Time filter

Source Type

Boulder, CO, United States

The University of Colorado Boulder is a public research university located in Boulder, Colorado, United States. It is the flagship university of the University of Colorado system and was founded five months before Colorado was admitted to the union in 1876. According to The Public Ivies: America's Flagship Public Universities , it is considered one of the thirty "Public Ivy League" schools.In 2010, the university consisted of nine colleges and schools and offered over 150 academic programs and enrolled 29,952 students. Eleven Nobel Laureates, nine MacArthur Fellows, and 18 astronauts have been affiliated with CU-Boulder as students, researchers, or faculty members in its history. The university received nearly US$454 million in sponsored research in 2010 to fund programs like the Laboratory for Atmospheric and Space Physics, and JILA.Colorado Buffaloes competes in nine intercollegiate sports in the NCAA Division I Pacific-12 Conference. The Buffaloes have won 26 NCAA championships: 19 in skiing, six total in men's and women's cross country, and one in football. Approximately 1,500 students participate in 34 intercollegiate club sports annually as well. Wikipedia.

Ganesan V.,University of Texas at Austin | Jayaraman A.,University of Colorado at Boulder
Soft Matter | Year: 2014

Polymer nanocomposites are a class of materials that consist of a polymer matrix filled with inorganic/organic nanoscale additives that enhance the inherent macroscopic (mechanical, optical and electronic) properties of the polymer matrix. Over the past few decades such materials have received tremendous attention from experimentalists, theoreticians, and computational scientists. These studies have revealed that the macroscopic properties of polymer nanocomposites depend strongly on the (microscopic) morphology of the constituent nanoscale additives in the polymer matrix. As a consequence, intense research efforts have been directed to understand the relationships between interactions, morphology, and the phase behavior of polymer nanocomposites. Theory and simulations have proven to be useful tools in this regard due to their ability to link molecular level features of the polymer and nanoparticle additives to the resulting morphology within the composite. In this article we review recent theory and simulation studies, presenting briefly the methodological developments underlying PRISM theories, density functional theory, self-consistent field theory approaches, and atomistic and coarse-grained molecular simulations. We first discuss the studies on polymer nanocomposites with bare or un-functionalized nanoparticles as additives, followed by a review of recent work on composites containing polymer grafted or functionalized nanoparticles as additives. We conclude each section with a brief outlook on some potential future directions. This journal is © The Royal Society of Chemistry.

Koonce R.C.,Skagit Regional Clinics | Bravman J.T.,University of Colorado at Boulder
Journal of the American Academy of Orthopaedic Surgeons | Year: 2013

A link has been established between obesity and osteoarthritis (OA), but the precise relationship has yet to be defined. OA has a multifactorial etiology, and obesity is consistently identified as an independent and modifiable risk factor. The biomechanical relationship is intuitive: increased loads on articular cartilage cause subsequent wear and cartilage breakdown. Less intuitive, and possibly more important, are the systemic effects of obesity on OA. Promising investigations into relationships between lipid metabolism and OA have been rarely reported in the orthopaedic literature. These reports argue that, in obese patients, weight loss may not only help prevent OA but also may be an effective treatment strategy. Orthopaedic surgeons should be aware of the biomechanical and systemic implications of obesity with respect to OA so that patients may be counseled accordingly. Copyright 2013 by the American Academy of Orthopaedic Surgeons.

Stucky B.J.,University of Colorado at Boulder
Journal of Biomolecular Techniques | Year: 2012

Modern applications of Sanger DNA sequencing often require converting a large number of chromatogram trace files into high-quality DNA sequences for downstream analyses. Relatively few nonproprietary software tools are available to assist with this process. SeqTrace is a new, free, and open-source software application that is designed to automate the entire workflow by facilitating easy batch processing of large numbers of trace files. SeqTrace can identify, align, and compute consensus sequences from matching forward and reverse traces, filter low-quality base calls, and end-trim finished sequences. The software features a graphical interface that includes a full-featured chromatogram viewer and sequence editor. SeqTrace runs on most popular operating systems and is freely available, along with supporting documentation, at http://seqtrace. googlecode.com/.© 2012 ABRF.

Chen C.C.,Columbia University | Borden M.A.,University of Colorado at Boulder
Biomaterials | Year: 2011

Complement fixation to surface-conjugated ligands plays a critical role in determining the fate of targeted colloidal particles after intravenous injection. In the present study, we examined the immunogenicity of targeted microbubbles with various surface architectures and ligand surface densities using a flow cytometry technique. Targeted microbubbles were generated using a post-labeling technique with a physiological targeting ligand, cyclic arginine-glycine-asparagine (RGD), attached to the distal end of the poly(ethylene glycol) (PEG) moieties on the microbubble surface. Microbubbles were incubated in human serum, washed and then mixed with fluorescent antibodies specific for various serum components. We found that complement C3/C3b was the main human serum factor to bind in vitro to the microbubble surface, compared to IgG or albumin. We also investigated the effect of PEG brush architecture on C3/C3b fixation to the microbubble surface. RGD peptide was able to trigger a complement immune response, and complement C3/C3b fixation depended on microbubble size and RGD peptide surface density. When the targeting ligand was attached to shorter PEG chains that were shielded by a PEG overbrush layer (buried-ligand architecture), significantly less complement activation was observed when compared to the more traditional exposed-ligand motif. The extent of this protective role by the PEG chains depended on the overbrush length. Taken together, our results confirm that the buried-ligand architecture may significantly reduce ligand-mediated immunogenicity. More generally, this study illustrates the use of flow cytometry and microbubbles to analyze the surface interactions between complex biological media and surface-engineered biomaterials. © 2011 Elsevier Ltd.

Darling J.,University of Colorado at Boulder
Astrophysical Journal Letters | Year: 2011

We have detected and confirmed five water maser complexes in the Andromeda Galaxy (M31) using the Green Bank Telescope. These masers will provide the high brightness temperature point sources needed for proper motion studies of M31, enabling measurement of its full three-dimensional velocity vector and its geometric distance via proper rotation. The motion of M31 is the keystone of Local Group dynamics and a gateway to the dark matter profiles of galaxies in general. Our survey for water masers selected 206 luminous compact 24 μm emitting regions in M31 and was sensitive enough to detect any maser useful for ∼10 μas yr-1 astrometry. The newly discovered masers span the isotropic luminosity range (0.3-1.9) × 10-3 L⊙ in single spectral components and are analogous to luminous Galactic masers. The masers are distributed around the molecular ring, including locations close to the major and minor axes, which is nearly ideal for proper motion studies. We find no correlation between 24μm luminosity and water maser luminosity, suggesting that while water masers arise in star-forming regions, the nonlinear amplification pathways and beamed nature of the water masers means that they are not predictable based on IR luminosity alone. This suggests that there are additional bright masers to be found in M31. We predict that the geometric distance and systemic proper motion of M31 can be measured in 2-3 years with current facilities. A "moving cluster" observation of diverging masers as M31 approaches the Galaxy may be possible in the long term. © 2011. The American Astronomical Society. All rights reserved.

Witczak-Krempa W.,Perimeter Institute for Theoretical Physics | Chen G.,University of Colorado at Boulder | Kim Y.B.,University of Toronto | Kim Y.B.,Korea Institute for Advanced Study | Balents L.,University of California at Santa Barbara
Annual Review of Condensed Matter Physics | Year: 2014

We discuss phenomena arising from the combined influence of electron correlation and spin-orbit coupling (SOC), with an emphasis on emergent quantum phases and transitions in heavy transition metal compounds with 4d and 5d elements. A common theme is the influence of spin-orbital entanglement produced by SOC, which influences the electronic and magnetic structure. In the weak-to-intermediate correlation regime, we show how nontrivial band-like topology leads to a plethora of phases related to topological insulators (TIs). We expound these ideas using the example of pyrochlore iridates, showing how many novel phases, such as the Weyl semimetal, axion insulator, topological Mott insulator, and TIs, may arise in this context. In the strong correlation regime, we argue that spin-orbital entanglement fully or partially removes orbital degeneracy, reducing or avoiding the normally ubiquitous Jahn-Teller effect. As we illustrate for the honeycomb-lattice iridates and double perovskites, this leads to enhanced quantum fluctuations of the spin-orbital entangled states and the chance to promote exotic spin liquid and multipolar ordered ground states. Connections to experiments, materials, and future directions are discussed. © Copyright 2014 by Annual Reviews. All rights reserved.

Levesque E.M.,University of Colorado at Boulder | Richardson M.L.A.,Arizona State University
Astrophysical Journal | Year: 2014

We present our parameterizations of the log([Ne III]λ3869/[O II]λ3727) (Ne3O2) and log([O III]λ5007/[O II]λ3727) (O3O2) ratios as diagnostics of ionization parameter in star-forming galaxies. Our calibrations are based on the Starburst99/Mappings III photoionization models, which extend up to the extremely high values of ionization parameter found in high-redshift galaxies. While similar calibrations have been presented previously for O3O2, this is the first such calibration of Ne3O2. We illustrate the tight correlation between these two ratios for star-forming galaxies and discuss the underlying physics that dictates their very similar evolution. Based on this work, we propose the Ne3O2 ratio as a new and useful diagnostic of ionization parameter for star-forming galaxies. Given the Ne3O2 ratio's relative insensitivity to reddening, this ratio is particularly valuable for use with galaxies that have uncertain amounts of extinction. The short wavelengths of the Ne3O2 ratio can also be applied out to very high redshifts, extending studies of galaxies' ionization parameters out to z ∼ 1.6 with optical spectroscopy and z ∼ 5.2 with ground-based near-infrared spectra. © 2014. The American Astronomical Society. All rights reserved..

Caruthers M.H.,University of Colorado at Boulder
Biochemical Society Transactions | Year: 2011

Current methodologies used to synthesize DNA and RNA are reviewed. These focus on using controlled pore glass and microarrays on glass slides. ©The Authors Journal compilation ©2011 Biochemical Society.

Johnson P.T.J.,University of Colorado at Boulder | Thieltges D.W.,University of Otago
Journal of Experimental Biology | Year: 2010

Growing interest in ecology has recently focused on the hypothesis that community diversity can mediate infection levels and disease ('dilution effect'). In turn, biodiversity loss - a widespread consequence of environmental change - can indirectly promote increases in disease, including those of medical and veterinary importance. While this work has focused primarily on correlational studies involving vector-borne microparasite diseases (e.g. Lyme disease, West Nile virus), we argue that parasites with complex life cycles (e.g. helminths, protists, myxosporeans and many fungi) offer an excellent additional model in which to experimentally address mechanistic questions underlying the dilution effect. Here, we unite recent ecological research on the dilution effect in microparasites with decades of parasitological research on the decoy effect in macroparasites to explore key questions surrounding the relationship between community structure and disease. We find consistent evidence that community diversity significantly alters parasite transmission and pathology under laboratory as well as natural conditions. Empirical examples and simple transmission models highlight the diversity of mechanisms through which such changes occur, typically involving predators, parasite decoys, low competency hosts or other parasites. However, the degree of transmission reduction varies among diluting species, parasite stage, and across spatial scales, challenging efforts to make quantitative, taxon-specific predictions about disease. Taken together, this synthesis highlights the broad link between community structure and disease while underscoring the importance of mitigating ongoing changes in biological communities owing to species introductions and extirpations. © 2010, Published by The Company of Biologists Ltd.

Brakenridge G.R.,University of Colorado at Boulder
Icarus | Year: 2011

Early predictions that some supernovae release large quantities of prompt high energy photons are now corroborated by optical identification of core-collapse supernovae associated with extragalactic GRBS (beamed γ-ray bursts) and XRFS (beamed or un-beamed X-ray flashes). Given the in-galaxy supernova frequency and GRB and XRF recurrence statistics, significant Earth-incident events during the past several million years very likely occurred and nearby events should have affected the Earth and other planetary atmospheres, including terrestrial surface solar UV, the Earth's climate, and its ecology. The Younger Dryas Stadial (~12,900 to 11,550 calendar yr BP) began with sharply cooler temperatures in the Earth's northern hemisphere, regional drought, paleoecological evidence compatible with increased UV, and abrupt increases in cosmogenic 14C and 10Be in ice and marine cores and tree rings. In North America, stratigraphic and faunal sequences indicate that a major pulse of mammalian extinctions (at least 23-31 genera) began very close to 12,830 calendar yr BP and was sudden: deposits one century younger are devoid of diverse extinct fauna remains. A 10s beamed GRB within 2kpc of the Earth delivers 100kJm -2 fluence to the Earth's atmosphere, where it causes spallation and catalytic reactions depleting 35-50% O 3, and producing excess NO x species (which favor cooling, drought, and surface fertility), 14C, and 10Be. An un-beamed, 10 50erg hard photon impulse at ~250pc produces similar terrestrial atmospheric effects. A well-characterized massive star supernova, the unusually close Vela event (d=250±30pc; total energy of 1-2×10 51erg; age constrained from remnant nebula shock velocities considerations at 13,000-16,000yr and from the pulsar characteristic age at ~11,400yr) may have initiated the Younger Dryas climate change, and caused the extinction of the terminal Rancholabrean fauna. © 2011 Elsevier Inc.

Nozik A.J.,National Renewable Energy Laboratory | Nozik A.J.,University of Colorado at Boulder
Nano Letters | Year: 2010

Quantum confinement of electronic particles (negative electrons and positive holes) in nanocrystals produces unique optical and electronic properties that have the potential to enhance the power conversion efficiency of solar cells for photovoltaic and solar fuels production at lower cost. These approaches and applications are labeled third generation solar photon conversion. Prominent among these unique properties is the efficient formation of more than one electron-hole pair (called excitons in nanocrystals) from a single absorbed photon. In isolated nanocrystals that have three-dimensional confinement of charge carriers (quantum dots) or two-dimensional confinement (quantum wires and rods) this process is termed multiple exciton generation. This Perspective presents a summary of our present understanding of the science of optoelectronic properties of nanocrystals and a prognosis for and review of the technological status of nanocrystals and nanostructures for third generation photovoltaic cells and solar fuels production. © 2010 American Chemical Society.

Mirocha J.,University of Colorado at Boulder
Monthly Notices of the Royal Astronomical Society | Year: 2014

Evolution in the X-ray luminosity-star formation rate (LX-SFR) relation could provide the first evidence of a top-heavy stellar initial mass function in the early Universe, as the abundance of high-mass stars and binary systems are both expected to increase with decreasing metallicity. The sky-averaged (global) 21-cm signal has the potential to test this prediction via constraints on the thermal history of the intergalactic medium, since X-rays can most easily escape galaxies and heat gas on large scales. A significant complication in the interpretation of upcoming 21-cm measurements is the unknown spectrum of accreting black holes (BHs) at high-z, which depends on the mass of accreting objects and poorly constrained processes such as how accretion disc photons are processed by the disc atmosphere and host galaxy interstellar medium. Using a novel approach to solving the cosmological radiative transfer equation (RTE), we show that reasonable changes in the characteristic BH mass affects the amplitude of the 21-cm signal's minimum at the ̃10-20mK level - comparable to errors induced by commonly used approximations to the RTE - while modifications to the intrinsic disc spectrum due to Compton scattering (bound-free absorption) can shift the position of the minimum of the global signal by δz ≈ 0.5 (δz ≈ 2), and modify its amplitude by up to ≈10mK (≈50 mK) for a given accretion history. Such deviations are larger than the uncertainties expected of current global 21-cm signal extraction algorithms, and could easily be confused with evolution in the LX-SFR relation. © 2014 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Jayaraman A.,University of Colorado at Boulder
Journal of Polymer Science, Part B: Polymer Physics | Year: 2013

Macroscopic properties of polymer nanocomposites depend on the microscopic composite morphology of the constituent nanoparticles and polymer matrix. One way to control the spatial arrangement of the nanoparticles in the polymer matrix is by grafting the nanoparticle surfaces with polymers that can tune the effective interparticle interactions in the polymer matrix. A fundamental understanding of how graft and matrix polymer chemistries and molecular weight, grafting density, and nanoparticle size, and chemistry affect interparticle interactions is needed to design the appropriate polymer ligands to achieve the target morphology. Theory and simulations have proven to be useful tools in this regard due to their ability to link molecular level interactions to the morphology. In this feature article, we present our recent theory and simulation studies of polymer grafted nanoparticles with chemical and physical heterogeneity in grafts to calculate the effective interactions and morphology as a function of chemistry, molecular weights, grafting densities, and so forth. © 2013 Wiley Periodicals, Inc.

Mitrovica J.X.,Harvard University | Wahr J.,University of Colorado at Boulder
Annual Review of Earth and Planetary Sciences | Year: 2011

Modern predictions of the rotational stability of an ice age Earth reflect a convergence of two classic problems in geophysical analysisâ€" the modeling of the glacial isostatic adjustment (GIA) process and the rotational stability of terrestrial planets. Recent theoretical advances in this area have been motivated not by conventional applications, such as the inference of Earth's deep-mantle viscosity, but rather by efforts to address vexing problems in global climate change research. These advances have demonstrated that traditional calculations of the ongoing motion of the rotation pole relative to the surface geography, or true polar wander (TPW), driven by ice age loading have systematically overestimated this motion by up to a factor of 4 by underestimating by ∼â̂ 1% the background flattening of Earth's oblate form. The physics of this sensitivity is related to concepts that appear in canonical, mid-twentieth century discussions of Earth rotation, and avoiding the associated inaccuracy resolves numerous perplexing sensitivities evident in previous predictions of ice age TPW. Moreover, these updated predictions provide both an important step in reconciling a recently defined enigma of modern global sea-level rise and a robust framework for analyzing a suite of space-geodetic constraints on Earth's climate system. Copyright © 2011 by Annual Reviews. All rights reserved.

Ayres T.R.,University of Colorado at Boulder
Astronomical Journal | Year: 2014

The following is a progress report on the long-term coronal (T 1 MK) activity of α Centauri A (HD 128620: G2 V) and B (HD 128621: K1 V). Since 2005 Chandra X-Ray Observatory has carried out semiannual pointings on AB mainly with the High Resolution Camera but also on two occasions with the Low-Energy Transmission Grating Spectrometer fully resolving the close pair in all cases. During 2008-2013 Chandra captured the rise peak and initial decline of B's coronal luminosity. Together with previous high states documented by ROSAT and XMM-Newton the long-term X-ray record suggests a period of 8.1 ± 0.2 yr compared to 11 yr for the Sun with a minimum-to-peak contrast of 4.5 about half the typical solar cycle amplitude. Meanwhile the A component has been mired in a Maunder-Minimum-like low state since 2005 initially recognized by XMM-Newton. But now A finally appears to be climbing out of the extended lull. If interpreted simply as an overlong cycle the period would be 19.2 ± 0.7 yr with a minimum-to-peak contrast of 3.4. The short X-ray cycle of B and possibly long cycle of A are not unusual compared with the diverse (albeit much lower amplitude) chromospheric variations recorded for example by the HK Project. Further the deep low state of A also is not unusual but instead is similar to the L X/L bol of the Sun during recent minima of the sunspot cycle. © 2014. The American Astronomical Society. All rights reserved..

Ayres T.R.,University of Colorado at Boulder
Astrophysical Journal, Supplement Series | Year: 2010

StarCAT is a catalog of high resolution ultraviolet spectra of objects classified as "stars," recorded by Space Telescope Imaging Spectrograph (STIS) during its initial seven years of operations (1997-2004). StarCAT is based on 3184 echelle observations of 545 distinct targets, with a total exposure duration of 5.2 Ms. For many of the objects, broad ultraviolet coverage has been achieved by splicing echellegrams taken in two or more FUV (1150-1700) and/or NUV (1600-3100) settings. In cases of multiple pointings on conspicuously variable sources, spectra were separated into independent epochs. Otherwise, different epochs were combined to enhance the signal-to-noise ratio (S/N). A post-facto correction to the pipeline data sets compensated for subtle wavelength distortions identified in a previous study of the STIS calibration lamps. An internal "fluxing" procedure yielded coherent spectral energy distributions (SEDs) for objects with broadly overlapping wavelength coverage. The best StarCAT material achieves 300 m s-1 internal velocity precision; absolute accuracy at the 1 km s-1 level; photometric accuracy of order 4%; and relative flux precision several times better (limited mainly by knowledge of SEDs of UV standard stars). While StarCAT represents a milestone in the large-scale post-processing of STIS echellegrams, a number of potential improvements in the underlying "final" pipeline are identified. © 2010 The American Astronomical Society.

Sigmund O.,Technical University of Denmark | Maute K.,University of Colorado at Boulder
Structural and Multidisciplinary Optimization | Year: 2013

Topology optimization has undergone a tremendous development since its introduction in the seminal paper by Bendsøe and Kikuchi in 1988. By now, the concept is developing in many different directions, including "density", "level set", "topological derivative", "phase field", "evolutionary" and several others. The paper gives an overview, comparison and critical review of the different approaches, their strengths, weaknesses, similarities and dissimilarities and suggests guidelines for future research. © 2013 Springer-Verlag Berlin Heidelberg.

Ayres T.R.,University of Colorado at Boulder
Astrophysical Journal | Year: 2011

Alpha Persei (HD20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290-1430 far-ultraviolet (FUV) spectrum of α Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si IV 1400 doublet (T ∼ 8 × 10 4K), are very weak, as are the chromospheric C II 1335 multiplet (T ∼ 3 × 104K) and O I 1305 Å triplet. In fact, the Si IV features of α Per are not only narrower than those of later, G-type supergiants of similar L X/L bol, but are also fainter (in L Si IV/L bol) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on α Per finds the X-ray centroid offset from the stellar position by 9″, at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star. © 2011. The American Astronomical Society. All rights reserved.

Wei Y.,CAS Institute of Mechanics | Wu J.,CAS Institute of Mechanics | Yin H.,CAS Institute of Mechanics | Shi X.,CAS Institute of Mechanics | And 2 more authors.
Nature Materials | Year: 2012

The two-dimensional crystalline structures in graphene challenge the applicability of existing theories that have been used for characterizing its three-dimensional counterparts. It is crucial to establish reliable structureg-property relationships in the important two-dimensional crystals to fully use their remarkable properties. With the success in synthesizing large-area polycrystalline graphene, understanding how grain boundaries (GBs) in graphene alter its physical properties is of both scientific and technological importance. A recent work showed that more GB defects could counter intuitively give rise to higher strength in tilt GBs (ref. ). We show here that GB strength can either increase or decrease with the tilt, and the behaviour can be explained well by continuum mechanics. It is not just the density of defects that affects the mechanical properties, but the detailed arrangements of defects are also important. The strengths of tilt GBs increase as the square of the tilt angles if pentagong-heptagon defects are evenly spaced, and the trend breaks down in other cases. We find that mechanical failure always starts from the bond shared by hexagong-heptagon rings. Our present work provides fundamental guidance towards understanding how defects interact in two-dimensional crystals, which is important for using high-strength and stretchable graphene for biological and electronic applications. © 2012 Macmillan Publishers Limited. All rights reserved.

Koban L.,University of Colorado at Boulder | Koban L.,University of Geneva | Pourtois G.,Ghent University
Neuroscience and Biobehavioral Reviews | Year: 2014

Action monitoring allows the swift detection of conflicts, errors, and the rapid evaluation of outcomes. These processes are crucial for learning, adaptive behavior, and for the regulation of cognitive control. Our review discusses neuroimaging and electrophysiological studies that have explored the contribution of emotional and social factors during action monitoring. Meta-analytic brain activation maps demonstrate reliable overlap of error monitoring, emotional, and social processes in the dorsal mediofrontal cortex (dMFC), lateral prefrontal areas, and anterior insula (AI). Cumulating evidence suggests that action monitoring is modulated by trait anxiety and negative affect, and that activity of the dMFC and the amygdala during action monitoring might contribute to the 'affective tagging' of actions along a valence dimension. The role of AI in action monitoring may be the integration of outcome information with self-agency and social context factors, thereby generating more complex situation-specific and conscious emotional feeling states. Our review suggests that action-monitoring processes operate at multiple levels in the human brain, and are shaped by dynamic interactions with affective and social processes. © 2014 Elsevier Ltd.

Hasenfratz A.,University of Colorado at Boulder
Physical Review Letters | Year: 2012

I investigate an SU(3) gauge model with 12 fundamental fermions. The physically interesting region of this strongly coupled system can be influenced by an ultraviolet fixed point due to lattice artifacts. I suggest to use a gauge action with an additional negative adjoint plaquette term that lessens this problem. I also introduce a new analysis method for the 2-lattice matching Monte Carlo renormalization group technique that significantly reduces finite volume effects. The combination of these two improvements allows me to measure the bare step scaling function in a region of the gauge coupling where it is clearly negative, indicating a positive renormalization group β function and infrared conformality. © 2012 American Physical Society.

Trampedach R.,University of Colorado at Boulder | Stein R.F.,Michigan State University
Astrophysical Journal | Year: 2011

The scale length over which convection mixes mass in a star can be calculated as the inverse of the vertical derivative of the unidirectional (up or down) mass flux. This is related to the mixing length in the mixing length theory of stellar convection. We give the ratio of mass mixing length to pressure scale height for a grid of three-dimensional surface convection simulations, covering from 4300K to 6900K on the main sequence, and up to giants at log g = 2.2, all for solar composition. These simulations also confirm what is already known from solar simulations that convection does not proceed by discrete convective elements, but rather as a continuous, slow, smooth, warm upflow and turbulent, entropy deficient, fast down drafts. This convective topology also results in mixing on a scale comparable to the classic mixing length formulation, and is simply a consequence of mass conservation on flows in a stratified atmosphere. © 2011. The American Astronomical Society. All rights reserved.

Yu L.,National Renewable Energy Laboratory | Zunger A.,University of Colorado at Boulder
Physical Review Letters | Year: 2012

There are numerous inorganic materials that may qualify as good photovoltaic (PV) absorbers, except that the currently available selection principle-focusing on materials with a direct band gap of ∼1.3eV (the Shockley-Queisser criteria)-does not provide compelling design principles even for the initial material screening. Here we offer a calculable selection metric of "spectroscopic limited maximum efficiency (SLME)" that can be used for initial screening based on intrinsic properties alone. It takes into account the band gap, the shape of absorption spectra, and the material-dependent nonradiative recombination losses. This is illustrated here via high-throughput first-principles quasiparticle calculations of SLME for ∼260 generalized I pIII qVI r chalcopyrite materials. It identifies over 20 high-SLME materials, including the best known as well as previously unrecognized PV absorbers. © 2012 American Physical Society.

Godin O.A.,University of Colorado at Boulder
Physical Review Letters | Year: 2012

We consider linear waves in compressible fluids in a uniform potential field, such as a gravity field, and demonstrate that a particular type of wave motion, in which pressure remains constant in each fluid parcel, is supported by inhomogeneous fluids occupying bounded or unbounded domains. We present elementary, exact solutions of linearized hydrodynamics equations, which describe the new type of waves in the coupled ocean-atmosphere system. The solutions provide an extension of surface gravity waves in an incompressible fluid half-space with a free boundary to waves in compressible, three-dimensionally inhomogeneous, rotating fluids. © 2012 American Physical Society.

Zimmerman P.M.,Stanford University | Zhang Z.,Stanford University | Musgrave C.B.,University of Colorado at Boulder
Nature Chemistry | Year: 2010

Multi-exciton generation-"the creation of multiple charge carrier pairs from a single photon-has been reported for several materials and may dramatically increase solar cell efficiency. Singlet fission, its molecular analogue, may govern multi-exciton generation in a variety of materials, but a fundamental mechanism for singlet fission has yet to be described. Here, we use sophisticated ab initio calculations to show that singlet fission in pentacene proceeds through rapid internal conversion of the photoexcited state into a dark state of multi-exciton character that efficiently splits into two triplets. We show that singlet fission to produce a pair of triplet excitons must involve an intermediate state that (i) has a multi-exciton character, (ii) is energetically accessible from the optically allowed excited state, and (iii) efficiently dissociates into multiple electron-"hole pairs. The rational design of photovoltaic materials that make use of singlet fission will require similar ab initio analysis of multi-exciton states such as the dark state studied here. © 2010 Macmillan Publishers Limited. All rights reserved.

Hindman B.W.,University of Colorado at Boulder | Jain R.,University of Sheffield
Astrophysical Journal | Year: 2012

We examine the scattering of acoustic p-mode waves from a thin magnetic fibril embedded in a gravitationally stratified atmosphere. The scattering is mediated through the excitation of slow sausage waves on the magnetic tube, and only the scattering of the monopole component of the wave field is considered. Since such tube waves are not confined by the acoustic cavity and may freely propagate along the field lines removing energy from the acoustic wave field, the excitation of fibril oscillations is a source of acoustic wave absorption as well as scattering. We compute the mode mixing that is achieved and the absorption coefficients and phase shifts. We find that for thin tubes the mode mixing is weak and the absorption coefficient is small and is a smooth function of frequency over the physically relevant band of observed frequencies. The prominent absorption resonances seen in previous studies of unstratified tubes are absent. Despite the relatively small absorption, the phase shift induced can be surprisingly large, reaching values as high as 15° for f modes. Further, the phase shift can be positive or negative depending on the incident mode order and the frequency. © 2012. The American Astronomical Society. All rights reserved.

Cash W.,University of Colorado at Boulder
Astrophysical Journal | Year: 2011

External occulters, otherwise known as starshades, have been proposed as a solution to one of the highest priority yet technically vexing problems facing astrophysics - the direct imaging and characterization of terrestrial planets around other stars. New apodization functions, developed over the past few years, now enable starshades of just a few tens of meters diameter to occult central stars so efficiently that the orbiting exoplanets can be revealed and other high-contrast imaging challenges addressed. In this paper, an analytic approach to the analysis of these apodization functions is presented. It is used to develop a tolerance analysis suitable for use in designing practical starshades. The results provide a mathematical basis for understanding starshades and a quantitative approach to setting tolerances. © 2011. The American Astronomical Society. All rights reserved.

Matrosov S.Y.,University of Colorado at Boulder
Monthly Weather Review | Year: 2013

Narrow elongated regions of moisture transport known as atmospheric rivers (ARs), which affect the West oast of North America, were simultaneously observed over the eastern North Pacific Ocean by the polarorbiting CloudSat and Aqua satellites. The presence, location, and extent of precipitation regions associated with ARs and their properties were retrieved from measurements taken at 265 satellite crossings of AR formations during the three consecutive cool seasons of the 2006-09 period. Novel independent retrievals of R mean rain rate, precipitation regime types, and precipitation ice region properties from satellite measurements were performed. Relations between widths of precipitation bands and AR thicknesses (as defined y the integrated water vapor threshold of 20mm) were quantified. Precipitation regime partitioning indicated that "cold" precipitation with a significant amount of melting precipitating ice and "warm" rainfall conditions with limited or no ice in the atmospheric column were observed, on average, with similar frequencies,though the cold rainfall fraction had an increasing trend as AR temperature decreased. Rain rates were generally higher for the cold precipitation regime. Precipitating ice cloud and rainfall retrievals indicated a significant correlation between the total ice amounts and the resultant rain rate. Observationally based statistical relations were derived between the boundaries of AR precipitation regions and integrated ater vapor amounts and between the total content of precipitating ice and rain rate. No statistically significant differences ofARproperties were found for three different cool seasons, which were characterized bydiffering phases of El Ni~no-Southern Oscillation. © 2013 American Meteorological Society.

Yang H.,Rice University | Johns-Krull C.M.,University of Colorado at Boulder
Astrophysical Journal | Year: 2011

We present an analysis of high-resolution (R 50, 000) infrared K-band echelle spectra of 14 T Tauri stars (TTSs) in the Orion Nebula Cluster. We model Zeeman broadening in three magnetically sensitive Ti I lines near 2.2 μm and consistently detect kilogauss-level magnetic fields in the stellar photospheres. The data are consistent in each case with the entire stellar surface being covered with magnetic fields, suggesting that magnetic pressure likely dominates over gas pressure in the photospheres of these stars. These very strong magnetic fields might themselves be responsible for the underproduction of X-ray emission of TTSs relative to what is expected based on main-sequence star calibrations. We combine these results with previous measurements of 14 stars in Taurus and 5 stars in the TW Hydrae association to study the potential variation of magnetic field properties during the first 10 million years of stellar evolution, finding a steady decline in total magnetic flux with age. © 2011. The American Astronomical Society. All rights reserved.

Esposito L.W.,University of Colorado at Boulder
Annual Review of Earth and Planetary Sciences | Year: 2010

Cassini observations confirm that Saturn's rings are predominantly water ice. The particles in Saturn's rings cover a range of sizes, from dust to small moons. Occultation results show the particles form temporary elongated aggregates tens of meters across. Some of the ring structure is created by moons, others by various instabilities. Data from future Cassini measurements can help investigators decide if the rings are remnants of the Saturn nebula or fragments of a destroyed moon or comet. Copyright © 2010 by Annual Reviews. All rights reserved.

Tucker G.E.,University of Colorado at Boulder | Hancock G.R.,University of Newcastle
Earth Surface Processes and Landforms | Year: 2010

Geomorphology is currently in a period of resurgence as we seek to explain the diversity, origins and dynamics of terrain on the Earth and other planets in an era of increased environmental awareness. Yet there is a great deal we still do not know about the physics and chemistry of the processes that weaken rock and transport mass across a planet's surface. Discovering and refining the relevant geomorphic transport functions requires a combination of careful field measurements, lab experiments, and use of longer-term natural experiments to test current theory and develop new understandings. Landscape evolution models have an important role to play in sharpening our thinking, guiding us toward the right observables, and mapping out the logical consequences of transport laws, both alone and in combination with other salient processes. Improved quantitative characterization of terrain and process, and an ever-improving theory that describes the continual modification of topography by the many and varied processes that shape it, together with improved observation and qualitative and quantitative modelling of geology, vegetation and erosion processes, will provide insights into the mechanisms that control catchment form and function. This paper reviews landscape theory - in the form of numerical models of drainage basin evolution and the current knowledge gaps and future computing challenges that exist. © 2010 John Wiley & Sons, Ltd.

Frehlich R.,University of Colorado at Boulder
Quarterly Journal of the Royal Meteorological Society | Year: 2011

A consistent definition of 'truth' is presented to define the errors in a numerical weather prediction (NWP) forecast, analysis and observations resulting from the unresolved turbulent field. 'Truth' is defined as the convolution of the continuous atmospheric variables by the effective spatial filter of an NWP model. Direct measurements of atmospheric variables are represented as an instrument error and a convolution of the continuous atmospheric variables by the observation sampling function. This clearly separates the instrument error from the observation sampling error that describes the mismatch between the NWP model effective spatial filter and the observation sampling function. The ensemble average that defines error statistics is defined by an infinite number of atmospheric realizations with statistically similar random fluctuations in the unresolved model field. This results in large spatial variations in the observation sampling errors due to the atmospheric variations in turbulence statistics. Two approaches are discussed to describe these spatial variations: one that defines observation error referenced to each model coordinate and one that assigns observation error referenced to each observation coordinate. The observation-error statistics depend on the observation sampling function, the local spatial statistics of the turbulence field and the NWP model filter. The effects of imprecise knowledge of the shape of the model filter on observation sampling error are small for rawinsonde measurements and for observations that produce a linear average along a track. The modifications to data-assimilation algorithms (the maximum-likelihood (ML) method, minimum mean-square-error algorithms, Kalman filtering, variational data assimilation and ensemble data assimilation) to include the spatial variations in observation-error statistics are discussed. In addition, the generation of ensemble forecast members should be consistent with the spatial variations in total observation error. A rigorous definition of error statistics is essential for evaluating the many different types of current and future observing systems. © 2010 Royal Meteorological Society.

Yi R.,University of Colorado at Boulder | Fuchs E.,Howard Hughes Medical Institute
Current Topics in Developmental Biology | Year: 2012

MicroRNAs (miRs) comprise a class of tiny (∼ 19-24 nucleotide), noncoding RNAs that regulate gene expression posttranscriptionally. Since the discovery of the founding members lin-4 and let-7 as key regulators in the developing nematode, miRs have been found throughout the eukaryotic kingdom. Functions for miRs are wide-ranging and encompass embryogenesis, stem cell biology, tissue differentiation, and human diseases including cancers. In this chapter, we begin by acquainting our readers with miRs and introducing them to their biogenesis. Then, we focus on the roles of miRs in stem cells during tissue development and homeostasis. We use mammalian skin as our main paradigm, but we also consider miR functions in several different types of adult stem cells. We conclude by discussing future challenges that will lead to a comprehensive understanding of miR functions in stem cells and their lineages. © 2012 Elsevier Inc.

Nalewajko K.,University of Colorado at Boulder
Monthly Notices of the Royal Astronomical Society | Year: 2013

I present a systematic study of gamma-ray flares in blazars. For this purpose, I propose a very simple and practical definition of a flare as a period of time, associated with a given flux peak, during which the flux is above half of the peak flux. I select a sample of 40 brightest gamma-ray flares observed by Fermi Large Area Telescope during the first four years of its mission. The sample is dominated by four blazars: 3C 454.3, PKS 1510-089, PKS 1222+216 and 3C 273. For each flare, I calculate a light curve and variations of the photon index. For the whole sample, I study the distributions of the peak flux, peak luminosity, duration, time asymmetry, average photon index and photon index scatter. I find that (1) flares produced by 3C 454.3 are longer and have more complex light curves than those produced by other blazars; (2) flares shorter than 1.5 d in the source frame tend to be time asymmetric with the flux peak preceding the flare midpoint. These differences can be largely attributed to a smaller viewing angle of 3C 454.3 as compared to other blazars. Intrinsically, the gamma-ray emitting regions in blazar jets may be structured and consist of several domains. I find no regularity in the spectral gamma-ray variations of flaring blazars. © 2013 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.

Martin R.G.,University of Colorado at Boulder | Lubow S.H.,US Space Telescope Science Institute
Monthly Notices of the Royal Astronomical Society | Year: 2013

Discs that contain dead zones are subject to the gravo-magneto instability which ariseswhen the turbulence shifts from gravitational to magnetic.We have previously described this instability through a local analysis at some radius in the disc in terms of a limit cycle. A disc may be locally unstable over a radial interval. In this paper, we consider how the local instability model can describe global disc outbursts. The outburst is triggered near the middle of the range of locally unstable radii. The sudden increase in turbulence within high surface density material causes a snowplough of density that propagates both inwards and outwards. All radii inside the trigger radius become unstable, as well as locally unstable radii outside the trigger radius. In addition, a locally stable region outside the trigger radius may also become unstable as the gravitational instability is enhanced by the snowplough. For the circumstellar disc model we consider, we find that a quarter of the disc mass is accreted on to the central object during the outburst. The radius out to which the disc is globally unstable is twice that for which it is locally unstable. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Martinsson P.G.,University of Colorado at Boulder
Journal of Computational Physics | Year: 2013

A numerical method for variable coefficient elliptic problems on two-dimensional domains is presented. The method is based on high-order spectral approximations and is designed for problems with smooth solutions. The resulting system of linear equations is solved using a direct solver with O(N1.5) complexity for the pre-computation and O(NlogN) complexity for the solve. The fact that the solver is direct is a principal feature of the scheme, and makes it particularly well suited to solving problems for which iterative solvers struggle; in particular for problems with highly oscillatory solutions. Numerical examples demonstrate that the scheme is fast and highly accurate. For instance, using a discretization with 12 points per wavelength, a Helmholtz problem on a domain of size 100 × 100 wavelengths was solved to ten correct digits. The computation was executed on a standard laptop; it involved 1.6M degrees of freedom and required 100 s for the pre-computation, and 0.3 s for the actual solve. © 2013 Elsevier Inc.

Medeiros D.M.,University of Colorado at Boulder | Crump J.G.,University of Southern California
Developmental Biology | Year: 2012

Patterning of the vertebrate facial skeleton involves the progressive partitioning of neural-crest-derived skeletal precursors into distinct subpopulations along the anteroposterior (AP) and dorsoventral (DV) axes. Recent evidence suggests that complex interactions between multiple signaling pathways, in particular Endothelin-1 (Edn1), Bone Morphogenetic Protein (BMP), and Jagged-Notch, are needed to pattern skeletal precursors along the DV axis. Rather than directly determining the morphology of individual skeletal elements, these signals appear to act through several families of transcription factors, including Dlx, Msx, and Hand, to establish dynamic zones of skeletal differentiation. Provocatively, this patterning mechanism is largely conserved from mouse and zebrafish to the jawless vertebrate, lamprey. This implies that the diversification of the vertebrate facial skeleton, including the evolution of the jaw, was driven largely by modifications downstream of a conversed pharyngeal DV patterning program. © 2012 Elsevier Inc.

Fornberg B.,University of Colorado at Boulder | Lehto E.,Uppsala University
Journal of Computational Physics | Year: 2011

Radial basis functions (RBFs) are receiving much attention as a tool for solving PDEs because of their ability to achieve spectral accuracy also with unstructured node layouts. Such node sets provide both geometric flexibility and opportunities for local node refinement. In spite of requiring a somewhat larger total number of nodes for the same accuracy, RBF-generated finite difference (RBF-FD) methods can offer significant savings in computer resources (time and memory). This study presents a new filter mechanism, allowing such gains to be realized also for purely convective PDEs that do not naturally feature any stabilizing dissipation. © 2010 Elsevier Inc.

Doostan A.,University of Colorado at Boulder | Owhadi H.,California Institute of Technology
Journal of Computational Physics | Year: 2011

We propose a method for the approximation of solutions of PDEs with stochastic coefficients based on the direct, i.e., non-adapted, sampling of solutions. This sampling can be done by using any legacy code for the deterministic problem as a black box. The method converges in probability (with probabilistic error bounds) as a consequence of sparsity and a concentration of measure phenomenon on the empirical correlation between samples. We show that the method is well suited for truly high-dimensional problems. © 2011 Elsevier Inc.

Nawrotzki R.J.,University of Colorado at Boulder
Organization and Environment | Year: 2012

Prior research in the United States has found that liberals are generally more environmentally concerned than conservatives. The present study explores whether conservatives' opposition to environmental protection is solely a U.S. or a universal phenomenon and whether this association is contingent on country-level characteristics, such as development, environmental conditions, and communist history. Employing data for 19 countries from the International Social Survey Program module "Environment II," this article explores inter-country variations in the relationship between individual conservatism and environmental concern using multilevel modeling with cross-level interactions. The models reveal a number of intriguing associations. Most important, conservatives' support for environmental protection varies by country. This variation is a function of country-level characteristics. The strongest opposition of conservatives' toward environmental protection was observed in developed, capitalist nations, with superior environmental conditions. On the other hand, in less developed countries, and countries characterized by poor environmental quality, conservatives are more environmentally concerned than liberals. © 2012 SAGE Publications.

Seals D.R.,University of Colorado at Boulder
Journal of Applied Physiology | Year: 2014

Cardiovascular diseases (CVD) remain the leading cause of morbidity and mortality in modern societies, and advancing age is the major risk factor for CVD. Arterial dysfunction, characterized by large elastic artery stiffening and endothelial dysfunction, is the key event leading to age-associated CVD. Our work shows that regular aerobic exercise inhibits large elastic artery stiffening with aging (optimizes arterial compliance) and preserves endothelial function. Importantly, among previously sedentary late middle-aged and older adults, aerobic exercise improves arterial stiffness and enhances endothelial function in most groups and, therefore, also can be considered a treatment for age-associated arterial dysfunction. The mechanisms by which regular aerobic exercise destiffens large elastic arteries are incompletely understood, but existing evidence suggests that reductions in oxidative stress associated with decreases in both adventitial collagen (fibrosis) and advanced glycation end-products (structural protein cross-linking molecules), play a key role. Aerobic exercise preserves endothelial function with aging by maintaining nitric oxide bioavailability via suppression of excessive superoxide-associated oxidative stress, and by inhibiting the development of chronic low-grade vascular inflammation. Recent work from our laboratory supports the novel hypothesis that aerobic exercise may exert these beneficial effects by directly inducing protection to aging arteries against multiple adverse factors to which they are chronically exposed. Regular aerobic exercise should be viewed as a "first line" strategy for prevention and treatment of arterial aging and a vital component of a contemporary public health approach for reducing the projected increase in population CVD burden. Copyright © 2014 the American Physiological Society.

Srubar W.V.,University of Colorado at Boulder
Cement and Concrete Composites | Year: 2014

The development and implementation of a stochastic service-life model for chloride-induced corrosion in reinforced recycled-aggregate concrete is presented in this work. The 1D model accounts for recycled aggregates that have been initially contaminated with chlorides from previous in-service exposure. Using a probabilistic approach, the model is employed to predict the service life of normal- and recycled-aggregate reinforced concrete with and without aggregate pre-contamination. Specifically, the effect of (a) type and replacement ratio of reclaimed aggregate, (b) chloride boundary conditions, (c) initial aggregate chloride concentration, and (d) thickness of contaminated aggregate shells on time to corrosion cracking was investigated herein. Results suggest that certain levels of contamination may be permissible in the design of reclaimed-aggregate reinforced concrete structures. Furthermore, quality control standards that limit thresholds of recycled aggregate replacement ratios and aggregate purity should be based on anticipated exposure conditions and old mortar thicknesses rather than initial degrees of aggregate contamination. © 2014 Elsevier Ltd. All rights reserved.

Begelman M.C.,U.S. National Institute of Standards and Technology | Begelman M.C.,University of Colorado at Boulder
Astrophysical Journal Letters | Year: 2012

We propose that the growth of supermassive black holes is associated mainly with brief episodes of highly super-Eddington infall of gas ("hyperaccretion"). This gas is not swallowed in real time, but forms an envelope of matter around the black hole that can be swallowed gradually, over a much longer timescale. However, only a small fraction of the black hole mass can be stored in the envelope at any one time. We argue that any infalling matter above a few percent of the hole's mass is ejected as a result of the plunge in opacity at temperatures below a few thousand degrees kelvin, corresponding to the Hayashi track. The speed of ejection of this matter, compared to the velocity dispersion σ of the host galaxy's core, determines whether the ejected matter is lost forever or returns eventually to rejoin the envelope, from which it can be ultimately accreted. The threshold between matter recycling and permanent loss defines a relationship between the maximum black hole mass and σ that resembles the empirical M BH-σ relation. © 2012 The American Astronomical Society. All rights reserved.

McHenry C.S.,University of Colorado at Boulder
Current Opinion in Chemical Biology | Year: 2011

Bacterial replicases are complex, tripartite replicative machines. They contain a polymerase, Pol III, a β 2 processivity factor and a DnaX complex ATPase that loads β 2 onto DNA and chaperones Pol III onto the newly loaded β 2. Many bacteria encode both a full length τ and a shorter γ form of DnaX by a variety of mechanisms. The polymerase catalytic subunit of Pol III, α, contains a PHP domain that not only binds to prototypical e{open} Mg 2+-dependent exonuclease, but also contains a second Zn 2+-dependent proofreading exonuclease, at least in some bacteria. Replication of the chromosomes of low GC Gram-positive bacteria require two Pol IIIs, one of which, DnaE, appears to extend RNA primers a only short distance before handing the product off to the major replicase, PolC. Other bacteria encode a second Pol III (ImuC) that apparently replaces Pol V, required for induced mutagenesis in E. coli. Approaches that permit simultaneous biochemical screening of all components of complex bacterial replicases promise inhibitors of specific protein targets and reaction stages. © 2011 Elsevier Ltd.

Feder J.L.,University of Notre Dame | Egan S.P.,University of Notre Dame | Nosil P.,University of Colorado at Boulder | Nosil P.,University of Sheffield
Trends in Genetics | Year: 2012

The emerging field of speciation genomics is advancing our understanding of the evolution of reproductive isolation from the individual gene to a whole-genome perspective. In this new view it is important to understand the conditions under which 'divergence hitchhiking' associated with the physical linkage of gene regions, versus 'genome hitchhiking' associated with reductions in genome-wide rates of gene flow caused by selection, can enhance speciation-with-gene-flow. We describe here a theory predicting four phases of speciation, defined by changes in the relative effectiveness of divergence and genome hitchhiking, and review empirical data in light of the theory. We outline future directions, emphasizing the need to couple next-generation sequencing with selection, transplant, functional genomics, and mapping studies. This will permit a natural history of speciation genomics that will help to elucidate the factors responsible for population divergence and the roles that genome structure and different forms of hitchhiking play in facilitating the genesis of new biodiversity. © 2012 Elsevier Ltd.

Armitage P.J.,University of Colorado at Boulder
Annual Review of Astronomy and Astrophysics | Year: 2011

Protoplanetary disks are quasi-steady structures whose evolution and dispersal determine the environment for planet formation. I review the theory of protoplanetary disk evolution and its connection to observations. Substantial progress has been made in elucidating the physics of potential angular momentum transport processesincluding self-gravity, magnetorotational instability, baroclinic instabilities, and magnetic brakingand in developing testable models for disk dispersal via photoevaporation. The relative importance of these processes depends upon the initial mass, size, and magnetization of the disk, and subsequently on its opacity, ionization state, and external irradiation. Disk dynamics is therefore coupled to star formation, pre-main-sequence stellar evolution, and dust coagulation during the early stages of planet formation and may vary dramatically from star to star. The importance of validating theoretical models is emphasized, with the key observations being those that probe disk structure on the scales between 1 AU and 10 AU, where theory is most uncertain. © 2011 by Annual Reviews. All rights reserved.

Hazzard K.R.A.,University of Colorado at Boulder | Mueller E.J.,Cornell University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We describe how rescaling experimental data obtained from cold atom density profiles can reveal signatures of quantum criticality. We identify a number of important questions which can be answered by analyzing experimental data in this manner. We show that such experiments can distinguish different universality classes and that the signatures are robust against temperature, noise, and finite system size. © 2011 American Physical Society.

Vaida V.,University of Colorado at Boulder
Journal of Chemical Physics | Year: 2011

The importance of water in atmospheric and environmental chemistry initiated recent studies with results documenting catalysis, suppression and anti-catalysis of thermal and photochemical reactions due to hydrogen bonding of reagents with water. Water, even one water molecule in binary complexes, has been shown by quantum chemistry to stabilize the transition state and lower its energy. However, new results underscore the need to evaluate the relative competing rates between reaction and dissipation to elucidate the role of water in chemistry. Water clusters have been used successfully as models for reactions in gas-phase, in aqueous condensed phases and at aqueous surfaces. Opportunities for experimental and theoretical chemical physics to make fundamental new discoveries abound. Work in this field is timely given the importance of water in atmospheric and environmental chemistry. © 2011 American Institute of Physics.

Radzihovsky L.,University of Colorado at Boulder
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi gases, we formulate a low-energy theory of the Fulde-Ferrell and the Larkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability, and phase transitions in these enigmatic finite momentum-paired superfluids. Focusing on the unidirectional LO pair-density-wave state, which spontaneously breaks the continuous rotational and translational symmetries, we show that it is characterized by two Goldstone modes, corresponding to a superfluid phase and a smectic phonon. Because of the liquid-crystalline "softness" of the latter, at finite temperature the three-dimensional state is characterized by a vanishing LO order parameter, quasi-Bragg peaks in the structure and momentum distribution functions, and a "charge"-4, paired-Cooper-pairs, off-diagonal long-range order, with a superfluid-stiffness anisotropy that diverges near a transition into a nonsuperfluid state. In addition to conventional integer vortices and dislocations, the LO superfluid smectic exhibits composite half-integer vortex-dislocation defects. A proliferation of defects leads to a rich variety of descendant states, such as the charge-4 superfluid and Fermi-liquid nematics and topologically ordered nonsuperfluid states, that generically intervene between the LO state and the conventional superfluid and the polarized Fermi liquid at low and high imbalance, respectively. The fermionic sector of the LO gapless superconductor is also quite unique, exhibiting a Fermi surface of Bogoliubov quasiparticles associated with the Andreev band of states, localized on the array of the LO domain walls. © 2011 American Physical Society.

Levesque E.M.,University of Colorado at Boulder | Massey P.,Lowell Observatory
Astronomical Journal | Year: 2012

We present moderate-resolution spectroscopic observations of red supergiants (RSGs) in the low-metallicity Local Group galaxies NGC6822 (Z = 0.4 Z ⊙) and Wolf-Lundmark-Melotte (WLM; Z = 0.1 Z ⊙). By combining these observations with reduction techniques for multislit data reduction and flux calibration, we are able to analyze spectroscopic data of 16 RSGs in NGC6822 and spectrophotometric data of 11 RSGs in WLM. Using these observations, we determine spectral types for these massive stars, comparing them to Milky Way and Magellanic Cloud RSGs and thus extending observational evidence of the abundance-dependent shift of RSG spectral types to lower metallicities. In addition, we have uncovered two RSGs with unusually late spectral types (J000158.14-152332.2 in WLM, with a spectral type of M3 I, and J194453.46-144552.6 in NGC6822, with a spectral type of M4.5 I) and a third RSG (J194449.96-144333.5 in NGC6822) whose spectral type has varied from an M2.5 in 1997 to a K5 in 2008. All three of these stars could potentially be members of a recently discovered class of extreme RSG variables. © 2012. The American Astronomical Society. All rights reserved.

McKnight D.M.,University of Colorado at Boulder
Frontiers in Ecology and the Environment | Year: 2010

Efforts to communicate with children about ecological themes often emphasize environmental threats. For some children, however, this approach can backfire, as they try to avoid continued exposure to problems they cannot solve. Another innovative approach is to promote the development of environmental empathy and environmental literacy through the use of narrative. Children's books that use narrative to convey key concepts about a given ecosystem could potentially reach a broad audience by making information about the books available on the internet. Examples of this approach are a special New York City edition of a book in the Magic School Bus series (Scholastic Press) and the Schoolyard Book series produced by the Long Term Ecological Research Network program. © The Ecological Society of America.

Cappa C.D.,University of California at Davis | Jimenez J.L.,University of Colorado at Boulder
Atmospheric Chemistry and Physics | Year: 2010

Measurements of the sensitivity of organic aerosol (OA, and its components) mass to changes in temperature were recently reported by Huffman et al.∼(2009) using a tandem thermodenuder-aerosol mass spectrometer (TD-AMS) system in Mexico City and the Los Angeles area. Here, we use these measurements to derive quantitative estimates of aerosol volatility within the framework of absorptive partitioning theory using a kinetic model of aerosol evaporation in the TD. OA volatility distributions (or "basis-sets") are determined using several assumptions as to the enthalpy of vaporization (ΔH vap). We present two definitions of "non-volatile OA," one being a global and one a local definition. Based on these definitions, our analysis indicates that a substantial fraction of the organic aerosol is comprised of non-volatile components that will not evaporate under any atmospheric conditions; on the order of 50-80% when the most realistic ΔHvap assumptions are considered. The sensitivity of the total OA mass to dilution and ambient changes in temperature has been assessed for the various ΔHvap assumptions. The temperature sensitivity is relatively independent of the particular ΔHvap assumptions whereas dilution sensitivity is found to be greatest for the low (ΔH vap Combining double low line 50 kJ/mol) and lowest for the high (ΔHvap Combining double low line 150 kJ/mol) assumptions. This difference arises from the high ΔHvap assumptions yielding volatility distributions with a greater fraction of non-volatile material than the low ΔHvap assumptions. If the observations are fit using a 1 or 2-component model the sensitivity of the OA to dilution is unrealistically high. An empirical method introduced by Faulhaber et al. (2009) has also been used to independently estimate a volatility distribution for the ambient OA and is found to give results consistent with the high and variable ΔH vap assumptions. Our results also show that the amount of semivolatile gas-phase organics in equilibrium with the OA could range from ∼20% to 400% of the OA mass, with smaller values generally corresponding to the higher ΔHvap assumptions. The volatility of various OA components determined from factor analysis of AMS spectra has also been assessed. In general, it is found that the fraction of non-volatile material follows the pattern: biomass burning OA < hydrocarbon-like OA < semivolatile oxygenated OA < low-volatility oxygenated OA. Correspondingly, the sensitivity to dilution and the estimated amount of semivolatile gas-phase material for the OA factors follows the reverse order. Primary OA has a substantial semivolatile fraction, in agreement with previous results, while the non-volatile fraction appears to be dominated by oxygenated OA produced by atmospheric aging. The overall OA volatility is thus controlled by the relative contribution of each aerosol type to the total OA burden. Finally, the model/measurement comparison appears to require OA having an evaporation coefficient (γe) substantially greater than 10-2 at this point it is not possible to place firmer constraints on γe based on the observations. © 2010 Author(s).

Flowers R.M.,University of Colorado at Boulder | Schoene B.,Princeton University
Geology | Year: 2010

The timing and causes of the >1.0 km elevation gain of the southern African Plateau since Paleozoic time are widely debated. We report the first apatite and titanite (U-Th)/He thermochronometry data for southern Africa to resolve the unroofing history across a classic portion of the major escarpment that encircles the plateau. The study area encompasses ~1500 m of relief within Archean basement of the Barberton Greenstone Belt region of the eastern Kaapvaal craton. Titanite dates are Neoproterozoic. Apatite dates are Cretaceous, with most results clustering at ca. 100 Ma. Thermal history simulations confirm Mesozoic heating followed by accelerated cooling in mid-to Late Cretaceous time. The lower temperature sensitivity of the apatite (U-Th)/He method relative to previous thermochronometry in southern Africa allows tighter constraints on the Cenozoic thermal history than past work. The data limit Cenozoic temperatures east of the escarpment to ≤35 °C, and appear best explained by temperatures within a few degrees of the modern surface temperature. These results restrict Cenozoic unroofing to less than ~850 m, and permit negligible erosion since the Cretaceous. If substantial uplift of the southern African Plateau occurred in the Cenozoic as advocated by some workers, then it was not responsible for the majority of post-Paleozoic unroofing across the eastern escarpment. Significant Mesozoic unroofing is coincident with large igneous province activity, kimberlite magmatism, and continental rifting within and along the margins of southern Africa, compatible with a phase of plateau elevation gain due to mantle buoyancy sources associated with these events. © 2010 Geological Society of America.

Barth C.A.,University of Colorado at Boulder
Journal of Geophysical Research: Space Physics | Year: 2010

During geomagnetic storms, gravity waves propagate from the polar regions toward the equator heating the thermosphere at 140 km and higher. These gravity waves are produced by Joule heating that occurs at latitudes of 60° and higher. The heating leads to an increase in the density of nitric oxide at 140 km in the thermosphere. On some occasions, the increased nitric oxide diffuses downward to the 110 km level causing the nitric oxide density at that level to increase substantially. Two and a half years (11 March 1998-30 September 2000) of Student Nitric Oxide Explorer (SNOE) observations of nitric oxide were examined to look for occurrences of increased nitric oxide produced by Joule heating initiated gravity waves and to determine how often downflow of nitric oxide occurs. The results of this study show that gravity wave heating occurs frequently, about 12-14% of the time at 40 latitude. For about 50% of these events, downflow of nitric oxide from 140 km to 110-120 km occurs the following day. About 2-3% of the time, gravity waves propagate all the way to the 20N and S latitude band around the equator. On special occasions, downflow of nitric oxide occurs at the equator as the result of Joule heating occurring in the polar regions. This happened on five occasions during the two and a half year period in 1998-2000. Copyright 2010 by the American Geophysical Union.

It has been known for many years that the ability to exert behavioral control over an adverse event blunts the behavioral and neurochemical impact of the event. More recently, it has become clear that the experience of behavioral control over adverse events also produces enduring changes that reduce the effects of subsequent negative events, even if they are uncontrollable and quite different from the original event controlled. This review focuses on the mechanism by which control both limits the impact of the stressor being experienced and produces enduring, trans-situational "immunization". The evidence will suggest that control is detected by a corticostriatal circuit involving the ventral medial prefrontal cortex (mPFC) and the posterior dorsomedial striatum (DMS). Once control is detected, other mPFC neurons that project to stress-responsive brainstem (dorsal raphe nucleus, DRN) and limbic (amygdala) structures exert topedown inhibitory control over the activation of these structures that is produced by the adverse event. These structures, such as the DRN and amygdala, in turn regulate the proximate mediators of the behavioral and physiological responses produced by adverse events, and so control blunts these responses. Importantly, the joint occurrence of control and adverse events seems to produce enduring plastic changes in the topedown inhibitory mPFC system such that this system is now activated by later adverse events even if they are uncontrollable, thereby reducing the impact of these events. Other issues are discussed that include a) whether other processes such as safety signals and exercise, that lead to resistance/resilience, also use the mPFC circuitry or do so in other ways; b) whether control has similar effects and neural mediation in humans, and c) the relationship of this work to clinical phenomena. © 2014 The Author.

Lee S.S.,National Oceanic and Atmospheric Administration | Lee S.S.,University of Colorado at Boulder
Atmospheric Chemistry and Physics | Year: 2011

This study examines the dependence of aerosol-precipitation interactions on environmental humidity in a mesoscale cloud ensemble (MCE) which is composed of convective and stratiform clouds. The author found that increases in aerosol concentration enhance evaporative cooling, which raises not only the intensity of vorticity and entrainment but also that of downdrafts and low-level convergence. The increase in vorticity tends to suppress precipitation. The increase in low-level convergence tends to enhance precipitation by generating more secondary clouds in a muptiple-cloud system simulated here. At high humidity, the effect of the increased vorticity on cloud-liquid mass and, thus, precipitation is outweighed by that of the increased low-level convergence. This leads to the precipitation enhancement induced by the increase in aerosol concentration. When humidity lowers to mid humidity, the effect of aerosol on low-level convergence still dominates that on entrainment, leading to the precipitation enhancement with the increased aerosol concentration. With the lowest humidity in the current work, the effect of aerosol on entrainment dominates that on low-level convergence, leading to the precipitation suppression with the increased aerosol concentration. Hence, there is not only a competition between the effect of evaporation on vorticity and that on low-level convergence at a given humidity level but also the variation of the competition with the varying humidity. This competition and variation are absent in a single-cloud system where the effect of low-level convergence on secondary clouds is absent. This exemplifies a difference in the mechanism which controls aerosol-precipitation interactions between a single-cloud system and a multiple-cloud system. © 2011 Author(s).

Molnar P.,University of Colorado at Boulder
Bulletin of the Geological Society of America | Year: 2010

Although geomorphic observations suggest that the Sierra Nevada has tilted so that the crest has risen 1-2 km since late Miocene time, deuterium and oxygen-18 isotope concentrations in Cenozoic geologic materials decrease eastward across California and Nevada similarly to those in modern, orographically induced precipitation, as if little change in Sierra Nevadan elevations has occurred since Eocene time. Orographic precipitation, however, depends on the amount of moisture in the atmosphere, which in turn can be much larger in warm air, as in Eocene or Oligocene time and in summer, than in the cooler air characteristic of present-day, domi nantly winter, precipitation. Moreover, the integrated rainout of vapor, and hence presumably in stable isotope concentrations in the remaining vapor, depends largely on the difference in heights traversed by air masses, not slopes of mountain ranges. Thus, if due simply to orographically induced rainout, both Eocene and Oligocene variations in deuterium isotopes across the Sierra Nevada and Miocene-Quaternary differences in deuterium and oxygen isotopes between the Great Valley of California and the Basin and Range place only weak constraints on the slope or past elevations of the Sierra Nevada. They do not necessarily contradict the inference that the crest of the Sierra Nevada has risen 1000 m or more since late Miocene time. © 2010 Geological Society of America.

O'Toole E.T.,University of Colorado at Boulder | Dutcher S.K.,University of Washington
Cytoskeleton | Year: 2014

Correct centriole/basal body positioning is required for numerous biological processes, yet how the cell establishes this positioning is poorly understood. Analysis of centriolar/basal body duplication provides a key to understanding basal body positioning and function. Chlamydomonas basal bodies contain structural features that enable specific triplet microtubules to be specified. Electron tomography of cultures enriched in mitotic cells allowed us to follow basal body duplication and identify a specific triplet at which duplication occurs. Probasal bodies elongate in prophase, assemble transitional fibers (TF) and are segregated with a mature basal body near the poles of the mitotic spindle. A ring of nine-singlet microtubules is initiated at metaphase, orthogonal to triplet eight. At telophase/cytokinesis, triplet microtubule blades assemble first at the distal end, rather than at the proximal cartwheel. The cartwheel undergoes significant changes in length during duplication, which provides further support for its scaffolding role. The uni1-1 mutant contains short basal bodies with reduced or absent TF and defective transition zones, suggesting that the UNI1 gene product is important for coordinated probasal body elongation and maturation. We suggest that this site-specific basal body duplication ensures the correct positioning of the basal body to generate landmarks for intracellular patterning in the next generation. © 2013 Wiley Periodicals, Inc.

Lawrence D.M.,U.S. National Center for Atmospheric Research | Slater A.G.,University of Colorado at Boulder
Climate Dynamics | Year: 2010

Global climate models predict that terrestrial northern high-latitude snow conditions will change substantially over the twenty-first century. Results from a Community Climate System Model simulation of twentieth and twenty-first (SRES A1B scenario) century climate show increased winter snowfall (+10-40%), altered maximum snow depth (-5 ± 6 cm), and a shortened snow-season (-14 ± 7 days in spring, +20 ± 9 days in autumn). By conducting a series of prescribed snow experiments with the Community Land Model, we isolate how trends in snowfall, snow depth, and snow-season length affect soil temperature trends. Increasing snowfall, by countering the snowpack-shallowing influence of warmer winters and shorter snow seasons, is effectively a soil warming agent, accounting for 10-30% of total soil warming at 1 m depth and ~16% of the simulated twenty-first century decline in near-surface permafrost extent. A shortening snow season enhances soil warming due to increased solar absorption whereas a shallowing snowpack mitigates soil warming due to weaker winter insulation from cold atmospheric air. Snowpack deepening has comparatively less impact due to saturation of snow insulative capacity at deeper snow depths. Snow depth and snow-season length trends tend to be positively related, but their effects on soil temperature are opposing. Consequently, on the century timescale the net change in snow state can either amplify or mitigate soil warming. Snow state changes explain less than 25% of total soil temperature change by 2100. However, for the latter half of twentieth century, snow state variations account for as much as 50-100% of total soil temperature variations. © 2009 Springer-Verlag.

Vaida V.,University of Colorado at Boulder | Donaldson D.J.,University of Toronto
Physical Chemistry Chemical Physics | Year: 2014

We present a brief review of long wavelength, red-light initiated chemistry from excited vibrational levels of the ground electronic state of atmospheric trace species. When sunlight driven electronic state reactions are not effective, photochemical processes occurring by vibrational overtone excitation have been found to be important in reactions of oxidized atmospheric compounds (acids, alcohols and peroxides) prevalent in the Earth's atmosphere. This review focuses on the fundamental energetic, mechanistic and dynamical aspects of unimolecular reactions of vibrationally excited atmospheric species. We will discuss the relevance of these red light initiated reactions to address the discrepancies between atmospheric measurements and results of standard atmospheric models. © 2014 the Owner Societies.

Shull J.M.,University of Colorado at Boulder | Shull J.M.,University of Cambridge
Astrophysical Journal | Year: 2014

Our current view of galaxies considers them as systems of stars and gas embedded in extended halos of dark matter, much of it formed by the infall of smaller systems at earlier times. The true extent of a galaxy remains poorly determined, with the "virial radius" (R vir) providing a characteristic separation between collapsed structures in dynamical equilibrium and external infalling matter. Other physical estimates of the extent of gravitational influence include the gravitational radius, gas accretion radius, and "galactopause" arising from outflows that stall at 100-200 kpc over a range of outflow parameters and confining gas pressures. Physical criteria are proposed to define bound structures, including a more realistic definition of R vir(M *, Mh , z a ) for stellar mass M * and halo mass Mh , half of which formed at "assembly redshifts" ranging from z a 0.7-1.3. We estimate the extent of bound gas and dark matter around L* galaxies to be 200 kpc. The new virial radii, with mean 〈R vir〉 200 kpc, are 40%-50% smaller than values estimated in recent Hubble Space Telescope/Cosmic Origins Spectrograph detections of H I and O VI absorbers around galaxies. In the new formalism, the Milky Way stellar mass, log M * = 10.7 ± 0.1, would correspond to kpc for half-mass halo assembly at za = 1.06 ± 0.03. The frequency per unit redshift of low-redshift O VI absorption lines in QSO spectra suggests absorber sizes 150 kpc when related to intervening 0.1L* galaxies. This formalism is intended to clarify semantic differences arising from observations of extended gas in galactic halos, circumgalactic medium (CGM), and filaments of the intergalactic medium (IGM). Astronomers should refer to bound gas in the galactic halo or CGM, and unbound gas at the CGM-IGM interface, on its way into the IGM. © 2014. The American Astronomical Society. All rights reserved..

Caine N.,University of Colorado at Boulder
Annals of Glaciology | Year: 2010

Hydrologie and hydrochemical studies have been conducted in Green Lakes Valley, Colorado Front Range, USA, above 3550 m since 1982. They show a classic seasonal hydrograph dominated by snowmelt and an earlier date for the start of spring flow and for peak flow over the period of record. This is consistent with patterns found at lower elevations in Colorado and throughout western North America. They also show an increasing trend in flows in September and October of 2.6 ±0.7 mm a-1 which is not found elsewhere and cannot be accounted for by increased autumn precipitation and the melting of surface ice. Because this late-season increase is not found at the highest elevations or in basins in which there is no evidence of permafrost, it seems best explained by the thawing of alpine permafrost at intermediate elevations. This is corroborated by an increase in the concentration of base cations and silica, and particularly in Ca2+ and SO4 -, in the stream discharge starting in 2000. As with the physical hydrology, the geochemical signals have not been detected at the higher elevations in the basin, though they have previously been associated with streamflow from a small rock glacier in the valley. The combined evidence suggests the degradation of ice-rich permafrost on the north-facing slopes of the valley below 3700 m, where it has been detected at 3 m depth by geophysical surveys.

Scheeres D.J.,University of Colorado at Boulder
Acta Astronautica | Year: 2012

Small solar system bodies such as asteroids and comets are of significant interest for both scientific and human exploration missions. However, their orbital environments are among the most highly perturbed and extreme environments found in the solar system. Uncontrolled trajectories are highly unstable in general and may either impact or escape in timespans of hours to days. Even with active control, the chaotic nature of motion about these bodies can effectively randomize a trajectory within a few orbits, creating fundamental difficulties for the navigation of spacecraft in these environments. In response to these challenges our research has identified robust and stable orbit solutions and mission designs across the whole range of small body sizes and spin states that are of interest for scientific and human exploration. This talk will describe the challenges of exploring small bodies and present the practical solutions that have been discovered which enable their exploration across the range of small body types and sizes. © 2011 Elsevier Ltd. All rights reserved.

Yi R.,University of Colorado at Boulder | Fuchs E.,Howard Hughes Medical Institute | Fuchs E.,Rockefeller University
Cell Death and Differentiation | Year: 2010

Skin, the biggest organ in mammals, protects the body from environmental hazards and prevents dehydration. Embryonic skin morphogenesis and homeostasis of adult skin require an accurately controlled gene expression in a spatiotemporally specific manner. Recently, the identification of microRNAs (miRNAs) in skin has added a new dimension in the regulatory network and attracted significant interest in this novel layer of gene regulation. Mammalian skin with its easy accessibility, well-defined lineages and established genetic tools offers an ideal system to unravel the functions of miRNAs in mammalian development and stem cells. In the past few years, significant progress has been made in determining the expression patterns of miRNAs, exploring their functions in skin morphogenesis and differentiation, as well as probing their functions in human skin diseases, for example, skin cancer. In this review, we summarized current progress in the study of miRNA in mammalian skin, provided insights gained from recent studies and offered our views for remaining challenges. © 2010 Macmillan Publishers Limited All rights reserved.

Tripp E.A.,University of Colorado at Boulder | McDade L.A.,500 N College Avenue
Systematic Biology | Year: 2014

More than a decade of phylogenetic research has yielded a well-sampled, strongly supported hypothesis of relationships within the large (>4000 species) plant family Acanthaceae. This hypothesis points to intriguing biogeographic patterns and asymmetries in sister clade diversity but, absent a time-calibrated estimate for this evolutionary history, these patterns have remained unexplored. Here, we reconstruct divergence times within Acanthaceae using fossils as calibration points and experimenting with both fossil selection and effects of invoking a maximum age prior related to the origin of Eudicots. Contrary to earlier reports of a paucity of fossils of Lamiales (an order of ~23,000 species that includesAcanthaceae) and to the expectation that a largely herbaceous to soft-wooded and tropical lineagewould have fewfossils,we recovered 51 reports of fossil Acanthaceae. Rigorous evaluation of these for accurate identification, quality of age assessment and utility in dating yielded eight fossils judged to merit inclusion in analyses.With nearly 10 kb of DNA sequence data, we used two sets of fossils as constraints to reconstruct divergence times.We demonstrate differences in age estimates depending on fossil selection and that enforcement of maximum age priors substantially alters estimated clade ages, especially in analyses that utilize a smaller rather than larger set of fossils. Our results suggest that long-distance dispersal events explain present-day distributions better than do Gondwanan or northern land bridge hypotheses. This biogeographical conclusion is for the most part robust to alternative calibration schemes. Our data support a minimum of 13 Old World (OW) to New World (NW) dispersal events but, intriguingly, only one in the reverse direction. Eleven of these 13 were among Acanthaceae s.s., which comprises >90% of species diversity in the family. Remarkably, if minimum age estimates approximate true history, these 11 events occurred within the last ~20 myr even though Acanthaceae s.s is over 3 times as old. A simulation study confirmed that these dispersal events were significantly skewed toward the present and not simply a chance occurrence. Finally, we review reports of fossils that have been assigned to Acanthaceae that are substantially older than the lower Cretaceous estimate for Angiosperms as a whole (i.e., the general consensus that has resulted from several recent dating and fossil-based studies in plants). This is the first study to reconstruct divergence times among clades of Acanthaceae and sets the stage for comparative evolutionary research in this and related families that have until now been thought to have extremely poor fossil resources. © The Author(s) 2014.

McCain C.M.,University of Colorado at Boulder
Global Ecology and Biogeography | Year: 2010

Aim: Latitudinal- and regional-scale studies of reptile diversity suggest a predominant temperature effect, unlike many other vertebrate richness patterns which tend to be highly correlated with both temperature and water variables. Here I examine montane gradients in reptile species richness with separate analyses of snakes and lizards from mountains around the world to assess a predominant temperature effect and three additional theories of diversity, including a temperature-water effect, the species-area effect and the mid-domain effect (MDE). Location: Twenty-five elevational gradients of reptile diversity from temperate, tropical and desert mountains in both hemispheres, spanning 10.3° N to 46.1° N. Methods: Elevational gradients in reptile diversity are based on data from the literature. Of the 63 data sets found or compiled, only those with a high, unbiased sampling effort were used in analyses. Twelve predictions and three interactions of diversity theory were tested using nonparametric statistics, linear regressions and multiple regression with the Akaike information criterion (AIC). Results: Reptile richness and, individually, snake and lizard richness on mountains followed four distinct patterns: decreasing, low-elevation plateaus, low-elevation plateaus with mid-elevation peaks, and mid-elevation peaks. Elevational reptile richness was most strongly correlated with temperature. The temperature effect was mediated by precipitation; reptile richness was more strongly tied to temperature on wet gradients than on arid gradients. Area was a secondary factor of importance, whereas the MDE was not strongly associated with reptile diversity on mountains. Main conclusions: Reptile diversity patterns on mountains did not follow the predicted temperature-water effect, as all diversity patterns were found on both wet and dry mountains. But the influence of precipitation on the temperature effect most likely reflects reptiles' use of radiant heat sources (sunning opportunities) that are more widespread on arid mountains than wet mountains due to lower humidity, sparser vegetation and less cloud cover across low and intermediate elevations. © 2010 Blackwell Publishing Ltd.

Crimaldi J.P.,University of Colorado at Boulder
Journal of Experimental Biology | Year: 2012

Broadcast-spawning benthic invertebrates synchronously release sperm and eggs from separate locations into the surrounding flow, whereupon the process depends on structured stirring by the flow field (at large scales), and sperm motility and taxis (at small scales) to bring the gametes together. The details of the relevant physical and biological aspects of the problem that result in successful and efficient fertilization are not well understood. This review paper includes relevant work from both the physical and biological communities to synthesize a more complete understanding of the processes that govern fertilization success; the focus is on the role of structured stirring on the dispersal and aggregation of gametes. The review also includes a summary of current trends and approaches for numerical and experimental simulations of broadcast spawning. © 2012. Published by The Company of Biologists Ltd.

Gray K.,University of North Carolina at Chapel Hill | Schein C.,University of North Carolina at Chapel Hill | Ward A.F.,University of Colorado at Boulder
Journal of Experimental Psychology: General | Year: 2014

When something is wrong, someone is harmed. This hypothesis derives from the theory of dyadic morality, which suggests a moral cognitive template of wrongdoing agent and suffering patient (i.e., victim). This dyadic template means that victimless wrongs (e.g., masturbation) are psychologically incomplete, compelling the mind to perceive victims even when they are objectively absent. Five studies reveal that dyadic completion occurs automatically and implicitly: Ostensibly harmless wrongs are perceived to have victims (Study 1), activate concepts of harm (Studies 2 and 3), and increase perceptions of suffering (Studies 4 and 5). These results suggest that perceiving harm in immorality is intuitive and does not require effortful rationalization. This interpretation argues against both standard interpretations of moral dumbfounding and domain-specific theories of morality that assume the psychological existence of harmless wrongs. Dyadic completion also suggests that moral dilemmas in which wrongness (deontology) and harm (utilitarianism) conflict are unrepresentative of typical moral cognition. © 2014 American Psychological Association.

Awerbuch J.J.,University of Colorado at Boulder
IEEE Transactions on Power Electronics | Year: 2013

The effect of voltage ripple on the power output of a photovoltaic panel is calculated and tested experimentally. Voltage ripple induces a much larger power reduction than would be predicted from a conventional small-signal model of the panels I-V characteristic, even with small ripple amplitude. A simple expression is provided to calculate power reduction from rms ripple voltage, for any ripple waveform shape. The effect of ripple on power output can be much more severe under nonuniform irradiance as can result from partial shading. The results are important for consideration of double-line-frequency ripple in single-phase inverters; © 1986-2012 IEEE.

Eisenberg M.,University of Colorado at Boulder
International Journal of Child-Computer Interaction | Year: 2013

The era of affordable 3D printing is clearly underway; indeed, the historical patterns of growth in 3D printing are, in many ways, strikingly similar to those associated with the growth of home computing in the late 1970's. One of the prominent areas of increased interest in 3D printing is in the realm of education: fabrication tools are becoming available to college undergraduates and high school students, and even to younger children. Accompanying this burgeoning growth, however, there is an acute need to consider the ways in which 3D printing should develop, as a technology, in order to accommodate the abilities and activities of youngsters. This paper discusses a number of technological challenges to be overcome in making 3D printing truly available to children over the next decade. The most prominent challenges described here include: (a) expanding the range of physical media available for printing, (b)incorporating ideas derived from "pick-and-place" mechanisms into 3D printing, (c) exploring methods for creating portable and ubiquitous printing devices, (d) creating tools for hand-customization and finishing of tangible printed objects, and (e) devising software techniques for specifying, altering, and combining 3D elements in the context of printing. By facing these challenges, we can provide children (and adults) with a remarkably powerful and expressive means for creating all sorts of personalized artifacts. © 2013 Elsevier B.V..

Shaw T.A.,Courant Institute of Mathematical Sciences | Perlwitz J.,University of Colorado at Boulder
Journal of Climate | Year: 2010

The impact of stratospheric model configuration on modeled planetary-scale waves in Northern Hemisphere winter is examined using the Canadian Middle Atmosphere Model (CMAM). The CMAM configurations include a high-lid (0.001 hPa) and a low-lid (10 hPa) configuration, which were each run with and without conservation of parameterized gravity wave momentum flux. The planetary wave structure, vertical propagation, and the basic state are found to be in good agreement with reanalysis data for the high-lid conservative configuration with the exception of the downward-propagating wave 1 signal. When the lid is lowered and momentum is conserved, the wave characteristics and basic state are not significantly altered, with the exception of the downward-propagating wave 1 signal, which is damped by the act of conservation. When momentum is not conserved, however, the wave amplitude increases significantly near the lid, and there is a large increase in both the upward- and downward-propagating wave 1 signals and a significant increase in the strength of the basic state. The impact of conserving parameterized gravity wave momentum flux is found to be much larger than that of the model lid height. The changes to the planetary waves and basic state significantly impact the stratosphere-troposphere coupling in the different configurations. In the low-lid configuration, there is an increase in wave-reflection-type coupling over zonal-mean-type coupling, a reduction in stratospheric sudden warming events, and an increase in the northern annular mode time scale. Conserving gravity wave momentum flux in the low-lid configuration significantly reduces these biases. © 2010 American Meteorological Society.

De Alwis S.P.,University of Colorado at Boulder
Journal of High Energy Physics | Year: 2010

We discuss the calculation of soft supersymmery breaking terms in type IIB string theoretic models in the Large Volume Scenario (LVS). The suppression of FCNC gives a lower bound on the size of the compactification volume. This leads to soft terms which are strongly suppressed relative to the gravitino mass so that the dominant contribution to the gaugino massses comes from the Weyl anomaly. The other soft terms are essentially generated by the renormalization group running from the string scale to the TeV scale. © 2010 SISSA.

Hallowell M.,University of Colorado at Boulder
Construction Management and Economics | Year: 2010

Every year the construction industry accounts for a disproportionate injury rate when compared to the all-industry average. In recent years, incident rates have declined as a result of improvements in safety management. While there is a great deal of knowledge regarding the safety management strategies of highly effective construction firms, little is known about the cost-effectiveness of these strategies. Interviews with 26 representatives of construction firms headquartered in the US were undertaken to quantify the cost of implementing common safety programme elements by: (1) quantifying cost for each element per US$1 million of project scope; and (2) determining the distribution of safety funding to each element. Using these cost data and effectiveness ratings from previous research, the cost-effectiveness of 13 safety programme elements was quantified. The results indicate that the most cost-effective safety programme elements are subcontractor selection and management and upper management support and commitment. Alternatively, the least cost-effective elements are the employment of a full-time safety manager and record-keeping. The information presented in this paper may be used by practitioners to direct resource investments, strategically select a subset of safety programme elements when resources are limited, and to justify additional resource investment in accident prevention. © 2010 Taylor & Francis.

Hallowell M.,University of Colorado at Boulder
Construction Management and Economics | Year: 2010

Unsafe worker actions contribute greatly to the frequency and severity of construction injuries. Recently, contractors have expressed concern with the high rate of injuries that occur when workers violate company safety policies. To enhance knowledge associated with this topic the following four objectives were targeted: (1) quantifying the current level of safety risk as perceived by construction workers; (2) quantifying the risk tolerance of workers and managers; (3) comparing the risk perceptions and tolerance of workers with managers; and (4) identifying factors that may affect one's risk tolerance. Fifty-one risk perceptions were gathered through interviews with managers and workers of nine different construction firms in the Pacific Northwest region of the United States. The results indicate that the level of current perceived risk is approximately five times higher than the tolerable risk value, workers are most dissatisfied with the frequency of high severity injuries, and there is a statistically significant difference in the risk tolerance between workers and managers. The findings presented can be used by project managers to increase awareness of risk tolerances, current areas where workers feel improvement is most needed, and for goal setting. © 2010 Taylor & Francis.

Matrosov S.Y.,University of Colorado at Boulder
Journal of Atmospheric and Oceanic Technology | Year: 2010

Different relations between rainfall rate R and polarimetric X-band radar measurables were evaluated using the radar, disdrometer, and rain gauge measurements conducted during the 4-month-long field experiment. The specific differential phase shift KDP-based estimators generally show less scatter resulting from variability in raindrop size distributions than with the power-based relations. These estimators depend on model assumptions about the drop aspect ratios and are not applicable for lighter rainfalls. The polynomial approximation for the mean drop aspect ratio provides R-KDP relations that result overall in good agreement between the radar retrievals of rainfall accumulations and estimates from surface rain gauges. The accumulation data obtained from power estimators that use reflectivity Zeh and differential reflectivity ZDR measurements generally exhibit greater standard deviations with respect to the gauge measurements. Unlike the phase-based estimators, the power-based estimators have an advantage of being "point" measurements, thus providing continuous quantitative precipitation estimation (QPE) for the whole area of radar coverage. The uncertainty in the drop shape model can result in errors in the attenuation and differential attenuation correction procedures. These errors might provide biases of radar-derived QPE for the estimators that use power measurements. Overall, for all considered estimators, the radar-based total rainfall accumulations showed biases less than 10% (relative to gauges). The standard deviations of radar retrievals were about 23% for the mean Zeh-R relation, 17%-22% for the KDP-based estimators (depending on the drop shape model), and about 20%-32% for different Zeh-ZDR-based estimators. Comparing ZDR-based retrievals of mean mass raindrop size Dm (for Dm > 1 mm) with disdrometer-derived values reveals an about 20%-25% relative standard deviation between these two types of estimates. © 2010 American Meteorological Society.

Willcutt E.G.,University of Colorado at Boulder
Neurotherapeutics | Year: 2012

This article describes a comprehensive meta-analysis that was conducted to estimate the prevalence of attention-deficit/hyperactivity disorder (ADHD), as defined by the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). A systematic literature review identified 86 studies of children and adolescents (N = 163,688 individuals) and 11 studies of adults (N = 14,112 individuals) that met inclusion criteria for the meta-analysis, more than half of which were published after the only previous meta-analysis of the prevalence of ADHD was completed. Although prevalence estimates reported by individual studies varied widely, pooled results suggest that the prevalence of DSM-IV ADHD is similar, whether ADHD is defined by parent ratings, teacher ratings, or a best estimate diagnostic procedure in children and adolescents (5.9-7.1 %), or by self-report measures in young adults (5.0 %). Analyses of diagnostic subtypes indicated that the predominantly inattentive type is the most common subtype in the population, but individuals with the combined type are more likely to be referred for clinical services. Additional research is needed to determine the etiology of the higher prevalence of ADHD in males than females and to clarify whether the prevalence of ADHD varies as a function of socioeconomic status or ethnicity. Finally, there were no significant prevalent differences between countries or regions of the world after controlling for differences in the diagnostic algorithms used to define ADHD. These results provide important support for the diagnostic validity of ADHD, and argue against the hypothesis that ADHD is a cultural construct that is restricted to the United States or any other specific culture. © 2012 The American Society for Experimental NeuroTherapeutics, Inc.

Klein F.,Woods Hole Oceanographic Institution | McCollom T.M.,University of Colorado at Boulder
Earth and Planetary Science Letters | Year: 2013

We injected a CO2-rich hydrous fluid of seawater chlorinity into an ongoing, mildly reducing (H2(a q) ≈ 3 mmol/kg) serpentinization experiment at 230 °C and 35 MPa to examine the changes in fluid chemistry and mineralogy during mineral carbonation. The chemistry of 11 fluid samples was measured, speciated, and compared with MgO-SiO2-H2O-CO2 (MSHC) phase equilibria to approximate the reaction pathway from serpentinization to carbonation. Although the overall system was in apparent disequilibrium, the speciated activities of dissolved silica (aSiO2(a q)) and carbon dioxide (aCO2(a q)) evolved roughly along MSHC equilibrium phase boundaries, indicative of 4 distinct mineral assemblages over time: (1) serpentine-brucite (± magnesite) before the injection, to (2) serpentine-talc-magnesite 2 h after the injection, to (3) quartz-magnesite (48 h after injection), and (4) metastable olivine-magnesite (623 h after injection) until the experiment was terminated. Inspection of the solid reaction products revealed the presence of serpentine, magnesite, minor talc, and magnetite, in addition to relict olivine. Although quartz was saturated over a short segment of the experiment, it was not found in the solid reaction products. A marked and rapid change in fluid chemistry suggests that serpentinization ceased and precipitation of magnesite initiated immediately after the injection. A sharp decrease in pH after the injection promoted the dissolution of brucite and olivine, which liberated SiO2(a q) and dissolved Mg. Dissolved Mg was efficiently removed from the solution via magnesite precipitation, whereas the formation of talc was relatively sluggish. This process accounts for an increase in aSiO2(a q) to quartz saturation shortly after the injection of the CO2-rich fluid. Molecular dihydrogen (H2(a q)) was generated during serpentinization of olivine by oxidation of ferrous iron before the injection; however, no additional H2(a q) was generated after the injection. Speciation calculations suggest a strong affinity for the formation of methane (CH4(a q)) at the expense of CO2(a q) and H2(a q) after the injection, but increased CH4(a q) formation was not observed. These findings suggest that kinetically fast mineral carbonation dominates over sluggish CH4(a q) formation in mildly reducing serpentinization systems affected by injection of CO2-rich fluids. © 2013 Elsevier B.V.

Buma B.,University of Colorado at Boulder
Environmental Monitoring and Assessment | Year: 2012

Forest disturbances around the world have the potential to alter forest type and cover, with impacts on diversity, carbon storage, and landscape composition. These disturbances, especially fire, are common and often large, making ground investigation of forest recovery difficult. Remote sensing offers a means to monitor forest recovery in real time, over the entire landscape. Typically, recovery monitoring via remote sensing consists of measuring vegetation indices (e.g., NDVI) or index-derived metrics, with the assumption that recovery in NDVI (for example) is a meaningful measure of ecosystem recovery. This study tests that assumption using MODIS 16-day imagery from 2000 to 2010 in the area of the Colorado's Routt National Forest Hinman burn (2002) and seedling density counts taken in the same area. Results indicate that NDVI is rarely correlated with forest recovery, and is dominated by annual and perennial forb cover, although topography complicates analysis. Utility of NDVI as a means to delineate areas of recovery or non-recovery are in doubt, as bootstrapped analysis indicates distinguishing power only slightly better than random. NDVI in revegetation analyses should carefully consider the ecology and seasonal patterns of the system in question. © Springer Science+Business Media B.V. 2011.

Topping M.W.,University of Colorado at Boulder | Topping M.W.,University of California at Los Angeles | Michael Shull J.,University of Cambridge
Astrophysical Journal | Year: 2015

We compute the production rate of photons in the ionizing Lyman continua (LyC) of H I (λ ≤ 912 Å), He I (λ ≤ 504 Å), and He II (λ ≤ 228 Å) using recent stellar evolutionary tracks coupled to a grid of non-LTE, line-blanketed WM-basic model atmospheres. The median LyC production efficiency is Q LyC = (6 ± 2) × 1060 LyC photons per MO of star formation (range [3.1-9.4] × 1060), corresponding to a revised calibration of 1053.3 ± 0.2 photons s-1 per MO yr-1. Efficiencies in the helium continua are photons and photons at solar metallicity and larger at low metallicity. The critical star formation rate needed to maintain reionization against recombinations at z = 7 is for fiducial values of the intergalactic medium (IGM) clumping factor C H = 3 and LyC escape fraction f esc = 0.2. The boost in LyC production efficiency is an important ingredient, together with metallicity, C H, and f esc, in assessing whether IGM reionization was complete by z = 7. Monte Carlo sampled spectra of coeval starbursts during the first 5 Myr have intrinsic flux ratios of F(1500)/F(900) = 0.4-0.5 and F(912-)/F(912+) = 0.4-0.7 in the far-UV (1500 Å), the LyC (900 Å), and at the Lyman edge (912 Å). These ratios can be used to calibrate the LyC escape fractions in starbursts. © 2015. The American Astronomical Society. All rights reserved..

Jiang Y.,Qualcomm | Varanasi M.K.,University of Colorado at Boulder | Li J.,University of Florida
IEEE Transactions on Information Theory | Year: 2011

This paper presents an in-depth analysis of the zero forcing (ZF) and minimum mean squared error (MMSE) equalizers applied to wireless multiinput multioutput (MIMO) systems with no fewer receive than transmit antennas. In spite of much prior work on this subject, we reveal several new and surprising analytical results in terms of output signal-to-noise ratio (SNR), uncoded error and outage probabilities, diversity-multiplexing (D-M) gain tradeoff and coding gain. Contrary to the common perception that ZF and MMSE are asymptotically equivalent at high SNR, we show that the output SNR of the MMSE equalizer (conditioned on the channel realization) is ρmmse = ρzf+ηsnr, where ρzf is the output SNR of the ZF equalizer and that the gap ηsnr is statistically independent of ρzf and is a nondecreasing function of input SNR. Furthermore, as snr → ∞, ηsnr converges with probability one to a scaled F random variable. It is also shown that at the output of the MMSE equalizer, the interference-to-noise ratio (INR) is tightly upper bounded by ηsnr/ρzf. Using the decomposition of the output SNR of MMSE, we can approximate its uncoded error, as well as outage probabilities through a numerical integral which accurately reflects the respective SNR gains of the MMSE equalizer relative to its ZF counterpart. The ∈-outage capacities of the two equalizers, however, coincide in the asymptotically high SNR regime. We also provide the solution to a long-standing open problem: applying optimal detection ordering does not improve the D-M tradeoff of the vertical Bell Labs layered Space-Time (V-BLAST) architecture. It is shown that optimal ordering yields a SNR gain of 10log10 N dB in the ZF-V-BLAST architecture (where N is the number of transmit antennas) whereas for the MMSE-V-BLAST architecture, the SNR gain due to ordered detection is even better and significantly so. © 2011 IEEE.

Chen G.,University of Colorado at Boulder | Balents L.,University of California at Santa Barbara
Physical Review Letters | Year: 2013

Motivated by the recent indications of ferromagnetism in transition metal oxide heterostructures, we propose a possible mechanism to generate ferromagnetism for itinerant t2g systems in two spatial dimensions that does not rely on the coupling between local moments and conduction electrons. We particularly emphasize the orbital nature of different bands and show that when the Fermi level lies near the bottom of the upper bands, a nonperturbative interaction effect due to the quasi-one-dimensional nature of the upper bands may drive a transition to a state in which the upper bands are ferromagnetically polarized. In the quasi-one-dimensional limit, the full thermodynamics may be obtained exactly. We discuss the connection between our mechanism with several itinerant t2g systems that may have ferromagnetic instabilities. © 2013 American Physical Society.

Bowman K.,Jet Propulsion Laboratory | Henze D.K.,University of Colorado at Boulder
Geophysical Research Letters | Year: 2013

Quantifying the dependence of ozone direct radiative forcing (DRF) on the mixture and spatial distribution of precursor emissions is a key step towards understanding the impact of air quality standards on climate. We use here a combination of satellite observations of ozone and its radiative effect in conjunction with an adjoint chemical transport model to determine the ozone DRF due to global, anthropogenic NOx, CO, and non-methane hydrocarbons (NMHC) emissions regionally at 2° × 2.5° regions resolution. We show that 8% of the ozone DRF from the sum of all these emissions can be attributed to 15 regions, which are predominantly located in China and the United States (US). To achieve an equivalent reduction in ozone DRF, necessary emission reductions for each precursor vary intra-continentally by a factor of 3-10 and globally by over an order of magnitude. The contribution of NOx emissions to ozone DRF relative to CO and NMHC emissions within individual regions varies globally by nearly a factor of two. Key Points: Attribution of ozone radiative forcing to high resolution emissions 8% of the ozone DRF from global emissions can be attributed to 15 regions Emission reductions vary intra-continentally by 3-7 and globally by over 10. © 2012. American Geophysical Union.

Rast M.P.,University of Colorado at Boulder | Pinton J.-F.,Ecole Normale Superieure de Lyon
Physical Review Letters | Year: 2011

The mixing properties of turbulent flows are, at first order, related to the dynamics of separation of particle pairs. Scaling laws for the evolution in time of the mean distance between particle pairs r2(t) have been proposed since the pioneering work of Richardson. We analyze a model which shares some features with 3D experimental and numerical turbulence, and suggest that pure scaling laws are only subdominant. The dynamics is dominated by a very wide distribution of "delay times" td, the duration for which particle pairs remain together before their separation increases significantly. The delay time distribution is exponential for small separations and evolves towards a flat distribution at large separations. The observed r2(t) behavior is best understood as an average over separations that individually follow the Richardson-Obukhov scaling, r2 t3, but each only after a fluctuating time delay td, where td is distributed uniformly. © 2011 American Physical Society.

Mccain C.M.,University of Colorado at Boulder | Colwell R.K.,University of Connecticut
Ecology Letters | Year: 2011

Mountains are centres of global biodiversity, endemism and threatened species. Elevational gradients present opportunities for species currently living near their upper thermal limits to track cooler temperatures upslope in warming climates, but only if changes in precipitation are sufficiently in step with temperature. We model local population extirpation risk for a range of temperature and precipitation scenarios over the next 100years for 16848 vertebrate species populations distributed along 156 elevational gradients. Average population extirpation risks due to warming alone were <5%, but increased 10-fold, on average, when changes in precipitation were also considered. Under the driest scenarios (minimum predicted precipitation), local extirpation risks increased sharply (50-60%) and were especially worrisome for hydrophilic amphibians and montane Latin America (c. 80%). Realistic assessment of risks urgently requires improved monitoring of precipitation, better regional precipitation models and more research on the effects of changes in precipitation on montane distributions. © 2011 Blackwell Publishing Ltd/CNRS.

McCollom T.M.,University of Colorado at Boulder
Geochimica et Cosmochimica Acta | Year: 2013

Laboratory experiments were conducted to observe the effect of iron oxide and sulfide minerals on decomposition reactions of norvaline, a representative of a group of alkyl-α-amino acids observed in meteorites and prebiotic synthesis experiments. The primary products observed during heating of aqueous solutions of norvaline at temperatures of 156-186°C in the presence of minerals included CO2, NH3, butyric acid, and valeric acid. The products indicated that norvaline predominantly decomposed by a combination of pathways that included both decarboxylation followed rapidly by oxidative deamination (norvaline→butanamide+CO2→butyric acid+NH3) and deamination directly to valeric acid (norvaline→valeric acid+NH3). An experiment performed with alanine under similar conditions showed it decomposed by analogous reactions that produced acetic and propionic acids along with CO2 and NH3. For both amino acids, the presence of minerals accelerated decomposition rates as well as altered the final products of reaction, when compared with decomposition in the absence of mineral substrates. In addition, decomposition of norvaline was found to proceed much faster in the presence of the mineral assemblage hematite-magnetite-pyrite (HMP) than with the assemblage pyrite-pyrrhotite-magnetite (PPM), a trend that has been observed for several other organic compounds. The influence of minerals on decomposition reactions of these amino acids appears to be attributable to a combination of surface catalysis and production of dissolved sulfur compounds. Overall, the results indicate that minerals may exert a substantial influence on amino acid stability in many geologic environments, and emphasize the need to consider the impact of minerals when evaluating the lifetimes and decomposition rates of amino acids in terrestrial and planetary systems. Estimated half-lives for alkyl-α-amino acids based on the experimental results indicate that moderately hot hydrothermal environments (<∼100°C) would have been the most favorable for accumulation of these amino acids in the early solar system, and that the predominance of alkyl-α-amino acids in some meteorites may only be compatible with temperature remaining below about 60°C following their formation. © 2012 Elsevier Ltd.

McCollom T.M.,University of Colorado at Boulder | Seewald J.S.,Woods Hole Oceanographic Institution
Elements | Year: 2013

The process of serpentinization creates strongly reducing conditions and produces fluids that are highly enriched in molecular hydrogen and methane. Some microorganisms are able to exploit these compounds to gain metabolic energy and to generate biomass, leading to the development of biological communities based on chemical energy rather than photosynthesis. The abundance of chemical energy and favorable conditions for organic synthesis make serpentinites a strong candidate for the site of the origin of life on Earth, as well as a prime target in the search for life elsewhere in our Solar System.

Crow D.A.,University of Colorado at Boulder
Policy Studies Journal | Year: 2010

Research on the process of policy change often involves a direct or indirect analysis of the roles of policy entrepreneurs and the mass media. In Colorado, beginning in 1998, twelve communities decided to obtain water rights for recreational in-channel purposes such as kayaking and whitewater rafting. These water rights stirred political controversy within some communities in Colorado related to spending public money, appropriate uses of water, and the role of recreation in local economies. Using a comparative case study research method, this research analyzes the role that policy entrepreneurs and local media coverage of recreational water rights played in initiating policy change in local communities. The most critical finding from this study is that in communities where citizens acted as policy entrepreneurs there was more controversy, less positive media coverage, and more media coverage early in the process. This case contradicts the assumption that local media coverage helps to highlight policy problems within communities. It supports the idea that experts wield higher levels of influence than citizens in promoting policy agendas. © 2010 Policy Studies Organization.

Mendis D.A.,University of California at San Diego | Horanyi M.,University of Colorado at Boulder
Reviews of Geophysics | Year: 2013

Despite their small masses, comets have played an extraordinary role in enhancing our understanding of cosmic physics. It was the calculation of comet Halley's orbit and the successful prediction of its return in 1758 that firmly established the correctness of Newton's law of universal gravitation. It was the morphology of the dusty tails of comets that provided the earliest information of the nature of the interaction of solar electromagnetic radiation with dust, and it was the orientation and structure of the plasma tails of comets that led to the discovery of the solar wind. More recently, the role of the changing dusty plasma environments of comets as natural space laboratories for the study of dust-plasma interactions, and their physical and dynamical consequences, has been recognized. The forthcoming Rosetta-Philae rendezvous and lander mission will provide a unique opportunity to revisit the entire range of earlier observations of dusty plasma phenomena in a single comet, as it moves around the Sun. In this topical review, motivated by the Rosetta mission, we discuss the varying modes of interaction of the comet as it approaches the Sun, and the different dusty plasma phenomena that are expected in each case, drawing on the earlier observations, including their interpretations and prevailing open questions. Key PointsComets are a primary example where dusty plasma processes are at work.Rosetta is expected to observe dusty plasma phenomena.The interaction with the solar wind will change with distance from the Sun. ©2013. American Geophysical Union. All Rights Reserved.

Seals D.R.,University of Colorado at Boulder
Journal of Physiology | Year: 2013

The term 'translational research' was coined 20 years ago and has become a guiding influence in biomedical research. It refers to a process by which the findings of basic research are extended to the clinical research setting (bench to bedside) and then to clinical practice and eventually health policy (bedside to community). It is a dynamic, multidisciplinary research approach. The concept of translational physiology applies the translational research model to the physiological sciences. It differs from the traditional areas of integrative and clinical physiology by its broad investigative scope of basic research to community health. Translational physiology offers exciting opportunities, but presently is under-developed and -utilized. A key challenge will be to expand physiological research by extending investigations to communities of patients and healthy (or at risk) individuals. This will allow bidirectional physiological investigation throughout the translational continuum: basic research observations can be studied up to the population level, and mechanisms can be assessed by 'reverse translation' in clinical research settings and preclinical models based on initial observations made in populations. Examples of translational physiology questions, experimental approaches, roadblocks and strategies for promotion are discussed. Translational physiology provides a novel framework for physiology programs and an investigational platform for physiologists to study function from molecular events to public health. It holds promise for enhancing the completeness and societal impact of our work, while further solidifying the critical role of physiology in the biomedical research enterprise. © 2013 The Physiological Society.

Perkins T.T.,U.S. National Institute of Standards and Technology | Perkins T.T.,University of Colorado at Boulder
Annual Review of Biophysics | Year: 2014

Single-molecule optical-trapping experiments are now resolving the smallest units of motion in biology, including 1-base-pair steps along DNA. This review initially concentrates on the experimental problems with achieving 1-Å instrumental stability and the technical advances necessary to overcome these issues. Instrumental advances are complemented by insights in optical-trapping geometry and single-molecule motility assay development to accommodate the elasticity of biological molecules. I then discuss general issues in applying this measurement capability in the context of precision measurements along DNA. Such enhanced optical-trapping assays are revealing the fundamental step sizes of increasingly complex enzymes, as well as informative pauses in enzymatic motion. This information in turn is providing mechanistic insight into kinetic pathways that are difficult to probe by traditional assays. I conclude with a brief discussion of emerging techniques and future directions.Copyright © 2014 by Annual Reviews. All rights reserved.

Nowotny K.M.,University of Colorado at Boulder
Addictive Behaviors | Year: 2015

Background: Research has documented racial and ethnic disparities in utilization, access, continuity, and quality of care for psychiatric disorders including treatment for substance use disorders among those with similar need in the general community. Currently, the extent of racial and ethnic disparities in treatment within U.S. correctional facilities is unknown. Methods: This study examines race/ethnic disparities in treatment for drug dependent inmates using the 2004 Survey of Inmates in State Correctional Facilities. Fixed effects logistic regression is used to analyze treatment outcomes for 5180 inmates housed within 286 prisons. The analysis accounts for differences in background characteristics (i.e., age, gender, marital status, foreign born status, veteran status), socioeconomic characteristics (i.e., education, employment prior to incarceration), mental health (i.e., diagnosis with a serious mental illness), and incarceration experiences (i.e., current conviction, previous incarceration episodes, time served, additional sentencing requirements, external social support, disciplinary violations). Results: The findings identify a remarkable unmet need among drug dependent inmates in that less than one-half of drug dependent inmates had received any type of treatment in prison at the time of the interview with the most common treatment type being self-help groups. Compared to whites, drug dependent Latino inmates have significantly lower odds of utilizing treatment, yet there are no significant black--white disparities found. Conclusion: The current study suggests that treatment for drug dependent inmates needs to be expanded to include clinically or medically based treatment since the failure to address addictions in the criminal legal system has been identified as the single most significant reason for rearrest and recidivism once released. © 2014.

Bradley A.R.,University of Colorado at Boulder
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

A new form of SAT-based symbolic model checking is described. Instead of unrolling the transition relation, it incrementally generates clauses that are inductive relative to (and augment) stepwise approximate reachability information. In this way, the algorithm gradually refines the property, eventually producing either an inductive strengthening of the property or a counterexample trace. Our experimental studies show that induction is a powerful tool for generalizing the unreachability of given error states: it can refine away many states at once, and it is effective at focusing the proof search on aspects of the transition system relevant to the property. Furthermore, the incremental structure of the algorithm lends itself to a parallel implementation. © 2011 Springer-Verlag.

Wyatt M.G.,University of Colorado at Boulder | Curry J.A.,Georgia Institute of Technology
Climate Dynamics | Year: 2014

A hypothesized low-frequency climate signal propagating across the Northern Hemisphere through a network of synchronized climate indices was identified in previous analyses of instrumental and proxy data. The tempo of signal propagation is rationalized in terms of the multidecadal component of Atlantic Ocean variability-the Atlantic Multidecadal Oscillation. Through multivariate statistical analysis of an expanded database, we further investigate this hypothesized signal to elucidate propagation dynamics. The Eurasian Arctic Shelf-Sea Region, where sea ice is uniquely exposed to open ocean in the Northern Hemisphere, emerges as a strong contender for generating and sustaining propagation of the hemispheric signal. Ocean-ice-atmosphere coupling spawns a sequence of positive and negative feedbacks that convey persistence and quasi-oscillatory features to the signal. Further stabilizing the system are anomalies of co-varying Pacific-centered atmospheric circulations. Indirectly related to dynamics in the Eurasian Arctic, these anomalies appear to negatively feed back onto the Atlantic's freshwater balance. Earth's rotational rate and other proxies encode traces of this signal as it makes its way across the Northern Hemisphere. © 2013 Springer-Verlag Berlin Heidelberg.

Nievinski F.G.,Sao Paulo State University | Larson K.M.,University of Colorado at Boulder
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

Snowpacks provide reservoirs of freshwater. The amount stored and how fast it is released by melting are vital information for both scientists and water supply managers. GPS multipath reflectometry (GPS-MR) is a new technique that can be used to measure snow depth. Signal-to-noise ratio data collected by GPS instruments exhibit peaks and troughs as coherent direct and reflected signals go in and out of phase. These interference fringes are used to retrieve the unknown land surface characteristics. In this two-part contribution, a forward/inverse approach is offered for GPS-MR of snow depth. Part I starts with the physically based forward model utilized to simulate the coupling of the surface and antenna responses. A statistically rigorous inverse model is presented and employed to retrieve parameter corrections responsible for observation residuals. The unknown snow characteristics are parameterized, the observation/parameter sensitivity is illustrated, the inversion performance is assessed in terms of its precision and its accuracy, and the dependence of model results on the satellite direction is quantified. The latter serves to indicate the sensing footprint of the reflection. © 1980-2012 IEEE.

Blumenthal T.,University of Colorado at Boulder
Current Biology | Year: 2011

Some genes in the candidate early-branching eukaryote Giardia lamblia occur in separate pieces, transcribed from non-contiguous chromosomal locations. The pre-mRNAs from the separate pieces apparently find each other by regions of complementarity and are subsequently spliced together by the spliceosome. Could genes in pieces, transcribed into separate pre-mRNAs, have been an early feature of spliceosomal evolution? © 2011 Elsevier Ltd.

Wu C.,Duke University | Linden K.G.,University of Colorado at Boulder
Water Research | Year: 2010

The phototransformation of two organophosphorus pesticides, parathion and chlorpyrifos, by hydroxyl radicals and carbonate radicals in aqueous solution were studied. Addition of hydrogen peroxide increased the UV degradation rates of both pesticides and data were simulated through kinetic modeling. The second-order rate constants of parathion and chlorpyrifos with hydroxyl radical were determined to be 9.7 ± 0.5 × 109 and 4.9 ± 0.1 × 109 M-1 s-1, respectively. The presence of bi/carbonate ions reduced the pesticide degradation rates via scavenging of hydroxyl radical but the formation of carbonate radical also contributed to the degradation of the pesticides with second-order reaction rate constants of 2.8 ± 0.2 × 106 and 8.8 ± 0.4 × 106 M-1 s-1 for parathion and chlorpyrifos, respectively. The dual roles of bicarbonate ion in UV/H2O2 treatment systems, i.e., scavenging of hydroxyl radicals and formation of carbonate radicals, were examined and discussed using a simulative kinetic model. The transformation of pesticides by carbonate radicals at environmentally relevant bi/carbonate concentrations was shown to be a significant contributor to the environmental fate of the pesticides and it reshaped the general phototransformation kinetics of both pesticides in UV/H2O2 systems. © 2010 Elsevier Ltd.

Gustafson K.,University of Colorado at Boulder
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2016

Enlarging upon experiments and analysis that I did jointly some years ago, in which artificial (symbolic, neural-net and pattern) learning and generalization were compared with that of humans, I will emphasize the role of imagination (or lack thereof) in artificial, human and quantum cognition and decision-making processes. Then I will look in more detail at some of the 'engineering details' of its implementation (or lack thereof) in each of these settings. In other words, the question posed is: What is actually happening? For example, we previously found that humans overwhelmingly seek, create or imagine context in order to provide meaning when presented with abstract, apparently incomplete, contradictory or otherwise untenable decision-making situations. Humans are intolerant of contradiction and will greatly simplify to avoid it. They can partially correlate but do not average. Human learning is not Boolean. These and other human reasoning properties will then be taken to critique how well artificial intelligence methods and quantum mechanical modelling might compete with them in decision-making tasks within psychology and economics. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Kassoy D.R.,University of Colorado at Boulder
Combustion Theory and Modelling | Year: 2014

Systematic asymptotic methods are applied to the compressible conservation and state equations for a reactive gas, including transport terms, to develop a rational thermomechanical formulation for the ignition of a chemical reaction following time-resolved, spatially distributed thermal energy addition from an external source into a finite volume of gas. A multi-parameter asymptotic analysis is developed for a wide range of energy deposition levels relative to the initial internal energy in the volume when the heating timescale is short compared to the characteristic acoustic timescale of the volume. Below a quantitatively defined threshold for energy addition, a nearly constant volume heating process occurs, with a small but finite internal gas expansion Mach number. Very little added thermal energy is converted to kinetic energy. The gas expelled from the boundary of the hot, high-pressure spot is the source of mechanical disturbances (acoustic and shock waves) that propagate away into the neighbouring unheated gas. When the energy addition reaches the threshold value, the heating process is fully compressible with a substantial internal gas expansion Mach number, the source of blast waves propagating into the unheated environmental gas. This case corresponds to an extremely large non-dimensional hot-spot temperature and pressure. If the former is sufficiently large, a high activation energy chemical reaction is initiated on the short heating timescale. This phenomenon is in contrast to that for more modest levels of energy addition, where a thermal explosion occurs only after the familiar extended ignition delay period for a classical high activation reaction. Transport effects, modulated by an asymptotically small Knudsen number, are shown to be negligible unless a local gradient in temperature, concentration or velocity is exceptionally large. © 2013 Taylor & Francis.

Van Der Schee W.,University Utrecht | Romatschke P.,University of Colorado at Boulder | Pratt S.,Michigan State University
Physical Review Letters | Year: 2013

We present a fully dynamical simulation of central nuclear collisions around midrapidity at LHC energies. Unlike previous treatments, we simulate all phases of the collision, including the equilibration of the system. For the simulation, we use numerical relativity solutions to anti-de Sitter space/conformal field theory for the preequilibrium stage, viscous hydrodynamics for the plasma equilibrium stage, and kinetic theory for the low-density hadronic stage. Our preequilibrium stage provides initial conditions for hydrodynamics, resulting in sizable radial flow. The resulting light particle spectra reproduce the measurements from the ALICE experiment at all transverse momenta. © 2013 American Physical Society.

Pouquet A.,University of Colorado at Boulder | Pouquet A.,Computational and Information Systems Laboratory | Marino R.,Computational and Information Systems Laboratory
Physical Review Letters | Year: 2013

The ocean and the atmosphere, and hence the climate, are governed at large scale by interactions between pressure gradient and Coriolis and buoyancy forces. This leads to a quasigeostrophic balance in which, in a two-dimensional-like fashion, the energy injected by solar radiation, winds, or tides goes to large scales in what is known as an inverse cascade. Yet, except for Ekman friction, energy dissipation and turbulent mixing occur at a small scale implying the formation of such scales associated with breaking of geostrophic dynamics through wave-eddy interactions or frontogenesis, in opposition to the inverse cascade. Can it be both at the same time? We exemplify here this dual behavior of energy with the help of three-dimensional direct numerical simulations of rotating stratified Boussinesq turbulence. We show that efficient small-scale mixing and large-scale coherence develop simultaneously in such geophysical and astrophysical flows, both with constant flux as required by theoretical arguments, thereby clearly resolving the aforementioned contradiction. © 2013 American Physical Society.

Natu S.S.,Cornell University | Hazzard K.R.A.,University of Colorado at Boulder | Mueller E.J.,Cornell University
Physical Review Letters | Year: 2011

We study the time scales for adiabaticity of trapped cold bosons subject to a time-varying lattice potential using a dynamic Gutzwiller mean-field theory. We explain apparently contradictory experimental observations by demonstrating a clear separation of time scales for local dynamics (∼ms) and global mass redistribution (∼1s). We provide a simple explanation for the short and fast time scales, finding that while density or energy transport is dominated by low energy phonons, particle-hole excitations set the adiabaticity time for fast ramps. We show how mass transport shuts off within Mott-insulator domains, leading to a chemical potential gradient that fails to equilibrate on experimental time scales. © 2011 American Physical Society.

Whisman M.A.,University of Colorado at Boulder | Baucom D.H.,University of North Carolina at Chapel Hill
Clinical Child and Family Psychology Review | Year: 2012

Relationship functioning and individual mental health and well-being are strongly associated with one another. In this article, we first review the cross-sectional and longitudinal associations between relationship discord and various types of psychopathology, We then review findings suggesting that relationship discord is associated with poorer outcome for individual-based treatments for psychopathology and that, generally, relationship discord does not improve following individual-based treatments for psychopathology. Finally, we present a model for conceptualizing work with couples in which one partner has a psychiatric disorder and review the efficacy of couple-based interventions in the treatment for psychiatric disorders, with a focus on substance-related, mood, and anxiety disorders. © 2011 Springer Science+Business Media, LLC.

Bowman C.N.,University of Colorado at Boulder | Kloxin C.J.,50 Academy Street
Angewandte Chemie - International Edition | Year: 2012

Smart and responsive: Reversible transesterification reactions were recently used within a polymer network to create a covalently crosslinked material that is capable of being processed as well as mended and recycled. This work is highlighted in the context of the covalent adaptable network approach and illustrates the bond cleavage and reformation mechanism that enable the adaptability of these materials (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Krishnamachari R.T.,Risk Focus Inc. | Varanasi M.K.,University of Colorado at Boulder
IEEE Transactions on Signal Processing | Year: 2013

This paper analyzes multiple-input, multiple-output interference channels where each receiver knows its channels from all the transmitters and feeds back this information using a limited number of bits to all the other terminals. It is shown that as long as the feedback bit rate scales sufficiently fast with the signal-to-noise ratio, the transmitters can use an interference alignment strategy by treating the quantized channel estimates as being perfect to achieve the sum degrees of freedom of the interference channel attainable with perfect and global channel state information. A tradeoff between the feedback rate and the achievable degrees of freedom is established by showing that a slower scaling of feedback rate for any one user leads to commensurately fewer degrees of freedom for that user alone. It is then shown that under the same fixed transmission strategy but with random quantization, the above mentioned sufficient condition on the feedback scaling rate to attain a given sum degrees of freedom (up to the maximum attainable) is also necessary in this setting. © 1991-2012 IEEE.

Flowers R.M.,University of Colorado at Boulder | Kelley S.A.,New Mexico Institute of Mining and Technology
Geochimica et Cosmochimica Acta | Year: 2011

New apatite (U-Th)/He (AHe) and apatite fission-track (AFT) data were acquired for cratonic basement samples from an 80. m span of drillcore in northeastern Kansas. The short depth interval over which the samples were collected indicates that they should have undergone thermal histories that would be indistinguishable using low temperature thermochronometry techniques. Individual AHe dates from four samples range from 99 to 464. Ma. Three samples yield dates <300. Ma that display a correlation with apatite eU (9-34. ppm) and a weaker correlation with grain size. eU concentration maps of apatites from these samples reveal low to moderate zonation in eU. Results for a fourth sample are characterized by dates >300. Ma, higher eU (39-113. ppm), and substantial data dispersion uncorrelated with eU and grain size. These apatites have strong and variable eU zonation. AFT dates for five samples range from 242 to 291. Ma. The sample with the highest eU apatites and oldest AHe dates yields the youngest AFT results. These results are " inverted" , with AHe dates distinctly older than the corresponding AFT date.We explore both the causes of data dispersion and the overall compatibility of this cratonic dataset. We find that geologically reasonable thermal histories can (1) explain the distribution of the moderate eU AHe data when accounting for the influence of radiation damage, grain size, and eU zonation on apatite He diffusivity, (2) reproduce the observed dispersion in the high eU AHe data when using a viable range of eU zonation and grain size, and (3) explain the AFT data for the same samples. The AHe and AFT data are mutually consistent, and viable thermal histories successfully predict the observed pattern of older AHe than AFT dates for the high eU apatites. Together these results suggest that appropriately accounting for the known controls on apatite He diffusivity can explain the observed dispersion and " inverted" AHe and AFT results in some thermochronometry datasets. A range of AHe dates should be especially common in cratonic data, because small differences in apatite He diffusivity are amplified by the thermal histories that typify cratonic settings. We use these results to develop some guidelines for interpreting dispersed AHe datasets. First, date-eU and date-grain size correlations should be evaluated, and if these patterns occur they can be used to better resolve the thermal history. Second, for samples that yield inexplicably large dispersion of AHe dates uncorrelated with eU and crystal size, the appropriate strategy is either to reject these samples from the suite used for thermal history interpretation or to acquire additional data to help decipher the significance of the age distribution. © 2011 Elsevier Ltd.

Cazalilla M.A.,National Tsing Hua University | Cazalilla M.A.,Donostia International Physics Center | Rey A.M.,University of Colorado at Boulder
Reports on Progress in Physics | Year: 2014

We review recent experimental and theoretical progress on ultracold alkaline-earth Fermi gases with emergent SU(N) symmetry. Emphasis is placed on describing the ground-breaking experimental achievements of recent years. The latter include (1) the cooling to below quantum degeneracy of various isotopes of ytterbium and strontium, (2) the demonstration of optical Feshbach resonances and the optical Stern-Gerlach effect, (3) the realization of a Mott insulator of 173Yb atoms, (4) the creation of various kinds of Fermi-Bose mixtures and (5) the observation of many-body physics in optical lattice clocks. On the theory side, we survey the zoo of phases that have been predicted for both gases in a trap and loaded into an optical lattice, focusing on two and three dimensional systems. We also discuss some of the challenges that lie ahead for the realization of such phases such as reaching the temperature scale required to observe magnetic and more exotic quantum orders. The challenge of dealing with collisional relaxation of excited electronic levels is also discussed. © 2014 IOP Publishing Ltd.

Hoenger A.,University of Colorado at Boulder
Protoplasma | Year: 2014

Cryo-electron microscopy techniques and computational 3-D reconstruction of macromolecular assemblies are tightly linked tools in modern structural biology. This symbiosis has produced vast amounts of detailed information on the structure and function of biological macromolecules. Typically, one of two fundamentally different strategies is used depending on the specimens and their environment. A: 3-D reconstruction based on repetitive and structurally identical unit cells that allow for averaging, and B: tomographic 3-D reconstructions where tilt-series between approximately ±60 and ±70° at small angular increments are collected from highly complex and flexible structures that are beyond averaging procedures, at least during the first round of 3-D reconstruction. Strategies of group A are averaging-based procedures and collect large number of 2-D projections at different angles that are computationally aligned, averaged together, and back-projected in 3-D space to reach a most complete 3-D dataset with high resolution, today often down to atomic detail. Evidently, success relies on structurally repetitive particles and an aligning procedure that unambiguously determines the angular relationship of all 2-D projections with respect to each other. The alignment procedure of small particles may rely on their packing into a regular array such as a 2-D crystal, an icosahedral (viral) particle, or a helical assembly. Critically important for cryo-methods, each particle will only be exposed once to the electron beam, making these procedures optimal for highest-resolution studies where beam-induced damage is a significant concern. In contrast, tomographic 3-D reconstruction procedures (group B) do not rely on averaging, but collect an entire dataset from the very same structure of interest. Data acquisition requires collecting a large series of tilted projections at angular increments of 1-2° or less and a tilt range of ±60° or more. Accordingly, tomographic data collection exposes its specimens to a large electron dose, which is particularly problematic for frozen-hydrated samples. Currently, cryo-electron tomography is a rapidly emerging technology, on one end driven by the newest developments of hardware such as super-stabile microscopy stages as well as the latest generation of direct electron detectors and cameras. On the other end, success also strongly depends on new software developments on all kinds of fronts such as tilt-series alignment and back-projection procedures that are all adapted to the very low-dose and therefore very noisy primary data. Here, we will review the status quo of cryo-electron microscopy and discuss the future of cellular cryo-electron tomography from data collection to data analysis, CTF-correction of tilt-series, post-tomographic sub-volume averaging, and 3-D particle classification. We will also discuss the pros and cons of plunge freezing of cellular specimens to vitrified sectioning procedures and their suitability for post-tomographic volume averaging despite multiple artifacts that may distort specimens to some degree. © 2014 The Author(s).

Spielman S.E.,University of Colorado at Boulder
Cartography and Geographic Information Science | Year: 2014

Collective intelligence is the idea that under the right circumstances collections of individuals are smarter than even the smartest individuals in the group, that is a group has an "intelligence" that is independent of the intelligence of its members. The ideology of collective intelligence undergirds much of the enthusiasm about the use of "volunteered" or crowd-sourced geographic information. Literature from a variety of fields makes clear that not all groups possess collective intelligence, this article identifies four pre-conditions for the emergence of collective intelligence and then examines the extent to which collectively generated mapping systems satisfy these conditions. However, the "intelligence" collectively generated maps is hard to assess because there are two difficult to reconcile perspectives on map quality-the credibility perspective and the accuracy perspective. Much of the current literature on user-generated maps focuses on assessing the quality of individual contributions. However, because user-generated maps are complex social systems and because the quality of a contribution is difficult to assess this strategy may not yield an "intelligent" end product. The existing literature on collective intelligence suggests that the structure of groups is more important than the intelligence of group members. Applying this idea to user-generated maps suggests that systems should be designed to foster conditions known to produce collective intelligence rather than privileging particular contributions/contributors. The article concludes with some design recommendations and by considering the implications of collectively generated maps for both expert knowledge and traditional state sponsored mapping programs. © 2014 Cartography and Geographic Information Society.

McCollom T.M.,University of Colorado at Boulder
Annual Review of Earth and Planetary Sciences | Year: 2013

The synthesis of amino acids in the Miller-Urey spark-discharge experiments in the early 1950s inspired a strong interest in experimental studies of prebiotic organic chemistry that continues today. Over the years, many of the basic building blocks of life as we know it have been synthesized in the laboratory from simple ingredients, including amino acids, sugars, nucleobases, and membrane-forming lipids. Questions remain, however, concerning whether the conditions that allow synthesis of these compounds in the laboratory accurately simulate those that might have been present on the early Earth, and a closer convergence between plausible prebiotic conditions and laboratory simulations remains a challenge for experimentalists. © Copyright ©2013 by Annual Reviews. All rights reserved.

Giacomazzo B.,U.S. National Institute of Standards and Technology | Perna R.,University of Colorado at Boulder
Astrophysical Journal Letters | Year: 2013

By performing fully general relativistic magnetohydrodynamic simulations of binary neutron star mergers, we investigate the possibility that the end result of the merger is a stable magnetar. In particular, we show that, for a binary composed of two equal-mass neutron stars (NSs) of gravitational mass M ∼ 1.2 MȮ and equation of state similar to Shen et al. at high densities, the merger product is a stable NS. Such NS is found to be differentially rotating and ultraspinning with spin parameter J/M2 ∼ 0.86, where J is its total angular momentum, and it is surrounded by a disk of ≈0.1 MȮ. While in our global simulations the magnetic field is amplified by about two orders of magnitude, local simulations have shown that hydrodynamic instabilities and the onset of the magnetorotational instability could further increase the magnetic field strength up to magnetar levels. This leads to the interesting possibility that, for some NS mergers, a stable and magnetized NS surrounded by an accretion disk could be formed. We discuss the impact of these new results for the emission of electromagnetic counterparts of gravitational wave signals and for the central engine of short gamma-ray bursts. © 2013. The American Astronomical Society. All rights reserved.

Objects and structures gravitationally decoupled from the Hubble expansion will appear to shrink in angular size as the universe expands. Observations of extragalactic proper motions can thus directly reveal the cosmic expansion. Relatively static structures such as galaxies or galaxy clusters can potentially be used to measure the Hubble constant, and test masses in large scale structures can measure the overdensity. Since recession velocities and angular separations can be precisely measured, apparent proper motions can also provide geometric distance measurements to static structures. The apparent fractional angular compression of static objects is 15 μas yr-1 in the local universe; this motion is modulated by the overdensity in dynamic expansion-decoupled structures. We use the Titov et al. quasar proper motion catalog to examine the pairwise proper motion of a sparse network of test masses. Small-separation pairs (<200 Mpc comoving) are too few to measure the expected effect, yielding an inconclusive 8.3 ± 14.9 μas yr -1. Large-separation pairs (200-1500 Mpc) show no net convergence or divergence for z < 1, -2.7 ± 3.7 μas yr-1, consistent with pure Hubble expansion and significantly inconsistent with static structures, as expected. For all pairs a "null test" gives -0.36 ± 0.62 μas yr-1, consistent with Hubble expansion and excludes a static locus at ∼5-10σ significance for z ≃ 0.5-2.0. The observed large-separation pairs provide a reference frame for small-separation pairs that will significantly deviate from the Hubble flow. The current limitation is the number of small-separation objects with precise astrometry, but Gaia will address this and will likely detect the cosmic recession. © 2013. The American Astronomical Society. All rights reserved.

In this issue of Structure, Molnar and colleagues present a pair of important advances: (1) a method to analyze multiple signaling states in on-off switch proteins and (2) evidence for a scissors-type mechanism of on-off switching in a full-length, membrane-bound receptor of the sensor histidine-kinase class. © 2014 Elsevier Ltd.

Graham M.J.,Yale University | Frederick J.,Yale University | Byars-Winston A.,University of Wisconsin - Madison | Hunter A.-B.,University of Colorado at Boulder | Handelsman J.,Yale University
Science | Year: 2013

An evidence-based framework offers a guide for efforts to increase student persistence in STEM majors.

Gosling J.T.,University of Colorado at Boulder | Phan T.D.,University of California at Berkeley
Astrophysical Journal Letters | Year: 2013

Using Wind 3 s plasma and magnetic field data, we have identified nine reconnection exhausts within a solar wind disturbance on 1998 October 18-20 driven by a moderately fast interplanetary coronal mass ejection (ICME). Three of the exhausts within the ICME were associated with current sheets having local field shear angles, θ, ranging from 4° to 9°, the smallest reported values of θ yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02-0.04) plasma β, and very high (281-383 km s-1) Alfvén speed, VA. Low β allows reconnection to occur at small θ and high VA leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-θ current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma β or high VA. On the other hand, small-θ current sheets should be common in the lower solar corona, a plasma regime of extremely low β and extremely high VA. Our observations lend credence to models that predict that reconnection at small-θ current sheets is primarily responsible for coronal heating. © 2013. The American Astronomical Society. All rights reserved.

Costi R.,Hebrew University of Jerusalem | Saunders A.E.,University of Colorado at Boulder | Banin U.,Hebrew University of Jerusalem
Angewandte Chemie - International Edition | Year: 2010

Une key goal of nanocrystal research is the development of experimental methods to selectively control the composition and shape of nanocrystals over a wide range of material combinations. The ability to selectively arrange nanosized domains of metallic, semiconducting, and magnetic materials into a single hybrid nanoparticle offers an intriguing route to engineer nanomaterials with multiple functionalities or the enhanced properties of one domain. In this Review, we focus on recent strategies used to create semiconductor-metal hybrid nanoparticles, present the emergent properties of these multicomponent materials, and discuss their potential applicability in different technologies. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Peterson R.J.,University of Colorado at Boulder
Nuclear Physics A | Year: 2013

Two scaling relations, familiar from analyses of electron scattering and successful over limited kinematic ranges for hadron scattering, are applied to 45 charge exchange spectra from beams of protons and pions on carbon. As with scattering without charge exchange, the conditions that underlie scaling analyses of quasifree scattering are in doubt for intermediate energy hadron beams, and scaling analyses are tests of strong assumptions. Scaling for charge exchange reactions is found in the sense that scaled responses for both beam species and all beam energies are in near agreement over a limited but useful range of momentum transfers, especially at small energy losses where nucleon dynamic effects are strong. © 2013 Elsevier B.V.

Raison C.L.,Emory University | Lowry C.A.,University of Colorado at Boulder | Rook G.A.W.,University College London
Archives of General Psychiatry | Year: 2010

Context: Inflammation is increasingly recognized as contributing to the pathogenesis of major depressive disorder (MDD), even in individuals who are otherwise medically healthy. Most studies in search of sources for this increased inflammation have focused on factors such as psychosocial stress and obesity that are known to activate inflammatory processes and increase the risk for depression. However, MDD may be so prevalent in the modern world not just because proinflammatory factors are widespread, but also because we have lost contact with previously available sources of anti-inflammatory, immunoregulatory signaling. Objective: To examine evidence that disruptions in coevolved relationships with a variety of tolerogenic microorganisms that were previously ubiquitous in soil, food, and the gut, but that are largely missing from industrialized societies, may contribute to increasing rates of MDD in the modern world. Data Sources: Relevant studies were identified using PubMed and Ovid MEDLINE. Study Selection: Included were laboratory animal and human studies relevant to immune functioning, the hygiene hypothesis, and major depressive disorder identified via PubMed and Ovid MEDLINE searches. Data Extraction: Studies were reviewed by all authors, and data considered to be potentially relevant to the contribution of hygiene-related immune variables to major depressive disorder were extracted. Data Synthesis: Significant data suggest that a variety of microorganisms (frequently referred to as the "old friends") were tasked by coevolutionary processes with training the human immune system to tolerate a wide array of non-threatening but potentially proinflammatory stimuli. Lacking such immune training, vulnerable individuals in the modern world are at significantly increased risk of mounting inappropriate inflammatory attacks on harmless environmental antigens (leading to asthma), benign food contents and commensals in the gut (leading to inflammatory bowel disease), or self-antigens (leading to any of a host of autoimmune diseases). Loss of exposure to the old friends may promote MDD by increasing background levels of depressogenic cytokines and may predispose vulnerable individuals in industrialized societies to mount inappropriately aggressive inflammatory responses to psychosocial stressors, again leading to increased rates of depression. Conclusion: Measured exposure to the old friends or their antigens may offer promise for the prevention and treatment of MDD in modern industrialized societies. ©2010 American Medical Association. All rights reserved.

Johnson T.E.,University of Colorado at Boulder
Experimental Gerontology | Year: 2013

This communication will briefly review more than 30. years of research on aging using the nematode Caenorhabditis elegans ("The Worm") as carried out in the labs of Tom Johnson. We will highlight research directions initiated in the 1980's, which were exciting for those of us trying to turn over a new leaf in aging research. In this narrative, I will discuss primarily the science that I and my lab have been involved with for the last 30. years. This area has been fascinating to those studying the sociology of science as modern aging research has moved to replace the simplistic, poorly controlled and outright fictitious approaches seen in much of the previous aging research. © 2013 Elsevier Inc.

Wolter K.,University of Colorado at Boulder | Timlin M.S.,Midwestern University
International Journal of Climatology | Year: 2011

El Niño/Southern Oscillation (ENSO) remains the most important coupled ocean-atmosphere phenomenon to cause global climate variability on seasonal to interannual time scales. This paper addresses the need for a reliable ENSO index that allows for the historical definition of ENSO events in the instrumental record back to 1871. The Multivariate ENSO Index (MEI) was originally defined as the first seasonally varying principal component of six atmosphere-ocean (COADS) variable fields in the tropical Pacific basin. It provides for a more complete and flexible description of the ENSO phenomenon than single variable ENSO indices such as the SOI or Niño 3.4 SST. Here we describe our effort to boil the MEI concept down to its most essential components (based on SLP, SST) to enable historical analyses that more than double its period of record to 1871-2005. The new MEI.ext confirms that ENSO activity went through a lull in the early- to mid-20th century, but was just about as prevalent one century ago as in recent decades. We diagnose strong relationships between peak amplitudes of ENSO events and their duration, as well as between their peak amplitudes and their spacing (periodicity). Our effort is designed to help with the assessment of ENSO conditions through as long a record as possible to be able to differentiate between 'natural' ENSO behaviour in all its rich facets, and the 'Brave New World' of this phenomenon under evolving GHG-related climate conditions. So far, none of the behaviour of recent ENSO events appears unprecedented, including duration, onset timing, and spacing in the last few decades compared to a full century before then. © 2011 Royal Meteorological Society.

Dowell R.D.,University of Colorado at Boulder
Genome Biology | Year: 2011

Meta-analysis of human and mouse microarray data reveals conservation of patterns of gene expression that will help to better characterize the evolution of gene expression. © 2011 BioMed Central Ltd.

Pampel F.C.,University of Colorado at Boulder
Sociology of Health and Illness | Year: 2012

While sedentary leisure-time activities such as reading, going to movies, attending cultural events, going to sporting events, watching TV, listening to music, and socialising with friends would seem to contribute to excess weight, a perspective focusing on socioeconomic status (SES) differences in cultural tastes suggests the opposite, that some sedentary activities are associated with lower rather than higher body weight. This study aims to test theories of cultural distinction by examining relationships between leisure-time activities and body weight. Using 2007 data on 17 nations from the International Social Survey Program (ISSP), the analysis estimates relationships between the body mass index and varied leisure-time activities while controlling for SES, physical activities, and sociodemographic variables. Net of controls for SES and physical activities, participation time in cultural activities is associated with lower rather than higher body weight, particularly in high-income nations. The results suggest that both cultural activities and body weight reflect forms of distinction that separate SES-based lifestyles. © 2011 The Author. Sociology of Health & Illness © 2011 Foundation for the Sociology of Health & Illness/Blackwell Publishing Ltd.

Velicogna I.,University of California at Irvine | Velicogna I.,Jet Propulsion Laboratory | Wahr J.,University of Colorado at Boulder
Geophysical Research Letters | Year: 2013

Time-variable gravity data from the Gravity Recovery and Climate Experiment (GRACE) mission have been available since 2002 to estimate the mass balance of the Greenland and Antarctic Ice Sheets. We analyze current progress and uncertainties in GRACE estimates of ice sheet mass balance. We discuss the impacts of errors associated with spherical harmonic truncation, spatial averaging, temporal sampling, and leakage from other time-dependent signals (e.g., glacial isostatic adjustment (GIA)). The largest sources of error for Antarctica are the GIA correction, the omission of l=1 terms, nontidal changes in ocean mass, and measurement errors. For Greenland, the errors come mostly from the uncertainty in the scaling factor. Using Release 5.0 (RL05) GRACE fields for January 2003 through November 2012, we find a mass change of -258 - 41 Gt/yr for Greenland, with an acceleration of -31 - 6 Gt/yr2, and a loss that migrated clockwise around the ice sheet margin to progressively affect the entire periphery. For Antarctica, we report changes of -83 - 49 and -147 - 80 Gt/yr for two GIA models, with an acceleration of -12 - 9 Gt/yr 2 and a dominance from the southeast pacific sector of West Antarctica and the Antarctic Peninsula. Key Points Comprehensive review of error sources, their impact and how to deal with them Estimates ice sheet mass balance for latest, extended GRACE releases Rapid publication for input to IPCC AR5 ©2013. American Geophysical Union. All Rights Reserved.

Larson K.M.,University of Colorado at Boulder
Geophysical Research Letters | Year: 2013

Detection of volcanic plumes, especially ash-laden ones, is important both for public health and aircraft safety. A variety of geophysical tools and satellite data are used to monitor volcanic eruptions and to predict the movement of ash. However, satellite-based methods are restricted by time of day and weather, while radars are often unavailable because of cost/portability. Here a method is proposed to detect volcanic plumes using GPS signal strength data. The strengths and limitations of the method are assessed using GPS data collected during the 2008 and 2009 eruptions of the Okmok and Mt. Redoubt volcanoes. Plume detections using this GPS technique are consistent with independently collected seismic and radar data. ©2013. American Geophysical Union. All Rights Reserved.

Medeiros D.M.,University of Colorado at Boulder
Wiley Interdisciplinary Reviews: Developmental Biology | Year: 2013

The neural crest is an embryonic cell population that gives rise to an array of tissues and structures in adult vertebrates including most of the head skeleton. Because neural crest cells (NCCs), and many of their derivatives, are unique to vertebrates, the evolution of the neural crest is thought to have potentiated vertebrate origins and diversification. However, the lack of clear NCC homologs in invertebrate chordates has made it difficult to reconstruct the evolutionary history of modern NCCs. In this review, the development of NCCs in the basal jawless vertebrate, lamprey, is compared with the development of neural crest-like cells in a range of invertebrates to deduce features of the first NCCs and their evolutionary precursors. These comparisons demonstrate that most of the defining attributes of NCCs are widespread features of invertebrate embryonic ectoderm. In addition, they suggest ancient origins for the neural border domain and chondroid skeletal tissue in the first bilaterian, and show that NCCs must have evolved in a chordate with an unduplicated invertebrate-type genome. On the basis of these observations, a stepwise model for the evolution of NCCs involving heterotopic and heterochronic activation of ancient ectodermal gene programs and new responsiveness to preexisting inducing signals is proposed. In light of the phylogenetic distribution of neural crest-like cells, the deep homology of developmental gene networks, and the central role of evolutionary loss in deuterostome evolution, this article concludes with suggestions for future studies in a broad range of bilaterians to test key aspects of this model. © 2012 Wiley Periodicals, Inc.

Ervens B.,University of Colorado at Boulder | Ervens B.,National Oceanic and Atmospheric Administration
Chemical Reviews | Year: 2015

The aqueous phase of clouds and fogs represents a unique medium where chemical reactions can occur that do not take place in the gas phase. While it is qualitatively established that chemical processes in clouds are the main global sulfate source he relative contribution of SOA formation by aqueous phase processes in clouds and deliquesced aerosol particles to total SOA burden has not been quantified to date. Particles that act as cloud condensation nuclei (CCN) are modified in clouds in terms of their mass, composition, and morphology. The formation pathways of sulfate in the gas and aqueous phases, respectively, cause the modification of particles of different sizes. Therefore, different correlations for sulfate mass formed in either phase and wet deposition rates have been found. The efficiency of precipitation as a sink for particles strongly depends on the phase of precipitation. It can be summarized that clouds act as a global source of sulfate and likely also of SOA mass. The semivolatile nature of SOA constituents results in their partitioning between gas and particulate phases.

Uzdensky D.A.,University of Colorado at Boulder
Astrophysical Journal | Year: 2013

In this paper, we consider two outstanding intertwined problems in modern high-energy astrophysics: (1) the vertical-thermal structure of an optically thick accretion disk heated by the dissipation of magnetohydrodynamic turbulence driven by the magnetorotational instability (MRI), and (2) determining the fraction of the accretion power released in the corona above the disk. For simplicity, we consider a gas-pressure-dominated disk and assume a constant opacity. We argue that the local turbulent dissipation rate due to the disruption of the MRI channel flows by secondary parasitic instabilities should be uniform across most of the disk, almost up to the disk photosphere. We then obtain a self-consistent analytical solution for the vertical thermal structure of the disk, governed by the balance between the heating by MRI turbulence and the cooling by radiative diffusion. Next, we argue that the coronal power fraction is determined by the competition between the Parker instability, viewed as a parasitic instability feeding off of MRI channel flows, and other parasitic instabilities. We show that the Parker instability inevitably becomes important near the disk surface, leading to a certain lower limit on the coronal power. While most of the analysis in this paper focuses on the case of a disk threaded by an externally imposed vertical magnetic field, we also discuss the zero net flux case, in which the magnetic field is produced by the MRI dynamo itself, and show that most of our arguments and conclusions should be valid in this case as well. © 2013. The American Astronomical Society. All rights reserved..

Park H.S.,University of Colorado at Boulder
International Journal for Numerical Methods in Engineering | Year: 2010

The purpose of this article is to present a multiscale finite element method that captures nanoscale surface stress effects on the dynamic mechanical behavior of nanomaterials. The method is based upon arguments from crystal elasticity, i.e. the Cauchy-Born rule, but significantly extends the capability of the standard Cauchy-Born rule by accounting for critical nanoscale surface stress effects, which are well known to have a significant effect on the mechanics of crystalline nanostructures. We present the governing equations of motion including surface stress effects, and demonstrate that the methodology is general and thus enables simulations of both metallic and semiconducting nanostructures. The numerical examples on elastic wave propagation and dynamic tensile and compressive loading show the ability of the proposed approach to capture surface stress effects on the dynamic behavior of both metallic and semiconducting nanowires, and demonstrate the advantages of the proposed approach in studying the deformation of nanostructures at strain rates and time scales that are inaccessible to classical molecular dynamics simulations. © 2010 John Wiley & Sons, Ltd.

Andrews-Hanna J.R.,University of Colorado at Boulder
Neuroscientist | Year: 2012

During the many idle moments that comprise daily life, the human brain increases its activity across a set of midline and lateral cortical brain regions known as the "default network." Despite the robustness with which the brain defaults to this pattern of activity, surprisingly little is known about the network's precise anatomical organization and adaptive functions. To provide insight into these questions, this article synthesizes recent literature from structural and functional imaging with a growing behavioral literature on mind wandering. Results characterize the default network as a set of interacting hubs and subsystems that play an important role in "internal mentation"-the introspective and adaptive mental activities in which humans spontaneously and deliberately engage in every day. © The Author(s) 2012.

Belknap J.,University of Colorado at Boulder
Criminology | Year: 2015

Similar to many criminologists, my interest in pursuing this career was driven by a desire to improve responses to injustices, on both small and large scales. I believe that among criminologists, this dedication to effect changes in social and legal justice disproportionately drives those of us historically kept out of the academy due to our race, gender, class, sexual identity, and/or other marginalizations. Fortunately, there is a growing diversity among criminologists and this has had a powerful impact on expanding the scope and depth of the field. At the same time, I am concerned that academic training and university climates frequently work against our commitment to advancing social and legal justice changes, what I refer to as "criminology activism." This address is a call to action, stressing criminologists' responsibility to advocate for social and legal justice on small and large scales. Numerous types of criminology activism are identified (e.g., in research, service, and teaching), including the requisite to continue diversifying the representation of criminologists. © 2015 American Society of Criminology.

Van Blerkom J.,University of Colorado at Boulder
Mitochondrion | Year: 2011

The role of mitochondria as a nexus of developmental regulation in mammalian oogenesis and early embryogenesis is emerging from basic research in model species and from clinical studies in infertility treatments that require in vitro fertilization and embryo culture. Here, mitochondrial bioenergetic activities and roles in calcium homeostasis, regulation of cytoplasmic redox state, and signal transduction are discussed with respect to outcome in general, and as possible etiologies of chromosomal defects, maturation and fertilization failure in human oocytes, and as causative factors in early human embryo demise. At present, the ability of mitochondria to balance ATP supply and demand is considered the most critical factor with respect to fertilization competence for the oocyte and developmental competence for the embryo. mtDNA copy number, the timing of mtDNA replication during oocyte maturation, and the numerical size of the mitochondrial complement in the oocyte are evaluated with respect to their relative contribution to the establishment of developmental competence. Rather than net cytoplasmic bioenergetic capacity, the notion of functional compartmentalization of mitochondria is presented as a means by which ATP may be differentially supplied and localized within the cytoplasm by virtue of stage-specific changes in mitochondrial density and potential (δψm). Abnormal patterns of calcium release and sequestration detected at fertilization in the human appear to have coincident effects on levels of mitochondrial ATP generation. These aberrations are not uncommon in oocytes obtained after ovarian hyperstimulation for in vitro fertilization. The possibility that defects in mitochondrial calcium regulation or bioenergetic homeostasis could have negative downstream development consequences, including imprinting disorders, is discussed in the context of signaling pathways and cytoplasmic redox state. © 2010 Elsevier B.V. and Mitochondria Research Society.

Marden J.R.,University of Colorado at Boulder | Wierman A.,California Institute of Technology
Operations Research | Year: 2013

Game-theoretic tools are becoming a popular design choice for distributed resource allocation algorithms. A central component of this design choice is the assignment of utility functions to the individual agents. The goal is to assign each agent an admissible utility function such that the resulting game possesses a host of desirable properties, including scalability, tractability, and existence and efficiency of pure Nash equilibria. In this paper we formally study this question of utility design on a class of games termed distributed welfare games. We identify several utility design methodologies that guarantee desirable game properties irrespective of the specific application domain. Lastly, we illustrate the results in this paper on two commonly studied classes of resource allocation problems: "coverage" problems and "coloring" problems. © 2013 INFORMS.

George S.M.,University of Colorado at Boulder
Chemical Reviews | Year: 2010

Atomic layer deposition (ALD) which has emerged as an important technique for depositing thin films for a variety of applications has been reported. The necessity for continuous and pinhole-free films in semiconductor devices has driven the advancement of ALD. ALD is able to meet the needs for atomic layer control and conformal deposition using sequential, self-limiting surface reactions. The ALD of Al2O3 has developed as a model ALD system. ALD processing is also extendible to very large substrates and to parallel processing of multiple substrates. ALD is a gas phase method based on sequential, selflimiting surface reactions. ALD can deposit very conformal and ultrathin films on substrates with very high aspect ratios. ALD on high aspect ratio structures was then considered including an examination of the times required for conformal growth on high aspect ratio structures. The number of applications for ALD also continues to grow outside of the semiconductor arena.

Warner R.,University of Colorado at Boulder
British Journal of Psychiatry | Year: 2010

British hospital alternatives inherit some of their most valuable features, such as the use of small, domestic environments and the avoidance of coercion and confinement, from the early 19th-century moral management movement. The North American experience illustrates that these advantages can be lost if clinical benefits are overridden by cost and other practical concerns.

Ungar P.S.,University of Arkansas | Sponheimer M.,University of Colorado at Boulder
Science | Year: 2011

Diet changes are considered key events in human evolution. Most studies of early hominin diets focused on tooth size, shape, and craniomandibular morphology, as well as stone tools and butchered animal bones. However, in recent years, dental microwear and stable isotope analyses have hinted at unexpected diversity and complexity in early hominin diets. Some traditional ideas have held; others, such as an increasing reliance on hard-object feeding and a dichotomy between Australopithecus and Paranthropus, have been challenged. The first known evidence of C4 plant (tropical grasses and sedges) and hard-object (e.g., seeds and nuts) consumption dates to millions of years after the appearance of the earliest probable hominins, and there are no consistent trends in diet change among these species through time.

Eberle J.J.,University of Colorado at Boulder | Greenwood D.R.,Brandon University
Bulletin of the Geological Society of America | Year: 2012

Early-middle Eocene (ca. 53-38 Ma) sediments of the Eureka Sound Group in Can ada's Arctic Archipelago preserve evidence of lush mixed conifer-broadleaf rain forests, inhabited at times by alligators, turtles, and diverse mammals, including primates, tapirs, brontotheres, and hippo-like Coryphodon. This biota reflects a greenhouse world, offering a climatic and ecologic deep time analog of a mild ice-free Arctic that may be our best means to predict what is in store for the future Arctic if current climate change goes unchecked. In our review of the early-middle Eocene Arctic flora and vertebrate fauna, we place the Arctic fossil localities in historic, geographic, and stratigraphic context, and we provide an integrated synthesis and discussion of the paleobiology and paleo ecology of these Eocene Arctic forests and their vertebrate inhabitants. The abundance and diversity of tapirs and plagiomenids (both rare elements in midlatitude faunas), and the absence of artiodactyls, early horses, and the hyopsodontid "condylarth"Hyopsodus (well represented at midlatitude localities) are peculiar to the Eocene Arctic. The Eocene Arctic macro floras reveal a forested landscape analogous to the swamp-cypress and broadleaf floodplain forests of the modern southeastern United States. Multiple climate proxies indicate a mild temperate early-middle Eocene Arctic with winter temperatures at or just above freezing and summer temperatures of 20 °C (or higher), and high precipitation. At times, this high precipitation resulted in fresh water discharge into a nearly enclosed Arctic Ocean basin, sufficient to cause surface freshening of the Arctic Ocean, supporting mats of the floating fern Azolla. Fluctuating Arctic Ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges, allowing land plants and animals to disperse between North America and both Europe and Asia. © 2012 Geological Society of America.

Radzihovsky L.,University of Colorado at Boulder | Sheehy D.E.,Louisiana State University
Reports on Progress in Physics | Year: 2010

We present an overview of recent developments in species-imbalanced ('polarized') Feshbach-resonant Fermi gases. We summarize the current status of thermodynamics of these systems in terms of a phase diagram as a function of the Feshbach resonance detuning, polarization and temperature. We review instabilities of the s-wave superfluidity across the Bose-Einstein condensation-to-Bardeen-Cooper-Schrieffer crossover to phase separation, Fulde-Ferrell-Larkin-Ovchinnikov states, polarized molecular superfluidity and the normal state, driven by the species imbalance. We discuss different models and approximations of this system and compare their predictions with current experiments. © 2010 IOP Publishing Ltd.

Matrosov S.Y.,University of Colorado at Boulder
Journal of Geophysical Research: Atmospheres | Year: 2011

The spaceborne 94 GHz radar onboard the CloudSat polar orbiting satellite offers new opportunities in estimating parameters of precipitating cloud systems including hurricanes. CloudSat measurements can resolve the vertical extent of storms and hurricanes, thus providing a view of their complex structure. These measurements can be used to retrieve with high spatial resolution rainfall and ice content parameters in an atmospheric vertical column as the satellite moves over the precipitating systems. Two major Atlantic hurricanes of the 2008 season, Gustav and Ike, were observed by CloudSat near their landfalls on the coast of the Gulf of Mexico. CloudSat measurements indicated cloud top heights at around 14-16 km above the ground and extended areas of startiform-like precipitation with estimated rain rates in a range of about 3-12 mm h -1. The radar bright band features observed just below the freezing level were identifiable for most measured reflectivity profiles. Maximum retrieved ice water path values reached about 20,000 g m-2. CloudSat rain rate retrievals over land and water agreed reasonably well with approximately coincident estimates from surface precipitation radars in the areas where measurements from these radars were available and were not contaminated by melting layer returns. Hurricane Gustav remnants observed by CloudSat several days after the landfall were characterized by smaller values of rain rate and ice water path (∼2-3 mm h-1 and 1000-10,000 g m-2, correspondingly). The hurricane parameters retrieved from CloudSat measurements may complement data from other satellite sources, which are traditionally used for hurricane observations. © 2011 by the American Geophysical Union.

Behera S.K.,University of Colorado at Boulder
Journal of Power Sources | Year: 2011

Nanostructured Fe3O4 nanoparticles were prepared by a simple sonication assisted co-precipitation method. Transmission electron microscopy, X-ray diffraction and BET surface area analysis confirmed the formation of ∼20 nm crystallites that constitute ∼200 nm nanoclusters. Galvanostatic charge-discharge cycling of the Fe3O4 nanoaprticles in half cell configuration with Li at 100 mA g-1 current density exhibited specific reversible capacity of 1000 mAh g -1. The cells showed stability at high current charge-discharge rates of 4000 mA g-1 and very good capacity retention up to 200 cycles. After multiple high current cycling regimes, the cell always recovered to full reversible capacity of ∼1000 mAh g-1 at 0.1 C rate. © 2011 Elsevier B.V. All rights reserved.

Gumbel J.,University of Stockholm | Karlsson B.,University of Colorado at Boulder
Geophysical Research Letters | Year: 2011

The state of the mesosphere is connected to the lower atmosphere through various dynamical coupling processes. Nine years of Odin satellite observations of noctilucent clouds (NLC) have been analyzed as tracers for such processes. Inter-hemispheric coupling from the winter stratosphere and troposphere is confirmed to have a major influence on the summer mesosphere. Intra-hemispheric coupling from the spring/summer stratosphere, on the other hand, can control the onset of the NLC season. Most prominently, the southern NLC season 2010-2011 started with a delay of more than 20 days as compared to other years, which coincides with an exceptionally persistent polar vortex in the Antarctic stratosphere. Proposed mechanisms for the above teleconnections are based on the effect of lower atmospheric circulation on gravity wave filtering and, thus, on the dynamical forcing of the mesospheric circulation. Both intra-and inter-hemispheric coupling processes are needed for an understanding of the overall seasonal behavior of the summer mesosphere. Copyright 2011 by the American Geophysical Union.

Reznik D.,University of Colorado at Boulder
Physica C: Superconductivity and its Applications | Year: 2012

Stripe order where electrons self-organize into alternating periodic charge-rich and magnetically-ordered charge-poor parallel lines was proposed as a way of optimizing the kinetic energy of holes in a doped Mott insulator. Static stripes detected as extra peaks in diffraction patterns, appear in a number of oxide perovskites as well as some other systems. The more controversial dynamic stripes, which are not detectable by diffraction, may be universally present in copper oxide superconductors. Thus it is important to learn how to detect dynamic stripes as well as to understand their influence on electronic properties. This review article focuses on lattice vibrations (phonons) that might show signatures of the charge component of dynamic stripes. The first part of the article describes recent progress in learning about how the phonon signatures of different types of electronic charge fluctuations including stripes can be distinguished from purely structural instabilities and from each other. Then I will focus on the evidence for dynamic stripes in the phonon spectra of copper oxide superconductors. © 2012 Elsevier B.V. All rights reserved.

Hatzfeld D.,French National Center for Scientific Research | Molnar P.,University of Colorado at Boulder
Reviews of Geophysics | Year: 2010

We compare the geologic histories, the deep structures, and the present-day kinematics of deformation of the Himalaya and the adjacent Tibetan Plateau with those of the Zagros and Iranian Plateau to test geodynamic processes of continental collision. Shortly after India and Arabia collided with Eurasia, horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from India's and Arabia's underlying crystalline basement. Subsequently, slip on thrust faults stacked slices of India's basement to build the Himalaya on India's northern margin. Such faulting has not yet developed in the Zagros, where collision is more recent and Arabia penetrates into Eurasia more slowly than India does, so that postcollision convergence with Eurasia is less. The greater elevation, thicker crust, and more marked heterogeneity of the upper mantle beneath the Tibetan than beneath the Iranian Plateau also reflect a more advanced stage of development. Moreover, while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus, normal faulting, suggesting horizontal extension and crustal thinning, occurs within Tibet but not in Iran. Hence, the balance of forces that built the high Tibetan Plateau must have changed, apparently some time since ∼15 Ma. Removal of Tibetan mantle lithosphere could have altered that balance. If mantle lithosphere beneath the Iranian Plateau has been removed, however, the change in force balance has been too small to initiate normal faulting. Low seismic wave speeds in the uppermost mantle just beneath the Moho of both plateaus suggest (to us) that lithosphere beneath both is thin, consistent with late Cenozoic removal of it, but alternative explanations might account for these low speeds. Despite its apparently thin, and hence presumably weak, mantle lithosphere, much of central Iran undergoes little deformation. It illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small. Whereas differences between the two regions clearly depend on the amount that Arabia and India have penetrated into Eurasia, which scales with both the dates of collision and rates of convergence, we see no differences in the operative processes that depend on the present-day rates of convergence. Copyright © 2010 by the American Geophysical Union.

Robertson S.,University of Colorado at Boulder
Plasma Physics and Controlled Fusion | Year: 2013

The sheaths that occur at surfaces in laboratory and space plasmas are reviewed with an emphasis on numerical models that can be solved with modest computational resources. The surfaces in plasma may be the interior walls of confinement devices or inserted probes. Fluid and kinetic models are presented in some detail, and particle-in-cell models are discussed briefly. The numerical methods find the spatial profile of the potential, the particle densities near the surfaces and the current to the surfaces. Maxwellian electrons and cold ions are assumed at the outset and subsequently the models are expanded to encompass (1) multiple electron populations, (2) multiple ion species, (3) finite ion temperature, (4) surfaces that emit electrons such as heated cathodes or emissive probes and (5) surfaces that emit plasma as in the Q-machine. These complications may produce nonmonotonic sheaths in which the first derivative of the potential changes sign or double layers in which the second derivative changes sign. The effect of charge-exchange collisions on ion losses to the wall and on ion current to probes is discussed, but models with collisions of electron are omitted. Some recent advances are discussed, including experiments that measure the ion distribution function in sheaths using laser-induced fluorescence, experiments and numerical models on sheaths with multiple ion species and computational models of sheaths surrounding objects in flowing plasma. © 2013 IOP Publishing Ltd.

Bauer S.,Swiss Ornithological Institute | Bauer S.,Netherlands Institute of Ecology | Hoye B.J.,University of Colorado at Boulder | Hoye B.J.,Deakin University
Science | Year: 2014

Animal migrations span the globe, involving immense numbers of individuals from a wide range of taxa. Migrants transport nutrients, energy, and other organisms as they forage and are preyed upon throughout their journeys. These highly predictable, pulsed movements across large spatial scales render migration a potentially powerful yet underappreciated dimension of biodiversity that is intimately embedded within resident communities. We review examples from across the animal kingdom to distill fundamental processes by which migratory animals influence communities and ecosystems, demonstrating that they can uniquely alter energy flow, food-web topology and stability, trophic cascades, and the structure of metacommunities. Given the potential for migration to alter ecological networks worldwide, we suggest an integrative framework through which community dynamics and ecosystem functioning may explicitly consider animal migrations.

Peterson R.J.,University of Colorado at Boulder
Physical Review C - Nuclear Physics | Year: 2012

Five scaling relations familiar from analyses of inclusive electron scattering spectra on complex nuclei are applied to 65 inclusive continuum spectra of protons, positive kaons, and pions incident upon carbon. Beam energies range from 300 MeV to 18.3 GeV with momentum transfers such that the conditions for quasifree scattering are met, similar to those for many electron scattering analyses. Several very strong assumptions need to be made to apply these scaling analyses to hadrons, and so the requirement that these spectra come into agreement under a scaling analysis is a severe test of these assumptions. Scaling is found in the sense that the responses of four of the five systems considered do agree over a significant range of momentum transfers for the three hadron species over a wide range of beam energies. Responses other than those for quasifree scattering destroy the validity of scaling systems for hadrons at large angles or momentum transfers or high beam energies. © 2012 American Physical Society.

Degrand T.,University of Colorado at Boulder
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Results are presented for hadron spectroscopy with gauge groups SU(N) with N=3, 5, 7. Calculations use the quenched approximation. Lattice spacings are matched using the static potential. Meson spectra show independence on N and vacuum-to-hadron matrix elements scale as √N. The baryon spectrum shows the excitation levels of a rigid rotor. © 2012 American Physical Society.

Lee S.S.,University of Colorado at Boulder
Journal of the Atmospheric Sciences | Year: 2012

This study examines the effect of a mesoscale perturbation of aerosol on a larger-scale cloud system driven by deep convective clouds. An aerosol-perturbed domain of size 120 km is prescribed in the middle of the larger-scale domain of size 1100 km. Aerosol perturbations in the mesoscale domain result in an intensification of convection in a mesoscale convective system (MCS). This leads to an intensification of the larger-scale circulations, which in turn leads to an intensification of the larger-scale subsidence. While the invigorated convection enhances precipitation in the MCS, the intensified larger-scale subsidence acts to increase the larger-scale stability and thus to suppress convection and precipitation in the larger-scale domain. The suppression of precipitation in the larger-scale domain outweighs the enhancement of precipitation in the mesoscale domain, leading to suppressed precipitation over the entire domain. The ramifications of aerosol perturbations therefore need to be considered on scales much larger than the scale of the perturbation. © 2012 American Meteorological Society.

Romatschke P.,University of Colorado at Boulder
European Physical Journal C | Year: 2015

Flow signatures in experimental data from relativistic ion collisions are usually interpreted as a fingerprint of the presence of a hydrodynamic phase during the evolution of these systems. In this work, flow signatures arising from event-by-event viscous hydrodynamics are compared to those arising from event-by-event non-interacting particle dynamics (free streaming), both followed by a late-stage hadronic cascade, in $$d + \mathrm{Au}\,$$d+Au, $$^3\mathrm{He} + \mathrm{Au}\,$$3He+Auat $$\sqrt{s}=200$$s=200 GeV and $$p + \mathrm{Pb}\,$$p+Pbcollisions at $$\sqrt{s}=5$$s=5 TeV, respectively. For comparison, also $$\mathrm{Pb} + \mathrm{Pb}\,$$Pb+Pbcollisions at $$\sqrt{s}=2.76$$s=2.76 TeV are simulated. It is found that non-hydrodynamic evolution can give rise to radial flow equal to or larger than hydrodynamics with $$\eta /s=0.08$$η/s=0.08 in all simulated collision systems. In light-on-heavy-ion collisions, free streaming gives rise to triangular and quadrupolar flow comparable to or larger than that from hydrodynamics, but it generally leads to considerably smaller elliptic flow. As expected, free streaming leads to considerably less elliptic, triangular and quadrupolar flow than hydrodynamics in nucleus–nucleus collisions, such as event-by-event $$\mathrm{Pb} + \mathrm{Pb}\,$$Pb+Pbcollisions at $$\sqrt{s}=2.76$$s=2.76 TeV. © 2015, The Author(s).

McIntosh J.R.,University of Colorado at Boulder | Molodtsov M.I.,Russian Academy of Sciences | Ataullakhanov F.I.,Russian Academy of Sciences
Quarterly Reviews of Biophysics | Year: 2012

Mitosis is the process by which eukaryotic cells organize and segregate their chromosomes in preparation for cell division. It is accomplished by a cellular machine composed largely of microtubules (MTs) and their associated proteins. This article reviews literature on mitosis from a biophysical point of view, drawing attention to the assembly and motility processes required to do this complex job with precision. Work from both the recent and the older literature is integrated into a description of relevant biological events and the experiments that probe their mechanisms. Theoretical work on specific subprocesses is also reviewed. Our goal is to provide a document that will expose biophysicists to the fascination of this quite amazing process and provide them with a good background from which they can pursue their own research interests in the subject. © 2012 Cambridge University Press.

Karmakar S.,Qualcomm | Varanasi M.K.,University of Colorado at Boulder
IEEE Transactions on Information Theory | Year: 2012

The generalized degrees of freedom (GDoF) region of the MIMO Gaussian interference channel (IC) is obtained for the general case of an arbitrary number of antennas at each node and where the signal-to-noise ratios (SNRs) and interference-to-noise ratios vary with arbitrary exponents to a nominal SNR. The GDoF-optimal coding scheme involves message splitting and partial interference decoding and consists of linear Gaussian superposition coding of the private and common submessages that can be seen as jointly performing signal-space and signal-level interference alignment. The admissible degree of freedom (DoF)-splits between the private and common messages are also specified. A study of the GDoF region reveals various insights through the joint dependence of optimal interference management techniques at high SNR on the SNR exponents and the numbers of antennas at the four terminals. For instance, it reveals that, unlike in the scalar IC, treating interference as noise is not always GDoF-optimal even in the very weak interference regime. Moreover, while the DoF-optimal strategy that relies just on transmit/receive zero-forcing beamforming and time sharing is not GDoF optimal (and thus has an unbounded gap to capacity), the precise characterization of the very strong interference regimewhere single-user DoF performance can be achieved simultaneously for both usersdepends on the relative numbers of antennas at the four terminals and thus deviates from what it is in the single-input single-output case. For asymmetric numbers of antennas at the four nodes, the shape of the symmetric GDoF curve can be a distorted W curve to the extent that for certain multiple-input multiple-output ICs it is a V curve. © 1963-2012 IEEE.

Batey R.T.,University of Colorado at Boulder
Quarterly Reviews of Biophysics | Year: 2012

A riboswitch is a non-protein coding sequence capable of directly binding a small molecule effector without the assistance of accessory proteins to regulate expression of the mRNA in which it is embedded. Currently, over 20 different classes of riboswitches have been validated in bacteria with the promise of many more to come, making them an important means of regulating the genome in the bacterial kingdom. Strikingly, half of the known riboswitches recognize effector compounds that contain a purine or related moiety. In the last decade, significant progress has been made to determine how riboswitches specifically recognize these compounds against the background of many other similar cellular metabolites and transduce this signal into a regulatory response. Of the known riboswitches, the purine family containing guanine, adenine and 2′-deoxyguanosine-binding classes are the most extensively studied, serving as a simple and useful paradigm for understanding how these regulatory RNAs function. This review provides a comprehensive summary of the current state of knowledge regarding the structure and mechanism of these riboswitches, as well as insights into how they might be exploited as therapeutic targets and novel biosensors. © 2012 Cambridge University Press.

Mohr G.S.,Colorado State University | Lichtenstein D.R.,University of Colorado at Boulder | Janiszewski C.,University of Florida
Journal of Marketing | Year: 2012

Nutritional labels are mandatory on virtually all packaged food items sold in the United States. The nutritional information on these labels is reported on a "per-serving-size" basis. However, unbeknownst to many consumers, current Food and Drug Administration regulations allow manufacturers some discretion in setting serving sizes-a factor that the authors hypothesize has implications for consumer behavior. For example, adopting a smaller serving size allows marketers to reduce the reported calories, fat, sugar, and carbohydrates in a product serving, which in turn can influence the anticipated consequences of consumption. Three studies show that manipulating the serving size, and thus calories per serving, for equivalent consumption amounts influences the anticipated guilt of consumption, purchase intentions, and choice behavior. However, the results also show that individual difference and context variables, which heighten consumer attention to nutritional information in general, often focus attention on calorie information but not serving size. This leads to the counterintuitive finding that more nutritionally vigilant consumers are more heavily influenced by serving size manipulations. The authors discuss the managerial and public policy implications. © 2012, American Marketing Association.

Gosling J.T.,University of Colorado at Boulder
Space Science Reviews | Year: 2012

It is only within the last 5 years that we have learned how to recognize the unambiguous signature of magnetic reconnection in the solar wind in the form of roughly Alfvénic accelerated plasma flows embedded within bifurcated magnetic field reversal regions (current sheets). This paper provides a brief overview of what has since been learned about reconnection in the solar wind from both single and multi-spacecraft observations of these so-called reconnection exhausts. © 2011 Springer Science+Business Media B.V.

Blackmon M.H.,University of Colorado at Boulder
Behaviour and Information Technology | Year: 2012

This paper draws from cognitive psychology and cognitive neuroscience to develop a preliminary similarity-choice theory of how people allocate attention among information patches on webpages while completing search tasks in complex informational websites. Study 1 applied stepwise multiple regression to a large dataset and showed that success rate for web navigation tasks approaches 100% if a single information patch is highly similar in meaning to the user goal, and success rate falls dramatically if two or more information patches compete for the user's attention and if only one contains a link that leads to accomplishing the search goal. Study 2 (n=82) manipulated the independent variables task difficulty and website design and found statistically significant differences in success rate for both main effects and the interaction. Study 2 also found that the distribution of attention among available information patches was strongly determined by the rank ordering of semantic similarity between user goal and information patch but was not influenced by website designs with very different visual layouts. While these results offer verification of a similarity-choice theory of attention to information patches, caution is warranted in generalising too broadly from these results. © 2012 Copyright Taylor and Francis Group, LLC.

Lee Y.,University of Northern Iowa | Kozar K.A.,University of Colorado at Boulder
Decision Support Systems | Year: 2012

Developing a usable website is pivotal for e-business success. Researchers have devoted effort to develop metrics, guidelines and theories of website usability, yet there still is a lack of consensus on the multifaceted dimensions of website usability and lack of investigation of the nomological networks among website usability constructs. This study first investigated the common dimensions of website usability by integrating the findings of previous studies and a focus group study with website usability experts. Instruments to measure the constructs were developed and empirically validated. Then nomological networks between website usability constructs and between those constructs and online purchase intention and purchase were examined. Three field studies including two questionnaire surveys and a causal mapping analysis were conducted. The research identified ten website usability constructs with strong psychometric properties. A number of nomological networks between usability constructs were discovered, contributing to identification of sources of variances of purchase intention and purchase behavior. Findings of this study are expected to provide useful insights for practitioners to develop more usable websites and for researchers to better assess the effect of website usability on online customer behavior. © 2011 Elsevier B.V. All rights reserved.

Kleiber W.,University of Colorado at Boulder | Genton M.G.,King Abdullah University of Science and Technology
Biometrika | Year: 2013

We derive sufficient conditions for the cross-correlation coefficient of a multivariate spatial process to vary with location when the spatial model is augmented with nugget effects. The derived class is valid for any choice of covariance functions, and yields substantial flexibility between multiple processes. The key is to identify the cross-correlation coefficient matrix with a contraction matrix, which can be either diagonal, implying a parsimonious formulation, or a fully general contraction matrix, yielding greater flexibility but added model complexity. We illustrate the approach with a bivariate minimum and maximum temperature dataset in Colorado, allowing the two variables to be positively correlated at low elevations and nearly independent at high elevations, while still yielding a positive definite covariance matrix. © 2012 Biometrika Trust.

Root E.D.,University of Colorado at Boulder
Annals of the Association of American Geographers | Year: 2012

A rich history of research documents the effects of neighborhood-level socioeconomic status (SES) conditions on health outcomes. Recent criticism of the neighborhoods and health literature, however, has stressed several conceptual and methodological challenges not adequately addressed in previous research. Critics suggest that early work on neighborhoods and health gave little thought to the spatial scale at which SES factors influence a specific health outcome. This article discusses the concept of neighborhoods and health, reviews recent criticisms of existing work, and provides a case study that exemplifies how geographic methods can address one such criticism. Using data on birth defects in North Carolina, the case study examines the relation of SES to orofacial clefts (cleft lip and cleft palate) at different spatial scales. The Brown-Forsythe test is used to select optimal neighborhood size. Results are evaluated using logistic regression models to examine the relationship between SES measures and orofacial clefts, controlling for individual-level risk factors. Results indicate modest associations between neighborhood-level measures of poverty and cleft palate but no associations with cleft lip with or without cleft palate. © 2012 Copyright Taylor and Francis Group, LLC.

Nievinski F.G.,Sao Paulo State University | Larson K.M.,University of Colorado at Boulder
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

GPS multipath reflectometry (GPS-MR) is a technique that uses geodetic quality GPS receivers to estimate snow depth. The accuracy and precision of GPS-MR retrievals are evaluated at three different sites: grasslands, alpine, and forested. The assessment yields a correlation of 0.98 and an rms error of 6-8 cm for observed snow depths of up to 2.5 m. GPS-MR underestimates in situ snow depth by 10%-15% at these three sites, although the validation methods do not measure the same footprint as GPS-MR. © 1980-2012 IEEE.

Whisman M.A.,University of Colorado at Boulder
Health Psychology | Year: 2010

Objective: This study evaluated the association between loneliness and the metabolic syndrome, which refers to a clustering of factors that have been shown to increase risk for cardiovascular disease, diabetes, stroke, and mortality. A secondary purpose was to evaluate whether age moderated the association between loneliness and the metabolic syndrome. Design: Participants were 52 to 79 years old, and they were drawn from a population-based survey of people 50 years of age and older living in England (N = 3211). They completed a self-report measure of loneliness and a nurse visit that included collection of blood pressure, blood sample, and anthropometric measures. Main Outcome Measures: Self-reported loneliness and the metabolic syndrome. Results: After controlling for demographic variables and smoking status, loneliness was significantly associated with increasing likelihood of meeting criteria for the metabolic syndrome and with the individual criterion of central obesity. The association between loneliness and the metabolic syndrome was not moderated by age. Conclusion: Results suggest that loneliness is associated with the metabolic syndrome. Therefore, the metabolic syndrome may be among the pathways by which loneliness increases risk of morbidity and mortality. © 2010 American Psychological Association.

Lohse K.R.,University of Colorado at Boulder
Human Movement Science | Year: 2012

Lohse, Sherwood, and Healy (2010) found that an external focus of attention (FOA) improved performance in a dart-throwing task and reduced the time taken between throws, but using the time between trials as a measure of preparation time is relatively crude. Thus, the current experiment analyzed how FOA affects accuracy and pre-movement time in an isometric force production task, to study how FOA affected motor planning. In the current experiment, training with an external focus improved the accuracy of the isometric force production task during training and during retention and transfer testing. During training, an external FOA also significantly reduced pre-movement time in early trials. These findings are interpreted as reduced explicit control of movement as a function of an external FOA, and help to integrate FOA research with other motor control phenomena and neuropsychological theories of motor control. © 2011.

Frehlich R.,University of Colorado at Boulder
Journal of Atmospheric and Oceanic Technology | Year: 2013

Scanning Doppler lidar is a promising technology for improvements in short-term wind power forecasts since it can scan close to the surface and produce wind profiles at a large distance upstream (15-30 km) if the atmosphere has sufficient aerosol loading and there are no sizable blockages from terrain or large structures. However, successful measurements require a large spatial sampling domain and new estimation algorithms that can perform well in the very weak signal regime. The maximum likelihood (ML) algorithm in the spectral domain and a faster version based on the minimum mean-square-error (MSE) are investigated by numerical simulation and with actual scanning Doppler lidar data from the Lockheed Martin Coherent Technologies WindTracer lidar. In addition, the maximum range can be extended by simultaneous estimation of the wind speed and wind direction from a larger azimuth sector scan if the atmosphere is well behaved.Real-time operation is possible using the spectral data from the WindTracer lidar and a dedicated computer to interface with a data assimilation system. Analysis of the Doppler lidar data in the first few kilometers can be used to extract the turbulence conditions for improvements in real-time wind farm operations. © 2013 American Meteorological Society.

Larson K.M.,University of Colorado at Boulder
Journal of Geophysical Research: Solid Earth | Year: 2013

Positions derived from continuously operating GPS sites are used throughout the world for geophysical research. These positions are estimated assuming that the GPS signals have not been obstructed by either snow or ice on the GPS antenna. Unfortunately, in many regions of the world, this assumption is not correct. Snow and ice attenuate and scatter the GPS signal in a way that leads to significant positioning errors. These positioning outliers are typically removed by assuming geophysical models of displacement. In this study an algorithm is developed that uses signal strength data to determine when the GPS signal has been impacted by snow or ice. This information is then used to remove outliers in GPS coordinate time series. The signal strength-based algorithm was tested on 6 years of data from the EarthScope Plate Boundary Observatory network. The algorithm improves the precision of ~10% of these coordinate time series, with most of the improvement found for sites operating in Alaska. © 2013. American Geophysical Union. All Rights Reserved.

Arch J.J.,University of Colorado at Boulder
Comprehensive Psychiatry | Year: 2013

In a national US sample of pregnant women (n = 311), we investigated the question of who becomes highly anxious about pregnancy by examining putative sociodemographic, pregnancy- and mental health-related predictors of pregnancy anxiety. We also assessed the contribution of pregnancy anxiety to the risk of significant alcohol consumption during pregnancy. English-speaking pregnant women aged 18+ years were recruited online. Results indicated that sociodemographic factors (younger age, white, unmarried, lower education, lower household income, no previous children), feelings about current pregnancy (unwanted), and general anxiety (higher general and state anxiety) predicted higher pregnancy-related anxiety, whereas age, religiosity, number of weeks pregnant, unplanned pregnancy, and maternal depressive symptoms did not. Pregnancy anxiety was the single strongest predictor of alcohol drinking risk during pregnancy (p <.001, â̂†R2 =.10) a relationship that held after controlling for other significant predictors. Pregnancy anxiety also represented the strongest predictor of screening positively for drinking risk during pregnancy at the total T-ACE (an alcohol risk screener for pregnancy) level of 3+ (odds ratio 95% CI = 1.61-4.14, p <.001), though not at the level of 2+ (odds ratio 95% CI = 0.98-1.68, p =.07). We discuss implications for the link between maternal mental health and birth/ child outcomes. © 2013 Elsevier Inc.

Schoennagel T.,University of Colorado at Boulder | Nelson C.R.,University of Montana
Frontiers in Ecology and the Environment | Year: 2011

The US National Fire Plan (NFP) is among the largest forest-restoration initiatives worldwide, removing wildland fuels on about 11 million hectares and costing over $6 billion. We evaluated the extent to which areas treated under the NFP - from 2004 to 2008, in forest ecosystems outside the wildland-urban interface in 11 western states ("West") - were predicted to need restoration, due to disruption of fire regimes and expected fuels buildup. Fuel-reduction treatments were implemented on about 1% of the West's forested areas. Fortythree percent of the treated area was predicted to have high-restoration need - almost twice as much as expected, given the distribution of these forests. However, an equal amount was in mixed-or uncertain-need forests, and 14% occurred in low-need forests, suggesting that managers need additional information on fireregime disruptions in some forest ecosystems to help prioritize restoration activities. Only one-quarter of the West's forested area shows strong evidence of uncharacteristic fuels buildup, which is often emphasized as the primary cause of current wildfire problems, potentially directing attention away from other important drivers such as climate change and an expanding wildland-urban interface. © The Ecological Society of America.

Cranmer S.R.,University of Colorado at Boulder | Woolsey L.N.,Harvard - Smithsonian Center for Astrophysics
Astrophysical Journal | Year: 2015

The solar chromosphere contains thin, highly dynamic strands of plasma known as spicules. Recently, it has been suggested that the smallest and fastest (Type II) spicules are identical to intermittent jets observed by the Interface Region Imaging Spectrograph. These jets appear to expand out along open magnetic field lines rooted in unipolar network regions of coronal holes. In this paper we revisit a thirty-year-old idea that spicules may be caused by upward forces associated with Alfvén waves. These forces involve the conversion of transverse Alfvén waves into compressive acoustic-like waves that steepen into shocks. The repeated buffeting due to upward shock propagation causes nonthermal expansion of the chromosphere and a transient levitation of the transition region (TR). Some older models of wave-driven spicules assumed sinusoidal wave inputs, but the solar atmosphere is highly turbulent and stochastic. Thus, we model this process using the output of a time-dependent simulation of reduced magnetohydrodynamic turbulence. The resulting mode-converted compressive waves are strongly variable in time, with a higher TR occurring when the amplitudes are large and a lower TR when the amplitudes are small. In this picture, the TR bobs up and down by several Mm on timescales less than a minute. These motions produce narrow, intermittent extensions of the chromosphere that have similar properties as the observed jets and Type II spicules. © 2015. The American Astronomical Society. All rights reserved..

Horneck G.,German Aerospace Center | Klaus D.M.,University of Colorado at Boulder | Mancinelli R.L.,Search for Extraterrestrial Intelligence Institute
Microbiology and Molecular Biology Reviews | Year: 2010

The responses of microorganisms (viruses, bacterial cells, bacterial and fungal spores, and lichens) to selected factors of space (microgravity, galactic cosmic radiation, solar UV radiation, and space vacuum) were determined in space and laboratory simulation experiments. In general, microorganisms tend to thrive in the space flight environment in terms of enhanced growth parameters and a demonstrated ability to proliferate in the presence of normally inhibitory levels of antibiotics. The mechanisms responsible for the observed biological responses, however, are not yet fully understood. A hypothesized interaction of microgravity with radiation-induced DNA repair processes was experimentally refuted. The survival of microorganisms in outer space was investigated to tackle questions on the upper boundary of the biosphere and on the likelihood of interplanetary transport of microorganisms. It was found that extraterrestrial solar UV radiation was the most deleterious factor of space. Among all organisms tested, only lichens (Rhizocarpon geographicum and Xanthoria elegans) maintained full viability after 2 weeks in outer space, whereas all other test systems were inactivated by orders of magnitude. Using optical filters and spores of Bacillus subtilis as a biological UV dosimeter, it was found that the current ozone layer reduces the biological effectiveness of solar UV by 3 orders of magnitude. If shielded against solar UV, spores of B. subtilis were capable of surviving in space for up to 6 years, especially if embedded in clay or meteorite powder (artificial meteorites). The data support the likelihood of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Kim J.-E.,University of Colorado at Boulder | Joan Alexander M.,NorthWest Research Associates, Inc.
Journal of Climate | Year: 2013

Tropical precipitation characteristics are investigated using the Tropical Rainfall Measuring Mission (TRMM) 3-hourly estimates, and the result is compared with five reanalyses including the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim), Modern Era Retrospective Analysis for Research and Applications (MERRA), National Centers for Environmental Prediction (NCEP)-National Center for Atmospheric Research (NCAR) reanalysis (NCEP1), NCEP-U.S. Department of Energy (DOE) reanalysis (NCEP2), and NCEP-Climate Forecast System Reanalysis (CFSR). Precipitation characteristics are evaluated in terms of the mean, convectively coupled equatorial wave activity, frequency characteristics, diurnal cycle, and seasonality of regional precipitation variability associated with submonthly scale waves. Generally the latest reanalyses such as ERA-Interim, MERRA, and CFSR show better performances than NCEP1 and NCEP2. However, all the reanalyses are still different from observations. Besides the positive mean bias in the reanalyses, a spectral analysis revealed that the reanalyses have overreddened spectra with persistent rainfall. MERRA has the most persistent rainfall, and CFSR appears to have the most realistic variability. The diurnal cycle in NCEP1 is extremely exaggerated relative to TRMM. The low-frequency waves with the period longer than 3 days are relatively well represented in ERAInterim, MERRA, and CFSR, but all the reanalyses have significant deficiencies in representing convectively coupled equatorial waves and variability in the high-frequency range. © 2013 American Meteorological Society.

Schmidt L.,Columbia University | Braun E.K.,Columbia University | Wager T.D.,University of Colorado at Boulder | Shohamy D.,Columbia University
Nature Neuroscience | Year: 2014

Expectations have a powerful influence on how we experience the world. Neurobiological and computational models of learning suggest that dopamine is crucial for shaping expectations of reward and that expectations alone may influence dopamine levels. However, because expectations and reinforcers are typically manipulated together, the role of expectations per se has remained unclear. We separated these two factors using a placebo dopaminergic manipulation in individuals with Parkinson's disease. We combined a reward learning task with functional magnetic resonance imaging to test how expectations of dopamine release modulate learning-related activity in the brain. We found that the mere expectation of dopamine release enhanced reward learning and modulated learning-related signals in the striatum and the ventromedial prefrontal cortex. These effects were selective to learning from reward: neither medication nor placebo had an effect on learning to avoid monetary loss. These findings suggest a neurobiological mechanism by which expectations shape learning and affect. © 2014 Nature America, Inc. All rights reserved.

Winey M.,University of Colorado at Boulder | Bloom K.,University of North Carolina at Chapel Hill
Genetics | Year: 2012

The Saccharomyces cerevisiae mitotic spindle in budding yeast is exemplified by its simplicity and elegance. Microtubules are nucleated from a crystalline array of proteins organized in the nuclear envelope, known as the spindle pole body in yeast (analogous to the centrosome in larger eukaryotes). The spindle has two classes of nuclear microtubules: kinetochore microtubules and interpolar microtubules. One kinetochore microtubule attaches to a single centromere on each chromosome, while approximately four interpolar microtubules emanate from each pole and interdigitate with interpolar microtubules from the opposite spindle to provide stability to the bipolar spindle. On the cytoplasmic face, two to three microtubules extend from the spindle pole toward the cell cortex. Processes requiring microtubule function are limited to spindles in mitosis and to spindle orientation and nuclear positioning in the cytoplasm. Microtubule function is regulated in large part via products of the 6 kinesin gene family and the 1 cytoplasmic dynein gene. A single bipolar kinesin (Cin8, class Kin-5), together with a depolymerase (Kip3, class Kin-8) or minus-end-directed kinesin (Kar3, class Kin-14), can support spindle function and cell viability. The remarkable feature of yeast cells is that they can survive with microtubules and genes for just two motor proteins, thus providing an unparalleled system to dissect microtubule and motor function within the spindle machine. © 2012 by the Genetics Society of America.

Kamenetzky J.R.,University of Colorado at Boulder
Science and Public Policy | Year: 2013

Though the US National Science Foundation introduced a broader impacts criterion to their merit review process in 1997, policy evaluations remain still scarce. Reactions from different scientific fields varied. This paper aims to quantitatively compare the proposed broader impacts of 360 funded abstracts from biology, engineering, and mathematical/physical sciences. Specifically, it considers whether or not certain fields are more likely to propose certain types of broader impacts activities, whether women principal investigators are more likely to propose broader impacts, and the effect of grant size. This study demonstrates that cultural differences exist between scientific fields and also supports existing policy recommendations that encourage the creation of organizations and partnerships at university level to allow scientists to more easily participate in activities with broader impacts. Emphasizing broader impacts activities may also attract a more diverse scientific workforce, as many individuals do not pursue science because of a perceived lack of impact. © The Author 2012. Published by Oxford University Press. All rights reserved.

Strife S.,University of Colorado at Boulder
Journal of Environmental Education | Year: 2010

Recently the environmental movement has seen much success and progress under a newly-framed green paradigm. Yet, despite the proliferation of national attention to, and public interest in, the go-green mentality, environmental education still seems to be stuck within the old environmental paradigm. This critical essay shares lessons that environmental education can learn through incorporating a human benefits approach. Ultimately, this essay calls for a reflection on environmental education's presence within the budding sustainability movement and calls for the "humanization" of environmental education discourse and pedagogical practice. Copyright © 2010 Taylor & Francis Group, LLC.

Sivaselvan M.V.,University of Colorado at Boulder
International Journal for Numerical Methods in Engineering | Year: 2011

In this paper, we describe an algorithm for the incremental state update of elasto-plastic systems with softening. The algorithm uses a complementary pivoting technique and is based on casting the incremental state update as a complementarity problem. In developing the algorithm, we take advantage of the special features of solid and structural mechanics problems to achieve good computational performance, and hence the ability to compute numerical solutions to practical size problems. For example, the notion of a tangent stiffness matrix arises. Numerical examples using models of skeletal structures are presented to demonstrate the practicability of the algorithm. The numerical examples also raise some interesting questions about multiplicity of the solutions. © 2010 John Wiley & Sons, Ltd.

Pao L.,University of Colorado at Boulder | Johnson K.E.,Center for Research and Education in Wind
IEEE Control Systems Magazine | Year: 2011

Wind energy is a fast-growing interdisciplinary field that encompasses multiple branches of engineering and science. According to the World Wind Energy Association, the global installed capacity of wind turbines grew at an average rate of 27 per year over the years 20052009 [1]. At the end of 2009, the installed capacity in the United States was about 35,000 MW [2], while the worldwide installed capacity was approximately 160,000 MW (see Figure 1). Wind is recognized worldwide as a costeffective, environmentally friendly solution to energy shortages. © 2006 IEEE.

Tierney K.,University of Colorado at Boulder
Annual Review of Environment and Resources | Year: 2012

Disaster governance is an emerging concept in the disaster research literature that is closely related to risk governance and environmental governance. Disaster governance arrangements and challenges are shaped by forces such as globalization, world-system dynamics, social inequality, and sociodemographic trends. Governance regimes are polycentric and multiscale, show variation across the hazards cycle, and tend to lack integration and to be formulated in response to particular large-scale disaster events. Disaster governance is nested within and influenced by overarching societal governance systems. Although governance failures can occur in societies with stable governance systems, as the governmental response to Hurricane Katrina shows, poorly governed societies and weak states are almost certain to exhibit deficiencies in disaster governance. State-civil society relationships, economic organization, and societal transitions have implications for disaster governance. Various measures can be employed to assess disaster governance; more research is needed in this nascent field of study on factors that contribute to effective governance and on other topics, such as the extent to which governance approaches contribute to long-term sustainability. © Copyright ©2012 by Annual Reviews. All rights reserved.

Kirschner C.M.,University of Colorado at Boulder | Brennan A.B.,University of Florida
Annual Review of Materials Research | Year: 2012

Biofouling is a complex, dynamic problem that globally impacts both the economy and environment. Interdisciplinary research in marine biology, polymer science, and engineering has led to the implementation of bio-inspired strategies for the development of the next generation of antifouling marine coatings. Natural fouling defense mechanisms have been mimicked through chemical, physical, andor stimuli-responsive strategies. This review outlines the detrimental effects associated with biofouling, describes the theoretical basis for antifouling coating design, and highlights prominent advances in bio-inspired antifouling technologies. © Copyright ©2012 by Annual Reviews. All rights reserved.

McHenry C.S.,University of Colorado at Boulder
Annual Review of Biochemistry | Year: 2011

Bacterial replicases are complex, tripartite replicative machines. They contain a polymerase, polymerase III (Pol III), a βÎ2;2 processivity factor, and a DnaX complex ATPase that loads βÎ2 onto DNA and chaperones Pol III onto the newly loaded βÎ2. Bacterial replicases are highly processive, yet cycle rapidly during Okazaki fragment synthesis in a regulated way. Many bacteria encode both a full-length τ and a shorter γ form of DnaX by a variety of mechanisms. γappears to be uniquely placed in a single position relative to two τ protomers in a pentameric ring. The polymerase catalytic subunit of Pol III, α±, contains a PHP domain that not only binds to a prototypical εμ Mg 2+-dependent exonuclease, but also contains a second Zn 2+-dependent proofreading exonuclease, at least in some bacteria. This review focuses on a critical evaluation of recent literature and concepts pertaining to the above issues and suggests specific areas that require further investigation. © 2011 by Annual Reviews. All rights reserved.

Batey R.T.,University of Colorado at Boulder
Wiley Interdisciplinary Reviews: RNA | Year: 2011

Riboswitches are regulatory elements commonly found in the 5′ leader sequences of bacterial mRNAs that bind cellular metabolites to direct expression at either the transcriptional or translational level. The effectors of these RNAs are chemically diverse, including nucleobases and nucleosides, amino acids, cofactors, and second messenger molecules. Over the last few years, a number of structures have revealed the architectural means by which RNA creates binding pockets of high affinity and specificity for these compounds. For most effectors, there is a single class of associated riboswitches. However, eight individual classes of S-adenosylmethionine (SAM) and/or S-adenosylhomocysteine (SAH) responsive riboswitches that control various aspects of sulfur metabolism have been validated, revealing a diverse set of solutions to the recognition of these ubiquitous metabolites. This review focuses upon the structures of RNAs that bind SAM and SAH and how they discriminate between these compounds. © 2011 John Wiley & Sons, Ltd.

Dilling L.,University of Colorado at Boulder | Lemos M.C.,University of Michigan
Global Environmental Change | Year: 2011

In the past several decades, decision makers in the United States have increasingly called upon publicly funded science to provide "usable" information for policy making, whether in the case of acid rain, famine prevention or climate change policy. As demands for usability become more prevalent for publicly accountable scientific programs, there is a need to better understand opportunities and constraints to science use in order to inform policy design and implementation. Motivated by recent critique of the decision support function of the US Global Change Research Program, this paper seeks to address this issue by specifically examining the production and use of climate science. It reviews empirical evidence from the rich scholarship focused on climate science use, particularly seasonal climate forecasts, to identify factors that constrain or foster usability. It finds, first, that climate science usability is a function both of the context of potential use and of the process of scientific knowledge production itself. Second, nearly every case of successful use of climate knowledge involved some kind of iteration between knowledge producers and users. The paper argues that, rather than an automatic outcome of the call for the production of usable science, iterativity is the result of the action of specific actors and organizations who 'own' the task of building the conditions and mechanisms fostering its creation. Several different types of institutional arrangements can accomplish this task, depending on the needs and resources available. While not all of the factors that enhance usability of science for decision making are within the realm of the scientific enterprise itself, many do offer opportunities for improvement. Science policy mechanisms such as the level of flexibility afforded to research projects and the metrics used to evaluate the outcomes of research investment can be critical to providing the necessary foundation for iterativity and production of usable science to occur. © 2010 Elsevier Ltd.

Roettger M.E.,University of Colorado at Boulder | Swisher R.R.,Bowling Green State University
Criminology | Year: 2011

Nearly 13 percent of young adult men report that their biological father has served time in jail or prison; yet surprisingly little research has examined how a father's incarceration is associated with delinquency and arrest in the contemporary United States. Using a national panel of Black, White, and Hispanic males, this study examines whether experiencing paternal incarceration is associated with increased delinquency in adolescence and young adulthood. We find a positive association with paternal incarceration that is robust to controls for several structural, familial, and adolescent characteristics. Relative to males not experiencing a father's incarceration, our results show that those experiencing a father's incarceration have an increased propensity for delinquency that persists into young adulthood. Using a national probability sample, we also find that a father's incarceration is highly and significantly associated with an increased risk of incurring an adult arrest before 25 years of age. These observed associations are similar across groups of Black, White, and Hispanic males. Taken as a whole, our findings suggest benefits from public policies that focus on male youth "at risk" as a result of having an incarcerated father. © 2011 American Society of Criminology.

Duchateau J.,Free University of Colombia | Enoka R.M.,University of Colorado at Boulder
Brain Research | Year: 2011

Soon after Edward Liddell [1895-1981] and Charles Sherrington [1857-1952] introduced the concept of a motor unit in 1925 and the necessary technology was developed, the recording of single motor unit activity became feasible in humans. It was quickly discovered by Edgar Adrian [1889-1977] and Detlev Bronk [1897-1975] that the force exerted by muscle during voluntary contractions was the result of the concurrent recruitment of motor units and modulation of the rate at which they discharged action potentials. Subsequent studies found that the relation between discharge frequency and motor unit force was characterized by a sigmoidal function. Based on observations on experimental animals, Elwood Henneman [1915-1996] proposed a "size principle" in 1957 and most studies in humans focussed on validating this concept during various types of muscle contractions. By the end of the 20th C, the experimental evidence indicated that the recruitment order of human motor units was determined primarily by motoneuron size and that the occasional changes in recruitment order were not an intended strategy of the central nervous system. Fundamental knowledge on the function of Sherrington's "common final pathway" was expanded with observations on motor unit rotation, minimal and maximal discharge rates, discharge variability, and self-sustained firing. Despite the great amount of work on characterizing motor unit activity during the first century of inquiry, however, many basic questions remain unanswered and these limit the extent to which findings on humans and experimental animals can be integrated and generalized to all movements. © 2011 Elsevier B.V. All rights reserved.

Breed M.D.,University of Colorado at Boulder
Animal Behaviour | Year: 2014

Kin selection stands among W. D. Hamilton's most influential ideas. The purpose of this review is to assess the impact of Hamilton's ideas about kin selection on studies of social recognition. Kin selection theory predicts that animals should direct aid-giving behaviour to closely related animals, provided that a positive net benefit in inclusive fitness is achieved from the altruistic act. Kin recognition is the key proximate mechanism by which animals can sort more related from less related interactants in a population. Kin recognition also has the potential to allow fine distinctions among animals based on identity by descent. Following the publications of Hamilton's 1964 papers on kin selection, studies of kin recognition focused on four disparate behavioural contexts: identification of group membership, inbreeding avoidance, alarm calls and other forms of aid-giving, and parent-offspring interactions. Investigations of eusocial insects have focused on identification of group membership by phenotypes that are shared among all members of a colony. In birds and mammals, social structure is often based on individual recognition. Some species, particularly rodents, have the ability to make discriminations based on relatedness among animals that they have not previously met. Future studies of kin recognition should be less reliant on assumptions that all forms of societal closure are due to factors related to kin selection. These studies should acknowledge that the role of individual recognition in vertebrate societies is key to understanding the full texture of social interactions, and that individual recognition may be equally important in many other types of animals. Of particular interest will be the discovery of how information about kinship is integrated with information about individual identity. © 2014.

Su T.T.,University of Colorado at Boulder
Chromosoma | Year: 2011

Eukaryotic cells employ a plethora of conserved proteins and mechanisms to ensure genome integrity. In metazoa, these mechanisms must operate in the context of organism development. This mini-review highlights two emerging features of DNA damage responses in Drosophila: a crosstalk between DNA damage responses and components of the spindle assembly checkpoint, and increasing evidence for the effect of DNA damage on the developmental program at multiple points during the Drosophila life cycle. © 2011 Springer-Verlag.

Glantz M.H.,University of Colorado at Boulder
International Journal of Disaster Risk Science | Year: 2015

The troubled forecast of El Niño’s onset in 2014 requires an explanation as well as an open dialogue with the user community that depends on such an important forecast. A review of the forecasts on the Internet reflects two different perceptions about what transpired. The forecast community suggests they got it right, while the popular media suggests forecasters got it wrong. Why such a gap? The major El Niño that was alluded to by several organizations did not materialize when or even as expected. A science-fed media frenzy took place about an event considered in retrospect to have been an unusual borderline (weak) El Niño event, “trickiest ever to forecast.” That is understandable, as the science of El Niño is still on a learning curve. But it suggests that the forecasting of El Niño’s onset is still in an experimental phase and not yet operational. Forecasting its onset (as a specific event) should be separated from forecasting its behavior and impacts (as a process) once the onset has been assured. Whenever a forecast is made, someone is responding to it. Therefore, such a distinction is necessary for the benefit of those societies and economic sectors affected by El Niño. © 2015, The Author(s).

Godin O.A.,University of Colorado at Boulder
Journal of the Acoustical Society of America | Year: 2012

A theory of guided propagation of sound in layered, moving fluids is extended to include acoustic-gravity waves (AGWs) in waveguides with piecewise continuous parameters. The orthogonality of AGW normal modes is established in moving and motionless media. A perturbation theory is developed to quantify the relative significance of the gravity and fluid compressibility as well as sensitivity of the normal modes to variations in sound speed, flow velocity, and density profiles and in boundary conditions. Phase and group speeds of the normal modes are found to have certain universal properties which are valid for waveguides with arbitrary stratification. The Lamb wave is shown to be the only AGW normal mode that can propagate without dispersion in a layered medium. © 2012 Acoustical Society of America.

Ebel B.A.,University of Colorado at Boulder
Water Resources Research | Year: 2013

A series of virtual experiments were conducted using a one-dimensional numerical model of unsaturated flow (Hydrus-1D) to investigate the factors responsible for shifts in subsurface hydrologic response following wildfire. These virtual experiments used a series of well-characterized experimental plots in the area affected by the 2010 Fourmile Canyon Fire near Boulder, CO, USA, that cover north and south facing slope aspects for plots both affected and unaffected by wildfire. Inverse estimation of soil-hydraulic parameters allowed establishing "foundation simulations" that served as the basis for virtual experiments to test findings from interpretation of field and laboratory data and extend understanding beyond what could be gleaned from data alone. The numerical model virtual experiments showed that loss of transpiration because of vegetation combustion/mortality caused soils to be wetter at depths greater than 5 cm on both north and south facing slopes, which agrees with field observations. Loss of tree canopy interception contributed to wetter subsurface conditions and loss of litter/duff increased evaporation, drying soils, in the top few cm on north facing slopes. On south facing slopes, at depths shallower than 3 cm, the simulations did not reproduce the observed trends of drier soils after wildfire, which suggests that more robust methods are needed to simulate evaporation and soil-water retention at soil-water contents less than 0.05 cm3 cm-3. Simulated bottom boundary flux, a proxy for groundwater recharge, was greater in north facing burned plots by a factor of 3.5-5.2 and greater on south facing plots by a factor of 10.6-12.7, relative to unburned plots. © 2013. American Geophysical Union. All Rights Reserved.

Bernard J.A.,University of Colorado at Boulder | Mittal V.A.,Northwestern University
Psychological Medicine | Year: 2015

Within the NIMH Research Domain Criteria (RDoC) framework, dimensions of behavior are investigated across diagnoses with the goal of developing a better understanding of their underlying neural substrates. Currently, this framework includes five domains: cognitive, social, arousal/regulatory, negative, and positive valence systems. We argue that the inclusion of a motor systems domain is sorely needed as well. Independent of medication, distinct areas of motor dysfunction (e.g. motor planning/inhibition/learning/coordination, involuntary movements) commonly appear across a number of mental disorders (e.g. schizophrenia, bipolar disorder, autism, attention deficit hyperactivity disorder, Alzheimer's disease, depression) as well as neurological disorders accompanied by significant psychological symptoms (e.g. Parkinson's disease). In addition, motor systems are amenable to study across multiple levels of analysis from the cellular molecular level focusing on cytoarchitechtonics and neurotransmitter systems, to networks and circuits measured using neuroimaging, and finally at the level of overt behavioral performance. Critically, the neural systems associated with motor performance have been relatively well defined, and different circuits have been linked to distinct aspects of motor behavior. As such, they may also be differentially associated with symptoms and motor dysfunction across diagnoses, and be uniquely informative about underlying etiology. Importantly, motor signs can change across stages of illness; they are also often present in the prodromal phases of disease and closely linked with course, suggesting that these behaviors represent a core feature reflective of pathogenic processes. The inclusion of a motor domain would allow researchers to better understand psychopathology more broadly, and may also reveal important contributions to disease processes across diagnoses. © 2015 Cambridge University Press.

Colwell R.K.,University of Connecticut | Colwell R.K.,University of Colorado at Boulder | Dunn R.R.,North Carolina State University | Harris N.C.,North Carolina State University
Annual Review of Ecology, Evolution, and Systematics | Year: 2012

The extinction of a single species is rarely an isolated event. Instead, dependent parasites, commensals, and mutualist partners (affiliates) face the risk of coextinction as their hosts or partners decline and fail. Species interactions in ecological networks can transmit the effects of primary extinctions within and between trophic levels, causing secondary extinctions and extinction cascades. Documenting coextinctions is complicated by ignorance of host specificity, limitations of historical collections, incomplete systematics of affiliate taxa, and lack of experimental studies. Host shifts may reduce the rate of coextinctions, but they are poorly understood. In the absence of better empirical records of coextinctions, statistical models estimate the rates of past and future coextinctions, and based on primary extinctions and interactions among species, network models explore extinction cascades. Models predict and historical evidence reveals that the threat of coextinction is Influenced by both host and affiliate traits and is exacerbated by other threats, including habitat loss, climate change, and invasive species. © 2012 by Annual Reviews. All rights reserved.

Wu Y.,University of Washington | Cai X.-C.,University of Colorado at Boulder
Journal of Computational Physics | Year: 2014

Due to the rapid advancement of supercomputing hardware, there is a growing interest in parallel algorithms for modeling the full three-dimensional interaction between the blood flow and the arterial wall. In [4], Barker and Cai developed a parallel framework for solving fluid-structure interaction problems in two dimensions. In this paper, we extend the idea to three dimensions. We introduce and study a parallel scalable domain decomposition method for solving nonlinear monolithically coupled systems arising from the discretization of the coupled system in an arbitrary Lagrangian-Eulerian framework with a fully implicit stabilized finite element method. The investigation focuses on the robustness and parallel scalability of the Newton-Krylov algorithm preconditioned with an overlapping additive Schwarz method. We validate the proposed approach and report the parallel performance for some patient-specific pulmonary artery problems. The algorithm is shown to be scalable with a large number of processors and for problems with millions of unknowns. © 2013 Elsevier Inc.

Moore J.R.,Boston University | Leinwand L.,University of Colorado at Boulder | Warshaw D.M.,University of Vermont
Circulation Research | Year: 2012

Hypertrophic (HCM) and dilated (DCM) cardiomyopathies are inherited diseases with a high incidence of death due to electric abnormalities or outflow tract obstruction. In many of the families afflicted with either disease, causative mutations have been identified in various sarcomeric proteins. In this review, we focus on mutations in the cardiac muscle molecular motor, myosin, and its associated light chains. Despite the >300 identified mutations, there is still no clear understanding of how these mutations within the same myosin molecule can lead to the dramatically different clinical phenotypes associated with HCM and DCM. Localizing mutations within myosin's molecular structure provides insight into the potential consequence of these perturbations to key functional domains of the motor. Review of biochemical and biophysical data that characterize the functional capacities of these mutant myosins suggests that mutant myosins with enhanced contractility lead to HCM, whereas those displaying reduced contractility lead to DCM. With gain and loss of function potentially being the primary consequence of a specific mutation, how these functional changes trigger the hypertrophic response and lead to the distinct HCM and DCM phenotypes will be the future investigative challenge. © 2012 American Heart Association, Inc.

Hacker J.P.,Naval Postgraduate School, Monterey | Angevine W.M.,University of Colorado at Boulder
Monthly Weather Review | Year: 2013

Experiments with the single-column implementation of the Weather Research and Forecasting Model provide a basis for deducing land-atmosphere coupling errors in the model. Coupling occurs both through heat and moisture fluxes through the land-atmosphere interface and roughness sublayer, and turbulent heat, moisture, and momentum fluxes through the atmospheric surface layer. This work primarily addresses the turbulent fluxes, which are parameterized following the Monin-Obukhov similarity theory applied to the atmospheric surface layer. By combining ensemble data assimilation and parameter estimation, the model error can be characterized. Ensemble data assimilation of 2-m temperature and water vapor mixing ratio, and 10-m wind components, forces the model to follow observations during a month-long simulation for a column over the well-instrumented Atmospheric Radiation Measurement (ARM) Central Facility near Lamont, Oklahoma. One-hour errors in predicted observations are systematically small but nonzero, and the systematic errors measure bias as a function of local time of day. Analysis increments for state elements nearby (15 m AGL) can be too small or have the wrong sign, indicating systematically biased covariances and model error. Experiments using the ensemble filter to objectively estimate a parameter controlling the thermal land- atmosphere coupling show that the parameter adapts to offset the model errors, but that the errors cannot be eliminated. Results suggest either structural errors or further parametric errors that may be difficult to estimate. Experiments omitting atypical observations such as soil and flux measurements lead to qualitatively similar deductions, showing the potential for assimilating common in situ observations as an inexpensive framework for deducing and isolating model errors. © 2013 American Meteorological Society.

Slater A.G.,University of Colorado at Boulder | Lawrence D.M.,U.S. National Center for Atmospheric Research
Journal of Climate | Year: 2013

Permafrost is a characteristic aspect of the terrestrial Arctic and the fate of near-surface permafrost over the next century is likely to exert strong controls on Arctic hydrology and biogeochemistry. Using output from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), the authors assess its ability to simulate present-day and future permafrost. Permafrost extent diagnosed directly from each climate model's soil temperature is a function of the modeled surface climate as well as the ability of the land surface model to represent permafrost physics. For each CMIP5 model these two effects are separated by using indirect estimators of permafrost driven by climatic indices and compared to permafrost extent directly diagnosed via soil temperatures. Several robust conclusions can be drawn from this analysis. Significant air temperature and snow depth biases exist in some model's climates, which degrade both directly and indirectly diagnosed permafrost conditions. The range of directly calculated present-day (1986-2005) permafrost area is extremely large (~4-25×106 km2). Several land models contain structural weaknesses that limit their skill in simulating cold region subsurface processes. The sensitivity of future permafrost extent to temperature change over the present-day observed permafrost region averages (1.67±0.7)x106km2°C-1 but is a function of the spatial and temporal distribution of climate change. Because of sizable differences in future climates for the representative concentration pathway (RCP) emission scenarios, a wide variety of future permafrost states is predicted by 2100. Conservatively, the models suggest that for RCP4.5, permafrost will retreat from the present-day discontinuous zone. Under RCP8.5, sustainable permafrost will be most probable only in the Canadian Archipelago, Russian Arctic coast, and east Siberian uplands. © 2013 American Meteorological Society.

Hermele M.,University of Colorado at Boulder
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We construct a family of exactly solvable spin models that illustrate a mechanism for fractionalization in topologically ordered phases, dubbed the string flux mechanism. The essential idea is that an anyon of a topological phase can be endowed with fractional quantum numbers when the string attached to it slides over a background pattern of flux in the ground state. The string flux models that illustrate this mechanism are Zn quantum double models defined on specially constructed d-dimensional lattices, and possess Zn topological order for d≥2. The models have a unitary, internal symmetry G, where G is an arbitrary finite group. The simplest string flux model is a Z2 toric code defined on a bilayer square lattice, where G=Z2 is layer-exchange symmetry. In general, by varying the pattern of Zn flux in the ground state, any desired fractionalization class [element of H2(G,Zn)] can be realized for the Zn charge excitations. While the string flux models are not gauge theories, they map to Zn gauge theories in a certain limit, where they follow a magnetic route for the emergence of low-energy gauge structure. The models are analyzed by studying the action of G symmetry on Zn charge excitations, and by gauging the G symmetry. The latter analysis confirms that distinct fractionalization classes give rise to distinct quantum phases, except that classes [ω],[ω]-1H2(G,Zn) give rise to the same phase. We conclude with a discussion of open issues and future directions. © 2014 American Physical Society.

Roberts T.D.,University of Colorado at Boulder
Applied Geography | Year: 2011

Recent empirical investigations have illustrated the stochastic validity of the IPAT model. The preponderance of these studies shows that theoretical relationships of IPAT hold at large units of analysis. This research applies the stochastic transformation of the IPAT-STIRPAT-model in the southeastern US. Using county-level data, this research illustrates that population is a unit-elastic determinant of total carbon emissions. At the same time, various metrics of affluence present statistically mixed results for wealth as a determinant of environmental degradation. Other " sunbelt" technology variables designed to capture the effects of economic restructuring are significant, suggesting that post-Fordist geographies complicate the nature of the relationships in the identity model. © 2010 Elsevier Ltd.

Wager T.D.,University of Colorado at Boulder | Atlas L.Y.,National Center for Complementary and Integrative Health
Nature Reviews Neuroscience | Year: 2015

Placebo effects are beneficial effects that are attributable to the brain-mind responses to the context in which a treatment is delivered rather than to the specific actions of the drug. They are mediated by diverse processes-including learning, expectations and social cognition-and can influence various clinical and physiological outcomes related to health. Emerging neuroscience evidence implicates multiple brain systems and neurochemical mediators, including opioids and dopamine. We present an empirical review of the brain systems that are involved in placebo effects, focusing on placebo analgesia, and a conceptual framework linking these findings to the mind-brain processes that mediate them. This framework suggests that the neuropsychological processes that mediate placebo effects may be crucial for a wide array of therapeutic approaches, including many drugs. © 2015 Macmillan Publishers Limited.

Millan R.M.,Dartmouth College | Baker D.N.,University of Colorado at Boulder
Space Science Reviews | Year: 2012

Discovered in 1958, Earth's radiation belts persist in being mysterious and unpredictable. This highly dynamic region of near-Earth space provides an important natural laboratory for studying the physics of particle acceleration. Despite the proximity of the radiation belts to Earth, many questions remain about the mechanisms responsible for rapidly energizing particles to relativistic energies there. The importance of understanding the radiation belts continues to grow as society becomes increasingly dependent on spacecraft for navigation, weather forecasting, and more. We review the historical underpinning and observational basis for our current understanding of particle acceleration in the radiation belts. © 2012 The Author(s).

Jones M.,University of Colorado at Boulder | Love B.C.,University of Texas at Austin
Behavioral and Brain Sciences | Year: 2011

The prominence of Bayesian modeling of cognition has increased recently largely because of mathematical advances in specifying and deriving predictions from complex probabilistic models. Much of this research aims to demonstrate that cognitive behavior can be explained from rational principles alone, without recourse to psychological or neurological processes and representations. We note commonalities between this rational approach and other movements in psychology â€" namely, Behaviorism and evolutionary psychology â€" that set aside mechanistic explanations or make use of optimality assumptions. Through these comparisons, we identify a number of challenges that limit the rational program's potential contribution to psychological theory. Specifically, rational Bayesian models are significantly unconstrained, both because they are uninformed by a wide range of process-level data and because their assumptions about the environment are generally not grounded in empirical measurement. The psychological implications of most Bayesian models are also unclear. Bayesian inference itself is conceptually trivial, but strong assumptions are often embedded in the hypothesis sets and the approximation algorithms used to derive model predictions, without a clear delineation between psychological commitments and implementational details. Comparing multiple Bayesian models of the same task is rare, as is the realization that many Bayesian models recapitulate existing (mechanistic level) theories. Despite the expressive power of current Bayesian models, we argue they must be developed in conjunction with mechanistic considerations to offer substantive explanations of cognition. We lay out several means for such an integration, which take into account the representations on which Bayesian inference operates, as well as the algorithms and heuristics that carry it out. We argue this unification will better facilitate lasting contributions to psychological theory, avoiding the pitfalls that have plagued previous theoretical movements. © 2011 Cambridge University Press.

Marks M.J.,University of Colorado at Boulder
Biochemical Pharmacology | Year: 2013

This research update summarizes thirty years of studies on genetic influences on responses to the acute or chronic administration of nicotine. Early studies established that various inbred mice are differentially sensitive to the effects of the drug. Classical genetic analyses confirmed that nicotine effects on locomotion, body temperature and seizures are heritable. A significant inverse correlation between the locomotor and hypothermic effects and the density of nicotine binding sites suggested that differential expression α4β2-neuronal nicotinic acetylcholine receptor (nAChR) mediated some of this genetic variability. Subsequent studies with α4 and β2 nAChR null (decreased sensitivity) and gain of function mutants (increased sensitivity) supports the role of the α4β2*nAChR subtype. However, null mutant mice still respond to nicotine, indicating that other nAChR subtypes also mediate these responses. Mice differing in initial sensitivity to nicotine also differ in tolerance development following chronic treatment: those mice that are initially more sensitive to nicotine develop tolerance at lower treatment doses than less sensitivemice, indicating that tolerance is an adaptive response to the effects of nicotine. In contrast, the sensitivity of mice to pre-pulse inhibition of acoustic startle response is correlated with the expression of α7-nAChR. While genetic variability in nAChR expression and function is an important factor contributing to differences in response to nicotine, the observations that altered activity of opioid, glutamate, and cannabinoid receptors among others also change nicotine sensitivity reinforces the proposal that the genetics of nicotine response is more complex than differences in nAChRs. © 2013 Elsevier Inc. All rights reserved.

Smith M.K.,University of Maine, United States | Knight J.K.,University of Colorado at Boulder
Genetics | Year: 2012

To help genetics instructors become aware of fundamental concepts that are persistently difficult for students, we have analyzed the evolution of student responses to multiple-choice questions from the Genetics Concept Assessment. In total, we examined pretest (before instruction) and posttest (after instruction) responses from 751 students enrolled in six genetics courses for either majors or nonmajors. Students improved on all 25 questions after instruction, but to varying degrees. Notably, there was a subgroup of nine questions for which a single incorrect answer, called the most common incorrect answer, was chosen by.>20% of students on the posttest. To explore response patterns to these nine questions, we tracked individual student answers before and after instruction and found that particular conceptual difficulties about genetics are both more likely to persist and more likely to distract students than other incorrect ideas. Here we present an analysis of the evolution of these incorrect ideas to encourage instructor awareness of these genetics concepts and provide advice on how to address common conceptual difficulties in the classroom. © 2012 by the Genetics Society of America.

Park W.,University of Colorado at Boulder
Laser Physics Letters | Year: 2010

Silicon is an important material for integrated photonics applications. High refractive index and transparency in the infrared region makes it an ideal platform to implement nanostructures for novel optical devices. We fabricated silicon photonic crystals and experimentally demonstrated negative refraction and self-collimation. We also used heterodyne near-field scanning optical microscope to directly visualize the anomalous wavefronts. When the periodicity is much smaller than wave-length, silicon photonic crystal can be described by the effective medium theory. By engineering effective refractive index with silicon nanorod size, we demonstrated an all-dielectric cloak structure which can hide objects in front of a highly reflecting plane. The work discussed in this review shows the powerful design flexibility and versatility of silicon nanostructures. © 2010 by Astro Ltd.

Greene C.H.,University of Colorado at Boulder
Physics Today | Year: 2010

Can one extract key properties of atomic nuclei by studying the seemingly unrelated system of a few cold, interacting atoms in a quantum gas? The answer is a resounding yes. The reason for that unexpected connection, which links energies spanning some 18 orders of magnitude, can be traced to universality in few-body physics, the focus of this article. In some cases, studies of systems with just two, three, or four atoms have even helped researchers identify fundamental aspects of a degenerate quantum gas having more than 100000 particles. © American Institute of Physics.

In the mid-latitude mountains of North America, archaeological materials have been identified in association with kinetically stable "ice patches" that attracted animals and their human predators. The stable ice in these features exhibits little internal deformation or movement and can preserve otherwise perishable materials for millennia. Eight prehistoric sites have been identified in association with perennial ice patches within the Greater Yellowstone Area of Montana and Wyoming. Surveys in Colorado have produced paleobiological samples, but no definitive archaeological sites. Archaeological remains include ancient wooden dart shafts and fragments, wooden artifacts of unknown function, a wrapped leather object of unknown function, butchered animal remains, and chipped stone artifacts. Fragments of weapons ranging in age from 200 to 10 400 years suggest long-term continuity in ice patch hunting in the region. Paleobiological specimens range in age from several hundred to nearly 8000 years. Bighorn sheep (Ovis canadensis) is a presumed prey species, but the remains of bison (Bison bison) and other large ungulates also occur. Ice patches offer important insights into the use of high-elevation environments by Native Americans. Efforts are ongoing to build and maintain awareness of these resources among federal land managers and the public. © The Arctic Institute of North America.

Pielke R.A.,University of Colorado at Boulder | Wilby R.L.,Loughborough University
Eos | Year: 2012

Dynamical and statistical downscaling of multidecadal global climate models provides finer spatial resolution information for climate impact assessments [Wilby and Fowler, 2010]. Increasingly, some scientists are using the language of "prediction" with respect to future regional climate change and impacts [e.g., Hurrell et al., 2009; Shapiro et al., 2010], yet others note serious reservations about the capability of downscaling to provide detailed, accurate predictions [see Kerr, 2011]. Dynamic downscaling is based on regional climate models (usually just the atmospheric part) that have finer horizontal grid resolution of surface features such as terrain [Castro et al., 2005]. Statistical downscaling uses transfer functions (e.g., regression relationships) representing observed relationships between larger-scale atmospheric variables and local quantities such as daily precipitation and/or temperature [Wilby and Fowler, 2010]. These approaches have been successful in improving the skill of numerical weather prediction. Statistical downscaling can also be used as the benchmark (the control) against which dynamic downscaling skill is judged [Landsea and Knaff, 2000].

Mckinney J.C.,Kavli Institute for Particle Astrophysics and Cosmology | Uzdensky D.A.,University of Colorado at Boulder
Monthly Notices of the Royal Astronomical Society | Year: 2012

Prompt gamma-ray burst (GRB) emission requires some mechanism to dissipate an ultrarelativistic jet. Internal shocks or some form of electromagnetic dissipation are candidate mechanisms. Any mechanism needs to answer basic questions, such as what is the origin of variability, what radius does dissipation occur at, and how does efficient prompt emission occur. These mechanisms also need to be consistent with how ultrarelativistic jets form and stay baryon pure despite turbulence and electromagnetic reconnection near the compact object and despite stellar entrainment within the collapsar model. We use the latest magnetohydrodynamical models of ultrarelativistic jets to explore some of these questions in the context of electromagnetic dissipation due to the slow collisional and fast collisionless reconnection mechanisms, as often associated with Sweet-Parker and Petschek reconnection, respectively. For a highly magnetized ultrarelativistic jet and typical collapsar parameters, we find that significant electromagnetic dissipation may be avoided until it proceeds catastrophically near the jet photosphere at large radii (r~ 1013-1014cm), by which the jet obtains a high Lorentz factor (γ~ 100-1000), has a luminosity ofLj~ 1050-1051ergs-1, has observer variability time-scales of the order of 1s (ranging from 0.001 to 10s), achieves γθj~ 10-20 (for opening half-angle θj) and so is able to produce jet-breaks, and has comparable energy available for both prompt and afterglow emission. A range of model parameters are investigated and simplified scaling laws are derived. This reconnection switch mechanism allows for highly efficient conversion of electromagnetic energy into prompt emission and associates the observed prompt GRB pulse temporal structure with dissipation time-scales of some number of reconnecting current sheets embedded in the jet. We hope this work helps to motivate the development of self-consistent radiative compressible relativistic reconnection models. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Begelman M.C.,U.S. National Institute of Standards and Technology | Begelman M.C.,University of Colorado at Boulder
Monthly Notices of the Royal Astronomical Society | Year: 2012

We reformulate the adiabatic inflow-outflow solution (ADIOS) model for radiatively inefficient accretion flows, treating the inflow and outflow zones on an equal footing. For purely adiabatic flows (i.e. with no radiative losses), we show that the mass flux in each zone must satisfy with n= 1, in contrast to previous work in which 0 < n < 1 is a free parameter but in rough agreement with numerical simulations. We also demonstrate that the resulting two-zone ADIOS models are not dynamically self-consistent without the introduction of an energy source close in to the central regions of the flow; we identify this with the energy liberated by accretion. We explore the parameter space of non-radiative models and show that both powerful winds and gentle breezes are possible. When small radiative losses (with fixed efficiency) are included, any centrally injected energy flux is radiated away and the system reverts to a power-law behaviour with n≲ 1, where n falls in a small range determined by the fractional level of radiative losses. We also present an ADIOS model for hypercritical (super-Eddington) disc accretion, in which the radiative losses are closely related to the flow geometry. We suggest that hyperaccretion can lead to either winds or breezes. © 2012 The Author. Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Rudy J.W.,University of Colorado at Boulder
Brain Research | Year: 2015

The goal of this essay is to link the regulation of actin dynamics to the idea that the synaptic changes that support long-term potentiation and memory evolve in temporally overlapping stages - generation, stabilization, and consolidation. Different cellular/molecular processes operate at each stage to change the spine cytoarchitecture and, in doing so, alter its function. Calcium-dependent processes that degrade the actin cytoskeleton network promote a rapid insertion of AMPA receptors into the post synaptic density, which increases a spine's capacity to express a potentiated response to glutamate. Other post-translation events then begin to stabilize and expand the actin cytoskeleton by increasing the filament actin content of the spine and reorganizing it to be resistant to depolymerizing events. Disrupting actin polymerization during this stabilization period is a terminal event - the actin cytoskeleton shrinks and potentiated synapses de-potentiate and memories are lost. Late-arriving, new proteins may consolidate changes in the actin cytoskeleton. However, to do so requires a stabilized actin cytoskeleton. The now enlarged spine has properties that enable it to capture other newly transcribed mRNAs or their protein products and thus enable the synaptic changes that support LTP and memory to be consolidated and maintained. © 2014 Elsevier B.V. All rights reserved.

Degrand T.,University of Colorado at Boulder
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

I carry out a finite-size scaling study of the correlation length in SU(3) lattice gauge theory coupled to 12 fundamental flavor fermions, using recent data published by Fodor, Holland, Kuti, Nógradi and Schroeder. I make the assumption that the system is conformal in the zero-mass, infinite volume limit, that scaling is violated by both nonzero fermion mass and by finite volume, and that the scaling function in each channel is determined self-consistently by the data. From several different observables I extract a common exponent for the scaling of the correlation length ξ with the fermion mass m q, ξ∼mq-1/y m with y m∼1.35. Shortcomings of the analysis are discussed. © 2011 American Physical Society.

Lawrence D.M.,U.S. National Center for Atmospheric Research | Slater A.G.,University of Colorado at Boulder | Swenson S.C.,U.S. National Center for Atmospheric Research
Journal of Climate | Year: 2012

The representation of permafrost and seasonally frozen ground and their projected twenty-first century trends is assessed in the Community Climate System Model, version 4 (CCSM4) and the Community Land Model version 4 (CLM4). The combined impact of advances in CLM and a better Arctic climate simulation, especially for air temperature, improve the permafrost simulation in CCSM4 compared to CCSM3. Present-day continuous plus discontinuous permafrost extent is comparable to that observed [12.5×10 6 versus (11.8-14.6)× 10 6 km 2], but active-layer thickness (ALT) is generally too thick and deep ground (>15 m) temperatures are too warm in CCSM4. Present-day seasonally frozen ground area is well simulated (47.5 × 10 6 versus 48.1 × 10 6 km 2). ALT and deep ground temperatures are much better simulated in offline CLM4 (i.e., forced with observed climate), which indicates that the remaining climate biases, particularly excessive high-latitude snowfall biases, degrade the CCSM4 permafrost simulation. Near-surface permafrost (NSP) and seasonally frozen ground (SFG) area are projected to decline substantially during the twenty-first century [representative concentration projections (RCPs); RCP8.5: NSP by 9.0 × 10 6 km 2, 72%, SFG by 7.1 × 10 6, 15%; RCP2.6: NSP by 4.1 × 10 6, 33%, SFG by 2.1 × 10 6, 4%]. The permafrost degradation rate is slower (2000-50) than in CCSM3 by ~35% because of the improved soil physics. Under the low RCP2.6 emissions pathway, permafrost state stabilizes by 2100, suggesting that permafrost related feedbacks could be minimized if greenhouse emissions could be reduced. The trajectory of permafrost degradation is affected by CCSM4 climate biases. In simulations with this climate bias ameliorated, permafrost degradation in RCP8.5 is lower by ~29%. Further reductions of Arctic climate biases will increase the reliability of permafrost projections and feedback studies in earth system models. © 2012 American Meteorological Society.

Hasenfratz A.,University of Colorado at Boulder
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Strongly coupled gauge systems with many fermions are important in many phenomenological models. I use the 2-lattice matching Monte Carlo renormalization group method to study the fixed point structure and critical indexes of SU(3) gauge models with 8 and 12 flavors of fundamental fermions. With an improved renormalization group block transformation I am able to connect the perturbative and confining regimes of the Nf=8 flavor system, thus verifying its QCD-like nature. With Nf=12 flavors the data favor the existence of an infrared fixed point and conformal phase, though the results are also consistent with very slow walking. I measure the anomalous mass dimension in both systems at several gauge couplings and find that they are barely different from the free-field value. © 2010 The American Physical Society.

Subduction erosion occurs at all convergent plate boundaries, even if they are also accretionary margins. Frontal subduction erosion results from a combination of erosion and structural collapse of the forearc wedge into the trench, and basal subduction erosion by abrasion and hydrofracturing above the subduction channel. High rates of subduction erosion are associated with relatively high convergence rates (>60mm/yr) and low rates of sediment supply to the trench (<40km2/yr), implying a narrow and topographically rough subduction channel which is neither smoothed out nor lubricated by fine-grained water-rich turbidites such as are transported into the mantle below accreting plate boundaries. Rates of subduction erosion, which range up to >440km3/km/my, vary temporally as a function of these same factors, as well as the subduction of buoyant features such as seamount chains, submarine volcanic plateaus, island arcs and oceanic spreading ridge, due to weakening of the forearc wedge. Revised estimates of long-term rates of subduction erosion appropriate for selected margins, including SW Japan (≥30km3/km/my since 400Ma), SW USA (≥30km3/km/my since 150Ma), Peru and northern Chile (50-70km3/km/my since >150Ma), and central (115km3/km/my since 30Ma) and southernmost Chile (30-35km3/km/my since 15Ma), are higher than in previous compilations. Globally, subduction erosion is responsible for >1.7Armstrong Units (1AU=1km3/yr) of crustal loss, 33% of the ~5.25AU of yearly total crustal loss, and more than any one other of sediment subduction (1.65AU), continental lower crustal delamination (≥1.1AU), crustal subduction during continental collision (0.4AU), and/or subduction of rock-weathering generated chemical solute that is dissolved in oceanic crust (0.4AU). The paucity of pre-Neoproterozoic blueschists suggests that global rates of subduction erosion were probably greater in the remote past, perhaps due to higher plate convergence rates. Subducted sediments and crust removed from the over-riding forearc wedge by subduction erosion may remain in the crust by being underplated below the wedge, or these crustal debris may be carried deeper into the source region of arc magmatism and incorporated into arc magmas by either dehydration of the subducted slab and the transport of their soluble components into the overlying mantle wedge source of arc basalts, and/or bulk melting of the subducted crust to produce adakites. In selected locations such as in Chile, Costa Rica, Japan and SW USA, strong cases can be made for the temporal and spatial correlations of distinctive crustal isotopic characteristics of arc magmas and episodes or areas of enhanced subduction erosion. Nevertheless, overall most subducted crust and sediment, >90% (>3.0AU), is transported deeper into the mantle and neither underplated below the forearc wedge nor incorporated in arc magmas. The total current rate of return of continental crust into the deeper mantle, the most important process for which is subduction erosion, is equal to or greater than the estimates of the rate at which the crust is being replaced by arc and plume magmatic activity, indicating that currently the continental crust is probably slowly shrinking. However, rates of crustal growth may have been episodically more rapid in the past, most likely at times of supercontinent breakup, and conversely, rates of crustal destruction may have also been higher during times of supercontinent amalgamation. Thus the supercontinent cycle controls the relative rates of growth and/or destruction of the continental crust. Subduction erosion plays an important role in producing and maintaining this cycle by transporting radioactive elements from the crust into the mantle, perhaps as deep as the 670km upper-to-lower mantle transition, or even deeper down to the core-mantle boundary, where heating of this subducted crustal material initiates plumes and superplumes. © 2011 International Association for Gondwana Research.

Gurarie V.,University of Colorado at Boulder
Journal of Physics A: Mathematical and Theoretical | Year: 2013

Logarithmic operators and logarithmic conformal field theories are reviewed. Prominent examples considered here include c = -2 and c = 0 logarithmic conformal field theories. c = 0 logarithmic conformal field theories are especially interesting since they describe some of the critical points of a variety of longstanding problems involving a two dimensional quantum particle moving in a spatially random potential, as well as critical two dimensional self-avoiding random walks and percolation. Lack of classification of logarithmic conformal field theories remains a major impediment to progress towards finding complete solutions to these problems. © 2013 IOP Publishing Ltd.

Chwang E.,University of Colorado at Boulder
American Journal of Bioethics | Year: 2014

The U.S. Code of Federal Regulations governing federally funded research on human subjects assumes that harmful research is sometimes morally justifiable because the beneficiaries of that research share a particular vulnerability with its subjects. In this article, I argue against this assumption, which occurs in every subpart of the Code of Federal Regulations that deals with specific vulnerable populations (pregnant women, fetuses, neonates, prisoners, and children). I argue that shared vulnerability is no exception to the general principle that harming one person in order to benefit another is no more justifiable if the two people have traits in common. Further, shared vulnerability is not a reasonable proxy for any morally relevant desideratum of research, in particular the desire to benefit the worst off, the desire to avoid exploitation, and the desire to use vulnerable populations in research only when necessary. © 2014, Copyright © Taylor & Francis Group, LLC.

Whisman M.A.,University of Colorado at Boulder | Uebelacker L.A.,Brown University
Health Psychology | Year: 2012

Objective: Metabolic syndrome (MetS) is a constellation of features- central obesity, dyslipidemia, elevated blood pressure, and dysglycemia-that are associated with increased risk for cardiovascular disease, diabetes, stroke, and mortality. This longitudinal study was conducted to evaluate whether marital adjustment, which has been shown to predict a variety of health outcomes, increases risk for incidence of MetS. Methods: A population-based English sample of couples (N = 216 couples) completed a self-report measure of marital adjustment at baseline and nurse visits that included collection of blood pressure, blood samples, and anthropometric measures at baseline and 4-year follow-up. Multilevel modeling was used to evaluate the association between both partners' report of baseline marital adjustment and incidence of MetS, controlling for other baseline risk factors (demographics, current and previous smoking status, alcohol use, activity level, depressive symptoms, number of MetS criteria). Results: Gender moderated the association between marital adjustment and incidence of MetS. Follow-up analyses indicated that husbands' report of marital adjustment at baseline was significantly associated with incident MetS for wives at follow-up, controlling for baseline risk factors. Marital adjustment was not significantly associated with incident MetS for men. Conclusions: Findings suggest that MetS may be one mechanism by which poor marital adjustment increases risk for poor health outcomes in women. Improving marital adjustment may help prevent the incidence of MetS and improve health, particularly for women. © 2011 American Psychological Association.

Hughes J.E.,University of Colorado at Boulder
Journal of Environmental Economics and Management | Year: 2011

This paper provides evidence of market power in the transportation of ethanol used in reformulated gasoline and alternative transportation fuels. I estimate a reduced form model for railroad route-level prices. My identification strategy instruments for railroad entry, controls for selection and explicitly models capacity constraints. A detailed understanding of this industry is important because U.S. environmental policies seek to substantially expand ethanol use. Evidence of market power may alter the types of policies pursued by lawmakers. I find that ethanol shipment prices are lower for more competitive routes. I also find evidence that railroads price discriminate based on environmental regulation at route destinations. Monopolist prices for shipments to carbon monoxide non-attainment areas are 3% higher than shipments to other destinations. This price premium falls sharply with increased competition. This suggests a perverse result where environmental regulation increases the price of a clean input. © 2011 Elsevier Inc.

Behera S.K.,University of Colorado at Boulder
Chemical Communications | Year: 2011

Monodispersed Fe3O4 nanoparticles of size ∼10 nm were processed by a simple ultrasonic assisted co-precipitation method, mechanically mixed with graphene oxide, and thermally reduced to form a magnetite-graphene composite. Electrochemical characterization of the Fe 3O4-graphene nanocomposites showed excellent capacity in excess of 1200 mA h g-1, and exceptional stability during high current cycling for at least 1000 cycles. © 2011 The Royal Society of Chemistry.

Fluri J.L.,University of Colorado at Boulder
Environment and Planning D: Society and Space | Year: 2014

This paper examines embodied representations of state (in)security within three broad thematic categories: biometrics, prosthetics, and military biopower. This analysis elucidates the ways in which gender and race are put to work through representational framings of US state security. These framings, while diverse, offer similar taxonomies of inclusion–exclusion, security–insecurity, and violence against or care for certain bodies. This critical examination explicates how security is succinctly situated by autonomous state actors, ‘life politics’, and manipulations of the global–intimate through the lens of mimetic gendered and raced bodies. I argue that these various visual representations aid in reinforcing to the mainstream/white US citizen-subject that he or she remains secure within the immediate US homeland by way of the displacement of contemporary war violence elsewhere—rather than such violence circulating ‘everywhere’. A visual and discursive representation of security–insecurity illustrates a purposeful militarized illusion, inscribed through the many examples discussed in this paper. These disparate techniques shape US citizens’ imagination of ‘terror’ as potentially ‘everywhere’, while simultaneously situating the US military’s war ‘over there’ (elsewhere) as part of securing the homeland. These corporeal exemplifications help to situate security within the homeland and a/effectively shroud the flesh-and-bone devastation of US military violence elsewhere. © 2014 pion and its Licensors.

Persha L.,University of North Carolina at Chapel Hill | Andersson K.,University of Colorado at Boulder
Global Environmental Change | Year: 2014

Recent scholarship focuses on elite capture as a driver of social inequality and a source of policy failure across a wide range of governance initiatives. In the context of environmental governance, concerns center on perceived links between elite capture and decentralization, particularly in developing countries where decentralized natural resource governance has been widely implemented. But, there is limited empirical knowledge regarding if, and the conditions under which, decentralization might promote elite capture, or whether institutional design factors can militate against it. We examine how local institutional arrangements under forest sector decentralization affect the risk of elite capture of forest benefits, as well as the potential for a key institutional design factor (linkages to external organizations as an accountability-building mechanism) to mitigate this risk. We analyze forest product harvesting data as well as social, ecological, and institutional data from pre- and post-decentralization across 56 forests and 174 community groups in four countries. We employ hierarchical linear modeling to test the extent to which decentralization is associated with inequities in the distribution of forest harvest benefits within communities, and to characterize the institutional arrangements that affect elite capture outcomes. We find not only strong evidence for increased local rule-making under decentralization, but also significantly higher risk of elite capture of forest harvest benefits. This risk increases with increasing time since decentralization, but it is also substantially moderated in cases where an external organization was involved in organizing the local forest institution. Our findings highlight ways in which decentralization reforms are filtered by institutional arrangements to produce different outcomes, and generate new knowledge on micro-institutional factors that can reduce the risk of elite capture in decentralized environmental governance regimes. © 2013 Elsevier Ltd.

Featherstone N.A.,University of Colorado at Boulder | Miesch M.S.,High Altitude Observatory
Astrophysical Journal | Year: 2015

We present a series of 3D nonlinear simulations of solar-like convection, carried out using the Anelastic Spherical Harmonic code, that are designed to isolate those processes that drive and shape meridional circulations (MCs) within stellar convection zones. These simulations have been constructed so as to span the transition between solar-like differential rotation (DR; fast equator/slow poles) and "anti-solar" DR (slow equator/fast poles). Solar-like states of DR, which arise when convection is rotationally constrained, are characterized by a very different convective Reynolds stress (RS) than anti-solar regimes, wherein convection only weakly senses the Coriolis force. We find that the angular momentum transport by convective RS plays a central role in establishing the meridional flow profiles in these simulations. We find that the transition from single-celled to multi-celled MC profiles in strong and weak regimes of rotational constraint is linked to a change in the convective RS, which is a clear demonstration of gyroscopic pumping. Latitudinal thermal variations differ between these different regimes, with those in the solar-like regime conspiring to suppress a single cell of MC, whereas the cool poles and warm equator established in the anti-solar states tend to promote single-celled circulations. Although the convective angular momentum transport becomes radially inward at mid-latitudes in anti-solar regimes, it is the MC that is primarily responsible for establishing a rapidly rotating pole. We conclude with a discussion of how these results relate to the Sun, and suggest that the Sun may lie near the transition between rapidly rotating and slowly rotating regimes. © 2015. The American Astronomical Society. All rights reserved.

Rudy J.W.,University of Colorado at Boulder
Brain Research | Year: 2015

William James noted that memories could persist from minutes to weeks. This essay attempts to explain this variation by situating the explanation in the biochemistry of dendritic spines. Two outcomes are critical to generate the synaptic basis of memory: (1) the actin cytoskeleton in the spine must be degraded to permit (2) additional AMPA receptors (GluA1s) to enter new "hot spots" in the postsynaptic density. These initial outcomes can support short-lasting memories. The threshold for these events is low but the underlying synaptic changes cannot resist the endocytic processes that remove the added AMPA receptors. For the memory to persist the degraded actin cytoskeleton must be rebuilt and the vacated "hot spots" refilled with GluA2 receptors. A primary claim is that it is the stabilization of an enlarged actin cytoskeleton that is the target outcome that consolidates the synaptic basis of memory (see Lynch et al., 2007). The stabilized actin cytoskeleton has properties that enable it to garner the synaptic proteins it needs to self sustain the potentiated state and to benefit from activation of memory modulation systems. © 2014 Elsevier B.V. All rights reserved.

Medlin J.W.,University of Colorado at Boulder
ACS Catalysis | Year: 2011

The production of fuels and chemicals from biomass requires heterogeneous catalysts that facilitate selective reactions of highly functional oxygenates. Although designing catalysts for high selectivity is a universal challenge in heterogeneous catalysis research, the problem is particularly acute for highly functional molecules, which contain two or more functional groups that may react over metal surfaces. This perspective article focuses on recent efforts to develop structure-property relations on metal surfaces and catalysts for two classes of highly functional molecules: multifunctional oxygenates such as α,β-unsaturated aldehydes and furanic compounds, and polyfunctional oxygenates such as glycerol and other polyols. Recent results from comparative reaction studies over a variety of catalysts, surface science experiments, and computational investigations suggest an array of approaches for producing more selective catalysts, many relying on the addition of multiple metals or other surface modifiers. General strategies that appear to show promise in the selective reactions of unsaturated oxygenates and of polyols are discussed in detail. © 2011 American Chemical Society.

Weidman P.D.,University of Colorado at Boulder
Journal of Fluid Mechanics | Year: 2012

A modification of Homanns axisymmetric outer potential stagnation-point flow of strain rate a is obtained by adding periodic radial and azimuthal velocities of the form b r sin 2 θ and b r 2θ, respectively, where b is a shear rate. This leads to the discovery of a new family of asymmetric viscous stagnation-point flows depending on the shear-to-strain-rate ratio γ = b/a that exist over the range-∞ < γ < ∞ . Numerical solutions for the wall shear stress parameters and the displacement thicknesses are given and compared with their large-γ asymptotic behaviours. Sample similarity velocity profiles are also presented. © 2012 Cambridge University Press.

Ligand noninnocence occurs for complexes composed of redox-active ligands and metals, with frontier orbitals of similar energy. Usually methods of analysis can be used to define the charge distribution, and cases where the metal oxidation state and ligand charge are unclear are unusual. Ligands derived from o-benzoquinones can bond with metals as radical semiquinonates (SQ•-) or as catecholates (Cat2-). Spectroscopic, magnetic, and structural properties can be used to assess the metal and ligand charges. With the redox activity at both the metal and ligands, reversible multicomponent redox series can be observed using electrochemical methods. Steps in the series may occur at either the ligand or metal, and ligand substituent effects can be used to tune the range of ligand-based redox steps. Complexes that appear as intermediates in a ligand-based redox series may contain both SQ and Cat ligands "bridged" by the metal as mixed-valence complexes. Properties reflect the strength of metal-mediated interligand electronic coupling in the same way that ligand-bridged bimetallics conform to the Robin and Day classification scheme. In this review, we will focus specifically on complexes of first-row transition-metal ions coordinated with three ligands derived from tetrachloro-1,2-benzoquinone (Cl4BQ). The redox activity of this ligand overlaps with the potentials of common metal oxidation states, providing examples of metal- and ligand-based redox activity, in some cases, within a single redox series. The strength of the interligand electronic coupling is important in defining the separation between ligand-based couples of a redox series. The complex of ferric iron will be described as an example where coupling is weak, and the steps associated with the FeIII(Cl 4SQ)3/[FeIII(Cl4Cat) 3]3- redox series are observed over a narrow range in electrochemical potential. © 2011 American Chemical Society.

Goodrich J.A.,University of Colorado at Boulder | Tjian R.,Howard Hughes Medical Institute
Nature Reviews Genetics | Year: 2010

The eukaryotic core promoter recognition complex was generally thought to play an essential but passive role in the regulation of gene expression. However, recent evidence now indicates that core promoter recognition complexes together with 'non-prototypical' subunits may have a vital regulatory function in driving cell-specific programmes of transcription during development. Furthermore, new roles for components of these complexes have been identified beyond development; for example, in mediating interactions with chromatin and in maintaining active gene expression across cell divisions. © 2010 Macmillan Publishers Limited. All rights reserved.

Matrosov S.Y.,University of Colorado at Boulder
Journal of Applied Meteorology and Climatology | Year: 2011

Polarimetric X-band radar measurements of differential reflectivity Z DR in stratiform rainfall were used for retrieving mean mass-weighted raindrop diameters D m and estimating their spatial variability δD m at different scales. The Z DR data were calibrated and corrected for differential attenuation. The results revealed greater variability in D m for larger spatial scales. Mean values of δD m were respectively around 0.32-0.34, 0.28-0.30, and 0.24-0.26 mm at scales of 20, 10, and 4.5 km, which are representative of footprints of various spaceborne sensors. For a given spatial scale, δD m decreases when the mean value of D m increases. At the 20-km scale the decreasing trend exhibits a factor-of-1.7 decrease of δD m when the average D m changes from 1 to 2 mm. Estimation data suggest that this trend diminishes as the spatial scale decreases. Measurement noise and other uncertainties preclude accurate estimations ofD m variability at smaller spatial scales because for many data points estimated variability values are equal to or less than the expected retrieval errors. Even though they are important for retrievals of absolute values ofD m, the details of the drop shape-size relation did not significantly affect estimates of size spatial variability. The polarization cross coupling in simultaneous transmission-simultaneous receiving measurement mode presents another limiting factor for accurate estimations of D m. This factor, however, was not too severe in estimations of the size variability. There are indications that tuning the differential attenuation correction scheme might balance off some possible cross-coupling Z DR bias if differential phase accumulation is less than approximately 40°. © 2011 American Meteorological Society.

Pfeffer W.T.,University of Colorado at Boulder
Oceanography | Year: 2011

The present-day assessment of contributions to sea level rise from glaciers and ice sheets depends to a large degree on new technologies that allow efficient and precise detection of change in otherwise inaccessible polar regions. The creation of an overall research strategy, however, was set in early collaborative efforts nearly 30 years ago to assess and project the contributions of glaciers and ice sheets to sea level rise. Many of the research objectives recommended by those early collaborations were followed by highly successful research programs and led to significant accomplishments. Other objectives are still being pursued, with significant intermediate results, but have yet to mature into fully operational tools; among them is the fully deterministic numerical ice sheet model. Recognized as a crucial tool in 1983 by the first formal working group to be convened to quantitatively evaluate glaciers and ice sheet contributions to sea level in a CO2-warmed future environment, the deterministic numerical model of glacier and ice sheet behavior has been the ultimate prognostic tool sought by the glaciological research community ever since. Progress toward this goal has been thwarted, however, by lack of knowledge of certain physical processes, especially those associated with interactions of ice with the bedrock it rests on, and interactions of ice with the ocean and calving of icebergs. Over the last decade, when mass loss rates from Greenland and Antarctica started to accelerate, some means of projecting glacier and ice sheet changes became increasingly necessary, and alternatives to deterministic numerical models were sought. The result was a variety of extrapolation schemes that offer partial constraints on future glacier and ice sheet losses, but also contain significant uncertainties and rely on assumptions that are not always clearly expressed. This review examines the history of assessments of glacier and ice sheet contributions to sea level rise, and considers how questions asked 30 years ago shaped the nature of the research agenda being carried out today. © 2011 by The Oceanography Society. All rights reserved.

Templeton A.S.,University of Colorado at Boulder
Elements | Year: 2011

The rapid redox cycling of iron is one of the most pervasive geochemical processes catalyzed by microbial organisms. Numerous microbial metabolisms rely on transferring electrons to and from iron, even in "extreme" environments considered challenging for life due to high acidity, high alkalinity, high temperature, low organic content, or low water abundance. Recent efforts to explore the iron biogeochemistry of extreme systems, such as hydrothermal vents, seafoor basalts, serpentinizing systems, and acid mine drainage, have signifcantly expanded our expectations regarding the distribution and activity of iron-dependent life on Earth, and potentially other iron-rich silicate planets, such as Mars.

Yoshinaga-Itano C.,University of Colorado at Boulder
Journal of Deaf Studies and Deaf Education | Year: 2014

This document is a supplement to the year 2007 position statement of the Joint Committee on Infant Hearing and provides comprehensive guidelines for establishing strong early intervention (EI) systems with appropriate expertise to meet the needs of children who are deaf or hard of hearing (D/ HH). Optimal outcomes can only be achieved when there is high quality to the universal newborn hearing screening programs, the audiologic diagnostic process of confirmation that a child is D/HH and fitting of amplification, and the provision of appropriate, individualized, targeted, and highquality EI services. There are 12 best practice guidelines for EI programs that include the provision of timely referral to EI services with providers who have knowledge and skills in early childhood deafness and hearing loss, infusion within the system of partnerships with parents as well as professionals who are D/HH, longitudinal developmental assessments for monitoring the child's development, data management systems that include developmental outcomes, a process to monitor the fidelity of the intervention, and appropriate services for children with additional disabilities, those from non-English speaking families, and those from special populations, including unilateral hearing loss and auditory neuropathy/ dyssynchrony. © The Author 2013. Published by Oxford University Press. All rights reserved.

DeGrand T.,University of Colorado at Boulder
Reviews of Modern Physics | Year: 2016

Over the last few years lattice techniques have been used to investigate candidate theories of new physics beyond the standard model. This review gives a survey of results from these studies. Most of these investigations have been of systems of gauge fields and fermions that have slowly running coupling constants. A major portion of the review is a critical discussion of work in this particular subfield, first describing the methods used and then giving a compilation of results for specific models. © 2016 American Physical Society.

Yarus M.,University of Colorado at Boulder
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2011

The smallest ribozyme that carries out a complex group transfer is the sequence GUGGC-3', acting to aminoacylate GCCU-3' (and host a manifold of further reactions) in the presence of substrate PheAMP. Here, I describe the enzymatic rate, the characterization of about 20 aminoacyl-RNA and peptidyl-RNA products and the pathways of these GUGGC/GCCU reactions. Finally, the topic is evolution, and the potential implications of these data for the advent of translation itself. © 2011 The Royal Society.

Coady J.A.,University of Colorado at Boulder
Journal of Speech, Language, and Hearing Research | Year: 2013

Purpose: Previous studies have reported that children with specific language impairment (SLI) name pictures more slowly than do chronological age-matched (CAM)peers. Rapid naming depends on 2 factors known to be problematic for children with SLI-lexical retrieval and nonlinguistic speed of processing. Although all studies implicate a speed-of-processing deficit as a contributing factor, researchers do not agree on the influence of language factors. The purpose of the current study was to explore word frequency (WF) and phonotactic pattern frequency (PPF) as potential lexical factors contributing to the naming deficits experienced by children with SLI. Method: Three groups of children-20 children with SLI (Mage = 9;8 [years; months]), 20 younger vocabulary-matched (VM) controls, and 20 CAM controls-named pictures whose labels varied by WF and PPF. Results: Reaction time results revealed significant main effects of group (CAM < SLI = VM) and WF (high WF < low WF). Effects due to WF were comparable for all groups, but a significant Group × PPF interaction revealed that PPF effects were greater for children with SLI than for VM or CAM children. Conclusion: Results replicate previous findings of a naming deficit in children with SLI. Furthermore, results suggest that children with SLI are more vulnerable to increased competition from words with frequent phonotactic patterns, which also come from dense phonological neighborhoods. © American Speech-Language-Hearing Association.

Mistry K.S.,National Renewable Energy Laboratory | Mistry K.S.,University of Colorado at Boulder | Larsen B.A.,National Renewable Energy Laboratory | Blackburn J.L.,National Renewable Energy Laboratory
ACS Nano | Year: 2013

Here, we report a thorough study on the ability of fluorene-based semiconducting polymers to disperse large-diameter (average diameter âŸ̈d⟩ ≈ 1.3 nm) laser vaporization (LV) single-walled carbon nanotubes (SWCNTs). We demonstrate the ability to select purely semiconducting species using poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co- (6,6′-{2,2′-bipyridine})] (PFO-BPy) and poly[(9,9-dihexylfluorenyl- 2,7-diyl)-co-(9,10-anthracene)] (PFH-A), producing samples with narrow and bright excitonic emission relative to comparable aqueous dispersions. Rapid processing and high yields offer the ability to easily incorporate these semiconducting SWCNTs into commercially scalable applications, as demonstrated by large-area thin films prepared by ultrasonic spraying. By modifying the growth temperature of the LV synthesis, we demonstrate the ability to tune the range of diameters and chiralities within dispersions by exerting synthetic control over the composition of the starting material. This synthetic control allows us to show that PFH-A preferentially disperses near-armchair semiconducting SWCNTs over a large range of diameters (0.8 nm < d < 1.4 nm) and induces unique solvatochromic shifts for the excitonic transitions of nanotubes with particular chiral indices. © 2013 American Chemical Society.

Grover S.,National Renewable Energy Laboratory | Moddel G.,University of Colorado at Boulder
IEEE Journal of Photovoltaics | Year: 2011

The current-voltage (I-V) characteristics of metal/insulator/metal (MIM) diodes illuminated at optical frequencies are modeled using a semiclassical approach that accounts for the photon energy of the radiation. Instead of classical small-signal rectification, in which a continuous span of the dc I-V curve is sampled during rectification, at optical frequencies, the radiation samples the dc I-V curve at discrete voltage steps separated by the photon energy (divided by the electronic charge). As a result, the diode resistance and responsivity differ from their classical values. At optical frequencies, a diode with even a moderate forward-to-reverse current asymmetry exhibits high quantum efficiency. An analysis is carried out to determine the requirements imposed by the operating frequency on the circuit parameters of antenna-coupled diode rectifiers, which are also called rectennas. Diodes with low resistance and capacitance are required for the RC time constant of the rectenna to be smaller than the reciprocal of the operating frequency and to couple energy efficiently from the antenna. Existing MIM diodes do not meet the requirements to operate efficiently at visible-to-near-infrared wavelengths. © 2011 IEEE.

Vernerey F.J.,University of Colorado at Boulder
International Journal of Solids and Structures | Year: 2011

The presence of interfaces (such as cracks, membranes and bi-material boundaries) in hydrated porous media may have a significant effect on the nature of their deformation and interstitial fluid flow. In this context, the present paper introduces a mathematical framework to describe the mechanical behavior of interfaces in an elastic porous media filled with an inviscid fluid. While bulk deformation and flow are characterized by displacement gradient and variations in the fluid chemical potential, their counterpart in the interface are derived by defining adequate projections of strains and flow onto the plane of the interface. This operation results in the definition of three interface deformation and stress measures describing decohesion, mean tangential strain and relative tangential strain, as well as three interface fluid driving forces and flux representing normal flux, mean tangential flux and relative tangential flux. Consistent with this macroscopic description of interface behavior, a set of governing equations are then introduced by considering the conservation of mass and the balance of momentum in the mixture. In particular, we show that the coupled mechanisms of interface deformation and fluid flow are described by six differential equations for fluid flow and three equations for solid deformation. It is also shown that a simpler set of governing equation can be derived when incompressible constituents are considered. The behavior of the mixture is finally specified through a general linear constitutive relation that relies on the definition of quadratic strain energy and dissipation functions. While an large number of material constants are needed in the general case, we show that under simplifying assumptions, the behavior of the interface can be written in terms of only eight material constants. A summary and discussion is then provided on the proposed formulation and potential applications are suggested. © 2011 Elsevier Ltd. All rights reserved.

Servedio M.R.,University of North Carolina at Chapel Hill | Doorn G.S.V.,University of Bern | Kopp M.,University of Vienna | Frame A.M.,University of Bern | Nosil P.,University of Colorado at Boulder
Trends in Ecology and Evolution | Year: 2011

Speciation with gene flow is greatly facilitated when traits subject to divergent selection also contribute to non-random mating. Such traits have been called 'magic traits', which could be interpreted to imply that they are rare, special, or unrealistic. Here, we question this assumption by illustrating that magic traits can be produced by a variety of mechanisms, including ones in which reproductive isolation arises as an automatic by-product of adaptive divergence. We also draw upon the theoretical literature to explore whether magic traits have a unique role in speciation or can be mimicked in their effects by physically linked trait-complexes. We conclude that magic traits are more frequent than previously perceived, but further work is needed to clarify their importance. © 2011 Elsevier Ltd.

Hynes J.T.,University of Colorado at Boulder | Hynes J.T.,French National Center for Scientific Research
Annual Review of Physical Chemistry | Year: 2015

After my acceptance of the kind invitation from Todd Martýńez and Mark Johnson, Co-Editors of this journal, to write this article, I had to decide just how to actually do this, given the existence of a fairly personal and extended autobiographical account of recent vintage detailing my youth, education, and assorted experiences and activities at the University of Colorado, Boulder, and later also at Ecole Normale Supérieure in Paris (1). In the end, I settled on a differently styled recounting of the adventures with my students, postdocs, collaborators, and colleagues in trying to unravel, comprehend, describe, and occasionally even predict the manifestations and consequences of the myriad assortment of molecular dances that contribute to and govern the rates and mechanisms of chemical reactions in solution (and elsewhere). The result follows. © 2015 by Annual Reviews. All rights reserved.

Domingue B.,University of Colorado at Boulder
Psychometrika | Year: 2014

The axioms of additive conjoint measurement provide a means of testing the hypothesis that testing data can be placed onto a scale with equal-interval properties. However, the axioms are difficult to verify given that item responses may be subject to measurement error. A Bayesian method exists for imposing order restrictions from additive conjoint measurement while estimating the probability of a correct response. In this study an improved version of that methodology is evaluated via simulation. The approach is then applied to data from a reading assessment intentionally designed to support an equal-interval scaling. © 2013 The Psychometric Society.