Entity

Time filter

Source Type

Santa Barbara, CA, United States

The University of California, Santa Barbara is a public research university and one of the 10 general campuses of the University of California system. The main campus is located on a 1,022-acre site near Goleta, California, United States, 8 miles from Santa Barbara and 100 miles northwest of Los Angeles. Tracing its roots back to 1891 as an independent teachers' college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system.UCSB is one of America's Public Ivy universities, which recognizes top public research universities in the United States. The university is a comprehensive doctoral university and is organized into five colleges and schools offering 87 undergraduate degrees and 55 graduate degrees. UCSB was ranked 40th among "National Universities", 10th among U.S. public universities and 28th among Best Global Universities by U.S. News & World Report 's 2015 rankings. The university was also ranked 37th worldwide by the Times Higher Education World University Rankings and 41st worldwide by the Academic Ranking of World Universities in 2014.UC Santa Barbara is a "very high activity" research university and spent $233.9 million on research expenditures in the 2012 fiscal year, 91st largest in the United States. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics. Current UCSB faculty includes six Nobel Prize laureates, one Fields Medalist, 29 members of the National Academy of science, 27 members of the National Academy of Engineering, and 31 members of the American Academy of Arts and science. UCSB was the No. 3 host on the ARPAnet and was elected to the Association of American Universities in 1995.The UC Santa Barbara Gauchos compete in the Big West Conference of the NCAA Division I. The Gauchos have won NCAA national championships in men's soccer and men's water polo. Wikipedia.


Polchinski J.,University of California at Santa Barbara
Classical and Quantum Gravity | Year: 2012

A recent paper by Gambini et al (2011 Class. Quantum Grav. 28 155005) investigates the important issue of constraints from Lorentz invariance on Planck scale physics, arguing that the classic analysis of Collins et al (2004 Phys. Rev. Lett. 93 191301) is not generally valid. We argue that the new work is based on models that do not capture the relevant physics and that almost all models of observable high-energy Lorentz violation, and proposed Lorentz-violating theories of quantum gravity, are ruled out by low-energy tests; the only known exceptions are based on supersymmetry. © 2012 IOP Publishing Ltd.


Notarstefano G.,University of Salento | Bullo F.,University of California at Santa Barbara
IEEE Transactions on Automatic Control | Year: 2011

Distributed abstract programs are a novel class of distributed optimization problems where i) the number of variables is much smaller than the number of constraints and ii) each constraint is associated to a network node. Abstract optimization programs are a generalization of linear programs that captures numerous geometric optimization problems. We propose novel constraints consensus algorithms for distributed abstract programs with guaranteed finite-time convergence to a global optimum. The algorithms rely upon solving local abstract programs and exchanging the solutions among neighboring processors. The proposed algorithms are appropriate for networks with weak time-dependent connectivity requirements and tight memory constraints. We show how the constraints consensus algorithms may be applied to suitable target localization and formation control problems. © 2011 IEEE.


Dutton A.A.,Max Planck Institute for Astronomy | Treu T.,University of California at Santa Barbara
Monthly Notices of the Royal Astronomical Society | Year: 2014

Recent studies have shown that massive elliptical galaxies have total mass density profiles within an effective radius that can be approximated as . ρtot ∝ r -γ' with mean slope 〈γ'〉 = 2.08 ± 0.03 and scatter σγ' =0.16 ± 0.02. The small scatter of the slope (known as the bulge-halo conspiracy) is not generic in Λ cold dark matter (ΛCDM) based models and therefore contains information about the galaxy formation process. We compute the distribution of γ' for ΛCDM-based models that reproduce the observed correlations between stellar mass, velocity dispersion, and effective radius of early-type galaxies in the Sloan Digital Sky Survey. The models have a range of stellar initial mass functions (IMFs) and dark halo responses to galaxy formation. The observed distribution of γ' is well reproduced by a model with cosmologically motivated but uncontracted dark matter haloes, and a Salpeter-type IMF. Other models are on average ruled out by the data, even though they may happen in individual cases. Models with adiabatic halo contraction (and lighter IMFs) predict too small values of γ'. Models with halo expansion, or mass-follows-light predict too high values of γ'. Our study shows that the non-homologous structure of massive early-type galaxies can be precisely reproduced by ΛCDM models if the IMF is not universal and if mechanisms, such as feedback from active galactic nuclei, or dynamical friction, effectively on average counterbalance the contraction of the halo expected as a result of baryonic cooling. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ford P.C.,University of California at Santa Barbara
Chemical Science | Year: 2016

Over the past several decades, the photochemistry and photophysics of transition metal compounds has blossomed from a relatively niche topic to a major research theme. Applications arising from the elucidation of the fundamental principles defining this field now range from probing the rates and mechanisms of small molecules with metalloproteins to light activated molecular machines. Offered here is a personal perspective of metal complex photochemistry drawn from this author's long involvement with this field. Several examples are described. Topics include characterizing key excited states and tuning these to modify chemical reactivity and/or photoluminescence properties, as well as using photoreactions as an entry to reactive intermediates relevant to homogeneous catalysts. This is followed by discussions of applying these concepts to developing precursors and precursor-antenna conjugates for the photochemical delivery of small molecule bioregulators to physiological targets. © 2016 The Royal Society of Chemistry.


Zhang L.,University of California at Santa Barbara
Accounts of Chemical Research | Year: 2014

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C-H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety.In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry.For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C-C triple bond a surrogate of an α-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the α-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The α-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of "gold rush". © 2014 American Chemical Society.


Miao M.-S.,Beijing Computational Science Research Center | Miao M.-S.,University of California at Santa Barbara | Hoffmann R.,Cornell University
Accounts of Chemical Research | Year: 2014

ConspectusElectrides, in which electrons occupy interstitial regions in the crystal and behave as anions, appear as new phases for many elements (and compounds) under high pressure. We propose a unified theory of high pressure electrides (HPEs) by treating electrons in the interstitial sites as filling the quantized orbitals of the interstitial space enclosed by the surrounding atom cores, generating what we call an interstitial quasi-atom, ISQ.With increasing pressure, the energies of the valence orbitals of atoms increase more significantly than the ISQ levels, due to repulsion, exclusion by the atom cores, effectively giving the valence electrons less room in which to move. At a high enough pressure, which depends on the element and its orbitals, the frontier atomic electron may become higher in energy than the ISQ, resulting in electron transfer to the interstitial space and the formation of an HPE.By using a He lattice model to compress (with minimal orbital interaction at moderate pressures between the surrounding He and the contained atoms or molecules) atoms and an interstitial space, we are able to semiquantitatively explain and predict the propensity of various elements to form HPEs. The slopes in energy of various orbitals with pressure (s > p > d) are essential for identifying trends across the entire Periodic Table. We predict that the elements forming HPEs under 500 GPa will be Li, Na (both already known to do so), Al, and, near the high end of this pressure range, Mg, Si, Tl, In, and Pb. Ferromagnetic electrides for the heavier alkali metals, suggested by Pickard and Needs, potentially compete with transformation to d-group metals. © 2014 American Chemical Society.


Neher R.A.,Max Planck Institute for Developmental Biology | Shraiman B.I.,University of California at Santa Barbara
Genetics | Year: 2012

The accumulation of deleterious mutations is driven by rare fluctuations that lead to the loss of all mutation free individuals, a process known as Muller's ratchet. Even though Muller's ratchet is a paradigmatic process in population genetics, a quantitative understanding of its rate is still lacking. The difficulty lies in the nontrivial nature of fluctuations in the fitness distribution, which control the rate of extinction of the fittest genotype. We address this problem using the simple but classic model of mutation selection balance with deleterious mutations all having the same effect on fitness. We show analytically how fluctuations among the fittest individuals propagate to individuals of lower fitness and have dramatically amplified effects on the bulk of the population at a later time. If a reduction in the size of the fittest class reduces the mean fitness only after a delay, selection opposing this reduction is also delayed. This delayed restoring force speeds up Muller's ratchet. We show how the delayed response can be accounted for using a path-integral formulation of the stochastic dynamics and provide an expression for the rate of the ratchet that is accurate across a broad range of parameters. © 2012 by the Genetics Society of America.


Guarrotxena N.,CSIC - Institute of Polymer Science and Technology | Bazan G.C.,University of California at Santa Barbara
Advanced Materials | Year: 2014

Simultaneous detection of multiple proteins on a single spot can be efficiently achieved by using multiplexed surface-enhanced Raman spectroscopy (SERS)-encoded nanoparticle 'antitags' consisting of poly(ethylene glycol) (PEG)-protected silver dimers (and higher aggregates) and antibody-tagging entities. The effective SERS-based multivariate deconvolution approach guarantees an accurate and successful distinguishable identification of single and multiple proteins in complex samples. Their potential application in multiplexed SERS bioimaging technology can be easily envisaged. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Egele M.,Vienna University of Technology | Scholte T.,SAP | Kirda E.,Eurecom | Kruegel C.,University of California at Santa Barbara
ACM Computing Surveys | Year: 2012

Anti-virus vendors are confronted with a multitude of potentially malicious samples today. Receiving thousands of new samples every day is not uncommon. The signatures that detect confirmedmalicious threats are mainly still created manually, so it is important to discriminate between samples that pose a new unknown threat and those that are mere variants of known malware. This survey article provides an overview of techniques based on dynamic analysis that are used to analyze potentially malicious samples. It also covers analysis programs that employ these techniques to assist human analysts in assessing, in a timely and appropriate manner, whether a given sample deserves closer manual inspection due to its unknown malicious behavior. © 2012 ACM.


Shen K.J.,University of California at Berkeley | Bildsten L.,University of California at Santa Barbara
Astrophysical Journal | Year: 2014

The progenitor channel responsible for the majority of Type Ia supernovae is still uncertain. One emergent scenario involves the detonation of a He-rich layer surrounding a C/O white dwarf, which sends a shock wave into the core. The quasi-spherical shock wave converges and strengthens at an off-center location, forming a second, C-burning, detonation that disrupts the whole star. In this paper, we examine this second detonation of the double detonation scenario using a combination of analytic and numeric techniques. We perform a spatially resolved study of the imploding shock wave and outgoing detonation and calculate the critical imploding shock strengths needed to achieve a core C detonation. We find that He detonations in recent two-dimensional simulations yield converging shock waves that are strong enough to ignite C detonations in high-mass C/O cores, with the caveat that a truly robust answer requires multi-dimensional detonation initiation calculations. We also find that convergence-driven detonations in low-mass C/O cores and in O/Ne cores are harder to achieve and are perhaps unrealized in standard binary evolution. © 2014. The American Astronomical Society. All rights reserved.


Proulx S.R.,University of California at Santa Barbara
Genetics | Year: 2012

Gene duplication is arguably the most significant source of new functional genetic material. A better understanding of the processes that lead to the stable incorporation of gene duplications into the genome is important both because it relates to interspecific differences in genome composition and because it can shed light on why some classes of gene are more prone to duplication than others. Typically, models of gene duplication consider the periods before duplication, during the spread and fixation of a new duplicate, and following duplication as distinct phases without a common underlying selective environment. I consider a scenario where a gene that is initially expressed in multiple contexts can undergo mutations that alter its expression profile or its functional coding sequence. The selective regime that acts on the functional output of the allele copies carried by an individual is constant. If there is a potential selective benefit to having different coding sequences expressed in each context, then, regardless of the constraints on functional variation at the single-locus gene, the waiting time until a gene duplication is incorporated goes down as population size increases. © 2012 by the Genetics Society of America.


Pohl O.,TU Berlin | Stark H.,TU Berlin | Stark H.,University of California at Santa Barbara
Physical Review Letters | Year: 2014

Recent experiments with self-phoretic particles at low concentrations show a pronounced dynamic clustering [I. Theurkauff et al., Phys. Rev. Lett. 108, 268303 (2012)PRLTAO0031-900710.1103/PhysRevLett.108.268303]. We model this situation by taking into account the translational and rotational diffusiophoretic motion, which the active particles perform in their self-generated chemical field. Our Brownian dynamics simulations show pronounced dynamic clustering only when these two phoretic contributions give rise to competing attractive and repulsive interactions, respectively. We identify two dynamic clustering states and characterize them by power-law-exponential distributions. In case of mere attraction a chemotactic collapse occurs directly from the gaslike into the collapsed state, which we also predict by mapping our Langevin dynamics on the Keller-Segel model for bacterial chemotaxis. © 2014 American Physical Society.


Dexter J.,University of California at Berkeley | Blaes O.,University of California at Santa Barbara
Monthly Notices of the Royal Astronomical Society | Year: 2014

We propose a new model of the steep power-law state of luminous black hole X-ray binaries. The model uses the fact that at high luminosities, the inner radii of radiation pressure dominated accretion discs are expected to (i) become effectively optically thin and (ii) produce significant luminosities. The gas temperature therefore rises sharply inwards, producing local saturated Compton spectra with rapidly increasing peak energies. These spectra sum together to form a steep power-law tail to the spectrum. A given photon energy on this tail corresponds to a narrow range in radius, so that local vertical oscillations of the disc naturally produce high-quality high-frequency quasi-periodic oscillations (HFQPOs) in the hard X-ray band. The two lowest order modes have a robust frequency ratio of √7/3 ≃ 1.53. This model explains the appearance of steep power-law spectra and HFQPOs at high luminosity, the 3:2 HFQPO frequency ratios, and their association with the power-law spectral component. We predict an increase in QPO quality factor when the power spectrum is restricted to a narrower photon energy band, and an increase in HFQPO frequency at higher X-ray energies or lower luminosities. Future X-ray telescopes could detect additional HFQPOs from higher order modes. We demonstrate how this model could be used to measure black hole spin from HFQPOs, and qualitatively estimate the spin of GRO J1655-40 as a/M ∼ 0.4-0.7. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ford P.C.,University of California at Santa Barbara
Inorganic Chemistry | Year: 2010

Presented is an overview of the fundamental chemical properties of nitric oxide and nitrite ion In relation to the reactions with ferri- and ferroheme models and proteins potentially relevant to the roles of these species in mammalian biology. © 2010 American Chemical Society.


Isakov S.V.,ETH Zurich | Hastings M.B.,Duke University | Hastings M.B.,University of California at Santa Barbara | Melko R.G.,University of Waterloo
Nature Physics | Year: 2011

The Landau paradigm of classifying phases by broken symmetries was shown to be incomplete when it was realized that different quantum-Hall states can only be distinguished by more subtle, topological properties1. The role of topology as an underlying description of order has since branched out to include topological band insulators and certain featureless gapped Mott insulators with a topological degeneracy in the ground-state wavefunction. Despite intense work, very few candidates for such topologically ordered ′spin liquids′ exist. The main difficulty in finding systems that harbour spin-liquid states is the very fact that they violate the Landau paradigm, making conventional order parameters non-existent. Here, we describe a spin-liquid phase in a Bose-Hubbard model on the kagome lattice, and determine its topological order directly by means of a measure known as topological entanglement entropy. We thus identify a non-trivial spin liquid through its entanglement entropy as a gapped ground state with emergent Z 2 gauge symmetry. © 2011 Macmillan Publishers Limited. All rights reserved.


Vamvoudakis K.G.,University of California at Santa Barbara | Lewis F.L.,University of Texas at Arlington | Hudas G.R.,U.S. Army
Automatica | Year: 2012

Multi-agent systems arise in several domains of engineering and can be used to solve problems which are difficult for an individual agent to solve. Strategies for team decision problems, including optimal control, N-player games (H-infinity control and non-zero sum), and so on are normally solved for off-line by solving associated matrix equations such as the coupled Riccati equations or coupled Hamilton-Jacobi equations. However, using that approach players cannot change their objectives online in real time without calling for a completely new off-line solution for the new strategies. Therefore, in this paper we bring together cooperative control, reinforcement learning, and game theory to present a multi-agent formulation for the online solution of team games. The notion of graphical games is developed for dynamical systems, where the dynamics and performance indices for each node depend only on local neighbor information. It is shown that standard definitions for Nash equilibrium are not sufficient for graphical games and a new definition of "Interactive Nash Equilibrium" is given. We give a cooperative policy iteration algorithm for graphical games that converges to the best response when the neighbors of each agent do not update their policies, and to the cooperative Nash equilibrium when all agents update their policies simultaneously. This is used to develop methods for online adaptive learning solutions of graphical games in real time along with proofs of stability and convergence. © 2012 Elsevier Ltd. All rights reserved.


Hechinger R.F.,University of California at Santa Barbara
American Naturalist | Year: 2013

Energetics may provide a useful currency for studying the ecology of parasite assemblages within individual hosts. Parasite assemblages may also provide powerful models to study general principles of ecological energetics. Yet there has been little ecological research on parasite-host energetics, probably due to methodological difficulties. However, the scaling relationships of individual metabolic rate with body or cell size and temperature may permit us to tackle the energetics of parasite assemblages in hosts. This article offers the foundations and initial testing of a metabolic theory of ecology (MTE) framework for parasites in hosts. I first provide equations to estimate energetic flux through observed parasite assemblages. I then develop metabolic scaling theory for parasite abundance, energetics, and biomass in individual hosts. In contrast to previous efforts, the theory factors in both host and parasite metabolic scaling, how parasites use host space, and whether energy or space dictates carrying capacity. Empirical tests indicate that host energetic flux can set parasite carrying capacity, which decreases as predicted considering the scaling of host and parasite metabolic rates. The theory and results also highlight that the phenomenon of "energetic equivalence" is not an assumption of MTE but a possible outcome contingent on how species partition resources. Hence, applying MTE to parasites can lend mechanistic, quantitative, predictive insight into the nature of parasitism and can inform general ecological theory. © 2013 by The University of Chicago.


Hechinger R.F.,University of California at Santa Barbara
BMC Evolutionary Biology | Year: 2010

Background. The probability of being killed by external factors (extrinsic mortality) should influence how individuals allocate limited resources to the competing processes of growth and reproduction. Increased extrinsic mortality should select for decreased allocation to growth and for increased reproductive effort. This study presents perhaps the first clear cross-species test of this hypothesis, capitalizing on the unique properties offered by a diverse guild of parasitic castrators (body snatchers). I quantify growth, reproductive effort, and expected extrinsic mortality for several species that, despite being different species, use the same species' phenotype for growth and survival. These are eight trematode parasitic castratorsthe individuals of which infect and take over the bodies of the same host speciesand their uninfected host, the California horn snail. Results. As predicted, across species, growth decreased with increased extrinsic mortality, while reproductive effort increased with increased extrinsic mortality. The trematode parasitic castrator species (operating stolen host bodies) that were more likely to be killed by dominant species allocated less to growth and relatively more to current reproduction than did species with greater life expectancies. Both genders of uninfected snails fit into the patterns observed for the parasitic castrator species, allocating as much to growth and to current reproduction as expected given their probability of reproductive death (castration by trematode parasites). Additionally, species differences appeared to represent species-specific adaptations, not general plastic responses to local mortality risk. Conclusions. Broadly, this research illustrates that parasitic castrator guilds can allow unique comparative tests discerning the forces promoting adaptive evolution. The specific findings of this study support the hypothesis that extrinsic mortality influences species differences in growth and reproduction. © 2010 Hechinger; licensee BioMed Central Ltd.


Barnes J.W.,University of Idaho | Linscott E.,Oklahoma Baptist University | Shporer A.,University of California at Santa Barbara
Astrophysical Journal, Supplement Series | Year: 2011

We model the asymmetry of the KOI-13.01 transit lightcurve assuming a gravity-darkened rapidly rotating host star in order to constrain the system's spin-orbit alignment and transit parameters. We find that our model can reproduce the Kepler lightcurve for KOI-13.01 with a sky-projected alignment of λ = 23° 4° and with the star's north pole tilted away from the observer by 48° 4° (assuming M * = 2.05 M ⊙). With both these determinations, we calculate that the net misalignment between this planet's orbit normal and its star's rotational pole is 56° ± 4°. Degeneracies in our geometric interpretation also allow a retrograde spin-orbit angle of 124° ± 4°. This is the first spin-orbit measurement to come from gravity darkening and is one of only a few measurements of the full (not just the sky-projected) spin-orbit misalignment of an extrasolar planet. We also measure accurate transit parameters incorporating stellar oblateness and gravity darkening: R * = 1.756 ± 0.014 R⊙, R p = 1.445 ± 0.016 RJup, and i = 859 04. The new lower planetary radius falls within the planetary mass regime for plausible interior models for the transiting body. A simple initial calculation shows that KOI-13.01's circular orbit is apparently inconsistent with the Kozai mechanism having driven its spin-orbit misalignment; planet-planet scattering and stellar spin migration remain viable mechanisms. Future Kepler data will improve the precision of the KOI-13.01 transit lightcurve, allowing more precise determination of transit parameters and the opportunity to use the Photometric Rossiter-McLaughlin effect to resolve the prograde/retrograde orbit determination degeneracy. © 2011. The American Astronomical Society. All rights reserved.


Increasing migration into urbanized centers in the Solomon Islands poses a great threat to adjacent coral reef fisheries because of negative effects on the fisheries and because it further erodes customary management systems. Parrotfish fisheries are of particular importance because the feeding habits of parrotfish (scrape and excavate coral) are thought to be critical to the resilience of coral reefs and to maintaining coral reef health within marine protected areas. We investigated the ecological impact of localized subsistence and artisanal fishing pressure on parrotfish fisheries in Gizo Town, Western Solomon Islands, by analyzing the density and size distribution of parrotfishwith an underwater visual census (UVC), recall diary (i.e., interviews with fishers), and creel surveys to independently assess changes in abundance and catch-per-unit-effort (CPUE) over 2 years. We then compared parrotfish data from Gizo Town with equivalent data from sites open to and closed to fishing in Kida and Nusa Hope villages, which have different customary management regimes. Results indicated a gradient of customary management effectiveness. Parrotfish abundance was greater in customary management areas closed to fishing, especially with regard to larger fish sizes, than in areas open to fishing. The decline in parrotfish abundance from 2004 to 2005 in Gizo was roughly the same magnitude as the difference in abundance decline between inside and outside customary management marine reserves. Our results highlight how weak forms of customary management can result in the rapid decline of vulnerable fisheries around urbanized regions, and we present examples in which working customary management systems (Kinda and Nusa Hope) can positively affect the conservation of parrotfish-and reef fisheries in general-in the highly biodiverse Coral Triangle region. © 2009 Society for Conservation Biology.


Moon E.-G.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We study Skyrmion quantum numbers, charge, and statistics, in (2+1) dimension induced by quadratic band touching (QBT) fermions. It is shown that induced charge of Skyrmions is twice bigger than corresponding Dirac particles' and their statistics are always bosonic. Applying to the Bernal stacking bilayer graphene, we show that Skyrmions of quantum spin Hall are charge 4e bosons, so their condensation realizes charge 4e superconductivity. The phase transition could be of second order, and one candidate theory of the transition is an O(5) nonlinear sigma model with a nonzero Wess-Zumino-Witten term. We calculate the renormalization group beta function of the model perturbatively and propose a possible phase diagram. We also discuss how QBT fermions are different from two copies of Dirac particles. © 2012 American Physical Society.


Jani A.J.,University of California at Santa Barbara | Faeth S.H.,University of North Carolina at Greensboro | Gardner D.,U.S. Department of Agriculture
Ecology Letters | Year: 2010

Despite their minute biomass, microbial symbionts of plants potentially alter herbivory, diversity and community structure. Infection of grasses by asexual endophytic fungi often decreases herbivore loads and alters arthropod diversity. However, most studies to date have involved agronomic grasses and often consider only infection status (infected vs. uninfected), without explicitly measuring endophyte-produced alkaloids, which vary among endophyte isolates and may impact consumers. We combined field experiments and population surveys to investigate how endophyte infection and associated alkaloids influence abundances, species richness, evenness and guild structure of arthropod communities on a native grass, Achnatherum robustum (sleepygrass). Surprisingly, we found that endophyte-produced alkaloids were associated with increased herbivore abundances and species richness. Our results suggest that, unlike what has been found in agronomic grass systems, high alkaloid levels in native grasses may not protect host grasses from arthropod herbivores, and may instead more negatively affect natural enemies of herbivores. © 2009 Blackwell Publishing Ltd/CNRS.


Krechetnikov R.,University of California at Santa Barbara
Physics of Fluids | Year: 2010

In this work, the characteristic properties of the lubrication approximation are studied and its weak ellipticity is established, in contradistinction to the commonly accepted parabolic character of the lubrication equations resulting from the underlying unidirectional flow assumption. The weak ellipticity property allows the lubrication analysis to capture flow topologies around stagnation points, contact lines, and flows over edges, all of which normally require elliptic operators to be accounted for. This is used to explain the empirically observed overperformance of the lubrication approximation from the perspective of characteristic analysis. While the analysis is developed in the context of the classical Landau-Levich problem of dip-coating, which is known to possess an interfacial stagnation point both in the clean and surfactant interface cases, the analysis is general since the Landau-Levich equation is common to many other lubrication problems. The analytical approach presented here when applied to the surfactant interface case, also allows one to establish a new physical result: a variation of the bulk surfactant concentration is the necessary condition for the film thickening phenomenon in the Landau-Levich problem to occur due to surfactant-induced Marangoni effects. © 2010 American Institute of Physics.


Munday P.L.,James Cook University | Warner R.R.,University of California at Santa Barbara | Monro K.,Monash University | Pandolfi J.M.,University of Queensland | Marshall D.J.,Monash University
Ecology Letters | Year: 2013

An increasing number of short-term experimental studies show significant effects of projected ocean warming and ocean acidification on the performance on marine organisms. Yet, it remains unclear if we can reliably predict the impact of climate change on marine populations and ecosystems, because we lack sufficient understanding of the capacity for marine organisms to adapt to rapid climate change. In this review, we emphasise why an evolutionary perspective is crucial to understanding climate change impacts in the sea and examine the approaches that may be useful for addressing this challenge. We first consider what the geological record and present-day analogues of future climate conditions can tell us about the potential for adaptation to climate change. We also examine evidence that phenotypic plasticity may assist marine species to persist in a rapidly changing climate. We then outline the various experimental approaches that can be used to estimate evolutionary potential, focusing on molecular tools, quantitative genetics, and experimental evolution, and we describe the benefits of combining different approaches to gain a deeper understanding of evolutionary potential. Our goal is to provide a platform for future research addressing the evolutionary potential for marine organisms to cope with climate change. © 2013 John Wiley & Sons Ltd/CNRS.


Treat N.D.,Imperial College London | Chabinyc M.L.,University of California at Santa Barbara
Annual Review of Physical Chemistry | Year: 2014

Thin-film solar cells are an important source of renewable energy. The most efficient thin-film solar cells made with organic materials are blends of semiconducting polymers and fullerenes called the bulk heterojunction (BHJ). Efficient BHJs have a nanoscale phase-separated morphology that is formed during solution casting. This article reviews recent work to understand the nature of the phase-separation process resulting in the formation of the domains in polymer-fullerene BHJs. The BHJ is now viewed as a mixture of polymer-rich, fullerene-rich, and mixed polymer-fullerene domains. The formation of this structure can be understood through fundamental knowledge of polymer physics. The implications of this structure for charge transport and charge generation are given. Copyright © 2014 by Annual Reviews.


Treu T.,University of California at Santa Barbara
Annual Review of Astronomy and Astrophysics | Year: 2010

Strong lensing is a powerful tool to address three majorastrophysical issues: understanding the spatial distribution of mass at kiloparsec and subkiloparsec scale, where baryons and dark matter interact to shape galaxies as we see them; determining the overall geometry, content, and kinematics of the Universe; and studying distant galaxies, black holes, and active nuclei that are too small or too faint to be resolved or detected with current instrumentation. After summarizing strong gravitational lensing fundamentals, I present a selection of recent important results. I conclude by discussing the exciting prospects of strong gravitational lensing in the nextdecade. © 2010 by Annual Reviews.


Saleh A.A.M.,University of California at Santa Barbara | Simmons J.M.,Monarch Network Architects
Proceedings of the IEEE | Year: 2012

While all-optical networking had its origins in the research community a quarter of a century ago, the realization of the vision has not had a straight trajectory. The original goal of the all-optical network was based on keeping the data signals entirely in the optical domain from source to destination to eliminate the so-called electronic bottleneck, and to allow arbitrary signal formats, bitrates, and protocols to be transported. The latter property is referred to as transparency. When all-optical networks were finally commercialized around the turn of the century, however, a modified reality emerged; the quest for transparency was replaced by the more pragmatic objective of reducing the network cost and energy consumption. Moreover, especially for networks of large geographical extent, electronics were still present at some (relatively few) points along the data path, for signal regeneration and traffic grooming. This modified vision captures the state of today's networks, though terms like all-optical and transparent are still used to describe this technology. However, continued advancements are bringing back some aspects of the original transparency vision. In this paper, we review the evolution of all-optical networking, from the early vision to its present vibrant state, which was made possible by great advances in optical transmission and all-optical switching technologies. We describe the numerous benefits afforded by the technology, and its relative merits and drawbacks compared to competing technologies, sometimes referred to as opaque. We also discuss the remaining challenges and future directions of all-optical networking. While all-optical solutions permeate today's access, metro, and core networks, this paper focuses on the core. © 2012 IEEE.


Blaes O.,University of California at Santa Barbara
Space Science Reviews | Year: 2014

I provide a broad overview of the basic theoretical paradigms of black hole accretion flows. Models that make contact with observations continue to be mostly based on the four decade old alpha stress prescription of Shakura and Sunyaev (1973), and I discuss the properties of both radiatively efficient and inefficient models, including their local properties, their expected stability to secular perturbations, and how they might be tied together in global flow geometries. The alpha stress is a prescription for turbulence, for which the only existing plausible candidate is that which develops from the magnetorotational instability (MRI). I therefore also review what is currently known about the local properties of such turbulence, and the physical issues that have been elucidated and that remain uncertain that are relevant for the various alpha-based black hole accretion flow models. © 2013, Springer Science+Business Media Dordrecht.


Gurven M.,University of California at Santa Barbara
Social Science and Medicine | Year: 2012

Indigenous populations experience higher rates of poverty, disease and mortality than non-indigenous populations. To gauge current and future risks among Tsimane Amerindians of Bolivia, I assess mortality rates and growth early in life, and changes in risks due to modernization, based on demographic interviews conducted Sept. 2002-July 2005. Tsimane have high fertility (total fertility rate = 9) and infant mortality (13%). Infections are the leading cause of infant death (55%). Infant mortality is greatest among women who are young, monolingual, space births close together, and live far from town. Infant mortality declined during the period 1990-2002, and a higher rate of reported miscarriages occurred during the 1950-1989 period. Infant deaths are more frequent among those born in the wet season. Infant stunting, underweight and wasting are common (34%, 15% and 12%, respectively) and greatest for low-weight mothers and high parity infants. Regression analysis of infant growth shows minimal regional differences in anthropometrics but greater stunting and underweight during the first two years of life. Males are more likely to be underweight, wasted, and spontaneously aborted. Whereas morbidity and stunting are prevalent in infancy, greater food availability later in life has not yet resulted in chronic diseases (e.g. hypertension, atherosclerosis and diabetes) in adulthood due to the relatively traditional Tsimane lifestyle. © 2012 Elsevier Ltd.


Jaeggi A.V.,University of Zurich | Gurven M.,University of California at Santa Barbara
Evolutionary Anthropology | Year: 2013

The study of cooperation is rich with theoretical models and laboratory experiments that have greatly advanced our knowledge of human uniqueness, but have sometimes lacked ecological validity. We therefore emphasize the need to tie discussions of human cooperation to the natural history of our species and its closest relatives, focusing on behavioral contexts best suited to reveal underlying selection pressures and evolved decision rules. Food sharing is a fundamental form of cooperation that is well-studied across primates and is particularly noteworthy because of its central role in shaping evolved human life history, social organization, and cooperative psychology. Here we synthesize available evidence on food sharing in humans and other primates, tracing the origins of offspring provisioning, mutualism, trade, and reciprocity throughout the primate order. While primates may gain some benefits from sharing, humans, faced with more collective action problems in a risky foraging niche, expanded on primate patterns to buffer risk and recruit mates and allies through reciprocity and signaling, and established co-evolving social norms of production and sharing. Differences in the necessity for sharing are reflected in differences in sharing psychology across species, thus helping to explain unique aspects of our evolved cooperative psychology. © 2013 Wiley Periodicals, Inc.


Grafton S.T.,University of California at Santa Barbara
Experimental Brain Research | Year: 2010

Prehension, the capacity to reach and grasp, is the key behavior that allows humans to change their environment. It continues to serve as a remarkable experimental test case for probing the cognitive architecture of goal-oriented action. This review focuses on recent experimental evidence that enhances or modiWes how we might conceptualize the neural substrates of prehension. Emphasis is placed on studies that consider how precision grasps are selected and transformed into motor commands. Then, the mechanisms that extract action relevant information from vision and touch are considered. These include consideration of how parallel perceptual networks within parietal cortex, along with the ventral stream, are connected and share information to achieve common motor goals. On-line control of grasping action is discussed within a state estimation framework. The review ends with a consideration about how prehension Wts within larger action repertoires that solve more complex goals and the possible cortical architectures needed to organize these actions. © 2010 Springer-Verlag.


Dai D.,Zhejiang University | Bowers J.E.,University of California at Santa Barbara
Nanophotonics | Year: 2014

An effective solution to enhance the capacity of an optical-interconnect link is utilizing advanced multiplexing technologies, like wavelength-division-multiplexing (WDM), polarization-division multiplexing (PDM), spatial-division multiplexing (SDM), bi-directional multiplexing, etc. On-chip (de)multiplexers are necessary as key components for realizing these multiplexing systems and they are desired to have small footprints due to the limited physical space for on-chip optical interconnects. As silicon photonics has provided a very attractive platform to build ultrasmall photonic integrated devices with CMOS-compatible processes, in this paper we focus on the discussion of silicon-based (de)multiplexers, including WDM filters, PDM devices, and SDM devices. The demand of devices to realize a hybrid multiplexing technology (combining WDM, PDM and SDM) as well as a bidirectional multiplexing technologies are also discussed to achieve Peta-bit optical interconnects. © 2014 Science Wise Publishing & De Gruyter.


Neher R.A.,University of California at Santa Barbara | Leitner T.,Los Alamos National Laboratory
PLoS Computational Biology | Year: 2010

The evolutionary dynamics of HIV during the chronic phase of infection is driven by the host immune response and by selective pressures exerted through drug treatment. To understand and model the evolution of HIV quantitatively, the parameters governing genetic diversification and the strength of selection need to be known. While mutation rates can be measured in single replication cycles, the relevant effective recombination rate depends on the probability of coinfection of a cell with more than one virus and can only be inferred from population data. However, most population genetic estimators for recombination rates assume absence of selection and are hence of limited applicability to HIV, since positive and purifying selection are important in HIV evolution. Yet, little is known about the distribution of selection differentials between individual viruses and the impact of single polymorphisms on viral fitness. Here, we estimate the rate of recombination and the distribution of selection coefficients from time series sequence data tracking the evolution of HIV within single patients. By examining temporal changes in the genetic composition of the population, we estimate the effective recombination to be ρ = 1.4±0.6×10-5 recombinations per site and generation. Furthermore, we provide evidence that the selection coefficients of at least 15% of the observed non-synonymous polymorphisms exceed 0.8% per generation. These results provide a basis for a more detailed understanding of the evolution of HIV. A particularly interesting case is evolution in response to drug treatment, where recombination can facilitate the rapid acquisition of multiple resistance mutations. With the methods developed here, more precise and more detailed studies will be possible as soon as data with higher time resolution and greater sample sizes are available.


Gerig J.T.,University of California at Santa Barbara
Journal of Physical Chemistry B | Year: 2013

Molecular dynamics simulations have been used to explore solvent-solute intermolecular nuclear Overhauser effects (NOEs) on NMR (nuclear magnetic resonance) signals of [val5]angiotensin dissolved in 35% ethanol-water (v/v). Consideration of chemical shift, coupling constant and intramolecular NOE data suggest that conformations of the peptide are adequately sampled by simulations of up to 0.6 μs duration. Calculated cross relaxation terms at 0 and 25 C are compared to experimental values and to terms predicted using a particulate model of the solvent. Many calculated solvent NOEs are in agreement with experimental results; disagreements are particularly striking for hydrogens of the Phe8 residue of the peptide. Calculations show that individual molecules of either solvent component can spend many ns in association with the peptide but dipolar interactions within such a complex account for only a few percent of an observed cross relaxation rate. Most parts of the peptide interact selectively with ethanol. Diffusion of both solvent components is slowed when they are close to the peptide. Solvent-solute cross relaxation terms for acetic acid in the same solvent obtained from simulations agree with experiment. Preferential interactions of solvent molecules with acetic acid are largely absent, as are effects of this solute on solvent diffusion rates. © 2013 American Chemical Society.


Childs A.M.,University of Waterloo | Van Dam W.,University of California at Santa Barbara
Reviews of Modern Physics | Year: 2010

Quantum computers can execute algorithms that dramatically outperform classical computation. As the best-known example, Shor discovered an efficient quantum algorithm for factoring integers, whereas factoring appears to be difficult for classical computers. Understanding what other computational problems can be solved significantly faster using quantum algorithms is one of the major challenges in the theory of quantum computation, and such algorithms motivate the formidable task of building a large-scale quantum computer. This article reviews the current state of quantum algorithms, focusing on algorithms with superpolynomial speedup over classical computation and, in particular, on problems with an algebraic flavor. © 2010 The American Physical Society.


Draper P.,University of California at Santa Barbara | Rzehak H.,Albert Ludwigs University of Freiburg | Rzehak H.,University of Southern Denmark
Physics Reports | Year: 2016

The discovery of the Higgs boson is both a milestone achievement for the Standard Model and an exciting probe of new physics beyond the SM. One of the most important properties of the Higgs is its mass, a number that has proven to be highly constraining for models of new physics, particularly those related to the electroweak hierarchy problem. Perhaps the most extensively studied examples are supersymmetric models, which, while capable of producing a 125 GeV Higgs boson with SM-like properties, do so in non-generic parts of their parameter spaces. We review the computation of the Higgs mass in the Minimal Supersymmetric Standard Model, in particular the large radiative corrections required to lift mh to 125 GeV and their calculation via Feynman-diagrammatic and effective field theory techniques. This review is intended as an entry point for readers new to the field, and as a summary of the current status, including the existing analytic calculations and publicly-available computer codes. © 2016 Elsevier B.V..


Teel A.R.,University of California at Santa Barbara
IEEE Transactions on Automatic Control | Year: 2013

Matrosov's relaxation of Lyapunov conditions for uniform global asymptotic stability in time-varying systems is extended to stochastic, set-valued discrete-time systems. Nested Matrosov functions are used to give conditions for stability that complement invariance principles for time-invariant systems. Unlike invariance principles, Matrosov functions also can be applied to general time-varying systems. © 1963-2012 IEEE.


Turk M.,University of California at Santa Barbara
Pattern Recognition Letters | Year: 2014

People naturally interact with the world multimodally, through both parallel and sequential use of multiple perceptual modalities. Multimodal human-computer interaction has sought for decades to endow computers with similar capabilities, in order to provide more natural, powerful, and compelling interactive experiences. With the rapid advance in non-desktop computing generated by powerful mobile devices and affordable sensors in recent years, multimodal research that leverages speech, touch, vision, and gesture is on the rise. This paper provides a brief and personal review of some of the key aspects and issues in multimodal interaction, touching on the history, opportunities, and challenges of the area, especially in the area of multimodal integration. We review the question of early vs. late integration and find inspiration in recent evidence in biological sensory integration. Finally, we list challenges that lie ahead for research in multimodal human-computer interaction. © 2013 Elsevier B.V. All rights reserved.


Dorfler F.,ETH Zurich | Bullo F.,University of California at Santa Barbara
Automatica | Year: 2014

The emergence of synchronization in a network of coupled oscillators is a fascinating subject of multidisciplinary research. This survey reviews the vast literature on the theory and the applications of complex oscillator networks. We focus on phase oscillator models that are widespread in real-world synchronization phenomena, that generalize the celebrated Kuramoto model, and that feature a rich phenomenology. We review the history and the countless applications of this model throughout science and engineering. We justify the importance of the widespread coupled oscillator model as a locally canonical model and describe some selected applications relevant to control scientists, including vehicle coordination, electric power networks, and clock synchronization. We introduce the reader to several synchronization notions and performance estimates. We propose analysis approaches to phase and frequency synchronization, phase balancing, pattern formation, and partial synchronization. We present the sharpest known results about synchronization in networks of homogeneous and heterogeneous oscillators, with complete or sparse interconnection topologies, and in finite-dimensional and infinite-dimensional settings. We conclude by summarizing the limitations of existing analysis methods and by highlighting some directions for future research. © 2014 Elsevier Ltd. All rights reserved.


Neill C.,University of California at Santa Barbara
Nature Physics | Year: 2016

Statistical mechanics is founded on the assumption that all accessible configurations of a system are equally likely. This requires dynamics that explore all states over time, known as ergodic dynamics. In isolated quantum systems, however, the occurrence of ergodic behaviour has remained an outstanding question. Here, we demonstrate ergodic dynamics in a small quantum system consisting of only three superconducting qubits. The qubits undergo a sequence of rotations and interactions and we measure the evolution of the density matrix. Maps of the entanglement entropy show that the full system can act like a reservoir for individual qubits, increasing their entropy through entanglement. Surprisingly, these maps bear a strong resemblance to the phase space dynamics in the classical limit; classically, chaotic motion coincides with higher entanglement entropy. We further show that in regions of high entropy the full multi-qubit system undergoes ergodic dynamics. Our work illustrates how controllable quantum systems can investigate fundamental questions in non-equilibrium thermodynamics. © 2016 Nature Publishing Group


Yang J.J.,Hewlett - Packard | Strukov D.B.,University of California at Santa Barbara | Stewart D.R.,National Research Council Canada
Nature Nanotechnology | Year: 2013

Memristive devices are electrical resistance switches that can retain a state of internal resistance based on the history of applied voltage and current. These devices can store and process information, and offer several key performance characteristics that exceed conventional integrated circuit technology. An important class of memristive devices are two-terminal resistance switches based on ionic motion, which are built from a simple conductor/insulator/conductor thin-film stack. These devices were originally conceived in the late 1960s and recent progress has led to fast, low-energy, high-endurance devices that can be scaled down to less than 10 nm and stacked in three dimensions. However, the underlying device mechanisms remain unclear, which is a significant barrier to their widespread application. Here, we review recent progress in the development and understanding of memristive devices. We also examine the performance requirements for computing with memristive devices and detail how the outstanding challenges could be met. © 2013 Macmillan Publishers Limited. All rights reserved.


Artyukhin S.,Zernike Institute for Advanced Materials | Artyukhin S.,Rutgers University | Delaney K.T.,University of California at Santa Barbara | Spaldin N.A.,ETH Zurich | Mostovoy M.,Zernike Institute for Advanced Materials
Nature Materials | Year: 2014

Topological defects in ordered states with spontaneously broken symmetry often have unusual physical properties, such as fractional electric charge or a quantized magnetic field flux, originating from their non-trivial topology. Coupled topological defects in systems with several coexisting orders give rise to unconventional functionalities, such as the electric-field control of magnetization in multiferroics resulting from the coupling between the ferroelectric and ferromagnetic domain walls. Hexagonal manganites provide an extra degree of freedom: in these materials, both ferroelectricity and magnetism are coupled to an additional, non-ferroelectric structural order parameter. Here we present a theoretical study of topological defects in hexagonal manganites based on Landau theory with parameters determined from first-principles calculations. We explain the observed flip of electric polarization at the boundaries of structural domains, the origin of the observed discrete vortices, and the clamping between ferroelectric and antiferromagnetic domain walls. We show that structural vortices induce magnetic ones and that, consistent with a recent experimental report, ferroelectric domain walls can carry a magnetic moment. © 2014 Macmillan Publishers Limited.


Morriss-Andrews A.,Stanford University | Shea J.-E.,Stanford University | Shea J.-E.,University of California at Santa Barbara
Annual Review of Physical Chemistry | Year: 2015

Protein aggregation involves the self-assembly of normally soluble proteins into large supramolecular assemblies. The typical end product of aggregation is the amyloid fibril, an extended structure enriched in â-sheet content. The aggregation process has been linked to a number of diseases, most notably Alzheimer's disease, but fibril formation can also play a functional role in certain organisms. This review focuses on theoretical studies of the process of fibril formation, with an emphasis on the computational models and methods commonly used to tackle this problem. © 2015 by Annual Reviews. All rights reserved.


Adams F.C.,University of Michigan | Adams F.C.,University of California at Santa Barbara
Astrophysical Journal | Year: 2011

Recent observations indicate that some extrasolar planets observed in transit can experience mass loss from their surfaces.Motivated by these findings, this paper considers outflows from hot Jupiters in the regime where the flow is controlled by magnetic fields. Given the mass-loss rates estimated from current observations and from theoretical arguments magnetic fields will dominate the flow provided that field strength near the planet is greater than ~1 G, comparable to the surface fields of the Sun and Jupiter. The problem can be separated into an inner regime, near the planet, where the outflow is launched, and an outer regime where the flow follows (primarily) stellar field lines and interacts with the stellar wind. This paper concentrates on the flow in the inner regime. For a dipole planetary field with a spatially constant background contribution, we construct a set of orthogonal coordinates that follow the field lines and determine the corresponding differential operators. Under the assumption of isothermal flow, we analytically find the conditions required for escaping material to pass smoothly through the sonic transition and then estimate the mass outflow rates. These magnetically controlled outflows differ significantly from previous spherical models. The outflow rates are somewhat smaller, typically M ∼ 109 g s-1, and the flow is launched primarily from the polar regions of the planet. In addition, if the stellar wind is strong enough, the flow could be reversed and the planet could gain mass from the star. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


Rigol M.,Georgetown University | Srednicki M.,University of California at Santa Barbara
Physical Review Letters | Year: 2012

An isolated quantum many-body system in an initial pure state will come to thermal equilibrium if it satisfies the eigenstate thermalization hypothesis (ETH). We consider alternatives to ETH that have been proposed. We first show that von Neumann's quantum ergodic theorem relies on an assumption that is essentially equivalent to ETH. We also investigate whether, following a sudden quench, special classes of pure states can lead to thermal behavior in systems that do not obey ETH, namely, integrable systems. We find examples of this, but only for initial states that obeyed ETH before the quench. © 2012 American Physical Society.


Lei T.L.,University of California at Santa Barbara
Geographical Analysis | Year: 2013

The hub location problem has been widely used in analyzing hub-and-spoke systems. The basic assumption is that a large number of demands exist to travel from origins to destinations via a set of intermediate transshipment nodes. These intermediate nodes can be lost, due to reasons such as natural disasters, outbreaks of disease, labor strikes, and intentional attacks. This article presents a hub interdiction median (HIM) problem. It can be used to identify the set of critical facilities in a hub-and-spoke system that, if lost, leads to the maximal disruption of the system's service. The new model is formulated using integer linear programming. Special constraints are constructed to account for origin-to-destination demand following the least-cost route via the remaining hubs. Based on the HIM problem, two hub protection problems are defined that aim to minimize the system cost associated with the worst-case facility loss. Computational experiment results are presented along with a discussion of possible future work. © 2013 The Ohio State University.


D'Alessio L.,Boston University | D'Alessio L.,University of California at Santa Barbara | Polkovnikov A.,Boston University
Annals of Physics | Year: 2013

According to the second law of thermodynamics the total entropy of a system is increased during almost any dynamical process. The positivity of the specific heat implies that the entropy increase is associated with heating. This is generally true both at the single particle level, like in the Fermi acceleration mechanism of charged particles reflected by magnetic mirrors, and for complex systems in everyday devices. Notable exceptions are known in noninteracting systems of particles moving in periodic potentials. Here the phenomenon of dynamical localization can prevent heating beyond certain threshold. The dynamical localization is known to occur both at classical (Fermi-Ulam model) and at quantum levels (kicked rotor). However, it was believed that driven ergodic systems will always heat without bound. Here, on the contrary, we report strong evidence of dynamical localization transition in both classical and quantum periodically driven ergodic systems in the thermodynamic limit. This phenomenon is reminiscent of many-body localization in energy space. © 2013 Elsevier Inc.


Giddings S.B.,University of California at Santa Barbara
Foundations of Physics | Year: 2013

Some problems in finding a complete quantum theory incorporating gravity are discussed. One is that of giving a consistent unitary description of high-energy scattering. Another is that of giving a consistent quantum description of cosmology, with appropriate observables. While string theory addresses some problems of quantum gravity, its ability to resolve these remains unclear. Answers may require new mechanisms and constructs, whether within string theory, or in another framework. © 2011 Springer Science+Business Media, LLC.


Fowler S.J.,ETH Zurich | Spera F.J.,University of California at Santa Barbara
Journal of Petrology | Year: 2010

Diverse explanations exist for the large-volume catastrophic eruptions that formed the Bishop Tuff of Long Valley in eastern California, the Bandelier Tuff in New Mexico, and the tuffs of Yellowstone, Montana, USA. These eruptions are among the largest on Earth within the last 2 Myr. A common factor in recently proposed petrogenetic scenarios for each system is multistage processing, in which a crystal mush forms by crystal fractionation and is then remobilized to liberate high-silica liquids. Magma evolves in the lower crust in earlier phases. We have tested these scenarios quantitatively by performing phase equilibria calculations (MELTS) and comparing the results with observed liquid (glass) and phenocryst compositions. Although comparison of tuff samples from each ignimbrite reveals distinct phenocryst compositions and proportions, the computed results exhibit a remarkable degree of congruity among the systems, pointing to some underlying uniform behavior relevant to large-volume silicic ignimbrites. Computed liquid compositions derived from more than ~25% fractional crystallization of the parental melt in the deep crust are marked by SiO2 concentrations several weight per cent too low compared with the observed compositions, suggesting a limit on the extent of magma evolution by crystal fractionation in the deep crust. In all cases, the phase equilibria results and related considerations point to evolution dominated by crystal fractionation of a water-saturated mafic parental melt at shallow depths (~5 km). Parental melt compositions are consistent with those of observed regional primitive basalts erupted prior to ignimbrite eruption for each system in each region. Fractional crystallization of water-rich mafic melt at shallow levels leads inherently to destabilization near thermodynamic pseudoinvariant points at around 800°C within the melting interval close to, but above, the solidus. For each system, the magmas evolve to states of high exsolved H2O volume fraction even at 5 km depth, eventually exceeding the criterion for magma fragmentation of ~60 vol. % near the pseudoinvariant point temperature. Copious exsolution and possible expulsion of fluid occurs at this temperature, where the solid fraction in the magma changes almost discontinuously (isothermally) to significantly higher values. This instability mechanism acts as an eruption trigger by generating a gravitationally unstable arrangement of low-density, watersaturated magma beneath a thin (several kilometres) crustal lid. The trigger mechanism is common to fractional crystallization scenarios based on a variety of conditions, when crystallized solids and/or exsolved fluids are fractionated from residual melt isobarically (constant pressure) or isochorically (constant volume). In a single system, differences in liquid compositions resulting from constant volume versus constant pressure crystallization and expulsion versus retention of exsolved H2O are small compared with those arising from variations in initial water concentration, lithostatic pressure, and oxygen fugacity. It is these latter quantities that lie at the crux of the commonality in large-volume ignimbrite-forming eruptions, with a reasonable range of metamodel parameters. Scale analysis provides thermal timescales for fractional crystallization, including age ranges for discrete crystal populations. For the BishopTuff, the overall timescale for the Bishop magma body is >1 Myr. For the YellowstoneTuffs, calculated thermal timescales are consistent with recurrence intervals of ~600 kyr between successive caldera collapses. Although it is recognized that petrogenetic processes other than perfect fractional crystallization play a role in ignimbrite petrogenesis, by emphasizing common features the uniqueness of each system can be brought into better focus by sound and quantitative analysis. © The Author 2010. Published by Oxford University Press. All rights reserved.


Busby C.J.,University of California at Santa Barbara
Geosphere | Year: 2013

The Walker Lane belt of eastern California and western Nevada is the northernmost extension of the Gulf of California transtensional rift, where the process of continental rupture has not yet been completed, and rift initiation can be studied on land. GPS and earthquake focal mechanism studies demonstrate that the Walker Lane belt currently accommodates NW-SE-directed movement between the Sierra Nevada microplate and the North American plate, but the timing and nature of rift initiation remains unclear. I present a model for plate-margin-scale initiation of the Gulf of California and Walker Lane transtensional rifts at ca. 12 Ma; localization of rifting in both was initiated by thermal weakening in the axis of a subduction- related arc undergoing extension due to slab rollback, and thermal weakening in the arc was enhanced by stalling of the trenchward- migrating precursor arc against a thick Cretaceous batholithic lithospheric profile on its western margin. Rifting succeeded very quickly in the Gulf of California, due to stalling of Farallon slabs, but the Walker Lane transtensional rift has been unzipping northward along the axis of the Cascades arc, following the Mendocino triple junction. I infer that plate-margin-scale Walker Lane transtension was signaled by the development of an unusually large and voluminous transtensional arc volcanic center, the ca. 11.5-9 Ma Sierra Crest-Little Walker arc volcanic center. I show that the style of faulting in this large Miocene arc volcanic center closely matches that of Quaternary transtensional structures in the central Walker Lane, where it lies, and that it differs from southern and northern Walker Lane structures. This indicates that the temporal transition from E-W Basin and Range extension to NW-SE Walker Lane transtension occurred earlier than most workers have inferred. I also summarize new data which show that the central Sierra Nevada range front (from Long Valley to the Tahoe Basin) lies squarely within the Walker Lane belt, not to the west of it as previous workers have inferred. The leading tip of Walker Lane transtension is marked by large arc volcanic centers sited in transtensional stepovers; these include the ca. 11.5-9 Ma Sierra Crest-Little Walker volcanic center; north of that, the ca. 6.3-4.8 Ma Ebbetts Pass volcanic center; and north of that, the active Lassen volcanic center. In its wake, large rift volcanic centers are sited on transtensional stepovers or bends; these include the Long Valley and Coso volcanic fields. I predict that any <12 Ma large volcanic centers identified by future workers in the Sierra Nevada-Walker Lane region, or in the Gulf of California, will prove to be sited at major releasing bends or stepovers. © 2013 Geological Society of America.


Scherler D.,University of Potsdam | Bookhagen B.,University of California at Santa Barbara | Strecker M.R.,University of Potsdam
Nature Geoscience | Year: 2011

Controversy about the current state and future evolution of Himalayan glaciers has been stirred up by erroneous statements in the fourth report by the Intergovernmental Panel on Climate Change. Variable retreat rates and a paucity of glacial mass-balance data make it difficult to develop a coherent picture of regional climate-change impacts in the region. Here, we report remotely-sensed frontal changes and surface velocities from glaciers in the greater Himalaya between 2000 and 2008 that provide evidence for strong spatial variations in glacier behaviour which are linked to topography and climate. More than 65% of the monsoon-influenced glaciers that we observed are retreating, but heavily debris-covered glaciers with stagnant low-gradient terminus regions typically have stable fronts. Debris-covered glaciers are common in the rugged central Himalaya, but they are almost absent in subdued landscapes on the Tibetan Plateau, where retreat rates are higher. In contrast, more than 50% of observed glaciers in the westerlies-influenced Karakoram region in the northwestern Himalaya are advancing or stable. Our study shows that there is no uniform response of Himalayan glaciers to climate change and highlights the importance of debris cover for understanding glacier retreat, an effect that has so far been neglected in predictions of future water availability or global sea level. © 2011 Macmillan Publishers Limited. All rights reserved.


The objective of the study was to compare 9 cervical cancer screening strategies to the current screening standard (cytology with human papillomavirus [HPV] triage of atypical squamous cells of undetermined significance) for the detection of high-grade cervical disease. Women (n = 34,254) aged 30 years or older from the Addressing the Need for Advanced HPV Diagnostics (ATHENA) study underwent screening with cytology and HPV testing with simultaneous HPV16/18 genotyping; those with atypical squamous cells of undetermined significance cytology or greater or HPV-positive status were referred for colposcopy. In general, screening strategies that offered greater sensitivity also required more referral to colposcopy. HPV testing was more sensitive than cytology for detection of cervical intraepithelial neoplasia grade 2 or greater, but strategies that depended on cytology for triage of HPV-positive women decreased this sensitivity. Various strategies of cotesting with cytology increased sensitivity but did so by increasing testing. Strategies that included integrated HPV16/18 testing provided more efficient referral to colposcopy. Strategies that maximize detection of women at greatest risk of cervical intraepithelial neoplasia grade 3 or greater by immediate referral to colposcopy, with follow-up testing of women at intermediate risk, maximize the benefits of cervical cancer screening while decreasing the potential harm. Incorporating screening with HPV and triage of HPV-positive women by a combination of genotyping for HPV16/18 and cytology provided a good balance between maximizing sensitivity (benefit) and specificity by limiting the number of colposcopies (potential harm). Copyright © 2013 Mosby, Inc. All rights reserved.


Mattinson J.M.,University of California at Santa Barbara
Canadian Journal of Earth Sciences | Year: 2011

Tom Krogh was without a doubt the most influential U-Pb geochronologist of the modern era. His career was marked by a continuing series of breakthroughs, both revolutionary and evolutionary. His legacy is such that every lab around the world uses the methods he developed. After some fascinating insights into chemical leaching effects in zircon, Tom largely dropped this approach in favor of his enormously successful air abrasion technique, coupled with careful sample selection at the individual grain level. Here, I describe continued experiments with leaching and "step-wise dissolution" techniques, and how a series of alternating steps forward and setbacks eventually led to a new "chemical abrasion" or "CA-TIMS" method for selectively removing those domains within zircon that have lost Pb. Continuing to strive for improvements in analytical technique is perhaps the best way to honor Tom's many contributions and extend his legacy.


Wang M.,Nanyang Technological University | Wudl F.,University of California at Santa Barbara
Journal of Materials Chemistry | Year: 2012

Solar cells involving organic small molecules and polymers have attracted intense attention from chemists, physicists and materials scientists in the past decade. Efforts in materials synthesis and device processing have led to significant improvement of the power conversion efficiency, approaching 10%. In organic solar cells (OSCs), the morphology and the interface of the donor-acceptor (D-A) heterojunctions play a critical role in determining the device efficiency. In this article, we highlight recent progress on both materials synthesis and self-assembly and lithography techniques toward ordered nanostructures and well-defined D/A interfaces that are expected to enhance the performance of OSCs. © The Royal Society of Chemistry 2012.


All mammalian cone photopigments are derived from the operation of representatives from two opsin gene families (SWS1 and LWS in marsupial and eutherian mammals; SWS2 and LWS in monotremes), a process that produces cone pigments with respective peak sensitivities in the short and middle-to-long wavelengths. With the exception of a number of primate taxa, the modal pattern for mammals is to have two types of cone photopigment, one drawn from each of the gene families. In recent years, it has been discovered that the SWS1 opsin genes of a widely divergent collection of eutherian mammals have accumulated mutational changes that render them nonfunctional. This alteration reduces the retinal complements of these species to a single cone type, thus rendering ordinary color vision impossible. At present, several dozen species from five mammalian orders have been identified as falling into this category, but the total number of mammalian species that have lost short-wavelength cones in this way is certain to be much larger, perhaps reaching as high as 10% of all species. A number of circumstances that might be used to explain this widespread cone loss can be identified. Among these, the single consistent fact is that the species so affected are nocturnal or, if they are not technically nocturnal, they at least feature retinal organizations that are typically associated with that lifestyle. At the same time, however, there are many nocturnal mammals that retain functional short-wavelength cones. Nocturnality thus appears to set the stage for loss of functional SWS1 opsin genes in mammals, but it cannot be the sole circumstance. Copyright © Cambridge University Press 2012.


Hayes C.S.,University of California at Santa Barbara | Keiler K.C.,Pennsylvania State University
FEBS Letters | Year: 2010

tmRNA is a unique bi-functional RNA that acts as both a tRNA and an mRNA to enter stalled ribosomes and direct the addition of a peptide tag to the C terminus of nascent polypeptides. Despite a reasonably clear understanding of tmRNA activity, the reason for its absolute conservation throughout the eubacteria is unknown. Although tmRNA plays many physiological roles in different bacterial systems, recent studies suggest a general role for trans-translation in monitoring protein folding and perhaps other co-translational processes. This review will focus on these new hypotheses and the data that support them. © 2009 Federation of European Biochemical Societies.


Scheff T.J.,University of California at Santa Barbara
Aggression and Violent Behavior | Year: 2011

This essay outlines a cybernetic theory of violence, supporting and extending earlier studies, particularly Gilligan and Websdale. It spells out recursive, interactive processes of alienation and emotion. The theory proposes that most violence is caused by the interaction between alienation and what Gilligan called secret shame, shame about shame. Recursion need not stop in one round: there may be no natural limit for the resultant spirals. A chain reaction of vengefulness, a shame/anger derivative, can be produced in this way. Two spirals are described: shame/rage and shame/shame. Studies and accounts of multiple killings offer preliminary support. The idea may be applicable to collective behavior also, such as gratuitous wars. Websdale's cases of calmly planned familicide seem particularly relevant to the origins of wars, such as WWI, in which vengeance seems to have played a major part. It would appear that the humiliation-revenge cycle is the most dangerous element in human existence. The last section offers some tentative first steps toward decreasing violence. To the extent that the theory proposed here is true, we face the dilemma of how to present it to a civilization in which the social-emotional world is virtually invisible. © 2011 Elsevier Ltd.


Helie S.,Purdue University | Ell S.W.,University of Maine, United States | Ashby F.G.,University of California at Santa Barbara
Cortex | Year: 2015

This article focuses on the interaction between the basal ganglia (BG) and prefrontal cortex (PFC). The BG are a group of nuclei at the base of the forebrain that are highly connected with cortex. A century of research suggests that the role of the BG is not exclusively motor, and that the BG also play an important role in learning and memory. In this review article, we argue that one important role of the BG is to train connections between posterior cortical areas and frontal cortical regions that are responsible for automatic behavior after extensive training. According to this view, one effect of BG trial-and-error learning is to activate the correct frontal areas shortly after posterior associative cortex activation, thus allowing for Hebbian learning of robust, fast, and efficient cortico-cortical processing. This hypothesized process is general, and the content of the learned associations depends on the specific areas involved (e.g., associations involving premotor areas would be more closely related to behavior than associations involving the PFC). We review experiments aimed at pinpointing the function of the BG and the frontal cortex and show that these results are consistent with the view that the BG is a general purpose trainer for cortico-cortical connections. We conclude with a discussion of some implications of the integrative framework and how this can help better understand the role of the BG in many different tasks. © 2014 Elsevier Ltd.


Lipshutz B.H.,University of California at Santa Barbara | Ghorai S.,Sigma-Aldrich
Green Chemistry | Year: 2014

Traditional organic chemistry, and organic synthesis in particular, relies heavily on organic solvents, as most reactions involve organic substrates and catalysts that tend to be water-insoluble. Unfortunately, organic solvents make up most of the organic waste created by the chemical enterprise, whether from academic, industrial, or governmental labs. One alternative to organic solvents follows the lead of Nature: water. To circumvent the solubility issues, newly engineered "designer" surfactants offer an opportunity to efficiently enable many of the commonly used transition metal-catalyzed and related reactions in organic synthesis to be run in water, and usually at ambient temperatures. This review focuses on recent progress in this area, where such amphiphiles spontaneously self-aggregate in water. The resulting micellar arrays serve as nanoreactors, obviating organic solvents as the reaction medium, while maximizing environmental benefits. This journal is © the Partner Organisations 2014.


Mostofi Y.,University of California at Santa Barbara
IEEE Transactions on Mobile Computing | Year: 2013

In this paper, we develop a theoretical and experimental framework for the mapping of obstacles (including occluded ones), in a robotic cooperative network, based on a small number of wireless channel measurements. This would allow the robots to map an area before entering it. We consider three approaches based on coordinated space, random space, and frequency sampling, and show how the robots can exploit the sparse representation of the map in space, wavelet or spatial variations, in order to build it with minimal sensing. We then show the underlying tradeoffs of all the possible sampling, sparsity and reconstruction techniques. Our simulation and experimental results show the feasibility and performance of the proposed framework. More specifically, using our experimental robotic platform, we show preliminary results in successfully mapping a number of real obstacles and having see-through capabilities with real structures, despite the practical challenges presented by multipath fading. © 2002-2012 IEEE.


Dobler G.,University of California at Santa Barbara
Astrophysical Journal Letters | Year: 2012

Using seven-year data from the Wilkinson Microwave Anisotropy Probe, I identify a sharp "edge" in the microwave haze at high southern Galactic latitude (-55° < b < -35°) that is spatially coincident with the southern edge of the "Fermi haze/bubbles." This finding proves conclusively that the edge in the gamma rays is real (and not a processing artifact), demonstrates explicitly that the microwave haze and the gamma-ray bubbles are indeed the same structure observed at multiple wavelengths, and strongly supports the interpretation of the microwave haze as a separate component of Galactic synchrotron (likely generated by a transient event) as opposed to a simple variation of the spectral index of disk synchrotron. In addition, combining these data sets allows for the first determination of the magnetic field within a radio bubble using microwaves and gamma rays by taking advantage of the fact that the inverse Compton gamma rays are primarily generated by scattering of cosmic microwave background photons at these latitudes, thus minimizing uncertainty in the target radiation field. Assuming uniform volume emissivity, I find that the magnetic field within the southern Galactic microwave/gamma-ray bubble is 5μG above 6kpc off of the Galactic plane. © 2012. The American Astronomical Society. All rights reserved..


Atzberger P.J.,University of California at Santa Barbara
Journal of Computational Physics | Year: 2011

We present approaches for the study of fluid-structure interactions subject to thermal fluctuations. A mixed mechanical description is utilized combining Eulerian and Lagrangian reference frames. We establish general conditions for operators coupling these descriptions. Stochastic driving fields for the formalism are derived using principles from statistical mechanics. The stochastic differential equations of the formalism are found to exhibit significant stiffness in some physical regimes. To cope with this issue, we derive reduced stochastic differential equations for several physical regimes. We also present stochastic numerical methods for each regime to approximate the fluid-structure dynamics and to generate efficiently the required stochastic driving fields. To validate the methodology in each regime, we perform analysis of the invariant probability distribution of the stochastic dynamics of the fluid-structure formalism. We compare this analysis with results from statistical mechanics. To further demonstrate the applicability of the methodology, we perform computational studies for spherical particles having translational and rotational degrees of freedom. We compare these studies with results from fluid mechanics. The presented approach provides for fluid-structure systems a set of rather general computational methods for treating consistently structure mechanics, hydrodynamic coupling, and thermal fluctuations. © 2010 Elsevier Inc.


Shieh I.C.,University of California at Santa Barbara | Zasadzinski J.A.,University of Minnesota
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Contrast in confocal microscopy of phase-separated monolayers at the air-water interface can be generated by the selective adsorption of water-soluble fluorescent dyes to disordered monolayer phases. Optical sectioning minimizes the fluorescence signal from the subphase, whereas convolution of the measured point spread function with a simple box model of the interface provides quantitative assessment of the excess dye concentration associated with the monolayer. Coexisting liquid-expanded, liquid-condensed, and gas phases could be visualized due to differential dye adsorption in the liquid-expanded and gas phases. Dye preferentially adsorbed to the liquid-disordered phase during immiscible liquid-liquid phase coexistence, and the contrast persisted through the critical point as shown by characteristic circle-to-stripe shape transitions. The measured dye concentration in the disordered phase depended on the phase composition and surface pressure, and the dye was expelled from the film at the end of coexistence. The excess concentration of a cationic dye within the double layer adjacent to an anionic phospholipid monolayer was quantified as a function of subphase ionic strength, and the changes in measured excess agreed with those predicted by the mean-field Gouy-Chapman equations. This provided a rapid and noninvasive optical method of measuring the fractional dissociation of lipid headgroups and the monolayer surface potential.


Deacon R.T.,University of California at Santa Barbara
Review of Environmental Economics and Policy | Year: 2012

Managing fisheries by delegating authority to an association of users, often organized as a cooperative, is gaining increased attention as a strategy for implementing rights-based reform. Assigning rights to groups rather than individuals can facilitate coordination and collective action and enable efficiency gains similar to those achieved when a firm organizes inputs centrally. Evidence from developed country fisheries managed by cooperatives indicates that coordination gains can be substantial. Furthermore, these gains often take forms overlooked in the traditional fishery reform literature, including those from enhanced product recovery and quality, improved spatial and temporal deployment of effort, and reduced environmental damage. In developing countries, assigning management responsibility to user groups can facilitate user-based provision of public goods in situations where governments do not function well. Developing country fishery cooperatives commonly provide monitoring and enforcement of access limitations, limits on fishing effort, and actions to conserve shared stocks. This article reviews empirical evidence on the performance of fishery cooperatives in developed and developing countries. A key conclusion is that using a combination of rights-based instruments can achieve efficiencies that cannot be captured by any single instrument.(JEL: Q20, Q22, D23). © The Author 2012. Published by Oxford University Press on behalf of the Association of Environmental and Resource Economists. All rights reserved.


Bao G.,Georgia Institute of Technology | Mitragotri S.,University of California at Santa Barbara | Tong S.,Georgia Institute of Technology
Annual Review of Biomedical Engineering | Year: 2013

Recent advances in nanotechnology and growing needs in biomedical applications have driven the development of multifunctional nanoparticles. These nanoparticles, through nanocrystalline synthesis, advanced polymer processing, and coating and functionalization strategies, have the potential to integrate various functionalities, simultaneously providing (a) contrast for different imaging modalities, (b) targeted delivery of drug/gene, and (c) thermal therapies. Although still in its ancy, the field of multifunctional nanoparticles has shown great promise in emerging medical fields such as multimodal imaging, theranostics, and image-guided therapies. In this review, we summarize the techniques used in the synthesis of complex nanostructures, review the major forms of multifunctional nanoparticles that have emerged over the past few years, and provide a perceptual vision of this important field of nanomedicine. Copyright © 2013 by Annual Reviews.


Gerig J.T.,University of California at Santa Barbara
Journal of Physical Chemistry B | Year: 2012

Intermolecular nuclear Overhauser effects (NOEs) produced by interactions of methanol with [val5]angiotensin in 25% methanol-water at 0 °C were examined through molecular dynamics (MD) simulations and compared to experimental results. Calculated average 3JNHCαH spin coupling constants, conformation-sensitive chemical shift changes, and intramolecular 1H-1H NOEs indicated that peptide conformations present over the course of simulation trajectories of 100-300 ns are likely similar to those present in the experimental system. Calculated cross-relaxation terms for the methanol-peptide interactions showed the same trends as corresponding experimental data but were about a factor of 3 too large. The lack of agreement between observed and calculated cross-relaxation terms probably has origins in characteristics of the simulations that lead to overestimation of translational diffusion coefficients of the system components. Simulations confirmed the heterogeneity of the methanol-water solvent at the molecular level, with clusters of methanol and water molecules changing their size and composition on a subpicosecond time scale. Most peptide hydrogens are preferentially solvated by interactions with methanol molecules. Simulations suggest that diffusion of water and methanol molecules near the peptide is slowed as these species approach the peptide backbone. © 2012 American Chemical Society.


Passow U.,University of California at Santa Barbara
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2016

Significant amounts of oil accumulated at the sea surface and in a subsurface plume during the Deepwater Horizon (DwH) spill in the Gulf of Mexico (GoM) in 2010. A substantial fraction of this oil was removed from the marine environment by mechanical recovery or burning, or it reached shorelines, whereas another fraction remained within the marine environment, where it dispersed (chemically or naturally), emulsified or sedimented. After the DwH accident the sedimentation of hydrocarbons to the seafloor via rapidly sinking, oil-associated marine snow has become a focus of attention, and it has been hypothesized that marine snow formation significantly impacted the distribution of the oil from the DwH spill. Here, roller table experiments are presented that investigated the conditions inducing the formation of oil-associated marine snow, focusing especially on the effects of oil type, photochemical aging of oil, and the presence of phytoplankton or dispersant. Large, mucus-rich marine snow, termed microbial marine snow, formed in treatments incubated with the oil that had accumulated at the sea surface. This bacteria-mediated formation of up to cm-sized marine snow in the absence of particles >1 μm, represents a unique formation pathway different from that of the physical coagulation of particles. Microbial marine snow, albeit smaller, also formed in the presence of crude oil that had been aged for ≥3 weeks in sunlight, but no particles formed in the presence of unaltered crude. The dispersant Corexit 9500A (Corexit:oil ratio=1:100) impeded the formation of microbial marine snow, requiring a re-evaluation of the benefits and detriments of Corexit 9500A as a mediating measure. Phytoplankton aggregates also incorporated fossil carbon, providing an alternate pathway for the formation of oil-associated marine snow. The ubiquitous formation and rapid sedimentation of oil-rich marine snow can explain the high accumulation rate of flocculent material at the seafloor and on corals observed after the DwH spill. These results may raise awareness that oil spill response and assessment need to include sedimentation of hydrocarbons via marine snow as a significant distribution mechanism and may guide future modeling efforts and budget calculations. © 2014 Elsevier Ltd.


Valentine D.L.,University of California at Santa Barbara
Annual Review of Marine Science | Year: 2011

Our knowledge of physical, chemical, geological and biological processes affecting methane in the ocean and in underlying sediments is expanding at a rapid pace. On first inspection, marine methane biogeochemistry appears simple: Methane distribution in sediment is set by the deposition pattern of organic material, and the balance of sources and sinks keeps its concentration low in most waters. However, recent research reveals that methane is affected by complex biogeochemical processes whose interactions are understood only at a superficial level. Such processes span the deep-subsurface, near subsurface, and ocean waters, and relate primarily to the production, consumption, and transport of methane. The purpose of this synthesis is to examine select processes within the framework of methane biogeochemistry, to formulate hypotheses on how they might operate and interact with one another, and to consider their controls. Copyright © 2011 by Annual Reviews. All rights reserved.


Heeger A.J.,University of California at Santa Barbara
Advanced Materials | Year: 2014

The status of understanding of the operation of bulk heterojunction (BHJ) solar cells is reviewed. Because the carrier photoexcitation recombination lengths are typically 10 nm in these disordered materials, the length scale for self-assembly must be of order 10-20 nm. Experiments have verified the existence of the BHJ nanostructure, but the morphology remains complex and a limiting factor. Three steps are required for generation of electrical power: i) absorption of photons from the sun; ii) photoinduced charge separation and the generation of mobile carriers; iii) collection of electrons and holes at opposite electrodes. The ultrafast charge transfer process arises from fundamental quantum uncertainty; mobile carriers are directly generated (electrons in the acceptor domains and holes in the donor domains) by the ultrafast charge transfer (≈70%) with ≈30% generated by exciton diffusion to a charge separating heterojunction. Sweep-out of the mobile carriers by the internal field prior to recombination is essential for high performance. Bimolecular recombination dominates in materials where the donor and acceptor phases are pure. Impurities degrade performance by introducing Shockly-Read-Hall decay. The review concludes with a summary of the problems to be solved to achieve the predicted power conversion efficiencies of >20% for a single cell. The operation of bulk heterojunction (BHJ) solar cells is reviewed. Ultrafast charge transfer arises from fundamental quantum uncertainty as expressed by the uncertainty principle; mobile charges are generated directly by ultrafast charge transfer. Sweep-out of the mobile carriers by the internal field prior to recombination is essential to obtain a high performance, especially a high fill factor. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Bravyi S.,IBM | Hastings M.B.,University of California at Santa Barbara
Communications in Mathematical Physics | Year: 2011

Recently, the stability of certain topological phases of matter under weak perturbations was proven. Here, we present a short, alternate proof of the same result. We consider models of topological quantum order for which the unperturbed Hamiltonian H0 can be written as a sum of local pairwise commuting projectors on a D-dimensional lattice. We consider a perturbed Hamiltonian H = H0 + V involving a generic perturbation V that can be written as a sum of short-range bounded-norm interactions. We prove that if the strength of V is below a constant threshold value then H has well-defined spectral bands originating from the low-lying eigenvalues of H0. These bands are separated from the rest of the spectrum and from each other by a constant gap. The width of the band originating from the smallest eigenvalue of H0 decays faster than any power of the lattice size. © 2011 Springer-Verlag.


Toggweiler J.R.,National Oceanic and Atmospheric Administration | Lea D.W.,University of California at Santa Barbara
Paleoceanography | Year: 2010

The Earth became warmer and cooler during the ice ages along with changes in the Earth?s orbit, but the orbital changes themselves are not nearly large enough to explain the magnitude of the warming and cooling. Atmospheric CO 2 also rose and fell, but again, the CO2 changes are rather small in relation to the warming and cooling. So, how did the Earth manage to warm and cool by so much? Here we argue that, for the big transitions at least, the Earth did not warm and cool as a single entity. Rather, the south warmed instead at the expense of a cooler north through massive redistributions of heat that were set off by the orbital forcing. Oceanic CO2 was vented up to the atmosphere by the same redistributions. The north then warmed later in response to higher CO2 and a reduced albedo from smaller ice sheets. This form of northsouth displacement is actually very familiar, as it is readily observed during the Younger Dryas interval 13,000 years ago and in the various millennial-scale events over the last 90,000 years. © Copyright 2010 by the American Geophysical Union.


Grover T.,University of California at Santa Barbara
Physical Review Letters | Year: 2013

Given a specific interacting quantum Hamiltonian in a general spatial dimension, can one access its entanglement properties, such as the entanglement entropy corresponding to the ground state wave function? Even though progress has been made in addressing this question for interacting bosons and quantum spins, as yet there exist no corresponding methods for interacting fermions. Here we show that the entanglement structure of interacting fermionic Hamiltonians has a particularly simple form - the interacting reduced density matrix can be written as a sum of operators that describe free fermions. This decomposition allows one to calculate the Renyi entropies for Hamiltonians which can be simulated via determinantal quantum Monte Carlo calculations, while employing the efficient techniques hitherto available only for free fermions. The method presented works for the ground state, as well as for the thermally averaged reduced density matrix. © 2013 American Physical Society.


Yurovsky V.A.,Tel Aviv University | Yurovsky V.A.,University of California at Santa Barbara
Physical Review Letters | Year: 2014

Many-body systems of identical arbitrary-spin particles, with separable spin and spatial degrees of freedom, are considered. Their eigenstates can be classified by Young diagrams, corresponding to nontrivial permutation symmetries (beyond the conventional paradigm of symmetric-antisymmetric states). The present work obtains the following. (a) Selection rules for additional nonseparable (dependent on spins and coordinates) k-body interactions: the Young diagrams, associated with the initial and final states of a transition, can differ by relocation of no more than k boxes between their rows. (b) Correlation rules in which eigenstate-averaged local correlations of k particles vanish if k exceeds the number of columns (for bosons) or rows (for fermions) in the associated Young diagram. It also elucidates the physical meaning of the quantities conserved due to permutation symmetry - in 1929, Dirac identified those with characters of the symmetric group - relating them to experimentally observable correlations of several particles. The results provide a way to control the formation of entangled states belonging to multidimensional non-Abelian representations of the symmetric group. These states can find applications in quantum computation and metrology. © 2014 American Physical Society.


Young O.R.,University of California at Santa Barbara
Polar Record | Year: 2011

Many analysts argue that responding effectively to the transformative changes occurring in the Arctic will require the creation of an Arctic Ocean treaty or even a more comprehensive treaty covering the whole Arctic. This article explores this line of thinking critically. In doing so, it addresses three distinct but related questions: 1) Is there a need for an Arctic Ocean framework agreement? 2) Where should we focus our attention along the integration-fragmentation spectrum? 3) Would it help to make arrangements for Arctic governance legally binding? The conclusion is that the case for spending political capital on an effort to negotiate the terms of an Arctic Ocean treaty is weak. But this need not be regarded as a cause for pessimism. A more multidimensional Arctic governance complex is emerging and is likely to continue to develop during the coming years. Copyright © 2010 Cambridge University Press.


Kniehl B.A.,University of California at Santa Barbara
Physical Review Letters | Year: 2014

We consider a mixed system of Dirac fermions in a general parity-nonconserving theory and renormalize the propagator matrix to all orders in the pole scheme, in which the squares of the renormalized masses are identified with the complex pole positions and the wave-function renormalization (WFR) matrices are adjusted in compliance with the Lehmann-Symanzik-Zimmermann reduction formalism. We present closed analytic all-order expressions and their expansions through two loops for the renormalization constants in terms of the scalar, pseudoscalar, vector, and pseudovector parts of the unrenormalized self-energy matrix, which is computable from the one-particle-irreducible Feynman diagrams of the flavor transitions. We identify residual degrees of freedom in the WFR matrices and propose an additional renormalization condition to exhaust them. We then explain how our results may be generalized to the case of unstable fermions, in which we encounter the phenomenon of WFR bifurcation. In the special case of a solitary unstable fermion, the all-order-renormalized propagator is presented in a particularly compact form. © 2014 American Physical Society.


Jackson M.G.,University of California at Santa Barbara | Jellinek A.M.,University of British Columbia
Geochemistry, Geophysics, Geosystems | Year: 2013

The bulk composition of the silicate portion of the Earth (BSE) has long been assumed to be tied to chondrites, in which refractory, lithophile elements like Sm and Nd exist in chondritic relative abundances. However, the 142Nd/144Nd ratios of modern terrestrial samples are 18 ± 5 ppm higher than the ordinary-chondrite reservoir, and this challenges the traditional BSE model. Here we investigate a hypothesis that this terrestrial 142Nd excess is related to a Sm/Nd ratio 6% higher than chondritic. This Sm/Nd ratio yields a superchondritic 143Nd/ 144Nd (∼0.5130) similar to that identified in the highest 3He/4He mantle reservoir, and we argue that this reservoir represents the BSE composition for lithophile elements. We develop a compositional model for BSE in which the elevated Sm/Nd requires a shift of 143Nd/144Nd from 0.51263 (chondritic) to 0.51300. The new BSE composition is depleted in highly incompatible elements, including K, relative to the chondrite-based BSE, and offers a solution the "missing" 40Ar paradox. This BSE compositional model requires that >83% of the mantle is depleted to form continental crust. It also implies a ∼30% reduction in BSE U, Th and K, and therefore in the current rate of radiogenic heating and, thus, a proportional increase in the heat flow delivered to surface by plate tectonics. We explore thermal history models including effects related to a newly recognized evolution in the style of plate tectonics over Earth history: The lower radiogenic heat production may delay the onset of core convection and dynamo action to as late as 3.5 Gyr. ©2013. American Geophysical Union. All Rights Reserved.


Noffke N.,Old Dominion University | Awramik S.M.,University of California at Santa Barbara
GSA Today | Year: 2013

Benthic microorganisms form highly organized communities called "biofilms." A biofilm consists of the individual cells plus their extracellular polymeric substances (EPS). In marine and non-marine environments, benthic microbial communities interact with the physical sediment dynamics and other factors in the environment in order to survive. This interaction can produce distinctive sedimentary structures called microbialites. Binding, biostabilization, baffling, and trapping of sediment particles by microorganisms result in the formation of microbially induced sedimentary structures (MISS); however, if carbonate precipitation occurs in EPS, and these processes happen in a repetitive manner, a multilayered build-up can form-stromatolites. Stromatolites and MISS are first found in the early Archean, recording highly evolved microbial activity early in Earth's history. Whereas the stromatolites show enormous morphologic and taxonomic variation, MISS seem not to have changed in morphology since their first appearance. MISS might be the older relative, but due to the lack of well-preserved sedimentary rocks older than 3.5 billion years, the origin of both stromatolites and MISS remains uncertain.


Nuzhdin S.V.,University of Southern California | Turner T.L.,University of California at Santa Barbara
Current Opinion in Genetics and Development | Year: 2013

Building the connection between genetic and phenotypic variation is an important 'work in progress', and one that will enable proactive diagnosis and treatment in medicine, promote development of environment-targeted varieties in agriculture, and clarify the limits of species adaptation to changing environments in conservation. Quantitative trait loci (QTL) mapping and genome wide association (GWA) studies have recently been allied to an additional focus on 'hitchhiking' (HH) mapping - using changes in allele frequency due to artificial or natural selection. This older technique has been popularized by the falling costs of high throughput sequencing. Initial HH-resequensing experiments seem to have found many thousands of polymorphisms responding to selection. We argue that this interpretation appears too optimistic, and that the data might in fact be more consistent with dozens, rather than thousands, of loci under selection. We propose several developments required for sensible data analyses that will fully realize the great power of the HH technique, and outline ways of moving forward. © 2013 Elsevier Ltd.


Hastings M.B.,Duke University | Hastings M.B.,University of California at Santa Barbara
Physical Review Letters | Year: 2011

We propose a definition for topological order at nonzero temperature in analogy to the usual zero temperature definition that a state is topologically ordered, or "nontrivial", if it cannot be transformed into a product state (or a state close to a product state) using a local (or approximately local) quantum circuit. We prove that any two-dimensional Hamiltonian which is a sum of commuting local terms is not topologically ordered at T>0. We show that such trivial states cannot be used to store quantum information using certain stringlike operators. This definition is not too restrictive, however, as the four dimensional toric code does have a nontrivial phase at nonzero temperature. © 2011 American Physical Society.


Giddings S.B.,University of California at Santa Barbara | Sloth M.S.,CERN
Journal of Cosmology and Astroparticle Physics | Year: 2011

We calculate IR divergent graviton one-loop corrections to scalar correlators in de Sitter space, and show that the leading IR contribution may be reproduced via simple semiclassical consistency relations. One can likewise use such semiclassical relations to calculate leading IR corrections to correlators in slow-roll inflation. The regulated corrections shift the tensor/scalar ratio and consistency relation of single field inflation, and non-gaussianity parameters averaged over very large distances. For inflation of sufficient duration, for example arising from a chaotic inflationary scenario, these corrections become of order unity. First-order corrections of this size indicate a breakdown of the perturbative expansion, and suggest the need for a non-perturbative description of the corresponding regime. This is analogous to a situation argued to arise in black hole evolution, and to interfere with a sharp perturbative calculation of "missing information" in Hawking radiation. © 2011 IOP Publishing Ltd and SISSA.


Giddings S.B.,University of California at Santa Barbara | Giddings S.B.,CERN
Classical and Quantum Gravity | Year: 2011

A proposal for resolution of the information paradox is that 'nice slice' states, which have been viewed as providing a sharp argument for information loss, do not in fact do so as they do not give a fully accurate description of the quantum state of a black hole. This however leaves an information problem, which is to provide a consistent description of how information escapes when a black hole evaporates. While a rather extreme form of nonlocality has been advocated in the form of complementarity, this paper argues that is not necessary, and more modest nonlocality could solve the information problem. One possible distinguishing characteristic of scenarios is the information retention time. The question of whether such nonlocality implies acausality, and particularly inconsistency, is briefly addressed. The need for such nonlocality, and its apparent tension with our empirical observations of local quantum field theory, may be a critical missing piece in understanding the principles of quantum gravity. © 2011 IOP Publishing Ltd.


A diverse guild of digenean trematodes infects the New Zealand mud snail, Potamopyrgus antipodarum, as first intermediate host. This manuscript offers an initial systematic treatment of these trematodes and relies on published and new information. I list 20 trematode species, for which I provide taxonomic affinities, life-cycle information, and an identification key. A species account section presents photographs, diagnostic information, additional descriptive notes, and information on relevant research concerning the listed species. The major aim of this manuscript is to facilitate research on this trematode guild by providing information and identification tools, and by highlighting gaps in our knowledge. Copyright © 2012 · Magnolia Press.


Haddock S.H.D.,Monterey Bay Aquarium Research Institute | Moline M.A.,California Polytechnic State University, San Luis Obispo | Case J.F.,University of California at Santa Barbara
Annual Review of Marine Science | Year: 2010

Bioluminescence spans all oceanic dimensions and has evolved many times from bacteria to fish to powerfully influence behavioral and ecosystem dynamics. New methods and technology have brought great advances in understanding of the molecular basis of bioluminescence, its physiological control, and its significance in marine communities. Novel tools derived from understanding the chemistry of natural light-producing molecules have led to countless valuable applications, culminating recently in a related Nobel Prize. Marine organisms utilize bioluminescence for vital functions ranging from defense to reproduction. To understand these interactions and the distributions of luminous organisms, new instruments and platforms allow observations on individual to oceanographic scales. This review explores recent advances, including the chemical and molecular, phylogenetic and functional, community and oceanographic aspects of bioluminescence. © 2010 by Annual Reviews.


Lisiecki L.E.,University of California at Santa Barbara
Geophysical Research Letters | Year: 2010

A high-resolution marine proxy for atmospheric pCO2 is needed to clarify the phase lag between pCO2 and marine climate proxies and to provide a record of orbital-scale pCO2 variations before the oldest ice core measurement at 800 ka. Benthic δ13C data should record deep ocean carbon storage and, thus, atmospheric pCO2. This study finds that a modified δ13C gradient between the deep Pacific and intermediate North Atlantic (δ13CP- NA/2 correlates well with pCO2. δ13CP-NA/2 reproduces characteristic differences between pCO2 and ice volume during Late Pleistocene glaciations and indicates that pCO2 usually leads terminations by 0.2-3.7 kyr but lags by 3-10 kyr during two "failed" terminations at 535 and 745 ka. δ13C P- NA/2 gradually transitions from 41- to 100-kyr cyclicity from 1.3-0.7 Ma but has no secular trend in mean or amplitude since 1.5 Ma. The minimum pCO2 of the last 1.5 Myr is estimated to be 155 ppm at ∼920 ka. © 2010 by the American Geophysical Union.


Leifer I.,University of California at Santa Barbara
Journal of Geophysical Research: Oceans | Year: 2010

The fate of marine seep gases in the ocean and atmosphere is intimately connected with bubble and bubble-plume processes, which are strongly size- and depth-dependent. Size-dependent flux distributions, φ and vertical velocity functions, VZ(r), were measured with a video bubble measurement system in the Santa Barbara Channel, California. Several distinct plume types were identified for which size distributions were measured, major, minor, intermediate, and obstructed. A further vent class is elastic (which was observed but not quantified). In addition, any plume class could be oily. Minor plumes generally produced a lower emission flux, Q, and showed narrow, peaked that were well described as Gaussian. The radius of the dominant peak, R P, of minor plumes varied as Q0.40, with correlation coefficient, R2 = 0.84, in agreement with theoretical relationship of RP∼Q0.4 for Q above a critical flow rate. Oil contamination was found to affect RP and was not used in the fit. A probability distribution, (RP), for all Gaussian bubble plumes was itself well described by a combination of Gaussian functions, which were different for different seep areas. Major plumes showed a broad distribution including very small and very large bubbles and were well described by a power law with exponent a, which varied with Q according to a = 0.43 + 0.55 log(Q) with R2 = 0.77. One obstructed vent was analyzed and shared characteristics with the minor bubble plumes. Mixed bubble plume size distributions showed characteristics of both major and minor plume classes, i.e., were described by a combination of Gaussian functions and power laws, and were steeper (higher a) than major plumes for the same Q. Oily plumes produced complex, confused bubble size distributions. Upwelling velocities, V UP(r), were derived from VZ(r) and increased as V UP∼Q0.66 (R2 = 0.64); however, consideration of the more intense plumes (Q > 2 cm s-1) showed VUP∼Q0.35 in agreement with other published field measurements. Thus, the weaker bubble plumes were observed during the acceleration phase. © 2010 by the American Geophysical Union.


Kurin D.S.,University of California at Santa Barbara
American Journal of Physical Anthropology | Year: 2013

This study evaluates trepanations from five well-contextualized prehistoric sites in the south-central highlands of Andahuaylas, Peru. The emergence of trepanation in this region coincides with the collapse of the Wari Empire, ca. ad 1000. Thirty-two individuals from Andahuaylas, AMS radiocarbon dated to the early Late Intermediate Period (ca. ad 1000-1250), were found to have 45 total trepanations. Various surgical techniques were being employed concurrently throughout the region. Scraping trepanations evinced the highest survival rate; circular grooving, drilling and boring, and linear cutting were far less successful. Evidence of perioperative procedures like hair shaving, poultice application, and possible cranioplasty use aimed to ensure the survival of a trepanation recipient. Postmortem trepanations, also present in Andahuaylas, were likely executed on corpses as a means of better understanding cranial anatomy and improving techniques. Similarities in trepanation patterns throughout the region attest to common motivations to engage in surgery. Although moderate physical head trauma seems to be the impetus for intervention in many cases of trepanation, other motivations included physiological and possibly psychosomatic factors. Nevertheless, treatment was not for everyone. In Andahuaylas, trepanations were withheld from subadults, females, and those individuals who practiced cranial modification. Am J Phys Anthropol 152:484-494, 2013. © 2013 Wiley Periodicals, Inc. Copyright © 2013 Wiley Periodicals, Inc.


Adler P.B.,Utah State University | Ellner S.P.,Cornell University | Levine J.M.,University of California at Santa Barbara
Ecology Letters | Year: 2010

Despite decades of research documenting niche differences between species, we lack a quantitative understanding of their effect on coexistence in natural communities. We perturbed an empirical sagebrush steppe community model to remove the demographic effect of niche differences and quantify their impact on coexistence. With stabilizing mechanisms operating, all species showed positive growth rates when rare, generating stable coexistence. Fluctuation-independent mechanisms contributed more than temporal variability to coexistence and operated more strongly on recruitment than growth or survival. As expected, removal of stabilizing niche differences led to extinction of all inferior competitors. However, complete exclusion required 300-400 years, indicating small fitness differences among species. Our results show an 'excess' of niche differences: stabilizing mechanisms were not only strong enough to maintain diversity but were much stronger than necessary given the small fitness differences. The diversity of this community cannot be understood without consideration of niche differences. © 2010 Blackwell Publishing Ltd/CNRS.


Hacker B.R.,University of California at Santa Barbara | Kelemen P.B.,Lamont Doherty Earth Observatory | Behn M.D.,Woods Hole Oceanographic Institution
Earth and Planetary Science Letters | Year: 2011

Crust extracted from the mantle in arcs is refined into continental crust in subduction zones. During sediment subduction, subduction erosion, arc subduction, and continent subduction, mafic rocks become eclogite and may sink into the mantle, whereas more silica-rich rocks are transformed into felsic gneisses that are less dense than peridotite but more dense than the upper crust. These more felsic rocks rise buoyantly, undergo decompression melting and melt extraction, and are relaminated to the base of the crust. As a result of this process, such felsic rocks could form much of the lower crust. The lower crust need not be mafic and the bulk continental crust may be more silica rich than generally considered. © 2011 Elsevier B.V.


Spruell J.M.,University of California at Santa Barbara
Pure and Applied Chemistry | Year: 2010

This article highlights the emerging use of the interactions of radical p-dimers to drive both molecular recognition and switching processes within supramolecular systems and mechanically interlocked molecular architectures. The enhanced stability experienced by dimers of radical cation species when encapsulated, as compared to when they are free in solution, is driving their useful incorporation into functional systems. The redox stimulation used in the production of radical cation species provides the ideal trigger for molecular switching events. Moreover, the nature and strength of the radical dimerization events introduces a completely novel recognition motif within supramolecular and mechanically interlocked molecular systems, complementing well-established techniques and enabling new research opportunities to blossom. © 2010 IUPAC, Publication date (Web): 28 September 2010.


Lisiecki L.E.,University of California at Santa Barbara
Nature Geoscience | Year: 2010

Variations in the eccentricity (100,000 yr), obliquity (41,000 yr) and precession (23,000 yr) of Earths orbit have been linked to glacial-interglacial climate cycles. It is generally thought that the 100,000-yr glacial cycles of the past 800,000 yr are a result of orbital eccentricity. However, the eccentricity cycle produces negligible 100-kyr power in seasonal or mean annual insolation, although it does modulate the amplitude of the precession cycle. Alternatively, it has been suggested that the recent glacial cycles are driven purely by the obliquity cycle. Here I use statistical analyses of insolation and the climate of the past five million years to characterize the link between eccentricity and the 100,000-yr glacial cycles. Using cross-wavelet phase analysis, I show that the relative phase of eccentricity and glacial cycles has been stable since 1.2 Myr ago, supporting the hypothesis that 100,000-yr glacial cycles are paced by eccentricity. However, I find that the time-dependent 100,000-yr power of eccentricity has been anticorrelated with that of climate since 5 Myr ago, with strong eccentricity forcing associated with weaker power in the 100,000-yr glacial cycle. I propose that the anticorrelation arises from the strong precession forcing associated with strong eccentricity forcing, which disrupts the internal climate feedbacks that drive the 100,000-yr glacial cycle. This supports the hypothesis that internally driven climate feedbacks are the source of the 100,000-yr climate variations. © 2010 Macmillan Publishers Limited.


Yang Y.,University of California at Santa Barbara
Journal of Cleaner Production | Year: 2013

Life cycle studies of corn ethanol have largely centered on the fuel's carbon and energy benefits. However, with the recognition that this narrow focus falls short of addressing the environmental sustainability of fuel substitution, there is a growing body of literature that extends assessment to a broader range of impacts, such as eutrophication, smog formation, acidification, and water and land use. Using the USEtox impact assessment model, this study evaluates the life cycle freshwater ecotoxicity, human health cancer, and noncancer effects of U.S. corn ethanol and gasoline, which are less well understood in comparison to other impact categories. This study also takes into account spatial and temporal variations in corn production and ethanol conversion technologies. Results show that corn ethanol generates potentially larger freshwater ecotoxicity than gasoline due to releases of pesticides in corn growth, particularly, atrazine, acetochlor, chlorpyrifos, and cyfluthrin. So does corn ethanol have a higher potential noncancer impact due to releases of heavy metals through use of phosphate fertilizers. The two fuels seem to induce similar potential caner impacts. The results indicate that replacing gasoline with corn ethanol could further degrade water quality and exacerbate noncancer related human health issues. Overall, this study implies that environmental policymaking should consider a broader spectrum of impacts beyond carbon and energy to avoid or minimize potential environmental burden-shifting. © 2013 Elsevier Ltd. All rights reserved.


Hansma H.G.,University of California at Santa Barbara
Journal of Biomolecular Structure and Dynamics | Year: 2013

The mica hypothesis for the origin of life proposes that life originated between the sheets of muscovite mica. This paper elaborates on two ways that life resembles what might have originated between mica sheets. First, enzymes: The configurations and dynamics of enzymes, with their substrates, cofactors, and sometimes transition metal ions, often resemble mica sheets, with their open-and-shut motions, acting on small molecules between them, sometimes assisted by transition metal ions. Second, organisms: Mica world had the potential to be a community or ecosystem of prebiotic organisms in a way unlike other models for the origin of life. © 2012 Taylor & Francis.


Srednicki M.,University of California at Santa Barbara
Journal of Physics A: Mathematical and Theoretical | Year: 2011

The local Riemann hypothesis states that the zeros of the Mellin transform of a harmonic-oscillator eigenfunction (on a real or p-adic configuration space) have a real part 1/2. For the real case, we show that the imaginary parts of these zeros are the eigenvalues of the Berry-Keating Hamiltonian ĤBK = (x̂p̂+p̂x̂)/2 projected onto the subspace of oscillator eigenfunctions of a lower level. This gives a spectral proof of the local Riemann hypothesis for the reals, in the spirit of the Hilbert-Pólya conjecture. The p-adic case is also discussed. © 2011 IOP Publishing Ltd.


Eckstein M.P.,University of California at Santa Barbara
Journal of Vision | Year: 2011

Visual search, a vital task for humans and animals, has also become a common and important tool for studying many topics central to active vision and cognition ranging from spatial vision, attention, and oculomotor control to memory, decision making, and rewards. While visual search often seems effortless to humans, trying to recreate human visual search abilities in machines has represented an incredible challenge for computer scientists and engineers. What are the brain computations that ensure successful search? This review article draws on efforts from various subfields and discusses the mechanisms and strategies the brain uses to optimize visual search: the psychophysical evidence, their neural correlates, and if unknown, possible loci of the neural computations. Mechanisms and strategies include use of knowledge about the target, distractor, background statistical properties, location probabilities, contextual cues, scene context, rewards, target prevalence, and also the role of saliency, center-surround organization of search templates, andeye movement plans. I provide overviews of classic and contemporary theories of covert attention and eye movements during search explaining their differences and similarities. To allow the reader to anchor some of the laboratory findings to real-world tasks, the article includes interviews with three expert searchers: a radiologist, a fisherman, and a satellite image analyst. © ARVO.


Goodchild M.F.,University of California at Santa Barbara
Geomorphology | Year: 2011

Scale has many meanings, but in GIS two are of greatest significance: resolution and extent. Ideally models of physical process would be defined and tested on scale-free data. In practice spatial resolution will always be limited by cost, data volume, and other factors. Raster data are shown to be preferable to vector data for scientific research because they make spatial resolution explicit. The effects of resolution are discussed for two simple GIS functions. Three theoretical frameworks for discussing spatial resolution are introduced and explored. The problems of cross-scale inference, including the modifiable areal unit problem and the ecological fallacy, are described and illustrated. © 2010 Elsevier B.V.


Hayton T.W.,University of California at Santa Barbara
Dalton Transactions | Year: 2010

There is a growing interest in uranium coordination chemistry, particularly as it relates to metal-ligand multiple bonding, and in the last decade significant progress has been made in synthesizing oxo, imido, μ-nitrido, and carbene-containing complexes of uranium. This review summarizes the synthesis, structure and reactivity of these complexes, starting from the inception of the field in 1981. Particular attention is focused on the recent developments in this area, such as the synthesis of the bis(imido) analogues of the uranyl ion, and the isolation of the first μ-nitrido complexes of this element. © The Royal Society of Chemistry 2010.


Antunes D.J.,University of Lisbon | Hespanha J.P.,University of California at Santa Barbara | Silvestre C.J.,University of Lisbon
IEEE Transactions on Automatic Control | Year: 2012

We analyze impulsive systems with independent and identically distributed intervals between transitions. Our approach involves the derivation of novel results for Volterra integral equations with positive kernel. We highlight several applications of these results, and show that when applied to the analysis of impulsive systems they allow us to (i) provide necessary and sufficient conditions for mean square stability, stochastic stability and mean exponential stability, which can be equivalently tested in terms of a matrix eigenvalue computation, an LMI feasibility problem, and a Nyquist criterion condition; (ii) assess performance of the impulsive system by computing a second moment Lyapunov exponent. The applicability of our results is illustrated in a benchmark problem considering networked control systems with stochastically spaced transmissions, for which we can guarantee stability for inter-sampling times roughly twice as large as in previous papers. © 2011 IEEE.


Lisiecki L.E.,University of California at Santa Barbara
Climate of the Past | Year: 2010

The fact that the deep-ocean benthic δ13C minimum shifted from the North Pacific to the South Atlantic during the Last Glacial Maximum is often interpretted as evidence of a change in deep water circulation, such as the development of deep water ventilation in the North Pacific or a decrease in Southern Ocean overturning. This study re-evaluates the implications of changes in benthic δ13C gradients by comparing Pacific Deep Water (PDW) δ13C measurements with the values expected for the null hypothesis that PDW ventilation sources remained unchanged throughout the Late Pleistocene. The δ13C compositions of PDW, Northern Component Water (NCW) and Southern Component Water (SCW) are estimated from regional benthic δ13C stacks of 3ĝ€"6 sites. Changes in PDW δ13C and PDW-SCW δ13C gradients over the past 800 kyr are found to be well described by a constant mixture of 60% NCW and 40% SCW plus a constant Pacific remineralization offset of −0. 5ĝ€°. Thus, a change in PDW ventilation cannot be inferred solely on the basis of changes in the Pacific-South Atlantic benthic δ13C gradient. © Author(s) 2010.


Porter S.M.,University of California at Santa Barbara
Geobiology | Year: 2010

A longstanding question in paleontology has been the influence of calcite and aragonite seas on the evolution of carbonate skeletons. An earlier study based on 21 taxa that evolved skeletons during the Ediacaran through Ordovician suggested that carbonate skeletal mineralogy is determined by seawater chemistry at the time skeletons first evolve in a clade. Here I test this hypothesis using an expanded dataset comprising 40 well-defined animal taxa that evolved skeletons de novo in the last 600 Myr. Of the 37 taxa whose mineralogy is known with some confidence, 25 acquired mineralogies that matched seawater chemistry of the time, whereas only two taxa acquired non-matching mineralogies. (Ten appeared during times when seawater chemistry is not well constrained.) The results suggest that calcite and aragonite seas do have a strong influence on carbonate skeletal mineralogy, however, this appears to be true only at the time mineralized skeletons first evolve. Few taxa switch mineralogies (from calcite to aragonite or vice versa) despite subsequent changes in seawater chemistry, and those that do switch do not appear to do so in response to changing aragonite-calcite seas. This suggests that there may be evolutionary constraints on skeletal mineralogy, and that although there may be increased costs associated with producing a mineralogy not favored by seawater, the costs of switching mineralogies are even greater. © 2010 Blackwell Publishing Ltd.


Goodchild M.F.,University of California at Santa Barbara
Journal of Spatial Information Science | Year: 2010

It is 20 years since the term "geographic information science" was suggested to encompass the set of fundamental research issues that surround GIS. Two decades of GIScience have produced a range of accomplishments, in an expanding literature of research results as well as in the infrastructure of research. Several themes are suggested for future research, based both on gaps in what has been accomplished thus far, and on technology trends that will themselves raise research questions.


Berenstein D.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2015

Abstract: In this paper it is argued that the central charge extension of the Coulomb branch of N=4 SYM theory appears as a limit of Beisert’s central charge extension of the planar N=4 spin chain in the presence of boundaries. These boundaries are interpreted as D-branes that source the central charge and are realized as giant gravitons and dual giant gravitons in the AdS dual. The BPS states that correspond to short representations of the centrally extended algebra on the spin chain can stop from existing when they cross walls of stability that depend on the position of the branes. These walls can be understood easily at weak coupling in the SU(2) sector. © 2015, The Author(s).


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.


Young O.R.,University of California at Santa Barbara
Ambio | Year: 2012

Interacting forces of climate change and globalization are transforming the Arctic. Triggered by a non-linear shift in sea ice, this transformation has unleashed mounting interest in opportunities to exploit the region's natural resources as well as growing concern about environmental, economic, and political issues associated with such efforts. This article addresses the implications of this transformation for governance, identifies limitations of existing arrangements, and explores changes needed to meet new demands. It advocates the development of an Arctic regime complex featuring flexibility across issues and adaptability over time along with an enhanced role for the Arctic Council both in conducting policy-relevant assessments and in promoting synergy in interactions among the elements of the emerging Arctic regime complex. The emphasis throughout is on maximizing the fit between the socioecological features of the Arctic and the character of the governance arrangements needed to steer the Arctic toward a sustainable future. © 2012 Royal Swedish Academy of Sciences.


Krintz C.,University of California at Santa Barbara
IEEE Internet Computing | Year: 2013

AppScale is an open source distributed software system that implements a cloud platform as a service (PaaS). AppScale makes cloud applications easy to deploy and scale over disparate cloud fabrics, implementing a set of APIs and architecture that also makes apps portable across the services they employ. AppScale is API-compatible with Google App Engine (GAE) and thus executes GAE applications on-premise or over other cloud infrastructures, without modification. © 1997-2012 IEEE.


Manzoni S.,Duke University | Schimel J.P.,University of California at Santa Barbara | Porporato A.,Duke University
Ecology | Year: 2012

Soil heterotrophic respiration and nutrient mineralization are strongly affected by environmental conditions, in particular by moisture fluctuations triggered by rainfall events. When soil moisture decreases, so does decomposers' activity, with microfauna generally undergoing stress sooner than bacteria and fungi. Despite differences in the responses of individual decomposer groups to moisture availability (e.g., bacteria are typically more sensitive than fungi to water stress), we show that responses of decomposers at the community level are different in soils and surface litter, but similar across biomes and climates. This results in a nearly constant soil-moisture threshold corresponding to the point when biological activity ceases, at a water potential of about -14 MPa in mineral soils and -36 MPa in surface litter. This threshold is shown to be comparable to the soil moisture value where solute diffusion becomes strongly inhibited in soil, while in litter it is dehydration rather than diffusion that likely limits biological activity around the stress point. Because of these intrinsic constraints and lack of adaptation to different hydro-climatic regimes, changes in rainfall patterns (primary drivers of the soil moisture balance) may have dramatic impacts on soil carbon and nutrient cycling. © 2012 by the Ecological Society of America.


Bullmore E.T.,University of Cambridge | Bassett D.S.,University of California at Santa Barbara
Annual Review of Clinical Psychology | Year: 2011

Brain graphs provide a relatively simple and increasingly popular way of modeling the human brain connectome, using graph theory to abstractly define a nervous system as a set of nodes (denoting anatomical regions or recording electrodes) and interconnecting edges (denoting structural or functional connections). Topological and geometrical properties of these graphs can be measured and compared to random graphs and to graphs derived from other neuroscience data or other (nonneural) complex systems. Both structural and functional human brain graphs have consistently demonstrated key topological properties such as small-worldness, modularity, and heterogeneous degree distributions. Brain graphs are also physically embedded so as to nearly minimize wiring cost, a key geometric property. Here we offer a conceptual review and methodological guide to graphical analysis of human neuroimaging data, with an emphasis on some of the key assumptions, issues, and trade-offs facing the investigator. Copyright © 2011 by Annual Reviews. All rights reserved.


This study examined whether encoding conditions that encourage thoughts about the environment of evolutionary adaptation (EEA) are necessary to produce optimal recall in the adaptive memory paradigm. Participants were asked to judge a list of words for their relevance to personal survival under two survival-based scenarios. In one condition, the EEA-relevant context was specified (i.e., you are trying to survive on the savannah/grasslands). In the other condition, no context was specified (i.e., you are simply trying to stay alive). The two tasks produced virtually identical recall despite participants in the former condition reporting significantly more EEA context-relevant thoughts (i.e., the savannah) than did participants in the latter condition (who reported virtually no EEA-related thoughts). The findings are discussed in terms of (1) survival as a target of natural selection and (2) the role of evolutionary theory in understanding memory in modern humans. © 2012 Psychonomic Society, Inc.


Hansell D.A.,University of Miami | Carlson C.A.,University of California at Santa Barbara
Global Biogeochemical Cycles | Year: 2013

The global ocean holds one of Earth's major carbon reservoirs as dissolved organic matter (662 ± 32 PgC). Most of this material (>95%) is termed refractory dissolved organic carbon (RDOC) as Williams and Druffel (1987) found it to be old relative to the circulation time of the ocean. While RDOC within the modern ocean is thus perceived as vast and only slowly renewed, its mobilization has been implicated by Sexton et al. (2011) to explain Earth's transient warming events (i.e., hyperthermals) of the Paleocene and Eocene epochs (65-34 million years ago). Assessing this proposed function of RDOC as a rapidly (~5-10 kyr) exchangeable carbon reservoir is presently limited by insufficient knowledge of the responsible processes. Here we investigate the dynamics of RDOC in the deep Pacific Ocean, previously characterized by concentration gradients thought to be established by slow but systematic RDOC removal with circulation and aging of the water masses. We demonstrate that RDOC is instead conserved during much of its circulation, but that there exist localized sinks in the deep, far North Pacific and at mid depth in the subtropical South Pacific. Water mass mixing into these sink regions creates the observed RDOC gradients. Together, the Pacific sinks remove 7-29% of the 43 Tg RDOC added to the deep global ocean each year with overturning circulation, and point to an important but still unidentified control on the RDOC inventory of deep marine systems. ©2013. American Geophysical Union. All Rights Reserved.


Schaefer R.S.,University of California at Santa Barbara
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2014

Moving to music is intuitive and spontaneous, and music is widely used to support movement, most commonly during exercise. Auditory cues are increasingly also used in the rehabilitation of disordered movement, by aligning actions to sounds such as a metronome or music. Here, the effect of rhythmic auditory cueing on movement is discussed and representative findings of cued movement rehabilitation are considered for several movement disorders, specifically post-stroke motor impairment, Parkinson’s disease and Huntington’s disease. There are multiple explanations for the efficacy of cued movement practice. Potentially relevant, non-mutually exclusive mechanisms include the acceleration of learning; qualitatively different motor learning owing to an auditory context; effects of increased temporal skills through rhythmic practices and motivational aspects of musical rhythm. Further considerations of rehabilitation paradigm efficacy focus on specific movement disorders, intervention methods and complexity of the auditory cues. Although clinical interventions using rhythmic auditory cueing do not show consistently positive results, it is argued that internal mechanisms of temporal prediction and tracking are crucial, and further research may inform rehabilitation practice to increase intervention efficacy. © 2014 The Author(s) Published by the Royal Society. All rights reserved.


Sawyer R.F.,University of California at Santa Barbara
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Photon-photon interactions mediated by an atomic gas can effect efficient polarization exchanges between two beams, leaving the medium exactly in its initial state. In, e.g., hydrogen, the distance required for macroscopic exchange is of the order of one-tenth the distance in which the ordinary nonlinear index of refraction would induce a phase change of π. Several examples are worked out that show the variety of behaviors that can result, depending on the initial respective polarizations stated and the angle between the beams. Of particular interest are initial conditions in which there is no exchange at a mean-field level, conventionally believed to apply when the number of photons N is large. Then the full theory leads both to large exchange and to large entanglement between the beams. Our most solid results indicate that one would have to wait a time proportional to log[N] to see this effect, but there are some indications that this behavior can be circumvented. © 2014 American Physical Society.


Loaiciga A.H.,University of California at Santa Barbara
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

Equations are derived to calculate one-dimensional (vertical) consolidation settlement in aquifers caused by groundwater extraction. The settlement equations capture the effect that the decline in pore-water pressure caused by groundwater extraction has on increased vertical effective stress. The settlement equations for single-layered confined or unconfined aquifers and multiple-layered aquifers are derived by linking the increase in vertical effective stress to the reduction of the void ratio using the reconstructed field consolidation curve of aquifer sediments. This paper's approach blends groundwater hydraulics with the classical theory of one-dimensional consolidation widely used in geotechnical engineering. Closed-form consolidation settlement equations are presented for single-layer, homogeneous, isotropic confined aquifers with steady-state or transient groundwater flow and for single-layer, homogeneous, isotropic, unconfined aquifers under steady-state flow. The consolidation equations for consolidated settlement in heterogeneous, anisotropic, single-layer or multilayer aquifers are expressed as the numerical integration of the vertical strain induced by groundwater pumping. The numerical-integration settlement equations require the implementation of a groundwater simulation model to calculate the pore pressure decline within aquifer layers, followed by the calculation of the increase in vertical effective stress and the reduction in pore volume. One numerical example confirms the accuracy of this paper's approach to aquifer consolidation by comparing with the solution obtained with the three-dimensional poroelastic theory. © 2013 American Society of Civil Engineers.


Bimber B.,University of California at Santa Barbara
Journal of Information Technology and Politics | Year: 2014

This essay provides a descriptive interpretation of the role of digital media in the campaigns of Barack Obama in 2008 and 2012 with a focus on two themes: personalized political communication and the commodification of digital media as tools. The essay covers campaign finance strategy, voter mobilization on the ground, innovation in social media, and data analytics, and why the Obama organizations were more innovative than those of his opponents. The essay provides a point of contrast for the other articles in this special issue, which describe sometimes quite different campaign practices in recent elections across Europe. © Taylor & Francis Group, LLC.


Silva M.L.,University of California at Santa Barbara
Computers and Composition | Year: 2012

In the last ten years, libraries, individual departments, and professors have experimented with screen-capture software to develop edited tutorials, record in-class lectures via presentation software, and record think-aloud rationale for difficult problem sets. Moreover, screen-capture software has been used to provide visual/audio feedback for student writing. Currently, there is scant research on visual/audio feedback via screen-capture software in writing courses. The present study examines student perceptions and attitudes about two different modes and media of teacher feedback: Microsoft Word comments versus visual/audio commentary. The results indicate that the mode and medium of teacher feedback had an impact on students' perceptions about the rhetorical context of the revision process and perceptions about the teacher/student relationship. Students who preferred the visual/audio modality of the teacher commentary videos cited their conversational quality, clarification of expectations, and reference to more global issues in writing. On the other hand, students who preferred the Microsoft Word comments were more apt to discuss its indexical quality in that students could easily revise surface level features or locate the " problem" sentence. The results also indicate that an either/or approach to teacher feedback is not necessary. Students articulated the relevance of using a combination approach in which Microsoft Word comments and the teacher commentary videos could be used for different elements or stages of the writing process. As instructors transition to teaching within online contexts and experiment with new technologies, it is important to examine the significance of the mode and medium of teacher feedback in student perceptions, participation, and writing practices. © 2011 Elsevier Inc..


Janusonis S.,University of California at Santa Barbara
International Journal of Developmental Neuroscience | Year: 2014

Altered serotonin (5-hydroxytryptamine, 5-HT) signaling has been implicated in some developmental abnormalities of autism spectrum disorder (ASD). However, the presumed role of 5-HT in ASD raises new questions in fundamental neuroscience. Specifically, it is not clear if the current piecemeal approach to 5-HT signaling in the mammalian body is effective and whether new conceptual approaches may be required. This review briefly discusses 5-HT production and circulation in the central nervous system and outside of it, especially with regard to ASD, and proposes a more encompassing approach that questions the utility of the "neurotransmitter" concept. It then introduces the idea of a generalized 5-HT packet that may offer insights into possible links between serotonergic varicosities and blood platelets. These approaches have theoretical significance, but they are also well positioned to advance our understanding of some long-standing problems in autism research. © 2014 ISDN.


Fowler A.G.,University of California at Santa Barbara | Fowler A.G.,University of Melbourne
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Many physical systems considered promising qubit candidates are not, in fact, two-level systems. Such systems can leak out of the preferred computational states, leading to errors on any qubits that interact with leaked qubits. Without specific methods of dealing with leakage, long-lived leakage can lead to time-correlated errors. We study the impact of such time-correlated errors on topological quantum error correction codes, which are considered highly practical codes, using the repetition code as a representative case study. We show that, under physically reasonable assumptions, a threshold error rate still exists; however, performance is significantly degraded. We then describe simple additional quantum circuitry that, when included in the error detection cycle, restores performance to acceptable levels. © 2013 American Physical Society.


Lisiecki L.E.,University of California at Santa Barbara
Paleoceanography | Year: 2014

This study analyzes 39 Atlantic and seven Pacific benthic δ13C records to characterize obliquity and precession responses in Atlantic overturning since 3 Ma. Regional benthic δ13C stacks are also analyzed. A major transition in orbital responses is observed at 1.5-1.6 Ma coincident with the first glacial shoaling of Northern Component Water. Since ∼1.5 Ma, the phases of Atlantic benthic δ13C records from 2300 to 4000 m depth lag maximum obliquity by 59 (6.7 kyr) and June perihelion precession forcing by 133 (8.5 kyr). Comparison with North Atlantic sea surface temperature suggests that these orbital responses (particularly precession) in middle deep Atlantic δ13C are associated with changes in ocean heat transport and overturning rates. The mid-Pleistocene transition had little effect on the obliquity and precession phases of benthic δ13C but did result in a ∼50% decrease in the obliquity power of middle deep Atlantic δ13C at 0.6 Ma. Key Points Major transition in Atlantic circulation at 1.5 Ma Atlantic overturning has larger lag for precession than obliquity since 1.5 Ma Regional benthic δ13C stacks for 0-3 Ma ©2014. American Geophysical Union. All Rights Reserved.


Poulin D.,Universite de Sherbrooke | Hastings M.B.,Duke University | Hastings M.B.,University of California at Santa Barbara
Physical Review Letters | Year: 2011

We present a lower bound for the free energy of a quantum many-body system at finite temperature. This lower bound is expressed as a convex optimization problem with linear constraints, and is derived using strong subadditivity of von Neumann entropy and a relaxation of the consistency condition of local density operators. The dual to this minimization problem leads to a set of quantum belief propagation equations, thus providing a firm theoretical foundation to that approach. The minimization problem is numerically tractable, and we find good agreement with quantum Monte Carlo calculations for spin-12 Heisenberg antiferromagnet in two dimensions. This lower bound complements other variational upper bounds. We discuss applications to Hamiltonian complexity theory and give a generalization of the structure theorem of to trees in an appendix. © 2011 American Physical Society.


Sarkar S.,Indian Institute of Technology Gandhinagar | Wall A.C.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In this article we consider the second law of black holes (and other causal horizons) in theories where the gravitational action is an arbitrary function of the Lovelock densities. We show that there exists an entropy which increases locally, for linearized perturbations to regular Killing horizons. In addition to a classical increase theorem, we also prove a generalized second law for semiclassical, minimally coupled matter fields. © 2013 American Physical Society.


Berenstein D.,University of California at Santa Barbara
Annual Review of Nuclear and Particle Science | Year: 2014

This review discusses the status of string physics where the string tension is around the TeV scale. It covers model-building basics for perturbative strings, based on D-brane configurations. The effective low-energy physics description of such string constructions is analyzed: how anomaly cancellation is implemented, how fast proton decay is avoided, and how D-brane models lead to additional Z′ particles. This review also discusses direct search bounds for strings at the TeV scale, as well as theoretical issues with model building related to flavor physics and axions. Copyright © 2014 by Annual Reviews. All rights reserved.


Zhang Y.V.,Johns Hopkins University | Raghuwanshi R.P.,Johns Hopkins University | Shen W.L.,Johns Hopkins University | Montell C.,Johns Hopkins University | Montell C.,University of California at Santa Barbara
Nature Neuroscience | Year: 2013

Animals tend to reject bitter foods. However, long-term exposure to some unpalatable tastants increases acceptance of these foods. Here we show that dietary exposure to an unappealing but safe additive, camphor, caused the fruit fly Drosophila melanogaster to decrease camphor rejection. The transient receptor potential-like (TRPL) cation channel was a direct target for camphor in gustatory receptor neurons, and long-term feeding on a camphor diet led to reversible downregulation of TRPL protein concentrations. The turnover of TRPL was controlled by an E3 ubiquitin ligase, Ube3a. The decline in TRPL levels and increased acceptance of camphor reversed after returning the flies to a camphor-free diet long term. We propose that dynamic regulation of taste receptors by ubiquitin-mediated protein degradation comprises an important molecular mechanism that allows an animal to alter its taste behavior in response to a changing food environment. © 2013 Nature America, Inc. All rights reserved.


Hacker B.R.,University of California at Santa Barbara | Gerya T.V.,ETH Zurich
Tectonophysics | Year: 2013

Regional ultrahigh-pressure (UHP) metamorphic terranes exhibit a spectrum of lithological, structural and petrological characteristics that result from the geodynamic processes that formed and exhumed them. At least six geodynamic processes can be envisioned to have carried continental rocks to mantle depths: i) continental margin subduction, ii) microcontinent subduction, iii) sediment subduction, iv) intracontinental subduction, v) subduction erosion, and vi) foundering of a crustal root. Most of these processes have been investigated through numerical or analog models and most have been invoked for one or more specific occurrences of UHP rocks. At least six geodynamic processes can be envisioned to have exhumed UHP continental rocks: i) eduction, ii) microplate rotation, iii) crustal stacking, iv) slab rollback, v) channel flow, and vi) trans-mantle diapirs. Most of these processes have also been investigated through numerical or analog models and all have been invoked to explain the exhumation of at least one UHP terrane. More-detailed and systematic field investigations are warranted to assess the predictions of numerical models, and more-sophisticated and realistic numerical models are required to replicate and explain the petrological, structural, and chronological data obtained from UHP terranes. © 2013 Elsevier B.V.


Nesic D.,University of Melbourne | Teel A.R.,University of California at Santa Barbara | Zaccarian L.,University of Rome Tor Vergata
IEEE Transactions on Automatic Control | Year: 2011

We consider set-point regulation and L2 robust stability properties of a class of reset control systems consisting of a minimum-phase relative degree-one linear SISO plant controlled by a novel first-order reset element (FORE). These results rely on necessary and sufficient conditions for exponential and L2 finite gain stability of a class of planar reset systems consisting of a scalar linear plant controlled by the novel FORE. We show that the L2 gain of the planar reset system decreases to zero as the pole and/or the gain of the FORE are increased to infinity. A number of stability results, including Lyapunov conditions for Lp and exponential stability, for a larger class of reset and hybrid systems are presented and used to prove our main results. © 2011 IEEE.


Doerr N.R.,University of California at Santa Barbara
Behavioral Ecology and Sociobiology | Year: 2010

Many animals use signals to communicate their social status to conspecifics, and the social control hypothesis suggests that social interactions maintain the evolutionary stability of status signals: low-quality individuals signal at a low level to prevent high-quality individuals from "punishing" them. I examined whether the numbers of decorations at bowers are socially controlled in the great bowerbird (Ptilonorhynchus nuchalis). In two populations, I supplemented males with decorations to determine whether they (a) rejected supplemental decorations and (b) experienced increased bower destruction from rivals. In contrast to the social control hypothesis, males in both populations accepted most supplemental decorations. Though the mean destruction rate did not increase during supplementation in either population, one of the study populations (Townsville) exhibited a negative correlation between the numbers of decorations naturally displayed at bowers and the change in destruction rate during the experiment. Townsville males that naturally had few decorations at their bowers also had more decorations stolen by other males during supplementation than males that naturally had many decorations. These results suggest that the numbers of decorations at bowers are an honest signal of the male's ability to defend his display site from rivals in at least one population of the great bowerbird (Townsville), but they do not support the social control hypothesis because males at both sites failed to limit signal expression. I discuss how the external nature of bower decorations and their availability in the environment may influence the costs and benefits of decoration theft and social control. © 2010 The Author(s).


Martinis J.M.,University of California at Santa Barbara | Geller M.R.,University of Georgia
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

A controlled-phase gate was demonstrated in superconducting Xmon transmon qubits with fidelity reaching 99.4%, relying on the adiabatic interaction between the |11 and |02 states. Here we explain the theoretical concepts behind this protocol, which achieves fast gate times with only σz control of the Hamiltonian, based on a theory of nonlinear mapping of state errors to a power spectral density and use of optimal window functions. With a solution given in the Fourier basis, optimization is shown to be straightforward for practical cases of an arbitrary state change and finite bandwidth of control signals. We find that errors below 10-4 are readily achievable for realistic control wave forms. © 2014 American Physical Society.


Begley M.R.,University of California at Santa Barbara | Wadley H.N.G.,University of Virginia
Acta Materialia | Year: 2012

Micromechanical models are developed to explore the effect of embedded metal layers upon thermal cycling delamination failure of thermal barrier coatings (TBCs) driven by thickening of a thermally grown oxide (TGO). The effects of reductions in the steady-state (i.e. maximum) energy release rate (ERR) controlling debonding from large interface flaws and decreases in the thickening kinetics of TGO are investigated. The models are used to quantify the dependence of the ERR and delamination lifetime upon the geometry and constitutive properties of metal/TBC/TGO multilayers. Combinations of multilayer properties are identified which maximize the increase in delamination lifetime. It is found that even in the absence of TGO growth rate effects, the delamination lifetime of TBC systems with weak TGO/bond coat interfaces can be more than doubled by replacing 10-20% of the ceramic TBC layer with a metal whose ambient temperature yield stress is in the ∼100-200 MPa range. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Giddings S.B.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

A candidate parametrization is introduced, in an effective field theory framework, for the quantum information transfer from a black hole that is necessary to restore unitarity. This in particular allows for description of the effects of this information transfer in the black hole atmosphere, for example seen by infalling observers. In the presence of such information transfer, it is shown that infalling observers need not experience untoward violence. Moreover, the presence of general moderate-frequency couplings to field modes with high angular momenta offers a mechanism to enhance information transfer rates, commensurate with the increased energy flux, when a string is introduced to "mine" a black hole. Generic such models for nonviolent information transfer predict extra energy flux from a black hole, beyond that of Hawking. © 2013 American Physical Society.


Berenstein D.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In this paper I describe a collective coordinate approach to the study of giant graviton states and their excitations in various field theories. The method simplifies considerably the understanding of the emergent gauge symmetry of these configurations, as well as the calculation of the spectrum of strings stretched between the giant gravitons. There is a limit where these results reproduce the one-loop dispersion relation for giant magnons. I also show that this method gives rise to a simple geometric interpretation of a Higgs mechanism for the emergent gauge symmetry which parallels the holographic dual realization of these states: the effective Higgs condensate is the geometric separation of D-branes in the collective coordinate geometry. © 2013 American Physical Society.


Bouchbinder E.,Weizmann Institute of Science | Langer J.S.,University of California at Santa Barbara
Physical Review Letters | Year: 2011

Despite qualitative differences in their underlying physics, both hard and soft glassy materials exhibit almost identical linear rheological behaviors. We show that these nearly universal properties emerge naturally in a shear-transformation-zone theory of amorphous plasticity, extended to include a broad distribution of internal thermal-activation barriers. The principal features of this barrier-height distribution are predicted by nonequilibrium, effective-temperature thermodynamics. Our theoretical loss modulus G ′′(ω) has a peak at the α relaxation rate, and a power law decay of the form ω-ζ for higher frequencies, in quantitative agreement with experimental data. © 2011 American Physical Society.


Srednicki M.,University of California at Santa Barbara
Physical Review Letters | Year: 2011

The Hilbert-Pólya conjecture states that the imaginary parts of the zeros of the Riemann zeta function are eigenvalues of a quantum Hamiltonian. If so, conjectures by Katz and Sarnak put this Hamiltonian in the Altland-Zirnbauer universality class C. This implies that the system must have a nonclassical two-valued degree of freedom. In such a system, the dominant primitive periodic orbits contribute to the density of states with a phase factor of -1. This resolves a previously mysterious sign problem with the oscillatory contributions to the density of the Riemann zeros. © 2011 American Physical Society.


Dobler G.,University of California at Santa Barbara
Astrophysical Journal | Year: 2012

The microwave "haze" was first discovered with the initial release of the full sky data from the Wilkinson Microwave Anisotropy Probe (WMAP). It is diffuse emission toward the center of our Galaxy with spectral behavior that makes it difficult to categorize as any of the previously known emission mechanisms at those wavelengths. With now sevenyears of WMAP data publicly available, we have learned much about the nature of the haze, and with the release of data from the Fermi Gamma-Ray Space Telescope and the discovery of the gamma-ray haze/bubbles, we have had a spectacular confirmation of its existence at other wavelengths. As the WMAP mission winds down and the Planck mission prepares to release data, I take a last look at what WMAP has to tell us about the origin of this unique Galactic feature. Much like the gamma rays, the microwave haze/bubbles is/are elongated in latitude with respect to longitude by a factor of roughly two, and at high latitudes, the microwave emission cuts off sharply above 35° (compared to 50° in the gammas). The hard spectrum of electrons required to generate the microwave synchrotron is consistent with that required to generate gamma-ray emission via inverse Compton scattering, though it is likely that these signals result from distinct regions of the spectrum (10 GeV for the microwaves and 1 TeV for the gammas). While there is no evidence for significant haze polarization in the seven-year WMAP data, I demonstrate explicitly that it is unlikely such a signal would be detectable above the noise. © 2012. The American Astronomical Society. All rights reserved.


Banuls M.C.,Max Planck Institute of Quantum Optics | Cirac J.I.,Max Planck Institute of Quantum Optics | Hastings M.B.,University of California at Santa Barbara
Physical Review Letters | Year: 2011

When a nonintegrable system evolves out of equilibrium for a long time, local observables are in general expected to attain stationary expectation values, independent of the details of the initial state. But the thermalization of a closed quantum system is not yet well understood. Here we show that it presents indeed a much richer phenomenology than its classical counterpart. Using a new numerical technique, we identify two distinct regimes, strong and weak, occurring for different initial states. Strong thermalization, intrinsically quantum, happens when instantaneous local expectation values converge to the thermal ones. Weak thermalization, well known in classical systems, shows convergence to thermal values only after time averaging. Remarkably, we find a third group of states showing no thermalization, neither strong nor weak, to the time scales one can reliably simulate. © 2011 American Physical Society.


Langer J.S.,University of California at Santa Barbara
Reports on Progress in Physics | Year: 2014

This key-issues review is a plea for a new focus on simpler and more realistic models of glass-forming fluids. It seems to me that we have too often been led astray by sophisticated mathematical models that beautifully capture some of the most intriguing features of glassy behavior, but are too unrealistic to provide bases for predictive theories. As illustrations of what I mean, the first part of this article is devoted to brief summaries of imaginative, sensible, but disparate and often contradictory ideas for solving glass problems. Almost all of these ideas remain alive today, with their own enthusiastic advocates. I then describe numerical simulations, mostly by H Tanaka and coworkers, in which it appears that very simple, polydisperse systems of hard disks and spheres develop long range, Ising-like, bond-orientational order as they approach glass transitions. Finally, I summarize my recent proposal that topologically ordered clusters of particles, in disordered environments, tend to become aligned with each other as if they were two-state systems, and thus produce the observed Ising-like behavior. Neither Tanaka's results nor my proposed interpretation of them fit comfortably within any of the currently popular glass theories. © 2014 IOP Publishing Ltd.


Grover T.,University of California at Santa Barbara
Physical Review Letters | Year: 2014

We employ the recent results on the generalization of the central charge theorem to three spacetime dimensions to derive nonperturbative results for several strongly interacting quantum field theories, including quantum electrodynamics (QED-3), and the theory corresponding to certain quantum phase transitions in condensed matter systems. In particular, by demanding that the universal constant part of the entanglement entropy decreases along the renormalization group flow (F theorem), we find sufficient conditions for the stability of QED-3 against chiral symmetry breaking and confinement. Using similar ideas, we derive strong constraints on the nature of quantum critical points in condensed matter systems with topological order. © 2014 American Physical Society.


Halverson J.,University of California at Santa Barbara
Physical Review Letters | Year: 2013

We argue for the existence of additional constraints on SU(2) gauge theories in four dimensions when realized in ultraviolet completions admitting an analog of D-brane nucleation. In type II string compactifications these constraints are necessary and sufficient for the absence of cubic non-Abelian anomalies in certain nucleated SU(N>2) theories. It is argued that they appear quite broadly in the string landscape. Implications for particle physics are discussed; most realizations of the standard model in this context are inconsistent, unless extra electroweak fermions are added. © 2013 American Physical Society.


Adam T.C.,University of California at Santa Barbara
Oecologia | Year: 2011

Many species disperse during their lifetime. Two factors that can affect the performance of individuals following dispersal are the presence of conspecifics and intrinsic habitat quality at the settlement site. Detecting the influence of these factors can be difficult for at least two reasons: (1) the outcomes of interactions with conspecifics are often variable including both competition and facilitation, and (2) selection of high quality habitats often leads to positive covariance between habitat quality and density. In this study, I investigate positive and negative effects of resident blue streak cleaner wrasse (Labroides dimidiatus) on the growth and survival of recently settled conspecifics while accounting for habitat quality. Juvenile L. dimidiatus settle near adult conspecifics, but likely have to compete with resident adults for access to food. However, field experiments indicate that settlers have access to more resources at occupied sites, and as a result, grow faster despite evidence for competition with residents. This result is a direct consequence of two factors: (1) resident conspecifics facilitate settlers by attracting client fish, and (2) resident conspecifics are strongly associated with high quality habitat. These results highlight the need to simultaneously consider habitat quality and competitive and facilitative interactions between conspecifics when making inferences about ecological processes from spatial patterns of individual performance. © 2010 The Author(s).


Giddings S.B.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

If quantum mechanics governs nature, black holes must evolve unitarily, providing a powerful constraint on the dynamics of quantum gravity. Such evolution apparently must in particular be nonlocal, when described from the usual semiclassical geometric picture, in order to transfer quantum information into the outgoing state. While such transfer from a disintegrating black hole has the dangerous potential to be violent to generic infalling observers, this paper proposes the existence of a more innocuous form of information transfer, to relatively soft modes in the black hole atmosphere. Simplified models for such nonlocal transfer are described and parameterized, within a possibly more basic framework of networked Hilbert spaces. Sufficiently sensitive measurements by infalling observers may detect departures from Hawking's predictions, and in generic models black holes decay more rapidly. Constraints of consistency - internally and with known and expected features of physics - restrict the form of information transfer, and should provide important guides to discovery of the principles and mechanisms of the more fundamental nonlocal mechanics. © 2013 American Physical Society.


Xu C.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

It is well known that the Haldane phase of a one-dimensional spin-1 chain is a symmetry-protected topological (SPT) phase, which is described by a nonlinear sigma model (NLSM) with a Θ term at Θ=2π. In this work we study a three-dimensional (3d) SPT phase of a SU(2N) antiferromagnetic spin system with a self-conjugate representation on every site. The spin-ordered Néel phase of this system has a ground state manifold M=U(2N)U(N)×U(N), and this system is described by a NLSM defined with manifold M. Since the homotopy group π4[M]=Z for N>1, this NLSM can naturally have a Θ term. We will argue that when Θ=2π this NLSM describes a SPT phase. This SPT phase is protected by the SU(2N) spin symmetry, or its subgroup SU(N)×SU(N)ŠZ2, without assuming any other discrete symmetry. We will also construct a trial SU(2N) spin state on a 3d lattice; we argue that the long-wavelength physics of this state is precisely described by the aforementioned NLSM with Θ=2π. © 2013 American Physical Society.


Dumontet C.,French Institute of Health and Medical Research | Dumontet C.,UniversiteLyon 1 | Jordan M.A.,University of California at Santa Barbara
Nature Reviews Drug Discovery | Year: 2010

Microtubules are dynamic filamentous cytoskeletal proteins composed of tubulin and are an important therapeutic target in tumour cells. Agents that bind to microtubules have been part of the pharmacopoeia of anticancer therapy for decades and until the advent of targeted therapy, microtubules were the only alternative to DNA as a therapeutic target in cancer. The screening of a range of botanical species and marine organisms has yielded promising new antitubulin agents with novel properties. In the current search for novel microtubule-binding agents, enhanced tumour specificity, reduced neurotoxicity and insensitivity to chemoresistance mechanisms are the three main objectives. © 2010 Macmillan Publishers Limited. All rights reserved.


Xu C.,University of California at Santa Barbara | Senthil T.,Massachusetts Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We study the structure of the ground-state wave functions of bosonic symmetry protected topological (SPT) insulators in three space dimensions. We demonstrate that the differences with conventional insulators are captured simply in a dual vortex description. As an example, we show that a previously studied bosonic topological insulator with both global U(1) and time-reversal symmetry can be described by a rather simple wave function written in terms of dual "vortex ribbons." The wave function is a superposition of all the vortex-ribbon configurations of the boson, and a factor (-1) is associated with each self-linking of the vortex ribbons. This wave function can be conveniently derived using an effective field theory of the SPT phase in the strong-coupling limit, and it naturally explains all the phenomena of this SPT phase discussed previously. The ground-state structure for other three-dimensional (3D) bosonic SPT phases are also discussed similarly in terms of vortex loop gas wave functions. We show that our methods reproduce known results on the ground-state structure of some 2D SPT phases. © 2013 American Physical Society.


Fateev V.A.,CNRS Charles Coulomb Laboratory | Litvinov A.V.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2012

In these notes we consider integrable structure of the conformal field theory with the algebra of symmetries A = W n H, where W n is W-algebra and H is Heisenberg algebra. We found the system of commuting Integrals of Motion with relatively simple properties. In particular, this system has very simple spectrum and the matrix elements of special primary operators between its eigenstates have nice factorized form coinciding exactly with the contribution of the bifundamental multiplet to the Nekrasov partition function for U(n) gauge theories. © SISSA 2012.


Kelly B.C.,University of California at Santa Barbara | Shen Y.,Harvard - Smithsonian Center for Astrophysics
Astrophysical Journal | Year: 2013

We employ a flexible Bayesian technique to estimate the black hole (BH) mass and Eddington ratio functions for Type 1 (i.e., broad line) quasars from a uniformly selected data set of ∼58, 000 quasars from the Sloan Digital Sky Survey (SDSS) DR7. We find that the SDSS becomes significantly incomplete at MBH ≲ 3 × 108 M⊙ or L/L Edd ≲ 0.07, and that the number densities of Type 1 quasars continue to increase down to these limits. Both the mass and Eddington ratio functions show evidence of downsizing, with the most massive and highest Eddington ratio BHs experiencing Type 1 quasar phases first, although the Eddington ratio number densities are flat at z < 2. We estimate the maximum Eddington ratio of Type 1 quasars in the observable universe to be L/L Edd ∼ 3. Consistent with our results in Shen & Kelly, we do not find statistical evidence for a so-called sub-Eddington boundary in the mass-luminosity plane of broad-line quasars, and demonstrate that such an apparent boundary in the observed distribution can be caused by selection effect and errors in virial BH mass estimates. Based on the typical Eddington ratio in a given mass bin, we estimate growth times for the BHs in Type 1 quasars and find that they are comparable to or longer than the age of the universe, implying an earlier phase of accelerated (i.e., with higher Eddington ratios) and possibly obscured growth. The large masses probed by our sample imply that most of our BHs reside in what are locally early-type galaxies, and we interpret our results within the context of models of self-regulated BH growth. © 2013. The American Astronomical Society. All rights reserved.


Bousso R.,University of California at Berkeley | Engelhardt N.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

A future holographic screen is a hypersurface of indefinite signature, foliated by marginally trapped surfaces with area A(r). We prove that A(r) grows strictly monotonically. Future holographic screens arise in gravitational collapse. Past holographic screens exist in our own Universe; they obey an analogous area law. Both exist more broadly than event horizons or dynamical horizons. Working within classical general relativity, we assume the null curvature condition and certain generiticity conditions. We establish several nontrivial intermediate results. If a surface σ divides a Cauchy surface into two disjoint regions, then a null hypersurface N that contains σ splits the entire spacetime into two disjoint portions: the future-and-interior, K+; and the past-and-exterior, K-. If a family of surfaces σ(r) foliate a hypersurface, while flowing everywhere to the past or exterior, then the future-and-interior K+(r) grows monotonically under inclusion. If the surfaces σ(r) are marginally trapped, we prove that the evolution must be everywhere to the past or exterior, and the area theorem follows. A thermodynamic interpretation as a second law is suggested by the Bousso bound, which relates A(r) to the entropy on the null slices N(r) foliating the spacetime. In a companion letter, we summarize the proof and discuss further implications. © 2015 American Physical Society.


Dehay C.,French Institute of Health and Medical Research | Dehay C.,University of Lyon | Kennedy H.,French Institute of Health and Medical Research | Kennedy H.,University of Lyon | Kosik K.,University of California at Santa Barbara
Neuron | Year: 2015

Evolutionary expansion and complexification of the primate cerebral cortex are largely linked to the emergence of the outer subventricular zone (OSVZ), a uniquely structured germinal zone that generates the expanded primate supragranular layers. The primate OSVZ departs from rodent germinal zones in that it includes a higher diversity of precursor types, inter-related in bidirectional non-hierarchical lineages. In addition, primate-specific regulatory mechanisms are operating in primate cortical precursors via the occurrence of novel miRNAs. Here, we propose that the origin and evolutionary importance of the OSVZ is related to genetic changes in multiple regulatory loops and that cell-cycle regulation is a favored target for evolutionary adaptation of the cortex. © 2015 Elsevier Inc.


Jacobs G.H.,University of California at Santa Barbara
Ophthalmic and Physiological Optics | Year: 2010

There have been significant advances in our understanding of mammalian color vision over the past 15 years. This paper reviews a number of topics that have been central to these recent efforts, including: (1) the extent and nature of ultraviolet vision in mammals, (2) the evolutionary loss of short-wavelength-sensitive cones in some mammals, (3) the possible roles of rod signals in mammalian color vision, (4) the evolution of mammalian color vision, and (5) recent laboratory investigations of animal color vision. Successes in linking opsin genes and photopigments to color vision have been key to the progress made on each of these issues. © 2010 The Author, Ophthalmic and Physiological Optics © 2010 The College of Optometrists.


Donnelly W.,University of Maryland University College | Wall A.C.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Quantum fluctuations of matter fields contribute to the thermal entropy of black holes. For free minimally coupled scalar and spinor fields, this contribution is precisely the entanglement entropy. For gauge fields, Kabat found an extra negative divergent "contact term" with no known statistical interpretation. We compare this contact term to a similar term which arises for nonminimally coupled scalar fields. Although both divergences may be interpreted as terms in the Wald entropy, we point out that the contact term for gauge fields comes from a gauge-dependent ambiguity in Wald's formula. Revisiting Kabat's derivation of the contact term, we show that it is sensitive to the treatment of infrared modes. To explore these infrared issues, we consider two-dimensional compact manifolds, such as Euclidean de Sitter space, and show that the contact term arises from an incorrect treatment of zero modes. In a manifestly gauge-invariant reduced phase space quantization, the gauge field contribution to the entropy is positive, finite, and equal to the entanglement entropy. © 2012 American Physical Society.


Tilman D.,University of California at Santa Barbara | Clark M.,University of Minnesota
Nature | Year: 2014

Diets link environmental and human health. Rising incomes and urbanization are driving a global dietary transition in which traditional diets are replaced by diets higher in refined sugars, refined fats, oils and meats. By 2050 these dietary trends, if unchecked, would be a major contributor to an estimated 80 per cent increase in global agricultural greenhouse gas emissions from food production and to global land clearing. Moreover, these dietary shifts are greatly increasing the incidence of type II diabetes, coronary heart disease and other chronic non-communicable diseases that lower global life expectancies. Alternative diets that offer substantial health benefits could, if widely adopted, reduce global agricultural greenhouse gas emissions, reduce land clearing and resultant species extinctions, and help prevent such diet-related chronic non-communicable diseases. The implementation of dietary solutions to the tightly linked diet-environment-health trilemma is a global challenge, and opportunity, of great environmental and public health importance.


Way B.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Under a Scherk-Schwarz compactification, the anti-de Sitter soliton and black brane provide a dual description to a confinement/deconfinement phase transition. We extend this construction to asymptotically Lifshitz spacetimes. In particular, we show that there must be a phase transition between the soliton and black hole if the solutions exist. We also construct these solutions numerically and compute the phase diagram. © 2012 American Physical Society.


An H.,Perimeter Institute | Liu T.,University of California at Santa Barbara | Wang L.-T.,University of Chicago
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The ATLAS and CMS collaborations have announced discovery of a ∼125GeV Higgs boson, after a combined analysis of the diphoton and ZZ search channels. This observation has significant impact on low-energy supersymmetry. First, some fine-tuning is necessary to accommodate such a Higgs mass in the minimal supersymmetric Standard Model (MSSM) because the tree-level mass of the SM-like Higgs boson in the MSSM is relatively small. We study the possibility of lifting the mass of the SM-like Higgs boson by a non-decoupling a D-term from an additional U(1) gauge symmetry. In particular, we focus on a gauged Peccei-Quinn symmetry which can also be related to a possible solution of the μ problem in the MSSM. In addition to the measurement of the mass of the Higgs, the data also reveals a tantalizing hint of a significantly enhanced diphoton signal rate, 1.56±0.43 and 1.9±0.5 times of the SM prediction in the CMS and ATLAS experiments, respectively. We demonstrate that such an enhancement can be accommodated in this MSSM extension. Anomaly cancellation requires the introduction of charged exotics. If some of them happen to be light and have sizable coupling to the SM-like Higgs boson, the diphoton signal rate can be enhanced significantly electroweak precision measurements provide stringent constraints on this model. Taking these into account, we identify two benchmark scenarios. We argue that they are representative of large classes of viable models beyond our current example which can consistently enhance the Higgs to diphoton rate. We also comment on possible signals of such light exotics at the LHC. © 2012 American Physical Society.


Campas O.,University of California at Santa Barbara
Seminars in Cell and Developmental Biology | Year: 2016

The sculpting of embryonic tissues and organs into their functional morphologies involves the spatial and temporal regulation of mechanics at cell and tissue scales. Decades of in vitro work, complemented by some in vivo studies, have shown the relevance of mechanical cues in the control of cell behaviors that are central to developmental processes, but the lack of methodologies enabling precise, quantitative measurements of mechanical cues in vivo have hindered our understanding of the role of mechanics in embryonic development. Several methodologies are starting to enable quantitative studies of mechanics in vivo and in situ, opening new avenues to explore how mechanics contributes to shaping embryonic tissues and how it affects cell behavior within developing embryos. Here we review the present methodologies to study the role of mechanics in living embryonic tissues, considering their strengths and drawbacks as well as the conditions in which they are most suitable. © 2016 Elsevier Ltd.


Dozier J.,University of California at Santa Barbara
Eos | Year: 2011

The world's mountain ranges accumulate substantial snow, whose melt produces the bulk of runoff and often combines with rain to cause floods. Worldwide, inadequate understanding and a reliance on sparsely distributed observations limit our ability to predict seasonal and paroxysmal runoff as climate changes, ecosystems adapt, populations grow, land use evolves, and societies make choices. To improve assessments of snow accumulation, melt, and runoff, scientists and community planners can take advantage of two emerging trends: (1) an ability to remotely sense snow properties from satellites at a spatial scale appropriate for mountain regions (10- to 100-meter resolution, coverage of the order of 100,000 square kilometers) and a daily temporal scale appropriate for the dynamic nature of snow and (2) The Fourth Paradigm [Hey et al., 2009], which posits a new scientific approach in which insight is discovered through the manipulation of large data sets as the evolutionary step in scientific thinking beyond the first three paradigms: empiricism, analyses, and simulation. The inspiration for the book's title comes from pioneering computer scientist Jim Gray, based on a lecture he gave at the National Academy of Sciences 3 weeks before he disappeared at sea.


Mafic and granodioritic magmas mingled to produce a swarm of microdiorite enclaves in the granodiorite. The enclaves and rare hornfels inclusions were carried upward in an oval-shaped pipe, 30 m long and 15 m wide, probably as a gas-driven mass to a point where an H2O-rich, superheated felsic melt intruded the pipe and the enclave mass, and upon abrupt undercooling, deposited orbicu lar shells of tangentially oriented micro crystals of sodic plagioclase, quartz, K-feldspar, and biotite on 20% of the enclaves and inclusions now located only against the north margin of the pipe. The mass of orbicular and nonorbicu lar enclaves was then injected by a quartz monzodiorite magma that now comprises the matrix among the enclaves. © 2011 Geological Society of America.


Meiburg E.,University of California at Santa Barbara | Kneller B.,University of Aberdeen
Annual Review of Fluid Mechanics | Year: 2010

The article surveys the current state of our understanding of turbidity currents, with an emphasis on their fluid mechanics. It highlights the significant role these currents play within the global sediment cycle, and their importance in environmental processes and in the formation of hydrocarbon reservoirs. Events and mechanisms governing the initiation of turbidity currents are reviewed, along with experimental observations and findings from field studies regarding their internal velocity and density structure. As turbidity currents propagate over the seafloor, they can trigger the evolution of a host of topographical features through the processes of deposition and erosion, such as channels, levees, and sediment waves. Potential linear instability mechanisms are discussed that may determine the spatial scales of these features. Finally, the hierarchy of available theoretical models for analyzing the dynamics of turbidity currents is outlined, ranging from dimensional analysis and integral models to both depth-averaged and depth-resolving simulation approaches. Copyright © 2010 by Annual Reviews. All rights reserved.


Janusonis S.,University of California at Santa Barbara
BMC Neuroscience | Year: 2014

Background: The activity of neurons is controlled by groups of neurotransmitter receptors rather than by individual receptors. Experimental studies have investigated some receptor interactions, but currently little information is available about transcriptional associations among receptors at the whole-brain level.Results: A total of 4950 correlations between 100 G protein-coupled neurotransmitter receptors were examined across 169 brain regions in the human brain using expression data published in the Allen Human Brain Atlas. A large number of highly significant correlations were found, many of which have not been investigated in hypothesis-driven studies. The highest positive and negative correlations of each receptor are reported, which can facilitate the construction of receptor sets likely to be affected by altered transcription of one receptor (such sets always exist, but their members are difficult to predict). A graph analysis isolated two large receptor communities, within each of which receptor mRNA levels were strongly cross-correlated.Conclusions: The presented systematic analysis shows that the mRNA levels of many G protein-coupled receptors are interdependent. This finding is not unexpected, since the brain is a highly integrated complex system. However, the analysis also revealed two novel properties of global brain structure. First, receptor correlations are described by a simple statistical distribution, which suggests that receptor interactions may be guided by qualitatively similar processes. Second, receptors appear to form two large functional communities, which might be differentially affected in brain disorders. © 2014 Janušonis; licensee BioMed Central Ltd.


Tilman D.,University of Minnesota | Balzer C.,University of California at Santa Barbara | Hill J.,University of Minnesota | Befort B.L.,University of Minnesota
Proceedings of the National Academy of Sciences of the United States of America | Year: 2011

Global food demand is increasing rapidly, as are the environmental impacts of agricultural expansion. Here, we project global demand for crop production in 2050 and evaluate the environmental impacts of alternative ways that this demand might be met. We find that per capita demand for crops, when measured as caloric or protein content of all crops combined, has been a similarly increasing function of per capita real income since 1960. This relationship forecasts a 100-110% increase in global crop demand from 2005 to 2050. Quantitative assessments show that the environmental impacts of meeting this demand depend on how global agriculture expands. If current trends of greater agricultural intensification in richer nations and greater land clearing (extensification) in poorer nations were to continue, ∼1 billion ha of land would be cleared globally by 2050, with CO 2-C equivalent greenhouse gas emissions reaching ∼3 Gt y -1 and N use ∼250 Mt y -1 by then. In contrast, if 2050 crop demand was met by moderate intensification focused on existing croplands of underyielding nations, adaptation and transfer of high-yielding technologies to these croplands, and global technological improvements, our analyses forecast land clearing of only ∼0.2 billion ha, greenhouse gas emissions of ∼1 Gt y -1, and global N use of ∼225 Mt y -1. Efficient management practices could substantially lower nitrogen use. Attainment of high yields on existing croplands of underyielding nations is of great importance if global crop demand is to be met with minimal environmental impacts.


Morin J.-F.,Free University of Colombia | Young O.,University of California at Santa Barbara
Global Governance | Year: 2013

Understanding the impact of regime complexes on global governance calls for creative policy thinking. This introduction provides a new and more precise definition of the concept of regime complex. It also suggests specific tools to characterize regime complexes and analyze their impacts on global governance. The articles in this issue deepen the analytical understanding of complexes by examining concrete examples in various domains of global governance such as piracy, taxation, energy, food security, emissions reduction, carbon sinks, biosafety, and refugee governance. In addition to providing an in-depth description of a variety of different regime complexes, this issue is innovative on three accounts: (1) it presents complexes as both barriers and opportunities for global governance and gives explanations for these diverse outcomes; (2) it shows how a broad spectrum of actors is necessary for understanding the creation and evolution of complexes; and (3) it qualifies former claims to the effect that only powerful actors can impact regime complexes. © 2013 Lynne Rienner Publishers, Inc.


Franco S.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2011

We introduce a correspondence between dimer models (and hence superconformal quivers) and the quantum Teichmüller space of the Riemann surfaces associated to them by mirror symmetry. Via the untwisting map, every brane tiling gives rise to a tiling of the Riemann surface with faces surrounding punctures. We explain how to obtain an ideal triangulation by dualizing this tiling. In order to do so, tiling nodes of valence greater than 3 (equivalently superpotential terms of order greater than 3 in the corresponding quiver gauge theories) must be decomposed by the introduction of 2-valent nodes. From a quiver gauge theory perspective, this operation corresponds to integrating-in massive fields. Fock coordinates in Teichmüller space are in one-to-one correspondence with chiral fields in the quiver. We present multiple explicit examples, including infinite families of theories, illustrating how the right number of Fock coordinates is generated by this procedure. Finally, we explain how Chekhov and Fock commutation relations between coordinates give rise to the commutators associated to dimer models by Goncharov and Kenyon in the context of quantum integrable systems. For generic dimer models (i.e. those containing nodes that are not 3-valent), this matching requires the introduction of a natural generalization of Chekhov and Fock rules. We also explain how urban renewal in the original brane tiling (Seiberg duality for the quivers) is mapped to flips of the ideal triangulation. © SISSA 2011.


Jacobson T.,University of California at Santa Barbara
Physical Review Letters | Year: 2016

A link between the semiclassical Einstein equation and a maximal vacuum entanglement hypothesis is established. The hypothesis asserts that entanglement entropy in small geodesic balls is maximized at fixed volume in a locally maximally symmetric vacuum state of geometry and quantum fields. A qualitative argument suggests that the Einstein equation implies the validity of the hypothesis. A more precise argument shows that, for first-order variations of the local vacuum state of conformal quantum fields, the vacuum entanglement is stationary if and only if the Einstein equation holds. For nonconformal fields, the same conclusion follows modulo a conjecture about the variation of entanglement entropy. © 2016 American Physical Society.


Heeger A.J.,University of California at Santa Barbara
Chemical Society Reviews | Year: 2010

There has been remarkable progress in the science and technology of semiconducting polymers during the past decade. The field has evolved from the early work on polyacetylene (the First Generation material) to a proper focus on soluble and processible polymers and co-polymers. The soluble poly(alkylthiophenes) and the soluble PPVs are perhaps the most important examples of the Second Generation of semiconducting polymers. Third Generation semiconducting polymers have more complex molecular structures with more atoms in the repeat unit. Important examples include the highly ordered and crystalline PDTTT and the ever-growing class of donor-acceptor co-polymers that has emerged in the past few years. Examples of the latter include the bithiophene-acceptor co-polymers pioneered by Konarka and the polycarbazole-acceptor co-polymers pioneered by Leclerc and colleagues. In this tutorial review, I will summarize progress in the basic physics, the materials science, the device science and the device performance with emphasis on the following recent studies of Third Generation semiconducting polymers: stable semiconducting polymers; self-assembly of bulk heterojunction (BHJ) materials by spontaneous phase separation; bulk heterojunction solar cells with internal quantum efficiency approaching 100%; high detectivity photodetectors fabricated from BHJ materials. © 2010 The Royal Society of Chemistry.


Joye S.B.,University of Georgia | MacDonald I.R.,Florida State University | Leifer I.,University of California at Santa Barbara | Asper V.,University of Southern Mississippi
Nature Geoscience | Year: 2011

The deep-sea hydrocarbon discharge resulting from the BP oil well blowout in the northern Gulf of Mexico released large quantities of oil and gaseous hydrocarbons such as methane into the deep ocean. So far, estimates of hydrocarbon discharge have focused on the oil released, and have overlooked the quantity, fate and environmental impact of the gas. Gaseous hydrocarbons turn over slowly in the deep ocean, and microbial consumption of these gases could have a long-lasting impact on oceanic oxygen levels. Here, we combine published estimates of the volume of oil released, together with provisional estimates of the oil to gas ratio of the discharged fluid, to determine the volume of gaseous hydrocarbons discharged during the spill. We estimate that the spill injected up to 500,000 t of gaseous hydrocarbons into the deep ocean and that these gaseous emissions comprised 40% of the total hydrocarbon discharge. Analysis of water around the wellhead revealed discrete layers of dissolved hydrocarbon gases between 1,000 and 1,300 m depth; concentrations exceeded background levels by up to 75,000 times. We suggest that microbial consumption of these gases could lead to the extensive and persistent depletion of oxygen in hydrocarbon-enriched waters. © 2011 Macmillan Publishers Limited. All rights reserved.


Potter W.J.,University of California at Santa Barbara
Journal of Broadcasting and Electronic Media | Year: 2010

Media literacy is a term that means many different things to different people- scholars, educators, citizen activists, and the general public. This article reviews the variety of definitions and presents a synthesis of commonalities thatmost definitions of media literacy share. The review presents an overview of how media literacy has been treated as an issue in curriculum design within the institution of education, and then how it has been treated as an intervention by parents and researchers. © 2010 Broadcast Education Association.


Giddings S.B.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The unitary crisis for black holes indicates an apparent need to modify local quantum field theory. This paper explores the idea that quantum mechanics and, in particular, unitarity are fundamental principles, but at the price of familiar locality. Thus, one should seek to parameterize unitary evolution, extending the field theory description of black holes, such that their quantum information is transferred to the external state. This discussion is set in a broader framework of unitary evolution acting on Hilbert spaces comprising subsystems. Here, various constraints can be placed on the dynamics, based on quantum information-theoretic and other general physical considerations, and one can seek to describe dynamics with minimal departure from field theory. While usual spacetime locality may not be a precise concept in quantum gravity, approximate locality seems an important ingredient in physics. In such a Hilbert-space approach an apparently coarser form of localization can be described in terms of tensor decompositions of the Hilbert space of the complete system. This suggests a general framework in which to seek a consistent description of quantum gravity, and approximate emergence of spacetime. Other possible aspects of such a framework-in particular, symmetries-are briefly discussed. © 2012 American Physical Society.


Giddings S.B.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Simple models for unitary black hole evolution are given in an effective Hilbert-space description, parameterizing a possible minimal relaxation of locality, with respect to semiclassical black hole geometry. © 2012 American Physical Society.


Wall A.C.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The generalized second law is proven for semiclassical quantum fields falling across a causal horizon, minimally coupled to general relativity. The proof is much more general than previous proofs in that it permits the quantum fields to be rapidly changing with time, and shows that entropy increases when comparing any slice of the horizon to any earlier slice. The proof requires the existence of an algebra of observables restricted to the horizon, satisfying certain axioms (determinism, ultralocality, local Lorentz invariance, and stability). These axioms are explicitly verified in the case of free fields of various spins, as well as 1+1 conformal field theories. The validity of the axioms for other interacting theories is discussed. © 2012 American Physical Society.


Adam T.C.,University of California at Santa Barbara
Journal of Animal Ecology | Year: 2012

Indirect interactions resulting from changes in organismal traits such as behaviour [i.e. trait-mediated indirect interactions (TMIIs)] are widespread in biological communities, yet few studies have explored the potential for mutualisms to initiate TMIIs. This study used a combination of behavioural observations and manipulative field experiments to investigate potential TMIIs resulting from a mutualism between specialized cleaner fish and the 'clients' that visit cleaners for the removal of ectoparasites. Behavioural observations indicate that the bluestreak cleaner wrasse, Labroides dimidiatus, increases local predation pressure on corals at cleaner stations by attracting corallivorous butterflyfish to their territories. Observations of the ornate butterflyfish, Chaetodon ornatissimus, suggest a trade-off between seeking cleaning and foraging; individuals decreased their foraging rate at cleaner stations and shifted their diet to include a greater proportion of less preferred prey items. Nonetheless, predation pressure on corals was higher at cleaner stations because the spatial response of butterflyfish to cleaners more than compensated for their lower foraging rates. The results of a field experiment suggest that the greater predation pressure observed at cleaner stations may be sufficient to reduce the growth rate of the unpreferred coral Porites rus. Together, these results emphasize the need to consider mutualists as potential initiators of TMIIs and highlight the importance of integrating individual movement into conceptual analyses of TMIIs. © 2012 The Author. Journal of Animal Ecology © 2012 British Ecological Society.


Trumble B.C.,University of California at Santa Barbara
Proceedings. Biological sciences / The Royal Society | Year: 2014

Controversy over the adaptive significance of male hunting in subsistence societies hinges on the relative importance of familial provisioning and mate-quality signalling. This paper examines the proximate and ultimate motivations of hunting behaviour from a neuroendocrine perspective, using salivary testosterone and cortisol data collected before, during and after hunting focal follows from 31 Tsimane hunters aged 18-82 years. Despite circadian declines in hormone levels, testosterone and cortisol of Tsimane hunters increased at the time of a kill, and remained high as successful hunters returned home. Previous studies of hormonal changes during competitions find that high-stakes and success in the presence of relevant audiences result in increased neuroendocrine arousal. If men hunt primarily to provision their families, then an additional audience would not be expected to impact testosterone or cortisol, nor would the size of the animal killed. However, if signalling male quality by 'showing off' was a larger relative driver of men's hunting behaviour, one would expect greater hormonal response in cases where men returned with large sharable kills, especially in the presence of community members. Consistent with provisioning models of male hunting motivation, neither kill size nor encountering an audience of villagers while returning from hunting was associated with hormonal changes for successful hunters.


Marolf D.,University of California at Santa Barbara
Classical and Quantum Gravity | Year: 2015

Observables in gravitational systems must be non-local so as to be invariant under diffeomorphism gauge transformations. But at the classical level some such observables can nevertheless satisfy an exact form of microcausality. This property is conjectured to remain true at all orders in the semiclassical expansion, though with limitations at finite h or ℓPlanck. We also discuss related issues concerning observables in black hole spacetimes and comment on the senses in which they do and do not experience the form of chaos identified by Shenker and Stanford. In particular, in contrast to the situation in a reflecting cavity, this chaos does not afflict observables naturally associated with Hawking radiation for evaporating black holes. © 2015 IOP Publishing Ltd Printed in the UK.


Xu C.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We study three-dimensional Z2 topological phases enriched by Z2T time-reversal symmetry with bosonic bulk excitations. Some of these phases can be constructed by simply coupling the three-dimensional symmetry protected topological phases with Z2×Z2T symmetry to a deconfined Z 2 gauge field. Besides these simple phases, we also construct two special root phases, whose boundary can have an extra Z2 topological order in addition to their bulk topological order, and the boundary anyon excitations can have fractional time-reversal transformation T with T4=-1. In particular, the boundary e and m anyons of one of the two root phases are interchanged under time-reversal transformation, and they must be degenerate and orthogonal with each other. Eventually we obtain (Z2 )2âŠ(Z2)2 classification (8 different phases) for Z2T-enriched Z2 topological phases with bosonic bulk excitations in three dimensions. © 2013 American Physical Society.


Kasen D.,University of California at Santa Cruz | Bildsten L.,University of California at Santa Barbara
Astrophysical Journal | Year: 2010

We show that energy deposited into an expanding supernova remnant by a highly magnetic (B ∼ 5 × 1014 G) neutron star spinning at an initial period of Pi ≈ 2-20 ms can substantially brighten the light curve. For magnetars with parameters in this range, the rotational energy is released on a timescale of days to weeks, which is comparable to the effective diffusion time through the supernova remnant. The late time energy injection can then be radiated without suffering overwhelming adiabatic expansion losses. The magnetar input also produces a central bubble that sweeps ejecta into an internal dense shell, resulting in a prolonged period of nearly constant photospheric velocity in the observed spectra. We derive analytic expressions for the light curve rise time and peak luminosity as a function of B and Pi , and the properties of the supernova ejecta that allow for direct inferences about the underlying magnetar in bright supernovae. We perform numerical radiation hydrodynamic calculations of a few specific instances and compare the resulting light curves to observed events. Magnetar birth is likely to impact more than a few percent of all core-collapse supernovae, and may naturally explain some of the brightest events ever seen (e.g., SN 2005ap and SN 2008es) at L ≳ 1044 ergs s-1. © 2010. The American Astronomical Society. All rights reserved.


Mason C.F.,University of Wyoming | Plantinga A.J.,University of California at Santa Barbara
Journal of Environmental Economics and Management | Year: 2013

Carbon offsets are a frequently discussed tool for reducing the costs of an emissions reduction policy. However, offsets have a basic problem stemming from asymmetric information. Sellers of offsets have private information about their opportunity costs, leading to concerns about whether offsets are additional. Non-additional offsets can undermine a cap-and-trade program or, if the government purchases them directly, result in enormous government expenditures. We analyze contracts for carbon sequestration in forests that mitigate the asymmetric information problem. Landowners are offered a menu of two-part contracts that induces them to reveal their type. Under this scheme, the government is able to identify ex post how much additional forest each landowner contributes and minimize ex ante its expenditures on carbon sequestration. To explore the performance of the contracting scheme, we conduct a national-scale simulation using an econometric model of land-use change. The results indicate that for an increase in forest area of 61 million acres, government expenditures are $5.3 billion lower under the contracting approach compared to a uniform subsidy offered to all landowners. This compares to an increase in private opportunity costs of just $110 million dollars under the contracts. Thus, the contracting scheme is preferable from society's perspective. © 2013 Elsevier Inc.


Bergstrom T.C.,University of California at Santa Barbara
Proceedings of the National Academy of Sciences of the United States of America | Year: 2014

This paper applies the theory of the evolution of risk-taking in the presence of idiosyncratic and environmental risks to the example of food hoarding by animals and explores implications of the resulting theory for human attitudes toward risk.


Grover T.,University of California at Santa Barbara | Vishwanath A.,University of California at Berkeley
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Bosonic integer quantum Hall (IQH) phases are a class of symmetry-protected topological (SPT) phases that, similar to the fermionic IQH states, support a quantized Hall conductance. They, however, require interactions for their realization. Here, we study quantum Hall plateau transitions between a trivial insulator and a bosonic IQH phase, in a clean system. Generically, we find an intervening superfluid phase. The presence of additional symmetries, however, can potentially lead to a direct transition between these phases. We employ a fermionic parton description that captures both the insulating phases as well as the transition between them. The critical theory is massless QED-3 with N f=2 fermion flavors. The fermions have a surprisingly simple interpretation: they are vortices of the superfluid. Therefore, the universal conductivity at the transition, assuming it is continuous, equals the universal resistivity of Dirac fermions in QED-3. We also briefly comment on sigma model descriptions of the transition and the surface states of related three-dimensional SPT phases. © 2013 American Physical Society.


Singh A.,University of California at San Diego | Hespanha J.P.,University of California at Santa Barbara
IEEE Transactions on Automatic Control | Year: 2011

In the stochastic formulation of chemical kinetics, the differential equation that describes the time evolution of the lower-order statistical moments for the number of molecules of the different species involved, is generally not closed, in the sense that the right-hand side of this equation depends on higher-order moments. Recent work has proposed a moment closure technique based on derivative-matching, which closes the moment equations by approximating higher-order moments as nonlinear functions of lower-order moments. We here provide a mathematical proof of this moment closure technique, and highlight its performance through comparisons with alternative methods. These comparisons reveal that this moment closure technique based on derivative-matching provides more accurate estimates of the moment dynamics, especially when the population size is small. Finally, we show that the accuracy of the proposed moment closure scheme can be arbitrarily increased by incurring additional computational effort. © 2006 IEEE.


Squires T.M.,University of California at Santa Barbara | Mason T.G.,University of California at Los Angeles
Annual Review of Fluid Mechanics | Year: 2010

In microrheology, the local and bulk mechanical properties of a complex fluid are extracted from the motion of probe particles embedded within it. In passive microrheology, particles are forced by thermal fluctuations and probe linear viscoelasticity, whereas active microrheology involves forcing probes externally and can be extended out of equilibrium to the nonlinear regime. Here we review the development, present state, and future directions of this field. We organize our review around the generalized Stokes-Einstein relation (GSER), which plays a central role in the interpretation of microrheology. By discussing the Stokes and Einstein components of the GSER individually, we identify the key assumptions that underpin each, and the consequences that occur when they are violated. We conclude with a discussion of two techniques-multiple particle-tracking and nonlinear microrheology-that have arisen to handle systems in which the GSER breaks down. Copyright © 2010 by Annual Reviews. All rights reserved.


Wereley S.T.,Purdue University | Meinhart C.D.,University of California at Santa Barbara
Annual Review of Fluid Mechanics | Year: 2010

Microfluidic devices are becoming increasingly common and are seen in applications ranging from biology to nanotechnology and manufacturing. Flow behavior in these small domains can often be counterintuitive because of the low Reynolds number or the relative importance of surface forces. Micro-particle image velocimetry (μPIV) is a quantitative method that can be used to characterize the performance of such microfluidic systems with spatial resolutions better than one micron. Illustrating the impact of this measurement technique, more than 100 journal articles are published per year that feature μPIV velocity measurements. This article discusses the fundamentals of the technique, its theoretical background, and several applications. Copyright © 2010 by Annual Reviews. All rights reserved.


Gu Z.-C.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Recently, the Grassmann-tensor-entanglement renormalization group (GTERG) algorithm has been proposed as a generic variational approach to study strongly correlated boson/fermion systems. However, the weakness of such a simple variational approach is that generic Grassmann tensor product states (GTPS) with large inner dimension D will contain a large number of variational parameters which are hard to be determined through usual minimization procedures. In this paper, we first introduce a standard form of GTPS which significantly simplifies the representations. Then we describe a simple imaginary-time-evolution algorithm to efficiently update the GTPS based on the fermion coherent state representation and show that all the algorithms developed for usual tensor product states (TPS) can be implemented for GTPS in a similar way. Finally, we study the environment effect for the GTERG approach and propose a simple method to further improve its accuracy. We demonstrate our algorithms by studying some simple two-dimensional free and interacting fermion systems on honeycomb lattice, including both off-critical and critical cases. © 2013 American Physical Society.


Fisher M.C.,Imperial College London | Henk D.A.,Imperial College London | Briggs C.J.,University of California at Santa Barbara | Brownstein J.S.,Harvard University | And 3 more authors.
Nature | Year: 2012

The past two decades have seen an increasing number of virulent infectious diseases in natural populations and managed landscapes. In both animals and plants, an unprecedented number of fungal and fungal-like diseases have recently caused some of the most severe die-offs and extinctions ever witnessed in wild species, and are jeopardizing food security. Human activity is intensifying fungal disease dispersal by modifying natural environments and thus creating new opportunities for evolution. We argue that nascent fungal infections will cause increasing attrition of biodiversity, with wider implications for human and ecosystem health, unless steps are taken to tighten biosecurity worldwide. © 2012 Macmillan Publishers Limited. All rights reserved.


Mayhew C.G.,Robert Bosch GmbH | Sanfelice R.G.,University of Arizona | Teel A.R.,University of California at Santa Barbara
IEEE Transactions on Automatic Control | Year: 2011

It is well known that controlling the attitude of a rigid body is subject to topological constraints. We illustrate, with examples, the problems that arise when using continuous and (memoryless) discontinuous quaternion-based state-feedback control laws for global attitude stabilization. We propose a quaternion-based hybrid feedback scheme that solves the global attitude tracking problem in three scenarios: full state measurements, only measurements of attitude, and measurements of attitude with angular velocity measurements corrupted by a constant bias. In each case, the hybrid feedback is dynamic and incorporates hysteresis-based switching using a single binary logic variable for each quaternion error state. When only attitude measurements are available or the angular rate is corrupted by a constant bias, the proposed controller is observer-based and incorporates an additional quaternion filter and bias observer. The hysteresis mechanism enables the proposed scheme to simultaneously avoid the unwinding phenomenon and sensitivity to arbitrarily small measurement noise that is present in discontinuous feedbacks. These properties are shown using a general framework for hybrid systems, and the results are demonstrated by simulation. © 2011 IEEE.


Rademaker L.,University of California at Santa Barbara | Ortuno M.,University of Murcia
Physical Review Letters | Year: 2016

Recently, it has been suggested that the many-body localized phase can be characterized by local integrals of motion. Here we introduce a Hilbert-space-preserving renormalization scheme that iteratively finds such integrals of motion exactly. Our method is based on the consecutive action of a similarity transformation using displacement operators. We show, as a proof of principle, localization and the delocalization transition in interacting fermion chains with random on-site potentials. Our scheme of consecutive displacement transformations can be used to study many-body localization in any dimension, as well as disorder-free Hamiltonians. © 2016 American Physical Society.


Larson K.P.,University of British Columbia | Cottle J.M.,University of California at Santa Barbara
Tectonics | Year: 2014

Detailed quartz lattice preferred orientation (LPO) data define two structural discontinuities in the exhumed high-grade metamorphic core of the Himalaya exposed in the upper Tama Kosi region of east central Nepal. The structures are marked by abrupt breaks in a general trend of up structural section increasing quartz LPO-defined deformation temperatures. Deformation associated with the upper structural discontinuity, which occurs within sillimanite grade rocks, is postpeak metamorphism in both the hanging wall and the footwall. New geochronologic data constrain the timing of metamorphism in the hanging wall of the upper discontinuity to between 24 and 16Ma, indistinguishable from previously published ages for the footwall. Movement across this structure represents Early Miocene strain localization and thickening in the Himalayan midcrust. Movement across the lower discontinuity, which occurs between staurolite and kyanite grade rocks, appears to be synmetamorphic with material in its footwall at approximately 10Ma, but postpeak metamorphism for material in its hanging wall. This movement is interpreted to reflect the underplating and incorporation of material into the metamorphic core. The recognition of two thrust-sense discontinuities in the exhumed Himalayan core in the Tama Kosi region is consistent with other similar structures recognized along the Himalaya. The widespread nature of these structures reinforces that they are important to our understanding of the evolution of the kinematics of large, hot orogens. Key Points Two structural discontinuities are outlined through quartz petrofabrics The discontinuities facilitated thickening of the Himalayan midcrust Similar recently identified structures occur orogen-wide ©2014. American Geophysical Union. All Rights Reserved.


Samuel C.E.,University of California at Santa Barbara
Current Topics in Microbiology and Immunology | Year: 2012

Double-stranded RNA (dsRNA) functions both as a substrate of ADARs and also as a molecular trigger of innate immune responses. ADARs, adenosine deaminases that act on RNA, catalyze the deamination of adenosine (A) to produce inosine (I) in dsRNA. ADARs thereby can destablize RNA structures, because the generated I:U mismatch pairs are less stable than A:U base pairs. Additionally, I is read as G instead of A by ribosomes during translation and by viral RNA-dependent RNA polymerases during RNA replication. Members of several virus families have the capacity to produce dsRNA during viral genome transcription and replication. Sequence changes (A-G, and U-C) characteristic of A-I editing can occur during virus growth and persistence. Foreign viral dsRNA also mediates both the induction and the action of interferons. In this chapter our current understanding of the role and significance of ADARs in the context of innate immunity, and as determinants of the outcome of viral infection, will be considered. © 2011 Springer-Verlag Berlin Heidelberg.


Vallee-Belisle A.,University of Montreal | Vallee-Belisle A.,University of California at Santa Barbara | Michnick S.W.,University of Montreal
Nature Structural and Molecular Biology | Year: 2012

To understand how proteins fold, assemble and function, it is necessary to characterize the structure and dynamics of each state they adopt during their lifetime. Experimental characterization of the transient states of proteins remains a major challenge because high-resolution structural techniques, including NMR and X-ray crystallography, cannot be directly applied to study short-lived protein states. To circumvent this limitation, we show that transient states during protein folding can be characterized by measuring the fluorescence of tryptophan residues, introduced at many solvent-exposed positions to determine whether each position is native-like, denatured-like or non-native-like in the intermediate state. We use this approach to characterize a late-folding-intermediate state of the small globular mammalian protein ubiquitin, and we show the presence of productive non-native interactions that suggest a 'flycatcher' mechanism of concerted binding and folding. © 2012 Nature America, Inc. All rights reserved.


Hartnett G.S.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2015

Abstract: Solutions corresponding to finite temperature (anti)-D3 and M2 branes localised in flux backgrounds are constructed in a linear approximation. The flux backgrounds considered are toy models for the IR of the Klebanov-Strassler solution and its M-theory analogue, the Cvetič-Gibbons-Lü-Pope solution. Smooth solutions exist for either sign charge, in stark contrast with the previously considered case of smeared black branes. That the singularities of the anti-branes in the zero temperature extremal limit can be shielded behind a finite temperature horizon indicates that the singularities are physical and resolvable by string theory. As the charge of the branes grows large and negative, the flux at the horizon increases without bound and diverges in the extremal limit, which suggests a resolution via brane polarisation à la Polchinski-Strassler. It therefore appears that the anti-brane singularities do not indicate a problem with the SUSY-breaking metastable states corresponding to expanded anti-brane configurations in these backgrounds, nor with the use of these states in constructing the de Sitter landscape. © 2015, The Author(s).


Morrison D.R.,University of California at Santa Barbara | Taylor W.,Massachusetts Institute of Technology
Journal of High Energy Physics | Year: 2015

Abstract: We analyze non-Higgsable clusters of gauge groups and matter that can arise at the level of geometry in 4D F-theory models. Non-Higgsable clusters seem to be generic features of F-theory compactifications, and give rise naturally to structures that include the nonabelian part of the standard model gauge group and certain specific types of potential dark matter candidates. In particular, there are nine distinct single nonabelian gauge group factors, and only five distinct products of two nonabelian gauge group factors with matter, including SU(3) × SU(2), that can be realized through 4D non-Higgsable clusters. There are also more complicated configurations involving more than two gauge factors; in particular, the collection of gauge group factors with jointly charged matter can exhibit branchings, loops, and long linear chains. © 2015, The Author(s).


Rosenhaus V.,University of California at Santa Barbara | Smolkin M.,University of California at Berkeley
Journal of High Energy Physics | Year: 2015

Abstract: We continue the study of entanglement entropy for a QFT through a perturbative expansion of the path integral definition of the reduced density matrix. The universal entanglement entropy for a CFT perturbed by a relevant operator is calculated to second order in the coupling. We also explore the geometric dependence of entanglement entropy for a deformed planar entangling surface, finding surprises at second order. © 2015, The Author(s).


Shaghoulian E.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2015

Abstract: We propose a formalism for counting the microstates of a class of three-dimensional black holes which are not asymptotically AdS. The formalism rests on the invariance of a dual field theory under a generalized modular transformation and is extended to Rindler horizons by a singular limit. We also obtain logarithmic corrections. © 2015, The Author(s).


Suh S.,University of California at Santa Barbara | Yee S.,University of Minnesota
Chemosphere | Year: 2011

The rapid increase in human mobilization of phosphorus has raised concerns on both its supply security and its impact on the environment. Increasing the efficiency of phosphorus use is an approach to mitigate the adverse impacts associated with phosphorus consumption. This study estimates the life-cycle phosphorus use-efficiency of the US food system. A framework for accounting phosphorus stocks and flows is developed, and the account was populated with data. A map of phosphorus stocks and flows around the US food system is drawn and phosphorus use-efficiency was calculated. The results show that only 15% of the total phosphorus extracted from nature for the provision of food is eventually ingested by humans and the rest is lost to the environment. Major losses occur during the livestock, meat and dairy production and crop cultivation stage, where about 66% of the total phosphorus extracted is lost to the environment. The results also show that other losses of phosphorus including household food waste, mining waste, and fertilizer manufacturing waste are not negligible, which constitute about 19% of the total phosphorus extracted for food purpose. A data quality assessment and sensitivity analysis was performed to identify data quality hotspots and to envisage effective measures to improving phosphorus use-efficiency. Improving yields of livestock and crop cultivation without additional phosphorus input and reducing household food waste are shown to be effective measures to improve life-cycle phosphorus use-efficiency. The results highlight the need of a concerted effort by all entities along the life-cycle for efficient use of phosphorus. © 2011 Elsevier Ltd.


Giddings S.B.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2015

Abstract: If quantum gravity respects the principles of quantum mechanics, suitably generalized, it may be that a more viable approach to the theory is through identifying the relevant quantum structures rather than by quantizing classical spacetime. This viewpoint is supported by difficulties of such quantization, and by the apparent lack of a fundamental role for locality. In finite or discrete quantum systems, important structure is provided by tensor factorizations of the Hilbert space. However, even in local quantum field theory properties of the generic type III von Neumann algebras and of long range gauge fields indicate that factorization of the Hilbert space is problematic. Instead it is better to focus on the structure of the algebra of observables, and in particular on its subalgebras corresponding to regions. This paper suggests that study of analogous algebraic structure in gravity gives an important perspective on the nature of the quantum theory. Significant departures from the subalgebra structure of local quantum field theory are found, working in the correspondence limit of long-distances/low-energies. Particularly, there are obstacles to identifying commuting algebras of localized operators. In addition to suggesting important properties of the algebraic structure, this and related observations pose challenges to proposals of a fundamental role for entanglement. © 2015, The Author(s).


Mattinson J.M.,University of California at Santa Barbara
Elements | Year: 2013

U-Pb geochronology has its roots in a spectacular decade of discovery. Within about ten years of the discovery of radioactivity in 1896, old ideas about the nature of matter were overthrown and the seeds of geochronology were planted. After giants of physics like Ernest Rutherford moved on to other research, Arthur Holmes nurtured the new field of geochronology, combining physics, chemistry, and geology to produce the earliest quantitative geologic timescale. Over the following decades, geochronology experienced a series of revolutionary and evolutionary advances, and became a vital part of almost all fields of geology.


Horowitz G.T.,University of California at Santa Barbara
Classical and Quantum Gravity | Year: 2011

This article is intended to introduce gravitational physicists to recent developments in which general relativity is being used to describe certain aspects of condensed matter systems, e.g., superconductivity. © 2011 IOP Publishing Ltd.


Yee C.-H.,Rutgers University | Balents L.,University of California at Santa Barbara
Physical Review X | Year: 2015

Motivated by the commonplace observation of Mott insulators away from integer filling, we construct a simple thermodynamic argument for phase separation in first-order doping-driven Mott transitions. We show how to compute the critical dopings required to drive the Mott transition using electronic structure calculations for the titanate family of perovskites, finding good agreement with experiment. The theory predicts that the transition is percolative and should exhibit Coulomb frustration.


Vannozzi C.,University of California at Santa Barbara
Physics of Fluids | Year: 2012

Boundary integral simulations and scaling theory were employed to study the effects of insoluble surfactant surface diffusivity Ds and concentration Γon the coalescence process of two equal-sized viscous drops. The drops underwent head-on collisions in a biaxial extensional flow, in the Stokes flow limit and low capillary numbers. The simulations were compared with the drainage time experiments of Yoon et al. [Phys. Fluids19, 023102 (2007)10.1063/1.2409735] concerned with a polymeric system, polybutadiene (PBd) drops in a polydimethylsyloxane (PDMS) matrix, stabilized by block-copolymers acting as insoluble surfactants to explain the mechanism underneath their findings. An ad hoc equation of state, derived by mean field theory, specific for the block-copolymers in the experiments of Yoon et al. , able to match the experimental surface tension data without fitting parameters, was used. We were able to reproduce the experimental drainage time data, although an additional attractive force, besides the usual van der Waals interactions, had to be introduced for high block-copolymer concentrations, probably as a result of the entropic attraction between the two facing dry brushes formed in the thin film between the two drops. According to simulations, the puzzling experimental drainage time transition for low surfactant concentrations, from high drainage time to low drainage time as Ca increases, was a consequence of the oscillating behavior of the minimum film thickness, which takes place for Marangoni numbers Ma < 5 and surface Peclet number Pes > 60. In this regard, a master curve was obtained for the scaled relative minimum film thickness attained during the oscillation as a function of Ma. This enabled to determine both the minimum value of the dimensionless attractive forces to avoid coalescence for each concentration studied and the range of Ma that favors early coalescence. The coalescence process was found very sensitive to Pes and for Pes O(100-1000) even trace amounts of surfactants can be as effective stabilizers as high surfactant concentrations. Moreover, for the polymeric system of interest, the range of Ds in which the drainage time changes from the saturation value to the clean interface value was computed as a function of the surfactant concentration. In the specific, for the PDMS/PBd system of interest the Ds range studied was O(10-12-10-5 cm2 s-1). Additionally, our scaling analysis further validates our simulations, also highlighting the effect on the drainage process of the different parameters, in particular, of the external pushing force, which is increased compared to a clean interface system, as Pes is increased or as the surfactant concentration is increased, because of the reduction in the interfacial mobility of the drop. Finally, our study suggests that matching simulations with four-roll mill drainage time experiments can be an effective method to determine block-copolymer surface diffusivity. © 2012 American Institute of Physics.


Krechetnikov R.,University of California at Santa Barbara
Physics of Fluids | Year: 2012

This work presents an analytical study of the structure of steady Marangoni-driven singularities in the context of chemical-reaction driven tip-streaming, which identifies the conditions when such singularities are observable. As motivated by experimental observations of the conical symmetry of the problem, one can construct self-similar solutions of the Stokes equations, which are singular at the tip; these solutions, however, provide no information on the thread structure which is responsible for a resolution of the singularity via tip-streaming. The cone-tip singularity is resolved here with the help of asymptotic matching of the cone and thread solutions using slender jet approximation, which gives an explicit asymptotic formula for the thread radius and thus of the emitted droplets size as a function of physical parameters governing the problem. © 2012 American Institute of Physics.


Sawyer R.F.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Photon-photon interactions, as described with the standard Heisenberg-Euler interaction, can transform plane polarization of the CMB into circular polarization, in the period right after last scattering. We estimate the distribution of the resulting circular polarization parameters, as constrained by confining observations to very small angular regions of large plane polarization, and find results of the order of 10-9 for the Stokes parameter V in some of these regions. © 2015 American Physical Society.


Nakamura S.,University of California at Santa Barbara
Angewandte Chemie - International Edition | Year: 2015

In the 1980s, all known material systems possessing the necessary properties for blue-light emission had shortcomings, thus negating their utilization in efficient LEDs. Gallium nitride (GaN) was one possible candidate, though, at the time, no p-type or active layer could be created. These challenges were ultimately overcome by Shuji Nakamura, who describes the path to the first blue GaN LED in his Nobel Lecture. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lutchyn R.M.,Microsoft | Skrabacz J.H.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Inspired by a recent experimental observation of the zero-bias tunneling conductance in superconductor-semiconductor nanowire devices, we consider here transport properties of the junctions consisting of a nanowire (Luttinger liquid) coupled to a topological superconductor characterized by the presence of Majorana zero-energy end states. The presence of the Majorana modes leads to a quantization of the zero-bias tunneling conductance at zero temperature. In order to understand this phenomenon, we have developed a framework, based on real-time Keldysh technique, which allows one to compute tunneling conductance at finite temperature and voltage in a realistic experimental setup. Our approach allows one to understand this transport phenomenon from a more general perspective by including the effect of interactions in the nanowire, which sometimes results in a drastic departure from the noninteracting predictions. Thus, our results provide a key insight for the tunneling experiments aiming at detecting Majorana particles in one-dimensional nanowire devices. © 2013 American Physical Society.


Birnir B.,University of California at Santa Barbara
Journal of Nonlinear Science | Year: 2013

In 1941 Kolmogorov and Obukhov postulated the existence of a statistical theory of turbulence, which allows the computation of statistical quantities that can be simulated and measured in a turbulent system. These are quantities such as the moments, the structure functions and the probability density functions (PDFs) of the turbulent velocity field. In this paper we will outline how to construct this statistical theory from the stochastic Navier-Stokes equation. The additive noise in the stochastic Navier-Stokes equation is generic noise given by the central limit theorem and the large deviation principle. The multiplicative noise consists of jumps multiplying the velocity, modeling jumps in the velocity gradient. We first estimate the structure functions of turbulence and establish the Kolmogorov-Obukhov 1962 scaling hypothesis with the She-Leveque intermittency corrections. Then we compute the invariant measure of turbulence, writing the stochastic Navier-Stokes equation as an infinite-dimensional Ito process, and solving the linear Kolmogorov-Hopf functional differential equation for the invariant measure. Finally we project the invariant measure onto the PDF. The PDFs turn out to be the normalized inverse Gaussian (NIG) distributions of Barndorff-Nilsen, and compare well with PDFs from simulations and experiments. © 2013 Springer Science+Business Media New York.


BenTov Y.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2015

Abstract: I study the prospect of generating mass for symmetry-protected fermions without breaking the symmetry that forbids quadratic mass terms in the Lagrangian. I focus on 1+1 spacetime dimensions in the hope that this can provide guidance for interacting fermions in 3+1 dimensions. I first review the SO(8) Gross-Neveu model and emphasize a subtlety in the triality transformation. Then I focus on the “m = 0” manifold of the SO(7) Kitaev-Fidkowski model. I argue that this theory exhibits a phenomenon similar to “parity doubling” in hadronic physics, and this leads to the conclusion that the fermion propagator vanishes when pμ = 0. I also briefly explore a connection between this model and the two-channel, single-impurity Kondo effect. This paper may serve as an introduction to topological superconductors for high energy theorists, and perhaps as a taste of elementary particle physics for condensed matter theorists. © 2015, The Author(s).


Hubeny V.E.,Center for Particle Theory | Rangamani M.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2012

We propose a measure of holographic information based on a causal wedge construction. The motivation behind this comes from an attempt to understand how boundary field theories can holographically reconstruct spacetime. We argue that given the knowledge of the reduced density matrix in a spatial region of the boundary, one should be able to reconstruct at least the corresponding bulk causal wedge. In attempt to quantify the 'amount of information' contained in a given spatial region in field theory, we consider a particular bulk surface (specifically a co-dimension two surface in the bulk spacetime which is an extremal surface on the boundary of the bulk causal wedge), and propose that the area of this surface, measured in Planck units, naturally quantifies the information content. We therefore call this area the causal holographic information. We also contrast our ideas with earlier studies of holographic entanglement entropy. In particular, we establish that the causal holographic information, whilst not being a von Neumann entropy, curiously enough agrees with the entanglement entropy in all cases where one has a microscopic understanding of entanglement entropy. © 2012 SISSA.


Halverson J.,University of California at Santa Barbara | Taylor W.,Massachusetts Institute of Technology
Journal of High Energy Physics | Year: 2015

Abstract: We explore a large class of F-theory compactifications to four dimensions. We find evidence that gauge groups that cannot be Higgsed without breaking supersymmetry, often accompanied by associated matter fields, are a ubiquitous feature in the landscape of N=1$$ \mathcal{N}=1 $$ 4D F-theory constructions. In particular, we study 4D F-theory models that arise from compactification on threefold bases that are ℙ1$$ {\mathrm{\mathbb{P}}}^1 $$ bundles over certain toric surfaces. These bases are one natural analogue to the minimal models for base surfaces for 6D F-theory compactifications. Of the roughly 100,000 bases that we study, only 80 are weak Fano bases in which there are no automatic singularities on the associated elliptic Calabi-Yau fourfolds, and 98.3% of the bases have geometrically non-Higgsable gauge factors. The ℙ1$$ {\mathrm{\mathbb{P}}}^1 $$-bundle threefold bases we analyze contain a wide range of distinct surface topologies that support geometrically non-Higgsable clusters. Many of the bases that we consider contain SU(3) × SU(2) seven-brane clusters for generic values of deformation moduli; we analyze the relative frequency of this combination relative to the other four possible two-factor non-Higgsable product groups, as well as various other features such as geometrically non-Higgsable candidates for dark matter structure and phenomenological (SU(2)-charged) Higgs fields. © 2015, The Author(s).


Morrison D.R.,University of California at Santa Barbara | Park D.S.,Massachusetts Institute of Technology
Journal of High Energy Physics | Year: 2012

The Mordell-Weil group of an elliptically fibered Calabi-Yau threefold X contains information about the abelian sector of the six-dimensional theory obtained by compactifying F-theory on X. After examining features of the abelian anomaly coefficient matrix and U(1) charge quantization conditions of general F-theory vacua, we study Calabi- Yau threefolds with Mordell-Weil rank-one as a first step towards understanding the features of the Mordell-Weil group of threefolds in more detail. In particular, we generate an interesting class of F-theory models with U(1) gauge symmetry that have matter with both charges 1 and 2. The anomaly equations - which relate the Néron-Tate height of a section to intersection numbers between the section and fibral rational curves of the manifold - serve as an important tool in our analysis. © 2012 SISSA.


Mayfield M.M.,University of Queensland | Levine J.M.,University of California at Santa Barbara
Ecology Letters | Year: 2010

Though many processes are involved in determining which species coexist and assemble into communities, competition is among the best studied. One hypothesis about competition's contribution to community assembly is that more closely related species are less likely to coexist. Though empirical evidence for this hypothesis is mixed, it remains a common assumption in certain phylogenetic approaches for inferring the effects of environmental filtering and competitive exclusion. Here, we relate modern coexistence theory to phylogenetic community assembly approaches to refine expectations for how species relatedness influences the outcome of competition. We argue that two types of species differences determine competitive exclusion with opposing effects on relatedness patterns. Importantly, this means that competition can sometimes eliminate more different and less related taxa, even when the traits underlying the relevant species differences are phylogenetically conserved. Our argument leads to a reinterpretation of the assembly processes inferred from community phylogenetic structure. © 2010 Blackwell Publishing Ltd/CNRS.


Heemskerk I.,University of California at Santa Barbara
Journal of High Energy Physics | Year: 2012

We extend the construction of field operators in AdS as smeared single trace operators in the boundary CFT to gauge fields and gravity. Bulk field operators in a fixed gauge can be thought of as non-local gauge invariant observables. Non-local commutators result from the Gauss law constraint, which for gravity implies a perturbative notion of holography. We work out these commutators in a generalized Coulomb gauge and obtain leading order smearing functions in radial gauge. © SISSA 2012.


Jacobs G.H.,University of California at Santa Barbara
Advances in Experimental Medicine and Biology | Year: 2012

Color vision is conventionally defined as the ability of animals to reliably discriminate among objects and lights based solely on differences in their spectral properties. Although the nature of color vision varies widely in different animals, a large majority of all vertebrate species possess some color vision and that fact attests to the adaptive importance this capacity holds as a tool for analyzing the environment. In recent years dramatic advances have been made in our understanding of the nature of vertebrate color vision and of the evolution of the biological mechanisms underlying this capacity. In this chapter I review and comment on these advances. © 2012 Landes Bioscience and Springer Science+Business Media.


Kramer E.M.,Harvard University | Hodges S.A.,University of California at Santa Barbara
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2010

The ranunculid genus Aquilegia holds extraordinary promise as a model system for investigating a wide range of questions relating to the evolution and ecology of petals. New genetic and genomic resources, including an extensive EST database, BAC libraries and physical maps, as well as virus-induced gene silencing are facilitating this research on multiple fronts. At the developmental genetic level, Aquilegia has been important for elucidating the developmental programme for specifying petals and petaloid characteristics. Data suggest that duplication events among the petal and stamen identity genes have resulted in sub- and neofunctionalization. This expansion of gene function does not include the petaloidy of Aquilegia sepals, however, which does not depend on the same loci that control identity of the second whorl petals. Of special interest is the elaboration of the petal into a nectar spur, a major innovation for the genus. Intra- and interspecific variation in the shape and colour of petals, especially the spurs, has been shown to be adaptative for different pollinators. Thus, understanding the genetic basis of these traits will help us connect the ecological interactions driving speciation with the genetic changes responsible for remodelling morphology. Progress in this area has focused on the multiple, parallel transitions in flower colour and nectar spur length across the genus. For flower colour, upstream transcription factors appear to be primarily targets of natural selection. Thus research in Aquilegia spans the initial evolution of petals and petaloidy to the diversification of petal morphology to the ecological basis of petal form, thereby providing a comprehensive picture of the evolutionary biology of this critical angiosperm feature. © 2010 The Royal Society.


Kilpatrick A.M.,University of California at Santa Cruz | Briggs C.J.,University of California at Santa Barbara | Daszak P.,Wildlife Trust
Trends in Ecology and Evolution | Year: 2010

Emerging infectious diseases are increasingly recognized as key threats to wildlife. Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, has been implicated in widespread amphibian declines and is currently the largest infectious disease threat to biodiversity. Here, we review the causes of Bd emergence, its impact on amphibian populations and the ecology of Bd transmission. We describe studies to answer outstanding issues, including the origin of the pathogen, the effect of Bd relative to other causes of population declines, the modes of Bd dispersal, and factors influencing the intensity of its transmission. Chytridiomycosis is an archetypal emerging disease, with a broad host range and significant impacts on host populations and, as such, poses a crucial challenge for wildlife managers and an urgent conservation concern. © 2009 Elsevier Ltd. All rights reserved.


Potter A.C.,University of California at Berkeley | Vasseur R.,University of California at Berkeley | Vasseur R.,Lawrence Berkeley National Laboratory | Parameswaran S.A.,University of California at Irvine | Parameswaran S.A.,University of California at Santa Barbara
Physical Review X | Year: 2015

We study the dynamical melting of "hot" one-dimensional many-body localized systems. As disorder is weakened below a critical value, these nonthermal quantum glasses melt via a continuous dynamical phase transition into classical thermal liquids. By accounting for collective resonant tunneling processes, we derive and numerically solve an effective model for such quantum-to-classical transitions and compute their universal critical properties. Notably, the classical thermal liquid exhibits a broad regime of anomalously slow subdiffusive equilibration dynamics and energy transport. The subdiffusive regime is characterized by a continuously evolving dynamical critical exponent that diverges with a universal power at the transition. Our approach elucidates the universal long-distance, low-energy scaling structure of many-body delocalization transitions in one dimension, in a way that is transparently connected to the underlying microscopic physics. We discuss experimentally testable signatures of the predicted scaling properties.


Bookhagen B.,University of California at Santa Barbara | Strecker M.R.,University of Potsdam
Earth and Planetary Science Letters | Year: 2012

The tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern Central Andes of northwestern Argentina cause strong contrasts in elevation, rainfall, and surface-process regimes. The climatic gradient in this region ranges from the wet, windward eastern flanks (~2m/yr rainfall) to progressively drier western basins and ranges (~0.1m/yr) bordering the arid Altiplano-Puna Plateau. In this study, we analyze the impact of spatiotemporal climatic gradients on surface erosion: First, we present 41 new catchment-mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns. Second, we re-evaluate paleoclimatic records from the Calchaquíes basin (66°W, 26°S), a large intermontane basin bordered by high (>4.5km) mountain ranges, to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late Pleistocene and Holocene. Three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time: (1) First-order spatial patterns of erosion rates can be explained by a simple specific stream power (SSP) approach. We explicitly account for discharge by routing high-resolution, satellite derived rainfall. This is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge. This relation indicates that erosion rates (ER) scale with ER~SSP 1.4 on cosmogenic-nuclide time scales. (2) We identify an intrinsic channel-slope behavior in different climatic compartments. Channel slopes in dry areas (<0.25m/yr rainfall) are slightly steeper than in wet areas (>0.75m/yr) with equal drainage areas, thus compensating lower amounts of discharge with steeper slopes. (3) Erosion rates can vary by an order of magnitude between presently dry (~0.05mm/yr) and well-defined late Pleistocene humid (~0.5mm/yr) conditions within an intermontane basin. Overall, we document a strong climatic impact on erosion rates and channel slopes. We suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport, which is primarily responsible for maintaining the balance between surface uplift, erosion, sediment routing and transient storage in the orogen. © 2012 Elsevier B.V..


Nakamura S.,University of California at Santa Barbara
Annalen der Physik | Year: 2015

Shuji Nakamura discovered p-type doping in Gallium Nitride (GaN) and developed blue, green, and white InGaN based light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid-state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize in Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions. © 2015 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Kleinermanns K.,Heinrich Heine University Dusseldorf | Nachtigallova D.,Czech Institute of Organic Chemistry And Biochemistry | de Vries M.S.,University of California at Santa Barbara
International Reviews in Physical Chemistry | Year: 2013

Biochemical reactions are subject to the particular environmental conditions of planet earth, including solar irradiation. How DNA responds to radiation is relevant to human health because radiation damage can affect genetic propagation and lead to cancer and is also important for our understanding of how life on earth developed. A reductionist approach to unravelling the detailed photochemistry seeks to establish intrinsic properties of individual DNA building blocks, followed by extrapolation to larger systems, to incorporate interactions between the building blocks and the role of the biomolecular environment. Advances in both experimental and computational techniques have lead to increasingly detailed insights in the excited state dynamics of DNA bases in isolation as well as the role of the solvent and intermolecular interactions. This review seeks to summarise current findings and understanding. © 2013 Copyright Taylor and Francis Group, LLC.


Hacker B.R.,University of California at Santa Barbara | Abers G.A.,Lamont Doherty Earth Observatory
Journal of Geophysical Research: Solid Earth | Year: 2012

The growing capability to measure seismic velocities in subduction zones has led to an unusual observation: VP/VS ratios as low as 1.65 with VS ∼ ∼ 4.7 km/s in the mantle wedge of some subduction zones. This is difficult to explain because most minerals have V P/VS ratios >1.75, and some of the likely alteration phases in mantle rocks, like antigorite, phlogopite, clinohumite and chlorite have isotropic high VP/VS ratios. It is possible that these measurements are biased by anisotropy in rock fabric or by the raypaths through these regions, leading to relatively high VS estimates and/or relatively low VP estimates compared with isotropic averages. Strong anisotropy has been documented in several mantle wedges, but its effect on velocity estimates are typically ignored. Anisotropic peridotites may produce the observed VP/VS ratios if olivine [100] axes are perpendicular rather than parallel to raypaths, consistent with typical seismic sampling geometries and with fabric predictions for wedge corner flow. Hence, low VP/VS ratios may be an indicator of strong anisotropy, rather than unusual composition, and may provide a useful additional constraint on orientation and strength of the rock fabric. © 2012. American Geophysical Union. All Rights Reserved.


Soto F.A.,University of California at Santa Barbara | Wasserman E.A.,University of Iowa
Frontiers in Neural Circuits | Year: 2014

Behavioral studies of object recognition in pigeons have been conducted for 50 years, yielding a large body of data. Recent work has been directed toward synthesizing this evidence and understanding the visual, associative, and cognitive mechanisms that are involved. The outcome is that pigeons are likely to be the non-primate species for which the computational mechanisms of object recognition are best understood. Here, we review this research and suggest that a core set of mechanisms for object recognition might be present in all vertebrates, including pigeons and people, making pigeons an excellent candidate model to study the neural mechanisms of object recognition. Behavioral and computational evidence suggests that error-driven learning participates in object category learning by pigeons and people, and recent neuroscientific research suggests that the basal ganglia, which are homologous in these species, may implement error-driven learning of stimulus-response associations. Furthermore, learning of abstract category representations can be observed in pigeons and other vertebrates. Finally, there is evidence that feed forward visual processing, a central mechanism in models of object recognition in the primate ventral stream, plays a role in object recognition by pigeons. We also highlight differences between pigeons and people in object recognition abilities, and propose candidate adaptive specializations which may explain them, such as holistic face processing and rule-based category learning in primates. From a modern comparative perspective, such specializations are to be expected regardless of the model species under study. The fact that we have a good idea of which aspects of object recognition differ in people and pigeons should be seen as an advantage over other animal models. From this perspective, we suggest that there is much to learn about human object recognition from studying the “simple” brains of pigeons. © 2014 Soto and Wasserman.


Proulx S.R.,University of California at Santa Barbara
Theoretical Population Biology | Year: 2011

Several groups have recently modeled evolutionary transitions from an ancestral allele to a beneficial allele separated by one or more intervening mutants. The beneficial allele can become fixed if a succession of intermediate mutants are fixed or alternatively if successive mutants arise while the previous intermediate mutant is still segregating. This latter process has been termed stochastic tunneling. Previous work has focused on the Moran model of population genetics. I use elementary methods of analyzing stochastic processes to derive the probability of tunneling in the limit of large population size for both Moran and Wright-Fisher populations. I also show how to efficiently obtain numerical results for finite populations. These results show that the probability of stochastic tunneling is twice as large under the Wright-Fisher model as it is under the Moran model. © 2011 Elsevier Inc.


Kaz D.M.,Harvard University | McGorty R.,Harvard University | Mani M.,Harvard University | Brenner M.P.,Harvard University | And 2 more authors.
Nature Materials | Year: 2012

Young's law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This has been used to explain why colloids often bind to liquid interfaces, and has been exploited in emulsification, water purification, mineral recovery, encapsulation and the making of nanostructured materials. However, little is known about the dynamics of binding. Here we show that the adsorption of polystyrene microspheres to a water/oil interface is characterized by a sudden breach and an unexpectedly slow relaxation. The relaxation appears logarithmic in time, indicating that complete equilibration may take months. Surprisingly, viscous dissipation appears to play little role. Instead, the observed dynamics, which bear strong resemblance to ageing in glassy systems, agree well with a model describing activated hopping of the contact line over nanoscale surface heterogeneities. These results may provide clues to longstanding questions on colloidal interactions at an interface. © 2012 Macmillan Publishers Limited. All rights reserved.


Jaeggi A.V.,University of California at Santa Barbara
Proceedings. Biological sciences / The Royal Society | Year: 2013

Helping, i.e. behaviour increasing the fitness of others, can evolve when directed towards kin or reciprocating partners. These predictions have been tested in the context of food sharing both in human foragers and non-human primates. Here, we performed quantitative meta-analyses on 32 independent study populations to (i) test for overall effects of reciprocity on food sharing while controlling for alternative explanations, methodological biases, publication bias and phylogeny and (ii) compare the relative effects of reciprocity, kinship and tolerated scrounging, i.e. sharing owing to costs imposed by others. We found a significant overall weighted effect size for reciprocity of r = 0.20-0.48 for the most and least conservative measure, respectively. Effect sizes did not differ between humans and other primates, although there were species differences in in-kind reciprocity and trade. The relative effect of reciprocity in sharing was similar to those of kinship and tolerated scrounging. These results indicate a significant independent contribution of reciprocity to human and primate helping behaviour. Furthermore, similar effect sizes in humans and primates speak against cognitive constraints on reciprocity. This study is the first to use meta-analyses to quantify these effects on human helping and to directly compare humans and other primates.


Minkler S.R.K.,TU Dortmund | Lipshutz B.H.,University of California at Santa Barbara | Krause N.,TU Dortmund
Angewandte Chemie - International Edition | Year: 2011

Micelles to the rescue: Two amphiphiles are shown to afford air-stable aqueous gold catalyst solutions with excellent reactivity and recyclability. Various α-functionalized allenes can be cycloisomerized smoothly and efficiently with this system at room temperature. Addition of NaCl to the reaction mixture affords larger micelles and induces faster reactions. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wan Z.,University of California at Santa Barbara
Remote Sensing of Environment | Year: 2014

According to the radiance-based (R-based) validation of the collection-5 or version-5 (C5 or V5) Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) land-surface temperature (LST) level-2 products at 42 sites in a wide LST range in different seasons and years, the LST errors are within ±. 2. K (within ±. 1. K in most cases) for all the sites but six bare soil sites. The V5 LSTs are underestimated by more than 2. K and up to 4.5. K at the desert site near In-salah, Algeria. Three refinements were implemented in the V6.3.0 daily LST Product Generation Executive (PGE)16 code: 1) refine the original viewing angle dependent split-window algorithm by adding two sets of coefficients separately for retrieval of daytime and nighttime LSTs at bare soil pixels in the hot and warm bare soil zone (HAWBSZ) within latitude range from 38° to 49.5°, 2) adjust the emissivity difference in bands 31 and 32 for bare soil pixels in HAWBSZ, and 3) incorporate the new refined split-window algorithm into the day/night algorithm for retrieving surface emissivity and temperature values at 6. km grids in HAWBSZ. The V6.3.0 PGE16 code was tested with C6 Aqua and Terra MODIS input data over a period of one year or longer in selected tile regions. The resulting C6 level-2 LST products were evaluated at five bare soil sites in north Africa, where radiosonde observation data for atmospheric temperature and water vapor profiles are available, with 12 R-based validation data sets as follows: the mean LST error is within ±. 0.6. K in 10 validate data sets, 0.8. K in one data set (for daytime LSTs at SVU site) and 1.9. K in another set (for daytime LSTs at Farafra site). The standard deviation of the C6 LST validation errors is less than 0.5. K in all the 12 validation data sets but the data set for daytime LSTs at Farafra site at 0.7. K. Statistical and viewing angle dependence analyses of the retrieved surface emissivity values also indicate that the C6 level-3 LST products are much better than the previous C4.1 and C5 products. © 2013 Elsevier Inc.


Nakamura S.,University of California at Santa Barbara | Krames M.R.,Soraa Inc
Proceedings of the IEEE | Year: 2013

The history of development for gallium-nitride-based light-emitting diodes (LEDs) is reviewed. We identify two broad developments in GaN-based LED technology: first, the key breakthroughs that enabled the development of GaN-based devices on foreign substrates like sapphire (first-generation LEDs), and, second, a new wave of devices benefiting from developments in GaN substrate manufacturing, which has led to native bulk-GaN-based LEDs with unprecedented performance characteristics that portend a disruptive shift in LED output power density and the corresponding cost of generating light. © 1963-2012 IEEE.


Burkov A.A.,University of Waterloo | Hook M.D.,University of Waterloo | Balents L.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present a study of "nodal-semimetal" phases in which nondegenerate conduction and valence bands touch at points (the "Weyl semimetal") or lines (the "line-node semimetal") in three-dimensional momentum space. We discuss a general approach to such states by perturbation of the critical point between a normal insulator (NI) and a topological insulator (TI), breaking either time-reversal (TR) or inversion symmetry. We give an explicit model realization of both types of states in a NI-TI superlattice structure with broken TR symmetry. Both the Weyl and the line-node semimetals are characterized by topologically protected surface states, although in the line-node case, some additional symmetries must be imposed to retain this topological protection. The edge states have the form of "Fermi arcs" in the case of the Weyl semimetal: these are chiral gapless edge states, which exist in a finite region in momentum space, determined by the momentum-space separation of the bulk Weyl nodes. The chiral character of the edge states leads to a finite Hall conductivity. In contrast, the edge states of the line-node semimetal are "flat bands": these states are approximately dispersionless in a subset of the two-dimensional edge Brillouin zone, given by the projection of the line node onto the plane of the edge. We discuss unusual transport properties of the nodal semimetals and, in particular, point out quantum critical-like scaling of the dc and optical conductivities of the Weyl semimetal and similarities to the conductivity of graphene in the line-node case. © 2011 American Physical Society.


Slater P.B.,University of California at Santa Barbara
Journal of Physics A: Mathematical and Theoretical | Year: 2013

We report major advances in the research program initiated in 'Moment-based evidence for simple rational-valued Hilbert-Schmidt generic 2 × 2 separability probabilities' (Slater and Dunkl 2012 J. Phys. A: Math. Theor. 45 095305). A highly succinct separability probability function P(α) is put forth, yielding for generic (nine-dimensional) two-rebit systems, , (15-dimensional) two-qubit systems, and (27-dimensional) two-quater(nionic)bit systems, . This particular form of P(α) was obtained by Qing-Hu Hou by applying Zeilberger's algorithm ('creative telescoping') to a fully equivalent - but considerably more complicated - expression containing six 7F6 hypergeometric functions (all with argument ). That hypergeometric form itself had been obtained using systematic, high-accuracy probability-distribution-reconstruction computations. These employed 7501 determinantal moments of partially transposed 4 × 4 density matrices, parameterized by . From these computations, exact rational-valued separability probabilities were discernible. The (integral/half-integral) sequences of 32 rational values then served as input to the Mathematica FindSequenceFunction command, from which the initially obtained hypergeometric form of P(α) emerged. © 2013 IOP Publishing Ltd.


Hormoz S.,University of California at Santa Barbara
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

A heat engine undergoes a cyclic operation while in equilibrium with the net result of conversion of heat into work. Quantum effects such as superposition of states can improve an engine's efficiency by breaking detailed balance, but this improvement comes at a cost due to excess entropy generated from collapse of superpositions on measurement. We quantify these competing facets for a quantum ratchet composed of an ensemble of pairs of interacting two-level atoms. We suggest that the measurement postulate of quantum mechanics is intricately connected to the second law of thermodynamics. More precisely, if quantum collapse is not inherently random, then the second law of thermodynamics can be violated. Our results challenge the conventional approach of simply quantifying quantum correlations as a thermodynamic work deficit. © 2013 American Physical Society.


Currie J.,Princeton University | Rossin-Slater M.,University of California at Santa Barbara
Journal of Policy Analysis and Management | Year: 2015

Mounting evidence across different disciplines suggests that early-life conditions can have consequences on individual outcomes throughout the life cycle. Relative to other developed countries, the United States fares poorly on standard indicators of early-life health, and this disadvantage may have profound consequences not only for population well-being, but also for economic growth and competitiveness in a global economy. In this paper, we first discuss the research on the strength of the link between early-life health and adult outcomes, and then provide an evidence-based review of the effectiveness of existing U.S. policies targeting the early-life environment. We conclude that there is a robust and economically meaningful relationship between early-life conditions and well-being throughout the life cycle, as measured by adult health, educational attainment, labor market attachment, and other indicators of socioeconomic status. However, there is some variation in the degree to which current policies in the United States are effective in improving early-life conditions. Among existing programs, some of the most effective are the Special Supplemental Program for Women, Infants, and Children (WIC), home visiting with nurse practitioners, and high-quality, center-based early-childhood care and education. In contrast, the evidence on other policies such as prenatal care and family leave is more mixed and limited. © 2014 by the Association for Public Policy Analysis and Management.


Teel A.R.,University of California at Santa Barbara
Proceedings of the American Control Conference | Year: 2014

For a class of stochastic hybrid systems, we characterize the sets to which bounded solutions converge. We show that each sample path converges to a weakly totally recurrent in probability set. This characterization is often tighter than the usual assertion that a solution converges to a weakly invariant set. Consequently, the results here can be viewed as a generalization of the invariance principle, to a broad class of stochastic hybrid systems that admit non-unique solutions. © 2014 American Automatic Control Council.


Jeong K.C.,University of Florida | Sexton J.A.,University of California at Santa Barbara | Vogel J.P.,University of Washington
PLoS Pathogens | Year: 2015

Modulation of host cell function is vital for intracellular pathogens to survive and replicate within host cells. Most commonly, these pathogens utilize specialized secretion systems to inject substrates (also called effector proteins) that function as toxins within host cells. Since it would be detrimental for an intracellular pathogen to immediately kill its host cell, it is essential that secreted toxins be inactivated or degraded after they have served their purpose. The pathogen Legionella pneumophila represents an ideal system to study interactions between toxins as it survives within host cells for approximately a day and its Dot/Icm type IVB secretion system (T4SS) injects a vast number of toxins. Previously we reported that the Dot/Icm substrates SidE, SdeA, SdeB, and SdeC (known as the SidE family of effectors) are secreted into host cells, where they localize to the cytoplasmic face of the Legionella containing vacuole (LCV) in the early stages of infection. SidJ, another effector that is unrelated to the SidE family, is also encoded in the sdeC-sdeA locus. Interestingly, while over-expression of SidE family proteins in a wild type Legionella strain has no effect, we found that their over-expression in a ∆sidJ mutant completely inhibits intracellular growth of the strain. In addition, we found expression of SidE proteins is toxic in both yeast and mammalian HEK293 cells, but this toxicity can be suppressed by co-expression of SidJ, suggesting that SidJ may modulate the function of SidE family proteins. Finally, we were able to demonstrate both in vivo and in vitro that SidJ acts on SidE proteins to mediate their disappearance from the LCV, thereby preventing lethal intoxication of host cells. Based on these findings, we propose that SidJ acts as a metaeffector to control the activity of other Legionella effectors. © 2015 Jeong et al.


Donnelly W.,University of California at Santa Barbara | Wall A.C.,Institute for Advanced Study
Physical Review Letters | Year: 2015

The vacuum entanglement entropy of Maxwell theory, when evaluated by standard methods, contains an unexpected term with no known statistical interpretation. We resolve this two-decades old puzzle by showing that this term is the entanglement entropy of edge modes: classical solutions determined by the electric field normal to the entangling surface. We explain how the heat kernel regularization applied to this term leads to the negative divergent expression found by Kabat. This calculation also resolves a recent puzzle concerning the logarithmic divergences of gauge fields in 3+1 dimensions. © 2015 American Physical Society.


Marolf D.,University of California at Santa Barbara
Physical Review Letters | Year: 2015

This Letter refines arguments forbidding nonlinear dynamical gravity from appearing in the low energy effective description of field theories with local kinematics, even for those with instantaneous long-range interactions. Specifically, we note that gravitational theories with universal coupling to energy - an intrinsically nonlinear phenomenon - are characterized by Hamiltonians that are pure boundary terms on shell. In order for this to be the low energy effective description of a field theory with local kinematics, all bulk dynamics must be frozen and, thus, irrelevant to the construction. The result applies to theories defined either on a lattice or in the continuum, and requires neither Lorentz invariance nor translation invariance. © 2015 American Physical Society.


Langer J.S.,University of California at Santa Barbara
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

Numerical simulations by Tanaka and co-workers indicate that glass-forming systems of moderately polydisperse hard-core particles, in both two and three dimensions, exhibit diverging correlation lengths. These correlations are described by Ising-like critical exponents, and are associated with diverging, Vogel-Fulcher-Tamann, structural relaxation times. Related simulations of thermalized hard disks indicate that the curves of pressure versus packing fraction for different polydispersities exhibit a sequence of transition points, starting with a liquid-hexatic transition for the monodisperse case, and crossing over with increasing polydispersity to glassy, Ising-like critical points. I propose to explain these observations by assuming that glass-forming fluids contain twofold degenerate, locally ordered clusters of particles, similar to the two-state systems that have been invoked to explain other glassy phenomena. This paper starts with a brief statistical derivation of the thermodynamics of thermalized, hard-core particles. It then discusses how a two-state, Ising-like model can be described within that framework in terms of a small number of statistically relevant, internal state variables. The resulting theory agrees accurately with the simulation data. I also propose a rationale for the observed relation between the Ising-like correlation lengths and the Vogel-Fulcher-Tamann formula. © 2013 American Physical Society.


Mordecai E.A.,University of California at Santa Barbara
Ecological Monographs | Year: 2011

Pathogens, like other consumers, mediate the outcome of competitive interactions between their host species. Ongoing efforts to integrate pathogens into plant community ecology could be accelerated by greater conceptual unification. Research on plant pathogens has mainly focused on a variety of disparate mechanisms-the Janzen-Connell hypothesis, plant-soil feedbacks, competition-defense trade-offs, escape of invasive plants from their enemies, and epidemic-driven community shifts-with limited recognition of how these mechanisms fit into the broader context of plant coexistence. Here, I extend an emerging theoretical framework for understanding species coexistence to include various pathogen impacts on plant communities. Pathogens can promote coexistence by regulating relative abundance or by reducing the disparities between species in fitness that make coexistence more difficult. Conversely, pathogens may undermine coexistence by creating positive feedbacks or by increasing between-species fitness differences. I review the evidence for these pathogenmediated mechanisms, and I reframe the major hypotheses in a community ecology context in order to understand how the mechanisms are related. This approach generates predictions about how various modes of pathogen attack affect plant coexistence, even when direct impacts on host relative abundance are difficult to measure. Surprisingly, no study gives direct empirical evidence for pathogen effects on mutual invasibility, a key criterion for coexistence. Future studies should investigate the relationship between pathogen attack and host relative abundance, in order to distinguish between mechanisms. © 2011 by the Ecological Society of America.


Gerig J.T.,University of California at Santa Barbara
Journal of Physical Chemistry B | Year: 2014

Various computational models of trifluoroethanol (TFE) and water have been explored with the goal of finding a system for molecular dynamics (MD) simulations that reliably predict properties of 40% TFE-water (v/v) and can be used in studies of peptide-solvent nuclear cross-relaxation. Models derived by modification of TFE parameters developed by Fioroni et al. (J. Phys. Chem. B 2000, 104, 12347), in combination with either TIP4P-Ew or TIP5P-E water, were most successful. Simulations of 40% TFE-TIP4P-Ew water evidenced separation of the system into large TFE-rich and water-rich domains. With TIP5P-E water, simulations showed aggregation of each solvent component into small clusters. Nuclear spin dipolar interactions between solvent fluorines and the methyl hydrogens of acetate ion dissolved in 40% TFE-water were calculated. The cross-relaxation parameter σHF reckoned for the TFE-TIP5P-E system agreed with experiment while the value calculated using the TFE-TIP4P-Ew system was too low. While the TFE-TIP5P-E model of 40% TFE-water leads to good predictions of the system density, translational diffusion coefficients, and a solvent-solute cross-relaxation parameter, this model performs poorly in predicting the enthalpy of mixing. Preliminary studies of 20% TFE-water and 50% TFE-water suggest that the model will perform with the same characteristics for mixtures that have compositions near 40% TFE-water. © 2014 American Chemical Society.


Starr A.,University of California at Santa Barbara
Cultural Studies - Critical Methodologies | Year: 2010

This article analyzes the development of "local food" institutions from a social movements perspective. Over the last decade, institutions that "shorten the links" between producer and consumer have developed through a diverse collaboration of many social sectors (farmers, agronomic experts, retailers, chefs, food writers, and several distinct consumer sectors). Some agronomists and rural sociologists critical of the globalization and industrialization of agriculture have recognized this development as heralding Polanyian "reembedding" of market exchanges in social relations. This article analyzes whether and how local food is a social movement, using new social movement theory as an analytic framework. © 2010 Sage Publications.


Clarke K.C.,University of California at Santa Barbara
Professional Geographer | Year: 2011

Understanding the Changing Planet lacks the spark of wonder and synthesis that initially attracted me into geography. Its structure around compelling questions reflects disciplinary fragmentation and the model of interdisciplinary science favored in the late twentieth century. It is suggested that geography can move beyond the "big tent with three poles" approach, to a twenty-first-century hyper disciplinary model where content, science, analysis, and synthesis blur and a new bottom-up science can emerge. In this science, new theory and even grand unified theory might be possible. As discussed in Understanding the Changing Planet, the Web and the emergence of volunteered geographic information are examples. This would make study of the whole earth and its systems "a respectable object for scholarly efforts." © Copyright 2011 by Association of American Geographers.


Carter Ohlmann J.,University of California at Santa Barbara
Oceanography | Year: 2011

This article presents observations of near-surface current trajectories made with water-following drifters in the Philippine Archipelago. The data describe small-scale flows around obstacles and provide some snapshots of regional currents that both add insight into conceptual views of circulation on a variety of scales. The most interesting tracks are those collected in San Bernardino Strait, where the interaction of energetic tidal flows with small islands, seamounts, and headlands give rise to flows with vorticity and strain rate that can exceed 100f on scales < 1 km. The observations show some of the high Rossby number flows that challenge regional circulation models. Much of the data inform subgridscale motions that models must presently parameterize. © 2011 by The Oceanography Society.


Tavakolifard M.,Norwegian University of Science and Technology | Almeroth K.C.,University of California at Santa Barbara
IEEE Network | Year: 2012

Computational applications now go beyond personal computing, facilitating collaboration and social interactions. Social computing is an area of information technology concerned with the intersection of human and social studies connected by computer networks. The primary goal of this article is to provide a brief survey of three popular social computing services: recommender systems, trust/reputation systems, and social networks. We approach these services from a data representation perspective and discuss two of their main challenges: network sparsity and coldstart problems. We also present a novel graph model, which provides an abstract taxonomy and a common data representation model for the three services. We are mainly motivated by the power of graph theory in data representation and analysis for social computing services. Through this model, we believe that it becomes clearer that data from different contexts can be related such that new solutions can be explored; thus, it may provide illumination for the aforementioned problems and stimulate new research. © 2012 IEEE.


Padilla-Gamino J.L.,University of California at Santa Barbara
Proceedings. Biological sciences / The Royal Society | Year: 2013

Ocean warming and ocean acidification, both consequences of anthropogenic production of CO2, will combine to influence the physiological performance of many species in the marine environment. In this study, we used an integrative approach to forecast the impact of future ocean conditions on larval purple sea urchins (Strongylocentrotus purpuratus) from the northeast Pacific Ocean. In laboratory experiments that simulated ocean warming and ocean acidification, we examined larval development, skeletal growth, metabolism and patterns of gene expression using an orthogonal comparison of two temperature (13°C and 18°C) and pCO2 (400 and 1100 μatm) conditions. Simultaneous exposure to increased temperature and pCO2 significantly reduced larval metabolism and triggered a widespread downregulation of histone encoding genes. pCO2 but not temperature impaired skeletal growth and reduced the expression of a major spicule matrix protein, suggesting that skeletal growth will not be further inhibited by ocean warming. Importantly, shifts in skeletal growth were not associated with developmental delay. Collectively, our results indicate that global change variables will have additive effects that exceed thresholds for optimized physiological performance in this keystone marine species.


Sun K.,University of Maryland University College | Gu Z.,University of California at Santa Barbara | Katsura H.,Gakushuin University | Das Sarma S.,University of Maryland University College
Physical Review Letters | Year: 2011

We report the theoretical discovery of a class of 2D tight-binding models containing nearly flatbands with nonzero Chern numbers. In contrast with previous studies, where nonlocal hoppings are usually required, the Hamiltonians of our models only require short-range hopping and have the potential to be realized in cold atomic gases. Because of the similarity with 2D continuum Landau levels, these topologically nontrivial nearly flatbands may lead to the realization of fractional anomalous quantum Hall states and fractional topological insulators in real materials. Among the models we discover, the most interesting and practical one is a square-lattice three-band model which has only nearest-neighbor hopping. To understand better the physics underlying the topological flatband aspects, we also present the studies of a minimal two-band model on the checkerboard lattice. © 2011 American Physical Society.


Vannozzi C.,University of California at Santa Barbara
Journal of Fluid Mechanics | Year: 2012

Head-on collisions of two equal-sized viscous drops in a biaxial extensional flow were simulated using the boundary integral method in the Stokes flow limit, for capillary numbers of the order of 10 -4-10 -1, typical of flow-induced coalescence experiments. At a certain point in time, during the drainage process, the flow was abruptly stopped and the time-dependent dynamics of drop deformation (relaxation) was followed to discern whether the pair of drops would eventually coalesce. The concept of coalescence probability was used to study the evolution of probable collisions. The polymeric system of polybutadiene (PBd) drops undergoing head-on collisions in a polydimethylsiloxane (PDMS) matrix, previously well-characterized both experimentally and numerically by Yoon et al. (Phys. Fluid, vol. 19, 2007, 102102), in which both fluids were Newtonian under the experimental conditions, was used as our reference. Film shapes, velocity profiles and pressure distributions were studied for initially parabolic or dimpled thin film shapes. It was shown that micrometre-sized drops undergoing relaxation can coalesce in the capillary number range studied, which also included cases of hindered coalescence and cases in which the flow interaction time for the collision was smaller than the drainage time; thus, this phenomenon could influence the final drop size distribution of blends. Further, these findings could be of interest in interpreting stop-strain experiments, in the case of a sudden change in flow conditions and in population balance studies of drops in blends. © 2012 Cambridge University Press.


Turner T.L.,University of California at Santa Barbara | Hahn M.W.,Indiana University Bloomington
Molecular Ecology | Year: 2010

Populations of the malaria mosquito, Anopheles gambiae, are comprised of at least two reproductively isolated, sympatric populations. In this issue, White et al. (2010) use extensive sampling, high-density tiling microarrays, and an updated reference genome to clarify and expand our knowledge of genomic differentiation between these populations. It is now clear that DNA near the centromeres of all three chromosomes are in near-perfect disequilibrium with each other. This is in stark contrast to the remaining 97% of the assembled genome, where fixed differences between populations have not been found, and many polymorphisms are shared. This pattern, coupled with direct evidence of hybridization in nature, supports models of "mosaic" speciation, where ongoing hybridization homogenizes variation in most of the genome while loci under strong selection remain in disequilibrium with each other. However, unambiguously demonstrating that selection maintains the association of these pericentric "speciation islands" in the face of gene flow is difficult. Low recombination at all three loci complicates the issue, and increases the probability that selection unrelated to the speciation process alters patterns of variation in these loci. Here, we discuss these different scenarios in light of this new data. © 2010 Blackwell Publishing Ltd.


Qi X.-L.,University of California at Santa Barbara | Qi X.-L.,Stanford University | Zhang S.-C.,Stanford University
Reviews of Modern Physics | Year: 2011

Topological insulators are new states of quantum matter which cannot be adiabatically connected to conventional insulators and semiconductors. They are characterized by a full insulating gap in the bulk and gapless edge or surface states which are protected by time-reversal symmetry. These topological materials have been theoretically predicted and experimentally observed in a variety of systems, including HgTe quantum wells, BiSb alloys, and Bi 2Te3 and Bi2Se3 crystals. Theoretical models, materials properties, and experimental results on two-dimensional and three-dimensional topological insulators are reviewed, and both the topological band theory and the topological field theory are discussed. Topological superconductors have a full pairing gap in the bulk and gapless surface states consisting of Majorana fermions. The theory of topological superconductors is reviewed, in close analogy to the theory of topological insulators. © 2011 American Physical Society.