Imlay J.A.,Urbana University
Current Opinion in Microbiology | Year: 2015
Microorganisms are vulnerable to elevated levels of intracellular reactive oxygen species (ROS). This situation has led to proposals that many natural stresses might be toxic specifically because they accelerate endogenous ROS formation. Such a mechanism has been convincingly demonstrated for redox-cycling compounds. However, the evidence is much weaker for most other stressors. The hypothesis that clinical antibiotics generate lethal ROS stress has attracted much attention, and the author discusses some aspects of evidence that support or oppose this idea. Importantly, even if all cellular electron flow were somehow diverted to ROS formation, the resultant doses of H2O2 and O2- would more likely be bacteriostatic than bacteriocidal unless key defense mechanisms were simultaneously blocked. © 2015 Elsevier Ltd.
Crutcher R.M.,Urbana University
Annual Review of Astronomy and Astrophysics | Year: 2012
This review examines observations of magnetic fields in molecular clouds and what those observations tell us about the theory of molecular cloud evolution and star formation. First, the review briefly summarizes classes of theoretical models of molecular clouds and specific predictions of the models that can be tested by observation. Then, the review describes the techniques for observing and mapping magnetic fields in molecular clouds, followed by discussion of important examples of observational studies using each technique. A synthesis of results from all observational techniques summarizes the current state, which is that though magnetic fields generally dominate turbulence, there is no definitive evidence for magnetic fields dominating gravity in molecular clouds or for ambipolar-diffusion-driven star formation. Finally, the review discusses prospects for advances in our observational capabilities with telescopes and instruments now beginning operation or under construction. Copyright © 2012 by Annual Reviews.
Brieher W.M.,Urbana University
Current opinion in cell biology | Year: 2013
Classical cadherin adhesion receptors exert many of their biological effects through close cooperation with the cytoskeleton. Much attention has focused on attempting to understand the physical interactions between cadherin molecular complexes and cortical actin filaments. In this review we aim to draw attention to other issues that highlight the diverse and dynamic cytoskeletons that contribute to cadherin function. First, we discuss the regulation of actin filament dynamics in the cadherin-based junctional cytoskeleton, focusing on the emerging role of Arp2/3 as a junctional actin nucleator and its implications for actin homeostasis at junctions. Second, we review recent developments in understanding the impact of microtubules on cadherin function. Together, these emphasize that cadherins cooperate with multiple dynamic cytoskeletal networks at cell-cell junctions. Copyright © 2012 Elsevier Ltd. All rights reserved.
Phillips P.,Urbana University
Reviews of Modern Physics | Year: 2010
High-temperature superconductivity in the copper-oxide ceramics remains an unsolved problem because we do not know what the propagating degrees of freedom are in the normal state. As a result, we do not know what are the weakly interacting degrees of freedom which pair up to form the superconducting condensate. That the electrons are not the propagating degrees of freedom in the cuprates is seen most directly from experiments that show spectral weight redistributions over all energy scales. In the correct low-energy theory, such rearrangements are minimized. This review focuses on the range of experimental consequences such ultraviolet-infrared mixings have on the normal state of the cuprates, such as the pseudogap, midinfrared band, temperature dependence of the Hall number, the superfluid density, and a recent theoretical advance which permits the identification of the propagating degrees of freedom in a doped Mott insulator. Within this theory, a wide range of phenomena which typify the normal state of the cuprates is shown to arise including T linear resistivity. © 2010 The American Physical Society.
Hartwig J.F.,Urbana University
Chemical Society Reviews | Year: 2011
The borylation of alkanes and arenes has become some of the most practical C-H bond functionalization chemistry. Most striking is the high regioselectivity of these reactions. Rhodium and ruthenium complexes catalyze with exquisite selectivity the borylation of methyl C-H bonds over methylene or methine C-H bonds. Iridium complexes catalyze, with high steric control, the borylation of one aromatic C-H bond over another. In contrast, iridium-catalyzed borylation of heteroaromatic C-H bonds is more controlled by electronic effects. Detailed information on these selectivities and mechanistic information on the origins of this regioselectivity will be described in this critical review (95 references). © 2011 The Royal Society of Chemistry.
Slichter C.P.,Urbana University
Reports on Progress in Physics | Year: 2014
In 1952, Overhauser proposed a method for transferring the large electron spin polarization of conduction electrons in a metal to the metal nuclei, enhancing their polarization one thousand fold. Such an enhancement method is called dynamic nuclear polarization (DNP). The article explains his idea, describes the experiments of Carver and Slichter that confirmed his proposal, their demonstration that the method was not limited to metals, describes the nature of immediate impact on the magnetic resonance community, discusses why DNP was not broadly utilized for many years, explains in simple terms how the method works and reports on the new developments in experimental methods that have given DNP an active and exciting future. © 2014 IOP Publishing Ltd.
Augspurger C.K.,Urbana University
Ecology | Year: 2013
Climate change, with both warmer spring temperatures and greater temperature fluctuations, has altered phenologies, possibly leading to greater risk of spring frost damage to temperate deciduous woody plants. Phenological observations of 20 woody species from 1993 to 2012 in Trelease Woods, Champaign County, Illinois, USA, were used to identify years with frost damage to vegetative and reproductive phases. Local temperature records were used in combination with the phenological observations to determine what combinations of the two were associated with damage. Finally, a long-term temperature record (1889-1992) was evaluated to determine if the frequency of frost damage has risen in recent decades. Frost <-1.7°C occurred after bud-break in 14 of the 20 years of observation. Frost damage occurred in five years in the interior and in three additional years at only the forest edge. The degree of damage varied with species, life stage, tissue (vegetative or reproductive), and phenological phase. Common features associated with the occurrence of damage to interior plants were (1) a period of unusual warm temperatures in March, followed by (2) a frost event in April with a minimum temperature <-6.1°C with (3) a period of 16-33 days between the extremes. In the long-term record, 10 of 124 years met these conditions, but the yearly probability of frost damage increased significantly, from 0.03 during 1889-1979 to 0.21 during 1980-2012. When the criteria were 'softened' to <-1.7°C in April and an interval of 16-37 days, 31 of 124 years met the conditions, and the yearly damage probability increased significantly to 0.19 for 1889-1979 and 0.42 for 1980-2012. In this forest, the combination of warming trends and temperature variability (extremes) associated with climate change is having ecologically important effects, making previously rare frost damage events more common. © 2013 by the Ecological Society of America.
Fields B.D.,Urbana University
Annual Review of Nuclear and Particle Science | Year: 2011
Big bang nucleosynthesis (BBN) theory, together with the precise WMAP cosmic baryon density, makes tight predictions for the abundances of the lightest elements. Deuterium and 4He measurements agree well with expectations, but 7Li observations lie below the BBN+WMAP prediction by a factor of three to four. This 45-σ mismatch constitutes the so-called cosmic lithium problem; disparate solutions are possible. First, astrophysical systematics in the observations could exist but are increasingly constrained. Second, nuclear physics experiments provide a wealth of well-measured cross-section data, but 7Be destruction could be enhanced by unknown or poorly measured resonances. Third, physics beyond the Standard Model could alter the 7Li abundance, although deuterium and 4He must remain unperturbed. In this review, we discuss such scenarios, highlighting decaying supersymmetric particles and time-varying fundamental constants. Present and planned experiments could reveal which (if any) of these proposed solutions is correct. © 2011 by Annual Reviews. All rights reserved.
Baldeck C.A.,Urbana University
Proceedings. Biological sciences / The Royal Society | Year: 2013
Both habitat filtering and dispersal limitation influence the compositional structure of forest communities, but previous studies examining the relative contributions of these processes with variation partitioning have primarily used topography to represent the influence of the environment. Here, we bring together data on both topography and soil resource variation within eight large (24-50 ha) tropical forest plots, and use variation partitioning to decompose community compositional variation into fractions explained by spatial, soil resource and topographic variables. Both soil resources and topography account for significant and approximately equal variation in tree community composition (9-34% and 5-29%, respectively), and all environmental variables together explain 13-39% of compositional variation within a plot. A large fraction of variation (19-37%) was spatially structured, yet unexplained by the environment, suggesting an important role for dispersal processes and unmeasured environmental variables. For the majority of sites, adding soil resource variables to topography nearly doubled the inferred role of habitat filtering, accounting for variation in compositional structure that would previously have been attributable to dispersal. Our results, illustrated using a new graphical depiction of community structure within these plots, demonstrate the importance of small-scale environmental variation in shaping local community structure in diverse tropical forests around the globe.
Li X.,Urbana University
Current Opinion in Solid State and Materials Science | Year: 2012
Metal assisted chemical etching (MacEtch) is a recently developed anisotropic wet etching method that is capable of producing high aspect ratio semiconductor nanostructures from patterned metal film. In this review article, we highlight the characteristics of MacEtch of silicon (Si) including controllability of the produced sidewall roughness, the inherent high aspect ratio, the weak crystal orientation dependence, impurity doping and solution concentration dependent porosity, as well as the applicability of MacEtch to non-Si based semiconductor materials including III-V compound semiconductors. Also reviewed are applications of MacEtch produced high aspect ratio Si nanostructures in photovoltaics, where the p-n junction can be in the planar Si tray, core-shell, or axial geometry, with nanowire, micropillar, or hole arrays serving as light trapping or carrier collection structures. The prospect of using MacEtch to improve the cost and efficiency of photovoltaic cells is discussed. © 2012 Elsevier Ltd. All rights reserved.