Evolution of the potential-energy surface of amorphous silicon

The link between the energy surface of bulk systems and their dynamical properties is generally difficult to establish. Using the activation-relaxation technique (ART nouveau), we follow the change in the barrier distribution of a model of amorphous silicon as a function of the degree of relaxation. We find that while the barrier-height distribution, calculated from the initial minimum, is a unique function that depends only on the level of distribution, the reverse-barrier height distribution, calculated from the final state, is independent of the relaxation, following a different function. Moreover, the resulting gained or released energy distribution is a simple convolution of these two distributions indicating that the activation and relaxation parts of a the elementary relaxation mechanism are completely independent. This characterized energy landscape can be used to explain nano-calorimetry measurements.Comment: 5 pages, 4 figure

Environmental Federalism in the European Union and the United States

The United States (US) and the European Union (EU) are federal systems in which the responsibility for environmental policy-making is divided or shared between the central government and the (member) states. The attribution of decision-making power has important policy implications. This chapter compares the role of central and local authorities in the US and the EU in formulating environmental regulations in three areas: automotive emissions for health related (criteria) pollutants, packaging waste, and global climate change. Automotive emissions are relatively centralised in both political systems. In the cases of packaging waste and global climate change, regulatory policy-making is shared in the EU, but is primarily the responsibility of local governments in the US. Thus, in some important areas, regulatory policy-making is more centralised in the EU. The most important role local governments play in the regulatory process is to help diffuse stringent local standards through more centralised regulations, a dynamic which has become recently become more important in the EU than in the US.

Tryptophan- and arginine-rich antimicrobial peptides: Structures and mechanisms of action

AbstractAntimicrobial peptides encompass a number of different classes, including those that are rich in a particular amino acid. An important subset are peptides rich in Arg and Trp residues, such as indolicidin and tritrpticin, that have broad and potent antimicrobial activity. The importance of these two amino acids for antimicrobial activity was highlighted through the screening of a complete combinatorial library of hexapeptides. These residues possess some crucial chemical properties that make them suitable components of antimicrobial peptides. Trp has a distinct preference for the interfacial region of lipid bilayers, while Arg residues endow the peptides with cationic charges and hydrogen bonding properties necessary for interaction with the abundant anionic components of bacterial membranes. In combination, these two residues are capable of participating in cation–π interactions, thereby facilitating enhanced peptide–membrane interactions. Trp sidechains are also implicated in peptide and protein folding in aqueous solution, where they contribute by maintaining native and nonnative hydrophobic contacts. This has been observed for the antimicrobial peptide from human lactoferrin, possibly restraining the peptide structure in a suitable conformation to interact with the bacterial membrane. These unique properties make the Arg- and Trp-rich antimicrobial peptides highly active even at very short peptide lengths. Moreover, they lead to structures for membrane-mimetic bound peptides that go far beyond regular α-helices and β-sheet structures. In this review, the structures of a number of different Trp- and Arg-rich antimicrobial peptides are examined and some of the major mechanistic studies are presented

The Fueling Diagram: Linking Galaxy Molecular-to-Atomic Gas Ratios to Interactions and Accretion

To assess how external factors such as local interactions and fresh gas accretion influence the global ISM of galaxies, we analyze the relationship between recent enhancements of central star formation and total molecular-to-atomic (H2/HI) gas ratios, using a broad sample of field galaxies spanning early-to-late type morphologies, stellar masses of 10^(7.2-11.2) Msun, and diverse stages of evolution. We find that galaxies occupy several loci in a "fueling diagram" that plots H2/HI vs. mass-corrected blue-centeredness, a metric tracing the degree to which galaxies have bluer centers than the average galaxy at their stellar mass. Spiral galaxies show a positive correlation between H2/HI and mass-corrected blue-centeredness. When combined with previous results linking mass-corrected blue-centeredness to external perturbations, this correlation suggests a link between local galaxy interactions and molecular gas inflow/replenishment. Intriguingly, E/S0 galaxies show a more complex picture: some follow the same correlation, some are quenched, and a distinct population of blue-sequence E/S0 galaxies (with masses below key transitions in gas richness) defines a separate loop in the fueling diagram. This population appears to be composed of low-mass merger remnants currently in late- or post-starburst states, in which the burst first consumes the H2 while the galaxy center keeps getting bluer, then exhausts the H2, at which point the burst population reddens as it ages. Multiple lines of evidence suggest connected evolutionary sequences in the fueling diagram. In particular, tracking total gas-to-stellar mass ratios within the diagram provides evidence of fresh gas accretion onto low-mass E/S0s emerging from central starbursts. Drawing on a comprehensive literature search, we suggest that virtually all galaxies follow the same evolutionary patterns found in our broad sample.Comment: 24 pages, 11 figures (table 4 available at http://user.physics.unc.edu/~dstark/table4_csv.txt), accepted for publication in Ap

The importance of sulfur for the behavior of highly-siderophile elements during Earth’s differentiation

AbstractThe highly siderophile elements (HSEs) are widely used as geochemical tracers for Earth’s accretion and core formation history. It is generally considered that core formation strongly depleted the Earth’s mantle in HSEs, which were subsequently replenished by a chondritic late veneer. However, open questions remain regarding the origin of suprachondritic Ru/Ir and Pd/Ir ratios that are thought to be characteristic for the primitive upper mantle. In most core-formation models that address the behavior of the HSEs, light elements such as S entering the core have not been taken into account and high P–T experimental data for S-bearing compositions are scarce. Here we present a comprehensive experimental study to investigate the effect of increasing S concentration in the metal on HSE metal–silicate partitioning at 2473K and 11GPa. We show that the HSEs become less siderophile with increasing S concentrations in the metal, rendering core-forming metal less efficient in removing the HSEs from the mantle if S is present. Furthermore, we investigated the FeS sulfide–silicate partitioning of the HSEs as a function of pressure (7–21GPa) and temperature (2373–2673K). The sulfide–silicate partition coefficient for Pt increases strongly with P, whereas those for Pd, Ru and Ir all decrease. The combined effect is such that above ∼20GPa Ru becomes less chalcophile than Pt, which is opposite to their behavior in the metal–silicate system where Ru is always more siderophile than Pt. The newly determined experimental results are used in a simple 2-stage core formation model that takes into account the effect of S on the behavior of the HSEs during core formation. Results of this model show that segregation of a sulfide liquid to the core from a mantle with substantial HSE concentrations plays a key role in reproducing Earth’s mantle HSE abundances. As Ru and Pd are less chalcophile than Pt and Ir at high P–T, some Ru and Pd remain in the mantle after sulfide segregation. Addition of the late veneer then raised the concentrations of all HSE to their current levels. Suprachondritic Ru/Ir and Pd/Ir ratios of the mantle can thus be explained by a combination of sulfide segregation together with the addition of a late veneer without the need to invoke unknown chondritic material

Transcriptome analysis of the sex pheromone gland of the noctuid moth Heliothis virescens

<p>Abstract</p> <p>Background</p> <p>The chemical components of sex pheromones have been determined for more than a thousand moth species, but so far only a handful of genes encoding enzymes responsible for the biosynthesis of these compounds have been identified. For understanding the evolution of moth sexual communication, it is essential to know which genes are involved in the production of specific pheromone components and what controls the variation in their relative frequencies in the pheromone blend. We used a transcriptomic approach to characterize the pheromone gland of the Noctuid moth <it>Heliothis virescens</it>, an important agricultural pest, in order to obtain substantial general sequence information and to identify a range of candidate genes involved in the pheromone biosynthetic pathway.</p> <p>Results</p> <p>To facilitate identifying sets of genes involved in a broad range of processes and to capture rare transcripts, we developed our majority of ESTs from a normalized cDNA library of <it>Heliothis virescens </it>pheromone glands (PG). Combining these with a non-normalized library yielded a total of 17,233 ESTs, which assembled into 2,082 contigs and 6,228 singletons. Using BLAST searches of the NR and Swissprot databases we were able to identify a large number of putative unique gene elements (unigenes), which we compared to those derived from previous transcriptomic surveys of the larval stage of <it>Heliothis virescens</it>. The distribution of unigenes among GO Biological Process functional groups shows an overall similarity between PG and larval transcriptomes, but with distinct enrichment of specific pathways in the PG. In addition, we identified a large number of candidate genes in the pheromone biosynthetic pathways.</p> <p>Conclusion</p> <p>These data constitute one of the first large-scale EST-projects for Noctuidae, a much-needed resource for exploring these pest species. Our analysis shows a surprisingly complex transcriptome and we identified a large number of potential pheromone biosynthetic pathway and immune-related genes that can be applied to population and systematic studies of <it>Heliothis virescens </it>and other Noctuidae.</p

The Conservation Reserve Program: Economic Implications for Rural America

This report estimates the impact that high levels of enrollment in the Conservation Reserve Program (CRP) have had on economic trends in rural counties since the program's inception in 1985 until today. The results of a growth model and quasi-experimental control group analysis indicate no discernible impact by the CRP on aggregate county population trends. Aggregate employment growth may have slowed in some high-CRP counties, but only temporarily. High levels of CRP enrollment appear to have affected farm-related businesses over the long run, but growth in the number of other nonfarm businesses moderated CRP's impact on total employment. If CRP contracts had ended in 2001, simulation models suggest that roughly 51 percent of CRP land would have returned to crop production, and that spending on outdoor recreation would decrease by as much as $300 million per year in rural areas. The resulting impacts on employment and income vary widely among regions having similar CRP enrollments, depending upon local economic conditions.Community/Rural/Urban Development, Land Economics/Use,

Encoded and updated spatial working memories share a common representational format in alpha activity

Working memory (WM) flexibly updates information to adapt to the dynamic environment. Here, we used alpha-band activity in the EEG to reconstruct the content of dynamic WM updates and compared this representational format to static WM content. An inverted encoding model using alpha activity precisely tracked both the initially encoded position and the updated position following an auditory cue signaling mental updating. The timing of the update, as tracked in the EEG, correlated with reaction times and saccade latency. Finally, cross-training analyses revealed a robust generalization of alpha-band reconstruction of WM contents before and after updating. These findings demonstrate that alpha activity tracks the dynamic updates to spatial WM and that the format of this activity is preserved across the encoded and updated representations. Thus, our results highlight a new approach for measuring updates to WM and show common representational formats during dynamic mental updating and static storage

The structure of the antimicrobial active center of lactoferricin B bound to sodium dodecyl sulfate micelles

AbstractLactoferricin B (LfcinB) is a 25-residue antimicrobial peptide released from bovine lactoferrin upon pepsin digestion. The antimicrobial center of LfcinB consists of six residues (RRWQWR-NH2), and it possesses similar bactericidal activity to LfcinB. The structure of the six-residue peptide bound to sodium dodecyl sulfate (SDS) micelles has been determined by NMR spectroscopy and molecular dynamics refinement. The peptide adopts a well defined amphipathic structure when bound to SDS micelles with the Trp sidechains separated from the Arg residues. Additional evidence demonstrates that the peptide is oriented in the micelle such that the Trp residues are more deeply buried in the micelle than the Arg and Gln residues