Selective gating to vibrational modes through resonant X ray scattering

The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X ray scattering RIXS study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X ray excitation to different core excited potential energy surfaces PESs will act as spatial gates to selectively probe the particular ground state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra high resolution RIXS measurements for gas phase water with state of the art simulation

One dimensional cuts through multidimensional potential energy surfaces by tunable x rays

The concept of the potential energy surface PES and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to near degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close lying vibrational levels. We show here that resonant inelastic x ray scattering RIXS constitutes an ideal probe for revealing one dimensional cuts through the ground state PES of molecular systems, even far away from the equilibrium geometry, where the independent mode picture is broken. We strictly link the center of gravity of close lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one dimensional Hamiltonian along the propagation coordinate of the core excited wave packet. This concept, combined with directional and site selectivity of the core excited states, allows us to experimentally extract cuts through the ground state PES along three complementary directions for the showcase H2O molecul

A study of the water molecule using frequency control over nuclear dynamics in resonant X ray scattering

In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X ray scattering RIXS spectra of H 2O, D 2O and HDO. We demonstrate that electronically elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X ray frequency across core excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied system

Ultrafast dissociation features in RIXS spectra of the water molecule

In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X ray scattering RIXS spectra of gas phase water via the lowest dissociative core excited state 1s amp; 8722;1O4a11 amp; 12297;. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state 1b amp; 8722;114a11 amp; 12297; of the molecule. The spectral feature has signatures of ultrafast dissociation UFD in the core excited state, as we show by means of ab initio calculations and time dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core excited state resonance, we can understand and single out the molecular and atomic like contributions in the decay to the lowest valence excited state. Our study is complemented by a theoretical discussion of RIXS in the case of isotopically substituted water HDO and D2O where the nuclear dynamics is significantly affected by the heavier fragments mas

An Information Theory Approach to Hypothesis Testing in Criminological Research

Background: This research demonstrates how the Akaike information criterion (AIC) can be an alternative to null hypothesis significance testing in selecting best fitting models. It presents an example to illustrate how AIC can be used in this way. Methods: Using data from Milwaukee, Wisconsin, we test models of place-based predictor variables on street robbery and commercial robbery. We build models to balance explanatory power and parsimony. Measures include the presence of different kinds of businesses, together with selected age groups and social disadvantage. Results: Models including place-based measures of land use emerged as the best models among the set of tested models. These were superior to models that included measures of age and socioeconomic status. The best models for commercial and street robbery include three measures of ordinary businesses, liquor stores, and spatial lag. Conclusions: Models based on information theory offer a useful alternative to significance testing when a strong theoretical framework guides the selection of model sets. Theoretically relevant ‘ordinary businesses’ have a greater influence on robbery than socioeconomic variables and most measures of discretionary businesses

Compatibility of quantitative X-ray spectroscopy with continuous distribution models of water at ambient conditions

The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 +/- 2.1% donated and accepted hydrogen bonds per molecule, pointing to a continuous-distribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray-matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscale-length correlations within the continuous distribution remains open

Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering

Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding

Prevalence of Influenza A viruses in wild migratory birds in Alaska: Patterns of variation in detection at a crossroads of intercontinental flyways

<p>Abstract</p> <p>Background</p> <p>The global spread of the highly pathogenic avian influenza H5N1 virus has stimulated interest in a better understanding of the mechanisms of H5N1 dispersal, including the potential role of migratory birds as carriers. Although wild birds have been found dead during H5N1 outbreaks, evidence suggests that others have survived natural infections, and recent studies have shown several species of ducks capable of surviving experimental inoculations of H5N1 and shedding virus. To investigate the possibility of migratory birds as a means of H5N1 dispersal into North America, we monitored for the virus in a surveillance program based on the risk that wild birds may carry the virus from Asia.</p> <p>Results</p> <p>Of 16,797 birds sampled in Alaska between May 2006 and March 2007, low pathogenic avian influenza viruses were detected in 1.7% by rRT-PCR but no highly pathogenic viruses were found. Our data suggest that prevalence varied among sampling locations, species (highest in waterfowl, lowest in passerines), ages (juveniles higher than adults), sexes (males higher than females), date (highest in autumn), and analytical technique (rRT-PCR prevalence = 1.7%; virus isolation prevalence = 1.5%).</p> <p>Conclusion</p> <p>The prevalence of low pathogenic avian influenza viruses isolated from wild birds depends on biological, temporal, and geographical factors, as well as testing methods. Future studies should control for, or sample across, these sources of variation to allow direct comparison of prevalence rates.</p

Meta-analysis identifies novel risk loci and yields systematic insights into the biology of male-pattern baldness

Life & Brain GmbH; the BONFOR programme of the University of Bonn; and the Agency for Science, Technology and Research (A*STAR). M.M.N. is a member of the DFG Excellence Cluster ImmunoSensation

Sleep in Elite Athletes and Nutritional Interventions to Enhance Sleep

Sleep has numerous important physiological and cognitive functions that may be particularly important to elite athletes. Recent evidence, as well as anecdotal information, suggests that athletes may experience a reduced quality and/or quantity of sleep. Sleep deprivation can have significant effects on athletic performance, especially submaximal, prolonged exercise. Compromised sleep may also influence learning, memory, cognition, pain perception, immunity and inflammation. Furthermore, changes in glucose metabolism and neuroendocrine function as a result of chronic, partial sleep deprivation may result in alterations in carbohydrate metabolism, appetite, food intake and protein synthesis. These factors can ultimately have a negative influence on an athlete’s nutritional, metabolic and endocrine status and hence potentially reduce athletic performance. Research has identified a number of neurotransmitters associated with the sleep–wake cycle. These include serotonin, gamma-aminobutyric acid, orexin, melanin-concentrating hormone, cholinergic, galanin, noradrenaline, and histamine. Therefore, nutritional interventions that may act on these neurotransmitters in the brain may also influence sleep. Carbohydrate, tryptophan, valerian, melatonin and other nutritional interventions have been investigated as possible sleep inducers and represent promising potential interventions. In this review, the factors influencing sleep quality and quantity in athletic populations are examined and the potential impact of nutritional interventions is considered. While there is some research investigating the effects of nutritional interventions on sleep, future research may highlight the importance of nutritional and dietary interventions to enhance sleep