Recent results on the Higgs boson candidate in the two-photon decay channel at ATLAS

This paper is intended to give an overview of the results of the ATLAS experiment at the LHC presented in December 2012 for the H → γγ channel using 4.8 fb−1 of data taken in 2011 at √s = 7TeV and 13.0 fb−1 of data taken in 2012 at √s = 8TeV

Assessing the vulnerability of stream communities and the consistency and use of biotic indices in least-disturbed streams

The need in freshwater conservation is to understand the current status of aquatic biota so that we can recognize when degradation or changes occur. Because stream habitats and communities are dynamic, it is important to understand the natural variability through time and space so that departures may be used to make inferences on stability or instability. Additionally, attempting to predict aquatic communities that are more likely to experience a change in diversity, abundance, and function from anthropogenic impacts may help to prioritize locations for management action. Finally, assessing the consistency of various biotic indices (quantitative tools used to convey lotic ecosystem health) will aid in conveying a more holistic depiction of stream condition and to prioritize locations and biota for management action. To address each of the aforementioned data gaps, we used fish and aquatic invertebrate community data collected from 1988 to 2013 from 88 sites within seven National Park Service (NPS) units represented within the Heartland Inventory and Monitoring Network. The fish community (Index of Biotic Integrity) at each of the seven NPS units was less temporally variable than spatially variable. This relationship was not found with aquatic invertebrate community (Hilsenhoff Biotic Index) in that only three of the seven NPS units were less temporally variable than spatially variable

Ab initio investigation of intermolecular interactions in solid benzene

A computational strategy for the evaluation of the crystal lattice constants and cohesive energy of the weakly bound molecular solids is proposed. The strategy is based on the high level ab initio coupled-cluster determination of the pairwise additive contribution to the interaction energy. The zero-point-energy correction and non-additive contributions to the interaction energy are treated using density functional methods. The experimental crystal lattice constants of the solid benzene are reproduced, and the value of 480 meV/molecule is calculated for its cohesive energy

Low-Energy Scale Excitations in the Spectral Function of Organic Monolayer Systems

Using high-resolution photoemission spectroscopy we demonstrate that the electronic structure of several organic monolayer systems, in particular 1,4,5,8-naphthalene tetracarboxylic dianhydride and Copper-phtalocyanine on Ag(111), is characterized by a peculiar excitation feature right at the Fermi level. This feature displays a strong temperature dependence and is immediatly connected to the binding energy of the molecular states, determined by the coupling between the molecule and the substrate. At low temperatures, the line-width of this feature, appearing on top of the partly occupied lowest unoccupied molecular orbital of the free molecule, amounts to only $\approx 25$ meV, representing an unusually small energy scale for electronic excitations in these systems. We discuss possible origins, related e.g. to many-body excitations in the organic-metal adsorbate system, in particular a generalized Kondo scenario based on the single impurity Anderson model.Comment: 6 pages, 3 figures, accepted as PRB Rapid Communication

Aquatic Invasive Species Change Ecosystem Services from the World\u27s Largest Wild Sockeye Salmon Fisheries in Alaska

This study combines a multi-method approach to structured expert judgment with market valuation to forecast fisheries damages from introduced invasive species. The method is applied to a case study of Alaska’s first submersed aquatic invasive plant, Elodea spp., threatening Alaska’s salmon fisheries. Assuming that Elodea spp. remains unmanaged, estimated mean damages to commercial sockeye fisheries aggregated across Alaska amount to a potential $159 million annually with a 5$577 million annually ($2015 USD). The associated mean loss of natural capital amounts to$5.1 billion cumulatively over the next 100 years reaching $400 million after 10 years. Results from the expert elicitation indicate that there is a 35% chance of positive net benefits associated with the believed positive effects of Elodea spp. on sockeye salmon (Oncorhynchus nerka). Despite the potential for positive net gains, the magnitude of the most probable damage estimate may justify substantial investment in keeping productive freshwater systems free of aquatic invasive species. The damage estimate for Alaska is significantly larger than similar estimates in the Great Lakes where ecosystems are already impaired by multiple aquatic invasive species, underscoring the value of keeping functioning ecosystems with global market value productive. This study is the first to estimate ecosystem service loss associated with introduction of an aquatic invasive species to freshwater habitat that supports the world’s most valuable wild sockeye salmon fisheries. Important policy implications related to natural resource management and efficient allocation of scarce resources are discusse

All-optical measurement of the hot electron sheath driving laser ion acceleration from thin foils

We present experimental results from an all-optical diagnostic method to directly measure the evolution of the hot-electron distribution driving the acceleration of ions from thin foils using high-intensity lasers. Central parameters of laser ion acceleration such as the hot-electron density, the temperature distribution and the conversion efficiency from laser pulse energy into hot electrons become comprehensively accessible with this technique.Deutsche Forschungsgemeinschaft (DFG) (contract number TR18)Germany. Bundesministerium für Bildung und Forschung (contract number 03ZIK445)Germany. Bundesministerium für Bildung und Forschung (contract number 03ZIK052

Measurement of Magnetic-Field Structures in a Laser-Wakefield Accelerator

Experimental measurements of magnetic fields generated in the cavity of a self-injecting laser-wakefield accelerator are presented. Faraday rotation is used to determine the existence of multi-megagauss fields, constrained to a transverse dimension comparable to the plasma wavelength and several plasma wavelengths longitudinally. The fields are generated rapidly and move with the driving laser. In our experiment, the appearance of the magnetic fields is correlated to the production of relativistic electrons, indicating that they are inherently tied to the growth and wavebreaking of the nonlinear plasma wave. This evolution is confirmed by numerical simulations, showing that these measurements provide insight into the wakefield evolution with high spatial and temporal resolution

Nuclear dynamics of singlet exciton fission: a direct observation in pentacene single crystals

Singlet exciton fission (SEF) is a key process in the development of efficient opto-electronic devices. An aspect that is rarely probed directly, and yet has a tremendous impact on SEF properties, is the nuclear structure and dynamics involved in this process. Here we directly observe the nuclear dynamics accompanying the SEF process in single crystal pentacene using femtosecond electron diffraction. The data reveal coherent atomic motions at 1 THz, incoherent motions, and an anisotropic lattice distortion representing the polaronic character of the triplet excitons. Combining molecular dynamics simulations, time-dependent density functional theory and experimental structure factor analysis, the coherent motions are identified as collective sliding motions of the pentacene molecules along their long axis. Such motions modify the excitonic coupling between adjacent molecules. Our findings reveal that long-range motions play a decisive part in the disintegration of the electronically correlated triplet pairs, and shed light on why SEF occurs on ultrafast timescales

High resolution monochromator for inelastic scattering studies of high energy phonons using undulator radiation at the advanced photon source

A monochromator for use at 13.84 keV with a calculated bandpass of 5.2 meV was designed built, and tested. Tuning was performed by rotating the inner crystal of a pair of nested silicon channel-cut crystals. The inner crystal employs the (884) reflection, and the outer crystal employs a collimating asymmetric (422) reflection (dynamical asymmetry factor, b, equal to {minus}17.5). Tests were done with a double-crystal Si(111) pre-monochromator situated upstream of the high resolution monochromator and a Si(777) backscattering crystal situated downstream. For this optical arrangement an ideal value of 6.3 meV as calculated by x-ray dynamical diffraction theory applies for the FWHM of the convolution of the net monochromator reflectivity function with that of the Si(777) reflection. This calculated value is to be compared to the value of 7.1 meV measured by tuning the high resolution monochromator. Measured efficiencies were less than ideal by a factor of 3.2 to 4.9, where the larger flux reduction factors were found with higher positron storage ring currents