913 research outputs found
Electron attachment to SF6 and lifetimes of SF6- negative ions
We study the process of low-energy electron capture by the SF6 molecule. Our
approach is based on the model of Gauyacq and Herzenberg [J. Phys. B 17, 1155
(1984)] in which the electron motion is coupled to the fully symmetric
vibrational mode through a weakly bound or virtual s state. By tuning the two
free parameters of the model, we achieve an accurate description of the
measured electron attachment cross section and good agreement with vibrational
excitation cross sections of the fully symmetric mode. An extension of the
model provides a limit on the characteristic time of intramolecular vibrational
relaxation in highly-excited SF6-. By evaluating the total vibrational spectrum
density of SF6-, we estimate the widths of the vibrational Feshbach resonances
of the long-lived negative ion. We also analyse the possible distribution of
the widths and its effect on the lifetime measurements, and investigate
nonexponential decay features in metastable SF6-.Comment: 22 pages, 10 figures, submitted to Phys. Rev.
Stochastic analysis of surface roughness
For the characterization of surface height profiles we present a new
stochastic approach which is based on the theory of Markov processes. With this
analysis we achieve a characterization of the complexity of the surface
roughness by means of a Fokker-Planck or Langevin equation, providing the
complete stochastic information of multiscale joint probabilities. The method
was applied to different road surface profiles which were measured with high
resolution. Evidence of Markov properties is shown. Estimations for the
parameters of the Fokker-Planck equation are based on pure, parameter free data
analysis
Modeling the impact of sea-spray on particle concentrations in a coastal city
Abstract 18 An atmospheric chemistry-transport model is used to assess the impacts of sea-spray chemistry 19 on the particle composition in and downwind of a coastal city -Vancouver, British Columbia. 20 Reactions in/on sea-spray affect the entire particle ensemble and particularly the size distribution 21 of particle nitrate. 2
Ecological Consequences of Anomalies in Atmospheric Moisture and Snowpack
Although increased frequency of extremeâweather events is one of the most secure predictions associated with contemporary climate change, effects of such events on distribution and abundance of climateâsensitive species remain poorly understood. Montane ecosystems may be especially sensitive to extreme weather because of complex abiotic and biotic interactions that propagate from climateâdriven reductions in snowpack. Snowpack not only protects subnivean biotas from extreme cold, but also influences forage availability through timing of meltâoff and water availability. We related relative abundances of an alpine mammal, the American pika (Ochotona princeps), to measures of weather and snowpack dynamics over an 8âyr period that included before and after a year of recordâlow snowpack in Washington, USA. We sought to (1) quantify any change in pika abundance associated with the snowpack anomaly and (2) identify aspects of weather and snowpack that influenced abundance of pikas. Pikas showed a 1âyr lag response to the snowpack anomaly and exhibited marked declines in abundance at elevations below 1,400 m simultaneous with increased abundances at higher elevations. Atmospheric moisture, indexed by vapor pressure deficit (VPD), was especially important, evidenced by strong support for the topâranked model that included the interaction of VPD with snowpack duration. Notably, our novel application of VPD from gridded climate data for analyses of animal abundances shows strong potential for improving species distribution models because VPD represents an important aspect of weather that influences the physiology and habitat of biota. Pikas were apparently affected by cold stress without snowpack at mid elevations, whereas changes to forage associated with snowpack and VPD were influential at high and low elevations. Our results reveal context dependency in pika responses to weather and illustrate how snow drought can lead to rapid change in the abundance of subnivean animals
Recommended from our members
Modeling the impact of sea-spray on particle concentrations in a coastal city
An atmospheric chemistry-transport model is used to assess the impacts of sea-spray chemistry on the particle composition in and downwind of a coastal city--Vancouver, British Columbia. Reactions in/on sea-spray affect the entire particle ensemble and particularly the size distribution of particle nitrate. Urban air quality, and particularly airborne particles, is a major concern in terms of human health impacts. Sea-spray is known to be a major component of the particle ensemble at coastal sites yet relatively few air quality models include the interaction of gases with sea-spray and the fate of the particles produced. Sea-spray is not an inert addition to the particle ensemble because heterogeneous chemistry in/on sea-spray droplets changes the droplets composition and the particle size distribution, which impacts deposition and the ion balance in different particle size fractions. It is shown that the ISOPART model is capable of simulating gas and particle concentrations in the coastal metropolis of Vancouver and the surrounding valley. It is also demonstrated that to accurately simulate ambient concentrations of particles and reactive/soluble gases in a coastal valley it is absolutely critical to include heterogeneous chemistry in/on sea-spray. Partitioning of total particle-NO{sub 3}{sup -} between sea-spray and NH{sub 4}NO{sub 3} is highly sensitive to the amount of sea-spray present, and hence the initial vertical profile, sea-spray source functions [48] and the wind speed. When a fixed wind speed is used to initialize the sea-spray vertical profiles, as expected, the sea-spray concentration decays with distance inland, but the particle-NO{sub 3}{sup -} concentration decays more slowly because it is also a function of the uptake rate for HNO{sub 3}. The simulation results imply model analyses of air quality in coastal cities conducted without inclusion of sea-spray interactions may yield highly misleading results in terms of emission sensitivities of the PM size distribution. The sensitivity of the model results to the initial sea spray profile further suggests there would be great benefit in better definition of the vertical profile of size resolved sea-spray for use in such model studies
Review: Transport Losses in Market Weight Pigs: I. A Review of Definitions, Incidence, and Economic Impact
Transport losses (dead and nonambulatory pigs) present animal welfare, legal, and economic challenges to the US swine industry. The objectives of this review are to explore 1) the historical perspective of transport losses; 2) the incidence and economic implications of transport losses; and 3) the symptoms and metabolic characteristics of fatigued pigs. In 1933 and 1934, the incidence of dead and nonambulatory pigs was reported to be 0.08 and 0.16%, respectively. More recently, 23 commercial field trials (n = 6,660,569 pigs) were summarized and the frequency of dead pigs, nonambulatory pigs, and total transport losses at the processing plant were 0.25, 0.44, and 0.69% respectively. In 2006, total economic losses associated with these transport losses were estimated to cost the US pork industry approximately $46 million. Furthermore, 0.37 and 0.05% of the nonambulatory pigs were classified as either fatigued (nonambulatory, noninjured) or injured, respectively, in 18 of these trials (n = 4,966,419 pigs). Fatigued pigs display signs of acute stress (open-mouth breathing, skin discoloration, muscle tremors) and are in a metabolic state of acidosis, characterized by low blood pH and high blood lactate concentrations; however, the majority of fatigued pigs will recover with rest. Transport losses are a multifactorial problem consisting of people, pig, facility design, management, transportation, processing plant, and environmental factors, and, because of these multiple factors, continued research efforts are needed to understand how each of the factors and the relationships among factors affect the well-being of the pig during the marketing process
Evidence of fatal skeletal injuries on Malapa Hominins 1 and 2
Malapa is one of the richest early hominin sites in Africa and the discovery site of the hominin
species, Australopithecus sediba. The holotype and paratype (Malapa Hominin 1 and 2, or MH1 and
MH2, respectively) skeletons are among the most complete in the early hominin record. Dating to
approximately two million years BP, MH1 and MH2 are hypothesized to have fallen into a natural pit
trap. All fractures evident on MH1 and MH2 skeletons were evaluated and separated based on wet
and dry bone fracture morphology/characteristics. Most observed fractures are post-depositional, but
those in the right upper limb of the adult hominin strongly indicate active resistance to an impact,
while those in the juvenile hominin mandible are consistent with a blow to the face. The presence of
skeletal trauma independently supports the falling hypothesis and supplies the first evidence for the
manner of death of an australopith in the fossil record that is not attributed to predation or natural
death.The National Research Foundation of South Africa (NRF)http://www.nature.com/scientificreportsam201
Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions
Previous and present "academic" research aiming at atomic scale understanding
is mainly concerned with the study of individual molecular processes possibly
underlying materials science applications. Appealing properties of an
individual process are then frequently discussed in terms of their direct
importance for the envisioned material function, or reciprocally, the function
of materials is somehow believed to be understandable by essentially one
prominent elementary process only. What is often overlooked in this approach is
that in macroscopic systems of technological relevance typically a large number
of distinct atomic scale processes take place. Which of them are decisive for
observable system properties and functions is then not only determined by the
detailed individual properties of each process alone, but in many, if not most
cases also the interplay of all processes, i.e. how they act together, plays a
crucial role. For a "predictive materials science modeling with microscopic
understanding", a description that treats the statistical interplay of a large
number of microscopically well-described elementary processes must therefore be
applied. Modern electronic structure theory methods such as DFT have become a
standard tool for the accurate description of individual molecular processes.
Here, we discuss the present status of emerging methodologies which attempt to
achieve a (hopefully seamless) match of DFT with concepts from statistical
mechanics or thermodynamics, in order to also address the interplay of the
various molecular processes. The new quality of, and the novel insights that
can be gained by, such techniques is illustrated by how they allow the
description of crystal surfaces in contact with realistic gas-phase
environments.Comment: 24 pages including 17 figures, related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Validation of the SF-36 in patients with endometriosis.
OBJECTIVES: Endometriosis presents with significant pain as the most common symptom. Generic health measures can allow comparisons across diseases or populations. However, the Medical Outcomes Study Short Form 36 (SF-36) has not been validated for this disease. The goal of this study was to validate the SF-36 (version 2) for endometriosis. METHODS: Using data from two clinical trials (N = 252 and 198) of treatment for endometriosis, a full complement of psychometric analyses was performed. Additional instruments included a pain visual analog scale (VAS); a physician-completed questionnaire based on patient interview (modified Biberoglu and Behrman--B&B); clinical global impression of change (CGI-C); and patient satisfaction with treatment. RESULTS: Bodily pain (BP) and the Physical Component Summary Score (PCS) were correlated with the pain VAS at baseline and over time and the B&B at baseline and end of study. In addition, those who had the greatest change in BP and PCS also reported the greatest change on CGI-C and patient satisfaction with treatment. Other subscales showed smaller, but significant, correlations with change in the pain VAS, CGI-C, and patient satisfaction with treatment. CONCLUSIONS: The SF-36--particularly BP and the PCS--appears to be a valid and responsive measure for endometriosis and its treatment
- âŠ