8,030 research outputs found
A Monte Carlo Method for Fermion Systems Coupled with Classical Degrees of Freedom
A new Monte Carlo method is proposed for fermion systems interacting with
classical degrees of freedom. To obtain a weight for each Monte Carlo sample
with a fixed configuration of classical variables, the moment expansion of the
density of states by Chebyshev polynomials is applied instead of the direct
diagonalization of the fermion Hamiltonian. This reduces a cpu time to scale as
compared to for the
diagonalization in the conventional technique; is the dimension
of the Hamiltonian. Another advantage of this method is that parallel
computation with high efficiency is possible. These significantly save total
cpu times of Monte Carlo calculations because the calculation of a Monte Carlo
weight is the bottleneck part. The method is applied to the double-exchange
model as an example. The benchmark results show that it is possible to make a
systematic investigation using a system-size scaling even in three dimensions
within a realistic cpu timescale.Comment: 6 pages including 4 figure
Collagen Fibrillogenesis in Tissues, in Solution and from Modeling: A Synthesis
Collagen fibril formation has been studied in tissues by light and electron microscopy; in solution by light scattering and microscopy; and from modeling based on the amino acid sequence of type I collagen. Taken together these studies indicate that collagen fibril assembly involves a stepwise formation of intermediate aggregates in which each intermediate is formed from earlier aggregates. In this sequence, monomeric collagen contributes only to the formation of early aggregates; and fibrils grow in length by the addition of intermediate aggregates to the end of a subfibril and in width by lateral wrapping of subfibrils. Modeling based on amino acid sequence data of possible intermolecular charge-charge interactions indicate 2 different kinds, one which promotes linear aggregation and the other which promotes lateral aggregation. The effects of different colla-gens and coprecipitants such as glycoproteins and proteoglycans can begin to be explained by their influence on the character of intermediate subassemblies. Ultrastructural data from 2 tissues, embryonic cornea and tendon, indicate that the site of fibril growth and assembly is at the cell surface
Physical determinants of vesicle mobility and supply at a central synapse
Encoding continuous sensory variables requires sustained synaptic signalling. At several sensory synapses, rapid vesicle supply is achieved via highly mobile vesicles and specialized ribbon structures, but how this is achieved at central synapses without ribbons is unclear. Here we examine vesicle mobility at excitatory cerebellar mossy fibre synapses which sustain transmission over a broad frequency bandwidth. Fluorescent recovery after photobleaching in slices from VGLUT1Venus knock-in mice reveal 75% of VGLUT1-containing vesicles have a high mobility, comparable to that at ribbon synapses. Experimentally constrained models establish hydrodynamic interactions and vesicle collisions are major determinants of vesicle mobility in crowded presynaptic terminals. Moreover, models incorporating 3D reconstructions of vesicle clouds near active zones (AZs) predict the measured releasable pool size and replenishment rate from the reserve pool. They also show that while vesicle reloading at AZs is not diffusion-limited at the onset of release, diffusion limits vesicle reloading during sustained high-frequency signalling
Experimentally induced root mortality increased nitrous oxide emission from tropical forest soils
We conducted an experiment on sand and clay tropical forest soils to test the shortâterm effect of root mortality on the soilâatmosphere flux of nitrous oxide, nitric oxide, methane, and carbon dioxide. We induced root mortality by isolating blocks of land to 1 m using trenching and root exclusion screening. Gas fluxes were measured weekly for ten weeks following the trenching treatment. For nitrous oxide there was a highly significant increase in soilâatmosphere flux over the ten weeks following treatment for trenched plots compared to control plots. N2O flux averaged 37.5 and 18.5 ng N cmâ2 hâ1 from clay trenched and control plots and 4.7 and 1.5 ng N cmâ2 hâ1 from sand trenched and control plots. In contrast, there was no effect for soilâatmosphere flux of nitric oxide, carbon dioxide, or methane
Fine root dynamics and trace gas fluxes in two lowland tropical forest soils
Fine root dynamics have the potential to contribute significantly to ecosystem-scale biogeochemical cycling, including the production and emission of greenhouse gases. This is particularly true in tropical forests which are often characterized as having large fine root biomass and rapid rates of root production and decomposition. We examined patterns in fine root dynamics on two soil types in a lowland moist Amazonian forest, and determined the effect of root decay on rates of C and N trace gas fluxes. Root production averaged 229 ( 35) and 153 ( 27) gm 2 yr 1 for years 1 and 2 of the study, respectively, and did not vary significantly with soil texture. Root decay was sensitive to soil texture with faster rates in the clay soil (k5 0.96 year 1) than in the sandy loam soil (k5 0.61 year 1),leading to greater standing stocks of dead roots in the sandy loam. Rates of nitrous oxide (N2O) emissions were significantly greater in the clay soil (13 1ngNcm 2 h 1) than in the sandy loam (1.4 0.2 ngNcm 2 h 1). Root mortality and decay following trenching doubled rates of N2O emissions in the clay and tripled them in sandy loam over a 1-year period. Trenching also increased nitric oxide fluxes, which were greater in the sandy loam than in the clay. We used trenching (clay only) and a mass balance approach to estimate the root contribution to soil respiration. In clay soil root respiration was 264â380 gCm 2 yr 1, accounting for 24% to 35% of the total soil CO2 efflux. Estimates were similar using both approaches. In sandy loam, root respiration rates were slightly higher and more variable (521 206 gCm2 yr 1) and contributed 35% of the total soil respiration. Our results show that soil heterotrophs strongly dominate soil respiration in this forest, regardless of soil texture. Our results also suggest that fine root mortality and decomposition associated with disturbance and land-use change can contribute significantly to increased rates of nitrogen trace gas emissions
Tumor antigen(s) in cells productively infected by wild-type polyoma virus and mutant NG-18
Fe XVII X-ray Line Ratios for Accurate Astrophysical Plasma Diagnostics
New laboratory measurements using an Electron Beam Ion Trap (EBIT) and an
x-ray microcalorimeter are presented for the n=3 to n=2 Fe XVII emission lines
in the 15 {\AA} to 17 {\AA} range, along with new theoretical predictions for a
variety of electron energy distributions. This work improves upon our earlier
work on these lines by providing measurements at more electron impact energies
(seven values from 846 to 1185 eV), performing an in situ determination of the
x-ray window transmission, taking steps to minimize the ion impurity
concentrations, correcting the electron energies for space charge shifts, and
estimating the residual electron energy uncertainties. The results for the
3C/3D and 3s/3C line ratios are generally in agreement with the closest theory
to within 10%, and in agreement with previous measurements from an independent
group to within 20%. Better consistency between the two experimental groups is
obtained at the lowest electron energies by using theory to interpolate, taking
into account the significantly different electron energy distributions.
Evidence for resonance collision effects in the spectra is discussed.
Renormalized values for the absolute cross sections of the 3C and 3D lines are
obtained by combining previously published results, and shown to be in
agreement with the predictions of converged R-matrix theory. This work
establishes consistency between results from independent laboratories and
improves the reliability of these lines for astrophysical diagnostics. Factors
that should be taken into account for accurate diagnostics are discussed,
including electron energy distribution, polarization, absorption/scattering,
and line blends.Comment: 29 pages, including 7 figure
The Frequency of Sexual Perpetration in College Men: A Systematic Review of Reported Prevalence Rates from 2000-2017
Background: The prevalence of sexual perpetration in college men is unknown. Prior reviews of sexual violence prevalence rates have produced wide-ranging estimates, likely due to wide variation in measurement strategies.
Objectives: This paper systematically reviewed research findings (from 2000-2017) regarding prevalence rates of sexual perpetration in college men and measurement strategies.
Data Sources: PsycINFO and Web of Science databases.
Eligibility Criteria: Empirical reports published between 2000-2017 that included male participants, available in English, and reported lifetime prevalence findings in Canadian or American college students.
Participants: Data from 78 independent samples including 25,524 college men.
Results: The average prevalence rate of any sexual perpetration was 29.3% (SD = 16.8), and the average rate of rape was 6.5% (SD = 6.3). Studies that used non-Sexual Experiences Survey (SES) based questionnaires recorded higher prevalence rates (41.5%) than SES-using studies (26.2%). At least sixteen different sexual perpetration questionnaires were identified. Modifying standardized questionnaires was extremely common; this was reported in over half the studies. Studies using modified standardized questionnaires found higher prevalence rates of sexual perpetration than studies using non-modified standardized questionnaires.
Limitations: This report focused exclusively on college men in the United States and Canada.
Conclusions and Implications: On average, 29% of college males report engaging in behaviors defined as sexual perpetration; however, there was a strong influence of measurement strategy on reported rates
How To Be An Advocate: Summary of âRealizing ABCTâs Mission In A Politicized Worldâ Presented by Lynn Bufka, Anita Brown, Brandon Gaudiano, Megan Gordan-Kane, Lauren Macivor Thompson, and Laura Seligman
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