2,062 research outputs found
Quark-gluon vertex with an off-shell O(a)-improved chiral fermion action
We perform a study the quark-gluon vertex function with a quenched Wilson
gauge action and a variety of fermion actions. These include the domain wall
fermion action (with exponentially accurate chiral symmetry) and the Wilson
clover action both with the non-perturbatively improved clover coefficient as
well as with a number of different values for this coefficient. We find that
the domain wall vertex function behaves very well in the large momentum
transfer region. The off-shell vertex function for the on-shell improved clover
class of actions does not behave as well as the domain wall case and,
surprisingly, shows only a weak dependence on the clover coefficient
for all components of its Dirac decomposition and across all momenta. Including
off-shell improvement rotations for the clover fields can make this action
yield results consistent with those from the domain wall approach, as well as
helping to determine the off-shell improved coefficient .Comment: 11 pages, 13 figures, REVTeX
Dire Wolf Collects his Due While the Boys Sit by the Fire: Why Michigan Cannot Afford to Buy into the Death Penalty
Optimal search strategies for hidden targets
What is the fastest way of finding a randomly hidden target? This question of
general relevance is of vital importance for foraging animals. Experimental
observations reveal that the search behaviour of foragers is generally
intermittent: active search phases randomly alternate with phases of fast
ballistic motion. In this letter, we study the efficiency of this type of two
states search strategies, by calculating analytically the mean first passage
time at the target. We model the perception mecanism involved in the active
search phase by a diffusive process. In this framework, we show that the search
strategy is optimal when the average duration of "motion phases" varies like
the power either 3/5 or 2/3 of the average duration of "search phases",
depending on the regime. This scaling accounts for experimental data over a
wide range of species, which suggests that the kinetics of search trajectories
is a determining factor optimized by foragers and that the perception activity
is adequately described by a diffusion process.Comment: 4 pages, 5 figures. to appear in Phys. Rev. Let
Enhancing Interdisciplinary Attitudes and Achievement via Integrated Biology and Chemistry
Success in undergraduate biology courses relies upon a firm grounding in chemical principles. We sought to raise students’ awareness of the connection between these two disciplines and to improve their understanding of each by carrying out a pilot project that integrated the curricula of Principles of Chemistry II (CHEM1212K) and Principles of Biology I (BIOL1107K) during the Fall 2016 semester. The study involved two course pairs: one section of each course delivered in the traditional non-integrated manner and a second pair of sections that were integrated across the chemistry and biology disciplines in both the scope and sequence of the content delivery. Both integrated and non-integrated sections were taught by the same instructors, who have expertise in both chemistry and biology to ensure a full understanding of both courses’ content. Attitudinal surveys administered at the beginning and end of the semester showed that students in the integrated BIOL/CHEM section of our pilot study appreciated the delivery of an integrated curriculum and improved their awareness of the connections between the two disciplines. End-of-course assessments of topic mastery demonstrated improvements in the integrated students’ capacity to understand and apply both biology and chemistry topics compared to students in the non-integrated sections
First Calculation of Hyperon Axial Couplings from Lattice QCD
In this work, we report the first lattice calculation of hyperon axial
couplings, using the 2+1-flavor MILC configurations and domain-wall fermion
valence quarks. Both the and axial couplings are computed for
the first time in lattice QCD. In particular we find that and .Comment: 5 pages, 2 figure
Effects of environmental variables on invasive amphibian activity: using model selection on quantiles for counts
Many different factors influence animal activity. Often, the value of an environmental variable may influence significantly the upper or lower tails of the activity distribution. For describing relationships with heterogeneous boundaries, quantile regressions predict a quantile of the conditional distribution of the dependent variable. A quantile count model extends linear quantile regression methods to discrete response variables, and is useful if activity is quantified by trapping, where there may be many tied (equal) values in the activity distribution, over a small range of discrete values. Additionally, different environmental variables in combination may have synergistic or antagonistic effects on activity, so examining their effects together, in a modeling framework, is a useful approach. Thus, model selection on quantile counts can be used to determine the relative importance of different variables in determining activity, across the entire distribution of capture results. We conducted model selection on quantile count models to describe the factors affecting activity (numbers of captures) of cane toads (Rhinella marina) in response to several environmental variables (humidity, temperature, rainfall, wind speed, and moon luminosity) over eleven months of trapping. Environmental effects on activity are understudied in this pest animal. In the dry season, model selection on quantile count models suggested that rainfall positively affected activity, especially near the lower tails of the activity distribution. In the wet season, wind speed limited activity near the maximum of the distribution, while minimum activity increased with minimum temperature. This statistical methodology allowed us to explore, in depth, how environmental factors influenced activity across the entire distribution, and is applicable to any survey or trapping regime, in which environmental variables affect activity
Impact of Lattice Strangeness Asymmetry Data in the CTEQ-TEA Global Analysis
We study the impact of lattice data on the determination of the strangeness
asymmetry distribution in the general
CTEQ-TEA global analysis of parton distribution functions (PDFs) of the proton.
Firstly, we find that allowing a nonvanishing , at the initial
~GeV scale, in a global PDF analysis leads to a CT18As fit with
similar quality to CT18A. Secondly, including the lattice data in the
CT18As\_Lat fit greatly reduces the -PDF error band size in the large-
region. To further reduce its error would require more precise lattice data,
extended to smaller values. We take ATLAS 7 TeV and production
data, SIDIS di-muon production data, structure function data, E866 NuSea
data, and E906 SeaQuest data as examples to illustrate the implication of
CT18As and CT18As\_Lat fits. The parametrization dependence for PDF ratio
is analyzed with CT18As2 and CT18As2\_Lat
fits as results.Comment: 37 pages, 19 figures. arXiv admin note: text overlap with
arXiv:2204.0794
Nucleon structure with two flavors of dynamical domain-wall fermions
We present a numerical lattice quantum chromodynamics calculation of
isovector form factors and the first few moments of the isovector structure
functions of the nucleon. The calculation employs two degenerate dynamical
flavors of domain-wall fermions, resulting in good control of chiral symmetry
breaking. Non-perturbative renormalization of the relevant quark currents is
performed where necessary. The inverse lattice spacing, , is about 1.7
GeV. We use degenerate up and down dynamical quark masses around 1, 3/4 and 1/2
the strange quark mass. The physical volume of the lattice is about
. The ratio of the isovector vector to axial charges, ,
trends a bit lower than the experimental value as the quark mass is reduced
toward the physical point. We calculate the momentum-transfer dependences of
the isovector vector, axial, induced tensor and induced pseudoscalar form
factors. The Goldberger-Treiman relation holds at low momentum transfer and
yields a pion-nucleon coupling, , where the quoted
error is only statistical. We find that the flavor non-singlet quark momentum
fraction and quark helicity fraction
overshoot their experimental values after linear chiral extrapolation. We
obtain the transversity, in
at 2 GeV and a twist-3 polarized moment, , appears small, suggesting that
the Wandzura-Wilczek relation holds approximately. We discuss the systematic
errors in the calculation, with particular attention paid to finite-volume
effects, excited-state contamination, and chiral extrapolations.Comment: 28 pages in two columns; 37 figures, 12 table
Global and regional effects of the photochemistry of CH_3O_2NO_2: evidence from ARCTAS
Using measurements from the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) experiment, we show that methyl peroxy nitrate (CH_3O_2NO_2) is present in concentrations of ~5–15 pptv in the springtime arctic upper troposphere. We investigate the regional and global effects of CH_3O_2NO_2 by including its chemistry in the GEOS-Chem 3-D global chemical transport model. We find that at temperatures below 240 K inclusion of CH_3O_2NO_2 chemistry results in decreases of up to ~20 % in NO_x, ~20 % in N_2O_5, ~5 % in HNO3, ~2 % in ozone, and increases in methyl hydrogen peroxide of up to ~14 %. Larger changes are observed in biomass burning plumes lofted to high altitude. Additionally, by sequestering NO_x at low temperatures, CH_3O_2NO_2 decreases the cycling of HO_2 to OH, resulting in a larger upper tropospheric HO_2 to OH ratio. These results may impact some estimates of lightning NO_x sources as well as help explain differences between models and measurements of upper tropospheric composition
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