1,104 research outputs found
Determining a reasonable range of relative numerical tolerance values for simulating deterministic models of biochemical reactions
What values of relative numerical tolerance should be chosen in simulation of a deterministic model of a biochemical reaction is unclear, which impairs the modeling effort since the simulation outcomes of a model may depend on the relative numerical tolerance values. In an attempt to provide a guideline to selecting appropriate numerical tolerance values in simulation of in vivo biochemical reactions, reasonable numerical tolerance values were estimated based on the uncertainty principle and assumptions of related cellular parameters. The calculations indicate that relative numerical tolerance values can be reasonably set at or around 10^4 for the concentrations expressed in ng/L. This work also suggests that further reducing relative numerical values may result in erroneous simulation results.Plant Biology, Ecology, and Evolutio
Effects of Fermi energy, dot size and leads width on weak localization in chaotic quantum dots
Magnetotransport in chaotic quantum dots at low magnetic fields is
investigated by means of a tight binding Hamiltonian on L x L clusters of the
square lattice. Chaoticity is induced by introducing L bulk vacancies. The
dependence of weak localization on the Fermi energy, dot size and leads width
is investigated in detail and the results compared with those of previous
analyses, in particular with random matrix theory predictions. Our results
indicate that the dependence of the critical flux Phi_c on the square root of
the number of open modes, as predicted by random matrix theory, is obscured by
the strong energy dependence of the proportionality constant. Instead, the size
dependence of the critical flux predicted by Efetov and random matrix theory,
namely, Phi_c ~ sqrt{1/L}, is clearly illustrated by the present results. Our
numerical results do also show that the weak localization term significantly
decreases as the leads width W approaches L. However, calculations for W=L
indicate that the weak localization effect does not disappear as L increases.Comment: RevTeX, 8 postscript figures include
Evolutionary Genomics of Genes Involved in Olfactory Behavior in the Drosophila melanogaster Species Group
Previous comparative genomic studies of genes involved in olfactory behavior in Drosophila focused only on particular gene families such as odorant receptor and/or odorant binding proteins. However, olfactory behavior has a complex genetic architecture that is orchestrated by many interacting genes. In this paper, we present a comparative genomic study of olfactory behavior in Drosophila including an extended set of genes known to affect olfactory behavior. We took advantage of the recent burst of whole genome sequences and the development of powerful statistical tools to analyze genomic data and test evolutionary and functional hypotheses of olfactory genes in the six species of the Drosophila melanogaster species group for which whole genome sequences are available. Our study reveals widespread purifying selection and limited incidence of positive selection on olfactory genes. We show that the pace of evolution of olfactory genes is mostly independent of the life cycle stage, and of the number of life cycle stages, in which they participate in olfaction. However, we detected a relationship between evolutionary rates and the position that the gene products occupy in the olfactory system, genes occupying central positions tend to be more constrained than peripheral genes. Finally, we demonstrate that specialization to one host does not seem to be associated with bursts of adaptive evolution in olfactory genes in D. sechellia and D. erecta, the two specialists species analyzed, but rather different lineages have idiosyncratic evolutionary histories in which both historical and ecological factors have been involved
Population Genetics of Duplicated Alternatively Spliced Exons of the Dscam Gene in Daphnia and Drosophila
In insects and crustaceans, the Down syndrome cell adhesion molecule (Dscam) occurs in many different isoforms. These are produced by mutually exclusive alternative splicing of dozens of tandem duplicated exons coding for parts or whole immunoglobulin (Ig) domains of the Dscam protein. This diversity plays a role in the development of the nervous system and also in the immune system. Structural analysis of the protein suggested candidate epitopes where binding to pathogens could occur. These epitopes are coded by regions of the duplicated exons and are therefore diverse within individuals. Here we apply molecular population genetics and molecular evolution analyses using Daphnia magna and several Drosophila species to investigate the potential role of natural selection in the divergence between orthologs of these duplicated exons among species, as well as between paralogous exons within species. We found no evidence for a role of positive selection in the divergence of these paralogous exons. However, the power of this test was low, and the fact that no signs of gene conversion between paralogous exons were found suggests that paralog diversity may nonetheless be maintained by selection. The analysis of orthologous exons in Drosophila and in Daphnia revealed an excess of non-synonymous polymorphisms in the epitopes putatively involved in pathogen binding. This may be a sign of balancing selection. Indeed, in Dr. melanogaster the same derived non-synonymous alleles segregate in several populations around the world. Yet other hallmarks of balancing selection were not found. Hence, we cannot rule out that the excess of non-synonymous polymorphisms is caused by segregating slightly deleterious alleles, thus potentially indicating reduced selective constraints in the putative pathogen binding epitopes of Dscam
Measurement of Muon Neutrino Quasi-Elastic Scattering on Carbon
The observation of neutrino oscillations is clear evidence for physics beyond
the standard model. To make precise measurements of this phenomenon, neutrino
oscillation experiments, including MiniBooNE, require an accurate description
of neutrino charged current quasi-elastic (CCQE) cross sections to predict
signal samples. Using a high-statistics sample of muon neutrino CCQE events,
MiniBooNE finds that a simple Fermi gas model, with appropriate adjustments,
accurately characterizes the CCQE events observed in a carbon-based detector.
The extracted parameters include an effective axial mass, M_A^eff = 1.23+/-0.20
GeV, that describes the four-momentum dependence of the axial-vector form
factor of the nucleon; and a Pauli-suppression parameter, kappa =
1.019+/-0.011. Such a modified Fermi gas model may also be used by future
accelerator-based experiments measuring neutrino oscillations on nuclear
targets.Comment: 5 pages, 3 figure
Measurement of the \nu_\mu charged current \pi^+ to quasi-elastic cross section ratio on mineral oil in a 0.8 GeV neutrino beam
Using high statistics samples of charged current interactions,
MiniBooNE reports a measurement of the single charged pion production to
quasi-elastic cross section ratio on mineral oil (CH), both with and
without corrections for hadron re-interactions in the target nucleus. The
result is provided as a function of neutrino energy in the range 0.4 GeV 2.4 GeV with 11% precision in the region of highest statistics. The
results are consistent with previous measurements and the prediction from
historical neutrino calculations.Comment: 4 pages, 2 figure
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
Design and construction of the MicroBooNE Cosmic Ray Tagger system
The MicroBooNE detector utilizes a liquid argon time projection chamber
(LArTPC) with an 85 t active mass to study neutrino interactions along the
Booster Neutrino Beam (BNB) at Fermilab. With a deployment location near ground
level, the detector records many cosmic muon tracks in each beam-related
detector trigger that can be misidentified as signals of interest. To reduce
these cosmogenic backgrounds, we have designed and constructed a TPC-external
Cosmic Ray Tagger (CRT). This sub-system was developed by the Laboratory for
High Energy Physics (LHEP), Albert Einstein center for fundamental physics,
University of Bern. The system utilizes plastic scintillation modules to
provide precise time and position information for TPC-traversing particles.
Successful matching of TPC tracks and CRT data will allow us to reduce
cosmogenic background and better characterize the light collection system and
LArTPC data using cosmic muons. In this paper we describe the design and
installation of the MicroBooNE CRT system and provide an overview of a series
of tests done to verify the proper operation of the system and its components
during installation, commissioning, and physics data-taking
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