2,802 research outputs found
Vacuum Condensates and the Anomalous Magnetic Moment of a Dirac Fermion
We address anticipated fermion-antifermion and dimension-4 gauge-field
vacuum-condensate contributions to the magnetic portion of the fermion-photon
vertex function in the presence of a vacuum with nonperturbative content, such
as that of QCD. We discuss how inclusion of such condensate contributions may
lead to a vanishing anomalous magnetic moment, in which case vacuum condensates
may account for the apparent consistency between constituent quark masses
characterizing baryon magnetic moments and those characterizing baryon
spectroscopy.Comment: 32 pages, 5 figures. Submitted to Foundations of Physics (1999
Steady State of Pedestrian Flow in Bottleneck Experiments
Experiments with pedestrians could depend strongly on initial conditions.
Comparisons of the results of such experiments require to distinguish carefully
between transient state and steady state. In this work, a feasible algorithm -
Cumulative Sum Control Chart - is proposed and improved to automatically detect
steady states from density and speed time series of bottleneck experiments. The
threshold of the detection parameter in the algorithm is calibrated using an
autoregressive model. Comparing the detected steady states with previous
manually selected ones, the modified algorithm gives more reproducible results.
For the applications, three groups of bottleneck experiments are analysed and
the steady states are detected. The study about pedestrian flow shows that the
difference between the flows in all states and in steady state mainly depends
on the ratio of pedestrian number to bottleneck width. When the ratio is higher
than a critical value (approximately 115 persons/m), the flow in all states is
almost identical with the flow in steady state. Thus we have more possibilities
to compare the flows from different experiments, especially when the detection
of steady states is difficult.Comment: 19 pages, 7 figure
An HMM-based Comparative Genomic Framework for Detecting Introgression in Eukaryotes
One outcome of interspecific hybridization and subsequent effects of
evolutionary forces is introgression, which is the integration of genetic
material from one species into the genome of an individual in another species.
The evolution of several groups of eukaryotic species has involved
hybridization, and cases of adaptation through introgression have been already
established. In this work, we report on a new comparative genomic framework for
detecting introgression in genomes, called PhyloNet-HMM, which combines
phylogenetic networks, that capture reticulate evolutionary relationships among
genomes, with hidden Markov models (HMMs), that capture dependencies within
genomes. A novel aspect of our work is that it also accounts for incomplete
lineage sorting and dependence across loci.
Application of our model to variation data from chromosome 7 in the mouse
(Mus musculus domesticus) genome detects a recently reported adaptive
introgression event involving the rodent poison resistance gene Vkorc1, in
addition to other newly detected introgression regions. Based on our analysis,
it is estimated that about 12% of all sites withinchromosome 7 are of
introgressive origin (these cover about 18 Mbp of chromosome 7, and over 300
genes). Further, our model detects no introgression in two negative control
data sets. Our work provides a powerful framework for systematic analysis of
introgression while simultaneously accounting for dependence across sites,
point mutations, recombination, and ancestral polymorphism
Diagnosing the role of observable distribution shift in scientific replications
Many researchers have identified distribution shift as a likely contributor
to the reproducibility crisis in behavioral and biomedical sciences. The idea
is that if treatment effects vary across individual characteristics and
experimental contexts, then studies conducted in different populations will
estimate different average effects. This paper uses ``generalizability" methods
to quantify how much of the effect size discrepancy between an original study
and its replication can be explained by distribution shift on observed
unit-level characteristics. More specifically, we decompose this discrepancy
into ``components" attributable to sampling variability (including publication
bias), observable distribution shifts, and residual factors. We compute this
decomposition for several directly-replicated behavioral science experiments
and find little evidence that observable distribution shifts contribute
appreciably to non-replicability. In some cases, this is because there is too
much statistical noise. In other cases, there is strong evidence that
controlling for additional moderators is necessary for reliable replication
19.2% Efficient InP Heterojunction Solar Cell with Electron-Selective TiO2 Contact.
We demonstrate an InP heterojunction solar cell employing an ultrathin layer (∼10 nm) of amorphous TiO2 deposited at 120 °C by atomic layer deposition as the transparent electron-selective contact. The TiO2 film selectively extracts minority electrons from the conduction band of p-type InP while blocking the majority holes due to the large valence band offset, enabling a high maximum open-circuit voltage of 785 mV. A hydrogen plasma treatment of the InP surface drastically improves the long-wavelength response of the device, resulting in a high short-circuit current density of 30.5 mA/cm2 and a high power conversion efficiency of 19.2%
Spatially Explicit Large-Scale Environmental Risk Assessment of Pharmaceuticals in Surface Water in China
With improving healthcare and an aging population, the consumption of human pharmaceuticals in China has been increasing dramatically. Environmental risks posed by many active pharmaceutical ingredients (APIs) are still unknown. This study used a spatially explicit dilution-factor methodology to model predicted environmental concentrations (PECs) of 11 human-use APIs in surface water for a preliminary environmental risk assessment (ERA). Median PECs in surface water across China range between 0.01 and 8.0 × 103 ng/L for the different APIs, under a moderate patient use scenario. Higher environmental risks of APIs in surface water are in regions with high water stress, e.g., northern China. Levonorgestrel, estradiol, ethinyl estradiol and abiraterone acetate were predicted to potentially pose a high or moderate environmental risk in China if consumption levels reach those in Europe. Relative risks of these four APIs have the potential to be among those chemicals with the highest impact on surface water in China when compared to the risks associated with other regulated chemicals, including triclosan and some standard water quality parameters including BOD5 (5-day biological oxygen demand), COD (chemical oxygen demand), Cu, Zn, and Hg and linear alkylbenzene sulfonate. This method could support the regulation of this category of chemicals and risk mitigation strategies in China
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