16,673 research outputs found
Distance to Multiple Kinematic Components of Quasar Outflows: VLT Observations of QSO 2359-1241 and SDSS J0318-0600
Using high resolution VLT spectra, we study the multi-component outflow
systems of two quasars exhibiting intrinsic Fe II absorption (QSO 2359-1241 and
SDSS J0318-0600). From the extracted ionic column densities and using
photoionization modeling we determine the gas density, total column density,
and ionization parameter for several of the components. For each object the
largest column density component is also the densest, and all other components
have densities of roughly 1/4 of that of the main component. We demonstrate
that all the absorbers lie roughly at the same distance from the source.
Further, we calculate the total kinetic luminosities and mass outflow rates of
all components and show that these quantities are dominated by the main
absorption component.Comment: 27 pages, 5 figure
Using collaborative online international learning as an approach to promote curricula internationalization in engineering
E-learning tools: engaging our students?
Since Generation Z students have grown up around WIFI-laptops, video game, etc. they expect technology to be involved in teaching approaches, however students' perception towards e-learning tools indicate that 80% of students (∼180 students) prefer a face-to-face approach.(undefined
Peaks of Otter Salamander (Plethodon hubrichti) Condition: Optimal Elevations for This Montane Species of Salamander
Undergraduate
Basi
Evaluating the Applicability of the Fokker-Planck Equation in Polymer Translocation: A Brownian Dynamics Study
Brownian dynamics (BD) simulations are used to study the translocation
dynamics of a coarse-grained polymer through a cylindrical nanopore. We
consider the case of short polymers, with a polymer length, N, in the range
N=21-61. The rate of translocation is controlled by a tunable friction
coefficient, gamma_{0p}, for monomers inside the nanopore. In the case of
unforced translocation, the mean translocation time scales with polymer length
N as ~ (N-N_p)^alpha, where N_p is the average number of monomers in the
nanopore. The exponent approaches the value alpha=2 when the pore friction is
sufficiently high, in accord with the prediction for the case of the
quasi-static regime where pore friction dominates. In the case of forced
translocation, the polymer chain is stretched and compressed on the cis and
trans sides, respectively, for low gamma_{0p}. However, the chain approaches
conformational quasi-equilibrium for sufficiently large gamma_{0p}. In this
limit the observed scaling of with driving force and chain length
supports the FP prediction that is proportional to N/f_d for sufficiently
strong driving force. Monte Carlo simulations are used to calculate
translocation free energy functions for the system. The free energies are used
with the Fokker-Planck equation to calculate translocation time distributions.
At sufficiently high gamma_{0p}, the predicted distributions are in excellent
agreement with those calculated from the BD simulations. Thus, the FP equation
provides a valid description of translocation dynamics for sufficiently high
pore friction for the range of polymer lengths considered here. Increasing N
will require a corresponding increase in pore friction to maintain the validity
of the FP approach. Outside the regime of low N and high pore friction, the
polymer is out of equilibrium, and the FP approach is not valid.Comment: 13 pages, 11 figure
Phylogenetic surveillance of viral genetic diversity and the evolving molecular epidemiology of human immunodeficiency virus type 1
With ongoing generation of viral genetic diversity and increasing levels of migration, the global human immunodeficiency virus type 1 (HIV-1) epidemic is becoming increasingly heterogeneous. In this study, we investigate the epidemiological characteristics of 5,675 HIV-1 pol gene sequences sampled from distinct infections in the United Kingdom. These sequences were phylogenetically analyzed in conjunction with 976 complete-genome and 3,201 pol gene reference sequences sampled globally and representing the broad range of HIV-1 genetic diversity, allowing us to estimate the probable geographic origins of the various strains present in the United Kingdom. A statistical analysis of phylogenetic clustering in this data set identified several independent transmission chains within the United Kingdom involving recently introduced strains and indicated that strains more commonly associated with infections acquired heterosexually in East Africa are spreading among men who have sex with men. Coalescent approaches were also used and indicated that the transmission chains that we identify originated in the late 1980s to early 1990s. Similar changes in the epidemiological structuring of HIV epidemics are likely to be taking in place in other industrialized nations with large immigrant populations. The framework implemented here takes advantage of the vast amount of routinely generated HIV-1 sequence data and can provide epidemiological insights not readily obtainable through standard surveillance methods
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