3,880 research outputs found
Stability and instability of a random multiple access model with adaptive energy harvesting
We introduce a model for the classical synchronised multiple access system
with a single transmission channel and a randomised transmission protocol
(ALOHA). We assume in addition that there is an energy harvesting mechanism,
and any message transmission requires a unit of energy. Units of energy arrive
randomly and independently of anything else. We analyse stability and
instability conditions for this model
RIDDLE: Race and ethnicity Imputation from Disease history with Deep LEarning
Anonymized electronic medical records are an increasingly popular source of
research data. However, these datasets often lack race and ethnicity
information. This creates problems for researchers modeling human disease, as
race and ethnicity are powerful confounders for many health exposures and
treatment outcomes; race and ethnicity are closely linked to
population-specific genetic variation. We showed that deep neural networks
generate more accurate estimates for missing racial and ethnic information than
competing methods (e.g., logistic regression, random forest). RIDDLE yielded
significantly better classification performance across all metrics that were
considered: accuracy, cross-entropy loss (error), and area under the curve for
receiver operating characteristic plots (all ). We made specific
efforts to interpret the trained neural network models to identify, quantify,
and visualize medical features which are predictive of race and ethnicity. We
used these characterizations of informative features to perform a systematic
comparison of differential disease patterns by race and ethnicity. The fact
that clinical histories are informative for imputing race and ethnicity could
reflect (1) a skewed distribution of blue- and white-collar professions across
racial and ethnic groups, (2) uneven accessibility and subjective importance of
prophylactic health, (3) possible variation in lifestyle, such as dietary
habits, and (4) differences in background genetic variation which predispose to
diseases
Elasticity-based polymer sorting in active fluids: A Brownian dynamics study
While the dynamics of polymer chains in equilibrium media is well understood
by now, the polymer dynamics in active non-equilibrium environments can be very
different. Here we study the dynamics of polymers in a viscous medium
containing self-propelled particles in two dimensions by using Brownian
dynamics simulations. We find that the polymer center of mass exhibits a
superdiffusive motion at short to intermediate times and the motion turns
normal at long times, but with a greatly enhanced diffusivity. Interestingly,
the long time diffusivity shows a non-monotonic behavior as a function of the
chain length and stiffness. We analyze how the polymer conformation and the
accumulation of the self-propelled particles, and therefore the directed motion
of the polymer, are correlated. At the point of maximal polymer diffusivity,
the polymer has preferentially bent conformations maintained by the balance
between the chain elasticity and the propelling force generated by the active
particles. We also consider the barrier crossing dynamics of actively-driven
polymers in a double-well potential. The barrier crossing times are
demonstrated to have a peculiar non-monotonic dependence, related to that of
the diffusivity. This effect can be potentially utilized for sorting of
polymers from solutions in \textit{in vitro} experiments.Comment: 11 pages, 7 figure
Annealing Effect for Supersolid Fraction in He
We report on experimental confirmation of the non-classical rotational
inertia (NCRI) in solid helium samples originally reported by Kim and Chan. The
onset of NCRI was observed at temperatures below ~400 mK. The ac velocity for
initiation of the NCRI suppression is estimated to be ~10 m/sec. After an
additional annealing of the sample at K for 12 hours, ~ 10% relative
increase of NCRI fraction was observed. Then after repeated annealing with the
same conditions, the NCRI fraction was saturated. It differs from Reppy's
observation on a low pressure solid sample.Comment: to be published in J. of Low Temp. Phys. (QFS2006 proceedings
Quasiclassical theory of non-adiabatic tunneling in nanocontacts induced by phase-controlled ultrashort light pulses
We theoretically investigate tunneling through free-space or dielectric
nanogaps between metallic nanocontacts driven by ultrashort ultrabroadband
light pulses. For this purpose we develop a time-dependent quasiclassical
theory being especially suitable to describe the tunneling process in the
non-adiabatic regime, when this process can be significantly influenced by the
photon absorption as the electron moves in the classically forbidden region.
Firstly, the case of driving by an ideal half-cycle pulse is studied. For
different distances between the contacts, we analyze the main solutions having
the form of a quasiclassical wave packet of the tunneling electron and an
evanescent wave of the electron density. For each of these solutions the
resulting tunneling probability is determined with the exponential accuracy
inherent to the method. We identify a crossover between two tunneling regimes
corresponding to both solutions in dependence on the field strength and
intercontact distance that can be observed in the corresponding behaviour of
the tunneling probability. Secondly, considering realistic temporal profiles of
few-femtosecond pulses, we demonstrate that the preferred direction of the
electron transport through the nanogap can be controlled by changing the
carrier-envelope phase of the pulse, in agreement with recent experimental
findings and numerical simulations. We find analytical expressions for the
tunneling probability, determining the resulting charge transfer in dependence
on the pulse parameters. Further, we determine temporal shifts of the outgoing
electron trajectories with respect to the peaks of the laser field in
dependence on the pulse phase and illustrate when the non-adiabatical character
of the tunneling process is particularly important.Comment: 38 pages, 13 figure
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