12,347 research outputs found
On the Swimming of \textit{Dictyostelium} amoebae
Traditionally, the primary mode for locomotion of amoeboid cells was thought
to be crawling on a substrate. Recently, it has been experimentally shown that
\textit{Dictostelium} amoeba and neutrophils can also swim in a directed
fashion. The mechanisms for amoeboid crawling and swimming were hypothesized to
be similar. In this letter, we show that the shape changes generated by a
crawling \textit{D. discoideum} cell are consistent with swimming.Comment: letter submitted to PNA
Mobility and Saturation Velocity in Graphene on SiO2
We examine mobility and saturation velocity in graphene on SiO2 above room
temperature (300-500 K) and at high fields (~1 V/um). Data are analyzed with
practical models including gated carriers, thermal generation, "puddle" charge,
and Joule heating. Both mobility and saturation velocity decrease with rising
temperature above 300 K, and with rising carrier density above 2x10^12 cm^-2.
Saturation velocity is >3x10^7 cm/s at low carrier density, and remains greater
than in Si up to 1.2x10^13 cm^-2. Transport appears primarily limited by the
SiO2 substrate, but results suggest intrinsic graphene saturation velocity
could be more than twice that observed here
Axinos as Dark Matter
Supersymmetric extensions of the Standard Model that incorporate the axion
solution to the strong CP problem necessarily contain also the axino, the
fermionic partner of the axion. In contrast to the neutralino and the
gravitino, the axino mass is generically not of the order of the
supersymmetry-breaking scale and can be much smaller. The axino is therefore an
intriguing candidate for a stable superpartner. In a previous Letter [1] it was
shown that axinos are a natural candidate for cold dark matter in the Universe
when they are generated non-thermally through out-of-equilibrium neutralino
decays. Here, we extend the study of non-thermal production and include a
competing thermal production mechanism through scatterings and decays of
particles in the plasma. We identify axino masses in the range of tens of MeV
to several GeV (depending on the scenario) as corresponding to cold axino
relics if the reheating temperature \treh is less than about
5\times10^4\gev. At higher \treh and lower mass, axinos could constitute
warm dark matter. In the scenario with axinos as relics, the gravitino problem
finds a natural solution. The lightest superpartner of the Standard Model
spectrum remains effectively stable in high-energy detectors but may be either
neutral or charged. The usual highly restrictive constraint \abundchi\lsim1
on the relic abundance of the lightest neutralino becomes void.Comment: 38 pages, a version to be published at JHE
Surplus Angle and Sign-flipped Coulomb Force in Projectable Horava-Lifshitz Gravity
We obtain the static spherically symmetric vacuum solutions of
Horava-Lifshitz gravity theory, imposing the detailed balance condition only in
the UV limit. We find the solutions in two different coordinate systems, the
Painlev\'e-Gullstrand coordinates and the Poincare coordinates, to examine the
consequences of imposing the projectability condition. The solutions in two
coordinate systems are distinct due to the non-relativistic nature of the HL
gravity. In the Painleve-Gullstrand coordinates complying with the
projectability condition, the solution involves an additional integration
constant which yields surplus angle and implies attractive Coulomb force
between same charges.Comment: 13 page
Dilaton Stabilization and Inflation in the D-brane World
We study the dilaton stabilization in the D-brane world in which a D-brane
constitutes our universe. The dilaton can be stabilized due to the interplay
between the D-brane tension and the negative scalar curvature of extra
dimensions. Cosmic evolution of the dilaton is investigated with the obtained
dilaton potential and it is found that inflation can be realized before the
settlement of the dilaton.Comment: 10 pages, abstract correcte
Neutron and muon-induced background studies for the AMoRE double-beta decay experiment
AMoRE (Advanced Mo-based Rare process Experiment) is an experiment to search
a neutrinoless double-beta decay of Mo in molybdate crystals. The
neutron and muon-induced backgrounds are crucial to obtain the zero-background
level (< counts/(keVkgyr)) for the AMoRE-II experiment,
which is the second phase of the AMoRE project, planned to run at YEMI
underground laboratory. To evaluate the effects of neutron and muon-induced
backgrounds, we performed Geant4 Monte Carlo simulations and studied a
shielding strategy for the AMORE-II experiment. Neutron-induced backgrounds
were also included in the study. In this paper, we estimated the background
level in the presence of possible shielding structures, which meet the
background requirement for the AMoRE-II experiment
Standard Error of Empirical Bayes Estimate in NONMEM® VI.
The pharmacokinetics/pharmacodynamics analysis software NONMEM® output provides model parameter estimates and associated standard errors. However, the standard error of empirical Bayes estimates of inter-subject variability is not available. A simple and direct method for estimating standard error of the empirical Bayes estimates of inter-subject variability using the NONMEM® VI internal matrix POSTV is developed and applied to several pharmacokinetic models using intensively or sparsely sampled data for demonstration and to evaluate performance. The computed standard error is in general similar to the results from other post-processing methods and the degree of difference, if any, depends on the employed estimation options
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