2,635 research outputs found
An exactly soluble noisy traveling wave equation appearing in the problem of directed polymers in a random medium
We calculate exactly the velocity and diffusion constant of a microscopic
stochastic model of evolving particles which can be described by a noisy
traveling wave equation with a noise of order . Our model can be
viewed as the infinite range limit of a directed polymer in random medium with
sites in the transverse direction. Despite some peculiarities of the
traveling wave equations in the absence of noise, our exact solution allows us
to test the validity of a simple cutoff approximation and to show that, in the
weak noise limit, the position of the front can be completely described by the
effect of the noise on the first particle.Comment: 5 page
Media Influence on Youth: Scientific Evidence, Policy Considerations, and the History of Media Self-Regulation
This invited commentary reviews the survey research described in Examining the Relationship between Media use and Aggression, Sexuality, and Body Image and situates this research within the recent history of entertainment media regulation
Efficient hepatitis C virus particle formation requires diacylglycerol acyltransferase-1.
Hepatitis C virus (HCV) infection is closely tied to the lipid metabolism of liver cells. Here we identify the triglyceride-synthesizing enzyme diacylglycerol acyltransferase-1 (DGAT1) as a key host factor for HCV infection. DGAT1 interacts with the viral nucleocapsid core and is required for the trafficking of core to lipid droplets. Inhibition of DGAT1 activity or RNAi-mediated knockdown of DGAT1 severely impairs infectious virion production, implicating DGAT1 as a new target for antiviral therapy
Some algebraic properties of differential operators
First, we study the subskewfield of rational pseudodifferential operators
over a differential field K generated in the skewfield of pseudodifferential
operators over K by the subalgebra of all differential operators.
Second, we show that the Dieudonne' determinant of a matrix
pseudodifferential operator with coefficients in a differential subring A of K
lies in the integral closure of A in K, and we give an example of a 2x2 matrix
differential operator with coefficients in A whose Dieudonne' determiant does
not lie in A.Comment: 15 page
On the relevance of polyynyl-substituted PAHs to astrophysics
We report on the absorption spectra of the polycyclic aromatic hydrocarbon
(PAH) molecules anthracene, phenanthrene, and pyrene carrying either an ethynyl
(-C2H) or a butadiynyl (-C4H) group. Measurements were carried out in the mid
infrared at room temperature on grains embedded in CsI pellets and in the near
ultraviolet at cryogenic temperature on molecules isolated in Ne matrices. The
infrared measurements show that interstellar populations of
polyynyl-substituted PAHs would give rise to collective features in the same
way non-substituted PAHs give rise to the aromatic infrared bands. The main
features characteristic of the substituted molecules correspond to the
acetylenic CH stretching mode near 3.05 mum and to the almost isoenergetic
acetylenic CCH in- and out-of-plane bending modes near 15.9 mum.
Sub-populations defined by the length of the polyynyl side group cause
collective features which correspond to the various acetylenic CC stretching
modes. The ultraviolet spectra reveal that the addition of an ethynyl group to
a non-substituted PAH molecule results in all its electronic transitions being
redshifted. Due to fast internal energy conversion, the bands at shorter
wavelengths are significantly broadened. Those at longer wavelengths are only
barely affected in this respect. As a consequence, their relative peak
absorption increases. The substitution with the longer butadiynyl chain causes
the same effects with a larger magnitude, resulting in the spectra to show a
prominent if not dominating pi-pi* transition at long wavelength. After
discussing the relevance of polyynyl-substituted PAHs to astrophysics, we
conclude that this class of highly conjugated, unsaturated molecules are valid
candidates for the carriers of the diffuse interstellar bands.Comment: 29 pages, 9 figures, accepted for publication in ApJ 2 April 201
A phenomenological theory giving the full statistics of the position of fluctuating pulled fronts
We propose a phenomenological description for the effect of a weak noise on
the position of a front described by the Fisher-Kolmogorov-Petrovsky-Piscounov
equation or any other travelling wave equation in the same class. Our scenario
is based on four hypotheses on the relevant mechanism for the diffusion of the
front. Our parameter-free analytical predictions for the velocity of the front,
its diffusion constant and higher cumulants of its position agree with
numerical simulations.Comment: 10 pages, 3 figure
Current facilitation by plasmon resonances between parallel wires of finite length
The current voltage (IV) characteristics for perpendicular transport through
two sequentially coupled wires of finite length is calculated analytically. The
transport within a Coulomb blockade step is assisted by plasmon resonances that
appear as steps in the IV characteristics with positions and heights depending
on inter- and intrawire interactions. In particular, due to the interwire
interactions, the peak positions shift to lower voltages in comparison to the
noninteracting wires which reflects the facilitation of current by
interactions. The interwire interactions are also found to enhance the
thermally activated current.Comment: 5 pages, 1figur
- …