2,920 research outputs found
Mean--field electrodynamics: Critical analysis of various analytical approaches to the mean electromotive force
There are various analytical approaches to the mean electromotive force crucial in mean--field electrodynamics, with
and
being velocity and magnetic field fluctuations. In most cases the
traditional approach, restricted to the second--order correlation
approximation, has been used. Its validity is only guaranteed for a range of
conditions, which is narrow in view of many applications, e.g., in
astrophysics. With the intention to have a wider range of applicability other
approaches have been proposed which make use of the so--called
--approximation, reducing correlations of third order in and
to such of second order. After explaining some basic features of the
traditional approach a critical analysis of the approaches of that kind is
given. It is shown that they lead in some cases to results which are in clear
conflict with those of the traditional approach. It is argued that this
indicates shortcomings of the --approaches and poses serious restrictions
to their applicability. These shortcomings do not result from the basic
assumption of the --approximation. Instead, they seem to originate in
some simplifications made in order to derive without really solving
the equations governing and . A starting point for a new
approach is described which avoids the conflict.Comment: 32 pages, no figures; accepted by Geophys. Astrophys. Fluid Dynam. A
quenching formula for \alpha and a section on comparisons with numerical
simulations added; references amended; changes in presentation and languag
Continuations of Hermitian indefinite functions and corresponding canonical systems : an example
M. G. Krein established a close connection between the continuation problem of positive definite functions from a finite interval to the real axis and the inverse spectral problem for differential operators. In this note we study such a connection for the function f(t) = 1 − |t|, t - R, which is not positive definite on R: its restrictions fa := f|(−2a,2a) are positive definite if a ≤ 1 and have one negative square if a > 1. We show that with f a canonical differential equation or a Sturm-Liouville equation can be associated which have a singularity
Do women behave more reciprocally than men? Gender differences in real effort dictator games
We analyze dictator allocation decisions in an experiment where the recipients have to earn the pot to be divided with a real-effort task. As the recipients move before the dictators, their effort decisions resemble the first move in a trust game. Depending on the recipients' performance, the size of the pot is either high or low. We compare this real-effort treatment to a baseline treatment where the pot is a windfall gain and where a lottery determines the pot size. In the baseline treatment, reciprocity cannot play a role. We find that female dictators show reciprocity and decrease their taking-rates significantly in the real-effort treatment. This treatment effect is larger when female dictators make a decision on recipients who successfully generated a large pot compared to the case where the recipients performed poorly. By contrast, there is no treatment effect with male dictators, who generally exhibit more sefish behavior. --Gender,Reciprocity,Dictator Game,Real Effort
Granular Structure Determined by Terahertz Scattering
Light-scattering in the terahertz region is demonstrated for granular matter.
A quantum-cascade laser is used in a benchtop setup to determine the
angle-dependent scattering of spherical grains as well as coffee powder and
sugar grains. For the interpretation of the form factors for the scattering
from single particles one has to go beyond the usual Rayleigh-Gans-Debye theory
and apply calculations within Mie theory. In addition to single scattering also
collective correlations can be identified and extracted as a static structure
factor.Comment: 7 pages, 12 figure
The hidden cost of downsizing: demotivating the remaining employees
There may be substantial costs associated with the 'survival syndrome' phenomenon, write Frank Drzensky and Matthias Hein
A nonstructural polypeptide encoded by immediate-early transcription unit 1 of murine cytomegalovirus is recognized by cytolytic T lymphocytes
We have constructed target cells by cotransfection of the MHC gene Ld and fragments of murine cytomegalovirus (MCMV) DNA coding for nonstructural immediate-early (IE) proteins. Transfectants were tested by using CTL clone IE1 with specificity for an IE epitope presented in association with Ld. Data show that clone IE1 recognizes a product of the ie1 transcription unit of MCMV, and that its specificity is shared by approximately 25% of polyclonal IE-specific CTL. The results provide the first definite evidence that expression of a herpes virus IE gene encoding a regulatory protein gives rise to antigen expression detectable by specific CT
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