1,886 research outputs found
No evidence for an effect of testosterone administration on delay discounting in male university students
SummaryIntertemporal choices between a smaller sooner and a larger delayed reward are one of the most important types of decisions humans face in their everyday life. The degree to which individuals discount delayed rewards correlates with impulsiveness. Steep delay discounting has been associated with negative outcomes over a wide range of behaviors such as addiction. However, little is known about the biological foundations of delay discounting. Here, we examine a potential causal link between delay discounting and testosterone, a hormone which has been associated with other types of impulsive behavior. In our double-blind placebo-controlled study 91 healthy young men either received a topical gel containing 50mg of testosterone (N=46) or a placebo (N=45) before participating in a delay discounting task with real incentives. Our main finding is that a single dose administration of testosterone did not lead to significant differences in discount rates between the placebo and the testosterone group. Within groups and in the pooled sample, no significant relationship between testosterone and discount rates was observed. At the same time, we do replicate standard findings from the delay discounting literature such as a magnitude-of-rewards effect on discount rates. In sum, our findings suggest that circulating testosterone does not have a significant effect on delay discounting in young men
Boundary Effects on Dynamic Behavior of Josephson-Junction Arrays
The boundary effects on the current-voltage characteristics in
two-dimensional arrays of resistively shunted Josephson junctions are examined.
In particular, we consider both the conventional boundary conditions (CBC) and
the fluctuating twist boundary conditions (FTBC), and make comparison of the
obtained results. It is observed that the CBC, which have been widely adopted
in existing simulations, may give a problem in scaling, arising from rather
large boundary effects; the FTBC in general turn out to be effective in
reducing the finite-size effects, yielding results with good scaling behavior.
To resolve the discrepancy between the two boundary conditions, we propose that
the proper scaling in the CBC should be performed with the boundary data
discarded: This is shown to give results which indeed scale well and are the
same as those from the FTBC.Comment: RevTex, Final version to appear in Phys. Rev.
Vortex dynamics for two-dimensional XY models
Two-dimensional XY models with resistively shunted junction (RSJ) dynamics
and time dependent Ginzburg-Landau (TDGL) dynamics are simulated and it is
verified that the vortex response is well described by the Minnhagen
phenomenology for both types of dynamics. Evidence is presented supporting that
the dynamical critical exponent in the low-temperature phase is given by
the scaling prediction (expressed in terms of the Coulomb gas temperature
and the vortex renormalization given by the dielectric constant
) both for RSJ and TDGL
and that the nonlinear IV exponent a is given by a=z+1 in the low-temperature
phase. The results are discussed and compared with the results of other recent
papers and the importance of the boundary conditions is emphasized.Comment: 21 pages including 15 figures, final versio
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Ultrafast optically induced spin transfer in ferromagnetic alloys
The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism
Accretion, Outflows, and Winds of Magnetized Stars
Many types of stars have strong magnetic fields that can dynamically
influence the flow of circumstellar matter. In stars with accretion disks, the
stellar magnetic field can truncate the inner disk and determine the paths that
matter can take to flow onto the star. These paths are different in stars with
different magnetospheres and periods of rotation. External field lines of the
magnetosphere may inflate and produce favorable conditions for outflows from
the disk-magnetosphere boundary. Outflows can be particularly strong in the
propeller regime, wherein a star rotates more rapidly than the inner disk.
Outflows may also form at the disk-magnetosphere boundary of slowly rotating
stars, if the magnetosphere is compressed by the accreting matter. In isolated,
strongly magnetized stars, the magnetic field can influence formation and/or
propagation of stellar wind outflows. Winds from low-mass, solar-type stars may
be either thermally or magnetically driven, while winds from massive, luminous
O and B type stars are radiatively driven. In all of these cases, the magnetic
field influences matter flow from the stars and determines many observational
properties. In this chapter we review recent studies of accretion, outflows,
and winds of magnetized stars with a focus on three main topics: (1) accretion
onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and
(3) winds from isolated massive magnetized stars. We show results obtained from
global magnetohydrodynamic simulations and, in a number of cases compare global
simulations with observations.Comment: 60 pages, 44 figure
The range and level of impurities in CO2 streams from different carbon capture sources
For CO2 capture and storage deployment, the impact of impurities in the gas or dense phase CO2 stream arising from fossil fuel power plants, or large scale industrial emitters, is of fundamental importance to the safe and economic transportation and storage of the captured CO2. This paper reviews the range and level of impurities expected from the main capture technologies used with fossil-fuelled power plants in addition to other CO2 emission-intensive industries. Analysis is presented with respect to the range of impurities present in CO2 streams captured using pre-combustion, post-combustion and oxy-fuel technologies, in addition to an assessment of the different parameters affecting the CO2 mixture composition. This includes modes of operation of the power plant, and different technologies for the reduction and removal of problematic components such as water and acid gases (SOx/NOx). A literature review of data demonstrates that the purity of CO2 product gases from carbon capture sources is highly dependent upon the type of technology used. This paper also addresses the CO2 purification technologies available for the removal of CO2 impurities from raw oxy-fuel flue gas, such as Hg and non-condensable compounds. CO2 purities of over 99% are achievable using post-combustion capture technologies with low levels of the main impurities of N2, Ar and O2. However, CO2 capture from oxy-fuel combustion and integrated gasification combined cycle power plants will need to take into consideration the removal of non-condensables, acid gas species, and other contaminants. The actual level of CO2 purity required will be dictated by a combination of transport and storage requirements, and process economics
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
Search for the standard model Higgs boson in tau final states
We present a search for the standard model Higgs boson using hadronically
decaying tau leptons, in 1 inverse femtobarn of data collected with the D0
detector at the Fermilab Tevatron ppbar collider. We select two final states:
tau plus missing transverse energy and b jets, and tau+ tau- plus jets. These
final states are sensitive to a combination of associated W/Z boson plus Higgs
boson, vector boson fusion and gluon-gluon fusion production processes. The
observed ratio of the combined limit on the Higgs production cross section at
the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of
115 GeV.Comment: publication versio
Search for W' bosons decaying to an electron and a neutrino with the D0 detector
This Letter describes the search for a new heavy charged gauge boson W'
decaying into an electron and a neutrino. The data were collected with the D0
detector at the Fermilab Tevatron proton-antiproton Collider at a
center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity
of about 1 inverse femtobarn. Lacking any significant excess in the data in
comparison with known processes, an upper limit is set on the production cross
section times branching fraction, and a W' boson with mass below 1.00 TeV can
be excluded at the 95% C.L., assuming standard-model-like couplings to
fermions. This result significantly improves upon previous limits, and is the
most stringent to date.Comment: submitted to Phys. Rev. Let
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