16,389 research outputs found
Micromagnetic Simulation of Nanoscale Films with Perpendicular Anisotropy
A model is studied for the theoretical description of nanoscale magnetic
films with high perpendicular anisotropy. In the model the magnetic film is
described in terms of single domain magnetic grains with Ising-like behavior,
interacting via exchange as well as via dipolar forces. Additionally, the model
contains an energy barrier and a coupling to an external magnetic field.
Disorder is taken into account in order to describe realistic domain and domain
wall structures. The influence of a finite temperature as well as the dynamics
can be modeled by a Monte Carlo simulation.
Many of the experimental findings can be investigated and at least partly
understood by the model introduced above. For thin films the magnetisation
reversal is driven by domain wall motion. The results for the field and
temperature dependence of the domain wall velocity suggest that for thin films
hysteresis can be described as a depinning transition of the domain walls
rounded by thermal activation for finite temperatures.Comment: Revtex, Postscript Figures, to be published in J. Appl.Phy
Study of Scalar Top Quarks in the Neutralino and Chargino Decay Channel
The scalar top discovery potential has been studied with a full-statistics
background simulation at sqrt(s)=500 GeV and L = 500 fb-1 for the TESLA
project. The beam polarization is very important to measure the scalar top
mixing angle and to determine its mass. The latest estimation of the beam
polarization parameters is applied. This study includes e+ polarization, which
improves the sensitivity. For a 180 GeV scalar top at minimum production cross
section, we obtain delta(m) = 0.8 GeV and delta(cosT) = 0.008 in the neutralino
decay channel, and delta(m) = 0.5 GeV and delta(cosT) = 0.004 in the chargino
decay channel.Comment: 4 pages, 6 figures, Proc. LCWS Chicago, November 200
A Highly Selective First-Level Muon Trigger With MDT Chamber Data for ATLAS at HL-LHC
Highly selective triggers are essential for the physics programme of the
ATLAS experiment at HL-LHC where the instantaneous luminosity will be about an
order of magnitude larger than the LHC instantaneous luminosity in Run 1. The
first level muon trigger rate is dominated by low momentum muons below the
nominal trigger threshold due to the moderate momentum resolution of the
Resistive Plate and Thin Gap trigger chambers. The resulting high trigger rates
at HL-LHC can be sufficiently reduced by using the data of the precision Muon
Drift Tube chambers for the trigger decision. This requires the implementation
of a fast MDT read-out chain and of a fast MDT track reconstruction algorithm
with a latency of at most 6 microseconds. A hardware demonstrator of the fast
read-out chain has been successfully tested at the HL-LHC operating conditions
at the CERN Gamma Irradiation Facility. The fast track reconstruction algorithm
has been implemented on a fast trigger processor
Executive compensation and the susceptibility of firms to hostile takeovers : An empirical investigation of the U.S. oil industry
We investigate the suggested substitutive relation between executive compensation and the disciplinary threat of takeover imposed by the market for corporate control. We complement other empirical studies on managerial compensation and corporate control mechanisms in three distinct ways. First, we concentrate on firms in the oil industry for which agency problems were especially severe in the 1980s. Due to the extensive generation of excess cash flow, product and factor market discipline was ineffective. Second, we obtain a unique data set drawn directly from proxy statements which accounts not only for salary and bonus but for the value of all stock-market based compensation held in the portfolio of a CEO. Our data set consists of 51 firms in the U.S. oil industry from 1977 to 1994. Third, we employ ex ante measures of the threat of takeover at the individual firm level which are superior to ex post measures like actual takeover occurrence or past incidence of takeovers in an industry. Results show that annual compensation and, to a much higher degree, stock-based managerial compensation increase after a firm becomes protected from a hostile takeover. However, clear-cut evidence that CEOs of protected firms receive higher compensation than those of firms considered susceptible to a takeover cannot be found
Radiative return method as a tool in hadronic physics
A short review of both theoretical and experimental aspects of the radiative
return method is presented. It is emphasised that the method gives not only
possibility of the independent from the scan method measurement of the hadronic
cross section, but also can provide information concerning details of the
hadronic interactions. New developments in the PHOKHARA event generator are
also reviewed. The 3 pion and kaon pair production is implemented within the
version 5.0 of the program, together with contributions of the radiative phi
decays to the 2 pion final states.
Missing NLO radiative corrections to the e+e- -> mu+ mu- gamma process will
be implemented in the forthcoming version of the generator
Evolutionary Markovian Strategies in 2 x 2 Spatial Games
Evolutionary spatial 2 x 2 games between heterogeneous agents are analyzed
using different variants of cellular automata (CA). Agents play repeatedly
against their nearest neighbors 2 x 2 games specified by a rescaled payoff
matrix with two parameteres. Each agent is governed by a binary Markovian
strategy (BMS) specified by 4 conditional probabilities [p_R, p_S, p_T, p_P]
that take values 0 or 1. The initial configuration consists in a random
assignment of "strategists" among the 2^4= 16 possible BMS. The system then
evolves within strategy space according to the simple standard rule: each agent
copies the strategy of the neighbor who got the highest payoff. Besides on the
payoff matrix, the dominant strategy -and the degree of cooperation- depend on
i) the type of the neighborhood (von Neumann or Moore); ii) the way the
cooperation state is actualized (deterministically or stochastichally); and
iii) the amount of noise measured by a parameter epsilon. However a robust
winner strategy is [1,0,1,1].Comment: 18 pages, 8 figures (7 of these figures contain 4 encapsulapted
poscript files each
Modeling the X-ray Contribution of X-ray Binary Jets
Astrophysical jets exist in both XRBs and AGN, and seem to share common
features, particularly in the radio. While AGN jets are known to emit X-rays,
the situation for XRB jets is not so clear. Radio jets have been resolved in
several XRBs in the low/hard state, establishing that some form of outflow is
routinely present in this state. Interestingly, the flat-to-inverted radio
synchrotron emission associated with these outflows strongly correlates with
the X-ray emission in several sources, suggesting that the jet plasma plays a
role at higher frequencies. In this same state, there is increasing evidence
for a turnover in the IR/optical where the flat-to-inverted spectrum seems to
connect to an optically thin component extending into the X-rays. We discuss
how jet synchrotron emission is likely to contribute to the X-rays, in addition
to inverse Compton up-scattering, providing a natural explanation for these
correlations and the turnover in the IR/optical band. We present model
parameters for fits to several sources, and address some common misconceptions
about the jet model.Comment: 4 pages, 1 Table, conference proceedings for "The Physics of
Relativistic Jets in the Chandra and XMM Era, Bologna, 2002", Eds. G.
Brunetti, D. E. Harris, R. M. Sambruna & G. Sett
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