20,497 research outputs found
Jarzynski equation for a simple quantum system: Comparing two definitions of work
The validity of the Jarzynski equation for a very simple, exactly solvable
quantum system is analyzed. The implications of two different definitions of
work proposed in the literature are investigated. The first one derives from
measurements of the system energy at the beginning and at the end of the
process under consideration making the work a classical stochastic variable
with transition probabilities derived from quantum mechanics. In the second
definition an operator of work is introduced and the average in the Jarzynski
equation is a quantum expectation value. For the first definition a general
quantum mechanical version of the Jarzynski equation is known to hold. For the
second one the Jarzynski equation fails to yield the free energy difference at
low temperature.Comment: 5 papes, 1 figure largly rewritten and slightly enlarged versio
On the electromagnetic force on a polarizable body
The force on a macroscopic polarizable body in an inhomogenous
electromagnetic field is calculated for three simple exactly solvable
situations. Comparing different approaches we pinpoint possible pitfalls and
resolve recent confusion about the force density in ferrofluids.Comment: 8 pages, 3 figures, submitted to Am. J. Phy
Digital data reformatter/deserializer
A method and apparatus is presented for reformatting and de-serializing a serially-received sequence of data words, each consisting of a fixed number of binary data bits. A block of nm bits is serially fed into a shift register or serially-connected group of shift registers. In lieu of the(nm-1)th shifts, the bits are rearranged within the shift register in parallel fashion, according to a prescribed scheme. Shifting then continues, until the first bit of each data word appears in the last bit position in the shift register, at which time that data word is shifted in parallel into an output buffer stage, from which it is outputted in parallel, after a fixed delay
Hadronic photon interactions at high energies
A simple phenomenological introduction to the physics of multi-pomeron
exchange amplitudes in connection with the Abramovski-Gribov-Kancheli (AGK)
cutting rules is given. The AGK cutting rules are applied to obtain qualitative
and quantitative predictions on multiparticle production at high energies. On
this basis, particle production in hadron-hadron scattering, photoproduction,
and in particular the transition to deep-inelastic scattering is discussed.Comment: LaTeX, 6 pages, 6 ps-figs, sprocl.sty, talk given by R. Engel at
"XXVI International Symposium on Multiparticle Dynamics" held in Faro,
Portugal, September 199
A new possibility to monitor collisions of relativistic heavy ions at LHC and RHIC
We consider the radiation of particles of one bunch in the collective field
of the oncoming bunch, called coherent bremsstrahlung (CBS). The main
characteristics of CBS for LHC (in the Pb-Pb mode) and for RHIC are calculated.
At LHC about photons per second are expected for
photon energies eV. It seems that CBS
can be a potential tool for optimizing collisions and for measuring beam
parameters. The bunch length can be found from the critical energy of the CBS
spectrum; the transverse bunch size is related to the photon rate. A specific
dependence of photon rate on the impact parameter between the beams allows for
a fast control over the beam displacement.Comment: 9 pages + 4 figures, latex with poscript figures uuencode
Spin Hall effect in a two-dimensional electron gas in the presence of a magnetic field
We study the spin Hall effect of a two-dimensional electron gas in the
presence of a magnetic field and both the Rashba and Dresselhaus spin-orbit
interactions. We show that the value of the spin Hall conductivity, which is
finite only if the Zeeman spin splitting is taken into account, may be tuned by
varying the ratio of the in-plane and out-of-plane components of the applied
magnetic field. We identify the origin of this behavior with the different role
played by the interplay of spin-orbit and Zeeman couplings for in-plane and
out-of-plane magnetic field components.Comment: 5 pages, 5 figures, submitte
Impact of Uncertainties in Hadron Production on Air-Shower Predictions
At high energy, cosmic rays can only be studied by measuring the extensive
air showers they produce in the atmosphere of the Earth. Although the main
features of air showers can be understood within a simple model of successive
interactions, detailed simulations and a realistic description of particle
production are needed to calculate observables relevant to air shower
experiments. Currently hadronic interaction models are the main source of
uncertainty of such simulations. We will study the effect of using different
hadronic models available in CORSIKA and CONEX on extensive air shower
predictions.Comment: 12 pages, 6 figures, to appear in the proceedings of International
Conference on Interconnection between High Energy Physics and Astroparticle
Physics: From Colliders to Cosmic Rays, Prague, Czech Republic, 7-13 Sep 200
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