1,273,111 research outputs found
Drastic Reduction of Shot Noise in Semiconductor Superlattices
We have found experimentally that the shot noise of the tunneling current
through an undoped semiconductor superlattice is reduced with respect to the
Poissonian noise value , and that the noise approaches 1/3 of that value
in superlattices whose quantum wells are strongly coupled. On the other hand,
when the coupling is weak or when a strong electric field is applied to the
superlattice the noise becomes Poissonian. Although our results are
qualitatively consistent with existing theories for one-dimensional mulitple
barriers, the theories cannot account for the dependence of the noise on
superlattice parameters that we have observed.Comment: 4 Pages, 3Figure
From Wave Geometry to Fake Supergravity
The `Wave Geometry' equation of the pre-WWII Hiroshima program is also the
key equation of the current `fake supergravity' program. I review the status of
(fake) supersymmetric domain walls and (fake) pseudo-supersymmetric
cosmologies. An extension of the domain-wall/cosmology correspondence to a
triple correspondence with instantons shows that `pseudo-supersymmetry' has
another interpretation as Euclidean supersymmetry.Comment: 14 pages. Minor Revisions to original. To appear in proceedings of
the 5th International Symposium on Quantum Theory and Symmetries (QTS5),
Vallodolid, July 2007. in version
Radiative collisional heating at the Doppler limit for laser-cooled magnesium atoms
We report Monte Carlo wave function simulation results on cold collisions
between magnesium atoms in a strong red-detuned laser field. This is the normal
situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate
due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical
trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We
find that radiative heating does not seem to affect the Doppler limit in this
case. We also describe a channelling mechanism due to the missing Q branch in
the excitation scheme, which could lead to a suppression of inelastic
collisions, and find that this mechanism is not present in our simulation
results due to the multistate character of the excitation process.Comment: 4 pages, RevTeX 4; v2 contains minor revisions based on referee
comments (5 pages
Mode doubling and tripling in reaction-diffusion patterns on growing domains: A piece-wise linear model
Reaction-diffusion equations are ubiquitous as models of biological pattern formation. In a recent paper [4] we have shown that incorporation of domain growth in a reaction-diffusion model generates a sequence of quasi-steady patterns and can provide a mechanism for increased reliability of pattern selection. In this paper we analyse the model to examine the transitions between patterns in the sequence. Introducing a piecewise linear approximation we find closed form approximate solutions for steady-state patterns by exploiting a small parameter, the ratio of diffusivities, in a singular perturbation expansion. We consider the existence of these steady-state solutions as a parameter related to the domain length is varied and predict the point at which the solution ceases to exist, which we identify with the onset of transition between patterns for the sequence generated on the growing domain. Applying these results to the model in one spatial dimension we are able to predict the mechanism and timing of transitions between quasi-steady patterns in the sequence. We also highlight a novel sequence behaviour, mode-tripling, which is a consequence of a symmetry in the reaction term of the reaction-diffusion system
Universality and the five-dimensional Ising model
We solve the long-standing discrepancy between Monte Carlo results and the
renormalization prediction for the Binder cumulant of the five-dimensional
Ising model. Our conclusions are based on accurate Monte Carlo data for systems
with linear sizes up to L=22. A detailed analysis of the corrections to scaling
allows the extrapolation of these results to L=\infinity. Our determination of
the critical point, K_c=0.1139150 (4), is more than an order of magnitude more
accurate than previous estimates.Comment: 6 pages LaTeX, 1 PostScript figure. Uses cite.sty (included) and
epsf.sty. Also available as PostScript and PDF file at
http://www.tn.tudelft.nl/tn/erikpubs.htm
Exact treatment of dispersion relations in pp and p\=p elastic scattering
Based on a study of the properties of the Lerch's transcendent, exact closed
forms of dispersion relations for amplitudes and for derivatives of amplitudes
in pp and p\=p scattering are introduced. Exact and complete expressions are
written for the real parts and for their derivatives at based on given
inputs for the energy dependence of the total cross sections and of the slopes
of the imaginary parts. The results are prepared for application in the
analysis of forward scattering data of the pp and p\=p systems at all energies,
where exact and precise representations can be written.Comment: 23 pages, 1 figur
Physical mechanism of the (tri)critical point generation
We discuss some ideas resulting from a phenomenological relation recently
declared between the tension of string connecting the static quark-antiquark
pair and surface tension of corresponding cylindrical bag. This relation
analysis leads to the temperature of vanishing surface tension coefficient of
the QGP bags at zero baryonic charge density as T_\sigma = 152.9 +- 4.5 MeV. We
develop the view point that this temperature value is not a fortuitous
coincidence with the temperature of (partial) chiral symmetry restoration as
seen in the lattice QCD simulations. Besides, we argue that T_\sigma defines
the QCD (tri)critical endpoint temperature and claim that a negative value of
surface tension coefficient recently discovered is not a sole result, but
should also exist in ordinary liquids at the supercritical temperatures.Comment: Talk given at the Conference "Critical Point and Onset of
Deconfinement (CPOD)" that held on August 23 - 29, 2010, JINR, Dubna, Russia.
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Abstract not available
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