962 research outputs found
Deeply-Virtual Compton Scattering on Deuterium and Neon at HERMES
We report the first observation of azimuthal beam-spin asymmetries in hard
electroproduction of real photons off nuclei. Attributed to the interference
between the Bethe-Heitler process and the deeply-virtual Compton scattering
process, the asymmetry gives access to the latter at the amplitude level. This
process appears to be the theoretically cleanest way to access generalized
parton distributions. The data presented here have been accumulated by the
HERMES experiment at DESY, scattering the HERA 27.6 GeV positron beam off
deuterium and neon gas targets.Comment: 5 pages, 6 figures. Talk given by F. Ellinghaus at the "15th
International Spin Physics Symposium", SPIN 2002, September 9-14, 2002, BNL,
Upton, NY, USA. To be published in the proceeding
Stability of strained heteroepitaxial systems in (1+1) dimensions
We present a simple analytical model for the determination of the stable
phases of strained heteroepitaxial systems in (1+1) dimensions. In order for
this model to be consistent with a subsequent dynamic treatment, all
expressions are adjusted to an atomistic Lennard-Jones system. Good agreement
is obtained when the total energy is assumed to consist of two contributions:
the surface energy and the elastic energy. As a result, we determine the stable
phases as a function of the main ``control parameters'' (binding energies,
coverage and lattice mismatch). We find that there exists no set of parameters
leading to an array of islands as a stable configuration. We however show that
a slight modification of the model can lead to the formation of stable arrays
of islands.Comment: 11 pages, 14 figures, submitted to Physical Review
On the efficient numerical solution of lattice systems with low-order couplings
We apply the Quasi Monte Carlo (QMC) and recursive numerical integration
methods to evaluate the Euclidean, discretized time path-integral for the
quantum mechanical anharmonic oscillator and a topological quantum mechanical
rotor model. For the anharmonic oscillator both methods outperform standard
Markov Chain Monte Carlo methods and show a significantly improved error
scaling. For the quantum mechanical rotor we could, however, not find a
successful way employing QMC. On the other hand, the recursive numerical
integration method works extremely well for this model and shows an at least
exponentially fast error scaling
Systematically extending classical nucleation theory
The foundation for any discussion of first-order phse transitions is
Classical Nucleation Theory(CNT). CNT, developed in the first half of the
twentieth century, is based on a number of heuristically plausible assumtptions
and the majority of theoretical work on nucleation is devoted to refining or
extending these ideas. Ideally, one would like to derive CNT from a more
fundamental description of nucleation so that its extension, development and
refinement could be developed systematically. In this paper, such a development
is described based on a previously established (Lutsko, JCP 136:034509, 2012 )
connection between Classical Nucleation Theory and fluctuating hydrodynamics.
Here, this connection is described without the need for artificial assumtions
such as spherical symmetry. The results are illustrated by application to CNT
with moving clusters (a long-standing problem in the literature) and the
constructrion of CNT for ellipsoidal clusters
Deeply Virtual Compton Scattering at HERA
Deeply virtual Compton scattering has recently been studied by three HERA
experiments, H1, ZEUS and HERMES, covering a broad range of kinematic regimes.
We present cross section measurements of the two collider experiments in the
kinematic region 2<Q^2<100 GeV^2 and 30<W<140 GeV, and compare them to
QCD-based calculations. HERMES measurements of azimuthal asymmetries and their
kinematical dependences are presented for Q^2>1 GeV^2 and 2<W<7 GeV.Comment: 4 pages, 8 figures, submitted to ICHEP 2002 proceedings; citations
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Absence of non-trivial asymptotic scaling in the Kashchiev model of polynuclear growth
In this brief comment we show that, contrary to previous claims [Bartelt M C
and Evans J W 1993 {\it J.\ Phys.\ A} 2743], the asymptotic
behaviour of the Kashchiev model of polynuclear growth is trivial in all
spatial dimensions, and therefore lies outside the Kardar-Parisi-Zhang
universality class.Comment: 3 pages, 4 postscript figures, uses eps
Mise en ligne d'un microscope digitalisé et télécommandé
On décrit la mise en ligne avec un calculateur d'un microscope digitalisé en x, y, z, et télécommandé, pour les mesures dans l'émulsion ionographique
The Pion Charge Form Factor via Pion Electroproduction on the Proton
Middelkoop, G. van [Promotor]Blok, H.P. [Copromotor]Mack, D.J. [Copromotor
Nucleation Rates of Water and Heavy Water using Equations of State
The original formula of Gibbs for the reversible work of critical nucleus formation is evaluated in three approximate ways for ordinary and heavy water. The least approximate way employs an equation of state to evaluate the pressure difference between the new and old phases. This form of the theory yields a temperature dependence for the nucleation rate close to that observed experimentally. This is a substantial improvement over the most commonly used (and most approximate) form of classical theory.©2004 American Institute of Physics
Improving the initial guess for the Newton-Raphson protocol in time-dependent simulations
A general linearisation procedure for the consistent tangent of a
small-strain visco-plastic material model is presented in this note. The
procedure is based on multi-variable linearisation around a so-called
'reference state'. In particular, the linerarisation of the time integration
scheme is found to yield an extra term compared to classical expressions, which
only appears because the material response is time-dependent. It has the effect
of yielding a very accurate initial guess for the Newton-Raphson protocol based
on the ongoing viscous flow. It is shown, using a modern variational FFT-based
solver, that the extra term reduces both the CPU time and the number of
Newton-Raphson iterations by around a factor two.Comment: Journal of Computational Physics, 202
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