6,998 research outputs found
An Overview of a Grid Architecture for Scientific Computing
This document gives an overview of a Grid testbed architecture proposal for
the NorduGrid project. The aim of the project is to establish an inter-Nordic
testbed facility for implementation of wide area computing and data handling.
The architecture is supposed to define a Grid system suitable for solving data
intensive problems at the Large Hadron Collider at CERN. We present the various
architecture components needed for such a system. After that we go on to give a
description of the dynamics by showing the task flow
Coupling between Rydberg states and Landau levels of electrons trapped on liquid helium
We investigate the coupling between Rydberg states of electrons trapped on a
liquid Helium surface and Landau levels induced by a perpendicular magnetic
field. We show that this realises a prototype quantum system equivalent to an
atom in a cavity, where their coupling strength can be tuned by a parallel
magnetic field. We determine experimentally the renormalisation of the atomic
transition energies induced by the coupling to the cavity, which can be seen as
an analogue of the Lamb shift. When the coupling is sufficiently strong the
transition between the ground and first excited Rydberg states splits into two
resonances corresponding to dressed states with vacuum and one photon in the
cavity. Our results are in quantitative agreement with the energy shifts
predicted by the effective atom in a cavity model where all parameters are
known with high accuracy
Isochoric thermal conductivity of solid nitrogen
The isochoric thermal conductivity of solid nitrogen has been investigated on
four samples of different densities in the temperature interval from 20 K to
the onset of melting. In alfa-N2 the isochoric thermal conductivity exhibits a
dependence weaker than 1/T; in beta-N2 it increases slightly with temperature.
The experimental results are discussed within a model in which the heat is
transported by low-frequency phonons or by "diffusive" modes above the mobility
boundary. The growth of the thermal conductivity in beta-N2 is attributed to
the decreasing "rotational" component of the total thermal resistance, which
occurs as the rotational correlations between the neighboring molecules become
weaker.Comment: Postscript 12 pages, 3 figures, 1 table. To be published in 200
On the nonlinear NMR and magnon BEC in antiferromagnetic materials with coupled electron-nuclear spin precession
We present a new study of nonlinear NMR and Bose-Einstein Condensation (BEC)
of nuclear spin waves in antiferromagnetic MnCO3 with coupled electron and
nuclear spins. In particular, we show that the observed behaviour of NMR
signals strongly contradicts the conventional description of paramagnetic
ensembles of noninteracting spins based on the phenomenological Bloch
equations. We present a new theoretical description of the coupled
electron-nuclear spin precession, which takes into account an indirect
relaxation of nuclear spins via the electron subsystem. We show that the
magnitude of the nuclear magnetization is conserved for arbitrary large
excitation powers, which is drastically different from the conventional heating
scenario derived from the Bloch equations. This provides strong evidence that
the coherent precession of macroscopic nuclear magnetization observed
experimentally can be identified with BEC of nuclear spin waves with k=0.Comment: 12 pages, 8 figure
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