103 research outputs found
Formalism of collective electron excitations in fullerenes
We present a detailed formalism for the description of collective electron
excitations in fullerenes in the process of the electron inelastic scattering.
Considering the system as a spherical shell of a finite width, we show that the
differential cross section is defined by three plasmon excitations, namely two
coupled modes of the surface plasmon and the volume plasmon. The interplay of
the three plasmons appears due to the electron diffraction of the fullerene
shell. Plasmon modes of different angular momenta provide dominating
contributions to the differential cross section depending on the transferred
momentum.Comment: 11 pages, 2 figures; submitted to the special issue "Atomic Cluster
Collisions: Structure and Dynamics from the Nuclear to the Biological Scale"
of Eur. Phys. J.
Quantum non-demolition (QND) modulation of quantum interference
We propose an experiment where quantum interference between two different
paths is modulated by means of a QND measurement on one or both the arm of the
interferometer. The QND measurement is achieved in a Kerr cell. We illustrate a
scheme for the realisation of this experiment and some further developments.Comment: accepted for publicatio
Noise limits in matter-wave interferometry using degenerate quantum gases
We analyze the phase resolution limit of a Mach-Zehnder atom interferometer
whose input consists of degenerate quantum gases of either bosons or fermions.
For degenerate gases, the number of atoms within one de Broglie wavelength is
larger than unity, so that atom-atom interactions and quantum statistics are no
longer negligible. We show that for equal atom numbers, the phase resolution
achievable with fermions is noticeably better than for interacting bosons.Comment: 4 pages, 5 figure
Role of electromagnetically induced transparency in resonant four-wave-mixing schemes.
Published versio
The Stern-Gerlach Experiment Revisited
The Stern-Gerlach-Experiment (SGE) of 1922 is a seminal benchmark experiment
of quantum physics providing evidence for several fundamental properties of
quantum systems. Based on today's knowledge we illustrate the different
benchmark results of the SGE for the development of modern quantum physics and
chemistry.
The SGE provided the first direct experimental evidence for angular momentum
quantization in the quantum world and thus also for the existence of
directional quantization of all angular momenta in the process of measurement.
It measured for the first time a ground state property of an atom, it produced
for the first time a `spin-polarized' atomic beam, it almost revealed the
electron spin. The SGE was the first fully successful molecular beam experiment
with high momentum-resolution by beam measurements in vacuum. This technique
provided a new kinematic microscope with which inner atomic or nuclear
properties could be investigated.
The original SGE is described together with early attempts by Einstein,
Ehrenfest, Heisenberg, and others to understand directional quantization in the
SGE. Heisenberg's and Einstein's proposals of an improved multi-stage SGE are
presented. The first realization of these proposals by Stern, Phipps, Frisch
and Segr\`e is described. The set-up suggested by Einstein can be considered an
anticipation of a Rabi-apparatus. Recent theoretical work is mentioned in which
the directional quantization process and possible interference effects of the
two different spin states are investigated.
In full agreement with the results of the new quantum theory directional
quantization appears as a general and universal feature of quantum
measurements. One experimental example for such directional quantization in
scattering processes is shown. Last not least, the early history of the
`almost' discovery of the electron spin in the SGE is revisited.Comment: 50pp, 17 fig
Mapping Vesta: First Results from Dawn’s Survey Orbit
The geologic objectives of the Dawn Mission [1] are
to derive Vesta’s shape, map the surface geology,
understand the geological context and contribute to
the determination of the asteroids’ origin and
evolution.Geomorphology and distribution of surface features
will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral
measurements of the surface will provide evidence of
the compositional characteristics of geological units.
Age information, as derived from crater sizefrequency
distributions, provides the stratigraphic
context for the structural and compositional mapping
results, thus revealing the geologic history of Vesta.
We present here the first results of the Dawn mission
from data collected during the approach to Vesta, and
its first discrete orbit phase – the Survey Orbit, which
lasts 21 days after the spacecraft had established a
circular polar orbit at a radius of ~3000 km with a
beta angle of 10°-15°
Consensus on the standardization of terminology in thrombotic thrombocytopenic purpura and related thrombotic microangiopathies
Essentials An international collaboration provides a consensus for clinical definitions. This concerns thrombotic microangiopathies and thrombotic thrombocytopenic purpura (TTP). The consensus defines diagnosis, disease monitoring and response to treatment. Requirements for ADAMTS-13 are given. Summary: Background Thrombotic thrombocytopenic purpura (TTP) and hemolytic\ue2\u80\u93uremic syndrome (HUS) are two important acute conditions to diagnose. Thrombotic microangiopathy (TMA) is a broad pathophysiologic process that leads to microangiopathic hemolytic anemia and thrombocytopenia, and involves capillary and small-vessel platelet aggregates. The most common cause is disseminated intravascular coagulation, which may be differentiated by abnormal coagulation. Clinically, a number of conditions present with microangiopathic hemolytic anemia and thrombocytopenia, including cancer, infection, transplantation, drug use, autoimmune disease, and pre-eclampsia and hemolysis, elevated liver enzymes and low platelet count syndrome in pregnancy. Despite overlapping clinical presentations, TTP and HUS have distinct pathophysiologies and treatment pathways. Objectives To present a consensus document from an International Working Group on TTP and associated thrombotic microangiopathies (TMAs). Methods The International Working Group has proposed definitions and terminology based on published information and consensus-based recommendations. Conclusion The consensus aims to aid clinical decisions, but also future studies and trials, utilizing standardized definitions. It presents a classification of the causes of TMA, and criteria for clinical response, remission and relapse of congenital and immune-mediated TTP
Nucleosynthesis Constraints on a Massive Gravitino in Neutralino Dark Matter Scenarios
The decays of massive gravitinos into neutralino dark matter particles and
Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may
alter the primordial light-element abundances. We present here details of a new
suite of codes for evaluating such effects, including a new treatment based on
PYTHIA of the evolution of showers induced by hadronic decays of massive,
unstable particles such as a gravitino. We also develop an analytical treatment
of non-thermal hadron propagation in the early universe, and use this to derive
analytical estimates for light-element production and in turn on decaying
particle lifetimes and abundances. We then consider specifically the case of an
unstable massive gravitino within the constrained minimal supersymmetric
extension of the Standard Model (CMSSM). We present upper limits on its
possible primordial abundance before decay for different possible gravitino
masses, with CMSSM parameters along strips where the lightest neutralino
provides all the astrophysical cold dark matter density. We do not find any
CMSSM solution to the cosmological Li7 problem for small m_{3/2}. Discounting
this, for m_{1/2} ~ 500 GeV and tan beta = 10 the other light-element
abundances impose an upper limit m_{3/2} n_{3/2}/n_\gamma < 3 \times 10^{-12}
GeV to < 2 \times 10^{-13} GeV for m_{3/2} = 250 GeV to 1 TeV, which is similar
in both the coannihilation and focus-point strips and somewhat weaker for tan
beta = 50, particularly for larger m_{1/2}. The constraints also weaken in
general for larger m_{3/2}, and for m_{3/2} > 3 TeV we find a narrow range of
m_{3/2} n_{3/2}/n_\gamma, at values which increase with m_{3/2}, where the Li7
abundance is marginally compatible with the other light-element abundances.Comment: 74 pages, 40 Figure
UHECR as Decay Products of Heavy Relics? The Lifetime Problem
The essential features underlying the top-down scenarii for UHECR are
discussed, namely, the stability (or lifetime) imposed to the heavy objects
(particles) whatever they be: topological and non-topological solitons,
X-particles, cosmic defects, microscopic black-holes, fundamental strings. We
provide an unified formula for the quantum decay rate of all these objects as
well as the particle decays in the standard model. The key point in the
top-down scenarii is the necessity to adjust the lifetime of the heavy object
to the age of the universe. This ad-hoc requirement needs a very high
dimensional operator to govern its decay and/or an extremely small coupling
constant. The natural lifetimes of such heavy objects are, however, microscopic
times associated to the GUT energy scale (sim 10^{-28} sec. or shorter). It is
at this energy scale (by the end of inflation) where they could have been
abundantly formed in the early universe and it seems natural that they decayed
shortly after being formed.Comment: 11 pages, LaTex, no figures, updated versio
Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates
We present a theory of the density correlations that appear in an atomic
Bose-Einstein condensate as a consequence of the dynamical Casimir emission of
pairs of Bogoliubov phonons when the atom-atom scattering length is modulated
in time. Different regimes as a function of the temporal shape of the
modulation are identified and a simple physical picture of the phenomenon is
discussed. Analytical expressions for the density correlation function are
provided for the most significant limiting cases. This theory is able to
explain some unexpected features recently observed in numerical calculations of
Hawking radiation from analog black holes
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