12,184 research outputs found
Notes on drift theory
It is shown that there is a simpler way to derive the average guiding center drift of a distribution of particles than via the so-called single particle analysis. Based on this derivation it is shown that the entire drift formalism can be considerably simplified, and that results for low order anisotropies are more generally valid than is usually appreciated. This drift analysis leads to a natural alternative derivation of the drift velocity along a neutral sheet
Direct comparison of the performance of CZT detectors contacted with various metals
Cadmium Zinc Telluride (CZT) achieves excellent spatial resolution and good
energy resolution over the broad energy range from several keV into the MeV
energy range. In this paper we present the results of a systematic study of the
performance of CZT detectors manufacturered by Orbotech (before IMARAD)
depending on surface preparation, contact materials and contact deposition. The
standard Orbotech detectors have the dimension of 2.0 x 2.0 x 0.5 cm. They have
a pixellated In anode with 8 x 8 pixels and a monolithic In cathode. Using the
same CZT substrates several times, we have made a direct comparison of the
performance of different contact materials by replacing the cathode and/or the
anode contacts with several high-workfunction metals. We present the
performance of the detectors and conclude with an overview over our ongoing
detector optimization.Comment: 8 pages, 5 figures, to appear in the proceedings of the conference
5922, "Hard X-Ray and Gamma-Ray Detector Physics VII" on the "Optics &
Photonics 2005" SPIE Symposium, July 31- August 4, 2005, San Diego, C
Kinematic analysis of handwriting movements in patients with Alzheimer's disease, mild cognitive impairment, depression and healthy subjects
A variety of studies have demonstrated that motor disorders, parkinsonism and extrapyramidal motor symptoms (EPMS) are common in patients with Alzheimer's disease (AD). Several studies have reported an association of EPMS with severity, progression and poor prognosis of AD. The majority of these studies used clinical assessments for the rating of EPMS. In this study, kinematic handwriting analysis was used to quantify differences in fine hand motor function in patients with probable AD and mild cognitive impairment (MCl, as an assumed initial stage of AD) compared to depressed patients and healthy controls. Both patients with MCl and patients with probable AD exhibited loss of fine motor performance. Movements of AD patients were significantly less regular than those of healthy controls. Copyright (C) 2003 S. Karger AG, Basel
P02.147. Emotions matter: sustained reductions in chronic non-structural pain after a brief, manualized emotional processing program
Indirect Self-Modulation Instability Measurement Concept for the AWAKE Proton Beam
AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment,
is a proof-of-principle R&D experiment at CERN using a 400 GeV/c proton beam
from the CERN SPS (longitudinal beam size sigma_z = 12 cm) which will be sent
into a 10 m long plasma section with a nominal density of approx. 7x10^14
atoms/cm3 (plasma wavelength lambda_p = 1.2mm). In this paper we show that by
measuring the time integrated transverse profile of the proton bunch at two
locations downstream of the AWAKE plasma, information about the occurrence of
the self-modulation instability (SMI) can be inferred. In particular we show
that measuring defocused protons with an angle of 1 mrad corresponds to having
electric fields in the order of GV/m and fully developed self-modulation of the
proton bunch. Additionally, by measuring the defocused beam edge of the
self-modulated bunch, information about the growth rate of the instability can
be extracted. If hosing instability occurs, it could be detected by measuring a
non-uniform defocused beam shape with changing radius. Using a 1 mm thick
Chromox scintillation screen for imaging of the self-modulated proton bunch, an
edge resolution of 0.6 mm and hence a SMI saturation point resolution of 1.2 m
can be achieved.Comment: 4 pages, 4 figures, EAAC conference proceeding
Scales for co-compact embeddings of virtually free groups
Let be a group which is virtually free of rank at least 2 and let
be the family of totally disconnected, locally
compact groups containing as a co-compact lattice.
We prove that the values of the scale function with respect to groups in
evaluated on the subset have only finitely
many prime divisors. This can be thought of as a uniform property of the family
.Comment: 12 pages; key words: uniform lattice, virtually free group, totally
disconnected group, scale function (Error in references corrected in version
2
Mutual Event Observations of Io's Sodium Corona
We have measured the column density profile of Io's sodium corona using 10 mutual eclipses between the Galilean satellites. This approach circumvents the problem of spatially resolving Io's corona directly from Io's bright continuum in the presence of atmospheric seeing and telescopic scattering. The primary goal is to investigate the spatial and temporal variations of Io's corona. Spectra from the Keck Observatory and McDonald Observatory from 1997 reveal a corona that is only approximately spherically symmetric around Io. Comparing the globally averaged radial sodium column density profile in the corona with profiles measured in 1991 and 1985, we find that there has been no significant variation. However, there appears to be a previously undetected asymmetry: the corona above Io's sub-Jupiter hemisphere is consistently more dense than above the anti-Jupiter hemisphere
Atomic Bose-Fermi mixtures in an optical lattice
A mixture of ultracold bosons and fermions placed in an optical lattice
constitutes a novel kind of quantum gas, and leads to phenomena, which so far
have been discussed neither in atomic physics, nor in condensed matter physics.
We discuss the phase diagram at low temperatures, and in the limit of strong
atom-atom interactions, and predict the existence of quantum phases that
involve pairing of fermions with one or more bosons, or, respectively, bosonic
holes. The resulting composite fermions may form, depending on the system
parameters, a normal Fermi liquid, a density wave, a superfluid liquid, or an
insulator with fermionic domains. We discuss the feasibility for observing such
phases in current experiments.Comment: 4 pages, 1 eps figure, misprints correcte
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