3,111 research outputs found
Tune Determination of Strongly Coupled Betatron Oscillations in a Fast-Ramping Synchrotron
Tune identification - i.e. attribution of the spectral peak to a particular
normal mode of oscillations - can present a significant difficulty in the
presence of strong transverse coupling when the normal mode with a lower
damping rate dominates spectra of Turn-by-Turn oscillations in both planes. The
introduced earlier phased sum algorithm helped to recover the weaker normal
mode signal from the noise, but by itself proved to be insufficient for
automatic peak identification in the case of close phase advance distribution
in both planes. To resolve this difficulty we modified the algorithm by taking
and analyzing Turn-by-Turn data for two different ramps with the beam
oscillation excited in each plane in turn. Comparison of the relative
amplitudes of Fourier components allows for automatic correct tune
identification. The proposed algorithm was implemented in the Fermilab Booster
B38 console application and successfully used in tune, coupling and
chromaticity measurements.Comment: 3 pp. 3rd International Particle Accelerator Conference (IPAC 2012)
20-25 May 2012, New Orleans, Louisian
Thermal stress cycling of GaAs solar cells
A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance
A mobile system for active otpical pollution monitoring
The remote monitoring of atmospheric pollutants can now be performed in several ways. Laser radar techniques have proven their ability to reveal the spatial distribution of different species or particles. Classical optical techniques can also be used, but yield the average concentration over a given path and hence no range resolution. One such technique is Differential Optical Absorption Spectroscopy, DOAS. Such schemes can be used to monitor paths that a preliminary lidar investigation has shown to be of interest. Having previously had access to a mobile lidar system, a new system has been completed. The construction builds on experience from using the other system and it is meant to be more of a mobile optical laboratory than just a lidar system. A complete system description is given along with some preliminary usage. Future uses are contemplated
Observation of Instabilities of Coherent Transverse Ocillations in the Fermilab Booster
The Fermilab Booster - built more than 40 years ago - operates well above the
design proton beam intensity of 4x10**12 ppp. Still, the Fermilab neutrino
experiments call for even higher intensity of 5.5x10**12 ppp. A multitude of
intensity related effects must be overcome in order to meet this goal including
suppression of coherent dipole instabilities of transverse oscillations which
manifest themselves as a sudden drop in the beam current. In this report we
present the results of observation of these instabilities at different tune,
coupling and chromaticity settings and discuss possible cures.Comment: 3 pp. 3rd International Particle Accelerator Conference (IPAC 2012)
20-25 May 2012, New Orleans, Louisian
Estrategias de formulación de los mercados de abasto y su influencia en la sociedad y cultura
Los mercados de abasto es una de las infraestructuras más antiguas de comercialización que convive con el retail moderno, manteniendo su posicionamiento, gracias no solo a la ventaja competitiva del producto fresco sino a los impactos sociales y culturales que generan. Por otro lado los supermercados y su gran desarrollo logÃstico operacional y fuerte crecimiento, han modificado los hábitos de compra del consumidor, con la creación de distintos formatos de venta, posicionándose cada vez más en la preferencia de compra, pudiéndose perder ese potencial beneficio sociocultural, por lo que los mercados de abasto tradicionales necesitan implementar nuevas estrategias que les permita seguir desarrollando esos aspectos relevantes de la sociedad, recuperando sus orÃgenes de ser edificaciones potencialmente influyentes de su entorno, a través de intervenciones que generan vinculaciones sociales y culturales, encontrándose en la investigación soluciones como: Beneficios sociales a través de la integración estratégica de comerciantes y vecinos, Beneficios urbanos a través de la integración con su entorno, Beneficios culturales a través de nuevos servicios con valor agregado, mejoras de los servicios internos implementando el diseño emocional y merchandising en la exhibición
The relaxation dynamics of a simple glass former confined in a pore
We use molecular dynamics computer simulations to investigate the relaxation
dynamics of a binary Lennard-Jones liquid confined in a narrow pore. We find
that the average dynamics is strongly influenced by the confinement in that
time correlation functions are much more stretched than in the bulk. By
investigating the dynamics of the particles as a function of their distance
from the wall, we can show that this stretching is due to a strong dependence
of the relaxation time on this distance, i.e. that the dynamics is spatially
very heterogeneous. In particular we find that the typical relaxation time of
the particles close to the wall is orders of magnitude larger than the one of
particles in the center of the pore.Comment: 9 pages of Latex, 4 figure
Short Musculoskeletal Function Assessment:normative data of the Dutch population
The Short Musculoskeletal Function Assessment (SMFA) is widely used in both research and clinical practice. Despite its frequent use, normative data of the SMFA have remained limited. Aim of this study was to gather normative data for the Dutch SMFA (SMFA-NL). The SMFA-NL consists of two indices (function index and bother index) and four subscales (upper extremity dysfunction, lower extremity dysfunction, mental and emotional problems, and problems with daily activities). A total of 900 patients were invited to fill in the SMFA-NL. Six age groups (18-24, 25-34, 35-44, 45-54, 55-64, and 65-75 years) were constructed. Analysis of variance, t tests, and regression analyses were used to assess age and gender effects. The response rate was 97 %. There was a significant difference between men and women in scores on all indices and subscales (range p <0.001 to p = 0.002), except for the upper extremity dysfunction subscale (p = 0.06). A significant interaction effect was found between gender and age for the upper extremity dysfunction subscale; a larger decrease in score with increasing age was observed for women, compared with men. Significant differences were found between age groups for the bother index (p <0.001), lower extremity dysfunction subscale (p = 0.001), and the problems with daily activities subscale (p = 0.002). Significant differences in SMFA-NL scores were found between men and women and between different age groups. These SMFA-NL normative data provide an opportunity of benchmarking health status of participants with musculoskeletal disorders or injuries against their age- and gender-matched peers in the Dutch population
The Magnetic Sensitivity of the Ba II D1 and D2 Lines of the Fraunhofer Spectrum
The physical interpretation of the spectral line polarization produced by the
joint action of the Hanle and Zeeman effects offers a unique opportunity to
obtain empirical information about hidden aspects of solar and stellar
magnetism. To this end, it is important to achieve a complete understanding of
the sensitivity of the emergent spectral line polarization to the presence of a
magnetic field. Here we present a detailed theoretical investigation on the
role of resonance scattering and magnetic fields on the polarization signals of
the Ba II D1 and D2 lines of the Fraunhofer spectrum, respectively at 4934 \AA\
and 4554 \AA. We adopt a three-level model of Ba II, and we take into account
the hyperfine structure that is shown by the Ba and Ba
isotopes. Despite of their relatively small abundance (18%), the contribution
coming from these two isotopes is indeed fundamental for the interpretation of
the polarization signals observed in these lines. We consider an optically thin
slab model, through which we can investigate in a rigorous way the essential
physical mechanisms involved (resonance polarization, Zeeman, Paschen-Back and
Hanle effects), avoiding complications due to radiative transfer effects. We
assume the slab to be illuminated from below by the photospheric solar
continuum radiation field, and we investigate the radiation scattered at 90
degrees, both in the absence and in the presence of magnetic fields,
deterministic and microturbulent. We show in particular the existence of a
differential magnetic sensitivity of the three-peak Q/I profile that is
observed in the D2 line in quiet regions close to the solar limb, which is of
great interest for magnetic field diagnostics.Comment: 40 pages, 1 table and 19 figures. Accepted for publication in The
Astrophysical Journal (ApJ
Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry
We present transport measurements of a tunable silicon
metal-oxide-semiconductor double quantum dot device with lateral geometry.
Experimentally extracted gate-to-dot capacitances show that the device is
largely symmetric under the gate voltages applied. Intriguingly, these gate
voltages themselves are not symmetric. Comparison with numerical simulations
indicates that the applied gate voltages serve to offset an intrinsic asymmetry
in the physical device. We also show a transition from a large single dot to
two well isolated coupled dots, where the central gate of the device is used to
controllably tune the interdot coupling.Comment: 4 pages, 3 figures, to be published in Applied Physics Letter
Isotope shift calculations for atoms with one valence electron
This work presents a method for the ab initio calculation of isotope shift in
atoms and ions with one valence electron above closed shells. As a zero
approximation we use relativistic Hartree-Fock and then calculate correlation
corrections. The main motivation for developing the method comes from the need
to analyse whether different isotope abundances in early universe can
contribute to the observed anomalies in quasar absorption spectra. The current
best explanation for these anomalies is the assumption that the fine structure
constant, alpha, was smaller at early epoch. We test the isotope shift method
by comparing the calculated and experimental isotope shift for the alkali and
alkali-like atoms Na, MgII, K, CaII and BaII. The agreement is found to be
good. We then calculate the isotope shift for some astronomically relevant
transitions in SiII and SiIV, MgII, ZnII and GeII.Comment: 11 page
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