16,456 research outputs found
Excitations of the Fractional Quantum Hall State and the Generalized Composite Fermion Picture
We present a generalization of the composite Fermion picture for a
muticomponent quantum Hall plasma which contains particle with different
effective charges. The model predicts very well the low-lying states of a
quantum Hall state found in numerical diagonalization.Comment: 5 pages, 3 figure
Capacitive pressure transducer system
Closed loop capacitive pressure transducer with extended frequency response for very low pressure measurement
X-ray Amorphous Components of Antarctica Dry Valley Soils: Weathering Implications for Mars
The Antarctic Dry Valleys (ADV) comprise the largest ice-free region of Antarctica. Precipitation usually occurs as snow, relative humidity is frequently low, and mean annual temperatures are about -20C [1]. Substantial work has focused on soil formation in the ADVs [2], however, little work has focused on the mineralogy of secondary alteration phases. The dominant weathering process in the ADV region is physical weathering, however, chemical weathering has been well documented [3]. The occurrence of chemical weathering processes are suggested by the presence of clay minerals and iron and titanium oxides in soil. Previously we have investigated soils from two sites in the ADVs and have shown evidence of chemical weathering by the presence of clay minerals (vermiculite, smectite), short-range ordered (SRO) and/or X-ray amorphous materials, and Fe- and Tioxides as well as the presence of discrete calcite crystals [4, 5]. The Chemistry and Mineralogy (CheMin) instrument onboard the Mars Curiosity rover has detected abundant amounts (approx. 25-30 wt. %) of X-ray amorphous materials in a windblown deposit or soil (Rocknest) and in a sedimentary rocks [6,7,8]. The occurrence of large amounts of X-ray amorphous materials in Mars sediments is surprising because these materials are usually present in small quantities in terrestrial environments. The objective of this study is to further characterize the chemistry and mineralogy, specifically the secondary alteration mineralogy and the presence of X-ray amorphous material, of soils from two sites we have previously studied, a subxerous soil in Taylor Valley, and an ultraxerous soil in University Valley. While the chemical alteration processes and mineralogy of the ADV has been documented previously, there has been limited discussion on the occurrence and formation of X-ray amorphous and SRO materials in Antarctica soils. The process of aqueous alteration in the ADVs may have implications for pedogenic processes on Mars, and may lead to a better understanding to the abundance of amorphous material found in sediments in Gale crater
Strategic Outsourcing: Evidence from the British Companies
Outsourcing has become an increasingly popular option for many organisations. But they vary in terms of activities being outsourced, reasons for and benefits from outsourcing, and how the decision was made. This article presents an empirical research on fourteen companies. It found out, a) in most cases it was the ‘peripheral’ support activity being outsourced with cost reduction as the primary driver; b) outsourcing decision was being made early in the process without active involvement of the in-house provider; and c) there were problems in supplier selection and management. The research identified pre-outsourcing decision process and post-outsourcing management as the two key areas that gave cause for concern, and offered recommendations for improvement
The (In)Stability of Planetary Systems
We present results of numerical simulations which examine the dynamical
stability of known planetary systems, a star with two or more planets. First we
vary the initial conditions of each system based on observational data. We then
determine regions of phase space which produce stable planetary configurations.
For each system we perform 1000 ~1 million year integrations. We examine
upsilon And, HD83443, GJ876, HD82943, 47UMa, HD168443, and the solar system
(SS). We find that the resonant systems, 2 planets in a first order mean motion
resonance, (HD82943 and GJ876) have very narrow zones of stability. The
interacting systems, not in first order resonance, but able to perturb each
other (upsilon And, 47UMa, and SS) have broad regions of stability. The
separated systems, 2 planets beyond 10:1 resonance, (we only examine HD83443
and HD168443) are fully stable. Furthermore we find that the best fits to the
interacting and resonant systems place them very close to unstable regions. The
boundary in phase space between stability and instability depends strongly on
the eccentricities, and (if applicable) the proximity of the system to perfect
resonance. In addition to million year integrations, we also examined stability
on ~100 million year timescales. For each system we ran ~10 long term
simulations, and find that the Keplerian fits to these systems all contain
configurations which may be regular on this timescale.Comment: 37 pages, 49 figures, 13 tables, submitted to Ap
Triple cascade behaviour in QG and drift turbulence and generation of zonal jets
We study quasigeostrophic (QG) and plasma drift turbulence within the Charney-Hasegawa-Mima (CHM) model. We focus on the zonostrophy, an extra invariant in the CHM model, and on its role in the formation of zonal jets. We use a generalized Fjørtoft argument for the energy, enstrophy, and zonostrophy and show that they cascade anisotropically into nonintersecting sectors in k space with the energy cascading towards large zonal scales. Using direct numerical simulations of the CHM equation, we show that zonostrophy is well conserved, and the three invariants cascade as predicted by the Fjørtoft argument
Fractional quantum Hall effect and electron correlations in partially filled first excited Landau level
We present a quantitative study of most prominent incompressible quantum Hall
states in the partially filled first excited Landau level (LL1) which have been
recently studied experimentally by Choi et al. The pseudopotential describing
the electron - electron interaction in LL1 is harmonic at short range. It
produces a series of incompressible states which is different from its LL0
counterpart. The numerical data indicate that the most prominent states
, 7/3, and 8/3 are not produced by Laughlin correlated electrons,
but result from a tendency of electrons to form pairs or larger clusters which
eventually become Laughlin correlated. States with smaller gaps at filling
factors 14/5, 16/7, 11/5, 19/7 are Laughlin correlated electron or hole states
and fit Jain's sequence of filled levels.Comment: 4 pages, 7 figure
Neutrino Fluxes from Active Galaxies: a Model-Independent Analysis
There are tantalizing hints that jets, powered by supermassive black holes at
the center of active galaxies, are true cosmic proton accelerators. They
produce photons of TeV energy, possible higher, and may be the enigmatic source
of the highest energy cosmic rays. Photoproduction of neutral pions by
accelerated protons on UV light is the source of the highest energy photons, in
which most of the bolometric luminosity of the galaxy may be emitted. The case
that proton beams power active galaxies is, however, far from conclusive.
Neutrinos from the decay of charged pions represent an uncontrovertible
signature for the proton induced cascades. We show that their flux can be
estimated by model-independent methods, based on dimensional analysis and
textbook particle physics. Our calculations also demonstrate why different
models for the proton blazar yield very similar results for the neutrino flux,
consistent with the ones obtained here.Comment: Latex 2.09 with epsf.sty. 12 pages, 2 postscript figures. Compressed
postscript version of paper with figures also available soon at
http://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-982.ps.Z or at
ftp://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-982.ps.
The joint US/UK 1990 epoch world magnetic model
A detailed summary of the data used, analyses performed, modeling techniques employed, and results obtained in the course of the 1990 Epoch World Magnetic Modeling effort are given. Also, use and limitations of the GEOMAG algorithm are presented. Charts and tables related to the 1990 World Magnetic Model (WMM-90) for the Earth's main field and secular variation in Mercator and polar stereographic projections are presented along with useful tables of several magnetic field components and their secular variation on a 5-degree worldwide grid
Quantum Hall Spherical Systems: the Filling Fraction
Within the newly formulated composite fermion hierarchy the filling fraction
of a spherical quantum Hall system is obtained when it can be expressed as an
odd or even denominator fraction. A plot of as a function
of for a constant number of particles (up to N=10001) exhibits structure
of the fractional quantum Hall effect. It is confirmed that
for all particle-hole conjugate systems, except systems with , and
.Comment: 3 pages, Revtex, 7 PostScript figures, submitted to Phys. Rev. B
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