1,004 research outputs found
Spin Susceptibility of an Ultra-Low Density Two Dimensional Electron System
We determine the spin susceptibility in a two dimensional electron system in
GaAs/AlGaAs over a wide range of low densities from 2cm to
4cm. Our data can be fitted to an equation that describes
the density dependence as well as the polarization dependence of the spin
susceptibility. It can account for the anomalous g-factors reported recently in
GaAs electron and hole systems. The paramagnetic spin susceptibility increases
with decreasing density as expected from theoretical calculations.Comment: 5 pages, 2 eps figures, to appear in PR
Magnetic tight-binding and the iron-chromium enthalpy anomaly
We describe a self consistent magnetic tight-binding theory based in an
expansion of the Hohenberg-Kohn density functional to second order, about a non
spin polarised reference density. We show how a first order expansion about a
density having a trial input magnetic moment leads to the Stoner--Slater rigid
band model. We employ a simple set of tight-binding parameters that accurately
describes electronic structure and energetics, and show these to be
transferable between first row transition metals and their alloys. We make a
number of calculations of the electronic structure of dilute Cr impurities in
Fe which we compare with results using the local spin density approximation.
The rigid band model provides a powerful means for interpreting complex
magnetic configurations in alloys; using this approach we are able to advance a
simple and readily understood explanation for the observed anomaly in the
enthalpy of mixing.Comment: Submitted to Phys Rev
Layer dependent band dispersion and correlations using tunable Soft X-ray ARPES
Soft X-ray Angle-Resolved Photoemission Spectroscopy is applied to study
in-plane band dispersions of Nickel as a function of probing depth. Photon
energies between 190 and 780 eV were used to effectively probe up to 3-7
layers. The results show layer dependent band dispersion of the Delta_2
minority-spin band which crosses the Fermi level in 3 or more layers, in
contrast to known top 1-2 layers dispersion obtained using ultra-violet rays.
The layer dependence corresponds to an increased value of exchange splitting
and suggests reduced correlation effects in the bulk compared to the surface.Comment: 7 pages, 3 figures Revised text and figur
Accounting students' IT applicaton skills over a 10-year period
This paper reports on the changing nature of a range of information technology (IT) application skills that students declare on entering an accounting degree over the period from 1996 to 2006. Accounting educators need to be aware of the IT skills students bring with them to university because of the implications this has for learning and teaching within the discipline and the importance of both general and specific IT skills within the practice and craft of accounting. Additionally, IT skills constitute a significant element within the portfolio of employability skills that are increasingly demanded by employers and emphasized within the overall Higher Education (HE) agenda. The analysis of students' reported IT application skills on entry to university, across a range of the most relevant areas of IT use in accounting, suggest that their skills have continued to improve over time. However, there are significant differential patterns of change through the years and within cohorts. The paper addresses the generalizability of these findings and discusses the implications of these factors for accounting educators, including the importance of recognising the differences that are potentially masked by the general increase in skills; the need for further research into the changing nature, and implications, of the gender gap in entrants' IT application skills; and the low levels of entrants' spreadsheet and database skills that are a cause for concern
Russell Lecture: Dark Star Formation and Cooling Instability
Optically thin cooling gas at most temperatures above 30K will make
condensations by pressure pushing material into cool dense regions. This works
without gravity. Cooling condensations will flatten and become
planar/similarity solutions. Most star formation may start from cooling
condensations - with gravity only important in the later stages. The idea that
some of the dark matter could be pristine white dwarfs that condensed slowly on
to planetary sized seeds without firing nuclear reactions is found lacking.
However, recent observations indicate fifty times more halo white dwarfs than
have been previously acknowledged; enough to make the halo fraction observed as
MACHOS.
A cosmological census shows that only 1% of the mass of the Universe is of
known constitution.Comment: 32 Pages, Latex (uses aastex & natbib), 5 eps figures, submitted to
ApJ April 200
Integral Relaxation Time of Single-Domain Ferromagnetic Particles
The integral relaxation time \tau_{int} of thermoactivating noninteracting
single-domain ferromagnetic particles is calculated analytically in the
geometry with a magnetic field H applied parallel to the easy axis. It is shown
that the drastic deviation of \tau_{int}^{-1} from the lowest eigenvalue of the
Fokker-Planck equation \Lambda_1 at low temperatures, starting from some
critical value of H, is the consequence of the depletion of the upper potential
well. In these conditions the integral relaxation time consists of two
competing contributions corresponding to the overbarrier and intrawell
relaxation processes.Comment: 8 pages, 3 figure
Magnetic Anisotropy of a Single Cobalt Nanoparticle
Using a new microSQUID set-up, we investigate magnetic anisotropy in a single
1000-atoms cobalt cluster. This system opens new fields in the characterization
and the understanding of the origin of magnetic anisotropy in such
nanoparticles. For this purpose, we report three-dimensional switching field
measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix.
We are able to separate the different magnetic anisotropy contributions and
evidence the dominating role of the cluster surface.Comment: 4 pages, 8 figure
Tunneling Anisotropic Magnetoresistance in Co/AlOx/Au Tunnel Junctions
We observe spin-valve-like effects in nano-scaled thermally evaporated
Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and
depends on the relative orientation of the magnetization direction of the Co
electrode with respect to the current direction. We attribute this effect to a
two-step magnetization reversal and an anisotropic density of states resulting
from spin-orbit interaction. The results of this study points to future
applications of novel spintronics devices involving only one ferromagnetic
layer.Comment: 11 pages, 5 figures. Accpted for publishing on Nano Letters, 200
Lattice-dynamics of a Disordered solid-solid Interface
Generic properties of elastic phonon transport at a disordered interface are
studied. The results show that phonon transmittance is a strong function of
frequency and the disorder correlation length. At frequencies lower than the
van Hove singularity the transmittance at a given frequency increases as the
correlation length decreases. At low frequencies, this is reflected by
different power-laws for phonon conductance across correlated and uncorrelated
disordered interfaces which are in approximate agreement with perturbation
theory of an elastic continuum. These results can be understood in terms of
simple mosaic and two-colour models of the interface.Comment: 17 pages, 5 figures, submitted to PR
Mass migration of juvenile Queen Conch (Strombus gigas) in the Bahamas
We summarize the available information for a mass migration of juvenile queen conch in the Bahamas. The migration was observed from April through June, 1987 over a large seagrass meadow and adjacent sand-algal plain at 1-5 m depths. Component aggregations ranged from 40-190 m in length and 1-6 m in width, with a maximum density of 319 conch/m2. Migrants averaged 101 mm in shell length, which ranged from 67-145 mm, and were of a similar size as non-migrants in the area The migration was directional towards ebb tidal flow and moved approximately 250 m, at rates of 2.7 - 4.8 m/d, from April until its dissociation in June. Given the characteristics of the migrants and aggregations, we conclude that a key function of the mass migration was as a dispersal mechanism for asynchronously emerged l+ year class of juvenile queen conch; other potential functions include reduction of predation-induced mortality and efficient utilization of food resources
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