56,125 research outputs found
Measuring carrier density in parallel conduction layers of quantum Hall systems
An experimental analysis for two parallel conducting layers determines the
full resistivity tensor of the parallel layer, at magnetic fields where the
other layer is in the quantum Hall regime. In heterostructures which exhibit
parallel conduction in the modulation-doped layer, this analysis quantitatively
determines the charge density in the doping layer and can be used to estimate
the mobility. To illustrate one application, experimental data show magnetic
freeze-out of parallel conduction in a modulation doped heterojunction. As
another example, the carrier density of a minimally populated second subband in
a two-subband quantum well is determined. A simple formula is derived that can
estimate the carrier density in a highly resistive parallel layer from a single
Hall measurement of the total system.Comment: 7 pages, 7 figure
Dynamics of the Young Binary LMC Cluster NGC 1850
In this paper we have examined the age and internal dynamics of the young
binary LMC cluster NGC 1850 using BV CCD images and echelle spectra of 52
supergiants. Isochrone fits to a BV color-magnitude diagram revealed that the
primary cluster has an age of Myr while the secondary member
has Myr. BV surface brightness profiles were constructed out
to R 40 pc, and single-component King-Michie (KM) models were applied. The
total cluster luminosity varied from L = 2.60 - 2.65
L\sol\ and L = 1.25 - 1.35 as the anisotropy radius
varied from infinity to three times the scale radius with the isotropic models
providing the best agreement with the data. Of the 52 stars with echelle
spectra, a subset of 36 were used to study the cluster dynamics. The KM radial
velocity distributions were fitted to these velocities yielding total cluster
masses of 5.4 - 5.9 M\sol\ corresponding to M/L =
0.02 M\sol/L\sol\ or M/L = 0.05 M\sol/L\sol.
A rotational signal in the radial velocities has been detected at the 93\%
confidence level implying a rotation axis at a position angle of 100\deg. A
variety of rotating models were fit to the velocity data assuming cluster
ellipticities of . These models provided slightly better
agreement with the radial velocity data than the KM models and had masses that
were systematically lower by a few percent. The preferred value for the slope
of a power-law IMF is a relatively shallow, x = 0.29 \pmm{+0.3}{-0.8}
assuming the B-band M/L or x = 0.71 \pmm{+0.2}{-0.4} for the V-band.Comment: 41 pages (figures available via anonymous FTP as described below
A general review of concepts for reducing skin friction, including recommendations for future studies
Four main concepts which have significantly reduced skin friction in experimental studies are discussed; suction, gaseous injection, particle additives, and compliant wall. It is considered possible that each of these concepts could be developed and applied in viable skin friction reduction systems for aircraft application. Problem areas with each concept are discussed, and recommendations for future studies are made
Uniqueness of infrared asymptotics in Landau gauge Yang-Mills theory II
We present a shortened and simplified version of our proof
\cite{Fischer:2006vf} of the uniqueness of the scaling solution for the
infrared asymptotics of Green functions in Landau gauge Yang-Mills theory. The
simplification relates to a new RG-invariant arrangement of Green functions
applicable to general theories. As before the proof relies on the necessary
consistency between Dyson-Schwinger equations (DSEs) and functional
renormalisation group equations (FRGs). We also demonstrate the existence of a
specific scaling solution for both, DSEs and FRGs, that displays uniform and
soft kinematic singularities.Comment: 12 pages, 10 figure
Emissivity measurements of reflective surfaces at near-millimeter wavelengths
We have developed an instrument for directly measuring the emissivity of reflective surfaces at near-millimeter wavelengths. The thermal emission of a test sample is compared with that of a reference surface, allowing the emissivity of the sample to be determined without heating. The emissivity of the reference surface is determined by one’s heating the reference surface and measuring the increase in emission. The instrument has an absolute accuracy of Δe = 5 x 10^-4 and can reproducibly measure a difference in emissivity as small as Δe = 10^-4 between flat reflective samples. We have used the instrument to measure the emissivity of metal films evaporated on glass and carbon fiber-reinforced plastic composite surfaces. We measure an emissivity of (2.15 ± 0.4) x 10^-3 for gold evaporated on glass and (2.65 ± 0.5) x 10^-3 for aluminum evaporated on carbon fiber-reinforced plastic composite
Fluids with quenched disorder: Scaling of the free energy barrier near critical points
In the context of Monte Carlo simulations, the analysis of the probability
distribution of the order parameter , as obtained in simulation
boxes of finite linear extension , allows for an easy estimation of the
location of the critical point and the critical exponents. For Ising-like
systems without quenched disorder, becomes scale invariant at the
critical point, where it assumes a characteristic bimodal shape featuring two
overlapping peaks. In particular, the ratio between the value of at
the peaks () and the value at the minimum in-between ()
becomes -independent at criticality. However, for Ising-like systems with
quenched random fields, we argue that instead should be observed, where is the
"violation of hyperscaling" exponent. Since is substantially non-zero,
the scaling of with system size should be easily detectable in
simulations. For two fluid models with quenched disorder, versus
was measured, and the expected scaling was confirmed. This provides further
evidence that fluids with quenched disorder belong to the universality class of
the random-field Ising model.Comment: sent to J. Phys. Cond. Mat
Developing a multi-metric habitat index for wadeable streams in Illinois (T-25-P-001). Annual Segment Report to the Illinois Department of Natural Resources.
Illinois Department of Natural Resources Grant/Contract No: (T-25-P-001)This project was initiated to describe key aquatic habitat characteristics and their association to anthropogenic disturbance by developing a field based, rapid assessment method for qualitatively monitoring instream conditions using a multi-metric habitat index. We have developed and applied a method for rating disturbance in wadeable streams throughout Illinois and collected information on physical habitat at 299 sites to date. Index development is in the preliminary stages with field work to continue during the summer of 2008. This report summarizes work performed for the period ending April 30, 2008 (Appendix A contains Eastern Illinois University subcontract annual report).INHS Technical Report Prepared for Illinois Department of Natural Resource
Reaching Approximate Byzantine Consensus with Multi-hop Communication
We address the problem of reaching consensus in the presence of Byzantine
faults. In particular, we are interested in investigating the impact of
messages relay on the network connectivity for a correct iterative approximate
Byzantine consensus algorithm to exist. The network is modeled by a simple
directed graph. We assume a node can send messages to another node that is up
to hops away via forwarding by the intermediate nodes on the routes, where
is a natural number. We characterize the necessary and
sufficient topological conditions on the network structure. The tight
conditions we found are consistent with the tight conditions identified for
, where only local communication is allowed, and are strictly weaker for
. Let denote the length of a longest path in the given network. For
and undirected graphs, our conditions hold if and only if and the node-connectivity of the given graph is at least , where
is the total number of nodes and is the maximal number of Byzantine
nodes; and for and directed graphs, our conditions is equivalent to
the tight condition found for exact Byzantine consensus.
Our sufficiency is shown by constructing a correct algorithm, wherein the
trim function is constructed based on investigating a newly introduced minimal
messages cover property. The trim function proposed also works over
multi-graphs.Comment: 24 pages, 1 figure. arXiv admin note: text overlap with
arXiv:1203.188
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