1,220 research outputs found
Applicability of siberian placer mining technology to Alaska
The result of Perestroyka and Glasnost has been an awakening of potential for cooperation between East and West. Nowhere has that been better demonstrated than
between Alaska and Magadan Province, USSR.
This report summarizes a one year effort financed by ASTF, with participation
from several technical organizations, to establish contacts with the Siberian placer mining industry. The purpose of the project was to provide initial assessment of the Soviet technology for placer mining in permafrost. A ten day trip to Magadan province by an ASTF team and a similar length visit to Alaska by the Soviet mining group representing the All Union Scientific and Research Institute of Gold and Rare Metals, (VNII-I), Magadan are described. The report also reviews translated data on mining in permafrost and describes surface and underground placer mining technology developed by the Soviets. The report also lists relevant publications on Soviet mining research and state of the art Soviet mining technology and expertise
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Remote sensing of cloud properties using ground-based measurements of zenith radiance
We have conducted the first extensive field test of two new methods to retrieve optical properties for overhead clouds that range from patchy to overcast. The methods use measurements of zenith radiance at 673 and 870 nm wavelengths and require the presence of green vegetation in the surrounding area. The test was conducted at the Atmospheric Radiation Measurement Program Oklahoma site during September–November 2004. These methods work because at 673 nm (red) and 870 nm (near infrared (NIR)), clouds have nearly identical optical properties, while vegetated surfaces reflect quite differently. The first method, dubbed REDvsNIR, retrieves not only cloud optical depth τ but also radiative cloud fraction. Because of the 1-s time resolution of our radiance measurements, we are able for the first time to capture changes in cloud optical properties at the natural timescale of cloud evolution. We compared values of τ retrieved by REDvsNIR to those retrieved from downward shortwave fluxes and from microwave brightness temperatures. The flux method generally underestimates τ relative to the REDvsNIR method. Even for overcast but inhomogeneous clouds, differences between REDvsNIR and the flux method can be as large as 50%. In addition, REDvsNIR agreed to better than 15% with the microwave method for both overcast and broken clouds. The second method, dubbed COUPLED, retrieves τ by combining zenith radiances with fluxes. While extra information from fluxes was expected to improve retrievals, this is not always the case. In general, however, the COUPLED and REDvsNIR methods retrieve τ to within 15% of each other
The incidence and make up of ability grouped sets in the UK primary school
The adoption of setting in the primary school (pupils ability grouped across classes for particular subjects) emerged during the 1990s as a means to raise standards. Recent research based on 8875 children in the Millennium Cohort Study showed that 25.8% of children in Year 2 were set for literacy and mathematics and a further 11.2% of children were set for mathematics or literacy alone. Logistic regression analysis showed that the best predictors of being in the top set for literacy or mathematics were whether the child was born in the Autumn or Winter and cognitive ability scores. Boys were significantly more likely than girls to be in the bottom literacy set. Family circumstances held less importance for setting placement compared with the child’s own characteristics, although they were more important in relation to bottom set placement. Children in bottom sets were significantly more likely to be part of a long-term single parent household, have experienced poverty, and not to have a mother with qualifications at NVQ3 or higher levels. The findings are discussed in relation to earlier research and the implications for schools are set out
Surface and capillary transitions in an associating binary mixture model
We investigate the phase diagram of a two-component associating fluid mixture
in the presence of selectively adsorbing substrates. The mixture is
characterized by a bulk phase diagram which displays peculiar features such as
closed loops of immiscibility. The presence of the substrates may interfere the
physical mechanism involved in the appearance of these phase diagrams, leading
to an enhanced tendency to phase separate below the lower critical solution
point. Three different cases are considered: a planar solid surface in contact
with a bulk fluid, while the other two represent two models of porous systems,
namely a slit and an array on infinitely long parallel cylinders. We confirm
that surface transitions, as well as capillary transitions for a large
area/volume ratio, are stabilized in the one-phase region. Applicability of our
results to experiments reported in the literature is discussed.Comment: 12 two-column pages, 12 figures, accepted for publication in Physical
Review E; corrected versio
Phenomenological glass model for vibratory granular compaction
A model for weakly excited granular media is derived by combining the free
volume argument of Nowak et al. [Phys. Rev. E 57, 1971 (1998)] and the
phenomenological model for supercooled liquids of Adam and Gibbs [J. Chem.
Phys. 43, 139 (1965)]. This is made possible by relating the granular
excitation parameter \Gamma, defined as the peak acceleration of the driving
pulse scaled by gravity, to a temperature-like parameter \eta(\Gamma). The
resulting master equation is formally identical to that of Bouchaud's trap
model for glasses [J. Phys. I 2, 1705 (1992)]. Analytic and simulation results
are shown to compare favourably with a range of known experimental behaviour.
This includes the logarithmic densification and power spectrum of fluctuations
under constant \eta, the annealing curve when \eta is varied cyclically in
time, and memory effects observed for a discontinuous shift in \eta. Finally,
we discuss the physical interpretation of the model parameters and suggest
further experiments for this class of systems.Comment: 2 references added; some figure labels tweaked. To appear in PR
Existence and stability of viscoelastic shock profiles
We investigate existence and stability of viscoelastic shock profiles for a
class of planar models including the incompressible shear case studied by
Antman and Malek-Madani. We establish that the resulting equations fall into
the class of symmetrizable hyperbolic--parabolic systems, hence spectral
stability implies linearized and nonlinear stability with sharp rates of decay.
The new contributions are treatment of the compressible case, formulation of a
rigorous nonlinear stability theory, including verification of stability of
small-amplitude Lax shocks, and the systematic incorporation in our
investigations of numerical Evans function computations determining stability
of large-amplitude and or nonclassical type shock profiles.Comment: 43 pages, 12 figure
Searching for the Slater Transition in the Pyrochlore CdOsO with Infrared Spectroscopy
Infrared reflectance measurements were made on the single crystal pyrochlore
CdOsO in order to examine the transformations of the
electronic structure and crystal lattice across the boundary of the metal
insulator transition at . All predicted IR active phonons are
observed in the conductivity over all temperatures and the oscillator strength
is found to be temperature independent. These results indicate that charge
ordering plays only a minor role in the MIT and that the transition is strictly
electronic in nature. The conductivity shows the clear opening of a gap with
. The gap opens continuously, with a temperature
dependence similar to that of BCS superconductors, and the gap edge having a
distinct dependence. All of these
observables support the suggestion of a Slater transition in CdOsO.Comment: 4 pages, 4 figure
Modulational Instability in Equations of KdV Type
It is a matter of experience that nonlinear waves in dispersive media,
propagating primarily in one direction, may appear periodic in small space and
time scales, but their characteristics --- amplitude, phase, wave number, etc.
--- slowly vary in large space and time scales. In the 1970's, Whitham
developed an asymptotic (WKB) method to study the effects of small
"modulations" on nonlinear periodic wave trains. Since then, there has been a
great deal of work aiming at rigorously justifying the predictions from
Whitham's formal theory. We discuss recent advances in the mathematical
understanding of the dynamics, in particular, the instability of slowly
modulated wave trains for nonlinear dispersive equations of KdV type.Comment: 40 pages. To appear in upcoming title in Lecture Notes in Physic
Comparison of two non-primitive methods for path integral simulations: Higher-order corrections vs. an effective propagator approach
Two methods are compared that are used in path integral simulations. Both
methods aim to achieve faster convergence to the quantum limit than the
so-called primitive algorithm (PA). One method, originally proposed by
Takahashi and Imada, is based on a higher-order approximation (HOA) of the
quantum mechanical density operator. The other method is based upon an
effective propagator (EPr). This propagator is constructed such that it
produces correctly one and two-particle imaginary time correlation functions in
the limit of small densities even for finite Trotter numbers P. We discuss the
conceptual differences between both methods and compare the convergence rate of
both approaches. While the HOA method converges faster than the EPr approach,
EPr gives surprisingly good estimates of thermal quantities already for P = 1.
Despite a significant improvement with respect to PA, neither HOA nor EPr
overcomes the need to increase P linearly with inverse temperature. We also
derive the proper estimator for radial distribution functions for HOA based
path integral simulations.Comment: 17 pages, latex, 6 postscript figure
Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host
Combining molecular dynamics and Monte Carlo simulation we study defect
structures around an elongated colloidal particle embedded in a nematic liquid
crystal host. By studying nematic ordering near the particle and the
disclination core region we are able to examine the defect core structure and
the difference between two simulation techniques. In addition, we also study
the torque on a particle tilted with respect to the director, and modification
of this torque when the particle is close to the cell wall
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