959 research outputs found
Kinetic Theory for Electron Dynamics Near a Positive Ion
A theoretical description of time correlation functions for electron
properties in the presence of a positive ion of charge number Z is given. The
simplest case of an electron gas distorted by a single ion is considered. A
semi-classical representation with a regularized electron - ion potential is
used to obtain a linear kinetic theory that is asymptotically exact at short
times. This Markovian approximation includes all initial (equilibrium) electron
- electron and electron - ion correlations through renormalized pair
potentials. The kinetic theory is solved in terms of single particle
trajectories of the electron - ion potential and a dielectric function for the
inhomogeneous electron gas. The results are illustrated by a calculation of the
autocorrelation function for the electron field at the ion. The dependence on
charge number Z is shown to be dominated by the bound states of the effective
electron - ion potential. On this basis, a very simple practical representation
of the trajectories is proposed and shown to be accurate over a wide range
including strong electron - ion coupling. This simple representation is then
used for a brief analysis of the dielectric function for the inhomogeneous
electron gas.Comment: 30 pages, 5 figures, submitted to Journal of Statistical Mechanics:
Theory and Experimen
Linear Response for Confined Particles
The dynamics of fluctuations is considered for electrons near a positive ion
or for charges in a confining trap. The stationary nonuniform equilibrium
densities are discussed and contrasted. The linear response function for small
perturbations of this nonuniform state is calculated from a linear Markov
kinetic theory whose generator for the dynamics is exact in the short time
limit. The kinetic equation is solved in terms of an effective mean field
single particle dynamics determined by the local density and dynamical
screening by a dielectric function for the non-uniform system. The
autocorrelation function for the total force on the charges is discussed.Comment: 4 pages, 1 figure. Results presented at the "International Conference
on Strongly Coupled Coulomb Systems", Camerino, Italy, July 2008. Submitted
for publication in the conference proceedings (special issue of Journal of
Physics A
Theoretical Description of Coulomb Balls - Fluid Phase
A theoretical description for the radial density profile of a finite number
of identical charged particles confined in a harmonic trap is developed for
application over a wide range of Coulomb coupling (or, equivalently,
temperatures) and particle numbers. A simple mean field approximation
neglecting correlations yields a density profile which is monotonically
decreasing with radius for all temperatures, in contrast to molecular dynamics
simulations and experiments showing shell structure at lower temperatures. A
more complete theoretical description including charge correlations is
developed here by an extension of the hypernetted chain approximation,
developed for bulk fluids, to the confined charges. The results reproduce all
of the qualitative features observed in molecular dynamics simulations and
experiments. These predictions are then tested quantitatively by comparison
with new benchmark Monte Carlo simulations. Quantitative accuracy of the theory
is obtained for the selected conditions by correcting the hypernetted chain
approximation with a representation for the associated bridge functions.Comment: 10 figures, submitted to Physical Review
Regulated expression of human A γ-, β-, and hybrid γ β-globin genes in transgenic mice: manipulation of the developmental expression patterns.
We have introduced the human fetal gamma- and adult beta-globin genes into the germ line of mice. Analysis of the resulting transgenic mice shows that the human gamma-globin gene is expressed like an embryonic mouse globin gene; the human beta-globin gene is expressed (as previously shown) like an adult mouse globin gene. These results imply that the regulatory signals for tissue- and developmental stage-specific expression of the globin genes have been conserved between man and mouse but that the timing of the signals has changed. Because the two genes are expressed differently, we introduced a hybrid gamma beta-globin gene construct. The combination of the regulatory sequences resulted in the expression of the hybrid gene at all stages in all the murine erythroid tissues
World Mineral Production 2009-13
The latest edition of this annual publication from the British Geological Survey (BGS) is now available to download. This volume contains mineral production statistics for the five year period from 2009 to 2013, for more than 70 mineral commodities, by country worldwide.
It is the latest publication from the World Mineral Statistics dataset which began in 1913. The information contained in the dataset, and associated publications, is compiled from a wide range of sources: home and overseas government departments, national statistical offices, specialist commodity authorities, company reports, and a network of contacts throughout the world.
The database compilers aim for integrity and accuracy in the data and, for quality control purposes, participate in international specialist groups, and maintain close links with other mineral statistics providers in Europe and North America. The data provides essential mineral intelligence for:
⢠security of supply issues
⢠economic analyses
⢠environmental issues
⢠sustainable development planning
⢠regulation and policy issues
⢠commercial strategic planning
The data are available in the following formats:
⢠Annual publication of âWorld Mineral Productionâ and its predecessors, which can be downloaded in pdf from our World Archive
⢠MS Excel for years from 1992 via our data download tool
⢠The most recent editions are available to purchase in hard copy from the BGS online shop
⢠One off reports such as those shown lower down this page, available for download in pd
World mineral production 2010-14
The latest edition of this annual publication from the British Geological Survey (BGS). This volume contains mineral production statistics for the five year period from 2010 to 2014, for more than 70 mineral commodities, by country worldwide.
It is the latest publication from the World Mineral Statistics dataset which began in 1913. The information contained in the dataset, and associated publications, is compiled from a wide range of sources: home and overseas government departments, national statistical offices, specialist commodity authorities, company reports, and a network of contacts throughout the world.
The database compilers aim for integrity and accuracy in the data and, for quality control purposes, participate in international specialist groups, and maintain close links with other mineral statistics providers in Europe and North America
Packet Switched vs. Time Multiplexed FPGA Overlay Networks
Dedicated, spatially configured FPGA interconnect
is efficient for applications that require high throughput connections
between processing elements (PEs) but with a limited degree
of PE interconnectivity (e.g. wiring up gates and datapaths).
Applications which virtualize PEs may require a large number
of distinct PE-to-PE connections (e.g. using one PE to simulate
100s of operators, each requiring input data from thousands of
other operators), but with each connection having low throughput
compared with the PEâs operating cycle time. In these highly interconnected
conditions, dedicating spatial interconnect resources
for all possible connections is costly and inefficient. Alternatively,
we can time share physical network resources by virtualizing
interconnect links, either by statically scheduling the sharing
of resources prior to runtime or by dynamically negotiating
resources at runtime. We explore the tradeoffs (e.g. area, route
latency, route quality) between time-multiplexed and packet-switched
networks overlayed on top of commodity FPGAs. We
demonstrate modular and scalable networks which operate on
a Xilinx XC2V6000-4 at 166MHz. For our applications, time-multiplexed,
offline scheduling offers up to a 63% performance
increase over online, packet-switched scheduling for equivalent
topologies. When applying designs to equivalent area, packet-switching
is up to 2Ă faster for small area designs while time-multiplexing
is up to 5Ă faster for larger area designs. When
limited to the capacity of a XC2V6000, if all communication is
known, time-multiplexed routing outperforms packet-switching;
however when the active set of links drops below 40% of the
potential links, packet-switched routing can outperform time-multiplexing
Finite-temperature quantum effects on confined charges
A quantum system of N Coulomb charges confined within a harmonic trap is considered over a wide range of densities and temperatures. A recently described construction of an equivalent classical system is applied in order to exploit the rather complete classical description of harmonic confinement via liquid-state theory. Here, the effects of quantum mechanics on that representation are described with attention focused on the origin and nature of shell structure. The analysis extends from the classical strong Coulomb coupling conditions of dusty plasmas to the opposite limit of low temperatures and large densities characteristic of warm, dense matter.close0
Some Problems in Density Functional Theory
Though calculations based on density functional theory (DFT) are used
remarkably widely in chemistry, physics, materials science, and biomolecular
research and though the modern form of DFT has been studied for almost 60
years, some mathematical problems remain. For context, we provide an outline of
the basic structure of DFT, then pose several questions regarding both its
time-independent and time-dependent forms. Progress on any of these would aid
in development of better approximate functionals and in interpretation
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