12,537 research outputs found
Nearsightedness of Electronic Matter
In an earlier paper, W. Kohn had qualitatively introduced the concept of
"nearsightedness" of electrons in many-atom systems. It can be viewed as
underlying such important ideas as Pauling's "chemical bond," "transferability"
and Yang's computational principle of "divide and conquer." It describes the
fact that, for fixed chemical potential, local electronic properties, like the
density , depend significantly on the effective external potential only
at nearby points. Changes of that potential, {\it no matter how large}, beyond
a distance have {\it limited} effects on local electronic
properties, which rapidly tend to zero as function of . In the
present paper, the concept is first sharpened for representative models of
uncharged fermions moving in external potentials, followed by a discussion of
the effects of electron-electron interactions and of perturbing external
charges.Comment: final for
Commentary : has financial development made the world riskier?
Greenspan, Alan ; Financial markets ; Monetary policy ; Banks and banking, Central
Edge Electron Gas
The uniform electron gas, the traditional starting point for density-based
many-body theories of inhomogeneous systems, is inappropriate near electronic
edges. In its place we put forward the appropriate concept of the edge electron
gas.Comment: 4 pages RevTex with 7 ps-figures included. Minor changes in
title,text and figure
Panel discussion: inflation targeting
Monetary policy ; Banks and banking, Central ; European Central Bank
Precision laser range finder system design for Advanced Technology Laboratory applications
Preliminary system design of a pulsed precision ruby laser rangefinder system is presented which has a potential range resolution of 0.4 cm when atmospheric effects are negligible. The system being proposed for flight testing on the advanced technology laboratory (ATL) consists of a modelocked ruby laser transmitter, course and vernier rangefinder receivers, optical beacon retroreflector tracking system, and a network of ATL tracking retroreflectors. Performance calculations indicate that spacecraft to ground ranging accuracies of 1 to 2 cm are possible
Do Different Neurons Age Differently? Direct Genome-Wide Analysis of Aging in Single Identified Cholinergic Neurons
Aplysia californica is a powerful experimental system to study the entire scope of genomic and epigenomic regulation at the resolution of single functionally characterized neurons and is an emerging model in the neurobiology of aging. First, we have identified and cloned a number of evolutionarily conserved genes that are age-related, including components of apoptosis and chromatin remodeling. Second, we performed gene expression profiling of different identified cholinergic neurons between young and aged animals. Our initial analysis indicates that two cholinergic neurons (R2 and LPl1) revealed highly differential genome-wide changes following aging suggesting that on the molecular scale different neurons indeed age differently. Each of the neurons tested has a unique subset of genes differentially expressed in older animals, and the majority of differently expressed genes (including those related to apoptosis and Alzheimer's disease) are found in aging neurons of one but not another type. The performed analysis allows us to implicate (i) cell specific changes in histones, (ii) DNA methylation and (iii) regional relocation of RNAs as key processes underlying age-related changes in neuronal functions and synaptic plasticity. These mechanisms can fine-tune the dynamics of long-term chromatin remodeling, or control weakening and the loss of synaptic connections in aging. At the same time our genomic tests revealed evolutionarily conserved gene clusters associated with aging (e.g., apoptosis-, telomere- and redox-dependent processes, insulin and estrogen signaling and water channels)
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