13,041 research outputs found
An oscillatory interference model of grid cell firing
We expand upon our proposal that the oscillatory interference mechanism proposed for the phase precession effect in place cells underlies the grid-like firing pattern of dorsomedial entorhinal grid cells (O'Keefe and Burgess (2005) Hippocampus 15:853-866). The original one-dimensional interference model is generalized to an appropriate two-dimensional mechanism. Specifically, dendritic subunits of layer 11 medial entorhinal stellate cells provide multiple linear interference patterns along different directions, with their product determining the firing of the cell. Connection of appropriate speed- and direction- dependent inputs onto dendritic subunits could result from an unsupervised learning rule which maximizes postsynaptic firing (e.g. competitive learning). These inputs cause the intrinsic oscillation of subunit membrane potential to. increase above theta frequency by an amount proportional to the animal's speed of running in the "preferred" direction. The phase difference between this oscillation and a somatic input at theta-frequency essentially integrates velocity so that the interference of the two oscillations reflects distance traveled in the preferred direction. The overall grid pattern is maintained in environmental location by phase reset of the grid cell by place cells receiving sensory input from the environment, and environmental boundaries in particular. We also outline possible variations on the basic model, including the generation of grid-like firing via the interaction of multiple cells rather than via multiple dendritic subunits. Predictions of the interference model are given for the frequency composition of EEG power spectra and temporal autocorrelograms of grid cell firing as functions of the speed and direction of running and the novelty of the environment. (C) 2007 Wiley-Liss, Inc
CREDIT SCORING, LOAN PRICING, AND FARM BUSINESS PERFORMANCE
In light of recent developments in agricultural credit evaluations, this study employs a multiperiod simulation model that endogenizes farm investment decisions, credit evaluations, and loan pricing based on the credit scoring procedures of agricultural lender. Model results show that credit-scored pricing yields time patterns of performance, credits classifications, and interest rates that parallel the firmÂ’s investment, financing, and debt servicing activities. Moreover, the lenderÂ’s price responses dampen growth incentives as credit worthiness diminished, stimulate growth as credit improves, and lead to similar capital structures over time.Agricultural Finance,
A MICROCOMPUTER ANALYSIS OF FARM FINANCIAL PERFORMANCE
This article describes the properties of the Farm Financial Simulation Model (FFSM). FFSM is a tool for analyzing the financial consequences of various managerial strategies and policy options that may be implemented in responding to farm financial stress. Various farm types from different geographical regions having differing enterprises, financial structures, tenure arrangements, and consumption patterns can be analyzed. The emphasis of FFSM is placed on modeling a farm's profitability, liquidity, solvency, and financial position and the model produces a coordinated set of financial statements and an extensive set of financial ratios over a four-year period.Farm Management,
On the parameterization dependence of the energy momentum tensor and the metric
We use results by Kirilin to show that in general relativity the nonleading
terms in the energy-momentum tensor of a particle depends on the
parameterization of the gravitational field. While the classical metric that is
calculated from this source, used to define the leading long-distance
corrections to the metric, also has a parameteriztion dependence, it can be
removed by a coordinate change. Thus the classical observables are
parameterization independent. The quantum effects that emerge within the same
calculation of the metric also depend on the parameterization and a full
quantum calculation requires the inclusion of further diagrams. However, within
a given parameterization the quantum effects calculated by us in a previous
paper are well defined. Flaws of Kirilin's proposed alternate metric definition
are described and we explain why the diagrams that we calculated are the
appropriate ones.Comment: 8 pages, 2 figure
Charge dynamics in the half-metallic ferromagnet CrO\u3csub\u3e2\u3c/sub\u3e
Infrared spectroscopy is used to investigate the electronic structure and charge carrier relaxation in crystalline films of CrO2 which is the simplest of all half-metallic ferromagnets. Chromium dioxide is a bad metal at room temperature but it has a remarkably low residual resistivity (\u3c5 \u3eμΩ cm) despite the small spectral weight associated with free carrier absorption. The infrared measurements show that low residual resistivity is due to the collapse of the scattering rate at ω\u3c2000 \u3ecm-1. The blocking of the relaxation channels at low v and T can be attributed to the unique electronic structure of a half-metallic ferromagnet. In contrast to other ferromagnetic oxides, the intraband spectral weight is constant below the Curie temperature
Use of aerial thermography in Canadian energy conservation programs
Recent developments in the use of aerial thermography in energy conservation programs within Canada were summarized. Following a brief review of studies conducted during the last three years, methodologies of data acquisition, processing, analysis and interpretation was discussed. Examples of results from an industrial oriented project were presented and recommendations for future basic work were outlined
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Adapting the International System of Units to the twenty-first century
We review the proposal of the International Committee for Weights and Measures
(Comité International des Poids et Mesures, CIPM), currently being considered by
the General Conference on Weights and Measures (Conférences Générales des Poids et
Mesures, CGPM), to revise the International System of Units (Le Système International
d’Unitès, SI). The proposal includes new definitions for four of the seven base units of
the SI, and a new form of words to present the definitions of all the units. The objective
of the proposed changes is to adopt definitions referenced to constants of nature, taken
in the widest sense, so that the definitions may be based on what are believed to be
true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and
mole are linked to exact numerical values of the mass of the international prototype of the
kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature
of water and the molar mass of carbon-12, respectively, in the new SI these units are linked
to exact numerical values of the Planck constant, the elementary charge, the Boltzmann
constant and the Avogadro constant, respectively. The new wording used expresses the
definitions in a simple and unambiguous manner without the need for the distinction
between base and derived units. The importance of relations among the fundamental
constants to the definitions, and the importance of establishing a mise en pratique for
the realization of each definition, are also discussed
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