Information In The Non-Stationary Case

Information estimates such as the ``direct method'' of Strong et al. (1998) sidestep the difficult problem of estimating the joint distribution of response and stimulus by instead estimating the difference between the marginal and conditional entropies of the response. While this is an effective estimation strategy, it tempts the practitioner to ignore the role of the stimulus and the meaning of mutual information. We show here that, as the number of trials increases indefinitely, the direct (or ``plug-in'') estimate of marginal entropy converges (with probability 1) to the entropy of the time-averaged conditional distribution of the response, and the direct estimate of the conditional entropy converges to the time-averaged entropy of the conditional distribution of the response. Under joint stationarity and ergodicity of the response and stimulus, the difference of these quantities converges to the mutual information. When the stimulus is deterministic or non-stationary the direct estimate of information no longer estimates mutual information, which is no longer meaningful, but it remains a measure of variability of the response distribution across time

Ecological effects of ditching and ditch-plugging in New England salt marshes

Anthropogenic activities in New England salt marshes have altered hydrologic flows in various ways, but unintended consequences from some of these habitat modifications have received little attention. Specifically, ditches have existed on salt marshes for decades, but the effects of these hydrologic alterations are only poorly understood. Ditch-plugging is a more recent methodology used for salt marsh habitat enhancement and mosquito control, but the long-term effects from this management practice are also unclear. I used natural tidal creeks and pools as controls to examine the effects resulting from ditching and plugging, respectively, on hydrology, soil characteristics, marsh surface elevation, plant characteristics, fish productivity, and trophic webs. Results indicated only slight differences in parameters sampled within habitat adjacent to ditches compared with creeks, and I infer minor ecological impact after 70+ years. Significant differences in hydrology, soil characteristics, marsh surface elevation, plant characteristics, fish productivity and trophic webs were observed in habitat adjacent to natural pools compared with ditch-plugs, and the many structural differences appear to result in ecological dissimilarities in function between the two habitats as well. The results of my study are important for natural resource managers to consider when planning salt marsh restoration and enhancement projects. The long-term legacy of ditch-plugs, especially as they pertain to changes in climate, may increase vulnerability of salt marshes to sea level rise and this conversion of ditches to ditch-plugs should not be undertaken without careful consideration

Descreening of Field Effect in Electrically Gated Nanopores

This modeling work investigates the electrical modulation characteristics of field-effect gated nanopores. Highly nonlinear current modulations are observed in nanopores with non-overlapping electric double layers, including those with pore diameters 100 times the Debye screening length. We attribute this extended field-effect gating to a descreening effect, i.e. the counter-ions do not fully relax to screen the gating potential due to the presence of strong ionic transport

An Economic Assessment of the 1999 Drought: Agricultural Impacts Are Severe Locally, but Limited Nationally

While the 1999 drought has had severe financial impacts on agricultural producers in the drought regions, its impact on U.S. agricultural production has been limited. The drought will reduce commodity receipts relative to 1998 by an estimated $1.29 billion. Estimated farm net income losses, including expected yield losses, increases in expenses, and insurance indemnities, will total$1.35 billion, about 3 percent of expected 1999 U.S. net farm income. Drought impacts in areas of the Northeast designated as extreme and severe drought are expected to reduce farmers' net income by nearly $840 million. The regions affected, the crops grown in those regions, the increased use of irrigation, and crop insurance coverage limited the drought's impacts on agriculture nationally. Drought also affects the rural population by reducing water supplies available for human and livestock consumption.Agricultural Finance, Farm Management,

Modification Of The Devonshire Formula For The Thermal Accommodation Coefficient Of Helium On Tungsten

The thermal accommodation coefficients (a.c.) of 3He and of 4He on clean tungsten were calculated using the Devonshire formula for temperatures between 70 and 600°K using realistic Morse potential parameters. The calculated a.c. values for 3He and 4He and the calculated ratios of the 4He to 3He values are compared with experimental data. The agreement is satisfactory if allowance is made for the error in the transition probability calculation used in the Devonshire formula

Schwinger variational principle applied to long-range potentials

We discuss an adaptation of the Schwinger variational principle which is particularly suitable for dealing with long-range potentials. The method treats the direct interaction potential exactly by numerical integration and assumes a separable representation of the Schwinger type for the exchange potential. The method should be very effective for obtaining the electronic continuum solutions of strongly polar molecular ions. The related photoionization cross sections can be shown to be variationally stable

ENVIRONMENTAL COMPLIANCE IN U.S. AGRICULTURAL POLICY: PAST PERFORMANCE AND FUTURE POTENTIAL

Since 1985, U.S. agricultural producers have been required to practice soil conservation on highly erodible cropland and conserve wetlands as a condition of farm program eligibility. This report discusses the general characteristics of compliance incentives, evaluates their effectiveness in reducing erosion in the program's current form, and explores the potential for expanding the compliance approach to address nutrient runoff from crop production. While soil erosion has, in fact, been reduced on land subject to Conservation Compliance, erosion is also down on land not subject to Conservation Compliance, indicating the influence of other factors. Analysis to isolate the influence of Conservation Compliance incentives from other factors suggests that about 25 percent of the decline in soil erosion between 1982 and 1997 can be attributed to Conservation Compliance. This report also finds that compliance incentives have likely deterred conversion of noncropped highly erodible land and wetland to cropland, and that a compliance approach could be used effectively to address nutrient runoff from crop production.conservation compliance, Sodbuster, Swampbuster, conservation policy, agri-environmental policy, nutrient management, buffer practices, Agricultural and Food Policy,

The Effect of Surface Impurities on the Thermal Accommodation of Rare Gases on a Tungsten Surface

A Rather Comprehensive Experimental Examination of the Effect of Surface Impurities (Potassium and Cesium) on the Thermal Accommodation of Rare Gases on a Tungsten Surface Has Been Made by Roach and Thomas. the Present Work Examines These Effects from a Theoretical Viewpoint with Particular Emphasis on the Effect on the Thermal Accommodation of Helium on a Tungsten Surface Caused by the Adsorption of Cesium Ions And/or Atoms. for This Examination, the Theory of Allen and Feuer Has Been Utilized using Reasonable Values of the Interaction Parameters for Helium with the Adsorbate as Well as the Force Constant for the Adsorbate-Substrate Bond. Resulting Values of the Accommodation Coefficients Are Compared with Experimental Values. © 1974 the Japan Society of Applied Physics

Revue du genre Coquilletidia (Diptera : Culididae) à Madagascar et description de la larve de Cq. grandidieri (Blanchard, 1905)

International audienceRESUME : Le genre Coquilletidia regroupe des moustiques impliqués dans la transmission de nombreuses arboviroses. Les adultes sont localement abondants et très agressifs pour l'homme. A Madagascar, ce genre concerne 3 espèces dont 2 endémiques qui n'ont pas encore été décrites au stade larvaire. Les auteurs décrivent une unique larve de Coquilletidia récoltée à Ankazobe, dans le Moyen Ouest malgache, à une altitude de 1200 mètres. La répartition des captures d'adultes de Coquilletidia dans les différentes zones bio-climatiques de Madagascar, d'une part, et les critères morphologiques différentiels, d'autre part, permettent d'attribuer cette larve à Cq. grandidieri