Transport on randomly evolving trees

The time process of transport on randomly evolving trees is investigated. By introducing the notions of living and dead nodes a model of random tree evolution is constructed which describes the spreading in time of objects corresponding to nodes. By using the method of the age-dependent branching processes we derive the joint distribution function of the number of living and dead nodes, and determine the correlation between these node numbers as a function of time. Also analyzed are the stochastic properties of the end-nodes; and the correlation between the numbers of living and dead end-nodes is shown to change its character suddenly at the very beginning of the evolution process. The survival probability of random trees is investigated and expressions are derived for this probability.Comment: 16 pages, 8 figures, published in Phys. Rev. E 72, 051101 (2005

Aircraft control system

A solar rechargeable, long-duration, span-loaded flying wing, having no fuselage or rudder. Having a two-hundred foot wingspan that mounts photovoltaic cells on most all of the wing's top surface, the aircraft uses only differential thrust of its eight propellers to turn, pitch and yaw. The wing is configured to deform under flight loads to position the propellers such that the control can be achieved. Each of five segments of the wing has one or more motors and photovoltaic arrays, and produces its own lift independent of the other segments, to avoid loading them. Five two-sided photovoltaic arrays, in all, are mounted on the wing, and receive photovoltaic energy both incident on top of the wing, and which is incident also from below, through a bottom, transparent surface

Costes de los sesgos de detección en el monitoreo de poblaciones basado en índices

Managers of wildlife populations commonly rely on indirect, count–based measures of the population in making decisions regarding conservation, harvest, or control. The main appeal in the use of such counts is their low material expense compared to methods that directly measure the population. However, their correct use rests on the rarely–tested but often–assumed premise that they proportionately reflect population size, i.e., that they constitute a population index. This study investigates forest management for the endangered Red–cockaded Woodpecker (Picoides borealis) and the Wood Thrush (Hylocichla mustelina) at the Piedmont National Wildlife Refuge in central Georgia, U.S.A. Optimal decision policies for a joint species objective were derived for two alternative models of Wood Thrush population dynamics. Policies were simulated under scenarios of unbiasedness, consistent negative bias, and habitat–dependent negative bias in observed Wood Thrush densities. Differences in simulation outcomes between biased and unbiased detection scenarios indicated the expected loss in resource objectives (here, forest habitat and birds) through decision–making based on biased population counts. Given the models and objective function used in our analysis, expected losses were as great as 11%, a degree of loss perhaps not trivial for applications such as endangered species management. Our analysis demonstrates that costs of uncertainty about the relationship between the population and its observation can be measured in units of the resource, costs which may offset apparent savings achieved by collecting uncorrected population counts.Los gestores de poblaciones de fauna silvestre a menudo toman decisiones relativas a la conservación, recolección o control a partir de medidas indirectas de la población basadas en recuentos. El principal atractivo que presenta este tipo de recuentos son los bajos costes de material, en comparación con otros métodos que miden la población de forma directa. Sin embargo, el correcto uso de los mismos depende de una premisa que suele darse por sentada, aunque rara vez se comprueba, y que consiste en suponer que reflejan proporcionalmente el tamaño de la población; es decir, que constituyen un índice poblacional. El presente estudio investiga la gestión forestal de dos especies en peligro de extinción: el pájaro carpintero de cresta roja (Picoides borealis) y el zorzal mustelino (Hylocichla mustelina) en la Reserva Nacional de Animales Salvajes de Piedmont, en Georgia central, Estados Unidos. Se simularon varias políticas de conservación bajo escenarios referentes a las densidades del zorzal mustelino insesgados, con un consistente sesgo negativo y con un sesgo negativo dependiente del hábitat. Las diferencias obtenidas con respecto a los resultados de simulación entre los escenarios de detección sesgados y los no sesgados indicaron la pérdida prevista en los objetivos en materia de recursos (en este caso, el hábitat y las aves del bosque) a través de una toma de decisiones basada en los recuentos poblacionales sesgados. Teniendo en cuenta los modelos y la función de los objetivos que hemos empleado en nuestro análisis, las pérdidas previstas ascendieron al 11%, lo que supone un porcentaje bastante significativo en aplicaciones tales como la gestión de especies en peligro de extinción. Nuestro análisis demuestra que los costes de incertidumbre acerca de la relación entre la población y su observación pueden medirse en unidades del recurso dado; es posible que estos costes compensen los ahorros aparentemente conseguidos mediante la recopilación de recuentos poblacionales no corregidos

Antimicrobial Susceptibilities of Aerobic Isolates from Respiratory Samples of Young New Zealand Horses

3rd Annual IEEE Energy Conversion Congress and Exposition, ECCE 2011, Phoenix, AZ, 17-22 September 2011This paper presents a method of mitigating the transient overshoots of DC-DC converters operating with large load disturbances. The method involves a small auxiliary power circuit with a complementary control scheme that provides a smooth absorption and release of excess energy from and to the main DC-DC converter in the events of large load changes. This control mechanism interactively mitigates the large transient overshoots which would otherwise appear at the converter output. Since the control scheme involves an adjustable-energy-storage feature, the proposed solution is effective for any level of step-load change within a pre-specified range.Department of Electronic and Information EngineeringRefereed conference pape

The High Cost of Reproduction in Sea Otters Necessitates Unique Physiological Adaptations

Resting Superimposed on inherently high basal metabolic demands, the additional energetic requirements of reproduction can push female sea otters beyond physiological limits. Indeed, the resulting energy imbalance contributes to disproportionately high rates of mortality at the end of lactation in this species. To examine and quantify metabolic changes associated with reproduction, we measured the resting metabolic rate (RMR) of a female sea otter across gestation, lactation and non-reproductive periods. Concurrently, measurements were made on a non-breeding control female. Our results suggest that RMR declines during gestation. Conversely, RMR increases during lactation, reaches a peak at 3–4 months postpartum, and remains elevated until weaning. Combining these direct measurements with published data, we found the cost of pup rearing to be significantly higher than previously estimated. High baseline energy demands and limited energy reserves, combined with significant lactation and pup rearing costs, appear to necessitate metabolic and thermal lability during key reproductive stages

Delineation of ligand binding and receptor signaling activities of purified P2Y receptors reconstituted with heterotrimeric G proteins

P2Y receptors are G protein coupled receptors that respond to extracellular nucleotides to promote a multitude of signaling events. Our laboratory has purified several P2Y receptors with the goal of providing molecular insight into their: (1) ligand binding properties, (2) G protein signaling selectivities, and (3) regulation by RGS proteins and other signaling cohorts. The human P2Y1 receptor and the human P2Y12 receptor, both of which are intimately involved in ADP-mediated platelet aggregation, were purified to near homogeneity and studied in detail. After high-level expression from recombinant baculovirus infection of Sf9 insect cells, approximately 50% of the receptors were successfully extracted with digitonin. Purification of nearly homogeneous epitope-tagged P2Y receptor was achieved using metal-affinity chromatography followed by other traditional chromatographic steps. Yields of purified P2Y receptors range from 10 to 100 μg/l of infected cells. Once purified, the receptors were reconstituted in model lipid vesicles along with their cognate G proteins to assess receptor function. Agonist-promoted increases in steady-state GTPase assays demonstrated the functional activity of the reconstituted purified receptor. We have utilized this reconstitution system to assess the action of various nucleotide agonists and antagonists, the relative G protein selectivity, and the influence of other proteins, such as phospholipase C, on P2Y receptor-promoted signaling. Furthermore, we have identified the RGS expression profile of platelets and have begun to assess the action of these RGS proteins in a reconstituted P2Y receptor/G protein platelet model

Drying and cracking mechanisms in a starch slurry

Starch-water slurries are commonly used to study fracture dynamics. Drying starch-cakes benefit from being simple, economical, and reproducible systems, and have been used to model desiccation fracture in soils, thin film fracture in paint, and columnar joints in lava. In this paper, the physical properties of starch-water mixtures are studied, and used to interpret and develop a multiphase transport model of drying. Starch-cakes are observed to have a nonlinear elastic modulus, and a desiccation strain that is comparable to that generated by their maximum achievable capillary pressure. It is shown that a large material porosity is divided between pore spaces between starch grains, and pores within starch grains. This division of pore space leads to two distinct drying regimes, controlled by liquid and vapor transport of water, respectively. The relatively unique ability for drying starch to generate columnar fracture patterns is shown to be linked to the unusually strong separation of these two transport mechanisms.Comment: 9 pages, 8 figures [revised in response to reviewer comments

Drying and cracking mechanisms in a starch slurry

Starch-water slurries are commonly used to study fracture dynamics. Drying starch-cakes benefit from being simple, economical, and reproducible systems, and have been used to model desiccation fracture in soils, thin film fracture in paint, and columnar joints in lava. In this paper, the physical properties of starch-water mixtures are studied, and used to interpret and develop a multiphase transport model of drying. Starch-cakes are observed to have a nonlinear elastic modulus, and a desiccation strain that is comparable to that generated by their maximum achievable capillary pressure. It is shown that a large material porosity is divided between pore spaces between starch grains, and pores within starch grains. This division of pore space leads to two distinct drying regimes, controlled by liquid and vapor transport of water, respectively. The relatively unique ability for drying starch to generate columnar fracture patterns is shown to be linked to the unusually strong separation of these two transport mechanisms.Comment: 9 pages, 8 figures [revised in response to reviewer comments

Discovery of very nearby ultracool dwarfs from DENIS

We report new spectroscopic results, obtained with UKIRT/CGS4, of a sample of 14 candidate ultracool dwarfs selected from the DENIS (Deep Near-Infrared Survey of the Southern Sky) database. A further object, selected from the 2MASS Second Incremental Release, was observed at a later epoch with the same instrument. Six objects are already known in the literature; we re-derive their properties. A further four prove to be very nearby (~10 pc) mid-to-late L-dwarfs, three unknown hitherto, two of which are almost certainly substellar. These findings increase the number of L-dwarfs known within ~10 pc by ~25%. The remainder of the objects discussed here are early L or very late M-type dwarfs lying between ~45 and 15 pc and are also new to the literature. Spectral types have been derived by direct comparison with J-,H- and K- band spectra of known template ultracool dwarfs given by Leggett et al. (ftp://ftp.jach.hawaii.edu/pub/ukirt/skl/dL.spectra/) For the known objects, we generally find agreement to within ~1 subclass with previously derived spectral types. Distances are determined from the most recent M_J vs. spectral type calibrations, and together with our derived proper motions yield kinematics for most targets consistent with that expected for the disk population; for three probable late M-dwarfs, membership of a dynamically older population is postulated. The very nearby L-type objects discussed here are of great interest for future studies of binarity and parallaxes.Comment: 4 pages, 2 figures, accepted in A&A Letter