ESTIMATING INSECTICIDE APPLICATION FREQUENCIES: A COMPARISON OF GEOMETRIC AND OTHER COUNT DATA MODELS

The number of insecticide applications made by an apple grower to control an insect infestation is modeled as a geometric random variable. Insecticide efficacy, rate per application, month of treatment, and method of application all have significant impacts on the expected number of applications. The number of applications to control a given insect population is dependent on the probability of achieving successful control with a given application. Results suggest that northeastern growers have the highest and mid-Atlantic growers the lowest probability of controlling an infestation with a given application. Results also indicate that scales require the least and moths the most number of applications. Growers are not responsive to per unit insecticide prices, but respond negatively to insecticide toxicity, supporting findings from previous pesticide demand analyses.Apples, Count data, Geometric, Insect control, Pesticides, Crop Production/Industries,

INFORMATION QUALITY, TECHNOLOGY DEPRECIATION, AND BT COTTON ADOPTION IN THE SOUTHEAST

In 1996, Bt cotton became one of the first genetically engineered crops to be available commercially. This study focuses on the various sources and quality of information about Bt cotton profitability available to farmers in the Southeast and assesses the relative importance of such information in the farmers' adoption decisions. A model of the individual decision to adopt is developed to incorporate two recent theories of the role of information quality (the "effective information" hypothesis and the "popularity" hypothesis) as well as the effect of current technology depreciation. The data show some support for all three factors as determinants of adoption.Crop Production/Industries,

Part I: A novel in-vitro system for simultaneous mechanical stimulation and time-lapse microscopy in 3D

To investigate the migration response of cells to changes in their biophysical environment, a novel uniaxial cell stimulation device (UCSD) has been designed and tested. The device is capable of applying very precise user-defined static or dynamic mechanical stimuli in a physiologically relevant strain window (up to 50%) and frequency bandwidth (up to 2Hz) to cells residing in a three-dimensional (3D) environment while single-cell migration is simultaneously measured by time-lapse microscopy. The system is an advancement over uniaxial loading devices reported to date in that it allows temporal and spatial quantification of migration as a function of the micromechanical environment. We make use of the favorable physical and biological properties of poly(ethylene glycol) hydrogels as model matrix and present a method for fabricating cell-containing hydrogel constructs. The 3D strain field within these constructs is modeled by finite element analysis. Fibroblasts reversibly altered their morphology and orientation in response to the strain field. In the succeeding companion paper we then exploit the system to analyze fibroblast motility induced by different stimulation regimes (refer to part II

Spatial Scaling in Model Plant Communities

We present an analytically tractable variant of the voter model that provides a quantitatively accurate description of beta-diversity (two-point correlation function) in two tropical forests. The model exhibits novel scaling behavior that leads to links between ecological measures such as relative species abundance and the species area relationship.Comment: 10 pages, 3 figure

Lunar base CELSS: A bioregenerative approach

During the twenty-first century, human habitation of a self-sustaining lunar base could become a reality. To achieve this goal, the occupants will have to have food, water, and an adequate atmosphere within a carefully designed environment. Advanced technology will be employed to support terrestrial life-sustaining processes on the Moon. One approach to a life support system based on food production, waste management and utilization, and product synthesis is outlined. Inputs include an atmosphere, water, plants, biodegradable substrates, and manufacutured materials such as fiberglass containment vessels from lunar resources. Outputs include purification of air and water, food, and hydrogen (H2) generated from methane (CH4). Important criteria are as follows: (1) minimize resupply from Earth; and (2) recycle as efficiently as possible

Part II: Fibroblasts preferentially migrate in the direction of principal strain

A growing body of evidence suggests that the sensory information from the cytoskeleton and integrins may be responsible for guiding migration during mechano- and haptotaxis. However, the dual function of these subcellular structures as mechano-sensors and -actuators is only partially understood. Using a new cell chamber described in the preceding companion paper (Ref to part I, Raeber etal. 2007a) we investigated the migration response of adhesion-dependent fibroblasts embedded 3-dimensionally within synthetic protease-sensitive poly(ethylene glycol) hydrogels to stepwise and cyclic mechanical loads. To that end, we developed a spatially and temporally resolved migration analysis technique capable of providing estimates of statistical cell migration parameters along and perpendicular to the main strain direction. Fibroblasts reoriented themselves in the direction of principal strain, increased their proteolytic migration activity and moved preferentially parallel to the principal strain axis. These results point to a possible correlation between planes of iso-strain and migration directio

Terrestrial Consequences of Spectral and Temporal Variability in Ionizing Photon Events

Gamma-Ray Bursts (GRBs) directed at Earth from within a few kpc may have damaged the biosphere, primarily though changes in atmospheric chemistry which admit greatly increased Solar UV. However, GRBs are highly variable in spectrum and duration. Recent observations indicate that short (~0.1 s) burst GRBs, which have harder spectra, may be sufficiently abundant at low redshift that they may offer an additional significant effect. A much longer timescale is associated with shock breakout luminosity observed in the soft X-ray (~10^3 s) and UV (~10^5 s) emission, and radioactive decay gamma-ray line radiation emitted during the light curve phase of supernovae (~10^7 s). Here we generalize our atmospheric computations to include a broad range of peak photon energies and investigate the effect of burst duration while holding total fluence and other parameters constant. The results can be used to estimate the probable impact of various kinds of ionizing events (such as short GRBs, X-ray flashes, supernovae) upon the terrestrial atmosphere. We find that the ultimate intensity of atmospheric effects varies only slightly with burst duration from 10^-1 s to 10^8 s. Therefore, the effect of many astrophysical events causing atmospheric ionization can be approximated without including time development. Detailed modeling requires specification of the season and latitude of the event. Harder photon spectra produce greater atmospheric effects for spectra with peaks up to about 20 MeV, because of greater penetration into the stratosphere.Comment: 30 pages, to be published in ApJ. Replaced for conformity with published version, including correction of minor typos and updated reference

Fixation and consensus times on a network: a unified approach

We investigate a set of stochastic models of biodiversity, population genetics, language evolution and opinion dynamics on a network within a common framework. Each node has a state, 0 < x_i < 1, with interactions specified by strengths m_{ij}. For any set of m_{ij} we derive an approximate expression for the mean time to reach fixation or consensus (all x_i=0 or 1). Remarkably in a case relevant to language change this time is independent of the network structure.Comment: 4+epsilon pages, two-column, RevTeX4, 3 eps figures; version accepted by Phys. Rev. Let

An exactly solvable coarse-grained model for species diversity

We present novel analytical results about ecosystem species diversity that stem from a proposed coarse grained neutral model based on birth-death processes. The relevance of the problem lies in the urgency for understanding and synthesizing both theoretical results of ecological neutral theory and empirical evidence on species diversity preservation. Neutral model of biodiversity deals with ecosystems in the same trophic level where per-capita vital rates are assumed to be species-independent. Close-form analytical solutions for neutral theory are obtained within a coarse-grained model, where the only input is the species persistence time distribution. Our results pertain: the probability distribution function of the number of species in the ecosystem both in transient and stationary states; the n-points connected time correlation function; and the survival probability, definned as the distribution of time-spans to local extinction for a species randomly sampled from the community. Analytical predictions are also tested on empirical data from a estuarine fish ecosystem. We find that emerging properties of the ecosystem are very robust and do not depend on specific details of the model, with implications on biodiversity and conservation biology.Comment: 20 pages, 4 figures. To appear in Journal of Statistichal Mechanic