Demonstration of event position reconstruction based on diffusion in the NEXT-white detector.

Noble element time projection chambers are a leading technology for rare event detection in physics, such as for dark matter and neutrinoless double beta decay searches. Time projection chambers typically assign event position in the drift direction using the relative timing of prompt scintillation and delayed charge collection signals, allowing for reconstruction of an absolute position in the drift direction. In this paper, alternate methods for assigning event drift distance via quantification of electron diffusion in a pure high pressure xenon gas time projection chamber are explored. Data from the NEXT-White detector demonstrate the ability to achieve good position assignment accuracy for both high- and low-energy events. Using point-like energy deposits from 83mKr calibration electron captures (E∼45 keV), the position of origin of low-energy events is determined to 2 cm precision with bias <1mm. A convolutional neural network approach is then used to quantify diffusion for longer tracks (E≥1.5 MeV), from radiogenic electrons, yielding a precision of 3 cm on the event barycenter. The precision achieved with these methods indicates the feasibility energy calibrations of better than 1% FWHM at Qßß in pure xenon, as well as the potential for event fiducialization in large future detectors using an alternate method that does not rely on primary scintillation.

Assembly rules for Greater Antillean Anolis lizards : Competition and random models compared.

Using previously published data, several models were constructed to predict the distribution of Anolis lizard species on a set of sites on Puerto Rico and Jamaica. The models form a series with increasing ecological detail. The simpler "null" models are based on randomly created species-site matrices using progressively greater dependency on the observed matrix. The remaining models hypothesize that competition is the most important biotic interaction determining the intra-island distribution of the lizards. "Simple" competition models test the predictive power of simple statistical descriptions relating intensity of competition and ecological variables such as niche overlap and body size ratios. More complicated models are based on the ecomorph model of Williams (1972) and use the lizard resourceuse data of several niche dimensions (e.g., perch diameter and height). These models are derived from Puerto Rican data and tested against Jamaican data. The primary statistical tool used to test the accuracy of these models in the kappa statistic (Fleiss 1973) which assesses the degree of agreement in a contingency table relative to that expected by chance. The model structure is based on generative grammars (Haefner 1981), but is also related to artificial intelligence expert systems. Model comparisons indicate the following. (1) Only those null models constrained by the marginals of the observed species-site matrix agree with observed data. (2) Simple competition models based on fixed size ratios and/or fixed levels of allowable overlap do not agree well. (3) A complex competition model developed for Puerto Rico also shows significant agreement with lizard distributions on Jamaica, but is not better than a constrained null model. (4) If allowance is made for the restricted distribution of A. sagrei, a recent colonist of Jamaica, agreement of the competition model increases dramatically. It is predicted that A. sagrei would persist following an experimental transplant to eastern Jamaica.

Parallel implementations of individual-based models in biology: bulletin- and non-bulletin-board approaches.

Particle-based models are simulations in which the discrete representation of physical phenomenon involves interacting particles. This paper studies the efficiency of two different methods of implementing these models on a network of UNIX workstations. Two data parallel methods of modeling particles are tested: bulletin-board and non-bulletin-board. In the former method, the programs communicate through a logically shared, associative memory called a bulletin-board. The simulated particles are distributed among the workstations dynamically as the processing load on the processors changes. In the latter method, the particles are divided amongst the networked workstations statically at load time. The simulated system is a collection of ants moving and foraging in a two-dimensional space. This paper analyzes and compares the execution times of both implementations for different combinations of particles and number of workstation, using speed-up, tuple granularity and communication cost as measures. Analysis shows that the bulletin-board method is better for particle-based simulations when the correct granularity is chosen.

An investigation of the external physician search process.

As a basis for better understanding the health care consumer and identifying ways to segment the health care market, the authors report the results of an empirical investigation of the external search process patients undertake to find a physician. The impact of a patient's perceived illness severity on this process also is investigated. Implications of the findings are discussed.

How phenotypic variation and life history trait correlation enhance mean fitness in prey populations.

The relative effects of phenotypic variation and trait correlations on mean population fitness are poorly understood. Moreover, when fitness is evaluated in the context of ecological processes such as predation, theoretical development is lacking. To address this deficiency, we simulate a predator-prey system, where the prey population is composed of three phenotypes that differ in fecundity and predator evasiveness. We use equilibrium population size and allele frequencies to examine the relative effects of trait variation and correlation on mean population fitness. When no correlation is present, increasing variance in either trait increases equilibrium population size. Negative correlations coupled with increasing variance in both traits increases equilibrium population size. Positive correlations are more likely to increase equilibrium population size when variances are inversely related. With respect to allele frequencies, as variance in both traits increases, populations with positive correlations experience greater loss of genetic diversity than those with negative correlations. Thus, selection as a dynamic ecological process (frequency-dependent predation) favors trade-offs, whether they are between trait means (negative correlations) or variances (positive correlations).

Conceptual frameworks and the philosophical foundations of general living systems theory.

The continued expansion and fragmentation of biological disciplines impede education, communication, and efficient advance of biological research. Reversing these trends may require a unification of theories and concepts from all levels of biological organization. One form of this unification is the statement of generalizations that apply to all living systems. We explore the philosophical foundations of general theories of living systems by analyzing conceptual frameworks as they apply to biology. This analysis examines the relation of empirical observation, theories, and conceptual frameworks within the context of an individual scientist's conceptual continuum. Also presented are a small set of translevel generalizations that articulate our conceptual framework of living systems in terms of organismic system organization, the environmental system-organismic system dyad, system capacity, and system incorporation. A set of procedural rules are stated which suggest minimum criteria for the evaluation of the explanatory adequacy of biological theories. The relation of this work to other similar analyses and syntheses of biological knowledge is discussed.