Simultaneous localization and mapping (SLAM): part II

This paper discusses the recursive Bayesian formulation of the simultaneous localization and mapping (SLAM) problem in which probability distributions or estimates of absolute or relative locations of landmarks and vehicle pose are obtained. The paper focuses on three key areas: computational complexity; data association; and environment representation.     

Variance and Convergence Analysis of Monte Carlo Line and Segment Sampling

Recently researchers have started employing Monte Carlo‐like line sample estimators in rendering, demonstrating dramatic reductions in variance (visible noise) for effects such as soft shadows, defocus blur, and participating media. Unfortunately, there is currently no formal theoretical framework to predict and analyze Monte Carlo variance using line and segment samples which have inherently anisotropic Fourier power spectra. In this work, we propose a theoretical formulation for lines and finite‐length segment samples in the frequency domain that allows analyzing their anisotropic power spectra using previous isotropic variance and convergence tools. Our analysis shows that judiciously oriented line samples not only reduce the dimensionality but also pre‐filter C⁰ discontinuities, resulting in further improvement in variance and convergence rates. Our theoretical insights also explain how finite‐length segment samples impact variance and convergence rates only by pre‐filtering discontinuities. We further extend our analysis to consider (uncorrelated) multi‐directional line (segment) sampling, showing that such schemes can increase variance compared to unidirectional sampling. We validate our theoretical results with a set of experiments including direct lighting, ambient occlusion, and volumetric caustics using points, lines, and segment samples.     

Accelerating geoscience and engineering system simulations on graphics hardware

Many complex natural systems studied in the geosciences are characterized by simple local-scale interactions that result in complex emergent behavior. Simulations of these systems, often implemented in parallel using standard central processing unit (CPU) clusters, may be better suited to parallel processing environments with large numbers of simple processors. Such an environment is found in graphics processing units (GPUs) on graphics cards.This paper discusses GPU implementations of three example applications from computational fluid dynamics, seismic wave propagation, and rock magnetism. These candidate applications involve important numerical modeling techniques, widely employed in physical system simulations, that are themselves examples of distinct computing classes identified as fundamental to scientific and engineering computing. The presented numerical methods (and respective computing classes they belong to) are: (1) a lattice-Boltzmann code for geofluid dynamics (structured grid class); (2) a spectral-finite-element code for seismic wave propagation simulations (sparse linear algebra class); and (3) a least-squares minimization code for interpreting magnetic force microscopy data (dense linear algebra class). Significant performance increases (between 10× and 30× in most cases) are seen in all three applications, demonstrating the power of GPU implementations for these types of simulations and, more generally, their associated computing classes.     

Prospects for insulin delivery by ex-vivo somatic cell gene therapy

The principle of insulin delivery by ex-vivo somatic cell gene therapy involves the removal of non-B-cell somatic cells (e.g. fibroblasts) from a diabetic patient, and genetically altering them in vitro to produce and secrete insulin. The cells can be grown in culture and returned to the donor as a source of insulin replacement. Cells modified in this way could be evaluated before implantation, and reserve stocks could be cryopreserved. By using the patient's own cells, the procedure should obviate the need for immunosuppression and overcome the problem of tissue supply, while avoiding a recurrence of cell destruction. Ex-vivo somatic cell gene therapy requires an accessible and robust cell type that is amenable to multiple transfections and subject to controlled proliferation. Special problems associated with the use of non-B-cell somatic cells include the processing of proinsulin to insulin, and the conferment of sensitivity to glucose-stimulated proinsulin biosynthesis and regulated insulin release. Preliminary studies using fibroblasts, pituitary cells, kidney (COS) cells and ovarian (CHO) cells suggest that these challenges could be met, and that ex-vivo somatic cell gene therapy offers a feasible approach to insulin replacement therapy.     

Taxometric analyses of sexual orientation and gender identity.

Taxa are nonarbitrary classes whose existence is an empirical question and not a matter of mere semantic convenience. Taxometric procedures detect whether numerical relations between purported indicators of conjectured taxa bear the hallmarks of true taxa. On the basis of theoretical considerations, the current study tested whether taxa underlie sexual orientation and related measures of gender identity. Two taxometric procedures, maximum covariance, making hits maximum (MAXCOV) and mean above minus below a cut (MAMBAC), were applied to Kinsey Scales and measures of childhood gender nonconformity and adult gender identity in a sample of nearly 5,000 members of the Australian Twin Registry. Results suggest that latent taxa underlie these measures. About 12–15% of men and 5–10% of women belong to latent taxa associated with homosexual preference. These percentages are greater than those of individuals who report homosexual preference, however, and hence it appears that an appreciable proportion of individuals in these taxa have heterosexual preference. An understanding of the origins of these latent taxa may be important to understanding the development of sexual orientation and gender identity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of antipredator responses in snakes: II. Effects of recent feeding on defensive behaviors of juvenile garter snakes (Thamnophis sirtalis).

The effect of having eaten a large meal (50% of body weight) on the defensive behavior of juvenile garter snakes (Thamnophis sirtalis) was investigated. Twenty-five 10-wk-old snakes were tested for antipredator responses (strikes) directed toward a threatening stimulus (moving and nonmoving human hand) before and after having eaten a large worm segment. Snakes directed significantly (p?     

Interaction between Macroinvertebrate Abundance and Habitat Use by Diving Ducks during Winter on Northeastern Lake Ontario

Although numbers of buffleheads (Bucephala albeola), common goldeneyes (Bucephala clangula) and long-tailed ducks (Clangula hyemalis) over-wintering on Lake Ontario have increased substantially over the past two decades, factors influencing habitat use and the potential for competition have not been investigated. The purpose of this study was to determine the relationship between prey availability and community structure of diving ducks during winter on northeastern Lake Ontario. Benthic and nektonic samples collected during fall, winter, and spring 2002–2004 indicated that macroinvertebrate numbers differed by location but generally did not decline throughout winter. Large accumulations of macroinvertebrates, apparently moved by wave action and currents, were documented in nearshore areas. Surveys showed that diving ducks congregated in mixed species flocks within areas of higher food abundance. Mixed species flocks were common in nearshore areas, likely because energydense foods (Amphipoda and Chironomidae) were abundant in the narrow zone of shallow water, close to shore. Although macroinvertebrate numbers likely affected habitat use by diving ducks, birds did not greatly reduce abundance of macroinvertebrates. It is unlikely that exploitative competition was occurring and interference competition appeared below threshold levels that would cause species to spatially segregate. Overall, our results suggest that food availability is not a limiting factor for buffleheads, common goldeneyes, or long-tailed ducks wintering on northeastern Lake Ontario.     

Colonization of broiler chicks by Salmonella typhimurium definitive phage type 104.

The prevalence of an antibiotic-resistant strain of Salmonella Typhimurium definitive phage type 104 (DT104) has increased dramatically in recent years resulting in increased morbidity and mortality in both animals and humans. Colonization and shedding of Salmonella Typhimurium DT104 was studied in broiler chickens in two trials. In trial 1, 180 day-of-hatch chicks (n = 60 per group, n = 30 per replicate) were challenged with 10(6) CFU DT104 (wild-type isolate from poultry) or were commingled with a seeder chick challenged with 10(6) CFU DT104. In trial 2, 360 day-of-hatch chicks (n = 120 per treatment, n = 30 per rep) were divided into three groups. Chicks in the susceptible group were commingled with two seeder chicks that were orally challenged with 10(7) CFU/bird of a pan-sensitive strain of Salmonella Typhimurium DT104. Chicks in the resistant group were commingled with two seeder chicks that were orally challenged with 10(7) CFU/bird DT104 used in trial 1. For both trials, a control group was not exposed to DT104, composite fecal samples were evaluated twice weekly for levels of Salmonella shedding and 20 chicks per group were necropsied weekly and their cecal contents were cultured. At hatch all groups were colonized with naturally occurring Salmonella Senftenberg and Salmonella Mbandaka (trial 1) or Salmonella Senftenberg and Salmonella Ohio (trial 2) prior to exposure to DT104. Throughout the study, the level of Salmonella spp. shedding in feces (trial 1 means 3.1, 2.9, and 3.0 log10 CFU per g feces for challenged, seeder, and control groups, respectively) or ceca (trial 2 means 2.9. 2.9. and 2.5 log10 CFU per g ceca for resistant, susceptible, and control groups, respectively) did not differ among groups. In trial 1, colonization of DT104 remained constant at higher levels in the challenged group (mean 87%, P < 0.01), increased over time in the seeder group (10 to 50%, P < 0.02) and was not recovered from the control chicks. Salmonella Mbandaka colonization remained steady within each group with challenge and seeder groups maintaining higher levels of colonization than the control group. Salmonella Senftenberg colonization levels tended to decline (P = .058) over time in the challenged group (20 to 0%) and significantly decreased (P < 0.01) over time for both the seeder (80 to 0%) and control chicks (85 to 10%). In trial 2, the percentage of chicks colonized with susceptible DT104 declined (r = 0.90, P < 0.05) over the course of the trial from 45 to 0%, while recovery of the resistant DT104 persisted at a mean percentage of 27%. DT104 was not recovered from the control chicks. Salmonella Ohio colonization levels tended to decline (r = 0.79, P > 0.05) over time in the control group (75 to 20%) and significantly decreased (P < 0.05) over time in both susceptible and resistant groups (40 to 10%, r = 0.82 and 55 to 5%, r = 0.85, respectively). Salmonella Senftenberg was recovered from the control group at low frequency throughout the trial and was not recovered from the other groups. For either trial, no apparent affect on morbidity or mortality was observed. Introduction of DT104 by commingling may induce colonization resulting in persistent high levels of shedding in flocks simultaneously with other Salmonella species.