State-space based mass event-history model I: many decision-making agents with one target

A dynamic decision-making system that includes a mass of indistinguishable agents could manifest impressive heterogeneity. This kind of nonhomogeneity is postulated to result from macroscopic behavioral tactics employed by almost all involved agents. A State-Space Based (SSB) mass event-history model is developed here to explore the potential existence of such macroscopic behaviors. By imposing an unobserved internal state-space variable into the system, each individual's event-history is made into a composition of a common state duration and an individual specific time to action. With the common state modeling of the macroscopic behavior, parametric statistical inferences are derived under the current-status data structure and conditional independence assumptions. Identifiability and computation related problems are also addressed. From the dynamic perspectives of system-wise heterogeneity, this SSB mass event-history model is shown to be very distinct from a random effect model via the Principle Component Analysis (PCA) in a numerical experiment. Real data showing the mass invasion by two species of parasitic nematode into two species of host larvae are also analyzed. The analysis results not only are found coherent in the context of the biology of the nematode as a parasite, but also include new quantitative interpretations.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS189 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

The effect of organic versus chemical fertilizers on insect pathogens

Insects such as the black cutworm are a major pest of seedling corn in Corn Belt states. Both the nematode Steinernema carpocapsae and the fungus Beauveria bassiana are potential biological control agents of this pest Because their survivability depends on moisture and they are affected adversely by nitrogen compounds, this project studied the effects of various fertilizers (fresh cow manure, composted cow manure, and urea) on these insect-killing organisms. Results showed that S. carpocapsae is more active in soils with no fertilizer amendment or with composted manure than with fresh manure or chemical fertilizer; B. bassiana is adversely affected by fresh manure. Investigation of factors that may enhance dispersal (which in turn may be a determining factor in the success of biological control) found that dispersal of two species of insect-killing nematodes was increased in the presence of earthworms

Chern classes and extraspecial groups

The mod-p cohomology ring of the extraspecial p-group of exponent p is studied for odd p. We investigate the subquotient ch(G) generated by Chern classes modulo the nilradical. The subring of ch(G) generated by Chern classes of one-dimensional representations was studied by Tezuka and Yagita. The subring generated by the Chern classes of the faithful irreducible representations is a polynomial algebra. We study the interplay between these two families of generators, and obtain some relations between them

Optimal Policies Search for Sensor Management

International audienceThis paper introduces a new approach to solve sensor management problems. Classically sensor management problems can be well formalized as Partially-Observed Markov Decision Processes (POMPD). The original approach developped here consists in deriving the optimal parameterized policy based on a stochastic gradient estimation. We assume in this work that it is possible to learn the optimal policy off-line (in simulation ) using models of the environement and of the sensor(s). The learned policy can then be used to manage the sensor(s). In order to approximate the gradient in a stochastic context, we introduce a new method to approximate the gradient, based on Infinitesimal Perturbation Approximation (IPA). The effectiveness of this general framework is illustrated by the managing of an Electronically Scanned Array Radar. First simulations results are finally proposed

Economic and health outcomes of capsule endoscopy: Opportunities for improved management of the diagnostic process for obscure gastrointestinal bleeding

The estimated annual incidence of gastrointestinal bleeding in the United States is approximately 100 episodes per 100,000 persons, resulting in 300,000 hospitalizations annually. Diagnostic tools such as radiologic studies and endoscopic examination often fail to identify a source of bleeding, resulting in a cycle of repetitive testing over months or even years. Costs associated with the diagnostic process, and with interim treatment for anemia and other symptoms, can be significant. The diagnostic process also takes a toll on the patient, in terms of worry, pain, and discomfort. Capsule endoscopy, a technology that received FDA clearance in August, 2001, consists of a video capsule that is ingested by the patient, and that transmits images to a wireless data recorder worn on the belt. The recorded stream of approximately 50,000 images can be reviewed on a computer workstation by a physician to identify nature and location of potential sources of bleeding. This paper presents a framework for economic analysis of this new technology. First, we present a review of the literature on the current diagnostic methods. Next, we present a conceptual model for examining contributors to costs in diagnosing obscure intestinal bleeds. We conclude by exploring the potential economic impact of the technology. Analysis of data from the first U.S. clinical trial of capsule endoscopy demonstrates its high diagnostic yield, and patient satisfaction. While further study is required, this analysis indicates that capsule endoscopy may reduce total medical utilization and costs and improve patient quality of life, when used for appropriate indications

Institutional and technological barriers to the use of open educational resources (OERs) in physiology and medical education

Open educational resources (OERs) are becoming increasingly common as a tool in education, particularly in medical and biomedical education. However, three key barriers have been identified to their use: (i) lack of awareness of OERs, (ii) lack of motivation to use OERs, and (iii) lack of training in the use of OERs. Here, we explore these three barriers with teachers of medical and biomedical science to establish how best to enhance the use of OERs to improve pedagogical outcomes. An online survey was completed by 209 educators, many of whom (68.4%) reported using OERs in their teaching, and almost all (99.5%) showing awareness of at least one OER. Results suggest that key problems that prevent educators from adopting OERs in their teaching include suitability for particular classes, time, and copyright. Most (81.8%) educators were somewhat, very, or extremely comfortable with OERs so there is no innate motivational barrier to adoption. A lack of training was reported by 13.9% of respondents, and 40% of respondents stated that there was little or no support from their institutions. OER users were no more comfortable with technology or better supported by departments, but tended to be aware of a greater number of sources of OERs. Our study illustrates key opportunities for the expansion of OER use in physiology and medical teaching: increased breadth of awareness, increased institutional support (including time, training, and copyright support), and greater sharing of diverse OERs to suit the range of teaching challenges faced by staff in different subdisciplines

mTORC2 signaling drives the development and progression of pancreatic cancer

mTOR signaling controls several critical cellular functions and is deregulated in many cancers, including pancreatic cancer. To date, most efforts have focused on inhibiting the mTORC1 complex. However, clinical trials of mTORC1 inhibitors in pancreatic cancer have failed, raising questions about this therapeutic approach. We employed a genetic approach to delete the obligate mTORC2 subunit Rictor and identified the critical times during which tumorigenesis requires mTORC2 signaling. Rictor deletion resulted in profoundly delayed tumorigenesis. Whereas previous studies showed most pancreatic tumors were insensitive to rapamycin, treatment with a dual mTORC1/2 inhibitor strongly suppressed tumorigenesis. In late-stage tumor-bearing mice, combined mTORC1/2 and PI3K inhibition significantly increased survival. Thus, targeting mTOR may be a potential therapeutic strategy in pancreatic cancer