Pion-Nucleon Scattering in a Large-N Sigma Model

We review the large-N_c approach to meson-baryon scattering, including recent interesting developments. We then study pion-nucleon scattering in a particular variant of the linear sigma-model, in which the couplings of the sigma and pi mesons to the nucleon are echoed by couplings to the entire tower of I=J baryons (including the Delta) as dictated by large-N_c group theory. We sum the complete set of multi-loop meson-exchange \pi N --> \pi N and \pi N --> \sigma N Feynman diagrams, to leading order in 1/N_c. The key idea, reviewed in detail, is that large-N_c allows the approximation of LOOP graphs by TREE graphs, so long as the loops contain at least one baryon leg; trees, in turn, can be summed by solving classical equations of motion. We exhibit the resulting partial-wave S-matrix and the rich nucleon and Delta resonance spectrum of this simple model, comparing not only to experiment but also to pion-nucleon scattering in the Skyrme model. The moral is that much of the detailed structure of the meson-baryon S-matrix which hitherto has been uncovered only with skyrmion methods, can also be described by models with explicit baryon fields, thanks to the 1/N_c expansion.Comment: This LaTeX file inputs the ReVTeX macropackage; figures accompany i

Cathelicidin-like Helminth Defence Molecules (HDMs) Absence of Cytotoxic, Anti-microbial and Anti-protozoan Activities Imply a Specific Adaptation to Immune Modulation

Host defence peptides (HDPs) are expressed throughout the animal and plant kingdoms. They have multifunctional roles in the defence against infectious agents of mammals, possessing both bactericidal and immune-modulatory activities. We have identified a novel family of molecules secreted by helminth parasites (helminth defence molecules; HDMs) that exhibit similar structural and biochemical characteristics to the HDPs. Here, we have analyzed the functional activities of four HDMs derived from Schistosoma mansoni and Fasciola hepatica and compared them to human, mouse, bovine and sheep HDPs. Unlike the mammalian HDPs the helminth-derived HDMs show no antimicrobial activity and are non-cytotoxic to mammalian cells (macrophages and red blood cells). However, both the mammalian- and helminth-derived peptides suppress the activation of macrophages by microbial stimuli and alter the response of B cells to cytokine stimulation. Therefore, we hypothesise that HDMs represent a novel family of HDPs that evolved to regulate the immune responses of their mammalian hosts by retaining potent immune modulatory properties without causing deleterious cytotoxic effects. © 2013 Thivierge et al

Comment letters to the National Commission on Commission on Fraudulent Financial Reporting, 1987 (Treadway Commission) Vol. 1

https://egrove.olemiss.edu/aicpa_sop/1661/thumbnail.jp

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Salmonella Cost Estimate Updated Using FoodNet Data

Salmonella infections due to contaminated food products make many people ill each year and are responsible for substantial economic costs. Salmonella infections are potentially serious and may be fatal, particularly for the elderly and people with weak immune systems (see box on Salmonella infections). However, most salmonellosis cases do not result in a visit to a medical facility and are never reported to public health agencies. The high proportion of unreported cases makes it difficult to determine the true incidence of salmonellosis, and has resulted in a wide range of estimates of the annual economic costs of foodborne Salmonella infections. Many Salmonella infections are caused by undercooked shell eggs, which may be contaminated by hens infected by Salmonella serotype Enteritidis, one of the most common Salmonella strains. Effective August 1999, Federal regulations will require that shell eggs packed for retail sale to consumers be stored and transported at or below 45 degrees Fahrenheit to reduce the risk of Salmonella infections. USO A was unable to make a definitive estimate of the potential economic benefits of this rule, partly because of the uncertainty about the economic costs of Salmonella infections. USDA shares federal regulatory responsibility for egg safety with the Food and Drug Administration (FDA), which recently proposed requiring safe handling labels on egg cartons to warn consumers about the risk of illness associated with Salmonellacontaminated shell eggs. Previous estimates of the economic costs due to foodborne Salmonella infections by USDA's Economic Research Service (ERS) were based on the best available estimates of the annual number of infections and the associated medical expenses and productivity losses. New information about the incidence, severity, and medical consequences of salmonellosis has since become available from the Foodborne Diseases Active Surveillance Network (FoodNet) and other sources, allowing us to refine the previous estimate