Roof Loads for Reliability Analysis of Lumber Properties Data

With load information reported in previous studies, distributions of maximum lifetime roof loads are developed in a form suitable for use in reliability analyses of lumber properties data. A lognormal distribution is chosen as best representing normalized maximum lifetime roof snow load.Examples are given in which contrasting lumber data sets are compared using the calculated load distributions and assuming that each set must provide equal reliability (equal safety) in the final design. A factor, k, resulting from this reliability analysis is shown to be a logical adjustment parameter for use in engineering design codes

A simulation model of intraherd transmission of foot and mouth disease with reference to disease spread before and after clinical diagnosis

Abstract. Intraherd transmission of foot and mouth disease virus (FMDV) was examined using a simulation model for a hypothetical 1,000-cow dairy, assuming clinical diagnosis was made when at least 1% (10 cows) or 5% (50 cows) had clinical signs of FMD, 1 index case cow, and transition state distributions for the latent, subclinically infectious, and clinically infectious periods of FMD calculated from published data. Estimates assumed for the number of animal-to-animal contacts (k) adequate for transmission ranged from 0.6 to 9.0 per hour (13.7-216.0 per day). A total of 40,000 iterations (5,000 for each scenario, assessing 4 adequate contact rates and 2 detection criteria) were run. The model predicted that FMD would not be diagnosed in the herd until 10.0-13.5 days after the index case cow had become infected, at which time between 65% and 97% of the cows (646-967 cows) to nearly 100% (978-996 cows) would already have become infected with the virus, if the number of cows showing clinical signs of FMD at the time of diagnosis were 10 or 50, respectively. At the time of diagnosis, the simulated number of infectious cattle varied substantially from 82-472 to 476-537 cows, depending on adequate contact rate and whether the diagnosis was made when 10 or 50 animals were showing clinical signs, respectively. The simulated number of infectious cows increased rapidly during the first few days after diagnosis. In the scenario where at least 10 cows showing clinical signs was necessary before a clinical diagnosis was made, each day after diagnosis, the number of infectious animals increased by nearly 100 to more than 200 cases per day up to day 5, assuming 0.57-9.0 animal-to-animal contacts per hour, respectively. Results obtained when it was assumed that at least 50 clinical cases were present at the time of diagnosis showed smaller relative increases because nearly one-half of the herd was projected to be infected at the time of diagnosis. From these results, it is clear that once an individual in a herd becomes infected with FMDV, herd infectivity is not static, rather it accelerates as would be expected as long as there are sufficient susceptible animals to sustain the increasing transmission rate, after which time the rate at which new infections occurs will diminish. Results indicate that biosecurity strategies aimed at minimizing both intraherd and interherd contact will be critical in minimizing the spread of FMD before the initial diagnosis is made. In addition, simulations suggest that very early clinical diagnosis of FMD and effective isolation or depopulation and disposal will be critical in limiting the number of infectious animals capable of transmitting the virus to other herds and thus in timely control of an epidemic. Early diagnosis will rely on early virus detection from animals in the preclinical phase of infection, rather than waiting for clinical signs to manifest in sufficient numbers to be noticed and to warrant investigation. Foot and mouth disease (FMD) is one of the most economically important livestock diseases in the world. In recent years, large-scale epidemics have been observed in Taiwan in 1997, 11 the UK in 2001

Chemistry courses as the turning point for premedical students

Previous research has documented that negative experiences in chemistry courses are a major factor that discourages many students from continuing in premedical studies. This adverse impact affects women and students from under-represented minority (URM) groups disproportionately. To determine if chemistry courses have a similar effect at a large public university, we surveyed 1,036 students from three entering cohorts at the University of California, Berkeley. We surveyed students at the beginning of their first year at the university and again at the end of their second year. All subjects had indicated an interest in premedical studies at the time they entered the university. We conducted follow-up interviews with a stratified sub-set of 63 survey respondents to explore the factors that affected their level of interest in premedical studies. Using a 10-point scale, we found that the strength of interest in premedical studies declined for all racial/ethnic groups. In the follow-up interviews, students identified chemistry courses as the principal factor contributing to their reported loss of interest. URM students especially often stated that chemistry courses caused them to abandon their hopes of becoming a physician. Consistent with reports over more than 50 years, it appears that undergraduate courses in chemistry have the effect of discouraging otherwise qualified students, as reflected in their admission to one of the most highly selective public universities in the US, from continuing in premedical studies, especially in the case of URM students. Reassessment of this role for chemistry courses may be overdue

Architecture of androgen receptor pathways amplifying glucagon-like peptide-1 insulinotropic action in male pancreatic β cells

Male mice lacking the androgen receptor (AR) in pancreatic β cells exhibit blunted glucose-stimulated insulin secretion (GSIS), leading to hyperglycemia. Testosterone activates an extranuclear AR in β cells to amplify glucagon-like peptide-1 (GLP-1) insulinotropic action. Here, we examined the architecture of AR targets that regulate GLP-1 insulinotropic action in male β cells. Testosterone cooperates with GLP-1 to enhance cAMP production at the plasma membrane and endosomes via: (1) increased mitochondrial production of CO2, activating the HCO3--sensitive soluble adenylate cyclase; and (2) increased Gαs recruitment to GLP-1 receptor and AR complexes, activating transmembrane adenylate cyclase. Additionally, testosterone enhances GSIS in human islets via a focal adhesion kinase/SRC/phosphatidylinositol 3-kinase/mammalian target of rapamycin complex 2 actin remodeling cascade. We describe the testosterone-stimulated AR interactome, transcriptome, proteome, and metabolome that contribute to these effects. This study identifies AR genomic and non-genomic actions that enhance GLP-1-stimulated insulin exocytosis in male β cells

Single-molecule experiments in biological physics: methods and applications

I review single-molecule experiments (SME) in biological physics. Recent technological developments have provided the tools to design and build scientific instruments of high enough sensitivity and precision to manipulate and visualize individual molecules and measure microscopic forces. Using SME it is possible to: manipulate molecules one at a time and measure distributions describing molecular properties; characterize the kinetics of biomolecular reactions and; detect molecular intermediates. SME provide the additional information about thermodynamics and kinetics of biomolecular processes. This complements information obtained in traditional bulk assays. In SME it is also possible to measure small energies and detect large Brownian deviations in biomolecular reactions, thereby offering new methods and systems to scrutinize the basic foundations of statistical mechanics. This review is written at a very introductory level emphasizing the importance of SME to scientists interested in knowing the common playground of ideas and the interdisciplinary topics accessible by these techniques. The review discusses SME from an experimental perspective, first exposing the most common experimental methodologies and later presenting various molecular systems where such techniques have been applied. I briefly discuss experimental techniques such as atomic-force microscopy (AFM), laser optical tweezers (LOT), magnetic tweezers (MT), biomembrane force probe (BFP) and single-molecule fluorescence (SMF). I then present several applications of SME to the study of nucleic acids (DNA, RNA and DNA condensation), proteins (protein-protein interactions, protein folding and molecular motors). Finally, I discuss applications of SME to the study of the nonequilibrium thermodynamics of small systems and the experimental verification of fluctuation theorems. I conclude with a discussion of open questions and future perspectives.Comment: Latex, 60 pages, 12 figures, Topical Review for J. Phys. C (Cond. Matt