The Stability of Double White Dwarf Binaries Undergoing Direct Impact Accretion

We present numerical simulations of dynamically unstable mass transfer in a double white dwarf binary with initial mass ratio, q = 0.4. The binary components are approximated as polytropes of index n = 3/2 and the initially synchronously rotating, semi-detached equilibrium binary is evolved hydrodynamically with the gravitational potential being computed through the solution of Poisson's equation. Upon initiating deep contact in our baseline simulation, the mass transfer rate grows by more than an order of magnitude over approximately ten orbits, as would be expected for dynamically unstable mass transfer. However, the mass transfer rate then reaches a peak value, the binary expands and the mass transfer event subsides. The binary must therefore have crossed the critical mass ratio for stability against dynamical mass transfer. Despite the initial loss of orbital angular momentum into the spin of the accreting star, we find that the accretor's spin saturates and angular momentum is returned to the orbit more efficiently than has been previously suspected for binaries in the direct impact accretion mode. To explore this surprising result, we directly measure the critical mass ratio for stability by imposing artificial angular momentum loss at various rates to drive the binary to an equilibrium mass transfer rate. For one of these driven evolutions, we attain equilibrium mass transfer and deduce that effectively q_crit has evolved to approximately 2/3. Despite the absence of a fully developed disk, tidal interactions appear effective in returning excess spin angular momentum to the orbit.Comment: 27 pages, 6 figures. Please see http://www.phys.lsu.edu/faculty/tohline/astroph/mftd07/ for animations and full resolution figures. Accepted for publication in the Astrophysical Journa

1-(1-Benzofuran-2-yl)-3-(4-chloro­phen­yl)prop-2-en-1-one

In the title compound, C17H11ClO2, the benzofuran ring system is almost planar (r.m.s. deviation = 0.011 Å) and forms a dihedral angle of 10.53 (6)° with the chloro­phenyl ring. No significant inter­molecular inter­actions are observed

Teachers developing assessment for learning: impact on student achievement

While it is generally acknowledged that increased use of formative assessment (or assessment for learning) leads to higher quality learning, it is often claimed that the pressure in schools to improve the results achieved by students in externally-set tests and examinations precludes its use. This paper reports on the achievement of secondary school students who worked in classrooms where teachers made time to develop formative assessment strategies. A total of 24 teachers (2 science and 2 mathematics teachers, in each of six schools in two LEAs) were supported over a six-month period in exploring and planning their approach to formative assessment, and then, beginning in September 1999, the teachers put these plans into action with selected classes. In order to compute effect sizes, a measure of prior attainment and at least one comparison group was established for each class (typically either an equivalent class taught in the previous year by the same teacher, or a parallel class taught by another teacher). The mean effect size was 0.32

Diabetes mellitus, insulin resistance, and metabolic syndrome in HIV-positive patients in South India

Insulin resistance, diabetes mellitus, and metabolic syndrome in patients with human immunodeficiency virus (HIV) infection are increasingly being reported in the global medical literature. This cross-sectional study was done to describe the occurrence of metabolic syndrome, diabetes mellitus, and insulin resistance in HIV-positive patients in a tertiary referral center in South India. A total of 60 patients who had HIV infection for 12 months or more were enrolled in the study. Of these, 30 patients were antiretroviral therapy (ART)-naïve, and 30 were treated with ART. Biochemical estimations (fasting blood glucose, 75 g oral glucose tolerance test, lipid profile, and fasting insulin) and anthropometric measurements (height, weight, and waist circumference) were performed for each patient. Metabolic syndrome was diagnosed using National Cholesterol Education Program–Adult Treatment Plan III criteria, and insulin resistance was calculated applying the homeostasis model assessment method. Diabetes mellitus, impaired fasting glycemia, and impaired glucose tolerance were diagnosed based on American Diabetes Association criteria. A high prevalence of metabolic syndrome was observed in patients with HIV (16/60), and was more prevalent in the ART-treated group (13/30; P = 0.028). Similarly, insulin resistance was also noted to be high (24/60), and of these patients, 15 were on ART. Seventy-five percent of patients with metabolic syndrome had insulin resistance. Diabetes was diagnosed in one patient who was ART-naïve and in six patients who were on ART. Our observations suggest an increased prevalence of metabolic syndrome, insulin resistance, and diabetes mellitus in ART-treated patients. These warrant attention and substantiation with larger studies. While ART improves survival, it may lead on to cardiovascular morbidity and mortality, especially in the Indian subcontinent where there is a genetic predisposition to cardiovascular risk

Electrochemical analysis of indigo carmine using polyarginine modified carbon paste electrode

Suitable electrocatalytic method is established for the selective determination of indigo carmine (IC) at polyarginine modified carbon paste electrode (PAMCPE). Surface morphological study of bare carbon paste electrode (CPE) and PAMPCE is done by field emission scanning electron microscopy (FESEM). The influence of different parameters such as IC concentration, solution pH and potential scan rate on the electrode responses is studied using cyclic and differential pulse voltammetry techniques. The prepared PAMCPE shows better electrochemical response towards IC than CPE. No interference is noticed at simultaneous presence of IC and riboflavin (RF) in the solution. The electrocatalytic current of IC at PAMPCE is varied linearly with its concentration in two separate ranges, from 2×10-7 to 10-6 M, and 1.5×10-6 to 3.5×10-6 M. Limits of detection (LOD) and quantification (LOQ) are determined as 2.53×10-8 and 8.43×10-8 M, respectively. The developed PAMCPE is showing successful reproducibility and stability. It is also found sensitive and reliable for trace amounts of IC in some real water and food samples. Since preparation of PAMCPE sensor is simple and easy, it could become a part of the standard method for determination of IC in real samples

A Genome-Wide Screen Identifies Genes That Affect Somatic Homolog Pairing in Drosophila

In Drosophila and other Dipterans, homologous chromosomes are in close contact in virtually all nuclei, a phenomenon known as somatic homolog pairing. Although homolog pairing has been recognized for over a century, relatively little is known about its regulation. We performed a genome-wide RNAi-based screen that monitored the X-specific localization of the male-specific lethal (MSL) complex, and we identified 59 candidate genes whose knockdown via RNAi causes a change in the pattern of MSL staining that is consistent with a disruption of X-chromosomal homolog pairing. Using DNA fluorescent in situ hybridization (FISH), we confirmed that knockdown of 17 of these genes has a dramatic effect on pairing of the 359 bp repeat at the base of the X. Furthermore, dsRNAs targeting Pr-set7, which encodes an H4K20 methyltransferase, cause a modest disruption in somatic homolog pairing. Consistent with our results in cultured cells, a classical mutation in one of the strongest candidate genes, pebble (pbl), causes a decrease in somatic homolog pairing in developing embryos. Interestingly, many of the genes identified by our screen have known roles in diverse cell-cycle events, suggesting an important link between somatic homolog pairing and the choreography of chromosomes during the cell cycle