Note on an integral equation of viscous flow theory

Summary The integral equation encountered by Van de Vooren and Veldman in a problem of viscous flow was recently solved by Brown by use of the Wiener-Hopf technique. In this note Brown's solution is re-derived by a different, function-theoretic method.     

Affective variables and school achievement: A study of possible causal influences.

Studied the predictive and causal relationship of affective variables and academic achievement (376 Ss in Grades 3–6), both concurrently and 1 yr later. Affective characteristics studied were general and academic self-concept, academic locus of control, and expectations for future academic achievement (Piers-Harris Children's Self-Concept Scale, Student's Perception of Ability Scale, Intellectual Achievement Responsibility Questionnaire, and the Projected Academic Performance Scale) whereas levels of achievement were ascertained by end-of-year grades. The findings indicate that affective variables, especially academic self-concept, made a small but significant contribution to school grades. The data suggest a possible reciprocal interaction between affective characteristics and school achievement. Implications for children experiencing learning difficulties are discussed. (French abstract) (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A novel genetic selection system for improved enantioselectivity of Bacillus subtilis lipase A

In directed evolution experiments, success often depends on the efficacy of screening or selection methods. Genetic selections have proven to be extremely valuable for evolving enzymes with improved catalytic activity, improved stability, or with altered substrate specificity. In contrast, enantioselectivity is a difficult parameter to select for. In this study, we present a successful strategy that not only selects for catalytic activity, but for the first time also for enantioselectivity, as demonstrated by the selection of Bacillus subtilis lipase A variants with inverted and improved enantioselectivity. A lipase mutant library in an aspartate auxotroph Escherichia coli was plated on minimal medium that was supplemented with the aspartate ester of the desired enantiomer (S)-(+)-1,2-O-isopropylidene-sn-glycerol. To inhibit growth of less enantioselective variants, a covalently binding phosphonate ester of the opposite (R)-(-)-1,2-O-isopropylidene-sn-glycerol enantiomer was added as well. After three selection rounds in which the selection pressure was increased by raising the phosphonate ester concentration, a mutant was selected with an improved enantioselectivity increased from an ee of -29.6 % (conversion 23.4 %) to an ee of +73.1 % (conversion 28.9 %) towards the (S)-(+)-enantiomer. Interestingly, its amino acid sequence showed that the acid of the catalytic triad had migrated to a position further along the loop that connects beta7 and alphaE; this shows that the position of the catalytic acid is not necessarily conserved in this lipase.     

Analysis of a second order gas-solid reaction in an isothermal spherical particle. Application to the reduction of oxides with gaseous substrates

The mass transport equation applying to a second order gas solid reaction taking place in an isothermal spherical particle is solved by the orthogonal collocation method, using 3, 5 and 8 point collocation. The results are compared with those obtained in earlier studies using different assumptions and calculation procedures.     

Algorithm for NO/sub 2/ vertical column retrieval from the ozone monitoring instrument

We describe the operational algorithm for the retrieval of stratospheric, tropospheric, and total column densities of nitrogen dioxide (NO/sub 2/) from earthshine radiances measured by the Ozone Monitoring Instrument (OMI), aboard the EOS-Aura satellite. The algorithm uses the DOAS method for the retrieval of slant column NO/sub 2/ densities. Air mass factors (AMFs) calculated from a stratospheric NO/sub 2/ profile are used to make initial estimates of the vertical column density. Using data collected over a 24-h period, a smooth estimate of the global stratospheric field is constructed. Where the initial vertical column densities exceed the estimated stratospheric field, we infer the presence of tropospheric NO/sub 2/, and recalculate the vertical column density (VCD) using an AMF calculated from an assumed tropospheric NO/sub 2/ profile. The parameters that control the operational algorithm were selected with the aid of a set of data assembled from stratospheric and tropospheric chemical transport models. We apply the optimized algorithm to OMI data and present global maps of NO/sub 2/ VCDs for the first time.     

Local Grid Refinement in Large-Eddy Simulation

A method for performing nested-grid calculations with a Large-Eddy Simulation (LES) code is described. The grid consists of a coarse mesh and a fine mesh which overlaps the coarse in some region. A standard finite-volume method is used on both meshes. By means of grid communication, the velocity and pressure at both meshes are matched. To check that large eddies which are already resolved on the coarse grid are not affected by the nesting procedure, a simple two-dimensional mixing layer is simulated. Several simulations of this flow have been carried out with a different number of grid points on the nested grid. It is found that, without much extra computational effort, the grid-nesting improves the turbulent statistics with respect to the results found on the coarse mesh. This improvement occurs first of all in the region where grid refinement is applied, but better results are also found on the coarse mesh outside the grid-refinement region. Furthermore, it is shown that the large-scale structures in this flow are not influenced by the boundary between the coarse and fine grid.     

Management of myocardial infarction: the proper priorities

We calculated the rates for perioperative mortality and fatal pulmonary embolism (PE) after primary total hip replacement in a single UK health region, using a regional arthroplasty register and the tracing service of the Office of National Statistics. During 1990, there were 2111 consecutive primary replacements in 2090 separate procedures. Within 42 days of operation a total of 19 patients had died (0.91%, 95% CI 0.55 to 1.42). Postmortem examination showed that four deaths (0.19%, 95% CI 0.05 to 0.49) were definitely due to PE. The overall perioperative mortality and fatal PE rates are low and in our study did not appear to be altered by the use of chemical thromboprophylaxis (perioperative mortality rate: one-tailed Fisher's exact test, p = 0.39; fatal PE rate: one-tailed Fisher's exact test, p = 0.56). The routine use of chemical thromboprophylaxis for primary THR is still controversial. The issue should be addressed by an appropriate randomised, prospective study using overall mortality and fatal PE rate as the main outcome measures, but the feasibility of such a study is questioned.     

Expression of p53, Bcl-2 and Bax in cisplatin-induced apoptosis in testicular germ cell tumour cell lines

We examined the sensitivity for cisplatin-induced apoptosis in a panel of four testicular germ cell tumour (TGCT) cell lines and monitored the cellular expression of the apoptosis-related proteins p53, Bcl-2 and Bax. Three of four TGCT cell lines (NT2, NCCIT and S2) were hypersensitive for cisplatin-induced apoptosis, while the TGCT cell line 2102 EP appeared to be resistant for cisplatin-induced apoptosis, even at relatively high drug concentrations (12.5 microM). For all four cell lines, the induction of apoptosis by cisplatin correlated with drug sensitivity in the MTT assay. The differences in chemosensitivity and induction of apoptosis could not be attributed to differences in cellular platinum accumulation, DNA platination or platinum-DNA adduct removal. We next analysed the relationship between p53 status and cisplatin-induced up-regulation of p53, and the susceptibility to cisplatin-induced apoptosis. Wild-type p53 containing NT2 and 2102 EP cells showed p53 up-regulation upon drug treatment, and NCCIT (mutant p53) and S2 (no p53 protein) cells did not. Consistently, the increase in wild-type p53 protein in NT2 and 2102 EP cells led to an increase in mRNA level of the p53 downstream gene p21/WAF/CIP, whereas mutant p53-containing NCCIT cells and p53-non-expressing S2 cells could not transactivate this p53-responsive gene. As NT2, NCCIT and S2 were readily triggered into apoptosis, while 2102 EP cells failed to undergo cisplatin-induced apoptosis, our data suggest that the presence of wild-type and/or transactivation-competent p53 might not be an absolute prerequisite for efficient induction of apoptosis in TGCT cell lines. Also endogenous levels of Bcl-2 and Bax expression did not correlate with cisplatin-induced apoptosis. In addition, the endogenous Bcl-2 and Bax expression was not affected by cisplatin treatment. The present study suggests that, at least in our panel of TGCT cell lines, hypersensitivity for cisplatin-induced apoptosis might not be necessarily correlated with the presence of wild-type p53 and is probably not associated with Bcl-2 and Bax expression.     

A diffusion problem in semiconductor technology

Summary This paper deals with a mathematical model of a SEM-EBIC experiment devised to measure the diffusion length of semiconductor materials. In the model the semiconductor material occupies a half-space, of which the plane bounding surface is partly covered by a semi-infinite current-collecting junction, the Schottky diode. A scanning electron microscope (SEM) is used to inject minority carriers into the material. It is assumed that injection occurs at a single point only. The injected minority carriers diffuse through the material and recombine in the bulk at a rate proportional to their local concentration. Recombination also occurs at the free surface of the material, not covered by the junction, where its rate is determined by the surface recombination velocity v. The mathematical model gives rise to a mixed-boundary-value problem for the diffusion equation, which is solved by means of the Wiener-Hopf technique. An analytical expression is derived for the measurable electron-beam-induced current (EBIC) caused by the minority carriers reaching the junction. The solution obtained is valid for all values of v, and special attention is given to the limiting cases v= and v=0. Asymptotic expansions of the induced current, which are usable when the injection point is more than a few diffusion lengths away from the edge of the junction, are derived as well.