Critical insulation thickness of a rectangular slab embedded with a periodic array of isothermal strips

We address the problem of two-dimensional heat conduction in a solid slab embedded with a periodic array of isothermal strips. The surfaces of the slab are subjected to a convective heat transfer boundary condition with a uniform heat transfer coefficient. Similar to the concept of critical insulation radius, associated with cylindrical and spherical configurations, we show that there exists a critical insulation thickness, associated with the slab, such that the total thermal resistance attains a minimum, i.e. a maximum heat transfer rate can be achieved. This result, which is not observed in one-dimensional heat conduction in a plane wall, is a consequence of the non-trivial coupling between conduction and convection that results in a 2D temperature distribution in the slab, and a non-uniform temperature on the surface of the slab. The findings of this work offer opportunities for improving the design of a broad range of engineering processes and products.     

Solar radiation modelling in the urban context

This paper describes alternative methods for predicting surface irradiance in the urban context. In this the focus is on means of accounting for the effects of nearby obstructions on reducing direct sky radiation and on contributing reflected radiation. The first two methods involve abstracting the urban skyline into an effective canyon using isotropic and anisotropic tilted surface irradiance models. The third predicts the irradiance contribution from two hemispheres which are discretised into patches––given the radiance of the sky and dominant obstructions (if these exist) and associated view factors––so that we have a new simplified radiosity algorithm (SRA). Results from the three methods (isotropic canyon (IC), anisotropic canyon (AC) and simplified radiosity algorithm (SRA)) are compared with a ‘truth model' under the following circumstances: (i) unobstructed sky, (ii) sky obstructed by black surfaces, (iii) sky obstructed by grey diffusely reflecting surfaces. Results show conclusively that the SRA offers superior accuracy at comparable speed to the canyon models. The SRA also compares well with a ray tracing program, it can handle urban scenes of arbitrary geometric complexity and is readily amenable for inclusion into standard computer programs that require surface irradiance as an input.     

Prostaglandins and mechanisms of preterm birth

Increased uterine contractility at term and preterm results first from activation and then stimulation of the myometrium. Activation can be provoked by mechanical stretch of the uterus, and by an endocrine pathway resulting from increased activity of the fetal hypothalamic-pituitary-adrenal axis. In sheep fetuses, increased cortisol output during pregnancy regulates expression of prostaglandin synthase type 2 (PGHS-2) in the placenta in an oestrogen-independent manner, resulting in increased concentrations of prostaglandin E2 (PGE2) in the fetal circulation. Later increases in maternal uterine expression of PGHS-2 require increases in oestrogen and lead to increased concentrations of PGF(2alpha) in the maternal circulation. Thus, regulation of PGHS-2 at term is differentially controlled in fetal (trophoblast) and maternal (uterine epithelium) tissue. This difference may reflect expression of glucocorticoid receptor but not oestrogen receptor (ER) in placental trophoblast cells. In women, cortisol also contributes to increased prostaglandin production in fetal tissues through upregulation of PGHS-2 (amnion and chorion) and downregulation of 15-OH prostaglandin dehydrogenase (PGDH; chorion trophoblasts). The effect of cortisol on expression of PGDH in the chorion reverses a tonic stimulatory effect of progesterone, potentially through a paracrine or autocrine action. In membranes, cortisol may be derived from cortisone through activity of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1, in addition to secretion from the maternal or fetal adrenal glands. In placenta, 11beta-HSD-2 oxidase activity predominates and expression of this enzyme is reduced with hypoxaemia and in placentae from pre-eclamptic pregnancies. In these circumstances, increased concentrations of maternal cortisol may cross into the fetal compartment, contributing to growth restriction and programming later life disease.     

走出困境——日本电子企业的创新征程

过去,日本电子企业凭借其对产品创新的专注,在全球市场中保持着领先地位.然而,世界其他地区的竞争者逐渐在生产力、财务业绩和品牌价值等方面超越了这些日企.为了走出逆境,日本电子企业必须力争成为全球创新者,并致力于五大艰难转型.     

Understanding coordination in computer-mediated versus face-to-face groups

Groups performed intellective and judgmental tasks in face-to-face (FTF) or computer-mediated communication (CMC) settings after coordination training or no training to determine the impact of CMC, training, and task type on group performance and coordination. Help seeking behaviors were stronger predictors of perceived and actual performance in CMC than FTF groups, but varied based on task type. In turn, training generally increased seeking behaviors, except non-task seeking behaviors in CMC groups; and seeking behaviors were stronger predictors for perceived performance in CMC than FTF groups. In addition, perceived performance was lower in CMC than FTF groups when untrained, but not when trained. Yet, performance agreement was similar on both tasks in FTF groups, but lower on the intellective than the judgmental task in CMC groups.     

Whose depression relates to discrepancies? Testing relations between informant characteristics and informant discrepancies from both informants' perspectives.

This study examined whether mothers' and children's depressive symptoms were each uniquely related to mother-child rating discrepancies on a multidimensional dyadic construct: domains associated with parental monitoring (i.e., Child Disclosure, Parental Knowledge, and Parental Solicitation). Participants included a community sample of 335 mother/female-caregiver and child dyads (182 girls, 153 boys; 9-16 years old). Children's depressive symptoms were consistently related to each of the three domains of mother-child discrepancies. Mothers' depressive symptoms were related to perceived discrepancies in two domains (Child Disclosure and Parental Knowledge). Furthermore, these relations could not be accounted for by other informant characteristics (maternal stress, child age, child gender, child ethnicity). Findings provide important empirical support for theory suggesting that both informants' perspectives meaningfully contribute to their discrepancies in perceived behavior. Consideration of both informants' perspectives leads to valuable information as to whether any particular characteristic is an important correlate of discrepancies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Work strain, health, and absenteeism: A meta-analysis.

Work strain has been argued to be a significant cause of absenteeism in the popular and academic press. However, definitive evidence for associations between absenteeism and strain is currently lacking. A theory focused meta-analysis of 275 effects from 153 studies revealed positive but small associations between absenteeism and work strain, psychological illness, and physical illness. Structural equation modeling results suggested that the strain-absence connection may be mediated by psychological and physical symptoms. Little support was received for the purported volitional distinction between absence frequency and time lost absence measures on the basis of illness. Among the moderators examined, common measurement, midterm and stable sources of variance, and publication year received support. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Langmuir-Blodgett films for nonlinear optical applications

Azo-benzene chromophores with an oxygen donor and five different end-groups have been attached to octadecyl chains or to polysiloxane backbones via hexadecyl spacer groups. These were deposited by the Langmuir-Blodgett (LB) technique using our own design of diamond-barrier trough. The LB deposition properties of the polymers were superior to those of the low molecular mass materials, which did not show second harmonic generation (SHG) as deposited monolayers. The strength of SHG from the polymers correlated with acceptor strength, but the maximum signal was only about 10% of that of hemicyanine. Only one of the polymers gave thick films of very high quality; this had a hydroxyl end-group and showed no SHG except when deposited from an acid subphase. This was presumed to result from protonation of the azo group to create an acceptor. The quality of the deposited films may correlate with their phase behaviour; the best material showed only a presumed soft crystalline phase. The film-forming properties of that film were remarkable; loss figures of around 2.5 dB cm^–1 have been recorded at 633 nm in films of 1.3 m thickness. Future work will seek to isolate and independently control the factors involved in good film formation and in high SHG.     

Floc morphology and size distributions of cohesive sediment in steady-state flow

Fractal dimensions of particle populations of cohesive sediment were examined during deposition experiments in an annular flume at four conditions of steady-state flow (0.058, 0.123, 0.212 and 0.323Pa). Light microscopy and an image analysis system were used to determine area, longest axis and perimeter of suspended solids. Four fractal dimensions (D, D(1), D(2), D(k)) were calculated from the slopes of regression lines of the relevant variables on double log plots. The fractal dimension D, which relates the projected area (A) to the perimeter (P) of the particle (P proportional, variant A(D/2)), increased from 1.25+/-0.005 at a shear stress of 0.058Pa to a maximum of 1.36+/-0.003 at 0.121Pa then decreased to 1.34+/-0.001 at 0.323Pa. The change in D indicated that particle boundaries became more convoluted and the shape of larger particles was more irregular at higher levels of shear stress. At the highest shear stress, the observed decrease in D resulted from floc breakage due to increased particle collisions. The fractal dimension D(1), which relates the longest axis (l) to the perimeter of the particle (P proportional to l(D1)), increased from 1.00+/-0.006 at a shear stress of 0.058Pa to a maximum of 1.25+/-0.003 at 0.325Pa. The fractal dimension D(2), which relates the longest axis with the projected area of the particle (A proportional to l(D(2)), increased from 1.35+/-0.014 at a shear stress of 0.058Pa to a maximum of 1.81+/-0.005 at 0.323Pa. The observed increases in D(1) and D(2) indicate that particles became more elongated with increasing shear stress. Values of the fractal dimension D(k), resulting from the Korcak's empirical law for particle population, decreased from 3.68+/-0.002 at a shear stress of 0.058Pa to 1.33+/-0.001 at 0.323Pa and indicate that the particle size distribution changed from a population of similar sized particles at low shear to larger flocculated particles at higher levels of shear. The results show that small particle clusters (micro-flocs) are the formational units of larger flocs in the water column and the stability of larger flocs is a function of the shear stress at steady state.