Phase-field modeling droplet dynamics with soluble surfactants

Using lattice Boltzmann approach, a phase-field model is proposed for simulating droplet motion with soluble surfactants. The model can recover the Langmuir and Frumkin adsorption isotherms in equilibrium. From the equilibrium equation of state, we can determine the interfacial tension lowering scale according to the interface surfactant concentration. The model is able to capture short-time and long-time adsorption dynamics of surfactants. We apply the model to examine the effect of soluble surfactants on droplet deformation, breakup and coalescence. The increase of surfactant concentration and attractive lateral interaction can enhance droplet deformation, promote droplet breakup, and inhibit droplet coalescence. We also demonstrate that the Marangoni stresses can reduce the interface mobility and slow down the film drainage process, thus acting as an additional repulsive force to prevent the droplet coalescence

Who Drops out? A Study of Secondary School Dropouts in Connecticut

The purpose of the study was to investigate the relationships between the dropout pattern and student characteristics such as gender, ethnicity and grade level among exited students from grade 7 to grade 12. The study included 57,709 students from grades 7-12 in the 2006-2007 school year in Connecticut. A logistic regression analysis was conducted to examine demographic factors related to student dropout pattern. This study provides empirical evidence of identifying secondary school students in Connecticut who were more likely to drop out. Identifying the groups of high risk students would help practitioners and policy makers to develop prevention programs or make interventions to reduce student attrition at the early stage, and thus, to close the achievement gap among these groups

Improving gas sensing properties of graphene by introducing dopants and defects: a first-principles study

The interactions between four different graphenes (including pristine, B- or N-doped and defective graphenes) and small gas molecules (CO, NO, NO2 and NH3) were investigated by using density functional computations to exploit their potential applications as gas sensors. The structural and electronic properties of the graphene-molecule adsorption adducts are strongly dependent on the graphene structure and the molecular adsorption configuration. All four gas molecules show much stronger adsorption on the doped or defective graphenes than that on the pristine graphene. The defective graphene shows the highest adsorption energy with CO, NO and NO2 molecules, while the B- doped graphene gives the tightest binding with NH3. Meanwhile, the strong interactions between the adsorbed molecules and the modified graphenes induce dramatic changes to graphene's electronic properties. The transport behavior of a gas sensor using B- doped graphene shows a sensitivity two orders of magnitude higher than that of pristine graphene. This work reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the appropriate dopant or defect

On the creep fatigue behavior of Metal Matrix Composites

The mechanical behaviour of Metal Matrix Composites (MMCs) subjected to a high temperature and cyclic load condition is difficult to understand. The significantly differing coefficients of thermal expansion between ceramic and metal give rise to micro thermal stresses. Their performance under varying load and high temperature is complex and inconsistent, where fatigue and creep damages become the main failures of MMCs. To improve current understanding of the relationship between creep fatigue interaction of MMCs, the history of thermal and mechanical loading, and the creep dwell period, a highly accurate but robust direct simulation technique on the basis of the Linear Matching Method (LMM) framework has been proposed in this paper, and been applied to model the fatigue and creep behaviour of MMCs. A homogenised FE model is considered in all analyses, which consist of continuous silicon carbide fibres embedded in a square 2024T3 aluminium alloy matrix array. Various factors that affect creep and fatigue behaviours of composites are analysed and discussed, including effects of the applied load level, dwell period and temperature on the MMC's performance. The effects of reversed plasticity on stress relaxation and creep deformation of MMC are investigated, and the behaviours of cyclically enhanced creep and elastic follow-up are presented. The applicability and accuracy of the proposed direct method has also been verified by the detailed step-by-step analysis via Abaqus

Assessment of β-D-Glucosidase Activity from Two Typical Strains of the Lactic Acid Bacteria, Oenococcus oeni, in China

β-D-glucosidase (βG) is one of the most interesting glycosidases for the hydrolysis of glycoconjugatedprecursors to release active aromatic compounds in musts and wines. Oenococcus oeni strains SD-2a and31MBR are widely used in Chinese wines to reduce the acidity. In the present study, the βG activity of thetwo strains was localised and partially characterised using synthetic substrate. The activity occurred inwhole cells, sonication supernatants and debris, but not in the culture supernatants for both strains. Wholecells of strain SD-2a possessed greater βG activity, while strain 31MBR showed higher enzyme activity inthe sonication supernatants. Strain 31MBR exhibited higher total enzyme activity than strain SD-2a. Theoptimum temperatures for βG from the two strains were 40ºС at pH 3.5 and 50ºС at pH 5.0, respectively.Ethanol at low concentrations had a positive effect on βG activity in both strains, while a wine-like pH (3.5)decreased the enzyme activity to a great extent. Whole cells of strain SD-2a showed the highest activityamong all samples tested under wine-like conditions. Thus, strain SD-2a proved to have potential foraroma improvement in winemaking

Organic petrology and geochemistry of mudstones from the lower Shahejie Formation in the Tanggu area of eastern China: evidence for the presence of an ancient saline lake

Mudstones in the Sha-3 member of the Shahejie Formation, in the Tanggu area of the Huanghua Depression, have been found to contain analcime and ankerite. Hydrothermal sedimentation has been invoked to explain the origin of these two minerals, raising the question of whether hydrothermal activity occurred at a sufficient scale to significantly raise the salinity of the depositional environment. We applied a suite of organic petrological and geochemical methods to directly address this question. Maceral composition, kerogen type, and the distribution of n-alkanes, hopanes, and steranes indicate that the organic matter contained in these mudstones and dolomitic mudstones is mainly derived from algae and bacteria. The dominant acritarch genera, C31R/C30 hopane ratio, gammacerane index, Pr/Ph ratio, and the relationship between Pr/n-C17 and Ph/n-C18 suggest that the mudstones and dolomitic mudstones were deposited in an anoxic, saline lacustrine environment. Tmax, biomarker maturity indices, the Thermal Alteration Index (TAI) and Acritarch Alteration Index (AAI), and vitrinite reflectance all indicate that the organic matter is at an immature to early mature stage. The estimated maximum paleotemperature is close to the present-day burial temperature, and much lower than the homogenization temperature of the analcime veins in dolostones. Combined with the absence of unresolved complex mixtures on the n-alkane pattern, this suggests that hydrothermal activity had a negligible impact on the salinity and alkalinity of the depositional lake

Variable metric proximal stochastic variance reduced gradient methods for nonconvex nonsmooth optimization

We study the problem of minimizing the sum of two functions. The first function is the average of a large number of nonconvex component functions and the second function is a convex (possibly nonsmooth) function that admits a simple proximal mapping. With a diagonal Barzilai-Borwein stepsize for updating the metric, we propose a variable metric proximal stochastic variance reduced gradient method in the mini-batch setting, named VM-SVRG. It is proved that VM-SVRG converges sublinearly to a stationary point in expectation. We further suggest a variant of VM-SVRG to achieve linear convergence rate in expectation for nonconvex problems satisfying the proximal Polyak-Lojasiewicz inequality. The complexity of VM-SVRG is lower than that of the proximal gradient method and proximal stochastic gradient method, and is the same as the proximal stochastic variance reduced gradient method. Numerical experiments are conducted on standard data sets. Comparisons with other advanced proximal stochastic gradient methods show the efficiency of the proposed method

A simulation of weak-light phase-locking for space laser interferometer

A simulation was investigated to better understand the impacts and effects of the additional technical noises on weak-light phase-locking for space laser interferometer. The result showed that the locking precision was limited by the phase readout noise when the laser frequency noise and clock jitter noise were removed, and this result was then confirmed by a benchtop experimental test. The required space laser interferometer noise floor was recovered from the simulation which proved the validity of the simulation program. © Published under licence by IOP Publishing Ltd.National Natural Science Foundation of China/61575209Chinese Academy of Sciences/XDB2303020