硫掺杂橄榄状BiVO4上可见光降解亚甲基蓝和甲醛水溶液性能

在无和有S源(Na₂S或硫脲)存在的条件下,采用十二胺辅助的醇-水热法制备了多孔单斜晶相结构的BiVO_4-δ和不同含量S掺杂的BiVO_4-δ光催化剂.利用多种手段表征了催化材料的物化性质,评价了它们在可见光照射下催化降解亚甲基蓝或甲醛的反应活性.结果表明,所制光催化剂为单斜白钨矿晶相结构,具有多孔橄榄状形貌,比表面积为8.4-12.5m²/g,带隙能为2.40-2.48eV.在S掺杂BiVO_4-δ表面同时含有Bi⁵⁺,Bi⁴⁺,V⁵⁺和V⁴⁺物种.S掺杂对BiVO_4-δ光催化剂的活性影响很大.在可见光下照射下,BiVO_4-δS_0.08光催化剂对亚甲基蓝和甲醛降解反应显示出最高的光催化活性,这与其较高的表面氧物种浓度和较低的带隙能相关.     

Formation and emission of tetraalkylammonium salt molecular ions sputtered from a gelatin matrix

A gelatin matrix was simultaneously doped with nine equimolar, homologous, tetraalkylammonium salts ranging in mass from 210 to 700 Da. Bombardment of the sample with kiloelectronvolt ions resulted in a nonidentical distribution of relative cation intensities with a maximum at m/z 242 for samples with a total salt concentration of 0.004 g of salt/g of gelatin. A rapid increase in relative intensities with increasing mass is observed for the low mass salts and is believed to be linked to changes in the ionization efficiencies. The changes in ionization efficiencies are likely related to decreasing coulombic attractive forces between the organic cation and the counterion. Disappearance cross-sections, determined from decay curves, indicate that sputter-induced damage increases with increasing mass of the cation. Fragment-to-intact cation ratios also suggest that damage accumulates fastest in the heaviest salts. These observations indicate that desorption yields of the organic salts in a gelatin matrix decrease with increasing mass. In addition, suppression of lower mass tetraalkylammonium salt intact cation intensities was observed for salt-in-gelatin concentrations greater than 10⁻³ g/g.     

Best cooperative partner selection and input resource reallocation using DEA

Reallocation of input resources (RIR) is a process by which certain decision making units (DMUs) reallocate resources among themselves; a process that occurs frequently in many enterprises. In this paper, a new data envelopment analysis (DEA) approach is developed to select the best cooperative partner DMU. Context-dependent DEA is used to identify the different levels of best-practice frontiers. Two DEA-based models are established for two cooperative scenarios, namely, resources pooling only and best-practice sharing. A cooperative method is applied to determine how to reallocate the input resources, and Shapley value is used to estimate the revenue changes that the various DMUs should expect after RIR. Two different situations with different objectives are considered. One objective is to maximize total revenue for the partnership, while the other is to maximize the Shapley value. The proposed approaches are illustrated with two examples.     

Anti-symplectic involutions with lagrangian fixed loci and their quotients

We study the lagrangian embedding as a fixed point set of anti-symplectic involution on a symplectic 4-manifold . Suppose the fixed loci of are the disjoint union of smooth Riemann surfaces ; then each component becomes a lagrangian submanifold. Furthermore, if one of the components is a Riemann surface of genus , then its quotient has vanishing Seiberg-Witten invariants. We will discuss some examples which allow an anti-symplectic involution with lagrangian fixed loci.

     

Three-dimensional vibration analysis of a torus with circular cross section

The free vibration characteristics of a torus with a circular cross section are studied by using the three-dimensional, small-strain, elasticity theory. A set of three-dimensional orthogonal coordinates system, comprising the polar coordinate (r, theta) at each circular cross section and the circumferential coordinate phi around the ring, is developed. Each of the displacement components u(r), v(theta), and w(phi) in the r, theta, and phi directions, respectively, is taken as a product of the Chebyshev polynomials in the r direction and the trigonometric functions in the theta and phi directions. Eigenfrequencies and vibration mode shapes have been obtained via a three-dimensional displacement-based extremum energy principle. Upper bound convergence of the first seven eigenfrequencies accurate to at least six significant figures is obtained by using only a few terms of the admissible functions. The eigenfrequency responses due to variation of the ratio of the radius of the ring centroidal axis to the cross-sectional radius are investigated in detail. Very accurate eigenfrequencies and deformed mode shapes of the three-dimensional vibration are presented. All major modes such as flexural thickness-shear modes, in-plane stretching modes, and torsional modes are included in the analysis. The results may serve as a benchmark reference for validating other computational techniques for the problem.     

What is 'unfreezable water', how unfreezable is it,and how much is there?

Water that remains unfrozen at temperatures below the equilibrium bulk freezing temperature, in the presence of ice, is sometimes called unfreezable or bound. This paper analyses the phenomenon in terms of quantitative measurements of the hydration interaction among membranes or macromolecules at freezing temperatures. These results are related to analogous measurements in which osmotic stress or mechanical compression is used to equilibrate water of hydration with a bulk phase. The analysis provides formulas to estimate, at a given sub-freezing temperature, the amount of unfrozen water due to equilibrium hydration effects. Even at tens of degrees below freezing, this hydration effect alone can explain an unfrozen water volume that considerably exceeds that of a single 'hydration shell' surrounding the hydrophilic surfaces. The formulas provided give a lower bound to the amount of unfrozen water for two reasons. First, the well-known freezing point depression due to small solutes is, to zeroth order, independent of the membrane or macromolecular hydration effect. Further, the unfrozen solution found between membranes or macromolecules at freezing temperatures has high viscosity and small dimensions. This means that dehydration of such systems, especially at freezing temperatures, takes so long that equilibrium is rarely achieved over normal experimental time scales. So, in many cases, the amount of unfrozen water exceeds that expected at equilibrium, which in turn usually exceeds that calculated for a single hydration shell.     

Improved cycle sequencing of GC-rich DNA template

Even when DNA sequencing of purified DNA template failed under the optimal condition, it can be generally contributed to high GC content. GC-rich region of template causes a secondary structure to produce shorter readable sequence. To solve this problem, the sequencing reaction was modified by using dimethyl sulfoxide (DMSO). It was found that 5% (v/v) of DMSO in the reaction mixture recovers sequencing signal intensity with reduced frequency of ambiguous bases. When DMSO was added to sequencing reaction of DNA template with normal GC content, it did not show any adverse effect. Sequencing accuracy and unambiguous base frequency were significantly improved at concentration of 2% to 5% (v/v) DMSO in GC-rich DNA template. DMSO has been empirically introduced to enhance the efficiency of PCR in GC-rich templates. However, the underlying mechanism of improved cycle sequencing by DMSO is unknown. Thus, cycle sequencing reaction was remodified with other additives such as N-methyl imidazole, N-methyl2-pyrrolidone, N-methyl-2-pyridone and glycerol, possessing the similar chemical properties as DMSO. Most of methyl nitrogen ring-containing chemicals did not improve sequencing accuracy, whereas only glycerol mimicked the positive effect of DMSO by the same extent. In the present study, we suggest that the treatment of DMSO improve cycle sequencing by the alteration of structural conformation of GC-rich DNA template.     

Target detection by an echolocating harbor porpoise (Phocoena phocoena)

Two echolocation experiments are described. They were conducted on the same harbor porpoise housed in a sea pen, one year apart at Neeltje Jans, The Netherlands. The aims were to determine the target detection ability of an echolocating harbor porpoise, with the ultimate goal to predict the distance at which harbor porpoises can detect fishing nets. In experiment 1, the maximum distance at which the 3-year-old porpoise could detect a 7.62-cm diameter water-filled stainless-steel sphere by echolocation was determined psychophysically. The 50%-current detection threshold was reached when the sphere was at a distance of 26 m from the porpoise's rostrum. In experiment 2, conducted a year later, the maximum detection distance for a 5.08-cm water-filled stainless-steel sphere was 15.9 m. The target strengths of both targets were measured using simulated harbor porpoise echolocation signals and the results, coupled with transmission-loss calculations, indicated that the echo levels received by the porpoise with the targets at the threshold ranges in the two experiments were only 1.3 dB apart. Together with information on the target strengths of various fishing nets, the results of the present study can be used to predict the distance at which the nets can be detected by harbor porpoises.     

Necessity and sufficiency of f being a divergence for vanishing of variational derivatives of f: General case

Concise proofs are presented for the necessity and sufficiency of f being a divergence for the variational derivatives of f to vanish identically, where f is a function of N functions of n variables, their partial derivatives to arbitrary order, and the n variables. The approach is conventional.