Van der Waals attraction between Stöber silica particles in a binary solvent system

Hydrophilic Stöber silica particles are stable in ethanol, but flocculation may be induced by the addition of sufficient cyclohexane. Low-shear rheological measurements indicated non-Newtonian behaviour beyond the critical cyclohexane concentration. The thickness and composition of the solvation layer around the particles were calculated from the adsorption excess isotherm on the basis of a multilayer adsorption model. The composition dependences of the Hamaker constants of the dispersion medium and the adsorption layer were obtained from optical dispersion measurements. A single-sheet, hard-sphere model predicted a weak van der Waals attraction in the ethanolic regime, but a strong attraction in the cyclohexane-rich region, in good accordance with the rheological properties of the dispersions and visual observations.     

Who Proved Haag's Theorem?

In physics literature, there are several different characterizations of Haag's theorem and its consequences for quantum field theory. These different versions of Haag's theorem are due in part to various generalizations and more “rigorous” proofs of Haag's theorem as well as to the fact that many of these proofs were done using different formulations of quantum field theory. As a result, there is confusion about what Haag's theorem is and when it was proved. This paper clears up some of these confusions by examining the history and development of Haag's theorem up to 1959. It is argued that the question of who proved Haag's theorem is tied up with what the theorem is taken to show.     

Spectral Analysis of Stochastic Phase Lockings and Stochastic Bifurcations in the Sinusoidally Forced van der Pol Oscillator with Additive Noise

Noise effects on the phase lockings and bifurcations in the sinusoidally forced van der Pol relaxation oscillator are investigated. Deterministic (noise-free) one-dimensional Poincaré mapping is extended to the iteration of the operator defined by a stochastic kernel function. Stochastic phase lockings and bifurcations are analyzed in terms of the density evolution by the operator. In particular, a new method which uses spectra (eigenvalues and eigenfunctions) of the operator to analyze stochastic bifurcations intensively is proposed.     

An Illustration of the Power of Structure Theory

There is a hierarchy of concepts of compact semigroups according to the degree of continuity of their multiplications: One-sided continuity, separate continuity, continuity. Each level of generality has its own fields of application and its own peculiarities. This is illustrated in a discussion of three seemingly rather unrelated examples from different branches of mathematics: number theory, functional analysis, logic.     

材料表面之间黏附过程分析

对两材料表面黏附过程进行了理论分析，得出了跳触距离的计算公式，发现跳触距离与试样的几何尺寸和系统的刚度有关，而且也受到相对湿度的影响. 利用单峰接触模型和幂律流体的本构方程，对材料表面吸附的水膜进行了动力学分析，改进了描述拉开力和停留时间关系的方程. 并利用自制的黏附力测试装置对跳触力和拉开力进行了测试和分析. 关键词： 黏附 范德华力 相对湿度 水膜     

The oscillation of stock price by majority orienting traders with investment position

We consider an interacting particle system for the stock price fluctuation. The change of the stock price with a feedback by the price considering the herding behavior (majority orienting behavior) of traders, gives the van der Pol equation as a deterministic approximation. Considering the investment position of each trader, we introduce the delayed van der Pol equation. The history of investment positions, for example sell or buy, of each trader for a stock makes a memory effect, which is modeled by using the time retardation. The delayed van der Pol equation model seems to be natural and explains typical phenomena, for example triangle pattern, volatility jumps, price jumps and price trends, known for the time series of a stock price.     

Synthesis and characterization of type-II textured tungsten disulfide thin films by vdWR process with Pb interfacial layer as texture promoter

The growth of type-II textured tungsten disulfide (WS₂) thin films by solid state reaction between the spray deposited WO₃ and gaseous sulfur vapors with Pb interfacial layer has been studied. X-ray diffraction (XRD) technique is used to measure the degree of preferred orientation ‘S’ and texture of WS₂ films. Scanning electron microscopy (SEM) and transmission electron microscopy techniques have been used to examine the microstructure and morphology. The electronic structure and chemical composition were studied using X-ray photoelectron spectroscopy (XPS). The use of Pb interfacial layer for the promotion of type-II texture in WS₂ thin films is successfully demonstrated. The presence of (0 0 3 l), (where l=1, 2, 3, …) family of planes in the XRD pattern indicates the strong type-II texture of WS₂ thin films. The crystallites exhibit rhombohedral (3R) structure. The large value of ‘S’ (1086) prompts the high degree of preferred orientation as well. The stratum of crystallites with their basal plane parallel to the substrate surface is seen in the SEM image. The EDS and XPS analyses confirm the tungsten to sulfur atomic ratio as 1:1.75. We purport that Pb interfacial layer enhances type-II texture of WS₂ thin films greatly.     

Inclusion property of (R,R)-(-)-trans-2,3,-bis(hydroxydiphenylmethyl)-1,4-dioxaspiro[4,4]nonane for aromatic components

An optically active host molecule, (R,R)-(-)-trans-2,3-bis(hydroxydiphenylmethyl)-1,4- dioxaspiro[4,4]nonane (1), is able to form inclusion complexes with nonpolar aromatic components such as benzene, toluene, p-xylene, mesitylene, and ethylbenzene. The host 1 crystallizes in the monoclinic space group C2 with a = 15.694(2), b = 9.326(2), c = 18.457(1) Å, = 10.34(1)°, and Z = 4. An inclusion complex (1-B) of 1 with benzene crystallizes in the orthorhombic space group P2₁2₁2 with a = 17.007(4), b = 19.670(5), c = 8.634(4) Å, and Z = 4. An inclusion complex (1-X) involving both 1 and p-xylene has the monoclinic space group P2₁ with a = 17.211(3), b = 20.143(3), c = 8.603(3) Å, = 92.64(2)°, and Z = 2. In the inclusion complexes, molecules of 1 are dimerized by intramolecular and intermolecular hydrogen bonds forming eight-membered (OH)₄ rings. The benzene and p-xylene molecules fit into the voids of the crystal packing of 1. In addition, the inclusion complexes are stabilized by van der Waals contacts between the hydrophobic sites. Thermal analysis of the inclusion complexes indicated that the number and the size of the alkyl group of the aromatic components affects the stability of the inclusion complexes.     

Evaluation of the van Deemter equation in terms of open‐ended flow to chromatography

Plate theory and adsorption theory are the main tools available for understanding chromatographic experiments. Both theories predict a Gaussian distribution of solute molecules within the tubular system. However, Gaussian concentration distributions are observed predominantly at slow linear flow rates, while asymmetric concentration distributions are observed at the linear flow rates most used in chromatography. Allegedly, this asymmetry originates from an inhomogeneous distribution of grain sizes in the column and column overload. However, it is an experimental fact that the distribution of chemicals within an injected volume of solute changes as a function of time, while the response is measured simultaneously. Accordingly, the obtained signal cannot be compared to the theory before some type of time‐based deconvolution of the data has been performed. Adjustments to high‐performance liquid chromatography data were thus proposed through empirical equations that describe the relevant time values, peak height, peak area, and parameters of the van Deemter equation. It was proposed that the transfer of solute from the front to the rear part of the pulse during laminar open‐ended flow occurs at rate that depends on the linear flow rate, and to a lesser extent, on properties of the response function.     

Coating for preventing nonspecific adhesion mediated biofouling in salty systems: Effect of the electrostatic and van der waals interactions

Development of anti-biofouling coating has attracted immense attention for reducing the massively detrimental effects of biofouling in systems ranging from ship hulls and surgical instruments to catheters, implants, and stents. In this paper, we propose a model to quantify the role of electrostatic and van der Waals (vdW) forces in dictating the efficacy of dielectric coating for preventing the nonspecific adhesion mediated biofouling in salty systems. The model considers a generic charged lipid-bilayer encapsulated vesicle-like structure representing the bio-organism. Also, we consider the fouling caused by the nonspecific adhesion of the bio-organism on the substrate, without accounting for the explicit structures (e.g., pili, appendages) or conditions (e.g., surface adhesins secreted by the organisms) involved in the adhesion of specific microorganism. The model is tested by considering the properties of actual coating materials and biofouling causing microorganisms (bacteria, fungi, algae). Results show that while the electrostatic-vdW effect can be significant in anti-biofouling action for cases where the salt concentration is relatively low (e.g., saline solution for surgical instruments), it might not be effective for marine environment where the salt concentration is much higher. The findings, therefore, point to a hitherto unexplored driving mechanism of anti-biofouling action of the coating. Such an identification will also enable the appropriate choices of the coating materials (e.g., possible dielectric material with volume charge) and other system parameters (e.g., salinity of the solution for storing the surgical instruments) that will significantly improve the efficiency of the coatings in preventing the nonspecific adhesion mediated biofouling.