Cycle and circle tests of balance in gain graphs: Forbidden minors and their groups

We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory     

Fine Dry Grinding of Zeolite in a Laboratory Ball Mill

This paper presents the importance and usage of natural zeolites, which was recently recognized in the industry. Therefore, the grinding properties of natural zeolite were studied with the emphasis on a kinetic study in a ball mill. The experimental mill employed was laboratory sized, 200 mm diameter, 191 mm length, providing a total mill volume of 6000 cm³, with a total mass of 5.62 kg of steel balls of 25 mm diameter with a charge of 20% of the mill volume and with a rotation speed of 76 rpm. The breakage parameters were determined by using single sized feed fractions of ?850+600 μm, ?600+425 μm, and ?425+300 μm for the zeolite samples. The S_i (specific rate of breakage) and B_{i, j} (primary breakage distribution) values were obtained for those feed size fractions in order to predict the product size distributions by simulation for comparison to the experimental data. From the experimental results, S_i values increased as the feed sizes became coarser, i.e., the highest S_i value was 0.85 min^?1 for ?850+600 μm, while the lowest S_i value was 0.65 min^?1 for ?425+300 μm feed ground in the mill. The B_{i, j} values obtained for the zeolite sample were γ=0.84, ?=0.61, and β=4.25. The breakage parameters obtained showed that the zeolite is broken faster than quartz and slower than calcite and barite in terms of the a_T values reported previously at the same experimental conditions. The simulations of the product size distributions of zeolite were in good agreement with the experimental data using a standard ball mill simulation program. The slowing‐down effect was also seen in the mill after 4 min. of grinding.     

Interactions between naproxen and maltoheptaose,the non-cyclic analog ofβ-cyclodextrin

The crystallinity of naproxen in solid combinations with amorphous maltoheptaose, the non-cyclic analog of -cyclodextrin, was assessed using differential scanning calorimetry supported by X-ray powder diffractometry. Cogrinding induced a decrease in drug crystalinity to an extent which depended on the grinding time, and was most pronounced for the combination of equimolecular composition. Thermal analysis showed that the mechanism behind the conversion of crystalline naproxen into the amorphous state by cogrinding with maltoheptaose differed from that with randomly substituted, amorphous -cyclodextrins. Interactions of naproxen with maltoheptaose in aqueous solution were studied by means of fluorescence spectroscopy, phase-solubility analysis, and computeraided molecular modelling. Maltoheptaose can wrap up naproxen, taking on a cyclic conformation and forming a pseudo inclusion complex (apparent binding constant K_{1: 1} = 1.0 × 10³ (–20%) L mol^–1 at 25 °C) which is about as stable as the true inclusion complex with -cyclodextrin in the lowest temperature range (0-100 K). A better complexing ability for naproxen in terms of binding constant values, however, was displayed by both native and derivatized -cyclodextrins, the hosts with covalently-bound cyclic structures.     

Effect of grinding on thermal reactivity of ceramic clay minerals

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.     

汽车车轮流场的数值模拟

首先以独立车轮为研究对象,以商用计算流体力学软件STAR—CD为工具,利用移动边界条件,并依据k-ε双方程高雷诺数湍流模型对三维定常不可压缩流N-S方程进行数值模拟计算．然后在合适尺寸的计算域下对3种不同宽度的静止和滚动车轮分别进行数值模拟计算,研究车轮宽度和来流速度对阻力系数的影响,将计算结果与实验结果进行了对比分析．计算结果表明,车轮宽度的减小以及来流速度的减小均明显降低汽车的气动阻力系数．     

三种固体转轮除湿系统的模拟比较

分别建立单级转轮系统、厚转轮系统以及两级转轮系统的模型.利用模型比较分析了三种系统的性能.结果显示两级系统处理的潜热、显热负荷和产生的冷量均为最大,但其COP在三者之中最低;厚转轮系统与单级系统的差异不显著.通过实际的两级除湿系统的实验结果,验证模拟结果的准确性.     

Modelling of squeal noise attenuation of ring damped wheels

The called vibratory instability squeal that appears in narrow curve or in end of braking is today uncontrolled and produced a high pitched noise very intense and unbearable. Many systems have been developed to limit acoustic emissions and particularly the metallic ring damping solution. Attenuation can reach 20 dB depending on the wheel type (Corail, safety wheel, etc.). However, the question is why this system has a various efficiency even on similar wheels and if this solution may be optimized. The aim of this paper is to understand the attenuation mechanisms of the ring dampers. Wheel modes susceptible to squeal are highlighted and numerical models are developed in order to simulate how the acoustic attenuation occur.     

Superspace groups and superstructures: NbS3

The application of superspace groups to short-period superstructures is considered. For niobium tri-sulfide this is worked out in detail. It is shown that in that case the superspace group provides more symmetry then given by the space group of the supercell. Its consequences for the structure, the diffraction pattern and tensor-properties are discussed.     

Atom-Efficient,Solvent-Free,Green Synthesis of Chalcones by Grinding

An improved Claisen–Schmidt condensation reaction of methyl ketones and aromatic aldehydes can be achieved by grinding at room temperature in the absence of solvents. This process is simple, efficient, economical, and environmentally benign compared to classical reactions.     

Efficient Method for Synthesis of the Derivatives of 5‐Arylidene Barbituric Acid Catalyzed by Aminosulfonic Acid With Grinding

Aminosulfonic acid is an environmentally friendly catalyst. Grinding a mixture of aromatic aldehydes, barbituric acid, and H₂NSO₃H at room temperature (without any solvent) gave 5‐arylidene barbituric acid in high yields, providing a simple and efficient route to synthesis of these compounds.