An approximate solution for the Couette–Poiseuille flow of the Giesekus model between parallel plates

An approximate analytical solution is derived for the Couette–Poiseuille flow of a nonlinear viscoelastic fluid obeying the Giesekus constitutive equation between parallel plates for the case where the upper plate moves at constant velocity, and the lower one is at rest. Validity of this approximation is examined by comparison to the exact solution during a parametric study. The influence of Deborah number (De) and Giesekus model parameter (α) on the velocity profile, normal stress, and friction factor are investigated. Results show strong effects of viscoelastic parameters on velocity profile and normal stress. In addition, five velocity profile types were obtained for different values of α, De, and the dimensionless pressure gradient (G).     

Optimized and validated initial-rate method for the determination of perindopril erbumine in tablets

A simple and sensitive kinetic spectrophotometric method for the determination of perindopril in pharmaceutical preparations is described. The method is based on the interaction of drug with 1-chloro-2,4-dinitrobenzene (CDNB) in dimethylsulfoxide (DMSO) at 40+/-1 degrees C. The reaction is followed spectrophotometrically by measuring the rate of change of the absorbance at 420 nm. Under the optimized experimental conditions, the calibration curve showed a linear relationship over the concentration range of 20-140 microg/ml. The activation parameter such as E(a), deltaH*, deltaS* and deltaG* for this reaction were calculated and found to be 27.31 kJ/mol, 24.69 kJ/mol, -138.84 J/K/mol and 61.50 kJ/mol, respectively. The method has been successfully applied to the determination of perindopril in commercial dosage forms. Statistical comparison of the results with the Abdellatef's spectrophotometric method shows excellent agreement and indicates no significant difference between the methods compared in terms of accuracy and precision.     

农田周围杂草带中普通田鼠种群数量的季节变动特征及杂草带年龄和植被之间的关系

本文中我们采用标志重捕方法从2003到2004年11月,对栖息在野花带的普通田鼠种群结构和数量动态进行比较系统的研究.结果表明,这两年中种群密度夏季最大分别达到410个体/ha和641个体/ha,春季最少分别达到166个体/ha和153个体/ha,从7月份开始增长,8月份种群密度减少并在11月份开始重新增长.种群中雌性个体数量比较多,雌性在种群中的居留时间比较长同时存活率比雄性高,这种现象导致种群数量的季节变化.种群周转率比较高,在两个捕鼠期间种群中的80%个体被更新,这表明普通田鼠在野花带中的活动非常活跃,不断与周围的其它种群进行交流,提高种群对环境的适应能力.种群中雌雄个体的领域之间没有年间变化,它们的活动领域比较小,领域长度2003年平均为11米,最长为37.5米,2004年平均为13米,最长为52米.本研究中我们没有找到环境因素和种群数量动态之间的相关关系.     

Investigation of the phase transition in lithium tantalate by Brillouin spectroscopy

The temperature dependences of the relaxation mode (the central peak) observed at temperatures in the vicinity of the phase transition from the polar phase 3m (C _3v ) to the paraelectric phase 3m (D _3d ) were examined for stoichiometric and congruent crystals of lithium tantalate. The Brillouin scattering measurements were performed on a six-pass Fabry-Perot interferometer (Sandercock tandem) in the frequency range 1–600 GHz. It was demonstrated that the width of the relaxation mode drastically decreases at temperatures close to the phase transition point. This effect was adequately described in terms of the critical slowing down. It was found that the critical slowing down in the stoichiometric crystal is more pronounced than that in the congruent crystal. Analysis of the revealed temperature dependence of the width of the relaxation mode allowed the conclusion that the phase transition in lithium tantalate predominantly occurs through the order-disorder mechanism.     

Synthesis of 1,3,4-mercapto-oxadiazole mono- and dinuclear copper(I) and copper(II) complexes and their microbiological activity

Mono- and dinuclear Cu(I) and Cu(II) complexes of 1,3,4-mercapto-oxadiazole derivatives were prepared and characterized by elemental analyses and standard spectroscopic techniques. The complexes were formulated as Cu(G-OX)₂, Cu₂(G-OX)₄(H₂O)₄, Cu(G-OX)₂L₂and Cu₂(G-OX)₂(PPh₃)₂; (G = H, MeO, Cl; L = Ph₃P, Ph₃As). The microbiological activity of the complexes was investigated against bacteria and fungi. All the complexes were active against Candida albicans, while the reactivity against bacteria varied. The antimicrobial activity of the [Cu(MeO-OX)₂(H₂O)₂]₂ complex was exceptionally better than that observed for any other metal complex against both bacteria and fungi.     

A rapid method for the microdetermination of sulfide using N-bromosuccinimide

Summary A new, rapid, convenient and accurate method for the determination of sulfide has been developed. N-Bromosuccinimide has been used for the displacement of iodine from potassium iodide which in turn reacts with sulfide and oxidises it to sulfur. N-Bromosuccinimide can be used as a primary standard and kept for several days if refrigerated and protected from light. Sulfide in the range of 0.6 to 13 mg can be determined with an average relative standard deviation of 1.02%.

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Zusammenfassung Ein neues Verfahren zur Sulfidbestimmung wurde entwickelt. N-Bromsuccinimid(I) dient zur Freisetzung von Jod aus KJ. Sulfid wird so zu elementarem Schwefel oxydiert. I kann als Standardlösung einige Tage im Dunklen gekühlt aufbewahrt werden. 0,6 bis 13 mg Sulfid können so mit einer relativen Standardabweichung von 1,02% bestimmt werden.

     

Photoparticle production in solid state detectors used for neutron dosimetry in the presence of photons

Photon-induced neutron, proton and alpha particle production in polyethylene and CR-39 has been estimated for the photon energy range of 2–30 MeV, using our previously established methods and photonuclear cross-section data for hydrogen, carbon and oxygen. The rarer isotopes of the constituents of CR-39 and polyethylene, namely ²H, ¹³C, ¹⁷O and ¹⁸O, have been taken into account. Neutrons and protons are produced in polyethylene and CR-39 for photon energies above 2.2 MeV, the (γ, np) threshold for ²H. Photoparticles produced in these materials may need to be taken into consideration when using them for neutron dosimetry in the presence of photons in this energy range, especially when the neutron flux is several orders of magnitude less than that of the photons.     

Unexpected products from the reaction of chalcones with cyanoguanidine

A new series of unexpected dihydrochalcones DHCs attached with cyanoiminopyrimidine moiety in addition to expected cyanoaminopyrimidines CAMPs were synthesized by efficient and facile method via reaction of cyanoguanidine with chalcone derivatives in the presence of EtONa.