Electric and dielectric properties of some gamma-irradiated cabal glasses

Electrical conductivity and dielectric properties have been studied for the glass system CaO---B₂O₃---Al₂O₃ in the temperature range 40–200°C. The substitution of 5% B₂O₃ by CaO or replacing 5% CaO by Na₂O or MgO cause a decrease in the conductivity, but the decrease obtained by soda is greater than that of magnesia. The activation energies of the tested glasses were calculated. All the glasses investigated showed a dielectric constant almost independent of temperature at fixed frequency. The effect of subjecting the glass to a constant dose of gamma-rays changes both the electrical conductivity and dielectric constant. The experimental results were discussed in relation to the specific conduction mechanism in such glasses. Also the effect of varying glass composition or temperature on the mobility or migration of current carrier was considered. The possible creation of induced defects in glass on irradiation was evaluated.     

Design of a modified three-rail shear test for shear fatigue of composites

There are various ways of determining the static in-plane shear properties of a fibre-reinforced composite. One of them is the standard three-rail shear test, as described in “ASTM D 4255/D 4255M The standard test method for in-plane shear properties of polymer matrix composite materials by the rail shear method”. This setup, however, requires drilling holes through the specimen. In this study, a new design based on friction and geometrical gripping, without the need of drilling holes through the composite specimen is presented. Quasi-static tests have been performed to assess the symmetry of the setup and the occurrence of buckling. Then, fatigue tests were done to assess the behaviour of the grips under fatigue loading conditions, yielding excellent results; the specimen fails under shear loading conditions in the loaded area. The material used to validate this setup was a carbon fabric-reinforced polyphenylene sulphide.

During fatigue, this material shows an increase in permanent deformation and a decrease in shear stiffness until a certain point in time, after which a drastic increase in deformation and temperature, higher than the softening temperature of the matrix occurs. Furthermore, the maximum value of the shear stress for fatigue with R=0 has a large influence on the fatigue lifetime.     

Eigenmobilities in background electrolytes for capillary zone electrophoresis. I. System eigenpeaks and resonance in systems with strong electrolytes

A background electrolyte system for capillary zone electrophoresis which is composed of three strong univalent ionic constituents is investigated. The ion 1 is considered as a counter-ion and two ions, 2 and 3, are considered as co-ions in relation to the analyte ion 4. We investigate the linearized model of electromigration in such a system and calculate the eigenvalues of a corresponding matrix. The model is formulated in such a way that the eigenvalues of the system are certain mobilities, which we call eigenmobilites, which characterize specific features of the electrophoretic migration. One of the eigenmobilities is the system eigenmobility u_S causing the rise of the system peak, called here the system eigenpeak. A situation when the analyte has the same mobility as the system eigenmobility, u₄=u_S, is analyzed in detail. We show that it leads to the resonance—the mutual jump in the concentration profile of both co-ions, 2 and 3, has a shape of the spatial derivation of the originally sampled analyte profile and, moreover, it grows linearly with time. After a sufficiently long time it can be “amplified” to any value. The resonance has then a great impact on signals of indirect detection methods, like indirect UV detection or conductivity detection. In the framework of the linearized model the relative velocity slope S_X, a measure of electromigration dispersion, is expressed as S_X=F(u₁+u₄)(u₂−u₄)(u₃−u₄)/[u₄(u_S−u₄)], where u_i is the mobility of the ith ion and F is the Faraday constant. As in practice the concentration of the analyte is not infinitely small and has a certain finite value, the analyte will be at the resonance severely dispersed to a much broader spatial interval. When a specific detector is used, the signal of such an analyte can apparently be missed without any notice.     

梯形交变加载作用下聚碳酸酯的应变与寿命

对聚碳酸酯在交变 持久载荷复合作用下应变与寿命研究表明 ,其疲劳 蠕变曲线与纯蠕变曲线十分相似 .加载时间周期越短和交变载荷变化越频繁 ,普弹应变阶段的斜率和应变越小 ,进入延迟弹性变形的平台应变阶段越早 .随每一次循环中的最大载荷加载保持时间延长 ,聚碳酸酯断裂寿命减小 .以最大载荷为恒载荷一直加载的纯蠕变曲线 ,平台最高 ,断裂时间最早 .而最大载荷加载作用时间为 0的纯疲劳曲线 ,平台最低 ,断裂时间最迟 .在交变 持久载荷复合作用下聚碳酸酯存在疲劳和蠕变的交互损伤 ,其断裂寿命N Nf 和 ∑t tr比纯疲劳或纯蠕变的断裂寿命低 ;断裂寿命减小 .并且 ,疲劳 蠕变的交互损伤程度与温度密切相关 .聚碳酸酯在较低温度的疲劳 蠕变交互损伤作用大于较高温度的交互损伤作用 .随温度升高 ,疲劳 蠕变断裂寿命下降是疲劳和蠕变各自的单独损伤增加所致     

甲苯-2,4-二氨基甲酸甲酯的光降解考察金红石TiO2颜料紫外屏蔽特性

以甲苯-2,4-二氨基甲酸甲酯(2,4-TDC)为分子探针模型,构建了一种新的评价金红石二氧化钛颜料紫外屏蔽性能的反应体系,系统地考察了反应条件对分子探针光降解的影响,并对一系列二氧化钛颜料紫外屏蔽性能进行了对比研究。结果表明,金红石二氧化钛作用下,2,4-TDC光降解过程符合一级反应动力学;随着二氧化钛颜料用量的增加,2,4-TDC光降解速率常数呈现指数次下降趋势;紫外光照下表面包覆的金红石二氧化钛颜料不能完全抑制·OH和h⁺活性物种的产生。根据2,4-TDC的光降解速率常数,能体现一系列工业金红石二氧化钛颜料紫外屏蔽性能差异。该方法具有条件温和、操作简便、实验周期短、结果重现性好等优点,将在二氧化钛颜料的紫外屏蔽性能测试中具有潜在的应用价值。     

混合三烃基锡衍生物的研究(Ⅱ)─一丁基二环己基锡羧酸酯的合成、结构表征及生物活性

合成了21个混合三烃基锡羧酸酯。利用红外光谱、核磁共振谱(¹H,¹³C,¹¹⁹Sn)和质谱表征了化合物的结构。对取代苯甲酸酯化合物,锡原子的化学位移δ(¹¹⁹Sn)与苯环上取代基的Hammett常数有很好的线性关系。化合物的生物活性测定结果表明,它们具有高效杀螨活性。     

Polymerization induced phase separation (PIPS) in a polymer dispersed liquid crystal (PDLC) system: A Monte-Carlo simulation approach

The polymerization induced phase separation (PIPS) process in a polymer dispersed liquid crystal (PDLC) system was studied by using Monte-Carlo (MC) simulation methods. In particular, the dependence of the phase separation between liquid crystal and polymer on the parameters, such as temperature γ = ε/kT, polymerization reactivity p and curing time t_c, was examined. It was found that the pair correlation function G(a, t) decreases with the decrease of temperature when the polymerization reactivity p is fixed. Our results also revealed that at a constant temperature, the final value of G(a) first increases with the increasing of p, and finally approaches a constant value. This observation provides us an effective way of controlling the size of liquid crystal droplets as well as their distributions. It was observed that the equilibrium value of G(a) increases as the curing time increases when both temperature and p are kept constant. This is another way of controlling the size of liquid crystal droplets.     

THEORY ON THE RADIATIONLESS TRANSITIONS IN LARGE POLYATOMIC MOLECULES

Abstract— The stationary perturbation theory of Robinson and Frosch is shown to be inadequate to describe the radiationless transitions in polyatomic molecules. An alternative theory of radiative transfer of excitation energy proposed by Franck and Sponer is considered. Evidence shows that this theory leads to a general mechanism for many radiationless transitions in semi-isolated molecules.
Empirically, the rate constants of the excitation transfer between states i and f of the same energy can be expressed by a simple equation: k_t-f=10¹³( f_i.f_f )^0.56sec^-1 where f 's are oscillator strengths to the ground state. This equation is accurate to within an order of magnitude for various processes, such as internal conversions and intersystem crossings with rates differing by 14 orders of magnitude.
The radiative transfer is the result of second order perturbation on the molecule by the radiation field. The equation of rate constant derived from the perturbation energy agrees fairly well with the above equation.     

RATE CONSTANTS FOR INTERACTION OF 1O21Δg) WITH AZIDE ION IN WATER

Abstract— The rate constant for quenching of ¹O₂ by azide ion in water was determined to be (5.0 ± 0.4) × 10⁸ M ⁻¹ s⁻¹ using a variety of sensitizers (including humic acids) and ¹O₂ acceptors. The apparent second-order rate constant decreases with pH below pH 5.5 in accordance with the protonation of azide ion to form hydrazoic acid (p K _a= 4.6). Quenching by hydrazoic acid is at least 2 orders of magnitude slower than by azide ion. Greater than 99% of all interactions between ¹O₂ and azide ion involve physical quenching rather than chemical reaction. Humic acid triplets are not significantly quenched by azide ion at concentrations less than 2 m M , allowing azide ion quenching to be used as a diagnostic test for the intermediacy of ¹O₂ in photosensitized oxidations in natural surface waters.     

Comparison of tear test methods

Tear strength is an important property of a rubber vulcanisate, particularly when considering it for applications such as cables, hoses and tyres. In the present study four test methods, as specified for vulcanised rubbers in British Standards (BS 903 Part A3 and BS 6899), have been investigated on five different compositions based on a nitrile natural rubber, an ethylene acrylic rubber, a polyurehane and undisclosed chloroprene elastomer. The objective of the study was to examine the influence of thickness, grain effects and strain rate on the tear strength. It was also intended to establish if the different tear test methods would rank materials in the same order and whether a constant ratio exists between the tear strength values obtained using the different methods for different materials.

Sample thicknesses in the range 0·5–3 mm and strain rates in the range 100–500 mm/min all produced small but significant variations in the tear strength, confirming that standardisation of these variables is very desirable. Grain effects were found to produce even larger variations in the test results, particularly for the trouser test pieces. It was found that the tests could be divided into two groups:

• (a) trouser and cable tests;

• (b) angle and crescent tests. The tests in each group ranked materials in the same order and the ratios between tests on different materials within each group was approximately the same.

     

Theoretical Study of Stability and Electronic Characteristics in Various Complexes of Psoralen as an Anticancer Drug in Gas Phase,Water and CCl4 Solutions

The present research employs density functional theory(DFT) computations to analyze the structure and energy of complexes formed by psoralen drug with alkali(Li⁺, Na⁺, K⁺) and alkaline earth(Be²⁺, Mg²⁺, Ca²⁺) metal cations. The computations are conducted on M06-2X/aug-cc-pVTZ level of theory in the gas phase and solution. The Atoms in Molecules(AIM) and natural bond orbital(NBO) analyses are applied to evaluating the characterization of bonds and the atomic charge distribution, respectively. The results show that the absolute values of binding energies decrease with going from the gas phase to the solution. Furthermore, the considered complexes in the water(as a polar solvent) are more stable than the CCl₄(as a non-polar solvent). The DFT based chemical reactivity indices, such as molecular orbital energies, chemical potential, hardness and softness are also investigated. The outcomes show that the considered complexes have high chemical stability and low reactivity from the gas phase to the solution. Finally, charge density distributions and chemical reactive sites of a typical complex explored in this study are obtained by molecular electrostatic potential surface.     

Evolution of the dynamic fatigue failure of the adhesion between rubber and polymer cords

The evolution of the dynamic fatigue of the adhesion in a tire carcass compound reinforced by polymer cords under cyclic loading was investigated using a self-developed fatigue test. The characteristic curves are used to explain the evolution of the fatigue failure of the adhesion between rubber and polymer cords. Three stages are identified during the evolution of the dynamic fatigue. Under stress-controlled mode by MTS-ETS (Mechanical Testing&Simulation–Elastomer Testing System), an equation to forecast the adhesion life of rubber/polymer cords composites has been developed. Under strain-controlled mode by MTS, a strain threshold value (87.8%) separating the evolution into two parts was identified. The effects of frequency on the adhesion were also investigated and suggest that, within the experimental range, regardless of the frequency, the adhesion life at a given stress amplitude is constant.     

Nonlinear dielectric effect in carbon tetrachloride solutions of iodobenzene

The results of measurements of Δ/E² as a function of concentration for CCl₄ solutions of iodobenzene are given and compared with earlier results for CCl₄ solutions of fluoro-, chloro- and bromo-benzene. Terms contributing to the molar saturation constant for pure halogeno-derivatives of benzene have been calculated, using Kielich's theory. The change of sign of Δ/E² for bromo- and iodo-benzene is explained.     

Study of self-association of water in supercritical CO2 by Monte Carlo simulation: Does water have a specific interaction with CO2?

The extent of the self-association of water in supercritical CO₂ has been investigated in a wide range of density and temperature by the test particle insertion technique. The results show that the association constant for water decreases with temperature and weakly depends on CO₂ density. This weak density dependence provides evidence for the lack of a strong specific CO₂–water interaction. Comparing calculated association constants with its gas-phase values shows that the association constant is at most ca. 38% lower than its gas-phase value in the high density–low temperature region. Inspection of the simulated radial distribution functions revealed that forming modest water–CO₂ complexes does not result in substantial interference in H-bonding of water molecules.     

恒电位库仑法研究硫在有机溶剂中的还原过程

实验证明,第1步还原E_(1/2)=-0.96V(文中所有的电位均相对于Ag参比电极);第2步E_(1/2)=-1.56V。该体系的特征是伴随的均相反应具有较低的速率常数,在一般的循环伏安法扫描时间内很难觉察到均相反应的进行。若采取时间窗较长的实验方法,将有利于观察伴随均相反应的动力学效应。恒电位库仑法时间域约为100～     

Analysis of Compact Fluorescent Lights for Use by Patients with Photosensitive Conditions

Ultraviolet radiation (UVR) is hazardous to patients with photosensitive skin disorders, such as lupus erythematosus, xeroderma pigmentosum and skin cancer. As such, these patients are advised to minimize their exposure to UVR. Classically, this is accomplished through careful avoidance of sun exposure and artificial tanning booths. Indoor light bulbs, however, are generally not considered to pose significant UVR hazard. We sought to test this notion by measuring the UV emissions of 19 different compact fluorescent light bulbs. The ability to induce skin damage was assessed with the CIE erythema action spectrum, ANSI S(λ) generalized UV hazard spectrum and the CIE photocarcinogenesis action spectrum. The results indicate that there is a great deal of variation amongst different bulbs, even within the same class. Although the irradiance of any given bulb is low, the possible daily exposure time is rather lengthy. This results in potential daily UVR doses ranging from 0.1 to 625 mJ cm⁻², including a daily UVB (290–320 nm) dose of 0.01 to 15 mJ cm⁻². Because patients are exposed continually over long time frames, this could lead to significant cumulative damage. It would therefore be prudent for patients to use bulbs with the lowest UV irradiance.     

磺化竹红菌素对蛋白质荧光猝灭机理的研究

本文详细研究了磺化竹红菌素对多种蛋白质在溶液状态下的荧光猝灭过程。结果表明,磺化竹红菌素对多种蛋白质荧光猝灭服从Stern-Volmer曲线,实验观察了温度、粘度、pH值和盐酸胍对荧光猝灭过程的影响。由于磺化竹红菌素是一两性分子,对于不同蛋白具有不同猝灭过程;磺化竹红菌素对蛋白质的荧光猝灭常数K_q在10¹³mol/L·s^-1左右,这说明,磺化竹红菌素是一种比其它蛋白质荧光猝灭剂更加有效的荧光猝灭剂。     

THE KINETICS OF REDUCTION OF CYTOCHROME c BY SEMI-REDUCED FLAVIN

Abstract— Flavin mononucleotide radicals, FMNH', generated by laser flash photolysis of FMN in the presence of the electron donors, histidine, guanosine monophosphate or EDTA, were found to reduce cytochrome c with an apparent rate constant of 6 ± 10⁷ M ⁻¹ s⁻¹. These flash photolysis results were, however, complicated by the electron donor radicals formed simultaneously which, particularly with EDTA, also lead to reduction of cytochrome c. Pulse radiolysis of a nitrous oxide saturated aqueous solution of FMN containing a high concentration of HCOONa, leads to the exclusive formation of FMNH'. By adding small concentrations of cytochrome c to this solution, a rate constant of 4.0 ± 10⁻¹ M ⁻¹ s⁻¹ was obtained for the reduction of cytochrome c by FMNH'. Replacement of the HCOONa by EDTA in such solutions leads to further routes for reduction of cytochrome c on radiolysis. as in the photolytic situation. The relevance of these results to flavin-photosensitised reduction of cytochrome c and other components of the mitochondrial electron transport chain is discussed.     

A new three-center model for diatomic bonds based on the spherical Gaussian bonding function

A new three-center model for diatomic bonds is proposed based on the spherical Gaussian bonding function. The characteristics of the model are that the magnitude of effective bond-charge described by the function is different for different observation points, and that the position of the bond-charge on the bond axis satisfies the energy variation principle.

According to the model and two additional assumptions, some theoretical formulas for bond properties, such as the total energy of system, dissociation energy, dipole moment, force constant and field gradients at nuclei, are derived. The calculated results are basically in agreement with the observed ones.

In addition, a comparison between the new model and the electrostatic three-center model proposed in a previous paper is discussed in brief.     

稀土乙酰丙酮络合物的激光拉曼和红外光谱(Ⅰ)

本文测定了15个一水稀土乙酰丙酮络合物的激光拉曼和红外光谱,在401、415cm~(-1)附近的拉曼谱带对不同稀土离子表现敏感,它们随原子序数变化呈现“四分组”效应,这是第一次在振动光谱中观察到的镧系递变规律。该系列络合物的振动频率变化亦符合镧系“斜W”效应的规律,这些特征规律为确认401、415cm^-1附近谱带为M-O拉伸振动提供了最好的证据。实验结果同时可用于讨论M-O键的性质。