The migration of gas-filled brine inclusions in rock salt under a temperature gradient

In natural halite crystals two sorts of inclusions will move if there exists a temperature gradient. The direction of moving brine inclusions is orientated towards the heat source. Brine inclusions which additionally contain more than 10% gas move towards the cold end of a specimen. This model is well known but detailed information about the migration mechanism of these so-called SORBY inclusions have been lacking in literature so far. In this paper it will be demonstrated that SORBY inclusions having a diameter of up to 20 micrometers can move undisturbed through the crystal. SORBY inclusions with a diameter of more than 20 micrometers are fixed and form droplets with their tips directed towards the cold side of the specimen. Later when the tips have grown the inclusions will emit a new daughter inclusion which can move through the crystal. The velocity of migration depends on the generation of daughters. Extended kinds of SORBY inclusions are stable for a long time. However, these can decay into many individuals which will move through the crystal like the others.     

Isomerization and Spin Generation in Polyacetylene

The isomerization of undoped (CH)_x was investigated in a combined Raman and ESR experiment. We find that the ESR linewidth, but not the spin concentration, is correlated with the degree of isomerization as determined from the Raman intensities. The spin concentratin does not change until the isomerization is well change untill the isomerization is well advanced. Hence the decrease in linewidth must be due to the increased mobility of the spins (solitons) rather than exchange interaction. The Spin qeneration is suggested to be due to Diels-Alder crosslinking. The Raman intensities indicate that there are two isomerization processes, with activation energies of 16 and 28 kcal/mole. Anomalous Raman scattering by cis (CH)_x excited with de ep red laser light provides additional evidence for defect structures.     

Generation and intermolecular trapping of a cage-annulated cycloalkylidenecarbene

Base-promoted reaction of 11-methylenepentacyclo[5.4.0.0^2,6.0^3,10.0^{5, 9}]undecan-8-one (5) with diethyl diazomethylphosphonate when performed in the presence of excess cyclohexene, resulted in the formation of the corresponding cycloalkylidenecarbene, 6, which subsequently was trapped in situ to afford 8-methylene-11-(7-bicyclo[4.1.0]heptylidene)pentacyclo-[5.4.0.0^{2, 6}.0^{3, 10}.0^{5, 9}]undecane (7, obtained in 44% yield as a mixture of exo, endo isomers). Subsequent reaction of 7 with dichlorocarbene (generated under phase transfer catalytic conditions) produced the corresponding mono- and di-:CCl₂ adducts [i.e., 8 (64% yield) and 9 (5% yield), respectively]. The structure of 9 was established unequivocally via application of single crystal X-ray analysis: Triclinic, P1¯, a = 6.276(2), b = 8.700(2), c = 18.550(3) Å, = 76.52(3), = 87.59(3), = 70.88(4)° Z = 2; D _calc 1.486 g cm^–3.     

Nonlinear Optical Crystals for Second Harmonic Generation

Crystallography Reports - Some important nonlinear optical crystal families in three spectral regions (DUV-FIR) have been discussed with reference to their anionic groups. In the M–F–IR...     

Generation of random network models with periodic boundary conditions

We have investigated a novel procedure for the generation of tetrahedral random network models compatible with periodic boundary conditions. Data for a sequence of such models is presented and critically examined.     

Use of Labels and Loops for the FIDAP Mesh Generation

The use of do-loops in connection with variables for the FIDAP mesh generation is demonstrated. Special focus is drawn on the advantage of labeling objects explicitly especially for more complicated meshes. These concepts are illustrated with the mesh generation for a three zone resistance furnace.     

长波红外用准相位匹配材料研究进展

8 ～ 12 μm长波红外波段激光在红外对抗系统、测距和瞄准系统、痕量气体监测、频谱分析和无线通信等多个领域具有重要的应用价值.随着红外固体激光器的波长不断向长波长扩展,急需长波红外非线性光学材料.但是CdSe、GaSe、ZnGeP2、AgGaSe2、LiInSe2、CdGeAs2、BaGa4Se7等非线性光学晶体受长波红外透过率、非线性系数、热导率、泵浦源波长的影响,而通过发展OP-GaAs、OP-GaP、OP-ZnSe等性能优异的准相位匹配材料来实现长波激光输出有望克服上述材料的缺点.本文主要对长波红外用准相位匹配材料进行梳理,分别从材料性能、制备技术,以及激光应用等方面综述它们的研究进展并对其应用潜质和技术瓶颈进行分析.     

Generation of dislocations on polished surfaces of dislocation free silicon wafers

This paper describes investigations into the influence of wafer defects (surface defects) on the generation of process induced crystal defects in dislocation-free n-type silicon material of both Czochralski and zone-floating techniques. The surface defects are artificial defects, which were produced by scratching with definite forces. The behaviour of scratched silicon surfaces as well as that of scratched and polished silicon surfaces was studied at room temperature and after heat treatment. The experimental results are discussed.     

Generation of VGaTeAsVAs Complexes in Tellurium-doped n-type GaAs by Low-temperature Annealing

It is shown that low-temperature annealing (T= 425 to 625 °C, t ⩾ 0.5 h) of tellurium-doped n-type GaAs crystals (n₀ = 2 × 10¹⁸ cm⁻³) leads to a generation of V_GaTe_AsV_As complexes as a result of a diffusion of arsenic vacancies to V_GaTe_As complexes or arsenic and gallium vacancies to isolated tellurium atoms. The observed regularities of generation of V_GaTe_AsV_As complexes as the annealing temperature and the annealing time are varied are well explained by the proposed model of diffusion-limited formation of V_GaTe_AsV_As complexes.     

Techniques for Generation of Supersaturation Applicable to the Precipitation of Barium Chromate

Possible techniques for generating supersaturation, which could be applied to precipitation of barium chromate from aqueous solution, are reviewed, and experimental work carried out to examine the feasibility of the more promising of these techniques are described. The process requirements of a reasonable rate of production of relatively large (∼ 100 μm) crystals of normal habit, are shown to be satisfied by the technique of precipitation from homogeneous solution (PFHS), employing urea hydrolysis to cause a controlled change in the solubility of barium chromate in an acidic aqueous medium. Some recent experimental work on urea hydrolysis, as applied to the precipitation of barium chromate, has been reanalysed and found to be in agreement with the generally accepted, pseudo-first order reaction model. The effects of urea hydrolysis on the precipitation process are discussed.     

CLBO晶体生长与紫外倍频性能研究

CLBO晶体是一种性能优良的新型激光紫外倍频晶体材料,本文采用改进的顶部籽晶法生长出大尺寸、高光学质量的CLBO晶体.用尺寸为6mm×5mm×10mm的CLBO四倍频样品测量了晶体对Nd:YAG,1064nm四倍频的紫外倍频性能,266nm激光输出功率达到780mW.针对CLBO晶体的潮解开裂问题,在CLBO倍频器工作和存放时,采用恒温加热套管保护,有效地防止了晶体的潮解开裂.     

Generation of molecular Bravais structures by the method of discrete modeling of packings

An algorithm for the generation of possible crystal structures consisting of molecules with the known shapes in the symmetry classes with one translationally independent molecule (the so-called molecular Bravais structures) has been proposed within the framework of the method of discrete modeling of packings in molecular structures. The algorithm was used to write a special complex of computer programs. Some examples of testing this complex on molecules with the structures determined earlier by the methods of X-ray diffraction analysis are also considered.     

Role of Spin States of Polymethine Dyes in the Generation of Electron-Hole Pairs

The spectral and luminescent properties of film composites based on photoconductive poly-N-epoxypropylcarbazole (PEPC) and electrically neutral polyvinylbutyral (PVB) with admixtures of polymethine dyes with various ionicities are studied. The external magnetic field effect on the spectral and luminescent properties of film composites based on PEPC with cationic polymethine and merocyanine dyes is studied. The magnetic field effect in the photogeneration of electron-hole pairs is explained by the participation of the singlet–triplet intersystem crossing of excited dye molecules.     

A Study of a Ferroelectric Liquid Crystal Using Second Optical Harmonic Generation

The phase-matched generation of the optical second harmonic was investigated in the chiral smectic C* phase of a classical ferroelectric liquid crystal (DOBAMBC). The phase-matching was achieved either by incidence angle or by temperature tuning. The temperature behaviour of the second order nonlinear susceptibility was studied.     

Generation of etch pits on sectional planes of unidirectionally solidified cd-zn eutectic samples

A series of experiments were carried out for generating defined etch pits on various sectional planes of unidirectionally solidified Cd-Zn eutectic samples. This was done as preliminaries of real structure investigations. For that purpose chemical, electrolytic, and ion beam procedures were tested.     

尺寸对NaYbF4纳米晶活性氧产生速率的影响

本文采用热分解法制备了NaYbF4纳米晶,并通过控制反应时间调节纳米晶尺寸来增加其比表面积,进而提高活性氧产率.通过TEM图像对NaYbF4纳米晶的尺寸进行表征.利用化学探针法检验NaYbF4纳米晶分散液中活性氧的产生,并计算了活性氧产生速率.结果表明纳米晶尺寸在影响Yb3+与O2的能量传递过程中占主导因素.同时,当生长时间较短时,晶格缺陷较多,无辐射弛豫过程增加,也影响活性氧产生速率.尺寸约8 nm时,NaYbF4纳米晶活性氧产生速率最大.     

PCD刀具切削各向同性热解石墨时石墨转移膜的形成机理

为研究石墨转移膜在刀具表面形成的可能性和演变规律及形成机理,采用聚晶金刚石(PCD)刀具进行了各向同性热解石墨切削试验.对刀具磨损区域形貌、表面加工质量和切削力进行了分析.根据试验结果分析表明:切削过程中PCD刀具后刀面上形成了一层石墨转移膜.石墨转移膜的形成机理以物理吸附作用和摩擦挤压为主.石墨晶体结构特性、石墨晶体缺陷和环境氛围是影响石墨转移膜形成的三个主要因素.刀具磨损、表面加工质量和切削力的变化情况与石墨转移膜的动态变化过程具有较高的一致性,石墨转移膜的形成可以有效地降低刀具磨损速度,提高表面加工质量,降低切削力.     

短程有序结构中宽带二次谐波产生的研究

本文从理论和数值模拟上分析了一种短程有序铁电畴结构中二次谐波的产生过程.这种短程有序结构是由一系列一定长度的周期极化铁电畴结构和任意长度的单畴结构交替构成.研究了结构参数对频率变化过程中频谱带宽和转换效率的影响.结果表明,转换效率可以通过增加短程有序结构的晶体长度得到提高,而频谱带宽的大小可以通过调节周期极化结构的长度加以控制.     

Field Dependence of 1 and 2 Photon Charge Generation in Anthracene and Phenazine

Charge carrier generation through photexcitation with strongly absorbed light and very weakly absorbed light has been compared for anthracene and phenazine crystals. No attempt was made to prepare clean surfaces, but purified crystals were used. The field dependence for strongly absorbed light was similar for both crystals, superlinear at low fields, linear at high fields. For weakly absorbed light, the photo generation of charge in anthracene could be described as Onsager type behavior, generation in phenazine could not. These results are discussed in terms of the charge generation process.