Quasipollucites and their mixed frameworks,block isomorphism,and superstructures

The structure type of analcime (ANA) is interpreted based on the basic block: a six-membered ring of tetrahedra which is generated by two template cations. The uncertainties in the composition and/or structure of alumophosphate, ferrisilicate, and titanosilicate pollucites, which are complicated by adding H₂O molecules and (OH)⁻ or O²⁻ anions, are eliminated. The block isomorphism and formation of super-structures in these pollucites is discussed. In view of the transformation of tetrahedral ANA frameworks into mixed ones, we propose that they be considered analcimoidal (quasipollucites).     

A Mössbauer effect study of Fe-site occupancy in Australasian tektites

A number of different splash-form Australasian tektites and one Muong Nong tektite from Laos have been investigated by room temperature ⁵⁷Fe Mössbauer effect spectroscopy. Multiple spectra of thailandite samples have been obtained in order to establish uncertainties in fitted parameters. Results indicate that most of the samples investigated have Fe³⁺/Fe²⁺ ratios that are close to zero. The Muong Nong tektite shows the largest Fe³⁺/Fe²⁺ ratio and this is interpreted in terms of proposed mechanisms for the formation of this class of tektite that have been presented in the literature.     

The kinetics of formation of A AuGeSi metallic glass

The glass-forming ability of a Au_0.778Ge_0.138Si_0.084 alloy is analyzed theoretically by computing a time-temperature-transformation curve which describes the time required to produce a barely detectable fraction of crystallization, at various temperatures. The calculation is based on an interpolated viscosity-temperature curve, this alloy being exceptional among metallic glass formers in that experimental viscous-flow data are available at both high and low temperatures. Allowing for uncertainties, the critical cooling rate for glass formation lies within the range 10⁶?10⁸ K/sec which is in satisfactory agreement with experimental estimates of cooling rates in splat quenching. This and previous comparisons for Ni and PdSi alloys suggest that the approach may have useful and general applicability to metallic glasses.     

Temporal evolution of sulfated zirconia sol–gel during dip coating: Analysis of mass drainage with time-varying refractive index

The formation of sulfated zirconia films from a sol–gel derived aqueous suspension is subjected to double-optical monitoring during batch dip coating. Interpretation of interferometric patterns, previously obscured by a variable refractive index, is now made possible by addition of its direct measurement by a polarimetric technique in real time. Significant sensitivity of the resulting physical thickness and refractive index curves (uncertainties of ±7 nm and ±0.005, respectively) to temporal film evolution is shown under different withdrawal speeds. As a first contribution to quantitative understanding of temporal film formation with varying nanostructure during dip coating, detailed analysis is directed to the stage of the process dominated by mass drainage, whose simple modeling with temporal t^−1/2 dependence is verified experimentally.     

Uncertainties in crystallization of hen‐egg white lysozyme: reproducibility issue

The reproducibility of biomacromolecular crystallization (tetragonal and orthorhombic lysozyme crystals) was studied by monitoring the evolution of protein concentration during the crystallization process using Mach‐Zehnder interferometer. It was found that formation of both tetragonal and orthorhombic crystals exhibited poor reproducibility. When the crystallization occurred under isothermal conditions, the protein concentration in the solution varied differently in different experiments under identical conditions (for both types of crystals). Moreover, in the case of orthorhombic lysozyme crystallization (under either isothermal or thermal gradient conditions), it is clear that the crystals could not be always readily formed. When formation of tetragonal lysozyme crystals was conducted at a temperature gradient condition, however, the evolution of concentration was reproducible. The phenomena found in this study revealed that biomacromolecular crystallization can be uncertain, which is probably caused by the process of nucleation. Such uncertainties will be harmful for the efforts of screening crystallization conditions for biomacromolecules. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Smectic Phase of p. p'-di-n-Heptylazoybenzene: A 1H NMR study of Its Anisotropy of Diamagnetic Susceptibility and of Its Use for Measuring Proton Chemical Shift Anisotropies

Abstract

The anisotropy of the diamagnetic susceptibility of the smectic liquid crystal p,p'-di-nheptylazoxybenzene (HAB) has been measured by use of ¹H NMR. The value of (X‖ - X⊥) is found as e.g. 1.418. 10^?6 at 318 K. Furthermore, we have observed local solvent effects of HAB on dissolved globular molecules, which are of the order of 0.10 to 0.19 ppm for methane, 0.37 to 0.44 ppm for tetramethylsilane, 0.35 to 0.40 ppm for tetramethylstannane, and 0.39 to 0.41 ppm for neopentane. These values are dependent on temperature and may lead to large uncertainties in the determination of proton chemical shift anisotropics. A theoretical treatment of the magnetic fields in the annulus of a double-wall tube and inside the inner tube filled with a smectic liquid crystal and variable angle between the applied field and the optic axis is also given.     

Quantum levitation of nanoparticles seen with ultracold neutrons

Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nanodroplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of the fields of fundamental interactions, neutron, surface and nanoparticle physics. Accounting for the interaction of UCNs with nanoparticles explains a recently discovered intriguing so-called “small heating” of UCNs in traps. It might be relevant to the striking conflict of the neutron lifetime experiments with smallest reported uncertainties by adding false effects there.     

Aklyl Chain Order Parameters and Phase Diagrams for Systems Containing Sodium n-Octanoate,Water, and Different Alcohols

Lamellar liquid crystalline phases containing sodium n-octanoate, water, and an alcohol have been studied by means of ²H NMR. Order parameters have been determined for the octanoate alkyl chain in systems containing ethanol, 1-propanol, 1-butanol, 1-pentanol, benzyl alcohol or 1, 8-octandiol. The straight chain alcohols yield decreasing octanoate order parameters with decreasing chain length. With 1, 8-octandiol the octanoate order parameters are somewhat smaller than with 1-propanol, indicating quite flexible octanoate hydrocarbon chains. Using mono-deuteriated benzyl alcohol. C₆H₅CHDOH, the S_CD as well as the S_HD (= S_HH ) order parameters were determined in the same measurement. A typical measurement yields |S _HD|-|S_CD | = 0.04 ± 0.04, where the error estimation includes the uncertainties in the quadrupole and the magnetic dipole-dipole coupling constants. It is stressed that in order to ascertain a significant difference between S_HH and S_CD , it is necessary to know the coupling constants with high accuracy. The phase diagram for the system sodium n-octanoate/water/benzyl alcohol was determined, mainly by ²H and ²³Na NMR.     

Crystal structure of tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato) aquolutetium(III)—Lu(fod)3. H2O

The crystal structure of Lu(fod)₃. H₂O has been solved by three-dimensional X-ray methods at room temperature. The space group isP and the cell dimensions area = 16·392,b = 22·492,c = 13·366 Å, = 91·83 °, = 119·93 °, = 90·00 °. There are four formula-units per unit cell;D _m = 1·66,D _c = 1·667 g cm^–3. Least-squares refinement of atomic and individual isotropic thermal parameters terminated withR = 0·128. This relatively highR factor is due to crystal decomposition, to the prohibitively large asymmetric unit which necessitated refinement in parts and also to the high vapour pressure of the compound and consequently large thermal vibrations in the structure. These factors caused large uncertainties especially in the positions of the atoms at the ends of the long side chains, but the more important geometry of the coordination polyhedra at the cores of the roughly spherical molecules have been firmly established. Except for orientation differences, the two crystallographically independent formula-units are very similar and both are dimerized through water molecules with hydrogen bonds across centres of symmetry. In each case the coordination of lutetium is seven-fold, with the geometry of a monocapped trigonal prism.     

Estimating accuracy of 17O NMR measurements in oxide glasses: Constraints and evidence from crystalline and glassy calcium and barium silicates

The use of ¹⁷O nuclear magnetic resonance (NMR) spectroscopy to measure site populations in silicate and aluminosilicate glasses has provided insights and challenges to conventional models of glass structure. In order to better understand the level of accuracy and precision achievable, we have synthesized crystalline barium metasilicate (BaSiO₃), barium orthosilicate (Ba₂SiO₄), tricalcium silicate (Ca₃SiO₅), a barium silicate glass ((BaO)_0.45(SiO₂)_0.55), and a calcium silicate glass ((CaO)_0.56(SiO₂)_0.44), and report ¹⁷O NMR spectra for all of these. After correcting the observed intensities for quadrupolar effects, we measure an NBO content of 66.7% ± 0.6% for the BaSiO₃, compared to the known value of 66.7%. Applying the same techniques for the glasses gives an NBO content of 58.8% ± 0.8% (vs. the expected 55.5% ± 1.4% from stoichiometry) for the barium silicate and 76.9% ± 1.2% (vs. 78.6% ± 1.4%) for the calcium silicate. Within our uncertainties, we find no evidence for deviation from conventional models of glass structure for the glasses studied here. We also see no NMR signal (detection limit of about 0.5%) at the expected position for “free” oxide ions (bonded only to Ca^2 +), as newly constrained by our data for crystalline Ca₃SiO₅, which contains this species.     

新型有机非线性光学晶体-L-苹果酸脲晶体生长的初步探讨

本文初步探讨了新型非线性光学晶体-L-苹果酸脲的晶体生长,研究结果表明,L-苹果酸脲晶体在甲醇、乙醇和水三种介质中的溶解度温度系数均较大,同温度下L-苹果酸脲晶体在水中的溶解度最大,无水甲醇次之,无水乙醇中最小.L-苹果酸脲晶体在无水甲醇中的成核自由能比在无水乙醇中的低得多,因此在无水甲醇中易于成核,晶核数多,晶体尺寸小,而在无水乙醇介质中,虽然成核相对比较困难一些,但有利于制备大的单晶,且发现低温有利于大晶体的生长.因此宜选择无水乙醇为晶体生长介质.L-苹果酸脲晶体在介质中以非均匀成核方式在试管壁成核长大,晶体呈棱柱状,生长过程中呈现台阶生长的特征.     

Study of liquid crystals at the institute of crystallography

The history of studying liquid crystal at the Shubnikov Institute of Crystallography is briefly reviewed. The scientific results of researchers from the institute (starting from the 1960s and leading to the formation of a new field of science: physics of liquid crystals) are presented. In particular, it is shown how the physics of electro-hydrodynamic instability was developed in the 1970s. The origin of the physics of photonic crystals is considered. The discovery of the ferroelectric properties of ultrathin films of polar molecules is described. A breakthrough in the molecular theory of ferroelectricity in liquid crystals in the new century is discussed. The entire abundance of liquid-crystalline phases and processes occurring in them is estimated. An analysis of the participation of researchers from the Institute of Crystallography in the development of liquid-crystal science demonstrates their valuable contribution, which offers perspectives of new studies in this field.     

Interferential method for determining the inclination angle of molecules in plane-parallel liquid crystalline layers

The interferential method is presented for determining the inclination angle θ of molecules in homogeneously ordered plane-parallel liquid crystalline layers. The essence of the method is the analysis of the changes in the layer transmission caused by the change in conditions of interference. The angle θ is calculated from the exact, explicit relation where from no limitations the size of the angle results. The measuring-stand is described that enabled the method to be put into practice. The results for the PCB layer are presented by way of example.     

Calculation of local electric fields in displacive-type ferroelectrics: LiNbO3

The method is suggested for calculating the intensity and potential of a local electric field in displacive-type ferroelectrics which is based on the introduction of a transitional zone between the region of the discrete localization of ions and the homogeneously polarized medium. The method is exemplified on the calculation of the contribution of Li⁺ ions to the local electric field in the lithium niobate structure. It is shown that the method provides fast convergence of the results in the calculation of the field intensity and high relative accuracy of the calculated electric-field potential inside the crystal. The contribution of the induced dipoles to the local electric field is calculated, and it is shown that the stability of the LiNbO₃ structure is provided by considerable anisotropy in the polarizability of Nb-O bonds. The method is applicable to any ionic crystal.     

Analysis of the dopant segregation effects at the floating zone growth of large silicon crystals

A computer simulation is carried out to study the dopant concentration fields in the molten zone and in the growing crystal for the floating zone (FZ) growth of large (> 100 mm) Si crystals with the needle-eye technique and with feed/crystal rotation. The mathematical model developed in the previous work is used to calculate the shape of the molten zone and the velocity field in the melt. The influence of melt convection on the dopant concentration field is considered. The significance of the rotation scheme of the feed rod and crystal on the dopant distribution is investigated. The calculated dopant concentration directly at the growth interface is used to determine the normalized lateral resistivity distribution in the single crystal. The calculated resistivity distributions are compared with lateral spreading resistivity measurements in the single crystal.     

Hydration of soda-lime glass

The hydration of soda-lime glass is studied using resonant nuclear reactions to measure the hydrogen and sodium profiles of hydrated glasses. The rate of growth of the surface layer of hydrated glass is initially proportional to the square root of time as is characteristic of diffusion controlled processes. After longer exposure a steady-state hydration profile is observed, which indicates that in addition to the diffusion controlled reaction there is a slow etching of the glass surface. The measured hydration profiles are discussed in relationship to the Doremus model of interdiffusing ions, which is found to be in good agreement with the data. This model is also discussed in relationship to measured hydration profiles of vacuum heated samples of hydrated glass.     

生长气氛和速度在金红石(TiO2)单晶体生长中的作用研究

本文研究了生长气氛和生长速度在焰熔法金红石单晶体生长中的作用,对比了晶体在空气中与在氧气中退火的结果,测定了晶体试样的摇摆曲线和透过率.研究表明:金红石单晶体的生长受炉膛气氛、生长界面温度和生长速度的影响;炉膛气氛决定晶体能否形成,是关键因素;炉膛气氛中的氧分压大于液固界面(即生长界面)处熔体的氧离解压是生长完整晶体的前提条件;晶体在退火过程中消除热应力,但更重要的是通过氧化反应消除氧空位,在氧气氛中退火,可明显缩短退火时间.在所优化的实验条件下制备的晶体,完整性较好,透过率为70～72;,与商用晶体的透过率基本一致.     

Fractal images of quasicrystals as an example of Penrose lattice

The Penrose lattice, an example of quasicrystals, is considered as a fractal set. The generation of these sets in the graph tree form is considered. The problem of percolation of informodynamic characteristics and fractal dimensions defined in terms of the information entropy is solved for the constructed graphs.     

Einfluß der Blockstruktur auf die Emissionseigenschaften von Laserrubinen

The laser energy of two rubies of different optical quality is measured in the relaxation regime. The adjustment and length of the resonator is varied and the polarisation of the emission is changed definetely. The results are interpreted in terms of mosaic structure and substructure of the rubies.     

Verteilung von Aktivatoren in Laser-Kristallen

The influence of growth conditions on the distribution coefficient and the radial distribution of activators in rubies and in neodynium doped yttrium-aluminium garnets is described. The distribution coefficient of chromium depends upon the composition of the growth atmosphere, whereas the distribution coefficient of neodymium is independent on it. The radial gradient of the activator concentration is proportional to the component of temperature gradient which is parallel to the phase interface. The shape of the phase interface of Czochralski-grown crystals conforms to the form of the isotherms, whereas of Verneuil-grown crystals is usually flat.