bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field‐induced Colour Change of Liquid Crystalline Dyes
Authors: Pelzl G. , Schubert H. , Zaschke H. , Demus D. 
Published: July 2007

AbstractPlanar oriented nematic layers and also partially oriented smectic C phases of certain diphenyl‐1,2,4,5‐tetrazine compounds due to their positive dielectric anisotropy can be oriented by an electric field (Freedericksz‐transition). The orientation is connected with a distinct change of absorption respectively colour. The mechanism of the effect is discussed. For both liquid crystalline phases the response times and decay times were measured.
Investigation of II—IV—V Systems by the Method of Differential Thermal Analysis
Authors: John M. , Hein K. , Buhrig E. 
Published: July 2007

AbstractIt is reported on experiences with the investigation of II—IV—V systems by DTA. Two different arrangements with different sensibility were used. Because of the high volatility of the component V, i.e. phosphorus, samples generally were put in sealed quartz ampoules. Because of the danger of ampoule bursting a special heating procedure was necessary. The results on various II—IV—V systems confirm and precise most of the data of the literature.
Zur Bestimmung von Aktivierungsparametern für die Stoffübergangs‐ und Stofftransportprozesse an AgCl‐ und AgBr‐Kristallen mittels radioaktiver Nuklide
Authors: Winzer A. 
Published: July 2007

AbstractEs wird über die mit Hilfe der Nuklide110mAg+,82Br−und36Cl−durchgeführten radiochemischen Messungen zur Bestimmung der Aktivierungsparameter für die Stoffübergangsprozesse beim AgCl und AgBr im Verlauf der Ostwald‐Reifung berichtet. Dazu wurde vorwiegend der Einfluß der thermischen Vorbehandlung sowie der Alterung des AgCl und AgBr auf die Aktivierungsparameter geprüft. Vergleichende Untersuchungen an den Systemen AgCl−(s)‐110mAg+(aq)und110mAgCl(s)‐Ag+(aq)ergaben, daß sowohl die Stoffübergangsprozesse am Kristall (Einbau der Ionen in das Kristallgitter bzw. Ablösung der Ionen von den Gitterplätzen) als auch die Stofftransportprozesse im Kristallgitter (Diffusion der Ag+‐Ionen über Zwischengitterplätze) geschwindigkeitsbestimmend sein können; die Dehydratation der Ag+‐Ionen sollte dagegen nicht dominieren, was auch durch Messungen in gemischten Lösungsmitteln bestätigt werden konnte.
OD Structures, — a Game and a Bit More
Authors: Dornberger‐Schiff K. 
Published: July 2007

AbstractThe notion of OD structures consisting of layers is explained, and visualization of its main features facilitated by a simple game: the player is asked to stack prefabricated layers periodic in 2 dimensions, which are all of the same kind or of a small number of different kinds, in accordance with some rules which correspond to the vicinity condition (VC).As shown, important features of the sequences of layers depend only on their symmetry (i.e. layer groups) and on geometrical features of any of the kinds of pairs, especially the layer group of any of the pairs.Table 1 shows that OD crystals consisting of layers occur amongst the most diverse chemical substances. In Tables 2 and 3 some examples of OD crystals with a variety of relations between crystallochemical entities and OD layers are listed.In the Appendix and Table 4 new and simplified formulae for the numberZv'(v)of possible positions of a certain layerLv′relative to the fixed position of its predecessor (or successor)Lvare given.
On Some Features of X‐Ray Powder Patterns of OD Structures
Authors: Fichtner‐Schmittler H. 
Published: July 2007

AbstractX‐ray powder data of OD crystals may be misinterpreted, if the OD character of the substance is not taken into account. For some typical OD structures, problems in connection with their identification and the determination of lattice parameters are discussed. Some features of X‐ray powder patterns, which — on principle — are relevant to all OD crystals are summarized.
HVEM Investigation of the Structure Change during Work Softening of Molybdenum
Authors: Luft A. , Brenner B. , Ritschel Ch. 
Published: July 2007

AbstractThe change of the dislocation structure of cold worked Mo single and polycrystals during reloading at T2 ⪆ 350 K has been studied by HVEM. The structure change was found to proceed in three discernible stages: i. formation of obstacle‐free zones by local annihilation of existing dislocations, ii. appearence of large scale slip in these zones, iii. blocking of slip zones by the formation of dislocation cell structure.
Electron Beam Induced Changes of the Real Structure of Semiconductors
Authors: Aseev A. L. , Astakhov V. M. , Pchelyakov O. P. , Heydenreich J. , Kästner G. , Hoehl D. 
Published: July 2007

AbstractThe formation of irradiation defects produced in a high voltage electron microscope (HVEM) has been studied in Ge and other semiconductor crystals in dependence on various thermal treatments and on covering of the specimen surface. It has been concluded that the defect formation depends — besides general features known for pure metals — also on the state of electrically neutral impurities. Besides, various interactions between dislocations and irradiation defects were observed.
Dislocation arrangements in cyclically deformed polycrystalline molybdenum
Authors: Mecke K. , Holste C. , Terentjev W. F. 
Published: July 2007

AbstractThe present paper deals with the cyclic stress‐strain behaviour of polycrystalline molybdenum at room temperature and the dislocation structures built up within this material during the fatigue process. A cyclic stress‐strain curve of molybdenum deformed in a strain‐controlled and symmetrical push‐pull test is shown. At strain amplitudes ea < 3 × 10−3 arrangements of relatively homogeneously distributed dislocations are observed in the stage of the stabilization of mechanical properties. The characteristics of these dislocation arrangements are similar to those of dislocation structures of unidirectionally deformed molybdenum single crystals. At strain amplitudes ea > 3 × 10−3 dislocation structures are developed with an inhomogeneous dislocation distribution (bundles structures). The dislocation density in the surface layers of fatigued specimens shows larger values than within the material. The cyclic deformation after a change from a small deformation amplitude to a larger one, or vice versa, is connected with characteristic changes of dislocation density.
On the description of symmetry of OD structures (III). Short symbols for OD groupoid families
Authors: Fichtner K. 
Published: July 2007

AbstractTwo kinds of short symbols are proposed: 1. The short symbol of any OD groupoid‐family consists of two parts: the symbol for the point group of the groupoid of partial symmetry operations and the symbol for the layer group. No information on the parameters is given. 2. The short symbol of any OD groupoid‐family consists of those parts that correspond to the lines of the full symbol. There is, however, only one of the partial symmetry operations given, which transform a layer into an adjacent layer. These short symbols are suitable for storage of the symmetry data of OD structures in computer operated data banks.
The polymorphism of some liquid crystalline 4′‐n‐alkyloxy‐3′‐nitro‐biphenylcarboxylic acids
Authors: Demus D. , Marzotko D. , Sharma N. K. , Wiegeleben A. 
Published: July 2007

AbstractThe substances of the homologous series
magnified image
with n = 6, 12, 14, 15, 16, 18 were investigated by calorimetry and microscopy. In the lower members exist nematic, smectic A and smectic C phases, in the homologs with n = 16 and 18 appear phases of the type smectic D with cubic structure. The kinetics of these phase transitions, in which smectic D is participating shows a strong dependence upon the experimental conditions. Supercooling, as well as, overheating effects were found. In the supercooled state we could detect for the first time smectic phases, which are metastable with respect to another liquid crystalline phase (SD).
Crystal growth from a calcium nitrate tetrahydrate melt
Authors: Pacák P. 
Published: July 2007

AbstractThe kinetics of growth of calcium nitrate tetrahydrate crystals from its melt were studied in the supercooling region ΔT = 0 — 65 K. The experimental results were compared with the theoretical equations, and it was found that the growth proceeds according to a dislocation mechanism at low supercooling values and changes to continuous growth governed by the melt viscosity at higher values of supercooling.
Surface topographic studies of MoSe2 single crystals
Authors: Agarwal M. K. , Patel H. B. , Patel J. V. 
Published: July 2007

AbstractSingle crystals of MoSe2 of fairly large size have been grown by the sublimation method. A careful study of microstructures on the as‐grown faces has revealed a variety of surface patterns. All these features have been critically studied and the implications have been discussed.
Trends in the thermal expansion coefficients of the AIBIIIC2VIand AIIBIVC2Vchalcopyrite compounds
Authors: Neumann H. 
Published: July 2007

AbstractEmpirical relations are derived for the average linear thermal expansion coefficient αLand the linear thermal expansion coefficients αaand αcof the lattice parametersaandc, respectively, of the AIBIIIC2IVand AIIBIVC2Vcompounds. It is shown that the thermal expansion coefficients of all tetrahedrally coordinated compounds can be described within the same model. The anisotropy of the thermal expansion coefficients depends essentially on the lattice constant ratioc/a. There exists a criticalc/avalue below of which αcbecomes negative.
A method for the determination of the cyclic stress‐strain curve of presistent slip bands in fatigued single crystals
Authors: Blochwitz C. , Kahle E. 
Published: July 2007

AbstractSingle crystals of pure nickel oriented for single slip were fatigued at constant total strain amplitude (εat) at room temperature. The dependence of the saturation resolved shear stress amplitudes (τas) on the saturation plastic resolved shear strain amplitudes (γaps) (cyclic stress‐strain curve — CSSC) was determined. In the plateau range of the CSSC the volume fraction f of persistent slip bands (PSBs) was found to be linearly related to γaps. The reduction of the total strain amplitude after saturation in the plateau range of the CSSC leads to the so‐called secondary CSSC with a slope n > 0 in the log‐log plot. From the secondary CSSC the ”︁true”︁ cyclic stress‐strain curve of the PSB‐volume (PSB‐CSSC) can be determined. The method is based on the two assumptions that firstly the PSB‐groups (or ”︁macrobands”︁) penetrate the whole cross‐section of the specimen and secondly the volume fraction of PSBs in the secondary range of the CSSC remains constant.
Field‐induced phase transition in lead magnesium niobate
Authors: Schmidt G. , Arndt H. , Cieminski J. V. , Petzsche T. , Voigt H.‐J. , Krainik N. N. 
Published: July 2007

AbstractThe temperature dependence of the dielectric constant, polarization, and elastic compliance as well as the field dependence of the polarization and strain at different temperatures was measured at lead magnesium niobate single crystals for three different directions. From the results some conclusions with respect to the symmetry of the field‐induced ferroelectric phases can be drawn. Below −70°C and after complete poling, the spontaneous polarization is probably directed along [111].
On the Mechanism of the Copper‐induced Hexagonal‐Cubic Transformation of Zinc Sulphide
Authors: Grus M. , Horodecki A. J. , Jankowska A. , Skowron A. 
Published: July 2007

AbstractThe influence 2H → 3C transition on the lattice constants, electron paramagnetic resonance and electroluminescence of ZnS: Cu, Mn was investigated. The effect of the electron gasionized donors interaction on the lattice constants of crystal is discussed. It is concluded that 2H → 3C transition is the first‐order phase transition.
Dynamic deformation of silicon‐rich V3Si single crystals at elevated temperatures
Authors: Bertram M. , Paufler P. , Kleinstück K. 
Published: July 2007

AbstractThe plastic deformation behaviour of the intermetallic phase V3Si (Cr3Si type) was investigated under dynamic conditions. The experiments revealed that V3Si deforms plastically at a strain rate of about 4.7 × 10−5s−1 above 1200°. Flow stress depends strongly on deformation temperature and strain rate. An alloy hardening by deviation from stoichiometric composition within the range of homogeneity is observed.
Studies on two‐dimensional nucleation
Authors: Vasudevan S. , Nagalingam S. , Dhanasekaran R. , Ramasamy P. 
Published: July 2007

AbstractAssuming a square shaped two‐dimensional nucleus, the expressions for critical size and critical free energy are derived. As an example of the relations derived, a system of ADP‐water at 300 K has been considered. Also a graph connecting the critical size and the supersaturation is drawn. Using the McDonald theory, the nucleation rate of two dimensional nucleus is derived.
Growth and etching of calcite crystals
Authors: Desai C. C. , George K. V. 
Published: July 2007

AbstractSingle crystals of calcite (CaCO3) have been grown by the method employed by GRUZENSKY, using an aquoeus solution of CaCl2 and a solid (NH4)2SO3, The chemical reaction takes place according to the following equation:
CaCl2 + (NH4)2SO3 CaCO3 + 2 NH4Cl
The crystals grown by this method are about 0.2 to 0.8 mm in edge dimensions.Synthetic calcite crystals have been cleaved along (100) planes and the cleavage surfaces have been studied by multiple beam interferometry. The interferograms have revealed that the cleavages are quite flat. The cleavage faces have also been chemically etched and the etch patterns studied optically. By etching a cleavage successively for three different periods it was found that the bottoms of the point‐bottomed pits follow a linear etch path. By etching a cleavage pair, one face in one etchant and the other face in a different etchant and by comparing the etch patterns produced, before and after polishing a cleavage face it has been shown that the etch pits nucleate at the sites of dislocations in the crystal. The etch patterns have also been compared with those produced on the cleavage faces of natural crystals. The density of dislocations in the syntheitc calctie crystals was generally less than the density of dislocations in the natural calcite crystals. The implications have been discussed.
Structure and morphology of metal oxide depositions on SiO2(II). Structural aspects of the intergrowth of metal oxides on quartz
Authors: Bräer K. , Müller E. 
Published: July 2007

AbstractThe oxides (TiO2, SnO2, GeO2) were deposited on the surfaces of quartz crystals ((1010), (1010), (0111), (0001)) and investigated by RHEED. Anatase and rutile were found for TiO2, the quartzisomorphous structure for GeO2 and for SnO2 apart from cassiterite a structure which was hitherto unknown. The epitaxy relations were derived and discussed from the aspect of structural chemistry.
X‐ray topographic investigation of growth defects in natural calcium fluoride crystals
Authors: Desai C. C. 
Published: July 2007

AbstractCalcium fluoride crystals have been cleaved along {111} faces and the freshly cleaved faces have been chemically etched in 2.6 N nitric acid solution. The etched faces have been optically studied. One‐to‐one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes. The same crystal has been studied using X‐ray topographic technique. By using 022‐ and 022 reflections, stereopair projection topographs were studied and compared with the optical micrographs. The close resemblance between dislocation etch pits and dislocation out‐crop images has been established. The orientation of the Burgers vectors of the dislocation lines has been identified using AgKα radiation with 111‐, 111‐ and 111 reflections. It has been confirmed that Burgers vectors of dislocation lines lie parallel to 〈110〉 directions. The implications are discussed.
Correlation between microhardness and dislocation mobility in crystals with a different type of bond
Authors: Boyarskaya Yu. S. , Grabko D. Z. , Dintu M. P. 
Published: July 2007

AbstractThe complex investigations of microhardness and dislocation mobility in temperature interval 77–873 K have been performed on ionic crystals, semimetals and covalent crystals. It is shown that the correlation between the microhardness and dislocation mobility exists as a whole only. The temperature change of microhardness is not often connected with the change of dislocation mobility. An “anomalous” behaviour of semimetals has been established – they have a small microhardness and a low dislocation mobility at a time.
Low‐angle grain boundaries in synthetic calcite crystals
Authors: Desai C. C. 
Published: July 2007

AbstractSingle crystals of calcite grown in this laboratory by the solution method have been cleaved along (100) planes and have been chemically etched in 20% NH4Cl and 5% citric acid solutions. Rows of equally spaced etch pits have been observed. By etching matched cleavage faces, correspondence has been established for low angle grain boundaries. Correspondence of grain boundaries has also been observed on the two sides of a thin plate 0.68 mm thick. It is observed that the density of pits in all the corresponding rows of matched cleavage faces and on the two sides of a thin plate is the same. Correspondence in the matching of four boundaries forming a node has also been observed on the matched faces and the relation na = nb = nc + nd (where n is the pit density along the boundary line) has also been established. The implications are discussed.
Epitaxial growth of silicon carbide layers by sublimation “Sandwich method” (II) structural defects and growth mechanism
Authors: Mokhov E. N. , Shulpina I. L. , Tregubova A. S. , Vodakov Yu. A. 
Published: July 2007

AbstractStructural defects of α‐SiC epitaxial layers grown by sublimation “sandwich‐method” in vacuum at the temperatures ranging from 1600 to 2100 °C have been investigated by X‐ray topography and optical microscopy methods. It was shown, that perfect SiC layers with the homogeneous polytype structure and small dislocation density (≦ 102 cm−2) may be obtained on the substrates with any crystallographic orientation at the conditions close to quasi‐equilibrium one. The presence of impurities and silicon deficiency in the vapour phase, lead usually to the deterioration of morphological and structural perfection of SiC layers. There are the following structural defects: uncoherent polytype inclusions (mainly β‐SiC), pores, dislocations, specific stacking faults. Morphological peculiarities of the SiC epitaxial layers and possible growth mechanisms are discussed.
Growth spirals of gadolinium gallium garnet (GGG) crystals
Authors: Naumowicz P. , Wieteska K. , Szarras S. , Cinak J. 
Published: July 2007

AbstractSlices cut from various locations in two GGG spirals grown by the Czochralski method have been studied using double crystal X‐ray topography. In selected regions of the slices the lattice parameter has been measured by a modified Bond method. An increase of lattice parameter has been found in the outer part of the crystal where growth bands have smaller periodicity than those in the central region of the spiral. An analysis of crystallization front changes allowed us to suppose that the asymmetry of the heat field around the growing crystal, and the forced convection of the melt, are responsible for the crystal's growing in the shape of a spiral.
A New Calcium Oxalate Monohydrate Produced by Thermal Dehydration of Weddellite
Authors: Schubert G. , Ziemer B. 
Published: July 2007

AbstractA high temperature‐Guinier photograph of weddellite power showed at 118 °C a transition to a so far unknown phase which transformed to β‐Ca(COO)2 at 135 °C and during cooling down to whewellite at 103 °C. X‐ray diffraction studies on single crystals revealed the new phase to have an orthorhombic symmetry with the lattice constant a = 12.088 Å, b = 10.112 Å, c = 14.634 Å, α = β = γ = 90°. There are very simple orientation relations to weddellite: a1 (wed) ∥ a (new phase), a2 (wed) ∥ b (new phase), c (wed) ∥ c (new phase). DTA/TG studies showed that the new phase is a calcium oxalate monohydrate.
Precipitation of Alkaline‐earth Metal Hydroxoberyllate, Hydroxoaluminates and Allied Salts from Aqueous Solution: Ionic Equilibria, Crystalline Phases and Precipitation Mechanisms
Authors: Packter A. 
Published: July 2007

AbstractThe precipitations of alkaline‐earth metal hydroxoberyllates and zincates, hydroxochromates (III), ferrates (III), aluminates and gallates, hydroxotitanates, zirconates and stannates (IV) and hydroxoantimonates (V) from different aqueous solutions are surveyed. The relevant ionic equilibria (hydroxoanion formation, precipitation of hydroxosalts, amphoteric metal hydroxides and alkaline‐earth metal hydroxides) that may influence these precipitations are examined. The crystalline phases precipitated from different systems are tabulated and precipitation mechanisms are analysed.
The accuracy of extrapolation methods; an automatic box–jenkins package sift
Authors: Hill Gareth , Fildes Robert 
Published: July 2007

AbstractHill and Woodworth (1980) proposed an algorithm suitable for identifying Box–Jenkins models automatically without reliance on the investigator. This paper first reviews the method. It is then used on the 111 series analysed by Anderson in the Makridakis forecasting competition. The results show that the automatic method of Hill and Woodworth is comparable in terms of accuracy to the full Box–Jenkins identification procedure.
General exponential smoothing and the equivalent arma process
Authors: McKenzie Ed. 
Published: July 2007

AbstractAlthough the basic principles of exponential smoothing and discounted least squares are easily understood, the full power of the technique is only rarely exploited. The reason for this failure lies in the complexity of the standard procedures. Often they require fairly complex mathematical models and use a variety of cumbersome algebraic manipulations. An alternative formulation for exponential smoothing is presented. It simplifies these procedures and allows an easier use of the full range of models. This new formulation is obtained by considering the relationship between general exponential smoothing (GES) and the well‐known ARMA process of Box and Jenkins. The three commonest seasonal models have only recently been considered for GES systems. They are discussed in some detail here. The computational requirements of the GES and equivalent ARMA procedures are reviewed and some recommendations for their application are made. The initialization of GES forecasting systems and the important problem of model selection is also discussed. A brief illustrative example is given.
Forecasting the economic recession in the U.K. 1979‐1982: A comparison of model‐based ex ante Forecasts
Authors: Barker Terry 
Published: July 2007

AbstractThis paper compares the forecasts of recession and recovery made by five non‐government U.K. teams modelling the economy (Cambridge Econometrics, the London Business School, the National Institute of Economic and Social Research, the Cambridge Economic Policy Group and the Liverpool Research Group). The paper concentrates on annual ex ante projections as published over the period 1978‐1982, i.e. forecasts made, before the event, of the onset, length, depth and character of the economic recession in the U.K. which began in 1979. The comparison is in terms of year by year changes in production, unemployment, prices and other variables. It concludes that no group was systematically better or worse than other groups (confirming U.S. experience) and that the groups tended to perform better in their chosen areas of specialization, e.g. medium‐term groups did better at forecasting the medium‐term outcome.