bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical chaperone therapy: clinical effect in murine GM1‐gangliosidosis
Authors: Suzuki Yoshiyuki , Ichinomiya Satoshi , Kurosawa Mieko , Ohkubo Masato , Watanabe Hiroshi , Iwasaki Hiroyuki , Matsuda Junichiro , Noguchi Yoko , Takimoto Kazuhiro , Itoh Masayuki , Tabe Miho , Iida Masami , Kubo Takatoshi , Ogawa Seiichiro , Nanba Eiji , Higaki Katsumi , Ohno Kousaku , Brady Roscoe O.
Published: November 2007

Certain low‐molecular‐weight substrate analogs act both as in vitro competitive inhibitors of lysosomal hydrolases and as intracellular enhancers (chemical chaperones) by stabilization of mutant proteins. In this study, we performed oral administration of a chaperone compound N‐octyl‐4‐epi‐β‐valienamine to GM1‐gangliosidosis model mice expressing R201C mutant human β‐galactosidase. A newly developed neurological scoring system was used for clinical assessment. N‐Octyl‐4‐epi‐β‐valienamine was delivered rapidly to the brain, increased β‐galactosidase activity, decreased ganglioside GM1, and prevented neurological deterioration within a few months. No adverse effect was observed during this experiment. N‐Octyl‐4‐epi‐β‐valienamine will be useful for chemical chaperone therapy of human GM1‐gangliosidosis. Ann Neurol 2007
Self‐reinforcing elastomer composites based on polyolefinic thermoplastic elastomer and thermotropic liquid crystalline polymer
Authors: Saikrasun Sunan , Amornsakchai Taweechai
Published: November 2007

In situ reinforcing elastomer composites based on Santoprene thermoplastic elastomer, a polymerized polyolefin compound of ethylene–propylene–diene monomer/polypropylene, and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a single‐screw extruder. The rheological behavior, morphology, mechanical, and thermal properties of the blends containing various LC3000 contents were investigated. All neat components and their blends exhibited shear thinning behavior. With increasing TLCP content, processability became easier because of the decrease in melt viscosity of the blends. Despite the viscosity ratio of dispersed phase to the matrix phase for the blend system is lower than 0.14, most of TLCP domains in the blends containing 5–10 wt % LC3000 appeared as droplets. At 20 wt % LC3000 or more, the domain size of TLCP became larger because of the coalescence of liquid TLCP threads that occurred during extrusion. The addition of LC3000 into the elastomer matrix enhanced the initial tensile modulus considerably whereas the extensibility of the blends remarkably decreased with addition of high TLCP level (>.20 wt %). The incorporation of LC3000 into Santoprene slightly improved the thermal resistance both in nitrogen and in air. Dynamic mechanical analysis results clearly showed an enhancement in dynamic moduli for the blends with 20–30 wt % LC3000. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Characterization of aminated poly(ethylene terephthalate) surfaces for biomedical applications
Authors: Nissen K. E. , Stuart B. H. , Stevens M. G. , Baker A. T.
Published: November 2007

Aminated poly(ethylene terephthalate) (PET) surfaces were characterized for their use as substrates for the attachment of biologically active molecules. Amines of different chain lengths, tetraethylenepentamine, triethylenetetraamine (TTETA), and diethylenetriamine (DETA), were investigated. X‐ray photoelectron spectroscopy was used to show that each amine introduced a comparable amount of nitrogen (5 atom %) to the PET surface. Contact‐angle and titration analyses indicated that the amination reaction was not restricted to the surface, with evidence of diffusion into the polymer by TTETA and DETA. As a result, degradation of the PET substrate, evidenced by mass loss, was observed to occur. Annealing of the PET films before amination at a temperature of 200°C reduced the extent of degradation without producing a decrease in the nitrogen content produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effects of nucleating agents on the porous structure of polyphenylene sulfide via thermally induced phase separation
Authors: Han Xuntong , Ding Huaiyu , Wang Lihua , Xiao Changfa
Published: November 2007

The different molecular weight Polyethylene glycol (PEG) was chosen to be the nucleating agent to investigate the effects of nucleating agents on the porous structure of polyphenylene sulfide (PPS) via thermally induced phase separation (TIPS). The pore structures were changed with the addition of PEG, due to the different mechanism on pattern formation. Moreover, some effecting factors, such as the molecular weight and concentration of PEG, were used to control the pore structure and size. With addition of nucleating agent, it can be estimated that the pore size (radius) should be about 0.5 ∼ 0.05 μm and the porosity should be above 70%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effect of poly(ethylene methyl acrylate) copolymer on thermal, morphological, and mechanical properties of polypropylene copolymer blown films
Authors: Gururajan Giri , Froude Victoria , Riutta Stephen , Thomas Aline , Gao Ian , Samuels S. L. , Massouda D. F. , Weinberg M. , Ogale A. A.
Published: November 2007

Blends of polypropylene copolymer (PP‐cp) and poly(ethylene methyl acrylate) [poly(EMA)] copolymer blends were processed by blown film extrusion. The orientation and crystallinity of PP‐cp matrix in the blend did not change significantly with the addition of EMA. The low machine direction and transverse direction tear strengths, which are observed for neat polypropylene blown films more than doubled at 6 wt % or higher content of EMA. The increase in tear properties was mainly attributed to a fine dispersion of EMA in the matrix with an average particle size of 100–500 nm and the formation of elongated domains. The dispersed nonrounded EMA domains, resulting from the blown‐film process, enhance better energy dissipation mechanism with the formation of an extended plastic zone in the blend films as compared with that in pure PP‐cp films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Dispersion polymerization of methyl methacrylate: Effect of stabilizer concentration
Authors: Jiang Sheng , David Sudol E. , Dimonie Victoria L. , El‐Aasser Mohamed S.
Published: November 2007

In dispersion polymerizations of methyl methacrylate (MMA), little difference was found in the polymerization kinetics with varying stabilizer (PVP K‐30) concentration, indicating that in contrast to emulsion polymerization, the kinetics of these dispersion polymerizations are independent of the number of particles. Comparing MMA precipitation and dispersion polymerizations revealed that nuclei formation in the latter results from precipitation polymerization occurring in the continuous phase, which can contribute significantly to the kinetics, and especially to the molecular weight distributions. No change was found in the molecular weight distribution of the PVP during a dispersion polymerization, nor was there any measurable difference between using fresh and recycled stabilizer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Influence of reaction media on pressure sensitivity of polyanilines doped with DBSA
Authors: de Souza Fernando Gomes , Anzai Thiago Koichi , Melo Príamo Albuquerque , Soares Bluma G. , Nele Márcio , Pinto José Carlos
Published: November 2007

The effect of the reaction medium on the final electrical performance of Pani doped with dodecylbenzene sulfonic acid (DBSA), Pani.DBSA, is analyzed in this manuscript. Pani.DBSA was synthesized through the one‐step route in nonaromatic media, in accordance with a mixture experimental design. Polymer samples were analyzed by UV–vis and WAXS to characterize the differences among the many prepared Pani.DBSA samples and to explain the observed conductivity and compression sensitivity characteristics. Obtained results were modeled in accordance with a standard empirical modeling approach. Based on the obtained experimental data and on the proposed empirical models, it is shown that addition of acetone and isopropanol into the aqueous media during the one‐step synthesis of Pani.DBSA materials must be encouraged. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The synthesis of block copolyetherketones based on 4,4′‐dichlorodiphenylketone, phenolphthaleine, and bisphenol A and investigation of their properties
Authors: Ozden S. , Charayev A. M. , Shaov A. H. , Bazheva R. C.
Published: November 2007

Block structured polyethers based on phenolphthaleine, 4,4′‐dichlorodiphenylketone, and bisphenol A with different degrees condensation (n = 1, 5, 10, and 20) were synthesized by means of acceptor‐catalytic polycondensation. Equaimolar quantities of chloranhydrides of iso‐ and terephthalic acids were used. Higher molecular masses were obtained from longer oligoketones with higher condensation degrees. Better molecular packing, increased thermal and mechanical properties were obtained with higher condensation degrees of oligoketones. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008
Mechanical, dynamic mechanical, morphological, thermal behavior and processability of polyaniline and ethylene 1‐octene based semi‐conducting composites
Authors: Bhadra Sambhu , Singha Nikhil K. , Khastgir Dipak
Published: November 2007

The polyaniline (PAni) was prepared by the oxidative emulsion polymerization of aniline. Different semi‐conducting composites were prepared by mixing this PAni with a polyolefinic thermoplastic elastomer namely ethylene 1‐octene copolymer (EN) with different ratio. The effect of composition on different mechanical, dynamic mechanical, and thermal properties of these composites and their processability were investigated. The results revealed that the increased incorporation of PAni in EN caused increase in the modulus, hardness, glass transition temperature (Tg), and apparent shear viscosity, but caused decrease in the tensile strength, elongation at rupture, damping character, and die‐swell during injection molding. The base matrix is thermoplastic elastomer for which vulcanization is not required. However, it is found that if such composites are subjected to electron beam (EB) radiation, they can undergo some cross‐linking. The introduction of crosslinks to such system through EB radiation improves mechanical properties. The flow behavior shows the material is pseudo‐plastic in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Alkaline treatment of diacetate fibers and subsequent cellulase degradation
Authors: He Jianxin , Tang Yuyuan , Wang Shan‐Yuan
Published: November 2007

The work investigated the degradation behavior of cellulose acetate (CA) fibers in NaOH solutions in heterogeneous conditions and the effect of alkaline treatment on cellulase degradation of CA fibers. Weight analysis and IR spectra showed that the weight loss of CA fibers immersed in NaOH solution chiefly depended on acetylation. Alkaline treatment promoted the degradation of CA fibers in cellulase solution by reason of deacetylation, especially when the degree of substitution (DS) of CA fibers reached 0.8, cellulase degradation increased most markedly. SEM revealed a smooth surface except some thin holes in the CA fibers after immersion in NaOH solution with a lower concentration because of the formation of alkaline cellulose, and only in a higher concentration such as 5.0N, it could be observed that microfibers perpendicular to fiber axis distributed over the surfaces of the fibers. 1NMR spectra suggested that only in a lower NaOH concentration (≤0.25N), deacetylation reaction was affected by the reactivities of ester groups at position 2, 3, and 6 in anhydroglucose unit, but did not follow the theoretical trend in the three positions. Moreover, the DS for polymer molecules in CA fibers were dispersive after alkaline treatment in heterogeneous condition and the DS of the product increased during sequent cellulase degradation. This was also demonstrated by the result of IR analysis and X‐ray diffraction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effect of foaming temperature and rubber grades on properties of natural rubber foams
Authors: Ariff Z. M. , Zakaria Z. , Tay L. H. , Lee S. Y.
Published: November 2007

Foaming temperature and grade of dry natural rubber were varied to evaluate their effects on the morphology and mechanical properties of natural rubber (NR) foams. Three different grades of NR were used; namely ENR‐25, SMR‐L, and SMR‐10. NR foams from these grades were produced at three different foaming temperatures, i.e. 140, 150, and 160°C. The study was carried out using formulated compositions containing sodium bicarbonate as the chemical blowing agent and were expanded using conventional compression molding technique via a heat transfer foaming process. The NR foams were characterized with respect to their relative foam density, density of crosslinking, cell size, compression stress, and compression set. Increase in foaming temperature resulted in lower relative density and larger cell size. It was also discovered that the crosslink density slightly decrease with increasing foaming temperature. For mechanical properties, the highest foam density resulted in the highest compression stress. Compression stress at 50% strain increased with increasing foaming temperature and ENR‐25 foam has the highest compression stress among the produced foams. The results showed that the morphology, physical, and mechanical properties of the rubber foams can be controlled closely by the foaming temperature and rubber grades. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Pilot test of prenatal surveillance for birth defects in South Texas
Authors: Ethen Mary K. , Canfield Mark A. , de Forest Peter , Trevino Jorge
Published: November 2007

BACKGROUND:

The Texas Birth Defects Registry (TBDR) does not access prenatal diagnostic facilities to ascertain cases. Objectives of the study were to determine how many cases may be missing from the registry as a result, and to assess the feasibility and utility of prenatal surveillance for birth defects, through a pilot test in one region of Texas.

METHODS:

A trained abstractor reviewed medical records of all patients with abnormal ultrasound findings during 2004 in all prenatal diagnostic facilities in Texas Health Region 11 (n = 6 facilities). When birth defects were prenatally detected, demographic and diagnostic data were abstracted. Prenatal abstractions were matched to cases in the TBDR. Those that did not match to registry cases were matched to vital records to determine where and when the pregnancy ended; delivery hospital medical records were reviewed for these cases.

RESULTS:

Approximately 760 patient charts were reviewed at prenatal diagnostic facilities and 365 were abstracted. Of these, 165 (45%) matched to cases in the TBDR. Delivery medical records were located and reviewed for 177 prenatal abstractions, with 170 (47%) indicating at delivery no defects monitored by the registry. Delivery records for one (0.3%) prenatal abstraction were not found by the hospital. Date and place of delivery were unknown for 22 (6%) prenatal abstractions. Only eight additional infants and fetuses (one twin pair) eligible for the registry were identified.

CONCLUSIONS:

For Texas Health Service Region 11, it is not necessary to conduct surveillance in prenatal diagnostic facilities, and to do so would be very labor‐intensive. Birth Defects Research (Part A) 79:788–791, 2007. © 2007 Wiley‐Liss, Inc.
Secondary structure inducing potential of β‐amino acids: Torsion angle clustering facilitates comparison and analysis of the conformation during MD trajectories
Authors: Guthöhrlein E. W. , Malešević M. , Majer Z. , Sewald N.
Published: November 2007

While numerous examples of β‐peptides—exclusively composed of β‐amino acids—have been investigated during the past decade, there are only few reports on the conformational preference of a single β‐amino acid when incorporated into a cyclopeptide. The conformational bias of β‐amino acids on the secondary structure of cyclopeptides has been investigated by NMR spectroscopy in combination with distance geometry (DG) and molecular dynamics (MD) calculations using experimental constraints. The atomic coordinate RMSD criterion usually employed for clustering of conformations after DG and MD calculations does not necessarily group similar peptide conformations, as there is an insufficient correlation between atomic coordinates and torsion angles. To improve on this shortcoming and to eliminate any arbitrary decisions during this process, a torsion angle clustering procedure has been implemented. For the cyclic pentapeptides cyclo‐(‐Val‐β‐Hala‐Phe‐Leu‐Ile‐) 1 and cyclo‐(‐Ser‐Pro‐Leu‐β‐Hasn‐Asp‐) 3, the β‐amino acid is found in the central position of an extended γ‐turn (pseudo γ‐turn, Ψγ‐turn), while the β‐Hpro residue in the cyclic hexapeptide cyclo‐(‐Ser‐β‐Hpro‐Leu‐Asn‐Ile‐Asp‐) 5 preferentially occupies position i+1 of a pseudo β‐turn (Ψβ‐turn). These results further corroborate the hypothesis of β‐amino acids being reliable inducers of secondary structure in cyclic penta‐ and hexapeptides. They can be employed in the de novo design of biologically active cyclopeptides in pharmaceutical research, since the three‐dimensional presentation of pharmacophoric groups in the side chains can be tailored by incorporation of β‐amino acids in strategic sequential positions. © 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 829–839, 2007.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
The effects of translation and sex on hypnotizability testing
Authors: Cardeña Etzel , Kallio Sakari , Terhune Devin B. , Buratti Sandra , Lööf Angelica
Published: November 2007

We compared hypnotizability between two samples from different universities in Sweden. One test was administered in Swedish (University of Skövde) using a translated Swedish version of the HGSHS : A (Bergman, Trenter and Kallio, 2003). At Lund University, the original English version of the HGSHS : A (Shor and Orne, 1962) was used and participants also completed the Inventory Scale of Hypnotic Depth (ISHD; Field, 1965). The results suggest that administering the HGSHS : A in English to Swedish University students may only slightly reduce hypnotizability scores. Because the HGSHS : A was designed to be used for the initial screening of hypnotic suggestibility, for most practical purposes the original version seems a valid choice among non‐English groups fluent in English. The data also support some recent findings about females exhibiting higher objective and subjective hypnotizability scores than male volunteers. Copyright © 2007 British Society of Experimental & Clinical Hypnosis. Published by John Wiley & Sons, Ltd.
Determination of enantiomeric excess of ethyl 3,5‐dihydroxy‐6‐benzyloxy hexanoate by chiral reverse phase high performance liquid chromatography
Authors: Liu Ji‐Hua , Yu Bo‐Yang , Chen Yi‐Jun
Published: November 2007

A simple and reliable chiral HPLC method was developed for the determination of enantiomeric excess of a chiral dihydroxy intermediate for the chemoenzymatic synthesis of side chain of statin drugs. After evaluating different columns and conditions, the four stereoisomers of ethyl 3,5‐dihydroxy‐6‐benzyloxy hexanoate were well resolved by a simple gradient elution on OD‐RH column, and the enantiomeric excess of the desired 3R,5S‐enantiomer was accurately measured. This study provides a simple, rapid, accurate, and reliable method to assess the enantiomeric quality of such important intermediates. Chirality, 2007. © 2007 Wiley‐Liss, Inc.
Computation of the J‐integral for large strains
Authors: Horváth Ágnes
Published: November 2007

The phenomenon of failure by catastrophic crack propagation in structural materials poses problems of design and analysis in many fields of engineering. Cracks are present to some degree in all structures. They may exist as basic defects in the constituent materials or they may be induced in construction or during service life.

Using the finite element method, a lot of papers deal with the calculation of stress intensity factors for two‐ and three‐dimensional geometries containing cracks of different shapes under various loadings to elastic bodies. In order to increase the accuracy of the results, special elements have been used. They are described together with methods for calculating the stress intensity factors from the computed results.

At the vicinity of a crack tip, the strains are not always small, but they may also be large. In this case, the J‐integral can also be applied to characterize the cracks in elastic or elastic–plastic bodies.

This paper describes the computation of the two‐dimensional J‐integral for large strains to elastic and elastic–plastic bodies and represents some numerical examples. Copyright © 2007 John Wiley & Sons, Ltd.
Polynomial basis functions on pyramidal elements
Authors: Bluck M. J. , Walker S. P.
Published: November 2007

Pyramidal elements are necessary to effect the transition from tetrahedral to hexahedral elements, a common requirement in practical finite element applications. However, existing pyramidal transition elements suffer from degeneracy or other numerical difficulties, requiring, at the least, warnings and care in their use. This paper presents a general technique for the construction of nodal basis functions on pyramidal finite elements. General forms for basis functions of arbitrary order are presented. The basis functions so derived are fully conformal and free of degeneracy. Copyright © 2007 John Wiley & Sons, Ltd.
Two‐ and three‐dimensional growth modes of nitride layers
Authors: Pakuła K. , Baranowski J. M. , Borysiuk J.
Published: November 2007

Heteroepitaxial three dimensional (3D) and two dimensional (2D) growth modes of nitride layers on sapphire substrates are discussed. It is shown that the 3D or 2D growth mode of AlGaN layers depends predominantly on the growth conditions of the underneath low temperature (LT) nucleation layer. Commonly described in literature 3D growth mode is achieved on LT GaN or AlN nucleation layer grown relatively fast. Successive growth of secondary layer at high temperature begins from separated sites, where individual 3D crystallites are formed. Threading dislocations present in crystallites bend on their facets, which reduces the quantity of dislocations. However, slight crystallographic misorientations between crystallites lead to the creation of new dislocations during coalescence of the crystallites. As a result, edge and mix dislocations appear at similar densities of about 109 cm‐2. Modification of growth conditions of LT AlN nucleation layer, especially reduction of their growth rate, leads to drastic changes in properties of the layer. Successive growth of secondary AlGaN layer at high temperature starts evenly on whole surface retaining atomic flatness. Thus growth at high temperature occurs only by 2D mode. Therefore, it is possible to grow a very thin AlGaN layers directly on top of LT nucleation layer. Such layers contain large number (1010 cm‐2) of edge dislocations, and relatively small number (less then 108 cm‐2) of mix dislocations. It is also shown that the decisive factor determining the growth mode of AlN nucleation layer is a growth of the first few atomic layers on substrate surface. The slow growth of these few first atomic layers decide about the 2D growth mode, and the fast one about the 3D one. The model explaining this difference is presented as well. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of crystal growth process of bulk Si and nitrides – a review
Authors: Kakimoto K. , Liu L. , Miyazawa H. , Nakano S. , Kashiwagi D. , Chen X. J. , Kangawa Y.
Published: November 2007

Heat and mass transfer during crystal growth of bulk Si and nitrides by using numerical analysis was studied. A three‐dimensional analysis was carried out to investigate temperature distribution and solid‐liquid interface shape of silicon for large‐scale integrated circuits and photovoltaic silicon. The analysis enables prediction of the solid‐liquid interface shape of silicon crystals. The result shows that the interface shape became bevel like structure in the case without crystal rotation. We also carried out analysis of nitrogen transfer in gallium melt during crystal growth of gallium nitride using liquid‐phase epitaxy. The result shows that the growth rate at the center was smaller than that at the center. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A stability diagram for crystal growth from the vapor – a review
Authors: Grasza K.
Published: November 2007

Stability of the solid‐vapor interface is investigated. Surface roughening and evolution of flat faces at the growth interface is considered in terms of relation between gradient of temperature in the crystal and gradient of concentration in the vapor. Stability diagram is proposed, based on experimental data. The diagram summarizes the various forms and structures, which can be obtained using a typical system for growth from the vapor. The critical lines for constitutional supersaturation and appearance of low and high index faces were plotted. This attempt to the problem of stability of the growth interface differs from the former investigations mainly in looking for dependence between temperature field and concentration field rather than between more absolute parameters like temperature and supersaturation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Preference for fcc atom stacking observed during growth of defect‐free LJ3281 clusters
Authors: Polak W.
Published: November 2007

Growth simulations of 3‐dimensional Lennard–Jones (LJ) clusters/nuclei from the vapor phase were carried out in order to estimate the role of kinetic and energetic effects in determining the internal structure of the clusters. The simulated growth was realized from N = 3281 up to ca. 10000 atoms at two reduced growth temperatures T* = 0.3 and 0.5 and the vapor atom concentration nv = 0.002 (in reduced units of LJ system). During growth at the low temperature, clusters evolve from octahedral to an irregular shape, while at the higher one they become spherical. Statistics of newly created structural units shows a strong preference for the formation of fcc units with their number approximately 3‐4 times larger than those of the hcp units. The possible explanation of this preference is by: (1) a larger surface diffusion leading to near spherical shape of clusters, (2) an energetic effect caused by different interaction energy of two fcc or hcp layers located on the neighboring {111} planes, and (3) an entropic effect in the form of disappearance of hcp island on the close‐packed fcc layers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct melt crystal growth of isotactic polybutene‐1 trigonal phase
Authors: Yamashita Motoi , Ueno Satoru
Published: November 2007

The morphology, crystalline structure and crystal growth kinetics of melt‐crystallized thin isotactic polybutene‐1 films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. It is demonstrated that a bypass of tetragonal phase crystallization and direct melt crystal growth of the trigonal phase can be achieved via self‐seeding at atmospheric pressure using solution‐grown trigonal crystals as nuclei. Electron microscopy and optical microscopy observations show that melt‐crystallized isotactic polybutene‐1 single crystals of the trigonal phase have rounded or hexagonal morphologies around 75°C. The growth rate of trigonal crystals in the melt has been obtained by in‐situ optical microscopy. The growth rate of trigonal crystals in the melt is 1/100 and 1/1000 that of tetragonal crystals in the melt around 70 and 90°C, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Initial stages of SiC crystal growth by PVT method
Authors: Tymicki E. , Grasza K. , Diduszko R. , Bożek R. , Gała M.
Published: November 2007

Initial stages of SiC crystal growth by Physical Vapor Transport method were investigated. The following features were observed: (a) many nucleation crystallization centres appeared on the seed surface during the initial stage of the growth, (b) at the same places many separate flat faces generated on the crystallization front, (c) the number of facets was dependent on the shape of the crystallization front and decreased during growth, (d) appearance of many facets lead to decrease of structural quality of crystals due to degradation of regions where crystallization steps from independent centres met. The results revealed that the optimal crystallization front should be slightly convex, which permits the growth of crystals with single nucleation centre and evolution of single facet on the crystallization front. The subjects of study were the shape and the morphology of growth interface. Defects in the crystallization fronts and wafers cut from the crystals were studied by optical microscopy, atomic force microscopy (AFM) combined with KOH etching and X‐ray diffraction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of growth kinetics and morphology of sodium fluorosilicate ice‐analogue crystals in solutions and gels
Authors: Krasiński M. J. , Krasińska K. R. , Ulanowski Z.
Published: November 2007

The effect of growth method (solution or gel growth) and growth conditions on the morphology of ice analogue crystals (sodium fluorosilicate) has been studied. Many habits typical for atmospheric ice crystals (hexagonal columns, plates, different types of stars or dendrites) were obtained during experiments. The dependence of growth rate of basal and prism faces of columnar crystals on supersaturation was measured for crystals growing by evaporation of solvent. The experiments establish evaporation rate and growth rate ranges at which appearance of certain types of crystals is most probable. The experiments have also shown that good quality sodium fluorosilicate crystals can be obtained in TMS gel. These crystals were significantly bigger than those obtained in solution. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the crucible bottom shape on the heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth
Authors: Tavakoli M. H. , Wilke H. , Crnogorac N.
Published: November 2007

For the seeding process of oxide Czochralski crystal growth, influence of the crucible bottom shape on the heat generation, temperature and flow field of the system and the seed‐melt interface shape have been studied numerically using the finite element method. The configuration usually used in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, gas and seed crystal. At first, the volumetric distribution of heat inside the metal crucible and afterheater inducted by the RF‐coil was calculated. Using this heat generation in the crucible wall as a source the fluid flow and temperature field of the entire system as well as the seed‐melt interface shape were determined. We have considered two cases, flat and rounded crucible bottom shape. It was observed that using a crucible with a rounded bottom has several advantages such as: (i) The position of the heat generation maximum at the crucible side wall moves upwards, compared to the flat bottom shape. (ii) The location of the temperature maximum at the crucible side wall rises and as a result the temperature gradient along the melt surface increases. (iii) The streamlines of the melt flow are parallel to the crucible bottom and have a curved shape which is similar to the rounded bottom shape. These important features lead to increasing thermal convection in the system and influence the velocity field in the melt and gas domain which help preventing some serious growth problems such as spiral growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Preparation and characterization of superconducting MgB2 rods
Authors: Orlińska N. , Zaleski A. , Paszula J. M. , Wokulski Z.
Published: November 2007

Superconducting Cu/Fe/MgB2 and Steel/Cu/MgB2 rods were prepared through the ex‐situ modified PIT technique with explosive consolidation method. The phase composition, microstructural features were investigated by X‐ray diffraction and scanning electron microscope. The AC susceptibility for a core samples was measured by the AC susceptometry. Measurements of the magnetization hysteresis loops were also carried out. It is found that no impurity phase was formed in MgB2 rods. In addition, it was found that grains in both Cu/Fe/MgB2 and Steel/Cu/MgB2 rods are densely packed. The magnetic measurements show that the critical temperature of Cu/Fe/MgB2 and Steel/Cu/MgB2 rods is 37.7 K and 37.6 K, respectively. The high critical current density of 9.22 × 105 A/cm2 (4.1 K, 0.2 T) was obtained for Steel/Cu/MgB2 rod. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallization of silicon thin films by current‐induced joule heating using a tungsten overcoat
Authors: Wu Gwo‐Mei , Wu Chen‐Yen
Published: November 2007

A modified crystallization process using current‐induced joule heating under vacuum is presented. A thin layer of high temperature resistant tungsten was sputtered on the amorphous silicon as the conducting and annealing medium. The thin film thickness was measured by α‐stepper. The high current density provided effective means in crystallizing the amorphous silicon layer. The crystalline morphology was studied by scanning electron microscopy (SEM) after Secco‐etch, transmission electron microscopy (TEM), and x‐ray diffraction (XRD), under different annealing conditions. The grain size was controlled in the range of 0.1‐0.5 μm and could be increased with annealing time. No tungsten silicide was found. Some defects were formed due to electron‐migration effect near the electrodes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling the growth of nitrides in ammonia‐rich environment
Authors: Krukowski S. , Kempisty P. , Strąk P. , Nowak G. , Czernecki R. , Leszczynski M. , Suski T. , Bockowski M. , Grzegory I.
Published: November 2007

Surface properties and the principal processes at the growth of gallium nitride on GaN (0001) face in ammonia‐based are modeled using DFT (density functional theory – SIESTA code) ab initio calculations and 2‐d diffusion analysis. The GaN growth methods are: ammonia‐source MBE, MOVPE, and also HVPE. The adiabatic trajectories, calculated for hydrogen‐rich and hydrogen‐free state of the GaN(0001) surface, include the adsorption of NH3, GaCl and HCl molecules and the desorption of Ga atoms. The adsorption of ammonia and GaCl has no energy barrier. Thus, in contrast to the results concerning Plasma‐Assisted Molecular Beam Epitaxy (PA MBE), proving that the GaN(0001) surface remains in metal‐rich state, these results indicate that, in the ammonia‐rich environment, typical for HVPE and MOVP growth, the GaN(0001) surface remains in the nitrogen‐rich state. In the case of HCl adsorption, the energy barrier depends on the surface coverage, and could reach 2.0 eV. The direct desorption of single Ga atom has the energy barrier, close to 7 eV. This indicates that Ga surface diffusion (growth controlling process) length is very large, leading to strong interaction of the step kinetics and the diffusion on the terraces. This interaction leads to double–step intertwined structures both in the case of dislocation‐mediated spiral growth and in the step flow growth mode. These morphologies, proposed by the geometric arguments, are observed in the atomic force microscopy (AFM) scans of the GaN(0001) surface. Additionally we have compared the interaction energy of two hydrogen atoms obtained in the DFT SIESTA and the high precision Gaussian in coupled cluster singles, double and perturbation triples CCSD(T) approximation. Both approaches yielded virtually identical interaction energy confirming the validity of DFT analysis of ammonia‐rich growth of GaN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
TEM investigations of GaN layers grown on silicon and sintered GaN nano‐ceramic substrates
Authors: Borysiuk J. , Caban P. , Strupiński W. , Gierlotka S. , Stelmakh S. , Janik J. F.
Published: November 2007

GaN nano‐ceramics were analyzed using transmission electron microscopy (TEM), showing that these ceramics are characterized by highly disoriented grains of the linear size of 100–150 nm. These GaN ceramics were used as substrates for GaN epitaxy in standard MOVPE conditions. For the comparison, MOVPE GaN layers on silicon substrates were grown using similar conditions. It is shown that MOVPE growth of GaN layers is highly anisotropic for both cases. However, the disorientation of the highly mismatched GaN layer on silicon is different from that characterizing GaN layer deposited on the ceramic substrate. In the latter case the disorientation is much higher, and three dimensional in nature, causing creation of polycrystalline structure having large number of the dislocations. In the case of the GaN layer grown on the silicon substrate the principal disorientation is due to rotation around c‐axis, causing creation of mosaic structure of edge dislocations. Additionally, it is shown that the typical grain size in AlN nucleation layer on Si is smaller, of order of 20 nm. These two factors contribute to pronounced differences in later stage of the growth of GaN layer on the ceramic. Due to high growth anisotropy an appropriately thick GaN layer can, eventually, develop flat surfaces suitable for construction of optoelectronic and electronic structures. As shown by the TEM data, this can be achieved only at the cost of creation of the relatively large density of dislocations and stacking faults. The latter defects were not observed for the GaN growth on Si substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thick GaN layers on sapphire with various buffer layers
Authors: Korbutowicz R. , Dumiszewska E. , Prażmowska J.
Published: November 2007

Thick GaN layers deposited in HVPE system on composite substrates made on sapphire substrates in Metalorganic Vapour Phase Epitaxy (MOVPE) system have been investigated. The following substrates were used: (00.1) sapphire substrates with AlN, AlN/GaN and GaN thin layers. The crystallographic structure and the quality of the epitaxial thick GaN layers were determined. Comparison of the three types of thick layers was performed. Significant differences were observed. It was found that thick GaN deposited on the simplest MOVPE‐GaN/sapphire composite substrate has comparable structure's properties as the other, more complicated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of post treatment on the photorefractive properties of Ru‐doped lithium niobate
Authors: Chiang Chang‐Hung , Chen Jyh‐Chen , Chang Jenq‐Yang , Lu Chung‐Wei
Published: November 2007

The effect of post treatment on the photorefractive properties of Ru‐doped lithium niobate was studied. The absorption spectra examination of Ru‐doped LiNbO3 crystals with different post treatments showed that the absorption coefficient at 530 nm increased after the reduced treatment was employed and the absorption edge of the reduced crystal shifted towards the infrared band. On the contrary, the trend reversed after the oxidized treatment was employed. In addition, the photorefractive properties were investigated with the two‐beam coupling method conducted via a 532 nm solid state laser. It was found that the oxidized Ru:LiNbO3 had smaller exponential gain coefficient and diffraction efficiency because the charges in the shallow level were exchanged to the deep level. On the other hand, the reduced Ru:LiNbO3 crystals had larger exponential gain coefficient and diffraction efficiency due to the increase of the Ru3+ which existed in the shallow level. The response times of both oxidized and reduced Ru:LiNbO3 were longer than those of the as‐grown ones. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence characteristics of undoped and Eu‐doped GdCa4O(BO3)3 single crystals and nanopowders
Authors: Solarz P. , Nikl M. , Kłos A. , Lisiecki R. , Ryba‐Romanowski W. , Rzepka A. , Ganschow S. , Pajączkowska A.
Published: November 2007

Single crystals of GdCa4O(BO3)3 (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling‐down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu3+ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu2+ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol‐gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd3+ at about 312 nm, whereas this emission dramatically decreases in Eu‐doped crystals upon X‐ray excitation, as well as in Eu‐doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125‐333 nm for Eu‐doped samples leads to strong emission in red coming from the 5D0 multiplet of Eu3+, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu‐doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd3+ 6P7/2 multiplet is 2.79 ms. The Eu3+ 5D0 decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu3+ luminescence in the 160‐200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd3+–O2– charge transfer was not observed in crystal obtained by the micropulling‐down method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of Nd, Yb – yttrium oxide nanopowders obtained by sol‐gel method
Authors: Rzepka A. , Ryba‐Romanowski W. , Diduszko R. , Lipińska L. , Pajączkowska A.
Published: November 2007

Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystal growth and scintillating properties of (Pr,Si)‐doped YAlO3
Authors: Zhuravleva M. , Novoselov A. , Mihokova E. , Mares J. A. , Vedda A. , Nikl M. , Yoshikawa A.
Published: November 2007

This paper deals with Pr‐doped and Pr, Si‐codoped YAlO3 single crystal growth by the micro‐pulling‐down method and investigation of their spectroscopic and scintillating properties. The Pr3+ 5d ‐4f radioluminescence intensity is more than 10 times higher than that of Bi4Ge3O12 standard sample, but the Si‐codoping decreases it. Absorption spectra of as‐grown and air‐annealed Si,Pr‐codoped YAlO3 samples show along with an onset of 4f ‐5d transition round 230 nm the induced absorption band at 400 nm which possibly related to a hole center absorption (Pr4+ or O‐). Thermoluminescence measurements above the room temperature were performed in order to monitor deep electron traps. Strong concentration dependence of thermoluminescence was observed for Pr:YAlO3 glow curves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of pure and Co2+‐doped Li2B4O7 single crystals
Authors: Piwowarska D. , Kaczmarek S. , Berkowski M.
Published: November 2007

Pure and Co‐doped Li2B4O7 (LBO) single crystals were grown by the Czochralski method. Starting concentrations of Co2O3 in the melt were: 0.5, 0.85 and 1 mol% relative to Li2CO3. Technological factors affecting the quality of both crystals were discussed. Optical absorption and EPR spectra were analyzed to define the oxidation states and lattice sites of cobalt ions. It was shown that Co2+ ions enter LBO crystal at octahedral Li+ site positions. Low‐temperature EPR measurements revealed that two types of Co2+ complexes can be distinguished in the Li2B4O7:Co crystals. Additional absorption calculated for γ‐irradiated crystals showed Vk type defects suggesting the creation of cation vacancies during growth. The concentration of the defects decreases with an increase of intentional Co concentration. Introduction of cobalt ions to LBO crystal is limited probably by the formation of cobalt ion pairs or by the entrance of cobalt as Co+. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoelectric and photothermal investigations of Zn1‐x‐yBexMnySe solid solutions
Authors: Firszt F. , Strzałkowski K. , Zakrzewski A. J. , Łęgowski S. , Męczyńska H. , Marasek A.
Published: November 2007

Zn1‐x‐yBexMnySe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence, photoelectric and photothermal properties of this material were investigated. Interpretation of the piezoelectrically detected photoacoustic spectra was performed using Jackson and Amer theory. From the spectral dependence of the amplitude and phase of photoacoustic signal as well as from photoluminescence spectra the variation of energy gap with composition was determined. The values of thermal diffusivity were derived from the dependence of photoacoustic signal on modulation frequency of the laser radiation illuminating the sample. The photoluminescence‐excitation spectra and photoconductivity spectra were measured. The origin of luminescence in Zn1‐x‐yBexMnySe was discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observation of individual dislocations in 6H and 4H SiC by means of back‐reflection methods of X‐ray diffraction topography
Authors: Wierzchowski W. , Wieteska K. , Balcer T. , Malinowska A. , Graeff W. , Hofman W.
Published: November 2007

SiC crystals of high structural perfection were investigated with several methods of X‐ray diffraction topography in Bragg‐case geometry. The methods included section and projection synchrotron white beam topography and monochromatic beam topography. The investigated 6H and 4H samples contained in large regions dislocations of density not exceeding 103 cm‐2. Most of them cannot be interpreted as hollow core dislocations (micro‐ or nano‐pipes). The concentration of the latter was lower than 102 cm‐2. The present investigation confirmed the possibility of revealing dislocations with all used methods. The quality of presently obtained Bragg‐case multi‐crystal and section images of dislocation enabled analysis based on comparison with numerically simulated images. The analysis confirmed the domination of screw‐type dislocations in the investigated crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic properties of zinc tris(thiourea) sulphate in a wide temperature range studied by Brillouin spectroscopy
Authors: Mielcarek S. , Trzaskowska A. , Mroz B. , Komorowski K.
Published: November 2007

The elastic properties of the zinc tris (thiourea) sulphate crystal were studied by Brillouin spectroscopy in the range 80 – 300 K. The measurements were made on single crystals obtained by the isothermal method. The temperature dependences of the Brillouin shift were determined for the crystal in the principal directions and in a few mixed directions on a tandem type spectrometer. The results revealed anomalies in the bulk wave propagation rate and in a few elastic constants at about 138 K. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)