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Structural Properties (structural + property)
Selected AbstractsOptical, Magnetic and Structural Properties of the Spin-Crossover Complex [Fe(btr)2(NCS)2]·H2O in the Light-Induced and Thermally Quenched Metastable StatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2007Vincent Legrand Abstract [Fe(btr)2(NCS)2]·H2O [btr = 4,4,-bis(1,2,4-triazole)] is thearchetype of highly cooperative and low-dimensional spin-crossover complexes, which exhibit low-spin (LS) to high-spin (HS) light-induced conversion at very low temperature. The structural reorganizations related to the light-induced and thermally induced LS,HS transitions were characterized by single-crystal X-ray diffraction below the relaxation temperature (T = 15 K < TLIESST) and at 130 K within the thermal hysteresis loop. We show that the LIESST and thermal spin transitions lead to the same structural variations, namely an elongation of the Fe,N bonds by 0.18 Å (Fe,NNCS) and 0.20 Å (Fe,Nbtr), on going from LS to HS, together with a reorientation of the NCS group by nearly 13°. The atomic displacement amplitudes, derived from the crystal structures, indicate lattice vibration modes of larger amplitudes and correlatively lower vibration frequencies in the HS state. The deformation of the crystal lattice as a function of temperature and laser excitation was quantitatively analyzed in terms of the HS and LS thermal-expansion (,HS and ,LS) and spin-transition spontaneous-strain (,) tensors. The eigendirections and eigenvalues of the , and , tensors correlate well with the weak and strong interactions in the solid and are responsible for the high cooperativity and low-dimensional behaviour. Magnetic and spectroscopic measurements were performed in all the different spin states and related to the structural findings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] 3,4-Dihydro-3H -pyrrol-2-imines as Conformationally Restrained 1,3-Diazabutadienes: Synthesis, Structural Properties and Protonation,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2009Simon Janich Abstract 5-Aryl-3,3,4,4-tetramethyl-3,4-dihydro-3H -pyrrol-2-imines,conformationally restrained 1,3-diazabuta-1,3-diene derivatives, were easily prepared by treating aryllithium species with 2,2,3,3-tetramethylsuccinonitrile (1). Trapping the reaction intermediate with chlorotrimethylsilane gave N -silylated compounds 2a,e, whereas aqueous workup gave N-H derivatives 3a,b. Pyrenyl-substituted compound 3b was characterised by X-ray diffraction studies, revealing the presence of both intermolecular aromatic face-to-face contacts and the formation of homodimers by twofold H-bonding. N -Silylated derivatives 2a,d were used successfully as nucleophilic components in palladium-catalysed C,N bond-forming reactions to obtain N -arylated compounds 5b,h,j,k,m and 7a,d. The UV spectra of compounds 5 and 7 exhibit long wavelength absorptions up to 462 nm for 7d, thus indicating extended ,,,* conjugation. Dihydropyrrolimine-based compounds with larger conjugated aryl substituents in the 5-position react with Brønsted and Lewis acids displaying a significant colour change that could be used to estimate the pKb of 3a to a value of ,4.5. Derivatives 2c,e and 3a,b, which are not N -arylated, are fluorescent with a Stokes shift of 107 nm (6034 cm,1) for 3a. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis and Structural Properties of New Oligodeoxynucleotide Analogues Containing a 2,,5,-Internucleotidic Squaryldiamide Linkage Capable of Formation of a Watson,Crick Base Pair with Adenine and a Wobble Base Pair with Guanine at the 3,-Downstream Junction SiteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004Kousuke Sato Abstract A TpT dimer analogue (U2,sq5,T), in which the 3,-5, phosphodiester linkage was replaced by a 2,-5, squaryldiamide linkage and the 5,-upstream T was replaced by a 3,-deoxyuridine, was synthesized in almost quantitative yield from diethyl squarate. This new dimer structural motif was designed to eliminate the squaryldiamide skeleton-induced overall strain in T3,sq5,T, previously incorporated into DNA fragments as a new TpT mimic, through the change in the connection mode from the 3,-5, linkage to a 2,-5, linkage. Spectral analyses of U2,sq5,T suggest that the overall structure of this dimer mimic is basically similar to that of TpT. A DNA 10mer 5,-d(CGCAU2,sq5,TAGCC)-3, incorporating this dimer was synthesized. From the CD analysis, it turned out that the overall structure of a DNA duplex of 5,-d(CGCAU2,sq5,TAGCC)-3,/3,-d(GCGTAATCGG)-5, is closer to that of the unmodified duplex than the DNA duplex of 5,-d(CGCAT3,sq5,TAGCC)-3,/3,-d(GCGTAATCGG)-5,. Interestingly, extensive Tm experiments suggest that d(CGCAU2,sq5,TAGCC)-3, exhibits intriguing inherent hybridization affinity not only for the completely complementary oligodeoxynucleotide 3,-d(GCGAATCGG)-5,, but also for 3,-d(GCGTAGTCGG)-5,, with a mismatched dG. The unique property of the 3,-downstream dT moiety of U2,sq5,T , the ability to recognize both dA and dG , was also supported by more detailed computational analysis of U2,sq5,T and TpT. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Evolution of Electrical, Chemical, and Structural Properties of Transparent and Conducting Chemically Derived Graphene Thin FilmsADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Cecilia Mattevi Abstract A detailed description of the electronic properties, chemical state, and structure of uniform single and few-layered graphene oxide (GO) thin films at different stages of reduction is reported. The residual oxygen content and structure of GO are monitored and these chemical and structural characteristics are correlated to electronic properties of the thin films at various stages of reduction. It is found that the electrical characteristics of reduced GO do not approach those of intrinsic graphene obtained by mechanical cleaving because the material remains significantly oxidized. The residual oxygen forms sp3 bonds with carbon atoms in the basal plane such that the carbon sp2 bonding fraction in fully reduced GO is ,0.80. The minority sp3 bonds disrupt the transport of carriers delocalized in the sp2 network, limiting the mobility, and conductivity of reduced GO thin films. Extrapolation of electrical conductivity data as a function of oxygen content reveals that complete removal of oxygen should lead to properties that are comparable to graphene. [source] Polyaniline Entrapped in Silver: Structural Properties and Electrical ConductivityADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Guy Nesher Abstract By employing the new methodology of entrapment of organic molecules within metals, we demonstrate the ability to modify the conductivity of a metal by suitable polymer entrapment. Specifically, polyaniline (PANI) in two molecular weights was entrapped in silver at different concentrations and a comprehensive comparison was preformed for a range of the composite properties, characterized by XRD, SEM, BET, TGA, and density measurements. Pressed films were utilized to measure the electrical conductivity of the composites in order to study the PANI-silver interactions at the molecular level and to establish a correlation between the microscopic morphology and the film conduction. Such correlations have been identified, and are interpreted. This work extends the functional applications of the new metallic composites and offers insight on the polymer-metal molecular level interactions. [source] A Randomized School-Based Jumping Intervention Confers Site and Maturity-Specific Benefits on Bone Structural Properties in Girls: A Hip Structural Analysis Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 3 2002M. A. Petit Abstract We compared 7-month changes in bone structural properties in pre- and early-pubertal girls randomized to exercise intervention (10-minute, 3 times per week, jumping program) or control groups. Girls were classified as prepubertal (PRE; Tanner breast stage 1; n = 43 for intervention [I] and n = 25 for control [C]) or early-pubertal (EARLY; Tanner stages 2 and 3; n = 43 for I and n = 63 for C). Mean ± SD age was 10.0 ± 0.6 and 10.5 ± 0.6 for the PRE and EARLY groups, respectively. Proximal femur scans were analyzed using a hip structural analysis (HSA) program to assess bone mineral density (BMD), subperiosteal width, and cross-sectional area and to estimate cortical thickness, endosteal diameter, and section modulus at the femoral neck (FN), intertrochanter (IT), and femoral shaft (FS) regions. There were no differences between intervention and control groups for baseline height, weight, calcium intake, or physical activity or for change over 7 months (p > 0.05). We used analysis of covariance (ANCOVA) to examine group differences in changes of bone structure, adjusting for baseline weight, height change, Tanner breast stage, and physical activity. There were no differences in change for bone structure in the PRE girls. The more mature girls (EARLY) in the intervention group showed significantly greater gains in FN (+2.6%, p = 0.03) and IT (+1.7%, p = 0.02) BMD. Underpinning these changes were increased bone cross-sectional area and reduced endosteal expansion. Changes in subperiosteal dimensions did not differ. Structural changes improved section modulus (bending strength) at the FN (+4.0%, p = 0.04), but not at the IT region. There were no differences at the primarily cortical FS. These data provide insight into geometric changes that underpin exercise-associated gain in bone strength in early-pubertal girls. [source] Structural Properties of Inertia Matrix and Gravity Vector of Dynamics of Rigid ManipulatorsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2002ba Ignacy In this paper, with the use of Euler-Lagrange formalism, it has been proven which joint variables can influence entries of the inertia matrix and the gravity vector of dynamics of a manipulator relative to the kinematic structure of the manipulator. Some formulas, alternative to well-known ones, are presented that allow us to compute the inertia matrix and the gravity vector without using a trace operator. These formulas are computationally inexpensive and provide an inspiration for interesting interpretations. Complexity indices are defined that are able to evaluate the complexity of dynamics of manipulators based on their kinematics. A key role of the accumulated pseudoinertia matrix of the manipulator has been shown. © 2002 Wiley Periodicals, Inc. [source] Contribution of the Starch, Protein, and Lipid Fractions to the Physical, Thermal, and Structural Properties of Amaranth (Amaranthus caudatus) Flour FilmsJOURNAL OF FOOD SCIENCE, Issue 5 2007D. Tapia-Blácido ABSTRACT:, Amaranth protein,lipid (PL) and protein (P) films were elaborated and compared with amaranth flour films in order to determine the contribution of the interactions between the biopolymer (starch and protein) and the lipids to the film properties. The films were made by the casting method, using the same glycerol concentration (0.9 g glycerol/100 g solution). A separation of the lipid fraction in the PL films and a polymorphic transformation of the corresponding fatty acids were observed by differential scanning calorimetry (DSC) and verified by an analysis of the microstructure by scanning electron microscopy (SEM). The flour films showed no separation of the lipid fraction, evidence that the lipids were strongly associated with the proteins and homogenously distributed throughout the starch network, contributing to the good mechanical properties when compared to the PL films and to the excellent barrier properties when compared to both the PL and P films. The protein-protein interactions also contributed to the mechanical properties of the flour films. The presence of proteins and lipids in the flour films had an important effect on film solubility, and also on the color and opacity of the films. This study showed that the flour film properties depended on the interactions formed by their polymers (starches and proteins) and by the lipid, on the distribution of these interactions within the film matrix and on the concentrations of each component in the film. [source] Dielectric and Structural Properties of Layer-Structured Sr1,xCaxBi2Nb2O9JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Shiming Huang Sr1,xCaxBi2Nb2O9 (x=0, 0.2, 0.4, 0.6, 0.8 and 1) ceramics were prepared by a conventional solid-state reaction method. Their dielectric and structural properties were investigated. X-ray diffraction analysis indicated that single-phase layered perovskites were obtained. For Ca-substituted specimens, a dielectric relaxation peak is observed in the temperature range of 30°,150°C, and there is a broader para-ferroelectric phase transition peak. The temperature of the maximum dielectric constant Tm increases linearly with increasing Ca content. Raman spectra indicate that a small amount of Ca2+ is incorporated into Bi sites in the Bi2O2 layers, and an increase in the degree of distortion of NbO6 octahedra for Ca-substituted specimens should be one of the reasons for the increase in Tm compared with SrBi2Nb2O9. [source] Thermodynamic and Structural Properties of Sodium Lithium Niobate Solid SolutionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Irina Pozdnyakova Thermodynamics of the Na1,xLixNbO3 system is investigated by high-temperature drop-solution calorimetry in molten 3Na2O,4MoO3 solvent at 973 K. Standard molar enthalpies of formation are derived. The estimated heats of transition between hypothetical and stable structures, lithium niobate and perovskite for NaNbO3 and vice versa for LiNbO3 are ,6 kJ/mol and ,10 kJ/mol, respectively. X-ray diffraction studies at room temperature showed for 0 ,x, 0.14 there are three phases based on different ordering of the perovskite type lattice: orthorhombic with a quadrupled reduced perovskite cell at 0 ,x, 0.02, orthorhombic with a doubled reduced perovskite cell at 0.015 ,x, 0.14, and rhombohedral at 0.08 ,x, 0.13. There are two two-phase (morphotropic) regions with coexistence of the two orthorhombic phases at 0.015 ,x, 0.02 and with the second orthorhombic phase coexisting with the rhombohedral phase at 0.08 ,x, 0.13. A reproducible anomaly in specific heat at ,600 K, not reported previously, has been observed in pure NaNbO3. Heat-capacity measurements confirm a phase transition at 553 K for 0.07 ,x, 0.09. With increasing lithium concentration, a gradual disappearance of high-temperature phase transitions associated with tilting of oxygen octahedra has been observed. [source] ChemInform Abstract: Crystal Growth, Structural Properties, and Photophysical Characterization of Ln4Na2K2M2O13 (M; Nb, Ta; Ln: Nd, Sm, Eu, Gd).CHEMINFORM, Issue 46 2009Thomas-C. Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Structural Properties of Multiferroic BiFeO3 under Hydrostatic Pressure.CHEMINFORM, Issue 44 2009Alexei A. Belik Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Probing the Electronic and Structural Properties of the Niobium Trimer Cluster and Its Mono- and Dioxides: Nb3On - and Nb3On (n = 0,2)CHEMINFORM, Issue 29 2009Hua-Jin Zhai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Plasmonic Cu2-xS Nanocrystals: Optical and Structural Properties of Copper-Deficient Copper(I) Sulfides.CHEMINFORM, Issue 28 2009Yixin Zhao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Optical and Structural Properties of a Eu(II)-Doped Silicoaluminate with Channel Structure and Partial Site Occupation.CHEMINFORM, Issue 8 2008Andreas Rief Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Dependence of Activity and Stability of Germanium Nitride Powder for Photocatalytic Overall Water Splitting on Structural Properties.CHEMINFORM, Issue 42 2007Kazuhiko Maeda Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A First-Principles Study of the Electronic and Structural Properties of ,-TaON.CHEMINFORM, Issue 27 2007Holger Wolff Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] ChemInform Abstract: Ni(II)-Doped CsCdBrCl2: Variation of Spectral and Structural Properties via Mixed-Halide Coordination.CHEMINFORM, Issue 15 2001S. R. Luethi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Syntheses and Structural Properties of 1,8-Diazacyclotetradeca-3,5,10,12-tetraynes.CHEMINFORM, Issue 2 2001Kirstin Hoevermann Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Solvent Effect on Relative Gibbs Free Energy and Structural Property of Eu3* to Yb3+ Ion Mutation: A Monte Carlo Simulation Study.CHEMINFORM, Issue 10 2002Hag-Sung Kim Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Output regulation of discrete-time linear plants subject to state and input constraintsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 8 2003Guoyong Shi Abstract Discrete-time output regulation of linear systems with state and/or input constraints on magnitude is considered. Structural properties of linear plants are identified under which the so-called constrained semi-global and global output regulation problems are solvable. As in the case of continuous-time systems, an important aspect of our development is a taxonomy of constraints showing a clear relationship between the constraint types and the output regulation results. Solvability conditions are developed for semi-global and global output regulation problems. Appropriate regulators are constructed for problems that are solvable. Copyright © 2003 John Wiley & Sons, Ltd. [source] Structural properties of orexins for activation of their receptorsJOURNAL OF PEPTIDE SCIENCE, Issue 4 2006Manja Lang Abstract The closely related neuropeptides orexin A and orexin B mediate their actions, including the regulation of sleep and appetite, by the activation of the orexin 1 and 2 receptors. To elucidate the structural prerequisites for receptor activation and subtype selectivity, we performed multiple amino acid substitutions within the sequence of orexin A and human orexin B-(6-28)-peptide and analyzed their solution structures by CD spectroscopy and their activity at both receptors in Ca2+ mobilization assays. For orexin A, we showed that the basic amino acids within the segment of residues 6,14 were important for the activation of both receptors. Furthermore, we showed that the restriction via disulfide bonds is not required to maintain the active structure of orexin A. The kink region of h orexin B has been shown to be important for Ox2R selectivity, which is not mediated by the restriction of the turn structure. Additionally, we showed that no particular secondary structure is required for receptor subtype selectivity. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. [source] Structural properties of network revenue management models: An economic perspectiveNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2006Alec Morton Abstract Many revenue management problems have a network aspect. In this paper, we argue that a network can be thought of as a system of substitutable and complementary products, and the value of a revenue management model should be supermodular or submodular in the availability of two resources as the resources are economic substitutes or complements. We demonstrate that this is true in the case of a two-resource dynamic stochastic revenue management model and show how this applies for multi-resource deterministic static revenue management models. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source] Optimal switchover times between two activities utilizing the same resourceNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2002M. Karakul Abstract The "gold-mining" decision problem is concerned with the efficient utilization of a delicate mining equipment working in a number of different mines. Richard Bellman was the first to consider this type of a problem. The solution found by Bellman for the finite-horizon, continuous-time version of the problem with two mines is not overly realistic since he assumed that fractional parts of the same mining equipment could be used in different mines and this fraction could change instantaneously. In this paper, we provide some extensions to this model in order to produce more operational and realistic solutions. Our first model is concerned with developing an operational policy where the equipment may be switched from one mine to the other at most once during a finite horizon. In the next extension we incorporate a cost component in the objective function and assume that the horizon length is not fixed but it is the second decision variable. Structural properties of the optimal solutions are obtained using nonlinear programming. Each model and its solution is illustrated with a numerical example. The models developed here may have potential applications in other areas including production of items requiring the same machine or choosing a sequence of activities requiring the same resource. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 186,203, 2002; DOI 10.1002/nav.10008 [source] Structural properties of ZnO polymorphs [phys. stat. sol. (b) 244, No. 5, 1538,1543 (2007)]PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007Jan Wróbel Abstract The corrected values for the band gaps Eg, width of valence p-band Wp, and d-band position Ed, calculated within the LDA+U approximation for ZnO polymorphs are provided. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatially resolved cathodoluminescence study on AlGaN layer fabricated by air-bridged lateral epitaxial growthPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Akihiko Ishibashi Abstract Structural properties of AlGaN layer on the GaN seed layer fabricated by air-bridged lateral epitaxial growth (ABLEG) have been studied by spatially resolved cathodoluminescence (CL) microscopy. The cross-sectional spatially resolved CL images of the ABLEG-AlGaN layer reveal that there are roughly three regions which have different main CL peaks. This result suggests that there are roughly three regions with the different Al contents. Before coalescence of the overgrown AlGaN wings, there are two regions of Al content, such as about 6.5, 10.6%. On the other hand, after coalescence of the wings, the Al content of the AlGaN layer becomes uniform (Al content = 8.9%). These results suggest that the facet growth of the overgrown AlGaN wings causes the modulation of Al content in the ABLEG-AlGaN layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and properties of In-rich InGaN films grown on (0001) sapphire by RF-MBEPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004M. Kurouchi Abstract We have performed detailed investigations of the optical properties of strain-free In-rich InxGa1,xN (0.61 , x , 1.0) films that were grown directly on (0001) sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy. In-composition dependence of photoluminescence peak energy for the InxGa1,xN films, measured at room temperature, exhibited a monotonic and smooth decrease with the increase in the In-composition, approaching to 0.66 eV of a strain-free InN film that was also grown directly on the sapphire substrate. The energy bowing parameter, b was determined to be 1.8 eV using these strain-free InxGa1,xN films. Structural properties of these films are also investigated in detail. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural properties of (Ga,Mn)Sb thin films on GaAs(111)A substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009J. Bak-Misiuk Abstract GaSb/GaAs(111)A layers with embedded Mn(Ga)Sb clusters have been grown by molecular beam epitaxy method at the substrate temperature of 450 °C. The results of structural characterization of (Ga,Mn)Sb with Mn concentration up to 8% are presented. Almost all Mn atoms introduced into the GaSb layers form hexagonal Mn(Ga)Sb clusters. Large hexagonal clusters with various shape and dimensions were detected by scanning electron microscopy. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural properties and mechanical behavior of injection molded composites of polypropylene and sisal fiberPOLYMER COMPOSITES, Issue 3 2002X. L. Xie Composites based on isotactic polypropylene (PP) and sisal fiber (SF) were prepared by melt mixing and injection molding. The melt mixing characteristics, thermal properties, morphology, crystalline structure, and mechanical behavior of the PP/SF composites were systematically investigated. The results show that the PP/SF composites can be melt mixed and injection molded under similar conditions as the PP homo-polymer. For the composites with low sisal fiber content, the fibers act as sites for the nucleation of PP spherulites, and accelerate the crystallization rate and enhance the degree of crystallinity of PP. On the other hand, when the sisal fiber content is high, the fibers hinder the molecular chain motion of PP, and retard the crystallization. The inclusion of sisal fiber induces the formation of ,-form PP crystals in the PP/SF composites and produces little change in the inter-planar spacing corresponding to the various diffraction peaks of PP. The apparent crystal size as indicated by the several diffraction peaks such as L(110),, L(040),, L(130), and L(300), of the , and ,-form crystals tend to increase in the PP/SF composites considerably. These results lead to the increase in the melting temperature of PP. Moreover, the stiffness of the PP/SF composites is improved by the addition of sisal fibers, but their tensile strength decreases because of the poor interfacial bonding. The PP/SF composites are toughened by the sisal fibers due to the formation of ,-form PP crystals and the pull-out of sisal fibers from the PP matrix, both factors retard crack growth. [source] Structural properties of trimers and tetramers of ribonuclease APROTEIN SCIENCE, Issue 10 2001Arianna Nenci Abstract Ribonuclease A aggregates (dimers, trimers, tetramers, pentamers) can be obtained by lyophilization from 40% acetic acid solutions. Each aggregate forms two conformational isomers distinguishable by different basic net charge. The crystal structure of the two dimers has recently been determined; the structure of the higher oligomers is unknown. The results of the study of the two trimeric and tetrameric conformers can be summarized as follows: (1) RNase A trimers and tetramers form by a 3D domain-swapping mechanism. N-terminal and C-terminal types of domain swapping could coexist; (2) the secondary structures of the trimeric and tetrameric conformers do not show significant differences if compared with the secondary structure of monomeric RNase A or its two dimers; (3) a different exposure of tyrosine residues indicates that in the aggregates they have different microenvironments; (4) the two trimeric and tetrameric conformers show different susceptibility to digestion by subtilisin; (5) dimers, trimers, and tetramers of RNase A show unwinding activity on double-helical poly(dA-dT) , poly(dA-dT), that increases as a function of the size of the oligomers; (6) the less basic conformers are more stable than the more basic ones, and a low concentration in solution of trimers and tetramers favors their stability, which is definitely increased by the interaction of the aggregates with poly(dA-dT) , poly(dA-dT); (7) the products of thermal dissociation of the two trimers indicate that their structures co ld be remarkably different. The dissociation products of the two tetramers allow the proposal of two models for their putative structures. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||