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1

Single crystal silicon as a low-temperature structural material  

Microsoft Academic Search

In neutron scattering applications, it is frequently desirable to construct a sample container from a material that is strong but has very little neutron absorption of scattering. Single crystal silicon is very good by these criteria but it is difficult to work with because of its brittleness. A technique for gluing silicon was developed that yields high strength joints at

P. R. Roach

1984-01-01

2

BAND STRUCTURES AND ABNORMAL BEHAVIOR OF ONE DIMENSIONAL PHOTONIC CRYSTAL CONTAINING NEGATIVE INDEX MATERIALS  

Microsoft Academic Search

AbstractWe have studied the optical properties,band structures and group velocities,of one dimensional photonic crystal (1-D PC) containing negative index materials using translational matrix method (TMM). The 1-D PC containing negative index materials is a periodic arrangement of positive index material (PIM) and negative index material (NIM). The observed group velocity of such structure is larger than the speed of light

Girijesh N. Pandey; Khem B. Thapa; Sanjeev Kumar Srivastava; Sant Prasad Ojha

2008-01-01

3

Exploring Materials: Liquid Crystals  

NSDL National Science Digital Library

In this activity, learners discover that the way a material behaves on the macroscale is affected by its structure on the nanoscale. Learners investigate the properties of a heat sensitive liquid crystal and make their own liquid crystal sensor to take home. This is a fun and engaging activity, especially since liquid crystals are used in many consumer products, including cell phone displays, laptop computer screens, strip thermometers, and even "mood" rings! SAFETY: learners must be supervised when doing this activity. They must wear safety glasses to protect their eyes. Before doing this activity, read through the Material Safety Data Sheets.

Network, Nanoscale I.; Sciencenter

2010-01-01

4

PYROGRAPHITE-A MATERIAL WITH ORIENTATED CRYSTAL STRUCTURE FOR USE IN REACTOR CONSTRUCTION  

Microsoft Academic Search

A material with marked anisotropic properties due to its laminated ; crystal structure is obtained by precipitating graphite from the gaseous phase ; onto a carrier which can be removed after having been used as a mold. Thermal ; and electric conductivity perpendicular to the lamination are l000 times less ; than parallel to it. Pyrographite withstands the erosive effect

Solow

1960-01-01

5

Theoretical Studies on the Electronic Structures and Properties of Complex Ceramic Crystals and Novel Materials  

SciTech Connect

This project is a continuation of a long program supported by the Office of Basic Energy Science in the Office of Science of DOE for many years. The final three-year continuation started on November 1, 2005 with additional 1 year extension to October 30, 2009. The project was then granted a two-year No Cost Extension which officially ended on October 30, 2011. This report covers the activities within this six year period with emphasis on the work completed within the last 3 years. A total of 44 papers with acknowledgement to this grant were published or submitted. The overall objectives of this project are as follows. These objectives have been evolved over the six year period: (1) To use the state-of-the-art computational methods to investigate the electronic structures of complex ceramics and other novel crystals. (2) To further investigate the defects, surfaces/interfaces and microstructures in complex materials using large scale modeling. (3) To extend the study on ceramic materials to more complex bioceramic crystals. (4) To initiate the study on soft condensed matters including water and biomolecules. (5) To focus on the spectroscopic studies of different materials especially on the ELNES and XANES spectral calculations and their applications related to experimental techniques. (6) To develop and refine computational methods to be effectively executed on DOE supercomputers. (7) To evaluate mechanical properties of different crystals and those containing defects and relate them to the fundamental electronic structures. (8) To promote and publicize the first-principles OLCAO method developed by the PI (under DOE support for many years) for applications to large complex material systems. (9) To train a new generation of graduate students and postdoctoral fellows in modern computational materials science and condensed matter physics. (10) To establish effective international and domestic collaborations with both experimentalists and theorists in materials research. Because of the large amount of work accomplished, a diverse class of materials covered and the desire for an easier reporting process, this report will list six categories (A to F) of major accomplishments and findings under the following headings with references to the published papers under DOE support. These six categories obviously have heavy overlaps. A complete list of published papers follows the brief description on each category. Each paper also indicates to which of the six categories the main accomplishment it belongs to. A. Electronic structure of complex and novel crystals B. Impurities, surfaces, interfaces and microstructures in ceramics C. Structures and properties of complex bioceramics D. Soft condensed matters E. Spectroscopic characterizations, XANES and ELNES spectroscopy F. Large-scale simulations

Ching, Wai-Yim

2012-01-14

6

Colloidal crystals as templates for porous materials  

Microsoft Academic Search

Close-packed colloidal crystals are promising precursors for novel materials, but only after appropriate methods are developed to fix their structure. A wide range of advanced materials has recently been synthesized by replicating the structure of colloidal crystals into durable solid matrices. Such materials with structured pores have promise as photonic crystals, catalysts, and membranes, and in a variety of other

Orlin D. Velev; Abraham M. Lenhoff

2000-01-01

7

Crystal Structure Refinements of Rhombohedral Symmetry Materials Containing Boron-Rich Icosahedra.  

National Technical Information Service (NTIS)

The crystal structures of several icosahedral boron-containing compounds have been refined using MoK alpha intensity data. Preparation of crystals differs from previous procedures, with boron carbide grown from molten copper and boron arsenide by arsenic ...

B. Morosin R. S. Feigelson T. L. Aselage

1987-01-01

8

Prediction and Design of Materials from Crystal Structures to Nanocrystal Morphology and Assembly  

NASA Astrophysics Data System (ADS)

Predictions of structure formation by computational methods have the potential to accelerate materials discovery and design. Here we present two computational approaches for the prediction of crystal structures and the morphology of nanoparticles. Many materials properties are controlled by composition and crystal structure. We show that evolutionary algorithms coupled to ab-initio relaxations can accurately predict the crystal structure and composition of compounds without any prior information about the system. We will discuss results for various systems including the prediction of unexpected quasi-1D and 2D electronic structures in Li-Be compounds under pressure [1] and of the crystal structure of the superconducting high-pressure phase of Eu [2]. The self-assembly of nanocrystals into mesoscale superlattices provides a path to the design of materials with tunable electronic, physical and chemical properties for various applications. The self-assembly is controlled by the nanocrystal shape and by ligand-mediated interactions between them. To understand this, it is necessary to know the effect of the ligands on the surface energies (which tune the nanocrystal shape), as well as the relative coverage of the different facets (which control the interactions). Density functional calculations for the binding energy of oleic acid-based ligands on PbSe nanocrystals determine the surface energies as a function of ligand coverage. The Wulff construction predicts the thermodynamic equilibrium shape of the PbSe nanocrystals as a function of the ligand coverage. We show that the different ligand binding energies on the 100 and 111 facets results in different ligand coverages on the facets and predict a transition in the equilibrium shape from octahedral to cubic when increasing the ligand concentration during synthesis. Our results furthermore suggest that the experimentally observed transformation of the nanocrystal superlattice structure from fcc to bcc is caused by the preferential detachment of ligands from particular facets, leading to anisotropic ligand coverage [3]. [4pt] [1] J. Feng, R. G. Hennig, N. W. Ashcroft and Roald Hoffmann. Nature 451, 445 (2008). [0pt] [2] W. Bi, Y. Meng, R. S. Kumar, A. L. Cornelius, W. W. Tipton, R. G. Hennig, Y. Zhang, C. Chen, and J. S. Schilling. Phys. Rev. B 83, 104106 (2011). [0pt] [3] J. J. Choi, C. R. Bealing, K. Bian, K. J. Hughes, W. Zhang, D.-M. Smilgies, R. G. Hennig, James R. Engstrom, and Tobias Hanrath. J. Am. Chem. Soc. 133, 3131 (2011).

Hennig, Richard

2012-02-01

9

Pattern information extraction from crystal structures  

Microsoft Academic Search

Abstract Determining the crystal structure parameters of a material is an important issue in crystallography and material science. Knowing,the crystal structure parameters helps in understanding the physical behavior of material. It can be difficult to obtain crystal parameters for complex structures, particularly those materials that show local symmetry,as well as global symmetry. This work provides a tool that extracts crystal

Erhan Okuyan; Ugur Gdkbay; Oguz Glseren

2007-01-01

10

Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields  

SciTech Connect

Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs.

Brandow, B.H.

1985-01-01

11

Structuring of material parameters in lithium niobate crystals with low-mass, high-energy ion radiation  

NASA Astrophysics Data System (ADS)

Ferroelectric lithium niobate crystals offer a great potential for applications in modern optics. To provide powerful optical components, tailoring of key material parameters, especially of the refractive index n and the ferroelectric domain landscape, is required. Irradiation of lithium niobate crystals with accelerated ions causes strong structured modifications in the material. The effects induced by low-mass, high-energy ions (such as 3He with 41 MeV, which are not implanted, but transmit through the entire crystal volume) are reviewed. Irradiation yields large changes of the refractive index ?n, improved domain engineering capability within the material along the ion track, and waveguiding structures. The periodic modification of ?n as well as the formation of periodically poled lithium niobate (PPLN) (supported by radiation damage) is described. Two-step knock-on displacement processes, 3He?Nb and 3He?O causing thermal spikes, are identified as origin for the material modifications.

Peithmann, K.; Eversheim, P.-D.; Goetze, J.; Haaks, M.; Hattermann, H.; Haubrich, S.; Hinterberger, F.; Jentjens, L.; Mader, W.; Raeth, N. L.; Schmid, H.; Zamani-Meymian, M.-R.; Maier, K.

2011-10-01

12

Nondestructive optical testing of the materials surface structure based on liquid crystals  

NASA Astrophysics Data System (ADS)

Thin layers of nematic liquid crystals (NLCs) may be used as recording media for visualizing structural and microrelief defects, distribution of low power physical fields and modifications of the surface. NLCs are more sensitive in comparison with cholesteric and smectic LCs having super molecular structures. The detecting properties of NLCs are based on local layers deformation, induced by surface fields and observed in polarizing microscope. The structural surface defects or physical field's distribution are dramatically change the distribution of surface tension. Surface defects recording becomes possible if NLC deformed structure is illuminated in transparent or reflective modes and observed in optical polarizing microscope and appearing image is compared with background structure. In this case one observes not the real defect but the local deformation in NLCs. The theory was developed to find out the real size of defects. The resolution of NLC layer is more than 2000 lines/mm. The fields of NLC application are solid crystals symmetry, minerals, metals, semiconductors, polymers and glasses structure inhomogeneities and optical coatings defects detecting. The efficiency of NLC method in biophotonics is illustrated by objective detecting cancer tissues character and visualizing the interaction traces of grippe viruses with antibodies. NLCs may detect solvent components structure in tea, wine and perfume giving unique information of their structure. It presents diagnostic information alternative to dyes and fluorescence methods. For the first time the structures of some juices and beverages are visualized to illustrate the unique possibilities of NLCs.

Tomilin, M. G.; Stafeev, S. K.

2011-08-01

13

Electro- and nonlinear optics of liquid crystal materials with nanoparticulate internal structure  

NASA Astrophysics Data System (ADS)

The combination of liquid crystals (LCs) and reconfigurable nanoparticulate networks results in most versatile materials for controlling light beams. These material systems can be used for developing multi-functional reconfigurable photonics and opto-electronics components and spatial light modulators with ultimate light modulating capabilities. We review here our results in laser recording of one and two-dimensional diffraction gratings and gratings with variable pitch. Nonlinear optical properties of LC with nanoparticulate internal networks and diffraction gratings laser-recorded in these materials are discussed. Nanoparticulate networks are capable of stabilizing the thermodynamic relaxation of photoinduced cis-isomers of molecules in photosensitive azobenzene LCs used as host for the nanoparticulate network leading to bistability of the phase state (anisotropic and isotropic) of the material, and reversible all-optical switching between those states.

Tabiryan, Nelson; Grozhik, Vladimir; Nersisyan, Sarik; Serak, Svetlana

2003-11-01

14

Band structure for a one-dimensional photonic crystal containing left-handed materials  

Microsoft Academic Search

The explicit dispersion equation for a one-dimensional periodic structure with alternative layers of left-handed material (LHM) and right-handed material (RHM) is given and analyzed. Some unusual phenomena such as spurious modes with complex frequencies, discrete modes and photon tunneling modes are observed in the band structure. The existence of spurious modes with complex frequencies is a common problem in the

Liang Wu; Sailing He; Linfang Shen

2003-01-01

15

Crystal structure and thermochemical properties of bis(1-octylammonium) tetrachlorochromate phase change materials  

NASA Astrophysics Data System (ADS)

A new crystalline complex (C8H17NH3)2CdCl4(s) (abbreviated as C8Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P-1 and Z = 2. The lattice potential energy of the title complex is calculated to be UPOT (C8Cd(s))=978.83 kJmol-1 from crystallographic data. Low-temperature heat capacities of the complex are measured by using a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.30.15 K, 10.150.23 kJmol-1, and 33.050.78 JK-1mol-1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by using the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.

Lu, Dong-Fei; Di, You-Ying; He, Dong-Hua

2012-08-01

16

Interference of electron diffracted beams from crystals and amorphous materials to measure their structure, mean inner potential and coherence properties  

NASA Astrophysics Data System (ADS)

This talk presents electron interferograms of crystals and amorphous materials used to measure their structure, mean inner potential and the coherence properties of their quasiparticles such as phonons, plasmons and, hopefully in the future, magnons. Recent methods of k-space interference has revealed that practically all electron intensities on the diffraction plane of a modern TEM have sufficient coherence to produce interferograms when self-interfered under a wide range of diffraction conditions. These diffraction intensities are of interest because they represent the material's atomic structure, which for amorphous materials has not yet been solved because of their complexity and missing phase information. For amorphous materials, two new methods of electron interference have been creaated. One is a wavefront-splitting method used for a-C, a-Si, a-Ge, SiO2, a-W and a-ZrNiFe metal. The other is an amplitude spitting method that interferes a crystal's Bragg diffracted beams that contains intensities of an amorphous thin film on the crystal's surface. The fringes in these interferograms have been produced to high scattering angles necessary to remove dynamic diffraction effects in order to measure the coherence of the quasiparticles. Although relative phase information of materials has been obtained, the absolute phase may be obtainable using a new electron holography microscope having multiple electron biprisms, an imaging energy filter and an excellent coherent source soon to be received by UVic and open for use by everyone. An immediate application of the wavefront-splitting method is as a new method to measure the spatial resolution of the TEM, which occurs at the shear angle for fringe disappearance that is easily controlled using the electron biprism and measured by a Fourier transform showing realization from previous possibilities.

Herring, Rodney

2010-10-01

17

Hydrothermal syntheses and crystal structures of hybrid materials based on Keggin cluster modified by iron complexes  

Microsoft Academic Search

Three new organic-inorganic hybrid complexes based on the Keggin polyoxometalates (POMs) modified by transition metal iron and N-ligand organic moiety: [Fe(phen)3]2 (1) [Fe(phen)2(H2O)]2??2H2O (2) and [Fe(phen)3]2??0.5H2O (3) (phen?=?1,10-phenanthroline) have been hydrothermally synthesized and structurally characterized. Crystal data for complex 1: C72H48Fe2M12N12O41PV, triclinic, , a?=?11.6618(2)?, b?=?13.8523(2)?, c?=?14.9168(2)?, ??=?105.87(3), ??=?93.103(2), ??=?96.609(2), V?=?2293.2(5)?, Z?=?1; for complex 2: C48H32Fe2PMo12N8O44, triclinic, , b?=?13.357(3)?, c?=?13.701(3)?, ??=?69.09(3),

Jingquan Sha; Jun Peng; Hongsheng Liu; Jing Chen; Aixiang Tian; Baoxia Dong; Pengpeng Zhang

2008-01-01

18

Syntheses, characterizations and crystal structures of two lead(II) phosphonate-sulfonate hybrid materials  

NASA Astrophysics Data System (ADS)

Hydrothermal reactions of lead(II) acetate with 5-sulfoisophthalic acid monosodium salt (NaH2BTS) and N-(phosphonomethyl)-N-methylglycine, MeN(CH2CO2H)(CH2PO3H2) (H3L1), or a new aminodiphosphonic acid, 3-Pyridyl-CH2N(CH2PO3H2)2 (H4L2), afforded two novel lead(II) phosphonate-sulfonate hybrids, namely, Pb3[L1][BTS][H2O].H2O 1 and Pb2[HL3][BTS].H2O 2 (H2L3=3-Pyridyl-CH2(Me)N(CH2PO3H2)). H2L3 was formed as a result of the decomposition of one phosphonate group in H4L2 during the reaction. Compound 1 crystallizes in the triclinic space group P1 with a=9.9148(4), b=10.4382(4), c=10.6926(2), ?=96.495(2), ?=110.599(2), ?=98.433(2), V=1008.31(6)3, and Z=2. The structure of compound 1 features a 3D network built from the interconnection of hexanuclear Pb6(L1)2 units and 1D double chains of lead(II) carboxylate-sulfonate. Compound 2 crystallizes in the monoclinic space group P21/c with a=9.5403(7), b=11.6170(8), c=19.7351(15), ?=97.918(2), V=2166.4(3)3, and Z=4. Compound 2 has a 3D network structure built by the cross-linkage of 1D double chains of lead(II) phosphonates and 2D layers of lead(II) carboxylate-sulfonate.

Song, Jun-Ling; Lei, Chong; Sun, Yan-Qiong; Mao, Jiang-Gao

2004-07-01

19

Two inorganic-organic hybrid materials based on polyoxometalate anions and methylene blue: Preparations, crystal structures and properties  

NASA Astrophysics Data System (ADS)

Two novel inorganic-organic hybrid materials based on an organic dye cation methylene blue (MB) and Lindqvist-type POM polyanions, [C22H18N3S]2Mo6O19 2DMF (1) and [C22H18N3S]2W6O19 2DMF (2) were synthesized under ambient conditions and characterized by CV, IR spectroscopy, solid diffuse reflectance spectrum, UV-vis spectra in DMF solution, luminescent spectrum and single crystal X-ray diffraction. Crystallographic data reveal that compounds 1 and 2 are isostructural and both crystallize in the triclinic space group P1. Their crystal structures present that the layers of organic molecules and inorganic anions array alternatively, and there exist strong ?? stacking interactions between dimeric MB cations and near distance interactions among organic dye cations, Lindqvist-type POM polyanions and DMF molecules. The solid diffuse reflectance spectra and UV-vis spectra in DMF solution appear new absorption bands ascribed to the charge-transfer transition between the cationic MB donor and the POM acceptors. Studies of the photoluminescent properties show that the formation of 1 and 2 lead to the fluorescence quenching of starting materials.

Nie, Shanshan; Zhang, Yaobin; Liu, Bin; Li, Zuoxi; Hu, Huaiming; Xue, Ganglin; Fu, Feng; Wang, Jiwu

2010-12-01

20

Hydrogenation-induced variation in crystal structure and heat capacity of magnetic regenerative material Er 3Ni  

NASA Astrophysics Data System (ADS)

In order to analyze the influence of hydrogenation on magnetic regenerative material Er 3Ni, the structures of Er 3Ni and its hydrides Er 3NiH x are tested by X-ray diffraction (XRD), and their magnetic properties and heat capacities are measured by a magnetic property measurement system (MPMS) and by a physical property measurement system (PPMS), respectively. The results show that different crystal structures can be formed by the hydrogenation at 293 K, while the Er 3NiH x does not go through magnetic transition above 2 K. The Er 3NiH x exhibits different specific heat features with that of original compound Er 3Ni, which could be attributed to the absence of magnetic transition and other effects caused by hydrogenation. The insertion of hydrogen atoms can lead to a larger specific heat than that of Er 3Ni in some certain temperature range.

Jin, T.; Li, C. H.; Tang, K.; Chen, L. X.; Xu, B.; Chen, G. B.

2011-05-01

21

Crystallization Behaviors of Ferroelectric and Piezoelectric Materials  

NASA Astrophysics Data System (ADS)

Crystallization represents a kind of phase transition, which can be regarded as a process related to bond formation and breaking. According to the chemical bonding characteristics of constituent atoms, the ideal morphology of LiNbO3 crystals has been successfully predicted by using the chemical bonding theory, which consists well with our experimental results. Some observations concerning the morphology evolution of KH2PO4 (KDP), NH4H2PO4 (ADP) and ZnO crystals can also be kinetically simulated by the present theory. The obtained results indicate that the microscopic constituent chemical bonds can help us to comprehensively understand the crystallization mechanism on the basis of quantitative calculations of growth rate in different crystal faces. The chemical bonding theory builds up a link between the crystallographic structure, growth morphology and microscopic chemical bonds of crystal materials, which provides us a useful microscopic tool to quantitatively understand single crystal growth behaviors.

Zhao, Xu; Sun, Congting; Si, Yunfei; Liu, Meinan; Xue, Dongfeng

22

Crystal growth in nanoporous framework materials.  

PubMed

Future applications of nanoporous materials will be in opto-electronic devices, magnetic and chemical sensors, shape-selective and bio-catalysis, structural materials and nuclear waste management. Crucially, in all such applications, an understanding of crystal growth to the same depth as has been achieved in semiconductor technology is needed. Therefore, defects, intergrowths, dopants and isomorphous substitution must be controlled, and crystal habit and size (e.g. single crystal films) must be fabricated with precision. These goals elude the community because of lack of understanding of crystal growth processes. Modern microscopy techniques including AFM, ultra-high resolution SEM and HREM coupled with theoretical calculations are beginning to reveal the details of these growth processes yielding the important thermodynamic data crucial to effect synthetic control such as: controlling defects; controlling intergrowths: introducing chirality; modifying surface access; altering diffusion pathways; controlling crystal habit; synthesising templated materials cheaply in order to render them economically viable; controlling crystal size for instance as single crystal films. In this paper we will discuss recent results including: the details of surface alteration processes in nanoporous materials, measured in situ, under different chemical environments and the ability to switch processes on and off by the control of growth conditions. Further we illustrate an approach to theoretically model the crystal growth in such complex systems which ultimately delivers activation energies for fundamental growth processes. PMID:17955807

Anderson, Michael W; Agger, Jonathan R; Meza, L Itzel; Chong, Chin B; Cundy, Colin S

2007-01-01

23

Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): a potential NLO material.  

PubMed

4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 623 mm(3)) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and (1)H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV). PMID:23624038

Dinakaran, Paul M; Kalainathan, S

2013-03-20

24

Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): A potential NLO material  

NASA Astrophysics Data System (ADS)

4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 6 2 3 mm3) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and 1H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV).

Dinakaran, Paul M.; Kalainathan, S.

2013-07-01

25

Comparative evaluation of different crystal-structured calcium sulfates as bone-filling materials.  

PubMed

The mechanical and handling properties and biological performances of two types of calcium sulfate (betaCS and alphaCS) as bone-filling materials were compared. The influence of two modifiers such as hydroxypropylmethylcellose (HPMC) and fibrin was also examined. alphaCS showed higher strength than, and similar setting time and injectability to those of betaCS. The degradation of CS in a simulated body fluid (SBF) was checked by measuring the amount of calcium released to SBF. alphaCS showed reduced calcium release than betaCS. The modifiers tended to increase the calcium release. The MC3T3-E1 preosteoblasts cultured on alphaCS showed higher levels of alkaline phosphatase (ALP) activity than those cultured on betaCS. alphaCS strongly promoted gene expression of osteoblast phenotypes including Runx2, alpha1(I) collagen, osteocalcin, and bone sialoprotein. There was no significant difference in cell adhesion and proliferation between two types of CS. The addition of modifiers to CS increased cell proliferation, ALP activity, and the gene expression. The osteoclastic differentiation of RAW264.7 monocytes was checked. The cells on both types of CS produced tartrate-resistant acid phosphatase (TRAP) activity with no significant difference. These cell response results indicated that alphaCS promoted osteoblast differentiation over betaCS but not osteoclast differentiation. Conclusively, a particular form of commercially available alphaCS possesses superior properties to betaCS in terms of mechanical properties and supports for osteoblast differentiation, suggesting that alphaCS could be an alternative to the conventionally used betaCS. The addition of HPMC and fibrin could further improve the feasibility of alphaCS as a bone-filling material. PMID:19507143

Woo, Kyung Mi; Yu, Bin; Jung, Hong-Moon; Lee, Yong-Keun

2009-11-01

26

Crystal growth and structure of L-methionine L-methioninium hydrogen maleatea new NLO material  

NASA Astrophysics Data System (ADS)

A new organic nonlinear optical (NLO) crystal from the amino acid family, viz., L-methionine L-methioninium hydrogen maleate (LMMM), has been grown by slow evaporation method from aqueous solution. Bulk crystals were grown using submerged seed solution method. The structure was elucidated using the single crystal x-ray diffraction data. The compound crystallized in the space group P21 and the unit cell contains a protonated L-methioninium cation and a zwitterionic methionine residue plus a maleate anion. The backbone conformation angles ?1 and ?2 are in cis and trans configurations for both the methionine and methioninium residues, respectively. Amino and carboxyl groups of the methioninium and methionine residues are connected through N-H...O hydrogen bonds leading to a ring R22(10) motif.

Natarajan, Subramanian; Rajan Devi, Neelamagam; Britto Dhas, Sathiya Dhas Martin; Athimoolam, Shanmuganarayanan

2008-04-01

27

Syntheses, crystal structures, thermal stabilities and luminescence of six M(II)-hydroxyphosphonoacetate materials  

SciTech Connect

Hydrothermal reactions of Zn{sup II}, Ba{sup II} or Co{sup II} ion with 2-hydroxyphosphonoacetic acid (H{sub 3}L) afforded six metal phosphonates, namely, [Zn{sub 5}(O{sub 3}PCH(OH)CO{sub 2}){sub 4}(C{sub 6}H{sub 9}N{sub 2}){sub 2}] (1), [(C{sub 4}H{sub 12}N{sub 2})Zn{sub 5}(O{sub 3}PCH(OH)CO{sub 2}){sub 4}(H{sub 2}O){sub 2}] (2), [(C{sub 3}H{sub 12}N{sub 2}){sub 0.5}Zn{sub 5}(HO{sub 3}PCH(OH)CO{sub 2})(O{sub 3}PCH(OH)CO{sub 2}){sub 3}(H{sub 2}O){sub 2}].0.75H{sub 2}O (3), [BaZn{sub 2}(O{sub 3}P CH(OH)CO{sub 2}){sub 2}] (4), [Ba(HO{sub 3}PCH(OH)CO{sub 2})] (5) and [(NH{sub 4}){sub 2}Co{sub 7}(HO{sub 3}PCH(OH) CO{sub 2}){sub 6}(HPO{sub 4}){sub 2}(H{sub 2}O){sub 6}].4H{sub 2}O (6). In 1, zinc tetrahedra ([ZnO{sub 4}]) and octahedra ([ZnO{sub 5}N], [ZnO{sub 6}]) are bridged by 2-hydroxyphosphonoacetate with penta- and hexadendate modes into a hybrid layer, which is further pillared by the 3-picolylamines to form a 3D structure through Zn-N bonds and hydrogen bondings. Both 2 and 3 are 3D framework encapsulating piperazine and 1,2-propanediamine cations, respectively. In solids 4-6, the cross-linkages of [ZnO{sub 4}], [BaO{sub 10}] and [CoO{sub 6}] polyhedral with 2-hydroxyphosphonoacetate form 3D frameworks. Solids 3 and 4 behave thermally stable up to 250 and 300 {sup o}C under air atmosphere, respectively. It is interesting that the peak emission of solid 3 displays a 10 nm red-shift after simple heat-treatment. -- Graphical abstract: Six new metal phosphonates exhibit layered or 3D frameworks based on 2-hydroxyphosphonoacetate with five new coordination modes. Display Omitted Research highlights: {yields} Metal phosphonates are layered or 3D frameworks. {yields} Metal phosphonates are stable up to 250-300 {sup o}C under air atmosphere. {yields} 2-Hydroxyphosphonoacetate displays five new coordination modes.

Fu, Ruibiao; Hu, Shengmin [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou, Fujian 350002 (China); Wu, Xintao, E-mail: wxt@fjirsm.ac.c [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou, Fujian 350002 (China)

2011-04-15

28

A 3.90 V iron-based fluorosulphate material for lithium-ion batteries crystallizing in the triplite structure  

SciTech Connect

Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, an intensive search has been made for new polyanionic compounds that have a higher potential for the Fe{sup 2+}/Fe{sup 3+} redox couple. Herein we push this potential to 3.90 V in a new polyanionic material that crystallizes in the triplite structure by substituting as little as 5 atomic per cent of Mn for Fe in Li(Fe{sub 1-{delta}}Mn{delta})SO{sub 4}F. Not only is this the highest voltage reported so far for the Fe{sup 2+}/Fe{sup 3+} redox couple, exceeding that of LiFePO{sub 4} by 450 mV, but this new triplite phase is capable of reversibly releasing and reinserting 0.7-0.8 Li ions with a volume change of 0.6% (compared with 7 and 10% for LiFePO{sub 4} and LiFeSO{sub 4}F respectively), to give a capacity of {approx}125 mA h g{sup -1}.

Barpanda, P.; Ati, M.; Melot, B.C.; Rousse, G.; Chotard, J-N.; Doublet, M-L.; Sougrati, M.T.; Corr, S.A.; Jumas, J-C.; Tarascon, J-M. (CNRS-UMR); (U. Kent)

2011-11-17

29

Station for X-ray structural analysis of materials and single crystals (including nanocrystals) on a synchrotron radiation beam from the wiggler at the Siberia-2 storage ring  

SciTech Connect

The design of the station for structural analysis of polycrystalline materials and single crystals (including nanoobjects and macromolecular crystals) on a synchrotron radiation beam from the superconducting wiggler of the Siberia-2 storage ring is described. The wiggler is constructed at the Budker Institute of Nuclear Physics of the Siberian Division of the Russian Academy of Sciences. The X-ray optical scheme of the station involves a (1, -1) double-crystal monochromator with a fixed position of the monochromatic beam and a sagittal bending of the second crystal, segmented mirrors bent by piezoelectric motors, and a (2{theta}, {omega}, {phi}) three-circle goniometer with a fixed tilt angle. Almost all devices of the station are designed and fabricated at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences. The Bruker APEX11 two-dimensional CCD detector will serve as a detector in the station.

Kheiker, D. M., E-mail: kheiker@nc.cryst.ras.ru; Kovalchuk, M. V. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Korchuganov, V. N. [Russian Research Centre 'Kurchatov Institute', Kurchatov Centre for Synchrotron Radiation and Nanotechnology (Russian Federation); Shilin, Yu. N.; Shishkov, V. A.; Sulyanov, S. N.; Dorovatovskii, P. V.; Rubinsky, S. V.; Rusakov, A. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2007-11-15

30

Crystal structure of magnesioneptunite  

NASA Astrophysics Data System (ADS)

The crystal structure of the new mineral magnesioneptunite (K0.8Na0.1-0.1)Na2Li(Ti0.39Mg0.34Fe0.27)2(Ti0.59Mg0.22Fe0.19)2[Si4O11]2(O,OH) from the xenolith of Verkhnechegemskaya caldera (Lakarga Mountain, North Caucasus) has been investigated by X-ray diffraction (XCalibur-S diffractometer, R = 0.0244): a = 16.3271(7) , b = 12.4788(4) , c = 9.9666(4) ? = 115.651(5), V = 1830.5(1) 3, sp. gr. C2/ c, Z = 4, and ?calcd = 3.152 g/cm3. The disordered distribution of Ti, Mg, and Fe atoms in the octahedra forming the basis of the cationic framework is established. It is shown that the isomorphic occupation of octahedral positions by cations of three types corresponds to the centrosymmetric crystal structure and is likely caused by the high-temperature crystallization of the mineral.

Karimova, O. V.; Yakubovich, O. V.; Zadov, A. E.; Ivanova, A. G.; Urusov, V. S.

2012-07-01

31

Physicomechanical model of the elastoplastic properties of materials taking account of the structural levels of deformation and the kinetic properties of real crystals  

NASA Astrophysics Data System (ADS)

On the basis of an earlier-proposed translational-rotational model of a continuous medium, reflecting a hierarchy of structural levels of deformation and destruction, the influence of diverse temperature-velocity conditions of loading on the properties of materials is investigated. The applicability of the theory for the description of unified equations of the mechanical properties of crystals in nonsteady conditions of deformation is established. Analysis and comparison of the calculations results with experiment is undertaken for uniaxial loading.

Likhachev, V. A.; Malinin, V. G.

1984-09-01

32

Two inorganicorganic hybrid materials based on polyoxometalate anions and methylene blue: Preparations, crystal structures and properties  

Microsoft Academic Search

Two novel inorganicorganic hybrid materials based on an organic dye cation methylene blue (MB) and Lindqvist-type POM polyanions, [C22H18N3S]2Mo6O19 2DMF (1) and [C22H18N3S]2W6O19 2DMF (2) were synthesized under ambient conditions and characterized by CV, IR spectroscopy, solid diffuse reflectance spectrum, UVvis spectra in DMF solution, luminescent spectrum and single crystal X-ray diffraction. Crystallographic data reveal that compounds 1 and 2

Shanshan Nie; Yaobin Zhang; Bin Liu; Zuoxi Li; Huaiming Hu; Ganglin Xue; Feng Fu; Jiwu Wang

2010-01-01

33

Vaterite crystals contain two interspersed crystal structures.  

PubMed

Calcite, aragonite, and vaterite are the three anhydrous polymorphs of calcium carbonate, in order of decreasing thermodynamic stability. Although vaterite is not commonly found in geological settings, it is an important precursor in several carbonate-forming systems and can be found in biological settings. Because of difficulties in obtaining large, pure, single crystals, the crystal structure of vaterite has been elusive for almost a century. Using aberration-corrected high-resolution transmission electron microscopy, we found that vaterite is actually composed of at least two different crystallographic structures that coexist within a pseudo-single crystal. The major structure exhibits hexagonal symmetry; the minor structure, existing as nanodomains within the major matrix, is still unknown. PMID:23620047

Kabalah-Amitai, Lee; Mayzel, Boaz; Kauffmann, Yaron; Fitch, Andrew N; Bloch, Leonid; Gilbert, Pupa U P A; Pokroy, Boaz

2013-04-26

34

A materials informatics approach for crystal chemistry  

NASA Astrophysics Data System (ADS)

This thesis addresses one of the fundamental questions in materials crystal chemistry, namely why do atoms arrange themselves in the way they do? The ability to broadly design and predict new phases [i.e. crystal structures] can be partly met using concepts that employ phase homologies. Homologous series of compounds are those that seem chemically diverse but can be expressed in terms of a mathematical formula that is capable of producing each chemical member in that crystal structure. A well-established strategy to help discover new compounds -- or at least to try to develop chemical design strategies for discovery -- is to search, organize and classify homologous compounds from known data. These classification schemes are developed with the hope that they can provide sufficient insight to help us forecast with some certainty, specific new phases or compounds. Yet, while the classification schemes (over a dozen have been reported in the last 50 years) have proved to be instructive, mostly in hindsight, but they have had limited impact, if at all, on the a priori design of materials chemistry. The aim of this research project is to develop a totally new approach to the study of chemical complexity in materials science using the tools of information theory and data science, which link diverse and high dimensional data derived from physical modeling and experiments. A very large scale binary AB2 crystallographic database is used as a data platform to develop a new data mining/informatics protocol based on high dimensional recursive partitioning schemes coupled to information theoretic measures to: (1) Identify which type of structure prototype is preferred over another for a given chemistry of compound; (2) discover new classification schemes of structure/chemistry/property relationships that classical homologies do not detect and finally we; (3) Extract and organize the underlying design rules for the formation of a given structure by quantitatively assessing the influence of multidimensional electronic structure attributes. Finally some applications of this new approach are demonstrated; including new ways for linking first principles calculations to crystal structure prediction and group theory to crystal structure transition.

Kong, Chang Sun

35

On the crystal structure and compressional behavior of talc: a mineral of interest in petrology and material science  

NASA Astrophysics Data System (ADS)

The crystal structure of a natural triclinic talc (1 Tc polytype) [with composition: (Mg2.93Fe0.06)?2.99(Al0.02Si3.97)?3.99O10(OH)2.10] has been investigated by single-crystal X-ray diffraction at 223 and 170 K and by single-crystal neutron diffraction at 20 K. Both the anisotropic X-ray refinements (i.e. at 223 and 170 K) show that the two independent tetrahedra are only slightly distorted. For the two independent Mg-octahedra, the bond distances between cation-hydroxyl groups are significantly shorter than the others. The ditrigonal rotation angle of the six-membered ring of tetrahedra is modest ( ? ~ 4). The neutron structure refinement shows that the hydrogen-bonding scheme in talc consists of one donor site and three acceptors (i.e. trifurcated configuration), all the bonds having OO ? 3.38 , HO ~ 2.8 , and O-HO ~ 111-116. The three acceptors belong to the six-membered ring of tetrahedra juxtaposed to the octahedral sheet. The vibrational regime of the proton site appears being only slightly anisotropic. The elastic behavior of talc was investigated by means of in situ synchrotron single-crystal diffraction up to 16 GPa (at room temperature) using a diamond anvil cell. No evidence of phase transition has been observed within the pressure range investigated. P- V data fit, with an isothermal third-order Birch-Murnaghan equation of state, results as follows: V 0 = 454.7(10) 3, K T0 = 56(3) GPa, and K' = 5.4(7). The "Eulerian finite strain" versus "normalized stress" plot yields: Fe(0) = 56(2) GPa and K' = 5.3(5). The compressional behavior of talc is strongly anisotropic, as reflected by the axial compressibilities (i.e. ?( a): ?( b): ?( c) = 1.03:1:3.15) as well as by the magnitude and orientation of the unit-strain ellipsoid (with ? 1: ? 2: ? 3 = 1:1.37:3.21). A comparison between the elastic parameters of talc obtained in this study with those previously reported is carried out.

Gatta, G. Diego; Merlini, Marco; Valdr, Giovanni; Liermann, Hanns-Peter; Nnert, Gwilherm; Rothkirch, Andr; Kahlenberg, Volker; Pavese, Alessandro

2013-02-01

36

Solvothermal crystal growth of functional materials  

Microsoft Academic Search

Hydrothermal crystal growth was associated with the development of ? -quartz single crystals for devices based on piezoelectric materials. This technology was then used to elaborate single crystals of different functional materials such as quartz-like oxides (AlPO4, GaPO4, GaAsO4, etc.), calcite CaCO3, etc. During the last few years two materials, GaN (using non-aqueous solvent) and ZnO, have been particularly investigated

Alain Largeteau; Stephane Darracq; Graziella Goglio; Gerard Demazeau

2008-01-01

37

Research on space structure materials  

NASA Astrophysics Data System (ADS)

An overview of the research conducted on space structure materials is presented. Major characteristics required for materials used for spacecraft structures operated in space for a long time were studied in the following aspects: (1) large specific strength and specific elasticity; (2) excellent characteristics stability; (3) excellent size stability; (4) large damping factor; and (5) excellent space environment resistance. Plastic-Metal Composite (PMC) and Metal-Metal Composite (MMC), most prosperous materials for space structures, were studied. Additionally hardened polyimide to withstand 300 C was under development as the main structural material for the H-2 Orbiting Plane (HOPE), and thermoplastic resin and liquid crystal composite were studied. MMC was deemed to be more prosperous material than PMC because of the superiority in physical properties. Joint research on radiation resistance of space structure materials was being conducted in cooperation with Takasaki Establishment of the Japan Atomic Energy Research Institute.

Yudate, Kouzou; Shibuta, Shigeto; Morino, Yoshiki

1992-08-01

38

Crystal Structure Lab  

NSDL National Science Digital Library

This activity is concerned with crystals, the basic building units that make up rocks and minerals. Students construct a model of the silicon-oxygen tetrahedron and discover that the smallest whole unit that could form a unique crystal is called a unit cell. They learn that a unit cell would have all the properties of a large crystal such as a diamond, but would be only molecular size (submicroscopic). If a crystal starts to form from a slowly cooling magma or from a drying up pool of salty sea water, unit cells add themselves one on top of another in order to develop the large crystals we can see and handle.

Fetcho, Ray

39

High Throughput Screening of Crystallization of Materials.  

National Technical Information Service (NTIS)

High throughput screening of crystallization of a target material is accomplished by simultaneously introducing a solution of the target material into a plurality of chambers of a microfabricated fluidic device. The microfabricated fluidic device is then ...

S. R. Quake C. L. Hansen J. M. Berger

2005-01-01

40

High Throughput Screening of Crystallization Materials.  

National Technical Information Service (NTIS)

High throughput screening of crystallization of a target material is accomplished by simultaneously introducing a solution of the target material into a plurality of chambers of a microfabricated fluidic device. The microfabricated fluidic device is then ...

C. L. Hansen J. M. Berger S. R. Quake

2006-01-01

41

Na/sub 4/Nb(PO/sub 4/)/sub 3/, a material with a reversible crystal-glass transformation: structural and optical comparison  

SciTech Connect

The phosphate Na/sub 4/Nb(PO/sub 4/)/sub 3/ exhibits a reversible crystal-phase change. Raman and optical investigations give evidence of the similarity between the covalent skeleton of the Nasicon-like crystalline phosphate and the network of the glass. Both types of materials contain octahedral NbO/sub 6/ groups with various Nb-O lengths. It is shown for the neodymium-doped glasses that these structural features induce a strong self concentration quenching of the Nd/sup 3 +/ emission.

El Jazouli, A.; Parent, C.; Dance, J.M.; Le Flem, G.; Hagenmuller, P.; Viala, J.C.

1988-06-01

42

Predicting crystal structure by merging data mining with quantum mechanics  

Microsoft Academic Search

Modern methods of quantum mechanics have proved to be effective tools to understand and even predict materials properties. An essential element of the materials design process, relevant to both new materials and the optimization of existing ones, is knowing which crystal structures will form in an alloy system. Crystal structure can only be predicted effectively with quantum mechanics if an

Christopher C. Fischer; Kevin J. Tibbetts; Dane Morgan; Gerbrand Ceder

2006-01-01

43

Synthetic Multifunctional Materials: Structure + ...  

National Technical Information Service (NTIS)

What are Synthetic Multifunctional Materials. Materials that are explicitly designed to realize multiple tasks. (Structure + power generation, + sensing, + self repair,) Inspiration Nature's materials (e.g., skin, bone): efficient, responsive, adaptable, ...

L. Christodoulou

2002-01-01

44

Salt crystallization in porous construction materials I Estimation of crystallization pressure  

Microsoft Academic Search

The crystallization process of soluble salts inside the natural and artificial porous materials partially immersed in different saline solutions has been studied. This procedure is used to simulate the conditions of exposure to salt weathering in which foundations and lower walls of building structures are within the zone of capillary rise of saline ground water.Crystallization pressures that can develop in

A. La Iglesia; V. Gonzlez; V. Lpez-Acevedo; C. Viedma

1997-01-01

45

Materials and structures  

Microsoft Academic Search

Materials and structures technology covers a wide range of technical areas. Some of the most pertinent issues for the Astrotech 21 missions include dimensionally stable structural materials, advanced composites, dielectric coatings, optical metallic coatings for low scattered light applications, low scattered light surfaces, deployable and inflatable structures (including optical), support structures in 0-g and 1-g environments, cryogenic optics, optical blacks,

Theodore T. Saito; Sharon L. Langenbeck; Ghanim Al-Jamily; Joe Arnold; Troy Barbee; Dan Coulter; Ben Dolgin; Buck Fichter; Patricia George; Paul Gorenstein

1992-01-01

46

Synthetic thermoelectric materials comprising phononic crystals  

DOEpatents

Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.

El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang

2013-08-13

47

Photosensitive liquid crystals with nanoparticulate internal structure  

NASA Astrophysics Data System (ADS)

Stabilization of thermodynamic relaxation of photoinduced cis isomers of azobenzene liquid-crystal molecules is observed in nanoparticulate networks. The phenomenon permits bistability of the phase state (anisotropic and isotropic) of the material and reversible all-optical switching between those states, resulting in strong changes in the light-scattering properties of the material. Recording of complex optical structures with high spatial resolution with the aid of laser beams of different wavelengths is demonstrated.

Tabiryan, N.; Grozhik, V.; Serak, S.

2002-11-01

48

An Example of Body-Centered Cubic Crystal Structure: The Atomium in Brussels as an Educative Tool for Introductory Materials Chemistry  

ERIC Educational Resources Information Center

|When students are introduced to the ways in which atoms are arranged in crystal structures, transposing the textbook illustrations into three-dimensional structures is difficult for some of them. To facilitate this transition, this article describes an approach to the study of the structure of solids through a well-known monument, the Atomium in

Pinto, Gabriel

2012-01-01

49

Teaching With Crystal Structures  

NSDL National Science Digital Library

Classifying a particle requires an understanding of the type of bonding that exists within and among the particles, which requires an understanding of atomic structure and electron configurations, which requires an understanding of the elements of periodi

Smithenry, Dennis W.

2009-09-01

50

Crystal growth in porous materialsI: The crystallization pressure of large crystals  

Microsoft Academic Search

A critical review of the existing literature on the pressure exerted by growing crystals in porous materials reveals that a number of different equations are in use. A derivation of an equation for the crystallization pressure based on the chemical potentials of the loaded and the unloaded faces of a growing crystal is provided. The equation obtained is compared to

Michael Steiger

2005-01-01

51

Manipulating the Crystal Growth of Organic Energetic Materials on Substrates  

NASA Astrophysics Data System (ADS)

Organic energetic materials (OMEs) have been attracted a lot of attention due to its wide application in military weapon. One of the most compelling researches is manipulating the crystal structure of OEMs due to their performances, such as ignition and burning rate, which depend strongly on the crystalline structure. The crystalline structure of OEMs on substrates has strong dependence on the experimental parameters, such as the deposition rate and external factors. This report demonstrates a new technique for manipulating the crystal growth of OEMs on substrates by micro-contact printing. The methodology depends on coating a polymer stamp with a surfactant, which has a strong affinity for the OEMs deposited on the substrate. The coated stamp selectively removes OEMs in contact areas when the stamp was lifted. And then the OEMs that were left on the substrates grew to the crystals. By careful choice facile film preparation method and optimal stamp pattern, this technique provides a new methodology for fabricating OEMs crystals from hexagon single crystals, dendrite crystals to micro-rod crystals and manipulating the size and distribution of these crystals.

Zhang, Xin; Zhang, Gengxin; Weeks, Brandon

2012-10-01

52

High-resolution 3D structural and optical analyses of hybrid or composite materials by means of scanning probe microscopy combined with the ultramicrotome technique: an example of application to engineering of liquid crystals doped with fluorescent quantum dots  

NASA Astrophysics Data System (ADS)

Combination of nanometer-scale 3D structural analysis with optical characterization of the same material is a challenging task. Its results may be important for nanophotonics, materials science, and quality control. We have developed a new technique for complementary high-resolution structural and optical characterization followed by optical spectroscopic and microscopic measurements accompanied by reconstruction of the 3D structure in the same area of the sample. The 3D structure is reconstructed by combination of ultramicrotomic and SPM techniques allowing the study of the 3D distribution of implanted nanoparticles and their effect on the matrix structure. The combination of scanning probe nanotomography (SPN) and optical microspectroscopy makes it possible to direct estimate how the 3D structural characteristics of materials affect their macroscopic optical properties. The technique developed has been applied to the engineering of materials made from cholesteric liquid crystals and fluorescent quantum dots (QDs). These materials permit photochemical patterning and image recording through the changes in the dissymmetry factor of circular polarization of QD emission. The differences in the polarisation images and morphological characteristics of the liquid crystal matrix have proved to be correlated with the arrangement of the areas of homogeneous distribution and nonhomogeneous clustering of QDs. The reconstruction of the 3D structure of the liquid crystal matrix in the areas of homogeneous QD distribution has shown that QDs embedded into cholesteric liquid crystal matrices do not perturb their periodic planar texture. The combined optical/SPM/ultramicrotome technique will be indispensable for evaluating the effects of inorganic nanoparticles on the organisation of organic and liquid crystal matrices, biomedical materials, cells, and tissues.

Mochalov, Konstantin E.; Efimov, Anton E.; Bobrovsky, Alexey Yu.; Agapov, Igor I.; Chistyakov, Anton A.; Oleinikov, Vladimir A.; Nabiev, Igor

2013-05-01

53

Crystal Structure of Beryllium Borohydride.  

National Technical Information Service (NTIS)

The crystal structure of Be(BH4)2 consists of a helical polymer of BH4Be and BH4 units. Within the BH4Be units there are two hydrogen bridges between B and Be, and in the helical polymer each B...Be contact has two hydrogen bridges. The hydrogen arrangeme...

D. S. Marynick W. N. Lipscomb

1971-01-01

54

Piezoelectricity, ferroelectricity, and crystal structure  

Microsoft Academic Search

By visualizing polar crystals as a network of permanent dipole moments, the piezo- and ferroelectric properties of dielectrics may be derived from the standpoint of molecular symmetry. This approach is used to clarify the relation between the sphalerite and wurtzite structures, the ferroelectric feedback effect in barium titanate, aspects of domain formation, and the interrelationship between ferro and piezoelectricity.

A. von Hippel

1952-01-01

55

Crystal structure of sorbitol dehydrogenase  

Microsoft Academic Search

Sorbitol dehydrogenase (SDH) is a distant relative to the alcohol dehydrogenases (ADHs) with sequence identities around 20%. SDH is a tetramer with one zinc ion per subunit. We have crystallized rat SDH and determined the structure by molecular replacement using a tetrameric bacterial ADH as search object. The conformation of the bound coenzyme is extended and similar to NADH bound

Kenth Johansson; Mustafa El-Ahmad; Christina Kaiser; Hans Jrnvall; Hans Eklund; Jan-Olov Hg; S. Ramaswamy

2001-01-01

56

Refinement of Hematite Crystal Structure.  

National Technical Information Service (NTIS)

The crystal structure of hematite, alpha-Fe2O3, has been refined as part of a continuing study of the behavior of phases in the Fe-O system during reduction and oxidation. Three-dimensional diffraction intensities were collected on two spherical single cr...

R. L. Blake T. Zoltai R. E. Hessevick L. W. Finger

1970-01-01

57

Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

Laser-driven acceleration holds great promise for significantly improving accelerating gradient. However, scaling the conventional process of structure-based acceleration in vacuum down to optical wavelengths requires a substantially different kind of structure. We require an optical waveguide that (1) is constructed out of dielectric materials, (2) has transverse size on the order of a wavelength, and (3) supports a mode with speed-of-light phase velocity in vacuum. Photonic crystals---structures whose electromagnetic properties are spatially periodic---can meet these requirements. We discuss simulated photonic crystal accelerator structures and describe their properties. We begin with a class of two-dimensional structures which serves to illustrate the design considerations and trade-offs involved. We then present a three-dimensional structure, and describe its performance in terms of accelerating gradient and efficiency. We discuss particle beam dynamics in this structure, demonstrating a method for keeping a beam confined to the waveguide. We also discuss material and fabrication considerations. Since accelerating gradient is limited by optical damage to the structure, the damage threshold of the dielectric is a critical parameter. We experimentally measure the damage threshold of silicon for picosecond pulses in the infrared, and determine that our structure is capable of sustaining an accelerating gradient of 300 MV/m at 1550 nm. Finally, we discuss possibilities for manufacturing these structures using common microfabrication techniques.

Cowan, Benjamin M.

2007-08-22

58

Bulk Crystal Growth - Methods and Materials  

NASA Astrophysics Data System (ADS)

This chapter covers the field of bulk single crystals of materials used in electronics and optoelectronics. These crystals are used in both active and passive modes (to produce devices directly in/on bulk-grown slices of material, or as substrates in epitaxial growth, respectively). Single-crystal material usually provides superior properties to polycrystalline or amorphous equivalents. The various bulk growth techniques are outlined, together with specific critical features, and examples are given of the types of materials (and their current typical sizes) grown by these techniques. Materials covered range from Group IV (Si, Ge, SiGe, diamond, SiC), Group III-V (such as GaAs, InP, nitrides) Group II-IV (including CdTe, ZnSe, MCT) through to a wide range of oxide/halide/phosphate/borate materials. This chapter is to be treated as a snapshot only; the interested reader is referred to the remainder of the chapters in this Handbook for more specific growth and characterization details on the various materials outlined in this chapter. This chapter also does not cover the more fundamental aspects of the growth of the particular materials covered; for these, the reader is again referred to relevant chapters within the Handbook, or to other sources of information in the general literature.

Capper, Peter

59

Crystal structure of lignin peroxidase  

Microsoft Academic Search

The crystal structure of lignin peroxidase (LiP) from the basidiomycete Phanerochaete chrysosporium has been determined to 2.6 [Angstrom] resolution by using multiple isomorphous replacement methods and simulated annealing refinement. Of the 343 residues, residues 3-335 have been accounted for in the electron density map, including four disulfide bonds. The overall three-dimensional structure is very similar to the only other peroxidase

S. L. Edwards; R. Raag; Hiroyuki Wariishi; M. H. Gold; T. L. Poulos

1993-01-01

60

Magnetic properties and crystal structure of FeTaAIN soft magnetic materials for MIG head (abstract)  

Microsoft Academic Search

Fe-based nitride films have been expected as promising head core materials used for high-density magnetic recording MIG head due to their large saturation flux density combined with excellent soft magnetic properties. Recent studies found that the addition of 813 at. % Ta in FeN resulted in a remarkable improvement of thermal stability. It was also reported that small amount of

Yiqun Li; Bingchu Cai; Xianglin Zeng; Dong Xu

1996-01-01

61

Crystal Structure of Bi  

SciTech Connect

The room temperature structures of the two-layer Aurivillius phases Bi{sub 2.5}Me{sub 0.5}Nb{sub 2}O{sub 9} (Me=Na, K) have been refined with the Rietveld method from powder neutron diffraction data ({lambda}=1.470 {angstrom}). They consist of (Bi{sub 2}O{sub 2}){sup 2+} layers interleaved with perovskite (Bi{sub 0.5}Me{sub 0.5}Nb{sub 2}O{sub 7}){sup 2-} (Me=Na, K) slabs. The structures were refined in the orthorhombic space group A2{sub 1}am, Z=4, and the unit cell parameters of the two oxides are a= 5.4937(3), b=5.4571(4), c=24.9169(14) {angstrom} and a=5.5005(8), b=5.4958(8), c=25.2524(16) {angstrom}, respectively. The orthorhombic distortion increases with decreasing Me+ cation size in the perovskite layer (Bi/Me){sup 2+} site and the lone pair electrons from the Bi{sup 3+} cation are influencing the site distortion. This is in agreement with other two-layer Aurivillius phases and originates from bonding requirements depending on size and electronic environment.

Borg, Stefan; Svensson, Goeran

2001-02-15

62

Artificially Structured Incommensurate Materials,  

National Technical Information Service (NTIS)

Modern ultrahigh vacuum deposition techniques such as Molecular Beam Epitaxy offer interesting opportunities for the fabrication of materials in which the incommensurate nature of the structure is expected to dominate the physical properties. The authors ...

R. Clarke R. Merlin

1987-01-01

63

Structural materials for NASP  

Microsoft Academic Search

Structural materials for the NASP X-30 experimental vehicle are briefly reviewed including titanium alloys, titanium-based metal-matrix composites, carbon-carbon composites, ceramic-matrix composites, and copper-matrix composites. Areas of application of these materials include the airframe where these materials would be used as lightweight skin panels for honeycomb-core, truss-core, or integrally stiffened thin sheet configuration; and the engine, where they would be used

Terence M. F. Ronald

1991-01-01

64

Vapor phase inclusion of ferrocene and its derivative in a microporous metal-organic porous material and its structural characterization by single crystal X-ray diffraction.  

PubMed

The inclusion of ferrocene and its derivative in metal-organic porous material MOF-5 is achieved by vapor diffusion; single-crystal X-ray diffraction studies using synchrotron radiation of ferrocene-loaded MOF-5 reveal well-ordered guest molecules packed into the pores. PMID:17009454

Kim, Hyunuk; Chun, Hyungphil; Kim, Ghyung-Hwa; Lee, Heung-Soo; Kim, Kimoon

2006-07-14

65

Crystal Structure of Neotame Anhydrate Polymorph G  

Microsoft Academic Search

Purpose. To determine the crystal structure of the neotame anhydrate polymorph G and to evaluate X-ray powder diffractometry (XRPD) with molecular modeling as an alternative method for determining the crystal structure of this conformationally flexible dipeptide.

Zedong Dong; Victor G. Young; Agam Sheth; Eric J. Munson; Steve A. Schroeder; Indra Prakash; David J. W. Grant

2002-01-01

66

American Mineralogist Crystal Structure Database  

NSDL National Science Digital Library

This database provides access to information on every crystal structure published in the American Mineralogist, the Canadian Mineralogist, European Journal of Mineralogy, and Physics and Chemistry of Minerals, as well as selected datasets from other journals. The data are searchable by mineral name, author, chemistry, cell parameters and symmetry, diffraction pattern, and a general search. There are also lists of minerals represented in the database and authors of publications cited.

Downs, R. T.; Hall-Wallace, M.

67

Platinum-Palladium Crystal Structures  

NASA Astrophysics Data System (ADS)

Being able to predict Platinum-Palladium ordering is important in discovering new alloys that have commercial and industrial applications. Using direct quantum mechanical calculations coupled with a lattice-based Hamiltonian called a cluster expansion, we can predict which crystal structures are thermodynamically stable for. In addition, a Monte Carlo simulation can be used in this model to determine the order-disorder transition temperatures. Knowing which structures are thermodynamically stable and their respective transition temperatures may help develop useful platinum palladium alloys.

Pratt, Weston

2009-10-01

68

The crystal structure of hopeite  

Microsoft Academic Search

The crystal structure of hopeite, Zns(POa)2.4Hro, has been solved by the Heavy Atom method from l42l graphite-monochromatized MoKa data and refined by full matrix least- squares to R = 0.026 (R. = 0.036). The structure is orthorhombic, pnma, a = 10.597(3), b : l8.3lE(8), c: 5.031(l) A, and Z: 4.Thezn atoms occur in two crystallographically distinct sites, one six-coordinated and

RooEnrcr J. Hrr; J. B. JoNes

69

Structural Materials: 95. Concrete  

SciTech Connect

Nuclear power plant concrete structures and their materials of construction are described, and their operating experience noted. Aging and environmental factors that can affect the durability of the concrete structures are identified. Basic components of a program to manage aging of these structures are identified and described. Application of structural reliability theory to devise uniform risk-based criteria by which existing facilities can be evaluated to achieve a desired performance level when subjected to uncertain demands and to quantify the effects of degradation is outlined. Finally, several areas are identified where additional research is desired.

Naus, Dan J [ORNL

2012-01-01

70

Shear induced structures in crystallizing cocoa butter  

Microsoft Academic Search

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear

Gianfranco Mazzanti; Sarah E. Guthrie; Eric B. Sirota; Alejandro G. Marangoni; Stefan H. J. Idziak

2004-01-01

71

Structural materials for NASP  

NASA Astrophysics Data System (ADS)

Structural materials for the NASP X-30 experimental vehicle are briefly reviewed including titanium alloys, titanium-based metal-matrix composites, carbon-carbon composites, ceramic-matrix composites, and copper-matrix composites. Areas of application of these materials include the airframe where these materials would be used as lightweight skin panels for honeycomb-core, truss-core, or integrally stiffened thin sheet configuration; and the engine, where they would be used in the hot gas path of the ramjet/scramjet, and in the inlet and nozzle areas.

Ronald, Terence M. F.

1991-12-01

72

Crystal Structure of Human ?-Galactosidase  

PubMed Central

GM1 gangliosidosis and Morquio B are autosomal recessive lysosomal storage diseases associated with a neurodegenerative disorder or dwarfism and skeletal abnormalities, respectively. These diseases are caused by deficiencies in the lysosomal enzyme ?-d-galactosidase (?-Gal), which lead to accumulations of the ?-Gal substrates, GM1 ganglioside, and keratan sulfate. ?-Gal is an exoglycosidase that catalyzes the hydrolysis of terminal ?-linked galactose residues. This study shows the crystal structures of human ?-Gal in complex with its catalytic product galactose or with its inhibitor 1-deoxygalactonojirimycin. Human ?-Gal is composed of a catalytic TIM barrel domain followed by ?-domain 1 and ?-domain 2. To gain structural insight into the molecular defects of ?-Gal in the above diseases, the disease-causing mutations were mapped onto the three-dimensional structure. Finally, the possible causes of the diseases are discussed.

Ohto, Umeharu; Usui, Kimihito; Ochi, Toshinari; Yuki, Kenjiro; Satow, Yoshinori; Shimizu, Toshiyuki

2012-01-01

73

Hertzian Fracture in Single Crystals with the Diamond Structure  

Microsoft Academic Search

Extension of an earlier theory of Hertzian fracture in brittle isotropic materials is here made to include the case of brittle single crystals, with particular reference to crystals having the diamond structure. A detailed description is first given of the inhomogeneous stress field in a flat, elastic specimen loaded normally with a hard sphere. The geometry of cracks growing in

B. R. Lawn

1968-01-01

74

Cavity-enhanced structural colour in extrudeable photonic crystals  

Microsoft Academic Search

Photonic crystals remain of significant interest because of the opportunity to modify a host of optical properties by structuring the material at the sub-wavelength scale, including enhanced light emission and absorption, superprism performance, and negative refraction. However until now photonic crystals have remained expensive to fabricate and control, and inconceivable to adopt in industrial processes because their assembly requires expensive

Jeremy Baumberg; David Snoswell; Andreas Kontogeorgos; Peter Spahn; Otto Pursiainen

2009-01-01

75

Polymer single crystal meets nanoparticle, toward ordered hybrid materials  

NASA Astrophysics Data System (ADS)

Judiciously selected polymer single crystal (PSC) systems can interplay with 1-D and 0-D nanoparticles, forming ordered hybrid structures. In this presentation, I will first focus on patterning PSCs on individual carbon nanotubes (CNT). Using both controlled solution crystallization, thin film crystallization and physical vapor deposition methods, CNTs were periodically decorated with PSCs, resulting in nano hybrid shish-kebab (NHSK) structures. Because the polymer kebabs can be easily removed, these unique NHSKs can serve as templates to fabricate a variety of CNTs-containing hybrid materials with controlled pattering on the CNT surface. Sub-20 nanometer alternating patterning was achieved by using crystalline block copolymers. The mechanism was attributed to the crystallization induced block copolymer phase separation. This pattern was successfully used to template nanoparticles (NP) pattering on CNTs. In the second part of the talk, I will discuss fabricating Janus NPs and patterning these NPs using PSCs. Single crystals of thiol-terminated polyethylene oxide (PEO) were incubated in a gold sol. Au-S bonds were formed between the AuNPs and the PEO single crystal surfaces. The inter-particle spacing was controlled by PEO molecular weights, the incubation time, and the annealing temperatures after incubation. The planar geometry of the PSCs led to Janus NP formation. A series of NP dimers, trimers and tetramers were synthesized. NP nanowires were also fabricated. We anticipate that this observation could lead to controlled synthesis of artificial molecules and NP chains for a variety of optical, electronic, and biomedical applications.

Li, Christopher

2009-03-01

76

Crystal structure of lignin peroxidase  

SciTech Connect

The crystal structure of lignin peroxidase (LiP) from the basidiomycete Phanerochaete chrysosporium has been determined to 2.6 [Angstrom] resolution by using multiple isomorphous replacement methods and simulated annealing refinement. Of the 343 residues, residues 3-335 have been accounted for in the electron density map, including four disulfide bonds. The overall three-dimensional structure is very similar to the only other peroxidase in this group for which a high-resolution crystal structure is available, cytochrome c peroxidase, despite the fact that the sequence identity is only [approx]20%, LiP has four disulfide bonds, while cytochrome c peroxidase has none, and Lip is larger (343 vs. 294 residues). The basic helical fold and connectivity defined by 11 helical segments with the heme sandwiched between the distal and proximal helices found in cytochrome c peroxidase is maintained in LiP. Both enzymes have a histidine as a proximal heme ligand, which is hydrogen bonded to a buried aspartic acid side chain. The distal or peroxide binding pocket also is similar, including the distal arginine and histidine. The most striking difference is that, whereas cytochrome c peroxidase has tryptophans contacting the distal and proximal heme surfaces, LiP has phenylalanines. This in part explains why, in the reaction with peroxides, cytochrome c peroxidase forms an amino acid-centered free radical, whereas LiP forms a porphyrin [pi] cation radical. 42 refs., 4 figs., 2 tabs.

Edwards, S.L. (Center for Advanced Research in Biotechnology, Rockville, MD (United States) National Institutes of Health, Bethesda, MD (United States)); Raag, R. (Center for Advanced Research in Biotechnology, Rockville, MD (United States)); Wariishi, Hiroyuki; Gold, M.H. (Oregon Graduate Institute of Science and Technology, Beaverton (United States)); Poulos, T.L. (Center for Advanced Reseaarch in Biotechnology, Rockville, MD (United States) Univ. of California, Irvine (United States))

1993-01-15

77

Light propagation in liquid crystals and liquid crystalline structures  

Microsoft Academic Search

Liquid crystals are optically complex materials, characterized in general by anisotropy, loss and chirality. Understanding light propagation both in uniform samples, and in stratified structures consisting of layers of such materials is of considerable interest for fundamental reasons. It is also essential for the effective use of these materials in technology. Light propagation in matter can be understood classically in

Haijun Yuan

2000-01-01

78

Photonic band structure of bcc colloidal crystals  

Microsoft Academic Search

Self-ordering colloidal systems are being recognized as possible candidates for optical photonic crystals. Such structures exhibit three-dimensional periodicity in refractive index, and possess lattice dimensions comparable to optical wavelengths. Recently, fcc colloidal crystals of water-suspended polystyrene microspheres were investigated in the context of photonic band structure. At lower polystyrene volume fractions, these colloidal suspensions crystallize in the bcc crystal lattice.

Ranjit D. Pradhan; John A. Bloodgood; George H. Watson

1997-01-01

79

Crystal structure of metarhodopsin II.  

PubMed

G-protein-coupled receptors (GPCRs) are seven transmembrane helix (TM) proteins that transduce signals into living cells by binding extracellular ligands and coupling to intracellular heterotrimeric G proteins (G???). The photoreceptor rhodopsin couples to transducin and bears its ligand 11-cis-retinal covalently bound via a protonated Schiff base to the opsin apoprotein. Absorption of a photon causes retinal cis/trans isomerization and generates the agonist all-trans-retinal in situ. After early photoproducts, the active G-protein-binding intermediate metarhodopsin II (Meta?II) is formed, in which the retinal Schiff base is still intact but deprotonated. Dissociation of the proton from the Schiff base breaks a major constraint in the protein and enables further activating steps, including an outward tilt of TM6 and formation of a large cytoplasmic crevice for uptake of the interacting C terminus of the G? subunit. Owing to Schiff base hydrolysis, Meta?II is short-lived and notoriously difficult to crystallize. We therefore soaked opsin crystals with all-trans-retinal to form Meta?II, presuming that the crystal's high concentration of opsin in an active conformation (Ops*) may facilitate all-trans-retinal uptake and Schiff base formation. Here we present the 3.0? and 2.85? crystal structures, respectively, of Meta?II alone or in complex with an 11-amino-acid C-terminal fragment derived from G? (G?CT2). G?CT2 binds in a large crevice at the cytoplasmic side, akin to the binding of a similar G?-derived peptide to Ops* (ref. 7). In the Meta?II structures, the electron density from the retinal ligand seamlessly continues into the Lys?296 side chain, reflecting proper formation of the Schiff base linkage. The retinal is in a relaxed conformation and almost undistorted compared with pure crystalline all-trans-retinal. By comparison with early photoproducts we propose how retinal translocation and rotation induce the gross conformational changes characteristic for Meta?II. The structures can now serve as models for the large GPCR family. PMID:21389988

Choe, Hui-Woog; Kim, Yong Ju; Park, Jung Hee; Morizumi, Takefumi; Pai, Emil F; Krauss, Norbert; Hofmann, Klaus Peter; Scheerer, Patrick; Ernst, Oliver P

2011-03-09

80

Intelligent materials and structures revisited  

Microsoft Academic Search

Presented are new definitions and interpretations for smartness and intelligence associated with materials, structures, and material systems (MS & MS). These newly proposed definitions complement and augment the present notion of smart and\\/or intelligent materials, structures and material systems, as accepted by our scientific community. These new definitions numerically quantify the concepts of smartness and intelligence for materials, structures and

Mohsen Shahinpoor

1996-01-01

81

Novel multifunctional organic semiconductor materials based on 4,8-substituted 1,5-naphthyridine: synthesis, single crystal structures, opto-electrical properties and quantum chemistry calculation.  

PubMed

A series of 4,8-substituted 1,5-naphthyridines (1a-1h) have been successfully synthesised by a Suzuki cross-coupling between 4,8-dibromo-1,5-naphthyridine (4) and the corresponding boronic acids (2a-2h) in the presence of catalytic palladium acetate in yields of 41.4-75.8% and have ben well characterized. They are thermally robust with high phase transition temperatures (above 186 C). Compounds 1b, 1e and 1f crystallized in the monoclinic crystal system with the space groups P2(1)/c, P2(1)/c and P2(1)/n, respectively. All of them show the lowest energy absorption bands (?(max)(Abs): 294-320 nm), revealing low optical band gaps (2.77-3.79 eV). These materials emit blue fluorescence with ?(max)(Em) ranging from 434-521 nm in dilute solution in dichloromethane and 400-501 nm in the solid state. 4,8-Substituted 1,5-naphthyridines 1a-1h have estimated electron affinities (EA) of (2.38-2.72 eV) suitable for electron-transport materials and ionization potentials (IP) of 4.85-5.04 eV facilitate excellent hole-injecting/hole-transport materials properties. Quantum chemical calculations using DFT B3LYP/6-31G* showed nearly identical the lowest unoccupied molecular orbitals (LUMO) of -2.39 to -2.19 eV and the highest occupied molecular orbitals (HOMO) of -5.33 to -6.84 eV. These results demonstrate the 4,8-substituted 1,5-naphthyridines 1a-1h with a simple architecture might be promising blue-emitting (or blue-green-emitting) materials, electron-transport materials and hole-injecting/hole-transport materials for applications for developing high-efficiency OLEDs. PMID:22790292

Wang, Kun-Yan; Chen, Chen; Liu, Jin-Fang; Wang, Qin; Chang, Jin; Zhu, Hong-Jun; Li, Chong

2012-07-13

82

Photonic Band Structure of fcc Colloidal Crystals  

Microsoft Academic Search

Polystyrene colloidal crystals form three dimensional periodic dielectric structures which can be used for photonic band structure measurements in the visible regime. From transmission measurements the photonic band structure of an fcc crystal has been obtained along the directions between the L point and the W point. Kossel line patterns were used for locating the symmetry points of the lattice

I. Inan Tarhan; George H. Watson

1996-01-01

83

Molecular and crystal structure of polycyclic nitramines  

Microsoft Academic Search

An X-ray structural investigation has been carried out for four polycyclic nitramines with an isowurtzitane structure. These\\u000a compounds are high-density, high-energy materials: 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diaza-tetracyclo(5.5.0.03,11.05,9)dodecane (4), 4,8,10,12-tetranitro-2,6-dioxa-4,8,10,12-tetrazatetracyclo (5.5.0.03,11.05,9)dodecane (5), and 4,6,10,12-tetranitro-2,8-dioxa-4,6,10,12-tetrazatetracyclo(5.5.0.03,11.05,9)-dodecane (6). Nitramine 5 crystallizes as triclinic (form ?, d\\u000a calc = 1.966 g\\/cm3) and trigonal (form ?, d\\u000a calc = 2.014 g\\/cm3) modifications. All amine nitrogen atoms have a nonplanar structure;

Yu. V. Gatilov; T. V. Rybalova; O. A. Efimov; A. A. Lobanova; G. V. Sakovich; S. V. Sysolyatin

2005-01-01

84

Advancements in MWIR window materials and structures  

NASA Astrophysics Data System (ADS)

To advance an area of technology requires an understanding of the current state of the art. For the past thirty years the standard material for durable window applications has been single crystal sapphire. Sapphire has proven to be a difficult material to replace although many attempts have been made. A variety of polycrystalline materials have been developed and characterized. Also, engineered structures such aerodynamic outer shapes with corrective optics to replace hemispherical shapes have been studied. Recently polycrystalline materials with nanometer-sized grains have been developed. A review of midwave optical window material development is presented with an emphasis on optical properties.

Thomas, M. E.; Tropf, W. J.

2013-06-01

85

Beyond crystals: the dialectic of materials and information  

PubMed Central

We argue for a convergence of crystallography, materials science and biology, that will come about through asking materials questions about biology and biological questions about materials, illuminated by considerations of information. The complex structures now being studied in biology and produced in nanotechnology have outstripped the framework of classical crystallography, and a variety of organizing concepts are now taking shape into a more modern and dynamic science of structure, form and function. Absolute stability and equilibrium are replaced by metastable structures existing in a flux of energy-carrying information and moving within an energy landscape of complex topology. Structures give place to processes and processes to systems. The fundamental level is that of atoms. As smaller and smaller groups of atoms are used for their physical properties, quantum effects become important; already we see quantum computation taking shape. Concepts move towards those in life with the emergence of specifically informational structures. We now see the possibility of the artificial construction of a synthetic living system, different from biological life, but having many or all of the same properties. Interactions are essentially nonlinear and collective. Structures begin to have an evolutionary history with episodes of symbiosis. Underlying all the structures are constraints of time and space. Through hierarchization, a more general principle than the periodicity of crystals, structures may be found within structures on different scales. We must integrate unifying concepts from dynamical systems and information theory to form a coherent language and science of shape and structure beyond crystals. To this end, we discuss the idea of categorizing structures based on information according to the algorithmic complexity of their assembly.

Cartwright, Julyan H. E.; Mackay, Alan L.

2012-01-01

86

Beyond crystals: the dialectic of materials and information.  

PubMed

We argue for a convergence of crystallography, materials science and biology, that will come about through asking materials questions about biology and biological questions about materials, illuminated by considerations of information. The complex structures now being studied in biology and produced in nanotechnology have outstripped the framework of classical crystallography, and a variety of organizing concepts are now taking shape into a more modern and dynamic science of structure, form and function. Absolute stability and equilibrium are replaced by metastable structures existing in a flux of energy-carrying information and moving within an energy landscape of complex topology. Structures give place to processes and processes to systems. The fundamental level is that of atoms. As smaller and smaller groups of atoms are used for their physical properties, quantum effects become important; already we see quantum computation taking shape. Concepts move towards those in life with the emergence of specifically informational structures. We now see the possibility of the artificial construction of a synthetic living system, different from biological life, but having many or all of the same properties. Interactions are essentially nonlinear and collective. Structures begin to have an evolutionary history with episodes of symbiosis. Underlying all the structures are constraints of time and space. Through hierarchization, a more general principle than the periodicity of crystals, structures may be found within structures on different scales. We must integrate unifying concepts from dynamical systems and information theory to form a coherent language and science of shape and structure beyond crystals. To this end, we discuss the idea of categorizing structures based on information according to the algorithmic complexity of their assembly. PMID:22615461

Cartwright, Julyan H E; Mackay, Alan L

2012-06-28

87

Biomimetic materials and structures  

NASA Astrophysics Data System (ADS)

An old-rooted endeavour of man, i.e. fabrication of material and structures taking inspiration from nature, is again actively pursued under a renewed name: biomimesis. This approach, once belonging to the realm of biological sciences, is based on the observation that, when one tries to embody our recognition criteria for biological organisms in an explicit list, nothing can be found on that list that cannot be mimicked by some inorganic system. Hence, a large variety of artifacts can be made, all possessing, to some extent, life-like features. Biomimetic arguments are today common reasoning in experimental studies about `origin-of-life' and in `advanced robotics'; a relatively new entry pertains to the area of `material science'.

de Rossi, Danilo

1996-04-01

88

Microchannel spatial light modulator using liquid crystal for modulating material  

NASA Astrophysics Data System (ADS)

Optical parallel processing is an attractive technique for treating today's vast quantities of information in parallel. In this field, a spatial light modulator which modulates the light in two dimensions is required. A microchannel spatial light modulator (MSLM) using LiNbO3 for a modulating material has been developed. However, it has physical limitations in readout light intensity, the spatial resolution and operating speed. In order to improve the characteristics of MSLM, liquid crystal (LC) is adopted for the modulating material. In this paper, the structure of the device and the operating principle are explained. The basic experimental results of the device are also shown.

Mukohzaka, Naohisa; Hara, Tsutomu; Suzuki, Yoshiji

1990-07-01

89

Discrete breathers in crystals with the NaCl structure  

NASA Astrophysics Data System (ADS)

In the recent decade, the spatially localized large-amplitude vibrational modes in defect-free crystals, referred to as discrete breathers (DBs), are intensively investigated in the materials science. This review reports the main results on gap DBs in crystals with the NaCl structure. The experimental proof of their existence in a NaI crystal is described. A number of molecular dynamics simulation results are presented, including new so far unpublished data. The properties of crystals potentially affected by the DBs are discussed.

Baimova, J. A.; Dmitriev, S. V.; Kistanov, A. A.; Potekaev, A. I.

2013-07-01

90

Artificially structured magnetic materials  

SciTech Connect

This document reports the progress made during the first six months of the current three-year DOE grant on Artificially Structured Magnetic Materials.'' However, because some of the results of our previous three-year DOE grant on Artificially Structured Superconductors'' continue to emerge, both topics are addressed in this Progress Report. This report describes progress with DOE funding during the current calendar year; description of the research to be conducted during the remaining six months of the current grant year; a description of the status of the graduate students working on this research; lists of the invited talks, seminars and colloquia, of other recognition of our research, and of the publications crediting DOE sponsorship; and a summary of current and pending federal support. Since the research proposed to be conducted during the next 2 1/2 years is described in detail in our DOE proposal, it is only briefly reviewed here.

Falco, C.M.

1990-09-28

91

Liquid Crystal Colloids: A Novel Composite Material Based on Liquid Crystals  

NASA Astrophysics Data System (ADS)

Liquid crystal colloids are composite materials made up of colloidal particles and liquid crystalline host fluids. After introducing various specific properties of liquid crystal collloids that are absent in conventional colloidal systems, we review our studies, based mainly on computer simulations using Landau-de Gennes theory, to elicudate those properties of liquid crystal colloids. We first present our attempts to investigate the orientational profiles and defect structures of a nematic liquid crystal around one colloidal particle. We successfully reproduce two configurations observed experimentally when strong homeotropic anchoring is imposed at the particle surface; one is a configuration with a hedgehog defect, and in the other, the particle is encircled by a ring defect referred to as a Saturn ring. Next we focus on the interaction between particles mediated by the elastic distortions of the host nematic liquid crystal. We calculate the interaction between particles carrying a hedgehog, and that between particles connected by a birefringent region called a bubble-gum. The properties of those interactions obtained numerically have been recently verified experimentally in a quantitative manner. We also review some of the important and attractive features of liquid crystal colloids not mentioned in the main part of the present paper.

Fukuda, Jun-ichi

2009-04-01

92

The crystal structure and crystallization temperature of equilibrium and metastable alloys and compounds  

NASA Astrophysics Data System (ADS)

The crystallization temperature of equilibrium V and Nb alloys and compounds is correlated with their crystal structure and phase diagrams. The production of superconducting materials under high pressure, in a thin-film state, or with superfast cooling requires increased superconductivity parameters. The temperature of the transition from a compound to a superconductor under superfast cooling and tempering depends on the chemical composition of the alloys and their crystal structure; the effects of superfast hardening on phase composition and transition temperature are analyzed for V and Nb binary and ternary alloys.

Frolova, T. M.; Efimov, Iu. V.; Savitskii, E. M.

1980-10-01

93

Structural, optical and electrical characteristics of a new NLO crystal  

NASA Astrophysics Data System (ADS)

A new nonlinear optical (NLO) organic crystal 1-[4-({(E)-[4-(methylsulfanyl)phenyl]methylidene}amino)phenyl]ethanone (MMP) has been grown by slow evaporation technique at ambient temperature. The crystal structure of MMP was determined by single crystal X-ray diffraction. MMP crystallizes in non-centrosymmetric monoclinic system with space group P21. The FT-IR spectrum recorded for new crystal confirmed the presence of various functional groups in the material. MMP was found to be thermally stable up to 300 C. The grown crystal was optically transparent in the wavelength range of 400-1100 nm. The second harmonic generation (SHG) efficiency of the crystal was measured by the classical powder technique using Nd:YAG laser and was found to be 4.13 times more efficient than reference material, urea. Third order nonlinear parameters were measured by employing the Z-scan technique. The laser damage threshold for MMP crystal was determined to be 4.26 GW/cm2. The Brewster angle technique was employed to measure the refractive index of the crystal and the values for green and red wavelengths were found to be 1.35 and 1.33, respectively. The dielectric and electrical measurements were carried out to study the different polarization mechanisms and conductivity of the crystal.

D'silva, E. D.; Krishna Podagatlapalli, G.; Venugopal Rao, S.; Dharmaprakash, S. M.

2012-09-01

94

Crystal structure transfer in core/shell nanowires.  

PubMed

Structure engineering is an emerging tool to control opto-electronic properties of semiconductors. Recently, control of crystal structure and the formation of a twinning superlattice have been shown for III-V nanowires. This level of control has not been obtained for Si nanowires, the most relevant material for the semiconductor industry. Here, we present an approach, in which a designed twinning superlattice with the zinc blende crystal structure or the wurtzite crystal structure is transferred from a gallium phosphide core wire to an epitaxially grown silicon shell. These materials have a difference in lattice constants of only 0.4%, which allows for structure transfer without introducing extra defects. The twinning superlattices, periodicity, and shell thickness can be tuned with great precision. Arrays of free-standing Si nanotubes are obtained by a selective wet-chemical etch of the core wire. PMID:21417242

Algra, Rienk E; Hocevar, Mora; Verheijen, Marcel A; Zardo, Ilaria; Immink, George G W; van Enckevort, Willem J P; Abstreiter, Gerhard; Kouwenhoven, Leo P; Vlieg, Elias; Bakkers, Erik P A M

2011-03-21

95

Structural, spectral and mechanical studies of bimetallic crystal: cadmium manganese thiocyanate single crystals  

NASA Astrophysics Data System (ADS)

A nonlinear optical bimetallic thiocyanate complex crystal, cadmium manganese thiocyanate (CMTC) has been successfully synthesized. The growth of single crystals of cadmium manganese thiocyanate has been accomplished from aqueous solution using slow evaporation method. The presence of manganese and cadmium in the synthesized material was confirmed through energy dispersive spectrum (EDS) analysis. Structural analysis was carried out using powder X-ray diffractometer (PXRD) and crystalline perfection of the grown crystals was ascertained by high-resolution X-ray diffraction (HRXRD) analysis. Fourier transform infrared (FTIR) spectrum was taken to confirm the functional groups. The transmittance spectrum of the crystal in the UV-visible region has been recorded and the cutoff wavelength has been determined. The dielectric measurements for the crystals were performed for various frequencies and temperatures. The mechanical properties were evaluated by Vickers microhardness testing, which reveals hardness and stiffness constant of the crystals.

Manikandan, M.; Vijaya Prasath, G.; Bhagavannarayan, G.; Vijayan, N.; Mahalingam, T.; Ravi, G.

2012-09-01

96

Crystal structures of proline-derived enamines  

PubMed Central

The isolation and structural characterization of both aldehyde- and ketone-derived proline enaminones are reported and discussed. Crystal structures of 10 proline enamines provide information on stereochemical aspects, i.e., double bond configuration and syn- vs. anti-positioning of the carboxylate relative to the enamine double bond. Furthermore, the obtained crystal structures are compared with the density functional theory-calculated structures of the ground and transition state and the postulated SeebachEschenmoser transition state.

Bock, Dominique Anna; Lehmann, Christian W.; List, Benjamin

2010-01-01

97

Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

We discuss simulated photonic crystal structure designs for laser-driven particle acceleration, focusing on three-dimensional planar structures based on the so-called ''woodpile'' lattice. We demonstrate guiding of a speed-of-light accelerating mode by a defect in the photonic crystal lattice and discuss the properties of this mode. We also discuss particle beam dynamics in the structure, presenting a novel method for focusing the beam. In addition we describe some potential coupling methods for the structure.

Cowan, B.; /SLAC

2005-09-19

98

Inorganic chiral 3-D photonic crystals with bicontinuous gyroid structure replicated from butterfly wing scales.  

PubMed

Three dimensional silica photonic crystals with the gyroid minimal surface structure have been synthesized. The butterfly Callophrys rubi was used as a biotemplate. This material represents a significant addition to the small family of synthetic bicontinuous photonic crystals. PMID:21818463

Mille, Christian; Tyrode, Eric C; Corkery, Robert W

2011-08-04

99

Crystal Structure of Chabazite K  

SciTech Connect

The crystal structure of the chabazite K with the formula (K{sub 1.33}Na{sub 1.02}Ca{sub 0.84})[Al{sub 4}Si{sub 8}O{sub 24}] {center_dot} 12.17H{sub 2}O from late hydrothermalites in the Khibiny alkaline massif (Kola Peninsula) is established by X-ray diffraction analysis (CAD4 four-circle diffractometer, {lambda}MoK{sub {alpha}} radiation, graphite monochromator, T = 193 K, 2{theta}{sub max} = 70 deg., R{sub 1} = 0.047 for 4745 reflections) on the basis of experimental data (6265 reflections) obtained from a twin (twinning parameter 0.535(1)): a = 13.831(3) A, c = 15.023(5) A, sp. gr. R3-barm, Z = 3, {rho}{sub calcd} = 2.016 g/cm{sup 3} . It is shown that cations occupy five independent positions in large cavities of the tetrahedral Al,Si,O anionic framework in potassium-rich chabazite. A comparative crystallochemical analysis of chabazites of different composition and origin is performed.

Yakubovich, O.V.; Gavrilenko, P.G.; Pekov, I.V. [Moscow State University, Vorob'evy gory, Moscow, 119992 (Russian Federation); Massa, W. [Philipps University, Marburg (Germany)

2005-07-15

100

Nanomedicine crystals-inspired optoelectronic device materials and processing  

NASA Astrophysics Data System (ADS)

Aim: Organic, biological materials and soft matters with optoelectronic donors and acceptors are postulated to be novel optoelectronic device materials. Methods: Molecular self-assemblies of nanomedicine crystals are employed by inelastic electron tunneling interaction force, which is a quantum force to make basic units of organic, biological and soft matter with optoelectronic donors and acceptors to be enlarged from nanometers to micrometers on silicon chips. Results: Self-assembled topographic structures and corresponding conducting with kondo effects and photoluminescence properties of self-assembled nanomedicine crystal building blocks are demonstrated by conducting atomic force microscopy (C-AFM) images and current-voltage curves, and laser micro- photoluminescence (PL) spectra. By contrast to top-down processing, the bottom-up processing of molecular self-assembly is low cost on large scale industrial manufacturing. Conclusion: The self-assembled nanomedicine crystal building blocks with optoelectronic donors and acceptors are candidates of novel optoelectronic device materials to be in the emerging discipline of information technology (IT) in its broadest sense, i.e. bioelectronics & biosensors, optoelectronic devices, data storage devices; simple to complex quantum entanglements and superposition for quantum bits computing, a novel strategy for 2020 IT and beyond.

Fang, Yan; Wang, Fangzhang; Wu, Rong

2011-11-01

101

A promising nonlinear optical material in the Mid-IR region: new results on synthesis, crystal structure and properties of noncentrosymmetric ?-HgBrCl.  

PubMed

This paper reports, for the first time, the nonlinear optical property of ?-HgBrCl, which was synthesized by a reaction of Hg2Cl2 and Br2 in EtOH. This reaction also gave ?-HgBrCl. And the single crystal structures of both ?- and ?-HgBrCl are presented and compared. ?-HgBrCl shows phase-matchable powder second harmonic generation (SHG) effect of about 2 times that of KH2PO4 (KDP). Its absorption edge in UV-vis spectrum locates at 366 nm, implying a wide band gap and therefore higher laser damage threshold. It also exhibits a relatively wide transparent window (from 0.4 to 20 ?m) and relatively good thermal stability. PMID:23695292

Dang, Yangyang; Meng, Xianggao; Jiang, Kui; Zhong, Cheng; Chen, Xingguo; Qin, Jingui

2013-05-21

102

Synthesis, crystal structure and thermal properties of Ca6(C12H14O4)4(CO3)(OH)2(H2O)x--a 3D inorganic hybrid material.  

PubMed

The inorganic-organic compound Ca(6)(1,3-adamantanedicarboxylate)(4)(CO(3))(OH)(2)(H(2)O)(x) with 0 < x < 15.2 was synthesized by hydrothermal methods. The crystal structure was determined on the basis of high resolution synchrotron powder diffraction data and poly-crystal measurements. The crystal structure of Ca(6)(C(12)H(14)O(4))(4)(CO(3))(OH)(2)(H(2)O)(14) is tetragonal, space group I4(1)/amd (141) with a = 29.12 , c = 15.85 , V = 13,440 (3) and Z = 8. The compound is classified as a 3D inorganic hybrid material with a 3-dimensional inorganic framework consisting of Ca and O, connected to 1,3-adamantanedicarboxylate anions. The structure shows hydrophilic channels in a diamond-like network. In between the channels there exist hydrophobic pores with surfaces defined by adamantane cages. The shortest distance between hydrogen atoms from different molecules in these pores is 3.6 . The largest hydrophilic cavity has a diameter of 10 and the pores connecting the channels have a diameter of 5 . In the as-synthesised state these channels are filled with water molecules. Reversible dehydration-rehydration occurs. The dehydrated compound easily takes up water from ambient air. PMID:22914759

Nielsen, Renie Birkedal; Norby, Poul; Kongshaug, Kjell Ove; Fjellvg, Helmer

2012-10-21

103

Intelligent materials and structures revisited  

NASA Astrophysics Data System (ADS)

Presented are new definitions and interpretations for smartness and intelligence associated with materials, structures, and material systems (MS & MS). These newly proposed definitions complement and augment the present notion of smart and/or intelligent materials, structures and material systems, as accepted by our scientific community. These new definitions numerically quantify the concepts of smartness and intelligence for materials, structures and material systems. In this context amino acid sequences and structures such as proteins are proposed to be the smartest material family and are given an MSQ of 1000. Correspondingly, ribonucleic acid sequences such as RNA and DNA macromolecular assemblies and structures are proposed to be the most intelligent material family and are given an MIQ of 1000. In the same category the proteins are given an MIQ of about 700. Ionic polymeric gels, shape memory alloys, electromagnetic (electrostrictive, piezoelectric, ferroelectric, ferromagnetic) materials, electrorheological fluids and magnetorheological fluids are then categorized under this hierarchy of smart/intelligent materials with MSQs and MIQs of smaller values. A similar classification is also applied to smart/intelligent structures with reference to simple cells such as bacteria and viruses such as T4 Bacteriophages. A number of examples are presented and the corresponding MSQs and MIQs are estimated to show that materials, structure and material systems can truly be numerically categorized in connection with their smartness and intelligence and thus be compared with biological and botanical structures and material systems.

Shahinpoor, Mohsen

1996-02-01

104

Structural characterization of thin film photonic crystals  

SciTech Connect

We quantitatively analyze the structure of thin film inverse-opal photonic crystals composed of ordered arrays of air pores in a background of titania. Ordering of the sphere template and introduction of the titania background were performed simultaneously in the thin film photonic crystals. Nondestructive optical measurements of backfilling with high refractive index liquids, angle-resolved reflectivity, and optical spectroscopy were combined with band-structure calculations. The analysis reveals a thin film photonic crystal structure with a very high filling fraction (92{endash}94%) of air and a substantial compression along the c axis ({similar_to}22{endash}25%).

Subramania, G.; Biswas, R.; Constant, K.; Sigalas, M. M.; Ho, K. M.

2001-06-15

105

Isotropic behavior of an anisotropic material: single crystal silicon  

NASA Astrophysics Data System (ADS)

Zero defect single crystal silicon (Single-Crystal Si), with its diamond cubic crystal structure, is completely isotropic in most properties important for advanced aerospace systems. This paper will identify behavior of the three most dominant planes of the Single-Crystal Si cube (110), (100) and (111). For example, thermal and optical properties are completely isotropic for any given plane. The elastic and mechanical properties however are direction dependent. But we show through finite element analysis that in spite of this, near-isotropic behavior can be achieved with component designs that utilize the optimum elastic modulus in directions with the highest loads. Using glass frit bonding to assemble these planes is the only bonding agent that doesn't degrade the performance of Single-Crystal Si. The most significant anisotropic property of Single-Crystal Si is the Young's modulus of elasticity. Literature values vary substantially around a value of 145 GPa. The truth is that while the maximum modulus is 185 GPa, the most useful <110< crystallographic direction has a high 169 GPa, still higher than that of many materials such as aluminum and invar. And since Poisson's ratio in this direction is an extremely low 0.064, distortion in the plane normal to the load is insignificant. While the minimum modulus is 130 GPa, a calculated average value is close to the optimum at approximately 160 GPa. The minimum modulus is therefore almost irrelevant. The (111) plane, referred to as the natural cleave plane survives impact that would overload the (110) and/or (100) plane due to its superior density. While mechanical properties vary from plane to plane each plane is uniform and response is predictable. Understanding the Single-Crystal Si diamond cube provides a design and manufacture path for building lightweight Single-Crystal Si systems with near-isotropic response to loads. It is clear then that near-isotropic elastic behavior is achievable in Single-Crystal Si components and will provide subsecond thermal equilibrium and sub-micron creep.

McCarter, Douglas R.; Paquin, Roger A.

2013-09-01

106

Composite Structural Materials.  

National Technical Information Service (NTIS)

The promise of filamentary composite materials, whose development may be considered as entering its second generation, continues to generate intense interest and applications activity. Fiber reinforced composite materials offer substantially improved perf...

G. S. Ansell R. G. Loewy S. E. Wiberley

1982-01-01

107

Refinement of the Crystal Structure of Nacrite  

Microsoft Academic Search

The crystal structure of nacrite from Pike's Peak district, Colorado, has been refined by least squares and electron density difference maps utilizing ten levels of data. Complete refinement was inhibited by thick domains involving a\\/3 interlayer shifts in the \\

Alice M. Blount; I. M. THREADGOLD; S. W. BAILEY

1969-01-01

108

ENHANCEMENT OF OMNIDIRECTIONAL REFLECTION BANDS IN ONE-DIMENSIONAL PHOTONIC CRYSTALS WITH LEFT-HANDED MATERIALS  

Microsoft Academic Search

In this paper we show, theoretically, that total omnidirec- tional reflected frequency band is enlarged considerably by using one- dimensional photonic crystal (PC) structure composed of alternate lay- ers of ordinary material (OM) and left handed material (LHM). From the analysis it is found that the proposed structure has very wide range of omnidirectional total frequency bands for both polarizations

Sanjeev Kumar Srivastava; Sant Prasad Ojha

2007-01-01

109

Crystal growth, characterization and structure refinement of neodymium[sup 3+] doped gehlenite, a new laser material (Ca[sub 2]Al[sub 2]SiO[sub 7])  

SciTech Connect

In order to find new Nd[sup 3+] laser materials pumpable by laser diode, gehlenite (Ca[sub 2]Al[sub 2]SiO[sub 7]) was chosen as a host matrix for neodymium ions. Large single crystals of Ca[sub 2[minus]x] Nd[sub x] Al[sub 2+x] Si[sub 1[minus]x] O[sub 7] (0 < x < 0.3) were obtained by Czochralski and floating zone methods. The main characteristics of these crystals (crystal perfection, thermal and mechanical behavior, optical properties...) were determined. The structure refinement revealed a structural disorder, occurring both on position and distribution of ions around Nd[sup 3+] and resulting in a broadening of the absorption bands. This means that less effort is required for diode laser pumping, and the laser effect has been observed. Therefore, Nd[sup 3+] doped Ca[sub 2]Al[sub 2]SiO[sub 7] appears as a good candidate as diode pumped laser.

Lejus, A.M.; Kahn-Harari, A.; Benitez, J.M.; Viana, B. (CNRS-URA1466, Paris (France). Lab. de Chimie Appliquee de l'Etat Solide)

1994-07-01

110

Structural, thermal and optical characterization of a Schiff base as a new organic material for nonlinear optical crystals and films with reversible noncentrosymmetry  

Microsoft Academic Search

Macroscopic single crystals of (E)-5-(diethylamino)-2-((3,5-dinitrophenylimino)methyl)phenol (DNP) were obtained from slow cooling of chloroform or dichlorometane saturated solutions at controlled temperature. X-ray diffraction analysis showed that this compound crystallizes in a noncentrosymmetric space group (P212121). Thermal analysis was performed and indicated that the crystals are stable until 260C. Second-order nonlinear optical properties of DNP were experimentally investigated in solution through EFISH

Mario Rodrguez; Gabriel Ramos-Ortz; Jos Luis Maldonado; Vctor M. Herrera-Ambriz; Oscar Domnguez; Rosa Santillan; Norberto Farfn; Keitaro Nakatani

2011-01-01

111

Liquid Crystal Colloids: A Novel Composite Material Based on Liquid Crystals  

Microsoft Academic Search

Liquid crystal colloids are composite materials made up of colloidal particles and liquid crystalline host fluids. After introducing various specific properties of liquid crystal collloids that are absent in conventional colloidal systems, we review our studies, based mainly on computer simulations using Landau-de Gennes theory, to elicudate those properties of liquid crystal colloids. We first present our attempts to investigate

Jun-ichi Fukuda

2009-01-01

112

Salt transport and crystallization in non-isothermal, partially saturated porous materials considering ions interaction model  

Microsoft Academic Search

Crystallizing salt changes the inner pore structure of materials. MIP tests of cement mortar and brick saturated with NaCl, Ca2Cl, Na2SO4 solutions were performed. The changes of porosity, pore size distribution and pore shape (ink-bottle type pores) were investigated by performing two intrusionextrusion cycles. The crystallization pressure bursts the mezopores. During salt crystallization the additional heat is released, which must

Marcin Koniorczyk

113

Self-monitoring structural materials  

Microsoft Academic Search

Self-monitoring (or intrinsically smart) structural materials, including concrete containing short carbon fibers, and polymer-matrix and carbon-matrix composites containing continuous carbon fibers, were reviewed. Each material is capable of monitoring its own reversible strain and damage through the effects of these on the electrical resistance of the material. This capability is valuable for structural control and structural health monitoring. Among these

D. D. L. Chung

1998-01-01

114

Simulation of Material Properties of Barium Titanate Single Crystal with Multidomain Structure Using Modified Time-Dependent Devonshire--Ginzburg--Landau Model  

NASA Astrophysics Data System (ADS)

We simulated and compared the material properties of the tetragonal phase of barium titanate for two types of multidomain structures, namely, multidomain-1 including both 90 and 180 domains, and multidomain-2 including only the 180 domain, and a monodomain by using a modified time-dependent Devonshire--Ginzburg--Landau model of two dimensions. We found that the piezoelectric coefficient d12 and dielectric susceptibility ?22 of muiltidomain-1 are about 6.5 times larger than those of the monodomain, and the large values of d12 and ?22 of multidomain-1 are explained by considering its peculiar multidomain structure. Moreover, we found that the piezoelectric coefficient d22 of muiltidomain-2 before polling is about one-half that of the monodomain, and that of muiltidomain-2 after polling is about two times larger than that before polling, whereas the value of ?22 before polling is three times larger than that after polling.

Imanaga, Syunji; Miura, Kaoru

2012-05-01

115

Methods of using structures including catalytic materials disposed within porous zeolite materials to synthesize hydrocarbons  

DOEpatents

Catalytic structures include a catalytic material disposed within a zeolite material. The catalytic material may be capable of catalyzing a formation of methanol from carbon monoxide and/or carbon dioxide, and the zeolite material may be capable of catalyzing a formation of hydrocarbon molecules from methanol. The catalytic material may include copper and zinc oxide. The zeolite material may include a first plurality of pores substantially defined by a crystal structure of the zeolite material and a second plurality of pores dispersed throughout the zeolite material. Systems for synthesizing hydrocarbon molecules also include catalytic structures. Methods for synthesizing hydrocarbon molecules include contacting hydrogen and at least one of carbon monoxide and carbon dioxide with such catalytic structures. Catalytic structures are fabricated by forming a zeolite material at least partially around a template structure, removing the template structure, and introducing a catalytic material into the zeolite material.

Rollins, Harry W. (Idaho Falls, ID); Petkovic, Lucia M. (Idaho Falls, ID); Ginosar, Daniel M. (Idaho Falls, ID)

2011-02-01

116

Liquid Crystal Photonic Band Gap Materials: The Tunable Electromagnetic Vacuum  

NASA Astrophysics Data System (ADS)

Photonic-Band-Gap (PBG) materials are a distinct class of dielectrics which facilitate the control over both propagation of light and the inhibition of spontaneous emission of light from atoms and molecules. The successful fabrication of such structures ( A. Birner et al., Phys. Stat. Sol (a) 165), 111 (1998); J.E.G.J. Wijnhoven and W.L. Vos, Science 281, 802 (1998) represents a great leap towards an integrated photonic. In this talk, we demonstrate that complete three-dimensional PBGs, spanning roughly 10% and 15% of the gap center frequency are attainable by incomplete infiltration of an opal with silicon and germanium, respectively (K. Busch und S. John, Phys. Rev. E 58), 3896 (1998). In addition, we show that when an optically birefringent nematic liquid crystal is infiltrated into the void regions of an inverse opal PBG material, the resulting composite material exhibits a completely tunable PBG (K. Busch und S. John, Phys. Rev. Lett. 83), 967 (1999). Measurements on analogous two-dimensional Photonic Crystals show that the photonic band edge may be shifted by more than 100 nm (S.W. Leonard et al., Phys. Rev. B (rapid), in press). note

Busch, Kurt

2000-03-01

117

Materials with layered structures. III. The system CoGa2S4CoIn2S4 and the crystal structure of CoGaInS4  

Microsoft Academic Search

The crystal structure of CoGaInS4 has been determined from single crystal X-ray diffraction data and refined to R = 0.03. It crystallizes in the trigonal FeGa2S4 type (space group P3m1, No. 164, a = 3.759(1), c = 12.184(2) , Z = 1) with the following cation distribution: (Co0.61In0.39Ga)t(Co0.39In0.61)oS4. The system xCoGa2S4-(1 - x)CoIn2S4 is quasibinary. The compound CoGaInS4 has a

H. Haeuseler; H. J. Stork; W. Cordes

1990-01-01

118

Pholcodine monohydrate: Crystal structure and polymorphism  

NASA Astrophysics Data System (ADS)

The first crystal structure elucidation of pholcodine monohydrate, an important antitussive active pharmaceutical ingredient is reported herein. The studied compound crystallizes in the orthorhombic system in the space group P212121. Each H2O molecule is shared by two pholcodine molecules via three strong hydrogen bonds. The detailed crystallization screening from several different organic solvents afforded single crystals with various quality, all exhibiting prism-to-needlelike micro morphology. The investigation of the obtained single crystals by means of several physico-chemical, solid-state instrumental techniques (FT-IR, DSC, TG/DTG and XRPD) proved that pholcodine monohydrate exists in a single crystalline modification, identical to the commercial form of the compound.

Petruevski, Gjorgji; Zba?nik, Marija; Kajdanoska, Marina; Ugarkovic, Sonja; Trim?eski, Vase; Kaitner, Branko; Jovanovski, Gligor; Makreski, Petre

2013-07-01

119

Smart materials and aerospace structures  

Microsoft Academic Search

Starting from the very definition of smart structures and smart materials, this paper addresses the fundamental mechanism of operation of some well known smart materials like piezoelectric ceramic\\/polymer, electrostrictive ceramic, magnetostrictive alloy, shape memory alloy, electroheological fluid, magnetoheological fluid, optical fibers and so on. It also describes briefly the working principles of the actuators and sensor based upon these materials.

K. Bandyopadhyay

1999-01-01

120

Natural photonic crystals: formation, structure, function  

NASA Astrophysics Data System (ADS)

The structure and properties of natural photonic crystals are discussed using the colored scales of the beetle Lamprocyphus augustus as an example. While the exact mechanism behind the formation of these biopolymeric photonic structures has yet to be fully explored, similarities of these structures to intracellular cubic membrane architectures are introduced. Some crucial parameters behind the formation of cubic membranes are discussed. Using these insights, intracellular cubic membrane structures are transformed into an extracellular environment.

Bartl, Michael H.; Dahlby, Michael R.; Barrows, Frank P.; Richens, Zachary J.; Terooatea, Tommy; Jorgensen, Matthew R.

2012-02-01

121

Structural, thermal and optical characterization of a Schiff base as a new organic material for nonlinear optical crystals and films with reversible noncentrosymmetry.  

PubMed

Macroscopic single crystals of (E)-5-(diethylamino)-2-((3,5-dinitrophenylimino)methyl)phenol (DNP) were obtained from slow cooling of chloroform or dichlorometane saturated solutions at controlled temperature. X-ray diffraction analysis showed that this compound crystallizes in a noncentrosymmetric space group (P2(1)2(1)2(1)). Thermal analysis was performed and indicated that the crystals are stable until 260 C. Second-order nonlinear optical properties of DNP were experimentally investigated in solution through EFISH technique and in solid state through the Kurtz-Perry powder technique. Crystals of compound DNP exhibited a second-harmonic signals 39 times larger than of the technologically useful potassium dihydrogenphosphate (KDP) under excitation at infrared wavelengths. In addition, the second-order nonlinear optical properties of DNP were also studied at visible wavelengths through the photorefractive effect and applied to demonstrate dynamic holographic reconstruction. PMID:21664174

Rodrguez, Mario; Ramos-Ortz, Gabriel; Maldonado, Jos Luis; Herrera-Ambriz, Vctor M; Domnguez, Oscar; Santillan, Rosa; Farfn, Norberto; Nakatani, Keitaro

2011-05-24

122

Structural, thermal and optical characterization of a Schiff base as a new organic material for nonlinear optical crystals and films with reversible noncentrosymmetry  

NASA Astrophysics Data System (ADS)

Macroscopic single crystals of (E)-5-(diethylamino)-2-((3,5-dinitrophenylimino)methyl)phenol ( DNP) were obtained from slow cooling of chloroform or dichlorometane saturated solutions at controlled temperature. X-ray diffraction analysis showed that this compound crystallizes in a noncentrosymmetric space group ( P212121). Thermal analysis was performed and indicated that the crystals are stable until 260 C. Second-order nonlinear optical properties of DNP were experimentally investigated in solution through EFISH technique and in solid state through the Kurtz-Perry powder technique. Crystals of compound DNP exhibited a second-harmonic signals 39 times larger than of the technologically useful potassium dihydrogenphosphate (KDP) under excitation at infrared wavelengths. In addition, the second-order nonlinear optical properties of DNP were also studied at visible wavelengths through the photorefractive effect and applied to demonstrate dynamic holographic reconstruction.

Rodrguez, Mario; Ramos-Ortz, Gabriel; Maldonado, Jos Luis; Herrera-Ambriz, Vctor M.; Domnguez, Oscar; Santillan, Rosa; Farfn, Norberto; Nakatani, Keitaro

2011-09-01

123

Crystal structure of plant photosystem I  

Microsoft Academic Search

Oxygenic photosynthesis is the principal producer of both oxygen and organic matter on Earth. The conversion of sunlight into chemical energy is driven by two multisubunit membrane protein complexes named photosystem I and II. We determined the crystal structure of the complete photosystem I (PSI) from a higher plant (Pisum sativum var. alaska) to 4.4 resolution. Its intricate structure shows

Adam Ben-Shem; Felix Frolow; Nathan Nelson

2003-01-01

124

Structure of crystals of hard colloidal spheres  

SciTech Connect

We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, {ital A},{ital B},{ital C}, which shows a high degree of randomness. Crystals grown slowly, while still containing many stacking faults, show a tendency towards face-centered-cubic packing: possible explanations for this observation are discussed.

Pusey, P.N.; van Megen, W.; Bartlett, P.; Ackerson, B.J.; Rarity, J.G.; Underwood, S.M. (Royal Signals and Radar Establishment, Malvern, WR14 3PS, United Kingsom (GB) Department of Applied Physics, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia School of Chemistry, Bristol University, Bristol, BS8 1TS, United Kingdom Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078)

1989-12-18

125

Structure of crystals of hard colloidal spheres  

Microsoft Academic Search

We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, {ital A},{ital B},{ital C}, which shows a high degree of randomness. Crystals grown slowly, while still containing many stacking faults, show a tendency towards face-centered-cubic packing:

P. N. Pusey; W. van Megen; P. Bartlett; B. J. Ackerson; J. G. Rarity; S. M. Underwood

1989-01-01

126

Structure of crystals of hard colloidal spheres  

Microsoft Academic Search

We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, A,B,C, which shows a high degree of randomness. Crystals grown slowly, while still containing many stacking faults, show a tendency towards face-centered-cubic packing: possible explanations for

P. N. Pusey; W. van Megen; P. Bartlett; B. J. Ackerson; J. G. Rarity; S. M. Underwood

1989-01-01

127

The Crystal and Molecular Structure of Fluorene  

Microsoft Academic Search

Fluorene, C13H10, crystallizes in the orthorhombic system, space group Pnam with four molecules per unit cell. The molecule possesses a plane of symmetry which is parallel to the (001) plane of the crystal. The structure has been determined by trial-and-error methods, followed (i) by a least-squares refinement and (ii) by two-dimensional Fourier syntheses. The results from the two methods of

D. M. Burns; J. Iball

1955-01-01

128

Crystal structure and stability of magnesium borohydride from first principles  

NASA Astrophysics Data System (ADS)

We present a structure model for constructing Mg(BH4)2 . The first-principles calculations reveal that some stable ground-state crystal structures of Mg(BH4)2 have the same or slightly lower energy than the I-4m2 structure predicted in a paper by Ozolins [Phys. Rev. Lett. 100, 135501 (2008)]. The possible mechanism for the anomalous stability originates from the fact that the charge transfer between different atoms is more homogeneous. The structure model can be anticipated to have potential application for predicting new stable structures of this group of homologous materials.

Zhou, Xiang-Feng; Qian, Quang-Rui; Zhou, Jian; Xu, Bo; Tian, Yongjun; Wang, Hui-Tian

2009-06-01

129

Optics of magnetic photonic crystals with mu-negative materials  

NASA Astrophysics Data System (ADS)

In this paper, we have made an analysis of the optics of magnetic photonic crystals having mu-negative materials. We consider the magnetic photonic crystal with different values of the magnetic permeability of the materials (PIM). Such materials will be affected by the applied magnetic field and can also exhibit the properties of superconducting materials. We infer that PhC with MNM and PIM materials can be used as tunable devices by choosing proper thickness, damping factor, and mu-value of the PIM.

Kumar, N.; Thapa, K. B.; Janma, Ram; Pandey, G. N.; Reena

2013-06-01

130

Single crystal growth and the electronic structure of orthorhombic Tl3PbBr5: A novel material for non-linear optics  

NASA Astrophysics Data System (ADS)

The X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces of a Tl3PbBr5 single crystal grown by the Bridgman-Stockbarger method have been measured. The present X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of Tl3PbBr5 single crystal surface. Total and partial densities of states of constituent atoms of low-temperature (LT) orthorhombic Tl3PbBr5 phase (space group P21212) have been calculated using the full potential linearized augmented plane wave (FP-LAPW) method. The FP-LAPW data reveal that contributions of the Br 4p-like states dominate in the valence band of LT-Tl3PbBr5; they contribute mainly into the top and the central portion of the valence band with also significant contributions throughout the whole valence-band region. The bottom of the valence band of LT-Tl3PbBr5 is composed mainly of the Tl 6s-like states, whilst the unoccupied Pb 6p- and Tl 6p-like states dominate at the bottom of the conduction band. We have explored the crystallochemistry and origin of the chemical bonds in Tl3PbBr5 with respect to the use as mid-IR non-linear optical crystals. Comparison of the spectral dependence to the second order susceptibilities for the titled crystals is performed with respect to the 3.39 ?m illuminated crystals. Possibility of the use of Tl3PbBr5 crystals as IR operated non-linear optical crystals is discussed.

Khyzhun, O. Y.; Bekenev, V. L.; Parasyuk, O. V.; Danylchuk, S. P.; Denysyuk, N. M.; Fedorchuk, A. O.; AlZayed, N.; Kityk, I. V.

2013-03-01

131

SITALL-A Crystallized Glass Candidate Armor Material.  

National Technical Information Service (NTIS)

A highly crystallized glass candidate armor material known as SITALL has been prepared in plate form suitable for ballistic test and evaluation in complex composite armor systems designed to defeat chemical and kinetic energy threats. Two comparative test...

M. Kliman

1994-01-01

132

Elastic constants and material properties of novel shaped liquid crystals  

NASA Astrophysics Data System (ADS)

We report the Frank elastic constants along with other material properties of the newly synthesized liquid crystals RB01115 and RB01189. These materials are being investigated due to their Y and H-shaped structures respectively and possible biaxial nature of the latter. At T* = (T / TNI) = 0.94, we found the extraordinary refractive index of RB01189 to be 1.548 while the ordinary index was 1.469. We applied magnetic fields to induce Freedericksz transitions in order to find the elastic constants and determined their values to be: K11 = 0.12 x 10-12 N, K22 = 5.6 x 10-12 N, and K33 = 4.6 x 10-12 N. For the Y-shaped RB0115 at T*=0.98, we found K11 = 2.8 x 10-12 N, K22 = 2.5 x 10-12 N, and K33 = 4.5 x 10-12 N. These constants are similar to values found for other materials with non-rod shaped or bent-core structure.

Schmitthenner, M.; Challa, P. K.; Gleeson, J. T.; Garg, S.

2013-03-01

133

Crystal structure of recombinant bovine neurocalcin  

Microsoft Academic Search

The crystal structure of calcium-bound unmyristoylated bovine neurocalcin from Escherichia coli has been determined at 2.4 resolution. The three-dimensional structure reveals a highly compact structure consisting of: (i) two pairs of calcium-binding EF-hands (EF1-EF2 and EF3-EF4); (ii) a calcium ion bound at EF2, EF3 and EF4 sites; and (iii) an EF1-hand that is disabled from calcium-binding due to a

Senadhi Vijay-Kumar; Vinod D. Kumar

1999-01-01

134

Photonic Crystal Structures with Tunable Structure Color as Colorimetric Sensors  

PubMed Central

Colorimetric sensing, which transduces environmental changes into visible color changes, provides a simple yet powerful detection mechanism that is well-suited to the development of low-cost and low-power sensors. A new approach in colorimetric sensing exploits the structural color of photonic crystals (PCs) to create environmentally-influenced color-changeable materials. PCs are composed of periodic dielectrics or metallo-dielectric nanostructures that affect the propagation of electromagnetic waves (EM) by defining the allowed and forbidden photonic bands. Simultaneously, an amazing variety of naturally occurring biological systems exhibit iridescent color due to the presence of PC structures throughout multi-dimensional space. In particular, some kinds of the structural colors in living organisms can be reversibly changed in reaction to external stimuli. Based on the lessons learned from natural photonic structures, some specific examples of PCs-based colorimetric sensors are presented in detail to demonstrate their unprecedented potential in practical applications, such as the detections of temperature, pH, ionic species, solvents, vapor, humidity, pressure and biomolecules. The combination of the nanofabrication technique, useful design methodologies inspired by biological systems and colorimetric sensing will lead to substantial developments in low-cost, miniaturized and widely deployable optical sensors.

Wang, Hui; Zhang, Ke-Qin

2013-01-01

135

Photonic crystal structures with tunable structure color as colorimetric sensors.  

PubMed

Colorimetric sensing, which transduces environmental changes into visible color changes, provides a simple yet powerful detection mechanism that is well-suited to the development of low-cost and low-power sensors. A new approach in colorimetric sensing exploits the structural color of photonic crystals (PCs) to create environmentally-influenced color-changeable materials. PCs are composed of periodic dielectrics or metallo-dielectric nanostructures that affect the propagation of electromagnetic waves (EM) by defining the allowed and forbidden photonic bands. Simultaneously, an amazing variety of naturally occurring biological systems exhibit iridescent color due to the presence of PC structures throughout multi-dimensional space. In particular, some kinds of the structural colors in living organisms can be reversibly changed in reaction to external stimuli. Based on the lessons learned from natural photonic structures, some specific examples of PCs-based colorimetric sensors are presented in detail to demonstrate their unprecedented potential in practical applications, such as the detections of temperature, pH, ionic species, solvents, vapor, humidity, pressure and biomolecules. The combination of the nanofabrication technique, useful design methodologies inspired by biological systems and colorimetric sensing will lead to substantial developments in low-cost, miniaturized and widely deployable optical sensors. PMID:23539027

Wang, Hui; Zhang, Ke-Qin

2013-03-28

136

Crystal growth of optical materials for advanced lasers  

SciTech Connect

During FY96, two specific projects were addressed, Yb-doped fluoroapatite and Cr:ZnSe crystals, which are being used as the gain media to develop diode-pumped solid-state lasers. Both materials have unique properties for near infrared to mid-infrared applications. However, defects in the crystals create optical losses and reduce the efficiency of the lasers. The source of the losses in the crystals were studied and techniques developed to reduce and/or eliminate defects to aid in the growth of high optical quality crystals to increase laser efficiency.

Schaffers, K.I.; Payne, S.A.

1997-02-04

137

Mechanochemical synthesis of nonstoichiometric nanocrystals La{sub 1-y}Ca{sub y}F{sub 3-y} with a tysonite structure and nanoceramic materials from CaF{sub 2} and LaF{sub 3} crystals  

SciTech Connect

The nonstoichiometric phases La{sub 1-y}Ca{sub y}F{sub 3-y} (y = 0.15, 0.20) with a tysonite (LaF{sub 3}) structure have been prepared for the first time by the mechanochemical synthesis from CaF{sub 2} and LaF{sub 3} crystals. The average size of coherent scattering regions is approximately equal to 10-30 nm. It has been shown that the compositions of the phases prepared by the mechanochemical synthesis are inconsistent with the phase diagram of the CaF{sub 2}-LaF{sub 3} system. The 'mechanohydrolysis' of the La{sub 1-y}Ca{sub y}F{sub 3-y} phase has been observed for the first time. Under these conditions, the La{sub 1-y}Ca{sub y}F{sub 3-y} phase partially transforms into lanthanum calcium oxyfluoride for a milling time of 180 min with intermediate sampling. The La{sub 1-y}Ca{sub y}F{sub 3-y} nanoceramic materials have been prepared from a powder of the mechanochemical synthesis product by pressing under a pressure of (2-6) x 10{sup 8} Pa at room temperature. The electrical conductivity of the synthesized materials at a temperature of 200 deg. C is equal to 4.9(6) x 10{sup -4} S/cm, and the activation energy of electrical conduction is 0.46(2) eV. These data for the nanoceramic materials coincide with those obtained for migration of fluorine vacancies in single-crystal tysonite fluoride materials.

Sobolev, B. P., E-mail: fluorides@ns.crys.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Sviridov, I. A.; Fadeeva, V. I. [Moscow State University, Faculty of Chemistry (Russian Federation); Sul'yanov, S. N.; Sorokin, N. I.; Zhmurova, Z. I. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Khodos, I. I. [Russian Academy of Sciences, Institute of Microelectronics Technology and High-Purity Materials (Russian Federation); Avilov, A. S.; Zaporozhets, M. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2008-09-15

138

Confined crystals of the smallest phase-change material.  

PubMed

The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales. PMID:23984706

Giusca, Cristina E; Stolojan, Vlad; Sloan, Jeremy; Brrnert, Felix; Shiozawa, Hidetsugu; Sader, Kasim; Rmmeli, Mark H; Bchner, Bernd; Silva, S Ravi P

2013-09-03

139

Polymerized lyotropic liquid crystals as contact lens materials  

NASA Astrophysics Data System (ADS)

When an aqueous solution of a hydrophilic monomer such as 2-hydroxyethylmetharylate (HEMA) is mixed with a surfactant at the correct proportions, the components self-assemble into a lytropic liquid crystal comprising a highly ordered periodic microstructure, and polymerization of the monomer and removal of the surfactant results in a macroporous hydrogel of potential importance as a material for contact lenses and other prostheses. The two most important properties of these structured polymers as contact lens materials are: (1) unlike simple hydrogels which have irregular pores with a highly polydispersed size distribution, these new materials have an extremely well-characterized-in fact, triply periodic-network of pores of identical size, which can be preselected so as to allow for the transport of proteins, mucins, and other components of the pre-ocular tear film; and (2) this pore size can be selected independently of the polymer concentration and crosslink density, unlike simple hydrogels where large pores can only be obtained by reducing the crosslink density and along with it the shear modulus. The pore diameter can be selected in the range 20-400 and possibly higher. A wide variety of surfactant systems that have been shown to yield materials of this degree of precision and versatility is reviewed.

Anderson, David M.; Strm, Pelle

1991-08-01

140

Confined Crystals of the Smallest Phase-Change Material  

PubMed Central

The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.

2013-01-01

141

Structural and optical properties of a new chalcone single crystal  

NASA Astrophysics Data System (ADS)

A new nonlinear optical material 1-(4-methylthiophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one with molecular formula C17H16O2S was synthesized by using the ClaisenSchmidt condensation reaction method. The Various functional groups present in the compound were identified using recorded FT-IR spectrum. The crystal growth parameters have been studied using solubility test and acetone is found to be a very good solvent for the crystal growth at an ambient temperature. The transparent high quality single crystals up to a size of 2622 mm3 were grown using the slow evaporation solution growth technique. UVvisible study was carried out and the spectrum reveals that the crystal is transparent in the entire visible region and absorptive in the UV region. The refractive index is determined using Brewster's angle method. The optical energy band gap of the material is measured using Tauc's plot and the direct method. The single crystal XRD of MMPP crystal shows the following cell parameters: a=5.9626(2) , b=15.3022(6) , c=16.0385(7) , ?=?=?=90, volume=1463.37(10) 3 with a space group of Pna21. The compound MMPP exhibits optical nonlinearity (NLO) and its second order NLO efficiency is 3.15 times to that of urea. The effect of functional groups OCH3 and SCH3 on the non-linearity as well as the structural property of the compound has been discussed. The crystal is thermally stable. High NLO efficiency, good thermal stability, good transparency and ability to grow as a high quality single crystal make this material very attractive for opto-electronic applications.

Rajesh Kumar, P. C.; Ravindrachary, V.; Janardhana, K.; Poojary, Boja

2012-09-01

142

Nanoscale Imaging of Mineral Crystals inside Biological Composite Materials Using X-Ray Diffraction Microscopy  

NASA Astrophysics Data System (ADS)

We for the first time applied x-ray diffraction microscopy to the imaging of mineral crystals inside biological composite materialsintramuscular fish boneat the nanometer scale resolution. We identified mineral crystals in collagen fibrils at different stages of mineralization. Based on the experimental results and biomineralization analyses, we suggested a dynamic model to account for the nucleation and growth of mineral crystals in the collagen matrix. The results obtained from this study not only further our understanding of the complex structure of bone, but also demonstrate that x-ray diffraction microscopy will become an important tool to study biological materials.

Jiang, Huaidong; Ramunno-Johnson, Damien; Song, Changyong; Amirbekian, Bagrat; Kohmura, Yoshiki; Nishino, Yoshinori; Takahashi, Yukio; Ishikawa, Tetsuya; Miao, Jianwei

2008-01-01

143

Crystal structure of Arabidopsis thaliana cytokinin dehydrogenase  

SciTech Connect

Since first discovered in Zea mays, cytokinin dehydrogenase (CKX) genes have been identified in many plants including rice and Arabidopsis thaliana, which possesses CKX homologues (AtCKX1-AtCKX7). So far, the three-dimensional structure of only Z. mays CKX (ZmCKX1) has been determined. The crystal structures of ZmCKX1 have been solved in the native state and in complex with reaction products and a slowly reacting substrate. The structures revealed four glycosylated asparagine residues and a histidine residue covalently linked to FAD. Combined with the structural information, recent biochemical analyses of ZmCKX1 concluded that the final products of the reaction, adenine and a side chain aldehyde, are formed by nonenzymatic hydrolytic cleavage of cytokinin imine products resulting directly from CKX catalysis. Here, we report the crystal structure of AtCKX7 (gene locus At5g21482.1, UniProt code Q9FUJ1).

Bae, Euiyoung; Bingman, Craig A.; Bitto, Eduard; Aceti, David J.; Phillips, Jr., George N. (UW)

2008-08-13

144

Developments in Aircraft Structural Materials.  

National Technical Information Service (NTIS)

An overview of recent and ongoing development in aircraft structural materials is given. In view of current and predicted usage the most important developments concern aluminum alloys and advanced composites. Developments in titanum alloys, high strength ...

R. J. H. Wanhill W. Vanderhoeven W. G. J. T. Hart

1979-01-01

145

Structural materials for fusion reactors  

Microsoft Academic Search

Fusion Reactors will require specially engineered structural materials, which will simultaneously satisfy the harsh conditions\\u000a such as high thermo mechanical stresses, high heat loads and severe radiation damage without compromising on safety considerations.\\u000a The fundamental differences between fusion and other nuclear reactors arise due to the 14MeV neutronics of structural materials.\\u000a There exists considerable uncertainty in the nuclear data at

P. M. Raole; S. P. Deshpande

2009-01-01

146

Microstructure and Crystal Structure in TAGS Compositions  

SciTech Connect

GeTe, a small bandgap semiconductor that has native p-type defects due to Ge vacancies, is an important constituent in the thermoelectric material known as TAGS. TAGS is an acronym for alloys of GeTe with AgSbTe{sub 2}, and compositions are normally designated as TAGS-x, where x is the fraction of GeTe. TAGS-85 is the most important with regard to applications, and there is also commercial interest in TAGS-80. The crystal structure of GeTe{sub 1+{delta}} has a composition-dependent phase transformation at a temperature ranging from 430 C ({delta} = 0) to {approx}400 C ({delta} = 0.02). The high-temperature form is cubic. The low-temperature form is rhombohedral for {delta} < 0.01, as is the case for good thermoelectric performance. Addition of AgSbTe{sub 2} shifts the phase transformation to lower temperatures, and one of the goals of this work is a systematic study of the dependence of transformation temperature on the parameter x. We present results on phase transformations and associated instabilities in TAGS compositions in the range of 70 at.% to 85 at.% GeTe.

Thompson, A. J. [Marlow Industries, Inc; Sharp, J [Marlow Industries, Inc; Rawn, Claudia J [ORNL

2009-01-01

147

Highly transparent ceramics with disordered crystal structure  

NASA Astrophysics Data System (ADS)

A highly transparent ceramic has been synthesized from Nd3+:Y2O3 to which 6 mol. % ZrO2 and 25 mol. % Sc2O3 or Lu2O3 were added for disordering the crystal structure. Nanopowders with an average particle size of 10-15 nm served as an initial material. They were compacted by the method of uniaxial static pressing combined with ultrasonic action on nanoparticles. The compacting pressure was 200 MPa; the power of the ultrasonic generator was 1.5 kW. It has been shown that the replacement of Y by isovalent Sc and Lu ions and by heterovalent Zr ions reduces the content of pores and the sizes of crystallites. The transparency of the Nd3+:Y2O3 ceramic with these additives reaches a maximum of 82.2%, and the 40% intensity level spectral band corresponding to the 4F3/2 ? 4I11/2 transition widens from 11.4 to 40 nm.

Osipov, V. V.; Khasanov, O. L.; Solomonov, V. I.; Shitov, V. A.; Orlov, A. N.; Platonov, V. V.; Spirina, A. V.; Luk'yashin, K. E.; Dvilis, E. S.

2010-08-01

148

Structural Materials for Space Applications.  

National Technical Information Service (NTIS)

The long-term performance of structural materials in the space environment is a key research activity within NASA. The primary concerns for materials in low Earth orbit (LEO) are atomic oxygen erosion and space debris impact. Atomic oxygen studies have in...

D. R. Tenney

1989-01-01

149

Requirements for structure determination of aperiodic crystals  

NASA Astrophysics Data System (ADS)

Using computer simulation, we compared the Patterson functions of one-dimensional (1D) randomly packed and quasiperiodic Fibonacci lattices with or without disorder, and a 2D Penrose lattice and random packing of pentagons (icosahedral glass model). Based on these comparisons, we derived some empirical guidelines for distinguishing ideal quasicrystals from aperiodic crystals with disorder using diffraction data. In contrast to periodic crystals, it is essential to include the background to obtain correct Patterson functions of the average structure since the background contains unresolved peaks. In particular, a Bragg peak scattering measurement cannot, in general, determine the structure of aperiodic crystals. Instead, a diffuse scattering measurement is required, which determines the absolute value of the diffraction background, in addition to the Bragg peaks. We further estimate that, dependent upon the disorder present, it is necessary to include up to 75% of the total diffracted intensity in any analysis.

Li, Xiao-Ou; Stern, Edward A.; Ma, Yanjun

1991-01-01

150

Crystal structure of methane oxidation enzyme determined  

SciTech Connect

A team of chemists has determined to 2.2-[angstrom] resolution the crystal structure of the hydroxylase protein of methane monooxygenase, the enzyme system responsible for the biological oxidation of methane. The hydroxylase, at a molecular weight of 251,000 daltons, if by far the largest component of methane monooxygenase. Although the crystal structure of the hydroxylase did not reveal any startling surprises about the enzyme-many features of the hydroxylase had been inferred previously from modeling and spectroscopic studies -- obtaining it is a significant achievement. For one thing, the crystal structure unambiguously confirms aspects of the enzyme structure that been at least somewhat speculative. The three-dimensional structure of the enzyme, the chemist say, also provides important insight into biological methane oxidation, including how methane, a relatively inert gas, might diffuse to and bind near the active site of the enzyme. The structure points to particular amino acid residues that are likely to participate in catalysis, and clarifies the structure of the dinuclear iron core of the enzyme.

Baum, R.

1994-01-10

151

Shear induced structures in crystallizing cocoa butter  

NASA Astrophysics Data System (ADS)

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear from the melt in temperature controlled Couette cells, at final crystallization temperatures of 17.5^oC, 20^oC and 22.5^oC in Beamline X10A of NSLS. The formation of phase X was observed at low shear rates (90 s-1) and low crystallization temperature (17.5^oC), but was absent at high shear (720 s-1) and high temperature (20^oC). The d-spacing and melting point suggest that this new phase is a mixture rich on two of the three major components of cocoa butter. We also found that, contrary to previous reports, the transition from phase II to phase V can happen through the intermediate phase IV, at high shear rates and temperature.

Mazzanti, Gianfranco; Guthrie, Sarah E.; Sirota, Eric B.; Marangoni, Alejandro G.; Idziak, Stefan H. J.

2004-03-01

152

Crystal and molecular structure of paclitaxel (taxol).  

PubMed Central

Paclitaxel (formerly called taxol), an important anticancer drug, inhibits cell replication by binding to and stabilizing microtubule polymers. As drug-receptor interactions are governed by the three-dimensional stereochemistries of both participants, we have determined the crystal structure of paclitaxel to identify its conformational preferences that may be related to biological activity. The monoclinic crystals contain two independent paclitaxel molecules in the asymmetric unit plus several water and dioxane solvent molecules. Taxane ring conformation is very similar in both paclitaxel molecules and is similar to the taxane ring conformation found in the crystal structure of the paclitaxel analogue docetaxel (formerly called taxotere). The two paclitaxel molecules have carbon-13 side-chain conformations that differ from each other and from that of the corresponding side chain in the docetaxel crystal structure. The carbon-13 side-chain conformation of one paclitaxel molecule is similar to what was proposed from NMR studies done in polar solvents, while that of the other paclitaxel molecule is different and hitherto unobserved. The paclitaxel molecules interact with each other and with solvent atoms through an extensive network of hydrogen bonds. Analysis of the hydrogen-bonding network together with structure-activity studies may suggest which atoms of paclitaxel are important for binding to microtubule receptors.

Mastropaolo, D; Camerman, A; Luo, Y; Brayer, G D; Camerman, N

1995-01-01

153

Crystal Structure of a Plectonemic RNA Supercoil  

PubMed Central

Genome packaging is an essential housekeeping process in virtually all organisms for proper storage and maintenance of genetic information. Although the extent and mechanisms of packaging vary, the process involves the formation of nucleic-acid superstructures. Crystal structures of DNA coiled coils indicate that their geometries can vary according to sequence and/or the presence of stabilizers such as proteins or small molecules. However, such superstructures have not been revealed for RNA. Here we report the crystal structure of an RNA supercoil, which displays one level higher molecular organization than previously reported structures of DNA coiled coils. In the presence of an RNA-binding protein, two interlocking RNA coiled coils of double-stranded RNA, a coil of coiled coils, form a plectonemic supercoil. Molecular dynamics simulations suggest that protein-RNA interaction is required for the stability of the supercoiled RNA. This study provides structural insight into higher-order packaging mechanisms of nucleic acids.

Stagno, Jason R.; Ma, Buyong; Li, Jess; Altieri, Amanda S.; Byrd, R. Andrew; Ji, Xinhua

2012-01-01

154

Crystal structure of a plectonemic RNA supercoil  

SciTech Connect

Genome packaging is an essential housekeeping process in virtually all organisms for proper storage and maintenance of genetic information. Although the extent and mechanisms of packaging vary, the process involves the formation of nucleic-acid superstructures. Crystal structures of DNA coiled coils indicate that their geometries can vary according to sequence and/or the presence of stabilizers such as proteins or small molecules. However, such superstructures have not been revealed for RNA. Here we report the crystal structure of an RNA supercoil, which displays one level higher molecular organization than previously reported structures of DNA coiled coils. In the presence of an RNA-binding protein, two interlocking RNA coiled coils of double-stranded RNA, a 'coil of coiled coils', form a plectonemic supercoil. Molecular dynamics simulations suggest that protein-RNA interaction is required for the stability of the supercoiled RNA. This study provides structural insight into higher order packaging mechanisms of nucleic acids.

Stagno, Jason R.; Ma, Buyong; Li, Jess; Altieri, Amanda S.; Byrd, R. Andrew; Ji, Xinhua (NCI); (Maryland)

2012-12-14

155

Structure analysis on synthetic emerald crystals  

NASA Astrophysics Data System (ADS)

Single crystals of emerald synthesized by means of the flux method were adopted for crystallographic analyses. Emerald crystals with a wide range of Cr3+-doping content up to 3.16 wt% Cr2O3 were examined by X-ray single crystal diffraction refinement method. The crystal structures of the emerald crystals were refined to R 1 (all data) of 0.019-0.024 and w R 2 (all data) of 0.061-0.073. When Cr3+ substitutes for Al3+, the main adjustment takes place in the Al-octahedron and Be-tetrahedron. The effect of substitution of Cr3+ for Al3+ in the beryl structure results in progressively lengthening of the Al-O distance, while the length of the other bonds remains nearly unchanged. The substitution of Cr3+ for Al3+ may have caused the expansion of a axis, while keeping the c axis unchanged in the emerald lattice. As a consequence, the Al-O-Si and Al-O-Be bonding angles are found to decrease, while the angle of Si-O-Be increases as the Al-O distance increases during the Cr replacement.

Lee, Pei-Lun; Lee, Jiann-Shing; Huang, Eugene; Liao, Ju-Hsiou

2013-05-01

156

Crystal Structure of Dipotassium Carbonate Trihydrate  

Microsoft Academic Search

The crystal structure of 2K2CO3?3H2O was determined by a sign-correlation procedure using three-dimensional data and refined by anisotropic least squares. The space group is C2?c with unit cell dimensions a = 11.887,b = 13.827,c = 7.112 and ? = 120.56. The structure consists of columns of hydrogen-bonded carbonate ions and water molecules within and between which lie the cations.

F. D. Hunter; G. A. Jeffrey

1967-01-01

157

Crystal structure of the 4-chromanone derivative.  

PubMed

The title compound was extracted from a natural product and its structure was characterized by an X-ray diffraction method. It crystallizes in the tetragonal space group P41 with cell parameters a = 15.832(10)A, c = 11.622(10)A, Z = 4; the final residual factor is R1 = 0.0769. The structure has both intra and intermolecular hydrogen bonds. PMID:15055979

Doreswamy, Beeranahally H; Mahendra, Madegowda; Devarajegowda, Hirihally C; Devaru, Venkatesh B; Anandalwar, Sridhar M; Prasad, Javaregowda S

2004-02-01

158

Structural Materials and Analytical Processes  

Microsoft Academic Search

\\u000a This is an introduction to the next three chapters, in which very interesting structures are dealt with, exhibiting impressive\\u000a similarity with advanced modern structures. These are the shields of Achilles and Ajax, consisting of successive laminates,\\u000a metallic for the former, of calfs leather for the latter. Such elements are called multi-layered structures, belonging to the wider class of composite materials.

S. A. Paipetis

159

Complex crystal structure of cesium-III.  

PubMed

The structure of Cs-III, stable between 4.2 and 4.3 GPa at room temperature, has been determined from single-crystal x-ray diffraction data. Rather than the simple fcc structure previously reported [Hall et al., Science 146, 1297 (1964)], the data yield a complex new type of elemental structure which is orthorhombic (space group C222(1)) with 84 atoms in the unit cell. No evidence could be found for the fcc form reported previously, even in a further experiment, conducted under conditions close to those used by Hall et al., which also yielded the 84-atom structure. PMID:11736587

McMahon, M I; Nelmes, R J; Rekhi, S

2001-11-30

160

Evolution of crystal structures in metallic elements  

NASA Astrophysics Data System (ADS)

Crystal structures of metals are often treated as dense packing of atomic spheres. Face-centered cubic and hexagonal close-packed structures are favored in many metals. Long-period-stacking structures such as 9R are sometimes formed. However, nonclose packed structures such as body centered cubic and ? are formed depending upon chemistry and process conditions. Even in metallic elements, it is a priori unknown how such close/nonclose packed structures are formed and what are their interrelationships. In the present study we show a simple algorithm for automated searching of the phase-transition pathway based upon first-principles calculations, which is applied to systematically pursue the evolution of crystal structures. Following the present algorithm, dynamical stability and interrelationships of different structures generated from a simple cubic structure are revealed for seven metallic elements. Effects of pressure are examined as well. The powerfulness of the automated method to investigate the nature of the phase transition and to predict as-yet-unknown metastable structures is demonstrated.

Togo, Atsushi; Tanaka, Isao

2013-05-01

161

The crystal structures of ? and ? * nitrogen  

NASA Astrophysics Data System (ADS)

The crystal structures of the high-pressure ? and ? * phases of nitrogen have been investigated using single-crystal x-ray diffraction. The structure of the ? phase is very similar to isostructural ?-O2 and comprises spherically disordered molecules, with a preference for avoiding pointing along the cubic <100> directions, and disklike molecules with a uniform distribution of orientations. The structure of the ? * phase is tetragonal and the space group is identified unambiguously as P42/ncm with unit cell parameters of a=8.603(5) A? and c=5.685(5) A? at 14.5 GPa. The orientations of the partially disordered molecules have been experimentally determined for the first time and are similar to those predicted on the basis of molecular dynamics simulations.

Stinton, G. W.; Loa, I.; Lundegaard, L. F.; McMahon, M. I.

2009-09-01

162

Crystal structure of low-symmetry rondorfite  

SciTech Connect

The crystal structure of an aluminum-rich variety of the mineral rondorfite with the composition Ca{sub 16}[Mg{sub 2}(Si{sub 7}Al)(O{sub 31}OH)]Cl{sub 4} from the skarns of the Verkhne-Chegemskoe plateau (the Kabardino-Balkarian Republic, the Northern Caucasus Region, Russia) was solved in the triclinic space group with the unit-cell parameters a = 15.100(2) A, b = 15.110(2) A, c = 15.092(2) A, {alpha} = 90.06(1) deg., {beta} = 90.01(1) deg., {gamma} = 89.93(1) deg., Z = 4, sp. gr. P1. The structural model consisting of 248 independent atoms was determined by the phase-correction method and refined to R = 3.8% with anisotropic displacement parameters based on all 7156 independent reflections with 7156 F > 3{sigma}(F). The crystal structure is based on pentamers consisting of four Si tetrahedra linked by the central Mg tetrahedron. The structure can formally be refined in the cubic space group (a = 15.105 A, sp. gr. Fd-bar 3, seven independent positions) with anisotropic displacement parameters to R = 2.74% based on 579 reflections with F > 3{sigma}(F) without accounting for more than 1000 observed reflections, which are inconsistent with the cubic symmetry of the crystal structure.

Rastsvetaeva, R. K. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)], E-mail: rast@ns.crys.ras.ru; Zadov, A. E. [NPO Neokhim (Russian Federation); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2008-03-15

163

Crystal structure of low-symmetry rondorfite  

SciTech Connect

The crystal structure of an aluminum-rich variety of the mineral rondorfite with the composition Ca{sub 16}[Mg{sub 2}(Si{sub 7}Al)(O{sub 31}OH)]Cl{sub 4} from the skarns of the Verkhne-Chegemskoe plateau (the Kabardino-Balkarian Republic, the Northern Caucasus Region, Russia) was solved in the triclinic space group with the unit-cell parameters a = 15.100(2) Angstrom-Sign , b = 15.110(2) Angstrom-Sign , c = 15.092(2) Angstrom-Sign , {alpha} = 90.06(1) Degree-Sign , {beta} = 90.01(1) Degree-Sign , {gamma} = 89.93(1) Degree-Sign , Z = 4, sp. gr. P1. The structural model consisting of 248 independent atoms was determined by the phase-correction method and refined to R = 3.8% with anisotropic displacement parameters based on all 7156 independent reflections with 7156 F > 3{sigma}(F). The crystal structure is based on pentamers consisting of four Si tetrahedra linked by the central Mg tetrahedron. The structure can formally be refined in the cubic space group (a = 15.105 Angstrom-Sign , sp. gr. Fd 3 bar , seven independent positions) with anisotropic displacement parameters to R = 2.74% based on 579 reflections with F > 3{sigma}(F) without accounting for more than 1000 observed reflections, which are inconsistent with the cubic symmetry of the crystal structure.

Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Zadov, A. E. [NPO Neokhim (Russian Federation); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2008-03-15

164

Crystal Structure of Toxoplasma gondii Porphobilinogen Synthase  

PubMed Central

Porphobilinogen synthase (PBGS) is essential for heme biosynthesis, but the enzyme of the protozoan parasite Toxoplasma gondii (TgPBGS) differs from that of its human host in several important respects, including subcellular localization, metal ion dependence, and quaternary structural dynamics. We have solved the crystal structure of TgPBGS, which contains an octamer in the crystallographic asymmetric unit. Crystallized in the presence of substrate, each active site contains one molecule of the product porphobilinogen. Unlike prior structures containing a substrate-derived heterocycle directly bound to an active site zinc ion, the product-bound TgPBGS active site contains neither zinc nor magnesium, placing in question the common notion that all PBGS enzymes require an active site metal ion. Unlike human PBGS, the TgPBGS octamer contains magnesium ions at the intersections between pro-octamer dimers, which are presumed to function in allosteric regulation. TgPBGS includes N- and C-terminal regions that differ considerably from previously solved crystal structures. In particular, the C-terminal extension found in all apicomplexan PBGS enzymes forms an intersubunit ?-sheet, stabilizing a pro-octamer dimer and preventing formation of hexamers that can form in human PBGS. The TgPBGS structure suggests strategies for the development of parasite-selective PBGS inhibitors.

Jaffe, Eileen K.; Shanmugam, Dhanasekaran; Gardberg, Anna; Dieterich, Shellie; Sankaran, Banumathi; Stewart, Lance J.; Myler, Peter J.; Roos, David S.

2011-01-01

165

Transmission properties of a double-periodic quasi-crystal containing single-negative materials  

Microsoft Academic Search

The transmission properties of a double-periodic quasi-crystal containing single-negative materials are investigated with the transfer matrix method and effective medium theory. It is shown that the double-periodic quasi-crystal has a single-negative band gap between the zeros of average permittivity and average permeability of the effective medium. These zeros are affected only by the filling factor of the structure, and are

S. Roshan Entezar; H. Rahimi

2011-01-01

166

Crystal structure of riboflavin synthase  

SciTech Connect

Riboflavin synthase catalyzes the dismutation of two molecules of 6,7-dimethyl-8-(1'-D-ribityl)-lumazine to yield riboflavin and 4-ribitylamino-5-amino-2,6-dihydroxypyrimidine. The homotrimer of 23 kDa subunits has no cofactor requirements for catalysis. The enzyme is nonexistent in humans and is an attractive target for antimicrobial agents of organisms whose pathogenicity depends on their ability to biosynthesize riboflavin. The first three-dimensional structure of the enzyme was determined at 2.0 {angstrom} resolution using the multiwavelength anomalous diffraction (MAD) method on the Escherichia coli protein containing selenomethionine residues. The homotrimer consists of an asymmetric assembly of monomers, each of which comprises two similar {beta} barrels and a C-terminal {alpha} helix. The similar {beta} barrels within the monomer confirm a prediction of pseudo two-fold symmetry that is inferred from the sequence similarity between the two halves of the protein. The {beta} barrels closely resemble folds found in phthalate dioxygenase reductase and other flavoproteins. The three active sites of the trimer are proposed to lie between pairs of monomers in which residues conserved among species reside, including two Asp-His-Ser triads and dyads of Cys-Ser and His-Thr. The proposed active sites are located where FMN (an analog of riboflavin) is modeled from an overlay of the {beta} barrels of phthalate dioxygenase reductase and riboflavin synthase. In the trimer, one active site is formed, and the other two active sites are wide open and exposed to solvent. The nature of the trimer configuration suggests that only one active site can be formed and be catalytically competent at a time.

Liao, D.-I.; Wawrzak, Z.; Calabrese, J.C.; Viitanen, P.V.; Jordan, D.B. (DuPont); (NWU)

2010-03-05

167

Comment on the paper "Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-Chloro 4-Nitrostilbene (CONS): A potential NLO material" by P.M. Dinakaran, S. Kalainathan [Spectrochim. Acta A 111 (2013) 123-130].  

PubMed

We argue that (trans)-4-chloro-4'-nitrostilbene is not a new organic nonlinear optical material as claimed by Dinakaran and Kalainathan [P.M. Dinakaran, S. Kalainathan, Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-Chloro 4-Nitrostilbene (CONS): a potential NLO material, Spectrochim. Acta A 111 (2013) 123-130], but instead a well-known compound whose synthesis, spectral data, single crystal structure and second harmonic generation (SHG) efficiency are well documented in the literature. The title paper is completely erroneous. PMID:24152596

Srinivasan, Bikshandarkoil R; Dhuri, Sunder N; Nadkarni, V S

2013-10-08

168

Monoolein lipid phases as incorporation and enrichment materials for membrane protein crystallization.  

SciTech Connect

The crystallization of membrane proteins in amphiphile-rich materials such as lipidic cubic phases is an established methodology in many structural biology laboratories. The standard procedure employed with this methodology requires the generation of a highly viscous lipidic material by mixing lipid, for instance monoolein, with a solution of the detergent solubilized membrane protein. This preparation is often carried out with specialized mixing tools that allow handling of the highly viscous materials while minimizing dead volume to save precious membrane protein sample. The processes that occur during the initial mixing of the lipid with the membrane protein are not well understood. Here we show that the formation of the lipidic phases and the incorporation of the membrane protein into such materials can be separated experimentally. Specifically, we have investigated the effect of different initial monoolein-based lipid phase states on the crystallization behavior of the colored photosynthetic reaction center from Rhodobacter sphaeroides. We find that the detergent solubilized photosynthetic reaction center spontaneously inserts into and concentrates in the lipid matrix without any mixing, and that the initial lipid material phase state is irrelevant for productive crystallization. A substantial in-situ enrichment of the membrane protein to concentration levels that are otherwise unobtainable occurs in a thin layer on the surface of the lipidic material. These results have important practical applications and hence we suggest a simplified protocol for membrane protein crystallization within amphiphile rich materials, eliminating any specialized mixing tools to prepare crystallization experiments within lipidic cubic phases. Furthermore, by virtue of sampling a membrane protein concentration gradient within a single crystallization experiment, this crystallization technique is more robust and increases the efficiency of identifying productive crystallization parameters. Finally, we provide a model that explains the incorporation of the membrane protein from solution into the lipid phase via a portal lamellar phase.

Wallace, E.; Dranow, D.; Laible, P. D.; Christensen, J.; Nollert, P. (Biosciences Division); (Emerald BioStructures)

2011-01-01

169

Changes in Electronic Structure and Chemical Bonding upon Crystallization of the Phase Change Material GeSb{sub 2}Te{sub 4}  

SciTech Connect

High-resolution photoelectron spectroscopy of in situ prepared films of GeSb{sub 2}Te{sub 4} reveals significant differences in electronic and chemical structure between the amorphous and the crystalline phase. Evidence for two different chemical environments of Ge and Sb in the amorphous structure is found. This observation can explain the pronounced property contrast between both phases and provides new insight into the formation of the amorphous state.

Klein, A.; Spaeth, B. [Darmstadt University of Technology, Institute of Materials Science, D-64287 Darmstadt (Germany); Dieker, H.; Steimer, C.; Wuttig, M. [RWTH Aachen, I. Institute of Physics (IA), D-52056 Aachen (Germany); Fons, P.; Kolobov, A. [Center for Applied Near-Field Optics Research (CAN-FOR), AIST, Tsukuba 305-8562 (Japan)

2008-01-11

170

Photonic crystal and photonic wire device structures  

NASA Astrophysics Data System (ADS)

Photonic devices that exploit photonic crystal (PhC) principles in a planar environment continue to provide a fertile field of research. 2D PhC based channel waveguides can provide both strong confinement and controlled dispersion behaviour. In conjunction with, for instance, various electro-optic, thermo-optic and other effects, a range of device functionality is accessible in very compact PhC channel-guide devices that offer the potential for high-density integration. Low enough propagation losses are now being obtained with photonic crystal channel-guide structures that their use in real applications has become plausible. Photonic wires (PhWs) can also provide strong confinement and low propagation losses. Bragg-gratings imposed on photonic wires can provide dispersion and frequency selection in device structures that are intrinsically simpler than 2D PhC channel guides--and can compete with them under realistic conditions.

De La Rue, Richard; Sorel, Marc; Johnson, Nigel; Rahman, Faiz; Ironside, Charles; Cronin, Lee; Watson, Ian; Martin, Robert; Jin, Chongjun; Pottier, Pierre; Chong, Harold; Gnan, Marco; Jugessur, Aju; Camargo, Edilson; Erwin, Grant; Md Zain, Ahmad; Ntakis, Iraklis; Hobbs, Lois; Zhang, Hua; Armenise, Mario; Ciminelli, Caterina; Coquillat, Dominique

2005-09-01

171

Fission fragment damage to crystal structures  

Microsoft Academic Search

AlO and ZrSiO show little change in properties when ; exposed to 10¹⁸ to 10¹⁹ nvt of thermal neutrons. When, however, a ; source of fission fragments is provided in the form of a UO dispersant, ; the grain boundaries and the peaks of the x-ray-diffraction profile disappear on ; irradiation. The crystal structure of UO is also destroyed when

B. Berman; M. L. Bleiberg; W. Yeniscavich

1960-01-01

172

Crystal structure of a Rad51 filament  

Microsoft Academic Search

Rad51, the major eukaryotic homologous recombinase, is important for the repair of DNA damage and the maintenance of genomic diversity and stability. The active form of this DNA-dependent ATPase is a helical filament within which the search for homology and strand exchange occurs. Here we present the crystal structure of a Saccharomyces cerevisiae Rad51 filament formed by a gain-of-function mutant.

Adam B Conway; Thomas W Lynch; Ying Zhang; Gary S Fortin; Cindy W Fung; Lorraine S Symington; Phoebe A Rice

2004-01-01

173

Crystal Structure of Kaolinite: Dimethylsulfoxide Intercalate  

Microsoft Academic Search

The crystal structure of the kaolinite : dimethylsulfoxide (DMSO) intercalate (P 1, a = 5.187(2), b = 8.964(3), c = 11.838(4) A, a = 91.53(1) ~ = 108.59(2) ~ T = 89.92(1)*) has been determined using spectroscopic and X-ray and neutron powder diffraction data. Both the X-ray and neutron powder diffraction patterns were refined. Solid-state ~3C, 298i, and 27A1 nuclear

J. G. Thompson; C. CUFF

1985-01-01

174

The crystal structure of potassium dimolybdate hydrate  

Microsoft Academic Search

K2Mo2O7 . H2O crystallizes in the triclinic system with unit-cell dimensions a = 7.640(1), b = 8.909(1), c = 7.654(1), , alpha = 109.42(1), beta = 95.75(1), gamma = 119.19(2), and space group P1 with Z = 2. The structure was solved by Patterson and Fourier methods. Of the 2361 unique reflections measured by counter techniques, 2229 with I >=

B. M. Gatehouse; A. J. Jozsa

1987-01-01

175

Lead pyrovanadate single crystal as a new SRS material  

SciTech Connect

Lead pyrovanadate Pb{sub 2}V{sub 2}O{sub 7} single crystals of optical quality suitable for laser experiments are obtained. Vibrational modes are identified based on the analysis of the polarised Raman spectra of the single crystals. The main parameters (width at half maximum, peak and integral intensities) of the spectral lines most promising for SRS conversion in this material are estimated. These parameters are compared with the corresponding parameters of the most frequently used lines of known Raman materials: yttrium and gadolinium vanadates, potassium and lead tungstates, and lead molybdate. (active media)

Basiev, Tasoltan T; Voronko, Yu K; Maslov, Vladislav A; Sobol, A A; Shukshin, V E [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2011-02-28

176

TOPICAL REVIEW: Lyotropic liquid crystal directed synthesis of nanostructured materials  

NASA Astrophysics Data System (ADS)

This review introduces and summarizes lyotropic liquid crystal (LLC) directed syntheses of nanostructured materials consisting of porous nanostructures and zero-dimensional (0-D), one-dimensional (1-D) and two-dimensional (2-D) nanostructures. After a brief introduction to the liquid crystals, the LLCs used to prepare mesoporous materials are discussed; in particular, recent advances in controlling mesostructures are summarized. The LLC templates directing the syntheses of nanoparticles, nanorods, nanowires and nanoplates are also presented. Finally, future development in this field is discussed.

Wang, Cuiqing; Chen, Dairong; Jiao, Xiuling

2009-04-01

177

Smart materials and aerospace structures  

NASA Astrophysics Data System (ADS)

Starting from the very definition of smart structures and smart materials, this paper addresses the fundamental mechanism of operation of some well known smart materials like piezoelectric ceramic/polymer, electrostrictive ceramic, magnetostrictive alloy, shape memory alloy, electroheological fluid, magnetoheological fluid, optical fibers and so on. It also describes briefly the working principles of the actuators and sensor based upon these materials. In addition to that an overview of the various applications and research dealing with the application of these smart materials in aerospace structures mainly in the context of vibration suppression, shape control and adaptive structures for their efficient functioning has been presented. On the whole the presentation stresses on actuators. Since it is the actuator not the sensor that is often the limiting factor in smart structure used for active control. Numerous investigations have been made and are on the way to improve upon the piezoelectric and electrostrictive actuator for greater generating force and larger stroke, as well as shape memory alloy actuator for fast response. Development of multilayer piezoelectric and electrostrictive actuator and discovery of precompressed piezoelectric element and actuator is a forward leap in that direction.

Bandyopadhyay, K.

1999-11-01

178

First-principles calculations of structural, elastic, electronic, and optical properties of perovskite-type KMgH3 crystals: novel hydrogen storage material.  

PubMed

We report a first-principles study of structural and phase stability in three different structures of perovskite-types KMgH(3) according to H position. While electronic and optical properties were measured only for stable perovskite-type KMgH(3), our calculated structural parameters are found in good agreement with experiment and other theoretical results. We also study the electronic charge density space distribution contours in the (200), (101), and (100) crystallographic planes, which gives better insight picture of chemical bonding between K-H, K-Mg-H, and Mg-H. Moreover, we have calculated the electronic band structure dispersion, total, and partial density of electron states to study the band gap origin and the contribution of s-band of H, s and p-band of Mg in the valence band, and d-band of K in the conduction band. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, and loss functions of stable KMgH(3) were calculated for photon energies up to 40 eV. PMID:21375346

Reshak, Ali H; Shalaginov, Mikhail Y; Saeed, Yasir; Kityk, I V; Auluck, S

2011-03-04

179

Crystallic silver amalgam--a novel electrode material.  

PubMed

A crystallic silver amalgam was found to be a suitable working electrode material for voltammetric determination of electrochemically reducible organic nitro-compounds. Optimum conditions for crystal growth were found, the crystal surface was investigated by atomic force microscopy in tapping mode and single crystals were used for the preparation of quasi-cylindrical single crystal silver amalgam electrode (CAgAE). An electrochemical behavior of this alternative electrode material was investigated in aqueous media by direct current voltammetry, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and adsorptive stripping voltammetry (AdSV) using 4-nitrophenol as a model compound. Applicable potential windows of the CAgAE were found comparable with those obtained at a hanging mercury drop electrode, providing high hydrogen overpotential, and polished silver solid amalgam electrode. Thanks to the smooth single crystal electrode surface, the effect of the passivation is not too pronounced, direct DPV determination of 100 ?mol l(-1) of 4-nitrophenol at CAgAEs in 0.2 mol l(-1) acetate buffer pH 4.8 provides a RSD around 1.5% (n = 15). DPV calibration curves of 4-nitrophenol are linear in the whole concentration range 1-100 ?mol l(-1) with a limit of quantification of 1.5 ?mol l(-1). The attempt to increase sensitivity by application of AdSV was not successful. The mechanism of 4-nitrophenol reduction at CAgAE was investigated by CV. PMID:21799953

Danhel, Ales; Mansfeldova, Vera; Janda, Pavel; Vyskocil, Vlastimil; Barek, Jiri

2011-07-28

180

Structural disorder in molecular framework materials.  

PubMed

It is increasingly apparent that many important classes of molecular framework material exhibit a variety of interesting and useful types of structural disorder. This tutorial review summarises a number of recent efforts to understand better both the complex microscopic nature of this disorder and also how it might be implicated in useful functionalities of these materials. We draw on a number of topical examples including topologically-disordered zeolitic imidazolate frameworks (ZIFs), porous aromatic frameworks (PAFs), the phenomena of temperature-, pressure- and desorption-induced amorphisation, partial interpenetration, ferroelectric transition-metal formates, negative thermal expansion in cyanide frameworks, and the mechanics and processing of layered frameworks. We outline the various uses of pair distribution function (PDF) analysis, dielectric spectroscopy, peak-shape analysis of powder diffraction data and single-crystal diffuse scattering measurements as means of characterising disorder in these systems, and we suggest a number of opportunities for future research in the field. PMID:23471316

Cairns, Andrew B; Goodwin, Andrew L

2013-06-21

181

High temperature structural insulating material  

DOEpatents

A high temperature structural insulating material useful as a liner for cylinders of high temperature engines through the favorable combination of high service temperature (above about 800.degree. C.), low thermal conductivity (below about 0.2 W/m.degree. C.), and high compressive strength (above about 250 psi). The insulating material is produced by selecting hollow ceramic beads with a softening temperature above about 800.degree. C., a diameter within the range of 20-200 .mu.m, and a wall thickness in the range of about 2-4 .mu.m; compacting the beads and a compatible silicate binder composition under pressure and sintering conditions to provide the desired structural form with the structure having a closed-cell, compact array of bonded beads.

Chen, Wayne Y. (Munster, IN)

1987-01-01

182

Crystal structure of the non-stoichiometric argyrodite compound Ag 7 x GeSe 5I 1 x ( x=0.31). A highly disordered silver superionic conducting material  

Microsoft Academic Search

Single crystals of the Ag6.69GeSe5I0.69 phase have been obtained by iodine transport of the iodine-partially substituted stoichiometric argyrodite compound Ag7GeSe5I. This phase crystallizes in the cubic space group F4?3m (argyrodite ?-phase, a=10.921(2) at ?100C, a=10.972(3) at 25C, Z=4). It is highly disordered both at anion and cation sites. Crystal structure refinements were completed by an anharmonic GramCharlier development

Renaud Belin; Laurent Aldon; Abdel Zerouale; Claude Belin; Michel Ribes

2001-01-01

183

Structure Determination of Nanocrystalline Materials  

NASA Astrophysics Data System (ADS)

Nanocrystalline materials play an important role in pristine and contaminated geochemical systems. In particular, the reactive surfaces of nanosized ferric and aluminum hydroxides are effective scavengers and transporters of metals and metalloids under aqueous conditions. Establishing the atomic arrangements of these nanocrystalline phases is an essential step towards understanding their structure-property relationships and their roles in geochemical environments. Solving the structures of nanosized materials, often forming with finite particle sizes less than 10 nm, is extremely challenging and often not feasible using conventional structure determination methods. Nanocrystalline ferrihydrite is one example of a material often referred to as being X-ray amorphous because it exhibits poorly defined diffraction maxima in conventional powder patterns. Such features primarily result from the effects caused by disorder and extremely small particle sizes and inhibits quantitative structure determination. This can be avoided by evaluating the atomic arrangement in real-space using total scattering methods combined with pair distribution function (PDF) analysis. PDF analysis is proving to be an essential tool in the study of nanocrystalline materials because it enables the incorporation of both the Bragg and diffuse scattering components and therefore information regarding the short-, intermediate-, and long-range ordering is attainable. We recently used this method to investigate the atomic structures of a number of important nanosized transition metal phases, including ferrihydrite. The initial study of synthetically-derived ferrihydrite resulted in the development of a new structure model for this phase. We are now expanding this investigation by evaluating samples of ferrihydrite occurring in natural settings which are inherently more complex formation environments due to the presence of organics and other metal and metalloid species. The total X-ray scattering method and PDF analysis will be introduced and experimental high-energy scattering data collected at a synchrotron facility will be presented.

Michel, F. M.

2007-12-01

184

Structure of organic/inorganic interface in assembled materials comprising molecular components. Crystal structure of the sensitizer Bis[(4,4{prime}-carboxy-2,2{prime}-bipyridine)(thiocyanato)]ruthenium(II)  

SciTech Connect

Structural data have been obtained for the photosensitizer bis[(4,4{prime}-carboxy-2,2{prime}-bipyridine)(thiocyanato)]ruthenium(II) (1) via X-ray diffraction analysis. Crystals of 1 are triclinic, a = 11.4663(4) {angstrom}, b = 12.5897(5) {angstrom}, c = 18.9329(7) {angstrom}, {alpha} = 75.238(2){degree}, {beta} = 89.611(2){degree}, {gamma} = 66.446(2){degree}, space group P{bar 1}, Z = 2, refinement to R = 0.0809, R{sub w} = 0.0950 for 4045 observed reflections. Structural models of sensitizer molecules anchoring to the TiO{sub 2} anatase surface and models of close-packed sensitizer monolayers with different anchoring types have been built by using experimental geometry of known organic Ti complexes and the X-ray structure of sensitizer 1. On the basis of a simple one-dimensional tight-binding model, it was suggested that possible modifications of TiO{sub 2}/sensitizer interface could enhance interfacial transparency for injected electrons.

Shklover, V.; Ovchinnikov, Yu.E.; Braginsky, L.S. [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Lab. of Crystallography; Zakeeruddin, S.M.; Graetzel, M. [Swiss Federal Inst. of Tech., Lausanne (Switzerland)

1998-09-01

185

Crystal Structure, Chemical Binding, and Lattice Properties  

NASA Astrophysics Data System (ADS)

This chapter starts with an overview of the ZnO crystal structure and its conjunction to the chemical binding. ZnO commonly occurs in the wurtzite structure. This fact is closely related to its tetrahedral bond symmetry and its prominent bond polarity. The main part of the first section deals with the ZnO wurtzite crystal lattice, its symmetry properties, and its geometrical parameters. Besides wurtzite ZnO, the other polytypes, zinc-blende and rocksalt ZnO are also briefly discussed. Subsequently, lattice constant variations and crystal lattice deformations are treated. This discussion starts with static lattice constant variations, induced by temperature or by pressure, as well as strain-induced static lattice deformation, which reduces the crystal symmetry. The impact of this symmetry reduction on the electrical polarization is the piezo effect, which is very much pronounced in ZnO and is exploited in many applications. See also Chap. 13. Dynamic lattice deformations manifest themselves as phonons and, in case of doping, as phonon-plasmon mixed states. The section devoted to phonons starts with a consideration of the vibration eigenmodes and their dispersion curves. Special attention is paid to the investigation of phonons by optical spectroscopy. The methods applied for this purpose are infrared spectroscopy and, more often, Raman spectroscopy. The latter method is very common for the structural quality assessment of ZnO bulk crystals and layers; it is also frequently used for the study of the incorporation of dopant and alloying atoms in the ZnO crystal lattice. Thus, it plays an important role with regard to possible optoelectronics and spintronics applications of ZnO. The final section of this chapter focuses on phonon-plasmon mixed states. These eigenstates occur in doped ZnO due to the strong coupling between collective free-carrier oscillations and lattice vibrations, which occurs due to the high bond polarity. Owing to the direct correlation of the plasmon-phonon modes to the electronic doping, they are an inherent property of ZnO samples, when applied in (opto-) electronics and spintronics. See also Chap. 12.

Geurts, J.

186

Crystal structures of the benzene and ethanol solvates of neotame  

Microsoft Academic Search

The benzene and ethanol solvates of neotame crystallized from solutions of neotame anhydrate in benzene and ethanol, respectively. The crystal structures of the two solvates were determined by single-crystal X-ray diffraction using synchrotron radiation. The benzene solvate crystallizes in the monoclinic space group, P21, Z = 2, with one neotame molecule and one benzene molecule per asymmetric unit. The cell

Zedong Dong; Victor G. Young; Eric J. Munson; Steve A. Schroeder; Indra Prakash; David J. W. Grant

2003-01-01

187

Structural materials for space mirrors  

NASA Astrophysics Data System (ADS)

Work leading to the development of XMM telescope mirrors is described. Although a carbon/epoxy composite structure was specified, a hot type of material was proposed. The further use of such technology in the development of substrates for space mirrors is discussed. The specifications for the plane plates used for the XMM telescope are presented. The advantages and disadvantages of various other materials in producing substrates for space mirrors are discussed. The potential uses of glass matrix ceramics reinforced with carbon or silicon carbide fibers is given particular attention.

Capitanio, C.

1990-06-01

188

[Band electronic structures and crystal packing forces  

SciTech Connect

We investigated the electronic and structural properties of low-dimensional materials and explored the structure-property correlations governing their physical properties. Progress was made on how to interpret the scanning tunneling microscopy and atomic force microscopy images of layered materials and on how to account for charge density wave instabilities in 2-D metals. Materials studied included transition metal chalcogenides, transition metal halides, organic conducting salts, Mo bronzes, A[sub 2]PdH[sub 2], fullerenes, squarate tetrahydrate polymers Fe, Cu(C[sub 4]O[sub 4])4[center dot]H[sub 2]O, BEDT salts, etc.

Not Available

1993-01-01

189

Nd-Doped Mixed Crystal Laser Material Research.  

National Technical Information Service (NTIS)

The mixed crystal system Y3(Al(x)Ga(1-x)5O12 was investigated at a laser host material for Nd(3+). Spectroscopic studies established that at the optimum composition a reduction by a factor of 3 in gain, as compared with YAlG (Y3Al5O12), is possible, and i...

W. C. Holton D. W. Bellavance F. J. Bruni M. deWit R. K. Watts

1974-01-01

190

Polymerized lyotropic liquid crystals as contact lens materials  

Microsoft Academic Search

When an aqueous solution of a hydrophilic monomer such as 2-hydroxyethylmetharylate (HEMA) is mixed with a surfactant at the correct proportions, the components self-assemble into a lytropic liquid crystal comprising a highly ordered periodic microstructure, and polymerization of the monomer and removal of the surfactant results in a macroporous hydrogel of potential importance as a material for contact lenses and

David M. Anderson; Pelle Strm

1991-01-01

191

Crystal structure of Cryptosporidium parvum pyruvate kinase.  

PubMed

Pyruvate kinase plays a critical role in cellular metabolism of glucose by serving as a major regulator of glycolysis. This tetrameric enzyme is allosterically regulated by different effector molecules, mainly phosphosugars. In response to binding of effector molecules and substrates, significant structural changes have been identified in various pyruvate kinase structures. Pyruvate kinase of Cryptosporidium parvum is exceptional among known enzymes of protozoan origin in that it exhibits no allosteric property in the presence of commonly known effector molecules. The crystal structure of pyruvate kinase from C. parvum has been solved by molecular replacement techniques and refined to 2.5 resolution. In the active site a glycerol molecule is located near the ?-phosphate site of ATP, and the protein structure displays a partially closed active site. However, unlike other structures where the active site is closed, the ?6' helix in C. parvum pyruvate kinase unwinds and assumes an extended conformation. In the crystal structure a sulfate ion is found at a site that is occupied by a phosphate of the effector molecule in many pyruvate kinase structures. A new feature of the C. parvum pyruvate kinase structure is the presence of a disulfide bond cross-linking the two monomers in the asymmetric unit. The disulfide bond is formed between cysteine residue 26 in the short N-helix of one monomer with cysteine residue 312 in a long helix (residues 303-320) of the second monomer at the interface of these monomers. Both cysteine residues are unique to C. parvum, and the disulfide bond remained intact in a reduced environment. However, the significance of this bond, if any, remains unknown at this time. PMID:23056503

Cook, William J; Senkovich, Olga; Aleem, Khadijah; Chattopadhyay, Debasish

2012-10-09

192

Crystal and molecular structure of Destruxin B.  

PubMed

The cyclic hexadepsipeptide mycotoxin Destruxin B, produced by Metarrhizium anisopliae, crystallizes in the orthorhombic space group P212121, with a = 11.010(2)A, b = 14.679(5)A, c = 21.273(7)A and Z = 4. The structure was solved by direct methods and refined by least-squares technique to a final unweighted R value of 0.051, for 3361 reflections with I greater than 3 sigma (I). The backbone of the peptide is asymmetric and is made of 5 trans peptide and ester units and 1 cis peptide unit. The backbone conformation of this cyclic depsipeptide is very similar to that of Roseotoxin B, an analogous mycotoxin produced by Trichothecium roseum. The conformation in the crystalline state also correlates well with the solution conformation, as reported from proton n.m.r. studies. The crystal packing is directed by van der Waals contacts. PMID:3366552

Steiner, J R; Barnes, C L

1988-02-01

193

Crystal growth, spectral, optical and thermal properties of semiorganic nonlinear optical material: Picolinic acid hydrochloride  

NASA Astrophysics Data System (ADS)

The bulk single crystal of 2-picolinic acid hydrochloride (PHCL) (a semi-organic nonlinear optical material of dimensions 25 15 10 mm3) was successfully grown by slow solvent evaporation technique. The XRD results revealed the cell parameters and the centrosymmetric nature of the crystal structure. FT-IR spectral study identified the functional groups, nature of bonding and their bond strength. The UV-Vis-NIR studies recognized the optical transmittance window and the lower cut off wavelength of the PHCL crystal and thus it could be performed as a NLO material. 1H NMR and 13CNMR spectra were correlated with the XRD standard for the molecular structure reveals harmony of the materials. Thermal properties of the crystal were studied by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA); the derived kinetic parameter values support the intuitive association of picolinicacid and HCl leads to the spontaneous formation of PHCL with a first order reaction. The presence of a proton and a proton acceptor groups provide the necessary stability to induce charge asymmetry in the PHCL structure. The load dependent hardness values of the crystal were measured by microhardness testing.

Gowri, S.; Uma Devi, T.; Sajan, D.; Surendra Dilip, C.; Chandramohan, A.; Lawrence, N.

2013-06-01

194

Crystal growth, spectral, optical and thermal properties of semiorganic nonlinear optical material: picolinic acid hydrochloride.  

PubMed

The bulk single crystal of 2-picolinic acid hydrochloride (PHCL) (a semi-organic nonlinear optical material of dimensions 251510 mm(3)) was successfully grown by slow solvent evaporation technique. The XRD results revealed the cell parameters and the centrosymmetric nature of the crystal structure. FT-IR spectral study identified the functional groups, nature of bonding and their bond strength. The UV-Vis-NIR studies recognized the optical transmittance window and the lower cut off wavelength of the PHCL crystal and thus it could be performed as a NLO material. (1)H NMR and (13)CNMR spectra were correlated with the XRD standard for the molecular structure reveals harmony of the materials. Thermal properties of the crystal were studied by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA); the derived kinetic parameter values support the intuitive association of picolinicacid and HCl leads to the spontaneous formation of PHCL with a first order reaction. The presence of a proton and a proton acceptor groups provide the necessary stability to induce charge asymmetry in the PHCL structure. The load dependent hardness values of the crystal were measured by microhardness testing. PMID:23557771

Gowri, S; Uma Devi, T; Sajan, D; Surendra Dilip, C; Chandramohan, A; Lawrence, N

2013-03-14

195

Chemical bond analysis of the correlation between crystal structure and nonlinear optical properties of complex crystals  

Microsoft Academic Search

Second order nonlinear optical (NLO) properties of single crystals with complex structures are studied, from the chemical bond viewpoint. Contributions of each type of constituent chemical bond to the total linearity and nonlinearity are calculated from the actual crystal structure, using the chemical bond theory of complex crystals and the modified bond charge model. We have quantitatively proposed certain relationships

Dongfeng Xue; Siyuan Zhang

1999-01-01

196

Crystal structure of MboIIA methyltransferase.  

SciTech Connect

DNA methyltransferases (MTases) are sequence-specific enzymes which transfer a methyl group from S-adenosyl-L-methionine (AdoMet) to the amino group of either cytosine or adenine within a recognized DNA sequence. Methylation of a base in a specific DNA sequence protects DNA from nucleolytic cleavage by restriction enzymes recognizing the same DNA sequence. We have determined at 1.74 {angstrom} resolution the crystal structure of a {beta}-class DNA MTase MboIIA (M {center_dot} MboIIA) from the bacterium Moraxella bovis, the smallest DNA MTase determined to date. M {center_dot} MboIIA methylates the 3' adenine of the pentanucleotide sequence 5'-GAAGA-3'. The protein crystallizes with two molecules in the asymmetric unit which we propose to resemble the dimer when M {center_dot} MboIIA is not bound to DNA. The overall structure of the enzyme closely resembles that of M {center_dot} RsrI. However, the cofactor-binding pocket in M {center_dot} MboIIA forms a closed structure which is in contrast to the open-form structures of other known MTases.

Osipiuk, J.; Walsh, M. A.; Joachimiak, A.; Biosciences Division; Univ. of Gdansk; Medical Research Council France

2003-09-15

197

Structure and Morphology of PEO-b-PLLA Diblock Copolymer Single Crystal  

NASA Astrophysics Data System (ADS)

Poly (L-lactide) (PLLA) is an important biodegradable synthetic polymer of interest for medical applications such as controlled drug delivery, resorbable sutures, medical implants, and scaffolds for tissue engineering. Combining PLLA with Poly (ethylene oxide) (PEO) to form a block copolymer PEO-b-PLLA has attracted the interests of material scientists because modifications of physical and chemical properties lead to an accelerated biodegradability. Generally, the rate of degradation strongly depends on the solid state structure of the material therefore clear understanding of crystallization behavior of PEO-b-PLLA is important. Crystallization of PEO-b-PLLA primarily depends on crystallization temperature (Tc). Solution cast thin film crystallization method was used to obtain the PEO-b-PLLA single crystals. At temperatures above Tm of PEO and below that of PLLA, PLLA crystallizes and forms lozenge-shaped single crystal .When cooled to room temperature, PEO begins to crystallize and form fractal-like single crystal on the top of already formed PLLA crystals. However, at temperatures below Tm of PEO, only the fractal-like PEO single crystals were observed. Structure and morphology of this novel single crystal was explored using TEM and AFM.

Li, Lingyu

2005-03-01

198

Report on artificially structured materials  

NASA Astrophysics Data System (ADS)

Advances in high-vacuum and semiconductor growth techniques have made it possible to tailor-make materials one atomic layer at a time. In this way materials not occurring in nature, with particularelectrical, magnetic optical, or mechanical properties ultimately may be designed and fabricated. The report describes the types of materials used, concentrating on GaAs and GaAlAs compounds; the structures involved, such as superlattices and heterostructures; the scientific opportunities in, for example, superconductor and semiconductor technologies; and the applications possible with ASMs. The report discusses the various fabrication, diagnostic, and characterization methods used in the production of ASMs. Finally, the report lists some of the difficulties confronting researchers, such as the need for easily-available, high-purity samples, and state-of-the-art equipment to fabricate ASMs. The report makes recommendations for federal funding support to allow the U.S. to maintain the lead in this field.

199

Bio-Inspired Approaches to Crystals with Composite Structures  

NASA Astrophysics Data System (ADS)

Advances in technology demand an ever-increasing degree of control over material structure, properties and function. As the properties of monolithic materials are necessary limited, one route to extending them is to create a composite by combining contrasting materials. The potential of this approach is beautifully illustrated by the formation of biominerals where organic macromolecules are combined with brittle minerals such as calcite to create crystals with considerable fracture toughness. This talk will discuss how bio-inspired approaches can be used to generate single crystals with composite crystals through a simple one-pot method. By precipitating calcite crystals in the presence of ``occlusion species'' ranging from latex particles, to organic and inorganic nanoparticles and finally small molecules we demonstrate that high amounts of foreign species can be incorporated through control over the additive surface chemistry, and that this can lead to an enhancement of the mechanical properties of the calcite. Occlusion of 20 nm anionic diblock copolymer micelles was achieved at levels of over 13 wt%, and the properties of the resuktant composite calcite crystals were measured using a range of techniques including IR spectroscopy, high resolution powder XRD and high resolution TEM. Incorporation of these macromolecules leads to crystals with structures and mechanical properties similar to those of biominerals. With sizes in the range of some intracrystalline proteins, the micelles act as ``pseudo-proteins'', thereby providing an excellent model system for investigation of the mechanism of macromolecule insertion within biominerals. Extension of these studies to the incorporation of small molecules (amino acids) again demonstrated high levels of incorporation without any change in the crystal morphology. Further, occlusion of these small molecules within the calcite lattice again resulted in a significant increase in the hardness of the calcite, a result which appears to derive from an increase in lattice strain on molecular occlusion. Finally, the generality of this strategy is demonstrated by its extension to the incorporation of inorganic particles such as magnetite and gold within calcite, leading to the formation of inorganic-inorganic composites.

Meldrum, Fiona

2013-03-01

200

Crystal structure of plant photosystem I  

NASA Astrophysics Data System (ADS)

Oxygenic photosynthesis is the principal producer of both oxygen and organic matter on Earth. The conversion of sunlight into chemical energy is driven by two multisubunit membrane protein complexes named photosystem I and II. We determined the crystal structure of the complete photosystem I (PSI) from a higher plant (Pisum sativum var. alaska) to 4.4 resolution. Its intricate structure shows 12 core subunits, 4 different light-harvesting membrane proteins (LHCI) assembled in a half-moon shape on one side of the core, 45 transmembrane helices, 167 chlorophylls, 3 Fe-S clusters and 2 phylloquinones. About 20 chlorophylls are positioned in strategic locations in the cleft between LHCI and the core. This structure provides a framework for exploration not only of energy and electron transfer but also of the evolutionary forces that shaped the photosynthetic apparatus of terrestrial plants after the divergence of chloroplasts from marine cyanobacteria one billion years ago.

Ben-Shem, Adam; Frolow, Felix; Nelson, Nathan

2003-12-01

201

Electronic structure of molecular crystals containing edge dislocations  

NASA Astrophysics Data System (ADS)

An attempt to model the electronic structure of molecular crystals containing an edge dislocation at the ab initio Hartree-Fock level is performed. The experimentally determined configurations for edge-type dislocations with the Burgers vector [001] in crystalline cyclotrimethylene trinitramine (RDX) and pentaetythritol tetranitrate (PETN) are theoretically simulated. It is shown that a shear stress, induced by the dislocations, produces local electronic states in the fundamental band gap of the crystal. These states are mainly formed by molecular orbitals of critical bonds (which are the N-NO2 group in RDX and the O-NO2 group in PETN) responsible for the stability of the materials. Optical absorption attributed to these electronic states is predicted and compared to the available experimental data. Properties of the defective solids are compared with those of the perfect crystals. Correlation of the electronic structure and sensitivity of the materials to initiation of a chemical reaction as well as some practical applications of the obtained results are discussed.

Kuklja, Maija M.; Kunz, A. Barry

2001-05-01

202

Crystal morphology variation in inkjet-printed organic materials  

NASA Astrophysics Data System (ADS)

The recent commercialization of piezoelectric-based drop-on-demand inkjet printers provides an additive processing platform for producing and micropatterning organic crystal structures. We report an inkjet printing approach where macro- and nano-scale energetic composites composed of cyclotrimethylenetrinitramine (RDX) crystals dispersed in a cellulose acetate butyrate (CAB) matrix are produced by direct phase transformation from organic solvent-based all-liquid inks. The characterization of printed composites illustrates distinct morphological changes dependent on ink deposition parameters. When 10 pL ink droplets rapidly formed a liquid pool, a coffee ring structure containing dendritic RDX crystals was produced. By increasing the substrate temperature, and consequently the evaporation rate of the pooled ink, the coffee ring structure was mitigated and shorter dendrites from up to 1 to 0.2 mm with closer arm spacing from 15 to 1 ?m were produced. When the nucleation and growth of RDX and CAB were confined within the evaporating droplets, a granular structure containing nanoscale RDX crystals was produced. The results suggest that evaporation rate and microfluidic droplet confinement can effectively be used to tailor the morphology of inkjet-printed energetic composites.

Ihnen, Andrew C.; Petrock, Anne M.; Chou, Tsengming; Samuels, Phillip J.; Fuchs, Brian E.; Lee, Woo Y.

2011-11-01

203

Tunable structural color in organisms and photonic materials for design of bioinspired materials  

NASA Astrophysics Data System (ADS)

In this paper, the key topics of tunable structural color in biology and material science are overviewed. Color in biology is considered for selected groups of tropical fish, octopus, squid and beetle. It is caused by nanoplates in iridophores and varies with their spacing, tilting angle and refractive index. These examples may provide valuable hints for the bioinspired design of photonic materials. 1D multilayer films and 3D colloidal crystals with tunable structural color are overviewed from the viewpoint of advanced materials. The tunability of structural color by swelling and strain is demonstrated on an example of opal composites.

Fudouzi, Hiroshi

2011-12-01

204

Characterisation of zeolitic materials with a HEU-type structure modified by transition metal elements: definition of acid sites in nickel-loaded crystals in the light of experimental and quantum-chemical results.  

PubMed

Nickel-loaded HEU-type zeolite crystals have been obtained by well-known synthetic procedures and characterised by X-ray fluorescence (XRF), scanning-electron microscopy/ energy-dispersive spectroscopy (SEM-EDS), FT-IR, diffuse reflectance UV/ Vis spectroscopy (DR(UV/Vis)S) and X-ray photoelectron spectroscopy (XPS) measurements as non-homoionic and non-stoichiometric substances containing exchangeable hydrated Ni2+ ions in the micropores and nickel hydroxide phases supported on the surface. Thermogravimetric analysis/differential gravimetry (TGA/DTG) and differential thermal analysis (DTA) demonstrated that full dehydration below approximately 400 degrees C follows a clearly endothermic process, whereas at higher temperatures the zeolite is amorphised and finally partially recrystallised to Ni(Al,Si) oxides, detected by powder X-ray powder diffraction (XRD). The solid acidity of NiHEU, initially determined by temperature-programmed desorption (TPD) of ammonia to be 8.93 mgg(-1) NH3, is attributed to the weak acid sites (fundamentally Lewis sites) resolved at approximately 183 degrees C, and to the strong acid sites (essentially Brnsted sites) resolved at approximately 461 degrees C in the TPD pattern. A more sophisticated study based on in situ/ex situ FT-IR with in situ/ex situ 27Al MAS NMR and pyridine (Py) as a probe molecule, revealed that the Lewis acid sites can be attributed primarily to Ni2+ ions, whereas the Brnsted ones can probably be associated with the surface-supported nickel hydroxide phases. The spectroscopic measurements in conjunction with powder XRD and 29Si MAS NMR data strongly suggest that distorted Al tetrahedra are formed during the dehydration process and Py chemisorption/complexation (NiHEU-Py), whereas the crystal structure is remarkably well preserved in the rehydrated material (NiHEU-Py/R). The structural, electronic, energetic and spectroscopic properties of all possible nickel(II) aqua and dihydroxy complexes absorbed in the zeolite micropores or supported on the zeolite surface were studied theoretically by density functional theory (DFT). The computed proton affinity, found to be in the range 182.0-210.0 kcalmol(-1), increases with increasing coordination number of the aqua and dihydroxy nickel(II) complexes. PMID:11575771

Godelitsas, A; Charistos, D; Tsipis, A; Tsipis, C; Filippidis, A; Triantafyllidis, C; Manos, G; Siapkas, D

2001-09-01

205

Structural contribution to the roughness of supersmooth crystal surface  

NASA Astrophysics Data System (ADS)

Technological advances in processing crystals (Si, sapphire ?-Al2O3, SiC, GaN, LiNbO3, SrTiO3, etc.) of substrate materials and X-ray optics elements make it possible to obtain supersmooth surfaces with a periodicity characteristic of the crystal structure. These periodic structures are formed by atomically smooth terraces and steps of nano- and subnanometer sizes, respectively. A model surface with such nanostructures is proposed, and the relations between its roughness parameters and the height of atomic steps are determined. The roughness parameters calculated from these relations almost coincide with the experimental atomic force microscopy (AFM) data obtained from 1 1 and 10 10 ?m areas on the surface of sapphire plates with steps. The minimum roughness parameters for vicinal crystal surfaces, which are due to the structural contribution, are calculated based on the approach proposed. A comparative analysis of the relief and roughness parameters of sapphire plate surfaces with different degrees of polishing is performed. A size effect is established: the relief height distribution changes from stochastic to regular with a decrease in the surface roughness.

Butashin, A. V.; Muslimov, A. E.; Kanevsky, V. M.; Deryabin, A. N.; Pavlov, V. A.; Asadchikov, V. E.

2013-05-01

206

Selective crystallization with preferred lithium-ion storage capability of inorganic materials  

PubMed Central

Lithium-ion batteries are supposed to be a key method to make a more efficient use of energy. In the past decade, nanostructured electrode materials have been extensively studied and have presented the opportunity to achieve superior performance for the next-generation batteries which require higher energy and power densities and longer cycle life. In this article, we reviewed recent research activities on selective crystallization of inorganic materials into nanostructured electrodes for lithium-ion batteries and discuss how selective crystallization can improve the electrode performance of materials; for example, selective exposure of surfaces normal to the ionic diffusion paths can greatly enhance the ion conductivity of insertion-type materials; crystallization of alloying-type materials into nanowire arrays has proven to be a good solution to the electrode pulverization problem; and constructing conversion-type materials into hollow structures is an effective approach to buffer the volume variation during cycling. The major goal of this review is to demonstrate the importance of crystallization in energy storage applications.

2012-01-01

207

Crystal structure of yeast Sco1  

SciTech Connect

The Sco family of proteins are involved in the assembly of the dinuclear CuA site in cytochrome c oxidase (COX), the terminal enzyme in aerobic respiration. These proteins, which are found in both eukaryotes and prokaryotes, are characterized by a conserved CXXXC sequence motif that binds copper ions and that has also been proposed to perform a thiol:disulfide oxidoreductase function. The crystal structures of Saccharomyces cerevisiae apo Sco1 (apo-ySco1) and Sco1 in the presence of copper ions (Cu-ySco1) were determined to 1.8- and 2.3-{angstrom} resolutions, respectively. Yeast Sco1 exhibits a thioredoxin-like fold, similar to that observed for human Sco1 and a homolog from Bacillus subtilis. The Cu-ySco1 structure, obtained by soaking apo-ySco1 crystals in copper ions, reveals an unexpected copper-binding site involving Cys181 and Cys216, cysteine residues present in ySco1 but not in other homologs. The conserved CXXXC cysteines, Cys148 and Cys152, can undergo redox chemistry in the crystal. An essential histidine residue, His239, is located on a highly flexible loop, denoted the Sco loop, and can adopt positions proximal to both pairs of cysteines. Interactions between ySco1 and its partner proteins yeast Cox17 and yeast COX2 are likely to occur via complementary electrostatic surfaces. This high-resolution model of a eukaryotic Sco protein provides new insight into Sco copper binding and function.

Abajian, Carnie; Rosenzweig, Amy C. (NWU)

2010-03-05

208

Biomolecular crystals for material applications and a mechanistic study of an iron oxide nanoparticle synthesis  

NASA Astrophysics Data System (ADS)

The three projects within this work address the difficulties of controlling biomolecular crystal formats (i.e. size and shape), producing 3-D ordered composite materials from biomolecular crystal templates, and understanding the mechanism of a practical iron oxide synthesis. The unifying thread consistent throughout these three topics is the development of methods to manipulate nanomaterials using a bottom-up approach. Biomolecular crystals are nanometer to millimeter sized crystals that have well ordered mesoporous solvent channels. The overall physical dimensions of these crystals are highly dependent on crystallization conditions. The controlled growth of micro- and nanoprotein crystals was studied to provide new pathways for creating smaller crystalline protein materials. This method produced tetragonal hen egg-white lysozyme crystals (250--100,000 nm) with near monodisperse size distributions (<15%). With this degree of control, existing protein crystal applications such as drug delivery and analytical sensors can reach their full potential. Applications for larger crystals with inherently ubiquitous pore structures could extend to materials used for membranes or templates. In this work, the porous structure of larger cowpea mosaic virus crystals was used to template metal nanoparticle growth within the body centered cubic crystalline network. The final composite material was found to have long range ordering of palladium and platinum nonocrystal aggregates (10nm) with symmetry consistent to the virus template. Nanoparticle synthesis itself is an immense field of study with an array of diverse applications. The final piece of this work investigates the mechanism behind a previously developed iron oxide synthesis to gain more understanding and direction to future synthesis strategies. The particle growth mechanism was found to proceed by the formation of a solvated iron(III)oleate complex followed by a reduction of iron (III) to iron (II). This unstable iron(II) nucleates to form a wustite (FeO) core which serves as an epitaxial surface for the magnetite (Fe3O4) shell growth. This method produces spherical particles (6-60nm) with relative size distributions of less than 15%.

Falkner, Joshua Charles

209

How evolutionary crystal structure prediction works--and why.  

PubMed

Once the crystal structure of a chemical substance is known, many properties can be predicted reliably and routinely. Therefore if researchers could predict the crystal structure of a material before it is synthesized, they could significantly accelerate the discovery of new materials. In addition, the ability to predict crystal structures at arbitrary conditions of pressure and temperature is invaluable for the study of matter at extreme conditions, where experiments are difficult. Crystal structure prediction (CSP), the problem of finding the most stable arrangement of atoms given only the chemical composition, has long remained a major unsolved scientific problem. Two problems are entangled here: search, the efficient exploration of the multidimensional energy landscape, and ranking, the correct calculation of relative energies. For organic crystals, which contain a few molecules in the unit cell, search can be quite simple as long as a researcher does not need to include many possible isomers or conformations of the molecules; therefore ranking becomes the main challenge. For inorganic crystals, quantum mechanical methods often provide correct relative energies, making search the most critical problem. Recent developments provide useful practical methods for solving the search problem to a considerable extent. One can use simulated annealing, metadynamics, random sampling, basin hopping, minima hopping, and data mining. Genetic algorithms have been applied to crystals since 1995, but with limited success, which necessitated the development of a very different evolutionary algorithm. This Account reviews CSP using one of the major techniques, the hybrid evolutionary algorithm USPEX (Universal Structure Predictor: Evolutionary Xtallography). Using recent developments in the theory of energy landscapes, we unravel the reasons evolutionary techniques work for CSP and point out their limitations. We demonstrate that the energy landscapes of chemical systems have an overall shape and explore their intrinsic dimensionalities. Because of the inverse relationships between order and energy and between the dimensionality and diversity of an ensemble of crystal structures, the chances that a random search will find the ground state decrease exponentially with increasing system size. A well-designed evolutionary algorithm allows for much greater computational efficiency. We illustrate the power of evolutionary CSP through applications that examine matter at high pressure, where new, unexpected phenomena take place. Evolutionary CSP has allowed researchers to make unexpected discoveries such as a transparent phase of sodium, a partially ionic form of boron, complex superconducting forms of calcium, a novel superhard allotrope of carbon, polymeric modifications of nitrogen, and a new class of compounds, perhydrides. These methods have also led to the discovery of novel hydride superconductors including the "impossible" LiH(n) (n=2, 6, 8) compounds, and CaLi(2). We discuss extensions of the method to molecular crystals, systems of variable composition, and the targeted optimization of specific physical properties. PMID:21361336

Oganov, Artem R; Lyakhov, Andriy O; Valle, Mario

2011-03-01

210

The crystal structure of vyuntspakhite: A redetermination  

NASA Astrophysics Data System (ADS)

The crystal structure of the mineral vyuntspakhite (Y, TR)6{Al2(OH)3[H1.48Si1.88O7][SiO4][SiO3(OH)]}2( a = 5.7551(11) , b = 14.752(3) , c = 15.906(4) , ? = 96.046(4), sp. gr. P21/ n, Z = 2), which had been established earlier in the pseudo-unit cell, is redetermined by X-ray diffraction ( R = 0.040, T = 100 K). The redetermination of the structure shows that pronounced pseudotranslation along the axis c' = c/3 is associated with the fact that Y( TR) atoms are related by a 1/3 translation along the [001] direction. Most of the hydrogen atoms are located. The crystal-chemical function of hydrogen bonds is analyzed. In the unit cell of vyuntspakhite, the cationic layers consisting of edge-sharing (Y, TR) eight-vertex polyhedra alternate along the b axis with mixed anionic layers composed of isolated Si tetrahedra (orthotetrahedra), Si2O7 double-tetrahedra (diortho) groups, Al five-vertex polyhedra, and Al2O8 double-tetrahedra groups linked by shared vertices and through hydrogen bonding.

Yakubovich, O. V.; Steele, I. M.

2009-09-01

211

The Crystal Structure of Human Argonaute2  

SciTech Connect

Argonaute proteins form the functional core of the RNA-induced silencing complexes that mediate RNA silencing in eukaryotes. The 2.3 angstrom resolution crystal structure of human Argonaute2 (Ago2) reveals a bilobed molecule with a central cleft for binding guide and target RNAs. Nucleotides 2 to 6 of a heterogeneous mixture of guide RNAs are positioned in an A-form conformation for base pairing with target messenger RNAs. Between nucleotides 6 and 7, there is a kink that may function in microRNA target recognition or release of sliced RNA products. Tandem tryptophan-binding pockets in the PIWI domain define a likely interaction surface for recruitment of glycine-tryptophan-182 (GW182) or other tryptophan-rich cofactors. These results will enable structure-based approaches for harnessing the untapped therapeutic potential of RNA silencing in humans.

Schirle, Nicole T.; MacRae, Ian J. (Scripps)

2012-07-18

212

Self-heating structural materials  

NASA Astrophysics Data System (ADS)

Self-heating structural materials, being useful for deicing and space heating, are reviewed. They include cement-matrix and polymer-matrix composites that are rendered self-heating through enhancing their effectiveness for resistance heating. The enhancement is attained by the use of electrically conductive fibers (continuous or discontinuous) and interlayers. The interlaminar interface between continuous carbon fiber laminae provides a two-dimensional array of heating elements. Power up to 6.5 W, maximum temperature up to 134 C and time to reach half of the maximum temperature rise down to 14 s have been attained.

Chung, D. D. L.

2004-06-01

213

Explosive scabbling of structural materials  

DOEpatents

A new approach to scabbling of surfaces of structural materials is disclosed. A layer of mildly energetic explosive composition is applied to the surface to be scabbled. The explosive composition is then detonated, rubbleizing the surface. Explosive compositions used must sustain a detonation front along the surface to which it is applied and conform closely to the surface being scabbled. Suitable explosive compositions exist which are stable under handling, easy to apply, easy to transport, have limited toxicity, and can be reliably detonated using conventional techniques.

Bickes, Jr., Robert W. (Albuquerque, NM); Bonzon, Lloyd L. (Albuquerque, NM)

2002-01-01

214

Crystal structure of Junin virus nucleoprotein.  

PubMed

Junin virus (JUNV) has been identified as the aetiological agent of Argentine haemorrhagic fever (AHF), which is a serious public health problem with approximately 5 million people at risk. It is treated as a potential bioterrorism agent because of its rapid transmission by aerosols. JUNV is a negative-sense ssRNA virus that belongs to the genus Arenavirus within the family Arenaviridae, and its genomic RNA contains two segments encoding four proteins. Among these, the nucleoprotein (NP) has essential roles in viral RNA synthesis and immune suppression, but the molecular mechanisms of its actions are only partially understood. Here, we determined a 2.2 crystal structure of the C-terminal domain of JUNV NP. This structure showed high similarity to the Lassa fever virus (LASV) NP C-terminal domain. However, both the structure and function of JUNV NP showed differences compared with LASV NP. This study extends our structural insight into the negative-sense ssRNA virus NPs. PMID:23884367

Zhang, Yinjie; Li, Le; Liu, Xiang; Dong, Shishang; Wang, Wenming; Huo, Tong; Guo, Yu; Rao, Zihe; Yang, Cheng

2013-07-24

215

Salt crystallization in porous construction materials. II. Mass transport and crystallization processes  

Microsoft Academic Search

In order to study the processes of salt weathering of monumental stones, several samples were partially immersed in sodium, potassium and magnesium sulphate solutions which ascended through their capillary network and, eventually, crystallized. This procedure pretends to simulate the conditions in which foundations and lower walls of building structures are, within the zone of capillary rise of saline groundwater. Mass

V. Lpez-Acevedo; C. Viedma; V. Gonzalez; A. La Iglesia

1997-01-01

216

Structures of Complex Crystals of Alkylammonium Salts with Aromatic Molecules  

Microsoft Academic Search

The complex crystal structures of dodecyltrimethylammonium chloride (DTAC) with catechol and hydroquinone were analysed by an X-ray diffraction method. Both complexes have isomorphous layered structures. The guest molecules locate between the interdigitated host molecules. Crystal structures are stabilized by mainly hydrogen bonds including water molecules. A cross-section balance between hydrophilic and hydrophobic parts is important for an energetically stable packing.

Keiichi Noguchi; Kenji Okuyama; Kulthida Vongbupnimit

1996-01-01

217

Some Lower Valence Vanadium Fluorides: Their Crystal Distortions, Domain Structures, Modulated Structures, Ferrimagnetism, and Composition Dependence.  

ERIC Educational Resources Information Center

|Describes some contemporary concepts unique to the structure of advanced solids, i.e., their crystal distortions, domain structures, modulated structures, ferrimagnetism, and composition dependence. (Author/CS)|

Hong, Y. S.; And Others

1980-01-01

218

Crystal structure of level zero extremal weight modules  

Microsoft Academic Search

We consider the crystal structure of the level zero extremal weight modules $V(\\\\lambda)$ using the crystal base of the quantum affine algebra constructed by Beck, Chari and Pressley. This approach yields an explicit form for the U^- extremal weight vectors in each connected component of the crystal of $V(\\\\lambda)$, which are given as Schur functions in the imaginary root vectors.

Jonathan Beck

2002-01-01

219

Tunable photonic structures from liquid crystal elastomers  

NASA Astrophysics Data System (ADS)

We investigated one-dimensional and two-dimensional optical diffraction structures fabricated in thin films of a sidechain light-sensitive liquid crystal elastomer (SC-LS-LCEs) by optical holographic lithography methods. The emphasis was on analysis of modifications of the periodicity of the recorded patterns induced by application of an external strain and by temperature modifications. The results show that due to rubber elasticity of the LCE films, relative modifications of the periodicity by 10% can easily be reached. In most cases tuning is reversible and linear with respect to the strain. Temperature induced tuning is most efficient in the region of phase transition from the nematic to the paranematic phase and provides relative periodicity modifications up to 30%.

Gregorc, Marko; Li, Hui; Domenici, Valentina; Drevenek-Olenik, Irena

2012-11-01

220

Crystal structures of saposins A and C.  

PubMed

Saposins A and C are sphingolipid activator proteins required for the lysosomal breakdown of galactosylceramide and glucosylceramide, respectively. The saposins interact with lipids, leading to an enhanced accessibility of the lipid headgroups to their cognate hydrolases. We have determined the crystal structures of human saposins A and C to 2.0 Angstroms and 2.4 Angstroms, respectively, and both reveal the compact, monomeric saposin fold. We confirmed that these two proteins were monomeric in solution at pH 7.0 by analytical centrifugation. However, at pH 4.8, in the presence of the detergent C(8)E(5), saposin A assembled into dimers, while saposin C formed trimers. Saposin B was dimeric under all conditions tested. The self-association of the saposins is likely to be relevant to how these small proteins interact with lipids, membranes, and hydrolase enzymes. PMID:16823039

Ahn, Victoria E; Leyko, Paul; Alattia, Jean-Ren; Chen, Lu; Priv, Gilbert G

2006-07-05

221

Crystal structure of a snake venom cardiotoxin  

SciTech Connect

Cardiotoxin V/sup II/4 from Naja mossambica crystallizes in space group P6/sub 1/ (a = b = 73.9 A; c = 59.0 A) with two molecules of toxin (molecular mass = 6715 Da) in the asymmetric unit. The structure was solved by using a combination of multiple isomorphous replacement and density modification methods. Model building and least-squares refinement led to an agreement factor of 27% for a data set to 3-A resolution prior to any inclusion of solvent molecules. The topology of the molecule is similar to that found in short and long snake neurotoxins, which block the nicotinic acetylcholine receptor. Major differences occur in the conformation of the central loop, resulting in a change in the concavity of the molecule. Hydrophobic residues are clustered in two distinct areas. The existence of stable dimeric entities in the crystalline state, with the formation of a six-stranded antiparallel ..beta.. sheet, may be functionally relevant.

Rees, B.; Samama, J.P.; Thierry, J.C.; Gilibert, M.; Fischer, J.; Schweitz, H.; Lazdunski, M.; Moras, D.

1987-05-01

222

Synthesis, crystal growth and characterization of a chiral compound (triphenylphosphine oxide cadmium iodide): A new semiorganic nonlinear optical material  

NASA Astrophysics Data System (ADS)

Synthesis of semiorganic material, triphenylphosphine oxide cadmium iodide (TPPOCdI), is reported for the first time. Employing the temperature reduction method, a crystal of size 1676 mm3 was grown from dimethyl sulfoxide (DMSO) solution. Three dimensional crystal structure of the grown crystal was determined by single crystal X-ray diffraction study. The complex crystallizes in the chiral orthorhombic space group P212121. FTIR study was carried out in order to confirm the presence of the functional groups. UV-vis-NIR spectral studies show that the crystal is transparent in the wavelength range of 290-1100 nm. The microhardness test was carried out, and the load hardness was measured. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. Second harmonic generation efficiency of the powdered TPPOCdI, tested using Nd: YAG laser, is 0.65 times that of potassium dihydrogen orthophosphate.

Santhakumari, R.; Ramamurthi, K.; Stoeckli-Evans, Helen; Hema, R.; Nirmala, W.

2011-05-01

223

Structural Materials for Fusion Reactor Blanket Systems.  

National Technical Information Service (NTIS)

Consideration of the required functions of the blanket and the general chemical, mechanical, and physical properties of candidate tritium breeding materials, coolants, structural materials, etc., leads to acceptable or compatible combinations of materials...

E. E. Bloom D. L. Smith

1984-01-01

224

Method and structure for passivating semiconductor material  

DOEpatents

A structure for passivating semiconductor material comprises a substrate of crystalline semiconductor material, a relatively thin film of carbon disposed on a surface of the crystalline material, and a layer of hydrogenated amorphous silicon deposited on the carbon film.

Pankove, Jacques I. (Princeton, NJ)

1981-01-01

225

Azine bridged silver coordination polymers: Powder X-ray diffraction route to crystal structure determination of silver benzotriazole  

Microsoft Academic Search

In continuation of our interest in solid-state structures of silver complexes of photographic importance, the structure for silver benzotriazole (AgBZT), has now been obtained. The preferred method for solving crystal structures is via single-crystal X-ray diffraction (XRD). However, for some materials, growing single crystals of appropriate size and quality is often difficult or even impossible. AgBZT is an example of

Manju. Rajeswaran; Thomas N. Blanton; David J. Giesen; David R. Whitcomb; Nicholas Zumbulyadis; Brian J. Antalek; Marcus M. Neumann; Scott T. Misture

2006-01-01

226

Cryogenic structural materials for superconducting magnets  

SciTech Connect

This paper reviews research in the United States and Japan on structural materials for high-field superconducting magnets. Superconducting magnets are used for magnetic fusion energy devices and for accelerators that are used in particle-physics research. The cryogenic structural materials that we review are used for magnet cases and support structures. We expect increased materials requirements in the future.

Dalder, E.N.C.; Morris, J.W. Jr.

1985-02-22

227

Structural, elastic, and electronic properties of new superhard isotropic cubic crystals of carbon nanotubes  

NASA Astrophysics Data System (ADS)

The models of new isotropic cubic crystals of single-layered carbon nanotubes are proposed. The structural, elastic, and electronic properties and the energies of formation of these crystals were calculated using the density functional-based tight binding (DFTB) method. The crystals proposed were found to exhibit extreme compression moduli (550-650 GPa) and a minimum compressibility (0.0018-0.0015 GPa-1); in this case, the type of conduction of the parent nanotubes was retained. For this reason, the above crystals are of interest for the development of new superhard materials with controllable electrophysical properties.

Enyashin, A. N.; Ivanovskii, A. L.

2008-05-01

228

Crystal chemistry, single crystal X-ray structure and magnetism of nickel manganese pyrophosphate  

SciTech Connect

A study of the crystal chemistry of the Ni[sub 2[minus]x]Mn[sub x]P[sub 2]O[sub 7] systems in powder form, 0 [le] x [le] 2, has revealed the existence of three solid solutions. When x < 0.10, the solution is isostructural with low temperature form, [alpha]-Ni[sub 2]P[sub 2]O[sub 7]. When 0.10 [le] x [le] 0.40, the structure of the solid solution is similar to that of [sigma]-Ni[sub 2]P[sub 2]O[sub 7]. When 0.60 [le] x [le] 2, a form similar to [beta]-Ni[sub 2]P[sub 2]O[sub 7] (or Mn[sub 2]P[sub 2]O[sub 7]) is seen. The single crystal structure of material corresponding to x = 0.816 has been determined in monoclinic space group Cm, a = 6.557(3), b = 8.738(5), c = 4.498(3), [beta] = 103.24(1)[degree], V = 240.6(2)[angstrom][sup 3], Z = 2, R/R[sub W] = 3.8/5.3% and shows a structural deformation of the parent lattice. The system shows antiferromagnetic interactions at low temperature.

Benkhouja, K.; Zahir, M.; Sadel, A. (Dept. de Chimie, ElJadida (Morocco)); Handizi, A.; Boukhari, A. (Univ. Mohammed 5, Rabat (Morocco)); Holt, E.M. (Oklahoma State Univ., Stillwater, OK (United States). Dept. of Chemistry); Aride, J. (E.N.S. Takaddoum, Rabat (Morocco)); Drillon, M. (GMI EHICS, Strasbourg (France))

1995-01-01

229

Composite materials and their use in structures  

Microsoft Academic Search

This book attempts to provide a basic fundamental understanding of the physical and mathematical aspects of the materials system and structures comprised of composite materials. The introduction discusses the nature and scope of composite materials, the strengthening processes used in the manufacture of alloys, and the needs for composite materials. Then various types of fiber-reinforced materials are examined, first by

J. R. Vinson; T. W. Chou

1975-01-01

230

Crystal Structure of Human Kynurenine Aminotransferase ll*  

SciTech Connect

Human kynurenine aminotransferase II (hKAT-II) efficiently catalyzes the transamination of knunrenine to kynurenic acid (KYNA). KYNA is the only known endogenous antagonist of N-methyl-d-aspartate (NMDA) receptors and is also an antagonist of 7-nicotinic acetylcholine receptors. Abnormal concentrations of brain KYNA have been implicated in the pathogenesis and development of several neurological and psychiatric diseases in humans. Consequently, enzymes involved in the production of brain KYNA have been considered potential regulatory targets. In this article, we report a 2.16 Angstroms crystal structure of hKAT-II and a 1.95 Angstroms structure of its complex with kynurenine. The protein architecture of hKAT-II reveals that it belongs to the fold-type I pyridoxal 5-phosphate (PLP)-dependent enzymes. In comparison with all subclasses of fold-type I-PLP-dependent enzymes, we propose that hKAT-II represents a novel subclass in the fold-type I enzymes because of the unique folding of its first 65 N-terminal residues. This study provides a molecular basis for future effort in maintaining physiological concentrations of KYNA through molecular and biochemical regulation of hKAT-II.

Han,Q.; Robinson, H.; Li, J.

2008-01-01

231

Study of the interfacial structures and behavior of smectic liquid crystals using synchrotron light source  

NASA Astrophysics Data System (ADS)

Grazing Incidence X-ray Scattering with a synchrotron X-ray source is used to study the depth dependence of the interfacial structure of smectic liquid crystal (8CB) hybrid films. The advancement and market potential of liquid crystal technologies lead to inventions of new materials and surface treatments. The knowledge of interfacial structures and behavior is very critical to these thin film devices such as Liquid Crystal Display. Photolithography in a clean room is adopted to make gratings on very thin glass, which offers better quality than conventional methods in terms of uniformity, reproducibility, reliability, and endurance. Liquid crystal thin films are bounded by a grated glass substrate and air, and have been studied as a function of both temperature and thickness. Experimental measurements indicate the existence of chevron, tilt, and bookshelf structure, as well as Twisted Grain Boundary (TGB) structure that has not previously been observed by X-ray in non-chiral smectic liquid crystals. These structures are a result of liquid crystal anchoring at two dissimilar competing confining surfaces, air-smectics and smectics-grating substrate. With deeper grating, smectic liquid crystals are more constrained in structure and more resilient to temperature change. The smectic phase also persisted at a higher temperature above the smectic-nematic transition point on a deeper grating substrate. When the thickness of liquid crystal samples is beyond a certain point, the smectic liquid crystal begins to form different layers. Chevron structures appear in most situations, which is consistent with previous research A TGB structure is not tamable in a thicker sample where liquid crystals tend to realign themselves in a more stable structure.

Hu, Yufei

2003-10-01

232

Synthesis of rare-earth selenate and selenite materials under "sol-gel" hydrothermal conditions: crystal structures and characterizations of La(HSeO3)(SeO4) and KNd(SeO4)2  

NASA Astrophysics Data System (ADS)

Two rare-earth compounds containing selenium atoms, La(HSeO3)(SeO4) with a new open framework structure and KNd(SeO4)2 with a layered structure, have been synthesized under "sol-gel" hydrothermal conditions for the first time. Single-crystals of La(HSeO3)(SeO4) crystallize in the monoclinic system (P21, a=8.5905(17), b=7.2459(14), c=9.5691(19), ?=104.91(3), Z=2, RAll=0.032). The structure contains puckered polyhedral layers made of LaOx (x=9,10) and SeO4 groups, which are connected via SeO3-uints to the 3D structure. The crytal structure of KNd(SeO4)2 (monoclinc, P21/c, a=8.7182(17), b=7.3225(15), c=11.045(2), ?=91.38(3), Z=4, RAll=0.051) contains honeycomb-like six-ring NdO9 polyhedra forming layers which are further decorated with SeO4 tetrahedra. The K+ ions occupy the interspaces of these layers and provide the charge balance.

Liu, Wei; Chen, Hao-Hong; Yang, Xin-Xin; Li, Mang-Rong; Zhao, Jing-Tai

2004-12-01

233

Anomalous variations of crystal habits and solution properties in the context of the crystallization medium structure  

NASA Astrophysics Data System (ADS)

The effect of the real structure of solutions on crystallization is one of the basic issues of crystallogenesis, which is also important for resolving problems of genetic mineralogy. The study of the NaNO3-H2O and KNO3-H2O model systems yielded new data on anomalous characteristics of crystal-forming systems, including morphological and kinetic properties of crystals, crystal-solution equilibrium, and physical properties of solutions (light scattering, thermal properties, IR parameters, pH), providing information on the structure of solutions. The internally consistent data confirm the previously suggested variations in structural heterogeneity of solutions related to minor (2-4%) variations in their composition, which result in numerous disturbances of monotonicity (thermal-concentration oscillations) in the liquidus curves of salts. It is shown that these variations can be caused by variable size and composition of crystal hydrate clusters. The experimental data indicate that the effect of the real solution structure on crystal morphology and crystal-solution equilibrium is enhanced in multicomponent systems, including natural crystal-forming systems. Anomalous faceting and habit, zoning, a sectorial structure of crystals, and nonuniform entrapment of admixtures cannot be ruled out in these systems.

Kiryanova, E. V.; Ugolkov, V. L.; Pyankova, L. A.; Filatov, S. K.

2009-12-01

234

Investigation of Structural Defects in CdZnTe Detector-Grade Crystals  

NASA Astrophysics Data System (ADS)

We investigated structural defects in CdZnTe detector-grade crystals grown under different conditions. Here, we report our findings from high-resolution electron microscopy [transmission electron microscopy (TEM) and scanning TEM (STEM)] and scanning electron microscopy integrated with energy-dispersive x-ray spectroscopy to characterize the material's structural and chemical composition. Combining these techniques gave us important information about the defects, their concentration, and the elemental composition of the CdZnTe crystals. Our experimental observations demonstrated some distinct nanostructural defects in the crystals that may play a major role in device performance.

Hossain, A.; Bolotnikov, A. E.; Camarda, G. S.; Gul, R.; Kim, K. H.; Kisslinger, K.; Yang, G.; Zhang, L. H.; James, R. B.

2012-10-01

235

Preparation and Crystal Structure of Paeonol  

Microsoft Academic Search

Paeonol was prepared by the extraction method from Moutan Cortex. Its crystal struc- ture was determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic sys- tem, space group P21\\/c with a = 6.724(4), b = 8.792(6), c = 14.689(10) , ? = 100.138(11), V = 854.8(10) 3, Mr = 166.17, Z = 4, F(000) = 352, Dc =

XU Xing-Youa

236

A review of fine structures of nanoporous materials as evidenced by microscopic methods.  

PubMed

This paper reviews diverse capabilities offered by modern electron microscopy techniques in studying fine structures of nanoporous crystals such as zeolites, silica mesoporous crystals, metal organic frameworks and yolk-shell materials. For the case of silica mesoporous crystals, new approaches that have been developed recently to determine the three-dimensionally periodic average structure, e.g., through self-consistent analysis of electron microscope images or through consideration of accidental extinctions, are presented. Various structural deviations in nanoporous materials from their average structures including intergrowth, surface termination, incommensurate modulation, quasicrystal and defects are demonstrated. Ibidem observations of the scanning electron microscope and atomic force microscope give information about the zeolite-crystal-growth mechanism, and an energy for unstitching a building-unit from a crystal surface is directly observed by an anatomic force microscope. It is argued how these observations lead to a deeper understanding of the materials. PMID:23349242

Liu, Zheng; Fujita, Nobuhisa; Miyasaka, Keiichi; Han, Lu; Stevens, Sam M; Suga, Mitsuo; Asahina, Shunsuke; Slater, Ben; Xiao, Changhong; Sakamoto, Yasuhiro; Anderson, Michael W; Ryoo, Ryong; Terasaki, Osamu

2013-01-24

237

Effectiveness of crystallization inhibitors in preventing salt damage in building materials  

Microsoft Academic Search

Salt crystallization in porous materials constitutes one of the most frequent causes of decay of buildings in a wide range of environments. Up to now no definitive solution exists to limit salt crystallization damage, unless of removing either the salt or the moisture. The possibility of making the process of salt crystallization less harmful by means of crystallization inhibitors has

Barbara Lubelli; Rob P. J. van Hees

2007-01-01

238

Model for the mechanical stress due to the salt crystallization in porous materials  

Microsoft Academic Search

This paper deals with the experimental investigation and the mathematical modelling of crystal growth in porous materials and resulting mechanical stress due to the crystallization pressure.Crystallization of potassium nitrate and of sodium sulphate was induced in two bricks by cooling down at constant rate. The measured temperatures describe indirectly the crystallization and the dissolution rates. Thus, the time-dependent amount of

R. M. Espinosa; L. Franke; G. Deckelmann

2008-01-01

239

Solid mechanics and material strength studies on the melt growth of bulk single crystals  

Microsoft Academic Search

Microdefects such as dislocations and macrocracking should be controlled during the crystal growth process to obtain high-quality bulk single crystals. Solid mechanics and material strength studies on the single crystals are of importance to solve the problems related to the generation and multiplication of dislocations and the cracking of single crystals. The present paper reviews such research activities that comprise

Noriyuki Miyazaki

2007-01-01

240

Electronic Structure of Rare-Earth Sesquisulfide Crystals  

Microsoft Academic Search

Single crystals of R2S3, R = Dy, Gd, Nd, and Y, have been grown by flame fusion in an argon plasma torch and by the Bridgman technique. The purification of R2O3 starting materials, synthesis and analysis of compound powders R2S3, crystal growth, analysis to determine if single crystals are produced, and measurement of electrical resistivity and thermoelectric power coefficient from

J. R. Henderson; M. Muramoto; E. Loh; John B. Gruber

1967-01-01

241

Crystal Structure of Cold Compressed Graphite  

NASA Astrophysics Data System (ADS)

Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp3 bonds and it provides an explanation to several features in experimental x-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to Z-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that Z-carbon is a transparent wide band-gap semiconductor with a hardness comparable to diamond.

Amsler, Maximilian; Flores-Livas, Jos A.; Lehtovaara, Lauri; Balima, Felix; Ghasemi, S. Alireza; Machon, Denis; Pailhs, Stphane; Willand, Alexander; Caliste, Damien; Botti, Silvana; San Miguel, Alfonso; Goedecker, Stefan; Marques, Miguel A. L.

2012-02-01

242

Impact testing of structural biological materials  

Microsoft Academic Search

Structural biological materials must be highly impact resistant, as appendages such as antlers and horns must sustain repeated, seasonal impact loads. Determining the impact damage progression along with the impact strength is very important for understanding how nature has optimized the structure and properties of biological materials in order to guide the design of superior bio-inspired synthetic materials. A drop

Steve Lee; Ekaterina E. Novitskaya; Brandon Reynante; Joshua Vasquez; Robert Urbaniak; Tsukasa Takahashi; Evan Woolley; Luca Tombolato; Po-Yu Chen; Joanna McKittrick

2011-01-01

243

Encoding crystal microstructure and chain folding in the chemical structure of synthetic polymers  

NASA Astrophysics Data System (ADS)

The development of robust methodologies to control the solid-state structure of polymeric materials by appropriate design of the macromolecular architecture has a crucial impact on the mechanical properties of these materials. Here, we demonstrate the feasibility of controlling chain folding of polymers by steric interactions only, in contrast to previous attempts aimed at engineering polymer crystallization through hydrogen bonding. In a linear synthetic macromolecule similar to polyethylene, we encoded structural instructions that are translated during a crystallization process to generate a unique, semi-crystalline morphology with structure-controlled crystal thickness of ~5 nm that remains constant over a wide temperature range. The molecular code consists of a linear backbone alternating crystallizable, long alkyl sequences of monodisperse sizes separated by short spacers containing side-chains and acting as stops and fold-controlling units. This simple strategy could be used to produce advanced polymeric materials with fine control of the crystalline and amorphous regions.

de Ten Hove, Cdric Le Fevere; Penelle, Jacques; Ivanov, Dimitri A.; Jonas, Alain M.

2004-01-01

244

Preparation of iridescent colloidal crystal coatings with variable structural colors.  

PubMed

Iridescent colloidal crystal coatings with variable structural colors were fabricated by incorporating carbon black nanoparticles (CB-NPs) into the voids of polystyrene (PS) colloidal crystals. The structural color of the colloid crystal coatings was not only greatly enhanced after the composition but also varied with observation angles. By changing the diameter of monodisperse PS colloids in the composites, colloidal crystal coatings with three primary colors for additive or subtractive combination were obtained. After incorporation of the PS/CB-NPs hybrid coatings into polydimethylsiloxane (PDMS) matrix, manmade opal jewelry with variable iridescent colors was made facilely. PMID:23938656

Cong, Hailin; Yu, Bing; Wang, Shaopeng; Qi, Limin; Wang, Jilei; Ma, Yurong

2013-07-29

245

Recovery of valuable materials from waste liquid crystal display panel.  

PubMed

Associated with the rapid development of the information and electronic industry, liquid crystal displays (LCDs) have been increasingly sold as displays. However, during the discarding at their end-of-life stage, significant environmental hazards, impacts on health and a loss of resources may occur, if the scraps are not managed in an appropriate way. In order to improve the efficiency of the recovery of valuable materials from waste LCDs panel in an environmentally sound manner, this study presents a combined recycling technology process on the basis of manual dismantling and chemical treatment of LCDs. Three key processes of this technology have been studied, including the separation of LCD polarizing film by thermal shock method the removal of liquid crystals between the glass substrates by the ultrasonic cleaning, and the recovery of indium metal from glass by dissolution. The results show that valuable materials (e.g. indium) and harmful substances (e.g. liquid crystals) could be efficiently recovered or separated through above-mentioned combined technology. The optimal conditions are: (1) the peak temperature of thermal shock to separate polarizing film, ranges from 230 to 240 degrees C, where pyrolysis could be avoided; (2) the ultrasonic-assisted cleaning was most efficient at a frequency of 40 KHz (P = 40 W) and the exposure of the substrate to industrial detergents for 10 min; and (3) indium separation from glass in a mix of concentrated hydrochloric acid at 38% and nitric acid at 69% (HCl:HNO(3):H(2)O = 45:5:50, volume ratio). The indium separation process was conducted with an exposure time of 30 min at a constant temperature of 60 degrees C. PMID:19157837

Li, Jinhui; Gao, Song; Duan, Huabo; Liu, Lili

2009-01-20

246

Recovery of valuable materials from waste liquid crystal display panel  

SciTech Connect

Associated with the rapid development of the information and electronic industry, liquid crystal displays (LCDs) have been increasingly sold as displays. However, during the discarding at their end-of-life stage, significant environmental hazards, impacts on health and a loss of resources may occur, if the scraps are not managed in an appropriate way. In order to improve the efficiency of the recovery of valuable materials from waste LCDs panel in an environmentally sound manner, this study presents a combined recycling technology process on the basis of manual dismantling and chemical treatment of LCDs. Three key processes of this technology have been studied, including the separation of LCD polarizing film by thermal shock method the removal of liquid crystals between the glass substrates by the ultrasonic cleaning, and the recovery of indium metal from glass by dissolution. The results show that valuable materials (e.g. indium) and harmful substances (e.g. liquid crystals) could be efficiently recovered or separated through above-mentioned combined technology. The optimal conditions are: (1) the peak temperature of thermal shock to separate polarizing film, ranges from 230 to 240 deg. C, where pyrolysis could be avoided; (2) the ultrasonic-assisted cleaning was most efficient at a frequency of 40 KHz (P = 40 W) and the exposure of the substrate to industrial detergents for 10 min; and (3) indium separation from glass in a mix of concentrated hydrochloric acid at 38% and nitric acid at 69% (HCl:HNO{sub 3}:H{sub 2}O = 45:5:50, volume ratio). The indium separation process was conducted with an exposure time of 30 min at a constant temperature of 60 deg. C.

Li Jinhui [Department of Environmental Science and Engineering, Tsinghua University (China); Sino-Italia Environmental Energy Building, Room 804, Haidian District, Beijing 100084 (China)], E-mail: jinhui@tsinghua.edu.cn; Gao Song; Duan Huabo; Liu Lili [Department of Environmental Science and Engineering, Tsinghua University (China)

2009-07-15

247

Synthesis, crystal structure, and transistor performance of tetracene derivatives.  

PubMed

The substitution of chloro or bromo groups in tetracene gives rise to the change of crystal structure, having a substantial effect on carrier transport. Halogenated tetracene derivatives were synthesized and grown into single crystals. Monosubstituted 5-bromo- and 5-chlorotetracenes have the herringbone-type structure, while 5,11-dichlorotetracene has the slipped pi stacking structure. Mobility of 5,11-dichlorotetracene was measured to be as high as 1.6 cm2/V.s in single-crystal transistors. The pi stacking structure, which enhances pi orbital overlap and facilitates carrier transport, may thus be responsible for this high mobility. PMID:15563126

Moon, Hyunsik; Zeis, Roswitha; Borkent, Evert-Jan; Besnard, Celine; Lovinger, Andrew J; Siegrist, Theo; Kloc, Christian; Bao, Zhenan

2004-12-01

248

Refinement of the crystal structure of rutherfordine.  

SciTech Connect

Rutherfordine, UO{sub 2}CO{sub 3} is orthorhombic, a 4.840(1), b 9.273(2), c 4.298(1) Angstroms, V192.90(7) Angstroms{sup 3}, space group lmm2,Z=2. The structure was refined to an R index of 2.2% on the basis of 306 unique data [|F{sub o}|/{sigma}(|F{sub o}|)>5] measured with MoK{alpha} X-radiation on a single-crystal diffractometer. The structure consists of neutral sheets of edge- and corner-sharing (UO{sub 8}) hexagonal bipyramids and (CO{sub 3}) triangles, as originally proposed by Christ et al. (1955); our refinement, however shows that (CO{sub 3}) groups in alternate layers have the same orientation, not opposite orientations as originally reported. The refined value of the U-O (uranyl) distance is strongly affected by the details of the absorption correction, ranging from 1.71 to 1.80 Angstroms as a function of the plate-glancing angle used in an empirical psi-scan absorption correction and as a function of the type of weighting scheme used in the refinement. The Gaussian-quadrature method of integration also shows similar problems, but they are less extreme. The preferred value for the U-O (uranyl) distance in rutherfordine is {approx}1.745 Angstroms; as rutherfordine contains no H atoms, the O(uranyl) atom is [1]-coordinated, and should have the shortest U-O(uranyl) distance stereochemically possible. The current work suggests that U-O(uranyl) values less than 1.745 Angstrom reported in other studies are adversely affected by less-than-optimum absorption corrections.

Finch, R. J.; Cooper, M. A.; Hawthorne, F. C.; Ewing, R. C.; Chemical Engineering; Univ. of Manitoba; Univ. of Michigan

1999-01-01

249

Requirements for structure determination of aperiodic crystals  

Microsoft Academic Search

Using computer simulation, we compared the Patterson functions of one-dimensional (1D) randomly packed and quasiperiodic Fibonacci lattices with or without disorder, and a 2D Penrose lattice and random packing of pentagons (icosahedral glass model). Based on these comparisons, we derived some empirical guidelines for distinguishing ideal quasicrystals from aperiodic crystals with disorder using diffraction data. In contrast to periodic crystals,

Xiao-Ou Li; Edward A. Stern; Yanjun Ma

1991-01-01

250

Materials physics of half-metallic magnetic oxide films by pulsed laser deposition: Controlling the crystal structure and near-surface properties of strontium iron molybdenum oxide and chromium oxide films  

NASA Astrophysics Data System (ADS)

The idea of half-metallic ferromagnets was first introduced by de Groot et al. in 1983 based on their calculations. The density of state at the Fermi level for half-metallic ferromagnet is completely polarized, meaning that only one of the spin up or spin down channel exists and has metallic behaviour while the other spin channel behaves as a semiconductor or insulator. This unusual electronic structure can be seen in different materials including Sr2FeMoO6, CrO2 and Mn-based Heusler alloys. The high spin polarization degree of the half-metallic ferromagnets makes them a perfect candidate to be used as a spin-injector/detector in spin-based electronics device (spintronics). However, the degree of spin polarization of these materials, particularly in the multilayered structure spintronic devices, strongly depends on the surface/interface quality and the presence of defects, which was the subject of the present study. Pulsed laser deposition (PLD) has been used to grow two examples of the half-metallic ferromagnets, namely, Sr2FeMoO6 and CrO2. The effects of the growth conditions (deposition temperature, gas pressure, laser power, target-to-substrate distance, post-annealing) and of the substrate lattice mismatch and thickness evolution have been studied. By optimizing the growth conditions, nanocrystalline Sr2FeMoO6 films have been grown on a Si(100) substrate for the first time. This single-phase Sr 2FeMoO6 film was obtained at a temperature as low as 600C, and it exhibits a high saturation magnetic moment of 3.4 muB per formula unit at 77 K. By using glancing-incidence X-ray diffraction with different incident beam angles, the crystal structure of the film was sampled as a function of depth. Despite the lack of good lattice matching with the Si substrate, a preferential orientation of the nanocrystals in the film was observed for the as-grown Sr2FeMoO6 films thicker than 60 nm. Furthermore, effects of the deposition temperature on the epitaxial growth of the Sr2FeMoO6 films on MgO(001) have been studied by means of high-resolution X-ray diffraction. The film grown at 800C was post-annealed in oxygen, producing epitaxial films of SrMoO4 on top of the Sr2FeMoO6 film. The corresponding magnetization data showed that the post-annealing treatment lowered the saturation magnetic moment from 3.4 muB per formula unit (or /f.u.) for the as-grown Sr2FeMoO6 film to 1.4 muB/f.u. after annealing. X-ray photoemission measurements as a function of sputtering time further revealed the presence of SrMoO4 on both the as-grown and annealed films, and their corresponding depth profiles indicated a thicker SrMoO 4 overlayer on the annealed film. The intensity ratios of the 3d features of Mo4+, Mo5+, and Mo6+ for Sr 2FeMoO6 remained unchanged with sputtering depth (after 160 s of sputtering), supporting the conclusion that the observed secondary phase (SrMoO4) was formed predominantly on the surface and not in the sub-grain boundaries of the as-grown Sr2FeMoO6 film. The epitaxial growth evolution of Sr2FeMoO6 films of different thickness on substrates of MgO(001), SrTiO3(100) and LaAlO3(100) have also been studied. For each thickness, surface morphology, grain size, film epitaxy, and crystal quality were determined by atomic force microscopy and X-ray diffraction (o-2theta scan and reciprocal space mapping). For thicker films (120 nm), high resolution X-ray diffraction studies revealed that SrMoO4 and other parasitic phases tend to forms on SrTiO3 and LaAlO3 substrates, but not on those grown on MgO substrates. As a second part of the project, single-phase CrO2 nanostructured thin films have been grown for the first time directly on MgO(001) by PLD from a metallic Cr target in an O2 environment. X-ray diffraction shows that these films are strained and consist of CrO2 crystallites with two possible epitaxial relationships to the substrate: either CrO 2(110) or CrO2(200) is parallel to MgO(001). X-ray photoemission further confirms that the films are primarily CrO2 covered with a thin CrO3 overlayer, and indicates its complete synthesis

Jalili, Helia

251

Inorganic-organic hybrid materials: synthesis and crystal structure determination from powder diffraction data of Pb2(O3PCH2C6H4CH2PO3)  

NASA Astrophysics Data System (ADS)

A new lead diphosphonate, Pb2(O3PCH2C6H4CH2PO3) was hydrothermally synthesized from tetraethyl /?,/?'-p-xylenediphos-phonate and Pb(NO3)2. The structure was solved and refined using X-ray powder diffraction data. It crystallizes in the monoclinic space group P21/c, with /a = 467.84(2), /b = 2007.98(9), /c = 639.10(2) pm, /? = 101.020(3), /V = 589.31(4) 106pm, /Z=2, wRp=0.034, Rp=0.027, RF2=0.061, RF=0.036. The structure is built from corner-linked [PbO4] polyhedra, containing a lone pair of electrons. These polyhedra are connected to layers by phosphonate groups, RPO32- and through the organic diphosphonic acid to a three-dimensional structure. Thermogravimetric as well as IR spectroscopic studies are also presented.

Irran, Elisabeth; Bein, Thomas; Stock, Norbert

2003-07-01

252

Salt crystallization as damage mechanism in porous building materialsa nuclear magnetic resonance study  

Microsoft Academic Search

Salts can damage building materials by chemical reactions or crystallization, which is a serious threat to cultural heritage. In order to develop better conservation techniques, more knowledge of the crystallization processes is needed.In a porous material, the size of a salt crystal is limited by the sizes of the pores. It has been predicted that as a consequence, the solubility

Lourens A. Rijniers; Leo Pel; Henk P. Huinink; Klaas Kopinga

2005-01-01

253

SMART MATERIALS IN INFLATABLE STRUCTURE APPLICATIONS  

Microsoft Academic Search

The focus of this work is to investigate the use of smart materials for vibration testing and control of inflated satellite components. Lightweight inflatable structures are a viable alternative in aerospace structure design. These structures, however, pose special problems in testing and in controlling vibrations due to their extremely lightweight, flexible, and high-damping properties. The smart materials offer the required

John A. Main

254

Growth of Crystals. Vol. 13  

Microsoft Academic Search

This book contains information on the crystallization of proteins, mechanisms and kinetics of crystal growth by vapor deposition, epitaxy, mechanisms and kinetics of crystal growth from the melt and from high-temperature solutions, growth of crystals from the melt, growth of crystals from solution, defect structure in crystals, and new materials (equipment for crystal growth). Specific articles include: equilibrium adsorption layers

E. I. Givargizov; E. A. D. White

1986-01-01

255

Structural Materials for Innovative Nuclear Systems  

SciTech Connect

This series of slides deal with: the goals for advanced fission reactor systems; the requirements for structural materials; a focus on two important types of materials: ODS and CMC; a focus on materials under irradiation (multiscale modelling, experimental simulation, 'smart' experiments in materials testing reactors); some concluding remarks.

Yvon, Pascal [Commissariat a l'energie atomique - CEA (France)

2011-07-01

256

Photochemical manipulation of colloidal structures in liquid-crystal colloids  

NASA Astrophysics Data System (ADS)

We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

Yamamoto, T.; Tabe, Y.; Yokoyama, H.

2007-05-01

257

Crystal structures at high pressures and temperatures  

NASA Astrophysics Data System (ADS)

The diamond anvil cell (DAC) is a unique instrument that can generate pressures equivalent to those inside planetary interiors (pressures on the order of 1 million atmospheres) under sustained conditions. When combined with a bright source of collimated x-rays, the DAC can be used to probe the structure of materials in-situ at ultra-high pressures. An understanding of the high-pressure structure of materials is important in determining what types of processes may take place in the Earth at great depths. Motivated by previous studies showing that xenon becomes metallic at pressures above 1 megabar (100 GPa), we examined the stable structures and reactivity of xenon at pressures approaching that of the core-mantle boundary in the Earth. Our findings indicate the transformation of xenon from face-centered cubic (fcc) to hexagonal close-packed (hcp) structures is kinetically hindered at room temperature, with the equilibrium fcc--hcp phase boundary at 21 (+/-3) gigapascals, a pressure lower than was previously thought. Additionally, we find no tendency on the part of xenon to form a metal alloy with iron or platinum to at least 100 to 150 gigapascals, making it unlikely that the Earth's core serves as a reservoir for primordial xenon. Measurements of the compressibility of natural (Mg.75,Fe .25)2SiO4 gamma-spinel at pressures of the Earth's transition zone yield a pressure derivative of the bulk modulus K0 ' = 6.3 (+/-0.3). As gamma-spinel is considered to be a dominant mineral phase of the transition-zone of the Earth's mantle (400--670 km depth), the relatively high value of K0' for gamma-spinel may help explain the rapid increase with depth of seismic velocities through the transition zone. The thermodynamics, mechanisms and kinetics of pressure-induced amorphization are not well understood. We report here new studies indicating little or no entropy difference between the crystalline and glassy states of Ca(OH) 2 (portlandite). Additional work on the pressure-induced amorphization of AlPO4 (berlinite) shows that this material, which is a close analog to quartz, shows a rich behavior that is dependent upon the pressure, temperature, stress-state and time-scales of the experimental conditions.

Caldwell, Wendel Alexander

2000-10-01

258

Rational Design, Theory and Molecular Architecture of Highly Ordered Stilbene and Stilbazole Systems for Nonlinear Optical Materials: Pi-Electron Theoretical Studies, Crystal Structure, High-T Functionalized Polymers, and Self - Multilayer Superlattices.  

NASA Astrophysics Data System (ADS)

The construction of chromophoric self-assembled multilayers as an approach to the synthesis of thin-film second-order nonlinear optical (NLO) materials is described. The self-assembled chromophore-containing multilayer structures are built up in the repeating reaction sequence: I _3Si(CH_2) _2C_6H_4 CH_2I (Cp), 4- (N,N-bis(3 -hydroxypropyl)amino) styryl-4^' -pyridine (Ch), Cl_3SiOSiCl _2OSiCl_3 (Si), polyvinylalcohol (PVA). The multilayer structures have been characterized by optical and XPS spectroscopy, advancing contact angle measurements, null ellipsometry, and NLO properties. The latter measurements reveal multilayer superlattices with good structural uniformity. Second -order susceptibilities were found to be chi _{rm zzz}^{(2)} = 2 times 10^ {-7} esu and chi_ {rm zzz}^{(2)} = 1.3 times 10^{ -7} esu at lambda = 1064 nm and 1900 nm respectively. chi_ {rm zzz}^{(2)} = 6 times 10^{ -7} esu. at 1064 nm for a single CpCh monolayer of estimated thickness 22A. A unified definition of hyperpolarizability tensors and the derivations of these susceptibilities via second quantization and pertubation theory is presented. Calculations of optical nonlinearities from second-order to fourth-order, using pi-electron model hamiltonians, have been performed on a variety of conjugated organic molecules. Excellent agreement between theoretical and available experimental second- and third-order susceptibilities for various nonlinear phenomena has been found. The PPP -SCF-MECI-DECI model is proved to be a computationally efficient, highly reliable scheme for understanding, predicting, and designing organic nonlinear optical chromophores. Large chromophores such as substituted stilbenes can be easily treated. S(+)-N- (p-(4-nitrostyryl)phenyl) prolinol (NSP) and its derivatives were synthesized and characterized. NSP crystallizes in a noncentrosymmetric orthorhombic space group P2_12_12 _1 with a = 7.631(8)A, b = 35.722(8)A, and c = 6.032(5)A. Final least-squares refinement gave R(F) = 0.14 for 1494 total reflections. It possesses very weak SHG properties because the chromophores are packed in an anti-parallel manner. NSP-functionalized poly(p -hydroxystyrene) and poly(2,6-dimethyl-1,4-phenylene oxide) were also prepared and characterized. In the NSP-PHS system (T_{rm g} = 173 ^circC), corona-poled 73% functionalized polymeric films yield the nonresonance second order susceptibility value, chi_{rm zzz} = 167 times 10^ {-9} esu. Reacting NSPONa with PPO(CH _2Br)_2<=ads to 158% functionalization; the corona-poled film gives a second order susceptibility chi_ {rm zzz} = 26.2 times 10^{-9} esu.

Li, Dequan

1990-01-01

259

Mechanochemical synthesis of nonstoichiometric nanocrystals La 1 ? y Ca y F 3 ? y with a tysonite structure and nanoceramic materials from CaF 2 and LaF 3 crystals  

Microsoft Academic Search

The nonstoichiometric phases La1 ? y\\u000a Ca\\u000a y\\u000a F3 ? y\\u000a (y = 0.15, 0.20) with a tysonite (LaF3) structure have been prepared for the first time by the mechanochemical synthesis from CaF2 and LaF3 crystals. The average size of coherent scattering regions is approximately equal to 1030 nm. It has been shown that the\\u000a compositions of the phases prepared

B. P. Sobolev; I. A. Sviridov; V. I. Fadeeva; S. N. Sulyanov; N. I. Sorokin; Z. I. Zhmurova; I. I. Khodos; A. S. Avilov; M. A. Zaporozhets

2008-01-01

260

Production of Flyash-Based Structural Materials.  

National Technical Information Service (NTIS)

This report describes bench-scale studies, pilot plant operations and process economics for the commercial production of structural materials. Raw materials used were flyash, bottom ash and boiler slag obtained from eastern, central and western coal areas...

C. F. Cockrell C. R. McFadden H. E. Shafer J. W. Leonard K. K. Humphreys

1972-01-01

261

Engineering Data on New Aerospace Structural Materials.  

National Technical Information Service (NTIS)

The major objectives of this research program were to evaluate newly developed materials of interest to the Air Force for potential structural airframe usage, and to provide 'data sheet' type presentations of engineering data for these materials. The effo...

H. Mindlin O. L. Deel P. E. Ruff

1975-01-01

262

Properties of Buoyant Materials and Structures.  

National Technical Information Service (NTIS)

This report is directed at furnishing information on the various kinds of materials which can be employed for the construction of flotation devices, a description of typical float structures comprised of the materials listed and generalized mathematical r...

J. Irgon C. Juhasz D. Z. Lippmann M. Armstrong M. P. Stoltenberg

1964-01-01

263

Fluoride crystals: materials for near-infrared solid state lasers  

NASA Astrophysics Data System (ADS)

In this work we present an overview of the best 2?m laser results obtained in Tm-doped fluoride hosts LiYF4(YLF), LiLuF4 (LLF) and BaY2F8 (BYF) and we report on the growth, spectroscopy and first laser test emission of a novel mixed material BaYLuF8 (BYLF), interesting as a variant of BYF material with a partial substitution of Y3+ ions by Lu3+. The novel host is interesting mainly because indications are that the mixed crystal would be sturdier than BYF. The addition of Lutetium would improve the thermo-mechanical properties going into the direction of high power applications, as suggest from works on YLF and its isomorph LLF. A detailed description of Czochralski growth of fluoride laser materials is provided, focusing on the growth parameters of the novel BYLF:Tm3+12% material grown. With regard of spectroscopy analysis, we report on the results obtained with BYLF host. Detailed absorption, fluorescence and lifetime measurements have been performed focusing on the 3H4 and 3F4 manifolds, the pumping and upper laser level. Moreover diode pumped CW laser emission at 2 ?m has been achieved in BYLF: Tm3+12% sample obtaining a slope efficiency of about 28% with respect to the absorbed power.

Parisi, Daniela; Veronesi, Stefano; Volpi, Azzurra; Gemmi, Mauro; Tonelli, Mauro; Cassanho, Arlete; Jenssen, Hans P.

2013-07-01

264

On the Crystal Structure of Ln  

SciTech Connect

The crystal structures of La{sub 2}O{sub 2}CO{sub 3} II and Nd{sub 2}O{sub 2}CO{sub 3} II have been shown by means of high-resolution powder neutron (PND) and synchrotron X-ray diffraction (SXRD) combined with selected area electron diffraction (SAED) studies to be far more complex than earlier anticipated, owing to ordering of carbonate groups between (Ln{sub 2}O{sub 2}{sup +2}){sub n} layers. In contrast to earlier descriptions, the carbonate groups appear to be rather regular. Relative to an average model, the SAED patterns show additional scattering in the form of closely distributed, but essentially discrete, spots along < 1/3, 1/3, 1 >. Most of the observed scattering, H, can be described as H=G{+-}m q{sub 1}+n q{sub 2}, where G is the Bragg reflections of the underlying average P6{sub 3}/mmc lattice, q1=[1/3, 1/3, {+-}1/2]*, q2=[1/3, 1/3, {+-}2/3]*, and m and n are integers. The additional scattering reflects ordering of the carbonate groups into trigonal layers between the (Ln{sub 2}O{sub 2}{sup +2}){sub n} layers, but it remains open whether q{sub 1} and q{sub 2} represent two separate structures with different stacking sequences of such layers or whether they correspond to an even more complex stacking sequence. In any case, some disorder and rotational domain twinning are present. Two structure models, one for each modulation wave vector, were constructed. Rietveld-type refinements of PND data of La{sub 2}O{sub 2}CO{sub 3} II were performed, approximating the complex, and at least partly disordered, stacking sequence as a two-phase mixture of the two modulated phases. Satisfactory convergence was achieved with R{sub p}=6.4%, R{sub wp}=8.3%, and {chi}{sup 2}=3.32. The isothermal expansivities, {alpha}{sub p}, for La{sub 2}O{sub 2}CO{sub 3} II and Nd{sub 2}O{sub 2}CO{sub 3} II between 298 and 893 K were determined as 2.92x10{sup {minus}5} and 2.70x10{sup {minus}5} K{sup {minus}1}, respectively.

Olafsen, Anja; Larsson, Ann-Kristin; Fjellvaag, Helmer; Hauback, Bjoern C.

2001-04-01

265

Space Structures Concepts and Materials.  

National Technical Information Service (NTIS)

An extension is presented of the evaluation of graphite/aluminum metal matrix composites (MMC) for space structures application. A tubular DWG graphite/aluminum truss assembly was fabricated having the structural integrity and thermal stability needed for...

A. M. Nowitzky E. C. Supan

1988-01-01

266

Ordering of crystal structure by ionizing radiation  

NASA Astrophysics Data System (ADS)

We have studied the action of ionizing radiation on defect-containing semiconductor crystals, metals, and alloys. Using modern methods for investigation of solids, Rutherford back scattering of channeled charged particles, x-ray diffraction, electron microscopy, and also calorimetric methods, we have established: a) irradiation (by x-ray beams, gamma rays, and electrons) of metals and alloys with an equivalent radiation dose less than 105 J/kg and of semiconductor crystals with a dose less than 103 J/kg does not lead to additional accumulation of defects but conversely leads to elimination of defects and transition of the crystal to a more equilibrium state; b) ionization processes play a determining role in rearrangment of defects in crystals exhibiting both semiconductor and metallic conductivity. We show that rearrangment of the crystal occurs as a result of stored energy in the crystal which is liberated due to chain reactions of annihilation of defects, initiated by ionization. Transition of the crystal to the equilibrium state is accompanied by improvement of its physical properties.

Chernov, I. P.; Momontov, A. P.; Cherdantsev, P. A.; Chakhlov, B. V.

1994-12-01

267

Structural Integrity of Intelligent Materials and Structures.  

National Technical Information Service (NTIS)

This report focuses on the development of micromechanical algorithms for shape memory alloy composite materials. The composite cylinders assemblage algorithm was utilized to determine the effective thermomechanical properties of shape memory alloy composi...

B. J. Sullivan K. W. Buesking

1994-01-01

268

Photonic crystals for monitoring fatigue phenomena in steel structures  

NASA Astrophysics Data System (ADS)

This paper introduces the concept and development of a strain sensing system for structural application based on the properties of photonic crystals. Photonic crystals are artificially created periodic structures, usually produced in the thinfilm form, where optical properties are tailored by a periodicity in the refractive index. The idea of using the crystal as a sensor is based on the observation that a distortion in the crystal structure produces a change in the reflected bandwidth. When a photonic crystal is designed to operate in the visible part of the spectrum, a permanent distortion of the film results in a change in its apparent color. This property makes photonic crystals suitable for permanent monitoring of structural elements, as any critical changes in the strain field can be promptly and easily detected by visual inspection. A simple and low-cost example of photonic crystals consists of opals synthesized by vertical deposition. In this contribution we introduce a target application for the fatigue monitoring of wind turbines, and then provide the reader with some basic information concerning modeling of the crystal architecture and fabrication of these structures. Next we discuss their application to strain measurement, specifying how reflection and transmission properties of the opals have to be designed to satisfy the expected strain response of the sensor. Finally, we present the preliminary results of a laboratory validation carried out on thin films applied to a rubber support.

Zonta, Daniele; Chiappini, Andrea; Chiasera, Alessandro; Ferrari, Maurizio; Pozzi, Matteo; Battisti, Lorenzo; Benedetti, Matteo

2009-03-01

269

Two Types of Anchoring Structure in Smectic Liquid Crystal Molecules  

Microsoft Academic Search

The anchoring structures of smectic liquid crystals, n-alkylcyanobiphenyl (mCB: m{=}8, 10, 12), on molybdenum disulfide (MoS2) are directly observed by scanning tunneling microscopy (STM) in order to analyze the alignment mechanism of liquid crystals. For 8CB, the anchoring structure is of the periodic monolayer type, while 10CB and 12CB take a bilayer structure in which there is no interdigitation of

Yasushi Iwakabe; Masahiko Hara; Katumi Kondo; Kenji Tochigi; Akio Mukoh; Anthony F. Garito; Hiroyuki Sasabe; Akira Yamada

1990-01-01

270

In vivo protein crystallization opens new routes in structural biology  

PubMed Central

Protein crystallization in cells has been observed several times in nature. However, owing to their small size these crystals have not yet been used for X-ray crystallographic analysis. We prepared nano-sized in vivogrown crystals of Trypanosoma brucei enzymes and applied the emerging method of free-electron laser-based serial femtosecond crystallography to record interpretable diffraction data. This combined approach will open new opportunities in structural systems biology.

Koopmann, Rudolf; Cupelli, Karolina; Redecke, Lars; Nass, Karol; DePonte, Daniel P; White, Thomas A; Stellato, Francesco; Rehders, Dirk; Liang, Mengning; Andreasson, Jakob; Aquila, Andrew; Bajt, Sasa; Barthelmess, Miriam; Barty, Anton; Bogan, Michael J; Bostedt, Christoph; Boutet, Sebastien; Bozek, John D; Caleman, Carl; Coppola, Nicola; Davidsson, Jan; Doak, R Bruce; Ekeberg, Tomas; Epp, Sascha W; Erk, Benjamin; Fleckenstein, Holger; Foucar, Lutz; Graafsma, Heinz; Gumprecht, Lars; Hajdu, Janos; Hampton, Christina Y; Hartmann, Andreas; Hartmann, Robert; Hauser, Gunter; Hirsemann, Helmut; Holl, Peter; Hunter, Mark S; Kassemeyer, Stephan; Kirian, Richard A; Lomb, Lukas; Maia, Filipe R N C; Kimmel, Nils; Martin, Andrew V; Messerschmidt, Marc; Reich, Christian; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Schlichting, Ilme; Schulz, Joachim; Seibert, M Marvin; Shoeman, Robert L; Sierra, Raymond G; Soltau, Heike; Stern, Stephan; Struder, Lothar; Timneanu, Nicusor; Ullrich, Joachim; Wang, Xiaoyu; Weidenspointner, Georg; Weierstall, Uwe; Williams, Garth J; Wunderer, Cornelia B; Fromme, Petra; Spence, John C H; Stehle, Thilo; Chapman, Henry N; Betzel, Christian; Duszenko, Michael

2012-01-01

271

Optical Response of Liquid Crystals in Colloid-Templated Structures  

Microsoft Academic Search

We report optical switching studies on nematic liquid crystals in self-assembled colloids. The liquid crystal may be imbibed into interstitial cavities of the assembled colloid, or can be incorporated into a network of positionally-ordered cavities obtained from a polymer replica of the colloid crystal. Our periodic host structures have lattice constants in the range of 0.5 to 1.5 microns. We

P. Mach; K. H. Lin; A. G. Yodh; D. A. Weitz; P. Wiltzius

2001-01-01

272

Structural material irradiations in FFTF  

SciTech Connect

Information is presented concerning the Materials Open Test Assembly (MOTA); instrumentation and control system; MOTA neutronic data; pressurized tube specimens; stress-rupture measurements for reactor materials; miniature specimen design; the Interim Examination and Maintenance (IEM) cell at the FFTF; support services; and general information concerning the FFTF.

Not Available

1985-01-01

273

The crystal structure of hexathallium(I) hexatellurodigermanate(III), Tl6[Ge2Te6  

Microsoft Academic Search

The new compound Tl6[Ge2Te6] was prepared by thermal synthesis from the elements. The material is triclinic, space group P1, with a = 9.471(2), b = 9.714(2), c = 10.389(2) , alpha = 89.39(1), beta = 97.27(1), gamma = 100.79(1), and Z = 2. The crystal structure was determined from single-crystal intensity data measured by means of an automated four-circle diffractometer

G. Eulenberger

1984-01-01

274

Effect of melt composition on the electrical properties and structure of undoped gallium arsenide single crystals  

SciTech Connect

We present results on the electrical properties and structure of single crystal GaAs, 40 mm in diameter, obtained by a combined synthesis process and grown by the Czochralski method in an inert gas at high pressure. For crystals of each group the composition of the starting melt was varied during growing between 46-54 at. % As. The intrinsic resistivity of the material was obtained by measuring the Hall effect at room temperature.

Koval'chuk, I.A.; Markov, A.V.; Mil'vidskii, M.G.

1988-07-01

275

Crystal structure of interleukin 8: Symbiosis of NMR and crystallography  

Microsoft Academic Search

The crystal structure of a host defense system chemotactic factor, interleukin 8, has been solved by molecular replacement using as a model the solution structure derived from nuclear magnetic resonance experiments. The structure was refined with 2 x-ray data to an R factor of 0.817. A comparison indicates some potential differences between the structure in solution and in the

E. T. Baldwin; I. T. Weber; R. St. Charles; Jiancheng Xuan; Kouji Matsushima; A. Wlodawer; E. Appella; G. M. Clore; A. M. Gronenborn; Masaki Yamada; B. F. P. Edwards

1991-01-01

276

Thermal Expansion and Structure of Crystallizing Glass.  

National Technical Information Service (NTIS)

The author carried out a complex study of the glasses with a composition close to spodumene during the isothermal crystallization process. Original samples differed in the type of catalyzer only. The results cover the changes in compression deformation, m...

E. S. Sorkin

1972-01-01

277

Electronic materials high- Tc superconductivity polymers and composites structural materials surface science and catalysts industry participation  

SciTech Connect

The fifth year of the Center for Advanced Materials was marked primarily by the significant scientific accomplishments of the research programs. The Electronics Materials program continued its work on the growth and characterization of gallium arsenide crystals, and the development of theories to understand the nature and distribution of defects in the crystals. The High-{Tc} Superconductivity Program continued to make significant contributions to the field in theoretical and experimental work on both bulk materials and thin films and devices. The Ceramic Processing group developed a new technique for cladding YBCO superconductors for high current applications in work with the Electric Power Research Institute. The Polymers and Composites program published a number of important studies involving atomistic simulations of polymer surfaces with excellent correlations to experimental results. The new Enzymatic Synthesis of Materials project produced its first fluorinated polymers and successfully began engineering enzymes designed for materials synthesis. The Structural Materials Program continued work on novel alloys, development of processing methods for advanced ceramics, and characterization of mechanical properties of these materials, including the newly-documented characterization of cyclic fatigue-crack propagation behavior in toughened ceramics. Finally, the Surface Science and Catalysis program made significant contributions to the understanding of microporous catalysts and the nature of surface structures and interface compounds.

Not Available

1988-01-01

278

Hydrothermal synthesis, crystal structure, and magnetic property of a three-dimensional inorganic-organic hybrid material: Mn(H2O)[HO3PCH2NH(CH2CO2)2  

NASA Astrophysics Data System (ADS)

A novel three-dimensional inorganic-organic hybrid compound, Mn(H2O)[HO3PCH2NH(CH2CO2)2] from a hydrothermal reaction of Mn (II) ion with N-(phosphonomethyl)iminodiacetic acid (H4PMIDA) was reported. The compound crystallizes in the monoclinic P21/n with cell dimensions of a=5.215(5), b=14.111(15), c=12.727(12), ?=93.646(16), V=934.6(16)3 and Z=4. In this structure each Mn atom is six-coordinated with the carboxylic groups and phosphonic groups to form layers along the bc plane. These layers are further connected with the organic moieties of H2PMIDA, resulting in a complicated three-dimensional network structure. Thermogravimetric analysis, IR spectrum and magnetic susceptibility of this compound are given.

Fan, Yong; Li, Guanghua; Shi, Zhan; Zhang, Dong; Xu, Jianing; Song, Tianyou; Feng, Shouhua

2004-11-01

279

Crystal and electronic structure of Li15Si4  

NASA Astrophysics Data System (ADS)

Silicon is one of the most promising anode materials for future rechargeable batteries because of its high theoretical capacity. New crystalline Li15Si4 was found as the fully electrochemical lithiated phase of crystalline Si or amorphous Si. Density functional theory was used to study the crystal and electronic structure of Li15Si4. Li15Si4 is formed by the unit figure in which six Li atoms surround a Si atom with two different Li-Si bond lengths. The Li atom has negative charge of 0.56-0.63 in Li15Si4. The average intercalation voltage for the lithium intercalation reaction from crystalline Si to Li15Si4 is 0.303 V, which is in good agreement with that predicted by the Coulometric titration experiment result for Li-Si alloys.

Kubota, Yoshiyuki; Escao, Mary Clare Sison; Nakanishi, Hiroshi; Kasai, Hideaki

2007-09-01

280

New alkali metal diphosphates how materials to preserve the security of the environment: CsNaCu(P2O7), Rb2Cu(P2O7) and CsNaCo(P2O7) synthesis and crystal structure determination  

NASA Astrophysics Data System (ADS)

In this work we describe preliminary results of the synthesis and of a crystal-chemical study of synthetic phosphates with transition metals. Due to the increasing requirements for environmental safety specialists from various industries, we are searching for sustainable forms of immobilization of hazardous waste during storage. We are also developing a component-based waste for new materials. In our continued exploratory synthesis of compounds containing transition-metals, we were able to produce the new diphosphate phases CsNaCu(P2O7), Rb2Cu(P2O7) and CsNaCo(P2O7). A crystal chemical study has allowed us to identify new phosphates. Crystals of CsNaCu(P2O7) (Phase 1) is orthorhombic, crystallizes in space group Pmn21, with a = 5.147(8), b = 15.126(2), c = 9.717(2) , V = 756.20 3, R1 = 0.066 and Rb2Cu(P2O7) (Phase 2) is orthorhombic as well, crystallizes in space group Pmcn, with a = 5.183(8), b = 10.096(1), c = 15.146(3) , V = 793.55 3, R1 = 0.063, they have been obtained by high-temperature reaction of RbNO3, CsNO3, Cu(NO3)2, NaOH and (NH4)4P2O7. Synthetic crystals of the phosphate of copper and rubidium were studied in detail by us on the structures of Rb2Cu(P2O7) and Rb2Cu3(P2O7)2 - new alkali metal copper diphosphates (CHERNYATIEVA et al., 2008). Here we report the synthesis, the structure and the properties of the title compounds and we compare these phases with the previously discovered K2CuP2O7 (ELMAADI et al., 1995) and CsNaMnP2O7 (HUANG et al., 1998). These structures crystallize in other space groups, although their structures are also based on 2-D layers, formed by P2O7 groups combined with polyhedra of the transition metals (CHERNYATIEVA et al., 2012). A crystal chemical study has allowed us to identify even new diphosphates CsNaCu(P2O7) (Phase 3). Crystals of CsNaCoP2O7 is monoclinic, space group P 21/n, with a = 7,424(2), b = 7,648(1), c = 12,931(3), ? = 90,71(2) , V = 734.2(3) 3 and R1 = 0.060. The structure is based framework of Co tetrahedra and P2O7 groups. The structure of the [Co(P2O7)]2-framework in more detail. The phosphate groups and tetrahedra coordinate cobalt ions form topology. This is a unique 4-coordination topology, where Co and P2O7 groups in the structure are topologically equivalent. References CHERNYATIEVA, A. P., KRIVOVICHEV, S. V., SPIRIDONOVA, D. V. (2008): International conference Inorganic Materials Dresden (2008) P3 - 143. CHERNYATIEVA, A. P, SPIRIDONOVA, D. V., KRIVOVICHEV, S. V. The crystal structures of two new synthetic compounds CsNaCu(P2O7) and Rb2Cu(P2O7), Acta Mineralogica-Petrographica (2012) Vol.7, p.25 EL MAADI, A., BOUKHARI, A., HOLT, E.M. (1995) Journal of Alloys Compounds, 223: 13-17. HUANG, Q., HWU, S. J., MO, X. H. (2001): Angewandte Chemie - International Edition, 40: 1690-1693.

Chernyatieva, Anastasiya; Filatova, Alyona; Spiridonova, Dariya; Krivovichev, Sergey

2013-04-01

281

Materials and Structures/Acee.  

National Technical Information Service (NTIS)

Light weight composites made from graphite fibers, glass, or man made materials held in an epoxy matrix, and their application to airframe design are reviewed. The Aircraft Energy Efficiency program is discussed. Characteristics of composites, acceptable ...

1981-01-01

282

Crystal structure of cholesteryl butanoate at 123 K  

Microsoft Academic Search

Cholesteryl butanoate has a complex crystal struc- ture that differs from those of the three main structure types for cholesteryl esters. It contains four molecules (C3LH5202) un- related by crystal symmetry. The molecules are packed in almost planar sheets and have molecular long axes nearly parallel. However, the molecules have different orientations about their long axes and furthermore, in a

Gye Won Han; B. M. Craven; David A. Langs

283

Crystal structures of drugs: advances in determination, prediction and engineering  

Microsoft Academic Search

Most marketed pharmaceuticals consist of molecular crystals. The arrangement of the molecules in a crystal determines its physical properties and, in certain cases, its chemical properties, and so greatly influences the processing and formulation of solid pharmaceuticals, as well as key drug properties such as dissolution rate and stability. A thorough understanding of the relationships between physical structures and the

Sharmistha Datta; David J. W. Grant

2004-01-01

284

Crystal structure and phototransistor behavior of N-substituted heptacence.  

PubMed

6,8,15,17-Tetraaza-1.18,4.5,9.10,13.14-tetrabenzoheptacene (TTH, 1) has been prepared and characterized by single-crystal X-ray structure analysis. A phototransistor device based on TTH single crystal demonstrated that TTH showed a good performance in signal amplification under the photoconductive effect as well as photocontrolled switches. PMID:22475002

Wu, Yuechao; Yin, Zongyou; Xiao, Jinchong; Liu, Yi; Wei, Fengxia; Tan, Ke Jie; Kloc, Christian; Huang, Ling; Yan, Qingyu; Hu, Fangzhong; Zhang, Hua; Zhang, Qichun

2012-04-09

285

Computational materials science aided design of glass ceramics and crystal properties (abstract only).  

PubMed

Today's high tech materials have in many cases highly specialized properties and designed functionalities. Materials parameters like high temperature stability, high stiffness and certain optical properties have to be optimized and in many cases an adaptation to given processes is necessary. Many materials are compounds or layered structures. Thus, surface and interface properties need to be considered as well. At the same time to some extent just a few atomic layers sometimes determine the properties of the material, as is well known in semiconductor and other thin film technologies. Therefore, a detailed understanding of the materials properties at the atomic scale becomes more and more important. In addition many high tech materials have to be of high purity or selective dopant concentrations have to be adjusted to fulfill the desired functionality. Modern materials developments successfully use computational materials science to achieve that goal. Improved software tools and continuously growing computational power allow us to predict macroscopic properties of materials on the basis of microscopic/atomic abinitio simulation approaches. At Schott, special materials, in particular glasses and glass ceramics, are produced for a variety of applications. For a glass ceramic all the above mentioned difficulties for materials development arise. The properties of a glass ceramic are determined by the interplay of crystalline phases embedded in an amorphous glass matrix. For materials development the understanding of crystal structures and their properties, surfaces and interface phenomena, and amorphous systems are necessary, likewise. Each by itself is already a challenging problem. Many crystal phases that are grown within the glass matrix do not exist as single crystals or are difficult to grow in reasonable amounts for experimental investigations. The only way to obtain the properties of these crystalline phases is through 'abinitio' simulations in the computer. In this presentation results of density functional theory (DFT) calculations of various crystal structures, mainly oxides, are discussed. The focus is on the thermomechanical and optical properties. We present elastic properties and the anisotropic Young's modulus for spinel structures, pyrosilicates and further oxides like rutile. Their influence on the stiffness of a resulting glass ceramic is discussed. The thermal expansion of glass ceramics is an important feature and is strongly dependent on the coefficient of thermal expansion (CTE) of the crystalline phases. For selective oxides the calculation of the CTE in the harmonic approximation is presented and a comparison with experiments is given. Optical devices for microlithography use CaF(2) crystal as a lens material. The optical properties and the influence of certain impurities in CaF(2) are crucial for the performance of such devices. 'Abinitio' simulation helps us here to estimate the formation of defects and color centers. Local density approximation screened exchange calculations for the optical properties of CaF(2) are presented as well as DFT simulation results for impurities and defects. PMID:21693894

Mannstadt, Wolfgang

2008-01-24

286

Structural and mechanical studies of cadmium manganese thiocyanate crystal  

NASA Astrophysics Data System (ADS)

Single crystals of cadmium manganese thiocyanate (CMTC) have been synthesized successfully and grown by slow evaporation method. The structural perfection of the grown crystals has been analyzed by High resolution X-ray diffraction (HRXRD), which shows the crystalline perfection of the grown crystal is quite good. Optical behavior was assessed by UV-Vis analysis and found that no absorption in the UV visible region and it may be useful for second harmonic applications. The mechanical hardness of the grown crystals was studied and Vicker's microhardness, Stiffness constant was calculated.

Manikandan, M. R.; Vijayaprasath, G.; babu, G. Anandha; Bhagavannarayan, G.; Vijayan, N.; Ravi, G.

2012-06-01

287

Solvent effects on morphology and crystal structure of solution-grown organic crystals  

NASA Astrophysics Data System (ADS)

Based on the measured solubility data of acenaphthene, fluoranthene and pyrene in six halogen derivative solvents, the solutes activity coefficients ((gamma) s) have been determined from Scatchard-Hildebrand solution theory and used as a measure of solute-solvent interactions for determination of observed solvent effect on growth morphology and intrinsic structure of solution grown crystals of these hydrocarbons. The growth morphologies of these crystals have been interpreted on the basis of PBC theory assumptions. Correlation between activity coefficients of the investigated solutes and morphology as well as structure of obtained crystals, are found.

Marciniak, Bernard; Rozycka-Sokolowska, Ewa; Pawliuk, W.

2001-04-01

288

Molecular structures and crystal packings of 2-styrylquinoxaline derivatives  

NASA Astrophysics Data System (ADS)

The crystal and molecular structures of 2-styrylquinoxaline derivatives with different substituents in the styryl fragment are determined. The degree of planarity of the molecules studied varies in a very wide range, from 1.7 to 33.5. In the ethylene fragment, the double bond is essentially localized. The bicycle-pedal disordering of the ethylene fragment is found in the crystals of the methoxy and oxyacetyl derivatives of 2-styrylquinoxaline. None of the packings contains packing motifs favorable for the photocycloaddition (PCA) reaction with single crystal retention. The crystal packings of these compounds and that of 2-(4-methylstyryl)quinoxaline are characterized by a stacking motif of the head-to-head type, which eliminates the possibility of PCA taking place with single crystal retention but is suitable for this reaction in polycrystalline films. The crystal packing of 2-(3,4-dimethoxystyryl)quinoxaline does not contain elements with stacking interactions.

Kuz'mina, L. G.; Sitin, A. G.; Gulakova, E. N.; Fedorova, O. A.; Lermontova, E. Kh.; Churakov, A. V.

2012-01-01

289

Computational study of the structure and mechanical properties of the molecular crystal rdx  

NASA Astrophysics Data System (ADS)

Molecular crystals constitute a class of materials commonly used as active pharmaceutical ingredients, energetic and high explosive materials. Like simpler crystalline materials, they possess a repeating lattice structure. However, the complexity of the structure -- due to having several entire molecules instead of atoms at each lattice site -- significantly complicates the relationship between the crystal structure and mechanical properties. Of particular interest to molecular crystals are the mechanically activated processes initiated by large deformations. These include polymorph transitions, slip deformation, cleavage fracture, or the transition to disordered states. Activation of slip systems is generally the preferred mode of deformation in molecular crystals because the long range order of the crystal and its associated properties are maintained. These processes change the crystal structure and affect the physiological absorption of advanced pharmaceutical ingredients and the decomposition of high explosives. This work used molecular dynamics to study the energetic molecule RDX, C3H6N6O6, as a model molecular crystal that is a commonly used military high explosive. Molecular dynamics is used to determine the crystal response to deformation by determination of elastic constants, polymorph transitions, cleavage properties, and energy barriers to slip. The cleavage and the free surface energy are determined through interface decohesion simulations and the attachment energy method. The energy barriers to slip are determined through the generalized stacking fault (GSF) procedure. To account for the steric contributions and elastic shearing due to the presence of flexible molecules, a modified calculation procedure for the GSF energy is proposed that enables the distinction of elastic shear energy from the energy associated with the interfacial displacement discontinuity at the slip plane. The unstable stacking fault energy from the GSF simulations is compared to the free surface energy to differentiate cleavage and slip planes. The results are found to be largely in agreement with available experimental data.

Munday, Lynn

290

An Assessment of New Materials Synthesis and Crystal Growth in United States  

Microsoft Academic Search

The committee of 16 members was drawn from the broad community of condensed-matter physicists and materials researchers, and included experts in bulk materials synthesis and crystal growth (oxide, intermetallic, semiconductor, and organic synthesis) and both experimentalists and theorists. It prepared a report to address the following tasks: (1) Define the research area of new materials synthesis and crystal growth, framing

Don C. Shapero; James C. Lancaster

2009-01-01

291

Managing Training Materials with Structured Text Design.  

ERIC Educational Resources Information Center

Describes characteristics of structured text design; benefits of its use in training; benefits for developers of training materials and steps in preparing training materials. A case study illustrating how the structured text design process solved the sales training needs of the Mercedes-Benz Truck Company is presented. (MBR)

Streit, Les D.; And Others

1986-01-01

292

Ordering the amorphous - Structures in PBD LED materials  

NASA Astrophysics Data System (ADS)

The class of 2,5 disubstituted-1,3,4-oxadiazoles containing a biphenyl unit on one side is intensively used as electron transport materials to enhance the performance of organic light emitting diodes (OLEDs). In contrast to the ongoing research on these materials insights in their structure-property relationships are still incomplete. To overcome the structural tentativeness and ambiguities the crystal structures of 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, that of the related compound 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole and of 2-(4-biphenylyl)-5-(2,6-dimethylphenyl)-1,3,4-oxadiazole are determined. A comparison with the results of GAUSSIAN03 calculations and similar compounds in the Cambridge Structural Database leads to a profound characterization.

Emmerling, Franziska; Orgzall, Ingo; Dietzel, Birgit; Schulz, Burkhard; Larrucea, Julen

2012-12-01

293

Determination of channeling perspectives for complex crystal structures  

SciTech Connect

Specification of the atomic arrangement for axes and planes of high symmetry is essential for crystal alignment using Rutherford backscattering and for studies of the lattice location of impurities in single crystals. By rotation of an inscribed orthogonal coordinate system, a visual image for a given perspective of a crystal structure can be specified. Knowledge of the atomic arrangement permits qualitative channeling perspectives to be visualized and calculation of continuum potentials for channeling. Channeling angular-yield profiles can then be analytically modeled and, subsequently, shadowing by host atoms of positions within the unit cell predicted. Software to calculate transformed atom positions for a channeling perspective in a single crystal are described and illustrated for the spinel crystal structure.

Allen, W.R.

1993-03-01

294

Structural Reorganization of Liquid Crystals Revealled by Fast Scanning Calorimeter  

NASA Astrophysics Data System (ADS)

Liquid crystal glass of 4-Cyano-4'-octylbiphenyl is obtained by rapid cooling with rates over 2000 Kelvin per second (K/s) on the chip calorimeter. The glass can crystallize easily upon heated above its glass transition temperature. Depending on the prior cooling rate and annealing history thereafter, melting-structural reorganization-remelting behavior similar to that of semicrystalline polymer can be observed during subsequent heating. The complex melting behavior is attributed to the transformation of metastable crystal forms formed during annealing or heating induced cold crystallization. Increasing the heating rate (>15000 K/s) can suppress the transformation and, additionally, enables us to capture the multiple N-I transition. This implies the coexistence of two different types of nematic states. To avoid above complex structural reorganization, one can anneal the sample at 260K for 2 seconds to get the stable crystal form.

Zhou, Dongshan; Jiang, Jing; Wang, Xiaoliang; Xue, Gi

2011-03-01

295

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements  

NASA Astrophysics Data System (ADS)

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr2+, Co2+, or Fe2+), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn2+, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.

Kramushchenko, D. D.; Ilyin, I. V.; Soltamov, V. A.; Baranov, P. G.; Kalinushkin, V. P.; Studenikin, M. I.; Danilov, V. P.; Il'ichev, N. N.; Shapkin, P. V.

2013-02-01

296

Detergent structure in tetragonal crystals of OmpF porin  

Microsoft Academic Search

Background: The high-resolution structures of five porins have been solved by X-ray crystallography including the trigonal crystal form of the trimeric OmpF porin from Escherichia coli. In an accompanying article, the structure of the tetragonal form of OmpF porin is presented. In contrast to the trigonal crystal form, the protein surfaces normally in contact with lipids in the membrane are

E Pebay-Peyroula; RM Garavito; JP Rosenbusch; M Zulauf; PA Timmins

1995-01-01

297

Crystal structure of a phospholipase D family member  

Microsoft Academic Search

The first crystal structure of a phospholipase D (PLD) family member has been determined at 2.0 resolution. The PLD superfamily is defined by a common sequence motif, HxK(x)4D(x)6GSxN, and includes enzymes involved in signal transduction, lipid biosynthesis, endonucleases and open reading frames in pathogenic viruses and bacteria. The crystal structure suggests that residues from two sequence motifs form a

Jeanne A. Stuckey; Jack E. Dixon

1999-01-01

298

The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study  

Microsoft Academic Search

The atomic structure of the potential photovoltaic materials Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) is discussed on the basis of a structural analysis of neutron powder diffraction data refined by the Rietveld analysis. Both compounds were found to crystallize in the kesterite type structure, but with a disorder within the CuZn layers at z=1\\/4 and 3\\/4. The latter causes CuZn and

Susan Schorr

2011-01-01

299

Photophysical properties and electronic structure of highly donor doped (110) layered perovskite material  

Microsoft Academic Search

Sr2Nb2O7, a donor doped (110) layered perovskite material was synthesized by solid state reaction method and studied for its photo physical properties. The morphology, crystal structure and optical properties were characterized respectively by SEM, XRD and UV-DRS spectroscopies. We performed the electronic band structure calculations on orthorhombic crystal structure of Sr2Nb2O7, within the framework of density functional theory (DFT) by

E. D. Jeong; M. G. Ha; M. S. Won; H. G. Kim; H. K. Pak; P. H. Borse; S. M. Ji; J. S. Lee

2006-01-01

300

Rhombohedral crystal structure of compounds containing boron-rich icosahedra  

Microsoft Academic Search

The crystal structures of several icosahedral boron containing compounds have been refined using Mo K? intensity data. Though these compounds, ?-boron, boron carbide, boron phosphide and boron arsenide, differ chemically, all have the same basic rhombohedral structure. The structures consist of icosahedral units bonded together with direct B-B bonds as well as other linkage units. Similarities in electron distributions are

B. Morosin; A. W. Mullendore; D. Emin; G. A. Slack

1986-01-01

301

Rhombohedral crystal structure of compounds containing boron-rich icosahedra  

Microsoft Academic Search

The crystal structures of several icosahedral boron containing compounds have been refined using Mo Kalpha intensity data. Though these compounds, alpha-boron, boron carbide, boron phosphide and boron arsenide, differ chemically, all have the same basic rhombohedral structure. The structures consist of icosahedral units bonded together with direct B-B bonds as well as other linkage units. Similarities in electron distributions are

B. Morosin; A. W. Mullendore; D. Emin; G. A. Slack

1986-01-01

302

Structure and vertical modes in finite 2D plasma crystals  

Microsoft Academic Search

The formation of finite 2D plasma crystals was numerically simulated to allow the investigation of structural symmetries for systems with various Debye lengths. For the case of increasing Debye length, a transition was discovered between a fully hexagonal structure and a structure having concentric rings along the outer edge and a hexagonal lattice in the interior. Additionally, the vertical as

K. Qiao; T. W. Hyde

2007-01-01

303

Structural Patterns in Polymer-Dispersed Liquid Crystal Films  

Microsoft Academic Search

Different methods for the creation of structural patterns in Polymer Dispersed Liquid Crystals (PDLC) are discussed and compared, with a special attention to the recent techniques of induced director pre-orientation and inhomogeneities creation in PDLC films. Examples of the periodic structural patterns obtained by means of different methods adopted during the PDLC preparation are reported. These PDLC with intrinsic structure

S. J. K?osowicz; O. Francescangeli; S. Di Bella

1999-01-01

304

The Durability of Various Crucible Materials for Aluminum Nitride Crystal growth by Sublimation  

SciTech Connect

Producing high purity aluminum nitride crystals by the sublimation-recondensation technique is difficult due to the inherently reactive crystal growth environment, normally at temperature in excess of 2100 C. The durability of the furnace fixture materials (crucibles, retorts, etc.) at such a high temperature remains a critical problem. In the present study, the suitability of several refractory materials for AlN crystal growth is investigated, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride. The thermal and chemical properties and performance of these materials in inert gas, as well as under AlN crystal growth conditions are discussed. TaC and NbC are the most stable crucible materials with very low elemental vapor pressures in the crystal growth system. Compared with refractory material coated graphite crucibles, HPBN crucible is better for AlN self-seeded growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density.

Liu,B.; Edgar, J.; Gu, Z.; Zhuang, D.; Raghothamachar, B.; Dudley, M.; Sarua, A.; Kuball, M.; Meyer, H.

2004-01-01

305

Engineering Materialism and Structural Integrity  

Microsoft Academic Search

SUMMARY Two prime engineering focuses are concerned with what might be termedmateri- alism', and with structural reliability. This paper discusses the interconnections between these in the context of the historical development of engineering capability, highlighting the associated risk in application and use of this capability, and the accrued bene ts for mankind. As successful engineering rests on communication skills, as

M. Neil James

1998-01-01

306

Crystal structure of Bacillus anthracis transpeptidase enzyme CapD.  

SciTech Connect

Bacillus anthracis elaborates a poly-{gamma}-d-glutamic acid capsule that protects bacilli from phagocytic killing during infection. The enzyme CapD generates amide bonds with peptidoglycan cross-bridges to anchor capsular material within the cell wall envelope of B. anthracis. The capsular biosynthetic pathway is essential for virulence during anthrax infections and can be targeted for anti-infective inhibition with small molecules. Here, we present the crystal structures of the {gamma}-glutamyltranspeptidase CapD with and without {alpha}-l-Glu-l-Glu dipeptide, a non-hydrolyzable analog of poly-{gamma}-d-glutamic acid, in the active site. Purified CapD displays transpeptidation activity in vitro, and its structure reveals an active site broadly accessible for poly-{gamma}-glutamate binding and processing. Using structural and biochemical information, we derive a mechanistic model for CapD catalysis whereby Pro{sup 427}, Gly{sup 428}, and Gly{sup 429} activate the catalytic residue of the enzyme, Thr{sup 352}, and stabilize an oxyanion hole via main chain amide hydrogen bonds.

Wu, R.; Richter, S.; Zhang, R.; Anderson, V. J.; Missiakas, D.; Joachimiak, A.; Biosciences Division; Univ. of Chicago

2009-09-04

307

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination  

NASA Astrophysics Data System (ADS)

Submicrometer single crystal diffractometry for highly accurate structure determination was developed using the extremely stable and highly brilliant synchrotron radiation from SPring-8. This was achieved using a microbeam focusing system and the submicrometer precision low-eccentric goniometer system. We demonstrated the structure analyses with 222 ?m3 cytidine, 600600300 nm3 BaTiO3, and 111 ?m3 silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendellsung method and do not require absorption and extinction corrections.

Yasuda, Nobuhiro; Fukuyama, Yoshimitsu; Toriumi, Koshiro; Kimura, Shigeru; Takata, Masaki

2010-06-01

308

Radiation Effects on Spacecraft Structural Materials  

SciTech Connect

Research is being conducted to develop an integrated technology for the prediction of aging behavior for space structural materials during service. This research will utilize state-of-the-art radiation experimental apparatus and analysis, updated codes and databases, and integrated mechanical and radiation testing techniques to investigate the suitability of numerous current and potential spacecraft structural materials. Also included are the effects on structural materials in surface modules and planetary landing craft, with or without fission power supplies. Spacecraft structural materials would also be in hostile radiation environments on the surface of the moon and planets without appreciable atmospheres and moons around planets with large intense magnetic and radiation fields (such as the Jovian moons). The effects of extreme temperature cycles in such locations compounds the effects of radiation on structural materials. This paper describes the integrated methodology in detail and shows that it will provide a significant technological advance for designing advanced spacecraft. This methodology will also allow for the development of advanced spacecraft materials through the understanding of the underlying mechanisms of material degradation in the space radiation environment. Thus, this technology holds a promise for revolutionary advances in material damage prediction and protection of space structural components as, for example, in the development of guidelines for managing surveillance programs regarding the integrity of spacecraft components, and the safety of the aging spacecraft. (authors)

Wang, Jy-An J.; Ellis, Ronald J.; Hunter, Hamilton T. [Oak Ridge National Laboratory (United States); Singleterry, Robert C. Jr. [NASA Langley Research Center, Hampton, VA 23681 (United States)

2002-07-01

309

Three-dimensional structure and defects in colloidal photonic crystals revealed by tomographic scanning transmission X-ray microscopy.  

PubMed

Self-assembled colloidal crystals have attracted major attention because of their potential as low-cost three-dimensional (3D) photonic crystals. Although a high degree of perfection is crucial for the properties of these materials, little is known about their exact structure and internal defects. In this study, we use tomographic scanning transmission X-ray microscopy (STXM) to access the internal structure of self-assembled colloidal photonic crystals with high spatial resolution in three dimensions for the first time. The positions of individual particles of 236 nm in diameter are identified in three dimensions, and the local crystal structure is revealed. Through image analysis, structural defects, such as vacancies and stacking faults, are identified. Tomographic STXM is shown to be an attractive and complementary imaging tool for photonic materials and other strongly absorbing or scattering materials that cannot be characterized by either transmission or scanning electron microscopy or optical nanoscopy. PMID:22260512

Hilhorst, Jan; van Schooneveld, Matti M; Wang, Jian; de Smit, Emiel; Tyliszczak, Tolek; Raabe, Jrg; Hitchcock, Adam P; Obst, Martin; de Groot, Frank M F; Petukhov, Andrei V

2012-02-07

310

Quasi-crystals-random structures or twins?  

Microsoft Academic Search

This paper discusses different ways of tiling a plane without defects by using two decorating elements. Four classes of structure with different tiling rules and different relative concentrations of the two elements are compared: Penrose tiling, microcrystalline twins, a random structure and a precipitated structure. The four structures have similar diffraction patterns exhibiting tenfold symmetry, but they differ in many

J. Wolny; L. Pytlik; B. Lebech

1988-01-01

311

Ordering of crystal structure by ionizing radiation  

Microsoft Academic Search

We have studied the action of ionizing radiation on defect-containing semiconductor crystals, metals, and alloys. Using modern methods for investigation of solids, Rutherford back scattering of channeled charged particles, x-ray diffraction, electron microscopy, and also calorimetric methods, we have established: a) irradiation (by x-ray beams, gamma rays, and electrons) of metals and alloys with an equivalent radiation dose less than

I. P. Chernov; A. P. Momontov; P. A. Cherdantsev; B. V. Chakhlov

1994-01-01

312

Omnidirectional reflection from the one-dimensional photonic crystal containing anisotropic left-handed material  

Microsoft Academic Search

We study the transmission properties in the one-dimensional\\u000aphotonic crystal containing alternate anisotropic left-handed\\u000amaterial (LHM) layers and regular isotropic right-handed material\\u000a(RHM) layers. For such an anisotropic case, the dispersion\\u000arelation from the Bloch theorem is derived and the Bragg gaps of\\u000athe periodic structure are observed. It is found that in the m=0\\u000aBragg gap, there is an

S. Wang; L. Gao

2005-01-01

313

Electronic and structural properties of partially crystallized silicon produced by solid-phase crystallization of as-deposited amorphous silicon  

SciTech Connect

Polycrystalline silicon produced by the solid-phase crystallization of low pressure chemical vapor deposited amorphous films is examined. Electrical activation energy measurements demonstrate that there is a progressive change in the nature of the dominant conduction paths as solid-phase crystallization proceeds. Film thickness is found to play an important role in determining these dominant conduction paths and thicker films are found to exhibit higher levels of hopping via localized states than thinner films annealed under the same conditions. The defect microstructure of annealed layers of a-Si takes the form of evolving dendrite crystals which coalesce with increasing time of annealing. Thinner films show increasing extent of lateral crystal growth consistent with a more extended state mode of conduction since few grain boundaries are seen by the dominant conduction path. Thicker films exhibit comparable grain sizes but a reduced lateral extent of crystallization. The balance between grain size and film thickness for increasing times of annealing will define the optimum electronic properties of the material. Dendritic grains are characterized by twin band core structures, and a high density of stacking faults are generally associated with grains from the first stages of nucleation.

Smith, J.P.; Eccleston, W. [Univ. of Liverpool (United Kingdom). Dept. of Electrical Engineering and Electronics; Brown, P.D.; Humphreys, C.J. [Univ. of Cambridge (United Kingdom). Dept. of Materials Science and Metallurgy

1999-01-01

314

Control of Nanoparticle Size, Crystal Structure and Growth of Layered Double Hydroxide by Hydrothermal Treatment  

NASA Astrophysics Data System (ADS)

Here, we showed the effect of hydrothermal treatment and aging process of urea hydrolysis on crystal structure, particle size and particle size distribution of Mg-Al layered double hydroxide (LDH) materials. The obtained materials were characterized by X-ray crystallography and scanning electron microscopy. The studied synthetic parameters showed a great influence on the physicochemical properties of the selected LDH materials. At insufficient conditions of hydrothermal treatments, the formed LDH particles were amorphous and the non-LDH phases dominated the X-ray diffraction chart. The crystal growth increased with increasing hydrothermal temperature. Aging process improved the crystal morphology up to18 hours, while further aging destroyed the LDH particles. The increase of hydrothermal aging led to a wide particle size distribution.

Berber, Mohamed R.; Hafez, Inas H.; Minagawa, Keiji; Katoh, Masahiro; Tanaka, Masami; Mori, Takeshi

315

Crystal Structures of Two Putative Phosphoheptose  

SciTech Connect

Structural genomic centers use both NMR spectroscopic and X-ray crystallographic methods to determine three-dimensional structures of proteins on a genomic scale in a high-throughput mode and to deposit in the PDB. The main goal of structural genomics is to determine a large number of protein structures to complement the ever-expanding database of genome sequences. Another role of structural genomics is to delineate the correspondence between sequence and structure space; a number of protein structures from otherwise unrelated (i.e., 8-10% sequence identity) families often prove to have remarkably similar folds. This finding, in turn, allows better understanding of the structure-function relationships in those proteins for which either structures are not available or cannot be experimentally determined.

Seetharaman,J.; Rajashankar, K.; Solarzano, V.; Kniewel, R.; Lima, C.; Bonanno, J.; Burley, S.; Swaminathan, S.

2006-01-01

316

Local liquid crystal alignment on patterned micrograting structures photofabricated by two photon excitation direct laser writing  

NASA Astrophysics Data System (ADS)

The authors demonstrate local alignment of nematic liquid crystal through the fabrication of local micrograting structures by curing an ultraviolet curable material via a two-photon excitation laser-lithography process. A local twisted-nematic region was prepared using one rubbed and one fabricated micrograting surface and the resulting cell was observed with a polarizing optical microscope. The polarization optical micrographs of the locally fabricated region suggest that liquid crystal molecules align parallel to the grating structure and that local alignment is achieved. We evaluate the anchoring energies of the fabricated microgratings by the torque balance method.

Lee, Chee Heng; Yoshida, Hiroyuki; Miura, Yusuke; Fujii, Akihiko; Ozaki, Masanori

2008-10-01

317

Revolutionary opportunities for materials and structures study  

SciTech Connect

The revolutionary opportunities for materials and structures study was performed to provide Government and Industry focus for advanced materials technology. Both subsonic and supersonic engine studies and aircraft fuel burn and DOC evaluation are examined. Year 2010 goal materials were used in the advanced engine studies. These goal materials and improved component aero yielded subsonic fuel burn and DOC improvements of 13.4 percent and 5 percent, respectively and supersonic fuel burn and DOC improvements of 21.5 percent and 18 percent, respectively. Conclusions are that the supersonic study engine yielded fuel burn and DOC improvements well beyond the program goals; therefore, it is appropriate that advanced material programs be considered.

Schweiger, F.A.

1987-02-01

318

Control and Computation in Smart Material Structures.  

National Technical Information Service (NTIS)

The research carried out dealt with mathematical modeling, computation, and model validation in smart material structures. In particular a focused study of laminated curved beam with embedded piezoceramic patches was conducted. There has been widespread i...

N. G. Medhin

1998-01-01

319

Optimal Design of Structures Incorporating 'Smart Materials'.  

National Technical Information Service (NTIS)

The purpose of this project was to develop a rigorous theoretical foundation of the design of structures incorporating general 'smart' materials, and to explore, extend and develop the use of sensors and actuators that employ 'finite length' paths. It is ...

P. D. Washabaugh J. E. Taylor A. M. Waas

1998-01-01

320

METALLURGICAL PROBLEMS OF NUCLEAR REACTORS. STRUCTURAL MATERIALS  

Microsoft Academic Search

After a survey of the specifically nuclear data of reactors, the ; different qualities, intrinsic and extrinsic, required for the structural ; materials of reactors are discussed. The effect of radiation on several aspects ; of their behavior is described. (tr-auth);

1958-01-01

321

Adapative Materials and Structures. A Workshop Report.  

National Technical Information Service (NTIS)

The objectives for the workshop were to explore the potential use of adaptive structural materials science and technology for military application. Understanding the current research in this area, and the potential opportunities to use this research by U....

2013-01-01

322

Crystal growth, thermal and optical studies of nonlinear optical material: Glycine potassium sulphate  

Microsoft Academic Search

A new nonlinear optical material glycine potassium sulphate (GPS) has been synthesized and optical quality crystals were grown from aqueous solution. This material has positive temperature coefficient revealed from the solubility studies. The grown crystals were characterized by employing several techniques such as single crystal and powder X-ray diffraction, thermo gravimetric analysis, FTIR and UVvisNIR spectra. The etching studies have

Ra. Shanmugavadivu; G. Ravi; A. Nixon Azariah

2006-01-01

323

Crystal structure of a theta-class glutathione transferase.  

PubMed Central

Glutathione S-transferases (GSTs) are a family of enzymes involved in the cellular detoxification of xenotoxins. Cytosolic GSTs have been grouped into four evolutionary classes for which there are representative crystal structures of three of them. Here we report the first crystal structure of a theta-class GST. So far, all available GST crystal structures suggest that a strictly conserved tyrosine near the N-terminus plays a critical role in the reaction mechanism and such a role has been convincingly demonstrated by site-directed mutagenesis. Surprisingly, the equivalent residue in the theta-class structure is not in the active site, but its role appears to have been replaced by either a nearby serine or by another tyrosine residue located in the C-terminal domain of the enzyme. Images

Wilce, M C; Board, P G; Feil, S C; Parker, M W

1995-01-01

324

The crystal structure of some rhenium and technetium dichalcogenides  

Microsoft Academic Search

The crystal structures of ReSe., ReS., ReSSe and TeS2 are determined using single crystal X-ray diffraction. The compounds are triclinic with space groupPl. ReSe., ReS, and ReSSe have a distorted CdCl2-type structure: TeS2 has a distorted Cd(OH)-type structure. In the case of ReS, there are two sandwiches in the unit cell, related by symmetry centers. The other compounds have one

H.-J. Lamfers; A. Meetsma; G. A. Wiegers; J. L. de Boer

1996-01-01

325

Nanomechanical resonant structures in single-crystal diamond  

NASA Astrophysics Data System (ADS)

With its host of outstanding material properties, single-crystal diamond is an attractive material for nanomechanical systems. Here, the mechanical resonance characteristics of freestanding, single-crystal diamond nanobeams fabricated by an angled-etching methodology are reported. Resonance frequencies displayed evidence of significant compressive stress in doubly clamped diamond nanobeams, while cantilever resonance modes followed the expected inverse-length-squared trend. Q-factors on the order of 104 were recorded in high vacuum. Results presented here represent initial groundwork for future diamond-based nanomechanical systems which may be applied in both classical and quantum applications.

Burek, Michael J.; Ramos, Daniel; Patel, Parth; Frank, Ian W.; Lon?ar, Marko

2013-09-01

326

Optical and structural properties of chalcone NLO single crystals  

NASA Astrophysics Data System (ADS)

Organic compound (E)-1-(4-methoxyphenyl)-3-(2,3,5-trichlorophenyl)prop-2-en-1-one [MPTCPP] with molecular formula C16H11Cl3O2 was synthesized using Claisen-Schmidt condensation reaction method. 1H NMR spectra was recorded to identify the various functional groups present in the compound and confirm the chemical structure. The single crystals were grown using slow evaporation solution growth technique. The UV-Visible spectrum study reveals that the crystal is transparent in the entire visible region and the absorption is observed at 364 nm. The Kurtz powder second harmonic generation (SHG) test shows that the MPTCPP is NLO active and its SHG efficiency is three times that of urea. Single crystal XRD study shows that the compound crystallizes in the monoclinic system with a space group Cc. The corresponding lattice parameters of the crystal are a = 28.215(5) , b = 3.9740(4) , c = 16.178(3) and V = 1503.0(4) 3. The micro hardness test was carried out and the work hardening coefficient value (n) of the crystal was found to be 1.48. This indicates that the crystal is hard and is suitable for device application. The thermal study reveals that the thermal stability of the crystal is good.

Rajesh Kumar, P. C.; Ravindrachary, V.; Janardhana, K.; Manjunath, H. R.; Karegouda, Prakash; Crasta, Vincent; Sridhar, M. A.

2011-11-01

327

Bone matrix like assemblies of collagen: From liquid crystals to gels and biomimetic materials  

Microsoft Academic Search

Skeletal tissues associate in close interaction, a dense organic matrix and a mineral network. In bone, the major structural protein is type I collagen, associated with inorganic crystals of hydroxyapatite. The three-dimensional arrangement of collagen fibrils in compact bone forms regularly ordered networks and a parallel was evidenced between these structures and molecular assemblies described in liquid crystals. Similar structures

Marie M. Giraud Guille; Gervaise Mosser; Christophe Helary; David Eglin

2005-01-01

328

Hexagonal structures for two-dimensional photonic crystals  

Microsoft Academic Search

Periodic dielectric structures have been recently proposed to inhibit spontaneous emission in semiconductors. From this suggestion, the new concepts of photonic band gap and photonic crystal have been developed. Zero-threshold lasers, waveguides, antenna substrates, filters and polarizers are promising applications. We propose a new class of two-dimensional periodic dielectric structures with hexagonal symmetry. We study the gap opening according to

D. Cassagne; C. Jouanin; D. Bertho

1996-01-01

329

Crystal structure solution from experimentally determined atomic pair distribution functions  

Microsoft Academic Search

The paper describes an extension of the Liga algorithm for structure solution from atomic pair distribution function (PDF), to handle periodic crystal structures with multiple elements in the unit cell. The procedure is performed in 2 separate steps - at first the Liga algorithm is used to find unit cell sites consistent with pair distances extracted from the experimental PDF.

Pavol Juhas; Luke Granlund; Saurabh R. Gujarathi; Phillip M. Duxbury; Simon J. L. Billinge

2010-01-01

330

Photonic crystals of diamond spheres with the opal structure  

NASA Astrophysics Data System (ADS)

Opal samples consisting of diamond spheres have been synthesized by chemical deposition in microwave plasma from a CH4/H2 mixture using templates of silicon inverse opal. The optical investigations have confirmed that the periodic structures prepared are structurally perfect three-dimensional photonic crystals.

Sovyk, D. N.; Ralchenko, V. G.; Kurdyukov, D. A.; Grudinkin, S. A.; Golubev, V. G.; Khomich, A. A.; Konov, V. I.

2013-05-01

331

On automation of the procedure for crystal structure model refinement  

NASA Astrophysics Data System (ADS)

The methods of automation of the procedure for crystal structure model refinement from experimental diffraction data, implemented in the ASTRA program package, are described. Such tools as statistical tests, parameter scanning, and data scanning reduce the time necessary for structural investigation. At strong correlations between parameters, especially when the data set is limited, parameter scanning has an advantage over the full-matrix refinement.

Dudka, A. P.

2008-03-01

332

Liquid crystal based electrically switchable Bragg structure for THz waves.  

PubMed

We demonstrate the first electronically switchable Bragg structure for THz frequencies. The structure works as stop-band filter and as mirror. It exhibits the 60 GHz broad stop-band around 300 GHz which can be removed by reorienting liquid crystal molecules in an external electric field. Our first proof-of-principle experiments agree very well with transfer matrix calculations. PMID:19399116

Wilk, Rafal; Vieweg, Nico; Kopschinski, Olaf; Koch, Martin

2009-04-27

333

Crystal Structure of Purine Nucleoside Phosphorylase from Thermus thermophilus  

Microsoft Academic Search

The purine nucleoside phosphorylase from Thermus thermophilus crystallized in space group P43212 with the unit cell dimensions a=131.9, and c=169.9, and one biologically active hexamer in the asymmetric unit. The structure was solved by the molecular replacement method and refined at a 1.9 resolution to an Rfree value of 20.8%. The crystals of the binary complex with sulfate ion and

Tahir H Tahirov; Eiji Inagaki; Noriyasu Ohshima; Tomoe Kitao; Chizu Kuroishi; Yoko Ukita; Koji Takio; Masanori Kobayashi; Seiki Kuramitsu; Shigeyuki Yokoyama; Masashi Miyano

2004-01-01

334

Crystal Structure of L-Histidinium 2-Nitrobenzoate  

PubMed Central

A new nonlinear optical organic compound, namely, L-histidinium 2-nitrobenzoate (abbreviated as LH2NB (I); ([C6H10N3O2]+ [C7H4NO4]?)), was synthesized. The molecular structure of LH2NB (I) was elucidated using single crystal X-ray diffraction technique. The second harmonic generation (SHG) efficiency of this compound is about two times that of the standard potassium dihydrogen phosphate crystals.

Natarajan, Subramanian; Moovendaran, Kalimuthu; Kalyana Sundar, Jeyaperumal; Ravikumar, Krishnan

2012-01-01

335

Crystal structure of a calcium sulfate-urea complex  

Microsoft Academic Search

The crystal structure of CaSO4 4(CH4N2) has been determined from 2695 x-ray intensities measured on a diffractometer, and refined anisotropically to anR-factor of 0.059. The pseudotetragonal crystals contain linear chains of CaSO4 which strongly resemble those in other CaSO4 phases. A common dodecahedral coordination of calcium ions in all these phases is demonstrated, and its implications in the conversion

J. P. R. De Villiers; J. C. A. Boeyens

1975-01-01

336

Boron-Oxygen Polyanion in the Crystal Structure of Tunellite.  

PubMed

The crystal structure of tunellite, SrO.3B(2)O(3).4H(2)O, with infinite sheets of composition n[B(6)O(9)(OH)(2)](2-), has cations and water molecules in the spaces within the sheets. Adjacent sheets are held together by hydrogen bonding through the water molecules. The boron-oxygen polyanions provide the first example in hydrated borate crystals of one oxygen linked to three borons. PMID:17751796

Clark, J R

1963-09-20

337

Crystal and molecular structure of glutaconic acid  

Microsoft Academic Search

Crystals of Glutaconic acid, C5O4H6, are triclinic, space group P\\u000a$${\\\\bar 1}$$\\u000a, with the cell dimensions (294 K), a = 4.843(1) , b = 10.188(1) , c = 12.609(1) , a = 83.46(1), = 80.02(1), ? = 78.71(1), V = 598.8(3) 3 with Dm = 1.47, Dx = 1.443 gcm -3. There are two independent molecules in the

Leonard Thomas; Thamarapu Srikrishnan

2003-01-01

338

Fine Structure of Electron Diffraction Beams from a Gold Crystal and from a Silver Film on a Gold Crystal  

Microsoft Academic Search

A study of the diffraction of low-speed electrons from a gold crystal has been made under the same conditions as those previously used for a silver crystal to determine the extent to which the previously observed fine structure characteristics depend on the nature of the atoms composing the crystal. For normal incidence there are many differences in the positions, structure,

H. E. Farnsworth

1933-01-01

339

Ensemble refinement of protein crystal structures  

PubMed Central

Summary X-ray crystallography typically uses a single set of coordinates and B-factors to describe macromolecular conformations. Refinement of multiple copies of the entire structure has been previously used in specific cases as an alternative means of representing structural flexibility. Here, we systematically validate this method using simulated diffraction data, and find ensemble refinement produces better representations of the distributions of atomic positions in the simulated structures than single conformer refinements. Comparison of principal components calculated from the refined ensembles and simulations shows that concerted motions are captured locally, but correlations dissipate over long distances. Ensemble refinement is also used on 50 experimental structures of varying resolution, and leads to decreases in R-free, implying that improvements in the representation of flexibility observed for the simulated structures may apply to real structures. These gains are essentially independent of resolution or data-to-parameter ratio, suggesting even structures at moderate resolution can benefit from ensemble refinement.

Levin, Elena J.; Kondrashov, Dmitry A.; Wesenberg, Gary E.; Phillips, George N.

2007-01-01

340

Synthesis and Structure Characterization of Forsterite Single Crystal  

NASA Astrophysics Data System (ADS)

Forsterite (Mg2SiO4), the low-pressure polymorph of magnesium orthosilicate, is of great importance in the upper mantle due to its aboundance. Up to now, only powder samples of forsterite can be synthesized due to the difficulty of its crystal growth. Therefore, the exact crystal structure of forsterite is still an open question. The crystal structure of forsterite was firstly studied in 1926 by Brown and Bragg. Numerous experimental investigations have been performed in order to get the structure of the olivine group minerals at ambient conditions and a variety of temperature and pressures by using the advent of the computer, the single crystal diffractometer and the diamond cell. However, there are still considerable uncertaintes regarding the accuracy of its unit-cell parameter values. In this study, we synthesized for the first time high quality single crystals of forsterite using the Quickpress piston-cylinder apparatus. The single crystal of forsterite was synthesized by direct reaction of stoichiometric amounts of MgO and amorphous SiO2 (Alfa Aesar, 99.999%) in the presence of ~10-11 wt% distilled water at 2.0GPa, 1723 K for 12h. A colorless single crystal of Mg2SiO4 with size dimensions 0.160.110.04 mm was selected for single crystal X-ray diffraction analysis. The intensity data were collected with a Rigaku R-AXIS RAPID IP diffractometer by oscillation scans using graphite- monochromated Mo-K?0?6?0?6?7677?0?6?0?6?7699 radiation (?=0.71073 ). Cell refinement and data reduction were accomplished with RAPID AUTO program. The crystal structure was solved by direct methods with the SHELXL crystallographic software package. Single crystal X-ray diffraction analysis shows a crystal structure of orthorhombic space group Pnma (No. 62) with a = 10.2073(11) , b = 5.9863(5) , c = 4.7611(4) and Z = 4. Our new data provides new constraints for theoretical investigations of the physical and chemistry properties and behaviors of forsterite under various pressures.

Wang, C.; Jin, S.; Wang, X.; Liu, X.; Fleet, M. E.; Jin, Z.

2006-12-01

341

Synthesis, growth, structural, spectroscopic and optical studies of a semiorganic NLO crystal: zinc guanidinium phosphate.  

PubMed

The semi-organic nonlinear optical (NLO) crystal, zinc guanidinium phosphate (ZGuP) has been grown through synthesis between zinc sulphate, guanidine carbonate and orthophosphoric acid from its aqueous solution by slow solvent evaporation technique. Solubility of the synthesized material has been determined for various temperatures using water as solvent. The grown crystal has been characterized by powder X-ray diffraction to confirm the crystal structure. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopy technique. (1)H and (13)C FT-NMR have been recorded to elucidate the molecular structure. The optical absorption study confirms the suitability of the crystal for device applications. The second harmonic generation (SHG) efficiency of ZGuP is found to be 1.825 times that of potassium dihydrogen phosphate (KDP). Thermal behavior of the grown crystals has been studied by thermogravimetric and differential thermal analysis. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. PMID:22079889

Suvitha, A; Murugakoothan, P

2011-10-20

342

Synthesis, growth, structural, spectroscopic and optical studies of a semiorganic NLO crystal: Zinc guanidinium phosphate  

NASA Astrophysics Data System (ADS)

The semi-organic nonlinear optical (NLO) crystal, zinc guanidinium phosphate (ZGuP) has been grown through synthesis between zinc sulphate, guanidine carbonate and orthophosphoric acid from its aqueous solution by slow solvent evaporation technique. Solubility of the synthesized material has been determined for various temperatures using water as solvent. The grown crystal has been characterized by powder X-ray diffraction to confirm the crystal structure. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopy technique. 1H and 13C FT-NMR have been recorded to elucidate the molecular structure. The optical absorption study confirms the suitability of the crystal for device applications. The second harmonic generation (SHG) efficiency of ZGuP is found to be 1.825 times that of potassium dihydrogen phosphate (KDP). Thermal behavior of the grown crystals has been studied by thermogravimetric and differential thermal analysis. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester.

Suvitha, A.; Murugakoothan, P.

2012-02-01

343

Structural, morphological and optical characteristics of KGd(WO4)2 crystals  

NASA Astrophysics Data System (ADS)

A KGd (WO sub 4) (sub 2) crystal, suitable as active laser material with Nd (sup + 3) doping, has a low-order symmetry which makes determination and normalization of its optical characteristics difficult. Its atomic structure is described by the P/2m group of spatial symmetry. A correspondence between the principal axes and the structure of this biaxial crystal was established by X-ray structural analyses with a URS-50IM X-ray diffractometer and a model F goniometer and optical measurements. Based on this study and plotting of the stereographic projection of such a crystal, its lattice parameters and optical indicatrix are found. Its optical orientation can be described as n sub g = b and n sub pc = 20 deg with the optical axes at an 86.5 deg angle to one another lying in the plane of the crystallographic b-axis zone.

Ananyeva, G. V.; Afanasyev, I. I.; Glazov, A. I.; Mamontov, I. Y.; Merkulyayeva, T. I.

1984-02-01

344

Structure of ice crystallized from supercooled water  

PubMed Central

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples.

Malkin, Tamsin L.; Murray, Benjamin J.; Brukhno, Andrey V.; Anwar, Jamshed; Salzmann, Christoph G.

2012-01-01

345

Structure of ice crystallized from supercooled water.  

PubMed

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples. PMID:22232652

Malkin, Tamsin L; Murray, Benjamin J; Brukhno, Andrey V; Anwar, Jamshed; Salzmann, Christoph G

2012-01-09

346

Dislocation-based crystal plasticity finite element modelling of polycrystalline material deformation  

NASA Astrophysics Data System (ADS)

The objective of this research is to develop an understanding of the mechanical behavior and dislocation microstructure evolution of copper single and polycrystals, and to delineate the physical and mechanical origins of spatially-localized plastic deformation. Traditional approaches to the study of plastic instabilities have either been based on kinematic considerations, such as finite strain effects and geometric softening, or physics-based concepts. In this study, we develop a framework that combines both approaches. A rate-independent crystal plasticity model was developed to incorporate micromechanics, crystallinity and microstructure into a continuum description of finite strain plasticity. A comprehensive dislocation density model based on rate theory is employed to determine the strain hardening behavior within each plastic slip system for the fcc crystal structure. Finite strain effects and the kinematics of crystal plasticity are coupled with the dislocation-density based model via the hardening matrix in crystal plasticity. ABAQUS/CAE is employed as a finite element method solver, and several user's subroutines were developed to model fcc crystals with 2 and 12 slip systems. The developed material models are applied to study single and polycrystal deformation behavior of copper. Interfaces between the ABAQUS user's subroutine Umat and the ABAQUS main code are developed to allow further extension of the current method. The results of the model are first compared to earlier simulations of localized shear bands in a single copper crystal showing the association of the shear band with defects, as illustrated by Asaro. Current simulations for bicrystals indicate that shear band localization initiates at the triple point junction between the two crystals and the free surface. Simulations carried out for polycrystals clearly illustrate the heterogeneous nature of plastic strain, and the corresponding spatial heterogeneity of the mobile dislocation density. The origins of the spatial heterogeneities are essentially geometric, as a result of constraints on grain rotation (finite strain effects), geometric softening due to plastic, unloading of neighboring crystals. The physical origins of plastic instabilities manifest themselves in the coupling between the dislocation densities and the localized kinematically-induced softening.

Liu, Chunlei

347

How to predict very large and complex crystal structures  

NASA Astrophysics Data System (ADS)

Evolutionary crystal structure prediction proved to be a powerful approach in discovering new materials. Certain limitations are encountered for systems with a large number of degrees of freedom (large systems) and complex energy landscapes (complex systems). We explore the nature of these limitations and address them with a number of newly developed tools. For large systems a major problem is the lack of diversity: any randomly produced population consists predominantly of high-energy disordered structures, offering virtually no routes toward the ordered ground state. We offer two solutions: first, modified variation operators that favor atoms with higher local order (a function we introduce here), and, second, construction of the first generation non-randomly, using pseudo-subcells with, in general, fractional atomic occupancies. This enhances order and diversity and improves energies of the structures. We introduce an additional variation operator, coordinate mutation, which applies preferentially to low-order (badly placed) atoms. Biasing other variation operators by local order is also found to produce improved results. One promising version of coordinate mutation, explored here, displaces atoms along the eigenvector of the lowest-frequency vibrational mode. For complex energy landscapes, the key problem is the possible existence of several energy funnels - in this situation it is possible to get trapped in one funnel (not necessarily containing the ground state). To address this problem, we develop an algorithm incorporating the ideas of abstract distance between structures. These new ingredients improve the performance of the evolutionary algorithm USPEX, in terms of efficiency and reliability, for large and complex systems.

Lyakhov, Andriy O.; Oganov, Artem R.; Valle, Mario

2010-09-01

348

Superconductivity in Layered Structure Organometallic Crystals.  

National Technical Information Service (NTIS)

Superconductivity persists in several, layered, transition metal dichalcogenide superconductors when the layers are spread apart to accommodate organic molecules between them. These materials are of interest not only because of their two-dimensional chara...

F. R. Gamble F. J. DiSalvo R. A. Klemm T. H. Geballe

1970-01-01

349

Ytterbium- and neodymium-doped vanadate laser hose crystals having the apatite crystal structure  

DOEpatents

Yb.sup.3+ and Nd.sup.3+ doped Sr.sub.5 (VO.sub.4).sub.3 F crystals serve as useful infrared laser media that exhibit low thresholds of oscillation and high slope efficiencies, and can be grown with high optical quality. These laser media possess unusually high absorption and emission cross sections, which provide the crystals with the ability to generate greater gain for a given amount of pump power. Many related crystals such as Sr.sub.5 (VO.sub.4).sub.3 F crystals doped with other rare earths, transition metals, or actinides, as well as the many structural analogs of Sr.sub.5 (VO.sub.4).sub.3 F, where the Sr.sup.2+ and F.sup.- ions are replaced by related chemical species, have similar properties.

Payne, Stephen A. (Castro Valley, CA); Kway, Wayne L. (Fremont, CA); DeLoach, Laura D. (Manteca, CA); Krupke, William F. (Pleasanton, CA); Chai, Bruce H. T. (Oviedo, FL)

1994-01-01

350

Ytterbium- and neodymium-doped vanadate laser hose crystals having the apatite crystal structure  

DOEpatents

Yb[sup 3+] and Nd[sup 3+] doped Sr[sub 5](VO[sub 4])[sub 3]F crystals serve as useful infrared laser media that exhibit low thresholds of oscillation and high slope efficiencies, and can be grown with high optical quality. These laser media possess unusually high absorption and emission cross sections, which provide the crystals with the ability to generate greater gain for a given amount of pump power. Many related crystals such as Sr[sub 5](VO[sub 4])[sub 3]F crystals doped with other rare earths, transition metals, or actinides, as well as the many structural analogs of Sr[sub 5](VO[sub 4])[sub 3]F, where the Sr[sup 2+] and F[sup [minus

Payne, S.A.; Kway, W.L.; DeLoach, L.D.; Krupke, W.F.; Chai, B.H.T.

1994-08-23

351

The crystal structure of Fe 2In 2Se 5, a FeIn 2Se 4-related polytype  

Microsoft Academic Search

Fe2In2Se5, a polytype of FeIn2Se4 (a material belonging to the II ? III2 VI4 family of semiconducting compounds) has been synthesized by conventional solid-state reaction of their constituent elements. The product of the reaction was sequentially used as starting material in the crystal growth process carried out by chemical transport using I2 as transporting agent. The crystal structure of a

C. Cedeo; G. Daz de Delgado; J. M. Delgado; L. M. de Chalbaud; V. Sagredo

2005-01-01

352

Angular structure of radiation scattered by monolayer of polydisperse droplets of nematic liquid crystal  

NASA Astrophysics Data System (ADS)

We considered light scattering by a polydisperse ensemble of droplets of a nematic liquid crystal. To model light scattering by a monolayer of polymer-dispersed spherical droplets of a nematic liquid crystal with cylindrical symmetry of its internal structure, we proposed a semianalytical modeling method. The method is based on interference approximation of the theory of multiple wave scattering, anomalous diffraction approximation, and effective-medium approximation. The method takes into account cooperative optical effects in concentrated, partially ordered layers and can be used to analyze the small-angle structure of the intensity of scattered radiation in relation to the concentration, size, polydispersity of liquid crystal droplets, orientation of their optical axes, and refractive indices of the liquid crystal and polymer. The obtained relations can be applied to solving direct and inverse problems of light scattering in composite liquid crystal materials using data of polarization measurements. We present graphical results of solving the direct problem for components of the polarization vector of scattered wave. These results illustrate the formation of an angular structure for monolayers with a high concentration of polydisperse droplets of the liquid crystal in the range of small scattering angles (0 < ? s ? 8).

Loiko, V. A.; Maschke, U.; Zyryanov, V. Ya.; Konkolovich, A. V.; Miskevich, A. A.

2011-01-01

353

Gastric lipase: crystal structure and activity  

Microsoft Academic Search

Fat digestion in humans requires not only the classical pancreatic lipase but also gastric lipase, which is stable and active despite the highly acidic stomach environment. We have solved the structure of recombinant human gastric lipase at 3.0 resolution, the first structure to be described within the mammalian acid lipase family. This globular enzyme (379 residues) consists of a

Stphane Canaan; Alain Roussel; Robert Verger; Christian Cambillau

1999-01-01

354

Structural Distortions and Modulations in Microporous Materials  

Microsoft Academic Search

This article will discuss some of the characteristics of the real structures of zeolites and clathrasils. For simplicity,\\u000a the term zeolite will be used for all classes of microporous materials. The term real structure indicates that the structure\\u000a under discussion is distorted from an ideal one, for example, by changing temperature, pressure, different chemical composition,\\u000a a chemical reaction, or adsorption\\/desorption

W. Depmeier

355

Structures and properties of materials recovered from high shock pressures  

SciTech Connect

Shock compression produces high dynamic pressures, densities, temperatures, and their quench rates. Because of these extreme conditions, shock compression produces materials with novel crystal structures, microstructures, and physical properties. Using a 6.5-m-long two-stage gun, we perform experiments with specimens up to 10 mm in diameter and 0.001--1 mm thick. For example, oriented disks of melt-textured superconducting YBa{sub 2}Cu{sub 3}O{sub 7} were shocked to 7 GPa without macroscopic fracture. Lattice defects are deposited in the crystal, which improve magnetic hysteresis at {approximately}1 kOe. A computer code has been developed to simulate shock compaction of 100 powder particles. Computations will be compared with experiments with 15--20 {mu}m Cu powders. The method is applicable to other powders and dynamic conditions.

Nellis, W.J.

1994-03-01

356

Complementary shapes in columnar liquid crystals: Structural control in homo- and heteronuclear bimetallic assemblies  

SciTech Connect

A comprehensive study of the liquid-crystalline properties of 51 bimetallic compounds based upon 1,3,5-triketonate and 1,3,5,7-tetraketonate ligands is reported. These materials are liquid crystalline when six or more side chains are appended to the mesogenic core, and only columnar phases were observed. Most of the liquid crystals were homonuclear dicopper complexes. Schiff-base derivatives of some of the triketones allowed for the synthesis of heteronuclear bimetallic liquid crystals. The NiCu and NiPd Schiff-base complexes are the first heteronuclear liquid crystals with proximate (strongly interacting) metal centers. Other heteronuclear complexes investigated were not liquid crystalline due to the tendency to retain coordinated solvent or to form strongly associated structures in the absence of axial ligands. The use of complementary shapes was demonstrated as a means to generate average relative organizations (correlations) between the complexes. The presence of these correlated structures was shown through comparisons of the structures, phase behavior, and the immiscibility between materials having the same phase but different shapes. Correlated structures were shown which produce average rotations of 90{degrees} and 180{degrees} between nearest-neighbor molecules. A crystal structure of one compound confirmed that a similar superstructure was exhibited in the solid state. In addition, it was found that the correlated structures exhibit relatively short (3.29 {angstrom}) correlations between the mesogens, thereby allowing for strong intermolecular interactions. The ability to control the orientation and relative position of transition metal centers in liquid crystals has applications in the design of new liquid-crystalline materials with useful magnetic and electronic properties. 32 refs., 8 figs., 8 tabs.

Serrette, A.G.; Lai, C.K.; Swager, T.M. [Univ. of Pennsylvania, Philadelphia, PA (United States)

1994-12-01

357

The crystal structure and superconducting properties of monatomic bromine  

Microsoft Academic Search

The crystal structure and superconducting properties of monatomic bromine under high pressure have been studied by first-principles calculations. We have found the following phase transition sequence with increasing pressure: from body-centered orthorhombic (bco, phase II) to body-centered tetragonal structure (bct, phase III) at 126 GPa, then to face-centered cubic structure (fcc, phase IV) at 157 GPa, which is stable at

Defang Duan; Xing Meng; Fubo Tian; Changbo Chen; Liancheng Wang; Yanming Ma; Tian Cui; Bingbing Liu; Zhi He; Guangtian Zou

2010-01-01

358

Structure of Widmanstatten crystals of ferrite and cementite  

Microsoft Academic Search

Structural analysis of Widmanstatten crystals in ?8, 10, and 5? carbon steel shows that Widmanstatten ferrite is first deposited\\u000a at the austenite grain boundaries in cast 50? steel. The intervals are filled with polyhedral ferrite. The plates of Widmanstatten\\u000a ferrite and cementite are laminar in structure. The layer thickness is ?10 3 nm or less. Analysis of the fine structure

I. A. Bataev; A. A. Bataev; V. G. Burov; Ya. S. Lizunkova; E. E. Zakharevich

2008-01-01

359

Relationship between Crystallization Behavior and Structure in Cocoa Butter  

Microsoft Academic Search

Cocoa butter was crystallized statically from the melt to various temperatures in the range of -20 to 26 C and annealed for up to 45 days. During this period, the polymorphism of the solid state was monitored using differential scanning calorimetry and powder X-ray diffraction. Moreover, the microstructure of the materials was imaged using polarized light microscopy. Below -15 C,

Alejandro G. Marangoni; Sara E. McGauley

2003-01-01

360

Effect of Mg2+ substitution on structural, dielectric, and transport properties of L-tartaric acid-nicotinamide organic crystals  

NASA Astrophysics Data System (ADS)

Single crystals of organic nonlinear optical material of pure and Mg2+ substituted L-tartaric acid-nicotinamide (LTN) were successfully grown by slow evaporation method at room temperature. The grown crystals have been subjected to single crystal X-ray diffraction to determine the unit cell dimensions and morphology. Powder XRD analysis confirms the structure and change in lattice parameter values for the doped crystals. The mode of vibration of different molecular groups present in LTN was identified by FTIR spectral analysis. The presence of magnesium in LTN crystals were confirmed by atomic absorption studies. Non-linear optical studies reveal that the SHG efficiency of the crystals is found to be increased in the presence of magnesium ions. The AC and DC conductivity, and dielectric studies were also carried out and reported for the first time. Dielectric measurements reveal that the dielectric constant of pure and doped crystals decreases with increase of frequency.

Gnanasambandam, C.; Perumal, S.

2010-02-01

361

Defectiveness of the crystal structure of electroerosion powders  

SciTech Connect

The fine structure and defectiveness of metal powder crystal lattices produced by electroerosion dispersion were examined. Dispersion was performed on granulated aluminum, Armco iron, carbon steels, and tungsten. The fine structure was examined by x-ray diffraction. Harmonic analysis was performed using a computer and a program which calculates not only the expansion coefficients of the functions into a Fourier series but also the microdistortions and the dimensions of the mosaic blocks. Electroerosion powders were found to have higher density of crystal lattice defects which can increase their chemical and catalytic activity, improve the metallic electroerosion powder passivation, and increase their corrosion resistance.

Fominskii, L.P.; Myuller, A.S.; Levchuk, M.V.

1988-03-01

362

Crystal structure of copper bis(tenuazonate) monohydrate  

Microsoft Academic Search

The crystal structure of copper bis(tenuazonate) monohydrate has been determined by X-ray diffraction from 968 counter-measured intensities. The thin flat crystals are monoclinic,P21, witha = 13.77(1),b = 15.51(1),c = 11.14(1) , = 109.5(2) , and two formula units, C20H26CuN2O6H2O, per asymmetric unit. The structure was refined by full-matrix least squares toR = 0.056. Because of the dimerization one copper

A. Dippenaar; C. W. Holzapfel; J. C. A. Boeyens

1977-01-01

363

Crystal chemistry and structure refinement of five hydrated calcium borates  

USGS Publications Warehouse

The crystal structures of the five known members of the series Ca2B6O11??xH2O (x = 1, 5, 5, 7, 9, and 13) have been refined by full-matrix least-squares techniques, yielding bond distances and angles with standard errors of less than 0??01 A?? and 0??5??, respectively. The results illustrate the crystal chemical principles that govern the structures of hydrated borate compounds. The importance of hydrogen bonding in the ferroelectric transition of colemanite is confirmed by more accurate proton assignments. ?? 1964.

Clark, J. R.; Appleman, D. E.; Christ, C. L.

1964-01-01

364

Identifying duplicate crystal structures: XTALCOMP, an open-source solution  

NASA Astrophysics Data System (ADS)

We describe the implementation of XTALCOMP, an efficient, reliable, and open-source library that tests if two crystal descriptions describe the same underlying structure. The algorithm has been tested and found to correctly identify duplicate structures in spite of the "real-world" difficulties that arise from working with numeric crystal representations: degenerate unit cell lattices, numerical noise, periodic boundaries, and the lack of a canonical coordinate origin. The library is portable, open, and not dependent on any external packages. A web interface to the algorithm is publicly accessible at http://xtalopt.openmolecules.net/xtalcomp/xtalcomp.html.

Lonie, David C.; Zurek, Eva

2012-03-01

365

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Crystal Structure and High Hardness Mechanism of Orthorhomic Si2N2O  

NASA Astrophysics Data System (ADS)

A quasi-single-phase orthorombic Si2N2O compound is obtained by hot-pressing sintering using homogeneous precursors as raw materials under nitrogen atmosphere. The bulk hardness of orthorombic Si2N2O (o-Si2N2O) is investigated by a nanoindenter experiment; the results show that o-Si2N2O with maximal value about 19GPa has a high hardness covalent crystal besides ?-Si3N4. It is discovered that the high hardness is mainly attributed to the unique crystal structure. The bridging O atoms in the o-Si2N2O are responsible for decreasing hardness. It is found that the Si-O bonds in the open tetrahedral crystal structure are more easily broken and tilted than other bonds.

Xiong, Lan-Tian; Cao, Mao-Sheng; Hou, Zhi-Ling

2009-07-01

366

Thermogravimetric analysis of selected condensed materials on a quartz crystal microbalance  

NASA Astrophysics Data System (ADS)

Employing a quartz crystal microbalance and a quadrupole mass spectrometer in a vacuum chamber, thermogravimetric analyses (TGA) and mass spectrometer analyses have been performed at low temperature on depositions of ammonia, acetone, methanol, toluene, isopropyl alcohol, water, para-xylene, and selected combinations. Deposition of a single species yielded a TGA curve characteristic of a pure substance. Homogeneous binary mixtures, like methanol and water, exhibited a desorption curve which included structure that was intermediate to that observed for pure materials. Sequential layering of one material on top of another also altered the TGA response, and the TGA curve shape was found to be a function of top-layer thickness for the water-on-methanol system. Backfilling the chamber with nitrogen or argon at a pressure of 1 Torr shifted the sublimation temperature of water about 20 K higher.

Bargeron, C. Brent; Phillips, Terry E.; Benson, Richard C.

1994-10-01

367

Crystal and molecular structure of biruthenocene  

Microsoft Academic Search

Crystalline biruthenocene is disordered at room temperature. The apparent symmetry ofP21c applies to an average structure only. Better resolution is achieved by refinement in the space groupP1. The room-temperature X-ray structure, as refined in both space groups, shows that the mutual orientation of cyclopentadienyl rings within a sandwich is not conformationally important and that it depends on intermolecular interactions.

Demetrius C. Levendis; Jan C. A. Boeyens; Eberhard W. Neuse

1982-01-01

368

Crystal structure of a eukaryotic phosphate transporter.  

PubMed

Phosphate is crucial for structural and metabolic needs, including nucleotide and lipid synthesis, signalling and chemical energy storage. Proton-coupled transporters of the major facilitator superfamily (MFS) are essential for phosphate uptake in plants and fungi, and also have a function in sensing external phosphate levels as transceptors. Here we report the 2.9? structure of a fungal (Piriformospora indica) high-affinity phosphate transporter, PiPT, in an inward-facing occluded state, with bound phosphate visible in the membrane-buried binding site. The structure indicates both proton and phosphate exit pathways and suggests a modified asymmetrical 'rocker-switch' mechanism of phosphate transport. PiPT is related to several human transporter families, most notably the organic cation and anion transporters of the solute carrier family (SLC22), which are implicated in cancer-drug resistance. We modelled representative cation and anion SLC22 transporters based on the PiPT structure to surmise the structural basis for substrate binding and charge selectivity in this important family. The PiPT structure demonstrates and expands on principles of substrate transport by the MFS transporters and illuminates principles of phosphate uptake in particular. PMID:23542591

Pedersen, Bjrn P; Kumar, Hemant; Waight, Andrew B; Risenmay, Aaron J; Roe-Zurz, Zygy; Chau, Bryant H; Schlessinger, Avner; Bonomi, Massimiliano; Harries, William; Sali, Andrej; Johri, Atul K; Stroud, Robert M

2013-03-31

369

Crystal structure of phosphorus-rich ellenbergerite  

SciTech Connect

The phosphorus-rich variety of ellenbergerite (Mg{sub 0.61}Ti{sub 0.08}{open_square}{sub 0.31}){sub 2}(Mg{sub 0.52}Al{sub 0.43}{open_square}{sub 0.05})= {sub 12}[SiO{sub 3}(O{sub 0.29}(OH){sub 0.71})]{sub 6} [(P{sub 0.71}Si{sub 0.20}{open_square}{sub 0.09})O{sub 3}OH]{sub 2}(OH){sub 6} was studied by X-ray diffraction and IR spectroscopy. The structure was refined in sp. gr. P6{sub 3}mc to R = 0.0248. The structure of phosphorus-rich ellenbergerite retains the octahedral framework observed in the structures of ellenbergerite, phosphoellenbergerite, ekatite, and a series of structurally related synthetic compounds. The structure of phosphorus-rich ellenbergerite differs from the structure of ellenbergerite primarily in that the Mg and Al cations in the phosphorus-rich variety are disordered in the octahedra of the framework, thereby leading to higher symmetry, and the channels of triangular cross section are occupied predominantly by P tetrahedra.

Zubkova, N. V., E-mail: dmitp@geol.msu.ru; Pushcharovskii, D. Yu. [Moscow State University, Faculty of Geology (Russian Federation); Pasero, M. [University of Pisa, Department of Earth Sciences (Italy); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation); Merlino, S. [University of Pisa, Department of Earth Sciences (Italy)

2007-03-15

370

Superconductivity in layered structure organometallic crystals.  

PubMed

Superconductivity persists in several, layered, transition metal dichalcogenide superconductors when the layers are spread apart to accommodate organic molecules between them. These materials are of interest not only because of their two-dimensional character but also because they may provide a means for examining hypotheses regarding organic molecules and superconductivity. PMID:17806773

Gamble, F R; Disalvo, F J; Klemm, R A; Geballe, T H

1970-05-01

371

Nano and micro-structuring of sensor materialsfrom molecule to cell detection  

Microsoft Academic Search

Self organisation is a key technique for the spontaneous and efficient structuring of materials for chemical sensing. For example, polymer materials are patterned by surface molecular imprinting via stamping techniques. Mass-sensitive measurements with quartz crystal microbalances (QCMs) prove that by this way fingerprints of enzymes, viruses and cells are generated which are capable of reversibly absorbing the imprint species. These

F. L. Dickert; O. Hayden; P. Lieberzeit; C. Haderspoeck; R. Bindeus; C. Palfinger; B. Wirl

2003-01-01

372

A hybrid computational-experimental approach for automated crystal structure solution.  

PubMed

Crystal structure solution from diffraction experiments is one of the most fundamental tasks in materials science, chemistry, physics and geology. Unfortunately, numerous factors render this process labour intensive and error prone. Experimental conditions, such as high pressure or structural metastability, often complicate characterization. Furthermore, many materials of great modern interest, such as batteries and hydrogen storage media, contain light elements such as Li and H that only weakly scatter X-rays. Finally, structural refinements generally require significant human input and intuition, as they rely on good initial guesses for the target structure. To address these many challenges, we demonstrate a new hybrid approach, first-principles-assisted structure solution (FPASS), which combines experimental diffraction data, statistical symmetry information and first-principles-based algorithmic optimization to automatically solve crystal structures. We demonstrate the broad utility of FPASS to clarify four important crystal structure debates: the hydrogen storage candidates MgNH and NH(3)BH(3); Li(2)O(2), relevant to Li-air batteries; and high-pressure silane, SiH(4). PMID:23178265

Meredig, Bryce; Wolverton, C

2012-11-25

373

Kinetics of non-isothermal crystallization process and activation energy for crystal growth in amorphous materials  

Microsoft Academic Search

An equation expressing the volume fraction,x, of crystals precipitating in a glass heated at a constant rate, a, was derived. When crystal particles grow m-dimensionally,x is expressed as In [- ln(1 -x)] = -n (na - 1.052mE\\/RT + Constant whereE is the activation energy for crystal growth andn is a numerical factor depending on the nucleation process. When the nuclei

Kazumasa Matusita; Takayuki Komatsu; Ryosuke Yokota

1984-01-01

374

Interface structure of the rubrene crystal field effect transistor  

NASA Astrophysics Data System (ADS)

The gate voltage effect on the surface structure of a rubrene field effect transistor (FET) is investigated by means of x-ray crystal truncation rod (CTR) scattering. Gate voltage ranging between 0 V and -70 V does not alter the CTR intensity profile of the rubrene FET, which reflects both the rubrene-air interface and the rubrene-substrate interface structures. Two possible structural models that explain the experimental results are proposed: (1) the gate voltage does not affect the structures of the two interfaces, or (2) the gate voltage does not affect the structure of the rubrene-air interface, and the other interface does not contribute to the CTR profile, because of the embossing of the rough substrate surface to the flat rubrene crystal surface.

Wakabayashi, Yusuke; Takeya, Jun; Kimura, Tsuyoshi

2011-11-01

375

Crystal structure study and investigation of solid-state cyclization for AMG 222, a channel hydrate.  

PubMed

In this study, we investigate the solid-state structure and stability of AMG 222 (5-(2-[2-(2-cyano-pyrrolidin-1-yl)-2-oxo-ethylamino]-propyl)-5-(1H-tetrazol-5-yl)-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-2,8 dicarboxylic acid bisdimethylamide), a small molecule DPP-IV inhibitor. Crystal structure of AMG 222 has been solved from single crystal X-ray analysis. Crystallographic data are as follows: monoclinic, P2(1) (no. 4), a=9.0327(5)?, b=18.6177(8)?, c=21.4927(10)?, ?=90.126(3), V=3614.4(3)?(3), Z=4. Based on single crystal structure, AMG 222 is a pentahydrate with the water molecules sitting in channels formed by the drug framework. There are three distinct crystal structures of AMG 222 between 0 and 95% relative humidity (RH), namely the anhydrate, hemihydrate, and pentahydrate forms. Solid-state stability of the GMP batch showed a high level of cyclized degradation product. It was postulated that the degradation was promoted by increased amorphous content generated as a result of excessive drying that was employed to remove residual crystallization solvent. Material produced using a modified procedure using a humidified nitrogen purge had lower amorphous content and lower levels of cyclic degradation when compared to the GMP batch. PMID:23182974

Kiang, Y-H; Nagapudi, Karthik; Liu, Jodi; Staples, Richard J; Jona, Janan

2012-11-23

376

CRYSTAL STRUCTURE ANALYSIS OF A PUTATIVE OXIDOREDUCTASE FROM KLEBSIELLA PNEUMONIAE  

SciTech Connect

Klebsiella pneumoniae, a gram-negative enteric bacterium, is found in nosocomial infections which are acquired during hospital stays for about 10% of hospital patients in the United States. The crystal structure of a putative oxidoreductase from K. pneumoniae has been determined. The structural information of this K. pneumoniae protein was used to understand its function. Crystals of the putative oxidoreductase enzyme were obtained by the sitting drop vapor diffusion method using Polyethylene glycol (PEG) 3350, Bis-Tris buffer, pH 5.5 as precipitant. These crystals were used to collect X-ray data at beam line X12C of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL). The crystal structure was determined using the SHELX program and refi ned with CNS 1.1. This protein, which is involved in the catalysis of an oxidation-reduction (redox) reaction, has an alpha/beta structure. It utilizes nicotinamide adenine dinucleotide phosphate (NADP) or nicotine adenine dinucleotide (NAD) to perform its function. This structure could be used to determine the active and co-factor binding sites of the protein, information that could help pharmaceutical companies in drug design and in determining the proteins relationship to disease treatment such as that for pneumonia and other related pathologies.

Baig, M.; Brown, A.; Eswaramoorthy, S.; Swaminathan, S.

2009-01-01

377

Crystal structures of Ti, Zr, and Hf under compression: Theory  

SciTech Connect

We have studied the crystal structures of Ti, Zr, and Hf under pressure by means of first-principles, total-energy calculations. The three metals are shown to exhibit a crystal structure sequence hcp[r arrow][omega][r arrow]bcc, with increasing pressure. This is in good agreement with experiment for Zr and Hf, whereas the bcc structure for Ti is a prediction. The calculated transition volumes as well as transition pressures compare fairly well with experiment. Also, the computed [ital c]/[ital a] ratio for hcp Ti, Zr, and Hf is found to be in good agreement with experiment. Similarly the calculated [ital c]/[ital a] ratio for Zr in the [omega] structure agrees well with measurement. The chemical bonding of the [omega] structure is shown to be quite different from what is normally the case in the transition metals, with a large degree of covalency. A search for the [omega] structure in Tc and Ru was fruitless yielding a stable hcp structure. At zero temperature and zero pressure the bcc crystal structure is found to be mechanically unstable for Ti, Zr, and Hf.

Ahuja, R. (Department of Physics, Uppsala University, Box 530, Uppsala (Sweden)); Wills, J.M. (Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Johansson, B.; Eriksson, O. (Department of Physics, Uppsala University, Box 530, Uppsala (Sweden))

1993-12-01

378

Photonic guiding structures in lithium niobate crystals produced by energetic ion beams  

NASA Astrophysics Data System (ADS)

A range of ion beam techniques have been used to fabricate a variety of photonic guiding structures in the well-known lithium niobate (LiNbO3 or LN) crystals that are of great importance in integrated photonics/optics. This paper reviews the up-to-date research progress of ion-beam-processed LiNbO3 photonic structures and reports on their fabrication, characterization, and applications. Ion beams are being used with this material in a wide range of techniques, as exemplified by the following examples. Ion beam milling/etching can remove the selected surface regions of LiNbO3 crystals via the sputtering effects. Ion implantation and swift ion irradiation can form optical waveguide structures by modifying the surface refractive indices of the LiNbO3 wafers. Crystal ion slicing has been used to obtain bulk-quality LiNbO3 single-crystalline thin films or membranes by exfoliating the implanted layer from the original substrate. Focused ion beams can either generate small structures of micron or submicron dimensions, to realize photonic bandgap crystals in LiNbO3, or directly write surface waveguides or other guiding devices in the crystal. Ion beam-enhanced etching has been extensively applied for micro- or nanostructuring of LiNbO3 surfaces. Methods developed to fabricate a range of photonic guiding structures in LiNbO3 are introduced. Modifications of LiNbO3 through the use of various energetic ion beams, including changes in refractive index and properties related to the photonic guiding structures as well as to the materials (i.e., electro-optic, nonlinear optic, luminescent, and photorefractive features), are overviewed in detail. The application of these LiNbO3 photonic guiding structures in both micro- and nanophotonics are briefly summarized.

Chen, Feng

2009-10-01

379

Constrained evolutionary algorithm for structure prediction of molecular crystals: methodology and applications.  

PubMed

Evolutionary crystal structure prediction proved to be a powerful approach for studying a wide range of materials. Here we present a specifically designed algorithm for the prediction of the structure of complex crystals consisting of well defined molecular units. The main feature of this new approach is that each unit is treated as a whole body, which drastically reduces the search space and improves the efficiency, but necessitates the introduction of new variation operators described here. To increase the diversity of the population of structures, the initial population and part (~20%) of the new generations are produced using space-group symmetry combined with random cell parameters, and random positions and orientations of molecular units. We illustrate the efficiency and reliability of this approach by a number of tests (ice, ammonia, carbon dioxide, methane, benzene, glycine and butane-1,4-diammonium dibromide). This approach easily predicts the crystal structure of methane A containing 21 methane molecules (105 atoms) per unit cell. We demonstrate that this new approach also has a high potential for the study of complex inorganic crystals as shown on examples of a complex hydrogen storage material Mg(BH(4))(2) and elemental boron. PMID:22610672

Zhu, Qiang; Oganov, Artem R; Glass, Colin W; Stokes, Harold T

2012-05-17

380

Estimation of diffusion anisotropy in microporous crystalline materials and optimization of crystal orientation in membranes  

NASA Astrophysics Data System (ADS)

The complex nature of the porous networks in microporous materials is primarily responsible for a high degree of intracrystalline diffusion anisotropy. Although this is a well-understood phenomenon, little attention has been paid in the literature with regards to classifying such anisotropy and elucidating its effect on the performance of membrane-based separation systems. In this paper, we develop a novel methodology to estimate full diffusion tensors based on the detailed description of the porous network geometry through our recent advances for the characterization of such networks. The proposed approach explicitly accounts for the tortuosity and complex connectivity of the porous framework, as well as for the variety of diffusion regimes that may be experienced by a guest molecule while it travels through the different localities of the crystal. Results on the diffusion of light gases in silicalite demonstrate good agreement with results from experiments and other computational techniques that have been reported in the literature. A comprehensive computational study involving 183 zeolite frameworks classifies these structures in terms of a number of anisotropy metrics. Finally, we utilize the computed diffusion tensors in a membrane optimization model that determines optimal crystal orientations. Application of the model in the context of separating carbon dioxide from nitrogen demonstrates that optimizing crystal orientation can offer significant benefit to membrane-based separation processes.

Gounaris, Chrysanthos E.; First, Eric L.; Floudas, Christodoulos A.

2013-09-01

381

CdTe:Ti crystals: materials for optical sensors in the near IR-region  

NASA Astrophysics Data System (ADS)

The Ti-doped CdTe semiinsulating crystals of high optical quality were grown by the vertical Bridgman technique. The complex optical, photoelectric and photorefractive measurements of CdTe doped with Ti atoms were carried out. It allowed to our knowledge for the first time to determine the photorefractive characteristics of these crystals. Studies of the optical absorption and photodiffusion current made it possible to determine the nature and energy structure of impurity and intrinsic defects as well as to establish their role in the photorefractive effect. It was shown that the excited 3T1(P) state is in resonance with the conduction band. As a result of it the auto-ionization of electrons to the conduction band under the laser excitation take place. The energy-level diagram both of impurity and intrinsic defects in the CdTe:Ti crystals was constructed. It was shown that titanium dopant have advantage over other dopants and that CdTe:Ti has better characteristics for a potential applications. Obtained parameters: high optical holographic gain coefficient (up to 0.60 cm-1), low background absorption (about 0.1 0.2 cm-1), high optical quality and homogeneity, almost electronic type photoconductivity (electron-hole competition factor equals 0.94) show that this material can be effectively used as sensor components for both optical and photoelectric applications in the near infrared region.

Gnatenko, Yuriy P.; Gamernyk, Roman V.; Borshch, Anatoly O.; Kukhtarev, Nickolai; Kukhtareva, Tatiana; Bukivskij, Petro M.; Faryna, Ivan O.; Volkov, Vladyslav I.; Paranchych, Stepan Y.; Paranchych, Lidia D.

382

Impact of polymers on crystal growth rate of structurally diverse compounds from aqueous solution.  

PubMed

The presence of an effective crystal growth inhibitor in solution is desirable to prolong supersaturation since residual crystalline material in an amorphous formulation resulting from the manufacturing process or formed during storage or dissolution can potentially have a significant impact on the extent and duration of supersaturation. In this study, the effectiveness of a group of chemically diverse polymers, including several recently synthesized cellulose derivatives, on solution crystal growth of three structurally diverse compounds (celecoxib, efavirenz, and ritonavir) was quantified at different extents of supersaturation and compared. Despite the different chemical properties and structures of the model compounds, nonspecific hydrophobic drug-polymer interactions appeared to be important in determining the impact of a given polymer on crystal growth for of all these drug compounds. Specific intermolecular interactions were also found to be important for crystal growth inhibition of celecoxib and efavirenz by the hydrophilic polymer, PVPVA. These interactive forces-hydrophobicity and specific intermolecular interactions-are likely to promote adsorption of the polymer onto the surface of the crystalline drugs, thus influencing crystal growth. The effectiveness of the polymers also depended on the rate of crystallization of the drug molecules. At a similar supersaturation ratio of ?1.2, ritonavir and celecoxib had slower normalized crystal growth rates (0.20 and 0.91 mg min(-1) m(-2), respectively), while the normalized crystal growth rate of efavirenz was significantly higher (2.97 mg min(-1) m(-2)), resulting in lower levels of crystal growth inhibition by the polymers for efavirenz. PMID:23597294

Ilevbare, Grace A; Liu, Haoyu; Edgar, Kevin J; Taylor, Lynne S

2013-05-02

383

Crystal structures of two engineered thiol trypsins.  

PubMed

We have determined the three-dimensional structures of engineered rat trypsins which mimic the active sites of two classes of cysteine proteases. The catalytic serine was replaced with cysteine (S195C) to test the ability of sulfur to function as a nucleophile in a serine protease environment. This variant mimics the cysteine trypsin class of thiol proteases. An additional mutation of the active site aspartate to an asparagine (D102N) created the catalytic triad of the papain-type cysteine proteases. Rat trypsins S195C and D102N,S195C were solved to 2.5 and 2.0 A, respectively. The refined structures were analyzed to determine the structural basis for the 10(6)-fold loss of activity of trypsin S195C and the 10(8)-fold loss of activity of trypsin D102N,S195C, relative to rat trypsin. The active site thiols were found in a reduced state in contrast to the oxidized thiols found in previous thiol protease structures. These are the first reported structures of serine proteases with the catalytic centers of sulfhydryl proteases. Structure analysis revealed only subtle global changes in enzyme conformation. The substrate binding pocket is unaltered, and active site amino acid 102 forms hydrogen bonds to H57 and S214 as well as to the backbone amides of A56 and H57. In trypsin S195C, D102 is a hydrogen-bond acceptor for H57 which allows the other imidazole nitrogen to function as a base during catalysis. In trypsin D102N,S195C, the asparagine at position 102 is a hydrogen-bond donor to H57 which places a proton on the imidazole nitrogen proximal to the nucleophile. This tautomer of H57 is unable to act as a base in catalysis.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2611228

McGrath, M E; Wilke, M E; Higaki, J N; Craik, C S; Fletterick, R J

1989-11-28

384

National Launch System: Structures and materials  

NASA Astrophysics Data System (ADS)

The National Launch System provides an opportunity to realize the potential of Al-Li. Advanced structures can reduce weights by 5-40 percent as well as relax propulsion system performance specifications and reduce requirements for labor and materials. The effect on costs will be substantial. Advanced assembly and process control technologies also offer the potential for greatly reduced labor during the manufacturing and inspection processes. Current practices are very labor-intensive and, as a result, labor costs far outweigh material costs for operational space transportation systems. The technological readiness of new structural materials depends on their commercial availability, producibility and materials properties. Martin Marietta is vigorously pursuing the development of its Weldalite 049 Al-Li alloys in each of these areas. Martin Marietta is also preparing to test an automated work cell concept that it has developed using discrete event simulation.

Bunting, Jack O.

1993-02-01

385

Structure and properties of hybrid composite materials  

NASA Astrophysics Data System (ADS)

The structure and interfacial interaction are studied in the hybrid aluminum-matrix composite materials fabricated by reactive casting combined with mechanical mixing of fillers with a metallic melt. The following types of hardening are considered: hardening by ceramic particles and by the phases formed as isolated inclusions or coatings on ceramic particles during in situ reactions. The hardness and tribological properties of the composite materials as functions of their compositions are discussed.

Chernyshova, T. A.; Kobeleva, L. I.; Bolotova, L. K.; Katin, I. V.

2013-03-01

386

SAW parameters on Y-cut langasite structured materials.  

PubMed

This paper presents results and investigations of several new, man-made piezoelectric single crystal, Czochralski-grown substrate materials for surface acoustic waves (SAW) applications. These materials, langanite (LGN), langatate (LGT), Sr3TaGa3Si2O14 (STGS), Sr3NbGa3Si2O14 (SNGS), Ca3TaGa3Si2O14 (CTGS), and Ca3NbGa3Si2O14 (CNGS), have the same structure as langasite (LGS) and are of the same crystal class as quartz. These compounds are denser than quartz, resulting in lower phase velocities. They also have higher coupling. Unlike quartz and lithium niobate, there is no degradation of material properties below the material melting points resulting in the possibility of extreme high-temperature operation (> 1000 degrees C). This paper gives a summary of extracted SAW material parameters for various propagation angles on Y-cut substrates of the six materials. Parameters included are electromechanical coupling, phase velocity, transducer capacitance, metal strip reflectivity, and temperature coefficient of frequency. Using previously published fundamental material constants, extracted parameters are compared with predictions for LGT and LGN. In addition, power flow angle and fractional frequency curvature data are reported for propagation angles on CTGS and CNGS Y-cut substrates that exhibit temperature compensation near room temperature. Detailed descriptions of the SAW parameter extraction techniques are given. A discussion of the results is provided, including a comparison of extracted parameters and an overview of possible SAW applications. PMID:17941393

Puccio, Derek; Malocha, Donald C; Saldanha, Nancy; da Cunha, Mauricio Pereira

2007-09-01

387

Band structures of phononic-crystal plates in the form of a sandwich-layered structure.  

PubMed

This study investigates the propagation of Lamb waves in phononic-crystal plates in the form of a sandwich-layered structure. The composite plates are composed of periodic layers bilaterally deposited on both sides of the homogeneous core layer. Using the analyses of the band structures and the transmission spectra, it is revealed that the core layer may induce significant modulations to the lower-order Lamb modes. The modulations are ascribed to the reshaped particle displacement fields of the eigenmodes. Prominently, the core layer made of soft material (rubber) combines the identical eigenmodes of the periodic layers into a pair of asymmetric and symmetric modes in which case the periodic layers vibrate independently. However, the core layer made of hard material (tungsten) or medium hardness material (silicon) couples the periodic layers tightly, in which case the composites vibrate as a whole. In addition, it is found that the phononic band gaps are very sensitive to the thickness of the core layer; this could be indispensable to practical applications such as bandgap tuning. PMID:22087902

Cheng, Y; Liu, X J; Wu, D J

2011-11-01

388

Evolution of aircraft/aerospace structures and materials symposium, Dayton, OH, April 24, 25, 1985, Proceedings  

SciTech Connect

Various papers on the evolution of aircraft and aerospace structures and materials are presented. The topics addressed include: XB-70 structures and materials advances, structural evolution from B-58 to F-16, advanced composites in construction of the Beech Starship, structural and material considerations for advanced fighters, the evolution of reciprocating engines at Lycoming, aircraft design from the myth of make-do to Mach 3, and the Wright Brothers' experience in the evolution of aircraft design, structures and materials. Also considered are: evolution of the turbofan aircraft engine, X-15 high-temperature advanced structure, X-20 structures overview, ASSET program for technology development, Shuttle Orbiter airframe, airframe design to achieve minimum cost, superplastically formed-diffusion bonded titanium technology transition case study, transition of advanced materials and structures in single crystal blades, and composites technology transfer and transition.

Not Available

1985-01-01

389

The diammoniate of diborane: Crystal structure and hydrogen release  

SciTech Connect

[(NH3)2BH2]+[BH4]- is formed from the room temperature decomposition of NH4+BH4-, via a NH3BH3 intermediate. Its crystal structure has been determined and contains disordered BH4- ions in 2 distinct sites. Hydrogen release is similar to that from NH3BH3 but with faster kinetics.

Bowden, Mark E.; Heldebrant, David J.; Karkamkar, Abhijeet J.; Proffen, Thomas E.; Schenter, Gregory K.; Autrey, Thomas

2010-10-12

390

The structure and vibrational frequencies of nitric acid hydrates crystals  

Microsoft Academic Search

The relevance of nitric acid hydrates in stratospheric processes has prompted a large number of investigations on the structure and physicochemical properties of these species. We are carrying out in our lab a study on the spectroscopy of crystals of nitric acid and the mono-, di- and trihydrates, NAM, NAD and NAT, respectively, as a first step to addressing more

R. Escribano; D. Fernndez; V. J. Herrero; B. Mat; A. Medialdea; M. A. Moreno; I. K. Ortega

2003-01-01

391

Yolk spherocrystal: The structure, composition and liquid crystal template  

Microsoft Academic Search

The structure and composition of the yolk spherocrystal, a biomineral developed in the egg yolk sac during the incubation of a chicken embryo, were investigated through various modern analytical methods. Additionally, inside the yolk sac, yolk liquid crystal, a liquid crystalline phase of lipid developed during the incubation of the embryo, was found and investigated. The spherocrystal was found to

Hua Tong; Peng Wan; Wentao Ma; Guirong Zhong; Lianxin Cao; Jiming Hu

2008-01-01

392

Electronic structure of molecular crystals containing edge dislocations  

Microsoft Academic Search

An attempt to model the electronic structure of molecular crystals containing an edge dislocation at the ab initio Hartree-Fock level is performed. The experimentally determined configurations for edge-type dislocations with the Burgers vector [001] in crystalline cyclotrimethylene trinitramine (RDX) and pentaetythritol tetranitrate (PETN) are theoretically simulated. It is shown that a shear stress, induced by the dislocations, produces local electronic

Maija M. Kuklja; A. Barry Kunz

2001-01-01

393

Unusual Features of Crystal Structures of Some Simple Copper Compounds  

ERIC Educational Resources Information Center

|Some simple copper compounds have unusual crystal structures. Cu[subscript 3]N is cubic with N atoms at centers of octahedra formed by 6 Cu atoms. Cu[subscript 2]O (cuprite) is also cubic; O atoms are in tetrahedra formed by 4 Cu atoms. These tetrahedra are linked by sharing vertices forming two independent networks without linkages between them.

Douglas, Bodie

2009-01-01

394

Crystal Structure of the 30s RIBOSOM and Its Use.  

National Technical Information Service (NTIS)

The invention provides an X-ray crystal structure of the 30S ribosome, obtained from Thermus thermophilus 30S subunit, having a tetragonal space group P4(sub 12)(sub 12) with unit cell dimensions of a=401.4.+-.4.0 (ANG), b=401.4.+-.4.0 (ANG), c=175.9.+-.5...

A. P. Carter B. T. Wimberly D. E. Brodersen V. Ramakrishnan

2001-01-01

395

Electronic Structure of Zinc Oxide and Related Crystals.  

National Technical Information Service (NTIS)

The aim of this investigati on is the elucidation of the electronic energy band structure of zinc oxide and related wurtzite-type crystals, including alloys of zinc oxide and zinc sulfide; zinc sulfide; zinc selenide; and zinc telluride. The principal fea...

F. Herman

1966-01-01

396

Crystal structure of tannase from Lactobacillus plantarum.  

PubMed

Tannins are water-soluble polyphenolic compounds in plants. Hydrolyzable tannins are derivatives of gallic acid (3,4,5-trihydroxybenzoic acid) or its meta-depsidic forms that are esterified to polyol, catechin, or triterpenoid units. Tannases are a family of esterases that catalyze the hydrolysis of the galloyl ester bond in hydrolyzable tannins to release gallic acid. The enzymes have found wide applications in food, feed, beverage, pharmaceutical, and chemical industries since their discovery more than a century ago, although little is known about them at the molecular level, including the details of the catalytic and substrate binding sites. Here, we report the first three-dimensional structure of a tannase from Lactobacillus plantarum. The enzyme displays an ?/? structure, featured by a large cap domain inserted into the classical serine hydrolase fold. A catalytic triad was identified in the structure, which is composed of Ser163, His451, and Asp419. During the binding of gallic acid, the carboxyl group of the molecule forges hydrogen-bonding interactions with the catalytic triad of the enzyme while the three hydroxyl groups make contacts with Asp421, Lys343, and Glu357 to form another hydrogen-bonding network. Mutagenesis studies demonstrated that these residues are indispensable for the activity of the enzyme. Structural studies of the enzyme in complex with a number of substrates indicated that the interactions at the galloyl binding site are the determinant force for the binding of substrates. The single galloyl binding site is responsible for the esterase and depsidase activities of the enzyme. PMID:23648840

Ren, Bin; Wu, Mingbo; Wang, Qin; Peng, Xiaohong; Wen, Hua; McKinstry, William J; Chen, Qianming

2013-05-03

397

Crystal structures of the ??-cerium phases  

PubMed Central

Endo et al. [Endo, S., Sasaki, H. & Mitsui, T. (1972) J. Phys. Soc. Jpn. 42, 882-885] have reported x-ray diffraction data for an unidentified phase of cerium metal observed in the 50- to 100-kbar range. It is shown that the unknown phase is a variant of the metastable monoclinic phase, ??-Ce, previously observed. The complete structure of the new form of ??-Ce is deduced.

Zachariasen, W. H.

1978-01-01

398

Spontaneous chiral crystallization of achiral materials and absolute asymmetric transformation in the chiral crystalline environment  

Microsoft Academic Search

Recently, the combination of chiral crystallization and the solid-state photoreaction has provided many successful examples\\u000a of absolute asymmetric synthesis.[1] In these reactions achiral materials adopted chiral arrangement only by spontaneous crystallization,\\u000a and optically active products are obtained from the topochemically controlled reaction with high ees (Figure 1).[2,3] This\\u000a method incurs a problem in crystallization of achiral molecules in chiral space

Masami Sakamoto

399

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface  

PubMed Central

Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

Parshin, Alexander M.; Gunyakov, Vladimir A.; Zyryanov, Victor Y.; Shabanov, Vasily F.

2013-01-01

400

Crystal Structure of the Bacillus subtilis Superoxide Dismutase  

SciTech Connect

The sodA gene of Bacillus subtilis was expressed in Escherichia coli, purified and crystallized. The crystal structure of MnSOD was solved by molecular replacement with four dimers per asymmetric unit and refined to an R factor of 21.1% at 1.8 {angstrom} resolution. The dimer structure is very similar to that of the related enzyme from B. anthracis. Larger structural differences were observed with the human MnSOD, which has one less helix in the helical domain and a longer loop between two -strands and also showed differences in three amino acids at the intersubunit interface in the dimer compared with the two bacterial MnSODs. These structural differences can be exploited in the design of drugs that selectively target the Bacillus enzymes.

Liu, Ping; Ewis, H.E.; Huang, Y.-J; Lu, C.-D.; Tai, P.C.; Weber, Irene T. (GSU)

2008-06-01

401

Effect of local structures on structural evolution during crystallization in undercooled metallic glass-forming liquids  

NASA Astrophysics Data System (ADS)

The effect of local structures on structural evolution during the crystallization of undercooled ZrCu metallic glass-forming liquid was studied via molecular dynamics simulations. It is found that body-centered-cubic (bcc)-like clusters play a key role in structural evolution during crystallization. In contrast to previous speculations, the number of bcc-like crystal nuclei does not change much before the onset of crystallization. Instead, the development of a bcc-like critical nucleus during annealing leads to a strong spatial correlation with other nuclei in its surroundings, forming a crystalline structure template. It is also found that the size distribution of bcc-like nuclei follows a power-law form with an exponential cutoff in the early stage of annealing, but changes to a pure power-law behavior just before the onset of crystallization. This implies that the crystalline structure template has fractal feature and the undercooled liquids evolve to a self-organized critical state before the onset of crystallization, which might trigger the subsequent rapid crystallization. According to the graph theory analysis, it is also found that the observed large scatter of the onset time of crystallization in different liquid samples results from the connectivity of the bcc-like clusters.

Wu, Z. W.; Li, M. Z.; Wang, W. H.; Song, W. J.; Liu, K. X.

2013-02-01

402

Analysis of voids in crystal structures: the methods of 'dual' crystal chemistry.  

PubMed

The theoretical basics of the analysis of voids in crystal structures by means of Voronoi-Dirichlet polyhedra (VDP) and of the graph theory are stated. Topological relations are considered between VDPs and atomic domains in a crystal field. These relations allow the separation of two non-intersecting topological subspaces in a crystal structure, whose connectednesses are defined by two finite 'reduced' graphs. The first, 'direct', subspace includes the atoms (VDP centres) and the network of interatomic bonds (VDP faces), the second, 'dual', one comprises the void centres (VDP vertices) and the system of channels (VDP edges) between them. Computer methods of geometrical-topological analysis of the 'dual' subspace are developed and implemented within the program package TOPOS. They are designed for automatically restoring the system of channels, visualizing and sizing voids and void conglomerates, dimensional analysis of continuous void systems, and comparative topological analysis of 'dual' subspaces for various substances. The methods of analysis of 'dual' and 'direct' subspaces are noted to differ from each other only in some details that allows the term 'dual' crystal chemistry to be introduced. The efficiency of the methods is shown with the analysis of compounds of different chemical nature: simple substances, ionic structures, superionic conductors, zeolites, clathrates, organic supramolecular complexes. PMID:12496460

Blatov, V A; Shevchenko, A P

2002-12-21

403

Crystal Structure of a ?-Catenin\\/Tcf Complex  

Microsoft Academic Search

The Wnt signaling pathway plays critical roles in embryonic development and tumorigenesis. Stimulation of the Wnt pathway results in the accumulation of a nuclear ?-catenin\\/Tcf complex, activating Wnt target genes. A crystal structure of ?-catenin bound to the ?-catenin binding domain of Tcf3 (Tcf3-CBD) has been determined. The Tcf3-CBD forms an elongated structure with three binding modules that runs antiparallel

Thomas A. Graham; Carole Weaver; Feng Mao; David Kimelman; Wenqing Xu

2000-01-01

404

Crystal structure of nitrile hydratase from a thermophilic Bacillus smithii  

Microsoft Academic Search

The crystal structure of the nitrile hydratase (NHase) from Bacillus smithii SC-J05-1 was determined. Our analysis of the structure shows that some residues that seem to be responsible for substrate recognition are different from those of other NHases. In particular, the Phe52 in the ? subunit of NHase from B. smithii covers the metal center partially like a small lid

Shinji Hourai; Misao Miki; Yoshiki Takashima; Satoshi Mitsuda; Kazunori Yanagi

2003-01-01

405

Crystal structure of a soluble CD28Fab complex  

Microsoft Academic Search

Naive T cell activation requires signaling by the T cell receptor and by nonclonotypic cell surface receptors. The most important costimulatory protein is the monovalent homodimer CD28, which interacts with CD80 and CD86 expressed on antigen-presenting cells. Here we present the crystal structure of a soluble form of CD28 in complex with the Fab fragment of a mitogenic antibody. Structural

Edward J Evans; Robert M Esnouf; Raquel Manso-Sancho; Robert J C Gilbert; John R James; Chao Yu; Janet A Fennelly; Cheryl Vowles; Thomas Hanke; Bjrn Walse; Thomas Hnig; Poul Srensen; David I Stuart; Simon J Davis

2005-01-01

406

The crystal structure of flap endonuclease-1 from Methanococcus jannaschii  

Microsoft Academic Search

Flap endonuclease-1 (FEN-1), a structure specific nuclease, is an essential enzyme for eukaryotic DNA replication and repair. The crystal structure of FEN-1 from Methanococcus jannaschii, determined at 2.0 resolution, reveals an active site with two metal ions residing on top of a deep cleft where several conserved acidic residues are clustered. Near the active site, a long flexible loop

Kwang Yeon Hwang; Kyuwon Baek; Hye-Yeon Kim; Yunje Cho

1998-01-01

407

The Gramicidin Pore: Crystal Structure of a Cesium Complex  

Microsoft Academic Search

Gramicidin, a linear polypeptide composed of hydrophobic amino acids with alternating L- and D- configurations, forms transmembrane ion channels. The crystal structure of a gramicidin-cesium complex has been determined at 2.0 angstrom resolution. In this structure, gramicidin forms a 26 angstrom long tube comprised of two polypeptide chains arranged as antiparallel beta strands that are wrapped into a left-handed helical

B. A. Wallace; K. Ravikumar

1988-01-01

408

Vaporization property and crystal structure of lithium metatitanate with excess Li  

NASA Astrophysics Data System (ADS)

The vaporization property and the crystal structure of lithium metatitanate with excess Li, which has been developed as an advanced tritium breeder, were studied. After synthesizing the lithium metatitanate specimens with Li/Ti = 2.0-2.3 (at mixing of the starting materials), the vaporization properties were investigated by measuring the mass losses during heating at 1173 K. The Li excessive specimens indicated higher rates of mass loss than the stoichiometric one during heating as long as excessive lithium atom exists. The crystal structures of stoichiometric and nonstoichiometric lithium metatitanates were discussed with the result of neutron diffraction and the refined structural parameters by Rietveld analysis. The refinement (Rwp = 7.98, Rp = 5.96 and Re = 2.58) suggested that lithium metatitanate with excess Li has ?-Li2TiO3 structure and excess Li atoms exist at unstable sites with the formation of reduced titanium or site vacancies.

Mukai, Keisuke; Sasaki, Kazuya; Terai, Takayuki; Suzuki, Akihiro; Hoshino, Tsuyoshi

2013-11-01

409

Crystal structure of interleukin 8: Symbiosis of NMR and crystallography  

SciTech Connect

The crystal structure of a host defense system chemotactic factor, interleukin 8, has been solved by molecular replacement using as a model the solution structure derived from nuclear magnetic resonance experiments. The structure was refined with 2 {angstrom} x-ray data to an R factor of 0.817. A comparison indicates some potential differences between the structure in solution and in the crystalline state. The analysis also predicts that residues 4 through 9 on the amino terminus and the {beta}-bend, which includes His-33, may be important for receptor binding.

Baldwin, E.T.; Weber, I.T.; St. Charles, R.; Xuan, Jiancheng; Matsushima, Kouji; Wlodawer, A. (National Cancer Inst., Frederick, MD (United States)); Appella, E.; Clore, G.M.; Gronenborn, A.M. (National Inst. of Health, Bethesda, MD (United States)); Yamada, Masaki (Dainippon Pharmaceutical Co., Ltd., Osaka (Japan)); Edwards, B.F.P. (Wayne State Univ. School of Medicine, Detroit, MI (United States))

1991-01-15

410

Modeling for ultrasonic nondestructive evaluation or columnar structures in anisotropic materials. Progress report  

SciTech Connect

The levitation zone refiner facility has been upgraded with a new crystal pulley. This produces larger crystals with better control of the crystallographic orientation. Progress also has been made toward controlled bicrystal production. Ultrasonic measurements and calculations have been performed to determine elastic constants and study velocity and alternation along principal directions in single crystal Ni; study velocity, attenuation and mode conversion along nonprincipal directions in single crystal Ni; and measure attenuation through two crystals coupled together with different orientations. Finite element development of ultrasonic wave propagation has been extended into material having cubic symmetry. Mode conversion for waves along nonprincipal directions has been demonstrated and preliminary work has been done on the two-crystal problem. Progress has advanced our understanding on techniques for ultrasonic inspection of oriented structures such as weldments and castings.

Dewey, B.R.; Oliver, B.F.; Adler, L.

1981-12-15

411

Crystal structure of triosephosphate isomerase from Trypanosoma cruzi in hexane  

PubMed Central

To gain insight into the mechanisms of enzyme catalysis in organic solvents, the x-ray structure of some monomeric enzymes in organic solvents was determined. However, it remained to be explored whether the structure of oligomeric proteins is also amenable to such analysis. The field acquired new perspectives when it was proposed that the x-ray structure of enzymes in nonaqueous media could reveal binding sites for organic solvents that in principle could represent the starting point for drug design. Here, a crystal of the dimeric enzyme triosephosphate isomerase from the pathogenic parasite Trypanosoma cruzi was soaked and diffracted in hexane and its structure solved at 2-? resolution. Its overall structure and the dimer interface were not altered by hexane. However, there were differences in the orientation of the side chains of several amino acids, including that of the catalytic Glu-168 in one of the monomers. No hexane molecules were detected in the active site or in the dimer interface. However, three hexane molecules were identified on the surface of the protein at sites, which in the native crystal did not have water molecules. The number of water molecules in the hexane structure was higher than in the native crystal. Two hexanes localized at <4 ? from residues that form the dimer interface; they were in close proximity to a site that has been considered a potential target for drug design.

Gao, Xiu-Gong; Maldonado, Ernesto; Perez-Montfort, Ruy; Garza-Ramos, Georgina; de Gomez-Puyou, Marietta Tuena; Gomez-Puyou, Armando; Rodriguez-Romero, Adela

1999-01-01

412

Artificial versus natural crystals: effective wave impedance of printed photonic bandgap materials  

Microsoft Academic Search

Printed metallo-dielectric photonic bandgap (PBG) materials are analyzed using an analytical approach based on multipole expansions for the scattered fields of individual scatterers and a transfer-matrix method for reconstructing the total scattered fields created by successive lattice planes of the artificial crystal. An effective description of the PBG medium is derived and its correspondence with natural crystals is further advanced

Chryssoula A. Kyriazidou; Harry F. Contopanagos; William M. Merrill; N. G. Alexpoulos

2000-01-01

413

Anisotropic material model and wave propagation simulations for shocked pentaerythritol tetranitrate single crystals  

Microsoft Academic Search

An anisotropic continuum material model was developed to describe the thermomechanical response of unreacted pentaerythritol tetranitrate (PETN) single crystals to shock wave loading. Using this model, which incorporates nonlinear elasticity and crystal plasticity in a thermodynamically consistent tensor formulation, wave propagation simulations were performed to compare to experimental wave profiles [J. J. Dick and J. P. Ritchie, J. Appl. Phys.

J. M. Winey; Y. M. Gupta

2010-01-01

414

Self-sensing structural composite materials  

Microsoft Academic Search

Self-sensing was attained in lightweight structural composite materials, including those with polymer (epoxy), carbon and ceramic (Si3N 4) matrices. Either a volume of the composite or the interlaminar interface in the composite was used as the sensor. The use of the interlaminar interface as a sensor is a new approach, which was found to be effective in continuous carbon fiber

Shoukai Wang

2002-01-01

415

Self-healing structural composite materials  

Microsoft Academic Search

A self-healing fiber-reinforced structural polymer matrix composite material is demonstrated. In the composite, a microencapsulated healing agent and a solid chemical catalyst are dispersed within the polymer matrix phase. Healing is triggered by crack propagation through the microcapsules, which then release the healing agent into the crack plane. Subsequent exposure of the healing agent to the chemical catalyst initiates polymerization

M. R. Kessler; N. R. Sottos; S. R. White

2003-01-01

416

Dynamic smart material and structural systems  

Microsoft Academic Search

Basic research in smart materials and structural systems and their development have demonstrated great potential for enhancing the functionality, serviceability and durability of civil and mechanical infrastructure systems and, as a result, offer the potential for significant contributions to the improvement of every nation's productivity, efficiency and quality of life. The intelligent renewal of aging and deteriorating civil and mechanical

A. B Flatau; K. P Chong

2002-01-01

417

Hierarchically structured materials for lithium batteries.  

PubMed

The lithium-ion battery (LIB) is one of the most promising power sources to be deployed in electric vehicles, including solely battery powered vehicles, plug-in hybrid electric vehicles, and hybrid electric vehicles. With the increasing demand for devices of high-energy densities (>500Whkg(-1)), new energy storage systems, such as lithium-oxygen (Li-O2) batteries and other emerging systems beyond the conventional LIB, have attracted worldwide interest for both transportation and grid energy storage applications in recent years. It is well known that the electrochemical performance of these energy storage systems depends not only on the composition of the materials, but also on the structure of the electrode materials used in the batteries. Although the desired performance characteristics of batteries often have conflicting requirements with the micro/nano-structure of electrodes, hierarchically designed electrodes can be tailored to satisfy these conflicting requirements. This work will review hierarchically structured materials that have been successfully used in LIB and Li-O2 batteries. Our goal is to elucidate (1) how to realize the full potential of energy materials through the manipulation of morphologies, and (2) how the hierarchical structure benefits the charge transport, promotes the interfacial properties and prolongs the electrode stability and battery lifetime. PMID:24067410

Xiao, Jie; Zheng, Jianming; Li, Xiaolin; Shao, Yuyan; Zhang, Ji-Guang

2013-09-25

418

Hierarchically structured materials for lithium batteries  

NASA Astrophysics Data System (ADS)

The lithium-ion battery (LIB) is one of the most promising power sources to be deployed in electric vehicles, including solely battery powered vehicles, plug-in hybrid electric vehicles, and hybrid electric vehicles. With the increasing demand for devices of high-energy densities (>500 Wh kg-1), new energy storage systems, such as lithium-oxygen (Li-O2) batteries and other emerging systems beyond the conventional LIB, have attracted worldwide interest for both transportation and grid energy storage applications in recent years. It is well known that the electrochemical performance of these energy storage systems depends not only on the composition of the materials, but also on the structure of the electrode materials used in the batteries. Although the desired performance characteristics of batteries often have conflicting requirements with the micro/nano-structure of electrodes, hierarchically designed electrodes can be tailored to satisfy these conflicting requirements. This work will review hierarchically structured materials that have been successfully used in LIB and Li-O2 batteries. Our goal is to elucidate (1) how to realize the full potential of energy materials through the manipulation of morphologies, and (2) how the hierarchical structure benefits the charge transport, promotes the interfacial properties and prolongs the electrode stability and battery lifetime.

Xiao, Jie; Zheng, Jianming; Li, Xiaolin; Shao, Yuyan; Zhang, Ji-Guang

2013-10-01

419

CORROSION OF STRUCTURAL MATERIALS IN IMPURE SANTOWAX  

Microsoft Academic Search

Corrosion rates were measured for a variety of structural materials ; exposed to commercially available terphenyls (Santowax) at elevated temperatures ; in agitatorautoclaves and in a pumped loop. Corrosion rates were determined as a ; function of water content, cover gas, fluid velocity, and temperature. A number ; of metals were found to be compatible with impure Santowax. Those of

Neymark

1963-01-01

420

Crystal structure and physical characterization of neotame methanol solvate  

Microsoft Academic Search

The crystal structure of the methanol solvate (empirical formula: 2C20H30N2O53CH3OH) of a new dipeptide sweetener, neotame (N-(3,3-dimethylbutyl)-L-a-aspartyl-L-phenylalanine 1-methyl ester), has been determined. Crystal data: a = 9.8989(1), b = 18.1331(1), c = 27.5725(1) , orthorhombic, space group P212121, with Z = 4. Each unit cell includes 8 neotame and 12 methanol molecules. Disorder exists in one neotame molecule and one

Zedong Dong; Victor G. Young; Brian E. Padden; Steve A. Schroeder; Indra Prakash; Eric J. Munson; David J. W. Grant

1999-01-01

421

Single Crystal Thin Films of Semiconductor and Piezoelectric Materials on Refractory Substrates.  

National Technical Information Service (NTIS)

Composites of single-crystal thin film piezoelectric ans semiconductor materials heteroepitaxially grown on insulating substrates were investigated for application to the generation, processing, and guiding of acoustic surface waves. Emphasis was on AlN a...

H. M. Manasevit J. E. Coker F. A. Pizzarello R. P. Ruth

1974-01-01

422

Materials Science and Technology, Volume 1, Structure of Solids  

NASA Astrophysics Data System (ADS)

This self-contained handbook focuses on the fundamentals important in all areas of solid-state science and serves as a foundation for the rest of the series. From the Contents: Steurer: Elements of Symmetry in Periodic Lattices, Quasicrystals. Pettifor: Electron Theory of Crystal Structure. Saccone/Ferro: Structure of Intermetallic Compounds and Phases. Steeb/Lamparter: Structure of Amorphous and Molten Alloys. Petry/Schober: Lattice Vibrations. Wollenberger: Point Defects in Crystals. Bacon: Dislocations in Crystals. Van Hove: Crystal Surfaces. Finnis/Rhle: Interfaces in Crystalline Solids.

Gerold, Volkmar

1996-12-01

423

Liquid crystal materials with asymmetric switching for microdisplay applications  

NASA Astrophysics Data System (ADS)

Liquid crystals are customarily used in several kinds of flat panel displays. Besides usual nematic liquid crystals, smectic tristate antiferroelectric liquid crystals have shown analogue grayscale and full color video rate at high-end devices with passive multiplexing. These devices ultimately are intended to be applied to small size devices on microdisplay applications. When a symmetric driving signal is applied, the electrooptic response of the devices usually consists of two symmetric hysteresis lobes. An asymmetric hysteresis cycle can be developed by using dissimilar aligning layers onto the two glass plates of the cell. This kind of devices can lead to analogue optical multistability, i.e., devices whose optical transmission may be arbitrarily set and maintained reducing or eliminating the bias voltage. In this work, a study of the asymmetric behavior of cells filled with commercial antiferroelectric liquid crystal is presented. Optical hysteresis cycles have been obtained applying a low frequency triangular waveform to the devices. Analogue grayscales have been generated only at one lobe of the hysteresis cycle. Electrical characterization has been carried out measuring the switching current of the cells test. Multiplexed driving waveforms have been applied with and without bias voltage in order to evaluate the stability of the optical transmission for video rate working. Results demonstrating analogue optical multistability on asymmetric antiferroelectric cells have been obtained. Narrow dynamic ranges, compatible with standard electronics for dynamic grayscale in data columns have been found. Preliminary measurements of the frequency dependence of impedance have been obtained on the capacitive device.

Urruchi, V.; Perez, I.; Pena, J. M. S.; Torres, J. C.; Manzanares, R.; Quintana, X.; Oton, J. M.

2005-07-01

424

Evolutionary crystal structure prediction: discovering new minerals in the deep Earth.  

NASA Astrophysics Data System (ADS)

Experimental determination of crystal structures at high pressure is often extremely difficult; given this and the strengths of quantum-mechanical simulations, theory presents an attractive tool to investigate matter at extreme conditions. However, crystal structure prediction on the basis of just the chemical formula has long been considered a formidable or even insoluble problem. Solving it would enable structural studies of planetary materials at extreme conditions [1,2] and probe changing chemistry at high pressure, solve structures where experimental data are insufficient, and design new materials entirely on the computer (once the structure is known, it is relatively easy to predict many of its properties e.g., [3]). Recently, we addressed this problem and devised a new method based on an ab initio evolutionary algorithm, which we implemented in the USPEX code (Universal Structure Predictor: Evolutionary Xtallography, [4-6]). USPEX uses ab initio free energy as evaluation function and features local optimization and spatial heredity, as well as further operators such as mutation and permutation. At given P-T conditions, USPEX finds the stable structure and a set of robust metastable structures, using no experimental information except the chemical composition. This method has been widely tested and applied to solve a number of important problems. In this talk I will discuss some of the applications of this method to a number of interesting materials at high pressure (C, O, S, MgSiO3, CO2, CaCO3, MgCO3). 1. Oganov A.R. & Ono S. (2004). Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D" layer. Nature 430, 445-448. 2. Oganov A.R., Ono S. (2005). The high pressure phase of alumina and implications for Earth's D" layer. Proc. Natl. Acad. Sci. 102, 10828-10831. 3. Oganov A.R., Brodholt J.P., Price G.D. (2001). The elastic constants of MgSiO3 perovskite at pressures and temperatures of the Earth's mantle. Nature 411, 934-937. 4. Oganov A.R., Glass C.W., Ono S. (2006). High-pressure phases of CaCO3: crystal structure prediction and experiment. Earth Planet. Sci. Lett. 241, 95-103. 5. Oganov A.R. & Glass C.W. (2006). Crystal Structure Prediction using ab initio evolutionary techniques: principles and applications. J. Chem. Phys, 124, art. 244704. 6. Glass C.W., Oganov A.R. & Hansen N. (2006). USPEX - evolutionary crystal structure prediction. Comp. Phys. Comm., in press.

Oganov, A. R.; Glass, C. W.

2006-12-01

425

Crystal structure of dimeric HIV-1 capsid protein.  

PubMed

X-ray diffraction analysis of a human immunodeficiency virus (HIV-1) capsid (CA) protein shows that each monomer within the dimer consists of seven alpha-helices, five of which are arranged in a coiled coil-like structure. Sequence assignments were made for two of the helices, and tentative connectivity of the remainder of the protein was confirmed by the recent solution structure of a monomeric N-terminal fragment. The C-terminal third of the protein is mostly disordered in the crystal. The longest helices in the coiled coil-like structure are separated by a long, highly antigenic peptide that includes the binding site of an antibody fragment complexed with CA in the crystal. The site of binding of the Fab, the position of the antigenic loop and the site of cleavage between the matrix protein and CA establish the side of the dimer that would be on the exterior of the retroviral core. PMID:8784350

Momany, C; Kovari, L C; Prongay, A J; Keller, W; Gitti, R K; Lee, B M; Gorbalenya, A E; Tong, L; McClure, J; Ehrlich, L S; Summers, M F; Carter, C; Rossmann, M G

1996-09-01

426

Crystal and electronic structures of LiNH2  

NASA Astrophysics Data System (ADS)

The crystal structure of LiNH2 was reinvestigated using powder neutron diffraction with high sensitivity. The compound crystallizes in the tetragonal space group I4 with lattice parameters a=b=5.034 42 (24) A?, c=10.255 58 (52) A?. It is found that H atoms occupy 8g1(0.2429, 0.1285, 0.1910) and 8g2 (0.3840, 0.3512, 0.1278) sites. The bond lengths between the nearest nitrogen and hydrogen atoms are 0.986 and 0.942 A?, respectively. The bond angle between H-N-H is about 99.97. These results are significantly different from those of previous experiments. The electronic structure was calculated according to the revised structural data. The calculated density of states and charge density distribution show strong ionic characteristics between the ionic Li+ cation and the covalent bonded [NH2]- anion.

Yang, J. B.; Zhou, X. D.; Cai, Q.; James, W. J.; Yelon, W. B.

2006-01-01

427

Crystal structure of a bacterial ribonuclease P RNA  

PubMed Central

The x-ray crystal structure of a 417-nt ribonuclease P RNA from Bacillus stearothermophilus was solved to 3.3- resolution. This RNA enzyme is constructed from a number of coaxially stacked helical domains joined together by local and long-range interactions. These helical domains are arranged to form a remarkably flat surface, which is implicated by a wealth of biochemical data in the binding and cleavage of the precursors of transfer RNA substrate. Previous photoaffinity crosslinking data are used to position the substrate on the crystal structure and to identify the chemically active site of the ribozyme. This site is located in a highly conserved core structure formed by intricately interlaced long-range interactions between interhelical sequences.

Kazantsev, Alexei V.; Krivenko, Angelika A.; Harrington, Daniel J.; Holbrook, Stephen R.; Adams, Paul D.; Pace, Norman R.

2005-01-01

428

Binary colloidal crystals  

Microsoft Academic Search

Binary crystals are crystals composed of two types of particles having different properties like size, mass density, charge etc. In this thesis several new approaches to make binary crystals of colloidal particles that differ in size, material and charge are reported We found a variety of crystal structures, amongst which five not seen before with colloids (LS3, LS6-, two LS8-

C. G. Christova-Zdravkova

2005-01-01

429

Influence of the starting materials used in the crystal growth process of CZT for gamma ray radiation applications  

NASA Astrophysics Data System (ADS)

The influences of two different ways of crystal growth preparations by using different starting materials on the detector properties have been investigated. The characterization has been carried out in terms of structural, optical, and electrical properties of the materials grown with the vertical gradient freeze method. The distributions of Zn and In at different axial positions with different crystals have been compared by using the Induced Coupled Plasma-Mass Spectroscopy technique. The size and density of Te inclusions within the materials have been identified by Infrared Microscopy. The luminescence behaviors have been investigated by studying the defects levels. Particularly, the currentvoltage characteristics and Gamma-ray Spectroscopy have been investigated by comparing the performance of detectors achieved from different axial directions of the ingots.

Zheng, Q.; Crocco, J.; Bensalah, H.; Wellmann, P.; Osvet, A.; Knecke, U.; Dierre, F.; Vela, O.; Perez, J. M.; Dieguez, E.

2013-10-01

430

Fundamental Aspects of the Electronic Structure, Materials Properties, and Lubrication Performance of Sputtered MoS2 Films.  

National Technical Information Service (NTIS)

Layered transition metal dichalcogenide (LTMD) compounds constitute a class of materials with unique and unusual properties based on the extreme degree of anisotropy in their layered crystal structures. LTMDs are formed by stacking sandwiches consisting o...

P. D. Fleischauer

1988-01-01

431

Omnidirectional reflection from one-dimensional quasi-periodic photonic crystal containing left-handed material  

Microsoft Academic Search

In this Letter, we study the properties of one-dimensional quasi-periodic photonic crystal containing left-handed material. In the light of the dispersion relation, we show that one-dimensional quasi-periodic photonic crystal can exhibit complete reflection at a given microwave frequency for all incident angles and both polarizations (s- and p-polarizations). The influence of left-handed material's permittivity and permeability on the omnidirectional reflection

H. X. da; C. Xu; Z. Y. Li

2005-01-01

432

Trapping of topological-structural defects in Coulomb crystals.  

PubMed

We study experimentally and theoretically structural defects which are formed during the transition from a laser cooled cloud to a Coulomb crystal, consisting of tens of ions in a linear radio frequency trap. We demonstrate the creation of predicted topological defects ("kinks") in purely two-dimensional crystals and also find kinks which show novel dynamical features in a regime of parameters not considered before. The kinks are always observed at the center of the trap, showing a large nonlinear localized excitation, and the probability of their occurrence saturates at ?0.5. Simulations reveal a strong anharmonicity of the kink's internal mode of vibration, due to the kink's extension into three dimensions. As a consequence, the periodic Peierls-Nabarro potential experienced by a discrete kink becomes a globally confining potential, capable of trapping one cooled defect at the center of the crystal. PMID:23581315

Mielenz, M; Brox, J; Kahra, S; Leschhorn, G; Albert, M; Schaetz, T; Landa, H; Reznik, B

2013-03-28

433

Crystal structure of TiNi nanoparticles obtained by Ar ion beam deposition  

Microsoft Academic Search

Nanoparticles are a state of matter that have properties different from either molecules or bulk solids, turning them into a very interesting class of materials to study. In the present work, the crystal structure of TiNi nanoparticles obtained by ion beam deposition is characterized. TiNi nanoparticles were obtained from TiNi wire samples by sputtering with Ar ions using a Gatan

A. Torres Castro; E. Lpez Cullar; U. Ortiz Mndez; M. Jos Yacamn

2008-01-01

434

Preparation, crystal and magnetic structure of the double perovskite Ba 2 FeWO 6  

Microsoft Academic Search

Single-phase polycrystalline material of the double perovskite Ba2FeWO6 was prepared and characterized by X-ray and neutron powder diffraction (NPD). The crystal structure was tetragonal with lattice parameters a=b=5.7479(4) and c=8.1444(9) at room temperature (295 K). NPD data at 10 K shows the evidence of an antiferromagnetic ordering of the Fe atoms. The reverse Monte Carlo powder (RMCPOW) technique

A. K. Azad; A. Mellergrd; S.-G. Eriksson; S. A. Ivanov; J. Eriksen; H. Rundlf

2002-01-01

435

Tuning of crystal structure and magnetic properties by exceptionally large epitaxial strains  

Microsoft Academic Search

Huge deformations of the crystal lattice can be achieved in materials with inherent structural instability by epitaxial straining. By coherent growth on seven different substrates the in-plane lattice constants of 50 nm thick Fe70Pd30 films are continuously varied. The maximum epitaxial strain reaches 8,3 % relative to the fcc lattice. The in-plane lattice strain results in a remarkable tetragonal distortion

J. Buschbeck; I. Opahle; M. Richter; U. K. Rossler; P. Klaer; M. Kallmayer; H. J. Elmers; G. Jakob; L. Schultz; S. Fahler

2009-01-01

436

Energetics and crystal chemical systematics among ilmenite, lithium niobate, and perovskite structures  

SciTech Connect

Transitions from chain silicates to garnet, ilmenite, and perovskite structures are important in deep earth geophysics and solid-state chemistry. Titanates and other oxides also show polymorphism among ilmenite, lithium niobate (metastable), and perovskite structures. This review brings together the evidence from the recent mineralogical and materials science literature linking the crystal chemistry, thermodynamics, and occurrence of these polymorphs at high pressure and temperature. A-site ordered multicomponent titanate perovskites are also discussed. A common feature of the perovskite structure is its high vibrational entropy.

Navrotsky, A. [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science

1998-10-01

437

Synthesis and crystal structure of CuZrTiO{sub 5}-A new crystal structure type  

SciTech Connect

A new compound, CuZrTiO{sub 5}, was synthesized as strongly pleochroic green crystals from the oxides between 995 and 1010 deg. C, 1 atm. Its crystal structure was determined by single crystal XRD, resulting in R (F{sup 2}>2sigma(F{sup 2}))=0.032 and wR (all data)=0.079). CuZrTiO{sub 5} is orthorhombic, space group P2{sub 1}2{sub 1}2{sub 1}, a=3.5871(3) A, b=6.6968(4) A, c=14.6679(9) A, V=352.35(4) A{sup 3}, Z=4. The <