Note: This page contains sample records for the topic crystal structure particle from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Crystal structure of an H\\/ACA box ribonucleoprotein particle  

Microsoft Academic Search

H\\/ACA ribonucleoprotein particles (RNPs) are a family of RNA pseudouridine synthases that specify modification sites through guide RNAs. They also participate in eukaryotic ribosomal RNA processing and are a component of vertebrate telomerases. Here we report the crystal structure, at 2.3 resolution, of an entire archaeal H\\/ACA RNP consisting of proteins Cbf5, Nop10, Gar1 and L7ae, and a single-hairpin H\\/ACA

Ling Li; Keqiong Ye

2006-01-01

2

Crystal structure of an H/ACA box ribonucleoprotein particle.  

PubMed

H/ACA ribonucleoprotein particles (RNPs) are a family of RNA pseudouridine synthases that specify modification sites through guide RNAs. They also participate in eukaryotic ribosomal RNA processing and are a component of vertebrate telomerases. Here we report the crystal structure, at 2.3 A resolution, of an entire archaeal H/ACA RNP consisting of proteins Cbf5, Nop10, Gar1 and L7ae, and a single-hairpin H/ACA RNA, revealing a modular organization of the complex. The RNA upper stem is bound to a composite surface formed by L7ae, Nop10 and Cbf5, and the RNA lower stem and ACA signature motif are bound to the PUA domain of Cbf5, thereby positioning middle guide sequences so that they are primed to pair with substrate RNA. Furthermore, Gar1 may regulate substrate loading and release. The structure rationalizes the consensus structure of H/ACA RNAs, suggests a functional role of each protein, and provides a framework for understanding the mechanism of RNA-guided pseudouridylation, as well as various cellular functions of H/ACA RNP. PMID:16943774

Li, Ling; Ye, Keqiong

2006-09-21

3

Single crystal particles of a mesoporous mixed transition metal oxide with a wormhole structure.  

PubMed

A new type of mesoporous mixed transition metal oxide of Nb and Ta (NbTa-TIT-1) has been prepared through a two-step calcination, which consists of single crystal particles with wormhole mesoporous structure. PMID:12240191

Lee, B; Lu, D; Kondo, J N; Domen, K

2001-10-21

4

Single crystal structure analysis of a single Sm2Fe17N3 particle  

NASA Astrophysics Data System (ADS)

We performed single crystal structure analysis of Sm2Fe17N3 using X-ray diffraction. A pick-up system combined with a micromanipulation tool driven by piezoelectric actuators and a microgripper was used. A single Sm2Fe17Nx particle with the diameter of about 20 ?m was picked up, and X-ray diffraction was measured using an X-ray diffractometer at the synchrotron radiation beamline at the Photon Factory, KEK. Single crystal structure analysis of a Sm2Fe17N3 particle was performed and the structure was successfully determined from X-ray diffraction patterns. The space group and the lattice constants were determined to be R-3m (#166) a = b = 8.7206 and c = 12.6345 , respectively. Atomic positions of Sm and Fe atoms were accurately determined by single crystal structure analysis of only one particle.

Inami, Nobuhito; Takeichi, Yasuo; Ueno, Tetsuro; Saito, Kotaro; Sagayama, Ryoko; Kumai, Reiji; Ono, Kanta

2014-05-01

5

Dependence of the crystal structure on particle size in barium titanate  

Microsoft Academic Search

The authors discuss the effect of the sample particle size on the crystal structure and the Curie temperature of BaTiO powder investigated in the particle size range 0.1 to 1.0 μm. The transformation from tetragonal to cubic symmetry occurs at a critical particle size of 0.12 μm at room temperature, and the Curie temperature drops below room temperature at the

Kenji Uchino; T. Hirose; E. Sadanaga

1989-01-01

6

The stability of a crystal with diamond structure for patchy particles with tetrahedral symmetry.  

PubMed

The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values of the range of the potential, with the aim of investigating the conditions under which a diamond crystal can be formed. We find that the diamond phase is never stable for our longer-ranged potential. At low temperatures and pressures, the fluid freezes into a body-centered-cubic solid that can be viewed as two interpenetrating diamond lattices with a weak interaction between the two sublattices. Upon compression, an orientationally ordered face-centered-cubic crystal becomes more stable than the body-centered-cubic crystal, and at higher temperatures, a plastic face-centered-cubic phase is stabilized by the increased entropy due to orientational disorder. A similar phase diagram is found for the shorter-ranged potential, but at low temperatures and pressures, we also find a region over which the diamond phase is thermodynamically favored over the body-centered-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centered-cubic solid explains why it is stable even though the enthalpy of the latter phase is lower. Some preliminary studies on the growth of the diamond structure starting from a crystal seed were performed. Even though the diamond phase is never thermodynamically stable for the longer-ranged model, direct coexistence simulations of the interface between the fluid and the body-centered-cubic crystal and between the fluid and the diamond crystal show that at sufficiently low pressures, it is quite probable that in both cases the solid grows into a diamond crystal, albeit involving some defects. These results highlight the importance of kinetic effects in the formation of diamond crystals in systems of patchy particles. PMID:20572725

Noya, Eva G; Vega, Carlos; Doye, Jonathan P K; Louis, Ard A

2010-06-21

7

The stability of a crystal with diamond structure for patchy particles with tetrahedral symmetry  

NASA Astrophysics Data System (ADS)

The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values of the range of the potential, with the aim of investigating the conditions under which a diamond crystal can be formed. We find that the diamond phase is never stable for our longer-ranged potential. At low temperatures and pressures, the fluid freezes into a body-centered-cubic solid that can be viewed as two interpenetrating diamond lattices with a weak interaction between the two sublattices. Upon compression, an orientationally ordered face-centered-cubic crystal becomes more stable than the body-centered-cubic crystal, and at higher temperatures, a plastic face-centered-cubic phase is stabilized by the increased entropy due to orientational disorder. A similar phase diagram is found for the shorter-ranged potential, but at low temperatures and pressures, we also find a region over which the diamond phase is thermodynamically favored over the body-centered-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centered-cubic solid explains why it is stable even though the enthalpy of the latter phase is lower. Some preliminary studies on the growth of the diamond structure starting from a crystal seed were performed. Even though the diamond phase is never thermodynamically stable for the longer-ranged model, direct coexistence simulations of the interface between the fluid and the body-centered-cubic crystal and between the fluid and the diamond crystal show that at sufficiently low pressures, it is quite probable that in both cases the solid grows into a diamond crystal, albeit involving some defects. These results highlight the importance of kinetic effects in the formation of diamond crystals in systems of patchy particles.

Noya, Eva G.; Vega, Carlos; Doye, Jonathan P. K.; Louis, Ard A.

2010-06-01

8

Crystal structure of a transfer-ribonucleoprotein particle that promotes asparagine formation  

PubMed Central

Four out of the 22 aminoacyl-tRNAs (aa-tRNAs) are systematically or alternatively synthesized by an indirect, two-step route requiring an initial mischarging of the tRNA followed by tRNA-dependent conversion of the non-cognate amino acid. During tRNA-dependent asparagine formation, tRNAAsn promotes assembly of a ribonucleoprotein particle called transamidosome that allows channelling of the aa-tRNA from non-discriminating aspartyl-tRNA synthetase active site to the GatCAB amidotransferase site. The crystal structure of the Thermus thermophilus transamidosome determined at 3 resolution reveals a particle formed by two GatCABs, two dimeric ND-AspRSs and four tRNAsAsn molecules. In the complex, only two tRNAs are bound in a functional state, whereas the two other ones act as an RNA scaffold enabling release of the asparaginyl-tRNAAsn without dissociation of the complex. We propose that the crystal structure represents a transient state of the transamidation reaction. The transamidosome constitutes a transfer-ribonucleoprotein particle in which tRNAs serve the function of both substrate and structural foundation for a large molecular machine.

Blaise, Mickael; Bailly, Marc; Frechin, Mathieu; Behrens, Manja Annette; Fischer, Frederic; Oliveira, Cristiano L P; Becker, Hubert Dominique; Pedersen, Jan Skov; Thirup, S?ren; Kern, Daniel

2010-01-01

9

Effects of Mn on the crystal structure of ?-Al(Mn,Fe)Si particles in A356 alloys  

NASA Astrophysics Data System (ADS)

In a commercial Al-7.0Si-0.38Mg cast alloy (A356) with 0.20 wt% Fe, added Mn modifies acicular ?-Al 5FeSi particles to less acicular ?-Al(Mn,Fe)Si in both crystallization and precipitation conditions. The crystal structure of ?-Al(Mn,Fe)Si changes from body-centered cubic (bcc)/ simple cubic (sc) to Pm3 structures in response to an increase in the bulk Mn content of the alloy. The ?-Al(Mn,Fe)Si particles (50-200 nm) precipitate during solution treatment and their precipitation temperature is about 485 C in the as-cast condition.

Kim, Hyun You; Park, Tea Young; Han, Sang Won; Lee, Hyuck Mo

2006-05-01

10

The crystal structure of the signal recognition particle Alu RNA binding heterodimer, SRP9/14.  

PubMed Central

The mammalian signal recognition particle (SRP) is an 11S cytoplasmic ribonucleoprotein that plays an essential role in protein sorting. SRP recognizes the signal sequence of the nascent polypeptide chain emerging from the ribosome, and targets the ribosome-nascent chain-SRP complex to the rough endoplasmic reticulum. The SRP consists of six polypeptides (SRP9, SRP14, SRP19, SRP54, SRP68 and SRP72) and a single 300 nucleotide RNA molecule. SRP9 and SRP14 proteins form a heterodimer that binds to the Alu domain of SRP RNA which is responsible for translation arrest. We report the first crystal structure of a mammalian SRP protein, that of the mouse SRP9/14 heterodimer, determined at 2.5 A resolution. SRP9 and SRP14 are found to be structurally homologous, containing the same alpha-beta-beta-beta-alpha fold. This we designate the Alu binding module (Alu bm), an additional member of the family of small alpha/beta RNA binding domains. The heterodimer has pseudo 2-fold symmetry and is saddle like, comprising a strongly curved six-stranded amphipathic beta-sheet with the four helices packed on the convex side and the exposed concave surface being lined with positively charged residues.

Birse, D E; Kapp, U; Strub, K; Cusack, S; Aberg, A

1997-01-01

11

Crystal Structure of an Aquabirnavirus Particle: Insights into Antigenic Diversity and Virulence Determinism?  

PubMed Central

Infectious pancreatic necrosis virus (IPNV), a pathogen of salmon and trout, imposes a severe toll on the aquaculture and sea farming industries. IPNV belongs to the Aquabirnavirus genus in the Birnaviridae family of bisegmented double-stranded RNA viruses. The virions are nonenveloped with a T=13l icosahedral capsid made by the coat protein VP2, the three-dimensional (3D) organization of which is known in detail for the family prototype, the infectious bursal disease virus (IBDV) of poultry. A salient feature of the birnavirus architecture is the presence of 260 trimeric spikes formed by VP2, projecting radially from the capsid. The spikes carry the principal antigenic sites as well as virulence and cell adaptation determinants. We report here the 3.4- resolution crystal structure of a subviral particle (SVP) of IPNV, containing 20 VP2 trimers organized with icosahedral symmetry. We show that, as expected, the SVPs have a very similar organization to the IBDV counterparts, with VP2 exhibiting the same overall 3D fold. However, the spikes are significantly different, displaying a more compact organization with tighter packing about the molecular 3-fold axis. Amino acids controlling virulence and cell culture adaptation cluster differently at the top of the spike, i.e., in a central bowl in IBDV and at the periphery in IPNV. In contrast, the spike base features an exposed groove, conserved across birnavirus genera, which contains an integrin-binding motif. Thus, in addition to revealing the viral antigenic determinants, the structure suggests that birnaviruses interact with different receptors for attachment and for cell internalization during entry.

Coulibaly, Fasseli; Chevalier, Christophe; Delmas, Bernard; Rey, Felix A.

2010-01-01

12

Nanodiamond particles forming photonic structures  

NASA Astrophysics Data System (ADS)

Colloid suspensions of irregularly shaped, highly charged detonation nanodiamond particles are found to have unexpected optical properties, similar to those of photonic crystals. This finding is all the more surprising since the particles used in this work are far more polydisperse than those typically forming photonic crystals. Intensely iridescent structures have been fabricated using the centrifugation of aqueous suspensions of nanodiamonds.

Grichko, Varvara; Tyler, Talmage; Grishko, Victor I.; Shenderova, Olga

2008-06-01

13

Nanodiamond particles forming photonic structures.  

PubMed

Colloid suspensions of irregularly shaped, highly charged detonation nanodiamond particles are found to have unexpected optical properties, similar to those of photonic crystals. This finding is all the more surprising since the particles used in this work are far more polydisperse than those typically forming photonic crystals. Intensely iridescent structures have been fabricated using the centrifugation of aqueous suspensions of nanodiamonds. PMID:21825753

Grichko, Varvara; Tyler, Talmage; Grishko, Victor I; Shenderova, Olga

2008-06-01

14

Crystallization of tetrahedral patchy particles in silico  

NASA Astrophysics Data System (ADS)

We investigate the competition between glass formation and crystallization of open tetrahedral structures for particles with tetrahedral patchy interactions. We analyze the outcome of such competition as a function of the potential parameters. Specifically, we focus on the separate roles played by the interaction range and the angular width of the patches, and show that open crystal structures (cubic and hexagonal diamond and their stacking hybrids) spontaneously form when the angular width is smaller than about 30. Evaluating the temperature and density dependence of the chemical potential of the fluid and of the crystal phases, we find that adjusting the patch width affects the fluid and crystal in different ways. As a result of the different scaling, the driving force for spontaneous self-assembly rapidly grows as the fluid is undercooled for small-width patches, while it only grows slowly for large-width patches, in which case crystallization is pre-empted by dynamic arrest into a network glass.

Romano, Flavio; Sanz, Eduardo; Sciortino, Francesco

2011-05-01

15

Ionic colloidal crystals of oppositely charged particles.  

PubMed

Colloidal suspensions are widely used to study processes such as melting, freezing and glass transitions. This is because they display the same phase behaviour as atoms or molecules, with the nano- to micrometre size of the colloidal particles making it possible to observe them directly in real space. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive, short-range attractive, hard-sphere-like and dipolar, can be realized and give rise to equilibrium phases. However, spherically symmetric, long-range attractions (that is, ionic interactions) have so far always resulted in irreversible colloidal aggregation. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to atomic systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external electric field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behaviour of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the production of binary crystals of micrometre-sized particles, which could find use as advanced materials for photonic applications. PMID:16148929

Leunissen, Mirjam E; Christova, Christina G; Hynninen, Antti-Pekka; Royall, C Patrick; Campbell, Andrew I; Imhof, Arnout; Dijkstra, Marjolein; van Roij, Ren; van Blaaderen, Alfons

2005-09-01

16

The crystal structure of the third signal-recognition particle GTPase FlhF reveals a homodimer with bound GTP  

PubMed Central

Flagella are well characterized as the organelles of locomotion and allow bacteria to react to environmental changes. The assembly of flagella is a multistep process and relies on a complex type III export machinery located in the cytoplasmic membrane. The FlhF protein is essential for the placement and assembly of polar flagella and has been classified as a signal-recognition particle (SRP)-type GTPase. SRP GTPases appeared early in evolution and form a unique subfamily within the guanine nucleotide binding proteins with only three members: the signal sequence-binding protein SRP54, the SRP receptor FtsY, and FlhF. We report the crystal structures of FlhF from Bacillus subtilis in complex with GTP and GMPPNP. FlhF shares SRP GTPase-specific features such as the presence of an N-terminal ?-helical domain and the I-box insertion. It forms a symmetric homodimer sequestering a composite active site that contains two head-to-tail arranged nucleotides similar to the heterodimeric SRP-targeting complex. However, significant differences to the GTPases of SRP and the SRP receptor include the formation of a stable homodimer with GTP as well as severe modifications and even the absence of motifs involved in regulation of the other two SRP GTPases. Our results provide insights into SRP GTPases and their roles in two fundamentally different protein-targeting routes that both rely on efficient protein delivery to a secretion channel.

Bange, Gert; Petzold, Georg; Wild, Klemens; Parlitz, Richard O.; Sinning, Irmgard

2007-01-01

17

Teaching with Crystal Structures: Helping Students Recognize and Classify the Smallest Repeating Particle in a Given Substance  

ERIC Educational Resources Information Center

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 periodic properties, and so on. Rather than getting tangled up in all of these concepts at the start

Smithenry, Dennis W.

2009-01-01

18

Crystal Structures as Geobarometers  

NSDL National Science Digital Library

This exercise is based on the recent formulation of a geobarometer based on the crystal structure of clinopyroxene (Nimis, 1995; 1998; 1999). This method relates structural parameters (e.g., the volumes of the unit cell and the M1 polyhedron) to the pressure at which the mineral crystallizes within basic and ultrabasic magmas. students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or Xtaldraw visualization software packages. students are instructed on how to examine the structures to determine pressure-sensitive crystallographic parameters students are then asked a series of questions related to what they learn.

Ratajeski, Kent

19

Derivative Crystal Structures  

Microsoft Academic Search

There exists a class of crystal structures which are derived from others by generalization. These are here designated derivative structures. A special case of derivative structure is the popular ``superstructure.'' The symmetry of a derivative structure is a subgroup of the symmetry of the basic structure. Here the term ``subgroup'' is used in a wider sense than common in mathematical

M. J. Buerger

1947-01-01

20

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

21

Crystal Lattice Structures  

NSDL National Science Digital Library

This site provides an index of common crystal lattice structures--arrangements of atoms in a crystalline substance. The structures are indexed by Strukturbericht designation, Pearson symbol, space group, and prototype. Each structure is illustrated and accompanied by a brief description. The structure graphics can be viewed online, downloaded for external viewing, or manipulated in virtual space using a Java applet.

22

Particle-Stabilized Defect Gel in Cholesteric Liquid Crystals  

Microsoft Academic Search

Dispersions of colloidal particles in cholesteric liquid crystals form an unusualsolid by stabilizing a network of linear defects under tension in the ideallayered structure of the cholesteric. The large length scales of the cholestericliquid crystals allowed direct observation of the network structure, and itsproperties were correlated with rheological measurements of elasticity. Thissystem serves as a model for a class of

Martin Zapotocky; Laurence Ramos; Philippe Poulin; T. C. Lubensky

1999-01-01

23

X-ray Crystal Structure of the Vault, Largest Ribonucleoprotein Particle, with a Molecular Weight of 10 MDa  

NASA Astrophysics Data System (ADS)

Vaults are among the largest cytoplasmic ribonucleoprotein particles and are found in numerous eukaryotic species. Although roles in multidrug resistance and innate immunity have been suggested, the cellular function remains unclear. We have determined the X-ray structure of rat liver vault at 3.5 resolution. A vault particle shell was composed of 78 MVP (Major vault protein) chains with 39-fold dihedral symmetry. The shoulder domain of MVP is structurally similar to SPFH (stomatin/prohibitin/flotillin/HflK/C) domain involved in lipid raft association.

Tanaka, Hideaki; Kato, Koji; Yamashita, Eiki

24

Passive particle dosimetry. [silver halide crystal growth  

NASA Technical Reports Server (NTRS)

Present methods of dosimetry are reviewed with emphasis on the processes using silver chloride crystals for ionizing particle dosimetry. Differences between the ability of various crystals to record ionizing particle paths are directly related to impurities in the range of a few ppm (parts per million). To understand the roles of these impurities in the process, a method for consistent production of high purity silver chloride, and silver bromide was developed which yields silver halides with detectable impurity content less than 1 ppm. This high purity silver chloride was used in growing crystals with controlled doping. Crystals were grown by both the Czochalski method and the Bridgman method, and the Bridgman grown crystals were used for the experiments discussed. The distribution coefficients of ten divalent cations were determined for the Bridgman crystals. The best dosimeters were made with silver chloride crystals containing 5 to 10 ppm of lead; other impurities tested did not produce proper dosimeters.

Childs, C. B.

1977-01-01

25

Olivine Crystal Structure  

NSDL National Science Digital Library

This exercise is based on recent crystallographic research on the olivine crystal structure published by Redfern et al. (2000). The authors of this study synthesized Fa50 olivine olivine (MgFeSiO4) in an experimental apparatus at temperatures ranging from 100 to 1250 °C, quenched the experiments, and used in situ neutron powder diffraction techniques to investigate changes in the synthesized olivines as a function of temperature. While this study reports cutting-edge materials research carried out with the latest crystallographic techniques, the results are educationally instructive and illustrate important concepts normally covered in an undergraduate mineralogy course. In this exercise, students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or XtalDraw visualization software packages. The students are instructed on how to manipulate the structures and are asked to plot some of the crystallographic data from this study on graphs using a spreadsheet program such as Excel.

Ratajeski, Kent

26

Crystal structure of daqingshanite  

Microsoft Academic Search

Daqinshanite, a new mineral recently discovered in China, is a kind of strontium-rare earth-bearing phosphate-carbonate. The\\u000a ideal formula is: (Sr, Ca, Ba), RF(PO4)(CO3)3. The mineral belongs to the trigonal system. The intensity data were collected with a single-crystal four-circle diffractometer.\\u000a The lattice parameters are given as:a=10.058(0.002) ;c=9.225(0.003) . Space group=R3m,Z=3. The crystal structure was solved by Patterson and electron density

Lulu Ximen; Zhizhong Peng

1985-01-01

27

Particle Waves and Audiofrequency Modes in Crystals.  

National Technical Information Service (NTIS)

Starting with the idea that wave mechanics should be useful in dealing with mechanical properties of solids, a connection between particle waves and deformation in crystals is developed. The connection is one in which Planck's constant h plays a prominent...

E. R. Fitzgerald

1964-01-01

28

Crystal Lattice Structures  

NSDL National Science Digital Library

The US Naval Research Laboratories (NRL) maintains this Website containing 2-D images (HTML) of 78 crystal lattice structures (e.g., body-centered-cubic, hexagonal-close packed, carbon, silicon). The index of structures can be searched by Pearson Symbol, Space Group, or Strukturbericht Designation. On each page, the structure can be viewed from different perspectives, and information about atomic number, vector diagrams, and atom coordinates is available. The site also contains a bibliography and a programming information page, both with hyperlinks.

29

Monodispersed Ultrafine Zeolite Crystal Particles by Microwave Hydrothermal Synthesis  

SciTech Connect

Microwave hydrothermal synthesis of zeolites is reviewed. Monodispersed ultrafine crystal particles of zeolite (Silicalite-1) have been synthesized in batch reactor vessels by microwave irradiation heating of aqueous basic silicate precursor solutions with tetra propyl ammonium hydroxide as the templating molecule. The effects of major process parameters (such as synthesis temperature, microwave heating rate, volume ratio (i.e., the volume of the initial synthesis solution over the total volume of the reactor vessel), and synthesis time on the zeolite particle characteristics are studied using a computer-controlled microwave reactor system that allows real-time monitoring and control of reaction medium temperature. The changes in the morphology, size and crystal structure of the particles are investigated using scanning electron microscope, dynamic light scattering, X-ray diffraction, and BET surface analysis. We have found that the synthesis temperature, volume ratio, and heating rate play a significant role in controlling the particle size, uniformity, and morphology. Microwave processing has generated new morphologies of zeolite particles (i.e., uniform block-shaped particles that contain mixed gel-nanocrystallites and agglomerated crystal particles) that could not be made by a conventional hydrothermal process. At higher synthesis temperature and lower volume ratio, irregular block-shaped particles were produced, whereas increasing the volume ratio promoted the formation of monodispersed single-crystal particles with uniform shape. Our results clearly demonstrate that faster microwave heating is advantageous to enhance the zeolite crystallization kinetics and produces larger-size crystal particles in shorter time. In addition, zeolite crystallization mechanisms, depending on the microwave heating rate, were also discussed.

Hu, Michael Z. [ORNL; Harris, Michael Tyrone [ORNL; Khatri, Lubna [ORNL

2008-01-01

30

Frustrated polymer crystal structures  

NASA Astrophysics Data System (ADS)

Several crystal structures or polymorphs of chiral or achiral polymers and biopolymers with three fold conformation of the helix have been found to conform to a common and -with one exception(Puterman, M. et al, J. Pol. Sci., Pol. Phys. Ed., 15, 805 (1977))- hitherto unsuspected packing scheme. The trigonal unit-cell contains three isochiral helices; the azimuthal setting of one helix differs significantly from that of the other two, leading to a so-called frustrated packing scheme, in which the environment of conformationally identical helices differs. Two variants of the frustrated scheme are analyzed. Similarities with frustrated two dimensional magnetic systems are underlined. Various examples of frustration in polymer crystallography are illustrated via the elucidation or reinterpretation of crystal phases or polymorphs of polyolefins, polyesters, cellulose derivatives and polypeptides. Structural manifestations (including AFM evidence) and morphological consequences of frustration are presented, which help diagnose the existence of this original packing of polymers.(Work done with L. Cartier, D. Dorset, S. Kopp, T. Okihara, M. Schumacher, W. Stocker.)

Lotz, B.; Strasbourg, 67083

1997-03-01

31

Inorganic Crystal Structure Database (ICSD)  

National Institute of Standards and Technology Data Gateway

SRD 84 FIZ/NIST Inorganic Crystal Structure Database (ICSD) (PC database for purchase) The Inorganic Crystal Structure Database (ICSD) is produced cooperatively by the Fachinformationszentrum Karlsruhe(FIZ) and the National Institute of Standards and Technology (NIST). The ICSD is a comprehensive collection of crystal structure data of inorganic compounds containing more than 140,000 entries and covering the literature from 1915 to the present.

32

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

33

Particle size effects on nanocolloidal interactions in nematic liquid crystals  

NASA Astrophysics Data System (ADS)

We study the interactions of submicrometer diameter silica particles, surface functionalized with DMOAP (N,N-dimethyl-n-octadecyl-3-aminopropyl-trimethoxysilyl chloride), in the nematic liquid crystal 5CB (pentylcyanobiphenil). Using the methods of video-tracking dark-field microscopy, we have measured the pair-binding energy of 35- to 450-nm-diameter silica particles, which is in the range between 100 and 1000 kBT. It is therefore high enough for the formation of thermally stable nanocolloidal pairs of 35 nm diameter. We find that smaller colloids with the diameter around 22 nm do not form thermally stable pairs, which seems to be currently the lower limit for nanocolloidal assembly in the nematic liquid crystals. We also study the particle interactions with point and Saturn-ring defects and discuss the possibility of hierarchical structures generated by particles of different sizes assembled by topological defects.

Ryzhkova, A. V.; Muevi?, I.

2013-03-01

34

Photonic Crystal Laser Accelerator Structures  

SciTech Connect

Photonic crystals have great potential for use as laser-driven accelerator structures. A photonic crystal is a dielectric structure arranged in a periodic geometry. Like a crystalline solid with its electronic band structure, the modes of a photonic crystal lie in a set of allowed photonic bands. Similarly, it is possible for a photonic crystal to exhibit one or more photonic band gaps, with frequencies in the gap unable to propagate in the crystal. Thus photonic crystals can confine an optical mode in an all-dielectric structure, eliminating the need for metals and their characteristic losses at optical frequencies. We discuss several geometries of photonic crystal accelerator structures. Photonic crystal fibers (PCFs) are optical fibers which can confine a speed-of-light optical mode in vacuum. Planar structures, both two- and three-dimensional, can also confine such a mode, and have the additional advantage that they can be manufactured using common microfabrication techniques such as those used for integrated circuits. This allows for a variety of possible materials, so that dielectrics with desirable optical and radiation-hardness properties can be chosen. We discuss examples of simulated photonic crystal structures to demonstrate the scaling laws and trade-offs involved, and touch on potential fabrication processes.

Cowan, Benjamin M

2003-05-21

35

Directed Discovery of Crystal Structures  

NSDL National Science Digital Library

This contribution is modified from a published exercise "Directed Discovery of Crystal Structures Using Ball-and-Stick Models" [Mogk, 1997] . While the published exercise is based on student exploration of traditional ball-and-stick models of crystal structures, this modified version uses a similar "discovery-based" approach and the latest online crystallographic information and visualization software to teach the spatial relationships and crystal-chemical rules that govern the crystal structures of common minerals and crystalline solids. A few changes in the content have been made from the published exercise, mainly to accommodate the new digital media.

Mogk, Dave; Ratajeski, Kent

36

Morphology and structure of biogenic magnetite particles  

Microsoft Academic Search

Blakemore1 found aquatic bacteria that swim along magnetic lines of force. Such bacteria have small particles of magnetite (magnetosomes) within them2,3 of various shapes3-5. We describe here the morphology and structure of bacterial magnetosomes investigated by high-resolution electron microscopy. From direct observation of various kinds of lattice images, the particles are determined to be single crystals with a hexagonal prism

Tsuyoshi Matsuda; Junji Endo; Nobuyuki Osakabe; Akira Tonomura; Tatsuo Arii

1983-01-01

37

Transport of particles in liquid crystals.  

PubMed

Colloidal particles in a liquid crystal (LC) behave very differently from their counterparts in isotropic fluids. Elastic nature of the orientational order and surface anchoring of the director cause long-range anisotropic interactions and lead to the phenomenon of levitation. The LC environment enables new mechanisms of particle transport that are reviewed in this work. Among them the motion of particles caused by gradients of the director, and effects in the electric field: backflow powered by director reorientations, dielectrophoresis in LC with varying dielectric permittivity and LC-enabled nonlinear electrophoresis with velocity that depends on the square of the applied electric field and can be directed differently from the field direction. PMID:24651158

Lavrentovich, Oleg D

2014-03-01

38

Effect of particle size and particle size distribution on physical characteristics, morphology and crystal structure of explosively compacted high-T(sub c) superconductors  

NASA Technical Reports Server (NTRS)

A superconductor, of composition Y(Ba,K,Na)2Cu3O(x)/F(y) and a composite of composition Y(Ba,K,Na)2Cu3O(x)/F(y) + Ag, with changing K, Na and F content but a constant silver content (Ag = 10 mass%) was prepared using a single heat treatment. the resulting material was ground in a corundum lined mill, separated to particle size fractions of 0-40 micron, 0-63 micron and 63-900 micron and explosively compacted, using an explosive pressure of 10(exp 4) MPa and a subsequent heat treatment. Best results were obtained with the 63-900 micron fraction of composition Y(Ba(1.95) K(0.01)Cu3O(x)F(0),(05)/Ag: porosity less than 0.01 cu cm/g and current density 2800 A/sq cm at 77K.

Kotsis, I.; Enisz, M.; Oravetz, D.; Szalay, A.

1995-01-01

39

Three-Dimensional 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 describe guiding of a speed-of-light accelerating mode by a defect in the photonic crystal lattice and discuss the properties of this mode, including particle beam dynamics and potential coupling methods for the structure. We also discuss possible materials and power sources for this structure and their effects on performance parameters, as well as possible manufacturing techniques and the required tolerances. In addition we describe the computational technique and possible improvements in numerical modeling that would aid development of photonic crystal structures.

Cowan, B.; /SLAC

2006-09-07

40

Crystals, Part II: Lattices and Structure.  

National Technical Information Service (NTIS)

Lists 715 domestic and foreign references added to the CFSTI collection during the period January 1959 through April 1965. Covers research on crystal lattices and lattice defects, crystal structure, crystal properties, optical properties, crystal processi...

1965-01-01

41

Thermal Expansion and Crystal Structure  

Microsoft Academic Search

In this investigation, the coefficients of thermal expansion of a number of crystals belonging to two structure types rutile and calcite have been studied by the x-ray method with a view to correlating thermal expansion with crystal structure. The crystals studied are MgF2, ZnF2, NiF2, MnF2, CoF2, FeF2, SnO2, PbO2, TiO2 (rutile), CrO2 and RuO2 belonging to the rutile type

K. V. Krishna Rao

1974-01-01

42

Use of Crystals for Beam Deflection in Particle Accelerators  

NASA Astrophysics Data System (ADS)

Charged particles interacting with a bent crystal can be trapped in channeling states and deflected by the atomic planes of the crystal lattice. The use of bent crystals for beam manipulation in particle accelerators is a well assessed concept rapidly evolving into practical applications. In the last three decades, a large number of experimental findings have contributed to clarify our knowledge and to improve our control of crystal-particle interactions. Bent crystals can impart angular deflections to the incoming particles, through channeling or volume reflection mechanisms. The efficiency of the latter mechanism has been found to be intrinsically very large, whilst the channeling efficiency has been improved by the increased technological expertize in crystal cutting and bending. In this paper, we review the recent milestones of the worldwide effort to propose a routine use of bent crystals in particle accelerators, with a specific attention to the proposals of promoting the use of bent crystals as primary element in beam halo collimation systems.

Scandale, Walter

43

Crystal Structure of Ettringite  

Microsoft Academic Search

ETTRINGITE (Ca6[Al(OH)6]2(SO4)3.26H2O) occurs as a natural mineral, and is technically important as a hydration product of Portland and supersulphated cements and in its use, as satin white, for coating paper. It forms hexagonal, prismatic crystals which in synthetic material are often highly elongated. Bannister, Hey and Bernal1 obtained unit-cell data (hexagonal: a 11.26, c 21.48 , space group P63\\/mmc, Z

A. Moore; H. F. W. TAYLOR

1968-01-01

44

Characterization of crystal structure in binary mixtures of latex globules.  

PubMed

Colloidal crystals formed by two types of polystyrene particles of different sizes (94 and 141 nm) at various number ratios (94:141 nm) are studied. Experiments showed that the formation time of crystals lengthens as the number ratio of the two components approaches 1:1. The dependence of the mean interparticle distance (D(0)), crystal structure and alloy structure on the number ratio of the two types of particles was studied by means of Kossel diffraction technique and reflection spectra. The results showed that as the number ratio decreased, the mean interparticle distance (D(0)) became larger. And the colloidal crystal in binary mixtures is more preferably to form the bcc structure. This study found that binary systems form the substitutional solid solution (sss)-type alloy structure in all cases except when the number ratio of two types of particles is 5:1, which results instead in the superlattice structure. PMID:18674779

Liu, Lei; Xu, Shenghua; Liu, Jie; Sun, Zhiwei

2008-10-01

45

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

46

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

47

The Surface Structure of Ground Metal Crystals  

NASA Technical Reports Server (NTRS)

The changes produced on metallic surfaces as a result of grinding and polishing are not as yet fully understood. Undoubtedly there is some more or less marked change in the crystal structure, at least, in the top layer. Hereby a diffusion of separated crystal particles may be involved, or, on plastic material, the formation of a layer in greatly deformed state, with possible recrystallization in certain conditions. Czochralski verified the existence of such a layer on tin micro-sections by successive observations of the texture after repeated etching; while Thomassen established, roentgenographically by means of the Debye-Scherrer method, the existence of diffused crystal fractions on the surface of ground and polished tin bars, which he had already observed after turning (on the lathe). (Thickness of this layer - 0.07 mm). Whether this layer borders direct on the undamaged base material or whether deformed intermediate layers form the transition, nothing is known. One observation ty Sachs and Shoji simply states that after the turning of an alpha-brass crystal the disturbance starting from the surface, penetrates fairly deep (approx. 1 mm) into the crystal (proof by recrystallization at 750 C).

Boas, W.; Schmid, E.

1944-01-01

48

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.

49

The structure of chemically modified detonation-synthesized nanodiamond particles  

Microsoft Academic Search

The results of studies of the structure of chemically modified detonation-synthesized nanodiamond (ND) particles by a set\\u000a of physical and chemical methods are reported. It is shown that the crystal structure, size, and the paramagnetic properties\\u000a of the particles persist during chemical modification processes. No nondiamond sp\\u000a 2 carbon is observed in the composition of the particles. The first experimental

I. I. Kulakova; V. V. Korolkov; R. Yu. Yakovlev; G. V. Lisichkin

2010-01-01

50

American Mineralogist Crystal Structure Database  

NSDL National Science Digital Library

The American Mineralogist Crystal Structure Database website, maintained by the Mineralogical Society of America and the Mineralogical Association of Canada and sponsored by the National Science Foundation, "includes every structure published in the American Mineralogist, The Canadian Mineralogist, and the European Journal of Mineralogy." The authors are also currently adding data from Physics and Chemistry of Minerals. Users can search the data by minerals, authors, chemistry, cell parameter and symmetry, or by a simple general search. This no frills website allows users to easily find and download data.

51

The crystal structure of dynamin  

PubMed Central

Dynamin-related proteins (DRPs) are multi-domain GTPases that function via oligomerization and GTP-dependent conformational changes to play central roles in regulating membrane structure across phylogenetic kingdoms. How DRPs harness self-assembly and GTP-dependent conformational changes to remodel membranes is not understood. Here we present the crystal structure of an assembly-deficient mammalian endocytic DRP, dynamin 1, lacking the proline-rich domain, in its nucleotide-free state. The dynamin 1 monomer is an extended structure with the GTPase domain and bundle signalling element positioned on top of a long helical stalk with the pleckstrin homology domain flexibly attached on its opposing end. Dynamin 1 dimer and higher order dimer multimers form via interfaces located in the stalk. Analysis of these interfaces provides insight into DRP family member specificity and regulation and provides a framework for understanding the biogenesis of higher order DRP structures and the mechanism of DRP-mediated membrane scission events.

Ford, Marijn G. J.; Jenni, Simon; Nunnari, Jodi

2014-01-01

52

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

53

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

54

American Mineralogist Crystal Structure Database  

NSDL National Science Digital Library

This database includes the crystal structure for every mineral published in the American Mineralogist, The Canadian Mineralogist, European Journal of Mineralogy and Physics, and Chemistry of Minerals. Data is now being imported from Acta Crystallographica as well. The database is maintained under the care of the Mineralogical Society of America and the Mineralogical Association of Canada. The data can be displayed or downloaded and are searchable by mineral, author, mineral chemistry, unit cell parameters and symmetry, diffraction pattern, or a general search. Links are provided to additional information and to crystallographic software.

55

The crystal structure of levyne  

Microsoft Academic Search

Summary Levyne, Ca27Na07K02[Al63Si117O36] 16.7 H2O, is rhombohedral, space group\\u000a$$R\\\\bar 3m$$\\u000a,ahex=13.338 andchex=23.014 . Its crystal structure is built up of layers of single and double six-membered rings of (Si, Al) O4 tetrahedra stacked according the model suggested fifteen years ago byBarrer andKerr. Cations are all disposed along the symmetry axis inside the levyne cage. One particular site is

S. Merlino; E. Galli; A. Alberti

1975-01-01

56

Nonlinear Phononic Periodic Structures and Granular Crystals.  

National Technical Information Service (NTIS)

In this chapter we describe the dynamic response of nonlinear phononic structures, focusing on granular crystals as the most prominent example. The chapter begins with a brief history of nonlinear lattices and with an introduction to granular crystals. It...

C. Daraio G. Theocharis N. Boechler

2012-01-01

57

The structural consequences of calcium crystal deposition.  

PubMed

Calcium pyrophosphate dihydrate and basic calcium phosphate (BCP) crystals are the most common calcium-containing crystals associated with rheumatic disease. Clinical manifestations of calcium crystal deposition include acute or chronic inflammatory and degenerative arthritides and certain forms of periarthritis. The intra-articular presence of BCP crystals correlates with the degree of radiographic degeneration. Calcium crystal deposition contributes directly to joint degeneration. Vascular calcification is caused by the deposition of calcium hydroxyapatite crystals in the arterial intima. These deposits may contribute to local inflammation and promote further calcification, thus aggravating the atherosclerotic process. Calcium crystal deposition results in substantial structural consequence in humans. PMID:24703349

Durcan, Laura; Bolster, Ferdia; Kavanagh, Eoin C; McCarthy, Geraldine M

2014-05-01

58

Single particle detection, manipulation and analysis with resonant optical trapping in photonic crystals.  

PubMed

We demonstrate a resonant optical trapping mechanism based on two-dimensional hollow photonic crystal cavities. This approach benefits simultaneously from the resonant nature and unprecedented field overlap with the trapped specimen. The photonic crystal structures are implemented in a 30 mm 12 mm optofluidic chip consisting of a patterned silicon substrate and an ultrathin microfluidic membrane for particle injection and control. Firstly, we demonstrate permanent trapping of single 250 and 500 nm-sized particles with sub-mW powers. Secondly, the particle induces a large resonance shift of the cavity mode amounting up to several linewidths. This shift is exploited to detect the presence of a particle within the trap and to retrieve information on the trapped particle. The individual addressability of multiple cavities on a single photonic crystal device is also demonstrated. PMID:23797114

Descharmes, Nicolas; Dharanipathy, Ulagalandha Perumal; Diao, Zhaolu; Tonin, Mario; Houdr, Romuald

2013-08-21

59

Particle interaction measurements in a Coulomb crystal using caged-particle motion.  

PubMed

A technique for characterizing the particle interaction potential of a Coulomb crystal is developed. The mean-square displacement (MSD) is measured, showing both caged- and superdiffusive-particle motions. By subtracting the center of mass of neighboring particles in computing MSD, only short-wavelength particle motions are retained. This yields the lattice Einstein frequency, which contains information about the interparticle forces and potentials. Video measurements of particle motions in a complex (dusty) plasma are used to demonstrate the technique. PMID:12005638

Quinn, R A; Goree, J

2002-05-13

60

Crystallization of micrometer-sized particles with molecular contours.  

PubMed

The crystallization of micrometer-sized particles with shapes mimicking those of tetrabenzoheptacene (TBH) and 1,2:5,6-dibenzanthracene (DBT), both flat polyacenes, in an electric field results in the formation of ordered 2D packings that mimic the plane group symmetries in their respective molecular crystal equivalents. Whereas the particles packed in low-density disordered arrangements under a gravitational gradient, dielectrophoresis (under an ac electric field) produced ordered high-density packings with readily identifiable plane group symmetry. The ordered colloidal assemblies were stable for hours, with the packing density decreasing slowly but with recognizable symmetry for up to 12 h for the TBH-shaped particles and up to 4 h for the DBT-shaped particles. This unexpected stability is attributed to jamming behavior associated with interlocking of the dogbone-shaped (TBH) and Z-block (DBT) particles, contrasting with the more rapid reduction of packing density and loss of hexagonal symmetry for disk-shaped particles upon removal of the electric field. The TBH-shaped and DBT-shaped particles assemble into the p2 plane group, which corresponds to the densest particle packing among the possible close-packed plane groups for these particle symmetries. The p2 symmetry observed for the TBH-shaped and DBT-shaped colloid crystal emulates the p2 symmetry of the (010) layers in their respective molecular crystals, which crystallize in monoclinic lattices. Notably, DBT-shaped particles also form ordered domains with pgg symmetry, replicating the plane group symmetry of the (100) layer in the orthorhombic polymorph of DBT. These observations illustrate that the 2D ordering of colloid particles can mimic the packing of molecules with similar shapes, demonstrating that packing can transcend length scales from the molecular to the colloidal. PMID:23984936

Song, Pengcheng; Olmsted, Brian K; Chaikin, Paul; Ward, Michael D

2013-11-12

61

Crystallization and preliminary X-ray diffraction analysis of apolipoprotein E-containing lipoprotein particles.  

PubMed

High-resolution structural information is available for several soluble plasma apolipoproteins (apos) in a lipid-free state. However, this information provides limited insight into structure-function relationships, as this class of proteins primarily performs its functions of lipid transport and modulation of lipid metabolism in a lipid-bound state on lipoprotein particles. Here, the possibility of generating homogeneous lipoprotein particles that could be crystallized was explored, opening the possibility of obtaining high-resolution structural information by X-ray crystallography. To test this possibility, apoE4 complexed with the phospholipid dipalmitoylphosphatidylcholine was chosen. Uniform particles containing 50% lipid and 50% apoE4 were obtained and crystallized using the hanging-drop method. Two crystal forms diffract to beyond 8 A resolution. PMID:16511213

Newhouse, Yvonne; Peters-Libeu, Clare; Weisgraber, Karl H

2005-11-01

62

Interaction of small spherical particles in confined cholesteric liquid crystals  

NASA Astrophysics Data System (ADS)

The theory of the elastic interaction of spherical colloidal particles immersed into a confined cholesteric liquid crystal is proposed. The case of weak anchoring on the particle surfaces is considered. We derive a general expression for the energy of the interaction between small spherical particles (with diameter much smaller than the cholesteric pitch) suspended in a cholesteric confined by two parallel planes. The resulting form of the interaction energy has a more complex spatial pattern and energy versus distance dependence than that in nematic colloids. The absence of translational symmetry related to helical periodicity and local nematic ordering in cholesteric liquid crystals manifest themselves in the complex nature of the interaction maps.

Lev, B. I.; Fukuda, Jun-ichi; Tovkach, O. M.; Chernyshuk, S. B.

2014-01-01

63

Simulations of Photonic Crystal and Dielectric Structures  

SciTech Connect

Dielectric materials and photonic crystal structures have electromagnetic properties that could potentially offer great benefits for accelerators. Computer simulation plays a critical role in designing, understanding, and optimizing these structures, especially the non-intuitive photonic crystal structures for which there is no relevant zeroth-order analytic model.

Werner, G. R. [Center for Integrated Plasma Studies, University of Colorado, Boulder, CO 80309 (United States)

2010-11-04

64

Photonic crystal devices formed by a charged-particle beam  

SciTech Connect

A photonic crystal device and method. The photonic crystal device comprises a substrate with at least one photonic crystal formed thereon by a charged-particle beam deposition method. Each photonic crystal comprises a plurality of spaced elements having a composition different from the substrate, and may further include one or more impurity elements substituted for spaced elements. Embodiments of the present invention may be provided as electromagnetic wave filters, polarizers, resonators, sources, mirrors, beam directors and antennas for use at wavelengths in the range from about 0.2 to 200 microns or longer. Additionally, photonic crystal devices may be provided with one or more electromagnetic waveguides adjacent to a photonic crystal for forming integrated electromagnetic circuits for use at optical, infrared, or millimeter-wave frequencies.

Lin, Shawn-Yu (Albuquerque, NM); Koops, Hans W. P. (Ober-Ramstadt, DE)

2000-01-01

65

Experimental modelling of single-particle dynamic processes in crystallization by controlled colloidal assembly.  

PubMed

In the last few decades, the controlled colloidal assembly was adopted as a new modelling technology for the study of the crystallization mechanism. In colloidal systems, the movement of particles is slow enough to follow and the particle dynamics can be monitored at the single-particle level using normal optical microscopes. So far, the studies of colloidal crystallization have produced a number of insights, which have significantly improved our understanding of crystallization. In this review, we summarize the recent advances in understanding the mechanism of crystallization, which were achieved using colloidal model systems, i.e., the kinetics of nucleation, growth and defect formation. Such model systems allow us to not only visualize some "atomic" details of nucleation and surface processes of crystallization, but also quantify previous models to such an extent that has never been achieved before by other approaches. In the case of nucleation, the quantitative observation of the kinetic process was made at the single-particle level; the results include the ideal case and the deviations from classical theories. The deviations include multi-step crystallization, supersaturation-driven structural mismatch nucleation, defect creation and migration kinetics, surface roughening, etc. It can be foreseen that this approach will become a powerful tool to study the fundamental process of crystallization and other phase transitions. PMID:24435291

Zhang, Tian Hui; Liu, Xiang Yang

2014-04-01

66

Crystal structure analysis of intermetallic compounds  

NASA Technical Reports Server (NTRS)

Study concerns crystal structures and lattice parameters for a number of new intermetallic compounds. Crystal structure data have been collected on equiatomic compounds, formed between an element of the Sc, Ti, V, or Cr group and an element of the Co or Ni group. The data, obtained by conventional methods, are presented in an easily usable tabular form.

Conner, R. A., Jr.; Downey, J. W.; Dwight, A. E.

1968-01-01

67

The structure of small, vapor-deposited particles. II - Experimental study of particles with hexagonal profile  

NASA Technical Reports Server (NTRS)

'Multiply-twinned' gold particles with hexagonal bright field TEM profile were determined to be icosahedra composed of 20 identical and twin-related tetrahedral building units that do not have an fcc structure. The crystal structure of these slightly deformed tetrahedra is rhombohedral. Experimental evidence supporting this particle model was obtained by selected-zone dark field and weak beam dark field electron microscopy. In conjunction with the results of part I, it has been concluded that multiply-twinned gold particles of pentagonal or hexagonal profile that are found during the early stages of the vapor deposition growth process on alkali halide surfaces do not have an fcc crystal structure, which is in obvious contrast to the structure of bulk gold.

Yacaman, M. J.; Heinemann, K.; Yang, C. Y.; Poppa, H.

1979-01-01

68

Sticky quartz crystal microbalance as a particle monitor  

NASA Astrophysics Data System (ADS)

Quartz crystal microbalances (QCM) have been used for over twenty years as contamination monitors in space satellites to measure film deposition on sensitive surfaces such optical mirrors, thermal radiators and solar arrays. However, it is only recently that miniature quartz crystal microbalances were used as particle monitors after the QCMs were coated with low outgassing grease to trap and measure the mass of particles impinging on the quartz surfaces. Results of these experiments utilizing 'sticky' QCMs are described for a series of wind- tunnel missile tests.

Uy, O. Manuel; Cain, Russell P.; Carkhuff, Bliss G.; Lennon, Andrew M.

1999-10-01

69

What can polymer crystal structure tell about polymer crystallization processes?  

NASA Astrophysics Data System (ADS)

Contrary to most or all other materials, crystallization of chiral but racemic polymers such as isotactic polypropylene is accompanied by a conformational rearrangement which leads to helical geometries: the building units of the crystal are helical stems, ? 10-20nm long, which can be either right-handed or left-handed. Helical hand cannot be reversed within the crystal structure: it is therefore a permanent marker and an indicator of molecular processes (in particular segregation/selection of helical hands) which take place during crystal growth, and more precisely during the crucial step of "efficient"helical stem deposition. The issue of proper helical hand selection during polymer crystal growth is mainly illustrated with isotactic polypropylene. Its various crystalline polymorphs (?, ?, ? and smectic) display virtually all possible combinations of helical hands, azimuthal settings and even non-parallel orientation of helix axes in space. Furthermore, a specific homoepitaxy which generates a lamellar branching in the ? phase "quadrites"and ?/? composite structures makes it possible a) to determine the helical hand and associated azimuthal setting of every stem in the crystalline entities and b) to determine the impact on the crystal structure and morphology of "mistakes"in helical hand of the depositing stem. Analysis of these morphologies demonstrates that the crystallization of isotactic polypropylene (and by implication of other achiral, helical polymers) is a highly sequential and "substrate-determined"process, i.e. that the depositing stem probes the topography of the growth face prior to attachment. These observations appear difficult to reconcile with crystallization schemes in which molecules (helical segments) are prearranged in a kind of pseudo-crystalline bundle (and as such, are not subjected to the high constraints of crystal symmetry) before deposition as a preassembled entity on the substrate.

Lotz, B.

2000-10-01

70

Crystallization media inhibit protein structural dynamics  

NASA Astrophysics Data System (ADS)

The first role of any crystallization solution is to reduce the solubility of proteins, so that it induces protein precipitation. Most times, protein precipitation does not lead to protein crystallization. Do crystallization solutions play any other roles that are crucial for protein crystallization? Here we report our studies that crystallization solutions suppress or inhibit protein structural dynamics. Photoactive yellow protein (PYP), a bacterial blue light photoreceptor protein, is employed as a model system in our study. We use time-resolved FTIR spectroscopic technique to probe the structural dynamics of proteins, including the proton transfer process and global conformational motions. We found that high concentration crystallization solutions (NH4)2SO4 strongly inhibit the structural dynamics of PYP upon blue light excitation. We will examine and discuss the mechanism in which crystallization solutions inhibit protein structural dynamics. The results are expected to provide insights to fundamental understanding of protein crystallization of water-soluble proteins. In addition, the data clearly demonstrates that the structural dynamics observed in crystalline conditions may be far from their natural structural dynamics for studies of protein structure-function relations.

Thubagere, Anupama; Kelemen, Lorand; Kaledhonkar, Sandip; Xie, Aihua

2007-03-01

71

Transition metal complexes with oligopeptides: single crystals and crystal structures.  

PubMed

The coordination chemistry of short chain peptides with transition metals is described in terms of the available crystal structures. Despite their high interest as synthetic models for metalloproteins and as building blocks for molecular materials based on the tuneable properties of oligopeptides, single crystal X-ray diffraction studies are scarce. A perusal of the most relevant results in this field allows us to define the main characteristics of oligopeptide-metal interactions, the fundamental problems for the crystallization of these complexes, and some hints to identify future promising approaches to advance the development of metallopeptide chemistry. PMID:24874062

Lillo, Vanesa; Galn-Mascars, Jos Ramn

2014-07-14

72

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

73

Crystal structure of a perfect carbyne  

NASA Astrophysics Data System (ADS)

The crystal structure of a perfect carbyne is calculated by the molecular mechanics methods. It is established that the carbyne crystals should consist of polycumulene chains arranged in hexagonal bundles. The unit cell of the perfect carbyne crystal is trigonal and contains one carbon atom. The unit cell parameters are as follows: a = b = c = 0.3580 nm, ? = ? = ? = 118.5, and space group P3 m1. The perfect carbyne single crystals have a stable structure at room temperature if the length of their constituent chains is larger than 500 nm.

Belenkov, E. A.; Mavrinsky, V. V.

2008-01-01

74

Crystal structure of a perfect carbyne  

SciTech Connect

The crystal structure of a perfect carbyne is calculated by the molecular mechanics methods. It is established that the carbyne crystals should consist of polycumulene chains arranged in hexagonal bundles. The unit cell of the perfect carbyne crystal is trigonal and contains one carbon atom. The unit cell parameters are as follows: a = b = c = 0.3580 nm, {alpha} = {beta} = {gamma} = 118.5{sup o}, and space group P3m1. The perfect carbyne single crystals have a stable structure at room temperature if the length of their constituent chains is larger than 500 nm.

Belenkov, E. A., E-mail: belenkov@csu.ru; Mavrinsky, V. V. [Chelyabinsk State University (Russian Federation)

2008-01-15

75

Microfluidic generation of magnetoresponsive Janus photonic crystal particles  

NASA Astrophysics Data System (ADS)

Janus particles with features of an anisotropic photonic band gap (PBG) structure and magnetic property have been achieved by phase separation and self-assembly of nanoparticles in microfluidic droplets. The resultant particles enable optical encoding and magnetically controllable motion, making them excellent functional encoded particles in biomedical applications.

Shang, Luoran; Shangguan, Fengqi; Cheng, Yao; Lu, Jie; Xie, Zhuoying; Zhao, Yuanjin; Gu, Zhongze

2013-09-01

76

Photonic crystals and glasses from monodisperse spherical mesoporous silica particles filled with nickel  

NASA Astrophysics Data System (ADS)

Films of photonic crystals and photonic glasses have been grown by the methods of vertical deposition and sedimentation from a suspension of monodisperse spherical mesoporous silica particles (MSMSP). A method of filling MSMSP pores with nickel, which is based on the adsorption and capillary phenomena in mesopores, has been developed. The composition and structure of the obtained materials have been studied.

Kurdyukov, D. A.; Eurov, D. A.; Stovpiaga, E. Yu.; Yakovlev, S. A.; Kirilenko, D. A.; Golubev, V. G.

2014-05-01

77

Metal oxide superconducting powder comprised of flake-like single crystal particles  

DOEpatents

Powder of a ceramic superconducting material is synthesized such that each particle of the powder is a single crystal having a flake-like, nonsymmetric morphology such that the c-axis is aligned parallel to the short dimension of the flake. Nonflake powder is synthesized by the normal methods and is pressed into pellets or other shapes and fired for excessive times to produce a coarse grained structure. The fired products are then crushed and ground producing the flake-like powder particles which exhibit superconducting characteristics when aligned with the crystal lattice.

Capone, Donald W. (Bolingbrook, IL); Dusek, Joseph (Downers Grove, IL)

1994-01-01

78

Metal oxide superconducting powder comprised of flake-like single crystal particles  

DOEpatents

Powder of a ceramic superconducting material is synthesized such that each particle of the powder is a single crystal having a flake-like, nonsymmetric morphology such that the c-axis is aligned parallel to the short dimension of the flake. Nonflake powder is synthesized by the normal methods and is pressed into pellets or other shapes and fired for excessive times to produce a coarse grained structure. The fired products are then crushed and ground producing the flake-like powder particles which exhibit superconducting characteristics when aligned with the crystal lattice. 3 figs.

Capone, D.W.; Dusek, J.

1994-10-18

79

A novel approach to identifying the elemental composition of individual residue particles retained in single snow crystals.  

PubMed

This study was carried out to describe the chemical characteristics of individual residual particles in hexagonal snow crystals, which can provide a clue to the aerosol removal mechanism during snowfall. In the present study, to collect snow crystal individually and to identify the elemental composition of individual residues retained in a hexagonal crystal, an orchestration of the replication technique and micro-particle induced X-ray emission (micro-PIXE) analysis was carried out. Information concerning the elemental compositions and their abundance in the snow crystals showed a severe crystal-to-crystal fluctuation. The residues retained in the hexagonal snow crystals were dominated primarily by mineral components, such as silica and calcium. Based on the elemental mask and the spectrum of micro-PIXE, it was possible to presume the chemical inner-structure as well as the elemental mixing state in and/or on the individual residues retained in single snow crystals. PMID:23934568

Ma, Chang-Jin; Hwang, Kyung-Chul; Kim, Ki-Hyun

2013-01-01

80

Quasi-periodic vertical structures of dusty plasma crystals  

Microsoft Academic Search

A semi-analytical model is proposed for understanding the quasi-periodic vertical structures in a plasma crystal, which are shown to be sustained by the combined effects of an ion flow, gravity and horizontal bonds of the dust particles. These structures are the manifestations of large-amplitude standing wake fields that lead to strong vertical bonds for the formation of an oriented hexagonal

Tzihong Chiueh; D. Ming-Ting Kuo

1999-01-01

81

Stepwise controlled immobilization of colloidal crystals formed by polymer-grafted silica particles.  

PubMed

Colloidal crystals formed by polymer-grafted silica particles were immobilized by a stepwise procedure consisting of gelation by radical copolymerization followed by solidification by ring-opening radical polymerization. In the first step, the poly(methyl methacrylate) (PMMA)-grafted silica colloidal crystal suspension was incorporated into the gel without altering the crystal structure by copolymerization of cross-linker, 1,2-dimethylacryloyloxyethane (DME) and methyl methacrylate (MMA). In the second step, ring-opening radical polymerization was performed after substituting the solvent with vinylidene-1,3-dioxolane. By this two-step procedure, the silica particle array of colloidal crystals was immobilized and made into durable material. PMID:16032862

Yoshinaga, Kohji; Fujiwara, Kumiko; Mouri, Emiko; Ishii, Masahiko; Nakamura, Hiroshi

2005-05-10

82

Defect structures in metallic photonic crystals  

SciTech Connect

We have investigated metallic photonic crystals built around a layer-by-layer geometry. Two different crystal structures (face-centered-tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7{endash}8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80{percent}), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations. {copyright} {ital 1996 American Institute of Physics.}

Oezbay, E.; Temelkuran, B. [Department of Physics, Bilkent University, Bilkent, Ankara 06533 (Turkey)] [Department of Physics, Bilkent University, Bilkent, Ankara 06533 (Turkey); Sigalas, M.; Tuttle, G.; Soukoulis, C.M.; Ho, K.M. [Ames Laboratory and Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory and Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States)

1996-12-01

83

Interaction between two spherical particles in a nematic liquid crystal  

NASA Astrophysics Data System (ADS)

We numerically investigate the interaction between two spherical particles in a nematic liquid crystal mediated by elastic distortions in the orientational order. We pay attention to the cases where two particles with equal radii R0 impose rigid normal anchoring on their surfaces and carry a pointlike topological defect referred to as a hyperbolic hedgehog. To describe the geometry of our system, we use bispherical coordinates, which prove useful in the implementation of boundary conditions at the particle surfaces and at infinity. We adopt the Landau de Gennes continuum theory in terms of a second-rank tensor order parameter Qij for the description of the orientational order of a nematic liquid crystal. We also utilize an adaptive mesh refinement scheme that has proven to be an efficient way of dealing with topological defects whose core size is much smaller than the particle size. When the two dipoles, composed of a particle and a hyperbolic hedgehog, are in parallel directions, the two-particle interaction potential is attractive for large interparticle distances D and proportional to D-3 as expected from the form of the dipole-dipole interaction, until the well-defined potential minimum at D?2.46 R0 is reached. For the antiparallel configuration with no hedgehogs between the two particles, the interaction potential is repulsive and behaves as D-2 for D?10 R0 , which is stronger than the dipole-dipole repulsion ( D-3 ) expected theoretically as an asymptotic behavior for large D .

Fukuda, Jun-Ichi; Stark, Holger; Yoneya, Makoto; Yokoyama, Hiroshi

2004-04-01

84

Structures of immature flavivirus particles  

PubMed Central

Structures of prM-containing dengue and yellow fever virus particles were determined to 16 and 25? resolution, respectively, by cryoelectron microscopy and image reconstruction techniques. The closely similar structures show 60 icosahedrally organized trimeric spikes on the particle surface. Each spike consists of three prM:E heterodimers, where E is an envelope glycoprotein and prM is the precursor to the membrane protein M. The pre-peptide components of the prM proteins in each spike cover the fusion peptides at the distal ends of the E glycoproteins in a manner similar to the organization of the glycoproteins in the alphavirus spikes. Each heterodimer is associated with an E and a prM transmembrane density. These transmembrane densities represent either an EE or prMprM antiparallel coiled coil by which each protein spans the membrane twice, leaving the C-terminus of each protein on the exterior of the viral membrane, consistent with the predicted membrane-spanning domains of the unprocessed polyprotein.

Zhang, Ying; Corver, Jeroen; Chipman, Paul R.; Zhang, Wei; Pletnev, Sergei V.; Sedlak, Dagmar; Baker, Timothy S.; Strauss, James H.; Kuhn, Richard J.; Rossmann, Michael G.

2003-01-01

85

Interaction of small spherical particles in confined cholesteric liquid crystals.  

PubMed

The theory of the elastic interaction of spherical colloidal particles immersed into a confined cholesteric liquid crystal is proposed. The case of weak anchoring on the particle surfaces is considered. We derive a general expression for the energy of the interaction between small spherical particles (with diameter much smaller than the cholesteric pitch) suspended in a cholesteric confined by two parallel planes. The resulting form of the interaction energy has a more complex spatial pattern and energy versus distance dependence than that in nematic colloids. The absence of translational symmetry related to helical periodicity and local nematic ordering in cholesteric liquid crystals manifest themselves in the complex nature of the interaction maps. PMID:24580248

Lev, B I; Fukuda, Jun-ichi; Tovkach, O M; Chernyshuk, S B

2014-01-01

86

Introduction to Crystal Structure: Bond Strength  

NSDL National Science Digital Library

This exercise is designed to familiarize students with some basic crystal structures The exercise helps students fully understand the nature and significance of ionic bonds and Pauling's second rule It also builds a bit on Pauling's first rule (radius ratio principle) It is one of several related activities, all of which are intended to help students understand the nature of ionic crystals

Perkins, Dexter

87

Compact Couplers for Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

Photonic crystal waveguides are promising candidates for laser-driven accelerator structures because of their ability to confine a speed-of-light mode in an all-dielectric structure. Because of the difference between the group velocity of the waveguide mode and the particle bunch velocity, fields must be coupled into the accelerating waveguide at frequent intervals. Therefore efficient, compact couplers are critical to overall accelerator efficiency. We present designs and simulations of high-efficiency coupling to the accelerating mode in a three-dimensional photonic crystal waveguide from a waveguide adjoining it at 90{sup o}. We discuss details of the computation and the resulting transmission. We include some background on the accelerator structure and photonic crystal-based optical acceleration in general.

Cowan, Benjamin; /Tech-X, Boulder; Lin, M.C.; /Tech-X, Boulder; Schwartz, Brian; /Tech-X, Boulder; Byer, Robert; /Stanford U., Phys. Dept.; McGuinness, Christopher; /Stanford U., Phys. Dept.; Colby, Eric; /SLAC; England, Robert; /SLAC; Noble, Robert; /SLAC; Spencer, James; /SLAC

2012-07-02

88

ICSD Web: the Inorganic Crystal Structure Database  

NSDL National Science Digital Library

This site contains a free demonstration version of the Inorganic Crystal Structure Database. This database contains a 3325 structure subset of the 76,480 inorganic structures as of 2004. The demo version can be queried and accessed by a web-interface which allows multiple methods of searching, and the resulting crystal structures can then be viewed online (with the CHIME plug-in) or downloaded for viewing with other visualization software. Also included on the site are updates of bug fixes, conditions of use and prices, tips for displaying the structures, a gallery of images, a flash movie, and instructions for installing a ICSD server.

Alan, Hewat

89

Role of Surface Area, Primary Particle Size, and Crystal Phase on Titanium Dioxide Nanoparticle Dispersion Properties  

PubMed Central

Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO2 samples, and one commercial Degussa TiO2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO2 isoelectric point was found to be dependent on particle size. As anatase TiO2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO2 nanoparticle IEP was found to be insensitive to particle crystal structure.

2011-01-01

90

Immobilization of semisoft colloidal crystals formed by polymer-brush-afforded hybrid particles.  

PubMed

An immobilization technique for semisoft colloidal crystals, which are ordered arrays of polymer-brush-afforded hybrid particles synthesized by surface-initiated living radical polymerization (SI-LRP), is reported. Silica particles were first grafted with well-defined block copolymers of poly(methyl methacrylate-co-hydroxyethyl methacrylate)-b-poly(methyl methacrylate), P(MMA-co-HEMA)-b-PMMA by SI-LRP, which gave a graft density as high as 0.7 chains/nm(2). The HEMA units reacted with 2-isocyanatoethyl methacrylate to introduce vinyl groups at the outer layer of the polymer-brush shell. The modified hybrid particles formed a colloidal crystal in a solution containing a small amount of free polymers with vinyl groups. The colloidal crystal was photoirradiated in the presence of a photoradical initiator to immobilize it through a cross-linking reaction among the vinyl groups. The structural analyses of the colloidal crystals before and after the photoirradiation were carried out by confocal laser scanning microscopy; the results showed that the periodic structures of the crystals were maintained after immobilization. PMID:24885119

Huang, Yun; Morinaga, Takashi; Tai, Yugo; Tsujii, Yoshinobu; Ohno, Kohji

2014-07-01

91

Formation of the structure of gold nanoclusters during crystallization  

NASA Astrophysics Data System (ADS)

The structure formation in gold nanoparticles 1.6-5.0 nm in diameter is studied by molecular dynamics simulation using a tight-binding potential. The simulation shows that the initial fcc phase in small Au clusters transforms into other structural modifications as temperature changes. As the cluster size increases, the transition temperature shifts toward the melting temperature of the cluster. The effect of various crystallization conditions on the formation of the internal structure of gold nanoclusters is studied in terms of microcanonical and canonical ensembles. The stability boundaries of various crystalline isomers are analyzed. The obtained dependences are compared with the corresponding data obtained for copper and nickel nanoparticles. The structure formation during crystallization is found to be characterized by a clear effect of the particle size on the stability of a certain isomer modification. Nickel and copper clusters are shown to exhibit common features in the formation of their structural properties, whereas gold clusters demonstrate much more complex behavior.

Gafner, Yu. Ya.; Goloven'ko, Zh. V.; Gafner, S. L.

2013-02-01

92

Formation of the structure of gold nanoclusters during crystallization  

SciTech Connect

The structure formation in gold nanoparticles 1.6-5.0 nm in diameter is studied by molecular dynamics simulation using a tight-binding potential. The simulation shows that the initial fcc phase in small Au clusters transforms into other structural modifications as temperature changes. As the cluster size increases, the transition temperature shifts toward the melting temperature of the cluster. The effect of various crystallization conditions on the formation of the internal structure of gold nanoclusters is studied in terms of microcanonical and canonical ensembles. The stability boundaries of various crystalline isomers are analyzed. The obtained dependences are compared with the corresponding data obtained for copper and nickel nanoparticles. The structure formation during crystallization is found to be characterized by a clear effect of the particle size on the stability of a certain isomer modification. Nickel and copper clusters are shown to exhibit common features in the formation of their structural properties, whereas gold clusters demonstrate much more complex behavior.

Gafner, Yu. Ya., E-mail: ygafner@khsu.ru; Goloven'ko, Zh. V.; Gafner, S. L. [Khakassian State University (Russian Federation)] [Khakassian State University (Russian Federation)

2013-02-15

93

Structures of cyano-biphenyl liquid crystals  

NASA Technical Reports Server (NTRS)

The structures of p-alkyl- p'-cyano- bicyclohexanes, C(n)H(2n+1) (C6H10)(C6H10) CN (n-CCH), and p-alkyl- p'-cyano- biphenyls, C(n)H(2n+1) (C6H4)(C6H4) CN (n-CBP), were studied. It is convenient to use an x ray image intensification device to search for symmetric x ray diffraction patterns. Despite the similarities in molecular structures of these compounds, very different crystal structures were found. For the smectic phase of 2CCH, the structure is close to rhombohedral with threefold symmetry. In contrast, the structure is close to hexagonal close-packed with two molecules per unit cell for 4CCH. Since intermolecular forces may be quite weak for these liquid crystals systems, it appears that crystal structures change considerably when the alkyl chain length is slightly altered. Different structures were also found in the crystalline phase of n-CBP for n = 6 to 9. For n = 7 to 9, the structures are close to monclinic. The structures are reminiscent of the smectic-A liquid crystal structures with the linear molecules slightly tilted away from the c-axis. In contrast, the structure is quite different for n = 6 with the molecules nearly perpendicular to the c-axis.

Chu, Yuan-Chao; Tsang, Tung; Rahimzadeh, E.; Yin, L.

1989-01-01

94

Tailoring of silicon crystals for relativistic-particle channeling  

NASA Astrophysics Data System (ADS)

In the last years, the research on channeling of relativistic particles has progressed considerably. A significant contribution has been provided by the development of techniques for quality improvement of the crystals. In particular, a planar etching of the surfaces of the silicon crystals proved useful to remove the superficial layer, which is a region very rich in imperfections, in turn leading to greater channeling efficiency. Micro-fabrication techniques, borrowed from silicon technology, may also be useful: micro-indentation and deposition of tensile or compressive layers onto silicon samples allow one to impart an even curvature to the samples. In this way, different topologies may be envisaged, such as a bent crystal for deflection of protons and ions or an undulator to force coherent oscillations of positrons and electrons.

Guidi, V.; Antonini, A.; Baricordi, S.; Logallo, F.; Malag, C.; Milan, E.; Ronzoni, A.; Stefancich, M.; Martinelli, G.; Vomiero, A.

2005-05-01

95

Crystal engineering: From design of crystal structures to fabrication of composite crystals  

NASA Astrophysics Data System (ADS)

This thesis reports how to design and control co-crystal structures from a kinetic point of view, and demonstrates the control of crystal morphology through understanding the kinetics and crystal structures. In chapter one, the in-situ atomic force microscope (AFM) was utilized to investigate how side chain on a glycine 2,5-diketopiperazine (GLYDKP) backbone can affect the assembly of GLYDKP, and showed that methyl groups cause larger energy barrier for crystallization. Because the introduction of functional group on the side chain could inevitably slow down the assembly process, a different approach should be considered. Chapter two shows that formic acid at low concentration can accelerate the assembly process without incorporating into the crystal structure. Because formic acid only crystallizes with GLYDKP in concentrated solution, these results prove that co-crystallization is a better method for incorporating functionalized molecules into a solid than direct modification of molecule itself. Chapter three focuses on the rational design of GLYDKP cocrystals by utilizing the observation found in chapter two. Structure of GLYDKP and formic acid crystal was analyzed to search possible guest molecules for cocrystal studies. This method successfully identified eleven molecules that crystallize with GLYDKP, and proved that crystal structure can be controlled through weak interactions such as C-HO=C and C-HCl interactions. Chapter four and chapter five explore the possibility of using self-assembled process to control morphology of crystals and surface epitaxy. Metal(II) bis(imidazolium 2,b-pyridinedicarboxylate) complexes were chosen and two morphologies associated with different metal ions were found: rhombohedral (Type I) and rectangular (Type II) crystals. In this study, an additive was found to change the morphology of crystal from type I to type II, and then methods of producing various shapes of composite crystals were also established. These self-assembled procedures of making composite crystals at micron scale are very promising, because the fabrication will only relies on solvent, additives, or combination of them without using sophisticated crystallizers.

Luo, Tzy-Jiun Mark

96

Structural properties of a C120 crystal  

NASA Astrophysics Data System (ADS)

With well-know models used for the study of orientational ordering transition in C60 crystal and with the crystallographic data from G-W. Wang and al.[Nature 387,583(1997)], this work aimed at characterizing a possible orientational ordering transition in C120 crystal. The C120 molecular structure used is based on MNDO optimization. With the same model, we have investigated the effect of the crystal surface on the ordering phase temperature. An orientational ordering phase transition was predicted to take place at 220K in the bulk and 175K at the surface.

Laforge, Christophe; Senet, Patrick; Lambin, Philippe

1998-08-01

97

Particle tracking from image sequences of complex plasma crystals  

SciTech Connect

In order to gather information about the physics of the complex plasma crystals from the experimental data, particles have to be tracked through a sequence of images. An application of the Kalman filter for that purpose is presented, using a one-dimensional approximation of the particle dynamics as a model for the filter. It is shown that Kalman filter is capable of tracking dust particles even with high levels of measurement noise. An inherent part of the Kalman filter, the innovation process, can be used to estimate values of the physical system parameters from the experimental data. The method is shown to be able to estimate the characteristic oscillation frequency from noisy data.

Hadziavdic, Vedad; Melandsoe, Frank; Hanssen, Alfred [Department of Physics and Technology, University of Tromsoe, NO-9037 Tromsoe (Norway)

2006-05-15

98

Particle beam and crabbing and deflecting structure  

DOEpatents

A new type of structure for the deflection and crabbing of particle bunches in particle accelerators comprising a number of parallel transverse electromagnetic (TEM)-resonant) lines operating in opposite phase from each other. Such a structure is significantly more compact than conventional crabbing cavities operating the transverse magnetic TM mode, thus allowing low frequency designs.

Delayen, Jean (Yorktown, VA)

2011-02-08

99

SINGLE CRYSTAL NIOBIUM TUBES FOR PARTICLE COLLIDERS ACCELERATOR CAVITIES  

SciTech Connect

The objective of this research project is to produce single crystal niobium (Nb) tubes for use as particle accelerator cavities for the Fermi laboratorys International Linear Collider project. Single crystal Nb tubes may have superior performance compared to a polycrystalline tubes because the absence of grain boundaries may permit the use of higher accelerating voltages. In addition, Nb tubes that are subjected to the high temperature, high vacuum crystallization process are very pure and well annealed. Any impurity with a significantly higher vapor pressure than Nb should be decreased by the relatively long exposure at high temperature to the high vacuum environment. After application of the single crystal process, the surfaces of the Nb tubes are bright and shiny, and the tube resembles an electro polished Nb tube. For these reasons, there is interest in single crystal Nb tubes and in a process that will produce single crystal tubes. To convert a polycrystalline niobium tube into a single crystal, the tube is heated to within a few hundred ?C of the melting temperature of niobium, which is 2477 ?C. RF heating is used to rapidly heat the tube in a narrow zone and after reaching the operating temperature, the hot zone is slowly passed along the length of the tube. For crystallization tests with Nb tubes, the traverse rate was in the range of 1-10 cm per hour. All the crystallization tests in this study were performed in a water-cooled, stainless steel chamber under a vacuum of 5 x10-6 torr or better. In earliest tests of the single crystal growth process, the Nb tubes had an OD of 1.9 cm and a wall thickness of 0.15 mm. With these relatively small Nb tubes, the single crystal process was always successful in producing single crystal tubes. In these early tests, the operating temperature was normally maintained at 2200 ?C, and the traverse rate was 5 cm per hour. In the next test series, the Nb tube size was increased to 3.8 cm OD and the wall thickness was increased 0.18 mm and eventually to 0.21 mm. Again, with these larger tubes, single crystal tubes were usually produced by the crystallization process. The power supply was generally operated at full output during these tests, and the traverse rate was 5 cm per hour. In a few tests, the traverse rate was increased to 10 cm per hour, and at the faster traverse rate, single crystal growth was not achieved. In these tests with a faster traverse rate, it was thought that the tube was not heated to a high enough temperature to achieve single crystal growth. In the next series of tests, the tube OD was unchanged at 3.8 cm and the wall thickness was increased to 0.30 mm. The increased wall thickness made it difficult to reach an operating temperature above 2,000 ?C, and although the single crystal process caused a large increase in the crystal grains, no single crystal tubes were produced. It was assumed that the operating temperature in these tests was not high enough to achieve single crystal growth. In FY 2012, a larger power supply was purchased and installed. With the new power supply, temperatures above the melting point of Nb were easily obtained regardless of the tube thickness. A series of crystallization tests was initiated to determine if indeed the operating temperature of the previous tests was too low to achieve single crystal growth. For these tests, the Nb tube OD remained at 3.8 cm and the wall thickness was 0.30 mm. The first test had an operating temperature of 2,000 ?C. and the operating temperature was increased by 50 ?C increments for each successive test. The final test was very near the Nb melting temperature, and indeed, the Nb tube eventually melted in the center of the tube. These tests showed that higher temperatures did yield larger grain sizes if the traverse rate was held constant at 5 cm per hour, but no single crystal tubes were produced even at the highest operating temperature. In addition, slowing the traverse rate to as low as 1 cm per hour did not yield a single crystal tube regardless of operating temperature. At this time, it

MURPHY, JAMES E [University of Nevada, Reno] [University of Nevada, Reno

2013-02-28

100

The crystal structure and crystal chemistry of fernandinite and corvusite  

USGS Publications Warehouse

Using type material of fernandinite from Minasragra, Peru, and corvusite from the Jack Claim, La Sal Mountains, Utah, the properties and crystal chemistry of these minerals have been determined by Rietveld analysis of the powder X-ray-diffraction patterns. The crystal structure of both species is isotypic with the V2O5 -type layer first found for ??-Ag0.68V2O5; it consists of chains of VO6 octahedra linked by opposite corners (parallel to b) condensed by edge-sharing to form the layer. The vanadium has average valence 4.8, and the resulting layer-charge is balanced by varying amounts of Ca, Na, and K in the interlayer region accompanied by labile water. This study has confirmed the validity of fernandinite as a unique mineral species. It is closely related to corvusite, from which it is distinguished on the basis of the dominant interlayer cation: Ca for fernandinite, Na for curvusite. -Authors

Evans, Jr, H. T.; Post, J. E.; Ross, D. R.; Nelen, J. A.

1994-01-01

101

Synthesis and crystal structure of maleopimaric acid.  

PubMed

The title compound maleopimaric acid was synthesized by a Diels-Alder reaction between maleic anhydride and Pinus elliottii engelm oleoresin at room temperature and it was characterized by single crystal X-ray diffraction. The white crystals crystallized in the orthorhombic system, space group P2(12121) with cell dimensions: a = 7.6960 (15) A, b = 11.851 (2) A, c = 24.577 (5) A, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, V = 2241.6(8) A(3), and R(1) = 0.0716, wR(2) = 0.1975. The two fused and unbridged cyclohexane rings form a trans ring junction with chair conformation with two methyl groups in axis positions, the anhydride ring is planar. Crystal water existed in the molecular and stabilized the structure through intermolecular hydrogen bonds. PMID:18626819

Rao, Xiaoping; Song, Zhanqian; Yao, Xujie; Han, Chunrui; Shang, Shibin

2008-01-01

102

Building Crystal Structure Ball Models Using Pre-Drilled Templates: Sheet Structures, Tridymite, and Cristobalite  

NSDL National Science Digital Library

This activity involves building crystal structure ball models in order to strengthen students' understanding of crystalline order, relative atomic size, atomic coordination, crystal chemistry, and crystal symmetry.

Hollocher, Kurt

103

Slip flow through colloidal crystals of varying particle diameter.  

PubMed

Slip flow of water through silica colloidal crystals was investigated experimentally for eight different particle diameters, which have hydraulic channel radii ranging from 15 to 800 nm. The particle surfaces were silylated to be low in energy, with a water contact angle of 83, as determined for a silylated flat surface. Flow rates through centimeter lengths of colloidal crystal were measured using a commercial liquid chromatograph for accurate comparisons of water and toluene flow rates using pressure gradients as high as 10(10) Pa/m. Toluene exhibited no-slip Hagen-Poiseuille flow for all hydraulic channel radii. For water, the slip flow enhancement as a function of hydraulic channel radius was described well by the expected slip flow correction for Hagen-Poiseuille flow, and the data revealed a constant slip length of 63 3 nm. A flow enhancement of 20 2 was observed for the smallest hydraulic channel radius of 15 nm. The amount of slip flow was found to be independent of shear rate over a range of fluid velocities from 0.7 to 5.8 mm/s. The results support the applicability of the slip flow correction for channel radii as small as 15 nm. The work demonstrates that packed beds of submicrometer particles enable slip flow to be employed for high-volume flow rates. PMID:23237590

Rogers, Benjamin J; Wirth, Mary J

2013-01-22

104

Slip Flow through Colloidal Crystals of Varying Particle Diameter  

PubMed Central

Slip flow of water through silica colloidal crystals was investigated experimentally for 8 different particle diameters, which have hydraulic channel radii ranging from 15 nm to 800 nm. The particle surfaces were silylated to be low in energy, with a water contact angle of 83, as determined for a silylated flat surface. Flow rates through centimeter lengths of colloidal crystal were measured using a commercial liquid chromatograph for accurate comparisons of water and toluene flow rates using pressure gradients as high as 1010 Pa/m. Toluene exhibited no-slip Hagen-Poiseuille flow for all hydraulic channel radii. For water, the slip flow enhancement as a function of hydraulic channel radius was described well by the expected slip flow correction for Hagen-Poiseuille flow, and the data revealed a constant slip length of 633 nm. A flow enhancement of 202 was observed for the smallest hydraulic channel radius of 15 nm. The amount of slip flow was found to be independent of shear rate over a range of fluid velocities from 0.7 to 5.8 mm/s. The results support the applicability of the slip flow correction for channel radii as small as 15 nm. The work demonstrates that packed beds of submicrometer particles enable slip flow to be employed for high volume flow rates.

Rogers, Benjamin J.; Wirth, Mary J.

2012-01-01

105

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

106

Particle Size Distribution and Magnetic Structure of Colloidal Ferrite Particles.  

NASA Astrophysics Data System (ADS)

A colloidal suspension of very fine magnetic particles is called a ferromagnetic liquid, or "ferrofluid". The colloidal particles are extremely small (~ 10 nm, or 100 angstrom) and are found to be very different in their magnetic properties from the bulk material. The size of such particles, defined by images observed by electron microscopy of a sample and called the physical size, usually ranges from 50 to 300 angstrom in diameter. Magnetic domain theory predicts that if the size of a particle is smaller than the critical value it will likely become single domain particle. The size of such a domain is called the magnetic moment size, or simply 'magnetic size', which is defined as the cube root of magnetic moment of a particle divided by 4pi/3 times the saturated magnetization of the bulk material (for a spherical particle). The first goal in this investigation is to determine the physical size and the magnetic size of particles in given samples. The second goal is to answer the question: if the magnetic size of a particle is smaller than the critical value, is the particle necessarily a single domain particle? If the particle magnetic size is smaller than its physical size, what is the magnetization distribution within the particle and the 'magnetic structure' of the particle?. The sample of colloidal particles used in this investigation is a water based Fe_3O _4 ferrofluid designated EMG805 made by Ferrofluidics Corp. In order to determine the dependence of various quantities on particle size, the sample was fractionationed using chromatographic techniques. The original sample was also diluted into different dilutions, which were used to obtain information about the effects of interparticle interactions. A colloid of CoFe_2O _4 suspended in kerosene obtained from G. E. Corp. was also investigated. Fractionation was not performed as kerosene is not compatible with the available gel. Its magnetic, physical and crystallite size distributions were also determined. Experiments employed electron microscopy, small angle neutron scattering with and without polarized neutrons, magnetization measurement and X-ray powder diffraction. It has been found that the independent domain model of colloidal particles should be replaced by a mixture model. (Abstract shortened with permission of author.).

Yu, Zhong Chen

107

Polymer Cholesteric Liquid Crystal Flakes for Particle Displays  

SciTech Connect

(B204)Polymer cholesteric liquid crystal (PCLC) flakes suspended in a moderately conductive host fluid reorient in the presence of an AC electric field within a specific frequency range, causing a dramatic change in flake reflectivity. PCLC flakes reflect light of a specific color and (circular) polarization, thereby eliminating the need for backlighting, color filters, and polarizers to attain unique optical effects. Reorientation can be seen in fields as low as several mili-volts per micron, and reorientation times are on the order of several hundred milliseconds, thereby approaching response times for both nematic liquid crystal displays and other particle displays. Applications for electro-optic devices, decorative commercial and consumer products, and displays, particularly electronic paper, are envisioned.

Kosc, T.Z.; Marshall, K.L.; Jacobs, S.D.

2003-07-15

108

Nanowire-Photonic Crystal Waveguide Hybrid Structure  

Microsoft Academic Search

We propose a class of nanocavities by combining nanowires and photonic crystal waveguides. Three-dimensional finite-difference time-domain techniques have been used to study the structures, and the simulation results show it is easy to achieve nanocavities with mode volumes less than 2(lambda\\/n)3 and Q values over 106 .

Chu-Cai Guo; Myung-Ki Kim; Se-Heon Kim; Yong-Hee Lee

2007-01-01

109

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

110

Nonviscous motion of a slow particle in a dust crystal under microgravity conditions  

NASA Astrophysics Data System (ADS)

Subsonic motion of a large particle moving through the bulk of a dust crystal formed by negatively charged small particles is investigated using the PK-3 Plus laboratory onboard the International Space Station. Tracing the particle trajectories shows that the large particle moves almost freely through the bulk of the plasma crystal, while dust particles move along characteristic ?-shaped pathways near the large particle. In the hydrodynamic approximation, we develop a theory of nonviscous dust particle motion about a large particle and calculate particle trajectories. Good agreement with experiment validates our approach.

Zhukhovitskii, D. I.; Fortov, V. E.; Molotkov, V. I.; Lipaev, A. M.; Naumkin, V. N.; Thomas, H. M.; Ivlev, A. V.; Schwabe, M.; Morfill, G. E.

2012-07-01

111

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

112

Crystal Structure of Human Enterovirus 71  

SciTech Connect

Enterovirus 71 is a picornavirus associated with fatal neurological illness in infants and young children. Here, we report the crystal structure of enterovirus 71 and show that, unlike in other enteroviruses, the 'pocket factor,' a small molecule that stabilizes the virus, is partly exposed on the floor of the 'canyon.' Thus, the structure of antiviral compounds may require a hydrophilic head group designed to interact with residues at the entrance of the pocket.

Plevka, Pavel; Perera, Rushika; Cardosa, Jane; Kuhn, Richard J.; Rossmann, Michael G. (Purdue); (Sentinext)

2013-04-08

113

The crystal structures of DNA Holliday junctions  

Microsoft Academic Search

Nearly 40 years ago, Holliday proposed a four-stranded complex or junction as the central intermediate in the general mechanism of genetic recombination. During the past two years, six single-crystal structures of such DNA junctions have been determined by three different research groups. These structures all essentially adopt the antiparallel stacked-X conformation, but can be classified into three distinct categories: RNADNA

P. Shing Ho; Brandt F Eichman

2001-01-01

114

Crystal and electronic structure of copper sulfides  

Microsoft Academic Search

Copper sulfides with different copper concentration exist in mineral form ranging from CuS to Cu2S. Among these, chalcosite Cu 2S, and digenite Cu1.8S were the subject of extensive research for decades mainly because of their use as the absorber in photovoltaic cells. Yet; their electronic structure is poorly understood because their crystal structure is complex. Most of the results published

Pavel Lukashev

2007-01-01

115

Crystal structure of a nonsymbiotic plant hemoglobin  

Microsoft Academic Search

Background: Nonsymbiotic hemoglobins (nsHbs) form a new class of plant proteins that is distinct genetically and structurally from leghemoglobins. They are found ubiquitously in plants and are expressed in low concentrations in a variety of tissues including roots and leaves. Their function involves a biochemical response to growth under limited O2 conditions.Results: The first X-ray crystal structure of a member

Mark S Hargrove; Eric Allen Brucker; Boguslaw Stec; Gautam Sarath; Ral Arredondo-Peter; Robert V Klucas; John S Olson; George N Phillips

2000-01-01

116

Computational studies of crystal structure and bonding.  

PubMed

The analysis, prediction, and control of crystal structures are frontier topics in present-day research in view of their importance for materials science, pharmaceutical sciences, and many other chemical processes. Computational crystallography is nowadays a branch of the chemical and physicals sciences dealing with the study of inner structure, intermolecular bonding, and cohesive energies in crystals. This chapter, mainly focused on organic compounds, first reviews the current methods for X-ray diffraction data treatment, and the new tools available both for quantitative statistical analysis of geometries of intermolecular contacts using crystallographic databases and for the comparison of crystal structures to detect similarities or differences. Quantum chemical methods for the evaluation of intermolecular energies are then reviewed in detail: atoms-in-molecules and other density-based methods, ab initio MO theory, perturbation theory methods, dispersion-supplemented DFT, semiempirical methods and, finally, entirely empirical atom-atom force fields. The superiority of analyses based on energy over analyses based on geometry is highlighted, with caveats on improvised definitions of some intermolecular chemical bonds that are in fact no more than fluxional approach preferences. A perspective is also given on the present status of computational methods for the prediction of crystal structures: in spite of great steps forward, some fundamental obstacles related to the kinetic-thermodynamic dilemma persist. Molecular dynamics and Monte Carlo methods for the simulation of crystal structures and of phase transitions are reviewed. These methods are still at a very speculative stage, but hold promise for substantial future developments. PMID:21506002

Gavezzotti, Angelo

2012-01-01

117

Structure of Cometary Dust Particles  

NASA Astrophysics Data System (ADS)

The recent encounter of Stardust with comet 81P/Wild 2 has provided highly spatially resolved data about dust particles in the coma. They show intense swarms and bursts of particles, suggest the existence of fragmenting low-density particles formed of higher density sub-micrometer components [1], and definitely confirm previous results (inferred from Giotto encounter with comet Grigg-Skjellerup [2] and remote light scattering observations [3]). The light scattering properties (mostly polarization, which does not depend upon disputable normalizations) of dust in cometary comae will be summarized, with emphasis on the spatial changes and on the wavelength and phase angle dependence. Experimental and numerical simulations are needed to translate these observed light scattering properties in terms of physical properties of the dust particles (e.g. size, morphology, albedo, porosity). New experimental simulations (with fluffy mixtures of sub-micron sized silica and carbon grains) and new numerical simulations (with fractal aggregates of homogeneous or core-mantled silicate and organic grains) will be presented. The results are in favor of highly porous particles built up (by ballistic-cluster-cluster agglomeration) from grains of interstellar origin. The perspectives offered by laboratory simulations with aggregates built under conditions representative of the early solar system on board the International Space Station will be presented, together with the perspectives offered by future experiments on board the Rosetta cometary probe. Supports from CNES and ESA are acknowledged [1] Tuzzolino et al., Science, 304, 1776, 2004, [2] N. McBride et al., Mon. Not. R. Astron. Soc., 289, p. 535-553, 1997, [3] Levasseur-Regourd and Hadamcik, J. Quant. Spectros. Radiat. Transfer, 79-80, 903-910, 2003.

Levasseur-Regourd, A. C.; Hadamcik, E.; Lasue, J.

2004-11-01

118

Crystal structure control in Au-free self-seeded InSb wire growth.  

PubMed

In this work we demonstrate experimentally the dependence of InSb crystal structure on the ratio of Sb to In atoms at the growth front. Epitaxial InSb wires are grown by a self-seeded particle assisted growth technique on several different III-V substrates. Detailed investigations of growth parameters and post-growth energy dispersive x-ray spectroscopy indicate that the seed particles initially consist of In and incorporate up to 20at.% Sb during growth. By applying this technique we demonstrate the formation of zinc-blende, 4H and wurtzite structure in the InSb wires (identified by transmission electron microscopy and synchrotron x-ray diffraction), and correlate this sequential change in crystal structure to the increasing Sb/In ratio at the particle-wire interface. The low ionicity of InSb and the large diameter of the wire structures studied in this work are entirely outside the parameters for which polytype formation is predicted by current models of particle seeded wire growth, suggesting that the V/III ratio at the interface determines crystal structure in a manner well beyond current understanding. These results therefore provide important insight into the relationship between the particle composition and the crystal structure, and demonstrate the potential to selectively tune the crystal structure in other III-V compound materials as well. PMID:21346304

Mandl, Bernhard; Dick, Kimberly A; Kriegner, Dominik; Keplinger, Mario; Bauer, Gnther; Stangl, Julian; Deppert, Knut

2011-04-01

119

Crystallization and preliminary X-ray diffraction analysis of recombinant hepatitis E virus-like particle  

PubMed Central

Hepatitis E virus (HEV) accounts for the majority of enterically transmitted hepatitis infections worldwide. Currently, there is no specific treatment for or vaccine against HEV. The major structural protein is derived from open reading frame (ORF) 2 of the viral genome. A potential oral vaccine is provided by the virus-like particles formed by a protein construct of partial ORF3 protein (residue 70123) fused to the N-terminus of the ORF2 protein (residues 112608). Single crystals obtained by the hanging-drop vapour-diffusion method at 293?K diffract X-rays to 8.3? resolution. The crystals belong to space group P212121, with unit-cell parameters a = 337, b = 343, c = 346?, ? = ? = ? = 90, and contain one particle per asymmetric unit.

Wang, Che-Yen; Miyazaki, Naoyuki; Yamashita, Tetsuo; Higashiura, Akifumi; Nakagawa, Atsushi; Li, Tian-Cheng; Takeda, Naokazu; Xing, Li; Hjalmarsson, Erik; Friberg, Claes; Liou, Der-Ming; Sung, Yen-Jen; Tsukihara, Tomitake; Matsuura, Yoshiharu; Miyamura, Tatsuo; Cheng, R. Holland

2008-01-01

120

Crystallization and preliminary X-ray diffraction analysis of recombinant hepatitis E virus-like particle.  

PubMed

Hepatitis E virus (HEV) accounts for the majority of enterically transmitted hepatitis infections worldwide. Currently, there is no specific treatment for or vaccine against HEV. The major structural protein is derived from open reading frame (ORF) 2 of the viral genome. A potential oral vaccine is provided by the virus-like particles formed by a protein construct of partial ORF3 protein (residue 70-123) fused to the N-terminus of the ORF2 protein (residues 112-608). Single crystals obtained by the hanging-drop vapour-diffusion method at 293 K diffract X-rays to 8.3 A resolution. The crystals belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 337, b = 343, c = 346 A, alpha = beta = gamma = 90 degrees , and contain one particle per asymmetric unit. PMID:18391436

Wang, Che-Yen; Miyazaki, Naoyuki; Yamashita, Tetsuo; Higashiura, Akifumi; Nakagawa, Atsushi; Li, Tian-Cheng; Takeda, Naokazu; Xing, Li; Hjalmarsson, Erik; Friberg, Claes; Liou, Der-Ming; Sung, Yen-Jen; Tsukihara, Tomitake; Matsuura, Yoshiharu; Miyamura, Tatsuo; Cheng, R Holland

2008-04-01

121

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

122

A tri-objective Particle Swarm Optimizer for designing line defect Photonic Crystal Waveguides  

NASA Astrophysics Data System (ADS)

This paper proposes a novel tri-objective approach for optimizing the structure of line defect Photonic Crystal Waveguides (PCW). A nature-inspired algorithm called Multi-Objective Particle Swarm Optimization (MOPSO) is employed as the optimizer. The three objectives considered are maximization of group index, maximization of bandwidth, and minimization of Group Velocity Dispersion (GVD). In addition, the optimization process is subject to five constraints in order to guarantee the feasibility of the structures obtained and prevent bad mixing in the final optimized structures. The results show that the tri-objective MOPSO is able to find 20 optimized structures for line defect PCW. The comparative study verifies the significant improvement of the optimized structures compared to current structures. Moreover, post analysis of the results reveals the importance of holes and their possible physical behaviours in line defect PCW. Finally, the implementation considerations and investigations show that the optimized structures are feasible for manufacturing with a resolution of 1 nm.

Mirjalili, Seyed Mohammad; Mirjalili, Seyedali; Lewis, Andrew; Abedi, Kambiz

2014-04-01

123

Crystal structure of columbite under high pressure  

NASA Astrophysics Data System (ADS)

The structural evolution of two columbites under pressure, one ferrocolumbite from Raode (Africa) and one manganocolumbite from Kragero (Norway), has been determined by single-crystal X-ray diffraction. Structural investigations at high pressure have been carried out on samples which were preliminarily annealed to attain the complete cation-ordered state. For each crystal, five complete datasets have been collected from room pressure up to ca. 7 GPa. Structure refinements converged to final discrepancy factors R ranging between 5.2 and 5.8% for both the crystals. Structure refinements of X-ray diffraction data at different pressures allowed characterisation of the mechanisms by which the columbite structure accommodates variations in pressure. A and B octahedral volumes in both samples decrease linearly as pressure increases, with a larger compression of the larger A site. The difference in polyhedral bulk moduli of the A sites for the two samples does not appear to relate directly to the octahedral sizes, the A site being more compressible in the Fe-rich sample than in the Mn-rich one. By far the most compressible direction in both the analysed samples is along b. The cations are in fact free to move along this direction, thus allowing the octahedral chains to slide over each other; this effect is particularly evident in the manganocolumbite sample which shows a steep shortening of interchain A-B distances along b.

Tarantino, Serena C.; Zema, Michele; Boffa Ballaran, Tiziana

2010-12-01

124

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

125

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

126

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

127

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

128

Quasi-periodic vertical structures of dusty plasma crystals  

NASA Astrophysics Data System (ADS)

A semi-analytical model is proposed for understanding the quasi-periodic vertical structures in a plasma crystal, which are shown to be sustained by the combined effects of an ion flow, gravity and horizontal bonds of the dust particles. These structures are the manifestations of large-amplitude standing wake fields that lead to strong vertical bonds for the formation of an oriented hexagonal lattice. The orientational symmetry breaking is caused by a gravity-induced thick sheath, which can preferentially accelerate a supersonic ion flow in the vertical direction. The electron and streaming ion densities and the electric potential are found to be all in phase in the plasma crystal, whereas the dust density is 180 degrees out of phase. With each dust layer playing a similar role as the plasma wall, the Bohm sheath criterion is also found to be satisfied. Crystal melting may also be qualitatively described by the present model when the horizontal bonds of the dust particles are sufficiently weakened.

Chiueh, Tzihong; Ming-Ting Kuo, D.

1999-04-01

129

The crystal structures of DNA Holliday junctions.  

PubMed

Nearly 40 years ago, Holliday proposed a four-stranded complex or junction as the central intermediate in the general mechanism of genetic recombination. During the past two years, six single-crystal structures of such DNA junctions have been determined by three different research groups. These structures all essentially adopt the antiparallel stacked-X conformation, but can be classified into three distinct categories: RNA-DNA junctions; ACC trinucleotide junctions; and drug-induced junctions. Together, these structures provide insight into how local and distant interactions help to define the detailed and general physical features of Holliday junctions at the atomic level. PMID:11406378

Ho, P S; Eichman, B F

2001-06-01

130

Crystal structure of ultrathin lamellar precipitates  

NASA Astrophysics Data System (ADS)

The crystal structure of lamellar precipitates formed in alloys 1213 (Al-Cu-Ag), V-1461 (Al-Cu-Li) and V-1469 (Al-Cu-Li-Ag) has been studied during age hardening. The experimental studies have been performed using transmission electron microscopy. The precipitates have {111} habits and thicknesses of several atomic planes. In diffraction patterns, these plates give a system of diffuse streaks. These ultrathin plates scatter electrons similar to two-dimensional crystal lattices. It is shown that thin plates of precipitates in alloys 1213, V-1461, and V-1469 give identical systems of diffuse streaks. The two-dimensional crystal lattices that give the system of these streaks have a hexagonal symmetry with the following orientation relationship: {ie481-1} and the lattice parameter a f = 0.495 nm (there is no lattice parameter c f for two-dimensional lattices). A sequence of the steps of reconstruction of the spatial structure of plane precipitates is proposed in terms of their thickness, structures of two-dimensional lattices, and type of precipitates (extrinsic or intrinsic). The influence of Ag on the structure of lamellar precipitates in the V-1469 alloy is discussed.

Alekseev, A. A.; Lukina, E. A.; Klochkova, Yu. Yu.

2013-06-01

131

Large-area optoelastic manipulation of colloidal particles in liquid crystals using photoresponsive molecular surface monolayers  

PubMed Central

Noncontact optical trapping and manipulation of micrometer- and nanometer-sized particles are typically achieved by use of forces and torques exerted by tightly focused high-intensity laser beams. Although they were instrumental for many scientific breakthroughs, these approaches find few technological applications mainly because of the small-area manipulation capabilities, the need for using high laser powers, limited application to anisotropic fluids and low-refractive-index particles, as well as complexity of implementation. To overcome these limitations, recent research efforts have been directed toward extending the scope of noncontact optical control through the use of optically-guided electrokinetic forces, vortex laser beams, plasmonics, and optofluidics. Here we demonstrate manipulation of colloidal particles and self-assembled structures in nematic liquid crystals by means of single-molecule-thick, light-controlled surface monolayers. Using polarized light of intensity from 1,000 to 100,000 times smaller than that in conventional optical tweezers, we rotate, translate, localize, and assemble spherical and complex-shaped particles of various sizes and compositions. By controlling boundary conditions through the monolayer, we manipulate the liquid crystal director field and the landscape of ensuing elastic forces exerted on colloids by the host medium. This permits the centimeter-scale, massively parallel manipulation of particles and complex colloidal structures that can be dynamically controlled by changing illumination or assembled into stationary stable configurations dictated by the memorized optoelastic potential landscape due to the last illumination pattern. We characterize the strength of optically guided elastic forces and discuss the potential uses of this noncontact manipulation in fabrication of novel optically- and electrically-tunable composites from liquid crystals and colloids.

Martinez, Angel; Mireles, Hector C.; Smalyukh, Ivan I.

2011-01-01

132

Crystal structure of ammonia monohydrate phase II.  

PubMed

We have determined the crystal structure of ammonia monohydrate phase II (AMH II) employing a combination of ab initio computational structure prediction and structure solution from neutron powder diffraction data using direct space methods. Neutron powder diffraction data were collected from perdeuterated AMH II using the D2B high-resolution diffractometer at the Institut Laue-Langevin. AMH II crystallizes in space-group Pbca with 16 formula units in a unit-cell of dimensions a = 18.8285(4) A, b = 6.9415(2) A, c = 6.8449(2) A, and V = 894.61(3) A3 [rho(calc)(deuterated) = 1187.56(4) kg m(-3)] at 502 MPa, 180 K. The structure is characterized by sheets of tessellated pentagons formed by orientationally ordered O-D...O, O-D...N, and N-D...O hydrogen-bonds; these sheets are stacked along the a-axis and connected by N-D...O hydrogen bonds alone. With the exception of the simple body-centered-cubic high-pressure phases of ammonia monohydrate and ammonia dihydrate, this is the first complex molecular structure of any of the high-pressure stoichiometric ammonia hydrates to be determined. The powder structure solution is complemented by an ab initio structure prediction using density functional theory which gives an almost identical hydrogen bonding network. PMID:19754191

Fortes, A Dominic; Suard, Emmanuelle; Leme-Cailleau, Marie-Hlne; Pickard, Christopher J; Needs, Richard J

2009-09-23

133

Epitaxial growth of a colloidal hard-sphere hcp crystal and the effects of epitaxial mismatch on crystal structure.  

PubMed

We demonstrate the epitaxial growth of hard-sphere hcp and double hcp crystals using a surface pattern that directly dictates the stacking sequence. A detailed three-dimensional analysis based on real-space measurements is performed on crystal structure as a function of template-crystal mismatch, which demonstrates the possibilities of colloidal epitaxy as a model system for studying the effects of a patterned substrate on crystal structure. Perfect template-induced hcp-crystal growth occurs at an isotropically deformed template. At deformed lattices we observe growth of a non-close-packed superstructure and of a perfect (100)-aligned fcc crystal. Small mismatches lead to increased out-of-plane displacements followed by a structural breakup in "crystal" grains where particle positions in successive layers are strictly periodic and "defect" grains where these positions are displaced with respect to each other. Large mismatches prevent crystallization in the surface layers. The volume fraction was found to vary drastically (up to about 20% ) as a function of template deformation. PMID:15244824

Hoogenboom, J P; van Langen-Suurling, A K; Romijn, J; van Blaaderen, A

2004-05-01

134

Phase behaviour of liquid-crystal monolayers of rod-like and plate-like particles.  

PubMed

Orientational and positional ordering properties of liquid crystal monolayers are examined by means of Fundamental-Measure Density Functional Theory. Particles forming the monolayer are modeled as hard parallelepipeds of square section of size ? and length L. Their shapes are controlled by the aspect ratio ? = L/? (>1 for prolate and <1 for oblate shapes). The particle centers of mass are restricted to a flat surface and three possible and mutually perpendicular orientations (in-plane and along the layer normal) of their uniaxial axes are allowed. We find that the structure of the monolayer depends strongly on particle shape and density. In the case of rod-like shapes, particles align along the layer normal in order to achieve the lowest possible occupied area per particle. This phase is a uniaxial nematic even at very low densities. In contrast, for plate-like particles, the lowest occupied area can be achieved by random in-plane ordering in the monolayer, i.e., planar nematic ordering takes place even at vanishing densities. It is found that the random in-plane ordering is not favorable at higher densities and the system undergoes an in-plane ordering transition forming a biaxial nematic phase or crystallizes. For certain values of the aspect ratio, the uniaxial-biaxial nematic phase transition is observed for both rod-like and plate-like shapes. The stability region of the biaxial nematic phase enhances with decreasing aspect ratios for plate-like particles, while the rod-like particles exhibit a reentrant phenomenon, i.e., a sequence of uniaxial-biaxial-uniaxial nematic ordering with increasing density if the aspect ratio is larger than 21.34. In addition to this, packing fraction inversion is observed with increasing surface pressure due to the alignment along the layers normal. At very high densities the nematic phase destabilizes to a nonuniform phases (columnar, smectic, or crystalline phases) for both shapes. PMID:24880324

Martnez-Ratn, Yuri; Varga, Szabolcs; Velasco, Enrique

2014-05-28

135

Observations on the crystal structures of lueshite  

NASA Astrophysics Data System (ADS)

Laboratory powder XRD patterns of the perovskite-group mineral lueshite from the type locality (Lueshe, Kivu, DRC) and pure NaNbO3 demonstrate that lueshite does not adopt the same space group ( Pbma; #57) as the synthetic compound. The crystal structures of lueshite (2 samples) from Lueshe, Mont Saint-Hilaire (Quebec, Canada) and Sallanlatvi (Kola, Russia) have been determined by single-crystal CCD X-ray diffraction. These room temperature X-ray data for all single-crystal samples can be satisfactorily refined in the orthorhombic space group Pbnm (#62). Cell dimensions, atomic coordinates of the atoms, bond lengths and octahedron tilt angles are given for four crystals. Conventional neutron diffraction patterns for Lueshe lueshite recorded over the temperature range 11-1,000 K confirm that lueshite does not adopt space group Pbma within these temperatures. Neutron diffraction indicates no phase changes on cooling from room temperature to 11 K. None of these neutron diffraction data give satisfactorily refinements but suggest that this is the space group Pbnm. Time-of-flight neutron diffraction patterns for Lueshe lueshite recorded from room temperature to 700 C demonstrate phase transitions above 550 C from Cmcm through P4 /mbm to above 650 C. Cell dimensions and atomic coordinates of the atoms are given for the three high-temperature phases. The room temperature to 400 C structures cannot be satisfactorily resolved, and it is suggested that the lueshite at room temperature consists of domains of pinned metastable phases with orthorhombic and/or monoclinic structures. However, the sequence of high-temperature phase transitions observed is similar to those determined for synthetic NaTaO3, suggesting that the equilibrated room temperature structure of lueshite is orthorhombic Pbnm.

Mitchell, Roger H.; Burns, Peter C.; Knight, Kevin S.; Howard, Christopher J.; Chakhmouradian, Anton R.

2014-06-01

136

The crystal structure of diphtheria toxin  

Microsoft Academic Search

The crystal structure of the diphtheria toxin dimer at 2.5 resolution reveals a Y-shaped molecule of three domains. The catalytic domain, called fragment A, is of the alpha + beta type. Fragment B actually consists of two domains. The transmembrane domain consists of nine alpha-helices, two pairs of which are unusually apolar and may participate in pH-triggered membrane insertion

Seunghyon Choe; Melanie J. Bennett; Gary Fujii; Paul M. G. Curmi; Katherine A. Kantardjieff; R. John Collier; David Eisenberg

1992-01-01

137

Vibrational Phonon Modes of Two-Dimensional Soft-Particle Colloidal Crystals with Hard-Particle Dopants  

NASA Astrophysics Data System (ADS)

We study the phonon modes of two-dimensional colloidal crystals consisting of random distributions of ``soft'' NIPA microgel particles and ``hard'' polystyrene particle dopants. Thus, the effective springs connecting nearest-neighbors are very stiff, very soft, or of intermediate stiffness, corresponding to three possible inter-particle potentials present in the crystals. We employ video microscopy to derive the phonon modes of corresponding ``shadow'' crystals with the same geometric configuration and interactions as the experimental colloidal system, but absent damping [1,2,3]. Long wavelength, Debye-like behavior is found at low frequencies, regardless of the number of hard polystyrene particles present in the crystal. Hard particles are primary participants at high frequencies, while soft spheres are primary participants at intermediate frequencies. [1] Chen et al., PRL 105, 025501 (2010). [2] Kaya et al., Science 329, 656 (2010). [3] Ghosh et al. PRL 104, 248305 (2010).

Gratale, Matthew; Yunker, Peter; Chen, Ke; Aptowicz, Kevin; Yodh, Arjun

2012-02-01

138

Crystal Structures of the ?2-Adrenergic Receptor  

NASA Astrophysics Data System (ADS)

G protein coupled receptors (GPCRs) constitute the largest family of membrane proteins in the human genome, and are responsible for the majority of signal transduction events involving hormones and neuro-transmitters across the cell membrane. GPCRs that bind to diffusible ligands have low natural abundance, are relatively unstable in detergents, and display basal G protein activation even in the absence of ligands. To overcome these problems two approaches were taken to obtain crystal structures of the ?2-adrenergic receptor (?2AR), a well-characterized GPCR that binds cate-cholamine hormones. The receptor was bound to the partial inverse agonist carazolol and co-crystallized with a Fab made to a three-dimensional epitope formed by the third intracellular loop (ICL3), or by replacement of ICL3 with T4 lysozyme. Small crystals were obtained in lipid bicelles (?2AR-Fab) or lipidic cubic phase (?2AR-T4 lysozyme), and diffraction data were obtained using microfocus technology. The structures provide insights into the basal activity of the receptor, the structural features that enable binding of diffusible ligands, and the coupling between ligand binding and G-protein activation.

Weis, William I.; Rosenbaum, Daniel M.; Rasmussen, Sren G. F.; Choi, Hee-Jung; Thian, Foon Sun; Kobilka, Tong Sun; Yao, Xiao-Jie; Day, Peter W.; Parnot, Charles; Fung, Juan J.; Ratnala, Venkata R. P.; Kobilka, Brian K.; Cherezov, Vadim; Hanson, Michael A.; Kuhn, Peter; Stevens, Raymond C.; Edwards, Patricia C.; Schertler, Gebhard F. X.; Burghammer, Manfred; Sanishvili, Ruslan; Fischetti, Robert F.; Masood, Asna; Rohrer, Daniel K.

139

Dynamic self-assembly and control of microfluidic particle crystals  

PubMed Central

Engineered two-phase microfluidic systems have recently shown promise for computation, encryption, and biological processing. For many of these systems, complex control of dispersed-phase frequency and switching is enabled by nonlinearities associated with interfacial stresses. Introducing nonlinearity associated with fluid inertia has recently been identified as an easy to implement strategy to control two-phase (solid-liquid) microscale flows. By taking advantage of inertial effects we demonstrate controllable self-assembling particle systems, uncover dynamics suggesting a unique mechanism of dynamic self-assembly, and establish a framework for engineering microfluidic structures with the possibility of spatial frequency filtering. Focusing on the dynamics of the particleparticle interactions reveals a mechanism for the dynamic self-assembly process; inertial lift forces and a parabolic flow field act together to stabilize interparticle spacings that otherwise would diverge to infinity due to viscous disturbance flows. The interplay of the repulsive viscous interaction and inertial lift also allow us to design and implement microfluidic structures that irreversibly change interparticle spacing, similar to a low-pass filter. Although often not considered at the microscale, nonlinearity due to inertia can provide a platform for high-throughput passive control of particle positions in all directions, which will be useful for applications in flow cytometry, tissue engineering, and metamaterial synthesis.

Lee, Wonhee; Amini, Hamed; Stone, Howard A.; Di Carlo, Dino

2010-01-01

140

Effect of polymer matrix on structure of Se particles formed in aqueous solutions during redox process  

SciTech Connect

Transmission electron microscopy and X-ray energy dispersive microanalysis study of the structure of particles formed during the reduction of Se(IV) to Se(0) in aqueous solutions in the presence of amphiphilic polymers showed the formation of Se/polymer composite particles. The content of carbon inside the particles can be as large as 80 at %. Polymers deeply influence the structure of particles. Depending on polymers, the composite particles may be unstable with time and they spontaneously evolve from Se/polymer composite particles to crystalline particles of monoclinic Se. For the stable ones, addition of bacterial cellulose Acetobacter xylinum gel-film can induce crystallization in the particles which expel the polymeric material. The Se/polymer composite particles and Se crystalline particles exhibit different sensitivity to electron irradiation and stiffness.

Suvorova, E. I., E-mail: suvorova@ns.crys.ras.ru; Klechkovskaya, V. V. [Shubnikov Institute of Crystallography of Russian Academy of Sciences (Russian Federation)

2010-12-15

141

Effect of polymer matrix on structure of Se particles formed in aqueous solutions during redox process  

NASA Astrophysics Data System (ADS)

Transmission electron microscopy and X-ray energy dispersive microanalysis study of the structure of particles formed during the reduction of Se(IV) to Se(0) in aqueous solutions in the presence of amphiphilic polymers showed the formation of Se/polymer composite particles. The content of carbon inside the particles can be as large as 80 at %. Polymers deeply influence the structure of particles. Depending on polymers, the composite particles may be unstable with time and they spontaneously evolve from Se/polymer composite particles to crystalline particles of monoclinic Se. For the stable ones, addition of bacterial cellulose Acetobacter xylinum gel-film can induce crystallization in the particles which expel the polymeric material. The Se/polymer composite particles and Se crystalline particles exhibit different sensitivity to electron irradiation and stiffness.

Suvorova, E. I.; Klechkovskaya, V. V.

2010-12-01

142

The crystal structure of Hiortdahlite II  

Microsoft Academic Search

Summary The crystal structure of Hiortdahlite II [triclinic P1,a = 11.012(6),b = 10.342(3),c = 7.359 (3) ,a = 89.92(2), = 109.21(5),y = 90.06(3)], was determined and refined using 1793 reflections toR1 = 0.069 and R2 = 0.066. The results of the structural study indicated that hiortdahlite II presents the modules which characterize the whole family of minerals related to

S. Merlino; N. Perchiazzi

1987-01-01

143

Fourier Analysis and Structure Determination--Part III: X-ray Crystal Structure Analysis.  

ERIC Educational Resources Information Center

Discussed is single crystal X-ray crystal structure analysis. A common link between the NMR imaging and the traditional X-ray crystal structure analysis is reported. Claims that comparisons aid in the understanding of both techniques. (MVL)

Chesick, John P.

1989-01-01

144

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.

145

Crystallization and Characterization of Galdieria sulphuraria RUBISCO in Two Crystal Forms: Structural Phase Transition Observed in P21 Crystal Form  

Microsoft Academic Search

We have isolated ribulose-1,5-bisphosphate-carboxylase\\/oxygenase (RUBISCO) from the red algae Galdieria Sulphuraria . The protein crystallized in two different crystal forms, the I422 crystal form being obtained from hi gh salt and the P2 1 crystal form being obtained from lower concentration of salt and PEG. We report here the crystallization, preliminary stages of structure determination and t he detection of

Michael Baranowski; Boguslaw Stec

2007-01-01

146

The structural instabilities in ferronematic based on liquid crystal with negative diamagnetic susceptibility anisotropy  

NASA Astrophysics Data System (ADS)

The studied ferronematic is a nematic liquid crystal (ZLI1695) of low negative anisotropy of the diamagnetic susceptibility (?a<0) doped with the magnetic particles Fe 3O 4. Structural instabilities are interpreted within Burylov and Raikher's theory. The high magnetic fields were oriented perpendicular (Freedericksz transition) or parallel to the initial director. Using capacitance measurements the Freedericksz threshold magnetic field of the ferronematic BFN, and the critical magnetic field Bmax, at which the initial parallel orientation between the director and the magnetic moment of magnetic particles breaks down, have been determined. The values of these quantities have been used to estimate the surface density of the anchoring energy W of liquid crystal molecules on the surface of the magnetic particles. The obtained values indicate a soft anchoring of the liquid crystal on the magnetic particles with a preferred parallel orientation of the magnetic moment of magnetic particles and the director.

Kop?ansk, Peter; Tomaovi?ov, Natlia; Konerack, Martina; Timko, Milan; Zviov, Vlasta; ber, Nndor; Fodor-Csorba, Katalin; Tth-Katona, Tibor; Vajda, Anik; Jadzyn, Jan; Beaugnon, Eric; Chaud, Xavier

2010-11-01

147

Inner structure of adsorbed ionic microgel particles.  

PubMed

Microgel particles of cross-linked poly(NIPAM-co-acrylic acid) with different acrylic acid contents are investigated in solution and in the adsorbed state. As a substrate, silicon with a poly(allylamine hydrochloride) (PAH) coating is used. The temperature dependence of the deswelling of the microgel particles was probed with atomic force microscopy (AFM). The inner structure of the adsorbed microgel particles was detected with grazing incidence small angle neutron scattering (GISANS). Small angle neutron scattering (SANS) on corresponding microgel suspensions was performed for comparison. Whereas the correlation length of the polymer network shows a divergence in the bulk samples, in the adsorbed microgel particles it remains unchanged over the entire temperature range. In addition, GISANS indicates changes in the particles along the surface normal. This suggests that the presence of a solid surface suppresses the divergence of internal fluctuations in the adsorbed microgels close to the volume phase transition. PMID:24920223

Wellert, Stefan; Hertle, Yvonne; Richter, Marcel; Medebach, Martin; Magerl, David; Wang, Weinan; Dem, Bruno; Radulescu, Aurel; Mller-Buschbaum, Peter; Hellweg, Thomas; von Klitzing, Regine

2014-06-24

148

Geometry of Crystal Structure with Defects. I. Euclidean Picture  

NASA Astrophysics Data System (ADS)

Continuously distributed defects of crystal structure are considered. The starting point is the Euclidean geometry of the ideal crystal lattice and the topological description of the distortion of the crystal structure. It is shown how the non-Euclidean geometry of distorted crystal structure, as well as the basic assumptions of the phenomenological plasticity theory concerning the deformation of a continuum, are related to those theories. A form for an affine connection describing continuously distributed dislocations is proposed.

Trzesowski, Andrzej

1987-04-01

149

The First Mammalian Aldehyde Oxidase Crystal Structure  

PubMed Central

Aldehyde oxidases (AOXs) are homodimeric proteins belonging to the xanthine oxidase family of molybdenum-containing enzymes. Each 150-kDa monomer contains a FAD redox cofactor, two spectroscopically distinct [2Fe-2S] clusters, and a molybdenum cofactor located within the protein active site. AOXs are characterized by broad range substrate specificity, oxidizing different aldehydes and aromatic N-heterocycles. Despite increasing recognition of its role in the metabolism of drugs and xenobiotics, the physiological function of the protein is still largely unknown. We have crystallized and solved the crystal structure of mouse liver aldehyde oxidase 3 to 2.9 ?. This is the first mammalian AOX whose structure has been solved. The structure provides important insights into the protein active center and further evidence on the catalytic differences characterizing AOX and xanthine oxidoreductase. The mouse liver aldehyde oxidase 3 three-dimensional structure combined with kinetic, mutagenesis data, molecular docking, and molecular dynamics studies make a decisive contribution to understand the molecular basis of its rather broad substrate specificity.

Coelho, Catarina; Mahro, Martin; Trincao, Jose; Carvalho, Alexandra T. P.; Ramos, Maria Joao; Terao, Mineko; Garattini, Enrico; Leimkuhler, Silke; Romao, Maria Joao

2012-01-01

150

Draft Crystal Structure of the Vault Shell at 9-? Resolution  

PubMed Central

Vaults are the largest known cytoplasmic ribonucleoprotein structures and may function in innate immunity. The vault shell self-assembles from 96 copies of major vault protein and encapsulates two other proteins and a small RNA. We crystallized rat liver vaults and several recombinant vaults, all among the largest non-icosahedral particles to have been crystallized. The best crystals thus far were formed from empty vaults built from a cysteine-tag construct of major vault protein (termed cpMVP vaults), diffracting to about 9- resolution. The asymmetric unit contains a half vault of molecular mass 4.65 MDa. X-ray phasing was initiated by molecular replacement, using density from cryo-electron microscopy (cryo-EM). Phases were improved by density modification, including concentric 24- and 48-fold rotational symmetry averaging. From this, the continuous cryo-EM electron density separated into domain-like blocks. A draft atomic model of cpMVP was fit to this improved density from 15 domain models. Three domains were adapted from a nuclear magnetic resonance substructure. Nine domain models originated in ab initio tertiary structure prediction. Three C-terminal domains were built by fitting poly-alanine to the electron density. Locations of loops in this model provide sites to test vault functions and to exploit vaults as nanocapsules.

Anderson, Daniel H; Kickhoefer, Valerie A; Sievers, Stuart A; Rome, Leonard H; Eisenberg, David

2007-01-01

151

Crystal structure of the dynein motor domain.  

PubMed

Dyneins are microtubule-based motor proteins that power ciliary beating, transport intracellular cargos, and help to construct the mitotic spindle. Evolved from ring-shaped hexameric AAA-family adenosine triphosphatases (ATPases), dynein's large size and complexity have posed challenges for understanding its structure and mechanism. Here, we present a 6 angstrom crystal structure of a functional dimer of two ~300-kilodalton motor domains of yeast cytoplasmic dynein. The structure reveals an unusual asymmetric arrangement of ATPase domains in the ring-shaped motor domain, the manner in which the mechanical element interacts with the ATPase ring, and an unexpected interaction between two coiled coils that create a base for the microtubule binding domain. The arrangement of these elements provides clues as to how adenosine triphosphate-driven conformational changes might be transmitted across the motor domain. PMID:21330489

Carter, Andrew P; Cho, Carol; Jin, Lan; Vale, Ronald D

2011-03-01

152

Continuous flow structuring of anisotropic biopolymer particles.  

PubMed

We review concepts and provide examples for the controlled structuring of biopolymer particles in hydrodynamic flow fields. The structuring concepts are grouped by the physical mechanisms governing drop deformation and shaping: (i) capillary structuring, (ii) shear and elongational structuring and (iii) confined flow methods. Non-spherical drops can be permanently structured if a solidification process, such as gelation or glass formation in the bulk or at the interface, is superimposed to the flow field. The physical and engineering properties of these processes critically depend on an elaborate balance between capillary phenomena, rheology, gel or glass formation kinetics, and bulk heat, mass and momentum transfer in multiphase fluids. This overview is motivated by the potential of non-spherical suspension particles, in particular those formed from 'natural' and 'sustainable' biopolymers, as rheology modifiers in food materials, consumer products, cosmetics or pharmaceuticals. PMID:19481192

Erni, Philipp; Cramer, Carsten; Marti, Irene; Windhab, Erich J; Fischer, Peter

2009-08-30

153

The Crystal Structure of Triuranyl Diphosphate Tetrahydrate  

Microsoft Academic Search

The hydrated neutral uranyl phosphate, (UO2)3(PO4)2(H2O)4, was synthesized by hydrothermal methods. Intensity data were collected using MoK? radiation and a CCD-based area detector. The crystal structure was solved by direct methods and refined by full-matrix least-squares techniques to agreement indices wR2=0.116 for all data, and R1=0.040, calculated for the 2764 unique observed reflections (?Fo??4?F). The compound is orthorhombic, space group

Andrew J. Locock; Peter C. Burns

2002-01-01

154

Crystal Structure of Marburg Virus VP24.  

PubMed

The VP24 protein plays an essential, albeit poorly understood role in the filovirus life cycle. VP24 is only 30% identical between Marburg virus and the ebolaviruses. Furthermore, VP24 from the ebolaviruses is immunosuppressive, while that of Marburg virus is not. The crystal structure of Marburg virus VP24, presented here, reveals that although the core is similar between the viral genera, Marburg VP24 is distinguished by a projecting ?-shelf and an alternate conformation of the N-terminal polypeptide. PMID:24574400

Zhang, Adrianna P P; Bornholdt, Zachary A; Abelson, Dafna M; Saphire, Erica Ollmann

2014-05-01

155

Elasticity of some mantle crystal structures. II.  

NASA Technical Reports Server (NTRS)

The single-crystal elastic constants are determined as a function of pressure and temperature for rutile structure germanium dioxide (GeO2). The data are qualitatively similar to those of rutile TiO2 measured by Manghnani (1969). The compressibility in the c direction is less than one-half that in the a direction, the pressure derivative of the shear constant is negative, and the pressure derivative of the bulk modulus has a relatively high value of about 6.2. According to an elastic strain energy theory, the negative shear modulus derivative implies that the kinetic barrier to diffusion decreases with increasing pressure.

Wang, H.; Simmons, G.

1973-01-01

156

A structural analysis of small vapor-deposited 'multiply twinned' gold particles  

NASA Technical Reports Server (NTRS)

High resolution selected zone dark field, Bragg reflection imaging and weak beam dark field techniques of transmission electron microscopy were used to determine the structure of small gold particles vapor deposited on NaCl substrates. Attention was focused on the analysis of those particles in the 50-150 A range that have pentagonal or hexagonal bright field profiles. These particles have been previously described as multiply twinned crystallites composed of face-centered cubic tetrahedra. The experimental evidence of the present studies can be interpreted on the assumption that the particle structure is a regular icosahedron or decahedron for the hexagonal or the pentagonal particles respectively. The icosahedron is a multiply twinned rhombohedral crystal and the decahedron is a multiply twinned body-centered orthorhombic crystal, each of which constitutes a slight distortion from the face-centered cubic structure.

Yang, C. Y.; Heinemann, K.; Yacaman, M. J.; Poppa, H.

1979-01-01

157

Crystal structure of the Baykovite mineral  

SciTech Connect

The X-ray crystal structure of baykovite, [Ca{sub 1.07}Mg{sub 0.62}Ti{sub 0.31}(Al{sub 0.55}Si{sub 0.45}){sub 2}O{sub 6}][Al(Mg{sub 0.77}Ti{sub 1.17}Al{sub 0.06}){sub 2}O{sub 4}] - a mineral of the enigmatite structural group - was determined: sp gr. P{bar 1}, a = 10.425(2), b = 10.799(2), c = 8.924(2) {Angstrom}, {alpha} = 105.98(2), {beta} = 96.05(2), {gamma} = 124.76(1){degrees}, V= 748.425, Z= 2, and R = 0.046. Baykovite is shown to be close to rhoenite varieties, which are characterized by their anomalous composition with a high content of titanium in two oxidation states: Ti{sup +3} and Ti{sup +4}. The structures of enigmatite-group compounds are described as disomatic structures formed from spinel and pyroxene moieties. A scheme of cation distribution over the equivalent positions in the enigmatite-group structures is proposed based on the assumption that individual fragments inherit the main features of the parent structures. 8 refs., 2 figs., 5 tabs.

Arakcheeva, A.V. [Baikov Institute of Metallurgy, Moscow (Russian Federation)

1995-03-01

158

Computational prediction of organic crystal structures and polymorphism  

NASA Astrophysics Data System (ADS)

The development of a robust manufacturing process for solid organic materials, such as pharmaceuticals, can be complicated when the molecules crystallize in different solid forms, including polymorphs. The diverse challenges to computational chemistry in computing the relative thermodynamic stability of different potential crystal structures for a range of organic molecules are outlined. Once the crystal structures which are thermodynamically feasible have been obtained, then comparison with the experimentally known polymorphs can provide interesting insights into crystallization behaviour. Although the computational prediction of polymorphism requires modelling the kinetic factors that can influence crystallization, the computational prediction of the crystal energy landscape is already a valuable complement to experimental searches for polymorphs.

Price, S. L.

159

Structural ordering and glass forming of soft spherical particles with harmonic repulsions.  

PubMed

We carry out dissipative particle dynamics simulations to investigate the dynamic process of phase transformation in the system with harmonic repulsion particles. Just below the melting point, the system undergoes liquid state, face-centered cubic crystallization, body-centered cubic crystallization, and reentrant melting phase transition upon compression, which is in good agreement with the phase diagram constructed previously via thermodynamic integration. However, when the temperature is decreased sufficiently, the system is trapped into an amorphous and frustrated glass state in the region of intermediate density, where the solid phase and crystal structure should be thermodynamically most stable. PMID:24712813

Sun, Bin; Sun, Zhiwei; Ouyang, Wenze; Xu, Shenghua

2014-04-01

160

Structural ordering and glass forming of soft spherical particles with harmonic repulsions  

NASA Astrophysics Data System (ADS)

We carry out dissipative particle dynamics simulations to investigate the dynamic process of phase transformation in the system with harmonic repulsion particles. Just below the melting point, the system undergoes liquid state, face-centered cubic crystallization, body-centered cubic crystallization, and reentrant melting phase transition upon compression, which is in good agreement with the phase diagram constructed previously via thermodynamic integration. However, when the temperature is decreased sufficiently, the system is trapped into an amorphous and frustrated glass state in the region of intermediate density, where the solid phase and crystal structure should be thermodynamically most stable.

Sun, Bin; Sun, Zhiwei; Ouyang, Wenze; Xu, Shenghua

2014-04-01

161

Structural and spectroscopic studies on calcium succinate single crystals  

NASA Astrophysics Data System (ADS)

Calcium succinate crystals have been grown by gel aided solution growth technique. The structure of the crystal is solved by single crystal XRD analysis. The Crystal structure of the title compound is triclinic having space group P(1) Powder XRD studies confirmed the good crystalline nature of the sample. The different functional groups and their assigned vibrations are discussed by FT-IR and FT Raman spectroscopic studies.

Binitha, M. P.; Pradyumnan, P. P.

2014-04-01

162

Track-Structure Simulations for Charged Particles  

PubMed Central

Monte-Carlo track-structure simulations provide a detailed and accurate picture of radiation transport of charged particles through condensed matter of biological interest. Liquid water serves as surrogate for soft tissue and is used in most Monte-Carlo track-structure codes. Basic theories of radiation transport and track-structure simulations are discussed and differences to condensed history codes highlighted. Interaction cross sections for electrons, protons, alpha particles, light and heavy ions are required input data for track-structure simulations. Different calculation methods, including the plane-wave Born approximation, the dielectric theory, and semi-empirical approaches are presented using liquid water as a target. Low-energy electron transport and light ion transport are discussed as areas of special interest.

Dingfelder, Michael

2013-01-01

163

Crystal structure of yeast Sco1.  

PubMed

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-A 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. PMID:16570183

Abajian, Carnie; Rosenzweig, Amy C

2006-06-01

164

Crystal structure of human nicotinamide riboside kinase.  

PubMed

Nicotinamide riboside kinase (NRK) has an important role in the biosynthesis of NAD(+) as well as the activation of tiazofurin and other NR analogs for anticancer therapy. NRK belongs to the deoxynucleoside kinase and nucleoside monophosphate (NMP) kinase superfamily, although the degree of sequence conservation is very low. We report here the crystal structures of human NRK1 in a binary complex with the reaction product nicotinamide mononucleotide (NMN) at 1.5 A resolution and in a ternary complex with ADP and tiazofurin at 2.7 A resolution. The active site is located in a groove between the central parallel beta sheet core and the LID and NMP-binding domains. The hydroxyl groups on the ribose of NR are recognized by Asp56 and Arg129, and Asp36 is the general base of the enzyme. Mutation of residues in the active site can abolish the catalytic activity of the enzyme, confirming the structural observations. PMID:17698003

Khan, Javed A; Xiang, Song; Tong, Liang

2007-08-01

165

Crystal Structure of Human Nicotinamide Riboside Kinase  

SciTech Connect

Nicotinamide riboside kinase (NRK) has an important role in the biosynthesis of NAD{sup +} as well as the activation of tiazofurin and other NR analogs for anticancer therapy. NRK belongs to the deoxynucleoside kinase and nucleoside monophosphate (NMP) kinase superfamily, although the degree of sequence conservation is very low. We report here the crystal structures of human NRK1 in a binary complex with the reaction product nicotinamide mononucleotide (NMN) at 1.5 {angstrom} resolution and in a ternary complex with ADP and tiazofurin at 2.7 {angstrom} resolution. The active site is located in a groove between the central parallel {beta} sheet core and the LID and NMP-binding domains. The hydroxyl groups on the ribose of NR are recognized by Asp56 and Arg129, and Asp36 is the general base of the enzyme. Mutation of residues in the active site can abolish the catalytic activity of the enzyme, confirming the structural observations.

Khan,J.; Xiang, S.; Tong, L.

2007-01-01

166

A mathematical theory of classical particle channeling in perfect crystals  

SciTech Connect

The problem is formulated as the motion of positively charged particles in a classical Hamiltonian system with potential representing the lattice of a perfect, static crystal. The phenomenon of channeling is defined as those motions with large total energy which avoid close encounters with nuclei, in other words as those motions which attain no more than a fixed small value of potential energy. For these motions, a nondimensionalization converts the physical Hamiltonian into nearly integrable form with small parameter equal to the ratio of maximum potential energy to total energy. It is shown that motions near KAM invariant tori are nonchanneling trajectories, in the sense that such trajectories quickly surpass the maximum allowed value of potential energy for channeling. Using techniques from Fourier analysis, functional analysis, and number theory, a purely mathematical result on the rate of ergodization of nonresonant geodesic flow on the flat Euolidean torus is derived and is then used to bound the maximum time until close encounters with nuclei for nonchanneling trajectories. Away from KAM tori and near low-order resonances, channeling motions are shown to exist and to be stable for times exponentially long in the small parameter. This is accomplished with techniques from the proof of Nekhoroshev's theorem on exponential estimates of stability times for nearly integrable Hamiltonian systems. The heuristically-derived continuum models from channeling physics are shown to coincide with the leading order terms in the resonant normal forms appearing in the proof of Nekhoroshev's theorem.

Dumas, H.S.

1988-01-01

167

Structural studies on orbivirus proteins and particles.  

PubMed

X-ray and electron microscopy analysis of Bluetongue virus (BTV), the type species of the Orbivirus genus within the family Reoviridae, have revealed various aspects of the organisation and structure of the proteins that form the viral capsid. Orbiviruses have a segmented dsRNA genome, which imposes constraints on their structure and life cycle. The atomic structure of the BTV core particle, the key viral component which transcribes the viral mRNA within the cell cytoplasm, revealed the architecture and assembly of the major core proteins VP7 and VP3. In addition, these studies formed the basis for a plausible model for the organisation of the dsRNA viral genome and the arrangement of the viral transcriptase complex (composed of the RNA-dependent RNA polymerase, the viral capping enzyme and RNA helicase) that resides within the core particle. Electron cryo-microscopy of the viral particle has shown how the two viral proteins VP2 and VP5 are arranged to form the outer capsid, with distinct packing arrangements between them and the core protein VP7. By comparison of the outer capsid proteins of orbiviruses with those of other nonturreted members of the family Reoviridae, we are able to propose a more detailed model of these structures and possible mechanisms for cell entry. Further structural results are also discussed including the atomic structure of an N-terminal domain of nonstructural protein NS2, a protein involved in virus genome assembly and morphogenesis. PMID:16909901

Stuart, D I; Grimes, J M

2006-01-01

168

Crystal Structure of Human Spermine Synthase  

PubMed Central

The crystal structures of two ternary complexes of human spermine synthase (EC 2.5.1.22), one with 5?-methylthioadenosine and spermidine and the other with 5?-methylthioadenosine and spermine, have been solved. They show that the enzyme is a dimer of two identical subunits. Each monomer has three domains: a C-terminal domain, which contains the active site and is similar in structure to spermidine synthase; a central domain made up of four ?-strands; and an N-terminal domain with remarkable structural similarity to S-adenosylmethionine decarboxylase, the enzyme that forms the aminopropyl donor substrate. Dimerization occurs mainly through interactions between the N-terminal domains. Deletion of the N-terminal domain led to a complete loss of spermine synthase activity, suggesting that dimerization may be required for activity. The structures provide an outline of the active site and a plausible model for catalysis. The active site is similar to those of spermidine synthases but has a larger substrate-binding pocket able to accommodate longer substrates. Two residues (Asp201 and Asp276) that are conserved in aminopropyltransferases appear to play a key part in the catalytic mechanism, and this role was supported by the results of site-directed mutagenesis. The spermine synthase5?-methylthioadenosine structure provides a plausible explanation for the potent inhibition of the reaction by this product and the stronger inhibition of spermine synthase compared with spermidine synthase. An analysis to trace possible evolutionary origins of spermine synthase is also described.

Wu, Hong; Min, Jinrong; Zeng, Hong; McCloskey, Diane E.; Ikeguchi, Yoshihiko; Loppnau, Peter; Michael, Anthony J.; Pegg, Anthony E.; Plotnikov, Alexander N.

2008-01-01

169

On the Crystallization of Small Silica Particles in Circumstellar Environments  

NASA Astrophysics Data System (ADS)

Infrared Space Observatory (ISO) observations have revealed the presence of crystalline silicate dust in circumstellar environments of some evolved stars (e.g. Waters et al. 1996, A&A 315, L361). Molster et al. (2001, A&A 366, 923), for instance, reported the discovery of a carbon-rich AGB star surrounded by a highly crystalline silicate dust shell as indicated by the high resolution ISO-SWS spectrum. However, it is still a matter of debate, whether the presence of crystalline dust is restricted only to certain phases of the stellar evolution (e.g. Kemper et al. 2000, A&A 369, 132). In order to understand the process, which leads to the formation of crystalline structures in circumstellar environments, the microphysical rearrangement of small silica particles is investigated by means of molecular dynamic calculations. The results indicate a dynamic coexistence of `amorphous'-like and symmetrical, `crystalline' structures. Such rearrangement processes depend on the energy transfer to the grain governed by the physical conditions of the astrophysical environment. Therefore, the effect of the degree of crystallinity on optical properties is additionally exemplified by Mie calculations. Some implications regarding the condensation and the mineralogy of silicate dust particles in the circumstellar environments of AGB and post-AGB objects are discussed.

John, M.; Mller, E.; Patzer, B.; Lttke, M.; Sedlmayr, E.

170

Morphology, crystal structure, phase transitions and blend compatibility of thermotropic liquid crystal terpolyesters  

Microsoft Academic Search

The morphology, crystal structure, phase transitions and blend compatibility of a series of semiflexible thermotropic liquid crystal terpolyesters (LCPs) were studied to understand their crystallization behavior and establish relationships between their microstructure and physical properties. Main characterization methods were electron microscopy and diffraction, and differential scanning calorimetry. The LCPs were composed of equimolar amounts of p-oxybenzoate, p-dioxyphenyl, and aliphatic segments,

Clara Lena Gonzalez-Costoso

1997-01-01

171

Cluster-Structured Adaptive Particle Swarm Optimization  

NASA Astrophysics Data System (ADS)

A new cluster-structured Particle Swarm Optimization (PSO) with interaction and diversity of parameters is proposed in this letter. After a swarm of PSO is divided into some sub-swarms (clusters), interactions between sub-swarms and diversity of PSO parameters are added so as to improve the search ability of PSO in the proposed cluster-structured PSO. The feasibility and the advantage of the proposed cluster-structured PSO are demonstrated through numerical simulations using two typical optimization test problems.

Yazawa, Kazuyuki; Motoki, Makoto; Ishigame, Atsushi; Yasuda, Keiichiro

172

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

2013-10-01

173

In situ proteolysis for protein crystallization and structure determination.  

PubMed

We tested the general applicability of in situ proteolysis to form protein crystals suitable for structure determination by adding a protease (chymotrypsin or trypsin) digestion step to crystallization trials of 55 bacterial and 14 human proteins that had proven recalcitrant to our best efforts at crystallization or structure determination. This is a work in progress; so far we determined structures of 9 bacterial proteins and the human aminoimidazole ribonucleotide synthetase (AIRS) domain. PMID:17982461

Dong, Aiping; Xu, Xiaohui; Edwards, Aled M; Chang, Changsoo; Chruszcz, Maksymilian; Cuff, Marianne; Cymborowski, Marcin; Di Leo, Rosa; Egorova, Olga; Evdokimova, Elena; Filippova, Ekaterina; Gu, Jun; Guthrie, Jennifer; Ignatchenko, Alexandr; Joachimiak, Andrzej; Klostermann, Natalie; Kim, Youngchang; Korniyenko, Yuri; Minor, Wladek; Que, Qiuni; Savchenko, Alexei; Skarina, Tatiana; Tan, Kemin; Yakunin, Alexander; Yee, Adelinda; Yim, Veronica; Zhang, Rongguang; Zheng, Hong; Akutsu, Masato; Arrowsmith, Cheryl; Avvakumov, George V; Bochkarev, Alexey; Dahlgren, Lars-Gran; Dhe-Paganon, Sirano; Dimov, Slav; Dombrovski, Ludmila; Finerty, Patrick; Flodin, Susanne; Flores, Alex; Grslund, Susanne; Hammerstrm, Martin; Herman, Maria Dolores; Hong, Bum-Soo; Hui, Raymond; Johansson, Ida; Liu, Yongson; Nilsson, Martina; Nedyalkova, Lyudmila; Nordlund, Pr; Nyman, Tomas; Min, Jinrong; Ouyang, Hui; Park, Hee-won; Qi, Chao; Rabeh, Wael; Shen, Limin; Shen, Yang; Sukumard, Deepthi; Tempel, Wolfram; Tong, Yufeng; Tresagues, Lionel; Vedadi, Masoud; Walker, John R; Weigelt, Johan; Welin, Martin; Wu, Hong; Xiao, Ting; Zeng, Hong; Zhu, Haizhong

2007-12-01

174

Nanoscale structure intercrystalline interactions in fat crystal networks  

Microsoft Academic Search

The functional attributes of fat-structured food products such as butter, margarine, chocolate, and ice cream are strongly influenced by the structure and physical properties of an underlying fat crystal network present in the material. Fat crystal networks are arranged in a hierarchical manner with characteristic and quantifiable nano and mesoscale structures. Recent studies carried out by our group have demonstrated

Nuria C. Acevedo; Fernanda Peyronel; Alejandro G. Marangoni

2011-01-01

175

Datamining Protein Structure Databanks for Crystallization Patterns of Proteins  

Microsoft Academic Search

A study of 345 protein structures selected among 1500 structures determined by Nuclear Magnetic Resonance (NMR) methods, revealed useful correlation between crystallization properties and several parameters for the studied proteins. NMR methods of structure determination do not require the growth of protein crystals, and hence allow comparison of properties of proteins that have or have not been the subject of

Homayoun Valafar; James H. Prestegard; Faramarz Valafar

2002-01-01

176

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

177

Disorder in the crystals of trans-4-fluoroazoxybenzene. Synthesis, spectral properties, crystal structures and DFT calculations  

Microsoft Academic Search

Two crystals of trans-4-fluoroazoxybenzene were obtained using two different methods. Oxidation of 4-fluoroazobenzene provided crystals of trans-4-fluoroazoxybenzene (I) consisting of two isomers; 51% alpha (ONN) and 49% beta (NNO) isomer. From trans-amino-azoxybenzenes in Schiemann reaction it were obtained crystals of trans-4-fluoro-NNO-azoxybenzenes (II, beta isomer) containing 4.7% of the alpha-isomer according to the HPLC analysis. The crystal structures of I and

Krzysztof Ejsmont; Andrzej A. Domanski; Janusz B. Kyziol; Jacek Zaleski

2005-01-01

178

Disorder in the crystals of trans-4-fluoroazoxybenzene. Synthesis, spectral properties, crystal structures and DFT calculations  

Microsoft Academic Search

Two crystals of trans-4-fluoroazoxybenzene were obtained using two different methods. Oxidation of 4-fluoroazobenzene provided crystals of trans-4-fluoroazoxybenzene (I) consisting of two isomers; 51% ? (ONN) and 49% ? (NNO) isomer. From trans-amino-azoxybenzenes in Schiemann reaction it were obtained crystals of trans-4-fluoro-NNO-azoxybenzenes (II, ? isomer) containing 4.7% of the ?-isomer according to the HPLC analysis. The crystal structures of I and

Krzysztof Ejsmont; Andrzej A. Doma?ski; Janusz B. Kyzio?; Jacek Zaleski

2005-01-01

179

ENERGETIC PARTICLE DIFFUSION IN STRUCTURED TURBULENCE  

SciTech Connect

In the full-orbit particle simulations of energetic particle transport in plasmas, the plasma turbulence is typically described as a homogeneous superposition of linear Fourier modes. The turbulence evolution is, however, typically a nonlinear process, and, particularly in the heliospheric context, the solar wind plasma is inhomogeneous due to the transient structures, as observed by remote and in situ measurements. In this work, we study the effects of the inhomogeneities on energetic particle transport by using spatially distributed, superposed turbulence envelopes. We find that the cross-field transport is significantly reduced, when compared to the results obtained with homogeneous turbulence. The reduction can reach an order of magnitude when the enveloping breaks the wave phase coherence along the mean magnetic field direction.

Laitinen, T.; Dalla, S.; Kelly, J. [Jeremiah Horrocks Institute, University of Central Lancashire, PR1 2HE Preston (United Kingdom)

2012-04-20

180

Caged particle motion in a crystallized complex plasma  

Microsoft Academic Search

A technique was developed for characterizing the particle interaction potential in a strongly-coupled dusty plasma. Also known as a complex plasma, in analogy with complex fluids which contain small particles of solid matter, a dusty plasma is an ionized gas with small solid particles that gain a large electric charge. Because of strong inter-particle Coulomb repulsion, and external confinement, the

R. A. Quinn; J. Goree

2000-01-01

181

Positron Annihilation and Electronic Lattice Structure in Insulator Crystals  

Microsoft Academic Search

The dimensions of the electronic lattice structure of the hexagonal quartz crystal and the fcc CaF2 crystal have been measured by resolving characteristic markings on the angular-correlation curves as observed for the two gamma quanta emitted in the annihilation of positrons with electrons in these crystals.

Werner Brandt; Grard Coussot; Robert Paulin

1969-01-01

182

Crystal structure of oligoacenes under high pressure  

SciTech Connect

We report crystal structures of anthracene, tetracene, and pentacene under pressure. Energy dispersive x-ray diffraction experiments up to 9 GPa were performed. Quasiharmonic lattice dynamics calculations are compared to the experimental results and show excellent agreement. The results are discussed with particular emphasis on the pressure dependence of the unit cell dimensions and the rearrangement of the molecules. The high pressure data also allow an analysis of the equation of state of these substances as a function of molecular length. We report the bulk modulus of tetracene and pentacene (B{sub 0}=9.0 and 9.6 GPa, respectively) and its pressure derivative (B{sub 0}{sup '}=7.9 and 6.4, respectively). We find that the unit-cell volume and bulk modulus at ambient pressure follow a linear relationship with the molecular length.

Oehzelt, M.; Aichholzer, A.; Resel, R.; Heimel, G.; Venuti, E.; Della Valle, R. G. [Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria); School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States); Dipartimento di Chimica Fisica e Inorganica and INSTM-UdR Bologna, Universita di Bologna, Viale Risorgimento 4, I-40136 Bologna (Italy)

2006-09-01

183

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

184

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

185

Efficient method for predicting crystal structures at finite temperature: variable box shape simulations.  

PubMed

We present an efficient and robust method based on Monte Carlo simulations for predicting crystal structures at finite temperature. We apply this method, which is surprisingly easy to implement, to a variety of systems, demonstrating its effectiveness for hard, attractive, and anisotropic interactions, binary mixtures, semi-long-range soft interactions, and truly long-range interactions where the truly long-range interactions are treated using Ewald sums. In the case of binary hard-sphere mixtures, star polymers, and binary Lennard-Jones mixtures, the crystal structures predicted by this algorithm are consistent with literature, providing confidence in the method. Finally, we predict new crystal structures for hard asymmetric dumbbell particles, bowl-like particles and hard oblate cylinders and present the phase diagram for the oblate cylinders based on full free energy calculations. PMID:19905838

Filion, Laura; Marechal, Matthieu; van Oorschot, Bas; Pelt, Danil; Smallenburg, Frank; Dijkstra, Marjolein

2009-10-30

186

Asymmetric free-standing 2-D photonic crystal films and their Janus particles.  

PubMed

We report the fabrication of large area, thin asymmetric free-standing two-dimensional (2-D) photonic crystals. We fabricate large area 2-D close-packed monodisperse polystyrene (PS) particle monolayers at air/water interfaces by using our needle tip flow method. We then layer tetraethyl orthosilicate (TEOS) onto the 2-D array to form a thin TEOS layer on the 2-D particle array on water. The hemispheres of PS particles located within the TEOS phase swell such that the adjacent particle hemispheres fuse. After TEOS evaporation, we obtain a free-standing connected photonic crystal film of hemispheres that efficiently diffracts light. The other side of the photonic crystal film consists of a fused connecting thin, flat sheet. Reactive ion etching (RIE) of the asymmetric films forms unusual, rough particle 2-D arrays and 2-D flower-like arrays. Mechanical abrasion allows one to separate the resulting novel Janus particles. PMID:23869422

Zhang, Jian-Tao; Chao, Xing; Asher, Sanford A

2013-07-31

187

Structure and properties of detonation soot particles  

SciTech Connect

The influence of TNT/RDX (50/50) detonation parameters and conservation conditions of detonation products during their expansion in hermetic detonation chamber on structure and phase composition of the detonation carbon has been considered. Systematic studies made it possible to establish the real structure of detonation carbon depending on experimental conditions. It has been shown that both during explosion in a chamber and thermal annealing in vacuum the nanoparticles of diamond have the tendency to transform not into graphite particles, as was assumed earlier, but into onionlike structures of fullerene series, composed of closed concentric carbon shells, the so-called carbon onions. The nanometer carbon particles have been obtained which comprise a diamond nucleus surrounded by a graphite-like mantle composed of quasi-spherical carbon shells which are the intermediate products of annealing of nanodiamond. The influence of initial sizes of the diamond particles and temperature on the annealing of diamond has been studied. {copyright} {ital 1996 American Institute of Physics.}

MalKOV, I.Y.; Titiov, V.M. [Lavrentyev Institute of Hydrodynamics, SD RAS, Novosibirsk, 630090 (Russia)

1996-05-01

188

The Refined Crystal Structure of Cowpea Mosaic Virus at 2.8 Resolution  

Microsoft Academic Search

Comoviruses are a group of plant viruses in the picornavirus superfamily. The type member of comoviruses, cowpea mosaic virus (CPMV), was crystallized in the cubic space group I23, a = 317 and the hexagonal space group P6122, a = 451 , c = 1038 . Structures of three closely similar nucleoprotein particles were determined in the cubic form. The

Tianwei Lin; Zhongguo Chen; Ramakrishnan Usha; Cynthia V. Stauffacher; Jin-Bi Dai; Tim Schmidt; John E. Johnson

1999-01-01

189

Polymer induced changes of the crystallization scenario in suspensions of hard sphere like microgel particles  

NASA Astrophysics Data System (ADS)

We investigated the crystallization scenario of highly cross linked polystyrene particles dispersed in the good solvent 2-ethylnaphtalene and their mixtures with non-adsorbing low molecular weight polysterene polymer using time resolved static light scattering. The samples were prepared slightly below the melting volume fraction of the polymer free system. For the polymer free samples, we obtained polycrystalline solids via crystallization scenario known from hard sphere suspensions with little competition of wall crystal formation. Addition of non-adsorbing low molecular weight polystyrene polymer leads to a considerably slowing down of the bulk crystallization kinetics. We observed a delay of the precursor to crystal conversion for the bulk crystallization while the induction times for the wall nucleation are reduced. The increased polymer concentration thus shifts the balance between the two competing crystallization pathways giving the possibility to tune the relative amount of wall based crystals.

Beyer, Richard; Iacopini, Sara; Palberg, Thomas; Schpe, Hans Joachim

2012-06-01

190

Liquid-crystal patterns of rectangular particles in a square nanocavity  

NASA Astrophysics Data System (ADS)

Using density-functional theory in the restricted-orientation approximation, we analyze the liquid-crystal patterns and phase behavior of a fluid of hard rectangular particles confined in a two-dimensional square nanocavity of side length H composed of hard inner walls. Patterning in the cavity is governed by surface-induced order as well as capillary and frustration effects and depends on the relative values of the particle aspect ratio ??L/?, with L the length and ? the width of the rectangles (L??), and cavity size H. Ordering may be very different from bulk (H??) behavior when H is a few times the particle length L (nanocavity). Bulk and confinement properties are obtained for the cases ?=1, 3, and 6. In bulk the isotropic phase is always stable at low packing fractions ?=L??0 (with ?0 the average density) and nematic, smectic, columnar, and crystal phases can be stabilized at higher ? depending on ?: For increasing ? the sequence of isotropic to columnar is obtained for ?=1 and 3, whereas for ?=6 we obtain isotropic to nematic to smectic (the crystal being unstable in all three cases for the density range explored). In the confined fluid surface-induced frustration leads to fourfold symmetry breaking in all phases (which become twofold symmetric). Since no director distortion can arise in our model by construction, frustration in the director orientation is relaxed by the creation of domain walls (where the director changes by 90?); this configuration is necessary to stabilize periodic phases. For ?=1 the crystal becomes stable with commensurate transitions taking place as H is varied. These transitions involve structures with different number of peaks in the local density. In the case ?=3 the commensurate transitions involve columnar phases with different number of columns. In the case ?=6 the high-density region of the phase diagram is dominated by commensurate transitions between smectic structures; at lower densities there is a symmetry-breaking isotropic to nematic transition exhibiting nonmonotonic behavior with cavity size. Apart from the present application in a confinement setup, our model could be used to explore the bulk region near close packing in order to elucidate the possible existence of disordered phases at close packing.

Gonzlez-Pinto, Miguel; Martnez-Ratn, Yuri; Velasco, Enrique

2013-09-01

191

Synthesis and textural evolution of alumina particles with mesoporous structures  

SciTech Connect

Alumina particles with mesostructures were synthesized through a chemical precipitation method by using different inorganic aluminum salts followed by a heterogeneous azeotropic distillation and calcination process. The obtained mesoporous {gamma}-alumina particles were systematically characterized by the X-ray diffraction, transmission electron microscopy and nitrogen adsorption-desorption measurement. Effects of the aluminum salt counter anion, pH value and the azeotropic distillation process on the structural or textural evolution of alumina particles were investigated. It is found that Cl{sup -} in the reaction solution can restrain the textural evolution of the resultant precipitates into two-dimensional crystallized pseudoboehmite lamellae during the heterogeneous azeotropic distillation, and then transformed into {gamma}-Al{sub 2}O{sub 3} particles with mesostructures after further calcination at 1173 K, whereas coexisting SO{sub 4}{sup 2-} can promote above morphology evolution and then transformed into {gamma}-Al{sub 2}O{sub 3} nanofibers after calcination at 1173 K. Moreover nearly all materials retain relatively high specific surface areas larger than 100 m{sup 2} g{sup -1} even after calcinations at 1173 K. - Graphical abstract: Co-existing Cl{sup -} is beneficial for the formation of {gamma}-alumina nanoparticles with mesostructures during the precipitation process. Interparticle and intraparticle mesopores can be derived from acidic solution and near neutral solution, respectively.

Liu Xun [College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072 (China); Peng Tianyou, E-mail: typeng@whu.edu.c [College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072 (China); Yao Jinchun; Lv Hongjin; Huang Cheng [College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072 (China)

2010-06-15

192

Enabling tablet product development of 5-fluorocytosine through integrated crystal and particle engineering.  

PubMed

The antifungal drug, 5-fluorocytosine (FC), is marketed as a capsule (250 or 500 mg strength) instead of the preferred tablet dosage form. Through systematic characterization of solid-state properties, including mechanical properties, we identify tabletability and poor physical stability of FC as the problems that likely have prevented the successful development of a FC tablet product. We then design an FC oxalate 2:1 salt (FCOXA21), based on established relationship between crystal structure and properties, to address these deficient properties. FCOXA21 is subsequently used to develop a direct compression tablet product using predictive and material-sparing powder characterization tools, that is, ring shear cell for powder flowability and compaction simulator for powder tabletability. The initial tablet formulation, which contains 84.5% (wt %) FCOXA21, exhibits excellent tabletability but inadequate flowability. We solve the powder flowability problem through controlling the particle size of FCOXA21. A batch of FCOXA21 tablets (500 mg FC equivalent dose) is then prepared. Finally, systematic evaluation on tablet weight variation, content uniformity, friability, and dissolution using standard methods confirms the commercial manufacturability of FC tablets. Through this work, we have demonstrated the potential of integrated crystal and particle engineering in expediting the development of tablet products of challenging drugs using the economical direct compression process. PMID:24515970

Perumalla, Sathyanarayana Reddy; Sun, Changquan Calvin

2014-04-01

193

Large scale structures in liquid crystal/clay colloids  

NASA Astrophysics Data System (ADS)

Suspensions of three different clays in K15, a thermotropic liquid crystal, have been studied by optical microscopy and small angle x-ray scattering. The three clays were claytone AF, a surface treated natural montmorillonite, laponite RD, a synthetic hectorite, and mined sepiolite. The claytone and laponite were sterically stabilized whereas sepiolite formed a relatively stable suspension in K15 without any surface treatment. Micrographs of the different suspensions revealed that all three suspensions contained large scale structures. The nature of these aggregates was investigated using small angle x-ray scattering. For the clays with sheet-like particles, claytone and laponite, the flocs contain a mixture of stacked and single platelets. The basal spacing in the stacks was independent of particle concentration in the suspension and the phase of the solvent. The number of platelets in the stack and their percentage in the suspension varied with concentration and the aspect ratio of the platelets. The lath shaped sepiolite did not show any tendency to organize into ordered structures. Here the aggregates are networks of randomly oriented single rods.

van Duijneveldt, Jeroen S.; Klein, Susanne; Leach, Edward; Pizzey, Claire; Richardson, Robert M.

2005-04-01

194

The interaction of colloidal particles with weak homeotropic anchoring energy in homogeneous nematic liquid crystal cells.  

PubMed

We have investigated interactions of colloidal particles with weak homeotropic anchoring energy in homogeneous nematic liquid crystal cells. Particle-wall and inter-particle interactions were observed experimentally and analyzed using typical dipole-dipole and quadrupole-quadrupole interactions, including substrate effects as the image charges. Both experimental results matched well with the calculated results for the effective particle radius reflecting the weak anchoring. The effective radius is reduced by the amount of extrapolation length than the actual particle radius. The effective radii of polyethylene micro-particles were reduced to a coefficient ? (0.78 ? ? ? 0.52) times the actual radius with anchoring coefficients in the range of 3.8 10(-6) to 1.4 10(-6) J m(-2). The anchoring energy of the particles is, therefore, a key component for explaining liquid crystal colloidal systems. PMID:24647470

Kim, Sung-Jo; Kim, Jong-Hyun

2014-04-21

195

Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE  

NASA Astrophysics Data System (ADS)

The first real-time, in situ, investigation of the chemical composition of the residue of cirrus ice crystals was performed during July 2002. This study was undertaken on a NASA WB-57F high-altitude research aircraft as part of CRYSTAL-FACE, a field campaign which sought to further our understanding of the relation of clouds, water vapor, and climate by characterizing, among other parameters, anvil cirrus formed about the Florida peninsula. A counter flow virtual impactor (CVI) was used to separate cirrus ice from the unactivated interstitial aerosol particles and evaporate condensed-phase water. Residual material, on a crystal-by-crystal basis, was subsequently analyzed using the NOAA Aeronomy Laboratory's Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Sampling was performed from 5 to 15 km altitude and from 12 to 28 north latitude within cirrus originating over land and ocean. Chemical composition measurements provided several important results. Sea salt was often incorporated into cirrus, consistent with homogeneous ice formation by aerosol particles from the marine boundary layer. Size measurements showed that large particles preferentially froze over smaller ones. Meteoritic material was found within ice crystals, indicative of a relation between stratospheric aerosol particles and tropospheric clouds. Mineral dust was the dominant residue observed in clouds formed during a dust transport event from the Sahara, consistent with a heterogeneous freezing mechanism. These results show that chemical composition and size are important determinants of which aerosol particles form cirrus ice crystals.

Cziczo, D. J.; Murphy, D. M.; Hudson, P. K.; Thomson, D. S.

2004-02-01

196

Use of Pom Pons to Illustrate Cubic Crystal Structures.  

ERIC Educational Resources Information Center

Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)

Cady, Susan G.

1997-01-01

197

Growth and crystal structure of the BeAl 6O 10 single crystals  

NASA Astrophysics Data System (ADS)

Unlike earlier published works we have established incongruent melting for the compound BeAl 6O 10 (BHA). The conditions of growing crystals from their own melt with a superstoichiometric excess of BeO, using the Czochralski method, have been determined. The nature of inclusions in grown BHA crystals is described. On the basis of X-ray crystal structure analysis and data of spectroscopic studies the symmetry and space group of BHA crystal structure have been refined, as well as uncertainties arising in their interpretation are discussed.

Alimpiev, A. I.; Merkulov, A. A.; Solntsev, V. P.; Tsvetkov, E. G.; Matrosov, V. N.; Pestryakov, E. V.

2002-04-01

198

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

199

Crystal Structure of a "Nonfoldable" Insulin  

PubMed Central

Protein evolution is constrained by folding efficiency (foldability) and the implicit threat of toxic misfolding. A model is provided by proinsulin, whose misfolding is associated with ?-cell dysfunction and diabetes mellitus. An insulin analogue containing a subtle core substitution (LeuA16 ? Val) is biologically active, and its crystal structure recapitulates that of the wild-type protein. As a seeming paradox, however, ValA16 blocks both insulin chain combination and the in vitro refolding of proinsulin. Disulfide pairing in mammalian cell culture is likewise inefficient, leading to misfolding, endoplasmic reticular stress, and proteosome-mediated degradation. ValA16 destabilizes the native state and so presumably perturbs a partial fold that directs initial disulfide pairing. Substitutions elsewhere in the core similarly destabilize the native state but, unlike ValA16, preserve folding efficiency. We propose that LeuA16 stabilizes nonlocal interactions between nascent ?-helices in the A- and B-domains to facilitate initial pairing of CysA20 and CysB19, thus surmounting their wide separation in sequence. Although ValA16 is likely to destabilize this proto-core, its structural effects are mitigated once folding is achieved. Classical studies of insulin chain combination in vitro have illuminated the impact of off-pathway reactions on the efficiency of native disulfide pairing. The capability of a polypeptide sequence to fold within the endoplasmic reticulum may likewise be influenced by kinetic or thermodynamic partitioning among on- and off-pathway disulfide intermediates. The properties of [ValA16]insulin and [ValA16]proinsulin demonstrate that essential contributions of conserved residues to folding may be inapparent once the native state is achieved.

Liu, Ming; Wan, Zhu-li; Chu, Ying-Chi; Aladdin, Hassan; Klaproth, Birgit; Choquette, Meredith; Hua, Qing-xin; Mackin, Robert B.; Rao, J. Sunil; De Meyts, Pierre; Katsoyannis, Panayotis G.; Arvan, Peter; Weiss, Michael A.

2009-01-01

200

Wear particles of single-crystal silicon carbide in vacuum  

NASA Technical Reports Server (NTRS)

Sliding friction experiments, conducted in vacuum with silicon carbide /000/ surface in contact with iron based binary alloys are described. Multiangular and spherical wear particles of silicon carbide are observed as a result of multipass sliding. The multiangular particles are produced by primary and secondary cracking of cleavage planes /000/, /10(-1)0/, and /11(-2)0/ under the Hertzian stress field or local inelastic deformation zone. The spherical particles may be produced by two mechanisms: (1) a penny shaped fracture along the circular stress trajectories under the local inelastic deformation zone, and (2) attrition of wear particles.

Miyoshi, K.; Buckley, D. H.

1980-01-01

201

Anisotropic domain structure of KTiOPO{sub 4} crystals  

SciTech Connect

Highly anisotropic ferroelectric domain structure is observed in KTiOPO{sub 4} (KTP) crystals reversed by low electric field. The applied Miller--Weinreich model for sidewise motion of domain walls indicates that this anisotropy results from the peculiarities of KTP crystal lattice. The domain nuclei of dozen nanometer size, imaged by atomic force microscopy method, demonstrate regular hexagonal forms. The orientation of domain walls of the elementary nuclei coincides with the orientation of the facets of macroscopic KTP crystals. The observed strong domain elongation along one principal crystal axis allows us to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters. {copyright} 2001 American Institute of Physics.

Urenski, P.; Lesnykh, M.; Rosenwaks, Y.; Rosenman, G.; Molotskii, M.

2001-08-15

202

Spectroscopic, thermal and structural studies on manganous malate crystals  

NASA Astrophysics Data System (ADS)

Prismatic crystals of manganous malate have been prepared by controlled ionic diffusion in hydrosilica gel. The structure was elucidated using single crystal X-ray diffraction. The crystals are orthorhombic with space group Pbca. Vibrations of the functional groups were identified by the FTIR spectrum. Thermogravimetric and differential thermal analyses (TG-DTA) were carried out to explore the thermal decomposition pattern of the material. Structural information derived from FTIR and TG-DTA studies is in conformity with the single crystal XRD data.

Thomas, J.; Lincy, A.; Mahalakshmi, V.; Saban, K. V.

2013-01-01

203

Coarsening of extracellularly biosynthesized cadmium crystal particles induced by thioacetamide in solution.  

PubMed

A novel coarsening route for extracellularly biosynthesized cadmium nanocrystals was investigated for the first time. In this process, the white rot fungus Coriolus versicolor was employed to take up cadmium ions and synthesize extracellular cadmium crystal particles. The coarsening of the particles was induced by thioacetamide under certain conditions. Scanning electron microscopy showed that the formed cadmium crystal particles were coarsened from about 100nm to 2-3?m. The corresponding energy-dispersive X-ray spectra confirmed the presence of proteins in the particles. The maximum removal efficiency of Cd(II) increased from 17% to 87%, and the corresponding sorption capacity of biomass increased from 4 to 24mgg(-1) with the completion of the coarsening process. The properties of the coarsened particles were also examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis of fungal mycelial pellets embedded with the coarsened particles confirmed the formation of cubic crystalline cadmium sulfide particles. The TEM results suggest that the coarsened particles were composed of clusters of several smaller particles. The changes in the functional groups on the biomass surface were studied through Fourier transform infrared spectroscopy. Based on the results above, a possible mechanism for the formation and coarsening of cadmium crystal particle is also discussed. PMID:21489598

Chen, Gui-Qiu; Zou, Zheng-Jun; Zeng, Guang-Ming; Yan, Ming; Fan, Jia-Qi; Chen, An-Wei; Yang, Fan; Zhang, Wen-Juan; Wang, Liang

2011-05-01

204

Synthesis, crystal structure and vibrational spectroscopy of a nonlinear optical crystal: L-arginine maleate dihydrate  

NASA Astrophysics Data System (ADS)

From the aqueous solution containing L-arginine and maleic acid (C 4H 4O 4), crystals of L-arginine maleate dihydrate were grown. The crystal structure was determined by single crystal X-ray diffraction. In the triclinic unit cell (space group P1), the molecule contains one L-arginine cation, one maleate anion and two water molecules. The crystal can be described as an inclusion complex from its layer structure. The basic unit in L-arginine layer is centrosymmetric and the maleate anions exist in coplanarity. Hydrogen bond plays a great role in the construction of the crystal and nonlinear optical properties. The crystal was characterized by infrared (IR) and Raman spectra. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder second harmonic generation (SHG) experiment was investigated to explore its NLO properties.

Sun, Z. H.; Yu, W. T.; Cheng, X. F.; Wang, X. Q.; Zhang, G. H.; Yu, G.; Fan, H. L.; Xu, D.

2008-02-01

205

Programmably structured plasma waveguide for development of table-top photon and particle sources  

NASA Astrophysics Data System (ADS)

Programmable fabrication of longitudinal spatial structures in an optically preformed plasma waveguide in a gas jet was achieved, by using laser machining with a liquid-crystal spatial light modulator as the pattern mask. Fabrication of periodic structures with a minimal period of 200 ?m and density-ramp structures with a minimal slope length of 100 ?m was attained. The technique is useful for the optimization of various laser-plasma-based photon and particle sources.

Hung, T.-S.; Ho, Y.-C.; Chang, Y.-L.; Wong, S.-J.; Chu, H.-H.; Lin, J.-Y.; Wang, J.; Chen, S.-Y.

2012-06-01

206

Programmably structured plasma waveguide for development of table-top photon and particle sources  

SciTech Connect

Programmable fabrication of longitudinal spatial structures in an optically preformed plasma waveguide in a gas jet was achieved, by using laser machining with a liquid-crystal spatial light modulator as the pattern mask. Fabrication of periodic structures with a minimal period of 200 {mu}m and density-ramp structures with a minimal slope length of 100 {mu}m was attained. The technique is useful for the optimization of various laser-plasma-based photon and particle sources.

Hung, T.-S.; Ho, Y.-C.; Wong, S.-J.; Chen, S.-Y. [Department of Physics, National Central University, Jhong-Li 320, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Chang, Y.-L. [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Department of Physics, National Chung Cheng University, Chia-Yi 621, Taiwan (China); Chu, H.-H. [Department of Physics, National Central University, Jhong-Li 320, Taiwan (China); Lin, J.-Y. [Department of Physics, National Chung Cheng University, Chia-Yi 621, Taiwan (China); Wang, J. [Department of Physics, National Central University, Jhong-Li 320, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Department of Physics, National Taiwan University, Taipei 106, Taiwan (China)

2012-06-15

207

A two-level, discrete-particle approach for simulating ordered colloidal structures  

SciTech Connect

The authors devise a new, two-level discrete-particle model to simulate ordered colloidal structures with vastly different scales. The authors use the molecular dynamics paradigm with a Lennard-Jones-type potential to define colloidal particle system and dissipative particle dynamics (DPD) to model the solvent. The initially mixed, disordered particle ensemble undergoes a phase transition. The authors observe the spontaneous creation of spherical or rod-like micelles and their crystallization in stable hexagonal or worm-like structures, respectively. The ordered arrays obtained by using the particle model are similar to the two-dimensional colloidal crystals observed in laboratory experiments. The micelle shape depends on the ratio between the scaling factors of the colloid-colloid to colloid-solvent particle interactions. The properties of the DPD solvent, such as the strongly variable viscosity and partial pressure, determine the speed of crystallization. The intriguing features of colloidal arrays and their exotic symmetries, which persist also over two-dimensional domains, can be simulated numerically by using the two-level discrete-particle approach and are illustrated here.

Dzwinel, W.; Yuen, D.A.

2000-05-01

208

Structure analysis of crystal surfaces by low energy ion beams  

NASA Astrophysics Data System (ADS)

The impact collision mode of low-energy ion scattering (ICISS) with backscattering close to- and at 180 has been used to determine the surface structure of single crystals in a direct and straightforward way. The intensity of backscattered primary particles (noble gas ions and neutrals NICISS, or alkali ions ALICISS) are measured as a function of the polar and azimuthai angles with respect to the surface, supplying a real space image of the atom positions. Energy discrimination by means of a time of flight or electrostatic deflection technique, respectively makes the method surface mass selective. On the basis of shadowing (and blocking) of the primary particles the location of atoms in the surface near region has been determined, the reconstruction of several fcc (110) metal surfaces have been found to be of the missing row type. The NICISS method has also clear benefits for surface crystallographic investigation of binary component systems. The NiAl(111) surface consists of two types of surfaces, either Ni or Al terminated, separated by single steps. From NICISS survey patterns the complete information of surface and near surface "bulk" crystallography may be displayed in a single gray scale plot. For 'the As/Si(001) -1 2 surface an As overlayer consisting of As dimers with an interatomic distance of 2.55 has been found.

Niehus, H.

1988-06-01

209

Monolithic photonic crystals created by partial coalescence of core-shell particles.  

PubMed

Colloidal crystals and their derivatives have been intensively studied and developed during the past two decades due to their unique photonic band gap properties. However, complex fabrication procedures and low mechanical stability severely limit their practical uses. Here, we report stable photonic structures created by using colloidal building blocks composed of an inorganic core and an organic shell. The core-shell particles are convectively assembled into an opal structure, which is then subjected to thermal annealing. During the heat treatment, the inorganic cores, which are insensitive to heat, retain their regular arrangement in a face-centered cubic lattice, while the organic shells are partially fused with their neighbors; this forms a monolithic structure with high mechanical stability. The interparticle distance and therefore stop band position are precisely controlled by the annealing time; the distance decreases and the stop band blue shifts during the annealing. The composite films can be further treated to give a high contrast in the refractive index. The inorganic cores are selectively removed from the composite by wet etching, thereby providing an organic film containing regular arrays of air cavities. The high refractive index contrast of the porous structure gives rise to pronounced structural colors and high reflectivity at the stop band position. PMID:24520901

Lee, Joon-Seok; Lim, Che Ho; Yang, Seung-Man; Kim, Shin-Hyun

2014-03-11

210

Free energy and structure of calcium carbonate nanoparticles during early stages of crystallization  

NASA Astrophysics Data System (ADS)

We introduce a metadynamics based scheme for computing the free energy of nanoparticles as a function of their crystalline order. The method is applied to small nanoparticles of the biomineral calcium carbonate to determine the preferred structure during early stages of crystal growth. For particles 2 nm in diameter, we establish a large energetic preference for amorphous particle morphologies. Particles with partial crystalline order consistent with vaterite are also observed with substantially lower probability. The absence of the stable calcite phase and stability of the amorphous state support recent conjectures that calcite formation starts via the deposition of amorphous calcium carbonate.

Quigley, D.; Rodger, P. M.

2008-06-01

211

Evolutionary Crystal Structure Prediction and Novel High-Pressure Phases  

Microsoft Academic Search

\\u000a Prediction of stable crystal structures at given pressure-temperature conditions, based only on the knowledge of the chemical\\u000a composition, is a central problem of condensed matter physics. This extremely challenging problem is often termed crystal\\u000a structure prediction problem, and recently developed evolutionary algorithm USPEX (Universal Structure Predictor: Evolutionary\\u000a Xtallography) made an important progress in solving it, enabling efficient and reliable prediction

Artem R. Oganov; Yanming Ma; Andriy O. Lyakhov; Mario Valle; Carlo Gatti

2010-01-01

212

Structural study of Langmuir liquid crystal monolayer  

NASA Astrophysics Data System (ADS)

A systematic study is reported on monolayer characteristics of Ferroelectric Liquid Crystal (FLC) at the air-water interface, using surface pressure and surface potential isotherms at different temperatures. Dipole moment is calculated by using Helmholtz equation. No significant influence from the sub phase temperature was detected because liquid crystal remains in Sm-C* phase in temperature range 5C-40C. FLC was deposited on smooth quartz substrate with good transfer ratio. AFM topography reveals uniform deposition of liquid crystals having well defined domains.

Kaur, Ramneek; Raina, K. K.

2014-04-01

213

Novel photonic crystal cavities and related structures.  

SciTech Connect

The key accomplishment of this project is to achieve a much more in-depth understanding of the thermal emission physics of metallic photonic crystal through theoretical modeling and experimental measurements. An improved transfer matrix technique was developed to enable incorporation of complex dielectric function. Together with microscopic theory describing emitter radiative and non-radiative relaxation dynamics, a non-equilibrium thermal emission model is developed. Finally, experimental methodology was developed to measure absolute emissivity of photonic crystal at high temperatures with accuracy of +/-2%. Accurate emissivity measurements allow us to validate the procedure to treat the effect of the photonic crystal substrate.

Luk, Ting Shan

2007-11-01

214

Monodisperse spherical mesoporous silica particles: fast synthesis procedure and fabrication of photonic-crystal films.  

PubMed

A procedure for the synthesis of monodisperse spherical mesoporous silica particles (MSMSPs) via the controlled coagulation of silica/surfactant clusters into spherical aggregates with mean diameters of 250-1500nm has been developed. The synthesis is fast (taking less than 1h) because identical clusters are simultaneously formed in the reaction mixture. The results of microscopic, x-ray diffraction, adsorption and optical measurements allowed us to conclude that the clusters are ?15nm in size and have hexagonally packed cylindrical pore channels. The channel diameters in MSMSPs obtained with cethyltrimethylammonium bromide and decyltrimethylammonium bromide as structure-directing agents were 3.10.15 and 2.30.12nm, respectively. The specific surface area and the pore volume of MSMSP were, depending on synthesis conditions, 480-1095m(2)g(-1) and 0.50-0.65cm(3)g(-1). The MSMSP were used to grow opal-like photonic-crystal films possessing a hierarchical macro-mesoporous structure, with pores within and between the particles. A selective filling of mesopore channels with glycerol, based on the difference between the capillary pressures in macro- and mesopores, was demonstrated. It is shown that this approach makes it possible to control the photonic bandgap position in mesoporous opal films by varying the degree of mesopore filling with glycerol. PMID:23518601

Trofimova, E Yu; Kurdyukov, D A; Yakovlev, S A; Kirilenko, D A; Kukushkina, Yu A; Nashchekin, A V; Sitnikova, A A; Yagovkina, M A; Golubev, V G

2013-04-19

215

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

216

Crystal and magnetic structure of the uranium digermanide UGe 2  

Microsoft Academic Search

The crystal structure of the uranium digermanide UGe2 was determined and refined from single crystal X-ray diffraction data to R = 0.040, Rw = 0.052. UGe2 crystallizes with the orthorhombic ZrGa2 type (Cmcm) instead of the ZrSi2 type (Cmcm) as was previously assumed on the basis of rather old and unreliable results. Our magnetic study of a polycrystalline are melted

P. Boulet; A. Daoudi; M. Potel; H. Nol; G. M. Gross; G. Andr; F. Boure

1997-01-01

217

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

218

III-Nitride LEDs with photonic crystal structures.  

SciTech Connect

Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a {approx} 270-340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED's Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.

Wendt, Joel Robert; Sigalas, M. M. (Agilent Technologies, Palo Alto, CA); Epler, J. E. (Lumileds Lighting, San Jose, CA); Krames, M. R. (Lumileds Lighting, San Jose, CA); Li, D. (University of New Mexico, Albuquerque NM); Brueck, Stephen R. J. (University of New Mexico, Albuquerque NM); Shagam, M. (Boston University, Boston, MA); Gardner, N. F. (Lumileds Lighting, San Jose, CA); Wierer, Jonathan J. (Lumileds Lighting, San Jose, CA)

2005-02-01

219

III-nitride LEDs with photonic crystal structures  

NASA Astrophysics Data System (ADS)

Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a ~ 270 - 340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED"s Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.

Wierer, Jonathan J.; Krames, Michael R.; Epler, John E.; Gardner, Nathan F.; Wendt, Joel R.; Sigalas, Mihail M.; Brueck, Steven R. J.; Li, Dong; Shagam, Michael

2005-03-01

220

Crystal structure and characterization of pyrroloquinoline quinone disodium trihydrate  

PubMed Central

Background Pyrroloquinoline quinone (PQQ), a tricarboxylic acid, has attracted attention as a growth factor, and its application to supplements and cosmetics is underway. The product used for these purposes is a water-soluble salt of PQQ disodium. Although in the past, PQQ disodiumpentahydrates with a high water concentration were used, currently, low hydration crystals of PQQ disodiumpentahydrates are preferred. Results We prepared a crystal of PQQ disodium trihydrate in a solution of ethanol and water, studied its structure, and analyzed its properties. In the prepared crystal, the sodium atom interacted with the oxygen atom of two carboxylic acids as well as two quinones of the PQQ disodium trihydrate. In addition, the hydration water of the prepared crystal was less than that of the conventional PQQ disodium crystal. From the results of this study, it was found that the color and the near-infrared (NIR) spectrum of the prepared crystal changed depending on the water content in the dried samples. Conclusions The water content in the dried samples was restored to that in the trihydrate crystal by placing the samples in a humid environment. In addition, the results of X-ray diffraction (XRD) and X-ray diffraction-differential calorimetry (XRD-DSC) analyses show that the phase of the trihydrate crystal changed when the crystallization water was eliminated. The dried crystal has two crystalline forms that are restored to the original trihydrate crystals in 20% relative humidity (RH). This crystalline (PQQ disodium trihydrate) is stable under normal environment.

2012-01-01

221

Crystal Structure of Human Plasma Platelet-activating Factor Acetylhydrolase  

PubMed Central

Human plasma platelet-activating factor (PAF) acetylhydrolase functions by reducing PAF levels as a general anti-inflammatory scavenger and is linked to anaphylactic shock, asthma, and allergic reactions. The enzyme has also been implicated in hydrolytic activities of other pro-inflammatory agents, such as sn-2 oxidatively fragmented phospholipids. This plasma enzyme is tightly bound to low and high density lipoprotein particles and is also referred to as lipoprotein-associated phospholipase A2. The crystal structure of this enzyme has been solved from x-ray diffraction data collected to a resolution of 1.5. It has a classic lipase ?/?-hydrolase fold, and it contains a catalytic triad of Ser273, His351, and Asp296. Two clusters of hydrophobic residues define the probable interface-binding region, and a prediction is given of how the enzyme is bound to lipoproteins. Additionally, an acidic patch of 10 carboxylate residues and a neighboring basic patch of three residues are suggested to play a role in high density lipoprotein/low density lipoprotein partitioning. A crystal structure is also presented of PAF acetylhydrolase reacted with the organophosphate compound paraoxon via its active site Ser273. The resulting diethyl phosphoryl complex was used to model the tetrahedral intermediate of the substrate PAF to the active site. The model of interface binding begins to explain the known specificity of lipoprotein-bound substrates and how the active site can be both close to the hydrophobic-hydrophilic interface and at the same time be accessible to the aqueous phase.

Samanta, Uttamkumar; Bahnson, Brian J.

2008-01-01

222

Transport of particles by a thermally induced gradient of the order parameter in nematic liquid crystals.  

PubMed

We demonstrate manipulation and transport of microparticles and even fluorescent molecules by the thermally induced gradient of the order parameter in the nematic liquid crystal. We use IR light absorption of the tightly focused beam of laser tweezers to heat locally a thin layer of the nematic liquid crystal by several degrees. This creates a spatial gradient of temperature of the nematic liquid crystal over separations of several tens of micrometers. We show that a dipolar colloidal particle is attracted into the hot spot of the laser tweezers. The depth of the trapping potential scales linearly with particle radius, indicating that the trapping mechanism is due to elastic self-energy of the distorted nematic liquid crystal around the particle and softening of the elasticity with increased temperature of the liquid crystal. We also demonstrate that this thermal trapping mechanism is efficient down to the nanoscale, as fluorescent molecules are also transported into hotter regions of the liquid crystal. This effect is absent in the isotropic phase, which calls into question particle transport due to the Soret effect. PMID:23848699

karabot, M; Lokar, ; Muevi?, I

2013-06-01

223

Growth and Structure of Single-Crystal Films.  

National Technical Information Service (NTIS)

This research project was concerned with basic research on the growth and structure of single-crystal films of metals obtained by evaporation in ultra-high vaccum onto two types of substrates: mica and metal single-crystal films. The films were prepared i...

E. Grunbaum

1968-01-01

224

The importance of crystal structure to the water treatment industry  

SciTech Connect

The intention of this paper is to provide additional insights into the area of crystal structure, dispersion and crystal modification, particularly for the calcium salts of carbonate and sulphate. The application of the discussed approaches to real life systems will go a long way to ensure scale-free heat transfer equipment.

Caplan, G.

1986-01-01

225

Electronic structure of Cr{sup 3+} in forsterite crystals  

SciTech Connect

Specific properties of silicate crystals that make them promising in applications as active media for IR tunable lasers are discussed. The energy level structure of Cr{sup 3+} ions in a forsterite crystal field is analyzed. 4 refs., 3 tabs.

Avanesov, A.G.; Zhorin, V.V.; Pisarenko, V.F. [Kuban` State Univ., Krasnodar (Russian Federation)

1994-11-01

226

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

227

Optically Generated Reconfigurable Photonic Structures of Elastic Quasiparticles in Frustrated Cholesteric Liquid Crystals  

SciTech Connect

We describe laser-induced two-dimensional periodic photonic structures formed by localized particle-like excitations in an untwisted confined cholesteric liquid crystal. The individual particle-like excitations (dubbed 'Torons') contain three-dimensional twist of the liquid crystal director matched to the uniform background director field by topological point defects. Using both single-beam-steering and holographic pattern generation approaches, the periodic crystal lattices are tailored by tuning their periodicity, reorienting their crystallographic axes, and introducing defects. Moreover, these lattices can be dynamically reconfigurable: generated, modified, erased and then recreated, depending on the needs of a particular photonic application. This robust control is performed by tightly focused laser beams of power 10-100 mW and by low-frequency electric fields at voltages {approx}10 V applied to the transparent electrodes.

Smalyukh,, I. I.; Kaputa, D.; Kachynski, A. V.; Kuzmin, A. N.; Ackerman, P. J.; Twombly, C. W.; Lee, T.; Trivedi, R. P.; Prasad, P. N.

2012-03-26

228

Optically generated reconfigurable photonic structures of elastic quasiparticles in frustrated cholesteric liquid crystals.  

PubMed

We describe laser-induced two-dimensional periodic photonic structures formed by localized particle-like excitations in an untwisted confined cholesteric liquid crystal. The individual particle-like excitations (dubbed "Torons") contain three-dimensional twist of the liquid crystal director matched to the uniform background director field by topological point defects. Using both single-beam-steering and holographic pattern generation approaches, the periodic crystal lattices are tailored by tuning their periodicity, reorienting their crystallographic axes, and introducing defects. Moreover, these lattices can be dynamically reconfigurable: generated, modified, erased and then recreated, depending on the needs of a particular photonic application. This robust control is performed by tightly focused laser beams of power 10-100 mW and by low-frequency electric fields at voltages ~10 V applied to the transparent electrodes. PMID:22453364

Smalyukh, Ivan I; Kaputa, Daniel; Kachynski, Aliaksandr V; Kuzmin, Andrey N; Ackerman, Paul J; Twombly, Christopher W; Lee, Taewoo; Trivedi, Rahul P; Prasad, Paras N

2012-03-26

229

'Crystal Collimator' Measurement of CESR particle-beam Source Size  

SciTech Connect

We have measured electron and positron beam source size at CHESS when the Cornell Electron Storage Ring (CESR) is run dedicated for the production of synchrotron radiation. Horizontal source size at several beamlines is expected to shrink by a factor of two but synchrotron (visible) light measurements only provide the vertical size. Therefore a 'crystal collimator' using two Bragg reflection in dispersive (+,+) orientation has been built to image the horizontal (vertical) source by passing x-rays parallel to within 5 microradians to an imaging screen and camera. With the 'crystal collimator' we observe rms sizes of 1.2 mm horizontal by 0.28 mm vertical, in good agreement with the 1.27 mm size calculated from lattice functions, and 0.26 mm observed using a synchrotron light interferometer.

Finkelstein, K.D.; Bazarov, Ivan; White, Jeffrey; Revesz, Peter [Cornell High Energy Synchrotron Source (CHESS), Wilson Laboratory, Cornell University, Ithaca, New York 14853 (United States)

2004-05-12

230

Ultrasound-initiated structural transformations in liquid crystals (A review)  

Microsoft Academic Search

The results of the studies of structural transformations in liquid crystal layers with homeotropic and planar macrostructures\\u000a in the fields of longitudinal, surface, and shear ultrasonic waves are systematized and generalized.

O. A. Kapustina

2008-01-01

231

Crystal Structure and Molecular Motion of Solid Carbon Disulfide.  

National Technical Information Service (NTIS)

The crystal structure of CS2 was determined at two temperatures from intensity data measured with a proportional counter and a modified Weissenberg apparatus. The orthorhombic cell exhibited marked anisotropic thermal expansion. Positional and anisotropic...

N. C. Baenziger W. L. Duax

1967-01-01

232

A Trireticulate Crystal Structure: Trihydrogen Cobalticyanide and Trisilver Cobalticyanide.  

National Technical Information Service (NTIS)

The crystals trisilver cobalticyanide and trihydrogen cobalticyanide have been shown to have a trireticulate structure, with nearly regular cobalticyanide octahedra connected by nitrogen-silver-nitrogen bonds or by hydrogen bonds between the nitrogen atom...

L. Pauling P. Pauling

1968-01-01

233

Effect of detergent alkyl chain length on crystallization of a detergent-solubilized membrane protein:. correlation of protein-detergent particle size and particle-particle interaction with crystallization of the photosynthetic reaction center from Rhodobacter sphaeroides  

NASA Astrophysics Data System (ADS)

The effect of detergent alkyl chain length on the crystallization of detergent-solubilized membrane proteins was characterized using the reaction center (RC) from Rhodobacter sphaeroides as a model. Crystallization was performed in the presence of both n-alkyl-?-D-glucopyranosides, C nG, where the alkyl chain length, n, was varied from 8 to 10, and dodecyl-dimethylamine-N-oxide (C 12DAO). A pronounced effect of detergent chain length was found on the ability to crystallize the reaction center. Small-angle neutron scattering measurements (SANS) demonstrated that the variation in the ability to crystallize the reaction center is correlated with changes in the apparent radius of gyration, Rg, of the reaction center-detergent particle, reflecting changes in the size of the reaction center and strength of the inter-particle interactions. Specifically, reaction center crystallization in the absence of additional amphiphiles was found to occur only with octylglucoside, C 8G. Crystallization in the presence of longer chain detergents, C 9G, C 10G, C 12DAO, required the use of an additional small amphiphile, heptanetriol (HT). SANS measurements showed that the apparent Rg of the reaction center-detergent particle increased with increasing detergent chain length, and that the addition of HT reduces this parameter. The addition of HT was found to impede crystallization in the presence of C 8G. This inhibition could be reversed by increasing C 8G concentration with respect to HT, resulting in the formation of alternate crystal forms. Taken together, these results suggest that detergents and small molecule amphiphiles used in membrane protein crystallization must be chosen to optimize both the size and solubility of the protein-detergent particle. Data for the reaction center suggest that crystallization occurs within a restricted range of size of the protein-detergent complex.

Marone, Palma Ann; Thiyagarajan, P.; Wagner, Arlene M.; Tiede, David M.

1999-12-01

234

Observation of particle pairing in a two-dimensional plasma crystal  

NASA Astrophysics Data System (ADS)

The observation is presented of naturally occurring pairing of particles and their cooperative drift in a two-dimensional plasma crystal. A single layer of plastic microspheres was suspended in the plasma sheath of a capacitively coupled radio-frequency discharge in argon at a low pressure of 1 Pa. The particle dynamics were studied by combining the top-view and side-view imaging of the suspension. Cross-analysis of the particle trajectories allowed us to identify naturally occurring metastable pairs of particles. The lifetime of pairs was long enough for their reliable identification.

Zhdanov, S. K.; Nosenko, V.; Thomas, H. M.; Morfill, G. E.; Coudel, L.

2014-02-01

235

Allophycocyanin and phycocyanin crystal structures reveal facets of phycobilisome assembly.  

PubMed

X-ray crystal structures of the isolated phycobiliprotein components of the phycobilisome have provided high resolution details to the description of this light harvesting complex at different levels of complexity and detail. The linker-independent assembly of trimers into hexamers in crystal lattices of previously determined structures has been observed in almost all of the phycocyanin (PC) and allophycocyanin (APC) structures available in the Protein Data Bank. In this paper we describe the X-ray crystal structures of PC and APC from Synechococcus elongatus sp. PCC 7942, PC from Synechocystis sp. PCC 6803 and PC from Thermosynechococcus vulcanus crystallized in the presence of urea. All five structures are highly similar to other PC and APC structures on the levels of subunits, monomers and trimers. The Synechococcus APC forms a unique loose hexamer that may show the structural requirements for core assembly and rod attachment. While the Synechococcus PC assembles into the canonical hexamer, it does not further assemble into rods. Unlike most PC structures, the Synechocystis PC fails to form hexamers. Addition of low concentrations of urea to T. vulcanus PC inhibits this proteins propensity to form hexamers, resulting in a crystal lattice composed of trimers. The molecular source of these differences in assembly and their relevance to the phycobilisome structure is discussed. PMID:23201474

Marx, Ailie; Adir, Noam

2013-03-01

236

Elemental composition and morphology of ice-crystal residual particles in cirrus clouds and contrails  

Microsoft Academic Search

Aircraft sampling of residual particles from evaporated ice crystals was performed using a Counterflow Virtual Impactor. Samples of crystals taken in both contrails and cirrus clouds were compared with interstitial aerosols found in natural cirrus. The samples were analyzed with a scanning electron microscope which was equipped with a windowless energy-dispersive X-ray detector (SEM\\/EDX). In the contrail and cirrus cases

A Petzold; J Strm; S Ohlsson; F. P Schrder

1998-01-01

237

Direct Deposition of Aerosol Particles on an ATR Crystal for FTIR Spectroscopy Using an Electrostatic Precipitator  

Microsoft Academic Search

An electrostatic precipitator (ESP) has been developed for collecting aerosol samples for attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) from an aerosol chamber. The ESP deposits the aerosol particles directly onto the ATR crystal with high efficiency. The ESP-ATR spectra are observed to agree well with the spectrum of a filter sample, transferred by impression. ZnSe ATR crystals have

J. Ofner; H.-U. Krger; C. Zetzsch; H. Grothe

2009-01-01

238

Crystal Structure of KinS2-I.  

National Technical Information Service (NTIS)

An X-ray single-crystal structure determination has confirmed that KInS2-I has the TIGaSe2 structure. The bonding in KIn S2-I is highly covalent and exhibits both two-dimensional and three-dimensinal features. The structure is comprised of layers of verte...

C. K. Lowe-Ma D. O. Kipp T. A. Vanderan

1990-01-01

239

Crystal Structure of Bacillus subtilis ?-Amylase in Complex with Acarbose  

PubMed Central

The crystal structure of Bacillus subtilis ?-amylase, in complex with the pseudotetrasaccharide inhibitor acarbose, revealed an hexasaccharide in the active site as a result of transglycosylation. After comparison with the known structure of the catalytic-site mutant complexed with the native substrate maltopentaose, it is suggested that the present structure represents a mimic intermediate in the initial stage of the catalytic process.

Kagawa, Masayuki; Fujimoto, Zui; Momma, Mitsuru; Takase, Kenji; Mizuno, Hiroshi

2003-01-01

240

Vortex structure in superconducting iron pnictide single crystals  

NASA Astrophysics Data System (ADS)

The vortex structure in the iron pnictide single crystals Ba1- x K x Fe2As2 and Sr1- x K x Fe2As2 of the 122 type and SmFeAsO1- x F x of the 1111 type has been investigated using the decoration method. In all of the crystals under investigation, no regular vortex lattice has been revealed in the magnetic field range up to 200 Oe. The disordered vortex structure is discussed in view of the vortex pinning in single crystals.

Vinnikov, L. Ya.; Artemova, T. M.; Veshchunov, I. S.; Zhigadlo, N. D.; Karpinski, J.; Popovich, P.; Sun, D. L.; Lin, C. T.; Boris, A. V.

2009-10-01

241

X-ray crystal structures of a severely desiccated protein.  

PubMed

Unlike most protein crystals, form IX of bovine pancreatic ribonuclease A diffracts well when severely dehydrated. Crystal structures have been solved after 2.5 and 4 days of desiccation with CaSO4, at 1.9 and 2.0 A resolution, respectively. The two desiccated structures are very similar. An RMS displacement of 1.6 A is observed for main-chain atoms in each structure when compared to the hydrated crystal structure with some large rearrangements observed in loop regions. The structural changes are the result of intermolecular contacts formed by strong electrostatic interactions in the absence of a high dielectric medium. The electron density is very diffuse for some surface loops, consistent with a very disordered structure. This disorder is related to the conformational changes. These results help explain conformational changes during the lyophilization of protein and the associated phenomena of denaturation and molecular memory. PMID:10548049

Bell, J A

1999-10-01

242

Quantitative crystal structure descriptors from multiplicative congruential generators.  

PubMed

Special types of number-theoretic relations, termed multiplicative congruential generators (MCGs), exhibit an intrinsic sublattice structure. This has considerable implications within the crystallographic realm, namely for the coordinate description of crystal structures for which MCGs allow for a concise way of encoding the numerical structural information. Thus, a conceptual framework is established, with some focus on layered superstructures, which proposes the use of MCGs as a tool for the quantitative description of crystal structures. The multiplicative congruential method eventually affords an algorithmic generation of three-dimensional crystal structures with a near-uniform distribution of atoms, whereas a linearization procedure facilitates their combinatorial enumeration and classification. The outlook for homometric structures and dual-space crystallography is given. Some generalizations and extensions are formulated in addition, revealing the connections of MCGs with geometric algebra, discrete dynamical systems (iterative maps), as well as certain quasicrystal approximants. PMID:22338652

Hornfeck, Wolfgang

2012-03-01

243

Opto-electric particle manipulation on a bismuth silicon oxide crystal  

NASA Astrophysics Data System (ADS)

High-throughput manipulation of microparticles can be efficiently accomplished using electrokinetic effects. In this contribution, we demonstrate the two-dimensional investigation of internal space-charge fields inside a bismuth silicon oxide (BSO) crystal and their use for optically mediated particle trapping. The magnitude of the internal fields as well as the time constant for its build-up are measured by Zernike phase contrast and digital holography. The fast response time of a BSO crystal at very low light powers enables real-time generation of high electric field gradients. We demonstrate that this photoconductive material facilitates both electrophoretic and dielectrophoretic trapping of particles on an accessible surface.

Esseling, Michael; Glasener, Stefan; Volonteri, Federico; Denz, Cornelia

2012-04-01

244

Effect of Complex Inclusion Particles on the Solidification Structure of Fe-Ni-Mn-Mo Alloy  

NASA Astrophysics Data System (ADS)

The effect of combinations of several deoxidizers, i.e., Mg-Al, Mg-Ti, Al-Ti, and Ce-Al, on the solidification structure of Fe-2 mass pct Ni-1 mass pct Mn-1 mass pct Mo alloy melt was investigated using a melt sampling and quenching method. Using this method, we evaluated the catalytic potency of several complex inclusion particles by taking the inclusion evolution process into account. Fine equiaxed crystals were obtained in the Mg-Ti-deoxidized steel wherein the MgO(MgAl2O4)-TiN complex compounds formed. However, the longer the holding time at high temperatures, the larger the fraction of Ti2O3, and very fine TiN formed because of microsegregation during solidification, resulting in poor equiaxed crystals. When the steel was deoxidized with Mg-Al, the initial structure was dominantly columnar. However, the longer the holding time, the larger the fraction of MgAl2O4 spinel, resulting in the formation of fine equiaxed crystals. Ce-Al complex deoxidation provided a relatively small portion of equiaxed crystals, whereas Ti-Al deoxidation produced the fewest equiaxed crystals because of the formation of alumina. The effectiveness of each inoculant particle for the crystallization of the primary ?-iron was explained well by the lattice disregistry concept.

Park, Jun Seok; Lee, Changhee; Park, Joo Hyun

2012-12-01

245

Internal structure visualization and lithographic use of periodic toroidal holes in liquid crystals.  

PubMed

The formation of a large-area ordered structure by organic molecular soft building blocks is one of the most exciting interdisciplinary research areas in current materials science and nanotechnology. So far, several distinct organic building blocks--including colloids, block copolymers and surfactants--have been examined as potential materials for the creation of lithographic templates. Here, we report that perfect ordered arrays of toric focal conic domains (TFCDs) covering large areas can be formed by semi-fluorinated smectic liquid crystals. Combined with controlled geometry, that is, a microchannel, our smectic liquid-crystal system exhibits a high density of TFCDs that are arranged with remarkably high regularity. Direct visualization of the internal structure of the TFCDs clearly verified that the smectic layers were aligned normal to the side walls and parallel to the top surface, and merge with the circular profile on the bottom wall surface. Moreover, we demonstrate a new concept: smectic liquid-crystal lithography. Grown in microchannels from a mixture of liquid-crystal molecules and fluorescent particles, TFCDs of the smectic liquid crystals acted as a template, trapping particles in an ordered array. Our findings pose new theoretical challenges and potentially enable lithographic applications based on smectic liquid-crystalline materials. PMID:17934466

Yoon, Dong Ki; Choi, M C; Kim, Yun Ho; Kim, Mahn Won; Lavrentovich, Oleg D; Jung, Hee-Tae

2007-11-01

246

Model solution for volume reflection of relativistic particles in a bent crystal  

SciTech Connect

For volume reflection process in a bent crystal, exact analytic expressions for positively- and negatively-charged particle trajectories are obtained within a model of parabolic continuous potential in each interplanar interval, with the neglect of incoherent multiple scattering. In the limit of the crystal bending radius greatly exceeding the critical value, asymptotic formulas are obtained for the particle mean deflection angle in units of Lindhard's critical angle, and for the final beam profile. Volume reflection of negatively charged particles is shown to contain effects of rainbow scattering and orbiting, whereas with positively charged particles none of these effects arise within the given model. The model predictions are compared with experimental results and numerical simulations. Estimates of the volume reflection mean angle and the final beam profile robustness under multiple scattering are performed.

Bondarenco, M. V. [Kharkov Institute of Physics and Technology, 1 Academic St., 61108 Kharkov (Ukraine)

2010-10-15

247

Single particle studies of cirrus ice crystals during CRYSTAL-FACE  

Microsoft Academic Search

The NOAA Aeronomy Laboratory's Particle Analysis by Laser Mass Spectrometry (PALMS) instrument is able to determine the chemical composition of the particulate matter found in the atmosphere. Individual particles are brought into a vacuum system where aerodynamic diameter is ascertained by the time required for passage between two visible laser beams. An excimer laser is then pulsed to hit each

D. Cziczo; D. Murphy; P. Hudson; D. Thomson

2003-01-01

248

Symmetry breaking and interaction of colloidal particles in nematic liquid crystals  

NASA Astrophysics Data System (ADS)

We propose a general approach to the description of the long-ranged elastic interaction in the nematic colloids, based on the symmetry breaking of the director field. The type of the far-field interaction between particles immersed in a nematic host is determined by the way the symmetry is broken in the near-field region around the colloidal particle. This is caused both by the particle's shape and the anchoring at the surface. If the director field near the particle has a set of three symmetry planes, the far-field interaction falls off as d-5 with d being the distance between particles. If one symmetry plane is absent, a dipolar moment perpendicular to it is allowed and yields dipole-dipole interactions, which decays as d-3. If both the horizontal and vertical mirror symmetries are broken (it is equivalent to the case when the nonzero torque moment is applied to the particle by the nematic liquid crystal), the particles are shown to attract each other following the Coulomb law. We propose a simple method for the experimental observation of this Coulomb attraction. The behavior of colloid particles in curved director fields is analyzed. Quadrupolar particles with planar anchoring are shown to be attracted toward the regions with high splay deformations, while quadrupoles with homeotropic anchoring are depleted from such regions. When there are many colloidal particles in the nematic solvent, the distortions of the director from all of them are overlapped and lead to the exponential screening in the elastic pair interaction potential. This is a many-body interaction effect. This screening is essential in the real dense colloid systems, such as ferronematics-suspensions of magnetic cylindrical grains in the nematic liquid crystal. External magnetic field induces an elastic Yukawa attraction between them. We apply this attraction to the explanation of the cellular texture in magnetically doped liquid crystals.

Lev, B. I.; Chernyshuk, S. B.; Tomchuk, P. M.; Yokoyama, H.

2002-02-01

249

Magnetic nano-particles of Ni in MgO single crystals by ion implantation  

Microsoft Academic Search

Magnetic Ni nano-particles in the near surface regions of MgO single crystals have been synthesized by 64keV Ni ion implantation to 11017cm?2 followed by thermal annealing. Transmission electron microscopy (TEM) and magnetic properties measurement system (MPMS) equipped with a superconducting quantum interference device (SQUID) detector have been employed to characterize the microstructure and magnetic properties of the Ni nano-particles. The

S. Zhu; X. Xiang; X. T. Zu; L. M. Wang

2006-01-01

250

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

251

Crystallization of dienelactone hydrolase in two space groups: structural changes caused by crystal packing.  

PubMed

Dienelactone hydrolase (DLH) is a monomeric protein with a simple ?/?-hydrolase fold structure. It readily crystallizes in space group P212121 from either a phosphate or ammonium sulfate precipitation buffer. Here, the structure of DLH at 1.85? resolution crystallized in space group C2 with two molecules in the asymmetric unit is reported. When crystallized in space group P212121 DLH has either phosphates or sulfates bound to the protein in crucial locations, one of which is located in the active site, preventing substrate/inhibitor binding. Another is located on the surface of the enzyme coordinated by side chains from two different molecules. Crystallization in space group C2 from a sodium citrate buffer results in new crystallographic protein-protein interfaces. The protein backbone is highly similar, but new crystal contacts cause changes in side-chain orientations and in loop positioning. In regions not involved in crystal contacts, there is little change in backbone or side-chain configuration. The flexibility of surface loops and the adaptability of side chains are important factors enabling DLH to adapt and form different crystal lattices. PMID:25005082

Porter, Joanne L; Carr, Paul D; Collyer, Charles A; Ollis, David L

2014-07-01

252

Effect of flow structure at the onset of instability on barium sulfate precipitation in Taylor-Couette crystallizers  

NASA Astrophysics Data System (ADS)

The effect of the vortex flow by primary instability on the precipitation of barium sulfate crystals was examined in Taylor-Couette crystallizers. Experiments involving precipitation of barium sulfate under laminar flow (before the onset of instability) and vortex flow (after the onset of primary instability) at three different axial flow rates revealed that the vortex motion plays a critical role in fine-tuning crystal properties such as internal crystal structure, particle microstructure and morphology. While no clear trends in crystalline size were observed for laminar flow, all flowrates at the onset of instability resulted in smaller crystalline sizes that ranged between 40 nm and 50 nm. A decrease in the unit cell dimensions of the orthorhombic lattice structure was also observed after the onset of instability. For both laminar and vortex flow, shortening the residence time by increasing axial flow rate led to a substantial decrease in crystal size. It is also observed that the crystal size distribution (CSD) became much narrower after the emergence of vortices. Under vortex flow, an increase in axial flow resulted in even narrower crystal size distributions. Finally, the observed phenomena of smaller crystal size and narrow crystal size distribution under vortex flow are qualitatively explained by the analysis of particle trajetory.

Aljishi, Mohammad Fuad; Ruo, An-Cheng; Park, Jay Hoon; Nasser, Bader; Kim, Woo-Sik; Joo, Yong Lak

2013-06-01

253

Deliquescence and crystallization of ammonium sulfate-glutaric acid and sodium chloride-glutaric acid particles  

NASA Astrophysics Data System (ADS)

In the following, we report the deliquescence relative humidities (DRH) and crystallization relative humidities (CRH) of mixed inorganic-organic particles, specifically ammonium sulfate-glutaric acid and sodium chloride-glutaric acid particles. Knowledge of the DRH and CRH of mixed inorganic-organic particles is crucial for predicting the role of aerosol particles in the atmosphere. Our DRH results are in good agreement with previous measurements, but our CRH results are significantly lower than some of the previous measurements reported in the literature. Our studies show that the DRH and CRH of ammonium sulfate and sodium chloride only decreased slightly when the mole fraction of the acid was less than 0.4. If other organics in the atmosphere behave in a similar manner, then the DRH and CRH of mixed inorganic-organic atmospheric particles will only be slightly less than the DRH and CRH of pure inorganic particles when the organic mole fraction is less than 0.4. Our results also show that if the particles contain a significant amount of organics (mole fraction > 0.5) the crystallization relative humidity decreases significantly and the particles are more likely to remain in the liquid state. Further work is needed to determine if other organics species of atmospheric importance have a similar effect.

Pant, Atul; Fok, Abel; Parsons, Matthew T.; Mak, Jackson; Bertram, Allan K.

2004-06-01

254

Photocurable pickering emulsion for colloidal particles with structural complexity.  

PubMed

We prepared polymeric microparticles with coordinated patches using oil-in-water emulsion droplets which were stabilized by adsorbed colloidal polystyrene (PS) latex particles. The oil phase was photocurable ethoxylated trimethylolpropane triacrylate (ETPTA), and the particle-armored oil droplets were solidified by UV irradiation within a few seconds to produce ETPTA-PS composite microparticles without disturbing the structures. Large armored emulsion drops became raspberry-like particles, while small emulsion drops with a few anchored particles were transformed into colloidal clusters with well-coordinated patches. For high-molecular-weight PS particles with low chemical affinity to the ETPTA monomer, the morphology of the patchy particle was determined by the volume of the emulsion drop and the contact angle of the emulsion interface on the PS particle surface. Meanwhile, for low-molecular-weight PS particles with high affinity, the ETPTA monomers were likely to swell the adsorbed PS particles, and distinctive morphologies were induced during the shrinkage of emulsion drops and the phase separation of ETPTA from the swollen PS particles. In addition, colloidal particles with large open windows were produced by dissolving the PS particles from the patchy particles. We observed photoluminescent emission from the patchy particles in which dye molecules were dispersed in the ETPTA phase. Finally, we used Surface Evolver simulation to predict equilibrium structures of patchy particles and estimate surface energies which are essential to understand the underlying physics. PMID:18237213

Kim, Shin-Hyun; Yi, Gi-Ra; Kim, Kyu Han; Yang, Seung-Man

2008-03-18

255

Single-crystal growth, crystal and electronic structure of NaCoO 2  

Microsoft Academic Search

Single crystals of NaCoO2 have been successfully synthesized for the first time by a flux method at 1323K. A single-crystal X-ray diffraction study confirmed the trigonal R3?m space group and the lattice parameters a=2.8897(15)A?, c=15.609(3)A?. The crystal structure has been refined to the conventional values R=1.9% and wR=2.1% for 309 independent observed reflections. The electron density distribution of NaCoO2 has

Yasuhiko Takahashi; Yoshito Gotoh; Junji Akimoto

2003-01-01

256

Datamining protein structure databanks for crystallization patterns of proteins.  

PubMed

A study of 345 protein structures selected among 1,500 structures determined by nuclear magnetic resonance (NMR) methods, revealed useful correlations between crystallization properties and several parameters for the studied proteins. NMR methods of structure determination do not require the growth of protein crystals, and hence allow comparison of properties of proteins that have or have not been the subject of crystallographic approaches. One- and two-dimensional statistical analyses of the data confirmed a hypothesized relation between the size of the molecule and its crystallization potential. Furthermore, two-dimensional Bayesian analysis revealed a significant relationship between relative ratio of different secondary structures and the likelihood of success for crystallization trials. The most immediate result is an apparent correlation of crystallization potential with protein size. Further analysis of the data revealed a relationship between the unstructured fraction of proteins and the success of its crystallization. Utilization of Bayesian analysis on the latter correlation resulted in a prediction performance of about 64%, whereas a two-dimensional Bayesian analysis succeeded with a performance of about 75%. PMID:12594078

Valafar, Homayoun; Prestegard, James H; Valafar, Faramarz

2002-12-01

257

Crystal and quasicrystal structures in Al-Mn-Si alloys  

Microsoft Academic Search

It is shown that the alpha-(AlMnSi) crystal structure is closely (and systematically) related to that of the icosahedral Al-Mn-Si alloys. Using a modification of the 'projection' method of generating icosahedral structures from six-dimensional lattices, a simple description of the alpha-(AlMnSi) structure is found. This structure, and (it is conjectured) the icosahedral one, can also be described as a packing of

Veit Elser; C. L. Henley

1985-01-01

258

Designing smart particles for the assembly of complex macroscopic structures.  

PubMed

Particle get-together: Surface functionalization with a branched copolymer surfactant is used to create responsive inorganic particles that can self-assemble in complex structures. The assembly process is triggered by a pH switch that reversibly activates multiple hydrogen bonds between ceramic particles (see picture; yellow) and soft templates (n-decane; green). PMID:23780923

Garcia-Tunon, Esther; Barg, Suelen; Bell, Robert; Weaver, Jonathan V M; Walter, Claudia; Goyos, Lidia; Saiz, Eduardo

2013-07-22

259

Single-crystal structure of a covalent organic framework.  

PubMed

The crystal structure of a new covalent organic framework, termed COF-320, is determined by single-crystal 3D electron diffraction using the rotation electron diffraction (RED) method for data collection. The COF crystals are prepared by an imine condensation of tetra-(4-anilyl)methane and 4,4'-biphenyldialdehyde in 1,4-dioxane at 120 C to produce a highly porous 9-fold interwoven diamond net. COF-320 exhibits permanent porosity with a Langmuir surface area of 2400 m(2)/g and a methane total uptake of 15.0 wt % (176 cm(3)/cm(3)) at 25 C and 80 bar. The successful determination of the structure of COF-320 directly from single-crystal samples is an important advance in the development of COF chemistry. PMID:24143961

Zhang, Yue-Biao; Su, Jie; Furukawa, Hiroyasu; Yun, Yifeng; Gndara, Felipe; Duong, Adam; Zou, Xiaodong; Yaghi, Omar M

2013-11-01

260

Crystal structure of potassium titanyl phosphate doped with zirconium  

SciTech Connect

This paper reports on the results of precision X-ray structural investigations of single crystals of the compounds KTi{sub 0.96}Zr{sub 0.04}OPO{sub 4} (at 293 K) and KTi{sub 0.97}Zr{sub 0.03}OPO{sub 4} (at 293 and 105 K). No significant splitting of the positions occupied by potassium atoms is revealed. This result is in agreement with a considerable decrease in the electrical conductivity of potassium titanyl phosphate KTiOPO{sub 4} (KTP) crystals doped with zirconium (KTP: Zr) as compared to crystals of undoped potassium titanyl phosphate. It is established that the difference between the Ti-O bond lengths in chains formed by titanium octahedra is not a single structural parameter responsible for the nonlinear optical properties of crystals in this series.

Alekseeva, O. A., E-mail: olalex@ns.crys.ras.ru; Dudka, A. P.; Sorokina, N. I. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Pietraszko, A. [Polish Academy of Sciences, Institute of Low Temperature and Structure Research (Poland); Rabadanov, M. Kh. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Agapova, E. I.; Voronkova, V. I. [Lomonosov Moscow State University (Russian Federation); Simonov, V. I. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2007-07-15

261

Crystal structure of ScB/sub 12/  

SciTech Connect

The crystal structure of scandium dodecaboride was determined. The research material was a single crystal derived from an ingot obtained by fusion of metallic Sc and finely crystalline boron in an electric-arc furnace (Ar atmosphere). We used Laue, rotation, and inverse-lattice photography methods. The data confirmed that ScB/sub 12/ has a face-centered cubic structure. The investigation showed that with regard to the composition and structure of the resulting borides Sc exhibits complete analogy with Zr and is less similar to yttrium-group rare earth metals, for which the formation of tetraborides and hexaborides is characteristic.

Bruskov, V.A.; Zavalii, L.V.; Kuz'ma, Yu.B.

1988-08-01

262

Vulcanite, CuTe: hydrothermal synthesis and crystal structure refinement  

Microsoft Academic Search

Summary The crystal structure of the mineral vulcanite, CuTe [a?=?3.155(1), b?=?4.092(1), c?=?6.956(1)?; Z?=?2; space group: Pmmn,\\u000a No. 59] exhibits a pronounced layer structure with Te-Te distances between the CuTe layers of 4.019(1)?. Within a range up\\u000a to 4.2? the individual Cu atom is [4Te+4Cu+2Cu], the individual Te atom [4Cu+2Te+4Te] coordinated. Crystals of vulcanite\\u000a suitable for the present structure investigation were

F. Pertlik

2001-01-01

263

Symmetry building Monte Carlo-based crystal structure prediction  

NASA Astrophysics Data System (ADS)

Methods are presented that allow for the automatic increase and preservation of symmetry during global optimization of crystal structures. This systematic building of symmetry allows for its incorporation into structure prediction simulations even when the space group information is not known a priori. It is shown that simulations that build and maintain symmetry converge much more rapidly to ground state crystal structures than when symmetry is ignored, allowing for the treatment of unit cells much larger than would otherwise be possible, especially when beginning from the P1 space group.

Michel, Kyle Jay; Wolverton, C.

2014-05-01

264

Atomic- Resolution Crystal Structure of the Antiviral Lectin Scytovirin  

SciTech Connect

The crystal structures of the natural and recombinant antiviral lectin scytovirin (SVN) were solved by single-wavelength anomalous scattering and refined with data extending to 1.3 Angstroms and 1.0 Angstroms resolution, respectively. A molecule of SVN consists of a single chain 95 amino acids long, with an almost perfect sequence repeat that creates two very similar domains (RMS deviation 0.25 Angstroms for 40 pairs of Ca atoms). The crystal structure differs significantly from a previously published NMR structure of the same protein, with the RMS deviations calculated separately for the N- and C-terminal domains of 5.3 Angstroms and 3.7 Angstroms, respectively, and a very different relationship between the two domains. In addition, the disulfide bonding pattern of the crystal structures differs from that described in the previously published mass spectrometry and NMR studies.

Moulaei,T.; Botos, I.; Ziolkowska, N.; Bokesch, H.; Krumpe, L.; McKee, T.; O'Keefe, B.; Dauter, Z.; Wlodawer, A.

2007-01-01

265

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

266

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 C 16H 11Cl 3O 2 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

267

Refined Crystal Structures of Unligated Adenylosuccinate Synthetase from Escherichia coli  

Microsoft Academic Search

Crystal structures of unligated adenylosuccinate synthetase fromEscherichia coliin space groupsP21andP212121have been refined toR-factors of 0.199 and 0.206 against data to 2.0 and 2.5 , respectively. Bond lengths and angles deviate from expected values by 0.011 and 1.7 for theP21crystal form and by 0.015 and 1.7 for theP212121crystal form. The fold of the polypeptide chain is dominated by a

M. Mercedes Silva; Bradley W. Poland; Chad R. Hoffman; Herbert J. Fromm; Richard B. Honzatko

1995-01-01

268

Chemical space sampling in virtual screening by different crystal structures.  

PubMed

Retrospective virtual screening experiments were carried out to investigate the effects of combining hit lists from different crystal structures of the same target using consensus scoring. An in-house High Throughput Screening (HTS) dataset from PI3K-? was used and docked against five diverse PI3K-? crystal structures. The results show that consensus scoring prioritizes compounds that score moderately against individual crystal structures and is thus complementary to individual crystal structure screening leading to an increase in the diversity of hits. Enrichment factors (EFs) of the consensus score for two or three structures are often as high as or higher than the EF of the individual structures used in the consensus score. Combining four or five structures in the consensus score generally yields lower enrichments. Compounds in the top 500 of the consensus score that are also found in the top 500 of an individual X-ray structure used in the consensus score calculations yield the largest number of hits with the lowest number of false positives. PMID:20958920

Brooijmans, Natasja; Humblet, Christine

2010-12-01

269

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

270

Crystal structure of simple metals at high pressures  

Microsoft Academic Search

The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 1417, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a

Olga Degtyareva; Olga

2010-01-01

271

Etching effect on periodic domain structures of lithium niobate crystals  

Microsoft Academic Search

In order to improve the knowledge of the domain structure in LiNbO3 crystals, the effect of the etching process with HF:HNO3 (1:2 by vol.) has been studied. It has been found, by analyzing the superficial composition with the secondary ion mass spectrometry technique, that during the etching treatment, the fluorine ion diffuses into the crystal, mainly along the positive ferroelectric

V. Bermdez; F Caccavale; C Sada; F Segato; E Diguez

1998-01-01

272

Etching effect on periodic domain structures of lithium niobate crystals  

NASA Astrophysics Data System (ADS)

In order to improve the knowledge of the domain structure in LiNbO 3 crystals, the effect of the etching process with HF : HNO 3 (1 : 2 by vol.) has been studied. It has been found, by analyzing the superficial composition with the secondary ion mass spectrometry technique, that during the etching treatment, the fluorine ion diffuses into the crystal, mainly along the positive ferroelectric domain.

Bermdez, V.; Caccavale, F.; Sada, C.; Segato, F.; Diguez, E.

1998-07-01

273

Structure of blue phase III of cholesteric liquid crystals.  

PubMed

We report large scale simulations of the blue phases of cholesteric liquid crystals. Our results suggest a structure for blue phase III, the blue fog, which has been the subject of a long debate in liquid crystal physics. We propose that blue phase III is an amorphous network of disclination lines, which is thermodynamically and kinetically stabilized over crystalline blue phases at intermediate chiralities. This amorphous network becomes ordered under an applied electric field, as seen in experiments. PMID:21469836

Henrich, O; Stratford, K; Cates, M E; Marenduzzo, D

2011-03-11

274

The Host Guest Co-Crystal Approach to Supramolecular Structure  

Microsoft Academic Search

A host-guest co-crystal approach to supramolecular structure has been developed. Molecular functionalities have been identified that will self assemble via hydrogen bonds to give one dimensional ?-networks with defined intermolecular distances. Host molecules based on these functionalites can be co-crystallized with guest molecules, the characteristic distance defined by the host is thus imposed on the guest. Using this strategy, functional

John J. Kane; Tam Nguyen; Jun Xiao; Frank W. Fowler; Joseph W. Lauher

2001-01-01

275

Crystal structure of the extracellular segment of integrin V3  

Microsoft Academic Search

Integrins are heterodimeric receptors that mediate divalent cation-dependent cell-cell and cell-matrix adhesion through tightly regulated interactions with ligands. We have solved the crystal structure of the extracellular portion of integrin V{sup }3 at 3.1 Angstroms resolution. Its 12 domains assemble into an ovoid 'head' and two 'tails.' In the crystal, V{sup }3 is severely bent at a defined region in

J.-P. Xiong; T. Stehle; B. Diefenbach; R. Zhang; R. Dunker; D. L. Scott; A. Joachimiak; S. L. Goodman; M. A. Arnaout; Merck KGaA

2001-01-01

276

Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.  

PubMed

Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by solution. We predict that micrometer-sized particles and nanoparticles have the same equilibrium internal structure. The variation of liquid-vapor surface tension with solute concentration is a key factor in determining whether a solution-embedded ice core or vapor-exposed ice cap is the equilibrium structure of the aerosols. In agreement with experiments, we predict that the structure of mixed-phase HNO3-water particles, representative of polar stratospheric clouds, consists of an ice core surrounded by freeze-concentrated solution. The results of this work are important to determine the phase state and internal structure of sea spray ultrafine aerosols and other mixed-phase particles under atmospherically relevant conditions. PMID:24820354

Hudait, Arpa; Molinero, Valeria

2014-06-01

277

Observation and Analysis of Polymer Crystal Structures at the Stem Level. Implications Regarding Polymer Crystallization Processes.  

NASA Astrophysics Data System (ADS)

The building element of chain folded polymer crystals is the individual stem that spans the lamellar thickness. For chiral but racemic helical polymers such as polyolefins (e.g. isotactic and syndiotactic polypropylene and poly(1-butene)), stems can be right- or left-handed helices. These polymers can exist in various crystal polymorphs that are either "racemic" or "chiral" (made of both, or of only one helical hand). Upon crystallization, each stem has a conformational "choice", but must adapt to the crystal structure and, once crystallized, is characterized by a "conformational tag" (right or left hand). Various means exist to determine or observe helical hands in polyolefin lamellae: Atomic Force Microscopy on epitaxially crystallized samples, or, for the alpha phase of isotactic polypropylene, analysis of its specific lamellar branching. These observations and analyses indicate that the helical hand of stems is tightly determined by the substrate or growth face topography, i.e. indicate that the depositing stem probes and adapts to the surface structure prior to successful attachment. This "post-mortem" analysis of the crystal structure and stem chirality emphasizes the "sequential" nature of the growth process (successive attachment of individual stems). It is in line with early views on polymer crystallization. It is at variance with recently introduced models or scenarios that assume either some pre-ordering of the polymer melt as a result of spinodal decomposition and/or accretion of polymer chains in pseudo-crystalline bundles followed by (solid state) reorganization of the bundles to generate fully grown lamellae.

Lotz, Bernard

2003-03-01

278

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

279

Crystal and Magnetic Structure of UNi0.52  

NASA Astrophysics Data System (ADS)

We report the single crystal neutron diffraction studies done to resolve the room-temperature structure and the magnetic structure at 25 K of Uranium antimonide, UNi0.5Sb2. The time-of-flight single-crystal neutron diffraction experiments at room temperature and 25 K were done on the Single Crystal Diffractometer, SCD, at Los Alamos Neutron Science Center. Previous X-ray single crystal and neutron powder diffraction studies could not unambiguously resolve the structure because of the presence of hkl/2 type reflections. The studies were done on a 2 x 1 x 0.5 mm3 crystal and half-indexed reflections were observed corroborating the observations in previous studies. The room temperature structure that accounts for all the observed reflections is determined to be tetragonal P42/n m c with lattice parameters a = 4.333(2) and c = 17.868(6) respectively. The compound is found to order antiferromagnetically at 162 K and has a simple antiferromagnetic structure at 25 K with propagation vector q = (0, 0, 0) and with a moment of 1.82?B/U atom.

Kothapalli, Karunakar; Torikachvili, Milton; Nasreen, Farzana; Nakotte, Heinrich

2010-10-01

280

Facile synthesis of nanoporous carbons with controlled particle sizes by direct carbonization of monodispersed ZIF-8 crystals.  

PubMed

Nanoporous carbon particles with different particle sizes are synthesized by simple carbonization of monodispersed zeolitic imidazolate framework-8 (ZIF-8) crystals. Quartz crystal microbalance (QCM) study proves that the use of small-sized nanoporous carbon can lead to both a large adsorption uptake and a faster sensor response for toxic toluene molecules. PMID:23423451

Torad, Nagy L; Hu, Ming; Kamachi, Yuichiro; Takai, Kimiko; Imura, Masataka; Naito, Masanobu; Yamauchi, Yusuke

2013-03-28

281

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

282

Lactose particle engineering: Influence of ultrasound and anti-solvent on crystal habit and particle size  

NASA Astrophysics Data System (ADS)

This study focuses on ultrasound-assisted anti-solvent crystallization of lactose, expanding on previous studies and presenting, for the first time, the results of large scale implementation of sonocrystallization for lactose. The results further clarify the interplay between solution chemistry - namely the role of ?-lactose - and crystallization, representing a step forward in the fine tuning of lactose properties for pharmaceutical manufacturing applications. Batches manufactured at laboratory and pilot scales were extensively characterised, including an approach for the quantification of ?-lactose in ?-lactose based on powder X-ray diffraction (PXRD), which is described here.

Kougoulos, E.; Marziano, I.; Miller, P. R.

2010-11-01

283

Emergent Structures in Wave-Particle Systems  

Microsoft Academic Search

We study the motion of a particle with mass m on a vibrated string of length L and friction constant eta. The string is sinusoidally forced at both ends. We find that the particle has fixed points located at x=L\\/2 - npi\\/k, where k is the wavenumber of the waves on the string, and n is an integer. We find

Davit Sivil; Alfred Hubler

2004-01-01

284

Optimal modeling of atomic fluctuations in protein crystal structures for weak crystal contact interactions  

NASA Astrophysics Data System (ADS)

The accurate modeling of protein dynamics in crystalline states holds keys to the understanding of protein dynamics relevant to functions. In this study, we used coarse-grained elastic network models (ENMs) to explore the atomic fluctuations of a protein structure that interacts with its crystalline environment, and evaluated the modeling results using the anisotropic displacement parameters (ADPs) obtained from x-ray crystallography. To ensure the robustness of modeling results, we used three ENM schemes for assigning force constant combined with three boundary conditions for treating the crystalline environment. To explore the role of crystal contact interactions in the modeling of ADPs, we varied the strength of interactions between a protein structure and its environment. For a list of 83 high-resolution crystal structures, we found that the optimal modeling of ADPs, as assessed by a variety of metrics, is achieved for weak protein-environment interactions (compared to the interactions within a protein structure). As a result, the ADPs are dominated by contributions from rigid-body motions of the entire protein structure, and the internal protein dynamics is only weakly perturbed by crystal packing. Our finding of weak crystal contact interactions is also corroborated by the calculations of residue-residue contact energy within a protein structure and between protein molecules using a statistical potential.

Hafner, Jeffrey; Zheng, Wenjun

2010-01-01

285

The Crystal Structure of YB4.  

National Technical Information Service (NTIS)

A structure determination of YB4 was carried out in order to determine the boron positions in metal tetraborides. The structure proposed by earlier workers using the ThB4 was confirmed; however, significant departures in occupany of boron positions were n...

R. F. Giese V. I. Matkovich J. Economy

1965-01-01

286

Nanoscale structural features determined by AFM for single virus particles.  

PubMed

In this work, we propose "single-image analysis", as opposed to multi-image averaging, for extracting valuable information from AFM images of single bio-particles. This approach allows us to study molecular systems imaged by AFM under general circumstances without restrictions on their structural forms. As feature exhibition is a resolution correlation, we have performed AFM imaging on surfaces of tobacco mosaic virus (TMV) to demonstrate variations of structural patterns with probing resolution. Two AFM images were acquired with the same tip at different probing resolutions in terms of pixel width, i.e., 1.95 and 0.49 nm per pixel. For assessment, we have constructed an in silico topograph based on the three-dimensional crystal structure of TMV as a reference. The prominent artifacts observed in the AFM-determined shape of TMV were attributed to tip convolutions. The width of TMV rod was systematically overestimated by ~10 nm at both probing resolutions of AFM. Nevertheless, the effects of tip convolution were less severe in vertical orientation so that the estimated height of TMV by AFM imaging was in close agreement with the in silico X-ray topograph. Using dedicated image processing algorithms, we found that at low resolution (i.e., 1.95 nm per pixel), the extracted surface features of TMV can be interpreted as a partial or full helical repeat (three complete turns with ~7.0 nm in length), while individual protein subunits (~2.5 nm) were perceivable only at high resolution. The present study shows that the scales of revealed structural features in AFM images are subject to both probing resolution and processing algorithms for image analysis. PMID:24056758

Chen, Shu-wen W; Odorico, Michael; Meillan, Matthieu; Vellutini, Luc; Teulon, Jean-Marie; Parot, Pierre; Bennetau, Bernard; Pellequer, Jean-Luc

2013-11-21

287

Formation and crystal structure of metallic inclusions in a HPHT as-grown diamond single crystal  

NASA Astrophysics Data System (ADS)

One of the most important characteristics associated with crystal growth technology is the entrapment of inclusions by the growing crystal. Diamond single crystals prepared under high temperature-high pressure (HPHT) usually contain metallic inclusions. In the present paper, metallic inclusions in a diamond grown from a Fe-Ni-C system using the HPHT method have been, for the first time, systematically examined by transmission electron microscopy (TEM). Energy dispersive X-ray spectrometry (EDS) , combined with selected area electron diffraction (SAD) patterns, has been used to identify the chemical composition and crystal structure of the metallic inclusions. The metallic inclusions were found to be composed mainly of cubic ?-(FeNi), face-centered cubic (FeNi)23C6, ortho-rhombic Fe3C and hexagonal Ni3C, which may have been formed through the entrapment of molten catalyst by the growth front or through reaction of the trapped melt with contaminants in the diamond.

Yin, L.-W.; Wang, N.-W.; Zou, Z.-D.; Li, M.-S.; Sun, D.-S.; Zheng, P.-Z.; Yao, Z.-Y.

288

About the probability of close collisions during stochastic deflection of positively charged particles by a bent crystal  

NASA Astrophysics Data System (ADS)

The probability of close interactions of high-energy positively charged particle with atoms in a bent crystal was considered as a function of the angle between the initial particle momentum and the bending plane. The results of simulation of particle motion presented in the article show the great efficiency of high-energy positively charged particle deflection by a bent crystal due to the stochastic deflection mechanism and strong reduction of the probability of close collisions during the stochastic deflection in comparison to the planar channeling in a bent crystal.

Chesnokov, Yu. A.; Kirillin, I. V.; Scandale, W.; Shul'ga, N. F.; Truten', V. I.

2014-04-01

289

Crystal structure of simple metals at high pressures  

SciTech Connect

The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14-17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host-guest and incommensurately modulated structures found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.

Degtyareva, Olga (Edinburgh)

2010-10-22

290

Crystal structure tuning in GaAs nanowires using HCl.  

PubMed

The use of HCl during growth of nanowires presents new possibilities for controlling the growth dynamics and resulting nanowire properties. In this paper, we investigate the effects of in situ HCl on the growth of Au-seeded GaAs nanowires in a growth regime where both wurtzite and zinc blende crystal structures are possible to achieve. We find that HCl changes the crystal structure of the nanowires from pure wurtzite to defect-free zinc blende. By comparing the growth of wurtzite-zinc blende heterostructures with and without the addition of HCl, it is deduced that HCl mainly interacts with Ga species prior incorporation, reducing the amount of Ga available to contribute to the growth. We conclude that the change in crystal structure is related to the reduction of Ga adatoms, and demonstrate the realization of wurtzite-zinc blende heterostructures with atomically sharp interfaces achieved only by adding HCl. PMID:24931099

Jacobsson, Daniel; Lehmann, Sebastian; Dick, Kimberly A

2014-06-26

291

Crystal structures of gold, silver, and sodium chalcogenides: Sphenoidal interpretation  

SciTech Connect

The crystal structures of 13 chalcogenides of Na, Au(I), and Ag(I) in the Na{sub 2-n}(Au,Ag){sub n}(S,Se,Te) series, where 0 {<=} n {<=} 2, are interpreted from unified positions based on the sphenoidal representation. Its essence is in the consideration of the entire crystal space (with packing X atoms in the framework of close-packing, body-centered, or hybrid schemes) as a set of elementary space units (sphenoids). Unified one-dimensional associates of sphenoids, the so-called basic rods, with sets of possible atomic positions in them are selected for all structures. The mutual effect of the dimensional and stoichiometric ratios of all components on the features of filling rod positions is analyzed. New possibilities in the crystallochemical and crystal-geometry analysis of inorganic compounds whose structures are characterized by a relatively uniform distribution of atoms are demonstrated by the example of chalcogenides.

Bakakin, V. V., E-mail: bakakin@niic.nsc.ru [Russian Academy of Sciences, Institute of Inorganic Chemistry, Siberian Branch (Russian Federation)

2011-11-15

292

Magnetic and crystal structure of copper(II) fluoride  

Microsoft Academic Search

A powder sample of the monoclinic, weak ferromagnet CuF2 was investigated by neutron diffraction. Using the profile method, the crystal structure was refined and the spin configuration determined. The layer type structure with planar quadratic fluorine coordination of Cu2+ (3d9) and the magnetic structure are remarkably similar to those of AgF2. The spin configuration is however different from the magnetic

P. Fischer; W. Hlg; D. Schwarzenbach; H. Gamsjger

1974-01-01

293

The Crystal Structure of GXGD Membrane Protease FlaK  

SciTech Connect

The GXGD proteases are polytopic membrane proteins with catalytic activities against membrane-spanning substrates that require a pair of aspartyl residues. Representative members of the family include preflagellin peptidase, type 4 prepilin peptidase, presenilin and signal peptide peptidase. Many GXGD proteases are important in medicine. For example, type 4 prepilin peptidase may contribute to bacterial pathogenesis, and mutations in presenilin are associated with Alzheimer's disease. As yet, there is no atomic-resolution structure in this protease family. Here we report the crystal structure of FlaK, a preflagellin peptidase from Methanococcus maripaludis, solved at 3.6 {angstrom} resolution. The structure contains six transmembrane helices. The GXGD motif and a short transmembrane helix, helix 4, are positioned at the centre, surrounded by other transmembrane helices. The crystal structure indicates that the protease must undergo conformational changes to bring the GXGD motif and a second essential aspartyl residue from transmembrane helix 1 into close proximity for catalysis. A comparison of the crystal structure with models of presenilin derived from biochemical analysis reveals three common transmembrane segments that are similarly arranged around the active site. This observation reinforces the idea that the prokaryotic and human proteases are evolutionarily related. The crystal structure presented here provides a framework for understanding the mechanism of the GXGD proteases, and may facilitate the rational design of inhibitors that target specific members of the family.

J Hu; Y Xue; S Lee; Y Ha

2011-12-31

294

The crystal structure of GXGD membrane protease FlaK  

SciTech Connect

The GXGD proteases are polytopic membrane proteins with catalytic activities against membrane-spanning substrates that require a pair of aspartyl residues. Representative members of the family include preflagellin peptidase, type 4 prepilin peptidase, presenilin and signal peptide peptidase. Many GXGD proteases are important in medicine. For example, type 4 prepilin peptidase may contribute to bacterial pathogenesis, and mutations in presenilin are associated with Alzheimer's disease. As yet, there is no atomic-resolution structure in this protease family. Here we report the crystal structure of FlaK, a preflagellin peptidase from Methanococcus maripaludis, solved at 3.6 {angstrom} resolution. The structure contains six transmembrane helices. The GXGD motif and a short transmembrane helix, helix 4, are positioned at the centre, surrounded by other transmembrane helices. The crystal structure indicates that the protease must undergo conformational changes to bring the GXGD motif and a second essential aspartyl residue from transmembrane helix 1 into close proximity for catalysis. A comparison of the crystal structure with models of presenilin derived from biochemical analysis reveals three common transmembrane segments that are similarly arranged around the active site. This observation reinforces the idea that the prokaryotic and human proteases are evolutionarily related. The crystal structure presented here provides a framework for understanding the mechanism of the GXGD proteases, and may facilitate the rational design of inhibitors that target specific members of the family.

Hu, Jian; Xue, Yi; Lee, Sangwon; Ha, Ya (Yale-MED)

2011-09-20

295

Structural determination of a partially hemihedrally twinned actin crystal.  

PubMed

An orthorhombic actin crystal (space group P2(1)2(1)2(1), unit-cell parameters a = 101.6, b = 103.0, c = 127.0 angstroms) was converted into a partially hemihedrally twinned tetragonal crystal (space group P4(3), unit-cell parameters a = b = 101.5, c = 104.2 angstroms) by induced condensation. This condensation (decrease in the c axis) was caused by the flash-freezing of the crystal, with 30% PEG 400 as a cryoprotectant, prior to data collection. Diffraction data for the twinned tetragonal crystal were collected at 100 K to 3.0 angstroms resolution (99.8% completeness with an Rsym of 8.1%) using synchrotron radiation. The hemihedral twinning of the data was observed by self-rotation function analysis and was determined to have a partial twin fraction of 0.376 from intensity statistics. The structure, with two actin molecules in the crystallographic asymmetric unit, was determined by molecular-replacement methods and refined to an R factor of 0.193. As a consequence of the crystal lattice transformation from the orthorhombic P2(1)2(1)2(1) to the tetragonal P4(3) space group, actin-actin contacts were rearranged and an inter-actin dimer disulfide bond (Cys374) observed in the orthorhombic crystal form was broken in the tetragonal crystal form. PMID:15159563

Govindasamy, Lakshmanan; Reutzel, Robbie; Agbandje-McKenna, Mavis; McKenna, Robert

2004-06-01

296

Utilization of Protein Crystal Structures in Industry  

NASA Astrophysics Data System (ADS)

In industry, protein crystallography is used in mainly two technologies. One is structure-based drug design, and the other is structure-based enzyme engineering. Some successful cases together with recent advances are presented in this article. The cases include the development of an anti-influenza drug, and the introduction of engineered acid phosphatase to the manufacturing process of nucleotides used as umami seasoning.

Ishikawa, Kohki

297

Microscopic characterization of defect structure in RDX crystals.  

PubMed

Three batches of the commercial energetic material RDX, as received from various production locations and differing in sensitivity towards shock initiation, have been characterized with different microscopic techniques in order to visualize the defect content in these crystals. The RDX crystals are embedded in an epoxy matrix and cross-sectioned. By a treatment of grinding and polishing of the crystals, the internal defect structure of a multitude of energetic crystals can be visualized using optical microscopy, scanning electron microscopy and confocal scanning laser microscopy. Earlier optical micrographs of the same crystals immersed in a refractive index matched liquid could visualize internal defects, only not in the required detail. The combination of different microscopic techniques allows for a better characterization of the internal defects, down to inclusions of approximately 0.5 ?m in size. The defect structure can be correlated to the sensitivity towards a high-amplitude shock wave of the RDX crystals embedded in a polymer bonded explosive. The obtained experimental results comprise details on the size, type and quantity of the defects. These details should provide modellers with relevant and realistic information for modelling defects in energetic materials and their effect on the initiation and propagation of shock waves in PBX formulations. PMID:24117989

Bouma, R H B; Duvalois, W; Van der Heijden, A E D M

2013-12-01

298

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

2013-04-25

299

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

300

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

301

Mesoscopic structuring and yield stress of magnetofluidized fine particles  

NASA Astrophysics Data System (ADS)

The fluidization behavior of a bed of fine magnetizable particles excited by an externally applied magnetic field is found to depend on the aggregative nature of the particles before the field was applied. Usually nonaggregated particles organize in quasivertical local linear chains when the field is applied. In contrast, naturally aggregated particles form large-scale branched structures when magnetized by an external field. As a consequence the yield stress of magnetically stabilized beds of naturally aggregated particles is relatively increased and the bed can be stabilized at smaller field intensities. As expected from the magnetic cohesive force between magnetized particles, the yield stress is proportional to the square of the magnetic-field intensity, with a proportionality constant that depends on the mesoscopic organization on the magnetic particles. Remarkably, it is found that quasivertical chainlike structures are stable in spite of the fact that the magnetic field is applied in the horizontal direction.

Valverde, J. M.; Espin, M. J.; Quintanilla, M. A. S.; Castellanos, A.

2009-10-01

302

Doping and Defect Structure of Tetradymite-Type Crystals  

NASA Astrophysics Data System (ADS)

Nonstoichiometry of tetradymite-type crystals A{2/V}B{3/VI} that are grown from stoichiometric melts leads to the formation of native defects in the crystal lattice (predominantly antisite defects, A{B/-1} and vacancies V{B/+2} in the anion sublattice). This paper summarizes the basic ideas concerning a point defect model in A{2/V}B{3/VI} crystals. It turns out that a variety of doping elements interact with the native defects. Such interactions alter the concentration of free charge carriers, affect the doping efficiency, and modify the transport properties. Detailed understanding of the defect structure in tetradymite-type crystals is very important as it impacts on the efficiency of these materials when used as active elements in thermoelectric coolers.

Drasar, C.; Lostak, P.; Uher, C.

2010-09-01

303

Morphology, crystal structure, phase transitions and blend compatibility of thermotropic liquid crystal terpolyesters  

NASA Astrophysics Data System (ADS)

The morphology, crystal structure, phase transitions and blend compatibility of a series of semiflexible thermotropic liquid crystal terpolyesters (LCPs) were studied to understand their crystallization behavior and establish relationships between their microstructure and physical properties. Main characterization methods were electron microscopy and diffraction, and differential scanning calorimetry. The LCPs were composed of equimolar amounts of p-oxybenzoate, p-dioxyphenyl, and aliphatic segments, containing variable number, n, of methylenes. Most work was done with P7, n = 7, which has been reported to exhibit chain folding in thin films, with 100 A thick lamellae and unit cell dimensions of a = 8.3 A and b = 5.1 A. An analogue terpolyester, P7-X, with a chlorine pendant group was also investigated; although exhibiting mostly glassy behavior, crystallized samples had unit cell dimensions of a = 7.6 A and b = 5.0 A. Effects of crystallization conditions such as cooling rate, state from which crystallized, and annealing, in the melt and in solution, were analyzed using bulk samples, and quiescent and sheared films. The morphology was observed to be more sensitive to small changes in cooling rate as well as to the type of solvent, while crystal structure and phase transitions depended mostly on the state from which the sample was crystallized. Attempts to produce polymer single crystals, by a method called Confined Thin Film Melt Polymerization, resulted in the formation of oligomers with an average number of six repeat units. These samples produced macrocrystals with lateral dimensions of up to 0.65 mm, and diffraction measurements and thermal behavior similar to those of their corresponding bulk versions. Deviations from the typical p-oxybenzoate homopolymer crystal structures were observed for n = 3. Compatibility of P7 and P7-X in binary blends with polyethylene (PE), polyethylene terephthalate (PET), and nylon 6 (Ny6), was examined to evaluate the effect of the aliphatic segment in promoting good adhesion at the interphase. Partial compatibility was observed for PE blends, while miscibility was obtained in PET and Ny6 blends mixed at high temperatures due to the occurrence of transreactions.

Gonzalez-Costoso, Clara Lena

304

Novel Banded Structures in a Combined Main-Chain/Side-Chain Crystalline Polyester: from Liquid Crystals to Confined Crystals  

NASA Astrophysics Data System (ADS)

Characterization of banded structures obtained from liquid crystals to confined crystallization has been investigated using optical and atomic force microscopy. A combined main-chain/side-chain liquid crystalline (LC) polyester, PEFBP(n = 11), was focused on to illustrate the formation of interesting additional bands on crystallization. On macroscopic scales, both approaches can be applied to visualize the morphological changes in these banded textures. In tapping mode AFM, the 3-D topographic banding images are detected in the height image from 3.5 ?m LC bands to 50 nm confined crystal bands. The sub-surface fine features of edge-on crystal (KO) lamellae are differentiated in an extended chain conformation in the phase image. The formation of complicated banded structures from liquid crystals to confined crystallization is recognized as a new element: self-elongated 1-D crystal growth in the confined LC matrix on crystallization.

Ge, Jason J.; Wensheng; Zhou; Zhang, John Z.; Wang, Shy-Yeu; Harris, Frank W.; Cheng, Stephen Z. D.

2000-03-01

305

Structure and NLO property relationship in a novel chalcone co-crystal  

NASA Astrophysics Data System (ADS)

Single crystals of a chalcone co-crystal (C18H19NO4/C17H16NO3Br; 0.972/0.028) have been grown by slow evaporation from solution. The powder second harmonic generation (SHG) efficiency of this chalcone co-crystal is 7 times that of urea. The dependence of second harmonic (SH) intensity on particle size revealed the existence of phase matching direction in this crystal. The large SHG efficiency observed is mainly due to the unidirectional alignment of molecular dipoles, in which the dipole moment of each molecule adds to establish a net polarization. The weak N-H ???O hydrogen-bond interactions help to stabilize the noncentrosymmetric crystal packing and also contribute partly to the SHG. The better thermal stability, transparency and high laser damage resistance (>1.5 GW cm-2 at 532 nm, 8 ns) of this chalcone co-crystal indicate that it is a promising material for frequency doubling of diode lasers down to 470 nm. This molecule also shows a third-order NLO response and good optical limiting property of 8 ns laser pulses at 532 nm. The mechanism for optical limiting in this chalcone was attributed to two-photon induced excited state absorption that leads to reverse saturable absorption. The structure-property relationship in this chalcone and related compounds is discussed based on the experimental results and semiempherical hyperpolarizability calculations.

Ravindra, H. J.; Chandrashekaran, K.; Harrison, W. T. A.; Dharmaprakash, S. M.

2009-03-01

306

Photonics of liquid-crystal structures: A review  

SciTech Connect

The original results of studies of the electro-optical and laser effects which have been performed at the Laboratory of Liquid Crystals of the Institute of Crystallography, Russian Academy of Sciences, over the last few years are reviewed. Cholesteric liquid crystals as vivid representatives of photonic structures and their behavior in an electric field are considered in detail. The formation of higher harmonics in the periodic distribution of the director field in a helical liquid crystal structure and, correspondingly, the new (anharmonic) mode of electro-optical effects are discussed. Another group of studies is devoted to bistable light switching by an electric field in chiral nematics. Polarization diffraction gratings controlled by an electric field are also considered. The results of studies devoted to microlasers on various photonic structures with cholesteric and nematic liquid crystals are considered in detail. Particular attention is given to the new regime: leaky-mode lasing. Designs of liquid crystal light amplifiers and their polarization, field, and spectral characteristics are considered in the last section.

Palto, S. P., E-mail: palto@online.ru; Blinov, L. M.; Barnik, M. I.; Lazarev, V. V.; Umanskii, B. A.; Shtykov, N. M. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2011-07-15

307

[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

308

Chemical space sampling by different scoring functions and crystal structures.  

PubMed

Virtual screening has become a popular tool to identify novel leads in the early phases of drug discovery. A variety of docking and scoring methods used in virtual screening have been the subject of active research in an effort to gauge limitations and articulate best practices. However, how to best utilize different scoring functions and various crystal structures, when available, is not yet well understood. In this work we use multiple crystal structures of PI3 K-gamma in both prospective and retrospective virtual screening experiments. Both Glide SP scoring and Prime MM-GBSA rescoring are utilized in the prospective and retrospective virtual screens, and consensus scoring is investigated in the retrospective virtual screening experiments. The results show that each of the different crystal structures that was used, samples a different chemical space, i.e. different chemotypes are prioritized by each structure. In addition, the different (re)scoring functions prioritize different chemotypes as well. Somewhat surprisingly, the Prime MM-GBSA scoring function generally gives lower enrichments than Glide SP. Finally we investigate the impact of different ligand preparation protocols on virtual screening enrichment factors. In summary, different crystal structures and different scoring functions are complementary to each other and allow for a wider variety of chemotypes to be considered for experimental follow-up. PMID:20401681

Brooijmans, Natasja; Humblet, Christine

2010-05-01

309

Ab initio crystal structure prediction-I. Rigid molecules.  

PubMed

A new methodology for the prediction of molecular crystal structures using only the atomic connectivity of the molecule under consideration is presented. The approach is based on the global minimization of the lattice enthalpy of the crystal. The modeling of the electrostatic interactions is accomplished through a set of distributed charges that are optimally and automatically selected and positioned based on results of quantum mechanical calculations. A four-step global optimization algorithm is used for the identification of the local minima of the lattice enthalpy surface. A parallelized implementation of the algorithm permits a much more extensive search of the solution space than has hitherto been possible, allowing the identification of crystal structures in less frequently occurring space groups and with more than one molecule in the asymmetric unit. The algorithm has been applied successfully to the prediction of the crystal structures of 3-aza-bicyclo(3.3.1)nonane-2,4-dione (P2(1)/a, Z' = 1), allopurinol (P2(1)/c, Z' = 1), 1,3,4,6,7,9-hexa-azacycl(3.3.3)azine (Pbca, Z' = 2), and triethylenediamine (P6(3)/m, Z' = 1). In all cases, the experimentally known structure is among the most stable predicted structures, but not necessarily the global minimum. PMID:15622548

Karamertzanis, Panagiotis G; Pantelides, Constantinos C

2005-02-01

310

Crystal structure and vibrational spectral studies of a new organic-inorganic crystal: 4-Benzylpiperidinium trioxonitrate.  

PubMed

Single crystals of a new organic-inorganic crystal, 4-benzylpiperidinium trioxonitrate (4-BPPN) were grown by slow evaporation at room temperature and were characterized by X-ray diffraction, DTA-TG measurement, FT-IR and FT-Raman spectroscopies. The title compound crystallizes in the monoclinic system P21/c at room temperature with the following parameters: a=12.787(8), b=9.007(5), c=11.120(5), ?=95.974(2) and Z=4. Its crystal structure is packing of alternated inorganic and organic layers parallel to (a, c) planes. The different components are connected by a bi-dimensional network of N-H?O hydrogen bonds. The ability of ions to form spontaneous three-dimensional structure through N-H?O hydrogen bond is fully utilized. These hydrogen bonds give notable vibrational effects. The optimized molecular structure and the vibrational spectra were calculated by the Density Functional Theory (DFT) method using the B3LYP function with the 6-31G(d) basis set. All observed vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our DFT calculations as a primary source of attribution and also by comparison with the previous results for similar compounds. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. PMID:24755637

Kessentini, Yassmin; Ben Ahmed, Ali; Al-Juaid, Salih S; Mhiri, Tahar; Elaoud, Zakaria

2014-08-14

311

Molecular dynamics simulation of fast particle irradiation on the single crystal CeO2  

NASA Astrophysics Data System (ADS)

We used a molecular dynamics method to simulate structural relaxation caused by the high-energy-ion irradiation of single crystal CeO2. As the initial condition, we assumed high thermal energy was supplied to the individual atoms within a cylindrical region of nanometer-order diameter located in the center of the single crystal. The potential proposed by Inaba et al. was utilized to calculate interactions between atoms [H. Inaba, R. Sagawa, H. Hayashi, K. Kawamura, Solid State Ionics 122 (1999) 95-103]. The supplied thermal energy was first spent to change the crystal structure into an amorphous one within a short period of about 0.3 ps, then it was dissipated in the crystal. We compared the obtained results with those of computer simulations for UO2 and found that CeO2 was more stable than UO2 when supplied with high thermal energy.

Sasajima, Y.; Ajima, N.; Osada, T.; Ishikawa, N.; Iwase, A.

2013-11-01

312

Crystal structure of amylose complexes with small ligands.  

PubMed

Amylose complexes were prepared, as lamellar single crystals and polycrystalline powders, from aqueous solutions by adding small flavor molecules. The morphology, crystal structure, and thermal properties of complexes with fenchone, menthone, and geraniol were determined using transmission electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry. The crystal structure was found to be similar to that of V amylose complexes with isopropanol. This implies that the crystallosolvates contain sixfold helices packed in orthorhombic unit cells, with the ligands possibly lying in the interhelical space. Different drying procedures were also studied leading to less resolved X-ray diagrams. The thermoanalysis confirmed that complexes with a relatively high crystallinity were formed. PMID:14607368

Nuessli, Jeannette; Putaux, Jean Luc; Bail, Patricia Le; Bulon, Alain

2003-12-01

313

Crystal structures of carbonates up to Mbar pressures determined by single crystal synchrotron radiation diffraction  

NASA Astrophysics Data System (ADS)

The recent improvements at synchrotron beamlines, currently allow single crystal diffraction experiments at extreme pressures and temperatures [1,2] on very small single crystal domains. We successfully applied such technique to determine the crystal structure adopted by carbonates at mantle pressures. The knowledge of carbon-bearing phases is in fact fundamental for any quantitative modelling of global carbon cycle. The major technical difficulty arises after first order transitions or decomposition reactions, since original crystal (apx. 10x10x5 ?m3) is transformed in much smaller crystalline domains often with random orientation. The use of 3D reciprocal space visualization software and the improved resolution of new generation flat panel detectors, however, allow both identification and integration of each single crystal domain, with suitable accuracy for ab-initio structure solution, performed with direct and charge-flipping methods and successive structure refinements. The results obtained on carbonates, indicate two major crystal-chemistry trends established at high pressures. The CO32- units, planar and parallel in ambient pressure calcite and dolomite structures, becomes non parallel in calcite- and dolomite-II and III phases, allowing more flexibility in the structures with possibility to accommodate strain arising from different cation sizes (Ca and Mg in particular). Dolomite-III is therefore also observed to be thermodynamically stable at lower mantle pressures and temperatures, differently from dolomite, which undergoes decomposition into pure end-members in upper mantle. At higher pressure, towards Mbar (lowermost mantle and D'' region) in agreement with theoretical calculations [3,4] and other experimental results [5], carbon coordination transform into 4-fold CO4 units, with different polymerisation in the structure depending on carbonate composition. The second important crystal chemistry feature detected is related to Fe2+ in Fe-bearing magnesite, which spontaneously oxidises at HP/HT, forming Fe3+ carbonates, Fe3+ oxides and reduced carbon (diamonds). Single crystal diffraction approach allowed full structure determination of these phases, yielding to the discovery of few unpredicted structures, such as Mg2Fe2C4O13 and Fe13O19, which can be well reproduced in different experiments. Mg2Fe2C4O13 carbonate present truncated chain C4O13 groups, and Fe13O19 oxide, whose stoichiometry is intermediate between magnetite and hematite, is a one-layer structure, with features encountered in superconducting materials. The results fully support the ideas of unexpected complexities in the mineralogy of the lowermost mantle, and single crystal technique, once properly optimized in ad-hoc synchrotron beamlines, is fundamental for extracting accurate structural information, otherwise rarely accessible with other experimental techniques. References: [1] Merlini M., Hanfland M. (2013). Single crystal diffraction at Mbar conditions by synchrotron radiation. High Pressure Research, in press. [2] Dubrovinsky et al., (2010). High Pressure Research, 30, 620-633. [3] Arapan et al. (1997). Phys. Rev. Lett., 98, 268501. [4] Oganov et al. (2008) EPSL, 273, 38-47. [5] Boulard et al. (2011) PNAS, 108, 5184-5187.

Merlini, M.

2013-12-01

314

Precise characterization of grain structures, stacking disorders, and lattice disorders of a close-packed colloidal crystal  

NASA Astrophysics Data System (ADS)

The perpendicular fracture surface of a dried colloidal crystal with pillar-like grains, obtained by centrifugation of a dispersion of polystyrene particles, was observed using a scanning electron microscope. Many grain boundaries on the fracture surface were observed at the particle level. Most of the particles on the surface showed a face-centered cubic (FCC) array. Although some grains were single FCC ones, other FCC grains contained some stacking disorders. Most of the surface was covered with such grains, and the grain boundaries formed a mosaic-like pattern. From these results, we confirmed that the colloidal crystals obtained by centrifugation formed a bundle structure of pillar-like FCC grains. A fracture surface adjacent to the side wall of the growth cell was also observed. The surface was composed of several layers. In the uppermost layer closest to the wall, numerous point defects and mismatches of triangular lattices between the neighboring two-dimensional islands were observed. These mismatches and point defects probably generated several lattice defects in the crystal. Similar generation of lattice defects probably occurred at the bottom of the container or the growth front of the crystals. Screw dislocations were also found in the layers, although they were not observed frequently. From these results, it was concluded that two-dimensional nucleation growth and spiral growth probably occurred on the crystal-dispersion interfaces of colloidal crystals as well as on the surface of atomic crystals.

Suzuki, Yoshihisa; Mori, Atsushi; Fujiwara, Takahisa; Tamura, Katsuhiro

2011-05-01

315

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

2013-08-01

316

Crystal structure of human chorionic gonadotropin  

Microsoft Academic Search

The three-dimensional structure of human chorionic gonadotropin shows that each of its two different subunits has a similar topology, with three disulphide bonds forming a cystine knot. This same folding motif is found in some protein growth factors. The heterodimer is stabilized by a segment of the beta-subunit which wraps around the alpha-subunit and is covalently linked like a seat

A. J. Lapthorn; D. C. Harris; A. Littlejohn; J. W. Lustbader; R. E. Canfield; K. J. Machin; F. J. Morgan; N. W. Isaacs

1994-01-01

317

Crystal structure of photolysed carbonmonoxy-myoglobin  

NASA Astrophysics Data System (ADS)

MYOGLOBIN is a globular haem protein that reversibly binds lig-ands such as O2 and CO. Single photons of visible light can break the covalent bond between CO and the haem iron in carbonmonoxy-myoglobin (MbCO) and thus form an unstable intermediate, Mb*CO, with the CO inside the protein1,2. The ensuing rebinding process has been extensively studied as a model for the interplay of dynamics, structure and function in protein reactions. We have used X-ray crystallography at liquid-helium temperatures to determine the structure of Mb*CO to a resolution of 1.5 . The photodissociated CO lies on top of the haem pyrrole ring C. Comparison with the CO-bound and unligated myoglobin structures reveals that on photodissociation of the CO, the haem 'domes', the iron moves partially out of the haem plane, the iron proximal histidine bond is compressed, the F helix is strained and the distal histidine swings towards the outside of the ligand-binding pocket.

Schlichting, Ilme; Berendzen, Joel; Phillips, George N.; Sweet, Robert M.

1994-10-01

318

Collective aspects of charged particle track structure  

SciTech Connect

A plasmon generated by a swift charged particle constitutes a coherent excitation about the particle track. We discuss the representation of collective modes in impact parameter space when created by a swift ion or a fast electron, and the decay of these modes into localized excitations. Several alternative spatial representations are considered. We show that the high spatial resolution found in secondary electron emission measurements with scanning electron microscopy is consistent with the existence of the plasmon as an intermediary between the fast incident electron and the measured secondary electrons. 24 refs., 6 figs.

Basbas, G. (Physical Review Letters, Ridge, NY (USA)); Howie, A. (Cambridge Univ. (UK). Cavendish Lab.); Ritchie, R.H. (Oak Ridge National Lab., TN (USA) Tennessee Univ., Knoxville, TN (USA). Dept. of Physics)

1989-01-01

319

Viral capsomere structure, surface processes and growth kinetics in the crystallization of macromolecular crystals visualized by in situ atomic force microscopy  

NASA Astrophysics Data System (ADS)

In situ atomic force microscopy (AFM) was used to investigate surface evolution during the growth of single crystals of turnip yellow mosaic virus (TYMV), cucumber mosaic virus (CMV) and glucose isomerase. Growth of these crystals proceeded by two-dimensional (2D) nucleation. For glucose isomerase, from supersaturation dependencies of tangential step rates and critical step length, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated for different crystallographic directions. The molecular structure of the step edges, the adsorption of individual virus particles and their aggregates, and the initial stages of formation of 2D nuclei on the surfaces of TYMV and CMV crystals were recorded. The surfaces of individual TYMV virions within crystals were visualized, and hexameric and pentameric capsomers of the T=3 capsids were clearly resolved. This, so far as we are aware, is the first direct visualization of the capsomere structure of a virus by AFM. In the course of recording the in situ development of the TYMV crystals, a profound restructuring of the surface arrangement was observed. This transformation was highly cooperative in nature, but the transitions were unambiguous and readily explicable in terms of an organized loss of classes of virus particles from specific lattice positions.

Malkin, A. J.; Kuznetsov, Yu. G.; McPherson, A.

2001-11-01

320

Hierarchical self-assembly of telechelic star polymers: from soft patchy particles to gels and diamond crystals  

NASA Astrophysics Data System (ADS)

The design of self-assembling materials in the nanometer scale focuses on the fabrication of a class of organic and inorganic subcomponents that can be reliably produced on a large scale and tailored according to their vast applications for, e.g. electronics, therapeutic vectors and diagnostic imaging agent carriers, or photonics. In a recent publication (Capone et al 2012 Phys. Rev. Lett. 109 238301), diblock copolymer stars have been shown to be a novel system, which is able to hierarchically self-assemble first into soft patchy particles and thereafter into more complex structures, such as the diamond and cubic crystal. The self-aggregating single star patchy behavior is preserved from extremely low up to high densities. Its main control parameters are related to the architecture of the building blocks, which are the number of arms (functionality) and the fraction of attractive end-monomers. By employing a variety of computational and theoretical tools, ranging from the microscopic to the mesoscopic, coarse-grained level in a systematic fashion, we investigate the crossover between the formation of microstructure versus macroscopic phase separation, as well as the formation of gels and networks in these systems. We finally show that telechelic star polymers can be used as building blocks for the fabrication of open crystal structures, such as the diamond or the simple-cubic lattice, taking advantage of the strong correlation between single-particle patchiness and lattice coordination at finite densities.

Capone, Barbara; Coluzza, Ivan; Blaak, Ronald; Lo Verso, Federica; Likos, Christos N.

2013-09-01

321

Integrable structure of melting crystal model with external potentials  

Microsoft Academic Search

This is a review of the authors' recent results on an integrable structure of the melting crystal model with external potentials. The partition function of this model is a sum over all plane partitions (3D Young diagrams). By the method of transfer matrices, this sum turns into a sum over ordinary partitions (Young diagrams), which may be thought of as

Toshio Nakatsu; Kanehisa Takasaki

2008-01-01

322

Crystal Structure and Dielectric Properties of PZT Ferroelectric Ceramic Fibers  

Microsoft Academic Search

The crystal structures of PZT ceramic fibers with continuum spinning process were identified, showing a pure tetragonal phase of perovskite for the samples treated at around 900C. The microstructures of the PZT fibers were observed, displaying relatively complex evolution with the increasing of temperature during heat treatment. With the increasing of frequency, the dielectric constants and loss tangents became smaller

Z. X. Xiong; J. Pan; H. Xue; M. F. Mai; H. Qiu; L. F. Chen

2010-01-01

323

Theoretical strength and structural response of Cu crystal  

Microsoft Academic Search

The theoretical strength and structural response of FCC crystal Cu under uniaxial loading along one edge of a unit cell have been investigated with MAEAM. The stability criteria of the tetragonal system are extended to the generally stressed orthogonal system. The results show that, even if an orthorhombic path is applied, the deformation is spontaneously along the tetragonal Bain path

Jian-Min Zhang; Yan Yang; Ke-Wei Xu; Vincent Ji

2008-01-01

324

Green-Function Method for Electronic Structure of Periodic Crystals  

NASA Astrophysics Data System (ADS)

A new Green-function program for electronic-structure calculations for periodic crystals in shortly described and some modifications necessary for using the Intel iPSC/860 are given. The computing power of the iPSC/860 for the total-energy calculation of fcc Cu is compared to various other computers.

Zeller, R.

325

The Crystal and Molecular Structure of 3-Nitroperchlorylbenzene.  

National Technical Information Service (NTIS)

3-Nitroperchlorylbenzene forms acicular crystals, with space group Pbn21 (No. 33). There are four molecules in the unit cell with a=14.717, b=10.707, and c=5.032 A. The structure was solved from a sharpened three-dimensional Patterson function and refined...

K. N. Trueblood G. J. Palenik J. Donohue

1967-01-01

326

Crystal Structure and Stereochemistry Study of 2-Substituted Benzoxazole Derivatives  

PubMed Central

The structure of 2-[(4-chlorophenylazo) cyanomethyl] benzoxazole, C15H9ClN4O (I), has triclinic (P1?) symmetry. The structure displays NH ? N hydrogen bonding. The structure of 2-[(arylidene) cyanomethyl] benzoxazoles, C17H10N2O3 (II), has triclinic (P1?) symmetry. The structure displays CH ? N, CH ? C hydrogen bonding. In (I), the chlorophenyl and benzoxazole groups adopt a trans configuration with respect to the central cyanomethyle hydrazone moiety. Compound (II) crystallized with two molecules in the asymmetric unit shows cisoid conformation between cyano group and benzoxazole nitrogen, contrary to (I). In (II) the benzodioxole has an envelope conformation (the C17 atom is the flap atom). The molecular geometry obtained using molecular mechanics (MM) calculations has been discussed along with the results of single crystal analysis.

Mabied, Ahmed F.; Shalaby, Elsayed M.; Zayed, Hamdia A.; El-Kholy, Esmat; Farag, Ibrahim S. A.; Ahmed, Naima A.

2014-01-01

327

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

328

Domain structures in nematic liquid crystals on a polycarbonate surface.  

PubMed

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. PMID:23965955

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

2013-01-01

329

Study of crystal structure at high temperature phase in KIO 3 crystal by synchrotron powder X-ray diffraction  

Microsoft Academic Search

The accurate crystal structure of the I-phase in KIO3 crystal has been obtained at 530 K, for the first time, by the MEM\\/Rietveld analysis from high-energy X-ray powder-diffraction data. The crystal structure of the I-phase is the rhombohedral perovskite structure (space group R3m; Z=1). The MEM charge-density distributions reveal that the shorter IO bond exhibits a covalent bonding character and

Hirofumi Kasatani; Shinobu Aoyagi; Yoshihiro Kuroiwa; Kenichiro Yagi; Ryoko Katayama; Hikaru Terauchi

2003-01-01

330

Synthesis of Highly Charged, Monodisperse Polystyrene Colloidal Particles for the Fabrication of Photonic Crystals.  

PubMed

We have developed a series of emulsion polymerization recipes for the synthesis of highly charged, monodisperse polystyrene colloids of diameters between 100-400 nm. These spherical colloidal particles were crosslinked with divinyl benzene and functionalized with 1-allyloxy-2-hydroxypropane sulfonate. These highly charged, monodisperse colloidal particles readily self-assemble into robust three-dimensionally ordered crystalline colloidal arrays (CCAs). These CCAs operate as photonic crystals that Bragg diffract light in the ultraviolet, visible, and infrared regions of the spectrum. Copyright 2000 Academic Press. PMID:11071735

Reese; Guerrero; Weissman; Lee; Asher

2000-12-01

331

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

332

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

333

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 Claisen-Schmidt 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. UV-visible 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

334

Multiplexed DNA detection using spectrally encoded porous SiO2 photonic crystal particles  

PubMed Central

A particle-based multiplexed DNA assay based on encoded porous SiO2 photonic crystal disks is demonstrated. A spectral barcode is generated by electrochemical etch of a single-crystal silicon wafer using a programmed current-time waveform. A lithographic procedure is used to isolate cylindrical microparticles 25 microns in diameter and 10 microns thick, which are then oxidized, modified with a silane linker, and conjugated to various amino functionalized oligonucleotide probes via cyanuric chloride. It is shown that the particles can be decoded based on their reflectivity spectra, and that a multiple analyte assay can be performed in a single sample with a modified fluorescence microscope. The homogeneity of the reflectivity and fluorescence spectra, both within and across the microparticles is also reported.

Meade, Shawn O.; Chen, Michelle Y.

2009-01-01

335

Sample Preparation and Photoluminescence of ZnO Particles Embedded in Thin Alkali Halide Crystals  

NASA Astrophysics Data System (ADS)

We have prepared samples of ZnO particles embedded in thin alkali halide crystals by a melt growth method and have measured photoluminescence spectra at various temperatures. In the spectra measured at 8.5 K, free exciton (FE) and bound exciton (BE) emission lines are clearly recognized, while the well-known green band is hardly observed. The FE line appears at temperatures between 8.5 K and 300 K. The widths of both lines are very sharp and almost equal to that of ZnO epitaxial layers grown by a molecular beam epitaxy method. These results strongly suggest that high-quality ZnO particles can be well embedded in thin alkali halide crystals.

Harada, Yoshiyuki; Kondo, Hisao; Ichimura, Nobuko; Hashimoto, Satoshi

1999-11-01

336

Crystal structure of homoserine O-acetyltransferase from Leptospira interrogans  

Microsoft Academic Search

Homoserine O-acetyltransferase (HTA, EC 2.3.1.31) initiates methionine biosynthesis pathway by catalyzing the transfer of acetyl group from acetyl-CoA to homoserine. This study reports the crystal structure of HTA from Leptospira interrogans determined at 2.2 resolution using selenomethionyl single-wavelength anomalous diffraction method. HTA is modular and consists of two structurally distinct domainsa core ?\\/? domain containing the catalytic site and a

Mingzhu Wang; Lin Liu; Yanli Wang; Zhiyi Wei; Ping Zhang; Yikun Li; Xiaohua Jiang; Hang Xu; Weimin Gong

2007-01-01

337

Crystal structure of new AsS2 compound  

NASA Astrophysics Data System (ADS)

AsS2 single crystals have been obtained for the first time from an As2S3 melt at pressures above 6 GPa and temperatures above 800 K in the As2S3 ? AsS + AsS2 reaction. The monoclinic structure of the new high-pressure phase is solved by X-ray diffraction analysis and compared to the structure of high-pressure AsS phase, which was studied previously.

Bolotina, N. B.; Brazhkin, V. V.; Dyuzheva, T. I.; Lityagina, L. M.; Kulikova, L. F.; Nikolaev, N. A.; Verin, I. A.

2013-01-01

338

Crystal structure of cyclin-dependent kinase 2  

Microsoft Academic Search

Cyclin-dependent kinase 2 (CDK2) is a member of a highly conserved family of protein klnases that regulate the eukaryotic cell cycle. The crystal structures of the human CDK2 apoenzyme and its Mg2+ATP complex have been determined to 2.4 resolution. The structure is bi-lobate, like that of the cyclic AMP-dependent protein kinase, but contains a unique helix-loop segment that interferes with

Hendrik L. de Bondt; Jody Rosenblatt; Jarmila Jancarik; Heather D. Jones; David O. Morgant; Sung-Hou Kim

1993-01-01

339

Structures and properties of Fe-C fine particles prepared by AC arc discharge  

NASA Astrophysics Data System (ADS)

Fe-C fine particles are produced by an alternating arc discharge between iron and carbon electrodes in an Ar gas atmosphere at pressures of 8, 14 and 18 kPa. The crystal structure, morphology and surface composition have been studied, respectively, by X-ray diffraction, transmission electron microscopy, selected area electron diffraction and X-ray photoelectron spectroscopy. Magnetic properties and Curie temperatures have also been determined by a vibrating sample magnetometer. Results show that the particles are of two different crystal structures, one is hexagonal FeC and the other is cubic iron. The iron particles have a multi-layered structure composed of an ?-Fe core wrapped by Fe 3O 4, FeO and FeO(OH) shells. It is found that the compositions and the specific saturation magnetization of the Fe-C particles prepared in different pressures of Ar gas are not the same, but their Curie temperatures are all 5805C.

Li, Jian; Liu, Cunye; Zhao, Baogang; Lin, Yaoqiang; Deng, Zhaojing

1999-05-01

340

Self-powdering and nonlinear optical domain structures in ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3} crystals formed in glass  

SciTech Connect

Ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3}, (GMO), crystals are formed through the crystallization of 21.25Gd{sub 2}O{sub 3}-63.75MoO{sub 3}-15B{sub 2}O{sub 3} glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50-500 {mu}m spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called 'self-powdering phenomenon during crystallization' in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and a spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO{sub 4}){sup 2-} tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals. - Graphical abstract: This figure shows the polarized optical photograph at room temperature for a particle (piece) obtained by a heat treatment of the glass at 590 deg. C for 2 h in an electric furnace in air. This particle was obtained through the self-powdering behavior in the crystallization of glass. The periodic domain structure is observed. Ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3} crystals are formed in the particle, and second harmonic generations are detected, depending on the domain structure.

Tsukada, Y.; Honma, T. [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188 (Japan); Komatsu, T., E-mail: komatsu@mst.nagaokaut.ac.j [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188 (Japan)

2009-08-15

341

Crystal growth, structure analysis and characterisation of 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid single crystal  

NASA Astrophysics Data System (ADS)

Single crystal of dielectric material 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid has been grown by slow evaporation solution growth method. The grown crystal was harvested in 25 days. The crystal structure was analyzed by Single crystal X - ray diffraction. UV-vis-NIR analysis was performed to examine the optical property of the grown crystal. The thermal property of the grown crystal was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric measurements were carried out and the dielectric constant was calculated and plotted at all frequencies.

Sankari, R. Siva; Perumal, Rajesh Narayana

2014-04-01

342

Crystal Structure of Uronate Dehydrogenase from Agrobacterium tumefaciens*  

PubMed Central

Uronate dehydrogenase from Agrobacterium tumefaciens (AtUdh) belongs to the short-chain dehydrogenase/reductase superfamily and catalyzes the oxidation of d-galacturonic acid and d-glucuronic acid with NAD+ as a cofactor. We have determined the crystal structures of an apo-form of AtUdh, a ternary form in complex with NADH and product (substrate-soaked structure), and an inactive Y136A mutant in complex with NAD+. The crystal structures suggest AtUdh to be a homohexamer, which has also been observed to be the major form in solution. The monomer contains a Rossmann fold, essential for nucleotide binding and a common feature of the short-chain dehydrogenase/reductase family enzymes. The ternary complex structure reveals a product, d-galactaro-1,5-lactone, which is bound above the nicotinamide ring. This product rearranges in solution to d-galactaro-1,4-lactone as verified by mass spectrometry analysis, which agrees with our previous NMR study. The crystal structure of the mutant with the catalytic residue Tyr-136 substituted with alanine shows changes in the position of Ile-74 and Ser-75. This probably altered the binding of the nicotinamide end of NAD+, which was not visible in the electron density map. The structures presented provide novel insights into cofactor and substrate binding and the reaction mechanism of AtUdh. This information can be applied to the design of efficient microbial conversion of d-galacturonic acid-based waste materials.

Parkkinen, Tarja; Boer, Harry; Janis, Janne; Andberg, Martina; Penttila, Merja; Koivula, Anu; Rouvinen, Juha

2011-01-01

343

Magnetic nano-particles of Ni in MgO single crystals by ion implantation  

Microsoft Academic Search

Magnetic Ni nano-particles in the near surface regions of MgO single crystals have been synthesized by 64 keV Ni ion implantation to 1 1017 cm-2 followed by thermal annealing. Transmission electron microscopy (TEM) and magnetic properties measurement system (MPMS) equipped with a superconducting quantum interference device (SQUID) detector have been employed to characterize the microstructure and magnetic properties of

S. Zhu; X. Xiang; X. T. Zu; L. M. Wang

2006-01-01

344

Crystal structure and vibrational spectra of piperazinium bis(4-hydroxybenzenesulphonate) molecular-ionic crystal.  

PubMed

The piperazinium bis(4-hydroxybenzenesulphonate) crystallizes from water solution at room temperature in P2(1)/c space group of monoclinic system. The crystals are built up of doubly protonated piperazinium cations and ionized 4-hydroxybenzenesulphonate anions that interact through weak hydrogen bonds of O-H...O and N-H...O type. Mutual orientation of anions is determined by non-conventional hydrogen bonds of C-Hcdots, three dots, centeredpi type. Room temperature powder FT IR and FT Raman measurements were carried out. The vibrational spectra are in full agreement with the structure obtained from X-ray crystallography. The big single crystals of the title salt can be grown. PMID:17627870

Marchewka, M K; Pietraszko, A

2008-02-01

345

Structure of finite two-dimensional Yukawa lattices: dust crystals.  

PubMed

Dust particles in plasmas are often confined near the boundary between the plasma bulk and the sheath where the gravitation is balanced by electrostatic force. To keep dust particles from running away horizontally, an electrostatic potential is usually applied to the electrode surrounding these dusty plasmas and, under appropriate conditions, we have finite two-dimensional lattices of dust particles. Modeling the interaction between dust particles as the isotropic Yukawa interaction, structures of finite two-dimensional Yukawa systems at low temperatures have been analyzed both by numerical simulations and variational methods. The effect of the correlation energy between dust particles is shown to play an important role in the formation of the one-body distribution in these systems. PMID:11736277

Totsuji, H; Totsuji, C; Tsuruta, K

2001-12-01

346

Effect of Gravity Level on the Particle Shape and Size During Zeolite Crystal Growth  

NASA Technical Reports Server (NTRS)

A microscopic diffusion model is developed to represent solute transport in the boundary layer of a growing zeolite crystal. This model is used to describe the effect of gravity on particle shape and solute distribution. Particle dynamics and crystal growth kinetics serve as the boundary conditions of flow and convection-diffusion equations. A statistical rate theory is used to obtain the rate of solute transport across the growing interface, which is expressed in terms of concentration and velocity of solute species. Microgravity can significantly decrease the solute velocity across the growing interface compared to its earth-based counterpart. The extent of this reduction highly depends on solute diffusion constant in solution. Under gravity, the flow towards the crystal enhances solute transport rate across the growing interface while the flow away from crystals reduces this rate, suggesting a non-uniform growth rate and thus an elliptic final shape. However, microgravity can significantly reduce the influence of flow and obtain a final product with perfect spherical shape. The model predictions compare favorably with the data of space experiment of zeolites grown in space.

Song, Hong-Wei; Ilebusi, Olusegun J.; Sacco, Albert, Jr.

2003-01-01

347

Characterization of particles in the Phoenix aerosol, and structure refinements of hollandite minerals  

SciTech Connect

Approximately 8000 particles, collected at three sites, from the Phoenix aerosol were analyzed, using an analytical SEM. In general, the composition of the aerosol at all three sites was similar. About 75% of the total number of particles in the coarse size fraction (>1 ..mu..m) have mineral-like compositions and are primarily derived from local rocks and soils. The remaining coarse particles are mainly sulfates, Pb compounds from automobile emissions and other anthropogenic particles. The submicron particle fraction of the Phoenix aerosol consists largely of sulfates, Pb compounds emitted from automobiles and other anthropogenic particles; an estimated 60 to 80% of the submicron particles are sulfates. Single crystal x-ray structure refinements were completed for the hollandite minerals hollandite ((Ba/sub 75/Pb/sub 16/Na/sub 10/K/sub 04/) (Mn,Fe,Al)/sub 8/ (O,OH)/sub 16/), cryptomelane ((K/sub 94/Na/sub 25/Sr/sub 13/Ba/sub 10/) (Mn,Fe,Al)/sub 8/(O,OH)/sub 16/), and priderite ((K/sub 90/Ba/sub 35/) (Ti,Fe,Mg)/sub 8/O/sub 16/), yielding residuals of R = .0165, R = .0299, and R = .0096, respectively. The first two structures are monoclinic (I 2/m), and priderite is tetragonal (I 4/m).

Post, J.E.

1981-01-01

348

Attempt to form ultrafine particles with hydride and amorphous structure  

NASA Astrophysics Data System (ADS)

TiH 2 particles with fcc structure can be produced in an atmosphere of reduced pressure of H 2, instead of an ordinary inactive gas, by the gas evaporation technique. The habit of the particles grown in the intermediate zone of a smoke is determined by means of electron microscope to be dodecahedral and consists of 8 {111} and 4 {100}. As in the case of Ti particles, the growth mechanism can be considered as follows: The bcc TiH 2 particles initially formed, the high temperature phase, are transformed into fcc structure, the low temperature phase, through the martensite transformation with a slight change of the habit, from the rhombic dodecahedral to simple dodecahedral. For the preparation of amorphous particles, first the quenching rate of a particle, d T/d t was estimated to be more than 10 4C/s. The quenching rate was estimated from measurements of the temperature gradient around the evaporation source, d T/d x and the rising velocity of the particles along the convection flow of residual gas, d x/d t. The preparation of ultrafine particles of Pd 80Si 20 chosen as a test material was attempted. However, the particles showed crystalline rather than amorphous structure.

Yatsuya, S.; Yanagida, A.; Yamauchi, K.; Mihama, K.

1984-12-01

349

Controlling the crystal structure of Ni nanoparticles by the use of alkylamines  

NASA Astrophysics Data System (ADS)

Ni nanoparticles were prepared via thermal decomposition of nickel acetate tetrahydrate in the presence of long-chain amines, which acted as both solvents and reducing agents. By tuning the reaction temperature, Ni nanostructures with either hcp or fcc crystal structure were obtained. In principle, higher temperatures favored the formation of hcp nanoparticles. The employment of additional surfactants such as 1-adamantanecarboxylic acid and trioctylphosphine-oxide facilitated the tuning of the particles' growth limit. The size of the particles varied between 5 and 120 nm. The magnetic features of fcc-Ni nanoparticles were quite similar to the corresponding 'bulk' ones. On the other hand, the hcp-Ni particles showed weak magnetic features, reflected by low magnetization values, the absence of saturation magnetization and by blocking temperatures far below room temperature.

Mourdikoudis, S.; Simeonidis, K.; Vilalta-Clemente, A.; Tuna, F.; Tsiaoussis, I.; Angelakeris, M.; Dendrinou-Samara, C.; Kalogirou, O.

2009-09-01

350

Production, purification, crystallization and structure determination of H-1 Parvovirus  

PubMed Central

Crystals of H-1 Parvovirus (H-1PV), an antitumor gene-delivery vector, were obtained for DNA-containing capsids and diffracted X-rays to 2.7? resolution using synchrotron radiation. The crystals belonged to the monoclinic space group P21, with unit-cell parameters a = 255.4, b = 350.4, c = 271.6?, ?=90.34. The unit cell contained two capsids, with one capsid per crystallographic asymmetric unit. The H-1PV structure has been determined by molecular replacement and is currently being refined.

Halder, Sujata; Nam, Hyun-Joo; Govindasamy, Lakshmanan; Vogel, Michele; Dinsart, Christiane; Salome, Nathalie; McKenna, Robert; Agbandje-McKenna, Mavis

2012-01-01

351

Crystal structure of alpha poly-p-xylylene.  

NASA Technical Reports Server (NTRS)

A crystal structure of alpha poly-p-xylylene is proposed with the help of data of oriented crystals grown during polymerization. The unit cell is monoclinic with the parameters a = 8.57 A, b = 10.62 A, c = 6.54 A (chain axis), and beta = 101.3 deg. Four repeating units per cell lead to a calculated density of 1.185 g/cu cm and a packing density of 0.71. The probable space group is P2 sub 1/m.

Kubo, S.; Wunderlich, B.

1971-01-01

352

Electronic structures of lead iodide based low-dimensional crystals  

NASA Astrophysics Data System (ADS)

The electronic structures of three-dimensional and two-dimensional lead-halide-based crystals CH3NH3PbI3 and (C4H9NH3)2PbI4 are investigated by photoelectron spectroscopy and band calculations using the linear combination of atomic orbitals within the density-functional theory. For both crystals, the top of the valence band is found to consist mainly of the ?-antibonding states of Pb 6s and I 5p orbitals, and the bottom of the conduction band to be composed primarily of the ?-antibonding states of Pb 6p and I 5s orbitals. Photoelectron spectra of the valence-band region indicate that the electronic structures change depending on the dimensionality of the crystals. Based on the calculation results, the differences observed in the spectra are rationalized in terms of narrowing bandwidth as the dimensionality decreases from three to two dimensions. It is shown that the bandwidth narrowing of the two-dimensional crystal is due to zero dispersion in the vertical direction and the Jahn-Teller effect in the layered structure. These effects lead to a wideband gap and high exciton stability in (C4H9NH3)2PbI4.

Umebayashi, T.; Asai, K.; Kondo, T.; Nakao, A.

2003-04-01

353

Self-Assembly of Colloidal Particles on Template Structures  

NASA Technical Reports Server (NTRS)

I will discuss recent experiments from my lab, which use surface templates to induce ordered colloidal structures. Particle assembly driven by entropic depletion, fluid convection, and sedimentation will be described. Confocal microscopy was used to visualize most of these samples.

Yodh, Arjun G.

2002-01-01

354

Use of Pom Pons To Illustrate Cubic Crystal Structures  

NASA Astrophysics Data System (ADS)

In general chemistry classes, students are introduced to the ways in which atoms are arranged in cubic crystal structures. Transposing the textbook illustrations into three dimensional structures is difficult for some students. This transitions is easier if a three dimensional model is available for examination. Several 3D models are cited. A quick to assemble, inexpensive, colorful, and durable alternative to these models and styrofoam balls is the use of olefin pom pons. Different sized pom pons can be used to demonstrate how the atomic radius will vary when comparing the different types of cubic crystal unit cells. Being made of a coarse material, pom pons can be stacked to illustrate different packing arrangements such as hexagonal close-packed and cubic close-packed structures. Pom pons make great atoms.

Cady, Susan G.

1997-07-01

355

Uptake of different crystal structures of TiO? nanoparticles by Caco-2 intestinal cells.  

PubMed

The gastrointestinal uptake of different crystal structures of TiO2 was investigated using Caco-2 intestinal cells. Caco-2 monolayers exhibited time-dependent, saturable uptake of Ti from TiO2 exposures of 1 mgl(-1) over 24h, which was influenced by crystal type. Initial uptake rates were 5.3, 3.73, 3.58 and 4.48 nmol mg(-1)protein h(-1) for bulk, P25, anatase and rutile forms respectively. All exposures caused elevations of Ti in the cells relative to the control (ANOVA P<0.05). Electron micrographs of the Caco-2 monolayer showed the presence of particles inside the cells, and energy dispersive spectroscopy (EDS) confirmed the composition as TiO2. Incubating the cells with 120 IU nystatin (putative endocytosis inhibitor) or 100 ?mol l(-1) vanadate (ATPase inhibitor) caused large increases in Ti accumulation for all crystal types relative to controls (ANOVA P<0.05), except for the rutile form with vanadate. Incubating the cells with 90 ?mol l(-1) genistein (tyrosine kinase inhibitor) or 27 ?mol l(-1) chloropromazine (clathrin-mediated endocytosis inhibitor) caused a large decrease in Ti accumulation relative to the controls (ANOVA P<0.05). Cell viability measures were generally good (low LDH leak, normal cell morphology), but there were some changes in the electrolyte composition (K(+), Na(+), Ca(2+), Mg(2+)) of exposed cells relative to controls. A rise in total Ca(2+) concentration in the cells was observed for all TiO2 crystal type exposures. Overall, the data shows that Ti accumulation for TiO2 NP exposure in Caco-2 cells is crystal structure-dependent, and that the mechanism(s) involves endocytosis of intact particles. PMID:24576787

Gitrowski, Constantinos; Al-Jubory, Aliaa R; Handy, Richard D

2014-05-01

356

Trapping of Topological-Structural Defects in Coulomb Crystals  

NASA Astrophysics Data System (ADS)

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 kinks internal mode of vibration, due to the kinks 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.

Mielenz, M.; Brox, J.; Kahra, S.; Leschhorn, G.; Albert, M.; Schaetz, T.; Landa, H.; Reznik, B.

2013-03-01

357

Crystal structure and density of helium to 232 kbar  

NASA Technical Reports Server (NTRS)

The properties of helium and hydrogen at high pressure are topics of great interest to the understanding of planetary interiors. These materials constitute 95 percent of the entire solar system. A technique was presented for the measurement of X-ray diffraction from single-crystals of low-Z condenses gases in a diamond-anvil cell at high pressure. The first such single-crystal X-ray diffraction measurements on solid hydrogen to 26.5 GPa were presented. The application of this technique to the problem of the crystal structure, equation of state, and phase diagram of solid helium is reported. Crucial for X-ray diffraction studies of these materials is the use of a synchrotron radiation source which provides high brillance, narrow collimation of the incident and diffracted X-ray beams to reduce the background noise, and energy-dispersive diffraction techniques with polychromatic (white) radiation, which provides high detection efficiency.

Mao, H. K.; Wu, Y.; Jephcoat, A. P.; Hemley, R. J.; Bell, P. M.; Bassett, W. A.

1988-01-01

358

Light output enhancement of light-emitting diodes with photonic crystal structure  

Microsoft Academic Search

New light-emitting diodes (LED) structure constituted by the photonic crystal (PhC) is presented, and the effects of structure parameters are investigated. Relying on the results of investigation, the structure parameters of photonic crystal LED are optimized. By Using the FDTD algorithm, the enhancement factor of photonic crystal LED is calculated efficiently, and the optimum values of structure parameters are obtained

Xiaoling Wang; Chunhui Niu; Zhehai Zhou

2010-01-01

359

New 2-methylimidazole-dicarboxylic acid molecular crystals: crystal structure and proton conductivity.  

PubMed

Three new proton conducting molecular crystals, 2-methylimidazole glutarate, 2-methylimidazole suberate and 2-methylimidazole azelate, were obtained and their structure was determined by the x-ray diffraction method. The structure of the crystals was found to be of layer-type. A hydrogen bond network between the heterocycle, glutaric acid and water molecules was apparent in a single layer of 2-methylimidazole glutarate, whereas chains consisting of two heterocyclic molecules linked with hydrogen bonds with dicarboxylic acid were distinguished in a single layer of 2-methylimidazole suberate and azelate crystals. Thermal stability of the crystals was characterized by differential scanning calorimetry and the electrical conductivity was studied by the impedance spectroscopy method. The maximum conductivity of 2-methylimidazole glutarate pellets amounts to 3.3 10(-2)Sm(-1) at 325K, in the case of 2-methylimidazole suberate pellets the maximum conductivity is 2.4 10(-4)Sm(-1) at 348K and for 2-methylimidazole azelate pellets the maximum conductivity reaches 6.9 10(-4)Sm(-1) at 353K. PMID:21715785

Lawniczak, P; Pogorzelec-Glaser, K; Pawlaczyk, Cz; Pietraszko, A; Szcze?niak, L

2009-08-26

360

Photoinduced Directional Motions of Microparticles at Air--Liquid-Crystal Interfaces of Azobenzene-Doped Liquid-Crystal Films with Homeotropic or Homogeneous Alignment Structures  

NASA Astrophysics Data System (ADS)

We investigated the effects of liquid-crystal (LC) alignments on photoinduced motions of microparticles at air--LC interfaces of azobenzene-doped LC films. In homeotropically aligned LC films, the lattice spacings of pseudo-hexagonal structures of microparticles site-selectively exhibited reversible expansion or contraction on alternating irradiation with ultraviolet and visible light. The particle motions were probably driven by photochemical deformation of LC surfaces. In homogeneously aligned films, alternating irradiation induced macroscopic convective flows followed by rapid gathering or dispersion of linear chains of microparticles. Particle motions were significantly influenced by LC alignments as well as the light wavelength.

Yamamoto, Takahiro; Yoshida, Masaru

2012-10-01

361

Azimuthal structures of produced particles in heavy-ion interactions  

SciTech Connect

The angular structures of particles produced in {sup 208}Pb at 158 A GeV/c and {sup 197}Au at 11.6 A GeV/c induced interactions with Ag(Br) nuclei in emulsion detector have been investigated. Nonstatistical well-ordered ring-like structures of produced particles in azimuthal plane of a collision have been found, and their parameters have been determined.

Vokal, S., E-mail: vokal@sunhe.jinr.ru; Orlova, G. I. [VBLHEP, JINR (Russian Federation); Lehocka, S. [University of P. J. Safarik (Slovakia)

2009-02-15

362

Phase Transitions in Liquid Crystal Doped with Magnetic Particles of Different Shapes in Combined Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

We have studied the influence of electric and magnetic fields on the orientational structure of ferronematics based on a thermotropic nematic 4-trans-4^' } -n-hexylcyclohexyl-isothiocyanato-benzene (6CHBT). The 6CHBT liquid crystal has been dissolved in phenyl isothiocyanate and doped with rod-like or chain-like magnetic particles. In such a mixture, the phase transition from an isotropic to a nematic phase is via a droplet state, i.e., coexistence of nematic and isotropic phases. The obtained results showed that a combination of the electric and magnetic fields can change the character of a phase transition from the isotropic to the nematic phase via the droplet state in such systems. Moreover, magneto-dielectric measurements of structural transitions showed the magnetic field induced a shift of the phase transition temperature from the isotropic to the droplet state.

Tomaovi?ov, Natlia; Timko, Milan; Zviov, Vlasta; Hashim, Aneka; Jadzyn, Jan; Chaud, Xavier; Beaugnon, Eric; Kop?ansk, Peter

2014-05-01

363

Is the methanation reaction over Ru single crystals structure dependent?  

PubMed

The influence of monoatomic steps and defects on the methanation reaction over ruthenium has been investigated. The experiments are performed on a Ru(0 1 54) ruthenium single crystal, which contains one monoatomic step atom for each 27 terrace atoms. The methanation activity is measured at one bar of hydrogen and CO in a high pressure cell, which enables simultaneous measurements of the local reactivity of the well defined single crystal surface and the global reactivity of the entire crystal and its auxiliary support. By adding sulfur we observe that the measured activity from the well defined stepped front-side of the crystal is poisoned faster than the entire crystal containing more defects. We also observe that additional sputtering of the well-defined front-side increases the reactivity measured on the surface. Based on this, we conclude that the methanation reaction takes place on undercoordinated sites, such as steps and kinks, and that the methanation reaction is extremely structure dependent. Simulations of the flow, temperature, and product distributions in the high pressure cell are furthermore presented as supplementary information. PMID:21258708

Vendelbo, Sren B; Johansson, Martin; Nielsen, Jane H; Chorkendorff, Ib

2011-03-14

364

The crystal structure of GROEL at 2.8 {angstrom}.  

SciTech Connect

The crystal structure of Escherichia coli GroEL shows a porous cylinder of 14 subunits made of two nearly 7-fold rotationally symmetrical rings stacked back-to-back with dyad symmetry. The subunits consist of three domains: a large equatorial domain that forms the foundation of the assembly at its waist and holds the rings together; a large loosely structured apical domain that forms the ends of the cylinder; and a small slender intermediate domain that connects the two, creating side windows. The three-dimensional structure places most of the mutationally defined functional sites on the channel walls and its outward invaginations, and at the ends of the cylinder.

Braig, K.; Otwinowski, Z.; Hegde, R.; Boisvert, D.; Joachimiak, A.; Horwich, A. L.; Sigler, P. B.; Center for Mechanistic Biology and Biotechnology; Yale Univ. School of Medicine; Yale Univ. School of Medicine

1995-01-01

365

Effect of precursor particle size on the densification and crystallization behavior of mullite  

SciTech Connect

Stoichiometric mullite, 3Al[sub 2]O[sub 3][center dot]2SiO[sub 2], has been prepared from a variety of colloidal and solution precursors. In order to change the level of mixing, the size of the silica particles has been varied while keeping the alumina (boehmite) particle size constant. The effect of varying particle size on the crystallization and densification behavior has been studied. Densification behavior was characterized by measuring the bulk density of pellets as a function of heat treatment temperature and by dilatometry. Phase development was examined by thermal analysis and X-ray diffraction. Results showed that the formation of crystalline phases including mullite inhibited densification. The formation of mullite was controlled by the initial segregation of alumina and silica in the gel. A heat treatment time-temperature profile designed to optimize the densification of the colloidal powders was investigated in order to compare the ability of the different gels to densify.

Fahrenholtz, W.G.; Smith, D.M. (Univ. of New Mexico, Albuquerque, NM (United States).Center for micro-engineered ceramics); Cesarano, J. III (Sandia National Laboratories, Albuquerque, NM (United States). Inorganic Materials Chemistry Div.)

1993-02-01

366

Association of Suprathermal Particles with Coherent Structures and Shocks  

NASA Astrophysics Data System (ADS)

Various mechanisms have been proposed to explain observed suprathermal particle populations in the solar wind, including direct acceleration at flares, stochastic acceleration, shock acceleration and acceleration by random compression or reconnection sites. Using magnetic field and suprathermal ion data from ACE, we identify coherent structures and interplanetary shocks, and analyze the temporal association of energetic particle fluxes with these coherent structures. Coherent structures having a range of intensities are identified using the magnetic PVI statistic, essentially a normalized vector increment. A stronger association of particle flux in the 0.047-4.75 MeV range is found with intense magnetic discontinuities than is found with shocks. The main results presented are on ions, but similar results have been found for electrons. The average profile of suprathermal particles near shocks is consistent with the expectations of diffusive shock acceleration. Significant fluxes of energetic particles as well as high occurrence rates of strong discontinuities are found within four hours after the passage a shock. Beyond that there appears to be a sharper drop-off in energetic particle intensity. This evidence supports the view that multiple mechanisms contribute to the acceleration and transport of interplanetary suprathermal particles. To make a statement about any specific mechanism we also study observed pitch angle distributions as well as comparisons with test particle simulations.

Tessein, J.; Matthaeus, W. H.; Wan, M.; Osman, K.; Ruffolo, D. J.; Giacalone, J.

2013-12-01

367

Crystal growth and crystal structures of the LnMnO 3 perovskites: Ln=Nd, Sm, Eu and Gd  

Microsoft Academic Search

Single crystal of LnMnO3 (Ln=Nd, Sm, Eu and Gd) was grown by floating zone method, and the crystal structure was determined by single crystal X-ray diffractometry. The structure of LnMnO3 belongs to the orthorhombic system (space group is Pnma, No. 62) with the lattice parameters a?2ap, b?2ap, c?2ap and Z=4, where ap is ideal cubic perovskite cell parameter.

Takanori Mori; Naoki Kamegashira; Katsuyuki Aoki; Toetsu Shishido; Tsuguo Fukuda

2002-01-01

368

Optical and luminescent properties of a series of molybdate single crystals of scheelite crystal structure  

Microsoft Academic Search

The luminescent and reflectivity spectra of a series of the molybdates with the scheelite crystal structure were investigated using synchrotron radiation. The main features in reflectivity spectra in the energy range of 3.2-40 eV were analyzed. The luminescence spectra were measured under X-ray excitation and their relative intensities were explained in the frames of the configuration curves model.

D. Spassky; S. Ivanov; I. Kitaeva; V. Kolobanov; V. Mikhailin; L. Ivleva; I. Voronina

2005-01-01

369

EVOEvolutionary algorithm for crystal structure prediction  

NASA Astrophysics Data System (ADS)

We present EVOan evolution strategy designed for crystal structure search and prediction. The concept and main features of biological evolution such as creation of diversity and survival of the fittest have been transferred to crystal structure prediction. EVO successfully demonstrates its applicability to find crystal structures of the elements of the 3rd main group with their different spacegroups. For this we used the number of atoms in the conventional cell and multiples of it. Running EVO with different numbers of carbon atoms per unit cell yields graphite as the lowest energy structure as well as a diamond-like structure, both in one run. Our implementation also supports the search for 2D structures and was able to find a boron sheet with structural features so far not considered in literature. Program summaryProgram title: EVO Catalogue identifier: AEOZ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOZ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License version 3 No. of lines in distributed program, including test data, etc.: 23488 No. of bytes in distributed program, including test data, etc.: 1830122 Distribution format: tar.gz Programming language: Python. Computer: No limitations known. Operating system: Linux. RAM: Negligible compared to the requirements of the electronic structure programs used Classification: 7.8. External routines: Quantum ESPRESSO (http://www.quantum-espresso.org/), GULP (https://projects.ivec.org/gulp/) Nature of problem: Crystal structure search is a global optimisation problem in 3N+3 dimensions where N is the number of atoms in the unit cell. The high dimensional search space is accompanied by an unknown energy landscape. Solution method: Evolutionary algorithms transfer the main features of biological evolution to use them in global searches. The combination of the "survival of the fittest" (deterministic) and the randomised choice of the parents and normally distributed mutation steps (non-deterministic) provides a thorough search. Restrictions: The algorithm is in principle only restricted by a huge search space and simultaneously increasing calculation time (memory, etc.), which is not a problem for our piece of code but for the used electronic structure programs. Running time: The simplest provided case runs serially and takes 30 minutes to one hour. All other calculations run for significantly longer time depending on the parameters like the number and sort of atoms and the electronic structure program in use as well as the level of parallelism included.

Bahmann, Silvia; Kortus, Jens

2013-06-01

370

Nanoscale potassium niobate crystal structure and phase transition  

PubMed Central

Nanoscale potassium niobate (KNbO3) powders of orthorhombic structure were synthesized using the sol-gel method. The heat-treatment temperature of the gels had a pronounced effect on KNbO3 particle size and morphology. Field emission scanning electron microscopy and transmission electron microscopy were used to determine particle size and morphology. The average KNbO3 grain size was estimated to be less than 100 nm, and transmission electron microscopy images indicated that KNbO3 particles had a brick-like morphology. Synchrotron X-ray diffraction was used to identify the room-temperature structures using Rietveld refinement. The ferroelectric orthorhombic phase was retained even for particles smaller than 50 nm. The orthorhombic to tetragonal and tetragonal to cubic phase transitions of nanocrystalline KNbO3 were investigated using temperature-dependent powder X-ray diffraction. Differential scanning calorimetry was used to examine the temperature dependence of KNbO3 phase transition. The Curie temperature and phase transition were independent of particle size, and Rietveld analyses showed increasing distortions with decreasing particle size.

2011-01-01

371

Dependence of scintillation characteristics in the CsI(Tl) crystal on Tl* concentrations under electron and alpha particles excitations  

Microsoft Academic Search

This paper reports the emission spectra, pulse heights and decay curves of CsI(Tl) crystals with a Tl* concentration ranging from 10-6 mol to 10-2 mol, under electron and alpha particle excitations. Larger pulse heights from the crystals with Tl+concentration of more than 10-3 mol were observed for a higher ionization density of alpha particle excitation, compared with those of electron

M. M. Hamadaa; F. E. Costa; M. C. C. Pereira; S. Kubota

2000-01-01

372

Dependence of scintillation characteristics in the CsI(Tl) crystal on Tl+ concentrations under electron and alpha particles excitations  

Microsoft Academic Search

This paper reports the emission spectra, pulse heights, and decay curves of CsI(TI) crystals with a Tl+ concentration ranging from 10-6 to 10-2 mol under electron and alpha particle excitations. Larger pulse heights from the crystals with Tl+ concentration of more than 10-3 mol were observed for a higher ionization density of alpha particle excitation compared with those of electron

Margarida M. Hamada; Fabio E. Costa; Maria C. C. Pereira; Shinzou Kubota

2001-01-01

373

Three-dimensional structure of polystyrene colloidal crystal by synchrotron radiation X-ray phase-contrast computed tomography  

NASA Astrophysics Data System (ADS)

Colloidal crystal with long-range ordered structure has attracted great attention for their applications in various fields. Although perfect colloidal crystals have been achieved by some fabrications for utilization, little is known about their exact structures and internal defects. In this study, we use synchrotron radiation (SR) phase-contrast computed tomography (CT) to noninvasively access the internal structure of polystyrene (PS) colloidal crystals in three dimensions (3D). The phase-attenuation duality Paganin algorithm phase retrieval was employed to achieve a satisfactory contrast and outline of the spheres. After CT reconstruction, the positions of individual PS particles and structural defects are identified in three dimensions, and the local crystal structure is revealed. Further quantitative analysis of the void system in colloidal crystal illustrates that single voids can be mostly attributed to tetrahedron void of sphere close packing, but the interconnected voids with large volume induce a sphere volume fraction of 59.39 % that reflects a metastable glass behavior of colloidal crystal arrangement. The void orientation result reveals that the 3D close-packing difficulty mainly lies in the stacking of interlayer.

Fu, Yanan; Xie, Honglan; Deng, Biao; Du, Guohao; Chen, Rongchang; Xiao, Tiqiao

2014-06-01

374

Three-dimensional structure of polystyrene colloidal crystal by synchrotron radiation X-ray phase-contrast computed tomography  

NASA Astrophysics Data System (ADS)

Colloidal crystal with long-range ordered structure has attracted great attention for their applications in various fields. Although perfect colloidal crystals have been achieved by some fabrications for utilization, little is known about their exact structures and internal defects. In this study, we use synchrotron radiation (SR) phase-contrast computed tomography (CT) to noninvasively access the internal structure of polystyrene (PS) colloidal crystals in three dimensions (3D). The phase-attenuation duality Paganin algorithm phase retrieval was employed to achieve a satisfactory contrast and outline of the spheres. After CT reconstruction, the positions of individual PS particles and structural defects are identified in three dimensions, and the local crystal structure is revealed. Further quantitative analysis of the void system in colloidal crystal illustrates that single voids can be mostly attributed to tetrahedron void of sphere close packing, but the interconnected voids with large volume induce a sphere volume fraction of 59.39 % that reflects a metastable glass behavior of colloidal crystal arrangement. The void orientation result reveals that the 3D close-packing difficulty mainly lies in the stacking of interlayer.

Fu, Yanan; Xie, Honglan; Deng, Biao; Du, Guohao; Chen, Rongchang; Xiao, Tiqiao

2014-04-01

375

Planar photonic crystal structure with inherently single-mode waveguides  

NASA Astrophysics Data System (ADS)

A planar photonic crystal that allows inherently gap-guided single-mode waveguides is proposed and discussed. This novel structure consists of a two-dimensional lattice of silicon rods embedded on a thin silica slab sandwiched between two silica claddings whose refractive indices are slightly lower than the index of the silica core. The physical parameters of the structure, i.e., rod radius and core thickness, are optimized to maximize the bandgap width for odd modes. Lossless guided modes inside the bandgap and below the claddings' light cone are obtained by reducing the radius of a row of rods. The waveguide bandwidth can be increased by inserting a thin silicon dielectric waveguide instead of the row of rods. The proposed approach may overcome many of the common drawbacks in conventional holes-on-dielectric planar photonic crystal waveguides.

Martinez, Alejandro; Garcia, Jaime; Sanchez, Guillermo; Marti, Javier

2003-11-01

376

Structure development in silicon sheet by shaped crystallization  

NASA Technical Reports Server (NTRS)

Models are presented for the development of a parallel twinned structure of the 110 plane type and the 112 line type in silicon ribbons. The models are believed to be mutually compatible and operable. The first model relates the requirements for super-cooling during crystallization. The existence of reentrant angles associated with the twin structure is proposed to provide a rough interface to reduce super-cooling. The spacing of the twins is proposed to be limited by the geometrical relationship between the thermal gradient in the liquid and the dimensions of the twinned crystallization front. The second model relates the thermal stress configuration to detail dislocation reactions which would be expected to develop twins. While a specific dislocation mechanism cannot yet be defined, a number of alternatives are presented. All of these various dislocation mechanisms would result in the observed crystalline configuration and the choice among them is not critical.

Leipold, M. H.; De Angelis, R. J.

1978-01-01

377

Crystal structures of Aedes aegypti alanine glyoxylate aminotransferase.  

PubMed

Mosquitoes are unique in having evolved two alanine glyoxylate aminotransferases (AGTs). One is 3-hydroxykynurenine transaminase (HKT), which is primarily responsible for catalyzing the transamination of 3-hydroxykynurenine (3-HK) to xanthurenic acid (XA). Interestingly, XA is used by malaria parasites as a chemical trigger for their development within the mosquito. This 3-HK to XA conversion is considered the major mechanism mosquitoes use to detoxify the chemically reactive and potentially toxic 3-HK. The other AGT is a typical dipteran insect AGT and is specific for converting glyoxylic acid to glycine. Here we report the 1.75A high-resolution three-dimensional crystal structure of AGT from the mosquito Aedes aegypti (AeAGT) and structures of its complexes with reactants glyoxylic acid and alanine at 1.75 and 2.1A resolution, respectively. This is the first time that the three-dimensional crystal structures of an AGT with its amino acceptor, glyoxylic acid, and amino donor, alanine, have been determined. The protein is dimeric and adopts the type I-fold of pyridoxal 5-phosphate (PLP)-dependent aminotransferases. The PLP co-factor is covalently bound to the active site in the crystal structure, and its binding site is similar to those of other AGTs. The comparison of the AeAGT-glyoxylic acid structure with other AGT structures revealed that these glyoxylic acid binding residues are conserved in most AGTs. Comparison of the AeAGT-alanine structure with that of the Anopheles HKT-inhibitor complex suggests that a Ser-Asn-Phe motif in the latter may be responsible for the substrate specificity of HKT enzymes for 3-HK. PMID:16990263

Han, Qian; Robinson, Howard; Gao, Yi Gui; Vogelaar, Nancy; Wilson, Scott R; Rizzi, Menico; Li, Jianyong

2006-12-01

378

Electronic structure and optical spectra of oxyanion crystals  

Microsoft Academic Search

Band structure of lithium, sodium, and potassium nitrites, nitrates, chlorates, perchlorates, sulfites, and sulfates together\\u000a with the state density and the imaginary part of the complex dielectric permittivity is calculated by the DFT-LDA method with\\u000a the Perdew and Zunger (PZ) correlation potential using the software package CRYSTAL06 on the uniform grid comprising 512 points\\u000a of the Brillouin zone in the

Yu. N. Zhuravlev; D. V. Korabelnikov

2009-01-01

379

Lithium niobate: Summary of physical properties and crystal structure  

Microsoft Academic Search

Ferroelectric lithium niobate (LiNbO3) is widely used in integrated and guided-wave optics because of its favorable optical, piezoelectric, electro-optic, elastic, photoelastic, and photorefractive properties. However, detailed summaries of its pertinent physical properties and crystal structure are not readily available. In this tutorial paper, the important tensor physical properties and their mathematical descriptions are compiled and presented. The essential features of

R. S. Weis; T. K. Gaylord

1985-01-01

380

The crystal structure of SmPtSi  

Microsoft Academic Search

The ternary compound SmPtSi was found in studying the phase diagram of Sm-Pt-Si system (870 K). This work is concerned with the determination of the SmPtSi crystal structure. The X-ray diffraction study (using an RKD-57.3 camera and CrK radiation) of alloys obtained by fusion of the starting materials (Sm content is 0.9998, Pt and Si contents are 0.9999 mass fractions)

Zh. M. Barakatova; Yu. D. Seropegin; O. I. Bodak

1995-01-01

381

Structure of the Blue Phase of a Cholesteric Liquid Crystal  

Microsoft Academic Search

Bragg diffraction of visible and near-ultraviolet light in the blue phase of a cholesteric liquid crystal have been observed. It is found that there are two distinct blue phases: One is stable from about 0.5C below the clearing point to about 0.2C below it and has either a body-centered-cubic or simple-cubic structure. A second, clearly distinct phase appears in the

S. Meiboom; M. Sammon

1980-01-01

382

Crystal Structure of the West Nile Virus Envelope Glycoprotein  

Microsoft Academic Search

The envelope glycoprotein (E) of West Nile virus (WNV) undergoes a conformational rearrangement triggered by low pH that results in a class II fusion event required for viral entry. Herein we present the 3.0- crystal structure of the ectodomain of WNV E, which reveals insights into the flavivirus life cycle. We found that WNV E adopts a three-domain architecture that

Grant E. Nybakken; Christopher A. Nelson; Beverly R. Chen; Michael S. Diamond; Daved H. Fremont

2006-01-01

383

Crystal Structure of a Self-Spliced Group II Intron  

Microsoft Academic Search

Group II introns are self-splicing ribozymes that catalyze their own excision from precursor transcripts and insertion into new genetic locations. Here we report the crystal structure of an intact, self-spliced group II intron from Oceanobacillus iheyensis at 3.1 angstrom resolution. An extensive network of tertiary interactions facilitates the ordered packing of intron subdomains around a ribozyme core that includes catalytic

Navtej Toor; Kevin S. Keating; Sean D. Taylor; Anna Marie Pyle

2008-01-01

384

Crystal structure of the Src family tyrosine kinase Hck  

Microsoft Academic Search

The crystal structure of the haematopoietic cell kinase Hck has been determined at 2.6\\/2.9 resolution. Inhibition of enzymatic activity is a consequence of intramolecular interactions of the enzyme's Src-homology domains SH2 and SH3, with concomitant displacement of elements of the catalytic domain. The conformation of the active site has similarities with that of inactive cyclin-dependent protein kinases.

Frank Sicheri; Ismail Moarefi; John Kuriyan

1997-01-01

385

Redox-Coupled Crystal Structural Changes in Bovine Heart Cytochrome  

Microsoft Academic Search

Crystal structures of bovine heart cytochrome c oxidase in the fully oxidized, fully!reduced, azide-bound, and carbon monoxide-bound states were determined at 2.30,!2.35, 2.9, and 2.8 angstrom resolution, respectively. An aspartate residue apart from the!O 2 reduction site exchanges its effective accessibility to the matrix aqueous phase for!one to the cytosolic phase concomitantly with a significant decrease in the pK of

Shinya Yoshikawa; Kyoko Shinzawa-Itoh; Ryosuke Nakashima; Rieko Yaono; Eiki Yamashita; Noriko Inoue; Min Yao; Ming Jie Fei; Clare Peters Libeu; Tsunehiro Mizushima; Hiroshi Yamaguchi; Takashi Tomizaki; Tomitake Tsukihara

1998-01-01

386

Crystal Structures of Cisplatin Bound to a Human Copper Chaperone  

SciTech Connect

Copper trafficking proteins, including the chaperone Atox1 and the P{sub 1B}-type ATPase ATP7B, have been implicated in cellular resistance to the anticancer drug cisplatin. We have determined two crystal structures of cisplatin-Atox1 adducts that reveal platinum coordination by the conserved CXXC copper-binding motif. Direct interaction of cisplatin with this functionally relevant site has significant implications for understanding the molecular basis for resistance mediated by copper transport pathways.

Boal, Amie K.; Rosenzweig, Amy C.; (NWU)

2010-08-16

387

Crystal structures explain functional properties of two E. coli porins  

Microsoft Academic Search

Porins form aqueous channels that aid the diffusion of small hydrophilic molecules across the outer membrane of Gram-negative bacteria. The crystal structures of matrix porin and phosphoporin both reveal trimers of identical subunits, each subunit consisting of a 16-stranded anti-parallel beta-barrel containing a pore. A long loop inside the barrel contributes to a constriction of the channel where the charge

S. W. Cowan; T. Schirmer; G. Rummel; M. Steiert; R. Ghosh; R. A. Pauptit; J. N. Jansonius; J. P. Rosenbusch

1992-01-01

388

Nanoconfinement-Induced Structures in Chiral Liquid Crystals  

PubMed Central

We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution has been modified to represent the orientation dependence of the interaction between a pair of chiral liquid-crystal molecules. The liquid crystal is confined between a pair of planar and atomically smooth substrates onto which molecules are anchored in a hybrid fashion. Hybrid anchoring allows for the formation of helical structures in the direction perpendicular to the substrate plane without exposing the helix to spurious strains. At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality. More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II. If the distance between the confining substrates and molecular chirality are chosen properly, we see a third structure, which may be thought of as a hybrid, exhibiting mixed features of a cholesteric and a blue phase.

Melle, Michael; Theile, Madlona; Hall, Carol K.; Schoen, Martin

2013-01-01

389

Crystal structure of the integral membrane diacylglycerol kinase  

PubMed Central

Diacylglycerol kinase (DgkA) catalyzes the ATP-dependent phosphorylation of diacylglycerol to phosphatidic acid for use in shuttling water-soluble components to membrane derived oligosaccharide and lipopolysaccharide in the cell envelope of Gram-negative bacteria1. For half a century, this 121-residue kinase has served as a paradigm for investigating membrane protein enzymology1,3-7, folding8,9, assembly10-13, and stability1,14. Here, we present crystal structures for three functional forms of this unique and paradigmatic kinase, one of which is wild type (WT). These reveal a homo-trimeric enzyme with three transmembrane helices and an N-terminal amphiphilic helix per monomer. Bound lipid substrate and docked ATP identify the putative active site which is of the composite, shared site type. The crystal structures rationalize extensive biochemical and biophysical data on the enzyme. They are however at variance with a published solution NMR model2 in that domain swapping, a key feature of the solution form, is not observed in the crystal structures.

Li, Dianfan; Lyons, Joseph A.; Pye, Valerie E.; Vogeley, Lutz; Aragao, David; Kenyon, Colin P.; Shah, Syed T. A.; Doherty, Christine; Aherne, Margaret; Caffrey, Martin

2013-01-01

390

Structural contribution to the roughness of supersmooth crystal surface  

SciTech Connect

Technological advances in processing crystals (Si, sapphire {alpha}-Al{sub 2}O{sub 3}, SiC, GaN, LiNbO{sub 3}, SrTiO{sub 3}, 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 Multiplication-Sign 1 and 10 Multiplication-Sign 10 {mu}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., E-mail: amuslimov@mail.ru; Kanevsky, V. M.; Deryabin, A. N.; Pavlov, V. A.; Asadchikov, V. E. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2013-05-15

391

Growth and structural, optical, and electrical properties of zincite crystals  

SciTech Connect

An X-ray diffraction study of ZnO crystals grown by the hydrothermal method has revealed reflections that give grounds to assign them to the sp. gr. P3 rather than to P6{sub 3}mc. The distribution of Zn1, Zn2, O1, and O2 over structural positions, along with vacancies and incorporated zinc atoms, explains the dissymmetrization observed in terms of the kinetic (growth) phase transition of the order-disorder type, which is caused by ordering Zn and O atoms over structural positions. The color of crystals of refined compositions (Zn{sub 0.975}{open_square}{sub 0.025})Zn{sub i(0.015)}(O{sub 0.990}{open_square}{sub 0.010}) (green) and (Zn{sub 0.965}{open_square}{sub 0.035})Zn{sub i(0.035)}O (bright green) is related to different oxygen contents, which is confirmed by the results of electron probe X-ray microanalysis and absorption spectroscopy. The degree of the structural quality of crystals, their resistivity, and activation energy are also related to oxygen vacancies.

Kaurova, I. A., E-mail: kaurova_irina@mail.ru [Moscow Open State University (Russian Federation); Kuz'micheva, G. M. [Lomonosov State Academy of Fine Chemical Technology (Russian Federation)] [Lomonosov State Academy of Fine Chemical Technology (Russian Federation); Rybakov, V. B. [Moscow State University (Russian Federation)] [Moscow State University (Russian Federation)

2013-03-15

392

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

393

Nanoconfinement-induced structures in chiral liquid crystals.  

PubMed

We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution has been modified to represent the orientation dependence of the interaction between a pair of chiral liquid-crystal molecules. The liquid crystal is confined between a pair of planar and atomically smooth substrates onto which molecules are anchored in a hybrid fashion. Hybrid anchoring allows for the formation of helical structures in the direction perpendicular to the substrate plane without exposing the helix to spurious strains. At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality. More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II. If the distance between the confining substrates and molecular chirality are chosen properly, we see a third structure, which may be thought of as a hybrid, exhibiting mixed features of a cholesteric and a blue phase. PMID:23989605

Melle, Michael; Theile, Madlona; Hall, Carol K; Schoen, Martin

2013-01-01

394

Crystal structure of a soluble cleaved HIV-1 envelope trimer.  

PubMed

HIV-1 entry into CD4(+) target cells is mediated by cleaved envelope glycoprotein (Env) trimers that have been challenging to characterize structurally. Here, we describe the crystal structure at 4.7 angstroms of a soluble, cleaved Env trimer that is stabilized and antigenically near-native (termed the BG505 SOSIP.664 gp140 trimer) in complex with a potent broadly neutralizing antibody, PGT122. The structure shows a prefusion state of gp41, the interaction between the component gp120 and gp41 subunits, and how a close association between the gp120 V1/V2/V3 loops stabilizes the trimer apex around the threefold axis. The complete epitope of PGT122 on the trimer involves gp120 V1, V3, and several surrounding glycans. This trimer structure advances our understanding of how Env functions and is presented to the immune system, and provides a blueprint for structure-based vaccine design. PMID:24179159

Julien, Jean-Philippe; Cupo, Albert; Sok, Devin; Stanfield, Robyn L; Lyumkis, Dmitry; Deller, Marc C; Klasse, Per-Johan; Burton, Dennis R; Sanders, Rogier W; Moore, John P; Ward, Andrew B; Wilson, Ian A

2013-12-20

395

Crystal structure of inactive form of Rab3B  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer This is the first structural information of human Rab3B. Black-Right-Pointing-Pointer To provides a structural basis for the GDP/GTP switch in controlling the activity of Rab3. Black-Right-Pointing-Pointer The charge distribution of Rab3B indicates its unique roles in vesicular trafficking. -- Abstract: Rab proteins are the largest family of ras-related GTPases in eukaryotic cells. They act as directional molecular switches at membrane trafficking, including vesicle budding, cargo sorting, transport, tethering, and fusion. Here, we generated and crystallized the Rab3B:GDP complex. The structure of the complex was solved to 1.9 A resolution and the structural base comparison with other Rab3 members provides a structural basis for the GDP/GTP switch in controlling the activity of small GTPase. The comparison of charge distribution among the members of Rab3 also indicates their different roles in vesicular trafficking.

Zhang, Wei [Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Huazhong Normal University, Wuhan 430079 (China)] [Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Huazhong Normal University, Wuhan 430079 (China); Shen, Yang [Structural Genomics Consortium, University of Toronto, 101 College St., Toronto, Ontario, Canada M5G 1L7 (Canada)] [Structural Genomics Consortium, University of Toronto, 101 College St., Toronto, Ontario, Canada M5G 1L7 (Canada); Jiao, Ronghong [Department of Function Inspection, Hebei Provincial People's Hospital, Shijiazhuang 050051 (China)] [Department of Function Inspection, Hebei Provincial People's Hospital, Shijiazhuang 050051 (China); Liu, Yanli; Deng, Lingfu [Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Huazhong Normal University, Wuhan 430079 (China)] [Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Huazhong Normal University, Wuhan 430079 (China); Qi, Chao, E-mail: qichao@mail.ccnu.edu.cn [Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Huazhong Normal University, Wuhan 430079 (China)] [Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Huazhong Normal University, Wuhan 430079 (China)

2012-02-24

396

New rf structure for intermediate-velocity particles.  

National Technical Information Service (NTIS)

This paper describes an rf structure with high shunt impedance and good field stability for particle velocities 0.1 (= or <) (beta) (= or <) 0.5. Traditionally, the drift-tube linac (DTL) has been the structure of choice for this velocity range. The new s...

J. H. Billen F. L. Krawczyk R. L. Wood L. M. Young

1994-01-01

397

PowderSolve a complete package for crystal structure solution from powder diffraction patterns  

Microsoft Academic Search

Powder diffraction techniques are becoming increasingly popular as tools for the determination of crystal structures. The authors of this paper have developed a software package, named PowderSolve, to solve crystal structures from experi- mental powder diffraction patterns and have applied this package to solve the crystal structures of organic compounds with up to 18 variable degrees of freedom (defined in

G. E. Engel; S. Wilke; O. Knig; K. D. M. Harris; F. J. J. Leusen

1999-01-01

398

Surface and zeta-potentials of silver halide single crystals: pH-dependence in comparison to particle systems.  

PubMed

We have carried out surface and zeta-potential measurements on AgCl and AgBr single crystals. As for particle systems we find that, surprisingly and previously unnoted, the zeta-potential exhibits pH-dependence, while the surface potential does not. A possible interpretation of these observations is the involvement of water ions in the interfacial equilibria and in particular, stronger affinity of the hydroxide ion compared to the proton. The pH-dependence of the zeta-potential can be suppressed at sufficiently high silver concentrations, which agrees with previous measurements in particle systems where no pH-dependence was found at high halide ion concentrations. The results suggest a subtle interplay between the surface potential determining the halide and silver ion concentrations, and the water ions. Whenever the charge due to the halide and silver ions is sufficiently high, the influence of the proton/hydroxide ion on the zeta-potential vanishes. This might be related to the water structuring at the relevant interfaces which should be strongly affected by the surface potential. Another interesting observation is accentuation of the assumed water ion effect on the zeta-potential at the flat single crystal surfaces compared to the corresponding silver halide colloids. Previous generic MD simulations have indeed predicted that hydroxide ion adsorption is accentuated on flat/rigid surfaces. A thermodynamic model for AgI single crystals was developed to describe the combined effects of iodide, silver and water ions, based on two independently previously published models for AgI (that only consider constituent and background electrolyte ions) and inert surfaces (that only consider water and background electrolyte ions). The combined model correctly predicts all the experimentally observed trends. PMID:24863080

Selmani, Atia; Ltzenkirchen, Johannes; Kallay, Nikola; Preo?anin, Tajana

2014-06-18

399

Surface and zeta-potentials of silver halide single crystals: pH-dependence in comparison to particle systems  

NASA Astrophysics Data System (ADS)

We have carried out surface and zeta-potential measurements on AgCl and AgBr single crystals. As for particle systems we find that, surprisingly and previously unnoted, the zeta-potential exhibits pH-dependence, while the surface potential does not. A possible interpretation of these observations is the involvement of water ions in the interfacial equilibria and in particular, stronger affinity of the hydroxide ion compared to the proton. The pH-dependence of the zeta-potential can be suppressed at sufficiently high silver concentrations, which agrees with previous measurements in particle systems where no pH-dependence was found at high halide ion concentrations. The results suggest a subtle interplay between the surface potential determining the halide and silver ion concentrations, and the water ions. Whenever the charge due to the halide and silver ions is sufficiently high, the influence of the proton/hydroxide ion on the zeta-potential vanishes. This might be related to the water structuring at the relevant interfaces which should be strongly affected by the surface potential. Another interesting observation is accentuation of the assumed water ion effect on the zeta-potential at the flat single crystal surfaces compared to the corresponding silver halide colloids. Previous generic MD simulations have indeed predicted that hydroxide ion adsorption is accentuated on flat/rigid surfaces. A thermodynamic model for AgI single crystals was developed to describe the combined effects of iodide, silver and water ions, based on two independently previously published models for AgI (that only consider constituent and background electrolyte ions) and inert surfaces (that only consider water and background electrolyte ions). The combined model correctly predicts all the experimentally observed trends.

Selmani, Atia; Ltzenkirchen, Johannes; Kallay, Nikola; Preo?anin, Tajana

2014-06-01

400

Phase behavior of lyotropic rigid-chain polymer liquid crystal studied by dissipative particle dynamics  

NASA Astrophysics Data System (ADS)

The phase behavior of lyotropic rigid-chain liquid crystal polymer was studied by dissipative particle dynamics (DPD) with variations of the solution concentration and temperature. A chain of fused DPD particles was used to represent each mesogenic polymer backbone surrounded with the strongly interacted solvent molecules. The free solvent molecules were modeled as independent DPD particles, where each particle includes a lump of solvent molecules with the volume roughly equal to the solvated polymer segment. The simulation shows that smectic-B (SB), smectic-A (SA), nematic (N), and isotropic (I) phases exist within certain regions in the temperature and concentration parameter space. The temperature-dependent SB/SA, SA/N, and N/I phase transitions occur in the high concentration range. In the intermediate concentration range, the simulation shows coexistence of the anisotropic phases and isotropic phase, where the anisotropic phases can be the SB, SA, or N phases. Mole fraction and compositions of the coexisted phases are determined from the simulation, which indicates that concentration of rigid rods in isotropic phase increases as the temperature increases. By fitting the orientational distribution function of the systems, the biphasic coexistence is further confirmed. From the parameter ? obtained for the simulation, the distribution of the rigid rods in the two coexistence phases is quantitatively evaluated. By using model and simulation methods developed in this work, the phase diagrams of the lyotropic rigid-chain polymer liquid crystal are obtained. Incorporating the solvent particles in the DPD simulation is critical to predict the phase coexistence and obtain the phase diagrams.

Zhao, Tongyang; Wang, Xiaogong

2011-12-01

401

Computational method for the long time propagation of quantum channeled particles in crystals and carbon nanotubes  

NASA Astrophysics Data System (ADS)

This work reports on the computational method for the long time propagation of the quantum channeled particles in infinite and finite harmonic interaction wells and in a realistic carbon nanotube interaction potential well. This method is based on the Chebyshev global propagation method for solving of the corresponding time dependent Schrdinger equation. For comparison, the computational method based on the Crank-Nicolson propagation method is also presented. In the case of quantum particle motion in infinite harmonic potential well, when the analytical solution of the corresponding time-dependent Schrdinger equation exists, we show that the obtained propagation method is efficient, very accurate and numerically stable. It is superior with respect to the method based on the Crank-Nicolson propagation method. A detailed study of the long time quantum particle motion in the finite harmonic interaction potential well shows that the obtained computational method based on the Chebyshev global propagation method can be successfully applied for following of the channeled quantum particle in crystals and carbon nanotubes. This is demonstrated in the case of quantum particle motion in a realistic carbon nanotube interaction potential well.

?osi?, M.; Petrovi?, S.; Nekovi?, N.

2014-07-01

402

Relation between x-ray emission mechanism and crystal structure in LiNbO3  

NASA Astrophysics Data System (ADS)

x-ray emission in LiNbO3 is confirmed by thermal treatments in a vacuum system by a new cleaning method of the crystal. Detailed single-crystal high-temperature x-ray structure refinements were carried out at 297, 323, 373, 423 and 473 K, far below the phase transition (~1473 K). The unit cell dimensions a and V show a linear increase with temperature; however, the lattice parameter, c shows only a slight linear increase. The length of Nb O bonds in adjacent octahedra is almost constant below 423 K. It is suggested that the valence electron in Nb changes in the compound. Therefore, x-ray emission induced by charged particles including electrons can be considered to have a close relation to the electric charge of Nb in LiNbO3.

Nakanishi, Y.; Mizota, H.; Ito, Y.; Takano, M.; Fukao, S.; Yoshikado, S.; Ohyama, K.; Yamada, K.; Fukushima, S.

2006-05-01

403

Coherent transmission and reflection spectra of ordered structures from spherical alumina particles  

NASA Astrophysics Data System (ADS)

We have studied the transmission of light through a multilayer system of plane-parallel monolayers of monodisperse nonabsorbing spherical alumina particles under conditions of normal illumination in the wavelength range of 0.3-1.0 ?m. In the quasi-crystalline approximation of the theory of multiple scattering of waves, we have calculated the coefficients of coherent transmission and reflection of partially ordered monolayers of particles and monolayers of particles with a nearly regular packing (planar photonic crystals with a nonideal lattice). Based on these calculations, using the transfer matrix method, we have calculated the coefficients of coherent transmission and reflection of the multilayer system. The influence of the spatial distribution of particles in individual monolayers on the coherent transmission and reflection spectra of the system has been analyzed. Characteristic minima in transmission spectra of layers caused by the interference of waves have been described. One of these minima is determined by the concentration and optical properties of particles. It appears in the spectrum of a monolayer at ratios of wavelengths and particle sizes roughly corresponding to one of the main maxima of the extinction. The second minimum is determined by the regularity of distribution of particles in the plane of the monolayer. It occurs in the spectrum of the monolayer at particle sizes comparable with the wavelength. The third minimum is the photonic band gap. It appears in the spectrum of a multilayer structure at spacings between monolayers comparable with the wavelength and is caused by the periodicity of the structure. The results make it possible to solve problems of monitoring of the degree of ideality of packing of particles by analysis of the spectral dependences of the coefficients of coherent transmission and reflection, problems of creating multilayer selective reflectors and bandpass filters, diffusers, and other elements based on alumina, which is used, e.g., in novel display technologies. The results of calculations agree well with the available experimental data for the position of the photonic band gap.

Loiko, V. A.; Miskevich, A. A.

2013-08-01

404

Crystal structure of new AsS{sub 2} compound  

SciTech Connect

AsS{sub 2} single crystals have been obtained for the first time from an As{sub 2}S{sub 3} melt at pressures above 6 GPa and temperatures above 800 K in the As{sub 2}S{sub 3} {yields} AsS + AsS{sub 2} reaction. The monoclinic structure of the new high-pressure phase is solved by X-ray diffraction analysis and compared to the structure of high-pressure AsS phase, which was studied previously.

Bolotina, N. B., E-mail: bolotina@ns.crys.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Brazhkin, V. V.; Dyuzheva, T. I.; Lityagina, L. M.; Kulikova, L. F.; Nikolaev, N. A. [Russian Academy of Sciences, Vereshchagin Institute for High Pressure Physics (Russian Federation)] [Russian Academy of Sciences, Vereshchagin Institute for High Pressure Physics (Russian Federation); Verin, I. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)] [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2013-01-15

405

Crystal structure of a plasma membrane proton pump  

US Patent & Trademark Office Database

The present invention relates to a crystal structure of a plasma membrane proton pump type ATPase. The invention further describes method for identification of modulators of ATPases as well as uses of such modulators. Based on the provided three dimensional structure of the ATPase, various method, such as computer implemented methods may be used for identification of modulators, such putative modulators may be further analysed using in vitro and in vivo experiments to confirm there functionality. Several modulator interaction regions are described as target of regulation by ATPase modulators.

2013-11-05

406

Unified approach for determining tetragonal tungsten bronze crystal structures.  

PubMed

Tetragonal tungsten bronze (TTB) oxides are one of the most important classes of ferroelectrics. Many of these framework structures undergo ferroelastic transformations related to octahedron tilting deformations. Such tilting deformations are closely related to the rigid unit modes (RUMs). This paper discusses the whole set of RUMs in an ideal TTB lattice and possible crystal structures which can emerge owing to the condensation of some of them. Analysis of available experimental data for the TTB-like niobates lends credence to the obtained theoretical predictions. PMID:24815976

Smirnov, M; Saint-Grgoire, P

2014-05-01

407

Crystal structure, microstructure and magnetic properties of Ni nanoparticles elaborated by hydrothermal route  

NASA Astrophysics Data System (ADS)

We report on the crystal structure, microstructure and magnetic properties of Ni nanoparticles (NPs), with an average diameter of around 40 nm, produced by hydrothermal method. A series of Ni powders was synthesized at relatively low temperature (140 C) by varying the NaOH concentration. The crystal structure, microstructure and magnetic properties were investigated by means of XRD, MEB coupled to EDX and VSM magnetometry. The XRD patterns show Bragg reflections corresponding to Ni with face centred cubic (fcc) crystal structure. EDX spectra confirm the purity of Ni powders. Moreover, the SEM micrographs show that the Ni-NPs are agglomerated forming entities of 1-5 ?m in average size with different morphologies that change as the NaOH concentration increases. While those entities exhibit a flower-like form at the lowest concentration, a dendritic shape appears for the highest one. The room temperature values for the coercive field (<200 Oe) and saturation magnetization (?52 Am2/kg) were obtained from the magnetic hysteresis loops. We discuss about the influence of the particle morphology on the magnetic behaviour.

Bouremana, A.; Guittoum, A.; Hemmous, M.; Rahal, B.; Sunol, J. J.; Martnez-Blanco, D.; Blanco, J. A.; Gorria, Pedro; Benrekaa, N.

2014-05-01

408

Effect of crystal thickness and geometry on the alpha-particle resolution of CsI (Tl)  

USGS Publications Warehouse

The resolution of CsI(Tl) for Po210 alpha particles has been measured as a function of crystal thickness. The best resolution of a 12;-in. diam cylindrical crystal was obtained for a thickness of 0.38 mm, and the effect of thickness on the resolution is discussed. Based on the proposed model, a conical crystal was designed, which yielded a line width of 1.8% for Po 210 alpha particles with a selected photomultiplier tube. ?? 1960 The American Institute of Physics.

Martinez, P.; Senftle, F. E.

1960-01-01

409

Bonding in ruthenates: Insights from crystal structures and electronic structures  

NASA Astrophysics Data System (ADS)

Although the ruthenates with perovskite, Ruddlesden-Popper, and pyrochlore structures have received the most attention, the recent observation of non-Fermi-liquid behavior in La_4Ru_6O_19 [1] and the abrupt loss of the local moment in two-dimensional La_4Ru_2O_10 at about 150 K [2] has demonstrated the value of studying a wider range of ruthenate structure types. Both of these compounds deviate from the typical 4d transition metal orbital picture (triply degenerate t_2g states and doubly degenerate eg states). The physical properties of these compounds will be reviewed, and some of the structural and electronic features that lead to the unusual orbital arrangements of these compounds will be discussed. Attempts will be made to find some structural guidelines for distinguishing between "normal" and "unusual" bonding in ruthenates. [1] P. Khalifah, K. D. Nelson, R. Jin, Z. Q. Mao, Y. Liu, X. P. A. Gao, A. P. Ramirez, and R. J. Cava. "Non-Fermi-liquid behavior in La_4Ru_6O_19: A cubic, non-peroskite ruthenate with Ru-Ru bonding", Nature, 411, 669-71 (2001). [2] P. Khalifah, Q. Huang, Y. Liu, R. Jin, R. Osborn, H. W. Zanbergen and R. J. Cava, to be published.

Khalifah, Peter

2002-03-01

410

Electronic Structure of Tetragonal and Monoclinic TlS Crystals  

NASA Astrophysics Data System (ADS)

Thallium monosulfide, TlS, contains Tl1+ and Tl3+ ions and is classified as a mixed valence compound. TlS is also known to crystallize into two different structures, chain type tetragonal structure and layer type monoclinic structure. In this study, electronic structures of the tetragonal and monoclinic TlS have been studied using linear-muffin-tin-orbital (LMTO) calculations. The calculated band dispersions show that tetragonal TlS has an indirect gap from T(2?/a,0,0) to W(?/a,?/a,?/c), and that monoclinic TlS has a direct gap at ?. For both crystals, the main valence bands are composed of two parts. The lower valence bands are derived from Tl 6s-S 3p bonding states, while the upper valence bands are derived mainly from S 3p states. The top of the valence bands has some character of the Tl1+ 6s-S 3p antibonding state. For monoclinic TlS, the microscopic mechanism of the structural phase transition is argued in terms of the present band results. The calculated densities of states (DOSs) are also compared with previously reported photoemission data.

Shimosaka, Wataru; Kashida, Shoji

2004-06-01

411

Crystal structure and crystal chemistry of melanovanadite, a natural vanadium bronze.  

USGS Publications Warehouse

The crystal structure of melanovanadite from Minas Ragra, Peru, has been determined in space group P1. The triclinic unit cell (non-standard) has a 6.360(2), b 18.090(9), c 6.276(2) A, alpha 110.18(4)o, beta 101.62(3)o, gamma 82.86(4)o. A subcell with b' = b/2 was found by crystal-structure analysis to contain CaV4O10.5H2O. The subcell has a layer structure in which the vanadate sheet consists of corner-shared tetrahedral VO4 and double square-pyramidal V2O8 groups, similar to that previously found in synthetic CsV2O5. Refinement of the full structure (R = 0.056) showed that the Ca atom, which half-occupies a general position in the subcell, is 90% ordered at one of these sites in the whole unit cell. Bond length-bond strength estimates indicate that the tetrahedra contain V5+, and the square pyramids, V4+.-J.A.Z.

Konnert, J. A.; Evans, Jr, H. T.

1987-01-01

412

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. Program summaryProgram title: XtalComp Catalogue identifier: AEKV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: "New" (3-clause) BSD [1] No. of lines in distributed program, including test data, etc.: 3148 No. of bytes in distributed program, including test data, etc.: 21 860 Distribution format: tar.gz Programming language: C++ Computer: No restrictions Operating system: All operating systems with a compliant C++ compiler. Classification: 7.8 Nature of problem: Computationally identifying duplicate crystal structures taken from the output of modern solid state calculations is a non-trivial exercise for many reasons. The translation vectors in the description are not unique they may be transformed into linear combinations of themselves and continue to describe the same extended structure. The coordinates and cell parameters contain numerical noise. The periodic boundary conditions at the unit cell faces, edges, and corners can cause very small displacements of atomic coordinates to result in very different representations. The positions of all atoms may be uniformly translated by an arbitrary vector without modifying the underlying structure. Additionally, certain applications may consider enantiomorphic structures to be identical. Solution method: The XtalComp algorithm overcomes these issues to detect duplicate structures regardless of differences in representation. It begins by performing a Niggli reduction on the inputs, standardizing the translation vectors and orientations. A transform search is performed to identify candidate sets of rotations, reflections, and translations that potentially map the description of one crystal onto the other, solving the problems of enantiomorphs and rotationally degenerate lattices. The atomic positions resulting from each candidate transform are then compared, using a cell-expansion technique to remove periodic boundary issues. Computational noise is treated by comparing non-integer quantities using a specified tolerance. Running time: The test run provided takes less than a second to complete.

Lonie, David C.; Zurek, Eva

2012-03-01

413

Synthesis of bulk nanostructured aluminum containing in situ crystallized amorphous particles  

NASA Astrophysics Data System (ADS)

5083 Al containing in situ crystallized Al85Ni10La 5 amorphous particles (10% and 20% in volume fraction) was synthesized through a powder metallurgy route consisting of cold isostatic pressing, degassing and hot extrusion. The nanostructured 5083 Al powders (grain size 28 nm) were produced through mechanical milling in liquid nitrogen. The Al 85Ni10La5 powders were produced via gas atomization using helium gas and the fraction in the size range of <500 mesh (<25 mum), which appeared to be fully amorphous on the basis of X-ray diffraction studies, was isolated for further investigation. The amorphous Al85Ni10La5 alloy exhibited a glass transition at 259C (at a heating rate of 40C/min) and nanoscale crystallites (< 100 nm) with an equiaxed morphology formed during the subsequent crystallization reactions. At temperatures higher than 283C, only the equilibrium phases Al, Al3Ni and Al11La 3 were formed. An unusually high nucleation density (1021-22 /m3) was recorded in the crystallization process. The copious nucleation sites were rationalized from the presence of quenched-in Al nuclei, which were evidenced by isothermal calorimetric tracing (235C) and a direct HRTEM observation of the amorphous Al85Ni10La 5 powders. The feasibility of preparation of nanocrystalline/amorphous particles via melt spinning followed by ball milling was also studied. In the as-extruded composites, the amorphous Al85Ni10 La5 particles underwent complete crystallization resulting in a grain size of 100 200 nm; the 5083 Al matrix had a grain size around 200 nm in the fine-grained region interspersed by coarse-grained region with a grain size of 600 1500 nm. A metallurgical bond formed between the 5083 Al matrix and Al85Ni10La5 particles showing a grain-boundary-like interface. The compressive fracture strength of the as-extruded 10% and 20% Al85Ni10La5 composites were determined to be 1025 MPa and 837 MPa, respectively. The influence of secondary processing, i.e., swaging, following extrusion on the mechanical behavior was also studied. The coarse grain formation in cryomilled 5083 Al during the thermomechanical process was discussed and it was evident that grain rotation and coalescence played an important role in the overall mechanism.

Zhang, Zhihui

414

The tobacco mosaic virus particle: structure and assembly.  

PubMed Central

A short account is given of the physical and chemical studies that have led to an understanding of the structure of the tobacco mosaic virus particle and how it is assembled from its constituent coat protein and RNA. The assembly is a much more complex process than might have been expected from the simplicity of the helical design of the particle. The protein forms an obligatory intermediate (a cylindrical disk composed of two layers of protein units), which recognizes a specific RNA hairpin sequence. This extraordinary mechanism simultaneously fulfils the physical requirement for nucleating the growth of the helical particle and the biological requirement for specific recognition of the viral DNA.

Klug, A

1999-01-01

415

Hierarchical structures of ZnO spherical particles synthesized solvothermally  

NASA Astrophysics Data System (ADS)

We review the solvothermal synthesis, using a mixture of ethylene glycol (EG) and water as the solvent, of zinc oxide (ZnO) particles having spherical and flower-like shapes and hierarchical nanostructures. The preparation conditions of the ZnO particles and the microscopic characterization of the morphology are summarized. We found the following three effects of the ratio of EG to water on the formation of hierarchical structures: (i) EG restricts the growth of ZnO microcrystals, (ii) EG promotes the self-assembly of small crystallites into spheroidal particles and (iii) the high water content of EG results in hollow spheres.

Saito, Noriko; Haneda, Hajime

2011-12-01

416

Crystal structure of homoserine O-acetyltransferase from Leptospira interrogans  

SciTech Connect

Homoserine O-acetyltransferase (HTA, EC 2.3.1.31) initiates methionine biosynthesis pathway by catalyzing the transfer of acetyl group from acetyl-CoA to homoserine. This study reports the crystal structure of HTA from Leptospira interrogans determined at 2.2 A resolution using selenomethionyl single-wavelength anomalous diffraction method. HTA is modular and consists of two structurally distinct domains-a core {alpha}/{beta} domain containing the catalytic site and a helical bundle called the lid domain. Overall, the structure fold belongs to {alpha}/{beta} hydrolase superfamily with the characteristic 'catalytic triad' residues in the active site. Detailed structure analysis showed that the catalytic histidine and serine are both present in two conformations, which may be involved in the catalytic mechanism for acetyl transfer.

Wang Mingzhu [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101 (China); School of Life Sciences, IBP-USTC Joint Laboratory for Protein Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); Graduate University of Chinese Academy of Sciences, 19 Yuquan Road, Shijingshan District, Beijing 100049 (China); Liu Lin; Wang Yanli; Wei Zhiyi; Zhang Ping; Li Yikun; Jiang Xiaohua [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101 (China); School of Life Sciences, IBP-USTC Joint Laboratory for Protein Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); Xu Hang [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101 (China)], E-mail: hxu@moon.ibp.ac.cn; Gong Weimin [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101 (China); School of Life Sciences, IBP-USTC Joint Laboratory for Protein Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China)], E-mail: wgong@ibp.ac.cn

2007-11-30

417

Crystal structure of homoserine O-acetyltransferase from Leptospira interrogans.  

PubMed

Homoserine O-acetyltransferase (HTA, EC 2.3.1.31) initiates methionine biosynthesis pathway by catalyzing the transfer of acetyl group from acetyl-CoA to homoserine. This study reports the crystal structure of HTA from Leptospira interrogans determined at 2.2A resolution using selenomethionyl single-wavelength anomalous diffraction method. HTA is modular and consists of two structurally distinct domains--a core alpha/beta domain containing the catalytic site and a helical bundle called the lid domain. Overall, the structure fold belongs to alpha/beta hydrolase superfamily with the characteristic 'catalytic triad' residues in the active site. Detailed structure analysis showed that the catalytic histidine and serine are both present in two conformations, which may be involved in the catalytic mechanism for acetyl transfer. PMID:17927957

Wang, Mingzhu; Liu, Lin; Wang, Yanli; Wei, Zhiyi; Zhang, Ping; Li, Yikun; Jiang, Xiaohua; Xu, Hang; Gong, Weimin

2007-11-30

418

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