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1

Defect structures in nematic liquid crystals around charged particles  

Microsoft Academic Search

We numerically study the orientation deformations in nematic liquid crystals around charged particles. We set up a Ginzburg-Landau\\u000a theory with inhomogeneous electric field. If the dielectric anisotropy is positive, Saturn-ring defects are formed around the particles. For < 0 , novel ansa defects appear, which are disclination lines with their ends on the particle surface. We find unique defect\\u000a structures

Keisuke Tojo; Akira Furukawa; Takeaki Araki; Akira Onuki

2009-01-01

2

Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host.  

PubMed

Combining molecular dynamics and Monte Carlo simulation, we study defect structures around an elongated colloidal particle embedded in a nematic liquid crystal host. By studying nematic ordering near the particle and the disclination core region, we are able to examine the defect core structure and the difference between two simulation techniques. In addition, we also study the torque on a particle tilted with respect to the director, and modification of this torque when the particle is close to the cell wall. PMID:12005841

Andrienko, Denis; Allen, Michael P; Skacej, Gregor; Zumer, Slobodan

2002-03-15

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

Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host  

Microsoft Academic Search

Combining molecular dynamics and Monte Carlo simulation, we study defect structures around an elongated colloidal particle embedded in a nematic liquid crystal host. By studying nematic ordering near the particle and the disclination core region, we are able to examine the defect core structure and the difference between two simulation techniques. In addition, we also study the torque on a

Denis Andrienko; Michael P. Allen; Gregor Skacej; Slobodan Zumer

2002-01-01

5

3D manipulation of particles into crystal structures using holographic optical tweezers  

Microsoft Academic Search

We have developed holographic optical tweezers that can manipulate many particles simultaneously in three dimensions in order to create micro-crystal structures that extend over many tens of microns. The technique uses specific hologram-design algorithms to create structures that can be dynamically scaled or rotated about arbitrary axes. We believe the generation and control of pre-determined crystal-like structures have significant potential

Jonathan Leach; Gavin Sinclair; Pamela Jordan; Johannes Courtial; Miles J. Padgett; Jon Cooper; Zsolt J. Laczik

2004-01-01

6

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

7

Modeling the Structures Arising From Defect Bonding Among Colloidal Particles in a Cholesteric Liquid Crystal  

NASA Astrophysics Data System (ADS)

We use a lattice-Boltzmann algorithm to investigate the possible structures formed by interactions among spherical colloidal particles emersed in a cholesteric liquid crystal. Strong tangential anchoring is assumed at the particle surfaces, which for a given sphere, results in the formation of a pair of +1/2 defect lines, which originate on the sphere, spiral around it at some distance, and then terminate on it. When the helical pitch of the cholesteric is comparable in size to the particle diameter, these defects have the appearance of two handles emerging from the sphere. With more than one particle present, the handles from different spheres tend to join together, forming a type of bond between them. Both single and double bonding among particles is found to be possible. We present results showing chains and other types of structures produced with this type of bonding.

Mackay, Frances; Denniston, Colin

2010-03-01

8

Crystal structure of the nucleosome core particle at 2.8 resolution  

Microsoft Academic Search

The X-ray crystal structure of the nucleosome core particle of chromatin shows in atomic detail how the histone protein octamer is assembled and how 146 base pairs of DNA are organized into a superhelix around it. Both histone\\/histone and histone\\/DNA interactions depend on the histone fold domains and additional, well ordered structure elements extending from this motif. Histone amino-terminal tails

Karolin Luger; Armin W. Mder; Robin K. Richmond; David F. Sargent; Timothy J. Richmond

1997-01-01

9

Mechanism of Formation of Three Dimensional Structures of Particles Dispersed in a Liquid Crystal  

Microsoft Academic Search

Recently, colloidal dispersions of small particles in a nematic liquid crystal have been reported. These particles introduce topological defects in the liquid crystal, (H. Stark, Euro. Phys. J. B 10), 311 (1999).(T. C. Lubensky, D. Pettey, N. Currier, and H. Stark, Phys. Rev. E, 57), 610 (1998). and the liquid crystal introduces additional long-range forces between the colloidal particles(B. I.

John West; Anatoliy Glushchenko; Guangxun Liao; Yuriy Reznikov; Denis Andrienko; Michael Allen

2002-01-01

10

Crystallization of hard aspherical particles  

NASA Astrophysics Data System (ADS)

We use numerical simulations to study the crystallization of monodisperse systems of hard aspherical particles. We find that particle shape and crystallizability can be easily related to each other when particles are characterized in terms of two simple and experimentally accessible order parameters: one based on the particle surface-to-volume ratio and the other on the angular distribution of the perturbations away from the ideal spherical shape. We present a phase diagram obtained by exploring the crystallizability of 487 different particle shapes across the two-order-parameter spectrum. Finally, we consider the physical properties of the crystalline structures accessible to aspherical particles and discuss limits and relevance of our results.

Miller, William L.; Bozorgui, Behnaz; Cacciuto, Angelo

2010-04-01

11

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

12

Alteration of the nucleosomal DNA path in the crystal structure of a human nucleosome core particle  

Microsoft Academic Search

Gene expression in eukaryotes depends upon posi- tioning, mobility and packaging of nucleosomes; thus, we need the detailed information of the human nucleosome core particle (NCP) structure, which could clarify chromatin properties. Here, we report the 2.5 Acrystal structure of a human NCP. The overall structure is similar to those of other NCPs reported previously. However, the DNA path of

Yasuo Tsunaka; Naoko Kajimura; Shin-ichi Tate; Kosuke Morikawa

2005-01-01

13

Structure and crystallization of rapidly quenched Cu-(Zr or Hf)-Ti alloys containing nanocrystalline particles  

NASA Astrophysics Data System (ADS)

The structure and primary crystallization process of the melt-spun Cu60 (Zr or Hf)30Ti10 alloys were investigated. Compositional segregation in the diameter range of 5-10 nm was observed in the as-quenched state. In the high-resolution transmission electron microscopy images, nanocrystalline particles are observed in the glassy matrix, the size of which corresponds to the scale of compositional segregation. The glassy region has comparatively high Zr or Hf and Ti contents. In contrast, the Cu element is enriched in the nanocrystalline phases. The nanocrystalline phases are identified as the cubic structure with a lattice constant of approximately 0.5 nm. These results are recognized as the formation of novel structure consisting of the glassy and nanocrystalline phases. It is suggested that the precipitation of body-centred-cubic CuZr phase as a primary crystallization phase proceeds in the glassy phase, the nanocrystalline phase remaining in the Cu-Zr-Ti alloy. Meanwhile, the glassy and nanocrystalline phases are transformed to an orthorhombic Cu8Hf3 phase in the initial crystallization stage in the Cu-Hf-Ti alloy.

Kasai, M.; Saida, J.; Matsushita, M.; Osuna, T.; Matsubara, E.; Inoue, A.

2002-12-01

14

Crystal Structure of Yeast Rpn14, a Chaperone of the 19 S Regulatory Particle of the Proteasome*  

PubMed Central

The ubiquitin-proteasome pathway is a major proteolytic system in eukaryotic cells and regulates various cellular processes. The 26 S proteasome, the central enzyme of this pathway, consists of a proteolytic core particle and two 19 S regulatory particles (RPs) composed of ATPase (Rpt) and non-ATPase (Rpn) subunits. Growing evidence indicates that proteasome assembly is assisted by a variety of chaperones. In particular, it has been reported recently that Nas2, Nas6, Rpn14, and Hsm3 bind specific Rpt subunits, thereby contributing to the formation of 19 S RP. Rpn14 transiently binds to the C-terminal domain of the Rpt6 subunit (Rpt6-C) during maturation of the ATPase ring of 19 S RP. In this study, we determined the crystal structure of yeast Rpn14 at 2.0 resolution, which revealed that this chaperone consists of a unique N-terminal domain with unknown function and a C-terminal domain assuming a canonical seven-bladed ?-propeller fold. The Rpt6-binding site on Rpn14 was predicted based on structural comparison with the complex formed between Nas6 and Rpt3-C. The top face of Rpn14 exhibits a highly acidic surface area, whereas the putative interacting surface of Rpt6-C is basic. By inspection of structural data along with genetic and biochemical data, we determined the specific residues of Rpn14 and Rpt6 for complementary charge interactions that are required for 19 S RP assembly.

Kim, Sangwoo; Saeki, Yasushi; Fukunaga, Keisuke; Suzuki, Atsuo; Takagi, Kenji; Yamane, Takashi; Tanaka, Keiji; Mizushima, Tsunehiro; Kato, Koichi

2010-01-01

15

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

16

Characterization of synthetic nanocrystalline mackinawite: crystal structure, particle size, and specific surface area.  

PubMed

Iron sulfide was synthesized by reacting aqueous solutions of sodium sulfide and ferrous chloride for 3 days. By X-ray powder diffraction (XRPD), the resultant phase was determined to be primarily nanocrystalline mackinawite (space group: P4/nmm) with unit cell parameters a = b = 3.67 and c = 5.20 . Iron K-edge XAS analysis also indicated the dominance of mackinawite. Lattice expansion of synthetic mackinawite was observed along the c-axis relative to well-crystalline mackinawite. Compared with relatively short-aged phase, the mackinawite prepared here was composed of larger crystallites with less elongated lattice spacings. The direct observation of lattice fringes by HR-TEM verified the applicability of Bragg diffraction in determining the lattice parameters of nanocrystalline mackinawite from XRPD patterns. Estimated particle size and external specific surface area (SSA(ext)) of nanocrystalline mackinawite varied significantly with the methods used. The use of Scherrer equation for measuring crystallite size based on XRPD patterns is limited by uncertainty of the Scherrer constant (K) due to the presence of polydisperse particles. The presence of polycrystalline particles may also lead to inaccurate particle size estimation by Scherrer equation, given that crystallite and particle sizes are not equivalent. The TEM observation yielded the smallest SSA(ext) of 103 m(2)/g. This measurement was not representative of dispersed particles due to particle aggregation from drying during sample preparation. In contrast, EGME method and PCS measurement yielded higher SSA(ext) (276-345 m(2)/g by EGME and 424 130 m(2)/g by PCS). These were in reasonable agreement with those previously measured by the methods insensitive to particle aggregation. PMID:21085620

Jeong, Hoon Y; Lee, Jun H; Hayes, Kim F

2008-01-15

17

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

18

Quartz crystal particle microbalance (QCPM)  

NASA Astrophysics Data System (ADS)

The QCPM has been developed to monitor particulate contamination in a space environment. The QCPM is similar in design to a TQCM in that it uses a thermoelectric device to control temperature and In Line Doublet Crystals to maintain frequency stability under solar radiation. The QCPM is coated with a thin layer of a vacuum fluid having a very low vapor pressure. At 0 degrees Celsius, the fluid is in a viscous liquid state and particles that fall onto the QCPM stick to its surface. Periodically, the particles are weighed by cooling the QCPM to -60 degrees Celsius to solidify the fluid and couple the particulates to the oscillator mass of the crystal. The results from a Scanning Electron Microscope and the Energy Dispersions Analysis by X-ray are presented showing the size, shape and composition of particles that contaminated surfaces flown on the Spacelab 1 Mission. Aluminum particles occurred in the greatest numbers and had diameters ranging between 0.5 to 10 micrometer.

McKeown, Daniel; Corbin, William E.; Fox, Marvin G.

1999-10-01

19

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

20

Ferroelectric Particles in Liquid Crystals: Recent Frontiers  

Microsoft Academic Search

In this article we describe electro-optical properties of recently discovered ferroelectric particles\\/liquid crystal colloids. We show that the presence of ferroelectric particles in a liquid crystal changes its birefringence and dielectric anisotropy. In contrast to the traditional time consuming and expensive chemical synthetic methods, this method to create liquid crystals with enhanced properties is relatively simple and has a great

Anatoliy Glushchenko; Chae Il Cheon; John West; Fenghua Li; Ebru Byktanir; Yuri Reznikov; Alexander Buchnev

2006-01-01

21

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

22

Microtubule particle dispersion in liquid crystal hosts  

Microsoft Academic Search

Microtubule particles and metal-coated microtubules were dispersed in various host liquid crystal mixtures. Dispersion effects were evaluated as a function of liquid crystal type, viscosity, dielectric anisotropy and surface interaction. Experimental results indicated that all the types of liquid crystals studied were aligned perpendicular to the microtubule surfaces, regardless of liquid crystal composition or various surface coatings used on the

A. M. Lackner; K. C. Lim; J. D. Margerum; E. Sherman

1993-01-01

23

Teaching With Crystal Structures  

NSDL National Science Digital Library

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

Smithenry, Dennis W.

2009-09-01

24

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

25

Size effect on the crystal phase of cobalt fine particles  

Microsoft Academic Search

We have synthesized Co fine particles with the average diameter (D) of less than 500 by sputtering Co in a somewhat high inert-gas pressure. It has been found that there is a close relationship between the particle size and the crystal phase; that is, pure fcc (beta) phase for D=400 . Precise structural characterizations have revealed that the beta

Osamu Kitakami; Hisateru Sato; Yutaka Shimada; Futami Sato; Michiyoshi Tanaka

1997-01-01

26

Particle tracking microrheology of lyotropic liquid crystals.  

PubMed

We present comprehensive results on the microrheological study of lyotropic liquid crystalline phases of various space groups constituted by water-monoglyceride (Dimodan) mixtures. In order to explore the viscoelastic properties of these systems, we use particle tracking of probe colloidal particles suitably dispersed in the liquid crystals and monitored by diffusing wave spectroscopy. The identification of the various liquid crystalline phases was separately carried out by small-angle X-ray scattering. The restricted motion of the particles was monitored and identified by the decay time of intensity autocorrelation function and the corresponding time-dependent mean square displacement (MSD), which revealed space group-dependent behavior. The characteristic time extracted by the intersection of the slopes of the MSD at short and long time scales, provided a characteristic time which could be directly compared with the relaxation time obtained by microrheology. Further direct comparison of microrheology and bulk rheology measurements was gained via the Laplace transform of the generalized time-dependent MSD, yielding the microrheology storage and loss moduli, G'(?) and G''(?), in the frequency domain ?. The general picture emerging from the microrheology data is that all liquid crystals exhibit viscoelastic properties in line with results from bulk rheology and the transition regime (elastic to viscous) differs according to the specific liquid crystal considered. In the case of the lamellar phase, a plastic fluid is measured by bulk rheology, while microrheology indicates viscoelastic behavior. Although we generally find good qualitative agreement between the two techniques, all liquid crystalline systems are found to relax faster when studied with microrheology. The most plausible explanation for this difference is due to the different length scales probed by the two techniques: that is, microscopical relaxation on these structured fluids, is likely to occur at shorter time scales which are more suitably probed by microrheology, whereas bulk, macroscopic relaxations occurring at longer time scales can only be probed by bulk rheology. PMID:21510686

Alam, Mohammad Mydul; Mezzenga, Raffaele

2011-04-21

27

Influence of Sedimentation on Crystallization of Charged Colloidal Particles  

NASA Astrophysics Data System (ADS)

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions on dynamic behavior of a colloidal system. Experiments on crystallization of charged colloidal microspheres with diameter of 98 nm dispersed in density-matched and -unmatched media (mixtures of H2O and D2O in proper proportion) are compared to examine the influence of sedimentation. Reflection spectra of colloidal suspensions were used to monitor the crystallization process. Results showed that the crystal size of the density-unmatched (namely, in the presence of sedimentation) sample grew faster than that of the density-matched (in the absence of sedimentation) case at the initial stage of the crystallization, and then the latter overtook and outstripped the former. To explain these observations, we assume that in the settling of crystals sedimentation facilitates result in more particles getting into the crystal structures. However, as the crystals increase to varying sizes, the settling velocities become large and hydrodynamic friction strips off some particles from the delicate crystal structures. Overall, the sedimentation appears to accelerate the crystal size growth initially and then retard the growth. In addition, the crystal structures formed under microgravity were more closely packed than that in normal gravity.

Du, Xuan; Xu, Sheng-hua; Sun, Zhi-wei; Liu, Lei

2012-06-01

28

Self-assembling behavior of cellulose Nanoparticles during freeze-drying: effect of suspension concentration, particle size, crystal structure, and surface charge.  

PubMed

Cellulose nanocrystals and cellulose nanofibers with I and II crystalline allomorphs (designated as CNC I, CNC II, CNF I, and CNF II) were isolated from bleached wood fibers by alkaline pretreatment and acid hydrolysis. The effects of concentration, particle size, surface charge, and crystal structure on the lyophilization-induced self-assembly of cellulose particles in aqueous suspensions were studied. Within the concentration range of 0.5 to 1.0 wt %, cellulose particles self-organized into lamellar structured foam composed of aligned membrane layers with widths between 0.5 and 3 ?m. At 0.05 wt %, CNC I, CNF I, CNC II, and CNF II self-assembled into oriented ultrafine fibers with mean diameters of 0.57, 1.02, 1.50, and 1.00 ?m, respectively. The size of self-assembled fibers became larger when more hydroxyl groups and fewer sulfates (weaker electrostatic repulsion) were on cellulose surfaces. Possible formation mechanism was inferred from ice growth and interaction between cellulose nanoparticles in liquid-crystalline suspensions. PMID:23544667

Han, Jingquan; Zhou, Chengjun; Wu, Yiqiang; Liu, Fangyang; Wu, Qinglin

2013-04-12

29

Crystal structure of magnesioneptunite  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

30

Vaterite crystals contain two interspersed crystal structures.  

PubMed

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

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

2013-04-26

31

Structure of crystals of hard colloidal spheres  

SciTech Connect

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

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

1989-12-18

32

Structure of crystals of hard colloidal spheres  

Microsoft Academic Search

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

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

1989-01-01

33

Structure of crystals of hard colloidal spheres  

Microsoft Academic Search

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

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

1989-01-01

34

Colloidal Particles: Crystals, Glasses, and Gels  

NASA Astrophysics Data System (ADS)

Colloidal particles are microscopic solid particles suspended in a fluid. Colloids are small enough that thermal energy drives their dynamics and ensures equilibration with the suspending fluid; they are also large enough that their positions and motions can be measured precisely using optical methods, such as light scattering and laser-scanning confocal fluorescence microscopy. Colloidal suspensions are a powerful model system for the study of other phenomena in condensed matter physics, where the collective phase behavior of the solid particles mimics that of other condensed systems. We review three classes of interacting colloidal particles, crystals, glasses, and gels, each of which represents fascinating properties of colloidal particles as well as a model for more general types of materials and their behavior.

Lu, Peter J.; Weitz, David A.

2013-04-01

35

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

36

Effect of the crystal structure of small precursor particles on the growth of ?-NaREF4 (RE = Sm, Eu, Gd, Tb) nanocrystals  

NASA Astrophysics Data System (ADS)

The origin of the narrow particle size distributions obtained in the oleic acid-based synthesis of hexagonal phase ?-NaREF4 nanocrystals (RE = Sm, Eu, Gd, Tb) has been investigated. Compared to the standard synthesis, the growth conditions were simplified by using small purified particles of either ?-NaREF4 (cubic phase) or ?-NaREF4 (hexagonal phase) as single-source precursors, thereby avoiding the complications arising from the simultaneous presence of molecular educts and intermediately formed small particles. The study shows that ?-phase as well as ?-phase particles grow by Ostwald-ripening but narrow particle size distributions of the ?-NaREF4 product particles are only obtained when ?-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of ?-NaSmF4, ?-NaEuF4, ?-NaGdF4 and ?-NaTbF4 particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems.The origin of the narrow particle size distributions obtained in the oleic acid-based synthesis of hexagonal phase ?-NaREF4 nanocrystals (RE = Sm, Eu, Gd, Tb) has been investigated. Compared to the standard synthesis, the growth conditions were simplified by using small purified particles of either ?-NaREF4 (cubic phase) or ?-NaREF4 (hexagonal phase) as single-source precursors, thereby avoiding the complications arising from the simultaneous presence of molecular educts and intermediately formed small particles. The study shows that ?-phase as well as ?-phase particles grow by Ostwald-ripening but narrow particle size distributions of the ?-NaREF4 product particles are only obtained when ?-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of ?-NaSmF4, ?-NaEuF4, ?-NaGdF4 and ?-NaTbF4 particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems. Electronic supplementary information (ESI) available: XRD patterns of the samples, particle size histograms from TEM and DLS measurements, Rietveld fits, emission spectra of NaGdF4:Eu particles with different Eu3+ concentrations and weighted amounts of NaREF4 precursor particles for the synthesis of the final products. See DOI: 10.1039/c2nr33083k

Vo, Benjamin; Nordmann, Jrg; Uhl, Andreas; Komban, Rajesh; Haase, Markus

2012-12-01

37

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

38

Quadrupolar particles in a nematic liquid crystal: Effects of particle size and shape  

Microsoft Academic Search

We investigate the effects of particle size and shape on the quadrupolar (Saturn-ring-like) defect structures formed by a nematic liquid crystal around nm-sized and mum -sized particles with spherical and spherocylindrical shapes. We also report results for the potentials of mean force in our systems, calculated using a mesoscale theory for the tensor order parameter Q of the nematic. Our

Francisco R. Hung

2009-01-01

39

Quadrupolar particles in a nematic liquid crystal: Effects of particle size and shape  

Microsoft Academic Search

We investigate the effects of particle size and shape on the quadrupolar (Saturn ring-like) defect structures formed by a nematic liquid crystal (NLC) around nm- and micron-sized particles with spherical, spherocylindrical and cubic shapes. Our calculations, based on a Landau-de Gennes expansion in terms of the tensor order parameter Q, indicate that for pairs of nanoparticles in close proximity, the

Francisco R. Hung

2009-01-01

40

Effect of the crystal structure of small precursor particles on the growth of ?-NaREF4 (RE = Sm, Eu, Gd, Tb) nanocrystals.  

PubMed

The origin of the narrow particle size distributions obtained in the oleic acid-based synthesis of hexagonal phase ?-NaREF(4) nanocrystals (RE = Sm, Eu, Gd, Tb) has been investigated. Compared to the standard synthesis, the growth conditions were simplified by using small purified particles of either ?-NaREF(4) (cubic phase) or ?-NaREF(4) (hexagonal phase) as single-source precursors, thereby avoiding the complications arising from the simultaneous presence of molecular educts and intermediately formed small particles. The study shows that ?-phase as well as ?-phase particles grow by Ostwald-ripening but narrow particle size distributions of the ?-NaREF(4) product particles are only obtained when ?-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of ?-NaSmF(4), ?-NaEuF(4), ?-NaGdF(4) and ?-NaTbF(4) particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems. PMID:23235555

Vo, Benjamin; Nordmann, Jrg; Uhl, Andreas; Komban, Rajesh; Haase, Markus

2012-12-13

41

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

42

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

NASA Astrophysics Data System (ADS)

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.

1995-04-01

43

Fabrication of Artificial Crystal Architectures by Micro-Manipulation of Spherical Particles  

NASA Astrophysics Data System (ADS)

Materials with three-dimensional periodic structures have the potential to produce photonic effects such as photonic crystals. We therefore developed a fabrication technique for such structured materials through assembly of monosized spherical micro-particles. First, a three-dimensional particle array system was designed and manufactured. In this system, a robotic micro-manipulator accurately positions spherical particles onto the lattice points, and subsequently, fiber lasers micro-weld contact points between neighboring particles. One-dimensional arrays were constructed using monosized tin particles with the diameter of 400 um. Moreover, on the basis of optimized laser conditions, we successfully constructed three-dimensional crystals such as those of diamond structures. The diamond structure, in particular, is expected to evolve towards a practical photonic crystal device, since it possesses the largest photonic band gap among all the crystal structures.

Takagi, Kenta; Kawasaki, Akira

2008-02-01

44

A Measurement System for the Phase Retardation of Liquid Crystal Particles Under an Electric Field Effect  

Microsoft Academic Search

The optical characteristics of LCDs, e.g. their brightness, contrast ratio and response time, are sensitive to the structural parameters of the liquid crystal cells. This study develops a phase retardation measurement system using a laser interferometer, a liquid crystal cell and a function generator. When the liquid crystal particles are subjected to an electric field effect, their orientation changes, causing

Cheng-Chi Wang; Ming-Jyi Jang; Pei-Ling Ko

2006-01-01

45

Photonic crystal devices formed by a charged-particle beam  

Microsoft Academic Search

A photonic crystal device and method are disclosed. 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

S. Y. Lin; H. W. P. Koops

2000-01-01

46

Photonic crystal devices formed by a charged-particle beam  

Microsoft Academic Search

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

Shawn-Yu Lin; Hans W. P. Koops

2000-01-01

47

The flow structure in the near field of jets and its effect on cavitation inception, and, Implementation of ferroelectric liquid crystal and birefringent crystal for image shifting in particle image velocimetry  

NASA Astrophysics Data System (ADS)

Cavitation experiments performed in the near field of a 50-mm diameter (D) jet at ReD = 5 105, showed inception in the form of inclined ``cylindrical'' bubbles at axial distances (x/D) less than 0.55, with indices of 2.5. On tripping the boundary layer, cavitation inception occurred at x/D ~ 2, as distorted ``spherical'' bubbles with inception indices of 1.7. To investigate these substantial differences, the near field of the jet was measured using Particle Image Velocimetry (PIV). Data on the primary flow, the strength distribution of the ``streamwise''vortices and the velocity profiles within the initial boundary layers were obtained. The untripped case showed a direct transition to three-dimensional flow in the near field (x/D < 0.7) even before rolling up to distinct vortex rings. Strong ``streamwise'' vortices with strengths up to 25% of the jet velocity times the characteristic wavelength were seen. Cavitation inception occurred in the core of these vortices. In contrast, in the tripped jet the vortex sheet rolled up to the familiar Kelvin- Helmholtz vortex rings with weak secondary vortices. Using the measured nuclei distribution, strengths and straining of the ``streamwise'' structures, the rates of cavitation events were estimated. The estimated results match very well with the measured cavitation rates. Also, the Reynolds stresses in the near field of the jet show similar trends and magnitudes to those of Browand & Latigo (1979) and Bell & Mehta (1990) for a plane shear layer. In the second part of this essay we discuss the implementation of electro-optical image shifting to resolve directional ambiguity in PIV measurements. The technique uses a ferroelectric liquid crystal (FLC) as an electro-optic half wave plate and a birefringent crystal (calcite) as the shifter. The system can be used with non-polarized light sources and fluorescent particles. The minimum shifting time is approximately 100?s. This compact electrooptical device usually is positioned in front of the camera lens, though it has also been mounted inside the lens body. This device extensively was used to acquire data in the near field of the jet, which is discussed in Chapter 2. Sample vector maps from a turbulent multidirectional flow are also included.

Gopalan, Shridhar

1999-10-01

48

Quadrupolar particles in a nematic liquid crystal: Effects of particle size and shape  

NASA Astrophysics Data System (ADS)

We investigate the effects of particle size and shape on the quadrupolar (Saturn-ring-like) defect structures formed by a nematic liquid crystal around nm-sized and ?m -sized particles with spherical and spherocylindrical shapes. We also report results for the potentials of mean force in our systems, calculated using a mesoscale theory for the tensor order parameter Q of the nematic. Our results indicate that for pairs of nm-sized particles in close proximity, the nematic forms entangled hyperbolic defect structures regardless of the shape of the nanoparticles. In our calculations with nanoparticles we did not observe any other entangled or unentangled defect structures, in contrast to what was reported for pairs of ?m -sized spherical particles. Such a finding suggests that the entangled hyperbolic defect structures are the most stable for pairs of nanoparticles in close proximity. For pairs of ?m -sized particles, our results indicate that the nematic forms entangled figure-of-eight defect structures around pairs of spheres and spherocylinders. Our results suggest that the transition between entangled hyperbolic and figure-of-eight defect structures takes place when the diameter of the particle is between D=100nm and 1?m . We have also calculated the torques that develop when pairs of spherocylindrical nanoparticles in a nematic approach each other. Our calculations suggest that the nematic-mediated interactions between the nm-sized particles are fairly strong, up to 5700 kBT for the case of pairs of spherocylindrical nanoparticles arranged with their long axis parallel to each other. Furthermore, these interactions can make the particles to bind together at specific locations, and thus could be used to assemble the particles into ordered structures with different morphologies.

Hung, Francisco R.

2009-02-01

49

Pattern information extraction from crystal structures  

Microsoft Academic Search

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

Erhan Okuyan; Ugur Gdkbay; Oguz Glseren

2007-01-01

50

INTERACTION BETWEEN SPHERICAL PARTICLES IN A DEFORMED LIQUID CRYSTAL  

Microsoft Academic Search

We study how the initial deformation of a nematic liquid crystal affects the interaction between particles mediated by the elastic deformation of a nematic liquid crystal. We calculate the interaction energy between particles in a hybrid nematic cell, homeotropic on the surface of one confining plate and tangential (director can rotate freely) on the other. We find an analytic form

Jun-ichi Fukuda; Keiko M. Aoki; Bohdan I. Lev; Hiroshi Yokoyama

2004-01-01

51

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

52

Crystal Structure of Beryllium Borohydride.  

National Technical Information Service (NTIS)

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

D. S. Marynick W. N. Lipscomb

1971-01-01

53

Piezoelectricity, ferroelectricity, and crystal structure  

Microsoft Academic Search

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

A. von Hippel

1952-01-01

54

Crystal structure of sorbitol dehydrogenase  

Microsoft Academic Search

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

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

2001-01-01

55

Refinement of Hematite Crystal Structure.  

National Technical Information Service (NTIS)

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

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

1970-01-01

56

Crystal structure of lignin peroxidase  

Microsoft Academic Search

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

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

1993-01-01

57

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

58

Crystal Structure of Neotame Anhydrate Polymorph G  

Microsoft Academic Search

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

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

2002-01-01

59

Formation of a crystal of Brownian particles under a uniform external force  

NASA Astrophysics Data System (ADS)

To keep the formation of colloidal crystal under a centrifugation in mind, we study ordering of Brownian particles under a uniform external force. When the force is added to Brownian particles distributing uniformly in the system, the particles drift and the density of particles near walls increases. Ordering of particles on the walls occurs at first and ordering in bulk occurs in succession. In bulk, both the clusters with face-centered cubic structure and those with the hexagonal close-packed structure appear. The distribution of cluster sizes changes with the direction of external force.

Sato, Masahide; Katsuno, Hiroyasu; Suzuki, Yoshihisa

2013-03-01

60

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.

61

The structure of small penta-twinned gold particles  

NASA Astrophysics Data System (ADS)

The structural feathers of penta-twinned gold particles (size between 2 and 6 nm) generated by gas evaporation have been investigated by high resolution TEM. The structural characteristic of penta-twinned particles is different from that of quasi-crystals that the five coherent or incoherent twin boundaries separating the twin oriented segments do not join up along a common edge. The lattice parameter is reduced by 4 5% in comparison to that of bulk gold. The formation of the penta-twinned particles is proposed to occur by particle collision. The particles were observed to be crystalline at ambient temperature.

Gao, Pei-Yu; Kunath, W.; Gleiter, H.; Weiss, K.

1989-03-01

62

Old and New Particle Structure  

Microsoft Academic Search

This discussion will compare the old concept of the structure of matter with Nature. How did the ancient model affect scientific thinking leading science down blind pathways producing paradoxes? What instead is the simple logic and surprising consequences of Nature's choice, the Wave Structure of Matter? The old concept due to the Greek Democritus was a discrete particle like a

Milo Wolff

2002-01-01

63

Platinum-Palladium Crystal Structures  

NASA Astrophysics Data System (ADS)

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

Pratt, Weston

2009-10-01

64

The crystal structure of hopeite  

Microsoft Academic Search

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

RooEnrcr J. Hrr; J. B. JoNes

65

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

66

Dynamics of a nematic liquid crystal around a spherical particle  

Microsoft Academic Search

We present the results of our numerical calculations that focus on the dynamics of a nematic liquid crystal around a spherical particle imposing strong homeotropic anchoring at the surface. The first part of this article is devoted to the discussion of the effect of an external magnetic or electric field on the director configuration of a nematic liquid crystal. With

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

2004-01-01

67

Two-dimensional metal nano-particles and layers in dielectric calcium fluoride crystals  

NASA Astrophysics Data System (ADS)

Highly aggregated color centers in wide-band-gap dielectric calcium fluoride crystal, heated in a reduction atmosphere of Ca vapors (an "additive coloration" of the crystal), have been studied using spectroscopic and atomic-force microscopic techniques. These centers are large aggregates of anion vacancies and electrons that transform into metal structures. Evolution of these structures with increasing the number of such components has been traced from individual two-dimensional particles to large metal film fragments.

Angervaks, A. E.; Shcheulin, A. S.; Ryskin, A. I.; Fedorov, P. P.; Gainutdinov, R. V.

2013-02-01

68

Crystallization mechanisms in convective particle assembly.  

PubMed

Colloidal particles are continuously assembled into crystalline particle coatings using convective fluid flows. Assembly takes place inside a meniscus on a wetting reservoir. The shape of the meniscus defines the profile of the convective flow and the motion of the particles. We use optical interference microscopy, particle image velocimetry, and particle tracking to analyze the particles' trajectory from the liquid reservoir to the film growth front and inside the deposited film as a function of temperature. Our results indicate a transition from assembly at a static film growth front at high deposition temperatures to assembly in a precursor film with high particle mobility at low deposition temperatures. A simple model that compares the convective drag on the particles to the thermal agitation explains this behavior. Convective assembly mechanisms exhibit a pronounced temperature dependency and require a temperature that provides sufficient evaporation. Capillary mechanisms are nearly temperature independent and govern assembly at lower temperatures. The model fits the experimental data with temperature and particle size as variable parameters and allows prediction of the transition temperatures. While the two mechanisms are markedly different, dried particle films from both assembly regimes exhibit hexagonal particle packings. We show that films assembled by convective mechanisms exhibit greater regularity than those assembled by capillary mechanisms. PMID:22559295

Born, Philip; Munoz, Andres; Cavelius, Christian; Kraus, Tobias

2012-05-18

69

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

70

Crystal structure of lignin peroxidase  

SciTech Connect

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

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

1993-01-15

71

Configuration of Nematic Liquid Crystals around Particles under External Fields  

Microsoft Academic Search

We present the results of our numerical attempts to simulate the configuration of a nematic liquid crystal around a spherical particle. We focus on the effect of an external field, such as a magnetic field or a flow field, on the director configuration and the topological defects accompanied by the particles. The use of adaptive mesh refinement together with a

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

2004-01-01

72

Photonic band structure of bcc colloidal crystals  

Microsoft Academic Search

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

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

1997-01-01

73

Crystal structure of metarhodopsin II.  

PubMed

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

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

2011-03-09

74

Methane hydrate crystallization mechanism from in-situ particle sizing  

SciTech Connect

A new experimental setup that makes possible in-situ determinations of the population density function of the methane hydrate particles during its crystallization in a pressurized reactor is used. Thanks to this equipment, new results can be obtained, in particular concerning the granular aspects of the crystallization processes and the influence of the stirring rate. These results are discussed in the framework of a model including gas absorption, primary and secondary nucleation, crystal growth, agglomeration, and breakage. From this discussion, the relevant processes and parameters of methane hydrate crystallization can be determined and quantified.

Herri, J.M. [Ecole des Mines de Saint-Etienne (France)]|[Institut Francais du Petrole, Rueil-Malmaison (France); Pic, J.S.; Gruy, F.; Cournil, M. [Ecole des Mines de Saint-Etienne (France)

1999-03-01

75

Photonic Band Structure of fcc Colloidal Crystals  

Microsoft Academic Search

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

I. Inan Tarhan; George H. Watson

1996-01-01

76

Design of a Highly Focused Photonic Crystal Lens Using Boolean Particle Swarm Optimization  

Microsoft Academic Search

The Boolean particle swarm optimization technique in conjunction with the scattering matrix method is proposed to design two dimensional photonic crystal based structures. The potential of this approach is illustrated in a lens design problem. The resulting lens has a superb F-number of 0.39. Furthermore, the effectiveness of this method in comparison with a genetic algorithm based optimization procedure is

Alireza Marandi; Farzaneh Afshinmanesh; Poman P. M. So

2008-01-01

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

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

79

Crystal structures of proline-derived enamines  

PubMed Central

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

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

2010-01-01

80

Application of channeling in bent crystals to charged particle beams  

SciTech Connect

The process of channeling of charged particle beams in bent crystals is described, including the effects of angular acceptance, spatial acceptance, normal dechanneling, bending dechanneling, and surface acceptance. Some bending applications that have been tried and future possibilities are reviewed. 29 refs., 30 figs. (LEW)

Carrigan, R.A. Jr.

1986-03-01

81

Manipulation of dielectric particles using photonic crystal cavities  

NASA Astrophysics Data System (ADS)

The authors present a theoretical study of the optical trapping forces on dielectric particles occurring in the highly localized evanescent field of planar photonic crystal (PC) cavities. These forces are evaluated by means of finite element simulations for particle sizes ranging from several nanometers to micrometers, and characteristic size-dependent changes of the trapping behavior are found. The authors introduce the phenomenon of self-induced trapping due to the resonance shift of the cavity and propose a transport mechanism based on alternating excitation of different cavity modes. Thus, PC cavities are promising candidates for applications involving the manipulation and arrangement of dielectric particles.

Barth, Michael; Benson, Oliver

2006-12-01

82

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

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

Structures of immature flavivirus particles.  

PubMed

Structures of prM-containing dengue and yellow fever virus particles were determined to 16 and 25 A 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. PMID:12773377

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

2003-06-01

86

Synthesis of crystals and particles by crystallization and polymerization in droplet-based microfluidic devices  

Microsoft Academic Search

The recent advances in crystallization and polymerization assisted by droplet-based microfluidics to synthesize micro-particles\\u000a and micro-crystals are reviewed in this paper. Droplet-based microfluidic devices are powerful tools to execute some precise\\u000a controls and operations on the flow inside microchannels by adjusting fluid dynamics parameters to produce monodisperse emulsions\\u000a or multiple-emulsions of various materials. Major features of this technique are producing

Jingtao Wang; Jin Zhang; Junjie Han

2010-01-01

87

Structural characterization of thin film photonic crystals  

SciTech Connect

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

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

2001-06-15

88

Transfer-printing and host-guest properties of 3D supramolecular particle structures.  

PubMed

Mechanically robust and crystalline supramolecular particle structures have been constructed by decoupling nanoparticle assembly and supramolecular glue infiltration into a sequential process. First, beta-cyclodextrin (CD)-functionalized polystyrene particles (d approximately 500 nm) were assembled on a CD-functionalized surface via convective assembly to form highly ordered, but mechanically unstable, particle crystals. Subsequently, the crystals were infiltrated by a solution of adamantyl-functionalized dendrimers, functioning as a supramolecular glue to bind neighboring particles together and to couple the entire particle crystal to the CD surface, both in a noncovalent manner. The supramolecular particle crystals are highly robust, as witnessed by their ability to withstand agitation by ultrasonication. When assembled on a poly(dimethylsiloxane) (PDMS) stamp, the dendrimer-infiltrated particle crystals could be transfer-printed onto a CD-functionalized target surface. By variation of the geometry and size of the PDMS stamps, single particle lines, interconnected particle rings, and V-shaped particle assemblies were obtained. The particle structures served as 3D receptors for the binding of (multiple) complementary guest molecules, indicating that the supramolecular host functionalities of the particle crystals were retained throughout the fabrication process. PMID:20356024

Ling, Xing Yi; Phang, In Yee; Reinhoudt, David N; Vancso, G Julius; Huskens, Jurriaan

2009-04-01

89

Refinement of the Crystal Structure of Nacrite  

Microsoft Academic Search

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

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

1969-01-01

90

About the mechanisms of high-energy charged particle deflection by a bent crystal  

Microsoft Academic Search

Computer simulations of the passage of high-energy charged particle beams through a bent crystal near a crystallographic axis are presented. The influence of the magnitude of the particle charge, of the particle charge sign and of incoherent scattering processes by thermal oscillations of the crystal's atoms and by the atomic electrons of the crystal on the beam deflection efficiency is

A. A. Greenenko; N. F. Shul'ga

2001-01-01

91

Interaction between two spherical particles in a nematic liquid crystal.  

PubMed

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 Q(ij) 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 approximately 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 less than or approximately equal 10R0, which is stronger than the dipole-dipole repulsion (approximately D-3 ) expected theoretically as an asymptotic behavior for large D. PMID:15169032

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

2004-04-30

92

Ordering of crystal structure by ionizing radiation  

NASA Astrophysics Data System (ADS)

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

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

1994-12-01

93

Highly transparent ceramics with disordered crystal structure  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

94

Pholcodine monohydrate: Crystal structure and polymorphism  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

95

Strategies for crystallizing a chromatin protein in complex with the nucleosome core particle.  

PubMed

The molecular details of how chromatin factors and enzymes interact with the nucleosome are critical to understanding fundamental genetic processes including cell division and gene regulation. A structural understanding of such processes has been hindered by the difficulty in producing diffraction-quality crystals of chromatin proteins in complex with the nucleosome. We describe here the steps used to grow crystals of the 300-kDa RCC1 chromatin factor/nucleosome core particle complex that diffract to 2.9- resolution. These steps include both pre- and postcrystallization strategies potentially useful to other complexes. We screened multiple variant RCC1/nucleosome core particle complexes assembled using different RCC1 homologs and deletion variants, and nucleosomes containing nucleosomal DNA with different sequences and lengths, as well as histone deletion variants. We found that using RCC1 from different species produced different crystal forms of the RCC1/nucleosome complex consistent with key crystal packing interactions mediated by RCC1. Optimization of postcrystallization soaks to dehydrate the crystals dramatically improved the diffraction quality of the RCC1/nucleosome crystal from 5.0- to 2.9- resolution. PMID:23928047

Makde, Ravindra D; Tan, Song

2013-08-06

96

Random hcp and fcc structures in thermoresponsive microgel crystals  

NASA Astrophysics Data System (ADS)

Monodisperse thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles having a diameter of 520 nm were synthesized by free-radical precipitation polymerization and centrifuged to obtain a concentrated suspension. The centrifuged mother suspension was made to self-order into a crystalline state by repeated annealing beyond the volume phase transition (VPT) of the particles. We report here the three-dimensional (3D) real space structure, determined using a confocal laser scanning microscope, of PNIPAM microgel crystal samples prepared by two different recrystallized routes: (1) solidifying a shear melted colloidal liquid (referred as as-prepared sample) and (2) slow cooling of a colloidal liquid (referred as recrystallized sample). We have recorded images of several regions of the crystal with each region containing 15 horizontal crystal planes for determining the in-plane [two-dimensional (2D)] and 3D pair-correlation functions. The 2D pair-correlation function g(r) revealed hexagonal long-range order of particles in the layers with a lattice constant of 620 nm. The analysis of stacking sequence of layers recorded on as-prepared sample has revealed the existence of stacking disorder with an average stacking probability ?~0.42. This value of ? together with the analysis of 3D pair-correlation function determined from particle positions revealed the structure of microgel crystals in the as-prepared sample to be random hexagonal close packing. We report the first observation of a split second peak in the 3D g(r) of the microgel crystals obtained from a shear melted liquid. Upon melting the sample above VPT and recrystallizing it the split second peak disappeared and the crystals are found to have a face centered cubic (fcc) structure with ?~0.95. From simulations, the split second peak is shown to arise from the displacement of some of the B-planes from the ideal hcp positions. The present results are discussed in light of those reported for charged and hard sphere colloidal crystals and plausible reasons for observing two different structures are also explained.

Brijitta, J.; Tata, B. V. R.; Joshi, R. G.; Kaliyappan, T.

2009-08-01

97

Natural photonic crystals: formation, structure, function  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

98

Crystal structure of plant photosystem I  

Microsoft Academic Search

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

Adam Ben-Shem; Felix Frolow; Nathan Nelson

2003-01-01

99

The Crystal and Molecular Structure of Fluorene  

Microsoft Academic Search

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

D. M. Burns; J. Iball

1955-01-01

100

Soviet research on crystal channeling of charged particle beams  

NASA Astrophysics Data System (ADS)

This report presents an overview of Soviet research in charged particle beam channeling in crystals from 1972 to the present, and the resulting electromagnetic emission, including Soviet proposals for channeling emission lasers in the X-ray region of the spectrum. It analyzes Soviet attitudes toward crystal channeling of charged particles as a subject of research, describes performers of the research, and indicates the level of effort involved. It presents a brief history of crystal channeling research, the differences between channeling and other kinds of electromagnetic radiation, the definition of the main research issues, and estimates of the potential capabilities of channeling radiation, all based on the Soviet viewpoint. It then describes Soviet proposals for laser systems utilizing the channeling radiation mechanism, and analyzes Soviet experimental work involving the observation and measurement of channeling radiation. The author concludes that the outstanding feature of Soviet research in this area is the optimistic belief of Soviet specialists in the technological potential of this research, but finds that the role of the laser proposals in Soviet planning is ambiguous.

Kassel, S.

1985-03-01

101

Ordering of crystal structure by ionizing radiation  

Microsoft Academic Search

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

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

1994-01-01

102

Crystal structure of recombinant bovine neurocalcin  

Microsoft Academic Search

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

Senadhi Vijay-Kumar; Vinod D. Kumar

1999-01-01

103

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

104

Theory of Interaction and Structure Formation in Liquid Crystal Colloids and Emulsion  

Microsoft Academic Search

This article is semi review our result about interaction and structure formation in liquid crystal colloids and emulsion. We treat colloidal and emulsion systems in liquid crystal using effectively describing the elastic interaction. Here we consider a system whose interactions are presumably well-understood and the phase transition in which can be studied in the scale of macro particle resolution

B. Lev; H. Yokoyama

2005-01-01

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

Requirements for structure determination of aperiodic crystals  

NASA Astrophysics Data System (ADS)

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

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

1991-01-01

107

Crystal structure of methane oxidation enzyme determined  

SciTech Connect

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

Baum, R.

1994-01-10

108

Shear induced structures in crystallizing cocoa butter  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

109

Crystal and molecular structure of paclitaxel (taxol).  

PubMed Central

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

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

1995-01-01

110

Crystal Structure of a Plectonemic RNA Supercoil  

PubMed Central

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

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

2012-01-01

111

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

112

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

113

Crystal Structure of Dipotassium Carbonate Trihydrate  

Microsoft Academic Search

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

F. D. Hunter; G. A. Jeffrey

1967-01-01

114

Crystal structure of the 4-chromanone derivative.  

PubMed

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

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

2004-02-01

115

Complex crystal structure of cesium-III.  

PubMed

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

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

2001-11-30

116

Construction and crystal structure of recombinant STNV capsids.  

PubMed

A codon-optimised gene has been expressed in Escherichia coli to produce the coat protein (CP) of the Satellite Tobacco Necrosis Virus. This protein assembles in vivo into capsids closely resembling those of the T=1 wild-type virus. These virus-like particles (VLPs) package the recombinant mRNA transcript and can be disassembled and reassembled using different buffer conditions. The X-ray crystal structure of the VLP has been solved and refined at 1.4 resolution and shown to be very similar to that of wild-type Satellite Tobacco Necrosis Virus, except that icosahedral symmetry constraints could be removed to reveal differences between subunits, presumably owing to crystal packing. An additional low-resolution X-ray crystal structure determination revealed well-ordered RNA fragments lodged near the inside surface of the capsid, close to basic clusters formed by the N-terminal helices that project into the interior of the particle. The RNA consists of multiple copies of a 3-bp helical stem, with a single unpaired base at the 3' end, and probably consists of a number of short stem-loops where the loop region is disordered. The arrangement of the RNA is different from that observed in other satellite viruses. PMID:21839089

Lane, Stephen W; Dennis, Caitriona A; Lane, Claire L; Trinh, Chi H; Rizkallah, Pierre J; Stockley, Peter G; Phillips, Simon E V

2011-08-03

117

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

118

Stability and dynamics of crystals and glasses of motorized particles  

PubMed Central

Many of the large structures of the cell, such as the cytoskeleton, are assembled and maintained far from equilibrium. We study the stabilities of various structures for a simple model of such a far-from-equilibrium organized assembly in which spherical particles move under the influence of attached motors. From the variational solutions of the many-body master equation for Brownian motion with motorized kicking we obtain a closed equation for the order parameter of localization. Thus, we obtain the transition criterion for localization and stability limits for the crystalline phase and frozen amorphous structures of motorized particles. The theory also allows an estimate of nonequilibrium effective temperatures characterizing the response and fluctuations of motorized asemblies.

Shen, Tongye; Wolynes, Peter G.

2004-01-01

119

Lagrangian Coherent Structures for Inertial Particles  

NASA Astrophysics Data System (ADS)

In this talk, I will discuss recent results on the asymptotics of inertial (i.e., finite-size) particle motion. The asymptotic particle motion turns out to be governed by a slow manifold that can be constructed explicitly up to any order of precision. Particle motions synchronize with inertial Lagrangian coherent structures (ILCS) obtained from the reduced dynamics on the slow manifold. For larger particle sizes, the slow manifold develops local instabilities that can be located analytically. As applications, I discuss droplet motion in hurricanes, source inversion for contaminants in an urban environment, and predator-prey interaction in jellyfish feeding.

Haller, G.; Sapsis, T.

2009-04-01

120

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

121

The crystal structures of ? and ? * nitrogen  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

122

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

123

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

124

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

125

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

126

Electron Cryomicroscopy of Membrane Proteins: Specimen Preparation for Two-Dimensional Crystals and Single Particles  

PubMed Central

Membrane protein structure and function can be studied by two powerful and highly complementary electron cryomicroscopy (cryo-EM) methods: electron crystallography of two-dimensional (2D) crystals and single particle analysis of detergent-solubilized protein complexes. To obtain the highest-possible resolution data from membrane proteins, whether prepared as 2D crystals or single particles, cryo-EM samples must be vitrified with great care. Grid preparation for cryo-EM of 2D crystals is possible by back-injection, the carbon sandwich technique, drying in sugars before cooling in the electron microscope, or plunge-freezing. Specimen grids for single particle cryo-EM studies of membrane proteins are usually produced by plunge-freezing protein solutions, supported either by perforated or a continuous carbon film substrate. This review outlines the different techniques available and the suitability of each method for particular samples and studies. Experimental considerations in sample preparation and preservation include the protein itself and the presence of lipid or detergent. The appearance of cryo-EM samples in different conditions is also discussed.

Schmidt-Krey, Ingeborg; Rubinstein, John L.

2010-01-01

127

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

128

Colloidal assembly: the road from particles to colloidal molecules and crystals.  

PubMed

Colloidal particles may be considered as building blocks for materials, just like atoms are the bricks of molecules, macromolecules, and crystals. Periodic arrays of colloids (colloidal crystals) have attracted much interest over the last two decades, largely because of their unique photonic properties. The archetype opal structures are based on close-packed arrays of spheres of submicrometer diameter. Interest in structuring materials at this length scale, but with more complex features and ideally by self-assembly processes, has led to much progress in controlling features of both building blocks and assemblies. The necessary ingredients include colloids, colloidal clusters, and colloidal "molecules" which have special shapes and the ability to bind directionally, the control over short-range and long-range interactions, and the capability to place and orientate these bricks. This Review highlights recent experimental and theoretical progress in the assembly of colloids larger than 50 nm. PMID:21038335

Li, Fan; Josephson, David P; Stein, Andreas

2011-01-10

129

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

130

Photonic crystal and photonic wire device structures  

NASA Astrophysics Data System (ADS)

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

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

2005-09-01

131

Design of sustained release fine particles using two-step mechanical powder processing: particle shape modification of drug crystals and dry particle coating with polymer nanoparticle agglomerate.  

PubMed

We attempted to prepare sustained release fine particles using a two-step mechanical powder processing method; particle-shape modification and dry particle coating. First, particle shape of bulk drug was modified by mechanical treatment to yield drug crystals suitable for the coating process. Drug crystals became more rounded with increasing rotation speed, which demonstrates that powerful mechanical stress yields spherical drug crystals with narrow size distribution. This process is the result of destruction, granulation and refinement of drug crystals. Second, the modified drug particles and polymer coating powder were mechanically treated to prepare composite particles. Polymer nanoparticle agglomerate obtained by drying poly(meth)acrylate aqueous dispersion was used as a coating powder. The porous nanoparticle agglomerate has superior coating performance, because it is completely deagglomerated under mechanical stress to form fine fragments that act as guest particles. As a result, spherical drug crystals treated with porous agglomerate were effectively coated by poly(meth)acrylate powder, showing sustained release after curing. From these findings, particle-shape modification of drug crystals and dry particle coating with nanoparticle agglomerate using a mechanical powder processor is expected as an innovative technique for preparing controlled-release coated particles having high drug content and size smaller than 100 ?m. PMID:23796831

Kondo, Keita; Ito, Natsuki; Niwa, Toshiyuki; Danjo, Kazumi

2013-06-21

132

Photosensitive liquid crystals with nanoparticulate internal structure  

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

133

Fission fragment damage to crystal structures  

Microsoft Academic Search

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

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

1960-01-01

134

Crystal structure of a Rad51 filament  

Microsoft Academic Search

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

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

2004-01-01

135

Crystal Structure of Kaolinite: Dimethylsulfoxide Intercalate  

Microsoft Academic Search

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

J. G. Thompson; C. CUFF

1985-01-01

136

The crystal structure of potassium dimolybdate hydrate  

Microsoft Academic Search

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

B. M. Gatehouse; A. J. Jozsa

1987-01-01

137

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

NASA Astrophysics Data System (ADS)

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

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

138

Bio-Inspired Approaches to Crystals with Composite Structures  

NASA Astrophysics Data System (ADS)

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

Meldrum, Fiona

2013-03-01

139

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.

140

Characterization of colloidal crystal film of polystyrene particles at the air-suspension interface  

Microsoft Academic Search

An aqueous suspension of polystyrene (PS) particles gave rise to a distinct color when a water-soluble volatile solvent, such as methanol or acetone, was added and left to evaporate. The color was caused by the formation of a colloidal crystal film of PS particles at the air-suspension interface. The colloidal crystal formation was possibly induced by the shear flow of

Yoshiro Imura; Hiroko Nakazawa; Emi Matsushita; Clara Morita; Takeshi Kondo; Takeshi Kawai

2009-01-01

141

Field Use of a Simple Technique for Identifying Silver Iodide Particles as Snow Crystal Nuclei.  

National Technical Information Service (NTIS)

A procedure is presented for identifying those silver iodide particles in ice crystals that have behaved as snow crystal nuclei. The new technique is based on the principle that any submicron particle can act as a nucleus in its own supersaturated solutio...

F. P. Parungo J. O. Rhea

1970-01-01

142

Crystal structures of the benzene and ethanol solvates of neotame  

Microsoft Academic Search

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

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

2003-01-01

143

Crystal structure of Cryptosporidium parvum pyruvate kinase.  

PubMed

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

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

2012-10-09

144

In situ X-ray crystallographic study of the structural evolution of colloidal crystals upon heating  

PubMed Central

The structural evolution of colloidal crystals made of polystyrene hard spheres has been studied in situ upon incremental heating of a crystal in a temperature range below and above the glass transition temperature of polystyrene. Thin films of colloidal crystals having different particle sizes were studied in transmission geometry using a high-resolution small-angle X-ray scattering setup at the P10 Coherence Beamline of the PETRA III synchrotron facility. The transformation of colloidal crystals to a melted state has been observed in a narrow temperature interval of less than 10?K.

Zozulya, A. V.; Meijer, J.-M.; Shabalin, A.; Ricci, A.; Westermeier, F.; Kurta, R. P.; Lorenz, U.; Singer, A.; Yefanov, O.; Petukhov, A. V.; Sprung, M.; Vartanyants, I. A.

2013-01-01

145

Crystal and molecular structure of Destruxin B.  

PubMed

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

Steiner, J R; Barnes, C L

1988-02-01

146

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

Microsoft Academic Search

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

Dongfeng Xue; Siyuan Zhang

1999-01-01

147

Crystal structure of MboIIA methyltransferase.  

SciTech Connect

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

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

2003-09-15

148

Formation of lamellar structures from spherical particles.  

PubMed

We report disorder to lamellar transition in a system of spherically symmetric particles where the interparticle potential consists of a short-ranged attraction and a longer-ranged repulsion. The system provides a simplified model for aqueous dispersions of colloidal particles and globular proteins that may exhibit stable/metastable clusters or microscopic phases. By using a non-mean-field density functional theory, we predict that under appropriate conditions, a lamellar phase with alternating condensed and dilute layers of particles is thermodynamically more stable than a uniform disordered phase at the same temperature and molecular number density. Formation of the lamellar structure may prohibit the macroscopic fluid-fluid phase transition. At a given condition, the width of the condensed lamellar layers increases with the overall particle density but the trend is opposite for the dilute lamellar layers. A minimal lamellar periodicity is obtained when the condensed and dilute layers have approximately the same thickness. PMID:19405634

Li, Zhidong; Wu, Jianzhong

2009-04-28

149

Crystal structure of plant photosystem I  

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

150

Molecular and crystal structure of polycyclic nitramines  

Microsoft Academic Search

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

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

2005-01-01

151

Track-structure simulations for charged particles.  

PubMed

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 a 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 compared to condensed history codes highlighted. Interaction cross sections for electrons, protons, alpha particles, and 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. PMID:23032889

Dingfelder, Michael

2012-11-01

152

Interaction of photonic crystals with nanoscopic particles: towards novel (bio)sensing techniques  

NASA Astrophysics Data System (ADS)

We investigate the potential of photonic crystals (PCs) for use as novel sensing devices. For this purpose we study the interaction of nanoscopic dielectric particles with the near field of planar PCs by means of 3D FEM calculations. In particular, we have simulated PC waveguide structures incorporating a single cavity-like defect that interacts with a single dielectric nanosphere in a liquid environment. The resonance of the PC cavity shifts in the presence of the particle, as can be monitored by corresponding transmission measurements. As a second aspect, we investigate the mechanical forces acting on the particle due to the high field gradient in the cavity when in resonance. These forces give rise to a stable trapping of the particle in the cavity in analogy to the trapping in optical tweezers. In combination with microfluidic devices this gives prospect to novel techniques for ultra-sensitive detection and spectroscopy with only minimal amounts of analyte. We also present a scheme for experimental investigations of the particle-PC interaction, which makes use of an optical tweezer to actively move dielectric nanospheres in the near field of the PC, and which allows both for fluorescence as well as very sensitive force measurements.

Barth, Michael; Benson, Oliver

2006-05-01

153

Microstructure Observation of Crystal-Originated Particles on Silicon Wafers  

NASA Astrophysics Data System (ADS)

Microstructure shape of crystal-originated particles (COP's) on mirror-polished silicon wafers (a) as received, (b) cleaned with NH4OH/H2O2/H2O solution (SC-1), and (c) annealed at high temperature (1150 C) in O2/N2 mixture or in H2, were observed using a scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM). Elemental analysis of the COP's was also made using TEM-energy dispersion X-ray spectroscope (EDX). The COP was a pyramidal pit with {111} sidewalls, or a vertical cave having some facets of {111}. In a part of the COP, oxygen was detected by TEM-EDX. It was suggested that the microstructure shape of the COP's has been determined until the mirror polishing is finished. The size of the COP becomes larger and the slopes of the COP become gentler after an anneal in 3% O2/N2 at 1150 C for 4 h and removal of the SiO2 layer by HF solution. The depth of the COP becomes shallower, its size larger and its corners rounder by annealing in H2 at 1100 C for 1 min. The COP's disappear by anealing in H2 at 1150 C for 4 h.

Miyazaki, Morimasa; Miyazaki, Sumio; Yanase, Yoshio; Ochiai, Takashi; Shigematsu, Tatsuhiko

1995-12-01

154

Population structure and particle swarm performance  

Microsoft Academic Search

The effects of various population topologies on the particle swarm algorithm were systematically investigated. Random graphs were generated to specifications, and their performance on several criteria was compared. What makes a good population structure? We discovered that previous assumptions may not have been correct

James Kennedy; Rui Mendes

2002-01-01

155

Pseudo-steady rates of crystal nucleation in suspensions of charged colloidal particles  

Microsoft Academic Search

We develop an analytical model to describe crystal nucleation in suspensions of charged colloidal particles. The particles are assumed to interact with a repulsive hard-core Yukawa potential. The thermodynamic properties of the suspensions are determined by mapping onto an effective hard-sphere system using perturbation theory. Hydrodynamic effects are calculated by approximating particle interactions with the excluded shell potential. The rates

Narendra M Dixit; Charles F Zukoski

2003-01-01

156

Effective Interatomic Forces from One-Particle Crystal Field Parameters.  

National Technical Information Service (NTIS)

Theoretical results are obtained for the crystal field coefficient which enable to develop an approach to the use of the crystal field data for the derivation of information on the effective interatomic forces in crystals. The method is applied to the mag...

S. Adam G. Adam A. Corciovei

1982-01-01

157

Crystal structure of yeast Sco1  

SciTech Connect

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

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

2010-03-05

158

Binary colloidal crystals  

Microsoft Academic Search

Binary crystals are crystals composed of two types of particles having different properties like size, mass density, charge etc. In this thesis several new approaches to make binary crystals of colloidal particles that differ in size, material and charge are reported We found a variety of crystal structures, amongst which five not seen before with colloids (LS3, LS6-, two LS8-

C. G. Christova-Zdravkova

2005-01-01

159

The crystal structure of vyuntspakhite: A redetermination  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

160

The Crystal Structure of Human Argonaute2  

SciTech Connect

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

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

2012-07-18

161

Observation of channeling and volume reflection in bent crystals for high-energy negative particles  

NASA Astrophysics Data System (ADS)

Deflection due to planar channeling and volume reflection in short bent silicon crystals was observed for the first time for 150 GeV/c negative particles, ?- mesons, at one of the secondary beams of the CERN SPS. The deflection efficiency was about 30% for channeling and higher than 80% for volume reflection. Volume reflection occurs, in spite of the attractive character of the forces acting between the particles and the crystal planes, in a wide angular range of the crystal orientations determined by the crystal bend angle.

Scandale, W.; Vomiero, A.; Bagli, E.; Baricordi, S.; Dalpiaz, P.; Fiorini, M.; Guidi, V.; Mazzolari, A.; Vincenzi, D.; Milan, R.; Mea, Gianantonio Della; Vallazza, E.; Afonin, A. G.; Chesnokov, Yu. A.; Maisheev, V. A.; Yazynin, I. A.; Golovatyuk, V. M.; Kovalenko, A. D.; Taratin, A. M.; Denisov, A. S.; Gavrikov, Yu. A.; Ivanov, Yu. M.; Lapina, L. P.; Malyarenko, L. G.; Skorobogatov, V. V.; Suvorov, V. M.; Vavilov, S. A.; Bolognini, D.; Hasan, S.; Mattera, A.; Prest, M.; Shiraishi, S.

2009-11-01

162

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

163

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

2013-07-19

164

Crystal structure of Junin virus nucleoprotein.  

PubMed

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

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

2013-07-24

165

Structures of Complex Crystals of Alkylammonium Salts with Aromatic Molecules  

Microsoft Academic Search

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

Keiichi Noguchi; Kenji Okuyama; Kulthida Vongbupnimit

1996-01-01

166

New scintillating media based on liquid crystals for particle detectors  

Microsoft Academic Search

The study results of optical, photoluminiscent and scintillation properties of a liquid crystal 4-pentyl-4\\/'-cyanobiphenyl are presented. The scintillation light output of this liquid crystal is about 35% of crystal anthracene, its main decay time constants are 4 and 14ns, and the maximum of light emission spectrum is about 400nm. The light output of a dissolution of green emitting light scintillation

M. I. Barnik; S. G. Yudin; V. G. Vasil'chenko; S. V. Golovkin; A. M. Medvedkov; A. S. Solovjev

2000-01-01

167

New scintillating media based on liquid crystals for particle detectors  

Microsoft Academic Search

The study results of optical, photoluminiscent and scintillation properties of a liquid crystal 4-pentyl-4?-cyanobiphenyl are presented. The scintillation light output of this liquid crystal is about 35% of crystal anthracene, its main decay time constants are 4 and 14ns, and the maximum of light emission spectrum is about 400nm. The light output of a dissolution of green emitting light scintillation

M. I. Barnik; S. G. Yudin; V. G. Vasil'chenko; S. V. Golovkin; A. M. Medvedkov; A. S. Solovjev

2000-01-01

168

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

169

Crystal structure of level zero extremal weight modules  

Microsoft Academic Search

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

Jonathan Beck

2002-01-01

170

Controlling the electronic structure of nanocrystal assemblies by variation of the particle-particle interaction  

NASA Astrophysics Data System (ADS)

The change in the electronic structure of germanium nanocrystals is investigated as their concentration is increased from noninteracting, individual particles to assembled arrays of particles. The electronic structure of the individual nanoclusters shows clear effects due to quantum confinement which are lost in the concentrated assemblies of bare particles. When the surface of the individual particles is passivated, they retain their quantum confinement properties also upon assembly. These effects are interpreted in terms of a particle-particle interaction model.

Bostedt, C.; van Buuren, T.; Willey, T. M.; Terminello, L. J.

2004-11-01

171

Particle Structures of Encapsulated Milkfat Powders  

Microsoft Academic Search

Emulsions of milkfat (cream or anhydrous butteroil), carbohydrate (sucrose, modified starch or all-purpose flour), nonfat dry milk and mono- and di-glycerides as emulsifying agents were prepared and spray dried, yielding free-flowing powders containing 400, 500 or 600 g\\/kg milkfat. Structural features of the powders were evaluated by optical and scanning electron microscopy. Powder particles were generally spherical in shape, with

C. I. Onwulata; P. W. Smith; P. H. Cooke; V. H. Holsinger

1996-01-01

172

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

173

Determination of Particle Size Distribution of Salt Crystals in Aqueous Slurries.  

National Technical Information Service (NTIS)

A method for determining particle size distribution of water-soluble crystals in aqueous slurries is described. The salt slurries, containing sodium salts of predominantly nitrate, but also nitrite, sulfate, phosphate, aluminates, carbonate, and hydroxide...

A. G. Miller

1977-01-01

174

Diffraction phenomena in spontaneous and stimulated radiation by relativistic particles in crystals (Review)  

SciTech Connect

This report discusses: the dispersion characteristics of parametric x-ray radiation (PXR) and diffraction radiation of oscillator; cooperative effects in x-radiation by charged particles in crystals; and diffraction x-radiation by relativistic oscillator.

Baryshevsky, V.G. [Inst. of Nuclear Problems, Minsk (Belarus); Dubovskaya, I.Ya. [Lawrence Berkeley Lab., CA (United States)

1991-12-01

175

Carbon Particle Inclusions in SiC Single Crystals Prepared by Sublimation.  

National Technical Information Service (NTIS)

Several experiments were performed to clarify the process of carbon particle inclusion in crystals grown by Lely's sublimation procedure. Special attention was paid to the effect of the cavity wall, recrystallization temperature, and the increasing heatin...

H. Tanaka Y. Inomata

1971-01-01

176

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

177

Synthesis and textural evolution of alumina particles with mesoporous structures  

NASA Astrophysics Data System (ADS)

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 ?-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- 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 ?-Al2O3 particles with mesostructures after further calcination at 1173 K, whereas coexisting SO42- can promote above morphology evolution and then transformed into ?-Al2O3 nanofibers after calcination at 1173 K. Moreover nearly all materials retain relatively high specific surface areas larger than 100 m2 g-1 even after calcinations at 1173 K.

Liu, Xun; Peng, Tianyou; Yao, Jinchun; Lv, Hongjin; Huang, Cheng

2010-06-01

178

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

179

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

180

Crystal structures of saposins A and C.  

PubMed

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

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

2006-07-05

181

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

182

Ultrastructure of Calcareous Dinophytes (Thoracosphaeraceae, Peridiniales) with a Focus on Vacuolar Crystal-Like Particles  

PubMed Central

Biomineralization in calcareous dinophytes (Thoracosphaeracaea, Peridiniales) takes place in coccoid cells and is presently poorly understood. Vacuolar crystal-like particles as well as collection sites within the prospective calcareous shell may play a crucial role during this process at the ultrastructural level. Using transmission electron microscopy, we investigated the ultrastructure of coccoid cells at an early developmental stage in fourteen calcareous dinophyte strains (corresponding to at least ten species of Calciodinellum, Calcigonellum, Leonella, Pernambugia, Scrippsiella, and Thoracosphaera). The shell of the coccoid cells consisted either of one (Leonella, Thoracosphaera) or two matrices (Scrippsiella and its relatives) of unknown element composition, whereas calcite is deposited in the only or the outer layer, respectively. We observed crystal-like particles in cytoplasmic vacuoles in cells of nine of the strains investigated and assume that they are widespread among calcareous dinophytes. However, similar structures are also found outside the Thoracosphaeraceae, and we postulate an evolutionarily old physiological pathway (possibly involved in detoxification) that later was specialized for calcification. We aim to contribute to a deeper knowledge of the biomineralization process in calcareous dinophytes.

Zinssmeister, Carmen; Keupp, Helmut; Tischendorf, Gilbert; Kaulbars, Freya; Gottschling, Marc

2013-01-01

183

Temperature dependence of magnetic domain structures of Co particles fabricated by electron beam lithography  

Microsoft Academic Search

Submicron-sized Co particles were fabricated by patterning single crystal Co thin films, and their magnetic domain structures were observed by magnetic force microscopy (MFM) with temperature up to 200 C. The Co films (220 nm in thickness) were epitaxially deposited onto Al2O3 [001] single-crystal substrates by electron beam evaporation, and from these films (with their c-axis parallel to the surface

Y. Kageyama; T. Suzuki

2005-01-01

184

Theoretical problems in the crystallization of hard sphere colloidal particles  

Microsoft Academic Search

In this paper we demonstrate the utility of density functional theories in providing unified descriptions of two problems associated with colloidal crystallization. The first problem involves crystallization in a fixed volume. The result is a time dependent pressure and, hence, density. This process is further complicated during growth by the presence of a depletion zone in advance of the growing

Robert Wild; Peter Harrowell

2000-01-01

185

Morphology of Tropical Cirrus Crystals Derived from Single Particle and Bulk Property Analysis  

Microsoft Academic Search

The bulk density, surface area, asphericity and fractal dimensions of crystals in tropical cirrus clouds are derived by combining complementary measurement techniques that were employed during the CRYSTAL\\/FACE experiment in July, 2002. The instruments that are used in this derivation are the Cloud, Aerosol and Precipitation Spectrometer (CAPS) that measures single particle properties, the cloud integrating nephelometer (CIN) that measures

G. B. Raga; D. Baumgardner; G. Kok; B. Anderson; T. Garrett; E. Weinstock; J. Smith

2003-01-01

186

Fredericksz Transition Threshold in Nematic Liquid Crystals Filled with Ferroelectric NanoParticles  

Microsoft Academic Search

A key liquid crystalline property for electro-optic applications is the Fredericksz threshold electric field. There has been recent experimental interest in liquid crystal-based colloidal suspensions in which the colloidal nanoparticles both possess a permanent electric polarization and provide strong director anchoring on the particle surface. Such suspensions are sometimes known as Filled Liquid Crystals. Our calculations suggest, in qualitative agreement

V. Yu. Reshetnyak; S. M. Shelestiuk; T. J. Sluckin

2006-01-01

187

Novel memory effect found in nematic liquid crystal\\/fine particle system  

Microsoft Academic Search

Novel liquid crystalline composites composed of a nematic two-frequency-addressing liquid crystal and organized clay mineral (about 1 wt %) have been prepared. The particles of clay mineral were dispersed homogeneously in the liquid crystal. The composite cells became transparent within 50ms when a 60 Hz electric field was applied. The transparent state was maintained after the field was switched off.

Masaya Kawasumi; Naoki Hasegawa; Arimitsu Usuki; Akane Okada

1996-01-01

188

Direct opal-like structures consisting of monodisperse polymer particles and synthesis of the related inverse structures  

NASA Astrophysics Data System (ADS)

Three-dimensional periodic solid-state film structures with a face-centered cubic lattice and a high degree of perfection have been prepared from monodisperse particles of styrene copolymers with methacrylic acid. It has been shown that these structures can be successfully used not only as model objects for studying specific features of light propagation in photonic crystals but also as templates for synthesizing inverse opal-like structures. The influence of the degree of hydrophilization of the surface layer of polymer particles forming a polymer template and the template synthesis conditions on the quality of an inverse opal-like TiO2-based structure has been analyzed.

Menshikova, A. Yu.; Shevchenko, N. N.; Bugakov, I. V.; Yakimansky, A. V.; Sel'Kin, A. V.

2011-06-01

189

Photochemical manipulation of colloidal structures in liquid-crystal colloids  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

190

Liquid Crystal Formation in Suspensions of Hard Rodlike Colloidal Particles: Direct Observation of Particle Arrangement and Self-Ordering Behavior  

Microsoft Academic Search

We successfully prepared monodisperse, hard rodlike colloidal particles with a wide range of length-to-width ratios (L\\/W). In their suspensions liquid crystals, or nematic (N) and smectic (Sm) phases, spontaneously appeared. The size of the particles made it possible to directly observe their arrangement and dynamics with an optical microscope. The phase behavior observed exhibited an I (isotropic)-Sm transition for L\\/W=3.5

Hideatsu Maeda; Yoshiko Maeda

2003-01-01

191

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

192

Crystal Structure of Human Kynurenine Aminotransferase ll*  

SciTech Connect

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

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

2008-01-01

193

The crystal structural evolution of nano-Si anode caused by lithium insertion and extraction at room temperature  

Microsoft Academic Search

The crystal structure and morphology of nanosized Si particles and wires after Li-insertion\\/extraction electrochemically have been studied by ex-situ XRD, Raman spectroscopy and electronic microscopy. It is confirmed that the insertion of lithium ions at room temperature destroys the crystal structure of Si gradually and leads to the formation of metastable amorphous LiSi alloy. Furthermore, local ordered structure of Si

Hong Li; Xuejie Huang; Liquan Chen; Guangwen Zhou; Ze Zhang; Dapeng Yu; Yu Jun Mo; Ning Pei

2000-01-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

195

Predicting crystal structure by merging data mining with quantum mechanics  

Microsoft Academic Search

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

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

2006-01-01

196

Lapping performance guide of poly-crystal diamond particles through morphological analysis  

Microsoft Academic Search

Morphological properties of fine diamond particles are intimately related to applications for fine processing such as wearing and polishing of advanced industrial materials and products. The authors are improving and refining particles of poly-crystal diamonds made by an explosive method through size-sorting and shape classification. Obtained products, of micron sizes, have been tested on the lapping rates with the peripheral

T. Shibata; K. Shinohara; T. Uchiyama; M. Otani

2001-01-01

197

Motion of Crystal Particles by the Electromagnetic Vibrations in Mg-Cu-Y Bulk Metallic Glasses  

NASA Astrophysics Data System (ADS)

The method for producing Mg-Cu-Y and Fe-Co-B-Si-Nb bulk metallic glasses using electromagnetic vibrations is effective in forming the metallic glass phase. Disappearance or decrement of clusters by the electromagnetic vibrations applied to the liquid state is considered to cause suppression of crystal nucleation, because the electromagnetic vibrations vibrate the clusters vigorously in the melt. The purpose of this study was to investigate motion of the crystal particles by the electromagnetic vibrations in Mg-Cu-Y bulk metallic glasses. The electromagnetic vibration force vibrated the crystal particles or the clusters that become crystal nuclei in the melt, because the electric current for the electromagnetic vibrations concentrates in those. Thus, the electromagnetic vibrations were found to select vibration particles from the melt. Moreover, it was considered that composites for which second phases or other compounds are dispersed into the metallic glass phase or a nanostructure phase can be produced by the electromagnetic vibration process.

Tamura, Takuya; Maehara, Yuuki; Omura, Naoki; Miwa, Kenji

2008-08-01

198

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

199

Preparation and Crystal Structure of Paeonol  

Microsoft Academic Search

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

XU Xing-Youa

200

Morphological Population Balance Models for the Dynamic Evolution of Particle Shape and Size Distribution in Protein Crystallization  

Microsoft Academic Search

Protein crystallization is known to be affected by many factors and inherently difficult to control. Being able to model the crystal growth, especially at process scale for the population of particles in a reactor rather than for a single particle, will no doubt greatly help the formulation and manufacture of protein crystals. In this paper, a morphological population balance model

Jing J. Liu; Cai Y. Ma; Yang D. Hu; Xue Z. Wang

2009-01-01

201

Structural Aspects of Saltatory Particle Movement  

PubMed Central

A variety of cells possess particles which show movements statistically different from Brownian movements. They are characterized by discontinuous jumps of 230 at velocities of 0.55 /sec or more. A detailed analysis of these saltatory, jumplike movements makes it most likely that they are caused by transmission of force to the particles by a fiber system in the cell outside of the particle itself. Work with isolated droplets of cytoplasm from algae demonstrates a set of fibers involved in both cytoplasmic streaming and saltatory motion, suggesting that both phenomena are related to the same force-generating set of fibers. Analysis of a variety of systems in which streaming and/or saltatory movement occurs reveals two types of fiber systems spatially correlated with the movement, microtubules and 50 A microfilaments. The fibers in Nitella (alga) are of the microfilament type. In other systems (melanocyte processes, mitotic apparatus, nerve axons) microtubules occur. A suggestion is made, based on work on cilia, that a microtubule-microfilament complex may be present in those cases in which only microtubules appear to be present, with the microfilament closely associated with or buried in the microtubule wall. If so, then microfilaments, structurally similar to smooth muscle filaments, may be a force-generating element in a very wide variety of saltatory and streaming phenomena.

Rebhun, Lionel I.

1967-01-01

202

Unconventional structure-assisted optical manipulation of high-index nanowires in liquid crystals.  

PubMed

Stable optical trapping and manipulation of high-index particles in low-index host media is often impossible due to the dominance of scattering forces over gradient forces. Here we explore optical manipulation in liquid crystalline structured hosts and show that robust optical manipulation of high-index particles, such as GaN nanowires, is enabled by laser-induced distortions in long-range molecular alignment, via coupling of translational and rotational motions due to helicoidal molecular arrangement, or due to elastic repulsive interactions with confining substrates. Anisotropy of the viscoelastic liquid crystal medium and particle shape give rise to a number of robust unconventional trapping capabilities, which we use to characterize defect structures and study rheological properties of various thermotropic liquid crystals. PMID:22453452

Engstrm, David; Varney, Michael C M; Persson, Martin; Trivedi, Rahul P; Bertness, Kris A; Goksr, Mattias; Smalyukh, Ivan I

2012-03-26

203

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

2013-03-22

204

Microstructure and Crystal Structure in TAGS Compositions  

SciTech Connect

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

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

2009-01-01

205

Preparation of iridescent colloidal crystal coatings with variable structural colors.  

PubMed

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

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

2013-07-29

206

Structurally coloured secondary particles composed of black and white colloidal particles.  

PubMed

This study investigated the colourful secondary particles formed by controlling the aggregation states of colloidal silica particles and the enhancement of the structural colouration of the secondary particles caused by adding black particles. We obtained glossy, partially structurally coloured secondary particles in the absence of NaCl, but matte, whitish secondary particles were obtained in the presence of NaCl. When a small amount of carbon black was incorporated into both types of secondary particles, the incoherent multiple scattering of light from the amorphous region was considerably reduced. However, the peak intensities in the reflection spectra, caused by Bragg reflection and by coherent single wavelength scattering, were only slightly decreased. Consequently, a brighter structural colour of these secondary particles was observed with the naked eye. Furthermore, when magnetite was added as a black particle, the coloured secondary particles could be moved and collected by applying an external magnetic field. PMID:23917891

Takeoka, Yukikazu; Yoshioka, Shinya; Teshima, Midori; Takano, Atsushi; Harun-Ur-Rashid, Mohammad; Seki, Takahiro

2013-08-01

207

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

PubMed

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

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

2004-12-01

208

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

209

Requirements for structure determination of aperiodic crystals  

Microsoft Academic Search

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

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

1991-01-01

210

Crystal structure of bet3 reveals a novel mechanism for Golgi localization of tethering factor TRAPP  

Microsoft Academic Search

Transport protein particle (TRAPP) is a large multiprotein complex involved in endoplasmic reticulumtoGolgi and intra-Golgi traffic. TRAPP specifically and persistently resides on Golgi membranes. Neither the mechanism of the subcellular localization nor the function of any of the individual TRAPP components is known. Here, the crystal structure of mouse Bet3p (bet3), a conserved TRAPP component, reveals a dimeric structure with

Yeon-Gil Kim; Eun Ju Sohn; Jawon Seo; Kong-Joo Lee; Heung-Soo Lee; Inhwan Hwang; Malcolm Whiteway; Michael Sacher; Byung-Ha Oh

2004-01-01

211

Crystal structures of histone Sin mutant nucleosomes reveal altered proteinDNA interactions  

Microsoft Academic Search

Here we describe 11 crystal structures of nucleosome core particles containing individual point mutations in the structured regions of histones H3 and H4. The mutated residues are located at the two protein-DNA interfaces flanking the nucleosomal dyad. Five of the mutations partially restore the in vivo effects of SWI\\/SNF inactivation in yeast. We find that even nonconservative mutations of these

Uma M Muthurajan; Yunhe Bao; Lawrence J Forsberg; Rajeswari S Edayathumangalam; Pamela N Dyer; Cindy L White; Karolin Luger

2004-01-01

212

Crystal structure of a core spliceosomal protein interface.  

PubMed

The precise excision of introns from precursor mRNAs (pre-mRNAs) in eukaryotes is accomplished by the spliceosome, a complex assembly containing five small nuclear ribonucleoprotein (snRNP) particles. Human p14, a component of the spliceosomal U2 and U11/U12 snRNPs, has been shown to associate directly with the pre-mRNA branch adenosine early in spliceosome assembly and within the fully assembled spliceosome. Here we report the 2.5-A crystal structure of a complex containing p14 and a peptide derived from the p14-associated U2 snRNP component SF3b155. p14 contains an RNA recognition motif (RRM), the surface of which is largely occluded by a C-terminal alpha-helix and a portion of the SF3b155 peptide. An analysis of RNA.protein crosslinking to wild-type and mutant p14 shows that the branch adenosine directly interacts with a conserved aromatic within a pocket on the surface of the complex. This result, combined with a comparison of the structure with known RRMs and pseudoRRMs as well as model-building by using the electron cryomicroscopy structure of a spliceosomal U11/U12 di-snRNP, suggests that p14.SF3b155 presents a noncanonical surface for RNA recognition at the heart of the mammalian spliceosome. PMID:16432215

Schellenberg, Matthew J; Edwards, Ross A; Ritchie, Dustin B; Kent, Oliver A; Golas, Monika M; Stark, Holger; Lhrmann, Reinhard; Glover, J N Mark; MacMillan, Andrew M

2006-01-23

213

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

2013-06-03

214

Polymer Cholesteric Liquid Crystal Flakes for Particle Displays  

Microsoft Academic Search

(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.

Tanya Z. Kosc; Ken L. Marshall; Stephen D. Jacobs

2003-01-01

215

Studies of NanoParticle Doped Liquid Crystal Mixtures  

Microsoft Academic Search

Liquid crystals (LCs) are rod-shaped molecules which can diffuse freely like liquid and orient themselves under the influence of electric field with the long axis of molecules pointing in the same direction. Carbon nanotubes and bucky balls are ideal LC dopants because of their strength, conductivity, flexibility and novel electrical characteristics. LCs doped with C60 show enhancement of the director

Gupta Sureshchandra J; Pradnya Prabhu; Arvind Singh; Balakrishna Sreeram; Vinita Dhulia; Bhakti S. Yadav; Anita Kanwar

2009-01-01

216

On the Crystal Structure of Ln  

SciTech Connect

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

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

2001-04-01

217

Photonic Crystal Structures with Tunable Structure Color as Colorimetric Sensors  

PubMed Central

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

Wang, Hui; Zhang, Ke-Qin

2013-01-01

218

Photonic crystal structures with tunable structure color as colorimetric sensors.  

PubMed

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

Wang, Hui; Zhang, Ke-Qin

2013-03-28

219

Photonic crystals for monitoring fatigue phenomena in steel structures  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

220

Two Types of Anchoring Structure in Smectic Liquid Crystal Molecules  

Microsoft Academic Search

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

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

1990-01-01

221

Crystallization, melting, and structure of water nanoparticles at atmospherically relevant temperatures.  

PubMed

Water nanoparticles play an important role in atmospheric processes, yet their equilibrium and nonequilibrium liquid-ice phase transitions and the structures they form on freezing are not yet fully elucidated. Here we use molecular dynamics simulations with the mW water model to investigate the nonequilibrium freezing and equilibrium melting of water nanoparticles with radii R between 1 and 4.7 nm and the structure of the ice formed by crystallization at temperatures between 150 and 200 K. The ice crystallized in the particles is a hybrid form of ice I with stacked layers of the cubic and hexagonal ice polymorphs in a ratio approximately 2:1. The ratio of cubic ice to hexagonal ice is insensitive to the radius of the water particle and is comparable to that found in simulations of bulk water around the same temperature. Heating frozen particles that contain multiple crystallites leads to Ostwald ripening and annealing of the ice structures, accompanied by an increase in the amount of ice at the expense of the liquid water, before the particles finally melt from the hybrid ice I to liquid, without a transition to hexagonal ice. The melting temperatures T(m) of the nanoparticles are not affected by the ratio of cubic to hexagonal layers in the crystal. T(m) of the ice particles decreases from 255 to 170 K with the particle size and is well described by the Gibbs-Thomson equation, T(m)(R) = T(m)(bulk) - K(GT)/(R - d), with constant K(GT) = 82 5 Knm and a premelted liquid of width d = 0.26 0.05 nm, about one monolayer. The freezing temperatures also decrease with the particles' radii. These results are important for understanding the composition, freezing, and melting properties of ice and liquid water particles under atmospheric conditions. PMID:22452637

Johnston, Jessica C; Molinero, Valeria

2012-04-05

222

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

223

Optical Response of Liquid Crystals in Colloid-Templated Structures  

Microsoft Academic Search

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

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

2001-01-01

224

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

225

Structure of hard-sphere fluid and precursor structures to crystallization  

NASA Astrophysics Data System (ADS)

The structural origin of the commonly observed split second peak of the radial distribution function of a supercooled or glassy liquid is examined in this work using the hard-sphere fluid as an example. A novel approach to the analysis of the microscopic structure of a fluid is described, which permits the decomposition of both the radial distribution function and bond-angle distribution function of a system of particles into contributions from a small number of ring structures. The method uses a modified shortest-path definition of rings appropriate to the analysis of the medium-range structure of dense systems. It is shown that the split peak is an indicator of the emergence of precursor structures to crystal formation. The origin of the split peak provides a structural link between fluid and crystalline phases and our results suggest that it is neither a structural feature peculiar to glassy phases nor a smooth structural continuation of the stable-fluid phase. This structural feature of simple glassy systems is more appropriately described as a signifier of the frustration of emerging crystalline order in a fluid.

O'Malley, Brendan; Snook, Ian

2005-08-01

226

Liquid crystal phase behaviour of attractive disc-like particles.  

PubMed

We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids. PMID:23965962

Wu, Liang; Jackson, George; Mller, Erich A

2013-08-08

227

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

228

Thermal Expansion and Structure of Crystallizing Glass.  

National Technical Information Service (NTIS)

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

E. S. Sorkin

1972-01-01

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

PARTICLE IMAGE VELOCIMETRY AND THERMOMETRY USING THERMOCHROMIC LIQUID CRYSTALS  

Microsoft Academic Search

Summary In recent years Thermochromic Liquid Crystals (TLCs) have been successfully used in non-intrusive heat transfer and fluid mechanics studies. Application of TLC tracers allows instantaneous measurement of the temperature and velocity fields for two-dimensional cross-section of flow. Here we present the review of the development of techniques for visualising and analysing flow images with TLC tracers we used over

Tomasz A. KOWALEWSKI

231

Crystal structure of cholesteryl butanoate at 123 K  

Microsoft Academic Search

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

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

232

Hertzian Fracture in Single Crystals with the Diamond Structure  

Microsoft Academic Search

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

B. R. Lawn

1968-01-01

233

Cavity-enhanced structural colour in extrudeable photonic crystals  

Microsoft Academic Search

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

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

2009-01-01

234

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

Microsoft Academic Search

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

Sharmistha Datta; David J. W. Grant

2004-01-01

235

Crystal structure and phototransistor behavior of N-substituted heptacence.  

PubMed

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

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

2012-04-09

236

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

237

Glass crystallization synthesis of ultrafine hexagonal M-type ferrites: Particle morphology and magnetic characteristics  

Microsoft Academic Search

This review concerns the synthesis and functional properties of ultrafine particles of M-type hexagonal ferrites prepared\\u000a by the most advanced process of oxide glass crystallization. Hexaferrite phase formation during the heat treatment of multicomponent\\u000a oxide glasses of various chemical compositions containing boron and\\/or silicon oxides as glass formers is considered. This\\u000a route is useful to prepare assemblies of single-crystal strontium

P. E. Kazin; L. A. Trusov; D. D. Zaitsev; Yu. D. Tretyakov

2009-01-01

238

Measurement of the size distribution of fat crystals using a laser particle counter  

Microsoft Academic Search

A new method that uses a laser particle counter has been developed to measure the size of fat crystals. The fat crystals were\\u000a suspended in isobutanol in the ratio of 1?25,000. The solid and liquid fat recovery after being in contact with isobutanol\\u000a for 24 hr, fatty acid composition of the solid and liquid fractions, DSC melting behavior and polarized

P. Chawla; J. M. deMan

1990-01-01

239

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

240

Structural and mechanical studies of cadmium manganese thiocyanate crystal  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

241

Discrete breathers in crystals with the NaCl structure  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

242

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

NASA Astrophysics Data System (ADS)

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

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

1980-10-01

243

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

NASA Astrophysics Data System (ADS)

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

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

2001-04-01

244

Coalescence of particles of liquid crystal phase in coking residual petroleum stocks  

SciTech Connect

This paper investigates the coalescence of the mesophase or liquid crystal phase in the carbonization of petroleum residua by means of direct observation with a ''hot stage'' microscope as specified. The sequence of microphotographs reflects the successive process of coalescence of three mesophase particles. Studies of the process reveal a new mechanism of particle coalesence--the formation of a liquid crystal bridge--that has a substantial influence on the formation of the solid matric and the purposeful regulation of which offers the possibility of obtaining coke with preassigned properties.

Kapustin, S.M.; Stolonogov, I.I.; Syunyaev, Z.I.; Zaitseva, N.P.

1983-11-01

245

Molecular structures and crystal packings of 2-styrylquinoxaline derivatives  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

246

Structural, optical and electrical characteristics of a new NLO crystal  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

247

Determination of channeling perspectives for complex crystal structures  

SciTech Connect

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

Allen, W.R.

1993-03-01

248

Structural Reorganization of Liquid Crystals Revealled by Fast Scanning Calorimeter  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

249

Detergent structure in tetragonal crystals of OmpF porin  

Microsoft Academic Search

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

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

1995-01-01

250

Crystal structure of a phospholipase D family member  

Microsoft Academic Search

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

Jeanne A. Stuckey; Jack E. Dixon

1999-01-01

251

Design of a 3D Digital Liquid Crystal Particle Thermometry and Velocimetry (3DDLCPT\\/V) System  

Microsoft Academic Search

A novel 3D Digital Liquid Crystal Particle Thermometry and Velocimetry (3DDLCPT\\/V) system has been designed and fabricated. By combining 3D Defocusing Particle Image Velocimetry (3DDPIV) and Digital Particle Image Thermometry (DPIT) into one system, this technique provides simultaneous temperature and velocity data using temperature-sensitive liquid crystal particles (LCP) as flow sensors. A custom water-filled prism corrects for astigmatism caused by

Rob Grothe; Greg Rixon; Dana Dabiri

2007-01-01

252

Symmetry breaking and interaction of colloidal particles in nematic liquid crystals.  

PubMed

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. PMID:11863547

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

2002-01-25

253

DYNAMIC PARTICLE SYSTEMS FOR OBJECT STRUCTURE EXTRACTION  

Microsoft Academic Search

A new deformable model based on the use of a particle system is introduced. By defining the local behavior of each particle, the system behaves as an active contour model showing a variable topology and regularization properties. The efficiency of the particle system is illustrated by two applications: the first one concerns the use of the system as a skeleton

OLIVIER LAVIALLE; FRANCK ANGELLA; CHRISTIAN GERMAIN; PIERRE BAYLOU

254

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

255

Rhombohedral crystal structure of compounds containing boron-rich icosahedra  

Microsoft Academic Search

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

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

1986-01-01

256

Rhombohedral crystal structure of compounds containing boron-rich icosahedra  

Microsoft Academic Search

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

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

1986-01-01

257

Structure and vertical modes in finite 2D plasma crystals  

Microsoft Academic Search

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

K. Qiao; T. W. Hyde

2007-01-01

258

Structural Patterns in Polymer-Dispersed Liquid Crystal Films  

Microsoft Academic Search

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

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

1999-01-01

259

The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite  

Microsoft Academic Search

The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic

F. Franco; L. A. Prez-Maqueda; J. L. Prez-Rodr??guez

2004-01-01

260

Preparation and characterization of pluronic-colloidal silicon dioxide composite particles as liquid crystal precursor.  

PubMed

The purpose of this study was to produce spray-dried Pluronic-colloidal silicon dioxide (Aerosil) composite particles as a liquid crystal precursor that would form a liquid crystalline phase upon hydration. A Pluronic-colloidal silicon dioxide dispersion in isopropyl alcohol was spray-dried to obtain composite particles using different concentrations of Aerosil. Polarizing microscopy, gelation, gel melting, and rheological studies were employed to characterize the composite particles. The composite particles obtained were irregular, with concave depression. Gelation was found to decrease with the addition of Aerosil, while gel melting was found to increase with the concentration of Aerosil. Rheological studies showed an increase in elasticity as well as viscosity with an increase in the concentration of Aerosil. Composite particles showed improved gelation and rheological properties. These composite particles and the process by which they were obtained may be useful for designing various drug delivery systems. PMID:17285743

Maheshwari, Manish; Paradkar, Anant; Yamamura, Shigeo; Kadam, Shivajirao

2006-01-01

261

Structure and dynamics of suspensions of nanoparticles in nematic liquid crystals  

NASA Astrophysics Data System (ADS)

A hierarchical modeling approach has been adopted to examine the structure and dynamics of nanoparticles suspended in liquid crystals. A molecular model is used to predict the defects that arise in nanoparticle assemblies, as well as their response to applied flow fields. The model is solved by resorting to a radial basis function based technique. The validity of the model and our numerical results are established by direct comparison to results from molecular dynamics simulations of nanoparticles in nematic and isotropic liquid crystals. Results for particle diffusion and aggregation at equilibrium and in flowing systems are then used to interpret our experimental data for a variety of systems.

Gettelfinger, Brian; Koenig, Gary; Moreno-Razo, Jose; Hernadez-Ortiz, Juan; Abbott, Nicholas; de Pablo, Juan

2009-03-01

262

Migration of suspended particles and topological defects within a nematic liquid crystal in anisotropic microfluidic devices  

NASA Astrophysics Data System (ADS)

Devendra et al. (2010) have explored the mobility of particles in periodic anisotropic arrays of obstacles. They observed that the particles migrate away from the applied force at angles that depend on the size of the particle, suggesting a method for microfluidic separation. Rovner et al. (2010) have shown that a lift force redirects particles in a nematic liquid crystal at an angle to the applied force that depends on the anchoring of the nematic director at the surface of the particle. Combining these approaches for separation of particles, we have investigated the behavior of the nematic 4-cyano-4'-pentylbiphenyl (5CB), both with and without suspended particles, flowing inside microfluidic devices containing arrays of obstacles. We report a certain degree of control over generation of topological defects in the nematic order, which we image using polarized microscopy, and control of the flow direction of these defects and suspended particles. The results suggest new ways to conduct microfluidic separation, as well as a new, controlled method for investigating the behavior of liquid crystal defects in flow.

Flower, Nicholas; Devendra, Raghavendra; Rovner, Joel; Leheny, Robert; Drazer, German

2011-11-01

263

Numerical study of structural phase transitions in a vertically confined plasma crystal  

NASA Astrophysics Data System (ADS)

Dusty plasmas consists of an ionized gas containing small (usually negatively charged) particles. Dusty plasmas are of interest in both astrophysics and space physics as well as in research in plasma processing and nanofabrication. In this work, the formation of plasma crystals confined in an external one-dimensional parabolic potential well is simulated for a normal experimental environment employing a computer code called BOX_TREE. Such crystals are layered systems, with each layer a two dimensional lattice composed of grain particles. The number of layers is dependent upon the external potential parameter. For constant layer number, the intralayer structure transits from a square lattice to a hexagonal (triangular) lattice as the confining potential decreases. For hexagonal lattices, both hcp and fcc characteristics were found but hcp structures dominate. The relative thickness of the system was also examined. The results were compared with previous experimental and theoretical results and found to agree.

Qiao, K.; Hyde, T. W.

2006-01-01

264

The effect of budesonide particle mass on drug particle detachment from carrier crystals in adhesive mixtures during inhalation.  

PubMed

The different fine particle fractions (FPFs) that are obtained, when different dry powder inhalers (DPIs) are used for the same powder formulation at the same flow rate, is the result of different powder de-agglomeration efficiencies for these DPIs. For adhesive mixtures, this is the efficiency with which the kinetic energy of the air flow through the DPI is converted into separation forces that detach drug particles from carrier crystals. We investigated the effect of drug particle diameter (mass) on drug-carrier separation during inhalation with three different inhalers (Sofotec Novolizer, Inhalator Ingelheim and a special test inhaler), at two different flow rates (30 and 60l/min). Two different size fractions were used as carrier material (45-63 and 100-150 microm). We measured decreasing amounts of residual drug on the carrier crystals after inhalation with increasing drug particle mass for all inhalers at both flow rates. The observed trends were the same for both carrier fractions. The decrease in residual drug on carrier is in agreement with increasing FPFs in an Erweka impactor. However, it has been calculated that the magnitude of the effect decreases with increasing de-agglomeration efficiency. PMID:12191698

Dickhoff, B H J; Ellison, M J H; de Boer, A H; Frijlink, H W

2002-09-01

265

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

266

Fabrication of electromagnetic crystals with a complete diamond structure by stereolithography  

Microsoft Academic Search

Three-dimensional electromagnetic or photonic crystals with periodic variations of the dielectric constants were fabricated by a rapid prototyping method called stereolithography. Millimeter-order epoxy lattices with a diamond structure were designed to reflect electromagnetic waves by forming an electromagnetic bandgap in the GHz range. Titanium oxide-based ceramic particles were dispersed into the lattice to control the dielectric constant, resulting in the

Soshu Kirihara; Yoshinari Miyamoto; Katsuhiro Takenaga; Mitsuo Wada Takeda; Kenji Kajiyama

2002-01-01

267

Some Specific Features of Coherent Radiation and Particle Propagation in Crystals.  

National Technical Information Service (NTIS)

Scattering of the high energy particles channeled through crystals on the lattice phonons is reviewed and has proved to play an important role at large penetration depths. Then the occurence of two distinct peaks is shown to be predicted by the theory for...

G. Adam S. Adam G. M. Gavrilenko D. Mikhalake V. K. Fedyanin

1982-01-01

268

Nonlinear optical probe of molecular structure on colloidal particle surfaces  

Microsoft Academic Search

The structure of molecules adsorbed at the colloidal particle surface has great influence on how the colloidal particles interact among themselves and with the environment. In this presentation we show that Second Harmonic Generation from molecules adsorbed at the particle surface can be used for determining the orientation of the molecules at this buried interface. The determination is facilitated by

Shih-Hui Jen

2005-01-01

269

Particle structure control through intraparticle reactions by spray pyrolysis  

Microsoft Academic Search

Spray pyrolysis is a dropletparticle conversion process comprising of the evaporation of solvents, precipitation of the solutes, decomposition of the solutes, sintering of the formed phases, etc. Purposive control of the reactions within every droplet or particle makes it possible to control the structure, phase composition and shape of the prepared particles. By introducing reactions into every droplets or precisely

Shenglei Che; Osamu Sakurai; Kazuo Shinozaki; Nobuyasu Mizutani

1998-01-01

270

Crystal structure transfer in core/shell nanowires.  

PubMed

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

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

2011-03-21

271

Quasi-crystals-random structures or twins?  

Microsoft Academic Search

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

J. Wolny; L. Pytlik; B. Lebech

1988-01-01

272

Colloid-induced structure in liquid crystal media.  

PubMed

The structural perturbations induced by colloidal particles immersed in a model nematic subjected to an external field are calculated employing integral equation methods. Maps of the density-orientational distribution about a colloidal particle are obtained, and these provide a microscopic picture of the colloid's nematic coat. We focus on colloidal particles that favor homeotropic anchoring, but planar anchoring cases are also considered. The range and structure of the nematic coat is shown to be significantly influenced by the nature of the anchoring, the size of the colloidal particle, the range and strength of the colloid-nematogen interaction, and the external field strength. All of these factors are discussed. PMID:15836424

Sokolovska, T G; Sokolovskii, R O; Patey, G N

2005-03-22

273

Selective cleavage of periodic mesoscale structures: two-dimensional replication of binary colloidal crystals into dimpled gold nanoplates.  

PubMed

Specific crystallographic planes of binary colloidal crystals consisting of silica nanoparticles are two-dimensionally replicated on the surface of gold nanoplates. The selectivity of the surface patterns is explained by the geometrical characteristics of the binary colloidal crystals as templates. The binary colloidal crystals with the AlB(2)- and NaZn(13)-type structures are fabricated from aqueous dispersions of stoichiometrically mixed silica nanoparticles with different sizes. The stoichiometry is precisely controlled on the basis of a seed growth of silica nanoparticles. Dimpled gold nanoplates are formed by the two-dimensional growth of gold between partially cleaved surfaces of templates. The selectivity of the surface patterns is explained using the AlB(2)-type binary colloidal crystal as a template. The surface pattern is determined by the preferential cleavage of the plane with the lowest density of particle-particle connections. The tendency to form well-defined cleavage in binary colloidal crystals is crucial to formation of dimpled gold nanoplates, which is explained using the NaZn(13)-type binary colloidal crystal as a template. Its complex structure does not show well-defined cleavage, and only distorted nanoplates are obtained. Therefore, the mechanism of the two-dimensional replication of binary colloidal crystals is reasonably explained on the basis of their periodic mesoscale structures and crystal-like properties. PMID:22524635

Kuroda, Yoshiyuki; Sakamoto, Yasuhiro; Kuroda, Kazuyuki

2012-05-04

274

Effect of confining walls on the interaction between particles in a nematic liquid crystal  

NASA Astrophysics Data System (ADS)

We investigate theoretically how the confining walls of a nematic cell affect the interaction of particles mediated by the elastic deformation of a nematic liquid crystal. We consider the case where strong homeotropic or planar anchoring is imposed on the flat parallel walls so that the director on the wall surfaces is fixed and uniform alignment is achieved in the bulk. This set-up is more realistic experimentally than any other previous theoretical studies concerning the elastic-deformation-mediated interactions that assume an infinite medium. When the anchoring on the particle surfaces is weak, an exact expression of the interaction between two particles can be obtained. The two-body interaction can be regarded as the interaction between one particle and an infinite array of 'mirror images' of the other particle. We also obtain the 'self-energy' of one particle, the interaction of a particle with confining walls, which is interpreted along the same way as the interaction of one particle with its mirror images. We show that the walls play a different role in homeotropic and planar cells, which is attributed to the difference in the symmetry of the cells. We also present the landscapes of the interaction energy when one particle is fixed and demonstrate that the interaction is sensitively dependent on the fixed particle as well as the interparticle distance.

Fukuda, Jun-ichi; Lev, Bohdan I.; Yokoyama, Hiroshi

2003-06-01

275

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

276

Force between colloidal particles in a nematic liquid crystal studied by optical tweezers  

NASA Astrophysics Data System (ADS)

We measure the dependence of the interparticle force F on the distance R between two colloidal particles with hyperbolic hedgehog defects in a nematic liquid crystal using optical tweezers. The particle-defect pair can be regarded as an elastic dipole in the electrostatic analogy. In a parallel configuration, where the dipole vectors are parallel with each other, F is attractive and proportional to R-4 . However, F becomes repulsive at small R due to the existence of a defect between the particles. In an antiparallel configuration, where the particles directly face each other, F is repulsive over the whole range of R and proportional to R-3.6 . In another antiparallel configuration, where two hyperbolic hedgehog defects directly face each other, F is proportional to R-3.6 and F at small R turns out to be attractive upon tilting the dipoles. Furthermore, we yield the force between particles connected by a stringlike defect called a bubblegum defect.

Takahashi, Kenji; Ichikawa, Masatoshi; Kimura, Yasuyuki

2008-02-01

277

Synthesis and Crystallization of Nano-Ceria Particles by Solvothermal Routes  

NASA Astrophysics Data System (ADS)

Cerium oxides (CeO2) were synthesized by two steps solvothermal routes. First, a precursor was precipitated using solutions of cerium (III) nitrate and ammonia, and then this precursor was treated via solvothermal techniques in an autoclave. Narrow distribution of CeO2 particle size, between 10 to 15 nm, was achieved in different solvents. Hard agglomerates of nano-CeO2 were mitigated in an ethanol solvent. Most of crystal particles were in the shape of a quadrangle for the precursor. Morphology of CeO2 particles gradually changed after the precursor was treated by solvothermal techniques. There were both quadrangular and symmetrically hexagonal particles at an alkaline pH value. Alternatively, the quadrangular particles disappeared, instead of geometrically unsymmetrical hexagon with decreasing pH to a more acid value. The evolution mechanism of the morphology was discussed. These results have important implications for recognizing and controlling the crystalline shape by solvothermal techniques.

Fu, Cong; Li, Ruixing; Zhang, Yue

278

Analysis of wave curvature experiments for monomodal explosives with different crystal quality and particle size characteristics  

SciTech Connect

Wood-Kirkwood theory reaction zone thickness determinations and computer simulations of wave curvature experiments of two sets of explosives are presented. One set included explosives composed of RDX with different crystal quality characteristics. The other set of explosives was composed of monomodal explosives made from fine, coarse and very coarse sieved RDX and bimodal explosives made from combining the fine and very coarse RDX. The calculated reaction zone thickness was found to be greater for explosives with higher RDX crystal quality and for those of higher mean particle size. A simplified two-term ignition and growth reactive model parameterized by embedded gauge experiments was used in CTH hydrocode simulations of the wave curvature experiments for the explosives where crystal quality was varied. The simulations under-predicted the axial position lag seen in experiment and predicted as seen in experiment, that the explosive containing the higher quality crystals had a greater axial position lag.

Sutherland, G. T. [Technology Development Department, Naval Surface Warfare Center, Indian Head, MD 20640 (United States); Lemar, E. R.; Marcus, M. H. [Energetics Technology Department, Naval Surface Warfare Center, Indian Head, MD 20640 (United States)

2007-12-12

279

Enhanced Magneto-Optical Properties of Suspensions of Spindle Type Mono-Dispersed Hematite NanoParticles in Liquid Crystal  

Microsoft Academic Search

We explored how to increase liquid crystal sensitivity to external magnetic fields. Suspensions consisting of a mixture of liquid crystal and spindle type mono-dispersed hematite nano-particles at concentrations lower than 1wt% were prepared. The Fredericksz transition threshold for the suspensions appeared to be lower than for the pure liquid crystal. It was proved that adding canted antiferromagnetic nano-particles in liquid

E. Ouskova; O. Buluy; C. Blanc; H. Dietsch; A. Mertelj

2010-01-01

280

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

281

The crystal structure of some rhenium and technetium dichalcogenides  

Microsoft Academic Search

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

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

1996-01-01

282

Optical and structural properties of chalcone NLO single crystals  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

283

Hexagonal structures for two-dimensional photonic crystals  

Microsoft Academic Search

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

D. Cassagne; C. Jouanin; D. Bertho

1996-01-01

284

Crystal structure solution from experimentally determined atomic pair distribution functions  

Microsoft Academic Search

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

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

2010-01-01

285

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

286

On automation of the procedure for crystal structure model refinement  

NASA Astrophysics Data System (ADS)

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

Dudka, A. P.

2008-03-01

287

Liquid crystal based electrically switchable Bragg structure for THz waves.  

PubMed

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

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

2009-04-27

288

Crystal Structure of Purine Nucleoside Phosphorylase from Thermus thermophilus  

Microsoft Academic Search

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

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

2004-01-01

289

Crystal Structure of L-Histidinium 2-Nitrobenzoate  

PubMed Central

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

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

2012-01-01

290

Crystal structure of a calcium sulfate-urea complex  

Microsoft Academic Search

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

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

1975-01-01

291

Boron-Oxygen Polyanion in the Crystal Structure of Tunellite.  

PubMed

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

Clark, J R

1963-09-20

292

Morphology of Tropical Cirrus Crystals Derived from Single Particle and Bulk Property Analysis  

NASA Astrophysics Data System (ADS)

The bulk density, surface area, asphericity and fractal dimensions of crystals in tropical cirrus clouds are derived by combining complementary measurement techniques that were employed during the CRYSTAL/FACE experiment in July, 2002. The instruments that are used in this derivation are the Cloud, Aerosol and Precipitation Spectrometer (CAPS) that measures single particle properties, the cloud integrating nephelometer (CIN) that measures ensemble light scattering and the Harvard Total Water (HTW) sensor that measures the vapor concentration of evaporated cloud particles. The asphericity of particles smaller than 50 ? m is determined by comparing the forward and backward scattering light spectra that is measured with the CAPS. The ratio of the areas under the forward and back scattering spectra is proportional to the asymmetry factor and can be used in radiative transfer calculations for evaluating the flux of radiation through the cirrus layers. The fractal dimension of ice crystals larger than 200 ? m is also derived from the CAPS measurements and is a measure of the crystal "roughness", related to the surface area and bulk density. The bulk density is estimated from CAPS and HTW measurements by calculating the volume of particles from the measured size distribution and then deriving the bulk density that would give an ice water content comparable to that measured by the HTW. The evaluation produces a family of curves relating ice crystal effective diameter and bulk density to ice water content. The behavior of these curves under different temperature conditions provides information on the type and age of ice crystals. The ice crystal surface areas are derived in a similar fashion by comparing the scattering coefficient calculated from the size distributions and direct measurements with the CIN. As with the derivation of bulk density, the surface area computed by this technique depends on the assumed shapes of the crystals. The average fractal dimension, asphericity factor, surface area and bulk density are sensitive to cloud temperature, distance from cloud top and cloud age. Contrail crystals are clearly distinguishable from natural cirrus by much lower fractal dimensions and smaller asphericity.

Raga, G. B.; Baumgardner, D.; Kok, G.; Anderson, B.; Garrett, T.; Weinstock, E.; Smith, J.

2003-12-01

293

Crystal and molecular structure of glutaconic acid  

Microsoft Academic Search

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

Leonard Thomas; Thamarapu Srikrishnan

2003-01-01

294

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

2013-09-09

295

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

296

Ensemble refinement of protein crystal structures  

PubMed Central

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

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

2007-01-01

297

Synthesis and Structure Characterization of Forsterite Single Crystal  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

298

Structures and phase transitions of a vertically confined plasma crystal  

NASA Astrophysics Data System (ADS)

Dusty plasmas consist of an ionized gas containing small (usually negatively charged) particles. Dusty plasmas are of interest in both astrophysics and space physics as well as in research in plasma processing and nanofabrication. In this work, the formation of plasma crystals confined in an external one-dimensional parabolic potential well is simulated for a normal experimental environment employing a computer code called BOX_TREE. Such crystals are layered systems, with each layer a 2D lattice composed of grain particles. The number of layers is dependent in part upon the external potential parameter. The transition from 1 to 2 layers is specifically analyzed with dispersion relations for the vertical dust lattice wave obtained at the transition point and the transition shown to be induced by the vertical dust lattice instability.

Qiao, K.; Hyde, T. W.

299

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

300

Structure of ice crystallized from supercooled water.  

PubMed

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

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

2012-01-09

301

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

PubMed

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

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

2012-02-07

302

The effect of reaction temperature on the particle size, structure and magnetic properties of coprecipitated CoFe 2O 4 nanoparticles  

Microsoft Academic Search

Magnetic nanoparticles of cobalt ferrite have been synthesized at different temperatures without any subsequent heat treatment. The particle size, crystal structure and magnetic properties of as-synthesized particles were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and vibrating sample magnetometer. The nanoparticles are of cubic spinel structure and equiaxial shape. The average size of nanoparticles increases

Yuqiu Qu; Haibin Yang; Nan Yang; Yuzun Fan; Hongyang Zhu; Guangtian Zou

2006-01-01

303

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

DOEpatents

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

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

1994-01-01

304

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

DOEpatents

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

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

1994-08-23

305

Gastric lipase: crystal structure and activity  

Microsoft Academic Search

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

Stphane Canaan; Alain Roussel; Robert Verger; Christian Cambillau

1999-01-01

306

The crystal structure and superconducting properties of monatomic bromine  

Microsoft Academic Search

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

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

2010-01-01

307

Structure of Widmanstatten crystals of ferrite and cementite  

Microsoft Academic Search

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

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

2008-01-01

308

High-resolution transmission electron microscopy of structural changes at and near surfaces of ZnTe crystals  

Microsoft Academic Search

Structural changes on and near surfaces of ZnTe crystals were observed by the surface profile imaging method in a high-resolution transmission electron microscope (HRTEM) with 200 kV accelerating voltage. It was found that ZnO particles form under electron irradiation on surfaces originally covered with a thin amorphous layer. For amorphous coverages thicker than about 7 nm, ZnO particles were not

X. G. Ning; M. Avalos-Borja; H. Q. Ye

1996-01-01

309

Response characteristics of GSO(Ce) crystal to intermediate-energy ?-particles  

NASA Astrophysics Data System (ADS)

Characteristics of a GSO(Ce) crystal were investigated in terms of the light output response and the peak-to-total efficiency for impinging intermediate-energy ?-particles. Experiments were carried out using ?-particles of energies ranging from 143 to 718 MeV with primary ? beams of 400 and 718 MeV. It has been demonstrated that the experimental results are explained well by calculations in the same manner as for protons and deuterons. In particular, no particle identity dependence of scintillation quenching phenomena have been observed between protons, deuterons and ?-particles. Furthermore, good linearity is confirmed in the higher energy range up to 718 MeV. The peak-to-total efficiency was accounted for by calculations using ?-nucleus reaction cross-sections.

Imamura, M.; Yamashita, Y.; Evtoukhovitch, P.; Hohara, S.; Kalinikov, V.; Kallies, W.; Khumutov, N.; Kin, T.; Kuchinski, N.; Maki, D.; Matsufuji, N.; Moisenko, A.; Mzavia, D.; Samoilov, V.; Tsamalaidze, Z.; Uozumi, Y.; Wakabayashi, G.

2006-08-01

310

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

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) 95103]. 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

Defectiveness of the crystal structure of electroerosion powders  

SciTech Connect

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

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

1988-03-01

313

Crystal structure of copper bis(tenuazonate) monohydrate  

Microsoft Academic Search

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

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

1977-01-01

314

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

315

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

NASA Astrophysics Data System (ADS)

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

Lonie, David C.; Zurek, Eva

2012-03-01

316

Tunable Liquid Crystal Random Laser Radiation Based on Photonic Crystal Micro-Cavity  

Microsoft Academic Search

The tunable liquid crystal random lasers is produced by filled liquid crystal which doped laser dye and scattering particles to the slab photonic crystal defect based on liquid crystal refractive index sensitive to changes in temperature and electric field properties, narrow-band filter characteristics of photonic crystal micro-cavity. The structure of liquid crystal tunable random lasers designed. By use of Maxwell

Xiang-zhong Qian

2011-01-01

317

Crystal and molecular structure of biruthenocene  

Microsoft Academic Search

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

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

1982-01-01

318

Forming Nanocrystalline Structures in Metal Particle Impact  

NASA Astrophysics Data System (ADS)

Grain refinement by plastic deformation is becoming increasingly popular as a way of producing metals with improved properties, such as higher mechanical strength. Surface treatment techniques in which a metallic substrate is bombarded with metallic particles can generate nanocrystalline layers in the impact zone. Understanding the physical mechanisms underlying this grain refinement is crucial for achieving an improvement of existing experimental processes. In this article, we propose a numerical framework combining finite element (FE) simulations with a dislocation-based material model to predict the evolution of the microstructure under particle impact. A single particle normally impacting on a metallic substrate was simulated at different initial velocities. The simulations were compared with previously reported numerical and experimental data. The results indicate that our model accurately captures the grain refinement in the impact zone for a broad range of velocities. This approach provides valuable information on the formation of nanocrystalline layers in both the substrate and the impacting particle. Its potential applications include processes involving surface treatment by high velocity particles, such as shot peening, surface mechanical attrition treatment, kinetic metallization, cold spray, etc.

Lemiale, Vincent; Estrin, Yuri; Kim, Hyoung Seop; O'Donnell, Robert

2010-12-01

319

Forming Nanocrystalline Structures in Metal Particle Impact  

NASA Astrophysics Data System (ADS)

Grain refinement by plastic deformation is becoming increasingly popular as a way of producing metals with improved properties, such as higher mechanical strength. Surface treatment techniques in which a metallic substrate is bombarded with metallic particles can generate nanocrystalline layers in the impact zone. Understanding the physical mechanisms underlying this grain refinement is crucial for achieving an improvement of existing experimental processes. In this article, we propose a numerical framework combining finite element (FE) simulations with a dislocation-based material model to predict the evolution of the microstructure under particle impact. A single particle normally impacting on a metallic substrate was simulated at different initial velocities. The simulations were compared with previously reported numerical and experimental data. The results indicate that our model accurately captures the grain refinement in the impact zone for a broad range of velocities. This approach provides valuable information on the formation of nanocrystalline layers in both the substrate and the impacting particle. Its potential applications include processes involving surface treatment by high velocity particles, such as shot peening, surface mechanical attrition treatment, kinetic metallization, cold spray, etc.

Lemiale, Vincent; Estrin, Yuri; Kim, Hyoung Seop; O'Donnell, Robert

2011-10-01

320

Crystal structure of a eukaryotic phosphate transporter.  

PubMed

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

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

2013-03-31

321

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

322

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

323

The effect of crystal tilt on high resolution micrographs of small metal particles  

SciTech Connect

The structure of small (1.5-5 nm) metal particles has been studied by high resolution transmission electron microscopy. For particles of this size, it is not possible to use tilting techniques (selected area diffraction), which means that the microscopist has to rely on the image when deciding in which direction the particle is viewed. This work points out some of the problems of intuitive determination of the viewing direction. (DLC)

Malm, J.O. (Lund Univ. (Sweden). Dept. of Inorganic Chemistry 2); O'Keefe, M.A. (Lawrence Berkeley Lab., CA (United States))

1993-01-01

324

Interface structure of the rubrene crystal field effect transistor  

NASA Astrophysics Data System (ADS)

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

Wakabayashi, Yusuke; Takeya, Jun; Kimura, Tsuyoshi

2011-11-01

325

CRYSTAL STRUCTURE ANALYSIS OF A PUTATIVE OXIDOREDUCTASE FROM KLEBSIELLA PNEUMONIAE  

SciTech Connect

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

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

2009-01-01

326

Crystal structure and stability of magnesium borohydride from first principles  

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

327

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

SciTech Connect

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

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

1993-12-01

328

Crystal structures of two engineered thiol trypsins.  

PubMed

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

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

1989-11-28

329

[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

330

Studying mechanical microcontacts of fine particles with the quartz crystal microbalance  

Microsoft Academic Search

To study micromechanical adhesion, glass particles were deposited on a quartz crystal microbalance (QCM). Beforehand, a 160nm-thick film of polystyrene (PS) had been spin-coated on the gold surface of the QCM. Shifts in the resonance frequency were monitored versus the oscillation amplitude. The aim was to analyse how QCM experiments reflect the state of adhesion. During oscillation, the motion of

Ewa Vittorias; Michael Kappl; Hans-Jrgen Butt; Diethelm Johannsmann

2010-01-01

331

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

332

Forming Nanocrystalline Structures in Metal Particle Impact  

Microsoft Academic Search

Grain refinement by plastic deformation is becoming increasingly popular as a way of producing metals with improved properties, such as higher mechanical strength. Surface treatment techniques in which a metallic substrate is bombarded with metallic particles can generate nanocrystalline layers in the impact zone. Understanding the physical mechanisms underlying this grain refinement is crucial for achieving an improvement of existing

Vincent Lemiale; Yuri Estrin; Hyoung Seop Kim; Robert O'Donnell

2011-01-01

333

Forming Nanocrystalline Structures in Metal Particle Impact  

Microsoft Academic Search

Grain refinement by plastic deformation is becoming increasingly popular as a way of producing metals with improved properties, such as higher mechanical strength. Surface treatment techniques in which a metallic substrate is bombarded with metallic particles can generate nanocrystalline layers in the impact zone. Understanding the physical mechanisms underlying this grain refinement is crucial for achieving an improvement of existing

Vincent Lemiale; Yuri Estrin; Hyoung Seop Kim; Robert O'Donnell

2010-01-01

334

The diammoniate of diborane: Crystal structure and hydrogen release  

SciTech Connect

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

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

2010-10-12

335

Light propagation in liquid crystals and liquid crystalline structures  

Microsoft Academic Search

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

Haijun Yuan

2000-01-01

336

The structure and vibrational frequencies of nitric acid hydrates crystals  

Microsoft Academic Search

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

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

2003-01-01

337

Yolk spherocrystal: The structure, composition and liquid crystal template  

Microsoft Academic Search

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

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

2008-01-01

338

Electronic structure of molecular crystals containing edge dislocations  

Microsoft Academic Search

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

Maija M. Kuklja; A. Barry Kunz

2001-01-01

339

Unusual Features of Crystal Structures of Some Simple Copper Compounds  

ERIC Educational Resources Information Center

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

Douglas, Bodie

2009-01-01

340

Crystal Structure of the 30s RIBOSOM and Its Use.  

National Technical Information Service (NTIS)

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

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

2001-01-01

341

Electronic Structure of Zinc Oxide and Related Crystals.  

National Technical Information Service (NTIS)

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

F. Herman

1966-01-01

342

Crystal structure of tannase from Lactobacillus plantarum.  

PubMed

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

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

2013-05-03

343

Crystal structures of the ??-cerium phases  

PubMed Central

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

Zachariasen, W. H.

1978-01-01

344

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface  

PubMed Central

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

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

2013-01-01

345

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

346

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

347

Structural and optical properties of a new chalcone single crystal  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

348

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

PubMed

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

Blatov, V A; Shevchenko, A P

2002-12-21

349

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

Microsoft Academic Search

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

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

2000-01-01

350

Crystal structure of nitrile hydratase from a thermophilic Bacillus smithii  

Microsoft Academic Search

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

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

2003-01-01

351

Crystal structure of a soluble CD28Fab complex  

Microsoft Academic Search

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

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

2005-01-01

352

The crystal structure of flap endonuclease-1 from Methanococcus jannaschii  

Microsoft Academic Search

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

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

1998-01-01

353

The Gramicidin Pore: Crystal Structure of a Cesium Complex  

Microsoft Academic Search

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

B. A. Wallace; K. Ravikumar

1988-01-01

354

Forming Nanocrystalline Structures in Metal Particle Impact  

Microsoft Academic Search

Grain refinement by plastic deformation is becoming increasingly popular as a way of producing metals with improved properties,\\u000a such as higher mechanical strength. Surface treatment techniques in which a metallic substrate is bombarded with metallic\\u000a particles can generate nanocrystalline layers in the impact zone. Understanding the physical mechanisms underlying this grain\\u000a refinement is crucial for achieving an improvement of existing

Vincent Lemiale; Yuri Estrin; Hyoung Seop Kim; Robert ODonnell

355

Kinematic Structure of Helicity Amplitudes for Massless Particles.  

National Technical Information Service (NTIS)

A study is made of the kinematic structure of helicity amplitudes describing scattering with massless particles of arbitrary helicities, using certain basic analyticity assumptions on the M functions. The behaviors of the amplitudes at the thresholds and ...

L. N. Chang Y. C. Leung

1969-01-01

356

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

357

Crystal Structure of Cold Compressed Graphite  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

358

Crystal structure of interleukin 8: Symbiosis of NMR and crystallography  

SciTech Connect

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

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

1991-01-15

359

Crystal structure of triosephosphate isomerase from Trypanosoma cruzi in hexane  

PubMed Central

To gain insight into the mechanisms of enzyme catalysis in organic solvents, the x-ray structure of some monomeric enzymes in organic solvents was determined. However, it remained to be explored whether the structure of oligomeric proteins is also amenable to such analysis. The field acquired new perspectives when it was proposed that the x-ray structure of enzymes in nonaqueous media could reveal binding sites for organic solvents that in principle could represent the starting point for drug design. Here, a crystal of the dimeric enzyme triosephosphate isomerase from the pathogenic parasite Trypanosoma cruzi was soaked and diffracted in hexane and its structure solved at 2-? resolution. Its overall structure and the dimer interface were not altered by hexane. However, there were differences in the orientation of the side chains of several amino acids, including that of the catalytic Glu-168 in one of the monomers. No hexane molecules were detected in the active site or in the dimer interface. However, three hexane molecules were identified on the surface of the protein at sites, which in the native crystal did not have water molecules. The number of water molecules in the hexane structure was higher than in the native crystal. Two hexanes localized at <4 ? from residues that form the dimer interface; they were in close proximity to a site that has been considered a potential target for drug design.

Gao, Xiu-Gong; Maldonado, Ernesto; Perez-Montfort, Ruy; Garza-Ramos, Georgina; de Gomez-Puyou, Marietta Tuena; Gomez-Puyou, Armando; Rodriguez-Romero, Adela

1999-01-01

360

Structures of ?-FeOOH Particles Formed in the Presence of Ti(IV), Cr(III), and Cu(II) Ions  

Microsoft Academic Search

?-FeOOH particles were prepared by aging aqueous FeCl3 solutions containing Ti(IV), Cr(III), and Cu(II) at room temperature for 360 days. The structures of the formed particles were investigated by various techniques including TEM, XRD, XAFS, and adsorption of N2 and H2O. Ti(IV) markedly impeded the crystallization and particle growth of ?-FeOOH by coprecipitation with Fe(III) and disturbing the short-range structure

Tatsuo Ishikawa; Taiki Motoki; Ryuichi Katoh; Akemi Yasukawa; Kazuhiko Kandori; Takenori Nakayama; Fumio Yuse

2002-01-01

361

Direct measurement of force between colloidal particles in a nematic liquid crystal  

NASA Astrophysics Data System (ADS)

The interparticle force between two colloidal particles in a nematic liquid crystal is directly measured as a function of the interparticle distance R by two different experimental methods: the free-release method and the optical tweezing method. The obtained force between an elastic 'dipole', which constitutes a colloidal particle and an accompanying hyperbolic hedgehog defect, confirms previous theoretical predictions that the force is attractive and proportional to R-4. We also observe that a repulsive component emerges at short distances to preclude direct contact of the particles. We find that the magnitudes of the forces obtained by the two methods are different. The origin of this discrepancy is discussed by a comparison between the static and the non-static measurements.

Takahashi, Kenji; Ichikawa, Masatoshi; Kimura, Yasuyuki

2008-02-01

362

Crystal structure and physical characterization of neotame methanol solvate  

Microsoft Academic Search

The crystal structure of the methanol solvate (empirical formula: 2C20H30N2O53CH3OH) of a new dipeptide sweetener, neotame (N-(3,3-dimethylbutyl)-L-a-aspartyl-L-phenylalanine 1-methyl ester), has been determined. Crystal data: a = 9.8989(1), b = 18.1331(1), c = 27.5725(1) , orthorhombic, space group P212121, with Z = 4. Each unit cell includes 8 neotame and 12 methanol molecules. Disorder exists in one neotame molecule and one

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

1999-01-01

363

Hopping and diffusion of ultrasoft particles in cluster crystals in the explicit presence of a solvent.  

PubMed

We have investigated diffusion and hopping processes in a cluster crystal formed from mesoscopic, ultrasoft particles. In contrast to previous contributions we have explicitly included in our investigations the microscopic solvent by using a simulation scheme that takes the induced hydrodynamic interactions into account as faithfully as possible. In our investigations we first focused on the processes of migration of the ultrasoft particles. By evaluating dynamical correlation functions we were able to demonstrate that the presence of the solvent does indeed have an important impact on the diffusion and hopping processes of the particles: this applies in particular to the diffusive behaviour, to the angular orientation of the jump events and to the spatial extents of these events. In a second set-up we have added non-cluster-forming ultrasoft particles to the system, investigating thus the impact of the solvent and that of the mutual interaction of the two species of ultrasoft particles on their respective dynamic behaviours. Our investigations clearly demonstrate, beside the expected significant role that the solvent plays in this set-up, that diffusion and the jump processes show distinct differences for the two particle species. PMID:23552457

Montes-Saralegui, Marta; Nikoubashman, Arash; Kahl, Gerhard

2013-04-03

364

Crystallization and preliminary structure of beef heart mitochondrial cytochrome-bc1 complex.  

PubMed

The method reported for isolation of ubiquinol-cytochrome-c reductase complex from submitochondrial particles was modified to yield a preparation for crystallization. The cytochrome bc1 complex was first crystallized in large thin plate form and diffracts X-rays to 7 A resolution in the presence of mother liquor. This crystalline complex was enzymatically active and contains ten protein subunits. It had 33 mol phospholipid and 0.6 mol ubiquinone per mol protein. With slightly modified crystallization conditions, different crystal forms were obtained. Crystals grown in the presence of 20% glycerol diffracted X-rays up to 2.9 A resolution using a synchrotron source. Four heavy atom derivatives have been obtained. The 3-D structure of the cytochrome bc1 complex was solved to 3.4 A resolution. Crystalline cytochrome bc1 complex is a dimer: most of the masses of core proteins I and II protrudes from the matrix side of the membrane, whereas the cytochrome b protein is located mainly within the membrane. There are 13 transmembrane helices in each monomer. Most of the mass of cytochrome c1 and iron-sulfur protein including their redox centers are located on the cytoplasmic side of the membrane. The distances between these redox centers have been determined, and several electron transfer inhibitor binding sites in the complex have been located. PMID:8688450

Yu, C A; Xia, J Z; Kachurin, A M; Yu, L; Xia, D; Kim, H; Deisenhofer, J

1996-07-18

365

Structural features of a Lennard-Jones system at melting and crystallization  

NASA Astrophysics Data System (ADS)

The structural features of the crystallization and melting of a system of particles whose pair interaction is described by the Lennard-Jones potential have been considered. The bond order parameter method is used to quantitatively describe the orientational short-range order. The rotational invariants of the second ( q l ) and third ( w l ) orders are calculated for each particle of the system. These calculations require only information on the snapshot of atom positions, which is quite easily obtained in experiments, and provide the distribution functions of particles in q l and w l (where l is the rank of an invariant; the results for l = 4, 6 are presented), which are important characteristics of the phase state of the system. It has been shown that the cumulant of the distribution of particles in w 6 is very sensitive to the destruction/formation of the short-range orientational order in the Lennard-Jones system and, correspondingly, can be used as a criterion of the melting and crystallization of this system.

Klumov, B. A.

2013-05-01

366

Crystal structure of dimeric HIV-1 capsid protein.  

PubMed

X-ray diffraction analysis of a human immunodeficiency virus (HIV-1) capsid (CA) protein shows that each monomer within the dimer consists of seven alpha-helices, five of which are arranged in a coiled coil-like structure. Sequence assignments were made for two of the helices, and tentative connectivity of the remainder of the protein was confirmed by the recent solution structure of a monomeric N-terminal fragment. The C-terminal third of the protein is mostly disordered in the crystal. The longest helices in the coiled coil-like structure are separated by a long, highly antigenic peptide that includes the binding site of an antibody fragment complexed with CA in the crystal. The site of binding of the Fab, the position of the antigenic loop and the site of cleavage between the matrix protein and CA establish the side of the dimer that would be on the exterior of the retroviral core. PMID:8784350

Momany, C; Kovari, L C; Prongay, A J; Keller, W; Gitti, R K; Lee, B M; Gorbalenya, A E; Tong, L; McClure, J; Ehrlich, L S; Summers, M F; Carter, C; Rossmann, M G

1996-09-01

367

Crystal and electronic structures of LiNH2  

NASA Astrophysics Data System (ADS)

The crystal structure of LiNH2 was reinvestigated using powder neutron diffraction with high sensitivity. The compound crystallizes in the tetragonal space group I4 with lattice parameters a=b=5.034 42 (24) A?, c=10.255 58 (52) A?. It is found that H atoms occupy 8g1(0.2429, 0.1285, 0.1910) and 8g2 (0.3840, 0.3512, 0.1278) sites. The bond lengths between the nearest nitrogen and hydrogen atoms are 0.986 and 0.942 A?, respectively. The bond angle between H-N-H is about 99.97. These results are significantly different from those of previous experiments. The electronic structure was calculated according to the revised structural data. The calculated density of states and charge density distribution show strong ionic characteristics between the ionic Li+ cation and the covalent bonded [NH2]- anion.

Yang, J. B.; Zhou, X. D.; Cai, Q.; James, W. J.; Yelon, W. B.

2006-01-01

368

Crystal structure of a bacterial ribonuclease P RNA  

PubMed Central

The x-ray crystal structure of a 417-nt ribonuclease P RNA from Bacillus stearothermophilus was solved to 3.3- resolution. This RNA enzyme is constructed from a number of coaxially stacked helical domains joined together by local and long-range interactions. These helical domains are arranged to form a remarkably flat surface, which is implicated by a wealth of biochemical data in the binding and cleavage of the precursors of transfer RNA substrate. Previous photoaffinity crosslinking data are used to position the substrate on the crystal structure and to identify the chemically active site of the ribozyme. This site is located in a highly conserved core structure formed by intricately interlaced long-range interactions between interhelical sequences.

Kazantsev, Alexei V.; Krivenko, Angelika A.; Harrington, Daniel J.; Holbrook, Stephen R.; Adams, Paul D.; Pace, Norman R.

2005-01-01

369

Trapping of topological-structural defects in Coulomb crystals.  

PubMed

We study experimentally and theoretically structural defects which are formed during the transition from a laser cooled cloud to a Coulomb crystal, consisting of tens of ions in a linear radio frequency trap. We demonstrate the creation of predicted topological defects ("kinks") in purely two-dimensional crystals and also find kinks which show novel dynamical features in a regime of parameters not considered before. The kinks are always observed at the center of the trap, showing a large nonlinear localized excitation, and the probability of their occurrence saturates at ?0.5. Simulations reveal a strong anharmonicity of the kink's internal mode of vibration, due to the kink's extension into three dimensions. As a consequence, the periodic Peierls-Nabarro potential experienced by a discrete kink becomes a globally confining potential, capable of trapping one cooled defect at the center of the crystal. PMID:23581315

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

2013-03-28

370

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

PubMed

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

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

2011-11-01

371

Experimental observation of the crystallization of hard-sphere colloidal particles by sedimentation onto flat and patterned surfaces  

Microsoft Academic Search

We present a confocal microscopy study of 1.55mum monodisperse silica hard spheres as they sediment and crystallize at the bottom wall of a container. If the particles sediment onto a feature less flat wall, the two bottom layers crystallize simultaneously and layerwise growth follows. If the wall is replaced by a hexagonal template, only layerwise growth occurs. Our results complement

I. B. Ramsteiner; K. E. Jensen; D. A. Weitz; F. Spaepen

2009-01-01

372

Synthesis and crystal structure of CuZrTiO{sub 5}-A new crystal structure type  

SciTech Connect

A new compound, CuZrTiO{sub 5}, was synthesized as strongly pleochroic green crystals from the oxides between 995 and 1010 deg. C, 1 atm. Its crystal structure was determined by single crystal XRD, resulting in R (F{sup 2}>2sigma(F{sup 2}))=0.032 and wR (all data)=0.079). CuZrTiO{sub 5} is orthorhombic, space group P2{sub 1}2{sub 1}2{sub 1}, a=3.5871(3) A, b=6.6968(4) A, c=14.6679(9) A, V=352.35(4) A{sup 3}, Z=4. The structure is topologically similar to In{sub 2}TiO{sub 5} but differs in space group and cation coordination. CuZrTiO{sub 5} has relatively regular TiO{sub 6} polyhedra, but coordination is 7+1 for Zr, and 4+2 for Cu due to the Jahn-Teller effect. Ordering of the long Cu-O bonds causes reduction in symmetry relative to In{sub 2}TiO{sub 5}. Layers of Cu alternate with Ti+Zr on (001), giving rise to a distinct cleavage. Bond valence sums on Ti and Zr are far from ideal, which appears due to the limited ability of this structural topology to avoid close next-nearest neighbour distances. - Graphical abstract: The new compound CuZrTiO{sub 5} is orthorhombic (P2{sub 1}2{sub 1}2{sub 1}), with a=3.5871(3) A, b=6.6968(4) A, c=14.6679(9) A. The structure, determined with single crystal XRD, represents a new crystal structure type that is a slight distortion of that of In{sub 2}TiO{sub 5} but differs in space group and cation coordination.

Troitzsch, Ulrike [Research School of Earth Sciences, Australian National University, Canberra ACT 0200 (Australia); Christy, Andrew G., E-mail: Andrew.Christy@anu.edu.a [Research School of Earth Sciences, Australian National University, Canberra ACT 0200 (Australia); Willis, Anthony C. [Research School of Chemistry, Australian National University, Canberra ACT 0200 (Australia); Ellis, David J. [Research School of Earth Sciences, Australian National University, Canberra ACT 0200 (Australia)

2010-03-15

373

Structural development in ultrafine particles of zirconia produced from sol-gel  

SciTech Connect

The pH of the solution that hydrous zirconia is precipitated from appears to define the crystal structure formed after calcination of the material at 400-600{degree}C. A metastable tetragonal structure was obtained for either low (less than about 5) or high (greater than about 13) pH. The tetragonal phase formed at high pH is much more stable than that obtained at a low pH at a calcination temperature of 500{degree}C. Detailed structural studies were undertaken using transmission electron microscopy, X-ray diffraction and BET surface area. The results obtained from these analyses do not support the crystallite size theory, which states that the tetragonal particles of less than 300 {angstrom} are stabilized against the t {yields} m transformation. It was observed that the time taken to attain the final pH of the solution in contact with the precipitate in the pH range 7-11, plays a dominant role in determining the crystal structure of the zirconium oxide after calcination at 500{degree}C. The dependence of the crystal structure on the rate of precipitation is observed only in the pH range 7-11. Rapid precipitation in this pH range yields predominantly monoclinic zirconia, whereas slow (8 hours) precipitation produces the tetragonal phase. At a pH of approximately 13.0, only the tetragonal phase is formed from both slowly and rapidly precipitated hydrous oxide. The results indicate that both the pH of the supernatant liquid and the time taken to attain this pH play dominant roles in determining the crystal structure of zirconia formed after calcination of the hydrous oxide. The factors that determine the crystal phase are therefore imparted in a mechanism of precipitation that depends upon the pH, and it is inferred that it is the hydroxyl concentration that is the dominant factor.

Srinivasan, R.

1989-01-01

374

Crystallizing Membrane Proteins for Structure Determination using Lipidic Mesophases  

PubMed Central

A detailed protocol for crystallizing membrane proteins by using lipidic mesophases is described. This method has variously been referred to as the lipidic cubic phase or in meso method. The method has been shown to be quite versatile in that it has been used to solve X-ray crystallographic structures of prokaryotic and eukaryotic proteins, proteins that are monomeric, homo- and hetero-multimeric, chromophore-containing and chromophore-free, and alpha-helical and beta-barrel proteins. Recent successes using in meso crystallization are the human engineered beta2-adrenergic and adenosine A2a G protein-coupled receptors. Protocols are presented for reconstituting the membrane protein into the monoolein-based mesophase, and for setting up crystallizations in the manual mode. Additional steps in the overall process, such as crystal harvesting, are to be addressed in future video articles. The time required to prepare the protein-loaded mesophase and to set up a crystallization plate manually is about one hour.

Caffrey, Martin; Porter, Christopher

2010-01-01

375

Crystal and molecular structure of didemnin A, an antiviral depsipeptide.  

PubMed

The molecular structure of didemnin A, the parent compound of a series of antiviral cytotoxic depsipeptides extracted from a marine tunicate Trididemnum solidum of the family of Didemnidae, has been determined by single-crystal X-ray diffraction. In the crystal, didemnin A molecules form pseudo-symmetric dimeric pair. The two molecules in the dimer are held together by strong N--H center dot center dot center dot O and N--H center dot center dot center dot N hydrogen bonds. A chloride ion, placed almost symmetrically between the dimeric pair, forms N--H center dot center dot center dot Cl hydrogen bonds (3.19 and 3.23 Angstrom) with both the molecules. The two independent molecules in the structure have closely similar geometry. For each molecule, the 23-membered depsipeptide ring assumes a folded conformation in the shape of a 'bent figure-of-eight' similar to that observed in the didemnin B crystal structure. The major conformational differences in the macrocycle of didemnin A and didemnin B are around the Hip residue. The root mean-square (RMS) difference of 20 of the 23 endocyclic torsion angles for the two structures is less than 10 degrees, while the three bond torsions in the Hip residue vary by about 50 degrees. The macrocycle conformation is stabilized by a transannular N--H center dot center dot center dot O hydrogen bond linking the isostatine amide group with the leucine carbonyl group. The truncated linear chain is folded back toward the macrocyclic ring and is held by a N--H center dot center dot center dot O hydrogen bond between the leucine amide group and Me-Leu carbonyl group. The transannular hydrogen bond in the didemnin A structure (N4--H center dot center dot center dot O3 = 2.83 Angstrom in both molecule a and molecule b) is noticeably stronger than that observed in the didemnin B structure (3.02 Angstrom). The X-ray structure of didemnin A is generally consistent with that obtained by NMR studies. Within the crystal, the molecules are packed in zig-zag chains formed by intermolecular O--H center dot center dot center dot O hydrogen bonds. The crystal structure and packing of didemnin A are quite different from that of the didemnin B structure. PMID:8907495

Hossain, M B; Van Der Helm, D; Antel, J; Sheldrick, G M; Weinheimer, A J; Sanduja, S K

376

The crystal structure of a heptameric archaeal Sm protein: Implications for the eukaryotic snRNP core  

Microsoft Academic Search

Sm proteins form the core of small nuclear ribonucleoprotein particles (snRNPs), making them key components of several mRNA-processing assemblies, including the spliceosome. We report the 1.75- crystal structure of SmAP, an Sm-like archaeal protein that forms a heptameric ring perforated by a cationic pore. In addition to providing direct evidence for such an assembly in eukaryotic snRNPs, this structure (i)

Cameron Mura; Duilio Cascio; Michael R. Sawaya; David S. Eisenberg

2001-01-01

377

The Rapid Crystallization Strategy for Structure-Based Inhibitor Design  

NASA Astrophysics Data System (ADS)

RAPID (Rapid Approaches to Pathogen Inhibitor Discovery) is an integrated center for structural biology, computational chemistry, and medicinal chemistry at Uppsala University, Sweden. The main target of the structural biology section is Mycobacterium tuberculosis. Key concepts in the crystallization strategy include minimal screening and buffer optimization. Examples are presented showing how these concepts have been successful in RAPID projects. Three screening methods are used: vapor-diffusion, micro-batch, and microfluidics. Our experiences may be relevant for other small, academic laboratories involved in structure-based inhibitor design.

Bergfors, Terese

378

Crystal structure prediction using the minima hopping method  

NASA Astrophysics Data System (ADS)

A structure prediction method is presented based on the minima hopping method. To escape local minima, moves on the configurational enthalpy surface are performed by variable cell shape molecular dynamics. To optimize the escape steps the initial atomic and cell velocities are aligned to low curvature directions of the current local minimum. The method is applied to both silicon crystals and well-studied binary Lennard-Jones mixtures. For the latter new putative ground state structures are presented. It is shown that a high success rate is achieved and a reliable prediction of unknown ground state structures is possible.

Amsler, Maximilian; Goedecker, Stefan

2010-12-01

379

Crystal structure of inactive form of Rab3B  

SciTech Connect

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 {angstrom} 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; Shen, Yang; Jiao, Ronghong; Liu, Yanli; Deng, Lingfu; Qi, Chao (Hebei); (Toronto); (Huazhong)

2012-06-28

380

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

NASA Astrophysics Data System (ADS)

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.

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

2005-01-01

381

Preliminary crystal structure of Acinetobacter glutaminasificans glutaminase-asparaginase.  

PubMed

The preliminary structure of a glutaminase-asparaginase from Acinetobacter glutaminasificans is reported. The structure was determined at 3.0-A resolution with a combination of phase information from multiple isomorphous replacement at 4-5-A resolution and phase improvement and extension by two density modification techniques. The electron density map was fitted by a polypeptide chain that was initially polyalanine. This was subsequently replaced by a polypeptide with an amino acid sequence in agreement with the sizes and shapes of the side chain electron densities. The crystallographic R factor is 0.300 following restrained least squares refinement with data to 2.9-A resolution. The A. glutaminasificans glutaminase-asparaginase subunit folds into two domains: the aminoterminal domain contains a five-stranded beta sheet surrounded by five alpha helices, while the carboxyl-terminal domain contains three alpha helices and less regular structure. The connectivity is not fully determined at present, due in part to the lack of a complete amino acid sequence. The A. glutaminasificans glutaminase-asparaginase structure has been used successfully to determine the relative orientations of the molecules in crystals of Pseudomonas 7A glutaminase-asparaginase, in crystals of Vibrio succinogenes asparaginase, and in a new crystal form of Escherichia coli asparaginase (space group 1222, one subunit per asymmetric unit). PMID:3275637

Ammon, H L; Weber, I T; Wlodawer, A; Harrison, R W; Gilliland, G L; Murphy, K C; Sjlin, L; Roberts, J

1988-01-01

382

Crystal structure of group II chaperonin in the open state  

PubMed Central

SUMMARY Thermosomes are group II chaperonins responsible for protein refolding in an ATP-dependent manner. Little is known regarding the conformational changes of thermosomes during their functional cycle due to lack of high-resolution structure in open state. Here we report the first complete crystal structure of thermosome (rATcpn?) in open state from Acidianus tengchongensis. There is a ~30 rotation of the apical and lid domains compared to the previous closed structure. Besides, the structure reveals a conspicuous hydrophobic patch in the lid domain and residues locating in this patch are conserved across species. Both the closed and open forms of rATcpn? were also reconstructed by electron microscopy (EM). Structural fitting revealed the detailed conformational change from open to closed state. Structural comparison as well as protease K digestion indicated only ATP binding without hydrolysis does not induce chamber closure of thermosome.

Huo, Yanwu; Hu, Zhongjun; Zhang, Kai; Wang, Li; Zhai, Yujia; Zhou, Qiangjun; Lander, Gabe; Zhu, Jiang; He, Yongzhi; Pang, Xiaoyun; Xu, Wei; Bartlam, Mark; Dong, Zhiyang; Sun, Fei

2011-01-01

383

Electronic and crystal structure of NiTi martensite  

SciTech Connect

All of the first-principles electronic-structure calculations for the martensitic structure of NiTi have used the experimental atomic parameters reported by Michal and Sinclair [Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. {bold B37}, 1803 (1981)]. We have used first-principles, full-potential, linear muffin-tin orbital calculations to examine the total energy of all the experimental martensitic structures reported in the literature. We find that another crystal structure, that of Kudoh {ital et al.} [Acta Metall. Mater. {bold 33}, 2049 (1985)], has the lowest total energy at zero temperature. Ground-state and formation energies were calculated for all of the experimental structures. Total and local densities of states were calculated and compared with each other for the structures of both Kudoh {ital et al.} and Michal and Sinclair thinsp {copyright} {ital 1998} {ital The American Physical Society}

Sanati, M. [Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221 (United States)]|[Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Albers, R.C. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Pinski, F.J. [Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221 (United States)

1998-11-01

384

Electronic and crystal structure of NiTi martensite  

NASA Astrophysics Data System (ADS)

All of the first-principles electronic-structure calculations for the martensitic structure of NiTi have used the experimental atomic parameters reported by Michal and Sinclair [Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. B37, 1803 (1981)]. We have used first-principles, full-potential, linear muffin-tin orbital calculations to examine the total energy of all the experimental martensitic structures reported in the literature. We find that another crystal structure, that of Kudoh et al. [Acta Metall. Mater. 33, 2049 (1985)], has the lowest total energy at zero temperature. Ground-state and formation energies were calculated for all of the experimental structures. Total and local densities of states were calculated and compared with each other for the structures of both Kudoh et al. and Michal and Sinclair

Sanati, Mahdi; Albers, R. C.; Pinski, F. J.

1998-11-01

385

Friction drag of a spherical particle in a liquid crystal above the isotropic-nematic transition  

NASA Astrophysics Data System (ADS)

We study the friction drag of a spherical particle in the isotropic phase of a nematic liquid crystal close to the isotropic-nematic transition point. To describe the orientational order in the liquid crystal, the second-rank tensor order parameter Q?? is employed. We solve the hydrodynamic equations for Q?? and the fluid velocity ? in order to determine the friction drag. In our discussion of the friction drag, we concentrate on four parameters: the temperature, the surface order parameter, the particle radius, and the Ericksen number Er (characterizing the ratio of the viscous force to the elastic force). The temperature dependence of the friction drag agrees well with experiments that show an increasing friction drag when the isotropic-nematic phase transition is approached from above. Furthermore the friction drag increases with the surface order parameter due to the more pronounced surface nematic layer, and for larger particles it is less affected by this layer. Finally, we observe that in the range of Er we study, the friction drag is almost independent of Er although flow-induced order occurs for sufficiently large Er and surface order parameter.

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

2005-08-01

386

Friction drag of a spherical particle in a liquid crystal above the isotropic-nematic transition.  

PubMed

We study the friction drag of a spherical particle in the isotropic phase of a nematic liquid crystal close to the isotropic-nematic transition point. To describe the orientational order in the liquid crystal, the second-rank tensor order parameter Qalphabeta is employed. We solve the hydrodynamic equations for Qalphabeta and the fluid velocity nu in order to determine the friction drag. In our discussion of the friction drag, we concentrate on four parameters: the temperature, the surface order parameter, the particle radius, and the Ericksen number Er (characterizing the ratio of the viscous force to the elastic force). The temperature dependence of the friction drag agrees well with experiments that show an increasing friction drag when the isotropic-nematic phase transition is approached from above. Furthermore the friction drag increases with the surface order parameter due to the more pronounced surface nematic layer, and for larger particles it is less affected by this layer. Finally, we observe that in the range of Er we study, the friction drag is almost independent of Er although flow-induced order occurs for sufficiently large Er and surface order parameter. PMID:16196579

Fukuda, Jun-ichi; Stark, Holger; Yokoyama, Hiroshi

2005-08-05

387

Large electronic bandwidth in solution-processable pyrene crystals: The role of close-packed crystal structure  

Microsoft Academic Search

We examine the interdependence of structural and electronic properties of two substituted pyrene crystals by means of combined spectroscopic probes and density-functional theory calculations. One derivative features n-hexyl side groups, while the other one contains branched silanyl groups. Both derivatives form triclinic crystal structures when grown from solution, but the electronic dispersion behavior is significantly different due to differences in

Francoise Provencher; Jean-Frederic Laprade; Gabrielle Simard; Nicolas Berube; Michel Cote; Carlos Silva

2009-01-01

388

Effect of the polydispersion in the crystallization and micro-structure of the high charged colloids  

NASA Astrophysics Data System (ADS)

In this work we investigate the effect of the polydipersion in the crystallization and micro-structure of the high charged colloids particles with tow and three different types and different concentrations of that types. This results were obtained by computer simulation, the particles interaction was modeled by a screened Coulomb potential. We used 4000 particles in our simulation cell to let them evolution from an initial random configuration, periodic boundary conditions was imposed to simulate the bulk. The temporal evolutions of the configuration show long-ranged self-ordering and a crystalline transition, the crystalline nucleation depend of the concentrations of different kinds as well as of types of particle. The common neighbor analysis (CNA) exhibit the competition of two micro-structures, icosahedral and bcc, in the equilibrium bcc crystalline order is dominant with relative abundance over the other micro-structures. 1.- U. Gasser, Eric R. Weeks et al, Science, 292 (258), 2001. 2.- Stefan Auer, Daan Frenkel, Letter of Nature, 409 (1020), 2001. 3.- J.P. Hoogenboom, et al , Phys. Rev. Leeters, 89 (256104), 2002. 4.- M. Ch'avez-P'aez, E. Urrutia-Bauelos and M. Medina --Noyola, Phys. Rev. E, 58 (681),1998 5.- Andrew S. Clarke and Hannes J'onsson, Phys. Rev. E, 47 (3975), 1993.

Urrutia-Bauelos, Efran; Aranda-Espinosa, Helim; Chasvez-Paez, Martin

2008-03-01

389

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

390

How evolutionary crystal structure prediction works--and why.  

PubMed

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

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

2011-03-01

391

The crystal structure of methenyltetrahydromethanopterin cyclohydrolase from Methanobrevibacter ruminantium.  

PubMed

Methenyltetrahydromethanopterin cyclohydrolase (Mch) is involved in the methanogenesis pathway of archaea as a C1 unit carrier where N(5) -formyl-tetrahydromethanopterin is converted to methenyl-tetrahydromethanopterin. Mch from Methanobrevibacter ruminantium was cloned, purified, crystallized and its crystal structure solved at 1.37 resolution. A biologically active trimer, the enzyme is composed of two domains including an N-terminal domain of six ?-helices encompassing a series of four ?-sheets and a predominantly anti-parallel ?-sheet at the C-terminus flanked on one side by ?-helices. Sequence and structural alignments have helped identify residues involved in substrate binding and trimer formation. Proteins 2013; 81:2064-2070. 2013 Wiley Periodicals, Inc. PMID:23873651

Carbone, Vincenzo; Schofield, Linley R; Beattie, Amy K; Sutherland-Smith, Andrew J; Ronimus, Ron S

2013-08-23

392

The crystal structure of LiVP2O7  

NASA Astrophysics Data System (ADS)

The structure of the vanadium(III) pyrophosphate LiVP2O7 was determined by single-crystal X-ray diffraction data. The title compound, which is isostructural with LiFeP2O7, crystallizes in the monoclinic space group P21 (No. 4) with a = 4.8048(6), b = 8.113(1), c = 6.9393(9) , ? = 109.01(1), V = 255.75(7) 3, Z = 2, and R = 0.022 for 607 unique reflections. The Li+ cations, which are located in the tunnels which are formed by corner-sharing VO6 octahedra and P2O7 groups, are each coordinated by four oxygen atoms in a geometry with the same general shape as that of SF4. The structure is discussed along with NaVP2O7 and CsVP2O7.

Lii, K. H.; Wang, Y. P.; Chen, Y. B.; Wang, S. L.

1990-06-01

393

Development and testing of quartz crystal microbalances for missions to measure particle fluxes from minor solar system bodies  

Microsoft Academic Search

An instrument is being developed to measure the mass flux and size distribution of particles striking a spacecraft operating in the vicinity of airless minor solar system bodies including asteroids, small moons, and comets. We are developing and testing quartz crystal microbalances (QCMs) with robust particle capture coatings coupled with advanced oscillator electronics. The instrument is an extension the QCMs

J. Stephens; B. Gustafson; K. Waldemarsson

2003-01-01

394

A method for structural analysis of disordered particle systems  

NASA Astrophysics Data System (ADS)

We present a brief overview of a method which can identify different 3D local structures in ordered and disordered systems. Its effectiveness is demonstrated in the analysis of the structures of sphere packings, the structural evolution of a rapid cooling process of silver liquid, and the inner structure of a metal nanocluster. Quantifying local structures by means of a topological criterion, this method is parameter-free and scale-independent, and can generally be used for structural analysis of amorphous systems involving atoms or particles at different length scales.

Tian, Z. A.; Dong, K. J.; Yu, A. B.

2013-06-01

395

Crystal Structures of Aedes Aegypt Alanine Glyoxylate Aminotransferase  

SciTech Connect

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 1.75{angstrom} 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 2.1{angstrom} 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.

Han,Q.; Robinson, H.; Gao, Y.; Vogelaar, N.; Wilson, S.; Rizzi, M.; Li, J.

2006-01-01

396

Structural refinements on a sodium. beta. -aluminogallate crystal and a parent Nd sup 3+ -exchanged crystal  

SciTech Connect

X ray structural refinements are performed on a sodium {beta}-aluminogallate single crystal and on the corresponding Nd{sup 3+}-exchanged compound, which presents potential laser applications. In the hexagonal unit cells (a = b = 5.667 {angstrom}, c = 22.663 {angstrom}, Z = 2 for the Na{sup +} compound and a = b = 5.644, c = 22.610 {angstrom} for the Nd-exchanged compound), the study of ion distribution reveals a single position for the rare-earth active ion, a highly disordered distribution of sodium ions in the mirror-planes of the structure and a nonrandom localization of gallium in the available sites.

Kahn-Harari, A.; Aka, G.; Thery, J. (C.N.R.S., Paris (France))

1991-03-01

397

Tuning the self-assembled monolayer formation on nanoparticle surfaces with different curvatures: Investigations on spherical silica particles and plane-crystal-shaped zirconia particles  

PubMed Central

The ordering of dodecyl-chain self-assembled monolayers (SAM) on different nanoscopic surfaces was investigated by FT-IR studies. As model systems plane-crystal-shaped ZrO2 nanoparticles and spherical SiO2 nanoparticles were examined. The type of capping agent was chosen dependent on the substrate, therefore dodecylphosphonic acid and octadecylphosphonic acid were used for ZrO2 and dodecyltrimethoxysilane for SiO2 samples. The plane ZrO2 nanocrystals yielded more ordered alkyl-chain structures whereas spherical SiO2 nanoparticles showed significantly lower alkyl-chain ordering. Submicron-sized silica spheres revealed a significantly higher alkyl chain ordering, comparable to an analogously prepared SAM on a non-curved plane oxidized Si-wafer. In the case of ZrO2 nanocrystals an intense alkyl-chain alignment could be disturbed by decreasing the grafting density from the maximum of 2.1molecules/nm2 through the variation of coupling agent concentration to lower values. Furthermore, the co-adsorption of a different coupling agent, such as phenylphosphonic acid for ZrO2 and phenyltrimethoxysilane for SiO2, resulted in a significantly lower alkyl-chain ordering for ZrO2 plane crystals and for large SiO2 spherical particles at high grafting density. An increasing amount of order-disturbing molecules leads to a gradual decrease in alkyl-chain alignment on the surface of the inorganic nanoparticles. In the case of the ZrO2 nanoparticle system it is shown via dynamic light scattering (DLS) that the mixed monolayer formation on the particle surface impacts the dispersion quality in organic solvents such as n-hexane.

Feichtenschlager, Bernhard; Lomoschitz, Christoph J.; Kickelbick, Guido

2011-01-01

398

Tuning the self-assembled monolayer formation on nanoparticle surfaces with different curvatures: investigations on spherical silica particles and plane-crystal-shaped zirconia particles.  

PubMed

The ordering of dodecyl-chain self-assembled monolayers (SAM) on different nanoscopic surfaces was investigated by FT-IR studies. As model systems plane-crystal-shaped ZrO(2) nanoparticles and spherical SiO(2) nanoparticles were examined. The type of capping agent was chosen dependent on the substrate, therefore dodecylphosphonic acid and octadecylphosphonic acid were used for ZrO(2) and dodecyltrimethoxysilane for SiO(2) samples. The plane ZrO(2) nanocrystals yielded more ordered alkyl-chain structures whereas spherical SiO(2) nanoparticles showed significantly lower alkyl-chain ordering. Submicron-sized silica spheres revealed a significantly higher alkyl chain ordering, comparable to an analogously prepared SAM on a non-curved plane oxidized Si-wafer. In the case of ZrO(2) nanocrystals an intense alkyl-chain alignment could be disturbed by decreasing the grafting density from the maximum of 2.1 molecules/nm(2) through the variation of coupling agent concentration to lower values. Furthermore, the co-adsorption of a different coupling agent, such as phenylphosphonic acid for ZrO(2) and phenyltrimethoxysilane for SiO(2), resulted in a significantly lower alkyl-chain ordering for ZrO(2) plane crystals and for large SiO(2) spherical particles at high grafting density. An increasing amount of order-disturbing molecules leads to a gradual decrease in alkyl-chain alignment on the surface of the inorganic nanoparticles. In the case of the ZrO(2) nanoparticle system it is shown via dynamic light scattering (DLS) that the mixed monolayer formation on the particle surface impacts the dispersion quality in organic solvents such as n-hexane. PMID:21549385

Feichtenschlager, Bernhard; Lomoschitz, Christoph J; Kickelbick, Guido

2011-03-21

399

Preparation of immunoblot test stripes from a Rubella virus-like particles dye crystal complex as antigen.  

PubMed

Stably transfected Chinese hamster ovary (CHO24S) cells were the source for Rubella virus-like particles (RVLP) containing all structural proteins (E1, E2, C and their dimers). RVLP are secreted from the CHO24S cells into the medium and the time-point for collecting the medium with the highest yield of >100 kDa proteins (with 17 mg protein from 10 ml cell culture supernatant) was after 2 days of incubation. Different methods for RVLP isolation from the cell culture supernatants were assessed by SDS-PAGE and Western blotting (using sera positive or negative for Rubella virus (RV)-specific antibodies or an anti-E1 monoclonal antibody). A combination of membrane filtration with a rapid, novel gradient ultracentrifugation step (using Coomassie brilliant blue G crystals as adsorbens for RVLP that facilitated virus isolation) was the most suitable technique. 132 RV-positive human sera (RV IgG > 20 IU/ml by commercial ELISA) were tested by our "self made" immunoblot test stripes (using RVLP adsorbed to dye crystals as antigen) for the presence or absence of antibodies specific for RV structural proteins. 57.6% of these sera had antibodies against E1, E2 and C, 31% against E1 and C, and 1.5% against E1 only, whereas 3.8% had no RV specific antibodies and only 6.0% were equivocal which demonstrated that these "self made" test stripes can reliably differentiate RV antibody specificities. PMID:15868096

Giessauf, A; Flaim, M; Walder, G; Dierich, M P; Wrzner, R

2005-05-02

400

Crystal structure of the sodiumpotassium pump  

Microsoft Academic Search

The Na+,K+-ATPase generates electrochemical gradients for sodium and potassium that are vital to animal cells, exchanging three sodium ions for two potassium ions across the plasma membrane during each cycle of ATP hydrolysis. Here we present the X-ray crystal structure at 3.5 resolution of the pig renal Na+,K+-ATPase with two rubidium ions bound (as potassium congeners) in an occluded state

J. Preben Morth; Bjrn P. Pedersen; Mads S. Toustrup-Jensen; Thomas L.-M. Srensen; Janne Petersen; Jens Peter Andersen; Bente Vilsen; Poul Nissen

2007-01-01

401

Crystal Structure of the Human Laminin Receptor Precursor  

SciTech Connect

The human laminin receptor (LamR) interacts with many ligands, including laminin, prions, Sindbis virus, and the polyphenol (-)-epigallocatechin-3-gallate (EGCG), and has been implicated in a number of diseases. LamR is overexpressed on tumor cells, and targeting LamR elicits anti-cancer effects. Here, we report the crystal structure of human LamR, which provides insights into its function and should facilitate the design of novel therapeutics targeting LamR.

Jamieson,K.; Wu, J.; Hubbard, S.; Meruelo, D.

2008-01-01

402

THE CRYSTAL STRUCTURE OF RbUF  

Microsoft Academic Search

The compound RbUF has a hexagonal crystal structure with ; the parameters a\\/sub o\\/ = 8.195 plus or minus 0.002 A and c\\/sub o\\/ = 16.437 ; plus or minus 0.002 A. This compound is believed to be isomorphous to KU\\/sub ; 6\\/F and KThF. (auth) uranium hexafluoride -chlorine ; trifluoride -hydrogen fluoride from a knowledge of the behavior of

1958-01-01

403

Crystal structure of a substrate-free aspartate transporter.  

PubMed

Archaeal glutamate transporter homologs catalyze the coupled uptake of aspartate and three sodium ions. After the delivery of the substrate and sodium ions to the cytoplasm, the empty binding site must reorient to the outward-facing conformation to reset the transporter. Here, we report a crystal structure of the substrate-free transporter GltTk from Thermococcus kodakarensis, which provides insight into the mechanism of this essential step in the translocation cycle. PMID:24013209

Jensen, Sonja; Guskov, Albert; Rempel, Stephan; Hnelt, Inga; Slotboom, Dirk Jan

2013-09-08

404

Crystal structure of bacterial multidrug efflux transporter AcrB  

Microsoft Academic Search

AcrB is a major multidrug exporter in Escherichia coli. It cooperates with a membrane fusion protein, AcrA, and an outer membrane channel, TolC. We have determined the crystal structure of AcrB at 3.5 resolution. Three AcrB protomers are organized as a homotrimer in the shape of a jellyfish. Each protomer is composed of a transmembrane region 50 thick and a

Satoshi Murakami; Ryosuke Nakashima; Eiki Yamashita; Akihito Yamaguchi

2002-01-01

405

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

406

Interplay between size and crystal structure of molybdenum dioxide nanoparticles--synthesis, growth mechanism, and electrochemical performance.  

PubMed

A detailed study is presented on the formation of MoO(2) nanoparticles from the dissolution of the precursor to the final rodlike product, with a focus on the exploration of the inorganic reaction occurring ahead of the nucleation step, and interplay between size and crystal structure of MoO(2). In situ X-ray absorption spectroscopy experiments show that the crystallization and the growth process of MoO(2) nanorods is initiated by rapid reduction of the MoO(2) Cl(2) precursor in benzyl alcohol and acetophenone. This reaction triggers the nucleation of 2 nm MoO(2) particles with spherical shape and hexagonal crystal structure. The transformation from spheres into rods emerges as a complex process driven by oriented attachment. High-resolution transmission electron microscopy and X-ray diffraction results provide evidence that the 2 nm particles first aggregate into 5-20 nm-large oriented assemblies. The increase in particle size induces the phase transition from hexagonal to the less symmetrical monoclinic crystal structure, and finally the transformation into rods. Is it shown that electrodes for lithium-ion batteries based on MoO(2) nanorods have a long-term cycling life. The specific discharge capacity even after 200 cycles at a discharge rate of 1 C is about 300 Ah kg(-1) . PMID:21294267

Koziej, Dorota; Rossell, Marta D; Ludi, Bettina; Hintennach, Andreas; Novk, Petr; Grunwaldt, Jan-Dierk; Niederberger, Markus

2010-12-20

407

Automated detection and characterization of microstructural features: application to eutectic particles in single crystal Ni-based superalloys  

NASA Astrophysics Data System (ADS)

Serial sectioning methods continue to produce an abundant amount of image data for quantifying the three-dimensional nature of material microstructures. Here, we discuss a methodology to automate detecting and characterizing eutectic particles taken from serial images of a production turbine blade made of a heat-treated single crystal Ni-based superalloy (PWA 1484). This method includes two important steps for unassisted eutectic particle characterization: automatically identifying a seed point within each particle and segmenting the particle using a region growing algorithm with an automated stop point. Once detected, the segmented eutectic particles are used to calculate microstructural statistics for characterizing and reconstructing statistically representative synthetic microstructures for single crystal Ni-based superalloys. The significance of this work is its ability to automate characterization for analysing the 3D nature of eutectic particles.

Tschopp, M. A.; Groeber, M. A.; Fahringer, R.; Simmons, J. P.; Rosenberger, A. H.; Woodward, C.

2010-03-01

408

Polymer crystallization enabled nanotube functionalization: Morphology, structure and applications  

NASA Astrophysics Data System (ADS)

Carbon Nanotubes (CNT) have attracted tremendous attention and numerous potential applications have been proposed. In this thesis study, a unique means to modify CNT surface with polymer crystals via controlled polymer crystallization method has been developed. CNTs were wrapped in polymer single crystal lamellae in a periodic manner, resulting in nano hybrid shish-kebab (NHSK) structures. The periodicity of the polymer lamellae can be varied from 20-150 nm. The kebabs are 5 nm thick (along CNT direction) with a lateral size of 20 nm to micrometers, which can be readily controlled by varying crystallization conditions. PE, Nylon 66 and PE-b-SBR were successfully decorated on single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT), as well as vapor grown carbon nanofibers (CNF). The formation mechanism was attributed to "size dependent soft epitaxy". Efforts were focused on PE/SWNT system to understand the growth mechanism and the effect of experimental parameters on the periodicity. It was found that weight ratio of SWNT and PE (defined as R) played an important role and periodicity increases with increasing R. This was attributed to a reduced polymer concentration at the crystal growth front. Since NHSK formation conditions depend upon CNT structures, it further provides a unique opportunity for CNT separation. Applications of using NHSK in CNT dispersions, separation and nanocomposites have also been successfully developed. This unique means is different from all the reported methods and it opens a gateway to achieving periodically functionalized CNT for a variety of applications ranging from nanocomposites, sensors, fuel cells etc.

Li, Lingyu

409

Syntheses and Crystal Structures of the Lanthanum Titanium Oxyselenides La  

SciTech Connect

The new compounds La{sub 4}Ti{sub 2}O{sub 4}Se{sub 5} and La{sub 6}Ti{sub 3}O{sub 5}Se{sub 9} have been obtained from stoichiometric reactions of La, Ti, TiO{sub 2}, and Se in fused-silica tubes at 1223 K. Potassium halide fluxes were used to promote the crystallization. The compounds have been characterized by single-crystal X-ray diffraction methods. La{sub 4}Ti{sub 2}O{sub 4}Se{sub 5} crystallizes in the orthorhombic space group Cmcm with eight formula units in a cell at 153 K of dimensions a=3.9695(4) {angstrom}, b=33.115(3) {angstrom}, c=18.6380(18) {angstrom}. The five independent La atoms in the structure are found in four different coordination polyhedra, namely tricapped trigonal prism, bicapped trigonal prism, square antiprism, and 7-octahedron, whereas the three independent Ti atoms have octahedral coordination. The crystal structure comprises infinite layers that stack along the b-axis. Two adjacent layers are linked by La-Se bonds. La{sub 4}Ti{sub 2}O{sub 4}Se{sub 5} represents the first rare-earth titanium oxychalcogenide containing only Ti{sup 3+} cations. La{sub 6}Ti{sub 3}O{sub 5}Se{sub 9} crystallizes in the monoclinic space group C2/m with four formula units in a cell at 153 K of dimensions a=43.999(6) {angstrom}, b=3.9454(6) {angstrom}, c=11.1093(16) {angstrom}, {beta}=96.882(2){degree}. The six independent La atoms in the structure are found in three different coordination polyhedra, namely tricapped trigonal prism, bicapped trigonal prism, and 7-octahedron. The four independent Ti atoms have octahedral coordination. The crystal structure comprises infinite condensed layers of composition {sub {infinity}}{sup 2}[La{sub 2}Ti{sub 1}O{sub 2}Se{sub 3}] that stack successively with extended slabs of composition {sub {infinity}}{sup 2}[La{sub 4}Ti{sub 2}O{sub 3}Se{sub 6}] along the a-axis. La{sub 6}Ti{sub 3}O{sub 5}Se{sub 9} is a mixed-valence compound in which two-thirds of the Ti cations are Ti{sup 3+} and one-third are Ti{sup 4+}.

Tougait, Olivier; Ibers, James A.

2001-03-01

410

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

411

Flow-Induced Crystallization Precursor Structure in Entangled Polymer Melt.  

NASA Astrophysics Data System (ADS)

Flow-induced crystallization has long been an important subject in polymer processing. Varying processing conditions can produce different morphologies, which lead to different properties. Recent studies indicated that the final morphology is in fact dictated by the initial formation of crystallization precursor structures (i.e., shish kebabs) under flow. In this talk, factors that affect the shish-kebab formation in entangled polymer melts are systematically reviewed, including the concept of coil-stretch transition, chain dynamics, critical orientation molecular weight, phase transition during shish and kebab formations. In particular, recent experimental results from in-situ rheo-X-ray studies and ex-situ microscopic examinations have been presented to illustrate several new findings of flow-induced shish-kebab structures in polymer melts. (1) The shish entity consists of stretched chains (or chain segments) that can be in the amorphous, mesomorphic or crystalline state. (2) The kebab entity mainly arises from the crystallization of coiled chains (or chain segments), which seems to follow a diffusion-control growth process. (3) A shish-kebab structure with multiple shish was seen in the ultra-high molecular weight polyethylene (UHMWPE) precursor. Based on the above results and recent simulation work from other laboratories, a modified molecular mechanism for the shish-kebab formation in entangled melt is presented.

Hsiao, Benjamin

2006-03-01

412

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

2013-08-28

413

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

NASA Astrophysics Data System (ADS)

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 P63 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 (Zn0.975?0.025)Zn i(0.015)(O0.990?0.010) (green) and (Zn0.965?0.035)Zn 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.; Kuz'micheva, G. M.; Rybakov, V. B.

2013-03-01

414

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

415

The crystal structure of acidic ?-galactosidase from Aspergillus oryzae.  

PubMed

The crystal structure of the industrially important Aspergillus oryzae ?-galactosidase has been determined at 2.60 resolution. The Ao-?-gal is a large (985 residues) monomeric multi-domain enzyme that has a catalytic (?/?)8-barrel domain. An electron density map revealed extensive N-glycosylation between the domain interfaces suggesting that the oligosaccharide-chains would have a stabilizing role for the structure of Ao-?-gal. Comparison of structure with other ?-galactosidase structures of glycoside hydrolase family 35 revealed a number of hydrophobic residues, which may contribute favorably to the stabilization of the structure. The role of a high number of acidic residues in Ao-?-gal is also discussed. PMID:23688418

Maksimainen, Mirko M; Lampio, Anja; Mertanen, Mirka; Turunen, Ossi; Rouvinen, Juha

2013-05-17

416

Technegas: a study of particle structure, size and distribution  

Microsoft Academic Search

Technegas (TcG) was produced using a commercially available TcG generator. The structure and size distribution of TcG particles were examined by means of the following methods: (a) transmission electron microscopy (TEM), range: 1 nm-100 m; (b) time-of-flight mass spectroscopy (MS), range: < 3 nm; (c) photon correlation spectroscopy (PCS), range: 3 nm-3 m. The TEM images showed graphite particles (size

M. Lemb; T. H. Oei; H. Eifert; B. Gnther

1993-01-01

417

Structure and morphology of small palladium particles (2-6 nm) supported on MgO micro-cubes  

NASA Astrophysics Data System (ADS)

Small MgO cubes were prepared in a controlled atmosphere and protected against air contamination. Their clean surfaces were used as supports for Pd particles (2-6 nm) vacuum-deposited from a Knudsen cell in the same chamber. The Pd particles epitaxially oriented on the substrate were observed by HRTEM, microdiffraction and convergent-beam electron diffraction. An isotropic lattice expansion was determined by microdiffraction on isolated particles, increasing between 2% and 8% for particle sizes decreasing from 6 to 2 nm. From the HRTEM images of particles observed in two directions, parallel and perpendicular to the interface with the MgO substrate, the particles were characterized as single crystals with fcc structure and octahedral shape. The octahedra are truncated by (001) planes at the top and at the interface.

Giorgio, S.; Henry, C. R.; Chapon, C.; Penisson, J. M.

1990-02-01

418

Nonlinear optical probe of molecular structure on colloidal particle surfaces  

NASA Astrophysics Data System (ADS)

The structure of molecules adsorbed at the colloidal particle surface has great influence on how the colloidal particles interact among themselves and with the environment. In this presentation we show that Second Harmonic Generation from molecules adsorbed at the particle surface can be used for determining the orientation of the molecules at this buried interface. The determination is facilitated by nonlinear Rayleigh-Gans-Debye analysis of polarization and scattering angle dependent SHG. The first demonstration is performed on the cationic Malachite Green (MG) molecule adsorbed on three types of polystyrene microspheres with different surface composition and charges.

Jen, Shih-Hui

2005-03-01

419

Structural Insights Into The Regulatory Particle Of The Proteasome From Methanocaldococcus jannaschii  

PubMed Central

Summary Eukaryotic proteasome consists of a core particle (CP), which degrades unfolded protein, and a regulatory particle (RP), which is responsible for recognition, ATP-dependent unfolding and translocation of polyubiquitinated substrate protein. In the archaea Methanocaldococcus jannaschii, the RP is a homohexameric complex of proteasome-activating nucleotidase (PAN). Here we report the crystal structures of essential elements of the archaeal proteasome: the CP, the ATPase domain of PAN, and a distal subcomplex that is likely the first to encounter substrate. The distal subcomplex contains a coiled-coil segment and an OB-fold domain, both of which appear to be conserved in the eukaryotic proteasome. The OB domains of PAN form a hexameric ring with a 13- pore, which likely constitutes the outermost constriction of the substrate translocation channel. These studies reveal structural codes and architecture of the complete proteasome, identify potential substrate-binding sites, and uncover unexpected asymmetry in the RP of archaea and eukaryotes.

Zhang, Fan; Hu, Min; Tian, Geng; Zhang, Ping; Finley, Daniel; Jeffrey, Philip D.; Shi, Yigong

2010-01-01

420

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 particle data from the Advanced Composition Explorer (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 Partial Variance of Increments statistic, essentially a normalized vector increment. A stronger association of energetic particle flux in the 0.047-4.75 MeV range is found with intense magnetic discontinuities than is found with shocks. Nevertheless, the average profile of suprathermals near shocks is quite consistent with standard models of diffusive shock acceleration, while a significant amount of the energetic particles measured and strong discontinuities are found by ACE within six hours of a shock. This evidence supports the view that multiple mechanisms contribute to the acceleration and transport of interplanetary suprathermal particles.

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

2013-10-01

421

Crystal structure of single crystals of nonlinear optical L-histidinium trichloroacetate  

NASA Astrophysics Data System (ADS)

Single crystals of a new histidinium salt: L-histidinium trichloroacetate {abbreviated as LHTCA; [(C3N2H4) CH2CH (NH3) (CO2)]+ CCl3COO-} were grown by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in a non-centrosymmetric space group P21 of monoclinic system with cell parameters a = 5.4505(18) , b = 25.769(8) , c = 9.210(2) and ? = 99.98(2) with Z = 4. The structure has been refined to an R-value of 0.05 for 2539 observed reflections using three-dimensional X-ray diffraction data. The vibrational structure of the compound confirms the presence of various functional groups in the molecule. The UV Vis NIR spectrum shows a good transparency in the whole of the region from ultraviolet to near IR. The Kurtz Perry powder SHG measurement confirms the frequency doubling of the crystal and its powder SHG efficiency was measured as deff = 0.33 deff (KDP).

Gokul Raj, S.; Ramesh Kumar, G.; Mohan, R.; Varghese, Babu; Jayavel, R.

2006-12-01

422

Electromagnetic Structure of the Nucleon with Many-Particle Structure  

Microsoft Academic Search

The electric and magnetic form factors of nucleons are treated on the basis of the model in which the nucleon has a ``central part'' with spin one half, which is composed of three urbaryons (like quarks) and whose extent is of the order of magnitude of the nucleon Compton wave length. These quarks need not have a ``particle-nature'' in all

Yukiko Kinoshita; Tsunehiro Kobayashi; Shigeru Machida; Mikio Namiki

1966-01-01

423

RNA is a structural element in retrovirus particles.  

PubMed

A single retroviral protein, Gag, is sufficient for virus particle assembly. While Gag is capable of specifically packaging the genomic RNA into the particle, this RNA species is unnecessary for particle assembly in vivo. In vitro, nucleic acids profoundly enhance the efficiency of assembly by recombinant Gag proteins, apparently by acting as "scaffolding" in the particle. To address the participation of RNA in retrovirus assembly in vivo, we analyzed murine leukemia virus particles that lack genomic RNA because of a deletion in the packaging signal of the viral RNA. We found that these particles contain cellular mRNA in place of genomic RNA. This result was particularly evident when Gag was expressed by using a Semliki Forest virus-derived vector: under these conditions, the Semliki Forest virus vector-directed mRNA became very abundant in the cells and was readily identified in the retroviral virus-like particles. Furthermore, we found that the retroviral cores were disrupted by treatment with RNase. Taken together, the data strongly suggest that RNA is a structural element in retrovirus particles. PMID:11320254

Muriaux, D; Mirro, J; Harvin, D; Rein, A

2001-04-24

424

RNA is a structural element in retrovirus particles  

PubMed Central

A single retroviral protein, Gag, is sufficient for virus particle assembly. While Gag is capable of specifically packaging the genomic RNA into the particle, this RNA species is unnecessary for particle assembly in vivo. In vitro, nucleic acids profoundly enhance the efficiency of assembly by recombinant Gag proteins, apparently by acting as scaffolding in the particle. To address the participation of RNA in retrovirus assembly in vivo, we analyzed murine leukemia virus particles that lack genomic RNA because of a deletion in the packaging signal of the viral RNA. We found that these particles contain cellular mRNA in place of genomic RNA. This result was particularly evident when Gag was expressed by using a Semliki Forest virus-derived vector: under these conditions, the Semliki Forest virus vector-directed mRNA became very abundant in the cells and was readily identified in the retroviral virus-like particles. Furthermore, we found that the retroviral cores were disrupted by treatment with RNase. Taken together, the data strongly suggest that RNA is a structural element in retrovirus particles.

Muriaux, Delphine; Mirro, Jane; Harvin, Demetria; Rein, Alan

2001-01-01

425

Physicochemical properties and plastic crystal structures of phosphonium fluorohydrogenate salts.  

PubMed

Fluorohydrogenate salts of quaternary phosphonium cations with alkyl and methoxy groups (tetraethylphosphonium (P(2222)(+)), triethyl-n-pentylphosphonium (P(2225)(+)), triethyl-n-octylphosphonium (P(2228)(+)), and triethylmethoxymethylphosphonium (P(222(101))(+))) have been synthesized by the metatheses of anhydrous hydrogen fluoride and the corresponding phosphonium bromide or chloride precursors. The three salts with asymmetric cations, P(222m)(FH)(2.1)F (m = 5, 8, and 101), are room temperature ionic liquids (ILs) and are characterized by differential scanning calorimetry, density, viscosity, and conductivity measurements. Linear sweep voltammetry using a glassy carbon working electrode shows these phosphonium fluorohydrogenate ILs have wide electrochemical windows (>4.9 V) with the lowest viscosity and highest conductivity in the known phosphonium-based ILs. Thermogravimetry shows their thermal stabilities are also improved compared to previously reported alkylammonium cation-based fluorohydrogenate salts. Differential scanning calorimetry and X-ray diffraction revealed that tetraethylphosphonium fluorohydrogenate salt, P(2222)(FH)(2)F, exhibits two plastic crystal phases. The high temperature phase has a hexagonal lattice, which is the first example of a plastic crystal phase with an inverse nickel arsenide-type structure, and the low-temperature phase has an orthorhombic lattice. The high-temperature plastic crystal phase exhibits a conductivity of 5 mS cm(-1) at 50 C, which is the highest value for the neat plastic crystals. PMID:21666902

Enomoto, Takeshi; Kanematsu, Shunsuke; Tsunashima, Katsuhiko; Matsumoto, Kazuhiko; Hagiwara, Rika

2011-06-10

426

Crystal structure of the carbon monoxide complex of human cytoglobin.  

PubMed

Cytoglobin (Cgb) is a vertebrate heme-containing globin-protein expressed in a broad range of mammalian tissues. Unlike myoglobin, Cgb displays a hexa-coordinated (bis-hystidyl) heme iron atom, having the heme distal His81(E7) residue as the endogenous sixth ligand. In the present study, we crystallized human Cgb in the presence of a reductant Na?S?O? under a carbon monoxide (CO) atmosphere, and determined the crystal structure at 2.6 A resolution. The CO ligand occupies the sixth axial position of the heme ferrous iron. Eventually, the imidazole group of His81(E7) is expelled from the sixth position and swings out of the distal heme pocket. The flipping motion of the His81 imidazole group accompanies structural readjustments of some residues (Gln62, Phe63, Gln72, and Ser75) in both the CD-corner and D-helix regions of Cgb. On the other hand, no significant structural changes were observed in other Cgb regions, for example, on the proximal side. These structural alterations that occurred as a result of exogenous ligand (CO) binding are clearly different from those observed in other vertebrate hexa-coordinated globins (mouse neuroglobin, Drosophila melanogaster hemoglobin) and penta-coordinated sperm whale myoglobin. The present study provides the structural basis for further discussion of the unique ligand-binding properties of Cgb. PMID:21254233

Makino, Masatomo; Sawai, Hitomi; Shiro, Yoshitsugu; Sugimoto, Hiroshi

2011-01-20

427

Crystal structure of the 80S yeast ribosome.  

PubMed

The first X-ray structure of the eukaryotic ribosome at 3.0? resolution was determined using ribosomes isolated and crystallized from the yeast Saccharomyces cerevisiae (Ben-Shem A, Garreau de Loubresse N, Melnikov S, Jenner L, Yusupova G, Yusupov M: The structure of the eukaryotic ribosome at 3.0 A resolution. Science 2011, 334:1524-1529). This accomplishment was possible due to progress in yeast ribosome biochemistry as well as recent advances in crystallographic methods developed for structure determination of prokaryotic ribosomes isolated from Thermus thermophilus and Escherichia coli. In this review we will focus on the development of isolation procedures that allowed structure determination (both cryo-EM and X-ray crystallography) to be successful for the yeast S. cerevisiae. Additionally we will introduce a new nomenclature that facilitates comparison of ribosomes from different species and kingdoms of life. Finally we will discuss the impact of the yeast 80S ribosome crystal structure on perspectives for future investigations. PMID:22884264

Jenner, Lasse; Melnikov, Sergey; Garreau de Loubresse, Nicolas; Ben-Shem, Adam; Iskakova, Madina; Urzhumtsev, Alexandre; Meskauskas, Arturas; Dinman, Jonathan; Yusupova, Gulnara; Yusupov, Marat

2012-08-08

428

The crystal structure of human GDP-L-fucose synthase.  

PubMed

Human GDP-l-fucose synthase, also known as FX protein, synthesizes GDP-l-fucose from its substrate GDP-4-keto-6-deoxy-d-mannose. The reaction involves epimerization at both C-3 and C-5 followed by an NADPH-dependent reduction of the carbonyl at C-4. In this paper, the first crystal structure of human FX protein was determined at 2.37 resolution. The asymmetric unit of the crystal structure contains four molecules which form two homodimers. Each molecule consists of two domains, a Rossmann-fold NADPH-binding motif and a carboxyl terminal domain. Compared with the Escherichia coli GDP-l-fucose synthase, the overall structures of these two enzymes have four major differences. There are four loops in the structure of human FX protein corresponding to two ?-helices and two ?-sheets in that of the E. coli enzyme. Besides, there are seven different amino acid residues binding with NAPDH comparing human FX protein with that from E. coli. The structure of human FX reveals the key catalytic residues and could be useful for the design of drugs for the treatment of inflammation, auto-immune diseases, and possibly certain types of cancer. PMID:23774504

Zhou, Huan; Sun, Lihua; Li, Jian; Xu, Chunyan; Yu, Feng; Liu, Yahui; Ji, Chaoneng; He, Jianhua

2013-06-16

429

Theory of elastic interaction between arbitrary colloidal particles in confined nematic liquid crystals.  

PubMed

We develop the method proposed by Chernyshuk and Lev [Phys. Rev. E 81, 041701 (2010)] for theoretical investigation of elastic interactions between colloidal particles of arbitrary shape and chirality (polar as well as azimuthal anchoring) in the confined nematic liquid crystal (NLC). General expressions for six different types of multipole elastic interactions are obtained in the confined NLC: monopole-monopole (Coulomb type), monopole-dipole, monopole-quadrupole, dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The obtained formulas remain valid in the presence of the external electric or magnetic fields. The exact equations are found for all multipole coefficients for the weak anchoring case. For the strong anchoring coupling, the connection between the symmetry of the shape or director and multipole coefficients is obtained, which enables us to predict which multipole coefficients vanish and which remain nonzero. The particles with azimuthal helicoid anchoring are considered as an example. Dipole-dipole interactions between helicoid cylinders and cones are found in the confined NLC. In addition, the banana-shaped particles in homeotropic and planar nematic cells are considered. It is found that the dipole-dipole interaction between banana-shaped particles differs greatly from the dipole-dipole interaction between the axially symmetrical particles in the nematic cell. There is a crossover from attraction to repulsion between banana particles along some directions in nematic cells. It is shown that monopoles do not "feel" the type of nematic cell: monopole-monopole interaction turns out to be the same in homeotropic and planar nematic cells and converges to the Coulomb law as thickness increases, L??. PMID:23367965

Tovkach, O M; Chernyshuk, S B; Lev, B I

2012-12-26

430

Theory of elastic interaction between arbitrary colloidal particles in confined nematic liquid crystals  

NASA Astrophysics Data System (ADS)

We develop the method proposed by Chernyshuk and Lev [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.81.041701 81, 041701 (2010)] for theoretical investigation of elastic interactions between colloidal particles of arbitrary shape and chirality (polar as well as azimuthal anchoring) in the confined nematic liquid crystal (NLC). General expressions for six different types of multipole elastic interactions are obtained in the confined NLC: monopole-monopole (Coulomb type), monopole-dipole, monopole-quadrupole, dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The obtained formulas remain valid in the presence of the external electric or magnetic fields. The exact equations are found for all multipole coefficients for the weak anchoring case. For the strong anchoring coupling, the connection between the symmetry of the shape or director and multipole coefficients is obtained, which enables us to predict which multipole coefficients vanish and which remain nonzero. The particles with azimuthal helicoid anchoring are considered as an example. Dipole-dipole interactions between helicoid cylinders and cones are found in the confined NLC. In addition, the banana-shaped particles in homeotropic and planar nematic cells are considered. It is found that the dipole-dipole interaction between banana-shaped particles differs greatly from the dipole-dipole interaction between the axially symmetrical particles in the nematic cell. There is a crossover from attraction to repulsion between banana particles along some directions in nematic cells. It is shown that monopoles do not feel the type of nematic cell: monopole-monopole interaction turns out to be the same in homeotropic and planar nematic cells and converges to the Coulomb law as thickness increases, L??.

Tovkach, O. M.; Chernyshuk, S. B.; Lev, B. I.

2012-12-01

431

Crystal structures of intermediates in the nitroalkane oxidase reaction.  

PubMed

The flavoenzyme nitroalkane oxidase is a member of the acyl-CoA dehydrogenase superfamily. Nitroalkane oxidase catalyzes the oxidation of neutral nitroalkanes to nitrite and the corresponding aldehydes or ketones. Crystal structures to 2.2 A resolution or better of enzyme complexes with bound substrates and of a trapped substrate-flavin adduct are described. The D402N enzyme has no detectable activity with neutral nitroalkanes [Valley, M. P., and Fitzpatrick, P. F. (2003) J. Am. Chem. Soc. 125, 8738-8739]. The structure of the D402N enzyme crystallized in the presence of 1-nitrohexane or 1-nitrooctane shows the presence of the substrate in the binding site. The aliphatic chain of the substrate extends into a tunnel leading to the enzyme surface. The oxygens of the substrate nitro group interact both with amino acid residues and with the 2'-hydroxyl of the FAD. When nitroalkane oxidase oxidizes nitroalkanes in the presence of cyanide, an electrophilic flavin imine intermediate can be trapped [Valley, M. P., Tichy, S. E., and Fitzpatrick, P. F. (2005) J. Am. Chem. Soc. 127, 2062-2066]. The structure of the enzyme trapped with cyanide during oxidation of 1-nitrohexane shows the presence of the modified flavin. A continuous hydrogen bond network connects the nitrogen of the CN-hexyl-FAD through the FAD 2'-hydroxyl to a chain of water molecules extending to the protein surface. Together, our complementary approaches provide strong evidence that the flavin cofactor is in the appropriate oxidation state and correlates well with the putative intermediate state observed within each of the crystal structures. Consequently, these results provide important structural descriptions of several steps along the nitroalkane oxidase reaction cycle. PMID:19265437

Hroux, Annie; Bozinovski, Dragana M; Valley, Michael P; Fitzpatrick, Paul F; Orville, Allen M

2009-04-21

432

Crystal structure of heat shock locus V (HslV) from Escherichia?coli  

PubMed Central

Heat shock locus V (HslV; also called ClpQ) is the proteolytic core of the ATP-dependent protease HslVU in Escherichia coli. It has sequence similarity with the ?-type subunits of the eukaryotic and archaebacterial proteasomes. Unlike these particles, which display 72-point symmetry, it is a dimer of hexamers with 62-point symmetry. The crystal structure of HslV at 3.8-? resolution, determined by isomorphous replacement and symmetry averaging, shows that in spite of the different symmetry of the particle, the fold and the contacts between subunits are conserved. A tripeptide aldehyde inhibitor, acetyl-Leu-Leu-norleucinal, binds to the N-terminal threonine residue of HslV, probably as a hemiacetal, relating HslV also functionally to the proteasomes of archaea and eukaryotes.

Bochtler, Matthias; Ditzel, Lars; Groll, Michael; Huber, Robert

1997-01-01

433

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

434

N-methylcodeinium iodide--crystal structure and spectroscopic elucidation.  

PubMed

The correlation between the structure and the spectroscopic properties of N-methylcodeinium iodide (1) has been studied, using the methods of single crystal X-ray diffraction, IR-LD spectroscopy of oriented samples as a suspension in nematic liquid crystals, UV-vis spectroscopy and 1H and 13C NMR spectroscopy. HPLC tandem mass spectrometry (HPLC ESI MS/MS) and thermal methods were also employed. Quantum chemical calculations have been performed with a view to obtaining the electronic structure and vibrational properties of the title compound. Compound (1) crystallizes in the space group P2(1)2(1)2(1) and its cations and anions are joined by moderate intermolecular OH...I- interaction of length 3.442A. The codeine molecule exhibits the classical T-shape for opiates. A dihedral angle value of 86.4(5) degrees between the A/B/C and D/E planes is obtained. Rings A and B are effectively coplanar with an interplanar angle of 3.6(3) degrees. PMID:19233715

Seidel, R W; Bakalska, B R; Kolev, T; Vassilev, D; Mayer-Figge, H; Spiteller, M; Sheldrick, W S; Koleva, B B

2009-01-31

435

Simultaneous occurrence of structure-directed and particle-resonance-induced phononic gaps in colloidal films.  

PubMed

We report on the observation of two hypersonic phononic gaps of different nature in three-dimensional colloidal films of nanospheres using Brillouin light scattering. One is a Bragg gap occurring at the edge of the first Brillouin zone along a high-symmetry crystal direction. The other is a hybridization gap in crystalline and amorphous films, originating from the interaction of the band of quadrupole particle eigenmodes with the acoustic effective-medium band, and its frequency position compares well with the computed lowest eigenfrequency. Structural disorder eliminates the Bragg gap, while the hybridization gap is robust. PMID:18518452

Still, T; Cheng, W; Retsch, M; Sainidou, R; Wang, J; Jonas, U; Stefanou, N; Fytas, G

2008-05-13

436

Structure of finite sphere packings via exact enumeration: Implications for colloidal crystal nucleation  

NASA Astrophysics Data System (ADS)

We analyze the geometric structure and mechanical stability of a complete set of isostatic and hyperstatic sphere packings obtained via exact enumeration. The number of nonisomorphic isostatic packings grows exponentially with the number of spheres N, and their diversity of structure and symmetry increases with increasing N and decreases with increasing hyperstaticity H?Nc-NISO, where Nc is the number of pair contacts and NISO=3N-6. Maximally contacting packings are in general neither the densest nor the most symmetric. Analyses of local structure show that the fraction f of nuclei with order compatible with the bulk (rhcp) crystal decreases sharply with increasing N due to a high propensity for stacking faults, five- and near-fivefold symmetric structures, and other motifs that preclude rhcp order. While f increases with increasing H, a significant fraction of hyperstatic nuclei for N as small as 11 retain non-rhcp structure. Classical theories of nucleation that consider only spherical nuclei, or only nuclei with the same ordering as the bulk crystal, cannot capture such effects. Our results provide an explanation for the failure of classical nucleation theory for hard-sphere systems of N?10 particles; we argue that in this size regime, it is essential to consider nuclei of unconstrained geometry. Our results are also applicable to understanding kinetic arrest and jamming in systems that interact via hard-core-like repulsive and short-ranged attractive interactions.

Hoy, Robert S.; Harwayne-Gidansky, Jared; O'Hern, Corey S.

2012-05-01

437

Refinement of the crystal structure of tetragonal Al2Cu  

NASA Astrophysics Data System (ADS)

New single-crystal X-ray diffraction data have been obtained for the ?-phase of aluminum-copper (Al2Cu). Results of the refinement are presented. The structure is found to be in accordance with the one determined by . The compound crystallizes in the tetragonal space group I4/mcm (No. 140) with a unit cell of dimensions a = 6.067(1) and c = 4.877(1) . There are four formula-units per unit cell. A full-matrix least-squares refinement with 237 observed reflections and 8 parameters converged to RF = 0.032 (wR = 0.037). In addition to more accurate values for the lattice parameters and the atomic coordinates, anisotropic temperature factors are obtained.

Meetsma, A.; de Boer, J. L.; van Smaalen, S.

1989-12-01

438

Crystal structure of jinshajiangite from the Norra Kaerr complex (Sweden)  

SciTech Connect

The structure of the mineral jinshajiangite from the Norra Kaerr alkaline complex (Sweden) was determined by single-crystal X-ray diffraction and refined to R = 6.7%. The monoclinic unit-cell parameters are a = 5.350(2) A, b = 6.909(6) A, c = 20.96(1) A, {beta} = 99.83(4){sup o}, sp. gr. P2/m. This mineral is an Fe-rich analogue of surkhobite and perraultite, but it crystallizes in a different space group, and the unit-cell parameters a and b are two times smaller than those of these two minerals. The framework of jinshajiangite from Norra Kaerr contains narrow and wide channels, which are occupied by Ca, Na, Ba, and K atoms in an ordered fashion.

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

2008-07-15

439

Syntheses and crystal structures of three barium uranium sulfides  

NASA Astrophysics Data System (ADS)

The barium uranium sulfides Ba3.69US6, BaUS3, and BaU2S5 have been synthesized at 1273, 1323, and 1323 K, respectively. The structures of these compounds have been determined by single-crystal X-ray diffraction methods. They crystallize in space groups D3d6-R3c, D2h16-Pnma, and C2h5-P21/c, respectively. Among these three ternaries and Ba2US6 the coordination geometries about the U atoms vary considerably. Ba3.69US6 is a mixed U4+/U5+compound whereas the others are U4+ compounds. The decreasing dimensionality of the four compounds with increasing Ba-to-U content shows the expected trend.

Mesbah, Adel; Ibers, James A.

2013-03-01

440

Crystal structure of deltarhodopsin-3 from Haloterrigena thermotolerans.  

PubMed

Deltarhodopsin, a new member of the microbial rhodopsin family, functions as a light-driven proton pump. Here, we report the three-dimensional structure of deltarhodopsin (dR3) from Haloterrigena thermotolerans at 2.7 resolution. A crystal belonging to space group R32 (a, b = 111.71 , c = 198.25 ) was obtained by the membrane fusion method. In this crystal, dR3 forms a trimeric structure as observed for bacteriorhodopsin (bR). Structural comparison of dR with bR showed that the inner part (the proton release and uptake pathways) is highly conserved. Meanwhile, residues in the protein-protein contact region are largely altered so that the diameter of the trimeric structure at the cytoplasmic side is noticeably larger in dR3. Unlike bR, dR3 possesses a helical segment at the C-terminal region that fills the space between the AB and EF loops. A significant difference is also seen in the FG loop, which is one residue longer in dR3. Another peculiar property of dR3 is a highly crowded distribution of positively charged residues on the cytoplasmic surface, which may be relevant to a specific interaction with some cytoplasmic component.Proteins 2013; 2013 Wiley Periodicals, Inc. PMID:23625688

Zhang, Jin; Mizuno, Katsuhide; Murata, Yuki; Koide, Hideaki; Murakami, Midori; Ihara, Kunio; Kouyama, Tsutomu

2013-06-20