BIOLOGICAL REVIEWS, Issue 3 2005
Jean-François Ponge
ABSTRACT More realistic approaches are needed to understand the complexity of ecological systems. Emergent properties of real systems can be used as a basis for a new, neither reductionist nor holistic, approach. Three systems, termed here BUBBLEs, WAVEs and CRYSTALS, have been identified as exhibiting emergent properties. They are non-hierarchical assemblages of individual components, with amplification and connectedness being two main principles that govern their build-up, maintenance and mutual relationships. Examples from various fields of biological and ecological science are referred to, ranging from individual organisms to landscapes. [source]

Dynamics of Dislocations in a 2D Plasma Crystal

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 4-5 2009
V. Nosenko
Abstract Recent experimental results on the dislocation dynamics in a two-dimensional plasma crystal are reviewed. A single layer of micron-size microspheres was suspended in the sheath of a capacitively coupled rf discharge. The particles self-organized in a triangular lattice. Edge dislocations were created in pairs in this plasma crystal when the internal shear stress built up above a threshold, due to the crystal's slow differential rotation. Basic stages of dislocation nucleation were identified and studied, from gradual pile-up of shear strain in the crystal to eventual escape of free dislocations. After nucleation, dislocations moved supersonically with respect to the shear waves and generated shear-wave Mach cones (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Crystal structure of a polar nematogen 4-(trans- 4-undecylcyclohexyl) isothiocyanatobenzene

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007
S. Biswas
Abstract Crystal and molecular structures of a nematogenic compound 4-(trans- 4-undecylcyclohexyl) isothiocyanatobenzene (11CHBT) have been determined by direct methods using single crystal X-ray diffraction data. The compound (C24H37N1S1) crystallizes in the monoclinic system with the space group P21/c and Z = 4. The unit cell parameters are a = 5.5539(11) Å, b = 8.1341(10) Å, c = 51.494(5) Å, and (= 91.127(14)0. The structure was refined to Rw = 0.051. The molecule is found to be slightly bow-shaped though the alkyl chain is in all- trans conformation. The phenyl ring and the alkyl chain are planar and the cyclohexyl group is in chair conformation. The isothiocyanato groups are almost linear. Parallel imbricated mode of packing of the molecules is found in the crystalline state which is precursor to the nematic phase structure. There are many van der Waals' interactions particularly in the isothiocyanato benzene part of the molecule. Of the various associated pairs of molecules the one having anti-parallel configuration with overlaps in the isothiocyanato phenyl group probably exists in both the crystalline and the nematic phases. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Configuration of Octahedral Metal Compounds , Equilibrium, Crystal and Molecular Structure of Nickel(II) Complexes of Linear N2O4, N4S2 or N6 Donors Set Atoms Ligands

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2004
Aminou Mohamadou
Abstract Two new nickel(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesised as perchlorate salts and characterised by X-ray crystallography and ligand-field spectroscopy. In both complexes the Ni2+ ion is hexacoordinate. The cation [Ni(pydado)]2+ is pseudo-octahedral with the two pyridyl groups in trans position; all Ni,N and Ni,O bond lengths are practically equivalent. In [Ni(pydadt)]2+ complex, however, the size of the thioether sulfur atoms imposes a C2v symmetry; the pyridyl groups and the sulfur atoms are in trans positions and all Ni,N bond lengths are equivalent. The comparison of these structures with those of octahedral cobalt, copper and zinc complexes with the same ligands shows that their configurations depend not only on the nature of the two central donor atoms of the ligand, but also on the nature of the metallic ion. In aqueous solution, the stability constants of the NiII chelates with these two ligands, determined by potentiometry, show the formation of [Ni(LH)]3+ and [NiL]2+ species in all cases. The chelating power of the pydadt ligand is slightly greater than that of pydado. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

In the Search of Glycogen Phosphorylase Inhibitors: Synthesis of C- D -Glycopyranosylbenzo(hydro)quinones , Inhibition of and Binding to Glycogen Phosphorylase in the Crystal,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2007
Li He
Abstract Penta- O -acetyl-,- D -glycopyranoses and 1,4-dimethoxybenzene led selectively by electrophilic substitution to C-,- D -glycopyranosyl-1,4-dimethoxybenzenes which were converted by simple and efficient reactions (oxidation, reduction and deacetylation) to the corresponding C-glycosylhydro- and C-glycosylbenzoquinones, with either an acetylated or deprotected sugar moiety. C-,- D -Glucosylbenzoquinone 19 and C-,- D -Glucosylhydroquinone 23 were found to be competitive inhibitors of rabbit muscle glycogen phosphorylase b (GPb), with respect to the substrate ,- D -glucose-1-phosphate, with Ki values of 1.3 and 0.9 mM, respectively, whereas C-,- D -glucosylhydroquinone 17 was not effective up to a concentration of 8 mM. In order to elucidate the structural basis of inhibition, we determined the crystal structures of 19 and 23 in complex with GPb at a 2.03,2.05 Å resolution. The complex structures reveal that the inhibitors can be accommodated at the catalytic site at approximately the same position as ,- D -glucose and stabilise the transition state conformation of the 280s loop by making several favourable contacts to Asp283 and Asn284 of this loop. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

MBSJ MCC Young Scientist Award 2009 REVIEW: Structural basis of protein disulfide bond generation in the cell

GENES TO CELLS, Issue 9 2010
Kenji Inaba
The formation of protein disulfide bonds is an oxidative reaction that is crucial for the folding and maturation of many secreted and membrane proteins. Both prokaryotic and eukaryotic cells possess various disulfide oxidoreductases and redox-active cofactors to accelerate this oxidative reaction in a correct manner. Crystal or solution structures have been solved for some of the oxidoreductases in the past 10 years, leading to remarkable progress in the field of thiol-based redox cell biology. Consequently, structural and mechanistic similarities in the disulfide bond formation pathways have been uncovered. This review highlights the molecular basis of the elaborate oxidative systems operating in the Escherichia coli periplasm, the endoplasmic reticulum lumen and the mitochondrial intermembrane space. The accumulated knowledge provides important insights into how protein and redox homeostasis are maintained in the cell. [source]

A Stimuli-Responsive, Photoluminescent, Anthracene-Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical Processes

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
Yoshimitsu Sagara
Abstract Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable,stable phase transition induced by external stimuli is prepared. A 2,6-diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6-diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid-crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic-columnar phase transition induced by heating or mechanical shearing for this 2,6-diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable,stable LC phase transition. [source]

Analysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum Oxidxe

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Sang-Wan Ryu
Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source]

Further Characterisation of the 91500 Zircon Crystal

GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2004
Michael Wiedenbeck
zircon 91500; matériau de référence; intercomparaison entre techniques; valeurs de travail This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses. Cet article présente les résultats d'une nouvelle caractérisation du zircon 91500, dont des données de microanalyse par sonde électronique, d'analyse par ablation laser en couplage à un ICP-MS, d'analyse par sonde ionique (SIMS) et d'analyse par fluorination laser. Le but de cette étude etait de démontrer que ce large monocristal de zircon pouvait être utilisé pour la calibration d'analyses in situ de Terres Rares et des isotopes de I'Oxygène, et en même temps de fournir des valeurs "de travail" pour un certain nombre de systémes géochimiques cruciaux. En complément des tests systématiques d'homogénéité de I'échantillon, tant chimiquement que structurellement, /'ex/sfence, dans le zircon 91500, de zonages visibles en électrons retro diffusés et en cathodoluminescence, est décrite en détail, line comparaison en aveugle des résultats obtenus par LA-ICP-MS et par SIMS, dans des laboratoires différents, montre que les différences systématiques entre les ensembles de données obtenues par ces deux techniques sont très faibles. De plus, I'utilisation du verre NIST SRM 610 comme calibrant lors de I'analyse par SIMS n'introduit qu'une erreur systématique très faible si ce n'est inexistante sur les résultats du zircon. Sur la base des analyses par fluorination laser et par SIMS, le zircon 91500 semble être parfaitement adapte a son utilisation pour la calibration d'analyses isotopiques in situ d'oxygène. [source]

UV-vis-Induced Vitrification of a Molecular Crystal,

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2007
T. Naito
Abstract A charge-transfer complex of 2,5-dimethyl- N,N,-dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)2, defined as ,) is irreversibly transformed by UV-vis illumination. Depending on the illumination conditions, three new types of solids (defined as ,, ,, and ,) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid-state, high-resolution, cross-polarization magic angle spinning (CP-MAS) 13C,NMR, elemental analysis (EA), mass spectrometry (MS), X-ray absorption fine structure (XAFS), and powder X-ray diffraction (XRD). The CP-MAS, EA, MS, and XAFS results indicate that compound , is a glass state of Ag(DM)2. The transformation from crystalline (,) to amorphous (,) solid Ag(DM)2 is an irreversible exothermic glass transition (glass-transition temperature 155.2,°C; ,H,=,,126.8,kJ,mol,1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound , (Ag(DM)1.5) consists of silver nanoparticles (diameter (7,±,2),nm ) dispersed in a glassy matrix of neutral DM molecules. The N,CN,Ag coordination bonds of the , form are not maintained in the , form. Decomposition of , by intense illumination results in a white solid (,), identified as being composed of silver nanoparticles (diameter (60,±,10),nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both , and , are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver. [source]

Silicon-Based Near-Visible Logpile Photonic Crystal

ADVANCED MATERIALS, Issue 37 2010
Ganapathi Subramania
A nanocavity structure is embedded inside a silicon logpile photonic crystal that demonstrates tunable absorption behavior at near visible wavelengths well beyond the absorption edge of silicon. This is due to silicon's indirect bandgap resulting in a relatively slow increase in the absorption of silicon with decreasing wavelength. Our results open up the possibility of utilizing the wide, complete three dimensional photonic gap enabled by the large refractive index of silicon to create three dimensional photonic crystal based devices well into the visible regime. [source]

Self-Assembled Organic,Inorganic Hybrid Elastic Crystal via Biomimetic Mineralization

ADVANCED MATERIALS, Issue 33 2010
Halei Zhai
Organic,inorganic hybrid rhombs with regular shape and a lamellar superstructure are biomimetically fabricated by the cooperative self-assembly of bovine serum albumin (BSA), sodium bis-2-ethylhexyl sulfosuccinate (AOT), and calcium phosphate (see figure). Although crystalline calcium phosphate is the main component, the hybrid crystals are elastic and they can be flexible under external stresses. [source]

Photonic Crystal Formed by the Imaginary Part of the Refractive Index

ADVANCED MATERIALS, Issue 24 2010
Juntao Li
A periodic array of dye-doped disks that form a 2D photonic lattice is fabricated and characterized. The array was generated by interference lithography, and the voids of the template were filled by SU8 without doping. This creates a photonic lattice with a uniform real part of the refractive index, but a periodically modulated imaginary part. The structure is characterized by diffraction measurements; the structure only diffracts light in the spectral range where the dye absorbs, hence acts like a truly imaginary index photonic crystal. [source]

N -substituted bis(tetrazol-5-yl)diazenes: Synthesis, spectra, X-ray molecular and crystal structures, and quantum-chemical DFT calculations

HETEROATOM CHEMISTRY, Issue 1 2010
Tatiyana V. Serebryanskaya
N -Substituted bis(tetrazol-5-yl)diazenes (substituents are 1-CH3 (3a), 1-Ph (3b), 2-CH3 (3c), and 2- tBu (3d)) were synthesized by oxidative coupling of corresponding 5-aminotetrazoles. All compounds were characterized with 1H and 13C NMR, IR- and UV-spectroscopy, and thermal analysis. Crystal and molecular structures of bis(1-phenyltetra- zol-5-yl)diazene (3b) and bis(2- tert -butyltetrazol-5-yl)diazene (3d) were determined by single crystal X-ray diffraction. Molecules of these compounds are trans-isomers in solid. According to X-Ray data, 3b molecule is S-trans-S-trans conformer, however 3d is S-cis-S-cis one. Quantum-chemical investigation of geometry and relative stability of cis- and trans-isomers and stable conformations of compounds 3a,d was carried out. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:24,35, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20574 [source]

Crystal and molecular structures of atropisomeric N -aryl-1,2,3,4-tetrahydro-3,3-dimethyl-2,4-quinolinediones

HETEROATOM CHEMISTRY, Issue 3 2008
Mario Cetina
The crystal structures of N -aryl-1,2,3,4-tetrahydro-3,3-dimethyl-2,4-quinolinediones bearing methoxy- (1), methyl- (2), and chloro- (3) substituents in 2,-position of the phenyl ring have been determined by X-ray crystal structure analysis. The heterocyclic ring in 1,3 adopts an envelope conformation, with the smallest ring puckering in the ortho-chloro derivative 3. The N -aryl ring is almost perpendicular with respect to the quinoline-2,4-dione ring. The corresponding dihedral angle values are 83.2(1)°, 80.0(9)°, and 83.4(2)° in 1, 2 and 3, respectively. The hydrogen bond of CH,,,O type joins the molecules of the ortho-methoxy derivative 1 into dimers. The supramolecular structure also contains two CH,,,, interactions that link the hydrogen-bonded dimers into sheets. In ortho-methyl derivative 2, one CH,,,, interaction generates infinite chains, whereas two CH,,,O hydrogen bonds and three CH,,,, interactions in the ortho-chloro derivative 3 form three-dimensional framework. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:325,331, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20436 [source]

Log-Pile TiO2 Photonic Crystal for Light Control at Near-UV and Visible Wavelengths

ADVANCED MATERIALS, Issue 4 2010
Ganapathi Subramania
Three-dimensional photonic crystals with an omnidirectional bandgap at visible frequencies can have significant impact on solid-state lighting and solar-energy conversion. Using a procedure based on multistep electron-beam lithographic processing, a 9-layer log-pile photonic crystal is fabricated composed of 70-nm-wide titanium dioxide rods with 250-nm lattice spacing that exhibit a stacking direction bandgap between 400,nm and 500,nm (see image). [source]

Piezoelectric and Electric-Field-Induced Properties of a Ferroelectric Bent-Core Liquid Crystal

ADVANCED MATERIALS, Issue 37 2009
Antal Jákli
A new adamantane bent-core liquid crystal exhibiting a metastable ferroelectric phase with large polarization is synthesized and characterized. The material shows reversible switching between a birefringent (opaque) and an optically isotropic (clear) state. In the clear state, the observed piezoelectric constant is comparable to those of commercial solid-state piezotransducers. [source]

Isolation of transcripts from Diabrotica virgifera virgifera LeConte responsive to the Bacillus thuringiensis toxin Cry3Bb1

INSECT MOLECULAR BIOLOGY, Issue 3 2010
A. Sayed
Abstract Crystal (Cry) proteins derived from Bacillus thuringiensis (Bt) have been widely used as a method of insect pest management for several decades. In recent years, a transgenic corn expressing the Cry3Bb1 toxin has been successfully used for protection against corn rootworm larvae (genus Diabrotica). The biological action of the Bt toxin in corn rootworms has not yet been clearly defined. Because development of resistance to Bt by corn rootworms will have huge economic and ecological costs, insight into larval response to Bt toxin is highly desirable. We identified 19 unique transcripts that are differentially expressed in D. virgifera virgifera larvae reared on corn transgenic for Cry3Bb1. Putative identities of these genes were consistent with impacts on metabolism and development. Analysis of highly modulated transcripts resulted in the characterization of genes coding for a member of a cysteine-rich secretory protein family and a glutamine-rich membrane protein. A third gene that was isolated encodes a nondescript 132 amino acid protein while a fourth highly modulated transcript could not be further characterized. Expression patterns of these four genes were strikingly different between susceptible and resistant western corn rootworm populations. These genes may provide useful targets for monitoring of Bt exposure patterns and resistance development in pest and non-target insect populations. [source]

Nanorod-Driven Orientational Control of Liquid Crystal for Polarization-Tailored Electro-Optic Devices

ADVANCED MATERIALS, Issue 9 2009
Somobrata Acharya
Dispersion of ultranarrow ZnS nanorods of molecular dimensions encapsulated by a fluid-like soft organic layer in the nematic liquid crystal (LC ZLI-4792) results in a novel soft-matter-type blend with previously unachieved electro-optic properties. The local ordering of the nanorods significantly affects the global ordering of the blend, allowing a more rapid response. [source]

Internally Referenced Ammonia Sensor Based on an Electrochemically Prepared Porous SiO2 Photonic Crystal,

ADVANCED MATERIALS, Issue 22 2007
H. King
An oxidized porous silicon photonic crystal possessing two reflectance peaks is infused with bromothymol blue, yielding a pH-responsive ammonia vapor sensor. One reflectance peak overlaps the absorbance band of the deprotonated dye while the other appears in a "clear" spectral region. Simultaneous monitoring of both reflectance peaks corrects for large changes in probe light intensity. [source]

A Two-Dimensional KTiOPO4 Photonic Crystal Grown Using a Macroporous Silicon Template,

ADVANCED MATERIALS, Issue 17 2006
A. Peña
2D KTiOPO4 photonic crystals are fabricated using a silicon membrane of air holes as a template. Columns of KTiOPO4 are grown by liquid-phase epitaxy from a substrate into such air holes. The crystallographic orientation of the columns is the same as that of the substrate. The photonic-crystal properties of the fabricated structures and their capability to generate second-harmonic light are experimentally demonstrated. [source]

Self-Assembled Silica Photonic Crystal as a Liquid-Crystal Alignment Layer and its Electro-optic Applications in Fabry,Perot Cavity Structures,

ADVANCED MATERIALS, Issue 19 2004
Y. Ha
Microgrooves on self-assembled photonic-crystal (PC) films align liquid crystals (LCs) without any additional rubbing or surface treatment. Nematic (see Figure and inside cover) or twisted-nematic LCs can be formed, depending on the relative orientation of the microgrooved films. A LC Fabry,Perot (FP) cavity was fabricated using these PC films, and electro-optic tuning of FP cavity modes is demonstrated. [source]

Nucleation of Hydroxyapatite Crystal through Chemical Interaction with Collagen

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000
Sang-Hoon Rhee
The nucleation of hydroxyapatite (HAp) crystal through chemical interaction with collagen was investigated. A collagen membrane was soaked in a supersaturated simulated body fluid (1.5 SBF) solution with ion concentrations at 1.5 times that of normal simulated body fluid (1.0 SBF). A few carbonate-containing HAp crystals were formed mostly on the edge-side of the collagen membrane after 4 weeks. In the Fourier-transform infrared spectometry (FTIR) results, the carboxylate band of the collagen membrane showed red chemical shifts after the formation of HAp crystals, which coincided well with the decrease of the calculated bond orders of the carboxylate group when chelated with a calcium ion, which emulated the first-step nucleation of HAp crystal on the carboxylate group of collagen. The result implies that the binding of a calcium ion to the carboxylate group of collagen is one of the key factors for the nucleation of HAp crystals in a 1.5 SBF solution. [source]

Synergistic Ordering of Side-Group Liquid Crystal Polymer and Small Molecule Liquid Crystal: Order and Phase Behavior of Nematic Polymer Solutions,

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19-20 2007
Neal R. Scruggs
Abstract Addition of a small-molecule liquid crystal (5CB) to a cyanobiphenyl-based side-group liquid crystal polymer (SGLCP) stabilizes nematic order, increasing the isotropization temperature (TNI) more than 15,°C. Despite synergistic ordering at high concentration, small amounts of polymer destabilize nematic order. Even though TNI(SGLCP) is 27,°C greater than TNI(5CB), 2H NMR shows that the order parameter of the SGLCP is less than that of 5CB at concentrations for which monodomains were accessible (,10 wt.-%). The results imply that nematic order is frustrated in the bulk polymer and addition of small molecule LC relaxes this frustration by allowing greater configurational freedom. Conversely, adding small amounts of polymer to the bulk 5CB introduces frustration, resulting in the strong asymmetry of the phase diagram. [source]

Crystal mismatched layers in pentagonal nanorods and nanoparticles

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010
L. M. Dorogin
Abstract Pentagonal nanorods (PNRs) and nanoparticles (PNPs) covered by mismatched shell layers are theoretically investigated. Mechanical stresses and elastic energies of such objects are calculated analytically and analyzed in the framework of linear isotropic elasticity. Difference between elastic modules of core and shell is taken into account. The threshold radiuses as the minimal radiuses of PNR and PNP for which the formation of the shell layer is energetically favorable are found. The threshold radius is approximately 10,nm for PNPs and 100,nm for PNRs of typical face-centered cubic (FCC) metals. The optimal magnitudes of mismatch parameter giving the maximal energy release for shelled PNRs and PNPs are determined. [source]

Multiscale simulation of polycrystal mechanics of textured ,-Ti alloys using ab initio and crystal-based finite element methods

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008
D. Ma
Abstract Crystal-based finite element methods (FEM) are versatile continuum approaches for predicting mechanical properties and deformation-induced crystallographic textures. They can be applied to both, elastic,plastic and elastic problems. The methodology is based on (i) a detailed understanding of the underlying crystal deformation mechanisms and (ii) a number of constitutive material parameters that are often difficult to measure. First principle calculations, that take into account the discrete nature of matter at the atomic scale, are an alternative way to study mechanical properties of single crystals without using empirical parameters. In this study we demonstrate how to combine these two well-established modeling tools, viz., ab initio modeling and crystal mechanical FEM, for an improved approach to design of polycrystalline materials. The combination is based on (i) the determination of basic thermodynamic and elastic parameter trends in metallurgical alloy design using density-functional (DFT) calculations (P. Hohenberg and W. Kohn, Phys. Rev. 136, B864 (1964), W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965) [1, 2], respectively) and (ii) the up-scale transfer of these results into crystal-based finite element simulations which take into account the anisotropic nature of the elastic,plastic deformation of metals. The method is applied to three body-centered cubic (bcc, ,) Ti,Nb alloys for bio-medical applications. The study addresses two technological processes, namely, the prediction of texture evolution during cold rolling (elastic-plastic problem) and elastic bending of textured polycrystals (elastic problem). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Crystal packing in vicinal diols CnHm(OH)2

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002
Carolyn Pratt Brock
The O,H,O bonds in vic -diols CnHm(OH)2 have been studied using data retrieved from the Cambridge Structural Database. About half of these diols form complete, or almost complete, sets of intermolecular O,H,O bonds (i.e. two satisfied donors per molecule). For this half of the structures the frequencies of high-symmetry space groups and of structures with Z,,>,1 (more than one molecule in the asymmetric unit) are substantially elevated. The most common motif among fully bonded structures is an dimer, which can be linked in a variety of ways to form one-, two- or even three-dimensional patterns. Most of the other half of the vic -diols form simple O,H,O chains in which each OH group participates in only one intermolecular hydrogen bond. The space-group frequencies for this second group of structures are unexceptional. The most important factor determining the extent of O,H,O bond formation is the degree of substitution of the vic -diol. The spatial segregation of OH groups that is necessary for the formation of O,H,O bonds is found to make the dense filling of space more difficult because the intermolecular spacings that are appropriate for the O,H,O bonds may be inappropriate for the rest of the molecule. [source]

Berichtigung: Strong Two-Photon Excited Fluorescence and Stimulated Emission from an Organic Single Crystal of an Oligo(Phenylene Vinylene)

ANGEWANDTE CHEMIE, Issue 36 2010
Fei Gao
No abstract is available for this article. [source]

A Strategy for Retrospectively Mapping the Growth History of a Crystal,

ANGEWANDTE CHEMIE, Issue 30 2010
Benjamin
Wie Baumringe zählen: Ein neue Strategie zur Untersuchung von Kristallwachstumsprozessen beruht auf der retrospektiven Analyse fertiger Kristalle. Die Zusammensetzung der wachsenden Kristalloberflächen variiert während des Kristallwachstums, während die Kristallstruktur unverändert bleibt, und die Zusammensetzungsverteilung im Kristall wird durch konfokale Raman-Mikrospektrometrie erfasst (siehe Bild). [source]

An Isolated CO2 Adduct of a Nitrogen Base: Crystal and Electronic Structures,

ANGEWANDTE CHEMIE, Issue 20 2010
Claude Villiers Dr.
Jetzt auch im Kristall: CO2 bindet reversibel an das Guanidinderivat TBD. Die Struktur des zwitterionischen Addukts wurde durch Röntgenbeugung und Rechnungen untersucht (siehe Bild; links: C,blau, H,weiß, N,rosa, O,rot), und in Lösung wurde NMR-spektroskopisch ein fluxionales Verhalten nachgewiesen. [source]