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Sample records for accompanying structural phase

  1. First-order metal-insulator transition not accompanied by the structural phase transition observed in VO2-based devices

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak; Chae, Byung-Gyu; Kim, Bong-Jun; Lee, Yong-Wook; Yun, Sun-Jin; Kang, Kwang-Yong

    2006-03-01

    An abrupt first-order metal-insulator transition (MIT) is observed during the application of a switching pulse voltage to VO2-based two-terminal devices. When the abrupt MIT occurs, the structural phase transition (SPT) is investigated by a micro- Raman spectroscopy and a micro-XRD. The result shows that the MIT is not accompanied with the structural phase transition (SPT); the abrupt MIT is prior to the SPT. Moreover, any switching pulse over a threshold voltage of 7.1 V for the MIT enabled the device material to transform efficiently from an insulator to a metal. The measured delay time from the source switching pulse to an induced MIT pulse is an order of 20 nsec which is much less than a delay time of about one msec deduced by thermal model. This indicates that the first-order MIT does not occur due to thermal. We think this MIT is the Mott transition. (Reference: New J. Phys. 6 (1994) 52 (www.njp.org), Appl. Phys. Lett. 86 (2005) 242101, Physica B 369 (2005. December) xxxx)

  2. Ge L{sub 3}-edge x-ray absorption near-edge structure study of structural changes accompanying conductivity drift in the amorphous phase of Ge{sub 2}Sb{sub 2}Te{sub 5}

    SciTech Connect

    Mitrofanov, K. V.; Kolobov, A. V. Fons, P.; Wang, X.; Tominaga, J.; Tamenori, Y.; Uruga, T.; Ciocchini, N.; Ielmini, D.

    2014-05-07

    A gradual uncontrollable increase in the resistivity of the amorphous phase of phase-change alloys, such as Ge{sub 2}Sb{sub 2}Te{sub 5}, known as drift, is a serious technological issue for application of phase-change memory. While it has been proposed that drift is related to structural relaxation, no direct structural results have been reported so far. Here, we report the results of Ge L{sub 3}-edge x-ray absorption measurements that suggest that the drift in electrical conductivity is associated with the gradual conversion of tetrahedrally coordinated Ge sites into pyramidal sites, while the system still remains in the amorphous phase. Based on electronic configuration arguments, we propose that during this process, which is governed by the existence of lone-pair electrons, the concentration of free carriers in the system decreases resulting in an increase in resistance despite the structural relaxation towards the crystalline phase.

  3. Infrared spectroscopic characterization of dehydration and accompanying phase transition behaviors in NAT-topology zeolites

    SciTech Connect

    Wang, Hsiu-Wen; Bishop, David

    2012-01-01

    Relative humidity (PH2O, partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite, scolecite, and mesolite) were studied under controlled temperature and known PH2O conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction. Dehydration was characterized by the disappearance of internal H2O vibrational modes. The loss of H2O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily via the thermal motion of guest Na?/Ca2? cations and H2O molecules. The observation of different interactions of H2O molecules and Na?/Ca2? cations with host aluminosilicate frameworks under highand low-PH2O conditions indicated the development of different local strain fields, arising from cation H2O interactions in NAT-type channels. These strain fields influence the Si O/Al O bond strength and tilting angles within and between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm-1 in natrolite, 2,276 cm-1 in scolecite, and 2,176 and 2,259 cm-1 in mesolite) result from strong cation H2O Al Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na?/Ca2? cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm-1 absorption bands in mesolite also appear to be related to Na?/Ca2? order disorder that occur when mesolite loses its Ow4 H2O molecules.

  4. Mechanochromism of piroxicam accompanied by intermolecular proton transfer probed by spectroscopic methods and solid-phase changes.

    PubMed

    Sheth, Agam R; Lubach, Joseph W; Munson, Eric J; Muller, Francis X; Grant, David J W

    2005-05-11

    Structural and solid-state changes of piroxicam in its crystalline form under mechanical stress were investigated using cryogenic grinding, powder X-ray diffractometry, diffuse-reflectance solid-state ultraviolet-visible spectroscopy, variable-temperature solid-state (13)C nuclear magnetic resonance spectroscopy, and solid-state diffuse-reflectance infrared Fourier transform spectroscopy. Crystalline piroxicam anhydrate exists as colorless single crystals irrespective of the polymorphic form and contains neutral piroxicam molecules. Under mechanical stress, these crystals become yellow amorphous piroxicam, which has a strong propensity to recrystallize to a colorless crystalline phase. The yellow color of amorphous piroxicam is attributed to charged piroxicam molecules. Variable-temperature solid-state (13)C NMR spectroscopy indicates that most of the amorphous piroxicam consists of neutral piroxicam molecules; the charged species comprise only about 8% of the amorphous phase. This ability to quantify the fractions of charged and neutral molecules of piroxicam in the amorphous phase highlights the unique capability of solid-state NMR to quantify mixtures in the absence of standards. Other compounds of piroxicam, which are yellow, are known to contain zwitterionic piroxicam molecules. The present work describes a system in which proton transfer accompanies both solid-state disorder and a change in color induced by mechanical stress, a phenomenon which may be termed mechanochromism of piroxicam. PMID:15869285

  5. Simulation of phase structures

    SciTech Connect

    Lawson, J.

    1995-04-20

    This memo outlines a procedure developed by the author to extract information from phase measurements and produce a simulated phase structure for use in modeling optical systems, including characteristic optics for the Beamlet and NIF laser systems. The report includes an IDL program listing.

  6. First-Order Structural Change Accompanied by Yb Valence Transition in YbInCu4

    NASA Astrophysics Data System (ADS)

    Tsutsui, Satoshi; Sugimoto, Kunihisa; Tsunoda, Ryoma; Hirose, Yusuke; Mito, Takeshi; Settai, Rikio; Mizumaki, Masaichiro

    2016-06-01

    A diffraction experiment using high-energy X-rays was carried out on YbInCu4. Below the Yb valence transition temperature, the splitting of Bragg peaks was detected in high-order reflections. No superlattice reflections accompanying the valence ordering were found below the transition temperature. These experimental findings indicate that a structural change from a cubic structure to a tetragonal structure without valence ordering occurs at the transition temperature. Such a structural change free from any valence ordering is difficult to understand only in terms of Yb valence degrees of freedom. This means that the structural change may be related to electronic symmetries such as quadrupolar degrees of freedom as well as to the change in Yb valence.

  7. Activation of Alpha Chymotrypsin by Three Phase Partitioning Is Accompanied by Aggregation

    PubMed Central

    Rather, Gulam Mohmad; Mukherjee, Joyeeta; Halling, Peter James; Gupta, Munishwar Nath

    2012-01-01

    Precipitation of alpha chymotrypsin in the simultaneous presence of ammonium sulphate and t-butanol (three phase partitioning) resulted in preparations which showed self aggregation of the enzyme molecules. Precipitation with increasing amounts of ammonium sulphate led to increasing size of aggregates. While light scattering estimated the hydrodynamic diameter of these aggregates in the range of 242–1124 nm; Nanoparticle tracking analysis (NTA) gave the value as 130–462 nm. Scanning electron microscopy and gel filtration on Sephadex G-200 showed extensive aggregation in these preparations. Transmission electron microscopy showed that the aggregates had irregular shapes. All the aggregates had about 3× higher catalytic activity than the native enzyme. These aggregates did not differ in λmax of fluorescence emission which was around 340 nm. However, all the aggregates showed higher fluorescence emission intensity. Far-UV and near-UV circular dichroism also showed no significant structural changes as compared to the native molecule. Interestingly, HPLC gel filtration (on a hydroxylated silica column) gave 14 nm as the diameter for all preparations. Light scattering of preparations in the presence of 10% ethylene glycol also dissociated the aggregates to monomers of 14 nm. Both these results indicated that hydrophobic interactions were the driving force behind this aggregation. These results indicate: (1) Even without any major structural change, three phase partitioning led to protein molecules becoming highly prone to aggregation. (2) Different methods gave widely different estimates of sizes of aggregates. It was however possible to reconcile the data obtained with various approaches. (3) The nature of the gel filtration column is crucial and use of this technique for refolding and studying aggregation needs a rethink. PMID:23239966

  8. Evolution of structure during phase transitions

    SciTech Connect

    Martin, J.E.; Wilcoxon, J.P.; Anderson, R.A.

    1996-03-01

    Nanostructured materials can be synthesized by utilizing the domain growth that accompanies first-order phase separation. Structural control can be achieved by appropriately selecting the quench depth and the quench time, but in order to do this in a mindful fashion one must understand the kinetics of domain growth. The authors have completed detailed light scattering studies of the evolution of structure in both temperature- and field-quenched phase transitions in two and three dimensional systems. They have studied these systems in the quiescent state and in shear and have developed theoretical models that account for the experimental results.

  9. Supersolid phase accompanied by a quantum critical point in the intermediate coupling regime of the Holstein model.

    PubMed

    Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo

    2014-12-31

    We reveal that electron-phonon systems described by the Holstein model on a bipartite lattice exhibit, away from half filling, a supersolid (SS) phase characterized by coexisting charge order (CO) and superconductivity (SC), and an accompanying quantum critical point (QCP). The SS phase, demonstrated by the dynamical mean-field theory with a quantum Monte Carlo impurity solver, emerges in the intermediate-coupling regime, where the peak of the Tc dome is located and the metal-insulator crossover occurs. On the other hand, in the weak- and strong-coupling regimes the CO-SC boundary is of first order with no intervening SS phases. The QCP is associated with the continuous transition from SS to SC and characterized by a reentrant behavior of the SS around it. We further show that the SS-SC transition is hallmarked by diverging charge fluctuations and a kink (peak) in the superfluid density. PMID:25615362

  10. Supersolid Phase Accompanied by a Quantum Critical Point in the Intermediate Coupling Regime of the Holstein Model

    NASA Astrophysics Data System (ADS)

    Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo

    2014-12-01

    We reveal that electron-phonon systems described by the Holstein model on a bipartite lattice exhibit, away from half filling, a supersolid (SS) phase characterized by coexisting charge order (CO) and superconductivity (SC), and an accompanying quantum critical point (QCP). The SS phase, demonstrated by the dynamical mean-field theory with a quantum Monte Carlo impurity solver, emerges in the intermediate-coupling regime, where the peak of the Tc dome is located and the metal-insulator crossover occurs. On the other hand, in the weak- and strong-coupling regimes the CO-SC boundary is of first order with no intervening SS phases. The QCP is associated with the continuous transition from SS to SC and characterized by a reentrant behavior of the SS around it. We further show that the SS-SC transition is hallmarked by diverging charge fluctuations and a kink (peak) in the superfluid density.

  11. Site-Specific Structural Variations Accompanying Tubular Assembly of the HIV-1 Capsid Protein

    PubMed Central

    Bayro, Marvin J.; Chen, Bo; Yau, Wai-Ming; Tycko, Robert

    2014-01-01

    The 231-residue capsid (CA) protein of HIV-1 spontaneously self-assembles into tubes with a hexagonal lattice that is believed to mimic the surface lattice of conical capsid cores within intact virions. We report the results of solid state nuclear magnetic resonance (NMR) measurements on HIV-1 CA tubes that provide new information regarding changes in molecular structure that accompany CA self-assembly, local dynamics within CA tubes, and possible mechanisms for the generation of lattice curvature. This information is contained in site-specific assignments of signals in two- and three-dimensional solid state NMR spectra, conformation-dependent 15N and 13C NMR chemical shifts, detection of highly dynamic residues under solution NMR conditions, measurements of local variations in transverse spin relaxation rates of amide 1H nuclei, and quantitative measurements of site-specific 15N-15N dipole-dipole couplings. Our data show that most of the CA sequence is conformationally ordered and relatively rigid in tubular assemblies and that the structures of N-terminal and C-terminal domains (NTD and CTD) observed in solution are largely retained. However, specific segments, including the N-terminal β-hairpin, the cyclophilin A binding loop, the inter-domain linker, segments involved in intermolecular NTD-CTD interactions, and the C-terminal tail, have substantial static or dynamical disorder in tubular assemblies. Other segments, including the 310-helical segment in CTD, undergo clear conformational changes. Structural variations associated with curvature of the CA lattice appear to be localized in the inter-domain linker and intermolecular NTD-CTD interface, while structural variations within NTD hexamers, around local three-fold symmetry axes, and in CTD-CTD dimerization interfaces are less significant. PMID:24370930

  12. Grain size dependence of elastic anomalies accompanying the α β phase transition in polycrystalline quartz

    NASA Astrophysics Data System (ADS)

    McKnight, Ruth E. A.; Moxon, T.; Buckley, A.; Taylor, P. A.; Darling, T. W.; Carpenter, M. A.

    2008-02-01

    The effects of grain size on the elastic properties of quartz through the α-β phase transition have been investigated by resonant ultrasound spectroscopy. It is found that there are three regimes, dependent on grain size, within which elastic properties show different evolutions with temperature. In the large grain size regime, as represented by a quartzite sample with ~100-300 µm grains, microcracking is believed to occur in the vicinity of the transition point, allowing grains to pull apart. In the intermediate grain size regime, as represented by novaculite (1-5 µm grain size) and Ethiebeaton agate (~120 nm grain size), bulk and shear moduli through the transition follow closely the values expected from averages of single crystal data. The novaculite sample, however, has a transition temperature ~7 °C higher than that of single crystal quartz. This is assumed to be due to the development of internal pressure arising from anisotropic thermal expansion. In the small grain size region, agates from Mexico (~65 nm) and Brazil (~50 nm) show significant reductions in the amount of softening of the bulk modulus as the transition point is approached from below. This is consistent with a tendency for the transition to become more second order in character. The apparent changes towards second order character do not match quantitative predictions for samples with homogeneous strain across elastically clamped nanocrystals, however. Some of the elastic variations are also due to the presence of moganite in these samples. True 'nanobehaviour' for quartz in ceramic samples thus appears to be restricted to grain sizes of less than ~50 nm.

  13. Shearing instabilities accompanying high-pressure phase transformations and the mechanics of deep earthquakes

    PubMed Central

    Green, Harry W.

    2007-01-01

    Deep earthquakes have been a paradox since their discovery in the 1920s. The combined increase of pressure and temperature with depth precludes brittle failure or frictional sliding beyond a few tens of kilometers, yet earthquakes occur continually in subduction zones to ≈700 km. The expected healing effects of pressure and temperature and growing amounts of seismic and experimental data suggest that earthquakes at depth probably represent self-organized failure analogous to, but different from, brittle failure. The only high-pressure shearing instabilities identified by experiment require generation in situ of a small fraction of very weak material differing significantly in density from the parent material. This “fluid” spontaneously forms mode I microcracks or microanticracks that self-organize via the elastic strain fields at their tips, leading to shear failure. Growing evidence suggests that the great majority of subduction zone earthquakes shallower than 400 km are initiated by breakdown of hydrous phases and that deeper ones probably initiate as a shearing instability associated with breakdown of metastable olivine to its higher-pressure polymorphs. In either case, fault propagation could be enhanced by shear heating, just as is sometimes the case with frictional sliding in the crust. Extensive seismological interrogation of the region of the Tonga subduction zone in the southwest Pacific Ocean provides evidence suggesting significant metastable olivine, with implication for its presence in other regions of deep seismicity. If metastable olivine is confirmed, either current thermal models of subducting slabs are too warm or published kinetics of olivine breakdown reactions are too fast. PMID:17468397

  14. Jahn-Teller solitons, structural phase transitions, and phase separation.

    PubMed

    Clougherty, Dennis P

    2006-02-01

    It is demonstrated that under common conditions a molecular solid subject to Jahn-Teller interactions supports stable Q-ball-like nontopological solitons. Such solitons represent a localized lump of excess electric charge in periodic motion accompanied by a time-dependent shape distortion of a set of adjacent molecules. The motion of the distortion can correspond to a true rotation or to a pseudorotation about the symmetric shape configuration. These solitons are stable for Jahn-Teller coupling strengths below a critical value; however, as the Jahn-Teller coupling approaches this critical value, the size of the soliton diverges signaling an incipient structural phase transition. The soliton phase mimics features commonly attributed to phase separation in complex solids. PMID:16486846

  15. Jahn-Teller Solitons, Structural Phase Transitions, and Phase Separation

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis P.

    2006-02-01

    It is demonstrated that under common conditions a molecular solid subject to Jahn-Teller interactions supports stable Q-ball-like nontopological solitons. Such solitons represent a localized lump of excess electric charge in periodic motion accompanied by a time-dependent shape distortion of a set of adjacent molecules. The motion of the distortion can correspond to a true rotation or to a pseudorotation about the symmetric shape configuration. These solitons are stable for Jahn-Teller coupling strengths below a critical value; however, as the Jahn-Teller coupling approaches this critical value, the size of the soliton diverges signaling an incipient structural phase transition. The soliton phase mimics features commonly attributed to phase separation in complex solids.

  16. Electrochromic behavior of a lambda-MnO{sub 2} electrode accompanying Li{sup +}-insertion in an aqueous phase

    SciTech Connect

    Kanoh, Hirofumi; Hirotsu, Takahiro; Ooi, Kenta

    1996-03-01

    Electrochemical insertion/extraction reactions of spinel-type manganese oxide with Li{sup +} ions have been extensively studied from the standpoint of the development of alternative materials for secondary batteries. electrochromic properties of thin manganese oxide films have been examined for application to electrochromic materials. Electrochromism of spinel-type manganese oxide accompanying an Li{sup +}-insertion in an aqueous phase was examined by visual light spectrometry. An absorbance spectrum for lithiated manganese oxide gave lower absorbance in the wave-length range < 700 nm than did an Li{sup +}-extracted one. The greatest difference was observed at {approximately} 450 nm and is explained by the difference between the spectra for Mn{sup 3+} and Mn{sup 4+}. A reversible change in absorbance at 450 nm occurred with the Li{sup +}-insertion/extraction reaction. Cyclic voltammetry indicated that the absorbance change couples with the electrochemical response of the manganese oxide to Li{sup +} ions.

  17. In situ SAXS observation on metal-salt-derived alumina sol-gel system accompanied by phase separation.

    PubMed

    Tokudome, Yasuaki; Nakanishi, Kazuki; Kanamori, Kazuyoshi; Hanada, Teiichi

    2010-12-15

    The structure formation process of hierarchically porous alumina gels has been investigated by in situ small angle X-ray scattering (SAXS). The measurement was performed on the sol-gel solution containing aluminum chloride hexahydrate (AlCl(3)·6H(2)O), poly(ethylene oxide) (PEO), and propylene oxide (PO). The temporal divergence of scattering intensity in the low q regime was observed in the early stage of reaction, indicating that the occurrence of spinodal-decomposition-type phase separation. Detailed analysis of the SAXS profiles revealed that phase separation occurs between weakly branched polymerizing aluminum hydroxide (AH) and PEO. Further progress of the condensation reaction forms phase-separated two phases, that is, AH-rich phase and PEO-rich phase with the micrometer-range heterogeneity. The growth and aggregation of primary particles occurs in the phase-separated AH-rich domain, and therefore, the addition of PEO influences on the structure in nanometer regime as well as micrometer regime. The moderate stability of oligomeric species allows homogeneous condensation reaction parallel to phase separation and successful formation of hierarchically porous alumina gel. PMID:20822775

  18. Orientational bonding of phases accompanying directed crystallization of the eutectic of the system Si-TiSi2

    NASA Astrophysics Data System (ADS)

    Derevyagina, L. S.; Butkevich, L. M.

    1987-09-01

    The characteristic features of structure formation in cast and direct crystallized alloys of the system Si-TiSi2 were studied. It is shown that the predominant orientation of the bonding of the phases in directionally crystallized eutectics (DE) of the system Si-TiSi2, observed at the stage of steady-state growth, already appears on the surface of nucleation, which apparently indicates that the nucleation of the phases in the alloys of this system is of an epitaxial character.

  19. Structural alteration of cell wall pectins accompanies pea development in response to cold.

    PubMed

    Baldwin, Laëtitia; Domon, Jean-Marc; Klimek, John F; Fournet, Françoise; Sellier, Hélène; Gillet, Françoise; Pelloux, Jérôme; Lejeune-Hénaut, Isabelle; Carpita, Nicholas C; Rayon, Catherine

    2014-08-01

    Pea (Pisum sativum) cell wall metabolism in response to chilling was investigated in a frost-sensitive genotype 'Terese' and a frost-tolerant genotype 'Champagne'. Cell walls isolated from stipules of cold acclimated and non-acclimated plants showed that cold temperatures induce changes in polymers containing xylose, arabinose, galactose and galacturonic acid residues. In the tolerant cultivar Champagne, acclimation is accompanied by increases in homogalacturonan, xylogalacturonan and highly branched Rhamnogalacturonan I with branched and unbranched (1→5)-α-arabinans and (1→4)-β-galactans. In contrast, the sensitive cultivar Terese accumulates substantial amounts of (1→4)-β-xylans and glucuronoxylan, but not the pectins. Greater JIM7 labeling was observed in Champagne compared to Terese, indicating that cold acclimation also induces an increase in the degree of methylesterification of pectins. Significant decrease in polygalacturonase activities in both genotypes were observed at the end of cold acclimation. These data indicate a role for esterified pectins in cold tolerance. The possible functions for pectins and their associated arabinans and galactans in cold acclimation are discussed. PMID:24837358

  20. Hippocampal Structural Plasticity Accompanies the Resulting Contextual Fear Memory Following Stress and Fear Conditioning

    ERIC Educational Resources Information Center

    Giachero, Marcelo; Calfa, Gaston D.; Molina, Victor A.

    2013-01-01

    The present research investigated the resulting contextual fear memory and structural plasticity changes in the dorsal hippocampus (DH) following stress and fear conditioning. This combination enhanced fear retention and increased the number of total and mature dendritic spines in DH. Intra-basolateral amygdala (BLA) infusion of midazolam prior to…

  1. The charge redistribution accompanying slip and cleavage: Electronic structure calculations in alloy design

    SciTech Connect

    Eberhart, M.E.; Woodward, C.; Giamei, A.F.

    1999-08-01

    Extracting full information from electronic structure calculations requires the ability to compare differences in bonding between two molecules or solids. Often these comparisons use qualitative models of the chemical bond in an unsuccessful attempt to account for subtle variations in molecular properties. Correlating electronic structure with properties requires an unambiguous and quantifiable description of the chemical bond. Here, the authors show that such a description is contained within the geometric properties of the charge density, which can be obtained from quantum mechanical calculations. This description is used to rationalize the previously unexplained variation in the mechanical properties of a series of ordered intermetallic alloys. The ease with which this description of chemical bonding can be applied to problems, which have defied simple bonding explanations, suggests that it may be useful in accounting for the properties of any molecular system which arise from the making, breaking, or rearrangement of bonds.

  2. Redox-dependent functional switching of plant proteins accompanying with their structural changes

    PubMed Central

    Chi, Yong Hun; Paeng, Seol Ki; Kim, Min Ji; Hwang, Gwang Yong; Melencion, Sarah Mae B.; Oh, Hun Taek; Lee, Sang Yeol

    2013-01-01

    Reactive oxygen species (ROS) can be generated during the course of normal aerobic metabolism or when an organism is exposed to a variety of stress conditions. It can cause a widespread damage to intracellular macromolecules and play a causal role in many degenerative diseases. Like other aerobic organisms plants are also equipped with a wide range of antioxidant redox proteins, such as superoxide dismutase, catalase, glutaredoxin, thioredoxin (Trx), Trx reductase, protein disulfide reductase, and other kinds of peroxidases that are usually significant in preventing harmful effects of ROS. To defend plant cells in response to stimuli, a part of redox proteins have shown to play multiple functions through the post-translational modification with a redox-dependent manner. For the alternative switching of their cellular functions, the redox proteins change their protein structures from low molecular weight to high molecular weight (HMW) protein complexes depending on the external stress. The HMW proteins are reported to act as molecular chaperone, which enable the plants to enhance their stress tolerance. In addition, some transcription factors and co-activators have function responding to environmental stresses by redox-dependent structural changes. This review describes the molecular mechanism and physiological significance of the redox proteins, transcription factors and co-activators to protect the plants from environmental stresses through the redox-dependent structural and functional switching of the plant redox proteins. PMID:23898340

  3. Alteration of citrine structure by hydrostatic pressure explains the accompanying spectral shift

    PubMed Central

    Barstow, Buz; Ando, Nozomi; Kim, Chae Un; Gruner, Sol M.

    2008-01-01

    A protein molecule is an intricate system whose function is highly sensitive to small external perturbations. However, no examples that correlate protein function with progressive subangstrom structural perturbations have thus far been presented. To elucidate this relationship, we have investigated a fluorescent protein, citrine, as a model system under high-pressure perturbation. The protein has been compressed to produce deformations of its chromophore by applying a high-pressure cryocooling technique. A closely spaced series of x-ray crystallographic structures reveals that the chromophore undergoes a progressive deformation of up to 0.8 Å at an applied pressure of 500 MPa. It is experimentally demonstrated that the structural motion is directly correlated with the progressive fluorescence shift of citrine from yellow to green under these conditions. This protein is therefore highly sensitive to subangstrom deformations and its function must be understood at the subangstrom level. These results have significant implications for protein function prediction and biomolecule design and engineering, because they suggest methods to tune protein function by modification of the protein scaffold. PMID:18768811

  4. Microbial community structure accompanied with electricity production in a constructed wetland plant microbial fuel cell.

    PubMed

    Lu, Lu; Xing, Defeng; Ren, Zhiyong Jason

    2015-11-01

    This study reveals the complex structure of bacterial and archaeal communities associated with a Canna indica plant microbial fuel cell (PMFC) and its electricity production. The PMFC produced a maximum current of 105 mA/m(2) by utilizing rhizodeposits as the sole electron donor without any external nutrient or buffer supplements, which demonstrates the feasibility of PMFCs in practical oligotrophic conditions with low solution conductivity. The microbial diversity was significantly higher in the PMFC than non-plant controls or sediment-only controls, and pyrosequencing and clone library reveal that rhizodeposits conversion to current were carried out by syntrophic interactions between fermentative bacteria (e.g., Anaerolineaceae) and electrochemically active bacteria (e.g., Geobacter). Denitrifying bacteria and acetotrophic methanogens play a minor role in organics degradation, but abundant hydrogenotrophic methanogens and thermophilic archaea are likely main electron donor competitors. PMID:26066972

  5. IgG4-related disease in the sinonasal cavity accompanied by intranasal structure loss.

    PubMed

    Inoue, Akiko; Wada, Kota; Matsuura, Kentaro; Osafune, Hiroshi; Ida, Yutaro; Kosakai, Arifumi; Edamatsu, Hideo

    2016-02-01

    IgG4-related disease was recently proposed under the classification of systemic chronic inflammatory disease. In the field of otolaryngology, organ-specific diagnostic criteria have been established for the occurrence of this condition in the salivary glands, but not in the sinonasal cavity. Here we report a case involving a 70-year-old man with IgG4-related disease in the sinonasal cavity. The patient, with the chief complaint of nasal bleeding, first visited a physician. However, the patient experienced recurrent bleeding with intranasal structure loss and was subsequently referred to our hospital. His IgG4 level was elevated, and histopathological examination of a tissue sample obtained from the edematous sphenoid sinus showed increased IgG4-positive plasma cells and storiform fibrosclerosis. A definitive diagnosis of IgG4-related rhinosinusitis was made on the basis of comprehensive criteria for IgG4-related disease. The disease showed a progressively destructive course that was clearly different from that of chronic sinusitis and represented a very rare case of IgG4-related rhinosinusitis. IgG4-related disease originating in the sinonasal cavity is rare, and, to the best of our knowledge, this is the first primary case of IgG4-related disease that originated in one side of the sinonasal cavity and showed progressive destruction. PMID:26104224

  6. Proteomic analysis of oil body membrane proteins accompanying the onset of desiccation phase during sunflower seed development

    PubMed Central

    Thakur, Anita; Bhatla, Satish C

    2015-01-01

    A noteworthy metabolic signature accompanying oil body (OB) biogenesis during oilseed development is associated with the modulation of the oil body membranes proteins. Present work focuses on 2-dimensional polyacrylamide gel electrophoresis (2-D PAGE)-based analysis of the temporal changes in the OB membrane proteins analyzed by LC-MS/MS accompanying the onset of desiccation (20–30 d after anthesis; DAA) in the developing seeds of sunflower (Helianthus annuus L.). Protein spots unique to 20–30 DAA stages were picked up from 2-D gels for identification and the identified proteins were categorized into 7 functional classes. These include proteins involved in energy metabolism, reactive oxygen scavenging, proteolysis and protein turnover, signaling, oleosin and oil body biogenesis-associated proteins, desiccation and cytoskeleton. At 30 DAA stage, exclusive expressions of enzymes belonging to energy metabolism, desiccation and cytoskeleton were evident which indicated an increase in the metabolic and enzymatic activity in the cells at this stage of seed development (seed filling). Increased expression of cruciferina-like protein and dehydrin at 30 DAA stage marks the onset of desiccation. The data has been analyzed and discussed to highlight desiccation stage-associated metabolic events during oilseed development. PMID:26786011

  7. Proteomic analysis of oil body membrane proteins accompanying the onset of desiccation phase during sunflower seed development.

    PubMed

    Thakur, Anita; Bhatla, Satish C

    2015-01-01

    A noteworthy metabolic signature accompanying oil body (OB) biogenesis during oilseed development is associated with the modulation of the oil body membranes proteins. Present work focuses on 2-dimensional polyacrylamide gel electrophoresis (2-D PAGE)-based analysis of the temporal changes in the OB membrane proteins analyzed by LC-MS/MS accompanying the onset of desiccation (20-30 d after anthesis; DAA) in the developing seeds of sunflower (Helianthus annuus L.). Protein spots unique to 20-30 DAA stages were picked up from 2-D gels for identification and the identified proteins were categorized into 7 functional classes. These include proteins involved in energy metabolism, reactive oxygen scavenging, proteolysis and protein turnover, signaling, oleosin and oil body biogenesis-associated proteins, desiccation and cytoskeleton. At 30 DAA stage, exclusive expressions of enzymes belonging to energy metabolism, desiccation and cytoskeleton were evident which indicated an increase in the metabolic and enzymatic activity in the cells at this stage of seed development (seed filling). Increased expression of cruciferina-like protein and dehydrin at 30 DAA stage marks the onset of desiccation. The data has been analyzed and discussed to highlight desiccation stage-associated metabolic events during oilseed development. PMID:26786011

  8. Regulation of Photochemical Energy Transfer Accompanied by Structural Changes in Thylakoid Membranes of Heat-Stressed Wheat

    PubMed Central

    Marutani, Yoko; Yamauchi, Yasuo; Miyoshi, Akihito; Inoue, Kanako; Ikeda, Ken-ichi; Mizutani, Masaharu; Sugimoto, Yukihiro

    2014-01-01

    Photosystems of higher plants alleviate heat-induced damage in the presence of light under moderate stressed conditions; however, in the absence of light (i.e., in the dark), the same plants are damaged more easily. (Yamauchi and Kimura, 2011) We demonstrate that regulating photochemical energy transfer in heat-treated wheat at 40 °C with light contributed to heat tolerance of the photosystem. Chlorophyll fluorescence analysis using heat-stressed wheat seedlings in light showed increased non-photochemical quenching (NPQ) of chlorophyll fluorescence, which was due to thermal dissipation that was increased by state 1 to state 2 transition. Transmission electron microscopy revealed structural changes in thylakoid membranes, including unstacking of grana regions under heat stress in light. It was accompanied by the phosphorylation of thylakoid proteins such as D1 and D2 proteins and the light harvesting complex II proteins Lhcb1 and Lhcb2. These results suggest that heat stress at 40 °C in light induces state 1 to state 2 transition for the preferential excitation of photosystem I (PSI) by phosphorylating thylakoid proteins more strongly. Structural changes of thylakoid membrane also assist the remodeling of photosystems and regulation of energy distribution by transition toward state 2 probably contributes to plastoquione oxidation; thus, light-driven electrons flowing through PSI play a protective role against PSII damage under heat stress. PMID:25514410

  9. Simple syllabic calls accompany discrete behavior patterns in captive Pteronotus parnellii: an illustration of the motivation-structure hypothesis.

    PubMed

    Clement, Matthew J; Kanwal, Jagmeet S

    2012-01-01

    Mustached bats, Pteronotus parnellii, are highly social and vocal. Individuals of this species roost in tight clusters, and emit an acoustically rich repertoire of calls whose behavioral significance is largely unknown. We recorded their social and vocal behaviors within a colony housed under semi-natural conditions. We also quantified the spatial spread of each bat's roosting location and discovered that this was relatively fixed and roughly confined to an individual's body width. The spatial precision in roosting was accompanied by an equally remarkable match between specific vocalizations and well-timed, discrete, identifiable postures/behaviors, as revealed by logistic regression analysis. The bodily behaviors included crouching, marking, yawning, nipping, flicking, fighting, kissing, inspecting, and fly-bys. Two echolocation-like calls were used to maintain spacing in the colony, two noisy broadband calls were emitted during fights, two tonal calls conveyed fear, and another tonal call signaled appeasement. Overall, the results establish that mustached bats exhibit complex social interactions common to other social mammals. The correspondence of relatively low frequency and noisy, broadband calls with aggression, and of tonal, high frequency calls with fear supports Morton's Motivation-Structure hypothesis, and establishes a link between motivation and the acoustic structure of social calls emitted by mustached bats. PMID:22693429

  10. Controlling the Al-doping profile and accompanying electrical properties of rutile-phased TiO2 thin films.

    PubMed

    Jeon, Woojin; Rha, Sang Ho; Lee, Woongkyu; Yoo, Yeon Woo; An, Cheol Hyun; Jung, Kwang Hwan; Kim, Seong Keun; Hwang, Cheol Seong

    2014-05-28

    The role of Al dopant in rutile-phased TiO2 films in the evaluation of the mechanism of leakage current reduction in Al-doped TiO2 (ATO) was studied in detail. The leakage current of the ATO film was strongly affected by the Al concentration at the interface between the ATO film and the RuO2 electrode. The conduction band offset of the interface increased with the increase in the Al dopant concentration in the rutile TiO2, which reduced the leakage current in the voltage region pertinent to the next-generation dynamic random access memory application. However, the Al doping in the anatase TiO2 did not notably increase the conduction band offset even with a higher Al concentration. The detailed analyses of the leakage conduction mechanism based on the quantum mechanical transfer-matrix method showed that Schottky emission and Fowler-Nordheim tunneling was the dominant leakage conduction mechanism in the lower and higher voltage regions, respectively. The chemical analyses using X-ray photoelectron spectroscopy corroborated the electrical test results. PMID:24749990

  11. Formation Structural Phase Gradients in Rail Steel During Long-Term Operation

    NASA Astrophysics Data System (ADS)

    Ivanov, Yu F.; Morozov, K. V.; Peregudov, O.; Gromov, V. E.; Popova, N. A.; Nikonenko, E. N.

    2016-01-01

    The paper presents results of the structural and phase analysis of the surface layer composition in the type R65 rail steel in its original state and after long-term operation. It is shown that long-term operation of rail steel is accompanied by its structural and phase modification at a depth of not less than 2 mm. The structural elements are detected that can be stress concentrators.

  12. Structural and dynamical transformations between neighboring dense microemulsion phases

    SciTech Connect

    Kotlarchyk, M. ); Sheu, E.Y. ); Capel, M. )

    1992-07-15

    A small-angle x-ray scattering (SAXS) study of dense AOT-water-decane microemulsions (AOT denotes sodium bis(2-ethylhexyl) sulfosuccinate) was undertaken in order to delineate clearly the phase behavior and corresponding structural transitions for AOT-plus-water volume fractions ranging from {phi}=0.60 to 0.95. Spectra were collected for temperatures between {ital T}=3 and 65 {degree}C. The resulting {ital T}-vs-{phi} phase diagram indicates three distinct structural domains when the water-to-AOT molar ratio is fixed at {ital W}=40.8, namely, the previously investigated {ital L}{sub 2} droplet phase, a high-temperature {ital L}{sub {alpha}} lamellar phase, and a low-temperature {ital L}{sub 3} phase consisting of randomly connected lamellar sheets. A significantly wide coexistence region accompanies the droplet-to-lamellar phase transition, which is demonstrated to be first order. For {ital W} between 15 and 40, an analysis of the lamellar structure using a one-dimensional paracrystal model produces a Hosemann {ital g} factor indicative of an approximately constant variation in the lamellar spacing of about 8%. The SAXS study was supplemented by dielectric-relaxation, shear-viscosity, and quasielastic light-scattering measurements in order to substantiate the observed phase transitions and further our understanding of the structural and dynamical properties of the {ital L}{sub 3} phase. It was found that the {ital L}{sub 3} phase exhibits Newtonian behavior up to a shear rate of 790 s{sup {minus}1}, in contradiction to previous theoretical considerations. The phase exhibits two distinct relaxation modes. A relaxation time of {similar to}1 ms characterizes the Brownian motion of a single lamellar sheet, while the motion of the entire interconnected sheet assembly has a relaxation time on the order of 1 s.

  13. Phase structure of soliton molecules

    SciTech Connect

    Hause, A.; Hartwig, H.; Seifert, B.; Stolz, H.; Boehm, M.; Mitschke, F.

    2007-06-15

    Temporal optical soliton molecules were recently demonstrated; they potentially allow further increase of data rates in optical telecommunication. Their binding mechanism relies on the internal phases, but these have not been experimentally accessible so far. Conventional frequency-resolved optical gating techniques are not suited for measurement of their phase profile: Their algorithms fail to converge due to zeros both in their temporal and their spectral profile. We show that the VAMPIRE (very advanced method of phase and intensity retrieval of E-fields) method performs reliably. With VAMPIRE the phase profile of soliton molecules has been measured, and further insight into the mechanism is obtained.

  14. Phase structure of soliton molecules

    NASA Astrophysics Data System (ADS)

    Hause, A.; Hartwig, H.; Seifert, B.; Stolz, H.; Böhm, M.; Mitschke, F.

    2007-06-01

    Temporal optical soliton molecules were recently demonstrated; they potentially allow further increase of data rates in optical telecommunication. Their binding mechanism relies on the internal phases, but these have not been experimentally accessible so far. Conventional frequency-resolved optical gating techniques are not suited for measurement of their phase profile: Their algorithms fail to converge due to zeros both in their temporal and their spectral profile. We show that the VAMPIRE (very advanced method of phase and intensity retrieval of E -fields) method performs reliably. With VAMPIRE the phase profile of soliton molecules has been measured, and further insight into the mechanism is obtained.

  15. Structural-phase states and wear resistance of surface formed on steel by surfacing

    SciTech Connect

    Kapralov, Evgenie V.; Raykov, Sergey V.; Vaschuk, Ekaterina S.; Budovskikh, Evgenie A. Gromov, Victor E.; Ivanov, Yuri F.

    2014-11-14

    Investigations of elementary and phase structure, state of defect structure and tribological characteristics of a surfacing, formed on a low carbon low-alloy steel by a welding method were carried out. It was revealed that a surfacing, formed on a steel surface is accompanied by the multilayer formation, and increases the wear resistance of the layer surfacing as determined.

  16. Incommensurate Structure of Phosphorus Phase IV

    SciTech Connect

    Fujihisa, Hiroshi; Gotoh, Yoshito; Yamawaki, Hiroshi; Sakashita, Mami; Takeya, Satoshi; Honda, Kazumasa; Akahama, Yuichi; Kawamura, Haruki; Ohishi, Yasuo

    2007-04-27

    There are six known phases for phosphorus at room temperature under high pressure. Only the structure of phase IV, which exists from 107 GPa to 137 GPa, remains unsolved. We performed a powder x-ray diffraction experiment and a Rietveld analysis and successfully determined its structure to be an incommensurately modulated structure by only 1 site of atomic position. High-pressure phases of halogens and chalcogens have previously been shown to have a similar modulated structure; however, phosphorus phase IV is different from them and was shown to be the third case.

  17. Reconstructive phase transition in (NH4)3TiF7 accompanied by the ordering of TiF6 octahedra.

    PubMed

    Molokeev, Maxim; Misjul, S V; Flerov, I N; Laptash, N M

    2014-12-01

    An unusual phase transition P4/mnc → Pa\\bar 3 has been detected after cooling the (NH4)3TiF7 compound. Some TiF6 octahedra, which are disordered in the room-temperature tetragonal structure, become ordered in the low-temperature cubic phase due to the disappearance of the fourfold axis. Other TiF6 octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.5-1.8 Å that implies a reconstructive phase transition. It was supposed that phases P4/mbm and Pm\\bar 3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm\\bar 3m → P4/mbm → P4/mnc → Pa\\bar 3. The interrelation between (NH4)3TiF7, (NH4)3GeF7 and (NH4)3PbF7 is found, which allows us to suppose phase transitions in relative compounds. PMID:25449615

  18. Structure of the low-temperature phase of hexafluoroethane

    NASA Astrophysics Data System (ADS)

    Klimenko, N. A.; Gal'tsov, N. N.; Prokhvatilov, A. I.

    2010-02-01

    X-Ray studies of C2F6 polycrystals have been performed in the temperature interval 6-140K. The low-temperature phase is found to have a monoclinic structure with lattice parameters at 6K a =8.9725Å, b =4.9546Å, c =9.3936Å, and β =95.07deg. The unit cell contains four molecules. The x-ray data are analyzed together with previously obtained neutron diffraction data. On this basis the space symmetry group P21/m(C2h2) is proposed for the low-temperature phase of C2F6. It is determined that the orientational structural phase transition at 103.97K of the monoclinic lattice into a cubic body-centered lattice is accompanied by a large volume jump ΔV /V=4.01%. This explains the large overcooling and overheating observed for the phases in solid hexafluoroethane. A detailed comparative analysis is performed of the crystal structure and physical properties of the solid phases of ethane and the haloethanes C2F6, C2Cl6, and C2Br6.

  19. A novel phase shifting structured illumination microscopy

    NASA Astrophysics Data System (ADS)

    Singh, Veena; Dubey, Vishesh; Ahmad, Azeem; Singh, Gyanendra; Mehta, D. S.

    2016-03-01

    This paper describes a new and novel phase shifting technique for qualitative as well as quantitative measurement in microscopy. We have developed a phase shifting device which is robust, inexpensive and involves no mechanical movement. In this method, phase shifting is implemented using LED array, beam splitters and defocused projection of Ronchi grating. The light from the LEDs are made incident on the beam splitters at spatially different locations. Due to variation in the geometrical distances of LEDs from the Ronchi grating and by sequentially illuminating the grating by switching on one LED at a time the phase shifted grating patterns are generated. The phase shifted structured patterns are projected onto the sample using microscopic objective lens. The phase shifted deformed patterns are recorded by a CCD camera. The initial alignment of the setup involves a simple procedure for the calibration for equal fringe width and intensity such that the phase shifted fringes are at equal phase difference. Three frame phase shifting algorithm is employed for the reconstruction of the phase map. The method described here is fully automated so that the phase shifted images are recorded just by switching of LEDs and has been used for the shape measurement of microscopic industrial objects. The analysis of the phase shifted images provides qualitative as well as quantitative information about the sample. Thus, the method is simple, robust and low cost compared to PZT devices commonly employed for phase shifting.

  20. Structures of diamond-like phases

    SciTech Connect

    Greshnyakov, V. A.; Belenkov, E. A.

    2011-07-15

    The diamond-like phases containing carbon atoms with the same degree of hybridization, which is close to sp{sup 3}, are classified. It is found that twenty such phases can exist, and ten of them are described for the first time. Molecular mechanics and semi-empirical quantum-mechanical methods are used to calculate the geometrically optimized structures of diamond-like phase clusters and to determine their structural parameters and properties, such as the density, the bulk modulus, and the sublimation energy. The difference between the properties of the diamond-like phases and those of diamond is found to be determined by the difference between the structures of these phases and diamond.

  1. Structural phase transitions in monolayer molybdenum dichalcogenides

    NASA Astrophysics Data System (ADS)

    Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo

    2015-03-01

    The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

  2. Shock-induced structural phase transition, plasticity, and brittle cracks in aluminum nitride ceramic.

    PubMed

    Branicio, Paulo S; Kalia, Rajiv K; Nakano, Aiichiro; Vashishta, Priya

    2006-02-17

    Atomistic mechanisms of fracture accompanying structural phase transformation (SPT) in AlN ceramic under hypervelocity impact are investigated using a 209 x 10(6) atom molecular-dynamics simulation. The shock wave generated by the impact splits into an elastic wave and a slower SPT wave that transforms the wurtzite structure into the rocksalt phase. The interaction between the reflected elastic wave and the SPT wave front generates nanovoids and dislocations into the wurtzite phase. Nanovoids coalesce into mode I cracks while dislocations give rise to kink bands and mode II cracking. PMID:16606007

  3. Exploring structural phase transitions of ion crystals

    PubMed Central

    Yan, L. L.; Wan, W.; Chen, L.; Zhou, F.; Gong, S. J.; Tong, X.; Feng, M.

    2016-01-01

    Phase transitions have been a research focus in many-body physics over past decades. Cold ions, under strong Coulomb repulsion, provide a repealing paradigm of exploring phase transitions in stable confinement by electromagnetic field. We demonstrate various conformations of up to sixteen laser-cooled 40Ca+ ion crystals in a home-built surface-electrode trap, where besides the usually mentioned structural phase transition from the linear to the zigzag, two additional phase transitions to more complicated two-dimensional configurations are identified. The experimental observation agrees well with the numerical simulation. Heating due to micromotion of the ions is analysed by comparison of the numerical simulation with the experimental observation. Our investigation implies very rich and complicated many-body behaviour in the trapped-ion systems and provides effective mechanism for further exploring quantum phase transitions and quantum information processing with ultracold trapped ions. PMID:26865229

  4. Neutral line chaos and phase space structure

    NASA Technical Reports Server (NTRS)

    Burkhart, Grant R.; Speiser, Theodore W.; Martin, Richard F., Jr.; Dusenbery, Paul B.

    1991-01-01

    Phase space structure and chaos near a neutral line are studied with numerical surface-of-section (SOS) techniques and analytic methods. Results are presented for a linear neutral line model with zero crosstail electric field. It was found that particle motion can be divided into three regimes dependening on the value of the conserved canonical momentum, Py, and the conserved Hamiltonian, h. The phase space structure, using Poincare SOS plots, is highly sensitive to bn = Bn/B0 variations, but not to h variations. It is verified that the slow motion preserves the action, Jz, as evaluated by Sonnerup (1971), when the period of the fast motion is smaller than the time scale of the slow motion. Results show that the phase space structure and particle chaos depend sensitively upon Py and bn, but are independent of h.

  5. Synthesis, Structure, and Pressure-Induced Polymerization of Li 3 Fe(CN) 6 Accompanied with Enhanced Conductivity

    DOE PAGESBeta

    Li, Kuo; Zheng, Haiyan; Hattori, Takanori; Sano-Furukawa, Asami; Tulk, Christopher A.; Molaison, Jamie; Feygenson, Mikhail; Ivanov, Ilia N.; Yang, Wenge; Mao, Ho-kwang

    2015-11-17

    By providing a new route to synthesize inorganic/organic conductors with tunable composition and properties, pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3Fe(CN)6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction andmore » Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. Moreover, the conductivity of the polymer is above 10–3 S·cm–1, which reaches the range of conductive polymers. Our investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.« less

  6. Structural phase transition in evolving networks.

    PubMed

    Kim, Sang-Woo; Noh, Jae Dong

    2009-08-01

    A network as a substrate for dynamic processes may have its own dynamics. We propose a model for networks which evolve together with diffusing particles through a coupled dynamics and investigate emerging structural property. The model consists of an undirected weighted network of fixed mean degree and randomly diffusing particles of fixed density. The weight w of an edge increases by the amount of traffics through its connecting nodes or decreases by a constant factor. Edges are removed with the probability P(rew)=1/(1+w) and replaced by new ones having w=0 at random locations. We find that the model exhibits a structural phase transition between the homogeneous phase characterized by an exponentially decaying degree distribution and the heterogeneous phase characterized by the presence of hubs. The hubs emerge as a consequence of a positive feedback between the particle and the edge dynamics. PMID:19792212

  7. Lightweight solar concentrator structures, phase 2

    NASA Technical Reports Server (NTRS)

    Williams, Brian E.; Kaplan, Richard B.

    1993-01-01

    This report summarizes the results of the program conducted by Ultramet under SBIR Phase 2 Contract NAS3-25418. The objective of this program was to develop lightweight materials and processes for advanced high accuracy Space Solar Concentrators using rigidized foam for the substrate structure with an integral optical surface.

  8. Progressive deformation of ultramafic rocks accompanied with deflection of layered structure and mylonitization culminating into a pseudotachylyte-bearing seismogenic fault - a field evidence of plastic instability

    NASA Astrophysics Data System (ADS)

    Ueda, T.; Obata, M.

    2011-12-01

    Plastic instability leading to rupture nucleation and propagetion (e.g. Hobbs et al.1986, Kelemen and Hirth, 2007) is an attractive hypothesis for deep earthquakes but lacked clear field evidences. 1D across-fault shear localization observed in some places (e.g. Jin et al.1998) is not clear if the deformation is directly related with seismicity. We present a clear field evidence of plastic instability as guided by pyroxenite/peridotite layering deflection structure (hereafter called LD structure, see figure) accompanied with mylonitization in spinel(Sp)-peridotite facies (P>~1GPa) in Balmuccia peridotite, Ivrea-Verbano Zone, Italy. The studied area contains abundant PST-bearing faults and N-S trending primary pyroxenite layers. Many faults in the area cut pyroxenite layers, but LD structure is found only in one place presented here. Many PSTs in the area have been (re)crystallized in Sp-peridotite facies, and have typically ultramylonitic texture (Ueda et al., 2008) with some injection veins. The fault with LD structure is situated in a fault system, which has two dominant attitudes with regional N-S extension. The shear strain of LD structure measured on outcrop surface is ~2.0. Near the fault, elongated Opx porphyroclasts (ellipses in figure) oblique to local layering are visible in peridotite. The dominant deformation textures are dynamic recrystallization in peridotite and kinking or undulatory extinction in pyroxenite. The mineral assemblages of the mylonite neoblast in the peridotite and the pyroxenite are Ol+Opx+Cpx+Sp+hornblende(Hbl), Cpx+Opx+Sp, respectively. Hbl typically occur only in neoblast. In the vicinity (several hundreds of micron) of the fault, dolomite(Dol) also occur in equilibrium with the assemblage above. The recrystallized grain sizes are 20-50 microns in peridotite and 10-30 microns in pyroxenite. The rarity of LD structure is consistent with general conception that deformation processes which lead to dynamic rupture initiation ought to be

  9. Structural assembly demonstration experiment, phase 1

    NASA Technical Reports Server (NTRS)

    Akin, David L.; Bowden, Mary L.; Miller, Rene H.

    1983-01-01

    The goal of this phase of the structural assembly and demonstration experiment (SADE) program was to begin to define a shuttle flight experiment that would yield data to compare on-orbit assembly operations of large space structures with neutral buoyancy simulations. In addition, the experiment would be an early demonstration of structural hardware and human capabilities in extravehicular activity (EVA). The objectives of the MIT study, as listed in the statement of work, were: to provide support in establishing a baseline neutral buoyancy testing data base, to develop a correlation technique between neutral buoyancy test results and on-orbit operations, and to prepare the SADE experiment plan (MSFC-PLAN-913).

  10. Phase and structural transformations in annealed copper coatings in relation to oxide whisker growth

    NASA Astrophysics Data System (ADS)

    Dorogov, M. V.; Priezzheva, A. N.; Vlassov, S.; Kink, I.; Shulga, E.; Dorogin, L. M.; Lõhmus, R.; Tyurkov, M. N.; Vikarchuk, A. A.; Romanov, A. E.

    2015-08-01

    We describe structural and phase transformation in copper coatings made of microparticles during heating and annealing in air in the temperature range up to 400 °C. Such thermal treatment is accompanied by intensive CuO nanowhisker growth on the coating surface and the formation of the layered oxide phases (Cu2O and CuO) in the coating interior. X-ray diffraction and focused ion beam (FIB) are employed to characterize the multilayer structure of annealed copper coatings. Formation of volumetric defects such as voids and cracks in the coating is demonstrated.

  11. Phasing macromolecular structures via structure-invariant algebra.

    PubMed

    Hauptman, H; Han, F

    1993-01-01

    Owing to the breakdown of Friedel's law when anomalous scatterers are present, unique values of the three-phase structure invariants in the whole range from 0 to 2pi are determined by measured values of diffraction intensities alone. Two methods are described for going from presumed known values of these invariants to the values of the individual phases. The first, dependent on a scheme for resolving the 2pi ambiguity in the estimate omega(HK) of the triplet phi(H) + phi(K) + phi(-H-K), solves by least squares the resulting redundant system of linear equations phi(H) + phi(K) + phi(-H-K) = omega(HK). The second attempts to minimize the weighted sum of squares of differences between the true values of the cosine and sine invariants and their estimates. The latter method is closely related to one based on the 'minimal principle' which determines the values of a large set of phases as the constrained global minimum of a function of all the phases in the set. Both methods work in the sense that they yield values of the individual phases substantially better than the values of the initial estimates of the triplets. However, the second method proves to be superior to the first but requires, in addition to estimates of the triplets, initial estimates of the values of the individual phases. PMID:15299539

  12. Electronic structure engineering of various structural phases of phosphorene.

    PubMed

    Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K

    2016-07-21

    We report the tailoring of the electronic structures of various structural phases of phosphorene (α-P, β-P, γ-P and δ-P) based homo- and hetero-bilayers through in-plane mechanical strains, vertical pressure and transverse electric field by employing density functional theory. In-plane biaxial strains have considerably modified the electronic bandgap of both homo- and hetero-bilayers while vertical pressure induces metallization in the considered structures. The γ-P homo-bilayer structure showed the highest ultimate tensile strength (UTS ∼ 6.21 GPa) upon in-plane stretching. Upon application of a transverse electric field, the variation in the bandgap of hetero-bilayers was found to be strongly dependent on the polarity of the applied field which is attributed to the counterbalance between the external electric field and the internal field induced by different structural phases and heterogeneity in the arrangements of atoms of each surface of the hetero-bilayer system. Our results demonstrate that the electronic structures of the considered hetero- and homo-bilayers of phosphorene could be modified by biaxial strain, pressure and electric field to achieve the desired properties for future nano-electronic devices. PMID:27334095

  13. Source parameters of a M4.8 and its accompanying repeating earthquakes off Kamaishi, NE Japan: Implications for the hierarchical structure of asperities and earthquake cycle

    USGS Publications Warehouse

    Uchida, N.; Matsuzawa, T.; Ellsworth, W.L.; Imanishi, K.; Okada, T.; Hasegawa, A.

    2007-01-01

    We determine the source parameters of a M4.9 ?? 0.1 'characteristic earthquake' sequence and its accompanying microearthquakes at ???50 km depth on the subduction plate boundary offshore of Kamaishi, NE Japan. The microearthquakes tend to occur more frequently in the latter half of the recurrence intervals of the M4.9 ?? 0.1 events. Our results show that the microearthquakes are repeating events and they are located not only around but also within the slip area for the 2001 M4.8 event. From the hierarchical structure of slip areas and smaller stress drops for the microearthquakes compared to the M4.8 event, we infer the small repeating earthquakes rupture relatively weak patches in and around the slip area for the M4.8 event and their activity reflects a stress concentration process and/or change in frictional property (healing) at the area. We also infer the patches for the M4.9 ?? 0.1 and other repeating earthquakes undergo aseismic slip during their interseismic period. Copyright 2007 by the American Geophysical Union.

  14. Urinary Lipocalin Protein in a Female Rodent with Correlation to Phases in the Estrous Cycle: An Experimental Study Accompanied by In Silico Analysis

    PubMed Central

    Saibaba, Ganesan; Alagesan, Alagersamy; Rengarajan, Rengasamy Lakhsminarayanan; Archunan, Govindaraju

    2013-01-01

    Male urinary lipocalin family proteins, practically odorant-binding proteins but also could be pheromones by themselves, in rodents act as a shuttle for chemosignal communication and facilitate delivery of the signals for access to congeners. However, presence of this protein in urine of female rodents has not yet been reported. Therefore, the present investigation was carried out to find if lipocalin family protein is present in the urine of female house rat and, if so, to find whether its expression differs between the phases in the estrous cycle. The rat urinary protein was separated in single dimensional gel electrophoresis. A 14.5 kDa lipocalin protein appeared in the urine prominently during the estrus and metestrus phases compared to proestrus and diestrus phases. The expression of this protein in the urine was very low in ovariectomized rats. MALDI-TOF/MS analysis affirmed the 14.5 kDa protein as a lipocalin family protein. Analysis adopting bio-informatics tools further proved the protein as a lipocalin family member. Thus, this study for the first time demonstrated the presence of a lipocalin family protein in the urine of a female rodent and it was highly expressed during estrus phase. This lipocalin protein in female rat urine may facilitate a chemosignal function independently of a pheromone or in association with a specific pheromone. PMID:23967199

  15. Macromolecular structure phasing by neutron anomalous diffraction

    PubMed Central

    Cuypers, Maxime G.; Mason, Sax A.; Mossou, Estelle; Haertlein, Michael; Forsyth, V. Trevor; Mitchell, Edward P.

    2016-01-01

    In this report we show for the first time that neutron anomalous dispersion can be used in a practical manner to determine experimental phases of a protein crystal structure, providing a new tool for structural biologists. The approach is demonstrated through the use of a state-of-the-art monochromatic neutron diffractometer at the Institut Laue-Langevin (ILL) in combination with crystals of perdeuterated protein that minimise the level of hydrogen incoherent scattering and enhance the visibility of the anomalous signal. The protein used was rubredoxin in which cadmium replaced the iron at the iron-sulphur site. While this study was carried out using a steady-state neutron beam source, the results will be of major interest for capabilities at existing and emerging spallation neutron sources where time-of-flight instruments provide inherent energy discrimination. In particular this capability may be expected to offer unique opportunities to a rapidly developing structural biology community where there is increasing interest in the identification of protonation states, protein/water interactions and protein-ligand interactions – all of which are of central importance to a wide range of fundamental and applied areas in the biosciences. PMID:27511806

  16. Macromolecular structure phasing by neutron anomalous diffraction.

    PubMed

    Cuypers, Maxime G; Mason, Sax A; Mossou, Estelle; Haertlein, Michael; Forsyth, V Trevor; Mitchell, Edward P

    2016-01-01

    In this report we show for the first time that neutron anomalous dispersion can be used in a practical manner to determine experimental phases of a protein crystal structure, providing a new tool for structural biologists. The approach is demonstrated through the use of a state-of-the-art monochromatic neutron diffractometer at the Institut Laue-Langevin (ILL) in combination with crystals of perdeuterated protein that minimise the level of hydrogen incoherent scattering and enhance the visibility of the anomalous signal. The protein used was rubredoxin in which cadmium replaced the iron at the iron-sulphur site. While this study was carried out using a steady-state neutron beam source, the results will be of major interest for capabilities at existing and emerging spallation neutron sources where time-of-flight instruments provide inherent energy discrimination. In particular this capability may be expected to offer unique opportunities to a rapidly developing structural biology community where there is increasing interest in the identification of protonation states, protein/water interactions and protein-ligand interactions - all of which are of central importance to a wide range of fundamental and applied areas in the biosciences. PMID:27511806

  17. Distortional phase transitions accompanying spin reorientation in the intermetallide Tb/sub 0. 5/Nd/sub 0. 5/Fe/sub 2/

    SciTech Connect

    Ilyushin, A.S.; Kakhadze, S.O.; Makhmud, I.A.

    1988-01-01

    The thermal expansion and spin reorientation in the intermetallide Tb/sub 0.5/Nd/sub 0.5/Fe/sub 2/ at temperatures ranging from 4.2 to 300/sup 0/K were studied by the method of low-temperature x-ray diffractometry. It was established that with spin reorientation in Tb/sub 0.5/Nd/sub 0.5/Fe/sub 2/ the orientation of the magnetic moment vector changes from <111> to <110> with the formation of corner magnetic phases.

  18. Tantalum-cadmium film coatings: Preparation, phase composition, and structure

    NASA Astrophysics Data System (ADS)

    Tuleushev, Yu. Zh.; Volodin, V. N.; Zhakanbaev, E. A.

    2015-01-01

    Ion-plasma sputtering and codeposition of ultrafine Ta and Cd particles were used for the first time to prepare solid solutions, namely, alloys with up to 66.2 at % Cd in the form of coatings; the fact of such a production confirms the thermal-fluctuation melting and coalescence of small particles. When the coatings are formed by tantalum and cadmium nanolayers, the mutual dissolution of the components takes place, which is accompanied by the formation of solid solutions of one metal in the other. When the cadmium concentration is above 44 at %, the β-Ta tetragonal lattice transforms into the α-Ta body-centered cubic lattice. Beginning from 74.4 at % Cd, a hexagonal structure typical of cadmium is formed, and tantalum is present in the coatings in the form of amorphous phase. The formation of β-Ta- and Cd-based interstitial and α-Ta-based substitute solid solutions is stated. At 700°C, cadmium evaporates from Ta-based solid solutions, and porous tantalum is formed. The evaporation of cadmium from coatings, which consist of the mixture of tantalum solid solution in cadmium and amorphous tantalum, leads to the formation of tantalum characterized by a highly developed surface. The prepared Ta-based materials assume the technological application of the results of the investigation.

  19. Coupled magnetic, structural, and electronic phase transitions in FeRh

    NASA Astrophysics Data System (ADS)

    Lewis, L. H.; Marrows, C. H.; Langridge, S.

    2016-08-01

    The B2-ordered intermetallic magnetic compound FeRh exhibits a thermodynamically first-order phase transition in the vicinity of room temperature that makes it a highly intriguing subject for both fundamental and applied study. On heating through the transition the magnetic character changes from antiferromagnetic to ferromagnetic order with an accompanying large increase in the electrical conductivity and an abrupt expansion in the lattice structure. Accompanying these effects is a very large entropy change comprising both magnetic and lattice contributions. As well as being driven by temperature, these coupled phase transitions may be driven by the application or removal of a magnetic field, or, because of the extremely strong lattice-spin interactions present in this compound, by an applied strain (pressure), and combinations thereof. In addition to these driving factors, the transition temperature can also be tuned by both compositional and finite size effects. Building from historical work on bulk forms of FeRh, the effects of extrinsic and intrinsic parameter variation on the coupled magnetic, structural, and electronic phase transitions are reviewed here, with special attention directed to phenomena that manifest themselves in thin films. Overall, the rich manner in which the physical properties of FeRh change at the phase transition has potential for a wide range of technological applications in areas such as thermally-assisted magnetic recording media, CFC-free magnetic cooling, sensors for energy management, and novel spintronic devices.

  20. Large entropy change accompanying two successive magnetic phase transitions in TbMn{sub 2}Si{sub 2} for magnetic refrigeration

    SciTech Connect

    Li, Guoxing; Cheng, Zhenxiang E-mail: cheng@uow.edu.au; Fang, Chunsheng; Dou, Shixue; Wang, Jianli E-mail: cheng@uow.edu.au; Ren, Qingyong

    2015-05-04

    Structural and magnetic properties in TbMn{sub 2}Si{sub 2} are studied by variable temperature X-ray diffraction, magnetization, electrical resistivity, and heat capacity measurements. TbMn{sub 2}Si{sub 2} undergoes two successive magnetic transitions at around T{sub c1} = 50 K and T{sub c2} = 64 K. T{sub c1} remains almost constant with increasing magnetic field, but T{sub c2} shifts significantly to higher temperature. Thus, there are two partially overlapping peaks in the temperature dependence of magnetic entropy change, i.e., −ΔS{sub M} (T). The different responses of T{sub c1} and T{sub c2} to external magnetic field, and the overlapping of −ΔS{sub M} (T) around T{sub c1} and T{sub c2} induce a large refrigerant capacity (RC) within a large temperature range. The large reversible magnetocaloric effect (−ΔS{sub M}{sup peak} ∼ 16 J/kg K for a field change of 0–5 T) and RC (=396 J/kg) indicate that TbMn{sub 2}Si{sub 2} could be a promising candidate for low temperature magnetic refrigeration.

  1. SSME structural dynamic model development, phase 2

    NASA Technical Reports Server (NTRS)

    Foley, M. J.; Wilson, V. L.

    1985-01-01

    A set of test correlated mathematical models of the SSME High Pressure Oxygen Turbopump (HPOTP) housing and rotor assembly was produced. New analysis methods within the EISI/EAL and SPAR systems were investigated and runstreams for future use were developed. The LOX pump models have undergone extensive modification since the first phase of this effort was completed. The rotor assembly from the original model was abandoned and a new, more detailed model constructed. A description of the new rotor math model is presented. Also, the pump housing model was continually modified as additional test data have become available. This model is documented along with measured test results. Many of the more advanced features of the EAL/SPAR finite element analysis system were exercised. These included the cyclic symmetry option, the macro-element procedures, and the fluid analysis capability. In addition, a new tool was developed that allows an automated analysis of a disjoint structure in terms of its component modes. A complete description of the implementation of the Craig-Bampton method is given along with two worked examples.

  2. Analysis of structure and phase composition of rails subjected to differential hardening at different regimes

    SciTech Connect

    Gromov, V. E. Morozov, K. V. Konovalov, S. V.; Alsaraeva, K. V.; Semina, O. A.; Ivanov, Yu. F.; Volkov, K. V.

    2014-11-14

    Differential hardening of rails by compressed air in different regimes is accompanied by formation of morphologically different structure, being formed according to the diffusion mechanism of γ↔α transformation and consisting of grains of lamellar pearlite, free ferrite and grains of ferrite-carbide mixture. By methods of transmission electron microscopy the layer by layer analysis of differentially hardened rails has been carried out, the quantitative parameters of the structure, phase composition and dislocation substructure have been established and their comparison has been made for different regimes of hardening. It has been found that the structure-phase states being formed have gradient character, defined by the hardening regime, direction of study from the surface of rolling and by depth of location of layer under study.

  3. Phase transitions and domain structures in multiferroics

    NASA Astrophysics Data System (ADS)

    Vlahos, Eftihia

    2011-12-01

    Thin film ferroelectrics and multiferroics are two important classes of materials interesting both from a scientific and a technological prospective. The volatility of lead and bismuth as well as environmental issues regarding the toxicity of lead are two disadvantages of the most commonly used ferroelectric random access memory (FeRAM) materials such as Pb(Zr,Ti)O3 and SrBi2Ta2O9. Therefore lead-free thin film ferroelectrics are promising substitutes as long as (a) they can be grown on technologically important substrates such as silicon, and (b) their T c and Pr become comparable to that of well established ferroelectrics. On the other hand, the development of functional room temperature ferroelectric ferromagnetic multiferroics could lead to very interesting phenomena such as control of magnetism with electric fields and control of electrical polarization with magnetic fields. This thesis focuses on the understanding of material structure-property relations using nonlinear optical spectroscopy. Nonlinear spectroscopy is an excellent tool for probing the onset of ferroelectricity, and domain dynamics in strained ferroelectrics and multiferroics. Second harmonic generation was used to detect ferroelectricity and the antiferrodistortive phase transition in thin film SrTiO3. Incipient ferroelectric CaTiO3 has been shown to become ferroelectric when strained with a combination of SHG and dielectric measurements. The tensorial nature of the induced nonlinear polarization allows for probing of the BaTiO3 and SrTiO3 polarization contributions in nanoscale BaTiO3/SrTiO3 superlattices. In addition, nonlinear optics was used to demonstrate ferroelectricity in multiferroic EuTiO3. Finally, confocal SHG and Raman microscopy were utilized to visualize polar domains in incipient ferroelectric and ferroelastic CaTiO3.

  4. Phase structures of holographic screen thermodynamics

    NASA Astrophysics Data System (ADS)

    Jiang, Wei-Jian; Chen, Yi-Xin; Li, Jian-Long

    2014-07-01

    Holographic screens are the generalization of the event horizon of a black hole in entropic force scheme, which are defined by setting Newton potential ϕ constant, i.e. e2ϕ = c = const. We demonstrate that the integrated first law of thermodynamics is equivalent to the (r-r) component of Einstein equations, so that we strengthen the correspondence between thermodynamics and gravity. We show that there are not only the first law of thermodynamics, but also kinds of phase transitions of holographic screens. These phase transitions are characterized by the discontinuity of their heat capacities. In (n+1)-dimensional Reissner-Nordström-anti-de Sitter (RN-AdS) spacetime, we analyze three kinds of phase transitions, which are of the holographic screens with Q = 0 (charge), constant Φ (electrostatic potential) and nonzero constant Q. In the Q = 0 case, only the holographic screens with 0≤c<1 can undergo phase transition. In the constant Φ case, the constraints become as 0<= c+16˜ {Γ }2Φ 2<1, where ˜ {Γ } is a dimensional-dependent parameter. By verifying the Ehrenfest equations, we show that the phase transitions in this case are all second order phase transitions. In the constant Q case, there might be two, or one, or no phase transitions of holographic screens, depending on the values of Q and c.

  5. Observation of Exchange Anisotropy in Single-Phase Layer-Structured Oxides with Long Periods

    PubMed Central

    Huang, Yan; Wang, Guopeng; Sun, Shujie; Wang, Jianlin; Peng, Ranran; Lin, Yue; Zhai, Xiaofang; Fu, Zhengping; Lu, Yalin

    2015-01-01

    A remarkable exchange bias effect arising from the temperature-dependent interaction among the ferromagnetic-like cluster glasses and antiferromagnetic regions was observed in a newly developed single-phase multiferroic compound of Bi10Fe6Ti3O30 which has a nine-layer Aurivillius structure. Inhomogeneous distribution of magnetic Fe ions inside this long-period layered structure was experimentally identified via the atomic level imaging. The results confirmed the presence of the short-range magnetic ordering (the cluster glassy state) and the canted antiferromagnetism, and then the direct interaction among them was further confirmed. Finding of this new single-phase material accompanying this remarkable exchange bias effect would be beneficial to both basic physics understanding and the potential device development. PMID:26487509

  6. Heat capacity, p-T phase diagram, and structure of Rb2KTiOF5

    NASA Astrophysics Data System (ADS)

    Fokina, V. D.; Flerov, I. N.; Molokeev, M. S.; Pogorel'Tsev, E. I.; Bogdanov, E. V.; Krylov, A. S.; Bovina, A. F.; Voronov, V. N.; Laptash, N. M.

    2008-11-01

    Elpasolite Rb2KTiOF5 (space group, Fm bar 3 m, Z = 4) was synthesized using a solid-phase reaction method. The temperature dependences of the heat capacity, the unit cell parameters, the structure, the permittivity, the response to an external pressure, and the Raman spectra were studied. A nonferroelectric phase transition was revealed at T 0 = 215 K; the transition is accompanied by a tetragonal distortion of the unit cell (space group I4/ m, Z = 10) and a change in the entropy (Δ S 0 = Rln8), which is anomalously large for perovskite-like oxyfluorides with atomic cations. The specific features of the mechanism of structure distortion are discussed in combination with the previous experimental data obtained for cryolite (NH4)3TiOF5 and elpasolite Rb2KGaF6.

  7. Synthesis of alloys with controlled phase structure

    DOEpatents

    Guthrie, S.E.; Thomas, G.J.; Bauer, W.; Yang, N.Y.C.

    1999-04-20

    A method is described for preparing controlled phase alloys useful for engineering and hydrogen storage applications. This novel method avoids melting the constituents by employing vapor transport, in a hydrogen atmosphere, of an active metal constituent, having a high vapor pressure at temperatures {approx_equal}300 C and its subsequent condensation on and reaction with the other constituent (substrate) of an alloy thereby forming a controlled phase alloy and preferably a single phase alloy. It is preferred that the substrate material be a metal powder such that diffusion of the active metal constituent, preferably magnesium, and reaction therewith can be completed within a reasonable time and at temperatures {approx_equal}300 C thereby avoiding undesirable effects such as sintering, local compositional inhomogeneities, segregation, and formation of unwanted second phases such as intermetallic compounds. 4 figs.

  8. Synthesis of alloys with controlled phase structure

    DOEpatents

    Guthrie, Stephen Everett; Thomas, George John; Bauer, Walter; Yang, Nancy Yuan Chi

    1999-04-20

    A method for preparing controlled phase alloys useful for engineering and hydrogen storage applications. This novel method avoids melting the constituents by employing vapor transport, in a hydrogen atmosphere, of an active metal constituent, having a high vapor pressure at temperatures .apprxeq.300 C. and its subsequent condensation on and reaction with the other constituent (substrate) of an alloy thereby forming a controlled phase alloy and preferably a single phase alloy. It is preferred that the substrate material be a metal powder such that diffusion of the active metal constituent, preferably magnesium, and reaction therewith can be completed within a reasonable time and at temperatures .apprxeq.300 C. thereby avoiding undesirable effects such as sintering, local compositional inhomogeneities, segregation, and formation of unwanted second phases such as intermetallic compounds.

  9. Using a plenoptic sensor to reconstruct vortex phase structures.

    PubMed

    Wu, Chensheng; Ko, Jonathan; Davis, Christopher C

    2016-07-15

    A branch point problem and its solution commonly involve recognizing and reconstructing a vortex phase structure around a singular point. In laser beam propagation through random media, the destructive phase contributions from various parts of a vortex phase structure will cause a dark area in the center of the beam's intensity profile. This null of intensity can, in turn, prevent the vortex phase structure from being recognized. In this Letter, we show how to use a plenoptic sensor to transform the light field of a vortex beam so that a simple and direct reconstruction algorithm can be applied to reveal the vortex phase structure. As a result, we show that the plenoptic sensor is effective in detecting branch points and can be used to reconstruct phase distortion in a beam in a wide sense. PMID:27420487

  10. Phase structure of a single urban intersection: a simulation study

    NASA Astrophysics Data System (ADS)

    Ebrahim Foulaadvand, M.; Fukui, M.; Belbasi, S.

    2010-07-01

    We study the phase structure of a cellular automata model proposed by Belbasi and Foulaadvand to describe the vehicular traffic flow at the intersection of two perpendicular streets. A set of traffic lights operating in a fixed-time scheme controls the traffic flow. A closed boundary condition is applied to the streets, each of which conducts a unidirectional flow. Streets are single-lane and cars cannot turn upon reaching the intersection. Via extensive Monte Carlo simulations it is shown that the model phase diagram consists of ten phases. The flow characteristics in each phase are investigated and the types of phase transitions between phases are specified.

  11. Dual-phase Cr-Ta alloys for structural applications

    DOEpatents

    Liu, Chain T.; Brady, Michael P.; Zhu, Jiahong; Tortorelli, Peter F.

    2001-01-01

    Dual phase alloys of chromium containing 2 to 11 atomic percent tantalum with minor amounts of Mo, Cr, Ti, Y, La, Cr, Si and Ge are disclosed. These alloys contain two phases including Laves phase and Cr-rich solid solution in either eutectic structures or dispersed Laves phase particles in the Cr-rich solid solution matrix. The alloys have superior mechanical properties at high temperature and good oxidation resistance when heated to above 1000.degree. C. in air.

  12. Phase structure of fuzzy black holes

    NASA Astrophysics Data System (ADS)

    Digal, S.; Govindarajan, T. R.; Gupta, Kumar S.; Martin, X.

    2012-01-01

    Noncommutative deformations of the BTZ black holes are described by non- commutative cylinders. We study the scalar fields in this background. The spectrum is studied analytically and through numerical simulations we establish the existence of novel `stripe phases'. These are different from stripes on Moyal spaces and stable due to topo- logical obstruction.

  13. Phase structure of QCD for heavy quarks

    NASA Astrophysics Data System (ADS)

    Fischer, Christian S.; Luecker, Jan; Pawlowski, Jan M.

    2015-01-01

    We investigate the nature of the deconfinement and Roberge-Weiss transition in the heavy quark regime for finite real and imaginary chemical potential within the functional approach to continuum QCD. We extract the critical phase boundary between the first-order and crossover regions and also explore tricritical scaling. Our results confirm previous ones from finite volume lattice studies.

  14. Atomic Structure and Phase Transformations in Pu Alloys

    SciTech Connect

    Schwartz, A J; Cynn, H; Blobaum, K M; Wall, M A; Moore, K T; Evans, W J; Farber, D L; Jeffries, J R; Massalski, T B

    2008-04-28

    Plutonium and plutonium-based alloys containing Al or Ga exhibit numerous phases with crystal structures ranging from simple monoclinic to face-centered cubic. Only recently, however, has there been increased convergence in the actinides community on the details of the equilibrium form of the phase diagrams. Practically speaking, while the phase diagrams that represent the stability of the fcc {delta}-phase field at room temperature are generally applicable, it is also recognized that Pu and its alloys are never truly in thermodynamic equilibrium because of self-irradiation effects, primarily from the alpha decay of Pu isotopes. This article covers past and current research on several properties of Pu and Pu-(Al or Ga) alloys and their connections to the crystal structure and the microstructure. We review the consequences of radioactive decay, the recent advances in understanding the electronic structure, the current research on phase transformations and their relations to phase diagrams and phase stability, the nature of the isothermal martensitic {delta} {yields} {alpha}{prime} transformation, and the pressure-induced transformations in the {delta}-phase alloys. New data are also presented on the structures and phase transformations observed in these materials following the application of pressure, including the formation of transition phases.

  15. 2D ice from first principles: structures and phase transitions

    NASA Astrophysics Data System (ADS)

    Chen, Ji; Schusteritsch, Georg; Pickard, Chris J.; Salzmann, Christoph G.; Michaelides, Angelos

    Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression the pentagonal structure becomes the most stable and persists up to ca. 2 GPa at which point square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. We also find a double layer AA stacked square ice phase, which clarifies the difference between experimental observations and earlier force field simulations. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and width.

  16. Phase and structural transformations in metallic iron under the action of heavy ions and recoil nuclei.

    PubMed

    Alekseev, I; Novikov, D

    2014-02-01

    By the use of various modes of Mössbauer spectroscopy after effects of irradiation of metal iron with (12)C(4+) and (14)N(5+) ions of medium energies, and alpha-particles and the (208)Tl, (208,212)Pb, and (216)Po recoil from a (228)Th-source have been studied. The experimental data obtained in the study enabled various types of external and internal radiation to be compared in regard to the damage they cause, as well as to their effect on the structure-, phase composition- and corrosion resistance properties of metallic iron. Irradiation with (12)C(4+) and (14)N(5+) ions is accompanied by both structural disordering of the α-Fe lattice, and the appearance of γ-phase in the bulk metal. This is indicated by a single line which is 2 to 3-fold broadened (as compared to the lines of the magnetic sextet). This is a result of a strong local heating of the lattice in the thermal spike area with a subsequent instant cooling-down and recrystallization of this "molted" area. Irradiation of iron foils with (12)C(4+)- and (14)N(5+) ions and with recoil nuclei does provoke corrosion processes (the formation of γ-FeOOH) and is accompanied by an intensive oxidation of the metal. PMID:24378918

  17. Structure evolution and piezoelectric properties across the morphotropic phase boundary of Sm-substituted BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Shi, Xin Xin; Liu, Xiao Qiang; Chen, Xiang Ming

    2016-02-01

    The evolution of structure, ferroelectric, and piezoelectric properties in Bi1-xSmxFe0.99Ti0.01O3 ceramics was extensively investigated within the entire morphotropic phase boundary region with 0 ≤ x ≤ 0.20. A sequential phase transition of R3c-Pna21-Pbnm with increasing Sm content was revealed by Rietveld refinement of the X-ray diffraction data together with the macroscopic ferroelectric measurements. Both ferroelectric and piezoelectric properties showed a great enhancement in the vicinity of the R3c/Pna21 (polar-to-polar) phase boundary, which should be caused by the field-induced phase transition between these two phases. Such field-induced phase transition might be essentially accompanied by a change of magnetic state, which indicated a way of controlling magnetism by means of electric field.

  18. Distillation tray structural parameter study: Phase 1

    NASA Technical Reports Server (NTRS)

    Winter, J. Ronald

    1991-01-01

    The purpose here is to identify the structural parameters (plate thickness, liquid level, beam size, number of beams, tray diameter, etc.) that affect the structural integrity of distillation trays in distillation columns. Once the sensitivity of the trays' dynamic response to these parameters has been established, the designer will be able to use this information to prepare more accurate specifications for the construction of new trays. Information is given on both static and dynamic analysis, modal response, and tray failure details.

  19. Structural Evidence for a Fast-Ion Transition in the High-Pressure Rocksalt Phase of Silver Iodide

    NASA Astrophysics Data System (ADS)

    Keen, D. A.; Hull, S.; Hayes, W.; Gardner, N. J. G.

    1996-12-01

    This Letter describes neutron diffraction measurements of the rocksalt structured phase of AgI at high pressure and temperature and the structural disorder which accompanies its high conductivity. In contrast to the first-order structural phase transition which results in fast-ionic α-AgI at ambient pressure, the fast-ionic behavior in rocksalt structured AgI occurs above a diffuse transition with a small anomaly in lattice parameter and a continuous increase in occupation of interstitial tetrahedral sites with increasing temperature. There are approximately 10 times more defects in the fast-ionic phase of rocksalt AgI than in isostructural AgBr at ambient pressure, 1 K below melting.

  20. Strain induced incommensurate structures in vicinity of reconstructive phase transitions

    NASA Astrophysics Data System (ADS)

    Korzhenevskii, A. L.; Dmitriev, V.

    2015-09-01

    General conditions controlling the formation of incommensurate phases in crystals undergoing reconstructive phase transitions are analyzed in the framework of a model-free phenomenological approach. A universal trend to stabilizing such intermediate phases in the vicinity of reconstructive phase transitions stems from the fact that certain high-order improper Lifshitz invariants reduce at such transformations to ones bi-linearly coupling critical displacement gradients and strains or even to the proper Lifshitz invariant. The approach developed here introduces a universal mechanism for the formation both of premartensite incommensurate phases and complex structures with giant unit cells, as found in some elemental crystals at high pressure.

  1. Phase decorrelation of coherent structures in a free shear layer

    NASA Technical Reports Server (NTRS)

    Ho, Chih-Ming; Zohar, Yitshak; Foss, Judith K.; Buell, Jeffrey C.

    1991-01-01

    The vortices near the origin of an initially laminar mixing layer have a single frequency with a well-defined phase; i.e., there is little phase jitter. Further downstream, however, the phase jitter increases suddenly. Even when the flow is forced, this same transition is observed. The forcing partially loses its influence because of the decorrelation of the phase between the forcing signal and the passing coherent structures. In the present investigation, this phenomenon is documented and the physical mechanism responsible for the phase decorrelation is identified.

  2. Structural comparison of nickel electrodes and precursor phases

    NASA Technical Reports Server (NTRS)

    Cornilsen, Bahne C.; Shan, Xiaoyin; Loyselle, Patricia

    1989-01-01

    Researchers summarize previous Raman spectroscopic results and discuss important structural differences in the various phases of active mass and active mass precursors. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to x rays (i.e., does not scatter x rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging are discussed. The oxidation states and dopant contents are explained in terms of the nonstoichiometric structures.

  3. Transitions between imperfectly ordered crystalline structures: A phase switch Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Wilms, Dorothea; Wilding, Nigel B.; Binder, Kurt

    2012-05-01

    A model for two-dimensional colloids confined laterally by “structured boundaries” (i.e., ones that impose a periodicity along the slit) is studied by Monte Carlo simulations. When the distance D between the confining walls is reduced at constant particle number from an initial value D0, for which a crystalline structure commensurate with the imposed periodicity fits, to smaller values, a succession of phase transitions to imperfectly ordered structures occur. These structures have a reduced number of rows parallel to the boundaries (from n to n-1 to n-2, etc.) and are accompanied by an almost periodic strain pattern, due to “soliton staircases” along the boundaries. Since standard simulation studies of such transitions are hampered by huge hysteresis effects, we apply the phase switch Monte Carlo method to estimate the free energy difference between the structures as a function of the misfit between D and D0, thereby locating where the transitions occur in equilibrium. For comparison, we also obtain this free energy difference from a thermodynamic integration method: The results agree, but the effort required to obtain the same accuracy as provided by phase switch Monte Carlo would be at least three orders of magnitude larger. We also show for a situation where several “candidate structures” exist for a phase, that phase switch Monte Carlo can clearly distinguish the metastable structures from the stable one. Finally, applying the method in the conjugate statistical ensemble (where the normal pressure conjugate to D is taken as an independent control variable), we show that the standard equivalence between the conjugate ensembles of statistical mechanics is violated.

  4. High Pressure Phase Transformations in Heavy Rare Earth Metals and Connections to Actinide Crystal Structures

    SciTech Connect

    Vohra, Yogesh K.; Sangala, Bagvanth Reddy; Stemshorn, Andrew K.; Hope, Kevin M.

    2008-07-01

    High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp {yields} Sm-type {yields} dhcp {yields} distorted fcc (hR-24) {yields} monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures. (authors)

  5. Phase structure rewrite systems in information retrieval

    NASA Technical Reports Server (NTRS)

    Klingbiel, P. H.

    1985-01-01

    Operational level automatic indexing requires an efficient means of normalizing natural language phrases. Subject switching requires an efficient means of translating one set of authorized terms to another. A phrase structure rewrite system called a Lexical Dictionary is explained that performs these functions. Background, operational use, other applications and ongoing research are explained.

  6. Different structures of monoclinic martensitic phases in titanium nickelide

    NASA Astrophysics Data System (ADS)

    Voronin, V. I.; Naish, V. E.; Novoselova, T. V.; Pushin, V. G.; Sagaradze, I. V.

    2000-03-01

    The detailed theoretical and experimental analysis has been undertaken to bring to light the true structure of the monoclinic phase in titanium nickelide (NiTi). Theoretical models for such a phase have been proposed to describe the experimental data. In addition to the well-known B19‧ phase two more structures - new monoclinic M phase with Cm space group and triclinic phase with P1 space group - have been produced and analyzed in detail. Diffraction patterns have been obtained from different NiTi samples by using the neutron diffractometer IVV2 at different temperatures. From the refinement by DBWS-9411 program all these neutron patterns have been decoded successfully. The proposed new structures and stereotype B19‧ one agree with correspondent experimental data and the agreement is quite good.

  7. STAEBL: Structural tailoring of engine blades, phase 2

    NASA Technical Reports Server (NTRS)

    Hirschbein, M. S.; Brown, K. W.

    1984-01-01

    The Structural Tailoring of Engine Blades (STAEBL) program was initiated at NASA Lewis Research Center in 1980 to introduce optimal structural tailoring into the design process for aircraft gas turbine engine blades. The standard procedure for blade design is highly iterative with the engineer directly providing most of the decisions that control the design process. The goal of the STAEBL program has been to develop an automated approach to generate structurally optimal blade designs. The program has evolved as a three-phase effort with the developmental work being performed contractually by Pratt & Whitney Aircraft. Phase 1 was intended as a proof of concept in which two fan blades were structurally tailored to meet a full set of structural design constraints while minimizing DOC+I (direct operating cost plus interest) for a representative aircraft. This phase was successfully completed and was reported in reference 1 and 2. Phase 2 has recently been completed and is the basis for this discussion. During this phase, three tasks were accomplished: (1) a nonproprietary structural tailoring computer code was developed; (2) a dedicated approximate finite-element analysis was developed; and (3) an approximate large-deflection analysis was developed to assess local foreign object damage. Phase 3 is just beginning and is designed to incorporated aerodynamic analyses directly into the structural tailoring system in order to relax current geometric constraints.

  8. Structured illumination quantitative phase microscopy for enhanced resolution amplitude and phase imaging

    PubMed Central

    Chowdhury, Shwetadwip; Izatt, Joseph

    2013-01-01

    Structured illumination microscopy (SIM) is an established microscopy technique typically used to image samples at resolutions beyond the diffraction limit. Until now, however, achieving sub-diffraction resolution has predominantly been limited to intensity-based imaging modalities. Here, we introduce an analogue to conventional SIM that allows sub-diffraction resolution, quantitative phase-contrast imaging of optically transparent objects. We demonstrate sub-diffraction resolution amplitude and quantitative-phase imaging of phantom targets and enhanced resolution quantitative-phase imaging of cells. We report a phase accuracy to within 5% and phase noise of 0.06 rad. PMID:24156044

  9. Two Dimensional Ice from First Principles: Structures and Phase Transitions.

    PubMed

    Chen, Ji; Schusteritsch, Georg; Pickard, Chris J; Salzmann, Christoph G; Michaelides, Angelos

    2016-01-15

    Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here, we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression, the pentagonal structure becomes the most stable and persists up to ∼2  GPa, at which point the square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and the width. PMID:26824547

  10. Two Dimensional Ice from First Principles: Structures and Phase Transitions

    NASA Astrophysics Data System (ADS)

    Chen, Ji; Schusteritsch, Georg; Pickard, Chris J.; Salzmann, Christoph G.; Michaelides, Angelos

    2016-01-01

    Despite relevance to disparate areas such as cloud microphysics and tribology, major gaps in the understanding of the structures and phase transitions of low-dimensional water ice remain. Here, we report a first principles study of confined 2D ice as a function of pressure. We find that at ambient pressure hexagonal and pentagonal monolayer structures are the two lowest enthalpy phases identified. Upon mild compression, the pentagonal structure becomes the most stable and persists up to ˜2 GPa , at which point the square and rhombic phases are stable. The square phase agrees with recent experimental observations of square ice confined within graphene sheets. This work provides a fresh perspective on 2D confined ice, highlighting the sensitivity of the structures observed to both the confining pressure and the width.

  11. High pressure structural phase transitions of PbPo

    NASA Astrophysics Data System (ADS)

    Bencherif, Y.; Boukra, A.; Zaoui, A.; Ferhat, M.

    2012-09-01

    First-principles calculations have been performed to investigate the high pressure phase transitions and dynamical properties of the less known lead polonium compound. The calculated ground state parameters for the NaCl phase show good agreement with the experimental data. The obtained results show that the intermediate phase transition for this compound is the orthorhombic Pnma phase. The PbPo undergoes from the rocksalt to Pnma phase at 4.20 GPa. Further structural phase transition from intermediate to CsCl phase has been found at 8.5 GPa. In addition, phonon dispersion spectra were derived from linear-response to density functional theory. In particular, we show that the dynamical properties of PbPo exhibit some peculiar features compared to other III-V compounds. Finally, thermodynamics properties have been also addressed from quasiharmonic approximation.

  12. Structural and thermodynamic properties of Fe{sub 1.12}Te with multiple phase transitions

    SciTech Connect

    Cherian, Dona Elizabeth, Suja; Rößler, S.; Koz, C.; Schwarz, U.; Wirth, S.; Tsirlin, A. A.

    2014-03-28

    The parent compound of iron chalcogenide superconductors, Fe{sub 1+y}Te, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe{sub 1.12}Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11≤y≤0.13. On cooling, an antiferromagnetic transition, T{sub N}≈57 K is observed. A closer examination of powder diffraction data suggests that the transition at T{sub N} is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at T{sub S} with T{sub S}structural coupling in this material.

  13. Phase stability, electronic structure and phonons in CsGeI3

    NASA Astrophysics Data System (ADS)

    Huang, Ling-Yi; Lambrecht, Walter

    Because Ge is smaller than Sn and Pb, CsGeI3 is promising to overcome the stability problems of the perovskite forms of CsSnI3 and CsPbI3 halides toward the denser yellow phase in which octahedra are edge as well as cornersharing in one dimensional chains. This phase has higher gaps and is unsuitable for photovoltaics. CsGeI3 and other trihalide germanates are found to exist in the cubic perovskite phase at high temperature but in a rhombohedral phase in which the Ge is displaced toward three of the halogen neighbors in its surrounding octahedron, accompanied by a rhombohedral distortion of the lattice vectors. We will present density functional total energy calculations and band structures obtained within the quasi-particle self-consistent GW method for both the cubic and rhombohedral phase of CsGeI3. For the latter, we find a gap of 1.6 eV in excellent agreement with recent experiments on its absorption edge. We will also present optical dielectric function and effective mass results for this material and discuss the trends for different types of distortions in halides depending on the chemical composition. The phonons at the Brillouin zone center are calculated and compared to experimental Raman spectra. NSF and DOE.

  14. Pressure-Induced Phase Transition in Guanidinium Perchlorate: A Supramolecular Structure Directed by Hydrogen Bonding and Electrostatic Interactions

    SciTech Connect

    Li, Shourui; Li, Qian; Wang, Kai; Tan, Xiao; Zhou, Mi; Li, Bing; Liu, Bingbing; Zou, Guangtian; Zou, Bo

    2012-01-20

    In situ Raman spectroscopy and synchrotron X-ray diffraction (XRD) experiments have been performed to investigate the response of guanidinium perchlorate (C(NH{sub 2}){sub 3}{sup +} {center_dot} ClO{sub 4}{sup -}, GP) to high pressures of {approx}11 GPa. GP exhibits a typical supramolecular structure of two-dimensional (2D) hydrogen-bonded ionic networks at ambient conditions. A subtle phase transition, accompanied by the symmetry transformation from R3m to C2, has been confirmed by obvious changes in both Raman and XRD patterns at 4.5 GPa. The phase transition is attributed to the competition between hydrogen bonds and close packing of the supramolecular structure at high pressure. Hydrogen bonds have been demonstrated to evolve into a distorted state through the phase transition, accompanied by the reduction in separation of oppositely charged ions in adjacent sheet motifs. A detailed mechanism of the phase transition, as well as the cooperativity between hydrogen bonding and electrostatic interactions, is discussed by virtue of the local nature of the structure.

  15. Low temperature phase transition and crystal structure of CsMgPO{sub 4}

    SciTech Connect

    Orlova, Maria; Khainakov, Sergey; Michailov, Dmitriy; Perfler, Lukas; Langes, Christoph; Kahlenberg, Volker; Orlova, Albina

    2015-01-15

    CsMgPO{sub 4} doped with radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at temperatures close to ambient conditions (∼−40 °C) was observed. Information about such kind of structural changes is important in order to understand whether it can cause any problem for medical use of this compound. The phase transition has been investigated in detail using synchrotron powder diffraction, Raman spectroscopy and DFT calculations. The structure undergoes a transformation from an orthorhombic modification, space group Pnma (RT phase) to a monoclinic polymorph, space group P2{sub 1}/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2) Å, b=8.95501(1) Å, c=5.50344(2) Å, β=90.68583(1)°, V=472.198(3) Å{sup 3}. CsMgPO{sub 4} belongs to the group of framework compounds and is made up of strictly alternating MgO{sub 4}- and PO{sub 4}-tetrahedra sharing vertices. The cesium counter cations are located in the resulting channel-like cavities. Upon the transformation a combined tilting of the tetrahedra is observed. A comparison with other phase transitions in ABW-type framework compounds is given. - Graphical abstract: Structural behavior of β-tridymite-type phosphate CsMgPO{sub 4}, considered as potential chemical form for radioactive Cs-source has been studied at near ambient temperatures. A phase transition at (∼−40 °C) has been found and investigated. It has been established that the known orthorhombic RT modification, space group Pnma, adopts a monoclinic cell with space group P2{sub 1}/n at low temperatures. In this paper, we present results of structural analysis of changes accompanying this phase transition and discuss its possible impact on the application properties. - Highlights: • β-Tridymite type phosphate CsMgPO{sub 4} undergoes so called translationengleiche phase transition of index 2 at −40 °C. • The structure

  16. A Phase-Field Method for Simulating Fluid-Structure Interactions in Multi-Phase Flow

    NASA Astrophysics Data System (ADS)

    Zheng, Xiaoning; Karniadakis, George

    2015-11-01

    We investigate two-phase flow instabilities by numerical simulations of fluid structure interactions in two-phase flow. The first case is a flexible pipe conveying two fluids, which exhibits self-sustained oscillations at high Reynolds number and tension related parameter. Well-defined two-phase flow patterns, i.e., slug flow and bubbly flow, are observed. The second case is external two-phase cross flow past a circular cylinder, which induces a Kelvin-Helmholtz instability due to density stratification. We solve the Navier-Stokes equation coupled with the Cahn-Hilliard equation and the structure equation in an arbitrary Lagrangian Eulerian (ALE) framework. For the fluid solver, a spectral/hp element method is employed for spatial discretization and backward differentiation for time discretization. For the structure solver, a Galerkin method is used in Lagrangian coordinates for spatial discretization and the Newmark- β scheme for time discretization.

  17. Detecting the temporal structure of intermittent phase locking

    PubMed Central

    Ahn, Sungwoo; Park, Choongseok; Rubchinsky, Leonid L.

    2011-01-01

    This study explores a method to characterize temporal structure of intermittent phase locking in oscillatory systems. When an oscillatory system is in a weakly synchronized regime away from a synchronization threshold, it spends most of the time in parts of its phase space away from synchronization state. Therefore characteristics of dynamics near this state (such as its stability properties/Lyapunov exponents or distributions of the durations of synchronized episodes) do not describe system’s dynamics for most of the time. We consider an approach to characterize the system dynamics in this case, by exploring the relationship between the phases on each cycle of oscillations. If some overall level of phase locking is present, one can quantify when and for how long phase locking is lost, and how the system returns back to the phase-locked state. We consider several examples to illustrate this approach: coupled skewed tent maps, which stability can be evaluated analytically, coupled Rössler and Lorenz oscillators, undergoing through different intermittencies on the way to phase synchronization, and a more complex example of coupled neurons. We show that the obtained measures can describe the differences in the dynamics and temporal structure of synchronization/desynchronization events for the systems with similar overall level of phase locking and similar stability of synchronized state. PMID:21867267

  18. Detecting the temporal structure of intermittent phase locking.

    PubMed

    Ahn, Sungwoo; Park, Choongseok; Rubchinsky, Leonid L

    2011-07-01

    This study explores a method to characterize the temporal structure of intermittent phase locking in oscillatory systems. When an oscillatory system is in a weakly synchronized regime away from a synchronization threshold, it spends most of the time in parts of its phase space away from the synchronization state. Therefore characteristics of dynamics near this state (such as its stability properties and Lyapunov exponents or distributions of the durations of synchronized episodes) do not describe the system's dynamics for most of the time. We consider an approach to characterize the system dynamics in this case by exploring the relationship between the phases on each cycle of oscillations. If some overall level of phase locking is present, one can quantify when and for how long phase locking is lost, and how the system returns back to the phase-locked state. We consider several examples to illustrate this approach: coupled skewed tent maps, the stability of which can be evaluated analytically; coupled Rössler and Lorenz oscillators, undergoing through different intermittency types on the way to phase synchronization; and a more complex example of coupled neurons. We show that the obtained measures can describe the differences in the dynamics and temporal structure of synchronization and desynchronization events for the systems with a similar overall level of phase locking and similar stability of the synchronized state. PMID:21867267

  19. Detecting the temporal structure of intermittent phase locking

    NASA Astrophysics Data System (ADS)

    Ahn, Sungwoo; Park, Choongseok; Rubchinsky, Leonid L.

    2011-07-01

    This study explores a method to characterize the temporal structure of intermittent phase locking in oscillatory systems. When an oscillatory system is in a weakly synchronized regime away from a synchronization threshold, it spends most of the time in parts of its phase space away from the synchronization state. Therefore characteristics of dynamics near this state (such as its stability properties and Lyapunov exponents or distributions of the durations of synchronized episodes) do not describe the system’s dynamics for most of the time. We consider an approach to characterize the system dynamics in this case by exploring the relationship between the phases on each cycle of oscillations. If some overall level of phase locking is present, one can quantify when and for how long phase locking is lost, and how the system returns back to the phase-locked state. We consider several examples to illustrate this approach: coupled skewed tent maps, the stability of which can be evaluated analytically; coupled Rössler and Lorenz oscillators, undergoing through different intermittency types on the way to phase synchronization; and a more complex example of coupled neurons. We show that the obtained measures can describe the differences in the dynamics and temporal structure of synchronization and desynchronization events for the systems with a similar overall level of phase locking and similar stability of the synchronized state.

  20. Structural comparison of nickel electrodes and precursor phases

    NASA Technical Reports Server (NTRS)

    Cornilsen, Bahne C.; Shan, Xiaoyin; Loyselle, Patricia

    1989-01-01

    A summary of previous Raman spectroscopic results and a discussion of important structural differences in the various phases of active mass and active mass precurors are presented. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to X-rays (i.e., does not scatter X-rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge, cobalt addition, and aging will be discussed and related to electrode properties. Important structural differences include NiO2 layer stacking, nonstoichiometry (especially cation-deficit nonstoichiometry), disorder, dopant content, and water content. The results indicate that optimal nickel active mass is non-close packed and nonstoichiometric. The formation process transforms precursor phases into this structure. Therefore, the precursor disorder, or lack thereof, influences this final active mass structure and the rate of formation. Aging processes induce structural change which is believed to be detrimental. The role of cobalt addition can be appreciated in terms of structures favored or stabilized by the dopant. In recent work, the in situ Raman technique to characterize the critical structural parameters was developed. An in situ method relates structure, electrochemistry, and preparation. In situ Raman spectra of cells during charge and discharge, either during cyclic voltammetry or under constant current conditions were collected. With the structure-preparation knowledge and the in situ Raman tool, it will be possible to define the structure-property-preparation relations in more detail. This instrumentation has application to a variety of electrode systems.

  1. Atomic structure and pressure-induced phase transformations in a phase-change alloy

    NASA Astrophysics Data System (ADS)

    Xu, Ming

    Phase-change materials exist in at least two phases under the ambient condition. One is the amorphous state and another is crystalline phase. These two phases have vastly different physical properties, such as electrical conductivity, optical reflectivity, mass density, thermal conductivity, etc. The distinct physical properties and the fast transformation between amorphous and crystalline phases render these materials the ability to store information. For example, the DVD and the Blue-ray discs take advantage of the optical reflectivity contrast, and the newly developed solid-state memories make use of the large conductivity difference. In addition, both the amorphous and crystalline phases in phase-change memories (PCMs) are very stable at room temperature, and they are easy to be scaled up in the production of devices with large storage density. All these features make phase-change materials the ideal candidates for the next-generation memories. Despite of the fast development of these new memory materials in industry, many fundamental physics problems underlying these interesting materials are still not fully resolved. This thesis is aiming at solving some of the key issues in phase-change materials. Most of phase-change materials are composed of Ge-Sb-Te constituents. Among all these Ge-Sb-Te based materials, Ge2Sb2Te5 (GST) has the best performance and has been frequently studied as a prototypical phase-change material. The first and foremost issue is the structure of the two functioning phases. In this thesis, we investigate the unique atomic structure and bonding nature of amorphous GST (a-GST) and crystalline GST ( c-GST), using ab initio tools and X-ray diffraction (XRD) methods. Their local structures and bonding scenarios are then analyzed using electronic structure calculations. In order to gain insight into the fast phase transformation mechanism, we also carried out a series of high-pressure experiments on GST. Several new polymorphs and their

  2. Structural phase transition and electronic properties in samarium chalcogenides

    NASA Astrophysics Data System (ADS)

    Panwar, Y. S.; Aynyas, Mahendra; Pataiya, J.; Sanyal, Sankar P.

    2016-05-01

    The electronic structure and high pressure properties of samarium monochalcogenides SmS, SmSe and SmTe have been reported by using tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). The total energy as a function of volume is evaluated. It is found that these monochalcogenides are stable in NaCl-type structure under ambient pressure. We predict a structural phase transition from NaCl-type (B1-phase) structure to CsCl-type (B2-type) structure for these compounds. Phase transition pressures were found to be 1.7, 4.4 and 6.6 GPa, for SmS, SmSe and SmTe respectively. Apart from this, the lattice parameter (a0), bulk modulus (B0), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed that these compounds exhibit metallic character. The calculated values of equilibrium lattice parameter and phase transition pressure are in general good agreement with available data.

  3. Topological defect transformation and structural transition of two-dimensional colloidal crystals across the nematic to smectic-A phase transition

    NASA Astrophysics Data System (ADS)

    Zuhail, K. P.; Sathyanarayana, P.; Seč, D.; Čopar, S.; Škarabot, M.; Muševič, I.; Dhara, S.

    2015-03-01

    We observe that topological defects in nematic colloids are strongly influenced by the elasticity and onset of smectic layering across the nematic (N ) to smectic-A (Sm A ) phase transition. When approaching the Sm A phase from above, the nematic hyperbolic hedgehog defect that accompanies a spherical colloidal inclusion is transformed into a focal conic line in the Sm A phase. This phase transformation has a strong influence on the pairwise colloidal interaction and is responsible for a structural transition of two-dimensional colloidal crystals. The pretransitional behavior of the point defect is supported by Landau-de Gennes Q -tensor modeling accounting for the increasing elastic anisotropy.

  4. Phase structure in a chiral model of nuclear matter

    SciTech Connect

    Phat, Tran Huu; Anh, Nguyen Tuan; Tam, Dinh Thanh

    2011-08-15

    The phase structure of symmetric nuclear matter in the extended Nambu-Jona-Lasinio (ENJL) model is studied by means of the effective potential in the one-loop approximation. It is found that chiral symmetry gets restored at high nuclear density and a typical first-order phase transition of the liquid-gas transition occurs at zero temperature, T=0, which weakens as T grows and eventually ends up with a second-order critical point at T=20 MeV. This phase transition scenario is confirmed by investigating the evolution of the effective potential versus the effective nucleon mass and the equation of state.

  5. Hydrogen isotope effects on the structural phase transition of NH₃BH₃

    SciTech Connect

    Navarra, Maria Assunta; Karkamkar, Abhijeet; Autrey, Tom; Cantelli, Rosario; Rispoli, Pasquale; Paolone, Annalisa; Palumbo, Oriele

    2011-07-01

    A systematic study of the structural phase transition of NH₃BH₃ and of its fully deuterated analogue was performed combining DSC and anelastic spectroscopy measurements. The transition is accompanied by a latent heat, and therefore is of the 1st order. On the deuterated sample the enthalpy variation is reduced of more than 20%, from 1.29 to 1.01 kJ/mol and the transition is shifted by -1.5 K toward higher temperatures. Both NH₃BH₃ and ND₃BD₃ display a temperature hysteresis between cooling and heating, thus denoting that the phase transition is of first-order. In addition, this hysteresis is extremely small (-0.5 K) indicating that the coexistence region between the two phases is very narrow. During isothermal ageing, the transformation of the low-temperature orthorhombic phase into the high-temperature tetragonal one occurs with a time constant of -16 min in NH₃BH₃ and -64 min in ND₃BD₃, evidencing a drastic slowing down of kinetics in the deuterated compound.

  6. Synthesis, Structure, and Pressure-Induced Polymerization of Li 3 Fe(CN) 6 Accompanied with Enhanced Conductivity

    SciTech Connect

    Li, Kuo; Zheng, Haiyan; Hattori, Takanori; Sano-Furukawa, Asami; Tulk, Christopher A.; Molaison, Jamie; Feygenson, Mikhail; Ivanov, Ilia N.; Yang, Wenge; Mao, Ho-kwang

    2015-11-17

    By providing a new route to synthesize inorganic/organic conductors with tunable composition and properties, pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3Fe(CN)6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. Moreover, the conductivity of the polymer is above 10–3 S·cm–1, which reaches the range of conductive polymers. Our investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.

  7. Structural Phase Transitions by Design in Monolayer Alloys.

    PubMed

    Duerloo, Karel-Alexander N; Reed, Evan J

    2016-01-26

    Two-dimensional monolayer materials are a highly anomalous class of materials under vigorous exploration. Mo- and W-dichalcogenides are especially unusual two-dimensional materials because they exhibit at least three different monolayer crystal structures with strongly differing electronic properties. This intriguing yet poorly understood feature, which is not present in graphene, may support monolayer phase engineering, phase change memory and other applications. However, knowledge of the relevant phase boundaries and how to engineer them is lacking. Here we show using alloy models and state-of-the-art density functional theory calculations that alloyed MoTe2-WTe2 monolayers support structural phase transitions, with phase transition temperatures tunable over a large range from 0 to 933 K. We map temperature-composition phase diagrams of alloys between pure MoTe2 and pure WTe2, and benchmark our methods to analogous experiments on bulk materials. Our results suggest applications for two-dimensional materials as phase change materials that may provide scale, flexibility, and energy consumption advantages. PMID:26647117

  8. Pulsed phase thermography for defect detection of honeycomb structure

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Feng, Lichun; Li, Yanhong; Zhang, Cunlin

    2009-07-01

    Pulse Phase Thermography (PPT) has been reported as a powerful technique of the thermal NDE. In this paper, the authors show that the original phase-images of two kinds of honeycomb structure defects by PPT based on Fast Fourier Transform (FFT) for the signal of temperature-time of each pixel. One is the artificial defects in honeycomb structure core under surface skin, and the defects can be identified easily. The other is disbonding defect between surface skin and core, and the difference is apparent compared with bonding and no-bonding between surface skin and core. To improve the signal to noise ratio for defect inspection of honeycomb structure, the temperature decay curve of each pixel is smoothed by moving average filter and then fitted by exponential function. After FFT on the fitted data of temperature, the fitted phase-images of two kinds of honeycomb structure defects are given. Compared with the original thermal-images of PT and original phase-images, the calculated phase-images are much more improved. Another advantage is the data could be represented by coefficients of fitting functions, and the storage of data could be greatly reduced. At last, the calculation process of temperature decay curve and analysis of the influence caused by increasing sampling time and frequency are given.

  9. Structural phase transition and electronic properties of NdBi

    SciTech Connect

    Sahu, Ashvini K.; Patiya, Jagdish; Sanyal, Sankar P.

    2015-06-24

    The structural and electronic properties of NdBi from an electronic structure calculation have been presented. The calculation is performed using self-consistent tight binding linear muffin tin orbital (TB-LMTO) method within the local density approximation (LDA). The calculated equilibrium structural parameters are in good agreement with the available experimental results. It is found that this compound shows metallic behavior under ambient condition and undergoes a structural phase transition from the NaCl structure to the CsCl structure at the pressure 20.1 GPa. The electronic structures of NdBi under pressure are investigated. It is found that NdBi have metallization and the hybridizations of atoms in NdBi under pressure become stronger.

  10. The Effect of Thermal Annealing on Structural-phase Changes in the Ni-Ti Alloy Implanted with Krypton Ions

    NASA Astrophysics Data System (ADS)

    Poltavtseva, V. P.; Kislitsin, S. B.; Ghyngazov, S. A.

    2016-06-01

    The influence of thermal annealing within the temperature range 100-300°C on the structural-phase state of a Ni-Ti alloy with shape memory effect (SME) implanted with 84Kr ions at the energies E = 280 keV and 1.75 MeV/nucl and the fluences within 5·1012-1·1020 ion/m2 is investigated. For the samples modified by 84Kr ions at E = 1.75 MeV/nucl up to the fluences 1·1020 and 5·1012 ion/m2, the formation of a martensitic NiTi phase with the B19 ' structure, responsible for the SME, is revealed at the annealing temperatures 100 and 300°C, respectively, in the near-surface region corresponding to the outrange area. This is accompanied by the formation of nanosized NiTi particles in the R-phase. As the implantation fluence increases, the probability of their formation decreases. It is shown that annealing of the implanted structures can increase the strength of the Ni-Ti alloy. The degree of hardening is determined by the value of annealing temperature, and an increase in strength is primarily due to ordering of the radiation-induced defect structures (phases). A correlation between the onset temperature of a forward martensitic transition and the structural-phase state of the thermally annealed Ni-Ti alloy is established.

  11. Phase contrast without phase plates and phase rings--optical solutions for improved imaging of phase structures.

    PubMed

    Piper, Timm; Piper, Jörg

    2013-10-01

    Using the optical methods described, phase specimens can be observed with a modified light microscope in enhanced clarity, purified from typical artifacts which are apparent in standard phase contrast illumination. In particular, haloing and shade-off are absent, lateral and vertical resolution are maximized and the image quality remains constant even in problematic preparations which cannot be well examined in normal phase contrast, such as specimens beyond a critical thickness or covered by obliquely situated cover slips. The background brightness and thus the range of contrast can be continuously modulated and specimens can be illuminated in concentric-peripheral, axial or paraxial light. Additional contrast effects can be achieved by spectral color separation. Normal glass or mirror lenses can be used; they do not need to be fitted with a phase plate or a phase ring. The methods described should be of general interest for all disciplines using phase microscopy. PMID:23913620

  12. Effect of point defects and disorder on structural phase transitions

    SciTech Connect

    Toulouse, J.

    1997-06-01

    Since the beginning in 1986, the object of this project has been Structural Phase Transitions (SPT) in real as opposed to ideal materials. The first stage of the study has been centered around the role of Point Defects in SPT`s. Our intent was to use the previous knowledge we had acquired in the study of point defects in non-transforming insulators and apply it to the study of point defects in insulators undergoing phase transitions. In non-transforming insulators, point defects, in low concentrations, marginally affect the bulk properties of the host. It is nevertheless possible by resonance or relaxation methods to study the point defects themselves via their local motion. In transforming solids, however, close to a phase transition, atomic motions become correlated over very large distances; there, even point defects far removed from one another can undergo correlated motions which may strongly affect the transition behavior of the host. Near a structural transition, the elastic properties win be most strongly affected so as to either raise or decrease the transition temperature, prevent the transition from taking place altogether, or simply modify its nature and the microstructure or domain structure of the resulting phase. One of the well known practical examples is calcium-stabilized zirconia in which the high temperature cubic phase is stabilized at room temperature with greatly improved mechanical properties.

  13. Thickness-induced structural phase transformation of layered gallium telluride.

    PubMed

    Zhao, Q; Wang, T; Miao, Y; Ma, F; Xie, Y; Ma, X; Gu, Y; Li, J; He, J; Chen, B; Xi, S; Xu, L; Zhen, H; Yin, Z; Li, J; Ren, J; Jie, W

    2016-07-28

    The thickness-dependent electronic states and physical properties of two-dimensional materials suggest great potential applications in electronic and optoelectronic devices. However, the enhanced surface effect in ultra-thin materials might significantly influence the structural stability, as well as the device reliability. Here, we report a spontaneous phase transformation of gallium telluride (GaTe) that occurred when the bulk was exfoliated to a few layers. Transmission electron microscopy (TEM) results indicate a structural variation from a monoclinic to a hexagonal structure. Raman spectra suggest a critical thickness for the structural transformation. First-principle calculations and thermodynamic analysis show that the surface energy and the interlayer interaction compete to dominate structural stability in the thinning process. A two-stage transformation process from monoclinic (m) to tetragonal (T) and then from tetragonal to hexagonal (h) is proposed to understand the phase transformation. The results demonstrate the crucial role of interlayer interactions in the structural stability, which provides a phase engineering strategy for device applications. PMID:27198938

  14. Self-Structured Conductive Filament Nanoheater for Chalcogenide Phase Transition.

    PubMed

    You, Byoung Kuk; Byun, Myunghwan; Kim, Seungjun; Lee, Keon Jae

    2015-06-23

    Ge2Sb2Te5-based phase-change memories (PCMs), which undergo fast and reversible switching between amorphous and crystalline structural transformation, are being utilized for nonvolatile data storage. However, a critical obstacle is the high programming current of the PCM cell, resulting from the limited pattern size of the optical lithography-based heater. Here, we suggest a facile and scalable strategy of utilizing self-structured conductive filament (CF) nanoheaters for Joule heating of chalcogenide materials. This CF nanoheater can replace the lithographical-patterned conventional resistor-type heater. The sub-10 nm contact area between the CF and the phase-change material achieves significant reduction of the reset current. In particular, the PCM cell with a single Ni filament nanoheater can be operated at an ultralow writing current of 20 μA. Finally, phase-transition behaviors through filament-type nanoheaters were directly observed by using transmission electron microscopy. PMID:26039415

  15. Electronic Structure and Phase Stability of PdPt Nanoparticles.

    PubMed

    Ishimoto, Takayoshi; Koyama, Michihisa

    2016-03-01

    To understand the origin of the physicochemical nature of bimetallic PdPt nanoparticles, we theoretically investigated the phase stability and electronic structure employing the PdPt nanoparticles models consisting of 711 atoms (ca. 3 nm). For the Pd-Pt core-shell nanoparticle, the PdPt solid-solution phase was found to be a thermodynamically stable phase in the nanoparticle as the result of difference in surface energy of Pd and Pt nanoparticles and configurational entropy effect, while it is well known that the Pd and Pt are the immiscible combination in the bulk phase. The electronic structure of nanoparticles is conducted to find that the electron transfer occurs locally within surface and subsurface layers. In addition, the electron transfer from Pd to Pt at the interfacial layers in core-shell nanoparticles is observed, which leads to unique geometrical and electronic structure changes. Our results show a clue for the tunability of the electronic structure of nanoparticles by controlling the arrangement in the nanoparticles. PMID:26862885

  16. Spontaneous phase transitions in magnetic films with a modulated structure

    SciTech Connect

    Arzamastseva, G. V.; Evtikhov, M. G.; Lisovskii, F. V. Mansvetova, E. G.

    2011-09-15

    The influence of monoperiodic and biperiodic bias fields on the nucleation of domain structures in quasi-uniaxial magnetic films near the Curie point has been studied experimentally. The main types of observed nonuniform magnetic moment distributions have been established and chains of a devil's staircase phase transitions are shown to be realized when the films are slowly cooled.

  17. Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition.

    PubMed

    Mauguière, Frédéric A L; Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Farantos, Stavros C; Wiggins, Stephen

    2015-10-15

    We re-examine the prototypical roaming reaction--hydrogen atom roaming in formaldehyde decomposition--from a phase space perspective. Specifically, we address the question "why do trajectories roam, rather than dissociate through the radical channel?" We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs, we show that in the roaming region, there is an unstable periodic orbit whose stable and unstable manifolds define a conduit that both encompasses all roaming trajectories exiting the formaldehyde well and shepherds them toward the H2···CO well. PMID:26499774

  18. Quasinormal modes and the phase structure of strongly coupled matter

    NASA Astrophysics Data System (ADS)

    Janik, Romuald A.; Jankowski, Jakub; Soltanpanahi, Hesam

    2016-06-01

    We investigate the poles of the retarded Green's functions of strongly coupled field theories exhibiting a variety of phase structures from a crossover up to different first order phase transitions. These theories are modeled by a dual gravitational description. The poles of the holographic Green's functions appear at the frequencies of the quasinormal modes of the dual black hole background. We focus on quantifying linearized level dynamical response of the system in the critical region of phase diagram. Generically non-hydrodynamic degrees of freedom are important for the low energy physics in the vicinity of a phase transition. For a model with linear confinement in the meson spectrum we find degeneracy of hydrodynamic and non-hydrodynamic modes close to the minimal black hole temperature, and we establish a region of temperatures with unstable non-hydrodynamic modes in a branch of black hole solutions.

  19. Capturing the Magnetic and Structural Phase Transition of Ferh using Extreme Ultraviolet Light

    NASA Astrophysics Data System (ADS)

    Zusin, Dmitriy; Grychtol, Patrik; Gentry, Christian; Murnane, Margaret; Kapteyn, Henry; Canton, Sophie; Knut, Ronny; Shaw, Justin; Nembach, Hans; Silva, Thomas; Ceballos, Alejandro; Bordel, Catherine; Fischer, Peter; Hellman, Frances

    2015-03-01

    The temperature dependent transition from the anti-ferromagnetic to the ferromagnetic phase in FeRh is accompanied by a modification of its crystal lattice. The interplay between the magnetic and the structural transition is a matter of strong debate. It is important to better understand the mechanism(s) of the transition since it can be induced by femtosecond laser pulses and, unlike slower (nanosecond) magnetic phase transitions, does not seem to be limited by heat transfer. In this work, we use extreme ultraviolet light generated by a tabletop high harmonics source to perform element-selective investigations of the temperature-dependent magneto-optical response of a thin film FeRh sample. We study the optically induced phase transition using two ultrafast pump-probe spectroscopy approaches: by monitoring the time-resolved transversal magneto-optical Kerr effect (T-MOKE) and the transient change in reflectivity. PF acknowledges support from BES MSD DOE # DE-AC02-05-CH11231 and LFRIR program (# 2012K1A4A3053565) through NRF Korea funded by MEST, and JILA from DOE # DE-FG02-09ER4665.

  20. Structure and phase behavior in five-component microemulsions

    SciTech Connect

    Billman, J.F. ); Kaler, E.W. )

    1990-03-01

    Droplet-to-bicontinuous structure transitions in a family of five-component microemulsions formed with sodium 4-(1{prime}-heptylnonyl)benzenesulfonate, isobutyl alcohol, D{sub 2}O, sodium chloride, and alkanes with even carbon numbers from octane to hexadecane are probed by using small-angle neutron scattering, electrical conductivity, and NMR self-diffusion measurements. The phase behavior and structure of these microemulsions are intimately linked and depend on salinity and the chain length of the alkane. Both the range of salt concentration in which the three-phase region is observed and the range of microemulsion water volume fraction within the three-phase region decrease with decreasing alkane chain length. Further, the appearance of the three-phase region is preceded by droplet-to-bicontinuous transitions. Microemulsions not exhibiting three-phase regions become bicontinuous only when they contain equal amounts of oil and water. The coincidence of the so-called percolation thresholds as determined by using electrical conductivity and self-diffusion measurements shows that electrical conduction in a dispersion of water droplets occurs with the exchange of material between the droplets.

  1. Structural phase stability in nanocrystalline titanium to 161 GPa

    SciTech Connect

    Velisavljevic, Nenad; Jacobsen, Matthew K.; Vohra, Yogesh K.

    2014-09-16

    Nanocrystalline titanium (nc-Ti) metal was investigated up to 161 GPa at room temperature using a diamond anvil cell. X-ray diffraction and electrical resistance techniques were used to investigate the compressibility and structural phase stability. nc-Ti is observed to undergo three structural phase transitions at high pressures, starting with α → ω at 10GPa and followed by ω → γ at 127GPa and γ → δ at 140GPa. The observed structural phase transitions, as well as compressibility, are consistent with previously reported values for coarse grained Ti (c-Ti). The high pressure experiments on nc-Ti samples do no show any significant variation of the α → ω transition pressure under varying nonhydrostatic conditions. This is in sharp contrast to c-Ti, where a significant decrease in the α → ω transition pressure is observed under increasing nonhydrostatic conditions. As a result, this would indicate that the decrease in grain size in nano grained titanium makes the α → ω phase transition less sensitive to shear stresses as compared to bulk or c-Ti.

  2. Structural phase transitions in EuNbO3 perovskite

    NASA Astrophysics Data System (ADS)

    Kususe, Yoshiro; Yoshida, Suguru; Fujita, Koji; Akamatsu, Hirofumi; Fukuzumi, Masafumi; Murai, Shunsuke; Tanaka, Katsuhisa

    2016-07-01

    The crystal structures of europium niobate, EuNbO3, have been examined over a wide temperature range between 20 and 500 K using synchrotron X-ray diffraction. We have observed two successive structural phase transitions at 360 and 460 K. Below 350 K, EuNbO3 adopts an orthorhombic perovskite structure (space group Imma), which is characterized by NbO6 octahedral tilting about the pseudocubic two-fold axis. The result differs from previous reports in which EuNbO3 was assigned to a cubic aristotype (space group Pm 3 barm) of perovskite at room temperature. At around 360 K, EuNbO3 undergoes a first-order phase transition to a tetragonal symmetry (space group I4/mcm) with the NbO6 octahedral tilting about the pseudocubic four-fold axis. As the temperature is further increased, the I4/mcm tetragonal phase changes into the Pm 3 barm cubic aristotype at 460 K. The tetragonal-to-cubic transformation is characterized as a continuous phase transition.

  3. Structural phase stability in nanocrystalline titanium to 161 GPa

    DOE PAGESBeta

    Velisavljevic, Nenad; Jacobsen, Matthew K.; Vohra, Yogesh K.

    2014-09-16

    Nanocrystalline titanium (nc-Ti) metal was investigated up to 161 GPa at room temperature using a diamond anvil cell. X-ray diffraction and electrical resistance techniques were used to investigate the compressibility and structural phase stability. nc-Ti is observed to undergo three structural phase transitions at high pressures, starting with α → ω at 10GPa and followed by ω → γ at 127GPa and γ → δ at 140GPa. The observed structural phase transitions, as well as compressibility, are consistent with previously reported values for coarse grained Ti (c-Ti). The high pressure experiments on nc-Ti samples do no show any significant variationmore » of the α → ω transition pressure under varying nonhydrostatic conditions. This is in sharp contrast to c-Ti, where a significant decrease in the α → ω transition pressure is observed under increasing nonhydrostatic conditions. As a result, this would indicate that the decrease in grain size in nano grained titanium makes the α → ω phase transition less sensitive to shear stresses as compared to bulk or c-Ti.« less

  4. Dual-phase steel structure visualized by extremely slow electrons.

    PubMed

    Mikmeková, Šárka; Yamada, Katsumi; Noro, Hisato

    2015-12-01

    Mechanical properties of complex steels are affected by their multi-phase structure. Scanning electron microscopy (SEM) is routinely used for characterizing dual-phase (DP) steels, although the identification of steel constituents is not straightforward. In fact, there are several ways of enabling the ferrite-martensite segmentation by SEM, and a wide range of electron energies can be utilized. This study demonstrates the phase identification of DP steels at high, low and extremely low landing energies of the primary electrons from tens of keV to tens of eV. Visualization of the specimen surface at very low landing energies has been achieved by inserting an earthed detector between the pole piece and the negatively biased specimen. This 'cathode lens mode' enables the use of the full energy range up to the primary electron energies. It has been found that extremely slow electrons (<100 eV) are exceptionally suitable for separation of the martensite from the ferrite matrix due to high surface sensitivity, enabling visualization of very fine features. Moreover, the channelling contrast is significantly suppressed at the landing energy of tens of eV of the primary electrons, which enables separation of the phases clearly even in the images acquired at low magnification. The contrast between the phases at tens of eV can be explained by the different thickness of native oxide covering the martensite and the ferrite phase. PMID:26497974

  5. Structured illumination diffraction phase microscopy for broadband, sub-diffraction resolution, quantitative phase imaging

    PubMed Central

    Chowdhury, Shwetadwip; Izatt, Joseph A.

    2015-01-01

    Structured illumination microscopy (SIM) is an established technique that allows sub-diffraction resolution imaging by heterodyning high sample frequencies into the system’s passband via structured illumination. However, until now, SIM has been typically used to achieve sub-diffraction resolution for intensity-based imaging. Here, we present a novel optical setup that uses structured illumination with a broadband-light source to obtain noise-reduced, sub-diffraction resolution, quantitative-phase (QPM) imaging of cells. We compare this with a previous work for sub-diffraction QPM imaging via SIM that used a laser source, and was thus still corrupted by coherent noise. PMID:24562266

  6. Structural phase transitions in trigonal Selenium induce the formation of a disordered phase

    NASA Astrophysics Data System (ADS)

    Pal, Anirban; Gohil, Smita; Sengupta, Surajit; Poswal, H. K.; Sharma, Surinder M.; Ghosh, Shankar; Ayyub, Pushan

    2015-10-01

    Arguments based on the Mermin-Wagner theorem suggest that the quasi-1D trigonal phase of Se should be unstable against long wavelength perturbations. Consisting of parallel Se-Se chains, this essentially fragile solid undergoes a partial transition to a monoclinic structure (consisting of 8-membered rings) at low temperatures (≈50 K), and to a distorted trigonal phase at moderate pressures (≈3GPa). Experimental investigations on sub-millimeter-sized single crystals provide clear evidence that these transitions occur via a novel and counter-intuitive route. This involves the reversible formation of an intermediate, disordered structure that appears as a minority phase with increasing pressure as well as with decreasing temperature. The formation of the disordered state is indicated by: (a) a ‘Boson-peak’ that appears at low temperatures in the specific heat and resonance Raman data, and (b) a decrease in the intensity of Raman lines over a relatively narrow pressure range. We complement the experimental results with a phenomenological model that illustrates how a first order structural transition may lead to disorder. Interestingly, nanocrystals of trigonal Se do not undergo any structural transition in the parameter space studied; neither do they exhibit signs of disorder, further underlining the role of disorder in this type of structural transition.

  7. New cubic structure compounds as actinide host phases

    NASA Astrophysics Data System (ADS)

    Stefanovsky, S. V.; Yudintsev, S. V.; Livshits, T. S.

    2010-03-01

    Various compounds with fluorite (cubic zirconia) and fluorite-derived (pyrochlore, zirconolite) structures are considered as promising actinide host phases at immobilization of actinide-bearing nuclear wastes. Recently some new cubic compounds — stannate and stannate-zirconate pyrochlores, murataite and related phases, and actinide-bearing garnet structure compounds were proposed as perspective matrices for complex actinide wastes. Zirconate pyrochlore (ideally Gd2Zr2O7) has excellent radiation resistance and high chemical durability but requires high temperatures (at least 1500 °C) to be produced by hot-pressing from sol-gel derived precursor. Partial Sn4+ substitution for Zr4+ reduces production temperature and the compounds REE2ZrSnO7 may be hot-pressed or cold pressed and sintered at ~1400 °C. Pyrochlore, A2B2O7-x (two-fold elementary fluorite unit cell), and murataite, A3B6C2O20-y (three-fold fluorite unit cell), are end-members of the polysomatic series consisting of the phases whose structures are built from alternating pyrochlore and murataite blocks (nano-sized modules) with seven- (2C/3C/2C), five- (2C/3C), eight- (3C/2C/3C) and three-fold (3C — murataite) fluorite unit cells. Actinide content in this series reduces in the row: 2C (pyrochlore) > 7C > 5C > 8C > 3C (murataite). Due to congruent melting murataite-based ceramics may be produced by melting and the firstly segregated phase at melt crystallization is that with the highest fraction of the pyrochlore modules in its structure. The melts containing up to 10 wt. % AnO2 (An = Th, U, Np, Pu) or REE/An fraction of HLW form at crystallization zoned grains composed sequentially of the 5C → 8C → 3C phases with the highest actinide concentration in the core and the lowest — in the rim of the grains. Radiation resistance of the "murataite" is comparable to titanate pyrochlores. One more promising actinide hosts are ferrites with garnet structure. The matrices containing sometime complex fluorite

  8. The Relationship Between ENSO Phases and Southern Hemisphere Jet Structure

    NASA Astrophysics Data System (ADS)

    Loeb, N.

    2015-12-01

    Tropical convection affects Southern Hemisphere jet dynamics through the process of mass outflow in the upper troposphere and lower stratosphere and through radiation of planetary wave trains through the connecting westerly waveguide. Seasonal changes and El Nino Southern Oscillation (ENSO) phases have an impact on the structure of the Subtropical, Polar and Polar Night Jet in the high latitude Southern Hemisphere. Through reanalysis of ERA-Interim data sets, an investigation of the different southern hemispheric jet structures that result from the various phases of ENSO. A classification of months into categories of El Niño, neutral and La Niña and then further sub classify the El Niño and La Niña into strong, moderate and weak events. The strength of the polar jet and subtropical jet vary greatly between the El Niño and La Niña episodes and also vary in latitudinal placement. Also, the structure of the jets vary between the Atlantic, Pacific and Indian Ocean Basins. Seasonal progression also has an impact on the structure and shape of the polar and subtropical jets. During the Winter in the Southern Atlantic Ocean, a more diffuse jet structure occurs during La Nina while a more focused jet structure is favored in El Niño periods. In addition, a strong link between the Polar-Night Jet and and the tropospheric polar jet is discovered.

  9. Thermal expansion accompanying the glass-liquid transition and crystallization

    NASA Astrophysics Data System (ADS)

    Jiang, M. Q.; Naderi, M.; Wang, Y. J.; Peterlechner, M.; Liu, X. F.; Zeng, F.; Jiang, F.; Dai, L. H.; Wilde, G.

    2015-12-01

    We report the linear thermal expansion behaviors of a Zr-based (Vitreloy 1) bulk metallic glass in its as-cast, annealed and crystallized states. Accompanying the glass-liquid transition, the as-cast Vitreloy 1 shows a continuous decrease in the thermal expansivity, whereas the annealed glass shows a sudden increase. The crystallized Vitreloy 1 exhibits an almost unchanged thermal expansivity prior to its melting. Furthermore, it is demonstrated that the nucleation of crystalline phases can induce a significant thermal shrinkage of the supercooled liquid, but with the growth of these nuclei, the thermal expansion again dominates. These results are explained in the framework of the potential energy landscape, advocating that the configurational and vibrational contributions to the thermal expansion of the glass depend on both, structure and temperature.

  10. Anomalies in the Young modulus at structural phase transitions in rare-earth cobaltites RBaCo{sub 4}O{sub 7} (R = Y, Tm-Lu)

    SciTech Connect

    Kazei, Z. A. Snegirev, V. V.; Andreenko, A. S.; Kozeeva, L. P.

    2011-08-15

    The elastic properties of rare-earth cobaltites RBaCo{sub 4}O{sub 7} (R = Y, Tm-Lu) have been experimentally studied in the temperature range of 80-300 K. The strong softening of the Young modulus {Delta}E(T)/E{sub 0} Almost-Equal-To -(0.1-0.2) of cobaltites with Lu and Yb ions has been revealed, which is due to the instability of the crystal structure upon cooling and is accompanied by an inverse jump at the second-order structural phase transition. The softening of the Young modulus and the jump at the phase transition decrease by an order of magnitude and the transition temperature T{sub s} and hysteresis {Delta}T{sub s} increase from a compound with Lu to that with Tm. A large softening of the Young modulus at the structural transition in Lu- and Yb cobaltites indicates that the corresponding elastic constant goes to zero, whereas this constant in Tm cobaltite is not a 'soft' mode of the phase transition. It has been found that the structural phase transition in Lu- and Yb cobaltites is accompanied by a large absorption maximum at the phase transition point and an additional maximum in the low-temperature phase and absorption anomalies in Tm cobaltite is an order of magnitude smaller.

  11. Micellar structures in lyotropic liquid crystals and phase transitions

    NASA Astrophysics Data System (ADS)

    Saupe, A.; Xu, S. Y.; Plumley, Sulakshana; Zhu, Y. K.; Photinos, P.

    1991-05-01

    The formation of micellar nematics is discussed with emphasis on the transitions between nematic phases and nematic-smectic transitions. Phase diagrams for MTAB/l-decanol/D,O systems show a direct transition between uniaxial nematics. Electrical conductivity and birefringence measurements on a mixture of sodium decylsulfate. 1-decanol, D,O demonstrate, on the other hand, the existence of a biaxial nemantic range that separates the Uniaxial nematics. On a mixture of cesium perflouroctanoate and H 2O the electrical conductivity and rotational viscosity are used to discuss the relevant features of nematic-lamellar-smectic transitions. The formation of elongated ribbon-like micelles at the nematic-smectic transition is suggested. Transitions between different nematic phases in the MTAB system may be connected with a structural change from long micelles with a fairly circular cross section to similar micelles with a more elliptical cross section.

  12. Structural transition from L1{sub 0} phase to A1 phase in FePt films caused by ion irradiation

    SciTech Connect

    Hasegawa, T.; Li, G.Q.; Pei, W.; Saito, H.; Ishio, S.; Taguchi, K.; Yamakawa, K.; Honda, N.; Ouchi, K.; Aoyama, T.; Sato, I.

    2006-03-01

    The effect of ion irradiation (B{sup +},Cr{sup +},Ga{sup +}, and Nb{sup +}) on the crystalline structure and magnetic properties of L1{sub 0} (face-centered tetragonal structure) FePt films was investigated. Irradiating with Cr{sup +}, Ga{sup +}, and Nb{sup +} ions of less than 1 at. % (1.6x10{sup 15} ions/cm{sup 2}) dose yielded an almost ideal structural transition from the L1{sub 0} to A1 (face-centered cubic structure) phase withoutdamage to the surface of the film. This structural transition was accompanied by a change in magnetic properties from a hard magnet with a coercivity H{sub c} of {approx}7 kOe to a soft magnet with H{sub c}<1 kOe. A two-dimensional pattern composed of hard magnetic L1{sub 0} and soft magnetic A1 phases was fabricated by using a focused Ga{sup +} ion beam.

  13. Irradiation induced structural change in Mo2Zr intermetallic phase

    DOE PAGESBeta

    Gan, J.; Keiser, Jr., D. D.; Miller, B. D.; Eriksson, N.; Sohn, Y. H.; Kirk, M.

    2016-05-14

    The Mo2Zr phase has been identified as a major interaction product at the interface of U-10Mo and Zr. Transmission electron microscopy in-situ irradiation with Kr ions at 200 °C with doses up to 2.0E + 16 ions/cm2 was carried out to investigate the radiation stability of the Mo2Zr. The Mo2Zr undergoes a radiation-induced structural change, from a large cubic (cF24) to a small cubic (cI2), along with an estimated 11.2% volume contraction without changing its composition. The structural change begins at irradiation dose below 1.0E + 14 ions/cm2. Furthermore, the transformed Mo2Zr phase demonstrates exceptional radiation tolerance with the developmentmore » of dislocations without bubble formation.« less

  14. Deep mantle structure and the postperovskite phase transition.

    PubMed

    Helmberger, D; Lay, T; Ni, S; Gurnis, M

    2005-11-29

    Seismologists have known for many years that the lowermost mantle of the Earth is complex. Models based on observed seismic phases sampling this region include relatively sharp horizontal discontinuities with strong zones of anisotropy, nearly vertical contrasts in structure, and small pockets of ultralow velocity zones (ULVZs). This diversity of structures is beginning to be understood in terms of geodynamics and mineral physics, with dense partial melts causing the ULVZs and a postperovskite solid-solid phase transition producing regional layering, with the possibility of large-scale variations in chemistry. This strong heterogeneity has significant implications on heat transport out of core, the evolution of the magnetic field, and magnetic field polarity reversals. PMID:16217029

  15. Phase structure of mathcal{N} = 2* SYM on ellipsoids

    NASA Astrophysics Data System (ADS)

    Marmiroli, Daniele

    2016-06-01

    We analyse the phase structure of an mathcal{N} = 2 massive deformation of mathcal{N} = 4 SYM theory on a four-dimensional ellipsoid using recent results on supersymmetric localisation. Besides the 't Hooft coupling λ, the relevant parameters appearing in the theory and discriminating between the different phases are the hypermultiplet mass M and the deformation (or squashing) parameter Q. Geometric deformation manifests itself as an effective mass term, thus braking the conformal invariance of the theory with massless hypermultiplets. The structure of perturbative corrections around the spherical geometry is analysed in the details and a systematic computational procedure is given, together with the first few corrections. The master field approximation of the matrix model associated to the analytically continued theory in the regime Q 2 M and on the compact space is exactly solvable and does not display any phase transition, similarly to mathcal{N} = 2 SU ( N) SYM with 2 N massive hypermultiplets. In the strong coupling limit, equivalent in our settings to the decompactification of the four-dimensional ellipsoid, we find evidence that the theory undergoes an infinite number of phase transitions starting at finite coupling and accumulating at λ = 8. Quite interestingly, the threshold points at which transitions occur can be pushed towards the weak coupling region by drifting Q to the value 2 M.

  16. Z(2) gauge neural network and its phase structure

    NASA Astrophysics Data System (ADS)

    Takafuji, Yusuke; Nakano, Yuki; Matsui, Tetsuo

    2012-11-01

    We study general phase structures of neural-network models that have Z(2) local gauge symmetry. The Z(2) spin variable Si=±1 on the i-th site describes a neuron state as in the Hopfield model, and the Z(2) gauge variable J=±1 describes a state of the synaptic connection between j-th and i-th neurons. The gauge symmetry allows for a self-coupling energy among J’s such as JJJ, which describes reverberation of signals. Explicitly, we consider the three models; (I) an annealed model with full and partial connections of J, (II) a quenched model with full connections where J is treated as a slow quenched variable, and (III) a quenched three-dimensional lattice model with the nearest-neighbor connections. By numerical simulations, we examine their phase structures paying attention to the effect of the reverberation term, and compare them with each other and with the annealed 3D lattice model which has been studied beforehand. By noting the dependence of thermodynamic quantities upon the total number of sites and the connectivity among sites, we obtain a coherent interpretation to understand these results. Among other things, we find that the Higgs phase of the annealed model is separated into two stable spin-glass phases in the quenched models (II) and (III).

  17. The solid phase of ginkgolide K: Structure and physicochemical properties

    NASA Astrophysics Data System (ADS)

    Zhang, Yiwen; Zhang, Guoshun; Wang, Zhenzhong; Lv, Yang; Xiao, Wei

    2016-05-01

    Four solvates of ginkgolide K with dimethyl sulfoxide(I), water molecule(II), acetone-isopropyl alcohol(III), methanol-ethanol(IV) and one solvate-free (V) have been described in this work. And the solid-state techniques such as X-ray diffraction, thermal analysis and Fourier transform infrared spectroscopy were used for characterization of the solid phases. The single crystal structures of ginkgolide K solvates (I-IV) have been determined. Ginkgolide K shows strong inflexibility and solvents being incorporated in the crystal structure results in it forming polymorphs via the diverse hydrogen bond interactions.

  18. Phase Diagrams and Electronic Structure of II-VI Alloys

    NASA Astrophysics Data System (ADS)

    de Gironcoli, Stefano

    1998-03-01

    Among II-VI wide-gap semiconductor solid solutions, Zn_xMg_1-xS_ySe_1-y alloy is the most studied for its potential applications in the blue-green light-emitter technology. In spite of this enormous technological interest little is known about its fundamental thermodynamical and structural properties. In this work the structural and thermodynamical properties of the Zn_xMg_1-xS_ySe_1-y solid solutions are determined by a combination of the computational alchemy (S. de Gironcoli, P. Giannozzi, and S. Baroni, Phys. Rev. Lett. 66), 2116 (1991); N. Marzari, S. de Gironcoli, and S. Baroni, Phys. Rev. Lett. 72, 4001 (1994). and the cluster expansion (S.-H. Wei, L. G. Ferreira, and A. Zunger, Phys. Rev. B 41), 8240 (1990). methods with Monte Carlo simulations. We determine the phase diagram of the alloy and show that the system is completely mixible at the tipical growth temperatures and phase separates at lower temperatures into two or three phases. The homogeneous phase is characterized by a large amount of short-range order occurring among first-nearest neighbors. Electronic-structure calculations, performed extending the special quasi-random structures approach (A. Zunger, S.-H. Wei, L. G. Ferreira, and J. E. Bernard, Phys. Rev. Lett. 65), 353 (1990). to the quaternary alloy case, indicate that the energy gap of the alloy is rather sensitive to this short-range order.

  19. Synthesis, structure and phase behavior of liquid crystalline polyurethanes

    SciTech Connect

    Papadimitrakopoulos, F.

    1993-01-01

    This dissertation describes the synthesis, structure and phase behavior of polyurethanes based on the mesogenic biphenol 4,4'-bis (6-hydroxyhexoxy)biphenyl (BHHBP) and meta substituted tolylene/phenylene diisocynates. The structure-property relationships were determined as a function of hydrogen-bonding, the position of the methyl group in the tolylene diisocyanate moiety (TDI) and the biphenol moiety. The liquid crystalline phase (mesophase) and crystalline phase were investigated primarily with differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and infrared spectroscopy. The influence of H-bonding on the structure and phase behavior of 1,4-LCPU-6 was determined by the synthesis of high molecular weight N-Methyl2,4-LCPU-65, using a novel high temperature polymerization of a biscarbamoyl chloride with the BHHBP mesogenic diol. In contrast to the regular ([alpha], [omega]-hexane diol) based polyurethanes (PUs), BHHBP derived polyurethanes (LCPUs) crystallize rapidly from their melts. Hexafluoroisopropanol fast solvent-evaporation casting or rapid cooling from the melt resulted in thin films or bulk samples with a glassy mesophase morphology. During the subsequent heating scan, the mesophase to crystal transition occurs. Highly oriented fibers were obtained for the mesogenic polyurethanes. Atomistic molecular simulations coupled with X-ray intensity refinement allowed determination of the crystalline chain conformation and packing characteristics for the 2,6-LCPU-6 and 1,3-LCPU-6 (2,6-TDI and 1,3-Phenylene Diisocynate (1,3-PDI) derived LCPUs). On the basis of structural similarity and well resolved WAXS powder patterns similar analysis was extended to the regular polyurethanes as well (2,6-PU-6 and 1,3-PU-6). The good correlation polymers suggest that melting is primarily controlled by the dissociation of H-bonds in the ordered domains.

  20. Structural Phase Transitions and Water Dynamics in Uranyl Fluoride Hydrates.

    PubMed

    Miskowiec, Andrew; Kirkegaard, Marie C; Huq, Ashfia; Mamontov, Eugene; Herwig, Kenneth W; Trowbridge, Lee; Rondinone, Adam; Anderson, Brian

    2015-12-10

    We report a novel production method for uranium oxyfluoride [(UO2)7F14(H2O)7]·4H2O, referred to as structure D. Structure D is produced as a product of hydrating anhydrous uranyl fluoride, UO2F2, through the gas phase at ambient temperatures followed by desiccation by equilibration with a dry environment. We follow the structure of [(UO2)7F14(H2O)7]·4H2O through an intermediate, liquid-like phase, wherein the coordination number of the uranyl ion is reduced to 5 (from 6 in the anhydrous structure), and a water molecule binds as an equatorial ligand to the uranyl ion. Quasielastic neutron scattering results compare well with previous measurements of mineral hydrates. The two groups of structurally distinct water molecules in D perform restricted motion on a length scale commensurate with the O-H bond (r = 0.92 Å). The more tightly bound equatorial ligand waters rotate slower (Dr = 2.2 ps(-1)) than their hydrogen-bonded partners (Dr = 28.7 ps(-1)). PMID:26575434

  1. Duality, phase structures, and dilemmas in symmetric quantum games

    SciTech Connect

    Ichikawa, Tsubasa . E-mail: tsubasa@post.kek.jp; Tsutsui, Izumi

    2007-03-15

    Symmetric quantum games for 2-player, 2-qubit strategies are analyzed in detail by using a scheme in which all pure states in the 2-qubit Hilbert space are utilized for strategies. We consider two different types of symmetric games exemplified by the familiar games, the Battle of the Sexes (BoS) and the Prisoners' Dilemma (PD). These two types of symmetric games are shown to be related by a duality map, which ensures that they share common phase structures with respect to the equilibria of the strategies. We find eight distinct phase structures possible for the symmetric games, which are determined by the classical payoff matrices from which the quantum games are defined. We also discuss the possibility of resolving the dilemmas in the classical BoS, PD, and the Stag Hunt (SH) game based on the phase structures obtained in the quantum games. It is observed that quantization cannot resolve the dilemma fully for the BoS, while it generically can for the PD and SH if appropriate correlations for the strategies of the players are provided.

  2. Universality class of the structural phase transition in the normal phase of cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Najafi, M. N.; Tavana, A.

    2016-08-01

    The tetragonal-orthorhombic structural phase transition of oxygen atoms in the basal plane of YBa2Cu3O6 +δ high-TC cuprate superconductors is studied numerically. By mapping the system onto the asymmetric next-nearest-neighbor Ising model, we characterize this phase transition. Results indicate the degrees of critical behavior. We show that this phase transition occurs at the temperature TC≃0.148 eV in the thermodynamic limit. By analyzing the critical exponents, it is found that this universality class displays some common features, with the two-dimensional three-state Potts model universality class, although the possibility of other universality classes cannot be ruled out. Conformal invariance at T =Tc is investigated using the Schramm-Loewner evolution (SLE) technique, and it is found that the SLE diffusivity parameter for this system is 3.34 ±0.01 .

  3. Inner Core Structure Behind the PKP Core Phase Triplication

    NASA Astrophysics Data System (ADS)

    Blom, N.; Paulssen, H.; Deuss, A. F.; Waszek, L.

    2015-12-01

    Despite its small size, the Earth's inner core plays an important role in the Earth's dynamics. Because it is slowly growing, its structure - and the variation thereof with depth - may reveal important clues about the history of the core, its convection and the resulting geodynamo. Learning more about this structure has been a prime effort in the past decades, leading to discoveries about anisotropy, hemispheres and heterogeneity in the inner core in general. In terms of detailed structure, mainly seismic body waves have contributed to these advances. However, at depths between ~100-200 km, the seismic structure is relatively poorly known. This is a result of the PKP core phase triplication and the existence of strong precursors to PKP phases, whose simultaneous arrival hinders the measurement of inner core waves PKIKP at epicentral distances between roughly 143-148°. As a consequence, the interpretation of deeper structure also remains difficult. To overcome these issues, we stack seismograms in slowness and time, separating PKP and PKIKP phases which arrive simultaneously, but with different slowness. We apply this method to study the inner core's Western hemisphere between South and Central America using paths travelling in the quasi-polar direction between epicentral distances of 140-150°. This enables us to measure PKiKP-PKIKP differential travel times up to greater epicentral distance than has previously been done. The resulting differential travel time residuals increase with epicentral distance, indicating a marked increase in seismic velocity with depth compared to reference model AK135 for the studied polar paths. Assuming a homogeneous outer core, these findings can be explained by either (i) inner core heterogeneity due to an increase in isotropic velocity, or (ii) increase in anisotropy over the studied depth range. Our current data set cannot distinguish between the two hypotheses, but in light of previous work we prefer the latter interpretation.

  4. Surface modification induced phase transformation and structure variation on the rapidly solidified recast layer of titanium

    SciTech Connect

    Tsai, Ming-Hung; Haung, Chiung-Fang; Shyu, Shih-Shiun; Chou, Yen-Ru; Lin, Ming-Hong; Peng, Pei-Wen; and others

    2015-08-15

    In this study, neodymium-doped yttrium orthovanadate (Nd:YVO{sub 4}) as a laser source with different scanning speeds was used on biomedical Ti surface. The microstructural and biological properties of laser-modified samples were investigated by means of optical microscope, electron microscope, X-ray diffraction, surface roughness instrument, contact angle and cell cytotoxicity assay. After laser modification, the rough volcano-like recast layer with micro-/nanoporous structure and wave-like recast layer with nanoporous structure were generated on the surfaces of laser-modified samples, respectively. It was also found out that, an α → (α + rutile-TiO{sub 2}) phase transition occurred on the recast layers of laser-modified samples. The Ti surface becomes hydrophilic at a high speed laser scanning. Moreover, the cell cytotoxicity assay demonstrated that laser-modified samples did not influence the cell adhesion and proliferation behaviors of osteoblast (MG-63) cell. The laser with 50 mm/s scanning speed induced formation of rough volcano-like recast layer accompanied with micro-/nanoporous structure, which can promote cell adhesion and proliferation of MG-63 cell on Ti surface. The results indicated that the laser treatment was a potential technology to enhance the biocompatibility for titanium. - Highlights: • Laser induced the formation of recast layer with micro-/nanoporous structure on Ti. • An α → (α + rutile-TiO{sub 2}) phase transition was observed within the recast layer. • The Ti surface becomes hydrophilic at a high speed laser scanning. • Laser-modified samples exhibit good biocompatibility to osteoblast (MG-63) cell.

  5. [Wernicke encephalopathy accompanying linitis plastica].

    PubMed

    Soós, Zsuzsanna; Salamon, Mónika; Oláh, Roland; Czégeni, Anna; Salamon, Ferenc; Folyovich, András; Winkler, Gábor

    2014-01-01

    Wernicke encephalopathy (or Wernicke-Korsakoff encephalopathy) is a rarely diagnosed neurological disorder, which is caused by vitamin B1 deficiency. In the classical form it is characterized by a typical triad (confusion, oculomotor disturbance and ataxia), however, in the majority of the cases only confusion is present. It can be frequently observed in subjects with chronic alcohol consumption, but it may accompany different pathological states of which end stage malignant diseases are the most importants, where confusion may have different backgrounds. The authors present the case of an old male patient with advanced gastric cancer recognised and treated vitamin B1 deficiency, and they draw attention to difficulties of the diagnosis of Wernicke's disease. PMID:24379094

  6. Optimized Structures for Low-Profile Phase Change Thermal Spreaders

    NASA Astrophysics Data System (ADS)

    Sharratt, Stephen Andrew

    Thin, low-profile phase change thermal spreaders can provide cooling solutions for some of today's most pressing heat flux dissipation issues. These thermal issues are only expected to increase as future electronic circuitry requirements lead to denser and potentially 3D chip packaging. Phase change based heat spreaders, such as heat pipes or vapor chambers, can provide a practical solution for effectively dissipating large heat fluxes. This thesis reports a comprehensive study of state-of-the-art capillary pumped wick structures using computational modeling, micro wick fabrication, and experimental analysis. Modeling efforts focus on predicting the shape of the liquid meniscus inside a complicated 3D wick structure. It is shown that this liquid shape can drastically affect the wick's thermal resistance. In addition, knowledge of the liquid meniscus shape allows for the computation of key parameters such as permeability and capillary pressure which are necessary for predicting the maximum heat flux. After the model is validated by comparison to experimental results, the wick structure is optimized so as to decrease overall wick thermal resistance and increase the maximum capillary limited heat flux before dryout. The optimized structures are then fabricated out of both silicon and copper using both traditional and novel micro-fabrication techniques. The wicks are made super-hydrophilic using chemical and thermal oxidation schemes. A sintered monolayer of Cu particles is fabricated and analyzed as well. The fabricated wick structures are experimentally tested for their heat transfer performance inside a well controlled copper vacuum chamber. Heat fluxes as high as 170 W/cm2 are realized for Cu wicks with structure heights of 100 μm. The structures optimized for both minimized thermal resistance and high liquid supply ability perform much better than their non-optimized counterparts. The super-hydrophilic oxidation scheme is found to drastically increase the maximum

  7. Structure, Hydrodynamics, and Phase Transition of Freely Suspended Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Clark, Noel A.

    2000-01-01

    Smectic liquid crystals are phases of rod shaped molecules organized into one dimensionally (1D) periodic arrays of layers, each layer being between one and two molecular lengths thick. In the least ordered smectic phases, the smectics A and C, each layer is a two dimensional (2D) liquid. Additionally there are a variety of more ordered smectic phases having hexatic short range translational order or 2D crystalline quasi long range translational order within the layers. The inherent fluid-layer structure and low vapor pressure of smectic liquid crystals enable the long term stabilization of freely suspended, single component, layered fluid films as thin as 30A, a single molecular layer. The layering forces the films to be an integral number of smectic layers thick, quantizing their thickness in layer units and forcing a film of a particular number of layers to be physically homogeneous with respect to its layer structure over its entire area. Optical reflectivity enables the precise determination of the number of layers. These ultrathin freely suspended liquid crystal films are structures of fundamental interest in condensed matter and fluid physics. They are the thinnest known stable condensed phase fluid structures and have the largest surface-to-volume ratio of any stable fluid preparation, making them ideal for the study of the effects of reduced dimensionality on phase behavior and on fluctuation and interface phenomena. Their low vapor pressure and quantized thickness enable the effective use of microgravity to extend the study of basic capillary phenomena to ultrathin fluid films. Freely suspended films have been a wellspring of new liquid crystal physics. They have been used to provide unique experimental conditions for the study of condensed phase transitions in two dimensions. They are the only system in which the hexatic has been unambiguously identified as a phase of matter, and the only physical system in which fluctuations of a 2D XY system and

  8. An Overview of 2014 SBIR Phase I and Phase II Materials Structures for Extreme Environments

    NASA Technical Reports Server (NTRS)

    Nguyen, Hung D.; Steele, Gynelle C.; Morris, Jessica R.

    2015-01-01

    NASA's Small Business Innovation Research (SBIR) program focuses on technological innovation by investing in development of innovative concepts and technologies to help NASA mission directorates address critical research needs for Agency programs. This report highlights nine of the innovative SBIR 2014 Phase I and Phase II projects that emphasize one of NASA Glenn Research Center's six core competencies-Materials and Structures for Extreme Environments. The technologies cover a wide spectrum of applications such as high temperature environmental barrier coating systems, deployable space structures, solid oxide fuel cells, and self-lubricating hard coatings for extreme temperatures. Each featured technology describes an innovation, technical objective, and highlights NASA commercial and industrial applications. This report provides an opportunity for NASA engineers, researchers, and program managers to learn how NASA SBIR technologies could help their programs and projects, and lead to collaborations and partnerships between the small SBIR companies and NASA that would benefit both.

  9. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  10. Electronic structure and crystal phase stability of palladium hydrides

    SciTech Connect

    Houari, Abdesalem; Matar, Samir F.; Eyert, Volker

    2014-11-07

    The results of electronic structure calculations for a variety of palladium hydrides are presented. The calculations are based on density functional theory and used different local and semilocal approximations. The thermodynamic stability of all structures as well as the electronic and chemical bonding properties are addressed. For the monohydride, taking into account the zero-point energy is important to identify the octahedral Pd-H arrangement with its larger voids and, hence, softer hydrogen vibrational modes as favorable over the tetrahedral arrangement as found in the zincblende and wurtzite structures. Stabilization of the rocksalt structure is due to strong bonding of the 4d and 1s orbitals, which form a characteristic split-off band separated from the main d-band group. Increased filling of the formerly pure d states of the metal causes strong reduction of the density of states at the Fermi energy, which undermines possible long-range ferromagnetic order otherwise favored by strong magnetovolume effects. For the dihydride, octahedral Pd-H arrangement as realized, e.g., in the pyrite structure turns out to be unstable against tetrahedral arrangement as found in the fluorite structure. Yet, from both heat of formation and chemical bonding considerations, the dihydride turns out to be less favorable than the monohydride. Finally, the vacancy ordered defect phase Pd{sub 3}H{sub 4} follows the general trend of favoring the octahedral arrangement of the rocksalt structure for Pd:H ratios less or equal to one.

  11. Structural Phase Transitions and Water Dynamics in Uranyl Fluoride Hydrates

    DOE PAGESBeta

    Miskowiec, Andrew J.; Kirkegaard, Marie C.; Huq, Ashfia; Mamontov, Eugene; Herwig, Kenneth W.; Trowbridge, Lee D.; Rondinone, Adam Justin; Anderson, Brian B.

    2015-11-17

    We report a novel production method for uranium oxy uoride [(UO2)7F14(H2O)7] 4H2O, referred to as structure D. Structure D is produced as a product of hydrating anhydrous uranyl uoride, UO2F2, through the gas phase at ambient temperatures fol- lowed by desiccation by equilibration with a dry environment. We follow the structure of [(UO2)7F14(H2O)7] 4H2O through an intermediate, liquid-like phase, wherein the coordination number of the uranyl ion is reduced to 5 (from 6 in the anhydrous struc- ture), and a water molecule binds as an equatorial ligand to the uranyl ion. Quasielas- tic neutron scattering results compare well with previousmore » measurements of mineral hydrates. The two groups of structurally distinct water molecules in D perform re- stricted motion on a length scale commensurate with the O{H bond (r = 0.92 A). The more tightly bound equatorial ligand waters rotate slower (Dr = 2.2 ps-1) than their hydrogen-bonded partners (Dr = 28.7 ps-1).« less

  12. Structural Phase Transitions and Water Dynamics in Uranyl Fluoride Hydrates

    SciTech Connect

    Miskowiec, Andrew J.; Kirkegaard, Marie C.; Huq, Ashfia; Mamontov, Eugene; Herwig, Kenneth W.; Trowbridge, Lee D.; Rondinone, Adam Justin; Anderson, Brian B.

    2015-11-17

    We report a novel production method for uranium oxy uoride [(UO2)7F14(H2O)7] 4H2O, referred to as structure D. Structure D is produced as a product of hydrating anhydrous uranyl uoride, UO2F2, through the gas phase at ambient temperatures fol- lowed by desiccation by equilibration with a dry environment. We follow the structure of [(UO2)7F14(H2O)7] 4H2O through an intermediate, liquid-like phase, wherein the coordination number of the uranyl ion is reduced to 5 (from 6 in the anhydrous struc- ture), and a water molecule binds as an equatorial ligand to the uranyl ion. Quasielas- tic neutron scattering results compare well with previous measurements of mineral hydrates. The two groups of structurally distinct water molecules in D perform re- stricted motion on a length scale commensurate with the O{H bond (r = 0.92 A). The more tightly bound equatorial ligand waters rotate slower (Dr = 2.2 ps-1) than their hydrogen-bonded partners (Dr = 28.7 ps-1).

  13. Structures of two intermediate phases between the B1 and B2 phases of PbS under high pressure

    SciTech Connect

    Li, Yanchun E-mail: liuj@ihep.ac.cn; Lin, Chuanlong; Li, Xiaodong; Liu, Jing E-mail: liuj@ihep.ac.cn; Xu, Jian; Li, Gong

    2014-12-15

    The structural transitions of PbS were investigated at pressures up to 50 GPa using synchrotron powder and single crystal X-ray diffraction (XRD) methods in diamond anvil cells. We found two intermediate phases between the B1 phase under atmospheric pressure and the B2 phase at 21.1 GPa, which is different to previous reports. The structures of these two intermediate phases were indexed as B27 and B33, respectively. Their structural parameters were investigated using density functional theory (DFT) calculations. Our results provide a new insight into understanding the transition pathway between the B1 and B2 phases in PbS.

  14. Pressure dependence of the local structure of iridium ditelluride across the structural phase transition

    NASA Astrophysics Data System (ADS)

    Paris, E.; Joseph, B.; Iadecola, A.; Marini, C.; Ishii, H.; Kudo, K.; Pascarelli, S.; Nohara, M.; Mizokawa, T.; Saini, N. L.

    2016-04-01

    The local structure of IrTe2 has been studied by iridium L3-edge x-ray absorption spectroscopy (XAS) measurements as a function of pressure, performed at two temperatures (100 and 295 K) across the structural phase transition at ˜270 K. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectra show pressure-dependent anomalies, suggesting phase transitions that are characterized by different local atomic displacements. The high-temperature phase of IrTe2 (trigonal at 295 K) reveals a clear anomaly in the Ir-Te correlations at ˜4 GPa, while the low-temperature phase (at 100 K) shows a smaller change at ˜6 GPa, likely to be associated with transitions in lower-symmetry phases. XANES spectra, measuring higher-order atomic correlations, also show nonlinear pressure dependence in the local geometry at the anomalous pressures. These nonlinear changes suggest that IrTe2 goes through lower local symmetry phases with increasing pressure.

  15. Macromolecular ab initio phasing enforcing secondary and tertiary structure

    PubMed Central

    Millán, Claudia; Sammito, Massimo; Usón, Isabel

    2015-01-01

    Ab initio phasing of macromolecular structures, from the native intensities alone with no experimental phase information or previous particular structural knowledge, has been the object of a long quest, limited by two main barriers: structure size and resolution of the data. Current approaches to extend the scope of ab initio phasing include use of the Patterson function, density modification and data extrapolation. The authors’ approach relies on the combination of locating model fragments such as polyalanine α-helices with the program PHASER and density modification with the program SHELXE. Given the difficulties in discriminating correct small substructures, many putative groups of fragments have to be tested in parallel; thus calculations are performed in a grid or supercomputer. The method has been named after the Italian painter Arcimboldo, who used to compose portraits out of fruit and vegetables. With ARCIMBOLDO, most collections of fragments remain a ‘still-life’, but some are correct enough for density modification and main-chain tracing to reveal the protein’s true portrait. Beyond α-helices, other fragments can be exploited in an analogous way: libraries of helices with modelled side chains, β-strands, predictable fragments such as DNA-binding folds or fragments selected from distant homologues up to libraries of small local folds that are used to enforce nonspecific tertiary structure; thus restoring the ab initio nature of the method. Using these methods, a number of unknown macromolecules with a few thousand atoms and resolutions around 2 Å have been solved. In the 2014 release, use of the program has been simplified. The software mediates the use of massive computing to automate the grid access required in difficult cases but may also run on a single multicore workstation (http://chango.ibmb.csic.es/ARCIMBOLDO_LITE) to solve straightforward cases. PMID:25610631

  16. Analysis of Lipoplex Structure and Lipid Phase Changes

    SciTech Connect

    Koynova, Rumiana

    2012-07-18

    Efficient delivery of genetic material to cells is needed for tasks of utmost importance in the laboratory and clinic, such as gene transfection and gene silencing. Synthetic cationic lipids can be used as delivery vehicles for nucleic acids and are now considered the most promising nonviral gene carriers. They form complexes (lipoplexes) with the polyanionic nucleic acids. A critical obstacle for clinical application of the lipid-mediated DNA delivery (lipofection) is its unsatisfactory efficiency for many cell types. Understanding the mechanism of lipid-mediated DNA delivery is essential for their successful application, as well as for a rational design and synthesis of novel cationic lipoid compounds for enhanced gene delivery. A viewpoint now emerging is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids. In particular, recent studies showed that the phase evolution of lipoplex lipids upon interaction and mixing with membrane lipids appears to be decisive for transfection success: specifically, lamellar lipoplex formulations, which were readily susceptible to undergoing lamellar-nonlamellar phase transition upon mixing with cellular lipids and were found rather consistently associated with superior transfection potency, presumably as a result of facilitated DNA release. Thus, understanding the lipoplex structure and the phase changes upon interacting with membrane lipids is important for the successful application of the cationic lipids as gene carriers.

  17. Phase behavior and local structure of liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Fynewever, Herb

    In this work we use a combination of theory and computer simulation to study the phase behavior of liquid crystalline polymers and the local structure of polymer melts. We review experimental and simulation evidence which shows that long and stiff molecules form orientationally ordered phases at packing fractions intermediate between the liquid and the solid. With the aid of a two-molecule simulation, we are able to apply Onsager's theory [Ann. N. Y. Acad. Sci. 51, 627 (1949)] for liquid crystal formation to flexible molecules without any additional approximations. Our results have a quantitative advantage over other theories in comparison with computer simulation data such as for the liquid-liquid crystal phase diagram. We also study the local structure of polymer melts using a two-molecule simulation to apply the density functional theories of Donley, Curro, and McCoy [J. Chem. Phys. 101 , 3205 (1994)1; and Yethiraj and Woodward [J. Chem. Phys 102 , 5499 (1995)]. The accuracy of these methods rivals that of integral equation theories in their predictions of local order. Further, the two-molecule simulation facilitates a more direct calculation of the equation of state via the monitoring of orientational correlations.

  18. Magnetic phase structure of Saturn's 10.7 h oscillations

    NASA Astrophysics Data System (ADS)

    Yates, J. N.; Southwood, D. J.; Dougherty, M. K.

    2015-04-01

    A source of Saturn's magnetic 10.7 h period oscillations has yet to be identified. The oscillations are known to consist of signals with slightly different periods from separate northern and southern sources. Here we present a novel way of examining observations, focusing on signal phase. We show that although the signals are highly periodic they are usually not sinusoidal and that there are differences in both phase structure and polarization between the outer magnetosphere (on the nightside) and the inner dipolar region. Paying particular attention to the deep midtail passes of 2006, the contrasting behavior between the inner and outer regions is clear with approximate sinusoidal behavior in the dipolar region and a pulse-like signal once per cycle in the tail. The latter structure seems to indicate that tail magnetic stress is released impulsively once per cycle in the tail. After equinox, in 2010-2011, we find a different picture in the premidnight sector. The predetermined northern and southern frequencies are closer together and apparently show sudden shifts. Our signal reconstruction approach finds instances where it is likely that the narrow band filtering is not able to track completely the basic north and south periods as we find phase jumps indicating unpredicted beats.

  19. Structural and topological phase transitions on the German Stock Exchange

    NASA Astrophysics Data System (ADS)

    Wiliński, M.; Sienkiewicz, A.; Gubiec, T.; Kutner, R.; Struzik, Z. R.

    2013-12-01

    We find numerical and empirical evidence for dynamical, structural and topological phase transitions on the (German) Frankfurt Stock Exchange (FSE) in the temporal vicinity of the worldwide financial crash. Using the Minimal Spanning Tree (MST) technique, a particularly useful canonical tool of the graph theory, two transitions of the topology of a complex network representing the FSE were found. The first transition is from a hierarchical scale-free MST representing the stock market before the recent worldwide financial crash, to a superstar-like MST decorated by a scale-free hierarchy of trees representing the market’s state for the period containing the crash. Subsequently, a transition is observed from this transient, (meta)stable state of the crash to a hierarchical scale-free MST decorated by several star-like trees after the worldwide financial crash. The phase transitions observed are analogous to the ones we obtained earlier for the Warsaw Stock Exchange and more pronounced than those found by Onnela-Chakraborti-Kaski-Kertész for the S&P 500 index in the vicinity of Black Monday (October 19, 1987) and also in the vicinity of January 1, 1998. Our results provide an empirical foundation for the future theory of dynamical, structural and topological phase transitions on financial markets.

  20. Analysis of lipoplex structure and lipid phase changes.

    PubMed

    Koynova, Rumiana

    2010-01-01

    Efficient delivery of genetic material to cells is needed for tasks of utmost importance in the laboratory and clinic, such as gene transfection and gene silencing. Synthetic cationic lipids can be used as delivery vehicles for nucleic acids and are now considered the most promising nonviral gene carriers. They form complexes (lipoplexes) with the polyanionic nucleic acids. A critical obstacle for clinical application of the lipid-mediated DNA delivery (lipofection) is its unsatisfactory efficiency for many cell types. Understanding the mechanism of lipid-mediated DNA delivery is essential for their successful application, as well as for a rational design and synthesis of novel cationic lipoid compounds for enhanced gene delivery. A viewpoint now emerging is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids. In particular, recent studies showed that the phase evolution of lipoplex lipids upon interaction and mixing with membrane lipids appears to be decisive for transfection success: specifically, lamellar lipoplex formulations, which were readily susceptible to undergoing lamellar-nonlamellar phase transition upon mixing with cellular lipids and were found rather consistently associated with superior transfection potency, presumably as a result of facilitated DNA release. Thus, understanding the lipoplex structure and the phase changes upon interacting with membrane lipids is important for the successful application of the cationic lipids as gene carriers. PMID:20013412

  1. Phase-field-crystal methodology for modeling of structural transformations.

    PubMed

    Greenwood, Michael; Rottler, Jörg; Provatas, Nikolas

    2011-03-01

    We introduce and characterize free-energy functionals for modeling of solids with different crystallographic symmetries within the phase-field-crystal methodology. The excess free energy responsible for the emergence of periodic phases is inspired by classical density-functional theory, but uses only a minimal description for the modes of the direct correlation function to preserve computational efficiency. We provide a detailed prescription for controlling the crystal structure and introduce parameters for changing temperature and surface energies, so that phase transformations between body-centered-cubic (bcc), face-centered-cubic (fcc), hexagonal-close-packed (hcp), and simple-cubic (sc) lattices can be studied. To illustrate the versatility of our free-energy functional, we compute the phase diagram for fcc-bcc-liquid coexistence in the temperature-density plane. We also demonstrate that our model can be extended to include hcp symmetry by dynamically simulating hcp-liquid coexistence from a seeded crystal nucleus. We further quantify the dependence of the elastic constants on the model control parameters in two and three dimensions, showing how the degree of elastic anisotropy can be tuned from the shape of the direct correlation functions. PMID:21517507

  2. Crystal structure and phase transition of thermoelectric SnSe.

    PubMed

    Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

    2016-06-01

    Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed. PMID:27240762

  3. High-throughput determination of structural phase diagram and constituent phases using GRENDEL.

    PubMed

    Kusne, A G; Keller, D; Anderson, A; Zaban, A; Takeuchi, I

    2015-11-01

    Advances in high-throughput materials fabrication and characterization techniques have resulted in faster rates of data collection and rapidly growing volumes of experimental data. To convert this mass of information into actionable knowledge of material process-structure-property relationships requires high-throughput data analysis techniques. This work explores the use of the Graph-based endmember extraction and labeling (GRENDEL) algorithm as a high-throughput method for analyzing structural data from combinatorial libraries, specifically, to determine phase diagrams and constituent phases from both x-ray diffraction and Raman spectral data. The GRENDEL algorithm utilizes a set of physical constraints to optimize results and provides a framework by which additional physics-based constraints can be easily incorporated. GRENDEL also permits the integration of database data as shown by the use of critically evaluated data from the Inorganic Crystal Structure Database in the x-ray diffraction data analysis. Also the Sunburst radial tree map is demonstrated as a tool to visualize material structure-property relationships found through graph based analysis. PMID:26469294

  4. High-throughput determination of structural phase diagram and constituent phases using GRENDEL

    NASA Astrophysics Data System (ADS)

    Kusne, A. G.; Keller, D.; Anderson, A.; Zaban, A.; Takeuchi, I.

    2015-11-01

    Advances in high-throughput materials fabrication and characterization techniques have resulted in faster rates of data collection and rapidly growing volumes of experimental data. To convert this mass of information into actionable knowledge of material process-structure-property relationships requires high-throughput data analysis techniques. This work explores the use of the Graph-based endmember extraction and labeling (GRENDEL) algorithm as a high-throughput method for analyzing structural data from combinatorial libraries, specifically, to determine phase diagrams and constituent phases from both x-ray diffraction and Raman spectral data. The GRENDEL algorithm utilizes a set of physical constraints to optimize results and provides a framework by which additional physics-based constraints can be easily incorporated. GRENDEL also permits the integration of database data as shown by the use of critically evaluated data from the Inorganic Crystal Structure Database in the x-ray diffraction data analysis. Also the Sunburst radial tree map is demonstrated as a tool to visualize material structure-property relationships found through graph based analysis.

  5. Femtosecond resolution of soft mode dynamics in structural phase transitions

    NASA Technical Reports Server (NTRS)

    Dougherty, Thomas P.; Wiederrecht, Gary P.; Nelson, Keith A.; Garrett, Mark H.; Jensen, Hans P.; Warde, Cardinal

    1992-01-01

    The microscopic pathway along which ions or molecules in a crystal move during structural phase transition can often be described in terms of a collective vibrational mode of the lattice. In many cases, this mode, called a 'soft' phonon mode because of its characteristically low frequency near the phase transition temperature, is difficult to characterize through conventional frequency-domain spectroscopies such as light or neutron scattering. A femtosecond time-domain analog of light-scattering spectroscopy called impulsive stimulated Raman scattering (ISRS) has been used to examine the soft modes of two perovskite ferroelectric crystals. The low-frequency lattice dynamics of KNbO3 and BaTiO3 are clarified in a manner that permits critical evaluation of microscopic models for their ferroelectric transitions. The results illustrate the advantages of ISRS over conventional Raman spectroscopy of low-frequency, heavily damped soft modes.

  6. [How to accompany a suicidal patient].

    PubMed

    Dorfman Lerner, B

    1986-06-01

    In this paper the author offers the prospective T.C. an orientation for the treatment of patients who have intended suicide. After examining general questions such as who and when people commit suicide, she presents an "Assessment of self-destructive potentiality" by Tabachnik & Farberow as a guide to the best prevention of the suicidal act. The metapsychological view of Freud as regards the repressed homicidal motivation in suicide is complemented by the views of Garma and Abadi. In respect to the process of accompaniment in these cases, the author suggests the appearance of four phases (simultaneous or in succession) that are: 1. the presence and the regard in which what is important for the patient is that the T.C. is there and affectionately regards him; 2. the listening, in which the T.C. provides facilities for the patient to speak; 3. the key word, in which "I comprehend" is the privileged T.C. expression; and 4. the dialogue. Within phase 3. discrimination can be made between different psycholinguistic aspects of the key expression, such as: a) its constituting aspects; b) its catarctic or economic aspect; c) its meaning a recognition of the patient's identity; and d) the emergence of hope. Also, as suicide is the end point of different psychopathologies, a brief indication of possible T.C. responses is given. In all these, the principal aim is to help the patient to elaborate a new life project. A clinical successful example shows how three T.C. were included in the treatment of a suicidal patient to accompany her in the recognition and tolerance of her own and others' aggressive feelings. Some philosophical considerations are added. PMID:3788628

  7. Molecular-dynamics simulation of tweed structure and the ω phase in Ni-Al

    NASA Astrophysics Data System (ADS)

    Becquart, C. S.; Clapp, P. C.; Rifkin, J. A.

    1993-07-01

    Using computer molecular dynamics (CMD) we have studied the occurrence of tweed structure and of the ω phase in Ni62.5Al37.5. Tweed is a mottled structure that is observed prior to transformations such as martensitic transformations. In some cases, it has been found to accompany ω-phase formation. The characteristic features of tweed have been simulated. To achieve the 62.5-37.5 composition we started with a 50%-50% stoichiometry in which some aluminum atoms were replaced by nickel. Two different lattices were used: one where the nickel atoms were distributed at random on the aluminum sublattice (referred to as the disordered B2 array) and one where they were arranged in an ordered manner (ordered supercell bcc). To describe the forces that interact between the atoms an embedded-atom method was chosen with an interatomic potential derived by Voter and Chen [1] [in Characterization of Defects in Materials, edited by R. W. Siegal, J. R. Weertman, and R. Sinclair, MRS Symposia Proceedings No. 82 (Materials Research Society, Pittsburgh, 1987)], which has been designed to fit some properties of Ni3Al, and some of NiAl, while maintaining good behavior for compositions in between. In the case of the disordered B2 array, diffuse streakings were observed in the diffraction patterns of the structures obtained from the CMD simulations, mainly along the <110>* directions but some also along the <112>* direction. The <112>* streaking is usually associated with the formation of the ω phase. However, with the ordered array, virtually no streaking appeared, strongly suggesting that heterogeneous defects (such as compositional disorder) are necessary to induce both tweed structure and the ω phase. The main type of streaking is typically seen on diffraction patterns of materials displaying tweed. By plotting the positions of the atoms and their displacements after the CMD runs we also noticed <110>\\{100\\} shears, again in the disordered lattice. The influence of temperature on

  8. A phased approach to enable hybrid simulation of complex structures

    NASA Astrophysics Data System (ADS)

    Spencer, Billie F.; Chang, Chia-Ming; Frankie, Thomas M.; Kuchma, Daniel A.; Silva, Pedro F.; Abdelnaby, Adel E.

    2014-08-01

    Hybrid simulation has been shown to be a cost-effective approach for assessing the seismic performance of structures. In hybrid simulation, critical parts of a structure are physically tested, while the remaining portions of the system are concurrently simulated computationally, typically using a finite element model. This combination is realized through a numerical time-integration scheme, which allows for investigation of full system-level responses of a structure in a cost-effective manner. However, conducting hybrid simulation of complex structures within large-scale testing facilities presents significant challenges. For example, the chosen modeling scheme may create numerical inaccuracies or even result in unstable simulations; the displacement and force capacity of the experimental system can be exceeded; and a hybrid test may be terminated due to poor communication between modules (e.g., loading controllers, data acquisition systems, simulation coordinator). These problems can cause the simulation to stop suddenly, and in some cases can even result in damage to the experimental specimens; the end result can be failure of the entire experiment. This study proposes a phased approach to hybrid simulation that can validate all of the hybrid simulation components and ensure the integrity large-scale hybrid simulation. In this approach, a series of hybrid simulations employing numerical components and small-scale experimental components are examined to establish this preparedness for the large-scale experiment. This validation program is incorporated into an existing, mature hybrid simulation framework, which is currently utilized in the Multi-Axial Full-Scale Sub-Structuring Testing and Simulation (MUST-SIM) facility of the George E. Brown Network for Earthquake Engineering Simulation (NEES) equipment site at the University of Illinois at Urbana-Champaign. A hybrid simulation of a four-span curved bridge is presented as an example, in which three piers are

  9. Ab initio molecular crystal structures, spectra, and phase diagrams.

    PubMed

    Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni

    2014-09-16

    Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling

  10. Stabilizing the hexagonal close packed structure of hard spheres with polymers: Phase diagram, structure, and dynamics.

    PubMed

    Edison, John R; Dasgupta, Tonnishtha; Dijkstra, Marjolein

    2016-08-01

    We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures. PMID:27497577

  11. Stabilizing the hexagonal close packed structure of hard spheres with polymers: Phase diagram, structure, and dynamics

    NASA Astrophysics Data System (ADS)

    Edison, John R.; Dasgupta, Tonnishtha; Dijkstra, Marjolein

    2016-08-01

    We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures.

  12. Phase chemistry, structure, and radiation effects in lunar samples.

    PubMed

    Arrhenius, G; Asunmaa, S; Drever, J I; Everson, J; Fitzgerald, R W; Frazer, J Z; Fujita, H; Hanor, J S; Lal, D; Liang, S S; Macdougall, D; Reid, A M; Sinkankas, J; Wilkening, L

    1970-01-30

    Phase chemistry, structure, and radiation effects were studied in rock, breccia, and soil samples. The regolith apparently developed in the final stages of accretion and was modified by later impact processes and radiation weathering. Exposure ages indicate transfer of buried igneous rock fragments to the near surface late in lunar history. With a few exceptions igneous rock fragments, soil, and breccia share the same distinctive chemistry, probably acquired before accretion of the moon. The igneous rocks texturally resemble basaltic achondrites, and the soil and breccias contain glassy spheres analogous to chondrules. PMID:17781535

  13. Structure of compact stars in a pion superfluid phase

    NASA Astrophysics Data System (ADS)

    Mao, Shijun

    2014-06-01

    The gross structure of compact stars composed of pion superfluid quark matter is investigated in the frame of the Nambu-Jona-Lasinio model. Under the Pauli-Villars regularization scheme, the uncertainty of the thermodynamic functions for inhomogeneous states is cured, and the Larkin-Ovchinnikov-Fulde-Ferrel state that appeared in the hard cutoff scheme is removed from the phase diagram of the pion superfluid. Different from the unpaired quark matter and color superconductor, the strongly coupled pion superfluid is a possible candidate of compact stars with mass M ≃3M⊙ and radius R ≃14 km.

  14. PHASE STRUCTURE OF TWISTED EGUCHI-KAWAI MODEL.

    SciTech Connect

    ISHIKAWA,T.; AZEYANAGI, T.; HANADA, M.; HIRATA, T.

    2007-07-30

    We study the phase structure of the four-dimensional twisted Eguchi-Kawai model using numerical simulations. This model is an effective tool for studying SU(N) gauge theory in the large-N limit and provides a nonperturbative formulation of the gauge theory on noncommutative spaces. Recently it was found that its Z{sub n}{sup 4} symmetry, which is crucial for the validity of this model, can break spontaneously in the intermediate coupling region. We investigate in detail the symmetry breaking point from the weak coupling side. Our simulation results show that the continuum limit of this model cannot be taken.

  15. Evolutionary dynamics and the phase structure of the minority game

    NASA Astrophysics Data System (ADS)

    Yuan, Baosheng; Chen, Kan

    2004-06-01

    We show that a simple evolutionary scheme, when applied to the minority game (MG), changes the phase structure of the game. In this scheme each agent evolves individually whenever his wealth reaches the specified bankruptcy level, in contrast to the evolutionary schemes used in the previous works. We show that evolution greatly suppresses herding behavior, and it leads to better overall performance of the agents. Similar to the standard nonevolutionary MG, the dependence of the standard deviation σ on the number of agents N and the memory length m can be characterized by a universal curve. We suggest a crowd-anticrowd theory for understanding the effect of evolution in the MG.

  16. Shadows of anyons and the entanglement structure of topological phases

    PubMed Central

    Haegeman, J.; Zauner, V.; Schuch, N.; Verstraete, F.

    2015-01-01

    The low-temperature dynamics of quantum systems are dominated by the low-energy eigenstates. For two-dimensional systems in particular, exotic phenomena such as topological order and anyon excitations can emerge. While a complete low-energy description of strongly correlated systems is hard to obtain, essential information about the elementary excitations is encoded in the eigenvalue structure of the quantum transfer matrix. Here we study the transfer matrix of topological quantum systems using the tensor network formalism and demonstrate that topological quantum order requires a particular type of ‘symmetry breaking' for the fixed point subspace. We also relate physical anyon excitations to domain-wall excitations at the level of the transfer matrix. This formalism enables us to determine the structure of the topological sectors in two-dimensional gapped phases very efficiently, therefore opening novel avenues for studying fundamental questions related to anyon condensation and confinement. PMID:26440783

  17. Nonlinear instabilities driven by coherent phase-space structures

    NASA Astrophysics Data System (ADS)

    Lesur, Maxime

    2012-10-01

    Coherent phase-space (PS) structures are an important feature of plasma turbulence. They can drive nonlinear instabilities [1], intermittency in drift-wave turbulence [2], and transport [3]. We aim at a comprehensive understanding of turbulence, not just as an ensemble of waves, as quasilinear theory implies, but as a mixture of coupled waves and localized structures. This work, which focuses on isolated PS structures, is a fundamental advance in this direction. We analyze the effects of self-binding negative fluctuations (PS holes) on stability, intermittency and anomalous resistivity, both analytically and numerically. We present a new theory which describes the growth of a hole or clump [4]. We find that PS holes grow nonlinearly, independently of linear stability. Numerical simulations clarify the physics of nonlinear instabilities in both subcritical and supercritical conditions. When many resonances are unstable, several holes can coalesce into one main macro-scale structure, which survives much longer than a quasilinear diffusion time, suggesting that it may be crucial to resolve phase-space turbulence in analytical and numerical studies of transport. These findings are applied to two fundamental paradigms of plasma physics: bump-on-tail instabilities in 1D electronic plasma and current-driven ion-acoustic instabilities electron-ion plasma. Our results expose important limits of routinely-used linear and quasilinear theories.[4pt] [1] T.H. Dupree, Phys. Fluids 15, 334 (1972); R.H. Berman et al., Phys. Rev. Lett. 48, 1249 (1982).[0pt] [2] P.W. Terry, P.H. Diamond, and T.S. Hahm, Phys. Fluids B 2, 2048 (1990).[0pt] [3] H. Biglari et al., Phys. Fluids 31, 2644 (1988); Y. Kosuga et al., Phys. Plasmas 18, 122305 (2011).[0pt] [4] M. Lesur, P.H. Diamond, submitted to Phys. Rev. Lett.

  18. Polarization-phase tomography of biological fluids polycrystalline structure

    NASA Astrophysics Data System (ADS)

    Dubolazov, A. V.; Vanchuliak, O. Ya.; Garazdiuk, M.; Sidor, M. I.; Motrich, A. V.; Kostiuk, S. V.

    2013-12-01

    Our research is aimed at designing an experimental method of Fourier's laser polarization phasometry of the layers of human effusion for an express diagnostics during surgery and a differentiation of the degree of severity (acute - gangrenous) appendectomy by means of statistical, correlation and fractal analysis of the coherent scattered field. A model of generalized optical anisotropy of polycrystal networks of albumin and globulin of the effusion of appendicitis has been suggested and the method of Fourier's phasometry of linear (a phase shift between the orthogonal components of the laser wave amplitude) and circular (the angle of rotation of the polarization plane) birefringence with a spatial-frequency selection of the coordinate distributions for the differentiation of acute and gangrenous conditions have been analytically substantiated. Comparative studies of the efficacy of the methods of direct mapping of phase distributions and Fourier's phasometry of a laser radiation field transformed by the dendritic and spherolitic networks of albumin and globulin of the layers of effusion of appendicitis on the basis of complex statistical, correlation and fractal analysis of the structure of phase maps.

  19. 10 CFR 9.56 - Accompanying persons.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... for Information, Access Or Amendment of Records Maintained About Them § 9.56 Accompanying persons. An individual requesting access to records about himself may be accompanied by another individual of his own choosing. Both the individual requesting access and the individual accompanying him shall sign the...

  20. 19 CFR 148.4 - Accompanying articles.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 19 Customs Duties 2 2012-04-01 2012-04-01 false Accompanying articles. 148.4 Section 148.4 Customs... (CONTINUED) PERSONAL DECLARATIONS AND EXEMPTIONS General Provisions § 148.4 Accompanying articles. (a) Generally. Articles shall be considered as accompanying a passenger or brought in by him if the...

  1. 19 CFR 148.4 - Accompanying articles.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 19 Customs Duties 2 2014-04-01 2014-04-01 false Accompanying articles. 148.4 Section 148.4 Customs... (CONTINUED) PERSONAL DECLARATIONS AND EXEMPTIONS General Provisions § 148.4 Accompanying articles. (a) Generally. Articles shall be considered as accompanying a passenger or brought in by him if the...

  2. 19 CFR 148.4 - Accompanying articles.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 19 Customs Duties 2 2013-04-01 2013-04-01 false Accompanying articles. 148.4 Section 148.4 Customs... (CONTINUED) PERSONAL DECLARATIONS AND EXEMPTIONS General Provisions § 148.4 Accompanying articles. (a) Generally. Articles shall be considered as accompanying a passenger or brought in by him if the...

  3. 19 CFR 148.4 - Accompanying articles.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 2 2011-04-01 2011-04-01 false Accompanying articles. 148.4 Section 148.4 Customs... (CONTINUED) PERSONAL DECLARATIONS AND EXEMPTIONS General Provisions § 148.4 Accompanying articles. (a) Generally. Articles shall be considered as accompanying a passenger or brought in by him if the...

  4. 19 CFR 148.4 - Accompanying articles.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 2 2010-04-01 2010-04-01 false Accompanying articles. 148.4 Section 148.4 Customs... (CONTINUED) PERSONAL DECLARATIONS AND EXEMPTIONS General Provisions § 148.4 Accompanying articles. (a) Generally. Articles shall be considered as accompanying a passenger or brought in by him if the...

  5. Structural phase transitions and superconductivity in lanthanum copper oxides

    SciTech Connect

    Crawford, M.K.; Harlow, R.L.; McCarron, E.M.

    1996-12-31

    Despite the enormous effort expended over the past ten years to determine the mechanism underlying high temperature superconductivity in cuprates there is still no consensus on the physical origin of this fascinating phenomenon. This is a consequence of a number of factors, among which are the intrinsic difficulties in understanding the strong electron correlations in the copper oxides, determining the roles played by antiferromagnetic interactions and low dimensionality, analyzing the complex phonon dispersion relationships, and characterizing the phase diagrams which are functions of the physical parameters of temperature and pressure, as well as the chemical parameters of stoichiometry and hole concentration. In addition to all of these intrinsic difficulties, extrinsic materials issues such as sample quality and homogeneity present additional complications. Within the field of high temperature superconductivity there exists a subfield centered around the material originally reported to exhibit high temperature superconductivity by Bednorz and Mueller, Ba doped La{sub 2}CuO{sub 4}. This is structurally the simplest cuprate superconductor. The authors report on studies of phase differences observed between such base superconductors doped with Ba or Sr. What these studies have revealed is a fascinating interplay of structural, magnetic and superconducting properties which is unique in the field of high temperature superconductivity and is summarized in this paper.

  6. Design of reconfigurable and structured spiral phase mask for optical security system

    NASA Astrophysics Data System (ADS)

    Lin, Chao; Shen, Xueju

    2016-07-01

    We propose the design and use of structured spiral phase mask as keys in optical security systems. A protocol for the generation of this deterministic and reconfigurable phase mask is demonstrated. Experimental results of the proposed phase masks employed in the double random phase encoding (DRPE) system is presented. To show the advantages of this structured phase mask (SPM) over the random phase mask (RPM), both the encryption and decryption behaviors of the SPM and RPM are compared.

  7. Investigation of Structural Phase Transitions on Wurtzite Gallium Nitride Surfaces

    NASA Astrophysics Data System (ADS)

    Chen, Tianjiao; Chinchore, Abhijit; Liu, Yinghao; Wang, Kangkang; Lin, Wenzhi; Smith, Arthur

    2009-03-01

    Surface structures of wurtzite gallium nitride (w-GaN) have been investigated previously,[1][2] and it is well known that above 300K there exist order-disorder phase transitions. For N-polar w-GaN (000-1) at 300K, a family of surface reconstructions occurs, including 1x1, 3x3, 6x6, and c(6x12). Not much is known, however, about what happens to these structures as they are cooled below 300K. We have recently developed a new epitaxy/analysis system, including a sample stage which can be both heated and cooled. The N-polar w-GaN surfaces are prepared using rf N-plasma-assisted molecular beam epitaxy, and monitored in-situ using reflection high energy electron diffraction (RHEED). The approach is to monitor the [11-20] and [10-10] RHEED diffractions during cryogenic cooling, starting with the 1x1 or 3x3 structures. A critical issue to explore is the interrelationship between surface gallium concentration and structural deformation. This study may provide the missing link to new reconstructions of w-GaN recently observed using LT scanning tunneling microscopy.[3] This work is supported by NSF (Grant No. 0730257). [1] A. R. Smith et al., Phys. Rev. Lett. 79, 3934 (1997). [2] A. R. Smith et al., Surface Science 423, 70 (1999). [3] D. Acharya, S.-W. Hla et al., unpublished.

  8. Structural phase transitions of sodium nitride at high pressure

    NASA Astrophysics Data System (ADS)

    Vajenine, G. V.; Wang, X.; Efthimiopoulos, I.; Karmakar, S.; Syassen, K.; Hanfland, M.

    2009-06-01

    The structural evolution of recently characterized sodium nitride Na3N as a function of pressure was investigated at room temperature by the angle-dispersive powder x-ray diffraction in a diamond-anvil cell up to 36 GPa. The rather open cubic anti- ReO3 -type structure stable at ambient pressure is followed by a series of four high-pressure modifications. Along the route, the coordination number for the nitride anion increases from 6 in Na3N-I to 8 in hexagonal Li3N -type Na3N-II , 9 in orthorhombic anti- YF3 -type Na3N-III , 11 in hexagonal Cu3P -type Na3N-IV , and finally 14 in cubic Li3Bi -type Na3N-V structures. The experimental data are compared to the results of total-energy calculations and are discussed with regard to the structural details of the five phases and their equations of state.

  9. Structures, electronic properties and stability phase diagrams for copper(I/II) bromide surfaces.

    PubMed

    Altarawneh, Mohammednoor; Marashdeh, Ali; Dlugogorski, Bogdan Z

    2015-04-14

    This study presents a comprehensive periodic slab DFT investigation into structures, electronic properties and thermodynamic stability of all plausible terminations of CuBr and CuBr2 surfaces. We first estimate lattice constants, formation and cohesive energies for the two bulk copper bromides before proceeding to analyse geometrical and electronic features of CuBr and CuBr2 configurations. Surface geometries exhibit, to a large extent, corresponding bulk structures. Nevertheless, certain CuBr2 surfaces experience a downward displacement of the topmost Cu-containing layers. We plot total and projected density of states for bulk and surface geometries of these two copper bromides and calculate their associated Bader's electronic charges. Electronic structure analysis for the bulk and surfaces of these two copper bromides show that CuBr bulk and its most stable surface (CuBr(001)_Br) do not exhibit any metallic character, whereas CuBr2 bulk and its most stable surface (CuBr2(001)_Br) both exhibit metallic characters. The formalism of the ab initio atomistic thermodynamics affords the construction of energy phase diagrams. We predict that the CuBr(001) surface, truncated with Br atoms, is the most stable structure among the considered CuBr slabs at all physically meaningful ranges of the chemical potential of bromine. This surface resembles a c(2 × 2)-bromine sheet that was characterised experimentally from initial interaction of Br2 with a Cu(100) surface. We find that surfaces terminated with the electronegative bromine atoms, if accompanied by significant relaxation, tend to be more stable. Calculated surface energies predict the shapes of CuBr and CuBr2 nanoparticles as the chemical potential of bromine changes. PMID:25760395

  10. Insight into the microscopic structure of an AdS black hole from a thermodynamical phase transition.

    PubMed

    Wei, Shao-Wen; Liu, Yu-Xiao

    2015-09-11

    Comparing with an ordinary thermodynamic system, we investigate the possible microscopic structure of a charged anti-de Sitter black hole completely from the thermodynamic viewpoint. The number density of the black hole molecules is introduced to measure the microscopic degrees of freedom of the black hole. We found that the number density suffers a sudden change accompanied by a latent heat when the black hole system crosses the small-large black hole coexistence curve, while when the system passes the critical point, it encounters a second-order phase transition with a vanishing latent heat due to the continuous change of the number density. Moreover, the thermodynamic scalar curvature suggests that there is a weak attractive interaction between two black hole molecules. These phenomena might cast new insight into the underlying microscopic structure of a charged anti-de Sitter black hole. PMID:26406818

  11. Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing

    PubMed Central

    Terwilliger, Thomas C.; Bunkóczi, Gábor; Hung, Li-Wei; Zwart, Peter H.; Smith, Janet L.; Akey, David L.; Adams, Paul D.

    2016-01-01

    A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. A simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment is presented. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined. In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. This means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure. PMID:26960122

  12. Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing.

    PubMed

    Terwilliger, Thomas C; Bunkóczi, Gábor; Hung, Li Wei; Zwart, Peter H; Smith, Janet L; Akey, David L; Adams, Paul D

    2016-03-01

    A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. A simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment is presented. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined. In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. This means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure. PMID:26960122

  13. Evolution of molecular crystal optical phonons near structural phase transitions

    NASA Astrophysics Data System (ADS)

    Michki, Nigel; Niessen, Katherine; Xu, Mengyang; Markelz, Andrea

    Molecular crystals are increasingly important photonic and electronic materials. For example organic semiconductors are lightweight compared to inorganic semiconductors and have inexpensive scale up processing with roll to roll printing. However their implementation is limited by their environmental sensitivity, in part arising from the weak intermolecular interactions of the crystal. These weak interactions result in optical phonons in the terahertz frequency range. We examine the evolution of intermolecular interactions near structural phase transitions by measuring the optical phonons as a function of temperature and crystal orientation using terahertz time-domain spectroscopy. The measured orientation dependence of the resonances provides an additional constraint for comparison of the observed spectra with the density functional calculations, enabling us to follow specific phonon modes. We observe crystal reorganization near 350 K for oxalic acid as it transforms from dihydrate to anhydrous form. We also report the first THz spectra for the molecular crystal fructose through its melting point.

  14. Structural-phase state and creep of mixed nitride fuel

    NASA Astrophysics Data System (ADS)

    Konovalov, I. I.; Tarasov, B. A.; Glagovsky, E. M.

    2016-04-01

    By the analysis of thermal creep data in conjunction with structural-phase state the most likely mechanisms of UN creep are considered. An equation relating the thermal and radiation creep of nitride fuel with such important parameters as plutonium content, porosity, grain size, the content of impurities of transition metals and oxygen, the carbon content has been suggested. At stationary operating parameters in reactor the creep of nitride fuel with technical purity is defined by the thermal component at mechanism of intergranular slip and by the radiation component, which plays a significant role at temperatures below 1100°C. Both types of creep in a first approximation have a linear dependence on the stress.

  15. Electronic structure and phase equilibria in ternary substitutional alloys

    SciTech Connect

    Traiber, A.J.S.; Allen, S.M.; Turchi, P.E.A.; Waterstrat, R.M.

    1996-04-26

    A reliable, consistent scheme to study phase equilibria in ternary substitutional alloys based on the tight-binding approximation is presented. With electronic parameters from linear muffin-tin orbital calculations, the computed density of states and band structures compare well with those from more accurate {ital ab}{ital initio} calculations. Disordered alloys are studied within the tight-binding coherent-potential approximation extended to alloys; energetics of ordered systems are obtained through effective pair interactions computed with the general perturbation method; and partially ordered alloys are studied with a novel simplification of the molecular coherent-potential approximation combined with the general perturbation method. The formalism is applied to bcc-based Zr-Ru-Pd alloys which are promising candidates for medical implant devices. Using energetics obtained from the above scheme, we apply the cluster- variation method to study phase equilibria for particular pseudo- binary alloys and show that results are consistent with observed behavior of electronic specific heat coefficient with composition for Zr{sub 0.5}(Ru, Pd){sub 0.5}.

  16. The peculiar phase structure of random graph bisection

    SciTech Connect

    Percus, Allon G; Istrate, Gabriel; Goncalves, Bruno T; Sumi, Robert Z

    2008-01-01

    The mincut graph bisection problem involves partitioning the n vertices of a graph into disjoint subsets, each containing exactly n/2 vertices, while minimizing the number of 'cut' edges with an endpoint in each subset. When considered over sparse random graphs, the phase structure of the graph bisection problem displays certain familiar properties, but also some surprises. It is known that when the mean degree is below the critical value of 2 log 2, the cutsize is zero with high probability. We study how the minimum cutsize increases with mean degree above this critical threshold, finding a new analytical upper bound that improves considerably upon previous bounds. Combined with recent results on expander graphs, our bound suggests the unusual scenario that random graph bisection is replica symmetric up to and beyond the critical threshold, with a replica symmetry breaking transition possibly taking place above the threshold. An intriguing algorithmic consequence is that although the problem is NP-hard, we can find near-optimal cutsizes (whose ratio to the optimal value approaches 1 asymptotically) in polynomial time for typical instances near the phase transition.

  17. Electronic structure, phase transitions and diffusive properties of elemental plutonium

    NASA Astrophysics Data System (ADS)

    Setty, Arun; Cooper, B. R.

    2003-03-01

    We present a SIC-LDA-LMTO based study of the electronic structure of the delta, alpha and gamma phases of plutonium, and also of the alpha and gamma phases of elemental cerium. We find excellent agreement with the experimental densities and magnetic properties [1]. Furthermore, detailed studies of the computational densities of states for delta plutonium, and comparison with the experimental photoemission spectrum [2], provide evidence for the existence of an unusual fluctuating valence state. Results regarding the vacancy formation and self-diffusion in delta plutonium will be presented. Furthermore, a study of interface diffusion between plutonium and steel (technologically relevant in the storage of spent fuel) or other technologically relevant alloys will be included. Preliminary results regarding gallium stabilization of delta plutonium, and of plutonium alloys will be presented. [1] M. Dormeval et al., private communication (2001). [2] A. J. Arko, J. J. Joyce, L. Morales, J. Wills, and J. Lashley et. al., Phys. Rev. B, 62, 1773 (2000). [3] B. R. Cooper et al, Phil. Mag. B 79, 683 (1999); B.R. Cooper, Los Alamos Science 26, 106 (2000)); B.R. Cooper, A.K. Setty and D.L.Price, to be published.

  18. Structure of ionospheric irregularities from amplitude and phase scintillation observations

    SciTech Connect

    Bhattacharyya, A.; Rastogi, R.G. )

    1991-04-01

    The mutual coherence function Gamma 2, or the second moment of the complex amplitude of a radio wave which traverses through equatorial F region irregularities, is computed from amplitude and phase scintillation data. Theoretically, the equation satisfied by the coherence function has an analytic solution over the whole range of scintillation strength. This solution is directly related to the structure function for the phase fluctuations produced by the irregularities. Hence, the shape of the correlation function for variations in the total electron content along the signal path can be derived from the computed values of Gamma 2. With a suitable power-law model for the irregularities, an 'intermediate break scale', this scale, as well as the rms density fluctuation are deduced from a comparison of computed values for short-time lags with those expected from theory. During a postsunset scintillation event, this scale is found to increase with local time. In the context of the generalized Rayleigh-Taylor instability, which is the likely source of the irregularities, this increase may be attributed to a decline in the effective electric field prevailing in the region of the irregularities. 26 refs.

  19. Structure and phase behavior of aqueous methylcellulose solutions

    NASA Astrophysics Data System (ADS)

    McAllister, John; Schmidt, Peter; Lodge, Timothy; Bates, Frank

    2015-03-01

    Cellulose ethers (CE) constitute a multi-billion dollar industry, and have found end uses in a broad array of applications from construction materials, food products, personal care products, and pharmaceuticals for more than 80 years. Methylcellulose (MC, with the trade name METHOCEL™) is a CE in which there is a partial substitution of -OH groups with -OCH3 groups. This results in a polymer that is water-soluble at low temperatures, and aqueous solutions of MC display gelation and phase separation at higher temperatures. The nature of MC gelation has been debated for many years, and this project has made significant advances in the understanding of the solution properties of CEs. We have characterized a fibrillar structure of MC gels by cryogenic transmission electron microscopy (cryo-TEM) and small angle neutron scattering (SANS). Using light scattering, turbidity measurements, and dynamic mechanical spectroscopy (DMS) we report that MC microphase separates by nucleation and growth of fibril aggregates, and is a different process from LCST phase separation.

  20. Structure and single-phase regime of boron carbides

    NASA Astrophysics Data System (ADS)

    Emin, David

    1988-09-01

    The boron carbides are composed of twelve-atom icosahedral clusters which are linked by direct covalent bonds and through three-atom intericosahedral chains. The boron carbides are known to exist as a single phase with carbon concentrations from about 8 to about 20 at. %. This range of carbon concentrations is made possible by the substitution of boron and carbon atoms for one another within both the icosahedra and intericosahedral chains. The most widely accepted structural model for B4C (the boron carbide with nominally 20% carbon) has B11C icosahedra with C-B-C intericosahedral chains. Here, the free energy of the boron carbides is studied as a function of carbon concentration by considering the effects of replacing carbon atoms within B4C with boron atoms. It is concluded that entropic and energetic considerations both favor the replacement of carbon atoms with boron atoms within the intericosahedral chains, C-B-C-->C-B-B. Once the carbon concentration is so low that the vast majority of the chains are C-B-B chains, near B13C2, subsequent substitutions of carbon atoms with boron atoms occur within the icosahedra, B11C-->B12. Maxima of the free energy occur at the most ordered compositions: B4C,B13C2,B14C. This structural model, determined by studying the free energy, agrees with that previously suggested by analysis of electronic and thermal transport data. These considerations also provide an explanation for the wide single-phase regime found for boron carbides. The significant entropies associated with compositional disorder within the boron carbides, the high temperatures at which boron carbides are formed (>2000 K), and the relatively modest energies associated with replacing carbon atoms with boron atoms enable the material's entropy to be usually important in determining its composition. As a result, boron carbides are able to exist in a wide range of compositions.

  1. Alopecia of IFN-gamma knockout mouse as a model for disturbance of the hair cycle: a unique arrest of the hair cycle at the anagen phase accompanied by mitosis.

    PubMed

    Hirota, Ryuichiro; Tajima, Sadao; Yoneda, Yukio; Tamayama, Takumi; Watanabe, Masahito; Ueda, Kouichi; Kubota, Takahiro; Yoshida, Ryotaro

    2002-09-01

    Interferon-gamma(-/-) (IFN-gamma(-/-)) and IFN-gamma(+/+) C57BL/6 mice (3 weeks of age) completed the production of morphogenesis-derived hair. Around 6 weeks of age, however, most of the IFN-gamma(-/-) but none of the IFN-gamma(+/+) mice began to lose hairs in the dorsal and occipital areas in the absence of inflammatory reactions, and the alopecia was sustained for at least several 10-week periods of observation. A single subcutaneous injection of IFN-gamma to IFN-gamma(-/-) mice at 3, but not 4, 5, or 8 weeks of age could protect all the mice from alopecia, revealing that the lack of IFN-gamma around 3 weeks of age is directly responsible for the alopecia. Histologic features showed that the hair follicles of the IFN-gamma(+/+) mice passed through the anagen (4-5 weeks of age) and catagen/telogen ( approximately 6 weeks of age) phases, whereas those of IFN-gamma(-/-) mice (5 weeks of age or older) stayed in the anagen phase. TUNEL and bromodeoxyuridine experiments suggested that an arrest with unlimited DNA synthesis of the hair cycle in the anagen phase by the lack of IFN-gamma-dependent apoptosis in the midfollicle region and diffuse shedding of previously formed hair induced alopecia in IFN-gamma(-/-) mice. PMID:12396715

  2. Phase Space Dissimilarity Measures for Structural Health Monitoring

    SciTech Connect

    Bubacz, Jacob A; Chmielewski, Hana T; Pape, Alexander E; Depersio, Andrew J; Hively, Lee M; Abercrombie, Robert K; Boone, Shane

    2011-11-01

    A novel method for structural health monitoring (SHM), known as the Phase Space Dissimilarity Measures (PSDM) approach, is proposed and developed. The patented PSDM approach has already been developed and demonstrated for a variety of equipment and biomedical applications. Here, we investigate SHM of bridges via analysis of time serial accelerometer measurements. This work has four aspects. The first is algorithm scalability, which was found to scale linearly from one processing core to four cores. Second, the same data are analyzed to determine how the use of the PSDM approach affects sensor placement. We found that a relatively low-density placement sufficiently captures the dynamics of the structure. Third, the same data are analyzed by unique combinations of accelerometer axes (vertical, longitudinal, and lateral with respect to the bridge) to determine how the choice of axes affects the analysis. The vertical axis is found to provide satisfactory SHM data. Fourth, statistical methods were investigated to validate the PSDM approach for this application, yielding statistically significant results.

  3. Investigating the Structure of Multicomponent Gel-Phase Lipid Bilayers.

    PubMed

    Hartkamp, Remco; Moore, Timothy C; Iacovella, Christopher R; Thompson, Michael A; Bulsara, Pallav A; Moore, David J; McCabe, Clare

    2016-08-23

    Single- and multicomponent lipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC), isostearyl isostearate, and heptadecanoyl heptadecanoate in the gel phase are studied via molecular dynamics simulations. It is shown that the structural properties of multicomponent bilayers can deviate strongly from the structures of their single-component counterparts. Specifically, the lipid mixtures are shown to adopt a compact packing by offsetting the positioning depths at which different lipid species are located in the bilayer. This packing mechanism affects the area per lipid, the bilayer height, and the chain tilt angles and has important consequences for other bilayer properties, such as interfacial hydrogen bonding and bilayer permeability. In particular, the simulations suggest that bilayers containing isostearyl isostearate or heptadecanoyl heptadecanoate are less permeable than pure 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine or DSPC bilayers. Furthermore, hydrogen-bond analysis shows that the residence times of lipid-water hydrogen bonds depend strongly on the bilayer composition, with longer residence times for bilayers that have a higher DSPC content. The findings illustrate and explain the fundamental differences between the properties of single- and multicomponent bilayers. PMID:27558724

  4. From local structure to nanosecond recrystallization dynamics in AgInSbTe phase-change materials

    NASA Astrophysics Data System (ADS)

    Matsunaga, Toshiyuki; Akola, Jaakko; Kohara, Shinji; Honma, Tetsuo; Kobayashi, Keisuke; Ikenaga, Eiji; Jones, Robert O.; Yamada, Noboru; Takata, Masaki; Kojima, Rie

    2011-02-01

    Phase-change optical memories are based on the astonishingly rapid nanosecond-scale crystallization of nanosized amorphous ‘marks’ in a polycrystalline layer. Models of crystallization exist for the commercially used phase-change alloy Ge2Sb2Te5 (GST), but not for the equally important class of Sb-Te-based alloys. We have combined X-ray diffraction, extended X-ray absorption fine structure and hard X-ray photoelectron spectroscopy experiments with density functional simulations to determine the crystalline and amorphous structures of Ag3.5In3.8Sb75.0Te17.7 (AIST) and how they differ from GST. The structure of amorphous (a-) AIST shows a range of atomic ring sizes, whereas a-GST shows mainly small rings and cavities. The local environment of Sb in both forms of AIST is a distorted 3+3 octahedron. These structures suggest a bond-interchange model, where a sequence of small displacements of Sb atoms accompanied by interchanges of short and long bonds is the origin of the rapid crystallization of a-AIST. It differs profoundly from crystallization in a-GST.

  5. Can I solve my structure by SAD phasing? Anomalous signal in SAD phasing

    DOE PAGESBeta

    Terwilliger, Thomas C.; Bunkóczi, Gábor; Hung, Li-Wei; Zwart, Peter H.; Smith, Janet L.; Akey, David L.; Adams, Paul D.

    2016-03-01

    A key challenge in the SAD phasing method is solving a structure when the anomalous signal-to-noise ratio is low. We present a simple theoretical framework for describing measurements of anomalous differences and the resulting useful anomalous correlation and anomalous signal in a SAD experiment. Here, the useful anomalous correlation is defined as the correlation of anomalous differences with ideal anomalous differences from the anomalous substructure. The useful anomalous correlation reflects the accuracy of the data and the absence of minor sites. The useful anomalous correlation also reflects the information available for estimating crystallographic phases once the substructure has been determined.more » In contrast, the anomalous signal (the peak height in a model-phased anomalous difference Fourier at the coordinates of atoms in the anomalous substructure) reflects the information available about each site in the substructure and is related to the ability to find the substructure. A theoretical analysis shows that the expected value of the anomalous signal is the product of the useful anomalous correlation, the square root of the ratio of the number of unique reflections in the data set to the number of sites in the substructure, and a function that decreases with increasing values of the atomic displacement factor for the atoms in the substructure. In conclusion, this means that the ability to find the substructure in a SAD experiment is increased by high data quality and by a high ratio of reflections to sites in the substructure, and is decreased by high atomic displacement factors for the substructure.« less

  6. Structural phase field crystal approach for modeling graphene and other two-dimensional structures

    NASA Astrophysics Data System (ADS)

    Seymour, Matthew; Provatas, Nikolas

    2016-01-01

    This paper introduces a new structural phase field crystal (PFC) type model that expands the PFC methodology to a wider class of structurally complex crystal structures than previously possible. Specifically, our approach allows for stabilization of graphene, as well as its coexistence with a disordered phase. It also preserves the ability to model the usual triangular and square lattices previously reported in two-dimensional (2D) PFC studies. Our approach is guided by the formalism of classical field theory, wherein the free-energy functional is expanded to third order in PFC density correlations. It differs from previous PFC approaches in two main features. First, it utilizes a hard-sphere repulsion to describe two-point correlations. Second, and more important, is that it uses a rotationally invariant three-point correlation function that provides a unified way to control the formation of crystalline structures that can be described by a specific bond angle, such as graphene, triangular, or square symmetries. Our approach retains much of the computational simplicity of previous PFC models and allows for efficient simulation of nucleation and growth of polycrystalline 2D materials. In preparation for future applications, this paper details the mathematical derivation of the model and its equilibrium properties and uses dynamical simulations to demonstrate defect structures produced by the model.

  7. Crustal Viscosity Structure Estimated from Multi-Phase Mixing Theory

    NASA Astrophysics Data System (ADS)

    Shinevar, W. J.; Behn, M. D.; Hirth, G.

    2014-12-01

    Estimates of lower crustal viscosity are typically constrained by analyses of isostatic rebound, post seismic creep, and laboratory-derived flow laws for crustal rocks and minerals. Here we follow a new approach for calculating the viscosity structure of the lower continental crust. We use Perple_X to calculate mineral assemblages for different crustal compositions. Effective viscosity is then calculated using the rheologic mixing model of Huet et al. (2014) incorporating flow laws for each mineral phase. Calculations are performed along geotherms appropriate for the Basin and Range, Tibetan Plateau, Colorado Plateau, and the San Andreas Fault. To assess the role of crustal composition on viscosity, we examined two compositional gradients extending from an upper crust with ~67 wt% SiO2 to a lower crust that is either: (i) basaltic with ~53 wt% SiO2 (Rudnick and Gao, 2003), or (ii) andesitic with ~64% SiO2 (Hacker et al., 2011). In all cases, the middle continental crust has a viscosity that is 2-3 orders of magnitude greater than that inferred for wet quartz, a common proxy for mid-crustal viscosities. An andesitic lower crust results in viscosities of 1020-1021 Pa-s and 1021-1022 Pa-s for hotter and colder crustal geotherms, respectively. A mafic lower crust predicts viscosities that are an order of magnitude higher for the same geotherm. In all cases, the viscosity calculated from the mixing model decreases less with depth compared to single-phase estimates. Lastly, for anhydrous conditions in which alpha quartz is stable, we find that there is a strong correlation between Vp/Vs and bulk viscosity; in contrast, little to no correlation exists for hydrous conditions.

  8. Ultrafast measurements of the magnetic and structural phase transition of FeRh in the extreme ultraviolet range

    NASA Astrophysics Data System (ADS)

    Zusin, Dmitriy; Grychtol, Patrik; Turgut, Emrah; Kapteyn, Henry; Murnane, Margaret; Knut, Ronny; Shaw, Justin; Nembach, Hans; Silva, Thomas; Ceballos, Alejandro; Bordel, Catherine; Fischer, Peter; Hellman, Frances

    2014-03-01

    The temperature dependent transition from the anti-ferromagnetic to the ferromagnetic phase in FeRh is accompanied by a modification of its crystal lattice. In spite of extensive investigations, the interplay between the magnetic and the structural transition is still a matter of strong debate. A better understanding of the phase transition mechanism(s) is important, since the transition can be induced by femtosecond laser pulses and does not seem to be limited by heat transfer, as is the case in magnetic phase transitions that occur on longer (nanosecond) time scales. In this work, we use extreme ultraviolet radiation generated by a tabletop high harmonics source to perform element-selective investigations of the temperature-dependent magneto-optical response of a thin film FeRh sample. We study the optically induced phase transition using two ultrafast pump-probe spectroscopy approaches: by monitoring the time-resolved transversal magneto-optical Kerr effect (T-MOKE) and the transient change in reflectivity. P.F. acknowledges support from BES MSD DOE # DE-AC02-05-CH11231 and JILA from DOE # DE-FG02-09ER4665.

  9. A Phase-tracking Snow Micro-structure Model

    NASA Astrophysics Data System (ADS)

    Slaughter, A. E.; Zabaras, N.

    2012-12-01

    Utilizing a methodology derived from models for phase transitions in alloy solidification [1], a 3D finite element (FE) model for snow metamorphism was developed. Avalanches are known to occur due to the existence of a weak-layer of faceted crystals, which form due to temperature gradients within the snow through a process known as kinetic metamorphism [2]. In general, snow models are limited in their ability to model these microstructural changes, especially in three dimensions, and rely on effective properties. To enhance the tools available to avalanche researchers a finite element model was developed capable of tracking vapor deposition within the snow. This is accomplished using a fixed-domain, stabilized finite element solution for the energy, mass, momentum, and transport equations. Using a level-set parameter the domain is separated into either solid or fluid components and along the phase-change boundary a "mushy-zone" is establish [1, 3]. This zone is modeled as porous media that includes the effects of shrinkage and density changes [1]. The basis of the model is the open-source C++ libMesh FE library, as such the model includes adaptive mesh coarsening and refinement and relies on domain decomposition for optimum parallel performance. This work is the initial phase of an ongoing research project that aims to demonstrate the ability to model snow at the micro-structural level and move away from the common coarse, effective property modeling techniques. It will serve as the deterministic basis for a multi-scale, stochastic model of snow that will account for uncertainties such as poorly understood growth properties and measurement variability. Future applications may include the inclusion of liquid melt and include external forces, yielding a comprehensive thermo-mechanical model that could evolve and fracture. [1] D. Samanta, N. Zabaras (2005), Modelling convection in solidification processes using stabilized finite element techniques, J. Numer. Meth. Eng

  10. Phase-field modeling of ferroelectric to paraelectric phase boundary structures in single-crystal barium titanate

    NASA Astrophysics Data System (ADS)

    Woldman, Alexandra Y.; Landis, Chad M.

    2016-03-01

    Ferroelectric perovskite materials have been shown to exhibit a large electrocaloric effect near phase transitions. We develop a computational model based on a phase-field approach to characterize the structure of ferroelectric to paraelectric phase boundaries for planar configurations under generalized plane strain with temperatures near the Curie temperature. A nonlinear finite element method is used to solve for the phase boundary structure of a representative unit cell with a 180° ferroelectric laminate for a range of domain widths. The temperature at which the phase boundary can be found increases with domain width, approaching the Curie temperature asymptotically. The excess free energy density per unit area of the boundary increases with domain width. As expected, closure domains form between the ferroelectric and paraelectric phase, and the shape of the closure domains evolves from triangular to needle-shaped as the domain width increases. The entropy jump across the phase boundary is quantified and is shown to increase with domain width as well. A planar configuration with a 90° ferroelectric laminate is investigated, but shown to be physically unlikely due to the high stress levels required to achieve strain compatibility between the phases. Possible three-dimensional structures of the ferroelectric-paraelectric phase boundary are also discussed.

  11. Structural properties, phase stability, elastic properties and electronic structures of Cu-Ti intermetallics

    NASA Astrophysics Data System (ADS)

    Chen, Shuai; Duan, Yong-Hua; Huang, Bo; Hu, Wen-Cheng

    2015-11-01

    The structural properties, phase stabilities, anisotropic elastic properties and electronic structures of Cu-Ti intermetallics have been systematically investigated using first principles based on the density functional theory. The calculated equilibrium structural parameters agree well with available experimental data. The ground-state convex hull of formation enthalpies as a function of Cu content is slightly symmetrical at CuTi with a minimal formation enthalpy (-13.861 kJ/mol of atoms), which indicates that CuTi is the most stable phase. The mechanical properties, including elastic constants, polycrystalline moduli and anisotropic indexes, were evaluated. G/B is more pertinent to hardness than to the shear modulus G due to the high power indexes of 1.137 for G/B. The mechanical anisotropy was also characterized by describing the three-dimensional (3D) surface constructions. The order of elastic anisotropy is Cu4Ti3 > Cu3Ti2 > α-Cu4Ti > Cu2Ti > CuTi > β-Cu4Ti > CuTi2. Finally, the electronic structures were discussed and Cu2Ti is a semiconductor.

  12. RPF101, a new capsaicin-like analogue, disrupts the microtubule network accompanied by arrest in the G2/M phase, inducing apoptosis and mitotic catastrophe in the MCF-7 breast cancer cells

    SciTech Connect

    Sá-Júnior, Paulo Luiz de; Pasqualoto, Kerly Fernanda Mesquita; Ferreira, Adilson Kleber; Tavares, Maurício Temotheo; Damião, Mariana Celestina Frojuello Costa Bernstorff; Azevedo, Ricardo Alexandre de; Câmara, Diana Aparecida Dias; Pereira, Alexandre; Madeiro de Souza, Dener; Parise Filho, Roberto

    2013-02-01

    Breast cancer is the world's leading cause of death among women. This situation imposes an urgent development of more selective and less toxic agents. The use of natural molecular fingerprints as sources for new bioactive chemical entities has proven to be a quite promising and efficient method. Capsaicin, which is the primary pungent compound in red peppers, was reported to selectively inhibit the growth of a variety tumor cell lines. Here, we report for the first time a novel synthetic capsaicin-like analogue, RPF101, which presents a high antitumor activity on MCF-7 cell line, inducing arrest of the cell cycle at the G2/M phase through a disruption of the microtubule network. Furthermore, it causes cellular morphologic changes characteristic of apoptosis and a decrease of Δψm. Molecular modeling studies corroborated the biological findings and suggested that RPF101, besides being a more reactive molecule towards its target, may also present a better pharmacokinetic profile than capsaicin. All these findings support the fact that RPF101 is a promising anticancer agent. -- Highlights: ► We report for the first time that RPF101 possesses anticancer properties. ► RPF101 induces apoptosis of human breast cancer cells. ► RPF 101 decreases mitochondrial potential and induces DNA fragmentation.

  13. Actinic imaging and evaluation of phase structures on EUV lithography masks

    SciTech Connect

    Mochi, Iacopo; Goldberg, Kenneth; Huh, Sungmin

    2010-09-28

    The authors describe the implementation of a phase-retrieval algorithm to reconstruct phase and complex amplitude of structures on EUV lithography masks. Many native defects commonly found on EUV reticles are difficult to detect and review accurately because they have a strong phase component. Understanding the complex amplitude of mask features is essential for predictive modeling of defect printability and defect repair. Besides printing in a stepper, the most accurate way to characterize such defects is with actinic inspection, performed at the design, EUV wavelength. Phase defect and phase structures show a distinct through-focus behavior that enables qualitative evaluation of the object phase from two or more high-resolution intensity measurements. For the first time, phase of structures and defects on EUV masks were quantitatively reconstructed based on aerial image measurements, using a modified version of a phase-retrieval algorithm developed to test optical phase shifting reticles.

  14. Investigation of new phases in the Ba-Si phase diagram under high pressure using ab initio structural search.

    PubMed

    Shi, Jingming; Cui, Wenwen; Flores-Livas, José A; San-Miguel, Alfonso; Botti, Silvana; Marques, Miguel A L

    2016-03-01

    Barium silicides are versatile materials that have attracted attention for a variety of applications in electronics and optoelectronics. Using an unbiased structural search based on a particle-swarm optimization algorithm combined with density functional theory calculations, we investigate systematically the ground-state phase stability and the structural diversity of Ba-Si binaries under high pressure. The phase diagram turns out to be quite intricate, with several compositions stabilizing/destabilizing as a function of pressure. In particular, we identify novel phases of BaSi, BaSi2, BaSi3, and BaSi5 that might be synthesizable experimentally over a wide range of pressures. Our results not only clarify and complete the previously known structural phase diagram, but also provide new insights for understanding the Ba-Si binary system. PMID:26923068

  15. Phase Structure of the Random Zq Models in 2D

    NASA Astrophysics Data System (ADS)

    Sasamoto, T.; Nishimori, H.

    We discuss the phase diagram of the random Zq models in two dimensions. It is argued that, when q is large enough, there exist three phases in the phase diagram with two axes being the temperature and the strength of randomness. Our conlusions are derived based on the application of the duality arguments for random systems, which have been formulated recently by Maillard et al.

  16. Nonequilibrium Phase Chemistry in High Temperature Structure Alloys

    NASA Technical Reports Server (NTRS)

    Wang, R.

    1991-01-01

    Titanium and nickel aluminides of nonequilibrium microstructures and in thin gauge thickness were identified, characterized and produced for potential high temperature applications. A high rate sputter deposition technique for rapid surveillance of the microstructures and nonequilibrium phase is demonstrated. Alloys with specific compositions were synthesized with extended solid solutions, stable dispersoids, and specific phase boundaries associated with different heat treatments. Phase stability and mechanical behavior of these nonequilibrium alloys were investigated and compared.

  17. A novel route for fabricating metal-polymer composite nanoparticles with phase-separated structures.

    PubMed

    Yabu, Hiroshi; Koike, Kazutaka; Motoyoshi, Kiwamu; Higuchi, Takeshi; Shimomura, Masatsugu

    2010-07-15

    Au nanoparticles (NPs) and polymer composite particles with phase-separation structures were prepared based on phase separation structures. Au NPs were successfully synthesized in amphiphilic block-copolymer micelles, and then composite particles were formed by a simple solvent evaporation process from Au NPs and polymer solution. The phase separated structures (Janus and Core-shell) were controlled by changing the combination of polymers having differing hydrophobicity. PMID:21567522

  18. The structure and dynamics of amorphous and crystalline phases of ice

    SciTech Connect

    Klug, D. D.; Tse, J. S.; Tulk, C. A.; Svensson, E. C.; Swainson, I.; Loong, C.-K.

    2000-07-14

    The structures of the high and low-density amorphous phases of ice are studied using several techniques. The diffraction patterns of high and low density amorphous ice are analyzed using reverse Monte Carlo methods and compared with molecular dynamics simulations of these phases. The spectra of crystalline and amorphous phases of ice obtained by Raman and incoherent inelastic neutron scattering are analyzed to yield structural features for comparison with the results of molecular dynamics and Reverse Monte Carlo analysis. The structural details obtained indicate that there are significant differences between the structure of liquid water and the amorphous phases of ice.

  19. Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability

    SciTech Connect

    Soo, Y. L.; Chen, P. J.; Huang, S. H.; Shiu, T. J.; Tsai, T. Y.; Chow, Y. H.; Lin, Y. C.; Weng, S. C.; Chang, S. L.; Wang, G.; Cheung, C. L.; Sabirianov, R. F.; Mei, W. N.; Namavar, F.; Haider, H.; Garvin, K. L.; Lee, J. F.; Lee, H. Y.; Chu, P. P.

    2008-12-01

    Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO{sub 2}) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO{sub 2} nanocrystal sample prepared by a sol-gel method. Variations in local structures due to thermal annealing were observed and analyzed. Most importantly, our x-ray results provide direct experimental evidence for the existence of oxygen vacancies arising from local disorder and distortion of the oxygen sublattice in nanocrystalline ZrO{sub 2}. These oxygen vacancies are regarded as the essential stabilizing factor for the nanostructurally stabilized cubic zirconia.

  20. Seismic Safety Margins Research Program (Phase I). Project IV. Structural building response; Structural Building Response Review

    SciTech Connect

    Healey, J.J.; Wu, S.T.; Murga, M.

    1980-02-01

    As part of the Phase I effort of the Seismic Safety Margins Research Program (SSMRP) being performed by the University of California Lawrence Livermore Laboratory for the US Nuclear Regulatory Commission, the basic objective of Subtask IV.1 (Structural Building Response Review) is to review and summarize current methods and data pertaining to seismic response calculations particularly as they relate to the objectives of the SSMRP. This material forms one component in the development of the overall computational methodology involving state of the art computations including explicit consideration of uncertainty and aimed at ultimately deriving estimates of the probability of radioactive releases due to seismic effects on nuclear power plant facilities.

  1. Liquid phase reaction-bonding of structural ceramics and composites

    SciTech Connect

    Chiang, Y.M. . Dept. of Materials Science and Engineering)

    1988-01-01

    Synthesis of ceramics via the reaction of a solid precursor with either a gas or liquid phase has a number of advantages compared to conventional sintering technology. These advantages are known for gas-phase processes. The authors have explored the potential for synthesizing high performance ceramics in the model system reaction-bonded silicon carbide, in which liquid silicon is used to infiltrate carbonaceous preforms. In this paper results are presented that illustrate the use of alloyed-melts to obtain dense silicon carbide composites with residual refractory silicide phases, such as MoSi/sub 2/, rather than the residual silicon phase which has heretofore limited high temperature properties. Infiltration processing considerations, such as the ultimate infiltration dimensions possible in the presence of simultaneous reaction, are discussed. Microstructure and mechanical properties characterization in the SIC-MoSi/sub 2/ system are presented. Other refractory ceramics systems to which liquid-phase reaction-bonding may be applied are discussed.

  2. Structural evolution of calcite at high temperatures: Phase V unveiled

    PubMed Central

    Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi

    2013-01-01

    The calcite form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240 K under a CO2 atmosphere of ~0.4 MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985 K and ~1240 K. PMID:24084871

  3. Representation of higher-order statistical structures in natural scenes via spatial phase distributions.

    PubMed

    MaBouDi, HaDi; Shimazaki, Hideaki; Amari, Shun-Ichi; Soltanian-Zadeh, Hamid

    2016-03-01

    Natural scenes contain richer perceptual information in their spatial phase structure than their amplitudes. Modeling phase structure of natural scenes may explain higher-order structure inherent to the natural scenes, which is neglected in most classical models of redundancy reduction. Only recently, a few models have represented images using a complex form of receptive fields (RFs) and analyze their complex responses in terms of amplitude and phase. However, these complex representation models often tacitly assume a uniform phase distribution without empirical support. The structure of spatial phase distributions of natural scenes in the form of relative contributions of paired responses of RFs in quadrature has not been explored statistically until now. Here, we investigate the spatial phase structure of natural scenes using complex forms of various Gabor-like RFs. To analyze distributions of the spatial phase responses, we constructed a mixture model that accounts for multi-modal circular distributions, and the EM algorithm for estimation of the model parameters. Based on the likelihood, we report presence of both uniform and structured bimodal phase distributions in natural scenes. The latter bimodal distributions were symmetric with two peaks separated by about 180°. Thus, the redundancy in the natural scenes can be further removed by using the bimodal phase distributions obtained from these RFs in the complex representation models. These results predict that both phase invariant and phase sensitive complex cells are required to represent the regularities of natural scenes in visual systems. PMID:26278166

  4. Inherent structures of phase-separating binary mixtures: Nucleation, spinodal decomposition, and pattern formation

    NASA Astrophysics Data System (ADS)

    Sarkar, Sarmistha; Bagchi, Biman

    2011-03-01

    An energy landscape view of phase separation and nonideality in binary mixtures is developed by exploring their potential energy landscape (PEL) as functions of temperature and composition. We employ molecular dynamics simulations to study a model that promotes structure breaking in the solute-solvent parent binary liquid, at low temperatures. The PEL of the system captures the potential energy distribution of the inherent structures (IS) of the system and is obtained by removing the kinetic energy (including that of intermolecular vibrations). The broader distribution of the inherent structure energy for structure breaking liquid than that of the structure making liquid demonstrates the larger role of entropy in stabilizing the parent liquid of the structure breaking type of binary mixtures. At high temperature, although the parent structure of the structure breaking binary mixture is homogenous, the corresponding inherent structure is found to be always phase separated, with a density pattern that exhibits marked correlation with the energy of its inherent structure. Over a broad range of intermediate inherent structure energy, bicontinuous phase separation prevails with interpenetrating stripes as signatures of spinodal decomposition. At low inherent structure energy, the structure is largely phase separated with one interface where as at high inherent structure energy we find nucleation type growth. Interestingly, at low temperature, the average inherent structure energy () exhibits a drop with temperature which signals the onset of crystallization in one of the phases while the other remains in the liquid state. The nonideal composition dependence of viscosity is anticorrelated with average inherent structure energy.

  5. [Phase transition in polymer blends and structure of ionomers and copolymers

    SciTech Connect

    Not Available

    1993-01-01

    The main thrust of the program in the past 3 years are summarized: SAXS instrumentation development; structure and dynamics of macro- and supra-molecules, phase transitions in polymer blends and solutions, structure of ionomers, and fractals and anisotropic systems.

  6. Phase structure of a holographic double monolayer Dirac semimetal

    NASA Astrophysics Data System (ADS)

    Grignani, Gianluca; Marini, Andrea; Pigna, Adriano-Costantino; Semenoff, Gordon W.

    2016-06-01

    We study a holographic D3/probe-D5-brane model of a double monolayer Dirac semimetal in a magnetic field and in the presence of a nonzero temperature. Intra-and inter-layer exciton condensates can form by varying the balanced charge density on the layers, the spatial separation and the temperature. Constant temperature phase diagrams for a wide range of layer separations and charge densities are found. The presence of a finite temperature makes the phase diagrams extremely rich and in particular leads to the appearance of a symmetric phase which was missing at zero temperature.

  7. Amplitude and phase transmission characteristics of parallel-coupled dual racetrack silicon microresonator structure

    NASA Astrophysics Data System (ADS)

    Zhou, Yating; Abbaslou, Siamak; Gatdula, Robert; Jiang, Wei

    2015-12-01

    Parallel-coupled dual racetrack silicon microresonator structures are fabricated and characterized. With an integrated Mach-Zehnder interferometer, the full information of amplitude and phase of the structure is obtained experimentally. The spectral characteristics of the amplitude and phase are shown to be in reasonable agreement with simulation results, considering possible small structure variations in fabrication. The structure is potentially useful for developing modulators for advanced modulation formats.

  8. Stress reduction in phase-separated, cross-linked networks: influence of phase structure and kinetics of reaction

    PubMed Central

    Szczepanski, Caroline R.; Stansbury, Jeffrey W.

    2014-01-01

    A mechanism for polymerization shrinkage and stress reduction was developed for heterogeneous networks formed via ambient, photo-initiated polymerization-induced phase separation (PIPS). The material system used consists of a bulk homopolymer matrix of triethylene glycol dimethacrylate (TEGDMA) modified with one of three non-reactive, linear prepolymers (poly-methyl, ethyl and butyl methacrylate). At higher prepolymer loading levels (10–20 wt%) an enhanced reduction in both shrinkage and polymerization stress is observed. The onset of gelation in these materials is delayed to a higher degree of methacrylate conversion (~15–25%), providing more time for phase structure evolution by thermodynamically driven monomer diffusion between immiscible phases prior to network macro-gelation. The resulting phase structure was probed by introducing a fluorescently tagged prepolymer into the matrix. The phase structure evolves from a dispersion of prepolymer at low loading levels to a fully co-continuous heterogeneous network at higher loadings. The bulk modulus in phase separated networks is equivalent or greater than that of poly(TEGDMA), despite a reduced polymerization rate and cross-link density in the prepolymer-rich domains. PMID:25418999

  9. Stationary phases with special structural properties for high-throughput separation techniques: preparation, characterization and applications.

    PubMed

    Buszewski, Boguslaw; Welerowicz, Tomasz

    2004-06-01

    Stationary phases with specific structural properties for high-throughput liquid chromatographic (LC) techniques are described. Special attention was paid to phases with special structural properties, mainly containing internal functional group (e.g. amide). Such materials are generally called "embedded phases". There are phases created in amidation process of aminopropylated silica gel, especially phases based on biological compounds, like phospholipids and cholesterol, which are called immobilized artificial membranes (IAM's). The synthesis and applications of polar embedded amide LC stationary phases were also reviewed. Methods of characterization of synthesized packing materials were presented, with general focusing on spectroscopic measurements like (13C and 29Si CP/MAS NMR and FT-IR), elemental and thermal analysis as well as chromatographic quantitative structure-retention relationships (QSRR) and extended chemometric tests. The potential applications of various dedicated stationary phases in a high-throughput LC screening procedures were also presented. PMID:15200378

  10. Structure of new carbon phases from carbyne nanorings

    SciTech Connect

    Belenkov, E. A. Shabiev, F. K.

    2007-03-15

    Model calculations of hypothetical carbon structures composed of carbon atoms in the sp-hybridization state have been performed by the molecular-mechanics and ab initio methods. The possibility of stable existence of 1D, 2a, and 3a chain structures from carbon nano rings is established. A mechanism of synthesis of such structures is proposed.

  11. Structure analysis of turbulent liquid phase by POD and LSE techniques

    SciTech Connect

    Munir, S. Muthuvalu, M. S.; Siddiqui, M. I.; Heikal, M. R. Aziz, A. Rashid A.

    2014-10-24

    In this paper, vortical structures and turbulence characteristics of liquid phase in both single liquid phase and two-phase slug flow in pipes were studied. Two dimensional velocity vector fields of liquid phase were obtained by Particle image velocimetry (PIV). Two cases were considered one single phase liquid flow at 80 l/m and second slug flow by introducing gas at 60 l/m while keeping liquid flow rate same. Proper orthogonal decomposition (POD) and Linear stochastic estimation techniques were used for the extraction of coherent structures and analysis of turbulence in liquid phase for both cases. POD has successfully revealed large energy containing structures. The time dependent POD spatial mode coefficients oscillate with high frequency for high mode numbers. The energy distribution of spatial modes was also achieved. LSE has pointed out the coherent structured for both cases and the reconstructed velocity fields are in well agreement with the instantaneous velocity fields.

  12. Ultrasonic phased array inspection imaging technology for NDT of offshore platform structures

    NASA Astrophysics Data System (ADS)

    Shan, Baohua; Wang, Hua; Liang, Yongning; Duan, Zhongdong; Ou, Jinping

    2008-03-01

    In order to improve inspection result repetition and flaw ration veracity of manual ultrasonic inspection of offshore platform structure, an ultrasonic phased array inspection imaging technology for NDT of offshore platform structures is proposed in this paper. Aimed at the practical requirement of tubular joint welds inspection of offshore platform structures, the ultrasonic phased array inspection imaging system for offshore platform structures is developed, which is composed of computer, ultrasonic circuit system, scanning device, phased array transducer and inspection imaging software system. The experiment of Y shape tubular joint model of 60 degree is performed with the ultrasonic phased array inspection imaging system for offshore platform structures, the flaws characteristic could be exactly estimated and the flaws size could be measured through ultrasonic phased array inspection imaging software system for offshore platform structures. Experiment results show that the ultrasonic phased array inspection imaging technology for offshore platform structures is feasible, the ultrasonic phased array inspection imaging system could detect flaws in tubular joint model, the whole development trend of flaws is factually imaging by the ultrasonic phased array inspection technology of offshore platform structures.

  13. A note on the relationship between turbulent coherent structures and phase correlation

    SciTech Connect

    Kang, Yanfei; Belušić, Danijel Smith-Miles, Kate

    2014-06-15

    Various definitions of coherent structures exist in turbulence research, but a common assumption is that coherent structures have correlated spectral phases. As a result, randomization of phases is believed, generally, to remove coherent structures from the measured data. Here, we reexamine these assumptions using atmospheric turbulence measurements. Small-scale coherent structures are detected in the usual way using the wavelet transform. A considerable percentage of the detected structures are not phase correlated, although some of them are clearly organized in space and time. At larger scales, structures have even higher degree of spatiotemporal coherence but are also associated with weak phase correlation. A series of specific examples are shown to demonstrate this. These results warn about the vague terminology and assumptions around coherent structures, particularly for complex real-world turbulence.

  14. Statistical energy analysis of complex structures, phase 2

    NASA Technical Reports Server (NTRS)

    Trudell, R. W.; Yano, L. I.

    1980-01-01

    A method for estimating the structural vibration properties of complex systems in high frequency environments was investigated. The structure analyzed was the Materials Experiment Assembly, (MEA), which is a portion of the OST-2A payload for the space transportation system. Statistical energy analysis (SEA) techniques were used to model the structure and predict the structural element response to acoustic excitation. A comparison of the intial response predictions and measured acoustic test data is presented. The conclusions indicate that: the SEA predicted the response of primary structure to acoustic excitation over a wide range of frequencies; and the contribution of mechanically induced random vibration to the total MEA is not significant.

  15. Phase structure of one-dimensional interacting Floquet systems. II. Symmetry-broken phases

    NASA Astrophysics Data System (ADS)

    von Keyserlingk, C. W.; Sondhi, S. L.

    2016-06-01

    Recent work suggests that a sharp definition of "phase of matter" can be given for periodically driven "Floquet" quantum systems exhibiting many-body localization. In this work, we propose a classification of the phases of interacting Floquet localized systems with (completely) spontaneously broken symmetries; we focus on the one-dimensional case, but our results appear to generalize to higher dimensions. We find that the different Floquet phases correspond to elements of Z (G ) , the center of the symmetry group in question. In a previous paper [C. W. von Keyserlingk and S. L. Sondhi, preceding paper, Phys. Rev. B 93, 245145 (2016)], 10.1103/PhysRevB.93.245145, we offered a companion classification of unbroken, i.e., paramagnetic phases.

  16. Phase structure of one-dimensional interacting Floquet systems. I. Abelian symmetry-protected topological phases

    NASA Astrophysics Data System (ADS)

    von Keyserlingk, C. W.; Sondhi, S. L.

    2016-06-01

    Recent work suggests that a sharp definition of "phase of matter" can be given for some quantum systems out of equilibrium, first for many-body localized systems with time-independent Hamiltonians and more recently for periodically driven or Floquet localized systems. In this work, we propose a classification of the finite Abelian symmetry-protected phases of interacting Floquet localized systems in one dimension. We find that the different Floquet phases correspond to elements of ClG×AG , where ClG is the undriven interacting classification, and AG is a set of (twisted) one-dimensional representations corresponding to symmetry group G . We will address symmetry-broken phases in a subsequent paper C. W. von Keyserlingk and S. L. Sondhi, following paper, Phys. Rev. B 93, 245146 (2016), 10.1103/PhysRevB.93.245146.

  17. The solid state structures of the high and low temperature phases of dimethylcadmium.

    PubMed

    Hanke, Felix; Hindley, Sarah; Jones, Anthony C; Steiner, Alexander

    2016-08-01

    The solid state structure of dimethylcadmium, a classic organometallic compound with a long history, has remained elusive for almost a century. X-ray crystallography and density functional theory reveal similar phase behaviour as in dimethylzinc. The high temperature tetragonal phase, α-Me2Cd, exhibits two-dimensional disorder, while the low temperature monoclinic phase, β-Me2Cd, is ordered. Both phases contain linearly coordinated cadmium atoms. While the methyl groups are staggered in the α-phase, they are eclipsed in the β-phase. PMID:27457504

  18. The Molecular Structure of the Liquid Ordered Phase

    NASA Astrophysics Data System (ADS)

    Lyman, Edward

    2014-03-01

    Molecular dynamics simulations reveal substructures within the liquid-ordered phase of lipid bilayers. These substructures, identified in a 10 μsec all-atom trajectory of liquid-ordered/liquid-disordered coexistence (Lo/Ld) , are composed of saturated hydrocarbon chains packed with local hexagonal order, and separated by interstitial regions enriched in cholesterol and unsaturated chains. Lipid hydrocarbon chain order parameters calculated from the Lo phase are in excellent agreement with 2H NMR measurements; the local hexagonal packing is also consistent with 1H-MAS NMR spectra of the Lo phase, NMR diffusion experiments, and small angle X-ray- and neutron scattering. The balance of cholesterol-rich to local hexagonal order is proposed to control the partitioning of membrane components into the Lo regions. The latter have been frequently associated with formation of so-called rafts, platforms in the plasma membranes of cells that facilitate interaction between components of signaling pathways.

  19. Structural phase transitions and topological defects in ion Coulomb crystals

    SciTech Connect

    Partner, Heather L.; Nigmatullin, Ramil; Burgermeister, Tobias; Keller, Jonas; Pyka, Karsten; Plenio, Martin B.; Retzker, Alex; Zurek, Wojciech Hubert; del Campo, Adolfo; Mehlstaubler, Tanja E.

    2014-11-19

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed non-adiabatically. For a second order phase transition, the Kibble-Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  20. Non Abelian structures and the geometric phase of entangled qudits

    SciTech Connect

    Oxman, L.E. Khoury, A.Z.

    2014-12-15

    In this work, we address some important topological and algebraic aspects of two-qudit states evolving under local unitary operations. The projective invariant subspaces and evolutions are connected with the common elements characterizing the su(d) Lie algebra and their representations. In particular, the roots and weights turn out to be natural quantities to parametrize cyclic evolutions and fractional phases. This framework is then used to recast the coset contribution to the geometric phase in a form that generalizes the usual monopole-like formula for a single qubit.

  1. Phase separation and emergent structures in an active nematic fluid

    PubMed Central

    Putzig, Elias; Baskaran, Aparna

    2015-01-01

    We consider a phenomenological continuum theory for an active nematic fluid and show that there exists a universal, model independent instability which renders the homogeneous nematic state unstable to order fluctuations. Using numerical and analytic tools we show that, in the vicinity of a critical point, this instability leads to a phase separated state in which the ordered regions form bands in which the direction of nematic order is perpendicular to the direction of density gradient. We argue that the underlying mechanism that leads to this phase separation is a universal feature of active fluids of different symmetries. PMID:25375491

  2. Crystal structure, phase, and electrical conductivity of nanocrystalline W₀.₉₅Ti(₀.₀₅)O₃ thin films.

    PubMed

    Kalidindi, N R; Manciu, F S; Ramana, C V

    2011-03-01

    W(0.95)Ti(0.05)O(3) films were fabricated using sputter-deposition onto Si(100) wafers in by varying the growth temperature from room temperature (RT) to 500 °C. X-ray diffraction (XRD), high-resolution scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS), and Raman spectroscopy (RS) were performed to investigate the effect of temperature on the growth behavior, crystal structure, texturing, surface morphology, and chemical bonding of W(0.95)Ti(0.5)O(3) films. The results indicate that the effect of temperature is significant on the growth and microstructure of W(0.95)Ti(0.05)O(3) films. XRD results indicate that the effect of Ti is remarkable on the crystallization of WO(3). W(0)(.95)Ti(0.05)O(3) films grown at temperatures <300 °C are amorphous compared to pure WO(3) crystalline films crystallizing at 200 °C. Phase transformation is induced in W(0)(.95)Ti(0.05)O(3) resulting in tetragonal structure at ≥300 °C. The structural changes were also reflected in the intensities of -W-O-W- vibrational modes in RS measurements. The SEM imaging analysis indicates that the phase transformations are accompanied by a characteristic change in surface morphology. Room temperature electrical conductivity of W(0.95)Ti(0.05)O(3) films increases from 0.63 to 27 (Ω m)(-1) with increasing temperature from RT to 400 °C due to improved structural order. Electrical conductivity exhibit a decrease at 500 °C (7.4 (Ω m)(-1)) due to disordering induced by Ti segregation, which is confirmed by XRD and RS measurements. PMID:21323357

  3. Structure and composition of phases occurring in austenitic stainless steels in thermal and irradiation environments

    SciTech Connect

    Lee, E.H.; Maziasz, P.J.; Rowcliffe, A.F.

    1980-01-01

    Transmission electron diffraction techniques coupled with quantitative x-ray energy dispersive spectroscopy have been used to characterize the phases which develop in austenitic stainless steels during exposure to thermal and to irradiation environments. In AISI 316 and Ti-modified stainless steels some thirteen phases have been identified and characterized in terms of their crystal structure and chemical composition. Irradiation does not produce any completely new phases. However, as a result of radiation-induced segregation principally of Ni and Si, and of enhanced diffusion rates, several major changes in phase relationships occur during irradiation. Firstly, phases characteristic of remote regions of the phase diagram appear unexpectedly and dissolve during postirradiation annealing (radiation-induced phases). Secondly, some phases develop with their compositions significantly altered by the incorporation of Ni or Si (radiation-modified phases).

  4. SPAR improved structure-fluid dynamic analysis capability, phase 2

    NASA Technical Reports Server (NTRS)

    Pearson, M. L.

    1984-01-01

    An efficient and general method of analyzing a coupled dynamic system of fluid flow and elastic structures is investigated. The improvement of Structural Performance Analysis and Redesign (SPAR) code is summarized. All error codes are documented and the SPAR processor/subroutine cross reference is included.

  5. Design, fabrication, and test of lightweight shell structure, phase 2

    NASA Technical Reports Server (NTRS)

    1974-01-01

    A cylindrical shell skirt structure 4.57 m (180 in.) in diameter and 3.66 m (144 in.) high was subjected to a design and analysis study using a wide variety of structural materials and concepts. The design loading of 1225.8 N/cm (700 lb/in.) axial compression and 245.2 N/cm (140 lb/in.) torsion is representative of that expected on a typical space tug skirt section. Structural concepts evaluated included honeycomb sandwich, truss, isogrid, and skin/stringer/frame. The materials considered included a wide variety of structural metals as well as glass, graphite, and boron-reinforced composites. The most unique characteristic of the candidate designs is that they involve the use of very thin-gage material. Fabrication and structural test of small panels and components representative of many of the candidate designs served to demonstrate proposed fabrication techniques and to verify design and analysis methods.

  6. Elongated silica nanoparticles with a mesh phase mesopore structure by fluorosurfactant templating.

    PubMed

    Tan, Bing; Dozier, Alan; Lehmler, Hans-Joachim; Knutson, Barbara L; Rankin, Stephen E

    2004-08-17

    Mesoporous silica materials with pore structures such as 2D hexagonal close packed, bicontinuous cubic, lamellar, sponge, wormhole-like, and rectangular have been made by using surfactant templating sol-gel processes. However, there are still some "intermediate" phases, in particular mesh phases, that are formed by surfactants but which have not been made into analogous silica pore structures. Here, we describe the one-step synthesis of mesoporous silica with a mesh phase pore structure. The cationic fluorinated surfactant 1,1,2,2-tetrahydroperfluorodecylpyridinium chloride (HFDePC) is used as the template. Like many fluorinated surfactants, HFDePC forms intermediate phases in water (including a mesh phase) over a wider range of compositions than do hydrocarbon surfactants. The materials produced by this technique are novel elongated particles in which the layers of the mesh phase are oriented orthogonal to the main axis of the particles. PMID:15301475

  7. Tuning phase structures of a symmetrical diblock copolymer with a patterned electric field.

    PubMed

    Kan, Di; He, Xuehao

    2016-05-11

    Electric fields can induce the orientation of the phase interfaces of block copolymers and provide a potential method to tune polymer phase structures for nanomaterial manufacture. In this work, we applied self-consistent field theory to study the self-assembly of a diblock copolymer confined between two parallel neutral substrates on which a set of electrodes was imposed to form a patterned electric field. The results showed that an alternatively distributed electric field can induce the formation of a parallel lamellar phase structure, which exists stably only in the system with selective substrates. The phase structure was proved to be sensitive to the characteristics of the electric field distribution, such as the strength of the electric field, the size and position of the electrodes, and the corresponding phase diagram was calculated in detail. The transition pathway of the phase structure from the perpendicular layered phase to the parallel layered phase was further analysed using the minimum energy path method. It is shown that the path and the active energy barrier of the phase transition depend on the electric field strength. Compound electric field patterns that can be designed to control the formation of novel and complex microphase structures were also examined. PMID:27102422

  8. Phase structure of the linear σ model in R1+1

    NASA Astrophysics Data System (ADS)

    Abramova, S. V.; Efimov, G. V.; Nedelko, S. N.

    1995-11-01

    The phase structure of the two-dimensional linear σ model is investigated within the method based on canonical transformations and the renormalization group formalism. The phase diagram in the (Y,G) plane is constructed, where Y and G are the Yukawa and boson self-interaction coupling constants. The Hamiltonians describing the system in each phase are obtained. It is shown that the contribution of pseudoscalar fields diminishes the vacuum energy density in the phase with broken chiral symmetry. This results in a rather complicated phase structure of the linear σ model. The most representative features of the phase picture are the dynamical breaking of chiral symmetry for an arbitrary small Yukawa coupling and the presence of critical and triple points in the phase diagram.

  9. A review on the structure of cold-compressed graphite phase

    NASA Astrophysics Data System (ADS)

    Zhai, Jinhui; Wan, Ajun; Wu, Wenbin

    2015-12-01

    The room-temperature structural phase transition of graphite at elevated hydrostatic pressure has drawn considerable scientific interest for its fundamental importance in condensed matter physics and materials science over the past few decades. A pressure-induced phase transition has been demonstrated in previous experiments by the measurement of electrical resistance, optical spectrum, X-ray diffraction spectrum, inelastic X-ray scattering and Raman spectroscopy. However, the nature of the cold-compressed graphite phase has been puzzling the experts and pioneers in the field of high pressure research due to some inherent factors, until recently a monoclinic structure, i.e. M-carbon, stands out from the other structure candidates and successfully accounts for the crystal structure of the cold-compressed graphite phase both in theory and experiment that eventually putting an end to this long-lasting controversial issue. This paper reviews the recent progress on the pressure-induced phase transitions of graphite at room temperature especially for the theoretical investigations. The review will focus on the recent proposed novel carbon allotropes as candidate structures of the cold-compressed graphite phase by using different crystal structure prediction methods. The history of structure determination of cold-compressed graphite phase is discussed.

  10. Fertility reduction programmes should accompany land reforms.

    PubMed

    Atiku, J

    1994-01-01

    Changes in population size both affect and are affected by the rate of development. With the total world population estimated to be 5.7 billion in mid-1994 and annual growth at 1.7%, declines in total fertility rates and overall growth rates in developing countries have not been sufficient to precipitate a decline in actual numbers. The population of developing countries has doubled from 1962 to 1994. The highest growth rates are expected to be in sub-Saharan Africa, but the largest absolute increase in population is expected to occur in Asia. Uganda's population has increased from 4.9 to 16.7 million from 1948 to 1991. At the current rate of increase (2.5%) and taking AIDS into account, Uganda's population is expected to double in 28 years. Rapid population growth in developing countries can be explained by the following factors: 1) high levels of morbidity and mortality which threaten child survival and encourage large families; 2) early marriage which extends reproductive activity; 3) a high value placed on children, especially sons; 4) unmet needs for family planning; 5) widespread poverty which causes children to be viewed as old age security; and 6) population momentum which would contribute to growth even if replacement fertility were achieved because of the current age-sex structure of the population. The impact of rapid population growth on development requires further study, but some things are clear. Economic development is hindered when the number of dependent and poor individuals in a population increases. High rates of fertility result in poor infant and maternal health. The provision of social welfare services and the capacity for providing basic services such as health care, education, safe water, and sanitation is strained by rapid population growth. Also, the quality of the environment is adversely affected by rapid population growth. Population policies should be developed for each country and should emphasize activities to improve individual

  11. Phase equilibria, fluid structure, and diffusivity of a discotic liquid crystal.

    PubMed

    Cienega-Cacerez, Octavio; Moreno-Razo, José Antonio; Díaz-Herrera, Enrique; Sambriski, Edward John

    2014-05-14

    Molecular Dynamics simulations were performed for the Gay-Berne discotic fluid parameterized by GB(0.345, 0.2, 1.0, 2.0). The volumetric phase diagram exhibits isotropic (IL), nematic (ND), and two columnar phases characterized by radial distribution functions: the transversal fluid structure varies between a hexagonal columnar (CD) phase (at higher temperatures and pressures) and a rectangular columnar (CO) phase (at lower temperatures and pressures). The slab-wise analysis of fluid dynamics suggests the formation of grain-boundary defects in the CO phase. Longitudinal fluid structure is highly periodic with narrow peaks for the CO phase, suggestive of a near-crystalline (yet diffusive) system, but is only short-ranged for the CD phase. The IL phase does not exhibit anisotropic diffusion. Transversal diffusion is more favorable in the ND phase at all times, but only favorable at short times for the columnar phases. In the columnar phases, a crossover occurs where longitudinal diffusion is favored over transversal diffusion at intermediate-to-long timescales. The anomalous diffusivity is pronounced in both columnar phases, with three identifiable contributions: (a) the rattling of discogens within a transient "interdigitation" cage, (b) the hopping of discogens across columns, and (c) the drifting motion of discogens along the orientation of the director. PMID:24718439

  12. Genetic algorithm prediction of crystal structure of metastable Si-IX phase

    SciTech Connect

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Yangang; Wang, Cai-Zhuang; Ho, Kai-Ming

    2013-12-14

    We performed genetic algorithm search for the atomic structure of the long Lime unsolved Si-IX phase. We found two new structures with space groups of P4(2)/m and P-4, respectively, which have lattice parameters in excellent agreement with the experimental data. The phonon calculations showed that the P4(2)/m structure exhibits a soft phonon mode, while the P-4 structure is dynamically stable. Our calculation also showed that the P-4 structure is a meta-stable structure in a pressure range from 0 to 40 GPa, The Si-IX phase could be a mixed phase consisting of the P4(2)/m and the P-4 structures. Published by Elsevier Ltd.

  13. Mesoscopic simulation of phase behaviors and structures in an amphiphile-solvent system

    NASA Astrophysics Data System (ADS)

    Yamada, Kohtaro; Yasuno, Emiko; Kawabata, Youhei; Okuzono, Tohru; Kato, Tadashi

    2014-06-01

    We have performed a three-dimensional simulation of mesoscopic structures in a mixture of AB amphiphilic molecule and C solvent by employing the density-functional theory under the conditions that (i) the size of the AB is much larger than C and (ii) the affinity between A and B is much larger than the affinity between B and C. First, we have calculated the free energy of five periodic structures, i.e., the lamellar phase, hexagonally packed cylinders, body-centered-cubic spheres, face-centered-cubic spheres, and gyroid phase for different sets of the concentration of AB (ϕ¯AB) and the χ parameter (χAC). By comparing the free energies for these structures, the χAC-ϕ ¯AB phase diagram has been obtained. In addition to these periodic structures, it has been shown that nonperiodic structures such as spherical and rodlike micelles can be obtained although they might be metastable phase.

  14. Experimental phasing for structure determination using membrane-protein crystals grown by the lipid cubic phase method

    SciTech Connect

    Li, Dianfan; Pye, Valerie E.; Caffrey, Martin

    2015-01-01

    Very little information is available in the literature concerning the experimental heavy-atom phasing of membrane-protein structures where the crystals have been grown using the lipid cubic phase (in meso) method. In this paper, pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine labelling as applied to an integral membrane kinase crystallized in meso are described. An assay to assess cysteine accessibility for mercury labelling of membrane proteins is introduced. Despite the marked increase in the number of membrane-protein structures solved using crystals grown by the lipid cubic phase or in meso method, only ten have been determined by SAD/MAD. This is likely to be a consequence of the technical difficulties associated with handling proteins and crystals in the sticky and viscous hosting mesophase that is usually incubated in glass sandwich plates for the purposes of crystallization. Here, a four-year campaign aimed at phasing the in meso structure of the integral membrane diacylglycerol kinase (DgkA) from Escherichia coli is reported. Heavy-atom labelling of this small hydrophobic enzyme was attempted by pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine incorporation. Strategies and techniques for special handling are reported, as well as the typical results and the lessons learned for each of these approaches. In addition, an assay to assess the accessibility of cysteine residues in membrane proteins for mercury labelling is introduced. The various techniques and strategies described will provide a valuable reference for future experimental phasing of membrane proteins where crystals are grown by the lipid cubic phase method.

  15. Phases and structures of sunset yellow and disodium cromoglycate mixtures in water

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Akihiro; Smith, Gregory P.; Yi, Youngwoo; Xu, Charles; Biffi, Silvia; Serra, Francesca; Bellini, Tommaso; Zhu, Chenhui; Clark, Noel A.

    2016-01-01

    We study phases and structures of mixtures of two representative chromonic liquid crystal materials, sunset yellow FCF (SSY) and disodium cromoglycate (DSCG), in water. A variety of combinations of isotropic, nematic (N ), and columnar (also called M ) phases are observed depending on their concentrations, and a phase diagram is made. We find a tendency for DSCG-rich regions to show higher-order phases while SSY-rich regions show lower-order ones. We observe uniform mesophases only when one of the materials is sparse in the N phases. Their miscibility in M phases is so low that essentially complete phase separation occurs. X-ray scattering and spectroscopy studies confirm that SSY and DSCG molecules do not mix when they form chromonic aggregates and neither do their aggregates when they form M phases.

  16. Phases and structures of sunset yellow and disodium cromoglycate mixtures in water.

    PubMed

    Yamaguchi, Akihiro; Smith, Gregory P; Yi, Youngwoo; Xu, Charles; Biffi, Silvia; Serra, Francesca; Bellini, Tommaso; Zhu, Chenhui; Clark, Noel A

    2016-01-01

    We study phases and structures of mixtures of two representative chromonic liquid crystal materials, sunset yellow FCF (SSY) and disodium cromoglycate (DSCG), in water. A variety of combinations of isotropic, nematic (N), and columnar (also called M) phases are observed depending on their concentrations, and a phase diagram is made. We find a tendency for DSCG-rich regions to show higher-order phases while SSY-rich regions show lower-order ones. We observe uniform mesophases only when one of the materials is sparse in the N phases. Their miscibility in M phases is so low that essentially complete phase separation occurs. X-ray scattering and spectroscopy studies confirm that SSY and DSCG molecules do not mix when they form chromonic aggregates and neither do their aggregates when they form M phases. PMID:26871132

  17. A composite phase diagram of structure H hydrates using Schreinemakers' geometric approach

    USGS Publications Warehouse

    Mehta, A.P.; Makogon, T.Y.; Burruss, R.C.; Wendlandt, R.F.; Sloan, E.D.

    1996-01-01

    A composite phase diagram is presented for Structure H (sH) clathrate hydrates. In this work, we derived the reactions occurring among the various phases along each four-phase (Ice/Liquid water, liquid hydrocarbon, vapor, and hydrate) equilibrium line. A powerful method (though seldom used in chemical engineering) for multicomponent equilibria developed by Schreinemakers is applied to determine the relative location of all quadruple (four-phase) lines emanating from three quintuple (five-phase) points. Experimental evidence validating the approximate phase diagram is also provided. The use of Schreinemakers' rules for the development of the phase diagram is novel for hydrates, but these rules may be extended to resolve the phase space of other more complex systems commonly encountered in chemical engineering.

  18. Structural phase transition of merocyanine J-aggregate induced by ion-recombination in the aqueous sub-phase

    NASA Astrophysics Data System (ADS)

    Kato, Noritaka; Saito, Kentaro; Uesu, Yoshiaki

    2000-08-01

    By using the sub-phase, which contains two different kinds of counter-ions, we found a reversible thermochromic transition between different J-aggregate states of amphiphilic merocyanine dye (MD) molecules in the monolayer at the air-water interface. This chromatic change is attributed to the structural phase transition of MD J-aggregate crystallites induced by the mutual recombination of different counter-ions to MD molecules. The drastic morphological change of the MD monolayer during the transition is revealed by the in-situ observation using a multipurpose non-linear optical microscope.

  19. Structural Phase Transitions and Metallized Phenomena in Arsenic Telluride under High Pressure.

    PubMed

    Zhao, Jinggeng; Yang, Liuxiang; Yu, Zhenhai; Wang, Yong; Li, Chunyu; Yang, Ke; Liu, Zhiguo; Wang, Yi

    2016-04-18

    In this study, first-principle calculations, in situ angle-dispersive X-ray diffraction, and in situ electrical resistance measurements were performed on arsenic telluride (As2Te3) under high pressure. Structural phase transitions and metallized phenomena were observed from the calculated and experimental results. Upon compression, α-As2Te3 transforms into phases α' and α″ at ∼5.09 and ∼13.2 GPa, respectively, with two isostructural phase transitions. From 13.2 GPa, As2Te3 starts to transform into phase γ, with one first-order monoclinic to monoclinic crystal structural phase transition. According to the first-principle calculations and electrical resistance measurements, the structural phase transitions in the compression process induce the transformation from an insulator (phase α) across a semimetal (phase α') into a metal (phases α″ and γ). The evolution of the structure and transport property upon compression on As2Te3 is helpful for understanding the properties of other A2B3-type compounds under high pressure. PMID:27035163

  20. Comparing two tetraalkylammonium ionic liquids. I. Liquid phase structure

    NASA Astrophysics Data System (ADS)

    Lima, Thamires A.; Paschoal, Vitor H.; Faria, Luiz F. O.; Ribeiro, Mauro C. C.; Giles, Carlos

    2016-06-01

    X-ray scattering experiments at room temperature were performed for the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N1114][NTf2], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N1444][NTf2]. The peak in the diffraction data characteristic of charge ordering in [N1444][NTf2] is shifted to longer distances in comparison to [N1114][NTf2], but the peak characteristic of short-range correlations is shifted in [N1444][NTf2] to shorter distances. Molecular dynamics (MD) simulations were performed for these ionic liquids using force fields available from the literature, although with new sets of partial charges for [N1114]+ and [N1444]+ proposed in this work. The shifting of charge and adjacency peaks to opposite directions in these ionic liquids was found in the static structure factor, S(k), calculated by MD simulations. Despite differences in cation sizes, the MD simulations unravel that anions are allowed as close to [N1444]+ as to [N1114]+ because anions are located in between the angle formed by the butyl chains. The more asymmetric molecular structure of the [N1114]+ cation implies differences in partial structure factors calculated for atoms belonging to polar or non-polar parts of [N1114][NTf2], whereas polar and non-polar structure factors are essentially the same in [N1444][NTf2]. Results of this work shed light on controversies in the literature on the liquid structure of tetraalkylammonium based ionic liquids.

  1. Comparing two tetraalkylammonium ionic liquids. I. Liquid phase structure.

    PubMed

    Lima, Thamires A; Paschoal, Vitor H; Faria, Luiz F O; Ribeiro, Mauro C C; Giles, Carlos

    2016-06-14

    X-ray scattering experiments at room temperature were performed for the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N1114][NTf2], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N1444][NTf2]. The peak in the diffraction data characteristic of charge ordering in [N1444][NTf2] is shifted to longer distances in comparison to [N1114][NTf2], but the peak characteristic of short-range correlations is shifted in [N1444][NTf2] to shorter distances. Molecular dynamics (MD) simulations were performed for these ionic liquids using force fields available from the literature, although with new sets of partial charges for [N1114](+) and [N1444](+) proposed in this work. The shifting of charge and adjacency peaks to opposite directions in these ionic liquids was found in the static structure factor, S(k), calculated by MD simulations. Despite differences in cation sizes, the MD simulations unravel that anions are allowed as close to [N1444](+) as to [N1114](+) because anions are located in between the angle formed by the butyl chains. The more asymmetric molecular structure of the [N1114](+) cation implies differences in partial structure factors calculated for atoms belonging to polar or non-polar parts of [N1114][NTf2], whereas polar and non-polar structure factors are essentially the same in [N1444][NTf2]. Results of this work shed light on controversies in the literature on the liquid structure of tetraalkylammonium based ionic liquids. PMID:27306015

  2. Phase structure of cold magnetized color superconducting quark matter

    NASA Astrophysics Data System (ADS)

    Allen, PG; Grunfeld, AG; Scoccola, NN

    2016-04-01

    The influence of intense magnetic fields on the behavior of color superconducting cold quark matter is investigated using an SU(2) f NJL-type model for which a novel regulation scheme is introduced. In such a scheme the contributions which are explicitly dependent on the magnetic field turn out to be finite and, thus, do not require to be regularized. As a result of this, non-physical oscillations that arise from regularizing magnetic field dependent terms are naturally removed, and oscillations that are actually physical can be better appreciated. The phase diagrams in the ẽB – μ plane are presented for different values of the diquark coupling.

  3. Inherent structures of phase-separating binary mixtures: nucleation, spinodal decomposition, and pattern formation.

    PubMed

    Sarkar, Sarmistha; Bagchi, Biman

    2011-03-01

    An energy landscape view of phase separation and nonideality in binary mixtures is developed by exploring their potential energy landscape (PEL) as functions of temperature and composition. We employ molecular dynamics simulations to study a model that promotes structure breaking in the solute-solvent parent binary liquid, at low temperatures. The PEL of the system captures the potential energy distribution of the inherent structures (IS) of the system and is obtained by removing the kinetic energy (including that of intermolecular vibrations). The broader distribution of the inherent structure energy for structure breaking liquid than that of the structure making liquid demonstrates the larger role of entropy in stabilizing the parent liquid of the structure breaking type of binary mixtures. At high temperature, although the parent structure of the structure breaking binary mixture is homogenous, the corresponding inherent structure is found to be always phase separated, with a density pattern that exhibits marked correlation with the energy of its inherent structure. Over a broad range of intermediate inherent structure energy, bicontinuous phase separation prevails with interpenetrating stripes as signatures of spinodal decomposition. At low inherent structure energy, the structure is largely phase separated with one interface where as at high inherent structure energy we find nucleation type growth. Interestingly, at low temperature, the average inherent structure energy () exhibits a drop with temperature which signals the onset of crystallization in one of the phases while the other remains in the liquid state. The nonideal composition dependence of viscosity is anticorrelated with average inherent structure energy. PMID:21517506

  4. Interatomic force constants and effective Hamiltonians for structural phase transitions

    NASA Astrophysics Data System (ADS)

    Kumar, Anil; Rabe, Karin M.

    2011-03-01

    Expansion of the total energy of a crystal around a high-symmetry reference structure provides information about material properties including the phonon dispersion, responses to applied fields, magnetostructural coupling, and structural transitions. For complex oxides, parameterization of the structural energetics by real-space interatomic force constants (IFCs) provides a computationally convenient and physically transparent way of analyzing these properties. By projection into a subspace containing the relevant degrees of freedom, one can construct an effective Hamiltonian to study properties that are not readily accessible with DFT based calculations, including properties at finite temperature or long length scales. It is well known that first-principles density-functional-theory (DFT) based-calculations can be systematically used to determine real-space IFCs of materials; this is part of several first-principles packages including ABINIT and Quantum Espresso. Here, we discuss a simple and efficient approach for construction of first-principles effective Hamiltonians which uses this computational capability to generate and compute the quadratic inter-cell parameters in a single step. We illustrate the method through the application to systems for which effective Hamiltonians have previously been constructed, and show how this approach facilitates the construction of effective Hamiltonians for new classes of crystal structures.

  5. Magnetic structures in the magnetic phase diagram of Ho2RhIn8

    NASA Astrophysics Data System (ADS)

    Čermák, Petr; Prokeš, Karel; Ouladdiaf, Bachir; Boehm, Martin; Kratochvílová, Marie; Javorský, Pavel

    2015-04-01

    The magnetic phase diagram of the tetragonal Ho2RhIn8 compound has similar features to many related systems, revealing a zero magnetic field AF1 and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase were not reported yet for any of the related compounds. In addition, only the Ho2RhIn8 phase diagram contains a small region of the incommensurate zero-field AF3 phase. We have performed a number of neutron diffraction experiments on single crystals of Ho2RhIn8 using several diffractometers including experiments in both horizontal and vertical magnetic fields up to 4 T. We present details of the magnetic structures in all magnetic phases of the rich phase diagram of Ho2RhIn8 . The Ho magnetic moments point along the tetragonal c axis in every phase. The ground-state AF1 phase is characterized by propagation vector k =(1 /2 ,0 ,0 ) . The more complex ferrimagnetic AF2 phase is described by four propagation vectors k0=(0 ,0 ,0 ) ,k1=(1 /2 ,0 ,0 ) ,k2=(0 ,1 /2 ,1 /2 ) ,k3=(1 /2 ,1 /2 ,1 /2 ) . The magnetic structure in the AF3 phase is incommensurate with kA F 3=(0.5 ,δ ,0 ) . Our results are consistent with theoretical calculations based on crystal field theory.

  6. Pressure Induced Structural Phase Transition in Actinide Monophospides: Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Makode, Chandrabhan; Sanyal, Sankar P.

    2011-07-01

    The structural and electronic properties of monophospides of Thorium, Uranium and Neptunium have been investigated using tight binding linear muffin-in-orbital (TB-LMTO) method within the local density approximation (LDA). From present study with the help of total energy calculations it is found that ThP, UP and NpP are stable in NaCl- type structure under ambient pressure. The structure stability of ThP, UP and NpP changes under the application of pressure. We predict a structural phase transition from NaCl-type (B1-phase) structure to CsCl-type (B2-phase) structure for these phospides in the pressure range of 37.0-24.0 GPa (ThP to NpP). The calculated equilibrium lattice parameters and bulk modulus are in good agreement with experimental and theoretical work.

  7. Pressure induced structural phase transition in actinide mono-bismuthides: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Pataiya, J.; Makode, C.; Aynyas, M.; Sanyal, Sankar P.

    2013-06-01

    The structural and electronic properties of mono-bismuthides of Plutonium and Americium have been investigated using tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). From present study with the help of total energy calculations it is found that PuBi and AmBi are stable in NaCl - type structure under ambient pressure. The structure stability of PuBi and AmBi changes under the application of pressure. We predict a structural phase transition from NaCl-type (B1-phase) structure to CsCl-type (B2-phase) structure for these phospides in the pressure range of 45 - 4.5 GPa for PuBi and AmBi respectively. The calculated equilibrium lattice parameters and bulk modulus are in good agreement with experimental and theoretical work.

  8. Phase composition and structure of aluminum Al-Cu-Si-Sn-Pb alloys

    NASA Astrophysics Data System (ADS)

    Belov, N. A.; Stolyarova, O. O.; Murav'eva, T. I.; Zagorskii, D. L.

    2016-06-01

    The structure and phase composition of cast and heat treated Al-Cu-Si-Sn-Pb alloys containing 6 wt % Sn, 2 wt % Pb, 0-4 wt % Cu, 0-10 wt % Si have been studied using calculations and experimental methods. Polythermal and isothermal sections are reported, which indicate the existence of two liquid phases. It was found that the low-melting phase is inhomogeneous and consists of individual leadand tin-based particles.

  9. Broadband reflected wavefronts manipulation using structured phase gradient metasurfaces

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Peng; Wan, Le-Le; Chen, Tian-Ning; Song, Ai-Ling; Du, Xiao-Wen

    2016-06-01

    Acoustic metasurface (AMS) is a good candidate to manipulate acoustic waves due to special acoustic performs that cannot be realized by traditional materials. In this paper, we design the AMS by using circular-holed cubic arrays. The advantages of our AMS are easy assemble, subwavelength thickness, and low energy loss for manipulating acoustic waves. According to the generalized Snell's law, acoustic waves can be manipulated arbitrarily by using AMS with different phase gradients. By selecting suitable hole diameter of circular-holed cube (CHC), some interesting phenomena are demonstrated by our simulations based on finite element method, such as the conversion of incoming waves into surface waves, anomalous reflections (including negative reflection), acoustic focusing lens, and acoustic carpet cloak. Our results can provide a simple approach to design AMSes and use them in wavefront manipulation and manufacturing of acoustic devices.

  10. Phase structures of 4D stringy charged black holes in canonical ensemble

    NASA Astrophysics Data System (ADS)

    Jia, Qiang; Lu, J. X.; Tan, Xiao-Jun

    2016-08-01

    We study the thermodynamics and phase structures of the asymptotically flat dilatonic black holes in 4 dimensions, placed in a cavity a la York, in string theory for an arbitrary dilaton coupling. We consider these charged black systems in canonical ensemble for which the temperature at the wall of and the charge inside the cavity are fixed. We find that the dilaton coupling plays the key role in the underlying phase structures. The connection of these black holes to higher dimensional brane systems via diagonal (double) and/or direct dimensional reductions indicates that the phase structures of the former may exhaust all possible ones of the latter, which are more difficult to study, under conditions of similar settings. Our study also shows that a diagonal (double) dimensional reduction preserves the underlying phase structure while a direct dimensional reduction has the potential to change it.

  11. Structure, scaling, and phase transition in the optimal transport network.

    PubMed

    Bohn, Steffen; Magnasco, Marcelo O

    2007-02-23

    The structure and properties of optimal networks depend on the cost functional being minimized and on constraints to which the minimization is subject. We show here two different formulations that lead to identical results: minimizing the dissipation rate of an electrical network under a global constraint is equivalent to the minimization of a power-law cost function introduced by Banavar et al. [Phys. Rev. Lett. 84, 4745 (2000)10.1103/PhysRevLett.84.4745]. An explicit scaling relation between the currents and the corresponding conductances is derived, proving the potential flow nature of the latter. Varying a unique parameter, the topology of the optimized networks shows a transition from a tree topology to a very redundant structure with loops; the transition corresponds to a discontinuity in the slope of the power dissipation. PMID:17359138

  12. Mechanical surface waves accompany action potential propagation.

    PubMed

    El Hady, Ahmed; Machta, Benjamin B

    2015-01-01

    Many diverse studies have shown that a mechanical displacement of the axonal membrane accompanies the electrical pulse defining the action potential (AP). We present a model for these mechanical displacements as arising from the driving of surface wave modes in which potential energy is stored in elastic properties of the neuronal membrane and cytoskeleton while kinetic energy is carried by the axoplasmic fluid. In our model, these surface waves are driven by the travelling wave of electrical depolarization characterizing the AP, altering compressive electrostatic forces across the membrane. This driving leads to co-propagating mechanical displacements, which we term Action Waves (AWs). Our model allows us to estimate the shape of the AW that accompanies any travelling wave of voltage, making predictions that are in agreement with results from several experimental systems. Our model can serve as a framework for understanding the physical origins and possible functional roles of these AWs. PMID:25819404

  13. Ocular myasthenia gravis accompanied by anosmia.

    PubMed

    Chen, Ying; Wang, Li; Zhou, Li; Gao, Ying

    2016-02-01

    We report a case of ocular myasthenia gravis (MG) accompanied by anosmia. A 76-year-old man had idiopathic anosmia of 2-year duration. Four months before consultation, he began to have drooping in the right upper eyelid along with muscle soreness, distension, and pain in the nape. His tongue was dark-red with a thin and white coating; his pulse was wiry and slippery. According to Traditional Chinese Medicine, eyelid drooping and anosmia are the main signs of liver constraint and spleen deficiency. In Western Medicine, the diagnosis was ocular MG and idiopathic anosmia. Our patient, along with the literature, suggests that anosmia may be an early symptom before MG. MG accompanied by anosmia could be a special subtype of MG according to antibody production and symptoms. PMID:26946629

  14. Mechanical surface waves accompany action potential propagation

    NASA Astrophysics Data System (ADS)

    El Hady, Ahmed; Machta, Benjamin B.

    2015-03-01

    Many diverse studies have shown that a mechanical displacement of the axonal membrane accompanies the electrical pulse defining the action potential (AP). We present a model for these mechanical displacements as arising from the driving of surface wave modes in which potential energy is stored in elastic properties of the neuronal membrane and cytoskeleton while kinetic energy is carried by the axoplasmic fluid. In our model, these surface waves are driven by the travelling wave of electrical depolarization characterizing the AP, altering compressive electrostatic forces across the membrane. This driving leads to co-propagating mechanical displacements, which we term Action Waves (AWs). Our model allows us to estimate the shape of the AW that accompanies any travelling wave of voltage, making predictions that are in agreement with results from several experimental systems. Our model can serve as a framework for understanding the physical origins and possible functional roles of these AWs.

  15. Crystalline structure in the confined-deconfined mixed phase: Neutron stars as an example

    SciTech Connect

    Glendenning, N.K.

    1996-04-18

    We review the differences in first order phase transition of single and multi-component systems, and then discuss the crystalline structure expected to exist in the mixed confined deconfined phase of hadronic matter. The particular context of neutron stars is chosen for illustration. The qualitative results are general and apply for example to the vapor-liquid transition in subsaturated asymmetric nuclear matter.

  16. Experimental phasing for structure determination using membrane-protein crystals grown by the lipid cubic phase method

    PubMed Central

    Li, Dianfan; Pye, Valerie E.; Caffrey, Martin

    2015-01-01

    Despite the marked increase in the number of membrane-protein structures solved using crystals grown by the lipid cubic phase or in meso method, only ten have been determined by SAD/MAD. This is likely to be a consequence of the technical difficulties associated with handling proteins and crystals in the sticky and viscous hosting mesophase that is usually incubated in glass sandwich plates for the purposes of crystallization. Here, a four-year campaign aimed at phasing the in meso structure of the integral membrane diacylglycerol kinase (DgkA) from Escherichia coli is reported. Heavy-atom labelling of this small hydrophobic enzyme was attempted by pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine incorporation. Strategies and techniques for special handling are reported, as well as the typical results and the lessons learned for each of these approaches. In addition, an assay to assess the accessibility of cysteine residues in membrane proteins for mercury labelling is introduced. The various techniques and strategies described will provide a valuable reference for future experimental phasing of membrane proteins where crystals are grown by the lipid cubic phase method. PMID:25615865

  17. Structural phase transitions in ionic conductor Bi2O3 by temperature dependent XPD and XAS

    NASA Astrophysics Data System (ADS)

    Zhu, Yingcai; An, Pengfei; Yu, Meijuan; Marcelli, Augusto; Liu, Yong; Hu, Tiandou; Xu, Wei

    2016-05-01

    The superionic behavior of cubic δ-phase Bi2O3, a metastable phase at high temperature, is of great interests from both scientific and technological perspectives. With the highest ionic conductivity among all known compounds, the δ-phase Bi2O3 possesses promising applications in solid-oxide fuel cells. Previous investigations pointed out the α to δ- phase transition occurs during the heating process, as supported by the X-ray and Neutron diffraction experiments. Through in situ measurements of the long-range order structure and the local structure by X-ray powder diffraction and X-ray absorption spectroscopy, we investigated the evolution of the structures under different temperatures. Both techniques provided ample evidence that the existence of meta-stable β-phase are crucial for forming the defective fluorite cubic δ phase. Our finding suggested that the phase transition from tetragonal β-phase to δ-phase is an influencing factor for the generation of the oxygen-ion pathways.

  18. Submicrometer photonic structure fabrication by phase spatial-light-modulator-based interference lithography.

    PubMed

    Behera, Saraswati; Kumar, Manish; Joseph, Joby

    2016-04-15

    We present a large-area and single-step fabrication approach based on phase spatial light modulator (SLM)-assisted interference lithography for the realization of submicrometer photonic structures on photoresist. A multimirror beam steering unit is used to reflect the SLM-generated phase-engineered beams leading to a large angle between interfering beams while also preserving the large area of the interfering plane beams. Both translational and rotational periodic submicrometer structures are experimentally realized. This approach increases the flexibility of interference lithography to fabricate more complex submicrometer photonic structures and photonic metamaterial structures for future applications. PMID:27082372

  19. Analysis of the structure of synthetic and natural melanins by solid-phase

    SciTech Connect

    Duff, G.A.; Roberts, J.E.; Foster, N.

    1988-09-06

    The structures of one synthetic and two natural melanins are examined by solid-state NMR using cross polarization, magic angle sample spinning, and high-power proton decoupling. The structural features of synthetic dopa malanin are compared to those of melanin from malignant melanoma cells grown in culture and sepia melanin from squid ink. Natural abundance /sup 13/C and /sup 15/N spectra show resonances consistent with known pyrrolic and indolic structures within the heterogeneous biopolymer; /sup 13/C spectra indicate the presence of aliphatic residues in all three materials. These solid-phase experiments illustrate the promise of solid-phase NMR for elucidating structural from insoluble biomaterials.

  20. Metastatic Basal Cell Carcinoma Accompanying Gorlin Syndrome

    PubMed Central

    Bilir, Yeliz; Gokce, Erkan; Ozturk, Banu; Deresoy, Faik Alev; Yuksekkaya, Ruken; Yaman, Emel

    2014-01-01

    Gorlin-Goltz syndrome or basal cell nevus syndrome is an autosomal dominant syndrome characterized by skeletal anomalies, numerous cysts observed in the jaw, and multiple basal cell carcinoma of the skin, which may be accompanied by falx cerebri calcification. Basal cell carcinoma is the most commonly skin tumor with slow clinical course and low metastatic potential. Its concomitance with Gorlin syndrome, resulting from a mutation in a tumor suppressor gene, may substantially change morbidity and mortality. A 66-year-old male patient with a history of recurrent basal cell carcinoma was presented with exophthalmus in the left eye and the lesions localized in the left lateral orbita and left zygomatic area. His physical examination revealed hearing loss, gapped teeth, highly arched palate, and frontal prominence. Left orbital mass, cystic masses at frontal and ethmoidal sinuses, and multiple pulmonary nodules were detected at CT scans. Basal cell carcinoma was diagnosed from biopsy of ethmoid sinus. Based on the clinical and typical radiological characteristics (falx cerebri calcification, bifid costa, and odontogenic cysts), the patient was diagnosed with metastatic skin basal cell carcinoma accompanied by Gorlin syndrome. Our case is a basal cell carcinoma with aggressive course accompanying a rarely seen syndrome. PMID:25506011

  1. Influence of the interfacial phase on the structural integrity and oxygen permeability of a dual-phase membrane.

    PubMed

    Sun, Ming; Chen, Xinwei; Hong, Liang

    2013-09-25

    Compositing fluorite Ce0.8Gd0.2O2-δ (CGO) oxide with perovskite La0.4Ba0.6Fe0.8Zn0.2O3-δ (LBFZ) oxide leads to the formation of a minor interfacial BaCeO3 phase upon sintering at 1400 °C. This interfacial composition assures a gastight ceramic membrane with fine grain-boundary structure, in which the LBFZ phase exhibits an improved oxygen permeability over the pristine LBFZ membrane on the same volumetric basis. The presence of the BaCeO3 phase effectively preserves the structural integrity of the composition by limiting the interfacial diffusion of barium ions between LBFZ and CGO. In comparison, replacing CGO with Y0.08Zr0.92O2-δ in the system results in a substantially low oxygen flux due to an overwhelming interfacial diffusion and, consequently, a heavy degradation of LBFZ. Besides structural reinforcement, the high interface between LBFZ and CGO benefits oxygen transport, as is proven through variation of the oxygen partial pressure on the feed side of the membrane and operation temperature. Furthermore, the trade-off between LBFZ loading and interfacial diffusion yields an optimal CGO loading at 40 wt %, which exhibits an oxygen flux of 0.84 cm(3)/cm(2)·min at 950 °C. In summary, the minor interfacial binding between CGO and LBFZ grains is constructive in easing oxygen crossover in the phase boundary with the exception of maintaining membrane structural stability under oxygen permeation conditions. PMID:23977996

  2. Structure and phase composition of samples in the Nb-C system

    SciTech Connect

    Markhasev, B.I.; Dzhamarov, S.S.; Klyugvant, V.V.; Pioro, N.C.; Smirnov, V.P.

    1985-09-01

    The structure and phase composition of samples in the Nb-C system have been repeatedly studied over a wide interval of carbon concentrations, yet many questions remain. To define more accurately the formation conditions of Nb/sub 4/C/sub 3/ and to ascertain the structure and phase composition of materials based on niobium carbide, the authors studied samples of compositions between NbCo /SUB .58/ and NbCo /SUB .98/ .

  3. Guided Lamb wave based 2-D spiral phased array for structural health monitoring of thin panel structures

    NASA Astrophysics Data System (ADS)

    Yoo, Byungseok

    2011-12-01

    In almost all industries of mechanical, aerospace, and civil engineering fields, structural health monitoring (SHM) technology is essentially required for providing the reliable information of structural integrity of safety-critical structures, which can help reduce the risk of unexpected and sometimes catastrophic failures, and also offer cost-effective inspection and maintenance of the structures. State of the art SHM research on structural damage diagnosis is focused on developing global and real-time technologies to identify the existence, location, extent, and type of damage. In order to detect and monitor the structural damage in plate-like structures, SHM technology based on guided Lamb wave (GLW) interrogation is becoming more attractive due to its potential benefits such as large inspection area coverage in short time, simple inspection mechanism, and sensitivity to small damage. However, the GLW method has a few critical issues such as dispersion nature, mode conversion and separation, and multiple-mode existence. Phased array technique widely used in all aspects of civil, military, science, and medical industry fields may be employed to resolve the drawbacks of the GLW method. The GLW-based phased array approach is able to effectively examine and analyze complicated structural vibration responses in thin plate structures. Because the phased sensor array operates as a spatial filter for the GLW signals, the array signal processing method can enhance a desired signal component at a specific direction while eliminating other signal components from other directions. This dissertation presents the development, the experimental validation, and the damage detection applications of an innovative signal processing algorithm based on two-dimensional (2-D) spiral phased array in conjunction with the GLW interrogation technique. It starts with general backgrounds of SHM and the associated technology including the GLW interrogation method. Then, it is focused on the

  4. Theory of structural phase transition in MgTi{sub 2}O{sub 4}

    SciTech Connect

    Talanov, V. M.; Shirokov, V. B.; Ivanov, V. V.; Talanov, M. V.

    2015-01-15

    A theory of phase transition in MgTi{sub 2}O{sub 4} is proposed based on a study of the order-parameter symmetry, thermodynamics, and mechanisms of formation of the atomic and orbital structure of the low-symmetry MgTi{sub 2}O{sub 4} phase. The critical order parameter (which induces a phase transition) is determined. It is shown that the calculated MgTi{sub 2}O{sub 4} tetragonal structure is a result of displacements of magnesium, titanium, and oxygen atoms; ordering of oxygen atoms; and the participation of d{sub xy}, d{sub xz}, and d{sub yz} orbitals. The contribution of noncritical representations to ion displacements is proven to be insignificant. The existence of various metal clusters in the tetragonal phase has been established by calculation in correspondence with experimental data. It is shown (within the Landau theory of phase transitions) that phase states can be changed as a result of both first- and second-order phase transitions: the high-symmetry phase borders two low-symmetry phases by second-order transition lines, while the border between low-symmetry phases is a first-order transition line.

  5. High pressure structural, electronic, and optical properties of polymorphic InVO4 phases

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Appalakondaiah, S.; Vaitheeswaran, G.

    2016-02-01

    In the present work, we report a detailed density functional theory calculation on polymorphic InVO4 phases by means of projector augmented wave method. The computed first-order structural phase transformation from orthorhombic (Cmcm) to monoclinic (P2/c) structure is found to occur around 5.6 GPa along with a large volume collapse of 16.6%, which is consistent with previously reported experimental data. This transformation also leads to an increase in the coordination number of vanadium atom from 4 to 6. The computed equilibrium and high pressure structural properties of both InVO4 phases, including unit cell parameters, equation of state, and bulk moduli, are in good agreement with the available experimental data. In addition, compressibility is found to be highly anisotropic and the b-axis being more compressible than the other for both the structures. Electronic band structures for both the phases were calculated, and the band gaps for orthorhombic and monoclinic InVO4 are found to be 4.02 and 1.67 eV, respectively, within the Tran-Blaha Modified Becke-Johnson potential as implemented in linearized augmented planewave method. We further examined the optical properties such as dielectric function, refractive index, and absorption spectra for both the structures. From the implications of these results, it can be proposed that the high pressure InVO4 phase can be more useful than orthorhombic phase for photo catalytic applications.

  6. Local structure, composition, and crystallization mechanism of a model two-phase "composite nanoglass".

    PubMed

    Chattopadhyay, Soma; Kelly, S D; Shibata, Tomohiro; Balasubramanian, M; Srinivasan, S G; Du, Jincheng; Banerjee, Rajarshi; Ayyub, Pushan

    2016-02-14

    We report a detailed study of the local composition and structure of a model, bi-phasic nanoglass with nominal stoichiometry Cu55Nb45. Three dimensional atom probe data suggest a nanoscale-phase-separated glassy structure having well defined Cu-rich and Nb-rich regions with a characteristic length scale of ≈3 nm. However, extended x-ray absorption fine structure analysis indicates subtle differences in the local environments of Cu and Nb. While the Cu atoms displayed a strong tendency to cluster and negligible structural order beyond the first coordination shell, the Nb atoms had a larger fraction of unlike neighbors (higher chemical order) and a distinctly better-ordered structural environment (higher topological order). This provides the first experimental indication that metallic glass formation may occur due to frustration arising from the competition between chemical ordering and clustering. These observations are complemented by classical as well as ab initio molecular dynamics simulations. Our study indicates that these nanoscale phase-separated glasses are quite distinct from the single phase nanoglasses (studied by Gleiter and others) in the following three respects: (i) they contain at least two structurally and compositionally distinct, nanodispersed, glassy phases, (ii) these phases are separated by comparatively sharp inter-phase boundaries, and (iii) thermally induced crystallization occurs via a complex, multi-step mechanism. Such materials, therefore, appear to constitute a new class of disordered systems that may be called a composite nanoglass. PMID:26874493

  7. Initial phases for the development of a Structural Geology database

    NASA Astrophysics Data System (ADS)

    Tikoff, Basil; Babaie, Hassan; Clark, Ryan; Newman, Juile; Walker, Doug

    2014-05-01

    We are at the beginning stages of developing a Data System for Structural Geology and Tectonics (SG&T). This activity is prompted by the necessity of reporting our data from government-funded projects and the lack of any existing database. SG&T data is complex for a variety of reasons, including the wide range of temporal and spatial scales (many orders of magnitude each), the complex three-dimensional geometry of some geological structures, inherent spatial nature of the data, and the difficulty of making temporal inferences from spatial observations. To successful implement the step of developing a SG&T data system, we must simultaneously solve three problems: 1) How to digitize SG&T data; 2) How to design a software system that is applicable; and 3) How to construct a very flexible user interface. To address the first problem, we introduce the "Spot" concept, which allows tracking of hierarchical and spatial relations between structures at all scales, and will link map scale, mesoscale, and laboratory scale data. A Spot, in this sense, is analogous to the beam size of analytical equipment used for in situ analysis of rocks; it is the size over which a measurement or quantity is applicable. A Spot can be a single measurement, an aggregation of individual measurements, or even establish relationships between numerous other Spots. We propose to implement both a Spot and a more traditional Mapping mode for data input. The final challenge is to construct a user interface that is intuitive, open source, and spans as many operating systems and devices as possible. For these reasons, we propose to develop a web-application that can run in both a connected (on the internet) and disconnected mode. Our hope is to have extensive and international community input into the data system development process.

  8. Calorimetric, spectroscopic and structural investigations of phase polymorphism in [Ru(NH3)6](BF4)3. Part I

    NASA Astrophysics Data System (ADS)

    Dołęga, Diana; Mikuli, Edward; Inaba, Akira; Górska, Natalia; Hołderna-Natkaniec, Krystyna; Nitek, Wojciech

    2013-01-01

    Four crystalline phases of the coordination compound [Ru(NH3)6](BF4)3 are identified by adiabatic calorimetry. Three phase transitions, one at TC3(IV→III)=30.7 K, the second at TC2(III→II)=91.7 K (both accompanied by comparable entropy changes 3.0 and 3.1 J K-1 mol-1, respectively) and the third at TC1(II→I)=241.6 K (accompanied by an entropy change of 8.1 J K-1 mol-1) were discovered. X-ray single crystal diffraction (at 293 K) demonstrates that phase I is a highly dynamic disordered cubic phase (Fm3¯m, No. 225) with two types of BF4- anions differing in a degree of disorder. In phase II (at 170 K) the structure remains cubic (Ia3¯, No. 206), with two different types of cations and four different types of anions. Splitting of certain IR bands connected with NH3 ligands at the observed phase transitions suggests a lowering of the symmetry of the [Ru(NH3)6]3+ complex cation. Both NH3 ligands and BF4- anions perform fast reorientations (τR≈10-12 s), which are significantly slowed down below the phase transition at TC3. 1H NMR studies led to estimate the values of the activation energy of NH3 ligands reorientation in the phases II and I as equal to ˜8 kJ mol-1. In phase I the whole hexammineruthenium(III) cations reorientation as a tumbling process can be noticed. The activation energy value of this motion is ˜24 kJ mol-1. 19F NMR studies give the values of the activation energy of BF4- anions reorientation as ˜6 kJ mol-1. Above the phase transition temperature half of BF4- anions perform a tumbling motion with Ea≈8 kJ mol-1.

  9. Structural Phase Transition in AuZn Alloys

    SciTech Connect

    Winn,B.L.; Shapiro, S.M.; Lashley, J.C.; Opeil, C.; Ratcliff, W.

    2009-05-03

    AuxZn1-x alloys undergo a shape memory martensitic transformation whose temperature and nature (continuous or discontinuous) is strongly composition dependent. Neutron diffraction experiments were performed on single crystals of x=50 and 52 to explore the structural changes occurring at the transition temperature. A transverse modulation with wavevector q0=(1/3,1/3,0) develops below the transition temperature, with no observable change in lattice parameter. However, the Bragg peak width shows a broadening suggesting an unresolved rhombohedral distortion similar to what has been observed in NiTi-Fe alloys.

  10. Accelerated safety analyses - structural analyses Phase I - structural sensitivity evaluation of single- and double-shell waste storage tanks

    SciTech Connect

    Becker, D.L.

    1994-11-01

    Accelerated Safety Analyses - Phase I (ASA-Phase I) have been conducted to assess the appropriateness of existing tank farm operational controls and/or limits as now stipulated in the Operational Safety Requirements (OSRs) and Operating Specification Documents, and to establish a technical basis for the waste tank operating safety envelope. Structural sensitivity analyses were performed to assess the response of the different waste tank configurations to variations in loading conditions, uncertainties in loading parameters, and uncertainties in material characteristics. Extensive documentation of the sensitivity analyses conducted and results obtained are provided in the detailed ASA-Phase I report, Structural Sensitivity Evaluation of Single- and Double-Shell Waste Tanks for Accelerated Safety Analysis - Phase I. This document provides a summary of the accelerated safety analyses sensitivity evaluations and the resulting findings.

  11. Structural ceramics incorporating whiskers, platelets, and particulate phases

    SciTech Connect

    Becher, P.F.; Hsueh, C.H.; Alexander, K.B.; Lin, H.T.; Warwick, W.H.; Westmoreland, C.G.; Waters, S.B.

    1995-02-01

    Advances in the development of ceramics toughened with whiskers, particles or platelets are reviewed with emphasis on the development of both fracture strength and toughness. In the systems described here, the primary focus is on toughening attained by crack bridging processes (e.g., frictional bridging and pullout) in the wake of the crack tip. Examples of the influence of resultant improvements in other mechanical properties (e.g., strength, fatigue, and thermal shock resistance) are also given for whisker-reinforced aluminas. It is shown that similar increases in fracture toughness may also be brought about by the incorporation of platelet phases in ceramics, either by their addition or by their formation during densification. In addition, the development of ceramic matrix composites containing transformable tetragonal zirconia grains is discussed. Here, it is shown that both the zirconia grain size and content, combined with thermal expansion mismatch stresses, influence the transformability of the zirconia and the resultant transformation toughening effects. Examples reveal that by addressing the microstructural characteristics, as well as the reinforcement and matrix properties, high strength toughened ceramics with exceptional damage resistance can be developed.

  12. Fluorinated microemulsions: A study of the phase behavior and structure

    SciTech Connect

    LoNostro, P.; Choi, S.M.; Chen, S.H.; Ku, C.Y.

    1999-06-24

    Fluorinated surfactants have been studied for their peculiar property to form micellar aggregates in water and oils (hydrocarbons or fluorocarbons) and to produce stable microemulsions. Because of their capacity to dissolve large amounts of gases (such as oxygen and carbon dioxide) and for their characteristic physicochemical properties, fluorocarbons have been tested for specific medical purposes, and their microemulsions are among the most promising candidates for the production of suitable blood substitutes and other biocompatible fluids. The authors have synthesized a new partially fluorinated nonionic surfactant, namely, F(CF{sub 2}){sub 7}-CO-(OCH{sub 2}CH{sub 2}){sub 7.2}OCH{sub 3} (I), that forms stable microemulsions with water and perfluorocarbons such as perfluorooctane (PFO). In this paper the authors describe for the first time the phase behaviors of perfluorooctanoic acid (PFOA) in water/PFH and in water/PFO, and that of ester I in water/PFO. Small-angle neutron-scattering (SANS) experiments provide a detailed description of the microstructure of the H{sub 2}O/PFO/PFOA ternary system.

  13. Phase Behavior of a Single Structured Ionomer Chain in Solution

    DOE PAGESBeta

    Aryal, Dipak; Etampawala, Thusitha; Perahia, Dvora; Grest, Gary S.

    2014-08-14

    Structured polymers offer a means to tailor transport pathways within mechanically stable manifolds. Here we examine the building block of such a membrane, namely a single large pentablock co-polymer that consist of a center block of a randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability,using molecular dynamics simulations. The polymer structure in a cyclohexane-heptane mixture, a technologically viable solvent, and in water, a poor solvent for all segments and a ubiquitous substance is extracted. In all solvents the pentablock collapsed into nearly spherical aggregates where the ionic block is segregated. Inmore » hydrophobic solvents, the ionic block resides in the center, surrounded by swollen intermix of flexible and end blocks. In water all blocks are collapsed with the sulfonated block residing on the surface. Our results demonstrate that solvents drive different local nano-segregation, providing a gateway to assemble membranes with controlled topology.« less

  14. Phase Behavior of a Single Structured Ionomer Chain in Solution

    SciTech Connect

    Aryal, Dipak; Etampawala, Thusitha; Perahia, Dvora; Grest, Gary S.

    2014-08-14

    Structured polymers offer a means to tailor transport pathways within mechanically stable manifolds. Here we examine the building block of such a membrane, namely a single large pentablock co-polymer that consist of a center block of a randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability,using molecular dynamics simulations. The polymer structure in a cyclohexane-heptane mixture, a technologically viable solvent, and in water, a poor solvent for all segments and a ubiquitous substance is extracted. In all solvents the pentablock collapsed into nearly spherical aggregates where the ionic block is segregated. In hydrophobic solvents, the ionic block resides in the center, surrounded by swollen intermix of flexible and end blocks. In water all blocks are collapsed with the sulfonated block residing on the surface. Our results demonstrate that solvents drive different local nano-segregation, providing a gateway to assemble membranes with controlled topology.

  15. A Rhombohedral Phase of Lipid Containing a Membrane Fusion Intermediate Structure

    PubMed Central

    Yang, Lin; Huang, Huey W.

    2003-01-01

    We constructed the electron density distribution from the x-ray diffraction of a phase of phospholipid that exhibited rhombohedral symmetry. To determine the phases of the diffraction amplitudes, we first extended the well-known one-dimensional swelling method for planar bilayers to a three-dimensional method applicable to a layered system containing in-plane structures, such as rhombohedral structures. The complete phase determination was accomplished by a combination of the swelling method and Luzzati's pattern recognition method. The constructed electron density distribution showed that in each unit cell, two apposed monolayers merged across the water layer and developed into an hourglass structure consistent with a postulated membrane fusion intermediate state called a stalk. The observation of the stalk structure lends a strong support to the stalk hypothesis for membrane fusion and opens a way to measure the structural parameters in the fusion pathway. PMID:12609882

  16. Structural Stability and Phase Transitions in K8Si46 Clathrate under High Pressure

    NASA Astrophysics Data System (ADS)

    Tse, John S.; Desgreniers, Serge; Li, Zhi-Qiang; Ferguson, Michael R.; Kawazoe, Yoshiyuki

    2002-10-01

    The structural stability of type-I K8Si46 clathrate has been investigated at high pressure by synchrotron x-ray diffraction. In contrast to that observed in the Na-doped structure-II analogue [

    A. San-Miguel et al., Phys. Rev. Lett. 83, 5290 (1999)
    ], no phase separation into the β-Sn Si structure was identified at 11 GPa. Instead, K8Si46 is found to undergo a transition to an isostructural positional disordered phase at around 15 GPa. Ab initio phonon band structure calculations reveal a novel phenomenon of phonon instabilities of K atoms in the large cavities is responsible for this transition. Above 32 GPa, the new structure transforms into an amorphous phase.

  17. Novel structural motifs in low energy phases of LiAlH4.

    PubMed

    Amsler, Maximilian; Flores-Livas, José A; Huan, Tran Doan; Botti, Silvana; Marques, Miguel A L; Goedecker, Stefan

    2012-05-18

    We identify a class of novel low energy phases of the hydrogen storage material LiAlH4 by using the ab initio minima hopping crystal structure prediction method. These phases are, unlike previous predictions and known structures of similar materials, characterized by polymeric networks consisting of Al atoms interlinked with H atoms. The most stable structure is a layered ionic crystal with P21/c symmetry, and it has lower free energy than the previously reported structure over a wide range of temperatures. Furthermore, we carry out x-ray diffraction, phonon, and GW band-structure analysis in order to characterize this phase. Its experimental synthesis would have profound implications for the study of dehydrogenation and rehydrogenation processes and the stability problem of LiAlH4 for hydrogen storage applications. PMID:23003156

  18. The systems Sr-Zn-{l_brace}Si,Ge{r_brace}: Phase equilibria and crystal structure of ternary phases

    SciTech Connect

    Romaka, V.V.; Falmbigl, M.; Grytsiv, A.; Rogl, P.

    2012-02-15

    Phase relations have been established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD) for the Sr-poor part of the ternary systems Sr-Zn-Si at 800 Degree-Sign C and Sr-Zn-Ge at 700 Degree-Sign C. In the Sr-Zn-Si system one new ternary compound SrZn{sub 2+x}Si{sub 2-x} (0{<=}x{<=}0.45) with CeAl{sub 2}Ga{sub 2} structure and a statistical mixture of Zn/Si in the 4e site was found. Neither a type-I nor a type-IX clathrate phase was encountered. This system is characterized by formation of two further phases, i.e. SrZn{sub 1-x}Si{sub 1+x} with ZrBeSi-type (0.16{<=}x{<=}0.22) and SrZn{sub 1-x}Si{sub 1+x} with AlB{sub 2}-type (0.35{<=}x{<=}0.65) with a random distribution of Zn/Si atoms in the 2c site. For the Sr-Zn-Ge system, the homogeneity regions of the isotypic phases SrZn{sub 1-x}Ge{sub 1+x} with ZrBeSi-type (0{<=}x{<=}0.17) and AlB{sub 2}-type (0.32{<=}x{<=}0.56), respectively, have been determined. Whereas the germanide SrZn{sub 2+x}Ge{sub 2-x} (CeAl{sub 2}Ga{sub 2}-type) is characterized by a homogeneity region (0{<=}x{<=}0.5), the clathrate type-I phase Sr{sub 8}Zn{sub 8}Ge{sub 38} shows a point composition. - Graphical abstract: Phase equilibria of ternary compounds in the Sr-Zn-Si-system at 800 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Phase equilibria in the Sr-Zn-Si-system are established at 800 Degree-Sign C. Black-Right-Pointing-Pointer Phase equilibria in the Sr-Zn-Ge-system are established at 700 Degree-Sign C. Black-Right-Pointing-Pointer Crystal structures of the ternary compounds were confirmed by X-ray powder diffraction. Black-Right-Pointing-Pointer All ternary compounds except the clathrate-I in the Ge-system are characterized by a homogeneity region.

  19. Structural and magnetic dynamics of a laser induced phase transition in FeRh.

    PubMed

    Mariager, S O; Pressacco, F; Ingold, G; Caviezel, A; Möhr-Vorobeva, E; Beaud, P; Johnson, S L; Milne, C J; Mancini, E; Moyerman, S; Fullerton, E E; Feidenhans'l, R; Back, C H; Quitmann, C

    2012-02-24

    We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (τ(1)~30 ps). This is significantly faster than the magnetic response (τ(2)~60 ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented. PMID:22463562

  20. Structural and Magnetic Dynamics of a Laser Induced Phase Transition in FeRh

    NASA Astrophysics Data System (ADS)

    Mariager, S. O.; Pressacco, F.; Ingold, G.; Caviezel, A.; Möhr-Vorobeva, E.; Beaud, P.; Johnson, S. L.; Milne, C. J.; Mancini, E.; Moyerman, S.; Fullerton, E. E.; Feidenhans'L, R.; Back, C. H.; Quitmann, C.

    2012-02-01

    We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (τ1˜30ps). This is significantly faster than the magnetic response (τ2˜60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.

  1. Modulated magnetic phase of structurally heterogeneous easy-plane weak ferromagnets

    NASA Astrophysics Data System (ADS)

    Dzhuraev, D. R.; Niyazov, L. N.; Sokolov, B. Yu.

    2016-06-01

    The modulated magnetic phase of a structurally heterogeneous easy-plane weak ferromagnet is considered in terms of the thermodynamic Landau theory of phase transitions. The temperature and field dependences of the main magnetic order modulation parameters are determined. The results obtained are compared with the experimental data obtained for the orientational phase transition into a modulated magnetic state that occurs in hematite and iron borate crystals doped with diamagnetic ions to create structural heterogeneity. The proposed theoretical model is shown to describe the entire set of experimental results consistently with some exceptions.

  2. Ramsdellite-structured LiTiO 2: A new phase predicted from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Koudriachova, M. V.

    2008-06-01

    A new phase of highly lithiated titania with potential application as an anode in Li-rechargeable batteries is predicted on the basis of ab initio calculations. This phase has a composition LiTiO2 and may be accessed through electrochemical lithiation of ramsdellite-structured TiO2 at the lowest potential reported for titanium dioxide based materials. The potential remains constant over a wide range of Li-concentrations. The new phase is metastable with respect to a tetragonally distorted rock salt structure, which hitherto has been the only known polymorph of LiTiO2.

  3. Discrete phase-space structure of n-qubit mutually unbiased bases

    SciTech Connect

    Klimov, A.B.; Romero, J.L.; Bjoerk, G.; Sanchez-Soto, L.L.

    2009-01-15

    We work out the phase-space structure for a system of n qubits. We replace the field of real numbers that label the axes of the continuous phase space by the finite field GF(2{sup n}) and investigate the geometrical structures compatible with the notion of unbiasedness. These consist of bundles of discrete curves intersecting only at the origin and satisfying certain additional properties. We provide a simple classification of such curves and study in detail the four- and eight-dimensional cases, analyzing also the effect of local transformations. In this way, we provide a comprehensive phase-space approach to the construction of mutually unbiased bases for n qubits.

  4. Outer Belt Radial Transport Signatures in Drift Phase Structure - Case Studies

    NASA Astrophysics Data System (ADS)

    O'Brien, T. P., III; Kwan, B. P.; Skov, T. M.; Claudepierre, S. G.; Roeder, J. L.; Green, J. C.; Fennell, J. F.

    2015-12-01

    During geomagnetic storms, the Earth's outer radiation belt experiences enhanced radial transport. Different modes of radial transport have different temporal signatures in the particle phase-space density on timescales shorter than a drift period. We use such drift phase structure in time series particle flux observations to identify transport signatures of impulsive and oscillatory drift resonant transport. We perform multiple case studies of geomagnetic storms using particle flux taken near geostationary orbit. We estimate the radial diffusion coefficients from the drift phase structures. We show how these radial diffusion coefficients derived from particle data compare to transport coefficients deduced from wave observations.

  5. Outer Belt Radial Transport Signatures in Drift Phase Structure - Case Studies

    NASA Astrophysics Data System (ADS)

    O'Brien, Paul; Green, Janet; Fennell, Joseph; Claudepierre, Seth; Roeder, James; Kwan, Betty; Mulligan Skov, Tamitha

    2016-07-01

    During geomagnetic storms, the Earth's outer radiation belt experiences enhanced radial transport. Different modes of radial transport have different temporal signatures in the particle phase-space density on timescales shorter than a drift period. We use such drift phase structure in time series particle flux observations to identify transport signatures of impulsive and oscillatory drift resonant transport. We perform multiple case studies of geomagnetic storms using particle flux taken near geostationary orbit. We estimate the radial diffusion coefficients from the drift phase structures. We show how these radial diffusion coefficients derived from particle data compare to transport coefficients deduced from wave observations.

  6. Three-phase inductive-coupled structures for contactless PHEV charging system

    NASA Astrophysics Data System (ADS)

    Lee, Jia-You; Shen, Hung-Yu; Li, Cheng-Bin

    2016-07-01

    In this article, a new-type three-phase inductive-coupled structure is proposed for the contactless plug-in hybrid electric vehicle (PHEV) charging system regarding with SAE J-1773. Four possible three-phase core structures are presented and subsequently investigated by the finite element analysis. To study the correlation between the core geometric parameter and the coupling coefficient, the magnetic equivalent circuit model of each structure is also established. In accordance with the simulation results, the low reluctance and the sharing of flux path in the core material are achieved by the proposed inductive-coupled structure with an arc-shape and three-phase symmetrical core material. It results in a compensation of the magnetic flux between each phase and a continuous flow of the output power in the inductive-coupled structure. Higher coupling coefficient between inductive-coupled structures is achieved. A comparison of coupling coefficient, mutual inductance, and self-inductance between theoretical and measured results is also performed to verify the proposed model. A 1 kW laboratory scale prototype of the contactless PHEV charging system with the proposed arc-shape three-phase inductive-coupled structure is implemented and tested. An overall system efficiency of 88% is measured when two series lithium iron phosphate battery packs of 25.6 V/8.4 Ah are charged.

  7. Direct phase selection of initial phases from single-wavelength anomalous dispersion (SAD) for the improvement of electron density and ab initio structure determination

    SciTech Connect

    Chen, Chung-De; Huang, Yen-Chieh; Chiang, Hsin-Lin; Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan; Chen, Chun-Jung

    2014-09-01

    A novel direct phase-selection method to select optimized phases from the ambiguous phases of a subset of reflections to replace the corresponding initial SAD phases has been developed. With the improved phases, the completeness of built residues of protein molecules is enhanced for efficient structure determination. Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (ϕ{sub 1} and ϕ{sub 2}) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ{sub DS} list as a criterion to select optimized phases ϕ{sub am} from ϕ{sub 1} or ϕ{sub 2} of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases ϕ{sub SAD} has been developed. Based on this work, reflections with an angle θ{sub DS} in the range 35–145° are selected for an optimized improvement, where θ{sub DS} is the angle between the initial phase ϕ{sub SAD} and a preliminary density-modification (DM) phase ϕ{sub DM}{sup NHL}. The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.

  8. Phase Correlations and Topological Measures of Large-Scale Structure

    NASA Astrophysics Data System (ADS)

    Coles, P.

    The process of gravitational instability initiated by small primordial density perturbations is a vital ingredient of cosmological models that attempt to explain how galaxies and large-scale structure formed in the Universe. In the standard picture (the "concordance" model), a period of accelerated expansion ("inflation") generated density fluctuations with simple statistical properties through quantum processes (Starobinsky [82], [83], [84]; Guth [39]; Guth & Pi [40]; Albrecht & Steinhardt [2]; Linde [55]). In this scenario the primordial density field is assumed to form a statistically homogeneous and isotropic Gaussian random field (GRF). Over years of observational scrutiny this paradigm has strengthened its hold in the minds of cosmologists and has survived many tests, culminating in those furnished by the Wilkinson Microwave Anisotropy Probe (WMAP; Bennett et al. [7]; Hinshaw et al. [45].

  9. Efficient structures for geosynchronous spacecraft solar arrays, phase 4

    NASA Technical Reports Server (NTRS)

    Adams, L. R.

    1982-01-01

    Efficient structures for geosynchronous spacecraft solar arrays were investigated. The STACBEAM (stacking triangular articulated compact beam) concept was selected. The primary component, the solar array blanket, is stored in a folded configuration and is deployed by controlled linear extension. Blanket stiffness is attained by axially tensioning the blanket and by providing periodic lateral ribs and standoffs which attach the blanket to the beam at several places along its length. The STACBEAM deploys sequentially (one bay at a time) using a deployer of sufficient rigidity so that beam stiffness is not degraded during deployment. The beam does not rotate during deployment, thus making blanket beam attachment possible in the packaged condition. In addition to high bending stiffness, the STACBEAM possesses high torsional rigidity due to nonflexible diagonals. The concept is adaptable to various size and loading requirements by changing member diameter and baylength, thus affecting the ratio of packaged and deployed length.

  10. Phase transformation of Ca{sub 4}[Al{sub 6}O{sub 12}]SO{sub 4} and its disordered crystal structure at 1073 K

    SciTech Connect

    Kurokawa, Daisuke; Takeda, Seiya; Colas, Maggy; Asaka, Toru; Thomas, Philippe; Fukuda, Koichiro

    2014-07-01

    The phase transformation of Ca{sub 4}[Al{sub 6}O{sub 12}]SO{sub 4} and the crystal structure of its high-temperature phase were investigated by differential thermal analysis, temperature-dependent Raman spectroscopy and high-temperature X-ray powder diffraction (CuKα{sub 1}). We determined the starting temperature of the orthorhombic-to-cubic transformation during heating (=711 K) and that of the reverse transformation during cooling (=742 K). The thermal hysteresis was negative (=−31 K), suggesting the thermoelasticity of the transformation. The space group of the high temperature phase is I4{sup ¯}3m with the unit-cell dimensions of a=0.92426(2) nm and V=0.78955(2) nm{sup 3} (Z=2) at 1073 K. The initial structural model was derived by the direct methods and further refined by the Rietveld method. The final structural model showed the orientational disordering of SO{sub 4} tetrahedra. The maximum-entropy method-based pattern fitting method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. At around the transformation temperature during heating, the vibrational spectra, corresponding to the Raman-active SO{sub 4} internal stretching mode, showed the continuous and gradual change in the slope of full width at half maximum versus temperature curve. This strongly suggests that the orthorhombic-to-cubic phase transformation would be principally accompanied by the statistical disordering in orientation of the SO{sub 4} tetrahedra, without distinct dynamical reorientation. - Graphical abstract: (Left) Three-dimensional electron-density distributions of the SO{sub 4} tetrahedron with the split-atom model, and (right) a bird's eye view of electron densities on the plane parallel to (111). - Highlights: • Crystal structure of Ca{sub 4}[Al{sub 6}O{sub 12}]SO{sub 4} at 1073 K is determined by powder XRD. • The atom arrangements are represented by the split-atom model

  11. Phenomenological thermodynamics and the structure formation mechanism of the CuTi₂S₄ rhombohedral phase.

    PubMed

    Talanov, Michail V; Shirokov, Vladimir B; Talanov, Valery M

    2016-04-21

    The theory of structural phase transition in CuTi2S4 is proposed. The symmetry of order parameters, thermodynamics and the mechanism of the atomic structure formation of the rhombohedral Cu-Ti-thiospinel have been studied. The critical order parameter inducing the phase transition has been found. Within the Landau theory of phase transitions, it is shown that the phase state may change from the high-symmetry cubic disordered Fd3[combining macron]m phase to the low-symmetry ordered rhombohedral R3[combining macron]m phase as a result of phase transition of the first order close to the second order. It is shown that the rhombohedral structure of CuTi2S4 is formed as a result of the displacements of all types of atoms and the ordering of Cu-atoms (1 : 1 order type in tetrahedral spinel sites), Ti-atoms (1 : 1 : 6 order type in octahedral spinel sites), and S-atoms (1 : 1 : 3 : 3 order type). The Cu- and Ti-atoms form metal nanoclusters which are named a "bunch" of dimers. The "bunch" of dimers in CuTi2S4 is a new type of self-organization of atoms in frustrated spinel-like structures. It is shown that Ti-atoms also form other types of metal nanoclusters: trimers and tetrahedra. PMID:27035866

  12. A search for the ground state structure and the phase stability of tantalum pentoxide.

    PubMed

    Pérez-Walton, S; Valencia-Balvín, C; Padilha, A C M; Dalpian, G M; Osorio-Guillén, J M

    2016-01-27

    Tantalum pentoxide (Ta2O5) is a wide-gap semiconductor that presents good catalytic and dielectric properties, conferring to this compound promising prospective use in a variety of technological applications. However, there is a lack of understanding regarding the relations among its crystalline phases, as some of them are not even completely characterized and there is currently no agreement about which models better explain the crystallographic data. Additionally, its phase diagram is unknown. In this work we performed first-principles density functional theory calculations to study the structural properties of the different phases and models of Ta2O5, the equation of state and the zone-centered vibrational frequencies. From our results, we conclude that the phases that are built up from only distorted octahedra instead of combinations with pentagonal and/or hexagonal bipyramids are energetically more favorable and dynamically stable. More importantly, this study establishes that, given the pressure range considered, the B-phase is the most favorable structure and there is no a crystallographic phase transition to another phase at high-pressure. Additionally, for the equilibrium volume of the B-phase and the λ-model, the description of the electronic structure and optical properties were performed using semi-local and hybrid functionals. PMID:26702713

  13. A search for the ground state structure and the phase stability of tantalum pentoxide

    NASA Astrophysics Data System (ADS)

    Pérez-Walton, S.; Valencia-Balvín, C.; Padilha, A. C. M.; Dalpian, G. M.; Osorio-Guillén, J. M.

    2016-01-01

    Tantalum pentoxide (Ta2O5) is a wide-gap semiconductor that presents good catalytic and dielectric properties, conferring to this compound promising prospective use in a variety of technological applications. However, there is a lack of understanding regarding the relations among its crystalline phases, as some of them are not even completely characterized and there is currently no agreement about which models better explain the crystallographic data. Additionally, its phase diagram is unknown. In this work we performed first-principles density functional theory calculations to study the structural properties of the different phases and models of Ta2O5, the equation of state and the zone-centered vibrational frequencies. From our results, we conclude that the phases that are built up from only distorted octahedra instead of combinations with pentagonal and/or hexagonal bipyramids are energetically more favorable and dynamically stable. More importantly, this study establishes that, given the pressure range considered, the B-phase is the most favorable structure and there is no a crystallographic phase transition to another phase at high-pressure. Additionally, for the equilibrium volume of the B-phase and the λ-model, the description of the electronic structure and optical properties were performed using semi-local and hybrid functionals.

  14. Structural phase transition in CuFe{sub 2}O{sub 4} spinel

    SciTech Connect

    Balagurov, A. M. Bobrikov, I. A.; Maschenko, M. S.; Sangaa, D.; Simkin, V. G.

    2013-09-15

    A structural transition with a reduction in symmetry of the high temperature cubic phase (sp. gr. Fd3m) to the tetragonal phase (sp. gr. I4{sub 1}/amd) and the appearance of a ferrimagnetic structure occur in CuFe{sub 2}O{sub 4} copper ferrite at T Almost-Equal-To 440 Degree-Sign C. It is established by an experiment on a high-resolution neutron diffractometer that the temperature at which long-range magnetic order occurs is higher than that of tetragonal phase formation. When cooling CuFe{sub 2}O{sub 4} spinel from 500 Degree-Sign C, the equilibrium coexistence of both phases is observed in a fairly wide temperature range ({approx}40 Degree-Sign C). The composition studied is a completely inverse spinel in the cubic phase, and in the tetragonal phase the inversion parameter does not exceed few percent (x = 0.06 {+-} 0.04). At the same time, the phase formed upon cooling has a classical value of tetragonal distortion ({gamma} Almost-Equal-To 1.06). The character of temperature changes in the structural parameters during the transition from cubic to tetragonal phase indicates that this transition is based on the Jahn-Teller distortion of (Cu,Fe)O{sub 6} octahedra rather than the mutual migration of copper and iron atoms.

  15. Reinvestigation of the gas-phase structure of tris(trifluoromethyl)arsine

    NASA Astrophysics Data System (ADS)

    Berger, Raphael J. F.; Mitzel, Norbert W.

    2010-08-01

    The gas-phase structure of tris(trifluoromethyl)arsine (As(CF)3) at ambient temperature has been re-investigated by means of electron diffraction. Substantial higher accuracy in structural parameters compared to the previous investigation has been achieved. In contrast to the previously reported C3v structure we found C3 symmetry. Selected r structure parameters are: As-C = 2.007(2) Å; C-As-C = 95.5(3)°. The experimental structure parameters are compared to parameters obtained in HF/TZVPP and MP2/TZVPP calculations, the latter being in excellent agreement with the experimental structure.

  16. Systematic comparison of crystalline and amorphous phases: Charting the landscape of water structures and transformations

    SciTech Connect

    Pietrucci, Fabio; Martoňák, Roman

    2015-03-14

    Systematically resolving different crystalline phases starting from the atomic positions, a mandatory step in algorithms for the prediction of structures or for the simulation of phase transitions, can be a non-trivial task. Extending to amorphous phases and liquids which lack the discrete symmetries, the problem becomes even more difficult, involving subtle topological differences at medium range that, however, are crucial to the physico-chemical and spectroscopic properties of the corresponding materials. Typically, system-tailored order parameters are devised, like global or local symmetry indicators, ring populations, etc. We show that a recently introduced metric provides a simple and general solution to this intricate problem. In particular, we demonstrate that a map can be traced displaying distances among water phases, including crystalline as well as amorphous states and the liquid, consistently with experimental knowledge in terms of phase diagram, structural features, and preparation routes.

  17. Structure and transformations of metastable phases. in Zr-Nb and Ti-V alloys

    NASA Astrophysics Data System (ADS)

    Cuello, G. J.; Aurelio, G.; Fernández Guillermet, A.; Campo, J.

    An experimental study is presented of the effect of an isothermal heat treatment (`aging') upon the structural properties of three metastable phases in Zr-Nb and Ti-V alloys, viz. α (hcp), β (bcc) and Ω, formed by quenching the alloys from 1273 K. Using neutron-diffraction experiments, the constitution of the aged alloys and the structural parameters of the resulting aged phases were determined. By combining lattice-parameter measurements with previously established correlations in the Zr-Nb and Ti-V systems, new information on the composition of the aged phases was obtained. For long aging times the α and β phases seem to be approaching equilibrium conditions, which opens up the possibility of using quenching-and-aging experiments to gain insight into the metastable phase diagram of these systems, which is not accurately known from experiments.

  18. Pressure induced structural phase transition of OsB 2: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Ren, Fengzhu; Wang, Yuanxu; Lo, V. C.

    2010-04-01

    Orthorhombic OsB 2 was synthesized at 1000 °C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2. An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3/ mmc structure (high-pressure phase) is stable for OsB 2. We expect the phase transition can be further confirmed by the experimental work.

  19. Structural Properties and Phase Behavior of Crosslinked Networks in Polymer Solutions

    PubMed Central

    Benmouna, Farida; Zemmour, Samira; Benmouna, Mustapha

    2016-01-01

    ABSTRACT Structural properties and phase behavior of crosslinked networks embedded in polymer solutions are theoretically investigated. The partial structure factor of the network is calculated using a matrix formulation of the random phase approximation and the forward scattering limit is correlated with the phase behavior. Swelling and deswelling processes are analyzed in terms of the polymer concentration, the mismatch of solvent quality with respect to polymer and network, the polymers incompatibility and their characteristic sizes. Most studies reported so far in the literature have focussed on the swelling of crosslinked networks and gels in pure solvents but the correlation of the structural properties with the phase behavior in the presence of high molecular weight polymers in solution has not been given sufficient attention. The present work is intended to fill this gap in view of the current efforts to develop novel drug encapsulating and targeted delivery devices. PMID:27134310

  20. Structural Collapse of the Hydroquinone-Formic Acid Clathrate: A Pressure-Medium-Dependent Phase Transition.

    PubMed

    Eikeland, Espen; Thomsen, Maja K; Madsen, Solveig R; Overgaard, Jacob; Spackman, Mark A; Iversen, Bo B

    2016-03-14

    The energy landscape governing a new pressure-induced phase transition in the hydroquinone-formic acid clathrate is reported in which the host structure collapses, opening up the cavity channels within which the guest molecules migrate and order. The reversible isosymmetric phase transition causes significant changes in the morphology and the birefringence of the crystal. The subtle intermolecular interaction energies in the clathrate are quantified at varying pressures using novel model energies and energy frameworks. These calculations show that the high-pressure phase forms a more stable host network at the expense of less-stable host-guest interactions. The phase transition can be kinetically hindered using a nonhydrostatic pressure-transmitting medium, enabling the comparison of intermolecular energies in two polymorphic structures in the same pressure range. Overall this study illustrates a need for accurate intermolecular energies when analyzing self-assembly structures and supramolecular aggregates. PMID:26879515

  1. Structural evolution of La-Cr-O thin films: Part I. Microstructure and phase development

    SciTech Connect

    Orlovskaya, N.; Coratolo, A.; Lugovy, M.; Johnson, C.D.; Gemmen, R.S.

    2006-12-05

    The structural evolution of La–Cr–O thin films and the formation mechanisms of the LaCrO3 perovskite phase have been studied. X-ray amorphous La–Cr–O protective coatings were deposited by magnetron sputtering on metallic interconnect materials. During the annealing of the material in air a two-step phase transition from La–Cr–O to a monoclinic LaCrO4 monazite and further to an orthorhombic LaCrO3 perovskite phase was observed. The formation of a fine nanoporous structure is a result of the significant increase in density of the final LaCrO3 perovskite in comparison with monazite LaCrO4 phase. While the porous structure was not sought after for this application, these distinctive nanostructures may have numerous applications in catalysis, separation membranes or for other SOFC components.

  2. Structural transformation of Sb-based high-speed phase-change material.

    PubMed

    Matsunaga, Toshiyuki; Kojima, Rie; Yamada, Noboru; Kubota, Yoshiki; Kifune, Kouichi

    2012-12-01

    The crystal structure of a phase-change recording material (the compound Ag(3.4)In(3.7)Sb(76.4)Te(16.5)) enclosed in a vacuum capillary tube was investigated at various temperatures in a heating process using a large Debye-Scherrer camera installed in BL02B2 at SPring-8. The amorphous phase of this material turns into a crystalline phase at around 416 K; this crystalline phase has an A7-type structure with atoms of Ag, In, Sb or Te randomly occupying the 6c site in the space group. This structure was maintained up to around 545 K as a single phase, although thermal expansion of the crystal lattice was observed. However, above this temperature, phase separation into AgInTe(2) and Sb-Te transpired. The first fragment, AgInTe(2), reliably maintained its crystal structure up to the melting temperature. On the other hand, the atomic configuration of the Sb-Te gradually varied with increasing temperature. This gradual structural transformation can be described as a continuous growth of the modulation period γ. PMID:23165592

  3. Phase dependent structural and electronic properties of lanthanum orthophosphate (LaPO4)

    NASA Astrophysics Data System (ADS)

    Neupane, M. R.; Garrett, G. A.; Rudin, S.; Andzelm, J. W.

    2016-05-01

    We study the phase-dependent structural and electronic properties of bulk LaPO4, using density functional theory (DFT). The applicability of conventional semi-local and hybrid functionals in predicting structural and electronic properties of monoclinic and hexagonal LaPO4 is evaluated by comparing results to available experimental data. The monoclinic LaPO4 was found to be more stable than the hexagonal phase in ambient conditions with a small energy difference, suggesting a possibility of a phase transition. Both the phases in the bulk form are found to be diamagnetic with indirect energy gaps. These results are consistent with available experimental results. In the monoclinic phase, the hybrid functionals predict indirect band gap at about 8 eV. Furthermore, the calculated indirect–direct transition energy offset (ΔE) in the hexagonal phase was three times lower than the monoclinic phase. Our calculations based on hybrid functionals also reveal that the states near the conduction band edge in the hexagonal LaPO4 are strongly hybridized between La and PO4 states. By analyzing the band dispersion around the band edges, we show that the hexagonal phase has lighter electron effective mass, as compared to the monoclinic phase. With a larger energy gap, smaller ΔE, and smaller electron effective mass, the hexagonal LaPO4 might be a promising candidate material as an n-type transparent oxide.

  4. Pressure-induced phase transition and structural properties of CrO2

    NASA Astrophysics Data System (ADS)

    Wu, H. Y.; Chen, Y. H.; Deng, C. R.; Su, X. F.

    2012-08-01

    The structural properties and pressure-induced phase transitions of CrO2 have been investigated using the pseudopotential plane-wave method based on the density functional theory (DFT). The rutile-type (P42/mnm), CaCl2-type (Pnnm), pyrite-type (Pā3), and CaF2-type (Fm-3m) phases of CrO2 have been considered. The structural properties such as lattice parameters, bulk moduli and its pressure derivative are consistent with the available experimental data. The second-order phase-transition pressure of CrO2 from the rutile phase to CaCl2 phase is 10.9 GPa, which is in good agreement with the experimental result. The sequence of these phases is rutile-type → CaCl2-type → pyrite-type → CaF2-type with the phase-transition pressures 10.9, 23.9, and 144.5 GPa, respectively. The equation of state of different phases has also been presented. It is more difficult to compress with the increase of pressure for different phases of CrO2.

  5. Phase dependent structural and electronic properties of lanthanum orthophosphate (LaPO4).

    PubMed

    Neupane, M R; Garrett, G A; Rudin, S; Andzelm, J W

    2016-05-25

    We study the phase-dependent structural and electronic properties of bulk LaPO4, using density functional theory (DFT). The applicability of conventional semi-local and hybrid functionals in predicting structural and electronic properties of monoclinic and hexagonal LaPO4 is evaluated by comparing results to available experimental data. The monoclinic LaPO4 was found to be more stable than the hexagonal phase in ambient conditions with a small energy difference, suggesting a possibility of a phase transition. Both the phases in the bulk form are found to be diamagnetic with indirect energy gaps. These results are consistent with available experimental results. In the monoclinic phase, the hybrid functionals predict indirect band gap at about 8 eV. Furthermore, the calculated indirect-direct transition energy offset (ΔE) in the hexagonal phase was three times lower than the monoclinic phase. Our calculations based on hybrid functionals also reveal that the states near the conduction band edge in the hexagonal LaPO4 are strongly hybridized between La and PO4 states. By analyzing the band dispersion around the band edges, we show that the hexagonal phase has lighter electron effective mass, as compared to the monoclinic phase. With a larger energy gap, smaller ΔE, and smaller electron effective mass, the hexagonal LaPO4 might be a promising candidate material as an n-type transparent oxide. PMID:27114454

  6. High-temperature structural phase transitions in neighborite: a high-resolution neutron powder diffraction investigation

    NASA Astrophysics Data System (ADS)

    Knight, Kevin S.; Price, G. David; Stuart, John A.; Wood, Ian G.

    2015-01-01

    The nature of the apparently continuous structural phase transition at 1,049 K in the perovskite-structured, MgSiO3 isomorph, neighborite (NaMgF3), from the orthorhombic ( Pbnm) hettotype phase to the cubic () aristotype structure, has been re-investigated using high-resolution, time-of-flight neutron powder diffraction. Using data collected at 1 K intervals close to the nominal phase transition temperature, the temperature dependence of the intensities of superlattice reflections at the M point and the R point of the pseudocubic Brillouin zone indicate the existence of a new intermediate tetragonal phase in space group P4/ mbm, with a narrow phase field extending from ~1,046.5 to ~1,048.5 K, at ambient pressure. Group theoretical analysis shows that the structural transitions identified in this study, Pbnm- P4/ mbm, and P4/ mbm-, are permitted to be second order. The observation of the tetragonal phase resolves the longstanding issue of why the high-temperature phase transition, previously identified as Pbnm-, and which would be expected to be first order under Landau theory, is in fact found to be continuous. Analysis of the pseudocubic shear strain shows it to vary with a critical exponent of 0.5 implying that the phase transition from Pbnm to P4/ mbm is tricritical in character. The large librational modes that exist in the MgF6 octahedron at high temperature, and the use of Gaussian probability density functions to describe atomic displacements, result in apparent bond shortening in the Mg-F distances, making mode amplitude determination an unreliable method for determination of the critical exponent from internal coordinates. Crystal structures are reported for the three phases of NaMgF3 at 1,033 K ( Pbnm), 1,047 K ( P4/ mbm) and 1,049 K ().

  7. Structural properties and high-temperature reactions of the metastable Ω phase in Zr Nb alloys

    NASA Astrophysics Data System (ADS)

    Aurelio, Gabriela; Fernández Guillermet, Armando; Cuello, Gabriel J.; Campo, Javier

    2005-05-01

    This article presents an experimental study and a systematic phenomenological analysis of the structural properties and the high-temperature reactions of the Ω phase formed by quenching ('q') bcc (β) Zr-Nb alloys. In the first part of the work an extensive database with lattice parameters (LPs) for the Ω q and the untransformed β q phase is developed on the basis of neutron diffraction measurements. Various striking features of the LP vs. composition relations are detected, and a new method of analysis is applied which involves the concept of a 'reference behavior' (RB) describing the probable properties of each individual phase if it were unaffected by the other structures in the heterogeneous alloys. In this way, a detailed evaluation is performed of the effects of Ω q/β q coherence strains upon the LPs of these two phases. In the second part of the work, neutron thermodiffraction studies are reported of the structural properties of the Ω q + β q two-phase alloys at 300 K ⩽ T ⩽ 650 K. Extensive LP vs. time results are discussed. On this basis, the structural properties of the Ω a phase formed isothermally upon aging ('a') are established, and compared with those of the Ω q phase. In addition, new information is discussed on the evolution of the Ω a + β a system toward thermodynamic equilibrium. Moreover, it is shown how the present method of analysis may also be used to obtain indirect information of both theoretical and practical interest. In particular, considerable evidence is presented indicating that the Nb content of the Ω a phase decreases upon aging whereas that of β a increases. Finally, it is shown how these composition changes might be used to reconcile much of the long-standing conflicting reports concerning the structural properties of the Ω q and Ω a metastable phases.

  8. Phase-Modulated Hierarchical Surface Structures by Interfering Laser Beams

    SciTech Connect

    Daniel, Claus; Dahotre, Narendra B

    2006-01-01

    A high-energy laser interference direct modulation technique is proposed to develop surfaces for energy-efficient performance based on microstructure and physical parameter control. By producing the surface features or particles at the nano to micron scale in an orderly and/or parallel manner with a lateral long-range order, the surfaces can be configured for highly improved surface response for a host of properties, including wear and friction. Laser interference direct modulation can lead to an optimized composite of metallurgical (localized alloyed or composite regions) and topographic textures. The technique is rapid prototyping, low cost and one-step method that can be well-integrated into existing production lines without the need for any special atmosphere. It is usable for complex geometries of the components and the surface can be modulated for nano-micro scale features on large areas. The present paper describes the principle behind the laser interference technique configured for surface modulation and provides the definitions of surface structures (features) evolved. Some examples of laser-based surface modulation of materials systems are presented.

  9. Crystal structure and phase transitions in perovskite-like C(NH{sub 2}){sub 3}SnCl{sub 3}

    SciTech Connect

    Szafranski, Marek Stahl, Kenny

    2007-08-15

    X-ray single-crystal diffraction, high-temperature powder diffraction and differential thermal analysis at ambient and high pressure have been employed to study the crystal structure and phase transitions of guanidinium trichlorostannate, C(NH{sub 2}){sub 3}SnCl{sub 3}. At 295 K the crystal structure is orthorhombic, space group Pbca, Z=8, a=7.7506(2) A, b=12.0958(4) A and c=17.8049(6) A, solved from single-crystal data. It is perovskite-like with distorted corner-linked SnCl{sub 6} octahedra and with ordered guanidinium cations in the distorted cuboctahedral voids. At 400 K the structure shows a first-order order-disorder phase transition. The space group is changed to Pnma with Z=4, a=12.1552(2) A, b=8.8590(2) A and c=8.0175(1) A, solved from powder diffraction data and showing disordering of the guanidinium cations. At 419 K, the structure shows yet another first-order order-disorder transformation with disordering of the SnCl{sub 3}{sup -} part. The space group symmetry is maintained as Pnma, with a=12.1786(2) A, b=8.8642(2) A and c=8.0821(2) A. The thermodynamic parameters of these transitions and the p-T phase diagram have been determined and described. - Graphical abstract: The perovskite-like crystals of C(NH{sub 2}){sub 3}SnCl{sub 3} undergo two successive first-order phase transitions at 400 and 419 K, both accompanied by an essential order-disorder contribution. The p-T phase diagram exhibits a singular point at 219 MPa and 443 K.

  10. Bi surfactant control of ordering and surface structure in GaInP grown by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Jun, S. W.; Lee, R. T.; Fetzer, C. M.; Shurtleff, J. K.; Stringfellow, G. B.; Choi, C. J.; Seong, T.-Y.

    2000-10-01

    The surfactant Bi has been added during organometallic vapor phase epitaxial growth (OMVPE) of GaInP using the precursor trimethylbismuth. The addition of a small amount of Bi during growth results in disordered material using conditions that would otherwise produce highly ordered GaInP. Significant changes in the surface structure are observed to accompany the disordering. Atomic force microscopy measurements show that Bi causes an order of magnitude increase in step velocity, leading to the complete elimination of three-dimensional islands for growth on singular (001) GaAs substrates, and a significant reduction in surface roughness. Surface photoabsorption measurements indicate that Bi reduces the number of [1¯10] P dimers on the surface. Secondary ion mass spectroscopy measurements reveal that the Bi is rejected from the bulk, even though it changes the surface reconstruction. Clearly, Bi acts as a surfactant during OMVPE growth of GaInP. The difference in band gap energy caused by the reduction in order parameter during growth is measured using photoluminescence to be about 110 meV for layers grown on singular substrates. Disorder/order/disorder heterostructures were successfully produced in GaInP with a constant solid composition by modulating the TMBi flow rate during growth.

  11. Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS

    PubMed Central

    Lai, Xiaofang; Liu, Ying; Lü, Xujie; Zhang, Sijia; Bu, Kejun; Jin, Changqing; Zhang, Hui; Lin, Jianhua; Huang, Fuqiang

    2016-01-01

    Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS. PMID:27498699

  12. Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS.

    PubMed

    Lai, Xiaofang; Liu, Ying; Lü, Xujie; Zhang, Sijia; Bu, Kejun; Jin, Changqing; Zhang, Hui; Lin, Jianhua; Huang, Fuqiang

    2016-01-01

    Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS. PMID:27498699

  13. Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS

    NASA Astrophysics Data System (ADS)

    Lai, Xiaofang; Liu, Ying; Lü, Xujie; Zhang, Sijia; Bu, Kejun; Jin, Changqing; Zhang, Hui; Lin, Jianhua; Huang, Fuqiang

    2016-08-01

    Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS.

  14. Real-time implementation of an interactive jazz accompaniment system

    NASA Astrophysics Data System (ADS)

    Deshpande, Nikhil

    Modern computational algorithms and digital signal processing (DSP) are able to combine with human performers without forced or predetermined structure in order to create dynamic and real-time accompaniment systems. With modern computing power and intelligent algorithm layout and design, it is possible to achieve more detailed auditory analysis of live music. Using this information, computer code can follow and predict how a human's musical performance evolves, and use this to react in a musical manner. This project builds a real-time accompaniment system to perform together with live musicians, with a focus on live jazz performance and improvisation. The system utilizes a new polyphonic pitch detector and embeds it in an Ableton Live system - combined with Max for Live - to perform elements of audio analysis, generation, and triggering. The system also relies on tension curves and information rate calculations from the Creative Artificially Intuitive and Reasoning Agent (CAIRA) system to help understand and predict human improvisation. These metrics are vital to the core system and allow for extrapolated audio analysis. The system is able to react dynamically to a human performer, and can successfully accompany the human as an entire rhythm section.

  15. Gas Phase Structure of Amino Acids: La-Mb Studies

    NASA Astrophysics Data System (ADS)

    Mata, I. Pena S.; Sanz, M. E.; Vaquero, V.; Cabezas, C.; Perez, C.; Blanco, S.; López, J. C.; Alonso, J. L.

    2009-06-01

    Recent improvements in our laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectrometer such as using Laval-type nozzles and picoseconds Nd:YAG lasers (30 to 150 ps) have allowed a major step forward in the capabilities of this experimental technique as demonstrated by the last results in serine cysteine and threonine^a for which seven, six and seven conformers have been respectively identified. Taking advantage of these improvements we have investigated the natural amino acids metionine, aspartic and glutamic acids and the γ-aminobutyric acid (GABA) with the aim of identify and characterize their lower energy conformers. Searches in the rotational spectra have lead to the identification of seven conformers of metionine, six and five of aspartic and glutamic acids, respectively, and seven for the γ-aminobutyric. These conformers have been unambiguously identified by their spectroscopic constants. In particular the ^{14}N nuclear quadrupole coupling constants, that depend heavily on the orientation of the amino group with respect to the principal inertial axes of the molecule, prove to be a unique tool to distinguish unambigously between conformations with similar rotational constants. For the γ-aminobutyric acid two of the seven observed structures are stablized by an intramolecular interaction n-π*. Two new conformers of proline have been identified together with the two previously observed. J. L. Alonso, C. Pérez, M. E. Sanz, J. C. López, S. Blanco, Phys.Chem.Chem.Phys., 2009, 11, 617. D. B. Atkinson, M. A. Smith, Rev. Sci. Instrum. 1995, 66, 4434 S. Blanco, M. E. Sanz, J. C. López, J. L. Alonso, Proc. Natl. Acad. Sci. USA2007, 104, 20183. M. E. Sanz, S. Blanco, J. C. López, J. L. Alonso, Angew. Chem. Int. Ed.,2008, 120, 6312. A. Lesarri, S. Mata, E. J. Cocinero, S. Blanco, J.C. López, J. L. Alonso, Angew. Chem. Int. Ed. , 2002, 41, 4673

  16. Titanium α-ω phase transformation pathway and a predicted metastable structure

    DOE PAGESBeta

    Zarkevich, Nickolai A.; Johnson, Duane D.

    2016-01-15

    A titanium is a highly utilized metal for structural lightweighting and its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT + U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We also find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure.

  17. Thick strings, the liquid crystal blue phase, and cosmological large-scale structure

    NASA Technical Reports Server (NTRS)

    Luo, Xiaochun; Schramm, David N.

    1992-01-01

    A phenomenological model based on the liquid crystal blue phase is proposed as a model for a late-time cosmological phase transition. Topological defects, in particular thick strings and/or domain walls, are presented as seeds for structure formation. It is shown that the observed large-scale structure, including quasi-periodic wall structure, can be well fitted in the model without violating the microwave background isotropy bound or the limits from induced gravitational waves and the millisecond pulsar timing. Furthermore, such late-time transitions can produce objects such as quasars at high redshifts. The model appears to work with either cold or hot dark matter.

  18. Titanium α -ω phase transformation pathway and a predicted metastable structure

    NASA Astrophysics Data System (ADS)

    Zarkevich, N. A.; Johnson, D. D.

    2016-01-01

    As titanium is a highly utilized metal for structural lightweighting, its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT + U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure.

  19. Structural damage detection based on the reconstructed phase space for reinforced concrete slab: Experimental study

    NASA Astrophysics Data System (ADS)

    Nie, Zhenhua; Hao, Hong; Ma, Hongwei

    2013-02-01

    In this paper, a parameter based on geometry changes of the reconstructed multidimensional phase space of the measured vibration signals for structural damage identification is proposed. The choice of the proper delay time steps and embedding dimensions for phase space reconstruction of linear systems is discussed. Using the determined delay time and embedding dimensions, an index Changes of Phase Space Topology (CPST) with multiple embedding dimensions is calculated and then used to identify the structural damage. To demonstrate the reliability of the proposed method, vibration test data corresponding to different damage states of a continuous reinforced concrete slab is used to calculate the CPST value for damage identification. The results indicate that except the measurement points at structural supports, the CPST values at all the measurement points on the structure increase with structural damage level irrespective of the damage location, indicating that using a single or a minimum number of measurement points and their CPST value can effectively identify damage existence in the structure. The traditional modal-based indices are also calculated using the same vibration data for comparison. It is found that the proposed method with CPST is the most sensitive to structural damage than any modal-based index. The results demonstrate that the proposed method with CPST value is very effective in identifying damage existence in the structure. Although it cannot quantify the damage, it can be a good candidate for continuous structural health monitoring because it needs only a few sensors to detect damage existence in the entire structure.

  20. First principle calculations of structural phase transition and electronic properties in AmTe

    SciTech Connect

    Pataiya, Jagdeesh Makode, C.; Aynyas, Mahendra; Singh, A.; Sanyal, S. P.

    2015-06-24

    The tight-binding linear muffin-tin orbital (TB-LMTO) with in the local density approximation is used to calculate total energy, lattice parameters, bulk modulus, density of states and energy band structure of americium telluride at ambient as well as at high pressure. It is found that AmTe is stable in NaCl – type structure under ambient pressure. The phase transition pressure was found to be 15.0 GPa from NaCl-type (B{sub 1}-phase) structure to CsCl-type (B{sub 2}-phase) structure for this compound. From energy band diagram it is observed that AmTe exhibit metallic behaviour. The calculated ground state properties such as lattice parameters and bulk modulus are in general good agreement with the available results.

  1. First principle calculations of structural phase transition and electronic properties in AmTe

    NASA Astrophysics Data System (ADS)

    Pataiya, Jagdeesh; Aynyas, Mahendra; Makode, C.; Singh, A.; Sanyal, S. P.

    2015-06-01

    The tight-binding linear muffin-tin orbital (TB-LMTO) with in the local density approximation is used to calculate total energy, lattice parameters, bulk modulus, density of states and energy band structure of americium telluride at ambient as well as at high pressure. It is found that AmTe is stable in NaCl - type structure under ambient pressure. The phase transition pressure was found to be 15.0 GPa from NaCl-type (B1-phase) structure to CsCl-type (B2-phase) structure for this compound. From energy band diagram it is observed that AmTe exhibit metallic behaviour. The calculated ground state properties such as lattice parameters and bulk modulus are in general good agreement with the available results.

  2. Magnetic and structural phase transitions in erbium at low temperatures and high pressures

    SciTech Connect

    Thomas, Sarah A.; Tsoi, Georgiy M.; Wenger, Lowell E.; Vohra, Yogesh K.

    2012-02-07

    Electrical resistance and crystal structure measurements have been carried out on polycrystalline erbium (Er) at temperatures down to 10 K and pressures up to 20 GPa. An abrupt change in the slope of the resistance is observed with decreasing temperature below 84 K, which is associated with the c-axis modulated (CAM) antiferromagnetic (AFM) ordering of the Er moments. With increasing pressure the temperature of the resistance slope change and the corresponding AFM ordering temperature decrease until vanishing above 10.6 GPa. The disappearance of the slope change in the resistance occurs at similar pressures where the hcp structural phase of Er is transformed to a nine-layer {alpha}-Sm structural phase, as confirmed by our high-pressure synchrotron x-ray diffraction studies. These results suggest that the disappearance in the AFM ordering of Er moments is strongly correlated to the structural phase transition at high pressures and low temperatures.

  3. Elastic energy and phase structure in a continuous spin Ising chain with applications to chiral homopolymers.

    PubMed

    Chernodub, M N; Lundgren, Martin; Niemi, Antti J

    2011-01-01

    We present a numerical Monte Carlo analysis of the phase structure in a continuous spin Ising chain that describes chiral homopolymers. We find that depending on the value of the Metropolis temperature, the model displays the three known nontrivial phases of polymers: At low temperatures the model is in a collapsed phase, at medium temperatures it is in a random walk phase, and at high temperatures it enters the self-avoiding random walk phase. By investigating the temperature dependence of the specific energy we confirm that the transition between the collapsed phase and the random walk phase is a phase transition, while the random walk phase and self-avoiding random walk phase are separated from each other by a crossover transition. We propose that the model can be applied to characterize the statistical properties of protein folding. For this we compare the predictions of the model to a phenomenological elastic energy formula, proposed by J. Lei and K. Huang [e-print arXiv:1002.5013; Europhys. Lett. 88, 68004 (2009)] to describe folded proteins. PMID:21405680

  4. Elastic energy and phase structure in a continuous spin Ising chain with applications to chiral homopolymers

    NASA Astrophysics Data System (ADS)

    Chernodub, M. N.; Lundgren, Martin; Niemi, Antti J.

    2011-01-01

    We present a numerical Monte Carlo analysis of the phase structure in a continuous spin Ising chain that describes chiral homopolymers. We find that depending on the value of the Metropolis temperature, the model displays the three known nontrivial phases of polymers: At low temperatures the model is in a collapsed phase, at medium temperatures it is in a random walk phase, and at high temperatures it enters the self-avoiding random walk phase. By investigating the temperature dependence of the specific energy we confirm that the transition between the collapsed phase and the random walk phase is a phase transition, while the random walk phase and self-avoiding random walk phase are separated from each other by a crossover transition. We propose that the model can be applied to characterize the statistical properties of protein folding. For this we compare the predictions of the model to a phenomenological elastic energy formula, proposed by J. Lei and K. Huang [e-print arXiv:1002.5013; Europhys. Lett.EULEEJ0295-507510.1209/0295-5075/88/68004 88, 68004 (2009)] to describe folded proteins.

  5. Amphipols Outperform Dodecylmaltoside Micelles in Stabilizing Membrane Protein Structure in the Gas Phase

    PubMed Central

    2014-01-01

    Noncovalent mass spectrometry (MS) is emerging as an invaluable technique to probe the structure, interactions, and dynamics of membrane proteins (MPs). However, maintaining native-like MP conformations in the gas phase using detergent solubilized proteins is often challenging and may limit structural analysis. Amphipols, such as the well characterized A8-35, are alternative reagents able to maintain the solubility of MPs in detergent-free solution. In this work, the ability of A8-35 to retain the structural integrity of MPs for interrogation by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is compared systematically with the commonly used detergent dodecylmaltoside. MPs from the two major structural classes were selected for analysis, including two β-barrel outer MPs, PagP and OmpT (20.2 and 33.5 kDa, respectively), and two α-helical proteins, Mhp1 and GalP (54.6 and 51.7 kDa, respectively). Evaluation of the rotationally averaged collision cross sections of the observed ions revealed that the native structures of detergent solubilized MPs were not always retained in the gas phase, with both collapsed and unfolded species being detected. In contrast, ESI-IMS-MS analysis of the amphipol solubilized MPs studied resulted in charge state distributions consistent with less gas phase induced unfolding, and the presence of lowly charged ions which exhibit collision cross sections comparable with those calculated from high resolution structural data. The data demonstrate that A8-35 can be more effective than dodecylmaltoside at maintaining native MP structure and interactions in the gas phase, permitting noncovalent ESI-IMS-MS analysis of MPs from the two major structural classes, while gas phase dissociation from dodecylmaltoside micelles leads to significant gas phase unfolding, especially for the α-helical MPs studied. PMID:25495802

  6. Structural phase transitions in Bi2Se3 under high pressure

    PubMed Central

    Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-kwang

    2015-01-01

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3. PMID:26522818

  7. Structural phase transitions in Bi2Se3 under high pressure

    DOE PAGESBeta

    Yu, Zhenhai; Gu, Genda; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Mao, Ho -kwang

    2015-11-02

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint thatmore » the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.« less

  8. Structural phase transitions in Bi2Se3 under high pressure.

    PubMed

    Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-kwang

    2015-01-01

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3. PMID:26522818

  9. Structural phase diagram of Sr2-xCaxRuO4

    NASA Astrophysics Data System (ADS)

    Gutmann, Matthias; Radaelli, Paolo; Chapon, Laurent; Mandrus, David

    2003-03-01

    The structural phase diagram of Sr2-xCaxRuO4 has been mapped for 0structure) and determine the local structure by means of the Pair Distribution Function analysis. The main results of this work will be presented.

  10. Structure imaging and vanadium substitution in cubic TiCr2 Laves phase

    NASA Astrophysics Data System (ADS)

    Ghosh, Chanchal; Sharma, Vinit; Basu, Joysurya; Ramachandran, Divakar; Mohandas, E.

    2015-08-01

    Properties of Laves phase compounds can be tailored by alloying and microstructural engineering. V-substituted cubic TiCr2 Laves phase has been studied to understand the location of V atoms in the lattice, by structural imaging and first-principle computations. Even though Ti, V and Cr appear next to each other in the periodic table, V preferentially replaces the Ti lattice producing anti-site defects. The defect formation energy for V substitution in Ti and in Cr lattice is 0.29 and 0.40 eV, respectively. V replacement in the Ti lattice generates atomic scale strain. Atomic numbers of V, Ti and Cr being very close, this phase is not quite suitable for incoherent imaging for understanding the structure and the chemistry. Instead, difference in channelling behaviour of electron waves along the Ti columns and along the Cr columns could be exploited to preferentially image the individual atom columns. Nature of the exit phase wave, phase and amplitude has been used to understand the contrast qualitatively. The intensity distribution of any particular atom column that is disturbed by the presence of foreign atom has been used to detect the position of V atoms. This method could be extended to study other Laves phases and complex intermetallic structures to understand their structure, defects and interfaces.

  11. Pressure induced structural phase transition of OsB{sub 2}: First-principles calculations

    SciTech Connect

    Ren Fengzhu; Wang Yuanxu; Lo, V.C.

    2010-04-15

    Orthorhombic OsB{sub 2} was synthesized at 1000 deg. C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB{sub 2}. An analysis of the calculated enthalpy shows that orthorhombic OsB{sub 2} can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6{sub 3}/mmc structure (high-pressure phase) is stable for OsB{sub 2}. We expect the phase transition can be further confirmed by the experimental work. - Abstract: Graphical Abstract Legend (TOC Figure): Table of Contents Figure Pressure induced structural phase transition from the orthorhombic structure to the hexagonal one for OsB{sub 2} takes place under 10.8 GPa (0 K), 10.35 GPa (300, 1000 K) by the first-principles predictions.

  12. Phase Synchronization and Desynchronization of Structural Response Induced by Turbulent and External Sound

    NASA Technical Reports Server (NTRS)

    Maestrello, Lucio

    2002-01-01

    Acoustic and turbulent boundary layer flow loadings over a flexible structure are used to study the spatial-temporal dynamics of the response of the structure. The stability of the spatial synchronization and desynchronization by an active external force is investigated with an array of coupled transducers on the structure. In the synchronous state, the structural phase is locked, which leads to the formation of spatial patterns while the amplitude peaks exhibit chaotic behaviors. Large amplitude, spatially symmetric loading is superimposed on broadband, but in the desynchronized state, the spectrum broadens and the phase space is lost. The resulting pattern bears a striking resemblance to phase turbulence. The transition is achieved by using a low power external actuator to trigger broadband behaviors from the knowledge of the external acoustic load inducing synchronization. The changes are made favorably and efficiently to alter the frequency distribution of power, not the total power level. Before synchronization effects are seen, the panel response to the turbulent boundary layer loading is discontinuously spatio-temporally correlated. The stability develops from different competing wavelengths; the spatial scale is significantly shorter than when forced with the superimposed external sound. When the external sound level decreases and the synchronized phases are lost, changes in the character of the spectra can be linked to the occurrence of spatial phase transition. These changes can develop broadband response. Synchronized responses of fuselage structure panels have been observed in subsonic and supersonic aircraft; results from two flights tests are discussed.

  13. The study of the structural stability of the spiral laser beams propagation through inhomogeneous phase medium

    NASA Astrophysics Data System (ADS)

    Zinchik, Alexander A.; Muzychenko, Yana B.

    2015-06-01

    This paper discusses theoretical and experimental results of the investigation of light beams that retain their intensity structure during propagation and focusing. Spiral laser beams are a family of laser beams that preserve the structural stability up to scale and rotation with the propagation. Properties of spiral beams are of practical interest for laser technology, medicine and biotechnology. Researchers use a spiral beams for movement and manipulation of microparticles. Functionality laser manipulators can be significantly enhanced by using spiral beams whose intensity remains invariable. It is well known, that these beams has non-zero orbital angular momentum. Spiral beams have a complicated phase distribution in cross section. In this paper we investigate the structural stability of the laser beams having a spiral phase structure by passing them through an inhomogeneous phase medium. Laser beam is passed through a medium is characterized by a random distribution of phase in the range 0..2π. The modeling was performed using VirtualLab 5.0 (manufacturer LightTrans GmbH). Compared the intensity distribution of the spiral and ordinary laser beam after the passage of the inhomogeneous medium. It is shown that the spiral beams exhibit a significantly better structural stability during the passage phase heterogeneous environments than conventional laser beams. The results obtained in the simulation are tested experimentally. Experimental results show good agreement with the theoretical results.

  14. Phase matching of backward second harmonic generation assisted by lattice structure in collagen tissues.

    PubMed

    Shen, Mengzhe; Zeng, Haishan; Tang, Shuo

    2015-10-01

    Phase matching of backward second harmonic generation (SHG) in a periodic structure of collagen fibrils is investigated through theoretical modeling, simulation, and experiments. The lattice structure of collagen fibrils is considered to provide a virtual momentum for assisting the phase matching of backward SHG. Phase matching over a relatively wide excitation wavelength range is achieved by tilting the angle of the fundamental excitation and SHG wave vectors. The SHG intensity in the periodic structure is simulated to quantify the phase matching effect. The effect of the fundamental excitation and the SHG emission angles on the peak excitation wavelength of the SHG excitation spectrum is further validated in experiments, where the excitation and emission angles are controlled by spatial filtering. It is found that an optimized excitation wavelength exists for a certain collagen fibril structure, which shifts toward a shorter wavelength when the excitation and emission angles are increased. Our results show that the lattice structure of collagen fibrils can assist the phase matching, providing a mechanism for generating backward SHG in multiphoton microscopy. PMID:26502229

  15. Phase matching of backward second harmonic generation assisted by lattice structure in collagen tissues

    NASA Astrophysics Data System (ADS)

    Shen, Mengzhe; Zeng, Haishan; Tang, Shuo

    2015-10-01

    Phase matching of backward second harmonic generation (SHG) in a periodic structure of collagen fibrils is investigated through theoretical modeling, simulation, and experiments. The lattice structure of collagen fibrils is considered to provide a virtual momentum for assisting the phase matching of backward SHG. Phase matching over a relatively wide excitation wavelength range is achieved by tilting the angle of the fundamental excitation and SHG wave vectors. The SHG intensity in the periodic structure is simulated to quantify the phase matching effect. The effect of the fundamental excitation and the SHG emission angles on the peak excitation wavelength of the SHG excitation spectrum is further validated in experiments, where the excitation and emission angles are controlled by spatial filtering. It is found that an optimized excitation wavelength exists for a certain collagen fibril structure, which shifts toward a shorter wavelength when the excitation and emission angles are increased. Our results show that the lattice structure of collagen fibrils can assist the phase matching, providing a mechanism for generating backward SHG in multiphoton microscopy.

  16. Changes in protein structure monitored by use of gas‐phase hydrogen/deuterium exchange

    PubMed Central

    Beeston, Helen S.; Ault, James R.; Pringle, Steven D.; Brown, Jeffery M.

    2015-01-01

    The study of protein conformation by solution‐phase hydrogen/deuterium exchange (HDX) coupled to MS is well documented. This involves monitoring the exchange of backbone amide protons with deuterium and provides details concerning the protein's tertiary structure. However, undesired back‐exchange during post‐HDX analyses can be difficult to control. Here, gas‐phase HDX‐MS, during which labile hydrogens on amino acid side chains are exchanged in sub‐millisecond time scales, has been employed to probe changes within protein structures. Addition of the solvent 2,2,2‐trifluoroethanol to a protein in solution can affect the structure of the protein, resulting in an increase in secondary and/or tertiary structure which is detected using circular dichroism. Using a Synapt G2‐S ESI‐mass spectrometer modified to allow deuterated ammonia into the transfer ion guide (situated between the ion mobility cell and the TOF analyser), gas‐phase HDX‐MS is shown to reflect minor structural changes experienced by the proteins β‐lactoglobulin and ubiquitin, as observed by the reduction in the level of deuterium incorporation. Additionally, the use of gas‐phase HDX‐MS to distinguish between co‐populated proteins conformers within a solution is demonstrated with the disordered protein calmodulin; the gas‐phase HDX‐MS results correspond directly with complementary data obtained by use of ion mobility spectrometry‐MS. PMID:25603979

  17. Slab stagnation and buckling in the mantle transition zone: Rheology, phase transition, trench migration, and seismic structure

    NASA Astrophysics Data System (ADS)

    Bina, Craig; Cizkova, Hana

    2014-05-01

    Subducting slabs may exhibit buckling instabilities and consequent folding behavior in the mantle transition zone for various combinations of dynamical parameters, accompanied by temporal variations in dip angle, plate velocity, and trench retreat. Parameters governing such behavior include both viscous forces (slab and mantle rheology) and buoyancy forces (slab thermal structure and mineral phase relations). 2D numerical experiments show that many parameter sets lead to slab deflection at the base of the transition zone, typically accompanied by quasi-periodic oscillations (consistent with previous scaling analyses) in largely anticorrelated plate and rollback velocities, resulting in undulating stagnant slabs as buckle folds accumulate subhorizontally atop the lower mantle. Slab interactions with mantle phase transitions are important components of this process (Bina and Kawakatsu, 2010; Čížková and Bina, 2013). For terrestrial parameter sets, trench retreat is found to be nearly ubiquitous, and trench advance is quite rare - due to both rheological structure and ridge-push effects (Čížková and Bina, 2013). Recent analyses of global plate motions indicate that significant trench advance is also rare on Earth, being largely restricted to the Izu-Bonin arc (Matthews et al., 2013). Consequently, we explore the conditions necessary for terrestrial trench advance through dynamical models involving the unusual geometry associated with the Philippine Sea region. Detailed images of buckled stagnant slabs are difficult to resolve due to smoothing effects inherent in seismic tomography, but velocity structures computed for compositionally layered slabs, using laboratory data on relevant mineral assemblages, can be spatially low-pass filtered for comparison with tomographic images of corresponding resolution. When applied to P-wave velocity anomalies from stagnant slab material beneath northeast China, model slabs which undulate due to compound buckling fit

  18. Extinction of Oct-3/4 gene expression in embryonal carcinoma [times] fibroblast somatic cell hybrids is accompanied by changes in the methylation status, chromatin structure, and transcriptional activity of the Oct-3/4 upstream region

    SciTech Connect

    Ben-Shushan, E.; Pikarsky, E.; Klar, A.; Bergman, Y. )

    1993-02-01

    The OCT-3/4 gene provides an excellent model system with which to study the extinction phenomenon in somatic cell hybrids. The molecular mechanism that underlies the extinction of a tissue-specific transcription factor in somatic cell hybrides is evaluated and compared with its down-regulation in retinoic acid treated embryonal carcinoma cells. This study draws a connection between the shutdown of OCT-3/4 expression in retinoic acid (RA)-differentiated embryonal carcinoma (EC) cells and its extinction in hybrid cells. This repression of OCT-3/4 expression is achieved through changes in the methylation status, chromatin structure, and transcriptional activity of the OCT-3/4 upstream regulatory region. 59 refs.

  19. Phase behavior and self-organized structures of diglycerol monolaurate in different nonpolar organic solvents.

    PubMed

    Shrestha, Lok Kumar; Sato, Takaaki; Aramaki, Kenji

    2007-06-01

    Nonaqueous phase behavior and reverse micellar structures of diglycerol monolaurate (DGL) in different nonpolar organic solvents, such as n-decane, n-tetradecane, and n-hexadecane, have been studied over a wide range of compositions and temperatures. The equilibrium phases are identified by means of visual observation and small-angle X-ray scattering (SAXS). A solid phase present at lower temperature swells small amount of oils and transforms into a lamellar liquid crystalline structure at higher temperature. The melting temperature of the solid phase is virtually constant at all mixing ratios of the surfactant and oil. With the further increase of temperature, the liquid crystal transforms into an isotropic single-liquid phase near the surfactant axis, whereas there is a coexistence region of two isotropic phases near the solvent axis. The area of the two-liquid (II) phase region depends largely on the hydrocarbon chain length of the oils, the longer chain leading to the wider II area. Accordingly, the DGL surfactant is most miscible with decane, exhibiting a reduced miscibility with increasing solvent hydrocarbon chain length. Increasing temperature enhances the dissolution tendency of the surfactant in oil, where the two-liquid phase transforms into an isotropic single phase. SAXS analysis based on the GIFT technique is used to characterize the structure of the reverse micellar aggregates in the isotropic single-phase liquids. We have demonstrated that instead of changing polarity or a functional group of the solvent molecules, if we optimize the hydrophilic nature of the surfactant head group, the alkyl chain length of the solvent oils can serve as a tunable parameter of the micellar geometry. The hydrophilic surfactant DGL interestingly forms cylindrical micelles in nonpolar oils, decane, and tetradecane in the dilute region above the II phase region. The micellar size shows temperature dependence behavior, and the micellar length goes on increasing with

  20. Atomically resolved structural determination of graphene and its point defects via extrapolation assisted phase retrieval

    SciTech Connect

    Latychevskaia, Tatiana; Fink, Hans-Werner

    2015-01-12

    Previously reported crystalline structures obtained by an iterative phase retrieval reconstruction of their diffraction patterns seem to be free from displaying any irregularities or defects in the lattice, which appears to be unrealistic. We demonstrate here that the structure of a nanocrystal including its atomic defects can unambiguously be recovered from its diffraction pattern alone by applying a direct phase retrieval procedure not relying on prior information of the object shape. Individual point defects in the atomic lattice are clearly apparent. Conventional phase retrieval routines assume isotropic scattering. We show that when dealing with electrons, the quantitatively correct transmission function of the sample cannot be retrieved due to anisotropic, strong forward scattering specific to electrons. We summarize the conditions for this phase retrieval method and show that the diffraction pattern can be extrapolated beyond the original record to even reveal formerly not visible Bragg peaks. Such extrapolated wave field pattern leads to enhanced spatial resolution in the reconstruction.

  1. Structural phase study in un-patterned and patterned PVDF semi-crystalline films

    SciTech Connect

    Pramod, K. Gangineni, Ramesh Babu

    2014-04-24

    This work explores the structural phase studies of organic polymer- polyvinylidene fluoride (PVDF) thin films in semi-crystallized phase and nano-patterned PVDF thin films. The nanopatterns are transferred with the CD layer as a master using soft lithography technique. The semi-crystalline PVDF films were prepared by a still and hot (SH) method, using a homemade spin coater that has the proficiency of substrate heating by a halogen lamp. Using this set up, smooth PVDF thin films in semi-crystalline α-phase were prepared using 2-Butanone as solvent. XRD, AFM and confocal Raman microscope have been utilized to study the structural phase, crystallinity and quality of the films.

  2. Phase structure and magnetic properties of Mn{sub 3}Ga{sub 2} alloy

    SciTech Connect

    Lu, Q. M. Yu, F.; Yue, M.; Zhang, H. G.; Li, Y. Q.; Liu, Y. Q.; Zhang, J. X.; Yan, X. L.

    2014-05-07

    In this paper, Mn{sub 3}Ga{sub 2} alloys with high saturation magnetization and high Curie temperatures were prepared by levitation melting high pure Mn and Ga elements followed by annealing. The effect of annealing temperature on phase structure and magnetic properties was investigated by means of x-ray diffraction and a vibrating sample magnetometer. A single phase alloy Mn{sub 3}Ga{sub 2}, which has tetragonal P4/mmm structure, was obtained with an annealing temperature of 773 K and annealing time of 24 h. The hysteresis curve of its easy axis for this single phase alloy shows that the room temperature coercivity and saturation magnetization are 4.18 kOe and 50.81 emu/g, respectively. The thermomagnetic curves indicate that the Curie temperature is about 650 K and a phase transformation occurs above 823 K.

  3. Phase stability, mechanical property, and electronic structure of an Mg-Ca system.

    PubMed

    Zhou, Peng; Gong, H R

    2012-04-01

    First principle calculations reveal that Mg-Ca phases are energetically favorable with negative heats of formation within the entire composition range, and that a strong chemical bonding is formed between Mg and Ca atoms. Calculations also show that the composition has an important effect on mechanical properties of Mg-Ca, and that the Mg-Ca phases with an Mg composition of less than 50 at.% would be good candidates as degradable bone materials in terms of Young's modulus and ductility. In addition, it is found out that Mg(3)Ca, MgCa and MgCa(3) have phase sequences of BCC→HCP, BCC→HCP and FCC→HCP under high pressure, respectively, and that Ca plays a dominant role in determining the electronic structures and stable crystal structures of various Mg-Ca phases. PMID:22402162

  4. Structural phase study in un-patterned & patterned PVDF semi-crystalline films

    NASA Astrophysics Data System (ADS)

    Pramod, K.; Gangineni, Ramesh Babu

    2014-04-01

    This work explores the structural phase studies of organic polymer- polyvinylidene fluoride (PVDF) thin films in semi-crystallized phase and nano-patterned PVDF thin films. The nanopatterns are transferred with the CD layer as a master using soft lithography technique. The semi-crystalline PVDF films were prepared by a still and hot (SH) method, using a homemade spin coater that has the proficiency of substrate heating by a halogen lamp. Using this set up, smooth PVDF thin films in semi-crystalline α-phase were prepared using 2-Butanone as solvent. XRD, AFM & confocal Raman microscope have been utilized to study the structural phase, crystallinity and quality of the films.

  5. Oxygen Tuned Local Structure and Phase-Change Performance of Germanium Telluride.

    PubMed

    Zhou, Xilin; Du, Yonghua; Behera, Jitendra K; Wu, Liangcai; Song, Zhitang; Simpson, Robert E

    2016-08-10

    The effect of oxygen on the local structure of Ge atoms in GeTe-O materials has been investigated. Oxygen leads to a significant modification to the vibrational modes of Ge octahedra, which results from a decrease in its coordination. We find that a defective octahedral Ge network is the crucial fingerprint for rapid and reversible structural transitions in GeTe-based phase change materials. The appearance of oxide Raman modes confirms phase separation into GeO and TeO at high level O doping. Counterintuitively, despite the increase in crystallization temperature of oxygen doped GeTe-O phase change materials, when GeTe-O materials are used in electrical phase change memory cells, the electrical switching energy is lower than the pure GeTe material. This switching energy reduction is ascribed to the smaller change in volume, and therefore smaller enthalpy change, for the oxygen doped GeTe materials. PMID:27430363

  6. Ultra-Fast Structural Studies of Shock-Induced Phase Transitions in Bismuth

    NASA Astrophysics Data System (ADS)

    McMahon, Malcolm

    2015-06-01

    The study of structural phase transitions via dynamic compression has a long and illustrious history. But, due to the absence of suitably bright x-ray sources, it is only relatively recently that the structures of some of these high-pressure phases have been determined. Over the last 25 years, static compression studies have revealed the great structural complexity that exists in many high-pressure phases, and DFT calculations predict that such complexity will continue to pressures as yet unattainable experimentally. Are these same complex structures formed on shock timescales, and, if so, can we determine their structures with certainty via x-ray diffraction? The recent advent of x-ray free electron lasers (XFELs) now provides us with x-ray sources that are ideally suited to structural studies of shock-compressed matter on nanosecond timescales. In this talk I will describe results from recent experiments on the MEC beamline at the LCLS on diffraction studies of the phase transitions in bismuth, and look forward to what will be possible in the Euro-XFEL after its start-up in 2017.

  7. Phase improvement via the Phantom Derivative technique: ancils that are related to the target structure.

    PubMed

    Carrozzini, Benedetta; Cascarano, Giovanni Luca; Giacovazzo, Carmelo

    2016-04-01

    Density modification is a general standard technique which may be used to improve electron density derived from experimental phasing and also to refine densities obtained by ab initio approaches. Here, a novel method to expand density modification is presented, termed the Phantom derivative technique, which is based on non-existent structure factors and is of particular interest in molecular replacement. The Phantom derivative approach uses randomly generated ancil structures with the same unit cell as the target structure to create non-existent derivatives of the target structure, called phantom derivatives, which may be used for ab initio phasing or for refining the available target structure model. In this paper, it is supposed that a model electron density is available: it is shown that ancil structures related to the target obtained by shifting the target by origin-permissible translations may be employed to refine model phases. The method enlarges the concept of the ancil, is as efficient as the canonical approach using random ancils and significantly reduces the CPU refinement time. The results from many real test cases show that the proposed methods can substantially improve the quality of electron-density maps from molecular-replacement-based phases. PMID:27050134

  8. Structural properties of a three-dimensional all- sp sup 2 phase of carbon

    SciTech Connect

    Liu, A.Y.; Cohen, M.L. ); Hass, K.C.; Tamor, M.A. )

    1991-03-15

    We have studied the structural properties of a recently proposed, hypothetical, all-{ital sp}{sup 2} phase of carbon, using the first-principles pseudopotential total-energy method. Our results are compared with those of an earlier tight-binding calculation. While the two calculations yield equilibrium volumes and bond lengths that are in excellent agreement, there are discrepancies in the cohesive energy, elastic constants, and predicted stability of this phase.

  9. The topological pressure-temperature phase diagram and crystal structures of the dimorphic system spiperone.

    PubMed

    Robert, B; Perrin, M-A; Coquerel, G; Céolin, R; Rietveld, I B

    2016-03-01

    The topological pressure-temperature phase diagram for the dimorphism of spiperone, a potent neuroleptic drug, has been constructed using literature data and improved crystal structures obtained with new crystallographic data from single-crystal X-ray diffraction at various temperatures. It is inferred that form II, which is the more dense form and exhibits the lower melting temperature, becomes the more stable phase under pressure. Under ambient conditions, form I is more stable. PMID:26601885

  10. Using Molecular Replacement Phasing to Study the Structure and Function of RNA.

    PubMed

    Marcia, Marco

    2016-01-01

    In recent years a wide variety of RNA molecules regulating fundamental cellular processes has been discovered. Therefore, RNA structure determination is experiencing a boost and many more RNA structures are likely to be determined in the years to come. The broader availability of experimentally determined RNA structures implies that molecular replacement (MR) will be used more and more frequently as a method for phasing future crystallographic structures. In this report we describe various aspects relative to RNA structure determination by MR. First, we describe how to select and create MR search models for nucleic acids. Second, we describe how to perform MR searches on RNA using available crystallographic software. Finally, we describe how to refine and interpret the successful MR solutions. These protocols are applicable to determine novel RNA structures as well as to establish structural-functional relationships on existing RNA structures. PMID:26227047

  11. The ACOSTA accompanying measure A2106.

    PubMed

    Thayer, C; De Moor, G; Van Goor, J

    1994-10-01

    At a time when the informatics and telecommunications industries are looking for new markets to exploit in relation, for example, to the emerging ISDN and broadband communications networks, there is a need to create a broad consensus in Europe by bringing together systematically the relevant industries including telecom service providers, health care providers, insurance organisations, standardisation experts and policy makers. The aim of the ACOSTA (Consensus Formation and Standardisation Promotion) Accompanying Measure is the creation of more general awareness of the relevant environment among all the parties, better specification of common requirements and options taking better account of the real needs of the users, and enlargement of the common market in health care telematics. PMID:7889758

  12. Sacral Perineural Cyst Accompanying Disc Herniation

    PubMed Central

    Ju, Chang Il; Shin, Ho; Kim, Hyeun Sung

    2009-01-01

    Although most of sacral perineural cysts are asymptomatic, some may produce symptoms. Specific radicular pain may be due to distortion, compression, or stretching of nerve root by a space occupying cyst. We report a rare case of S1 radiculopathy caused by sacral perineural cyst accompanying disc herniation. The patient underwent a microscopic discectomy at L5-S1 level. However, the patient's symptoms did not improved. The hypesthesia persisted, as did the right leg pain. Cyst-subarachnoid shunt was set to decompress nerve root and to equalize the cerebrospinal fluid pressure between the cephalad thecal sac and cyst. Immediately after surgery, the patient had no leg pain. After 6 months, the patient still remained free of leg pain. PMID:19352483

  13. Sacral perineural cyst accompanying disc herniation.

    PubMed

    Ju, Chang Il; Shin, Ho; Kim, Seok Won; Kim, Hyeun Sung

    2009-03-01

    Although most of sacral perineural cysts are asymptomatic, some may produce symptoms. Specific radicular pain may be due to distortion, compression, or stretching of nerve root by a space occupying cyst. We report a rare case of S1 radiculopathy caused by sacral perineural cyst accompanying disc herniation. The patient underwent a microscopic discectomy at L5-S1 level. However, the patient's symptoms did not improved. The hypesthesia persisted, as did the right leg pain. Cyst-subarachnoid shunt was set to decompress nerve root and to equalize the cerebrospinal fluid pressure between the cephalad thecal sac and cyst. Immediately after surgery, the patient had no leg pain. After 6 months, the patient still remained free of leg pain. PMID:19352483

  14. The Mechanism of Atomization Accompanying Solid Injection

    NASA Technical Reports Server (NTRS)

    Castleman, R A , Jr

    1933-01-01

    A brief historical and descriptive account of solid injection is followed by a detailed review of the available theoretical and experimental data that seem to throw light on the mechanism of this form of atomization. It is concluded that this evidence indicates that (1) the atomization accompanying solid injection occurs at the surface of the liquid after it issues as a solid stream from the orifice; and (2) that such atomization has a mechanism physically identical with the atomization which takes place in an air stream, both being due merely to the formation, at the gas-liquid interface, of fine ligaments under the influence of the relative motion of gas and liquid, and to their collapse, under the influence of surface tension, to form the drops in the spray.

  15. Phase Transformation of U3O8 and Enhanced Structural Stability at Extreme Conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Fuxiang; Lang, Maik; Ewing, Rodney

    2013-06-01

    A powder sample of β-U3O8 was pressurized at room temperature up to 37.5 GPa with a symmetric diamond anvil cell. XRD patterns clearly indicated that a phase transition occurred between 3-11 GPa. The high-pressure phase is a fluorite-like structure. The fluorite-like structure is stable up to 37.5 GPa. The high-pressure phase was then laser heated to over 1700 K in the diamond anvil cell at high pressure conditions. No phase transition was found at high pressure/ temperature conditions, and the fluorite-like structure of U3O8 is even fully quenchable. The lattice parameter of the fluorite-like high-pressure phase is 5.425 Å at ambient conditions, which is smaller than that of the stoichiometric UO2. Previous experiments have shown that the stoichiometric uranium dioxide (UO2) is not stable at high pressure conditions and starts to transform to a cotunnite structure at ~30 GPa. When heating the sample at high pressure, the critical transtion pressure is greatly reduced. However, the fluorite-like high-pressure phase of U3O8 is very stable at high pressure/high temperature conditions. The enhanced phase stability is believed to be related to the presence of extra oxygen (or U vacancies) in the structure. This work was supported by Materials Science of Actinides, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0001089.

  16. Enhancement of magnetism by structural phase transition in MoS{sub 2}

    SciTech Connect

    Yan, Shiming; Qiao, Wen; He, Xueming; Zhong, Wei Du, Youwei; Guo, Xiaobing; Xi, Li

    2015-01-05

    The magnetic properties of 2H phase of MoS{sub 2} (2H-MoS{sub 2}) and 1T phase of MoS{sub 2} (1T-MoS{sub 2}) were investigated both experimentally and theoretically. Lithium (Li) intercalation method was used to prepare single-layer MoS{sub 2} sheets. It was found that pristine MoS{sub 2} (2H-MoS{sub 2}) exhibited weak diamagnetism. After exfoliating by Li intercalation, the crystal structure transformed from 2H to 1T phase, and the magnetism was significantly enhanced from diamagnetism to paramagnetism accordingly. With further annealing in argon atmosphere, the 2H phase recovered gradually from 1T phase, and the magnetism decreased correspondingly. Using crystal field theory and combining the results of first principle calculation, we conclude that the enhanced magnetism can be attributed to the Mo atoms of 1T-MoS{sub 2}.

  17. Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations

    PubMed Central

    Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

    2013-01-01

    Ir1−xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280 K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

  18. Group Lifting Structures For Multirate Filter Banks, II: Linear Phase Filter Banks

    SciTech Connect

    Brislawn, Christopher M

    2008-01-01

    The theory of group lifting structures is applied to linear phase lifting factorizations for the two nontrivial classes of two-channel linear phase perfect reconstruction filter banks, the whole-and half-sample symmetric classes. Group lifting structures defined for the reversible and irreversible classes of whole-and half-sample symmetric filter banks are shown to satisfy the hypotheses of the uniqueness theorem for group lifting structures. It follows that linear phase lifting factorizations of whole-and half-sample symmetric filter banks are therefore independent of the factorization methods used to compute them. These results cover the specification of user-defined whole-sample symmetric filter banks in Part 2 of the ISO JPEG 2000 standard.

  19. Average Structure Evolution of δ-phase Pu-Ga Alloys

    SciTech Connect

    Smith, Alice Iulia; Page, Katharine L.; Gourdon, Olivier; Siewenie, Joan E.; Richmond, Scott; Saleh, Tarik A.; Ramos, Michael; Schwartz, Daniel S.

    2015-03-30

    [Full Text] Plutonium metal is a highly unusual element, exhibiting six allotropes at ambient pressure, from room temperature to its melting point. Many phases of plutonium metal are unstable with temperature, pressure, chemical additions, and time. This strongly affects structure and properties, and becomes of high importance, particularly when considering effects on structural integrity over long time periods. The fcc δ-phase deserves additional attention, not only in the context of understanding the electronic structure of Pu, but also as one of the few high-symmetry actinide phases that can be stabilized down to ambient pressure and room temperature by alloying it with trivalent elements. We will present results on recent work on aging of Pu-2at.%Ga and Pu-7at.%Ga alloys

  20. Experimental phase determination of the structure factor from Kossel line profile

    PubMed Central

    Faigel, G.; Bortel, G.; Tegze, M.

    2016-01-01

    Kossel lines are formed when radiation from point x-ray sources inside a single crystal are diffracted by the crystal itself. In principle, Kossel line patterns contain full information on the crystalline structure: phase and magnitude of the structure factors. The phase is coded into the profile of the lines. Although this was known for a long time, experimental realization has not been presented. In this work we demonstrate experimentally that phases can be directly determined from the profile of the Kossel lines. These measurements are interesting not only theoretically, but they would facilitate structure solution of samples within extreme conditions, such as high pressure, high and low temperatures, high magnetic fields and extremely short times. The parallel measurement of many diffraction lines on a stationary sample will allow a more efficient use of the new generation of x-ray sources the X-ray free electron lasers (XFELs). PMID:26965321

  1. Experimental phase determination of the structure factor from Kossel line profile.

    PubMed

    Faigel, G; Bortel, G; Tegze, M

    2016-01-01

    Kossel lines are formed when radiation from point x-ray sources inside a single crystal are diffracted by the crystal itself. In principle, Kossel line patterns contain full information on the crystalline structure: phase and magnitude of the structure factors. The phase is coded into the profile of the lines. Although this was known for a long time, experimental realization has not been presented. In this work we demonstrate experimentally that phases can be directly determined from the profile of the Kossel lines. These measurements are interesting not only theoretically, but they would facilitate structure solution of samples within extreme conditions, such as high pressure, high and low temperatures, high magnetic fields and extremely short times. The parallel measurement of many diffraction lines on a stationary sample will allow a more efficient use of the new generation of x-ray sources the X-ray free electron lasers (XFELs). PMID:26965321

  2. Cystic lesions accompanying extra-axial tumours.

    PubMed

    Lohle, P N; Wurzer, H A; Seelen, P J; Kingma, L M; Go, K G

    1999-01-01

    We examined the mechanism of cyst formation in extra-axial tumours in the central nervous system (CNS). Cyst fluid, cerebrospinal fluid (CSF) and blood plasma were analysed in eight patients with nine peritumoral cysts: four with meningiomas, two with intracranial and two spinal intradural schwannomas. Measuring concentrations of various proteins [albumin, immunoglobulin G (IgG), IgA, alpha 2-macroglobulin and IgM] in cyst fluid, CSF and blood plasma provides insight into the state of the semipermeability of the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier. Peritumoral cysts accompanying intra-axial brain tumours are the end result of disruption of the BBB and oedema formation. Unlike intra-axial tumours which lie embedded within nervous tissue, extra-axial tumours tend to be separated from nervous tissue by arachnoid and pia mater. High concentrations of proteins were measured in the cyst fluid, approaching blood plasma levels, suggesting a local barrier disruption, and passage across the arachnoid, pia mater and cortical/medullary layer into the CNS parenchyma, leaving the protein concentrations of CSF practically unchanged. We confirmed that very high concentrations of protein are to be found in tumour cysts, plasma proteins forming almost 90% of the total protein in the cyst. We review current hypotheses on the pathogenesis of cysts accompanying neoplasms, particularly meningiomas and schwannomas, and conclude that the majority of proteins in cyst fluid in extra-axial, intradural meningiomas and schwannomas are plasma proteins. This provides a strong argument for pathogenesis of extra-axial intradural tumour cysts in favour of leakage of plasma proteins out of the tumour vessels into the nervous tissue. PMID:9987761

  3. Crystal structures and phase formation thermodynamics of iron-gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Mukherjee, Pinaki

    Alloy nanoparticles are being increasingly used in wide variety of applications (catalysis, contrast enhancement in magnetic resonance imaging, etc.). Knowledge of crystal structure and phase formation of the alloy nanoparticles is critical for these applications. Anomalous thermodynamic behavior and unusual phase formation have been reported for nanoparticles with size below 10 nm. In the present work, inert gas condensation (IGC) has been used to produce Au-Fe nanoclusters of varied compositions with a mean size between 5-10 nm. Here, the nanoclusters below 10 nm display complete solubility between Fe and Au in Fex Au1-x (0.3 < x < 0.8) alloys. The as-deposited clusters are single-crystalline but crystallinity is poor with significant disorder. New structural phases have been obtained for as-deposited clusters that are inconsistent with the equilibrium phase diagram. The as-deposited structures were either bcc for x > 0.65 and fcc for x < 0.65, with lattice parameters expanded relative to elemental and rule-of mixtures values, suggesting the presence of self-interstitials. The as-deposited clusters were ferromagnetic at room temperature. Heat treatment at 600°C for 15 minutes followed by furnace cooling resulted in the size-dependent transformation of the clusters into additional, non-equilibrium structures that depended on cluster composition, while larger clusters followed bulk behavior. At about 65 atom % Fe, clusters transformed to a well-ordered, single fcc phase with a lattice parameter of 0.363 nm, whereas the phase diagram predicted two-phase equilibrium. The stabilization of a single fcc phase was explained by a thermodynamic analysis. This analysis suggests that the single phase stability in the Fe-Au nanoparticles arises from the fact that the introduction of a phase boundary is energetically opposed. Heat treatment of as-deposited particles results in L12 and L1 0ordered structures near 1:3, 3:1 and 1:1 (Fe:Au) stoichiometries respectively

  4. Lattice vibrations and instabilities in tungsten phases from electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Grimvall, G.; Einarsdotter, K.; Sadigh, B.; Köpe, B.; Ozolinš, V.

    1998-03-01

    Phonon dispersion curves are calculated for bcc and fcc W, as a function of atomic volume. The range of phonon stability in the fcc phase is mapped out in the Brillouin zone. Incipient instabilities in the bcc phase are studied, and compared with related instabilities in, e.g., bcc Ti and Zr. A molecular-dynamics type analysis is also performed. Implications are discussed for binary phase diagrams AB where elements A and B have different lattice structures, one of them being dynamically unstable.

  5. Electronic Structure and Phase Transition in Ferroelectic Sn2P2S6 Crystal

    PubMed Central

    Glukhov, Konstantin; Fedyo, Kristina; Banys, Juras; Vysochanskii, Yulian

    2012-01-01

    An analysis of the P2S6 cluster electronic structure and its comparison with the crystal valence band in the paraelectric and ferroelectric phases has been done by first-principles calculations for Sn2P2S6 ferroelectrics. The origin of ferroelectricity has been outlined. It was established that the spontaneous polarization follows from the stereochemical activity of the electron lone pair of tin cations, which is determined by hybridization with P2S6 molecular orbitals. The chemical bonds covalence increase and rearrangement are related to the valence band changes at transition from the paraelectric phase to the ferroelectric phase. PMID:23203069

  6. Two-dimensional Mueller matrix phase tomography of self-similarity birefringence structure of biological tissues

    NASA Astrophysics Data System (ADS)

    Ushenko, V. O.

    2012-10-01

    This work presents the possibility of phase tomography of optical-anisotropic multilayered biological structures. The superposition approach of polarization manifestation of optical anisotropy of polycrystalline protein networks is proposed. The optical model of polycrystalline networks of biological tissues protein fibrils is presented. The technique of phase tomography based on determining the coordinate distributions of Mueller-matrix elements of biological tissues is suggested. The results of investigating the interrelation between the values of statistical (statistical moments of the 1st- 4th order) parameters are presented. They characterize the coordinate distributions of phase shifts of biological tissue layer of different optical thickness and the degree of muscle dystrophy.

  7. Enhanced ferromagnetism in Mn-doped TiO 2 films during the structural phase transition

    NASA Astrophysics Data System (ADS)

    Xu, J. P.; Lin, Y. B.; Lu, Z. H.; Liu, X. C.; Lu, Z. L.; Wang, J. F.; Zou, W. Q.; Lv, L. Y.; Zhang, F. M.; Du, Y. W.

    2006-12-01

    The crystal structures and magnetic properties of Ti 0.9747Mn 0.0253O 2 films prepared by sol-gel dip coating have been investigated. Room temperature ferromagnetism was observed both in the films of pure anatase phase and of mixed anatase and rutile phases. For the first time, enhancement of the ferromagnetism was revealed as the phase transition from anatase to rutile occurs: from 0.7±0.01μ B/Mn to 1.1±0.05μ B/Mn. The possible mechanism for the observed magnetism enhancement is discussed.

  8. A portable ultrasonic phased array device for tabular joint weld inspection of offshore platform structures

    NASA Astrophysics Data System (ADS)

    Shan, Baohua; Li, Jingan; Duan, Zhongdong; Ou, Jinping; Shen, Wei

    2012-05-01

    To meet the inspection need for complex tabular joints weld of offshore platform structures, a portable ultrasonic phased array inspection device is developed. The integrated device is small and portable. As designed, the device can implement different algorithm of the ultrasonic phased array inspection technology. With proposed inspection plan, the experiment of Y tubular joint model was performed in lab. Experiment results indicate that the possible ultrasonic phased array inspection device can detect and visualize the flaws on Y tubular joint weld, which are nearly consistent with the actual condition.

  9. Study of structural phase transitions in (NH 4) 2SnBr 6 by Raman scattering

    NASA Astrophysics Data System (ADS)

    Negita, K.; Nakamura, N.; Chihara, H.

    1980-06-01

    The two successive phase transitions in (NH 4) 2SnBr 6 were examined by low- frequency Raman scattering experiments. Two low frequency modes which were assigned to the rotary modes of SnBr 2-6 ions showed soft-mode like behavior in the lowest temperature phase. It was proposed that the higher phase transition is structural in nature associated with the soft rotary mode of the anions whereas the lower one is of an order-disorder type with respect to the relative orientations of the ammonium ions.

  10. First-Principles Study of Lattice Dynamics, Structural Phase Transition, and Thermodynamic Properties of Barium Titanate

    NASA Astrophysics Data System (ADS)

    Zhang, Huai-Yong; Zeng, Zhao-Yi; Zhao, Ying-Qin; Lu, Qing; Cheng, Yan

    2016-08-01

    Lattice dynamics, structural phase transition, and the thermodynamic properties of barium titanate (BaTiO3) are investigated by using first-principles calculations within the density functional theory (DFT). It is found that the GGA-WC exchange-correlation functional can produce better results. The imaginary frequencies that indicate structural instability are observed for the cubic, tetragonal, and orthorhombic phases of BaTiO3 and no imaginary frequencies emerge in the rhombohedral phase. By examining the partial phonon density of states (PDOSs), we find that the main contribution to the imaginary frequencies is the distortions of the perovskite cage (Ti-O). On the basis of the site-symmetry consideration and group theory, we give the comparative phonon symmetry analysis in four phases, which is useful to analyze the role of different atomic displacements in the vibrational modes of different symmetry. The calculated optical phonon frequencies at Γ point for the four phases are in good agreement with other theoretical and experimental data. The pressure-induced phase transition of BaTiO3 among four phases and the thermodynamic properties of BaTiO3 in rhombohedral phase have been investigated within the quasi-harmonic approximation (QHA). The sequence of the pressure-induced phase transition is rhombohedral→orthorhombic→tetragonal→cubic, and the corresponding transition pressure is 5.17, 5.92, 6.65 GPa, respectively. At zero pressure, the thermal expansion coefficient αV, heat capacity CV, Grüneisen parameter γ, and bulk modulus B of the rhombohedral phase BaTiO3 are estimated from 0 K to 200 K.

  11. Cryogenic Ion Mobility-Mass Spectrometry: Tracking Ion Structure from Solution to the Gas Phase.

    PubMed

    Servage, Kelly A; Silveira, Joshua A; Fort, Kyle L; Russell, David H

    2016-07-19

    Electrospray ionization (ESI) combined with ion mobility-mass spectrometry (IM-MS) is adding new dimensions, that is, structure and dynamics, to the field of biological mass spectrometry. There is increasing evidence that gas-phase ions produced by ESI can closely resemble their solution-phase structures, but correlating these structures can be complicated owing to the number of competing effects contributing to structural preferences, including both inter- and intramolecular interactions. Ions encounter unique hydration environments during the transition from solution to the gas phase that will likely affect their structure(s), but many of these structural changes will go undetected because ESI-IM-MS analysis is typically performed on solvent-free ions. Cryogenic ion mobility-mass spectrometry (cryo-IM-MS) takes advantage of the freeze-drying capabilities of ESI and a cryogenically cooled IM drift cell (80 K) to preserve extensively solvated ions of the type [M + xH](x+)(H2O)n, where n can vary from zero to several hundred. This affords an experimental approach for tracking the structural evolution of hydrated biomolecules en route to forming solvent-free gas-phase ions. The studies highlighted in this Account illustrate the varying extent to which dehydration can alter ion structure and the overall impact of cryo-IM-MS on structural studies of hydrated biomolecules. Studies of small ions, including protonated water clusters and alkyl diammonium cations, reveal structural transitions associated with the development of the H-bond network of water molecules surrounding the charge carrier(s). For peptide ions, results show that water networks are highly dependent on the charge-carrying species within the cluster. Specifically, hydrated peptide ions containing lysine display specific hydration behavior around the ammonium ion, that is, magic number clusters with enhanced stability, whereas peptides containing arginine do not display specific hydration around the

  12. Rotational tunneling of methyl groups in low temperature phases of mesitylene: potentials and structural implications.

    PubMed

    Prager, M; Grimm, H; Natkaniec, I

    2005-07-01

    Mesitylene can be stabilized at He temperature in three solid phases of so far unknown crystal structures. Rotational tunneling of methyl groups is based on rotational potentials and used to characterize structural aspects. In phase III found after the first fast cooling of the sample three nonequivalent methyl rotors with splittings of 2.7, 4.1 and 16.3 microeV are observed. Three other unresolved bands are identified by their librational modes. In the second phase II the metastability is emphasized by tunneling energies still changing at temperatures T< or = 12 K. Above this temperature tunneling bands at 6.6, 12.5, 15.0 and 18.3 microeV evolve in the manner characteristic of coupling to phonons. In the equilibrium phase I a single tunnel splitting of 10.2 microeV represents all methyl groups. A unit cell containing a single molecule at a site of threefold symmetry explains quantitatively this spectrum. Phases II and III most likely contain two nonequivalent molecules in the unit cell with no local symmetry in phase II and a mirror plane in phase III. The good moderator properties for neutrons are most likely not connected to the low energy tunneling bands but to a dense vibrational phonon density of states. PMID:16189568

  13. Structure and phase behaviour of diblock copolymer monolayers investigated by means of Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Słyk, Edyta; Rżysko, Wojciech; Bryk, Paweł

    2015-10-01

    We use grand canonical Monte Carlo simulation paired with multiple histogram reweighting, hyperparallel tempering and finite size scaling to investigate the structure and phase behaviour of monolayers of diblock copolymers. The chain molecules are arranged on the square lattice and we consider both fully flexible and rod-coil polymer models. In contrast to the majority of previous studies we assume that the interactions between the segments belonging to one of the two subunits are weaker than the remaining segment-segment interactions. We find that when the diblock copolymer is fully flexible, this choice of the interactions leads to a suppression of the ordered phase, and the phase behaviour is analogous to that of the fully flexible homopolymer model. However, when one of the subunits is rigid, we observe the formation of a novel hairpin chessboard ordered structure with fully stretched chains bent in the middle. The topology of the phase diagram depends on the chain length. For shorter chains the global phase diagram features a critical point and a triple point. For longer chains the gas—disordered liquid phase transition is suppressed and only the order-disorder transition remains stable. The resulting phase diagram is of the swan neck type.

  14. Phase equilibria, crystal structure and oxygen content of intermediate phases in the Y-Ba-Co-O system

    NASA Astrophysics Data System (ADS)

    Urusova, A. S.; Cherepanov, V. A.; Aksenova, T. V.; Gavrilova, L. Ya.; Kiselev, E. A.

    2013-06-01

    The phase equilibria in the Y-Ba-Co-O system were systematically studied at 1373 K in air. The intermediate phases formed in the Y-Ba-Co-O system at 1373 K in air were: YBaCo2O5+δ, YBaCo4O7 and BaCo1-yYyO3-δ (0.09≤y≤0.42). It was shown that YBaCo2O5+δ possesses tetragonal structure with the 3ap×3ap×2ap superstructure (sp. gr. P4/mmm). High-temperature X-ray diffraction analysis of the YBaCo2O5+δ in the temperature range from 298 K up to 1073 K under Po2=0.21 аtm has not shown any phase transformations. The value of oxygen content for the YBaCo2O5+δ at room temperature was estimated as 5.40 and at 1323 K it was equal to 5.04. Thermal expansion of sample shows a linear characteristics and the average thermal expansion coefficient (TEC) is about 13.8×10-6, K-1 in the temperature range 298-1273 K. The homogeneity range and crystal structure of the BaCo1-yYyO3-δ (0.09≤y≤0.42) solid solutions were determined by X-ray diffraction of quenched samples. All BaCo1-yYyO3-δ solid solutions were found to have cubic structure (sp. gr. Pm3m). The unit cell parameters were refined using Rietveld full-profile analysis. Oxygen nonstoichiometry of BaCo1-yYyO3-δ solid solutions with 0.1≤y≤0.4 was measured by means of thermogravimetric technique within the temperature range 298-1373 K in air. Thermal expansion of BaCo1-yYyO3-δ (у=0.0; 0.1; 0.2; 0.3) samples was studied within the temperature range 298-1200 K in air. The projection of isothermal-isobaric phase diagram for the Y-Ba-Co-O system to the compositional triangle of metallic components was presented.

  15. Influence of LC Content on the Phase Structures of Side-Chain Liquid

    SciTech Connect

    Tenneti, K.; Chen, X; Li, C; Shen, Z; Wan, X; Fan, X; Zhou, Q; Rong, L; Hsiao, B

    2009-01-01

    We report the phase structures of a series of poly(styrene-block-{l_brace}3'-[4-(4-n-dodecyloxybenzoyloxy)benzoyloxy]-4-(12-methacryloyloxydodecyloxy)benzoyloxybiphenyl{r_brace}) (PS-b-PMAC) side-chain liquid crystalline block copolymers (SC LCBCP). The SC liquid crystalline polymer was formed by side attaching a bent-core mesogen to the polymer backbone using a 12-carbon spacer. The phase structure of the high and low fPMAC samples were investigated using differential scanning calorimetry, small-angle and wide-angle X-ray scattering, and transmission electron microscopy techniques. The PS coil block and PMAC LC block phase separate into a lamellar morphology in all of the samples investigated (volume fraction of PMAC fPMAC 0.31-0.65). However, both the LC phase and the orientation of the hierarchical structure under mechanical shear showed strong dependence on the LC content. Samples having a high fPMAC (0.5-0.65) showed a SmC2 LC phase (Smectic C denotes the LC molecules are tilted with respect to the layer normal, and 2 represents a bilayered structure), similar to that observed in PMAC homopolymers. Upon mechanical shear, these smectic layers oriented parallel to the shear plane and the BCP lamellae oriented perpendicular to the shear plane with the layer normal parallel to the vorticity direction. In samples having a lower fPMAC, the BCP lamellae laid parallel to the shear plane and the LC phase structure in these samples was columnar rectangular. A detailed structural and morphological study will be reported.

  16. Phase equilibria, crystal structure and oxygen content of intermediate phases in the Y–Ba–Co–O system

    SciTech Connect

    Urusova, A.S.; Cherepanov, V.A. Aksenova, T.V.; Gavrilova, L.Ya.; Kiselev, E.A.

    2013-06-01

    The phase equilibria in the Y–Ba–Co–O system were systematically studied at 1373 K in air. The intermediate phases formed in the Y–Ba–Co–O system at 1373 K in air were: YBaCo₂O5+δ, YBaCo₄O₇ and BaCo1–yYyO3–δ (0.09≤y≤0.42). It was shown that YBaCo₂O5+δ possesses tetragonal structure with the 3aₚ×3aₚ×2aₚ superstructure (sp. gr. P4/mmm). High-temperature X-ray diffraction analysis of the YBaCo₂O5+δ in the temperature range from 298 K up to 1073 K under Po₂=0.21 atm has not shown any phase transformations. The value of oxygen content for the YBaCo₂O5+δ at room temperature was estimated as 5.40 and at 1323 K it was equal to 5.04. Thermal expansion of sample shows a linear characteristics and the average thermal expansion coefficient (TEC) is about 13.8×10⁻⁶, K⁻¹ in the temperature range 298–1273 K. The homogeneity range and crystal structure of the BaCo1–yYyO3–δ (0.09≤y≤0.42) solid solutions were determined by X-ray diffraction of quenched samples. All BaCo1–yYyO3–δ solid solutions were found to have cubic structure (sp. gr. Pm3m). The unit cell parameters were refined using Rietveld full-profile analysis. Oxygen nonstoichiometry of BaCo1–yYyO3–δ solid solutions with 0.1≤y≤0.4 was measured by means of thermogravimetric technique within the temperature range 298–1373 K in air. Thermal expansion of BaCo1–yYyO3–δ (y=0.0; 0.1; 0.2; 0.3) samples was studied within the temperature range 298–1200 K in air. The projection of isothermal–isobaric phase diagram for the Y–Ba–Co–O system to the compositional triangle of metallic components was presented. - Graphical abstract: A projection of isobaric isothermal phase diagram of the Y–Ba–Co–O system to the metallic components

  17. Inelastic light scattering measurements of structural phase coexistence in ferrimagnetic spinel Mn3O4

    NASA Astrophysics Data System (ADS)

    Gleason, Samuel; Byrum, Taylor; Thaler, Alexander; MacDougall, Gregory; Cooper, S. Lance

    2015-03-01

    The ferrimagnetic spinel Mn3O4 has a number of functional properties, e.g., magnetodielectricity, that are ascribed to a coupling between the spins and lattice of this material. Such a coupling is manifested in the symmetry-lowering structural distortion that occurs when Mn3O4 magnetically orders at T = 33 K. A recent x-ray diffraction study2 of polycrystalline Mn3O4 found that this distortion is not fully realized, i.e., the high-symmetry and low-symmetry structures coexist below T = 33 K due to strains from lattice mismatch. To extend this work, we use variable-pressure and variable-magnetic-field inelastic light scattering spectroscopy to study structural phase coexistence in single crystals of Mn3O4. We confirm the coexistence of tetragonal (high-symmetry) and orthorhombic (low-symmetry) phases below T = 33 K. Furthermore, we demonstrate that the application of hydrostatic pressure suppresses the remnant tetragonal phase, while the application of magnetic field can bolster this phase. These results indicate that microscopic descriptions of functional behavior in Mn3O4 should consider effects due to structural phase coexistence. [2] M. C. Kemei, et al., Phys. Rev. B 89, 174410 (2014). Research was supported by the U.S. Department of Energy under Award DE-FG02-07ER46453. T. Byrum was partially supported by the National Science Foundation under Grant Number DGE-1144245.

  18. Structural disorder in the paraelectric phase of the Fe3B7O13Br boracite

    NASA Astrophysics Data System (ADS)

    Shuvaeva, V. A.; Lysenko, K. A.; Antipin, M. Yu.

    2011-04-01

    A structural model of the cubic paraelectric phase of a Fe3B7O13Br crystal belonging to the boracite family has been developed using the data obtained by single-crystal X-ray diffraction with due regard for the results of extended X-ray absorption fine structure (EXAFS) spectroscopy. It has been shown that the best agreement between the data obtained by these two methods is achieved within a model assuming a disorder in the arrangement of both the Fe and Br atoms and a high degree of correlation of their displacements. It has been found that, during the phase transition from the rhombohedral ferroelectric phase to the cubic paraelectric phase, no significant transformation of the structure is observed on a local level. In this case, a change in the macroscopic symmetry occurs predominantly as a result of the variation in the set of possible spatial orientations of stable structural fragments, which is characteristic of order-disorder phase transitions.

  19. Magnetostructural phase transitions and magnetocaloric effect in Tb-Dy-Ho-Co-Al alloys with a Laves phase structure

    NASA Astrophysics Data System (ADS)

    Tereshina, I. S.; Chzhan, V. B.; Tereshina, E. A.; Khmelevskyi, S.; Burkhanov, G. S.; Ilyushin, A. S.; Paukov, M. A.; Havela, L.; Karpenkov, A. Yu.; Cwik, J.; Koshkid'ko, Yu. S.; Miller, M.; Nenkov, K.; Schultz, L.

    2016-07-01

    The influence of simultaneous substitution within the rare earth (R) and Co sublattices on the structural, magnetic, and magnetocaloric properties of the Laves phase RCo2-type compounds is studied. Main attention is devoted to the studies of the magnetostructural phase transitions and the transition types with respect to the alloy composition. Multicomponent alloys Tbx(Dy0.5Ho0.5)1-xCo2 and Tbx(Dy0.5Ho0.5)1-xCo1.75Al0.25 were prepared with the use of high purity metals. Majority of the Tbx(Dy0.5Ho0.5)1-xCo2 alloys exhibit magnetic transitions of the first-order type and a large magnetocaloric effect. The substitution of Al for Co in Tbx(Dy0.5Ho0.5)1-xCo2 increases the Curie temperature (TC) but changes the transition type from first-to the second-order. The discussion of the physical mechanisms behind the observed phenomena is given on the basis of the first principles electronic-structure calculations taking into account both the atomic disorder and the magnetic disorder effects at finite temperatures. The advantage of Al-containing materials is that sufficiently high magnetocaloric effect values are preserved at T > TC.

  20. Lattice Dynamical Interpretation of the Structure of \\zeta-Phase AgZn

    NASA Astrophysics Data System (ADS)

    Yamada, Yasusada; Noda, Yukio

    1988-04-01

    The crystal structure of \\zeta-phase AgZn has been reconsidered. It is shown that the static structure of \\zeta-AgZn is expressible in terms of (i) two types of lattice waves (phonon modes) and (ii) one type of probability density wave of Zn atom site-occupation. It is noted that the relevant phonon modes are the soft modes existing commonly in bcc Hume-Rothery alloys. It is pointed out that \\zeta-AgZn shares the common origin of stabilization with 9R martensites and ω-phase.

  1. Structural organization of replicon domains during DNA synthetic phase in the mammalian nucleus

    SciTech Connect

    Nakamura, H.; Morita, T.; Sato, C.

    1986-01-01

    In mammalian cells, it has been shown that adjacent multiple DNA replicons, termed a replicon cluster or a replicon domain, are replicated coordinately in a defined temporal order during the DNA synthetic (S) phase. However, no intranuclear structure of this replicon domain has been revealed in the nucleus labelled with (/sup 3/H)thymidine at the limited resolution level of autoradiography. Bu immunofluorescent staining with antibody against 5-bromodeoxyuridine (BrdU), we succeeded in detecting novel, intranuclear ring-like structures of replicating replicon domains that were organized temporarily during the S phase of mammalian cells with incorporated BrdU.

  2. New structural picture of the Ge2Sb2Te5 phase-change alloy.

    PubMed

    Liu, X Q; Li, X B; Zhang, L; Cheng, Y Q; Yan, Z G; Xu, M; Han, X D; Zhang, S B; Zhang, Z; Ma, E

    2011-01-14

    Using electron microscopy and diffraction techniques, as well as first-principles calculations, we demonstrate that as much as 35% of the total Ge atoms in the cubic phase of Ge2Sb2Te5 locate in tetrahedral environments. The Ge-vacancy interactions play a crucial stabilizing role, leading to Ge-vacancy pairs and the sharing of vacancies that clusters tetrahedral Ge into domains. The Ge2Sb2Te5 structure with coexisting octahedral and tetrahedral Ge produces optical and structural properties in good agreement with experimental data and explains the property contrast as well as the rapid transformation in this phase-change alloy. PMID:21405239

  3. Structural and phase changes in carbides of the high-speed steel upon heat treatment

    NASA Astrophysics Data System (ADS)

    Chaus, A. S.

    2016-07-01

    The effect of austenitizing temperature on structural and phase changes in carbides of the tungsten-molybdenum high-speed steel has been studied. The results of metallographic analysis and energy dispersive microanalysis have been discussed. It has been shown that an increase in austenitizing temperature from 1180 to 1260°C causes structural transformations in carbide particles of eutectic origin crushed upon hot plastic deformation, which are related to their dissolution and coalescence, and changes in the phase composition of the carbides themselves.

  4. Dynamics of Structural Transformations between Lamellar and Inverse Bicontinuous Cubic Lyotropic Phases

    SciTech Connect

    Conn, Charlotte E.; Ces, Oscar; Mulet, Xavier; Seddon, John M.; Templer, Richard H.; Finet, Stephanie; Winter, Roland

    2006-03-17

    The liquid crystalline lamellar (L{sub {alpha}}) to double-diamond inverse bicontinuous cubic (Q{sub II}{sup D}) phase transition for the amphiphile monoelaidin in excess water exhibits a remarkable sequence of structural transformations for pressure or temperature jumps. Our data imply that the transition dynamics depends on a coupling between changes in molecular shape and the geometrical and topological constraints of domain size. We propose a qualitative model for this coupling based on theories of membrane fusion via stalks and existing knowledge of the structure and energetics of bicontinuous cubic phases.

  5. Damping and structural control of the JPL phase 0 testbed structure

    NASA Technical Reports Server (NTRS)

    Fanson, James L.; Chu, Cheng-Chih; Lurie, Boris J.; Smith, Roy S.

    1991-01-01

    This paper describes recent advances in structural quieting technology as applied to active truss structures intended for high precision space based optics applications. The active structure incorporates piezoelectric active members which exert control forces internal to the structure and thereby improve the structure's dimensional stability. The control architecture involves two layers of feedback control. The first utilizes collocated measurements of force and velocity at the active member to achieve active damping, the second utilizes noncollocated measurements of acceleration at the location of a simulated optical component to achieve structural stabilization. The local control loops are based on the concept of impedance matching, the global control loops are designed using robust control methods. These two levels of control are intended to operate simultaneously; however, in this paper each approach is applied individually. The combined implementation is left for future work.

  6. System identification and structural control on the JPL Phase B testbed

    NASA Technical Reports Server (NTRS)

    Chu, Cheng-Chih; Obrien, John F.; Lurie, Boris J.

    1993-01-01

    The primary objective of NASA's CSI program at JPL is to develop and demonstrate the CSI technology required to achieve high precision structural stability on large complex optical class spacecraft. The focus mission for this work is an orbiting interferometer telescope. Toward the realization of such a mission, a series of evolutionary testbed structures are being constructed. The JPL's CSI Phase B testbed is the second structure constructed in this series which is designed to study the pathlength control problem of the optical train of a stellar interferometer telescope mounted on a large flexible structure. A detailed description of this testbed can be found. This paper describes our efforts in the first phase of active structural control experiments of Phase B testbed using the active control approach where a single piezoelectric active member is used as an actuation device and the measurements include both colocated and noncolocated sensors. Our goal for this experiment is to demonstrate the feasibility of active structural control using both colocated and noncolocated measurements by means of successive control design and loop closing. More specifically, the colocated control loop was designed and closed first to provide good damping improvement over the frequency range of interest. The noncolocated controller was then designed with respect to a partially controlled structure to further improve the performance. Based on our approach, experimental closed-loop results have demonstrated significant performance improvement with excellent stability margins.

  7. Pressure induced structural phase transition and electronic properties of actinide monophospides: Ab-initio calculations

    NASA Astrophysics Data System (ADS)

    Makode, Chandrabhan; Sanyal, Sankar P.

    2011-09-01

    We have investigated the structural and electronic properties of monophospides of thorium, uranium and neptunium. The total energy as a function of volume is obtained by means of the self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). From the present study with the help of total energy calculations it is found that ThP, UP and NpP are stable in NaCl-type structure at ambient pressure. The structural stability of ThP, UP and NpP changes under the application of pressure. We predict a structural phase transition from NaCl-type (B 1-phase) structure to CsCl-type (B 2-phase) structure for these phospides in the pressure range of 37.0-24.0 GPa (ThP-NpP). We also calculate lattice parameter ( a0), bulk modulus ( B0), band structure and density of states. From energy band diagram it is observed that ThP, UP and NpP exhibit metallic behavior. The calculated equilibrium lattice parameters and bulk modulus are in good agreement with experimental and theoretical work.

  8. Crystal structures of three intermetallic phases in the Mo-Pt-Si system

    SciTech Connect

    Joubert, J.-M.; Tokaychuk, Ya.; Cerny, R.

    2010-01-15

    The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. All three structures are representative of new structure types. Both the X (MoPt{sub 2}Si{sub 3}, Pmc2{sub 1}, oP12, a=3.48438(6), b=9.1511(2), c=5.48253(8) A) and Y (MoPt{sub 3}Si{sub 4}, Pnma, oP32, a=5.51210(9), b=3.49474(7), c=24.3090(4) A) phases derive from PtSi (FeAs type) structure while the Z phase (ideal composition Mo{sub 32}Pt{sub 20}Si{sub 16}, refined composition Mo{sub 29.9(2)}Pt{sub 21.0(3)}Si{sub 17.1(1)}, Cc, mC68, a=13.8868(3), b=8.0769(2), c=9.6110(2) A, beta=100.898(1){sup o}) present similarities with the group of Frank-Kasper phases. - Graphical abstract: The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. The three structures represent new structure types.

  9. Effect of lattice anharmonicity in the structural phase transformation of Laves phase HfV2 alloy: A first-principles investigation

    SciTech Connect

    Krcmar, Maja; Fu, Chong Long

    2013-01-01

    First-principles theory was developed to study the structural phase transformations in the Laves phase HfV2 alloy. We explored the energy landscape and established the role of lattice anharmonicity underlying the structural phase transitions. Our approach is based on a phenomenological Landau theory for the structural phase transition and a mean-field approximation for the free energy. First-principles calculations were utilized to obtain the distortion energy as a function of relevant deformations, and to deduce parameters for constructing the free energy. Our result for the phase transition temperature of HfV2 is in good agreement with experiment. We find that the high-temperature cubic C15 phase is stabilized by the effect of lattice anharmonicity. The theory also predicts an anomalous increase in shear modulus with increasing temperature for systems where the anharmonicity is pronounced.

  10. On linear structure and phase rotation invariant properties of block M-PSK modulation codes

    NASA Technical Reports Server (NTRS)

    Kasami, Tadao; Takata, Toyoo; Fujiwara, Toru; Lin, Shu

    1991-01-01

    Two important structural properties of block M(=2')-ary PSK modulation codes, linear structure and phase symmetry, are investigated. An M-ary modulation code is first represented as a code with symbols from the integer group S(MPSK) = (0,1,2,...M-1) under modulo-M addition. Then the linear structure of block MPSK modulation codes over S(M-PSK) with respect to modulo-M vector addition is defined, and conditions are derived under which a block MPSK modulation code is linear. Once the linear structure is developed, the phase symmetry of block M-PSK modulation codes is studied. In particular, a necessary and sufficient condition for a block MPSK modulation code that is linear as a binary code to be invariant under 2 h 180 deg/M phase rotation (for h = 1 to l) is derived. Finally, a list of short 8PSK and 16PSK modulation codes is given, together with their linear structure and the smallest phase rotation for which a code is invariant.

  11. Mesoscopic simulation of phase behaviors and structures in an amphiphile-solvent system.

    PubMed

    Yamada, Kohtaro; Yasuno, Emiko; Kawabata, Youhei; Okuzono, Tohru; Kato, Tadashi

    2014-06-01

    We have performed a three-dimensional simulation of mesoscopic structures in a mixture of AB amphiphilic molecule and C solvent by employing the density-functional theory under the conditions that (i) the size of the AB is much larger than C and (ii) the affinity between A and B is much larger than the affinity between B and C. First, we have calculated the free energy of five periodic structures, i.e., the lamellar phase, hexagonally packed cylinders, body-centered-cubic spheres, face-centered-cubic spheres, and gyroid phase for different sets of the concentration of AB (ϕ[over ¯]_{AB}) and the χ parameter (χ_{AC}). By comparing the free energies for these structures, the χ_{AC}-ϕ[over ¯]_{AB} phase diagram has been obtained. In addition to these periodic structures, it has been shown that nonperiodic structures such as spherical and rodlike micelles can be obtained although they might be metastable phase. PMID:25019779

  12. Phase Structure and Cyclic Deformation in Eutectic Tin-Lead Alloy: A Numerical Analysis

    SciTech Connect

    FANG,HUEI ELIOT; Li,W; SHEN,Y.-L

    1999-09-09

    This study is devoted to providing a mechanistic rationale of coarsening induced failure in solder alloys during thermomechanical fatigue. Micromechanical modeling of cyclic deformation of eutectic tin-lead alloy was undertaken using the finite element method. The models consist of regularly arranged tin-rich and lead-rich phases, simulating the lamellar array and colony structure in a typical eutectic system. A fine structure and a coarse structure, bearing the same phase fraction but different in the aspect ratio of each lead-rich layer and in the number of lead-rich layers in each colony, are utilized for representing the microstructure before and after coarsening, respectively. Both phases are treated as elastic-plastic solids with their respective properties. For simplicity the creep effect is ignored without compromising the main objective of this study. Cyclic loading under pure shear and uniaxial conditions is modeled. It is found that both the fine and coarse structures exhibit essentially the same macroscopic stress-strain response. The coarse structure, however, shows a greater maximum effective plastic strain on a local scale throughout the deformation. The numerical result implies that, in a solder joint, a locally coarsened region may not be mechanically weaker than its surrounding, but it is subject to early damage initiation due to accumulated plasticity. Other implications regarding solder alloy failure and micromechanical modeling of two-phase materials are discussed.

  13. An integer programming approach to the phase problem for centrosymmetric structures.

    PubMed

    Vaia, Anastasia; Sahinidis, Nikolaos V

    2003-09-01

    The problem addressed in this paper is the determination of three-dimensional structures of centrosymmetric crystals from X-ray diffraction measurements. The 'minimal principle' that a certain quantity is minimized only by the crystal structure is employed to solve the phase problem. The mathematical formulation of the minimal principle is a nonconvex nonlinear optimization problem. To date, local optimization techniques and advanced computer architectures have been used to solve this problem, which may have a very large number of local optima. In this paper, the minimal principle model is reformulated for the case of centrosymmetric structures into an integer programming problem in terms of the missing phases. This formulation is solvable by well established combinatorial optimization techniques that are guaranteed to provide the global optimum in a finite number of steps without explicit enumeration of all possible combinations of phases. Computational experience with the proposed method on a number of structures of moderate complexity is provided and demonstrates that the approach yields a fast and reliable method that resolves the crystallographic phase problem for the case of centrosymmetric structures. PMID:12944609

  14. Structure and phase behavior of a confined nanodroplet composed of the flexible chain molecules.

    PubMed

    Kim, Soon-Chul; Kim, Eun-Young; Seong, Baek-Seok

    2011-04-28

    A polymer density functional theory has been employed for investigating the structure and phase behaviors of the chain polymer, which is modelled as the tangentially connected sphere chain with an attractive interaction, inside the nanosized pores. The excess free energy of the chain polymer has been approximated as the modified fundamental measure-theory for the hard spheres, the Wertheim's first-order perturbation for the chain connectivity, and the mean-field approximation for the van der Waals contribution. For the value of the chemical potential corresponding to a stable liquid phase in the bulk system and a metastable vapor phase, the flexible chain molecules undergo the liquid-vapor transition as the pore size is reduced; the vapor is the stable phase at small volume, whereas the liquid is the stable phase at large volume. The wide liquid-vapor coexistence curve, which explains the wide range of metastable liquid-vapor states, is observed at low temperature. The increase of temperature and decrease of pore size result in a narrowing of liquid-vapor coexistence curves. The increase of chain length leads to a shift of the liquid-vapor coexistence curve towards lower values of chemical potential. The coexistence curves for the confined phase diagram are contained within the corresponding bulk liquid-vapor coexistence curve. The equilibrium capillary phase transition occurs at a higher chemical potential than in the bulk phase. PMID:21528975

  15. Calorimetric, spectroscopic and structural investigations of phase polymorphism in [Ru(NH{sub 3}){sub 6}](BF{sub 4}){sub 3}. Part I

    SciTech Connect

    Dolega, Diana; Mikuli, Edward; Inaba, Akira; Gorska, Natalia; Holderna-Natkaniec, Krystyna; Nitek, Wojciech

    2013-01-15

    Four crystalline phases of the coordination compound [Ru(NH{sub 3}){sub 6}](BF{sub 4}){sub 3} are identified by adiabatic calorimetry. Three phase transitions, one at T{sub C3}(IV{yields}III)=30.7 K, the second at T{sub C2}(III{yields}II)=91.7 K (both accompanied by comparable entropy changes 3.0 and 3.1 J K{sup -1} mol{sup -1}, respectively) and the third at T{sub C1}(II{yields}I)=241.6 K (accompanied by an entropy change of 8.1 J K{sup -1} mol{sup -1}) were discovered. X-ray single crystal diffraction (at 293 K) demonstrates that phase I is a highly dynamic disordered cubic phase (Fm3{sup Macron }m, No. 225) with two types of BF{sub 4}{sup -} anions differing in a degree of disorder. In phase II (at 170 K) the structure remains cubic (Ia3{sup Macron }, No. 206), with two different types of cations and four different types of anions. Splitting of certain IR bands connected with NH{sub 3} ligands at the observed phase transitions suggests a lowering of the symmetry of the [Ru(NH{sub 3}){sub 6}]{sup 3+} complex cation. Both NH{sub 3} ligands and BF{sub 4}{sup -} anions perform fast reorientations ({tau}{sub R} Almost-Equal-To 10{sup -12} s), which are significantly slowed down below the phase transition at T{sub C3}. {sup 1}H NMR studies led to estimate the values of the activation energy of NH{sub 3} ligands reorientation in the phases II and I as equal to {approx}8 kJ mol{sup -1}. In phase I the whole hexammineruthenium(III) cations reorientation as a tumbling process can be noticed. The activation energy value of this motion is {approx}24 kJ mol{sup -1}. {sup 19}F NMR studies give the values of the activation energy of BF{sub 4}{sup -} anions reorientation as {approx}6 kJ mol{sup -1}. Above the phase transition temperature half of BF{sub 4}{sup -} anions perform a tumbling motion with E{sub a} Almost-Equal-To 8 kJ mol{sup -1}. - Graphical abstract: A series of complementary methods, such as Adiabatic Calorimetry, Differential Scanning Calorimetry, Fourier

  16. Crystal Structures of Endotaxic Phases in Europium Potassium Silicate Having a Pellyite Unit Cell

    SciTech Connect

    Rastsvetaeva, R. K. Aksenov, S. M.; Taroev, V. K.

    2010-11-15

    The structures of three phases of the synthesized europium potassium silicate were determined by X-ray diffraction. Two of these phases crystallize in a new structural type. The chemical formulas of the phases were determined. The orthorhombic unit-cell parameters of all three phases are equal: a = 14.852(1) A, b = 15.902(1) A, c = 7.243(1) A, sp. gr. P2{sub 1}2{sub 1}2 (phase I) and sp. gr. Pbam (phases II and III). The structures were solved by direct methods and refined from X-ray diffraction data collected from one crystal to R = 0.0271, 0.0479, and 0.0582 based on 4370, 3320, and 2498 reflections, respectively, with |F| > 3{sigma}(F). The crystal- chemical formulas of the phases (Z = 4) are K{sub 3}Eu{sub 3+}[Si{sub 6}O{sub 15}] . 2H{sub 2}O, K{sub 3}Eu{sup 3+}[Si{sub 6}O{sub 13}(OH){sub 4}] . 2H{sub 2}O, and K{sub 3}Eu{sup 3+}[Si{sub 4}O{sub 9.5}(OH)](OH){sub 2}. 5.5H{sub 2}O. The structure of phase I consists of silicon-oxygen sheets [Si{sub 6}O{sub 15}] analogous to those found in the isostructural compound K{sub 3}Nd[Si{sub 6}O{sub 15}] . 2H{sub 2}O. In the structures of phases II and III, the ribbons [Si{sub 6}O{sub 17}] and [Si{sub 8}O{sub 21}] run along the shortest c axis and are linked together by Eu{sup 3+} octahedra and trigonal prisms to form three-dimensional layered and framework structures containing K atoms between the sheets and in the channels. The fragments are also linked through hydrogen bonds with the participation of OH groups and water molecules.

  17. Pressure-induced structural, electronic, and magnetic phase transitions in FeCl2 studied by x-ray diffraction and resistivity measurements

    NASA Astrophysics Data System (ADS)

    Rozenberg, G. Kh.; Pasternak, M. P.; Gorodetsky, P.; Xu, W. M.; Dubrovinsky, L. S.; Le Bihan, T.; Taylor, R. D.

    2009-06-01

    High-pressure (HP) synchrotron x-ray diffraction (XRD) studies were carried out in FeCl2 (TN≈24K) together with resistivity (R) studies at various temperatures and pressures to 65 GPa using diamond-anvil cells. This work follows a previous HP F57e Mössbauer study in which two pressure-induced (PI) electronic transitions were found interpreted as: (i) quenching of the orbital-term contribution to the hyperfine field concurring with a tilting of the magnetic moment by 55° , and (ii) collapse of the magnetism concurring with a sharp decrease in the isomer shift. The R(P,T) studies affirm that the cause of the collapse of the magnetism is a PI p-d correlation breakdown, leading to an insulator-metal transition at ˜45GPa and is not due to a spin crossover (S=2→S=0) . The structure response to the pressure evolution of the two electronic phase transitions starting at low pressures (LP), through an intermediate phase (IP) 30-57 GPa, and culminating in a high-pressure phase, P>32GPa , can clearly be quantified. The IP-HP phases coexist through the 32-57 GPa range in which the HP abundance increases monotonically at the expense of the IP phase. At the LP-IP interface no volume change is detected, yet the c axis increases and the a axis shrinks by 0.21 and 0.13Å , respectively. The fit of the equation of state of the combined LP-IP phases yields a bulk modulus K0=35.3(1.8)GPa . The intralayer Cl-Cl distances increase but no change is observed in Fe-Cl bond length nor are there substantial changes in the interlayer spacing. The pressure-induced electronic IP-HP transition leads to a first-order structural phase transition characterized by a decrease in Fe-Cl bond length and an abrupt drop in V(P) by ˜3.5% accompanying the correlation breakdown. In this transition no symmetry change is detected and the XRD data could be satisfactorily fitted with the CdI2 structure. The bulk modulus of the HP phase is practically the same as that of the LP-IP phases suggesting

  18. A layered approach to structural control system design for the JPL phase B testbed

    NASA Technical Reports Server (NTRS)

    Chu, Cheng-Chih; O'Brien, John

    1993-01-01

    This paper describes our efforts in structural control experiments for a flexible precision structure using both passive and active control. Specifically, a layered structural control approach utilizing passive viscous dampers, colocated and noncolocated active control is used. The passive dampers and active colocated control loops are used to enhance stability and robustness and the noncolocated multivariable controller is designed with respect to a partially controlled structure to further improve the performance. Our approach to the multivariable design problem requires not only a state space model description of the plant, but also an accompanying uncertainty model. To support the multivariable robust control design development, a significant effort in system identification was undertaken. The process of identification and identified results are discussed. Noncolocated controllers are designed using the H(infinity)/mu-synthesis methodology. The order of the controller is typically large, hence, model reduction is performed for practical digital implementation on a real-time control system developed at JPL. Finally, experimental results are presented and some of lessons are discussed.

  19. Mechanical properties of 15%Mn steel with fine lamellar structure consisting of ferrite and austenite phases

    NASA Astrophysics Data System (ADS)

    Ueji, R.; Okitsu, Y.; Nakamura, T.; Takagi, Y.; Tanaka, Y.

    2010-07-01

    New steel with fine lamellar structure consisting of austenite and ferrite was developed. 15mass%Mn-3%Al-3%Si steel sheet was used in this study. First of all, the effect of the cooling rate on the microstructure was examined. The cooling at the slower speed of 100 deg/hour created the dual phase structure consisting of both austenite and ferrite. The additional rolling developed the fine lamellar duplex structure. Improvement of both the tensile strength and elongation was achieved by rolling. The strength increases furthermore by the rolling up to larger reduction. The 90% rolled sheet shows high tensile strength around 1000MPa with large elongation (15%-20%). These results indicate that the multi-phased structure with controlled lamellar morphology is beneficial for the management of both high strength and large ductility.

  20. Substrate stiffness-modulated registry phase correlations in cardiomyocytes map structural order to coherent beating

    NASA Astrophysics Data System (ADS)

    Dasbiswas, K.; Majkut, S.; Discher, D. E.; Safran, Samuel A.

    2015-01-01

    Recent experiments show that both striation, an indication of the structural registry in muscle fibres, as well as the contractile strains produced by beating cardiac muscle cells can be optimized by substrate stiffness. Here we show theoretically how the substrate rigidity dependence of the registry data can be mapped onto that of the strain measurements. We express the elasticity-mediated structural registry as a phase-order parameter using a statistical physics approach that takes the noise and disorder inherent in biological systems into account. By assuming that structurally registered myofibrils also tend to beat in phase, we explain the observed dependence of both striation and strain measurements of cardiomyocytes on substrate stiffness in a unified manner. The agreement of our ideas with experiment suggests that the correlated beating of heart cells may be limited by the structural order of the myofibrils, which in turn is regulated by their elastic environment.

  1. The effects of bonded interactions on the structural phase properties of flexible elastic homopolymer

    NASA Astrophysics Data System (ADS)

    Qi, Kai; Liewehr, Benjamin; Koci, Tomas; Pattanasiri, Busara; Williams, Matthew; Bachmann, Michael

    By means of advanced parallel-tempering replica-exchange Monte Carlo methods we systematically examine the effects of an asymmetric bond potential between the bonded monomers on the structural formations of an elastic flexible polymer model. Employing microcanonical inflection-point analysis and conformational analysis based on a suitable set of structural order parameters, we identify diverse structural phases in the low-temperature region of the microcanonical hyperphase diagram. In addition to the icosahedral phase occurring if the symmetry of the bonded interaction is broken by strong bonded Lennard-Jones potential, amorphous structures with bihexagonal cores appear for small values of the asymmetry control parameter in the bond potential. Another remarkable feature is the observation of the hierarchy of freezing transitions associated with the formation of the surface layer after nucleation.

  2. Substrate stiffness-modulated registry phase correlations in cardiomyocytes map structural order to coherent beating.

    PubMed

    Dasbiswas, K; Majkut, S; Discher, D E; Safran, Samuel A

    2015-01-01

    Recent experiments show that both striation, an indication of the structural registry in muscle fibres, as well as the contractile strains produced by beating cardiac muscle cells can be optimized by substrate stiffness. Here we show theoretically how the substrate rigidity dependence of the registry data can be mapped onto that of the strain measurements. We express the elasticity-mediated structural registry as a phase-order parameter using a statistical physics approach that takes the noise and disorder inherent in biological systems into account. By assuming that structurally registered myofibrils also tend to beat in phase, we explain the observed dependence of both striation and strain measurements of cardiomyocytes on substrate stiffness in a unified manner. The agreement of our ideas with experiment suggests that the correlated beating of heart cells may be limited by the structural order of the myofibrils, which in turn is regulated by their elastic environment. PMID:25597833

  3. High-Temperature Superconductors as Electromagnetic Deployment and Support Structures in Spacecraft. [NASA NIAC Phase I

    NASA Technical Reports Server (NTRS)

    Getliffe, Gwendolyn V.; Inamdar, Niraj K.; Masterson, Rebecca; Miller, David W.

    2012-01-01

    This report, concluding a one-year NIAC Phase I study, describes a new structural and mechanical technique aimed at reducing the mass and increasing the deployed-to-stowed length and volume ratios of spacecraft systems. This technique uses the magnetic fields generated by electrical current passing through coils of high-temperature superconductors (HTSs) to support spacecraft structures and deploy them to operational configurations from their stowed positions inside a launch vehicle fairing.

  4. Area modulation grating for sinusoidal structure illumination on phase-measuring profilometry.

    PubMed

    Xian, T; Su, X

    2001-03-10

    Sinusoidal structured illumination is used widely in three-dimensional (3-D) sensing and machine vision. Phase algorithms, for example, in phase-measuring profilometry, are inherently free of errors only with perfect sinusoidal fringe projection. But it is difficult to produce a perfect sinusoidal grating. We propose a new concept, area modulation, to improve the sinusoidality of structured illumination. A binary-coded picture is made up of many micrometer units. An aperture is open in every micrometer unit, and its area is determined by the value of the sinusoidal function. When such a grating is projected onto an object surface, the image of the grating becomes sinusoidal because of the convolution function of an optical system. We have designed and manufactured an area modulation grating for sinusoidal structure illumination using a large-scale integration technique. The area modulation grating has been used in the high-precision phase-measuring profilometry system, and the phase errors caused by the area modulation grating are reduced to 0.1%. The grating guaranteed the entire measuring accuracy to a 1% equivalent wavelength. The experimental results proved that area modulation grating would be of significant help in improving the phase-measurement accuracy of the 3-D sensing system. PMID:18357106

  5. Structural phase modification in Cu incorporated nanostructured zinc sulfide thin films

    NASA Astrophysics Data System (ADS)

    Chalana, S. R.; Jolly Bose, R.; Reshmi Krishnan, R.; Kavitha, V. S.; Sreeja Sreedharan, R.; Mahadevan Pillai, V. P.

    2016-08-01

    Cu incorporated zinc sulfide (ZnS) films are prepared by a RF magnetron sputtering technique and the influence of Cu doping concentration on the structural, morphological and optical properties is systematically analyzed using techniques like grazing incidence X-Ray diffraction (GIXRD), micro-Raman spectroscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and UV-vis spectroscopy. XRD examination of the as-prepared films revealed the presence of polycrystalline structure with co-existence of cubic and hexagonal phases in the pure and lower Cu incorporated films. Increase in Cu doping concentration causes a gradual phase transformation from mixed phase to cubic phase. Micro-Raman spectra further confirms the structural phase modifications with the addition of Cu in ZnS. Morphological analysis shows compact distribution of elongated grain geometry with good connectivity and detectable grain boundary in the pure and Cu incorporated films. Increase in Cu incorporation results in the systematic reduction of RMS surface roughness. EDS analysis confirms the incorporation of Cu and surface vacancy defects in the doped films. All the films are transparent in the visible region and band gap calculation by Tauc plot shows that increase in Cu incorporation results in band gap renormalization.

  6. Structural evolution of epitaxial SrCoO{sub x} films near topotactic phase transition

    SciTech Connect

    Jeen, Hyoungjeen; Lee, Ho Nyung

    2015-12-15

    Control of oxygen stoichiometry in complex oxides via topotactic phase transition is an interesting avenue to not only modifying the physical properties, but utilizing in many energy technologies, such as energy storage and catalysts. However, detailed structural evolution in the close proximity of the topotactic phase transition in multivalent oxides has not been much studied. In this work, we used strontium cobaltites (SrCoO{sub x}) epitaxially grown by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven evolution of the structure, electronic, and magnetic properties. We grew coherently strained SrCoO{sub 2.5} thin films and performed post-annealing at various temperatures for topotactic conversion into the perovskite phase (SrCoO{sub 3-δ}). We clearly observed significant changes in electronic transport, magnetism, and microstructure near the critical temperature for the topotactic transformation from the brownmillerite to the perovskite phase. Nevertheless, the overall crystallinity was well maintained without much structural degradation, indicating that topotactic phase control can be a useful tool to control the physical properties repeatedly via redox reactions.

  7. Phase Structure of Strong-Field Tunneling Wave Packets from Molecules

    NASA Astrophysics Data System (ADS)

    Liu, Ming-Ming; Li, Min; Wu, Chengyin; Gong, Qihuang; Staudte, André; Liu, Yunquan

    2016-04-01

    We study the phase structure of the tunneling wave packets from strong-field ionization of molecules and present a molecular quantum-trajectory Monte Carlo model to describe the laser-driven dynamics of photoelectron momentum distributions of molecules. Using our model, we reproduce and explain the alignment-dependent molecular frame photoelectron spectra of strong-field tunneling ionization of N2 reported by M. Meckel et al. [Nat. Phys. 10, 594 (2014)]. In addition to modeling the low-energy photoelectron angular distributions quantitatively, we extract the phase structure of strong-field molecular tunneling wave packets, shedding light on its physical origin. The initial phase of the tunneling wave packets at the tunnel exit depends on both the initial transverse momentum distribution and the molecular internuclear distance. We further show that the ionizing molecular orbital has a critical effect on the initial phase of the tunneling wave packets. The phase structure of the photoelectron wave packet is a key ingredient for modeling strong-field molecular photoelectron holography, high-harmonic generation, and molecular orbital imaging.

  8. Structural evolution of epitaxial SrCoOx films near topotactic phase transition

    SciTech Connect

    Jeen, Hyoung Jeen; Lee, Ho Nyung

    2015-12-18

    Control of oxygen stoichiometry in complex oxides via topotactic phase transition is an interesting avenue to not only modifying the physical properties, but utilizing in many energy technologies, such as energy storage and catalysts. However, detailed structural evolution in the close proximity of the topotactic phase transition in multivalent oxides has not been much studied. In this work, we used strontium cobaltites (SrCoOx) epitaxially grown by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven evolution of the structure, electronic, and magnetic properties. We grew coherently strained SrCoO2.5thin films and performed post-annealing at various temperatures for topotactic conversion into the perovskite phase (SrCoO3-δ). We clearly observed significant changes in electronic transport, magnetism, and microstructure near the critical temperature for the topotactic transformation from the brownmillerite to the perovskite phase. Furthermore, the overall crystallinity was well maintained without much structural degradation, indicating that topotactic phase control can be a useful tool to control the physical properties repeatedly via redox reactions.

  9. Structural evolution of epitaxial SrCoOx films near topotactic phase transition

    DOE PAGESBeta

    Jeen, Hyoung Jeen; Lee, Ho Nyung

    2015-12-18

    Control of oxygen stoichiometry in complex oxides via topotactic phase transition is an interesting avenue to not only modifying the physical properties, but utilizing in many energy technologies, such as energy storage and catalysts. However, detailed structural evolution in the close proximity of the topotactic phase transition in multivalent oxides has not been much studied. In this work, we used strontium cobaltites (SrCoOx) epitaxially grown by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven evolution of the structure, electronic, and magnetic properties. We grew coherently strained SrCoO2.5thin films and performed post-annealing at various temperatures for topotacticmore » conversion into the perovskite phase (SrCoO3-δ). We clearly observed significant changes in electronic transport, magnetism, and microstructure near the critical temperature for the topotactic transformation from the brownmillerite to the perovskite phase. Furthermore, the overall crystallinity was well maintained without much structural degradation, indicating that topotactic phase control can be a useful tool to control the physical properties repeatedly via redox reactions.« less

  10. Mapping strain modulated electronic structure perturbations in mixed phase bismuth ferrite thin films

    SciTech Connect

    Krishnan, P.S. Sanakara R.; Aguiar, Jeffery A.; Ramasse, Q. M.; Kepaptsoglou, D. M.; Liang, W. I.; Chu, Y. H.; Browning, Nigel D.; Munroe, Paul R.; Nagarajan, Valanoor

    2015-01-01

    Strain engineering of epitaxial ferroelectrics has emerged as a powerful method to tailor the electromechanical response of these materials, although the effect of strain at the atomic scale and the interplay between lattice displacements and electronic structure changes are not yet fully understood. Here, using a combination of scanning transmission electron microscopy (STEM) and density functional theory (DFT), we systematically probe the role of epitaxial strain in mixed phase bismuth ferrite thin films. Electron energy loss O K and Fe L2,3 edge spectra acquired across the rhombohedral (R)-tetragonal (T) phase boundary reveal progressive, and systematic changes, in electronic structure going from one phase to the other. The comparison of the acquired spectra, with theoretical simulations using DFT, suggests a breakage in the structural symmetry across the boundary due to the simultaneous presence of increasing epitaxial strain and off- axial symmetry in the T phase. This implies that the imposed epitaxial strain plays a significant role in not only changing the crystal-field geometry, but also the bonding environment surrounding the central iron cation at the interface thus providing new insights and a possible link to understand how the imposed strain could perturb magnetic ordering in the T phase BFO.

  11. Structural evolution of epitaxial SrCoOx films near topotactic phase transition

    NASA Astrophysics Data System (ADS)

    Jeen, Hyoungjeen; Lee, Ho Nyung

    2015-12-01

    Control of oxygen stoichiometry in complex oxides via topotactic phase transition is an interesting avenue to not only modifying the physical properties, but utilizing in many energy technologies, such as energy storage and catalysts. However, detailed structural evolution in the close proximity of the topotactic phase transition in multivalent oxides has not been much studied. In this work, we used strontium cobaltites (SrCoOx) epitaxially grown by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven evolution of the structure, electronic, and magnetic properties. We grew coherently strained SrCoO2.5 thin films and performed post-annealing at various temperatures for topotactic conversion into the perovskite phase (SrCoO3-δ). We clearly observed significant changes in electronic transport, magnetism, and microstructure near the critical temperature for the topotactic transformation from the brownmillerite to the perovskite phase. Nevertheless, the overall crystallinity was well maintained without much structural degradation, indicating that topotactic phase control can be a useful tool to control the physical properties repeatedly via redox reactions.

  12. Phase Structure of Strong-Field Tunneling Wave Packets from Molecules.

    PubMed

    Liu, Ming-Ming; Li, Min; Wu, Chengyin; Gong, Qihuang; Staudte, André; Liu, Yunquan

    2016-04-22

    We study the phase structure of the tunneling wave packets from strong-field ionization of molecules and present a molecular quantum-trajectory Monte Carlo model to describe the laser-driven dynamics of photoelectron momentum distributions of molecules. Using our model, we reproduce and explain the alignment-dependent molecular frame photoelectron spectra of strong-field tunneling ionization of N_{2} reported by M. Meckel et al. [Nat. Phys. 10, 594 (2014)]. In addition to modeling the low-energy photoelectron angular distributions quantitatively, we extract the phase structure of strong-field molecular tunneling wave packets, shedding light on its physical origin. The initial phase of the tunneling wave packets at the tunnel exit depends on both the initial transverse momentum distribution and the molecular internuclear distance. We further show that the ionizing molecular orbital has a critical effect on the initial phase of the tunneling wave packets. The phase structure of the photoelectron wave packet is a key ingredient for modeling strong-field molecular photoelectron holography, high-harmonic generation, and molecular orbital imaging. PMID:27152800

  13. Enhanced power factor via the control of structural phase transition in SnSe

    NASA Astrophysics Data System (ADS)

    Yu, Hulei; Dai, Shuai; Chen, Yue

    2016-05-01

    Tin selenide has attracted much research interest due to its unprecedentedly high thermoelectric figure of merit (ZT). For real applications, it is desirable to increase the ZT value in the lower-temperature range, as the peak ZT value currently exists near the melting point. It is shown in this paper that the structural phase transition plays an important role in boosting the ZT value of SnSe in the lower-temperature range, as the Cmcm phase is found to have a much higher power factor than the Pnma phase. Furthermore, hydrostatic pressure is predicted to be extremely effective in tuning the phase transition temperature based on ab-initio molecular dynamic simulations; a remarkable decrease in the phase transition temperature is found when a hydrostatic pressure is applied. Dynamical stabilities are investigated based on phonon calculations, providing deeper insight into the pressure effects. Accurate band structures are obtained using the modified Becke-Johnson correction, allowing reliable prediction of the electrical transport properties. The effects of hydrostatic pressure on the thermal transport properties are also discussed. Hydrostatic pressure is shown to be efficient in manipulating the transport properties via the control of phase transition temperature in SnSe, paving a new path for enhancing its thermoelectric efficiency.

  14. Phase-Field Methods for Structure Evolution in Sheared Multiphase Systems

    NASA Technical Reports Server (NTRS)

    Badalassi, Vittorio; Ceniceros, Hector; Banerjee, Sanjoy

    2002-01-01

    A homogeneous disordered phase separates into ordered structures when quenched into a broken-symmetry phase. The competition of broken-symmetry phases to select an equilibrium state may be studied in terms of coarse-grained order parameters described by a suitable Landau free-energy function. A network of equilibrium-phase domains develops on quenching and coarsens with time with a topology that may be controlled by shear. We use three-dimensional simulations, in which time-dependent models for conserved-order parameters coupled to Navier-Stokes fluid models are solved, to investigate the evolution of such domains, e.g. spinodal decompositions of polymeric materials under shear. The numerical problems are formidable because of the strong nonlinearities inherent in the coupled model, and these are amongst the first 3D calculations undertaken. In linear shear fields we find stable nanostrings, also recently seen in experiments. The affinity of the ordered phases to boundaries plays a role in the form of the structures that develop, with stacked plate-like phase distributions emerging under certain conditions. Such methods appear quite promising for design and analysis of multiphase and complex fluid formulations. The behavior of foams in such conditions is of particular interest in microgravity environments. Additional information can be found in the original extended abstract.

  15. Enhanced power factor via the control of structural phase transition in SnSe

    PubMed Central

    Yu, Hulei; Dai, Shuai; Chen, Yue

    2016-01-01

    Tin selenide has attracted much research interest due to its unprecedentedly high thermoelectric figure of merit (ZT). For real applications, it is desirable to increase the ZT value in the lower-temperature range, as the peak ZT value currently exists near the melting point. It is shown in this paper that the structural phase transition plays an important role in boosting the ZT value of SnSe in the lower-temperature range, as the Cmcm phase is found to have a much higher power factor than the Pnma phase. Furthermore, hydrostatic pressure is predicted to be extremely effective in tuning the phase transition temperature based on ab-initio molecular dynamic simulations; a remarkable decrease in the phase transition temperature is found when a hydrostatic pressure is applied. Dynamical stabilities are investigated based on phonon calculations, providing deeper insight into the pressure effects. Accurate band structures are obtained using the modified Becke-Johnson correction, allowing reliable prediction of the electrical transport properties. The effects of hydrostatic pressure on the thermal transport properties are also discussed. Hydrostatic pressure is shown to be efficient in manipulating the transport properties via the control of phase transition temperature in SnSe, paving a new path for enhancing its thermoelectric efficiency. PMID:27193260

  16. Enhanced power factor via the control of structural phase transition in SnSe.

    PubMed

    Yu, Hulei; Dai, Shuai; Chen, Yue

    2016-01-01

    Tin selenide has attracted much research interest due to its unprecedentedly high thermoelectric figure of merit (ZT). For real applications, it is desirable to increase the ZT value in the lower-temperature range, as the peak ZT value currently exists near the melting point. It is shown in this paper that the structural phase transition plays an important role in boosting the ZT value of SnSe in the lower-temperature range, as the Cmcm phase is found to have a much higher power factor than the Pnma phase. Furthermore, hydrostatic pressure is predicted to be extremely effective in tuning the phase transition temperature based on ab-initio molecular dynamic simulations; a remarkable decrease in the phase transition temperature is found when a hydrostatic pressure is applied. Dynamical stabilities are investigated based on phonon calculations, providing deeper insight into the pressure effects. Accurate band structures are obtained using the modified Becke-Johnson correction, allowing reliable prediction of the electrical transport properties. The effects of hydrostatic pressure on the thermal transport properties are also discussed. Hydrostatic pressure is shown to be efficient in manipulating the transport properties via the control of phase transition temperature in SnSe, paving a new path for enhancing its thermoelectric efficiency. PMID:27193260

  17. Novel device structure for phase change memory toward low-current operation

    NASA Astrophysics Data System (ADS)

    Kim, Eunha; Kang, Nam Soo; Yang, Hyung-Jun; Sutou, Yuji; Song, Yun-Heub

    2015-09-01

    We present a novel device architecture for low set and reset currents in phase change random access memory (PCRAM). In this structure, the sidewall of phase-change film is contacted with the vertical heating layer. In particular, to realize a small contact area of under 50 nm2 for low reset current, this structure includes stacked layers consisting of extremely thin phase change material (PCM) and conduction films, the fabrication method of which is proposed. We estimated set and reset currents for the proposed structure by the device simulation method. Here, we confirmed that a contact area of 30 nm2 in this structure, where Ge2Sb2Te5 is used as PCM, provides a reset current of 13.5 µA and a set current of 4 µA, which are promising for the scaling down of PCM. Furthermore, it is confirmed that the thinner PCM in this structure provides less thermal disturbance to the neighboring cell. From the results, we expect this structure to be a promising candidate for a high-density nonvolatile memory architecture with PCM.

  18. Crystal lattice and band structure of the intermediate high-pressure phase of PbSe.

    PubMed

    Streltsov, S V; Manakov, A Yu; Vokhmyanin, A P; Ovsyannikov, S V; Shchennikov, V V

    2009-09-23

    In the present paper the results of fitting synchrotron diffraction data are obtained for the intermediate high-pressure phase (9.5 GPa) of the lead selenide based compound Pb(1-x)Sn(x)Se (x = 0.125)-an optoelectronic as well as a thermoelectric material-for two types of lattice symmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parameters and positions of atoms for the above mentioned structures have been used in calculations of the electron structure of high-pressure phases. The main difference between the electronic properties for Cmcm and Pnma structures established in electronic structure calculations is that in the first one the PbSe compound was found to be a metal, while in the second a small semiconductor gap (E(G) = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitude larger than those calculated for the Pnma lattice. In the optimized, Pnma structure within a generalized gradient approximation (GGA), the band gap increases up to E(G) = 0.27 eV. The result coincides with the data on thermoelectric power and electrical resistance data pointing to a semiconductor gap of ∼0.2 eV at ∼9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediate phase compared with the Cmcm one. PMID:21832372

  19. Transient Structures and Possible Limits of Data Recording in Phase-Change Materials.

    PubMed

    Hu, Jianbo; Vanacore, Giovanni M; Yang, Zhe; Miao, Xiangshui; Zewail, Ahmed H

    2015-07-28

    Phase-change materials (PCMs) represent the leading candidates for universal data storage devices, which exploit the large difference in the physical properties of their transitional lattice structures. On a nanoscale, it is fundamental to determine their performance, which is ultimately controlled by the speed limit of transformation among the different structures involved. Here, we report observation with atomic-scale resolution of transient structures of nanofilms of crystalline germanium telluride, a prototypical PCM, using ultrafast electron crystallography. A nonthermal transformation from the initial rhombohedral phase to the cubic structure was found to occur in 12 ps. On a much longer time scale, hundreds of picoseconds, equilibrium heating of the nanofilm is reached, driving the system toward amorphization, provided that high excitation energy is invoked. These results elucidate the elementary steps defining the structural pathway in the transformation of crystalline-to-amorphous phase transitions and describe the essential atomic motions involved when driven by an ultrafast excitation. The establishment of the time scales of the different transient structures, as reported here, permits determination of the possible limit of performance, which is crucial for high-speed recording applications of PCMs. PMID:26035229

  20. Increased spatial variance accompanies reorganization of two continental shelf ecosystems.

    PubMed

    Litzow, Michael A; Urban, J Daniel; Laurel, Benjamin J

    2008-09-01

    Phase transitions between alternate stable states in marine ecosystems lead to disruptive changes in ecosystem services, especially fisheries productivity. We used trawl survey data spanning phase transitions in the North Pacific (Gulf of Alaska) and the North Atlantic (Scotian Shelf) to test for increases in ecosystem variability that might provide early warning of such transitions. In both time series, elevated spatial variability in a measure of community composition (ratio of cod [Gadus sp.] abundance to prey abundance) accompanied transitions between ecosystem states, and variability was negatively correlated with distance from the ecosystem transition point. In the Gulf of Alaska, where the phase transition was apparently the result of a sudden perturbation (climate regime shift), variance increased one year before the transition in mean state occurred. On the Scotian Shelf, where ecosystem reorganization was the result of persistent overfishing, a significant increase in variance occurred three years before the transition in mean state was detected. However, we could not reject the alternate explanation that increased variance may also have simply been inherent to the final stable state in that ecosystem. Increased variance has been previously observed around transition points in models, but rarely in real ecosystems, and our results demonstrate the possible management value in tracking the variance of key parameters in exploited ecosystems. PMID:18767612

  1. Liquid-Gas Relative Permeabilities in Fractures: Effects of Flow Structures, Phase Transformation and Surface Roughness

    SciTech Connect

    Chih-Ying Chen

    2005-06-30

    Two-phase flow through fractured media is important in petroleum, geothermal, and environmental applications. However, the actual physics and phenomena that occur inside fractures are poorly understood, and oversimplified relative permeability curves are commonly used in fractured reservoir simulations. In this work, an experimental apparatus equipped with a high-speed data acquisition system, real-time visualization, and automated image processing technology was constructed to study three transparent analog fractures with distinct surface roughnesses: smooth, homogeneously rough, and randomly rough. Air-water relative permeability measurements obtained in this study were compared with models suggested by earlier studies and analyzed by examining the flow structures. A method to evaluate the tortuosities induced by the blocking phase, namely the channel tortuosity, was proposed from observations of the flow structure images. The relationship between the coefficients of channel tortuosity and the relative permeabilities was studied with the aid of laboratory experiments and visualizations. Experimental data from these fractures were used to develop a broad approach for modeling two-phase flow behavior based on the flow structures. Finally, a general model deduced from these data was proposed to describe two-phase relative permeabilities in both smooth and rough fractures. For the theoretical analysis of liquid-vapor relative permeabilities, accounting for phase transformations, the inviscid bubble train models coupled with relative permeability concepts were developed. The phase transformation effects were evaluated by accounting for the molecular transport through liquid-vapor interfaces. For the steam water relative permeabilities, we conducted steam-water flow experiments in the same fractures as used for air-water experiments. We compared the flow behavior and relative permeability differences between two-phase flow with and without phase transformation effects

  2. The structural phase transitions of aminoguanidinium(1+) dihydrogen phosphate-study of crystal structures, vibrational spectra and thermal behavior

    SciTech Connect

    Nemec, Ivan . E-mail: agnemec@natur.cuni.cz; Machackova, Zorka; Teubner, Karel; Cisarova, Ivana; Vanek, Premysl; Micka, Zdenek

    2004-12-01

    Aminoguanidinium(1+) dihydrogen phosphate was prepared by crystallization from aqueous solution. On the basis of the results of DSC measurements, X-ray structural analysis was carried out at temperatures of 160, 215 and 293K for three aminoguanidinium(1+) dihydrogen phosphate phases (vertical bar >222K vertical bar P1-bar (2) vertical bar Z=2 vertical bar non-ferroic vertical bar melting point 408K; II vertical bar 201-222K vertical bar P1-bar (2) vertical bar Z=2 vertical bar non-ferroic vertical bar-; III vertical bar <201K vertical bar P1-bar (2) vertical bar Z=4 vertical bar non-ferroic vertical bar-). The triclinic unit cell dimensions (a=6.8220(2), b=7.1000(2), c=7.4500(2)A, {alpha}=86.925(2){sup o}, {beta}=80.731(2){sup o}, {gamma}=79.630(2){sup o}, V=350.21(2)A{sup 3}-phase I) are similar for all three structural phases with the exception of phase III, where doubling of the c-axis length leads to an increase in the volume to 692.34(3)A{sup 3}. The crystal structure of all three modifications consists of parallel layers of dihydrogen phosphate anions that are interconnected by aminoguanidinium(1+) cations through hydrogen bonds of the N-H...O type. The planar aminoguanidinium(1+) cations are oriented almost parallel to each other and are perpendicular to the anion layers. The primary differences amongst phases I, II and III lie in the location of the H atom in the short O-H...O bonds connecting the dihydrogen phosphate anions in layers. The FTIR and FT Raman spectra of natural and deuterated compounds were recorded and interpreted. The FTIR spectra were studied down to a temperature of 90K.

  3. Mechanical Surface Waves Accompany Action Potential Propagation

    NASA Astrophysics Data System (ADS)

    Machta, Benjamin; El Hady, Ahmed

    2015-03-01

    The action potential (AP) is the basic mechanism by which information is transmitted along neuronal axons. Although the excitable nature of axons is understood to be primarily electrical, many experimental studies have shown that a mechanical displacement of the axonal membrane co-propagates with the electrical signal. While the experimental evidence for co-propagating mechanical waves is diverse and compelling, there is no consensus for their physical underpinnings. We present a model in which these mechanical displacements arise from the driving of mechanical surface waves, in which potential energy is stored in elastic deformations of the neuronal membrane and cytoskeleton while kinetic energy is stored in the movement of the axoplasmic fluid. In our model these surface waves are driven by the traveling wave of electrical depolarization that characterizes the AP, altering the electrostatic forces across the membrane as it passes. Our model allows us to predict the shape of the displacement that should accompany any traveling wave of voltage, including the well-characterized AP. We expect our model to serve as a framework for understanding the physical origins and possible functional roles of these AWs in neurobiology. See Arxiv/1407.7600

  4. Prediction of structural and metal-to-semiconductor phase transitions in nanoscale MoS2, WS2, and other transition metal dichalcogenide zigzag ribbons

    NASA Astrophysics Data System (ADS)

    Güller, F.; Llois, A. M.; Goniakowski, J.; Noguera, C.

    2015-02-01

    While MoS2 and WS2 nanostructures gain an increasing importance in a number of recent technological applications, the control of their structure as a function of their size and their environment appears of prominent importance. In the present study which relies on first-principles simulations, we predict the dimerized 1T ' structural phase to be the actual ground state of MoS2, WS2, and MoSe2 zigzag nanoribbons of small width and monolayer thickness. We assign this result to the competition between edge energy—which favors the nonpolar 1T ' edges over the polar 1H edges—and the energy of atoms in the center of the ribbons—which favors the 1H ground state of the infinite monolayers. A metal-to-semiconductor transition accompanies the structural transition. At variance, ZrS2 zigzag ribbons are predicted to display the 1T structure whatever their width. In compounds of major technological importance, such structural and electronic flexibility associated with polarity effects opens the possibility for controlling the ribbon type during synthesis.

  5. Merwinite-structured phases as a potential host of alkalis in the upper mantle

    NASA Astrophysics Data System (ADS)

    Bindi, Luca; Safonov, Oleg G.; Zedgenizov, Dmitriy A.

    2015-08-01

    Two previously unknown Na- and K-rich phases were synthesized near the solidus of the model CMAS lherzolite interacted with the CaCO3 + Na2CO3 + KCl melt at 7 GPa. They coexist with forsterite, garnet and chloride-carbonate melt. Stoichiometry and unit-cell parameters measured by means of powder diffraction indicate that one of the phases corresponds to (K,Na)2Ca4Mg2Si4O15 (with about 0.1 a.p.f.u. Al). Although single-crystal X-ray measurements of this phase did not allow the solution of the crystal structure, we suggest that the structure of this phase includes mixed SiO4 and Si2O7 units. Single-crystal diffraction experiments of the other alkali-rich phase with composition (Ca2.06Na0.86K0.08)Σ=3.00(Mg0.53Si0.45Al0.03)Σ=1.01Si2.00O8 showed that it exhibits the merwinite structure, space group P21/ a, with lattice parameters a = 12.987(2), b = 5.101(1), c = 9.130(2) Å, β = 92.36(1)°, V = 604.3(2) Å3, and Z = 4. The structure was refined to R 1 = 0.031 using 2619 independent reflections. In the structure, Na is hosted at the large Ca sites, whereas Si replaces Mg at the octahedral site and occurs in the usual tetrahedral coordination. Ordering-induced distortion provokes a change in coordination of the (Ca, Na) atoms with respect to pure merwinite. Merwinite phases with lower K + Na contents (0.08-0.18 a.p.f.u.) coexist with forsterite, clinopyroxene and immiscible carbonate-chloride and silicate melts at higher temperatures (up to 1510 °C) at 7 and 5.5 GPa. These phases (including alkali-rich ones at solidus) show a general formula [Ca3-2 x (Na,K)2 x ][Mg1- x Si x ]Si2O8 (with x up to 0.45), where the Na + K content negatively correlates with Ca and positively correlates with Si. The present experimental and crystal-chemical data prove that merwinite-structured phases may be efficient hosts for alkalis in the upper mantle. They are mineralogical indicators of either the interaction of mantle peridotites with alkaline carbonatitic liquids or high

  6. Pressure-Induced Phase Transition in Hydrogen-Bonded Supramolecular Structure: Guanidinium Nitrate

    SciTech Connect

    Wang, Run; Li, Shourui; Wang, Kai; Duan, Defang; Tang, Lingyun; Cui, Tian; Liu, Bingbing; Cui, Qiliang; Liu, Jing; Zou, Bo; Zou, Guangtian

    2010-08-04

    In situ Raman scattering and synchrotron X-ray diffraction have been used to investigate the effects of high pressure on the structural stability of guanidinium nitrate (C(NH{sub 2}){sub 3}{sup +} {center_dot} NO{sub 3}{sup -}, GN), a representative two-dimensional supramolecular architecture of hydrogen-bonded rosette network. This study has confirmed a structural phase transition observed by Raman scattering and X-ray diffraction at {approx}1 GPa and identified it as a space group change from C2 to P2{sub 1}. The high-pressure phase remained stable up to 22 GPa. We discussed the pressure-induced changes in N-H stretching vibration in Raman spectra and proposed that this phase transition is due to the rearrangements of the hydrogen-bonding networks.

  7. Novel phases of lithium-aluminum binaries from first-principles structural search

    NASA Astrophysics Data System (ADS)

    Sarmiento-Pérez, Rafael; Cerqueira, Tiago F. T.; Valencia-Jaime, Irais; Amsler, Maximilian; Goedecker, Stefan; Romero, Aldo H.; Botti, Silvana; Marques, Miguel A. L.

    2015-01-01

    Intermetallic Li-Al compounds are on the one hand key materials for light-weight engineering, and on the other hand, they have been proposed for high-capacity electrodes for Li batteries. We determine from first-principles the phase diagram of Li-Al binary crystals using the minima hopping structural prediction method. Beside reproducing the experimentally reported phases (LiAl, Li3Al2, Li9Al4, LiAl3, and Li2Al), we unveil a structural variety larger than expected by discovering six unreported binary phases likely to be thermodynamically stable. Finally, we discuss the behavior of the elastic constants and of the electric potential profile of all Li-Al stable compounds as a function of their stoichiometry.

  8. Novel phases of lithium-aluminum binaries from first-principles structural search

    SciTech Connect

    Sarmiento-Pérez, Rafael; Cerqueira, Tiago F. T.; Botti, Silvana; Marques, Miguel A. L.; Valencia-Jaime, Irais; Amsler, Maximilian; Goedecker, Stefan; Romero, Aldo H.

    2015-01-14

    Intermetallic Li–Al compounds are on the one hand key materials for light-weight engineering, and on the other hand, they have been proposed for high-capacity electrodes for Li batteries. We determine from first-principles the phase diagram of Li–Al binary crystals using the minima hopping structural prediction method. Beside reproducing the experimentally reported phases (LiAl, Li{sub 3}Al{sub 2}, Li{sub 9}Al{sub 4}, LiAl{sub 3}, and Li{sub 2}Al), we unveil a structural variety larger than expected by discovering six unreported binary phases likely to be thermodynamically stable. Finally, we discuss the behavior of the elastic constants and of the electric potential profile of all Li–Al stable compounds as a function of their stoichiometry.

  9. Escherichia coli MltA: MAD phasing and refinement of a tetartohedrally twinned protein crystal structure.

    PubMed

    Barends, Thomas R M; de Jong, René M; van Straaten, Karin E; Thunnissen, Andy Mark W H; Dijkstra, Bauke W

    2005-05-01

    Crystals were grown of a mutant form of the bacterial cell-wall maintenance protein MltA that diffracted to 2.15 A resolution. When phasing with molecular replacement using the native structure failed, selenium MAD was used to obtain initial phases. However, after MAD phasing the crystals were found to be tetartohedrally twinned, hampering correct space-group determination and refinement. A refinement protocol was designed to take tetartohedral twinning into account and was successfully applied to refine the structure. The refinement protocol is described and the reasons for the failure of molecular replacement and the success of MAD are discussed in terms of the effects of the tetartohedral twinning. PMID:15858272

  10. Simplified Aerodynamic and Structural Modeling for Oblique All-Wing Aircraft. Phase 2: Structures

    NASA Technical Reports Server (NTRS)

    Kroo, Ilan (Principal Investigator)

    1994-01-01

    Any aircraft preliminary design study requires a structural model of the proposed configuration. The model must be capable of estimating the structural weight of a given configuration, and of predicting the deflections which will result from foreseen flight and ground loads. The present work develops such a model for the proposed Oblique All Wing airplane. The model is based on preliminary structural work done by Jack Williams and Peter Rudolph at Mdng, and is encoded in a FORTRAN program. As a stand-alone application, the program can calculate the weight CG location, and several types of structural deflections; used in conjunction with an aerodynamics model, the program can be used for mission analysis or sizing studies.

  11. Phase-field crystal model for a diamond-cubic structure.

    PubMed

    Chan, V W L; Pisutha-Arnond, N; Thornton, K

    2015-05-01

    We present a structural phase-field crystal model [M. Greenwood et al., Phys. Rev. Lett. 105, 045702 (2010)] that yields a stable dc structure. The stabilization of a dc structure is accomplished by constructing a two-body direct correlation function (DCF) approximated by a combination of two Gaussian functions in Fourier space. A phase diagram containing a dc-liquid phase coexistence region is calculated for this model. We examine the energies of solid-liquid interfaces with normals along the [100], [110], and [111] directions. The dependence of the interfacial energy on a temperature parameter, which controls the heights of the peaks in the two-body DCF, is described by a Gaussian function. Furthermore, the dependence of the interfacial energy on the peak widths of the two-body DCF, which controls the excess energy associated with interfaces, defects, and strain, is described by an inverse power law. These relationships can be used to parametrize the phase-field crystal model for the dc structure to match solid-liquid interfacial energies to those measured experimentally or calculated from atomistic simulations. PMID:26066277

  12. Diagnostic efficiency of Mueller-matrix polarization reconstruction system of the phase structure of liver tissue

    NASA Astrophysics Data System (ADS)

    Zabolotna, Natalia I.; Pavlov, Sergii V.; Radchenko, Kostiantyn O.; Stasenko, Vladyslav A.; Wójcik, Waldemar; Kussambayeva, Nazym

    2015-12-01

    The application field of using the Mueller-matrix polarizing reconstruction system of phase structure of biological layer for optical-anisotropic parameters differentiation of histological sections of healthy and rat's liver with hepatitis were investigated. Comparison of system informativity with known systems on indexes of sensitivity, specificity and balanced accuracy were performed.

  13. Phase matching in second-harmonic generation using artificial periodic structures.

    NASA Technical Reports Server (NTRS)

    Tang, C. L.; Bey, P. P.

    1973-01-01

    The use of artificial periodic structures, consisting of spatial modulations of the linear and nonlinear susceptibilities of a nonlinear optical medium, to achieve phase matching in second-harmonic generation is analyzed. Dispersion relations and approximate formulas for the second-harmonic fields generated under various conditions are obtained and used to evaluate the experimental situation.

  14. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating

    PubMed Central

    Li, Yao; Duerloo, Karel-Alexander N.; Wauson, Kerry; Reed, Evan J.

    2016-01-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for MoxW1−xTe2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices. PMID:26868916

  15. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating.

    PubMed

    Li, Yao; Duerloo, Karel-Alexander N; Wauson, Kerry; Reed, Evan J

    2016-01-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for Mo(x)W(1-x)Te2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices. PMID:26868916

  16. Electronic structure, phase transition, and elastic properties of ScC under high pressure

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Xin; Zhu, Jun; Hao, Yan-Jun; Li, Zi-Yuan; Chen, Long-Qing; Ji, Guang-Fu

    2015-12-01

    The structural properties and the phase transition for scandium carbide (ScC) have been studied in NaCl (B1), CsCl (B2), ZB (B3), WZ (B4), NiAs (B81), WC (B h ), and Pmmn structures by using the pseudopotential plane-wave method in the framework of the density functional theory. Our theoretical results show that the most stable structure is the B1 phase, contrary to the result of Rahim et al. The phase transitions B1 → Pmmn and Pmmn → B2 are predicted at 83.7 and 109.7 GPa, respectively. At the same time, we find that the B3, B4, B81, and B h phases are not stable over the whole pressure range considered. In particular, the elastic constants of Pmmn-ScC under high pressure are obtained successfully. The effects of pressure on the elastic properties of B1-ScC and Pmmn-ScC are also predicted. The Debye temperatures Θ and the sound velocities of these two structures are estimated from the elastic constants, and by analyzing G/ B, the brittle-ductile behavior of ScC is assessed. In addition, the density of states of B1-ScC at high pressures is also discussed.

  17. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating

    NASA Astrophysics Data System (ADS)

    Li, Yao; Duerloo, Karel-Alexander N.; Wauson, Kerry; Reed, Evan J.

    2016-02-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for MoxW1-xTe2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices.

  18. Exploiting the Burkholderia pseudomallei acute phase antigen BPSL2765 for structure-based epitope discovery/design in structural vaccinology.

    PubMed

    Gourlay, Louise J; Peri, Claudio; Ferrer-Navarro, Mario; Conchillo-Solé, Oscar; Gori, Alessandro; Rinchai, Darawan; Thomas, Rachael J; Champion, Olivia L; Michell, Stephen L; Kewcharoenwong, Chidchamai; Nithichanon, Arnone; Lassaux, Patricia; Perletti, Lucia; Longhi, Renato; Lertmemongkolchai, Ganjana; Titball, Richard W; Daura, Xavier; Colombo, Giorgio; Bolognesi, Martino

    2013-09-19

    We solved the crystal structure of Burkholderia pseudomallei acute phase antigen BPSL2765 in the context of a structural vaccinology study, in the area of melioidosis vaccine development. Based on the structure, we applied a recently developed method for epitope design that combines computational epitope predictions with in vitro mapping experiments and successfully identified a consensus sequence within the antigen that, when engineered as a synthetic peptide, was selectively immunorecognized to the same extent as the recombinant protein in sera from melioidosis-affected subjects. Antibodies raised against the consensus peptide were successfully tested in opsonization bacterial killing experiments and antibody-dependent agglutination tests of B. pseudomallei. Our strategy represents a step in the development of immunodiagnostics, in the production of specific antibodies and in the optimization of antigens for vaccine development, starting from structural and physicochemical principles. PMID:23993463

  19. Electronic and structural phase transitions induced by uniaxial strains in monolayer SnSe

    NASA Astrophysics Data System (ADS)

    Wu, Yabei; Gao, Weiwei; Zhang, Peihong; Ren, Wei

    Two dimensional (2D) materials have attracted unprecedented research interest owing to their unique properties that are suitable for various applications. Recent research has started to explore 2D materials beyond graphene; examples include transition metal dichalcogenides and black phosphorus. Bulk SnSe is a layered semiconductor which exists in two phases. The low temperature Pnma phase has an indirect band gap of 0.89 eV and a direct band gap of 1.3 eV, while the high temperature Cmcm phase is stabilized at T >800 K. In this talk, we will present first-principles investigations of the effects of strains on the electronic and structural properties of SnSe. We find that uniaxial strains are an effective means to tune the properties single layer SnSe, and may also induce phase transitions in this system.

  20. Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2.

    PubMed

    He, Hai; Lu, Pengfei; Wu, Liyuan; Zhang, Chunfang; Song, Yuxin; Guan, Pengfei; Wang, Shumin

    2016-12-01

    First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries. PMID:27416903

  1. Surface based cardiac and respiratory motion extraction for pulmonary structures from multi-phase CT

    NASA Astrophysics Data System (ADS)

    von Berg, Jens; Barschdorf, Hans; Blaffert, Thomas; Kabus, Sven; Lorenz, Cristian

    2007-03-01

    During medical imaging and therapeutic interventions, pulmonary structures are in general subject to cardiac and respiratory motion. This motion leads potentially to artefacts and blurring in the resulting image material and to uncertainties during interventions. This paper presents a new automatic approach for surface based motion tracking of pulmonary structures and reports on the results for cardiac and respiratory induced motion. The method applies an active shape approach to ad-hoc generated surface representations of the pulmonary structures for phase to phase surface tracking. Input of the method are multi-phase CT data, either cardiac or respiratory gated. The iso-surface representing the transition between air or lung parenchyma to soft tissue, is triangulated for a selected phase p 0. An active shape procedure is initialised in the image of phase p I using the generated surface in p 0. The used internal energy term penalizes shape deformation as compared to p 0. The process is iterated for all phases p i to p i+1 of the complete cycle. Since the mesh topology is the same for all phases, the vertices of the triangular mesh can be treated as pseudo-landmarks defining tissue trajectories. A dense motion field is interpolated. The motion field was especially designed to estimate the error margins for radiotherapy. In the case of respiratory motion extraction, a validation on ten biphasic thorax CT images (2.5mm slice distance) was performed with expert landmarks placed at vessel bifurcations. The mean error on landmark position was below 2.6mm. We further applied the method to ECG gated images and estimated the influence of the heart beat on lung tissue displacement.

  2. Phase Behavior and Nanoscale Structure of Phospholipid Membranes Incorporated with Acylated C14-Peptides

    PubMed Central

    Pedersen, Tina B.; Kaasgaard, Thomas; Jensen, Morten Ø.; Frokjaer, Sven; Mouritsen, Ole G.; Jørgensen, Kent

    2005-01-01

    The thermotropic phase behavior and lateral structure of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers containing an acylated peptide has been characterized by differential scanning calorimetry (DSC) on vesicles and atomic force microscopy (AFM) on mica-supported bilayers. The acylated peptide, which is a synthetic decapeptide N-terminally linked to a C14 acyl chain (C14-peptide), is incorporated into DPPC bilayers in amounts ranging from 0–20 mol %. The calorimetric scans of the two-component system demonstrate a distinct influence of the C14-peptide on the lipid bilayer thermodynamics. This is manifested as a concentration-dependent downshift of both the main phase transition and the pretransition. In addition, the main phase transition peak is significantly broadened, indicating phase coexistence. In the AFM imaging scans we found that the C14-peptide, when added to supported gel phase DPPC bilayers, inserts preferentially into preexisting defect regions and has a noticeable influence on the organization of the surrounding lipids. The presence of the C14-peptide gives rise to a laterally heterogeneous bilayer structure with coexisting lipid domains characterized by a 10 Å height difference. The AFM images also show that the appearance of the ripple phase of the DPPC lipid bilayers is unaffected by the C14-peptide. The experimental results are supported by molecular dynamics simulations, which show that the C14-peptide has a disordering effect on the lipid acyl chains and causes a lateral expansion of the lipid bilayer. These effects are most pronounced for gel-like bilayer structures and support the observed downshift in the phase-transition temperature. Moreover, the molecular dynamics data indicate a tendency of a tryptophan residue in the peptide sequence to position itself in the bilayer headgroup region. PMID:16100273

  3. Structural Phase Transitions in AuIn2 at High Pressure

    NASA Astrophysics Data System (ADS)

    Clark, S. M.; Speziale, S.; Voltolini, M.; Godwal, B. K.; Jeanloz, R.

    2007-12-01

    The intermetallic compound AuIn2 provides an analog for the high-pressure phases of SiO2, as it is initially in the Fm3m fluorite (CaF2) structure. Synchrotron-based angular-dispersive x-ray diffraction (Advanced Light Source beamline 12.2.2) reveals subtle anomalies in the pressure variation of normalized stress (F) versus Eulerian strain (f) around 3 GPa, coinciding with anomalies observed in fusion, transport and optical data, and potentially associated with the onset of an electronic phase transition. Our diamond-cell experiments (gasketted sample with methanol-ethanol pressure medium) show continuous broadening of diffraction peaks beyond 12 GPa, leading to amorphization near 24 GPa. On further increase of pressure, a crystalline phase appears around 28 GPa and persists upon unloading from 30 GPa to about 5 GPa, then reverting back to the original CaF2 phase. We find the sequence of pressure-induced phase transition documented for CaF2 (fluorite structure Fm3m - PbCl2 Pnma - Ni2In-type P63/mmc and a combination of PbCl2 and Ni2In) to be inadequate in fitting the observed high-pressure diffraction patterns of AuIn2. However, the post-cotunnite structure of PbCl2, BaCl2, BaBr2 and SnCl2 (P1121/c, Z=8) is able to account for most of the prominent peaks in our high-pressure diffraction patterns (a=10.983, b=9.875, c=4.350, À=96.6). Many oxides of geophysical interest occur in the CaF2 structure, and study of intermetallic compounds such as AuIn2 may prove useful in suggesting high-pressure metallic phases for these oxides.

  4. ALCHEMI of NbCr{sub 2}/V C15-structured Laves phase

    SciTech Connect

    Kotula, P.G.; Chu, F.; Mitchell, T.E.; Anderson, I.M.; Bentley, J.

    1996-05-01

    Laves-phase intermetallics are of potential interest for use as high temperature structural materials, of which NbCr{sub 2}-based C15- structured Laves phases are particularly attractive. Vanadium-alloyed NbCr{sub 2} Laves phases have been studies. The defect mechanism of a ternary Laves phase is crucial to understanding its physical metallurgy and deformation behavior. It is suggested based on the Nb- Cr-V phase diagram and first-principles total energy and electronic structure calculations for NbCr{sub 2} that V should occupy the B sites in C15-structured AB{sub 2}. In this paper, ALCHEMI is employed to examine this assumption for one composition of a V- alloyed NbCr{sub 2} C15 Laves phase. A Nb-Cr-V alloy of composition Nb{sub 33}Cr{sub 42}V{sub 25} was prepared by arc-melting followed by annealing at 1400{degrees}C for 120 h. Specimens were prepared for microanalysis by cutting 3 mm discs followed by dimpling and ion milling. Energy-dispersive X-ray (EDX) spectra were acquired with a Philips CM30 operating at 300 kV and equipped with a Kevex Quantum detector. Fourteen spectra were collected near <014> over a range of [400] excitations between symmetry and beyond [12 0 0]. Owing to the high accelerating voltage (and therefore relatively flat Ewald sphere) used for these experiments, it was difficult to eliminate non- systematic reflections, although attempts were made to minimize this effect. Spectra were also acquired with a Philips CM12 operating at 120 kV and equipped with an EDAX superUTW detector. Nine spectra were collected near <334> over a range of [440] excitations between symmetry and [880]. Site-distributions were extracted from the data by multivariate statistical analysis (MSA) with delocalization correction as described elsewhere.

  5. High pressure structural phase transitions of TiO2 nanomaterials

    NASA Astrophysics Data System (ADS)

    Quan-Jun, Li; Bing-Bing, Liu

    2016-07-01

    Recently, the high pressure study on the TiO2 nanomaterials has attracted considerable attention due to the typical crystal structure and the fascinating properties of TiO2 with nanoscale sizes. In this paper, we briefly review the recent progress in the high pressure phase transitions of TiO2 nanomaterials. We discuss the size effects and morphology effects on the high pressure phase transitions of TiO2 nanomaterials with different particle sizes, morphologies, and microstructures. Several typical pressure-induced structural phase transitions in TiO2 nanomaterials are presented, including size-dependent phase transition selectivity in nanoparticles, morphology-tuned phase transition in nanowires, nanosheets, and nanoporous materials, and pressure-induced amorphization (PIA) and polyamorphism in ultrafine nanoparticles and TiO2-B nanoribbons. Various TiO2 nanostructural materials with high pressure structures are prepared successfully by high pressure treatment of the corresponding crystal nanomaterials, such as amorphous TiO2 nanoribbons, α-PbO2-type TiO2 nanowires, nanosheets, and nanoporous materials. These studies suggest that the high pressure phase transitions of TiO2 nanomaterials depend on the nanosize, morphology, interface energy, and microstructure. The diversity of high pressure behaviors of TiO2 nanomaterials provides a new insight into the properties of nanomaterials, and paves a way for preparing new nanomaterials with novel high pressure structures and properties for various applications. Project supported by the National Basic Research Program of China (Grant No. 2011CB808200), the National Natural Science Foundation of China (Grant Nos. 11374120, 11004075, 10979001, 51025206, 51032001, and 21073071), and the Cheung Kong Scholars Programme of China.

  6. VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

    SciTech Connect

    Rao Popuri, Srinivasa; Artemenko, Alla; Labrugere, Christine; Miclau, Marinela; Villesuzanne, Antoine; Pollet, Michaël

    2014-05-01

    Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.

  7. Formation mechanism of primary phases and eutectic structures within undercooled Pb-Sb-Sn ternary alloys

    NASA Astrophysics Data System (ADS)

    Wang, Weili; Dai, Fuping; Wei, Bingbo

    2007-08-01

    The solidification characteristics of three types of Pb-Sb-Sn ternary alloys with different primary phases were studied under substantial undercooling conditions. The experimental results show that primary (Pb) and SbSn phases grow in the dendritic mode, whereas primary (Sb) phase exhibits faceted growth in the form of polygonal blocks and long strips. (Pb) solid solution phase displays strong affinity with SbSn intermetallic compound so that they produce various morphologies of pseudobinary eutectics, but it can only grow in the divorced eutectic mode together with (Sb) phase. Although (Sb) solid solution phase and SbSn intermetallic compound may grow cooperatively within ternary eutectic microstructures, they seldom form pseudobinary eutectics independently. The (Pb)+(Sb)+SbSn ternary eutectic structure usually shows lamellar morphology, but appears as anomalous eutectic when its volume fraction becomes small. EDS analyses reveal that all of the three primary (Pb), (Sb) and SbSn phases exhibit conspicuous solute trapping effect during rapid solidification, which results in the remarkable extension of solute solubility.

  8. A novel benzoxazine/cyanate ester blend with sea-island phase structures.

    PubMed

    Li, Xiaodan; Luo, Xiaoyong; Gu, Yi

    2015-07-15

    A novel cardanol-based benzoxazine (C-BOZ)/bisphenol A dicyanate ester (BADCy) blend with sea-island phase structures was successfully prepared via reaction-induced phase separation. The introduction of a long-chain alkyl group on the benzene ring significantly enhanced the thermodynamic differences between C-BOZ and BADCy. With the increase of the BADCy content, the Flory-Huggins interaction parameter (χ) of the blend decreased. By adjusting the ratio of the two components, sea-island phase separations were observed in C-BOZ/BADCy blends during the curing process. The dispersed phase was a C-BOZ rich phase, while the matrix was the crosslinked network composed of triazine rings and ring-opened C-BOZ. On the DMA curves of 9/1, 8/2 and 7/3 cured blends, there were two distinct Tgs. But with the increase of the BADCy content, the extent of phase separation was reduced. When the ratio reached 5/5, there was only one Tg because the viscosity of the blend was too high for phase separation to occur. PMID:26138358

  9. Isopycnic Phases and Structures in H2O/CO2/Ethoxylated Alcohol Surfactant Mixtures

    NASA Technical Reports Server (NTRS)

    Paulaitis, Michael E.; Zielinski, Richard G.; Kaler, Eric W.

    1996-01-01

    Ternary mixtures of H2O and CO2 with ethoxylated alcohol (C(i)E(j)) surfactants can form three coexisting liquid phases at conditions where two of the phases have the same density (isopycnic phases). Isopycnic phase behavior has been observed for mixtures containing the surfactants C8E5, C10E6, and C12E6, but not for those mixtures containing either C4E1 or CgE3. Pressure-temperature (PT) projections for this isopycnic three-phase equilibrium were determined for H2O/CO2/C8E5 and H2O/CO2/C10E6 mixtures at temperatures from approximately 25 to 33 C and pressures between 90 and 350 bar. As a preliminary to measuring the microstructure in isopycnic three component mixtures, phase behavior and small angle neutron scattering (SANS) experiments were performed on mixtures of D2O/CO2/ n-hexaethyleneglycol monododecyl ether (C12E6) as a function of temperature (25-31 C), pressure (63.1-90.7 bar), and CO2 composition (0-3.9 wt%). Parameters extracted from model fits of the SANS spectra indicate that, while micellar structure remains essentially unchanged, critical concentration fluctuations increase as the phase boundary and plait point are approached.

  10. Phase ordering and its effect on magnetic and structural properties of FeRh ultrathin films

    NASA Astrophysics Data System (ADS)

    Yap, Q. J.; Qiu, J. J.; Luo, P.; Ying, J. F.; Han, G. C.; Laughlin, D. E.; Zhu, J.-G.; Kanbe, T.; Shige, T.

    2014-07-01

    Applications using FeRh for controllable exchange coupling of two magnetic layers with in-plane and out-of-plane anisotropies require ultrathin (˜10 nm) films with pure antiferromagnetic (AF) FeRh α″ phase at room temperature (RT). However, it is also well known that the antiferromagnetic-ferromagnetic (AF-FM) transition of FeRh is sensitive to composition and deteriorates at low thicknesses. Hence, in this work, we study the composition-dependent phase ordering of co-sputtered FeRh thin films at ultrathin thicknesses of ˜10 nm. As the ultrathin films get richer in Rh, the appearance of α″ phase is typically characterized magnetically by a sudden drop in RT moment, and structurally by a slight decrease in degree of B2 chemical ordering with a sharp decrease in c-axis lattice constant. These observations are consistent with the FeRh phase diagram where FeRh abruptly enters the AF α″ phase once it becomes slightly disordered. Dependences of magnetic transition parameters on composition were also described. Moreover, higher sputtering powers possibly allow the formation of purer α″ phase with less γ-face centered cubic phase impurities. Consequently, a composition optimized 10 nm film shows a relatively low residual moment (13.5 emu/cc), thus suggesting good AF phase formation. In addition, correlation of the magnetic transition parameters with the crystal structural parameters reveal that the maximum rate of AF-FM transition (Rmax,h) and the corresponding total change in magnetization (ΔMh) interestingly shows linear dependence on the c-axis lattice constant, but would depart from this linearity under certain conditions, i.e., when grain sizes were large, crystallinity was improved and Fe content was high.

  11. Formation of Asymmetrical Structured Silica Controlled by a Phase Separation Process and Implication for Biosilicification

    PubMed Central

    Shi, Jia-Yuan; Yao, Qi-Zhi; Li, Xi-Ming; Zhou, Gen-Tao; Fu, Sheng-Quan

    2013-01-01

    Biogenetic silica displays intricate patterns assembling from nano- to microsize level and interesting non-spherical structures differentiating in specific directions. Several model systems have been proposed to explain the formation of biosilica nanostructures. Of them, phase separation based on the physicochemical properties of organic amines was considered to be responsible for the pattern formation of biosilica. In this paper, using tetraethyl orthosilicate (TEOS, Si(OCH2CH3)4) as silica precursor, phospholipid (PL) and dodecylamine (DA) were introduced to initiate phase separation of organic components and influence silica precipitation. Morphology, structure and composition of the mineralized products were characterized using a range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), infrared spectra (IR), and nitrogen physisorption. The results demonstrate that the phase separation process of the organic components leads to the formation of asymmetrically non-spherical silica structures, and the aspect ratios of the asymmetrical structures can be well controlled by varying the concentration of PL and DA. On the basis of the time-dependent experiments, a tentative mechanism is also proposed to illustrate the asymmetrical morphogenesis. Therefore, our results imply that in addition to explaining the hierarchical porous nanopatterning of biosilica, the phase separation process may also be responsible for the growth differentiation of siliceous structures in specific directions. Because organic amine (e.g., long-chair polyamines), phospholipids (e.g., silicalemma) and the phase separation process are associated with the biosilicification of diatoms, our results may provide a new insight into the mechanism of biosilicification. PMID:23585878

  12. Formation of asymmetrical structured silica controlled by a phase separation process and implication for biosilicification.

    PubMed

    Shi, Jia-Yuan; Yao, Qi-Zhi; Li, Xi-Ming; Zhou, Gen-Tao; Fu, Sheng-Quan

    2013-01-01

    Biogenetic silica displays intricate patterns assembling from nano- to microsize level and interesting non-spherical structures differentiating in specific directions. Several model systems have been proposed to explain the formation of biosilica nanostructures. Of them, phase separation based on the physicochemical properties of organic amines was considered to be responsible for the pattern formation of biosilica. In this paper, using tetraethyl orthosilicate (TEOS, Si(OCH2CH3)4) as silica precursor, phospholipid (PL) and dodecylamine (DA) were introduced to initiate phase separation of organic components and influence silica precipitation. Morphology, structure and composition of the mineralized products were characterized using a range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), infrared spectra (IR), and nitrogen physisorption. The results demonstrate that the phase separation process of the organic components leads to the formation of asymmetrically non-spherical silica structures, and the aspect ratios of the asymmetrical structures can be well controlled by varying the concentration of PL and DA. On the basis of the time-dependent experiments, a tentative mechanism is also proposed to illustrate the asymmetrical morphogenesis. Therefore, our results imply that in addition to explaining the hierarchical porous nanopatterning of biosilica, the phase separation process may also be responsible for the growth differentiation of siliceous structures in specific directions. Because organic amine (e.g., long-chair polyamines), phospholipids (e.g., silicalemma) and the phase separation process are associated with the biosilicification of diatoms, our results may provide a new insight into the mechanism of biosilicification. PMID:23585878

  13. Detailed requirements document for the integrated structural analysis system, phase B

    NASA Technical Reports Server (NTRS)

    Rainey, J. A.

    1976-01-01

    The requirements are defined for a software system entitled integrated Structural Analysis System (ISAS) Phase B which is being developed to provide the user with a tool by which a complete and detailed analysis of a complex structural system can be performed. This software system will allow for automated interface with numerous structural analysis batch programs and for user interaction in the creation, selection, and validation of data. This system will include modifications to the 4 functions developed for ISAS, and the development of 25 new functions. The new functions are described.

  14. Stability of self-interstitial clusters with C15 Laves phase structure in iron

    NASA Astrophysics Data System (ADS)

    Dézerald, L.; Marinica, M.-C.; Ventelon, Lisa; Rodney, D.; Willaime, F.

    2014-06-01

    The energetics and stability of self-interstitial clusters with C15 Laves phase structure in iron are investigated by Density Functional Theory (DFT) calculations. First, the properties of bulk C15 are examined. The C15 structure is shown to be mechanically and dynamically stable. Second, the influence of the calculation scheme on the energy difference between C15, ring and loop configurations of di-, tri-, tetra- and octa-interstitial clusters is studied. These calculations confirm that, according to DFT, the C15 structure has by far the lowest energy of all known configurations of tetra- and octa-interstitial clusters in bcc-Fe.

  15. Structural properties of the zircon- and scheelite-type phases of YVO4 at high pressure

    NASA Astrophysics Data System (ADS)

    Wang, X.; Loa, I.; Syassen, K.; Hanfland, M.; Ferrand, B.

    2004-08-01

    The laser host material yttrium orthovanadate YVO4 with a tetragonal zircon-type structure has been studied by angle-dispersive powder x-ray diffraction in a diamond anvil cell up to 26GPa (T=300K) . In situ diffraction confirms that the compound undergoes a nonreversible transformation to a scheelite-type structure at a pressure of 8.5GPa . The equations of state of the zircon and scheelite phases and changes in internal structural parameters are reported. The effect of pressure on the distorted tetrahedral and dodecahedral coordinations of the V and Y ions, respectively, is discussed.

  16. Drifting Pulsating Structure in the Post-maximum Phase of the May 13, 2005 Flare

    NASA Astrophysics Data System (ADS)

    Jiřička, K.; Karlický, M.

    A high-frequency drifting pulsating structure observed in the post-maximum flare phase is analysed in detail. Using the Aschwanden and Benz model (1997) of the solar atmosphere the altitude of the radio source of this structure is estimated and compared with the loop height derived from the distance of the Hα flare ribbons. It was found that for the emission on the harmonic frequency the radio source is close to the flare-loop top. It supports the idea that this drifting pulsating structure is generated in the so-called termination shock.

  17. High pressure structural phase transition of osmium nitride (OsN)

    NASA Astrophysics Data System (ADS)

    Sarwan, Madhu; Abdul Shukoor, V.; Dubey, Ritu; Singh, Sadhna

    2015-05-01

    The structural phase transition and relative volume change of OsN compound has been investigated by means of interaction potential model (IPM) which consists of Coulomb interaction, three-body interaction (TBI), van der Waal interaction (vdW) and short range overlap repulsive interactions up to second neighbor ions. It is found that the OsN transforms from zinc-blende structure (B3) to rock-salt structure (B1) at 87.0 GPa. The second order elastic constants are also investigated. These results are compared with available results.

  18. Atomic force microscopy studies of domain structures in phase-separated monolayers

    NASA Astrophysics Data System (ADS)

    Xiao, Shou-Jun; Wu, Hai-Ming; Yang, Xiao-Min; Wei, Yu; Tai, Zi-Hou; Sun, Xing-Zhong

    1994-10-01

    Domain structures were studied with atomic force microscopy (AFM) in binary phase-separated monolayer films composed of 5, 10, 15-triphenyl-20-(4-dl-α-phenylalanylamindo) phenyl porphyrin (TPPP) and one of a series of fatty acids which are arachidic acid (AA), palmitic acid (PA), and lauric acid (LA). The liquid-condensed (LC) domain structures of AA and PA were observed in their corresponding mixed monolayers. However, instead of the fatty acid domain, a liquid-expanded (LE) domain structure of TPPP appears in the mixed monolayer of LA/TPPP.

  19. Measurement of wavefront structure from large aperture optical components by phase shifting interferometry

    SciTech Connect

    Wolfe, C.R.; Lawson, J.K.; Kellam, M.; Maney, R.T.; Demiris, A.

    1995-05-12

    This paper discusses the results of high spatial resolution measurement of the transmitted or reflected wavefront of optical components using phase shifting interferometry with a wavelength of 6328 {angstrom}. The optical components studied range in size from approximately 50 mm {times} 100 mm to 400 mm {times} 750 mm. Wavefront data, in the form of 3-D phase maps, have been obtained for three regimes of scale length: ``micro roughness``, ``mid-spatial scale``, and ``optical figure/curvature.`` Repetitive wavefront structure has been observed with scale lengths from 10 mm to 100 mm. The amplitude of this structure is typically {lambda}/100 to {lambda}/20. Previously unobserved structure has been detected in optical materials and on the surfaces of components. We are using this data to assist in optimizing laser system design, to qualify optical components and fabrication processes under study in our component development program.

  20. Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

    NASA Astrophysics Data System (ADS)

    Li, Chunyu; Ke, Feng; Hu, Qingyang; Yu, Zhenhai; Zhao, Jinggeng; Chen, Zhiqiang; Yan, Hao

    2016-04-01

    Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr2S3) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr2S3 near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7-15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr2S3 based applications under extreme conditions.

  1. Structural Isomerization of the Gas Phase 2-NORBORNYL Cation Revealed with Infrared Spectroscopy and Computational Chemistry

    NASA Astrophysics Data System (ADS)

    Mauney, Daniel; Mosley, Jonathan; Duncan, Michael A.

    2014-06-01

    The non-classical structure of the 2-norborny cation (C_7H11+) which was at the center of "the most heated chemical controversy of our time" has been observed in the condensed phase and recently using X-ray crystallography. However, no gas phase vibrational spectrum has been collected. The C_7H11+ cation is produced via H_3+ protonation of norbornene by pulsed discharge in a supersonic expansion of H_2/Ar. Ions are mass-selected and probed using infrared photodissociation spectroscopy. Due to high exothermicity, protonation via H_3+ leads to a structural isomerization to the global minimum structure 1,3-dimethylcyclopentenyl (DMCP+). Experiments are currently being conducted to find softer protonation techniques that could lead to the authentic 2-norbornyl cation. Schleyer,P.v.R. et. al.; Stable Carbocation Chemistry, John Wiley & Sons,Inc.; New York, 1997, Chapter 2

  2. Structural and phase transformation of apatite and quartz in the indentation process single crystals

    SciTech Connect

    Chaikina, Marina

    2014-11-14

    Using the method of scanning and high-resolution electron microscopy, the zones of indentation by scratching for apatite and quartz single crystals were investigated. The textural, structural and phase transformations revealed have been conventionally ascribed to “deformation” and “diffusion” processes of plastic deformation. In zones of indentation by scratching of single crystals there have been two levels of structural transformations revealed, with a sharp boundary between them, at a stress equal to the theoretical ultimate stress limit (σ{sub TSL}). In the top zone of scratches, within the range of stress from the microhardness value H{sub s} up to the σ{sub TSL} value the substance undergoes profound structural and phase transformations. In the bed of scratches at the stress value lower than σ{sub TSL} values, single crystal fragmentation occurs with the formation of blocks and steps.

  3. Selective Sequence for the Peptide-Triggered Phase Transition of Lyotropic Liquid-Crystalline Structures.

    PubMed

    Liu, Qingtao; Dong, Yao-Da; Boyd, Ben J

    2016-05-24

    A novel concept of using mixed lipids to construct selective peptide-sequence-sensing lyotropic liquid-crystalline (LLC) dispersion systems was investigated. The LLC systems were constructed using a mixture of phytantriol, a lipid that forms lyotropic liquid-crystalline phases, and a novel synthesized peptide-lipid (peplipid) for sensing a target peptide with the RARAR sequence. The internal structure of the dispersed LLC particles was converted from the lamellar structure (liposomes) to the inverse bicontinuous cubic phase (cubosomes) in the presence of the target peptide. The addition of common human proteins did not induce any structural change, indicating a high selectivity of interaction with the target peptide. The concept has potential for the design of targeted controlled release drug delivery agents. PMID:27148806

  4. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show

  5. Structural and magnetic phase transitions in CeCu6 -xTx (T =Ag ,Pd )

    NASA Astrophysics Data System (ADS)

    Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.

    2015-12-01

    The structural and the magnetic properties of CeCu6 -xAgx (0 ≤x ≤0.85 ) and CeCu6 -xPdx (0 ≤x ≤0.4 ) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6 -xAgx and CeCu6 -xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (P n m a ) to a monoclinic (P 21/c ) phase at 240 K. In CeCu6 -xAgx , the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈0.1 . The structural transition in CeCu6 -xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6 -xAgx and CeCu6 -xPdx , exhibit a magnetic quantum critical point (QCP), at x ≈0.2 and x ≈0.05 , respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ10 δ2), where δ1˜0.62 ,δ2˜0.25 ,x =0.125 for CeCu6 -xPdx and δ1˜0.64 ,δ2˜0.3 ,x =0.3 for CeCu6 -xAgx . The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  6. Effect of structural phase transformation in FeGaO{sub 3} on its magnetic and ferroelectric properties

    SciTech Connect

    Lone, A. G. Bhowmik, R. N.

    2015-06-24

    We investigate the structural phase transformation from orthorhombic to rhombohedral structure in FeGaO{sub 3} by adopting a combined effect of mechanical alloying/milling and solid state sintering techniques. The structural phase formation of the FeGaO{sub 3} compound has been characterized by X-ray diffraction pattern. Mechanical milling played a significant role on the stabilization of rhombohedral phase in FeGaO{sub 3}, where as high temperature sintering stabilized the system in orthorhombic phase. A considerable difference has been observed in magnetic and ferroelectric properties of the system in two phases. The system in rhombohedral (R-3c) phase exhibited better ferromagnetic and of ferroelectric properties at room temperature in comparison to orthorhombic (Pc2{sub 1}n) phase. The rhombohedral phase appears to be good for developing metal doped hematite system for spintronics applications and in that process mechanical milling played an important role.

  7. Pressure-induced phase transitions and structural properties of CoF2: An ab-initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Kürkçü, Cihan; Merdan, Ziya; Öztürk, Hülya

    2016-04-01

    The crystal structure of CoF2 was studied theoretically using first-principles density functional theory (DFT) methods within the generalized gradient approximation (GGA) and local density approximation (LDA) under rapid hydrostatic pressure up to 144 GPa. CoF2 undergoes a structural phase transformation from the rutile-type tetragonal parent phase with space group P42/mnm to the CaCl2-type orthorhombic parent phase with space group Pnnm at 64 GPa with GGA and at 96 GPa with LDA methods. Another phase transformation occurs from the CaCl2-type structure to monoclinic parent phase with space group P21/c at 96 GPa with a GGA method. These phase transitions are also studied by enthalpy and total energy calculations. According to these calculations, we obtained the first phase transformation at about 6.5 GPa both GGA and LDA methods and the later phase transformation at about 45 GPa with the GGA method.

  8. Structural and magnetic phase transition in samarium hydrogen system SmHx (x=1, 2, 3)

    NASA Astrophysics Data System (ADS)

    Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Santhosh, M.; Iyakutti, K.

    2015-06-01

    We report ab-initio calculations for the structural and magnetic phase transition of SmHx (x= 1, 2, 3) using the Vienna ab-initio simulation package (VASP). The non-spin polarized (NSP) and spin polarized (SP) calculations are performed for these hydrides at normal and high pressure. It is found that these compounds are stable in ferromagnetic state at normal pressure. The calculated lattice parameters and bulk modulus of these hydrides are in good agreement with the available experimental results. A pressure-induced structural phase transition from cubic to hexagonal phase in SmH and SmH2 and hexagonal to cubic phase in SmH3 is predicted. A pressure-induced ferromagnetic to nonmagnetic phase transition is observed in SmH, SmH2 and SmH3 at the pressures of 104 GPa, 76 GPa and 81 GPa respectively. Ferromagnetism is quenched in mono, di and tri hydrides at high pressures.

  9. Electronic structure of low-pressure and high-pressure phases of silicon disulfide

    NASA Astrophysics Data System (ADS)

    Bletskan, D. I.; Vakulchak, V. V.; Glukhov, K. E.

    2014-07-01

    Self-consistent density functional theory calculations of band spectra, densities of states as well as the spatial distribution of valence electron charge density were carried out for the low-pressure α-phase and the high-pressure β-phase of SiS2. Group-theoretical analysis performed for both phases enabled the symmetry of wave functions in a number of high-symmetry points of the Brillouin zone as well as the structure of valence band representations to be found. Based on the calculations of the band structure, the orthorhombic α-phase of SiS2 was determined to be an indirect-gap semiconductor with the band gap E gi = 2.44 eV (T 1 → X 8 transition), while the β-phase was shown to be direct gap with E gd = 2.95 eV (Г 3 → Г 2 transition). The calculated energy distribution of the total density of states in the valence band of α-SiS2 qualitatively and quantitatively correlates with the main experimental features of the X-ray photoelectron spectrum.

  10. The Structure and Phase Diagram of Chiral Alkyl-Serine Monolayers on Mercury

    SciTech Connect

    L Tamam; D Medina; T Menahem; Y Mastai; E Sloutskin; S Yefet; M Deutsch

    2011-12-31

    The structure of liquid-mercury-supported Langmuir films (LFs) of chiral serine-modified fatty acid molecules was studied as a function of length, n = 8-22 carbons, temperature, T = 5-25 C, and surface coverage, A {approx} 40-200 {angstrom}{sup 2} per molecule, for both homochiral and heterochiral compounds. Using surface pressure {pi}-area A isotherms and surface-specific synchrotron X-ray diffraction methods the phase diagram was determined in detail. No lateral order was found for phases comprising surface-parallel molecules, in contrast with unmodified fatty acid LFs on mercury. For phases comprising standing-up molecules, long range lateral order was found for n {>=} 12, but no order for n = 8. The molecules in the ordered phases are extended, and tilt rigidly by {approx}40{sup o} from the surface normal. The homochiral LFs pack in an oblique, single-molecule, unit cell. The heterochiral LFs pack in a body-centered rectangular unit cell, containing two molecules. Unlike unmodified fatty acid LFs, the structure of the standing-up phase does not vary with n, T or A. The interactions underlying these characteristics, and the role of chirality, are discussed.

  11. A novel actuator phasing method for ultrasonic de-icing of aircraft structures

    NASA Astrophysics Data System (ADS)

    Borigo, Cody J.

    Aircraft icing is a critical concern for commercial and military rotorcraft and fixed-wing aircraft. In-flight icing can lead to dramatic decreases in lift and increases in drag that have caused more than a thousand deaths and hundreds of accidents over the past three decades alone. Current ice protection technologies have substantial drawbacks due to weight, power consumption, environmental concerns, or incompatibility with certain structures. In this research, an actuator phasing method for ultrasonic de-icing of aircraft structures was developed and tested using a series of finite element models, 3D scanning laser Doppler vibrometer measurements, and experimental de-icing tests on metallic and composite structures including plates and airfoils. An independent actuator analysis method was developed to allow for practical evaluation of many actuator phasing scenarios using a limited number of finite element models by properly calculating the phased stress fields and electromechanical impedance curves using a complex coupled impedance model. A genetic algorithm was utilized in conjunction with a series of finite element models to demonstrate that phase inversion, in which only in-phase and anti-phase signal components are applied to actuators, can be utilized with a small number of phasing combinations to achieve substantial improvements in de-icing system coverage. Finite element models of a 48"-long airfoil predicted that phase inversion with frequency sweeping can provide an improvement in the shear stress coverage levels of up to 90% compared to frequency sweeping alone. Experimental evaluation of the phasing approach on an icing grid showed a 189% improvement in de-icing coverage compared to frequency sweeping alone at comparable power levels. 3D scanning laser Doppler vibrometer measurements confirmed the increased variation in the surface vibration field induced by actuator phasing compared to unphased frequency sweeping. Additional contributions were made

  12. Atomic density functional and diagram of structures in the phase field crystal model

    NASA Astrophysics Data System (ADS)

    Ankudinov, V. E.; Galenko, P. K.; Kropotin, N. V.; Krivilyov, M. D.

    2016-02-01

    The phase field crystal model provides a continual description of the atomic density over the diffusion time of reactions. We consider a homogeneous structure (liquid) and a perfect periodic crystal, which are constructed from the one-mode approximation of the phase field crystal model. A diagram of 2D structures is constructed from the analytic solutions of the model using atomic density functionals. The diagram predicts equilibrium atomic configurations for transitions from the metastable state and includes the domains of existence of homogeneous, triangular, and striped structures corresponding to a liquid, a body-centered cubic crystal, and a longitudinal cross section of cylindrical tubes. The method developed here is employed for constructing the diagram for the homogeneous liquid phase and the body-centered iron lattice. The expression for the free energy is derived analytically from density functional theory. The specific features of approximating the phase field crystal model are compared with the approximations and conclusions of the weak crystallization and 2D melting theories.

  13. Spin Echo Attenuation of Restricted Diffusion as a Discord of Spin Phase Structure

    PubMed

    Stepisnik

    1998-04-01

    By using the particle probability density we analyze the spin echo attenuation of particles, diffusing in a bounded region. It provides a means to expand a nonuniform spin phase distribution into a series of waves that characterize the geometry and boundary conditions of confinement. Random motion disrupts the initial phase structure created by applied gradients and consequently discords its structure waves. By assuming the spin phase fluctuation and/or the randomness of spin phase distribution in the subensemble as a Gaussian stochastic process, we derive a new analytical expression for the echo attenuation related to the particle velocity correlation. For a diffusion in porous structure we get the expression featuring the same "diffusive diffraction" patterns as those being found and explained by P. T. Callaghan and A. Coy ("Principles of Nuclear Magnetic Resonance Microscopy," Oxford Univ. Press, Oxford (1991); J. Chem. Phys. 101, 4599-4609 (1994)) with the use of propagator theory. With the new approach we cast a new light on the phenomena and derive analitically how the diffusive diffractions appear when the sequence of finite or even modulated gradients are applied. The method takes into account the non-Markovian character of restricted diffusion, and therefore the echo dependence on the diffusion lengths and on the strength of applied gradient differs from the results of authors assuming the Markovian diffusion either by dealing with the diffusion propagators or by the computer simulation of Fick's diffusion. Copyright 1998 Academic Press. PMID:9571110

  14. Atomistic structures of metastable and amorphous phases in ion-irradiated magnesium aluminate spinel

    NASA Astrophysics Data System (ADS)

    Ishimaru, Manabu; Hirotsu, Yoshihiko; Afanasyev-Charkin, Ivan V.; Sickafus, Kurt E.

    2002-02-01

    Ion-beam-induced microstructures in magnesium aluminate (MgAl2O4) spinel have been examined using transmission electron microscopy (TEM). Irradiations were performed at cryogenic temperature (~120 K) on MgAl2O4 spinel single-crystal surfaces with (111) orientation, using 180 keV neon (Ne+) ions to ion fluences ranging from 1016 to 1017 Ne+ cm-2. Cross-sectional TEM observations indicated that the MgAl2O4 spinel transforms first into a metastable crystalline phase and then into an amorphous phase under these irradiation conditions. On the basis of selected-area electron diffraction and high-resolution TEM, we concluded that Ne-ion-beam irradiation induces an ordered spinel-to-disordered rock-salt-like structural phase transformation. Atomistic structures of amorphous MgAl2O4 were also examined on the basis of atomic pair distribution functions. We compared the experimentally obtained results with previous theoretically calculated results for the metastable and amorphous phases of MgAl2O4, and discussed the validity of the proposed ion-beam-induced structural changes in MgAl2O4 spinel.

  15. Stability of ultrafine lamellar structures during aging in two-phase {gamma}-TiAl alloys

    SciTech Connect

    Maziasz, P.J.; Liu, C.T.; Wright, J.L.

    1997-08-01

    Two-phase {gamma}-tail alloys such as PM Ti-47Al-2Cr-2Nb or Ti-47Al- 2Cr-1Nb-Ta hot extruded above the {alpha}-transus temperature have unique refined-colony/ultrafine lamellar structures. These lamellar microstructures consist of very fine laths of the {gamma} and {alpha}{sub 2} phases, with average interlamellar spacings of 100 nm and {alpha}{sub 2}-{alpha}{sub 2} spacings of 200 nm, and are dominated by {gamma}/{alpha}{sub 2} interfaces. This ultrafine lamellar structure remains stable during 900 C heat treatment for 2 h, but becomes unstable after 4 h at 982 C. This structure remains stable in both alloys after aging for >5000 h at 800 C but disappears completely at 1000 C. Continuous coarsening begins with dissolution of fine {alpha}{sub 2} lamellea. The aged Ta-modified alloy shows similar lamellar coarsening behavior within the colonies but has more discontinuous coarsening of the intercolony {gamma} with new precipitation of coarse {alpha}{sub 2} and {beta} phase particles. Analytical electron microscopy show that changes in {alpha}{sub 2} phase composition correlate with microstructural instability.

  16. Structural organisation and phase behaviour of a stratum corneum lipid analogue: ceramide 3A.

    PubMed

    Garidel, Patrick

    2006-05-21

    The thermotropic phase behaviour and structural organisation of ceramide N-linoeoyl-phytosphingosine (ceramide 3A) is investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Its polymorphism and structural properties are compared with two ceramides of the type III class with various hydrocarbon chain saturation degrees. After hydration the main phase transition temperature of ceramide 3A is found at 76 degrees C with a phase transition enthalpy of +29 kJ mol(-1). Analysing the frequency of methylene stretching vibrations (by infrared spectroscopy) reveals that the fluidity (amount of trans-gauche isomers) is strongly increased for ceramide 3A compared to its stearoyl ceramide type III analogue. After lipid hydration, the acyl chains of all investigated phytosphingosine ceramides of type III adopt a hexagonal-like chain packing. The amide I and amide II vibrations are quite sensitive to the phase transition of the ceramide. The corresponding band analysis reveals strong inter- and intramolecular hydrogen bonds between the amide and hydroxyl groups in the ceramide head groups. The H-bonding network and conformation of the head group of ceramide 3A is only slightly influenced by hydration. The water penetration capacity of ceramide 3A is, however, considerably larger compared to other phytosphingosine derivatives. The structural and organisational properties of ceramides of type III class are discussed with respect to their physiological relevancies for the stratum corneum lipid barrier property of the skin. PMID:16688309

  17. Evolution of Surface Structure and Phase Separation in GaInAsSb

    SciTech Connect

    C.J. Vineis; C.A. Wang; D.R. Calawa

    2000-08-21

    Atomic force microscopy was used to study changes in the surface step structure of GaInAsSb layers with varying degrees of phase separation. The layers were grown by organometallic vapor phase epitaxy on (001) GaSb substrates with 2{sup o} miscut angles toward (-1-11)A, (1-11)B, and (101). Alloy decomposition was observed by contrast modulations in plan-view transmission electron microscopy, and broadening in x-ray diffraction and photoluminescence peaks. GaInAsSb layers with a minimal degree of phase separation exhibit a step-bunched step structure. A gradual degradation in the periodicity of the step structure is observed as the alloy decomposes into GaAs- and InSb-rich regions. The surface eventually develops trenches to accommodate the local strain associated with composition variations, which are on the order of a few percent. The surface composition is affected by substrate miscut angle, and although phase separation cannot be eliminated, its extent can be reduced by growing on substrates miscut toward (1-11)B.

  18. Structural transformations in amorphous ↔ crystalline phase change of Ga-Sb alloys

    SciTech Connect

    Edwards, T. G.; Sen, S.; Hung, I.; Gan, Z.; Kalkan, B.; Raoux, S.

    2013-12-21

    Ga-Sb alloys with compositions ranging between ∼12 and 50 at. % Ga are promising materials for phase change random access memory applications. The short-range structures of two such alloys with compositions Ga{sub 14}Sb{sub 86} and Ga{sub 46}Sb{sub 54} are investigated, in their amorphous and crystalline states, using {sup 71}Ga and {sup 121}Sb nuclear magnetic resonance spectroscopy and synchrotron x-ray diffraction. The Ga and Sb atoms are fourfold coordinated in the as-deposited amorphous Ga{sub 46}Sb{sub 54} with nearly 40% of the constituent atoms being involved in Ga-Ga and Sb-Sb homopolar bonding. This necessitates extensive bond switching and elimination of homopolar bonds during crystallization. On the other hand, Ga and Sb atoms are all threefold coordinated in the as-deposited amorphous Ga{sub 14}Sb{sub 86}. Crystallization of this material involves phase separation of GaSb domains in Sb matrix and a concomitant increase in the Ga coordination number from 3 to 4. Results from crystallization kinetics experiments suggest that the melt-quenching results in the elimination of structural “defects” such as the homopolar bonds and threefold coordinated Ga atoms in the amorphous phases of these alloys, thereby rendering them structurally more similar to the corresponding crystalline states compared to the as-deposited amorphous phases.

  19. High pressure phase transitions in scheelite structured fluoride: ErLiF{sub 4}

    SciTech Connect

    Garg, Nandini; Mishra, A.K.; Poswal, H.K.; Tyagi, A.K.; Sharma, Surinder M

    2015-09-15

    Our synchrotron based angle dispersive x-ray diffraction studies on scheelite structured ErLiF{sub 4} show that it undergoes two phase transitions, at ~11.5 and ~15.5 GPa to lower symmetry monoclinic phases, before becoming (irreversibly) amorphous at ~28 GPa. The first high pressure phase transformation to the fergusonite structure (space group I2/a) is found to be of thermodynamically second order. The second high pressure phase could be fitted to the P2/c space group, but detailed analysis rules out the wolframite structure (P2/c space group), common to many scheelite compounds under high pressures. We also suggest that despite the ionic character of the LiF{sub 4} tetrahedra, the compressibility of LnLiF{sub 4} (Ln=Eu–Lu) kind of scheelites is more affected by the LnF{sub 8} dodecahedra than the LiF{sub 4} tetrahedra. - Graphical abstract: Volume per formula unit of the scheelite and high pressure phases of ErLiF{sub 4} as a function of pressure. - Highlights: • ErLiF{sub 4} transforms to fergusonite and P2/c phase at high pressure. • Polyhedra of LnF{sub 8} affects compressibility of LnLiF{sub 4} (Ln=Eu–Lu) more than LiF{sub 4}. • Amorphization pressure varies inversely in LnLiF{sub 4} with ionic size of Ln cation. • In ErLiF{sub 4}a/c ratio reduces with pressure in contrast to reported increase in YLiF{sub 4}.

  20. Self-Assembly of Soft Colloids with Multi-scale Phase-Separated Structures

    NASA Astrophysics Data System (ADS)

    Sosa, Chris; Prud'Homme, Robert K.; Priestley, Rodney D.

    The ability of polymers and block co-polymers to self-assemble into highly-ordered structures in bulk two-dimensional films under specific environmental conditions has allowed in recent years for the fabrication of nano-porous membranes, nano-structured surfaces, and sacrificial templates for the preparation of inorganic nanomaterials with well-defined geometries. Extending these fairly specific fabrication techniques to the creation of similar three-dimensional colloidal structures in bulk solutions, however, has proven quite challenging despite the significant need for heterogeneously-structured colloidal materials in medicine and industry. Here we present a strategy for controlling the structural heterogeneity of soft polymer particles along multiple length scales by inducing the rapid phase-separation of polymer mixtures through a continuous nanoprecipitation process. DOE SCGF Fellowship Program.