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Sample records for afm transition temperature

  1. First principles simulation of temperature dependent electronic transition of FM-AFM phase BFO.

    PubMed

    Bian, Liang; Xu, Jin-bao; Song, Mian-xin; Dong, Fa-qin; Dong, Hai-liang; Shi, Fa-Nian; Zhang, Xiao-Yan; Duan, Tao

    2015-04-01

    Understanding how temperature affects the electronic transitions of BFO is important for design of BiFeO3 (BFO)-based temperature-sensitive device. Hitherto, however, there have been only very limited reports of the quantitative simulation. Here, we used density functional theory (DFT) and two-dimensional correlation analysis (2D-CA) techniques to calculate the systematic variations in electronic transitions of BFO crystal, over a range of temperature (50~1500 K). The results suggest that the heat accumulation accelerates the O-2p(4) orbital splitting, inducing the Fe(3+)-3d(5) → Fe(2+)-3d(5)d(0) charge disproportionation. The origin is observed as the temperature-dependent electron transfer process changes from threefold degeneracy to twofold degeneracy. Additionally, the crystallographic orientation (111) can be used to control the 2p-hole-induced electronic transition as O → unoccupied Fe(3+)-3d(5), in comparison to the O → Bi-6p(3) + Fe(3+)-3d(5)d(0) on the orientations (001) and (101). This study offers new perspective on the improvement of BFO-based temperature-sensitive device. PMID:25786830

  2. BOREAS AFM-06 Mean Temperature Profile Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides temperature profiles at 15 heights, containing the variables of virtual temperature, vertical velocity, the speed of sound, and w-bar. The data are stored in tabular ASCII files. The mean temperature profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  3. Development of portable experimental set-up for AFM to work at cryogenic temperature

    NASA Astrophysics Data System (ADS)

    Agarwal, D. H.; Bhatt, P. M.; Pathan, A. M.; Patel, Hitarthi; Joshi, U. S.

    2012-06-01

    We report on the designing aspects and fabrication of low temperature atomic force microscope (AFM) to study the surface structures of nanomaterials. Several key features of design including liquid nitrogen reservoir, vacuum chamber, vibration isolation table etc. have been presented. The whole set up was assembled in-house at a fairly low cost to be used with any commercial AFM system. The surface morphology of important oxide (In0.94Sn0.04)2O3 (ITO) thin film nanostructures has been investigated using the cryogenic AFM set up.

  4. Controlled AFM detachments and movement of nanoparticles: gold clusters on HOPG at different temperatures

    NASA Astrophysics Data System (ADS)

    Tripathi, Manoj; Paolicelli, Guido; D'Addato, Sergio; Valeri, Sergio

    2012-06-01

    The effect of temperature on the onset of movement of gold nanoclusters (diameter 27 nm) deposited on highly oriented pyrolytic graphite (HOPG) has been studied by atomic force microscopy (AFM) techniques. Using the AFM with amplitude modulation (tapping mode AFM) we have stimulated and controlled the movement of individual clusters. We show how, at room temperature, controlled detachments and smooth movements can be obtained for clusters having dimensions comparable to or smaller than the tip radius. Displacement is practically visible in real time and it can be started and stopped easily by adjusting only one parameter, the tip amplitude oscillation. Analysing the energy dissipation signal at the onset of nanocluster sliding we evaluated a detachment threshold energy as a function of temperature in the range 300-413 K. We also analysed single cluster thermal induced displacement and combining this delicate procedure with AFM forced movement behaviour we conclude that detachment threshold energy is directly related to the activation energy of nanocluster diffusion and it scales linearly with temperature as expected for a single-particle thermally activated process.

  5. Temperature Dependence Study of Noncontact Afm Images Using Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Nejat Pishkenari, Hossein; Meghdari, Ali

    The effect of temperature on the noncontact atomic force microscopy (NC-AFM) surface imaging is investigated with the aid of molecular dynamics (MD) analysis based on the Sutton-Chen (SC) interatomic potential. Particular attention is devoted to the tip and sample flexibility at different temperatures. When a gold coated probe is brought close to the Au (001) surface at high temperatures, the tip and surface atoms are pulled together and their distance becomes smaller. The tip and sample atoms displacement varies in the different environment temperatures and this leads to the different interaction forces. Along this line, to study the effect of temperature on the resulting images, we have employed the well-known NC-AFM model and carried out realistic non-equilibrium MD 3D simulations of atomic scale imaging at different close approach positions to the surface.

  6. Nano-scale temperature dependent visco-elastic properties of polyethylene terephthalate (PET) using atomic force microscope (AFM).

    PubMed

    Grant, Colin A; Alfouzan, Abdulrahman; Gough, Tim; Twigg, Peter C; Coates, Phil D

    2013-01-01

    Visco-elastic behaviour at the nano-level of a commonly used polymer (PET) is characterised using atomic force microscopy (AFM) at a range of temperatures. The modulus, indentation creep and relaxation time of the PET film (thickness=100 μm) is highly sensitive to temperature over an experimental temperature range of 22-175°C. The analysis showed a 40-fold increase in the amount of indentation creep on raising the temperature from 22°C to 100°C, with the most rapid rise occurring above the glass-to-rubber transition temperature (T(g)=77.1°C). At higher temperatures, close to the crystallisation temperature (T(c)=134.7°C), the indentation creep reduced to levels similar to those at temperatures below T(g). The calculated relaxation time showed a similar temperature dependence, rising from 0.6s below T(g) to 1.2s between T(g) and T(c) and falling back to 0.6s above T(c). Whereas, the recorded modulus of the thick polymer film decreases above T(g), subsequently increasing near T(c). These visco-elastic parameters are obtained via mechanical modelling of the creep curves and are correlated to the thermal phase changes that occur in PET, as revealed by differential scanning calorimetry (DSC). PMID:22750040

  7. 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.

  8. The role of growth temperature in the adhesion and mechanics of pathogenic L. monocytogenes: an AFM study.

    PubMed

    Gordesli, Fatma Pinar; Abu-Lail, Nehal I

    2012-01-17

    The adhesion strengths of pathogenic L. monocytogenes EGDe to a model surface of silicon nitride were quantified using atomic force microscopy (AFM) in water for cells grown under five different temperatures (10, 20, 30, 37, and 40 °C). The temperature range investigated was chosen to bracket the thermal conditions in which L. monocytogenes survive in the environment. Our results indicated that adhesion force and energy quantified were at their maximum when the bacteria were grown at 30 °C. The higher adhesion observed at 30 °C compared to the adhesion quantified for bacterial cells grown at 37, 40, 20, and 10 °C was associated with longer and denser bacterial surface biopolymer brushes as predicted from fitting a model of steric repulsion to the approach distance-force data as well from the results of protein colorimetric assays. Theoretically predicted adhesion energies based on soft-particle DLVO theory agreed well with the adhesion energies computed from AFM force-distance retraction data (r(2) = 0.94); showing a minimum energy barrier to adhesion at 30 °C. PMID:22133148

  9. Membrane Transition Temperature Determines Cisplatin Response.

    PubMed

    Raghunathan, Krishnan; Ahsan, Aarif; Ray, Dipankar; Nyati, Mukesh K; Veatch, Sarah L

    2015-01-01

    Cisplatin is a classical chemotherapeutic agent used in treating several forms of cancer including head and neck. However, cells develop resistance to the drug in some patients through a range of mechanisms, some of which are poorly understood. Using isolated plasma membrane vesicles as a model system, we present evidence suggesting that cisplatin induced resistance may be due to certain changes in the bio-physical properties of plasma membranes. Giant plasma membrane vesicles (GPMVs) isolated from cortical cytoskeleton exhibit a miscibility transition between a single liquid phase at high temperature and two distinct coexisting liquid phases at low temperature. The temperature at which this transition occurs is hypothesized to reflect the magnitude of membrane heterogeneity at physiological temperature. We find that addition of cisplatin to vesicles isolated from cisplatin-sensitive cells result in a lowering of this miscibility transition temperature, whereas in cisplatin-resistant cells such treatment does not affect the transition temperature. To explore if this is a cause or consequence of cisplatin resistance, we tested if addition of cisplatin in combination with agents that modulate GPMV transition temperatures can affect cisplatin sensitivity. We found that cells become more sensitive to cisplatin when isopropanol, an agent that lowers GPMV transition temperature, was combined with cisplatin. Conversely, cells became resistant to cisplatin when added in combination with menthol that raises GPMV transition temperatures. These data suggest that changes in plasma membrane heterogeneity augments or suppresses signaling events initiated in the plasma membranes that can determine response to cisplatin. We postulate that desired perturbations of membrane heterogeneity could provide an effective therapeutic strategy to overcome cisplatin resistance for certain patients. PMID:26484687

  10. Membrane Transition Temperature Determines Cisplatin Response

    PubMed Central

    Raghunathan, Krishnan; Ahsan, Aarif; Ray, Dipankar; Nyati, Mukesh K.; Veatch, Sarah L.

    2015-01-01

    Cisplatin is a classical chemotherapeutic agent used in treating several forms of cancer including head and neck. However, cells develop resistance to the drug in some patients through a range of mechanisms, some of which are poorly understood. Using isolated plasma membrane vesicles as a model system, we present evidence suggesting that cisplatin induced resistance may be due to certain changes in the bio-physical properties of plasma membranes. Giant plasma membrane vesicles (GPMVs) isolated from cortical cytoskeleton exhibit a miscibility transition between a single liquid phase at high temperature and two distinct coexisting liquid phases at low temperature. The temperature at which this transition occurs is hypothesized to reflect the magnitude of membrane heterogeneity at physiological temperature. We find that addition of cisplatin to vesicles isolated from cisplatin-sensitive cells result in a lowering of this miscibility transition temperature, whereas in cisplatin-resistant cells such treatment does not affect the transition temperature. To explore if this is a cause or consequence of cisplatin resistance, we tested if addition of cisplatin in combination with agents that modulate GPMV transition temperatures can affect cisplatin sensitivity. We found that cells become more sensitive to cisplatin when isopropanol, an agent that lowers GPMV transition temperature, was combined with cisplatin. Conversely, cells became resistant to cisplatin when added in combination with menthol that raises GPMV transition temperatures. These data suggest that changes in plasma membrane heterogeneity augments or suppresses signaling events initiated in the plasma membranes that can determine response to cisplatin. We postulate that desired perturbations of membrane heterogeneity could provide an effective therapeutic strategy to overcome cisplatin resistance for certain patients. PMID:26484687

  11. The ReactorAFM: Non-contact atomic force microscope operating under high-pressure and high-temperature catalytic conditions

    SciTech Connect

    Roobol, S. B.; Cañas-Ventura, M. E.; Bergman, M.; Spronsen, M. A. van; Onderwaater, W. G.; Tuijn, P. C. van der; Koehler, R.; Frenken, J. W. M.; Ofitserov, A.; Baarle, G. J. C. van

    2015-03-15

    An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image model catalysts such as those consisting of metal nanoparticles on flat oxide supports in a gas atmosphere up to 6 bar and at a temperature up to 600 K, while the catalytic activity can be measured using mass spectrometry. The high-pressure reactor is placed inside an Ultrahigh Vacuum (UHV) system to supplement it with standard UHV sample preparation and characterization techniques. To demonstrate that this instrument successfully bridges both the pressure gap and the materials gap, images have been recorded of supported palladium nanoparticles catalyzing the oxidation of carbon monoxide under high-pressure, high-temperature conditions.

  12. The ReactorAFM: Non-contact atomic force microscope operating under high-pressure and high-temperature catalytic conditions

    NASA Astrophysics Data System (ADS)

    Roobol, S. B.; Cañas-Ventura, M. E.; Bergman, M.; van Spronsen, M. A.; Onderwaater, W. G.; van der Tuijn, P. C.; Koehler, R.; Ofitserov, A.; van Baarle, G. J. C.; Frenken, J. W. M.

    2015-03-01

    An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image model catalysts such as those consisting of metal nanoparticles on flat oxide supports in a gas atmosphere up to 6 bar and at a temperature up to 600 K, while the catalytic activity can be measured using mass spectrometry. The high-pressure reactor is placed inside an Ultrahigh Vacuum (UHV) system to supplement it with standard UHV sample preparation and characterization techniques. To demonstrate that this instrument successfully bridges both the pressure gap and the materials gap, images have been recorded of supported palladium nanoparticles catalyzing the oxidation of carbon monoxide under high-pressure, high-temperature conditions.

  13. Radiation pressure excitation of Low Temperature Atomic Force & Magnetic Force Microscope (LT-AFM/MFM) for Imaging

    NASA Astrophysics Data System (ADS)

    Karci, Ozgur; Celik, Umit; Oral, Ahmet; NanoMagnetics Instruments Ltd. Team; Middle East Tech Univ Team

    2015-03-01

    We describe a novel method for excitation of Atomic Force Microscope (AFM) cantilevers by means of radiation pressure for imaging in an AFM for the first time. Piezo excitation is the most common method for cantilever excitation, but it may cause spurious resonance peaks. A fiber optic interferometer with 1310 nm laser was used both to measure the deflection of cantilever and apply a force to the cantilever in a LT-AFM/MFM from NanoMagnetics Instruments. The laser power was modulated at the cantilever`s resonance frequency by a digital Phase Lock Loop (PLL). The force exerted by the radiation pressure on a perfectly reflecting surface by a laser beam of power P is F = 2P/c. We typically modulate the laser beam by ~ 800 μW and obtain 10nm oscillation amplitude with Q ~ 8,000 at 2.5x10-4 mbar. The cantilever's stiffness can be accurately calibrated by using the radiation pressure. We have demonstrated performance of the radiation pressure excitation in AFM/MFM by imaging a hard disk sample between 4-300K and Abrikosov vortex lattice in BSCCO single crystal at 4K to for the first time.

  14. Low-temperature bitumen stiffness and viscous paraffinic nano- and micro-domains by cryogenic AFM and PDM.

    PubMed

    Masson, J-F; Leblond, V; Margeson, J; Bundalo-Perc, S

    2007-09-01

    In an effort to better understand the structure and behaviour of bitumen in low temperature, we describe the first use of cryogenic atomic force microscopy and phase detection microscopy to characterize bitumen nano- and micro-structures. The results were interpreted in light of glass transition temperatures (T(g)s) for bitumen fractions. The domains visible by microscopy, the catana, peri and para phases, were attributed to domains rich in asphaltenes, naphthene and polar aromatics, and saturates, respectively. Between -10 degrees C and -30 degrees C, atomic force microscopy images revealed topographic features not visible in atomic force microscopy images acquired at room temperature. According to phase detection microscopy and T(g)s, the features were assigned to viscous unfrozen saturates. Upon cooling to -72 degrees C, unfrozen domains of 20-400 nm were observed. These domains were found in the paraphase rich in saturates and in the periphase rich in naphthene aromatics and polar aromatics. The findings indicate that new viscous domains form upon cooling to low temperatures owing to phase segregation, and that some bitumens are never entirely rigid in low temperatures. PMID:17760614

  15. Dielectric determination of the glass transition temperature (T sub g)

    NASA Technical Reports Server (NTRS)

    Ries, Heidi R.

    1990-01-01

    The objective is to determine the glass transition temperature of a polymer using a dielectric dissipation technique. A peak in the dissipation factor versus temperature curve is expected near the glass transition temperature T sub g. It should be noted that the glass transition is gradual rather than abrupt, so that the glass transition temperature T sub g is not clearly identifiable. In this case, the glass transition temperature is defined to be the temperature at the intersection point of the tangent lines to the dissipation factor versus temperature curve above and below the transition region, as illustrated.

  16. Elasticity and Inverse Temperature Transition in Elastin

    DOE PAGESBeta

    Perticaroli, Stefania; Ehlers, Georg; Jalarvo, Niina; Katsaras, John; Nickels, Jonathan D.

    2015-09-22

    Structurally, elastin is protein and biomaterial that provides elasticity and resilience to a range of tissues. This work provides insights into the elastic properties of elastin and its peculiar inverse temperature transition (ITT). These features are dependent on hydration of elastin and are driven by a similar mechanism of hydrophobic collapse to an entropically favorable state. Moreover, when using neutron scattering, we quantify the changes in the geometry of molecular motions above and below the transition temperature, showing a reduction in the displacement of water-induced motions upon hydrophobic collapse at the ITT. Finally, we measured the collective vibrations of elastinmore » gels as a function of elongation, revealing no changes in the spectral features associated with local rigidity and secondary structure, in agreement with the entropic origin of elasticity.« less

  17. Elasticity and Inverse Temperature Transition in Elastin

    SciTech Connect

    Perticaroli, Stefania; Ehlers, Georg; Jalarvo, Niina; Katsaras, John; Nickels, Jonathan D.

    2015-09-22

    Structurally, elastin is protein and biomaterial that provides elasticity and resilience to a range of tissues. This work provides insights into the elastic properties of elastin and its peculiar inverse temperature transition (ITT). These features are dependent on hydration of elastin and are driven by a similar mechanism of hydrophobic collapse to an entropically favorable state. Moreover, when using neutron scattering, we quantify the changes in the geometry of molecular motions above and below the transition temperature, showing a reduction in the displacement of water-induced motions upon hydrophobic collapse at the ITT. Finally, we measured the collective vibrations of elastin gels as a function of elongation, revealing no changes in the spectral features associated with local rigidity and secondary structure, in agreement with the entropic origin of elasticity.

  18. Elasticity and Inverse Temperature Transition in Elastin.

    PubMed

    Perticaroli, Stefania; Ehlers, Georg; Jalarvo, Niina; Katsaras, John; Nickels, Jonathan D

    2015-10-15

    Elastin is a structural protein and biomaterial that provides elasticity and resilience to a range of tissues. This work provides insights into the elastic properties of elastin and its peculiar inverse temperature transition (ITT). These features are dependent on hydration of elastin and are driven by a similar mechanism of hydrophobic collapse to an entropically favorable state. Using neutron scattering, we quantify the changes in the geometry of molecular motions above and below the transition temperature, showing a reduction in the displacement of water-induced motions upon hydrophobic collapse at the ITT. We also measured the collective vibrations of elastin gels as a function of elongation, revealing no changes in the spectral features associated with local rigidity and secondary structure, in agreement with the entropic origin of elasticity. PMID:26722771

  19. Electron anions and the glass transition temperature.

    PubMed

    Johnson, Lewis E; Sushko, Peter V; Tomota, Yudai; Hosono, Hideo

    2016-09-01

    Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca12Al14O32](2+) ⋅ (e(-))2, we demonstrate that electron anions in this system behave as glass modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. The concentration of such electron anions is a consequential control parameter: It invokes materials evolution pathways and properties not available in conventional glasses, which opens a unique avenue in rational materials design. PMID:27559083

  20. Effect of incubation temperature on the self-assembly of regenerated silk fibroin: a study using AFM.

    PubMed

    Zhong, Jian; Liu, Xunwei; Wei, Daixu; Yan, Juan; Wang, Ping; Sun, Gang; He, Dannong

    2015-05-01

    Understanding effect of temperature on the molecular self-assembly process will be helpful to unravel the structure-function relationship of biomolecule and to provide important information for the bottom-up approach to nanotechnology. In this work, the effect of incubation temperature on the secondary structures and morphological structures of regenerated silk fibroin (RSF) was systematically studied using atomic force microscopy and Fourier Transform infrared spectroscopy. The effect of incubation temperature on RSF self-assembly was dependent on RSF concentration. For the RSF solution with relatively low concentrations (15 μg/mL and 60 μg/mL), the increase of the incubation temperature mainly accelerated the formation and aggregation of antiparallel β-sheet protofibrils and decreased the formation of random coil protofilaments/globule-like molecules. For the RSF solution with relatively high concentrations (300 μg/mL and 1.5mg/mL), the increase of the incubation temperature mainly accelerated the formation and aggregation of antiparallel β-sheet RSF features (protofibrils and globule-like features) and decreased the formation of random coil bead-like features. This work implies that the morphology and conformation of biomacromolecules could be tuned by controlling the incubation temperature. Further, it will be beneficial to basic understanding of the nanoscale structure formation in different silk-based biomaterials. PMID:25748848

  1. Tethered poly(2-isopropyl-2-oxazoline) chains: temperature effects on layer structure and interactions probed by AFM experiments and modeling.

    PubMed

    An, Junxue; Liu, Xiaoyan; Linse, Per; Dėdinaitė, Andra; Winnik, Françoise M; Claesson, Per M

    2015-03-17

    Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 °C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature. PMID:25686020

  2. Magnetization and compensation temperature in transition metal -- rare earth multilayers: a mean-field approach

    NASA Astrophysics Data System (ADS)

    Tornau, E. E.; Šmakov, J.; Lapinskas, S.; Rosengren, A.

    1998-03-01

    Mean-field theory is used to explain the magnetization as a function of layer thickness in transition metal -- rare earth multilayers. Long-range dipole interactions are included along with FM nearest neighbor interactions within the layers and AF nearest neighbor interactions at the interface. The obtained dependencies of saturation magnetization and compensation temperature on layer thickness agree with experimental data on Tb/Co multilayers( L. Ertl, G. Endl, and H. Hoffmann, J. Magn. Magn. Mater. 113, 227 (1992).). The saturation magnetization is constant for very thin films (the behavior characteristic to Tb - Co alloys) but it decreases with increase of layer thickness. At thick enough films the magnetization starts to increase again confirming the importance of the long - range forces. The compensation temperature also decreases with layer thickness. The proposed theory is extended to calculate the magnetization of FM/AFM layers with a spacer layer in between.

  3. An experimental UHV AFM-STM device for characterizing surface nanostructures under stress/strain at variable temperature.

    PubMed

    Nahas, Y; Berneau, F; Bonneville, J; Coupeau, C; Drouet, M; Lamongie, B; Marteau, M; Michel, J; Tanguy, P; Tromas, C

    2013-10-01

    A compression setup fully integrated in an ultra high vacuum chamber is presented. The system has been designed to combine in situ mechanical test together with near field microscopy at variable temperature, from 90 to 600 K. Compressive stress can be applied on the samples up to 500 MPa at different strain rates ranging from 10(-6) s(-1) to 10(-2) s(-1). The setup performances are highlighted through investigations on Au and Ni3(Al,Ta) single crystals. In particular, it is demonstrated that the high mechanical stability of the original apparatus allows us to follow in situ the evolution of the same area of interest over a large range of temperature and to keep the high spatial resolution offered by near field microscopy, even at high strain levels. PMID:24182173

  4. Size dependence of transition temperature in polymer nanowires.

    PubMed

    Nakanishi, Sana; Yoshikawa, Hirofumi; Shoji, Satoru; Sekkat, Zouheir; Kawata, Satoshi

    2008-03-27

    We studied the effect of changing temperature on the mechanical properties of nanosized poly(methyl methacrylate) wires fabricated by two-photon fabrication. At around room temperature, the nanowires showed a transition temperature where the shear modulus suddenly changed. This transition temperature was observed to decrease more than 40 K by decreasing the radius of the nanowires from 450 to 150 nm. This size is several times larger in nanowires than reported values of polymer thin film thickness showing a depression of the glass transition temperature. PMID:18318534

  5. EBSD and AFM observations of the microstructural changes induced by low temperature plasma carburising on AISI 316

    NASA Astrophysics Data System (ADS)

    Corujeira Gallo, Santiago; Dong, Hanshan

    2011-10-01

    Low temperature plasma carburising (LTPC) has been increasingly accepted as a hardening process for austenitic stainless steels because it produces a good combination of tribological and corrosion properties. The hardening mechanism is based on the supersaturation of the austenitic structure with carbon, which greatly hardens the material, significantly expands the fcc unit cell, produces high levels of compressive residual stresses and, ultimately, leads to the occurrence of deformation bands and rotation of the crystal lattice. The microstructural changes introduced during plasma carburising have a significant impact on the mechanical, tribological and corrosion performance and, for this reason, the microstructure of expanded austenite or S-phase has been extensively studied. However, modern surface characterisation techniques could provide new insights into the formation mechanism of S-phase layers. In this work, backscattered electron diffraction and atomic force microscopy were used to characterise the surface layers of expanded austenite produced by LTPC in an active screen furnace. Based on the experimental results, the plastic deformation, its dependence on crystallographic orientation, the evolution of grain boundaries, and their effects on mechanical, tribological and corrosion properties are discussed.

  6. Qplus AFM driven nanostencil.

    PubMed

    Grévin, B; Fakir, M; Hayton, J; Brun, M; Demadrille, R; Faure-Vincent, J

    2011-06-01

    We describe the development of a novel setup, in which large stencils with suspended silicon nitride membranes are combined with atomic force microscopy (AFM) regulation by using tuning forks. This system offers the possibility to perform separate AFM and nanostencil operations, as well as combined modes when using stencil chips with integrated tips. The flexibility and performances are demonstrated through a series of examples, including wide AFM scans in closed loop mode, probe positioning repeatability of a few tens of nanometer, simultaneous evaporation of large (several hundred of micron square) and nanoscopic metals and fullerene patterns in static, multistep, and dynamic modes. This approach paves the way for further developments, as it fully combines the advantages of conventional stenciling with the ones of an AFM driven shadow mask. PMID:21721701

  7. Temperature-assisted morphological transition in CuPc thin films

    NASA Astrophysics Data System (ADS)

    Bae, Yu Jeong; Pham, Thi Kim Hang; Kim, Tae Hee

    2016-05-01

    Ex-situ and in-situ morphological analyses were performed for Cu-phthalocyanine (CuPc) organic semiconductor films by using atomic force microscopy (AFM) and reflection high-energy electron diffraction (RHEED). The focus was the effects of post-annealing on the structural characteristics of CuPc films grown on MgO(001) layers by using an ultra-high-vacuum thermal evaporator. Sphere-to-nanofibril and 2-D to 3-D morphological transitions were observed with increasing CuPc thickness beyond 3 nm. The surface morphology and the crystallinity were drastically improved after an additional cooling of the post-annealed CuPc films thinner than 3 nm. Our results highlight that molecular orientation and structural ordering can be effectively controlled by using different temperature treatments and a proper combination of material, film thickness, and substrate.

  8. PREFACE: Non-contact AFM Non-contact AFM

    NASA Astrophysics Data System (ADS)

    Giessibl, Franz J.; Morita, Seizo

    2012-02-01

    Kelvin probe force microscopy for Si surfaces by taking account of chemical forces Masaru Tsukada, Akira Masago and Mamoru Shimizu Reversal of atomic contrast in scanning probe microscopy on (111) metal surfaces M Ondrácek, C González and P Jelínek Mechanical properties of H2Pc self-assembled monolayers at the single molecule level by noncontact atomic force microscopy Han-Qing Mao, Na Li, Xi Chen and Qi-Kun Xue High-resolution imaging of C60 molecules using tuning-fork-based non-contact atomic force microscopy R Pawlak, S Kawai, S Fremy, T Glatzel and E Meyer NC-AFM contrast formation on the calcite (101¯4) surface Philipp Rahe, Jens Schütte and Angelika Kühnle Imaging and manipulation of adatoms on an alumina surface by noncontact atomic force microscopy G H Simon, M Heyde and H-J Freund Three-dimensional scanning force/tunneling spectroscopy at room temperature Yoshiaki Sugimoto, Keiichi Ueda, Masayuki Abe and Seizo Morita Imaging and manipulation of the Si(100) surface by small-amplitude NC-AFM at zero and very low applied biasA Sweetman, R Danza, S Gangopadhyay and P Moriarty Manipulation of individual water molecules on CeO2(111) S Torbrügge, O Custance, S Morita and M Reichling FM-AFM imaging of a commercial polyethylene film immersed in n-dodecaneTakumi Hiasa, Tomoki Sugihara, Kenjiro Kimura and Hiroshi Onishi

  9. FM-AFM crossover in vanadium oxide nanomaterials

    NASA Astrophysics Data System (ADS)

    Demishev, S. V.; Chernobrovkin, A. L.; Glushkov, V. V.; Grigorieva, A. V.; Goodilin, E. A.; Sluchanko, N. E.; Samarin, N. A.; Semeno, A. V.

    2010-01-01

    The magnetic properties of nanomaterials based on vanadium oxide (multiwall nanotubes, nanorods, and nanolayers) have been investigated in the temperature range of 1.8-220 K by high-frequency (60-GHz) EPR. A transition from a ferromagnetic temperature dependence to an antiferromagnetic temperature dependence has been observed in nanorods and nanotubes with a decrease in the temperature. The FM-AFM crossover observed near T C ˜ 110 K is accompanied by a low-temperature increase in the Curie constant by a factor of 2.7-7. The comparison of the experimental data for various VO x nanoparticles indicates that the most probable cause of the change in the type of magnetic interaction is a change in the concentration of V4+ magnetic ions.

  10. Recovery Temperature, Transition, and Heat Transfer Measurements at Mach 5

    NASA Technical Reports Server (NTRS)

    Brinich, Paul F.

    1961-01-01

    Schlieren, recovery temperature, and heat-transfer measurements were made on a hollow cylinder and a cone with axes alined parallel to the stream. Both the cone and cylinder were equipped with various bluntnesses, and the tests covered a Reynolds number range up to 20 x 10(exp 6) at a free-stream Mach number of 4.95 and wall to free-stream temperature ratios from 1.8 to 5.2 (adiabatic). A substantial transition delay due to bluntness was found for both the cylinder and the cone. For the present tests (Mach 4.95), transition was delayed by a factor of 3 on the cylinder and about 2 on the cone, these delays being somewhat larger than those observed in earlier tests at Mach 3.1. Heat-transfer tests on the cylinder showed only slight effects of wall temperature level on transition location; this is to be contrasted to the large transition delays observed on conical-type bodies at low surface temperatures at Mach 3.1. The schlieren and the peak-recovery-temperature methods of detecting transition were compared with the heat-transfer results. The comparison showed that the first two methods identified a transition point which occurred just beyond the end of the laminar run as seen in the heat-transfer data.

  11. Connection between the glass transition temperature Tg and the Arrhenius temperature TA in supercooled liquids

    NASA Astrophysics Data System (ADS)

    Novikov, V. N.

    2016-08-01

    At high temperatures the structural relaxation time in liquids has Arrhenius temperature dependence. At lowering temperature, temperature dependence changes to a super Arrhenius at some temperature TA. This temperature is an important point for the structural relaxation dynamics in supercooled liquids because it reflects the transition to collective relaxation. Here we derive a relation between TA, the glass transition temperature Tg and fragility. We show that the ratio Tg/TA increases with increasing fragility of a liquid. The derived relation is in agreement with the experimental data in a series of molecular, hydrogen bonding and two inorganic glass-formers.

  12. Structural transition of spinel compound NiCr2O4 at ferrimagnetic transition temperature

    NASA Astrophysics Data System (ADS)

    Ishibashi, H.; Yasumi, T.

    Magnetic properties and crystal structure of spinel compound NiCr2O4 have been investigated by magnetization and high-resolution X-ray powder diffraction measurements. The structural transition from tetragonal to orthorhombic symmetry was observed at ferrimagnetic transition temperature. This crystal distortion is related to the magnetic ordering of ferrimagnetic component.

  13. Superconducting transition temperature in heterogeneous ferromagnet-superconductor systems

    NASA Astrophysics Data System (ADS)

    Pokrovsky, Valery L.; Wei, Hongduo

    2004-03-01

    We study the superconducting phase transition in two systems: ferromagnet-superconductor bilayer (FSB) and a thin superconducting film with a periodic array of magnetic dots (SFMD) upon it. We show that this transition is of the first order in FSB and of the second order in SFMD. The shift of the transition temperature ΔTc due to the presence of a ferromagnetic layer may be positive or negative in the FSB and is always negative in the SFMD. The dependence of ΔTc on geometrical factors and external magnetic field is found. Theory is extended to multilayers.

  14. Temperature range of the liquid-glass transition

    NASA Astrophysics Data System (ADS)

    Sanditov, D. S.; Darmaev, M. V.; Sanditov, B. D.

    2016-02-01

    It has been shown that the currently used method for calculating the temperature range of δ T g in the glass transition equation qτ g = δ T g as the difference δ T g = ( T 12- T 13) results in overestimated values, which is explained by the assumption of a constant activation energy of glass transition in deriving the calculation equation ( T 12 and T 13 are the temperatures corresponding to the logarithmic viscosity values of logη = 12 and logη = 13). The methods for the evaluation of δ T g using the Williams-Landel-Ferry equation and the model of delocalized atoms are considered, the results of which are in satisfactory agreement with the product qτ g ( q is the cooling rate of the melt and τ g is the structural relaxation time at the glass transition temperature). The calculation of τ g for inorganic glasses and amorphous organic polymers is proposed.

  15. Anomalous metastability in a temperature-driven transition

    NASA Astrophysics Data System (ADS)

    Ibáñez Berganza, M.; Coletti, P.; Petri, A.

    2014-06-01

    The Langer theory of metastability provides a description of the lifetime and properties of the metastable phase of the Ising model field-driven transition, describing the magnetic-field-driven transition in ferromagnets and the chemical-potential-driven transition of fluids. An immediate further step is to apply it to the study of a transition driven by the temperature, as the one exhibited by the two-dimensional Potts model. For this model, a study based on the analytical continuation of the free energy (Meunier J. L. and Morel A., Eur. Phys. J. B, 13 (2000) 341) predicts the anomalous vanishing of the metastable temperature range in the large-system-size limit, an issue that has been controversial since the eighties. By a GPU algorithm we compare the Monte Carlo dynamics with the theory. For temperatures close to the transition we obtain agreement and characterize the dependence on the system size, which is essentially different with respect to the Ising case. For smaller temperatures, we observe the onset of stationary states with non-Boltzmann statistics, not predicted by the theory.

  16. High-Temperature Phase Transition in Enstatite : Raman Spectroscopic Results

    NASA Astrophysics Data System (ADS)

    Reynard, B.; Bass, J.

    2003-12-01

    (Mg,Fe)SiO3 enstatite has various polymorphs of which orthoenstatite with space group Pbca is the most common in natural rocks. The existence of a high temperature form has been suggested from various experiments but its symmetry remains unknown. Recent high-temperature Brillouin measurements on nearly pure MgSiO3 show that this transition is first order with a strong hysteresis (Tc at about 1200-1250° C with increasing temperature, Tc around 1000° C with decreasing temperature; Jackson et al, 2003). It is accompanied by strong pretransitional softening of some elastic constants and has some important consequences in the understanding of upper mantle seismic properties especially in hot regions. In order to more fully understand the nature of this transition and possibly the structural changes associated with it, we have performed in situ Raman spectroscopy on pure enstatite up to the transition temperature. The transition is observed in the same temperature range with increasing temperature, and is characterized by a decrease of the number of Raman modes, which can be interpreted as the transition to a space group with reduced Wigner-Seitz cell. Pretransitional effects are observed especially on a low frequency mode at 80 cm-1, which displays pronounced anharmonic behaviour. Possible space groups are Pbcn (protoenstatite), C2/c (high-clinoenstatite) or a previously unreported Cmca structure. The latter is a supergroup of Pbca and could account for the pretransitional softening. On decreasing temperature, backtransformation to orthoenstatite is marked by the appearance of cracks along simple crystallographic directions, which eventually leads to the breaking of the submillimeter-sized single crystals used as starting materials. Areas of untransformed high-temperature phase can be preserved down to about 750° C. This large hysteresis is strongly controlled by crystal shape and size as well as thermal history. In a parallel experiments, needle shaped thin (5x50

  17. Fluorinated epoxy resins with high glass transition temperatures

    NASA Technical Reports Server (NTRS)

    Griffith, James R.

    1991-01-01

    Easily processed liquid resins of low dielectric constants and high glass transition temperatures are useful for the manufacture of certain composite electronic boards. That combination of properties is difficult to acquire when dielectric constants are below 2.5, glass transition temperatures are above 200 C and processability is of conventional practicality. A recently issued patent (US 4,981,941 of 1 Jan. 1991) teaches practical materials and is the culmination of 23 years of research and effort and 15 patents owned by the Navy in the field of fluorinated resins of several classes. In addition to high fluorine content, practical utility was emphasized.

  18. Plastic Instability in Amorphous Selenium near its Glass Transition Temperature

    SciTech Connect

    Su, Caijun; Lamanna Jr, James; Gao, Yanfei; Oliver, Warren C.; Pharr, George M

    2010-01-01

    Deformation behavior of amorphous selenium near its glass transition temperature (31 C) has been investigated by uniaxial compression and nanoindentation creep tests. Cylindrical specimens compressed at high temperatures and low strain rates deform into drum-like shape, while tests at low temperatures and high strain rates lead to fragmentation. These results agree nicely with the stress exponent and kinetic activation parameters extracted from the nanoindentation creep tests by using a similarity analysis. The dependence of deformation modes on temperature and strain rate is understood as a consequence of material instability and strain localization in the rate-dependent solids.

  19. Zero temperature phase transitions in quantum Heisenberg ferromagnets

    SciTech Connect

    Sachdev, S.; Senthil, T.

    1996-10-01

    The purpose of this work is to understand the zero temperature phases and the phase transitions of Heisenberg spin systems which can have an extensive, spontaneous magnetic moment, this entails a study of quantum transitions with an order parameter which is also a non-abelian conserved charge. To this end, we introduce and study a new class of lattice models of quantum rotors. We compute their mean-field phase diagrams and present continuum, quantum field-theoretic descriptions of their low energy properties in different regimes. We argue that, in spatial dimension {ital d}=1, the phase transitions in itinerant Fermi systems are in the same universality class as the corresponding transitions in certain rotor models. We discuss implications of our results for itinerant fermions systems in higher {ital d} and for other physical systems. Copyright {copyright} 1996 Academic Press, Inc.

  20. Connecting Photospheric Magnetic Fields and Transition Temperature Plasma Emission

    NASA Astrophysics Data System (ADS)

    Schmit, Donald

    2016-05-01

    The connectivity of quiet sun magnetic fields is not well understood. One observational obstacle to probe this question has been the sparse spectral observations spanning the transition temperatures (3×104 K< T < 1×105K) between the chromosphere and corona. The Si IV lines observed by IRIS provide a rich dataset to address the structure of the cool quiet sun. We use over 900 deep exposures from IRIS to map the correlation between transition-temperature emission structures and magnetic field concentrations. Ultimately, our aim is to discern the topology and energetic equilibrium of the magnetic structures that span the quiet sun. We use both a potential field model and a snapshot of the Bifrost 3D MHD simulation to interpret our emission data. In a broad sense, we find there is a clear correlation between magnetic fields and strong Si IV emission. However, more pointed statistics suggest that the relationship is quite complex. We do not find evidence for cool loops longer than 3 Mm in length, but we see ubiquitous, smooth emission nearly everywhere in the quiet sun. Emission voids on scales larger than 8 Mm cannot be well explained by their proximity to magnetic fields. This evidence suggests that weak-field transition-temperature loops contribute significantly to quiet sun transition-temperature emission measure, and evolutionary effects likely play a role in structuring the magnetic atmosphere.

  1. Low temperature magnetic transitions of single crystal HoBi

    SciTech Connect

    Fente, A.; Suderow, H.; Vieira, S.; Nemes, N. M.; Garcia-Hernandez, M.; Budko, Sergei L.; Canfield, Paul C.

    2013-09-04

    We present resistivity, specific heat and magnetization measurements in high quality single crystals of HoBi, with a residual resistivity ratio of 126. We find, from the temperature and field dependence of the magnetization, an antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields, into a series of up to five metamagnetic phases.

  2. Room temperature magnetism and metal to semiconducting transition in dilute Fe doped Sb1-xSex semiconducting alloy thin films

    NASA Astrophysics Data System (ADS)

    Agrawal, Naveen; Sarkar, Mitesh; Chawda, Mukesh; Ganesan, V.; Bodas, Dhananjay

    2015-02-01

    The magnetism was observed in very dilute Fe doped alloy thin film Fe0.008Sb1-xSex, for x = 0.01 to 0.10. These thin films were grown on silicon substrate using thermal evaporation technique. Structural, electrical, optical, charge carrier concentration measurement, surface morphology and magnetic properties were observed using glancing incidence x-ray diffraction (GIXRD), four probe resistivity, photoluminescence, Hall measurement, atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques, respectively. No peaks of iron were seen in GIXRD. The resistivity results show that activation energy increases with increase in selenium (Se) concentration. The Arrhenius plot reveals metallic behavior below room temperature. The low temperature conduction is explained by variable range-hopping mechanism, which fits very well in the temperature range 150-300 K. The decrease in density of states has been observed with increasing selenium concentration (x = 0.01 to 0.10). There is a metal-to-semiconductor phase transition observed above room temperature. This transition temperature is Se concentration dependent. The particle size distribution ˜47-61 nm is evaluated using AFM images. These thin films exhibit ferromagnetic interactions at room temperature.

  3. Hydration states of AFm cement phases

    SciTech Connect

    Baquerizo, Luis G.; Matschei, Thomas; Scrivener, Karen L.; Saeidpour, Mahsa; Wadsö, Lars

    2015-07-15

    The AFm phase, one of the main products formed during the hydration of Portland and calcium aluminate cement based systems, belongs to the layered double hydrate (LDH) family having positively charged layers and water plus charge-balancing anions in the interlayer. It is known that these phases present different hydration states (i.e. varying water content) depending on the relative humidity (RH), temperature and anion type, which might be linked to volume changes (swelling and shrinkage). Unfortunately the stability conditions of these phases are insufficiently reported. This paper presents novel experimental results on the different hydration states of the most important AFm phases: monocarboaluminate, hemicarboaluminate, strätlingite, hydroxy-AFm and monosulfoaluminate, and the thermodynamic properties associated with changes in their water content during absorption/desorption. This data opens the possibility to model the response of cementitious systems during drying and wetting and to engineer systems more resistant to harsh external conditions.

  4. AFM indentation study of breast cancer cells

    SciTech Connect

    Li, Q.S.; Lee, G.Y.H.; Ong, C.N.; Lim, C.T.

    2008-10-03

    Mechanical properties of individual living cells are known to be closely related to the health and function of the human body. Here, atomic force microscopy (AFM) indentation using a micro-sized spherical probe was carried out to characterize the elasticity of benign (MCF-10A) and cancerous (MCF-7) human breast epithelial cells. AFM imaging and confocal fluorescence imaging were also used to investigate their corresponding sub-membrane cytoskeletal structures. Malignant (MCF-7) breast cells were found to have an apparent Young's modulus significantly lower (1.4-1.8 times) than that of their non-malignant (MCF-10A) counterparts at physiological temperature (37 deg. C), and their apparent Young's modulus increase with loading rate. Both confocal and AFM images showed a significant difference in the organization of their sub-membrane actin structures which directly contribute to their difference in cell elasticity. This change may have facilitated easy migration and invasion of malignant cells during metastasis.

  5. Temperature Mediated Morphological Transition during Drying of Spray Colloidal Droplets.

    PubMed

    Biswas, Priyanka; Sen, D; Mazumder, S; Basak, C B; Doshi, P

    2016-03-15

    Understanding how a tiny dilute evaporative colloidal spray droplet gets transformed into a microgranule with a characteristic morphology is crucial from scientific as well as technological points of view. In the present work, it is demonstrated that the morphology and the size distribution of the microcapsules can be tuned simply by adjusting the drying temperature. Shape and size of the capsules are quantified at four different drying temperatures. It is shown that the morphology transits gradually from sphere to toroid with increasing temperature keeping the average volume-fraction of the correlated nanoparticles nearly unaffected for the synthesized granules. A plausible mechanism for the chronological pathway of such morphological transformation is illustrated. Computer simulation corroborates the experimentally observed morphological transition. The variation in hollowness and buckling tendency of the capsules are elucidated by scattering and imaging techniques. PMID:26900937

  6. Temperature-induced Lifshitz transition in WTe2

    DOE PAGESBeta

    Wu, Yun; Jo, Na Hyun; Ochi, Masayuki; Huang, Lunan; Mou, Daixiang; Bud’ko, Sergey L.; Canfield, P. C.; Trivedi, Nandini; Arita, Ryotaro; Kaminski, Adam

    2015-10-12

    In this study, we use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X–Γ–X direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at T≃160 K, associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potential μ(T)more » due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at T≈175 K and a breakdown of Kohler’s rule in the 70–140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals.« less

  7. Temperature-Induced Lifshitz Transition in WTe2

    NASA Astrophysics Data System (ADS)

    Wu, Yun; Jo, Na Hyun; Ochi, Masayuki; Huang, Lunan; Mou, Daixiang; Bud'ko, Sergey L.; Canfield, P. C.; Trivedi, Nandini; Arita, Ryotaro; Kaminski, Adam

    2015-10-01

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X -Γ -X direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at T ≃160 K , associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potential μ (T ) due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at T ≈175 K and a breakdown of Kohler's rule in the 70-140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals.

  8. Temperature-Induced Lifshitz Transition in WTe2.

    PubMed

    Wu, Yun; Jo, Na Hyun; Ochi, Masayuki; Huang, Lunan; Mou, Daixiang; Bud'ko, Sergey L; Canfield, P C; Trivedi, Nandini; Arita, Ryotaro; Kaminski, Adam

    2015-10-16

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X-Γ-X direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at T≃160  K, associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potential μ(T) due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at T≈175  K and a breakdown of Kohler's rule in the 70-140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals. PMID:26550889

  9. Effect of interface roughness on superconducting transition temperatures of Nb/Co multilayers

    NASA Astrophysics Data System (ADS)

    Liu, L. Y.; Chacón Hernandez, U. D.; Xing, Y. T.; Suguihiro, N. M.; Haeussler, D.; Baggio-Saitovitch, E.; Jäger, W.; Solórzano, I. G.

    2016-03-01

    Superconductor (SC)/ferromagnet (FM) Nb/Co multilayers have been produced by magnetron-sputtering with a 100 nm thickness of Nb and 5, 10, and 20 nm of Co. The superconducting properties have been investigated by electric transport measurements. It was found that the thicker Co layers decrease the superconducting transition temperature (Tc) less than the thinner ones. In order to understand this unexpected behavior, the microstructure of the layers has been investigated by means of Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and by energy-dispersive X-ray spectroscopy line scan analyses in scanning TEM (STEM) mode. It was found that the decisive parameter which determines the effect of magnetic layers on Tc of the superconducting layers is not only the roughness (R), but the ratio of the roughness to thickness (dCo) of the magnetic Co layer, δ = R /dCo. For δ > 1 the magnetic stray field of the magnetic layers is the main reason for the Tc reduction.

  10. Rheological transitions in high-temperature volcanic fault zones

    NASA Astrophysics Data System (ADS)

    Okumura, Satoshi; Uesugi, Kentaro; Nakamura, Michihiko; Sasaki, Osamu

    2015-05-01

    Silicic magma experiences shear-induced brittle fracturing during its ascent, resulting in the formation of a magmatic fault at the conduit margin. Once the fault is formed, frictional behavior of the fault controls the magma ascent process. We observed torsional deformation of a magmatic fault gouge in situ at temperatures of 800 and 900°C using synchrotron radiation X-ray radiography. The torsional deformation rate was set at 0.1-10 rpm, corresponding to equivalent slip velocities of 2.27 × 10-5-1.74 × 10-3 m s-1 and shear strain rates of 0.014-1.16 s-1. The normal stresses used were 1, 5, and 10 MPa. The magmatic fault showed frictional sliding as well as viscous flow even above the glass transition temperature. The transition between frictional sliding and viscous flow depends on temperature, deformation rate, and normal stress on the fault. At 900°C, the fault showed viscous deformation at a normal stress of 10 MPa, while frictional sliding was predominant at 800°C. We propose the ratio of timescales of fault healing and deformation as a criterion for transition between frictional sliding and viscous flow. The experimentally calibrated criterion infers that frictional sliding is predominant from ~500 m in depth during explosive eruption; this may explain rapid magma ascent without efficient outgassing. Frictional heating would in turn enhance fault healing, resulting in the reverse transition from frictional sliding to viscous flow, followed by deceleration of magma ascent. Therefore, cyclic transitions between frictional sliding and viscous flow are a possible explanation for the cyclic behavior of lava effusion.

  11. Pressure variation of reentrant transition temperature in liquid crystals.

    PubMed

    Srivastava, A; Sa, D; Singh, S

    2007-02-01

    High pressure experimental studies show that in certain mesogenic materials, the nematic-smectic A (N-Sm A) transition temperature T(AN) exhibits nonlinear pressure dependence. As a consequence, the material shows reentrant phenomena that is a phase sequence nematic -- smectic A -- reentrant nematic appears. The characteristic features of this phenomenon have been addressed here within the framework of Landau-de-Gennes theory, where the coupling between nematic and smectic A order parameters (gamma, lambda(eff)) plays an important role. The cubic coupling gamma is chosen to be negative in order to form Sm A phase whereas the biquadratic coupling lambda(eff) is made large and positive to obtain reentrant behaviour. In the present work, we incorporate the pressure dependence in the theory through gamma and lambda(eff) which justifies the experimental pressure dependence in the reentrant transition temperature [Formula: see text]. The pressure dependence of gamma and lambda(eff) are employed in the calculation of excess specific heat capacity near the reentrant transition. The computed heat capacity shows strong pressure dependence near the reentrant transition which can be confirmed from high pressure measurement. PMID:17342375

  12. Scaled down glass transition temperature in confined polymer nanofibers.

    PubMed

    Wang, Hongxia; Chang, Tongxin; Li, Xiaohui; Zhang, Weidong; Hu, Zhijun; Jonas, Alain M

    2016-08-11

    Arrays of polymer nanostructures have been widely used in many novel devices and nanofabrication methods. The glass transition temperature, which is a key parameter influencing the long-term stability of polymer nanostructures, has not yet been systematically studied and well understood. Here we study this technological and fundamental issue with polymers of different values of molar mass M confined in nanocylinders of a varying diameter D. The glass transition temperature Tg loses its dependence on the molar mass for D ≲ 100 nm, a range in which the relative depression of Tg varies as D(-0.44). For higher cylinder diameters, Tg progressively recovers its dependence on the molar mass. This is quantitatively reproduced by a model based on an equilibrium interfacial excess of free volume, which needs to be created unless provided by the chain ends. Our findings suggest that the structural perturbations during nanofabrication may strongly affect the long-term stability of arrays of polymer nanostructures. PMID:27476991

  13. Graphical representation for thermal equilibrium when transition temperatures are present

    NASA Astrophysics Data System (ADS)

    Rojas, Roberto

    2016-01-01

    We propose the use of graphics in order to get a quick insight of the thermal equilibrium of two bodies, when a transition temperature is present in the interval between both initial temperatures. We have found two convenient variables in order to represent the mathematical condition for the partial or complete transition of each component. In mixing hot water and cold ice, the proposed graphical representation exhibits straight lines separating four regions corresponding to different equilibrium states, going from one containing just ice up to the other containing just water, and two states in between with increased ice or increased water. This graphical representation helps to avoid typical student errors in learning elementary physics.

  14. Predicting Glass Transition Temperatures of Polyarylethersulphones Using QSPR Methods

    PubMed Central

    Hamerton, Ian; Howlin, Brendan J.; Kamyszek, Grzegorz

    2012-01-01

    The technique of Quantitative Structure Property Relationships has been applied to the glass transition temperatures of polyarylethersulphones. A general equation is reported that calculates the glass transition temperatures with acceptable accuracy (correlation coefficients of between 90–67%, indicating an error of 10–30% with regard to experimentally determined values) for a series of 42 reported polyarylethersulphones. This method is quite simple in assumption and relies on a relatively small number of parameters associated with the structural unit of the polymer: the number of rotatable bonds, the dipole moment, the heat of formation, the HOMO eigenvalue, the molar mass and molar volume. For smaller subsets of the main group (based on families of derivatives containing different substituents) the model can be simplified further to an equation that uses the volume of the substituents as the principal variable. PMID:22719884

  15. Trapped resonant fermions above the superfluid transition temperature

    SciTech Connect

    Cheng, C.-H.; Yip, S.-K.

    2007-01-01

    We investigate trapped resonant fermions with unequal populations within the local density approximation above the superfluid transition temperature. By tuning the attractive interaction between fermions via Feshbach resonance, the system evolves from weakly interacting fermi gas to strongly interacting fermi gas, and finally becomes a Bose-Fermi mixture. The density profiles of fermions are examined and compared with experiments. We also point out the simple relationships between the local density, the axial density, and the gas pressure within the local density approximation.

  16. CosmoTransitions: Computing cosmological phase transition temperatures and bubble profiles with multiple fields

    NASA Astrophysics Data System (ADS)

    Wainwright, Carroll L.

    2012-09-01

    I present a numerical package (CosmoTransitions) for analyzing finite-temperature cosmological phase transitions driven by single or multiple scalar fields. The package analyzes the different vacua of a theory to determine their critical temperatures (where the vacuum energy levels are degenerate), their supercooling temperatures, and the bubble wall profiles which separate the phases and describe their tunneling dynamics. I introduce a new method of path deformation to find the profiles of both thin- and thick-walled bubbles. CosmoTransitions is freely available for public use.Program summaryProgram Title: CosmoTransitionsCatalogue identifier: AEML_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEML_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 8775No. of bytes in distributed program, including test data, etc.: 621096Distribution format: tar.gzProgramming language: Python.Computer: Developed on a 2009 MacBook Pro. No computer-specific optimization was performed.Operating system: Designed and tested on Mac OS X 10.6.8. Compatible with any OS with Python installed.RAM: Approximately 50 MB, mostly for loading plotting packages.Classification: 1.9, 11.1.External routines: SciPy, NumPy, matplotLibNature of problem: I describe a program to analyze early-Universe finite-temperature phase transitions with multiple scalar fields. The goal is to analyze the phase structure of an input theory, determine the amount of supercooling at each phase transition, and find the bubble-wall profiles of the nucleated bubbles that drive the transitions.Solution method: To find the bubble-wall profile, the program assumes that tunneling happens along a fixed path in field space. This reduces the equations of motion to one dimension, which can then be solved using the overshoot

  17. Moisture adsorption isotherms and glass transition temperature of pectin.

    PubMed

    Basu, Santanu; Shivhare, U S; Muley, S

    2013-06-01

    The moisture adsorption isotherms of low methoxyl pectin were determined at 30-70°C and water activity ranging from 0.11 to 0.94. The moisture adsorption isotherms revealed that the equilibrium moisture content increased with water activity. Increase in temperature, in general, resulted in decreased equilibrium moisture content. However in some cases, equilibrium moisture content values increased with temperature at higher water activities. Selected sorption models (GAB, Halsey, Henderson, Oswin, modified Oswin) were tested for describing the adsorption isotherms. Parameters of each sorption models were determined by nonlinear regression analysis. Oswin model gave the best fit for pectin sorption behaviour. Isosteric heat of sorption decreased with increase in moisture content and varied between 14.607 and 0.552 kJ/mol. Glass transition temperature decreased with increase in moisture content of pectin. PMID:24425957

  18. Temperature-Induced Lifshitz Transition in WTe2

    NASA Astrophysics Data System (ADS)

    Jo, Na Hyun; Wu, Yun; Ochi, Masayuki; Huang, Lunan; Mou, Daixiang; Bud'Ko, Sergey L.; Canfield, P. C.; Trivedi, Nandini; Arita, Ryotaro; Kaminski, Adam

    We use thermoeletric power (TEP), temperature- and field-dependent resistivity, and ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X - Γ - X direction. We find a rare example of a temperature-induced Lifshitz transition at T ~ 160 K. Temperature dependent TEP shows a change of slope at T ~ 175 K and Kohler's rule was breakdown in the 70-140 K range. ARPES temperature scans confirm that the hole pockets completely disappear around 160 K. Our electronic structure calculations show a clear and substantial shift of the chemical potential μ (T) due to the semimetal nature of this material driven by modest changes in temperature. [PRL 115, 166602 (2015)] This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358; Betty Moore Foundation EPiQS Initiative (Grant No. GBMF4411); and CEM, a NSF MRSEC, under Grant No. DMR-1420451.

  19. Measurement of the glass transition temperature of elastomer systems

    SciTech Connect

    Sircar, A.K.; Chartoff, R.P.

    1994-09-01

    The glass transition temperature of polymers depends on both the experimental procedures and the experimental techniques used for its evaluation. However, the value of the published data is often diminished because these details are omitted. Examples are cited to show how the magnitude of differential scanning calorimetry (DSC) T{sub g} depends on the T{sub g} location and different calibration methods. Some comments are also made about thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) methods, although these are treated only briefly. The factors that are unique to elastomer glass transition temperatures are: (1) the difficulties of calibration of the instruments at subambient temperature, (2) increase of T{sub g} by the extent of vulcanization and filler loading, (3) differences due to microstructure and microphase separation, and (4) the availability of different grades of the same elastomer with different composition or added components, which alter their T{sub g}. Thus, the literature value of T{sub g} should include not only the calibration and procedure for the experiment, but also the exact name and description of the elastomer with the number index, the recipe used, and the cure conditions.

  20. Model of High Temperature Phase Transitions in Metals

    NASA Astrophysics Data System (ADS)

    Filippov, E. S.

    2016-04-01

    On the basis of the assumption of the electron density fluctuation at the band degradation, a calculation parameter (the radius R) of the half-width of the probability distribution over the coordinate R is identified at the level of the maximum electron density fluctuation (at a maximum of the Gaussian function). Based on an analysis of the crystallization process and high polymorphic transformations bcc → fcc, the reasons for the formation of bcc, fcc, hexagonal, and tetragonal structures from the liquid phase, as well as for the high temperature bcc → hcp transition in the solid phase are established using the calculated parameter (the radius R) in the solid and liquid phases.

  1. Phase transition of carbonate solvent mixture solutions at low temperatures

    NASA Astrophysics Data System (ADS)

    Okumura, Takefumi; Horiba, Tatsuo

    2016-01-01

    The phase transition of carbonate solvent mixture solutions consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and LiPF6 salt have been studied for improving the low temperature performance of lithium-ion batteries. The Li ion conductivity at 25 °C was maximum at x = 0.3 in a series of 1 M LiPF6 mixed carbonate solvents compositions consisting of ECxDMC0.5-0.5xEMC0.5-0.5x (x = 0 to 0.6), while the maximum tended to shift to x = 0.2 as the temperature lowered. The differential scanning calorimetry results showed that the freezing temperature depressions of EC in the 1 M LiPF6 solution were larger than those of the DMC or EMC. The chemical shift of 7Li nuclear magnetic resonance changed from a constant to increasing at around x = 0.3, which could be reasonably understood by focusing on the change in solvation energy calculated using Born equation. However, in the region of a high EC concentration of over x = 0.3 (EC/LiPF6 > 4) in the 1 M LiPF6 solution, the free EC from the solvation to the lithium ions seems to reduce the freezing temperature depression of the EC, and thus, decreases the ionic conductivity of the solution at low temperatures, due to the EC freezing.

  2. Simultaneous Determination of Glass Transition Temperatures of Several Polymers

    PubMed Central

    He, Jiang; Liu, Wei; Huang, Yao-Xiong

    2016-01-01

    Aims A simple and easy optical method is proposed for the determination of glass transition temperature (Tg) of polymers. Methods & Results Tg was determined using the technique of microsphere imaging to monitor the variation of the refractive index of polymer microsphere as a function of temperature. It was demonstrated that the method can eliminate most thermal lag and has sensitivity about six fold higher than the conventional method in Tg determination. So the determined Tg is more accurate and varies less with cooling/heating rate than that obtained by conventional methods. The most attractive character of the method is that it can simultaneously determine the Tg of several polymers in a single experiment, so it can greatly save experimental time and heating energy. Conclusion The method is not only applicable for polymer microspheres, but also for the materials with arbitrary shapes. Therefore, it is expected to be broadly applied to different fundamental researches and practical applications of polymers. PMID:26985670

  3. Determination of the glass transition temperature of cyclodextrin polymers.

    PubMed

    Tabary, Nicolas; Garcia-Fernandez, Maria Jose; Danède, Florence; Descamps, Marc; Martel, Bernard; Willart, Jean-François

    2016-09-01

    The aim of this work was to determine the main physical characteristics of β-cyclodextrin polymers, well known for improving complexation capacities and providing enhanced and sustained release of a large panel of drugs. Two polymers were investigated: a polymer of β-cyclodextrin (polyβ-CD) and a polymer of partially methylated (DS=0.57) β-cyclodextrin (polyMe-β-CD). The physical characterizations were performed by powder X-ray diffraction and differential scanning calorimetry. The results indicate that these polymers are amorphous and that their glass transition is located above the thermal degradation point of the materials preventing their direct observation and thus their full characterization. We could however estimate the virtual glass transition temperatures by mixing the polymers with different plasticizers (trehalose and mannitol) which decreases Tg sufficiently to make the glass transition observable. Extrapolation to zero plasticizer concentration then yield the following Tg values: Tg (polyMe-β-CD)=317°C±5°C and Tg (polyβ-CD)=418°C±6°C. PMID:27185128

  4. Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

    NASA Astrophysics Data System (ADS)

    Zhao, K.; Xia, X. X.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

    2011-04-01

    We report a high entropy metallic glass of Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

  5. Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

    SciTech Connect

    Zhao, K.; Xia, X. X.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

    2011-04-04

    We report a high entropy metallic glass of Zn{sub 20}Ca{sub 20}Sr{sub 20}Yb{sub 20}(Li{sub 0.55}Mg{sub 0.45}){sub 20} via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

  6. Finite temperature quantum critical transport near the Mott transition

    NASA Astrophysics Data System (ADS)

    Terletska, Hanna; Dobrosavljevic, Vladimir

    2010-03-01

    We use Dynamical Mean-Field Theory to study incoherent transport above the critical end-point temperature Tc of the single band Hubbard model at half-filling. By employing an eigenvalue analysis for the free energy functional, we are able to precisely identify the crossover temperature T*(U) separating the Fermi liquid and the Mott insulating regimes. Our calculations demonstrate that a broad parameter range exist around the crossover line, where the family of resistivity curves displays simple scaling behavior. This is interpreted as a manifestation of quantum criticality controlled by the T=0 Mott transition, which is ``interrupted'' by the emergence of the coexistence dome at T < Tc . We argue that in situations where the critical temperature Tc is significantly reduced, so that the coexistence region is reduced or even absent (as in two-band, particle-hole asymmetric models, where this is found even in the clean d->∞ limit [1, 2]), similar critical scaling properties should persist down to much lower temperatures, resembling quantum critical transport similar to that found in a number of experiments [2]. [1] A. Amaricci, G. Sordi, and M. J. Rosenberg, Phys. Rev. Lett. 101, 146403 (2008) [2] A. Camjayi, K. Haule, V. Dobrosavljevic, and G. Kotliar, Nature Physics, 4, 932 (2008)

  7. Transition temperature range of thermally activated nickel-titanium archwires

    PubMed Central

    SPINI, Tatiana Sobottka; VALARELLI, Fabrício Pinelli; CANÇADO, Rodrigo Hermont; de FREITAS, Karina Maria Salvatore; VILLARINHO, Denis Jardim

    2014-01-01

    Objectives The shape memory resulting from the superelasticity and thermoelastic effect is the main characteristic of thermally activated NiTi archwires and is closely related to the transition temperature range (TTR). The aim of this study was to evaluate the TTR of thermally activated NiTi archwires commercially available. Material and Methods Seven different brands of 0.019"x0.025" thermally activated nickel-titanium archwires were tested as received by differential scanning calorimetry (DSC) over the temperature range from -100°C to 150°C at 10°C/min. Results All thermally activated NiTi archwires analyzed presented stage transformation during thermal scanning with final austenitic temperature (Af) ranging from 20.39°C to 45.42°C. Three brands of NiTi archwires presented Af close to the room temperature and, this way, do not present properties of shape memory and pseudoelasticity that are desirable in clinical applications. Conclusions The thermally activated NiTi archwires present great variability in the TTR and the elastic parameters of each NiTi archwire should be provided by the manufacturers, to allow achievement of the best clinical performance possible. PMID:24676581

  8. Pattern formation and control in polymeric systems: From Minkowski measures to in situ AFM imaging

    NASA Astrophysics Data System (ADS)

    Jacobs, Karin

    2014-03-01

    Thin liquid polymer films are not only of great technical importance, they also exhibit a variety of dynamical instabilities. Some of them may be desired, some rather not. To analyze and finally control pattern formation, modern thin film theories are as vital as techniques to characterize the morphologies and structures in and on the films. Examples for the latter are atomic force microscopy (AFM) as well as scattering techniques. The talk will introduce into the practical applications of Minkowski measures to characterize patterns and explain what thin film properties (e.g. capillary number, solid/liquid boundary condition, glass transition temperature, chain mobility) can further be extracted including new technical possibilities by AFM and scattering techniques.

  9. Microwave response of high transition temperature superconducting thin films

    NASA Technical Reports Server (NTRS)

    Miranda, Felix Antonio

    1991-01-01

    We have studied the microwave response of YBa2Cu3O(7 - delta), Bi-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O high transition temperature superconducting (HTS) thin films by performing power transmission measurements. These measurements were carried out in the temperature range of 300 K to 20 K and at frequencies within the range of 30 to 40 GHz. Through these measurements we have determined the magnetic penetration depth (lambda), the complex conductivity (sigma(sup *) = sigma(sub 1) - j sigma(sub 2)) and the surface resistance (R(sub s)). An estimate of the intrinsic penetration depth (lambda approx. 121 nm) for the YBa2Cu3O(7 - delta) HTS has been obtained from the film thickness dependence of lambda. This value compares favorably with the best values reported so far (approx. 140 nm) in single crystals and high quality c-axis oriented thin films. Furthermore, it was observed that our technique is sensitive to the intrinsic anisotropy of lambda in this superconductor. Values of lambda are also reported for Bi-based and Tl-based thin films. We observed that for the three types of superconductors, both sigma(sub 1) and sigma(sub 2) increased when cooling the films below their transition temperature. The measured R(sub s) are in good agreement with other R(sub S) values obtained using resonant activity techniques if we assume a quadratic frequency dependence. Our analysis shows that, of the three types of HTS films studied, the YBa2Cu3O(7 - delta) thin film, deposited by laser ablation and off-axis magnetron sputtering are the most promising for microwave applications.

  10. Supported phospholipid bilayer interaction with components found in typical room-temperature ionic liquids - a QCM-D and AFM study

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Quartz crystal microbalance with dissipation monitoring and atomic force microscopy were combined to evaluate the defects created by room-temperature ionic liquid anion and cation in a supported phospholipid bilayer composed of Zwitterionic lipids on a silica surface. The cation 1-octyl-3-methyl im...

  11. Influence of entanglements on glass transition temperature of polystyrene

    NASA Astrophysics Data System (ADS)

    Ougizawa, Toshiaki; Kinugasa, Yoshinori

    2013-03-01

    Chain entanglement is essential behavior of polymeric molecules and it seems to affect many physical properties such as not only viscosity of melt state but also glass transition temperature (Tg). But we have not attained the quantitative estimation because the entanglement density is considered as an intrinsic value of the polymer at melt state depending on the chemical structure. Freeze-drying method is known as one of the few ways to make different entanglement density sample from dilute solution. In this study, the influence of entanglements on Tg of polystyrene obtained by the freeze-dried method was estimated quantitatively. The freeze-dried samples showed Tg depression with decreasing the concentration of precursor solution due to the lower entanglement density and their depressed Tg would be saturated when the almost no intermolecular entanglement was formed. The molecular weight dependence of the maximum value of Tg depression was discussed.

  12. Moderate temperature sodium cells. I - Transition metal disulfide cathodes

    NASA Technical Reports Server (NTRS)

    Abraham, K. M.; Pitts, L.; Schiff, R.

    1980-01-01

    TiS2, VS2, and Nb(1.1)S2 transition metal disulfides were evaluated as cathode materials for a moderate temperature rechargeable Na cell operating at 130 C. The 1st discharge of TiS2 results in a capacity of 0.85 eq/mole; approximately half of the Na in the 1st phase spanning the Na range from zero to 0.30 and almost all the Na in the 2nd phase spanning the 0.37 to 0.80 range are rechargeable. VS2 intercalates up to one mole of Na/mole of VS2 in the 1st discharge; the resulting Na(x)VS2 ternary consists of 3 phases in the 3 ranges of Na from zero to 1. Niobium disulfide undergoes a phase change in the 1st discharge; the average rechargeable capacity in extended cycling of this cathode is 0.50 eq/mole.

  13. Towards a better understanding of superconductivity at high transition temperatures

    NASA Astrophysics Data System (ADS)

    Hackl, R.; Hanke, W.

    2010-10-01

    We provide an overview over the following eleven contributions on superconductivity in copper-oxygen and iron-based compounds. The main objective of this volume is an improved general understanding of superconductivity at high transition temperatures. The key questions on the way towards understanding superconducting pairing beyond electron-phonon coupling are spelled out, and the present status of theoretical reasoning is summarized. The crucial experiments, their results and interrelations are discussed. The central result is that fluctuations of spin and charge contribute substantially to superconductivity and also to other ordering phenomena. Methodically, the simultaneous analysis of results obtained from different experimental techniques such as photoelectron spectroscopy and neutron scattering, on one and the same sample, turned out to be of pivotal importance.

  14. Investigation of Glass Transition Temperature of Binary Tellurite Glasses

    SciTech Connect

    Chippy, L.; Unnithan, C. Harikuttan; Jayakumar, S.

    2011-10-20

    Five series of binary Tellurite glass samples containing Sb{sub 2}O{sub 4}, WO{sub 3}, Fe{sub 2}O{sub 3}, Na{sub 2}O and ZnO{sub 2} are studied in terms of the variation of glass transition temperature (T{sub g}). It is seen that Tg increases as Tellurite concentration decreases in the case of glasses containing metal oxides Sb{sub 2}O{sub 4} WO{sub 3}, and Fe{sub 2}O{sub 3} while T{sub g} shows a decreasing trend with that of Na{sub 2}O and ZnO and the corresponding changes in the network structure are accounted to possible extent. The structural variations are analyzed using the concept of electronegativity.

  15. Phase transition in finite density and temperature lattice QCD

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Chen, Ying; Gong, Ming; Liu, Chuan; Liu, Yu-Bin; Liu, Zhao-Feng; Ma, Jian-Ping; Meng, Xiang-Fei; Zhang, Jian-Bo

    2015-06-01

    We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of β and ma at the lattice size 24 × 122 × 6. The calculation was done in the Taylor expansion formalism. We are able to calculate the first and second order derivatives of ≤ft< {\\bar{\\psi} \\psi } \\right> in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and that the magnitude of \\bar{\\psi} \\psi decreases under the influence of finite chemical potential in both channels. Supported by National Natural Science Foundation of China (11335001, 11105153, 11405178), Projects of International Cooperation and Exchanges NSFC (11261130311)

  16. Structural basis of the temperature transition of Pf1 bacteriophage

    PubMed Central

    Thiriot, David S.; Nevzorov, Alexander A.; Opella, Stanley J.

    2005-01-01

    The filamentous bacteriophage Pf1 undergoes a reversible temperature-dependent transition that is also influenced by salt concentrations. This structural responsiveness may be a manifestation of the important biological property of flexibility, which is necessary for long, thin filamentous assemblies as a protection against shear forces. To investigate structural changes in the major coat protein, one- and two-dimensional solid-state NMR spectra of concentrated solutions of Pf1 bacteriophage were acquired, and the structure of the coat protein determined at 0°C was compared with the structure previously determined at 30°C. Despite dramatic differences in the NMR spectra, the overall change in the coat protein structure is small. Changes in the orientation of the C-terminal helical segment and the conformation of the first five residues at the N-terminus are apparent. These results are consistent with prior studies by X-ray fiber diffraction and other biophysical methods. PMID:15741342

  17. CHARACTERIZING TRANSITION TEMPERATURE GAS IN THE GALACTIC CORONA

    SciTech Connect

    Wakker, Bart P.; Savage, Blair D.; Fox, Andrew J.; Benjamin, Robert A.; Shapiro, Paul R. E-mail: savage@astro.wisc.edu E-mail: benjamir@uww.edu

    2012-04-20

    We present a study of the properties of the transition temperature (T {approx} 10{sup 5} K) gas in the Milky Way corona, based on the measurements of O VI, N V, C IV, Si IV, and Fe III absorption lines seen in the far-ultraviolet spectra of 58 sight lines to extragalactic targets, obtained with the Far-Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph. In many sight lines the Galactic absorption profiles show multiple components, which are analyzed separately. We find that the highly ionized atoms are distributed irregularly in a layer with a scale height of about 3 kpc, which rotates along with the gas in the disk, without an obvious gradient in the rotation velocity away from the Galactic plane. Within this layer the gas has randomly oriented velocities with a dispersion of 40-60 km s{sup -1}. On average the integrated column densities are log N(O VI) = 14.3, log N(N V) = 13.5, log N(C IV) = 14.2, log N(Si IV) = 13.6, and log N(Fe III) = 14.2, with a dispersion of just 0.2 dex in each case. In sight lines around the Galactic center and Galactic north pole, all column densities are enhanced by a factor {approx}2, while at intermediate latitudes in the southern sky there is a deficit in N(O VI) of about a factor of two, but no deficit for the other ions. We compare the column densities and ionic ratios to a series of theoretical predictions: collisional ionization equilibrium, shock ionization, conductive interfaces, turbulent mixing, thick disk supernovae, static non-equilibrium ionization (NIE) radiative cooling, and an NIE radiative cooling model in which the gas flows through the cooling zone. None of these models can fully reproduce the data, but it is clear that NIE radiative cooling is important in generating the transition temperature gas.

  18. Crystalline to amorphous phase transition of tin oxide nanocrystals induced by SHI at low temperature

    SciTech Connect

    Kumar, Vijay; Pratap, Deepti; Jain, Anshul; Agarwal, D. C.; Sulania, I.; Tripathi, A.; Chaudhary, R. J.; Chauhan, R. S.

    2012-06-05

    Tin oxide (SnO{sub 2}) thin films were deposited using pulsed laser deposition (PLD) technique on Si substrates. The as-deposited films were irradiated using 100 MeV Ag ions at different fluences ranging from 3x10{sup 13} to 3x10{sup 14} ions/cm{sup 2} at an incidence angle of 75 deg. with respect to surface normal at liquid nitrogen (LN2) temperature. The as-deposited and irradiated films have been characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques to study the modifications in structural and surface morphological properties. Nanocrystalline film become completely amorphous and nanograins of tin oxide disappeared from the surface as indicated by XRD spectra and AFM micrographs respectively.

  19. Pressure dependence of glass transition temperature of elastomeric glasses

    NASA Astrophysics Data System (ADS)

    Pae, K. D.; Tang, C.-L.; Shin, E.-S.

    1984-11-01

    The pressure dependence of the glass transition temperature Tg of two elastomers, Solithane 113 and 3,3-bis(azidomethyl)oxetane/tetrahydrofuran (BAMO/THF) has been determined, employing high-pressure differential thermal analysis (HP-DTA) and dielectric techniques, up to 8.5 kbar. The glasses of the elastomers were named the specific (or Pi glass) or the general glass depending on how the glasses were formed. A Pi glass was formed by lowering temperature under a constant pressure (Pi) and the pressure dependency of the Pi glass was determined after changing pressure only in the glassy state. The general glass consists of a series of specific glasses but the Tg is determined only at pressures under which the glass is formed. The Tg for both glasses increased with increasing pressure. However, the Tg for the Pi glass appears to level off at very high pressures while the Tg does not level off for the general glass. Thermodynamic analysis was made to show that for many general glasses dTg/dP=Δβ/(1+n)Δα holds, in which n=1 for Solithane and many other glasses. It is also shown that a modified Gibbs and DiMarzio theory can be used effectively to predict the observed experimental results.

  20. Does Brillouin light scattering probe the primary glass transition process at temperatures well above glass transition?

    NASA Astrophysics Data System (ADS)

    Voudouris, P.; Gomopoulos, N.; Le Grand, A.; Hadjichristidis, N.; Floudas, G.; Ediger, M. D.; Fytas, G.

    2010-02-01

    The primary α-relaxation time (τα) for molecular and polymeric glass formers probed by dielectric spectroscopy and two light scattering techniques (depolarized light scattering and photon correlation spectroscopy) relates to the decay of the torsional autocorrelation function computed by molecular dynamics simulation. It is well known that Brillouin light scattering spectroscopy (BLS) operating in gigahertz frequencies probes a fast (10-100 ps) relaxation of the longitudinal modulus M∗. The characteristic relaxation time, irrespective of the fitting procedure, is faster than the α-relaxation which obeys the non-Arrhenius Vogel-Fulcher-Tammann equation. Albeit, this has been noticed, it remains a puzzling finding in glass forming systems. The available knowledge is based only on temperature dependent BLS experiments performed, however, at a single wave vector (frequency). Using a new BLS spectrometer, we studied the phonon dispersion at gigahertz frequencies in molecular [o-terphenyl (OTP)] and polymeric [polyisoprene (PI) and polypropylene (PP)] glass formers. We found that the hypersonic dispersion does relate to the glass transition dynamics but the disparity between the BLS-relaxation times and τα is system dependent. In PI and PP, the former is more than one order of magnitude faster than τα, whereas the two relaxation times become comparable in the case of OTP. The difference between the two relaxation times appears to relate to the "breadth" of the relaxation time distribution function. In OTP the α-relaxation process assumes a virtually single exponential decay at high temperatures well above the glass transition temperature, in clear contrast with the case of the amorphous bulk polymers.

  1. Does Brillouin light scattering probe the primary glass transition process at temperatures well above glass transition?

    PubMed

    Voudouris, P; Gomopoulos, N; Le Grand, A; Hadjichristidis, N; Floudas, G; Ediger, M D; Fytas, G

    2010-02-21

    The primary alpha-relaxation time (tau(alpha)) for molecular and polymeric glass formers probed by dielectric spectroscopy and two light scattering techniques (depolarized light scattering and photon correlation spectroscopy) relates to the decay of the torsional autocorrelation function computed by molecular dynamics simulation. It is well known that Brillouin light scattering spectroscopy (BLS) operating in gigahertz frequencies probes a fast (10-100 ps) relaxation of the longitudinal modulus M*. The characteristic relaxation time, irrespective of the fitting procedure, is faster than the alpha-relaxation which obeys the non-Arrhenius Vogel-Fulcher-Tammann equation. Albeit, this has been noticed, it remains a puzzling finding in glass forming systems. The available knowledge is based only on temperature dependent BLS experiments performed, however, at a single wave vector (frequency). Using a new BLS spectrometer, we studied the phonon dispersion at gigahertz frequencies in molecular [o-terphenyl (OTP)] and polymeric [polyisoprene (PI) and polypropylene (PP)] glass formers. We found that the hypersonic dispersion does relate to the glass transition dynamics but the disparity between the BLS-relaxation times and tau(alpha) is system dependent. In PI and PP, the former is more than one order of magnitude faster than tau(alpha), whereas the two relaxation times become comparable in the case of OTP. The difference between the two relaxation times appears to relate to the "breadth" of the relaxation time distribution function. In OTP the alpha-relaxation process assumes a virtually single exponential decay at high temperatures well above the glass transition temperature, in clear contrast with the case of the amorphous bulk polymers. PMID:20170250

  2. High Glass Transition Temperature Renewable Polymers via Biginelli Multicomponent Polymerization.

    PubMed

    Boukis, Andreas C; Llevot, Audrey; Meier, Michael A R

    2016-04-01

    A novel and straightforward one-pot multicomponent polycondensation method was established in this work. The Biginelli reaction is a versatile multicomponent reaction of an aldehyde, a β-ketoester (acetoacetate) and urea, which can all be obtained from renewable resources, yielding diversely substituted 3,4-dihydropyrimidin-2(1H)-ones (DHMPs). In this study, renewable diacetoacetate monomers with different spacer chain lengths (C3, C6, C10, C20) were prepared via simple transesterification of renewable diols and commercial acetoacetates. The diacetoacetate monomers were then reacted with renewable dialdehydes, i.e., terephthalaldehyde and divanillin in a Biginelli type step-growth polymerization. The obtained DHMP polymers (polyDHMPs) displayed high molar masses, high glass transition temperatures (Tg) up to 203 °C and good thermal stability (Td5%) of 280 °C. The Tg of the polyDHMPs could be tuned by variation of the structure of the dialdehyde or the diacetoacetate component. PMID:26800511

  3. Effect of impurities on the transition temperature of a dilute dipolar trapped Bose gas

    NASA Astrophysics Data System (ADS)

    Yavari, H.; Afsaneh, E.

    2013-01-01

    By using a two-fluid model the effect of impurities on the transition temperature of a dipolar trapped Bose gas is investigated. By treating Gaussian spatial correlation for impurities from the interaction modified spectra of the system, the formula for the shift of the transition temperature is derived. The shift of the transition temperature contains essentially three contributions due to contact, dipole-dipole, and impurity interactions. Applying our results to dipolar Bose gases shows that the shift of the transition temperature due to impurities could be measured for an isotropic trap (dipole-dipole contribution is zero) and the Feshbach resonance technique (contact potential contribution is negligible).

  4. Glass transition temperature and topological constraints of sodium borophosphate glass-forming liquids

    NASA Astrophysics Data System (ADS)

    Jiang, Qi; Zeng, Huidan; Liu, Zhao; Ren, Jing; Chen, Guorong; Wang, Zhaofeng; Sun, Luyi; Zhao, Donghui

    2013-09-01

    Sodium borophosphate glasses exhibit intriguing mixed network former effect, with the nonlinear compositional dependence of their glass transition temperature as one of the most typical examples. In this paper, we establish the widely applicable topological constraint model of sodium borophosphate mixed network former glasses to explain the relationship between the internal structure and nonlinear changes of glass transition temperature. The application of glass topology network was discussed in detail in terms of the unified methodology for the quantitative distribution of each coordinated boron and phosphorus units and glass transition temperature dependence of atomic constraints. An accurate prediction of composition scaling of the glass transition temperature was obtained based on topological constraint model.

  5. Fe Spin Reorientation across the Metamagnetic Transition in Strained FeRh Thin Films

    NASA Astrophysics Data System (ADS)

    Bordel, C.; Juraszek, J.; Cooke, David W.; Baldasseroni, C.; Mankovsky, S.; Minár, J.; Ebert, H.; Moyerman, S.; Fullerton, E. E.; Hellman, F.

    2012-09-01

    A spin reorientation accompanying the temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition is reported in strained epitaxial FeRh thin films. Fe57 conversion electron Mössbauer spectrometry showed that the Fe moments have different orientations in FeRh grown on thick single-crystalline MgO and in FeRh grown on ion-beam-assist-deposited (IBAD) MgO. It was also observed, in both samples, that the Fe moments switch orientations at the AFM to FM phase transition. Perpendicular anisotropy was evidenced in the AFM phase of the film grown on IBAD MgO and in the FM phase of that grown on regular MgO. Density-functional theory calculations enabled this spin-reorientation transition to be accurately reproduced for both FeRh films across the AFM-FM phase transition and show that these results are due to differences in strain.

  6. Fe spin reorientation across the metamagnetic transition in strained FeRh thin films.

    PubMed

    Bordel, C; Juraszek, J; Cooke, David W; Baldasseroni, C; Mankovsky, S; Minár, J; Ebert, H; Moyerman, S; Fullerton, E E; Hellman, F

    2012-09-14

    A spin reorientation accompanying the temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition is reported in strained epitaxial FeRh thin films. (57)Fe conversion electron Mössbauer spectrometry showed that the Fe moments have different orientations in FeRh grown on thick single-crystalline MgO and in FeRh grown on ion-beam-assist-deposited (IBAD) MgO. It was also observed, in both samples, that the Fe moments switch orientations at the AFM to FM phase transition. Perpendicular anisotropy was evidenced in the AFM phase of the film grown on IBAD MgO and in the FM phase of that grown on regular MgO. Density-functional theory calculations enabled this spin-reorientation transition to be accurately reproduced for both FeRh films across the AFM-FM phase transition and show that these results are due to differences in strain. PMID:23005667

  7. High transition temperatures in molecular intercalates of FeSe

    NASA Astrophysics Data System (ADS)

    Blundell, Stephen

    2015-03-01

    Molecular groups can now be intercalated into iron-based superconductors with dramatic consequences on the superconducting properties. These species act as charge reservoirs, sources of electrical polarization, and also make subtle structural modifications to superconducting layers, all of which can make novel adjustments to the band structure that in turn can control superconducting properties. By synthesizing the compound Lix(NH2)y(NH3)1 -yFe2Se2 (x ~ 0.6; y ~ 0.2), in which lithium ions, lithium amide and ammonia (NH3) act as the spacer layer between FeSe layers, we have turned a 9 K superconductor into a 43 K superconductor. Further chemical modification allow us to produce a range of new superconducting materials which we have studied using a variety of techniques including muon-spin rotation. Recently, we have used hydrothermal reactions to produce layered lithium iron selenide hydroxides with chemical formula Li1-xFex(OH)Fe1-ySe and thereby producing compounds whose transition temperature can be tuned from zero up to about 40 K. Minimizing the concentration of iron vacancies in the iron selenide layer and simultaneously increasing the electron count on iron in the selenide layers enhance the superconducting properties in this family. Future prospects for new superconducting materials using these novel synthetic routes will be discussed, as will also our current understanding of the superconductivity in these materials. (Work performed in collaboration with S. J. Clarke and coworkers at Oxford, RAL and Durham, UK.) Work supported by EPSRC(UK).

  8. High transition-temperature SQUID magnetometers and practical applications

    SciTech Connect

    Dantsker, E

    1997-05-01

    The design, fabrication and performance of SQUID magnetometers based on thin films of the high-transition temperature superconductor YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) are described. Essential to the achieving high magnetic field resolution at low frequencies is the elimination of 1/f flux noise due to thermally activated hopping of flux vortices between pinning sites in the superconducting films. Through improvements in processing, 1/f noise in single layer YBCO thin films and YBCO-SrTiO{sub 3}-YBCO trilayers was systematically reduced to allow fabrication of sensitive SQUID magnetometers. Both single-layer directly coupled SQUID magnetometers and multilayer magnetometers were fabricated, based on the dc SQUID with bicrystal grain boundary Josephson junctions. Multilayer magnetometers had a lower magnetic field noise for a given physical size due to greater effective sensing areas. A magnetometer consisting of a SQUID inductively coupled to the multiturn input coil of a flux transformer in a flip-chip arrangement had a field noise of 27 fT Hz{sup {minus}1/2} at 1 Hz and 8.5 fT Hz{sup {minus}1/2} at 1 kHz. A multiloop multilayer SQUID magnetometer had a field noise of 37 fT Hz{sup {minus}1/2} at 1 Hz and 18 fT Hz{sup {minus}1/2} at 1 kHz. A three-axis SQUID magnetometer for geophysical applications was constructed and operated in the field in the presence of 60 Hz and radiofrequency noise. Clinical quality magnetocardiograms were measured using multilayer SQUID magnetometers in a magnetically shielded room.

  9. Magnetic biosensor using a high transition temperature SQUID

    NASA Astrophysics Data System (ADS)

    Grossman, Helene Lila

    A high transition temperature (Tc) Superconducting QUantum Interference Device (SQUID) is used to detect magnetically-labeled microorganisms. The targets are identified and quantified by means of magnetic relaxation measurements, with no need for unbound magnetic labels to be washed away. The binding rate between antibody-linked magnetic particles and targets can be measured with this technique. Installed in a "SQUID microscope," a YBa2Cu 3O7-delta SQUID is mounted on a sapphire rod thermally linked to a liquid nitrogen can; these components are enclosed in a fiberglass vacuum chamber. A thin window separates the vacuum chamber from the sample, which is at room temperature and atmospheric pressure. In one mode of the experiment, targets are immobilized on a substrate and immersed a suspension of ˜50 nm diameter superparamagnetic particles, coated with antibodies. A pulsed magnetic field aligns the magnetic dipole moments, and the SQUID measures the magnetic relaxation signal each time the field is turned off. Unbound particles relax within ˜50 mus by Brownian rotation, too fast for the SQUID system to measure. In contrast, particles bound to targets have their Brownian motion inhibited. These particles relax in ˜1 s by rotation of the internal dipole moment, and this Neel relaxation process is detected by the SQUID. This assay is demonstrated with a model system of liposomes carrying the FLAG epitope; the detection limit is (2.7 +/- 0.2) x 105 particles. The replacement of the SQUID with a gradiometer improves the detection limit to (7.0 +/- 0.7) x 103 particles. In an alternate mode of the experiment, freely suspended targets (larger than ˜1 mum diameter) are detected. Since the Brownian relaxation time of the targets is longer than the measurement time, particles bound to targets are effectively immobilized and exhibit Neel relaxation. Listeria monocytogenes are detected using this method; the sensitivity is (1.1 +/- 0.2) x 105 bacteria in 20 muL. For a 1 n

  10. Low temperature magnetic transition and high temperature oxidation in INCONEL alloy 718

    SciTech Connect

    Seehra, M.S.; Babu, V.S.

    1996-05-01

    X-ray diffraction and temperature dependent (5 K{endash}380 K) magnetic measurements have been carried out in INCONEL 718 superalloy before and after high temperature aging treatments (INCONEL is a trademark of the INCO family of companies). The nominal composition of this alloy is Ni (52.5{percent}), Cr (19.0{percent}), Fe (18.5{percent}), Nb (5.1{percent}), Mo (3.0{percent}), Ti (0.9{percent}), Al (0.5{percent}), Cu (0.15{percent}) and C (0.08{percent}) and it yields an x-ray diffraction pattern consisting of a fcc phase with {ital a}=3.5987 (3) A and an orthorhombic phase associated with {delta}{minus}Ni{sub 3}Nb. It is concluded that the fcc pattern is due to both the {gamma} austenitic phase and {gamma}{prime} Ni{sub 3}(Al,Ti) phase of alloy 718. The standard annealing and aging treatment carried out in air at temperatures between 621 and 982{degree}C produces surface oxides (Cr,Fe){sub 2}O{sub 3} and FeNbO{sub 4} (which are easily removed by etching and polishing) and contracts the lattice. Magnetic measurements show a distinct phase transition at {ital T}{sub {ital c}}=14 K, which has been attributed to the {gamma}{prime}{minus}Ni{sub 3}(Al,Ti) phase by the process of elimination and by observing that it has most of the characteristics of the weak itinerant ferromagnet Ni{sub 74.5}Al{sub 25.5}. This transition may have some effects on the cryogenic applications of this alloy. {copyright} {ital 1996 Materials Research Society.}

  11. QCD chiral transition temperature in a Dyson-Schwinger-equation context

    SciTech Connect

    Blank, M.; Krassnigg, A.

    2010-08-01

    We analyze the chiral phase transition with the help of the QCD gap equation. Various models for the effective interaction in rainbow truncation are contrasted with regard to the resulting chiral transition temperatures. In particular, we investigate possible systematic relations of the details of the effective interaction and the value of T{sub c}. In addition, we quantify changes to the transition temperature beyond the rainbow truncation.

  12. Molecular Motion in Polymers: Mechanical Behavior of Polymers Near the Glass-Rubber Transition Temperature.

    ERIC Educational Resources Information Center

    Sperling, L. H.

    1982-01-01

    The temperature at which the onset of coordinated segmental motion begins is called the glass-rubber transition temperature (Tg). Natural rubber at room temperature is a good example of a material above its Tg. Describes an experiment examining the response of a typical polymer to temperature variations above and below Tg. (Author/JN)

  13. An Overview of the Glass Transition Temperature of Synthetic Polymers.

    ERIC Educational Resources Information Center

    Beck, Keith R.; And Others

    1984-01-01

    Presents an overview of the glass-to-rubber transition, what it is, why it is important, and the major factors that influence it. Indicates that this information should be incorporated into chemistry curricula. (JN)

  14. Process for preparing high-transition-temperature superconductors in the Nb-Al-Ge system

    DOEpatents

    Giorgi, A.L.; Szklarz, E.G.

    1973-01-30

    The patent describes a process for preparing superconducting materials in the Nb-Al-Ge system having transition temperatures in excess of 19K. The process comprises premixing powdered constituents, pressing them into a plug, heating the plug to 1,450-1,800C for 30 minutes to an hour under vacuum or an inert atmosphere, and annealing at moderate temperatures for reasonably long times (approximately 50 hours). High transition-temperature superconductors, including those in the Nb3(Al,Ge) system, prepared in accordance with this process exhibit little degradation in the superconducting transition temperature on being ground to -200 mesh powder. (GRA)

  15. Magnetic-field-induced irreversible antiferromagnetic-ferromagnetic phase transition around room temperature in as-cast Sm-Co based SmCo7-xSix alloys

    NASA Astrophysics Data System (ADS)

    Feng, D. Y.; Zhao, L. Z.; Liu, Z. W.

    2016-04-01

    A magnetic-field-induced irreversible metamagnetic phase transition from antiferro- to ferromagnetism, which leads to an anomalous initial-magnetization curve lying outside the magnetic hysteresis loop, is reported in arc-melted SmCo7-xSix alloys. The transition temperatures are near room temperature, much higher than other compounds with similar initial curves. Detailed investigation shows that this phenomenon is dependent on temperature, magnetic field and Si content and shows some interesting characteristics. It is suggested that varying interactions between the Sm and Co layers in the crystal are responsible for the formation of a metastable AFM structure, which induces the anomalous phenomenon in as-cast alloys. The random occupation of 3g sites by Si and Co atoms also has an effect on this phenomenon.

  16. Effect of MnAs/GaAs(001) film accommodations on the phase-transition temperature

    SciTech Connect

    Iikawa, F.; Brasil, M.J.S.P.; Couto, O.D.D.; Adriano, C.; Giles, C.; Daeweritz, L.

    2004-09-20

    The phase-transition temperature of MnAs epitaxial films grown by molecular-beam epitaxy on GaAs(001) with different crystalline accommodations was studied by specular and grazing incidence x-ray diffraction. The transition temperature of MnAs films with tilted hexagonal c-axis orientations with respect to the GaAs substrate is higher than the most investigated nontilted films and reaches a value above room temperature, which is more suitable for device applications.

  17. Using Rare Gas Permeation to Probe Methanol Diffusion near the Glass Transition Temperature

    NASA Astrophysics Data System (ADS)

    Matthiesen, Jesper; Smith, R. Scott; Kay, Bruce D.

    2009-12-01

    The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition.

  18. Using rare gas permeation to probe methanol diffusion near the glass transition temperature.

    PubMed

    Matthiesen, Jesper; Smith, R Scott; Kay, Bruce D

    2009-12-11

    The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition. PMID:20366212

  19. Evidence for a finite-temperature phase transition in a bilayer quantum Hall system.

    PubMed

    Champagne, A R; Eisenstein, J P; Pfeiffer, L N; West, K W

    2008-03-01

    We study the Josephson-like interlayer tunneling signature of the strongly correlated nuT=1 quantum Hall phase in bilayer two-dimensional electron systems as a function of the layer separation, temperature, and interlayer charge imbalance. Our results offer strong evidence that a finite temperature phase transition separates the interlayer coherent phase from incoherent phases which lack strong interlayer correlations. The transition temperature is dependent on both the layer spacing and charge imbalance between the layers. PMID:18352740

  20. Evidence for a Finite-Temperature Phase Transition in a Bilayer Quantum Hall System

    NASA Astrophysics Data System (ADS)

    Champagne, A. R.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.

    2008-03-01

    We study the Josephson-like interlayer tunneling signature of the strongly correlated νT=1 quantum Hall phase in bilayer two-dimensional electron systems as a function of the layer separation, temperature, and interlayer charge imbalance. Our results offer strong evidence that a finite temperature phase transition separates the interlayer coherent phase from incoherent phases which lack strong interlayer correlations. The transition temperature is dependent on both the layer spacing and charge imbalance between the layers.

  1. Influence of film composition on the transition temperature of FeRh films

    NASA Astrophysics Data System (ADS)

    Jiang, M.; Chen, X. Z.; Zhou, X. J.; Wang, Y. Y.; Pan, F.; Song, C.

    2016-03-01

    We investigate the influences of film composition, tuned by argon growth pressure and palladium doping, on antiferromagnetic to ferromagnetic transition temperatures of FeRh films. Employing complementary characterizations we show that the CsCl-type FeRh grows on MgO (100) substrate epitaxially with a controllable transition temperature. Lower argon pressure, a suitable palladium doping are found to effectively decrease the transition temperature. In addition, the exploration about the influence of post-annealing time on un-doped FeRh films indicates that annealing procedure is helpful to improve the growth quality. The optimized growth parameter provides an opportunity to deposit ultrathin FeRh films (5 nm) with a clear antiferromagnetic to ferromagnetic transition. The manipulation of the transition temperature of FeRh would advance its use in antiferromagnetic spintronics.

  2. Boron-tuning transition temperature of vanadium dioxide from rutile to monoclinic phase

    SciTech Connect

    Zhang, J. J.; He, H. Y.; Xie, Y.; Pan, B. C.

    2014-11-21

    The effect of the doped boron on the phase transition temperature between the monoclinic phase and the rutile phase of VO{sub 2} has been studied by performing first-principles calculations. It is found that the phase transition temperature decreases linearly with increasing the doping level of B in each system, no matter where the B atom is in the crystal. More importantly, the descent of the transition temperature is predicted to be as large as 83 K/at. % B, indicating that the boron concentration of only 0.5% can cause the phase transition at room temperature. These findings provide a new routine of modulating the phase transition of VO{sub 2} and pave a way for the practicality of VO{sub 2} as an energy-efficient green material.

  3. Tracking the Verwey Transition in Single Magnetite Nanocrystals by Variable-Temperature Scanning Tunneling Microscopy.

    PubMed

    Hevroni, Amir; Bapna, Mukund; Piotrowski, Stephan; Majetich, Sara A; Markovich, Gil

    2016-05-01

    Variable-temperature scanning tunneling spectroscopy revealed a sharp Verwey transition in individual ∼10 nm magnetite nanocrystals prepared by the coprecipitation technique and embedded in the surface of a gold film. The transition was observed as a significant change in the electronic structure around the Fermi level, with an apparent band gap of ∼140-250 meV appearing below the transition temperature and a pseudogap of ∼75 ± 10 meV appearing above it. The transition temperature was invariably observed around 101 ± 2 K for different nanocrystals, as opposed to 123 K typically reported for stoichiometric bulk crystals. This suggests that the lowering of the transition temperature is an intrinsic finite size effect, probably due to the presence of the surface. PMID:27088645

  4. Structure-to-glass transition temperature relationships in high temperature stable condensation polyimides

    NASA Technical Reports Server (NTRS)

    Alston, W. B.; Gratz, R. F.

    1985-01-01

    The presence of a hexafluoroisopropylidene (6F) connecting group in aryl dianhydrides used to prepare aromatic condensation polyimides provides high glass transition temperature (T sub g) polyimides with excellent thermo-oxidative stability. The purpose of this study was to determine if a trifluorophenyl-ethylidene (3F) connecting group would have a similar effect on the T sub g of aromatic condensation polyimides. A new dianhydride containing the 3F connecting group was synthesized. This dianhydride and an aromatic diamine also containing the 3F connecting group were used together and in various combinations with known diamines or known dianhydrides, respectively, to prepare new 3F containing condensation polyimides. Known polyimides, including some with the 6F connecting linkage, were also prepared for comparison purposes. The new 3F containing polymers and the comparison polymers were prepared by condensation polymerization via the traditional amic-acid polymerization method in N,N-dimethylacetamide solvent. The solutions were characterized by determining their inherent viscosities and then were thermally converted into polyimide films under nitrogen atmosphere at 300 to 500 C, usually 350 C. The T sub g's of the films and resin discs were then determined by thermomechanical analysis and were correlated as a function of the final processing temperatures of the films and resin discs. The results showed that similarities existed in the T sub g's depending on the nature of the connecting linkage in the monomers used to prepare the condensation polyimides.

  5. Structural dynamics in FeRh during a laser-induced metamagnetic phase transition

    NASA Astrophysics Data System (ADS)

    Quirin, Florian; Vattilana, Michael; Shymanovich, Uladzimir; El-Kamhawy, Abd-Elmoniem; Tarasevitch, Alexander; Hohlfeld, Julius; von der Linde, Dietrich; Sokolowski-Tinten, Klaus

    2012-01-01

    Time-resolved x-ray diffraction with ultrashort x-ray pulses from a laser-produced plasma is used to study the lattice response of FeRh during a femtosecond laser-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition. Pump-probe measurements at initial sample temperatures below as well as above the AFM-to-FM transition temperature and for different laser pump fluences allowed to disentangle the various contributions driving lattice expansion. In particular, the data reveal that the structural changes associated with the magnetic phase transition occur on a time scale of a hundred picoseconds.

  6. Transition in Hypersonic Flows Including High-temperature Gas Effects

    NASA Technical Reports Server (NTRS)

    Stemmer, Christian

    2003-01-01

    Hypersonic transition poses a special challenge for direct numerical simulations. Comparable data from Wind-tunnel tests or free-flight testing are not available or not accurate enough for comparison. The wind-tunnel testing does not allow for the exact match to the free-flight conditions at such high Mach-numbers. Flat-plate boundary-layer transition at high Mach-numbers is investigated in this work. A simulation case was chosen where chemical non-equilibrium plays an important role but ionization can be neglected. The chosen case at an altitude of H=50Km lies close to one point on the descent path of the Space Shuttle. The failure of the Space Shuttle has shown that an improved vehicle for space transportation is imperative in the close future. Transition research for an improved space-transportation vehicle is crucial in order to estimate the heat load during re-entry.

  7. Depression of the Superfluid Transition Temperature in 4He by a Heat Flow

    NASA Astrophysics Data System (ADS)

    Yin, Liang; Lin, Peng; Qi, Xin

    2014-11-01

    The depression of the superfluid transition temperature Tλ in 4He by a heat flow Q is studied. A small sealed cell with a capillary is introduced and a stable and flat superfluid transition temperature plateau is easily obtained by controlling the temperature of the variable-temperature platform and the bottom chamber of the sealed cell. Owing to the depression effect of the superfluid transition temperature by the heat flow, the heat flow through the capillary is changed by the temperature control to obtain multiple temperature plateaus of different heat flows. The thermometer self-heating effect, the residual heat leak of the 4.2 K environment, the temperature difference on the He II liquid column, the Kapiza thermal resistance between the liquid helium and the copper surface of the sealed cell, the temperature gradient of the sealed cell, the static pressure of the He II liquid column and other factors have influence on the depression effect and the influence is analyzed in detail. Twenty experiments of the depression of the superfluid transition temperature in 4He by heat flow are made with four sealed cells in one year. The formula of the superfluid transition temperature pressured by the heat flow is Tλ (Q) = -0.00000103Q + 2.1769108, and covers the range 229 <= Q <= 6462 μW/cm2.

  8. Ferromagnetic Ground States with High Transition Temperatures in New Tetragonal Rare-Earth Compounds CeRu2Al2B and PrRu2Al2B

    NASA Astrophysics Data System (ADS)

    Matsuoka, Eiichi; Tomiyama, Yo; Sugawara, Hitoshi; Sakurai, Takahiro; Ohta, Hitoshi

    2012-04-01

    We report on the discovery of ferromagnetic ground states in the newly synthesized tetragonal compounds CeRu2Al2B and PrRu2Al2B. Polycrystalline samples of these compounds were synthesized and their magnetization M(B) and electrical resistivity ρ(T) were measured as functions of the magnetic field B and the temperature T. CeRu2Al2B is a metallic compound with trivalent Ce ions and is classified into a Kondo-lattice system: a Kondo-like -\\ln T dependence of ρ(T) is observed below 32 K. The cusp at TN{}Ce = 14.3 K and the steep increase at approximately TC{}Ce = 13 K observed in the magnetic susceptibility M/B(T) correspond to antiferromagnetic (AFM) and ferromagnetic (FM) transitions, respectively. TC{}Ce is the second highest transition temperature of the Ce-based ferromagnet with no other magnetic elements. PrRu2Al2B is also a metallic compound with trivalent Pr ions. The M/B(T) of PrRu2Al2B shows a cusp at TN{}Pr = 26 K and a steep increase at approximately TC{}Pr = 11 K, indicating that AFM and FM transitions occur at TN{}Pr and TC{}Pr, respectively.

  9. Probing the Glass Transition from Structural and Vibrational Properties of Zero-Temperature Glasses

    NASA Astrophysics Data System (ADS)

    Wang, Lijin; Xu, Ning

    2014-02-01

    We find that the density dependence of the glass transition temperature of Lennard-Jones (LJ) and Weeks-Chandler-Andersen (WCA) systems can be predicted from properties of the zero-temperature (T=0) glasses. Below a crossover density ρs, LJ and WCA glasses show different structures, leading to different vibrational properties and consequently making LJ glasses more stable with higher glass transition temperatures than WCA ones. Above ρs, structural and vibrational quantities of the T =0 glasses show scaling collapse. From scaling relations and dimensional analysis, we predict a density scaling of the glass transition temperature, in excellent agreement with simulation results. We also propose an empirical expression of the glass transition temperature using structural and vibrational properties of the T=0 glasses, which works well over a wide range of densities.

  10. Transition temperature and fracture mode of as-castand austempered ductile iron.

    PubMed

    Rajnovic, D; Eric, O; Sidjanin, L

    2008-12-01

    The ductile to brittle transition temperature is a very important criterion that is used for selection of materials in some applications, especially in low-temperature conditions. For that reason, in this paper transition temperature of as-cast and austempered copper and copper-nickel alloyed ductile iron (DI) in the temperature interval from -196 to +150 degrees C have been investigated. The microstructures of DIs and ADIs were examined by light microscope, whereas the fractured surfaces were observed by scanning electron microscope. The ADI materials have higher impact energies compared with DIs in an as-cast condition. In addition, the transition curves for ADIs are shifted towards lower temperatures. The fracture mode of Dls is influenced by a dominantly pearlitic matrix, exhibiting mostly brittle fracture through all temperatures of testing. By contrast, with decrease of temperature, the fracture mode for ADI materials changes gradually from fully ductile to fully brittle. PMID:19094047

  11. Glass transition temperature of a cationic polymethacrylate dependent on the plasticizer content - Simulation vs. experiment

    NASA Astrophysics Data System (ADS)

    Wagner, Karl G.; Maus, Martin; Kornherr, Andreas; Zifferer, Gerhard

    2005-04-01

    Atomistic molecular dynamics simulations ( NPT ensemble) are performed to compute the specific volume as a function of temperature of cationic polymethacrylate (Eudragit ® RS) with varying plasticizer (triethylcitrate) content ranging from pure polymer to a plasticizer weight proportion of 7.70%. The simulated glass transition temperature of these polymer-plasticizer blends is determined as the temperature marking the kink in the slope of specific volume vs. temperature plots. A linear dependence of the glass transition temperature on the plasticizer content is found. The computational findings are supported by differential scanning calorimetry experiments showing the same trend thus validating the applied computational method.

  12. Unraveling protein stabilization mechanisms: vitrification and water replacement in a glass transition temperature controlled system.

    PubMed

    Grasmeijer, N; Stankovic, M; de Waard, H; Frijlink, H W; Hinrichs, W L J

    2013-04-01

    The aim of this study was to elucidate the role of the two main mechanisms used to explain the stabilization of proteins by sugar glasses during drying and subsequent storage: the vitrification and the water replacement theory. Although in literature protein stability is often attributed to either vitrification or water replacement, both mechanisms could play a role and they should be considered simultaneously. A model protein, alkaline phosphatase, was incorporated in either inulin or trehalose by spray drying. To study the storage stability at different glass transition temperatures, a buffer which acts as a plasticizer, ammediol, was incorporated in the sugar glasses. At low glass transition temperatures (<50°C), the enzymatic activity of the protein strongly decreased during storage at 60°C. Protein stability increased when the glass transition temperature was raised considerably above the storage temperature. This increased stability could be attributed to vitrification. A further increase of the glass transition temperature did not further improve stability. In conclusion, vitrification plays a dominant role in stabilization at glass transition temperatures up to 10 to 20°C above storage temperature, depending on whether trehalose or inulin is used. On the other hand, the water replacement mechanism predominantly determines stability at higher glass transition temperatures. PMID:23360765

  13. A simplified ductile-brittle transition temperature tester

    NASA Technical Reports Server (NTRS)

    Arias, A.

    1973-01-01

    The construction and operation of a versatile, simplified bend tester is described. The tester is usable at temperatures from - 192 to 650 C in air. Features of the tester include a single test chamber for cryogenic or elevated temperatures, specimen alining support rollers, and either manual or motorized operation.

  14. Temperature-dependent phase transitions of a complex biological membrane in zeptoliter volumes

    SciTech Connect

    Nikiforov, Maxim; Hohlbauch, Sophia; King, William P; Voitchovsky, K; Contera, S Antoranz; Jesse, Stephen; Kalinin, Sergei V; Proksch, Roger

    2011-01-01

    Phase transitions in purple membrane have been a topic of debate for the past two decades. In this work we present studies of a reversible transition of purple membrane in the 50 60 C range in zeptoliter volumes under different heating regimes (global heating and local heating). The temperature of the reversible phase transition is 52 5 C for both local and global heating, supporting the hypothesis that this transition is mainly due to a structural rearrangement of bR molecules and trimers. To achieve high resolution measurements of temperature-dependent phase transitions, a new scanning probe microscopy-based method was developed. We believe that our new technique can be extended to other biological systems and can contribute to the understanding of inhomogeneous phase transitions in complex systems.

  15. Measuring the Transition Temperature of a Superconductor in a Pre-University Laboratory

    ERIC Educational Resources Information Center

    Ireson, Gren

    2006-01-01

    This article presents the methodology and results for a simple approach to the measurement of the transition temperature of a superconducting material, in a pre-university laboratory session, using readily available apparatus (and some liquid nitrogen).

  16. Glass Transition Temperature of Saccharide Aqueous Solutions Estimated with the Free Volume/Percolation Model.

    PubMed

    Constantin, Julian Gelman; Schneider, Matthias; Corti, Horacio R

    2016-06-01

    The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions has been predicted as a function of the water content by using the free volume/percolation model (FVPM). This model only requires the molar volume of water in the liquid and supercooled regimes, the molar volumes of the hypothetical pure liquid sugars at temperatures below their pure glass transition temperatures, and the molar volumes of the mixtures at the glass transition temperature. The model is simplified by assuming that the excess thermal expansion coefficient is negligible for saccharide-water mixtures, and this ideal FVPM becomes identical to the Gordon-Taylor model. It was found that the behavior of the water molar volume in trehalose-water mixtures at low temperatures can be obtained by assuming that the FVPM holds for this mixture. The temperature dependence of the water molar volume in the supercooled region of interest seems to be compatible with the recent hypothesis on the existence of two structure of liquid water, being the high density liquid water the state of water in the sugar solutions. The idealized FVPM describes the measured glass transition temperature of sucrose, glucose, and fructose aqueous solutions, with much better accuracy than both the Gordon-Taylor model based on an empirical kGT constant dependent on the saccharide glass transition temperature and the Couchman-Karasz model using experimental heat capacity changes of the components at the glass transition temperature. Thus, FVPM seems to be an excellent tool to predict the glass transition temperature of other aqueous saccharides and polyols solutions by resorting to volumetric information easily available. PMID:27176640

  17. On an anomalous kinetic in irradiated polymers around the glass transition temperature

    NASA Astrophysics Data System (ADS)

    Chipara, Mircea I.

    1997-08-01

    Anomalies occurring in irradiated polymers within the glass transition range, as reported by various authors are critically reviewed. A theoretical description for such processes, is developed within the free volume approximation. The discrepancies between the temperature at which such anomalies are noticed and the glass transition temperature have been ascribed to the fact that the volume of radiation-induced radicals is not equal with the segmental one. The agreement between experiment and theory is good.

  18. Sex reversal triggers the rapid transition from genetic to temperature-dependent sex.

    PubMed

    Holleley, Clare E; O'Meally, Denis; Sarre, Stephen D; Marshall Graves, Jennifer A; Ezaz, Tariq; Matsubara, Kazumi; Azad, Bhumika; Zhang, Xiuwen; Georges, Arthur

    2015-07-01

    Sex determination in animals is amazingly plastic. Vertebrates display contrasting strategies ranging from complete genetic control of sex (genotypic sex determination) to environmentally determined sex (for example, temperature-dependent sex determination). Phylogenetic analyses suggest frequent evolutionary transitions between genotypic and temperature-dependent sex determination in environmentally sensitive lineages, including reptiles. These transitions are thought to involve a genotypic system becoming sensitive to temperature, with sex determined by gene-environment interactions. Most mechanistic models of transitions invoke a role for sex reversal. Sex reversal has not yet been demonstrated in nature for any amniote, although it occurs in fish and rarely in amphibians. Here we make the first report of reptile sex reversal in the wild, in the Australian bearded dragon (Pogona vitticeps), and use sex-reversed animals to experimentally induce a rapid transition from genotypic to temperature-dependent sex determination. Controlled mating of normal males to sex-reversed females produces viable and fertile offspring whose phenotypic sex is determined solely by temperature (temperature-dependent sex determination). The W sex chromosome is eliminated from this lineage in the first generation. The instantaneous creation of a lineage of ZZ temperature-sensitive animals reveals a novel, climate-induced pathway for the rapid transition between genetic and temperature-dependent sex determination, and adds to concern about adaptation to rapid global climate change. PMID:26135451

  19. Deconfinement Transition and High Temperature Phase in Lattice Gauge Theories

    NASA Astrophysics Data System (ADS)

    Papa, Alessandro

    2002-09-01

    This paper is organized in two parts. In the first one, I present a recent determination of the critical exponent ν of the correlation length in 3D SU(3) and in 4D SU(2) pure gauge theories at finite temperature, by a new approach inspired by-universality and based on finite size scaling. Moreover, I discuss possible implications of universality on the spectrum of screening masses in 4D SU(2) just above the critical temperature. In the second part, I propose two topics, well known in the literature, to be investigated by numerical simulations on the lattice, namely the Polyakov loop model by Pisarski for the high temperature phase of 4D SU(N) pure gauge theories and the Roberge-Weiss formulation of 4D SU(N) gauge theories with fermions and with imaginary chemical potential.

  20. Broad resistive transition under magnetic field in high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo; Ni, Baorong

    1990-04-01

    A significantly broad resistive transition has been observed in high-temperature superconductors in magnetic fields, and its mechanism has been extensively discussed. A similar broad transition was observed by French et al. in 1967 even for low-temperature superconductors, where a variation in the magnetic field dependence of the resistance was measured for various current densities. The resistive properties in low-temperature superconductors are mainly determined by the fluxoid motion. Hence, this suggests that the resistive properties of high-temperature superconductors are similarly determined. In this paper, the broad resistive transition in high-temperature superconductors expected from the simple flux flow is estimated. The fluxoid motion in the longitudinal field geometry where the Lorentz force does not work is also discussed.

  1. Finite-temperature fluid-insulator transition of strongly interacting 1D disordered bosons.

    PubMed

    Michal, Vincent P; Aleiner, Igor L; Altshuler, Boris L; Shlyapnikov, Georgy V

    2016-08-01

    We consider the many-body localization-delocalization transition for strongly interacting one-dimensional disordered bosons and construct the full picture of finite temperature behavior of this system. This picture shows two insulator-fluid transitions at any finite temperature when varying the interaction strength. At weak interactions, an increase in the interaction strength leads to insulator [Formula: see text] fluid transition, and, for large interactions, there is a reentrance to the insulator regime. It is feasible to experimentally verify these predictions by tuning the interaction strength with the use of Feshbach or confinement-induced resonances, for example, in (7)Li or (39)K. PMID:27436894

  2. Phases transitions and interfaces in temperature-sensitive colloidal systems

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Schall, Peter

    2013-03-01

    Colloids are widely used because of their exceptional properties. Beside their own applications in food, petrol, cosmetics and drug industries, photonic, optical filters and chemical sensor, they are also known as powerful model systems to study molecular phase behavior. Here, we examine both aspects of colloids using temperature-sensitive colloidal systems to fully investigate colloidal phase behavior and colloidal assembly.

  3. Pressure-temperature phase transition diagram for wheat starch.

    PubMed

    Douzals, J P; Perrier-Cornet, J M; Coquille, J C; Gervais, P

    2001-02-01

    Wheat starch suspensions in water (5% dry matter) were subjected to various pressures (0.1-600 MPa) and temperatures (-20 to 96 degrees C) for 15 min. The gelatinization rate was measured after treatment by using microscopic measurements of the loss of birefringence of the granules. This method was previously calibrated by differential scanning calorimetry. Curves of isogelatinization were found to be quite similar to a pressure-temperature (P-T) diagram of unfolding proteins. Results were first analyzed by considering the thermodynamic aspects related to the dT/dP curve shifts. On the basis of equations already shown for proteins, the P-T gelatinization diagram of wheat starch would show different kinds of thermal contributions, suggesting endothermic, athermic, or exothermic melting reactions. Second, as a practical consequence, these previous P-T areas corresponded to specific gelatinization conditions as confirmed by hydration evaluation measured by starch swelling index. Depending on the pressure-temperature conditions, gelatinization would involve hydration. Lowering the pressure and temperature resulted in a complete gelatinization with less hydration in comparison with a thermal treatment at atmospheric pressure. A hydration model based on an energetic approach was proposed. PMID:11262043

  4. Electric field increases the phase transition temperature in the bilayer membrane of phosphatidic acid.

    PubMed

    Antonov, V F; Smirnova EYu; Shevchenko, E V

    1990-02-01

    The effect of the electric field on the phase transition temperature (Tc) of acidic 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA) and 1,2-dipalmitoyl-sn-glycero-3-thionphosphate (thion-DPPA) and zwitterion, i.e. 1,2-dipalmitoyl-rac-3-phosphocholine and 1,2-distearoyl-rac-glycero-3-phosphocholine (DPPC and DSPC), lipids has been investigated. The phase transition was detected using the jump-like increase effect in the conductance of the planar bilayer membrane. A voltage increase to 150 mV has been shown to increase the phase transition temperature in a bilayer lipid membrane (BLM) of phosphatidic acids (DPPA and thion-DPPA) by 8-12 degrees C while the transition temperature in the bilayer of zwitterion lipids (DPPC and DSPC) increases insignificantly. The increasing of Tt in BLM of acidic lipids is attributed to the voltage-induced changes in the molecule packing density. PMID:2340602

  5. Investigation of coal char-slag transition during oxidation: effect of temperature and residual carbon

    SciTech Connect

    Suhui Li; Kevin J. Whitty

    2009-04-15

    The transition of coal char to molten slag at high conversion was studied for a bituminous coal using a laminar entrained-flow reactor under oxidizing conditions. Post-oxidized char particles were analyzed by various techniques including loss-on-ignition, gas adsorption analysis, and scanning electron microscopy to determine carbon content, internal surface area and pore size distribution, and char morphology, respectively. These analyses provide information concerning the effect of temperature and residual carbon on the transition from porous char to molten slag. Results showed that, at temperatures above the ash flow temperature, the transition from porous char to molten slag occurred at about 90% conversion for the coal used in this study. No transition occurred at temperatures below the ash flow temperature. This finding explains previous observations that there is a coal-dependent critical carbon conversion at which the ash stickiness increases dramatically. This result also indicates that surface area can be used as a criterion for determining the critical conversion of the transition. In addition, it was found that the randomly overlapping pore model cannot be directly applied to predict the surface area evolution of char particles during the transition without considering the reopening of closed micropores during the initial reaction and the ash fusion effect. 33 refs., 9 figs., 2 tabs.

  6. Confinement effects on glass transition temperature, transition breadth, and expansivity: Comparison of ellipsometry and fluorescence measurements on polystyrene films

    NASA Astrophysics Data System (ADS)

    Kim, S.; Hewlett, S. A.; Roth, C. B.; Torkelson, J. M.

    2009-09-01

    Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T gof supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: ensuremath Tg(bulk)-Tg(23{ nm})= 10 circ C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T g where expansivity slowly decreases with decreasing T . As determined from expansivities, the T g breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T g reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T g ’s from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T g(bulk) - T g(23 nm) = 15° C via fluorescence. This small difference in the T g confinement effect reflects differences in how fluorescence and ellipsometry report “average T g ” with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution. in here

  7. Kappa-distributions and Temperature Structure of the Prominence-Corona Transition Region

    NASA Astrophysics Data System (ADS)

    Dzifčáková, Elena; Mackovjak, Šimon; Heinzel, Petr

    2014-01-01

    The influence of the electron κ - distributions on the differential emission measure (DEM) of the prominence-corona transition region (PCTR) derived from observed line intensities has been investigated. An important consequence of the κ - distribution is formation of the emission lines in much wider temperature ranges. The implications for the formation temperature of the observed SDO/AIA band emissions are shown.

  8. Monitoring of temperature-mediated adipose tissue phase transitions by refractive-index measurements

    NASA Astrophysics Data System (ADS)

    Yanina, I. Yu.; Popov, A. P.; Bykov, A. V.; Tuchin, V. V.

    2014-10-01

    Monitoring of temperature-mediated adipose tissue phase transitions were studied in vitro using an Abbe refractometer. The 1-2-mm thick porcine fat tissues slices were used in the experiments. The observed change in the tissue was associated with several phase transitions of lipid components of the adipose tissue. It was found that overall heating of a sample from the room to higher temperature led to more pronounced and tissue changes in refractive index if other experimental conditions were kept constant. We observed an abrupt change in the refractive index in the temperature range of 37-60 °C.

  9. Charge-transfer transitions in triarylamine mixed-valence systems: the effect of temperature

    NASA Astrophysics Data System (ADS)

    Coropceanu, V.; Lambert, C.; Nöll, G.; Brédas, J. L.

    2003-05-01

    The temperature dependence of inter-valence charger-transfer transitions has been investigated for three triarylamine-based mixed-valence systems: (bis-{4-[ N, N-di(4-methoxyphenyl)amino]-phenyl}butadiyne, 1+), (4,4 '-bis[ N, N-di(4-methoxyphenyl)amino] biphenyl, 2+), and ( N, N, N', N'-tetraphenyl-1,4-phenylenediamine, 3+). Although the band shape of 1+- 3+ changes with temperature, neither the position of the transition maximum nor the integral intensity are significantly affected by temperature. The shape of the absorption bands is analyzed in the framework of a dynamic vibronic model.

  10. Single ricin detection by AFM chemomechanical mapping

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This research reports a method of detecting ricin molecules immobilized on chemically modified gold (Au;111) surface by chemomechanically mapping the molecular interactions with a chemically modified Atomic Force Microscope (AFM) tip. AFM images resolved the different fold-up conformations of single...

  11. Microwave properties of high transition temperature superconducting thin films

    NASA Technical Reports Server (NTRS)

    Gordon, W. L.

    1991-01-01

    Extensive studies of the interaction of microwaves with YBa2Cu3O(7-delta), Bi-based, and Tl-based superconducting thin films deposited in several microwave substrates were performed. The data were obtained by measuring the microwave power transmitted through the film in the normal and the superconducting state and by resonant cavity techniques. The main motives were to qualify and understand the physical parameters such as the magnetic penetration depth, the complex conductivity, and the surface impedance, of high temperature superconducting (HTS) materials at microwave frequencies. Based on these parameters, the suitability of these HTS thin films is discussed for microwave applications.

  12. Investigations of Effects of Surface Temperature and Single Roughness Elements on Boundary-Layer Transition

    NASA Technical Reports Server (NTRS)

    Liepmann, Hans W; Fila, Gertrude H

    1947-01-01

    The laminar boundary layer and the position of the transition point were investigated on a heated flat plate. It was found that the Reynolds number of transition decreased as the temperature of the plate is increased. It is shown from simple qualitative analytical considerations that the effect of variable viscosity in the boundary layer due to the temperature difference produces a velocity profile with an inflection point if the wall temperature is higher than the free-stream temperature. This profile is confirmed by measurements. The instability of inflection-point profiles is discussed. Studies of the flow in the wake of large, two-dimensional roughness elements are presented. It is shown that a boundary-layer can separate and reattach itself to the wall without having transition take place.

  13. Does zero temperature decide on the nature of the electroweak phase transition?

    NASA Astrophysics Data System (ADS)

    Harman, Christopher P. D.; Huber, Stephan J.

    2016-06-01

    Taking on a new perspective of the electroweak phase transition, we investigate in detail the role played by the depth of the electroweak minimum ("vacuum energy difference"). We find a strong correlation between the vacuum energy difference and the strength of the phase transition. This correlation only breaks down if a negative eigen-value develops upon thermal corrections in the squared scalar mass matrix in the broken vacuum before the critical temperature. As a result the scalar fields slide across field space toward the symmetric vacuum, often causing a significantly weakened phase transition. Phenomenological constraints are found to strongly disfavour such sliding scalar scenarios. For several popular models, we suggest numerical bounds that guarantee a strong first order electroweak phase transition. The zero temperature phenomenology can then be studied in these parameter regions without the need for any finite temperature calculations. For almost all non-supersymmetric models with phenomenologically viable parameter points, we find a strong phase transition is guaranteed if the vacuum energy difference is greater than -8.8 × 107 GeV4. For the GNMSSM, we guarantee a strong phase transition for phenomenologically viable parameter points if the vacuum energy difference is greater than -6.9×107 GeV4. Alternatively, we capture more of the parameter space exhibiting a strong phase transition if we impose a simultaneous bound on the vacuum energy difference and the singlet mass.

  14. Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

    SciTech Connect

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-11-07

    High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Smtype→ dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GP and a temperature of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Furthermore, our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.

  15. On the high-temperature phase transitions of CsH2PO4: A polymorphic transition? A transition to a superprotonic conducting phase?

    NASA Astrophysics Data System (ADS)

    Ortiz, E.; Vargas, R. A.; Mellander, B.-E.

    1999-03-01

    X-ray diffraction, thermogravimetric (TGA), differential scanning calorimetric (DSC), and impedance analysis were used to study the reported high-temperature phase transitions at 107, 149, 230, and 256 °C in crystals of cesium dihydrogen phosphate, CsH2PO4 (CDP). Our results show strong evidence that at all these temperatures, the observed DSC or differential thermal analysis (DTA) endothermic effects appear only as a consequence of a dehydration process starting on the surface of the crystal. Our results thus show that the reported transition at 230 °C is not a polymorphic transition. This means that the monoclinic symmetry, stable at room temperature, with space group P21/m-C2k2, is maintained up to the final decomposition. Moreover, since we have not found any evidence for the existence of a superprotonic high-temperature phase above 230 °C, the high conductivity above 230 °C is thus only a consequence of the dehydration of the crystal surface.

  16. Scaling of the hysteresis in the glass transition of glycerol with the temperature scanning rate

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Zhen; Li, Ying; Zhang, Jin-Xiu

    2011-03-01

    By measuring the dependences of the temperature-dependent primary ("alpha") dielectric relaxation time behavior on the temperature scanning rate for the glass-forming glycerol, we study the scaling of hysteresis at the glass transition in glycerol. Based on the Vogel-Fulcher-Tammann (VFT) expression and the Angell's fragility concept, notable correlations of the systematic kinetic fragility, and of the hysteresis effect in the vitrification/fusion "alpha"-relaxation process of glycerol, with the temperature scanning rate, were reasonably analyzed and discussed. It was observed that the kinetic fragility m and the apparent glass-transition temperature hysteresis width Δ T_g^a, respectively, scaled the temperature scanning rate q as m ≈ αmq-γ and Δ T_g^a ≈ A0 + αqβ, at which the exponents, γ and β, were suggested to be characteristic of the resistance to the structure change or fragility change of the system during the glass transition. The observed scaling laws are quite similar to the scaling power law for the thermal hysteresis in the first-order phase transition (FOPT) of solids, providing a significant insight into the hysteresis effect in the glass transition of the glass-forming liquids.

  17. Body temperature-related structural transitions of monotremal and human hemoglobin.

    PubMed

    Digel, I; Maggakis-Kelemen, Ch; Zerlin, K F; Linder, Pt; Kasischke, N; Kayser, P; Porst, D; Temiz Artmann, A; Artmann, G M

    2006-10-15

    In this study, temperature-related structural changes were investigated in human, duck-billed platypus (Ornithorhynchus anatinus, body temperature T(b) = 31-33 degrees C), and echidna (Tachyglossus aculeatus, body temperature T(b) = 32-33 degrees C) hemoglobin using circular dichroism spectroscopy and dynamic light scattering. The average hydrodynamic radius (R(h)) and fractional (normalized) change in the ellipticity (F(obs)) at 222 +/- 2 nm of hemoglobin were measured. The temperature was varied stepwise from 25 degrees C to 45 degrees C. The existence of a structural transition of human hemoglobin at the critical temperature T(c) between 36-37 degrees C was previously shown by micropipette aspiration experiments, viscosimetry, and circular dichroism spectroscopy. Based on light-scattering measurements, this study proves the onset of molecular aggregation at T(c). In two different monotremal hemoglobins (echidna and platypus), the critical transition temperatures were found between 32-33 degrees C, which are close to the species' body temperature T(b). The data suggest that the correlation of the structural transition's critical temperature T(c) and the species' body temperature T(b) is not mere coincidence but, instead, is a more widespread structural phenomenon possibly including many other proteins. PMID:16844747

  18. Electronic transition above room temperature in CaMn{sub 7}O{sub 12} films

    SciTech Connect

    Huon, A.; Lang, A. C.; Moon, E. J.; Taheri, M. L.; May, S. J.; Saldana-Greco, D.; Lim, J. S.; Rappe, A. M.

    2015-10-05

    We report on the electronic phase transition in CaMn{sub 7}O{sub 12} quadruple perovskite films synthesized by oxide molecular beam epitaxy on SrLaAlO{sub 4} and La{sub 0.3}Sr{sub 0.7}Al{sub 0.65}Ta{sub 0.35}O{sub 3} substrates. We use x-ray diffraction and transmission electron microscopy to confirm that the CaMn{sub 7}O{sub 12} phase has been realized. Temperature dependent resistivity measurements reveal a signature of a charge ordering phase transition at ≈425 K, consistent with bulk CaMn{sub 7}O{sub 12}. The transition temperature is found to be relatively invariant to changes in the cation stoichiometry. Density functional theory calculations reveal the changes in atomic and electronic structure induced by the charge ordering transition.

  19. Phase Transition in all-trans-β-Carotene Crystal: Temperature-Dependent Raman Spectra.

    PubMed

    da Silva, Kleber J R; Paschoal, Waldomiro; Belo, Ezequiel A; Moreira, Sanclayton G C

    2015-09-24

    In this study, we studied the stability of an all-trans-β-carotene single crystal using Raman spectroscopy with line excitation at 632.8 nm, in the temperature range 20–300 K. The Raman spectra exhibit clear modifications in the spectral range of the lattice and internal vibrational modes. The temperature dependence of the most intense vibrational modes ν1 (1511 cm(–1)) and ν2 (1156 cm(–1)) that are related to the C═C and C—C stretching vibrations of the polyene chain, respectively, shows an upward shift on the Raman modes. This behavior is similar to that stated in the theoretical work of Wei-Long Liu et al. We conclude that the all-trans-β-carotene crystal undergoes a temperature-induced phase transition at approximately 219 K. This transition is interpreted as a rotation experienced by β-ring groups at each end of the all-trans-β-carotene molecule around the dihedral angle. At low temperatures, the new molecular configuration affects the sliding plane of the space group C2h(5)(P2(1)/n), and the phase transition leads to an unchanged monoclinic structure; however, the original space group is possibly lowered to the space group C2. In the temperature range 200–220 K, the spectral ratio (S) of the integrated intensities of the spectral modes around the symmetric and asymmetric stretching wavenumbers of the methyl group (CH3) changes as a function of temperature in agreement with the phase transition. Furthermore, according to phase transition undergone by the all-trans-β-carotene, the thermal results obtained by differential scanning calorimetry show an exothermic process that occurs near the transition temperature assigned by the Raman spectra. PMID:26335691

  20. Phase Transitions at Low Temperature (<77 K) by Means of Photopyroelectric Calorimetry

    NASA Astrophysics Data System (ADS)

    Oleaga, A.; Salazar, A.

    2012-11-01

    An ac photopyroelectric calorimeter has been designed and mounted to work at low temperatures (12 K to 77 K), where the sample is in a He atmosphere and with the detector region isolated from mechanical vibrations allowing the retrieval of high resolution measurements of thermal diffusivity and specific heat. The system has been used to study magnetic and ferroelectric phase transitions in RMnO3 (R = Sm, Tb, Dy). The high quality of the measurements has allowed study of the critical behavior of the transitions and extraction of their critical parameters. In the particular case of the antiferromagnetic-to-paramagnetic transition in SmMnO3, it belongs to the 3D-XY universality class while in the case of the lock-in, ferroelectric transition in TbMnO3, the results confirm that the transition is clearly second order.

  1. Impact of thermal expansion of substrates on phase transition temperature of VO2 films

    NASA Astrophysics Data System (ADS)

    Sakai, Joe; Zaghrioui, Mustapha; Matsushima, Masaaki; Funakubo, Hiroshi; Okimura, Kunio

    2014-09-01

    Non-epitaxial, (010)M1-oriented VO2 thin films were grown on various substrates [amorphous SiO2, Si (001), Al2O3 (0001), and CaF2 (001)] with Pt (111)/SiO2 buffer layers. Phase transition from MoO2-type monoclinic to rutile-type tetragonal structures of these VO2 layers was investigated with temperature-controlled micro-Raman spectroscopy. It was confirmed that substrates with larger thermal expansion coefficient cause larger out-of-plane lattice spacings of both Pt and VO2, and thus lower transition temperatures of VO2 films, as a result of higher in-plane shrinkage during cooling from the deposition temperature. The transition temperatures and aM1/2 lengths, estimated from bM1 lengths, of present samples were compared with previous reports in a strain—temperature phase diagram. The present results fit with previous reports better by assuming that in-plane lattice aspect ratio of VO2 films is not clamped by the substrates but is flexible during the temperature change. Thermal expansion of substrates is an essential parameter to be taken into account when one considers device application of the phase transition properties of VO2 films, especially thick or non-epitaxial.

  2. Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

    DOE PAGESBeta

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-11-07

    High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Smtype→ dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GP and a temperaturemore » of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Furthermore, our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.« less

  3. High Temperature Elastic Moduli Measurements and Phase Transition Studies of Novel Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Li, Guangyan; Adebisi, Resheed; Gladden, Josh

    2009-03-01

    Thermoelectric (TE) materials can be used to convert heat including waste heat to electrical power. They are one component to energy savings and independence. Silicon germanium (SiGe) and Zintl phase compounds are excellent candidates for high temperature applications. The mechanical properties of these materials need to be known before their actual applications in high temperature (1000C) environments. The temperature dependent elastic moduli of five different SiGe alloys were successfully measured using a high temperature resonant ultrasound spectroscopy (RUS) technique. A linear trend is generally observed up to 600C, a downward curvature especially in two n-type samples is noticeable at higher temperatures. Hysteresis is only observed in one of the n-type SiGe samples. Phase transitions, indicated by shifts in the natural frequencies of a Zintl sample, were observed near 792, 892, 931C. The nature of these transitions will be discussed.

  4. Temperature-driven transition from a semiconductor to a topological insulator

    NASA Astrophysics Data System (ADS)

    Wiedmann, Steffen; Jost, Andreas; Thienel, Cornelius; Brüne, Christoph; Leubner, Philipp; Buhmann, Hartmut; Molenkamp, Laurens W.; Maan, J. C.; Zeitler, Uli

    2015-05-01

    We report on a temperature-induced transition from a conventional semiconductor to a two-dimensional topological insulator investigated by means of magnetotransport experiments on HgTe/CdTe quantum well structures. At low temperatures, we are in the regime of the quantum spin Hall effect and observe an ambipolar quantized Hall resistance by tuning the Fermi energy through the bulk band gap. At room temperature, we find electron and hole conduction that can be described by a classical two-carrier model. Above the onset of quantized magnetotransport at low temperature, we observe a pronounced linear magnetoresistance that develops from a classical quadratic low-field magnetoresistance if electrons and holes coexist. Temperature-dependent bulk band structure calculations predict a transition from a conventional semiconductor to a topological insulator in the regime where the linear magnetoresistance occurs.

  5. Low Temperature Structural Phase Transition of Ba3NaIr2O9

    SciTech Connect

    Conrad, H.; Loye, Z; Kim, S; Macquart, R; Smith, M; Lee, Y; Vogt, T

    2009-01-01

    Single crystal X-ray and synchrotron X-ray powder diffraction have been used to probe the structure of Ba3NaIr2O9 from 300 K down to 20 K. Ba3NaIr2O9 is found to undergo a structural transition from hexagonal symmetry, P63/mmc, at ambient temperature to monoclinic symmetry, C2/c, at low temperature. The evolution of the unit cell volume upon cooling is indicative of a higher order structural transition, and the symmetry breaking becomes apparent as the temperature is decreased. The low temperature monoclinic structure of Ba3NaIr2O9 contains strongly distorted [NaO6] and [IrO6] octahedra in comparison to the room temperature hexagonal structure.

  6. Near-field resonance shifts of ferroelectric barium titanate domains upon low-temperature phase transition

    SciTech Connect

    Döring, Jonathan; Ribbeck, Hans-Georg von; Kehr, Susanne C.; Eng, Lukas M.; Fehrenbacher, Markus

    2014-08-04

    Scattering scanning near-field optical microscopy (s-SNOM) has been established as an excellent tool to probe domains in ferroelectric crystals at room temperature. Here, we apply the s-SNOM possibilities to quantify low-temperature phase transitions in barium titanate single crystals by both temperature-dependent resonance spectroscopy and domain distribution imaging. The orthorhombic-to-tetragonal structural phase transition at 263 K manifests in a change of the spatial arrangement of ferroelectric domains as probed with a tunable free-electron laser. More intriguingly, the domain distribution unravels non-favored domain configurations upon sample recovery to room temperature as explainable by increased sample disorder. Ferroelectric domains and topographic influences are clearly deconvolved even at low temperatures, since complementing our s-SNOM nano-spectroscopy with piezoresponse force microscopy and topographic imaging using one and the same atomic force microscope and tip.

  7. Pressure-induced irreversible phase transitions of the monoclinic GdOOH nanorods at ambient temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Chuanchao; Dai, Rucheng; Sui, Zhilei; Chen, Qiao; Wang, Zhongping; Yuan, Xiaodong; Zhang, Zengming; Ding, Zejun

    2014-09-01

    The structural transition of monoclinic GdOOH nanorods was studied by using a diamond anvil cell at room temperature with the probe of Eu3+ ion luminescence under pressures up to 21.4 GPa. The changes of luminescence spectra indicated that a pressure-induced phase transition from the monoclinic phase to the high pressure tetragonal phase occurs at 10.7 GPa for GdOOH nanorods, and the monoclinic GdOOH nanorods are gradually transformed into the tetragonal phase with increasing pressure. After releasing of pressure to the ambient, the high pressure tetragonal phase is retained, and the phase transition of GdOOH nanorods is irreversible.

  8. Transition of temperature coefficient of conductance in weakly coupled gold nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Guan, Changrong; Sun, Jinling; Peng, Lianmao; Liao, Jianhui

    2014-12-01

    A unique positive-to-negative transition of temperature coefficient of conductance (TCC) was observed in self-assembled close-packed Au nanoparticle (AuNP) arrays. The transition of TCC can be interpreted properly with a diffusive hopping model, in which the Coulomb charging energy Ea plays a significant role. Two parameters of AuNP arrays, the nearest neighboring number and the particle core size, have been varied to tune Ea. Our data show that the positive-to-negative transitions of TCC are relevant to both parameters, which confirms the validity of the diffusive hopping model.

  9. Finite temperature spin-dynamics and phase transitions in spin-orbital models

    SciTech Connect

    Chen, C.-C.

    2010-04-29

    We study finite temperature properties of a generic spin-orbital model relevant to transition metal compounds, having coupled quantum Heisenberg-spin and Ising-orbital degrees of freedom. The model system undergoes a phase transition, consistent with that of a 2D Ising model, to an orbitally ordered state at a temperature set by short-range magnetic order. At low temperatures the orbital degrees of freedom freeze-out and the model maps onto a quantum Heisenberg model. The onset of orbital excitations causes a rapid scrambling of the spin spectral weight away from coherent spin-waves, which leads to a sharp increase in uniform magnetic susceptibility just below the phase transition, reminiscent of the observed behavior in the Fe-pnictide materials.

  10. Reversible temperature regulation of electrical and thermal conductivity using liquid–solid phase transitions

    PubMed Central

    Zheng, Ruiting; Gao, Jinwei; Wang, Jianjian; Chen, Gang

    2011-01-01

    Reversible temperature tuning of electrical and thermal conductivities of materials is of interest for many applications, including seasonal regulation of building temperature, thermal storage and sensors. Here we introduce a general strategy to achieve large contrasts in electrical and thermal conductivities using first-order phase transitions in percolated composite materials. Internal stress generated during a phase transition modulates the electrical and thermal contact resistances, leading to large contrasts in the electrical and thermal conductivities at the phase transition temperature. With graphite/hexadecane suspensions, the electrical conductivity changes 2 orders of magnitude and the thermal conductivity varies up to 3.2 times near 18 °C. The generality of the approach is also demonstrated in other materials such as graphite/water and carbon nanotube/hexadecane suspensions. PMID:21505445

  11. Gas-liquid type phase transition in semiivietals at low temperatures and high magnetic fields

    NASA Astrophysics Data System (ADS)

    Mase, Shoichi; Fukami, Takeshi; Mori, Masatoshi; Inoue, Tomnio

    1982-07-01

    Remarkable anomalies have been found in the temperature and frequency dependences of the attenuation coefficient of sound waves in bismuth, antimony and pyrolytic graphite at low temperatures and high magnetic fields. The result for bismuth in particular is app]arently similar to those observed in second-order phase transition phenomena. On the basis of the Nakajima-Yoshioka-Kuramoto theory of the gas-liquid type phase transition in the electron-hole system, these anomalies are fairly well explained in terms of the fluctuation effect above the phase transition temperature, provided that the electron-hole correlation interaction is assumed to be sensitively dependent on the state of the overlapping of the electron and hole Landau levels.

  12. Variable defect structures cause the magnetic low-temperature transition in natural monoclinic pyrrhotite

    NASA Astrophysics Data System (ADS)

    Koulialias, D.; Kind, J.; Charilaou, M.; Weidler, P. G.; Löffler, J. F.; Gehring, A. U.

    2016-02-01

    Non-stoichiometric monoclinic 4C pyrrhotite (Fe7S8) is a major magnetic remanence carrier in the Earth's crust and in extraterrestrial materials. Because of its low-temperature magnetic transition around 30 K also known as Besnus transition, which is considered to be an intrinsic property, this mineral phase is easily detectable in natural samples. Although the physical properties of pyrrhotite have intensively been studied, the mechanism behind the pronounced change in magnetization at the low-temperature transition is still debated. Here we report magnetization experiments on a pyrrhotite crystal (Fe6.6S8) that consists of a 4C and an incommensurate 5C* superstructure that are different in their defect structure. The occurrence of two superstructures is magnetically confirmed by symmetric inflection points in hysteresis measurements above the transition at about 30 K. The disappearance of the inflection points and the associated change of the hysteresis parameters indicate that the two superstructures become strongly coupled to form a unitary magnetic anisotropy system at the transition. From this it follows that the Besnus transition in monoclinic pyrrhotite is an extrinsic magnetic phenomenon with respect to the 4C superstructure and therefore the physics behind it is in fact different from that of the well-known Verwey transition.

  13. Glass Transition in Thin Supported Polymer Films Probed by Temperature-Modulated Ellipsometry in Vacuum

    NASA Astrophysics Data System (ADS)

    Efremov, Mikhail; Nealey, Paul

    2010-03-01

    Glass transition in model glass-forming polymer coatings is probed by ellipsometry in vacuum. Novel temperature-modulated modification of the technique is used alongside with traditional linear temperature program [1]. Spin-cast 2 - 200 nm thick polystyrene (PS) and 10 - 200 nm thick poly(methyl methacrylate) (PMMA) films on silicon are studied. Measurements are performed at 10-6 - 10-8 torr residual gas pressure. Temperature modulation allows effective separation of reversible glass transition from accompanying irreversible processes. It is found that glass transition in both polymers demonstrates no appreciable dependence on film thickness for more than 20 nm thick coatings. The temperature of the transition (Tg) in thinnest PS films does depend on film thickness, but does not follow often accepted Tg(h)=Tg(∞)[1-(Ah)^δ] function (where h is film thickness, A and δ are constants). Effects of polymer molecular weight and substrate surface pre-treatment on glass transition will be discussed also.[4pt] [1]. M. Yu. Efremov, A. V. Kiyanova, and P. F. Nealey, Macromolecules, 41, 5978 (2008).

  14. Experimental evidence of ultrathin polymer film stratification by AFM force spectroscopy.

    PubMed

    Delorme, Nicolas; Chebil, Mohamed Souheib; Vignaud, Guillaume; Le Houerou, Vincent; Bardeau, Jean-François; Busselez, Rémi; Gibaud, Alain; Grohens, Yves

    2015-06-01

    By performing Atomic Force Microscopy measurements of pull-off force as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) films. Thermal transitions induce modifications in the surface energy, roughness and surface modulus that are clearly detected by AFM and related to PS chain relaxation mechanisms. We demonstrated the existence of three transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. The thickness of this region is estimated to be above 7nm. The detection of a transition only present for film thicker than the gyration radius Rg is linked to the dynamics of polymer chains in a bulk conformation (i.e. not in contact with the free interface). We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in terms of relaxation behavior. PMID:26087914

  15. Anomalous Increase in Nematic-Isotropic Transition Temperature in Dimer Molecules Induced by a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Salili, S. M.; Tamba, M. G.; Sprunt, S. N.; Welch, C.; Mehl, G. H.; Jákli, A.; Gleeson, J. T.

    2016-05-01

    We have determined the nematic-isotropic transition temperature as a function of an applied magnetic field in three different thermotropic liquid crystalline dimers. These molecules are comprised of two rigid calamitic moieties joined end to end by flexible spacers with odd numbers of methylene groups. They show an unprecedented magnetic field enhancement of nematic order in that the transition temperature is increased by up to 15 K when subjected to a 22 T magnetic field. The increase is conjectured to be caused by a magnetic-field-induced decrease of the average bend angle in the aliphatic spacers connecting the rigid mesogenic units of the dimers.

  16. ezAFM: A low cost Atomic Force Microscope(AFM)

    NASA Astrophysics Data System (ADS)

    Celik, Umit; Celik, Kubra; Aslan, Husnu; Kehribar, Ihsan; Dede, Munir; Ozgur Ozer, H.; Oral, Ahmet

    2012-02-01

    A low cost AFM, ezAFM is developed for educational purposes as well as research. Optical beam deflection method is used to measure the deflection of cantilever. ezAFM scanner is built using voice coil motors (VCM) with ˜50x50x6 μm scan area. The microscope uses alignment free cantilevers, which minimizes setup times. FPGA based AFM feedback Control electronics is developed. FPGA technology allows us to drive all peripherals in parallel. ezAFM Controller is connected to PC by USB 2.0 interface as well as Wi-Fi. We have achieved <5nm lateral and ˜0.01nm vertical resolution. ezAFM can image single atomic steps in HOPG and mica. An optical microscope with <3 μm resolution is also integrated into the system. ezAFM supports different AFM operation modes such as dynamic mode, contact mode, lateral force microscopy. Advanced modes like magnetic force microscopy and electric force microscopy will be implemented later on. The new ezAFM system provides, short learning times for student labs, quick setup and easy to transport for portable applications with the best price/performance ratio. The cost of the system starts from 15,000, with system performance comparable with the traditional AFM systems.

  17. Irreversible phase transitions in doped metal oxides as temperature sensors in explosions

    NASA Astrophysics Data System (ADS)

    Eilers, Hergen; Gunawidjaja, Ray; Myint, Thandar; Lightstone, James

    2011-06-01

    The temperature of post-detonation fireballs produced by advanced energetic formulations is commonly determined using optical methods such as pyrometry and spectral line fitting. These methods provide an average temperature mostly from the surface of the fireball. However, for many applications the ability to probe the internal temperature and temperature gradients within the fireball is highly desirable. One method that has shown promise is seeding micron to nano-sized temperature sensors into the fireball which can be collected and analyzed post-detonation. In this work, disordered Eu3+-doped nanoparticles were subjected to various heat treatments, incl. furnace, T-Jump, pulsed laser, and explosive heating. This treatment leads to irreversible phase transitions which are monitored by the Eu dopants. Optical signatures such as the ratio of electric and magnetic dipole transition intensities, energy level splitting, FWHM, etc. are evaluated to monitor the phase transitions. Also, the kinetics of particle growth is evaluated as an indicator for the time-dependence of the heating process. The information is used to establish a correlation with the temperature profile. Temperature profiles collected from a series of lab-based tests and small-scale detonations of an aluminized explosive will be presented. This work was supported by the Defense Threat Reduction Agency.

  18. Glass transition temperature and conductivity in Li2O and Na2O doped borophosphate glasses

    NASA Astrophysics Data System (ADS)

    Ashwajeet, J. S.; Sankarappa, T.; Ramanna, R.; Sujatha, T.; Awasthi, A. M.

    2015-08-01

    Two alkali doped Borophosphate glasses in the composition, (B2O3)0.2. (P2O5)0.3. (Na2O)(0.5-x). (Li2O)x, where x = 0.05 to 0.50 were prepared by standard melt quenching method at 1200K. Non-crystalline nature was confirmed by XRD studies. Room temperature density was measured by Archimedes principle. DC conductivity in the temperature range from 300K to 575K has been measured. Samples were DSC studied in the temperature range from 423K to 673K and glass transition temperature was determined. Glass transition temperature passed through minima for Li2O con.2centration between 0.25 and 0.30 mole fractions. Activation energy of conduction has been determined by analyzing temperature variation of conductivity determining Arrhenius law. Conductivity passed through minimum and activation passed through maximum for Li2O content from 0.25 to 0.30 mole fractions. Glass transition temperature passed through minimum for the same range of Li2O content. These results revealed mixed alkali effect taking place in these glasses. It is for the first time borophosphate glasses doped with Li2O and Na2O have been studied for density and dc conductivity and, the mixed alkali effect (MAE) has been observed.

  19. Temperature stability of intersubband transitions in AlN/GaN quantum wells

    SciTech Connect

    Berland, Kristian; Stattin, Martin; Farivar, Rashid; Sultan, D. M. S.; Hyldgaard, Per; Larsson, Anders; Wang, Shu Min; Andersson, Thorvald G.

    2010-07-26

    Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to 400 deg. C. The self-consistent Schroedinger-Poisson modeling includes temperature effects of the band gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by approx6 meV at 400 deg. C relative to its room temperature value.

  20. Measured and calculated wall temperatures on air-cooled turbine vanes with boundary layer transition

    NASA Astrophysics Data System (ADS)

    Liebert, C. H.; Gaugler, R. E.; Gladden, H. J.

    1982-11-01

    Convection cooled turbine vane metal wall temperatures experimentally obtained in a hot cascade for one vane design were compared with wall temperatures calculated with TACT1 and STAN5 computer codes which incorporated various models for predicting laminar-to-turbulent boundary layer transition. Favorable comparisons on both vane surface were obtained at high Reynolds number with only one of these transition models. When other models were used, temperature differences between calculated and experimental data obtained at the high Reynolds number were as much as 14 percent in the separation bubble region of the pressure surface. On the suction surface and at lower Reynolds number, predictions and data unsatisfactorily differed by as much as 22 percent. Temperature differences of this magnitude can represent orders of magnitude error in blade life prediction.

  1. Demonstration of glass transition temperature shift in thin supported polystyrene films by internal reference method

    NASA Astrophysics Data System (ADS)

    Efremov, Mikhail Yu.; Thode, Christopher; Nealey, Paul F.

    2013-02-01

    An internal reference method is used for the first time to clearly demonstrate the glass transition temperature (Tg) depression effect in 5 nm thick polystyrene films spin-cast on silicon wafers. Initially flat films exhibit depressed Tg at approximately 85 °C. Temperature-induced dewetting on hexamethyldisilazane-treated silicon substrates leads to formation of discontinuous films with average effective thickness of 15-30 nm. Dewetted films demonstrate Tg close to the bulk value (≈ 100 °C) and are used as internal references. Data both for continuous and discontinuous films are obtained in the same experimental run for the same sample, which allows direct comparison between datasets. Phase-modulated ellipsometry in vacuum is used to monitor glass transition. Both traditional linear temperature scan method and a novel temperature modulated technique have been employed in the measurements.

  2. Determination of Material Properties Near the Glass Transition Temperature for an Isogrid Boom

    NASA Technical Reports Server (NTRS)

    Blandino, Joseph R.; Woods-Vedeler, Jessica A. (Technical Monitor)

    2002-01-01

    Experiments were performed and results obtained to determine the temperature dependence of the modulus of elasticity for a thermoplastic isogrid tube. The isogrid tube was subjected to axial tensile loads of 0-100 lbf and strain was measured at room and elevated temperatures of 100, 120, 140, 160, 180, 190, and 200 F. These were based on tube manufacturer specifying an incorrect glass transition temperature of 210 F. Two protocols were used. For the first protocol the tube was brought to temperature and a tensile test performed. The tube was allowed to cool between tests. For the second protocol the tube was ramped to the desired test temperature and held. A tensile test was performed and the tube temperature ramped to the next test temperature. The second protocol spanned the entire test range. The strain rate was constant at 0.008 in/min. Room temperature tests resulted in the determination of an average modulus of 2.34 x 106 Psi. The modulus decreased above 100 F. At 140 F the modulus had decreased by 7.26%. The two test protocols showed good agreement below 160 F. At this point the glass transition temperature had been exceeded. The two protocols were not repeated because the tube failed.

  3. High-transition-temperature superconductors in the Nb-Al-Ge system

    DOEpatents

    Giorgi, A.L.; Szklarz, E.G.

    1972-09-26

    The patent describes superconducting materials of the nominal composition Nb(x)Al(y)Ge(l-y), where x is in the range of 1.9 to 2.8 and y is in the range of 0.5 to 0.9, having transition temperatures in the 19 -20K. range which are readily produced by annealing arc-melted compositions, or cold-pressed, heat-treated compositions at moderate temperatures for reasonably long times (about 50 hours).

  4. Room temperature broadband terahertz gains in graphene heterostructures based on inter-layer radiative transitions

    SciTech Connect

    Tang, Linlong; Du, Jinglei; Shi, Haofei Wei, Dongshan; Du, Chunlei

    2014-10-15

    We exploit inter-layer radiative transitions to provide gains to amplify terahertz waves in graphene heterostructures. This is achieved by properly doping graphene sheets and aligning their energy bands so that the processes of stimulated emissions can overwhelm absorptions. We derive an expression for the gain estimation and show the gain is insensitive to temperature variation. Moreover, the gain is broadband and can be strong enough to compensate the free carrier loss, indicating graphene based room temperature terahertz lasers are feasible.

  5. Spin orbital theory for the high temperature magnetic phase transitions in Yttrium orthovanadate

    NASA Astrophysics Data System (ADS)

    de Silva, Theja; Joshi, Anuvrat; Zhang, Fu Chun; Ma, Michael

    2003-03-01

    Motivated by recent diffraction experiments, we develope a theoritical model for Yttrium orthovanadate(YVO_3). The key parameters governing the system are on-site coulomb repulsion, Hund's coupling, crystal field splitting between 3d levels and hopping amplitude between nearest neighbor ions. Then, we use a mean field theory to illustrate the relevent physics of the system and verify the existence of the high temperature G-type orbital transition before C-type spin ordering at a lower temperature.

  6. EHL Transition Temperature Measurements on a Geostationary Operational Environmental Satellite (GOES) Filter Wheel Bearing

    NASA Technical Reports Server (NTRS)

    Jansen, Mark J.; Jones, William R., Jr.; Pepper, Stephen V.; Predmore, Roamer E.; Shogrin, Bradley A.

    2001-01-01

    The elastohydrodynamic lubrication (EHL) transition temperature was measured for a Geostationary Operational Environmental Satellite (GOES) sounder filter wheel bearing in a vacuum tribometer. Conditions included both an 89 N (20 lb.) hard and soft load, 600 rpm, temperatures between 23 C (73 F) and 85 C (185 F), and a vacuum of approximately 1.3 x 10(exp -5) Pa. Elastohydrodynamic to mixed lubrication started to occur at approximately 70 C (158 F).

  7. Effects of temperature and pressure on the glass transitions of plastic bonded explosives

    SciTech Connect

    Campbell, M.S.; Garcia, D.; Idar, D.

    1998-12-31

    Various plastic bonded explosives (PBXs) contain about 5-wt% polymer, plasticizer, and stabilizer as binder. The glass-transition temperature (T{sub g}) determines, in part, if the binder will reduce or increase the sensitivity of the PBX to impact. A soft binder reduces the impact sensitivity; however, too soft a binder compromises the mechanical strength below that desirable for dimensional stability. Glass transitions were measured by temperature modulated DSC for PBXs before and after pressing. Pressing temperature was 90 C. The T{sub g} of Estane, a polyester/polyurethane used in some PBX binders, was investigated. Only small changes were observed in the low temperature T{sub g} of the soft segments but larger changes were seen in the higher temperature transitions due to the relaxation of the hard segments. The T{sub g} of Kel F 800, a binder used in insensitive PBX 9502, was observed near ambient temperature. The PBX 9502 had a lower T{sub g} than the neat polymer. Mechanical strength will be measured for the samples.

  8. High-temperature heat capacity of Co3O4 spinel: thermally induced spin unpairing transition

    USGS Publications Warehouse

    Mocala, K.; Navrotsky, A.; Sherman, David M.

    1992-01-01

    A strong anomaly was found in the heat capacity of Co3O4 between 1000 K and the decomposition temperature. This anomaly is not related to the decomposition of Co3O4 to CoO. The measured entropy of transition, ??S=46??4 J mol-1 K-1 of Co3O4, supports the interpretation that this anomaly reflects a spin unpairing transition in octahedrally coordinated Co3+ cations. Experimental values of heat capacity, heat content and entropy of Co3O4 in the high temperature region are provided. The enthalpy of the spin unpairing transition is 53??4 kJ mol-1 of Co3O4. ?? 1992 Springer-Verlag.

  9. FAST TRACK COMMUNICATION: Characterization of frequency-dependent glass transition temperature by Vogel-Fulcher relationship

    NASA Astrophysics Data System (ADS)

    Bai, Yu; Jin, Li

    2008-08-01

    The complex mechanical modulus of polymer and polymer based composite materials showed a frequency-dependent behaviour during glass transition relaxation, which was historically modelled by the Arrhenius equation. However, this might not be true in a broad frequency domain based on the experience from the frequency dependence of the complex dielectric permittivity, which resulted from the same glass transition relaxation as for the complex mechanical modulus. Considering a good correspondence between dielectric and mechanical relaxation during glass transition, the Vogel-Fulcher relationship, previously proposed for the frequency dependence of dielectric permittivity, is introduced for that of the mechanical modulus; and the corresponding static glass transition temperature (Tf) was first determined for polymer and polymer based composite materials.

  10. Scenarios of transition to chaos competition in low-temperature plasma

    SciTech Connect

    Dimitriu, D. G.

    2013-11-13

    Dynamics of a fireball created in front of a positively biased electrode immersed into low-temperature plasma was experimentally investigated. By analyzing the time series of the oscillations of the current collected by the electrode, several successive scenarios of transitions to chaos were identified: by intermittencies, by cascade of sub-harmonic bifurcations and by quasi-periodicity (Ruelle-Takens scenario)

  11. CORRELATION OF THE GLASS TRANSITION TEMPERATURE OF PLASTICIZED PVC USING A LATTICE FLUID MODEL

    EPA Science Inventory

    A model has been developed to describe the composition dependence of the glass transition temperature (Tg) of polyvinyl chloride (PVC) + plasticizer mixtures. The model is based on Sanchez-Lacombe equation of state and the Gibbs-Di Marzio criterion, which states that th...

  12. Influence of grain size on transition temperature of thermochromic VO2

    NASA Astrophysics Data System (ADS)

    Miller, Mark J.; Wang, Junlan

    2015-01-01

    Vanadium(IV) oxide (VO2) is a unique material that undergoes a reversible phase transformation around 68 °C. The material could potentially be used as an energy-efficient coating for windows since its reflectance in the infrared (IR) increases significantly more than in the visible region. Currently, VO2 is limited by a transition temperature ( τ c ) that is too high, luminous transmittance that is too low or both. In this study, a transition temperature of 45 °C is achieved for a reactively sputtered, undoped film by restricting grain size to approximately 30 nm. It is concluded that a higher density of grain boundaries (smaller grain size) provides a greater number of nucleating defects which in turn reduces τ c . Similarly, a higher density of grain boundaries may reduce the hysteresis width (difference between transition temperatures in heating and cooling). Also in this study, a new set of optical performance metrics is proposed in which the solar spectrum is divided into the ultraviolet (UV), visible and near infrared (NIR) regions. This approach is more closely aligned with the goals of limiting UV, allowing luminous and modulating NIR transmission. Using these metrics, the optical properties of the low- τ c sample were: 2% UV transmittance, 47% luminous transmittance, and 23% NIR modulation (decrease from 43 to 33%). This study demonstrates that the grain size of VO2 should be viewed as an important parameter for controlling the transition temperature of the material.

  13. Low-temperature phase transition of ZnS: The critical role of ZnO

    SciTech Connect

    Lin, Po-Chang; Hua, Chi Chung; Lee, Tai-Chou

    2012-10-15

    Wurtzite zinc sulfide (WZ-ZnS) is a valuable wide-band-gap semiconductor. However, it is difficult to synthesize due to its high transition temperature (1020 Degree-Sign C). This study investigates the formation of WZ-ZnS particles using a ZnO template. Various phase structures of ZnS with the same size but different levels of ZnO content are generated during the annealing process. The transition temperature can be lowered significantly to below 350 Degree-Sign C. Furthermore, when the powders of ZnO and zinc-blende ZnS are mixed, large ZnS particles are not induced by ZnO to transform into WZ-ZnS. The results strongly suggest that grain size is an essential but not sufficient factor in the formation of WZ-ZnS at lower temperatures. - Graphical abstract: By controlling pH of the precursor, wurtzite ZnS particles can be generated at {approx}350 Degree-Sign C. The ZnO-template mechanism was proposed and discussed. Highlights: Black-Right-Pointing-Pointer Wurtzite ZnS particles were prepared by using simple wet chemistry. Black-Right-Pointing-Pointer pH of the precursor solution was adjusted to decrease the phase transition temperature of ZnS. Black-Right-Pointing-Pointer ZnO-template-inducing mechanism of ZnS phase transition was proposed and discussed.

  14. Physical properties of polyacrylamide gels probed by AFM and rheology

    NASA Astrophysics Data System (ADS)

    Abidine, Yara; Laurent, Valérie M.; Michel, Richard; Duperray, Alain; Iulian Palade, Liviu; Verdier, Claude

    2015-02-01

    Polymer gels have been shown to behave as viscoelastic materials but only a small amount of data is usually provided in the glass transition. In this paper, the dynamic moduli G\\prime and G\\prime\\prime of polyacrylamide hydrogels are investigated using both an AFM in contact force modulation mode and a classical rheometer. The validity is shown by the matching of the two techniques. Measurements are carried out on gels of increasing polymer concentration in a wide frequency range. A model based on fractional derivatives is successfully used, covering the whole frequency range. G\\text{N}0 , the plateau modulus, as well as several other parameters are obtained at low frequencies. The model also predicts the slope a of both moduli in the glass transition, and a transition frequency f\\text{T} is introduced to separate the gel-like behavior with the glassy state. Its variation with polymer content c gives a dependence f\\text{T}∼ c1.6 , in good agreement with previous theories. Therefore, the AFM data provides new information on the physics of polymer gels.

  15. Origin of thickness dependence of structural phase transition temperatures in highly strained BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Yang, Yongsoo; Beekman, Christianne; Siemons, Wolter; Schlepütz, Christian M.; Senabulya, Nancy; Clarke, Roy; Christen, Hans M.

    2016-03-01

    Two structural phase transitions are investigated in highly strained BiFeO3 thin films as a function of film thickness and temperature via synchrotron x-ray diffraction. Both transition temperatures (upon heating: monoclinic MC to monoclinic MA to tetragonal) decrease as the film becomes thinner. A film-substrate interface layer, evidenced by half-order peaks, contributes to this behavior, but at larger thicknesses (above a few nanometers), the temperature dependence results from electrostatic considerations akin to size effects in ferroelectric phase transitions, but observed here for structural phase transitions within the ferroelectric phase. For ultra-thin films, the tetragonal structure is stable to low temperatures.

  16. Temperature-driven phase transitions from first principles including all relevant excitations: The fcc-to-bcc transition in Ca

    NASA Astrophysics Data System (ADS)

    Grabowski, B.; Söderlind, P.; Hickel, T.; Neugebauer, J.

    2011-12-01

    The temperature-driven fcc-to-bcc phase transition in calcium is examined by a fully ab initio-based integrated technique including all relevant finite-temperature excitation mechanisms. The approach is based on density-functional-theory calculations with a controlled numerical stability of below 0.5 meV/atom for the electronic, quasiharmonic, and structural excitations and better than 1 meV/atom for the explicitly anharmonic contribution. The latter is achieved by successfully utilizing the recently developed hierarchical upsampled thermodynamic integration using Langevin dynamics method. This approach gives direct access to a numerically highly precise volume- and temperature-dependent free-energy surface and derived properties. It enables us to assign the remaining deviations from experiment to inherent errors of the presently available exchange-correlation functionals. Performing the full analysis with both of the conventional functionals, local density approximation and generalized gradient approximation, we demonstrate that—when considered on an absolute scale—thermodynamic properties are dictated by a strikingly similar free energy vs volume curve. Further, we show that, despite an error in the T=0 K energy difference between the two phases (≈6 meV in the present case), an excellent agreement of the temperature dependence of the Gibbs energy difference with experimentally derived data is feasible. This makes it possible, for instance, to unveil unreliable and possibly erroneous experimental input used in popular thermodynamic databases as we explicitly demonstrate for the isobaric heat capacity of calcium.

  17. Circulatory osmotic desalination driven by a mild temperature gradient based on lower critical solution temperature (LCST) phase transition materials.

    PubMed

    Mok, Yeongbong; Nakayama, Daichi; Noh, Minwoo; Jang, Sangmok; Kim, Taeho; Lee, Yan

    2013-11-28

    Abrupt changes in effective concentration and osmotic pressure of lower critical solution temperature (LCST) mixtures facilitate the design of a continuous desalination method driven by a mild temperature gradient. We propose a prototype desalination system by circulating LCST mixtures between low and high temperature (low T and high T) units. Water molecules could be drawn from a high-salt solution to the LCST mixture through a semipermeable membrane at a temperature lower than the phase transition temperature, at which the effective osmotic pressure of the LCST mixture is higher than the high-salt solution. After transfer of water to the high T unit where the LCST mixture is phase-separated, the water-rich phase could release the drawn water into a well-diluted solution through the second membrane due to the significant decrease in effective concentration. The solute-rich phase could be recovered in the low T unit via a circulation process. The molar mass, phase transition temperature, and aqueous solubility of the LCST solute could be tuneable for the circulatory osmotic desalination system in which drawing, transfer, release of water, and the separation and recovery of the solutes could proceed simultaneously. Development of a practical desalination system that draws water molecules directly from seawater and produces low-salt water with high purity by mild temperature gradients, possibly induced by sunlight or waste heat, could be attainable by a careful design of the molecular structure and combination of the circulatory desalination systems based on low- and high-molar-mass LCST draw solutes. PMID:24129795

  18. Transitions.

    ERIC Educational Resources Information Center

    Nathanson, Jeanne H., Ed.

    1993-01-01

    This theme issue on transitions for individuals with disabilities contains nine papers discussing transition programs and issues. "Transition Issues for the 1990s," by Michael J. Ward and William D. Halloran, discusses self-determination, school responsibility for transition, continued educational engagement of at-risk students, and service…

  19. Graphitic carbon anode temperature excursions reflect crystallographic phase transitions in lithium-ion cells

    NASA Astrophysics Data System (ADS)

    Srinivasan, Rengaswamy; Srinivasan, Lakshminarayan

    2015-10-01

    Surface temperature measurement of lithium-ion cells provides a limited view of internal physical processes during charging. Using a recently developed non-invasive battery internal temperature sensor, we now demonstrate that anode temperature reflects physically-based dynamics at the anode that were previously obscured by cell-surface measurements. First, using automated segmentation with a maximum-likelihood piecewise-linear statistical model, we show that features in the anode temperature reproducibly coincide with phase transitions into Stages IVd, IV and I of graphitic carbon lithiation at various charging rates. Second, we show that anode temperature peaks around 61% state of charge, intermediate between Stages II and I of the lithiated graphitic carbon. Third, we demonstrate a sharp and sustained increase in anode temperature at variable state of charge above 85%. These findings open the possibility for improved state-of-charge estimation and adaptive charging profiles that safely reduce charging time.

  20. Nano Mechanical Machining Using AFM Probe

    NASA Astrophysics Data System (ADS)

    Mostofa, Md. Golam

    Complex miniaturized components with high form accuracy will play key roles in the future development of many products, as they provide portability, disposability, lower material consumption in production, low power consumption during operation, lower sample requirements for testing, and higher heat transfer due to their very high surface-to-volume ratio. Given the high market demand for such micro and nano featured components, different manufacturing methods have been developed for their fabrication. Some of the common technologies in micro/nano fabrication are photolithography, electron beam lithography, X-ray lithography and other semiconductor processing techniques. Although these methods are capable of fabricating micro/nano structures with a resolution of less than a few nanometers, some of the shortcomings associated with these methods, such as high production costs for customized products, limited material choices, necessitate the development of other fabricating techniques. Micro/nano mechanical machining, such an atomic force microscope (AFM) probe based nano fabrication, has, therefore, been used to overcome some the major restrictions of the traditional processes. This technique removes material from the workpiece by engaging micro/nano size cutting tool (i.e. AFM probe) and is applicable on a wider range of materials compared to the photolithographic process. In spite of the unique benefits of nano mechanical machining, there are also some challenges with this technique, since the scale is reduced, such as size effects, burr formations, chip adhesions, fragility of tools and tool wear. Moreover, AFM based machining does not have any rotational movement, which makes fabrication of 3D features more difficult. Thus, vibration-assisted machining is introduced into AFM probe based nano mechanical machining to overcome the limitations associated with the conventional AFM probe based scratching method. Vibration-assisted machining reduced the cutting forces

  1. Critical temperature for the nuclear liquid-gas phase transition (from multifragmentation and fission)

    SciTech Connect

    Karnaukhov, V. A.; Oeschler, H.; Budzanowski, A.; Avdeyev, S. P.; Botvina, A. S.; Cherepanov, E. A.; Karcz, W.; Kirakosyan, V. V.; Rukoyatkin, P. A.; Skwirczynska, I.; Norbeck, E.

    2008-12-15

    Critical temperature T{sub c} for the nuclear liquid-gas phase transition is estimated from both the multifragmentation and fission data. In the first case, the critical temperature is obtained by analysis of the intermediate-mass-fragment yields in p(8.1 GeV) + Au collisions within the statistical model of multifragmentation. In the second case, the experimental fission probability for excited {sup 188}Os is compared with the calculated one with T{sub c} as a free parameter. It is concluded for both cases that the critical temperature is higher than 15 MeV.

  2. Observing the Temperature Dependent Transition of the GP2 Peptide Using Terahertz Spectroscopy

    PubMed Central

    Sun, Yiwen; Zhu, Zexuan; Chen, Siping; Balakrishnan, Jega; Abbott, Derek; Ahuja, Anil T.; Pickwell-MacPherson, Emma

    2012-01-01

    The GP2 peptide is derived from the Human Epidermal growth factor Receptor 2 (HER2/nue), a marker protein for breast cancer present in saliva. In this paper we study the temperature dependent behavior of hydrated GP2 at terahertz frequencies and find that the peptide undergoes a dynamic transition between 200 and 220 K. By fitting suitable molecular models to the frequency response we determine the molecular processes involved above and below the transition temperature (TD). In particular, we show that below TD the dynamic transition is dominated by a simple harmonic vibration with a slow and temperature dependent relaxation time constant and that above TD, the dynamic behavior is governed by two oscillators, one of which has a fast and temperature independent relaxation time constant and the other of which is a heavily damped oscillator with a slow and temperature dependent time constant. Furthermore a red shifting of the characteristic frequency of the damped oscillator was observed, confirming the presence of a non-harmonic vibration potential. Our measurements and modeling of GP2 highlight the unique capabilities of THz spectroscopy for protein characterization. PMID:23209703

  3. Significant increasing of onset temperature of FM transition in LSMO thin films

    NASA Astrophysics Data System (ADS)

    Chromik, Štefan; Štrbík, Vladimír; Dobročka, Edmund; Dujavová, Agáta; Reiffers, Marián; Liday, Jozef; Španková, Marianna

    2013-03-01

    La0.67Sr0.33MnO3 (LSMO) thin films with a significant increased onset temperature of ferromagnetic transition were prepared using an on-axis dc magnetron sputtering from a stoichiometric ceramic target onto one-side polished MgO (0 0 1). The highest temperature of insulator-metal transition was observed at TP = 416 K. Magnetization hysteresis curves taken at T = 398 K indicate the beginning of the ferromagnetic transition above 400 K. The negative magnetoresistance reaches 15% at a temperature of 400 K. We show that the LSMO thin films with increased temperature values of resistance peak TP and Curie temperature TC are characteristic by a proper microstructure with distorted orthorhombic unit cells. This microstructure is developed during the layer growth, it is not caused by the underlying substrate and it is linked with an appropriate pseudocubic out-of-plane lattice parameter ac⊥, splitted Bragg reflections in rocking curves and as well as in reciprocal space maps.

  4. What is the Actual Low-Temperature Glass Transition for Fish Flesh ?

    NASA Astrophysics Data System (ADS)

    Viriyarattanasak, Chotika; Kawai, Kiyoshi; Watanabe, Manabu; Suzuki, Toru

    We measured glass transition temperatures in the maximally freeze-concentrated phase (Tg') of tuna and cod tissue by differential scanning calorimetry (DSC) using an annealing technique. In our experiment, the Tg' (approximately -71°C) of tuna and cod tissue did not exhibit any significant change after isothermal holding for several weeks at a temperature higher than the Tg. Another Tg' appeared above -45°C when annealing was performed at a temperature higher than -60°C for one week. We also collected Tg' data for fish flesh from many published studies and discussed them in the light of our data. The Tg' values for fish flesh in most published reports are higher than -40°C, although there have been several reports that give values of around -70°C. The high glass transition temperature (i.e., -45°C) measured in our study agrees with most of the data in the literature. Furthermore, the results suggest that the glass transition behavior at the higher temperature may be correlated to the vitrification of protein itself.

  5. Superhigh moduli and tension-induced phase transition of monolayer gamma-boron at finite temperatures.

    PubMed

    Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi

    2016-01-01

    Two dimensional (2D) gamma-boron (γ-B28) thin films have been firstly reported by the experiments of the chemical vapor deposition in the latest study. However, their mechanical properties are still not clear. Here we predict the superhigh moduli (785 ± 42 GPa at 300 K) and the tension-induced phase transition of monolayer γ-B28 along a zigzag direction for large deformations at finite temperatures using molecular dynamics (MD) simulations. The new phase can be kept stable after unloading process at these temperatures. The predicted mechanical properties are reasonable when compared with our results from density functional theory. This study provides physical insights into the origins of the new phase transition of monolayer γ-B28 at finite temperatures. PMID:26979283

  6. Absence of low-temperature phase transitions in epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Tenne, D. A.; Xi, X. X.; Li, Y. L.; Chen, L. Q.; Soukiassian, A.; Zhu, M. H.; James, A. R.; Lettieri, J.; Schlom, D. G.; Tian, W.; Pan, X. Q.

    2004-05-01

    We have studied phase transitions in epitaxial BaTiO3 thin films by Raman spectroscopy. The films are found to remain in a single ferroelectric phase over the temperature range from 5 to 325 K. The low-temperature phase transitions characteristic of bulk BaTiO3 (tetragonal-orthorhombic-rhombohedral) are absent in the films. X-ray diffraction shows that the BaTiO3 films are under tensile strain due to the thermal expansion mismatch with the buffer layer. A phase-field calculation of the phase diagram and domain structures in BaTiO3 thin films predicts, without any priori assumption, that an orthorhombic phase with in-plane polarization is the thermodynamically stable phase for such values of tensile strain and temperature, consistent with the experimental Raman results.

  7. The Temperature Gradient and Transition Timescales as a Function of Topography in Complex Terrain

    NASA Astrophysics Data System (ADS)

    Higgins, C. W.; Hoch, S. W.; Pardyjak, E.

    2013-12-01

    Large portions of the Earth's surface are covered by mountainous areas, and understanding atmospheric flow over these regions is critical for weather prediction, (micro)climatological research, and dispersion modeling. Complex interactions between the topographic features, the synoptic forcing and the buoyant forcing drive flow patterns and flow regime transitions. As a part of the MATTERHORN field experiment, Distributed Temperature Sensing (DTS) technology was used to measure the vertical temperature gradient on an east facing slope across a 2km transect of granite ridge in the Utah west desert, from the base of the mountain to the middle slope. Thus, the temperature gradient is sampled above a wide range of topographic features, from valley formations to ridges, and over a wide range of slope and aspect angles. The relationship between these landforms and the timescales of morning and evening transitions is explored and presented.

  8. Superhigh moduli and tension-induced phase transition of monolayer gamma-boron at finite temperatures

    PubMed Central

    Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi

    2016-01-01

    Two dimensional (2D) gamma-boron (γ-B28) thin films have been firstly reported by the experiments of the chemical vapor deposition in the latest study. However, their mechanical properties are still not clear. Here we predict the superhigh moduli (785 ± 42 GPa at 300 K) and the tension-induced phase transition of monolayer γ-B28 along a zigzag direction for large deformations at finite temperatures using molecular dynamics (MD) simulations. The new phase can be kept stable after unloading process at these temperatures. The predicted mechanical properties are reasonable when compared with our results from density functional theory. This study provides physical insights into the origins of the new phase transition of monolayer γ-B28 at finite temperatures. PMID:26979283

  9. Low temperature magnetic phase transition and interlayer coupling in double-wall carbon nanotubes

    SciTech Connect

    Diamantopoulou, A.; Glenis, S.; Likodimos, V.; Guskos, N.

    2014-08-28

    The magnetic properties of double wall carbon nanotubes (DWCNTs) were investigated using electron spin resonance (ESR) spectroscopy. An asymmetric resonance line of low intensity was identified and analyzed by the superimposition of a narrow and a broad metallic lineshape, attributed to the distinct contributions of defect spins located on the inner and outer DWCNTs shells. The spin susceptibilities of both ESR components revealed a ferromagnetic phase transition at low temperatures (T < 10 K) with small variation in the corresponding Curie-Weiss temperatures, approaching closely that of metallic single wall carbon nanotubes. Interlayer coupling between the DWCNT layers is suggested to effectively reduce the difference between the transition temperatures for the inner and outer shells and enhance spin-spin interactions between defect spins via the RKKY-type interaction of localized spins with conduction electrons.

  10. Superhigh moduli and tension-induced phase transition of monolayer gamma-boron at finite temperatures

    NASA Astrophysics Data System (ADS)

    Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi

    2016-03-01

    Two dimensional (2D) gamma-boron (γ-B28) thin films have been firstly reported by the experiments of the chemical vapor deposition in the latest study. However, their mechanical properties are still not clear. Here we predict the superhigh moduli (785 ± 42 GPa at 300 K) and the tension-induced phase transition of monolayer γ-B28 along a zigzag direction for large deformations at finite temperatures using molecular dynamics (MD) simulations. The new phase can be kept stable after unloading process at these temperatures. The predicted mechanical properties are reasonable when compared with our results from density functional theory. This study provides physical insights into the origins of the new phase transition of monolayer γ-B28 at finite temperatures.

  11. Modified shape memory cyanate polymers with a wide range of high glass transition temperatures

    NASA Astrophysics Data System (ADS)

    Xie, Fang; Huang, Longnan; Liu, Yanju; Leng, Jinsong

    2012-04-01

    Shape memory cyanate polymers (SMCPs) are a new kind of smart materials, which have huge development potential and a promising future. A series of shape memory cyanate polymers were prepared by cyanate ester and varying content of a linear modifier. The thermal properties of the SMCPs were investigated by Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). The SMCPs we prepared have high glass transition temperature and show good heat resistance. The glass transition temperature Tg can be adjusted from 156.9°C to 259.6°C with the modifier. The initial temperature of thermal decomposition comes up to 300°C, which is enough high for the application in aerospace fields. The shape memory polymer we prepared shows a good shape memory effect, as the shape recovery time is less than 65s and the shape recovery rate reaches 95%.

  12. Temperature-induced phase transition in quartz nanocrystals dispersed in pseudotachylite

    NASA Astrophysics Data System (ADS)

    Vettegren, V. I.; Mamalimov, R. I.; Sobolev, G. A.; Kireenkova, S. M.; Morozov, Yu. A.; Smul'skaya, A. I.

    2013-05-01

    The size and concentration of α-quartz nanocrystals dispersed in samples of pseudotachylite and the internal stresses in these nanocrystals have been determined using infrared spectroscopy in the temperature range 300-800 K. Pseudotachylite is a product of intense crushing of granite that undergoes in the Earth's crust faults. It has been found that the size of the nanocrystals is ˜20 nm and does not depend on temperature. As the temperature increases, their concentration decreases monotonically and tends to zero at ˜650 K. This process is paralleled by a growth of the concentration of β-quartz nanocrystals. The α-quartz nanocrystal concentration regains its initial level with decreasing temperature. Thus, the α → β phase transition in quartz nanocrystals in pseudotachylite starts at temperatures lower by ˜500 K than that in the bulk of the macrocrystal (846 K), and is stretched by ˜350 K. At room temperature, the unit cell of nanocrystals is compressed by surface tension forces. These forces retard the α → β phase transition. The thermal expansion coefficient of nanocrystals is larger than that of macrocrystals, which entails a decrease of compression and a monotonic decrease of the concentration of α-quartz nanocrystals with increasing temperature.

  13. Practical Considerations for Determination of Glass Transition Temperature of a Maximally Freeze Concentrated Solution.

    PubMed

    Pansare, Swapnil K; Patel, Sajal Manubhai

    2016-08-01

    Glass transition temperature is a unique thermal characteristic of amorphous systems and is associated with changes in physical properties such as heat capacity, viscosity, electrical resistance, and molecular mobility. Glass transition temperature for amorphous solids is referred as (T g), whereas for maximally freeze concentrated solution, the notation is (T g'). This article is focused on the factors affecting determination of T g' for application to lyophilization process design and frozen storage stability. Also, this review provides a perspective on use of various types of solutes in protein formulation and their effect on T g'. Although various analytical techniques are used for determination of T g' based on the changes in physical properties associated with glass transition, the differential scanning calorimetry (DSC) is the most commonly used technique. In this article, an overview of DSC technique is provided along with brief discussion on the alternate analytical techniques for T g' determination. Additionally, challenges associated with T g' determination, using DSC for protein formulations, are discussed. The purpose of this review is to provide a practical industry perspective on determination of T g' for protein formulations as it relates to design and development of lyophilization process and/or for frozen storage; however, a comprehensive review of glass transition temperature (T g, T g'), in general, is outside the scope of this work. PMID:27193003

  14. L to H mode transition: Parametric dependencies of the temperature threshold

    DOE PAGESBeta

    Bourdelle, C.; Chone, L.; Fedorczak, N.; Garbet, Xavier; Beyer, P.; Citrin, J.; Fuhr, G.; Loarte, A.; Maggi, C. F.; Militello, F.; et al

    2015-06-15

    The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (Tth). They are based on the stabilization of the underlying turbulence by a mean radial electricmore » field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived Tth are tested versus magnetic field, density, effective charge. Furthermore, various robust experimental observations are reproduced, in particular Tth increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.« less

  15. L to H mode transition: Parametric dependencies of the temperature threshold

    SciTech Connect

    Bourdelle, C.; Chone, L.; Fedorczak, N.; Garbet, Xavier; Beyer, P.; Citrin, J.; Fuhr, G.; Loarte, A.; Maggi, C. F.; Militello, F.; Sarazin, Y.; Vermare, L.; Delabie, E.; Dif-Pradalier, G.

    2015-06-15

    The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (Tth). They are based on the stabilization of the underlying turbulence by a mean radial electric field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived Tth are tested versus magnetic field, density, effective charge. Furthermore, various robust experimental observations are reproduced, in particular Tth increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.

  16. L to H mode transition: parametric dependencies of the temperature threshold

    NASA Astrophysics Data System (ADS)

    Bourdelle, C.; Chôné, L.; Fedorczak, N.; Garbet, X.; Beyer, P.; Citrin, J.; Delabie, E.; Dif-Pradalier, G.; Fuhr, G.; Loarte, A.; Maggi, C. F.; Militello, F.; Sarazin, Y.; Vermare, L.; Contributors, JET

    2015-07-01

    The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (Tth). They are based on the stabilization of the underlying turbulence by a mean radial electric field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived Tth are tested versus magnetic field, density, effective charge. Various robust experimental observations are reproduced, in particular Tth increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.

  17. Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

    SciTech Connect

    Thomas, Sarah; Uhoya, Walter; Tsoi, Georgiy; Wenger, Lowell E; Vohra, Yogesh; Chesnut, Gary Neal; Weir, S. T.; Tulk, Christopher A; Moreira Dos Santos, Antonio F

    2012-01-01

    Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

  18. Reproducible technique for fabrication of thin films of high transition temperature superconductors

    NASA Astrophysics Data System (ADS)

    Mankiewich, P. M.; Scofield, J. H.; Skocpol, W. J.; Howard, R. E.; Dayem, A. H.

    1987-11-01

    A new process to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates is reported. The films have high transition temperatures (up to 91 K for a full resistive transition), high critical current densities (10 to the 6th A/sq cm at 81 K), and a reduced sensitivity to fabrication and environmental conditions. Because of the lower reactivity of the films, the authors have been able to pattern them in both the pre-annealed and postannealed states using conventional positive photoresist technology.

  19. High-pressure and high-temperature study of the phase transition in anhydrite

    NASA Astrophysics Data System (ADS)

    Ma, Y. M.; Zhou, Q.; He, Z.; Li, F. F.; Yang, K. F.; Cui, Q. L.; Zou, G. T.

    2007-10-01

    The high-pressure and high-temperature behaviors of anhydrite (CaSO4) are studied up to 53.5 GPa and 1800 K using double-sided laser heating Raman spectroscopy and x-ray diffraction in diamond anvil cells. The evidence of phase transition from an anhydrite structure to the monazite type was observed at about 2 GPa under cold compression. Another phase transition and a change in color of the sample from transparent to black have been also observed at a pressure of 33.2 GPa after laser heating. The new phase after laser heating persists to 53.5 GPa and 1800 K.

  20. 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 ().

  1. High temperature stress-induced ``double loop-like'' phase transitions in Bi-based perovskites

    NASA Astrophysics Data System (ADS)

    Webber, K. G.; Zhang, Y.; Jo, Wook; Daniels, J. E.; Rödel, J.

    2010-07-01

    Polycrystalline 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 samples were tested under uniaxial mechanical compression at various temperatures in the vicinity of the polar tetragonal to nonpolar tetragonal phase boundary. They are shown to display double loop-like stress-strain behavior, marked by a closed ferroelastic hysteresis loop. Thus, it forms a mechanical analog to the polarization-electric field hysteresis behavior of barium titanate above the Curie temperature. As temperature is increased there is an apparent loss of macroscopically observable ferroelasticity, despite the persistence of tetragonality. Macroscopic experimental results are discussed in conjunction with temperature-dependent and stress-dependent high-energy x-ray diffraction data. This reveals a phase transition below the Curie temperature, marked by a discontinuous change in lattice parameters and octahedral tilting during compressive mechanical loading.

  2. Tuning phase transition temperature of VO2 thin films by annealing atmosphere

    NASA Astrophysics Data System (ADS)

    Liu, Xingxing; Wang, Shao-Wei; Chen, Feiliang; Yu, Liming; Chen, Xiaoshuang

    2015-07-01

    A simple new way to tune the optical phase transition temperature of VO2 films was proposed by only controlling the pressure of oxygen during the annealing process. Vanadium films were deposited on glass by a large-scale magnetron sputtering coating system and then annealed in appropriate oxygen atmosphere to form the VO2 films. The infrared transmission change (at 2400 nm) is as high as 58% for the VO2 thin film on the glass substrate, which is very good for tuning infrared radiation and energy saving as smart windows. The phase transition temperature of the films can be easily tuned from an intrinsic temperature to 44.7 °C and 40.2 °C on glass and sapphire by annealing oxygen pressure, respectively. The mechanism is: V3+ ions form in the film when under anaerobic conditions, which can interrupt the V4+ chain and reduce the phase transition temperature. The existence of V3+ ions has been observed by x-ray photoelectron spectroscopy (XPS) experiments as proof.

  3. Temperature dependent electrical transport in single Ge nanowires near insulator-metal transition

    NASA Astrophysics Data System (ADS)

    Raychaudhuri, Arup Kumar; Seth, Shaili; Das, Kaustuv

    We report low temperature (4K <= T <= 300K) electrical transport in single strands of Germanium Nanowires of radius well below 50 nm. The nanowires, grown from vapour phase with Au catalyst have carrier concentrations ranging from intrinsic to near the insulator-metal transition boundary. The nanowires were characterized extensively by High Resolution Transmission Electron Microscope and established their crystalline quality. A single nanowire dispersed on a Si/SiO2 substrate was connected by Cr/Au contacts made by electron beam lithography in 2-probe / 4-probe configurations. The undoped nanowires have a room temperature resistivity (ρ) of 2 ohm.cm or more (estimated carrier concentration ~1015/cm3) and below the 25K (where it shows carrier freeze out) the ρ rises to high value of 35 ohm.cm. For nanowires with ρ <= .01 ohm.cm at 300K , low temperature ρ becomes finite, signaling transition to a metallic state with negative temperature co-efficient of ρ. The critical composition for the insulator-metal transition is more than an order higher than that observed in the bulk. At low T (<25K) resistivity data in this regime can be fitted to weak-localization form ρ =ρ0 - aTp/2 with ρ0 the NW's ~ 0.5-3.5 mohm.cm, with the exponent p ~ 3-4 as expected from theoretical predictions. Acknowldge Financial Support from Department od Science and Technology, Government of India for Sponsored Project.

  4. Transitions.

    ERIC Educational Resources Information Center

    Field, David; And Others

    1992-01-01

    Includes four articles: "Career Aspirations" (Field); "Making the Transition to a New Curriculum" (Baker, Householder); "How about a 'Work to School' Transition?" (Glasberg); and "Technological Improvisation: Bringing CNC to Woodworking" (Charles, McDuffie). (SK)

  5. Reversible transition between SDS@2β-CD microtubes and vesicles triggered by temperature.

    PubMed

    Zhou, Chengcheng; Cheng, Xinhao; Yan, Yun; Wang, Jide; Huang, Jianbin

    2014-04-01

    Switching between association and dissociation is the well-known strategy for constructing responsive materials based on the host-guest complexes of cyclodextrins (CDs). In this work, we report that temperature may also trigger self-assembly transition in the supramolecular system composed of sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD) at a molar ratio of 1:2. We reported previously that, at this ratio, SDS and β-CD form a channel-type SDS@2β-CD supramolecular unit, which further self-assembles into non-amphiphilic vesicles and microtubes driven by hydrogen bonding. Here, we report that the vesicles and microtubes can be reversibly switched between each other upon decreasing and increasing temperature. Control experiments in heavy water suggest that water molecules play a dominating role in the hydrogen bonding between SDS@2β-CD supramolecular units at lower concentration and higher temperature. Under opposite conditions, the hydrogen bonding between CDs is dominating. Therefore, for the 5% system, we observed a vesicle to microtube transition with a decreasing temperature, whereas for the 10% system, we observed the reverse process. Both processes are reversible. This is not only an example of temperature-triggered responsiveness in non-amphiphilic self-assemblies but also a new mode of responsiveness for the host-guest inclusion systems based on CDs. This temperature-responsive process is anticipated to shed light on the design and development of novel advanced materials. PMID:24601651

  6. Temperature-induced Lifshitz transition in WTe2

    SciTech Connect

    Wu, Yun; Jo, Na Hyun; Ochi, Masayuki; Huang, Lunan; Mou, Daixiang; Bud’ko, Sergey L.; Canfield, P. C.; Trivedi, Nandini; Arita, Ryotaro; Kaminski, Adam

    2015-10-12

    In this study, we use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X–Γ–X direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at T≃160 K, associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potential μ(T) due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at T≈175 K and a breakdown of Kohler’s rule in the 70–140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals.

  7. Growth Conditions and Cell Cycle Phase Modulate Phase Transition Temperatures in RBL-2H3 Derived Plasma Membrane Vesicles

    PubMed Central

    Gray, Erin M.; Díaz-Vázquez, Gladys; Veatch, Sarah L.

    2015-01-01

    Giant plasma membrane vesicle (GPMV) isolated from a flask of RBL-2H3 cells appear uniform at physiological temperatures and contain coexisting liquid-ordered and liquid-disordered phases at low temperatures. While a single GPMV transitions between these two states at a well-defined temperature, there is significant vesicle-to-vesicle heterogeneity in a single preparation of cells, and average transition temperatures can vary significantly between preparations. In this study, we explore how GPMV transition temperatures depend on growth conditions, and find that average transition temperatures are negatively correlated with average cell density over 15°C in transition temperature and nearly three orders of magnitude in average surface density. In addition, average transition temperatures are reduced by close to 10°C when GPMVs are isolated from cells starved of serum overnight, and elevated transition temperatures are restored when serum-starved cells are incubated in serum-containing media for 12h. We also investigated variation in transition temperature of GPMVs isolated from cells synchronized at the G1/S border through a double Thymidine block and find that average transition temperatures are systematically higher in GPMVs produced from G1 or M phase cells than in GPMVs prepared from S or G1 phase cells. Reduced miscibility transition temperatures are also observed in GPMVs prepared from cells treated with TRAIL to induce apoptosis or sphingomyelinase, and in some cases a gel phase is observed at temperatures above the miscibility transition in these vesicles. We conclude that at least some variability in GPMV transition temperature arises from variation in the local density of cells and asynchrony of the cell cycle. It is hypothesized that GPMV transition temperatures are a proxy for the magnitude of lipid-mediated membrane heterogeneity in intact cell plasma membranes at growth temperatures. If so, these results suggest that cells tune their plasma membrane

  8. Transition.

    ERIC Educational Resources Information Center

    Thompson, Sandy, Ed.; And Others

    1990-01-01

    This "feature issue" focuses on transition from school to adult life for persons with disabilities. Included are "success stories," brief program descriptions, and a list of resources. Individual articles include the following titles and authors: "Transition: An Energizing Concept" (Paul Bates); "Transition Issues for the 1990s" (William Halloran…

  9. Transition process of abrupt climate change based on global sea surface temperature over the past century

    NASA Astrophysics Data System (ADS)

    Yan, Pengcheng; Hou, Wei; Feng, Guolin

    2016-05-01

    A new detection method has been proposed to study the transition process of abrupt climate change. With this method, the climate system transiting from one stable state to another can be verified clearly. By applying this method to the global sea surface temperature over the past century, several climate changes and their processes are detected, including the start state (moment), persist time, and end state (moment). According to the spatial distribution, the locations of climate changes mainly have occurred in the Indian Ocean and western Pacific before the middle twentieth century, in the 1970s in the equatorial middle-eastern Pacific, and in the middle and southern Pacific since the end of the twentieth century. In addition, the quantitative relationship between the transition process parameters is verified in theory and practice: (1) the relationship between the rate and stability parameters is linear, and (2) the relationship between the rate and change amplitude parameters is quadratic.

  10. Response of water to electric fields at temperatures below the glass transition: A molecular dynamics analysis

    SciTech Connect

    Hu, Xiaohu; Elghobashi-Meinhardt, Nadia; Gembris, Daniel; Smith, Jeremy C

    2011-01-01

    The electric field dependence of the structure and dynamics of water at 77 K, i.e., below the glass transition temperature (136 K), is investigated using molecular dynamics simulations. Transitions are found at two critical field strengths, denoted E1 and E2. The transition around E1 3.5 V/nm is characterized by the onset of significant structural disorder, a rapid increase in the orientational polarization, and a maximum in the dynamical fluctuations. At E2 40 V/nm, the system crystallizes in discrete steps into a body-centered-cubic unit cell that minimizes the potential energy by simultaneous superpolarization of the water molecular dipoles and maximization of the intermolecular hydrogen bonds. The stepwise and discontinuous increase of the orientational polarization with the increasing electric field indicates that the dipole relaxation in the electric field is highly cooperative.

  11. The low temperature phase transition in octane and its possible generalisation to other n-alkanes

    NASA Astrophysics Data System (ADS)

    Neumann, M. A.; Johnson, M. R.; Radaelli, P. G.

    2001-05-01

    A neutron powder diffraction study of three n-alkanes, octane, nonane and pentadecane, down to 2 K is presented. The temperature dependence of the octane diffraction pattern reveals a solid state phase transition between 40 and 55 K, which involves a doubling of the unit cell in the b direction, the space group remaining P 1¯. Confirmation of the phase transition, which results in a doubling of the number of crystallographically inequivalent methyl groups, is sought in the published NMR, tunnelling data and neutron scattering, vibrational data. Density functional theory and force field techniques are used to simulate spectroscopic data based on the measured structures. While no unequivocal evidence is found in spectroscopic data, the published data does not rule out the existence of energetically inequivalent methyl groups. Indeed close inspection of the spectroscopic data for other n-alkanes suggests that the phase transition may be common to many alkanes.

  12. High pressure phase transitions in lawsonite at simultaneous high pressure and temperature: A single crystal study

    NASA Astrophysics Data System (ADS)

    O'Bannon, E. F., III; Vennari, C.; Beavers, C. C. G.; Williams, Q. C.

    2015-12-01

    Lawsonite (CaAl2Si2O7(OH)2.H2O) is a hydrous mineral with a high overall water content of ~11.5 wt.%. It is a significant carrier of water in subduction zones to depths greater than ~150 km. The structure of lawsonite has been extensively studied under room temperature, high-pressure conditions. However, simultaneous high-pressure and high-temperature experiments are scarce. We have conducted synchrotron-based simultaneous high-pressure and temperature single crystal experiments on lawsonite up to a maximum pressure of 8.4 GPa at ambient and high temperatures. We used a natural sample of lawsonite from Valley Ford, California (Sonoma County). At room pressure and temperature lawsonite crystallizes in the orthorhombic system with Cmcm symmetry. Room temperature compression indicates that lawsonite remains in the orthorhombic Cmcm space group up to ~9.0 GPa. Our 5.0 GPa crystal structure is similar to the room pressure structure, and shows almost isotropic compression of the crystallographic axes. Unit cell parameters at 5.0 GPa are a- 5.7835(10), b- 8.694(2), and c- 13.009(3). Single-crystal measurements at simultaneous high-pressure and temperature (e.g., >8.0 GPa and ~100 oC) can be indexed to a monoclinic P-centered unit cell. Interestingly, a modest temperature increase of ~100 oC appears to initiate the orthorhombic to monoclinic phase transition at ~0.6-2.4 GPa lower than room temperature compression studies have shown. There is no evidence of dehydration or H atom disorder under these conditions. This suggests that the orthorhombic to monoclinic transition could be kinetically impeded at 298 K, and that monoclinic lawsonite could be the dominant water carrier through much of the depth range of upper mantle subduction processes.

  13. Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

    NASA Astrophysics Data System (ADS)

    Böhmer, A. E.; Taufour, V.; Straszheim, W. E.; Wolf, T.; Canfield, P. C.

    2016-07-01

    The study of the iron-based superconductor FeSe has blossomed with the availability of high-quality single crystals, obtained through flux/vapor-transport growth techniques below the structural transformation temperature of its tetragonal phase, T ≈450 ∘C . Here, we report on the variation of sample morphology and properties due to small modifications in the growth conditions. A considerable variation of the superconducting transition temperature Tc, from 8.8 K to 3 K, which cannot be correlated with the sample composition, is observed. Instead, we point out a clear correlation between Tc and disorder, as measured by the residual resistivity ratio. Notably, the tetragonal-to-orthorhombic structural transition is also found to be quite strongly disorder dependent (Ts≈72 -90 K) and linearly correlated with Tc.

  14. Double sudden transitions of geometric discord at finite-temperature in the framework of stochastic description

    SciTech Connect

    Wu, Wei; Luo, Da-Wei; Xu, Jing-Bo

    2014-06-28

    We investigate the phenomenon of double sudden transitions in geometric quantum correlations for a system consisting of a bare qubit and a qubit locally coupled to its finite-temperature heat environment with an Ohmic spectrum in the framework of stochastic description. Moreover, we explore the possibility of protecting the geometric discord between the two qubits and prolonging the time during which the geometric discord remains constant by applying Bang-Bang pulses.

  15. Influence of grain size on transition temperature of thermochromic VO{sub 2}

    SciTech Connect

    Miller, Mark J.; Wang, Junlan

    2015-01-21

    Vanadium(IV) oxide (VO{sub 2}) is a unique material that undergoes a reversible phase transformation around 68 °C. The material could potentially be used as an energy-efficient coating for windows since its reflectance in the infrared (IR) increases significantly more than in the visible region. Currently, VO{sub 2} is limited by a transition temperature (τ{sub c}) that is too high, luminous transmittance that is too low or both. In this study, a transition temperature of 45 °C is achieved for a reactively sputtered, undoped film by restricting grain size to approximately 30 nm. It is concluded that a higher density of grain boundaries (smaller grain size) provides a greater number of nucleating defects which in turn reduces τ{sub c}. Similarly, a higher density of grain boundaries may reduce the hysteresis width (difference between transition temperatures in heating and cooling). Also in this study, a new set of optical performance metrics is proposed in which the solar spectrum is divided into the ultraviolet (UV), visible and near infrared (NIR) regions. This approach is more closely aligned with the goals of limiting UV, allowing luminous and modulating NIR transmission. Using these metrics, the optical properties of the low-τ{sub c} sample were: 2% UV transmittance, 47% luminous transmittance, and 23% NIR modulation (decrease from 43 to 33%). This study demonstrates that the grain size of VO{sub 2} should be viewed as an important parameter for controlling the transition temperature of the material.

  16. Spatially resolved quantitative mapping of thermomechanical properties and phase transition temperatures using scanning probe microscopy

    DOEpatents

    Jesse, Stephen; Kalinin, Sergei V; Nikiforov, Maxim P

    2013-07-09

    An approach for the thermomechanical characterization of phase transitions in polymeric materials (polyethyleneterephthalate) by band excitation acoustic force microscopy is developed. This methodology allows the independent measurement of resonance frequency, Q factor, and oscillation amplitude of a tip-surface contact area as a function of tip temperature, from which the thermal evolution of tip-surface spring constant and mechanical dissipation can be extracted. A heating protocol maintained a constant tip-surface contact area and constant contact force, thereby allowing for reproducible measurements and quantitative extraction of material properties including temperature dependence of indentation-based elastic and loss moduli.

  17. Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals.

    PubMed

    Hansen, G P; Krishnan, S; Hauge, R H; Margrave, J L

    1989-05-15

    The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium. PMID:20548762

  18. Method for preparing high transition temperature Nb/sub 3/Ge superconductors. [Patent application

    DOEpatents

    Newkirk, L.R.; Valencia, F.A.

    1975-06-26

    Bulk coatings of Nb/sub 3/Ge superconductors having transition temperatures in excess of 20/sup 0/K are readily formed by a chemical vapor deposition technique involving the coreduction of NbCl/sub 5/ and GeCl/sub 4/ in the presence of hydrogen. The NbCl/sub 5/ vapor may advantageously be formed quantitatively in the temperature range of about 250 to 260/sup 0/C by the chlorination of Nb metal provided the partial pressure of the product NbCl/sub 5/ vapor is maintained at or below about 0.1 atm.

  19. Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals

    NASA Technical Reports Server (NTRS)

    Hansen, George P.; Krishnan, Shankar; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium.

  20. Method for preparing high transition temperature Nb.sub.3 Ge superconductors

    DOEpatents

    Newkirk, Lawrence R.; Valencia, Flavio A.

    1977-01-01

    Bulk coatings of Nb.sub.3 Ge superconductors having transition temperatures in excess of 20 K are readily formed by a chemical vapor deposition technique involving the coreduction of NbCl.sub.5 and GeCl.sub.4 in the presence of hydrogen. The NbCl.sub.5 vapor may advantageously be formed quantitatively in the temperature range of about 250.degree. to 260.degree. C by the chlorination of Nb metal provided the partial pressure of the product NbCl.sub.5 vapor is maintained at or below about 0.1 atm.

  1. Glass-transition temperature gradient in nanocomposites: evidence from nuclear magnetic resonance and differential scanning calorimetry.

    PubMed

    Papon, Aurélie; Montes, Hélène; Hanafi, Mohamed; Lequeux, François; Guy, Laurent; Saalwächter, Kay

    2012-02-10

    The slowing-down of the dynamics of a polymer chain near a surface has been observed for many years now. Here we show that the behavior of model nanocomposites can be quantitatively described with a gradient of glass-transition temperature. We describe with a single parameter-the range of this gradient-the temperature and solvent effect on the spin relaxation dynamics. Moreover, this parameter allows a quantitative description of the nanocomposite calorimetric response from the one of the bulk polymer. PMID:22401088

  2. Temperature dependence of quasi-three level laser transition for long pulse Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Bidin, Noriah; Pourmand, Seyed Ebrahim; Sidi Ahmad, Muhamad Fakaruddin; Khrisnan, Ganesan; Mohd Taib, Nur Athirah; Nadia Adnan, Nurul; Bakhtiar, Hazri

    2013-02-01

    The influence of temperature and pumping energy on stimulated emission cross section and the laser output of quasi-three level laser transition are reported. Flashlamp is used to pump Nd:YAG laser rod. Distilled water is mixed with ethylene glycol to vary the temperature of the cooling system between -30 and 60 °C. The capacitor voltage of flashlamp driver is verified to manipulate the input energy within the range of 10-70 J. The line of interest in quasi-three level laser comprised of 938.5 and 946 nm. The stimulated emission cross section of both lines is found to be inversely proportional to the temperature but directly proportional to the input energy. This is attributed from thermal broadening effect. The changes of stimulated emission cross section and the output laser with respect to the temperature and input energy on line 946 nm are realized to be more dominant in comparison to 938.5 nm.

  3. Finite-temperature phase transitions in the SU (N ) Hubbard model

    NASA Astrophysics Data System (ADS)

    Yanatori, Hiromasa; Koga, Akihisa

    2016-07-01

    We investigate the SU (N ) Hubbard model for the multicomponent fermionic optical lattice system, combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method. We obtain the finite-temperature phase diagrams with N ≤6 and find that low-temperature properties depend on the parity of the components. The magnetically ordered state competes with the correlated metallic state in the system with an even number of components (N ≥4 ) , yielding the first-order phase transition. It is also clarified that in the odd-component system, the ordered state is realized at relatively lower temperatures and the critical temperature is constant in the strong coupling limit.

  4. Effect of thermal history on mechanical properties of polyetheretherketone below the glass transition temperature

    NASA Technical Reports Server (NTRS)

    Cebe, Peggy; Chung, Shirley Y.; Hong, Su-Don

    1987-01-01

    The effect of thermal history on the tensile properties of polyetheretherketone neat resin films was investigated at different test temperatures (125, 25, and -100) using four samples: fast-quenched amorphous (Q); quenched, then crystallized at 180 C (C180); slowly cooled (for about 16 h) from the melt (SC); and air-cooled (2-3 h) from the melt (AC). It was found that thermal history significantly affects the tensile properties of the material below the glass transition. Fast quenched amorphous films were most tough, could be drawn to greatest strain before rupture, and undergo densification during necking; at the test temperature of -100 C, these films had the best ultimate mechanical properties. At higher temperatures, the semicrystalline films AC and C180 had properties that compared favorably with the Q films. The SC films exhibited poor mechanical properties at all test temperatures.

  5. Low-temperature thermal conductances of amorphous dielectric microbridges in the diffusive to ballistic transition

    NASA Astrophysics Data System (ADS)

    Withington, S.; Goldie, D. J.; Velichko, A. V.

    2011-05-01

    Through a lossy acoustic-wave model we explore the effect of inelastic scattering on the low-temperature thermal conductances of amorphous dielectric microbridges in the diffusive to ballistic transition. The model gives not only the thermal flux as a function of geometry and temperature, but also the temperature distribution of the internal degrees of freedom that constitute the loss, which in turn can be used for calculating noise. The approach leads to powerful conceptual insights and provides a numerical framework for analyzing experimental data. SixNy tends to behave ballistically at low frequencies and diffusively at high frequencies, and when integrated over all frequency, the diffusive to ballistic transition becomes apparent at lengths of around a few hundred microns. It is possible to include flux-dependent acoustic loss, which leads to counterintuitive thermal behavior. A sample can behave diffusively when measured using a small temperature difference, but ballistically when measured using a large temperature difference. There is compelling circumstantial evidence that the effects of acoustic saturation have been seen, but not explicitly recognized, on many occasions.

  6. Temperature-dependent phase transition of ferroelectric perovskites: A Wang-Landau-DFT approach

    NASA Astrophysics Data System (ADS)

    Yuk, Simuck; Li, Ying Wai; Eisenbach, Markus; Cooper, Valentino

    Since the discovery of ferroelectricity in perovskite oxides, considerable efforts have been devoted to understanding their phase transition behaviors in terms of temperature, pressure, and composition. Such materials have regularly been used in transducer and actuator applications. As our first step to make accurate predictions of the crystal phases of more complex oxides such as Pb(ZrxTi1-x) O3, we have used the Wang-Landau (WL) algorithm and density functional theory (DFT) to examine the temperature-dependent phase transition of PbTiO3, BaTiO3, and KNbO3. DFT was employed to evaluate the energetics of important crystal-structure candidates, which were later used as the input for WL algorithm. In addition, we examine how the choice of exchange-correlation functionals affects our predictions of the relevant phase transition temperatures. Research supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division and the Office of Science Early Career Research Program (V.R.C.) and used resources at NERSC and OLCF.

  7. Low temperature synthesis, photoluminescence, magnetic properties of the transition metal doped wurtzite ZnS nanowires

    SciTech Connect

    Cao, Jian; Han, Donglai; Wang, Bingji; Fan, Lin; Fu, Hao; Wei, Maobin; Feng, Bo; Liu, Xiaoyan; Yang, Jinghai

    2013-04-15

    In this paper, we synthesized the transition metal ions (Mn, Cu, Fe) doped and co-doped ZnS nanowires (NWs) by a one-step hydrothermal method. The results showed that the solid solubility of the Fe{sup 2+} ions in the ZnS NWs was about two times larger than that of the Mn{sup 2+} or Cu{sup 2+} ions in the ZnS NWs. There was no phase transformation from hexagonal to cubic even in a large quantity transition metal ions introduced for all the samples. The Mn{sup 2+}/Cu{sup 2+}/Fe{sup 2+} related emission peaks can be observed in the Mn{sup 2+},Cu{sup 2+} and Fe{sup 2+} doped ZnS NWs. The ferromagnetic properties of the co-doped samples were investigated at room temperature. - graphical abstract: The stable wurtzite ZnS:TM{sup 2+} (TM=Mn, Cu, Fe) nanowires with room temperature ferromagnetism properties were obtained. The different elongation of unit cell caused by the different doped ions was observed. Highlights: ► The transition metal ions doped wurtzite ZnS nanowires were synthesized at 180 °C. ► There was no phase transformation from hexagonal to cubic even in a large quantity introduced for all the samples. ► The room temperature ferromagnetism properties of the co-doped nanowires were investigated.

  8. Relative permittivity behavior and temperature changes in linoleic acid during the phase transition

    NASA Astrophysics Data System (ADS)

    Kościesza, R.; Siegoczyński, R. M.; Rostocki, A. J.; Tefelski, D. B.; Kos, A.; Ejchart, W.

    2008-07-01

    In our earlier works several fatty liquids (edible oils and unsaturated fatty acids) which exhibit existence of a new phase induced by high pressure were presented. Conclusion of those experiments is that C=C bonds existence in these liquids plays a dominant role in a new phase occurrence. Relative permittivity in pure acids investigated till now seems to behave in specific way. That is why we decided to investigate linoleic acid (C18H32O2) under high pressure. In our experiment such quantities as: electric capacity, pressure and temperature were recorded. The experimental setup gives us also a possibility to conduct optical investigations. We observed a transmitted and scattered beams of close infrared light (λ = 800nm) in directions 0° and 90° towards the incident beam. Due to the rapid grow of temperature and the rapid change of transmitted and scattered beams we may say that observed phenomenon is a first order phase transition and a proof for the significant change of liquid structure. This paper contains time dependencies of permittivity, temperature, transmitted and scattered light intensity and also permittivity vs. pressure changes during the phase transition in linoleic acid and first of all measured data analysis which lets us explain the transition reasons.

  9. Synthesis of a metal oxide with a room-temperature photoreversible phase transition

    NASA Astrophysics Data System (ADS)

    Ohkoshi, Shin-Ichi; Tsunobuchi, Yoshihide; Matsuda, Tomoyuki; Hashimoto, Kazuhito; Namai, Asuka; Hakoe, Fumiyoshi; Tokoro, Hiroko

    2010-07-01

    Photoinduced phase-transition materials, such as chalcogenides, spin-crossover complexes, photochromic organic compounds and charge-transfer materials, are of interest because of their application to optical data storage. Here we report a photoreversible metal-semiconductor phase transition at room temperature with a unique phase of Ti3O5, λ-Ti3O5. λ-Ti3O5 nanocrystals are made by the combination of reverse-micelle and sol-gel techniques. Thermodynamic analysis suggests that the photoinduced phase transition originates from a particular state of λ-Ti3O5 trapped at a thermodynamic local energy minimum. Light irradiation causes reversible switching between this trapped state (λ-Ti3O5) and the other energy-minimum state (β-Ti3O5), both of which are persistent phases. This is the first demonstration of a photorewritable phenomenon at room temperature in a metal oxide. λ-Ti3O5 satisfies the operation conditions required for a practical optical storage system (operational temperature, writing data by short wavelength light and the appropriate threshold laser power).

  10. Temperature induced structural transitions from native to unfolded aggregated states of tobacco etch virus protease

    NASA Astrophysics Data System (ADS)

    Zhu, Guo-Fei; Ren, Si-Yan; Xi, Lei; Du, Lin-Fang; Zhu, Xiao-Feng

    2015-02-01

    Tobacco etch virus protease (TEVp) is widely used to remove fusion tags from recombinant proteins because of its high and unique specificity. This work describes the conformational and the thermodynamic properties in the unfolding/refolding process of TEVp3M (three-point mutant: L56V/S135G/S219V) induced by temperature. With temperature increasing from 20 to 100 °C, the CD spectra showed a transition trend from α-helix to β-sheet, and the fluorescence emission, synchronous fluorescence, ANS and RLS spectroscopy consistently revealed that the temperature-induced unfolding process behaved in a three-state manner, for there was a relatively stable intermediate state observed around 50 °C. The reversibility of thermal unfolding of TEVp3M further showed that the transition from the native to the intermediate state was reversible (below 50 °C), however the transition from the intermediate to the unfolded state was irreversible (above 60 °C). Moreover, aggregates were observed above 60 °C as revealed by SDS-PAGE, Thioflavin-T fluorescence and Congo red absorbance.

  11. The effects of shock wave compaction on the transition temperatures of A15 structure superconductors

    NASA Technical Reports Server (NTRS)

    Otto, G. H.

    1974-01-01

    Several superconductors with the A15 structure exhibit a positive pressure coefficient, indicating that their transition temperatures increase with applied pressure. Powders of the composition Nb3Al, Nb3Ge, Nb3(Al0.75Ge0.25), and V3Si were compacted by explosive shock waves. The superconducting properties of these materials were measured before and after compaction and it was found that regardless of the sign of the pressure coefficient, the transition temperature is always lowered. The decrease in transition temperature is associated with a decrease in the particle diameter. The shock wave passage through a 3Nb:1Ge powder mixture leads to the formation of at least one compound (probably Nb5Ge3). However, the formation of the A15 compound Nb3Ge is not observed. Elemental niobium powder can be compacted by converging shock waves close to the expected value of the bulk density. Under special circumstances a partial remelting in the center of the sample is observed.

  12. Transport properties of glass-forming liquids suggest that dynamic crossover temperature is as important as the glass transition temperature

    PubMed Central

    Mallamace, Francesco; Branca, Caterina; Corsaro, Carmelo; Leone, Nancy; Spooren, Jeroen; Chen, Sow-Hsin; Stanley, H. Eugene

    2010-01-01

    It is becoming common practice to partition glass-forming liquids into two classes based on the dependence of the shear viscosity η on temperature T. In an Arrhenius plot, ln η vs 1/T, a strong liquid shows linear behavior whereas a fragile liquid exhibits an upward curvature [super-Arrhenius (SA) behavior], a situation customarily described by using the Vogel–Fulcher–Tammann law. Here we analyze existing data of the transport coefficients of 84 glass-forming liquids. We show the data are consistent, on decreasing temperature, with the onset of a well-defined dynamical crossover η×, where η× has the same value, η× ≈ 103 Poise, for all 84 liquids. The crossover temperature, T×, located well above the calorimetric glass transition temperature Tg, marks significant variations in the system thermodynamics, evidenced by the change of the SA-like T dependence above T× to Arrhenius behavior below T×. We also show that below T× the familiar Stokes–Einstein relation D/T ∼ η-1 breaks down and is replaced by a fractional form D/T ∼ η-ζ, with ζ ≈ 0.85. PMID:21148100

  13. Evidence of liquid–liquid transition in glass-forming La50Al35Ni15 melt above liquidus temperature

    PubMed Central

    Xu, Wei; Sandor, Magdalena T.; Yu, Yao; Ke, Hai-Bo; Zhang, Hua-Ping; Li, Mao-Zhi; Wang, Wei-Hua; Liu, Lin; Wu, Yue

    2015-01-01

    Liquid–liquid transition, a phase transition of one liquid phase to another with the same composition, provides a key opportunity for investigating the relationship between liquid structures and dynamics. Here we report experimental evidences of a liquid–liquid transition in glass-forming La50Al35Ni15 melt above its liquidus temperature by 27Al nuclear magnetic resonance including the temperature dependence of cage volume fluctuations and atomic diffusion. The observed dependence of the incubation time on the degree of undercooling is consistent with a first-order phase transition. Simulation results indicate that such transition is accompanied by the change of bond-orientational order without noticeable change in density. The temperature dependence of atomic diffusion revealed by simulations is also in agreement with experiments. These observations indicate the need of two-order parameters in describing phase transitions of liquids. PMID:26165855

  14. Evidence of liquid-liquid transition in glass-forming La50Al35Ni15 melt above liquidus temperature

    NASA Astrophysics Data System (ADS)

    Xu, Wei; Sandor, Magdalena T.; Yu, Yao; Ke, Hai-Bo; Zhang, Hua-Ping; Li, Mao-Zhi; Wang, Wei-Hua; Liu, Lin; Wu, Yue

    2015-07-01

    Liquid-liquid transition, a phase transition of one liquid phase to another with the same composition, provides a key opportunity for investigating the relationship between liquid structures and dynamics. Here we report experimental evidences of a liquid-liquid transition in glass-forming La50Al35Ni15 melt above its liquidus temperature by 27Al nuclear magnetic resonance including the temperature dependence of cage volume fluctuations and atomic diffusion. The observed dependence of the incubation time on the degree of undercooling is consistent with a first-order phase transition. Simulation results indicate that such transition is accompanied by the change of bond-orientational order without noticeable change in density. The temperature dependence of atomic diffusion revealed by simulations is also in agreement with experiments. These observations indicate the need of two-order parameters in describing phase transitions of liquids.

  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. Temperature Measurements in the Solar Transition Region Using N III Line Intensity Ratios

    NASA Technical Reports Server (NTRS)

    Doron, R.; Doschek, G. A.; Laming, J. M.; Feldman, U.; Bhatia, A. K.

    2003-01-01

    UV emission from B-like N and O ions a rather rare opportunity for recording spectral lines in a narrow wavelength range that can potentially be used to derive temperatures relevant to the solar transition region. In these ions, the line intensity ratios of the type (2s2p(sup 2) - 2p(sup 3)) / (2s(sup 2)2p - 2s2p(sup 2)) are very sensitive to the electron temperature. Additionally, the lines involving the ratios fall within a range of only - 12 A; in N III the lines fall in the 980 - 992 A range and in O IV in the 780 - 791 A range. In this work, we explore the use of these atomic systems, primarily in N III, for temperature diagnostics of the transition region by analyzing UV spectra obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory (SOHO). The N III temperature-sensitive line ratios are measured in more than 60 observations. Most of the measured ratios correspond to temperatures in the range 5.7x10(exp 4) - 6.7x10(exp 4) K. This range is considerably lower than the calculated temperature of maximum abundance of N III, which is approx. 7.6x10(exp 4) K. Detailed analysis of the spectra further indicates that the measured ratios are probably somewhat overestimated due to resonant scattering effects in the 2s(sup 2)2p - 2s2p(sup 2) lines and small blends in the 2s2p(sup 2) - 2p3 lines. Actual lower ratios would only increase the disagreement between the ionization balance calculations and present temperature measurements based on a collisional excitation model. In the case of the O IV spectra, we determined that due to the close proximity in wavelength of the weak line (2s2p(sup 2)-2p3 transitions) to a strong Ne VIII line, sufficiently accurate ratio measurements cannot be obtained. Subject headings: atomic data --- atomic processes --- Sun: transition region --- Sun: U V radiation --- techniques: spectroscopic

  17. Plastic Deformation of Transition Zone Minerals: Effect of Temperature on Dislocation Mobility

    NASA Astrophysics Data System (ADS)

    Ritterbex, S.; Carrez, P.; Gouriet, K.; Cordier, P.

    2014-12-01

    Mantle convection is the fundamental process by which the Earth expels its internal heat. It is controlled at the microscopic scale by the motion of crystal defects responsable for plastic deformation at high temperature and pressure conditions of the deep Earth. In this study we focus on dislocations which are usually considered as the most efficient defects contributing to intracrystalline deformation. The influence of temperature is a key parameter in determining the behaviour of dislocations. We propose a model to describe the temperature-dependent mobility of dislocations based on a computational materials science approach, connecting the atomic to the grain scale. This provides elementary knowledge to both interpret seismic anisotropy and to improve geodynamic modelling. Here we focus on plastic deformation of the transition zone minerals wadsleyite and ringwoodite, dominating the boundary separating the upper from the lower mantle, a region over which the viscosity is thought to increase rapidly. Using the Peierls-Nabarro-Galerkin model enabled us to select potential glide planes, to predict the dislocation core structures and fundamental properties of both Mg2SiO4 high-pressure polymorphs integrating the non-elastic nature of dislocations from atomic scale based calculations. Macroscopic deformation results from the mobility of these distinct dislocations. High finite mantle temperatures activates unstable double-kink configurations on the dislocation line which allow the dislocation to move under stress. The original contribution of the present work is the formulation of a mobility law for dissociated dislocations as they occur in wadsleyite and ringwoodite. This permits us to predict the critical activation enthalpy required to overcome lattice friction associated to the onset of glide. From this, the effective glide velocities can be derived as a function of stress and temperature leading to the first lower bound estimates of transition zone viscosities

  18. The influence of initial temperature on flame acceleration and deflagration-to-detonation transition

    SciTech Connect

    Ciccarelli, G.; Boccio, J.L.; Ginsberg, T.

    1996-07-01

    The influence of initial mixture temperature on deflagration-to-detonation transition (DDT) has been investigated experimentally. The experiments were carried out in a 27-cm-inner diameter, 21.3-meter-long heated detonation tube, which was equipped with periodic orifice plates to promote flame acceleration. Hydrogen-air-steam mixtures were tested at a range of temperatures up to 650K and at an initial pressure of 0.1 MPa. In most cases, the limiting hydrogen mole fraction which resulted in transition to detonation corresponded to the mixture whose detonation cell size, {lambda}, was approximately equal to the inner diameter of the orifice plate, d (e.g., d/{lambda}{approximately}1). The only exception was in dry hydrogen-air mixtures at 650K where the DDT limit was observed to be 11 percent hydrogen, corresponding to a value of d/{lambda} equal to 5.5. For a 10.5 percent hydrogen mixture at 650K, the flame accelerated to a maximum velocity of about 120 m/s and then decelerated to below 2 m/s. This observation indicates that the d/{lambda} = 1 DDT limit criterion provides a necessary condition but not a sufficient one for the onset of DDT in obstacle-laden ducts. In this particular case, the mixture initial condition (i.e., temperature) resulted in the inability of the mixture to sustain flame acceleration to the point where DDT could occur. It was also observed that the distance required for the flame to accelerate to the onset of detonation was a function of both the hydrogen mole fraction and the mixture initial temperature. For example, decreasing the hydrogen mole fraction or increasing the initial mixture temperature resulted in longer transition distances.

  19. Conductance of AFM Deformed Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Maiti, Amitesh; Anatram, M. P.; Biegel, Bryan (Technical Monitor)

    2002-01-01

    This viewgraph presentation provides information on the electrical conductivity of carbon nanotubes upon deformation by atomic force microscopy (AFM). The density of states and conductance were computed using four orbital tight-binding method with various parameterizations. Different chiralities develop bandgap that varies with chirality.

  20. Contact nanomechanical measurements with the AFM

    NASA Astrophysics Data System (ADS)

    Geisse, Nicholas

    2013-03-01

    The atomic force microscope (AFM) has found broad use in the biological sciences largely due to its ability to make measurements on unfixed and unstained samples under liquid. In addition to imaging at multiple spatial scales ranging from micro- to nanometer, AFMs are commonly used as nanomechanical probes. This is pertinent for cell biology, as it has been demonstrated that the geometrical and mechanical properties of the extracellular microenvironment are important in such processes as cancer, cardiovascular disease, muscular dystrophy, and even the control of cell life and death. Indeed, the ability to control and quantify these external geometrical and mechanical parameters arises as a key issue in the field. Because AFM can quantitatively measure the mechanical properties of various biological samples, novel insights to cell function and to cell-substrate interactions are now possible. As the application of AFM to these types of problems is widened, it is important to understand the performance envelope of the technique and its associated data analyses. This talk will discuss the important issues that must be considered when mechanical models are applied to real-world data. Examples of the effect of different model assumptions on our understanding of the measured material properties will be shown. Furthermore, specific examples of the importance of mechanical stimuli and the micromechanical environment to the structure and function of biological materials will be presented.

  1. A Batch Fabricated SECM-AFM Probe

    NASA Astrophysics Data System (ADS)

    Dobson, P. S.; Macpherson, J. V.; Holder, M.; Weaver, J. M. R.

    2003-12-01

    A scheme for the fabrication of combined Scanning Electrochemical Microscopy — Atomic Force Microscopy (SECM-AFM) probes is presented for both silicon nitride and silicon cantilevers. The advantages over exsisting methods used for their production is explained. The process flow is described and initial results from electrodeposition of silver are presented.

  2. Direct Shear of Olivine Single Crystals at the Transition from Asthenospheric to Lithospheric Temperatures

    NASA Astrophysics Data System (ADS)

    Tielke, J. A.; Zimmerman, M. E.; Kohlstedt, D. L.

    2014-12-01

    Models of geodynamic processes require constitutive equations that describe the rheological properties of olivine-rich mantle rocks. An extensive database exists for high-temperature deformation of olivine single crystals and aggregates. However, extrapolation of flow laws derived from high-temperature experiments to temperatures typical of the lithospheric mantle results in significant overestimation of olivine strength. Although some studies have explored the low-temperature deformation of olivine, constitutive equations describing the rheological properties of the four dominate dislocation slip systems over a large range of temperature and stress conditions have yet to be established. To investigate the rheological properties of olivine single crystals deforming by dislocation creep at asthenospheric and lithospheric temperatures, a series of direct shear experiments were carried out. The direct shear geometry permits isolation of the four dominate dislocation slip systems, whereas only two slip systems can be independently activated during triaxial compression. The experiments were carried out in a gas-medium deformation apparatus at temperatures of 1000-1300°C, a confining pressure of 300 MPa, and shear stresses of 81 to 334 MPa that result in shear strain rates of 1.0 x 10-5 to 2.6 x 10-3 s-1. At high-temperature and low-stress conditions, strain rate follows a power law relationship with stress. At low-temperature and high-stress conditions, strain rate depends exponentially on stress. These observations are consistent with a transition from strain rate limited by a climb-controlled dislocation mechanism at higher temperatures to strain rate limited by a glide-controlled dislocation mechanism at lower temperatures.

  3. Transition-metal embedded carbon nitride monolayers: high-temperature ferromagnetism and half-metallicity

    NASA Astrophysics Data System (ADS)

    Choudhuri, Indrani; Kumar, Sourabh; Mahata, Arup; Rawat, Kuber Singh; Pathak, Biswarup

    2016-07-01

    High-temperature ferromagnetic materials with planar surfaces are promising candidates for spintronics applications. Using state-of-the-art density functional theory (DFT) calculations, transition metal (TM = Cr, Mn, and Fe) incorporated graphitic carbon nitride (TM@gt-C3N4) systems are investigated as possible spintronics devices. Interestingly, ferromagnetism and half-metallicity were observed in all of the TM@gt-C3N4 systems. We find that Cr@gt-C3N4 is a nearly half-metallic ferromagnetic material with a Curie temperature of ~450 K. The calculated Curie temperature is noticeably higher than other planar 2D materials studied to date. Furthermore, it has a steel-like mechanical stability and also possesses remarkable dynamic and thermal (500 K) stability. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N4 is as high as 137.26 μeV per Cr. Thereby, such material with a high Curie temperature can be operated at high temperatures for spintronics devices.High-temperature ferromagnetic materials with planar surfaces are promising candidates for spintronics applications. Using state-of-the-art density functional theory (DFT) calculations, transition metal (TM = Cr, Mn, and Fe) incorporated graphitic carbon nitride (TM@gt-C3N4) systems are investigated as possible spintronics devices. Interestingly, ferromagnetism and half-metallicity were observed in all of the TM@gt-C3N4 systems. We find that Cr@gt-C3N4 is a nearly half-metallic ferromagnetic material with a Curie temperature of ~450 K. The calculated Curie temperature is noticeably higher than other planar 2D materials studied to date. Furthermore, it has a steel-like mechanical stability and also possesses remarkable dynamic and thermal (500 K) stability. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N4 is as high as 137.26 μeV per Cr. Thereby, such material with a high Curie temperature can be operated at high temperatures for spintronics devices. Electronic supplementary information (ESI

  4. Magnetism in transition metal-substituted germanane: A search for room temperature spintronic devices

    NASA Astrophysics Data System (ADS)

    Sun, Minglei; Ren, Qingqiang; Zhao, Yiming; Wang, Sake; Yu, Jin; Tang, Wencheng

    2016-04-01

    Using first-principles calculations, we investigated the geometric structure, binding energy, and magnetic behavior of monolayer germanane substitutional doped with transition metals. Our work demonstrates that germanane with single vacancy forms strong bonds with all studied impurity atoms. Magnetism is observed for Ti, V, Cr, Mn, Fe, and Ni doping. Doping of Ti and Mn atoms results in half-metallic properties, while doping of Cr results in dilute magnetic semiconducting state. We estimate a Curie temperature of about 735 K for Mn-substituted system in the mean-field approximation at impurity concentration 5.56%. Furthermore, when increasing the impurity concentration to 12.5%, Curie temperatures of Ti and Mn-substituted systems are 290 and 1120 K, respectively. Our studies demonstrate the potential of Ti and Mn-substituted germanane for room temperature spintronic devices.

  5. Precise and millidegree stable temperature control for fluorescence imaging: Application to phase transitions in lipid membranes

    PubMed Central

    Farkas, Elaine R.; Webb, Watt W.

    2010-01-01

    We present the design of a custom temperature-controlled chamber suitable for water or oil immersion fluorescence microscopy and its application to phase behavior in lipid bilayer vesicles. The apparatus is self-contained and portable, suitable for multiuser microscopy facilities. It offers a higher temperature resolution and stability than any comparable commercial apparatus, on the order of millidegrees. We demonstrate the utility of the system in the study of miscibility transitions in model membranes. The temperature-dependent phase behavior of model membrane systems that display liquid-ordered (Lo) phase coexistence with the liquid-disordered (Ld) phase is relevant to understanding the existence of heterogeneities in biological cell plasma membranes, ubiquitously termed “lipid rafts.” PMID:20886984

  6. Scaling description of the yielding transition in soft amorphous solids at zero temperature.

    PubMed

    Lin, Jie; Lerner, Edan; Rosso, Alberto; Wyart, Matthieu

    2014-10-01

    Yield stress materials flow if a sufficiently large shear stress is applied. Although such materials are ubiquitous and relevant for industry, there is no accepted microscopic description of how they yield, even in the simplest situations in which temperature is negligible and in which flow inhomogeneities such as shear bands or fractures are absent. Here we propose a scaling description of the yielding transition in amorphous solids made of soft particles at zero temperature. Our description makes a connection between the Herschel-Bulkley exponent characterizing the singularity of the flow curve near the yield stress Σc, the extension and duration of the avalanches of plasticity observed at threshold, and the density P(x) of soft spots, or shear transformation zones, as a function of the stress increment x beyond which they yield. We argue that the critical exponents of the yielding transition may be expressed in terms of three independent exponents, θ, df, and z, characterizing, respectively, the density of soft spots, the fractal dimension of the avalanches, and their duration. Our description shares some similarity with the depinning transition that occurs when an elastic manifold is driven through a random potential, but also presents some striking differences. We test our arguments in an elasto-plastic model, an automaton model similar to those used in depinning, but with a different interaction kernel, and find satisfying agreement with our predictions in both two and three dimensions. PMID:25246567

  7. Variable Temperature FTIR Spectroscopy Of Transition Metal Complexes Using The SCN Reporter Ligand.

    NASA Astrophysics Data System (ADS)

    Herber, Rolfe H...

    1989-12-01

    Due to its large oscillator strength, as well as its position in the IR spectrum (ca. 2100 cm-1) which is relatively free of interferences, the CN stretch absorption in transition metal thiocyanate and iso-thiocyanate complexes has long been used as a diagnostic measure of both the ligand binding mode, as well as an indication of molecular point-group symmetry. In bis-SCN complexes of the first-row transition metals having (distorted) D, symmetry, cis complexes are expected to show two absorbances, corresponding to the sym and asym stretching modes, while for trans complexes (D,) having inversion symmetry, the sym stretch should be IR forbidden and Raman allowed, while the asym stretch is IR allowed and Raman forbidden. Similar considerations apply to square planar complexes (Cav and D). In this study, a number of octahedral and square planar transition metal bis-thiocyanate (isothiocyanate) complexes of Mn(II), Fe(II), Co(II), Ni(II),Cu(II), Ru(II) and Pt(II) have been synthesized, and characterized. by variable temperature IR spectroscopy both in KBr and Kel-F grease mull matrices. Depending on the steric requirements of the other ligands, the characteristic signature of the pseudohalide stretching mode is found to depend critically on the (near) degeneracy of the sym and asym CN stretching modes. Low temperature IR data, as well as supporting nmr and Raman spectroscopic results are required to completely characterize the geometry of these inorganic and metal organic complexes.

  8. Scaling description of the yielding transition in soft amorphous solids at zero temperature

    PubMed Central

    Lin, Jie; Lerner, Edan; Rosso, Alberto; Wyart, Matthieu

    2014-01-01

    Yield stress materials flow if a sufficiently large shear stress is applied. Although such materials are ubiquitous and relevant for industry, there is no accepted microscopic description of how they yield, even in the simplest situations in which temperature is negligible and in which flow inhomogeneities such as shear bands or fractures are absent. Here we propose a scaling description of the yielding transition in amorphous solids made of soft particles at zero temperature. Our description makes a connection between the Herschel–Bulkley exponent characterizing the singularity of the flow curve near the yield stress Σc, the extension and duration of the avalanches of plasticity observed at threshold, and the density P(x) of soft spots, or shear transformation zones, as a function of the stress increment x beyond which they yield. We argue that the critical exponents of the yielding transition may be expressed in terms of three independent exponents, θ, df, and z, characterizing, respectively, the density of soft spots, the fractal dimension of the avalanches, and their duration. Our description shares some similarity with the depinning transition that occurs when an elastic manifold is driven through a random potential, but also presents some striking differences. We test our arguments in an elasto-plastic model, an automaton model similar to those used in depinning, but with a different interaction kernel, and find satisfying agreement with our predictions in both two and three dimensions. PMID:25246567

  9. Effect of the glass transition of coating adhesive on temperature performance of fiber optic gyroscope and its optimization

    NASA Astrophysics Data System (ADS)

    Wang, Yueze; Wang, Tieshui; Ma, Lin; Yu, Hao; Liu, Bohan

    2015-10-01

    The fiber optic gyroscope (FOG)based on Sagnac effect has became to one of the most important sensors in developing due to light in quality, high accuracy, compact in dimension and long life and has played a very important role in both military and civil use. It is the most difficult problem that the FOG has an obvious bias drift caused by temperature change and temperature grade, so its application is limited to a great extent. Fiber coil is one of the most critical components in FOG. Here, the characteristic of temperature error of the fiber optical coil was analyzed. At first, by studying the glass transition of coating adhesive in the fiber coil, the element model of the fiber coil with the glass transition of coating adhesive in FOG was built. Then the discrete mathematics model of SHUPE error with the glass transition of coating adhesive in FOG was built. Finally, based on the temperature models mentioned above, the effects caused by the glass transition of coating adhesive on temperature performance of fiber optic gyroscope were analyzed. Theoretical analysis and experimental results show that effect caused by the glass transition of coating adhesive had seriously affected the temperature performance of FOG. By optimizing the glass transition temperature of coating adhesive, the SHUPE error of fiber coils can be reduced. At the same time, the amplitude uniformity of the SHUPE error can be improved greatly to reduce the difficulty in temperature compensation.

  10. Massive Temperature-Induced Metal—Insulator Transition in Individual Nanowires of a Non-Stoichiometric Vanadium Oxide Bronze

    SciTech Connect

    Patridge, C.; Wu, T; Jaye, C; Ravel, B; Takeuchi, E; Fischer, D; Sambandamurthy, G; Banerjee, S

    2010-01-01

    Metal-insulator transitions in strongly correlated materials, induced by varying either temperature or dopant concentration, remain a topic of enduring interest in solid-state chemistry and physics owing to their fundamental importance in answering longstanding questions regarding correlation effects. We note here the unprecedented observation of a four-orders-of-magnitude metal-insulator transition in single nanowires of {delta}-K{sub x}V{sub 2}O{sub 5}, when temperature is varied, which thus represents a rare new addition to the pantheon of materials exhibiting pronounced metal-insulator transitions in proximity to room temperature.

  11. Electronic structure changes across the metamagnetic transition in FeRh via hard X-ray photoemission.

    PubMed

    Gray, A X; Cooke, D W; Krüger, P; Bordel, C; Kaiser, A M; Moyerman, S; Fullerton, E E; Ueda, S; Yamashita, Y; Gloskovskii, A; Schneider, C M; Drube, W; Kobayashi, K; Hellman, F; Fadley, C S

    2012-06-22

    Stoichiometric FeRh undergoes a temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition at ~350 K. In this Letter, changes in the electronic structure accompanying this transition are investigated in epitaxial FeRh thin films via bulk-sensitive valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 5.95 keV. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density-functional theory. Changes in the 2p core levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results indicate that significant electronic structure changes over the entire valence-band region are involved in this AFM-FM transition. PMID:23004654

  12. Electronic Structure Changes across the Metamagnetic Transition in FeRh via Hard X-Ray Photoemission

    NASA Astrophysics Data System (ADS)

    Gray, A. X.; Cooke, D. W.; Krüger, P.; Bordel, C.; Kaiser, A. M.; Moyerman, S.; Fullerton, E. E.; Ueda, S.; Yamashita, Y.; Gloskovskii, A.; Schneider, C. M.; Drube, W.; Kobayashi, K.; Hellman, F.; Fadley, C. S.

    2012-06-01

    Stoichiometric FeRh undergoes a temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition at ˜350K. In this Letter, changes in the electronic structure accompanying this transition are investigated in epitaxial FeRh thin films via bulk-sensitive valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 5.95 keV. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density-functional theory. Changes in the 2p core levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results indicate that significant electronic structure changes over the entire valence-band region are involved in this AFM-FM transition.

  13. High-temperature phase transition and local structure of a hydrous anorthoclase

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Wang, Z. P.; Tian, Z. Z.; Xia, Q. K.; Li, G. W.

    2016-02-01

    The in situ Raman spectra of a hydrous anorthoclase at temperatures of 20-800 °C have been measured using a LABRAM-HR spectrometer and Linkam TS 1500 heating stage. The frequencies of modes at 54, 99, 130 and 162 cm-1 related to M-O vibrations decrease sharply and then increase drastically or keep steady at temperatures above 200 °C. A knee point can be clearly seen at about 200 °C for those modes. The frequency of the mode at 282 cm-1 shows little temperature dependence. However, for the two strongest modes at 471 and 512 cm-1, the frequencies decrease linearly with increasing temperature. From evolution of the frequencies of modes at 54, 99, 130 and 162 cm-1 with temperature, the following conclusions can be drawn: (1) The distance of the local M-O bond shortens rather than lengthens at temperatures above 200 °C; (2) The abrupt changes of the local structure of M site induce a collapse of the framework structure and displacive phase transition at 200 °C; and (3) The H atoms incorporated in anorthoclase are located at the M site. These results are indicative for the structure and properties of anorthoclase at deep earth conditions.

  14. Low-Cost, High Glass-Transition Temperature, Thermosetting Polyimide Developed

    NASA Technical Reports Server (NTRS)

    Chuang, Kathy C.

    1999-01-01

    PMR-15 polyimide, developed in the mid-1970's at the NASA Lewis Research Center, is recognized as a state-of-the-art high-temperature resin for composite applications in the temperature range of 500 to 550 F (260 to 288 C). PMR-15 offers easy processing and good property retention at a reasonable cost. For these reasons, it is widely used in both military and commercial aircraft engine components. Traditionally, polyimide composites have been designed for long-term use at 500 to 600 F over thousands of hours. However, new applications in reusable launch vehicles (RLV's) require lightweight materials that can perform for short times (tens of hours) at temperatures between 800 and 1000 F (425 and 538 C). Current efforts at Lewis are focused on raising the use temperature of polyimide composites by increasing the glass-transition temperature of the matrix resins. Achieving this dramatic increase in the upper use temperature without sacrificing polymer and composite processability is a major technical challenge.

  15. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

    NASA Technical Reports Server (NTRS)

    Cullers, Cheryl L.; Antolovich, Stephen D.

    1993-01-01

    The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature.

  16. Reproducible technique for fabrication of thin films of high transition temperature superconductors

    SciTech Connect

    Mankiewich, P.M.; Scofield, J.H.; Skocpol, W.J.; Howard, R.E.; Dayem, A.H.; Good, E.

    1987-11-23

    We report on a new process to make films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ using coevaporation of Y, Cu, and BaF/sub 2/ on SrTiO/sub 3/ substrates. The films have high transition temperatures (up to 91 K for a full resistive transition), high critical current densities (10/sup 6/ A/cm/sup 2/ at 81 K), and a reduced sensitivity to fabrication and environmental conditions. Because of the lower reactivity of the films, we have been able to pattern them in both the pre-annealed and post-annealed states using conventional positive photoresist technology.

  17. Light-Induced Temperature Transitions in Biodegradable Polymer and Nanorod Composites**

    PubMed Central

    Hribar, Kolin C.; Metter, Robert B.; Ifkovits, Jamie L.; Troxler, Thomas

    2010-01-01

    Shape-memory materials (including polymers, metals, and ceramics) are those that are processed into a temporary shape and respond to some external stimuli (e.g., temperature) to undergo a transition back to a permanent shape.[1, 2] Shape memory polymers are finding use in a range of applications from aerospace to fabrics, to biomedical devices and microsystem components.[3–5] For many applications, it would be beneficial to initiate heating with an external trigger (e.g., transdermal light exposure). In this work, we formulated composites of gold nanorods (<1% by volume) and biodegradable networks, where exposure to infrared light induced heating and consequently, shape transitions. The heating is repeatable and tunable based on nanorod concentration and light intensity and the nanorods did not alter the cytotoxicity or in vivo tissue response to the networks. PMID:19408258

  18. Bifurcation Theory of the Transition to Collisionless Ion-temperature-gradient-driven Plasma Turbulence

    SciTech Connect

    Kolesnikov, R.A.; Krommes, J.A.

    2005-09-22

    The collisionless limit of the transition to ion-temperature-gradient-driven plasma turbulence is considered with a dynamical-systems approach. The importance of systematic analysis for understanding the differences in the bifurcations and dynamics of linearly damped and undamped systems is emphasized. A model with ten degrees of freedom is studied as a concrete example. A four-dimensional center manifold (CM) is analyzed, and fixed points of its dynamics are identified and used to predict a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows. The exact value of that shift in terms of physical parameters is established for the model; the effects of higher-order truncations on the dynamics are noted. Multiple-scale analysis of the CM equations is used to discuss possible effects of modulational instability on scenarios for the transition to turbulence in both collisional and collisionless cases.

  19. Evidence for a Phase Transition in Silicate Melt at Extreme Pressure and Temperature Conditions

    NASA Astrophysics Data System (ADS)

    Spaulding, D. K.; McWilliams, R. S.; Jeanloz, R.; Eggert, J. H.; Celliers, P. M.; Hicks, D. G.; Collins, G. W.; Smith, R. F.

    2012-02-01

    Laser-driven shock compression experiments reveal the presence of a phase transition in MgSiO3 over the pressure-temperature range 300-400 GPa and 10 000-16 000 K, with a positive Clapeyron slope and a volume change of ˜6.3 (±2.0) percent. The observations are most readily interpreted as an abrupt liquid-liquid transition in a silicate composition representative of terrestrial planetary mantles, implying potentially significant consequences for the thermal-chemical evolution of extrasolar planetary interiors. In addition, the present results extend the Hugoniot equation of state of MgSiO3 single crystal and glass to 950 GPa.

  20. Zero-temperature Kosterlitz-Thouless transition in a two-dimensional quantum system

    SciTech Connect

    Castelnovo, Claudio . E-mail: castel@buphy.bu.edu; Chamon, Claudio . E-mail: chamon@buphy.bu.edu; Mudry, Christopher . E-mail: christopher.mudry@psi.ch; Pujol, Pierre . E-mail: pierre.pujol@ens-lyon.fr

    2007-04-15

    We construct a local interacting quantum dimer model on the square lattice, whose zero-temperature phase diagram is characterized by a line of critical points separating two ordered phases of the valence bond crystal type. On one side, the line of critical points terminates in a quantum transition inherited from a Kosterlitz-Thouless transition in an associated classical model. We also discuss the effect of a longer-range dimer interaction that can be used to suppress the line of critical points by gradually shrinking it to a single point. Finally, we propose a way to generalize the quantum Hamiltonian to a dilute dimer model in presence of monomers and we qualitatively discuss the phase diagram.

  1. BOREAS AFM-04 Twin Otter Aircraft Sounding Data

    NASA Technical Reports Server (NTRS)

    MacPherson, J. Ian; Desjardins, Raymond L.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-4 team used the National Research Council, Canada (NRC) Twin Otter aircraft to make sounding measurements through the boundary layer. These measurements included concentrations of carbon dioxide and ozone, atmospheric pressure, dry bulb temperature, potential temperature, dewpoint temperature, calculated mixing ratio, and wind speed and direction. Aircraft position, heading, and altitude were also recorded. Data were collected at both the Northern Study Area (NSA) and the Southern Study Area (SSA) in 1994 and 1996. These data are stored in tabular ASCII files. The Twin Otter aircraft sounding data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files also are available on a CD-ROM (see document number 20010000884).

  2. Impact of caramelization on the glass transition temperature of several caramelized sugars. Part I: Chemical analyses.

    PubMed

    Jiang, Bin; Liu, Yeting; Bhandari, Bhesh; Zhou, Weibiao

    2008-07-01

    This study aims to investigate the relationship between caramelization of several sugars including fructose, glucose, and sucrose and their glass transition temperature (Tg). Differential scanning calorimetry (DSC) was used for creating caramelized sugar samples as well as determining their glass transition temperature, which was found to decrease first and then increase as the holding time at the highest temperature increased. The extent of caramelization was quantified by UV-vis absorbance measurement and high-performance liquid chromatography analysis. Results showed that the amount of small molecules from the degradation of sugar increased very fast at the beginning of heating, and this increase slowed down in the later stage of caramelization. On the other hand, there was a lag phase in the formation of large molecules from the degradation of sugar at the beginning of heating, followed by a fast increase in the later stage of caramelization. The obtained results clearly indicate the impact of melting condition on the T g of sugars through formation of intermediates and end products of caramelization. Generally, when the heating condition is relatively mild, small molecules are formed first by decomposition of the sugar, which leads to a decrease of the overall Tg, and as the heating time becomes longer and/or the heating condition becomes more severe, polymerization takes over and more large molecules are formed, which results in an increase of the overall Tg. Mathematical modeling of the relationship will be presented as part II of the study in a separate paper. PMID:18553889

  3. Ab-initio study of the temperature effects on the optical properties of transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Molina-Sanchez, Alejandro; Palummo, Maurizia; Marini, Andrea; Wirtz, Ludger

    2015-03-01

    Research on ultra-thin two-dimensional materials has been booming since the discovery of graphene along with its interesting physical properties. The transition metal dichalcogenides as MoSare gaining considerable attention due to their potential application in photovoltaics and nanoscale transistors. The optical properties of these layered materials depend strongly on the number of layers. The paradigmatic example is the transition from indirect to direct bandgap when we change from multi-layer to single-layer MoS. In this work, we study the effects of the electron-phonon interaction on the optical properties of single-layer MoS. In the framework of the GW method we calculate the contribution of the electron-phonon coupling to the self-energy. This allows us to calculate the zero-point re-normalization of the quasi-particle energies and to include temperature effects. We discuss the bandgap dependence on the temperature, and the change in the linewidth of the quasi-particle states. The impact of temperature on the exciton states is also addressed.

  4. Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature.

    PubMed

    Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F

    2015-01-28

    Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties. PMID:25638003

  5. Techniques for Transition and Surface Temperature Measurements on Projectiles at Hypersonic Velocities- A Status Report

    NASA Technical Reports Server (NTRS)

    Wilder, M. C.; Bogdanoff, D. W.

    2005-01-01

    A research effort to advance techniques for determining transition location and measuring surface temperatures on graphite-tipped projectiles in hypersonic flight in a ballistic range is described. Projectiles were launched at muzzle velocities of approx. 4.7 km/sec into air at pressures of 190-570 Torr. Most launches had maximum pitch and yaw angles of 2.5-5 degrees at pressures of 380 Torr and above and 3-6 degrees at pressures of 190-380 Torr. Arcjet-ablated and machined, bead-blasted projectiles were launched; special cleaning techniques had to be developed for the latter class of projectiles. Improved methods of using helium to remove the radiating gas cap around the projectiles at the locations where ICCD (intensified charge coupled device) camera images were taken are described. Two ICCD cameras with a wavelength sensitivity range of 480-870 nm have been used in this program for several years to obtain images. In the last year, a third camera, with a wavelength sensitivity range of 1.5-5 microns [in the infrared (IR)], has been added. ICCD and IR camera images of hemisphere nose and 70 degree sphere-cone nose projectiles at velocities of 4.0-4.7 km/sec are presented. The ICCD images clearly show a region of steep temperature rise indicative of transition from laminar to turbulent flow. Preliminary temperature data for the graphite projectile noses are presented.

  6. Temperature-induced valence transition and associated lattice collapse in samarium fulleride.

    PubMed

    Arvanitidis, J; Papagelis, Konstantinos; Margadonna, Serena; Prassides, Kosmas; Fitch, Andrew N

    2003-10-01

    The different degrees of freedom of a given system are usually independent of each other but can in some materials be strongly coupled, giving rise to phase equilibria sensitively susceptible to external perturbations. Such systems often exhibit unusual physical properties that are difficult to treat theoretically, as exemplified by strongly correlated electron systems such as intermediate-valence rare-earth heavy fermions and Kondo insulators, colossal magnetoresistive manganites and high-transition temperature (high-T(c)) copper oxide superconductors. Metal fulleride salts-metal intercalation compounds of C60--and materials based on rare-earth metals also exhibit strong electronic correlations. Rare-earth fullerides thus constitute a particularly intriguing system--they contain highly correlated cation (rare-earth) and anion (C60) sublattices. Here we show, using high-resolution synchrotron X-ray diffraction and magnetic susceptibility measurements, that cooling the rare-earth fulleride Sm2.75C60 induces an isosymmetric phase transition near 32 K, accompanied by a dramatic isotropic volume increase and a samarium valence transition from (2 + epsilon) + to nearly 2 +. The negative thermal expansion--heating from 4.2 to 32 K leads to contraction rather than expansion--occurs at a rate about 40 times larger than in ternary metal oxides typically exhibiting such behaviour. We attribute the large negative thermal expansion, unprecedented in fullerene or other molecular systems, to a quasi-continuous valence transition from Sm(2+) towards the smaller Sm((2+epsilon)+), analogous to the valence or configuration transitions encountered in intermediate-valence Kondo insulators like SmS (ref. 3). PMID:14534581

  7. High Resolution Far Infrared Study of Antiferromagnetic Resonance Transitions in α-Fe2O3 (hematite)

    NASA Astrophysics Data System (ADS)

    Chou, Shin Grace; Plusquellic, David F.; Stutzman, Paul E.; Wang, Shuangzhen; Garboczi, Edward J.; Egelhoff, William F.

    2012-02-01

    In this study, we report high resolution optical measurements of the temperature dependence of the antiferromagnetic (AFM) transition in α-Fe2O3 (hematite) between (0.5 and 10) cm-1. The absorption peak position, over a large temperature range, is found to be in agreement with a modified spin-wave model at both the high and low temperature phases, where the temperature is above and below the Morin transition temperature, respectively. The high spectral resolution optical measurements as demonstrated in this study allow unprecedented zero-field spectral analysis of the zone center AFM magnon in a previously challenging spectral region, giving insights into the role of temperature and strain on the exchange and anisotropy interactions in the system. The results also suggest that the frequency-resolved measurement platform could be extended for room-temperature non-destructive examination and imaging applications for antiferromagnetic materials and devices.

  8. Effect of annealing temperature on magnetic phase transition in Fe3O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Jafari, A.; Farjami Shayesteh, S.; Salouti, M.; Boustani, K.

    2015-04-01

    Fe3O4 (magnetite) nanoparticles (NPs) were synthesized using a co-precipitation method, and then annealed at various temperatures between 50 and 850 °C for 1 h in air. After annealing, the NPs were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometer (VSM). The FTIR and XRD results indicated that Fe3O4 NPs were converted to γ-Fe2O3 (maghemite) by annealing at 250 °C for 1 h and then to α-Fe2O3 (hematite) on annealing in the range of 550-650 °C. The average crystallite size of the NPs estimated by the Debye-Scherrer equation increased from 6.6 to 37.6 nm by increasing annealing temperature from 50 to 850 °C. According to VSM results, the magnetite NPs were superparamagnetic and converted to the maghemite with superparamagnetic phase by annealing up to 550 °C. A phase transition from soft to hard ferromagnetic was occurred at annealing temperature 650 and 850 °C, respectively °C. This phase transition was attributed to the conversion of magnetite to hematite. The VSM analysis confirmed the XRD and FTIR results. The saturation magnetization (Ms) of Fe3O4 NPs was increased from 41.69 to 53.61 emu/g by increasing annealing temperature from 50 to 550 °C, and then decreased intensively to 0.49 emu/g after annealing at 850 °C. By increasing annealing temperature from 50 to 550, the crystallite size of NPs was increased from 6.6 to 12.7 and the coercive force (Hc) was reached to 4.20 Oe after annealing at 550 °C and then intensively increased to 1459.02 Oe for any further increasing of particle size up to 850 °C.

  9. Resistance anomaly near the superconducting transition temperature in short aluminum wires

    SciTech Connect

    Santhanam, P.; Chi, C.C.; Wind, S.J.; Brady, M.J.; Bucchignano, J.J. )

    1991-04-29

    We report a systematic experimental study of the superconducting resistive transition in one-dimensional Al wires of length 0.6 to 110 {mu}m. Shorter wires show a peak in resistance as a function of temperature near {ital T}{sub {ital c}}, with a value {ital above} the normal-state resistance. Near the peak, the resistance {ital decreases} sharply in a magnetic field of only a few Oe. In the same regime, the current-voltage characteristic resembles that of a superconductor-insulator-normal tunnel junction. These new results may be a manifestation of coherent effects in small superconducting samples.

  10. Effect of Wall Temperature on Roughness Induced Attachment-Line Transition

    NASA Technical Reports Server (NTRS)

    Dietz, Anthony; Coleman, Colin; Laub, Jim; Poll, D. I. A.; Nixon, David (Technical Monitor)

    1999-01-01

    An experiment on a cooled swept cylinder in a low-disturbance Mach 1.6 wind tunnel is described. The flow attachment line is disturbed by trip wires of varying size and the laminar/turbulent state of the downstream boundary layer is determined with a hot wire. The results demonstrate that although cooling the wall increases the stability of the boundary layer, it promotes roughness induced transition. Analysis of the data suggests that the attachment- line Reynolds number can account for the effect of wall cooling if the viscosity is evaluated at a particular reference temperature.

  11. Predicting the glass transition temperature as function of crosslink density and polymer interactions in rubber compounds

    NASA Astrophysics Data System (ADS)

    D'Escamard, Gabriella; De Rosa, Claudio; Auriemma, Finizia

    2016-05-01

    Crosslink sulfur density in rubber compounds and interactions in polymer blends are two of the composition elements that affect the rubber compound properties and glass transition temperature (Tg), which is a marker of polymer properties related to its applications. Natural rubber (NR), butadiene rubber (BR) and styrene-butadiene rubber (SBR) compounds were investigated using calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicate that the Di Marzio's and Schneider's Models predict with accuracy the dependence of Tg on crosslink density and composition in miscible blends, respectively, and that the two model may represent the base to study the relevant "in service" properties of real rubber compounds.

  12. Deviations of the glass transition temperature in amorphous conjugated polymer thin films

    NASA Astrophysics Data System (ADS)

    Liu, Dan; Osuna Orozco, Rodrigo; Wang, Tao

    2013-08-01

    The deviations of the glass transition temperature (Tg) in thin films of an amorphous conjugated polymer poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) are reported. Monotonic and nonmonotonic Tg deviations are observed in TFB thin films supported on Si-SiOx and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), respectively. A three-layer model is developed to fit both monotonic and nonmonotonic Tg deviations in these films. A 5-nm PEDOT:PSS capping layer was not found to be effective to remove the free-surface effect in Si-SiOx supported TFB films.

  13. Glass transition temperature of water confined in lipid membranes as determined by anelastic spectroscopy

    NASA Astrophysics Data System (ADS)

    Castellano, C.; Generosi, J.; Congiu, A.; Cantelli, R.

    2006-12-01

    The research of gene delivery vehicles used in gene therapy is focused on nonviral vectors like lipid membranes. Such vectors, nonimmunogenic and biodegradable, are formed by complexation of DNA with a mixture of cationic lipids and a neutral colipid which improve the transfection efficiency. A main topic related to lipid membrane dynamics is their capability to spontaneously confine water. At present the value of the glass transition temperature (Tg) is largely debated and determined only by some indirect methods. Here the authors show that anelastic spectroscopy allows the confined water Tg value to be directly identified in several lipid mixtures.

  14. Induced Interactions and the Superfluid Transition Temperature in a Three-Component Fermi Gas

    SciTech Connect

    Martikainen, J.-P.; Kinnunen, J. J.; Toermae, P.; Pethick, C. J.

    2009-12-31

    We study many-body contributions to the effective interaction between fermions in a three-component Fermi mixture. We find that effective interactions induced by the third component can lead to a phase diagram different from that predicted if interactions with the third component are neglected. As a result, in a confining potential a superfluid shell structure can arise even for equal populations of the components. We also find a critical temperature for the BCS transition in a {sup 6}Li mixture which can deviate strongly from the one in a weakly interacting two-component system.

  15. Anticorrelation between the parent charge transfer gap and maximum transition temperature in cuprates

    NASA Astrophysics Data System (ADS)

    Ruan, Wei; Hu, Cheng; Cai, Peng; Peng, Yingying; Li, Xintong; Hao, Zhenqi; Zhou, Xingjiang; Weng, Zheng-Yu; Wang, Yayu

    We use scanning tunneling spectroscopy to measure the electronic structure of the parent Mott insulator of three different types of cuprates. The charge transfer gap size exhibits pronounced variations, and more interestingly it shows an anticorrelation with the maximum superconducting transition temperature achieved at the optimal doping of each cuprate. This result suggests that the Mottness in parent cuprate plays a crucial role in determining the superconducting properties. In particular, reducing the electron correlation strength enhances superconductivity, which is consistent with the pairing mechanism based on the doped Mott insulator picture.

  16. High accuracy heat capacity measurements through the lambda transition of helium with very high temperature resolution

    NASA Technical Reports Server (NTRS)

    Fairbanks, W. M.; Lipa, J. A.

    1984-01-01

    A measurement of the heat capacity singularity of helium at the lambda transition was performed with the aim of improving tests of the Renormalization Group (RG) predictions for the static thermodynamic behavior near the singularity. The goal was to approach as closely as possible to the lambda-point while making heat capacity measurements of high accuracy. To do this, a new temperature sensor capable of unprecedented resolution near the lambda-point, and two thermal control systems were used. A short description of the theoretical background and motivation is given. The initial apparatus and results are also described.

  17. Low-transition-temperature mixtures (LTTMs): a new generation of designer solvents.

    PubMed

    Francisco, María; van den Bruinhorst, Adriaan; Kroon, Maaike C

    2013-03-11

    A new generation of designer solvents emerged in the last decade as promising green media for multiple applications, including separation processes: the low-transition-temperature mixtures (LTTMs). They can be prepared by mixing natural high-melting-point starting materials, which form a liquid by hydrogen-bond interactions. Among them, deep-eutectic solvents (DESs) were presented as promising alternatives to conventional ionic liquids (ILs). Some limitations of ILs are overcome by LTTMs, which are cheap and easy to prepare from natural and readily available starting materials, biodegradable, and renewable. PMID:23401138

  18. AFM-based force spectroscopy measurements of mature amyloid fibrils of the peptide glucagon

    NASA Astrophysics Data System (ADS)

    Dong, Mingdong; Bruun Hovgaard, Mads; Mamdouh, Wael; Xu, Sailong; Otzen, Daniel Erik; Besenbacher, Flemming

    2008-09-01

    We report on the mechanical characterization of individual mature amyloid fibrils by atomic force microscopy (AFM) and AFM-based single-molecule force spectroscopy (SMFS). These self-assembling materials, formed from the 29-residue amphiphatic peptide hormone glucagon, were found to display a reversible elastic behaviour. Based on AFM morphology and SMFS studies, we suggest that the observed elasticity is due to a force-induced conformational transition which is reversible due to the β-helical conformation of protofibrils, allowing a high degree of extension. The elastic properties of such mature fibrils contribute to their high stability, suggesting that the internal hydrophobic interactions of amyloid fibrils are likely to be of fundamental importance in the assembly of amyloid fibrils and therefore for the understanding of the progression of their associated pathogenic disorders. In addition, such biological amyloid fibril structures with highly stable mechanical properties can potentially be used to produce nanofibres (nanowires) that may be suitable for nanotechnological applications.

  19. Temperature dependence of the electronic transitions in BiFeO{sub 3} thin film studied by spectroscopic ellipsometry

    SciTech Connect

    Kang, T. D.; Jeon, B. C.; Moon, S. J.

    2015-04-07

    The temperature dependence of the electronic response of BiFeO{sub 3} thin film grown on a SrTiO{sub 3} substrate is investigated using spectroscopic ellipsometry. By analyzing the pseudodielectric function, we identify two d-d crystal field transitions of Fe{sup 3+} ions in the energy region between 1 and 2 eV. The d-d transitions show abnormal temperature dependence that cannot be attributed to conventional electron-phonon interactions. The origin of the abnormal temperature dependence is discussed in terms of spin-charge coupling. The temperature dependence of the charge transfer transitions located above 2.5 eV is characterized by standard critical point model analysis of the 2nd derivatives of the dielectric function. This analysis provides detailed information of the critical point parameters for charge transfer transitions.

  20. Detection of Pathogens Using AFM and SPR

    NASA Astrophysics Data System (ADS)

    Vaseashta, Ashok

    2005-03-01

    A priori detection of pathogens in food and water has become a subject of paramount importance. Several recent incidents have resulted in the government passing stringent regulations for tolerable amounts of contamination of food products. Identification and/or monitoring of bacterial contamination in food are critical. The conventional methods of pathogen detection require time-consuming steps to arrive disembark at meaningful measurement in a timely manner as the detection time exceeds the time in which perishable food recycles through the food chain distribution. The aim of this presentation is to outline surface plasmon resonance (SPR) and atomic force microscopy (AFM) as two methods for fast detect6ion of pathogens. Theoretical basis of SPR and experimental results of SPR and AFM on E. coli O157:H7 and prion are presented.

  1. Transition-metal embedded carbon nitride monolayers: high-temperature ferromagnetism and half-metallicity.

    PubMed

    Choudhuri, Indrani; Kumar, Sourabh; Mahata, Arup; Rawat, Kuber Singh; Pathak, Biswarup

    2016-08-01

    High-temperature ferromagnetic materials with planar surfaces are promising candidates for spintronics applications. Using state-of-the-art density functional theory (DFT) calculations, transition metal (TM = Cr, Mn, and Fe) incorporated graphitic carbon nitride (TM@gt-C3N4) systems are investigated as possible spintronics devices. Interestingly, ferromagnetism and half-metallicity were observed in all of the TM@gt-C3N4 systems. We find that Cr@gt-C3N4 is a nearly half-metallic ferromagnetic material with a Curie temperature of ∼450 K. The calculated Curie temperature is noticeably higher than other planar 2D materials studied to date. Furthermore, it has a steel-like mechanical stability and also possesses remarkable dynamic and thermal (500 K) stability. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N4 is as high as 137.26 μeV per Cr. Thereby, such material with a high Curie temperature can be operated at high temperatures for spintronics devices. PMID:27321785

  2. Retrogradation of Waxy Rice Starch Gel in the Vicinity of the Glass Transition Temperature

    PubMed Central

    Charoenrein, Sanguansri; Udomrati, Sunsanee

    2013-01-01

    The retrogradation rate of waxy rice starch gel was investigated during storage at temperatures in the vicinity of the glass transition temperature of a maximally concentrated system (Tg′), as it was hypothesized that such temperatures might cause different effects on retrogradation. The Tg′ value of fully gelatinized waxy rice starch gel with 50% water content and the enthalpy of melting retrograded amylopectin in the gels were investigated using differential scanning calorimetry. Starch gels were frozen to −30°C and stored at 4, 0, −3, −5, and −8°C for 5 days. The results indicated that the Tg′ value of gelatinized starch gel annealed at −7°C for 15 min was −3.5°C. Waxy rice starch gels retrograded significantly when stored at 4°C with a decrease in the enthalpy of melting retrograded starch in samples stored for 5 days at −3, −5, and −8°C, respectively, perhaps due to the more rigid glass matrix and less molecular mobility facilitating starch chain recrystallization at temperatures below Tg′. This suggests that retardation of retrogradation of waxy rice starch gel can be achieved at temperature below Tg′. PMID:26904602

  3. Charge transport mechanism and low temperature phase transitions in KIO3

    NASA Astrophysics Data System (ADS)

    Abdel Kader, M. M.; El-Kabbany, F.; Naguib, H. M.; Gamal, W. M.

    2013-04-01

    Our report deals with the measurement of some electrical properties, namely the ac conductivity σ(ω,T) and the complex dielectric permittivity epsilon*(ω, T) in the temperature interval 95K < T < 280K and at some selected frequencies (0.7kHz - 20kHz) for polycrystalline samples of potassium iodate KIO3 using a computerized RLC meter. The improper character of the ferroelectricity over the mentioned temperature range has been achieved by recording the ferroelectric hysteresis loops. The temperature dependence of each electrical parameter reveals that the compound undergoes two phase transitions at T ≈ 258K and at T ≈ 110K. The frequency dependent conductivity seems to be in accordance with the power law σ(ω,T)αωs(T) and the trend of temperature dependence of the frequency exponent s (0 < s < 1) suggests that the quantum mechanical tunneling (QMT) model is the main mechanism of the charge transport. Comparison with the behavior of the NH4IO3 in the same temperature range was outlined.

  4. Discrimination of biogenic and detrital magnetite through a double Verwey transition temperature

    NASA Astrophysics Data System (ADS)

    Chang, Liao; Heslop, David; Roberts, Andrew P.; Rey, Daniel; Mohamed, Kais J.

    2016-01-01

    Magnetite occurs widely in natural environments in both inorganic and biogenic forms. Discrimination of the origin of magnetite has important implications, from searching for past microbial activity to interpreting paleomagnetic and environmental magnetic records in a wide range of settings. In this study, we present rock magnetic and electron microscopic analyses of marine sediments from the continental margin of Oman. Low-temperature magnetic data reveal two distinct Verwey transition (Tv) temperatures that are associated with the presence of biogenic and inorganic magnetite. This interpretation is consistent with room temperature magnetic properties and is confirmed by electron microscopic analyses. Our study justifies the use of two distinct Tv temperatures as a diagnostic signature for discriminating inorganic and biogenic magnetite. Simple low-temperature magnetic measurements, therefore, provide a tool to recognize rapidly the origin of magnetite within natural samples. In addition, our analyses reveal progressive down-core dissolution of detrital and biogenic magnetite, but with preservation of significant amounts of fine-grained magnetite within sediments that have been subjected to severe diagenetic alteration. We demonstrate that preservation of magnetite in such environments is due to protection of fine-grained magnetite inclusions within silicate hosts. Our results, therefore, also provide new insights into diagenetic processes in marine sediments.

  5. Evidence for a finite temperature phase transition in a bilayer quantum Hall system

    NASA Astrophysics Data System (ADS)

    Champagne, A. R.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.

    2008-03-01

    We study the Joshepson-like interlayer tunneling signature of the quantum Hall bilayer excitonic state at total filling factor νT= 1 as a function of the layer separation, interlayer charge imbalance and temperature. The tunneling amplitude collapses to zero as either the temperature or interlayer spacing is increased. The interlayer tunneling amplitude dependences on the layer spacing at various temperatures are very similar, but the layer separations where the tunneling disappears scale linearly with temperature. Our results offer evidence [1] that a finite temperature phase transition separates the interlayer coherent phase from incoherent phases which lack strong interlayer correlations. The phase boundary is found to be re-entrant as a function of charge imbalance thus suggesting an intricate competition between the interlayer coherent phase and various independent layer states. This work was supported by the NSF and the DOE. [1] A.R. Champagne, J.P. Eisenstein, L.N. Pfeiffer, K.W. West, Cond-mat/0709.0718

  6. Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

    2004-01-01

    The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

  7. Characterizing Cell Mechanics with AFM and Microfluidics

    NASA Astrophysics Data System (ADS)

    Walter, N.; Micoulet, A.; Suresh, S.; Spatz, J. P.

    2007-03-01

    Cell mechanical properties and functionality are mainly determined by the cytoskeleton, besides the cell membrane, the nucleus and the cytosol, and depend on various parameters e.g. surface chemistry and rigidity, surface area and time available for cell spreading, nutrients and drugs provided in the culture medium. Human epithelial pancreatic and mammary cancer cells and their keratin intermediate filaments are the main focus of our work. We use Atomic Force Microscopy (AFM) to study cells adhering to substrates and Microfluidic Channels to probe cells in suspension, respectively. Local and global properties are extracted by varying AFM probe tip size and the available adhesion area for cells. Depth-sensing, instrumented indentation tests with AFM show a clear difference in contact stiffness for cells that are spread of controlled substrates and those that are loosely attached. Microfluidic Channels are utilized in parallel to evaluate cell deformation and ``flow resistance'', which are dependent on channel cross section, flow rate, cell nucleus size and the mechanical properties of cytoskeleton and membrane. The results from the study are used to provide some broad and quantitative assessments of the connections between cellular/subcellular mechanics and biochemical origins of disease states.

  8. Spatial glass transition temperature variations in polymer glass: application to a maltodextrin-water system.

    PubMed

    van Sleeuwen, Rutger M T; Zhang, Suying; Normand, Valéry

    2012-03-12

    A model was developed to predict spatial glass transition temperature (T(g)) distributions in glassy maltodextrin particles during transient moisture sorption. The simulation employed a numerical mass transfer model with a concentration dependent apparent diffusion coefficient (D(app)) measured using Dynamic Vapor Sorption. The mass average moisture content increase and the associated decrease in T(g) were successfully modeled over time. Large spatial T(g) variations were predicted in the particle, resulting in a temporary broadening of the T(g) region. Temperature modulated differential scanning calorimetry confirmed that the variation in T(g) in nonequilibrated samples was larger than in equilibrated samples. This experimental broadening was characterized by an almost doubling of the T(g) breadth compared to the start of the experiment. Upon reaching equilibrium, both the experimental and predicted T(g) breadth contracted back to their initial value. PMID:22268547

  9. Theoretical study of pressure dependence of transition temperature of In and Pb

    SciTech Connect

    Kumar, Priyank; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.

    2015-08-28

    Recently proposed structured local pseudopotential (PP) by Fiolhais et al. has been successfully used to compute superconducting state parameters (SSP): electron-phonon coupling strength (λ), Coulomb pseudopotential (μ*), critical temperature (T{sub c}), effective interaction strength (N{sub 0}V), isotopic effect parameter (α) and their pressure dependence of non-transition metals In and Pb as a test case. Pressure dependence of the Debye temperature has been computed by Gruneisen model. Present results are in good agreement with experimental and other theoretical results. Present study has been further extended to estimate volume (critical volume) at which λ=μ*, where Tc and N{sub 0}V becomes zero. The presently used model is found to be transferable at the extreme environment without any adjustment of parameters further alongwith its simplicity and predictivity.

  10. Phase transition and metallization of FeO at high pressures and temperatures

    SciTech Connect

    Fischer, Rebecca A.; Campbell, Andrew J.; Lord, Oliver T.; Shofner, Gregory A.; Dera, Przemyslaw; Prakapenka, Vitali B.

    2012-05-10

    Wuestite, Fe{sub 1-x}O, is an important component in the mineralogy of Earth's lower mantle and may also be a component of the core. Therefore its high pressure-temperature behavior, including its electronic structure, is essential to understanding the nature and evolution of Earth's deep interior. We performed X-ray diffraction and radiometric measurements on wuestite in a laser-heated diamond anvil cell, finding an insulator-metal transition at high pressures and temperatures. Our data show a negative slope for this apparently isostructural phase boundary, which is characterized by a volume decrease and emissivity increase. The metallic phase of FeO is stable at conditions of the lower mantle and core, which has implications for the high P-T character of Fe-O bonds, magnetic field propagation, and lower mantle conductivity.

  11. Characterization of natural low transition temperature mixtures (LTTMs): Green solvents for biomass delignification.

    PubMed

    Yiin, Chung Loong; Quitain, Armando T; Yusup, Suzana; Sasaki, Mitsuru; Uemura, Yoshimitsu; Kida, Tetsuya

    2016-01-01

    The aim of this work was to characterize the natural low transition temperature mixtures (LTTMs) as promising green solvents for biomass pretreatment with the critical characteristics of cheap, biodegradable and renewable, which overcome the limitations of ionic liquids (ILs). The LTTMs were derived from inexpensive commercially available hydrogen bond acceptor (HBA) and l-malic acid as the hydrogen bond donor (HBD) in distinct molar ratios of starting materials and water. The peaks involved in the H-bonding shifted and became broader for the OH groups. The thermal properties of the LTTMs were not affected by water while the biopolymers solubility capacity of LTTMs was improved with the increased molar ratio of water and treatment temperature. The pretreatment of oil palm biomass was consistence with the screening on solubility of biopolymers. This work provides a cost-effective alternative to utilize microwave hydrothermal extracted green solvents such as malic acid from natural fruits and plants. PMID:26253419

  12. Electronic, structural, and magnetic properties of LaMnO3 phase transition at high temperature

    NASA Astrophysics Data System (ADS)

    Rivero, Pablo; Meunier, Vincent; Shelton, William

    2016-01-01

    We develop a procedure to determine the portion of exact Hartree-Fock exchange interaction contained in a hybrid density functional to treat the range of electronic correlation governing the physics of a system as a function of a thermodynamical parameter. This includes systems that depend on physical parameters accessible to experiment (i.e., temperature, pressure, composition, etc.) or those composed of two or more materials such as heterostructures and interfaces. This approach is applied to LaMnO3, where we are able to simulate the high temperature insulator-to-metal transition (IMT) and observe a half-metallic orbital disorder ferromagnetic state using density functional theory. In particular, we show that the softening of the Q2 Jahn-Teller mode plays a central role in driving the IMT. These findings are likely to motivate the investigation of heterostructures and bulk materials that contain a range of electronic correlation in similar material systems.

  13. Applications of AFM for atomic manipulation and spectroscopy

    NASA Astrophysics Data System (ADS)

    Custance, Oscar

    2009-03-01

    Since the first demonstration of atom-by-atom assembly [1], atomic manipulation with scanning tunneling microscopy has yielded stunning realizations in nanoscience. A new exciting panorama has been recently opened with the possibility of manipulating atoms at surfaces using atomic force microscopy (AFM) [2-5]. In this talk, we will present two different approaches that enable patterning structures at semiconductor surfaces by manipulating individual atoms with AFM and at room temperature [2, 3]. We will discuss the physics behind each protocol through the analysis of the measured forces associated with these manipulations [3-5]. Another challenging issue in scanning probe microscopy is the ability to disclose the local chemical composition of a multi-element system at atomic level. Here, we will introduce a single-atom chemical identification method, which is based on detecting the forces between the outermost atom of the AFM tip and the atoms at a surface [6]. We demonstrate this identification procedure on a particularly challenging system, where any discrimination attempt based solely on topographic measurements would be impossible to achieve. [4pt] References: [0pt] [1] D. M. Eigler and E. K. Schweizer, Nature 344, 524 (1990); [0pt] [2] Y. Sugimoto, M. Abe, S. Hirayama, N. Oyabu, O. Custance and S. Morita, Nature Materials 4, 156 (2005); [0pt] [3] Y. Sugimoto, P. Pou, O. Custance, P. Jelinek, M. Abe, R. Perez and S. Morita, Science 322, 413 (2008); [0pt] [4] Y. Sugimoto, P. Jelinek, P. Pou, M. Abe, S. Morita, R. Perez and O. Custance, Phys. Rev. Lett. 98, 106104 (2007); [0pt] [5] M. Ternes, C. P. Lutz, C. F. Hirjibehedin, F. J. Giessibl and A. J. Heinrich, Science 319, 1066 (2008); [0pt] [6] Y. Sugimoto, P. Pou, M. Abe, P. Jelinek, R. Perez, S. Morita, and O. Custance, Nature 446, 64 (2007)

  14. Percolative switching in transition metal dichalcogenide field-effect transistors at room temperature

    NASA Astrophysics Data System (ADS)

    Paul, Tathagata; Ghatak, Subhamoy; Ghosh, Arindam

    2016-03-01

    We have addressed the microscopic transport mechanism at the switching or ‘on-off’ transition in transition metal dichalcogenide (TMDC) field-effect transistors (FETs), which has been a controversial topic in TMDC electronics, especially at room temperature. With simultaneous measurement of channel conductivity and its slow time-dependent fluctuation (or noise) in ultrathin WSe2 and MoS2 FETs on insulating SiO2 substrates where noise arises from McWhorter-type carrier number fluctuations, we establish that the switching in conventional backgated TMDC FETs is a classical percolation transition in a medium of inhomogeneous carrier density distribution. From the experimentally observed exponents in the scaling of noise magnitude with conductivity, we observe unambiguous signatures of percolation in a random resistor network, particularly, in WSe2 FETs close to switching, which crosses over to continuum percolation at a higher doping level. We demonstrate a powerful experimental probe to the microscopic nature of near-threshold electrical transport in TMDC FETs, irrespective of the material detail, device geometry, or carrier mobility, which can be extended to other classes of 2D material-based devices as well.

  15. Percolative switching in transition metal dichalcogenide field-effect transistors at room temperature.

    PubMed

    Paul, Tathagata; Ghatak, Subhamoy; Ghosh, Arindam

    2016-03-29

    We have addressed the microscopic transport mechanism at the switching or 'on-off' transition in transition metal dichalcogenide (TMDC) field-effect transistors (FETs), which has been a controversial topic in TMDC electronics, especially at room temperature. With simultaneous measurement of channel conductivity and its slow time-dependent fluctuation (or noise) in ultrathin WSe2 and MoS2 FETs on insulating SiO2 substrates where noise arises from McWhorter-type carrier number fluctuations, we establish that the switching in conventional backgated TMDC FETs is a classical percolation transition in a medium of inhomogeneous carrier density distribution. From the experimentally observed exponents in the scaling of noise magnitude with conductivity, we observe unambiguous signatures of percolation in a random resistor network, particularly, in WSe2 FETs close to switching, which crosses over to continuum percolation at a higher doping level. We demonstrate a powerful experimental probe to the microscopic nature of near-threshold electrical transport in TMDC FETs, irrespective of the material detail, device geometry, or carrier mobility, which can be extended to other classes of 2D material-based devices as well. PMID:26891381

  16. Systematics in the metal-insulator transition temperatures in vanadium oxides

    NASA Astrophysics Data System (ADS)

    Fisher, B.; Genossar, J.; Reisner, G. M.

    2016-01-01

    Nine of the known vanadium oxides, VO 2 - 1 / n (n - a positive or negative integer) with n = 2 - 6 , 8 , 9 , ∞ and -6, undergo metal-insulator transitions accompanied by structural transitions, at various temperatures TMIT (V7O13 is metallic above T=0). Among the persistent efforts to determine the driving force(s) of these transitions, electron-electron (Mott-like) and electron-phonon (Peierls-like) interactions, there were several attempts to find systematics in TMIT as function of n. Here we present an unexpectedly simple and illuminating systematics that holds for positive n: if TMIT is the absolute value of the difference between TM(n) and TP(n), which represent the contributions of electron-electron and electron-phonon interactions, respectively, all data points of TM-TP versus 1/n lie on, or close to, two simple straight lines; one is TM -TP =T∞(7 / n - 1) for V3O5, V4O7, V5O9, V7O13, V8O15, V9O17 and VO2 and the other is TM -TP =T∞(3 / n - 1) for V2O3, V6O11 and VO2.

  17. Influence of temperature on transit times and microwave noise performances of SiGe HBT

    NASA Astrophysics Data System (ADS)

    Diaz-Albarran, L. M.; Ramirez-Garcia, E.; Zerounian, N.; Aniel, F.; Rodriguez-Mendez, L. M.; Valdez-Perez, D.; Galaz-Larios, M. C.; Enciso-Aguilar, M. A.

    2016-03-01

    The influence of temperature (300 K and 40 K) on intrinsic transit times and microwave noise performances of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) is investigated. At 300 K, we compared measured and modelled S-parameters and four noise parameters, and we found a good agreement. At 40 K, we compared measured and modelled S-parameters, and we deduced noise performances from the S-parameter measurements. The electric model includes correlated junction noise sources and a proper extraction of the transit times involved in these sources. Moreover, the microwave noise model considers all the physical phenomena that impact noise performances in SiGe HBTs. We analysed three devices having different Ge content (10%-20%, 10%-25% and 10%-30%). At 40 K, the device with 10%-25% reaches one of the lowest base transit times (τ B), the lowest minimum noise figure (NFmin), and the lowest equivalent noise resistance (R n), for operation frequencies up to the maximum device dynamic performances (f ≈ f T) These results demonstrate the excellent potential to develop cryogenic applications of SiGe HBTs.

  18. Pairing phase transition: A finite-temperature relativistic Hartree-Fock-Bogoliubov study

    NASA Astrophysics Data System (ADS)

    Li, Jia Jie; Margueron, Jérôme; Long, Wen Hui; Van Giai, Nguyen

    2015-07-01

    Background: The relativistic Hartree-Fock-Bogoliubov (RHFB) theory has recently been developed and it provides a unified and highly predictive description of both nuclear mean-field and pairing correlations. Ground-state properties of finite nuclei can accurately be reproduced without neglecting exchange (Fock) contributions. Purpose: Finite-temperature RHFB (FT-RHFB) theory has not yet been developed, leaving yet unknown its predictions for phase transitions and thermal excitations in both stable and weakly bound nuclei. Method: FT-RHFB equations are solved in a Dirac Woods-Saxon (DWS) basis considering two kinds of pairing interactions: finite or zero range. Such a model is appropriate for describing stable as well as loosely bound nuclei since the basis states have correct asymptotic behavior for large spatial distributions. Results: Systematic FT-RH(F)B calculations are performed for several semimagic isotopic/isotonic chains comparing the predictions of a large number of Lagrangians, among which are PKA1, PKO1, and DD-ME2. It is found that the critical temperature for a pairing transition generally follows the rule Tc=0.60 Δ (0 ) for a finite-range pairing force and Tc=0.57 Δ (0 ) for a contact pairing force, where Δ (0 ) is the pairing gap at zero temperature. Two types of pairing persistence are analyzed: type I pairing persistence occurs in closed subshell nuclei while type II pairing persistence can occur in loosely bound nuclei strongly coupled to the continuum states. Conclusions: This FT-RHFB calculation shows very interesting features of the pairing correlations at finite temperature and in finite systems such as pairing re-entrance and pairing persistence.

  19. Observation of a Low-Temperature, Dynamically Driven, Structural Transition in a Polypeptide by Solid State NMR Spectroscopy

    PubMed Central

    Bajaj, Vikram S.; van der Wel, Patrick C.A.; Griffin, Robert G.

    2009-01-01

    At reduced temperatures, proteins and other biomolecules are generally found to exhibit dynamic as well as structural transitions. This includes a so-called protein glass transition that is universally observed in systems cooled between 200–230K, and which is generally attributed to interactions between hydrating solvent molecules and protein side chains. However, there is also experimental and theoretical evidence for a low-temperature transition in the intrinsic dynamics of the protein itself, absent any solvent. Here, we use low-temperature solid state NMR to examine site specific fluctuations in atomic structure and dynamics in the absence of solvents. In particular, we employ magic angle spinning NMR to examine a structural phase transition associated with dynamic processes in a solvent-free polypeptide, N-f-MLF-OH, lattice at temperatures as low as 90K. This transition is characterized by the appearance of an extra set of lines in 1D 15N spectra as well as additional cross peaks in 2D 13C-13C and 13C-15N spectra. Interestingly, the gradual, temperature-dependent appearance of the new spectral component is not accompanied by the line broadening typical of dynamic transitions. A direct comparison between the spectra of N-f-MLF-OH and the analog N-f-MLF-OMe, which does not display this transition, indicates a correlation of the structural transition to the temperature dependent motion of the aromatic phenylalanine side chain. Several quantitative solid state NMR experiments were employed to provide site-specific measurements of structural and motional features of the observed transition. PMID:19067520

  20. Equation of state and phase transition of antigorite under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Yang, Cuiping; Inoue, Toru; Yamada, Akihiro; Kikegawa, Takumi; Ando, Jun-ichi

    2014-03-01

    The equation of state of natural antigorite has been determined up to ∼10 GPa and 500 °C by in situ X-ray diffraction in a cubic type multi-anvil apparatus, MAX80, located at the Photon Factory-Advanced Ring at the High Energy Accelerator Research Organization (KEK), and the temperature dependence of the bulk modulus was determined for the first time by high pressure and high temperature X-ray diffraction based on a series of direct measurements. No dehydration occurred during the entire experimental process, and no significant deviatoric stress was observed after heating. The room temperature P-V data below 7 GPa have been fit to the Birch-Murnaghan equation of state, yielding V0,300 K = 366.9(7) Å3, K0, 300 K = 65.2(31) GPa, and the pressure derivative K‧ fixed to 6.1. The high pressure phase transition was observed through volume softening behavior at around 7 GPa, and the dP/dT slope seems to be flat or slightly positive, which is consistent with the recent report by Bezacier et al. (2013). The high temperature Birch-Murnaghan equation of state was used to fit the P-V-T data below 7 GPa. Since the present experimental data was obtained by energy dispersive X-ray diffraction at high pressure and high temperature, the resolution was slightly lower than that obtained by the angle dispersive X-ray method. So the bulk modulus K0, 300 K and the pressure derivative K‧ were fixed to 62.9 GPa and 6.1, respectively, which was obtained by single crystal X-ray diffraction in a diamond anvil cell by means of the angle dispersive method (Nestola et al., 2010) during fitting. From the fitting, we obtained V0, 300 K = 367.3(2) Å3, dK/dT = -0.0265(41) GPa/K, thermal expansion α0 = 3.92(50) × 10-5/K. The temperature dependence of the bulk modulus was larger than the value calculated empirically (Holland and Powell, 1998). The thermal expansion of antigorite is larger than the results from the previous study. The compression of antigorite is very anisotropic along

  1. Soil temperature and water dynamics on contrasting aspects in the rain-snow transition zone

    NASA Astrophysics Data System (ADS)

    Link, T. E.; Seyfried, M. S.; Bryden, S.; McNamara, J. P.; Klos, P. Z.

    2013-12-01

    Understanding how complex terrain affects ecohydrological and biogeochemical processes in the critical zone has become increasingly important as the global climate changes. Soils modulate both fluxes and are therefore central to this understanding. We are particularly interested in soil temperature and water content because they exert strong controls on hydrologic and biogeochemical fluxes and ecological processes. We measured soil water (θ) and temperature (Ts) profiles at three paired locations in mountainous, complex terrain in SW Idaho, USA (~43°latitude). Each pair consisted of a soil profile of temperature and water content from a depth of 5 cm to bedrock (50 to 110 cm) on opposing north and south facing slopes at the same elevation. The sites are located near the rain/snow transition elevation for the area (1600 m) on steep slopes (25 to 40°) with sparse vegetative cover. We measured dramatic differences between the two slopes, with a difference of 9°C (at 50 cm) in August. Differences between slopes were smaller in winter, about 4° C. The Ts difference between two opposing slopes at identical elevations that we measured is practically the same as the difference between Ts measured on nearly level ground but separated by 1000 m in elevation. This implies that we need to consider two snowmelt seasons within a given watershed based on aspect. We expected θ on north facing soils to decline more slowly and later in the year the south facing soils due to the evaporative demand differential. We did not observe this and, in fact, θ on the two slopes responded similarly during spring and early summer. This is attributed to two factors. First, spring rains were sufficient to maintain relatively high soil water storage on both slopes. Second, the denser vegetative cover on the north-facing slopes counters the lesser evaporative demand. Results suggest that as climate warms, south facing slopes will be the first to transition from a five hydrologic season system

  2. Glass Transition Temperature of Polyetherimide: Relationship between Thin Films and Nanoporous Materials

    NASA Astrophysics Data System (ADS)

    Ozisik, Rahmi; Liu, Tong; Siegel, Richard W.

    2006-03-01

    The glass transition temperature (Tg) of nanoporous polyetherimide (PEI) was investigated using differential scanning calorimetry. Nanosized pores were created by spin coating a solution of PEI and polycaprolactone-diol (PCLD) in their common solvent dichloromethane. The nanoporous structure was created by fast phase separation during spin coating and subsequent removal of PCLD with acetone. Atomic force microscopy, scanning electron microscopy and statistical methods were used to characterize the pore structure. The glass transition temperatures of both the thin PEI films and nanoporous PEI samples were lower than that of bulk PEI. The Tg of nanoporous PEI was found to depend strongly on pore volume fraction. A Monte Carlo simulation was performed to investigate the relationship between thin films and nanoporous systems. The distribution of nearest neighbor distances (h) were obtained from the Monte Carlo simulation, which was biased to create the pore size distribution obtained from experiments. Various moments of h was calculated and used to compare the findings to thin film data.

  3. Impact of caramelization on the glass transition temperature of several caramelized sugars. Part II: Mathematical modeling.

    PubMed

    Jiang, Bin; Liu, Yeting; Bhandari, Bhesh; Zhou, Weibiao

    2008-07-01

    Further to part I of this study, this paper discusses mathematical modeling of the relationship between caramelization of several sugars including fructose, glucose, and sucrose and their glass transition temperatures ( T g). Differential scanning calorimetry (DSC) was used for creating caramelized sugar samples and determining their glass transition temperatures ( T g). UV-vis absorbance measurement and high-performance liquid chromatography (HPLC) analysis were used for quantifying the extent of caramelization. Specifically, absorbances at 284 and 420 nm were obtained from UV-vis measurement, and the contents of sucrose, glucose, fructose, and 5-hydroxymethyl-furfural (HMF) in the caramelized sugars were obtained from HPLC measurements. Results from the UV and HPLC measurements were correlated with the Tg values measured by DSC. By using both linear and nonlinear regressions, two sets of mathematical models were developed for the prediction of Tg values of sugar caramels. The first set utilized information obtained from both UV-vis measurement and HPLC analysis, while the second set utilized only information from the UV-vis measurement, which is much easier to perform in practice. As a caramelization process is typically characterized by two stages, separate models were developed for each of the stages within a set. Furthermore, a third set of nonlinear equations were developed, serving as criteria to decide at which stage a caramelized sample is. The models were evaluated through a validation process. PMID:18553880

  4. Transitional properties of supersolitons in a two electron temperature warm multi-ion plasma

    NASA Astrophysics Data System (ADS)

    Varghese, Steffy S.; Ghosh, S. S.

    2016-08-01

    The existence domain of an ion acoustic supersoliton and its transition to a regular kind of solitary wave have been explored in detail using Sagdeev pseudopotential technique for a two electron temperature warm multi-ion plasma having two species of ions. It was found that both the cold to hot electron temperature ratio and their respective ambient densities play a deterministic role for the existence of a supersoliton, as well as its transitional processes to a regular solitary wave. Analogous to a double layer solution, which often marks the boundary of the existence domain of a regular solitary wave, a "curve of inflection" determines the boundary of the existence domain of a supersoliton. The characteristics of the "curve of inflection," in turn, depend on the respective concentrations of the two ion species. It is observed that the supersolitons are actually a subset of a more general kind of solutions which are characterized by a fluctuation in the corresponding charge separation which precedes their maximum amplitude. It is also observed that these novel kinds of solitary structures, including supersolitons, occur only for a very narrow range of parameters near constant amplitude beyond which the wave breaks.

  5. A high pressure low temperature study on rare earth compounds: Semiconductor to metal transition

    NASA Astrophysics Data System (ADS)

    Neuenschwander, J.; Wachter, P.

    1990-01-01

    This work studies the pressure induced semiconductor to metal transition (SMT) in several rare earth compounds. This SMT is accompanied by a valence instability. Single crystalline semiconducting TmSe 1- xTe x, Tm 1- xEu xSe and SmS 1- xSe x alloys are investigated under high pressure at low temperatures. Measurements of electrical resistivity, magnetic susceptibility, neutron diffraction, volume and optical properties are presented and discussed. A very unusual peak structure in the resistivity-pressure relation of TmSe 1- xTe x at low temperatures is observed. A discussion of the novel feature involves the concept of the excitonic insulator and f-d hybridization. The magnetic behavior of the Tm and Eu based compounds is significantly influenced by the SMT. This is thought to be mainly due to the additional coupling between the rare earth moments via free carriers which are present in the metallic state. In SmS 1- xSe x a considerable softening of the lattice is observed before the valence transition occurs. It is speculated that Poisson's ratio might become negative already in the semiconducting state.

  6. A high pressure low temperature study on rare earth compounds: Semiconductor to metal transition

    NASA Astrophysics Data System (ADS)

    Neuenschwander, J.; Wachter, P.

    1989-12-01

    This work studies the pressure induced semiconductor to metal transition (SMT) in several rare earth compounds. This SMT is accompanied by a valence instability. Single crystalline semiconducting TmSe1-xTex, Tm1-xEuxSe and SmS1-xSex alloys are investigated under high pressure at low temperatures. Measurements of electrical resistivity, magnetic susceptibility, neutron diffraction, volume and optical properties are presented and discussed. A very unusual peak structure in the resistivity-pressure relation of TmSe1-xTex at low temperatures is observed. A discussion of the novel feature involves the concept of the excitonic insulator and f-d hybridization. The magnetic behavior of the Tm and Eu based compounds is significantly influenced by the SMT. This is thought to be mainly due to the additional coupling between the rare earth moments via free carriers which are present in the metallic state. In SmS1-xSex a considerable softening of the lattice is observed before the valence transition occurs. It is speculated that Poisson's ratio might become negative already in the semiconducting state.

  7. 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.

  8. AFM probing of polymer/nanofiller interfacial adhesion and its correlation with bulk mechanical properties in a poly(ethylene terephthalate) nanocomposite.

    PubMed

    Aoyama, Shigeru; Park, Yong Tae; Macosko, Christopher W; Ougizawa, Toshiaki; Haugstad, Greg

    2014-11-01

    The interfacial adhesion between polymer and nanofiller plays an important role in affecting the properties of nanocomposites. The detailed relationship between interfacial adhesion and bulk properties, however, is unclear. In this work, we developed an atomic force microscopy (AFM)-based abrasive scanning methodology, as applied to model laminate systems, to probe the strength of interfacial adhesion relevant to poly(ethylene terephthalate) (PET)/graphene or clay nanocomposites. Graphite and mica substrates covered with ∼2 nm thick PET films were abrasively sheared by an AFM tip as a model measurement of interfacial strength between matrix PET and dispersed graphene and clay, respectively. During several abrasive raster-scan cycles, PET was shear-displaced from the scanned region. At temperatures below the PET glass transition, PET on graphite exhibited abrupt delamination (i.e., full adhesive failure), whereas PET on mica did not; rather, it exhibited a degree of cohesive failure within the shear-displaced layer. Moreover, 100-fold higher force scanning procedures were required to abrade through an ultimate "precursor" layer of PET only ∼0.2-0.5 nm thick, which must be largely disentangled from the matrix polymer. Thus, the adhesive interface of relevance to the strength of clay-filler nanocomposites is between matrix polymer and strongly bound polymer. At 90 °C, above the bulk PET glass transition temperature, the PET film exhibited cohesive failure on both graphite and mica. Our results suggest that there is little difference in the strength of the relevant interfacial adhesion in the two nanocomposites within the rubbery dynamic regime. Further, the bulk mechanical properties of melt mixed PET/graphene and PET/clay nanocomposites were evaluated by dynamic mechanical analysis. The glassy dynamic storage modulus of the PET/clay nanocomposite was higher than that of PET/graphene, correlating with the differences in interfacial adhesion probed by AFM. PMID

  9. Molecular relaxation behavior and isothermal crystallization above glass transition temperature of amorphous hesperetin.

    PubMed

    Shete, Ganesh; Khomane, Kailas S; Bansal, Arvind Kumar

    2014-01-01

    The purpose of this paper was to investigate the relaxation behavior of amorphous hesperetin (HRN), using dielectric spectroscopy, and assessment of its crystallization kinetics above glass transition temperature (Tg ). Amorphous HRN exhibited both local (β-) and global (α-) relaxations. β-Relaxation was observed below Tg , whereas α-relaxation prominently emerged above Tg . β-Relaxation was found to be of Johari-Goldstein type and was correlated with α-process by coupling model. Secondly, isothermal crystallization experiments were performed at 363 K (Tg + 16.5 K), 373 K (Tg + 26.5 K), and 383 K (Tg + 36.5 K). The kinetics of crystallization, obtained from the normalized dielectric strength, was modeled using the Avrami model. Havriliak-Negami (HN) shape parameters, αHN and αHN .βHN , were analyzed during the course of crystallization to understand the dynamics of amorphous phase during the emergence of crystallites. HN shape parameters indicated that long range (α-like) were motions affected to a greater extent than short range (β-like) motions during isothermal crystallization studies at all temperature conditions. The variable behavior of α-like motions at different isothermal crystallization temperatures was attributed to evolving crystallites with time and increase in electrical conductivity with temperature. PMID:24186540

  10. Transition-metal-based magnetic refrigerants for room-temperature applications.

    PubMed

    Tegus, O; Brück, E; Buschow, K H J; de Boer, F R

    2002-01-10

    Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field. PMID:11805828

  11. Low temperature magneto-structural transitions in Mn3Ni20P6

    NASA Astrophysics Data System (ADS)

    Cedervall, Johan; Beran, Premysl; Vennström, Marie; Danielsson, Therese; Ronneteg, Sabina; Höglin, Viktor; Lindell, David; Eriksson, Olle; André, Gilles; Andersson, Yvonne; Nordblad, Per; Sahlberg, Martin

    2016-05-01

    X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm 3 barm (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic antiferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k=(0 0 ½) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 ~0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K.

  12. The Effects of Dislocations on the Verwey Transition as Observed by Transmission Electron Microscopy and Low Temperature Magnetic Measurements

    NASA Astrophysics Data System (ADS)

    Lindquist, A. K.; Feinberg, J. M.; Harrison, R. J.; Loudon, J.; Newell, A. J.

    2014-12-01

    Pure magnetite experiences a first order phase transition, called the Verwey transition, at ~120K whereby the mineral's crystal structure changes from cubic to monoclinic. This transformation has a profound effect on the magnetic properties of magnetite. Internal and external stresses have been shown to affect the onset of the Verwey transition, but the processes by which this occurs have not been observed. To further investigate this behavior, we used transmission electron microscopy on deformed magnetite samples to simultaneously image dislocations, magnetic domain walls, and low-temperature twins while cooling through the Verwey transition. To relate the observed changes to more readily-measurable bulk sample magnetic behavior, we made low-temperature magnetic measurements using SQUID magnetometry. According to these low temperature measurements, the temperature of the phase transition is depressed by as much as 6°C in the deformed samples. Combining these two techniques allows us, for the first time, to observe the Verwey transition in a defect-rich area and to observe the manner in which dislocations, and their associated stress fields, influence and impede the growth of twin structures as magnetite is cooled through the Verwey transition.

  13. Homogeneous and inhomogeneous sources of optical transition broadening in room temperature CdSe/ZnS nanocrystal quantum dots

    SciTech Connect

    Wolf, M.; Berezovsky, J.

    2014-10-06

    We perform photoluminescence excitation measurements on individual CdSe/ZnS nanocrystal quantum dots (NCQDs) at room temperature to study optical transition energies and broadening. The observed features in the spectra are identified and compared to calculated transition energies using an effective mass model. The observed broadening is attributed to phonon broadening, spectral diffusion, and size and shape inhomogeneity. The former two contribute to the broadening transitions in individual QDs, while the latter contributes to the QD-to-QD variation. We find that phonon broadening is often not the dominant contribution to transition line widths, even at room temperature, and that broadening does not necessarily increase with transition energy. This may be explained by differing magnitude of spectral diffusion for different quantum-confined states.

  14. Effect of free surface roughness on the apparent glass transition temperature in thin polymer films measured by ellipsometry.

    PubMed

    Efremov, Mikhail Yu

    2014-12-01

    Ellipsometry is one of the standard methods for observation of glass transition in thin polymer films. This work proposes that sensitivity of the method to surface morphology can complicate manifestation of the transition in a few nm thick samples. Two possible mechanisms of free surface roughening in the vicinity of glass transition are discussed: roughening due to lateral heterogeneity and roughening associated with thermal capillary waves. Both mechanisms imply an onset of surface roughness in the glass transition temperature range, which affects the experimental data in a way that shifts apparent glass transition temperature. Effective medium approximation models are used to introduce surface roughness into optical calculations. The results of the optical modeling for a 5 nm thick polystyrene film on silicon are presented. PMID:25554303

  15. Raman study of the Verwey transition in magnetite at high-pressure and low-temperature: Effect of Al doping

    NASA Astrophysics Data System (ADS)

    Gasparov, L.; Shirshikova, Z.; Pekarek, T. M.; Blackburn, J.; Struzhkin, V.; Gavriliuk, A.; Rueckamp, R.; Berger, H.

    2012-08-01

    We employed Raman spectroscopy to investigate how the hydrostatic pressure affects the temperature of the Verwey transition in pure (Fe3O4) and Al-doped (Fe2.8Al0.2O4) magnetite. In both samples, pressure suppresses the transition. The Al-doped sample displays no transition above 8 GPa. We do not observe such discontinuity in a pure magnetite, which suggests that the discontinuity is doping driven. Our Clausius-Clapeyron formula based analysis of the pressure-transition temperature dependence is in excellent agreement with our data in pure magnetite. The Al doping leads to a smaller entropy change and larger volume expansion consistent with partial charge ordering at the transition.

  16. Formation of supported lipid bilayers on silica: relation to lipid phase transition temperature and liposome size.

    PubMed

    Jing, Yujia; Trefna, Hana; Persson, Mikael; Kasemo, Bengt; Svedhem, Sofia

    2014-01-01

    DPPC liposomes ranging from 90 nm to 160 nm in diameter were prepared and used for studies of the formation of supported lipid membranes on silica (SiO2) at temperatures below and above the gel to liquid-crystalline phase transition temperature (Tm = 41 °C), and by applying temperature gradients through Tm. The main method was the quartz crystal microbalance with dissipation (QCM-D) technique. It was found that liposomes smaller than 100 nm spontaneously rupture on the silica surface when deposited at a temperature above Tm and at a critical surface coverage, following a well-established pathway. In contrast, DPPC liposomes larger than 160 nm do not rupture on the surface when adsorbed at 22 °C or at 50 °C. However, when liposomes of this size are first adsorbed at 22 °C and at a high enough surface coverage, after which they are subject to a constant temperature gradient up to 50 °C, they rupture and fuse to a bilayer, a process that is initiated around Tm. The results are discussed and interpreted considering a combination of effects derived from liposome-surface and liposome-liposome interactions, different softness/stiffness and shape of liposomes below and above Tm, the dynamics and thermal activation of the bilayers occurring around Tm and (for liposomes containing 33% of NaCl) osmotic pressure. These findings are valuable both for preparation of supported lipid bilayer cell membrane mimics and for designing temperature-responsive material coatings. PMID:24651504

  17. Analysis of the thermally stimulated discharge current around glass-rubber transition temperature in polyethylene terephthalate

    NASA Astrophysics Data System (ADS)

    Neagu, Eugen R.; Marat-Mendes, Jose N.; Das-Gupta, Dilip K.; Neagu, Rodica M.; Igreja, Rui

    1997-09-01

    The nature of the thermally stimulated discharge current (TSDC) for polyethylene terephthalate samples in the temperature range from room temperature to above glass-rubber transition temperature of the amorphous phase is analyzed. The well conditioning of the sample is strictly necessary in order to have a good reproducibility and accuracy of results. A main peak was observed whose maximum temperature moves towards a lower value with the decreasing of the amount of charge that flows through the sample during polarization. The peak position changes as well, if the sample is polarized in air or in oxygen and the nature of change is more important in the case of oxygen. The shape of the peak is complex and at least four shoulders have been identified around 85, 90, 105, and 125 °C using the cleaning technique. The activation energy tends to increase with repetition of the TSDC runs, in the glass-rubber transition temperature range, in the case when the cleaning technique is used for the peaks separation. For the conditioned samples, there is a good agreement between the experimental results and the analytical expression of the current, particularly in the region where it reaches a maximum, and so relevant values for the characteristic parameters of the peak are determined. The time interval of the short circuiting of the sample, at room temperature, before the TSDC measurement, strongly influences the initial rise of the current and consequently the parameters of the peak. A possible redistribution of the internal field arising from the injected charge, the heterocharge, and the existing charge in the sample as received, has been put forward to account for the experimental evidences. The conclusion is that the current is mainly determined by the space-charge released from the traps that are likely continuously distributed in energy. For the stated polarization conditions, the charge is released from the shallow traps with an activation energy in the range 0.23-0.32 e

  18. Densification and depression in glass transition temperature in polystyrene thin films.

    PubMed

    Vignaud, G; S Chebil, M; Bal, J K; Delorme, N; Beuvier, T; Grohens, Y; Gibaud, A

    2014-10-01

    Ellipsometry and X-ray reflectivity were used to characterize the mass density and the glass transition temperature of supported polystyrene (PS) thin films as a function of their thickness. By measuring the critical wave vector (qc) on the plateau of total external reflection, we evidence that PS films get denser in a confined state when the film thickness is below 50 nm. Refractive indices (n) and electron density profiles measurements confirm this statement. The density of a 6 nm (0.4 gyration radius, Rg) thick film is 30% greater than that of a 150 nm (10Rg) film. A depression of 25 °C in glass transition temperature (Tg) was revealed as the film thickness is reduced. In the context of the free volume theory, this result seems to be in apparent contradiction with the fact that thinner films are denser. However, as the thermal expansion of thinner films is found to be greater than the one of thicker films, the increase in free volume is larger for thin films when temperature is raised. Therefore, the free volume reaches a critical value at a lower Tg for thinner films. This critical value corresponds to the onset of large cooperative movements of polymer chains. The link between the densification of ultrathin films and the drop in their Tg is thus reconciled. We finally show that at their respective Tg(h) all films exhibit a critical mass density of about 1.05 g/cm(3) whatever their thickness. The thickness dependent thermal expansion related to the free volume is consequently a key factor to understand the drop in the Tg of ultrathin films. PMID:25209183

  19. Effective AFM cantilever tip size: methods for in-situ determination

    NASA Astrophysics Data System (ADS)

    Maragliano, Carlo; Glia, Ayoub; Stefancich, Marco; Chiesa, Matteo

    2015-01-01

    In atomic force microscopy (AFM) investigations, knowledge of the cantilever tip radius R is essential for the quantitative interpretation of experimental observables. Here we propose two techniques to rapidly quantify in-situ the effective tip radius of AFM probes. The first method is based on the strong dependency of the minimum value of the free amplitude required to observe a sharp transition from attractive to repulsive force regimes on the AFM probe radius. Specifically, the sharper the tip, the smaller the value of free amplitude required to observe such a transition. The key trait of the second method is to treat the tip-sample system as a capacitor. Provided with an analytical model that takes into account the geometry of the tip-sample’s capacitance, one can quantify the effective size of the tip apex fitting the experimental capacitance versus distance curve. Flowchart-like algorithms, easily implementable on any hardware, are provided for both methods, giving a guideline to AFM practitioners. The methods’ robustness is assessed over a wide range of probes of different tip radii R (i.e. 4 < R < 50 nm) and geometries. Results obtained from both methods are compared with the nominal values given by manufacturers and verified by acquiring scanning electron microscopy images. Our observations show that while both methods are reliable and robust over the range of tip sizes tested, the critical amplitude method is more accurate for relatively sharp tips (4 nm < R < 10 nm).

  20. Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

    NASA Astrophysics Data System (ADS)

    Holmlid, Leif; Kotzias, Bernhard

    2016-04-01

    Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H2N(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H4(0) and H3(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H2N(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected.

  1. The effect of deuteration and doping on the phase transition temperature of grown glycine phosphite single crystals

    SciTech Connect

    Perumal, R.; Chandru, A. Lakshmi; Babu, S. Moorthy

    2014-04-24

    The Glycinium Phosphite (GPI) compound is a representative of hydrogen-bonded ferroelectric crystals. The ordering of protons could be expected below the room temperature (225 K). Crystals grown from the milipore water as well as deuterated solvents respectively. The corresponding hydrogen bond distance was stretched out due to the effect of isotopic substitution that increase the phase transition temperature. Further to improve the phase transition temperature, GPI crystal was doped with organic complexing agent and various metals and the obtained results are presented.

  2. Absence of low temperature phase transitions and enhancement of ferroelectric transition temperature in highly strained BaTiO{sub 3} epitaxial films grown on MgO Substrates

    SciTech Connect

    Kumar, Satish; Kumar, Dhirendra; Sathe, V. G.; Kumar, Ravi; Sharma, T. K.

    2015-04-07

    Recently, a large enhancement in the ferroelectric transition temperature of several oxides is reported by growing the respective thin films on appropriate substrates. This phenomenon is correlated with high residual strain in thin films often leading to large increase in the tetragonality of their crystal structure. However, such an enhancement of transition temperature is usually limited to very thin films of ∼10 nm thickness. Here, we report growth of fully strained epitaxial thin films of BaTiO{sub 3} of 400 nm thickness, which are coherently grown on MgO substrates by pulsed laser deposition technique. Conventional high resolution x-ray diffraction and also the reciprocal space map measurements confirm that the film is fully strained with in-plane tensile strain of 5.5% that dramatically increases the tetragonality to 1.05. Raman measurements reveal that the tetragonal to cubic structural phase transition is observed at 583 K, which results in an enhancement of ∼200 K. Furthermore, temperature dependent Raman studies on these films corroborate absence of all the low temperature phase transitions. Numerical calculations based on thermodynamical model predict a value of the transition temperature that is greater than 1500 °C. Our experimental results are therefore in clear deviation from the existing strain dependent phase diagrams.

  3. Origins of the two simultaneous mechanisms causing glass transition temperature reductions in high molecular weight freestanding polymer films

    SciTech Connect

    Prevosto, Daniele E-mail: Prevosto@df.unipi.it; Capaccioli, Simone; Ngai, K. L. E-mail: Prevosto@df.unipi.it

    2014-02-21

    From ellipsometry measurements, Pye and Roth [Phys. Rev. Lett. 107, 235701 (2011)] presented evidence of the presence of two glass transitions originating from two distinctly different and simultaneous mechanisms to reduce the glass transition temperature within freestanding polystyrene films with thickness less than 70 nm. The upper transition temperature T{sub g}{sup u}(h) is higher than the lower transition temperature T{sub g}{sup l}(h) in the ultrathin films. After comparing their data with the findings of others, using the same or different techniques, they concluded that new theoretical interpretation is needed to explain the two transitions and the different dependences of T{sub g}{sup u}(h) and T{sub g}{sup l}(h) on film thickness and molecular weight. We address the problem based on advance in delineating the different viscoelastic mechanisms in the glass-rubber transition zone of polymers. Theoretical considerations as well as experiments have shown in time-scales immediately following the segmental α-relaxation are the sub-Rouse modes with longer length scale but shorter than that of the Rouse modes. The existence of the sub-Rouse modes in various polymers including polystyrene has been repeatedly confirmed by experiments. We show that the sub-Rouse modes can account for the upper transition and the properties observed. The segmental α-relaxation is responsible for the lower transition. This is supported by the fact that the segmental α-relaxation in ultrathin freestanding PS films had been observed by dielectric relaxation measurements and photon correlation spectroscopy. Utilizing the temperature dependence of the segmental relaxation times from these experiments, the glass transition temperature T{sub g}{sup α} associated with the segmental relaxation in the ultrathin film is determined. It turns out that T{sub g}{sup α} is nearly the same as T{sub g}{sup l}(h) of the lower transition, and hence definitely segmental α-relaxation is the

  4. BOREAS AFM-6 Surface Meteorological Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) collected surface meteorological data from 21 May to 20 Sep 1994 near the Southern Study Area-Old Jack Pine (SSA-OJP) tower site. The data are in tabular ASCII files. The surface meteorological data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  5. Temperature dependent absorption measurement of various transition metal doped laser materials

    NASA Astrophysics Data System (ADS)

    Horackova, Lucie; Šulc, Jan; Jelinkova, Helena; Jambunathan, Venkatesan; Lucianetti, Antonio; Mocek, Tomás.

    2015-05-01

    In recent years, there has been a vast development of high energy class lasers of the order of 100 J to kJ level which have potential applications in the field of science and technology. Many such systems use the gain media cooled at cryogenic temperatures which will help in enhancing the spectroscopic and thermo-optical properties. Nevertheless, parasitic effects like amplified spontaneous emission enhance and affect the overall efficiency. The best way to suppress this effect is to use cladding element attached to the gain material. Based on these facts, this work was focused on the systematic investigation of temperature dependent absorption of several materials doped with transition metals, which can be used as cladding, as laser gain material, or as passive Q-switching element. The Ti:sapphire, Cr:YAG, V:YAG, and Co:MALO samples were measured in temperature range from 80 K to 330 K by step of 50 K. Using Beer-Lambert law we estimated the absorption coefficient of these materials.

  6. High-Temperature Elasticity, Cation Disorder and Magnetic Transition in Magnesioferrite

    SciTech Connect

    Antao,S.; Jackson, I.; Li, B.; Kung, J.; Chen, J.; Hassan, I.; Liebermann, R.; Parise, J.

    2007-01-01

    The elastic moduli of magnesioferrite spinel, MgFe2O4, and their temperature dependence have been determined for the first time by ultrasonic measurements on a polycrystalline specimen. The measurements were carried out at 300 MPa and to 700 C in a gas-medium high-pressure apparatus. On heating, both the elastic bulk (K S) and shear (G) moduli decrease linearly to 350 C. By combining with extant thermal-expansion data, the values for the room-temperature K S and G, and their temperature derivatives are as follows: K 0 = 176.3(7) GPa, G 0 = 80.1(2) GPa, ({partial_derivative}K S/{partial_derivative}T) P = -0.032(3) GPa K-1 and ({partial_derivative}G/{partial_derivative}T) P = -0.012(1) GPa K-1. Between 350 and 400 C, there are abrupt increases of 1.4% in both of the elastic moduli; these closely coincide with the magnetic Curie transition that was observed by thermal analyses at about 360 C.

  7. Low temperature structural phase transition in hafnium and zirconium tetrafluoride trihydrates

    NASA Astrophysics Data System (ADS)

    Dey, S. K.; Dey, C. C.; Saha, S.

    2016-04-01

    From time-differential perturbed angular correlation (TDPAC) measurements, the monoclinic and triclinic crystal structures in hafnium and zirconium tetrafluoride trihydrates are found to be present simultaneously in both the compounds. From previous TDPAC and XRD investigations, a monoclinic crystal structure for HfF4·3H2O but, for its analogues zirconium compound, a triclinic structure was reported. Contrary to earlier reports, the triclinic fraction in HfF4·3H2O is found to be maximum (80%) at room temperature. In fact, the triclinic crystal structure of HfF4·3H2O is reported here which was not known prior to this report. In ZrF4·3H2O, a strong signal (80-90%) for the triclinic structure is found at room temperature while the monoclinic fraction appears as a weak signal (10-15%). Structural phase transitions in these trihydrate compounds have been observed in the temperature range 298-333 K.

  8. Lee-Yang zero distribution of high temperature QCD and the Roberge-Weiss phase transition

    NASA Astrophysics Data System (ADS)

    Nagata, Keitaro; Kashiwa, Kouji; Nakamura, Atsushi; Nishigaki, Shinsuke M.

    2015-05-01

    Canonical partition functions and Lee-Yang zeros of QCD at finite density and high temperature are studied. Recent lattice simulations confirm that the free energy of QCD is a quartic function of quark chemical potential at temperature slightly above pseudocritical temperature Tc, as in the case with a gas of free massless fermions. We present analytic derivation of the canonical partition functions and Lee-Yang zeros for this type of free energy using the saddle point approximation. We also perform lattice QCD simulation in a canonical approach using the fugacity expansion of the fermion determinant and carefully examine its reliability. By comparing the analytic and numerical results, we conclude that the canonical partition functions follow the Gaussian distribution of the baryon number, and the accumulation of Lee-Yang zeros of these canonical partition functions exhibit the first-order Roberge-Weiss phase transition. We discuss the validity and applicable range of the result and its implications both for theoretical and experimental studies.

  9. Hydrogen detonation and detonation transition data from the High-Temperature Combustion Facility

    SciTech Connect

    Ciccarelli, G.; Boccio, J.L.; Ginsberg, T.; Finfrock, C.; Gerlach, L.; Tagawa, H.; Malliakos, A.

    1995-12-31

    The BNL High-Temperature Combustion Facility (HTCF) is an experimental research tool capable of investigating the effects of initial thermodynamic state on the high-speed combustion characteristic of reactive gas mixtures. The overall experimental program has been designed to provide data to help characterize the influence of elevated gas-mixture temperature (and pressure) on the inherent sensitivity of hydrogen-air-steam mixtures to undergo detonation, on the potential for flames accelerating in these mixtures to transition into detonations, on the effects of gas venting on the flame-accelerating process, on the phenomena of initiation of detonations in these mixtures by jets of hot reactant product,s and on the capability of detonations within a confined space to transmit into another, larger confined space. This paper presents results obtained from the completion of two of the overall test series that was designed to characterize high-speed combustion phenomena in initially high-temperature gas mixtures. These two test series are the intrinsic detonability test series and the deflagration-to-detonation (DDT) test series. A brief description of the facility is provided below.

  10. Disentangling Cooper-pair formation above the transition temperature from the pseudogap state in the cuprates

    SciTech Connect

    Kondo, Takeshi; Hamaya, Yoichiro; Palczewski, Ari D.; Takeuchi, Tsunehiro; Wen, J. S.; Xu, Z. J.; Gu, Genda; Schmalian, Joerg; Kaminski, Adam

    2010-12-05

    The discovery of the pseudogap in the cuprates created significant excitement as it was believed to be a signature of pairing, in some cases above room temperature. Indeed, a number of experiments detected phase-fluctuating superconductivity above the transition temperature T{sub c}. However, several recent experiments reported that the pseudogap and superconducting state are characterized by different energy scales and probably compete with each other, leaving open the question of whether the pseudogap is caused by pair formation. Here we report the discovery of a spectroscopic signature of pair formation and demonstrate that in a region commonly referred to as the pseudogap, two distinct states coexist: one that is due to pair formation and persists to an intermediate temperature T{sub pair} < T* and a second - the 'proper' pseudogap - characterized by the loss of spectral weight and anomalies in transport properties that extends up to T*. T{sub pair} has a value around 120-150 K even for materials with very different T{sub c} values and it probably sets a limit on the highest attainable T{sub c} in the cuprates

  11. Disentangling Cooper-pair formation above the transition temperature from the pseudogap state in the cuprates

    SciTech Connect

    Kondo, Takeshi; Hamaya, Yoichiro; Palczewski, Ari D.; Takeuchi, Tsunehiro; Wen, J. S.; Xu, Z. J.; Gu, Genda; Schmalian, Jorg; Kaminski, Adam

    2010-12-05

    The discovery of the pseudogap in the cuprates created significant excitement as it was believed to be a signature of pairing, in some cases above room temperature. Indeed, a number of experiments detected phase-fluctuating superconductivity above the transition temperature T{sub c}. However, several recent experiments reported that the pseudogap and superconducting state are characterized by different energy scales, and probably compete with each other, leaving open the question of whether the pseudogap is caused by pair formation. Here we report the discovery of a spectroscopic signature of pair formation and demonstrate that in a region commonly referred to as the pseudogap, two distinct states coexist: one that is due to pair formation and persists to an intermediate temperature T{sub pair}

  12. High antiferromagnetic transition temperature of a honeycomb compound SrRu2O6

    DOE PAGESBeta

    Tian, Wei; Svoboda, Chris; Ochi, M.; Matsuda, M.; Cao, Huibo; Cheng, J. -G.; Sales, B. C.; Mandrus, D.; Arita, R.; Trivedi, Nandini; et al

    2015-09-14

    We study the high-temperature magnetic order in a quasi-two-dimensional honeycomb compound SrRu2O6 by measuring magnetization and neutron powder diffraction with both polarized and unpolarized neutrons. SrRu2O6 crystallizes into the hexagonal lead antimonate (PbSb2O6, space group P31m) structure with layers of edge-sharing RuO6 octahedra separated by Sr2+ ions. SrRu2O6 is found to order at TN = 565 K with Ru moments coupled antiferromagnetically both in plane and out of plane. The magnetic moment is 1.30(2) μB/Ru at room temperature and is along the crystallographic c axis in the G-type magnetic structure. We perform density functional calculations with constrained random-phase approximation (RPA)more » to obtain the electronic structure and effective intra- and interorbital interaction parameters. The projected density of states shows strong hybridization between Ru 4d and O 2p. By downfolding to the target t2g bands we extract the effective magnetic Hamiltonian and perform Monte Carlo simulations to determine the transition temperature as a function of interand intraplane couplings. We find a weak interplane coupling, 3% of the strong intraplane coupling, permits three-dimensional magnetic order at the observed TN .« less

  13. Hydrogen detonation and detonation transition data from the High-Temperature Combustion Facility

    SciTech Connect

    Ciccarelli, G.; Boccio, J.L.; Ginsberg, T.; Finfrock, C.

    1996-03-01

    The BNL High-Temperature Combustion Facility (HTCF) is an experimental research tool capable of investigating the effects of initial thermodynamic state on the high-speed combustion characteristic of reactive gas mixtures. The overall experimental program has been designed to provide data to help characterize the influence of elevated gas-mixture temperature (and pressure) on the inherent sensitivity of hydrogen-air-steam mixtures to undergo detonation, on the potential for flames accelerating in these mixtures to transition into detonations, on the effects of gas venting on the flame-accelerating process, on the phenomena of initiation of detonations in these mixtures by jets of hot reactant products, and on the capability of detonations within a confined space to transmit into another, larger confined space. This paper presents results obtained from the completion of two of the overall test series that was designed to characterize high-speed combustion phenomena in initially high-temperature gas mixtures. These two test series are the intrinsic detonability test series and the deflagration-to-detonation (DDT) test series. A brief description of the facility is provided below.

  14. High antiferromagnetic transition temperature for a layered hexagonal compound: SrRu2O6

    NASA Astrophysics Data System (ADS)

    Yan, Jiaqiang

    4d or 5d transition metal oxides (TMOs) are less correlated and have a larger bandwidth than 3d TMOs. A high magnetic ordering temperature for 4d/5d TMOs is not expected. It was therefore a surprise when a perovskite, SrTcO3, was reported to order magnetically around 1000 K. Unfortunately, the radioactive nature of Tc prevented further investigation of the underlying mechanism for the high magnetic ordering temperature. Here we report antiferromagnetic order of SrRu2O6 >at 565 K. Two features distinguish this compound from SrTcO3: (1) SrRu2O6 is not radioactive, which allows the study of the underlying physics by a large variety of techniques as well as the possible fine tuning of the magnetic ground state; and (2) SrRu2O6 crystallizes into a quasi-two-dimensional structure with layers of edge-sharing RuO6 octahedra separated by nonmagnetic Sr layers. Our density functional calculations and Monte Carlo simulations suggest an origin of the reduced moment size and the high Neel temperature. Work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and by the CEM and NSF MRSEC under Grant No. DMR-1420451.

  15. Kinetics of HMX and Phase Transitions: Effects of Grain Size at Elevated Temperature

    SciTech Connect

    Saw, C K

    2002-06-13

    To date a global kinetic rate law has not been written to accurately describe solid-solid phase transformations of HMX and TATB where contributions from grain size effects, binder contents, and impurity levels are explicitly defined. Our recent work presented at the 2001 SCCM topical APS meeting, Atlanta, GA, demonstrated one can not confidently use the second harmonic generation (SHG) diagnostic to study energetic material phase transitions where non-uniform grain size distributions are present. For example, in HMX, the early arrival of SHG before the XRD in the SHG/XRD simultaneous high temperature experiment clearly indicates the partial molecular conversion from centrosymmetric to non-centrosymmetric without any structural changes as exhibit by the XRD pattern. This conversion is attributed to the changes of the surface molecules due to the differences in potential between the surface and the bulk. The present paper reports on accurate XRD measurements following changes of {beta}-HMX to {delta}-HMX at elevated temperature. The results are compared for sample with 2 different grain sizes for HMX. We report accurate temperature dependent lattice parameters and hence volume and linear thermal expansion coefficients along each crystallographic axis. We have also conducted kinetic studies of the behavior of 2 grain-sizes of HMX and concluded that their kinetics, are drastically different.

  16. High-temperature ferromagnetism in transition metal implanted wide-bandgap semiconductors

    NASA Astrophysics Data System (ADS)

    Raley, Jeremy A.

    The field of spin transport electronics (spintronics) is a viable candidate for advancing computing and communication technologies. Material with both semiconductor and magnetic properties, which is commonly called a dilute magnetic semiconductor (DMS), will prove most useful in the fabrication of spintronic devices. In order to produce a DMS at above room temperature, transition metals (TMs) were implanted into host semiconductors of p-GaN, Al0.35Ga0.65N, or ZnO. Magnetic hysteresis measurements using a superconducting quantum interference device (SQUID) magnetometer show that some of the material combinations clearly exhibit ferromagnetism above room temperature. The most promising materials for creating spintronic devices using ion implantation are p-GaN:Mn, Al0.35Ga0.65N:Cr, and Fe-implanted ZnO nanotips on Al2O3. Temperature-dependent magnetization measurements confirm that indications of ferromagnetism are due to DMS behavior. Photo- and cathodoluminescence measurements show that implantation damage is recovered and the implanted TMs are incorporated into the semiconductor. As progress is made toward realizing practical spintronic devices, the work reported here will be useful for determining material combinations and implantation conditions that will yield the needed materials.

  17. Temperature dependence of thermal conductivity of VO2 thin films across metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Kizuka, Hinako; Yagi, Takashi; Jia, Junjun; Yamashita, Yuichiro; Nakamura, Shinichi; Taketoshi, Naoyuki; Shigesato, Yuzo

    2015-05-01

    Thermal conductivity of a 300-nm-thick VO2 thin film and its temperature dependence across the metal-insulator phase transition (TMIT) were studied using a pulsed light heating thermoreflectance technique. The VO2 and Mo/VO2/Mo films with a VO2 thickness of 300 nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO2 films were deposited by reactive rf magnetron sputtering using a V2O3 target and an Ar-O2 mixture gas at 645 K. The VO2 films consisted of single phase VO2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 × 10-1 to 5.3 × 10-4 Ω cm across the TMIT of around 325-340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4 W m-1 K-1 across the TMIT. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law.

  18. Morphology and Mechanical Properties of Poly(Ethylene Terephthalate) Stretched Above the Glass Transition Temperature

    NASA Astrophysics Data System (ADS)

    Todorov, Lyudmil V.; Viana, Júlio C.

    2007-04-01

    This study presents an experimental investigation into the development of the strain-induced morphology of amorphous poly(ethylene terephthalate), PET, stretched above its glass transition temperature. The present work aims at: i) defining the most important processing parameters that govern the structure formation and its significance; ii) characterising the mechanical properties of uniaxial stretched glassy PET, as an approach for industrial stretch-blow moulding techniques; iii) establishing structure-properties relationships. Compression moulded amorphous PET was uniaxial stretched with variations of following stretching parameters: stretching temperature, Tst, stretching velocity, Vst, and stretching ratio, λst, that were varied in two levels according to a L8 Taguchi orthogonal array. The developed morphologies were observed by differential scanning calorimetry (DSC), birefringence and Wide-Angle X-ray Scattering (WAXS). The mechanical behaviour was assessed in tensile testing at 15 mm.min-1 and room temperature. The results were treated by a statistical ANOVA tool. A strong thermal and mechanical coupling is evidenced in the stretching process, significantly influencing the morphology development. The main stretching parameters controlling microstructure formation were defined. The relationships between the microstructure and mechanical properties were established too.

  19. High antiferromagnetic transition temperature of the honeycomb compound SrRu2O6

    NASA Astrophysics Data System (ADS)

    Tian, W.; Svoboda, C.; Ochi, M.; Matsuda, M.; Cao, H. B.; Cheng, J.-G.; Sales, B. C.; Mandrus, D. G.; Arita, R.; Trivedi, N.; Yan, J.-Q.

    2015-09-01

    We study the high-temperature magnetic order in a quasi-two-dimensional honeycomb compound SrRu2O6 by measuring magnetization and neutron powder diffraction with both polarized and unpolarized neutrons. SrRu2O6 crystallizes into the hexagonal lead antimonate (PbSb2O6 , space group P 3 ¯1 m ) structure with layers of edge-sharing RuO6 octahedra separated by Sr2 + ions. SrRu2O6 is found to order at TN=565 K with Ru moments coupled antiferromagnetically both in plane and out of plane. The magnetic moment is 1.30(2) μB/Ru at room temperature and is along the crystallographic c axis in the G-type magnetic structure. We perform density functional calculations with constrained random-phase approximation (RPA) to obtain the electronic structure and effective intra- and interorbital interaction parameters. The projected density of states shows strong hybridization between Ru 4 d and O 2 p . By downfolding to the target t2 g bands we extract the effective magnetic Hamiltonian and perform Monte Carlo simulations to determine the transition temperature as a function of inter- and intraplane couplings. We find a weak interplane coupling, 3% of the strong intraplane coupling, permits three-dimensional magnetic order at the observed TN.

  20. Air-sea temperature decoupling in western Europe during the last interglacial-glacial transition

    NASA Astrophysics Data System (ADS)

    Sánchez Goñi, María Fernanda; Bard, Edouard; Landais, Amaelle; Rossignol, Linda; D'Errico, Francesco

    2013-10-01

    A period of continental ice growth between about 80,000 and 70,000 years ago was controlled by a decrease in summer insolation, and was among the four largest ice expansions of the past 250,000 years. The moisture source for this ice sheet expansion, known as the Marine Isotope Stage (MIS) 5a/4 transition, has been proposed to be the warm subpolar and northern subtropical Atlantic Ocean. However, the mechanism by which glaciers kept growing through three suborbital cooling events within this period, which were associated with iceberg discharge in the North Atlantic and cooling over Greenland, is unclear. Here we reconstruct parallel records of sea surface and air temperatures from marine microfossil and pollen data, respectively, from two sediment cores collected within the northern subtropical gyre. The thermal gradient between the cold air and warmer sea increased throughout the MIS5a/4 transition, and was marked by three intervals of even more pronounced thermal gradients associated with the C20, C19 and C18' cold events. We argue that the warm ocean surface along the western European margin provided a source of moisture that was transported, through northward-tracking storms, to feed ice sheets in colder Greenland, northern Europe and the Arctic.

  1. Nanosecond Ultrasonics to Study Phase Transitions in Solid and Liquid Systems at High Pressure and Temperature

    SciTech Connect

    Bonner, B P; Berge, P A; Carlson, S C; Farber, D L; Akella, J

    2007-03-21

    This report describes the development of a high-frequency ultrasonic measurement capability for application to the study of phase transitions at elevated pressure and temperature. We combined expertise in various aspects of static high-pressure technique with recent advances in wave propagation modeling, ultrasonic transducer development, electronic methods and broadband instrumentation to accomplish the goals of this project. The transduction and electronic systems have a demonstrated bandwidth of 400 MHz, allowing investigations of phenomena with characteristic times as short as 2.5 nS. A compact, pneumatically driven moissanite anvil cell was developed and constructed for this project. This device generates a high-pressure environment for mm dimension samples to pressures of 3 GPa. Ultrasonic measurements were conducted in the moissanite cell, an LLNL multi-anvil device and in a modified piston cylinder device. Measurements for water, and elemental tantalum, tin and cerium demonstrate the success of the methods. The {gamma}-{alpha} phase transition in cerium was clearly detected at {approx}0.7 GPa with 75 MHz longitudinal waves. These results have direct application to important problems in LLNL programs, as well as seismology and planetary science.

  2. Temperature Dependence of Magnetically Active Charge Excitations in Magnetite across the Verwey Transition.

    PubMed

    Taguchi, M; Chainani, A; Ueda, S; Matsunami, M; Ishida, Y; Eguchi, R; Tsuda, S; Takata, Y; Yabashi, M; Tamasaku, K; Nishino, Y; Ishikawa, T; Daimon, H; Todo, S; Tanaka, H; Oura, M; Senba, Y; Ohashi, H; Shin, S

    2015-12-18

    We study the electronic structure of bulk single crystals and epitaxial films of Fe_{3}O_{4}. Fe 2p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model-and in contrast to an earlier peak assignment-we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above T_{V} and its T-dependent evolution. The Fe 2p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at E_{F} for the polaronic half metal with a remnant order above T_{V} and a clear gap formation below T_{V}. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B-site electronic states, consistent with resistivity and optical spectra. PMID:26722935

  3. Temperature Dependence of Magnetically Active Charge Excitations in Magnetite across the Verwey Transition

    NASA Astrophysics Data System (ADS)

    Taguchi, M.; Chainani, A.; Ueda, S.; Matsunami, M.; Ishida, Y.; Eguchi, R.; Tsuda, S.; Takata, Y.; Yabashi, M.; Tamasaku, K.; Nishino, Y.; Ishikawa, T.; Daimon, H.; Todo, S.; Tanaka, H.; Oura, M.; Senba, Y.; Ohashi, H.; Shin, S.

    2015-12-01

    We study the electronic structure of bulk single crystals and epitaxial films of Fe3 O4 . Fe 2 p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T ) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model—and in contrast to an earlier peak assignment—we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above TV and its T -dependent evolution. The Fe 2 p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at EF for the polaronic half metal with a remnant order above TV and a clear gap formation below TV. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B -site electronic states, consistent with resistivity and optical spectra.

  4. Deviations of the glass transition temperature in amorphous conjugated polymer thin films.

    PubMed

    Liu, Dan; Osuna Orozco, Rodrigo; Wang, Tao

    2013-08-01

    The deviations of the glass transition temperature (T(g)) in thin films of an amorphous conjugated polymer poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) are reported. Monotonic and nonmonotonic T(g) deviations are observed in TFB thin films supported on Si-SiOx and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), respectively. A three-layer model is developed to fit both monotonic and nonmonotonic T(g) deviations in these films. A 5-nm PEDOT:PSS capping layer was not found to be effective to remove the free-surface effect in Si-SiOx supported TFB films. PMID:24032856

  5. A Physically-Based Correlation of Irradiation-Induced Transition Temperature Shifts for RPV Steels1

    SciTech Connect

    Eason, Ernest D.; Odette, George Robert; Nanstad, Randy K; Yamamoto, Takuya

    2013-01-01

    This paper presents a physically-based, empirically calibrated model for estimating irradiation-induced transition temperature shifts in reactor pressure vessel steels, based on a broader database and more complete understanding of embrittlement mechanisms than was available for earlier models. Brief descriptions of the underlying radiation damage mechanisms and the database are included, but the emphasis is on the model and the quality of its fit to U.S. power reactor surveillance data. The model is compared to a random sample of surveillance data that were set aside and not used in fitting and to selected independent data from test reactor irradiations, in both cases showing good ability to predict data that were not used for calibration. The model is a good fit to the surveillance data, with no significant residual error trends for variables included in the model or additional variables that could be included.

  6. On-the-fly transition search and applications to temperature-accelerated dynamics

    NASA Astrophysics Data System (ADS)

    Shim, Yunsic; Amar, Jacques

    2015-03-01

    Temperature-accelerated dynamics (TAD) is a powerful method to study non-equilibrium processes and has been providing surprising insights for a variety of systems. While serial TAD simulations have been limited by the roughly N3 increase in the computational cost as a function of the number of atoms N in the system, recently we have shown that by carrying out parallel TAD simulations which combine spatial decomposition with our semi-rigorous synchronous sublattice algorithm, significantly improved scaling is possible. However, in this approach the size of activated events is limited by the processor size while the dynamics is not exact. Here we discuss progress in improving the scaling of serial TAD by combining the use of on-the-fly transition searching with our previously developed localized saddle-point method. We demonstrate improved performance for the cases of Ag/Ag(100) annealing and Cu/Cu(100) growth. Supported by NSF DMR-1410840.

  7. Temperature effects on superfluid phase transition in Bose-Hubbard model with three-body interaction

    NASA Astrophysics Data System (ADS)

    Kopeć, T. K.; Szymański, M. W.

    2014-10-01

    We theoretically investigate the effect of the three-body on-site interactions on the Mott-insulator-superfluid transition for ultracold bosonic atoms in the framework of the Bose-Hubbard model. In particular, we explore the combined effects of three-body interaction and finite temperature on the phase diagram in detail. In order to handle system with strong local interactions a resolvent expansion technique based on the contour integral representation of the partition function has been devised. Subsequently, we derive the Landau-type expansion for the free energy in terms of the superfluid order parameter and find the phase diagrams depicting the relationships between various physical quantities of interest.

  8. Thickness dependence of the charge-density-wave transition temperature in VSe{sub 2}

    SciTech Connect

    Yang, Jiyong; Liu, Yan; Du, Haifeng; Ning, Wei; Zheng, Guolin; Jin, Chiming; Han, Yuyan; Wang, Ning; Tian, Mingliang Zhang, Yuheng; Wang, Weike; Yang, Zhaorong

    2014-08-11

    A set of three-dimensional charge-density-wave (3D CDW) VSe{sub 2} nano-flakes with different thicknesses were obtained by the scotch tape-based micro-mechanical exfoliation method. Resistivity measurements showed that the 3D CDW transition temperature T{sub p} decreases systematically from 105 K in bulk to 81.8 K in the 11.6 nm thick flake. The Hall resistivity ρ{sub xy} of all the flakes showed a linear dependent behavior against the magnetic field with a residual electron concentration of the order of ∼10{sup 21} cm{sup −3} at 5 K. The electron concentration n increases slightly as the thickness d decreases, possibly due to the CDW gap is reduced with the decrease of the thickness.

  9. High transition temperature superconductor/insulator bilayers for the development of ultra-fast electronics

    SciTech Connect

    Sirena, M.; Félix, L. Avilés; Haberkorn, N.

    2013-07-29

    High transition temperature superconductor (HTc)/SrTiO{sub 3} (STO) bilayers were fabricated by sputtering deposition on (100) STO substrates. Their transport and morphological properties were characterized using conductive atomic force microscopy. The STO barriers present good insulating properties, with long attenuation lengths (λ ∼ 1 nm) which reduce the junction resistance and increase the operating critical current. The samples present roughness values smaller than 1 nm, with an extremely low density of surface defects (∼5 × 10{sup −5} defects/μm{sup 2}). The high control of the barrier quality over large defect free surfaces is encouraging for the development of microelectronics devices based in HTc Josephson junctions.

  10. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    SciTech Connect

    Zhang, Wen; Zhou, Zhaofeng Zhong, Yuan; Zhang, Ting; Huang, Yongli; Sun, Changqing

    2015-11-15

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (T{sub N}) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the T{sub N} by adjusting the atomic cohesive energy. The T{sub N} is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the T{sub N} of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  11. Electrical detection of the temperature induced melting transition of a DNA hairpin covalently attached to gold interdigitated microelectrodes

    PubMed Central

    Brewood, Greg P.; Rangineni, Yaswanth; Fish, Daniel J.; Bhandiwad, Ashwini S.; Evans, David R.; Solanki, Raj; Benight, Albert S.

    2008-01-01

    The temperature induced melting transition of a self-complementary DNA strand covalently attached at the 5′ end to the surface of a gold interdigitated microelectrode (GIME) was monitored in a novel, label-free, manner. The structural state of the hairpin was assessed by measuring four different electronic properties of the GIME (capacitance, impedance, dissipation factor and phase angle) as a function of temperature from 25°C to 80°C. Consistent changes in all four electronic properties of the GIME were observed over this temperature range, and attributed to the transition of the attached single-stranded DNA (ssDNA) from an intramolecular, folded hairpin structure to a melted ssDNA. The melting curve of the self-complementary single strand was also measured in solution using differential scanning calorimetry (DSC) and UV absorbance spectroscopy. Temperature dependent electronic measurements on the surface and absorbance versus temperature values measured in solution experiments were analyzed assuming a two-state process. The model analysis provided estimates of the thermodynamic transition parameters of the hairpin on the surface. Two-state analyses of optical melting data and DSC measurements provided evaluations of the thermodynamic transition parameters of the hairpin in solution. Comparison of surface and solution measurements provided quantitative evaluation of the effect of the surface on the thermodynamics of the melting transition of the DNA hairpin. PMID:18628294

  12. THE ELECTRON TEMPERATURE OF THE SOLAR TRANSITION REGION AS DERIVED FROM EIS AND SUMER

    SciTech Connect

    Muglach, K.; Landi, E.; Doschek, G. A.

    2010-01-01

    We use UV and extreme-UV emission lines observed in quiet regions on the solar disk with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument and the Extreme Ultraviolet Imaging Spectrometer (EIS) to determine the electron temperature in solar transition region plasmas. Prominent emission lines of O IV and O VI are present in the solar spectrum, and the measured intensity line ratios provide electron temperatures in the range of log T = 5.6-6.1. We find that the theoretical O IV and O VI ion formation temperatures are considerably lower than our derived temperatures. The line ratios expected from a plasma in ionization equilibrium are larger by a factor of about 2-5 than the measured line ratios. A careful cross-calibration of SUMER and EIS has been carried out, which excludes errors in the relative calibration of the two instruments. We checked for other instrumental and observational effects, as well as line blending, and can exclude them as a possible source of the discrepancy between theoretical and observed line ratios. Using a multi-thermal quiet-Sun differential emission measure changes the theoretical line ratio by up to 28% which is not sufficient as an explanation. We also explored additional excitation mechanisms. Photoexcitation from photospheric blackbody radiation, self-absorption, and recombination into excited levels cannot be a possible solution. Adding a second Maxwellian to simulate the presence of non-thermal, high-energy electrons in the plasma distribution of velocities also did not solve the discrepancy.

  13. High-temperature nuclear magnetic resonance study of phase transition kinetics in LiNaSO{sub 4}

    SciTech Connect

    Shakhovoy, R. A. E-mail: r.a.shakhovoy@gmail.com; Sarou-Kanian, V.; Rakhmatullin, A.; Véron, E.; Bessada, C.

    2015-12-28

    A new high-temperature NMR technique for measurements of the phase transition kinetics in solids has been developed. The technique allows measuring the time evolution of the volume of the appearing phase at controlled cooling rates. Developed method was applied to study the phase transition kinetics in the superionic conductor LiNaSO{sub 4}. It was revealed that the phase transition in LiNaSO{sub 4} is governed by the diffusion-controlled growth of nuclei (“germs”). An effect of the crystallite rearrangement in the LiNaSO{sub 4} powder after cooling through the phase transition was also revealed. This effect was studied by means of high-temperature XRD and NMR.

  14. Use of dynamic mechanical analysis (DMA) to determine critical transition temperatures in frozen biomaterials intended for lyophilization.

    PubMed

    Gearing, John; Malik, Kiran P; Matejtschuk, Paul

    2010-08-01

    Dynamic mechanical analysis is widely used to determine glass transitions in solid state materials. However, here we demonstrate the application of DMA for the determination of glass transitions (Tg') in the frozen liquid state by means of a steel sample pocket. The use of the pocket allows frozen material to be analysed and glass transition events demonstrated. In addition, it allows weak glass transitions to be detected clearly in some complex formulations where they can be obscured by eutectic and other strong thermal events when other methods such as DSC or DTA are used. Classical excipients (trehalose, lactose, dextran) were analysed and shown to give reproducible Tg' values, though with values slightly higher than those obtained by DSC. Finally, several complex real biological materials, typical of those encountered when freeze drying biological and biopharmaceutical materials, were analysed and the potential value of DMA demonstrated to determine the relevant glass transition temperatures for use in cryobiology and freeze drying. PMID:20430020

  15. An unusual isotope effect in a high-transition-temperature superconductor

    SciTech Connect

    Gweon, G.-H.; Sasagawa, T.; Zhou, S.Y.; Graf, J.; Takagi, H.; Lee, D.-H.; Lanzara, A.

    2004-04-01

    In conventional superconductors, the electron pairing that allows superconductivity is caused by exchange of virtual phonons, which are quanta of lattice vibration. For high-transition-temperature (high-Tc) superconductors, it is far from clear that phonons are involved in the pairing at all. For example, the negligible change in Tc of optimally doped Bi2Sr2CaCu2O8 (Bi2212) upon oxygen isotope substitution (16O to 18O leads to Tc decreasing from 92 to 91 K) has often been taken to mean that phonons play an insignificant role in this material. Here we provide a detailed comparison of the electron dynamics of Bi2212 samples containing different oxygen isotopes, using angle-resolved photoemission spectroscopy. Our data show definite and strong isotope effects. Surprisingly, the effects mainly appear in broad high-energy humps, commonly referred to as ''incoherent peaks''. As a function of temperature and electron momentum, the magnitude of the isotope effect closely correlates with the superconducting gap--that is, the pair binding energy. We suggest that these results can be explained in a dynamic spin-Peierls picture, where the singlet pairing of electrons and the electron-lattice coupling mutually enhance each other.

  16. Low-temperature optical spectroscopy of single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Plechinger, Gerd; Nagler, Philipp; Schüller, Christian; Korn, Tobias

    In recent years, layered materials beyond graphene have attracted immense interest in the scientific community. Among those, particularly the semiconducting transition metal dichalcogenides (TMDCs) in their monolayer form are in the focus of the current research due to their intriguing optical properties and their potential application in valleytronic-based devices. The optical properties are governed by excitonic features, even at room temperature. The excitons in monolayer TMDCs have unusually large binding energies due to the two-dimensional carrier confinement and weak dielectric screening. Here, we investigate the photoluminescence spectra of monolayer TMDCs at low temperatures. We present clear evidence for the existence of biexcitons in monolayer WS2, exhibiting a superlinear behavior in excitation-power-dependent measurements. Applying a gate-voltage in a FET-configuration, we can identify charge-neutral and negatively charged excitons (trions) in the optical spectrum of different TMDCs. The trion binding energies range in the order of 30 meV. The evolution of the excitonic peaks under the application of external magnetic fields give further insight into the internal structure of these materials.

  17. Epitaxial growth of higher transition-temperature VO2 films on AlN/Si

    NASA Astrophysics Data System (ADS)

    Slusar, Tetiana; Cho, Jin-Cheol; Kim, Bong-Jun; Yun, Sun Jin; Kim, Hyun-Tak

    2016-02-01

    We report the epitaxial growth and the mechanism of a higher temperature insulator-to-metal-transition (IMT) of vanadium dioxide (VO2) thin films synthesized on aluminum nitride (AlN)/Si (111) substrates by a pulsed-laser-deposition method; the IMT temperature is TIMT ≈ 350 K. X-ray diffractometer and high resolution transmission electron microscope data show that the epitaxial relationship of VO2 and AlN is VO2 (010) ‖ AlN (0001) with VO2 [101] ‖ AlN [ 2 1 ¯ 1 ¯ 0 ] zone axes, which results in a substrate-induced tensile strain along the in-plane a and c axes of the insulating monoclinic VO2. This strain stabilizes the insulating phase of VO2 and raises TIMT for 10 K higher than TIMT single crystal ≈ 340 K in a bulk VO2 single crystal. Near TIMT, a resistance change of about four orders is observed in a thick film of ˜130 nm. The VO2/AlN/Si heterostructures are promising for the development of integrated IMT-Si technology, including thermal switchers, transistors, and other applications.

  18. Chiral phase transition in QED3 at finite temperature and impurity potential

    NASA Astrophysics Data System (ADS)

    Yin, Pei-Lin; Wei, Wei; Xiao, Hai-Xiao; Feng, Hong-Tao; Liu, Xiao-Jun; Zong, Hong-Shi

    2016-01-01

    In a realistic interacting system described by (2 +1 )-dimensional quantum electrodynamics (QED3 ), there is always a certain number of impurities by which fermions are scattered. In general, impurity scattering can generate a finite density of states at the Fermi level, which screens the temporal component of the gauge field. This effect is expected to weaken dynamical fermion mass generation. Within the Born approximation, by introducing a damping term in the energy component of the fermion propagator, the influences of finite temperature and impurity scattering on the chiral phase transition in QED3 are investigated. Pursuing this aim, we solve the Dyson-Schwinger equations for the fermion and boson propagators to the leading order in 1 /Nf expansion at zero frequency and then calculate the chiral condensate, the chiral susceptibility, and the thermal susceptibility within a range of the impurity scattering rates Γ and the numbers of fermion flavors Nf. It is found that impurity scattering leads to an obvious suppression of the dynamical fermion mass generation and critical temperature Tc.

  19. The biological stimuli for governing the phase transition temperature of the "smart" polymer PNIPAM in water.

    PubMed

    Umapathi, Reddicherla; Reddy, P Madhusudhana; Kumar, Awanish; Venkatesu, Pannuru; Chang, Chi-Jung

    2015-11-01

    A lack of sufficient knowledge regarding the behaviour of stimuli-responsive polymers to biological stimuli hinders the potential use of responsive polymers as biomaterials and medical devices. Hence, in this study, we demonstrate the impact of various globular proteins on the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) in an aqueous solution through the use of fluorescence spectroscopy, dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy and field-emission scanning electron microscopy (FESEM). Furthermore, we describe the molecular interaction of PNIPAM with proteins by the MolDock method. Our experimental and docking studies revealed that such proteins as α-chymotrypsin (CT), insulin (In) and haemoglobin (Hb) decreased the lower critical solution temperature (LCST) of the polymer, whereas succinyl-concanavalin A (SCA) increased the LCST of PNIPAM. The LCST changed upon increasing the concentration of protein from 0.5mg/mL to 1mg/mL. The thermoresponsive behaviour of PNIPAM can be significantly altered by the functional groups present in the protein. The findings of the present study can be used in the engineering of bioresponsive smart PNIPAM-based devices. PMID:26320570

  20. Structural transition in sputter-deposited amorphous germanium films by aging at ambient temperature

    NASA Astrophysics Data System (ADS)

    Okugawa, M.; Nakamura, R.; Ishimaru, M.; Watanabe, K.; Yasuda, H.; Numakura, H.

    2016-06-01

    The structure of amorphous Ge (a-Ge) films prepared by sputter-deposition and the effects of aging at ambient temperature and pressure were studied by pair-distribution-function (PDF) analysis from electron scattering and molecular dynamics simulations. The PDFs of the as-deposited and aged samples for 3-13 months showed that the major peaks for Ge-Ge bonds decrease in intensity and broaden with aging for up to 7 months. In the PDFs of a-Ge of molecular dynamics simulation obtained by quenching liquid at different rates, the major peak intensities of a slowly cooled model are higher than those of a rapidly cooled model. Analyses on short- and medium-range configurations show that the slowly cooled model includes a certain amount of medium-range ordered (MRO) clusters, while the rapidly cooled model includes liquid-like configurations rather than MRO clusters. The similarity between experimental and computational PDFs implies that as-deposited films are similar in structure to the slowly cooled model, whereas the fully aged films are similar to the rapidly cooled model. It is assumed that as they undergo room-temperature aging, the MRO clusters disintegrate and transform into liquid-like regions in the same matrix. This transition in local configurations is discussed in terms of instability and the non-equilibrium of nanoclusters produced by a vapor-deposition process.

  1. Temperature-Induced Irreversible Phase Transition From Perovskite to Diamond But Pressure-Driven Back-Transition in an Ammonium Copper Formate.

    PubMed

    Shang, Ran; Chen, Sa; Wang, Bing-Wu; Wang, Zhe-Ming; Gao, Song

    2016-02-01

    The compound [CH3 CH2 NH3][Cu(HCOO)3] undergoes a phase transition at 357 K, from a perovskite to a diamond structure, by heating. The backward transition can be driven by pressure at room temperature but not cooling under ambient or lower pressure. The rearrangement of one long copper-formate bond, the switch of bridging-chelating mode of the formate, the alternation of N-H⋅⋅⋅O H-bonds, and the flipping of ethylammonium are involved in the transition. The strong N-H⋅⋅⋅O H-bonding probably locks the metastable diamond phase. The two phases display magnetic and electric orderings of different characters. PMID:26709724

  2. Characterization of polycrystalline VO2 thin film with low phase transition temperature fabricated by high power impulse magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen

    2016-04-01

    VO2 is a unique material that undergoes a reversible phase transformation around 68∘C. Currently, applications of VO2 on smart windows are limited by its high transition temperature. In order to reduce the temperature, VO2 thin film was fabricated on quartz glass substrate by high power impulse magnetron sputtering with a modulated pulsed power. The phase transition temperature has been reduced to as low as 32∘C. In addition, the VO2 film possesses a typical metal-insulator transition. X-ray diffraction and selected area electron diffraction patterns reveal that an obvious lattice distortion has been formed in the as-deposited polycrystalline VO2 thin film. X-ray photoelectron spectroscopy proves that oxygen vacancies have been formed in the as-deposited thin film, which will induce a lattice distortion in the VO2 thin film.

  3. Size Dependence of a Temperature-Induced Solid-Solid Phase Transition in Copper(I) Sulfide

    SciTech Connect

    Rivest, Jessy B; Fong, Lam-Kiu; Jain, Prashant K; Toney, Michael F; Alivisatos, A Paul

    2011-07-24

    Determination of the phase diagrams for the nanocrystalline forms of materials is crucial for our understanding of nanostructures and the design of functional materials using nanoscale building blocks. The ability to study such transformations in nanomaterials with controlled shape offers further insight into transition mechanisms and the influence of particular facets. Here we present an investigation of the size-dependent, temperature-induced solid-solid phase transition in copper sulfide nanorods from low- to high-chalcocite. We find the transition temperature to be substantially reduced, with the high chalcocite phase appearing in the smallest nanocrystals at temperatures so low that they are typical of photovoltaic operation. Size dependence in phase trans- formations suggests the possibility of accessing morphologies that are not found in bulk solids at ambient conditions. These other- wise-inaccessible crystal phases could enable higher-performing materials in a range of applications, including sensing, switching, lighting, and photovoltaics.

  4. Superfluid transition temperature across the BCS-BEC crossover induced by a synthetic non-Abelian gauge field

    NASA Astrophysics Data System (ADS)

    Vyasanakere, Jayanth P.; Shenoy, Vijay B.

    2013-03-01

    A non-Abelian gauge field that induces a spin-orbit coupling on the motion of fermions engenders a BCS-BEC crossover even for weakly attracting fermions. The transition temperature at large spin-orbit coupling is known to be determined by the mass of the emergent boson - the rashbon. We obtain the transition temperature of the system as a function of the spin-orbit coupling by constructing and studying a Gaussian fluctuation (Nozieres-Schmitt-Rink) theory. These results will help guide the upcoming experiments on spin-orbit coupled fermions. In addition, this work suggests a route to enhance the transition temperature of a weakly attracting fermionic system by tuning the spin-orbit coupling. Work supported by CSIR, DST, DAE India

  5. The impact of room temperature polymorphism in K doped NaTaO3 on structural phase transition behaviour

    NASA Astrophysics Data System (ADS)

    Arulnesan, Shamanthini William; Kayser, Paula; Kennedy, Brendan J.; Knight, Kevin S.

    2016-06-01

    Temperature dependent high resolution neutron diffraction studies demonstrate that the sequence and temperatures of the crystallographic phase transitions in NaTaO3 are not impacted by doping with 1% K to form Na0.99K0.01TaO3. Rietveld analysis of the neutron diffraction data shows the structural transitions to be: Pbnm ↔ 723       K Cmcm ↔ 803   K P 4 / nbm ↔ 893   K Pm 3 bar m . The two orthorhombic polymorphs, Pbnm and Cmcm, differ fundamentally in the distortion and tilting of the octahedra, such that they cannot be obtained from each other via a continuous phase transition resulting in their co-existence between RT and 723 K. Chemical doping, does however, dramatically impact on the amount of the metastable Cmcm phase observed at room temperature.

  6. Thermal diffusivity of spinels at elevated temperature: implications for heat transfer in the transition zone

    NASA Astrophysics Data System (ADS)

    Hofmeister, A. M.

    2006-12-01

    The dependence of the vibrational component of thermal diffusivity (D) of spinel-family minerals on chemical composition, disorder, and temperature (T) is discerned using laser-flash measurements of single-crystals up to 1850 K, and used along with data on garnets and radiative transfer calculations to constrain heat transport in Earth's transition zone (TZ). Laser-flash analysis lacks the systematic errors associated with conventional methods, namely, corruption with radiative transfer, and thermal contact losses. Chemical compositions are synthetic disordered spinel, 4 natural samples near MgAl2O4; 4 natural hercynites (Mg,Fe,Al)3O4], nearly ZnAl2O4, and 2 magnetites [Fe3O4]. The magnetic transition is manifest as a lambda curve in 1/D, but otherwise, 1/D is described by low-order polynomial fits with temperature. Ordered, MgAl2O4 has D(298K) = 7.78 mm2/s, which should approximate that of γ-Mg2SiO4. At 298 K, D decreases strongly as cation substitution or Mg-Al disorder increases: D(298K) for ringwoodite is estimated as 5.8 mm2/s. However, above 1400 K, D becomes constant: this limit (Dsat=0.70-1.07 mm2/s) weakly depends on composition and disorder and is analogous to the Dulong-Petit limit in heat capacity (Cp). Mantle garnets have Dsat=0.65 mm2/s (Hofmeister 2006 Phys Chem Min.). To obtain TZ values, we use d(lnD)/dP= (4γth 2/3)KT, literature data on bulk modulus and thermal Gruneisen parameter, density from PREM, and Cp=1.3 J/g-K, which depends weakly on composition, T, and P. Average thermal conductivity (k)in the TZ is 5-6 W/m-K, depending on garnet proportion, and increase with P. Radiative transfer provides ca 1 W/m-K, depending on Fe content and grain-size (Hofmeister 2005 J. Geodyn.). Our estimate of large k = 6-7 W/m-K is twice recent estimates, and is a consequence of phonon saturation revealed by laser-flash measurements. Efficient vibrational transport of heat in the TZ and deeper stabilizes against convection, as does the positive temperature

  7. Fine tuning the color-transition temperature of thermoreversible polydiacetylene/zinc oxide nanocomposites: The effect of photopolymerization time.

    PubMed

    Traiphol, Nisanart; Faisadcha, Kunruethai; Potai, Ruttayapon; Traiphol, Rakchart

    2015-02-01

    An ability to control the thermochromic behaviors of polydiacetylene (PDA)-based materials is very important for their utilization. Recently, our group has developed the PDA/zinc oxide (ZnO) nanocomposites, which exhibit reversible thermochromism (Traiphol et al., 2011). In this study, we present our continuation work demonstrating a rather simple method for fine tuning their color-transition temperature. The PDA/ZnO nanocomposites are prepared by varying photopolymerization time, which in turn affects the length of PDA conjugated backbone. We have found that the increase of photopolymerization time from 1 to 120min results in systematically decrease of the color-transition temperature from about 85 to 40°C. These PDA/ZnO nanocomposites still exhibit reversible thermochromism. The PDA/ZnO nanocomposites embedded in polyvinyl alcohol films show two-step color-transition processes, the reversible blue to purple and then irreversible purple to orange. Interestingly, the increase of photopolymerization time causes an increase of the irreversible color-transition temperature. Our method is quite simple and cheap, which can provide a library of PDA-based materials with controllable color-transition temperature. PMID:25463181

  8. Garnet-to-perovskite transition in Gd3Sc2Ga3O12 at high pressure and high temperature.

    PubMed

    Lin, Chuanlong; Liu, Jing; Lin, Jung-Fu; Li, Xiaodong; Li, Yanchun; Zhang, Qingli; Xiong, Lun; Li, Rui

    2013-01-01

    The structural phase transition of gadolinium-scandium-gallium garnet (Gd(3)Sc(2)Ga(3)O(12), GSGG) has been studied at high pressure and high temperature using the synchrotron X-ray diffraction technique in a laser-heated diamond anvil cell. The GSGG garnet transformed to an orthorhombic perovskite structure at approximately 24 GPa after laser heating to 1500-2000 K. The garnet-to-perovskite phase transition is associated with an ∼8% volume reduction and an increase in the coordination number of the Ga(3+) or Sc(3+) ion. The orthorhombic perovskite GSGG has bulk modulus B(0) = 194(15) GPa with B(0)' = 5.3(8), exhibiting slightly less compression than the cubic garnet structure of GSGG with B(0) = 157(15) GPa and B(0)' = 6.5(10). Upon compression at room temperature, the cubic GSGG garnet became amorphous at ∼65 GPa. Coupled with the amorphous-to-perovskite phase transition in Y(3)Fe(5)O(12) and Gd(3)Ga(5)O(12) at high-pressure-temperature conditions, we conclude that amorphization should represent a new thermodynamic state resulting from hindrance of the garnet-to-perovskite phase transition, whereas the garnet-to-amorphous transition in rare-earth garnets should be kinetically hindered at room temperature. PMID:23240758

  9. Temperature-Modulated Ellipsometry in Vacuum: A New Tool for Probing Glass Transition in Thin Supported Polymer Films

    NASA Astrophysics Data System (ADS)

    Efremov, Mikhail; Soofi, Shauheen; Kiyanova, Anna; Cerrina, Franco; Nealey, Paul

    2009-03-01

    Observation of glass transition in thin polymer films is a good example of experimental challenges that measurements at the nanoscale may present. The standard technique in the field, ellipsometry, has been advanced by state-of-the-art approaches: measurements in vacuum and temperature modulation. Glass transition in 5 -- 200 nm thick spin-cast polystyrene (PS) and poly(methyl methacrylate) (PMMA) films on silicon has been studied at 10-6 -- 10-8 torr residual gas pressure, using both linear and modulated temperature scans [1, 2]. A well-defined glass transition in 5 nm thick PS and 10 nm thick PMMA films is observed. Factors that can alter glass transition temperature assignment will be discussed. Residual gas can affect data even at the pressures mentioned above [1]. An ionization gauge, the standard vacuum equipment, causes sample deterioration [1]. Temperature modulation effectively separates reversible glass transition from accompanying irreversible processes [2]. [1]. M. Yu. Efremov, S. S. Soofi, A. V. Kiyanova, C. J. Munoz, P. Burgardt, F. Cerrina, and P. F. Nealey, Rev. Sci. Instr., 79, 043903 (2008). [2]. M. Yu. Efremov, A. V. Kiyanova, and P. F. Nealey, Macromolecules, 41, 5978 (2008).

  10. Effect of sugar addition on glass transition temperatures of cassava starch with low to intermediate moisture contents.

    PubMed

    Figueroa, Yetzury; Guevara, Marvilan; Pérez, Adriana; Cova, Aura; Sandoval, Aleida J; Müller, Alejandro J

    2016-08-01

    This work studies how sucrose (S) addition modifies the thermal properties of cassava starch (CS). Neat CS and CS-S blends with 4, 6 and 8% sugar contents (CS-S-4%, CS-S-6% and CS-S-8%) were prepared and analyzed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA), in a wide range of moisture levels (2-20%). In equilibrated samples with moisture contents lower than 10%, twoendothermic steps were observed during first DSC heating scans and two corresponding relaxation maxima in tan δ were detected by DMTA. The first transition, detected at around 45-55°C by both DSC and DMTA, is frequently found in starchy foods, while the second observed at higher temperatures is associated to the glass transition temperature of the blends. At higher moisture contents, only one thermal transition was observed. Samples analyzed immediately after cooling from the melt (i.e., after erasing their thermal history), exhibited a single glass transition temperature, regardless of their moisture content. Addition of sugar promotes water plasticization of CS only at high moisture contents. In the low moisture content range, anti-plasticization was observed for both neat and sugar-added CS samples. Addition of sugar decreases the moisture content needed to achieve the maximum value of the glass transition temperature before plasticization starts. The results of this work may be valuable for the study of texture establishment in low moisture content extruded food products. PMID:27112870

  11. M(5)-silicon (M= titanium, niobium, molybdenum) based transition-metal silicides for high temperature applications

    NASA Astrophysics Data System (ADS)

    Tang, Zhihong

    2007-12-01

    Transition metal silicides are being considered for future engine turbine components at temperatures up to 1600ºC. Although significant improvement in high temperature strength, room temperature fracture toughness has been realized in the past decade, further improvement in oxidation resistance is needed. Oxidation mechanism of Ti5Si3-based alloys was investigated. Oxidation behavior of Ti5Si3-based alloy strongly depends on the atmosphere. Presence of Nitrogen alters the oxidation behavior of Ti5Si3 by nucleation and growth of nitride subscale. Ti5Si3.2 and Ti5Si3C0.5 alloys exhibited an excellent oxidation resistance in nitrogen bearing atmosphere due to limited dissolution of nitrogen and increased Si/Ti activity ratio. MoSi2 coating developed by pack cementation to protect Mo-based Mo-Si-B composites was found to be effective up to 1500ºC. Shifting coating composition to T1+T2+Mo3Si region showed the possibility to extend the coating lifetime above 1500ºC by more than ten times via formation of slow growing Mo3Si or T2 interlayer without sacrificing the oxidation resistance of the coating. The phase equilibria in the Nb-rich portion of Nb-B system has been evaluated experimentally using metallographic analysis and differential thermal analyzer (DTA). It was shown that Nbss (solid solution) and NbB are the only two primary phases in the 0-40 at.% B composition range, and the eutectic reaction L ↔ Nbss + NbB was determined to occur at 2104+/-5°C by DTA.

  12. [AFM fishing of proteins under impulse electric field].

    PubMed

    Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

    2016-05-01

    A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell. PMID:27562998

  13. The effect of initial temperature on flame acceleration and deflagration-to-detonation transition phenomenon

    SciTech Connect

    Ciccarelli, G.; Boccio, J.L.; Ginsberg, T.; Finfrock, C.; Gerlach, L.; Tagawa, H.; Malliakos, A.

    1998-05-01

    The High-Temperature Combustion Facility at BNL was used to conduct deflagration-to-detonation transition (DDT) experiments. Periodic orifice plates were installed inside the entire length of the detonation tube in order to promote flame acceleration. The orifice plates are 27.3-cm-outer diameter, which is equivalent to the inner diameter of the tube, and 20.6-cm-inner diameter. The detonation tube length is 21.3-meters long, and the spacing of the orifice plates is one tube diameter. A standard automobile diesel engine glow plug was used to ignite the test mixture at one end of the tube. Hydrogen-air-steam mixtures were tested at a range of temperatures up to 650K and at an initial pressure of 0.1 MPa. In most cases, the limiting hydrogen mole fraction which resulted in DDT corresponded to the mixture whose detonation cell size, {lambda}, was equal to the inner diameter of the orifice plate, d (e.g., d/{lambda}=1). The only exception was in the dry hydrogen-air mixtures at 650K where the DDT limit was observed to be 11 percent hydrogen, corresponding to a value of d/{lambda} equal to 5.5. For a 10.5 percent hydrogen mixture at 650K, the flame accelerated to a maximum velocity of about 120 mIs and then decelerated to below 2 mIs. By maintaining the first 6.1 meters of the vessel at the ignition end at 400K, and the rest of the vessel at 650K, the DDT limit was reduced to 9.5 percent hydrogen (d/{lambda}=4.2). This observation indicates that the d/{lambda}=1 DDT limit criteria provides a necessary condition but not a sufficient one for the onset of DDT in obstacle laden ducts. In this particular case, the mixture initial condition (i.e., temperature) resulted in the inability of the mixture to sustain flame acceleration to the point where DDT could occur. It was also observed that the distance required for the flame to accelerate to the point of detonation initiation, referred to as the run-up distance, was found to be a function of both the hydrogen mole fraction

  14. BOREAS AFM-6 Boundary Layer Height Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  15. BOREAS AFM-06 Mean Wind Profile Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Administration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides wind profiles at 38 heights, containing the variables of wind speed; wind direction; and the u-, v-, and w-components of the total wind. The data are stored in tabular ASCII files. The mean wind profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  16. Temperature-Induced Aggregate Transitions in Mixtures of Cationic Ammonium Gemini Surfactant with Anionic Glutamic Acid Surfactant in Aqueous Solution.

    PubMed

    Ji, Xiuling; Tian, Maozhang; Wang, Yilin

    2016-02-01

    The aggregation behaviors of the mixtures of cationic gemini surfactant 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol (C12C4(OH)2C12Br2) and anionic amino acid surfactant N-dodecanoylglutamic acid (C12Glu) in aqueous solution of pH = 10.0 have been studied. The mixture forms spherical micelles, vesicles, and wormlike micelles at 25 °C by changing mixing ratios and/or total surfactant concentration. Then these aggregates undergo a series of transitions upon increasing the temperature. Smaller spherical micelles transfer into larger vesicles, vesicles transfer into solid spherical aggregates and then into larger irregular aggregates, and entangled wormlike micelles transfer into branched wormlike micelles. Moreover, the larger irregular aggregates and branched micelles finally lead to precipitation and clouding phenomenon, respectively. All these transitions are thermally reversible, and the transition temperatures can be tuned by varying the mixing ratios and/or total concentration. These temperature-dependent aggregate transitions can be elucidated on the basis of the temperature-induced variations in the dehydration, electrostatic interaction, and hydrogen bonds of the headgroup area and in the hydrophobic interaction between the hydrocarbon chains. The results suggest that the surfactants carrying multiple binding sites will greatly improve the regulation ability and temperature sensitivity. PMID:26750978

  17. Physical properties of FeRh alloys: The antiferromagnetic to ferromagnetic transition

    NASA Astrophysics Data System (ADS)

    Kudrnovský, J.; Drchal, V.; Turek, I.

    2015-01-01

    The electronic, magnetic, thermodynamical, and transport properties of FeRh alloys are studied from first principles. We present a unified approach to the phase stability, an estimate of exchange interactions in various magnetic phases, and transport properties including the effect of temperature which are all based on the same electronic-structure model. Emphasis is put on the transition between the ferromagnetic (FM) and antiferromagnetic (AFM) phases. Such a study is motivated by a recent suggestion of FeRh as a room-temperature antiferromagnetic memory resistor. The theory predicts the order-disorder transformation from the hypothetical disordered bcc phase into ordered B2 phase. Comparison of exchange interactions in the magnetically ordered FM and AFM phases with corresponding spin-disordered counterparts allows us to identify relevant interactions which are precursors of magnetically ordered phases. The most important result is the explanation of a dramatic decrease of the resistivity accompanying the AFM to FM phase transition which is due to the spin disorder present in the system. The study of the anisotropic magnetoresistance in the AFM phase found recently experimentally is extended also to finite temperatures.

  18. The mechanism of lamellar-to-inverted hexagonal phase transitions: a study using temperature-jump cryo-electron microscopy.

    PubMed Central

    Siegel, D P; Green, W J; Talmon, Y

    1994-01-01

    The lamellar/inverted hexagonal (L alpha/HII) phase transition can be very fast, despite the drastic change in the topology of the lipid/water interfaces. The first structures to form in this transition may be similar to those that mediate membrane fusion in many lipid systems. To study the transition mechanism and other dynamic phenomena in membrane dispersions, we constructed an apparatus to rapidly trigger the transition and then vitrify the specimens to preserve the structure of transient intermediates. The apparatus applies millisecond-long temperature jumps of variable size to aqueous dispersions of lipids on electron microscope grids at times 9-16 ms before specimen vitrification. The vitrified specimens are then examined by cryo-transmission electron microscopy. Dispersions of egg phosphatidylethanolamine completed the transition within 9 ms when superheated by 20 K. Similar transition times have been observed in dioleoylphosphatidylethanolamine via time-resolved x-ray diffraction. N-monomethylated dioleoylphosphatidylethanolamine dispersions superheated to lesser extent exhibited slower transitions and more complex morphology. The structure of the first intermediates to form in the transition process could not be determined, probably because the intermediates are labile on the time scale of sample cooling and vitrification (< 1 ms) and because of the poor contrast developed by some of these small structures. However, the results are more compatible with a transition mechanism based on "stalk" intermediates than a mechanism involving inverted micellar intermediates. Temperature-jump cryo-transmission electron microscopy should be useful in studying dynamic phenomena in biomembranes, large protein complexes, and other colloidal dispersions. It should be especially helpful in studying the mechanism of protein-induced membrane fusion. Images FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 10 PMID:8161694

  19. AFM CHARACTERIZATION OF RAMAN LASER INDUCED DAMAGE ON CDZNTECRYSTAL SURFACES

    SciTech Connect

    Teague, L.; Duff, M.

    2008-10-07

    High quality CdZnTe (or CZT) crystals have the potential for use in room temperature gamma-ray and X-ray spectrometers. Over the last decade, the methods for growing high quality CZT have improved the quality of the produced crystals however there are material features that can influence the performance of these materials as radiation detectors. The presence of structural heterogeneities within the crystals, such as twinning, pipes, grain boundaries (polycrystallinity), and secondary phases (SPs) can have an impact on the detector performance. There is considerable need for reliable and reproducible characterization methods for the measurement of crystal quality. With improvements in material characterization and synthesis, these crystals may become suitable for widespread use in gamma radiation detection. Characterization techniques currently utilized to test for quality and/or to predict performance of the crystal as a gamma-ray detector include infrared (IR) transmission imaging, synchrotron X-ray topography, photoluminescence spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. In some cases, damage caused by characterization methods can have deleterious effects on the crystal performance. The availability of non-destructive analysis techniques is essential to validate a crystal's quality and its ability to be used for either qualitative or quantitative gamma-ray or X-ray detection. The work presented herein discusses the damage that occurs during characterization of the CZT surface by a laser during Raman spectroscopy, even at minimal laser powers. Previous Raman studies have shown that the localized annealing from tightly focused, low powered lasers results in areas of higher Te concentration on the CZT surface. This type of laser damage on the surface resulted in decreased detector performance which was most likely due to increased leakage current caused by areas of higher Te concentration. In this study

  20. On-Orbit Measurement of the Superconductive Transition Temperatures of YBa2Cu3O(7-x) Thick Films

    NASA Technical Reports Server (NTRS)

    Hooker, Matthew W.

    1997-01-01

    Thick film superconductors were integrated into hybrid circuits and tested in the Materials In Devices As Superconductors (MIDAS) spaceflight experiment which operated autonomously aboard the MIR space station for 90 days. MIDAS was designed to cool the circuits from 300 to 75K, maintain the temperature at 75K for 28 days, and warm the circuits back to 300K. This cycle was performed a total of three times, during which the superconductive transition temperature was measured during each cool-down and warm-up portion of the experiment. All of the thick films used in this experiment exhibited superconductive transition temperatures of approximately 87K, and no significant differences in the resistance versus temperature properties of the materials were observed among the data collected during pre-flight, flight, and post-flight operations.

  1. Influence of the calcining temperature on the superconducting transition and critical current of Y-Ba-Cu-oxide compound

    NASA Astrophysics Data System (ADS)

    Lee, H. K.; Kwon, H. C.; Kim, I. S.; Park, J. C.

    1988-01-01

    Superconducting transition and critical current of a Y-Ba-Cu-oxide compound prepared by ceramic technique have been studied for the samples which have the same nominal composition and sintering conditions, while systematically varying the calcining temperature from 850 to 1000 °C. It was observed that the shape of the superconducting transition in resistivity measurement markedly depends on the calcining temperature. All samples showed metallic behavior in normal state and samples which have lower resistivity showed higher critical current density. The resistivity just above onset temperature decreased with increasing the calcining temperature up to 950 °C, but above 975 °C the opposite behavior was observed. This behavior was discussed in connection with x-ray diffraction patterns of the samples.

  2. Monte Carlo Comparisons to a Cryogenic Dark Matter Search Detector with Low Transition-Edge-Sensor Transition Temperature

    SciTech Connect

    Leman, S.W.; McCarthy, K.A.; Brink, P.L.; Cabrera, B.; Cherry, M.; Silva, E.Do Couto E; Figueroa-Feliciano, E.; Kim, P.; Mirabolfathi, N.; Pyle, M.; Resch, R.; Sadoulet, B.; Serfass, B.; Sundqvist, K.M.; Tomada, A.; Young, B.A.; /Santa Clara U.

    2012-06-05

    We present results on phonon quasidiffusion and Transition Edge Sensor (TES) studies in a large, 3-inch diameter, 1-inch thick [100] high purity germanium crystal, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare calibration data with results from a Monte Carlo which includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels. The phonon energy is then parsed into TES based phonon readout channels and input into a TES simulator.

  3. Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

    2015-01-01

    Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.

  4. Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

    PubMed Central

    Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

    2015-01-01

    Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality. PMID:25600001

  5. Equation of state and Kosterlitz-Thouless transition temperature in two-dimensional Fermi gases: An analytical approach

    NASA Astrophysics Data System (ADS)

    Klawunn, Michael

    2016-08-01

    We study Fermi gases in two dimensions at low temperatures with attractive interactions. Analytic results are derived for the equation of state and the Kosterlitz-Thouless transition temperature as functions of the two-body binding energy and the density of the gas. Our results for the equation of state and the pressure of the gas strongly deviate from the mean field predictions. However, they are in reasonable agreement with Monte-Carlo calculations and recent experiments with cold atomic gases.

  6. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature.

    PubMed

    Yin, Qiuzhen

    2013-02-14

    Glacial-interglacial cycles characterized by long cold periods interrupted by short periods of warmth are the dominant feature of Pleistocene climate, with the relative intensity and duration of past and future interglacials being of particular interest for civilization. The interglacials after 430,000 years ago were characterized by warmer climates and higher atmospheric concentrations of carbon dioxide than the interglacials before, but the cause of this climatic transition (the so-called mid-Brunhes event (MBE)) is unknown. Here I show, on the basis of model simulations, that in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic bottom water formation and Southern Ocean ventilation. My results also show that strong westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and by changes in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward systematic difference in the astronomical parameters between the interglacials before and after 430,000 years ago. Rather than being a real 'event', the apparent MBE seems to have resulted from a series of individual interglacial responses--including notable exceptions to the general pattern--to various combinations of insolation conditions. Consequently, assuming no anthropogenic interference, future interglacials may have pre- or post-MBE characteristics without there being a systematic change in forcings. These findings are a first step towards understanding the magnitude change of the interglacial carbon dioxide concentration around 430

  7. Glass-Transition Temperature Profile Measured in a Wood Cell Wall Using Scanning Thermal Expansion Microscope (SThEM)

    NASA Astrophysics Data System (ADS)

    Antoniow, J. S.; Maigret, J.-E.; Jensen, C.; Trannoy, N.; Chirtoc, M.; Beaugrand, J.

    2012-11-01

    This study aims to assess the in situ spatial distribution of glass-transition temperatures ( T g) of the main lignocellulosic biopolymers of plant cell walls. Studies are conducted using scanning thermal expansion microscopy to analyze the cross-section of the cell wall of poplar. The surface topography is mapped over a range of probe-tip temperatures to capture the change of thermal expansion on the sample surface versus temperature. For different temperature values chosen between 20 °C and 250 °C, several quantitative mappings were made to show the spatial variation of the thermal expansion. As the glass transition affects the thermal expansion coefficient and elastic modulus considerably, the same data line of each topography image was extracted to identify specific thermal events in their topographic evolution as a function of temperature. In particular, it is shown that the thermal expansion of the contact surface is not uniform across the cell wall and a profile of the glass-transition temperature could thus be evidenced and quantified corresponding to the mobility of lignocellulosic polymers having a role in the organization of the cell wall structures.

  8. Study on the effect of transition curve to the dynamic characteristics of high-temperature superconducting maglev

    NASA Astrophysics Data System (ADS)

    Qian, Nan; Zheng, Botian; Gou, Yanfeng; Chen, Ping; Zheng, Jun; Deng, Zigang

    2015-12-01

    High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary.

  9. Measuring the glass transition temperature of EPDM roofing materials: Comparison of DMA, TMA, and DSC techniques

    SciTech Connect

    Paroli, R.M.; Penn, J.

    1994-09-01

    Two ethylene-propylene-diene monomer (EPDM) roofing membranes were aged at 100 C for 7 and 28 days. The T{sub g} of these membranes was then determined by dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), and differential scanning calorimetry (DSC) and the results compared. It was found that: (1) T{sub g} data can be obtained easily using the DMA and TMA techniques. The DSC method requires greater care due to the broad step change in the baseline which is associated with heavily plasticized materials. (2) The closest correspondence between techniques was for TMA and DSC (half-height). The latter, within experimental error, yielded the same glass transition temperature before and after heat-aging. (3) The peak maxima associated with tan{delta} and E{double_prime} measurements should be cited with T{sub g} values as significant differences can exist. (4) The T{sub g}(E{double_prime}) values were closer to the T{sub g}(TMA) and T{sub g}(DSC) data than were the T{sub g}(tan{delta}) values. Data obtained at 1 Hz (or possibly less) should be used when making comparisons based on various techniques. An assessment of T{sub g} values indicated that EPDM 112 roofing membrane is more stable than the EPDM 111 membrane. The T{sub g} for EPDM 112 did not change significantly with heat-aging for 28 days at 130 C.

  10. Study of glass transition temperature (Tg) of novel stress-sensitive composites using molecular dynamic simulation

    NASA Astrophysics Data System (ADS)

    Koo, B.; Liu, Y.; Zou, J.; Chattopadhyay, A.; Dai, L. L.

    2014-09-01

    This study investigates the glass transition temperature (Tg) of novel stress-sensitive composites capable of detecting a damage precursor using molecular dynamics (MD) simulations. The molecular structures of a cross-linked epoxy network (which consist of epoxy resin, hardener and stress-sensitive material) have been simulated and experimentally validated. The chemical constituents of the molecular structures are di-glycidyl ether of bisphenol F (DGEBF: epoxy resin), di-ethylene tri-amine (DETA: hardener) and tris-(cinnamoyloxymethyl)-ethane (TCE: stress-sensitive material). The cross-linking degree is varied by manipulating the number of covalent bonds through tuning a cutoff distance between activated DGEBF and DETA during the non-equilibrium MD simulation. A relationship between the cross-linking degree and Tgs has been studied numerically. In order to validate a proposed MD simulation framework, MD-predicted Tgs of materials used in this study have been compared to the experimental results obtained by the differential scanning calorimetry (DSC). Two molecular models have been constructed for comparative study: (i) neat epoxy (epoxy resin with hardener) and (ii) smart polymer (neat epoxy with stress-sensitive material). The predicted Tgs show close agreement with the DSC results.

  11. Length Scales of Local Glass Transition Temperature Gradients Near Soft and Hard Polymer-Polymer Interfaces

    NASA Astrophysics Data System (ADS)

    Baglay, Roman; Roth, Connie

    Polymer-polymer interfaces are ubiquitous in polymer blends and block copolymers, while opening up another avenue for the study of interfacial perturbations to the local glass transition temperature Tg(z). We have previously reported the full local Tg(z) profile across a glassy-rubbery polymer interface between polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA), an 80 K difference in bulk Tg [Baglay & Roth, J Chem Phys 2015, 143, 111101]. By using local fluorescence measurements, we revealed how the Tg(z) profile extends hundreds of nanometers away from the interface showing an asymmetric behavior penetrating deeper into the glassy PS side relative to the composition profile. Here, we extend these measurements to investigate how the local Tg profile in PS varies when in contact with a variety of immiscible polymers whose Tgs vary between +90 K and -80 K relative to the bulk Tg of PS, so-called hard vs. soft confinement. The data reveal that the onset of local Tg deviation from bulk in PS occurs at two distinct length scales, which depend on whether PS is the low Tg component (hard confinement) or the high Tg component (soft confinement). In addition, we explore the influence of finite system size on the range of dynamics by the introduction of periodic boundary conditions, as is commonly encountered in computer simulations or block copolymer systems.

  12. Using Combined Computational Techniques to Predict the Glass Transition Temperatures of Aromatic Polybenzoxazines

    PubMed Central

    Mhlanga, Phumzile; Wan Hassan, Wan Aminah; Hamerton, Ian; Howlin, Brendan J.

    2013-01-01

    The Molecular Operating Environment software (MOE) is used to construct a series of benzoxazine monomers for which a variety of parameters relating to the structures (e.g. water accessible surface area, negative van der Waals surface area, hydrophobic volume and the sum of atomic polarizabilities, etc.) are obtained and quantitative structure property relationships (QSPR) models are formulated. Three QSPR models (formulated using up to 5 descriptors) are first used to make predictions for the initiator data set (n = 9) and compared to published thermal data; in all of the QSPR models there is a high level of agreement between the actual data and the predicted data (within 0.63–1.86 K of the entire dataset). The water accessible surface area is found to be the most important descriptor in the prediction of Tg. Molecular modelling simulations of the benzoxazine polymer (minus initiator) carried out at the same time using the Materials Studio software suite provide an independent prediction of Tg. Predicted Tg values from molecular modelling fall in the middle of the range of the experimentally determined Tg values, indicating that the structure of the network is influenced by the nature of the initiator used. Hence both techniques can provide predictions of glass transition temperatures and provide complementary data for polymer design. PMID:23326419

  13. Terbium-Doped VO2 Thin Films: Reduced Phase Transition Temperature and Largely Enhanced Luminous Transmittance.

    PubMed

    Wang, Ning; Duchamp, Martial; Dunin-Borkowski, Rafal E; Liu, Shiyu; Zeng, XianTing; Cao, Xun; Long, Yi

    2016-01-26

    Vanadium dioxide (VO2) is a well-known thermochromic material with large IR modulating ability, promising for energy-saving smart windows. The main drawbacks of VO2 are its high phase transition temperature (τ(c) = 68°C), low luminous transmission (T(lum)), and weak solar modulating ability (ΔT(sol)). In this paper, the terbium cation (Tb(3+)) doping was first reported to reduce τ(c) and increase T(lum) of VO2 thin films. Compared with pristine VO2, 2 at. % doping level gives both enhanced T(lum) and ΔT(sol) from 45.8% to 54.0% and 7.7% to 8.3%, respectively. The T(lum) increases with continuous Tb(3+) doping and reaches 79.4% at 6 at. % doping level, representing ∼73.4% relative increment compared with pure VO2. This has surpassed the best reported doped VO2 thin films. The enhanced thermochromic properties is meaningful for smart window applications of VO2 materials. PMID:26729057

  14. Ordering of p-n-alkoxybenzoic acids at phase transition temperatures: a comparative computational analysis.

    PubMed

    Ajeetha, Narayanan; Ojha, Durga Prasad; Pisipati, Venkata Gopala Krishna Murthy

    2006-01-01

    A comparative analysis of molecular ordering of nematogenic p-n-alkoxybenzoic acids has been carried out with respect to translatory and orientational motions for the acids with seven (7OBAC), eight (8OBAC), nine (9OBAC) and 10 (10OBAC) carbon atoms in the alkyl chain. The CNDO/2 method has been used to compute the net atomic charge and dipole moment components at each atomic center. Modified Rayleigh-Schrodinger perturbation theory with multicentered-multipole expansion method has been used to evaluate long-range intermolecular interactions while a '6-exp' potential function has been assumed for short-range interactions. The total interaction-energy values obtained by these computations were used to calculate the probability of each configuration at the phase-transition temperature using the Maxwell-Boltzmann formula. The flexibility of various configurations has been studied in terms of variation of probability due to small departures from the most probable configuration. A comparative picture of molecular parameters like total energy, binding energy and total dipole moment has been given. An attempt has been made to explain the nematogenicity of these acids in terms of their relative order with the molecular parameter introduced in this paper. PMID:16311756

  15. Effect of Hydrogenation on the Glass Transition Temperatures of Novel Ring-Opened Polynorbornenes

    NASA Astrophysics Data System (ADS)

    Burns, Adam; Li, Sheng; Register, Richard

    2013-03-01

    Ring-opening metathesis polymerization (ROMP) of norbornene-type monomers has been demonstrated as a facile way to produce block copolymers incorporating semicrystalline, glassy, and rubbery blocks. Of particular interest are block copolymers, made by ROMP, with thermoplastic elastomeric properties. For this application we seek blocks with glass transition temperatures (Tg) in excess of 100 oC. To this end, novel substituted norbornene-type monomers with large, rigid substituents have been investigated. A key consequence of the ROMP mechanism is that unsaturation in the monomer is preserved in the polymer. Unsaturation in the polymer backbone is susceptible to degradation; therefore, hydrogenation is required to enhance the long-term stability of these polymers. Hydrogenation can also have a significant impact on the thermal behavior. To investigate this, we have synthesized ROMP polymers of 5-phenyl-2-norbornene and 5-cyclohexyl-2-norbornene. Hydrogenation yielded derivatives with saturated backbones. This series of polymers provides a systematic study on the influence of hydrogenation on the Tg of glassy ROMP polymers. We find that saturation of the side group increases the Tg by 14 oC, irrespective of backbone saturation. Conversely, saturation of the backbone reduces Tg by 17 oC for both aromatic and cycloaliphatic side groups. When compared to analogous studies on other ROMP polymers, it becomes clear that these trends are difficult to predict, highlighting the importance of experimental measurements.

  16. The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

    NASA Astrophysics Data System (ADS)

    Schmidt, J. A.; Johnson, M. S.; McBane, G. C.; Schinke, R.

    2012-08-01

    Global three dimensional potential energy surfaces and transition dipole moment functions are calculated for the lowest singlet and triplet states of carbonyl sulfide at the multireference configuration interaction level of theory. The first ultraviolet absorption band is then studied by means of quantum mechanical wave packet propagation. Excitation of the repulsive 2 1A' state gives the main contribution to the cross section. Excitation of the repulsive 1 1A″ state is about a factor of 20 weaker at the absorption peak (Eph ≈ 45 000 cm-1) but becomes comparable to the 2 1A' state absorption with decreasing energy (35 000 cm-1) and eventually exceeds it. Direct excitation of the repulsive triplet states is negligible except at photon energies Eph < 38 000 cm-1. The main structure observed in the cross section is caused by excitation of the bound 2 3A″ state, which is nearly degenerate with the 2 1A' state in the Franck-Condon region. The structure observed in the low energy tail of the spectrum is caused by excitation of quasi-bound bending vibrational states of the 2 1A' and 1 1A″ electronic states. The absorption cross sections agree well with experimental data and the temperature dependence of the cross section is well reproduced.

  17. Critical dynamics of the O(n)-symmetric relaxational models below the transition temperature

    NASA Astrophysics Data System (ADS)

    Täuber, U. C.; Schwabl, F.

    1992-08-01

    The critical dynamics of the O(n)-symmetric relaxational models with either nonconserved (model A) or conserved order parameter (model B) are studied below the transition temperature. As a consequence of Goldstone's theorem, the transverse modes are massless, implying infrared divergences in the theory along the entire coexistence curve. These Goldstone singularities can be treated within the field-theoretical formulation of the dynamical renormalization group by using the generalized regularization scheme as introduced by Amit and Goldschmidt, which has already been applied on the statics of the φ4 model below Tc by Lawrie. We extend the formalism in several respects: (i) we generalize it to dynamical phenomena, (ii) taking advantage of the fact that the theory is exactly treatable in the coexistence limit, we do not use the ɛ expansion; (iii) the flow equations are solved numerically, thus allowing for a detailed description of the crossover from the critical isotropic Heisenberg fixed point to the infrared-stable coexistence fixed point. We calculate the static susceptibilities as well as the dynamical correlation functions for models A and B within the complete crossover region, identifying the asymptotic coexistence anomalies and also a pronounced intermediate minimum of the effective critical exponents. Furthermore, the longitudinal dynamical correlation function GL(q,ω) displays an anomalous line shape.

  18. Solid-to-fluid DNA transition inside HSV-1 capsid close to the temperature of infection

    SciTech Connect

    Sae-Ueng, Udom; Li, Dong; Zuo, Xiaobing; Huffman, Jamie B.; Homa, Fred L.; Rau, Donald; Evilevitch, Alex

    2014-10-01

    DNA in the human Herpes simplex virus type 1 (HSV-1) capsid is packaged to a tight density. This leads to tens of atmospheres of internal pressure responsible for the delivery of the herpes genome into the cell nucleus. In this study we show that, despite its liquid crystalline state inside the capsid, the DNA is fluid-like, which facilitates its ejection into the cell nucleus during infection. We found that the sliding friction between closely packaged DNA strands, caused by interstrand repulsive interactions, is reduced by the ionic environment of epithelial cells and neurons susceptible to herpes infection. However, variations in the ionic conditions corresponding to neuronal activity can restrict DNA mobility in the capsid, making it more solid-like. This can inhibit intranuclear DNA release and interfere with viral replication. In addition, the temperature of the human host (37 °C) induces a disordering transition of the encapsidated herpes genome, which reduces interstrand interactions and provides genome mobility required for infection.

  19. BOREAS AFM-2 Wyoming King Air 1994 Aircraft Sounding Data

    NASA Technical Reports Server (NTRS)

    Kelly, Robert D.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The BOREAS AFM-2 team used the University of Wyoming King Air aircraft during IFCs 1, 2, and 3 in 1994 to collected pass-by-pass fluxes (and many other statistics) for the large number of level (constant altitude), straight-line passes used in a variety of flight patterns over the SSA and NSA and areas along the transect between these study areas. The data described here form a second set, namely soundings that were incorporated into nearly every research flight by the King Air in 1994. These soundings generally went from near the surface to above the inversion layer. Most were flown immediately after takeoff or immediately after finishing the last flux pattern of that particular day's flights. The parameters that were measured include wind direction, wind speed, west wind component (u), south wind component (v), static pressure, air dry bulb temperature, potential temperature, dewpoint, temperature, water vapor mixing ratio, and CO2 concentration. Data on the aircraft's location, attitude, and altitude during data collection are also provided. These data are stored in tabular ASCH files. The data files are available on a CD-ROM (see document number 20010000884) or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  20. Studying post-etching silicon crystal defects on 300mm wafer by automatic defect review AFM

    NASA Astrophysics Data System (ADS)

    Zandiatashbar, Ardavan; Taylor, Patrick A.; Kim, Byong; Yoo, Young-kook; Lee, Keibock; Jo, Ahjin; Lee, Ju Suk; Cho, Sang-Joon; Park, Sang-il

    2016-03-01

    Single crystal silicon wafers are the fundamental elements of semiconductor manufacturing industry. The wafers produced by Czochralski (CZ) process are very high quality single crystalline materials with known defects that are formed during the crystal growth or modified by further processing. While defects can be unfavorable for yield for some manufactured electrical devices, a group of defects like oxide precipitates can have both positive and negative impacts on the final device. The spatial distribution of these defects may be found by scattering techniques. However, due to limitations of scattering (i.e. light wavelength), many crystal defects are either poorly classified or not detected. Therefore a high throughput and accurate characterization of their shape and dimension is essential for reviewing the defects and proper classification. While scanning electron microscopy (SEM) can provide high resolution twodimensional images, atomic force microscopy (AFM) is essential for obtaining three-dimensional information of the defects of interest (DOI) as it is known to provide the highest vertical resolution among all techniques [1]. However AFM's low throughput, limited tip life, and laborious efforts for locating the DOI have been the limitations of this technique for defect review for 300 mm wafers. To address these limitations of AFM, automatic defect review AFM has been introduced recently [2], and is utilized in this work for studying DOI on 300 mm silicon wafer. In this work, we carefully etched a 300 mm silicon wafer with a gaseous acid in a reducing atmosphere at a temperature and for a sufficient duration to decorate and grow the crystal defects to a size capable of being detected as light scattering defects [3]. The etched defects form a shallow structure and their distribution and relative size are inspected by laser light scattering (LLS). However, several groups of defects couldn't be properly sized by the LLS due to the very shallow depth and low

  1. Magnetization processes and transitions between two antiferromagnetic spin configurations in single-crystalline MnSn2

    NASA Astrophysics Data System (ADS)

    Duan, T. F.; Ren, W. J.; Liu, W.; Zhang, Z. D.

    2016-08-01

    The magnetic structure of MnSn2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field (H) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H-T phase diagram has been established.

  2. A room-temperature phase transition in maximum microcline. Absorption in the far infrared (10 200 cm-1) in the temperature range 110 300 K

    NASA Astrophysics Data System (ADS)

    Wyncke, B.; McMillan, P. F.; Brown, W. L.; Openshaw, R. E.; Bréhat, F.

    1981-02-01

    The far infrared powder absorption spectra (10 200 cm-1) for a maximum microcline sample (obtained by ion-exchange from Amelia albite) and for a natural maximum microcline were measured at steps of 10 K on lowering and raising the temperature between 300 and 110 K. Of the absorption bands at 97.5, 113.5, 137.5, 148, and 157 cm-1 occurring at room temperature, those at 157 and eventually 148 cm-1 showed evidence of a phase transition and only that at 157 cm-1 showed hysteresis. The transition occurs at 245±5 K on lowering the temperature and the low-temperature form can be superheated to 300 K in the case of the ion-exchange sample. Oriented thin sections parallel to (001) and (010) were also measured to 110 K as a function of the direction of the electric vector E, but could not be unambiguously interpreted. Though the effect is very slight it is tentatively proposed that the phase transition (already characterized by calorimetry and lattice parameters) involves changes in K-O and T-O-T bonds.

  3. Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition

    NASA Astrophysics Data System (ADS)

    Zhou, Xianzhong; Matthes, Frank; Bürgler, Daniel E.; Schneider, Claus M.

    2016-01-01

    The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

  4. Finite temperature topological phase transitions and emergence of Dirac semi-metallic phases in a Kondo lattice

    NASA Astrophysics Data System (ADS)

    Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Lee, Ting-Kuo; Mou, Chung-Yu

    The energy gap in Dirac materials controls the topology and critical behaviors of the quantum phase transition associated with the critical point when the gap vanishes. However, it is often difficult to access the critical point as it requires tunablity of electronic structures. Here by exploiting the many-body screening interaction of localized spins and conduction electrons in a Kondo lattice, we demonstrate that the electronic band structures in a Kondo lattice are tunable in temperature. When spin-orbit interactions are included, we find that below the Kondo temperature, the Kondo lattice is a strong topological insulator at low temperature and undergoes a topological transition to a weak topological insulator at a higher temperature TD. At TD, Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our results indicate that the topological phase transition though a Dirac semi-metallic phase at finite temperatures also manifests profound physics and results in critical-like behavior both in magnetic and transport properties near TD. We acknowledge support from NCTS and Ministry of Science and Technology (MoST), Taiwan.

  5. Particle deformation induced by AFM tapping under different setpoint voltages

    NASA Astrophysics Data System (ADS)

    Wu, Chung-Lin; Farkas, Natalia; Dagata, John A.; He, Bo-Ching; Fu, Wei-En

    2014-09-01

    The measured height of polystyrene nanoparticles varies with setpoint voltage during atomic force microscopy (AFM) tapping-mode imaging. Nanoparticle height was strongly influenced by the magnitude of the deformation caused by the AFM tapping forces, which was determined by the setpoint voltage. This influence quantity was studied by controlling the operational AFM setpoint voltage. A test sample consisting of well-dispersed 60-nm polystyrene and gold nanoparticles co-adsorbed on poly-l-lysine-coated mica was studied in this research. Gold nanoparticles have not only better mechanical property than polystyrene nanoparticles, but also obvious facets in AFM phase image. By using this sample of mixed nanoparticles, it allows us to confirm that the deformation resulted from the effect of setpoint voltage, not noise. In tapping mode, the deformation of polystyrene nanoparticles increased with decreasing setpoint voltage. Similar behavior was observed with both open loop and closed loop AFM instruments.

  6. Striking role of non-bridging oxygen on glass transition temperature of calcium aluminosilicate glass-formers

    SciTech Connect

    Bouhadja, M.; Jakse, N.; Pasturel, A.

    2014-06-21

    Molecular dynamics simulations are used to study the structural and dynamic properties of calcium aluminosilicate, (CaO-Al{sub 2}O{sub 3}){sub 1−x}(SiO{sub 2}){sub x}, glass formers along three joins, namely, R = 1, 1.57, and 3, in which the silica content x can vary from 0 to 1. For all compositions, we determined the glass-transition temperature, the abundances of the non-bridging oxygen, triclusters, and AlO{sub 5} structural units, as well as the fragility from the temperature evolution of the α-relaxation times. We clearly evidence the role played by the non-bridging oxygen linked either to Al atoms or Si atoms in the evolution of the glass-transition temperature as well as of the fragility as a function of silica content along the three joins.

  7. From a Single-Band Metal to a High-Temperature Superconductor via Two Thermal Phase Transitions

    SciTech Connect

    He, R.-H.; Hashimoto, M.; Karapetyan, H.; Koralek, J.D.; Hinton, J.P.; Testaud, J.P.; Nathan, V.; Yoshida, Y.; Yao, H.; Tanaka, K.; Meevasana, W.; Moore, R.G.; Lu, D.H.; Mo, S.-K.; Ishikado, M.; Eisaki, H.; Hussain, Z.; Devereaux, T.P.; Kivelson, S.A.; Orenstein, J.; Kapitulnik, A.

    2011-11-08

    The nature of the pseudogap phase of cuprate high-temperature superconductors is one of the most important unsolved problems in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally-doped Bi2201 crystals. We observe the coincident onset at T* of a particle-hole asymmetric antinodal gap, a non-zero Kerr rotation, and a change in the relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T{sub c}), entangled in an energy-momentum dependent fashion with the pre-existing pseudogap features.

  8. Electroclinic effect in a chiral paranematic liquid-crystal layer above the bulk nematic-to-isotropic transition temperature

    NASA Astrophysics Data System (ADS)

    Nemitz, Ian R.; Lacaze, Emmanuelle; Rosenblatt, Charles

    2016-02-01

    Electroclinic measurements are reported for two chiral liquid crystals above their bulk chiral isotropic-nematic phase transition temperatures. It is found that an applied electric field E induces a rotation θ [∝Ε] of the director in the very thin paranematic layers that are induced by the cell's two planar-aligning substrates. The magnitude of the electroclinic coefficient dθ/dE close to the transition temperature is comparable to that of a bulk chiral nematic, as well as to that of a parasmectic region above a bulk isotropic-to-chiral smectic-A phase. However, dθ/dE in the paranematic layer varies much more slowly with temperature than in the parasmectic phase, and its relaxation time is slower by more than three orders of magnitude than that of the bulk chiral nematic electroclinic effect.

  9. Adsorbate migration effects on continuous and discontinuous temperature-dependent transitions in the quality factors of graphene nanoresonators.

    PubMed

    Jiang, Jin-Wu; Wang, Bing-Shen; Park, Harold S; Rabczuk, Timon

    2014-01-17

    We perform classical molecular dynamics simulation to investigate the mechanisms underpinning the unresolved, experimentally observed temperature-dependent scaling transition in the quality factors of graphene nanomechanical resonators (GNMRs). Our simulations reveal that the mechanism underlying this temperature scaling phenomenon is the out-of-plane migration of adsorbates on GNMRs. Specifically, the migrating adsorbate undergoes frequent collisions with the GNMR, which strongly influences the resulting mechanical oscillation, and thus the quality factors. We also predict a discontinuous transition in the quality factor at a lower critical temperature, which results from the in-plane migration of the adsorbate. Overall, our work clearly demonstrates the strong effect of adsorbate migration on the quality factors of GNMRs. PMID:24334407

  10. Thermopower analysis of metal-insulator transition temperature modulations in vanadium dioxide thin films with lattice distortion

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2015-07-01

    Insulator-to-metal (MI) phase transition in vanadium dioxide (V O2) thin films with controlled lattice distortion was investigated by thermopower measurements. V O2 epitaxial films with different crystallographic orientations, grown on (0001 ) α -A l2O3 , (11 2 ¯0 ) α -A l2O3 , and (001 ) Ti O2 substrates, showed significant decrease of absolute value of Seebeck coefficient (S ) from ˜200 to 23 μ V K-1 , along with a sharp drop in electrical resistivity (ρ ) , due to the transition from an insulator to a metal. The MI transition temperatures observed both in ρ (Tρ) and S (TS) for the V O2 films systematically decrease with lattice shrinkage in the pseudorutile structure along the c axis, accompanying a broadening of the MI transition temperature width. Moreover, the onset TS, where the insulating phase starts to become metallic, is much lower than the onset Tρ. This difference is attributed to the sensitivity of S for the detection of hidden metallic domains in the majority insulating phase, which cannot be detected in ρ measurements. Consequently, S measurements provide a straightforward and excellent approach for a deeper understanding of the MI transition process in V O2 .

  11. An observed connection between wintertime temperature anomalies over Northwest China and weather regime transitions in North Atlantic

    NASA Astrophysics Data System (ADS)

    Li, Chao; Zhang, Qingyun

    2015-04-01

    In this study, the association between wintertime temperature anomalies over Northwest China and the weather regime transitions in North Atlantic on synoptic scale is analyzed by using observational surface air temperature (SAT) data and atmospheric reanalysis data. Daily SAT anomaly and duration time are used in order to define SAT anomaly cases. Differences with regard to the circulation anomalies over the Ural Mountains and the upstream North Atlantic area are evident. It is found that the colder than normal SAT is caused by the enhanced Ural high and associated southward flow over Northwest China. Time-lagged composites reveal possible connections between the SAT anomalies and the different development phases of the North Atlantic Oscillation (NAO). The Ural highs tend to be strengthened during the negative phase of NAO (NAO-) to Atlantic ridge transition, which are closely related to the downstream-propagating Rossby wave activity. The opposite circulation patterns are observed in the warm SAT cases. A cyclonic circulation anomaly is distinctly enhanced over the Urals during the positive phase of NAO (NAO+) to Scandinavian blocking transition, which would cause warmer SAT over Northwest China. Further analyses suggest that the intensified zonal wind over North Atlantic would favor the NAO- to Atlantic ridge transition, while the weakened zonal wind may be responsible for the transition between NAO+ and Scandinavian blocking.

  12. Microrheology using a custom-made AFM

    NASA Astrophysics Data System (ADS)

    Kosgodagan Acharige, Sebastien; Benzaquen, Michael; Steinberger, Audrey

    In the past few years, a new method was developed to measure local properties of liquids (X. Xiong et al., Phys. Rev. E 80, 2009). This method consists of gluing a micron-sized glass fiber at the tip of an AFM cantilever and probing the liquid with it. In ENS Lyon, this method was perfected (C. Devailly et al., EPL, 106 5, 2014) with the help of an interferometer developped in the same laboratory (L. Bellon et al., Opt. Commun. 207 49, 2002 and P. Paolino et al., Rev. Sci. Instrum. 84, 2013), which background noise can reach 10-14 m /√{ Hz } . This method allows us to measure a wide range of viscosities (1 mPa . s to 500 mPa . s) of transparent and opaque fluids using a small sample volume ( 5 mL). In this presentation, I will briefly describe the interferometer developped in ENS Lyon, then explain precisely the microrheology measurements and then compare the experimental results to a model developped by M. Benzaquen. This work is supported financially by the ANR project NANOFLUIDYN (Grant Number ANR-13-BS10-0009).

  13. Manufacturing process of nanofluidics using afm probe

    NASA Astrophysics Data System (ADS)

    Karingula, Varun Kumar

    A new process for fabricating a nano fluidic device that can be used in medical application is developed and demonstrated. Nano channels are fabricated using a nano tip in indentation mode on AFM (Atomic Force Microscopy). The nano channels are integrated between the micro channels and act as a filter to separate biomolecules. Nano channels of 4 to7 m in length, 80nm in width, and at varying depths from 100nm to 850 nm allow the resulting device to separate selected groups of lysosomes and other viruses. Sharply developed vertical micro channels are produced from a deep reaction ion etching followed by deposition of different materials, such as gold and polymers, on the top surface, allowing the study of alternative ways of manufacturing a nanofluidic device. PDMS (Polydimethylsiloxane) bonding is performed to close the top surface of the device. An experimental setup is used to test and validate the device by pouring fluid through the channels. A detailed cost evaluation is conducted to compare the economical merits of the proposed process. It is shown that there is a 47:7% manufacturing time savings and a 60:6% manufacturing cost savings.

  14. BOREAS AFM-07 SRC Surface Meteorological Data

    NASA Technical Reports Server (NTRS)

    Osborne, Heather; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Young, Kim; Wittrock, Virginia; Shewchuck, Stan; Smith, David E. (Technical Monitor)

    2000-01-01

    The Saskatchewan Research Council (SRC) collected surface meteorological and radiation data from December 1993 until December 1996. The data set comprises Suite A (meteorological and energy balance measurements) and Suite B (diffuse solar and longwave measurements) components. Suite A measurements were taken at each of ten sites, and Suite B measurements were made at five of the Suite A sites. The data cover an approximate area of 500 km (North-South) by 1000 km (East-West) (a large portion of northern Manitoba and northern Saskatchewan). The measurement network was designed to provide researchers with a sufficient record of near-surface meteorological and radiation measurements. The data are provided in tabular ASCII files, and were collected by Aircraft Flux and Meteorology (AFM)-7. The surface meteorological and radiation data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  15. Comparison of two adaptive temperature-based replica exchange methods applied to a sharp phase transition of protein unfolding-folding

    NASA Astrophysics Data System (ADS)

    Lee, Michael S.; Olson, Mark A.

    2011-06-01

    Temperature-based replica exchange (T-ReX) enhances sampling of molecular dynamics simulations by autonomously heating and cooling simulation clients via a Metropolis exchange criterion. A pathological case for T-ReX can occur when a change in state (e.g., folding to unfolding of a protein) has a large energetic difference over a short temperature interval leading to insufficient exchanges amongst replica clients near the transition temperature. One solution is to allow the temperature set to dynamically adapt in the temperature space, thereby enriching the population of clients near the transition temperature. In this work, we evaluated two approaches for adapting the temperature set: a method that equalizes exchange rates over all neighbor temperature pairs and a method that attempts to induce clients to visit all temperatures (dubbed "current maximization") by positioning many clients at or near the transition temperature. As a test case, we simulated the 57-residue SH3 domain of alpha-spectrin. Exchange rate equalization yielded the same unfolding-folding transition temperature as fixed-temperature ReX with much smoother convergence of this value. Surprisingly, the current maximization method yielded a significantly lower transition temperature, in close agreement with experimental observation, likely due to more extensive sampling of the transition state.

  16. Characterization of polymers in the glass transition range: Time-temperature and time-aging time superposition in polycarbonate

    SciTech Connect

    Pesce, J.J.; Niemiec, J.M.; Chiang, M.Y.

    1995-12-31

    Here we present time-temperature and time-aging time superposition data for a commercial grade polycarbonate. The data reduction is performed for dynamic-mechanical data obtained in torsion over a range of temperatures from 103.6 to 144.5{degrees}C and aging times to 16 h. For time-temperature superposition the results show the deviation of the sub-T{sub g} response from the WTF equation. Two response regimes are observed: at temperatures far below T{sub g} the log(a{sub T}) is linear in T, followed by a transition towards the WLF behavior as T{sub g} is approached. The temperature at which the behavior changes from a linear dependence of log(aT) on T to the transition-type behavior is found to depend on the aging time. This temperature decreases as aging time increases. The time-aging time response is found to behave in a normal way. At temperatures far below T{sub g} the log(a{sub te}) vs log(t{sub e}) is constant and has a slope somewhat less than unity. However, nearer to T{sub g} the slope decreases and there is a second regime in which the aging virtually ceases. In this polycarbonate, above 136.9{degrees}C, no aging is observed.

  17. Quantum phase transitions and Berezinskii-Kosterlitz-Thouless temperature in a two-dimensional spin-orbit-coupled Fermi gas

    NASA Astrophysics Data System (ADS)

    Devreese, Jeroen P. A.; Tempere, Jacques; Sá de Melo, Carlos A. R.

    2015-10-01

    We study the effect of spin-orbit coupling on both the zero-temperature and nonzero-temperature behavior of a two-dimensional Fermi gas. We include a generic combination of Rashba and Dresselhaus terms into the system Hamiltonian, which allows us to study both the experimentally relevant equal-Rashba-Dresselhaus (ERD) limit and the Rashba-only (RO) limit. At zero temperature, we derive the phase diagram as a function of the two-body binding energy and Zeeman field. In the ERD case, this phase diagram reveals several topologically distinct uniform superfluid phases, classified according to the nodal structure of the quasiparticle excitation energies. Furthermore, we use a momentum-dependent SU(2) rotation to transform the system into a generalized helicity basis, revealing that spin-orbit coupling induces a triplet pairing component of the order parameter. At nonzero temperature, we study the Berezinskii-Kosterlitz-Thouless (BKT) phase transition by including phase fluctuations of the order parameter up to second order. We show that the superfluid density becomes anisotropic due to the presence of spin-orbit coupling (except in the RO case). This leads both to elliptic vortices and antivortices, and to anisotropic sound velocities. The latter prove to be sensitive to quantum phase transitions between topologically distinct phases. We show further that at a fixed nonzero Zeeman field, the BKT critical temperature is increased by the presence of ERD spin-orbit coupling. Subsequently, we demonstrate that the Clogston limit becomes infinite: TBKT remains nonzero at all finite values of the Zeeman field. We conclude by extending the quantum phase transition lines to nonzero temperature, using the nodal structure of the quasiparticle spectrum, thus connecting the BKT critical temperature with the zero-temperature results.

  18. The Effects of Electron Radiation on the Glass Transition Temperature of a Polyetherimide.

    NASA Astrophysics Data System (ADS)

    Kern, Kristen Tulloch

    The effects of electron radiation on a polyetherimide (PEI), Ultem^{cdot}, were investigated. In particular, the changes in the glass transition temperature (T_{g} ) with absorbed radiation dose were studied. The polymer was exposed to mono-energetic beams of 100-keV electrons and 1.0-MeV electrons for doses up to 100 megagray (MGy). Dosimetry for the exposures was based on Monte -Carlo simulations of the transfer of energy from an energetic electron to the polymer and on comparison to Nylon standards. Dynamic mechanical analysis was used to determine the T _{g} for non-exposed PEI and the changes in T_{g} resulting from irradiation. The T_{g} did not change significantly for doses up to and including 75 MGy, while a significant increase in T_ {g} occurred for a dose of 100 MGy. The cross-link and chain scission densities in the irradiated PEI were determined using infrared spectroscopy. The cross -link density increased with dose for all doses investigated. The chain scission density increased with dose for doses up to 75 MGy, but was lower for a dose of 100 MGy than for a dose of 75 MGy. Radical population kinetics, based in part on data from an electron paramagnetic resonance study, were correlated with the cross-link density and chain scission density to investigate the mechanism for the observed density variations with dose. The radical population simulations suggest that chain scissioning occurs less readily when the average radical separation during the exposure is less than three molecular radii. Finally, a model for the combined effects of cross-linking and chain scissioning is proposed which combines a statistical-mechanical model for the change in T_{g} with cross-link density and a free-volume model for the change in T _{g} with chain scission density.

  19. Deep water temperature, carbonate ion, and ice volume changes across the Eocene-Oligocene climate transition

    NASA Astrophysics Data System (ADS)

    Pusz, A. E.; Thunell, R. C.; Miller, K. G.

    2011-06-01

    Paired benthic foraminiferal stable isotope and Mg/Ca data are used to estimate bottom water temperature (BWT) and ice volume changes associated with the Eocene-Oligocene Transition (EOT), the largest global climate event of the past 50 Myr. We utilized ODP Sites 1090 and 1265 in the South Atlantic to assess seawater δ18O (δw), Antarctic ice volume, and sea level changes across the EOT (˜33.8-33.54 Ma). We also use benthic δ13C data to reconstruct the sources of the deep water masses in this region during the EOT. Our data, together with previously published records, indicate that a pulse of Northern Component Water influenced the South Atlantic immediately prior to and following the EOT. Benthic δ18O records show a 0.5‰ increase at ˜33.8 Ma (EOT-1) that represents a ˜2°C cooling and a small (˜10 m) eustatic fall that is followed by a 1.0‰ increase associated with Oi-1. The expected cooling of deep waters at Oi-1 (˜33.54 Ma) is not apparent in our Mg/Ca records. We suggest the cooling is masked by coeval changes in the carbonate saturation state (Δ[CO32-]) which affect the Mg/Ca data. To account for this, the BWT, ice volume, and δw estimates are corrected for a change in the Δ[CO32-] of deep waters on the basis of recently published work. Corrected BWT at Sites 1090 and 1265 show a ˜1.5°C cooling coincident with Oi-1 and an average δw increase of ˜0.75‰. The increase in ice volume during Oi-1 resulted in a ˜70 m drop in global sea level and the development of an Antarctic ice sheet that was near modern size or slightly larger.

  20. How melt stretching affect the brittle-ductile transition temperature of polymer glasses

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Wang, Shi-Qing

    2013-03-01

    Upon increasing temperature a brittle polymer glass can turn ductile. PMMA is a good example. For a while this brittle-ductile transition (BDT) was thought to be determined by the emergence of a secondary relaxation....1-3 On the other hand, it has been known for a long time...4-6 that predeformation in the melt state (e.g., melt stretching) can also make brittle glasses behave in a ductile manner. This transformation has recently received a satisfactory explanation based on a picture of structural hybrid for polymer glasses....7 It appears that BDT is dictated by the relative mechanical characteristics of the primary structure (due to the van der Waals bonds) and the chain network. The present work, based on conventional Instron tensile extension tests and DMA tests, shows that melt stretching does not alter the secondary relaxation behavior of PMMA and PC yet can turn them the brittle PMMA ductile and the ductile PC brittle. Moreover, sufficient melt stretching makes the brittle PS ductile although it does not produce any secondary relaxation process..1. Monnerie, L.; Laupretre, F.; Halary, J. L. Adv. Polym. Sci2005, 187, 35-213. 2. Monnerie, L.; Halary, J. L.; Kausch, H. Adv. Polym. Sci2005, 187, 215-364. 3. Wu, S. J. Appl. Polym. Sci.1992, 46, (4), 619-624. 4. Vincent, P. I. Polymer1960, 1, (0), 425-444. 5. Harris, J. S.; Ward, I. M. J. Mater. Sci.1970, 5, (7), 573-579. 6. Ender, D. H.; Andrews, R. D. J. Appl. Phys.1965, 36, (10), 3057-3062. 7. Zartman, G. D.; Cheng, S.; Li, X.; Lin, F.; Becker, M. L.; Wang, S.-Q. Macromolecules2012, 45, (16), 6719-6732.

  1. Time-dependent surface adhesive force and morphology of RBC measured by AFM.

    PubMed

    Wu, Yangzhe; Hu, Yi; Cai, Jiye; Ma, Shuyuan; Wang, Xiaoping; Chen, Yong; Pan, Yunlong

    2009-04-01

    Atomic force microscopy (AFM) is a rapidly developing tool recently introduced into the evaluation of the age of bloodstains, potentially providing legal medical experts useful information for forensic investigation. In this study, the time-dependent, morphological changes of red blood cells (RBC) under three different conditions (including controlled, room-temperature condition, uncontrolled, outdoor-environmental condition, and controlled, low-temperature condition) were observed by AFM, as well as the cellular viscoelasticity via force-vs-distance curve measurements. Firstly, the data indicate that substrate types have different effects on cellular morphology of RBC. RBC presented the typical biconcave shape on mica, whereas either the biconcave shape or flattened shape was evident on glass. The mean volume of RBCs on mica was significantly larger than that of cells on glass. Surprisingly, the adhesive property of RBC membrane surfaces was substrate type-independent (the adhesive forces were statistically similar on glass and mica). With time lapse, the changes in cell volume and adhesive force of RBC under the controlled room-temperature condition were similar to those under the uncontrolled outdoor-environmental condition. Under the controlled low-temperature condition, however, the changes in cell volume occurred mainly due to the collapse of RBCs, and the curves of adhesive force showed the dramatic alternations in viscoelasticity of RBC. Taken together, the AFM detections on the time-dependent, substrate type-dependent, environment (temperature/humidity)-dependent changes in morphology and surface viscoelasticity of RBC imply a potential application of AFM in forensic medicine or investigations, e.g., estimating age of bloodstain or death time. PMID:19019689

  2. BOREAS AFM-03-NCAR Electra 1994 Aircraft Sounding Data

    NASA Technical Reports Server (NTRS)

    Lenschow, Donald H.; Oncley, Steven P.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-3 team used the National Center for Atmospheric Research's (NCAR) Electra aircraft to make sounding measurements to study the planetary boundary layer using in situ and remote-sensing measurements. Measurements were made of wind speed and direction, air pressure and temperature, potential temperature, dewpoint, mixing ratio of H, O, CO, concentration, and ozone concentration. Twenty-five research missions were flown over the Northern Study Area (NSA), Southern Study Area (SSA), and the transect during BOREAS Intensive Field Campaigns (IFCs) 1, 2, and 3 during 1994. All missions had from four to ten soundings through the top of the planetary boundary layer. This sounding data set contains all of the in situ vertical profiles through the boundary layer top that were made (with the exception of 'porpoise' maneuvers). Data were recorded in one-second time intervals. These data are stored in tabular ASCII files. The NCAR Electra 1994 aircraft sounding data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  3. BOREAS AFM-12 1-km AVHRR Seasonal Land Cover Classification

    NASA Technical Reports Server (NTRS)

    Steyaert, Lou; Hall, Forrest G.; Newcomer, Jeffrey A. (Editor); Knapp, David E. (Editor); Loveland, Thomas R.; Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-12 team's efforts focused on regional scale Surface Vegetation and Atmosphere (SVAT) modeling to improve parameterization of the heterogeneous BOREAS landscape for use in larger scale Global Circulation Models (GCMs). This regional land cover data set was developed as part of a multitemporal one-kilometer Advanced Very High Resolution Radiometer (AVHRR) land cover analysis approach that was used as the basis for regional land cover mapping, fire disturbance-regeneration, and multiresolution land cover scaling studies in the boreal forest ecosystem of central Canada. This land cover classification was derived by using regional field observations from ground and low-level aircraft transits to analyze spectral-temporal clusters that were derived from an unsupervised cluster analysis of monthly Normalized Difference Vegetation Index (NDVI) image composites (April-September 1992). This regional data set was developed for use by BOREAS investigators, especially those involved in simulation modeling, remote sensing algorithm development, and aircraft flux studies. Based on regional field data verification, this multitemporal one-kilometer AVHRR land cover mapping approach was effective in characterizing the biome-level land cover structure, embedded spatially heterogeneous landscape patterns, and other types of key land cover information of interest to BOREAS modelers.The land cover mosaics in this classification include: (1) wet conifer mosaic (low, medium, and high tree stand density), (2) mixed coniferous-deciduous forest (80% coniferous, codominant, and 80% deciduous), (3) recent visible bum, vegetation regeneration, or rock outcrops-bare ground-sparsely vegetated slow regeneration bum (four classes), (4) open water and grassland marshes, and (5) general agricultural land use/ grasslands (three classes). This land cover mapping approach did not detect small subpixel-scale landscape

  4. Investigation on onset voltage and conduction channel temperature in voltage-induced metal-insulator transition of vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Yoon, Joonseok; Kim, Howon; Mun, Bongjin Simon; Park, Changwoo; Ju, Honglyoul

    2016-03-01

    The characteristics of onset voltages and conduction channel temperatures in the metal-insulator transition (MIT) of vanadium dioxide (VO2) devices are investigated as a function of dimensions and ambient temperature. The MIT onset voltage varies from 18 V to 199 V as the device length increases from 5 to 80 μm at a fixed width of 100 μm. The estimated temperature at local conduction channel increases from 110 to 370 °C, which is higher than the MIT temperature (67 °C) of VO2. A simple Joule-heating model is employed to explain voltage-induced MIT as well as to estimate temperatures of conduction channel appearing after MIT in various-sized devices. Our findings on VO2 can be applied to micro- to nano-size tunable heating devices, e.g., microscale scanning thermal cantilevers and gas sensors.

  5. Graft copolymers that exhibit temperature-induced phase transitions over a wide range of pH

    NASA Astrophysics Data System (ADS)

    Chen, Guohua; Hoffman, Allan S.

    1995-01-01

    THERE are many potential applications of 'intelligent' aqueous polymer systems1-8 in medicine, biotechnology, industry and in environmental problems9-13. Many of these polymer systems undergo reversible phase transitions-for example, abrupt changes in volume-in response to external stimuli such as temperature, pH or the nature of the solvent. Most of the polymers studied previously are responsive to only one kind of stimulus. But for some applications, independent responsiveness to several factors, such as temperature and pH, may be required. Here we describe a polymer that undergoes marked solubility changes in water in response to temperature and/or pH changes. The polymer is prepared by grafting temperature-sensitive side chains onto a pH-sensitive backbone. We also find that block copolymers, in which the temperature- and pH-sensitive units alternate along the chain, show similar behaviour.

  6. Mixing it up - Measuring diffusion in supercooled liquid solutions of methanol and ethanol at temperatures near the glass transition

    SciTech Connect

    Matthiesen, Jesper; Smith, R. Scott; Kay, Bruce D.

    2011-03-17

    Do liquid mixtures, cooled to temperatures below their freezing point, behave as normal liquids? We address this question using nanoscale films of methanol and ethanol supercooled liquid solutions of varying composition (7 -93% methanol) at temperatures near their glass transition,Tg. The permeation of Kr through these films is used to determine the diffusivities of the supercooled liquid mixtures. We find that the temperature dependent diffusivities of the mixtures are well-fit by a Vogel-Fulcher-Tamman equation indicating that the mixtures exhibit fragile behavior at temperatures just above their Tg. Further, for a given temperature, the composition dependent diffusivity is well-fit by a Vignes-type equation, i.e. the diffusivity of any mixture can be predicted using an exponential weighting of the diffusion of the pure methanol and ethanol diffusivities. These results show that deeply supercooled liquid mixtures can be used to provide valuable insight into the properties of normal liquid mixtures.

  7. Bismuth doping strategies in GeTe nanowires to promote high-temperature phase transition from rhombohedral to face-centered cubic structure

    SciTech Connect

    Zhang, Jie; Huang, Rong; Wei, Fenfen; Cheng, Guosheng; Kong, Tao

    2014-11-17

    The phase transition of Bi-doped (∼3 at. %) GeTe nanowires from a rhombohedral (R) to a face-centered cubic (C) structure was observed in in situ high-temperature X-ray diffraction. The promotion of high-temperature R-C phase transition by a doping approach was revealed. Ab initio energy calculations of doped GeTe at various Bi doping concentrations were performed to interpret the promoted temperature-induced phase transitions. Those results indicated that the total energy differences between R and C structures of doped GeTe decreased as Bi doping concentrations increased, which facilitated R-C phase transitions.

  8. Changes in core electron temperature fluctuations across the ohmic energy confinement transition in Alcator C-Mod plasmas

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A. E.; Howard, N. T.; Oi, C. Y.; Rice, J. E.; Gao, C.; Ennever, P.; Porkolab, M.; Parra, F.; Mikkelsen, D.; Ernst, D.; Walk, J.; Hughes, J. W.; Irby, J.; Kasten, C.; Hubbard, A. E.; Greenwald, M. J.; the Alcator C-Mod Team

    2013-08-01

    The first measurements of long wavelength (kyρs < 0.3) electron temperature fluctuations in Alcator C-Mod made with a new correlation electron cyclotron emission diagnostic support a long-standing hypothesis regarding the confinement transition from linear ohmic confinement (LOC) to saturated ohmic confinement (SOC). Electron temperature fluctuations decrease significantly (∼40%) crossing from LOC to SOC, consistent with a change from trapped electron mode (TEM) turbulence domination to ion temperature gradient (ITG) turbulence as the density is increased. Linear stability analysis performed with the GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) shows that TEMs are dominant for long wavelength turbulence in the LOC regime and ITG modes are dominant in the SOC regime at the radial location (ρ ∼ 0.8) where the changes in electron temperature fluctuations are measured. In contrast, deeper in the core (ρ < 0.8), linear stability analysis indicates that ITG modes remain dominant across the LOC/SOC transition. This radial variation suggests that the robust global changes in confinement of energy and momentum occurring across the LOC/SOC transition are correlated to local changes in the dominant turbulent mode near the edge.

  9. Study of relaxation and transport processes by means of AFM based dielectric spectroscopy

    SciTech Connect

    Miccio, Luis A.

    2014-05-15

    Since its birth a few years ago, dielectric spectroscopy studies based on atomic force microscopy (AFM) have gained a growing interest. Not only the frequency and temperature ranges have become broader since then but also the kind of processes that can be studied by means of this approach. In this work we analyze the most adequate experimental setup for the study of several dielectric processes with a spatial resolution of a few nanometers by using force mode AFM based dielectric spectroscopy. Proof of concept experiments were performed on PS/PVAc blends and PMMA homopolymer films, for temperatures ranging from 300 to 400 K. Charge transport processes were also studied by this approach. The obtained results were analyzed in terms of cantilever stray contribution, film thickness and relaxation strength. We found that the method sensitivity is strongly coupled with the film thickness and the relaxation strength, and that it is possible to control it by using an adequate experimental setup.

  10. Molecular Dynamic Simulations of Interaction of an AFM Probe with the Surface of an SCN Sample

    NASA Technical Reports Server (NTRS)

    Bune, Adris; Kaukler, William; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Molecular dynamic (MD) simulations is conducted in order to estimate forces of probe-substrate interaction in the Atomic Force Microscope (AFM). First a review of available molecular dynamic techniques is given. Implementation of MD simulation is based on an object-oriented code developed at the University of Delft. Modeling of the sample material - succinonitrile (SCN) - is based on the Lennard-Jones potentials. For the polystyrene probe an atomic interaction potential is used. Due to object-oriented structure of the code modification of an atomic interaction potential is straight forward. Calculation of melting temperature is used for validation of the code and of the interaction potentials. Various fitting parameters of the probe-substrate interaction potentials are considered, as potentials fitted to certain properties and temperature ranges may not be reliable for the others. This research provides theoretical foundation for an interpretation of actual measurements of an interaction forces using AFM.

  11. Mobility of Supercooled liquid Toluene, Ethylbenzene, and Benzene near their Glass Transition Temperatures Investigated using Inert Gas Permeation

    SciTech Connect

    May, Robert A.; Smith, R. Scott; Kay, Bruce D.

    2013-11-21

    We investigate the mobility of supercooled liquid toluene, ethylbenzene, and benzene near their respective glass transition temperatures (Tg). The permeation rate of Ar, Kr, and Xe through the supercooled liquid created when initially amorphous overlayers heated above their glass transition temperature is used to determine the diffusivity. Amorphous benzene crystallizes at temperatures well below its Tg and as a result the inert gas underlayer remains trapped until the onset of benzene desorption. In contrast, for toluene and ethylbenzene the onset of inert gas permeation is observed at temperatues near Tg. The inert gas desorption peak temperature as a function of the heating rate and overlayer thickness is used to quantify the diffusivity of supercooled liquid toluene and ethylbenzene from 115 K to 135 K. In this temperature range, diffusivities are found to vary across five orders of magnitude (~10-14 to 10-9 cm2/s). These data are compared to viscosity measurements and used to determine the low temperature fractional Stokes-Einstein exponent. Efforts to determine the diffusivity of a mixture of benzene and ethylbenzene are detailed, and the effect of mixing these materials on benzene crystallization is explored using infrared spectroscopy.

  12. Investigation of K X-ray intensity ratios of some 4d transition metals depending on the temperature.

    PubMed

    Özdemir, Yüksel; Kavaz, Esra; Ahmadi, Nader; Ertuğrul, Mehmet; Ekinci, Neslihan

    2016-09-01

    In this paper, we have studied the intensity ratios Kβ/Kα depending on the temperature for transition elements Mo, Nb, Zr and Y by 59.5keV γ-rays from a 100 mCi (241)Am radioisotope point source. The Kα and Kβ emission spectra of Mo, Nb, Zr and Y were measured by using a Si (Li) solid-state detector at temperature between 40 and 400°C. σKα and σKβ production cross-sections, Kβ/Kα intensity ratios, asymmetry factor, energy shifts and full width half maximum (FWHM) values of the elements have been calculated. Temperature-dependent changes of the parameters are tabulated and given in the graphical forms. Based on the results obtained, Kβ/Kα X-ray intensity ratios of the elements are dependent on the temperature. It is shown that σKβ fluorescence cross sections of Mo, Nb and Zr have more increase rate than σKα fluorescence cross sections with increasing temperature. For Y, σKα and σKβ production cross-sections firstly decrease, then increase. In general, Kβ/Kα X-ray intensity ratios tend to increase with increasing temperature. Some significant shifts are observed in Kα and Kβ emission spectra of Mo and Y. These results may contribute to the XRF studies of transition metals. PMID:27380197

  13. Development of DMBZ-15 High-Glass-Transition-Temperature Polyimides as PMR-15 Replacements Given R&D 100 Award

    NASA Technical Reports Server (NTRS)

    Chuang, Kathy

    2004-01-01

    PMR-15, a high-temperature polyimide developed in the mid-1970s at the NASA Lewis Research Center,1 offers the combination of low cost, easy processing, and good high-temperature performance and stability. It has been recognized as the leading polymer matrix resin for carbon-fiber-reinforced composites used in aircraft engine components. The state-of-the-art PMR-15 polyimide composite has a glass-transition temperature (Tg) of 348 C (658 F). Since composite materials must be used at temperatures well below their glass-transition temperature, the long-term use temperatures of PMR-15 composites can be no higher than 288 C (550 F). In addition, PMR-15 is made from methylene dianiline (MDA), a known liver toxin. Concerns about the safety of workers exposed to MDA during the fabrication of PMR-15 components and about the environmental impact of PMR-15 waste disposal have led to the industry-wide implementation of special handling procedures to minimize the health risks associated with this material. These procedures have increased manufacturing and maintenance costs significantly and have limited the use of PMR-15 in commercial aircraft engine components.

  14. Temperature and pressure shift of the Cs clock transition in the presence of buffer gases: Ne, N2, Ar

    NASA Astrophysics Data System (ADS)

    Kozlova, Olga; Guérandel, Stéphane; de Clercq, Emeric

    2011-06-01

    The ground-state hyperfine resonance line of alkali-metal atoms is frequency shifted in the presence of noble or molecular gases. The buffer gases used in vapor-cell atomic clocks thus induce a temperature-dependent shift of the clock transition frequency. We report on measurements of the pressure and temperature dependence of the Cs clock transition frequency in the presence of Ne, Ar, and N2 buffer gases. The pressure in the sealed glass vapor cells is measured by means of the shift of the Cs D1 line. We have also investigated the temperature dependence of the optical shift. From these measurements, we infer the pressure and temperature coefficients of the hyperfine frequency shift. It is then possible to predetermine gas mixture ratios that cancel the temperature sensitivity at a given temperature. This prediction is confirmed experimentally for Ar-N2 mixtures. These results can be useful for improving the long-term frequency stability of Cs vapor-cell clocks.

  15. Segmental calibration for commercial AFM in vertical direction

    NASA Astrophysics Data System (ADS)

    Shi, Yushu; Gao, Sitian; Lu, Mingzhen; Li, Wei; Xu, Xuefang

    2013-01-01

    Atomic force microscopy (AFM) is most widely applied in scientific research and industrial production. AFM is a scanning probe imaging and measuring device, useful for physical and chemical studies. Depends on its basic structure, microscopic surface pattern can be measured and captured by mechanically scanning. Its vertical and horizon resolution can reach to 0.01nm and 0.1nm. Commonly the measurement values of commercial AFM are directly from scanning piezoelectric tube, so that it not a traceable value. In order to solve the problem of commercial AFM's traceability, step height standard references are applied to calibrate the piezoelectric ceramic housing in scanning tube. All of the serial of step height standard references, covering the commercial AFM vertical scale, are calibrated by Metrology AFM developed by National Institute of Metrology (NIM), China. Three interferometers have been assembled in its XYZ axis, therefore the measurement value can directly trace to laser wavelength. Because of nonlinear characteristic of PZT, the method of segmental calibration is proposed. The measurement scale can be divided into several subsections corresponding to the calibrated values of the series of step height standards references. By this method the accuracy of measurements can be ensured in each segment measurement scale and the calibration level of the whole instrument can be promoted. In order to get a standard step shape by commercial AFM, substrate removal method is applied to deal with the bow shape problem.

  16. The Gardner Transition: A new approach for understanding low-temperature glasses

    NASA Astrophysics Data System (ADS)

    Charbonneau, Patrick

    Recent theoretical advances in the mean-field theory of glasses predict the existence deep in the glass phase of a novel phase transition, a so-called Gardner transition. This transition signals the emergence of a complex free energy landscape composed of a marginally stable hierarchy of sub-basins within a broad glass metabasin. It is thus the onset of marked changes in thermal and transport properties of glasses, and ultimately leads to the unusual critical behavior at jamming. The Gardner transition itself is immediately related to a diverging (i) characteristic relaxation time, (ii) caging susceptibility and (iii) correlation length of the caging heterogeneity as well as aging, even in well-thermalized glasses. We have detected some of these signatures both in a mean-field model and in standard hard-sphere glass formers. We find the results to quantitatively agree with theory in the former and qualitatively so in the latter, which suggest that the transition should be detectable in a wide array of numerical and experimental systems. Interestingly, although the Gardner transitions is primarily associated with structural glass formers, we also find features of the transition in crystals of polydisperse particles once the landscape becomes rough.

  17. Raman and AFM study of gamma irradiated plastic bottle sheets

    SciTech Connect

    Ali, Yasir; Kumar, Vijay; Dhaliwal, A. S.; Sonkawade, R. G.

    2013-02-05

    In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV {sup 60}Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFM observations.

  18. Dynamics of the nanoneedle probe in trolling mode AFM.

    PubMed

    Abdi, Ahmad; Pishkenari, Hossein Nejat; Keramati, Ramtin; Minary-Jolandan, Majid

    2015-05-22

    Atomic force microscopy (AFM), as an indispensable tool for nanoscale characterization, presents major drawbacks for operation in a liquid environment arising from the large hydrodynamic drag on the vibrating cantilever. The newly introduced 'Trolling mode' (TR-mode) AFM resolves this complication by using a specialized nanoneedle cantilever that keeps the cantilever outside of the liquid. Herein, a mechanical model with a lumped mass was developed to capture the dynamics of such a cantilever with a nanoneedle tip. This new developed model was applied to investigate the effects of the needle-liquid interface on the performance of the AFM, including the imaging capability in liquid. PMID:25915451

  19. AFM Studies of Conformational Changes in Proteins and Peptides

    NASA Astrophysics Data System (ADS)

    Ploscariu, Nicoleta; Sukthankar, Pinakin; Tomich, John; Szoszkiewicz, Robert

    2015-03-01

    Here, we present estimates of molecular stiffness and mechanical energy dissipation factors for some examples of proteins and peptides. The results are obtained from AFM force spectroscopy measurements. To determine molecular stiffness and mechanical energy dissipation factors we developed a model based on measuring several resonance frequencies of an AFM cantilever in contact with either single protein molecule or peptides adsorbed on arbitrary surface. We used compliant AFM cantilevers with a small aspect ratio - a ratio of length to width - in air and in liquid, including biologically relevant phosphate buffered saline medium. Department of Physics.

  20. Raman study of the Verwey transition in Magnetite at high-pressure and low-temperature; effect of Al doping

    NASA Astrophysics Data System (ADS)

    Gasparov, Lev; Shirshikova, Z.; Pekarek, T. M.; Blackburn, J.; Struzhkin, V.; Gavriliuk, A.; Rueckamp, R.; Berger, H.

    2012-02-01

    We report high-pressure low-temperature Raman measurements of the Verwey transition in pure and Al --doped magnetite (Fe3O4) Al-doped magnetite Fe2.8Al0.2O4 (TV=116.5K) displays a nearly linear decrease of the transition temperature with an increase of pressure yielding dP/dTV=-0.096±0.013 GPa/K. In contrast pure magnetite displays a significantly steeper slope of the PT equilibrium line with dP/dTV = -0.18±0.013 GPa/K. Contrary to earlier high pressure resistivity reports we do not observe quantum critical point behavior at 8 GPa in the pure magnetite. Our data indicates that Al doping leads to a smaller entropy change and larger volume expansion at the transition. The trends displayed by the data are consistent with the mean field model of the transition that assumes charge ordering in magnetite.

  1. Nonanalytic microscopic phase transitions and temperature oscillations in the microcanonical ensemble: An exactly solvable one-dimensional model for evaporation

    NASA Astrophysics Data System (ADS)

    Hilbert, Stefan; Dunkel, Jörn

    2006-07-01

    We calculate exactly both the microcanonical and canonical thermodynamic functions (TDFs) for a one-dimensional model system with piecewise constant Lennard-Jones type pair interactions. In the case of an isolated N -particle system, the microcanonical TDFs exhibit (N-1) singular (nonanalytic) microscopic phase transitions of the formal order N/2 , separating N energetically different evaporation (dissociation) states. In a suitably designed evaporation experiment, these types of phase transitions should manifest themselves in the form of pressure and temperature oscillations, indicating cooling by evaporation. In the presence of a heat bath (thermostat), such oscillations are absent, but the canonical heat capacity shows a characteristic peak, indicating the temperature-induced dissociation of the one-dimensional chain. The distribution of complex zeros of the canonical partition may be used to identify different degrees of dissociation in the canonical ensemble.

  2. Low-temperature phase transitions in a soluble oligoacene and their effect on device performance and stability

    SciTech Connect

    Ward, J. W.; Goetz, K. P.; Obaid, A.; Diemer, P. J.; Jurchescu, O. D.; Payne, M. M.; Anthony, J. E.; Day, C. S.

    2014-08-25

    The use of organic semiconductors in high-performance organic field-effect transistors requires a thorough understanding of the effects that processing conditions, thermal, and bias-stress history have on device operation. Here, we evaluate the temperature dependence of the electrical properties of transistors fabricated with 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene, a material that has attracted much attention recently due to its exceptional electrical properties. We have discovered a phase transition at T = 205 K and discuss its implications on device performance and stability. We examined the impact of this low-temperature phase transition on the thermodynamic, electrical, and structural properties of both single crystals and thin films of this material. Our results show that while the changes to the crystal structure are reversible, the induced thermal stress yields irreversible degradation of the devices.

  3. Temperature-dependent study of isotropic nematic transition for a Gay Berne fluid using density-functional theory

    NASA Astrophysics Data System (ADS)

    Singh, Ram Chandra

    2007-09-01

    We have used the density-functional theory to study the effect of varying temperature on the isotropic-nematic transition of a fluid of molecules interacting via the Gay-Berne intermolecular potential. The nematic phase is found to be stable with respect to isotropic phase in the temperature range 0.80<=T*<=1.25. Pair correlation functions needed as input information in density-functional theory is calculated using the Percus-Yevick integral equation theory. We find that the density-functional theory is good for studying the isotropic-nematic transition in molecular fluids if the values of the pair-correlation functions in the isotropic phase are known accurately. We have also compared our results with computer simulation results wherever they are available.

  4. Low-temperature phase transitions in a soluble oligoacene and their effect on device performance and stability

    NASA Astrophysics Data System (ADS)

    Ward, J. W.; Goetz, K. P.; Obaid, A.; Payne, M. M.; Diemer, P. J.; Day, C. S.; Anthony, J. E.; Jurchescu, O. D.

    2014-08-01

    The use of organic semiconductors in high-performance organic field-effect transistors requires a thorough understanding of the effects that processing conditions, thermal, and bias-stress history have on device operation. Here, we evaluate the temperature dependence of the electrical properties of transistors fabricated with 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene, a material that has attracted much attention recently due to its exceptional electrical properties. We have discovered a phase transition at T = 205 K and discuss its implications on device performance and stability. We examined the impact of this low-temperature phase transition on the thermodynamic, electrical, and structural properties of both single crystals and thin films of this material. Our results show that while the changes to the crystal structure are reversible, the induced thermal stress yields irreversible degradation of the devices.

  5. Temperature Dependence of the Damping Constant Close to the I-II Phase Transition in s-TRIAZINE

    NASA Astrophysics Data System (ADS)

    Kavruk, D.; Yurtseven, H.

    The damping constant is calculated here at various temperatures for the Raman mode II in s-triazine using the soft mode-hard mode coupling model. The temperature dependence of the order parameter is used as the input data to calculate the damping constant of the Raman mode studied in this coupling model for s-triazine close to the I-II transition (Tc = 198 K). The soft mode-hard mode coupling model which considers the coupling of the soft acoustic mode with the optic modes in s-triazine, is fitted to the observed halfwidths of the Raman mode II close to the I-II phase transition in this crystal.

  6. Observations of Near-Surface Heat-Flux and Temperature Profiles Through the Early Evening Transition over Contrasting Surfaces

    NASA Astrophysics Data System (ADS)

    Jensen, Derek D.; Nadeau, Daniel F.; Hoch, Sebastian W.; Pardyjak, Eric R.

    2016-06-01

    Near-surface turbulence data from the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program are used to study countergradient heat fluxes through the early evening transition. Two sites, subjected to similar large-scale forcing, but with vastly different surface and sub-surface characteristics, are considered. The Playa site is situated at the interior of a large dry lakebed desert with high sub-surface soil moisture, shallow water table, and devoid of vegetation. The Sagebrush site is located in a desert steppe region with sparse vegetation and little soil moisture. Countergradient sensible heat fluxes are observed during the transition at both sites. The transition process is both site and height dependent. At the Sagebrush site, the countergradient flux at 5 m and below occurs when the sign change of the sensible heat flux precedes the local temperature gradient sign change. For 10 m and above, the countergradient flux occurs when the sign change of the sensible heat flux follows the local temperature gradient sign change. At the Playa site, the countergradient flux at all tower levels occurs when the sign change of the sensible heat flux follows the local temperature gradient sign change. The phenomenon is explained in terms of the mean temperature and heat-flux evolution. The temperature gradient sign reversal is a top-down process while the flux reversal occurs nearly simultaneously at all heights. The differing countergradient behaviour is primarily due to the different subsurface thermal characteristics at the two sites. The combined high volumetric heat capacity and high thermal conductivity at the Playa site lead to small vertical temperature gradients that affect the relative magnitude of terms in the heat-flux tendency equation. A critical ratio of the gradient production to buoyant production of sensible heat flux is suggested so as to predict the countergradient behaviour.

  7. High-temperature spin transition in coordination compounds of iron(II) with triazoles

    SciTech Connect

    Lavrenova, L.G.; Ikorskii, V.N.; Varnek, V.A.; Oglezneva, I.M.; Larionov, S.V.

    1986-12-01

    Methods for the synthesis of the complexes FeL/sub 3/(NO/sub 3/)/sub 2/, where L = 1,2,4-triazole (TR) (I) and 4-amino-1,2,4-triazole (ATR) (II), Fe(ATR)/sub 2.5/Cl/sub 2/ x H/sub 2/O (III), and Fe(TR)/sub 2/Cl/sub 2/ (IV) have been developed. A high-temperature (340-350/sup 0/K) reversible transition of Fe/sup II/ from the low-spin (LS) state to the high-spin (HS) state has been discovered during the study of the magnetic properties of complexes I-III. The plots of the dependence of ..mu../sub eff/ on T display hysteresis. Thus, the complexes of Fe/sup II/ with triazoles comprise a new group of compounds having this special feature. Complex III has different values of ..mu../sub eff/ at 300/sup 0/K, depending on the synthesis conditions. The plots of the dependence of ..mu../sub eff/ on T for complexes I and II and for III are different. Complex IV is basically a high-spin complex with a weakly expressed dependence of ..mu../sub eff/ on T. The Moessbauer spectra for complexes I and II and for a sample of III with ..mu../sub eff/ = 0.86 Bohr magneton at 300/sup 0/K display singlet lines with a value of delta typical of Fe/sup II/ in the LS state. In the spectra of samples of III with ..mu../sub eff/(T) = 2.05 Bohr magnetons at 300/sup 0/K there are peaks for the HS form along with the line of the LS form, the complex having two modifications in the HS form with different values of epsilon. The data form diffuse reflectance spectroscopy and the values of delta and ..mu../sub eff/ point out the octahedral coordination of Fe/sup II/, the presence of an FeN/sub 6/ chromophore in complexes I and II, and the presence of an FeN/sub 4/Cl/sub 2/ chromophore in III and IV. From an analysis of the IR spectra in the region of the torsional vibrations of the ring it follows that the ligands L are coordinated by the ring N(1) and N(2) atoms, indicating that the ligands L have bridging function.

  8. The peculiar behavior of the glass transition temperature of amorphous drug-polymer films coated on inert sugar spheres.

    PubMed

    Dereymaker, Aswin; Van Den Mooter, Guy

    2015-05-01

    Fluid bed coating has been proposed in the past as an alternative technology for manufacturing of drug-polymer amorphous solid dispersions, or so-called glass solutions. It has the advantage of being a one-step process, and thus omitting separate drying steps, addition of excipients, or manipulation of the dosage form. In search of an adequate sample preparation method for modulated differential scanning calorimetry analysis of beads coated with glass solutions, glass transition broadening and decrease of the glass transition temperature (Tg ) were observed with increasing particle size of crushed coated beads and crushed isolated films of indomethacin (INDO) and polyvinylpyrrolidone (PVP). Substituting INDO with naproxen gave comparable results. When ketoconazole was probed or the solvent in INDO-PVP films was switched to dichloromethane (DCM) or a methanol-DCM mixture, two distinct Tg regions were observed. Small particle sizes had a glass transition in the high Tg region, and large particle sizes had a glass transition in the low Tg region. This particle size-dependent glass transition was ascribed to different residual solvent amounts in the bulk and at the surface of the particles. A correlation was observed between the deviation of the Tg from that calculated from the Gordon-Taylor equation and the amount of residual solvent at the Tg of particles with different sizes. PMID:25702912

  9. Locating of normal transitions in a Bi2223 high temperature superconducting coil by non-contact voltage measurement method

    NASA Astrophysics Data System (ADS)

    Nanato, N.; Nishiyama, K.

    2015-12-01

    Locating of normal transitions in high temperature superconducting (HTS) coils is important for protection and safety design of HTS apparatus. A general method to locate the normal transitions is to measure resistive voltages along HTS windings by many voltage taps directly soldered to the HTS coils. However, electrical insulation characteristics of the HTS coils are deteriorated because it is necessary to remove electrical insulations of the HTS wires for the soldering. It is a serious problem especially for AC HTS coils to which high voltages are applied. Therefore the authors have presented a non-contact voltage measurement method that can detect the resistive voltages without removing the insulations by voltage dividing capacitors. So far the authors have verified the principle of the non-contact method. In this paper, a method to locate the normal transitions in a Bi2223 HTS coil based on the non-contact method is proposed. The proposed method can not only detect the normal transitions but also locate their positions. It is experimentally confirmed that the proposed method is useful for locating the normal transitions.

  10. Mg doping of thermochromic VO2 films enhances the optical transmittance and decreases the metal-insulator transition temperature

    NASA Astrophysics Data System (ADS)

    Mlyuka, N. R.; Niklasson, G. A.; Granqvist, C. G.

    2009-10-01

    Thermochromic films of MgxV1-xO2 were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by ˜3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by ˜10% when the Mg content was ˜7 at. %. Our results point at the usefulness of these films for energy efficient fenestration.

  11. Preparation, crystal structure, and electrical properties of thallium monosulfide in the vicinity of high-temperature phase transitions

    NASA Astrophysics Data System (ADS)

    Aliev, V. P.; Gasimov, Sh. G.; Mammadov, T. G.; Mammadov, T. S.; Nadjafov, A. I.; Seyidov, Mirhasan Yu.

    2006-12-01

    Single crystals of thallium monosulfide TlS with excess sulfur (4 at. %) are grown. The existence of monoclinic (of the TlGaSe2 type), tetragonal ordered (of the TlS type), and subtetragonal phases of thallium monosulfide is revealed using x-ray powder diffraction. The temperature dependences of the electrical conductivity and permittivity of thallium monosulfide single crystals indicate that, in the temperature range 401 411 K, these crystals undergo a phase transition to a state with superionic conduction.

  12. Thermal stress modification in regenerated fiber Bragg grating via manipulation of glass transition temperature based on CO₂-laser annealing.

    PubMed

    Lai, Man-Hong; Lim, Kok-Sing; Gunawardena, Dinusha S; Yang, Hang-Zhou; Chong, Wu-Yi; Ahmad, Harith

    2015-03-01

    In this work, we have demonstrated thermal stress relaxation in regenerated fiber Bragg gratings (RFBGs) by using direct CO₂-laser annealing technique. After the isothermal annealing and slow cooling process, the Bragg wavelength of the RFBG has been red-shifted. This modification is reversible by re-annealing and rapid cooling. It is repeatable with different cooling process in the subsequent annealing treatments. This phenomenon can be attributed to the thermal stress modification in the fiber core by means of manipulation of glass transition temperature with different cooling rates. This finding in this investigation is important for accurate temperature measurement of RFBG in dynamic environment. PMID:25723423

  13. Investigation of effective base transit time and current gain modulation of light-emitting transistors under different ambient temperatures

    SciTech Connect

    Yang, Hao-Hsiang; Tu, Wen-Chung; Wang, Hsiao-Lun; Wu, Chao-Hsin

    2014-11-03

    In this report, the modulation of current gain of InGaP/GaAs light-emitting transistors under different ambient temperatures are measured and analyzed using thermionic emission model of quantum well embedded in the transistor base region. Minority carriers captured by quantum wells gain more energy at high temperatures and escape from quantum wells resulting in an increase of current gain and lower optical output, resulting in different I-V characteristics from conventional heterojunction bipolar transistors. The effect of the smaller thermionic lifetime thus reduces the effective base transit time of transistors at high temperatures. The unique current gain enhancement of 27.61% is achieved when operation temperature increase from 28 to 85 °C.

  14. DEFLAGRATION-TO-DETONATION TRANSITION IN LX-04 AS A FUNCTION OF LOADING DENSITY, TEMPERATURE, AND CONFINEMENT

    SciTech Connect

    Sandusky, H W; Granholm, R H; Bohl, D G; Hare, D E; Vandersall, K S; Garcia, F

    2005-06-01

    The potential for deflagration-to-detonation transition (DDT) in LX-04 (85/15 HMX/Viton) is being evaluated as a function of loading density, temperature, and confinement. In the high confinement arrangement, a matrix of tests will be performed with the LX-04 loaded at {approx}50, 70, 90, and {approx}99 %TMD; and temperatures of ambient, 160 C, and 190 C, at each loading density. A more limited set of tests at medium confinement will be conducted. As expected, LX-04 does not undergo DDT at near TMD loadings in both medium and high confinement, although the later still results in significant fragmentation. In high confinement at pour density (50.3 %TMD), LX-04 does not transit to detonation at 160 C, but does at ambient and 190 C with the shortest run distance to detonation (l) at ambient temperature. With a 70% TMD loading at ambient temperature, l was even less. The limited ambient temperature measurements for l in high confinement are similar to previous data for 91/9 HMX/wax, which has nearly the same %volume of HMX as LX-04.

  15. DEFLAGRATION-TO-DETONATION TRANSITION IN LX-04 AS A FUNCTION OF LOADING DENSITY, TEMPERATURE, AND CONFINEMENT

    SciTech Connect

    Sandusky, H W; Granholm, R H; Bohl, D G; Vandersall, K S; Hare, D E; Garcia, F

    2006-06-20

    The potential for deflagration-to-detonation transition (DDT) in LX-04 (85/15 HMX/Viton) is being evaluated as a function of loading density, temperature, and confinement. In the high confinement arrangement, a matrix of tests is nearly completed with the LX-04 loaded at {approx} 51, 70, 90, and {approx} 99% of theoretical maximum density (TMD); and temperatures of ambient, 160 C, and 190 C at each loading density. A more limited set of tests with {approx}99 %TMD loadings at medium confinement were conducted at temperatures of ambient and 186 C. LX-04 does not undergo DDT at near TMD loadings in both medium and high confinement, although the latter still results in significant fragmentation. Most porous beds in high confinement undergo DDT, with the minimum run distance to detonation (l) for a 70 %TMD loading at ambient temperature. LX-04 does not transit to detonation for a pour density (51.3 %TMD) loading at 160 C, but does at 190 C with a longer l than at ambient. The limited ambient temperature measurements for l in high confinement are similar to previous data for 91/9 HMX/wax, which has nearly the same %volume of HMX as LX-04.

  16. The influence of copper precipitation and plastic deformation hardening on the impact-transition temperature of rolled structural steels

    NASA Astrophysics Data System (ADS)

    Aróztegui, Juan J.; Urcola, José J.; Fuentes, Manuel

    1989-09-01

    Commercial electric arc melted low-carbon steels, provided as I beams, were characterized both microstructurally and mechanically in the as-rolled, copper precipitation, and plastically pre-deformed conditions. Inclusion size distribution, ferrite grain size, pearlite volume fraction, precipitated volume fraction of copper, and size distribution of these precipitates were deter-mined by conventional quantitative optical and electron metallographic techniques. From the tensile tests conducted at a strain rate of 10-3 s-1 and impact Charpy V-notched tests carried out, stress/strain curves, yield stress, and impact-transition temperature were obtained. The spe-cific fractographic features of the fracture surfaces also were quantitatively characterized. The increases in yield stress and transition temperature experienced upon either aging or work hard-ening were related through empirical relationships. These dependences were analyzed semi-quantitatively by combining microscopic and macroscopic fracture criteria based on measured fundamental properties (fracture stress and yield stress) and observed fractographic parameters (crack nucleation distance and nuclei size). The rationale developed from these fracture criteria allows the semiquantitative prediction of the temperature transition shifts produced upon aging and work hardening. The values obtained are of the right order of magnitude.

  17. Measurement of the volatility and glass transition temperatures of glasses produced during the DWPF startup test program

    SciTech Connect

    Marra, J.C.; Harbour, J.R.

    1995-10-18

    The Defense Waste Processing Facility (DWPF) will immobilize high-level radioactive waste currently stored in underground tanks at the Savannah River Site by incorporating the waste into a glass matrix. The molten waste glass will be poured into stainless steel canisters which will be welded shut to produce the final waste form. One specification requires that any volatiles produced as a result of accidentally heating the waste glass to the glass transition temperature be identified. Glass samples from five melter campaigns, run as part of the DWPF Startup Test Program, were analyzed to determine glass transition temperatures and to examine the volatilization (by weight loss). Glass transition temperatures (T{sub g}) for the glasses, determined by differential scanning calorimetry (DSC), ranged between 445 C and 474 C. Thermogravimetric analysis (TGA) scans showed that no overall weight loss occurred in any of the glass samples when heated to 500 C. Therefore, no volatility will occur in the final glass product when heated up to 500 C.

  18. Linear-in-temperature resistivity close to a topological metal insulator transition in ultra-multi valley fcc-ytterbium

    NASA Astrophysics Data System (ADS)

    Enderlein, Carsten; Fontes, Magda; Baggio-Saitovich, Elisa; Continentino, Mucio A.

    2016-01-01

    The semimetal-to-semiconductor transition in fcc-Yb under modest pressure can be considered a picture book example of a metal-insulator transition of the Lifshitz type. We have performed transport measurements at low temperatures in the closest vicinity of the transition and related DFT calculations of the Fermi surface. Our resistivity measurements show a linear temperature dependence with an unusually low dρ / dT at low temperatures approaching the MIT. The calculations suggest fcc-ytterbium being an ultra-multi valley system with 24 electron and 6 hole pockets in the Brillouin zone. Such Fermi surface topology naturally supports the appearance of strongly correlated phases. An estimation of the quasiparticle-enhanced effective mass shows that the scattering rate is by at least two orders of magnitude lower than in other materials which exhibit linear-in-T behavior at a quantum critical point. However, we cannot exclude an excessive effective mass enhancement, when the van Hove singularity touches the Fermi level.

  19. Half-Metallic Behavior in Doped Sr2CrOsO6 Double Perovskite with High Transition Temperature.

    PubMed

    Samanta, Kartik; Sanyal, Prabuddha; Saha-Dasgupta, Tanusri

    2015-01-01

    Half-metallic magnets with metallic behavior in one spin channel and insulating in the other, have attracted considerable attention due to their potential application possibility. The spin-dependent nature of the carrier scattering due to half-metallic nature of these materials, allows for the resistance to be strongly influenced by the low magnetic field. However, the operating temperatures of such known materials are generally low, opening up the need for half-metallic magnets with high transition temperatures. The double perovskites having general formula A2BB'O6 with alternating ordered arrangement of two transition metal sites, B and B' offer an attractive possibility in this respect. Here, we consider the case of Sr2CrOsO6, which is a ferrimagnetic insulator with transition temperature (Tc) of 725 K, highest ever known in the oxide family, and show that moderate amount of La and Na doping at Sr site can drive the compound half-metallic with high Tc. PMID:26446395

  20. High temperature phase transition in SOFC anodes based on Sr{sub 2}MgMoO{sub 6-{delta}}

    SciTech Connect

    Marrero-Lopez, D.; Pena-Martinez, J.; Ruiz-Morales, J.C.; Martin-Sedeno, M.C.; Nunez, P.

    2009-05-15

    The double perovskite Sr{sub 2}MgMoO{sub 6-{delta}} has been recently reported as an efficient anode material for solid oxide fuel cells (SOFCs). In the present work, this material have been investigated by high temperature X-ray diffraction (XRD), differential scanning calorimetry (DSC) and impedance spectroscopy to further characterise its properties as SOFC anode. DSC and XRD measurements indicate that Sr{sub 2}MgMoO{sub 6-{delta}} exhibits a reversible phase transition around 275 deg. C from triclinic (I1-bar) with an octahedral tilting distortion to cubic (Fm3-barm) without octahedral distortion. This phase transition is continuous with increasing temperature without any sudden cell volume change during the phase transformation. The main effect of the phase transformation is observed in the electrical conductivity with a change in the activation energy at low temperature. La{sup 3+} and Fe-substituted Sr{sub 2}MgMoO{sub 6-{delta}} phases were also investigated, however these materials are unstable under oxidising conditions due to phase segregations above 600 deg. C. - Graphical abstract: The double perovskite Sr{sub 2}MgMoO{sub 6}, recently proposed as an efficient SOFC anode for direct hydrocarbon oxidation, exhibits a reversible structural phase transition from triclinic to cubic at 275 deg. C.

  1. Southern Ocean and Antarctic Peninsula Temperatures During Critical Climate Transitions of the Cenozoic Constrained by Clumped Isotope Thermometry

    NASA Astrophysics Data System (ADS)

    Dill, R.; Eagle, R.; Henry, D.; Praskin, S.; Mering, J. A.; Petryshyn, V. A.; Priyadarshi, A.; Rycroft, L.; Vollmer, T.; Chea, Y.; Dix, J.; Aguilar, A.; Supakkul, K.; Tran, B.; Lipel, Z.; Flores, S.; Riesselman, C. R.; Taviani, M.; Marenssi, S.; Harwood, D. M.; Lunt, D. J.; Valdes, P. J.; Meckler, A. N.; Tripati, A.

    2014-12-01

    The Southern Ocean and Antarctica play fundamental roles in the global climate system. These polar regions are a major area for the net loss of heat to space. Ice storage on Antarctica also influences the global water cycle. Through upwelling of deep waters, the Southern Ocean is an important regulator of atmospheric CO2. To better constrain the evolution of paleoclimate in this region over major climate transitions of the Cenozoic, we estimated ocean temperatures using clumped isotope thermometry. Clumped isotope thermometry is a thermodynamically-based stable isotope thermometer that can be used to constrain temperatures previously estimated using other paleothermometers (which in turn leads to constraints on ice volume), as it allows the exclusion of water isotope composition from temperature estimates (unlike the δ18O thermometer). We previously have published calibrations for foraminifera and mollusks, two of the major archives used in this study. Critical transitions investigated include the Eocene-Oligocene boundary and the Middle Miocene Climate Transition. Study sites include Seymour Island (Antarctic Peninsula), ANDRILL (Southern McMurdo Sounds), Ocean Drilling Program (ODP) Sites 689/690 (Weddell Sea), and ODP 744 (Kerguelen Plateau). Results will be compared to GCM output.

  2. A Physically Based Correlation of Irradiation-Induced Transition Temperature Shifts for RPV Steels

    SciTech Connect

    Eason, Ernest D.; Odette, George Robert; Nanstad, Randy K; Yamamoto, Takuya

    2007-11-01

    The reactor pressure vessels (RPVs) of commercial nuclear power plants are subject to embrittlement due to exposure to high-energy neutrons from the core, which causes changes in material toughness properties that increase with radiation exposure and are affected by many variables. Irradiation embrittlement of RPV beltline materials is currently evaluated using Regulatory Guide 1.99 Revision 2 (RG1.99/2), which presents methods for estimating the shift in Charpy transition temperature at 30 ft-lb (TTS) and the drop in Charpy upper shelf energy (ΔUSE). The purpose of the work reported here is to improve on the TTS correlation model in RG1.99/2 using the broader database now available and current understanding of embrittlement mechanisms. The USE database and models have not been updated since the publication of NUREG/CR-6551 and, therefore, are not discussed in this report. The revised embrittlement shift model is calibrated and validated on a substantially larger, better-balanced database compared to prior models, including over five times the amount of data used to develop RG1.99/2. It also contains about 27% more data than the most recent update to the surveillance shift database, in 2000. The key areas expanded in the current database relative to the database available in 2000 are low-flux, low-copper, and long-time, high-fluence exposures, all areas that were previously relatively sparse. All old and new surveillance data were reviewed for completeness, duplicates, and discrepancies in cooperation with the American Society for Testing and Materials (ASTM) Subcommittee E10.02 on Radiation Effects in Structural Materials. In the present modeling effort, a 10% random sample of data was reserved from the fitting process, and most aspects of the model were validated with that sample as well as other data not used in calibration. The model is a hybrid, incorporating both physically motivated features and empirical calibration to the U.S. power reactor surveillance

  3. Growth temperature-dependent metal-insulator transition of vanadium dioxide epitaxial films on perovskite strontium titanate (111) single crystals

    NASA Astrophysics Data System (ADS)

    Wang, Liangxin; Yang, Yuanjun; Zhao, Jiangtao; Hong, Bin; Hu, Kai; Peng, Jinlan; Zhang, Haibin; Wen, Xiaolei; Luo, Zhenlin; Li, Xiaoguang; Gao, Chen

    2016-04-01

    Vanadium dioxide (VO2) epitaxial films were grown on perovskite single-crystal strontium titanate (SrTiO3) substrates by reactive radio-frequency magnetron sputtering. The growth temperature-dependent metal-insulator transition (MIT) behavior of the VO2 epitaxial films was then investigated. We found that the order of magnitude of resistance change across the MIT increased from 102 to 104 with increasing growth temperature. In contrast, the temperature of the MIT does not strongly depend on the growth temperature and is fairly stable at about 345 K. On one hand, the increasing magnitude of the MIT is attributed to the better crystallinity and thus larger grain size in the (010)-VO2/(111)-SrTiO3 epitaxial films at elevated temperature. On the other hand, the strain states do not change in the VO2 films deposited at various temperatures, resulting in stable V-V chains and V-O bonds in the VO2 epitaxial films. The accompanied orbital occupancy near the Fermi level is also constant and thus the MIT temperatures of VO2 films deposited at various temperatures are nearly the same. This work demonstrates that high-quality VO2 can be grown on perovskite substrates, showing potential for integration into oxide heterostructures and superlattices.

  4. Phase transition in Ba{sub 2}In{sub 2}O{sub 5} studied by in situ high temperature X-ray diffraction using synchrotron radiation

    SciTech Connect

    Rey, J. F. Q.; Ferreira, F. F.; Muccillo, E. N. S.

    2009-01-29

    The order-disorder phase transition in Ba{sub 2}In{sub 2}O{sub 5} high-temperature ionic conductor was systematically studied by in situ high-temperature X-ray diffraction using synchrotron radiation and electrical conductivity. Pure barium indate was prepared by solid state reactions at 1300 deg. C. The room-temperature structural characterization showed a high degree of phase homogeneity in the prepared material. The reduction of the order-disorder phase transition temperature was verified by electrical conductivity and high-temperature X-ray diffraction. The observed features were explained based on Fourier-transform infrared spectroscopy results that revealed the presence of hydroxyl species in the crystal lattice. The increase of the intensity of few diffraction peaks near the phase transition temperature suggests the formation of a superstructure before the orthorhombic-to-tetragonal phase transition.

  5. Exploring thermal and mechanical properties of selected transition elements under extreme conditions: Experiments at high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Hrubiak, Rostislav

    Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents: • An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K). • An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T.. • New phase diagrams created for Hf, Ti and Zr from experimental data. • P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope. • New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams. • First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled); All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature); Complete thermodynamic data for selected elements from standard to extreme conditions. The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software, tabulated values of all thermodynamic and volume data for the 13 metals at high P-T are included in the APPENDIX. In the APPENDIX, a description of several other high-pressure studies of selected

  6. Ability of Lactobacillus rhamnosus GAF01 to remove AFM1 in vitro and to counteract AFM1 immunotoxicity in vivo.

    PubMed

    Abbès, Samir; Salah-Abbès, Jalila Ben; Sharafi, Hakimeh; Jebali, Rania; Noghabi, Kambiz Akbari; Oueslati, Ridha

    2013-01-01

    Aflatoxin M1 (AFM1) has been detected in many parts of the world both in raw milk and many dairy products, causing great economic losses and human disease. Unfortunately, there are few studies dealing with AFM1 immunotoxicity/interactions with lactic acid bacteria for potential application as a natural preventive agent. The aim of this study was to isolate (from dairy products) food-grade probiotic bacteria able to degrade/bind AFM1 in vitro and evaluate whether the same organism(s) could impart a protective role against AFM1-induced immunotoxicity in exposed Balb/c mice. Bacteria (Lactobacillus plantarum MON03 and L. rhamnosus GAF01) were isolated from Tunisian artisanal butter and then tested for abilities to eliminate AFM1 from phosphate-buffered saline (PBS) and reconstituted milk (containing 0.05, 0.10, and 0.20 µg AFM1/ml) after 0, 6, and 24 h at 37°C. Results showed that the selected bacteria could 'remove' AFM1 both in PBS and skimmed milk. The binding abilities of AFM1 by L. plantarum MON03 and L. rhamnosus GAF01 strains (at 10(8) CFU/ml) in PBS and reconstituted milk ranged, respectively, from 16.1-78.6% and 15.3-95.1%; overall, L. rhamnosus showed a better potential for removal than L. plantarum. 'Removal' appeared to be by simple binding; the bacteria/AFM1 complex was stable and only a very small proportion of mycotoxin was released back into the solution. L. rhamnosus GAF01 had the highest binding capacity and was selected for use in the in vivo study. Those results indicated that use of the organism prevented AFM1-induced effects on total white and red blood cells, and lymphocyte subtypes, after 15 days of host treatment. These studies clearly indicated that L. rhamnosus GAF01 was able to bind AFM1 in vitro and-by mechanisms that might also be related to a binding effect-counteract AFM1-induced immunotoxicity. Moreover, by itself, this bacterium was not toxic and could potentially be used as an additive in dairy products and in biotechnology for

  7. The influence of hydrogen on the transition from power-law creep to low-temperature plasticity of olivine at lithospheric temperatures

    NASA Astrophysics Data System (ADS)

    Tielke, Jacob; Zimmerman, Mark; Kohlstedt, David

    2015-04-01

    At high-temperature (asthenospheric) conditions, strain rate of olivine-rich mantle rocks follows a power-law dependence on stress. At lower-temperature (lithospheric) conditions, strain rate exhibits an exponential dependence on stress. However, the influence of water (hydrogen) on the transition from high-temperature to low-temperature behavior is poorly constrained. To investigate the influence of water on the transition in flow regimes at lithospheric conditions, deformation experiments on single crystals of San Carlos olivine under both wet (hydrogen-rich) and dry (hydrogen-poor) conditions were carried out. Crystals were oriented relative to the applied load to exert the maximum shear stress on the (100)[001] and (001)[100] dislocation slip systems, which are the dominate (weakest) slip systems at both low temperatures and under wet conditions. Experiments were carried out using a gas-medium apparatus with high resolution in stress (±2 MPa) and temperature (±2°C). For the wet experiments, hydrogen was supplied to the crystals using talc sealed in nickel jackets. Deformation experiments were carried out in either triaxial compression or direct shear geometries at 1000-1300°C, differential stresses of 120 to 670 MPa, and resultant strain rates of 6 x 10-6 to 4 x 10-4 s-1. At high-temperature, under dry conditions, strain rate is a power-law function of stress with a stress exponent of 3.5 and an Arrhenius function of temperature with an activation energy of 520 kJ/mol. At low-temperature and high-stress conditions, under dry conditions, strain rate increases exponentially with increasing stress with an activation energy of 360 kJ/mol. These observations are consistent with a transition from a climb-controlled dislocation mechanism at higher temperatures to a glide-controlled dislocation mechanism at lower temperatures for hydrogen-poor olivine crystals. Under wet conditions, the strain rate dependence on stress follows a power-law relationship with a stress

  8. Atomic force microscopy combined with optical tweezers (AFM/OT)

    NASA Astrophysics Data System (ADS)

    Pierini, F.; Zembrzycki, K.; Nakielski, P.; Pawłowska, S.; Kowalewski, T. A.

    2016-02-01

    The role of mechanical properties is essential to understand molecular, biological materials, and nanostructures dynamics and interaction processes. Atomic force microscopy (AFM) is the most commonly used method of direct force evaluation, but due to its technical limitations this single probe technique is unable to detect forces with femtonewton resolution. In this paper we present the development of a combined atomic force microscopy and optical tweezers (AFM/OT) instrument. The focused laser beam, on which optical tweezers are based, provides us with the ability to manipulate small dielectric objects and to use it as a high spatial and temporal resolution displacement and force sensor in the same AFM scanning zone. We demonstrate the possibility to develop a combined instrument with high potential in nanomechanics, molecules manipulation and biological studies. AFM/OT equipment is described and characterized by studying the ability to trap dielectric objects and quantifying the detectable and applicable forces. Finally, optical tweezers calibration methods and instrument applications are given.

  9. Magnetocaloric effect and critical behavior in Pr0.5Sr0.5MnO3: an analysis of the validity of the Maxwell relation and the nature of the phase transitions.

    PubMed

    Caballero-Flores, R; Bingham, N S; Phan, M H; Torija, M A; Leighton, C; Franco, V; Conde, A; Phan, T L; Yu, S C; Srikanth, H

    2014-07-16

    The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr0.5Sr0.5MnO3, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at TC ~ 247 K, and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at TN ~ 165 K. We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, ΔSM) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of ΔSM calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the field- and temperature-dependent magnetization [Formula: see text] curves, and hence the [Formula: see text] curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature TC, but a noticeable discrepancy is present for [Formula: see text]. This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix. PMID:24945593

  10. Concentration- and Temperature-Induced Phase Transitions in PrAlO3-SrTiO3 System.

    PubMed

    Vasylechko, Leonid; Stepchuk, Roman; Prots, Yuri; Rosner, Helge

    2016-12-01

    Single-phase mixed aluminates-titanates Pr1-x Sr x Al1-x Ti x O3 (x = 0.1, 0.2, 0.3, 0.5, 0.7) with rhombohedral perovskite structure were prepared by solid-state reaction technique at 1823-1873 K. Morphotropic rhombohedral-to-cubic phase transition in Pr1-x Sr x Al1-x Ti x O3 series is predicted to occur at x = 0.88. The temperature-induced structural phase transition R  [Formula: see text]  с - Pm [Formula: see text]  m in Pr0.5Sr0.5Al0.5Ti0.5O3, detected at 930 K by in situ high-temperature X-ray synchrotron powder diffraction, occurs at considerably lower temperature as the corresponding transformation in the parent compound PrAlO3 (1770 K). Such remarkable drop of the transition temperature is explained by gradual decrease of the perovskite structure deformation in the Pr1-x Sr x Al1-x Ti x O3 series with increasing Sr and Ti contents as a consequence of the increasing Goldschmidt tolerance factor. For Pr0.3Sr0.7Al0.3Ti0.7O3 phase, a sequence of the low-temperature phase transformation R  [Formula: see text]  с - Immb(C2/m) - I4/mcm was detected. PMID:26759353

  11. Nanoscale structural features determined by AFM for single virus particles.

    PubMed

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

    2013-11-21

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

  12. The Conductance of Nanotubes Deformed by the AFM Tip

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Maiti, Amitesh; Anantram, M. P.

    2003-01-01

    The conductance drop under AFM-tip deformation can be explained by stretching of the tube length. NT sensors can be built utilizing uniform stretching. Single sp3 bond cross section cannot block electrons, because another conducting path may exist. AFM tip which forms sp3 bonds with the tube will decrease conductance. In the "table experiment" a conductance drop of 2 orders of magnitude happened only after some bonds were broken.

  13. Characterization of the interaction between AFM tips and surface nanobubbles.

    PubMed

    Walczyk, Wiktoria; Schönherr, Holger

    2014-06-24

    While the presence of gaseous enclosures observed at various solid-water interfaces, the so-called "surface nanobubles", has been confirmed by many groups in recent years, their formation, properties, and stability have not been convincingly and exhaustively explained. Here we report on an atomic force microscopy (AFM) study of argon nanobubbles on highly oriented pyrolitic graphite (HOPG) in water to elucidate the properties of nanobubble surfaces and the mechanism of AFM tip-nanobubble interaction. In particular, the deformation of the nanobubble-water interface by the AFM tip and the question whether the AFM tip penetrates the nanobubble during scanning were addressed by this combined intermittent contact (tapping) mode and force volume AFM study. We found that the stiffness of nanobubbles was smaller than the cantilever spring constant and comparable with the surface tension of water. The interaction with the AFM tip resulted in severe quasi-linear deformation of the bubbles; however, in the case of tip-bubble attraction, the interface deformed toward the tip. We tested two models of tip-bubble interaction, namely, the capillary force and the dynamic interaction model, and found, depending on the tip properties, good agreement with experimental data. The results showed that the tip-bubble interaction strength and the magnitude of the bubble deformation depend strongly on tip and bubble geometry and on tip and substrate material, and are very sensitive to the presence of contaminations that alter the interfacial tension. In particular, nanobubbles interacted differently with hydrophilic and hydrophobic AFM tips, which resulted in qualitatively and quantitatively different force curves measured on the bubbles in the experiments. To minimize bubble deformation and obtain reliable AFM results, nanobubbles must be measured with a sharp hydrophilic tip and with a cantilever having a very low spring constant in a contamination-free system. PMID:24856074

  14. Structural disorder and its effect on the superconducting transition temperature in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

    SciTech Connect

    Su, X.; Zuo, F.; Schlueter, J.A.; Kelly, M.E.; Williams, J.M.

    1998-06-01

    In this paper, we report direct evidence of a structural transition in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br near 80 K and the effect of disorder on the superconducting transition temperature. By cooling the sample from above 80 K, the interlayer magnetoresistance displays a bumplike feature, which increases sharply with increasing cooling rate. The rapidly cooled sample has a much larger resistivity and a lower transition temperature, which decreases linearly with increasing resistivity near the transition temperature. We propose that rapid cooling quenches the sample into a disordered state. Localized moments in the disordered state reduce the superconducting transition temperature. {copyright} {ital 1998} {ital The American Physical Society}

  15. Gate-tuned superconductor-insulator transition in (Li,Fe)OHFeSe

    NASA Astrophysics Data System (ADS)

    Lei, B.; Xiang, Z. J.; Lu, X. F.; Wang, N. Z.; Chang, J. R.; Shang, C.; Zhang, A. M.; Zhang, Q. M.; Luo, X. G.; Wu, T.; Sun, Z.; Chen, X. H.

    2016-02-01

    The antiferromagnetic (AFM) insulator-superconductor transition has always been a center of interest in the underlying physics of unconventional superconductors. However, in the family of iron-based high-Tc superconductors, no intrinsic superconductor-insulator transition has been confirmed so far. Here, we report a first-order transition from superconductor to AFM insulator with a strong charge doping induced by ionic gating in the thin flakes of single crystal (Li,Fe)OHFeSe. The superconducting transition temperature (Tc) is continuously enhanced with electron doping by ionic gating up to a maximum Tc of 43 K, and a striking superconductor-insulator transition occurs just at the verge of optimal doping with highest Tc. A phase diagram of temperature-gating voltage with the superconductor-insulator transition is mapped out, indicating that the superconductor-insulator transition is a common feature for unconventional superconductivity. These results help to uncover the underlying physics of iron-based superconductivity as well as the universal mechanism of high-Tc superconductivity. Our finding also suggests that the gate-controlled strong charge doping makes it possible to explore novel states of matter in a way beyond traditional methods.

  16. Metal-insulator transition in antiferromagnetic Ba1−xKxMn2As2 (0≤x≤0.4) single crystals studied by 55Mn and 75As NMR

    SciTech Connect

    Yeninas, Steven; Pandey, Abhishek; Ogloblichev, V.; Mikhalev, K.; Johnston, David C.; Furukawa, Yuji

    2013-12-23

    The magnetic structure and metal-insulator transition in antiferromagnetic (AFM) BaMn2As2 and Ba1−xKxMn2As2 single crystals have been investigated by 55Mn and 75As nuclear magnetic resonance (NMR) measurements. In the parent AFM insulator BaMn2As2 with a Néel temperature TN=625 K, we observed a 55Mn zero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from the field dependence of the 55Mn spectra and 75As NMR spectra below TN. In hole-doped crystals with x>0.01, similar 55Mn ZFNMR spectra were observed and the AFM state was revealed to be robust up to x=0.4 with the ordered moment nearly independent of x. The nuclear spin-lattice relaxation rates (1/T1) for both nuclei in the doped samples follow the Korringa relation T1T=const, indicating a metallic state. This confirms the coexistence of AFM ordered localized Mn spins and conduction carriers from a microscopic point of view. From the x dependence of (T1T)−1/2 for both nuclei, we conclude that this transition is caused by vanishing of the hole concentration as the transition is approached from the metallic side.

  17. Winter to Spring Transition in Europe 48-45 degrees N: From Temperature Control by Advection to Control by Insolation

    NASA Technical Reports Server (NTRS)

    Otterman, J.; Ardizzone, J.; Atlas, R.; Hu, H.; Jusem, J. C.; Starr, D.

    1999-01-01

    As established in previous studies, and analyzed further herein for the years 1988-1998, warm advection from the North Atlantic is the predominant control of the surface-air temperature in northern-latitude Europe in late winter. This thesis is supported by the substantial correlation Cti between the speed of the southwesterly surface winds over the eastern North Atlantic, as quantified by a specific Index Ina, and the 2-meter level temperature Ts over central Europe (48-54 deg N; 5-25 deg E), for January, February and early March. In mid-March and subsequently, the correlation Cti drops drastically (quite often it is negative). The change in the relationship between Ts and Ina marks a transition in the control of the surface-air temperature. As (a) the sun rises higher in the sky, (b) the snows melt (the surface absorptivity can increase by a factor of 3.0), (c) the ocean-surface winds weaken, and (d) the temperature difference between land and ocean (which we analyze) becomes small, absorption of insolation replaces the warm advection as the dominant control of the continental temperature. We define the onset of spring by this transition, which evaluated for the period of our study occurs at pentad 16 (Julian Date 76, that is, March 16). The control by insolation means that the surface is cooler under cloudy conditions than under clear skies. This control produces a much smaller interannual variability of the surface temperature and of the lapse rate than prevailing in winter, when the control is by advection. Regional climatic data would be of greatest value for agriculture and forestry if compiled for well-defined seasons. For continental northern latitudes, analysis presented here of factors controlling the surface temperature appears an appropriate tool for this task.

  18. Temperature effect on the build-up of exponentially growing polyelectrolyte multilayers. An exponential-to-linear transition point.

    PubMed

    Vikulina, Anna S; Anissimov, Yuri G; Singh, Prateek; Prokopović, Vladimir Z; Uhlig, Katja; Jaeger, Magnus S; von Klitzing, Regine; Duschl, Claus; Volodkin, Dmitry

    2016-03-21

    In this study, the effect of temperature on the build-up of exponentially growing polyelectrolyte multilayer films was investigated. It aims at understanding the multilayer growth mechanism as crucially important for the fabrication of tailor-made multilayer films. Model poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers were assembled in the temperature range of 25-85 °C by layer-by-layer deposition using a dipping method. The film growth switches from the exponential to the linear regime at the transition point as a result of limited polymer diffusion into the film. With the increase of the build-up temperature the film growth rate is enhanced in both regimes; the position of the transition point shifts to a higher number of deposition steps confirming the diffusion-mediated growth mechanism. Not only the faster polymer diffusion into the film but also more porous/permeable film structure are responsible for faster film growth at higher preparation temperature. The latter mechanism is assumed from analysis of the film growth rate upon switching of the preparation temperature during the film growth. Interestingly, the as-prepared films are equilibrated and remain intact (no swelling or shrinking) during temperature variation in the range of 25-45 °C. The average activation energy for complexation between PLL and HA in the multilayers calculated from the Arrhenius plot has been found to be about 0.3 kJ mol(-1) for monomers of PLL. Finally, the following processes known to be dependent on temperature are discussed with respect to the multilayer growth: (i) polymer diffusion, (ii) polymer conformational changes, and (iii) inter-polymer interactions. PMID:26911320

  19. Modeling the Interaction between AFM Tips and Pinned Surface Nanobubbles.

    PubMed

    Guo, Zhenjiang; Liu, Yawei; Xiao, Qianxiang; Schönherr, Holger; Zhang, Xianren

    2016-01-26

    Although the morphology of surface nanobubbles has been studied widely with different AFM modes, AFM images may not reflect the real shapes of the nanobubbles due to AFM tip-nanobubble interactions. In addition, the interplay between surface nanobubble deformation and induced capillary force has not been well understood in this context. In our work we used constraint lattice density functional theory to investigate the interaction between AFM tips and pinned surface nanobubbles systematically, especially concentrating on the effects of tip hydrophilicity and shape. For a hydrophilic tip contacting a nanobubble, its hydrophilic nature facilitates its departure from the bubble surface, displaying a weak and intermediate-range attraction. However, when the tip squeezes the nanobubble during the approach process, the nanobubble shows an elastic effect that prevents the tip from penetrating the bubble, leading to a strong nanobubble deformation and repulsive interactions. On the contrary, a hydrophobic tip can easily pierce the vapor-liquid interface of the nanobubble during the approach process, leading to the disappearance of the repulsive force. In the retraction process, however, the adhesion between the tip and the nanobubble leads to a much stronger lengthening effect on nanobubble deformation and a strong long-range attractive force. The trends of force evolution from our simulations agree qualitatively well with recent experimental AFM observations. This favorable agreement demonstrates that our model catches the main intergradient of tip-nanobubble interactions for pinned surface nanobubbles and may therefore provide important insight into how to design minimally invasive AFM experiments. PMID:26751634

  20. Temperature and Pressure Dependent Phase Transitions of β'-LiZr2(PO4)3 Studied by Raman Spectroscopy.

    PubMed

    Kamali, K; Ravindran, T R

    2016-03-31

    LiZr2(PO4)3 (LZP) belongs to the NASICON family of compounds whose ionic conductivity can be tuned by substitution of different cations or by increasing the temperature or pressure. Besides its conductivity, thermal and electrochemical stability makes it useful as a cathode material for lithium-ion energy storage devices. Temperature dependent Raman spectroscopic studies were carried out on the monoclinic (β') phase of LZP in the temperature range 298-853 K. A reversible structural phase transition driven by disorder in lithium sites is observed at 603 K. The spectral data enable an understanding of dynamics of the mobile Li ion and PO4 internal modes across the orthorhombic structural phase transition. On the basis of these studies, a reported change in the conductivity around 600 K is explained. High pressure Raman spectroscopic measurements on β'-LiZr2(PO4)3 reveal the onset of a structural phase transformation at 3.8 GPa and amorphization above 10 GPa. On decompression from 26 GPa, the amorphous phase remains unchanged, indicating irreversible nature of pressure-induced amorphization. Three low frequency Raman modes at 100, 124, and 144 cm(-1), which soften with an increase in pressure could be the driving force for the phase transition at 3.8 GPa. Pressure-induced phase transition prior to amorphization in β'-LiZr2(PO4)3 could be due to collapse of Zr-O-P bond angles. Pressure-induced amorphization in this compound might be due to kinetic hindrance of equilibrium decomposition. PMID:26959504

  1. B to D(D*)e{nu}{sub e} transitions at finite temperature in QCD

    SciTech Connect

    Azizi, K.; Er, N.

    2010-05-01

    In this article, we work out the properties of the B, D, and D* mesons as well as the B{yields}D(D*)e{nu}{sub e} decay properties at finite temperature QCD. The behavior of the masses, decay constants and widths of the B, D, and D* mesons in terms of the temperature is studied. The temperature dependency of the form factors responsible for such decays are also obtained. These temperature-dependent form factors are used to investigate the variation of the branching ratios with respect to the temperature. It is shown that the branching ratios do not change up to T/T{sub c}=0.3, however they start to diminish with increasing the temperature after this region and vanish at the critical or deconfinement temperature.

  2. Phase lamination in a t-J bilayer at finite temperature

    NASA Astrophysics Data System (ADS)

    Voo, Khee-Kyun

    2016-05-01

    A bilayered t- J model is investigated with a slave boson mean field theory. A spontaneous phase lamination (PL) into a layer dominated by antiferromagnetism (AFM) and a layer dominated by superconductivity (SC) is found at a low doping density and low temperature regime. Raising the temperature removes the PL and SC, turns the system into a homogeneously antiferromagnetic (AF) bilayer, and eventually a homogeneously paramagnetic bilayer at high temperature. The PL circumvents the competition between AFM and SC, and may result in a higher superconducting transition temperature. The density of states of low energy single particle excitation in the homogeneously AF state at intermediate temperature is reduced by the AF scattering. The relation between this study and the bilayered superconducting cuprates is discussed.

  3. Nonuniqueness of H23 and H2 field-temperature transition lines in spin-glasses

    NASA Astrophysics Data System (ADS)

    Wenger, L. E.; Mydosh, J. A.

    1984-04-01

    Including the magnetic field dependence on the superparamagnetic relaxation time τ, "transition" lines in the H-T plane are obtained for constant τ. These lines follow the relation TH-T0~Hν where ν~23 except for H-->0 which shows a crossover to ν=2. Thus a power law similar to that derived from mean-field models of spin-glasses is obtained, based strictly on a superparamagnetic relaxation-time approach. This questions the conclusion that experimental observations of H-T lines are solely the result of a mean-field phase transition.

  4. Structural phase transitions in EuFe[subscript 2]As[subscript 2] superconductor at low temperatures and high pressures

    SciTech Connect

    Uhoya, Walter O.; Tsoi, Georgiy M.; Vohra, Yogesh K.; McGuire, Michael A.; Sefat, Athena S.

    2011-09-20

    The crystal structure of EuFe{sub 2}As{sub 2} has been studied up to a pressure of 35 GPa and down to a temperature of 8 K using temperature dependent x-ray diffraction in a diamond anvil cell at a synchrotron source. At 4.3 GPa, we have detected a structural phase transition from a high temperature tetragonal phase with I4/mmm space group to a low temperature orthorhombic phase with Fmmm space group around 120 K. With the application of pressure at a low temperature of 10 K, the orthorhombic phase is suppressed and a phase change to a collapsed tetragonal phase with I4/mmm space group is observed at 11 GPa. This collapsed tetragonal phase is similar to the one observed at ambient temperature and pressure above 8.5 GPa. We have shown that the collapsed tetragonal phase of EuFe{sub 2}As{sub 2} has the same pressure-volume (P-V) equation of state at ambient temperature and at 10 K, implying that the high pressure phase of EuFe{sub 2}As{sub 2} has a negligible thermal expansion coefficient.

  5. Gel formation and low-temperature intramolecular conformation transition of a triple-helical polysaccharide lentinan in water.

    PubMed

    Zhang, Yangyang; Xu, Xiaojuan; Zhang, Lina

    2008-10-01

    The gelation behavior of the triple-helical polysaccharide lentinan fractions having different molecular weights in water at 25 degrees C were studied by using a rheometer. The analysis of concentration and molecular weight dependence of shear stress and shear viscosity showed that aqueous lentinan is a typical shear-thinning fluid, possessing potential as a viscosity control agent, and that a weak gel with entangled network structure formed. The dynamic oscillatory behavior of lentinan in the temperature range of 1-15 degrees C was also investigated by rheologic method. The storage modulus G' and complex viscosity eta* increased first with decreasing temperature, and underwent a maximum centered at 7-9 degrees C, and then decreased with further decreasing temperature. This abnormal phenomenon was ascribed to formation of rigid structure in the gel state, which was confirmed by the experimental results from micro-DSC. The micro-DSC curves showed that an endothermic peak appeared at 7-9 degrees C for lentinan in water upon heating, which was attributable to the intramolecular order-disorder structure transition similar to triple-helical polysaccharide schizophyllan. Namely, at lower temperature, the side glucose residues of lentinan (triplix II) formed a well-organized triple-helical structure (triplix I) through hydrogen-bonding with the surrounding water molecules. Moreover, this conformation transition was proved to be thermally reversible. PMID:18506809

  6. Phase transitions and hydrogen bonding in deuterated calcium hydroxide: High-pressure and high-temperature neutron diffraction measurements

    SciTech Connect

    Iizuka, Riko; Komatsu, Kazuki; Kagi, Hiroyuki; Nagai, Takaya; Sano-Furukawa, Asami; Hattori, Takanori; Gotou, Hirotada; Yagi, Takehiko

    2014-10-15

    In situ neutron diffraction measurements combined with the pulsed neutron source at the Japan Proton Accelerator Research Complex (J-PARC) were conducted on high-pressure polymorphs of deuterated portlandite (Ca(OD){sub 2}) using a Paris–Edinburgh cell and a multi-anvil press. The atomic positions including hydrogen for the unquenchable high-pressure phase at room temperature (phase II′) were first clarified. The bent hydrogen bonds under high pressure were consistent with results from Raman spectroscopy. The structure of the high-pressure and high-temperature phase (Phase II) was concordant with that observed previously by another group for a recovered sample. The observations elucidate the phase transition mechanism among the polymorphs, which involves the sliding of CaO polyhedral layers, position modulations of Ca atoms, and recombination of Ca–O bonds accompanied by the reorientation of hydrogen to form more stable hydrogen bonds. - Graphical abstract: Crystal structures of high-pressure polymorphs of Ca(OD){sub 2}, (a) at room temperature (phase II′) and (b) at high temperature (phase II), were obtained from in situ neutron diffraction measurements. - Highlights: • We measured in situ neutron diffraction of high-pressure polymorphs of Ca(OD){sub 2}. • Hydrogen positions of the high-pressure phase are first determined. • The obtained hydrogen bonds reasonably explain Raman peaks of OH stretching modes. • A phase transition mechanism among the polymorphs is proposed.

  7. Atom probe, AFM, and STM studies on vacuum-fired stainless steels.

    PubMed

    Stupnik, A; Frank, P; Leisch, M

    2009-04-01

    The surface morphology of grades 304L and 316LN stainless steels, after low-temperature bake-out process and vacuum annealing, has been studied by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). The local elemental composition on the surface before and after thermal treatment has been investigated by atom probe (AP) depth profiling measurements. After vacuum annealing, AFM and STM show significant changes in the surface structure and topology. Recrystallization and surface reconstruction is less pronounced on the 316LN stainless steel. AP depth profiling analyses result in noticeable nickel enrichment on the surface of grade 304L samples. Since hydrogen recombination is almost controlled by surface structure and composition, a strong influence on the outgassing behaviour by the particular surface microstructure can be deduced. PMID:19167824

  8. Preparation and Characterization of a Novel Epoxy Molding Compound with Low Storage Modulus at High Temperature and Low Glass-Transition Temperature

    NASA Astrophysics Data System (ADS)

    Cui, Hui-wang; Li, Dong-sheng; Fan, Qiong

    2012-09-01

    Epoxy molding compound (EMC) has been widely used as a main material for encapsulation and protection of semiconductor packages because of its low cost, high moisture resistance, high heat resistance, and good mechanical performance. Due to the extensive application of lead-free solder in place of Sn-Pb, soldering temperature is higher than before; this demands that EMC, which is usually used for lead-free solder, should have extremely low thermal stress and excellent stability at elevated temperatures. In this work, 1,3-propanediol bis(4-aminobenzoate) (PBA) was added to an EMC product to form a novel epoxy molding compound (FEMC). PBA had very limited effect on the process feasibility of EMC, and caused reduction of the storage modulus by 40% to 50% at high temperatures and reduction of the glass-transition temperature by more than 10°C, which are very helpful to reduce thermal stress buildup during high-temperature soldering processes. The increases of the tab pull force of copper- and silver-plated lead frames within EMC due to PBA were up to 58% and 117%, respectively. With increasing PBA content in the EMC, water absorption increased in a linear fashion, so the amount of PBA added to the EMC should be limited, preferably to not more than 1%.

  9. Hydrogen-doping induced reduction in the phase transition temperature of VO2: a first-principles study.

    PubMed

    Cui, Yuanyuan; Shi, Siqi; Chen, Lanli; Luo, Hongjie; Gao, Yanfeng

    2015-08-28

    VO2 is a promising thermochromic material that can intelligently control the transmittance of sunlight in the near-infrared region in response to temperature change, although the high phase transition temperature (Tc) of 340 K restricts its wide application. Our first-principles calculations show that hydrogen is an efficient dopant which can stabilize the metallic VO2 phase at ambient temperature through reducing Tc by 38 K/at% H. The reduction in Tc is coupled with the changes in atomic and electronic structures, i.e., the V-V chains feature the dimerization characteristics in H-doped VO2(R) and the V-O bonds become less ionic due to the formation of a typical H-O covalent bond. In addition, hydrogen-doped VO2 is more sensitive to external strain as compared with pure VO2, implying that Tc can be further regulated through a combination of H-doping and strain. PMID:26214593

  10. Temperature-Dependent Energy Gap Shift and Thermally Activated Transition in Multilayer CdTe/ZnTe Quantum Dots.

    PubMed

    Man, Minh Tan; Lee, Hong Seok

    2015-10-01

    We investigated the influence of growth conditions on carrier dynamics in multilayer CdTe/ZnTe quantum dots (QDs) by monitoring the temperature dependence of the photoluminescence emission energy. The results were analyzed using the empirical Varshni and O'Donnell relations for temperature variation of the energy gap shift. Best fit values showed that the thermally activated transition between two different states occurs due to band low-temperature quenching with values separated by 5.0-6.5 meV. The addition of stack periods in multilayer CdTe/ZnTe QDs plays an important role in the energy gap shift, where the exciton binding energy is enhanced, and, conversely, the exciton-phonon coupling strength is suppressed with an average energy of 19.3-19.8 meV. PMID:26726473

  11. Tension-induced phase transition of single-layer molybdenum disulphide (MoS2) at low temperatures.

    PubMed

    Zhao, Junhua; Kou, Liangzhi; Jiang, Jin-Wu; Rabczuk, Timon

    2014-07-25

    We show that the hexagonal structure of single-layer molybdenum disulphide (MoS2), under uniaxial tension along a zigzag direction for large deformations, can transfer to a new quadrilateral structure by molecular dynamics (MD) simulations when the temperature is below 40 K. The new phase remains stable after unloading, even at room temperature. The Young's modulus of the new phase along the zigzag direction is about 2.5 times higher than that of normal MoS2. Checking against density functional theory calculations shows that the new phase is preserved and displays excellent electrical conductivity. Our results provide physical insights into the origins of the new phase transition of MoS2 at low temperatures. PMID:24980057

  12. Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure

    PubMed Central

    Ji, Cheng; Levitas, Valery I.; Zhu, Hongyang; Chaudhuri, Jharna; Marathe, Archis; Ma, Yanzhang

    2012-01-01

    Disordered structures of boron nitride (BN), graphite, boron carbide (BC), and boron carbon nitride (BCN) systems are considered important precursor materials for synthesis of superhard phases in these systems. However, phase transformation of such materials can be achieved only at extreme pressure–temperature conditions, which is irrelevant to industrial applications. Here, the phase transition from disordered nanocrystalline hexagonal (h)BN to superhard wurtzitic (w)BN was found at room temperature under a pressure of 6.7 GPa after applying large plastic shear in a rotational diamond anvil cell (RDAC) monitored by in situ synchrotron X-ray diffraction (XRD) measurements. However, under hydrostatic compression to 52.8 GPa, the same hBN sample did not transform to wBN but probably underwent a reversible transformation to a high-pressure disordered phase with closed-packed buckled layers. The current phase-transition pressure is the lowest among all reported direct-phase transitions from hBN to wBN at room temperature. Usually, large plastic straining leads to disordering and amorphization; here, in contrast, highly disordered hBN transformed to crystalline wBN. The mechanisms of strain-induced phase transformation and the reasons for such a low transformation pressure are discussed. Our results demonstrate a potential of low pressure–room temperature synthesis of superhard materials under plastic shear from disordered or amorphous precursors. They also open a pathway of phase transformation of nanocrystalline materials and materials with disordered and amorphous structures under extensive shear. PMID:23129624

  13. Tunable Ferromagnetic Transition Temperature and Vertical Hysteretic Shift in SrRuO3 Films Integrated on Si(001).

    PubMed

    Zheng, Ming; Wang, Wei

    2016-06-01

    SrRuO3 thin films have been epitaxially integrated on complementary metal oxide semiconductor (CMOS) compatible Si(001) substrates via pulsed laser deposition using a unique buffer layer (SrTiO3/TiN) approach. When the oxygen pressure during deposition was controlled, a dramatic suppression in the ferromagnetic transition temperature (TC) of up to 53 K was observed, caused by the growth-induced ruthenium vacancies rather than the oxygen vacancies. The ruthenium vacancies can also effectively tune the vertical magnetization shift (Mshift) in hysteresis loops, and thus we achieved a giant Mshift of 240%. Transport and magnetic measurements reveal that these appreciable physical phenomena are closely related to the ruthenium defect-induced local disorder and complex effects due to the strongly hybridized p-d orbitals as well as the induced lattice distortion. These observations indicate the importance of ruthenium defects in controlling the vertical magnetization shift and ferromagnetic transition temperature in this transitional metal oxide. PMID:27203399

  14. Use of shear-stress-sensitive, temperature-insensitive liquid crystals for hypersonic boundary-layer transition detection

    SciTech Connect

    Aeschliman, D.P.; Croll, R.H.; Kuntz, D.W.

    1997-04-01

    The use of shear-stress-sensitive, temperature-insensitive (SSS/TI) liquid crystals (LCs) has been evaluated as a boundary-layer transition detection technique for hypersonic flows. Experiments were conducted at Mach 8 in the Sandia National Laboratories Hypersonic Wind Tunnel using a flat plate model at near zero-degree angle of attack over the freestream unit Reynolds number range 1.2-5.8x10{sup 6}/ft. Standard 35mm color photography and Super VHS color video were used to record LC color changes due to varying surface shear stress during the transition process for a range of commercial SSS liquid crystals. Visual transition data were compared to an established method using calorimetric surface heat-transfer measurements to evaluate the LC technique. It is concluded that the use of SSS/TI LCs can be an inexpensive, safe, and easy to use boundary-layer transition detection method for hypersonic flows. However, a valid interpretation of the visual records requires careful attention to illumination intensity levels and uniformity, lighting and viewing angles, some prior understanding of the general character of the flow, and the selection of the appropriate liquid crystal for the particular flow conditions.

  15. Observation of an ultrahigh-temperature ferromagnetic-like transition in iron-contaminated multiwalled carbon nanotube mats

    NASA Astrophysics Data System (ADS)

    Zhao, Guo-Meng; Beeli, Pieder

    2008-06-01

    We report magnetic measurements up to 1200 K on iron-contaminated multiwalled carbon nanotube mats with a Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show a ferrromagnetic transition at about 1000 K and a ferromagnetic-like transition at about 1275 K. The ferromagnetic transition at about 1000 K is associated with an Fe impurity phase and its saturation magnetization is in quantitative agreement with the Fe concentration measured by an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the ferromagnetic-like phase (at 1275 K) is about 4 orders of magnitude larger than that expected from the measured concentration of Co or CoFe. We show that this ultrahigh-temperature ferromagnetic-like (UHTFL) transition is not consistent with ferromagnetism of any Fe-carbon phases, carbon-based phases, or magnetic impurities. Alternatively, the observed magnetic behavior of the UHTFL phase is phenomenologically explained in terms of the paramagnetic Meissner effect (orbital ferromagnetism) due to the existence of π Josephson junctions in a granular superconductor.

  16. [In situ experimental study of phase transition of calcite by Raman spectroscopy at high temperature and high pressure].

    PubMed

    Liu, Chuan-jiang; Zheng, Hai-fei

    2012-02-01

    The phase transitions of calcite at high temperature and high pressure were investigated by using hydrothermal diamond anvil cell combined with Raman spectroscopy. The result showed that the Raman peak of 155 cm(-1) disappeared, the peak of 1 087 cm(-1) splited into 1083 and 1 090 cm(-1) peaks and the peak of 282 cm(-1) abruptly reduced to 231 cm(-1) at ambient temperature when the system pressure increased to 1 666 and 2 127 MPa respectively, which proved that calcite transformed to calcite-II and calcite-III. In the heating process at the initial pressure of 2 761 MPa and below 171 degrees C, there was no change in Raman characteristic peaks of calcite-III. As the temperature increased to 171 degrees C, the color of calcite crystal became opaque completely and the symmetric stretching vibration peak of 1 087 cm(-1), in-plane bending vibration peak of 713 cm(-1) and lattice vibration peaks of 155 and 282 cm(-1) began to mutate, showing that the calcite-III transformed to a new phase of calcium carbonate at the moment. When the temperature dropped to room temperature, this new phase remained stable all along. It also indicated that the process of phase transformation from calcite to the new phase of calcium carbonate was irreversible. The equation of phase transition between calcite-III and new phase of calcium carbonate can be determined by P(MPa) = 9.09T x (degrees C) +1 880. The slopes of the Raman peak (v1 087) of symmetrical stretching vibration depending on pressure and temperature are dv/dP = 5.1 (cm(-1) x GPa(-1)) and dv/dT = -0.055 3(cm(-1) x degrees C(-1)), respectively. PMID:22512172

  17. Bulk electronic structure of FeRh undergoing metamagnetic transition via hard x-ray photoemission

    NASA Astrophysics Data System (ADS)

    Gray, Alexander; Cooke, David; Kruger, Peter; Bordel, Catherine; Fullerton, Eric; Ueda, Shigenori; Kobayashi, Keisuke; Hellman, Frances; Fadley, Charles

    2012-02-01

    In this study changes in the electronic structure accompanying a temperature-induced metamagnetic transition from anti-ferromagnetic to ferromagnetic order are investigated in strained epitaxial FeRh thin films via valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 6 keV. At such high photon energy, the resulting inelastic mean-free paths of the photoemitted electrons and therefore the average probing depths are on the order of 60 å, corresponding to about 20 unit cells and ensuring truly bulk-sensitive measurement. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density functional theory. Changes in the Fe 2p core-levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results suggest that significant electronic structure changes are involved in this AFM-FM transition.

  18. High temperature-induced phase transitions in Sr{sub 2}GdRuO{sub 6} complex perovskite

    SciTech Connect

    Triana, C.A.; Corredor, L.T.; Landinez Tellez, D.A.; Roa-Rojas, J.

    2011-12-15

    Highlights: Black-Right-Pointing-Pointer Crystal structure, thermal expansion and phase transitions at high-temperature of Sr{sub 2}GdRuO{sub 6} perovskite has been investigated. Black-Right-Pointing-Pointer X-ray diffraction pattern at 298 K of Sr{sub 2}GdRuO{sub 6} corresponds to monoclinic perovskite-type structure with P2{sub 1}/n space group. Black-Right-Pointing-Pointer Evolution of X-ray diffraction patterns at high-temperature shows that the Sr{sub 2}GdRuO{sub 6} perovskite suffers two-phase transitions. Black-Right-Pointing-Pointer At 573 K the X-ray diffraction pattern of Sr{sub 2}GdRuO{sub 6} corresponds to monoclinic perovskite-type structure with I2/m space group. Black-Right-Pointing-Pointer At 1273 K the Sr{sub 2}GdRuO{sub 6} perovskite suffers a complete phase-transition from monoclinic I2/m (no. 12) to tetragonal I4/m (no. 87). -- Abstract: The crystal structure behavior of the Sr{sub 2}GdRuO{sub 6} complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K {<=} T {<=} 1273 K. Measurements of X-ray diffraction at room-temperature and Rietveld analysis of the experimental patterns show that this compound crystallizes in a monoclinic perovskite-like structure, which belongs to the P2{sub 1}/n (no. 14) space group and 1:1 ordered arrangement of Ru{sup 5+} and Gd{sup 3+} cations over the six-coordinate M sites. Experimental lattice parameters were obtained to be a =5.8103(5) Angstrom-Sign , b =5.8234(1) Angstrom-Sign , c =8.2193(9) Angstrom-Sign , V = 278.11(2) Angstrom-Sign {sup 3} and angle {beta} = 90.310(5) Degree-Sign . The high-temperature analysis shows the occurrence of two-phase transitions on this material. First, at 573 K it adopts a monoclinic perovskite-type structure with I2/m (no. 12) space group with lattice parameters a = 5.8275(6) Angstrom-Sign , b = 5.8326(3) Angstrom-Sign , c = 8.2449(2) Angstrom-Sign , V = 280.31(3) Angstrom-Sign {sup 3} and angle {beta} = 90.251(3) Degree-Sign . Close

  19. Temperature-induced reversible self-assembly of diphenylalanine peptide and the structural transition from organogel to crystalline nanowires.

    PubMed

    Huang, Renliang; Wang, Yuefei; Qi, Wei; Su, Rongxin; He, Zhimin

    2014-01-01

    Controlling the self-assembly of diphenylalanine peptide (FF) into various nanoarchitectures has received great amounts of attention in recent years. Here, we report the temperature-induced reversible self-assembly of diphenylalanine peptide to microtubes, nanowires, or organogel in different solvents. We also find that the organogel in isopropanol transforms into crystalline flakes or nanowires when the temperature increases. The reversible self-assembly in polar solvents may be mainly controlled by electronic and aromatic interactions between the FF molecules themselves, which is associated with the dissociation equilibrium and significantly influenced by temperature. We found that the organogel in the isopropanol solvent made a unique transition to crystalline structures, a process that is driven by temperature and may be kinetically controlled. During the heating-cooling process, FF preferentially self-assembles to metastable nanofibers and organogel. They further transform to thermodynamically stable crystal structures via molecular rearrangement after introducing an external energy, such as the increasing temperature used in this study. The strategy demonstrated in this study provides an efficient way to controllably fabricate smart, temperature-responsive peptide nanomaterials and enriches the understanding of the growth mechanism of diphenylalanine peptide nanostructures. PMID:25520600

  20. Temperature-induced reversible self-assembly of diphenylalanine peptide and the structural transition from organogel to crystalline nanowires

    PubMed Central

    2014-01-01

    Controlling the self-assembly of diphenylalanine peptide (FF) into various nanoarchitectures has received great amounts of attention in recent years. Here, we report the temperature-induced reversible self-assembly of diphenylalanine peptide to microtubes, nanowires, or organogel in different solvents. We also find that the organogel in isopropanol transforms into crystalline flakes or nanowires when the temperature increases. The reversible self-assembly in polar solvents may be mainly controlled by electronic and aromatic interactions between the FF molecules themselves, which is associated with the dissociation equilibrium and significantly influenced by temperature. We found that the organogel in the isopropanol solvent made a unique transition to crystalline structures, a process that is driven by temperature and may be kinetically controlled. During the heating-cooling process, FF preferentially self-assembles to metastable nanofibers and organogel. They further transform to thermodynamically stable crystal structures via molecular rearrangement after introducing an external energy, such as the increasing temperature used in this study. The strategy demonstrated in this study provides an efficient way to controllably fabricate smart, temperature-responsive peptide nanomaterials and enriches the understanding of the growth mechanism of diphenylalanine peptide nanostructures. PMID:25520600