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Sample records for 41-j transition temperature

  1. 78 FR 5773 - Notification of Proposed Production Activity, Generac Power Systems, Inc., Subzone 41J...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-28

    ...., Subzone 41J, (Generators, Pressure Washers, Engines and Other Related Components), Whitewater, Edgerton..., Wisconsin. The facilities are used for the production of generators, pressure washers, engines and other.../elements; catalytic converters; pressure washers; water jet project machines and parts; bearings;...

  2. 78 FR 29322 - Foreign-Trade Zone 41-Milwaukee, Wisconsin; Authorization of Production Activity; Subzone 41J...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-20

    ... FR 5773, 01-28-2013). The FTZ Board has determined that no further review of the activity is... Activity; Subzone 41J; Generac Power Systems, Inc. (Generators, Pressure Washers, Engines and Other...

  3. 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.

  4. Elasticity and Inverse Temperature Transition in Elastin

    DOE PAGES

    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

  5. 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.

  6. 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

  7. A universal reduced glass transition temperature for liquids

    NASA Technical Reports Server (NTRS)

    Fedors, R. F.

    1979-01-01

    Data on the dependence of the glass transition temperature on the molecular structure for low-molecular-weight liquids are analyzed in order to determine whether Boyer's reduced glass transition temperature (1952) is a universal constant as proposed. It is shown that the Boyer ratio varies widely depending on the chemical nature of the molecule. It is pointed out that a characteristic temperature ratio, defined by the ratio of the sum of the melting temperature and the boiling temperature to the sum of the glass transition temperature and the boiling temperature, is a universal constant independent of the molecular structure of the liquid. The average value of the ratio obtained from data for 65 liquids is 1.15.

  8. 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.

  9. Ternary transition metal phosphides: High-temperature superconductors

    PubMed Central

    Barz, H.; Ku, H. C.; Meisner, G. P.; Fisk, Z.; Matthias, B. T.

    1980-01-01

    Two systems of ternary transition metal phosphides with the ordered Fe2P-type hexagonal structure are reported. They have the general formula MRuP and MOsP, in which M can be Ti, Zr, or Hf. An onset of the superconducting transition temperature as high as 13.0 K is reported for the ZrRuP compound. PMID:16592838

  10. Multiple phase transitions in rare earth tetraborides at low temperature

    NASA Astrophysics Data System (ADS)

    Fisk, Z.; Maple, M. B.; Johnston, D. C.; Woolf, L. D.

    1981-09-01

    We report the temperature dependence of the magnetic susceptibility of single crystals of PrB 4, GdB 4, TbB 4, HoB 4 and TmB 4, both parallel and perpendicular to the tetragonal c-axis. We also present low temperature resistance measurements on crytals of GdB 4 through TmB 4. Two magnetic phase transitions are found for TbB 4, DyB 4, HoB 4 and TmB 4. For the latter two compounds, the lower transitions appear to be first order. For HoB 4, we have measured the low temperature specific heat. The lower transition in TbB 4 and HoB 4 is rapidly depressed upon dilution with YB 4.

  11. Transition temperature of a weakly interacting Bose gas

    SciTech Connect

    Kao, Yee-Mou; Jiang, T. F.

    2006-04-15

    We report a theoretical study of the transition temperature of a trapped interacting dilute Bose gas. The system is treated like a two-fluid model consisting of a thermal component and a condensate component. Through the calculation of the energy spectra, the origins of various effects on the transition temperature are derived. We found that the interactive shift is affected by both the thermal component and the condensate component. The latter effect, which is about 34% of the former, has never been reported so far. With these two effects, our calculated interactive shift agrees very well with the recent measurement.

  12. Correlation of irradiation-induced transition temperature increases from C sub v and K sub Jc /K sub Ic data

    SciTech Connect

    Hiser, A.L. )

    1990-03-01

    Reactor pressure vessel (RPV) surveillance capsules contain Charpy-V (C{sub v}) specimens, but many do not contain fracture toughness specimens; accordingly, the radiation-induced shift (increase) in the brittle-to-ductile transition region ({Delta}T) is based upon the {Delta}T determined from notch ductility (C{sub v}) tests. Since the ASME K{sub Ic} and K{sub IR} reference fracture toughness curves are shifted by the {Delta}T from C{sub v}, assurance that this {Delta}T does not underestimate {Delta}T associated with the actual irradiated fracture toughness is required to provide confidence that safety margins do not fall below assumed levels. To assess this behavior, comparisons of {Delta}T's defined by elastic-plastic fracture toughness and C{sub v} tests have been made using data from RPV base and weld metals in which irradiations were made under test reactor conditions. Using as-measure'' fracture toughness values (K{sub Jc}), average comparisons between {Delta}T(C{sub v}) and {Delta}T(K{sub Jc}) are: (a) All data: {Delta}T(K{sub Jc} 100 MPa{radical}{bar m}) = {Delta}T(C{sub v} 41 J) +10{degree}C; (b) Plates only: {Delta}T(K{sub Jc} 100 MPa{radical}{bar m}) = {Delta}T(C{sub v} 41 J) +15{degree}C; and (c) Welds only: {Delta}T(K{sub Jc} 100 MPa{radical}{bar m}) = {Delta}T(C{sub v} 41 J) {minus}1{degree}C. Fluence rate is found to have no significant effect on the relationship between {Delta}T(C{sub v}) and {Delta}T(K{sub Jc}). 12 refs., 12 figs., 5 tabs.

  13. 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.

  14. 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.

  15. Temperature Dependence in Desorption Induced by Electronic Transitions.

    NASA Astrophysics Data System (ADS)

    Heinz, T. F.; Misewich, J. A.

    1996-03-01

    The process of desorption induced by electronic transitions (DIET) is a subject of great theoretical and experimental interest. We have extended the classic MGR model for DIET to include initial thermal excitation of the adsorbate. In the MGR model, an electronic transition causes the adsorbate to move on excited potential energy surface. Desorption ensues whenever the adsorbate stays in the excited state long enough to acquire the necessary energy to escape from the surface. At finite temperatures, the initial transition occurs from a distribution of ground-state vibrational energies and momenta. Compared with the zero temperature desorption yield some components of the finite-temperature distribution will have enhanced yields while others will have suppressed yields. Averaging over the initial distribution, we find that the desorption yield increases substantially with temperature, particularly for short excited-state lifetimes. These findings and their extension to the multiple excitation regime are relevant to understanding the long-time scale response observed in femtosecond two-pulse correlation measurements of O_2/Pd(111). J. A. Misewich et al., J. Chem. Phys. 100, 736 (1994)

  16. 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.

  17. Temperature-induced Lifshitz transition in WTe2

    DOE PAGES

    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

  18. 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

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. Rubberlike Dynamics in Sulphur above the {lambda}-Transition Temperature

    SciTech Connect

    Monaco, G.; Crapanzano, L.; Crichton, W.; Mezouar, M.; Verbeni, R.; Bellissent, R.

    2005-12-16

    The high-frequency acoustic dynamics of sulfur across the liquid-liquid, {lambda} transition has been studied using inelastic x-ray scattering. The combination of these high-frequency data with lower frequency, literature data indicates that liquid sulfur develops, in the high-temperature, polymeric solution phase, some characteristic features of a rubber. In particular, entanglement coupling among polymeric chains plays a relevant role in the dynamics of this liquid phase.

  4. 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

  5. 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.

  6. Pressure effect on inverse temperature transitions: biological implications

    NASA Astrophysics Data System (ADS)

    Urry, Dan W.; Hayes, Larry C.; Channe Gowda, D.; Parker, Timothy M.

    1991-07-01

    Elastic protein-based polymers of the form poly [ fx(VPGXG), fv(VPGVG)], where fx and fv are mole fractions with fx+ fv=1, exhibit inverse temperature transitions in the form of a phase separation in which folding and aggregation of polymer chains into more-ordered states of the condensed (coacervate) phase occurs on raising the temperature. When X = Trp, Phe or Tyr, an increase in pressure causes a substantial increase in the temperature of the transition. The data are interpreted to indicate that water molecules surrounding the aromatic side chains of Trp(W), Phe(F) or Tyr(Y) occupy less volume than water molecules in bulk water. The calculated volume change for poly[0.8(GVGVP), 0.2(GFGVP)], for example, on going from coacervate phase, where hydrophobic associations have largely eliminated waters of hydrophobic hydration, to be dispersed in water where the hydrophobic moieties are surrounded by water is 80 cm 3/mol of mean pentamers or some 400 cm 3/mol of (GFGVP). The results provide an understanding of the source of pressure effects in biological systems and for the capacity to design materials capable of exhibiting baromechanical transduction.

  7. 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.

  8. Finite Temperature Deconfining Transition in the BRST Formalism

    NASA Astrophysics Data System (ADS)

    Hata, H.; Taniguchi, Y.

    1995-04-01

    We present a toy model study of the high temperature deconfining transition in Yang-Mills theory as a breakdown of the confinement condition proposed y Kugo and Ojima. Our toy model is a kind of topological field theory obtained from the Yang-Mills theory by taking the limit of vanishing gauge coupling constant gYM --> 0, and therefore the gauge field Aμ is constrained to the pure-gauge configuration Aμ = g†partialμg. At zero temperature this model has been known to satisfy the confinement condition of Kugo and Ojima which requires the absence of the massless Nambu-Goldstone-like mode coupled to the BRST-exact color current. In the finite temperature case based on the real-time formalism, our model in 3 + 1 dimensions is reduced, by the Parisi-Sourlas mechanism, the the ``sum'' of chiral models in 1 + 1 dimensions with various boundary conditions of the group element g(t, x) at the ends of the time contour. We analyze the effective potential of the SU(2) model and find that the deconfining transition in fact occurs due to the contribution of the sectors with non-periodic boundary conditions.

  9. Investigation of low glass transition temperature on COTS PEM's reliability for space applications

    NASA Technical Reports Server (NTRS)

    Sandor, M.; Agarwal, S.; Peters, D.; Cooper, M. S.

    2003-01-01

    Plastic Encapsulated Microelectronics (PEM) reliability is affected by many factors. Glass transition temperature (Tg) is one such factor. In this presentation issues relating to PEM reliability and the effect of low glass transition temperature epoxy mold compounds are presented.

  10. 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.

  11. Glass transition temperatures in nanoscale equilibrated polystyrene droplets

    NASA Astrophysics Data System (ADS)

    Daley, Chad; Forrest, James

    2013-03-01

    Measurements of thin film glass transition temperature (Tg) in thin polymer films are only made possible through the metastability of the film with respect to dewetting. Even in the melt state, such samples are not in thermal equilibrium, and resulting Tg values may not be conclusive. In this talk we discuss recent measurements of Tg for equilibrium polystyrene droplets on silicon substrates as measured through their thermal expansion with true non-contact atomic force microscopy. These measurements show promise to not only definitively address the continuing controversy surrounding thin film Tg measurements, but are also readily applied to study non-polymeric glass formers.

  12. 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.

  13. High-transition-temperature shape memory alloy film

    NASA Astrophysics Data System (ADS)

    Johnson, A. David; Martynov, Valery V.; Shahoian, Erik J.

    1995-05-01

    Using conventional magnetron sputtering deposition processes three different types of shape memory alloys (FeNi based, CuAl based and TiNi based) were examined as potential candidates for the production of high temperature SMA thin film. CuAlNi and TiNiHf SMA were successfully deposited on silicon wafers and thin films of 4 - 20 micrometers were produced. After annealing at approximately equals 500 degree(s)C both CuAlNi and TiNiHf films exhibited reversible high temperature martensitic transition. For CuAlNi thin films, annealing itself was found to be inadequate for obtaining transformation intervals corresponding to that of the target. To deal with the problem it is expected that additional quenching after solid solution heat treatment will be necessary. Of the three alloys examined, the most promising candidate for high temperature thin film microactuators is TiNiHf. It was found that by changing the Hf content in the target, the transformation start temperature of thin films can be easily adjusted in a temperature range from 100 degree(s)C to 200 degree(s)C.

  14. Temperature-modulated synchronization transition in coupled neuronal oscillators

    NASA Astrophysics Data System (ADS)

    Sato, Yasuomi D.; Okumura, Keiji; Ichiki, Akihisa; Shiino, Masatoshi; Câteau, Hideyuki

    2012-03-01

    We study two firing properties to characterize the activities of a neuron: frequency-current (f-I) curves and phase response curves (PRCs), with variation in the intrinsic temperature scaling parameter (μ) controlling the opening and closing of ionic channels. We show a peak of the firing frequency for small μ in a class I neuron with the I value immediately after the saddle-node bifurcation, which is entirely different from previous experimental reports as well as model studies. The PRC takes a type II form on a logarithmic f-I curve when μ is small. Then, we analyze the synchronization phenomena in a two-neuron network using the phase-reduction method. We find common μ-dependent transition and bifurcation of synchronizations, regardless of the values of I. Such results give us helpful insight into synchronizations tuned with a sinusoidal-wave temperature modulation on neurons.

  15. 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

  16. 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

  17. 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.

  18. Local Glass Transition Temperature Gradients Near Polymer-Polymer Interfaces

    NASA Astrophysics Data System (ADS)

    Baglay, Roman; Roth, Connie

    2015-03-01

    For decades the glass transition in confined systems has been studied with the hopes of uncovering the governing length scales that impact these dynamics. However, understanding length scales of local gradients in glass transition temperature (Tg) near a free surface have been hampered by limitations of how to treat the enhanced mobility at the free surface theoretically. We have previously reported on the local Tg in multilayer structures made from high molecular weight polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA), a weakly immiscible system with a ~ 7 nm interfacial width. Using ultrathin (10-15 nm) pyrene-labeled layers inserted into the multilayer structure at different positions (z) from the glassy-rubbery interface, we were able to map the local Tg(z) profile across this glassy-rubbery interface with temperature-dependent fluorescence intensity measurements. Our work revealed an asymmetric local mobility gradient propagating hundreds of nanometers away from the glassy-rubbery PS-PnBMA interface into the glassy PS and rubbery PnBMA sides before bulk Tgs were recovered far from the interface. Here we extend these measurements to investigate how the local Tg(z) profile in PS varies when in contact with a variety of immiscible polymers whose Tgs vary between +90 K to -80 K relative to the Tg of PS, so-called hard vs soft confinement.

  19. Homology of interatomic forces and Debye temperatures in transition metals

    NASA Astrophysics Data System (ADS)

    Guillermet, A. Fernández; Grimvall, G.

    1989-07-01

    Using experimental data on the entropy S at intermediate temperatures, corrected for an electronic term to get the vibrational entropy, we obtain well-defined and accurate ``entropy Debye temperatures'' FTHETA=FTHETAS. From FTHETAS we define a quantity with the dimension of a force constant, kS==M(kBFTHETA/ħ)2, where M is the atomic mass. Similarly, data on the low-temperature vibrational heat capacity and the elastic coefficients yield Debye temperatures FTHETAC and FTHETAelas and corresponding force constants kC and kelas. The ratios of kS for the 4d-5d pairs Zr,Hf, Nb,Ta, Mo,W, Tc,Re, Ru,Os, Rh,Ir, and Pd,Pt are remarkably constant, (kS)4d/(kS)5d =0.76+/-0.01, in spite of varying crystal structures. Further, (kC)4d/(kC)5d =0.70+/-0.07 and (kelas)4d/(kelas)5d =0.69+/-0.08. The corresponding force-constant ratios k3d/k4d vary more. This correlates with an approximately constant atomic-volume ratio Ω4d/Ω5d=0.99+/-0.02, while Ω3d/Ω4d=0.81+/-0.05 shows irregularities, mainly of magnetic origin. As a basis for our analysis, we review low-temperature Debye temperatures FTHETAelas and FTHETAC and the bulk modulus B of the transition metals.

  20. 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.

  1. 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.

  2. 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.

  3. Correlation between average melting temperature and glass transition temperature in metallic glasses

    NASA Astrophysics Data System (ADS)

    Lu, Zhibin; Li, Jiangong

    2009-02-01

    The correlation between average melting temperature (⟨Tm⟩) and glass transition temperature (Tg) in metallic glasses (MGs) is analyzed. A linear relationship, Tg=0.385⟨Tm⟩, is observed. This correlation agrees with Egami's suggestion [Rep. Prog. Phys. 47, 1601 (1984)]. The prediction of Tg from ⟨Tm⟩ through the relationship Tg=0.385⟨Tm⟩ has been tested using experimental data obtained on a large number of MGs. This relationship can be used to predict and design MGs with a desired Tg.

  4. Equation of state and QCD transition at finite temperature

    SciTech Connect

    Bazavov, A; Bhattacharya, T; Cheng, M; Christ, N H; DeTar, C; Ejiri, S; Gottlieb, S; Gupta, R; Heller, U M; Huebner, K; Jung, C; Karsch, F; Laermann, E; Levkova, L; Miao, C; Mawhinney, R D; Petreczky, P; Schmidt, C; Soltz, R A; Soeldner, W; Sugar, R; Toussaint, D; Vranas, P

    2009-03-25

    We calculate the equation of state in 2+1 flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent N{sub {tau}} = 8. Calculations have been performed with two different improved staggered fermion actions, the asqtad and p4 actions. Overall, we find good agreement between results obtained with these two O(a{sup 2}) improved staggered fermion discretization schemes. A comparison with earlier calculations on coarser lattices is performed to quantify systematic errors in current studies of the equation of state. We also present results for observables that are sensitive to deconfining and chiral aspects of the QCD transition on N{sub {tau}} = 6 and 8 lattices. We find that deconfinement and chiral symmetry restoration happen in the same narrow temperature interval. In an Appendix we present a simple parametrization of the equation of state that can easily be used in hydrodynamic model calculations. In this parametrization we also incorporated an estimate of current uncertainties in the lattice calculations which arise from cutoff and quark mass effects. We estimate these systematic effects to be about 10 MeV.

  5. Gap-modulation infrared spectroscopy of high transition temperature superconductors

    PubMed Central

    Little, William A.; Collman, James P.

    1988-01-01

    Conventional methods of determining the coupling factor α2(ω)F(ω) for the newly discovered high transition temperature (Tc) cuprate superconductors by using tunneling and infrared measurements have thus far failed to show the cause of the very high Tc of these compounds. This is due in part to difficulties in sample preparation for tunneling studies and to difficulties in obtaining good data at relatively high tunneling voltages. Also, in IR (infrared) measurements, small differences in absorptivity between the normal and superconducting state can be masked by changes in the phonon occupation at high and low temperatures. Here we propose a technique for determing the coupling constant, which should be less dependent on the surface quality of the sample than with tunneling and should allow measurements at higher energies with greater precision than do tunneling or simple IR observations. This should make possible a definitive determination of any possible exciton contribution to this coupling term, which would appear at energies well above the range where conventional IR or tunneling measurements are effective. PMID:16593950

  6. Determination of the liquid crystals phase transition temperatures using optical rotation effect

    NASA Astrophysics Data System (ADS)

    Niu, Xiao-ling; Liu, Wei-guo; Liu, Peng; Cai, Chang-long

    2011-11-01

    Using optical rotation effect, a sensitive, simple optical analytical system is developed for determining the phase transition temperatures of liquid crystals (LCs). When a monochromatic polarized light passes through LCs sample and analyzer, the light intensity changes with temperature. Especially, during the phase transition process, the intensity varies greatly due to optical rotation effect. The variation of light intensity versus variation of temperature curve shows the phase transition temperatures of LCs clearly. The phase transition temperatures of three cholesteric liquid crystals (ChLCs) and a nematic liquid crystals (NLCs) were detected by this method, and compared with those of the differential scanning calorimetry (DSC) and polarized light microscope (PLM) methods.

  7. Temperature dependence of the soft mode for structural phase transitions in highly anisotropic systems

    SciTech Connect

    Bishop, A.R.; Kerr, W.C.

    1986-01-01

    It is shown that describing the dynamics of structural phase transition in highly anisotropic systems requires the introduction of another characteristic temperature is addition to the transition temperature. This soft-mode temperature is identified with the minimum of the soft-mode frequency and results from the appearance of the 1-d soliton propagation along the chains. 1 ref., 3 figs.

  8. Effect of interband interactions on the pressure dependence on transition temperature of MgB2

    NASA Astrophysics Data System (ADS)

    Ogbuu, Okechukwu A.; Abah, Obinna

    2015-12-01

    A two-band BCS model with interactions, both phonon and non-phonon induced interactions, were employed to investigate the pressure dependence on superconducting transition temperature of two-band superconductor. We derived the transition temperature and its pressure dependence within Bogoliubov--Valatin formalism for magnesium diboride superconductor. We examined the influence of interband interactions on transition temperature at varying pressure and analyzed the relevance of this calculation in magnesium diboride, MgB2.

  9. The Structural Bases for Polymer Glass-Transition Temperatures

    NASA Astrophysics Data System (ADS)

    Shen, Jialong; Tonelli, Alan

    2015-03-01

    The glass-transition temperatures (Tgs) observed for chemically distinct polymers range over several hundred K, and the molecular bases for this wide variability are largely unknown, though the following three factors are often mentioned as being pivotal: 1. Their inherent conformational flexibilities; 2. The sizes or steric bulk of their side-chains; and 3. Their inter-chain interactions. These three factors are generally interdependent, making it difficult to predict or even rationalize the Tgs of polymers. Structurally analogous aliphatic copolyesters, copolyamides, and copoly(ester/amide)s can be synthesized to produce amorphous samples with Tgs that are unaffected either by crystallinity or polymer chain lengths. Their conformations are virtually identical, and each can be synthesized with or without side-chains, so we can begin to evaluate the relative importance of the above three factors. The Tgs of un-branched analogous samples should differ solely due to factor 3., while analogous samples with singly-branched repeat units should provide a measure of the relative importance of factors 1. and 2.

  10. Finite-temperature twisted-untwisted transition of the kagome lattice

    NASA Astrophysics Data System (ADS)

    Bedi, Deshpreet; Rocklin, D. Zeb; Mao, Xiaoming

    Mechanical instability governs many fascinating phenomena in nature, including jamming, glass transitions, and structural phase transitions. Although mechanical instability in athermal systems is well understood, how thermal fluctuations modify such transitions remains largely unexplored. Recent studies reveal that, due to the large number of floppy modes that emerge at mechanical instability, intriguing new phenomena occur, such as fluctuation-driven first-order transitions and order-by-disorder. In this talk, we present an analytic study of the finite-temperature rigidity transition for the kagome lattice. Our model exhibits a zero-temperature continuous twisted-untwisted transition as the sign of the next-nearest-neighbor spring constant changes. At finite temperature, we show that the divergent contribution of floppy modes to the vibrational entropy renormalizes this spring constant, resulting in a first-order transition. We also propose an experimental manifestation of this transition in the system of self-assembling triblock Janus particles.

  11. 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.

  12. Processing of transition metal silicides for high-temperature applications

    SciTech Connect

    Deevi, S.C.; Sikka, V.K.

    1995-12-31

    The authors review and discuss recent developments in the processing and mechanical properties of MoSi{sub 2} and its composites. High-temperature creep rates of MoSi{sub 2} and its composites are compared to those of several intermetallics and discussed in relation to grain-size effects. Thermophysical properties of MoSi{sub 2} and Si{sub 3}N{sub 4} are compared, and the need for functionally graded composites of MoSi{sub 2}-Si{sub 3}N{sub 4} is discussed. This is followed by a discussion of combustion synthesis, reaction synthesis and densification, in-situ composite development, and reactive hot extrusion of metal-silicon mixtures. In combustion synthesis, a heterogeneous reaction occurs between liquid Si and Mo powder to form MoSi{sub 2}. This technique can be applied to obtain composites and alloys of MoSi{sub 2} and various other transition-metal silicides. In-situ synthesis of a composite of MoSi{sub 2}-Al{sub 2}O{sub 3} was carried out by reacting a thermite mixture consisting of MoO{sub 3}, Al, and Si powders. X-ray characterization of the products obtained at various temperatures reveals that the mechanism consists of a reduction of MoO{sub 3} by Al to MoO{sub 2}, followed by a simultaneous oxidation of Al to Al{sub 2}O{sub 3} and a synthesis reaction between reduced Mo and Si to form MoSi{sub 2}. The rate-determining step is found to be reduction of MoO{sub 2} by Al and oxidation of Al to Al{sub 2}O{sub 3}. The thermite reaction was moderated by adding Mo and Si to the mixture of MoO{sub 3}, Al, and Si, such that the ratio of MoSi{sub 2} to the thermite was in the range of 60:40 to 90:10. Reactive extrusion of metal-silicon mixtures of 3Ni-Si and Co-2Si results in a dense product with at least two phases.

  13. 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.}

  14. 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.

  15. 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)

  16. Glass transition temperatures of liquid prepolymers obtained by thermal penetrometry

    NASA Technical Reports Server (NTRS)

    Potts, J. E., Jr.; Ashcraft, A. C.

    1973-01-01

    Thermal penetrometry is experimental technique for detecting temperature at which frozen prepolymer becomes soft enough to be pierced by weighted penetrometer needle; temperature at which this occurs is called penetration temperature. Apparatus used to obtain penetration temperatures can be set up largely from standard parts.

  17. 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)

  18. 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)

  19. 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

  20. 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.

  1. 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.

  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. 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.

  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. Room Temperature Semiconductor-Metal Transition of MoTe2 Thin Films Engineered by Strain.

    PubMed

    Song, Seunghyun; Keum, Dong Hoon; Cho, Suyeon; Perello, David; Kim, Yunseok; Lee, Young Hee

    2016-01-13

    We demonstrate a room temperature semiconductor-metal transition in thin film MoTe2 engineered by strain. Reduction of the 2H-1T' phase transition temperature of MoTe2 to room temperature was realized by introducing a tensile strain of 0.2%. The observed first-order SM transition improved conductance ∼10 000 times and was made possible by an unusually large temperature-stress coefficient, which results from a large volume change and small latent heat. The demonstrated strain-modulation of the phase transition temperature is expected to be compatible with other TMDs enabling the 2D electronics utilizing polymorphism of TMDs along with the established materials. PMID:26713902

  6. Temperature and magnetic field induced multiple magnetic transitions in DyAg(2).

    PubMed

    Arora, Parul; Chattopadhyay, M K; Sharath Chandra, L S; Sharma, V K; Roy, S B

    2011-02-01

    The magnetic properties of the rare-earth intermetallic compound DyAg(2) are studied in detail with the help of magnetization and heat capacity measurements. It is shown that the multiple magnetic phase transitions can be induced in DyAg(2) both by temperature and magnetic field. The detailed magnetic phase diagram of DyAg(2) is determined experimentally. It was already known that DyAg(2) undergoes an incommensurate to commensurate antiferromagnetic phase transition close to 10 K. The present experimental results highlight the first order nature of this phase transition, and show that this transition can be induced by magnetic field as well. It is further shown that another isothermal magnetic field induced transition or metamagnetic transition exhibited by DyAg(2) at still lower temperatures is also of first order nature. The multiple magnetic phase transitions in DyAg(2) give rise to large peaks in the temperature dependence of the heat capacity below 17 K, which indicates its potential as a magnetic regenerator material for cryocooler related applications. In addition it is found that because of the presence of the temperature and field induced magnetic phase transitions, and because of short range magnetic correlations deep inside the paramagnetic regime, DyAg(2) exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between 10 and 60 K.

  7. Influences of structural mismatch on morphology, phase transition temperature, segmental dynamics and color-transition behaviors of polydiacetylene vesicles.

    PubMed

    Pattanatornchai, Thanutpon; Charoenthai, Nipaphat; Traiphol, Rakchart

    2014-10-15

    In this contribution, we report a systematic study of polydiacetylene (PDA) vesicles fabricated by mixing two types of monomers, 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA). These diacetylene (DA) monomers constitute the same head group but different alkyl chain length, which in turn causes structural mismatch within the PDA layers. The PCDA:TCDA ratios are 100, 75, 50, 25 and 0mol%. Morphologies and properties of these PDA vesicles are explored by utilizing laser light scattering, transmission electron microscopy, differential scanning calorimetry, temperature-dependent nuclear magnetic resonance spectroscopy (NMR) and spin-lattice relaxation time (T1) measurements. An increase in DA mole ratio to 50mol% leads to significant increase in particle size. The mixed PDA vesicles also exhibit irregular shape with rather rough surface. The mismatch of alkyl side chain causes the drop of phase transition temperature. For the system of mixed poly(PCDA50:TCDA50), its transition temperature is lower than those of the pure PDAs. The NMR line shape analysis detects an abrupt change of proton signal adjacent to the PDA head group during the blue/red color-transition process. The T1 measurements also reveal different local environments of PDA alkyl side chains in the blue and red phases. The mismatch of PDA side chains causes significant drop of the color-transition temperature. PMID:25086392

  8. Influences of structural mismatch on morphology, phase transition temperature, segmental dynamics and color-transition behaviors of polydiacetylene vesicles.

    PubMed

    Pattanatornchai, Thanutpon; Charoenthai, Nipaphat; Traiphol, Rakchart

    2014-10-15

    In this contribution, we report a systematic study of polydiacetylene (PDA) vesicles fabricated by mixing two types of monomers, 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA). These diacetylene (DA) monomers constitute the same head group but different alkyl chain length, which in turn causes structural mismatch within the PDA layers. The PCDA:TCDA ratios are 100, 75, 50, 25 and 0mol%. Morphologies and properties of these PDA vesicles are explored by utilizing laser light scattering, transmission electron microscopy, differential scanning calorimetry, temperature-dependent nuclear magnetic resonance spectroscopy (NMR) and spin-lattice relaxation time (T1) measurements. An increase in DA mole ratio to 50mol% leads to significant increase in particle size. The mixed PDA vesicles also exhibit irregular shape with rather rough surface. The mismatch of alkyl side chain causes the drop of phase transition temperature. For the system of mixed poly(PCDA50:TCDA50), its transition temperature is lower than those of the pure PDAs. The NMR line shape analysis detects an abrupt change of proton signal adjacent to the PDA head group during the blue/red color-transition process. The T1 measurements also reveal different local environments of PDA alkyl side chains in the blue and red phases. The mismatch of PDA side chains causes significant drop of the color-transition temperature.

  9. 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.

  10. 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).

  11. Deconfinement Phase Transition at Finite Temperature in the Dual Ginzburg-Landau Theory

    NASA Astrophysics Data System (ADS)

    Ichie, H.; Suganuma, H.; Toki, H.

    We find deconfinement phase transition into the quark-gluon-plasma at finite temperature and then show a possibility of QGP formation process due to the interaction of color-flux-tubes in dual Ginzburg-Landau (DGL) theory.

  12. 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.

  13. 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

  14. In situ wetting state transition on micro- and nanostructured surfaces at high temperature.

    PubMed

    Wang, Jingming; Liu, Meng; Ma, Rui; Wang, Qianbin; Jiang, Lei

    2014-09-10

    We studied the in situ transition of the droplets' wetting state on the heated solid surfaces. The wetting behaviors of four micro- and nanostructured surfaces with different chemical components were studied. These parameters included the maximum contact areas (MCA), the maximum evaporation areas (MEA) and the wetting transition temperature (T(trans)). The reduction in MEAs has a specific transition process from wetting (Wenzel state) or partial wetting (Wenzel-Cassie intermediate state) to nonwetting (Cassie State) as the surface temperature rises. When the MEAs drop to zero at a critical temperature (T(trans)), the droplets rebound from the heated surfaces to complete the wetting transition process. The chemical compounds and the surfaces' rough structure play an important role in the droplets' wetting transition behavior. Before FAS-modification, microstructures can increase the MCAs, MEAs, and T(trans). However, the microstructures are less effective at increasing the MEAs and T(trans) than changes to nanostructures. After FAS-modification, both the nano- and microstructures reduce the T(trans). On the FAS-MNSi surfaces, the MEAs are always zero--the droplets rebounded at room temperature, and the wetting transition did occur. We propose two high-temperature mechanisms to explain these transition phenomena.

  15. ATOMIC AND MOLECULAR PHYSICS: High-Temperature Raman Investigation on Phase Transition of LBO Crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Xia; Wan, Song-Ming; Yin, Shao-Tang; You, Jing-Lin

    2009-11-01

    The high-temperature Raman spectroscopy technique is applied to investigate the phase transition of LiB3O5 crystal. The result shows that the crystal is stable in the range of 293-893 K. When the temperature increases up to above 1107K, the phase transition occurs. In the liquid phase, Li2B4O7 crystal precipitates out. Up to 1173K, the Li2B4O7 crystal disappears in the melt.

  16. 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.

  17. Temperature dependence of the lowest excitonic transition for an InAs ultrathin quantum well

    NASA Astrophysics Data System (ADS)

    Singh, S. D.; Porwal, S.; Sharma, T. K.; Rustagi, K. C.

    2006-03-01

    Temperature dependent photoluminescence and photoreflectance techniques are used to investigate the lowest excitonic transition of InAs ultrathin quantum well. It is shown that the temperature dependence of the lowest energy transition follows the band gap variation of GaAs barrier, which is well reproduced by calculated results based on the envelope function approximation with significant corrections due to strain and temperature dependences of the confinement potential. A redshift in photoluminescence peak energy compared to photoreflectance is observed at low temperatures. This is interpreted to show that the photoluminescence signal originates from the recombination of carriers occupying the band-tail states below the lowest critical point.

  18. Surface self-diffusion constants at low temperature: Monte Carlo transition state theory with importance sampling

    SciTech Connect

    Voter, A.F.; Doll, J.D.

    1984-06-01

    We present an importance-sampling method which, when combined with a Monte Carlo procedure for evaluating transition state theory rates, allows computation of classically exact, transition state theory surface diffusion constants at arbitrarily low temperature. In the importance-sampling method, a weighting factor is applied to the transition state region, and Metropolis steps are chosen from a special distribution which facilitates transfer between the two important regions of configuration space: the binding site minimum and the saddle point between two binding sites. We apply the method to the diffusion of Rh on Rh(111) and Rh on Rh(100), in the temperature range of existing field ion microscope experiments.

  19. 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

  20. Theory of the jamming transition at finite temperature.

    PubMed

    DeGiuli, E; Lerner, E; Wyart, M

    2015-04-28

    A theory for the microscopic structure and the vibrational properties of soft sphere glass at finite temperature is presented. With an effective potential, derived here, the phase diagram and vibrational properties are worked out around the Maxwell critical point at zero temperature T and pressure p. Variational arguments and effective medium theory identically predict a non-trivial temperature scale T(∗) ∼ p((2-a)/(1-a)) with a ≈ 0.17 such that low-energy vibrational properties are hard-sphere like for T ≳ T(∗) and zero-temperature soft-sphere like otherwise. However, due to crossovers in the equation of state relating T, p, and the packing fraction ϕ, these two regimes lead to four regions where scaling behaviors differ when expressed in terms of T and ϕ. Scaling predictions are presented for the mean-squared displacement, characteristic frequency, shear modulus, and characteristic elastic length in all regions of the phase diagram. PMID:25933770

  1. 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.

  2. 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

  3. Modelling of the size effect's influence on the critical temperature of the nanowires’ phase transition

    NASA Astrophysics Data System (ADS)

    Leonid, Afremov; Aleksandr, Petrov

    2016-08-01

    Influence of the size effect on the magnetic phase transition's temperature and magnetic moment of the nanowires was modelled based on “average spin” method. As it was shown that Curie temperature was increased with nanowires’ sizes increase. The calculated value of the critical exponent of the spin-spin correlations v = 0.737 is close to experimental value.

  4. Ab Initio Simulations of Temperature Dependent Phase Stability and Martensitic Transitions in NiTi

    NASA Technical Reports Server (NTRS)

    Haskins, Justin B.; Thompson, Alexander E.; Lawson, John W.

    2016-01-01

    For NiTi based alloys, the shape memory effect is governed by a transition from a low-temperature martensite phase to a high-temperature austenite phase. Despite considerable experimental and computational work, basic questions regarding the stability of the phases and the martensitic phase transition remain unclear even for the simple case of binary, equiatomic NiTi. We perform ab initio molecular dynamics simulations to describe the temperature-dependent behavior of NiTi and resolve several of these outstanding issues. Structural correlation functions and finite temperature phonon spectra are evaluated to determine phase stability. In particular, we show that finite temperature, entropic effects stabilize the experimentally observed martensite (B19') and austenite (B2) phases while destabilizing the theoretically predicted (B33) phase. Free energy computations based on ab initio thermodynamic integration confirm these results and permit estimates of the transition temperature between the phases. In addition to the martensitic phase transition, we predict a new transition between the B33 and B19' phases. The role of defects in suppressing these phase transformations is discussed.

  5. 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.

  6. Temperature induced transition from hexagonal to circular pits in graphite oxidation by O2

    NASA Astrophysics Data System (ADS)

    Delehouzé, Arnaud; Rebillat, Francis; Weisbecker, Patrick; Leyssale, Jean-Marc; Epherre, Jean-Francois; Labrugère, Christine; Vignoles, Gérard L.

    2011-07-01

    We report on an in-situ monitoring of graphite oxidation using a high temperature environmental scanning electron microscope. A morphological transition is clearly identified around 1040 K between hexagonal pits at low temperatures and circular pits at high temperatures, with apparently no change in the kinetic law. A kinetic Monte Carlo model allows rationalizing these findings in terms of the competitive oxidation of armchair and zig-zag edge sites and provides an estimate of the rate laws associated to these two events. Extended to three dimensions, the model also explains the "in-depth" transition between the stepwise hexagons and the hemispheres observed by atomic force microscopy.

  7. 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.

  8. 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.

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

    PubMed

    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 12 h. 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

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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 → Sm-type → 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 GPa and a temperature of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. 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.

  12. Determination of the glass-transition temperature of proteins from a viscometric approach.

    PubMed

    Monkos, Karol

    2015-03-01

    All fully hydrated proteins undergo a distinct change in their dynamical properties at glass-transition temperature Tg. To determine indirectly this temperature for dry albumins, the viscosity measurements of aqueous solutions of human, equine, ovine, porcine and rabbit serum albumin have been conducted at a wide range of concentrations and at temperatures ranging from 278 K to 318 K. Viscosity-temperature dependence of the solutions is discussed on the basis of the three parameters equation resulting from Avramov's model. One of the parameter in the Avramov's equation is the glass-transition temperature. For all studied albumins, Tg of a solution monotonically increases with increasing concentration. The glass-transition temperature of a solution depends both on Tg for a dissolved dry protein Tg,p and water Tg,w. To obtain Tg,p for each studied albumin the modified Gordon-Taylor equation was applied. This equation describes the dependence of Tg of a solution on concentration, and Tg,p and a parameter depending on the strength of the protein-solvent interaction are the fitting parameters. Thus determined the glass-transition temperature for the studied dry albumins is in the range (215.4-245.5)K.

  13. Effects of temperature factor of cone nose-tip on a transition to turbulence

    NASA Astrophysics Data System (ADS)

    Bountin, D. A.; Gromyko, Yu. V.; Polivanov, P. A.; Sidorenko, A. A.; Nastobursky, A. S.; Maslov, A. A.

    2016-10-01

    During the flight of a hypersonic vehicle the areas of local heating of the surface can appear due to various reasons: the local separation zone, the incident shock wave, the joints of different materials and so forth. These areas change the temperature factor, i.e. the ratio of the surface temperature to the recovery temperature. Previous studies have shown that a local change of the temperature factor strongly influences the position of the laminar-turbulent transition in hypersonic boundary layer [1]. It was also shown that the degree of this effect depends on the position of the local heating/cooling area of the model surface. The leading edge or nose-tip of the model is an important area where the processes of receptivity occur. Disturbances converted to inner pulsation of the boundary layer is gradually increasing downstream, provoking non-linear processes, resulting in a laminar-turbulent transition. It is well known that the bluntness of model-tip substantially shifts transition position downstream. On the other hand the biggest heat loads occurs in the area of nose of reentry vehicle sufficiently changing temperature of nose-tip. Behavior of disturbances when changing the temperature factor of a blunt nose has not yet been investigated. In this paper the effect of temperature factor of blunt nose-tip change on the development of the perturbation of the boundary layer and the position of the transition was studied.

  14. Shock-induced phase transition of Tin: experimental study with velocity and temperature measurements

    NASA Astrophysics Data System (ADS)

    Chauvin, Camille; Bouchkour, Zakaria; Sinatti, Frédéric; Petit, Jacques

    2015-06-01

    To investigate polymorphic transition and melting on release of Tin, experiments under shock wave compression have been carried out from 10 GPa to 44 GPa with both velocity and temperature measurements. Interface Sn/LiF velocity has been recorded using PDV measurement technique and interface Sn/LiF temperature has been performed thnks to an optical pyrometer appropriate to detect low and high temperature (respectively under 1000 K and upper 1000 K). While PDV measurements are common and accurate, temperature remains often imprecise due to the lack of knowledge of the emissivity of the sample. Nevertheless, temperature profiles show singularities particularly during phase transition, not visible on velocity profiles. The use of an emissive layer at the interface Sn/LiF allows to estimate an accurate temperature measurement which can be compared to our numerical calculations. The profiles of velocity record and radiance record are in a good agreement in chronometry and display the polymorphic transition and the melting on release of Tin. This presentation will discuss the evidence of phase transitions on temperature measurements, the complementarity with velocity data and the advantages of an emissive layer.

  15. Determination of the ductile-brittle transition temperature from the microplastic-strain rate

    NASA Astrophysics Data System (ADS)

    Andreev, A. K.; Solntsev, Yu. P.

    2008-04-01

    The possibility of the determination of the tendency of cast and deformed steels to brittle fracture using the temperature dependence of the small-plastic-strain rate is studied. The temperature corresponding to the maximum in this curve is found to indicate an abrupt decrease in the steel plasticity, which makes it possible to interpret it as the ductile-brittle transition temperature depending only on the structure of a material.

  16. 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.

  17. 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

  18. 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.

  19. Association between in-transit loss, internal trailer temperature, and distance traveled by Ontario market hogs.

    PubMed

    Haley, Charles; Dewey, Catherine E; Widowski, Tina; Friendship, Robert

    2008-10-01

    An observational study was conducted from July to October 2004 to determine the association between in-transit losses of swine and internal trailer temperature after controlling for loading density, trip distance, herd size, and random trip effect. A convenience sample of 3 trucking companies was used to collect temperature, relative humidity, and global positioning data for 104 trips that delivered 21,834 pigs from 371 producers to Ontario abattoirs. The association between in-transit loss and trailer temperature was determined using the 90th percentiles of internal temperature for each trip. Average loading density was 0.36 m2/100 kg pig (range 0.28 to 0.50 m2/100 kg pig). Average in-transit loss was 0.12%; however, 94% of producers experienced no losses. As the 90th percentile of internal trailer temperature increased from a range of 8.6 degrees C to 23.3 degrees C to a range of 23.4 degrees C to 26.1degreesC, average in-transit loss ratio increased approximately 3-fold, with an additional 2-fold increase as the range increased from 26.2 degrees C to 28.9 degrees C to 29.0 degrees C to 30.5 degrees C. As the 90th percentile of temperature increased by 1degreesC over the full range of temperatures in this study, in-transit loss was expected to increase 1.26 times. The in-transit loss was expected to decrease 0.81 times for each 50-km increase in distance traveled between the farm and the abattoir. PMID:19086369

  20. 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.

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

    DOE PAGES

    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

  2. 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.

  3. 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.

  4. Reversible temperature regulation of electrical and thermal conductivity using liquid-solid phase transitions.

    PubMed

    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.

  5. Structural parameters determining the transition temperature of tetragonal KH2PO4-type crystals

    NASA Astrophysics Data System (ADS)

    Ichikawa, M.; Amasaki, D.; Gustafsson, T.; Olovsson, I.

    2001-09-01

    A systematic study of the structural parameters determining the ferroelectric phase transition temperature Tc in tetragonal KH2PO4 (KDP)-type crystals MH2XO4 has been performed by searching the correlation between different structural parameters and Tc. It has been revealed that the transition temperature is determined not only by the hydrogen-bond distance R, as reported earlier, but also by the distortion of XO4 (via O-X-O angle α1) and the packing of M and XO4 along the c axis (via the rotation angle θ around the c axis); α1 reflects the dipole moment of XO4 and θ may influence the amplitude of optical vibration of M and XO4. The contribution of each structural part to the transition temperature Tc in the tetragonal KDP family has been revealed in a comprehensive way for ferroelectrics.

  6. Low-temperature fabrication of VO2 thin film on ITO glass with a Mott transition

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen

    2016-09-01

    Polycrystalline Vanadium dioxide (VO2) thin film can be fabricated on glass substrates by high power impulse magnetron sputtering at a relative high temperature. In order to apply an effective bias voltage on substrate and control the energy of the ions impinged to the substrate, conductive indium-tin oxide (ITO) glass was used as the substrate. UV-visible-near IR transmittance spectra and X-ray diffraction (XRD) patterns of the as-deposited films exhibited that M-VO2 thin film with a metal-insulator transition temperature of 37∘C was fabricated successfully at 300∘C with a bias voltage of ‑200V, and the calculated average crystalline size of this film was about 12nm. XRD patterns at varied temperatures showed that the structural change of MIT of the VO2 thin film was suppressed during the phase transition process, and a pure Mott transition was obtained.

  7. 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

  8. 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.

  9. Variation of internal friction with time in metallic glasses near glass transition temperature

    NASA Astrophysics Data System (ADS)

    Hiki, Y.; Miyauchi, Y.; Karasawa, R.; Tamura, R.

    2013-02-01

    Internal friction (IF) of a bulk metallic glass Zr55Cu30Al10Ni5 has been measured near and below/above the glass transition temperature Tg. The specimen is prepared by rapid cooling the liquid mother alloy through casting into a copper ingot. The size of the specimen is about 30 mm × 2 mm × 0.8 mm. The amorphous state of the specimen is checked by the X-ray diffraction, and the temperatures of glass transition (Tg=666 K) and crystallization (Tx=746 K) are determined by the DSC method. The specimen is stabilized by annealing at Tg-10 K for 10 h. The IF measurement is performed by using DMA (TA Instrument) apparatus at the frequency of 0.1 Hz. The deformation mode of vibration is the cantilever bending. The specimen is kept at a constant temperature T, and the IF value Q-1 is measured as a function of duration time t( = 0˜2.5×104s). The temperature is controlled by the apparatus. The measurement is successively carried out at various temperatures T = (Tg-50K)˜(Tg+50K). The Q-1-vs-t behavior is different in different temperature ranges. At lower and higher temperatures, Q-1-vs-t shows the single relaxation. At temperatures near Tg, Q-1-vs-t appears to be quite irregular. These results are considered on the basis of the characteristics of the glass-forming materials and the glass transition.

  10. 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.

  11. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature.

    PubMed

    Bordignon, Enrica; Nalepa, Anna I; Savitsky, Anton; Braun, Lukas; Jeschke, Gunnar

    2015-10-29

    For structural characterization by pulsed EPR methods, spin-labeled macromolecules are routinely studied at cryogenic temperatures. The equilibration of the conformational ensemble during shock-freezing occurs to a good approximation at the glass transition temperature (Tg). In this work, we used X-band power saturation continuous wave (cw) EPR to obtain information on the glass transition temperatures in the microenvironment of nitroxide radicals in solvents or bound to different sites in proteins. The temperature dependence of the saturation curve of nitroxide probes in pure glycerol or ortho-terphenyl showed detectable transitions at the respective Tg values, with the latter solvent characterized by a sharper change of the saturation properties, according to its higher fragility. In contrast, nitroxide probes in a glycerol/water mixture showed a discontinuity in the saturation properties close to the expected glass transition temperature, which made the determination of Tg complicated. Low-temperature W-band cw EPR and W-band ELDOR-detected NMR experiments demonstrated that the discontinuity is due to local rearrangements of H-bonds between water molecules and the nitroxide reporter group. The change in the network of H-bonds formed between the nitroxide and water molecules that occurs around Tg was found to be site-dependent in spin-labeled proteins. This effect can therefore be modulated by neighboring residues with different steric hindrances and/or charge distributions and possibly by the glycerol enrichment on protein surfaces. In conclusion, if the thermal history of the sample is carefully reproduced, the nitroxide probe is extremely sensitive in reporting site-specific changes in the H-bonding to water molecules close to Tg and local glass transition temperatures in spin-labeled macromolecules. PMID:26266707

  12. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature.

    PubMed

    Bordignon, Enrica; Nalepa, Anna I; Savitsky, Anton; Braun, Lukas; Jeschke, Gunnar

    2015-10-29

    For structural characterization by pulsed EPR methods, spin-labeled macromolecules are routinely studied at cryogenic temperatures. The equilibration of the conformational ensemble during shock-freezing occurs to a good approximation at the glass transition temperature (Tg). In this work, we used X-band power saturation continuous wave (cw) EPR to obtain information on the glass transition temperatures in the microenvironment of nitroxide radicals in solvents or bound to different sites in proteins. The temperature dependence of the saturation curve of nitroxide probes in pure glycerol or ortho-terphenyl showed detectable transitions at the respective Tg values, with the latter solvent characterized by a sharper change of the saturation properties, according to its higher fragility. In contrast, nitroxide probes in a glycerol/water mixture showed a discontinuity in the saturation properties close to the expected glass transition temperature, which made the determination of Tg complicated. Low-temperature W-band cw EPR and W-band ELDOR-detected NMR experiments demonstrated that the discontinuity is due to local rearrangements of H-bonds between water molecules and the nitroxide reporter group. The change in the network of H-bonds formed between the nitroxide and water molecules that occurs around Tg was found to be site-dependent in spin-labeled proteins. This effect can therefore be modulated by neighboring residues with different steric hindrances and/or charge distributions and possibly by the glycerol enrichment on protein surfaces. In conclusion, if the thermal history of the sample is carefully reproduced, the nitroxide probe is extremely sensitive in reporting site-specific changes in the H-bonding to water molecules close to Tg and local glass transition temperatures in spin-labeled macromolecules.

  13. 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.

  14. 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.

  15. 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.

  16. Transition temperature to the superconducting phase of QCD at high baryon density

    SciTech Connect

    Brown, William E.; Liu, James T.; Ren, Hai-cang

    2000-09-01

    Recent interest in the study of color superconductivity has focused on the regime of high baryon density where perturbative QCD may be employed. Based on the dominant one-gluon-exchange interaction, both the transition temperature and zero temperature gap have been determined to leading order in the coupling g. While the leading non-BCS behavior T{sub C}{approx}{mu}g{sup -5}e{sup -{kappa}}{sup /g} is easily obtained, the pre-exponential factor has proved more difficult to evaluate. Focusing on the transition temperature, we present a perturbative derivation of this factor, exact to leading order in g. This approach is first motivated by the study of a toy model and involves working to second order in the perturbative expansion. We compare this result to the zero temperature gap. Additionally, we extend the analysis to the case of higher angular momentum for longitudinal and transverse quark pairing. (c) 2000 The American Physical Society.

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

  18. Hilbert-Glass Transition: New Universality of Temperature-Tuned Many-Body Dynamical Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Pekker, David; Refael, Gil; Altman, Ehud; Demler, Eugene; Oganesyan, Vadim

    2014-01-01

    We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. One example of such a transition is the recently proposed many-body localization-delocalization transition, in which transport coefficients vanish at a critical temperature with no singularities in thermodynamic observables. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here, we develop a real-space renormalization group method for excited states that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1 D disordered transverse-field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using the real-space renormalization group method for excited states we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by nonanalyticities in the low-frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

  19. High-temperature tolerance in anhydrobiotic tardigrades is limited by glass transition.

    PubMed

    Hengherr, S; Worland, M R; Reuner, A; Brümmer, F; Schill, R O

    2009-01-01

    Survival in microhabitats that experience extreme fluctuations in water availability and temperature requires special adaptations. To withstand such environmental conditions, tardigrades, as well as some nematodes and rotifers, enter a completely desiccated state known as anhydrobiosis. We examined the effects of high temperatures on fully desiccated (anhydrobiotic) tardigrades. Nine species from the classes Heterotardigrada and Eutardigrada were exposed to temperatures of up to 110 degrees C for 1 h. Exposure to temperatures of up to 80 degrees C resulted in a moderate decrease in survival. Exposure to temperatures above this resulted in a sharp decrease in survival, with no animals of the families Macrobiotidae and Echiniscidae surviving 100 degrees C. However, Milnesium tardigradum (Milnesidae) showed survival of >90% after exposure to 100 degrees C; temperatures above this resulted in a steep decrease in survival. Vitrification is assumed to play a major role in the survival of anhydrobiotic organisms during exposure to extreme temperatures, and consequently, the glass-transition temperature (T(g)) is critical to high-temperature tolerance. In this study, we provide the first evidence of the presence of a glass transition during heating in an anhydrobiotic tardigrade through the use of differential scanning calorimetry.

  20. 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.

  1. Effects of confinement on the glass transition temperature of molecular liquids

    SciTech Connect

    Zhang, J.; Liu, G.; Jonas, J.

    1992-04-16

    Differential scanning calorimetry was used to analyze the effects of confinement on the glass transition of temperature, T{sub g}, of several molecular liquids in porous silica glasses. For all the liquids, confinement lowers the observed T{sub g}. A linear relationship between the inverse of the silica glass pore radius and T{sub g} was also observed. The relative temperature depression due to confinement was less than the freezing point depression. 40 refs., 1 fig., 1 tab.

  2. 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).

  3. 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).

  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. 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.

  6. Temperature limits in laser cooling of free atoms with three-level cascade transitions

    NASA Astrophysics Data System (ADS)

    Cruz, Flavio C.; Sundheimer, Michael L.; Magno, Wictor C.

    2013-06-01

    We employ semiclassical theoretical analysis to study laser cooling of free atoms using three-level cascade transitions, where the upper transition is much weaker than the lower one. This represents an alternate cooling scheme, particularly useful for group II atoms. We find that temperatures below the Doppler limits associated with each of these transitions are expected. The lowest temperatures arise from a remarkable increase in damping and reduced diffusion compared to two-level cooling. They are reached at the two-photon resonance, where there is a crossing between the narrow and the partially dark dressed states, and can be estimated simply by the usual Doppler limit considering the decay rate of the optical coherence between these states.

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

    NASA Astrophysics Data System (ADS)

    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 → 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 7Li or 39K.

  8. Local temperature redistribution and structural transition during joule-heating-driven conductance switching in VO2.

    PubMed

    Kumar, Suhas; Pickett, Matthew D; Strachan, John Paul; Gibson, Gary; Nishi, Yoshio; Williams, R Stanley

    2013-11-13

    Joule-heating induced conductance-switching is studied in VO2 , a Mott insulator. Complementary in situ techniques including optical characterization, blackbody microscopy, scanning transmission X-ray microscopy (STXM) and numerical simulations are used. Abrupt redistribution in local temperature is shown to occur upon conductance-switching along with a structural phase transition, at the same current.

  9. 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.

  10. 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...

  11. 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.

  12. Upper critical fields and superconducting transition temperatures of some zirconium-base amorphous transition-metal alloys

    NASA Astrophysics Data System (ADS)

    Karkut, M. G.; Hake, R. R.

    1983-08-01

    Superconducting upper critical fields Hc2(T), transition temperatures Tc and normal-state electrical resistivities ρn have been measured in the amorphous transition-metal alloy series Zr1-xCox, Zr1-xNix, (Zr1-xTix)0.78Ni0.22, and (Zr1-xNbx)0.78Ni0.22. Structural integrity of these melt-spun alloys is indicated by x-ray, density, bend-ductility, normal-state electrical resistivity, superconducting transition width, and mixed-state flux-pinning measurements. The specimens display Tc=2.1-3.8 K, ρn=159-190 μΩ cm, and |(dHc2dT)Tc|=28-36 kG/K. These imply electron mean free paths l~2-6 Å, zero-temperature Ginzburg-Landau coherence distances ξG0~50-70 Å, penetration depths λG0~(7-10)×103 Å, and extremely high dirtiness parameters ξ0l~300-1300. All alloys display Hc2(T) curves with negative curvature and (with two exceptions) fair agreement with the standard dirty-limit theory of Werthamer, Helfand, Hohenberg, and Maki (WHHM) for physically reasonable values of spin-orbit-coupling induced, electron-spin-flip scattering time τso. This is in contrast to the anomalously elevated Hc2(T) behavior which is nearly linear in T that is observed by some, and the unphysically low-τso fits to WHHM theory obtained by others, for various amorphous alloys. Current ideas that such anomalies may be due to alloy inhomogeneity are supported by present results on two specimens for which relatively low-τso fits of Hc2(T) to WHHM theory are coupled with superconductive evidence for inhomogeneity: relatively broad transitions at Tc and Hc2 current-density-dependent transitions at Hc2 and (in one specimen) a J-dependent, high-H (>Hc2), resistive "beak effect." In the Zr1-xCox and Zr1-xNix series, Tc decreases linearly with x (and with unfilled-shell average electron-to-atom ratio < ea > in the range 5.05<=< ea ><=6.40 in fair agreement with previous results for these systems and contrary to the Tc vs < ea > behavior of both amorphous and crystalline transition-metal alloys formed

  13. Topological effects on transition temperatures and response functions in three-dimensional Fermi superfluids

    NASA Astrophysics Data System (ADS)

    Anderson, Brandon M.; Wu, Chien-Te; Boyack, Rufus; Levin, K.

    2015-10-01

    We investigate the effects of topological order on the transition temperature, Tc, and response functions in spin-orbit-coupled fermionic superfluids with a transverse Zeeman field in three dimensions. Our calculations include fluctuation effects beyond mean-field theory and are compatible with f -sum rules. In the topological phase we find that Tc can be as large as 10 % of the Fermi temperature, which should be experimentally accessible in cold-gas experiments. At higher temperatures, above Tc, the spin and density response functions provide signatures of topological phases via the recombination or amplification of frequency-dependent peaks.

  14. 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.

  15. Low temperature magnetic properties of monoclinic pyrrhotite with particular relevance to the Besnus transition

    NASA Astrophysics Data System (ADS)

    Volk, Michael W. R.; Gilder, Stuart A.; Feinberg, Joshua M.

    2016-10-01

    Monoclinic pyrrhotite (Fe7S8) owes its ferrimagnetism to an ordered array of Fe vacancies. Its magnetic properties change markedly around 30 K, in what is known as the Besnus transition. Plausible explanations for the Besnus transition are either due to changes in crystalline anisotropy from a transformation in crystal symmetry or from the establishment of a two-phase system with magnetic interaction between the two phases. To help resolve this discrepancy, we measured hysteresis loops every 5° and back field curves every 10° in the basal plane of an oriented single crystal of monoclinic pyrrhotite at 300 K and every two kelvin from 50 K through the Besnus transition until 20 K. Between 50 and 30 K, hysteresis loops possess double inflections between crystallographic a-axes and only a single inflection parallel to the a-axes. Magnetization energy calculations and relative differences of the loops show a six-fold symmetry in this temperature range. We propose that the inflections stem from magnetic axis switching, which is both field and temperature dependent, in a manner somewhat analogous to an isotropic point where magnetocrystalline constants change their sign. The Besnus transition is best characterized by changes in magnetic remanence and coercivity over a 6° temperature span (28-34 K) with a maximum rate of change at 30 K. A surprising yet puzzling finding is that the coercivity ratio becomes less than unity below the transition when four-fold symmetry arises. Because the changes in magnetic parameters are linked to the crystal structure, we conclude the Besnus transition owes its origin to a distortion of the crystallographic axes below 30 K rather than an apparition of a two-phase system. An isothermal magnetization of natural pyrrhotite cycled from room temperature to successively lower temperatures through the Besnus transition decreases 2-4 times less than equivalent grain sizes of magnetite, with less than a 10% loss in remanence between 300 K and

  16. 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.

  17. 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

  18. Dielectric spectroscopy for the determination of the glass transition temperature of pharmaceutical solid dispersions.

    PubMed

    O'Donnell, Kevin P; Woodward, W H Hunter

    2015-06-01

    The purpose of this study was to evaluate analytical techniques for the measurement of the glass transition temperature of HPMC and formulated solid dispersions thereof. Unmodified samples of various grades of HPMC and solid dispersions of HPMC and itraconazole produced by hot melt extrusion were analyzed by thermomechanical analysis, differential scanning calorimetry, thermally stimulated depolarization current and dielectric spectroscopy. It was found that dielectric spectroscopy offers the best accuracy and reproducibility for analysis of the base HPMC powders regardless of the substitution type or viscosity grade and that the obtained results were not frequency dependent. The results of dielectric measurements of solid dispersions prepared by hot melt extrusion were compared with predicted values of the Gordon-Taylor equation. It was found that time-temperature superposition effects and small molecule frequency dependence makes broadly applying determination of the glass transition temperature in drug dispersions by dielectric spectroscopy prohibitively difficult.

  19. 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%.

  20. Controllable release from high-transition temperature magnetoliposomes by low-level magnetic stimulation.

    PubMed

    Spera, Romina; Apollonio, Francesca; Liberti, Micaela; Paffi, Alessandra; Merla, Caterina; Pinto, Rosanna; Petralito, Stefania

    2015-07-01

    High-transition temperature liposomes with embedded coated magnetite nanoparticles were prepared using the thin lipid film hydration method in order to obtain magnetoliposomes not sensitive to temperature increase (at least up to 50°C). Accordingly, drug can be released from such magnetoliposomes using a low-level electromagnetic field as triggering agent, while no delivery would be obtained with temperature increase within the physiological acceptable range. The hypothesized release mechanism involves mechanical stress of the liposome membrane due to nanoparticles oscillations and it is investigated by means of a numerical model evaluated using multiphysics simulations. The carrier content was repetitively released by switching on and off a 20kHz, 60A/m magnetic field. The results indicated high reproducibility of cycle-to-cycle release induced by the magnetic-impelled motions driving to the destabilization of the bilayer rather than the liposome phase transition or the destruction of the liposome structure.

  1. Controllable release from high-transition temperature magnetoliposomes by low-level magnetic stimulation.

    PubMed

    Spera, Romina; Apollonio, Francesca; Liberti, Micaela; Paffi, Alessandra; Merla, Caterina; Pinto, Rosanna; Petralito, Stefania

    2015-07-01

    High-transition temperature liposomes with embedded coated magnetite nanoparticles were prepared using the thin lipid film hydration method in order to obtain magnetoliposomes not sensitive to temperature increase (at least up to 50°C). Accordingly, drug can be released from such magnetoliposomes using a low-level electromagnetic field as triggering agent, while no delivery would be obtained with temperature increase within the physiological acceptable range. The hypothesized release mechanism involves mechanical stress of the liposome membrane due to nanoparticles oscillations and it is investigated by means of a numerical model evaluated using multiphysics simulations. The carrier content was repetitively released by switching on and off a 20kHz, 60A/m magnetic field. The results indicated high reproducibility of cycle-to-cycle release induced by the magnetic-impelled motions driving to the destabilization of the bilayer rather than the liposome phase transition or the destruction of the liposome structure. PMID:26042528

  2. 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.

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

    DOE PAGES

    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

  4. 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.

  5. 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

  6. Composition dependence of the phase transition temperature in SrxBa1-xNb2O6

    NASA Astrophysics Data System (ADS)

    David, C.; Granzow, T.; Tunyagi, A.; Wöhlecke, M.; Woike, Th.; Betzler, K.; Ulex, M.; Imlau, M.; Pankrath, R.

    2004-06-01

    The temperature dependence of the spontaneous polarization in strontium-barium-niobate single crystals with varying Sr/Ba ratio is presented. The temperature of the relaxor phase-transition is determined from the inflexion point of the curve of the ferroelectric polarization versus temperature. The influence of the Sr/Ba ratio in the crystal on the transition temperature is discussed within an effective field approach.

  7. 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.

  8. 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)

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. In Situ Observation of Gypsum-Anhydrite Transition at High Pressure and High Temperature

    NASA Astrophysics Data System (ADS)

    Liu, Chuan-Jiang; Zheng, Hai-Fei

    2012-04-01

    An in-situ Raman spectroscopic study of gypsum-anhydrite transition under a saturated water condition at high pressure and high temperature is performed using a hydrothermal diamond anvil cell (HDAC). The experimental results show that gypsum dissolvs in water at ambient temperature and above 496 MPa. With increasing temperature, the anhydrite (CaSO4) phase precipitates at 250-320°C in the pressure range of 1.0-1.5GPa, indicating that under a saturated water condition, both stable conditions of pressure and temperature and high levels of Ca and SO4 ion concentrations in aqueous solution are essential for the formation of anhydrite. A linear relationship between the pressure and temperature for the precipitation of anhydrite is established as P(GPa) = 0.0068T-0.7126 (250°C<=T<=320°C). Anhydrite remained stable during rapid cooling of the sample chamber, showing that the gypsum-anhydrite transition involving both dissolution and precipitation processes is irreversible at high pressure and high temperature.

  14. 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.

  15. Multiple high-temperature transitions driven by dynamical structures in NaI

    NASA Astrophysics Data System (ADS)

    Manley, M. E.; Jeffries, J. R.; Lee, H.; Butch, N. P.; Zabalegui, A.; Abernathy, D. L.

    2014-06-01

    Multiple, consecutive high-temperature transitions in NaI involving dynamical order and/or localization in the energy-momentum spectrum but not in the average crystal structure are revealed by lattice dynamics, x-ray lattice spacing, and heat-capacity measurements. Distinctive energy-momentum patterns and lattice distortions indicate dynamical structures forming within randomly stacked planes, rather than the isolated point-defect-like intrinsic localized modes predicted. Transition entropies are accounted for by vibrational entropy changes, and the transition enthalpies are explained by the strain energy of forming stacking-fault-like planar distortions deduced from x-ray-diffraction peak shifts. The vibrational entropy of the dynamical structures stabilizes surrounding elastic distortions.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    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.

  17. 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.

  18. Organization versus frustration: low temperature transitions in a gelatine-based gel

    NASA Astrophysics Data System (ADS)

    Philipp, M.; Müller, U.; Sanctuary, R.; Baller, J.; Krüger, J. K.

    2008-09-01

    A commercial physical gel composed of gelatine, water and glycerol shows a sol-gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not observable in the longitudinal acoustic mode measured at hypersonic frequencies with Brillouin spectroscopy. Depending on the thermal treatment of the investigated material during the sol-gel transition and within the gel state, Brillouin spectroscopy reflects tremendously different hypersonic dynamics. These distinct dynamics are responsible for the formation of different glassy states at low temperatures including that of a glass-ceramic. The large variety of super-cooled and glassy states is attributed to distinct distributions of the gel's constituents within the samples. Surprisingly, the same gel state can be produced either by annealing the gel over months or by the non-equilibrium effect of thermo-diffusion (Soret effect) in the course of some minutes.

  19. 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.

  20. 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.

  1. Effect of the degree of substitution in the transition temperatures and hydrophobicity of hydroxypropyl cellulose esters.

    PubMed

    López-Velázquez, Delia; Hernández-Sosa, Armando R; Pérez, Ernesto

    2015-07-10

    We have synthesized and characterized five members of a homologous series of side chain polymers of hydroxypropyl cellulose esters obtained by homogeneous esterification with 6-[4'-(ethoxycarbonyl)biphenyl-4-yloxy]hexanoic acid. Two acylation procedures were studied. One procedure involved the acid chloride derivative and the other one was the activation of that acid with N,N'-carbonyldiimidazol. The second method yielded esters with higher degree of substitution, DS¯. The esters, with DS¯ ranging from 26 to about 66%, were characterized by FTIR, NMR, solution viscometry, TGA, DSC, polarized optical microscopy, and X-ray diffraction, in order to study the effect of the degree of substitution on the hydrophobicity, on the transition temperatures and on their potential liquid crystal properties. It has been found that the hydrophobicity and the transition temperatures of the HPC derivatives are very much dependent on the degree of acylation. The esters with high DS¯ values showed liquid crystal properties.

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

    DOE PAGES

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

    2016-07-29

    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 alsomore » found to be quite strongly disorder dependent (Ts≈72–90K) and linearly correlated with Tc.« less

  3. Improving the efficiency of Monte Carlo simulations of systems that undergo temperature-driven phase transitions

    NASA Astrophysics Data System (ADS)

    Velazquez, L.; Castro-Palacio, J. C.

    2013-07-01

    Recently, Velazquez and Curilef proposed a methodology to extend Monte Carlo algorithms based on a canonical ensemble which aims to overcome slow sampling problems associated with temperature-driven discontinuous phase transitions. We show in this work that Monte Carlo algorithms extended with this methodology also exhibit a remarkable efficiency near a critical point. Our study is performed for the particular case of a two-dimensional four-state Potts model on a square lattice with periodic boundary conditions. This analysis reveals that the extended version of Metropolis importance sampling is more efficient than the usual Swendsen-Wang and Wolff cluster algorithms. These results demonstrate the effectiveness of this methodology to improve the efficiency of MC simulations of systems that undergo any type of temperature-driven phase transition.

  4. Effect of the degree of substitution in the transition temperatures and hydrophobicity of hydroxypropyl cellulose esters.

    PubMed

    López-Velázquez, Delia; Hernández-Sosa, Armando R; Pérez, Ernesto

    2015-07-10

    We have synthesized and characterized five members of a homologous series of side chain polymers of hydroxypropyl cellulose esters obtained by homogeneous esterification with 6-[4'-(ethoxycarbonyl)biphenyl-4-yloxy]hexanoic acid. Two acylation procedures were studied. One procedure involved the acid chloride derivative and the other one was the activation of that acid with N,N'-carbonyldiimidazol. The second method yielded esters with higher degree of substitution, DS¯. The esters, with DS¯ ranging from 26 to about 66%, were characterized by FTIR, NMR, solution viscometry, TGA, DSC, polarized optical microscopy, and X-ray diffraction, in order to study the effect of the degree of substitution on the hydrophobicity, on the transition temperatures and on their potential liquid crystal properties. It has been found that the hydrophobicity and the transition temperatures of the HPC derivatives are very much dependent on the degree of acylation. The esters with high DS¯ values showed liquid crystal properties. PMID:25857978

  5. The Transition to Collisionless Ion-temperature-gradient-driven Plasma Turbulence: A Dynamical Systems Approach

    SciTech Connect

    R.A. Kolesnikov; J.A. Krommes

    2004-10-21

    The transition to collisionless ion-temperature-gradient-driven plasma turbulence is considered by applying dynamical systems theory to a model with ten degrees of freedom. Study of a four-dimensional center manifold predicts a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows and establishes the exact value of that shift in terms of physical parameters. For insight into fundamental physical mechanisms, the method provides a viable alternative to large simulations.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  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. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. Enhanced Volcanic Degassing Decoupled Atmospheric CO2 and Temperature During the Last Interglacial-Glacial Transition

    NASA Astrophysics Data System (ADS)

    Rupke, L.; Knorr, G.; Hasenclever, J.; Köhler, P.; Morgan, J. P.; Garofalo, K.; Barker, S.; Lohmann, G.; Hall, I. R.

    2015-12-01

    Evidence from the joint interpretation of proxy data as well as geodynamical and biogeochemical modeling results point to complex interactions between sea level drawdown, volcanic degassing, and atmospheric CO2 that hampered the climate system's decent into the last ice age. Ice core data shows that atmospheric CO2 dropped abruptly into glacial Marine Isotope Stage (MIS) 4 at ~71 ka, while Antarctic temperatures display a more gradual decline between ~85 ka to ~71 ka across the MIS 5/4 transition. Based on 2D and 3D geodynamical simulations, we show that a ~60-100 m sea level drop associated with the MIS 5/4 transition led to a significant increase in magma and possibly CO2 flux at mid-ocean ridges (MOR) and oceanic hotspot volcanoes. The MOR signal is assessed with 2D thermomechanical models that account for mantle melting and resolve the flux of incompatible carbon dioxide. These models have been run at different spreading rates and integrated with the global distribution of opening rates to compute global variations in magma and CO2 flux across the MIS 5/4 transition. 3D plume models have been used to quantify the impact of a dropping sea level on oceanic hotspot melting and CO2 release. Here a wide range of simulations with differing plume fluxes, lithospheric thicknesses as well as speeds, and plume excess temperatures have been integrated with data from ~40 hotspots in order to compute a global signal. Biogeochemical carbon cycle modeling shows that the predicted increase in volcanic emissions is likely to have raised atmospheric CO2 by up to 15 ppmv, sufficient to explain the bulk of the decoupling between temperature and atmospheric CO2 during the global change to pronounced glacial conditions across the MIS 5/4 transition.

  2. Temperature-Dependent Line Shift and Broadening of CO Infrared Transitions.

    PubMed

    Drascher; Giesen; Wang; Schmücker; Schieder; Winnewisser; Joubert; Bonamy

    1998-12-01

    The temperature dependence of lineshift and broadening of the rovibrational transitions R(18) and R(20) of the CO fundamental band, perturbed by Ar, N2, O2, and H2, have been measured with high frequency accuracy and at temperatures between 160 and 270 K in steps of 20 K. A wavelength stabilized tunable diode laser spectrometer has been combined with a low temperature long path cell of 134 m absorption length and 1 m basis length. For all measurements the CO pressure was below 0.1 mbar to avoid self-shift and self-broadening. In case of line broadening the temperature dependence is quite well reproduced by an exponential relation, b(T) = b(T0)(T/T0)-n. For all foreign gases, the exponent n has been obtained (0.53 temperatures, but there is no exponential behavior of the shift versus temperature. The line broadening and shift for CO with Ar and the broadening of CO by N2 and O2 have been compared to calculations from the semi-classical theory of Robert and Bonamy. Sufficient agreement has been achieved for the line broadening, while the calculated shifts are for all temperatures larger than the measured values. Copyright 1998 Academic Press.

  3. High-temperature, structural disorder, phase transitions, and piezoelectric properties of GaPO{sub 4}

    SciTech Connect

    Haines, J.; Cambon, O.; Prudhomme, N.; Fraysse, G.; Keen, D. A.; Chapon, L. C.; Tucker, M. G.

    2006-01-01

    Gallium orthophosphate was studied at high temperature up to 1303 K by total neutron scattering and 1173 K by piezoelectric measurements. Rietveld refinements at 1223 K confirm the stability of the structural distortion in the {alpha}-quartz-type phase with an average tilt angle {delta}=18.8 deg. at this temperature. In contrast, reverse Monte Carlo (RMC) refinements of total neutron scattering data indicate that, whereas the degree of structural disorder initially slowly varies over a very large temperature interval in the {alpha}-quartz-type phase, an increase in disorder is observed beginning above 1023 K. Piezoelectric measurements indicate that the quality factor (Q) of GaPO{sub 4} resonators remains stable up to this temperature above which the piezoelectric properties of the material degrade. This degradation can be correlated to the increase in structural disorder. RMC refinements indicate that the high-temperature {beta}-cristobalite-type phase at 1303 K is characterized by significant thermally induced disorder with oxygen atom density forming a continuous ring around the vector joining neighboring gallium and phosphorous atoms. Gallium phosphate may be expected to retain its piezoelectric properties up to within 200 K of the phase transition temperature and as a consequence be used in applications at temperatures slightly above 1000 K.

  4. Low-temperature structure anomalies in CuNCN. Manifestations of RVB phase transitions?

    PubMed

    Tchougréeff, A L; Dronskowski, R

    2013-10-30

    We propose a new frustrated Heisenberg antiferromagnetic model with spatially anisotropic exchange parameters Jc, Ja, and Jac, extending along the c, a, and a ± c (c-a-ca model) lattice directions, and apply it to describe the fascinating physics of copper carbodiimide, CuNCN, assuming the resonating valence bond (RVB) type of its phases. This explains within a unified picture the intriguing absence of magnetic order in CuNCN. We further present a parameters-temperature phase diagram of the c-a-ca-RVB model in the high-temperature approximation. Eight different phases including Curie and Pauli paramagnets (respectively, in disordered and 1D- or Q1D-RVB phases) and (pseudo)gapped (quasi-Arrhenius) paramagnets (2D-RVB phases) are possible. By adding magnetostriction and elastic terms to the model, we derive possible structural manifestations of RVB phase transitions. Assuming a sequence of RVB phase transitions to occur in CuNCN with decreasing temperature, several anomalies observed in the temperature course of the lattice constants are explained.

  5. 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

  6. 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

  7. Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition.

    PubMed

    Elderfield, H; Ferretti, P; Greaves, M; Crowhurst, S; McCave, I N; Hodell, D; Piotrowski, A M

    2012-08-10

    Earth's climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum. PMID:22879512

  8. The coronal and transition region temperature structure of a solar active region

    NASA Technical Reports Server (NTRS)

    Levine, R. H.; Pye, J. P.

    1980-01-01

    Using measurements of EUV and X-ray spectral lines, the differential emission measure vs electron temperature from the transition region to the corona of an active region (electron temperature between 100,000 and 5,000,000 K) is derived. The total emission measure and radiative losses are of the order 3 x 10 to the 48th/cu cm and 4 x 10 to the 26th ergs/sec, respectively. The emission measure at electron temperatures greater than approximately 1,000,000 K (i.e. that mainly responsible for the X-ray emission) is about 75% of the total. The use of the Mg x line at 625 A as an indicator of coronal electron density is also examined. A set of theoretical energy balance models of coronal loops in which the loop divergence is a variable parameter is presented and compared with the observations.

  9. Low temperature phase transition and crystal structure of CsMgPO4

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    CsMgPO4 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 P21/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) Å3. CsMgPO4 belongs to the group of framework compounds and is made up of strictly alternating MgO4- and PO4-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.

  10. 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

  11. Pressure and temperature induced high spin-low spin phase transition: Macroscopic and microscopic consideration

    NASA Astrophysics Data System (ADS)

    Levchenko, G.; Khristov, A.; Kuznetsova, V.; Shelest, V.

    2014-08-01

    The behavior under pressure of the high spin-low spin phase transition in the coordination compounds containing 3d ions is analyzed using thermodynamic and microscopic approaches. For thermodynamic approach the mean field model with interactions between spin-crossover molecules is considered. Microscopic model takes into account the interaction of d electrons of the transition metal ions with full symmetric distortions of the ligands. The relationship of the thermodynamic interaction parameters with microscopic ones is installed and shown how the quantum-mechanical interactions form the cooperativity of the system. Within the microscopic model the temperature and pressure dependences of the high spin fraction in 2-D compounds {Fe(3-Fpy)2[M(CN)4]} (M=Pd, Pt) are simulated and microscopic parameters are evaluated. It is concluded that different experimental behaviors of the temperature and pressure induced spin transitions are determined by different variations of the inelastic and elastic energies under pressure, and vibrational component of the free energy drives the ST equally with electronic part.

  12. Transits

    NASA Astrophysics Data System (ADS)

    Gilliland, Ronald L.

    Transits of the planets Mercury and especially Venus have been exciting events in the development of astronomy over the past few hundred years. Just two years ago the first transiting extra-solar planet, HD 209458b, was discovered, and subsequent studies during transit have contributed fundamental new knowledge. From the photometric light curve during transit one obtains a basic confirmation that the radial velocity detected object is indeed a planet by allowing precise determination of its mass and radius relative to these stellar quantities. From study of spectroscopic changes during transit it has been possible to probe for individual components of the transiting planets atmosphere. Planet transits are likely to become a primary tool for detection of new planets, especially other Earth-like planets with the Kepler Discovery Mission. Looking ahead, the additional aperture of the James Webb Space Space Telescope promises to allow the first possibility of studying the atmosphere of extra-solar Earth-analogue planets, perhaps even providing the first evidence of direct relevance to the search for signs of life on other planets.

  13. Rapid Discrimination of Biogenic and Detrital Magnetite Through a Double Verwey Transition Temperature

    NASA Astrophysics Data System (ADS)

    Chang, L.; Heslop, D.; Roberts, A. P.; Rey, D.; Mohamed, K.

    2015-12-01

    Magnetite occurs widely in natural environments in both inorganic and biogenic forms. Discrimination of the origin of magnetite in natural environments 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 detailed rock magnetic and electron microscopic results from marine sediment samples from the continental margin of Oman. Low-temperature magnetic measurements reveal two distinct Verwey transition temperatures (Tv) 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 magnetic signature for discriminating inorganic and biogenic magnetite. Simple low-temperature magnetic measurement (i.e., low-temperature warming of a saturation remanence after field cooling) provides a tool to recognize rapidly the origin of magnetite particles within natural samples. In addition, our analyses reveal progressive down-core dissolution of detrital and biogenic magnetite. We also observe preservation of significant amounts of fine-grained magnetite within sediments that have been subjected to severe diagenetic alteration, despite the expectation that small magnetite grains are prone to dissolution in anoxic marine environments. Preservation of magnetite in such environments is most likely due to protection of fine-grained magnetite inclusions by coarse-grained silicate host minerals.

  14. 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.

  15. 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.

  16. 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.

  17. Rheological, optical, and thermal characterization of temperature-induced transitions in liquid crystal ferrosuspensions

    NASA Astrophysics Data System (ADS)

    Diestra-Cruz, Heberth; Rinaldi, Carlos; Acevedo, Aldo

    2012-04-01

    Liquid crystal ferrosuspensions (LCFs) were obtained by inclusion of magnetic microparticles in a nematic liquid crystal (NLC) at mass fractions of up to 20%. The phase transition of the NLC promotes the formation of a space filling particle network and an enhancement of the mechanical properties. Polarized optical microscopy (POM) and differential scanning calorimetry were used to study microparticle network formation. POM images show that an anisotropic particle structure formed when an external magnetic field was applied, whereas a quasihomogeneous cellular network is obtained in the absence of the field. A jump in the viscoelastic moduli at the isotropic-nematic transition temperature of the NLC was observed for all particle concentrations and applied magnetic fields. Experimental results also showed that the rheological response of the LCFs increased with magnetic field and tend to saturate at high fields. A linear relation between the particle mass fraction and the saturation value of the storage modulus was found.

  18. 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

  19. Photoemission Study of VO2 Above and Below the Transition Temperature

    NASA Astrophysics Data System (ADS)

    Moreschini, Luca; Chang, Young Jun; Innocenti, Davide; Walter, Andrew L.; Denlinger, Jonathan; Bostwick, Aaron; Rotenberg, Eli

    2012-02-01

    Angle-resolved photoemission (ARPES) experiments on VO2 have traditionally been hindered by the quality of cleaved single crystals. The lack of a clear metal-insulator transition (MIT) in low photon energy measurements has even lead to the assumption of a surface region with a different electronic structure. WIth the in situ pulsed-laser-deposition (PLD) system available on beamline 7.0.1 at the Advanced Light Source we have grown VO2(001) films on a TiO2 substrate and measured the band structure above and below the transition temperature. We discuss our results in comparison with the available calculations, and we show that the MIT is clearly visible for photon energies within the UV range.

  20. 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.

  1. Lifshitz transitions and zero point lattice fluctuations in sulfur hydride showing near room temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Jarlborg, Thomas

    2015-11-01

    Emerets's experiments on pressurized sulfur hydride have shown that H3S metal has the highest known superconducting critical temperature Tc = 203 K. The Emerets data show pressure induced changes of the isotope coefficient between 0.25 and 0.5, in disagreement with Eliashberg theory which predicts a nearly constant isotope coefficient.We assign the pressure dependent isotope coefficient to Lifshitz transitions induced by pressure and zero point lattice fluctuations. It is known that pressure could induce changes of the topology of the Fermi surface, called Lifshitz transitions, but were neglected in previous papers on the H3S superconductivity issue. Here we propose thatH3S is a multi-gap superconductor with a first condensate in the BCS regime (located in the large Fermi surface with high Fermi energy) which coexists with second condensates in the BCS-BEC crossover regime (located on the Fermi surface spots with small Fermi energy) near the and Mpoints.We discuss the Bianconi-Perali-Valletta (BPV) superconductivity theory to understand superconductivity in H3S since the BPV theory includes the corrections of the chemical potential due to pairing and the configuration interaction between different condensates, neglected by the Eliashberg theory. These two terms in the BPV theory give the shape resonance in superconducting gaps, similar to Feshbach resonance in ultracold fermionic gases, which is known to amplify the critical temperature. Therefore this work provides some key tools useful in the search for new room temperature superconductors.

  2. 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

  3. Transitions in Convection of a Low Prandtl Number Fluid Driven by a Horizontal Temperature Gradient

    NASA Astrophysics Data System (ADS)

    Hung, Ming-Cheng

    The transitions in convection of a low Prandtl number fluid (mercury) contained in enclosed rectangular cavities driven by horizontal temperature gradients were investigated. These cavities have insulating top, bottom and side boundaries. The other two end walls are highly conducting. The temperatures on the conducting walls were varied to control the temperature gradient inside. Both the temperature and the velocity of the fluid inside the cavity were measured. A traversing system allowed the probe position to be changed with the cavity always sealed. The temperature gradient, controlled by a computer, was ramped very slowly. At every 0.2 or 0.12 degree the ramping was held and a data file of several hours was taken. The Prandtl number of the fluid was varied from 0.025 to 0.035 by changing the average temperature. The cavity size effect on the transitions was investigated. The primary (large) cavity had aspect ratio (length:height:width) of 17.8:1:17.8 (height = 0.9 cm). The other cavities for size effect investigation were shorter and narrower. Fourier transform was used to analyze the time series. Phase portraits were constructed in 3d using time delay method and correlation dimensions were computed for some trajectories. For the large cavity, the observed onset of the longitudinal oscillatory state at Grashof number Gr = 18490 was far above the predicted value of 10610 for an infinite long cavity (height/length = 0). At low Grashof numbers, the flow was time independent. As Gr was increased, it changed to a noisy state with a periodic component and then became purely chaotic. Finally the longitudinal oscillatory state appeared with two frequencies and noise. The longitudinal oscillatory state was observed to be a standing wave with a wavelength of about 3 cm. The critical Gr was affected by the cavity width and length. The narrower the cavity, the more stable the flow. The critical Gr for oscillation decreased as the length was increased. An unusual

  4. Determination of L(alpha)-H(II) phase transition temperature for 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine.

    PubMed

    Toombes, Gilman E S; Finnefrock, Adam C; Tate, Mark W; Gruner, Sol M

    2002-05-01

    The thermodynamic properties of fully-hydrated lipids provide important information about the stability of membranes and the energetic interactions of lipid bilayers with membrane proteins (Nagle and Scott, Physics Today, 2:39, 1978). The lamellar/inverse hexagonal (L(alpha)-H(II)) phase transition of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) water mixtures is a first-order transition and, therefore, at constant pressure, must have a thermodynamically well-defined equilibrium transition temperature. The observed transition temperature is known to be dependent upon the rate at which the temperature is changed, which accounts for the many different values in the literature. X-ray diffraction was used to study the phase transition of fully-hydrated DOPE to determine the rate-independent transition temperature, T(LH). Samples were heated or cooled for a range of rates, 0.212 < r < 225 degrees C/hr, and the rate-dependent apparent phase transition temperatures, T(A)(r) were determined from the x-ray data. By use of a model-free extrapolation method, the transition temperature was found to be T(LH) = 3.33 +/- 0.16 degrees C. The hysteresis, /T(A)(r) - T(LH)/, was identical for heating and cooling rates, +/-r, and varied as /r/beta for beta approximately 1/4. This unexpected power-law relationship is consistent with a previous study (Tate et al., Biochemistry, 31:1081-1092, 1992) but differs markedly from the exponential behavior of activation barrier kinetics. The methods used in this study are general and provide a simple way to determine the true mesomorphic phase transition temperatures of other lipid and lyotropic systems.

  5. Determination of L(alpha)-H(II) phase transition temperature for 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine.

    PubMed Central

    Toombes, Gilman E S; Finnefrock, Adam C; Tate, Mark W; Gruner, Sol M

    2002-01-01

    The thermodynamic properties of fully-hydrated lipids provide important information about the stability of membranes and the energetic interactions of lipid bilayers with membrane proteins (Nagle and Scott, Physics Today, 2:39, 1978). The lamellar/inverse hexagonal (L(alpha)-H(II)) phase transition of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) water mixtures is a first-order transition and, therefore, at constant pressure, must have a thermodynamically well-defined equilibrium transition temperature. The observed transition temperature is known to be dependent upon the rate at which the temperature is changed, which accounts for the many different values in the literature. X-ray diffraction was used to study the phase transition of fully-hydrated DOPE to determine the rate-independent transition temperature, T(LH). Samples were heated or cooled for a range of rates, 0.212 < r < 225 degrees C/hr, and the rate-dependent apparent phase transition temperatures, T(A)(r) were determined from the x-ray data. By use of a model-free extrapolation method, the transition temperature was found to be T(LH) = 3.33 +/- 0.16 degrees C. The hysteresis, /T(A)(r) - T(LH)/, was identical for heating and cooling rates, +/-r, and varied as /r/beta for beta approximately 1/4. This unexpected power-law relationship is consistent with a previous study (Tate et al., Biochemistry, 31:1081-1092, 1992) but differs markedly from the exponential behavior of activation barrier kinetics. The methods used in this study are general and provide a simple way to determine the true mesomorphic phase transition temperatures of other lipid and lyotropic systems. PMID:11964238

  6. 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.

  7. A molecular dynamics simulation of the melting points and glass transition temperatures of myo- and neo-inositol.

    PubMed

    Watt, Stephen W; Chisholm, James A; Jones, William; Motherwell, Sam

    2004-11-15

    The heat of sublimation, density, melting point, and glass transition temperature are calculated for myo- and neo-inositol, using the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field and molecular dynamics techniques. Our results show that the calculated heats of sublimation and density are very close to the experimental values for both compounds. Furthermore, our simulated melting temperatures for myo- and neo-inositol also compare very well to the experimentally obtained data. The glass transition temperatures for myo- and neo-inositol have been calculated to be ca. 494 K and ca. 518 K, respectively, and the shape of the volume versus temperature plots produced are typical for a glass transition. As a result, it is our view that the COMPASS force field suitably describes these two compounds in molecular simulations and that molecular dynamics techniques, combined with this force field, can be used to simulate the melt and glass transitions for such molecules.

  8. General approach for studying first-order phase transitions at low temperatures.

    PubMed

    Fiore, C E; da Luz, M G E

    2011-12-01

    By combining different ideas, a general and efficient protocol to deal with discontinuous phase transitions at low temperatures is proposed. For small T's, it is possible to derive a generic analytic expression for appropriate order parameters, whose coefficients are obtained from simple simulations. Once in such regimes simulations by standard algorithms are not reliable; an enhanced tempering method, the parallel tempering-accurate for small and intermediate system sizes with rather low computational cost-is used. Finally, from finite size analysis, one can obtain the thermodynamic limit. The procedure is illustrated for four distinct models, demonstrating its power, e.g., to locate coexistence lines and the phase density at the coexistence.

  9. 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.

  10. 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.

  11. Comparative High Field Magneto-transport Of Rare Earth Oxypnictides With Maximum Transition Temperatures

    SciTech Connect

    Balakirev, Fedor F; Migliori, A; Riggs, S; Hunte, F; Gurevich, A; Larbalestier, D; Boebinger, G; Jaroszynski, J; Ren, Z; Lu, W; Yang, J; Shen, X; Dong, X; Zhao, Z; Jin, R; Sefat, A; Mcguire, M; Sales, B; Christen, D; Mandrus, D

    2008-01-01

    We compare magnetotransport of the three iron-arsenide-based compounds ReFeAsO (Re=La, Sm, Nd) in very high DC and pulsed magnetic fields up to 45 and 54 T, respectively. Each sample studied exhibits a superconducting transition temperature near the maximum reported to date for that particular compound. While high magnetic fields do not suppress the superconducting state appreciably, the resistivity, Hall coefficient, and critical magnetic fields, taken together, suggest that the phenomenology and superconducting parameters of the oxypnictide superconductors bridges the gap between MgB{sub 2} and YBCO.

  12. 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.

  13. 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.

  14. Temperature-driven volume transition in hydrogels: Phase-coexistence and interface localization

    NASA Astrophysics Data System (ADS)

    Cirillo, E. N. M.; Nardinocchi, P.; Sciarra, G.

    2016-05-01

    We study volume transition phenomenon in hydrogels within the framework of Flory-Rehner thermodynamic modelling; we show that starting from different models for the Flory parameter different conclusions can be achieved, in terms of admissible coexisting equilibria of the system. In particular, with explicit reference to a one-dimensional problem we establish the ranges of both temperature and traction which allow for the coexistence of a swollen and a shrunk phase. Through consideration of an augmented Flory-Rehner free-energy, which also accounts for the gradient of volume changes, we determine the position of the interface between the coexisting phases, and capture the connection profile between them.

  15. 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.

  16. High transition temperature superconductor/insulator bilayers for the development of ultra-fast electronics

    NASA Astrophysics Data System (ADS)

    Sirena, M.; Félix, L. Avilés; Haberkorn, N.

    2013-07-01

    High transition temperature superconductor (HTc)/SrTiO3 (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 × 10-5 defects/μm2). 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.

  17. 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

  18. 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,

  19. 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.

  20. 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

  1. 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.

  2. Inverse isotope effect and the x dependence of the superconducting transition temperature in PdHx and PdDx

    NASA Technical Reports Server (NTRS)

    Klein, B. M.; Economou, E. N.; Papaconstantopoulos, D. A.

    1977-01-01

    First-principles electron-band-structure calculations and measured phonon properties are employed in a calculation of the concentration dependence of the superconducting transition temperatures for PdHx and PdDx, including the inverse isotope effect. Excellent agreement with the experimental results is obtained. Our model also gives a qualitative understanding of the enhanced transition temperatures in the palladium-noble-metal hydrides.

  3. Dynamical transition, hydrophobic interface, and the temperature dependence of electrostatic fluctuations in proteins

    NASA Astrophysics Data System (ADS)

    Lebard, David N.; Matyushov, Dmitry V.

    2008-12-01

    Molecular dynamics simulations have revealed a dramatic increase, with increasing temperature, of the amplitude of electrostatic fluctuations caused by water at the active site of metalloprotein plastocyanin. The increased breadth of electrostatic fluctuations, expressed in terms of the reorganization energy of changing the redox state of the protein, is related to the formation of the hydrophobic protein-water interface, allowing large-amplitude collective fluctuations of the water density in the protein’s first solvation shell. On top of the monotonic increase of the reorganization energy with increasing temperature, we have observed a spike at ≃220K also accompanied by a significant slowing of the exponential collective Stokes shift dynamics. In contrast to the local density fluctuations of the hydration-shell waters, these spikes might be related to the global property of the water solvent crossing the Widom line or undergoing a weak first-order transition.

  4. 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

  5. Jamming and unjamming transition of oil-in-water emulsions under continuous temperature change.

    PubMed

    Choi, Se Bin; Lee, Joon Sang

    2015-05-01

    To analyze the jamming and unjamming transition of oil-in-water emulsions under continuous temperature change, we simulated an emulsion system whose critical volume fraction was 0.3, which was validated with experimental results under oscillatory shear stress. In addition, we calculated the elastic modulus using the phase lag between strain and stress. Through heating and cooling, the emulsion experienced unjamming and jamming. A phenomenon-which is when the elastic modulus does not reach the expected value at the isothermal system-occurred when the emulsion system was cooled. We determined that this phenomenon was caused by the frequency being faster than the relaxation of the deformed droplets. We justified the relation between the frequency and relaxation by simulating the frequency dependency of the difference between the elastic modulus when cooled and the expected value at the same temperature. PMID:26064194

  6. Transport properties of a Tl-2201 film close to the critical temperature: The vortex glass transition

    SciTech Connect

    Chen, H.Q.; Johansson, L.G.; Ivanov, Z.G.

    1999-12-01

    The authors have studied the I-V characteristics of a Tl-2201 film at zero field. In the regime in which flux creep is the dominant dissipation mechanism, the J{sub c}-T curve is divided into two parts at a temperature T{sub g} (about 82 K), close to the critical temperature (84 K). The I-V characteristics around T{sub g} are well described using a flux creep model. Differential resistance (dV/dI) as a function of the measuring current shows a change in curvature close to T{sub g}. The I-V curves collapsed nicely into two branches by plotting (V/I)/{vert{underscore}bar}T-T{sub g}{vert{underscore}bar}{sup V(z{minus}1)} vs. (I/T)/{vert{underscore}bar}T{sub g}-T{vert{underscore}bar}{sup 2v}, indicating a current-reduced vortex glass transition.

  7. 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.

  8. 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.

  9. Superconducting fluctuation effects on the thermoelectric coefficient above the transition temperature

    NASA Astrophysics Data System (ADS)

    Reizer, M. Yu.; Sergeev, A. V.

    1994-10-01

    The quantum kinetic-equation method is applied to calculate the response of a metal to a temperature gradient above the superconducting transition temperature Tc. It is shown that the fluctuation correction to the thermoelectric coefficient of a three-dimensional superconductor is nonsingular near Tc. The fluctuation correction is more important in low-dimensional systems: it diverges as ln(T-Tc) in a thin film and as (T-Tc)1/2 in a filament. Applying the linear-response method, we confirm these results and prove microscopically the Onsager relation for this problem. We also demonstrate how more singular terms obtained in earlier papers are canceled out by other terms representing the corrections to the heat current operator. The universal relation, independent on the electron mean free path, between the electric and heat current operators for the fluctuating order parameter is obtained.

  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. Temperature-induced structural phase transitions in a two-dimensional self-assembled network.

    PubMed

    Blunt, Matthew O; Adisoejoso, Jinne; Tahara, Kazukuni; Katayama, Keisuke; Van der Auweraer, Mark; Tobe, Yoshito; De Feyter, Steven

    2013-08-14

    Two-dimensional (2D) supramolecular self-assembly at liquid-solid interfaces is a thermodynamically complex process producing a variety of structures. The formation of multiple network morphologies from the same molecular building blocks is a common occurrence. We use scanning tunnelling microscopy (STM) to investigate a structural phase transition between a densely packed and a porous phase of an alkylated dehydrobenzo[12]annulene (DBA) derivative physisorbed at a solvent-graphite interface. The influence of temperature and concentration are studied and the results combined using a thermodynamic model to measure enthalpy and entropy changes associated with the transition. These experimental results are compared to corresponding values obtained from simulations and theoretical calculations. This comparison highlights the importance of considering the solvent when modeling porous self-assembled networks. The results also demonstrate the power of using structural phase transitions to study the thermodynamics of these systems and will have implications for the development of predictive models for 2D self-assembly.

  12. 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.

  13. 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.

  14. 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

  15. Low transition temperature mixtures as innovative and sustainable CO2 capture solvents.

    PubMed

    Zubeir, Lawien F; Lacroix, Mark H M; Kroon, Maaike C

    2014-12-11

    The potential of three newly discovered low transition temperature mixtures (LTTMs) is explored as sustainable substituents for the traditional carbon dioxide (CO2) absorbents. LTTMs are mixtures of two solid compounds, a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), which form liquids upon mixing with melting points far below those of the individual compounds. In this work the HBD is lactic acid and the HBAs are tetramethylammonium chloride, tetraethylammonium chloride, and tetrabutylammonium chloride. These compounds were found to form LTTMs for the first time at molar ratios of HBD:HBA = 2:1. First, the LTTMs were characterized by determining the thermal operating window (e.g., decomposition temperature and glass transition temperature) and the physical properties (e.g., density and viscosity). Thereafter, the phase behavior of CO2 with the LTTMs has been measured using a gravimetric magnetic suspension balance operating in the static mode at 308 and 318 K and pressures up to 2 MPa. The CO2 solubility increased with increasing chain length, increasing pressure, and decreasing temperature. The Peng-Robinson equation of state was applied to correlate the phase equilibria. From the solubility data, thermodynamic parameters were determined (e.g., Henry's law coefficient and enthalpy of absorption). The heat of absorption was found to be similar to that in conventional physical solvents (-11.21 to -14.87 kJ·mol(-1)). Furthermore, the kinetics in terms of the diffusion coefficient of CO2 in all LTTMs were determined (10(-11)-10(-10) m(2)·s(-1)). Even though the CO2 solubilities in the studied LTTMs were found to be slightly lower than those in thoroughly studied conventional physical solvents, LTTMs are a promising new class of absorbents due to their low cost, their environmentally friendly character, and their easy tunability, allowing further optimization for carbon capture.

  16. Irreversibility temperatures in superconducting oxides: The flux-line-lattice melting, the glass-liquid transition, or the depinning temperatures

    SciTech Connect

    Xu, Y.; Suenaga, M. )

    1991-03-01

    The magnetic-field dependence of the irreversibility temperatures follows an {ital H}={ital a}(1{minus}{ital T}{sub {ital r}}({ital H})/{ital T}{sub {ital c}}(0)){sup {ital n}} relationship with {ital n}{congruent}1.5, for pure and alloyed YBa{sub 2}(Cu{sub 1{minus}{ital x}}M{sub {ital x}}){sub 3}O{sub 7+{delta}} with {ital x}=0 and 0.02, where {ital M}=Al, Fe, Ni, and Zn, measured for an applied field parallel to the {ital c} axis. However, for {ital M}=Ni and {ital x}=0.04 and 0.06, {ital n}{congruent}2.0. This relationship is not applicable for either Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} or (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} powders. It is also shown that the irreversibility temperature is a strong function of the magnetic hysteresis width {Delta}{ital M} for pure and alloyed YBa{sub 2}Cu{sub 3}O{sub 7}. These results and the measurements of the flux creep {Delta}{ital M}({ital t}) for these specimens suggest that {ital T}{sub {ital r}}({ital H}) is a depinning line rather than a lattice melting or glass-to-liquid phase-transition temperature. However, the conventional flux-creep model cannot account for all of the observed temporal dependences of {Delta}{ital M}({ital t}).

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. a Study of High Transition Temperature Superconductors: Mercury-Copper Oxide Systems

    NASA Astrophysics Data System (ADS)

    Kirven, Paul Douglas

    1995-01-01

    The Hg-based copper-oxides viz., HgBa _2Ca_{n-1}Cu_ nO _{2n+2+delta}, were discovered in 1993. A system consisting of many different, but related, compounds can be synthesized by including or substituting one or more elements in the original compound (e.g. Hg _{1-x}Pb_ x). In this thesis, the superconducting and normal state properties of several of these compounds were investigated. In the normal state electrical resistivity rho(T) is a linear function of temperature (T) and the magnetic susceptibility, X(T), is weakly paramagnetic. Many were observed to superconduct at very high temperatures. At 5 K up to 80% perfect diamagnetic X(T) was measured. The onset transition temperature (T_ c), where a specimen starts to superconduct, is observed to be as high as 135 K. Although T_ c is about 10 K higher than that of any previously known material, in many respects the properties of this new system are similar to that of other type II superconductors. Flux flow behavior and the nature of these type II superconductors was investigated via SQUID measurements and high field longitudinal magneto-resistance R(T,H) as a function of field and temperature. The study of flux motion allows one to observe Anderson-Kim type logarithimic flux creep at low temperature and field (T < 80K and B < 2T) and giant -flux flow at high temperature and field (80 < T < 130; B < 17T). Key parameters were determined. Some of which include reversibility temperature T*(H), critical field Hc, and pinning potential, Uo. Normal state properties which were also measured include the following: Curie constant, Curie-Weiss temperature (15-25 K), temperature independent susceptibility, and Sommerfeld constant (10-25 mJ/mol.Cu K^2). The values of these parameters of the Hg-based superconductors were compared to those of other superconductors. The results of this investigation are expected to yield a better understanding of this newest family of high temperature superconductors.

  4. 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

  5. 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.

  6. 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.

  7. Nucleation and temperature-driven phase transitions of silicene superstructures on Ag(1 1 1).

    PubMed

    Grazianetti, C; Chiappe, D; Cinquanta, E; Fanciulli, M; Molle, A

    2015-07-01

    Silicene grown on Ag(1 1 1) is characterized by several critical parameters. Among them, the substrate temperature plays a key role in determining the morphology during growth. However, an unexpected important role is also equally played by the post-deposition annealing temperature which determines the self-organization of silicene domains even in the submonolayer coverage regime and consecutive transitions between silicene with different periodicity. These temperature-driven phase transitions can be exploited to select the desired majority silicene phase, thus allowing for the manipulation of silicene properties.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. High antiferromagnetic transition temperature of a honeycomb compound SrRu2O6

    DOE PAGES

    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

  15. 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.

  16. 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

  17. 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}

  18. 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.

  19. 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.

  20. Measurement of the ductile to brittle transition temperature for waste tank cooling coils

    SciTech Connect

    Wiersma, B.J.

    1992-09-01

    Charpy impact tests were conducted on ASTM A106 carbon steel archived from SRS waste tanks to determine the susceptibility of the cooling coils to brittle fracture during a seismic event. The highest ductile to brittle transition temperature measured was [minus]5[degree]F and, with the addition of a 30[degree]F safety factor, the minimum safe operating temperature was determined to be 25[degree]F. Calculations also showed that a pre-existing circumferential flaw that is 2.2in. long would be necessary to initiate brittle fracture of the pipe. These results demonstrate that the pipes will not be susceptible to brittle fracture if the cooling water inlet temperature is lowered to 50[degree]F. Visual observation of the inner and outer walls of the pipe showed no localized attack or significant wall thinning. A 100--200 micron zinc coating is probably the reason for the lack of corrosion. A build-up of zinc slag occurred at pipe fittings where the weld had burned through. Although no attack was observed, the slag created several crevices which have the potential to trap the chromated water and initiate localized attack.

  1. Measurement of the ductile to brittle transition temperature for waste tank cooling coils

    SciTech Connect

    Wiersma, B.J.

    1992-09-01

    Charpy impact tests were conducted on ASTM A106 carbon steel archived from SRS waste tanks to determine the susceptibility of the cooling coils to brittle fracture during a seismic event. The highest ductile to brittle transition temperature measured was {minus}5{degree}F and, with the addition of a 30{degree}F safety factor, the minimum safe operating temperature was determined to be 25{degree}F. Calculations also showed that a pre-existing circumferential flaw that is 2.2in. long would be necessary to initiate brittle fracture of the pipe. These results demonstrate that the pipes will not be susceptible to brittle fracture if the cooling water inlet temperature is lowered to 50{degree}F. Visual observation of the inner and outer walls of the pipe showed no localized attack or significant wall thinning. A 100--200 micron zinc coating is probably the reason for the lack of corrosion. A build-up of zinc slag occurred at pipe fittings where the weld had burned through. Although no attack was observed, the slag created several crevices which have the potential to trap the chromated water and initiate localized attack.

  2. Lattice parameter, lattice disorder and resistivity of carbohydrate doped MgB2 and their correlation with the transition temperature.

    PubMed

    Kim, J H; Oh, Sangjun; Xu, X; Joo, Jinho; Rindfleisch, M; Tomsic, M; Dou, S X

    2009-12-01

    The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the transition temperature by carbon doping in MgB2. In this work, an extensive investigation on the effects of carbohydrate doping has been carried out. It is found that not only the a-axis but also the c-axis lattice parameter increases with the sintering temperature. A linear relation between the unit cell volume and the critical temperature is observed. Compared with the well known correlation between the lattice strain and the critical temperature, the X-ray peak broadening itself shows a closer correlation with the transition temperature. The residual resistivity and the critical temperature are linearly correlated with each other as well and its implication is further discussed.

  3. Calculation of the superconducting transition temperature of a graphene layer doped with titanium and palladium

    NASA Astrophysics Data System (ADS)

    Vazquez, Gerardo; Magana, Fernando; Salas-Torres, Osiris

    We explore the structural interactions between graphene and transition metals such as palladium (Pd) and titanium (Ti) and the possibility of inducing superconductivity in a graphene sheet in two cases, one by doping its surface with palladium atoms sit on the center of the hexagons of the graphene layer and other by covering the graphene layer with two layers of titanium metal atoms. The results here were obtained from first-principles density functional theory in the local density approximation. The Quantum-Espresso package was used with norm conserving pseudopotentials. All of the structures considered were relaxed to their minimum energy configuration. Phonon frequencies were calculated using the linear-response technique on several phonon wave-vector mesh. The electron-phonon coupling parameter was calculated with several electron momentum k-mesh. The superconducting critical temperature was estimated using the Allen-Dynes formula with μ* = 0.1 - 0.15. We note that palladium and titanium are good candidate materials to show a metal-to-superconductor transition. We thank Dirección General de Asuntos del Personal Académico de la Universidad Nacional Autónoma de México, partial financial support by Grant IN-106514 and we also thank Miztli Super-Computing center the technical assistance.

  4. 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.

  5. 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

  6. 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.

  7. Relation Between Glass Transition Temperatures in Polymer Nanocomposites and Polymer Thin Films

    NASA Astrophysics Data System (ADS)

    Kropka, Jamie; Pryamitsyn, Victor; Ganesan, Venkat

    2009-03-01

    Motivated by recent experiments, we examine within a percolation model whether there is a quantitative equivalence in the glass transition temperatures of polymer thin films and polymer nanocomposites (PNCs). Our results indicate that while the qualitative behaviors of these systems are similar, a quantitative equivalence cannot be established in general. However, we propose a phenomenological scaling collapse of our results which suggests a simple framework by which the results of the thin films may be used to quantitatively predict the properties of PNCs. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  8. 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.

  9. 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.

  10. Universal critical behavior and the transition temperature in (2+1)-flavor QCD

    SciTech Connect

    Schmidt, Christian

    2011-05-23

    We discuss the universal critical behavior in (2+1)-flavor QCD by analyzing lattice data from improved staggered fermions generated by the HotQCD Collaboration. We present recent results from two different lattice discretizations and various lattice spacings (N{sub {tau}} = 6,8,12) at fixed physical strange quark mass (m{sub s}) but varying light quark mass (m{sub l}). We find that the chiral order-parameter, i.e. the chiral condensate, shows the expected universal scaling that is associated with the critical point in the chiral limit already for light quark masses m{sub l}/m{sub s} < or approx. 0.05. From an analysis of the disconnected chiral susceptibility we estimate a preliminary value of the QCD transition temperature.

  11. 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.

  12. 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.

  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. High-temperature structural phase transition in the LiCu{sub 2}O{sub 2} multiferroic

    SciTech Connect

    Kamentsev, K. E.; Bush, A. A.; Tishchenko, E. A.; Ivanov, S. A.; Ottoson, M.; Mathieu, R.; Nordblad, P.

    2013-08-15

    The results of thermogravimetric, X-ray diffraction, and electrical studies of LiCu{sub 2}O{sub 2} single crystals in the temperature range 300-1100 K are presented. A reversible first-order phase transition between the orthorhombic and tetragonal phases is found to occur in these single crystals at T = 993 K. A pronounced peak on a differential thermal analysis curve and jumps in the unit cell parameters and the electrical resistivity are detected at the phase-transition temperature. The data on the crystal structure of LiCu{sub 2}O{sub 2} and the phase transition-induced change in the entropy determined in this work are used to conclude that the revealed phase transition is caused by the ordering-disordering of Li{sup +} and Cu{sup 2+} cations in their structural positions.

  15. Phase transitions as a function of material constants and temperature in intermetallic compounds of the terfenol-D type

    NASA Astrophysics Data System (ADS)

    Fridman, Yu. A.; Klevets, F. N.; Voĭtenko, A. P.

    2010-07-01

    A model of magnetic and magnetoelastic properties of intermetallic compounds has been considered with the inclusion of the influence of the “giant” magnetoelastic coupling and the biquadratic exchange interaction. The phase transitions as a function of material constants and temperature have been investigated in the framework of the proposed model. It has been demonstrated that the ferromagnetic and quadrupole phases can be formed in the system under consideration. In this case, the phase transition between these phases is a first-order transition and occurs through the intermediate, i.e., quadrupole-ferromagnetic, state. The dependences of the phase transition temperature on the Heisenberg and biquadratic exchange interaction constants have been obtained for compounds of the terfenol-D type.

  16. Glass transition temperature of honey as a function of water content as determined by differential scanning calorimetry.

    PubMed

    Kántor, Z; Pitsi, G; Thoen, J

    1999-06-01

    The glass transition of pure and diluted honey and the glass transition of the maximally freeze-concentrated solution of honey were investigated by differential scanning calorimetry (DSC). The glass transition temperature, of the pure honey samples accepted as unadulterated varied between -42 and -51 degrees C. Dilution of honey to 90 wt % honey content resulted in a shift of the glass transition temperature by -13 to -20 degrees C. The concentration of the maximally freeze-concentrated honey solutions, as expressed in terms of honey content is approximately 102-103%, i.e., slightly more concentrated in sugars than honey itself. The application of DSC measurements of and in characterization of honey may be considered, but requires systematic study on a number of honeys. PMID:10794630

  17. Towards the N{sub f} = 2 deconfinement transition temperature with O(a) improved Wilson fermions: An update

    SciTech Connect

    Brandt, Bastian B.; Wittig, Hartmut; Philipsen, Owe; Zeidlewicz, Lars

    2011-05-23

    We give an update on our current project to determine the transition temperature and the order of the deconfinement transition in the chiral limit of two flavour QCD. We use nonperturbatively O(a) improved Wilson fermions of the Sheikholeslami-Wohlert type, employing the efficient deflation accelerated DDHMC algorithm. We start at lattices with N{sub t{>=}}12 and pion masses below 600 MeV, aiming at chiral and continuum limits with light quarks.

  18. Proposed temperature-dependent conformational transition in D-amino acid oxidase: a differential scanning microcalorimetric study.

    PubMed Central

    Sturtevant, J M; Mateo, P L

    1978-01-01

    A number of authors have reported observations on D-amino acid oxidase [D-amino acid: O2 oxidoreductase (deaminating), EC 1.4.3.3.] that they have interpreted in terms of a temperature-dependent conformational transition having a van't Hoff enthalpy amounting to more than 1 cal per g of protein (1 cal = 4.184J). No indication of this transition is obtained by using a differential scanning calorimeter having a sensitivity considerably in excess of that required to detect such a transition. The implications of this discrepancy are discussed. PMID:26913

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Influence of the torsional potential on the glass transition temperature and the structure of amorphous polyethylene.

    PubMed

    Canales, Manel

    2009-05-01

    The effect of the torsional potential on several thermodynamic and structural properties of a system of polyethylene chains has been analyzed. To this end, molecular dynamics simulations of a coarse-grained model, whose sites interact through a force field with bending, torsional, and nonbonded terms, have been considered. The torsional potential has three stable configurations: gauche-, trans, and gauche+ . It has been modeled using a simple functional form with only two parameters: the trans-gauche and the gauche-gauche energy barriers. In order to analyze the influence of these parameters on the properties considered in this work, five models with different values of the torsional barriers have been considered. We have observed that the glass transition temperature, the intrachain radial distribution function, the radius of gyration, and the end to end distribution functions are very sensitive to the changes in the trans-gauche torsional barrier. Moreover, at low temperatures, the interchain radial distribution function, the orientational correlation function, and the volume distribution functions of the Voronoi polyhedra, that surround every site of the polymeric chains, also depend on the trans-gauche torsional barrier. On the contrary, the gauche-gauche energy barrier has a minor influence in the properties considered in this work.

  5. 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.

  6. Polarization induced water molecule dissociation below the first-order electronic-phase transition temperature.

    PubMed

    Das Arulsamy, Andrew; Kregar, Zlatko; Eleršič, Kristina; Modic, Martina; Subramani, Uma Shankar

    2011-09-01

    Hydrogen produced from the photocatalytic splitting of water is one of the reliable alternatives to replace the polluting fossil and the radioactive nuclear fuels. Here, we provide unequivocal evidence for the existence of blue- and red-shifting O-H covalent bonds within a single water molecule adsorbed on the MgO surface as a result of asymmetric displacement polarizabilities. The adsorbed H-O-H on MgO gives rise to one weaker H-O bond, while the other O-H covalent bond from the same adsorbed water molecule compensates this effect with a stronger bond. The weaker bond (nearest to the surface), the interlayer tunneling electrons and the silver substrate are shown to be the causes for the smallest dissociative activation energy on the MgO monolayer. The origin that is responsible to initiate the splitting mechanism is proven to be due to the changes in the polarizability of an adsorbed water molecule, which are further supported by the temperature-dependent static dielectric constant measurements for water below the first-order electronic-phase transition temperature.

  7. 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.

  8. Autohesion of semi-crystalline PEEK near and under the glass transition temperature

    NASA Astrophysics Data System (ADS)

    Awaja, Firas; Zhang, Shengnan; McKenzie, David R.

    2013-10-01

    Autohesion of semi-crystalline polymers under the glass transition temperature (Tg) is fundamentally difficult due to severe restriction in molecular chain mobility. We demonstrate that enhanced autohesion of semi-crystalline polyetheretherketone (PEEK) at temperatures close or under Tg can be achieved through plasma immersion ion implantation (PIII) treatment. Autohesive bonding strength of PEEK increased linearly with PIII bias voltage up to tenfold compared to untreated controls at 160 °C (Tg +10 °C). At 130 °C (Tg -20 °C), PIII treatment increased bonding strength of PEEK by more than fivefold compared to the untreated control. PIII treated surface exhibited higher surface energy, polar component and oxygen content. A model based on the formation of covalent bonds on the plasma treated PEEK by radicals present at the interface was found to predict the bonding strength above and below Tg. The major mechanism responsible for improved autohesion of PEEK near and under Tg is believed to be free radicals based covalent bonding assisted by an increase of surface wettability and reduction in surface crystal structure as was evidenced by SEM images.

  9. Molecular Weight Dependent and Independent Glass Transition Temperature Reductions Coexisting in High MW Free-Standing Polystyrene Films

    NASA Astrophysics Data System (ADS)

    Pye, Justin; Roth, Connie

    2012-02-01

    Using transmission ellipsometry, we have measured the thermal expansion of ultrathin, high molecular weight (MW), free-standing polystyrene films over an extended temperature range. For two different MWs, we observed two distinct reduced glass transition temperatures (Tgs), separated by up to 60 K, within single films with thicknesses h less than 70 nm. The lower transition follows the previously seen MW dependent, linear Tg(h) behavior, while we also observe the presence of a much stronger upper transition that is MW independent and exhibits the same Tg(h) dependence as supported and low MW free-standing films. This represents the first experimental evidence indicating that two separate mechanisms can act simultaneously on thin free-standing polymer films to propagate enhanced mobility from the free surface into the material. The change in thermal expansion through the transitions indicate that ˜90% of the film (matrix) solidifies at the upper transition with only ˜10% of the material remaining mobile, freezing in at the lower transition. Surprisingly, when we compare our results to the existing literature, and especially the low MW free-standing film data, we conclude that the upper transition encompasses the free surface region and associated gradient in dynamics. This leaves open the question about where the small (˜10%) fraction of material that has ultrafast, MW dependent dynamics resides within the film.

  10. Entropy dependence of viscosity and the glass-transition temperature of melts in the system diopside-anorthite

    NASA Astrophysics Data System (ADS)

    Taniguchi, H.

    1992-01-01

    Viscosities of diopside-anorthite melts were measured over the wide range of temperature (near the glass-transition temperature-1580°C/1bar) and pressure (5 20 kb/above the liquidus temperature). The measurements were carried out by the fibre-elongation method for low temperature and the counter-balanced sphere method for high temperature at 1 bar, and the sinking and floating spheres method for high temperature at high pressure. Some of the values obtained deviated slightly from those in the literature. The data on viscosity and the glasstransition temperature have been interpreted on the basis of the configurational entropy theory, by which temperature and compositional effects on viscosity were explained well. The configurational entropies at the glasstransition temperature of magmatic silicate melts are almost constant if we use an average molecular weight (amw) or “bead” as a unit; 8.0±1.2 J/K·amw, 1.1 ±0.2cal/K·bead. The latter value coincides well with the value from the literature for organic polymers. The negative deviation from linearity of the glass-transition temperature of intermediate melts may be interpreted as the effect of the mixing entropy. The calculated glasstransition temperature-composition curve using the mixing entropy agreed well with the experimental values.

  11. 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

  12. 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

  13. 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.

  14. Electrothermal actuation of metal-insulator transition in SmNiO3 thin film devices above room temperature

    NASA Astrophysics Data System (ADS)

    Ha, Sieu D.; Viswanath, B.; Ramanathan, Shriram

    2012-06-01

    We demonstrate that a metal-insulator phase transition can be electrothermally actuated in the correlated complex oxide SmNiO3 (SNO) above room temperature from current-voltage measurements on thin film two-terminal devices. We simulate the internal temperature of SmNiO3 as a function of applied dc power by a Joule heating mechanism with substrate/electrode dissipation and find good agreement with experiment and device scaling. The results are relevant towards integrating correlated oxide phase transition functionality into semiconductor electronic/optoelectronic platforms.

  15. 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

  16. Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures.

    PubMed

    Lee, Il-Hyung; Saha, Suvrajit; Polley, Anirban; Huang, Hector; Mayor, Satyajit; Rao, Madan; Groves, Jay T

    2015-03-26

    Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14-37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane.

  17. 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.

  18. 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.

  19. Temperature-Induced and Photo-Induced Phase Transition in a BistableMetal-Cyanide Polymer

    NASA Astrophysics Data System (ADS)

    Tokoro, Hiroko; Ohkoshi, Shin-ichi

    Studies that are related to thermal-induced phase transition and photo-induced phase transition are important issues in the field of solid state science. Rubidium manganese hexacyanoferrate RbMn[Fe(CN)6], one of the Prussian blue analogs, is a suitable system for observing thermal-induced and photo-induced phase transitions since this compound is a mixed-valence compound that has a strong cooperativity due to the CN ligand bridges. Here, we describe the crystal structure, magnetic properties, thermal-induced phase transition, and photo-induced phase collapse and photomagnetic effect based on photo-induced phase transition of RbMn[Fe(CN)6].

  20. 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

  1. 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

  2. Glass transition dynamics and boiling temperatures of molecular liquids and their isomers.

    PubMed

    Wang, Li-Min; Richert, Ranko

    2007-03-29

    The relation between a dynamic and a thermodynamic temperature, glass transition Tg and boiling point Tb, is investigated for various glass-forming liquids, with emphasis on monohydroxy alcohols. As is well known, Tb and Tg are positively correlated across a large variety of liquids. However, we found that the same quantities show a negative correlation within an isomeric series, i.e., Tb decreases with increasing Tg for different isomers of the same chemical formula. For the alcohol series, CnH2n+1OH with 3 < or = n < or = 10, a master curve of the negative Tg - Tb correlation is obtained if the temperatures are normalized to the respective values of the n-alkanols. This Tg - Tb dependence of isomeric liquids is linked to entropic effects and responsible for much of the scatter of the correlation observed for a large number of molecular organic glass-formers with 45 < Tg < 250 K. Dielectric relaxation is measured for three groups of isomers: (a) 3-methoxyl-1-butanol and 2-iso-propoxyethanol, (b) 1,4-, 1,2-, and 2,4-pentanediol, and (c) di-n- and di-iso-butyl phthalate. Two key parameters of the dynamics, fragility m and stretching exponent beta, are found to be indistinguishable within isomers of moderately different Tgs. Larger fragility differences are readily expected with pronounced structural change, but no systematic trend is observed within an isomer series. The results provide a useful tool for assessing Tg, m, and beta for marginal glass formers on the basis of their isomers.

  3. Neutron Diffraction and Electrical Transport Studies on Magnetic Transition in Terbium at High Pressures and Low Temperatures

    NASA Astrophysics Data System (ADS)

    Thomas, Sarah; Montgomery, Jeffrey; Tsoi, Georgiy; Vohra, Yogesh; Weir, Samuel; Tulk, Christopher; Moreira Dos Santos, Antonio

    2013-06-01

    Neutron diffraction and electrical transport measurements have been carried out on the heavy rare earth metal terbium at high pressures and low temperatures in order to elucidate its transition from a helical antiferromagnetic to a ferromagnetic ordered phase as a function of pressure. The electrical resistance measurements using designer diamonds show a change in slope as the temperature is lowered through the ferromagnetic Curie temperature. The temperature of the ferromagnetic transition decreases at a rate of -16.7 K/GPa till 3.6 GPa, where terbium undergoes a structural transition from hexagonal close packed (hcp) to an α-Sm phase. Above this pressure, the electrical resistance measurements no longer exhibit a change in slope. In order to confirm the change in magnetic phase suggested by the electrical resistance measurements, neutron diffraction measurements were conducted at the SNAP beamline at the Oak Ridge National Laboratory. Measurements were made at pressures to 5.3 GPa and temperatures as low as 90 K. An abrupt increase in peak intensity in the neutron diffraction spectra signaled the onset of magnetic order below the Curie temperature. A magnetic phase diagram of rare earth metal terbium will be presented to 5.3 GPa and 90 K based on these studies.

  4. 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.

  5. Freeze-out temperature and density in heavy-ion collisions at liquid-gas phase transition

    SciTech Connect

    Shlomo, Shalom

    2010-08-04

    The study of properties of hot nuclei and the search for liquid-gas phase transition in nuclei have been the subjects of many investigations in recent decades. We present a short and limited review of the theoretical and experimental status of determining the temperature and density of the disassembling nucleus from ratios of the yields of emitted fragments.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. Oxygen Isotopes Reveal Attenuation in Latitudinal Ocean Temperature Gradient during the Permian Icehouse to Hothouse Transition

    NASA Astrophysics Data System (ADS)

    Shultis, A. I.; Frank, T. D.; Fielding, C. R.

    2011-12-01

    To assess changes in paleolatitudinal temperature gradient in the Permian ocean system during the demise of the Late Paleozoic Ice Age (LPIA), we analyzed the oxygen isotope composition of high latitude brachiopod and bivalve shells and compared them to published low latitude isotope records. We selected brachiopods and Eurydesma bivalves of Early to Middle Permian age that lie along a transect extending from temperate paleolatitudes in Queensland to polar paleolatitudes in Tasmania. Using cathodoluminescence (CL) microscopy and elemental analyses, diagenically altered samples were separated from well-preserved samples for isotopic analysis. Samples that were nonluminescent were prepared for elemental screening, and brachiopod and bivalve samples that passed both CL and trace element screening methods were analyzed for oxygen and carbon isotopes. The δ18O values reveal a long-term decrease in the paleolatitudinal temperature gradient from Early Permian (Sakmarian) and late Middle Permian (Capitanian), which parallels the trend in climate associated with the demise of LPIA. Transient decreases from glacial to non-glacial epochs are also evident. The δ18O values from well-preserved samples are as high as 0.1% during glacial epoch P2 (287-280 Ma: late Sakmarian to mid-Artinskian) and drop to -3.0% in the nonglacial interval between P2 and glacial epoch P3 (273-268 Ma: late Kungurian to latest Roadian). High-latitude δ18O values then rise to -1.5% during P3 and drop to -3.8% during the subsequent nonglacial interval. Low latitude δ18O values from the literature are as high as -2.3% during the P2 and drop to -2.9% in the nonglacial interval between P2 and the P3. δ18O values then rise to -1.6% during P3. Low latitude δ18O values drop to -4.4% between P3 and P4 and rise again to -2.4% during the P4 glacial epoch (267-260 Ma: late Wordian to late Capitanian). This comparison of high and low latitude δ18O suggests that meridional sea surface temperature gradients

  12. Concentration- and Temperature-Induced Phase Transitions in PrAlO3-SrTiO3 System

    NASA Astrophysics Data System (ADS)

    Vasylechko, Leonid; Stepchuk, Roman; Prots, Yuri; Rosner, Helge

    2016-01-01

    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 overline{3} c - Pm overline{3} 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 overline{3} c - Immb( C2/ m) - I4/ mcm was detected.

  13. 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.

  14. 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.

  15. From a Single-Band Metal to a High-Temperature Superconductor via Two Thermal Phase Transitions

    NASA Astrophysics Data System (ADS)

    He, Rui-Hua; Hashimoto, M.; Karapetyan, H.; Koralek, J. D.; Hinton, J. P.; Testaud, J. P.; Nathan, V.; Yoshida, Y.; Yao, Hong; 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.; Shen, Z.-X.

    2011-03-01

    The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem 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 observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (Tc), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.

  16. 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

  17. Morin transition temperature in (0001)-oriented α-Fe2O3 thin film and effect of Ir doping

    NASA Astrophysics Data System (ADS)

    Shimomura, Naoki; Pati, Satya Prakash; Sato, Yuji; Nozaki, Tomohiro; Shibata, Tatsuo; Mibu, Ko; Sahashi, Masashi

    2015-05-01

    The structural properties and Morin transition in c-plane-oriented α-Fe2O3 and Ir-doped α-Fe2O3 thin films have been investigated. The enhancement of the Morin transition temperature (TM) in α-Fe2O3 film by Ir doping has been demonstrated. The TM in the c-plane-oriented α-Fe2O3 thin film was determined from the temperature-dependent in-plane magnetization and change of coercivity (Hc); this TM value was found close to that of bulk α-Fe2O3. The spin directions of non-doped and Ir-doped α-Fe2O3 at room temperature were also estimated from conversion electron Mössbauer spectroscopy measurements. We confirmed that Ir doping dramatically enhances the TM of α-Fe2O3 thin film.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Low-temperature magnetic transition in troilite: A simple marker for highly stoichiometric FeS systems

    NASA Astrophysics Data System (ADS)

    Cuda, J.; Kohout, T.; Tucek, J.; Haloda, J.; Filip, J.; Prucek, R.; Zboril, R.

    2011-11-01

    Low-temperature magnetic evolution of troilite sample, extracted from the Cape York IIIA octahedrite meteorite, was investigated by employing macroscopic magnetic measurement, Mössbauer spectroscopy, scanning electron microscopy (SEM) and backscattered electrons (BSE) microscopy, X-ray diffraction (XRD), electron microprobe analysis (EMA), and atomic absorption spectrometry (AAS). The study identified a magnetic transition at ≈70 K manifested itself in a similar manner as previously reported for troilite from the Bruderheim L6 chondrite meteorite. The data show that this transition is unlikely driven by impurity such as chromite and seems to be rather an intrinsic property of troilite. In this study, we unambiguously exclude the relation of this transition to the structural rearrangement like the Morin transition in hematite. Similarly, in-field Mössbauer data do not support the change of the canting angle in the spin structure of FeS above and below the transition. Mössbauer, XRD, and magnetic data, newly measured also for troilite from the Bruderheim L6 chondrite, demonstrate that both studied troilite samples exhibit nearly the same magnetic and structural characteristics. Thus, the nature of the transition occurring at ≈70 K in both samples has identical characteristics and its detection can be used as a simple general marker for highly stoichiometric FeS systems.

  3. Temperature-dependent transitions between normal and inverse isotope effects pertaining to the interaction of H-H and C-H bonds with transition metal centers.

    PubMed

    Parkin, Gerard

    2009-02-17

    Deuterium kinetic isotope effects (KIEs) serve as versatile tools to infer details about reaction mechanisms and the nature of transition states, while equilibrium isotope effects (EIEs) associated with the site preferences of hydrogen and deuterium enable researchers to study aspects of molecular structure. Researchers typically interpret primary deuterium isotope effects based on two simple guidelines: (i) the KIE for an elementary reaction is normal (k(H)/k(D) > 1) and (ii) the EIE is dictated by deuterium preferring to be located in the site corresponding to the highest frequency oscillator. In this Account, we evaluate the applicability of these rules to the interactions of H-H and C-H bonds with a transition metal center. Significantly, experimental and computational studies question the predictability of primary EIEs in these systems based on the notion that deuterium prefers to occupy the highest frequency oscillator. In particular, the EIEs for (i) formation of sigma-complexes by coordination of H-H and C-H bonds and (ii) oxidative addition of dihydrogen exhibit unusual temperature dependencies, such that the same system may demonstrate both normal (i.e., K(H)/K(D) > 1) and inverse (i.e., K(H)/K(D) < 1) values. The transition between a normal and inverse EIE indicates that these systems do not demonstrate the typical monotonic variation predicted by the van't Hoff relationship. Instead, the calculated EIEs in these systems are 0 at 0 K, increase to a value greater than 1, and then decrease to unity at infinite temperature. This unusual behavior may be rationalized by considering the individual factors that contribute to the EIE. Specifically, the EIE may be expressed in the form EIE = SYM x MMI x EXC x ZPE (where SYM is the symmetry factor, MMI is the mass-moment of inertia term, EXC is the excitation term, and ZPE is the zero-point energy term), and the distinctive temperature profile results from the inverse ZPE (enthalpy) and normal [SYM x MMI x EXC

  4. 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.

  5. 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.

  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. Temperature-induced phase transition and temperature sensing behavior in Yb3+ sensitized Er3+ doped YPO4 phosphors

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangtong; Fu, Zuoling; Sun, Zhen; Liu, Guofeng; Jeong, Jung Hyun; Wu, Zhijian

    2016-10-01

    YPO4:Er3+, Yb3+ microcrystals have been manufactured using hydrothermal synthesis and annealed at different temperature for 3 h. With the increases of calcination temperature, the phase transformation of yttrium phosphate from hexagonal to tetragonal phase is reported base on the representation of X-ray diffraction (XRD). Besides, the size and morphology of yttrium phosphate have been clearly observed by employing field-emission scanning electron microscopy (FE-SEM). By selective annealing temperature and doped concentration procedure, YPO4:1%Er3+, 15%Yb3+ phosphors that annealed at 1000 °C for 3 h after hydrothermal synthesis show the strongest luminescence intensity under a 980 nm laser diode excitation. The temperature sensing behavior of YPO4:1%Er3+, 15%Yb3+ phosphors has also been investigated in detail. The result indicated that YPO4:1%Er3+, 15%Yb3+ phosphors could be considered as potential materials for optical temperature sensors.

  8. Lower solar chromosphere-corona transition region. I - Theoretical models with small temperature gradients

    NASA Technical Reports Server (NTRS)

    Woods, D. Tod; Holzer, Thomas E.; Macgregor, Keith B.

    1990-01-01

    A study of transition region models including the effects of classical thermal conduction, heating, and radiative cooling is carried out with attention directed toward the problem of understanding the observed emission in the lower transition region. It is found that the observationally inferred emission measure curve implies a near-balance between heating and radiative cooling in the lower transition region, and that the presence of strong hydrogen Ly-alpha cooling leads to the existence of singularities in the solutions of the force balance and energy balance equations when such a near-balance between heating and cooling is assumed. These singularities place strong constraints on the nature of viable models of the lower transition region and must be considered when Ly-alpha cooling is important. Previously suggested explanations of the observed emission from the lower transition region are considered in the context of the results of the present study, and conditions for the applicability of these suggested explanations are discussed.

  9. 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.

  10. An evaluation of the transition temperature range of super-elastic orthodontic NiTi springs using differential scanning calorimetry.

    PubMed

    Barwart, O; Rollinger, J M; Burger, A

    1999-10-01

    Differential scanning calorimetry (DSC) was used to determine the transition temperature ranges (TTR) of four types of super-elastic orthodontic nickel-titanium coil springs (Sentalloy). A knowledge of the TTR provides information on the temperature at which a NiTi wire or spring can assume superelastic properties and when this quality disappears. The spring types in this study can be distinguished from each other by their characteristic TTR during cooling and heating. For each tested spring type a characteristic TTR during heating (austenite transformation) and cooling (martensite transformation) was evaluated. The hysteresis of the transition temperature, found between cooling and heating, was 3.4-5.2 K. Depending on the spring type the austenite transformation started (As) at 9.7-17.1 degrees C and finished (Af) at 29.2-37 degrees C. The martensite transformation starting temperature (Ms) was evaluated at 32.6-25.4 degrees C, while Mf (martensite transformation finishing temperature) was 12.7-6.5 degrees C. The results show that the springs become super-elastic when the temperature increases and As is reached. They undergo a loss of super-elastic properties and a rapid decrease in force delivery when they are cooled to Mf. For the tested springs, Mf and As were found to be below room temperature. Thus, at room temperature and some degrees lower, all the tested springs exert super-elastic properties. For orthodontic treatment this means the maintenance of super-elastic behaviour, even when mouth temperature decreases to about room temperature as can occur, for example, during meals.

  11. Oxygen Vacancy Induced Room-Temperature Metal-Insulator Transition in Nickelate Films and Its Potential Application in Photovoltaics.

    PubMed

    Wang, Le; Dash, Sibashisa; Chang, Lei; You, Lu; Feng, Yaqing; He, Xu; Jin, Kui-juan; Zhou, Yang; Ong, Hock Guan; Ren, Peng; Wang, Shiwei; Chen, Lang; Wang, Junling

    2016-04-20

    Oxygen vacancy is intrinsically coupled with magnetic, electronic, and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by postannealing at temperature lower than 300 °C and realize the reversible metal-insulator transition in epitaxial NdNiO₃ films. Importantly, over 6 orders of magnitude in the resistance modulation and a large change in optical bandgap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelate films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ∼50 emu/cm³ due to the formation of strongly correlated Ni²⁺ t(2g)⁶e(g)² states. The bandgap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelate-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. Two-photon microwave transitions and strong-field effects in a room-temperature Rydberg-atom gas

    NASA Astrophysics Data System (ADS)

    Anderson, D. A.; Schwarzkopf, A.; Miller, S. A.; Thaicharoen, N.; Raithel, G.; Gordon, J. A.; Holloway, C. L.

    2014-10-01

    We investigate two-photon Autler-Townes splitting and strong-field effects of 85Rb Rydberg atoms in a room-temperature vapor cell. To observe the level structure we employ electromagnetically induced transparency. We first study the two-photon 62 S1 /2-63 S1 /2 microwave transition using an electric-field reference measurement obtained with the one-photon 62 S1 /2-62 P3 /2 transition. We then study the 61 D5 /2-62 D5 /2 transition where the microwave electric-field range is extended up to ˜40 V /m . A Floquet analysis is used to model field-induced level shifts and state-mixing effects present in the strongly driven quantum systems under consideration. Calculations are found to be in good agreement with experimental observations.

  17. 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.

  18. 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.

  19. Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

    NASA Astrophysics Data System (ADS)

    Teknowijoyo, S.; Cho, K.; Tanatar, M. A.; Gonzales, J.; Böhmer, A. E.; Cavani, O.; Mishra, V.; Hirschfeld, P. J.; Bud'ko, S. L.; Canfield, P. C.; Prozorov, R.

    2016-08-01

    A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δ λ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature Tc increases by 0.4 K from Tc 0≈8.8 K while the structural transition temperature Ts decreases by 0.9 K from Ts 0≈91.2 K after electron irradiation. We discuss several explanations for the Tc enhancement and propose that local strengthening of the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Photo-assisted cyanation of transition metal nitrates coupled with room temperature C-C bond cleavage of acetonitrile.

    PubMed

    Zou, Shihui; Li, Renhong; Kobayashi, Hisayoshi; Liu, Juanjuan; Fan, Jie

    2013-03-01

    It is a challenge to use acetonitrile as a cyanating agent because of the difficulty in cleaving its C-CN bond. Herein, we report a mild photo-assisted route to conduct the cyanation of transition metal nitrates using acetonitrile as the cyanating agent coupled with room-temperature C-C bond cleavage. DFT calculations and experimental observations suggest a radical-involved reaction mechanism, which excludes toxicity from free cyanide ions.

  5. 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

  6. Experimental determination of the cooperative length scale of a glass-forming liquid near the glass transition temperature

    NASA Astrophysics Data System (ADS)

    Rizos, A. K.; Ngai, K. L.

    1999-01-01

    Photon correlation spectroscopy and dielectric relaxation are used to examine the molecular reorientation relaxation dynamics of a fragile glass-forming liquid Aroclor (a mixture of polychlorinated biphenyls), modified by the addition of low- and high-molecular-weight polyisoprene and polybutadiene as a function of temperature and polymer solute concentration. Concentration fluctuation contributes a temperature-dependent broadening of the relaxation spectrum of Aroclor. The rate of change of the Aroclor relaxation spectrum with temperature is more pronounced when the polymers added are of low molecular weight and exhibits a steplike decrease in the neighborhood of some characteristic molecular weight. The radius of gyration of the polymer with this characteristic molecular weight is about 15 Å, which determines the cooperative length scale L(T) of Aroclor to be approximately 30 Å near and above the glass transition temperature.

  7. 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.

  8. Phase transitions and the temperature dependence of the dielectric properties in tetragonally strained barium strontium titanate films

    NASA Astrophysics Data System (ADS)

    Alldredge, L. M. B.; Chang, Wontae; Kirchoefer, Steven W.; Pond, Jeffrey M.

    2009-02-01

    The dielectric properties of sputter-deposited Ba1-xSrxTiO3 (BST) thin films on (001) MgO substrates with in-plane or out-of-plane tetragonal lattice structure distortions were characterized as a function of temperature. A temperature-dependent interpolation calibration technique was developed for increased efficiency of the microwave measurements. The BST films showed significant differences in the ferroelectric phase transition due to lattice distortions with a strong temperature dependence of the in-plane dielectric behavior for films under tensile strain and a weak temperature dependence for films under compressive strain. The experimental data agreed well with theoretical modeling of the BST film strain effect based on Devonshire's theory.

  9. 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.

  10. 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.

  11. 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.

  12. Structural aspects of the. alpha. transition in stoichiometric FeS: Identification of the high-temperature phase

    SciTech Connect

    Keller-Besrest, F.; Collin, G. )

    1990-02-01

    Compounds of the Fe{sub 1-x}S system (O {le} {times} {le} O.125) are of NiAs type (a and c being the substructure lattice constants). For O {le} {times} {le} O.O5, the temperature-induced metal-nonmetal o transition is associated with a structural change. Powder studies identify the influence of x on the transition and especially on the superstructure reflection intensities of the hexagonal {radical}3a, 2c low-temperature (T < T{sub {alpha}}) phase. Crystal growth for compositions in the transition range is detailed. The structural study of a stoichiometric FeS crystal at various temperatures gives evidence for disorder phenomena in the pretransition range and for the exact nature of the hexagonal HT phase (T > T{sub {alpha}}) 2a,c (SG P6{sub 3}mc). Its structure refinement (R = 6.O%) rules out the previous tritwinned model of MnP type. The cationic lattice of this 2a,c modification is intermediate between the lattices of the LT {radical}a,2c phase and those of a pure NiAs phase.

  13. X-ray diffraction studies of lipid phase transitions in cholesterol-rich membranes at sub-zero temperatures.

    PubMed

    Finean, J B; Hutchinson, A L

    1988-01-01

    In X-ray diffraction studies of hydrated (greater than 60%) cholesterol/dioleoylphosphatidylcholine mixtures the lipid packing band showed an abrupt transition from liquid crystal-type to gel-type position and definition at a temperature which decreased progressively to almost -50 degrees C as the proportion of cholesterol was increased to a saturation level of about 50 mol%. Plots of transition temperature against composition (mol% cholesterol) and of peak position against composition provided evidence of a significant change in phospholipid configuration at about 20 mol% cholesterol. However, the data overall suggested a uniform dispersion of the cholesterol molecules in the phospholipid bilayer at all concentrations up to the saturation point. Parallel studies of hydrated lipid extract of erythrocyte membranes and of several cholesterol-rich membrane preparations showed a similar overall change from liquid crystal-type packing at +20 degrees C to a gel-type packing at -30 degrees C to -40 degrees C but without displaying a defined transition temperature.

  14. 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.

  15. 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

  16. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: From boiling point to glass transition temperature

    NASA Astrophysics Data System (ADS)

    Schmidtke, B.; Petzold, N.; Kahlau, R.; Rössler, E. A.

    2013-08-01

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10-12 s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature Tg is covered. We focus on low-Tg liquids for which the high-temperature limit τ ≅ 10-12 s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" Ecoop(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)], 10.1103/PhysRevE.86.041507. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a Ecoop(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon.

  17. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: from boiling point to glass transition temperature.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Rössler, E A

    2013-08-28

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10(-12) s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature T(g) is covered. We focus on low-T(g) liquids for which the high-temperature limit τ ≅ 10(-12) s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" E(coop)(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)]. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a E(coop)(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon. PMID:24007015

  18. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: from boiling point to glass transition temperature.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Rössler, E A

    2013-08-28

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10(-12) s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature T(g) is covered. We focus on low-T(g) liquids for which the high-temperature limit τ ≅ 10(-12) s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" E(coop)(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)]. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a E(coop)(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon.

  19. 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.

  20. From boiling point to glass transition temperature: Transport coefficients in molecular liquids follow three-parameter scaling

    NASA Astrophysics Data System (ADS)

    Schmidtke, B.; Petzold, N.; Kahlau, R.; Hofmann, M.; Rössler, E. A.

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10-12 s < τ(T) < 102 s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E∞ and a low-temperature regime for which Ecoop(T) ≡ E(T)-E∞ increases exponentially while cooling. A scaling is introduced, specifically Ecoop(T)/E∞ ∝ exp[-λ(T/TA-1)], where λ is a fragility parameter and TA a reference temperature proportional to E∞. In order to describe τ(T) still the attempt time τ∞ has to be specified. Thus, a single interaction parameter E∞ describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics.

  1. 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.

  2. From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Hofmann, M; Rössler, E A

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10(-12) s < τ(T) < 10(2) s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E(∞) and a low-temperature regime for which E(coop)(T) ≡ E(T)-E(∞) increases exponentially while cooling. A scaling is introduced, specifically E(coop)(T)/E(∞) [proportionality] exp[-λ(T/T(A)-1)], where λ is a fragility parameter and T(A) a reference temperature proportional to E(∞). In order to describe τ(T) still the attempt time τ(∞) has to be specified. Thus, a single interaction parameter E(∞) describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics. PMID:23214591

  3. From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Hofmann, M; Rössler, E A

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10(-12) s < τ(T) < 10(2) s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E(∞) and a low-temperature regime for which E(coop)(T) ≡ E(T)-E(∞) increases exponentially while cooling. A scaling is introduced, specifically E(coop)(T)/E(∞) [proportionality] exp[-λ(T/T(A)-1)], where λ is a fragility parameter and T(A) a reference temperature proportional to E(∞). In order to describe τ(T) still the attempt time τ(∞) has to be specified. Thus, a single interaction parameter E(∞) describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics.

  4. 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

  5. A Bayesian approach to infer the radial distribution of temperature and anisotropy in the transition zone from seismic data

    NASA Astrophysics Data System (ADS)

    Drilleau, M.; Beucler, E.; Mocquet, A.; Verhoeven, O.; Moebs, G.; Burgos, G.; Montagner, J.

    2013-12-01

    Mineralogical transformations and matter transfers within the Earth's mantle make the 350-1000 km depth range (considered here as the mantle transition zone) highly heterogeneous and anisotropic. Most of the 3-D global tomographic models are anchored on small perturbations from 1-D models such as PREM, and are secondly interpreted in terms of temperature and composition distributions. However, the degree of heterogeneity in the transition zone can be strong enough so that the concept of a 1-D reference seismic model may be addressed. To avoid the use of any seismic reference model, we developed a Markov chain Monte Carlo algorithm to directly interpret surface wave dispersion curves in terms of temperature and radial anisotropy distributions, considering a given composition of the mantle. These interpretations are based on laboratory measurements of elastic moduli and Birch-Murnaghan equation of state. An originality of the algorithm is its ability to explore both smoothly varying models and first-order discontinuities, using C1-Bézier curves, which interpolate the randomly chosen values for depth, temperature and radial anisotropy. This parameterization is able to generate a self-adapting parameter space exploration while reducing the computing time. Using a Bayesian exploration, the probability distributions on temperature and anisotropy are governed by uncertainties on the data set. The method was successfully applied to both synthetic data and real dispersion curves. Surface wave measurements along the Vanuatu- California path suggest a strong anisotropy above 400 km depth which decreases below, and a monotonous temperature distribution between 350 and 1000 km depth. On the contrary, a negative shear wave anisotropy of about 2 % is found at the top of the transition zone below Eurasia. Considering compositions ranging from piclogite to pyrolite, the overall temperature profile and temperature gradient are higher for the continental path than for the oceanic

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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.

  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

    Ji, Cheng; Levitas, Valery I; Zhu, Hongyang; Chaudhuri, Jharna; Marathe, Archis; Ma, Yanzhang

    2012-11-20

    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.

  13. 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

  14. 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

  15. The Hilbert-glass transitions: new universality of temperature-tuned many-body dynamical quantum criticality

    NASA Astrophysics Data System (ADS)

    Pekker, David; Refael, Gil; Altman, Ehud; Demler, Eugene; Oganesyan, Vadim

    2014-03-01

    We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here we develop a real-space renormalization group method for excited state (RSRG-X) that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1D disordered transverse field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using RSRG-X we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by non-analyticities in the low frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

  16. 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.

  17. [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

  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. Transition from Arrhenius to non-Arrhenius temperature dependence of structural relaxation time in glass-forming liquids: Continuous versus discontinuous scenario

    NASA Astrophysics Data System (ADS)

    Popova, V. A.; Surovtsev, N. V.

    2014-09-01

    The temperature dependences of α relaxation time τα(T) of three glass-forming liquids (salol, o-terphenyl, and α-picoline) were investigated by a depolarized light scattering technique. A detailed description of τα(T) near TA, the temperature of the transition from the Arrhenius law at high temperatures to a non-Arrhenius behavior of τα(T) at lower temperatures, was done. It was found that this transition is quite sharp. If the transition is described as switching from the Arrhenius law to the Vogel-Fulcher-Tammann law, it occurs within the temperature range of about 15 K or less. Most of the known expressions for τα(T) cannot describe this sharp transition. Our analysis revealed that this transition can be described either as a discontinuous transition in the spirit of the frustration-limited domain theory [D. Kivelson, G. Tarjus, X. Zhao, and S. A. Kivelson, Phys. Rev. E 53, 751 (1996), 10.1103/PhysRevE.53.751], implying a phase transition, or by a phenomenological expression recently suggested [B. Schmidtke, N. Petzold, R. Kahlau, M. Hofmann, and E. A. Rössler, Phys. Rev. E 86, 041507 (2012), 10.1103/PhysRevE.86.041507], where the activation energy includes the term depending exponentially on temperature.

  20. Low-temperature magnetic phase transitions in the multiferroic Nd0.9Dy0.1Fe3(BO3)4. Part 1. Transitions induced by magnetic fields directed along the trigonal symmetry axis. Spontaneous transitions with temperature changes

    NASA Astrophysics Data System (ADS)

    Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Kolodyazhnaya, M. P.; Zvyagin, A. A.; Bludov, A. N.; Pashchenko, V. A.; Gudim, I. A.

    2016-04-01

    The elastic and magnetic characteristics of single-crystal Nd0.9Dy0.1Fe3(BO3)4 are studied at low temperatures in zero magnetic field and in external fields H||C3. The temperature dependences of the acoustic mode velocities and the magnetic susceptibility manifest a transition of the magnetic subsystem into a magnetically ordered state and two successive, spontaneous spin-reorientation phase transitions. The possibility of a spontaneous transition into an incommensurate (spiral) magnetic phase in the crystal is discussed. It is shown that an external magnetic field directed along the trigonal axis of the crystal induces a sequence of spin-reorientation phase transitions. An H-T phase diagram (H||C3) is constructed for this compound.

  1. On the influence of porosity on the low-temperature brittle—ductile transition in siliciclastic rocks

    NASA Astrophysics Data System (ADS)

    Rutter, E. H.; Hadizadeh, J.

    A compilation of available experimental data, coupled with new results on Tennessee sandstone, shows that the low-temperature brittle faulting to cataclastic flow transition in siliciclastic rocks takes place at progressively higher confining pressures as porosity is reduced. The collapse of initial porosity compensates for the tendency for brittle deformation to be dilatant. According to a stability criterion, this in turn favours spreading of the cataclastic deformation throughout the rock volume instead of fault localization. At sufficiently high strains, dilatation, and hence fault localization, supervenes. From microstructural observations on Oughtibridge Ganister (7% porosity), deformed under conditions of the faulting to flow transition, the mechanism of pore collapse involves crushing and sliding on shear-oriented grain boundaries, with accumulation of wear products in the pore spaces. This explains the enhancement of pore collapse by differential stress relative to purely hydrostatic compression.

  2. Measurements of Thermal Conductivity of Superfluid Helium Near its Transition Temperature T(sub lambda) in a 2D Confinement

    NASA Technical Reports Server (NTRS)

    Jerebets, Sergei

    2004-01-01

    We report our recent experiments on thermal conductivity measurements of superfluid He-4 near its phase transition in a two-dimensional (2D) confinement under saturated vapor pressure. A 2D confinement is created by 2-mm- and 1-mm-thick glass capillary plates, consisting of densely populated parallel microchannels with cross-sections of 5 x 50 and 1 x 10 microns, correspondingly. A heat current (2 < Q < 400 nW/sq cm) was applied along the channels long direction. High-resolution measurements were provided by DC SQUID-based high-resolution paramagnetic salt thermometers (HRTs) with a nanokelvin resolution. We might find that thermal conductivity of confined helium is finite at the bulk superfluid transition temperature. Our 2D results will be compared with those in a bulk and 1D confinement.

  3. Temperature effects on failure thickness and deflagration-to-detonation transition in PBX 9502 and TATB

    SciTech Connect

    Asay, B.W.; McAfee, J.B.

    1993-01-01

    The deflagration-to-detonation (DDT) behavior of TATB has been investigated at high temperatures and severe confinement. comparison is made to other common explosives under similar confinement. TATB did not DDT under these conditions. The failure thickness of PBX 9502 at 250[degrees]C has also been determined. Two mm appears to be the limiting value at this temperature.

  4. Temperature effects on failure thickness and deflagration-to-detonation transition in PBX 9502 and TATB

    SciTech Connect

    Asay, B.W.; McAfee, J.B.

    1993-04-01

    The deflagration-to-detonation (DDT) behavior of TATB has been investigated at high temperatures and severe confinement. comparison is made to other common explosives under similar confinement. TATB did not DDT under these conditions. The failure thickness of PBX 9502 at 250{degrees}C has also been determined. Two mm appears to be the limiting value at this temperature.

  5. Temperature-Induced Transitions in the Structure and Interfacial Rheology of Human Meibum

    SciTech Connect

    Leiske, Danielle L.

    2012-01-01

    Meibomian lipids are the primary component of the lipid layer of the tear film. Composed primarily of a mixture of lipids, meibum exhibits a range of melt temperatures. Compositional changes that occur with disease may alter the temperature at which meibum melts.

  6. Temperature Dependences of Dielectric, Elastic and Piezoelectric Properties of KIO 3 Single Crystals Associated with the Successive Phase Transitions

    NASA Astrophysics Data System (ADS)

    Maeda, Masaki; Takagi, Masayoshi; Suzuki, Ikuo

    2000-01-01

    Pottasium iodate, KIO3, belongs to the perovskite structure and undergoes successive phase transitions at T1= 212°C, T2= 72.5°C, T3=-15°C, T4=-160°C and T5=-240°C, respectively. The temperature dependences of the dielectric, elastic and piezoelectic properties have been measured in the temperature range from -263°C to 330°C.The superionic conductivity was found in the temperature range above T2. Pronounced dielectric dispersions in the frequency range below 10 kHz were observed around -160°C and -240°C and the data were analyzed by fitting to the Davidson-Cole and Havriliak-Negami dispersion formulas, respectively. Both dielectric anomalies are ascribed to the orientaional glass-transitions. The piezoelectric and elastic properties have been investigsated by the resonance-antiresonance method. The piezoelectric and elastic anomalies were observed at T2 and T3.

  7. EFFECTS OF TRITIUM GAS EXPOSURE ON THE GLASS TRANSITION TEMPERATURE OF EPDM ELASTOMER AND ON THE CONDUCTIVITY OF POLYANILINE

    SciTech Connect

    Clark, E; Marie Kane, M

    2008-12-12

    Four formulations of EPDM (ethylene-propylene diene monomer) elastomer were exposed to tritium gas initially at one atmosphere and ambient temperature for between three and four months in closed containers. Material properties that were characterized include density, volume, mass, appearance, flexibility, and dynamic mechanical properties. The glass transition temperature was determined by analysis of the dynamic mechanical property data per ASTM standards. EPDM samples released significant amounts of gas when exposed to tritium, and the glass transition temperature increased by about 3 C. during the exposure. Effects of ultraviolet and gamma irradiation on the surface electrical conductivity of two types of polyaniline films are also documented as complementary results to planned tritium exposures. Future work will determine the effects of tritium gas exposure on the electrical conductivity of polyaniline films, to demonstrate whether such films can be used as a sensor to detect tritium. Surface conductivity was significantly reduced by irradiation with both gamma rays and ultraviolet light. The results of the gamma and UV experiments will be correlated with the tritium exposure results.

  8. Transport evidence of a magnetic quantum phase transition in electron-doped high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Yu, W.; Higgins, J. S.; Bach, P.; Greene, R. L.

    2007-07-01

    We present magnetotransport evidence for antiferromagnetism in films of the electron-doped cuprates Pr2-xCexCuO4 . Our results show clear signature of static or quasistatic antiferromagnetism up to optimal doping x=0.15 , with a quantum phase transition close to x=0.16 , and a coexistence of antiferromagnetism and superconductivity for 0.12⩽x⩽0.15 .

  9. Synthesis, crystal structure, and high-temperature phase transition of the novel plumbide Na2MgPb.

    PubMed

    Yamada, Takahiro; Ikeda, Takuji; Stoffel, Ralf P; Deringer, Volker L; Dronskowski, Richard; Yamane, Hisanori

    2014-05-19

    A hitherto unknown sodium magnesium plumbide, Na2MgPb, was synthesized by heating the constituent elements. Na2MgPb crystallizes in a hexagonal unit cell with the Li2CuAs-type structure (P63/mmc, Z = 2, a = 5.110(2) Å, c = 10.171(4) Å at 293 K). The compound furthermore displays polymorphism: high-temperature powder XRD measurements revealed that hexagonal Na2MgPb (dubbed the "α" phase) transforms to another hexagonal phase (β) which is existent at 493-553 K, and the β phase changes to a cubic structure (γ) at 533-633 K further. The molar volume of γ-Na2MgPb is approximately 9% and 13% smaller than the molar volumes of the α phase and the β phase, respectively (at 543 K). The electrical resistivity of Na2MgPb is 0.39 mΩ at 300 K; it rises with increasing temperature from 300 to 491 K, and then drops at 491 and 523 K. These abrupt changes in resistivity may be attributed to the α → β and β → γ phase transitions, respectively. To gain further insight into the structure of cubic γ-Na2MgPb, putative models with regular Heusler-type (Cu2MnAl-type) and inverse Heusler-type (Li2AgSb-type) arrangements were probed using first-principles computations based on density functional theory (DFT). These computations indicate that, for the cubic γ phase, an inverse Heusler-type structure is distinctly more stable than the alternative regular Heusler type (at 0 K); beyond that, ab initio thermochemistry was successfully used to verify the stability ordering (α-Na2MgPb being favorable at low temperature, γ-Na2MgPb at high temperature), albeit the theoretically predicted transition temperature of 900 K which is higher than observed in experiment.

  10. Degradation of Terfenol-D particle epoxy composites under low-frequency cyclic magneto-mechanical loading at the matrix glass transition start and finish temperatures

    NASA Astrophysics Data System (ADS)

    Armstrong, William D.; Shanmugham, Manikantan; Bailey, Harold

    2004-07-01

    The present paper presents cyclic strain amplitude and longitudinal strain measurements of longitudinally compressed Terfenol-D particle samples subjected to magneto-strain cycling. A comparison is made of the responses of material strain cycle tested at temperatures near the matrix glass transition start temperature, and material strain cycle tested at a temperature near the matrix glass transition finish temperature. The cyclic strain amplitude of the material was significantly larger when tested at a temperature near the matrix glass transition finish temperature. A useful range of longitudinal applied stress exists where the composite suffers little apparent degradation. Beyond this range the composite exhibits steadily decreasing cyclic strain amplitude with increases in longitudinal compressive stress magnitude.

  11. Kinetics of a bioactive compound (caffeine) mobility at the vicinity of the mechanical glass transition temperature induced by gelling polysaccharide.

    PubMed

    Jiang, Bin; Kasapis, Stefan

    2011-11-01

    An investigation of the diffusional mobility of a bioactive compound (caffeine) within the high-solid (80.0% w/w) matrices of glucose syrup and κ-carrageenan plus glucose syrup exhibiting distinct mechanical glass transition properties is reported. The experimental temperature range was from 20 to -60 °C, and the techniques of modulated differential scanning calorimetry, small deformation dynamic oscillation in shear, and UV spectrometry were employed. Calorimetric and mechanical measurements were complementary in recording the relaxation dynamics of high-solid matrices upon controlled heating. Predictions of the reaction rate theory and the combined WLF/free volume framework were further utilized to pinpoint the glass transition temperature (T(g)) of the two matrices in the softening dispersion. Independent of composition, calorimetry yielded similar T(g) predictions for both matrices at this level of solids. Mechanical experimentation, however, was able to detect the effect of adding gelling polysaccharide to glucose syrup as an accelerated pattern of vitrification leading to a higher value of T(g). Kinetic rates of caffeine diffusion within the experimental temperature range were taken with UV spectroscopy. These demonstrated the pronounced effect of the gelling κ-carrageenan/glucose syrup mixture to retard diffusion of the bioactive compound near the mechanical T(g). Modeling of the diffusional mobility of caffeine produced activation energy and fractional free-volume estimates, which were distinct from those of the carbohydrate matrix within the glass transition region. This result emphasizes the importance of molecular interactions between macromolecular matrix and small bioactive compound in glass-related relaxation phenomena.

  12. Determination of glass transition temperature of reduced graphene oxide-poly(vinyl alcohol) composites using temperature dependent Fourier transform infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Mahendia, Suman; Heena; Kandhol, Geeta; Deshpande, Uday P.; Kumar, Shyam

    2016-05-01

    In the present work, structural properties of reduced graphene oxide (RGO) synthesized using modified Hummer's method and its composites with Poly(vinyl alcohol) (PVA) fabricated using solution-cast method have been studied. The structural properties of prepared samples have been systematically studied through UV-Visible absorption, Raman, Fourier Transform Infrared (FTIR) and Differential Scanning Calorimeter (DSC) spectroscopy. Infrared spectroscopy indicates the grafting of PVA chains with graphene layer through the formation of H-bonding linkage in the composites. Temperature-dependent FTIR spectra of PVA-RGO composite films were recorded to obtain the glass transition temperature (Tg) and to study its molecular origin. From these spectra the values of Tg were obtained using two-dimensional (2D) mapping of the first derivative of the absorbance intensity with respect to temperature (dA/dT), over the space of wavenumber and temperature. The value of Tg obtained for pure PVA increases from 78 °C to 92 °C after loading 0.5 wt.% of RGO in PVA and can be attributed to the strong H-bonding interaction between polymer chains and grafted solid surface of RGO. These results are in good agreement with those obtained from DSC analysis. This clearly indicates that the thermal behavior of PVA gets modified with loading of RGO.

  13. The influence of temperature induced phase transition on the energy storage density of anti-ferroelectric ceramics

    SciTech Connect

    Yi, Jinqiao; Zhang, Ling; Xie, Bing; Jiang, Shenglin

    2015-09-28

    Anti-ferroelectric (AFE) composite ceramics of (Pb{sub 0.858}Ba{sub 0.1}La{sub 0.02}Y{sub 0.008})(Zr{sub 0.65}Sn{sub 0.3}Ti{sub 0.05})O{sub 3}-(Pb{sub 0.97}La{sub 0.02})(Zr{sub 0.9}Sn{sub 0.05} Ti{sub 0.05})O{sub 3} (PBLYZST-PLZST) were fabricated by the conventional solid-state sintering process (CS), the glass-aided sintering (GAS), and the spark plasma sintering (SPS), respectively. The influence of the temperature induced phase transition on the phase structure, hysteresis loops, and energy storage properties of the composite ceramics were investigated in detail. The measured results of X-ray diffraction demonstrate that the composite ceramics exhibit the perovskite phases and small amounts of non-functional pyrochlore phases. Compared with the CS process, the GAS and SPS processes are proven more helpful to suppress the diffusion behaviors between the PBLYZST and PLZST phases according to the field emission scanning electron microscopy, thereby being able to improve the contribution of PBLYZST phase to the temperature stability of the orthogonal AFE phase. When the ambient temperature rises from 25 °C to 125 °C, CS and GAS samples have undergone a phase transition from orthorhombic AFE phase to tetragonal AFE phase, which results in a sharp decline in the energy storage density. However, the phase transition temperature of SPS samples is higher than 125 °C, and the energy storage density only slightly decreases due to the disorder of material microstructure caused by the high temperature. As a result, the SPS composite ceramics obtain a recoverable high energy storage density of 6.46 J/cm{sup 3} and the excellent temperature stability of the energy storage density of 1.16 × 10{sup −2} J/°C·cm{sup 3}, which is 1.29 × 10{sup −2} J/°C·cm{sup 3} lower than that of CS samples and about 0.43 times as that of GAS samples.

  14. The influence of temperature induced phase transition on the energy storage density of anti-ferroelectric ceramics

    NASA Astrophysics Data System (ADS)

    Yi, Jinqiao; Zhang, Ling; Xie, Bing; Jiang, Shenglin

    2015-09-01

    Anti-ferroelectric (AFE) composite ceramics of (Pb0.858Ba0.1La0.02Y0.008)(Zr0.65Sn0.3Ti0.05)O3-(Pb0.97La0.02)(Zr0.9Sn0.05Ti0.05)O3 (PBLYZST-PLZST) were fabricated by the conventional solid-state sintering process (CS), the glass-aided sintering (GAS), and the spark plasma sintering (SPS), respectively. The influence of the temperature induced phase transition on the phase structure, hysteresis loops, and energy storage properties of the composite ceramics were investigated in detail. The measured results of X-ray diffraction demonstrate that the composite ceramics exhibit the perovskite phases and small amounts of non-functional pyrochlore phases. Compared with the CS process, the GAS and SPS processes are proven more helpful to suppress the diffusion behaviors between the PBLYZST and PLZST phases according to the field emission scanning electron microscopy, thereby being able to improve the contribution of PBLYZST phase to the temperature stability of the orthogonal AFE phase. When the ambient temperature rises from 25 °C to 125 °C, CS and GAS samples have undergone a phase transition from orthorhombic AFE phase to tetragonal AFE phase, which results in a sharp decline in the energy storage density. However, the phase transition temperature of SPS samples is higher than 125 °C, and the energy storage density only slightly decreases due to the disorder of material microstructure caused by the high temperature. As a result, the SPS composite ceramics obtain a recoverable high energy storage density of 6.46 J/cm3 and the excellent temperature stability of the energy storage density of 1.16 × 10-2 J/°C.cm3, which is 1.29 × 10-2 J/°C.cm3 lower than that of CS samples and about 0.43 times as that of GAS samples.

  15. The effects of mass flow on the temperature and abundance structure of the solar transition region

    NASA Technical Reports Server (NTRS)

    Woods, D. T.; Holzer, Thomas E.

    1991-01-01

    The density and temperature structure of a multicomponent plasma consisting of electrons, protons, ionized helium, and a trace minor ion species are computed. The equations of force and energy balance for this model are developed and solved. It is found that in the case of downflows the minor ion temperature can be significantly hotter than the electron temperature, and significant abundance enhancements are possible due to the slowdown of the minor species from the effect of the thermal force. A simple physical picture of the source of the thermal force is given.

  16. Long-range order in a high-density electron-hole system at room temperature during superradiant phase transition

    NASA Astrophysics Data System (ADS)

    Vasil'ev, Peter P.; Olle, Vojtech; Penty, Richard V.; White, Ian H.

    2013-11-01

    We have experimentally investigated the formation of off-diagonal long-range order and non-equilibrium BEC-like condensation in GaAs/AlGaAs heterostructures during superradiant (SR) emission at room temperature. The conclusive evidence of the establishment of phase coherence over a macroscopic range during the superradiant quantum phase transition is reported. The first-order spatial correlation function of the e-h system is determined by evaluating interference patterns of SR emission using Young's double slit.

  17. Large arctic temperature change at the Wisconsin-Holocene glacial transition

    SciTech Connect

    Cuffey, K.M.; Clow, G.D.; Alley, R.B.

    1995-10-20

    Analysis of borehole temperature and Greenland Ice Sheet Project II ice-core isotopic composition reveals that the warming from average glacial conditions to the Holocene in central Greenland was large, approximately 15{degrees}C. This is at least three times the coincident temperature change in the tropics and mid-latitudes. The coldest periods of the last glacial were probably 21{degrees}C colder than at present over the Greenland ice sheet. 47 refs., 3 figs., 1 tab.

  18. Large arctic temperature change at the Wisconsin-Holocene glacial transition

    USGS Publications Warehouse

    Cuffey, Kurt M.; Clow, G.D.; Alley, R.B.; Stuiver, M.; Waddington, E.D.; Saltus, R.W.

    1995-01-01

    Analysis of borehole temperature and Greenland Ice Sheet Project II ice-core isotopic composition reveals that the warming from average glacial conditions to the Holocene in central Greenland was large, approximately 15??C. This is at least three times the coincident temperature change in the tropics and mid-latitudes. The coldest periods of the last glacial were probably 21??C colder than at present over the Greenland ice sheet.

  19. Origins of the high temperature increase of the thermal conductivity of transition metal carbides from atomistic simulations.

    PubMed

    Crocombette, Jean-Paul

    2013-12-18

    To understand the unexpected increase of the thermal conductivity of transition metal carbides at high temperatures, we calculate, with atomistic simulations, the thermal conductivity of zirconium carbide (ZrC). To account for the common substoichiometry of this material, various numbers of carbon vacancies are considered. The vibrational part of the conductivity is calculated by empirical potential molecular dynamics while the electronic part is calculated from density functional theory electronic structure with the Kubo-Greenwood formula on selected atomic configurations generated by the same empirical potential. We find that the vibrational part of the conductivity is negligible at temperatures higher than 1500 K. The increase of thermal conductivity with temperature is quantitatively reproduced in the calculations. It appears for all compositions and proves to rely entirely on its electronic component. Three phenomena are found responsible for the rise of the thermal conductivity with temperature: the semi-metallic shape of the electronic density of states, the additional electrical resistivity induced by carbon vacancies and the rise of the density of states with either temperature or the concentration of vacancies.

  20. Kinetic arrest of field-temperature induced first order phase transition in quasi-one dimensional spin system Ca3Co2O6

    NASA Astrophysics Data System (ADS)

    De, Santanu; Kumar, Kranti; Banerjee, A.; Chaddah, P.

    2016-05-01

    We have found that the geometrically frustrated spin chain compound Ca3Co2O6 belonging to Ising like universality class with uniaxial anisotropy shows kinetic arrest of first order intermediate phase (IP) to ferrimagnetic (FIM) transition. In this system, dc magnetization measurements followed by different protocols suggest the coexistence of high temperature IP with equilibrium FIM phase in low temperature. Formation of metastable state due to hindered first order transition has also been probed through cooling and heating in unequal field (CHUF) protocol. Kinetically arrested high temperature IP appears to persist down to almost the spin freezing temperature in this system.

  1. Magnetostructural phase transition assisted by temperature in Ag-αMnO2: a density functional theory study.

    PubMed

    Ochoa, Francisco Sánchez; Huang, Zhiwei; Tang, Xingfu; Cocoletzi, Gregorio Hernández; Springborg, Michael

    2016-03-14

    A crystalline material formed by parallel chains of silver atoms inside one-dimensional tunnels of hollandite manganese dioxide, Ag-αMnO2, is investigated through first-principles total energy calculations. Two different magnetic phases have been identified; one structure containing linear Ag chains with an antiferromagnetic ordering in the direction perpendicular to the MnO2 tunnels for T = 0 K (I4/m) and another configuration with zigzag Ag chains in a non-magnetic regime for higher temperatures (P21/c). According to phonon dispersions, both structures are stable. On the other hand, the structure with linear Ag chains in the non-magnetic state is unstable. A critical temperature of Tc≃ 125 K for the magnetostructural phase transition between the two stable structures I4/m and P21/c is predicted.

  2. Temperature stability of transit time delay for a single-mode fibre in a loose tube cable

    NASA Technical Reports Server (NTRS)

    Bergman, L. A.; Eng, S. T.; Johnston, A. R.

    1983-01-01

    The effect of temperature on the transit-time delay of a loose-tube-type single-mode optical-fiber cable is investigated experimentally. A 1058-m length of cable was placed loosely coiled in an oven and used to connect a 820-nm single-mode laser diode to a high-speed avalanche-photodiode detector feeding a vector voltmeter; the signal was provided by a high-stability frequency-synthesized generator. Measurements were made every 2 C from -50 to 60 C and compared to those obtained with a 200-m lacquered bare fiber. The phase change of both fibers varied with temperature at a positive slope of 6-7 ppm/C. This value is significantly better than those reported for other cable types, suggesting the application of loose-fiber cables to long-haul gigabit digital transmissions or precision time-base distribution for VLBI.

  3. Ferroelectric Sm-Doped BiMnO3 Thin Films with Ferromagnetic Transition Temperature Enhanced to 140 K

    PubMed Central

    2014-01-01

    A combined chemical pressure and substrate biaxial pressure crystal engineering approach was demonstrated for producing highly epitaxial Sm-doped BiMnO3 (BSMO) films on SrTiO3 single crystal substrates, with enhanced magnetic transition temperatures, TC up to as high as 140 K, 40 K higher than that for standard BiMnO3 (BMO) films. Strong room temperature ferroelectricity with piezoresponse amplitude, d33 = 10 pm/V, and long-term retention of polarization were also observed. Furthermore, the BSMO films were much easier to grow than pure BMO films, with excellent phase purity over a wide growth window. The work represents a very effective way to independently control strain in-plane and out-of-plane, which is important not just for BMO but for controlling the properties of many other strongly correlated oxides. PMID:25141031

  4. Probing temperature-driven spin reorientation transition of GdFeCo film by Kerr loops and ferromagnetic resonance

    SciTech Connect

    He, Wei Liu, Hao-Liang; Cai, Jian-Wang; Cheng, Zhao-Hua; Wu, Hong-Ye

    2015-01-26

    The magnetic anisotropy is of both scientific and technological interest for magneto-optical material GdFeCo film. We characterize the magnetic anisotropy of a 20 nm GdFeCo film from 265 K to 320 K via Kerr loops and ferromagnetic resonance. With increasing temperature, both of the first-order uniaxial magnetic anisotropy and shape anisotropy increase. However, the competition between them causes a temperature-driven spin reorientation transition (SRT) and the effective perpendicular magnetic anisotropy decrease from 2.22 × 10{sup 4 }ergs/cm{sup 3} (288 K) to −1.56 × 10{sup 4 }ergs/cm{sup 3} (317 K). The positive second-order uniaxial magnetic anisotropy determines an easy-cone state as the mediated state during SRT.

  5. Ferroelectric InMnO3: Growth of single crystals, structure and high-temperature phase transitions

    NASA Astrophysics Data System (ADS)

    Bekheet, Maged F.; Svoboda, Ingrid; Liu, Na; Bayarjargal, Lkhamsuren; Irran, Elisabeth; Dietz, Christian; Stark, Robert W.; Riedel, Ralf; Gurlo, Aleksander

    2016-09-01

    To understand the origin of the ferroelectricity in InMnO3, single crystals with average size of 1 mm were grown in PbF2 flux at 950 °C. The results of single crystal X-ray diffraction, second harmonic generation and piezoresponse force microscopy studies of high-quality InMnO3 single crystals reveal that the room-temperature state in this material is ferroelectric with P63cm symmetry. The polar InMnO3 specimen undergoes a reversible phase transition from non-centrosymmetric P63cm structure to a centrosymmetric P63/mmc structure at 700 °C as confirmed by the in situ high-temperature Raman spectroscopic and synchrotron X-ray diffraction experiments.

  6. Superconducting transition temperature in two-dimensional doped repulsive Hubbard model: DCA+ simulations with continuous momentum dependence

    NASA Astrophysics Data System (ADS)

    Jiang, Mi; Staar, Peter; Maier, Thomas; Schulthess, Thomas

    2015-03-01

    DCA+ algorithm extends the dynamical cluster approximation (DCA) with continuous lattice self-energy to ensure better convergence with cluster size and delay the occurrence of the severe sign problem. This new algorithm enables a systematic investigation of the phase diagram of 2D Hubbard model relevant to the high temperature superconductors. We calculate the superconducting transition temperature Tc in the 2D repulsive Hubbard model on square lattice with nearest-neighbor hoppings for different doping levels, focussing on the intermediate correlation (U / t = 7) regime. This research was carried out with resources of the Oak Ridge Leadership Computing Facility (OLCF), the Swiss National Supercomputing Center (CSCS), and the Center for Nanophase Materials Sciences (CNMS).

  7. Observations on the brittle to ductile transition temperatures of B2 nickel aluminides with and without zirconium

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Noebe, R. D.; Bowman, R.

    1989-01-01

    The effect of a zirconium addition (0.05 at. pct) to a stoichiometric NiAl alloy on the brittle-to-ductile transition temperature (BDTT) of this alloy was investigated. Constant velocity tensile tests were conducted to fracture between 300 and 1100 K under initial strain rate 0.00014/sec, and the true stress and true strain values were determined from plots of load vs time after subtracting the elastic strain. The inelastic strain was measured under a traveling microscope. Microstructural characterization of as-extruded and fractured specimens was carried out by SEM and TEM. It was found that, while the addition of 0.05 at. pct Zr strengthened the NiAl alloy, it increased its BDTT; this shift in the BDTT could not be attributed either to variations in grain size or to impurity contents. Little or no room-temperature ductility was observed for either alloy.

  8. Electric-field-induced modification of the magnon energy, exchange interaction, and curie temperature of transition-metal thin films.

    PubMed

    Oba, M; Nakamura, K; Akiyama, T; Ito, T; Weinert, M; Freeman, A J

    2015-03-13

    The electric-field-induced modification in the Curie temperature of prototypical transition-metal thin films with the perpendicular magnetic easy axis, a freestanding Fe(001) monolayer and a Co monolayer on Pt(111), is investigated by first-principles calculations of spin-spiral structures in an external electric field (E field). An applied E field is found to modify the magnon (spin-spiral formation) energy; the change arises from the E-field-induced screening charge density in the spin-spiral states due to p-d hybridizations. The Heisenberg exchange parameters obtained from the magnon energy suggest an E-field-induced modification of the Curie temperature, which is demonstrated via Monte Carlo simulations that take the magnetocrystalline anisotropy into account.

  9. Zanclean/Piacenzian transition on Cyprus (SE Mediterranean): calcareous nannofossil and Sea Surface Temperatures evidence of sapropel formation

    NASA Astrophysics Data System (ADS)

    Athanasiou, Maria; Triantaphyllou, Maria; Bouloubassi, Ioanna; Dimiza, Margarita; Gogou, Alexandra; Klein, Vincent; Parinos, Constantine; Theodoroyu, George

    2016-04-01

    Quantitative analyses of calcareous nannofossils in the sediments of Pissouri South section on the island of Cyprus have produced a paleoceanographic record reflecting the paleoclimatic conditions during Zanclean/Piacenzian transition. According to the performed calcareous nannofossil biostratigraphy the studied section is correlated with MNN14/15 and MNN16 calcareous nannofossil biozones and is astronomically dated between 4.065 and 3.217 Ma. Intervals of increased organic carbon content along with the positive values of Florisphaera profunda, Helicosphaera sellii, Discoaster spp. and the subsequent increase of stratification S-index correspond to the sapropel deposition during periods of wetter climate and intense continental runoff especially from the river Nile. These layers are alternating with grey marly intervals, featured by the increased values of small placoliths of Reticulofenestra and Gephyrocapsa species, which are indicative of eutrophic conditions during intense surface waters mixing. Pissouri South section comprises a SSTs sequence using alkenone unsaturation index (Uk 37) providing with the first continuous record from SE Mediterranean covering the Zanclean/Piacenzian (Pliocene) transition (~ 4.1-3.2 Ma). Correlation of the total alkenone concentration to the calcareous nannofossil assemblage and especially representatives among Noelaerhabdaceae family revealed that Pseudoemiliania lacunosa probably had similar temperature sensitivity to that of Emiliania huxleyi, currently producing alkenones in present day oceans.Our data support the prevalence of a generally warm phase characterized by the absence of high-frequency climate variations in the southeastern Mediterranean during the Zanclean/Piacenzian (Early/Late Pliocene) transition.

  10. Temperature-induced shifts in selective pressure at a critical developmental transition.

    PubMed

    Gagliano, Monica; McCormick, Mark I; Meekan, Mark G

    2007-05-01

    Selective mortality within a population, based on the phenotype of individuals, is the foundation of the theory of natural selection. We examined temperature-induced shifts in the relationships among early life history traits and survivorship over the embryonic and larval stages of a tropical damselfish, Pomacentrus amboinensis. Our experiments show that temperature determines the intensity of selective mortality, and that this changes with ontogeny. The size of energy stores determined survival through to hatching, after which egg size became a good indicator of fitness as predicted by theoretical models. Yet, the benefits associated with egg size were not uniform among test temperatures. Initial egg size positively influenced larval survival at control temperature (29 degrees C). However, this embryonic trait had no effect on post-hatching longevity of individuals reared at the higher (31 degrees C) and lower (25 degrees C) end of the temperature range. Overall, our findings indicate that the outcome of selective mortality is strongly dependent on the interaction between environment conditions and intrinsic developmental schedules. PMID:17242907

  11. Mean ocean temperature change over the last glacial transition based on atmospheric changes in heavy noble mixing ratios

    NASA Astrophysics Data System (ADS)

    Bereiter, Bernhard; Severinghaus, Jeff; Shackleton, Sarah; Baggenstos, Daniel; Kawamura, Kenji

    2016-04-01

    On paleo-climatic timescales heavy noble gases (Krypton and Xenon) are passively cycled through the atmosphere-ocean system without seeing any significant sink or source. Since the solubility in water of each gas species is characterized by a specific temperature dependency, mixing ratios in the atmosphere change with changing ocean temperatures. In this study, we use this fact to reconstruct mean global ocean temperatures (MOT) over the course of the last glacial transition based on measurements of trapped air in the WAIS Divide ice core. We analyzed 70 ice samples with a recently developed method which determines the isotopic ratios of N2, Ar, Kr (and in some cases also of Xe, though with less precision) and the elemental ratios of Kr/N2, Xe/N2 and Xe/Kr. We use the isotope ratios to correct the elemental ratios for gravitational enrichment in the firn column. The corrected elemental ratios are then used in a simple box model to reconstruct MOT. The three elemental ratio pairs are first interpreted as independent measures of MOT and then combined to a single "best-estimate" MOT record with an average uncertainty of 0.27°C. We find a clear link to Antarctic temperatures and a LGM-Holocene change in MOT of 2.4°C. This value is in good agreement with results from marine sediment cores (which, however, have an uncertainty of 1°C). Our record provides an unprecedented constrain on ocean heat uptake over the last glacial transition and therefore gives new insights in the mechanisms underlying long term ocean heat fluxes. To our knowledge, this is the first time that MOT has been reconstructed in such great detail.

  12. A room-temperature phase transition in maximum microcline - Heat capacity measurements

    USGS Publications Warehouse

    Openshaw, R.E.; Hemingway, B.S.; Robie, R.A.; Krupka, K.M.

    1979-01-01

    The thermal hysteresis in heat capacity measurements recently reported (Openshaw et al., 1976) for a maximum microcline prepared from Amelia albite by fused-salt ion-exchange is described in detail. The hysteresis is characterized by two limiting and reproducible curves which differ by 1% of the measured heat capacities. The lower curve, denoted curve B, represents the values obtained before the sample had been cooled below 300 K. Measurements made immediately after cooling the sample below 250 K followed a second parallel curve, curve A, to at least 370 K. Values intermediate to the two limiting curves were also obtained. The transitions from the B to the A curve were rapid and observed to occur three times. The time required to complete the transition from the A to the B curve increased from 39 h to 102 h in the two times it was observed to occur. The hysteresis is interpreted as evidence of a phase change in microcline at 300??10 K The heat effect associated with the phase change has not been evaluated. ?? 1979 Springer-Verlag.

  13. Folding-unfolding transitions of Rv3221c on the pressure-temperature plane

    NASA Astrophysics Data System (ADS)

    Somkuti, Judit; Jain, Sriyans; Ramachandran, Srinivasan; ászló Smeller, L.

    2013-06-01

    Rv3221c is a biotin-binding protein found in Mycobacterium tuberculosis. It has been reported that an elevated temperature is needed for it to adopt a folded conformation. We determined the complete pressure-temperature phase diagram, and determined the thermodynamical parameters of the denaturation. The phase diagram follows well the Hawley theory. The secondary structure of the protein was found to contain predominantly beta sheet. The pressure unfolding was partially reversible, resulting in pressure-sensitive aggregates, besides the correctly refolded and biotin-bound fraction of proteins.

  14. Screening out the non-Arrhenius behaviour of nematic-isotropic transition by room temperature ionic liquid

    NASA Astrophysics Data System (ADS)

    Dan, K.; Datta, A.; Yoshida, Y.; Saito, G.; Yoshikawa, K.; Roy, M.

    2016-02-01

    Differential Scanning Calorimetry (DSC) and optical polarization microscopy of a mixture of the liquid crystalline material (N-(4-methoxybenzylidene)-4-butylaniline, MBBA) and a Fe-based room temperature ionic liquid 1-ethyl-3-methylimidazolium tetrachloroferrate ([Emim]+ [FeCl4]-, EMIF) indicate a decrease in the nematic-isotropic (N-I) phase transition temperature (TNI) with an increase in EMIF concentration, explained by a proposed model of Coulomb "screening" of MBBA quadrupoles by the EMIF ions along with ionic "self screening." DSC studies of EMIF-MBBA and pure EMIF and comparison with pure MBBA results show that the major transitions in pure EMIF have Arrhenius behaviour, but more importantly the previously found convex Arrhenius behaviour of the pristine MBBA [K. Dan et al., Europhys. Lett. 108, 36007 (2014)] becomes Arrhenius in the mixture, indicating a conversion of the entropic N-I activation barrier to an enthalpic one. In presence of EMIF, a drastic decrease in the intensity of out-of-plane distortions of benzene rings in MBBA is found from Fourier transform infrared spectroscopy, consistent with significant reduction in the conformational states of MBBA. This suppression of large amplitude motion is again consistent with a Coulomb screening and gives a molecular basis for the entropic-to-enthalpic conversion of the N-I activation barrier.

  15. Analysis of fracture toughness in the transition-temperature region of an Mn-Mo-Ni low-alloy steel

    NASA Astrophysics Data System (ADS)

    Kim, Sangho; Hwang, Byoungchul; Lee, Sunghak; Lee, Sunghak

    2003-06-01

    This study is concerned with the analysis of fracture toughness in the transition region of an Mn-Mo-Ni low-alloy steel, in accordance with the ASTM E1921 standard test method. Elastic-plastic cleavage fracture toughness ( K Jc ) was determined by three-point bend tests, using precracked Charpy V-notch (PCVN) specimens, and relationships between K Jc , the critical component of J ( J c ), critical distance ( X c ), stretch-zone width (SZW), local fracture stress, and plane-strain fracture toughness ( K Ic were discussed on the basis of the cleavage fracture behavior in the transition region. The master curve and the 95 pct confidence curves well explained the variation in the measured K Jc , and the Weibull slope measured on the Weibull plots was consistent with the theoretical slope of 4. Fractographic observation indicated that X c linearly increased with increasing J c , and that the SZW had a good correlation with K Jc , irrespective of the test temperature. In addition, the local fracture stress was independent of the test temperature, because the tempered bainitic steel used in this study showed a propagation-controlled cleavage fracture behavior.

  16. Preparation of a series of model poly(n-alkyl styrene)s and their viscoelasticity and glass transition temperatures

    NASA Astrophysics Data System (ADS)

    Matsushima, Satoru; Takano, Atsushi; Takahashi, Yoshiaki; Matsushita, Yushu

    Viscoelasticity and glass transition temperatures for linear polymers of many species have been investigated so far, and it is well-known that the melt viscosity for the linear polymers varies with molecular weight in essentially the same manner such as packing length theory. It is important to understand the relationship between the viscosity and the molecular structure of various kinds of linear polymers. To investigate the relationship deeply, viscoelastic measurements using linear polymer analogues which the molecular structure is systematically varied should be useful. For example, poly(n-alkyl-substituted polymers) such as poly(n-alkyl methacrylate)s are one of the good candidate. In this study, a series of poly(n-alkyl styrene)s with the different number of carbon atoms(n) in the side alkyl groups (n =1, 2, 3, 4, 6, 8, 10 and 12) were carefully synthesized by an anionic polymerization technique, and the viscoelasticity and the glass transition temperatures of the poly(n-alkyl styrene)s with high molecular weight (Mw >=4Me) and narrow molecular weight distribution (Mw/Mn <=1.1) were discussed.

  17. Validation of Force Fields of Rubber through Glass-Transition Temperature Calculation by Microsecond Atomic-Scale Molecular Dynamics Simulation.

    PubMed

    Sharma, Pragati; Roy, Sudip; Karimi-Varzaneh, Hossein Ali

    2016-02-25

    Microsecond atomic-scale molecular dynamics simulation has been employed to calculate the glass-transition temperature (Tg) of cis- and trans-1,4-polybutadiene (PB) and 1,4-polyisoprene (PI). Both all-atomistic and united-atom models have been simulated using force fields, already available in literature. The accuracy of these decade old force fields has been tested by comparing calculated glass-transition temperatures to the corresponding experimental values. Tg depicts the phase transition in elastomers and substantially affects various physical properties of polymers, and hence the reproducibility of Tg becomes very crucial from a thermodynamic point of view. Such validation using Tg also evaluates the ability of these force fields to be used for advanced materials like rubber nanocomposites, where Tg is greatly affected by the presence of fillers. We have calculated Tg for a total of eight systems, featuring all-atom and united-atom models of cis- and trans-PI and -PB, which are the major constituents of natural and synthetic rubber. Tuning and refinement of the force fields has also been done using quantum-chemical calculations to obtain desirable density and Tg. Thus, a set of properly validated force fields, capable of reproducing various macroscopic properties of rubber, has been provided. A novel polymer equilibration protocol, involving potential energy convergence as the equilibration criterion, has been proposed. We demonstrate that not only macroscopic polymer properties like density, thermal expansion coefficient, and Tg but also local structural characteristics like end-to-end distance (R) and radius of gyration (Rg) and mechanical properties like bulk modulus have also been equilibrated using our strategy. Complete decay of end-to-end vector autocorrelation function with time also supports proper equilibration using our strategy. PMID:26836395

  18. Validation of Force Fields of Rubber through Glass-Transition Temperature Calculation by Microsecond Atomic-Scale Molecular Dynamics Simulation.

    PubMed

    Sharma, Pragati; Roy, Sudip; Karimi-Varzaneh, Hossein Ali

    2016-02-25

    Microsecond atomic-scale molecular dynamics simulation has been employed to calculate the glass-transition temperature (Tg) of cis- and trans-1,4-polybutadiene (PB) and 1,4-polyisoprene (PI). Both all-atomistic and united-atom models have been simulated using force fields, already available in literature. The accuracy of these decade old force fields has been tested by comparing calculated glass-transition temperatures to the corresponding experimental values. Tg depicts the phase transition in elastomers and substantially affects various physical properties of polymers, and hence the reproducibility of Tg becomes very crucial from a thermodynamic point of view. Such validation using Tg also evaluates the ability of these force fields to be used for advanced materials like rubber nanocomposites, where Tg is greatly affected by the presence of fillers. We have calculated Tg for a total of eight systems, featuring all-atom and united-atom models of cis- and trans-PI and -PB, which are the major constituents of natural and synthetic rubber. Tuning and refinement of the force fields has also been done using quantum-chemical calculations to obtain desirable density and Tg. Thus, a set of properly validated force fields, capable of reproducing various macroscopic properties of rubber, has been provided. A novel polymer equilibration protocol, involving potential energy convergence as the equilibration criterion, has been proposed. We demonstrate that not only macroscopic polymer properties like density, thermal expansion coefficient, and Tg but also local structural characteristics like end-to-end distance (R) and radius of gyration (Rg) and mechanical properties like bulk modulus have also been equilibrated using our strategy. Complete decay of end-to-end vector autocorrelation function with time also supports proper equilibration using our strategy.

  19. Investigations of α-helix↔β-sheet transition pathways in a miniprotein using the finite-temperature string method

    SciTech Connect

    Ovchinnikov, Victor; Karplus, Martin

    2014-05-07

    A parallel implementation of the finite-temperature string method is described, which takes into account the invariance of coordinates with respect to rigid-body motions. The method is applied to the complex α-helix↔β-sheet transition in a β-hairpin miniprotein in implicit solvent, which exhibits much of the complexity of conformational changes in proteins. Two transition paths are considered, one derived from a linear interpolant between the endpoint structures and the other derived from a targeted dynamics simulation. Two methods for computing the conformational free energy (FE) along the string are compared, a restrained method, and a tessellation method introduced by E. Vanden-Eijnden and M. Venturoli [J. Chem. Phys. 130, 194103 (2009)]. It is found that obtaining meaningful free energy profiles using the present atom-based coordinates requires restricting sampling to a vicinity of the converged path, where the hyperplanar approximation to the isocommittor surface is sufficiently accurate. This sampling restriction can be easily achieved using restraints or constraints. The endpoint FE differences computed from the FE profiles are validated by comparison with previous calculations using a path-independent confinement method. The FE profiles are decomposed into the enthalpic and entropic contributions, and it is shown that the entropy difference contribution can be as large as 10 kcal/mol for intermediate regions along the path, compared to 15–20 kcal/mol for the enthalpy contribution. This result demonstrates that enthalpic barriers for transitions are offset by entropic contributions arising from the existence of different paths across a barrier. The possibility of using systematically coarse-grained representations of amino acids, in the spirit of multiple interaction site residue models, is proposed as a means to avoid ad hoc sampling restrictions to narrow transition tubes.

  20. Investigations of α-helix↔β-sheet transition pathways in a miniprotein using the finite-temperature string method

    PubMed Central

    Ovchinnikov, Victor; Karplus, Martin

    2014-01-01

    A parallel implementation of the finite-temperature string method is described, which takes into account the invariance of coordinates with respect to rigid-body motions. The method is applied to the complex α-helix↔β-sheet transition in a β-hairpin miniprotein in implicit solvent, which exhibits much of the complexity of conformational changes in proteins. Two transition paths are considered, one derived from a linear interpolant between the endpoint structures and the other derived from a targeted dynamics simulation. Two methods for computing the conformational free energy (FE) along the string are compared, a restrained method, and a tessellation method introduced by E. Vanden-Eijnden and M. Venturoli [J. Chem. Phys. 130, 194103 (2009)]. It is found that obtaining meaningful free energy profiles using the present atom-based coordinates requires restricting sampling to a vicinity of the converged path, where the hyperplanar approximation to the isocommittor surface is sufficiently accurate. This sampling restriction can be easily achieved using restraints or constraints. The endpoint FE differences computed from the FE profiles are validated by comparison with previous calculations using a path-independent confinement method. The FE profiles are decomposed into the enthalpic and entropic contributions, and it is shown that the entropy difference contribution can be as large as 10 kcal/mol for intermediate regions along the path, compared to 15–20 kcal/mol for the enthalpy contribution. This result demonstrates that enthalpic barriers for transitions are offset by entropic contributions arising from the existence of different paths across a barrier. The possibility of using systematically coarse-grained representations of amino acids, in the spirit of multiple interaction site residue models, is proposed as a means to avoid ad hoc sampling restrictions to narrow transition tubes. PMID:24811667

  1. High-temperature thermochemistry of transition metal borides, silicides and related compounds. Final report

    SciTech Connect

    Klemppa, Ole J.

    2000-10-01

    Earlier this year in collaboration with Dr. Susan V. Meschel we prepared a major review paper which gives a comprehensive summary of what our laboratory has accomplished with support from DOE. This paper is No.43 in the List of Publications provided. It was presented to TMS at its National Meeting in Nashville, TN last March. A copy of the manuscript of this paper was recently mailed to DOE. It has been submitted for publication in Journal of Alloys and Compounds. This review paper summarizes our observed trends in the enthalpies of formation of TR-X and RE-X compounds (where X is a IIIB or IVB element) in their dependence of the atomic number of the transition metal (TR) and the lanthanide metal (RE). In this paper our measured enthalpies of formation for each alloy family are compared for the 3d, 4d and 5d transition metal elements. We also compare our experimental results with predicted values based on Miedema's semi-empirical model. Data are presented for the carbides, silicides, germanides and stannides in Group IVB, and for the borides and aluminides in Group IIIB. During the past year (1999-2000) we have extended our work to compounds of the 3d, 4d and 5d elements with gallium (see papers No.40, No.41, and No.45 in the List of Publications). Fig. 1 (taken from No.45) presents a systematic picture of our experimental values for the most exothermic gallide compounds formed with the transition elements. This figure is characteristic of the other systematic pictures which we have found for the two other IIIB elements which we have studied and for the four IVB elements. These figures are all presented in Ref. No.43. This paper also illustrates how the enthalpy of formation of compounds of the IIIB and IVB elements with the lanthanide elements (with the exception of Pm, Eu and Yb) depend on the atomic number of RE. Finally our results for the RE-X compounds are compared with the predictions of Gschneidner (K.A. Gschneidner, Jr., J. Less Common Metals 17, 1

  2. Thermodynamic and spectroscopic analysis of the conformational transition of poly(vinyl alcohol) by temperature-dependent FTIR

    NASA Astrophysics Data System (ADS)

    Han, Shan; Luan, Ye-Mei; Pang, Shu-Feng; Zhang, Yun-Hong

    2015-03-01

    The conformational change of poly(vinyl alcohol) has been studied by Fourier transform infrared spectroscopy at various temperatures in the 4000-400 cm-1 region. The molecular motion and the trans/gauche content are sensitive to the Csbnd H, Csbnd C stretching modes. FTIR spectra show that the I2920/I2849 decreases from 1.84 to 1.0 with increasing temperature, companying the decrease in I1047/I1095 from 0.78 to 0.58, implying the conformational transition from trans to gauche in alkyl chain. Based on the van't Hoff relation, the enthalpies and entropies have been calculated in different temperatures, which are 4.61 kJ mol-1 and 15.23 J mol-1 K-1, respectively, in the region of 80-140 °C. From the Cdbnd O stretching mode and Osbnd H band, it can be concluded that the intermolecular hydrogen bonds decrease owing to elevating temperature, which leads to more gauche conformers.

  3. Molecular dynamics simulations to calculate glass transition temperature and elastic constants of novel polyethers.

    PubMed

    Sarangapani, Radhakrishnan; Reddy, Sreekantha T; Sikder, Arun K

    2015-04-01

    Molecular dynamics simulations studies are carried out on hydroxyl terminated polyethers that are useful in energetic polymeric binder applications. Energetic polymers derived from oxetanes with heterocyclic side chains with different energetic substituents are designed and simulated under the ensembles of constant particle number, pressure, temperature (NPT) and constant particle number, volume, temperature (NVT). Specific volume of different amorphous polymeric models is predicted using NPT-MD simulations as a function of temperature. Plots of specific volume versus temperature exhibited a characteristic change in slope when amorphous systems change from glassy to rubbery state. Several material properties such as Young's, shear, and bulk modulus, Poisson's ratio, etc. are predicted from equilibrated structures and established the structure-property relations among designed polymers. Energetic performance parameters of these polymers are calculated and results reveal that the performance of the designed polymers is comparable to the benchmark energetic polymers like polyNIMMO, polyAMMO and polyBAMO. Overall, it is worthy remark that this molecular simulations study on novel energetic polyethers provides a good guidance on mastering the design principles and allows us to design novel polymers of tailored properties.

  4. Preparation and phase transition behaviors of temperature-responsive 3-butoxy-2-hydroxypropyl hydroxyethyl celluloses.

    PubMed

    Tian, Ye; Ju, Benzhi; Zhang, Shufen; Duan, Xiuling; Dong, Daopeng

    2015-01-01

    2-Hydroxy-3-butoxypropyl hydroxyethyl celluloses (HBPEC), which are thermoresponsive polymers, are prepared by grafting butyl glycidyl ether onto hydroxyethyl cellulose. The effects of several factors on the cloud point (Tc) of the HBPEC are also investigated. The Tc of HBPEC can be tuned to a ranging from 17.0 to 43.0 °C by changing the molar substitution of hydrophobic groups. Increasing the concentration of HBPEC leads to a faster phase transition as well as a corresponding linear decrease in the Tc. A series of salts with common anions or cations are used to investigate the effects of specific anions or cations on the Tc of HBPEC aqueous solutions. It is discovered that the Tc of HBPEC is largely influenced by the variation of cation identity and concentration. Plotting Tc as a function of cation activity shows that the Tc can be classified by charge density. PMID:26230225

  5. Room temperature magneto-structural transition in Al for Sn substituted Ni-Mn-Sn melt spun ribbons

    NASA Astrophysics Data System (ADS)

    Maziarz, W.; Czaja, P.; Szczerba, M. J.; Przewoźnik, J.; Kapusta, C.; Żywczak, A.; Stobiecki, T.; Cesari, E.; Dutkiewicz, J.

    2013-12-01

    Martensitic and magnetic transformations in Ni48Mn39.5Sn12.5-xAlx (x=0, 1, 2, 3) Heusler alloy ribbons were investigated. It is demonstrated that both magnetic and structural transformations occur in all of the studied samples. It is also shown that substitution of Sn with Al causes the martensitic transformation (MT) and the reverse martensitic transformation (RMT) temperatures to increase to room temperature (ΔTMT=49 K; ΔTRMT=43 K), whereas the Curie temperature of martensite TCM decreases (ΔT=36 K) and the Curie temperature of austenite TCA remains practically insensitive to Al introduction. This then allows to tune TCA and the MT temperature leading to their coincidence at ambient temperature. The austenite phase with the L21 type structure has been identified to exist in all the samples regardless of composition. On the other hand the structure of martensite has been shown to be sensitive to composition. It has been determined as the 10 M martensite with (32¯) stacking sequence in Al free samples and the 4O martensite with the stacking periodicity (31¯) in Al containing samples. In addition, the splitting of the field cooling (FC) and the field heating (FH) thermo-magnetic curves at low (50 Oe) magnetic field and below the TCM has been attributed to intermartensitic transition. The application of large magnetic field (50 kOe) has shown the existence of two distinct ferromagnetic states with a considerable hysteresis loop. The properties of these materials make them promising for magnetocaloric applications.

  6. Low temperature transformation from antiferromagnetic to ferromagnetic order in impurity system Ge:As near the insulator-metal phase transition

    SciTech Connect

    Veinger, A. I.; Zabrodskii, A. G.; Tisnek, T. V.; Goloshchapov, S. I.; Semenikhin, P. V.; Makarova, T. L.

    2014-08-20

    The low-temperature transformation from antiparallel to parallel spin orientation in a nonmagnetic compensated system Ge:As semiconductor near the metal-insulator phase transition has been experimentally observed. This effect is manifested in the temperature dependences of the impurity magnetic susceptibility obtained by integration of the spin resonance absorption line. These dependences show that the spin density falls in the medium temperature range (10-100 K) and grows at low temperatures. The effect is confirmed by the specific temperature features of the g-factor and inverse magnetic susceptibility. As the relative content of a compensating impurity (gallium) is made lower than 0.7, the transition temperature begins to decrease and, at a degree of compensation < 0.3, falls outside the temperature range under study (i.e., below 2 K)

  7. Phase selective synthesis of quantum cutting nanophosphors and the observation of a spontaneous room temperature phase transition

    NASA Astrophysics Data System (ADS)

    Ghosh, Pushpal; Mudring, Anja-Verena

    2016-04-01

    Oxygen-free Eu3+-doped NaGdF4 nanocrystals with high quantum cutting efficiency are accessible at low temperatures (room temperature to 80 °C) using task-specific ionic liquids (ILs) as structure directing agents and only water as solvent. Selective tuning of the shape, morphology and, most importantly, the crystal phase of the host lattice is achieved by changing the alkyl side length, the H-bonding capabilities and the concentration of 1-alkyl-3-methylimidazolium bromide ILs, [Cnmim]Br. When using [C2mim]Br, hexagonal NaGdF4 nanoparticles are obtained. In the case of methylimidazolium bromides with longer pendant alkyl chains such as butyl (C4), octyl (C8) or decyl (C10), extremely small nanoparticles of the cubic polymorph form, which then convert even at room temperature (RT) to the thermodynamically favored hexagonal modification. To the best of our knowledge, this kind of spontaneous phase transition is not yet reported. The hexagonal nanomaterial shows a substantial quantum cutting efficiency (154%) whilst in the cubic material, the effect is negligible (107%). The easy yet highly phase selective green synthesis of the materials promises large scale industrial application in environmentally benign energy efficient lighting.Oxygen-free Eu3+-doped NaGdF4 nanocrystals with high quantum cutting efficiency are accessible at low temperatures (room temperature to 80 °C) using task-specific ionic liquids (ILs) as structure directing agents and only water as solvent. Selective tuning of the shape, morphology and, most importantly, the crystal phase of the host lattice is achieved by changing the alkyl side length, the H-bonding capabilities and the concentration of 1-alkyl-3-methylimidazolium bromide ILs, [Cnmim]Br. When using [C2mim]Br, hexagonal NaGdF4 nanoparticles are obtained. In the case of methylimidazolium bromides with longer pendant alkyl chains such as butyl (C4), octyl (C8) or decyl (C10), extremely small nanoparticles of the cubic polymorph form, which

  8. Soy Sauce Residue Oil Extracted by a Novel Continuous Phase Transition Extraction under Low Temperature and Its Refining Process.

    PubMed

    Zhao, Lichao; Zhang, Yong; He, Liping; Dai, Weijie; Lai, Yingyi; Yao, Xueyi; Cao, Yong

    2014-03-28

    On the basis of previous single-factor experiments, extraction parameters of soy sauce residue (SSR) oil extracted using a self-developed continuous phase transition extraction method at low temperature was optimized using the response surface methodology. The established optimal conditions for maximum oil yield were n-butane solvent, 0.5 MPa extraction pressure, 45 °C temperature, 62 min extraction time, and 45 mesh raw material granularity. Under these conditions, the actual yield was 28.43% ± 0.17%, which is relatively close to the predicted yield. Meanwhile, isoflavone was extracted from defatted SSR using the same method, but the parameters and solvent used were altered. The new solvent was 95% (v/v) ethanol, and extraction was performed under 1.0 MPa at 60 °C for 90 min. The extracted isoflavones, with 0.18% ± 0.012% yield, mainly comprised daidzein and genistein, two kinds of aglycones. The novel continuous phase transition extraction under low temperature could provide favorable conditions for the extraction of nonpolar or strongly polar substances. The oil physicochemical properties and fatty acids compositions were analyzed. Results showed that the main drawback of the crude oil was the excess of acid value (AV, 63.9 ± 0.1 mg KOH/g) and peroxide value (POV, 9.05 ± 0.3 mmol/kg), compared with that of normal soybean oil. However, through molecular distillation, AV and POV dropped to 1.78 ± 0.12 mg KOH/g and 5.9 ± 0.08 mmol/kg, respectively. This refined oil may be used as feedstuff oil. PMID:24650165

  9. Tuning the Transition Temperature of WSix Alloys for Use in Cryogenic Microcalorimeters

    NASA Astrophysics Data System (ADS)

    Cecil, T.; Gades, L.; Madden, T.; Yan, D.; Miceli, A.

    2016-07-01

    Microwave kinetic inductance detectors (MKID) provide a pathway to highly multiplexed, high-resolution, detectors. Over the past several years we have introduced the concept of the thermal kinetic inductance detector (TKID), which operates as a microcalorimeter. As with other microcalorimeters, the thermal noise of a TKID is reduced when the operating temperature is decreased. However, because the sensitivity of a TKID decreases as the operating temperature drops below 20 % of T_C, the T_C of the resonator material must be tuned to match the desired operating temperature. We have investigated the WSix alloy system as a material for these detectors. By co-sputtering from a Si and W2Si target, we have deposited WSix films with a tunable T_C that ranges from 5 K down to 500 mK. These films provide a large kinetic inductance fraction and relatively low noise levels. We provide results of these studies showing the T_C, resistivity, quality factors, and noise as a function of deposition conditions. These results show that WSix is a good candidate for TKIDs.

  10. Double metamagnetic transition in Sr4Ru3O10 investigated by low temperature magnetization measurements

    NASA Astrophysics Data System (ADS)

    Weickert, Dagmar Franziska; Civale, Leonardo; Jaime, Marcelo; Maiorov, Boris; Movshovich, Roman; Fittipaldi, R.; Granata, V.; Vecchione, A.; Tan, Teng; Salamon, Myron

    2015-03-01

    We report a study of the magnetization of the n =3 member of the Srn+1RunO3n+1 Ruddlesden-Popper series down to 3He temperatures. Sr4Ru3O10 exhibits ferromagnetism below 105 K with magnetic moments aligned along the crystallographic c-direction in the tetragonal crystal structure. Metamagnetism is observed at about 2 T below 50 K when a magnetic field is applied in the ab- plane. A recent study on high quality samples revealed that the metamagnetism has a substructure. We extend the studies to very low temperatures and found i) a clear double peak in dM/dH, ii) that the metamagnetism is accompanied by a reduction of the magnetic moment and iii) no further splitting of the metamagnetic anomalies to the lowest temperatures of 0.46 K. Furthermore, the measurements indicate a shift of both metamagnetic signatures to higher fields by rotating from H//ab to H / / c . We will discuss the phase diagram and possible ordered states. Research at LANL (magnetometry and data analysis) was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

  11. Diversity of electronic transitions and photoluminescence properties of p-type cuprous oxide films: A temperature-dependent spectral transmittance study

    SciTech Connect

    Yu, W. L. E-mail: zghu@ee.ecnu.edu.cn; Lin, Y. Z.; Zhu, X. W.; Cai, S. S.; Chen, L. L.; Shao, H. H.; Hu, Z. G. E-mail: zghu@ee.ecnu.edu.cn; Han, M. J.

    2015-01-28

    Cuprous oxide films have been deposited on quartz substrates by a sol-gel method under various annealing temperatures. The X-ray diffraction analysis and Raman scattering show that all the films are of pure Cu{sub 2}O phase. From comparison of photoluminescence with 488 and 325 nm laser excitations, the electronic transition energies and intensities present the annealing-temperature dependent behavior. The electronic band structures of the Cu{sub 2}O film annealed at 800 °C, especially for the contribution of exciton series and high energy transitions, have been investigated by temperature dependent transmittance. The extracted refraction index and the high frequency dielectric constant both abruptly decrease until the temperature rises up to 100 K. Six transitions can be clearly identified and the red shift trend of E{sub o3}-E{sub o5} transition energies with increasing the temperature can be found. Moreover, the anomalous behavior takes place at about 200 K from the E{sub o6} transition. The singularities indicate that the change in the crystalline and electronic band structure occurs as the temperature near 100 K and 200 K for the film.

  12. A novel powder sample holder for the determination of glass transition temperatures by DMA.

    PubMed

    Mahlin, Denny; Wood, John; Hawkins, Nicholas; Mahey, Jas; Royall, Paul G

    2009-04-17

    The use of a new sample holder for dynamic mechanical analysis (DMA) as a means to characterise the Tg of powdered hydroxypropyl methyl cellulose (HPMC) has been investigated. A sample holder was constructed consisting of a rectangular stainless steel container and a lid engineered to fit exactly within the walls of the container when clamped within a TA instruments Q800 DMA in dual cantilever configuration. Physical mixtures of HPMC (E4M) and aluminium oxide powders were placed in the holder and subjected to oscillating strains (1 Hz, 10 Hz and 100 Hz) whilst heated at 3 degrees C/min. The storage and loss modulus signals showed a large reduction in the mechanical strength above 150 degrees C which was attributed to a glass transition. Optimal experimental parameters were determined using a design of experiment procedure and by analysing the frequency dependence of Tg in Arrhenius plots. The parameters were a clamping pressure of 62 kPa, a mass ratio of 0.2 HPMC in aluminium oxide, and a loading mass of either 120 mg or 180 mg. At 1 Hz, a Tg of 177+/-1.2 degrees C (n=6) for powdered HPMC was obtained. In conclusion, the new powder holder was capable of measuring the Tg of pharmaceutical powders and a simple optimization protocol was established, useful in further applications of the DMA powder holder. PMID:19167475

  13. Techniques for Surface-Temperature Measurements and Transition Detection on Projectiles at Hypersonic Velocities--Status Report No. 2

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    The latest developments in a research effort to advance techniques for measuring surface temperatures and heat fluxes and determining transition locations on projectiles in hypersonic free flight in a ballistic range are described. Spherical and hemispherical titanium projectiles were launched at muzzle velocities of 4.6-5.8 km/sec into air and nitrogen at pressures of 95-380 Torr. Hemisphere models with diameters of 2.22 cm had maximum pitch and yaw angles of 5.5-8 degrees and 4.7-7 degrees, depending on whether they were launched using an evacuated launch tube or not. Hemisphere models with diameters of 2.86 cm had maximum pitch and yaw angles of 2.0-2.5 degrees. Three intensified-charge-coupled-device (ICCD) cameras with wavelength sensitivity ranges of 480-870 nm (as well as one infrared camera with a wavelength sensitivity range of 3 to 5 microns), were used to obtain images of the projectiles in flight. Helium plumes were used to remove the radiating gas cap around the projectiles at the locations where ICCD camera images were taken. ICCD and infrared (IR) camera images of titanium hemisphere projectiles at velocities of 4.0-4.4 km/sec are presented as well as preliminary temperature data for these projectiles. Comparisons were made of normalized temperature data for shots at approx.190 Torr in air and nitrogen and with and without the launch tube evacuated. Shots into nitrogen had temperatures 6% lower than those into air. Evacuation of the launch tube was also found to lower the projectile temperatures by approx.6%.

  14. High-temperature superfluidity of the two-component Bose gas in a transition metal dichalcogenide bilayer

    NASA Astrophysics Data System (ADS)

    Berman, Oleg L.; Kezerashvili, Roman Ya.

    2016-06-01

    The high-temperature superfluidity of two-dimensional dipolar excitons in two parallel transition metal dichalcogenide (TMDC) layers is predicted. We study Bose-Einstein condensation in the two-component system of dipolar A and B excitons. The effective mass, energy spectrum of the collective excitations, the sound velocity, and critical temperature are obtained for different TMDC materials. It is shown that in the Bogoliubov approximation, the sound velocity in the two-component dilute exciton Bose gas is always larger than in any one-component exciton system. The difference between the sound velocities for two-component and one-component dilute gases is caused by the fact that the sound velocity for a two-component system depends on the reduced mass of A and B excitons, which is always smaller than the individual mass of A or B exciton. Due to this fact, the critical temperature Tc for superfluidity for the two-component exciton system in a TMDC bilayer is about one order of magnitude higher than Tc in any one-component exciton system. We propose to observe the superfluidity of two-dimensional dipolar excitons in two parallel TMDC layers, which causes two opposite superconducting currents in each TMDC layer.

  15. Correlation Of Ortho-Positronium Intensity With Doppler Broadening For Rubber Above And Below The Glass Transition Temperature

    SciTech Connect

    Towry, Amanda; Quarles, C. A.

    2011-06-01

    Previous research has demonstrated a correlation between the Doppler broadening S parameter and the intensity of the ortho-positronium lifetime component in polymers that depends on the composition of the polymer. On the other hand, rubber polymers do not show this correlation and behave more like liquids for which the S parameter is essentially independent of the ortho-positronium intensity. The bubble model has been suggested as an explanation of the lack of correlation in analogy with liquids, but the bubble model applied to rubber is controversial. There are two important differences between the rubber and the polymers samples: first, the rubber samples at room temperature were all above the glass transition temperature (T{sub G}). Second, the rubber samples all contained sulfur and were vulcanized. These differences were investigated by first measuring the S parameter for six rubber samples below T{sub G} where the bubble model would not be expected to work. Second, raw rubber samples that did not contain any sulfur and were unvulcanized were studied at room temperature. The results show that the lack of correlation between the S parameter and the ortho-positronium intensity previously observed for vulcanized rubber is due to the inhibition of positronium formation by the sulfur in the vulcanized rubber samples rather than to the rubber being above T{sub G}.

  16. Sorption isotherms, thermodynamic properties and glass transition temperature of mucilage extracted from chia seeds (Salvia hispanica L.).

    PubMed

    Velázquez-Gutiérrez, Sandra Karina; Figueira, Ana Cristina; Rodríguez-Huezo, María Eva; Román-Guerrero, Angélica; Carrillo-Navas, Hector; Pérez-Alonso, César

    2015-05-01

    Freeze-dried chia mucilage adsorption isotherms were determined at 25, 35 and 40°C and fitted with the Guggenheim-Anderson-de Boer model. The integral thermodynamic properties (enthalpy and entropy) were estimated with the Clausius-Clapeyron equation. Pore radius of the mucilage, calculated with the Kelvin equation, varied from 0.87 to 6.44 nm in the temperature range studied. The point of maximum stability (minimum integral entropy) ranged between 7.56 and 7.63kg H2O per 100 kg of dry solids (d.s.) (water activity of 0.34-0.53). Enthalpy-entropy compensation for the mucilage showed two isokinetic temperatures: (i) one occurring at low moisture contents (0-7.56 kg H2O per 100 kg d.s.), controlled by changes in water entropy; and (ii) another happening in the moisture interval of 7.56-24 kg H2O per 100 kg d.s. and was enthalpy driven. The glass transition temperature Tg of the mucilage fluctuated between 42.93 and 57.93°C.

  17. Sorption isotherms, thermodynamic properties and glass transition temperature of mucilage extracted from chia seeds (Salvia hispanica L.).

    PubMed

    Velázquez-Gutiérrez, Sandra Karina; Figueira, Ana Cristina; Rodríguez-Huezo, María Eva; Román-Guerrero, Angélica; Carrillo-Navas, Hector; Pérez-Alonso, César

    2015-05-01

    Freeze-dried chia mucilage adsorption isotherms were determined at 25, 35 and 40°C and fitted with the Guggenheim-Anderson-de Boer model. The integral thermodynamic properties (enthalpy and entropy) were estimated with the Clausius-Clapeyron equation. Pore radius of the mucilage, calculated with the Kelvin equation, varied from 0.87 to 6.44 nm in the temperature range studied. The point of maximum stability (minimum integral entropy) ranged between 7.56 and 7.63kg H2O per 100 kg of dry solids (d.s.) (water activity of 0.34-0.53). Enthalpy-entropy compensation for the mucilage showed two isokinetic temperatures: (i) one occurring at low moisture contents (0-7.56 kg H2O per 100 kg d.s.), controlled by changes in water entropy; and (ii) another happening in the moisture interval of 7.56-24 kg H2O per 100 kg d.s. and was enthalpy driven. The glass transition temperature Tg of the mucilage fluctuated between 42.93 and 57.93°C. PMID:25659716

  18. High temperature thermoelectric properties of Zr and Hf based transition metal dichalcogenides: A first principles study

    SciTech Connect

    Yumnam, George; Pandey, Tribhuwan; Singh, Abhishek K.

    2015-12-21

    We investigate the electronic and thermal transport properties of bulk MX{sub 2} compounds (M = Zr, Hf and X = S, Se) by first-principles calculations and semi-classical Boltzmann transport theory. The band structure shows the confinement of heavy and light bands along the out of plane and in-plane directions, respectively. This results in high electrical conductivity (σ) and large thermopower leading to a high power factor (S{sup 2}σ) for moderate n-type doping. The phonon dispersion demonstrates low frequency flat acoustical modes, which results in low group velocities (v{sub g}). Consequently, lowering the lattice thermal conductivity (κ{sub latt}) below 2 W/m K. Low κ{sub latt} combined with high power factor results in ZT > 0.8 for all the bulk MX{sub 2} compounds at high temperature of 1200 K. In particular, the ZT{sub max} of HfSe{sub 2} exceeds 1 at 1400 K. Our results show that Hf/Zr based dichalcogenides are very promising for high temperature thermoelectric application.

  19. Structural phase transition of as-synthesized Sr-Mn nanoferrites by annealing temperature

    NASA Astrophysics Data System (ADS)

    Amer, M. A.; Meaz, T. M.; Attalah, S. S.; Ghoneim, A. I.

    2015-11-01

    The Sr0.2Mn0.8Fe2O4 nanoparticle ferrites were synthesized by the co-precipitation method and annealed at different temperatures T. XRD, TEM, FT-IR, VSM and Mössbauer techniques were used to characterize the samples. This study proved that the structural phase of nanoferrites was transformed from cubic spinel for T≤500 °C to Z-type hexagonal for T≥700 °C. The structural transformation was attributed to Jahn-Teller effect of the Mn3+ ions and/or atomic disorder existed in the crystal lattice. The obtained spectra and parameters for the samples were affected by the transformation process. The lattice constant a showed a splitting to a and c for T>500 °C. The lattice constant c, grain and crystallite size R, strain, octahedral B-site band position and force constant, Debye temperature, coercivity Hc, remnant magnetization, squareness and magnetic moment, spontaneous magnetization and hyperfine magnetic fields showed increase against T. The lattice constant a, distortion and dislocation parameters, specific surface area, tetrahedral A-site band position and force constant, threshold frequency, Young's and bulk moduli, saturation magnetization Ms, area ratio of B-/A-sites, A-site line width were decreased with T. Experimental and theoretical densities, porosity, Poison ratio, stiffness constants, rigidity modulus, B-site line width and spontaneous magnetization showed dependence on T, whereas Ms and Hc proved dependence on R.

  20. Probing the structural changes in the phase transitions of a Bi{sub 2}MoO{sub 6} catalyst: The nature of the intermediate-temperature phase

    SciTech Connect

    Sankar, G.; Roberts, M.A.; Thomas, J.M.

    1995-10-01

    The nature of the phase transitions of Bi{sub 2}MoO{sub 6} has been investigated by the combined use of X-ray diffraction and X-ray absorption spectroscopy. The distorted MoO{sub 6} octahedra in the low-temperature form are shown to undergo further distortion in the intermediate-temperature form before transforming to MoO{sub 4} tetrahedra in the high-temperature phase.

  1. Dielectric Dispersion, Diffuse Phase Transition, and Electrical Properties of BCT-BZT Ceramics Sintered at a Low-Temperature

    NASA Astrophysics Data System (ADS)

    Tian, Yongshang; Gong, Yansheng; Meng, Dawei; Li, Yuanjian; Kuang, Boya

    2015-08-01

    Lead-free ceramics 0.50Ba0.9Ca0.1TiO3-0.50BaTi1- x Zr x O3 (BCT-BZT) were prepared via sintering BCT and BZT nanoparticles, which were synthesized using a modified Pechini polymeric precursor method, at a low temperature of 1260°C. The relative densities of the ceramics prepared with different zirconium contents ( x) were all above 95.3%, reaching a maximum of 97% when x = 0.08. X-ray diffraction results confirmed the onset of phase transformation from orthorhombic to rhombohedral symmetry with increasing zirconium contents, and the polymorphic phase transition was observed at x = 0.10. The dielectric dispersion, diffuse phase transition (DPT), and relaxor-like ferroelectric characteristics as a function of zirconium content were thoroughly studied. Optimum physical properties, remnant polarization ( P r) = 16.4 μC/cm2, piezoelectric constant ( d 33) = ~240 pC/N, and electromechanical coupling factor ( k p) = 0.22, were obtained at x = 0.10. The findings of the current DPT behavior study of BCT-BZT ceramics are believed to be insightful to the development of ferroelectric materials.

  2. Differential scanning calorimetric evaluation of human meibomian gland secretions and model lipid mixtures: transition temperatures and cooperativity of melting

    PubMed Central

    Lu, Hua; Wojtowicz, Jadwiga C.; Butovich, Igor A.

    2013-01-01

    Meibomian gland secretions (or meibum) are produced by holocrine meibomian glands and are secreted in melted form onto the ocular surface of humans and animals to form a protective tear film lipid layer (TFLL). Its protective effect strongly depends on the composition and, hence, thermotropic behavior of meibum. The goal of our study was to quantitatively evaluate the melting characteristics of human meibum and model lipid mixtures using differential scanning microcalorimetry. Standard calorimetric parameters, e.g. changes in calorimetric enthalpy, transition temperatures T(m), cooperativity of melting etc. were assessed. We found that thermotropic behavior of meibum resembled that of relatively simple mixtures of unsaturated wax esters, but showed a lower change in calorimetric enthalpy, which can be indicative of a looser packing of lipids in meibum compared with pure standards and their simple mixtures. The cooperativity of melting of meibomian lipids was comparable to that of an equimolar mixture of four oleic-acid based wax esters. We demonstrated that the phase transitions in meibum start at about 10 to 15 °C and end at 35-36 °C, with T(m) being about 30 °C. The highly asymmetrical shape of the thermotropic peak of meibum is important for the physiology and biophysics of TFLL. PMID:23578711

  3. High-temperature desulfurization of gasifier effluents with rare earth and rare earth/transition metal oxides

    SciTech Connect

    Dooley, Kerry M.; Kalakota, Vikram; Adusumilli, Sumana

    2011-02-11

    We have improved the application of mixed rare-earth oxides (REOs) as hot gas desulfurization adsorbents by impregnating them on stable high surface area supports and by the inclusion of certain transition metal oxides. We report comparative desulfurization experiments at high temperature (900 K) using a synthetic biomass gasifier effluent containing 0.1 vol % H2S, along with H2, CO2, and water. More complex REO sorbents outperform the simpler CeO2/La2O3 mixtures, in some cases significantly. Supporting REOs on Al2O3 (~20 wt % REO) or ZrO2 actually increased the sulfur capacities found after several cycles on a total weight basis. Another major increase in sulfur capacity took place when MnOx or FeOx is incorporated. Apparently most of the Mn or Fe is dispersed on or near the surface of the mixed REOs because the capacities with REOs greatly exceeded those of Al2O3-supported MnOx or FeOx alone at these conditions. In contrast, incorporating Cu has little effect on sulfur adsorption capacities. Both the REO and transition metal/REO adsorbents could be regenerated completely using air for at least five repetitive cycles.

  4. Rheological transition in mantle convection with a composite temperature-dependent, non-Newtonian and Newtonian rheology

    NASA Technical Reports Server (NTRS)

    Van Den Berg, Arie P.; Yuen, David A.; Van Keken, Peter E.

    1995-01-01

    Numerical simulations of mantle convection with a composite temperature-dependent, Newtonian and non-Newtonian creep law have revealed a transition in the dominant creep mechanism with the increasing vigour of convection. Newtonian creep is found to dominate in the low Rayleigh number regime. With sufficiently high effective Rayleigh number, the overall creep mechanism in the convective flow becomes non-Newtonian. The transitional Rayleigh number increases strongly with the activation energy. These results would suggest a scenario that in the early epochs of Earth the flow in the mantle would have been governed by non-Newtonian rheology and would have exhibited both strong spatial and temporal fluctuations. With time the flow mechanism would behave like a Newtonian fluid and would have a different time-dependent character. In time-dependent Newtonian-dominated flows there are still localized features with distinctly non-Newtonian character. Our analysis of the relative contributions to the lateral viscosity field supports the idea that the inference of the nature of lateral viscosity heterogeneities by seismic tomography may be strongly contaminated by the dominant non-Newtonian contributions to the total lateral viscosity field.

  5. Flash X-Ray Diffraction System for Fast, Single-PulseTemperature and Phase Transition Measurements (Pre-print)

    SciTech Connect

    Michael J. Madlener; Dane V. Morgan

    2007-06-12

    A new, fast, single-pulse diagnostic for determining phase transitions and measuring the bulk temperature of polycrystalline metal objects has been developed. The diagnostic consists of a 37-stage Marx bank with a cable-coupled X-ray diode that produces a 35-ns pulse of mostly 0.71-{angstrom} monochromatic X rays and a P-43 fluor coupled to a cooled, charge-coupled device camera by a coherent fiber-optic bundle for detection of scattered X rays. The X-ray beam is collimated to a 1{sup o} divergence in the scattering plane with the combination of a 1.5-mm tungsten pinhole and a 1.5-mm-diameter molybdenum anode. X rays are produced by a high-energy electron beam transiting inward from the cathode to the anode in a needle-and-washer configuration. The anode's characteristic K-{alpha} X-ray emission lines are utilized for this diffraction system. The X-ray anode is heavily shielded in all directions other than the collimated beam. The X-ray diode has a sealed reentrant system, allowing X rays to be produced inside a vacuum containment vessel, close to the sample under study.

  6. Low-Temperature Synthesis of Tunable Mesoporous Crystalline Transition Metal Oxides and Applications as Au Catalyst Supports

    SciTech Connect

    Wang, Donghai; Ma, Zhen; Dai, Sheng; Liu, Jun; Nie, Zimin; Engelhard, Mark H.; Huo, Qisheng; Wang, Chong M.; Kou, Rong

    2008-09-04

    Mesoporous transition metal oxides are of great potential as catalyst supports, shape-selective catalysts, photocatalysts, and sensor materials. Previously stable crystalline mesoporous oxides were mostly obtained by thermally induced crystallization or by segregating the nanocrystals with an amorphous phase. Here we report a novel direct approach to crystalline mesoporous frameworks via the spontaneous growth and assembly of transition metal oxide nanocrystals (i.e., rutile TiO2, fluorite CeO2, cassiterite SnO2, and anatase SnxTi1-xO2) by oxidative hydrolysis and condensation in the presence of anionic surfactants. The influences of synthesis time, surfactants with different chain lengths, concentrations of the oxidant (i.e., hydrogen peroxide), and synthesis temperatures on the composition and morphologies of the resulting materials were investigated by X-ray diffraction (XRD), N2-sorption, transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). A mechanism for the templated synthesis of crystalline mesoporous metal oxides was tentatively proposed. To demonstrate the catalytic applications of these materials, gold nanoparticles were loaded on mesoporous rutile TiO2 and fluorite CeO2 supports, and their catalytic performance in CO oxidation and water-gas shift was surveyed. Au nanoparticles supported on the mesoporous crystalline metal oxides exhibit higher reactivity and excellent on-stream stability towards CO oxidation and water-gas shift reaction compared with commercial TiO2 and CeO2.

  7. Dependence of transition temperature on hole concentration per CuO2 sheet in the Bi-based superconductors

    NASA Technical Reports Server (NTRS)

    Zhao, J.; Seehra, M. S.

    1991-01-01

    The recently observed variations of the transition temperature (T sub c) with oxygen content in the Bi based (2212) and (2223) superconductors are analyzed in terms of p+, the hole concentration per CuO2 sheet. This analysis shows that in this system, T sub c increases with p+ initially, reaching maxima at p+ = 0.2 approx. 0.3, followed by monotonic decrease of T sub c with p+. The forms of these variations are similar to those observed in the La(2-x)Sr(x)CuO4 and YBa2Cu3Oy systems, suggesting that p+ may be an important variable governing superconductivity in the cuprate superconductors.

  8. Effect of Nanoconfinement on the Glass Transition Temperature and Small Molecule Diffusion in Polymers of Varying Backbone Stiffness

    NASA Astrophysics Data System (ADS)

    Deng, Hui; Mundra, Manish; Torkelson, John

    2010-03-01

    Fluorescence spectroscopy was used to determine the glass transition temperature in ultrathin supported bisphenol-A polysulfone (BPAPS) and bisphenol-A polycarbonate (BPAPC) films and compared to previous results for ultrathin supported polystyrene (PS) films. BPAPC and BPAPS are more rigid than PS due to the presence of aromatic rings in their polymer backbones. A dramatic increase in Tg-reduction upon confinement was seen for polymers with increased backbone stiffness. A fluorescence-multilayer film technique was then used to determine the diffusion coefficient of a small molecule probe in ultrathin supported PS films. A decrease in the diffusion coefficient of the probe was observed upon confinement of the PS films. This procedure is also being applied to ultrathin supported BPAPC and BPAPS films to explore the impact of polymer backbone rigidity on small molecule diffusion in nanoconfined polymers.

  9. Indium tin oxide films prepared by atmospheric plasma annealing and their semiconductor-metal conductivity transition around room temperature

    NASA Astrophysics Data System (ADS)

    Li, Yali; Li, Chunyang; He, Deyan; Li, Junshuai

    2009-05-01

    We report the synthesis of indium tin oxide (ITO) films using the atmospheric plasma annealing (APA) technique combined with the spin-coating method. The ITO film with a low resistivity of ~4.6 × 10-4 Ω cm and a high visible light transmittance, above 85%, was achieved. Hall measurement indicates that compared with the optimized ITO films deposited by magnetron sputtering, the above-mentioned ITO film has a higher carrier concentration of ~1.21 × 1021 cm-3 and a lower mobility of ~11.4 cm2 V-1 s-1. More interestingly, these electrical characteristics result in the semiconductor-metal conductivity transition around room temperature for the ITO films prepared by APA.

  10. Estimate bond angle dependence of superconducting transition temperature in NaFeAs with the first principle methods

    NASA Astrophysics Data System (ADS)

    Sun, Tieyu; Huang, Haitao; Peng, Biaolin; Zheng, Renkui; Lam, Chi-Hang; Tang, Tao; Wang, Yu

    2016-11-01

    The change of superconducting transition temperature (Tc) with bond angle in iron-pnictides was investigated by first-principles calculation based on density functional theory. A Green's function method was adopted to estimate the maximum eigenvalue of Eliashberg equation (an indicator of Tc) for NaFeAs with different bond angles. Through calculations the band structure of NaFeAs was obtained. It was found that hole pockets could form at the center of the first Brillion zone in the band structure, which confirmed the existence of superconductivity in NaFeAs. The upper limit of the Fe-As-Fe bond angle for superconductivity was found to be 121° and the highest Tc would occur at the angle of 108°.

  11. Influence of Irreversible Adsorption on the Glass Transition Temperature of Polymer Thin Films as Measured by Fluorescence

    NASA Astrophysics Data System (ADS)

    Burroughs, Mary; Priestley, Rodney

    2014-03-01

    Polymers confined to the nanometer length scale have been shown to exhibit deviations in the glass transition temperature (Tg) from the bulk. With the increasing use of confined polymers in nanotechnology, understanding and predicting this behavior is extremely relevant to industries ranging from pharmaceuticals to organic electronics. Recent work (Napolitano, Wübbenhorst, Nature Communications, 2, 260 (2011)) has connected deviations in Tg under confinement with irreversible physical adsorption of polymer chains at substrate interfaces. Here we investigate the influence of irreversibly adsorbed layers on the Tg of polystyrene (PS) thin films supported on silica via fluorescence. We examine the Tg of the brushes as a function of annealing time and irreversibly adsorbed layer thickness. By incorporating fluorescently labeled polymer layers into multilayered films of unlabeled polymer, we will examine the influence of brushes on adjacent layers dynamics. Finally, we will compare the results on PS with those of poly(methyl methacrylate).

  12. 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.

  13. Benchmark Transiting Brown Dwarf LHS 6343 C: Spitzer Secondary Eclipse Observations Yield Brightness Temperature and Mid-T Spectral Class

    NASA Astrophysics Data System (ADS)

    Montet, Benjamin T.; Johnson, John Asher; Fortney, Jonathan J.; Desert, Jean-Michel

    2016-05-01

    There are no field brown dwarf analogs with measured masses, radii, and luminosities, precluding our ability to connect the population of transiting brown dwarfs with measurable masses and radii and field brown dwarfs with measurable luminosities and atmospheric properties. LHS 6343 C, a weakly irradiated brown dwarf transiting one member of an M+M binary in the Kepler field, provides the first opportunity to probe the atmosphere of a non-inflated brown dwarf with a measured mass and radius. Here, we analyze four Spitzer observations of secondary eclipses of LHS 6343 C behind LHS 6343 A. Jointly fitting the eclipses with a Gaussian process noise model of the instrumental systematics, we measure eclipse depths of 1.06 ± 0.21 ppt at 3.6 μm and 2.09 ± 0.08 ppt at 4.5 μm, corresponding to brightness temperatures of 1026 ± 57 K and 1249 ± 36 K, respectively. We then apply brown dwarf evolutionary models to infer a bolometric luminosity {log}({L}\\star /{L}ȯ )=-5.16+/- 0.04. Given the known physical properties of the brown dwarf and the two M dwarfs in the LHS 6343 system, these depths are consistent with models of a 1100 K T dwarf at an age of 5 Gyr and empirical observations of field T5-6 dwarfs with temperatures of 1070 ± 130 K. We investigate the possibility that the orbit of LHS 6343 C has been altered by the Kozai–Lidov mechanism and propose additional astrometric or Rossiter–McLaughlin measurements of the system to probe the dynamical history of the system.

  14. One dimensional models of temperature and composition in the transition zone from a bayesian inversion of surface waves

    NASA Astrophysics Data System (ADS)

    Drilleau, M.; Beucler, E.; Mocquet, A.; Verhoeven, O.; Burgos, G.; Capdeville, Y.; Montagner, J.

    2011-12-01

    The transition zone plays a key role in the dynamics of the Earth's mantle, especially for the exchanges between the upper and the lower mantles. Phase transitions, convective motions, hot upwelling and/or cold downwelling materials may make the 400 to 1000 km depth range very anisotropic and heterogeneous, both thermally and chemically. A classical procedure to infer the thermal state and the composition is to interpret 3D velocity perturbation models in terms of temperature and mineralogical composition, with respect to a global 1D model. However, the strength of heterogeneity and anisotropy can be so high that the concept of a one-dimensional reference seismic model might be addressed for this depth range. Some recent studies prefer to directly invert seismic travel times and normal modes catalogues in terms of temperature and composition. Bayesian approach allows to go beyond the classical computation of the best fit model by providing a quantitative measure of model uncertainty. We implement a non linear inverse approach (Monte Carlo Markov Chains) to interpret seismic data in terms of temperature, anisotropy and composition. Two different data sets are used and compared : surface wave waveforms and phase velocities (fundamental mode and the first overtones). A guideline of this method is to let the resolution power of the data govern the spatial resolution of the model. Up to now, the model parameters are the temperature field and the mineralogical composition ; other important effects, such as macroscopic anisotropy, will be taken into account in the near future. In order to reduce the computing time of the Monte Carlo procedure, polynomial Bézier curves are used for the parameterization. This choice allows for smoothly varying models and first-order discontinuities. Our Bayesian algorithm is tested with standard circular synthetic experiments and with more realistic simulations including 3D wave propagation effects (SEM). The test results enhance the

  15. Effects of pressure and temperature on the M412 intermediate of the bacteriorhodopsin photocycle. Implications for the phase transition of the purple membrane.

    PubMed Central

    Tsuda, M; Govindjee, R; Ebrey, T G

    1983-01-01

    The effects of pressure and temperature on the decay kinetics of the M412 (M) intermediate in the photocycle of bacteriorhodopsin were studied to provide information about the phase transitions of the purple membrane lipids. The activation volume (delta V++) for the decay of M is expected to be different below and above a phase transition. However, no abrupt change in delta V++ was found from 3.5 degrees to 60 degrees C. But a sharp break was observed in a plot of the logarithm of the rate of M decay vs. pressure. Extrapolation of this break point to standard atmospheric pressure gives a temperature of -42 degrees C, which probably corresponds to the phase transition of the purple membrane lipids. This conclusion is supported by studies of the effect of pressure on the M kinetics of bacteriorhodopsin incorporated into dimyristoylphosphatidylcholine vesicles, whose phase transition has previously been characterized. PMID:6652216

  16. Glaciation and erosion of Eastern Greenland at the Eocene-Oligocene transition: Insights from low-temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Bernard, Thomas; Steer, Philippe; Gallagher, Kerry; Szulc, Adam; Whittam, Andrew

    2016-04-01

    Climate cooling through the Late Cenozoic was important in the evolution of glaciated mountain ranges. While the onset of accelerated Cenozoic exhumation is generally associated with the Quaternary at mid-latitudes, coincident with the local onset of glaciation, some high-latitude passive margins may have experienced earlier glaciation starting at 30-38 Ma or even 45 Ma. To address this issue, we use a set of new AFT data from 16 sub-vertical profiles sampled along the fjords of the central Eastern Greenland margin between 68° and 76° N, combined with new apatite (U-Th-Sm)/He (AHe) data from selected profiles. To infer thermal histories and exhumation from these profiles, we use the software QTQt. The modeling results show a major phase of exhumation in the East Greenland margin between 68° and 76° N starting at 30±5 Ma. The spatial distribution of the exhumation shows that normal faulting on East Greenland margin had no resolvable influence on exhumation related to the cooling phase. However, the timing is coincident with the dramatic worldwide fall of surface temperature at the Eocene-Oligocene transition. We therefore suggest that a transition from an Eocene fluvial to an Oligocene glacial-dominated landscape triggered a period of enhanced erosion. We infer from the thermal histories that around 2.7±1.9 km of erosion occurred close to the coast since the Eocene-Oligocene transition. This amount of erosion is consistent with the incision of the fjords and with the effective removal of 2.3±1.5 km of basalt thickness, deduced by the thermal modeling of a heating phase at 55±5 Ma. This phase of erosion is most strongly evidenced near the coast, suggesting either that continental ice extent was limited to the coastal areas or that erosion was less efficient outside these areas, leading to no obvious signal in thermochronometric data further north. Overall, this study provides the first onshore evidence of the onset of continental ice in East Greenland margin

  17. Universal low-temperature Ohmic contacts for quantum transport in transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Xu, Shuigang; Wu, Zefei; Lu, Huanhuan; Han, Yu; Long, Gen; Chen, Xiaolong; Han, Tianyi; Ye, Weiguang; Wu, Yingying; Lin, Jiangxiazi; Shen, Junying; Cai, Yuan; He, Yuheng; Zhang, Fan; Lortz, Rolf; Cheng, Chun; Wang, Ning

    2016-06-01

    Low carrier mobility and high electrical contact resistance are two major obstacles prohibiting explorations of quantum transport in TMDCs. Here, we demonstrate an effective method to establish low-temperature Ohmic contacts in boron nitride encapsulated TMDC devices based on selective etching and conventional electron-beam evaporation of metal electrodes. This method works for most extensively studied TMDCs in recent years, including MoS2, MoSe2, WSe2, WS2, and 2H-MoTe2. Low electrical contact resistance is achieved at 2 K. All of the few-layer TMDC devices studied show excellent performance with remarkably improved field-effect mobilities ranging from 2300 to 16 000 cm2 V‑1 s‑1, as verified by the high carrier mobilities extracted from Hall effect measurements. Moreover, both high-mobility n-type and p-type TMDC channels can be realized by simply using appropriate contact metals. Prominent Shubnikov–de Haas oscillations have been observed and investigated in these high-quality TMDC devices.

  18. Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. Paper 1: Estimate of the electron velocity distribution functions

    NASA Technical Reports Server (NTRS)

    Roussel-Dupre, R.

    1979-01-01

    It was shown that, in the presence of the steep temperature gradients characteristic of EUV models of the solar transition region, the electron and proton velocity distribution functions are non-Maxwellian and are characterized by high energy tails. The magnitude of these tails are estimated for a model of the transition region and the heat flux is calculated at a maximum of 30 percent greater than predicted by collision-dominated theory.

  19. Temperature dependence of Peierls-Hubbard phase transition in [Pd(cptn)2Br]Br2 studied by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Hosomi, Yuka; Yoshida, Shoji; Taninaka, Atsushi; Yoshida, Takefumi; Takaishi, Shinya; Takeuchi, Osamu; Yamashita, Masahiro; Shigekawa, Hidemi

    2016-08-01

    The temperature dependence of the Peierls-Hubbard phase transition in [Pd(cptn)2Br]Br2 (cptn: 1R,2R-diaminocyclopentane) was directly observed using a low-temperature scanning tunneling microscope. A short ligand without alkyl chains was used to form a rigid crystal lattice to reduce the effect of structural changes in the crystal with temperature. The hysteresis in the temperature dependence of the ratio between the areas of the charge density wave (CDW) state produced by the PdII-PdIV mixed-valence state and the Mott-Hubbard (MH) state with a PdIII-averaged valence state which is a characteristic of the first-order phase transition, was directly observed at the atomic scale. Pinning of the CDW phase by defects was observed below the critical temperature, suggesting the growth of the CDW phase with defects as nuclei.

  20. Raman microspectroscopy of noncancerous and cancerous human breast tissues. Identification and phase transitions of linoleic and oleic acids by Raman low-temperature studies.

    PubMed

    Brozek-Pluska, Beata; Kopec, Monika; Surmacki, Jakub; Abramczyk, Halina

    2015-04-01

    We present the results of Raman studies in the temperature range of 293-77 K on vibrational properties of linoleic and oleic acids and Raman microspectroscopy of human breast tissues at room temperature. Our results confirmed the significant role of unsaturated fatty acids in differentiation of noncancerous and cancerous breast tissues and the role of vibrational spectroscopy in phase transition identification. We have found that vibrational properties are very sensitive indicators to specify phases and phase transitions typical of unsaturated fatty acids at the molecular level. Using Raman spectroscopy we have identified high-temperature, middle-temperature and low-temperature phases of linoleic acid. Results obtained for linoleic acid were compared with parameters characteristic of α and γ phases of oleic acid - the parent compound of polyunsaturated fatty acids.

  1. Microwave properties of YBa2Cu3O(7-delta) high-transition-temperature superconducting thin films measured by the power transmission method

    NASA Technical Reports Server (NTRS)

    Miranda, F. A.; Gordon, W. L.; Bhasin, K. B.; Heinen, V. O.; Warner, J. D.

    1991-01-01

    The microwave response of YBa2Cu3O(7-delta) superconducting thin films deposited on LaAlO3, MgO, YSZ, and LaGaO3 substrates are studied. It is found that the microwave transmission properties are very weakly dependent on temperature in the normal state but change drastically upon transition to the superconducting state. In particular, the transmission decreases and there is a negative phase shift with respect to the phase at room temperature when the sample is cooled through its transition temperature. The magnetic penetration depth for all the films was determined from the surface reactance of the films. The microwave complex conductivity is determined in both the normal and the superconducting state. It is observed that both sigma1 and sigma2 increase in transition to the superconducting state. The surface resistivity is calculated for all the films.

  2. Temperature Dependencies of Linewidths, Positions, and Line Shifts of Spectral Transitions of Trivalent Neodymium Ions in Ceramic Nd3+:Y2O3

    NASA Astrophysics Data System (ADS)

    Pedraza, Francisco; Khachatryan, Edward; Dennis, Robert; Nash, Kelly; Sardar, Dhiraj

    2010-10-01

    Effects of temperature on widths and shifts of the spectral lines of Nd^3+ in Y2O3 polycrystalline ceramic have been investigated. The spectral lines corresponding to the inter-Stark transitions R1 -> Y1 (1074 nm) and R1-> X3 (914 nm) within the ^4F3/2 -> ^4I11/2 and ^4F3/2 -> ^4I9/2 transitions, respectively, have been studied. The widths of these lines and their shifts have been measured as a function of temperature in 10K- 300K range. The spectral linewidths of both transitions are found to increase with increasing temperature. This research was supported by the National Science Foundation Grant No. DMR-0934218.

  3. Thermodynamic studies on the ferroelectric phase transition in neutron irradiated (Li(sub x)K(1-x))2SO4 crystals at high temperature

    NASA Astrophysics Data System (ADS)

    Kassem, M. E.; El-Khatib, A. M.; Ammar, E. A.; Denton, M. M.

    1989-05-01

    Thermodynamic studies of (Li(x)K(1-x))2SO4, LKS, mixed crystals have been made in the concentration range (x=0.1,0.2,..., x=0.5). The thermal behavior has been investigated by differential thermal analysis, DTA, and differential scanning calorimeter, DSC, in the vicinity of high temperature phases. Also, the effect of the mixed neutron field of fast and thermal neutrons (10 percent of the reactor neutron pile is fast neutrons) on the thermal properties of mixed crystals was studied. The results show a change in the transition temperature Tc, as well as the value of specific heat Cp at transition temperature, due to the change of the stoichiometric ratio and the radiation doses. The changes of enthalpy and entropy of mixed crystals have been estimated numerically. The obtained small values of Delta S/R is characteristic of incommensurate phase transition as previously confirmed by the results of neutron diffraction technique.

  4. Physical stability of drugs after storage above and below the glass transition temperature: Relationship to glass-forming ability.

    PubMed

    Alhalaweh, Amjad; Alzghoul, Ahmad; Mahlin, Denny; Bergström, Christel A S

    2015-11-10

    Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (Tg) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12h at temperatures 20°C above or below the Tg. A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20°C below the Tg. Fourteen of the Class II compounds crystallized when stored above the Tg whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e.g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the Tg. The use of a large dataset revealed that molecular features related to aromaticity and π-π interactions reduce the inherent physical stability of amorphous drugs.

  5. The behavior of the electron density and temperature at Millstone Hill during the equinox transition study September 1984

    NASA Technical Reports Server (NTRS)

    Richards, P. G.; Torr, D. G.; Buonsanto, M. J.; Miller, K. L.

    1989-01-01

    The ionospheric electron density and temperature variations is simulated during the equinox transition study in September 1984 and the results are compared with measurements made at Millstone Hill. The agreement between the modeled and measured electron density and temperature for the quiet day (18 September) is very good but there are large differences on the day of the storm (19 September). On the storm day, the measured electron density decreases by a factor of 1.7 over the previous day, while the model density actually increases slightly. The model failure is attributed to an inadequate increase in the ratio of atomic oxygen to molecular neutral densities in the MSIS neutral atmosphere model, for this particular storm. A factor of 3 to 5 increase in the molecular to atomic oxygen density ratio at 300 km is needed to explain the observed decrease in electron density. The effect of vibrationally excited N sub 2 on the electron density were studied and found to be small.

  6. Size-induced effect upon the Néel temperature of the antiferro/paramagnetic transition in gadolinium oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Mutelet, B.; Keller, N.; Roux, S.; Flores-Gonzales, M. A.; Lux, F.; Martini, M.; Tillement, O.; Billotey, C.; Janier, M.; Villiers, C.; Novitchi, Ghenadie; Luneau, Dominique; Perriat, P.

    2011-10-01

    In this paper, we demonstrate that cubic gadolinium oxide is paramagnetic and follows the Curie-Weiss law from 20 K to room temperature for particles size comprised between 3.5 and 60 nm. The largest particles (60 nm) possess the macroscopic behaviour of Gd oxide with a Néel temperature, T N, close to 18 K (Gd oxide is antiferromagnetic below T N, paramagnetic above). Then size-induced effects can be encountered only for particles smaller than 60 nm. We find that the finite-size scaling model used for describing the size evolution of the antiferro/paramagnetic transition is valid for sizes comprised between 3.5 and 35 nm with parameters in excellent agreement with those usually found for antiferromagnetic materials. The correlation length (3.6 nm) is of the order of magnitude of a few lattice parameters and the critical exponent λ is found equal to 1.3, a value very close to that predicted by the three dimensional Heisenberg model ( λ=1.4).

  7. [Deactivation by SO2 of transition metal oxides modified low-temperature SCR catalyst for NOx reduction with NH3].

    PubMed

    Shen, Bo-xiong; Liu, Ting; Yang, Ting-ting; Xiong, Li-xian; Wang, Jing

    2009-08-15

    MnOx-CeOx/ACF catalyst was prepared by impregnation method, which exhibited high activity for low-temperature selective catalytic reduction of NOx over the temperature range 110-230 degrees C. Experiments results indicated that the catalyst yielded 80% NO conversion at 150 degrees C and 90% at 230 degrees C. The Oxides of Fe,Cu and V were added to the catalysts based on MnOx-CeOx/ACF. The additions of these transition metal oxides had a negative effect on the activity of the catalysts. Compared with MnOx-CeOx/ACF and Cu and V modified catalysts, NO conversion for Fe-MnOx-CeOx/ACF catalyst leveled off at nearly 75% in the first 6 h in the presence of SO2. Two mechanisms of catalyst deactivation by SO2 were discovered by the methods of X-ray photoelectron spectrum (XPS) and Fourier transform infrared spectra (FTIR), indicating that the catalysts were covered by ammonium sulfates and the metal oxides, acting as active components, were also sulfated by SO2 to form metal sulfates.

  8. Physical stability of drugs after storage above and below the glass transition temperature: Relationship to glass-forming ability

    PubMed Central

    Alhalaweh, Amjad; Alzghoul, Ahmad; Mahlin, Denny; Bergström, Christel A.S.

    2015-01-01

    Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (Tg) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12 h at temperatures 20 °C above or below the Tg. A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20 °C below the Tg. Fourteen of the Class II compounds crystallized when stored above the Tg whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e.g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the Tg. The use of a large dataset revealed that molecular features related to aromaticity and π–π interactions reduce the inherent physical stability of amorphous drugs. PMID:26341321

  9. Abrupt Sea Surface Temperature changes during The Last Glacial-Interglacial Transition in the Iberian margin: Sea Level implications

    NASA Astrophysics Data System (ADS)

    Rodrigues, Teresa; Grimalt, Joan; Abrantes, Fatima; Naughton, Filipa; Flores, José-Abel

    2010-05-01

    Uk'37-SST and organic terrestrial biomarkers were used to reconstruct Sea surface temperature (SST) and continental input in a shallow core (D13882) from the Tagus mud patch (Iberian margin) during last glacial and interglacial transition (LGIT). In the western Iberian margin the Heinrich 1 (H1) and the Younger Dryas (YD) represent two extreme episodes of cold sea surface temperature conditions mediated by a marine warm phase that coincides with the Bolling-Allerod event (B-A) in the neighbor continent. Following the YD event, an abrupt sea surface warming marks the beginning of the Holocene in this region. However, SST values and amplitude of variation recorded in core D13882 differ from deep sea core MD03- 2699 and other available palaeoclimate sequences from this region. While the SST values from most deep sea cores reflect the latitudinal gradient detected on the Iberian Peninsula during H1 and B-A, the shallow core (D13882) SSTs are colder than the ones recorded in the deep sea. This suggests that a supplementary input of cold freshwater coming from the continent reached shallow areas. This hypothesis is supported by the high terrigenous biomarkers and total organic carbon content as well as by the dominance of tetra alkenone in the Tagus mud patch. Furthermore, the comparison of all western Iberia SST records suggest that the SST increase during the B-A event started 1,000 yr before the meltwater pulse 1A (mwp-1A) and attained maximum values during or slightly after this sea level rise episode. Conversely, the sharp SST increase in the Iberian margin during the YD/Holocene transition, is synchronous with the meltwater pulse 1B (mwp-1B). The decrease of continental input in the Tagus mud patch confirms a sea level rise in the region. Thus, the synchronism between the maximum warming in the mid-latitudes of the western Iberian margin, in the adjacent landmasses and temperature in Greenland suggest that the mwp-1B, could have been initiated in the Northern

  10. Staggering Changes in Mediterranean Sea Surface Temperatures Coincide with Global Climate and Evolution Transitions during the Late Miocene - Pliocene

    NASA Astrophysics Data System (ADS)

    Tzanova, A.; Herbert, T.; Peterson, L.

    2012-12-01

    The Late Miocene warmer-than-modern Earth is a time of important transitions such as the C3/C4 photosynthesis transition, the appearance of the Sahara and the hominin evolution. The interconnections and drivers for climate and evolutionary change during this time, such as pCO2, albedo, vegetation and temperatures, are still speculative. The causal relationships can be better understood via paleoproxy records from sensitive to climate shifts areas such as the Mediterranean Sea. The Mediterranean Sea is a largely enclosed mid-latitude basin on the cusp of the subtropical climate zone formed after the closure of the Tethys. The enclosed nature of the Mediterranean Sea makes it sensitive to continental climate and shifts in climate zones with the advantage of resolution, preservation and detail usually reserved for marine records Here we present a continuous 30 kyr resolution, sea surface temperature (SST) record for the Mediterranean Sea (Late Miocene - Pliocene) from the well-dated, uplifted marine sequences of Monte dei Corvi in Northern Italy and Rosello in Sicily, Italy. The Late Miocene portion of the record is from the pelagic, uplifted Monte dei Corvi land section. The data from two organic paleothermometers UK'37 and TEX86, establish the Mediterranean Sea as notably warmer than present. SSTs were equivalent and even higher than the warmest parts of the modern ocean. For the oldest samples, ~ 12.9 Ma to ~8.1 Ma, UK'37 derived temperatures hovered close to 28oC and possibly even higher. A distinct cooling trend takes over starting at ~8.1 Ma and superimposed upon it are prominent, high variability, cold episodes lasting from ~7 Ma to 6 Ma. During these extreme episodes, reconstructed SSTs reach values comparable the modern eastern Mediterranean annual average SST of 19.5oC. The variability during this colder period is substantial, with temperature swings of as much as ~6-8 oC over 40 kyr. Continuous pelagic sedimentation resumes after the Messinian Salinity

  11. High antiferromagnetic transition temperature of a honeycomb compound SrRu2O6

    SciTech Connect

    Tian, Wei; Svoboda, Chris; Ochi, M.; Matsuda, M.; Cao, Huibo; Cheng, J. -G.; Sales, B. C.; Mandrus, D.; Arita, R.; Trivedi, Nandini; Yan, Jiaqiang

    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) 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 .

  12. Optimization of magnetostriction, coercive field and magnetic transition temperature in nanocrystalline TbDyFe+Zr/Nb multilayers

    NASA Astrophysics Data System (ADS)

    Fischer, S. F.; Kelsch, M.; Kronmüller, H.

    1999-06-01

    The magnetostrictive properties of TbDyFe/Nb multilayers containing 2 at% Zr as an additive have been investigated after different annealing treatments for the (Terfenol-D near) composition of [Tb 0.27Dy 0.73] 0.27Fe 0.73. The multilayer structure has been produced by ion-beam sputtering on a sapphire substrate. After 10 min annealing of the multilayers at temperatures from 873 to 973 K the parallel magnetostriction increased from λ‖(0.8 T)=265 to 520 ppm accompanied by an increase of the magnetic phase transition temperature from TC=333 to 592 K, while the increase of the coercive fields from μ0Hc<5 to 75 mT lies distinctively below 100 mT. These properties are suitable for applications of giant magnetostrictive films in microsystems where values of λ>500 ppm, TC>500 K and μ0Hc≪100 mT are required. Establishing a nanocrystalline microstructure with grain sizes d< dc˜15 nm ( dc is the critical grain diameter) smaller than the exchange length is essential for the combination of intrinsic magnetic properties (increased λ and TC) with soft magnetic properties ( μ0Hc of a few mT) as typical for an amorphous microstructure. It is shown by microstructural XRD and TEM investigations that such a nanocrystalline microstructure can be realized by a suitable heat treatment of TbDyFe+Zr/Nb multilayers. Introducing Nb spacer layers effectively reduces grain growth for certain annealing temperatures while Zr is assumed to play a dominant role in forming nucleation centers of nanograins. In combination, both effects can be well used to optimize the magnetostrictive layer properties.

  13. Overlap of quantum many-body states with a separable state and phase transitions in the Dicke model: Zero and finite temperature

    SciTech Connect

    Cui, H. T.

    2010-04-15

    Overlap with the separable state is introduced in this article for the purpose of characterizing the overall correlation in many-body systems. This definition has clear geometric and physical meaning and moreover can be considered as the generalization of the concept of the Anderson orthogonality catastrophe. As an exemplification, it is used to mark the phase transition in the Dicke model for zero and finite temperatures, and the discussion shows that it can faithfully reflect the phase transition properties of this model whether for zero or finite temperature. Furthermore, the overlap for the ground state also indicates the appearance of multipartite entanglement in the Dicke model.

  14. Current oscillations as a manifestation of spatio-temporal inhomogeneity of temperature distribution in vanadium dioxide films at semiconductor-metal phase transition

    SciTech Connect

    Aliev, V. Sh.; Bortnikov, S. G. Mzhelskiy, I. V.; Badmaeva, I. A.

    2014-10-06

    A spatial temperature distribution in VO{sub 2} film was first investigated at current oscillations using infrared microscope. The oscillations are revealed to arise from the periodic formation and disappearance of a narrow high-temperature channel in VO{sub 2} film. The nature of the oscillations in VO{sub 2} films is considered from the standpoint of a well-known phenomenon: spatio-temporal instability of current flow in homogeneous semiconductors. The temperature of the channel significantly exceeds the semiconductor-metal transition temperature being the cause of film destruction and oscillations cessation.

  15. Temperature measurement of cold atoms using single-atom transits and Monte Carlo simulation in a strongly coupled atom-cavity system

    SciTech Connect

    Li, Wenfang; Du, Jinjin; Wen, Ruijuan; Yang, Pengfei; Li, Gang; Zhang, Tiancai; Liang, Junjun

    2014-03-17

    We investigate the transmission of single-atom transits based on a strongly coupled cavity quantum electrodynamics system. By superposing the transit transmissions of a considerable number of atoms, we obtain the absorption spectra of the cavity induced by single atoms and obtain the temperature of the cold atom. The number of atoms passing through the microcavity for each release is also counted, and this number changes exponentially along with the atom temperature. Monte Carlo simulations agree closely with the experimental results, and the initial temperature of the cold atom is determined. Compared with the conventional time-of-flight (TOF) method, this approach avoids some uncertainties in the standard TOF and sheds new light on determining temperature of cold atoms by counting atoms individually in a confined space.

  16. Determination of the phase boundary of the omega to beta transition in Zr using in situ high-pressure and high-temperature X-ray diffraction

    SciTech Connect

    Ono, Shigeaki; Kikegawa, Takumi

    2015-05-15

    The high-pressure behavior of zirconium has been examined using the synchrotron X-ray diffraction technique to a pressure of 38 GPa and a temperature of 800 K employing a hydrothermal diamond anvil cell technique. The structural transition from the ω to the β phase was observed. This transition has a negative dP/dT gradient, which is in general agreement with those reported in previous studies. The transition boundary was determined to be, P (GPa)=41.2–0.025×T (K). The negative slope of the transition, dP/dT, determined in our study using the diamond anvil cell technique was less than half that estimated by the previous study using a large press apparatus. - Graphical abstract: Experimental results and phase boundary of the ω–β transition in Zr. - Highlights: • X-ray diffraction patterns of zirconium were measured by the synchrotron experiments. • High-pressure experiments were performed by an external-heated diamond anvil cell. • Phase diagram of zirconium was determined at high pressures and high temperatures. • Phase boundary between omega and beta transition has a negative dP/dT slope.

  17. Suppression of phase transitions at low temperature by chromium substitution in vanadium spinel Fe(V1-x Cr x )2O4.

    PubMed

    Kawaguchi, S; Ishibashi, H; Nagami, K; Kubota, Y

    2016-07-27

    Synchrotron powder diffraction, magnetization, and specific heat measurements have been used to investigate the structural and magnetic phase transitions in the spinel-type vanadate Fe(V1-x Cr x )2O4 (0.0  ⩽  x  ⩽  1.0). We observed five different transitions in our polycrystalline samples. The canted-type ferrimagnetic phase transition accompanied by the lattice distortion was suppressed by Cr substitution (x  =  0.2). Additionally, high-resolution synchrotron powder diffraction revealed that the low-temperature orthorhombic phase appears in FeV2O4 below 30 K and disappears by subtle Cr doping. In contrast, for x  ⩾  0.7, we observed a different magnetic transition of possibly conical-type ferrimagnetic ordering that did not induce significant lattice distortion at the transition temperature. We performed structural refinements for low-temperature phases and suggest that the crystal system of Fe(V1-x Cr x )2O4 at 15K is an orthorhombic lattice for all x values. In the orthorhombic phase, a unique behaviour was observed, with the lattice constants a and b approaching each other as Cr doping increased. This behaviour can be explained by the change of orbitally ordered states of the Fe(2+) ions. PMID:27250516

  18. Suppression of phase transitions at low temperature by chromium substitution in vanadium spinel Fe(V1‑x Cr x )2O4

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Ishibashi, H.; Nagami, K.; Kubota, Y.

    2016-07-01

    Synchrotron powder diffraction, magnetization, and specific heat measurements have been used to investigate the structural and magnetic phase transitions in the spinel-type vanadate Fe(V1‑x Cr x )2O4 (0.0  ⩽  x  ⩽  1.0). We observed five different transitions in our polycrystalline samples. The canted-type ferrimagnetic phase transition accompanied by the lattice distortion was suppressed by Cr substitution (x  =  0.2). Additionally, high-resolution synchrotron powder diffraction revealed that the low-temperature orthorhombic phase appears in FeV2O4 below 30 K and disappears by subtle Cr doping. In contrast, for x  ⩾  0.7, we observed a different magnetic transition of possibly conical-type ferrimagnetic ordering that did not induce significant lattice distortion at the transition temperature. We performed structural refinements for low-temperature phases and suggest that the crystal system of Fe(V1‑x Cr x )2O4 at 15K is an orthorhombic lattice for all x values. In the orthorhombic phase, a unique behaviour was observed, with the lattice constants a and b approaching each other as Cr doping increased. This behaviour can be explained by the change of orbitally ordered states of the Fe2+ ions.

  19. Phase transition kinetics of LiNi0.5Mn1.5O4 analyzed by temperature-controlled operando X-ray absorption spectroscopy.

    PubMed

    Takahashi, Ikuma; Arai, Hajime; Murayama, Haruno; Sato, Kenji; Komatsu, Hideyuki; Tanida, Hajime; Koyama, Yukinori; Uchimoto, Yoshiharu; Ogumi, Zempachi

    2016-01-21

    LiNi0.5Mn1.5O4 (LNMO) is a promising positive electrode material for lithium ion batteries because it shows a high potential of 4.7 V vs. Li/Li(+). Its charge-discharge reaction includes two consecutive phase transitions between LiNi0.5Mn1.5O4 (Li1) ↔ Li0.5Ni0.5Mn1.5O4 (Li0.5) and Li0.5 ↔ Ni0.5Mn1.5O4 (Li0) and the complex transition kinetics that governs the rate capability of LNMO can hardly be analyzed by simple electrochemical techniques. Herein, we apply temperature-controlled operando X-ray absorption spectroscopy to directly capture the reacting phases from -20 °C to 40 °C under potential step (chronoamperometric) conditions and evaluate the phase transition kinetics using the apparent first-order rate constants at various temperatures. The constant for the Li1 ↔ Li0.5 transition (process 1) is larger than that for the Li0.5 ↔ Li0 transition (process 2) at all the measured temperatures, and the corresponding activation energies are 29 and 46 kJ mol(-1) for processes 1 and 2, respectively. The results obtained are discussed to elucidate the limiting factor in this system as well as in other electrode systems.

  20. Multiple magnetic transitions and associated room temperature magneto-functionality in Ni2.048Mn1.312In0.64

    NASA Astrophysics Data System (ADS)

    Pramanick, S.; Dutta, P.; Chatterjee, S.; Giri, S.; Majumdar, S.

    2016-05-01

    Present work reports on the observation of multiple magnetic transitions in a Ni-excess ferromagnetic shape memory alloy with nominal composition Ni2.048Mn1.312In0.64. The magnetization data reveal two distinct thermal hystereses associated with two different phase transitions at different temperature regions. The high temperature magnetic hysteresis is due to the martensitic phase transition whereas the low temperature hysteresis occurs around the magnetic anomaly signifying the transition from a paramagnetic-like state to the ferromagnetic ground state within the martensite. Clear thermal hysteresis along with the sign of the curvatures of Arrott plot curves confirm the first-order nature of both the transitions. In addition, the studied alloy is found to be functionally rich with the observation of large magnetoresistance (-45% and -4% at 80 kOe) and magnetocaloric effect (+16.7 J kg-1 K-1 and -2.25 J kg-1 K-1 at 50 kOe) around these two hysteresis regions (300 K and 195 K respectively).

  1. Suppression of phase transitions at low temperature by chromium substitution in vanadium spinel Fe(V1-x Cr x )2O4.

    PubMed

    Kawaguchi, S; Ishibashi, H; Nagami, K; Kubota, Y

    2016-07-27

    Synchrotron powder diffraction, magnetization, and specific heat measurements have been used to investigate the structural and magnetic phase transitions in the spinel-type vanadate Fe(V1-x Cr x )2O4 (0.0  ⩽  x  ⩽  1.0). We observed five different transitions in our polycrystalline samples. The canted-type ferrimagnetic phase transition accompanied by the lattice distortion was suppressed by Cr substitution (x  =  0.2). Additionally, high-resolution synchrotron powder diffraction revealed that the low-temperature orthorhombic phase appears in FeV2O4 below 30 K and disappears by subtle Cr doping. In contrast, for x  ⩾  0.7, we observed a different magnetic transition of possibly conical-type ferrimagnetic ordering that did not induce significant lattice distortion at the transition temperature. We performed structural refinements for low-temperature phases and suggest that the crystal system of Fe(V1-x Cr x )2O4 at 15K is an orthorhombic lattice for all x values. In the orthorhombic phase, a unique behaviour was observed, with the lattice constants a and b approaching each other as Cr doping increased. This behaviour can be explained by the change of orbitally ordered states of the Fe(2+) ions.

  2. Measurements of Tc (Q,P): Depression of the Superfluid Transition Temperature by a Heat Current Along the Lambda Line

    NASA Technical Reports Server (NTRS)

    Liu, Yuan-Ming; Larson, Melora; Israelsson, Ulf

    1999-01-01

    We report experimental measurements of Tc (Q,P) for heat currents (Q) between I1and 100 micro W/sq cm and pressure (P) between SVP and 15 bar. The measurements were performed in a normal gravity environment, using the low-gravity simulator facility at JPL without the magnet being energized. The sample pressure was controlled to 0.1 micro bar using a hot volume, and a Straty-Adams capacitive pressure gauge. The total volume of helium in the sample cell and the hot volume was held constant using a pneumatic low temperature valve. A melting curve thermometer (MCT) measured the transition temperature (Tc) with a resolution of about 10 nK through a sidewall probe of the thermal conductivity sample cell. We employed the same measurement technique and procedure described by DAS. Preliminary results indicate that Tc (Q,P) depends very little on the pressure in the pressure range between SVP and 15 bar with a variation in the amplitude of Tc(Q,P) of less than about 5% observable in this pressure range. According to the Renormalization-group theory calculation by Haussmann and Dohm, the amplitude of Tc (Q,P) has a leading pressure-dependence term proportional to xi(sub 0) (sup (1/nu)), where xi(sub 0) is the correlation-length amplitude and nu is the correlation-length exponent. Thus, a small pressure dependence of the amplitude of Tc (Q,P) is expected since xi(sub 0) is very weakly dependent on pressure between SVP and 15 bar, consistent with our measurements.

  3. Order-parameter-aided temperature-accelerated sampling for the exploration of crystal polymorphism and solid-liquid phase transitions

    SciTech Connect

    Yu, Tang-Qing Vanden-Eijnden, Eric; Chen, Pei-Yang; Chen, Ming; Samanta, Amit; Tuckerman, Mark

    2014-06-07

    The problem of predicting polymorphism in atomic and molecular crystals constitutes a significant challenge both experimentally and theoretically. From the theoretical viewpoint, polymorphism prediction falls into the general class of problems characterized by an underlying rough energy landscape, and consequently, free energy based enhanced sampling approaches can be brought to bear on the problem. In this paper, we build on a scheme previously introduced by two of the authors in which the lengths and angles of the supercell are targeted for enhanced sampling via temperature accelerated adiabatic free energy dynamics [T. Q. Yu and M. E. Tuckerman, Phys. Rev. Lett. 107, 015701 (2011)]. Here, that framework is expanded to include general order parameters that distinguish different crystalline arrangements as target collective variables for enhanced sampling. The resulting free energy surface, being of quite high dimension, is nontrivial to reconstruct, and we discuss one particular strategy for performing the free energy analysis. The method is applied to the study of polymorphism in xenon crystals at high pressure and temperature using the Steinhardt order parameters without and with the supercell included in the set of collective variables. The expected fcc and bcc structures are obtained, and when the supercell parameters are included as collective variables, we also find several new structures, including fcc states with hcp stacking faults. We also apply the new method to the solid-liquid phase transition in copper at 1300 K using the same Steinhardt order parameters. Our method is able to melt and refreeze the system repeatedly, and the free energy profile can be obtained with high efficiency.

  4. Order-parameter-aided temperature-accelerated sampling for the exploration of crystal polymorphism and solid-liquid phase transitions

    NASA Astrophysics Data System (ADS)

    Yu, Tang-Qing; Chen, Pei-Yang; Chen, Ming; Samanta, Amit; Vanden-Eijnden, Eric; Tuckerman, Mark

    2014-06-01

    The problem of predicting polymorphism in atomic and molecular crystals constitutes a significant challenge both experimentally and theoretically. From the theoretical viewpoint, polymorphism prediction falls into the general class of problems characterized by an underlying rough energy landscape, and consequently, free energy based enhanced sampling approaches can be brought to bear on the problem. In this paper, we build on a scheme previously introduced by two of the authors in which the lengths and angles of the supercell are targeted for enhanced sampling via temperature accelerated adiabatic free energy dynamics [T. Q. Yu and M. E. Tuckerman, Phys. Rev. Lett. 107, 015701 (2011)]. Here, that framework is expanded to include general order parameters that distinguish different crystalline arrangements as target collective variables for enhanced sampling. The resulting free energy surface, being of quite high dimension, is nontrivial to reconstruct, and we discuss one particular strategy for performing the free energy analysis. The method is applied to the study of polymorphism in xenon crystals at high pressure and temperature using the Steinhardt order parameters without and with the supercell included in the set of collective variables. The expected fcc and bcc structures are obtained, and when the supercell parameters are included as collective variables, we also find several new structures, including fcc states with hcp stacking faults. We also apply the new method to the solid-liquid phase transition in copper at 1300 K using the same Steinhardt order parameters. Our method is able to melt and refreeze the system repeatedly, and the free energy profile can be obtained with high efficiency.

  5. Can We Determine Temperatures Associated with Critical Transitions During the Evolution of Metazoan life? Application of 'Clumped' Isotope Thermometry to the Neoproterozoic and Paleozoic

    NASA Astrophysics Data System (ADS)

    Defliese, W.; Gutierrez, M.; Flores, S.; Retallack, G.; Tripati, A.

    2015-12-01

    The evolution and development of metazoan life during the Neoproterozoic and Paleozoic was one of the largest and monumental events in Earth history. Conditions surrounding these events are uncertain, as there remain many questions about the types of environment transitions such as the development of multicellular life, evolution of hard shells, and the transitions of life to land took place in. While mass-47 clumped isotope signatures are prone to thermal resetting and diagenesis, it remains the best tool for reconstructing temperatures in uncertain regimes, and can be integrated along with traditional tools such as textural petrography and cathodoluminescence to screen for diagenetic alteration. In this context, we analyze suites of Neoproterozoic and Paleozoic sediments and brachiopods for clumped isotope temperatures, and combine with microscopy and stratigraphic data to infer diagenetic and burial histories of these rocks. Samples judged to be unaltered will be further analyzed for the conditions prevalent during critical transitions during the evolution of metazoan life.

  6. Nuclear Jacobi and Poincaré transitions at high spins and temperatures: Account of dynamic effects and large-amplitude motion

    NASA Astrophysics Data System (ADS)

    Mazurek, K.; Dudek, J.; Maj, A.; Rouvel, D.

    2015-03-01

    We present a theoretical analysis of the competition between the so-called nuclear Jacobi and Poincaré shape transitions as a function of spin at high temperatures. The latter condition implies the method of choice, a realistic version of the nuclear liquid drop model, here the Lublin-Strasbourg drop model. We address specifically the fact that the Jacobi and Poincaré shape transitions are accompanied by the flattening of the total nuclear energy landscape as a function of the relevant deformation parameters, which enforces large-amplitude oscillation modes that need to be taken into account. For that purpose we introduce an approximate form of the collective Schrödinger equation whose solutions are used to calculate the most probable deformations associated with the nuclear Jacobi and Poincaré transitions. We discuss selected aspects of the new description focusing on the critical-spin values for both types of these transitions.

  7. Low-Temperature Polymorphic Phase Transition in a Crystalline Tripeptide l-Ala-l-Pro-Gly·H2O Revealed by Adiabatic Calorimetry

    PubMed Central

    Markin, Alexey V.; Markhasin, Evgeny; Sologubov, Semen S.; Ni, Qing Zhe; Smirnova, Natalia N.; Griffin, Robert G.

    2015-01-01

    We demonstrate application of precise adiabatic vacuun calorimetry to observation of phase transition in the tripeptide l-alanyl-l-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuun calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide. PMID:25588051

  8. Transition-metal-free visible-light photoredox catalysis at room-temperature for decarboxylative fluorination of aliphatic carboxylic acids by organic dyes.

    PubMed

    Wu, Xinxin; Meng, Chunna; Yuan, Xiaoqian; Jia, Xiaotong; Qian, Xuhong; Ye, Jinxing

    2015-07-28

    We report herein an efficient, general and green method for decarboxylative fluorination of aliphatic carboxylic acids. By using a transition-metal-free, organocatalytic photoredox system, the reaction of various aliphatic carboxylic acids with the Selectfluor reagent afforded the corresponding alkyl fluorides in satisfactory yields under visible light irradiation at room temperature.

  9. Thermal-Driven Fluorite-Pyrochlore-Fluorite Phase Transitions of Gd2Zr2O7 Ceramics Probed in Large Range of Sintering Temperature

    NASA Astrophysics Data System (ADS)

    Zhou, Li; Huang, Zhangyi; Qi, Jianqi; Feng, Zhao; Wu, Dengxue; Zhang, Wei; Yu, Xiaohe; Guan, Yongbing; Chen, Xingtao; Xie, Landong; Sun, Kai; Lu, Tiecheng

    2016-01-01

    Fluorite (F)-pyrochlore (P)-fluorite (F) phase transitions of Gd2Zr2O7 were investigated from 573 K to 1873 K (300 °C to 1600 °C), by means of X-ray diffraction, infrared spectra (IR), and Raman spectra. The low-temperature F phase can stably exist below 1523 K (1250 °C) and the F-P transition occurs at 1523 K to 1573 K (1250 °C to 1300 °C). The ordering process of P phase forms at 1573 K to 1773 K (1300 °C to 1500 °C) and the ordering degree increases with increasing sintering temperature and heat preservation period. High-temperature phase transition from P to F occurs between 1773 K and 1823 K (1300 °C and 1550 °C). IR spectra of samples with different ordering degrees show an interesting shift at 510 cm-1. Raman spectra show that only the A1 g mode displays a significant change between F and P phases. This ordering degree and phase transition temperature studies would allow a more targeted experimental optimization of Gd2Zr2O7 to use in nuclear waste host, thermal barrier coatings, and solid oxide fuel cells.

  10. Ordering, incommensuration, and phase transitions in pyrrhotite. Part II: A high-temperature X-ray powder diffraction and thermomagnetic study

    SciTech Connect

    Li, F.; Franzen, H.F.

    1996-10-01

    High-temperature X-ray diffraction (HTXRD) has been combined with thermomagnetic measurements to study synthetic and natural pyrrhotites. The temperature dependence of the properties observed in DTA, thermomagnetic and diffraction measurements indicates that transitions consistently occur upon heating and cooling so long as the sample is kept below 400{degrees}C, but if the ultimate heating temperature is higher than 550{degrees}C the transitions are altered, probably due to the loss of sulfur. The previously proposed transition sequence for Fe{sub 7}S{sub 8} was supported by HTXRD observation, especially on natural monoclinic pyrrhotite. For intermediate pyrrhotite, the principal ordering was found to be the formation of Kagome nets, and it was found that the vertical stacking sequences that are commensurate along the c axis yield antiferromagnetic characteristics. Based on the changes observed in the HTXRD patterns it is proposed that the mechanism for an observed magnetic {lambda}-transition between the temperatures 150 and 250{degrees}C is the transformation of a commensurate structure with ABCD layering of Kagome nets into a vacancy-disordered structure with the same c modulation.

  11. Pre-Service Primary Science Teachers' Understandings of the Effect of Temperature and Pressure on Solid-Liquid Phase Transition of Water

    ERIC Educational Resources Information Center

    Yalcin, Fatma Aggul

    2012-01-01

    The aim of this study was to explore pre-service primary teachers' understandings of the effect of temperature and pressure on the solid-liquid phase transition of water. In the study a survey approach was used, and the sample consisted of one-hundred and three, third year pre-service primary science teachers. As a tool for data collection, a test…

  12. Selecting polymers for two-phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature.

    PubMed

    Bacon, Stuart L; Peterson, Eric C; Daugulis, Andrew J; Parent, J Scott

    2015-01-01

    Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection. PMID:26259846

  13. Selecting polymers for two-phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature.

    PubMed

    Bacon, Stuart L; Peterson, Eric C; Daugulis, Andrew J; Parent, J Scott

    2015-01-01

    Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection.

  14. Systematic Surface Phase Transition of Ag Thin Films by Iodine Functionalization at Room Temperature: Evolution of Optoelectronic and Texture Properties.

    PubMed

    Bashouti, Muhammad Y; Talebi, Razieh; Kassar, Thaer; Nahal, Arashmid; Ristein, Jürgen; Unruh, Tobias; Christiansen, Silke H

    2016-01-01

    We show a simple room temperature surface functionalization approach using iodine vapour to control a surface phase transition from cubic silver (Ag) of thin films into wurtzite silver-iodid (β-AgI) films. A combination of surface characterization techniques (optical, electronical and structural characterization) reveal distinct physical properties of the new surface phase. We discuss the AgI thin film formation dynamics and related transformation of physical properties by determining the work-function, dielectric constant and pyroelectric behavior together with morphological and structural thin film properties such as layer thickness, grain structure and texture formation. Notable results are: (i) a remarkable increase of the work-function (by 0.9 eV) of the Ag thin layer after short a iodine exposure time (≤60 s), with simultaneous increase of the thin film transparency (by two orders of magnitude), (ii) pinning of the Fermi level at the valance band maximum upon iodine functionalization, (iii) 84% of all crystallites grain were aligned as a result of the evolution of an internal electric field. Realizing a nano-scale layer stack composed of a dielectric AgI layer on top of a metallic thin Ag layer with such a simple method has some technological implications e.g. to realize optical elements such as planar optical waveguides. PMID:26899434

  15. Influence of manufacturing factors on physical stability and solubility of solid dispersions containing a low glass transition temperature drug.

    PubMed

    Sakurai, Atsushi; Sako, Kazuhiro; Maitani, Yoshie

    2012-01-01

    In this study, we investigated the effect of manufacturing factors such as particle size, water content and manufacturing method on the physical stability and solubility of solid dispersion formulations of a low-glass-transition-temperature (T(g)) drug. Solid dispersions were prepared from polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose (HPMC) by hot melt extrusion or spray drying. Water content of solid dispersions prepared by hot melt extrusion determined by dynamic moisture sorption measurement was increased drastically with relative humidity below a certain level of particle size. The blends with a lower water content (0.8%) prepared by hot melt extrusion during storage were more stable than those with a higher water content (3.5%) prepared by spray drying, which caused rapid recrystallization. Physical stability in the hot melt blends may be attributed to reduced molecular mobility due to a higher T(g). Dissolution study revealed that solid dispersions prepared by hot melt extrusion with the smallest particle size showed decreased solubility, attributed to reduced wetting properties (surface energy), which is not predictable by the Noyes-Whitney equation. Taken together, these results indicate that the control of particle size concerned in water content or wetting properties is critical to ensuring the physical stability or enhancing solubility of low-T(g) drugs. Further, hot melt extrusion, which can reduce water content, is a suitable manufacturing method for solid dispersions of low-T(g) drugs. PMID:23124559

  16. Synthesis and Characterization of Fluorescently Labeled Diblock Copolymers for Location-Specific Measurements of The Glass Transition Temperature

    NASA Astrophysics Data System (ADS)

    Christie, Dane; Register, Richard; Priestley, Rodney

    Interfaces play a determinant role in the size dependence of the glass transition temperature (Tg) of polymers confined to nanometric length scales. Interfaces are intrinsic in diblock copolymers, which, depending on their molecular weight and composition, are periodically nanostructured in the bulk. As a result diblock copolymers are model systems for characterizing the effect of interfaces on Tg in bulk nanostructured materials. Investigating the effect of intrinsic interfaces on Tg in diblock copolymers has remained unexplored due to their small periodic length scale. By selectively incorporating trace amounts of a fluorescent probe into a diblock copolymer, Tg can be characterized relative to the diblock copolymer's intrinsic interface using fluorescence spectroscopy. Here, pyrene is selectively incorporated into the poly(methyl methacrylate) (PMMA) block of lamellar forming diblock copolymers of poly(butyl- b-methyl methacrylate) (PBMA-PMMA). Preliminary results show a correlation of Tg as measured by fluorescence with the onset of Tg as measured by calorimetry in labeled homopolymers of PMMA. This result is consistent with previous characterizations of Tg using fluorescence spectroscopy. In selectively labeled diblock copolymers Tg is found to vary systematically depending on the distance of the probe from the PBMA-PMMA interface. We acknowledge funding from the Princeton Center for Complex Materials, a MRSEC supported by NSF Grant DMR 1420541.

  17. Effect of Interfaces on Self-diffusion and Glass Transition Temperature of Poly(isobutyl methacrylate) Thin Films

    NASA Astrophysics Data System (ADS)

    Katsumata, Reika; Dulaney, Austin; Ellison, Christopher

    2015-03-01

    In thin films, physical properties such as the glass transition temperature (Tg), modulus, and viscosity, are different compared to that in thick films due to higher interfacial area to volume ratio. However, the effects of film thickness and associated interfaces on self-diffusion are not well understood, partly because only a few techniques are available for such studies. In this study, we employed fluorescence recovery after patterned photobleaching to evaluate the self-diffusion coefficient (D) of fluorescently labeled poly(isobutyl methacrylate) (PiBMA, Mn = 11 kg/mol, PDI = 1.2). Films 16 - 300 nm in thickness were spin coated onto two substrates then D and Tg were examined: one set of films possessing attractive polymer/substrate interactions on silica substrates, and the other set possessing repulsive polymer/substrate interactions using poly(cyclohexylethylene) substrates. D was measured in the melt state (Tg + 48 K) and the D of thick films were identical to the bulk value regardless of the substrate type. The D of a ~ 19 nm thick film on a repulsive substrate was four times larger than its bulk value while Tg was increased by about 10-15 K. In contrast, attractive substrates typically do not affect D or Tg of PiBMA.

  18. Systematic Surface Phase Transition of Ag Thin Films by Iodine Functionalization at Room Temperature: Evolution of Optoelectronic and Texture Properties

    PubMed Central

    Bashouti, Muhammad Y.; Talebi, Razieh; Kassar, Thaer; Nahal, Arashmid; Ristein, Jürgen; Unruh, Tobias; Christiansen, Silke H.

    2016-01-01

    We show a simple room temperature surface functionalization approach using iodine vapour to control a surface phase transition from cubic silver (Ag) of thin films into wurtzite silver-iodid (β-AgI) films. A combination of surface characterization techniques (optical, electronical and structural characterization) reveal distinct physical properties of the new surface phase. We discuss the AgI thin film formation dynamics and related transformation of physical properties by determining the work-function, dielectric constant and pyroelectric behavior together with morphological and structural thin film properties such as layer thickness, grain structure and texture formation. Notable results are: (i) a remarkable increase of the work-function (by 0.9 eV) of the Ag thin layer after short a iodine exposure time (≤60 s), with simultaneous increase of the thin film transparency (by two orders of magnitude), (ii) pinning of the Fermi level at the valance band maximum upon iodine functionalization, (iii) 84% of all crystallites grain were aligned as a result of the evolution of an internal electric field. Realizing a nano-scale layer stack composed of a dielectric AgI layer on top of a metallic thin Ag layer with such a simple method has some technological implications e.g. to realize optical elements such as planar optical waveguides. PMID:26899434

  19. Influence of manufacturing factors on physical stability and solubility of solid dispersions containing a low glass transition temperature drug.

    PubMed

    Sakurai, Atsushi; Sako, Kazuhiro; Maitani, Yoshie

    2012-01-01

    In this study, we investigated the effect of manufacturing factors such as particle size, water content and manufacturing method on the physical stability and solubility of solid dispersion formulations of a low-glass-transition-temperature (T(g)) drug. Solid dispersions were prepared from polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose (HPMC) by hot melt extrusion or spray drying. Water content of solid dispersions prepared by hot melt extrusion determined by dynamic moisture sorption measurement was increased drastically with relative humidity below a certain level of particle size. The blends with a lower water content (0.8%) prepared by hot melt extrusion during storage were more stable than those with a higher water content (3.5%) prepared by spray drying, which caused rapid recrystallization. Physical stability in the hot melt blends may be attributed to reduced molecular mobility due to a higher T(g). Dissolution study revealed that solid dispersions prepared by hot melt extrusion with the smallest particle size showed decreased solubility, attributed to reduced wetting properties (surface energy), which is not predictable by the Noyes-Whitney equation. Taken together, these results indicate that the control of particle size concerned in water content or wetting properties is critical to ensuring the physical stability or enhancing solubility of low-T(g) drugs. Further, hot melt extrusion, which can reduce water content, is a suitable manufacturing method for solid dispersions of low-T(g) drugs.

  20. Second-phase segregation and micro strain/lattice parameter dependent transition temperature in polycrystalline MgB2

    NASA Astrophysics Data System (ADS)

    Cai, Qi; Liu, Yongchang; Guo, Qianying; Ma, Zongqing; Li, Huijun

    2016-10-01

    Un-doped, metal-doped, and carbon-doped MgB2 samples were prepared by furnace cooling and quenching to investigate the second phase behavior and the resultant critical current density J c performance under different heat treatment processes, which is infrequently mentioned, and to explore the strain/lattice parameter dependence of the superconducting transition temperature. To release the residual stress, quenching induced second-phase segregation in these MgB2 samples shows a negative effect on the J c. Nevertheless, the dislocations and the lattice distortion assisted the enhancement of the high-field J c in the un-doped and metal-doped MgB2 samples, which indicated that quenching could be technically applied for the fabrication of metal-sheathed MgB2 wires and tapes to obtain excellent J c. After evaluating the micro strain and the lattice parameters’ (c and a for hexagonal lattice) variation, a dome was observed in the illustration of the strain/lattice parameter c/a dependence of T c, which differed from the reported linear relation in previous work. This suggests that the c/a ratio and the strain may be the predominant parameters for scaling of the superconducting dome width in the superconducting phase diagram of MgB2.