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Sample records for ductile-to-brittle transition temperature

  1. Evaluation of Crashworthiness for SAE Materials under Ductile to Brittle Transition Temperature (DBTT

    Directory of Open Access Journals (Sweden)

    Amol Bhanage

    2014-10-01

    Full Text Available The concept of crashworthy coaches came into existence after a crash. This demands, avoid vehicle deformation of other/central parts. For this, the behaviour of plastic deformation of the material is necessary to be known. So, these results are required to study the crashworthy behaviour of the structure. In this research, Comparative study has been taken on the automotive materials of SAE 1026, SAE 4140, SAE 5120 and SAE8620. This paper presents the results of fracture toughness, impact energy and stress required for crack propagation from Charpy v-notch impact test and tensile test. The mechanical behaviour of SAE 1026, SAE 4140, SAE 5120 and SAE 8620 are important to describe response during actual loading condition properties used in the crash analysis of the component. The Charpy impact test was conducted at temperature ranging from room temperature 24°C, 0°C, -20°C, - 40°C, -60°C. Specimens oriented in T-L direction are tested. The materials SAE 1026, SAE 4140, SAE 5120 and SAE8620 shown that the ductile to brittle transition temperature, based on 19.5 J, 10.5 J, 113 J, 59.5 J, absorbed energy is about 1.2°C, -3°C, -38°C, -10°C respectively.

  2. Comparison of ductile-to-brittle transition curve fitting approaches

    Energy Technology Data Exchange (ETDEWEB)

    Cao, L.W. [School of Materials Science and Engineering, Beihang University (BUAA), Beijing 100191 (China)] [Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR (United Kingdom); Wu, S.J., E-mail: wusj@buaa.edu.cn [School of Materials Science and Engineering, Beihang University (BUAA), Beijing 100191 (China); Flewitt, P.E.J. [Interface Analysis Centre, University of Bristol, Bristol BS2 8BS (United Kingdom)] [School of Physics, HH Wills Laboratory, University of Bristol, BS8 1TL (United Kingdom)

    2012-05-15

    Ductile-to-brittle transition (DBT) curve fitting approaches are compared over the transition temperature range for reactor pressure vessel steels with different kinds of data, including Charpy-V notch impact energy data and fracture toughness data. Three DBT curve fitting methods have been frequently used in the past, including the Burr S-Weibull and tanh distributions. In general there is greater scatter associated with test data obtained within the transition region. Therefore these methods give results with different accuracies, especially when fitting to small quantities of data. The comparison shows that the Burr distribution and tanh distribution can almost equally fit well distributed and large data sets extending across the test temperature range to include the upper and lower shelves. The S-Weibull distribution fit is poor for the lower shelf of the DBT curve. Overall for both large and small quantities of measured data the Burr distribution provides the best description. - Highlights: Black-Right-Pointing-Pointer Burr distribution offers a better fit than that of a S-Weibull and tanh fit. Black-Right-Pointing-Pointer Burr and tanh methods show similar fitting ability for a large data set. Black-Right-Pointing-Pointer Burr method can fit sparse data well distributed across the test temperature. Black-Right-Pointing-Pointer S-Weibull method cannot fit the lower shelf well and show poor fitting quality.

  3. Synergetic effect of hardness and phosphorus grain-boundary segregation on the ductile-to-brittle transition temperature of 17-4 PH steel

    Science.gov (United States)

    Christien, F.; Le Gall, R.; Saindrenan, G.

    2003-11-01

    The influence of hardness and phosphorus grain-boundary segregation (PGBS) on the ductile-to-brittle transition temperature (DBTT) of a 17-4 PH martensitic steel was studied. Thermal treatments including long-time aging at low temperature were made to get different hardness levels and different PGBS amounts. A synergetic effect between PGBS and hardness on the DBTT of the steel is evidenced; in other words, the DBTT shift due to PGBS increases with hardness. If hardness is low enough, PGBS can even have no effect on the DBTT. A tentative interpretation of this synergetic effect is proposed, based on the assumption that the detrimental effect of PGBS on the grain-boundary cohesion increases with temperature.

  4. Evaluation of the ductile-to-brittle transition temperature of a silicon steel under various strain rate conditions with a servo-hydraulic high speed testing machine

    Science.gov (United States)

    Kwon, Junbeom; Huh, Hoon; Kim, Jae-song

    2017-07-01

    This paper is concerned with the construction of an empirical model of the Ductile-to-Brittle Transition Temperature (DBTT) for 3.4% silicon steel based on tensile test results at strain rates ranging from 0.001 s‒1 to 100 s‒1. Dynamic tensile tests are conducted using an in-house servo hydraulic tensile test machine at strain rates of 1 s‒1, 10 s‒1, and 100 s‒1 and quasi-static tensile tests are conducted using Instron 4206 at strain rates of 0.001 s‒1 and 0.01 s‒1 with an environmental chamber. Fracture elongations are measured by a DIC method during all tests using the high-speed camera for accurate measurement. The DBTT of 3.4% silicon steel is presented in terms of fracture strain with the variation of the temperature and the strain rate. It is demonstrated from the test results that the DBTT increases as the strain rate increases. An empirical model of the DBTT is constructed in terms of strain rate, temperature and fracture elongation. The parameters of the empirical model are calculated from experimental results obtained at various temperatures and strain rates.

  5. Understanding ductile-to-brittle transition of metallic glasses from shear transformation zone dilatation

    Directory of Open Access Journals (Sweden)

    M.Q. Jiang

    2015-08-01

    Full Text Available A theoretical model that takes into account the free-volume aided cooperative shearing of shear transformation zones (STZs is developed to quantitatively understand the ductile-to-brittle transition (DBT of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-type rearrangements to dilatational processes (termed tension transformation zones (TTZs.

  6. The Ductile to Brittle Transition Behavior of the Modified 9Cr-1Mo Steel and Its Laser Welds

    Institute of Scientific and Technical Information of China (English)

    H.C. Wu; R.K. Shiue; C. Chen

    2004-01-01

    The ductile to brittle transition temperature (DBTT) of the modified 9Cr-1Mo steel and its laser welds was studied. The increase in grain size of the weld structure ascended the DBTT of the steel significantly. The transformation of retained austenite at martensite interlath boundaries into untempered and/or twinned martensite could also contribute to increased DBTTs of the steel and its welds tempered at 540℃.

  7. Strain Rate Dependent Ductile-to-Brittle Transition of Graphite Platelet Reinforced Vinyl Ester Nanocomposites

    Directory of Open Access Journals (Sweden)

    Brahmananda Pramanik

    2014-01-01

    Full Text Available In previous research, the fractal dimensions of fractured surfaces of vinyl ester based nanocomposites were estimated applying classical method on 3D digital microscopic images. The fracture energy and fracture toughness were obtained from fractal dimensions. A noteworthy observation, the strain rate dependent ductile-to-brittle transition of vinyl ester based nanocomposites, is reinvestigated in the current study. The candidate materials of xGnP (exfoliated graphite nanoplatelets reinforced and with additional CTBN (Carboxyl Terminated Butadiene Nitrile toughened vinyl ester based nanocomposites that are subjected to both quasi-static and high strain rate indirect tensile load using the traditional Brazilian test method. High-strain rate indirect tensile testing is performed with a modified Split-Hopkinson Pressure Bar (SHPB. Pristine vinyl ester shows ductile deformation under quasi-static loading and brittle failure when subjected to high-strain rate loading. This observation reconfirms the previous research findings on strain rate dependent ductile-to-brittle transition of this material system. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Contribution of nanoreinforcement to the tensile properties is reported in this paper.

  8. Grain boundary chemistry and heat treatment effects on the ductile-to-brittle transition behavior of vanadium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kurtz, R.J.; Hamilton, M.L.; Li, H. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    One-third scale Charpy impact specimens of V-4Cr-4Ti were given the same heat treatments applied to equivalent specimens of V-5Cr-5Ti. Auger specimens of V-4Cr-4Ti were also heat treated with the Charpy specimens to enable grain boundary chemistry measurements. The microstructural, microchemical and Charpy impact response of V-4Cr-4Ti displayed trends similar to those observed for V-5Cr-5Ti. The results show that grain size plays an important role in determining the ductile-to-brittle transition temperature (DBTT) of these materials and that a threshold level of grain boundary segregant appears to be required to cause grain boundary embrittlement and intergranular fracture.

  9. Fracture toughness evaluation of 20MnMoNi55 pressure vessel steel in the ductile to brittle transition regime: Experiment & numerical simulations

    Science.gov (United States)

    Gopalan, Avinash; Samal, M. K.; Chakravartty, J. K.

    2015-10-01

    In this work, fracture behaviour of 20MnMoNi55 reactor pressure vessel (RPV) steel in the ductile to brittle transition regime (DBTT) is characterised. Compact tension (CT) and single edged notched bend (SENB) specimens of two different sizes were tested in the DBTT regime. Reference temperature 'T0' was evaluated according to the ASTM E1921 standard. The effect of size and geometry on the T0 was studied and T0 was found to be lower for SENB geometry. In order to understand the fracture behaviour numerically, finite element (FE) simulations were performed using Beremin's model for cleavage and Rousselier's model for ductile failure mechanisms. The simulated fracture behaviour was found to be in good agreement with the experiment.

  10. Ductile to Brittle Transition Behaviour of HSLA-65 Steel Welds: Dynamic Tear Testing

    Science.gov (United States)

    2011-01-01

    de transition obtenues antérieurement à l’aide de l’essai de choc Charpy. Un objectif secondaire de la présente étude consistait à comparer la méthode...dynamique de résistance à l’arrachement sont beaucoup plus élevées que celles obtenues à l’aide de l’essai de choc Charpy, ce qui appuie l’exigence...servir dans des conditions arctiques. Les résultats montrent que l’essai de choc Charpy ne constitue pas une méthode fiable permettant de déterminer le

  11. Characterisation of the fracture properties in the ductile to brittle transition region of the weld material of a reactor pressure vessel

    Energy Technology Data Exchange (ETDEWEB)

    Scibetta, M. [SCK-CEN, Boeretang 200, 2400 Mol (Belgium); Ferreno, D., E-mail: ferrenod@unican.es [University of Cantabria, ETS Ingenieros de Caminos, Av/Los Castros s/n, 39005 Santander (Spain); Gorrochategui, I. [Centro Tecnologico de Componentes (CTC), Parque Cientifico y Tecnologico de Cantabria, Isabel Torres No 1, 39011 Santander (Spain); Nuclenor, SA, C/Hernan Cortes 26, 39003 Santander (Spain); Lacalle, R. [University of Cantabria, ETS Ingenieros de Caminos, Av/Los Castros s/n, 39005 Santander (Spain); Walle, E. van [SCK-CEN, Boeretang 200, 2400 Mol (Belgium); Martin, J. [Nuclenor, SA, C/Hernan Cortes 26, 39003 Santander (Spain); Gutierrez-Solana, F. [University of Cantabria, ETS Ingenieros de Caminos, Av/Los Castros s/n, 39005 Santander (Spain)

    2011-04-15

    This work presents the results of the fracture characterisation of the weld material of a nuclear vessel, currently in service, in the ductile to brittle transition region. The tests consisted of Charpy impact and tensile tests, performed in the framework of the surveillance programme of the plant. Moreover, in the context of this research, K{sub Jc} fracture toughness tests on pre-cracked Charpy V notch specimens (evaluated according to the Master Curve methodology) together with some mini-tensile tests, were performed; non-irradiated and several irradiated material conditions were characterised. The analysis of the experimental results revealed some inconsistencies concerning the material embrittlement as measured through Charpy and K{sub Jc} fracture tests: in order to obtain an adequate understanding of the results, an extended experimental scope well beyond the regulatory framework was developed, including Charpy tests and K{sub Jc} fracture tests, both performed on reconstituted specimens. Moreover, Charpy specimens irradiated in the high flux BR2 material test reactor were tested with the same purpose. With this extensive experimental programme, a coherent and comprehensive description of the irradiation behaviour of the weld material in the transition region was achieved. Furthermore it revealed better material properties in comparison with the initial expectations based on the information obtained in the framework of the surveillance programme.

  12. 高氮奥氏体钢的韧脆转变与层错能的关系%Study on relationship between ductile to brittle transition and stacking fault energy of high nitrogen containing austenitic stainless steel

    Institute of Scientific and Technical Information of China (English)

    马玉喜

    2011-01-01

    在60℃至室温范围内,采用夏比冲击试验测定材料的韧一脆转变温度,并通过对冲击断口的X-射线测试层错能等方法,对几种不同含氮量奥氏体不锈钢在低温下发生韧一脆转变的现象进行了研究.结果表明:在超高氮奥氏体钢中,随氮质量分数的增加该钢种发生韧一脆转变的温度上升,层错能减少,韧性越来越差.%The DBTT of super-high nitrogen containing austenitic stainless steels was tested at temperatures between room-temperature and -60 ℃ by Charpy-type test, and its ductility and brittleness transition were investigated under low temperature by XRD method. The results show that the ductile to brittle transition temperature (DBTT) of high nitrogen containing austenitic stainless steels depends on the nitrogen content in the steel, and the DBTT is shifted from low temperature to high temperature. In addition,with the increase of nitrogen content, the stacking fault energy is decreased and the ductility is getting worse.

  13. Assessment of Ductile-to-Brittle Transition Behavior of Localized Microstructural Regions in a Friction-Stir Welded X80 Pipeline Steel with Miniaturized Charpy V-Notch Testing

    Science.gov (United States)

    Avila, Julian A.; Lucon, Enrico; Sowards, Jeffrey; Mei, Paulo Roberto; Ramirez, Antonio J.

    2016-06-01

    Friction-stir welding (FSW) is an alternative welding process for pipelines. This technology offers sound welds, good repeatability, and excellent mechanical properties. However, it is of paramount importance to determine the toughness of the welds at low temperatures in order to establish the limits of this technology. Ductile-to-brittle transition curves were generated in the present study by using a small-scale instrumented Charpy machine and miniaturized V-notch specimens (Kleinstprobe, KLST); notches were located in base metal, heat-affected, stirred, and hard zones within a FSW joint of API-5L X80 Pipeline Steel. Specimens were tested at temperatures between 77 K (-196 °C) and 298 K (25 °C). Based on the results obtained, the transition temperatures for the base material and heat-affected zone were below 173 K (-100 °C); conversely, for the stirred and hard zones, it was located around 213 K (-60 °C). Fracture surfaces were characterized and showed a ductile fracture mechanism at high impact energies and a mixture of ductile and brittle mechanisms at low impact energies.

  14. ``Global and local approaches of fracture in the ductile to brittle regime of a low alloy steel``; ``Approches globale et locale de la rupture dans le domaine de transition fragile-ductile d`un acier faiblement allie``

    Energy Technology Data Exchange (ETDEWEB)

    Renevey, S

    1998-12-31

    The study is a contribution to the prediction of flow fracture toughness of low alloy steel and to a better knowledge of fracture behavior in the ductile to brittle transition region. Experiments were performed on a nozzle cut-off from a pressurized water reactor vessel made of steels A508C13 type steel. Axisymmetrical notched specimens were tested to study the fracture onset in a volume element while pre-cracked specimens were used to investigate cleavage fracture after stable crack growth. Systematic observations of fracture surfaces showed manganese sulfide inclusions (MnS) at cleavage sites or in the vicinity. The experimental results were used for modelling by the local approach to fracture. In a volume element the fracture is described by an original probabilistic model. This model is based on volume fraction distributions of MnS inclusions gathered in clusters and on the assumption of a competition without interaction between ductile and cleavage fracture modes. This model was applied to pre-cracked specimens (CT specimens). It is able to describe the scatter in the toughness after a small stable crack growth if a temperature effect on the cleavage stress is assumed. So, the modelling is able to give a lower bound of fracture toughness as a function of temperature. (author) 100 refs.

  15. Geochronology Constraints on Transformation Age from Ductile to Brittle Deformation of the Shangma Fault and Its Tectonic Significance, Dabieshan, Central China

    Institute of Scientific and Technical Information of China (English)

    Wang Guocan; Wang Pu; Liu Chao; Wang An; Ye Runqing

    2008-01-01

    By a detailed investigation of geometry and kinematics of the Shangma (商麻) fault in Dabieshan (大别山),three different crust levels of extension movement have been recognized in sequence from the deep to the shallow:① low-angle ductile detachment shearing with top to the NW; ② low-angle normal fault with top to the NW or NWW in brittle or brittle-ductile transition domain; ③high-angle brittle normal fault with top to the W or NWW. Two samples were chosen for zircon U-Pb age dating to constrain the activity age of the Shangma fault. A bedding intrusive granitoid pegmatite vein that is parallel to the foliation of the low-angle ductile detachment shear zone of the country rock exhibits a lotus-joint type of boudinage deformation,showing syn-tectonic emplacing at the end of the ductile deformation period and deformation in the brittle-ductile transition domain. The zircon U-Pb dating of this granitoid pegmatite vein gives an age of (125.9±4.2) Ma,which expresses the extension in the brittle-ductile transition domain of the Shangma fault. The other sample,which is collected from a granite pluton cutting the foliation of the low-angle ductile detachment shear zone, gives a zircon U-Pb age of (118.8±4.1) Ma,constraining the end of the ductile detachment shearing. Then the transformation age from ductile to brittle deformation can be constrained between 126-119 Ma.Combined with the previous researches,the formation of the Luotian (罗田) dome,which is located to the east of the Shangma fault,can beconstrained during 150-126 Ma. This study gives a new time constraint to the evolution of the Dabie orogenic belt.

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

    Science.gov (United States)

    Rajnovic, D; Eric, O; Sidjanin, L

    2008-12-01

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

  17. Revealing the extra-high ductility and toughness of micro+duplex medium+Mn steel in a large temperature range from 200 ℃ to -196 ℃

    DEFF Research Database (Denmark)

    Cao, Wenquan; Hu, Jun; Dong, Han

    2014-01-01

    A medium-Mn steel (0.2C5Mn) was processed by intercritical annealing at different temperature (625℃ and 650℃) after forging and hot rolling. The microstructures were characterized by transmission electron microscopy and the mechanical properties were measured by tensile tests and impact tests...... be obtained in the temperature range from 200℃ to -196℃. And significantly delayed transition from ductile to brittle and no less than 200J impact toughness at -40℃ could be obtained in the ART-annealed medium-Mn steel. Based on the analysis of microstructure and mechanical properties, the enhanced ductility...... in the full temperature range could be ascribed to the phase transformation effect of austenite (TRIP effects), while the delayed ductile to brittle transition could be attributed to the enhanced austenite stability....

  18. High Ductility and Toughness of a Micro-duplex Medium-Mn Steel in a Large Temperature Range from -196 °C to 200 °C

    DEFF Research Database (Denmark)

    Chen, Si-lian; Hu, Jun; Zhang, Xiaodan

    2015-01-01

    A medium-Mn steel (0.2C5Mn) was processed by intercritical annealing at different temperatures (625 degrees C and 650 degrees C). An ultrafine-grained micro-duplex structure consisting of alternating austenite and ferrite laths was developed by austenite reverse transformation (ART) during...... and mechanical properties, it was found that the enhanced ductility was determined by the phase transformation effect 'of austenite (TRIP effect), while the delayed ductile to brittle transition was controlled by austenite stability....

  19. Effects of irradiation at low temperature on V-4Cr-4Ti

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, D.J.; Snead, L.L.; Zinkle, S.J. [Oak Ridge National Lab., TN (United States)] [and others

    1996-10-01

    Irradiation at low temperatures (100 to 275{degrees}C) to 0.5 dpa causes significant embrittlement and changes in the subsequent room temperature tensile properties of V-4Cr-4Ti. The yield strength and microhardness at room temperature increase with increasing irradiation temperature. The tensile flow properties at room temperature show large increases in strength and a complete loss of work hardening capacity with no uniform ductility. Embrittlement, as measured by an increase in the ductile-to-brittle transition temperature, increases with increasing irradiation temperature, at least up to 275{degrees}C. This embrittlement is not due to pickup of O or other interstitial solutes during the irradiation.

  20. Effects of Lower Drying-Storage Temperature on the Ductility of High-Burnup PWR Cladding

    Energy Technology Data Exchange (ETDEWEB)

    Billone, M. C. [Argonne National Lab. (ANL), Argonne, IL (United States); Burtseva, T. A. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-08-30

    The purpose of this research effort is to determine the effects of canister and/or cask drying and storage on radial hydride precipitation in, and potential embrittlement of, high-burnup (HBU) pressurized water reactor (PWR) cladding alloys during cooling for a range of peak drying-storage temperatures (PCT) and hoop stresses. Extensive precipitation of radial hydrides could lower the failure hoop stresses and strains, relative to limits established for as-irradiated cladding from discharged fuel rods stored in pools, at temperatures below the ductile-to-brittle transition temperature (DBTT).

  1. Estimation Uncertainty in the Determinatin of the Master Curve Reference Temperature

    Energy Technology Data Exchange (ETDEWEB)

    TL Sham; DR Eno

    2006-11-15

    The Master Curve Reference Temperature, T{sub 0}, characterizes the fracture performance of structural steels in the ductile-to-brittle transition region. For a given material, this reference temperature is estimated via fracture toughness testing. A methodology is presented to compute the standard error of an estimated T{sub 0} value from a finite sample of toughness data, in a unified manner for both constant temperature and multiple temperature test methods. Using the asymptotic properties of maximum likelihood estimators, closed-form expressions for the standard error of the estimate of T{sub 0} are presented for both test methods. This methodology includes statistically rigorous treatment of censored data, which represents an advance over the current ASTM E1921 methodology. Through Monte Carlo simulations of realistic constant temperature and multiple temperature test plans, the recommended likelihood-based procedure is shown to provide better statistical performance than the methods in the ASTM E1920 standards.

  2. ESTIMATION UNCERTAINTY IN THE DETERMINATION OF THE MASTER CURVE REFERENCE TEMPERATURE

    Energy Technology Data Exchange (ETDEWEB)

    Sham, Sam [ORNL; Eno, Daniel R [Bechtel Marine Propulsion Corporation

    2010-01-01

    The Master Curve Reference Temperature, T0, characterizes the fracture performance of structural steels in the ductile-to-brittle transition region. For a given material, this reference temperature is estimated via fracture toughness testing. A methodology is presented to compute the standard error of an estimated T0 value from a finite sample of toughness data, in a unified manner for both single temperature and multiple temperature test methods. Using the asymptotic properties of maximum likelihood estimators, closed-form expressions for the standard error of the estimate of T0 are presented for both test methods. This methodology includes statistically rigorous treatment of censored data, which represents an advance over the current ASTM E1921 methodology. Through Monte Carlo simulations of realistic single temperature and multiple temperature test plans, the recommended likelihood-based procedure is shown to provide better statistical performance than the methods in the ASTM E1921 standard.

  3. Effect of temperature and displacement rate on behaviour of as-cast AA5182 and Al–3.3%Cu alloys under tensile loading near solidus temperature

    Indian Academy of Sciences (India)

    Suyitno

    2013-08-01

    Hot cracking develops in the still semi-solid casting during the last stages of solidification. The micromechanism of its origin is not generally accepted. There exists considerable doubt whether it is initiated by a void or develops as an instantaneous crack. The aim of this work is to study the mechanism of fracture behaviour of aluminum alloys around solidus temperature. Tensile tests were performed on notched specimens of as-cast AA5182 and Al–3.3%Cu alloys using a Gleeble 3500® thermomechanical simulator. The effect of temperature and strain rate on the propagation of fracture in the semi-solid state has been studied to establish fracture mechanism. The transition from ductile to brittle mode of fracture has been observed around the solidus temperature. The fracture is intergranular and propagates through interdendritic channels.

  4. High temperature erosion of coated superalloys for gas turbines

    Energy Technology Data Exchange (ETDEWEB)

    Restall, J.E.; Stephenson, D.J.

    1987-04-01

    Particulate materials ingested with the intake air, together with other solids generated within the gas turbine, are known to have the potential of degrading the hot oxidized or corroded surfaces of static and rotating aerofoil components. The nature of the degradation may be primarily by oxidation, corrosion or erosion or through some form of interaction between these processes. These regimes are illustrated by reference to the metallurgical assessment of components withdrawn from a marine gas turbine and a turbine used for pressurized fluidized-bed combustion trials. The conditions under which surface coatings may be expected to enhance the erosion-corrosion resistance of hot-end turbine components are discussed. From laboratory erosion experiments, particular attention is directed towards the importance of oxide scale plasticity and the ductile-to-brittle transition temperature of the coating under various particle-loading conditions.

  5. Small punch tensile/fracture test data and 3D specimen surface data on Grade 91 ferritic/martensitic steel from cryogenic to room temperature.

    Science.gov (United States)

    Bruchhausen, Matthias; Lapetite, Jean-Marc; Ripplinger, Stefan; Austin, Tim

    2016-12-01

    Raw data from small punch tensile/fracture tests at two displacement rates in the temperature range from -196 °C to room temperature on Grade 91 ferritic/martensitic steel are presented. A number of specimens were analyzed after testing by means of X-ray computed tomography (CT). Based on the CT volume data detailed 3D surface maps of the specimens were established. All data are open access and available from Online Data Information Network (ODIN)https://odin.jrc.ec.europa.eu. The data presented in the current work has been analyzed in the research article "On the determination of the ductile to brittle transition temperature from small punch tests on Grade 91 ferritic-martensitic steel" (M. Bruchhausen, S. Holmström, J.-M. Lapetite, S. Ripplinger, 2015) [1].

  6. Effects of temperature and strain rate on the tensile properties of potassium-doped tungsten

    Energy Technology Data Exchange (ETDEWEB)

    Sasaki, Kenta, E-mail: k.sasaki@jupiter.qse.tohoku.ac.jp; Yabuuchi, Kiyohiro, E-mail: kiyohiro.yabuuchi@qse.tohoku.ac.jp; Nogami, Shuhei, E-mail: shuhei.nogami@qse.tohoku.ac.jp; Hasegawa, Akira, E-mail: akira.hasegawa@qse.tohoku.ac.jp

    2015-06-15

    Tensile tests were performed on pure and K-doped tungsten at temperatures from 25 to 700 °C and strain rates between 10{sup −5} and 10{sup −1} s{sup −1} in vacuum. The yield strength of both materials increased with increasing strain rate and decreasing temperature. The amount of change in the yield strength decreased with increasing temperature. The determination of activation volumes for plastic deformation highlighted that the rate-controlling process of the deformation behavior at lower temperatures was the same for both materials, namely, kink-pair formation on screw dislocations, and the process was not affected by potassium addition. The fracture strain of both materials increased with increasing strain rate and decreasing temperature, in the temperature range where the materials showed measurable ductility. K-doped W showed higher yield strength and a lower ductile-to-brittle transition temperature than pure W. No negative effect of K addition on strain rate- and temperature-induced changes in tensile properties was found. The analysis also highlighted the effectiveness of K addition, and of the grain refinement induced by it, for improving the mechanical properties of tungsten.

  7. Effects of temperature and strain rate on the tensile properties of potassium-doped tungsten

    Science.gov (United States)

    Sasaki, Kenta; Yabuuchi, Kiyohiro; Nogami, Shuhei; Hasegawa, Akira

    2015-06-01

    Tensile tests were performed on pure and K-doped tungsten at temperatures from 25 to 700 °C and strain rates between 10-5 and 10-1 s-1 in vacuum. The yield strength of both materials increased with increasing strain rate and decreasing temperature. The amount of change in the yield strength decreased with increasing temperature. The determination of activation volumes for plastic deformation highlighted that the rate-controlling process of the deformation behavior at lower temperatures was the same for both materials, namely, kink-pair formation on screw dislocations, and the process was not affected by potassium addition. The fracture strain of both materials increased with increasing strain rate and decreasing temperature, in the temperature range where the materials showed measurable ductility. K-doped W showed higher yield strength and a lower ductile-to-brittle transition temperature than pure W. No negative effect of K addition on strain rate- and temperature-induced changes in tensile properties was found. The analysis also highlighted the effectiveness of K addition, and of the grain refinement induced by it, for improving the mechanical properties of tungsten.

  8. Effect of Temperature on the Toughness of Locally Manufactured Low Alloy Steel SUP9 Used for Manufacturing Leaf Springs

    Directory of Open Access Journals (Sweden)

    Muhammad Ishaque Abro

    2011-10-01

    Full Text Available The effect of heat treatment on locally manufactured low alloy steel grade SUP9 most frequently used in making leaf springs for automobiles was studied. While for determination of toughness and hardness Charpy impact testing machine and Rockwell hardness tester were used. The cryogenic test temperatures were achieved by soaking the samples in liquid nitrogen and temperature was measured using digital thermometer capable of reading the temperature from -40-200oC. Hardening, tempering and austempering treatments were conducted using muffle furnace and salt bath furnace. After heat treatment samples were quenched in oil. The results of present work confirmed that toughness and hardness are inversely related with each other and are highly dependent on the type of heat treatment employed. Highest toughness was measured after austempering at 450oC. Effect of test temperature revealed that toughness of the samples increased significantly with decreasing temperature. DBTT (Ductile to Brittle Transition Temperature of the austempered samples was observed at -10oC, whereas, that of tempered samples could not be determined. Based on the test results authors wish to recommend the 600oC tempering temperature in place of 450oC where normally tempering is practiced in Alwin industry Karachi during manufacturing of leaf spring.

  9. Microstructure and tensile properties of tungsten at elevated temperatures

    Science.gov (United States)

    Shen, Tielong; Dai, Yong; Lee, Yongjoong

    2016-01-01

    In order to support the development of the 5 MW spallation target for the European Spallation Source, the effect of fabrication process on microstructure, ductile-to-brittle transition temperature (DBTT), tensile and fracture behaviour of powder-metallurgy pure tungsten materials has been investigated. A hot-rolled (HR) tungsten piece of 12 mm thickness and a hot-forged (HF) piece of about 80 mm thickness were used to simulate the thin and thick blocks in the target. The two tungsten pieces were characterized with metallography analysis, hardness measurement and tensile testing. The HR piece exhibits an anisotropic grain structure with an average size of about 330 × 140 × 40 μm in rolling, long transverse and short transverse (thickness) directions. The HF piece possesses a bimodal grain structure with about 310 × 170 × 70 μm grain size in deformed part and about 25 μm sized grains remained from sintering process. Hardness (HV0.2) of the HR piece is slightly greater than that of the HF one. The ductility of the HR tungsten specimens is greater than that of the HF tungsten. For the HF tungsten piece, specimens with small grains in gauge section manifest lower ductility but higher strength. The DBTT evaluated from the tensile results is 250-300 °C for the HR tungsten and about 350 °C for the HF tungsten.

  10. Fracture properties of neutron-irradiated martensitic 9Cr-WVTa steels below room temperature

    Science.gov (United States)

    Abe, F.; Narui, M.; Kayano, H.

    1994-09-01

    Fracture properties of the reduced activation martensitic 9Cr-1WVTa and 9Cr-3WVTa steels were investigated by carrying out instrumented Charpy impact tests and tensile tests at temperatures below room temperature after irradiation in the Japan Materials Testing Reactor at 493 and 538 K. Modified 9Cr-1MoVNb steel was also examined for comparison. The irradiation-induced increase in ductile-to-brittle transition temperature was 53, 26 and 40 K for the {1}/{3} size Charpy specimens of 9Cr-1WVTa, 9Cr-3WVTa and 9Cr-1MoVNb steels, respectively, which resulted primarily from the irradiation-induced increase in yield stress. The cleavage fracture stress was 1820-1870 MPa for the three steels in unirradiated conditions, which was scarcely affected by irradiation. The deflections to the maximum load and to the brittle fracture initiation were decreased by irradiation. In the tensile test, quasi-cleavage fracture occurred at 77 K in both unirradiated and irradiated conditions. The cleavage fracture stress was 1320-1380 MPa for the tensile specimens of the three steels, which was about 1.4 times smaller than that for the Charpy specimens.

  11. Membrane Transition Temperature Determines Cisplatin Response.

    Directory of Open Access Journals (Sweden)

    Krishnan Raghunathan

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

  12. A master curve-mechanism based approach to modeling the effects of constraint, loading rate and irradiation on the toughness-temperature behavior of a V-4Cr-4Ti alloy

    Energy Technology Data Exchange (ETDEWEB)

    Odette, G.R.; Donahue, E.; Lucas, G.E.; Sheckherd, J.W. [Univ. of California, Santa Barbara, CA (United States)

    1996-10-01

    The influence of loading rate and constraint on the effective fracture toughness as a function of temperature [K{sub e}(T)] of the fusion program heat of V-4Cr-4Ti was measured using subsized, three point bend specimens. The constitutive behavior was characterized as a function of temperature and strain rate using small tensile specimens. Data in the literature on this alloy was also analysed to determine the effect of irradiation on K{sub e}(T) and the energy temperature (E-T) curves measured in subsized Charpy V-notch tests. It was found that V-4Cr-4Ti undergoes {open_quotes}normal{close_quotes} stress-controlled cleavage fracture below a temperature marking a sharp ductile-to-brittle transition. The transition temperature is increased by higher loading rates, irradiation hardening and triaxial constraint. Shifts in a reference transition temperature due to higher loading rates and irradiation can be reasonably predicted by a simple equivalent yield stress model. These results also suggest that size and geometry effects, which mediate constraint, can be modeled by combining local critical stressed area {sigma}*/A* fracture criteria with finite element method simulations of crack tip stress fields. The fundamental understanding reflected in these models will be needed to develop K{sub e}(T) curves for a range of loading rates, irradiation conditions, structural size scales and geometries relying (in large part) on small specimen tests. Indeed, it may be possible to develop a master K{sub e}(T) curve-shift method to account for these variables. Such reliable and flexible failure assessment methods are critical to the design and safe operation of defect tolerant vanadium structures.

  13. Transition paths in molecules at finite temperature

    Science.gov (United States)

    Pinski, F. J.; Stuart, A. M.

    2010-05-01

    In the zero temperature limit, it is well known that in systems evolving via Brownian dynamics, the most likely transition path between reactant and product may be found as a minimizer of the Freidlin-Wentzell action functional. An analog for finite temperature transitions is given by the Onsager-Machlup functional. The purpose of this work is to investigate properties of Onsager-Machlup minimizers. We study transition paths for thermally activated molecules governed by the Langevin equation in the overdamped limit of Brownian dynamics. Using gradient descent in pathspace, we minimize the Onsager-Machlup functional for a range of model problems in one and two dimensions and then for some simple atomic models including Lennard-Jones seven-atom and 38-atom clusters, as well as for a model of vacancy diffusion in a planar crystal. Our results demonstrate interesting effects, which can occur at nonzero temperature, showing transition paths that could not be predicted on the basis of the zero temperature limit. However the results also demonstrate unphysical features associated with such Onsager-Machlup minimizers. As there is a growing literature that addresses transition path sampling by related techniques, these insights add a potentially useful perspective into the interpretation of this body of work.

  14. Modelling coupled to behaviour and damage; rupture criteria in the field of the PVDF transition; Modelisation couplee comportement endommagement et criteres de rupture dans le domaine de la transition du PVDF

    Energy Technology Data Exchange (ETDEWEB)

    Lafarge, M.

    2004-12-15

    Pipeline structures are used for the transport of crude oil in offshore fields. Flexible pipelines are made of an inner metallic layer, which accommodates flexural and tensile strains and of a PVDF layer, which guarantees watertightness. The aim of the study is to determine which conditions can lead to a risk of brittle fracture of the polymer material. The PVDF of interest was extruded without plasticizer and therefore it differs considerably from the standard industrial grade. The lack of plasticizer leads to a difficult extrusion, which creates significant porosity (10%). Several specimens with various geometries were tested in order to analyse the detrimental effect of a defect regarding damage evolution and fracture mechanisms. During the deformation process, the material is characterized by whitening due to void growth and material elongation. Ductile fracture of PVDF is promoted by high temperatures, low strain rates, low stress triaxiality ratios and flexural loading, whereas brittle fracture is favoured by low temperatures (T{<=}Tg = -42 C), high strain rates, high stress triaxiality ratios and tensile loading. The Gurson-Tvergaard-Needleman model, usually used for metallic materials, was employed to model behaviour and damage of PVDF material at various temperatures. Damage is essentially due to void growth and is described by using q1 and q2 parameters. The constitutive model has been successfully applied to account for all aspects of the mechanical behaviour of the material. Crazing is the failure mode and final fracture is assumed to occur when either, the maximum principal plastic strain at low stress triaxiality or the porosity at high stress triaxiality reaches respectively a critical value. Furthermore, the ductile to brittle transition criterion is found to be the maximum principal stress. This latter allows to explain both fracture mechanisms modes in flexural and tensile loading. (author)

  15. Temperature, transitivity, and the zeroth law

    DEFF Research Database (Denmark)

    Bergthorsson, Bjørn

    1977-01-01

    Different statements of the zeroth law are examined. Two types of statements—which characterize two aspects of temperature—are found. A new formulation of the zeroth law is given and a corollary is stated. By means of this corollary it is shown how temperature and transitivity are used to disclose...

  16. Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust

    Science.gov (United States)

    Wehrens, Philip; Berger, Alfons; Peters, Max; Spillmann, Thomas; Herwegh, Marco

    2016-12-01

    Mid-crustal deformation is classically characterized by the transition from ductile to brittle deformation defining the frictional-to-viscous transition (FVT). Here we investigate an exhumed continental mid-crustal basement section in order to envisage the relationship between ductile and brittle deformation at the FVT. Our detailed study from km- to micro-scale shows that, under greenschist metamorphic conditions, deformation is accommodated by a dense network of highly-localized ductile shear zones. In the investigated case it is not quartz which defines the overall ductile deformation behavior but the viscous granular deformation in shear zones with an ultrafine-grained polymineralic matrix consisting of quartz, feldspar, sheet silicates and epidote. During viscous granular flow mass transfer processes under the presence of fluids promote a chemo-mechanical mixing, resulting in grain size reduction and reaction softening. Coeval with this ductile deformation, fluid-assisted embrittlement occurs, as indicated by biotite-coated fractures, cataclasites and injection of non-cohesive polymineralic gouge material into secondary fractures inside the host rock. The embrittlement during predominant ductile deformation occurs in cycles, i.e. prolonged periods of slow viscous granular flow are interrupted by rapid brittle deformation. We interpret this fluid-assisted cyclic embrittlement evidenced by injection of the fluidized material into off-fault fractures as an alternative equivalent to pseudotachylites and as a microstructural indicator for paleo-seismic activity. With exhumation and associated cooling, localized deformation persists in the ultrafine-grained polymineralic shear zones but progressively transitions to cataclastic flow and finally to pressure-dependent frictional flow; always showing cycles of slow interseismic flow and fast seismic injection events. Overall, in the granitic crust of the Aar-massif, brittle and ductile deformation coexist up to

  17. Relating structural loading rate to tensing rate for fracture mechanics specimens

    NARCIS (Netherlands)

    Walters, C.L.; Przydatek, J.

    2014-01-01

    It is vely well-known that fracture toughness depends on loading rate. Higher strain rates can shift the ductile to brittle transition curve to higher temperatures, resulting in a more brittle structure at the same temperature. However, there is little effort to relate the testing rate to the

  18. Tectonic evolvement of metamorphic complexes at Jilin paleocontinental margin during the transition from late Archaean to early Proterozoic

    Institute of Scientific and Technical Information of China (English)

    SUN Zhongshi; DENG Jun; JIANG Yanguo; WANG Jianping; WANG Qingfei; WEI Yanguang

    2004-01-01

    The kinematics and dynamical process of tectonic evolvement of metamorphic complexes at the interim from late Archaean to early Proterozoic is one of the key problems in geosciences. For the disputation on the genesis of metamorphic complexes at the margin of Jilin palaeocontinent, this paper takes the example of Banshigou region, Jilin Province to discuss the dynamical evolution of palaeocontinent during the transition from late Archaean to early Proterozoic (2600-2000 Ma). On the time sequence, from center to palaeocontinental margin, it shows a series of dynamical movements including underplating, horizontal movement, subduction, intraplate extension and separation. And its corresponding sequence of kinematical modes is as follows: vertical movement, horizontal movement, extension and shearing in contact zone,uplift-sliding movement in paleocontinental margin and interformational sliding, resulting in such tectonite sequence, tectonic gneiss, gneissic complex, gneissic complex-mylonite, mylonite and fracture cleavage-mylonite, which consist of the main body of metamorphic complexes. Their palaeostresses are: < 20, 20.40, 21.72, 28.80 and 30.8-69.8 MPa respectively. The deformational metamorphic temperature is between hornblende and low-grade greenschist facies. The general deformational characters of Jilin palaeocontinent reflect a complete dynamic system of crust evolution, which indicates that the formation of the metamorphic complexes and the tectonic evolution are altered from vertical movement to compression to extension. It also indicates a continuous tectonic transformation from deep to shallow, and from ductile to brittle. The transformation between different dynamic mechanisms not only forms tectonic rocks, but also benefits the linking up, exchange and enrichment with rock-forming minerals and ore-forming elements.This research is helpful to classifying regional tectonic events and making further study on the evolution of palaeocontinental dynamics.

  19. Impact Behavior and Fracture Mechanism of Ductile Cast Iron with Minor Nickel Addition at Low Temperature%低镍球墨铸铁低温冲击性能及断裂机理研究

    Institute of Scientific and Technical Information of China (English)

    陈江; 黄兴民; 高杰维; 董海; 戴光泽

    2012-01-01

    使用激光共聚焦显微镜、扫描电镜和示波冲击等实验手段研究了镍元素(0.0%~0.9%,质量分数,下同)对球墨铸铁的微观组织和低温冲击性能的影响,对低温断裂机理进行了探讨.结果表明:含镍0.7%退火态球墨铸铁的韧脆转变温度低于-60℃,其-70℃下冲击功高于12J;适量镍元素添加能有效地细化晶粒和强化基体,改善球墨铸铁的低温冲击性能.%Utilizing laser confocal microscopy, SEM, instrumented impact and other experimental methods, the influence of nickel content(0. 0%-0. 9%,mass fraction, the same below) on the micro-structure and low temperature impact toughness of ductile cast iron(DCI) was investigated. The fracture mechanism of DCIs was studied further at different temperatures by using scanning electronic microscopy (SEM). The results show that ductile-to-brittle transition temperature of as-annealed DCIs with 0. 7% Ni content is lower than —60℃ , the impact energy of Charpy-type test is still higher than 12J at —70℃. Minor Ni addition of proper quantities might favor the grain refinement and matrix strengthen, low temperature impact toughness properties of DCIs are markedly improved.

  20. Parametric study of irradiation effects on the ductile damage and flow stress behavior in ferritic-martensitic steels

    Science.gov (United States)

    Chakraborty, Pritam; Biner, S. Bulent

    2015-10-01

    Ferritic-martensitic steels are currently being considered as structural materials in fusion and Gen-IV nuclear reactors. These materials are expected to experience high dose radiation, which can increase their ductile to brittle transition temperature and susceptibility to failure during operation. Hence, to estimate the safe operational life of the reactors, precise evaluation of the ductile to brittle transition temperatures of ferritic-martensitic steels is necessary. Owing to the scarcity of irradiated samples, particularly at high dose levels, micro-mechanistic models are being employed to predict the shifts in the ductile to brittle transition temperatures. These models consider the ductile damage evolution, in the form of nucleation, growth and coalescence of voids; and the brittle fracture, in the form of probabilistic cleavage initiation, to estimate the influence of irradiation on the ductile to brittle transition temperature. However, the assessment of irradiation dependent material parameters is challenging and influences the accuracy of these models. In the present study, the effects of irradiation on the overall flow stress and ductile damage behavior of two ferritic-martensitic steels is parametrically investigated. The results indicate that the ductile damage model parameters are mostly insensitive to irradiation levels at higher dose levels though the resulting flow stress behavior varies significantly.

  1. Electron anions and the glass transition temperature

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-08-24

    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. 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 new avenue in rational materials design.

  2. Effects of Microstructure on CVN Impact Toughness in Thermomechanically Processed High Strength Microalloyed Steel

    Science.gov (United States)

    Jia, Tao; Zhou, Yanlei; Jia, Xiaoxiao; Wang, Zhaodong

    2017-02-01

    Investigation on the correlation between microstructure and CVN impact toughness is of practical importance for the microstructure design of high strength microalloyed steels. In this work, three steels with characteristic microstructures were produced by cooling path control, i.e., steel A with granular bainite (GB), steel B with polygonal ferrite (PF) and martensite-austenite (M-A) constituent, and steel C with the mixture of bainitic ferrite (BF), acicular ferrite (AF), and M-A constituent. Under the same alloy composition and controlled rolling, similar ductile-to-brittle transition temperatures were obtained for the three steels. Steel A achieved the highest upper shelf energy (USE), while large variation of impact absorbed energy has been observed in the ductile-to-brittle transition region. With apparently large-sized PF and M-A constituent, steel B shows the lowest USE and delamination phenomenon in the ductile-to-brittle transition region. Steel C exhibits an extended upper shelf region, intermediate USE, and the fastest decrease of impact absorbed energy in the ductile-to-brittle transition region. The detailed CVN impact behavior is studied and then linked to the microstructural features.

  3. From ductile to brittle deformation: structural development and strain distribution along a crustal-scale shear zone in SW Finland

    Science.gov (United States)

    Torvela, Taija; Ehlers, Carl

    2010-07-01

    This study demonstrates the impact of variations in overall crustal rheology on crustal strength in relatively high P- T conditions at mid- to lower mid-crustal levels. In a crustal-scale shear zone, along-strike variations in the rheological competence result in large-scale deformation partitioning and differences in the deformation style and strain distribution. The structural behaviour of the crustal-scale Sottunga-Jurmo shear zone (SJSZ) in SW Finland is described. The shear zone represents a discontinuity between the amphibolite-to-granulite facies, dome-and-basin style crustal block to the north and the amphibolite facies rocks with dominantly steeply dipping structures to the south. The overall deformation style and resulting strains along the shear zone are greatly affected by the local lithology. The results of this study also have implications for the current tectonic models of the Palaeoproterozoic Fennoscandia. The most important implication is that the SJSZ, together with other structurally related shear zones, compartmentalised the far-field stresses, so that the late ductile structures within and south of the SJSZ can be allocated to a convergence from the south as late as ~1.79 Ga rather than to the Nordic orogeny from the west-northwest. It is further suggested that at ~1.79 Ga the stress regime was still compressive/transpressive and that the ~1.79 Ga magmatism in Åland at least initiated in a compressive setting. No extension or orogenic collapse, therefore, occurred in the Åland area while the rocks still were within the ductile regime.

  4. Metallurgical and mechanical behaviours of PWR fuel cladding tube oxidised at high temperature; Comportements metallurqigue et mecanique des materiaux de gainage du combustible REP oxydes a haute temperature

    Energy Technology Data Exchange (ETDEWEB)

    Stern, A

    2007-12-15

    were mechanically tested at various temperatures and for various mean oxygen contents. This allowed us, first, to establish ductile to brittle transition temperatures (for a given oxygen content), and second, to establish behaviour laws for those materials (function of oxygen content and temperature). It was thus possible to start some preliminary finite element calculations to describe the cladding behaviour under the standard technological ring compression test. (author)

  5. Glass transition and heavy oil dynamics at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Abivin, P.; Indo, K.; Cheng, Y.; Freed, D.; Taylor, S. D. [Schlumberger (Canada)], email: PAbivin@slb.com

    2011-07-01

    In the oil industry, the viscosity of crude oils is a key factor as it affects market value, field developments and the design of production strategies. In heavy oils, a glass transition occurs and previous work related this to oil's temperature-viscosity behavior. This study aimed at better characterizing heavy oil dynamics and the temperature dependency of viscosity. Experiments were conducted with differential scanning calorimetry and shear rate sweeps on heavy oils from Asia, South America and North America over a wide range of temperatures to measure their viscosities and characterize their glass transition. The glass transition was observed at around 210K and results showed that the Arrhenius model does not fit the experimental data at low temperatures but the WLF model does. This research provided a better understanding of heavy oil dynamics but further work is required to explain the viscosity-temperature behavior of heavy oils at low temperatures.

  6. Chiral phase transition in QED3 at finite temperature

    Science.gov (United States)

    Yin, Pei-Lin; Xiao, Hai-Xiao; Wei, Wei; Feng, Hong-Tao; Zong, Hong-Shi

    2016-12-01

    In the framework of Dyson-Schwinger equations, we employ two kinds of criteria (one kind is the chiral condensate, the other kind is thermodynamic quantities, such as the pressure, the entropy, and the specific heat) to investigate the nature of chiral phase transitions in QED3 for different fermion flavors. It is found that the chiral phase transitions in QED3 for different fermion flavors are all typical second-order phase transitions; the critical temperature and order of the chiral phase transition obtained from the chiral condensate and susceptibility are the same with that obtained by the thermodynamic quantities, which means that they are equivalent in describing the chiral phase transition; the critical temperature decreases as the number of fermion flavors increases and there is a boundary that separates the Tc-Nf plane into chiral symmetry breaking and restoration regions.

  7. Critical temperature for shape transitions in excited nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Martin, V. [Analisis Numerico, Facultad de Informatica, Universidad Politecnica de Madrid, E-28660, Madrid (Spain); Egido, J.L.; Robledo, L.M. [Departamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049, Madrid (Spain)

    2004-04-01

    The behavior of shell effects with temperature is studied within the framework of the finite-temperature Hartree-Fock-Bogoliubov theory with the Gogny force. Thermal shape fluctuations in the quadrupole degree of freedom are taken into account in the frame of the Landau theory. Numerical results for the superfluid-to-normal and deformed-to-spherical phase transitions are presented for the nucleus {sup 164}Er. We find that the critical temperature for the deformed-spherical shape transition is much lowered when the thermal shape fluctuations are considered. (orig.)

  8. A NEURAL NETWORK STUDY ON GLASS TRANSITION TEMPERATURE OF POLYMERS

    Institute of Scientific and Technical Information of China (English)

    Lin-xi Zhanga; De-lu Zhao; You-xing Huang

    2002-01-01

    In this paper, an artificial neural network model is adopted to study the glass transition temperature of polymers. In our artificial neural networks, the input nodes are the characteristic ratio C∞, the average molecular weight M, between entanglement points and the molecular weight Mmon of repeating unit. The output node is the glass transition temperature Tg,and the number of the hidden layer is 6. We found that the artificial neural network simulations are accurate in predicting the outcome for polymers for which it is not trained. The maximum relative error for predicting of the glass transition temperature is 3.47%, and the overall average error is only 2.27%. Artificial neural networks may provide some new ideas to investigate other properties of the polymers.

  9. Instrumented charpy impact tests of austenitic and ferritic steels

    Science.gov (United States)

    Yoshida, H.; Miyata, K.; Hayashi, Y.; Narui, M.; Kayano, H.

    1985-08-01

    The instrumented Charpy impact test was applied to commercial Mn-steel and ferritic steels before and after JMTR irradiation ( 6.5 × 10 22 n/m 2). The load-deflection curves show typical characteristics of the fracture properties of the specimens; i.e. linear elastic behaviour for the brittle fracture and elastic-plastic behaviour for the ductile fracture. The fracture deflection and the absorption energy (fracture energy) dropped rapidly at the temperature of ductile to brittle transition. The ductile-brittle transition temperatures (DBTTs) showed shifts of about 30 and 40 K due to the irradiation for 9Cr-1Mo and 9Cr-2Mo steels, respectively. In Mn-steel the transition from ductile to brittle did not appear at temperatures higher than 77 K. The lateral expansions measured from the scanning electron micrographs show good correspondence to the above results.

  10. Fluorinated epoxy resins with high glass transition temperatures

    Science.gov (United States)

    Griffith, James R.

    1991-01-01

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

  11. Chiral phase transition in QED$_3$ at finite temperature

    CERN Document Server

    Wei, Wei; Zong, Hong-Shi

    2016-01-01

    Chiral phase transition in (2+1)-dimensional quantum electrodynamics (QED$_3$) at finite temperature is investigated in the framework of truncated Dyson-Schwinger equations (DSEs). We go beyond the widely used instantaneous approximation and adopt a method that retains the full frequency dependence of the fermion self-energy. We also take further step to include the effects of wave-function renormalizations and introduce a minimal dressing of the bare vertex. Finally, with the more complete solutions of the truncated DSEs, we revisit the study of chiral phase transition in finite-temperature QED$_3$.

  12. Thermophysical and mechanical properties of Fe-(8-9)%Cr reduced activation steels

    Energy Technology Data Exchange (ETDEWEB)

    Zinkle, S.J.; Robertson, J.P.; Klueh, R.L. [Oak Ridge National Lab., TN (United States)

    1998-09-01

    The key thermophysical and mechanical properties for 8--9%Cr reduced activation ferritic/martensitic steels are summarized, including temperature-dependent tensile properties in the unirradiated and irradiated conditions, stress-rupture behavior, elastic constants, thermal conductivity, thermal expansion, specific heat, and ductile-to-brittle transition temperature. The estimated lower and upper temperatures limits for structural applications are 250 and 550 C due to radiation hardening/embrittlement and thermal creep considerations, respectively.

  13. Citrate increases glass transition temperature of vitrified sucrose preparations

    NARCIS (Netherlands)

    Kets, E.P.W.; Lipelaar, P.J.; Hoekstra, F.A.; Vromans, H.

    2004-01-01

    The aim of this study was to investigate the effect of sodium citrate on the properties of dried amorphous sucrose glasses. Addition of sodium citrate to a sucrose solution followed by freeze-drying or convective drying resulted in a glass transition temperature (T-g) that was higher than the well-s

  14. Depression of Glass Transition Temperatures of Polymer Networks by Diluents

    NARCIS (Netherlands)

    Brinke, Gerrit ten; Karasz, Frank E.; Ellis, Thomas S.

    1983-01-01

    A classical thermodynamic theory is used to derive expressions for the depression of the glass transition temperature Tg of a polymer network by a diluent. The enhanced sensitivity of Tg in cross-linked systems to small amounts of diluent is explained. Predictions of the theory are in satisfactory a

  15. ZrCuNiAl块体非晶合金的低温压缩变形行为%Compressive deformation behavior of ZrCuNiAl bulk metallic glass at low temperature

    Institute of Scientific and Technical Information of China (English)

    孙亚娟; 翟延慧

    2016-01-01

    Low temperature compression tests for the Zr 55.7 Cu23 Ni9 Al12.3 bulk metallic glass ( BMG) were carried out at the strain rate of 4 × 10 -4 s-1 and at the temperature of 143 K on Instron 5500 universal-testing machine , and the compressive deformation behavior of the Zr55.7 Cu23 Ni9 Al12.3 BMG during low temperature compression was investigated .The results show that the compressive yield strength and plasticity of the Zr55.7 Cu23 Ni9 Al12.3 BMG improve as testing temperature decreasing from 298 K to 143 K.Meanwhile, the phenomenon of ductile-to-brittle transition ( DBT) in traditional crystalline material is not observed with the decrease of temperature .The increase of yield strength is attributed to the nucleation of shear bands which requires a higher applied load at low temperature .Dense and multiple shear bands which are contributed to the enhanced ductility are observed on the side surface of the low temperature fractured samples .%采用Instron 5500万能试验机对Zr55.7 Cu23 Ni9 Al12.3块体非晶合金进行了应变速率为4×10-4 s-1、环境温度为143 K的低温压缩试验,研究了其低温压缩变形行为。结果表明,当测试环境温度从298 K(室温)降低到143 K时,该合金的强度和塑性均呈增加的趋势,且未出现传统晶态材料的冷脆性现象。分析表明,其屈服强度的增加源于低温下剪切带的形核需要更高的载荷,而低温下断口侧面高密度剪切带的形成导致了其塑性的增加。

  16. Cooling Dynamics Trough Transition Temperature of Niobium SRF Cavities Captured by Temperature Mapping

    CERN Document Server

    Martinello, M; Checchin, M; Grassellino, A; Crawford, A C; Melnychuk, A; Sergatskov, D A

    2015-01-01

    Cool-down dynamics of superconducting accelerating cavities became particularly important for obtaining very high quality factors in SRF cavities. Previous studies proved that when cavity is cooled fast, the quality factor is higher than when cavity is cooled slowly. This has been discovered to derive from the fact that a fast cool-down allows better magnetic field expulsion during the superconducting transition. In this paper we describe the first experiment where the temperature all around the cavity was mapped during the cavity cool-down through transition temperature, proving the existence of two different transition dynamics: a sharp superconducting-normal conducting transition during fast cool-down which favors flux expulsion and nucleation phase transition during slow cool-down, which leads to full flux trapping.

  17. Holographic Superconductor/Insulator Transition at Zero Temperature

    CERN Document Server

    Nishioka, Tatsuma; Takayanagi, Tadashi

    2009-01-01

    We analyze the five-dimensional AdS gravity coupled to a gauge field and a charged scalar field. Under a Scherk-Schwarz compactification, we show that the system undergoes a superconductor/insulator transition at zero temperature in 2+1 dimensions as we change the chemical potential. By taking into account a confinement/deconfinement transition, the phase diagram turns out to have a rich structure. We will observe that it has a similarity with the RVB (resonating valence bond) approach to high-Tc superconductors via an emergent gauge symmetry.

  18. Measurement of improved pressure dependence of superconducting transition temperature

    Science.gov (United States)

    Karmakar, S.

    2013-06-01

    We describe a technique for making electrical transport measurements in a diamond anvil cell at liquid helium temperature having in situ pressure measurement option, permitting accurate pressure determination at any low temperature during the resistance measurement scan. In general, for four-probe resistivity measurements on a polycrystalline sample, four fine gold wires are kept in contact with the sample with the help of the compression from the soft solid (usually alkali halides such as NaCl, KCl, etc.) acting as a pressure-transmitting medium. The actual pressure on the sample is underestimated if not measured from a ruby sphere placed adjacent to the sample and at that very low temperature. Here, we demonstrate the technique with a quasi-four-probe resistance measurement on an Fe-based superconductor in the temperature range 1.2-300 K and pressures up to 8 GPa to find an improved pressure dependence of the superconducting transition temperature.

  19. Temperature Triggered Structural Transitions in Surfactant organized Self Assemblies

    Science.gov (United States)

    Rose, J. Linet; Balamurugan, S.; Sajeevan, Ajin C.; Sreejith, Lisa

    2011-10-01

    Preparation & characterization of tunable fluids is an emerging area with potential application in many fields. Surfactants self assemble in aqueous solution to give a rich variety of phase structures, the size and shape of which can be tuned by additives like salts, alcohols, amines, aromatics etc or external stimuli such as light, temperature etc. The addition of long chain aliphatic alcohol has significant influence on the surfactant aggregation, as it promotes morphological growth of micelles. The cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB) with nonanol in presence of potassium bromide (KBr) shows thermo tunable viscosity behaviour and optical switching behaviour. The solution is visually observed to transform from a turbid and less viscous phase at low temperature to clear and considerably viscous phase at high temperature. Temperature induced changes in turbidity and viscosity are consistent with the transition from vesicle to worm like micelle. It is also worth emphasizing that the transition is thermo reversible, so that vesicles that are disrupted into micelles upon heating can be reformed upon cooling. The thermo tunable transition from turbid to transparent state and the concomitant changes in viscosity are promising for the use in smart windows, monitoring of tumor growth or in other stimuli based application.

  20. A Study of Solder Alloy Ductility for Cryogenic Applications

    Science.gov (United States)

    Lupinacci, A.; Shapiro, A. A.; Suh, J-O.; Minor, A. M.

    2013-01-01

    For aerospace applications it is important to understand the mechanical performance of components at the extreme temperature conditions seen in service. For solder alloys used in microelectronics, cryogenic temperatures can prove problematic. At low temperatures Sn-based solders undergo a ductile to brittle transition that leads to brittle cracks, which can result in catastrophic failure of electronic components, assemblies and spacecraft payloads. As industrial processes begin to move away from Pb-Sn solder, it is even more critical to characterize the behavior of alternative Sn-based solders. Here we report on initial investigations using a modified Charpy test apparatus to characterize the ductile to brittle transformation temperature of nine different solder systems.

  1. POLYMER CHAIN DIFFUSION AT A TEMPERATURE BELOW ITS BULK GLASS TRANSITION TEMPERATURE

    Institute of Scientific and Technical Information of China (English)

    Tisato Kajiyama; Daisuke Kawaguchi; Keiji Tanaka

    2003-01-01

    In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in the bulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtained results clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristic length scale of usual segmental motion even at a temperature below its bulk glass transition temperature, Tbg. This is consistent with our previous results that the surface glass transition temperature is much lower than the corresponding Tbg.Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.

  2. Predicting glass transition temperatures of polyarylethersulphones using QSPR methods.

    Directory of Open Access Journals (Sweden)

    Ian Hamerton

    Full Text Available 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.

  3. Magnetic transition temperatures follow crystallographic symmetry in samarium under high-pressures and low-temperatures

    Science.gov (United States)

    Johnson, Craig R.; Tsoi, Georgiy M.; Vohra, Yogesh K.

    2017-02-01

    Magnetic ordering temperatures in rare earth metal samarium (Sm) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to high-pressure up to 47 GPa and low-temperature to 10 K. The two magnetic transitions at 106 K and 14 K in the α-Sm phase, attributed to antiferromagnetic ordering on hexagonal and cubic layers respectively, collapse in to one magnetic transition near 10 GPa when Sm assumes a double hexagonal close packed (dhcp) phase. On further increase in pressure above 34 GPa, the magnetic transitions split again as Sm adopts a hexagonal-hP3 structure indicating different magnetic transition temperatures for different crystallographic sites. A model for magnetic ordering for the hexagonal-hP3 phase in samarium has been proposed based on the experimental data. The magnetic transition temperatures closely follow the crystallographic symmetry during α-Sm  →  dhcp  →  fcc/dist.fcc  →  hP3 structure sequence at high-pressures and low-temperatures.

  4. Fluctuational shift of nematic-isotropic phase transition temperature

    Science.gov (United States)

    Kats, E. I.

    2017-02-01

    In this work we discuss a macroscopic counterpart to the microscopic mechanism of the straightening dimer mesogens conformations, proposed recently by S.M. Saliti, M.G.Tamba, S.N. Sprunt, C.Welch, G.H.Mehl, A. Jakli, J.T. Gleeson (Phys. Rev. Lett. 116, 217801 (2016)) to explain their experimental observation of the unprecedentedly large shift of the nematic-isotropic transition temperature. Our interpretation is based on singular longitudinal fluctuations of the nematic order parameter. Since these fluctuations are governed by the Goldstone director fluctuations they exist only in the nematic state. External magnetic field suppresses the singular longitudinal fluctuations of the order parameter (similarly as it is the case for the transverse director fluctuations, although with a different scaling over the magnetic field). The reduction of the fluctuations changes the equilibrium value of the modulus of the order parameter in the nematic state. Therefore it leads to additional (with respect to the mean field contribution) fluctuational shift of the nematic-isotropic transition temperature. Our mechanism works for any nematic liquid crystals, however the magnitude of the fluctuational shift increases with decrease of the Frank elastic moduli. Since some of these moduli supposed to be anomalously small for so-called bent-core or dimer nematic liquid crystals, just these liquid crystals are promising candidates for the observation of the predicted fluctuational shift of the phase transition temperature.

  5. Internal coating of air cooled gas turbine blades

    Science.gov (United States)

    Ahuja, P. L.

    1979-01-01

    Six coating systems were evaluated for internal coating of decent stage (DS) eutectic high pressure turbine blades. Sequential deposition of electroless Ni by the hydrazine process, slurry Cr, and slurry Al, followed by heat treatment provided the coating composition and thickness for internal coating of DS eutectic turbine blades. Both NiCr and NiCrAl coating compositions were evaluated for strain capability and ductile to brittle transition temperature.

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

    Science.gov (United States)

    Wainwright, Carroll L.

    2012-09-01

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

  7. Taste and Temperature in Swallowing Transit Time after Stroke

    Directory of Open Access Journals (Sweden)

    Paula C. Cola

    2012-09-01

    Full Text Available Background: Oropharyngeal dysphagia is common in individuals after stroke. Taste and temperature are used in dysphagia rehabilitation. The influence of stimuli, such as taste and temperature, on swallowing biomechanics has been investigated in both healthy individuals and in individuals with neurological disease. However, some questions still remain unanswered, such as how the sequence of offered stimuli influences the pharyngeal response. The goal of the present study was to determine the influence of the sequence of stimuli, sour taste and cold temperature, on pharyngeal transit time during deglutition in individuals after stroke. Methods: The study included 60 individuals with unilateral ischemic stroke, 29 males and 31 females, aged 41–88 years (mean age: 66.2 years examined 0–50 days after ictus (median: 6 days, with mild to moderate oropharyngeal dysphagia. Exclusion criteria were hemorrhagic stroke patients, patients with decreased level of consciousness, and clinically unstable patients, as confirmed by medical evaluation. The individuals were divided into two groups of 30 individuals each. Group 1 received a nonrandomized sequence of stimuli (i.e. natural, cold, sour, and sour-cold and group 2 received a randomized sequence of stimuli. A videofluoroscopic swallowing study was performed to analyze the pharyngeal transit time. Four different stimuli (natural, cold, sour, and sour-cold were offered. The images were digitalized and specific software was used to measure the pharyngeal transit time. Since the values did not present regular distribution and uniform variances, nonparametric tests were performed. Results: Individuals in group 1 presented a significantly shorter pharyngeal transit time with the sour-cold stimulus than with the other stimuli. Individuals in group 2 did not show a significant difference in pharyngeal transit time between stimuli. Conclusions: The results showed that the sequence of offered stimuli influences

  8. Structural phase transitions in high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tatarenko, H.M. [Toulon Univ., 83 - Le Garde (France). Lab. des Materiaux Multiphases et Interfaces; Nihoul, G.E. [Toulon Univ., 83 - Le Garde (France). Lab. des Materiaux Multiphases et Interfaces

    1995-11-01

    This chapter is devoted to the study of the order-disorder like phase transitions which occur in the high-temperature superconductors (HTS). We mainly consider Lanthanium based compounds like La{sub 2}CuO{sub 4+{delta}} or La{sub 2-x}M{sub x}CuO{sub 4+{delta}} (where M is an alkali atom Ba, Sr, Ca, Na, K, ..) and Yttrium based superconductors like YBa{sub 2}Cu{sub 3}O{sub 6+{delta}}. Different kinds of ordered structures were found in these compounds by X-ray and neutron diffraction, as well as by High Resolution Electron Microscopy imaging and are described. The theoretical models, which describe the structural evolution as temperature and/or concentration of the different components vary, are considered in detail. The relation between structural instabilities and high-temperature superconductivity is discussed. (orig.)

  9. Anisotropy of the superconducting transition temperature under uniaxial pressure

    Science.gov (United States)

    Chen, X. J.; Lin, H. Q.; Yin, W. G.; Gong, C. D.; Habermeier, H.-U.

    2001-12-01

    The superconducting transition temperature Tc is calculated as a function of uniaxial pressure along the a, b, c directions for optimally doped YBa2Cu3O7-δ on the basis of a hole dispersion of the anisotropic t-J model. There is a good qualitative agreement with experiments. We show that the uniaxial pressure effect on Tc in the ab plane is due to the anisotropies of the hole dispersion and the in-plane pairing interaction, whereas the reduction of Tc under uniaxial compression along the c axis mainly results from the pressure-induced increase of hole concentration of the CuO2 plane.

  10. QSPR Study on the Glass Transition Temperature of Polyacrylates

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Structural parameters of 22 polyacrylic compounds were computed at two levels using Hartree-Fock and DFT methods. Based on the experimental data of glass transition temperature (Tg), four-parameter (energy of the lowest unoccupied molecular orbital (ELOMO), the highest positive charge (Qmax+), dipole moments (μ) and the next highest occupied molecular orbital (ENLOMO)) dependent equations were developed using structural parameters as theoretical descriptors. Especially, Tg dependent equation calculated at the HF/6-31G(d) level is more advantageous than others in view of their correlation and predictive abilities. This dependent equation was validated by variance inflation factors (VIF) and t-test methods.

  11. Can sigma models describe finite temperature chiral transitions?

    CERN Document Server

    Kocic, Aleksandar; Aleksandar KOCIC; John KOGUT

    1995-01-01

    Large-N expansions and computer simulations indicate that the universality class of the finite temperature chiral symmetry restoration transition in the 3D Gross-Neveu model is mean field theory. This is a counterexample to the standard 'sigma model' scenario which predicts the 2D Ising model universality class. We trace the breakdown of the standard scenario (dimensional reduction and universality) to the absence of canonical scalar fields in the model. We point out that our results could be generic for theories with dynamical symmetry breaking, such as Quantum Chromodynamics.

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

    Science.gov (United States)

    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. Direct investigations of deformation and yield induced structure transitions in polyamide 6 below glass transition temperature with WAXS and SAXS

    DEFF Research Database (Denmark)

    Guo, Huilong; Wang, Jiayi; Zhou, Chengbo;

    2015-01-01

    Deformation and yield induced structure transitions of polyamide 6 (PA6) were detected with the combination of the wide- and small-angle X-ray scattering (WAXS and SAXS) at 30 degrees C below glass transition temperature (T-g) of PA6. During deformation, gamma-alpha phase transition was found at ...

  14. Equation of state and QCD transition at finite temperature

    CERN Document Server

    Bazavov, A; Cheng, M; Christ, N H; DeTar, C; Ejiri, S; Gottlieb, Steven; 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; Söldner, W; Sugar, R; Toussaint, D; Vranas, P

    2009-01-01

    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 Nt=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^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 Nt=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 c...

  15. Lifted Temperature Minimum during the atmospheric evening transition

    Directory of Open Access Journals (Sweden)

    E. Blay-Carreras

    2014-11-01

    Full Text Available Observations of Lifted Temperature Minimum (LTM profiles in the nocturnal boundary layer were first reported by Ramdas and Atmanathan (1932. It was defined by the existence of a temperature minimum some centimeters above the ground. During the following decades, several research studies analyzed this phenomenon verifying its existence and postulating different hypothesis about its origin. The aim of this work is to study the existence and characteristics of LTM during the evening transition by using observations obtained during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST campaign. Data obtained from two masts instrumented with thermocouples and wind sensors at different heights close to the ground, and a mast with radiometers are used to study the role of mechanical turbulence and radiation in LTM development. The study shows that LTM profiles can be detected under calm conditions during the day–night transition, several hours earlier than reported in previous work. These conditions are fulfilled under weak synoptic forcing during local flow shifts associated with a mountain–plain circulation in relatively complex orography. Under these special conditions, turbulence becomes a crucial parameter in determining the ideal conditions for observing LTM profiles. Additionally, LTM observed profiles are also related to a change in the atmospheric radiative characteristics under calm conditions.

  16. Phase transition in finite density and temperature lattice QCD

    CERN Document Server

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

    2015-01-01

    We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of $\\beta$ and $ma$ at the lattice size $24\\times12^{2}\\times6$. The calculation was done in the Taylar expansion formalism. We are able to calculate the first and second order derivatives of $\\langle\\bar{\\psi}\\psi\\rangle$ in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and the magnitude of $\\bar{\\psi}\\psi$ decreases under the influence of finite chemical potential in both channels.

  17. Low-temperature transitions in cod and tuna determined by differential scanning calorimetry

    DEFF Research Database (Denmark)

    Jensen, Kristina Nedenskov; Jørgensen, Bo; Nielsen, Jette

    2003-01-01

    Differential scanning calorimetry measurements have revealed different thermal transitions in cod and tuna samples. Transition temperatures detected Lit -11degreesC, -15degreesC and -21degreesC were highly dependent on the annealing temperature. In tuna muscle an additional transition was observe...

  18. Low-temperature transitions in cod and tuna determined by differential scanning calorimetry

    DEFF Research Database (Denmark)

    Jensen, Kristina Nedenskov; Jørgensen, Bo; Nielsen, Jette

    2003-01-01

    Differential scanning calorimetry measurements have revealed different thermal transitions in cod and tuna samples. Transition temperatures detected Lit -11degreesC, -15degreesC and -21degreesC were highly dependent on the annealing temperature. In tuna muscle an additional transition was observed...

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

    Science.gov (United States)

    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.

  20. Functional Integral Approach to Transition Temperature of a Homogeneous Imperfect Bose Gas

    Institute of Scientific and Technical Information of China (English)

    HU Guang-Xi; DAI Xian-Xi; DAI Ji-Xin; William E. Evenson

    2004-01-01

    A functional integral approach (FIA) is introduced to calculate the transition temperature of a uniform imperfect Bose gas. With this approach we find that the transition temperature is higher than that of the corresponding ideal gas. We obtain the expression of the transition temperature shift as △Tc/To = 2.492 (na3) 1/6, where n is the density of particle number and a is the scattering length. The result has never been reported in the literature.

  1. Glass transition temperatures of epoxy resins by pulsed nuclear magnetic resonance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rutenberg, A.C.; Dorsey, G.F.; Peck, C.G.

    1976-04-21

    Pulsed nuclear magnetic resonance spectroscopy has been used to measure the glass transition temperatures of cured epoxy resins. These measurements make it possible to monitor the cure and determine the glass transition temperature as a function of the curing conditions and the concentration of the components. Knowledge of the glass transition temperature of the cured epoxies allows screening of them for a number of uses, including adhesives and coatings operations.

  2. Temperature-driven spin reorientation transition of magnetron sputtered nickel thin film

    Institute of Scientific and Technical Information of China (English)

    Song Xiao-Hui; Zhang Dian-Lin

    2008-01-01

    The temperature-driven spin reorientation transition of magnetron sputtered Ni/Si(111)systems has been studied.The relationship between ac initial susceptibility and temperature of nickel films with different thicknesses shows that the magnetization orientation changes from in-plane to out-of-plane with the increase of temperature.The temperature dependence of magnetoelastic,magneto-crystalline,and magnetostatic anisotropies determines the direction of the reorientation transition.The temperature-driven spin reorientation transition is supported by Hall coefficient measurements which show that its temperature dependence is similar to that of susceptibility.

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

    Science.gov (United States)

    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.

  4. Selective and low temperature transition metal intercalation in layered tellurides

    Science.gov (United States)

    Yajima, Takeshi; Koshiko, Masaki; Zhang, Yaoqing; Oguchi, Tamio; Yu, Wen; Kato, Daichi; Kobayashi, Yoji; Orikasa, Yuki; Yamamoto, Takafumi; Uchimoto, Yoshiharu; Green, Mark A.; Kageyama, Hiroshi

    2016-12-01

    Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries. Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored. Here we show that the layered telluride T2PTe2 (T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 °C for cadmium in Ti2PTe2). The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid.

  5. Equation of State and the Finite Temperature Transition in QCD

    CERN Document Server

    Gupta, Rajan

    2009-01-01

    This talk provides a summary of the results obtained by the HotQCD collaboration on the equation of state and the crossover transition in 2+1 flavor QCD. We investigate bulk thermodynamic quantities - energy density, pressure, entropy density, and the speed of sound over the temperature range 140 < T < 540 MeV. These results have been obtained on lattices of temporal size N_tau = 6 and 8 and with two improved staggered fermion actions, asqtad and p4. Our most extensive results are with masses of the two degenerate light quarks set at m_l = 0.1 m_s corresponding to the Goldstone pion mass m_pi between 220-260 MeV. In these simulations, the strange quark mass is tuned to its physical value and constant values of m_l/m_s define lines of constant physics. We also summarize the current state of results on observables sensitive to the chiral and deconfining physics -- the light and strange quark number susceptibilities, the chiral condensate and its susceptibility, and the renormalized Polyakov loop. Our resu...

  6. Creep performance of PVC aged at temperature relatively close to glass transition temperature

    Institute of Scientific and Technical Information of China (English)

    Zhi-hong ZHOU; Yao-long HE; Hong-jiu HU; Feng ZHAO; Xiao-long ZHANG

    2012-01-01

    In order to predict the mechanical performance of the polyvinyl chloride (PVC) at a high operating temperature,a series of short-term tensile creep tests (onetenth of the physical aging time) of the PVC are carried out at 63 ℃ with a small constant stress by a dynamic mechanical analyzer (DMA).The Struik-Kohlrausch (SK)formula and Struik shifting methods are used to describe these creep data for various physical aging time.A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters (the initial creep compliance,the characteristic retardation time,and the shape factor) determined by the aging time.It is shown that the momentary creep compliance curve of the PVC at 63 ℃ can be very well fitted by the SK formula for each aging time.However,the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures,and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinates have shown a nonlinear phenomenon. Moreover,the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case.Finally,the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.

  7. High transition-temperature SQUID magnetometers and practical applications

    Energy Technology Data Exchange (ETDEWEB)

    Dantsker, Eugene [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    The design, fabrication and performance of SQUID magnetometers based on thin films of the high-transition temperature superconductor YBa2Cu3O7-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-SrTiO3-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-1/2 at 1 Hz and 8.5 fT Hz-1/2 at 1 kHz. A multiloop multilayer SQUID magnetometer had a field noise of 37 fT Hz-1/2 at 1 Hz and 18 fT Hz-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.

  8. High transition-temperature SQUID magnetometers and practical applications

    Energy Technology Data Exchange (ETDEWEB)

    Dantsker, E [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

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

  9. Temperature- and electric-field-induced inverse Freedericksz transition in a nematogen with weak surface anchoring

    Science.gov (United States)

    Kumar, T. Arun; Sathyanarayana, P.; Sastry, V. S. S.; Takezoe, Hideo; Madhusudana, N. V.; Dhara, Surajit

    2010-07-01

    We report electric field dependence of the anchoring transition in a mesogen on cooling in a cell with perfluoropolymer treated surfaces. Below a crossover voltage Vco the transition is discontinuous between planar and homeotropic alignments, and as the temperature is lowered, the transition temperature decreases quadratically with the field. Above Vco the transition is continuous between planar and tilted alignments, the transition temperature decreasing essentially linearly with the rms field. We develop a simple model to account for these results and argue that the higher field regime corresponds to a temperature driven inverse Freedericksz transition in which the director orientation starts tilting at the weakly anchored surfaces while the tilt angle remains zero at the midplane of the cell.

  10. Modeling the nonlinear PMMA behavior near glass transition temperature: application to its thermoforming

    Science.gov (United States)

    Gilormini, P.; Chevalier, L.; Régnier, G.

    2011-01-01

    Using suitable constitutive equations, numerical simulation allows predicting the properties of transparencies that are thermoformed near their glass transition temperature. Such equations are presented, which describe the nonlinear viscoelastic behavior of poly(methyl methacrylate) at large deformations near glass transition. The simulation of the thermoforming of a transparency at constant and uniform temperature is performed and compared with experimental results.

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

    Science.gov (United States)

    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.

  12. Novel mechanism for temperature-independent transitions in flexible molecules: role of thermodynamic fluctuations.

    Science.gov (United States)

    Teslenko, V I; Petrov, E G; Verkhratsky, A; Krishtal, O A

    2010-04-30

    A novel physical mechanism is proposed to explain the temperature-independent transition reactions in molecular systems. The mechanism becomes effective in the case of conformation transitions between quasi-isoenergetic molecular states. It is shown that at room temperatures, stochastic broadening of molecular energy levels predominates the energy of low-frequency vibrations accompanying the transition. This leads to a cancellation of temperature dependence in the stochastically averaged rate constants. As an example, a physical interpretation of temperature-independent onset of P2X{3} receptor desensitization in neuronal membranes is provided.

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

    Science.gov (United States)

    Beck, Keith R.; And Others

    1984-01-01

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

  14. Transitions through critical temperatures in nematic liquid crystals

    KAUST Repository

    Majumdar, Apala

    2013-08-06

    We obtain estimates for critical nematic liquid crystal (LC) temperatures under the action of a slowly varying temperature-dependent control variable. We show that biaxiality has a negligible effect within our model and that these delay estimates are well described by a purely uniaxial model. The static theory predicts two critical temperatures: the supercooling temperature below which the isotropic phase loses stability and the superheating temperature above which the ordered nematic states do not exist. In contrast to the static problem, the isotropic phase exhibits a memory effect below the supercooling temperature in the dynamic framework. This delayed loss of stability is independent of the rate of change of temperature and depends purely on the initial value of the temperature. We also show how our results can be used to improve estimates for LC material constants. © 2013 American Physical Society.

  15. Interpretation of low-temperature data part 4: The low-temperature magnetic transition of monoclinic pyrrhotite

    NARCIS (Netherlands)

    Rochette, P.; Fillion, G.; Dekkers, M.J.

    2011-01-01

    Use of low temperature (LT) magnetic transitions to identify magnetic minerals that carry a remanence – either natural or laboratory-induced – at room temperature, is a classic tool in rock magnetism (e.g. Nagata et al., 1964; Kosterov, 2007). This particularly applies to magnetite (Verwey transitio

  16. Low-temperature structural phase transition in deuterated and protonated lithium acetate dihydrate

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, F., E-mail: schroeder@kristall.uni-frankfurt.d [Goethe-Universitaet Frankfurt am Main, Institut fuer Geowissenschaften, Abt. Kristallographie, Altenhoeferallee 1, 60438 Frankfurt am Main (Germany); Winkler, B.; Haussuehl, E. [Goethe-Universitaet Frankfurt am Main, Institut fuer Geowissenschaften, Abt. Kristallographie, Altenhoeferallee 1, 60438 Frankfurt am Main (Germany); Cong, P.T.; Wolf, B. [Goethe-Universitaet Frankfurt am Main, Physikalisches Institut, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main (Germany); Avalos-Borja, M. [Instituto Potosino de Investigacion Cientifica y Tecnologica, A.C. Camino a la Presa San Jose 2055, Col. Lomas 4 seccion CP 78216, San Luis Potosi (Mexico); Quilichini, M.; Hennion, B. [Laboratoire Leon Brillouin, CEN Saclay, 91191 Gif-sur-Yvette (France)

    2010-08-15

    Heat capacity measurements of protonated lithium acetate dihydrate show a structural phase transition at T = 12 K. This finding is in contrast to earlier work, where it was thought that only the deuterated compound undergoes a low temperature structural phase transition. This finding is confirmed by low temperature ultrasound spectroscopy, where the structural phase transition is associated with a velocity decrease of the ultrasonic waves, i.e. with an elastic softening. We compare the thermodynamic properties of the protonated and deuterated compounds and discuss two alternatives for the mechanism of the phase transition based on the thermal expansion measurements.

  17. Determining magnetic phase transitions temperatures in working magnetocaloric coolers bodies and gas cryorefrigerators regenerators

    Science.gov (United States)

    Karagusov, V. I.; Mayankov, I. V.

    2017-08-01

    Due to magnetic phase transitions rare-earth materials possess unique properties near the Curie and Neel temperatures, such as the magneto-caloric effect, the abnormally high heat capacity, the magnetic susceptibility and permeability extremes. Using rare earth materials in gas cryogenic refrigerators regenerators increases the efficiency, reduces the power consumption and allows reaching helium temperatures. The magneto-caloric effect has also extreme values near the Curie and Neel temperatures. The paper presents theoretical and experimental methods allowing to determine magnetic phase transitions temperatures in a wide range of low temperature materials with a various rare-earth components content and expected thermophysical properties of a certain rare-earth materials composition at the temperatures based on starting pure metals characteristics. The results analysis has shown that magnetic phase transitions temperatures are a linear function of the components concentration. Moreover, heat capacity values and MCE also depend linearly on the starting components concentration, which simplifies calculations significantly.

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

    Science.gov (United States)

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

    2011-02-09

    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.

  19. Pathological Behavior of Renormalization-Group Maps at High Fields and Above the Transition Temperature

    NARCIS (Netherlands)

    Enter, Aernout C.D. van; Fernández, Roberto; Kotecký, Roman

    We show that decimation transformations applied to high-q Potts models result in non-Gibbsian measures even for temperatures higher than the transition temperature. We also show that majority transformations applied to the Ising model in a very strong field at low temperatures produce non-Gibbsian

  20. Rheology across the Zero-Temperature Jamming Transition

    NARCIS (Netherlands)

    Paredes, J.; Michels, M.A.J.; Bonn, D.

    2013-01-01

    Many soft-matter systems show a transition between fluidlike and mechanically solidlike states when the volume fraction of the material, e.g., particles, drops, or bubbles is increased. Using an emulsion as a model system with a precisely controllable volume fraction, we show that the entire

  1. Predictions of Glass Transition Temperature for Hydrogen Bonding Biomaterials

    NARCIS (Netherlands)

    Sman, van der R.G.M.

    2013-01-01

    We show that the glass transition of a multitude of mixtures containing hydrogen bonding materials correlates strongly with the effective number of hydroxyl groups per molecule, which are available for intermolecular hydrogen bonding. This correlation is in compliance with the topological constraint

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

    Energy Technology Data Exchange (ETDEWEB)

    Nikiforov, Maxim P; Jesse, Stephen; Kalinin, Sergei V [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Hohlbauch, Sophia; Proksch, Roger [Asylum Research, Santa Barbara, CA 93117 (United States); King, William P [Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801 (United States); Voitchovsky, Kislon [Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Contera, Sonia Antoranz [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, Oxford (United Kingdom)

    2011-02-04

    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 deg. C range in zeptoliter volumes under different heating regimes (global heating and local heating). The temperature of the reversible phase transition is 52 {+-} 5 deg. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Nikiforov, Maxim [ORNL; Hohlbauch, Sophia [Asylum Research, Santa Barbara, CA; King, William P [University of Illinois, Urbana-Champaign; Voitchovsky, K [Massachusetts Institute of Technology (MIT); Contera, S Antoranz [University of Oxford; Jesse, Stephen [ORNL; Kalinin, Sergei V [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA

    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.

  4. Intrinsic noise sources in superconductors near the transition temperature

    Energy Technology Data Exchange (ETDEWEB)

    Galeazzi, M. E-mail: galeazzi@physics.miami.edu; Zuo, F.; Chen, C.; Ursino, E

    2004-03-11

    The performance of Transition Edge Sensors (TES) is limited by excess noise that is not predicted by the current theory of microcalorimeters and bolometers. The nature of this noise is currently unknown, but is likely to be dominated by fundamental physics of supeconductors. The University of Miami has recently started a joint effort between the microcalorimeter group and the superconductivity group to study and characterize the noise in TES. In particular, we plan to investigate the effect of flux motion due to self-field and external field and the effect of fluctuating order parameter by measuring the para-conductivity due to fluctuations in the number of Cooper pairs near the transition. We also plan to characterize the fundamental physical parameters of the TES to better predict their properties. In this paper we report our preliminary qualitative assessment of the problem, based on the literature, and we illustrate the experimental techniques that we plan to use for the investigation.

  5. Distributed Low Temperature Combustion: Fundamental Understanding of Combustion Regime Transitions

    Science.gov (United States)

    2016-09-07

    Excellent optical access for laser- based diagnostic measurements ; (ii) Accurate experimental control of boundary conditions; (iii) Aerodynamic flame...potential to extend methods based on bimodal approximations, such as the BML [21] framework , by permitting inter- mediate fluid states, which is of...identify the impact of the major chemical pathways on combustion mode transitions. The conceptual multifluid approach of Spalding can be used to avoid

  6. Glass Transition Temperature- and Specific Volume- Composition Models for Tellurite Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Riley, Brian J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Vienna, John D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2017-09-01

    This report provides models for predicting composition-properties for tellurite glasses, namely specific gravity and glass transition temperature. Included are the partial specific coefficients for each model, the component validity ranges, and model fit parameters.

  7. Predicting Glass Transition Temperature of Polyethylene/Graphene Nanocomposites by Molecular Dynamic Simulation

    Institute of Scientific and Technical Information of China (English)

    SHENG Yan-zhen; YANG Hua; LI Jun-yin; SUN Miao

    2013-01-01

    The glass transition temperature of polyethylene/graphene nanocomposites was investigated by molecular dynamic simulation.The specific volumes of three systems(polyethylene,polyethylene with a small graphene sheet and two small graphene sheets) were examined as a function of temperature.We found that the glass transition temperature decreases with increasing graphene.Then the van der Waals energy changes obviously with increasing graphene and the torsion energy also plays an important role in the glass transition of polymer.The radial distribution functions of the inter-molecular carbon atoms suggest the interaction between PE and graphene weakens with increasing graphene.These indicate that graphene can prompt the motion of chain segments of polymer and decrease the glass transition temperature (Tg) of polymer.

  8. Functional Integral Approach to the Transition Temperature of Attractive Interacting Bose Gas in Traps

    Institute of Scientific and Technical Information of China (English)

    HU Guang-Xi; DAI Xian-Xi

    2004-01-01

    The functional integral approach (FIA) is introduced to study the transition temperature of an imperfect Bose gas in traps.An interacting model in quantum statistical mechanics is presented.With the model we study a Bose gas with attractive interaction trapped in an external potential.We obtain the result that the transition temperature of a trapped Bose gas will slightly shift upwards owing to the attractive interacting force.Successful application of the FIA to Bose systems is demonstrated.

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

    Science.gov (United States)

    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.

  10. Molecular dynamics simulation for baryon-quark phase transition at finite temperature and density

    CERN Document Server

    Akimura, Y; Yoshinaga, N; Chiba, S; Akimura, Yuka; Maruyama, Toshiki; Yoshinaga, Naotaka; Chiba, Satoshi

    2005-01-01

    We study the baryon-quark phase transition in a molecular dynamics (MD) of quark degrees of freedom at finite temperature and density. The baryon state at low density and temperature, and the deconfined quark state at high density and temperature are reproduced. We investigate the equations of state of matters with different $u$-$d$-$s$ compositions. Then we draw phase diagrams in the temperature-density plane by this simulation. It is found that the baryon-quark transition is sensitive to the quark width.

  11. Temperature dependence of excitonic transition in ZnSe/ZnCdSe quantum wells

    Institute of Scientific and Technical Information of China (English)

    GUO Zi-zheng; LIANG Xi-xia; BAN Shi-liang

    2005-01-01

    A theoretical calculation for the temperature dependence of the excitonic transition in ZnSe/ZnCdSe quantum wells is performed. The exciton binding energy is calculated with a variational technique by considering the temperature-dependence parameters. Our results show that the exciton binding energy reduces linearly with temperature increasing. We find that the strain due to lattice mismatch and differential thermal expansion decreases with the temperature increasing.

  12. On the gauge dependence of vacuum transitions at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Garny, Mathias [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Konstandin, Thomas [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); European Organization for Nuclear Research (CERN), Geneva (Switzerland)

    2012-05-15

    In principle, observables as for example the sphaleron rate or the tunneling rate in a first-order phase transition are gauge-independent. However, in practice a gauge dependence is introduced in explicit perturbative calculations due to the breakdown of the gradient expansion of the effective action in the symmetric phase. We exemplify the situation using the effective potential of the Abelian Higgs model in the general renormalizable gauge. Still, we find that the quantitative dependence on the gauge choice is small for gauges that are consistent with the perturbative expansion.

  13. Phase transition, phase transition temperature and crystal structure of a new compound----Ca2PdWO6

    Institute of Scientific and Technical Information of China (English)

    傅正民; 李文秀

    1996-01-01

    A new compound Ca2PdWO6 has been synthesized by solid state sintering. The phase transition of this compound was investigated by means of differential thermal analysis (DTA), X-ray phase analysis, precise measurement of lattice parameters and other methods. It is discovered that the compound has a displacive phase transition of the first order at (806+5)C. The low temperature phase, a-Ca2PdWO6, belongs to orthorhombic system, with space group Pmm2. Its lattice parameters at room temperature are: a=0.79946nm, b=0.55404nm and c=0.58008nm. The measured density is Dm=6.26g/cm3, and each unit cell contains two formula weights. The high temperature phase, Ca2PdWO6, belongs to the cubic system, with space group fm3m and the lattice parameter is a = 0.810 3 nm at 860C; Z = 4. The calculated density is Dx=5.821g/cm3. The crystal structure of Ca2PdWO6 and Ca,PdWO6 was also determined by means of the X-ray polycrystal diffraction method. The factors influencing phase transition temperature are discussed in detail.

  14. Phase Transition and Micellization of Temperature Responsive Dextran-graft-poly (N-isopropylacrylamide) Polymers

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Phase behavior and micellization of dextran-graft-poly (N-isopropylacrylamide) (PNIPAAm) polymers in aqueous solution are investigated in this paper using DSC and AFM methods. It is found that with the increase of grafting (G%) of the copolymers the endothermic enthalpy during the phase transition increases significantly and the transition temperature decreases slightly. The phase transition behavior of the copolymers is scanning rate dependent. Micelles are formed whenever the solution temperature is raised above the LCST of the copolymers. It is proposed that by using this thermal responsive property of the copolymers, drugs could be incorporated into the micelles without employing any organic solvent.

  15. Study of the finite temperature transition in 3-flavor QCD using the R and RHMC algorithms

    CERN Document Server

    Cheng, M; Clark, M A; Jung, C; Kaczmarek, O; Karsch, Frithjof; Laermann, E; Mawhinney, R D; Miao, C; Petreczky, P; Petrov, K V; Schmidt, C; Söldner, W; Umeda, T; Van der Heide, J

    2006-01-01

    We study the finite temperature transition in QCD with three flavors of equal masses using the R and RHMC algorithm on lattices with temporal extent N_{\\tau}=4 and 6. For the transition temperature in the continuum limit we find r_0 T_c=0.429(8) for the light pseudo-scalar mass corresponding to the end point of the 1st order transition region. When comparing the results obtained with the R and RHMC algorithms for p4fat3 action we see no significant step-size errors down to a lightest pseudo-scalar mass of m_{ps} r_0=0.4.

  16. Assignment of the glass transition temperature using dielectric analysis: A review

    Energy Technology Data Exchange (ETDEWEB)

    Bidstrup, S.A. [Georgia Inst. of Technology, Atlanta, GA (United States). School of Chemical Engineering; Day, D.R. [Auburn International, Danvers, MA (United States)

    1994-09-01

    The use of dielectric analysis for the determination of the glass transition temperature for polymers is reviewed. Both a sharp increase in the permittivity and the dielectric loss peak have been correlated with the glass transition. Dielectric data for an epoxy resin and polyvinylchloride are presented and compared with data obtained by differential scanning calorimetry (DSC). The dielectric glass transition approaches the DSC glass transition as the frequency of the dielectric measurement is decreased. The effects of contact resistance and moisture on the dielectric measurement are also discussed.

  17. Dynamical transition of water in the grooves of DNA duplex at low temperature.

    Science.gov (United States)

    Biswal, Debasmita; Jana, Biman; Pal, Subrata; Bagchi, Biman

    2009-04-02

    At low temperature (below its freezing/melting temperature), liquid water under confinement is known to exhibit anomalous dynamical features. Here we study structure and dynamics of water in the grooves of a long DNA duplex using molecular dynamics simulations with TIP5P potential at low temperature. We find signatures of a dynamical transition in both translational and orientational dynamics of water molecules in both the major and the minor grooves of a DNA duplex. The transition occurs at a slightly higher temperature (T(GL) approximately 255 K) than the temperature at which the bulk water is found to undergo a dynamical transition, which for the TIP5P potential is at 247 K. Groove water, however, exhibits markedly different temperature dependence of its properties from the bulk. Entropy calculations reveal that the minor groove water is ordered even at room temperature, and the transition at T approximately 255 K can be characterized as a strong-to-strong dynamical transition. Confinement of water in the grooves of DNA favors the formation of a low density four-coordinated state (as a consequence of enthalpy-entropy balance) that makes the liquid-liquid transition stronger. The low temperature water is characterized by pronounced tetrahedral order, as manifested in the sharp rise near 109 degrees in the O-O-O angle distribution. We find that the Adams-Gibbs relation between configurational entropy and translational diffusion holds quite well when the two quantities are plotted together in a master plot for different region of aqueous DNA duplex (bulk, major, and minor grooves) at different temperatures. The activation energy for the transfer of water molecules between different regions of DNA is found to be weakly dependent on temperature.

  18. Transmutation-induced embrittlement of V-Ti-Ni and V-Ni alloys in HFIR

    Energy Technology Data Exchange (ETDEWEB)

    Ohnuki, S.; Takahashi, H. [Hokkaido Univ., Sapparo (Japan); Garner, F.A. [Pacific Northwest National Laboratory, Richland, WA (United States); Pawel, J.E. [Oak Ridge National Laboratory, TN (United States)] [and others

    1996-04-01

    Vanadium, V-1Ni, V-10Ti and V-10Ti-1Ni (at %) were irradiated in HFIR to doses ranging from 18 to 30 dpa and temperatures between 300 and 600C. Since the irradiation was conducted in a highly thermalized neutron spectrum without shielding against thermal neutrons, significant levels of chromium (15-22%) were formed by transmutation. The addition of such large chromium levels strongly elevated the ductile to brittle transition temperature. At higher irradiation temperatures radiation-induced segregation of transmutant Cr and solute Ti at specimen surfaces leads to strong increases in the density of the alloy.

  19. Miniature Precracked Charpy Specimens for Measuring the Master Curve Reference Temperature of RPV Steels at Impact Loading Rates

    Energy Technology Data Exchange (ETDEWEB)

    Lucon, E.; Scibetta, M.; Puzzolante, L.

    2008-10-15

    In the framework of the 2006 Convention, we investigated the applicability of fatigue precracked miniature Charpy specimens of KLST type (MPCC - B = 3 mm, W = 4 mm and L = 27 mm) for impact toughness measurements, using the well-characterized JRQ RPV steel. In the ductile to-brittle transition region, MPCC tests analyzed using the Master Curve approach and compared to data previously obtained from PCC specimens had shown a more ductile behavior and therefore un conservative results. In the investigation presented in this report, two additional RPV steels have been used to compare the performance of impact-tested MPCC and PCC specimens in the transition regime: the low-toughness JSPS steel and the high-toughness 20MnMoNi55 steel. The results obtained (excellent agreement for 20MnMoNi55 and considerable differences between T0 values for JSPS) are contradictory and do not presently allow qualifying the MPCC specimens as a reliable alternative to PCC samples for impact toughness measurements.

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

    Science.gov (United States)

    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.

  1. Sphere-to-rod transition of triblock copolymer micelles at room temperature

    Indian Academy of Sciences (India)

    R Ganguly; V K Aswal; P A Hassan; I K Gopalakrishnan; J V Yakhmi

    2004-08-01

    A room temperature sphere-to-rod transition of the polyethylene oxide-polypropylene oxide-polyethylene oxide-based triblock copolymer, (PEO)20 (PPO)70 (PEO)20 micelles have been observed in aqueous medium under the influence of ethanol and sodium chloride. Addition of 5-10% ethanol induces a high temperature sphere-to-rod transition of the micelles, which is brought to room temperature upon addition of NaCl. The inference about the change in the shape of the micelles has been drawn from small-angle neutron scattering (SANS) and viscosity studies.

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

    Science.gov (United States)

    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.

  3. Computational Intelligence Approach for Estimating Superconducting Transition Temperature of Disordered MgB2 Superconductors Using Room Temperature Resistivity

    Directory of Open Access Journals (Sweden)

    Taoreed O. Owolabi

    2016-01-01

    Full Text Available Doping and fabrication conditions bring about disorder in MgB2 superconductor and further influence its room temperature resistivity as well as its superconducting transition temperature (TC. Existence of a model that directly estimates TC of any doped MgB2 superconductor from the room temperature resistivity would have immense significance since room temperature resistivity is easily measured using conventional resistivity measuring instrument and the experimental measurement of TC wastes valuable resources and is confined to low temperature regime. This work develops a model, superconducting transition temperature estimator (STTE, that directly estimates TC of disordered MgB2 superconductors using room temperature resistivity as input to the model. STTE was developed through training and testing support vector regression (SVR with ten experimental values of room temperature resistivity and their corresponding TC using the best performance parameters obtained through test-set cross validation optimization technique. The developed STTE was used to estimate TC of different disordered MgB2 superconductors and the obtained results show excellent agreement with the reported experimental data. STTE can therefore be incorporated into resistivity measuring instruments for quick and direct estimation of TC of disordered MgB2 superconductors with high degree of accuracy.

  4. Shift in membrane miscibility transition temperature upon addition of short-chain alcohols

    Science.gov (United States)

    Schick, M.

    2016-12-01

    I consider the effect of a small concentration of a molecule, such as a short-chain alcohol, on the miscibility transition temperature of a giant plasma membrane vesicle. For concentrations sufficiently small such that the system can be treated as a dilute solution, the change in transition temperature is known to depend upon the extent of the molecule's partition into the coexisting liquid-disordered and liquid-ordered phases. Preferential partitioning into the former decreases the miscibility temperature, while preferential partitioning into the latter causes an increase. The analysis, combined with calculated values of the partition coefficient of saturated chains, illuminates the results of recent experiments on the change in miscibility transition temperatures with changing alcohol chain length, and makes several testable predictions.

  5. Equation of state and transition temperatures in the quark-hadron hybrid model

    Science.gov (United States)

    Miyahara, Akihisa; Torigoe, Yuhei; Kouno, Hiroaki; Yahiro, Masanobu

    2016-07-01

    We analyze the equation of state of 2 +1 flavor lattice QCD at zero baryon density by constructing a simple quark-hadron hybrid model that has both quark and hadron components simultaneously. We calculate the hadron and quark contributions separately and parameterize those to match with lattice QCD data. Lattice data on the equation of state are decomposed into hadron and quark components by using the model. The transition temperature is defined by the temperature at which the hadron component is equal to the quark one in the equation of state. The transition temperature thus obtained is about 215 MeV; this is somewhat higher than the chiral and the deconfinement pseudocritical temperatures defined by the temperature at which the susceptibility or the absolute value of the derivative of the order parameter with respect to temperature becomes maximum.

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

    Science.gov (United States)

    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.

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

    OpenAIRE

    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 (T g ′), as it was hypothesized that such temperatures might cause different effects on retrogradation. The T g ′ 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...

  8. Theoretical Study on Effects of Salt and Temperature on Denaturation Transition of Double-stranded DNA

    Institute of Scientific and Technical Information of China (English)

    DONG Rui-Xin; YAN Xun-Ling; PANG Xiao-Feng; JIANG Shan; LIU Sheng-Gang

    2004-01-01

    We investigate the statistical mechanics properties of a nonlinear dynamics model of the denaturation of the DNA double-helix and study the effects of salt concentration and temperature on denaturation transition of DNA. The specific heat, entropy, and denaturation temperature of the system versus salt concentration are obtained. These results show that the denaturation of DNA not only depends on the temperature but also is influenced by the salt concentration in the solution of DNA, which are in agreement with experimental measurement.

  9. Room temperature hysteretic spin transition in 1D iron(II) coordination polymers

    Energy Technology Data Exchange (ETDEWEB)

    Dirtu, Marinela M; Naik, Anil D; Marchand-Brynaert, Jacqueline; Garcia, Yann, E-mail: yann.garcia@uclouvain.b [Institut de la Matiere Condensee et des Nanosciences, Universite Catholique de Louvain, Place L. Pasteur 1, 1348, Louvain-la-Neuve (Belgium)

    2010-03-01

    The 1D spin transition compound [Fe(L1){sub 3}](ClO{sub 4}){sub 2} (1) with L1 ethyl-4H-1,2,4-triazol-4-yl-acetate, a novel neutral bidentate ligand, has been synthesised. The temperature dependence of the high-spin molar fraction derived from {sup 57}Fe Mossbauer spectroscopy reveals an exceptionally abrupt single step transition between low-spin and high-spin states with a hysteresis loop of width 5 K (T{sub c}{sup u} = 298 K and T{sub c}{sup {down_arrow}} = 293 K). This spin transition operating around room temperature presents striking reversible thermochromism from white at 295 K to pink at ice temperature, behaving as an optical alert towards temperature variations. This first order phase transition was additionally followed by differential scanning calorimetry in good agreement with Moessbauer spectroscopy data. The spin transition properties of a freshly prepared sample of 1, dried under a N{sub 2}(g) stream which was formulated as [Fe(L1){sub 3}](ClO{sub 4}){sub 2{center_dot}}MeOH (2), are shifted below room temperature (T{sub 1/2}{sup u} = 273 K and T{sub 1/2}{sup {down_arrow}} 263 K), thus showing a remarkable influence of solvent inclusion on the spin state of these chain compounds.

  10. Impact toughness of tungsten films deposited on martensite stainless steel

    Institute of Scientific and Technical Information of China (English)

    HUANG Ning-kang; YANG Bin; WANG De-zhi

    2005-01-01

    Tungsten films were deposited on stainless steel Charpy specimens by magnetron sputtering followed by electron beam heat treatment. Charpy impact tests and scanning electron microscopy were used to investigate the ductile-brittle transition behavior of the specimens. With decreasing test temperature the fracture mode was transformed from ductile to brittle for both kinds of specimens with and without W films. The data of the crack initiation energy, crack propagation energy, impact absorbing energy, fracture time and deflection as well as the fracture morphologies at test temperature of -70 ℃ show that W films can improve the impact toughness of stainless steel.

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

    Science.gov (United States)

    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.

  12. Investigation into the temperature dependence of isotropic- nematic phase transition of Gay- Berne liquid crystals

    Directory of Open Access Journals (Sweden)

    A Avazpour

    2014-12-01

    Full Text Available Density functional approach was used to study the isotropic- nematic (I-N transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic transition densities increase as the temperature increases. It was found that the new direct correlation function is suitable to study the isotropic- nematic transition of Gay- Berne liquids. Comparison to other works showed qualitative agreement

  13. Non-compact QED3 at finite temperature the confinement-deconfinement transition

    CERN Document Server

    Fiore, Roberto; Papa, Alessandro

    2008-01-01

    The confinement-deconfinement phase transition is explored by lattice numerical simulations in non-compact (2+1)-dimensional quantum electrodynamics with massive fermions at finite temperature. The existence of two phases, one with and the other without confinement of fractional charges, is related to the realization of the Z symmetry. The order parameter of this transition can be clearly identified. We show that it is possible to detect the critical temperature for a given value of the fermion mass, by exploiting suitable lattice operators as probes of the Z symmetry. Moreover, the large-distance behavior of the correlation of these operators permits to distinguish the phase with Coulomb-confinement from the Debye-screened phase. The resulting scenario is compatible with the existence of a Berezinsky-Kosterlitz-Thouless transition. Some investigations are presented on the possible relation between chiral and deconfinement transitions and on the role of ``monopoles''.

  14. Isotope shift of the ferromagnetic transition temperature in itinerant ferromagnets

    Science.gov (United States)

    Yanagisawa, Takashi; Hase, Izumi; Odagiri, Kosuke

    2017-02-01

    We present a theory of the isotope effect of the Curie temperature Tc in itinerant ferromagnets. The isotope effect in ferromagnets occurs via the electron-phonon vertex correction and the effective attractive interaction mediated by the electron-phonon interaction. The decrease of the Debye frequency increases the relative strength of the Coulomb interaction, which results in a positive isotope shift of Tc when the mass M of an atom increases. Following this picture, we evaluate the isotope effect of Tc by using the Stoner theory and a spin-fluctuation theory. When Tc is large enough as large as or more than 100 K, the isotope effect on Tc can be measurable. Recently, precise measurements on the oxygen isotope effect on Tc have been performed for itinerant ferromagnet SrRuO3 with Tc ∼ 160 K. A clear isotope effect has been observed with the positive shift of Tc ∼ 1 K by isotope substitution (16O →18O). This experimental result is consistent with our theory.

  15. Finite-temperature transition of the antiferromagnetic Heisenberg model on a distorted kagome lattice.

    Science.gov (United States)

    Masuda, Hiroshi; Okubo, Tsuyoshi; Kawamura, Hikaru

    2012-08-03

    Motivated by the recent experiment on kagome-lattice antiferromagnets, we study the zero-field ordering behavior of the antiferromagnetic classical Heisenberg model on a uniaxially distorted kagome lattice by Monte Carlo simulations. A first-order transition, which has no counterpart in the corresponding undistorted model, takes place at a very low temperature. The origin of the transition is ascribed to a cooperative proliferation of topological excitations inherent to the model.

  16. A statistical approach to the QCD phase transition --A mystery in the critical temperature

    OpenAIRE

    Ishii, Noriyoshi; Suganuma, Hideo

    2002-01-01

    We study the QCD phase transition based on the statistical treatment with the bag-model picture of hadrons, and derive a phenomenological relation among the low-lying hadron masses, the hadron sizes and the critical temperature of the QCD phase transition. We apply this phenomenological relation to both full QCD and quenched QCD, and compare these results with the corresponding lattice QCD results. Whereas such a statistical approach works well in full QCD, it results in an extremely large es...

  17. High-temperature NMR study of zeolite Na-A: Detection of a phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Janssen, R.; Tijink, G.A.H.; Veeman, W.S.; Maesen, T.L.M.; van Lent, J.F. (Univ. of Nijmegen (Netherlands))

    1989-01-26

    The zeolite Linde 4A is studied by {sup 23}Na, {sup 27}al, and {sup 29}Si NMR at temperatures up to 953 K. {sup 23}Na NMR shows that the quadrupole interaction of sodium ions sited at 6-rings decreases when the temperature increases. With the aid of two-dimensional nutation and exchange experiments it can be shown that large-amplitude motions of the sodium ions, which in principle could explain a decrease of quadrupole interactions, do not occur. The decrease of the quadrupole interaction can be interpreted in terms of a phase transition. From a comparison of the NMR spectra of {sup 23}Na and {sup 27}Al it is concluded that the zeolite framework undergoes a major structural change upon increasing the temperature, before the sodium ions are displaced at higher temperatures. The exchange of sodium ions for potassium ions shifts this transition to higher temperatures.

  18. Pressure- and temperature-driven phase transitions in HgTe quantum wells

    Science.gov (United States)

    Krishtopenko, S. S.; Yahniuk, I.; But, D. B.; Gavrilenko, V. I.; Knap, W.; Teppe, F.

    2016-12-01

    We present theoretical investigations of pressure- and temperature-driven phase transitions in HgTe quantum wells grown on a CdTe buffer. Using the eight-band k .p Hamiltonian we calculate evolution of energy-band structure at different quantum well widths with hydrostatic pressure up to 20 kbars and temperature ranging up to 300 K. In particular, we show that, in addition to temperature, tuning of hydrostatic pressure allows us to drive transitions between semimetal, band insulator, and topological insulator phases. Our realistic band-structure calculations reveal that the band inversion under hydrostatic pressure and temperature may be accompanied by nonlocal overlapping between conduction and valence bands. The pressure and temperature phase diagrams are presented.

  19. Lasing and high temperature phase transitions in atomic systems with dressed state polaritons

    CERN Document Server

    Chestnov, I Yu

    2013-01-01

    We consider the fundamental problem of high temperature phase transitions in the system of high density two-level atoms off-resonantly interacting with a pump field in the presence of optical collisions (OCs) and placed in the cavity. OCs are considered in the framework of thermalization of atomic dressed state (DS) population. For the case of a strong atom-field coupling condition we analyze the problem of thermodynamically equilibrium superradiant phase transition for the order parameter representing a real amplitude of cavity mode and taking place as a result of atomic DSs thermalization process. Such transition is also connected with condensed (coherent) properties of low branch (LB) DS-polaritons occurring in the cavity. For describing non-equilibrium phase transitions we derive Maxwell-Bloch like equations which account for cavity decay rate, collisional decay rate and spontaneous emission. Various aspects of transitions to laser field formation by using atomic DS levels for both positive and negative d...

  20. On the polymorphism of benzocaine; a low-temperature structural phase transition for form (II).

    Science.gov (United States)

    Chan, Eric J; Rae, A David; Welberry, T Richard

    2009-08-01

    A low-temperature structural phase transition has been observed for form (II) of benzocaine (BZC). Lowering the temperature doubles the b-axis repeat and changes the space group from P2(1)2(1)2(1) to P112(1) with gamma now 99.37 degrees. The structure is twinned, the twin rule corresponding to a 2(1) screw rotation parallel to a. The phase transition is associated with a sequential displacement parallel to a of zigzag bi-layers of ribbons perpendicular to b*. No similar phase transition was observed for form (I) and this was attributed to the different packing symmetries of the two room-temperature polymorphic forms.

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

    Science.gov (United States)

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

    2016-02-01

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

  2. Glass Transition Temperature of Water: from Simulations of Diffusion and Excess Entropy

    Institute of Scientific and Technical Information of China (English)

    LIU Jia; WANG Shu-Ying; ZHENG Cai-Ping; XIN Li-Juan; WANG Dan; SUN Min-Hua

    2007-01-01

    We report a computer simulation study of the glass transition of water with SP2 potential. The temperature dependences of the diffusion coefficient and the excess entropy on cooling process are calculated. It is found that both the diffusion coefficient and the excess entropy show a break point at 160K. Our results support the viewpoint that the glass transition temperature is 160K. According to the calculated viscosity, we obtain a fragility index of water to be 326, which is much larger than the value accepted before.

  3. LARGE MAGNETIC ENTROPY CHANGE NEAR CHARGE-ORDERED TRANSITION TEMPERATURE IN PEROVSKITE-TYPE MANGANITE

    Institute of Scientific and Technical Information of China (English)

    陈鹏; 都有为

    2001-01-01

    The magnetocaloric effect in polycrystalline of Pr1-xSrxMnO3 (x=0.33, 0.43, 0.50) has been investigated. A large magnetic entropy change (7.1J/kgK) was discovered in Pr0.5Sr0.5MnO3 under a low magnetic field of IT at charge-ordered state transition temperature (161K). The physical mechanism is related to a drastic magnetization change at a temperature where the field-induced magnetic, electron and structural phase transitions occur (from the antiferromagnetic charge-ordered state to the ferromagnetic charge-disordered state).

  4. The insulating-to-superconducting transition in europium high-temperature superconducting ceramics

    CERN Document Server

    Rosenbaum, R

    1997-01-01

    Experiment resistivity data on high-temperature superconducting ceramics of fully oxygenated EuBa sub 2 Cu sub 3 sub - sub x Co sub x O sub y show that the insulating-to-superconducting transitions take place at liquid-helium temperature, provided that the cobalt fraction x exceeds 0.3. The resistivity follows a simple power-law dependence rho propor to T sup - sup 1 sup / sup 2 , attributed to electron-electron interactions. A model based upon intrinsic Josephson tunnelling junctions is suggested to explain the transition from insulating to superconducting states. (author)

  5. Equilibrium and non-equilibrium properties of a relativistic gas at the transition temperature

    Science.gov (United States)

    Chacón-Acosta, Guillermo

    2016-11-01

    The Jüttner distribution function for equilibrium relativistic fluids has two well-known limits, the non-relativistic limit at low temperatures and ultra-relativistic limit for high temperatures. Recently, the description of this transition in velocity space in the system, from a gaussian to a bimodal distribution was made by Mendoza et al. Physically, it is a transition between a regime where the relativistic energy is dominated by kinetic to another where the rest energy dominates. It has been found that the critical temperature at which the relativistic corrections becomes relevant, depends just on the dimension of the system, this allowed a description in terms of the theory of critical points (Montakhab et al.). In this contribution a review of the thermodynamic quantities that are only dependent on the ratio between temperature and critical temperature, and the dimension is made. We will also analyze the effects of critical temperature on dissipative processes in simple special relativistic fluids. Particularly, purely relativistic terms that are usually proportional to the number density gradient are studied. The transport coefficients can be written in terms of the transition temperature, this will allow us to identify the lower order relativistic effects just in terms of the dimension of the system.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  8. Mechanics and chemical thermodynamics of phase transition in temperature-sensitive hydrogels

    Science.gov (United States)

    Cai, Shengqiang; Suo, Zhigang

    2011-11-01

    This paper uses the thermodynamic data of aqueous solutions of uncrosslinked poly( N-isopropylacrylamide) (PNIPAM) to study the phase transition of PNIPAM hydrogels. At a low temperature, uncrosslinked PNIPAM can be dissolved in water and form a homogenous liquid solution. When the temperature is increased, the solution separates into two liquid phases with different concentrations of the polymer. Covalently crosslinked PNIPAM, however, does not dissolve in water, but can imbibe water and form a hydrogel. When the temperature is changed, the hydrogel undergoes a phase transition: the amount of water in the hydrogel in equilibrium changes with temperature discontinuously. While the aqueous solution is a liquid and cannot sustain any nonhydrostatic stress in equilibrium, the hydrogel is a solid and can sustain nonhydrostatic stress in equilibrium. The nonhydrostatic stress can markedly affect various aspects of the phase transition in the hydrogel. We adopt the Flory-Rehner model, and show that the interaction parameter as a function of temperature and concentration obtained from the PNIPAM-water solution can be used to analyze diverse phenomena associated with the phase transition of the PNIPAM hydrogel. We analyze free swelling, uniaxially and biaxially constrained swelling of a hydrogel, swelling of a core-shell structure, and coexistent phases in a rod. The analysis is related to available experimental observations. Also outlined is a general theory of coexistent phases undergoing inhomogeneous deformation.

  9. Water sorption and glass transition temperatures in red raspberry (Rubus idaeus)

    Energy Technology Data Exchange (ETDEWEB)

    Syamaladevi, Roopesh M. [Biological Systems Engineering Department, Washington State University, PO Box 646120, Pullman, WA 99164-6120 (United States); Sablani, Shyam S., E-mail: ssablani@wsu.edu [Biological Systems Engineering Department, Washington State University, PO Box 646120, Pullman, WA 99164-6120 (United States); Tang, Juming [Biological Systems Engineering Department, Washington State University, PO Box 646120, Pullman, WA 99164-6120 (United States); Powers, Joseph; Swanson, Barry G. [School of Food Science, Washington State University, PO Box 6463760, Pullman, WA 99164-6376 (United States)

    2010-05-20

    Water sorption isotherms and glass transition temperatures of raspberries were determined to understand interactions between water and biopolymers. Water adsorption and desorption isotherms of raspberries were determined with an isopiestic method. Thermal transitions of raspberries equilibrated at selected water concentrations using adsorption and desorption were determined by differential scanning calorimetry (DSC). The sorption isotherm data were modeled by BET and GAB equations, while the plasticizing influence of water on glass transition was modeled by the Gordon-Taylor equation. Equilibrium water concentrations varied at equivalent water activities during adsorption and desorption indicating occurrence of hysteresis and irreversibility of thermodynamic processes. The monolayer water concentrations of 0.099 and 0.108 kg water/kg dry raspberry solids obtained by BET and GAB models during desorption were larger than those during adsorption (0.059 and 0.074 kg water/kg dry raspberry solids). The glass transition temperature of raspberries decreased with increasing water concentrations. The Gordon-Taylor parameters T{sub gs} and k obtained for raspberries during adsorption were 42.6 {sup o}C and 4.73 and during desorption were 44.9 {sup o}C and 5.03, respectively. The characteristic glass transition temperature of the maximally freeze concentrated solution T{sup '}{sub g} was -63.1 {+-} 5 {sup o}C and the onset of ice crystal melting temperature T{sup '}{sub m} was -32.3 {+-} 0.4 {sup o}C. Although the water activity differed significantly at equivalent water concentrations obtained using absorption or desorption, the glass transition temperatures of raspberries were dependent on the concentration of water present not the method of equilibration.

  10. Transition Temperatures of Thermotropic Liquid Crystals from the Local Binary Gray Level Cooccurrence Matrix

    Directory of Open Access Journals (Sweden)

    S. Sreehari Sastry

    2012-01-01

    Full Text Available This paper presents a method which combines the statistical analysis with texture structural analysis called Local Binary Gray Level Cooccurrence Matrix (LBGLCM to investigate the phase transition temperatures of thermotropic p,n-alkyloxy benzoic acid (nOBA, n=4,6,8,10 and 12 liquid crystals. Textures of the homeotropically aligned liquid crystal compounds are recorded as a function of temperature using polarizing optical microscope attached to the hot stage and high resolution camera. In this method, second-order statistical parameters (contrast, energy, homogeneity, and correlation are extracted from the LBGLCM of the textures. The changes associatedwiththe values of extracted parameters as a function of temperature are a helpful process to identify the phases and phase transition temperatures of the samples. Results obtained from this method have validity and are in good agreement with the literature.

  11. Molecular dynamics simulations on specific heat capacity and glass transition tempera-ture of liquid silver

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The embedded-atom method is adopted to simulate the specific heat capacity of liquid silver. The relationship between the specific heat capacity and the temperature above and below melting point is derived. The results show that there exists an anormaly of the specific heat capacity of liquid silver near 950 K. Simulated pair distribution functions show that the liquid-to-glass transition takes place at this temperature.

  12. Influence of irradiation on the ductile fracture of a reactor pressure vessel steel

    Science.gov (United States)

    Haušild, Petr; Kytka, Miloš; Karlík, Miroslav; Pešek, Pavel

    2005-05-01

    The mechanical properties of 15Ch2MFA steel were characterised by tensile and instrumented Charpy tests. The fracture surfaces of Charpy specimens broken in the ductile-to-brittle transition temperature range contain a certain proportion of ductile fracture correlated to fracture energy. Measured ductile crack lengths show the same dependence on fracture deflection and/or fracture energy for irradiated and non-irradiated specimens. The decrease of upper shelf energy with increasing neutron fluence could be explained by an increasing amount of shear fracture.

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

    Directory of Open Access Journals (Sweden)

    David Pekker

    2014-03-01

    Full Text Available 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-12-31

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

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

    CERN Document Server

    Cruz, Flavio C; Magno, Wictor C

    2013-01-01

    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.

  16. Material properties and glass transition temperatures of different thermoplastic starches after extrusion processing

    NARCIS (Netherlands)

    Janssen, Léon P.B.M.; Karman, Andre P.; Graaf, Robbert A. de

    2003-01-01

    Four different starch sources, namely waxy maize, wheat, potato and pea starch were extruded with the plasticizer glycerol, the latter in concentrations of 15, 20 and 25% (w/w). The glass transition temperatures of the resulting thermoplastic products were measured by Dynamic Mechanical Thermal Anal

  17. Time evolution of chiral phase transition at finite temperature and density in the linear sigma model

    Energy Technology Data Exchange (ETDEWEB)

    Sato, K.; Koide, Tomoi; Maruyama, Masahiro [Tohoku Univ., Faculty of Science, Sendai, Miyagi (Japan)

    1999-08-01

    There are various approaches to nonequilibrium system. We use the projection operator method investigated by F. Shibata and N. Hashitsume on the linear sigma model at finite temperature and density. We derive a differential equation of the time evolution for the order parameter and pion number density in chiral phase transition. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Dimitriu, D. G. [Faculty of Physics, Alexandru Ioan Cuza University, 11 Carol I Blvd., RO-700506 Iasi (Romania)

    2013-11-13

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

  19. Pressure-Driven Commensurate-Incommensurate Transition Low-Temperature Submonolayer Krypton on Graphite

    DEFF Research Database (Denmark)

    Nielsen, Mourits; Als-Nielsen, Jens Aage; Bohr, Jakob

    1981-01-01

    By using D2 gas as a source of two-dimensional spreading pressure, we have studied the commensurate-incommensurate (C-I) transition in submonolayer Kr on ZYX graphite at temperatures near 40 K. High-resolution synchrotron x-ray diffraction results show both hysteresis and C-I phase coexistence...

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

    Science.gov (United States)

    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...

  1. TRANSITION TEMPERATURE IN QCD WITH PHYSICAL LIGHT AND STRANGE QUARK MASSES.

    Energy Technology Data Exchange (ETDEWEB)

    KARSCH, F.

    2006-11-14

    We present results from a calculation of the transition temperature in QCD with two light (up, down) and one heavier (strange) quark mass as well as for QCD with three degenerate quark masses. Furthermore, we discuss first results from an ongoing calculation of the QCD equation of state with almost realistic light and strange quark masses.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    CERN Document Server

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

    2008-01-01

    Critical temperature Tc for the nuclear liquid-gas phase transition is stimated both from the multifragmentation and fission data. In the first case,the critical temperature is obtained by analysis of the IMF yields in p(8.1 GeV)+Au collisions within the statistical model of multifragmentation (SMM). In the second case, the experimental fission probability for excited 188Os is compared with the calculated one with Tc as a free parameter. It is concluded for both cases that the critical temperature is higher than 16 MeV.

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

    Institute of Scientific and Technical Information of China (English)

    LIU Chuan-Jiang; ZHENG Hai-Fei

    2012-01-01

    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℃ in the pressure range of 1.0 1.5 GPa,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℃≤T≤320℃).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.%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℃ in the pressure range of 1.0-1.5 Gpa, 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℃≤T≤320℃). Anhydrite remained stable during rapid cooling of the sample chamber, showing that the gypsum-anhydrite transition involving both dissolution and precipitation processes is

  6. Mathematical modeling of photoinitiated coating degradation: Effects of coating glass transition temperature and light stabilizers

    DEFF Research Database (Denmark)

    Kiil, Søren; G.de With, R.A.T.M.Van Benthem

    2013-01-01

    A mathematical model, describing coating degradation mechanisms of thermoset coatings exposed to ultraviolet radiation and humidity at constant temperature, was extended to simulate the behavior of a coating with a low glass transition temperature. The effects of adding light stabilizers (a UV...... absorber and a radical scavenger) to the coating were also explored. The extended model includes photoinitiated oxidation reactions, intrafilm oxygen permeability, water absorption and diffusion, reduction of crosslink density, absorption of ultraviolet radiation, a radical scavenger reaction......, and simulates the transient development of an oxidation zone. Simulations are in good agreement with experimental data for a fast degrading epoxy-amine coating with a glass transition temperature of −50°C. It was found that the degradation rate of the non-stabilized coating was influenced significantly...

  7. Finite-temperature phase transition of $N_{f}=3$ QCD with exact center symmetry

    CERN Document Server

    Misumi, Tatsuhiro; Itou, Etsuko

    2015-01-01

    For the $Z_{3}$-symmetric lattice QCD-like theory ($Z_3$-QCD), in which $SU(3)$ gauge theory is coupled with three fundamental Wilson quarks with flavor-dependent twisted boundary conditions, we calculate the expectation values of Polyakov loop and chiral condensate as functions of temperature on $16^3 \\times4$ and $20^3 \\times 4$ lattices with $m_{PS}/m_{V}=0.70$ fixed. We find the first-order phase transition with respect to the $Z_{3}$ center symmetry, where the Polyakov loop exhibits a hysteresis depending on the initial condition of thermalization process. We also show that the crossover behavior of chiral condensate around the critical temperature of the center transition and the manifestation of flavor symmetry breaking in the high-temperature phase.

  8. High-temperature phase transitions in SrHfO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, B.J.; Howard, C.J. [School of Chemistry, The University of Sydney, Sydney, New South Wales 2006 (Australia); Chakoumakos, B.C. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    1999-08-01

    The crystal structure of SrHfO{sub 3} has been studied at high temperatures using powder neutron diffraction and the Rietveld method. From 300 K to approximately 670 K the structure of SrHfO{sub 3} is orthorhombic ({ital Pnma}). By 870 K the material adopts a second orthorhombic structure ({ital Cmcm}). The material then undergoes a further phase transition and is tetragonal (I4/mcm) from {approximately}1000 to 1353 K. At higher temperatures ({gt}1360 K) the structure is the ideal cubic perovskite (Pm{bar 3}m). The angle of rotation of the oxygen octahedron in the tetragonal phase is taken as the order parameter and its temperature variation is consistent with a second order phase transition. {copyright} {ital 1999} {ital The American Physical Society}

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

    Science.gov (United States)

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

    2016-12-01

    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 backfield curves every 10° in the basal plane of an oriented single crystal of monoclinic pyrrhotite at 300 K and every 2 K 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 sixfold 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 fourfold 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 per cent loss in remanence between 300 and 150 K

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

    Science.gov (United States)

    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 in the range 5.05previous results for these systems and contrary to the Tc vs behavior of both amorphous and crystalline transition-metal alloys formed between near neighbors in the Periodic Table. Upper

  11. The Diurnal Temperature Cycle and Its Relation to Boundary-Layer Structure During the Morning Transition

    Science.gov (United States)

    Ketzler, G.

    2014-05-01

    The morning portion of the near-surface diurnal temperature cycle is analyzed in combination with heat-flux and vertical temperature-gradient data. During summer, mean diurnal cycles of temperature rates-of-change show periods that can be related to defined points of the morning transition (MT). The start of the MT is clearly marked with a temperature discontinuity, apparent even on individual days, while the end of the transition is apparent only when using averages over many days. The findings concerning the timing of the MT using temperature cycle analysis correspond well with studies using heat-flux measurements. Mean diurnal cycles of temperature rates-of-change for stations in different urban and valley positions show differences that can partly be explained by apparent effects of the surroundings. For the valley situation, the timing differences and their relation to station position in the valley are generally plausible, while urban effects on the diurnal cycle are apparent but less distinct, which may be due to the small number of stations used. The results indicate that warming already begins before heat-flux crossover, which is the current definition of the beginning of the MT. This definition should be extended to include the phase between the temperature rate-of-change crossover and heat-flux crossover, which represents the early part of the MT before warming reaches instrument level.

  12. A tool to evaluate local biophysical effects on temperature due to land cover change transitions

    Science.gov (United States)

    Perugini, Lucia; Caporaso, Luca; Duveiller, Gregory; Cescatti, Alessandro; Abad-Viñas, Raul; Grassi, Giacomo; Quesada, Benjamin

    2017-04-01

    Land Cover Changes (LCC) affect local, regional and global climate through biophysical variations of the surface energy budget mediated by albedo, evapotranspiration, and roughness. Assessment of the full climate impacts of anthropogenic LCC are incomplete without considering biophysical effects, but the high level of uncertainties in quantifying their impacts to date have made it impractical to offer clear advice on which policy makers could act. To overcome this barrier, we provide a tool to evaluate the biophysical impact of a matrix of land cover transitions, following a tiered methodological approach similar to the one provided by the IPCC to estimate the biogeochemical effects, i.e. through three levels of methodological complexity, from Tier 1 (i.e. default method and factors) to Tier 3 (i.e. specific methods and factors). In particular, the tool provides guidance for quantitative assessment of changes in temperature following a land cover transition. The tool focuses on temperature for two main reasons (i) it is the main variable of interest for policy makers at local and regional level, and (ii) temperature is able to summarize the impact of radiative and non-radiative processes following LULCC. The potential changes in annual air temperature that can be expected from various land cover transitions are derived from a dedicated dataset constructed by the JRC in the framework of the LUC4C FP7 project. The inputs for the dataset are air temperature values derived from satellite Earth Observation data (MODIS) and land cover characterization from the ESA Climate Change Initiative product reclassified into their IPCC land use category equivalent. This data, originally at 0.05 degree of spatial resolution, is aggregated and analysed at regional level to provide guidance on the expected temperature impact following specific LCC transitions.

  13. Towards an accurate and precise determination of the solid-solid transition temperature of enantiotropic systems

    Energy Technology Data Exchange (ETDEWEB)

    Herman, Christelle, E-mail: christelle.herman@ulb.ac.b [Universite Libre de Bruxelles, Transfers, Interfaces and Processes Department, Chemical Engineering Unit, 50 Avenue Franklin D-Roosevelt, CP 165/67, 1050 Bruxelles (Belgium); Leyssens, Tom [Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences, 1 Place Louis Pasteur, 1348 Louvain-La-Neuve (Belgium); Vermylen, Valerie [UCB Pharma, 60 Allee de la Recherche, 1070 Braine l' Alleud (Belgium); Halloin, Veronique; Haut, Benoit [Universite Libre de Bruxelles, Transfers, Interfaces and Processes Department, Chemical Engineering Unit, 50 Avenue Franklin D-Roosevelt, CP 165/67, 1050 Bruxelles (Belgium)

    2011-05-15

    Research highlights: We test two methods to obtain the solid-solid transition temperature of Etiracetam system, showing two enantiotropically related polymorphs. The first method, based on a thermodynamic development, is sensitive to the correctness of the data required. The second method is an experimental study of the stability thermal range of each morph. We identify the nature of crystals in suspension at equilibrium through Raman analysis. The solid-solid transition temperature is found equal to 303.65 K {+-} 0.5 K. - Abstract: This paper presents two distinct methods for the determination of the solid-solid transition temperature (T{sub tr}) separating the temperature ranges of stability of two crystallographic forms, hereafter called morphs, of a same substance. The first method, based on thermodynamic calculations, consists in determining T{sub tr} as the temperature at which the Gibbs free energies of the two morphs are equal to each other. For this purpose, some thermodynamic characteristics of both morphs are required, such as the specific heat capacities, the melting temperatures and the melting enthalpies. These are obtained using the Differential Scanning Calorimetry (DSC). In the second method, T{sub tr} is determined directly by an experimental study of the temperature ranges of stability of each morph. The three main originalities of the method developed are (i) to prepare samples composed by an isomassic mixture of crystals of both morphs, (ii) to set them in a thermostated and agitated suspension, and (iii) to use an in situ Raman spectroscopic probe for the determination of the crystallographic form of the crystals in suspension at equilibrium. Both methods are applied to determine the solid-solid transition temperature of the enantiotropic system of Etiracetam, and both of its two crystallographic forms so far identified, named morph I and morph II. The first method is shown to be very sensitive to the experimental data obtained by DSC while

  14. Kinetic criteria of glass formation and the pressure dependence of the glass transition temperature.

    Science.gov (United States)

    Schmelzer, Jürn W P

    2012-02-21

    An overview on different attempts of formulation of kinetic criteria of glass formation is given. It is analyzed which of the characteristic time scales-time of observation, time of relaxation, and time of change of external parameters-have to be employed to appropriately develop such criteria. Based on this analysis, a general model-independent kinetic criterion for glass formation is formulated. As a first consequence, it is shown that it is not-as often claimed-the Deborah number which governs glass formation. Based on this general kinetic criterion for glass formation, general expressions for the dependence of the glass transition temperature on pressure (and vice versa) are obtained being essentially ratios of the partial derivatives of the appropriate relaxation times with respect to pressure and temperature, respectively. Employing, as examples, further two different (free volume and entropy based) models for the description of viscous flow and relaxation, respectively, relations similar but, in general, not identical to the classical Ehrenfest relations describing second-order equilibrium phase transitions are obtained. In this way, it can be explained why one of the Ehrenfest's relations is usually fulfilled in glass transition and the other not and why the Prigogine-Defay ratio in glass transition is not equal to one as this is the case with Ehrenfest's ratio in second-order equilibrium phase transitions. © 2012 American Institute of Physics

  15. MICROSTRUCTURE AND INFRARED EMISSIVITY AT NORMAL TEMPERATURE IN TRANSITIONAL METAL OXIDES SYSTEM CERAMICS

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The fabrication of Fe2O3-MnO2-Co2O3-CuO system ceramics, and the composite system ceramics of transitional metal oxides-cordierite and transitional metal oxides-kaolinit are presented in this work. The research was carried out with the main attention to the infrared emissivity in the band of 8~14μm at room temperature,the microstructure of the ceramics and the relation between them. High infrared emissivities exceeding 0.9 in the band of 8~14μm at room temperature were gained in the transitional metal oxide ceramics and the composite system ceramics. It is suggested that the formation of inverse spinels and partially inverse spinels, such as Fe3O4, CoFe2O4, CuFe2O4 and CuMn2O4, is beneficial to the enhancement of the infrared emissivity of the transitional metal oxide ceramics. The transitional metal oxides play an important role in determining the infrared emissivity of the composite system ceramics.

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

    Science.gov (United States)

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

    2015-07-01

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

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

    Science.gov (United States)

    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.

  18. High-temperature and high-pressure phase transitions in uranium

    Science.gov (United States)

    Bouchet, J.; Bottin, F.

    2017-02-01

    The phase diagram of uranium has been explored up to 100 GPa and 2000 K by means of ab initio molecular dynamics (AIMD) simulations. The lattice dynamics and energetics of the stable phases observed experimentally in this range of pressure and temperature are studied in this work. The phonon spectra of the α and γ phases are shown to evolve strongly as a function of temperature, unveiling the huge anharmonic effects present in this material. If the elastics constants and the bulk and shear moduli of the γ phase do not disclose any temperature effects, the shear modulus of the α phase decreases strongly as a function of temperature. Using the pressure- and temperature-dependent vibrational density of states and the Gibbs free energy of these two structures, we found a line transition between the α and γ phases which slightly underestimates the experimental one. Coherently with experiments, the bct structure is never found stable between 0 and 100 GPa.

  19. Chemical composition effect on VVER-1000 RPV weld metal thermal aging

    Science.gov (United States)

    Gurovich, B. A.; Chernobaeva, A. A.; Erak, D. Yu; Kuleshova, E. A.; Zhurko, D. A.; Papina, V. B.; Skundin, M. A.; Maltsev, D. A.

    2015-10-01

    Temperature and fast neutron flux simultaneously affect the material of welded joints of reactor pressure vessels under irradiation. Understanding thermal aging effects on the weld metal allows for an explanation of the mechanisms that govern an increase in the ductile-to-brittle transition temperature of the reactor pressure vessel materials under long term irradiation at operation temperature. This paper reports on new results and reassessment of the VVER-1000 weld metal surveillance specimen database performed at the National Research Center "Kurchatov Institute". The current database of VVER-1000 weld metal thermal aging at 310-320 °C includes 50 transition temperature values with the maximum holding time of 208,896 h. The updated database completed with the information on intergranular fracture shear and phosphorous content in the grain boundaries has allowed us to propose a new mechanism of VVER-1000 weld materials thermal aging at 310-320 °C and develop models of ductile-to-brittle transition temperature shift for VVER-1000 weld metal during a long-term exposure at 310-320 °C.

  20. Predict the glass transition temperature of glycerol-water binary cryoprotectant by molecular dynamic simulation.

    Science.gov (United States)

    Li, Dai-Xi; Liu, Bao-Lin; Liu, Yi-shu; Chen, Cheng-lung

    2008-04-01

    Vitrification is proposed to be the best way for the cryopreservation of organs. The glass transition temperature (T(g)) of vitrification solutions is a critical parameter of fundamental importance for cryopreservation by vitrification. The instruments that can detect the thermodynamic, mechanical and dielectric changes of a substance may be used to determine the glass transition temperature. T(g) is usually measured by using differential scanning calorimetry (DSC). In this study, the T(g) of the glycerol-aqueous solution (60%, wt/%) was determined by isothermal-isobaric molecular dynamic simulation (NPT-MD). The software package Discover in Material Studio with the Polymer Consortium Force Field (PCFF) was used for the simulation. The state parameters of heat capacity at constant pressure (C(p)), density (rho), amorphous cell volume (V(cell)) and specific volume (V(specific)) and radial distribution function (rdf) were obtained by NPT-MD in the temperature range of 90-270K. These parameters showed a discontinuity at a specific temperature in the plot of state parameter versus temperature. The temperature at the discontinuity is taken as the simulated T(g) value for glycerol-water binary solution. The T(g) values determined by simulation method were compared with the values in the literatures. The simulation values of T(g) (160.06-167.51K) agree well with the DSC results (163.60-167.10K) and the DMA results (159.00K). We drew the conclusion that molecular dynamic simulation (MDS) is a potential method for investigating the glass transition temperature (T(g)) of glycerol-water binary cryoprotectants and may be used for other vitrification solutions.

  1. Glass Transition Temperature Depression at the Percolation Threshold in Carbon Nanotube-Epoxy Resin and Polypyrrole-Epoxy Resin Composites

    OpenAIRE

    Barrau, Sophie; Demont, Philippe; Maraval, Céline; Bernès, Alain; Lacabanne, Colette

    2005-01-01

    The glass transition temperatures of conducting composites, obtained by blending carbon nanotubes (CNTs) or polypyrrole (PPy) particles with epoxy resin, were investigated by using both differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). For both composites, dc and ac conductivity measurements revealed an electrical percolation threshold at which the glass transition temperature and mechanical modulus of the composites pass through a minimum.

  2. Analysis of the competition between brittle and ductile fracture: application for the mechanical behaviour of C-Mn and theirs welds; Etude de la competition dechirure ductile/rupture fragile: application de la tenue mecanique des tubes en acier C-Mn et de leurs joints soudes

    Energy Technology Data Exchange (ETDEWEB)

    Le Corre, V

    2006-09-15

    This study deals with the fracture behaviour of welded thin structures in the ductile to brittle transition range. It aims to propose a criterion to define the conditions for which the risk of fracture by cleavage does not exist on a cracked structure. The literature review shows that the difficulties of prediction of the fracture behaviour of a structure are related to the dependence of the fracture probability to the mechanical fields at the crack tip. The ductile to brittle transition range thus depends on the studied geometry of the structure. A threshold stress, below which cleavage cannot take place, is defined using fracture tests on notched specimens broken at very low temperature. The finite element numerical simulation of fracture tests onspecimens in the transition range shows a linear relationship between the fracture probability and the volume exceeding the threshold stress, thus showing the relevance of the proposed criterion. Moreover, several relations are established allowing to simplify the identification of the criterion parameters. The criterion is applied to a nuclear structural C-Mn steel, by focusing more particularly on the higher boundary of the transition range. A fracture test on a full-scale pipe is designed, developed, carried out and analysed using its numerical simulation. The results show firstly that, on the structure, the transition range is shifted in temperature, compared to laboratory specimens, due to the low plasticity constraint achieved in thin structures, and secondly that the threshold stress criterion allows to estimate simply this shift. (author)

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

    Directory of Open Access Journals (Sweden)

    Erin M Gray

    Full Text Available 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

  4. Pressure-temperature dependence of growth bottlenecks and phenotypic transitions of Escherichia coli

    Science.gov (United States)

    Kumar, Pradeep; Libchaber, Albert J.

    2012-02-01

    A vast majority of bacteria and archaea can grow in diverse environmental conditions. The range of those conditions include high pressures, high temperature, low temperature, high salinity, low and high pH etc. We investigate the growth bottlenecks and phenotypic transitions of Escherichia coli (E. coli), a mesophilic bacterium, as a function of pressure and temperature. We find that E.coli can grow and proliferate in a wide range of pressures (1-400 atm) and temperatures (23-40 deg C). Moreover, we find that the division time of E. coli increases monotonically upon increasing pressure and exhibits a sharp increase in division time at pressures between 250-400 atm for all the temperatures investigated in our experiments. The sharp change in division time is followed by a sharp change in phenotypic transition of E. Coli at high pressures where bacterial cells switch to an elongating cell type. We propose that this phenotypics changes in bacteria at high pressures is an irreversible stochastic process whereas the switching probability to elongating cell type increases with increasing pressure. Furthermore, we propose an irreversible stochastic model of cell phenotype switching. We find that model fits well the experimental data. We discuss our experimental results in the light of structural and so the functional changes in proteins and structural changes in membranes at different pressure and temperature.

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

    Science.gov (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Philipp, M; Mueller, U; Sanctuary, R; Baller, J; Krueger, J K [Laboratoire de Physique des Materiaux, Universite du Luxembourg, 162A, avenue de la Faiencerie, L-1511 (Luxembourg)], E-mail: martine.philipp@uni.lu

    2008-09-15

    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.

  7. Phase transitions in strongly coupled 3d Z(N) lattice gauge theories at finite temperature

    CERN Document Server

    Borisenko, O; Cortese, G; Fiore, R; Gravina, M; Papa, A; Surzhikov, I

    2012-01-01

    We perform an analytical and numerical study of the phase transitions in three-dimensional Z(N) lattice gauge theories at finite temperature for N>4. In the strong coupling limit these models are equivalent to a generalized version of the vector Potts models in two dimensions, where Polyakov loops play the role of Z(N) spins. The effective couplings of these two-dimensional spin models are calculated explicitly. It is argued that the effective spin models have two phase transitions of BKT type. This is confirmed by large-scale Monte Carlo simulations. Using a cluster algorithm we locate the position of the critical points and study the critical behavior across both phase transitions in details. In particular, we determine various critical indices, compute the helicity modulus, the average action and the specific heat. A scaling formula for the critical points with N is proposed.

  8. Transition temperature in QCD with physical light and strange quark masses

    CERN Document Server

    Karsch, F

    2007-01-01

    We present results from a calculation of the transition temperature in QCD with two light and one heavier (strange) quark mass on lattices with temporal extent N_t =4 and 6. Calculations with improved staggered fermions have been performed with a strange quark mass fixed close to its physical value and for various light to strange quark mass ratios that correspond to light pseudo-scalar masses in the range (150-500) MeV. From a combined extrapolation to the chiral (m_l -> 0) and continuum (aT -> 0) limits we obtain for the transition temperature at the physical point T_c = 192(7)(4) MeV. We also present first results from an ongoing calculation of the QCD equation of state with almost realistic light and strange quark masses.

  9. Structure of chiral phase transitions at finite temperature in abelian gauge theories

    Energy Technology Data Exchange (ETDEWEB)

    Fukazawa, Kenji [Kure National College of Technology, Kure (Japan); Inagaki, Tomohiro [Information Media Center, Hiroshima Univ., Hiroshima (Japan); Mukaigawa, Seiji [Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate Univ., Iwate (Japan); Muta, Taizo [Department of Physics, Hiroshima Univ., Hiroshima (Japan)

    2001-06-01

    The mechanism of chiral symmetry breaking is investigated in strong-coupling Abelian gauge theories at finite temperature. The Schwinger-Dyson equation in the Landau gauge is employed in the real time formalism and is solved numerically within the framework of the instantaneous exchange approximation, including the effect of the thermal mass for the photon propagator. It is found that the chiral symmetry is broken below the critical temperature T for sufficiently large coupling {alpha}. The chiral phase transition is found to be of second order, and the phase diagram in the T-{alpha} plane is obtained. It is investigated how the structure of the chiral phase transition is affected by the thermal mass in the photon propagator. (author)

  10. Structure of chiral phase transitions at finite temperature in Abelian gauge theories

    CERN Document Server

    Fukazawa, K; Mukaigawa, S; Muta, T; Fukazawa, Kenji; Inagaki, Tomohiro; Mukaigawa, Seiji; Muta, Taizo

    1999-01-01

    The mechanism of the chiral symmetry breaking is investigated in the strong-coupling Abelian gauge theories at finite temperature. The Schwinger-Dyson equation in Landau gauge is employed in the real time formalism and is solved numerically within the framework of the instantaneous exchange approximation including the effect of the hard thermal loop for the photon propagator. It is found that the chiral symmetry is broken below the critical temperature T for sufficiently large coupling. The chiral phase transition is found to be of the 2nd order and the phase diagram on the $T-\\alpha$ plane is obtained. It is investigated how the structure of the chiral phase transition is affected by the hard thermal loops in the photon propagator.

  11. Transition in Deformation Mechanism of AZ31 Magnesium Alloy during High-Temperature Tensile Deformation

    Directory of Open Access Journals (Sweden)

    Masafumi Noda

    2011-01-01

    Full Text Available Magnesium alloys can be used for reducing the weight of various structural products, because of their high specific strength. They have attracted considerable attention as materials with a reduced environmental load, since they help to save both resources and energy. In order to use Mg alloys for manufacturing vehicles, it is important to investigate the deformation mechanism and transition point for optimizing the material and vehicle design. In this study, we investigated the transition of the deformation mechanism during the high-temperature uniaxial tensile deformation of the AZ31 Mg alloy. At a test temperature of 523 K and an initial strain rate of 3×10−3 s-1, the AZ31 Mg alloy (mean grain size: ~5 μm exhibited stable deformation behavior and the deformation mechanism changed to one dominated by grain boundary sliding.

  12. Predicting the glass transition temperature of bioactive glasses from their molecular chemical composition.

    Science.gov (United States)

    Hill, Robert G; Brauer, Delia S

    2011-10-01

    A recently published paper (M.D. O'Donnell, Acta Biomaterialia 7 (2011) 2264-2269) suggests that it is possible to correlate the glass transition temperature (T(g)) of bioactive glasses with their molar composition, based on iterative least-squares fitting of published T(g) data. However, we show that the glass structure is an important parameter in determining T(g). Phase separation, local structural effects and components (intermediate oxides) which can switch their structural role in the glass network need to be taken into consideration, as they are likely to influence the glass transition temperature of bioactive glasses. Although the model suggested by O'Donnell works reasonably well for glasses within the composition range presented, it is oversimplified and fails for glasses outside certain compositional boundaries.

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

    Science.gov (United States)

    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.

  14. Laminar-Turbulent Transition: The change of the flow state temperature with the Reynolds number

    CERN Document Server

    Chekmarev, Sergei F

    2014-01-01

    Using the previously developed model to describe laminar/turbulent states of a viscous fluid flow, which treats the flow as a collection of coherent structures of various size (Chekmarev, Chaos, 2013, 013144), the statistical temperature of the flow state is determined as a function of the Reynolds number. It is shown that at small Reynolds numbers, associated with laminar states, the temperature is positive, while at large Reynolds numbers, associated with turbulent states, it is negative. At intermediate Reynolds numbers, the temperature changes from positive to negative as the size of the coherent structures increases, similar to what was predicted by Onsager for a system of parallel point-vortices in an inviscid fluid. It is also shown that in the range of intermediate Reynolds numbers the temperature exhibits a power-law divergence characteristic of second-order phase transitions.

  15. High Power, Room Temperature Terahertz Emitters Based on Dopant Transitions in 6H-Silicon Carbide

    Institute of Scientific and Technical Information of China (English)

    James Kolodzey; Guang-Chi Xuan; Peng-Cheng Lv; Nathan Sustersic; Xin Ma

    2014-01-01

    Electrically pumped high power terahertz (THz) emitters that operated above room temperature in a pulse mode were fabricated from nitrogen-doped n-type 6H-SiC. The emission spectra had peaks centered on 5 THz and 12 THz (20 meV and 50 meV) that were attributed to radiative transitions of excitons bound to nitrogen donor impurities. Due to the relatively deep binding energies of the nitrogen donors, above 100 meV, and the high thermal conductivity of the SiC substrates, the THz output power and operating temperature were significantly higher than previous dopant based emitters. With peak applied currents of a few amperes, and a top surface area of 1 mm2, the device emitted up to 0.5 mW at liquid nitrogen temperature (77 K), and tens of microwatts up to 333 K. This result is the highest temperature of THz emission reported from impurity-based emitters.

  16. Deformation and structure evolution of glassy poly(lactic acid) below the glass transition temperature

    DEFF Research Database (Denmark)

    Zhou, Chengbo; Li, Hongfei; Zhang, Yao;

    2015-01-01

    Poly(lactic acid) (PLA) is a bio-based and compostable thermoplastic polyester that has rapidly evolved into a competitive commodity material over the last decade. One key bottleneck in expanding the field of application of PLA is the control of its structure and properties. Therefore, in situ...... by differential scanning calorimetry (DSC). The obtained results showed that the deformation and yield stress of glassy PLA are strongly dependent on the stretching temperatures together with the transition from mesophase to mesocrystal and the formation of cavities. With the increase in drawing temperature...

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

    Science.gov (United States)

    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.

  18. Superfluid density and superconducting transition temperature in Bi-based cuprate single crystals.

    Science.gov (United States)

    Gasparov, L.; Tanner, D.; Berger, H.; Forro, L.; Margaritondo, G.

    2000-03-01

    We present temperature-dependent reflectance measurements for Bi-based cuprate single crystals in the frequency range from 100 to 40,000 cm-1 (0.012--5 eV). The optical conductivity is obtained by Kramers-Kronig analysis. We compare differently doped Bi-2212 (particularly in the underdoped regime) as well as Pr-doped Bi-2212 crystals by analyzing optical conductivity in the framework of a two-fluid approach. This approach allows us to study correlations between superfluid density and superconducting transition temperature of these materials.

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

    Science.gov (United States)

    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.

  20. Raman Scattering Spectroscopy of Phase Transition in n-Pentadecane under High Temperature and High Pressure

    Institute of Scientific and Technical Information of China (English)

    QIAO Er-Wei; ZHENG Hai-Fei; XU Bei

    2009-01-01

    The Raman spectroscopy of n-pentadecane is investigated in a moissanite anvil cell at normal temperatures and a diamond anvil cell under pressure to about 3000 MPa and at temperature from 298 to 573 K. Result indicates that at room temperature the vibration modes, assigned to the symmetric and asymmetric stretching of CH3 and CH2 stretching, shift to higher frequency and display a pressure dependent quasi-linear curve. A liquid-solid phase transition appears at a pressure of 150 MPa. The high temperature solidus line of n-pentadecane follows a quadratic function of P = 0.02369T2 - 9.117T + 725.58, in agreement with previous conclusion derived from studies of other hydrocarbons. Upon phase transition, fitting the experimental data obtained in a temperature range of 283-553 K to the Clausius-Clapeyron equation allows one to define the thermodynamic parameters of n-pentadecane of dP/dT = 0.04738T - 9.117.

  1. Above room temperature heat capacity and phase transition of lithium tetrahydroborate

    Energy Technology Data Exchange (ETDEWEB)

    El Kharbachi, A., E-mail: a.elkharbachi@simap.grenoble-inp.fr [Laboratoire de Science et Ingenierie des Materiaux et Procedes (SIMaP), CNRS-UMR 5266, Universite de Grenoble, 1130 rue de la Piscine, Domaine Universitaire, BP 75, 38402 Saint Martin d' Heres (France); Nuta, I.; Hodaj, F. [Laboratoire de Science et Ingenierie des Materiaux et Procedes (SIMaP), CNRS-UMR 5266, Universite de Grenoble, 1130 rue de la Piscine, Domaine Universitaire, BP 75, 38402 Saint Martin d' Heres (France); Baricco, M. [Dipartimento di Chimica I.F.M and NIS, Universita di Torino, via P. Giuria 9, 10125 Torino (Italy)

    2011-06-10

    Highlights: {yields} LiBH{sub 4} as hydrogen storage material. {yields} Thermodynamic properties of this compound are lacking in literature. Molar heat capacity, C{sub p,m}, of the different phases (ortho-phase, hexa-phase and liquid phase) needs to be determined. {yields} C{sub p,m} 'anomaly' is observed to be independent of the main phase transition. - Abstract: New calorimetric determinations of molar heat capacity C{sub p,m} of lithium tetrahydroborate (LiBH{sub 4}) were performed in order to analyze the origin of the previously observed 'anomaly' before the polymorphous transition at 386 K. The above room temperature dependence of LiBH{sub 4}C{sub p,m} was measured until approaching the melting point of the compound at 553 K and the abnormal behaviour was attributed to lattice defects independent of the main crystalline phase transition. As a result, lower entropy of the transition {Delta}{sub trs}S = 13.11 {+-} 0.23 J K{sup -1} mol{sup -1} than that proposed in literature was obtained, which is in agreement with the observed anisotropy and crystal density decrease before the transition from recent X-ray diffraction indexing. An estimate of the liquid C{sub p,m} of LiBH{sub 4} 'molten salt' is proposed.

  2. Effect of chain end group on surface glass transition temperature of thin polymer film

    Science.gov (United States)

    Jiang, Xiqun; Yang, Chang Zheng; Tanaka, Keiji; Takahara, Atsushi; Kajiyama, Tisato

    2001-04-01

    Surface glass transition behaviors of proton end capped poly(2-vinylpyridine) (P2VP-H) and perfluoroalkyl end capped poly(2-vinylpyridine) (P2VP-C 2C 8F) thin films were investigated based on temperature-dependent lateral force microscopic (TDLFM) measurement. It is found that the species of chain end groups have significant influence on the surface glass transition temperature of the thin polymer film. For both samples, it is revealed that the surface glass transition temperatures decrease significantly in comparison to the bulk ones, and the magnitude order of reduction in surface Tg for P2VP-C 2C 8F is larger than that for P2VP-H. The apparent activation energy of surface α-relaxation calculated from the Arrhenius plot is ca. 292±40 and 212±40 kJ/mol for P2VP-H and P2VP-C 2C 8F, respectively, and is much smaller than the bulk one. The depression of the surface Tg for thin polymer films is explained by the excess free volume induced by the enrichment of chain end groups at the surface.

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

    Science.gov (United States)

    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.

  4. A statistical approach to the QCD phase transition --A mystery in the critical temperature

    CERN Document Server

    Ishii, N; Ishii, Noriyoshi; Suganuma, Hideo

    2002-01-01

    We study the QCD phase transition based on the statistical treatment with the bag-model picture of hadrons, and derive a phenomenological relation among the low-lying hadron masses, the hadron sizes and the critical temperature of the QCD phase transition. We apply this phenomenological relation to both full QCD and quenched QCD, and compare these results with the corresponding lattice QCD results. Whereas such a statistical approach works well in full QCD, it results in an extremely large estimate of the critical temperature in quenched QCD, which indicates a serious problem in understanding of the QCD phase transition. This large discrepancy traces back to the fact that enough number of glueballs are not yet thermally excited at the critical temperature T_c \\simeq 280 MeV in quenched QCD due to the extremely small statistical factor as exp(-m_G/T_c) \\simeq 0.00207. This fact itself has a quite general nature independent of the particular choice of the effective model framework. We are thus arrive at a myste...

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

    Energy Technology Data Exchange (ETDEWEB)

    Orlova, Maria, E-mail: maria.p.orlova@gmail.com [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Khainakov, Sergey [Departamento de Química Física y Analítica, Universidad de Oviedo—CINN, 33006 Oviedo (Spain); Servicios Científico Técnicos, Universidad de Oviedo, 33006 Oviedo (Spain); Michailov, Dmitriy [Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation); Perfler, Lukas [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Langes, Christoph [Institute of Pharmacy, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Kahlenberg, Volker [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Orlova, Albina [Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation)

    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

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

    Science.gov (United States)

    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

  7. Temperature decline thermography for laminar-turbulent transition detection in aerodynamics

    Science.gov (United States)

    von Hoesslin, Stefan; Stadlbauer, Martin; Gruendmayer, Juergen; Kähler, Christian J.

    2017-09-01

    Detailed knowledge about laminar-turbulent transition and heat transfer distribution of flows around complex aerodynamic components are crucial to achieve highest efficiencies in modern aerodynamical systems. Several measurement techniques have been developed to determine those parameters either quantitatively or qualitatively. Most of them require extensive instrumentation or give unreliable results as the boundary conditions are often not known with the required precision. This work introduces the simple and robust temperature decline method to qualitatively detect the laminar-turbulent transition and the respective heat transfer coefficients on a surface exposed to an air flow, according to patent application Stadlbauer et al. (Patentnr. WO2014198251 A1, 2014). This method provides results which are less sensitive to control parameters such as the heat conduction into the blade material and temperature inhomogeneities in the flow or blade. This method was applied to measurements with NACA0018 airfoils exposed to the flow of a calibration-free jet at various Reynolds numbers and angles of attack. For data analysis, a post-processing method was developed and qualified to determine a quantity proportional to the heat transfer coefficient into the flow. By plotting this quantity for each pixel of the surface, a qualitative, two-dimensional heat transfer map was obtained. The results clearly depicted the areas of onset and end of transition over the full span of the model and agreed with the expected behavior based on the respective flow condition. To validate the approach, surface hotfilm measurements were conducted simultaneously on the same NACA profile. Both techniques showed excellent agreement. The temperature decline method allows to visualize laminar-turbulent transitions on static or moving parts and can be applied on a very broad range of scales—from tiny airfoils up to large airplane wings.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  10. Dependence of the brittle ductile transition on strain-rate-dependent critical homologous temperature

    Science.gov (United States)

    Davis, Paul M.

    2017-05-01

    Earthquakes mainly occur in crust or mantle that is below a critical temperature for the tectonic strain-rate, \\dot{e}_t, such that stress builds up to the breaking point before it can relax due to creep. Then long-range stress correlation gives rise to power law seismicity including large events. The limiting temperature depends on pressure, which is taken into account by finding a critical homologous temperature THc = T/TM above which earthquakes are rarely observed (where T, TM are temperature and average melting temperature of constituent minerals). We find that THc for ocean plates is ∼0.55. For California earthquakes, it is also close to 0.55. The uppermost mantle layer of oceanic plates of thickness ∼50 km is composed of harzburgite and depleted peridotite from which basalt has been removed to form ocean crust. Thus it has a higher melting temperature than the peridotite of the surrounding mantle, or the lower halves of plates. Thicknesses of seismicity in deep subduction zones, determined from 2-D polynomial fits to a relocated catalogue, are ∼50 km, which suggests that the earthquake channel is confined to this layer. We construct models to find homologous temperatures in slabs, and find that seismicity thicknesses are also, on average, confined to TH ≤ 0.55 ± 0.05. The associated rheology is compared with that obtained from flexure models of ocean lithosphere. The brittle-ductile transition occurs where viscosity drops from high values in the cold cores of slabs to values of 1022-1023 Pa s, that is, where creep strain-rates become comparable to tectonic rates. The cut-off for deep earthquakes is not sharp. However they appear unlikely to occur if homologous temperature is high TH > 0.55. Exceptions to the rule are anomalously deep earthquakes such as those beneath the Iceland and the Hawaiian hotspots, and the Newport Inglewood Fault. These are smaller events with short-range stress correlation, and can be explained if strain-rates are two to

  11. Influence of higher sodium substitutions on magnetic entropy change and transition temperature in lanthanum manganites

    Indian Academy of Sciences (India)

    N Sethulakshmi; I A Al Omari; M R Anantharaman

    2015-10-01

    Present investigation focuses on the variation of magnetic entropy change for higher sodium substitution above 50% in lanthanum manganites. Magnetic measurements indicated that all samples exhibit a ferromagnetic ordering near room temperature. Magnetic isotherms for different temperatures above and below 300 K were recorded and the magnetic entropy change for compositions belonging to La1−Na MnO3 for = 0.6 to 0.9 in steps of 0.1 was estimated for different applied magnetic fields. It has been found that the compositions having a Na substitution of 0.6 are having the largest entropy change, and the entropy change increases with applied magnetic field for all compositions. The change in entropy also decreases with increase in substitution of sodium. A notable change in transition temperature with Na concentration is also found in this sample series.

  12. Low temperature phase transition and crystal structure of CsMgPO4

    Science.gov (United States)

    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.

  13. Relevance of the axial anomaly at the finite-temperature chiral transition in QCD

    CERN Document Server

    Pelissetto, Andrea

    2013-01-01

    We address the issue of the relevance of the suppression of the U(1)_A symmetry breaking, induced by the axial anomaly, at the finite-temperature chiral QCD transition with two light flavors. If the U(1)_A breaking is substantially suppressed at the transition, the effective symmetry breaking that determines the universality class is U(2)_L X U(2)_R -> U(2)_V. We perform a high-order perturbative study of the renormalization-group (RG) flow of the corresponding three-dimensional (3D) multiparameter Phi theory that has the same order parameter and symmetry-breaking pattern. We confirm the existence of a stable fixed point (FP), and determine its attraction domain in the space of the bare quartic parameters. Therefore, the chiral QCD transition might be continuous also if the U(1)_A symmetry is effectively restored at Tc. However, the corresponding universality class differs from the O(4) vector universality class which would describe a continuous transition in the presence of a substantial U(1)_A symmetry brea...

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

    Science.gov (United States)

    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. First-principles prediction of new complex transition metal hydrides for high temperature applications.

    Science.gov (United States)

    Nicholson, Kelly M; Sholl, David S

    2014-11-17

    Metal hydrides with high thermodynamic stability are desirable for high-temperature applications, such as those that require high hydrogen release temperatures or low hydrogen overpressures. First-principles calculations have been used previously to identify complex transition metal hydrides (CTMHs) for high temperature use by screening materials with experimentally known structures. Here, we extend our previous screening of CTMHs with a library of 149 proposed materials based on known prototype structures and charge balancing rules. These proposed materials are typically related to known materials by cation substitution. Our semiautomated, high-throughput screening uses density functional theory (DFT) and grand canonical linear programming (GCLP) methods to compute thermodynamic properties and phase diagrams: 81 of the 149 materials are found to be thermodynamically stable. We identified seven proposed materials that release hydrogen at higher temperatures than the associated binary hydrides and at high temperature, T > 1000 K, for 1 bar H2 overpressure. Our results indicate that there are many novel CTMH compounds that are thermodynamically stable, and the computed thermodynamic data and phase diagrams should be useful for selecting materials and operating parameters for high temperature metal hydride applications.

  16. Enhancement of Curie temperature and transition temperature range induced by Al doping in Mn1-xAlxCoGe

    Science.gov (United States)

    Si, Xiaodong; Liu, Yongsheng; Lei, Wei; Xu, Juan; Du, Wenlong; Lin, Jia; Zhou, Tao; Lu, Xiaofei

    2016-12-01

    Mn1-xAlxCoGe alloys with a second order transition were produced by arc-melting method. The substitution of Mn by Al increased the Curie temperature (TC) from 260.5 K to 300.8 K, the magnetic entropy change (|ΔSM|) decreased from 3.78 J·Kg-1K-1 to 2.35 J·Kg-1K-1 under a field change of Δμ0H=5 T. In addition, the |ΔSM| well linearly depends on the H2/3 around TC. Furthermore, the relative cooling power (RCP) can reach 242.3 J·Kg-1 with a large full width at half maximum of |ΔSM| (75.5 K) for x=0.02. The decrease of |ΔSM| is explained by the corresponding monotonical decrease of magnetic moment per formula unit.

  17. Trends in low-temperature water–gas shift reactivity on transition metals

    DEFF Research Database (Denmark)

    Schumacher, Nana Maria Pii; Boisen, Astrid; Dahl, Søren;

    2005-01-01

    Low-temperature water–gas shift reactivity trends on transition metals were investigated with the use of a microkinetic model based on a redox mechanism. It is established that the adsorption energies for carbon monoxide and oxygen can describe to a large extent changes in the remaining activation...... and adsorption energies through linear correlations. In comparisons with experimental data it is found that the model predicts well the order of catalytic activities for transition metals, although it fails to quantitatively describe the experimental data. This discrepancy could be due to the assumption...... that the redox mechanism dominates and to the neglect of adsorbate interactions, which play an important role at high coverages. The model predicts that the activity of copper can be improved by increasing the strengths with which carbon monoxide and oxygen are bonded to the surface, thus suggesting possible...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-09-22

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

  19. Structural stability and phase transition of Bi 2 Te 3 under high pressure and low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, J. L.; Zhang, S. J.; Zhu, J. L.; Liu, Q. Q.; Wang, X. C.; Jin, C. Q.; Yu, J. C.

    2017-09-01

    Structural stability and phase transition of topological insulator Bi2Te3 were studied via angle-dispersive synchrotron radiation X-ray diffraction under high pressure and low temperature condition. The results manifest that the R-3m phase (phase I) is stable at 8 K over the pressure range up to 10 GPa and phase transition occurs between 8 K and 45 K at 8 GPa. According to the Birch-Murnaghan equation of state, the bulk modulus at ambient pressure B0 was estimated to be 45 ± 3 GPa with the assumption of B0' = 4. The structural robustness of phase I at 8 K suggests that the superconductivity below 10 GPa is related to phase I. Topological properties of superconducting Bi2Te3 phase under pressure were discussed.

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

    Science.gov (United States)

    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.

  1. Equilibrium free-energy differences at different temperatures from a single set of nonequilibrium transitions

    Science.gov (United States)

    Patra, Puneet Kumar; Bhattacharya, Baidurya

    2016-10-01

    Crook's fluctuation theorem (CFT) and Jarzynski equality (JE) are effective tools for obtaining free-energy difference Δ F (λA→λB,T0) through a set of finite-time protocol driven nonequilibrium transitions between two equilibrium states A and B [parametrized by the time-varying protocol λ (t ) ] at the same temperature T0. Using the generalized dimensionless work function Δ WG , we extend CFT to transitions between two nonequilibrium steady states (NESSs) created by a thermal gradient. We show that it is possible, provided the period over which the transitions occur is sufficiently long, to obtain Δ F (λA→λB,T0) for different values of T0, using the same set of finite-time transitions between these two NESSs. Our approach thus completely eliminates the need to make new samples for each new T0. The generalized form of JE arises naturally as the average of the exponentiated Δ WG . The results are demonstrated on two test cases: (i) a single particle quartic oscillator having a known closed form Δ F , and (ii) a one-dimensional ϕ4 chain. Each system is sampled from the canonical distribution at an arbitrary T' with λ =λA , then subjected to a temperature gradient between its ends, and after steady state is reached, the protocol change λA→λB is effected in time τ , following which Δ WG is computed. The reverse path likewise initiates in equilibrium at T' with λ =λB and the protocol is time reversed leading to λ =λA and the reverse Δ WG . Our method is found to be more efficient than either JE or CFT when free-energy differences at multiple T0's are required for the same system.

  2. Low-temperature thermal transport and thermopower of monolayer transition metal dichalcogenide semiconductors

    Science.gov (United States)

    Sengupta, Parijat; Tan, Yaohua; Klimeck, Gerhard; Shi, Junxia

    2017-10-01

    We study the low temperature thermal conductivity of single-layer transition metal dichalcogenides (TMDCs). In the low temperature regime where heat is carried primarily through transport of electrons, thermal conductivity is linked to electrical conductivity through the Wiedemann–Franz law (WFL). Using a k.p Hamiltonian that describes the K and K{\\prime} valley edges, we compute the zero-frequency electric (Drude) conductivity using the Kubo formula to obtain a numerical estimate for the thermal conductivity. The impurity scattering determined transit time of electrons which enters the Drude expression is evaluated within the self-consistent Born approximation. The analytic expressions derived show that low temperature thermal conductivity (1) is determined by the band gap at the valley edges in monolayer TMDCs and (2) in presence of disorder which can give rise to the variable range hopping regime, there is a distinct reduction. Additionally, we compute the Mott thermopower and demonstrate that under a high frequency light beam, a valley-resolved thermopower can be obtained. A closing summary reviews the implications of results followed by a brief discussion on applicability of the WFL and its breakdown in context of the presented calculations.

  3. RECOVERY OF AMORPHOUS POLY(ETHYLENE TEREPHTHALATE) FILM UNIAXIALLY DRAWN JUST BELOW THE GLASS TRANSITION TEMPERATURE

    Institute of Scientific and Technical Information of China (English)

    Nan-jian Sun; Juan Yang; De-yan Shen; Ren-yuan Qian

    2000-01-01

    Isothermal recovery in the macroscopic length of homogeneously deformed specimens of amorphous poly(ethylene terephthalate) (PET) film sample uniaxially drawn at 69℃ to the draw ratios λ0 = 1.26~2.20 were studied at temperatures around the glass transition temperature (Tg = 73 ℃). Experimental results indicate that the length recovery took place in two distinct steps: a fast first step (fast relaxation) followed by a slow second step (slow relaxation). The relaxation processes were accompanied by the reversion of trans-conformers (1340 cm-1) to gauche, and the dichroic function of the 1340 cm-1 band characterizing the segmental orientation along the chain direction decreased to a very low value at the end of the fast relaxation. This fact led us to assign the fast relaxation as the segmental orientation while the slow relaxation as relaxation of the global chain orientation. It was found that the slow relaxation follows a single exponential function, with relaxation times strongly dependent on the temperature resembling the glass transition process. The fast relaxation does not follow a single exponential decay, presumably a distribution of relaxation times is involved.

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

    Science.gov (United States)

    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.

  5. Effects of Stretching Ratio and Temperature on Phase Transition of Melt-spun Poly (Vinylidene Fluoride) Fibers

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hua; REN Ping; ZHANG Guifang; XIAO Changfa

    2006-01-01

    The effects of stretching ratio and stretching temperature on phase transition of melt-spun poly ( vinylidene fluoride ) fibers were investigated and analyzed by using scanning electron microscopy, wide angle Xray diffraction, differential scanning calorimetry and Fourier transfer infrared spectroscopy. The β phase exists in the as-spun fiber. The β phase content increases as the stretching ratio increases. When the stretching temperature is lower than 100 ℃ , enhancing temperature is good for the transition of phase α to β. By contrast, when the stretching temperature is higher than 100 ℃ , enhancing temperature is unfavourable for the transition of phase α to β. Increasing the draw temperature increases the α-phase content.

  6. Temperature dependence of the structure of protein hydration water and the liquid-liquid transition.

    Science.gov (United States)

    Accordino, S R; Malaspina, D C; Rodriguez Fris, J A; Alarcón, L M; Appignanesi, G A

    2012-03-01

    We study the temperature dependence of the structure and orientation of the first hydration layers of the protein lysozyme and compare it with the situation for a model homogeneous hydrophobic surface, a graphene sheet. We show that in both cases these layers are significantly better structured than bulk water. The geometrical constraint of the interface makes the water molecules adjacent to the surface lose one water-water hydrogen bond and expel the fourth neighbors away from the surface, lowering local density. We show that a decrease in temperature improves the ordering of the hydration water molecules, preserving such a geometrical effect. For the case of graphene, this favors an ice Ih-like local structuring, similar to the water-air interface but in the opposite way along the c axis of the basal plane (while the vicinal water molecules of the air interface orient a hydrogen atom toward the surface, the oxygens of the water molecules close to the graphene plane orient a lone pair in such a direction). In turn, the case of the first hydration layers of the lysozyme molecule is shown to be more complicated, but still displaying signs of both kinds of behavior, together with a tendency of the proximal water molecules to hydrogen bond to the protein both as donors and as acceptors. Additionally, we make evident the existence of signatures of a liquid-liquid transition (Widom line crossing) in different structural parameters at the temperature corresponding to the dynamic transition incorrectly referred to as "the protein glass transition."

  7. Temperature-Dependent Surface States and Transitions of Si(111)-7x7.

    Science.gov (United States)

    1984-09-01

    TRANSTONS OF Si(Il1)-7x7 by J. E. Demuth, B. N. J. Persson and A. J. Scheil-Sorokin Prepared for Publication in Physical Review Letters IBM T. J. Watson...NUMBER 24 PHYSICAL REVIEW LETTERS 12 DEiEMiER 1983 Temperature-Dependent Surface States and Transitions of Si(11l)-7x7 J. E. Demuth, B. N. J. Persson...8217 ’ " " " .. . .; " ’ " ’ " " " " "h " - -’ ; - ’ . . ": - - VOLUME 51, NUMBER 24 PHYSICAL REVIEW LETTERS 12

  8. A Simple System to Measure Superconducting Transition Temperature at High Pressure

    Institute of Scientific and Technical Information of China (English)

    YU Yong; ZHAI Guang-Jie; JIN Chang-Qing

    2009-01-01

    A simple hydride system is fabricated to measure the superconducting transition temperature Tc under high pressure using a diamond anvil cell (DAC). The system is designed with centrosymetric coils around the diamond that makes it easy to keep balance between the pick-up coil and the inductance coil, while the superconducting states can be modulated with a low-frequency small external magnetic field. Using the device we successfully obtain the Tc evolution as a function of applied pressure up to 10 GPa for YBa2 Cu3O6+δ superconductor single crystal.

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

    Energy Technology Data Exchange (ETDEWEB)

    Balakirev, Fedor F [Los Alamos National Laboratory; Migliori, A [MPA-NHMFL; Riggs, S [NHMFL-FSU; Hunte, F [NHMFL-FSU; Gurevich, A [NHMFL-FSU; Larbalestier, D [NHMFL-FSU; Boebinger, G [NHMFL-FSU; Jaroszynski, J [NHMFL-FSU; Ren, Z [CHINA; Lu, W [CHINA; Yang, J [CHINA; Shen, X [CHINA; Dong, X [CHINA; Zhao, Z [CHINA; Jin, R [ORNL; Sefat, A [ORNL; Mcguire, M [ORNL; Sales, B [ORNL; Christen, D [ORNL; Mandrus, D [ORNL

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  12. Effect of Indium on the Superconducting Transition Temperature of Tin Telluride

    Science.gov (United States)

    Zhong, Ruidan; Schneeloch, John; Shi, Xiaoya; Li, Qiang; Tranquada, John; Gu, Genda

    2013-03-01

    Indium-doped tin telluride is one of the most appealing topological superconductors. We have grown a series of Sn1-xInxTe crystals with different indium concentrations (0.1 <=x <=1.0). The results show indium doping improves the superconducting transition temperature significantly and is highly related to the indium concentration. The maximum Tc of indium-doped tin telluride polycrystalline is 4.5K for x =0.4. Single crystals of Sn1-xInxTe were also grown by the floating zone method, and their magnetic properties were characterized.

  13. BKT phase transitions in strongly coupled 3D Z(N) LGT at finite temperature

    OpenAIRE

    Borisenko, O.; V. Chelnokov; Cortese, G.; Fiore, R.; Gravina, M.; Papa, A.; Surzhikov, I.

    2012-01-01

    We investigate, both analytically and numerically, the phase diagram of three-dimensional Z(N) lattice gauge theories at finite temperature for N > 4. These models, in the strong coupling limit, are equivalent to a generalized version of vector Potts models in two dimension, with Polyakov loops playing the role of Z(N) spins. It is argued that the effective spin models have two phase transitions of infinite order (i.e. BKT). Using a cluster algorithm we confirm this conjecture, locate the pos...

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

    Science.gov (United States)

    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. BKT phase transitions in strongly coupled 3D Z(N) LGT at finite temperature

    CERN Document Server

    Borisenko, O; Cortese, G; Fiore, R; Gravina, M; Papa, A; Surzhikov, I

    2012-01-01

    We investigate, both analytically and numerically, the phase diagram of three-dimensional Z(N) lattice gauge theories at finite temperature for N > 4. These models, in the strong coupling limit, are equivalent to a generalized version of vector Potts models in two dimension, with Polyakov loops playing the role of Z(N) spins. It is argued that the effective spin models have two phase transitions of infinite order (i.e. BKT). Using a cluster algorithm we confirm this conjecture, locate the position of the critical points and extract various critical indices.

  16. Computer simulation of trails on a square lattice. II. Finite temperatures and the collapse transition

    Science.gov (United States)

    Meirovitch, H.; Lim, H. A.

    1989-04-01

    We study by the scanning simulation method trails on a square lattice at finite temperatures. This method constitutes a very efficient tool since it enables one to obtain results at many temperatures from a single sample generated at any given temperature. The tricritical temperature at which the collapse transition occurs is -ɛ/kBTt=1.086+/-0.002. The tricritical exponents of the trail shape and its free energy are, respectively, νt=0.569+/-0.008 and γt=1.133+/-0.024 (95% confidence limits). They are equal within the error bars to the exact values of self-attracting self-avoiding walks (SAW's). However, the crossover exponent φt=0.807+/-0.005 is significantly larger than the exact value 0.423 of SAW's. We also carry out a detailed scaling analysis near Tt and demonstrate that the various properties scale as predicted by theory. At sufficiently low temperatures (Tappears to be ~1.

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

    Science.gov (United States)

    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

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

    Directory of Open Access Journals (Sweden)

    Sanguansri Charoenrein

    2013-01-01

    Full Text Available 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 (, as it was hypothesized that such temperatures might cause different effects on retrogradation. The 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 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 . This suggests that retardation of retrogradation of waxy rice starch gel can be achieved at temperature below .

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

    Science.gov (United States)

    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 (T g '), as it was hypothesized that such temperatures might cause different effects on retrogradation. The T g ' 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 T g ' 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 T g '. This suggests that retardation of retrogradation of waxy rice starch gel can be achieved at temperature below T g '.

  20. Influence of microwave vacuum drying on glass transition temperature, gelatinization temperature, physical and chemical qualities of lotus seeds.

    Science.gov (United States)

    Zhao, Yingting; Jiang, Yajun; Zheng, Baodong; Zhuang, Weijing; Zheng, Yafeng; Tian, Yuting

    2017-08-01

    This study investigated the effects of microwave power density on effective moisture diffusion coefficient (Deff), glass transition temperature (Tg), gelatinization temperature (TP), physical and chemical qualities of lotus seeds during microwave vacuum drying. Deff increased by 42% and 127% at 15W/g and 20W/g, respectively, when compared with 10W/g. TP was negatively correlated with the relaxation times of T21 and T22, while Tg was negatively correlated with the relative areas A22. The rates of change of color were observed to be divided roughly into two periods, consisting of a rapid change caused by enzymatic browning and a slow change caused by non-enzymatic browning. An equation is provided to illustrate the relationship of k1 and k2 of Peleg's model depending on power density during rehydration kinetics. The samples at 20W/g exhibited the higher content of amino acid (540.19mg/100gd.b.) while lower starch (17.53g/100gd.b.).

  1. Effect of neutron irradiation on the mechanical properties of weld overlay cladding for reactor pressure vessel

    Science.gov (United States)

    Tobita, Tohru; Udagawa, Makoto; Chimi, Yasuhiro; Nishiyama, Yutaka; Onizawa, Kunio

    2014-09-01

    This study investigates the effects of high fluence neutron irradiation on the mechanical properties of two types of cladding materials fabricated using the submerged-arc welding and electroslag welding methods. The tensile tests, Charpy impact tests, and fracture toughness tests were conducted before and after the neutron irradiation with a fluence of 1 × 1024 n/m2 at 290 °C. With neutron irradiation, we could observe an increase in the yield strength and ultimate strength, and a decrease in the total elongation. All cladding materials exhibited ductile-to-brittle transition behavior during the Charpy impact tests. A reduction in the Charpy upper-shelf energy and an increase in the ductile-to-brittle transition temperature was observed with neutron irradiation. There was no obvious decrease in the elastic-plastic fracture toughness (JIc) of the cladding materials upon irradiation with high neutron fluence. The tearing modulus was found to decrease with neutron irradiation; the submerged-arc-welded cladding materials exhibited low JIc values at high temperatures.

  2. Effect of neutron irradiation on the mechanical properties of weld overlay cladding for reactor pressure vessel

    Energy Technology Data Exchange (ETDEWEB)

    Tobita, Tohru, E-mail: tobita.tohru@jaea.go.jp; Udagawa, Makoto; Chimi, Yasuhiro; Nishiyama, Yutaka; Onizawa, Kunio

    2014-09-15

    This study investigates the effects of high fluence neutron irradiation on the mechanical properties of two types of cladding materials fabricated using the submerged-arc welding and electroslag welding methods. The tensile tests, Charpy impact tests, and fracture toughness tests were conducted before and after the neutron irradiation with a fluence of 1 × 10{sup 24} n/m{sup 2} at 290 °C. With neutron irradiation, we could observe an increase in the yield strength and ultimate strength, and a decrease in the total elongation. All cladding materials exhibited ductile-to-brittle transition behavior during the Charpy impact tests. A reduction in the Charpy upper-shelf energy and an increase in the ductile-to-brittle transition temperature was observed with neutron irradiation. There was no obvious decrease in the elastic–plastic fracture toughness (J{sub Ic}) of the cladding materials upon irradiation with high neutron fluence. The tearing modulus was found to decrease with neutron irradiation; the submerged-arc-welded cladding materials exhibited low J{sub Ic} values at high temperatures.

  3. Theory of Temperature Dependence of the Magnetization in Rare-Earth-Transition-Metal Alloys

    DEFF Research Database (Denmark)

    Szpunar, B.; Lindgård, Per-Anker

    1977-01-01

    It is shown that the temperature dependence of the magnetic moments and Curie and ferrimagnetic compensation temperatures for Gdl-xTx (T = Co, Ni, and Fe) and Y1-xCox can be accounted for by a simple model assuming a RKKY interaction between the rare-earth moments and the transition-metal pseudo-spin......1-xCox durch ein einfaches Model1 erklärt werden können, das eine RKKY-Wechsel-wirkung zwischen den Momenten der Seltenen Erden und des Pseudo-Spins des Übergangsmetalls annimmt. Die Wechselwirkung wird durch ein effektives Legierungsmedium übermittelt, das mit der CPA-Theorie und elliptischen...

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

    Science.gov (United States)

    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.

  5. Three dimensional finite temperature SU(3) gauge theory near the phase transition

    CERN Document Server

    Bialas, Piotr; Morel, Andre; Petersson, Bengt

    2012-01-01

    We have measured the correlation function of Polyakov loops on the lattice in three dimensional SU(3) gauge theory near its finite temperature phase transition. Using a new and powerful application of finite size scaling, we furthermore extend the measurements of the critical couplings to considerably larger values of the lattice sizes, both in the temperature and space directions, than was investigated earlier in this theory. With the help of these measurements we perform a detailed finite size scaling analysis, showing that for the critical exponents of the two dimensional three state Potts model the mass and the susceptibility fall on unique scaling curves. This strongly supports the expectation that the gauge theory is in the same universality class. The Nambu-Goto string model on the other hand predicts that the exponent \

  6. Ionic Hamiltonians for transition metal atoms: effective exchange coupling and Kondo temperature

    Science.gov (United States)

    Flores, F.; Goldberg, E. C.

    2017-02-01

    An ionic Hamiltonian for describing the interaction between a metal and a d-shell transition metal atom having an orbital singlet state is introduced and its properties analyzed using the Schrieffer-Wolf transformation (exchange coupling) and the poor man’s scaling method (Kondo temperature). We find that the effective exchange coupling between the metal and the atom has an antiferromagnetic or a ferromagnetic interaction depending on the kind of atomic fluctuations, either S\\to S-1/2 or S\\to S+1/2 , associated with the metal-atom coupling. We present a general scheme for all those processes and calculate, for the antiferromagnetic interaction, the corresponding Kondo-temperature.

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

    Science.gov (United States)

    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.

  8. Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

    Directory of Open Access Journals (Sweden)

    J. C. Phillips

    2010-01-01

    Full Text Available I review the multiple successes of the discrete hard-wired dopant network model ZZIP, and comment on the equally numerous failures of continuum models, in describing and predicting the properties of ceramic superconductors. The prediction of transition temperatures can be regarded in several ways, either as an exacting test of theory, or as a tool for identifying theoretical rules for defining new homology models. Popular “first principle” methods for predicting transition temperatures in conventional crystalline superconductors have failed for cuprate HTSC, as have parameterized models based on CuO2 planes (with or without apical oxygen. Following a path suggested by Bayesian probability, it was found that the glassy, self-organized dopant network percolative model is so successful that it defines a new homology class appropriate to ceramic superconductors. The reasons for this success in an exponentially complex (non-polynomial complete, NPC problem are discussed, and a critical comparison is made with previous polynomial (PC theories. The predictions are successful for the superfamily of all ceramics, including new non-cuprates based on FeAs in place of CuO2.

  9. Pressure Dependence of the Glass Transition Temperature in the Fragile Glass Former Cumene

    Science.gov (United States)

    Raty, Jean-Yves; Baris Malcioglu, Osman; Bichara, Christophe

    2013-03-01

    The glass transition temperature, Tg, is one of the most important characteristics of glassy systems. While Tg has been measured for many systems at atmospheric pressure, direct measurement of the glass transition is difficult at high pressures due to small sample sizes and long time scales. Tg(P) measurements to date mostly involve extrapolations of high-pressure viscosity or relaxation data to η = 1013 P or t = 100 s, respectively. In this study we present direct measurement of Tg at pressures up to several GPa through a combination of pressure gradient tracking and observation of increases in the thermal expansion coefficient upon heating from the glass to the viscous liquid state. High pressures are attained through the use of a diamond anvil cell and precise temperatures are maintained via custom heating and cryogenic systems. By directly mapping this phase boundary, we can compare models for Tg(P). In addition, high-pressure analysis requiring knowledge of Tg at pressure will be greatly aided.

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

    Science.gov (United States)

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

    2002-01-10

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

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

    Science.gov (United States)

    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.

  12. Temperature-induced coupled–decoupled transition in perpendicular pseudo spin valves

    Science.gov (United States)

    Hamdi, M.; Mohseni, S. M.

    2017-03-01

    The effect of spacer and ferromagnetic layer thickness on temperature-dependent magnetostatic coupling in perpendicular magnetic anisotropy pseudo spin valves (PMA-PSVs) with the structure of [Ni/Co]5/Cu(d Cu)/[Ni/Co] n is explored theoretically. We introduce an effective field that controls the domain replication mechanism and coupling in PSVs. The decoupling temperature (T decoupling) can be determined by considering the temperature dependence of the effective field and the coercivity of the hard layer of the PSVs. This study reveals that by increasing the spacer layer thickness, the effective field decreases and T decoupling has an increasing trend. Furthermore, by increasing the hard ferromagnetic layer thickness, which is accompanied by an increase in the anisotropy of the layer, T decoupling again has an increasing trend. The results are comparable to recently reported experimental ones for PMA-PSVs with various spacer thicknesses, d Cu, and the number of bilayer repeats, n. As a practical result, this work gives a deep understanding of the magnetostatically driven domain replication mechanism and temperature-induced coupled–decoupled transitions in PMA-PSVs.

  13. Transition metal doping of GaSe implemented with low temperature liquid phase growth

    Science.gov (United States)

    Lei, Nuo; Sato, Youhei; Tanabe, Tadao; Maeda, Kensaku; Oyama, Yutaka

    2017-02-01

    Our group works on improving the conversion efficiencies of terahertz (THz) wave generation using GaSe crystals. The operating principle is based on difference frequency generation (DFG) which has the advantages such as high output power, a single tunable frequency, and room temperature operation. In this study, GaSe crystals were grown by the temperature difference method under controlled vapor pressure (TDM-CVP). It is a liquid phase growth method with temperature 300 °C lower than that of the Bridgman method. Using this method, the point defects concentration is decreased and the polytype can be controlled. The transition metal Ti was used to dope the GaSe in order to suppress free carrier absorption in the low frequency THz region. As a result, a deep acceptor level of 38 meV was confirmed as being formed in GaSe with 1.4 at% Ti doping. Compared with undoped GaSe, a decrease in carrier concentration ( 1014 cm-3) at room temperature was also confirmed. THz wave transmittance measurements reveal the tendency for the absorption coefficient to increase as the amount of dopant is increased. It is expected that there is an optimum amount of dopant.

  14. Low temperature magneto-structural transitions in Mn3Ni20P6

    Science.gov (United States)

    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.

  15. Phase transition studies of the exsoluted ilmenite-hematite at high pressure and temperature conditions

    Science.gov (United States)

    Kim, Y.; Secco, R.; Hwang, G.; Bao, X.; Ming, L.

    2011-12-01

    Ilmenite minerals found in Switzerland Alpe Arami peridotite massif indicate that these precipitates are metastable phases converted from the single perovskite phase during the ascending process in the mantle. After this work, lots of subsequent high pressure-temperature experiments on ilmenite itself and its solid solution phases were performed to check the phase boundary from the starting phase to perovskite structure. This study also aims to identify the phase transition sequence(s) of the exsoluted ilmenite-hematite specimen where its locality is the Allard Lake area, Quebac, Canada, under high pressure and high temperature conditions. Bulky ore sample consists of 76.2% ilmenite and 23.8% hematite in volume. Chemistry of ilmenite is Fe1.02Mg0.13Ti0.92O3 and that of hematite, Fe2O3. Lattice parameters of ilmenite are a=5.08287(2)Å, c=14.0511(1)Å, and those of hematite a=5.04378(4)Å, c=13.7757(2)Å. Walker-type large volume multi anvil cell was employed for high pressure and high temperature experiment up to 14GPa and 2400K, respectively. Recovered samples after high pressure-temperature treatment were subjected to identify the product phase(s) by the general area detector x-ray diffraction method with conventional x-radiation as well as the x-ray micro-diffraction technique using synchrotron radiation. Phase transition sequences observed are the followings: starting exsoluted ilmenite-hematite phase transforms to the single phase of perovskite, then this perovskite phase disproportionate into various kind of oxides. Phase boundaries to perovskite, then to oxides were determined to be P(GPa)=31.8 - 0.0178T(K), and P(GPa)=23.8 - 0.0072T(K), respectively. Present result is different from the previous reports of Syono et al. (1980)(i.e., P(GPa)=25.2 - 0.01T(K)) and Ming et al. (2006)(i.e., P(GPa)=16.0 - 0.0012T(K)). Based on the present results applied to the Alpe Arami peridotite massif, source region would be much shallower part at the upper mantle(i.e., 240km

  16. Evaluation of ductile-brittle transition temperature before and after neutron irradiation for RPV steels using small punch tests

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Min-Chul [Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353 (Korea, Republic of)]. E-mail: mckim@kaeri.re.kr; Oh, Yong Jun [Hanbat National University, Deogmyeong-dong, Yuseong-gu, Daejeon 305-719 (Korea, Republic of); Lee, Bong Sang [Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353 (Korea, Republic of)

    2005-08-01

    Small punch (SP) tests were performed to evaluate the ductile-brittle transition temperature before and after a neutron irradiation of reactor pressure vessel (RPV) steels produced by different manufacturing (refining) processes. The results were compared to the standard transition temperature shifts from the conventional Charpy tests and the Master Curve fracture toughness tests in accordance with the American Society for Testing and Materials (ASTM) standard E1921. Small punch specimens were taken from a 1/4t location of the vessel thickness and machined into a 10 mm x 10 mm x 0.5 mm dimension. The specimens were irradiated in the research reactors at Korea Atomic Energy Research Institute Nuclear Research Institute in the Czech Republic at the different fluence levels of about 290 deg C. Small punch tests were performed in the temperature range of RT to -196 deg C using a 2.4 mm diameter ball. For the materials before and after irradiation, the small punch transition temperatures (T {sub SP}), which are determined at the middle of the upper small punch energies, showed a linear correlation with the Charpy index temperature, T {sub 41J}. T {sub SP} from the irradiated samples was increased with the fluence levels and was well within the deviation range of the unirradiated data. However, the transition temperature shift from the Charpy test ({delta}T {sub 41J}) shows a better correlation with the transition temperature shift ({delta}T {sub SP(E)}) when a specific small punch energy level rather than the middle energy level of the small punch curve is used to determine the transition temperature. T {sub SP} also had a correlation with the reference temperature (T {sub 0}) from the Master Curve method using a pre-cracked Charpy V-notched (PCVN) specimen.

  17. The thermal conductivity of BaTiO3 in the neighbourhood of its ferroelectric transition temperatures

    NARCIS (Netherlands)

    Mante, A.J.H.; Volger, J.

    1967-01-01

    The thermal conductivity of single crystalline BaTiO3 has been measured in the temperature range of 100–500°K. In the neighbourhood of the transition temperature a reduction of the thermal conductivity is observed. This result can be explained in view of a current theory on ferroelectricity which in

  18. Bismuth Vanadate: A High-Pressure, High-Temperature Crystallographic Study of the Ferroelastic-Paraelastic Transition

    Science.gov (United States)

    Hazen, R. M.; Mariathasan, J. W. E.

    1982-05-01

    Lattice dimensions of bismuth vanadate have been determined under 37 different high-pressure or high-temperature conditions or a combination of these conditions. New high-pressure, high-temperature, single-crystal x-ray techniques were used to bracket the reversible monoclinic (ferroelastic) to tetragonal (paraelastic) transition.

  19. High temperature phase transition of mixed (PuO2 + ThO2) investigated by laser melting

    NARCIS (Netherlands)

    Böhler, R.; Cakir, P.; Benes, O.; Hein, H.; Konings, R.J.M.; Manara, D.

    2014-01-01

    A laser heating approach combined with fast pyrometry in a thermal arrest method was used to provide new data for the melting/solidification phase transition in mixed (PuO2 + ThO2) at high temperature. At low concentration of ThO2 in PuO2 a minimum in the solidification temperature in the pseudo bin

  20. Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

    Science.gov (United States)

    Holmlid, Leif; Kotzias, Bernhard

    2016-04-01

    Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H2N(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H4(0) and H3(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H2N(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected.

  1. Temperature dependence of the flux line lattice transition into square symmetry in superconducting LuNi2B2C

    DEFF Research Database (Denmark)

    Eskildsen, M.R.; Abrahamsen, A.B.; Kogan, V.G.;

    2001-01-01

    We have investigated the temperature dependence of the H parallel to c flux line lattice structural phase transition from square to hexagonal symmetry, in the tetragonal superconductor LuNi2B2C (T-c = 16.6 K). At temperatures below 10 K the transition onset field, H-2(T), is only weakly temperature...... dependent. Above 10 K, H-2(T) rises sharply, bending away from the upper critical field. This contradicts theoretical predictions of H-2(T) merging with the upper critical field and suggests that just below the H-c2(T) curve the flux line lattice might be hexagonal....

  2. Microstructure and low-temperature phase transition in Ni{sub 2}FeGa Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Liu Libao [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China) and Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China) and Harbin Institute of Technology at Weihai, Weihai 264209 (China)]. E-mail: lbliu@blem.ac.cn; Fu Shiyou [Harbin Institute of Technology at Weihai, Weihai 264209 (China); Liu Zhuhong [Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Wu Guangheng [Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Sun Xiudong [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Li Jianqi [Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

    2006-11-30

    The microstructure features and structural phase transition in the Ni{sub 2}FeGa alloy has been systematically investigated by means of transmission electron microscopy (TEM). A number of ordered states have been observed at room temperature; certain short-range orders are found to be in metastable states which are temperature sensitive and become invisible when annealed. In situ cooling TEM observations revealed evident structural changes along with the martensitic transition with T {sub c}{approx}145 K. Low-temperature microstructure domains, superstructures and variations of monoclinic distortion have been analyzed in detail.

  3. Kinetics of low-temperature transitions and a reaction rate theory from non-equilibrium distributions

    Science.gov (United States)

    Aquilanti, Vincenzo; Coutinho, Nayara Dantas; Carvalho-Silva, Valter Henrique

    2017-03-01

    This article surveys the empirical information which originated both by laboratory experiments and by computational simulations, and expands previous understanding of the rates of chemical processes in the low-temperature range, where deviations from linearity of Arrhenius plots were revealed. The phenomenological two-parameter Arrhenius equation requires improvement for applications where interpolation or extrapolations are demanded in various areas of modern science. Based on Tolman's theorem, the dependence of the reciprocal of the apparent activation energy as a function of reciprocal absolute temperature permits the introduction of a deviation parameter d covering uniformly a variety of rate processes, from those where quantum mechanical tunnelling is significant and d 0, corresponding to the Pareto-Tsallis statistical weights: these generalize the Boltzmann-Gibbs weight, which is recovered for d = 0. It is shown here how the weights arise, relaxing the thermodynamic equilibrium limit, either for a binomial distribution if d > 0 or for a negative binomial distribution if d kinetics, where transport phenomena accelerate processes as the temperature increases; (ii) the sub-Arrhenius kinetics, where quantum mechanical tunnelling propitiates low-temperature reactivity; (iii) the anti-Arrhenius kinetics, where processes with no energetic obstacles are rate-limited by molecular reorientation requirements. Particular attention is given for case (i) to the treatment of diffusion and viscosity, for case (ii) to formulation of a transition rate theory for chemical kinetics including quantum mechanical tunnelling, and for case (iii) to the stereodirectional specificity of the dynamics of reactions strongly hindered by the increase of temperature. This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.

  4. First-principles screening of complex transition metal hydrides for high temperature applications.

    Science.gov (United States)

    Nicholson, Kelly M; Sholl, David S

    2014-11-17

    Metal hydrides with enhanced thermodynamic stability with respect to the associated binary hydrides are useful for high temperature applications in which highly stable materials with low hydrogen overpressures are desired. Though several examples of complex transition metal hydrides (CTMHs) with such enhanced stability are known, little thermodynamic or phase stability information is available for this materials class. In this work, we use semiautomated thermodynamic and phase diagram calculations based on density functional theory (DFT) and grand canonical linear programming (GCLP) methods to screen 102 ternary and quaternary CTMHs and 26 ternary saline hydrides in a library of over 260 metals, intermetallics, binary, and higher hydrides to identify materials that release hydrogen at higher temperatures than the associated binary hydrides and at elevated temperatures, T > 1000 K, for 1 bar H2 overpressure. For computational efficiency, we employ a tiered screening approach based first on solid phase ground state energies with temperature effects controlled via H2 gas alone and second on the inclusion of phonon calculations that correct solid phase free energies for temperature-dependent vibrational contributions. We successfully identified 13 candidate CTMHs including Eu2RuH6, Yb2RuH6, Ca2RuH6, Ca2OsH6, Ba2RuH6, Ba3Ir2H12, Li4RhH4, NaPd3H2, Cs2PtH4, K2PtH4, Cs3PtH5, Cs3PdH3, and Rb2PtH4. The most stable CTMHs tend to crystallize in the Sr2RuH6 cubic prototype structure and decompose to the pure elements and hydrogen rather than to intermetallic phases.

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

    Science.gov (United States)

    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.

  6. Direct Measurement of the Pressure Dependence of the Glass Transition Temperature: A Comparison of Methods

    Science.gov (United States)

    Oliver, William, III; Ransom, Timothy; Cooper, James, III

    2013-03-01

    Two methods for the direct measurement of the pressure dependence of the glass-transition temperature Tg are presented and compared. These methods involve the use of the diamond anvil cell (DAC), and hence, enable the ability to measure Tg(P) to record high pressures of several GPa. Such studies are increasingly relevant as new methods have pushed other high-pressure experimental investigations of glass-forming systems into the same pressure regime. Both methods use careful ruby fluorescence measurements in the DAC as temperature is increased from the glass (TTg) . Method 1 observes the disappearance of pressure gradients as the viscous liquid region is entered, whereas method 2 involves observation of slope changes in the P-T curve during temperature ramps. Such slope changes are associated with the significant change in the volume expansion coefficient between the highly viscous, metastable, supercooled liquid state and the solid glassy state. In most cases, the two methods yield good agreement in the Tg(P) curve. Data will be presented for more than one glass-forming system, including the intermediate strength glass-forming system glycerol and the fragile glass former salol. We acknowledge support from the NSF under DMR-0552944

  7. Low Temperature Conductivity in n-Type Noncompensated Silicon below Insulator-Metal Transition

    Directory of Open Access Journals (Sweden)

    A. L. Danilyuk

    2017-01-01

    Full Text Available We investigate the transport properties of n-type noncompensated silicon below the insulator-metal transition by measuring the electrical and magnetoresistances as a function of temperature T for the interval 2–300 K. Experimental data are analyzed taking into account possible simple activation and hopping mechanisms of the conductivity in the presence of two impurity bands, the upper and lower Hubbard bands (UHB and LHB, resp.. We demonstrate that the charge transport develops with decreasing temperature from the band edge activation (110–300 K to the simple activation with much less energy associated with the activation motion in the UHB (28–90 K. Then, the Mott-type variable range hopping (VRH with spin dependent hops occurs (5–20 K. Finally, the VRH in the presence of the hard gap (HG between LHB and UHB (2–4 K takes place. We propose the empiric expression for the low T density of states which involves both the UHB and LHB and takes into account the crossover from the HG regime to the Mott-type VRH with increasing temperature. This allows us to fit the low T experimental data with high accuracy.

  8. Hydrogen detonation and detonation transition data from the High-Temperature Combustion Facility

    Energy Technology Data Exchange (ETDEWEB)

    Ciccarelli, G.; Boccio, J.L.; Ginsberg, T.; Finfrock, C. [Brookhaven National Lab., Upton, NY (United States)] [and others

    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.

  9. The influence of sour taste and cold temperature in pharyngeal transit duration in patients with stroke

    Directory of Open Access Journals (Sweden)

    Paula Cristina Cola

    2010-03-01

    Full Text Available CONTEXT: The effect of sour taste and food temperature variations in dysphagic patients has not been entirely clarified. OBJECTIVE: To determine the effect of sour and cold food in the pharyngeal transit times of patients with stroke. METHODS: Patients participating in this study were 30 right-handed adults, 16 of which were male and 14 were female, aged 41 to 88 (average age 62.3 years with ictus varying from 1 to 30 days (median of 6 days. To analyze the pharyngeal transit time a videofluoroscopy swallow test was performed. Each patient was observed during swallow of a 5 mL paste bolus given by spoon, totaling four different stimuli (natural, cold, sour and cold sour, one at a time, room temperature (22ºC and cold (8ºC were used. Later, the tests were analyzed using specific software to measure bolus transit time during the pharyngeal phase. RESULTS: The results showed that the pharyngeal transit time was significantly shorter during swallow of cold sour bolus when compared with other stimuli. Conclusion - Sour taste stimuli associated to cold temperature cause significant change in swallowing patterns, by shortening the pharyngeal transit time, which may lead to positive effects in patients with oropharyngeal dysphagia.CONTEXTO: O efeito do sabor azedo e as variações da temperatura dos alimentos em indivíduos disfágicos, ainda não foi totalmente esclarecidos. OBJETIVO: Verificar o efeito do sabor azedo e da temperatura fria no tempo de trânsito faríngeo da deglutição em indivíduos após acidente vascular encefálico hemisférico isquêmico. MÉTODOS: Participaram deste estudo 30 indivíduos adultos, sendo 16 do gênero masculino e 14 do feminino, destros, com faixa etária variando de 41 a 88 anos (média de 62,3 anos e ictus que variou de 1 a 30 dias (mediana de 6 dias. Para analisar o tempo de trânsito faríngeo da deglutição foi realizado o exame de videofluoroscopia da deglutição. Cada indivíduo foi observado durante a

  10. Evaluation of grain boundary embrittlement of phosphorus added F82H steel by SSTT

    Science.gov (United States)

    Kim, Byung Jun; Kasada, Ryuta; Kimura, Akihiko; Tanigawa, Hiroyasu

    2012-02-01

    Non-hardening embrittlement (NHE) can be happened by a large amount of He on grain boundaries over 500-700 appm of bulk He without hardening at fusion reactor condition. Especially, at high irradiation temperatures (>≈420 °C), NHE accompanied by intergranular fracture affects the severe accident and the safety of fusion blanket system. Small specimen tests to evaluate fracture toughness and Charpy impact properties were carried out for F82H steels with different levels of phosphorous addition in order to simulate the effects of NHE on the shift of transition curve. It was found that the ductile to brittle transition temperature (DBTT) and reference temperature ( T0) after phosphorous addition is shifted to higher temperatures and accompanied by intergranular fracture at transition temperatures region. The master curve approach for evaluation of fracture toughness change by the degradation of grain boundary strength was carried out by referring to the ASTM E1921.

  11. Holographic s + p insulator/superconductor phase transition at zero temperature

    Science.gov (United States)

    Li, Ran; Zi, Tieguang; Zhang, Hongbao

    2017-03-01

    We study the holographic s + p insulator/superconductor phase transition at zero temperature by using the model with a scalar triplet charged under an SU (2) gauge field in anti-de Sitter (AdS) soliton background. In this model, besides the insulator phase, s-wave condensate phase and p-wave condensate phase, the s + p coexisting condensate phase is found numerically when operator dimension Δ is greater than a critical value Δc. We also construct the complete phase diagram in Δ - μ plane, which shows the s + p coexisting region is very narrow. Furthermore, we calculate the corresponding conductivities for different phases. The delta function support for the real part of conductivity of the spontaneous breaking phases is also revealed numerically as expected for the superconducting phases.

  12. Holographic s+p insulator/superconductor phase transition at zero temperature

    Directory of Open Access Journals (Sweden)

    Ran Li

    2017-03-01

    Full Text Available We study the holographic s+p insulator/superconductor phase transition at zero temperature by using the model with a scalar triplet charged under an SU(2 gauge field in anti-de Sitter (AdS soliton background. In this model, besides the insulator phase, s-wave condensate phase and p-wave condensate phase, the s+p coexisting condensate phase is found numerically when operator dimension Δ is greater than a critical value Δc. We also construct the complete phase diagram in Δ−μ plane, which shows the s+p coexisting region is very narrow. Furthermore, we calculate the corresponding conductivities for different phases. The delta function support for the real part of conductivity of the spontaneous breaking phases is also revealed numerically as expected for the superconducting phases.

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

    Energy Technology Data Exchange (ETDEWEB)

    Sirena, M.; Félix, L. Avilés [Consejo Nacional de Investigaciones Científicas y Técnicas, Centro Atómico Bariloche, CNEA, Bustillo 9500, 8400 Bariloche (Argentina); Instituto Balseiro, Universidad Nacional de Cuyo and CNEA, 8400 Bariloche (Argentina); Haberkorn, N. [Consejo Nacional de Investigaciones Científicas y Técnicas, Centro Atómico Bariloche, CNEA, Bustillo 9500, 8400 Bariloche (Argentina)

    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.

  14. Optimizing the superconducting transition temperature and upper critical field of Sn1-xInxTe

    Science.gov (United States)

    Zhong, R. D.; Schneeloch, J. A.; Shi, X. Y.; Xu, Z. J.; Zhang, C.; Tranquada, J. M.; Li, Q.; Gu, G. D.

    2013-07-01

    Sn1-xInxTe is a possible candidate for topological superconductivity. Previous work has shown that substitution of In for Sn in the topological crystalline insulator SnTe results in superconductivity, with the transition temperature, Tc, growing with In concentration. We have performed a systematic investigation of Sn1-xInxTe for a broad range of x, synthesizing single crystals (by a modified floating-zone method) as well as polycrystalline samples. The samples have been characterized by x-ray diffraction, resistivity, and magnetization. For the single crystals, the maximum Tc is obtained at x=0.45 with a value of 4.5 K, as determined by the onset of diamagnetism.

  15. Enhancing the Superconducting Transition Temperature of BaSi2 by Structural Tuning

    Science.gov (United States)

    Flores-Livas, José A.; Debord, Régis; Botti, Silvana; San Miguel, Alfonso; Marques, Miguel A. L.; Pailhès, Stéphane

    2011-02-01

    We present a joint experimental and theoretical study of the superconducting phase of the layered binary silicide BaSi2. Compared with the AlB2 structure of graphite or diboridelike superconductors, in the hexagonal structure of binary silicides the sp3 arrangement of silicon atoms leads to corrugated sheets. Through a high-pressure synthesis procedure we are able to modify the buckling of these sheets, enhancing the superconducting transition temperature from 6 to 8.9 K when the silicon planes flatten out. By performing ab initio calculations based on density-functional theory we explain how the electronic and phonon properties are strongly affected by changes in the buckling. This mechanism is likely present in other intercalated layered superconductors, opening the way to the tuning of superconductivity through the control of internal structural parameters.

  16. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wen; Zhou, Zhaofeng, E-mail: zfzhou@xtu.edu.cn; Zhong, Yuan; Zhang, Ting; Huang, Yongli [Key Laboratory of Low-Dimensional Materials and Application Technologies(Ministry of Education)Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Changqing [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)

    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.

  17. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    2015-11-01

    Full Text Available Incorporating the bond order-length-strength (BOLS notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN 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 TN by adjusting the atomic cohesive energy. The TN 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 TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  18. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Science.gov (United States)

    Zhang, Wen; Zhou, Zhaofeng; Zhong, Yuan; Zhang, Ting; Huang, Yongli; Sun, Changqing

    2015-11-01

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN) 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 TN by adjusting the atomic cohesive energy. The TN 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 TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  19. Glass transition temperature of PIB, PDMS and PMMA from small-time simulations

    Science.gov (United States)

    Duki, Solomon; Tsige, Mesfin; Taylor, Philip

    2009-03-01

    We have applied some new techniques to obtain predictions of the glass transition temperatures Tg of poly(isobutylene), poly(dimethyl-siloxane), and poly(methyl methacrylate) from small-time atomistic molecular dynamics simulations. The different fragilities of these materials are reflected in the results of the simulations. One approach involved measurement of the apparent softening of the ``cage'' in which a monomer is bound, while another involved studying autocorrelation of a convolution of the velocity with a smoothing function in order to detect the frequency of escapes from the ``cage.'' To check the accuracy of the short-time methods, the Tg of the polymers was also found using conventional diffusion simulations in which the rate of increase of the root mean squared displacement of an atom, monomer, or molecule is measured at very long times. The economical short-time simulations yielded results for Tg that were identical to those of the computer-intensive long-time simulations.

  20. Reduced glass transition temperatures in thin polymer films: surface effect or artifact?

    Science.gov (United States)

    Bäumchen, O; McGraw, J D; Forrest, J A; Dalnoki-Veress, K

    2012-08-03

    We have examined the direct effect of manipulating the number of free surfaces on the measured glass transition temperature T(g) of thin polystyrene films. Thin films in the range 35 nm thickness and refractive index of freestanding films. By noting the change in slope in each of these quantities, a T(g) value can be assigned in quantitative agreement with previously reported results. For thin freestanding films this value is reduced from that of the bulk. The exact same films are then transferred to a Si substrate and the T(g) of the resulting supported film was determined. The T(g) values of the now supported films are the same as the bulk value and the same as previous reports of similar supported films. These experiments unambiguously show that free interfaces are the dominant cause of the T(g) reductions for the film thicknesses studied.

  1. Temperature-assisted morphological transition in CuPc thin films

    Science.gov (United States)

    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.

  2. Universal behavior of the transition temperature in irradiated iron pnictide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Weaver, B.D., E-mail: bradley.weaver@nrl.navy.mil

    2014-06-15

    Highlights: • Compare radiation damage effects on T{sub c} of conventional superconductors, high-T{sub c} cuprates and iron pnictides. • Analyze data using displacement damage dose methodology. • T{sub c} in irradiated pnictides behaves identically to cuprates despite differences in T{sub c}. • Conclude: Common element is defect-induced scattering of carriers out of 2-D planes. - Abstract: We show that, as in the cuprate superconductors, the superconducting transition temperature in irradiated iron pnictides decreases linearly with increasing induced defect concentration, largely independent of the initial onset T{sub c} or the incident particle’s mass or energy. We attribute this to depairing caused by scattering of Cooper pairs out of the quasi two-dimensional FeAs planes.

  3. Pairing phase transition: A Finite-Temperature Relativistic Hartree-Fock-Bogoliubov study

    CERN Document Server

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

    2015-01-01

    Background: The relativistic Hartree-Fock-Bogoliubov (RHFB) theory has recently been developed and it provides a unified and highly predictive description of both nuclear mean field and pairing correlations. Ground state properties of finite nuclei can accurately be reproduced without neglecting exchange (Fock) contributions. Purpose: Finite-temperature RHFB (FT-RHFB) theory has not yet been developed, leaving yet unknown its predictions for phase transitions and thermal excitations in both stable and weakly bound nuclei. Method: FT-RHFB equations are solved in a Dirac Woods-Saxon (DWS) basis considering two kinds of pairing interactions: finite or zero range. Such a model is appropriate for describing stable as well as loosely bound nuclei since the basis states have correct asymptotic behaviour for large spatial distributions. Results: Systematic FT-RH(F)B calculations are performed for several semi-magic isotopic/isotonic chains comparing the predictions of a large number of Lagrangians, among which are PK...

  4. The glass transition temperature and microstructure of polyurethane/epoxy resin interpenetrating polymer networks nanocomposites

    Institute of Scientific and Technical Information of China (English)

    JIA Qingming; ZHENG Maosheng; SHEN Renjie; CHEN Hongxiang

    2006-01-01

    Nanocomposites with various contents of organophilic montmorillonite (oMMT) have been prepared by adding oMMT to interpenetrating polymer networks (IPNs) of polyurethane and epoxy resin (PU/EP) which had been prepared by a sequential polymeric technique. DSC experiment indicates a novel phenomenon that the glass transition temperature (Tg) of the nanocomposites increases with the oMMT content up to 3 %, then decreases with further increasing oMMT content. In order to explain this phenomenon, crosslink density, hydrogen bonding in the hard segments, crystallization of the nanocomposites and the exfoliation degree of oMMT in the nanocomposites have been investigated by swelling method, FT-IR, XRD, SEM and TEM, respectively. The results indicate that the crosslink density and the hydrogen bonding index of the nanocomposites increase, but the crystallization degree of the nanocomposites decreases with increasing oMMT content. In addition, oMMT improves the network structure of PU/EP.

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

    Science.gov (United States)

    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.

  6. Enhancement in the Glass Transition Temperature in Latent Thiol-Epoxy Click Cured Thermosets

    Directory of Open Access Journals (Sweden)

    Dailyn Guzmán

    2015-04-01

    Full Text Available Tri and tetrafunctional thiol were used as curing agent for diglycidyl ether of bisphenol A (DGEBA catalyzed by a commercially available amine precursor, LC-80. Triglycidyl isocianurate (TGIC was added in different proportions to the mixture to increase rigidity and glass transition temperature (Tg. The cooperative effect of increasing functionality of thiol and the presence of TGIC in the formulation leads to an increased Tg without affecting thermal stability. The kinetics of the curing of mixtures was studied by calorimetry under isothermal and non-isothermal conditions. The latent characteristics of the formulations containing amine precursors were investigated by rheometry and calorimetry. The increase in the functionality of the thiol produces a slight decrease in the storage lifetime of the mixture. The materials obtained with tetrathiol as curing agent showed the highest values of Young’s modulus and Tg.

  7. Nanosecond Ultrasonics to Study Phase Transitions in Solid and Liquid Systems at High Pressure and Temperature

    Energy Technology Data Exchange (ETDEWEB)

    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.

  8. Low-temperature structural phase transition in synthetic libethenite Cu 2PO 4OH

    Science.gov (United States)

    Belik, Alexei A.; Naumov, Panče; Kim, Jungeun; Tsuda, Shunsuke

    2011-11-01

    Low-temperature structural properties of the synthetic mineral libethenite Cu 2PO 4OH were investigated by single-crystal X-ray diffraction, synchrotron X-ray powder diffraction, specific heat measurements, and Raman spectroscopy. A second-order structural phase transition from the Pnnm symmetry ( a=8.0553(8) Å, b=8.3750(9) Å, c=5.8818(6) Å at 180 K) to the P2 1/ n symmetry ( a=8.0545(8) Å, b=8.3622(9) Å, c=5.8755(6) Å, β=90.0012(15) at 120 K) was found at 160 K during cooling. At 120 K, the monoclinic angle is 90.0012(15) from single crystal X-ray data vs 90.083(1) from powder X-ray diffraction data. The P2 1/ n-to- Pnnm transition may be a general feature of the adamite-type compounds, M 2XO 4OH.

  9. Heat capacity and transition behavior of sucrose by standard, fast scanning and temperature-modulated calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Magoń, A. [Department of Chemistry, University of Technology, 35-959 Rzeszów (Poland); Wurm, A.; Schick, C. [Department of Physics, University of Rostock, 18057 Rostock (Germany); Pangloli, Ph.; Zivanovic, S. [Department of Food Science and Technology, University of Tennessee, Knoxville, TN 37996 (United States); Skotnicki, M. [Department of Pharmaceutical Technology, Poznan University of Medical Sciences, 60-780 Poznań (Poland); Pyda, M., E-mail: mpyda@utk.edu [Department of Chemistry, University of Technology, 35-959 Rzeszów (Poland)

    2014-08-10

    Highlights: • Experimental, apparent heat capacity of sucrose was investigated by advanced thermal analysis. • Vibrational heat capacity of solid state was linked with a low temperature experimental heat capacity of sucrose. • Equilibrium melting parameters of sucrose were determined. • Decomposition, superheating of crystalline sucrose during melting process were presented. • TGA, DSC, TMDSC, and FSC are useful tools for characterization of sucrose. - Abstract: The heat capacity (C{sub p}) of crystalline and amorphous sucrose was determined using standard and quasi-isothermal temperature modulated differential scanning calorimetry. The results were combined with the published data determined by adiabatic calorimetry, and the C{sub p} values are now reported for the wide 5–600 K range. The experimental C{sub p} of solid sucrose at 5–300 K was used to calculate the vibrational, solid C{sub p} based on the vibrational molecular motions. The calculated solid and liquid C{sub p} together with the transition parameters for equilibrium conditions were used as references for detailed quantitative thermal analysis of crystalline and amorphous sucrose. Melting temperature (T{sub m}) of the crystalline sucrose was identified in a broad 442–465 K range with a heat of fusion of 40–46 J/mol determined at heating rates 0.5–20 K/min, respectively. The equilibrium T{sub m} and heat of fusion of crystalline sucrose were estimated at zero heating rate as T{sup o}{sub m} = 424.4 K and ΔH{sup o}{sub f} = 32 kJ/mol, respectively. The glass transition temperature (T{sub g}) of amorphous sucrose was at 331 K with a change in C{sub p} of 267 J/(mol K) as it was estimated from reversing heat capacity by quasi-isothermal TMDSC on cooling. At heating rates less than 30 K/min, thermal decomposition occurred during melting, while at extreme rate of 1000 K/s, degradation was not observed. Data obtained by fast scanning calorimetry (FSC) at 1000 K/s, showed that T{sub m} was

  10. Chiral transition temperature and aspects of deconfinement in 2+1 flavor QCD with the HISQ/tree action

    CERN Document Server

    Bazavov, Alexei

    2012-01-01

    We present results on the chiral transition temperature Tc in 2+1 flavor QCD extrapolated to the continuum limit and the physical light quark mass. The extrapolations are based on the data from simulations on lattices with temporal extent Ntau=6, 8 and 12 with the HISQ/tree and Ntau=8 and 12 with the asqtad action. The chiral transition is analyzed in terms of universal O(N) scaling functions. After performing simultaneous asqtad and HISQ/tree continuum extrapolation the chiral transition temperature is Tc=154 +/- 9 MeV. We also discuss the deconfinement aspects of the transition in terms of the renormalized Polyakov loop, fluctuations and correlations of several conserved charges and the trace anomaly.

  11. Size Dependence of a Temperature-Induced Solid-Solid Phase Transition in Copper(I) Sulfide

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Zero-temperature transition and correlation-length exponent of the frustrated XY model on a honeycomb lattice

    Science.gov (United States)

    Granato, Enzo

    2012-02-01

    Phase coherence and vortex order in the fully frustrated XY model on a two-dimensional honeycomb lattice are studied by extensive Monte Carlo simulations using the parallel tempering method and finite-size scaling. No evidence is found for an equilibrium order-disorder or a spin/vortex-glass transition, suggested in previous simulation works. Instead, the scaling analysis of correlations of phase and vortex variables in the full equilibrated system is consistent with a phase transition where the critical temperature vanishes and the correlation lengths diverge as a power law with decreasing temperatures and corresponding critical exponents νph and νv. This behavior and the near agreement of the critical exponents suggest a zero-temperature transition scenario where phase and vortex variables remain coupled on large length scales.

  13. The impact of room temperature polymorphism in K doped NaTaO3 on structural phase transition behaviour

    Science.gov (United States)

    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.

  14. Epitaxial growth of higher transition-temperature VO2 films on AlN/Si

    Directory of Open Access Journals (Sweden)

    Tetiana Slusar

    2016-02-01

    Full Text Available 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.

  15. Measurement and modeling of the glass transition temperatures of multi-component solutions

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Binal N. [Department of Chemical and Environmental Engineering, University of Toledo, 2801 W. Bancroft Street, Toledo, OH 43606 (United States); Schall, Constance A. [Department of Chemical and Environmental Engineering, University of Toledo, 2801 W. Bancroft Street, Toledo, OH 43606 (United States)]. E-mail: cschall@eng.utoledo.edu

    2006-04-01

    Protein crystals are usually grown in multi-component aqueous solutions containing salts, buffers and other additives. To measure the X-ray diffraction data of the crystal, crystals are rapidly lowered to cryogenic temperatures. On flash cooling, ice frequently forms affecting the integrity of the sample. In order to eliminate this effect, substances called cryoprotectants are added to produce a glassy (vitrified) state rather than ice. Heretofore, the quantity of cryoprotectant needed to vitrify the sample has largely been established by trial and error. In this study, differential scanning calorimetry (DSC) was used to measure the melting (T {sub m}), devitrification (T {sub d}) and glass transition (T {sub g}) temperatures of solutions with a range of compositions typical of those used for growing protein crystals, with the addition of glycerol as cryoprotectant. The addition of cryoprotectant raises the T {sub g} and lowers the T {sub m} of bulk solution thereby decreasing the cooling rates required for vitrification of protein crystals. The theoretical T {sub g} value was calculated using the apparent volume fraction using the Miller/Fox equation extended for multi-component systems. The experimental values of T {sub g} were within approximately {+-}4% of that predicted by the model. Thus, the use of the model holds the promise of a rational method for the theoretical determination of the composition of cryoprotectant requirement of protein crystallization solutions.

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

    Science.gov (United States)

    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.

  17. An unusual isotope effect in a high-transition-temperature superconductor.

    Science.gov (United States)

    Gweon, G-H; Sasagawa, T; Zhou, S Y; Graf, J; Takagi, H; Lee, D-H; Lanzara, A

    2004-07-08

    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-T(c)) superconductors, it is far from clear that phonons are involved in the pairing at all. For example, the negligible change in T(c) of optimally doped Bi2Sr2CaCu2O8+delta (Bi2212; ref. 1) upon oxygen isotope substitution (16O --> 18O leads to T(c) 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.

  18. Delayed thermalization of X-rays absorbed in tin films far below the superconducting transition temperature

    Science.gov (United States)

    Stahle, C. K.; Kelley, R. L.; Moseley, S. H.; Szymkowiak, A. E.; Juda, M.; McCammon, D.; Zhang, J.

    1994-02-01

    As part of a program for developing high resolution X-ray detectors, we have deposited 4 μm thick Sn films on silicon calorimeters to serve as X ray absorbers. Thermistors in the silicon measured the temperature increase resulting from the thermalization of an X-ray photon. Silver-filled epoxy was placed on the Sn to establish a complete thermalization reference. The devices were operated near 0.1 K and below. Signal pulses resulting from the absorption of 6 keV photons in the Ag epoxy rose faster, peaked higher, and decayed to baseline more quickly than those resulting from absorption in the Sn. Taking the Ag pulse shape to be the impulse response of the detector, we deconvolved it from the average Sn pulse shape to obtain the thermalization function in the Sn. The result contained a slow component with a thermalization rate on the scale of several milliseconds. We consider this an indication of the quasiparticle recombination time in the Sn during the non-equilibrium condition following X-ray absorption. We were able to manipulate the thermalization by heating the device above the Sn transition temperature and varying the amount of magnetic field present upon cooling.

  19. Effect of bond length and radius on superconducting transition temperature for FeAs-based superconductors

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    By comparing the data of lattice parameters of more than 50 new FeAs-based high temperature superconductors in two syetems, the effect of bondlength on superconducting transition temperature (T C ) was found that, for both FeAs superconductor systems with similar ionic radii of cation A, the bond length L As-A between Arsenic atom and its nearest neighbor cation at the A site is in an inverse proportion to T C , i.e. the larger the bond length L As-A , the lower the T C . In addition, we also found a noticeable effect of ionic radius on T C , in which deviation from the tendency line of bond length vs. T C decreases with the increasing ionic radius. Both bond length-T C and ionic radii-T C relations indicate that the interaction of cation A and As ion have significant effect on superconductivity. The analysis on the electronic structure indicates that there exists the proximity of the secondary-outer p-orbit of the cation A and the 4s orbit of the As ion, both in energy space and in real space. Some high frequency individual vibrating modes would be established through exchange coupling on their inner orbits. It is worth of mention that the superconducting condensation is influenced by the interaction between the cation A and the As atoms.

  20. Predicting bioactive glass properties from the molecular chemical composition: glass transition temperature.

    Science.gov (United States)

    O'Donnell, Matthew D

    2011-05-01

    The glass transition temperature (T(g)) of inorganic glasses is an important parameter than can be used to correlate with other glass properties, such as dissolution rate, which governs in vitro and in vivo bioactivity. Seven bioactive glass compositional series reported in the literature (77 in total) were analysed here with T(g) values obtained by a number of different methods: differential thermal analysis, differential scanning calorimetry and dilatometry. An iterative least-squares fitting method was used to correlate T(g) from thermal analysis of these compositions with the levels of individual oxide and fluoride components in the glasses. When all seven series were fitted a reasonable correlation was found between calculated and experimental values (R(2)=0.89). When the two compositional series that were designed in weight percentages (the remaining five were designed in molar percentage) were removed from the model an improved fit was achieved (R(2)=0.97). This study shows that T(g) for a wide range in compositions (e.g. SiO(2) content of 37.3-68.4 mol.%) can be predicted to reasonable accuracy enabling processing parameters to be predicted such as annealing, fibre-drawing and sintering temperatures.

  1. Low temperature route for the synthesis of rare earth transition metal borides and their hydrides

    Energy Technology Data Exchange (ETDEWEB)

    Kramp, S.; Febri, M.; Joubert, J.C. [CNRS UMR 5628, Saint Martin d`Heres (France)

    1997-10-01

    Synthesis of rare earth-based alloys by the ORD technique consists in the reduction of rare earth oxides in a melt of calcium under argon, and simultaneous diffusion-reaction of the just formed rare earth metal with the other elements. This method has been applied with success to numerous ternary borides containing transition metals such as the magnetic alloys Y{sub 2}Co{sub 14}B, LnCo{sub 4}B, and YCo{sub 3}B{sub 2}. By using a small excess of Ca, boride particles grow in a viscous slurry media containing unreacted (melted) Ca and nanosize CaO particles. Single phase boride alloys can be obtained at 1000{degrees}C as loose micrometer-size particles of very high crystal quality as confirmed by the sharp diffraction peaks on the corresponding X-ray diagrams. Particles can be easily recovered by gentle wishing in diluted weak acid solution, and dried under vacuum at room temperature. This rather low temperature technique is particularly adapted to the synthesis of incongruent melting phases, as well as for the alloys containing volatile rare earth elements (Sm, Yb, Tb,...).

  2. A Low Temperature Route for the Synthesis of Rare Earth Transition Metal Borides and Their Hydrides

    Science.gov (United States)

    Kramp, S.; Febri, M.; Joubert, J. C.

    1997-10-01

    Synthesis of rare earth-based alloys by the ORD technique consists in the reduction of rare earth oxides in a melt of calcium under argon, and simultaneous diffusion-reaction of the just formed rare earth metal with the other elements. This method has been applied with success to numerous ternary borides containing transition metals such as the magnetic alloys Y2Co14B, LnCo4B, and YCo3B2. By using a small excess of Ca, boride particles grow in a viscous slurry media containing unreacted (melted) Ca and nanosize CaO particles. Single phase boride alloys can be obtained at 1000°C as loose micrometer-size particles of very high crystal quality as confirmed by the sharp diffraction peaks on the corresponding X-ray diagrams. Particles can be easily recovered by gentle washing in diluted weak acid solution, and dried under vacuum at room temperature. This rather low temperature technique is particularly adapted to the synthesis of incongruent melting phases, as well as for the alloys containing volatile rare earth elements (Sm, Yb, Tb,…).

  3. Novel Shape-Memory Polymer with Two Transition Temperature Based on Two Different Memory Mechanism

    Institute of Scientific and Technical Information of China (English)

    Liu Guoqin; Ding Xiaobing; Cao Yiping; Zheng Zhaohui; Peng Yuxing

    2004-01-01

    As an important kind of intelligent materials, shape-memory materials have been received increasing attention on account of their interesting properties and potential applications in recent years. Particularly, the rise of shape-memory polymers by far surpasses well-known metallic shape-memory alloys in their shape-memory properties. The advantages of polymers compared to other materials are their easier availability and their wide range of mechanical and physical properties. The polymers designed to exhibit a shape-memory effect require two components on the molecular level: crosslinks to determine the permanent shape and switching segments with Ttrans to fix the temporary shape. Up to now almost all papers on shape-memory polymers introduce switching segments with the covalent linking method. On the other hand, only several cases concern non-covalent interaction. However, the research works mentioned above is based on a single Ttrans (i.e., Tm or Tg).Following our previous work, here, we first report a novel kind of polymer consisted of PMMA-PEG semi-interpenetrating polymer networks (semi-IPN), which exhibiting independently two shape memory effects based on Tm and Tg, respectively. This result can also extend the shape memory polymer categories from one Ttrans to two Ttrans, and the combination of Tm and Tg give rise to an extremely excellent shape-memory effect.Two different shape memory behaviors of this material based on two transition temperatures were evaluated by bending test as follows: a straight strip of the specimen was folded at a temperature above Ttrans and kept in this shape. The so-deformed sample was cooled down to a temperature Tlow< Ttrans and the deforming stress were released. When the sample was heated up to the measuring temperature Thigh > Ttrans, it recovered its initial shape. The deformation angle θ f varied as a function of time and the ratio of the recovery was defined as θ f /180. The PMMA-PEG polymer behaved as a hard plastic

  4. Experiments of Brittle-Plastic Transition and Instability Modes of Juyongguan Granite at Different Temperatures and Pressures

    Institute of Scientific and Technical Information of China (English)

    Zhou Yongsheng; Jiang Haikun; He Changrong

    2003-01-01

    Three groups of experiments on brittle-plastic transition and instability modes of granite wereperformed in a triaxial vessel with solid pressure medium at high temperature and highpressure. The results of experiments show that brittle faulting is the major failure mode attemperature < 300℃, but crystal-plastic deformation is dominate at temperature > 800℃, andthere is a transition with increasing temperature from semi-brittle faulting to cataclnstic flowand semi-brittle flow at temperatures of 300 ~ 800℃. So, temperature is the most influentialfactor in brittle-plastic transition of granite and confining pressure is the second factor. Theresults also show that progressive failure of granite occurs at lower pressure or hightemperature where there is crystal plasticity, and sudden instability occurs at room temperatureand high pressure ( > 300MPa) or high temperature and great pressure(550℃600MPa ~ 650℃700MPa), and a broad regime of quasi-sudden instability exists between the T-P condition ofprogressive failure and sudden instability. So, instability modes of granite dependsimnitaneonsly on the pressure and temperature.

  5. Nonempirical Calculation of Superconducting Transition Temperatures in Light-Element Superconductors.

    Science.gov (United States)

    Arita, Ryotaro; Koretsune, Takashi; Sakai, Shiro; Akashi, Ryosuke; Nomura, Yusuke; Sano, Wataru

    2017-01-06

    Recent progress in the fully nonempirical calculation of the superconducting transition temperature (Tc ) is reviewed. Especially, this study focuses on three representative light-element high-Tc superconductors, i.e., elemental Li, sulfur hydrides, and alkali-doped fullerides. Here, it is discussed how crucial it is to develop the beyond Migdal-Eliashberg (ME) methods. For Li, a scheme of superconducting density functional theory for the plasmon mechanism is formulated and it is found that Tc is dramatically enhanced by considering the frequency dependence of the screened Coulomb interaction. For sulfur hydrides, it is essential to go beyond not only the static approximation for the screened Coulomb interaction, but also the constant density-of-states approximation for electrons, the harmonic approximation for phonons, and the Migdal approximation for the electron-phonon vertex, all of which have been employed in the standard ME calculation. It is also shown that the feedback effect in the self-consistent calculation of the self-energy and the zero point motion considerably affect the calculation of Tc . For alkali-doped fullerides, the interplay between electron-phonon coupling and electron correlations becomes more nontrivial. It has been demonstrated that the combination of density functional theory and dynamical mean field theory with the ab initio downfolding scheme for electron-phonon coupled systems works successfully. This study not only reproduces the experimental phase diagram but also obtains a unified view of the high-Tc superconductivity and the Mott-Hubbard transition in the fullerides. The results for these high-Tc superconductors will provide a firm ground for future materials design of new superconductors.

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

    Science.gov (United States)

    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.

  7. PECH和GAP的玻璃化转变温度研究%Glass-transition Temperature of PECH and GAP

    Institute of Scientific and Technical Information of China (English)

    宋晓庆; 周集义; 王文浩; 王建伟; 白森虎

    2008-01-01

    @@ Glycidyl azide polymer (GAP) is one of the most recognized and prominent azide polymer. Because of its superior properties,GAP is used extensively as a high energetic binder or plasticizer in propellants to increase burning and specific impulse. It is very important to research on the glass-transition temperature (Tg) of GAP and its precursor PECH (poly-epichlorohydrin) due to the Tg of binders is the key factor which can influence low temperature properties of solid propellants.

  8. Determination of the Glass Transition Temperature of Freestanding and Supported Azo-Polymer Thin Films by Thermal Assisted Atomic Force Microscopy

    Directory of Open Access Journals (Sweden)

    Chernykh Elena

    2017-01-01

    Full Text Available In this paper we introduce and apply the method for determination of the glass transition temperature of the sub-100 nm thick freestanding and supported polymer films based on thermally assisted atomic force microscopy (AFM. In proposed approach changes of the phase of an oscillating AFM cantilever are used to determine glass transition temperature. An anomalous decrease of the glass transition temperature for both free-standing and supported azobenzene-functionalized polymer thin films is shown.

  9. Robust metastable skyrmions and their triangular-square lattice structural transition in a high-temperature chiral magnet

    Science.gov (United States)

    Karube, K.; White, J. S.; Reynolds, N.; Gavilano, J. L.; Oike, H.; Kikkawa, A.; Kagawa, F.; Tokunaga, Y.; Rønnow, H. M.; Tokura, Y.; Taguchi, Y.

    2016-12-01

    Skyrmions, topologically protected nanometric spin vortices, are being investigated extensively in various magnets. Among them, many structurally chiral cubic magnets host the triangular-lattice skyrmion crystal (SkX) as the thermodynamic equilibrium state. However, this state exists only in a narrow temperature and magnetic-field region just below the magnetic transition temperature Tc, while a helical or conical magnetic state prevails at lower temperatures. Here we describe that for a room-temperature skyrmion material, β-Mn-type Co 8Zn 8Mn 4, a field-cooling via the equilibrium SkX state can suppress the transition to the helical or conical state, instead realizing robust metastable SkX states that survive over a very wide temperature and magnetic-field region. Furthermore, the lattice form of the metastable SkX is found to undergo reversible transitions between a conventional triangular lattice and a novel square lattice upon varying the temperature and magnetic field. These findings exemplify the topological robustness of the once-created skyrmions, and establish metastable skyrmion phases as a fertile ground for technological applications.

  10. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature.

    Science.gov (United States)

    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

  11. Monte Carlo Comparisons to a Cryogenic Dark Matter Search Detector with low Transition-Edge-Sensor Transition Temperature

    CERN Document Server

    Leman, S W; Brink, P L; Cabrera, B; Cherry, M; Silva, E Do Couto E; Figueroa-Feliciano, E; Kim, P; Mirabolfathi, N; Pyle, M; Resch, R; Sadoulet, B; Serfass, B; Sundqvist, K M; Tomada, A; Young, B A

    2011-01-01

    We present results on phonon quasidiffusion and Transition Edge Sensor (TES) studies in a large, 3 inch diameter, 1 inch thick [100] high purity germanium crystal, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare calibration data with results from a Monte Carlo which includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels. The phonon energy is then parsed into TES based phonon readout channels and input into a TES simulator.

  12. A modified golden gate attenuated total reflection (ATR) cell for monitoring phase transitions in multicomponent fluids at high temperatures.

    Science.gov (United States)

    Novitskiy, Alexander A; Ke, Jie; Comak, Gurbuz; Poliakoff, Martyn; George, Michael W

    2011-08-01

    A new continuous flow method using attenuated total reflection infrared (ATR-IR) spectroscopy has been developed for monitoring phase transitions in multicomponent fluids at high pressures and temperatures. Our approach uses Fourier transform infrared (FT-IR) and a modified Golden Gate attenuated total reflection (ATR) cell and exploits the fact that the absorbance of a vapor is much lower than that of the corresponding liquid to monitor the phase transition between vapor and liquid. We demonstrate that this method can provide quantitative measurements on both the dew point and the bubble point. We have validated our approach using three single-component systems (EtOH, MeOH, and H(2)O) and a binary system of EtOH + H(2)O, monitoring phase transitions at temperature up to 300 °C and pressure up to 10 MPa.

  13. Higgs boson resonance parameters and the finite temperature phase transition in a chirally invariant Higgs-Yukawa model

    Energy Technology Data Exchange (ETDEWEB)

    Bulava, John; Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Gerhold, Philip; Kallarackal, Jim; Nagy, Attila [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Humbolt-Univ. Berlin (Germany)

    2011-12-15

    We study a chirally invariant Higgs-Yukawa model regulated on a space-time lattice. We calculate Higgs boson resonance parameters and mass bounds for various values of the mass of the degenerate fermion doublet. Also, first results on the phase transition temperature are presented. In general, this model may be relevant for BSM scenarios with a heavy fourth generation of quarks. (orig.)

  14. Phase transitions at finite temperature and dimensional reduction for fermions and bosons

    CERN Document Server

    Kocic, Aleksandar

    1995-01-01

    In a recent Letter we discussed the fact that large-N expansions and computer simulations indicate that the universality class of the finite temperature chiral symmetry restoration transition in the 3D Gross-Neveu model is mean field theory. This was seen to be a counterexample to the standard 'sigma model' scenario which predicts the 2D Ising model universality class. In this article we present more evidence, both theoretical and numerical, that this result is correct. We develop a physical picture for our results and discuss the width of the scaling region (Ginzburg criterion), 1/N corrections, and differences between the dynamics of BCS superconductors and Gross-Neveu models. Lattices as large as 12 \\times 72^2 are simulated for both the N=12 and N=4 cases and the numerical evidence for mean field scaling is quite compelling. We point out that the amplitude ratio for the model's susceptibility is a particulartly good observable for distinguishing between the dimensional reduction and the mean field sceneri...

  15. Using combined computational techniques to predict the glass transition temperatures of aromatic polybenzoxazines.

    Directory of Open Access Journals (Sweden)

    Phumzile Mhlanga

    Full Text Available 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 T(g. 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 T(g. Predicted T(g values from molecular modelling fall in the middle of the range of the experimentally determined T(g 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.

  16. Solid-to-fluid DNA transition inside HSV-1 capsid close to the temperature of infection

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. Lattice paramenter, lattice disorder and resistivity of carbohydrate doepd MgB2 and their correlation with the transition temperature

    OpenAIRE

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

    2009-01-01

    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 know...

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

    Science.gov (United States)

    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.

  19. Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Xianzhong; Matthes, Frank; Bürgler, Daniel E., E-mail: d.buergler@fz-juelich.de; Schneider, Claus M. [Peter Grünberg Institut, Electronic Properties (PGI-6) and Jülich-Aachen Research Alliance, Fundamentals of Future Information Technology (JARA-FIT), Forschungszentrum Jülich, D-52425 Jülich (Germany)

    2016-01-15

    The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

  20. Magnetic surface domain imaging of uncapped epitaxial FeRh(001 thin films across the temperature-induced metamagnetic transition

    Directory of Open Access Journals (Sweden)

    Xianzhong Zhou

    2016-01-01

    Full Text Available The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001 thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001 surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. The Doping Effect on Conductivity and Glass Transition Temperature of Solid Polymeric Electrolyte Based on Polyvinylchloride (pvc)

    Science.gov (United States)

    Abd. Rahman, Mohd. Yusri; Mat Salleh, Muhammad; Abu Talib, Ibrahim; Yahaya, Muhamad

    2002-12-01

    Solid electrolyte materials have been widely used in electrochemical devices such as batteries, solar cells and displays. This is because of its advantages over the liquidmaterial.This paper is concerned with the preparation of solid polymeric electrolyte based on polyvinylchloride (PVC) and its conductivity .The effect of percentage by weight of dopant material (LiClO4) on conductivity and glass transition temperature of the electrolyte was studied by using differential scanning calorimeter (DSC) and impedance spectroscopy technique. The electrolyte doped with 4.8%wt LiClO4 exhibits the highest conductivitiy of 7 × 10-6Scm-1 at room temperature but has the lowest glass transition temperature of 36.37°C. The other results are presented in this paper.

  3. An observed connection between wintertime temperature anomalies over Northwest China and weather regime transitions in North Atlantic

    Science.gov (United States)

    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.

  4. An Observed Connection Between Wintertime Temperature Anomalies over Northwest China and Weather Regime Transitions in North Atlantic

    Institute of Scientific and Technical Information of China (English)

    李超; 张庆云

    2015-01-01

    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 defi ne SAT anomaly cases. Diff erences 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 fl ow over Northwest China. Time-lagged composites reveal possible connections between the SAT anomalies and the diff erent 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 intensifi ed 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.

  5. Radiation and annealing response of WWER 440 beltline welding seams

    Energy Technology Data Exchange (ETDEWEB)

    Viehrig, Hans-Werner, E-mail: h.w.viehrig@hzdr.de; Houska, Mario; Altstadt, Eberhard

    2015-01-15

    Highlights: • Investigation of the beltline welding seam from decommissioned reactor pressure vessels. • The Master Curve based reference temperature varies strongly through the thickness. • This variation is mainly caused by the intrinsic weld bead structure. • The Charpy-V based ductile-to-brittle temperature shift does not correspond to the prediction. • The mitigation of the irradiation induced embrittlement by annealing has been confirmed. - Abstract: The focus of this paper is on the irradiation response and the effect of thermal annealing in weld materials extracted from decommissioned WWER 440 reactor pressure vessels of the nuclear power plant Greifswald. The characterisation is based on the measurement of the hardness, the yield stress, the Master Curve reference temperature, T{sub 0}, and the Charpy-V transition temperature through the thickness of multi-layer beltline welding seams in the irradiated and the thermally annealed condition. Additionally, the weld bead structure was characterised by light microscopic studies. We observed a large variation in the through thickness T{sub 0} values in the irradiated as well as in thermally annealed condition. The T{sub 0} values measured with the T–S-oriented Charpy size SE(B) specimens cut from different thickness locations of the multilayer welding seams strongly depend on the intrinsic weld bead structure along the crack tip. The Master Curve, T{sub 0}, and Charpy-V, TT{sub 47J}, based ductile-to-brittle transition temperature progressions through the thickness of the multi-layer welding seam do not correspond to the forecast according to the Russian code. In general, the fracture toughness values at cleavage failure, K{sub Jc}, measured on SE(B) specimens from the irradiated and large-scale thermally annealed beltline welding seams follow the Master Curve description, but more than the expected number lie outside the curves for 2% and 98% fracture probability. In this case the test standard ASTM

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

    Science.gov (United States)

    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 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.

  7. Slow dynamics and glass transition in simulated free-standing polymer films: a possible relation between global and local glass transition temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Peter, S [Institut Charles Sadron, 6 rue Boussingault, 67083 Strasbourg Cedex (France); Meyer, H [Institut Charles Sadron, 6 rue Boussingault, 67083 Strasbourg Cedex (France); Baschnagel, J [Institut Charles Sadron, 6 rue Boussingault, 67083 Strasbourg Cedex (France); Seemann, R [Max Planck Institute for Dynamics and Self-Organization, D-37018 Goettingen (Germany)

    2007-05-23

    We employ molecular dynamics simulations to explore the influence that the surface of a free-standing polymer film exerts on its structural relaxation when the film is cooled toward the glass transition. Our simulations are concerned with the features of a coarse-grained bead-spring model in a temperature regime above the critical temperature T{sub c} of mode-coupling theory. We find that the film dynamics is spatially heterogeneous. Monomers at the free surface relax much faster than they would in the bulk at the same temperature T. The fast relaxation of the surface layer continuously turns into bulk-like relaxation with increasing distance y from the surface. This crossover remains smooth for all T, but its range grows on cooling. We show that it is possible to associate a gradient in critical temperatures T{sub c}(y) with the gradient in the relaxation dynamics. This finding is in qualitative agreement with experimental results on supported polystyrene (PS) films (Ellison and Torkelson 2003 Nat. Mater. 2 695). Furthermore we show that the y dependence of T{sub c}(y) can be expressed in terms of the depression of T{sub c}(h)-the global T{sub c} for a film of thickness h-if we assume that T{sub c}(h) is the arithmetic mean of T{sub c}(y) and parameterize the depression of T{sub c}(h) by T{sub c}(h) = T{sub c}/(1+h{sub 0}/h), a formula suggested by Herminghaus et al (2001 Eur. Phys. J. E 5 531) for the reduction of the glass transition temperature in supported PS films. We demonstrate the validity of this formula by comparing our simulation results to results from other simulations and experiments.

  8. The Effects of Electron Radiation on the Glass Transition Temperature of a Polyetherimide.

    Science.gov (United States)

    Kern, Kristen Tulloch

    The effects of electron radiation on a polyetherimide (PEI), Ultem^{cdot}, were investigated. In particular, the changes in the glass transition temperature (T_{g} ) with absorbed radiation dose were studied. The polymer was exposed to mono-energetic beams of 100-keV electrons and 1.0-MeV electrons for doses up to 100 megagray (MGy). Dosimetry for the exposures was based on Monte -Carlo simulations of the transfer of energy from an energetic electron to the polymer and on comparison to Nylon standards. Dynamic mechanical analysis was used to determine the T _{g} for non-exposed PEI and the changes in T_{g} resulting from irradiation. The T_{g} did not change significantly for doses up to and including 75 MGy, while a significant increase in T_ {g} occurred for a dose of 100 MGy. The cross-link and chain scission densities in the irradiated PEI were determined using infrared spectroscopy. The cross -link density increased with dose for all doses investigated. The chain scission density increased with dose for doses up to 75 MGy, but was lower for a dose of 100 MGy than for a dose of 75 MGy. Radical population kinetics, based in part on data from an electron paramagnetic resonance study, were correlated with the cross-link density and chain scission density to investigate the mechanism for the observed density variations with dose. The radical population simulations suggest that chain scissioning occurs less readily when the average radical separation during the exposure is less than three molecular radii. Finally, a model for the combined effects of cross-linking and chain scissioning is proposed which combines a statistical-mechanical model for the change in T_{g} with cross-link density and a free-volume model for the change in T _{g} with chain scission density.

  9. Effects of temperature on hy drostatic pressure-induced FE-AFE phase transition in PbLa(Zr, Sn, Ti)O3 ceramics

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Hydrostatic pressure-induced ferroelectricantiferroelectric (FE-AFE) phase transition and the pressure dependence of dielectric properties in La-doped Pb(Zr, Sn,Ti)O3 ceramics were researched; the effects of temperature on hydrostatic pressure-induced FE-AFE phase transition and dielectric properties of the samples were studied. It was found that the temperature made the FE-AFE phase transition pressure decrease, and there existed the behavior of dielectric frequency dispersion and phase transition diffusion in the dielectric-pressure spectrum. These phenomena were very useful to enrich and develop the knowledge on the diffused phase transition behavior of polycomponent relaxor ferroelectric.``

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

    Science.gov (United States)

    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.

    Science.gov (United States)

    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. Noncovalent Modulation of the Inverse Temperature Transition and Self-Assembly of Elastin-b-Collagen-like Peptide Bioconjugates.

    Science.gov (United States)

    Luo, Tianzhi; Kiick, Kristi L

    2015-12-16

    Stimuli-responsive nanostructures produced with peptide domains from the extracellular matrix offer great opportunities for imaging and drug delivery. Although the individual utility of elastin-like (poly)peptides and collagen-like peptides in such applications has been demonstrated, the synergistic advantages of combining these motifs in short peptide conjugates have surprisingly not been reported. Here, we introduce the conjugation of a thermoresponsive elastin-like peptide (ELP) with a triple-helix-forming collagen-like peptide (CLP) to yield ELP-CLP conjugates that show a remarkable reduction in the inverse transition temperature of the ELP domain upon formation of the CLP triple helix. The lower transition temperature of the conjugate enables the facile formation of well-defined vesicles at physiological temperature and the unexpected resolubilization of the vesicles at elevated temperatures upon unfolding of the CLP domain. Given the demonstrated ability of CLPs to modify collagens, our results not only provide a simple and versatile avenue for controlling the inverse transition behavior of ELPs, but also suggest future opportunities for these thermoresponsive nanostructures in biologically relevant environments.

  13. Development of DMBZ-15 High-Glass-Transition-Temperature Polyimides as PMR-15 Replacements Given R&D 100 Award

    Science.gov (United States)

    Chuang, Kathy

    2004-01-01

    PMR-15, a high-temperature polyimide developed in the mid-1970s at the NASA Lewis Research Center,1 offers the combination of low cost, easy processing, and good high-temperature performance and stability. It has been recognized as the leading polymer matrix resin for carbon-fiber-reinforced composites used in aircraft engine components. The state-of-the-art PMR-15 polyimide composite has a glass-transition temperature (Tg) of 348 C (658 F). Since composite materials must be used at temperatures well below their glass-transition temperature, the long-term use temperatures of PMR-15 composites can be no higher than 288 C (550 F). In addition, PMR-15 is made from methylene dianiline (MDA), a known liver toxin. Concerns about the safety of workers exposed to MDA during the fabrication of PMR-15 components and about the environmental impact of PMR-15 waste disposal have led to the industry-wide implementation of special handling procedures to minimize the health risks associated with this material. These procedures have increased manufacturing and maintenance costs significantly and have limited the use of PMR-15 in commercial aircraft engine components.

  14. Relaxation Mode Analysis and Markov State Relaxation Mode Analysis for Chignolin in Aqueous Solution at a Transition Temperature

    CERN Document Server

    Mitsutake, Ayori

    2015-01-01

    It is important to extract reaction coordinates or order parameters from protein simulations in order to investigate the local-minimum-energy states and the transition between them. The most popular method is principal component analysis, which extracts modes with large conformational fluctuation around an average structure. For protein systems, we recently have applied relaxation mode analysis, which investigate dynamics properties of structural fluctuations of proteins and extract slow relaxation modes. In this article, we apply relaxation mode analysis to extract reaction coordinates for the system, in which there are large conformational changes such as folding/unfolding simulation. We have performed a 750 ns simulation of chignolin at a transition temperature and observed many transitions between the most stable, misfolded and unfolded states. Here, we apply principal component analysis and relaxation mode analysis to the system. In relaxation mode analysis, we extract good reaction coordinates automatic...

  15. Direct measurement of the low-temperature spin-state transition in LaCoO3.

    Science.gov (United States)

    Klie, R F; Zheng, J C; Zhu, Y; Varela, M; Wu, J; Leighton, C

    2007-07-27

    LaCoO3 exhibits an anomaly in its magnetic susceptibility around 80 K associated with a thermally excited transition of the Co3+-ion spin. We show that electron energy-loss spectroscopy is sensitive to this Co3+-ion spin-state transition, and that the O K edge prepeak provides a direct measure of the Co3+ spin state in LaCoO3 as a function of temperature. Our experimental results are confirmed by first-principles calculations, and we conclude that the thermally excited spin-state transition occurs from a low to an intermediate spin state, which can be distinguished from the high-spin state.

  16. The Gardner Transition: A new approach for understanding low-temperature glasses

    Science.gov (United States)

    Charbonneau, Patrick

    Recent theoretical advances in the mean-field theory of glasses predict the existence deep in the glass phase of a novel phase transition, a so-called Gardner transition. This transition signals the emergence of a complex free energy landscape composed of a marginally stable hierarchy of sub-basins within a broad glass metabasin. It is thus the onset of marked changes in thermal and transport properties of glasses, and ultimately leads to the unusual critical behavior at jamming. The Gardner transition itself is immediately related to a diverging (i) characteristic relaxation time, (ii) caging susceptibility and (iii) correlation length of the caging heterogeneity as well as aging, even in well-thermalized glasses. We have detected some of these signatures both in a mean-field model and in standard hard-sphere glass formers. We find the results to quantitatively agree with theory in the former and qualitatively so in the latter, which suggest that the transition should be detectable in a wide array of numerical and experimental systems. Interestingly, although the Gardner transitions is primarily associated with structural glass formers, we also find features of the transition in crystals of polydisperse particles once the landscape becomes rough.

  17. Magnetic phase transitions and large magnetic entropy change with a wide temperature span in HoZn

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lingwei, E-mail: wei0396@hotmail.com [Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China); Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster (Germany); Yuan, Ye [Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Ion Beam Physics and Materials Research, P.O. Box 510119, 01314 Dresden (Germany); Zhang, Yikun [Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China); Pöttgen, Rainer [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster (Germany); Zhou, Shengqiang [Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Ion Beam Physics and Materials Research, P.O. Box 510119, 01314 Dresden (Germany)

    2015-09-15

    Highlights: • Magnetic phase transitions and magnetocaloric effect in HoZn were studied. • The critical properties of HoZn were systematically investigated. • The obtained critical exponents are satisfied with scaling theory. • A large reversible magnetocaloric effect in HoZn was observed. • HoZn could be a promising candidate for magnetic refrigeration. - Abstract: CsCl-type HoZn undergoes two successive magnetic phase transitions: (i) paramagnetic to ferromagnetic (FM) at T{sub C} ∼ 72 K and (ii) a spin reorientation (SR) at T{sub SR} ∼ 26 K. Magnetization and modified Arrott plots indicate that HoZn undergoes a second-order magnetic phase transition around T{sub C}. The obtained critical exponents have some small deviations from the mean-field theory, indicating a short range or a local magnetic interaction which is properly related to the coexistence of FM and SR transitions at low temperature. Two successive magnetic transitions in HoZn induce one broad pronounced peak together with a shoulder in the temperature dependence of the magnetic entropy change −ΔS{sub M}(T) curves, resulting in a wide temperature range with a large relative cooling power (RCP). For a field change of 0–7 T, the maximum value of −ΔS{sub M} is 15.2 J/kg K around T{sub C} with a large RCP value of 1124 J/kg. The large reversible magnetocaloric effect (MCE) and RC indicate that HoZn is a good candidate for active magnetic refrigeration.

  18. Critical point phase transition for finite temperature 3-flavor QCD with nonperturbatively O (a ) improved Wilson fermions at Nt=10

    Science.gov (United States)

    Jin, Xiao-Yong; Kuramashi, Yoshinobu; Nakamura, Yoshifumi; Takeda, Shinji; Ukawa, Akira

    2017-08-01

    We study the finite temperature phase structure for three-flavor QCD with a focus on locating the critical point, which separates the crossover and the first order phase transition region in the chiral regime of the Columbia plot. In this study, we employ the Iwasaki gauge action and the nonperturvatively O (a ) improved Wilson-Clover fermion action. We discuss the finite size scaling analysis, including the mixing of magnetizationlike and energylike observables. We carry out the continuum extrapolation of the critical point using newly generated data at the Nt=8 , 10 and estimate the upper bound of the critical pseudoscalar meson mass mPS ,E≲170 MeV and the critical temperature TE=134 (3 ) MeV . Our estimate of the upper bound is derived from the existence of the critical point as an edge of the first order phase transition while that of the staggered-type fermions with smearing is based on its absence.

  19. Temperature-dependent study of isotropic-nematic transition for a Gay-Berne fluid using density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Ram Chandra [Department of Physics, Hindustan Institute of Technology, 32, 34 Knowledge Park-III, Greater Noida-201306, UP (India)

    2007-09-19

    We have used the density-functional theory to study the effect of varying temperature on the isotropic-nematic transition of a fluid of molecules interacting via the Gay-Berne intermolecular potential. The nematic phase is found to be stable with respect to isotropic phase in the temperature range 0.80{<=}T*{<=}1.25. Pair correlation functions needed as input information in density-functional theory is calculated using the Percus-Yevick integral equation theory. We find that the density-functional theory is good for studying the isotropic-nematic transition in molecular fluids if the values of the pair-correlation functions in the isotropic phase are known accurately. We have also compared our results with computer simulation results wherever they are available.

  20. Driven-dissipative many-body systems with mixed power-law interactions: Bistabilities and temperature-driven phase transitions

    CERN Document Server

    Šibalić, Nikola; Adams, Charles S; Weatherill, Kevin J; Pohl, Thomas

    2015-01-01

    We investigate the non-equilibrium dynamics of a driven-dissipative spin ensemble with competing power-law interactions. Contrary to previous work on pure van der Waals systems, we demonstrate that the emergence of a dynamical phase transition and bistable steady states critically relies on the presence of a finite dipolar potential-core. Upon introducing random particle motion, we show that a finite gas temperature can drive a phase transition with regards to the spin degree of freedom and eventually leads to mean-field behaviour in the high-temperature limit. Our work reconciles contrasting observations of recent experiments with Rydberg atoms in the cold-gas and hot-vapour domain, and establishes an efficient theoretical framework in the latter regime.

  1. Analysis of fracture toughness in transition temperature region of a Mn-Mo-Ni low-alloy steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sang Ho; Hwang, Byoung Chul; Lee, Sung Hak [Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

    2002-08-01

    This study is concerned with the analysis of fracture toughness in the transition region of a Mn-Mo-Ni low-alloy steel according to ASTM E1921 standard test method. Elastic-plastic cleavage fracture toughness, K{sub Jc} was determined by 3-point bend tests, using precracked Charpy V-notch (PCVN) specimens, and then the measured K{sub Jc} values were interpreted by the 3-parameter Weibull distribution with a theoretical slope of 4. fractographic observation indicated that the critical distance from a precrack tip to a cleavage initiation site linearly increased with increasing the critical J(J{sub c}) value, and that the stretch zone width had a good correlation with K{sub Jc} value, irrespective of testing temperature. Relationship between J{sub c} and critical distance, local fracture stress, and plane strain fracture toughness were discussed on the basis of the cleavage fracture behavior in the transition temperature region.

  2. Effect of rare earth ions on transition temperature in perovskite materials by on-line ultrasonic studies

    Directory of Open Access Journals (Sweden)

    Sundararaman Sankarrajan

    2012-08-01

    Full Text Available On-line measurements of ultrasonic longitudinal velocity, shear velocity and longitudinal attenuation were carried out on R1-xSr xMnO3 perovskites (R = La, Pr, Nd and Sm for different compositions of Sr, at a fundamental frequency of 5 MHz over wide range of temperatures using the through-transmission method. The observed maxima/minima in velocities and attenuation have been discussed with decrease in ionic radii and composition. As a decrease in the ionic radii of rare earth elements leads to a decrease in transition temperature (Tc, the results that are observed show that measurement is one of the best tools to explore the structural/phase transition on-line velocity in perovskite manganese materials as a function of the ionic radii of rare earth elements.

  3. Alternative methods of determining phase transition temperatures of phospholipids that constitute liposomes on the example of DPPC and DMPC

    Energy Technology Data Exchange (ETDEWEB)

    Pentak, Danuta, E-mail: danuta.pentak@us.edu.pl

    2014-05-01

    Highlights: • New phase transition for DMPC was found. • FT-IR method is an important addition to the DSC studies. • The proposed method for determining the T{sub C} give very consistent results. - Abstract: In this work, alternatives to differential scanning calorimetry (DSC) as a method of determining the main phospholipid phase transition temperature are presented. The bilayer phase transitions from the ripple gel phase (P{sub β{sup ′}}) to the liquid-crystal phase (L{sub α}) of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were studied by differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) methods. In this work, two correlations between the DSC and FT-IR methods, and NMR and EPR methods are shown. The proposed methods allow for determining the T{sub C} temperature with a high degree of accuracy. Furthermore, a comparison of results obtained using the DSC and FT-IR methods allowed for an observation of a new DMPC phase transition. The liposomes analyzed in this work were obtained by the modified reverse-phase evaporation method (mREV)

  4. Freeze-Drying Above the Glass Transition Temperature in Amorphous Protein Formulations While Maintaining Product Quality and Improving Process Efficiency.

    Science.gov (United States)

    Depaz, Roberto A; Pansare, Swapnil; Patel, Sajal Manubhai

    2016-01-01

    This study explored the ability to conduct primary drying during lyophilization at product temperatures above the glass transition temperature of the maximally freeze-concentrated solution (Tg′) in amorphous formulations for four proteins from three different classes. Drying above Tg′ resulted in significant reductions in lyophilization cycle time. At higher protein concentrations, formulations freeze dried above Tg′ but below the collapse temperature yielded pharmaceutically acceptable cakes. However, using an immunoglobulin G type 4 monoclonal antibody as an example, we found that as protein concentration decreased, minor extents of collapse were observed in formulations dried at higher temperatures. No other impacts to product quality, physical stability, or chemical stability were observed in this study among the different drying conditions for the different proteins. Drying amorphous formulations above Tg′, particularly high protein concentration formulations, is a viable means to achieve significant time and cost savings in freeze-drying processes.

  5. Phase transition in a one-dimensional Ising ferromagnet at zero temperature using Glauber dynamics with a synchronous updating mode.

    Science.gov (United States)

    Sznajd-Weron, Katarzyna

    2010-09-01

    In the past decade low-temperature Glauber dynamics for the one-dimensional Ising system has been several times observed experimentally and occurred to be one of the most important theoretical approaches in a field of molecular nanomagnets. On the other hand, it has been shown recently that Glauber dynamics with the Metropolis flipping probability for the zero-temperature Ising ferromagnet under synchronous updating can lead surprisingly to the antiferromagnetic steady state. In this paper the generalized class of Glauber dynamics at zero temperature will be considered and the relaxation into the ground state, after a quench from high temperature, will be investigated. Using Monte Carlo simulations and a mean field approach, discontinuous phase transition between ferromagnetic and antiferromagnetic phases for a one-dimensional ferromagnet will be shown.

  6. Bonding at Compatible and Incompatible Amorphous Interfaces of Polystyrene and Poly(Methyl Methacrylate) Below the Glass Transition Temperature

    DEFF Research Database (Denmark)

    Boiko, Yuri M.; Lyngaae-Jørgensen, Jørgen

    2004-01-01

    Films of high-molecular-weight amorphous polystyrene (PS, M-w = 225 kg/mol, M-w/M-n = 3, T-g-bulk = 97degreesC, where T-g-bulk is the glass transition temperature of the bulk sample) and poly(methyl methacrylate) (PMMA, M-w = 87 kg/mol, M-w/M-n = 2, Tg-bulk = 109degreesC) were brought into contact...

  7. Determination of production efficiency, color, glass transition, and sticky point temperature of spray-dried pomegranate juice powder

    OpenAIRE

    Khalid Muzaffar; Sajad Ahmad Wani; Bijamwar Vilas Dinkarrao; Pradyuman Kumar

    2016-01-01

    The aim of the study was to determine the powder recovery, color characteristics, glass transition temperature (Tg), and sticky point (Ts) temperature of spray-dried pomegranate juice powder as affected by different concentrations of maltodextrin (DE 20). Five different combinations of pomegranate juice and maltodextrin (95:5, 90:10, 85:15, 80:20 and 75:25 v/w) were prepared and spray dried in a laboratory-type spray dryer. Increase in concentration of maltodextrin significantly increased the...

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  10. Growth temperature-dependent metal–insulator transition of vanadium dioxide epitaxial films on perovskite strontium titanate (111) single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Liangxin; Zhao, Jiangtao; Hong, Bin; Hu, Kai; Luo, Zhenlin [National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230029 (China); Yang, Yuanjun, E-mail: yangyuanjun@ustc.edu.cn, E-mail: cgao@ustc.edu.cn; Gao, Chen, E-mail: yangyuanjun@ustc.edu.cn, E-mail: cgao@ustc.edu.cn [National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230029 (China); Chinese Academy of Sciences Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026 (China); Peng, Jinlan; Zhang, Haibin; Wen, Xiaolei; Li, Xiaoguang [Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230027 (China)

    2016-04-14

    Vanadium dioxide (VO{sub 2}) epitaxial films were grown on perovskite single-crystal strontium titanate (SrTiO{sub 3}) substrates by reactive radio-frequency magnetron sputtering. The growth temperature-dependent metal–insulator transition (MIT) behavior of the VO{sub 2} epitaxial films was then investigated. We found that the order of magnitude of resistance change across the MIT increased from 10{sup 2} to 10{sup 4} 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)-VO{sub 2}/(111)-SrTiO{sub 3} epitaxial films at elevated temperature. On the other hand, the strain states do not change in the VO{sub 2} films deposited at various temperatures, resulting in stable V-V chains and V-O bonds in the VO{sub 2} epitaxial films. The accompanied orbital occupancy near the Fermi level is also constant and thus the MIT temperatures of VO{sub 2} films deposited at various temperatures are nearly the same. This work demonstrates that high-quality VO{sub 2} can be grown on perovskite substrates, showing potential for integration into oxide heterostructures and superlattices.

  11. How carbon nanotubes affect the cure kinetics and glass transition temperature of their epoxy composites? – A review

    Directory of Open Access Journals (Sweden)

    2009-09-01

    Full Text Available Motivated by the widespread and contradictory results regarding the glass transition temperature of carbon nanotube (CNT/epoxy composites, we reviewed and analyzed the literature results dealing with the effect of unmodified multiwall carbon nanotubes (MWNT on the cure behaviour of an epoxy resin (as a possible source of this discrepancy. The aim of this work was to clarify the effective role of unmodified multiwall carbon nanotubes on the cure kinetics and glass transition temperature (Tg of their epoxy composites. It was found that various authors reported an acceleration effect of CNT. The cure reaction was promoted in its early stage which may be due to the catalyst particles present in the CNT raw material. While SWNT may lead to a decrease of Tg due to their bundling tendency, results reported for MWNT suggested an increased or unchanged Tg of the composites. The present status of the literature does not allow to isolate the effect of MWNT on the Tg due to the lack of a study providing essential information such as CNT purity, glass transition temperature along with the corresponding cure degree.

  12. Temperature Dependence of the Raman Spectra and Phase Transition of Zirconia

    Institute of Scientific and Technical Information of China (English)

    尤静林; 蒋国昌; 杨松华; 马金昌; 徐匡迪

    2001-01-01

    A newly constructed high-temperature Raman spectrometer was used to study the temperature-dependence Raman spectra (up to 2023 K) and transformation of zirconia crystal. High-temperature Raman scattering is a useful tool in characterizing the different structures of zirconia and offers the possibility of identifying the phase transformation. It shows that monoclinic zirconia transforms to tetragonal phase at about 1440 K during the process of increasing temperature, but shows a lower transformation temperature from tetragonal to monoclinic phase at about 1323 K while the temperature decreases.

  13. A Physically Based Correlation of Irradiation-Induced Transition Temperature Shifts for RPV Steels

    Energy Technology Data Exchange (ETDEWEB)

    Eason, Ernest D. [Modeling and Computing Services, LLC; Odette, George Robert [UCSB; Nanstad, Randy K [ORNL; Yamamoto, Takuya [ORNL

    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

  14. Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling

    CERN Document Server

    Fujiwara, Masazumi; Tanaka, Akira; Toubaru, Kiyota; Zhao, Hong-Quan; Takeuchi, Shigeki; 10.1364/OE.20.019545

    2012-01-01

    We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling.

  15. Confirmation of temperature independence in the fluorescence lifetime of the 3P 0 → 3F 2 transition in praseodymium-doped fluoride glass

    Science.gov (United States)

    Nguyen, Thinh B.; Vella, Vince; Baxter, Greg W.; Collins, Stephen F.; Newman, Peter J.; MacFarlane, Douglas R.

    2006-05-01

    The dependence of the fluorescence lifetime from the 3P0 → 3F2 transition in praseodymium-doped fluoride glass as a function of dopant concentration and temperature was investigated. It was found that the fluorescence lifetime at the concentration of 7000 ppm was constant with temperature, confirming the prediction of temperature independence in the lifetime for this transition in Pr3+-doped ZBLAN glass.

  16. Winter to Spring Transition in Europe 48-45 degrees N: From Temperature Control by Advection to Control by Insolation

    Science.gov (United States)

    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.

  17. Temperature and host dependence of the transition interference between f–f and f–d transitions of Sm{sup 2+} in matlockites

    Energy Technology Data Exchange (ETDEWEB)

    Pal, Prodipta, E-mail: prodipta.pal08@gmail.com [Département de Chimie Physique,Sciences II, Université de Genève, 30, Quai Ernest-Ansermet, CH-1211 Genève 4 (Switzerland); Hagemann, Hans; Bill, Hans [Département de Chimie Physique,Sciences II, Université de Genève, 30, Quai Ernest-Ansermet, CH-1211 Genève 4 (Switzerland); Zhang, Jiahua [State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Eastern South Lake Road, Changchun 130033 (China)

    2015-05-15

    The absorption spectra of Sm{sup 2+} doped in MFX (M=Sr, Ba; X=Cl, Br) crystals were studied within the range of 20,000–35,000 cm{sup −1} as a function of temperature and host. The absorption bands observed were described with a simple model developed by Wood and Kaiser using group theory. The temperature and host dependence on the {sup 7}F{sub 0}→{sup 5}D{sub 3} Fano resonance lines were investigated. BaFCl:Sm{sup 2+} system showed a “normal” {sup 7}F{sub 0}→{sup 5}D{sub 3} transition at 4 K in spite of similar crystal structure and absorption profile with other MFX hosts. New Fano resonances were observed in the absorption spectra at higher energies (23,000–25,000 cm{sup −1}) for all MFX:Sm{sup 2+} systems at 4 K which persist up to room temperature. Preliminary energy level calculation showed that these resonance lines involve the interaction between higher excited {sup 5}L{sub J} states of 4f{sup 6} configuration and 4f{sup 5}5d{sup 1} configuration. - Highlights: • The absorption spectra of Sm{sup 2+} doped in MFX (M=Sr, Ba; X=Cl, Br) crystals within the range of as a function of temperature and host. • The absorption bands described with a simple model developed by Wood and Kaiser using group theory. • BaFCl:Sm{sup 2+} system showed a “normal” {sup 7}F{sub 0}→{sup 5}D{sub 3} transition at 4 K in spite of similar crystal structure and absorption profile with other MFX hosts. • New Fano resonances observed in the absorption spectra at higher energies (23,000–25,000 cm{sup −1}) for all MFX:Sm{sup 2+} systems at 4 K which persist up to room temperature.

  18. Effect of heat treatment on microstructure and fracture toughness of a V-5Cr-5Ti alloy

    Energy Technology Data Exchange (ETDEWEB)

    Li, H.; Hamilton, M.L.; Jones, R.H. [Pacific Northwest Lab., Richland, WA (United States)

    1995-04-01

    The purpose of this research is to investigate the effect of heat treatment on microstructure and fracture toughness in the range of {minus}50 to 100{degrees}C for a V-5Cr-5Ti alloy. Fracture toughness and impact tests were performed on a V-5Cr-5Ti alloy. Specimens annealed at 1125{degree}C for 1 h and furnace cooled in a vacuum of 1.33 x 10{sup {minus}5} Pa were brittle at room temperature and experienced a mixture of intergranular and cleavage fracture. The ductile to brittle transition temperature was estimated to be about 20{degree}C. When some specimens were given an additional annealing at 890{degree}C for 24 h, they became very ductile at room temperature and fractured by microvoid coalescence.

  19. Temperature Induced Solubility Transitions of Various Poly(2-oxazolines in Ethanol-Water Solvent Mixtures

    Directory of Open Access Journals (Sweden)

    Hanneke M. L. Lambermont-Thijs

    2010-08-01

    Full Text Available The solution behavior of a series of poly(2-oxazolines with different side chains, namely methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, phenyl and benzyl, are reported in ethanol-water solvent mixtures based on turbidimetry investigations. The LCST transitions of poly(2-oxazolines with propyl side chains and the UCST transitions of the poly(2-oxazolines with more hydrophobic side chains are discussed in relation to the ethanol-water solvent composition and structure. The poly(2-alkyl-2-oxazolines with side chains longer than propyl only dissolved during the first heating run, which is discussed and correlated to the melting transition of the polymers.

  20. Zero-temperature magnetic transition in an easy-axis Kondo lattice model.

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao

    2007-11-30

    We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.

  1. Towards the N_f=2 deconfinement transition temperature with O(a) improved Wilson fermions

    CERN Document Server

    Brandt, Bastian B; Wittig, Hartmut; Zeidlewicz, Lars

    2010-01-01

    A lot of effort in lattice simulations over the last years has been devoted to studies of the QCD deconfinement transition. Most state-of-the-art simulations use rooted staggered fermions, while Wilson fermions are affected by large systematic uncertainties, such as coarse lattices or heavy sea quarks. Here we report on an ongoing study of the transition, using two degenerate flavours of nonperturbatively $\\Ord(a)$ improved Wilson fermions. We start with $N_{t}=12$ and 16 lattices and pion masses of 600 to 450 MeV, aiming at chiral and continuum limits with light quarks.

  2. Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao

    2007-11-01

    We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.

  3. Radiation and annealing response of WWER 440 beltline welding seams

    Science.gov (United States)

    Viehrig, Hans-Werner; Houska, Mario; Altstadt, Eberhard

    2015-01-01

    The focus of this paper is on the irradiation response and the effect of thermal annealing in weld materials extracted from decommissioned WWER 440 reactor pressure vessels of the nuclear power plant Greifswald. The characterisation is based on the measurement of the hardness, the yield stress, the Master Curve reference temperature, T0, and the Charpy-V transition temperature through the thickness of multi-layer beltline welding seams in the irradiated and the thermally annealed condition. Additionally, the weld bead structure was characterised by light microscopic studies. We observed a large variation in the through thickness T0 values in the irradiated as well as in thermally annealed condition. The T0 values measured with the T-S-oriented Charpy size SE(B) specimens cut from different thickness locations of the multilayer welding seams strongly depend on the intrinsic weld bead structure along the crack tip. The Master Curve, T0, and Charpy-V, TT47J, based ductile-to-brittle transition temperature progressions through the thickness of the multi-layer welding seam do not correspond to the forecast according to the Russian code. In general, the fracture toughness values at cleavage failure, KJc, measured on SE(B) specimens from the irradiated and large-scale thermally annealed beltline welding seams follow the Master Curve description, but more than the expected number lie outside the curves for 2% and 98% fracture probability. In this case the test standard ASTM E1921 indicates the investigated multi-layer weld metal as not uniform. The multi modal Master Curve based approach describes the temperature dependence of the specimen size adjusted KJc-1T values well. Thermal annealing at 475 °C for 152 h results in the expected decrease of the hardness and tensile strength and the shift of Master Curve and Charpy-V based ductile-to-brittle transition temperatures to lower values.

  4. Intermediate-temperature Polymorphic Phase Transition in KH2PO4: A Synchrotron X-ray Diffraction Study

    Energy Technology Data Exchange (ETDEWEB)

    Botez, C.; Carbajal, D; Adiraju, V; Tackett, R; Chianelli, R

    2010-01-01

    We have used synchrotron X-ray diffraction to investigate the structural and chemical changes undergone by polycrystalline KH{sub 2}PO{sub 4} (KDP) upon heating within the 30-250 C temperature interval. Our data show evidence of a polymorphic transition at T {approx} 190 C from the room-temperature tetragonal KDP phase to a new intermediate-temperature monoclinic KDP modification (spacegroup P2{sub 1}/m and lattice parameters a = 7.590, b = 6.209, c = 4.530 {angstrom}, and {beta} = 107.36{sup o}). The monoclinic RDP polymorph remains stable upon further heating to 235 C, and is isomorphic to its RbH{sub 2}PO{sub 4} and CsH{sub 2}PO{sub 4} counterparts.

  5. Investigation of Regularities of Heat and Mass Transfer and Phase Transitions during Water Droplets Motion through High-Temperature Gases

    Directory of Open Access Journals (Sweden)

    Roman S. Volkov

    2014-06-01

    Full Text Available The macroscopic regularities of heat and mass transfer and phase transitions during water droplets motion through high-temperature (more than 1000 K gases have been investigated numerically and experimentally. Water droplet evaporation rates have been established. Gas and water vapors concentrations and also temperature values of gas-vapor mixture in small neighborhood and water droplet trace have been singled out. Possible mechanisms of droplet coagulation in high-temperature gas area have been determined. Experiments have been carried out with the optical methods of two-phase gas-vapor-droplet mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging” usage to assess the adequateness of developed heat and mass transfer models and the results of numerical investigations. The good agreement of numerical and experimental investigation results due to integral characteristics of water droplet evaporation has been received.

  6. Temperature-Dependent Energy Gap Shift and Thermally Activated Transition in Multilayer CdTe/ZnTe Quantum Dots.

    Science.gov (United States)

    Man, Minh Tan; Lee, Hong Seok

    2015-10-01

    We investigated the influence of growth conditions on carrier dynamics in multilayer CdTe/ZnTe quantum dots (QDs) by monitoring the temperature dependence of the photoluminescence emission energy. The results were analyzed using the empirical Varshni and O'Donnell relations for temperature variation of the energy gap shift. Best fit values showed that the thermally activated transition between two different states occurs due to band low-temperature quenching with values separated by 5.0-6.5 meV. The addition of stack periods in multilayer CdTe/ZnTe QDs plays an important role in the energy gap shift, where the exciton binding energy is enhanced, and, conversely, the exciton-phonon coupling strength is suppressed with an average energy of 19.3-19.8 meV.

  7. Effect of A-site cation substitution on magnetic transition temperature of (LaCa) MnO3

    Institute of Scientific and Technical Information of China (English)

    李可斌; 王守国; 程荣胜; 李西军; 侯登录; 聂向富; 张裕恒

    1999-01-01

    The ferromagnetic transition temperatures have been measured on two bathes of perovskite manganese oxides such as (La1-xRx)2/3Ca1/3MnO3(R=Ce, Pr, Nd, etc.) and La2/3(Ca1-yCd)y)1/3MnO3. It is found that the (La1-xRx)2/3Ca1/3MnO3 samples have obviously different Curie temperature TC although their (the average A-site cation radius) are almost identical, and the TC in the system of (La1-xRx)2/3Ca1/3MnO3 compounds increases with increasing y although decreases slightly. It is suggested that the Curie temperature should be influenced by the average local A-site magnetic moment in the ferromagnetic perovskite manganite system.

  8. Standard Guide for Predicting Radiation-Induced Transition Temperature Shift in Reactor Vessel Materials, E706 (IIF)

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2002-01-01

    1.1 This guide presents a method for predicting reference transition temperature adjustments for irradiated light-water cooled power reactor pressure vessel materials based on Charpy V-notch 30-ftlbf (41-J) data. Radiation damage calculative procedures have been developed from a statistical analysis of an irradiated material database that was available as of May 2000. The embrittlement correlation used in this guide was developed using the following variables: copper and nickel contents, irradiation temperature, and neutron fluence. The form of the model was based on current understanding for two mechanisms of embrittlement: stable matrix damage (SMD) and copper-rich precipitation (CRP); saturation of copper effects (for different weld materials) was included. This guide is applicable for the following specific materials, copper, nickel, and phosphorus contents, range of irradiation temperature, and neutron fluence based on the overall database: 1.1.1 MaterialsA 533 Type B Class 1 and 2, A302 Grade B, A302 G...

  9. Effect of heat-treatment on phase transition temperatures of a superelastic NiTi alloy for medical use

    Energy Technology Data Exchange (ETDEWEB)

    Yeung, K.W.K.; Cheung, K.M.C.; Lu, W.W.; Luk, K.D.K. [Univ. of Hong Kong (China). Dept. of Orthopaedic Surgery; Chung, C.Y. [City Univ. of Hong Kong, Kowloon (China). Dept. of Physics and Materials Science

    2002-07-01

    Surgical correction of scoliosis typically uses stainless steel or titanium alloy spinal instrumentation to straighten the scoliotic spine by 70% only. Our aim is to develop a method to overcome this by using an implantable superelastic (SE) nickel-titanium (NiTi) alloy rod, which will impose a continuous gradual correction force to the spine after the surgery so as to achieve a superior correction. More than 75 specimens made of a Ti-50.0 at% Ni alloy were treated by different heat treatment routes. The Austenitic transition temperature of the NiTi alloy can be adjusted to be available at 37.5 C by altering the heat treatment parameters: time and temperature of heat treatment. The experimental results showed that the heat treatment temperature should set between 400-500 C and the heat treatment time should be less than 60 minutes for the alloy. (orig.)

  10. Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure.

    Science.gov (United States)

    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.

  11. Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure

    Science.gov (United States)

    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

  12. Phase coexistence and pressure-temperature phase evolution of VO2(A ) nanorods near the semiconductor-semiconductor transition

    Science.gov (United States)

    Samanta, Sudeshna; Li, Quanjun; Cheng, Benyuan; Huang, Yanwei; Pei, Cuiying; Wang, Qinglin; Ma, Yanzhang; Wang, Lin

    2017-01-01

    A comprehensive understanding of the physical origins of the phase transition behaviors of transition metal oxides is still complex due to the interplay among competing interactions of comparable strengths tuning their nature. Widespread interest in such phase transitions has motivated explorations of nanocrystalline vanadium dioxide (VO2) in various forms and a long-running debate persists over the roles played by electron-electron correlation with lattice distortion. External stimuli like pressure and temperature have strong effects on the appearance, stability, and spacial distribution of the high-resistive (HR) and low-resistive (LR) phases accompanying their structural modification. Our comprehensive experiments establish the pressure-induced and thermally driven evolution of phase coexistence in VO2(A ) nanorods. Our experimental evidence supports coexisting HR and LR phases, where compression suppressed coexistence at ˜7 GPa, followed by a semiconductor-semiconductor transition at around ˜10 GPa with the absence of pressure-induced metallization. X-ray diffraction revealed lattice distortion with local microscopic strain inhomogeneity in the nanorods, without any discontinuity in the pressure-volume data. We further investigated the vibrational modes and relaxations of the samples related to their thermal expansions. We also found that the pressure-dependent hierarchy of microstructural densification contributed significantly to the resulting transport properties.

  13. Towards an improved calorimetric methodology for glass transition temperature determination in amorphous sugars

    National Research Council Canada - National Science Library

    Saavedra-Leos, M.Z; Alvarez-Salas, C; Esneider-Alcalá, M.A; Toxqui-Terán, A; Pérez-García, S.A; Ruiz-Cabrera, M.A

    2012-01-01

    .... Journal of Agricultural and Food Chemistry, 56, 5138-5147). Thermogravimetric analysis with simultaneous DSC was required to characterize the melting and thermal degradation temperatures of sugars...

  14. Insights into glass transition and relaxation behavior using temperature-modulated differential scanning calorimetry

    DEFF Research Database (Denmark)

    Guo, Xiaoju; Mauro, J.C.; Allan, D.C.;

    Temperature-modulated differential scanning calorimetry (TMDSC) is based on conventional DSC but with a sinusoidally modulated temperature path. Our simulations of TMDSC signals prove that the frequency correction of non-reversing heat flow can give a master curve within a certain range of freque......Temperature-modulated differential scanning calorimetry (TMDSC) is based on conventional DSC but with a sinusoidally modulated temperature path. Our simulations of TMDSC signals prove that the frequency correction of non-reversing heat flow can give a master curve within a certain range...

  15. Temperature-induced reversible self-assembly of diphenylalanine peptide and the structural transition from organogel to crystalline nanowires.

    Science.gov (United States)

    Huang, Renliang; Wang, Yuefei; Qi, Wei; Su, Rongxin; He, Zhimin

    2014-01-01

    Controlling the self-assembly of diphenylalanine peptide (FF) into various nanoarchitectures has received great amounts of attention in recent years. Here, we report the temperature-induced reversible self-assembly of diphenylalanine peptide to microtubes, nanowires, or organogel in different solvents. We also find that the organogel in isopropanol transforms into crystalline flakes or nanowires when the temperature increases. The reversible self-assembly in polar solvents may be mainly controlled by electronic and aromatic interactions between the FF molecules themselves, which is associated with the dissociation equilibrium and significantly influenced by temperature. We found that the organogel in the isopropanol solvent made a unique transition to crystalline structures, a process that is driven by temperature and may be kinetically controlled. During the heating-cooling process, FF preferentially self-assembles to metastable nanofibers and organogel. They further transform to thermodynamically stable crystal structures via molecular rearrangement after introducing an external energy, such as the increasing temperature used in this study. The strategy demonstrated in this study provides an efficient way to controllably fabricate smart, temperature-responsive peptide nanomaterials and enriches the understanding of the growth mechanism of diphenylalanine peptide nanostructures.

  16. Experimental determination of the peritectic transition temperature of MgB{sub 2} in the Mg–B phase diagram

    Energy Technology Data Exchange (ETDEWEB)

    Bohnenstiehl, S.D. [Department of Materials Science and Engineering, The Ohio State University, 143 Fontana Laboratories, 116 West 19th Avenue, Columbus, OH 43210 (United States); Susner, M.A., E-mail: susner.1@osu.edu [Department of Materials Science and Engineering, The Ohio State University, 143 Fontana Laboratories, 116 West 19th Avenue, Columbus, OH 43210 (United States); Dregia, S.A.; Sumption, M.D. [Department of Materials Science and Engineering, The Ohio State University, 143 Fontana Laboratories, 116 West 19th Avenue, Columbus, OH 43210 (United States); Donovan, J. [Center for Advanced Materials Characterization in Oregon, University of Oregon, 1443 East 13th Avenue, Eugene, OR 97403 (United States); Collings, E.W. [Department of Materials Science and Engineering, The Ohio State University, 143 Fontana Laboratories, 116 West 19th Avenue, Columbus, OH 43210 (United States)

    2014-01-20

    Highlights: • We have created a high pressure, high temperature material synthesis apparatus. • This apparatus is programmable and capable of various thermal analysis procedures. • Using our apparatus we have established the peritectic transition temperature of MgB{sub 2}. • This temperature is 300 °C lower than established values for the same pressure. • We have shown that this discrepancy is likely the result of impurities such as C. - Abstract: We have studied thermodynamic phase stability in the Mg–B system through use of a high-pressure, high-temperature apparatus consisting of a large pressure vessel and an RF induction heater. The incongruent melting temperature for MgB{sub 2} was found to be ∼1450 °C at 10 MPa using thermal analysis data applied to both MgB{sub 2} powder samples and Mg/B mixtures. The experimental temperature is ∼300 °C lower than temperatures shown in calculated phase diagrams of the Mg–B system at the same pressure and the discrepancy demonstrates the need for further experimental investigations of phase stability in binary Mg–B and ternary Mg–B–X systems. In this study C (as an impurity in boron) was found to have a large effect on the peritectic temperature, with a relatively small (0.7 wt% C) impurity concentration resulting in a ∼40 °C elevation of the peritectic temperature. Along with morphological characterization, XRD and EPMA analyses were used to identify phases and confirm the peritectic transformation in the Mg–B phase diagram.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Popova, V A; Surovtsev, N V

    2014-09-01

    The temperature dependences of α relaxation time τ(α)(T) of three glass-forming liquids (salol, o-terphenyl, and α-picoline) were investigated by a depolarized light scattering technique. A detailed description of τ(α)(T) near T(A), the temperature of the transition from the Arrhenius law at high temperatures to a non-Arrhenius behavior of τ(α)(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 τ(α)(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)], 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)], where the activation energy includes the term depending exponentially on temperature.

  19. Effect of deformation frequency on temperature and stress oscillations in cyclic phase transition of NiTi shape memory alloy

    Science.gov (United States)

    Yin, Hao; He, Yongjun; Sun, Qingping

    2014-07-01

    Distinctive temperature and stress oscillations can be observed in superelastic shape memory alloys (SMAs) when they subject to displacement-controlled cyclic phase transition. In this paper, we examine the effect of the deformation frequency on the thermal and mechanical responses of the polycrystalline superelastic NiTi rods under stress-induced cyclic phase transition. By synchronized measurement of the evolutions in overall temperature and stress-strain curve over the frequency range of 0.0004-1 Hz (corresponding average strain rate range of 4.8×10-5/s-1.2×10-1/s) in stagnant air, it was found that both the temperature evolution and the stress-strain curve vary significantly with the frequency and the number of cycles. For each frequency, steady-state cyclic thermal and mechanical responses of the specimen were reached after a transient stage, exhibiting stabilization. In the steady-state, the average temperature oscillated around a mean temperature plateau which increased monotonically with the frequency and rose rapidly in the high frequency range due to the rapid accumulation of hysteresis heat. The oscillation was mainly caused by the release and absorption of latent heat and increased with the frequency, eventually reaching a saturation value. The variations in the stress responses followed similar frequency dependence as the temperature. The steady-state stress-strain hysteresis loop area, as a measure of the material's damping capacity, first increased then decreased with the frequency in a non-monotonic manner. The experimental data were analyzed and discussed based on the simplified lumped heat transfer analysis and the Clausius-Clapeyron relationship, incorporating the inherent thermomechanical coupling in the material's response. We found that, for given material's properties and specimen geometries, all such frequency-dependent variations in temperature, stress and damping capacity were essentially determined by the competition between the time

  20. On the Frequency Correction in Temperature-Modulated Differential Scanning Calorimetry of Glass Transition

    DEFF Research Database (Denmark)

    Guo, Xiaoju; Mauro, J.C.; Allan, D.C.;

    2012-01-01

    Temperature-modulated differential scanning calorimetry (TMDSC) is based on conventional DSC but with a sinusoidally modulated temperature path. Simulations of TMDSC signals were performed for Corning EAGLE XG® glass over a wide range of modulation frequencies. Our results reveal that the frequen...

  1. Insights into glass transition and relaxation behavior using temperature-modulated differential scanning calorimetry

    DEFF Research Database (Denmark)

    Guo, Xiaoju; Mauro, J.C.; Allan, D.C.

    Temperature-modulated differential scanning calorimetry (TMDSC) is based on conventional DSC but with a sinusoidally modulated temperature path. Our simulations of TMDSC signals prove that the frequency correction of non-reversing heat flow can give a master curve within a certain range...

  2. Anomalous pressure dependence of the superconducting transition temperature of beta-pyrochlore AOs2O6 oxides.

    Science.gov (United States)

    Muramatsu, T; Takeshita, N; Terakura, C; Takagi, H; Tokura, Y; Yonezawa, S; Muraoka, Y; Hiroi, Z

    2005-10-14

    High-pressure effects on the superconducting transitions of beta-pyrochlore oxide superconductors AOs(2)O(6) (A = Cs,Rb,K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature T(c) first increases with increasing pressure in every compound and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa), and 10 K (0.6 GPa) for A = Cs, Rb, and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the coefficient A of the T(2) term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in T(c).

  3. Strain-induced high ferromagnetic transition temperature of MnAs epilayer grown on GaAs (110

    Directory of Open Access Journals (Sweden)

    Pan Guoqiang

    2011-01-01

    Full Text Available Abstract MnAs films are grown on GaAs surfaces by molecular beam epitaxy. Specular and grazing incidence X-ray diffractions are used to study the influence of different strain states of MnAs/GaAs (110 and MnAs/GaAs (001 on the first-order magnetostructural phase transition. It comes out that the first-order magnetostructural phase transition temperature T t, at which the remnant magnetization becomes zero, is strongly affected by the strain constraint from different oriented GaAs substrates. Our results show an elevated T t of 350 K for MnAs films grown on GaAs (110 surface, which is attributed to the effect of strain constraint from different directions. PACS: 68.35.Rh, 61.50.Ks, 81.15.Hi, 07.85.Qe

  4. Transition duct system with metal liners for delivering hot-temperature gases in a combustion turbine engine

    Energy Technology Data Exchange (ETDEWEB)

    Wiebe, David J.

    2017-04-11

    A transition duct system (10) for delivering hot-temperature gases from a plurality of combustors in a combustion turbine engine is provided. The system includes an exit piece (16) for each combustor. The exit piece may include a straight path segment (26) and an arcuate connecting segment (36). A respective straight metal liner (92) and an arcuate metal liner (94) may be each inwardly disposed onto a metal outer shell (38) along the straight path segment and the arcuate connecting segment (36) of the exit piece. Structural arrangements are provided to securely attach the respective liners in the presence of substantial flow path pressurization. Cost-effective serviceability of the transition duct systems is realizable since the liners can be readily removed and replaced as needed.

  5. Transition duct system with straight ceramic liner for delivering hot-temperature gases in a combustion turbine engine

    Energy Technology Data Exchange (ETDEWEB)

    Wiebe, David J.

    2017-05-16

    A transition duct system (10) for delivering hot-temperature gases from a plurality of combustors in a combustion turbine engine is provided. The system includes an exit piece (16) for each combustor. The exit piece may include a straight path segment (26) for receiving a gas flow from a respective combustor. A straight ceramic liner (40) may be inwardly disposed onto a metal outer shell (38) along the straight path segment of the exit piece. Structural arrangements are provided to securely attach the ceramic liner in the presence of substantial flow path pressurization. Cost-effective serviceability of the transition duct systems is realizable since the liner can be readily removed and replaced as needed.

  6. The effect of water temperature on food transit time and digestive enzymes activity in Caspian kutum (Rutilus kutum larvae

    Directory of Open Access Journals (Sweden)

    Nahid Ghysvandi

    2014-07-01

    Full Text Available The present study investigates the effects of water temperature on digestive enzymes activity and food transit time in Caspian kutum (Rutilus kutum larvae. Caspian kutum larvae (532 ± 0.05 and 543 ± 0.02 mg were divided into two groups with three replicates and reared at different water temperature i.e. 25.6 ± 0.4°C (T1 and 18.4 ± 0.1°C (T2. At the end of the experiment, sampling of intestine was performed at 0, 1, 3, 5, 8, 16, 24 and 30 h after feeding from each treatment. In T2, food was observed until 24 h after feeding and the intestine was empty 29 h after feeding, while in T1 19 h after feeding the intestine was empty. Digestive enzymes activities were higher in T2 treatment. The peaks of trypsin and alkaline phosphatase enzymes activity were found 8 h after feeding in T1, while occurred 16 h after feeding in T2. The highest chymotrypsin and alpha-amylase enzymes activity were observed 5 and 8h after feeding in T1 and T2, respectively. These results confirmed remarkable effects of temperature on food transit time and digestive enzymes activity of Caspian kutum.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    Science.gov (United States)

    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.

  9. Statistical analysis using the Bayesian nonparametric method for irradiation embrittlement of reactor pressure vessels

    Science.gov (United States)

    Takamizawa, Hisashi; Itoh, Hiroto; Nishiyama, Yutaka

    2016-10-01

    In order to understand neutron irradiation embrittlement in high fluence regions, statistical analysis using the Bayesian nonparametric (BNP) method was performed for the Japanese surveillance and material test reactor irradiation database. The BNP method is essentially expressed as an infinite summation of normal distributions, with input data being subdivided into clusters with identical statistical parameters, such as mean and standard deviation, for each cluster to estimate shifts in ductile-to-brittle transition temperature (DBTT). The clusters typically depend on chemical compositions, irradiation conditions, and the irradiation embrittlement. Specific variables contributing to the irradiation embrittlement include the content of Cu, Ni, P, Si, and Mn in the pressure vessel steels, neutron flux, neutron fluence, and irradiation temperatures. It was found that the measured shifts of DBTT correlated well with the calculated ones. Data associated with the same materials were subdivided into the same clusters even if neutron fluences were increased.

  10. Mechanisms and modeling of cleavage fracture in simulated heat-affected zone microstructures of a high-strength low alloy steel

    Science.gov (United States)

    Lambert-Perlade, A.; Sturel, T.; Gourgues, A. F.; Besson, J.; Pineau, A.

    2004-03-01

    The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of “crystallographic” bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the “Master-curve” (MC) approach, the Beremin model, and a “double-barrier” (DB) model) are applied to account for the ductile-to-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.

  11. Influence of the crack-tip hydride concentration on the fracture toughness of Zircaloy-4

    Energy Technology Data Exchange (ETDEWEB)

    Bertolino, G. [LMS, CNRS UMR7649, Ecole Polytechnique, 91128 Palaiseau cedex (France)]. E-mail: bertolin@cab.cnea.gov.ar; Perez Ipina, J. [CONICET (Argentina); Universidad Nacional del Comahue, 8300 Neuquen (Argentina); Meyer, G. [Centro Atomico Bariloche, CNEA, 8400 Bariloche (Argentina); CONICET (Argentina)

    2006-01-01

    The influence of a hydrogen concentration gradient at the crack-tip and hydride platelet orientation on the fracture toughness, fracture mode and micromechanisms of a Zircaloy-4 commercial alloy was studied. Fracture toughness was measured on CT specimens and the analysis was performed in terms of J-integral resistance curves at temperatures ranging from 293 to 473 K. Fracture toughness results of specimens containing higher hydrides concentration near the crack-tip region, preferentially orientated in the crack plane, were compared to those obtained from specimens with a homogeneous hydrogen distribution and different platelet orientation; specimens were obtained by charging them in loaded and unloaded condition, respectively. Changes on both macroscopic and microscopic fracture behaviour were observed at temperatures ranging from 293 to 343 K, and the results show the relevance of both hydride concentration and platelet orientation. The existence of a ductile-to-brittle transition is discussed at the light of these new results.

  12. Irradiation embrittlement of neutron-irradiated ferritic steel

    Science.gov (United States)

    Kayano, H.; Narui, M.; Ohta, S.; Morozumi, S.

    1985-08-01

    In this study three kinds of Fe-Cr ferritic steels were examined by the instrumented Charpy test and tensile test before and after JMTR irradiation ( 2.2×10 23 f.n./m 2). In the unirradiated samples, 100%-martensite 5Cr-2Mo steel showed the highest adsorbed energy and the highest toughness at low temperatures, follewed by the 9Cr-2Mo steel, and the 20%-martensite 5Cr-2Mo steel showed the third highest toughness. In the irradiated samples, however, thoughness was low as a whole, especially in 20%-martensite 5Cr-2Mo steel. It was clarified that 100%-martensite 5Cr-2Mo steel had the lowest Ductile-to-Brittle Transition Temperature (DBTT) and the highest fracture toughness, and that its DBTT and fracture toughness changed a little upon irradiation, showing excellent irradiation characteristics. The general equations were considered for correlation among strength, ductillity, DBTT and fracture toughness ( J value)

  13. Temperature-induced transitions in disordered proteins probed by NMR spectroscopy

    DEFF Research Database (Denmark)

    Kjærgaard, Magnus; Poulsen, Flemming Martin; Kragelund, Birthe Brandt

    2012-01-01

    Intrinsically disordered proteins are abundant in nature and perform many important physiological functions. Multidimensional NMR spectroscopy has been crucial for the understanding of the conformational properties of disordered proteins and is increasingly used to probe their conformational...... ensembles. Compared to folded proteins, disordered proteins are more malleable and more easily perturbed by environmental factors. Accordingly, the experimental conditions and especially the temperature modify the structural and functional properties of disordered proteins. NMR spectroscopy allows analysis...... of temperature-induced structural changes at residue resolution using secondary chemical shift analysis, paramagnetic relaxation enhancement, and residual dipolar couplings. This chapter discusses practical aspects of NMR studies of temperature-induced structural changes in disordered proteins....

  14. Particle Density in Zero Temperature Symmetry Restoring Phase Transitions in Four-Fermion Interaction Models

    Institute of Scientific and Technical Information of China (English)

    ZHOU Bang-Rong

    2004-01-01

    By means of critical behaviors of the dynamical fermion mass in four-fermion interaction models, we show by explicit calculations that when T = 0 the particle density will have a discontinuous jumping across the critical chemical potential μc in 2D and 3D Gross-Neveu (GN) model and these physically explain the first-order feature of the corresponding symmetry restoring phase transitions. For the second-order phase transitions in the 3D GN model when T → 0 and in 4D Nambu-Jona-Lasinio (NJL) model when T = 0, it is proven that the particle density itself will be continuous across μc but its derivative over the chemical potential μ will have a discontinuous jumping. The results give a physical explanation of implications of the tricritical point (T, μ) = (0,μc) in the 3D GN model. The discussions also show effectiveness of the critical analysis approach of phase transitions.

  15. Temperature-Induced Phase Transition of In2O3 from a Rhombohedral Structure to a Body-Centered Cubic Structure

    Institute of Scientific and Technical Information of China (English)

    YANG Lin-Hong; DONG Hong-Xing; SUN Zheng; SUN Liao-Xin; SHEN Xue-Chu; CHEN Zhang-Hai

    2011-01-01

    @@ We report an experimental study on the temperature-induced phase transition of three-dimensional nanosheetbased flower-like microspheres(NBFMs)of In2O3.Using InOOH as precursor, rhombohedral-In2O3 NBFMs are fabricated.Temperature-induced phase transition of In2O3 NBFMs from a rhombohedral(rh) structure to a body-centered cubic(bcc) structure is examined by Raman spectroscopy and x-ray diffraction.The critical phase transition temperature is found to be about 500℃.Photoluminescence(PL)spectra of In2O3 are measured before annealing and after annealing at different temperatures.The PL spectral results provide further evidence for the phase transition, confirming the fabrication of bcc-In2O3 NBFMs via a simple annealing method.

  16. Unified picture of the doping dependence of superconducting transition temperatures in alkali metal/ammonia intercalated FeSe

    OpenAIRE

    Guterding, Daniel; Jeschke, Harald O.; Hirschfeld, P. J.; Valenti, Roser

    2014-01-01

    In the recently synthesized Li$_x$(NH$_2$)$_y$(NH$_3$)$_z$Fe$_2$Se$_2$ family of iron chalcogenides a molecular spacer consisting of lithium ions, lithium amide and ammonia separates layers of FeSe. It has been shown that upon variation of the chemical composition of the spacer layer, superconducting transition temperatures can reach $T_c\\sim 44 \\mathrm{K}$, but the relative importance of the layer separation and effective doping to the $T_c$ enhancement is currently unclear. Using state of t...

  17. Variation in superconducting transition temperature due to tetragonal domains in two-dimensionally doped SrTiO3

    Science.gov (United States)

    Noad, Hilary; Spanton, Eric M.; Nowack, Katja C.; Inoue, Hisashi; Kim, Minu; Merz, Tyler A.; Bell, Christopher; Hikita, Yasuyuki; Xu, Ruqing; Liu, Wenjun; Vailionis, Arturas; Hwang, Harold Y.; Moler, Kathryn A.

    2016-11-01

    Strontium titanate is a low-temperature, non-Bardeen-Cooper-Schrieffer superconductor that superconducts to carrier concentrations lower than in any other system and exhibits avoided ferroelectricity at low temperatures. Neither the mechanism of superconductivity in strontium titanate nor the importance of the structure and dielectric properties for the superconductivity are well understood. We studied the effects of twin structure on superconductivity in a 5.5-nm-thick layer of niobium-doped SrTiO3 embedded in undoped SrTiO3. We used a scanning superconducting quantum interference device susceptometer to image the local diamagnetic response of the sample as a function of temperature. We observed regions that exhibited a superconducting transition temperature Tc≳ 10 % higher than the temperature at which the sample was fully superconducting. The pattern of these regions varied spatially in a manner characteristic of structural twin domains. Some regions are too wide to originate on twin boundaries; therefore, we propose that the orientation of the tetragonal unit cell with respect to the doped plane affects Tc. Our results suggest that the anisotropic dielectric properties of SrTiO3 are important for its superconductivity and need to be considered in any theory of the mechanism of the superconductivity.

  18. Glass Transition Temperature Measurement for Undercured Cyanate Ester Networks: Challenges, Tips, and Tricks (Briefing Charts)

    Science.gov (United States)

    2014-01-29

    temperature of a thermoplastic such as PVC exhibits a nearly fixed value regardless of processing-induces changes to the system • In contrast, the...Temp. (°C) A. R. Berens and I. M. Hodges, Macromolecules 1982, 15, 756 (digitized data from Fig. 2) Free-cooled PVC Bisphenol A dicyanate ester...Wet TMA Plasticization and degradation drop TG to near / below cure temperature Carbamate formation dilutes remaining –OCN groups, slows down in-situ

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

    Energy Technology Data Exchange (ETDEWEB)

    Maziarz, W. [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 W. Reymonta Str., 30-059 Kraków (Poland); Czaja, P., E-mail: p.czaja@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 W. Reymonta Str., 30-059 Kraków (Poland); Szczerba, M.J. [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 W. Reymonta Str., 30-059 Kraków (Poland); Przewoźnik, J.; Kapusta, C. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Department of Solid State Physics, Al. Mickiewicza 30, 30-059 Krakow (Poland); Żywczak, A.; Stobiecki, T. [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); Cesari, E. [Department de Fisica, Universitat de Illes Balears, Ctra. de Valldemossa, km 7.5, Palma de Mallorca E-07071 (Spain); Dutkiewicz, J. [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 W. Reymonta Str., 30-059 Kraków (Poland)

    2013-12-15

    Martensitic and magnetic transformations in Ni{sub 48}Mn{sub 39.5}Sn{sub 12.5−x}Al{sub x} (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 (ΔT{sub MT}=49 K; ΔT{sub RMT}=43 K), whereas the Curie temperature of martensite T{sub C}{sup M} decreases (ΔT=36 K) and the Curie temperature of austenite T{sub C}{sup A} remains practically insensitive to Al introduction. This then allows to tune T{sub C}{sup A} and the MT temperature leading to their coincidence at ambient temperature. The austenite phase with the L2{sub 1} 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{sup ¯}) stacking sequence in Al free samples and the 4O martensite with the stacking periodicity (31{sup ¯}) 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 T{sub C}{sup M} 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. - Highlights: • Al for Sn substituted Ni–Mn–Sn based ferromagnetic Heusler alloys were produced by melt spinning. • Martensitic, reverse martensitic and intermartensitic transformations were observed, their temperatures and magnitude changed with Al substitution. • Different types of martensite structures were identified depending on Al

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

    Science.gov (United States)

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

    Science.gov (United States)

    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.

  2. Temperature induced stress phase transition in CdTe quantum dots observed by dielectric constant and thermal diffusivity measurements

    Science.gov (United States)

    Moreira, S. G. C.; da Silva, E. C.; Mansanares, A. M.; Barbosa, L. C.; Cesar, C. L.

    2007-07-01

    The authors measured the dielectric constant by capacitance method and the thermal diffusivity by thermal lens technique in the temperature range from 20to300K for CdTe quantum dot doped borosilicate glass samples. Results show a huge difference between the thermal behavior of the pure glass matrix, without quantum dots, and of the doped glass, especially around 90 and 250K. The authors attributed this difference to the phase transition experienced by the CdTe nanocrystals due to the high pressure exerted by the glass matrix over the CdTe quantum dots. The temperature induced stress is caused by the thermal expansion coefficient mismatch between the quantum dot and the glass matrix.

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

    Energy Technology Data Exchange (ETDEWEB)

    He, Wei, E-mail: hewei@aphy.iphy.ac.cn; Liu, Hao-Liang; Cai, Jian-Wang; Cheng, Zhao-Hua, E-mail: zhcheng@aphy.iphy.ac.cn [State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Wu, Hong-Ye [Department of Physics, Baotou Teachers College, Baotou 014030 (China)

    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.

  4. Dieterici 气体对比态形式的转换温度%Transition Temperature Contrast State Dieterici Das

    Institute of Scientific and Technical Information of China (English)

    莫小梅; 赵金和; 黎远成

    2014-01-01

    The use of contrast - state forms of Dieterici state equation,analyze and export Joule - Thomson effect comparison and contrast transition temperature pressure relationship. And draw Dieterici equation by Matlab software conversion curves at different temperatures in contrast to the index,its comparative analysis and comparison of the conversion curve Miller equation.%运用对比态形式的 Dieterici 状态方程,分析和导出焦-汤效应的对比转换温度与对比压强关系式,并且通过 Matlab 软件绘制 Dieterici 方程在不同温度指数的对比转换曲线,将其与 Miller 方程的对比转换曲线进行比较分析。

  5. influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals.

    Science.gov (United States)

    Wunschel, Markus; Dinnebier, Robert E; Carlson, Stefan; Bernatowicz, Piotr; van Smaalen, Sander

    2003-02-01

    The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH(3))(3)](1)[Si(CH(3))(3)](3) (Bu1), and di-tert-butyl-bis(trimethylsilyl)silane, Si[C(CH(3))(3)](2)[Si(CH(3))(3)](2) (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm3m symmetry (Z = 4) with a = 13.2645 (2) A, V = 2333.87 (4) A(3) for Bu1 and a = 12.9673 (1) A, V = 2180.46 (3) A(3) for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at temperatures T(c) = 230 (5) K (Bu1) and T(c) = 250 (5) K (Bu2) into monoclinic structures with space group P2(1)/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) A, gamma = 109.477 (4) degrees, V = 4172.7 (8) A(3) and Z = 8 for Bu1and a = 17.0089 (9), b = 15.3159 (8), c = 15.9325 (8) A, gamma = 110.343 (3) degrees, V = 3891.7 (5) A(3) and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13-0.28 GPa for Bu1 and 0.20-0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell Volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependencies of the lattice parameters were observed. These anomalies are explained as additional disorder-order phase transitions.

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

    Science.gov (United States)

    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.

  7. Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves

    Science.gov (United States)

    Chiadini, Francesco; Fiumara, Vincenzo; Mackay, Tom G.; Scaglione, Antonio; Lakhtakia, Akhlesh

    2017-08-01

    The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a dissipative plasmonic material. Correspondingly, the ESWs transmute from Dyakonov-Tamm surface waves into surface-plasmon-polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results.

  8. Fast wettability transition from hydrophilic to superhydrophobic laser-textured stainless steel surfaces under low-temperature annealing

    Science.gov (United States)

    Ngo, Chi-Vinh; Chun, Doo-Man

    2017-07-01

    Recently, the fabrication of superhydrophobic metallic surfaces by means of pulsed laser texturing has been developed. After laser texturing, samples are typically chemically coated or aged in ambient air for a relatively long time of several weeks to achieve superhydrophobicity. To accelerate the wettability transition from hydrophilicity to superhydrophobicity without the use of additional chemical treatment, a simple annealing post process has been developed. In the present work, grid patterns were first fabricated on stainless steel by a nanosecond pulsed laser, then an additional low-temperature annealing post process at 100 °C was applied. The effect of 100-500 μm step size of the textured grid upon the wettability transition time was also investigated. The proposed post process reduced the transition time from a couple of months to within several hours. All samples showed superhydrophobicity with contact angles greater than 160° and sliding angles smaller than 10° except samples with 500 μm step size, and could be applied in several potential applications such as self-cleaning and control of water adhesion.

  9. Temperature-Induced Liquid-Liquid Transition in Metallic Melts: A Brief Review on the New Physical Phenomenon

    Directory of Open Access Journals (Sweden)

    Fang-Qiu Zu

    2015-03-01

    Full Text Available Understanding the nature of liquid structures and properties remains an open problem for many fundamental and applied fields. It is well known that there is no other defined phase line above liquidus (TL in phase diagrams of ordinary alloys. However, via resorts of internal friction, electric resistivity, thermal analysis, X-ray diffraction, solidification, etc., the results of our research on lots of single- and multiple-component melts show a novel physical image: temperature induced liquid-liquid structure transition (TI-LLST can occur above TL. Moreover, the solidification behaviors and structures out of the melts that experienced TI-LLST are distinct from those out of the melts before TI-LLST. In this paper, some typical examples of TI-LLST and characteristic aspects of the TI-LLST are briefly reviewed, in which the main contents are limited in our own achievements, although other groups have also observed similar phenomena using different methods. In the sense of phenomenology, TI-LLST reported here is quite different from other recognized liquid transitions, i.e., there are only a few convincing cases of liquid P, Si, C, H2O, Al2O3-Y2O3, etc. in which the transition occurs, either induced by pressure or at a supercooled state and near liquidus.

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

    Science.gov (United States)

    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.

  11. Phase transitions in Cd3P2 at high pressures and high temperatures

    DEFF Research Database (Denmark)

    Yel'kin, F.S.; Sidorov, V.A.; Waskowska, A.;

    2008-01-01

    The high-pressure, high-temperature structural behaviour of Cd3P2 has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0 GPa in compression....... The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7) GPa, which agrees quite well with the calculated value of 66.3 GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal...

  12. Analyzing temperature-induced transitions in disordered proteins by NMR spectroscopy and secondary chemical shift analyses

    DEFF Research Database (Denmark)

    Kjærgaard, Magnus; Poulsen, Flemming Martin; Kragelund, Birthe Brandt

    2012-01-01

    Intrinsically disordered proteins are abundant in nature and perform many important physiological functions. Multidimensional NMR spectroscopy has been crucial for the understanding of the conformational properties of disordered proteins and is increasingly used to probe their conformational...... ensembles. Compared to folded proteins, disordered proteins are more malleable and more easily perturbed by environmental factors. Accordingly, the experimental conditions and especially the temperature modify the structural and functional properties of disordered proteins. This chapter discusses practical...... aspects of NMR studies of temperature-induced structural changes in disordered proteins using chemical shifts....

  13. Zero-Temperature Magnetic Transition in an Easy-Axis Kondo Lattice Model --- An NRG Study

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Bulla, Ralf; Si, Qimiao

    2007-03-01

    Antiferromagnetic heavy fermion metals close to their quantum critical points display a richness in their physical properties unanticipated by the traditional approach to quantum criticality. Here we address the quantum transition of a spin-12 antiferromagnetic Kondo lattice model with an easy-axis anisotropy within the extended dynamical mean field theory. We derive results [1] in real frequency using the bosonic numerical renormalization group (bNRG) method and compare them with Quantum Monte Carlo results in Matsubara frequency. The bNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is nearly second order, with any jump in the magnetic order parameter not exceeding a few percents of the full moment. The bNRG results also display some subtle features; we discuss their possible origins and suggest means for further microscopic studies. [1] J.-X. Zhu, S. Kirchner, R. Bulla, and Q. Si, cond-mat/0607567.

  14. A unified model for de novo design of elastin-like polypeptides with tunable inverse transition temperatures.

    Science.gov (United States)

    McDaniel, Jonathan R; Radford, D Christopher; Chilkoti, Ashutosh

    2013-08-12

    Elastin-like polypeptides (ELPs) are stimulus-responsive peptide polymers that exhibit inverse temperature phase transition behavior, causing an ELP to aggregate above its inverse transition temperature (T(t)). Although this property has been exploited in a variety of biotechnological applications, de novo design of ELPs that display a specific T(t) is not trivial because the T(t) of an ELP is a complex function of several variables, including its sequence, chain length, polypeptide concentration, and the type and concentration of cosolutes in solution. This paper provides a quantitative model that predicts the T(t) of a family of ELPs (Val-Pro-Gly-Xaa-Gly, where Xaa = Ala and/or Val) from their composition, chain length, and concentration in phosphate buffered saline. This model will enable de novo prediction of the amino acid sequence and chain length of ELPs that will display a predetermined T(t) in physiological buffer within a specified concentration regime, thereby greatly facilitating the design of new ELPs for applications in medicine and biotechnology.

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

    Science.gov (United States)

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

    Science.gov (United States)

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

    2016-02-28

    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 (T(NI)) 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.

  17. δ-KIO 3·HIO 3: crystal structure, proton disorder and low temperature phase transition

    Science.gov (United States)

    Engelen, B.; Gavrilko, T.; Panthöfer, M.; Puchkovskaya, G.; Sekirin, I.

    2000-05-01

    δ-KIO 3·HIO 3, obtained by slowly cooling a concentrated solution of KIO 3 and HIO 3, has been investigated by means of single crystal X-ray diffraction measurements at ambient temperature and temperature dependent powder X-ray diffraction, dielectric, calorimetric and FT-IR and FT-Raman measurements. From the single crystal X-ray measurements, the I-O bonding scheme of the iodine atoms and the hydrogen bond system were determined. The crystal structure of δ-KIO 3·HIO 3 was found to consist of [I 3O 9H 3/2] 3/2- ions possibly originating from occupationally disordered [I 3O 9H 2] - and [I 3O 9H] 2- anions. These ions are connected via hydrogen bonds to form plane grids parallel (100) with the K + ions placed between them. Thus δ-KIO 3·HIO 3 should be formulated as K 3/2[I 3O 9H 3/2]. The temperature dependent FT-IR data give an evidence for a dynamic proton disorder at room temperature and for a proton ordering below 220 K, which may be regarded as a structural phase transition in the proton sublattice.

  18. Temperature-driven topological quantum phase transitions in a phase-change material Ge2Sb2Te5

    Science.gov (United States)

    Eremeev, S. V.; Rusinov, I. P.; Echenique, P. M.; Chulkov, E. V.

    2016-12-01

    The Ge2Sb2Te5 is a phase-change material widely used in optical memory devices and is a leading candidate for next generation non-volatile random access memory devices which are key elements of various electronics and portable systems. Despite the compound is under intense investigation its electronic structure is currently not fully understood. The present work sheds new light on the electronic structure of the Ge2Sb2Te5 crystalline phases. We demonstrate by predicting from first-principles calculations that stable crystal structures of Ge2Sb2Te5 possess different topological quantum phases: a topological insulator phase is realized in low-temperature structure and Weyl semimetal phase is a characteristic of the high-temperature structure. Since the structural phase transitions are caused by the temperature the switching between different topologically non-trivial phases can be driven by variation of the temperature. The obtained results reveal the rich physics of the Ge2Sb2Te5 compound and open previously unexplored possibility for spintronics applications of this material, substantially expanding its application potential.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ovchinnikov, Victor, E-mail: ovchinnv@georgetown.edu [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States); Karplus, Martin, E-mail: marci@tammy.harvard.edu [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States); Laboratoire de Chimie Biophysique, ISIS, Université de Strasbourg, 67000 Strasbourg (France)

    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. Integrated high-transition temperature magnetometer with only two superconducting layers

    DEFF Research Database (Denmark)

    Kromann, R.; Kingston, J.J.; Miklich, A.H.;

    1993-01-01

    are required, the SQUID body serving as the crossunder that completes the multiturn flux transformer. The highest temperature at which any of the magnetometers functioned was 76 K. At 60 K the magnetic field gain of this device was 63, and the magnetic field noise was 160 fT Hz-1/2 at 2 kHz, increasing to 3...

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

    Science.gov (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

  3. The Influence of Instrumented Striker Configuration on the Results of Dynamic Toughness Testing

    Energy Technology Data Exchange (ETDEWEB)

    Lucon, E.

    2008-09-15

    Several studies are available on the influence of the edge radius of instrumented strikers (ASTM - 8 mm or ISO - 2 mm) on the results of both non instrumented and instrumented Charpy tests. This paper investigates the effect of using either a 2 mm or a 8 mm striker when performing dynamic toughness tests at impact loading rates on precracked Charpy specimens. Existing data from tests run in the ductile-to-brittle region (dynamic Master Curve reference temperature) and in the upper shelf regime (ductile initiation fracture toughness and crack resistance curves) have been analyzed. The results show that 2 mm strikers tend to yield lower cleavage fracture toughness in the transition region (although the effect cannot be considered statistically significant), whereas the influence of striker configuration is negligible in the upper shelf regime when data are generated using the low-blow multiple-specimen technique.

  4. Recent progress on gas tungsten arc welding of vanadium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Grossbeck, M.L.; King, J.F.; Alexander, D.J. [Oak Ridge National Lab., TN (United States)] [and others

    1997-08-01

    Emphasis has been placed on welding 6.4 mm plate, primarily by gas tungsten arc (GTA) welding. The weld properties were tested using blunt notch Charpy testing to determine the ductile to brittle transition temperature (DBTT). Erratic results were attributed to hydrogen and oxygen contamination of the welds. An improved gas clean-up system was installed on the welding glove box and the resulting high purity welds had Charpy impact properties similar to those of electron beam welds with similar grain size. A post-weld heat treatment (PWHT) of 950{degrees}C for two hours did not improve the properties of the weld in cases where low concentrations of impurities were attained. Further improvements in the gas clean-up system are needed to control hydrogen contamination.

  5. Application of the small punch test to reactor pressure vessel integrity

    Energy Technology Data Exchange (ETDEWEB)

    Rosinski, S.T. [EPRI Nondestructive Evaluation Center, Charlotte, NC (United States); Viswanathan, R. [EPRI, Palo Alto, CA (United States); Foulds, J.R. [Failure Analysis Associates, Inc., Menlo Park, CA (United States)

    1998-07-01

    Based on prior success with fossil plant steels, EPRI is investigating the feasibility of applying the Small Punch test to determine the fracture toughness (K{sub ic}) of irradiated reactor pressure vessel (RPV) materials. The small punch test specimen is sufficiently small to alleviate future surveillance material availability concerns, as well as provide a means of direct vessel material interrogation by non-disruptive miniature sample removal and testing. A limited series of small punch tests on unirradiated and irradiated RPV steel materials has shown that the method can be used to estimate ductile-to-brittle transition temperatures and to determine the material fracture toughness (K{sub lc}, J{sub lc}). The results to date are described and the experimental difficulties that need to be resolved in achieving valid results are identified. (authors)

  6. Microstructural study of irradiated isotopically tailored F82H steel

    Energy Technology Data Exchange (ETDEWEB)

    Wakai, E. E-mail: wakai@realab01.tokai.jaeri.go.jp; Miwa, Y.; Hashimoto, N.; Robertson, J.P.; Klueh, R.L.; Shiba, K.; Abiko, K.; Furuno, S.; Jitsukawa, S

    2002-12-01

    The synergistic effect of displacement damage and hydrogen or helium atoms on microstructures in F82H steel irradiated at 250-400 deg. C to 2.8-51 dpa in HFIR has been examined using isotopes of {sup 54}Fe or {sup 10}B. Hydrogen atoms increased slightly the formation of dislocation loops and changed the Burgers vector for some parts of dislocation loops, and they also affected on the formation of cavity at 250 deg. C to 2.8 dpa. Helium atoms also influenced them at around 300 deg. C, and the effect of helium atoms was enhanced at 400 deg. C. Furthermore, the relations between microstructures and radiation-hardening or ductile to brittle transition temperature (DBTT) shift in F82H steel were discussed. The cause of the shift increase of DBTT is thought to be due to the hardening of dislocation loops and the formation of {alpha}{sup '}-precipitates on dislocation loops.

  7. Irradiation performance of 9--12 Cr ferritic/martensitic stainless steels and their potential for in-core application in LWRs

    Energy Technology Data Exchange (ETDEWEB)

    Jones, R.H.; Gelles, D.S.

    1993-08-01

    Ferritic-martensitic stainless steels exhibit radiation stability and stress corrosion resistance that make them attractive replacement materials for austenitic stainless steels for in-core applications. Recent radiation studies have demonstrated that 9% Cr ferritic/martensitic stainless steel had less than a 30C shift in ductile-to-brittle transition temperature (DBTT) following irradiation at 365C to a dose of 14 dpa. These steels also exhibit very low swelling rates, a result of the microstructural stability of these alloys during radiation. The 9 to 12% Cr alloys to also exhibit excellent corrosion and stress corrosion resistance in out-of-core applications. Demonstration of the applicability of ferritic/martensitic stainless steels for in-core LWR application will require verification of the irradiation assisted stress corrosion cracking behavior, measurement of DBTT following irradiation at 288C, and corrosion rates measurements for in-core water chemistry.

  8. Thermal Equation of State and Spin Transition of Fe-rich Carbonate at High Pressure and Temperature

    Science.gov (United States)

    Liu, J.; Lin, J.; Mao, Z.; Prakapenka, V.

    2013-12-01

    Magnesite [MgCO3] has been reported to be a potential stable phase as a major deep-carbon host at deep-mantle conditions, in which it is expected to contain approximately 20 mole% of iron in the lattice. Laboratory studies of Fe-bearing magnesite [(MgFe)CO3] across the spin transition at high P-T conditions can provide crucial constraints on the role and behavior of deep carbon in the geochemistry and geophysics of the Earth's mantle, and therefore the mantle's role in the global carbon cycle. In situ synchrotron X-ray diffraction experiments on natural magnesiosiderite [(Mg0.35Fe0.65)CO3] were conducted using resistive and laser-heated diamond anvil cells (DACs) up to 80 GPa and 1200 K. Based on thermal elastic modeling of the measured pressure-volume curves at given temperatures, we have derived thermal equation of state (EoS) parameters and the spin-crossover diagram of magnesiosiderite across the spin transition. These results show the spin crossover broadened and shifted toward higher pressures at elevated temperatures. Low-spin magnesiosiderite is denser and more incompressible than the high-spin phase at 1200 K and high pressures. Within the spin crossover at 1200 K, magnesiosiderite exhibits anomalous thermal elastic behaviors, including a dramatic increase in the thermal expansion coefficient and a drop in the isothermal bulk modulus and the bulk sound velocity, respectively. Compared with the end-member magnesite at relevant pressure-temperature conditions of the subducted slabs, the low-spin magnesiosiderite is denser and its unit cell volume is smaller than the end-member magnesite. Here we will present new experimental and thermodynamic modeling results to show how the lower-mantle low-spin Fe-bearing magnesite can become the major deep-carbon host mineral in the lower part of the lower mantle.

  9. Population transitions and temperature change in Minas Gerais, Brazil: a multidimensional approach

    Directory of Open Access Journals (Sweden)

    Alisson F. Barbieri

    2015-12-01

    Full Text Available Climate change will exacerbate the vulnerability of places and people around the world in the next decades, especially in less developed regions. In this paper, we investigate future scenarios of population vulnerability to climate change for the next 30 years in 66 regions of the state of Minas Gerais, Brazil. Based upon the Alkire & Foster Index, we integrate simulated and projected dimensions of population vulnerability into a Multidimensional Index, showing how scenarios of temperature change would affect each region's relative vulnerability in the future. Results suggest that economic and health dimensions are the highest contributors to increases in temperature-related vulnerability, with the poorest and agribusiness regions being the most impacted in decades to come.

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

    CERN Document Server

    LeBard, David N

    2008-01-01

    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 the top of the monotonic increase of the reorganization energy with increasing temperature, we have observed a spike at 220 K 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.

  11. Amorphous to nanocrystalline transition in HWCVD Si:H films by substrate temperature variation

    Energy Technology Data Exchange (ETDEWEB)

    Gogoi, Purabi; Jha, Himanshu S.; Agarwal, Pratima [Department of Physics, IIT Guwahati, Guwahati (India); Deva, Dinesh [Department of Chemical Engineering, IIT Kanpur, Kanpur (India)

    2010-04-15

    Thin films of hydrogenated silicon with band gap ranging from 2.0-2.34 eV are prepared at deposition rate 8-14A/sec in an indigenously fabricated HWCVD system keeping all parameters except substrate temperature fixed. The films grown at T{sub s}{<=}150 C are found to be pure amorphous, whereas the formation of nanocrystalline phase starts at T{sub s} {>=} 200 C. With increase in T{sub s}, crystalline fraction increases along with the increase in the band gap whereas the hydrogen content in the films and the deposition rate decreases. The variation of microstructure by varying substrate temperature without a significant decrease in deposition rate is useful for various device applications. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Composite self-similar solutions for relativistic shocks: The transition to cold fluid temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Margaret [School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Sari, Re' em [California Institute of Technology, MS 130-33, Pasadena, California 91125 (United States) and Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)

    2009-11-15

    The flow resulting from a strong ultrarelativistic shock moving through a stellar envelope with a polytropelike density profile has been studied analytically and numerically at early times while the fluid temperature is relativistic--that is, just before and after the shock breaks out of the star. Such a flow should expand and accelerate as its internal energy is converted to bulk kinetic energy; at late enough times, the assumption of relativistic temperatures becomes invalid. Here we present a new self-similar solution for the postbreakout flow when the accelerating fluid has bulk kinetic Lorentz factors much larger than unity but is cooling through p/n of order unity to subrelativistic temperatures. This solution gives a relation between a fluid element's terminal Lorentz factor and that element's Lorentz factor just after it is shocked. Our numerical integrations agree well with the solution. While our solution assumes a planar flow, we show that corrections due to spherical geometry are important only for extremely fast ejecta originating in a region very close to the stellar surface. This region grows if the shock becomes relativistic deeper in the star.

  13. Composite self-similar solutions for relativistic shocks: the transition to cold fluid temperatures

    CERN Document Server

    Pan, Margaret

    2008-01-01

    The flow resulting from a strong ultrarelativistic shock moving through a stellar envelope with a polytrope-like density profile has been studied analytically and numerically at early times while the fluid temperature is relativistic--that is, just before and just after the shock breaks out of the star. Such a flow should expand and accelerate as its internal energy is converted to bulk kinetic energy; at late enough times, the assumption of relativistic temperatures becomes invalid. Here we present a new self-similar solution for the post-breakout flow when the accelerating fluid has bulk kinetic Lorentz factors much larger than unity but is cooling through $p/n$ of order unity to subrelativistic temperatures. This solution gives a relation between a fluid element's terminal Lorentz factor and that element's Lorentz factor just after it is shocked. Our numerical integrations agree well with the solution. While our solution assumes a planar flow, we show that corrections due to spherical geometry are importan...

  14. Use of glass transition temperature for stabilization of board's cracks of Eucalyptus grandis

    Directory of Open Access Journals (Sweden)

    Fred W. Calonego

    2010-09-01

    Full Text Available The Eucalyptus grandis logs temperatures were determined and correlated with the board's cracks during steaming. Thermocouples were inserted in the logs center, registering their temperatures during steaming at 90"C. The logs were sawed and the board's cracks measured. It was concluded that: (1 the logistic S-shaped curve explains the logs temperature variation; (2 the logs with diameter of 20 to As temperaturas em toras de Eucalyptus grandis, durante a vaporização, foram determinadas e correlacionadas com as rachaduras das tábuas. Nos centros das toras foram inseridos termopares e registradas suas temperaturas durante a vaporização à 90"C. As toras foram desdobradas e as rachaduras das tábuas mensuradas. Concluiu-se que: (1 o modelo estatístico sigmoidal logístico explica a variação da temperatura nas toras; (2 as toras com 20 a <25, 25 a <30 e 30 a <35 cm de diâmetro apresentaram, respectivamente, 84,2"C, 73,1"C e 45,8"C ao final da vaporização; e (3 as rachaduras foramsignificativamente menores nas toras que atingiram a temperatura de transição vítrea.

  15. Strength, ductility, and ductile-brittle transition temperature for MFR (magnetic fusion reactor) candidate vanadium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Loomis, B.A.; Lee, R.H.; Smith, D.L.; Peterson, J.R.

    1987-09-01

    The dependence of the yield strength, tensile strength, elongation, and reduction in area on temperature for the V-15Ti-7.5Cr, V-20Ti, V-15Cr-5Ti, V-12Cr-5Ti, V-10Cr-5Ti, and V-3Ti-1Si alloys was determined from tensile tests at temperatures ranging from 25 to 700/sup 0/C. The strength of the alloys increased with an increase of the combined Cr and Ti concentration. The total elongation for the alloys ranged between 20% and 38%. The reduction in area ranged from 30% to 90%. The DBTT, which was determined from the temperature dependence of the reduction in area, was less than 25/sup 0/C for the V-15Ti-7.5Cr, V-20Ti, and V-3Ti-1Si alloys. The DBTT for the V-10Cr-5Ti, V-12Cr-5Ti, and V-15Cr-5Ti alloys was also less than 25/sup 0/C if these alloys were annealed to reduce the hydrogen concentration prior to the tensile test. If these latter alloys were not annealed prior to the tensile test, the DBTT ranged from 40/sup 0/C to 90/sup 0/C and the DBTT increased with an increase of the Cr concentration. A Cr/Ti concentration ratio of 0 to 0.5 in these alloys was found to cause the alloys to be less susceptible to hydrogen embrittlement. 14 refs., 4 figs., 3 tabs.

  16. Kinetics of low-temperature transitions and a reaction rate theory from non-equilibrium distributions.

    Science.gov (United States)

    Aquilanti, Vincenzo; Coutinho, Nayara Dantas; Carvalho-Silva, Valter Henrique

    2017-04-28

    This article surveys the empirical information which originated both by laboratory experiments and by computational simulations, and expands previous understanding of the rates of chemical processes in the low-temperature range, where deviations from linearity of Arrhenius plots were revealed. The phenomenological two-parameter Arrhenius equation requires improvement for applications where interpolation or extrapolations are demanded in various areas of modern science. Based on Tolman's theorem, the dependence of the reciprocal of the apparent activation energy as a function of reciprocal absolute temperature permits the introduction of a deviation parameter d covering uniformly a variety of rate processes, from those where quantum mechanical tunnelling is significant and d  0, corresponding to the Pareto-Tsallis statistical weights: these generalize the Boltzmann-Gibbs weight, which is recovered for d = 0. It is shown here how the weights arise, relaxing the thermodynamic equilibrium limit, either for a binomial distribution if d > 0 or for a negative binomial distribution if d theory for chemical kinetics including quantum mechanical tunnelling, and for case (iii) to the stereodirectional specificity of the dynamics of reactions strongly hindered by the increase of temperature.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'. © 2017 The Author(s).

  17. Evidence of a transition temperature for the optimum deposition of grafted monolayer coatings

    Science.gov (United States)

    Brzoska, J. B.; Shahidzadeh, N.; Rondelez, F.

    1992-12-01

    TECHNIQUES for surface modification are of considerable technological interest for the fabrication of water-repellent and anti-fouling coatings. Silanization1 (the chemical grafting of organic molecules onto a substrate via a trichlorosilane group) stands out among these techniques by virtue of its ability to provide highly compact coatings of optical quality, extreme chemical inertness and adjustable wettability2. Although the silanization reaction has been extensively characterized3-8, the properties of the grafted layers are still too variable for most commercial applications; for example, the quality of the grafted layers depends critically on the presence of trace amounts of water, and on the temperature at which the silanization reaction takes place9. Here we provide evidence for the existence of a near-ambient temperature threshold, Tc, which represents an upper bound for obtaining the highest-quality films. This threshold temperature is found to be an intrinsic property of the silane molecules: it depends linearly on their chain length, but is independent of the solvent used for the reaction. We suggest that Tc is analogous to the triple point in the phase diagram of Langmuir monolayers.

  18. Prediction of the spin transition temperature in Fe(II) one-dimensional coordination polymers: an anion based database.

    Science.gov (United States)

    Dîrtu, Marinela M; Rotaru, Aurelian; Gillard, Damien; Linares, Jorge; Codjovi, Epiphane; Tinant, Bernard; Garcia, Yann

    2009-08-17

    One-dimensional (1D) coordination polymers of formula [Fe(NH(2)trz)(3)]A.nH(2)O, {A = TiF(6)(2-), n = 0.5 (1) and n = 1 (2); A = ZrF(6)(2-), n = 0.5 (3) and n = 0 (4); A = SnF(6)(2-), n = 0.5 (5) and n = 1 (6); A = TaF(7)(2-), n = 3 (7) and n = 2.5 (8); A = GeF(6)(2-), n = 1 (9) and n = 0.5 (10), NH(2)trz = 4-amino-1,2,4-triazole} have been synthesized, fully characterized, and their spin crossover behavior carefully studied by SQUID magnetometry, Mossbauer spectroscopy, and differential scanning calorimetry. These materials display an abrupt and hysteretic spin transition around 200 K on cooling, as well as a reversible thermochromic effect. Accurate spin transition curves were derived by (57)Fe Mossbauer spectroscopy considering the corrected f factors for the high-spin and low-spin states determined employing the Debye model. The unusual hysteresis width of 3 (28 K), was attributed to a dense hydrogen bonding network involving the ZrF(6)(2-) counteranion and the 1D chains, an organization which is also revealed in [Cu(NH(2)trz)(3)]ZrF(6).H(2)O (11). Trinuclear spin crossover compounds of formula [Fe(3)(NH(2)trz)(10)(H(2)O)(2)](SbF(6))(6).S {S = 1.5CH(3)OH (12), 0.5C(2)H(5)OH (13)} were also obtained. A structural property relationship was derived between the volume of the inserted counteranion and the transition temperature T(1/2) of the 1D chains. Two linear size regimes were identified for monovalent anions (0.04 or= 0.11 nm(3)) with saturation around T(1/2) = 200 K. These characteristics allowed us to derive an anion based database that is of interest for the prediction of the transition temperature of such functional switchable materials. Diffuse reflectivity measurements under hydrostatic pressure for 3,4 combined with calorimetric data allow an estimation of the electrostatic pressure between cationic chains and counteranions in the crystal lattice of these materials. The chain length distribution that ranges between 1 and 4 nm was also derived.

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

    Science.gov (United States)

    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%.

  20. An unusual temperature induced isostructural phase transition in a scheelite, Li(0.5)Ce(0.5)MoO4.

    Science.gov (United States)

    Saha, Dipankar; Ranjan, Rajeev; Swain, Diptikanta; Narayana, Chandrabhas; Row, Tayur N Guru

    2013-06-07

    High resolution synchrotron X-ray diffraction, dielectric and Raman scattering study of a scheelite compound Li0.5Ce0.5MoO4 (LCM) revealed that it transforms to a self similar structure above 400 °C. The thermally induced isostructural phase transition (IPT), a phenomenon which has rarely been reported in the literature, is preceded by partial softening of the zone centre phonons followed by their hardening above the IPT transition temperature. The high temperature isostructural phase, which exhibits expanded lattice parameters and cell volume, nucleates and grows in the low temperature matrix over a very wide temperature range. Both the phases show nearly identical thermal expansion suggesting similarities in symmetry, unaltered coordination environments around the atoms across the transition.

  1. Pressure induced ionic-superionic transition in silver iodide at ambient temperature.

    Science.gov (United States)

    Han, Y H; Wang, H B; Troyan, I A; Gao, C X; Eremets, M I

    2014-01-28

    Silver iodide (AgI-V) is an archetypical ionic compound for studying the formation mechanism of a superionic state. Previous studies have proven that superionic AgI with high ionic conductivity greater than 0.1 Ω(-1)cm(-1) could only be obtained at high temperatures. We show in this paper that high pressure could also induce the superionic state in AgI even at ambient temperature. Using electrochemical impedance spectroscopy, we investigated Ag(+) ions diffusing in rock-salt structured AgI-III and KOH-type AgI-V under high pressures and directly observed the superionic state in AgI-V. The diffusion coefficient of AgI-V is ∼3.4 × 10(-4)-8.6 × 10(-4) cm(2)/s in the investigated pressure range of 12-17 GPa, comparable with those of superionic α-AgI and AgI-III'. By analyzing the half infinite length Warburg diffusion process, two parameters α and β, which closely relate to the disordered state of Ag(+) ions, have been determined and it was suggested that Ag(+) ions in AgI-V become disordered. The ionic conductivity of AgI-V is three orders of magnitude higher than that of AgI-III, and has reached around 0.1 Ω(-1)cm(-1). Evidence for all three, the diffusion coefficient, α and β, and conductivity have proven that AgI-V is a superionic conductor at ambient temperature.

  2. Ge(001)-(<2 1>, <0 3>)-Pb(<2 1>, <0 6>)↔Pb: Low-temperature two-dimensional phase transition

    DEFF Research Database (Denmark)

    Bunk, Oliver; Nielsen, Martin Meedom; Zeysing, J.H.;

    2001-01-01

    The Ge(001)-((2 1)(0 3))-Pb surface reconstruction with a lead coverage of 5/3 monolayer is on the borderline between the low-coverage covalently-bonded and high-coverage metallic lead overlayers. This gives rise to an unusual low-temperature phase transition with concomitant changes in the bonding...... configuration. Both the room-temperature and low-temperature phases of this system were investigated by surface x-ray diffraction using synchrotron radiation. The room-temperature Ge(001)-((2 1)(0 3)) phase is best described by a model with dynamically flipping germanium dimers underneath a distorted Pb(111......) overlayer with predominantly metallic properties. In the low-temperature Ge(001)-((2 1)(0 6)) phase the dimers are static and the interaction between adsorbate and substrate and within the adsorbate is stronger than at room temperature. These results suggest that the phase transition is of order...

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

    Science.gov (United States)

    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.

  4. EFFECTS OF INTERPARTICLE DISTANCE,TEMPERATURE AND INTERFACIAL ADHESION ON BRITTLE-DUCTILE TRANSITION FOR NYLON 6/ABS BLENDS

    Institute of Scientific and Technical Information of China (English)

    Shu-hao Qin; Jie Yu; Min He; Wei Yan

    2009-01-01

    The toughness of blends composed of nylon 6 and acrylonitrile-butadiene-styrene(ABS)compatibilized by using styrene-maleic anhydride(SMA)as a compatibilizer was measured over a wide temperature region.Results reveal that the combining effects of particle size and volume fraction of ABS on the toughness of nylon 6/ABS/SMA blends can be described through plotting brittle-ductile transition of the impact strength versus the interparticle distance(ID)on the assumption that ABS domains relieve the triaxial tension via internal cavitation or interfacial debonding.Moreover,the effect of interfacial adhesion on fracture behavior of nylon 6/ABS/SMA blends strongly depends upon the testing temperature.The difference of relation amomg temperature,fracture behavior and interfacial adhesion can be understood in terms of the deformation mechanisms,i.e.in the case of poor interfacial adhesion,the toughness lies on whether debonding existing at the interface relieves triaxial tension or not.It is believed that for good interfacial adhesion,internal cavitation followed by matrix shear yielding is a predominant factor for toughening.Furthermore,the fracture surface of these blends was probed to elucidate how interfacial adhesion affected the impact strength of the blends.

  5. In situ X-ray observation of phase transitions in ZnF2 under high pressure and high temperature

    Science.gov (United States)

    Kusaba, Keiji; Kikegawa, Takumi

    2008-02-01

    High-pressure and high-temperature behavior of ZnF 2 with the rutile-type structure was investigated using an energy-dispersive-type X-ray diffraction method. Two high-pressure phases were found in the range up to 15 GPa and 400 ∘C. The CaCl 2-type phase with an orthorhombic cell (space group: Pnnm) was clearly observed at 5.4 GPa and 400 ∘C. Further phase transition was induced above 10 GPa at room temperature. The single phase of the high-pressure phase was obtained at 15.3 GPa and 350 ∘C. The high-pressure phase was found to have the PdF 2-type structure with a cubic cell (space group: Pa-3). The single phase was observed above 4 GPa in a pressure-release process at room temperature, and completely reverted to a mixture of the rutile-type phase and the α- PbO 2-type phase at ambient condition. The high-pressure behavior of ZnF 2 was similar to that of MgF 2.

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

    Science.gov (United States)

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

    2015-05-05

    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.

  7. Molecular weight dependence of surface flow near the bulk glass transition temperature

    Science.gov (United States)

    Chai, Yu; Salez, Thomas; Benzaquen, Michael; Raphael, Elie; Forrest, James A.

    2014-03-01

    We present the study on molecular weight dependent sub-Tg surface dynamics of polymer thin films by using the Nano-step experiment [McGraw et al. Soft Matter 7, 7832 (2011)]. By varying the molecular weight, we are able to probe the surface dynamics of the free surface below Tg with the polymer size comparable to the surface depth. In particular, we define and use a correlation function to compare measured and calculated profiles to analyze the transition from the bulk flow to flow restricted to the surface region. Surprisingly, even for the polymers with Mw = 22,000 surface flow is still observed below the bulk Tg value. A numerical simulation of random walk is used to find the fraction of polymer of which all of the polymer segments are located in the free surface region. The simulation results indicate that there are still a significant fraction of polymer molecules where all segments are in the near free surface region. These molecules can undergo flow consistent with the experimental results.

  8. Standard test method for determination of reference temperature, to, for ferritic steels in the transition range

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2011-01-01

    1.1 This test method covers the determination of a reference temperature, To, which characterizes the fracture toughness of ferritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic KJc instabilities, or both. The specific types of ferritic steels (3.2.1) covered are those with yield strengths ranging from 275 to 825 MPa (40 to 120 ksi) and weld metals, after stress-relief annealing, that have 10 % or less strength mismatch relative to that of the base metal. 1.2 The specimens covered are fatigue precracked single-edge notched bend bars, SE(B), and standard or disk-shaped compact tension specimens, C(T) or DC(T). A range of specimen sizes with proportional dimensions is recommended. The dimension on which the proportionality is based is specimen thickness. 1.3 Median KJc values tend to vary with the specimen type at a given test temperature, presumably due to constraint differences among the allowable test specimens in 1.2. The degree of KJc variability among specimen types i...

  9. Temperature and frequency investigations of the electrical parameters in the TGS ferroelectric transition

    Energy Technology Data Exchange (ETDEWEB)

    Berbecaru, Ciceron [University of Bucharest, Faculty of Physics, Bucharest-Magurele 077125 (Romania)

    2010-05-15

    Pure and D: alanina doped triglycin sulphate (TGS) crystals were grown from aqueous solutions. Fresh cleaved, polished and silver paste painted samples were temperature and frequency investigated. Pure crystals show nonreproducible values of the permittivity and dielectric loss crossing up and down the Curie point. More stable and much lower values of the permittivity and dielectric loss could be noticed for D: alanina doped crystals. Permittivity and loss values show different frequencies behavior related to polar or nonpolar state of crystals. Frequency dependence of permittivity and loss behavior could be related to the general picture of relaxation of different polarization mechanisms and their contributions to permittivity and loss values for dielectric materials. Much smaller and stable values of permittivity and loss, vs. temperature and frequency, were found for doped crystals. Experimental results point out for a more stable structure with dipoles mobility decreased of doped vs. pure TGS crystals. Thus, higher figure of merit of doped TGS crystals point to a major advantage for technical applications (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Science.gov (United States)

    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. FePt nanoparticle formation with lower phase transition temperature by single shot plasma focus ion irradiation

    Science.gov (United States)

    Lin, J. J.; Roshan, M. V.; Pan, Z. Y.; Verma, R.; Lee, P.; Springham, S. V.; Tan, T. L.; Rawat, R. S.

    2008-07-01

    Uniform FePt nanoparticles were synthesized through nanostructuring of pulsed laser deposited FePt thin films by single shot H+ ion irradiation using a plasma focus device. The annealing temperature required for phase transition from low Ku face-centred cubic to high Ku face-centred tetragonal, for ion irradiated samples, is simultaneously lowered down to 400 °C. The energetic H+ ion irradiation significantly reduces the activation energy for atomic ordering by increasing the number of vacancies. The advantage of using a plasma focus device is that it can achieve nanostructuring in much shorter time, in single shot ion exposure with pulse duration of typically about a few hundreds of nanoseconds, as compared with much longer duration required by continuous ion sources.

  12. Effect of stoichiometry on the superconducting transition temperature in single crystalline 2H-NbS2

    Science.gov (United States)

    Lian, Hailong; Wu, Yueshen; Xing, Hui; Wang, Shun; Liu, Ying

    2017-07-01

    Single crystals of 2H-NbS2 are prepared by chemical vapor transport method under varying conditions. The residual resistivity ratio (RRR) of the as-grown single crystals is observed to change from 10 to 60, while the superconducting transition temperatures (Tc) remain around 6.2 K. Changes in stoichiometry were obtained by annealing in different conditions, resulting in sulfur deficient 2H-NbS2-y single crystals. Both Tc and RRR of the annealed samples are found to drop drastically when y increases from 0.05 to 0.10, which is argued to be the effect of enhanced electron scattering caused by the decreased interlayer coupling evidenced by the increase of the c-axis lattice constant after annealing, possibly due to Nb intercalation between layers.

  13. Critical endline of the finite temperature phase transition for 2 +1 flavor QCD around the SU(3)-flavor symmetric point

    Science.gov (United States)

    Kuramashi, Yoshinobu; Nakamura, Yoshifumi; Takeda, Shinji; Ukawa, Akira

    2016-12-01

    We investigate the critical endline of the finite temperature phase transition of QCD around the SU(3)-flavor symmetric point at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and nonperturbatively O (a )-improved Wilson-clover fermion action. The critical endline is determined by using the intersection point of kurtosis, employing the multiparameter, multiensemble reweighting method to calculate observables off the SU(3)-symmetric point, at the temporal size NT=6 and lattice spacing as low as a ≈0.19 fm . We confirm that the slope of the critical endline takes the value of -2 , and find that the second derivative is positive, at the SU(3)-flavor symmetric point on the Columbia plot parametrized with the strange quark mass ms and degenerated up-down quark mass ml.

  14. Enhancement of transition temperature in FexSe0.5Te0.5 film via iron vacancies

    Science.gov (United States)

    Zhuang, J. C.; Yeoh, W. K.; Cui, X. Y.; Kim, J. H.; Shi, D. Q.; Shi, Z. X.; Ringer, S. P.; Wang, X. L.; Dou, S. X.

    2014-06-01

    The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8 ≤ x ≤ 1) on superconductivity and electronic properties have been studied. A significant enhancement of the superconducting transition temperature (TC) up to 21 K was observed in the most Fe deficient film (x = 0.8). Based on the observed and simulated structural variation results, there is a high possibility that Fe vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows a strong relationship with the lattice strain effect induced by Fe vacancies. Importantly, the presence of Fe vacancies alters the charge carrier population by introducing electron charge carriers, with the Fe deficient film showing more metallic behavior than the defect-free film. Our study provides a means to enhance the superconductivity and tune the charge carriers via Fe vacancy, with no reliance on chemical doping.

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

    Science.gov (United States)

    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.

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

    CERN Document Server

    Montet, Benjamin T; Fortney, Jonathan J; Desert, Jean-Michel

    2016-01-01

    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 \\pm 0.21 ppt at 3.6 microns and 2.09 \\pm 0.08 ppt at 4.5 microns, corresponding to brightness temperatures of 1026 \\pm 57 K and 1249 \\pm 36 K, respectively. We then apply brown dwarf evolutionary models to infer a bolometric luminosity log(L_star / L_sun) = -5.16 \\pm 0.04. Given the known physica...

  17. Temperature and electric field induced metal-insulator transition in atomic layer deposited VO2 thin films

    Science.gov (United States)

    Tadjer, Marko J.; Wheeler, Virginia D.; Downey, Brian P.; Robinson, Zachary R.; Meyer, David J.; Eddy, Charles R.; Kub, Fritz J.

    2017-10-01

    Amorphous vanadium oxide (VO2) films deposited by atomic layer deposition (ALD) were crystallized with an ex situ anneal at 660-670 °C for 1-2 h under a low oxygen pressure (10-4 to 10-5 Torr). Under these conditions the crystalline VO2 phase was maintained, while formation of the V2O5 phase was suppressed. Electrical transition from the insulator to the metallic phase was observed in the 37-60 °C range, with an ROFF/RON ratio of up to about 750 and ΔTC ≅ 7-10 °C. Lateral electric field applied across two-terminal device structures induced a reversible phase change, with a room temperature transition field of about 25 kV/cm in the VO2 sample processed with the 2 h long O2 anneal. Both the width and slope of the field induced MIT I-V hysteresis were dependent upon the VO2 crystalline quality.

  18. Crystalline phase transition information induced by high temperature susceptibility transformations in bulk PMP-YBCO superconductor growth in-situ

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, C.P., E-mail: zhangcp6813@126.com [SMRC, Northwest Institute for Non-ferrous Metal Research, Xi’an (China); Physics Department, Université Joseph Fourier, Grenoble (France); State Key Lab of Solidification Processing, Northwest Polytechnical University, Xi’an (China); Chaud, X. [CRETA/CNRS, 25 avenue des martyrs, 38042 Grenoble Cedex 9 (France); Beaugnon, E. [Physics Department, Université Joseph Fourier, Grenoble (France); CRETA/CNRS, 25 avenue des martyrs, 38042 Grenoble Cedex 9 (France); Zhou, L. [SMRC, Northwest Institute for Non-ferrous Metal Research, Xi’an (China); State Key Lab of Solidification Processing, Northwest Polytechnical University, Xi’an (China)

    2015-01-15

    Highlights: • It was the first time we measured the susceptibility of bulk YBCO in powder-melting-process at high temperature up to 1060 °C. • It revealed that the crystalline phase transition of bulk PMP-YBCO growth in process. • A new discovery of Y123 phase pre-formed then melted in heating stage has been found. • It discovered that Y123 crystal solidification started at 1004 °C in cooling stage in PMP route. - Abstract: The dynamic susceptibility transformations of bulk HTSC PMP-YBCO growth have been investigated from 200 °C up to 1060 °C by the Faraday Balance in-situ. It revealed that the crystalline phase transitions of bulk PMP-YBCO growth in process. A new discovery of Y123 phase pre-formed then melted in heating stage has been found. It also discovered that Y123 crystal solidification started at 1004 °C in cooling stage. Before Y123 solidification the liquid phase CuO change to Cu{sub 2}O reciprocally as well as the copper ion valence changed between divalent Cu{sup 2+} and trivalent Cu{sup 1+} each other. It was essential to keep quantities of CuO phase instead of the Cu{sub 2}O for Y123 crystal solidification.

  19. Translational diffusion across a free-standing smectic film above the bulk smectic-A-isotropic transition temperature.

    Science.gov (United States)

    Śliwa, Izabela; Zakharov, A V

    2017-01-01

    Calculations of translational self-diffusion coefficient in free-standing smectic films during a series of layer-thinning transitions as the temperature is raised above the bulk smectic-A-isotropic transition have been carried out. A molecular model based upon the random walk theory is applied for calculating the translational diffusion coefficient (TDC) D_{∥} across the smectic film both in the bulk of the film, as well as in the vicinity of the bounding surfaces. Calculations of D_{∥} require the set of the orientational and translational order parameters (OPs) which have been obtained by using the extended McMillan approach with anisotropic forces. The effect of E on the orientational and translational OPs, as well as on the TDC of smectic films has been investigated. A reasonable agreement between the theoretically predicted and the experimentally obtained data on the TDC in the bulk of the partially fluorinated H10F5MOPP film has been obtained. We also found, in agreement with the experimentally observed behavior of D_{∥}(N)(N=25,13,11,10), that the translational diffusion coefficient in the bulk of the film gradually increases as the film thickness N is decreased.

  20. Detection of orbital fluctuations above the structural transition temperature in the iron pnictides and chalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Arham, H.Z.; Hunt, C.R.; Park, W.K.; Gillett, J.; Das, S.D.; Sebastian, S.E.; Xu, Z.J.; Lin, Z.W.; Li, Q.; Gu, G.; Thaler, Alexander; Ran, Sheng; Budko, Serguei L.; Canfield, Paul C.; Chung, D.Y.; Kanatzidis, M.G.; Greene, L.H.

    2012-06-18

    We use point-contact spectroscopy (PCS) to probe AEFe2As2 (AE=Ca, Sr, Ba) and Fe1+yTe. For AE=Sr,Ba we detect orbital fluctuations above TS while for AE=Ca these fluctuations start below TS. Co doping preserves the orbital fluctuations while K doping suppresses it. The fluctuations are only seen at those dopings and temperatures where an in-plane resistive anisotropy is known to exist. We predict an in-plane resistive anisotropy of Fe1+yTe above TS. Our data are examined in light of the recent work by Lee and Phillips (arXiv:1110.5917v2). We also study how joule heating in the PCS junctions impacts the spectra. Spectroscopic information is only obtained from those PCS junctions that are free of heating effects while those PCS junctions that are in the thermal regime display bulk resistivity phenomena.

  1. TRANSITION AND DECOMPOSITION TEMPERATURES OF CEMENT PHASES - A COLLECTION OF THERMAL ANALYSIS DATA

    Directory of Open Access Journals (Sweden)

    Nick C. Collier

    2016-10-01

    Full Text Available Thermal analysis techniques provide the cement chemist with valuable tools to qualify and quantify the products formed during the hydration of cementitious materials. These techniques are commonly used alongside complimentary techniques such as X-ray diffraction and electron microscopy/energy dispersive spectroscopy to confirm the composition of phases present and identify amorphous material unidentified by other techniques. The most common thermal analysis techniques used by cement chemists are thermogravimetry, differential thermal analysis and differential scanning calorimetry. In order to provide a useful reference tool to the cement chemist, this paper provides a brief summary of the temperatures at which phase changes occur in the most common cement hydrates in the range 0-800°C in order to aid phase identification.

  2. Phase Transition and EOS of Cinnabar (α-HgS) at High Pressure and High Temperature

    Institute of Scientific and Technical Information of China (English)

    FAN Da-Wei; ZHOU Wen-Ge; LIU Cong-Qiang; WAN Fang; XING Yin-Suo; LIU Jing; LI Yan-Chun; XIE Hong-Sen

    2009-01-01

    @@ Phase relations and equation of state (EOS) of natural cinnabar (α-HgS) are investigated by high-pressure and high-temperature synchrotron x-ray powder diffraction. The unambiguous cinnabar-rocksalt structure phase boundaries are determined to be Plower(Gpa)=15.54-0.014T(℃) and Pupper(Gpa)= 23.84 - 0.014T(℃) at 300--623K. With K' axed at 4, we obtain K0 = 37(4) Gpa, ( K/ T)p=-0.025(2) GPaK-1, and α0= 3.79(20)× 10-5 K-1 for the cinnabar phase of α-HgS. The ( K/ T)p and α0 of cinnabar phase are obtained for the first time. A nearly isotropic compression of cinnabar phase is observed by linear regressions.

  3. Electroabsorption spectroscopy of electronic transition for room-temperature ionic liquid molecules dispersed in a polymer matrix

    Energy Technology Data Exchange (ETDEWEB)

    Ito, Ryuichi; Funamoto, Yuuki [Department of Applied Chemistry, Muroran Institute of Technology, Muroran 050-8585 (Japan); Ohta, Nobuhiro [Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812 (Japan); Iimori, Toshifumi, E-mail: iimori@mmm.muroran-it.ac.jp [Department of Applied Chemistry, Muroran Institute of Technology, Muroran 050-8585 (Japan)

    2015-07-29

    Highlights: • We measure electric field effects on absorption spectra of ionic liquids. • Changes in dipole moment and polarizability on photoexcitation are determined. • Pyridinium ions show reorientation along electric fields in polymer matrix. • Lower limit of electric dipole moment in the ground state is evaluated. - Abstract: Electroabsorption spectroscopy of electronic transitions in the room-temperature ionic liquids (RTILs) 1-butylpyridinium bis(trifluoromethylsulfonyl)imide ([C{sub 4}py][NTf{sub 2}]) and 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide ([C{sub 4}mpy][NTf{sub 2}]) dispersed in poly(methyl methacrylate) (PMMA) is reported. [C{sub 4}py][NTf{sub 2}] shows a π → π{sup ∗} transition of the cation [C{sub 4}py]{sup +} with an absorption maximum at 258 nm. The changes in the dipole moment and the electronic polarizability between the excited and ground states are determined by analysis of the Stark effect in the absorption band. A field-induced reorientation effect of the pyridinium chromophore is observed at room temperature. This observation implies that the cation [C{sub 4}py]{sup +} is not rigidly fixed to the polymer matrix, which is consistent with the results of previous studies on hybrid materials of RTILs and PMMA. The lower limit of the dipole moment in the ground state is derived from analysis of the field-induced reorientation effect, and the results for [C{sub 4}mpy][NTf{sub 2}] are essentially the same as those for [C{sub 4}py][NTf{sub 2}].

  4. Reprint of “Heat capacity and transition behavior of sucrose by standard, fast scanning and temperature-modulated calorimetry”

    Energy Technology Data Exchange (ETDEWEB)

    Magoń, A. [Department of Chemistry, University of Technology, 35-959 Rzeszów (Poland); Wurm, A.; Schick, C. [Department of Physics, University of Rostock, 18057 Rostock (Germany); Pangloli, Ph.; Zivanovic, S. [Department of Food Science and Technology, University of Tennessee, Knoxville, TN 37996 (United States); Skotnicki, M. [Department of Pharmaceutical Technology, Poznan University of Medical Sciences, 60-780 Poznań (Poland); Pyda, M., E-mail: mpyda@utk.edu [Department of Chemistry, University of Technology, 35-959 Rzeszów (Poland)

    2015-03-10

    Highlights: • Experimental, apparent heat capacity of sucrose was investigated by advanced thermal analysis. • Vibrational heat capacity of solid state was linked with a low temperature experimental heat capacity of sucrose. • Equilibrium melting parameters of sucrose were determined. • Decomposition, superheating of crystalline sucrose during melting process were presented. • TGA, DSC, TMDSC, and FSC are useful tools for characterization of sucrose. - Abstract: The heat capacity (C{sub p}) of crystalline and amorphous sucrose was determined using standard and quasi-isothermal temperature modulated differential scanning calorimetry. The results were combined with the published data determined by adiabatic calorimetry, and the C{sub p} values are now reported for the wide 5–600 K range. The experimental C{sub p} of solid sucrose at 5–300 K was used to calculate the vibrational, solid C{sub p} based on the vibrational molecular motions. The calculated solid and liquid C{sub p} together with the transition parameters for equilibrium conditions were used as references for detailed quantitative thermal analysis of crystalline and amorphous sucrose. Melting temperature (T{sub m}) of the crystalline sucrose was identified in a broad 442–465 K range with a heat of fusion of 40–46 J/mol determined at heating rates 0.5–20 K/min, respectively. The equilibrium T{sub m} and heat of fusion of crystalline sucrose were estimated at zero heating rate as T{sup o}{sub m} = 424.4 K and ΔH{sup o}{sub f} = 32 kJ/mol, respectively. The glass transition temperature (T{sub g}) of amorphous sucrose was at 331 K with a change in C{sub p} of 267 J/(mol K) as it was estimated from reversing heat capacity by quasi-isothermal TMDSC on cooling. At heating rates less than 30 K/min, thermal decomposition occurred during melting, while at extreme rate of 1000 K/s, degradation was not observed. Data obtained by fast scanning calorimetry (FSC) at 1000 K/s, showed that T{sub m} was

  5. Ferroelectric InMnO{sub 3}: Growth of single crystals, structure and high-temperature phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Bekheet, Maged F., E-mail: maged.bekheet@ceramics.tu-berlin.de [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Fachgebiet Keramische Werkstoffe / Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin (Germany); Svoboda, Ingrid; Liu, Na [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Bayarjargal, Lkhamsuren [Institut für Geowissenschaften, Goethe-Universität, Altenhöferallee 1, d-60438 Frankfurt a.M. (Germany); Irran, Elisabeth [Institut für Chemie, Technische Universität Berlin, Straße des 17, Juni 135, 10623 Berlin (Germany); Dietz, Christian; Stark, Robert W.; Riedel, Ralf [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Gurlo, Aleksander [Fachgebiet Keramische Werkstoffe / Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin (Germany)

    2016-09-15

    To understand the origin of the ferroelectricity in InMnO{sub 3}, single crystals with average size of 1 mm were grown in PbF{sub 2} flux at 950 °C. The results of single crystal X-ray diffraction, second harmonic generation and piezoresponse force microscopy studies of high-quality InMnO{sub 3} single crystals reveal that the room-temperature state in this material is ferroelectric with P6{sub 3}cm symmetry. The polar InMnO{sub 3} specimen undergoes a reversible phase transition from non-centrosymmetric P6{sub 3}cm structure to a centrosymmetric P6{sub 3}/mmc structure at 700 °C as confirmed by the in situ high-temperature Raman spectroscopic and synchrotron X-ray diffraction experiments. - Graphical abstract: Piezoresponse fore microscopy (PFM) studies of high quality InMnO{sub 3} single crystal revealed that the room-temperature state of this material is ferroelectric with a clear cloverleaf pattern corresponding to six antiphase ferroelectric domains with alternating polarization ±P{sub z}. Display Omitted - Highlights: • InMnO{sub 3} single crystals with average size of 1 mm were grown in PbF{sub 2} flux at 950 °C. • The room-temperature state of InMnO{sub 3} is ferroelectric with polar P6{sub 3}cm structure. • PolarInMnO{sub 3} reversibly transforms to a centrosymmetric P6{sub 3}/mmc structure above 700 °C.

  6. KELT-9b: A giant planet with the temperature of a red dwarf star transiting an unevolved A0 star

    Science.gov (United States)

    Gaudi, B. Scott; Stassun, Keivan G.; Collins, Karen A.; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D.; Siverd, Robert; Crepp, Justin R.; Gonzales, Erica J.; Stevens, Daniel J.; Buchhave, Lars A.; Pepper, Joshua; Johnson, Marshall C.; Colon, Knicole D.; Jensen, Eric L. N.; Rodriguez, Joseph; KELT and KELT-FUN Collaborations

    2017-06-01

    We report the discovery of KELT-9b, the hottest, most irradiated known hot Jupiter, with a period of ~1.5 days, and radius and mass of ~1.8 Jupiter radii and ~2.7 Jupiter masses. The host is a massive (~2.3 solar masses), hot (effective temperature of ~9,600 K) rapidly-rotating (projected rotation velocity of ~100 km/s) A0 star. Given the implied planetary equilibrium temperature of ~3800 K and scale height of ~1000 km (assuming zero albedo and no heat redistribution), this system provides one of the best targets for detailed characterization of a hot Jupiter atmosphere under extreme irradiation. The planet has been confirmed via high-precision primary transit observations in multiple bands, a lack of companions in deep AO observations, radial velocity detection of the reflex motion of the star due to the companion, detection of the Doppler tomographic signal, and a detection of the secondary eclipse depth in the far-red optical (z) that implies a brightness temperature of ~4600 K, and thus exceptionally poor heat redistribution to the night side. We find that the planet is on a near-polar orbit, likely resulting in orbital precession that will be detectable within a few years. The brightness of the host, the extreme planet temperature, large planet-to-star radius ratio, large planetary atmospheric scale height, and short orbital period, make this an exceptional target for follow-up studies of the planet's atmosphere, which may exhibit unusual photochemistry due to the extreme amount of incident high-energy radiation.

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

    Science.gov (United States)

    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

  8. Detection of orbital fluctuations above the structural transition temperature in the iron pnictides and chalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Arham, H. Z.; Hunt, C. R.; Park, W. K.; Gillett, J.; Das, S. D.; Sebastian, S. E.; Xu, Z. J.; Wen, J. S.; Lin, Z. W.; Li, Q.; Gu, G.; Thaler, A.; Ran, S.; Bud' ko, S. L.; Canfield, P. C.; Chung, D. Y.; Kanatzidis, M. G.; Greene, L. H.

    2012-06-01

    We use point-contact spectroscopy (PCS) to probe AEFe2As2 (AE=Ca,Sr,Ba) and Fe1+yTe. For AE=Sr,Ba we detect orbital fluctuations above TS while for AE=Ca these fluctuations start below TS. Co doping preserves the orbital fluctuations while K doping suppresses it. The fluctuations are only seen at those dopings and temperatures where an in-plane resistive anisotropy is known to exist. We predict an in-plane resistive anisotropy of Fe1+yTe above TS. Our data are examined in light of the recent work by Lee and Phillips (arXiv:1110.5917v2). We also study how joule heating in the PCS junctions impacts the spectra. Spectroscopic information is only obtained from those PCS junctions that are free of heating effects while those PCS junctions that are in the thermal regime display bulk resistivity phenomena.

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

    CERN Document Server

    Arulsamy, Andrew Das; Elersic, Kristina; Modic, Martina; Subramani, Uma Shankar

    2011-01-01

    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 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 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...

  10. Size dependence of phase transition temperatures of ferromagnetic ,ferroelectric and superconductive nanocrystals

    Institute of Scientific and Technical Information of China (English)

    LANG Xing-you; JIANG Qing

    2007-01-01

    With the miniaturization of devices,size and interface effects become increasingly important for the properties and performances of nanomaterials.Here,we present a thermodynamic approach to the mechanism behind size-induced unusual behavior in the phase stabilities of ferromagnetic(FM),antiferromagnetic(AFM),ferroelectric (FE),and superconductive(SC)nanocrystals,which are different dramatically from their bulk counterparts.This method is based on the Lindemann criterion for melting,Mott's expression for the vibrational melting entropy,and the Shi model for the size-dependent melting temperature.Simple and unified functions,without any adjustable parameter,are established for the size and interface dependences of thermal and phase stabilities of FM,AFM,FE and SC nanocrystals.According to these analytic functions,as the size of nanocrystals is reduced,the thermal and phasestabilities may strengthen or weaken,depending on the confluence of the.surface/volume ratio of nanocrystals and the FM(AFM,FE or SC)/substrate interface situations.The validity of this model is confirmed by a large number of experimental results.This theory will be significant for the choice of materials and the design of devices for practicalapplication.

  11. Nucleation and crystallization kinetics of hydrated amorphous lactose above the glass transition temperature.

    Science.gov (United States)

    Schmitt, E A; Law, D; Zhang, G G

    1999-03-01

    The crystallization kinetics of amorphous lactose in the presence and absence of seed crystals were investigated at 57.5% relative humidity. Isothermal crystallization studies were conducted gravimetrically in an automated vacuum moisture balance at several temperatures between 18 and 32 degrees C. The crystallization rate constants were then determined from Johnson-Mehl-Avrami (JMA) treatment and isothermal activation energies were obtained from Arrhenius plots. Based on microscopic observations, a reaction order of 3 was used for JMA analysis. The nonisothermal activation energies were determined by differential scanning calorimetry using Kissinger's analysis. Isothermal activation energies for amorphous lactose with and without seed crystals were 89.5 (+/-5.6) kJ/mol and 186.5 (+/-17.6) kJ/mol, respectively. Nonisothermal activation energies with and without seed crystals were 71 (+/-7.5) kJ/mol and 80.9 (+/-8.9) kJ/mol, respectively. The similarity of the isothermal and nonisothermal activation energies for the sample with seeds suggested that crystallization was occurring by growth from a fixed number of preexisting nuclei. Markedly different isothermal and nonisothermal activation energies in the absence of seeds suggested a site-saturated nucleation mechanism, and therefore allowed calculation of an activation energy for nucleation of 317 kJ/mol.

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

    Science.gov (United States)

    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.

  13. Two-dimensional percolation transition at finite temperature: Phase boundary for in-plane magnetism in films with two atomic layers of Fe on W(110)

    Science.gov (United States)

    Belanger, R.; Venus, D.

    2017-02-01

    A two-dimensional (2D) percolation transition in Fe/W(110) ultrathin magnetic films occurs when islands in the second atomic layer percolate and resolve a frustrated magnetic state to produce long-range in-plane ferromagnetic order. Novel measurements of percolation using the magnetic susceptibility χ (θ ) as the films are deposited at a constant temperature, allow the long-range percolation transition to be observed as a sharp peak consistent with a critical phase transition. The measurements are used to trace the paramagnetic-to-ferromagnetic phase boundary between the T =0 percolation magnetic transition and the thermal Curie magnetic transition of the undiluted film. A quantitative comparison to critical scaling theory is made by fitting the functional form of the phase boundary. The fitted parameters are then used in theoretical expressions for χ (T ) in the critical region of the paramagnetic state to provide an excellent, independent representation of the experimental measurements.

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

    Science.gov (United States)

    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.

  15. Phase transition and high temperature thermoelectric properties of copper selenide Cu2-xSe (0 <= x <= 0.25)

    Science.gov (United States)

    Xiao, Xing-Xing; Xie, Wen-Jie; Tang, Xin-Feng; Zhang, Qing-Jie

    2011-08-01

    With good electrical properties and an inherently complex crystal structure, Cu2-xSe is a potential “phonon glass electron crystal" thermoelectric material that has previously not attracted much interest. In this study, Cu2-xSe (0 <= x <= 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu2-xSe were investigated in the temperature range of 300 K-750 K. The results of X-ray diffraction at room temperature show that Cu2-xSe compounds possess a cubic structure with a space group of Fm3m(#225) when 0.15 <= x <= 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 <= x <= 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu2Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.

  16. Role of single-point mutations and deletions on transition temperatures in ideal proteinogenic heteropolymer chains in the gas phase.

    Science.gov (United States)

    Olivares-Quiroz, L

    2016-07-01

    A coarse-grained statistical mechanics-based model for ideal heteropolymer proteinogenic chains of non-interacting residues is presented in terms of the size K of the chain and the set of helical propensities [Formula: see text] associated with each residue j along the chain. For this model, we provide an algorithm to compute the degeneracy tensor [Formula: see text] associated with energy level [Formula: see text] where [Formula: see text] is the number of residues with a native contact in a given conformation. From these results, we calculate the equilibrium partition function [Formula: see text] and characteristic temperature [Formula: see text] at which a transition from a low to a high entropy states is observed. The formalism is applied to analyze the effect on characteristic temperatures [Formula: see text] of single-point mutations and deletions of specific amino acids [Formula: see text] along the chain. Two probe systems are considered. First, we address the case of a random heteropolymer of size K and given helical propensities [Formula: see text] on a conformational phase space. Second, we focus our attention to a particular set of neuropentapeptides, [Met-5] and [Leu-5] enkephalins whose thermodynamic stability is a key feature on their coupling to [Formula: see text] and [Formula: see text] receptors and the triggering of biochemical responses.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  19. Accurate sequential detection of primary tumor and metastatic lymphatics using a temperature-induced phase transition nanoparticulate system

    Directory of Open Access Journals (Sweden)

    Oh KS

    2014-06-01

    Full Text Available Keun Sang Oh,1 Ji Young Yhee,2 Dong-Eun Lee,3 Kwangmeyung Kim,2 Ick Chan Kwon,2 Jae Hong Seo,4 Sang Yoon Kim,5 Soon Hong Yuk1,4 1College of Pharmacy, Korea University, Sejong, 2Biomedical Research Center, Korea Institute of Science and Technology, Seoul, 3Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeonbuk, 4Biomedical Research Center, Korea University Guro Hospital, Seoul, 5Department of Otolaryngology, Asan Medical Center, University of Ulsan, College of Medicine, Seoul, Republic of Korea Abstract: Primary tumor and tumor-associated metastatic lymphatics have emerged as new targets for anticancer therapy, given that these are difficult to treat using traditional chemotherapy. In this study, docetaxel-loaded Pluronic nanoparticles with Flamma™ (FPR-675, fluorescence molecular imaging dye; DTX/FPR-675 Pluronic NPs were prepared using a temperature-induced phase transition for accurate detection of metastatic lymphatics. Significant accumulation was seen at the primary tumor and in metastatic lymph nodes within a short time. Particle size, maximum drug loading capacity, and drug encapsulation efficiency of the docetaxel-loaded Pluronic NPs were approximately 10.34±4.28 nm, 3.84 wt%, and 94±2.67 wt%, respectively. Lymphatic tracking after local and systemic delivery showed that DTX/FPR-675 Pluronic NPs were more potent in tumor-bearing mice than in normal mice, and excised mouse lymphatics showed stronger near-infrared fluorescence intensity on the tumor-bearing side than on the non-tumor-bearing side at 60 minutes post-injection. In vivo cytotoxicity and efficacy data for the NPs demonstrated that the systemically administered NPs caused little tissue damage and had minimal side effects in terms of slow renal excretion and prolonged circulation in tumor-bearing mice, and rapid renal excretion in non-tumor-bearing mice using an in vivo real-time near-infrared fluorescence imaging system. These results

  20. Temperature Dependence of the Raman Frequency of an Internal Mode for SiO2-Moganite Close to the α-β Transition

    Directory of Open Access Journals (Sweden)

    Mustafa Cem Lider

    2012-01-01

    Full Text Available The temperature dependence of the 501 cm−1 frequency of the vibrational mode is analyzed for SiO2-moganite. The experimental data for the heating and cooling cycles of moganite from the literature is used for our analysis. The coexistence of α-β moganite is obtained over a finite temperature interval, and the α-β moganite transition at around 570 K is studied, as observed experimentally.

  1. Optical Temperature Sensing Behavior Through Stark Sublevels Transitions of Green and Red Upconversion Emissions for Er3+-Yb3+-Li+ Codoped TiO2 Phosphors.

    Science.gov (United States)

    He, Y Y; Wu, J L; Wang, X H; Feng, Z Q; Dong, B

    2016-04-01

    The Er3+-Yb3+-Li+ codoped TiO2 phosphors have been prepared by sol-gel method. The green and red upconversion emissions were observed under a 976 nm laser diode excitation, which were ascribed to 2H11/2 --> 4I15/2, 4S3/2(I)/4S3/2(II) -->4I15/2, and 4F9/2(I)/4F9/2(II) -->4I15/2 transitions of Er3+ Stark sublevels. The fluorescence intensity ratios (FIR), which are corresponding to the transitions of 2H11/2/(4S3/2(I)+4S3/2(II))--> 4I5/2, 4S3/2(I)/4S3/2(II) -->4I15/2, and 4F9/2(II)/4F9/2(II) -->4I15/2, have been studied as a function of temperature in the range of 303 673 K. The temperature sensitivities have been calculated at the maximum value of 0.0020 K-1, 0.0015 K-1, and 0.0011 K-1 at the temperatures of 427 K, 350 K, and 273 K for the three coupled energy level transitions, respectively. The Er3+-Yb3+-Li+ codoped Ti02 phosphor with different temperature sensitivities by Stark sublevels indicated that it is a promising material for application in optical temperature sensing at a wide range of temperature.

  2. Comparison between experiment and theory in the temperature variation of film tension above the bulk isotropic transition in free-standing liquid-crystal films.

    Science.gov (United States)

    Veum, M; Duelge, L; Droske, J; Nguyen, H T; Huang, C C; Mirantsev, L V

    2009-09-01

    Using differential scanning calorimetry, the transition enthalpies and temperatures for the bulk smectic-isotropic phase transition have been measured for a series of liquid-crystal compounds. For five compounds, those values were used as parameters in a microscopic mean-field model to predict the temperature dependence of the difference in free-energy density between a sample of material in a free-standing smectic film and that in the bulk. The model predicts a weak temperature dependence below the bulk clearing point and a pronounced monotonic increase with temperature above the transition temperature. The compounds used in this study were chosen specifically because they were also the subject of a previous independent experimental study [M. Veum, Phys. Rev. E 74, 011703 (2006)] that demonstrated a sudden monotonic increase in the free-standing film tension with temperature, which is qualitatively consistent with the predictions of the above-mentioned mean-field model. This study presents a direct and quantitative comparison between the predictions of the mean-field model and the results from previous tension experiments.

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

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Tang-Qing, E-mail: tangqing.yu@nyu.edu; Vanden-Eijnden, Eric, E-mail: eve2@cims.nyu.edu [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States); Chen, Pei-Yang; Chen, Ming [Department of Chemistry, New York University, New York, New York 10003 (United States); Samanta, Amit [Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544, USA and Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Tuckerman, Mark, E-mail: mark.tuckerman@nyu.edu [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States); Department of Chemistry, New York University, New York, New York 10003 (United States); NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai 200062 (China)

    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. Enhanced temperature-independent magnetoresistance below the metal–insulator transition temperature of epitaxial La0.2Nd0.4Ca0.4MnO3 thin films

    Indian Academy of Sciences (India)

    Darshan C Kundaliya; A A Tulapurkar; J John; R Pinto; R G Kulkarni

    2002-05-01

    Epitaxial La0.2Nd0.4Ca0.4MnO3 thin films have been deposited at 800°C on LaAlO3 substrate using pulsed laser deposition technique. The structural and magnetotransport properties of the films have been studied. The sharp peak in the temperature dependence of the resistance corresponding to metal-to-insulator transition (p) has been observed at a temperature of p =82 K, 97 K and 110 K for 0 Oe, 20 kOe and 40 kOe magnetic fields, respectively. The film exhibits a large nearly temperature-independent magnetoresistance around 99% in the temperature regime below p. The zero field-cooled (ZFC) and field-cooled (FC) magnetization data at 50 Oe shows irreversibility between the ZFC and FC close to the ferromagnetic transition temperature c = 250 K. The ZFC temperature data of the film displays ferromagnetic behavior for higher temperature regime c =250 K > T > p = 82 K, and a decrease in magnetization with decreasing temperature up to 5 K below 82 K exhibiting a sort of antiferromagnetic behavior in the low temperature regime ( < 82 K= p = N).

  5. Pressure effect of glass transition temperature in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Roseker, W.; Sikorski, M.

    2004-01-01

    Pressure effects on glass transition temperature and supercooled liquid region of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass have been investigated by performing in situ high-temperature and high-pressure x-ray powder diffraction measurements using synchrotron radiation. The glass transition...... was detected from the change of the slope of peak position as a function of temperature. It is found that the glass transition temperature increases with pressure by 4.4 K/GPa for the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass, and the supercooled liquid range decreases with pressure by 2.9 K/GPa in a pressure...... range of 0-2.2 GPa. This method opens a possibility to study the pressure effect of glass transition process in glassy systems under high pressures (>1 GPa). (C) 2004 American Institute of Physics....

  6. Enzymatic liquefaction of agarose above the sol-gel transition temperature using a thermostable endo-type β-agarase, Aga16B.

    Science.gov (United States)

    Kim, Jung Hyun; Yun, Eun Ju; Seo, Nari; Yu, Sora; Kim, Dong Hyun; Cho, Kyung Mun; An, Hyun Joo; Kim, Jae-Han; Choi, In-Geol; Kim, Kyoung Heon

    2017-02-01

    The main carbohydrate of red macroalgae is agarose, a heterogeneous polysaccharide composed of D-galactose and 3,6-anhydro-L-galactose. When saccharifying agarose by enzymes, the unique physical properties of agarose, namely the sol-gel transition and the near-insolubility of agarose in water, limit the accessibility of agarose to the enzymes. Due to the lower accessibility of agarose to enzymes in the gel state than to the sol state, it is important to prevent the sol-gel transition by performing the enzymatic liquefaction of agarose at a temperature higher than the sol-gel transition temperature of agarose. In this study, a thermostable endo-type β-agarase, Aga16B, originating from Saccharophagus degradans 2-40(T), was characterized and introduced in the liquefaction process. Aga16B was thermostable up to 50 °C and depolymerized agarose mainly into neoagarooligosaccharides with degrees of polymerization 4 and 6. Aga16B was applied to enzymatic liquefaction of agarose at 45 °C, which was above the sol-gel transition temperature of 1 % (w/v) agarose (∼35 °C) when cooling agarose. This is the first systematic demonstration of enzymatic liquefaction of agarose, enabled by determining the sol-gel temperature of agarose under specific conditions and by characterizing the thermostability of an endo-type β-agarase.

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

    Science.gov (United States)

    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.

  8. Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry.

    Science.gov (United States)

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

    2015-02-05

    We demonstrate application of precise adiabatic vacuum 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 vacuum 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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  11. Nuclear Jacobi and Poincar\\'e Transitions at High Spins and Temperatures: Account~of~Dynamic~Effects~and~Large-Amplitude Motion

    CERN Document Server

    Mazurek, K; Maj, A; Rouvel, D

    2013-01-01

    We present a theoretical analysis of the competition between so-called nuclear Jacobi and Poincar\\'e shape transitions in function of spin - at high temperatures. The latter condition implies the method of choice - a realistic version of the nuclear Liquid Drop Model (LDM), here: the Lublin-Strasbourg Drop (LSD) model. We address specifically the fact that the Jacobi and Poincar\\'e shape transitions are accompanied by the flattening of total nuclear energy landscape as function of the relevant deformation parameters what enforces large amplitude oscillation modes that need to be taken into account. For that purpose we introduce an approximate form of the collective Schr\\"odinger equation whose solutions are used to calculate the most probable deformations associated with both types of transitions and discuss the physical consequences in terms of the associated critical-spin values and transitions themselves.

  12. Thermochromic phase-transitions of GafChromic films studied by z-scan and temperature-dependent absorbance measurements.

    Science.gov (United States)

    Koulouklidis, A D; Cohen, S; Kalef-Ezra, J

    2013-11-01

    complicated. These shapes were attributed to a temperature-dependent (thermochromic) transition from the blue form to the conformer red form of the active material, a transition which appears to be irreversible at high intensities. This transition was incorporated into the open-aperture z-scan model which reproduced satisfactorily the corresponding experimental curves. Finally, the use of a chopped laser beam in the closed-aperture z-scan technique allowed artifact-free, high spatial resolution dose measurements using a laser beam of relatively high power. The model developed in the present study elucidates some of the effects related to film reading and the causes of some of the artifacts reported in the literature. Two-dimensional dose distributions can be assessed by z-scan; however, the merits of such a technique relative to those currently in use have to be further investigated.

  13. Observation of exchanging role of gold and silver nanoparticles in bimetallic thin film upon annealing above the glass transition temperature

    Science.gov (United States)

    Htet Kyaw, Htet; Tay Zar Myint, Myo; Hamood Al-Harthi, Salim; Maekawa, Toru; Yanagisawa, Keiichi; Sellai, Azzouz; Dutta, Joydeep

    2017-08-01

    The exchange role of gold (Au) and silver (Ag) in bimetallic films co-evaporated onto soda-lime glass substrates with Au-Ag volume ratios of 1:2, 1:1 and 2:1 have been demonstrated. Annealing of the films above the glass transition temperature in air led to non-alloying nature of the films, silver neutrals (Ag0) and gold nanoparticles (AuNPs) on the surface, along with silver nanoparticles (AgNPs) inside the glass matrix. Moreover, the size distribution and interparticle spacing of the AuNPs on the surface were governed by the Ag content in the deposited film. In contrast, the content of Au in the film played an opposite role leading to the migration of Ag ions (i.e. Ag0 being transformed to Ag ions after annealing in oxygen ambient) to form AgNPs inside the glass matrix. The higher the Au content in the film is, the more likely Ag0 to stay on the surface and impacts on the size distribution of AuNPs and consequently on the refractive index sensitivity measurements. Experimental realisation of this fact was reflected from the best performance for localized surface plasmon resonance (LSPR) sensitivity test achieved with Au-Ag ratio of 1:2. The Au/Ag/glass bimetallic dynamic results of this study can be pertinent to sensor applications integrated with optical devices.

  14. Edge effect and significant increase of the superconducting transition onset temperature of 2D superconductors in flat and curved geometries

    Science.gov (United States)

    Wong, Chi Ho; Lortz, Rolf

    2016-02-01

    In this paper, we present a simple method to model the curvature activated phonon softening in a 2D superconducting layer. The superconducting transition temperature Tc in the case of a 2D rectangular sheet, a hollow cylinder and a hollow sphere of one coherence length thickness is calculated by the quantum mechanical electron-phonon scattering matrix, and a series of collective lattice vibrations in the surface state. We will show that being extremely thin in a flat rectangular shape is not enough to significantly enhance the Tc through phonon softening. However, if a curvature is added, Tc can be strongly enhanced. The increase in Tc with respect to the bulk is greatest in a hollow sphere, intermediate in a hollow cylinder and weakest for the rectangular sheet, when systems of identical length scale are considered. In addition, we find that the edge effect of such a 2D sheet has a strong broadening effect on Tc in addition to the effect of order parameter phase fluctuations.

  15. Two-dimensional transition metal dichalcogenides with a hexagonal lattice: Room-temperature quantum spin Hall insulators

    Science.gov (United States)

    Ma, Yandong; Kou, Liangzhi; Li, Xiao; Dai, Ying; Heine, Thomas

    2016-01-01

    So far, several transition metal dichalcogenide (TMDC)-based two-dimensional (2D) topological insulators (TIs) have been discovered, all of them based on a tetragonal lattice. However, in 2D crystals, the hexagonal rather than the tetragonal symmetry is the most common motif. Here, based on first principles calculations, we propose a class of stable 2D TMDCs of composition MX2(M =Mo ,W ;X =S ,Se ,Te ) with a hexagonal lattice. They are all in the same stability range as other 2D TMDC allotropes that have been demonstrated experimentally, and they are identified to be practical 2D TIs with large band gaps ranging from 41 to 198 meV, making them suitable for applications at room temperature. Besides, in contrast to tetragonal 2D TMDCs, their hexagonal lattice will greatly facilitate the integration of theses novel TI state van der Waals crystals with other hexagonal or honeycomb materials and thus provide a route for 2D material-based devices for wider nanoelectronic and spintronic applications. The nontrivial band gaps of both WS e2 and WT e2 2D crystals are 198 meV, which are larger than that in any previously reported TMDC-based TIs. These large band gaps entirely stem from the strong spin orbit coupling strength within the d orbitals of Mo/W atoms near the Fermi level. Our findings broaden the scientific and technological impact of both 2D TIs and TMDCs.

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

    Science.gov (United States)

    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.

  17. Effects of grain size on fracture toughness in transition temperature region of Mn-Mo-Ni low-alloy steels

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sangho; Lee, Sunghak; Lee, Bong Sang

    2003-10-25

    An investigation was conducted into the effect of grain size on fracture toughness in the transition temperature region of Mn-Mo-Ni low-alloy steels used for nuclear pressure vessels. Three kinds of steels with different austenite grain sizes (AGS) were fabricated by varying the contents of Al and N, and their microstructures and mechanical properties were examined. Elastic-plastic cleavage fracture toughness, K{sub Jc}, was determined by three-point bend tests of precracked Charpy V-notch (PCVN) specimens according to ASTM E1921 standard test method. When the AGS decreased, the total number of carbides increased, while the size and the aspect ratio of carbides decreased. Local fracture stresses, estimated from a theoretical stress distribution in front of a crack tip, were found to be mainly determined by the 92nd% size of carbides. Cross-sectional areas beneath fracture surfaces were observed to understand microstructural features to affect the cleavage crack propagation behavior. The results showed that measured cleavage fracture units were smaller than AGSs, indicating that packet boundaries as well as austenite grain boundaries played an important role in the cleavage crack propagation. Based on the electron back-scatter diffraction (EBSD) results, the cleavage fracture units could also be matched with the effective grain sizes determined by the misorientation tolerance angle of 25 deg.

  18. Dust evolution in the transition towards the denser ISM: impact on dust temperature, opacity, and spectral index

    CERN Document Server

    Köhler, Melanie; Jones, Anthony P

    2015-01-01

    Variations in the observed dust emission and extinction indicate a systematic evolution of grain properties in the transition from the diffuse interstellar medium (ISM) to denser molecular clouds. The differences in the dust spectral energy distribution (SED) observed from the diffuse ISM to denser regions, namely an increase in the spectral index at long wavelengths, an increase in the FIR opacity, and a decrease in temperature, are usually assumed to be the result of changes in dust properties. We investigate if evolutionary processes, such as coagulation and accretion, are able to change the dust properties of grains in a way that is consistent with observations. We use a core-mantle grain model to describe diffuse ISM-type grains, and using DDA we calculate how the accretion of mantles and coagulation into aggregates vary the grain optical properties. We calculate the dust SED and extinction using DustEM and the radiative transfer code CRT. We show that the accretion of an aliphatic carbon mantle on diffu...

  19. QSPR Analysis of Copolymers by Recursive Neural Networks: Prediction of the Glass Transition Temperature of (Meth)acrylic Random Copolymers.

    Science.gov (United States)

    Bertinetto, Carlo Giuseppe; Duce, Celia; Micheli, Alessio; Solaro, Roberto; Tiné, Maria Rosaria

    2010-09-17

    The glass transition temperature (Tg ) of acrylic and methacrylic random copolymers was investigated by means of Quantitative Structure-Property Relationship (QSPR) methodology based on Recursive Neural Networks (RNN). This method can directly take molecular structures as input, in the form of labelled trees, without needing predefined descriptors. It was applied to three data sets containing up to 615 polymers (340 homopolymers and 275 copolymers). The adopted representation was able to account for the structure of the repeating unit as well as average macromolecular characteristics, such as stereoregularity and molar composition. The best result, obtained on a data set focused on copolymers, showed a Mean Average Residual (MAR) of 4.9 K, a standard error of prediction (S) of 6.1 K and a squared correlation coefficient (R(2) ) of 0.98 for the test set, with an optimal rate with respect to the training error. Through the treatment of homopolymers and copolymers both as separated and merged data sets, we also showed that the proposed approach is particularly suited for generalizing prediction of polymer properties to various types of chemical structures in a uniform setting.

  20. Thermal ionization induced metal-semiconductor transition and room temperature ferromagnetism in trivalent doped ZnO codoped with lithium

    Energy Technology Data Exchange (ETDEWEB)

    Sivagamasundari, A.; Chandrasekar, S.; Pugaze, R.; Kannan, R., E-mail: kannan@pec.edu [Department of Physics, Pondicherry Engineering College, Puducherry 605 014 (India); Rajagopan, S. [Department of Chemistry, Pondicherry Engineering College, Puducherry 605 014 (India)

    2014-03-07

    Thermal ionization induced metallic to semiconductor (MST) transition occurring at 460 K for Zn{sub 0.97}Al{sub 0.03}O, 463 K for Zn{sub 0.94}Al{sub 0.03}Li{sub 0.03}O, and 503 K for Zn{sub 0.91}Al{sub 0.03}Li{sub 0.03}Mn{sub 0.03}O has been found in the sol-gel synthesized (using hexamethylenetetramine), trivalent doped (Al, Mn) ZnO codoped with lithium. Increase in the thermally ionized carrier concentration due to Al doping is responsible for near band edge (NBE) peak shift causing Fermi level to move into conduction band making it metallic consistent with resistivity results. Free carrier (thermally activated) neutralization with ionized donor is responsible for semiconducting nature, which is supported from the free carrier screening produced energy shift in the NBE of photoluminescence peak. Furthermore, independently band gap shrinkage is also obtained from UV-Visible studies confirming localization induced MST. An anti-correlation is found between defect density (DLE) and room temperature ferromagnetism (RTFM) indicating intrinsic defects are not directly responsible for RTFM.