Immobilization of simulated radioactive soil waste containing cerium by self-propagating high-temperature synthesis

International Nuclear Information System (INIS)

Mao, Xianhe; Qin, Zhigui; Yuan, Xiaoning; Wang, Chunming; Cai, Xinan; Zhao, Weixia; Zhao, Kang; Yang, Ping; Fan, Xiaoling

2013-01-01

A simulated radioactive soil waste containing cerium as an imitator element has been immobilized by a thermite self-propagating high-temperature synthesis (SHS) process. The compositions, structures, and element leaching rates of products with different cerium contents have been characterized. To investigate the influence of iron on the chemical stability of the immobilized products, leaching tests of samples with different iron contents with different leaching solutions were carried out. The results showed that the imitator element cerium mainly forms the crystalline phases CeAl 11 O 18 and Ce 2 SiO 5 . The leaching rate of cerium over a period of 28 days was 10 −5 –10 −6 g/(m 2 day). Iron in the reactants, the reaction products, and the environment has no significant effect on the chemical stability of the immobilized SHS products

Immobilization of simulated radioactive soil waste containing cerium by self-propagating high-temperature synthesis

Science.gov (United States)

Mao, Xianhe; Qin, Zhigui; Yuan, Xiaoning; Wang, Chunming; Cai, Xinan; Zhao, Weixia; Zhao, Kang; Yang, Ping; Fan, Xiaoling

2013-11-01

A simulated radioactive soil waste containing cerium as an imitator element has been immobilized by a thermite self-propagating high-temperature synthesis (SHS) process. The compositions, structures, and element leaching rates of products with different cerium contents have been characterized. To investigate the influence of iron on the chemical stability of the immobilized products, leaching tests of samples with different iron contents with different leaching solutions were carried out. The results showed that the imitator element cerium mainly forms the crystalline phases CeAl11O18 and Ce2SiO5. The leaching rate of cerium over a period of 28 days was 10-5-10-6 g/(m2 day). Iron in the reactants, the reaction products, and the environment has no significant effect on the chemical stability of the immobilized SHS products.

Characterization of ceramics and intermetallics fabricated by self-propagating high-temperature synthesis

International Nuclear Information System (INIS)

Hurst, J.B.

1989-05-01

Three efforts aimed at investigating the process of self-propagating high temperature synthesis (SHS) for the fabrication of structural ceramics and intermetallics are summarized. Of special interest was the influence of processing variables such as exothermic dopants, gravity, and green state morphology in materials produced by SHS. In the first effort directed toward the fabrication of SiC, exothermic dopants of yttrium and zirconium were added to SiO2 or SiO2 + NiO plus carbon powder mix and processed by SHS. This approach was unsuccessful since it did not produce the desired product of crystalline SiC. In the second effort, the influence of gravity was investigated by examining Ni-Al microstructures which were produced by SHS combustion waves traveling with and opposite the gravity direction. Although final composition and total porosities of the combusted Ni-Al compounds were found to be gravity independent, larger pores were created in those specimens which were combusted opposite to the gravity force direction. Finally, it was found that green microstructure has a significant effect on the appearance of the combusted piece. Severe pressing laminations were observed to arrest the combustion front for TiC samples

Self-propagating high-temperature synthesis flammable range and dominant parameters for synthesizing several ceramics and intermetallic compounds under heat-loss condition

International Nuclear Information System (INIS)

Makino, Atsushi

1996-01-01

Extensive comparisons have been conducted between experimental and theoretical results for the nonadiabatic self-propagating high-temperature synthesis combustion characteristics of many solid-solid systems subjected to volumetric heat loss. The nonadiabatic flame propagation theory--which describes the premixed mode of bulk flame propagation supported by the nonpremixed reaction of dispersed nonmetal (or higher-melting point metal) particles in the liquid metal, with finite-rate reaction at the particle surface and temperature-sensitive Arrhenius-type condensed-phase mass diffusivity--is used to compare with experimental results with heat loss. Systems examined are ceramics (TiC, TiB 2 , and ZrB 2 ) and intermetallic compounds (NiAl, TiCo, and TiNi). By using a consistent set of physicochemical parameters for these systems, satisfactory quantitative agreement is demonstrated for the flammable range (defined in terms of the mixture ratio, degree of dilution, particle size, and/or compact diameter)

Fabrication of FeAl Intermetallic Foams by Tartaric Acid-Assisted Self-Propagating High-Temperature Synthesis

Directory of Open Access Journals (Sweden)

Krzysztof Karczewski

2018-04-01

Full Text Available Iron aluminides are intermetallics with interesting applications in porous form thanks to their mechanical and corrosion resistance properties. However, making porous forms of these materials is not easy due to their high melting points. We formed FeAl foams by elemental iron and aluminum powders sintering with tartaric acid additive. Tartaric acid worked as an in situ gas-releasing agent during the self-propagating high-temperature synthesis of FeAl intermetallic alloy, which was confirmed by X-ray diffraction measurements. The porosity of the formed foams was up to 36 ± 4%. In the core of the sample, the average equivalent circle diameter was found to be 47 ± 20 µm, while on the surface, it was 35 ± 16 µm; thus, the spread of the pore size was smaller than reported previously. To investigate functional applications of the formed FeAl foam, the pressure drop of air during penetration of the foam was examined. It was found that increased porosity of the material increased the flow of the air through the metallic foam.

Effect of C particle size on the mechanism of self-propagation high-temperature synthesis in the Ni-Ti-C system

International Nuclear Information System (INIS)

Yang, Y.F.; Wang, H.Y.; Wang, J.G.; Jiang, Q.C.

2011-01-01

Highlights: → We investigated the effect of C particle size on the self-propagating high temperature reaction mechanism. → Coarse C particle size (>38 μm) resulted in the formation of prior TiC x layer between Ti and C. → Prior TiC x layer control the whole reaction of Ni-Ti-C and domain the reaction kinetics. → The selection of C particle size is the most important factor to fabricate TiC/Ni composite using Ti, C and Ni mixtures. - Abstract: Effect of C particle size on the mechanism of self-propagation high-temperature synthesis (SHS) in the Ni-Ti-C system was investigated. Fine C particle resulted in a traditional mechanism of dissolution-precipitation while coarse C particle made the reaction be controlled by a mechanism of the diffusion of C through the TiC x layer. The whole process can be described: C atoms diffusing through the TiC x layer dissolved into the Ni-Ti liquid and TiC were formed once the liquid became supersaturated. Simultaneously, the heat generated from the TiC formation made the unstable TiC x layer break up. However, with the spread of Ti-Ni liquid, a new TiC x layer was formed again at the interface between spreading liquid and C particle. This process cannot stop until all the C particles are consumed completely.

Self-propagating high-temperature synthesis of Sr-doped LaMnO3 perovskite as oxidation catalyst

International Nuclear Information System (INIS)

Hirano, T.; Purwanto, H.; Watanabe, T.; Akiyama, T.

2007-01-01

Sr-doped LaMnO 3 perovskite oxide has been focused on as one of the alternative catalysts to precious metals such as platinum that are used for cleaning automotive emission gas. The conventional Solid-state reaction method is a popular productive process for perovskite oxide, however, it is time and energy consuming process because it requires repeated prolonged heat treatment at high temperatures. Therefore, the purposes of this work are to produce Sr-doped LaMnO 3 perovskite by using Self-propagating high-temperature synthesis (SHS) and experimentally examine the oxidation catalytic activity of the product for cleaning automotive emission gas. In the SHS, powders of La 2 O 3 , SrCO 3 , Mn and NaClO 4 were well mixed at the desired ratio and poured in a graphite crucible, where at one end it was ignited by using an electrically heated carbon foil. The wave of exothermic reaction due to oxidation of manganese propagated to the other end in a short time. The obtained products were characterized by means of XRD, FE-SEM, BET and particle size distribution analysis and then evaluated via catalytic oxidation tests by using propane in a fixed bed reactor at several temperatures. From the XRD analysis, the products had the desired composition of La 1-x Sr x MnO 3 (x = 0, 0.1, 0.2 and 0.4) perovskite, in which the replacing ratio x of La and Sr in the products was easily controlled by changing the mixing ratio of raw materials. The catalytic activity test showed that the samples exhibited good catalytic activity for propane oxidation over 200 deg. C , although the products had a relatively small surface area. SHS showed the potential for the production of a relatively inexpensive catalytic converter

Hydrophilic Graphene Preparation from Gallic Acid Modified Graphene Oxide in Magnesium Self-Propagating High Temperature Synthesis Process

Science.gov (United States)

Cao, Lei; Li, Zhenhuan; Su, Kunmei; Cheng, Bowen

2016-10-01

Hydrophilic graphene sheets were synthesized from a mixture of magnesium and gallic acid (GA) modified graphene oxide (GO) in a self-propagating high-temperature synthesis (SHS) process, and hydrophilic graphene sheets displayed the higher C/O ratio (16.36), outstanding conductivity (~88900 S/m) and excellent water-solubility. GO sheets were connected together by GA, and GA was captured to darn GO structure defects through the formation of hydrogen bonds and ester bonds. In SHS process, the most oxygen ions of GO reacted with magnesium to prevent the escape of carbon dioxide and carbon monoxide to from the structure defects associated with vacancies, and GA could take place the high-temperature carbonization, during which a large-area graphene sheets formed with a part of the structure defects being repaired. When only GO was reduced by magnesium in SHS process, and the reduced GO (rGO) exhibited the smaller sheets, the lower C/O ratio (15.26), the weaker conductivity (4200 S/m) and the poor water-solubility because rGO inevitably left behind carbon vacancies and topological defects. Therefore, the larger sheet, less edge defects and free structure defects associated with vacancies play a key role for graphene sheets good dispersion in water.

An assessment of the process of Self-propagating High-Temperature Synthesis for the fabrication of porous copper composite

International Nuclear Information System (INIS)

Moloodi, A.; Raiszadeh, R.; Vahdati-Khaki, J.; Babakhani, A.

2009-01-01

The present article describes the process of Self-propagating High-temperature Synthesis (SHS) that is employed for fabricating open cell copper-alumina composite foam. This foam was fabricated by the reactions between the powders of CuO, Al and C. The gas released during these reactions as well as the initial porosity of the green powder compact were suggested to be the sources of the produced pores. Further, the effect of C content and the precursor compressing pressure on the porosity content and morphology of the SHS product was determined. Optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were utilized to characterize the porous samples. The optimum weight fractions for blending the initial powders were determined to be 84 wt.% CuO, 9.5 wt.% Al, and 6.5 wt.% C, and the SHS reaction was sustainable only if the initial compacting pressure of the powders was between 100 and 300 MPa.

Thermodynamic and lattice parameter calculation of TiC x produced from Al-Ti-C powders by laser igniting self-propagating high-temperature synthesis

International Nuclear Information System (INIS)

Li, Y.X.; Hu, J.D.; Wang, H.Y.; Guo, Z.X.; Chumakov, A.N.

2007-01-01

TiC x has been formed by self-propagating high-temperature synthesis (SHS) from elemental powder mixtures with a range of C/Ti ratios. The combusting behavior of the powder mixtures was investigated. The effect of the processing variables on the lattice parameter and the composition of TiC were examined. The results show that lattice parameters of TiC x increase with the increase of C/Ti ratio. The variation of Gibbs free energy in Al-Ti-C system was studied based on the thermodynamics theory. The results show that TiC and Al 3 Ti phases are easier to form than Al 4 C 3 phase

Self-propagating high-temperature synthesis of La(Sr)Ga(Mg)O3-δ for electrolyte of solid oxide fuel cells

International Nuclear Information System (INIS)

Ishikawa, Hiroyuki; Enoki, Makiko; Ishihara, Tatsumi; Akiyama, Tomohiro

2007-01-01

This paper describes self-propagating high-temperature synthesis (SHS) of an electrolyte for solid oxide fuel (SOFC), in comparison to a conventional solid-state reaction method (SRM). Doped-lanthanum gallate: La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ (LSGM9182) and LSGM9173 as the SOFC electrolyte, was prepared by the SHS and sintered at different temperatures, for measuring the electrical conductivity of the sintered LSGM and the power generating performance at 1073 K, in comparison to the SRM. In the SHS, the LSGM powders with smaller size were obtained and easily sintered at the 100 K-lower temperature, 1673 K, than in the SRM. Most significantly, the electrical conductivity of the sintered LSGM9182 was as high as 0.11 S cm -1 and its maximum power density was a value of 245 mW cm -2 in the cell configuration of Ni/LSGM9182 (0.501 mm in thickness)/Sm 0.5 Sr 0.5 CoO 3 . The conclusion was that the proposed SHS-sintering method with many benefits of minimizing the energy requirement and the processing time in the production, easing temperature restriction for the sintering, and improving the electrolyte performance up to a conventional level is practicable for producing the LSGM-electrolyte of SOFC at an intermediate-temperature application

Self-propagating high-temperature synthesis of La(Sr)Ga(Mg)O{sub 3-{delta}} for electrolyte of solid oxide fuel cells

Energy Technology Data Exchange (ETDEWEB)

Ishikawa, Hiroyuki [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo 060-8628 (Japan); Enoki, Makiko [Department of Applied Chemistry, Faculty of Engineering, Kyusyu University, Fukuoka 812-8581 (Japan); Ishihara, Tatsumi [Department of Applied Chemistry, Faculty of Engineering, Kyusyu University, Fukuoka 812-8581 (Japan); Akiyama, Tomohiro [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo 060-8628 (Japan)]. E-mail: takiyama@eng.hokudai.ac.jp

2007-03-14

This paper describes self-propagating high-temperature synthesis (SHS) of an electrolyte for solid oxide fuel (SOFC), in comparison to a conventional solid-state reaction method (SRM). Doped-lanthanum gallate: La{sub 0.9}Sr{sub 0.1}Ga{sub 0.8}Mg{sub 0.2}O{sub 3-{delta}} (LSGM9182) and LSGM9173 as the SOFC electrolyte, was prepared by the SHS and sintered at different temperatures, for measuring the electrical conductivity of the sintered LSGM and the power generating performance at 1073 K, in comparison to the SRM. In the SHS, the LSGM powders with smaller size were obtained and easily sintered at the 100 K-lower temperature, 1673 K, than in the SRM. Most significantly, the electrical conductivity of the sintered LSGM9182 was as high as 0.11 S cm{sup -1} and its maximum power density was a value of 245 mW cm{sup -2} in the cell configuration of Ni/LSGM9182 (0.501 mm in thickness)/Sm{sub 0.5}Sr{sub 0.5}CoO{sub 3}. The conclusion was that the proposed SHS-sintering method with many benefits of minimizing the energy requirement and the processing time in the production, easing temperature restriction for the sintering, and improving the electrolyte performance up to a conventional level is practicable for producing the LSGM-electrolyte of SOFC at an intermediate-temperature application.

Effects of process parameters on tungsten boride production from WO{sub 3} by self propagating high temperature synthesis

Energy Technology Data Exchange (ETDEWEB)

Yazici, Sertac [Metallurgical and Materials Engineering Department, Istanbul Technical University, Maslak, Istanbul 34469 (Turkey); Derin, Bora, E-mail: bderin@itu.edu.tr [Metallurgical and Materials Engineering Department, Istanbul Technical University, Maslak, Istanbul 34469 (Turkey)

2013-01-01

Highlights: Black-Right-Pointing-Pointer We produced tungsten boride compounds by SHS method. Black-Right-Pointing-Pointer Mg containing byproducts were leached out by using a hot aqueous HCl media. Black-Right-Pointing-Pointer The ratio of W{sub 2}B{sub 5}/WB was found to be {approx}2.0 containing minor phases of W{sub 2}B and W. - Abstract: In the present study, the production parameters of tungsten boride compounds by self-propagating high-temperature synthesis (SHS) method and following leaching process were investigated. In the SHS stage, the products consisting of tungsten borides, magnesium oxide, magnesium borate, and also minor compounds were obtained by using different initial molar ratios of WO{sub 3}, Mg and B{sub 2}O{sub 3} as starting materials. In the leaching step, Mg containing byproducts, i.e. MgO and Mg{sub 3}B{sub 2}O{sub 6}, existed in the selected SHS product synthesized at 1:8:2.5 initial molar ratio of WO{sub 3}:Mg:B{sub 2}O{sub 3} were leached out by using aqueous HCl solution to obtain clean tungsten boride compounds at different experimental parameters which are time, acid concentration and temperature. The acid leaching experiments of the SHS product showed that optimum leaching conditions could be achieved by using 5.8 M HCl at 1/10 S/L ratio and the temperature of 80 Degree-Sign C for 60 min.

Functional Properties of Porous Ti-48.0 at.% Ni Shape Memory Alloy Produced by Self-Propagating High-Temperature Synthesis

Science.gov (United States)

Resnina, Natalia; Belyaev, Sergey; Voronkov, Andrew

2018-03-01

The functional behavior of the porous shape memory alloy produced by self-propagating high-temperature synthesis from the Ti-48.0 at.% Ni powder mixture was studied. It was found that a large unelastic strain recovered on unloading and it was not attributed to the pseudoelasticity effect. A decrease in deformation temperatures did not influence the value of strain that recovered on unloading, while the effective modulus decreased from 1.9 to 1.44 GPa. It was found that the porous Ti-48.0 at.% Ni alloy revealed the one-way shape memory effect, where the maximum recoverable strain was 5%. The porous Ti-48.0 at.% Ni alloy demonstrated the transformation plasticity and the shape memory effects on cooling and heating under a stress. An increase in stress did not influence the shape memory effect value, which was equal to 1%. It was shown that the functional properties of the porous alloy were determined by the TiNi phase consisted of the two volumes Ti49.3Ni50.7 and Ti50Ni50 where the martensitic transformation occurred at different temperatures. The results of the study showed that the existence of the Ti49.3Ni50.7 volumes in the porous Ti-48.0 at.% Ni alloy improved the functional properties of the alloy.

Preparation of Al-Ti-B grain refiner by SHS technology[Self-propagating High-temperature Synthesis

Energy Technology Data Exchange (ETDEWEB)

Nikitin, V.I.; Wanqi, J.I.E.; Kandalova, E.G.; Makarenko, A.G.; Yong, L.

2000-02-01

Since the discovery of the grain refinement effect of aluminum by titanium, especially with the existence of B or C in 1950, grain refiners are widely accepted in industry for microstructure control of aluminum alloys. Research on this topic is to obtain the highest grain refinement efficiency with the lowest possible addition of master alloy. It is widely accepted that the morphology and size of TiAl{sub 3} particles, which are known as heterogeneous nucleation centers, are important factors deterring the grain refinement efficiency. Fine TiAl{sub 3} particles are favorable. The grain refinement process shows a heredity phenomenon, which means that structural information from initial materials transfers through a melt to the final product. It is important to find the connection between microstructural parameters of the master alloy and the final product. To improve the quality of Al-Ti-B master alloys for the use as a grain refiner, a new method based on SHS (self-propagating high-temperature synthesis) technology has been developed in Samara State Technical University to produce the master alloys. SHS, as a new method for preparation of materials, was first utilized by Merzhanov in 1967. This method uses the energy from highly exothermic reactions to sustain the chemical reaction in a combustion wave. The advantages of SHS include simplicity, low energy requirement, and higher product purity. Because SHS reactions can take place between elemental reactants, it is easy to control product composition. The purposes of this investigation were to fabricate an SHS Al-5%Ti-1%B master alloy, to analyze its structure and to test its grain refining performance.

Fabrication of Titanium Diboride-Cu Composite by Self-High Temperature Synthesis plus Quick Press

Institute of Scientific and Technical Information of China (English)

Jinyong ZHANG; Zhengyi FU; Weimin WANG

2005-01-01

Titanium diboride based composites, good candidates for contact materials, have high hardness, Young's modulus,high temperature stability, and excellent electrical, thermal conductivity. However a good interface of TiB2/Cu is very difficult to achieve for oxidation of TiB2. To avoid this oxidation behavior, the in situ combusting synthesis technology, SHS, was used to prepare TiB2/Cu composite. Thecharacters of Ti-B-xCu SHS were studied in detail,such as combustion temperature, products phases and grain size. Based on the experimental results a proper technology way of self-high temperature synthesis plus quick press (SHS/QP) was determined and compact TiB2/Cu composites with relative density over than 97 pct of the theoretical were fabricated by this method. The properties and microstructures of these TiB2 based composites were also investigated.

Self-propagating high temperature synthesis and magnetic ...

Indian Academy of Sciences (India)

Unknown

phase composition, microstructure and magnetic properties of the combustion products. The effect ... The size and shapes of the ... Figure 3 shows the effect of combustion temperature on ... ducts at 1200°C are too hard to be ground easily and.

Computer modeling of the process of self-propagating high-temperature synthesis in thin system Ni-Al

International Nuclear Information System (INIS)

Poletayev, G.M.; Starostenkov, M.D.; Denisova, N.F.; Skakov, M.K.

2004-01-01

Full text: The process of synthesis of thermal phases of the system Ni-Al is studied through the method of molecular dynamics. As the object of investigation was chosen two-dimensional crystal, that corresponds to atomic packing laying at the plane of volumetric fcc crystal. Clean Ni was taken as a matrix crystal. A particle of clean Al is packed in the center of matrix block. Beyond the bounds of calculated block crystal packing is repeated with the help of periodical border conditions. The interaction between different pairs of atoms is set by pair potential function of Morse, considering interatomic bonding of the point of the sixth coordinate sphere. The allocation of speeds of atomic function in the system is set through the Boltzmann factor, depending the temperature. When the bicrystal is represented by the ideal atom packing and there are no vacancies , the process of structural adjustment is only observed at the temperature, that is higher than melting point. At that, structural adjustment is observed in circular mechanism of atom allocation, also through the border between phases of clean Ni and Al. As a result, Al particle is transformed, at the border between metals, fields of positional disorder and embryos of intermetallide phases NiAl 2 , Ni 2 Al, Ni 3 Al. The introduction of of free volume through the creation of vacancies significantly lowers the temperature of the beginning of the synthesis process of intermetallide phases. The greatest decrease in temperature to the point of 300 K happens, when the vacancies are located in Ni field of bicrystal, the beginning of the thermo-activation is directly connected with the distance from interphase borders. As the process of thermo-activation continues, vacancies located in Ni matrix right up to seventh neighborhood relatively the border bicrystal. During thermo-activation Al particles enter the field and activate the synthesis process

Morse oscillator propagator in the high temperature limit I: Theory

Energy Technology Data Exchange (ETDEWEB)

Toutounji, Mohamad, E-mail: Mtoutounji@uaeu.ac.ae

2017-02-15

In an earlier work of the author the time evolution of Morse oscillator was studied analytically and exactly at low temperatures whereupon optical correlation functions were calculated using Morse oscillator coherent states were employed. Morse oscillator propagator in the high temperature limit is derived and a closed form of its corresponding canonical partition function is obtained. Both diagonal and off-diagonal forms of Morse oscillator propagator are derived in the high temperature limit. Partition functions of diatomic molecules are calculated. - Highlights: • Derives the quantum propagator of Morse oscillator in the high temperature limit. • Uses the resulting diagonal propagator to derive a closed form of Morse oscillator partition function. • Provides a more sophisticated formula of the quantum propagator to test the accuracy of the herein results.

STUDY OF GRINDING PROCESS OF TITANIUM CARBIDE PRODUCED WITH SELF-PROPAGATING HIGH TEMPERATURE SYNTHESIS (SPHTS)

International Nuclear Information System (INIS)

Kovziridze, Z.; Tabatadze, G.; Donadze, G.; Lezhava, A.; Gventsadze, D.

2006-01-01

It is stated that the specific character of SPHTS-preparations of TiC_x consists in crystal lattice strength reflecting the condition of synthesis in ''burning wave''. The use of roentgenographic and other methods of analysis allows to estimate the effect of the conditions of synthesis, causing carbon sublattice defect on grinding intensity of TiC_x phases. Study of the kinetics of vibro-grinding of TiC_x-phases in ethanol and benzene medium allows to establish high grinding intensity of the phases close to stoichiometry and the possibility of high depresion powderds (S_s_p H'' 4.5-6 m"2/g). (author)

Self-organization of high intensity laser pulses propagating in gases

International Nuclear Information System (INIS)

Koga, James

2001-01-01

In recent years the development of high intensity short pulse lasers has opened up wide fields of science which had previously been difficult to study. Recent experiments of short pulse lasers propagating in air have shown that these laser pulses can propagate over very long distances (up to 12 km) with little or no distortion of the pulse. Here we present a model of this propagation using a modified version of the self-organized criticality model developed for sandpiles by Bak, Tang, and Weisenfeld. The additions to the sandpile model include the formation of plasma which acts as a threshold diffusion term and self-focusing by the nonlinear index of refraction which acts as a continuous inverse diffusion. Results of this simple model indicate that a strongly self-focusing laser pulse shows self-organized critical behavior. (author)

Mechanically activated combustion synthesis of molybdenum borosilicides for ultrahigh-temperature structural applications

Energy Technology Data Exchange (ETDEWEB)

Esparza, Alan A.; Shafirovich, Evgeny, E-mail: eshafirovich2@utep.edu

2016-06-15

The thermal efficiency of gas-turbine power plants could be dramatically increased by the development of new structural materials based on molybdenum silicides and borosilicides, which can operate at temperatures higher than 1300 °C with no need for cooling. A major challenge, however, is to simultaneously achieve high oxidation resistance and acceptable mechanical properties at high temperatures. Materials based on Mo{sub 5}SiB{sub 2} (called T{sub 2}) phase are promising materials that offer favorable combinations of high temperature mechanical properties and oxidation resistance. In the present paper, T{sub 2} phase based materials have been obtained using mechanically activated self-propagating high-temperature synthesis (MASHS). Upon ignition, Mo/Si/B/Ti mixtures exhibited a self-sustained propagation of a spinning combustion wave, but the products were porous, contained undesired secondary phases, and had low oxidation resistance. The “chemical oven” technique has been successfully employed to fabricate denser and stronger Mo{sub 5}SiB{sub 2}–TiC, Mo{sub 5}SiB{sub 2}–TiB{sub 2}, and Mo–Mo{sub 5}SiB{sub 2}–Mo{sub 3}Si materials. Among them, Mo{sub 5}SiB{sub 2}–TiB{sub 2} material exhibits the best oxidation resistance at temperatures up to 1500 °C. - Highlights: • Mechanical activation has enabled combustion synthesis of Mo{sub 5}SiB{sub 2} based materials. • For the first time, the fabrication of Mo{sub 5}SiB{sub 2}–TiB{sub 2} material has been reported. • Among the obtained materials, Mo{sub 5}SiB{sub 2}–TiB{sub 2} exhibits the best oxidation resistance.

A novel method for direct fabrication of ferromolybdenum using molybdenite via self-propagation high temperature synthesis

International Nuclear Information System (INIS)

Golmakani, M.H.; Vahdati khaki, J.; Babakhani, A.

2017-01-01

Direct production of ferromolybdenum from molybdenite (MoS 2 ), in the presence of lime as a desulfurizing reagent using combustion synthesis process is investigated. Thermodynamic calculations and measurement of the adiabatic temperature of the reaction denoted that the process is in agreement with the Merzhanov criterion for self-sustaining processes. The experimental results indicated a relatively complete separation between the molten metal droplets and the co-existing slag. The slag and metal phases were characterized by X-ray diffraction, electron microscopy and wet chemical analysis techniques. It was found that sulfur is mainly distributed into the slag in the form of solid calcium sulfide (CaS). The Lack of calcium oxide in the slag indicated a complete desulfurization reaction between lime and the sulfur in molybdenum sulfide. Characterization of the molted metal revealed that only two phases namely Fe 3 Mo 3 C and Fe 3 Mo exist in the melt. Mass balance calculations showed an Iron-molybdenum recovery greater than 85%. Analyses of the phases indicated that a significant amount of Fe 3 Mo 3 C phase (60–70 wt%) is present in ferromolybdenum molten droplets even though the raw materials were low in carbon. Chemical analysis and microstructural studies of the raw materials and the products showed that carbon is not present in sufficient quantities to produce this amount of Fe 3 Mo 3 C; therefore the structure of this phase should contain a high concentration of carbon vacancies. The deviation of Fe 3 Mo 3 C 1-x peaks in X-ray diffraction pattern compared to its standard reference peaks and a calculated 0.02% decrease in the lattice parameter of this phase are evidence of the presence of these carbon vacancies. - Highlights: • A new SHS method for direct fabrication of ferromolybdenum from MoS 2 is introduced. • Addition of CaO as an effective desulfurizing agent has been investigated. • Removing the oxidative roasting process, and sulfur gas emission

A novel method for direct fabrication of ferromolybdenum using molybdenite via self-propagation high temperature synthesis

Energy Technology Data Exchange (ETDEWEB)

Golmakani, M.H.; Vahdati khaki, J., E-mail: vahdati@um.ac.ir; Babakhani, A.

2017-06-15

Direct production of ferromolybdenum from molybdenite (MoS{sub 2}), in the presence of lime as a desulfurizing reagent using combustion synthesis process is investigated. Thermodynamic calculations and measurement of the adiabatic temperature of the reaction denoted that the process is in agreement with the Merzhanov criterion for self-sustaining processes. The experimental results indicated a relatively complete separation between the molten metal droplets and the co-existing slag. The slag and metal phases were characterized by X-ray diffraction, electron microscopy and wet chemical analysis techniques. It was found that sulfur is mainly distributed into the slag in the form of solid calcium sulfide (CaS). The Lack of calcium oxide in the slag indicated a complete desulfurization reaction between lime and the sulfur in molybdenum sulfide. Characterization of the molted metal revealed that only two phases namely Fe{sub 3}Mo{sub 3}C and Fe{sub 3}Mo exist in the melt. Mass balance calculations showed an Iron-molybdenum recovery greater than 85%. Analyses of the phases indicated that a significant amount of Fe{sub 3}Mo{sub 3}C phase (60–70 wt%) is present in ferromolybdenum molten droplets even though the raw materials were low in carbon. Chemical analysis and microstructural studies of the raw materials and the products showed that carbon is not present in sufficient quantities to produce this amount of Fe{sub 3}Mo{sub 3}C; therefore the structure of this phase should contain a high concentration of carbon vacancies. The deviation of Fe{sub 3}Mo{sub 3}C{sub 1-x} peaks in X-ray diffraction pattern compared to its standard reference peaks and a calculated 0.02% decrease in the lattice parameter of this phase are evidence of the presence of these carbon vacancies. - Highlights: • A new SHS method for direct fabrication of ferromolybdenum from MoS{sub 2} is introduced. • Addition of CaO as an effective desulfurizing agent has been investigated. • Removing the

Production of porous sintered materials using wastes of manufacturing engineering in self-propagating high-temperature synthesis

Directory of Open Access Journals (Sweden)

Y. S. Povstyana

2016-06-01

Full Text Available The increasing amount of wastes produced by the manufacturing engineering, as well as their physical and mechanical properties and restorability provide a search for sphere of their application. The actual problem of modern science is the utilization of wastes and using them in further production that will minimize their harmful impact on the environment and reduce the cost of expensive raw materials. Wastes are ideally suitable for the manufacture of porous permeable materials (filters. Powder metallurgy allows obtaining products with controlled filtration, physical and mechanical properties. Such materials are good filters for regeneration of technical liquids, oils, cooling fluids, sewage etc. The article analyzes the methods and technologies for the manufacture of porous ceramic materials and a new technology for their manufacture, which is based on use of mill scale and natural mineral – saponite as the main components. Compression technology provides products at low pressures and sintering by passing high-temperature synthesis. The proposed technology is characterized by low cost and good physical and mechanical properties of the product that gives a reason to use them for filtering and regeneration of technical liquids.

High temperature synthesis of ceramic composition by directed reaction of molten titanium or zirconium with boron carbide

International Nuclear Information System (INIS)

Johnson, W.B.

1990-01-01

Alternative methods of producing ceramics and ceramic composites include sintering, hot pressing and more recently hot isostatic pressing (HIP) and self-propagating high temperature synthesis (SHS). Though each of these techniques has its advantages, each suffers from several restrictions as well. Sintering may require long times at high temperatures and for most materials requires sintering aids to get full density. These additives can, and generally do, change (often degrade) the properties of the ceramic. Hot pressing and hot isostatic pressing are convenient methods to quickly prepare samples of some materials to full density, but generally are expensive and may damage some types of reinforcements during densification. This paper focuses on the preparation and processing of composites prepared by the directed reaction of molten titanium or zirconium with boron carbide. Advantages and disadvantages of this approach when compared to traditional methods are discussed, with reference to specific examples. Examples of microstructure are properties of these materials are reported

Preparation of lead oxide nanoparticles from cathode-ray tube funnel glass by self-propagating method.

Science.gov (United States)

Wang, Yu; Zhu, Jianxin

2012-05-15

This paper presents a novel process of extracting lead oxide nanoparticles from cathode-ray tube (CRT) funnel glass using self-propagating high-temperature synthesis (SHS) method. The impacts of added amount of funnel glass on the extraction ratio of lead, the lead extraction velocity and the micromorphology, as well as particle size of extracted nanoparticles were investigated. We found that self-propagating reaction in the presence of Mg and Fe(2)O(3) could separate lead preferentially and superfine lead oxide nanoparticles were obtained from a collecting chamber. The separation ratio was related closely to the amount of funnel glass added in the original mixture. At funnel glass addition of no more than 40wt.%, over 90wt.% of lead was recovered from funnel glass. High extraction yield reveals that the network structure of funnel glass was fractured due to the dramatic energy generated during the SHS melting process. The PbO nanoparticles collected show good dispersion and morphology with a mean grain size of 40-50nm. Copyright © 2012 Elsevier B.V. All rights reserved.

High temperature meson propagators with domain-wall quarks

International Nuclear Information System (INIS)

Lagae, J.-F.; Sinclair, D. K.

1999-01-01

We study the chiral properties of domain-wall quarks at high temperatures on an ensemble of quenched configurations. Low lying eigenmodes of the Dirac operator are calculated and used to check the extent to which the Atiyah-Singer index theorem is obeyed on lattices with finite N 5 . We calculate the connected and disconnected screening propagators for the lowest mass scalar and pseudoscalar mesons in the sectors of different topological charge and note that they behave as expected. Separating out the would-be zero eigenmodes enables us to accurately estimate the disconnected propagators with far less effort than would be needed otherwise

High temperature meson propagators with domain-wall quarks

International Nuclear Information System (INIS)

Lagaee, J.-F.; Sinclair, D.K.

2000-01-01

We study the chiral properties of domain-wall quarks at high temperatures on an ensemble of quenched configurations. Low lying eigenmodes of the Dirac operator are calculated and used to check the extent to which the Atiyah-Singer index theorem is obeyed on lattices with finite N 5 . We calculate the connected and disconnected screening propagators for the lowest mass scalar and pseudoscalar mesons in the sectors of different topological charge and note that they behave as expected. Separating out the would-be zero eigenmodes enables us to accurately estimate the disconnected propagators with far less effort than would be needed otherwise

Pulsed cathodoluminescence and Raman spectra of MoS{sub 2} and WS{sub 2} nanocrystals and their combination MoS{sub 2}/WS{sub 2} produced by self-propagating high-temperature synthesis

Energy Technology Data Exchange (ETDEWEB)

Bozheyev, Farabi, E-mail: farabi.bozheyev@gmail.com [Institute of High Technology Physics, National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk (Russian Federation); National Nanolaboratory, al-Farabi Kazakh National University, 71 al-Farabi Ave., 050000 Almaty (Kazakhstan); Nazarbayev University Research and Innovation System, 53 Kabanbay Batyr St., 010000 Astana (Kazakhstan); Valiev, Damir [Institute of High Technology Physics, National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk (Russian Federation); Nemkayeva, Renata [National Nanolaboratory, al-Farabi Kazakh National University, 71 al-Farabi Ave., 050000 Almaty (Kazakhstan)

2016-02-29

Molybdenum and tungsten disulfide nanoplates were produced by self-propagating high-temperature synthesis in argon atmosphere. This method provides an easy way to produce MoS{sub 2} and WS{sub 2} from nanoplates up to single- and several layers. The Raman peak intensities corresponding to in-plane E{sup 1}{sub 2g} and out-of-plane A{sub 1g} vibration modes and their shifts strongly depend on the thicknesses of the MoS{sub 2} and WS{sub 2} platelets indicating size-dependent scaling laws and properties. An electron beam irradiation of MoS{sub 2} and WS{sub 2} powders leads to an occurrence of pulsed cathodoluminescence (PCL) spectra at 575 nm (2.15 eV) and 550 nm (2.25 eV) characteristic to their intrinsic band gaps. For the combination of MoS{sub 2} and WS{sub 2} nanopowders, a PCL shoulder at 430 nm (2.88 eV) was observed, which is explained by the radiative electron-hole recombination at the MoS{sub 2}/WS{sub 2} grain boundaries. The luminescence decay kinetics of the MoS{sub 2}/WS{sub 2} nanoplates appears to be slower than for individual MoS{sub 2} and WS{sub 2} platelets due to a spatial separation of electrons and holes at MoS{sub 2}/WS{sub 2} junction resulting in extension of recombination time.

Laser induced self-propagating reduction and exfoliation of graphite oxide as an electrode material for supercapacitors

International Nuclear Information System (INIS)

Wang, Dewei; Min, Yonggang; Yu, Youhai; Peng, Bo

2014-01-01

Graphical abstract: - Highlights: • Few layers graphene was obtained by laser induced self-propagating reduction. • The process is ultrafast without assistance of any high temperate/vacuum environment. • The as-prepared graphene exhibits excellent electrochemical performance. • The superior capacitive behavior is owing to its unique structures. - Abstract: Focused laser beam induced self-propagating reaction has been developed for fabrication of graphene rapidly and efficiently through simultaneous reduction and exfoliation of graphite oxide (GO) process. This chemical-free approach can realize the reduction and exfoliation at room temperature without assistance of any high temperature/vacuum environment. We found that the small sized spot can trigger an ultrafast and highly thermal transferred process by self-propagating reaction at ambient conditions. Benefiting from its high surface area and unique structure, the laser induced self-propagating reaction reduced graphene (LIG) shows excellent capacitive performance. Considering that the cost-effective and feasible process, this facile technique presented here will not only provide a promising method for production of graphene on an industrial scale, but also put forward the application graphene materials in energy storage and conversion

Synthesis and characterization of actinide metal compounds formed by combustion

International Nuclear Information System (INIS)

Behrens, R.G.; King, M.A.

1985-01-01

This paper briefly describes the results of attempts to synthesize arsenides, phosphides, and antimonides of uranium and thorium using Self-Propagating High-Temperature Synthesis (SHS) techniques. This paper first summarizes the chemistry and thermodynamics of these chemical systems, describes SHS synthesis techniques, and then describes the results of the syntheses using data from powder x-ray diffraction, metallographic, and electron microprobe analyses

Alcohol synthesis in a high-temperature slurry reactor

Energy Technology Data Exchange (ETDEWEB)

Roberts, G.W.; Marquez, M.A.; McCutchen, M.S. [North Carolina State Univ., Raleigh, NC (United States)

1995-12-31

The overall objective of this contract is to develop improved process and catalyst technology for producing higher alcohols from synthesis gas or its derivatives. Recent research has been focused on developing a slurry reactor that can operate at temperatures up to about 400{degrees}C and on evaluating the so-called {open_quotes}high pressure{close_quotes} methanol synthesis catalyst using this reactor. A laboratory stirred autoclave reactor has been developed that is capable of operating at temperatures up to 400{degrees}C and pressures of at least 170 atm. The overhead system on the reactor is designed so that the temperature of the gas leaving the system can be closely controlled. An external liquid-level detector is installed on the gas/liquid separator and a pump is used to return condensed slurry liquid from the separator to the reactor. In order to ensure that gas/liquid mass transfer does not influence the observed reaction rate, it was necessary to feed the synthesis gas below the level of the agitator. The performance of a commercial {open_quotes}high pressure {close_quotes} methanol synthesis catalyst, the so-called {open_quotes}zinc chromite{close_quotes} catalyst, has been characterized over a range of temperature from 275 to 400{degrees}C, a range of pressure from 70 to 170 atm., a range of H{sub 2}/CO ratios from 0.5 to 2.0 and a range of space velocities from 2500 to 10,000 sL/kg.(catalyst),hr. Towards the lower end of the temperature range, methanol was the only significant product.

Ideal laser-beam propagation through high-temperature ignition Hohlraum plasmas.

Science.gov (United States)

Froula, D H; Divol, L; Meezan, N B; Dixit, S; Moody, J D; Neumayer, P; Pollock, B B; Ross, J S; Glenzer, S H

2007-02-23

We demonstrate that a blue (3omega, 351 nm) laser beam with an intensity of 2 x 10(15) W cm(-2) propagates nearly within the original beam cone through a millimeter scale, T(e)=3.5 keV high density (n(e)=5 x 10(20) cm(-3)) plasma. The beam produced less than 1% total backscatter at these high temperatures and densities; the resulting transmission is greater than 90%. Scaling of the electron temperature in the plasma shows that the plasma becomes transparent for uniform electron temperatures above 3 keV. These results are consistent with linear theory thresholds for both filamentation and backscatter instabilities inferred from detailed hydrodynamic simulations. This provides a strong justification for current inertial confinement fusion designs to remain below these thresholds.

Optimization of the Technological Synthesis of Refractory Compounds

Science.gov (United States)

Gaidar, S. M.; Karelina, M. Yu.; Prikhod'ko, V. M.; Volkov, A. A.

2017-12-01

The results of experimental studies, which are related to the regulation of the fractional composition of refractory compounds by roll milling in using controlled roll opening and unbalanced peripheral speeds of rollers, are reported. The content of prepared fine, middle, and coarse fractions is within 50-80%; in this case, the milling time of synthesis products is less than the time of ball milling by an order of magnitude. The application of roll milling for refining the products of self-propagating high-temperature synthesis can be most efficient in using together with heat-generating reactor to solve the main problem of self-propagating synthesis (SHS), which is a problem for recent several decades (the problem is the creation of intense automated production of refractory compounds in using continuous manufacturing cycle within a energotechnological system with the recovery of a great quantity of heat released during SHS).

Green frequency-doubled laser-beam propagation in high-temperature hohlraum plasmas.

Science.gov (United States)

Niemann, C; Berger, R L; Divol, L; Froula, D H; Jones, O; Kirkwood, R K; Meezan, N; Moody, J D; Ross, J; Sorce, C; Suter, L J; Glenzer, S H

2008-02-01

We demonstrate propagation and small backscatter losses of a frequency-doubled (2omega) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of 2 higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2omega laser-beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggest that good laser coupling into fusion hohlraums using 2omega light is possible.

Single Crystal Synthesis and STM Studies of High Temperature Superconductors

Science.gov (United States)

Barrientos, Alfonso

1997-01-01

This is a final report for the work initiated in September of 1994 under the grant NAG8-1085 - NASA/OMU, on the fabrication of bulk and single crystal synthesis, specific heat measuring and STM studies of high temperature superconductors. Efforts were made to fabricate bulk and single crystals of mercury based superconducting material. A systematic thermal analysis on the precursors for the corresponding oxides and carbonates were carried out to synthesized bulk samples. Bulk material was used as seed in an attempt to grow single crystals by a two-step self flux process. On the other hand bulk samples were characterized by x-ray diffraction, electrical resistivity and magnetic susceptibility, We studied the specific heat behavior in the range from 80 to 300 K. Some preliminary attempts were made to study the atomic morphology of our samples. As part of our efforts we built an ac susceptibility apparatus for measuring the transition temperature of our sintered samples.

High temperature initiation and propagation of cracks in 12%Cr-steel turbine disks

Directory of Open Access Journals (Sweden)

S. Foletti

2013-10-01

Full Text Available This work aims to study the crack propagation in 12%Cr steel for turbine disks. Creep Crack Growth (CCG tests on CT specimens have been performed to define the proper fracture mechanics which describes the initiation of the crack propagation and the crack growth behaviour for the material at high temperature. Results have been used to study the occurrence of crack initiation on a turbine disk at the extreme working temperature and stress level experienced during service, and validate the use of C* integral in correlating creep growth rate on the disk component, in case C* is numerically calculated through FEM analysis or calculated by the use of reference stress concept.

Synthesis of high quality single-walled carbon nanotubes via a catalytic layer reinforced by self-assembled monolayers

International Nuclear Information System (INIS)

Adhikari, Prashanta Dhoj; Song, Wooseok; Cha, Myoung-Jun; Park, Chong-Yun

2013-01-01

This work reports the synthesis of high quality single-walled carbon nanotubes (SWCNT) using a catalytic layer reinforced by self-assembled monolayers (SAM). Amine-SAM was introduced on a SiO 2 /Si substrate and then an iron nanoparticles solution was dropped on the substrate by spin-coating. This catalytic template was used to grow carbon nanotubes by chemical vapor deposition and the synthesized SWCNT were observed to be prominent, based on the size distribution. Highly dense SWCNT with a diameter of about 1.1-1.2 nm were produced at 800-850 °C. Moreover, the diameter distribution of the SWCNT was more selective at a growth temperature of 900 °C. These findings provide important insights for a SAM support layer that can play the role as a restriction for the agglomeration of iron catalyst and is promising for the synthesis of high quality SWCNT. - Highlights: • Fe nanoparticles on self-assembled monolayers (SAM) containing template is underlined. • Its catalytic behavior to synthesis single-walled carbon nanotubes is studied. • The role of SAM on catalytic template is explored

Effects of temperature on SCC propagation in high temperature water injected with hydrogen peroxide

International Nuclear Information System (INIS)

Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Yoshiyuki, Kaji; Yamamoto, Masahiro; Tsukada, Takashi

2012-09-01

To understand the stress corrosion cracking (SCC) behaviour of austenitic stainless steels (SSs) in the boiling water reactor (BWR) coolant environment, it is significant to investigate the effect of hydrogen peroxide (H 2 O 2 ) produced by the radiolysis of water on SCC under the various water chemistry and operational conditions. At the start-up or shut-down periods, for example, the conditions of radiation and temperature on the structural materials are different from those during the plant normal operation, and may be influencing on SCC behaviour. Therefore, the effect of temperature on SCC in high temperature water injected with H 2 O 2 was evaluated by SCC propagation test at the present study. Oxide films on the metal surface in crack were examined and the thermal equilibrium diagram was calculated to estimate the environmental situation in the crack. On the thermally sensitized type 304 SS, crack growth tests were conducted in high temperature water injected with H 2 O 2 to simulate water radiolysis in the core. Small CT type specimens with a width of 15.5 mm and thickness of 6.2 mm were machined from the sensitized SS. SCC growth tests were conducted in high temperature water injected with 100 ppb H 2 O 2 at 453 and 561 K. To minimize H 2 O 2 decomposition by a contact with metal surface of autoclave, the CT specimen was isolated from inner surface of the autoclave by the inner modules made of polytetrafluoroethylene (PTFE), and PTFE lining was also used for the inner surface of inlet and sampling tubes. Base on the measurement of sampled water, it was confirmed that 80-90 % of injected H 2 O 2 remained around the CT specimen in autoclave. Constant load at initial K levels of 11-20 MPam 1/2 was applied to the CT specimens during crack growth tests. After crack growth tests, CT specimens were split into two pieces on the plane of crack propagation. Scanning electron microscope (SEM) examination and laser Raman spectroscopy for outer oxide layer of oxide

Cermet materials prepared by combustion synthesis and metal infiltration

Science.gov (United States)

Holt, Joseph B.; Dunmead, Stephen D.; Halverson, Danny C.; Landingham, Richard L.

1991-01-01

Ceramic-metal composites (cermets) are made by a combination of self-propagating high temperature combustion synthesis and molten metal infiltration. Solid-gas, solid-solid and solid-liquid reactions of a powder compact produce a porous ceramic body which is infiltrated by molten metal to produce a composite body of higher density. AlN-Al and many other materials can be produced.

Self-propagating high temperature synthesis as a method of determination of formation heat of refractory compounds

International Nuclear Information System (INIS)

Maslov, V.M.; Neganov, A.S.; Borovinskaya, I.P.; Merzhanov, A.G.

1978-01-01

Determination possibility of formation heats of refractory compounds in the process of direct synthesis from elements in a special calorimeter in the combustion regime is studied. Determined are formation heats of carbides - ZrCsub(0.92), Hf Csub(0.93), TaCsub(0.86), borides - ZrB 2 , HfB 2 NbB, NbB 2 , TaB, TaB 2 , MoB and silicides - ZrSi, ZrSi 2 , MoSi 2 . The results of chemical and x-ray phase analyses of the synthesized compounds are also given. Total error of formation heat determination methods does not surpass 2.0%

Room temperature synthesis and high temperature frictional study of silver vanadate nanorods

Energy Technology Data Exchange (ETDEWEB)

Singh, D P; Aouadi, S M [Department of Physics, Southern Illinois University, Carbondale-62901 (United States); Polychronopoulou, K [Department of Chemistry, University of Cyprus, Nicosia, 1678 (Cyprus); Rebholz, C, E-mail: dineshpsingh@gmail.com, E-mail: saouadi@physics.siu.edu [Department of Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia, 1678 (Cyprus)

2010-08-13

We report the room temperature (RT) synthesis of silver vanadate nanorods (consisting of mainly {beta}-AgV O{sub 3}) by a simple wet chemical route and their frictional study at high temperatures (HT). The sudden mixing of ammonium vanadate with silver nitrate solution under constant magnetic stirring resulted in a pale yellow coloured precipitate. Structural/microstructural characterization of the precipitate through x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the high yield and homogeneous formation of silver vanadate nanorods. The length of the nanorods was 20-40 {mu}m and the thickness 100-600 nm. The pH variation with respect to time was thoroughly studied to understand the formation mechanism of the silver vanadate nanorods. This synthesis process neither demands HT, surfactants nor long reaction time. The silver vanadate nanomaterial showed good lubrication behaviour at HT (700 deg. C) and the friction coefficient was between 0.2 and 0.3. HT-XRD revealed that AgV O{sub 3} completely transformed into silver vanadium oxide (Ag{sub 2}V{sub 4}O{sub 11}) and silver with an increase in temperature from RT to 700 deg. C.

Room temperature synthesis and high temperature frictional study of silver vanadate nanorods.

Science.gov (United States)

Singh, D P; Polychronopoulou, K; Rebholz, C; Aouadi, S M

2010-08-13

We report the room temperature (RT) synthesis of silver vanadate nanorods (consisting of mainly beta-AgV O(3)) by a simple wet chemical route and their frictional study at high temperatures (HT). The sudden mixing of ammonium vanadate with silver nitrate solution under constant magnetic stirring resulted in a pale yellow coloured precipitate. Structural/microstructural characterization of the precipitate through x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the high yield and homogeneous formation of silver vanadate nanorods. The length of the nanorods was 20-40 microm and the thickness 100-600 nm. The pH variation with respect to time was thoroughly studied to understand the formation mechanism of the silver vanadate nanorods. This synthesis process neither demands HT, surfactants nor long reaction time. The silver vanadate nanomaterial showed good lubrication behaviour at HT (700 degrees C) and the friction coefficient was between 0.2 and 0.3. HT-XRD revealed that AgV O(3) completely transformed into silver vanadium oxide (Ag(2)V(4)O(11)) and silver with an increase in temperature from RT to 700 degrees C.

Self-Propagating Frontal Polymerization in Water at Ambient Pressure

Science.gov (United States)

Olten, Nesrin; Kraigsley, Alison; Ronney, Paul D.

2003-01-01

Advances in polymer chemistry have led to the development of monomers and initiation agents that enable propagating free-radical polymerization fronts to exist. These fronts are driven by the exothermicity of the polymerization reaction and the transport of heat from the polymerized product to the reactant monomer/solvent/initiator solution. The thermal energy transported to the reactant solution causes the initiator to decompose, yielding free radicals, which start the free radical polymerization process as discussed in recent reviews. The use of polymerization processes based on propagating fronts has numerous applications. Perhaps the most important of these is that it enables rapid curing of polymers without external heating since the polymerization process itself provides the high temperatures necessary to initiate and sustain polymerization. This process also enables more uniform curing of arbitrarily thick samples since it does not rely on heat transfer from an external source, which will necessarily cause the temperature history of the sample to vary with distance from the surface according to a diffusion-like process. Frontal polymerization also enables filling and sealing of structures having cavities of arbitrary shape without having to externally heat the structure. Water at atmospheric pressure is most convenient solvent to employ and the most important for practical applications (because of the cost and environmental issues associated with DMSO and other solvents). Nevertheless, to our knowledge, steady, self-propagating polymerization fronts have not been reported in water at atmospheric pressure. Currently, polymerization fronts require a high boiling point solvent (either water at high pressures or an alternative solvent such as dimethyl sulfoxide (DMSO) (boiling point 189 C at atmospheric pressure.) Early work on frontal polymerization, employed pressures up to 5000 atm in order to avoid boiling of the monomer/solvent/initiator solution. High

Propagation of sound wave in high density deuterium at high temperatures

International Nuclear Information System (INIS)

Inoue, Kazuko; Ariyasu, Tomio

1986-01-01

The velocity and the attenuation constant of sound wave have been calculated for high density (10 24 ∼ 10 27 /cm 3 ) deuterium at high temperatures (10 -1 ∼ 10 4 eV). This calculation was made to understand the fuel properties in inertial confinement fusion and to obtain the basic data for pellet design. The isentropic sound wave which propagates in deuterium in plasma state at temperature T i = T e , is dealt with. The velocity is derived using the modulus of bulk elasticity of the whole system and the modulus of shear elasticity due to ion-ion interaction. For the calculation of attenuation constant, the bulk and shear viscosity due to ion-ion interaction, the shear viscosity of free electron gas, and the thermal conductivity due to free electrons are considered. The condition of frequency for the existence of such isentropic sound wave is discussed. The possibility of penetration into the fuel pellet in inertial confinement fusion is also discussed. The followings have been found: (1) The sound velocity is determined mainly from the bulk elasticity. The contribution of the shear elasticity is small. The velocity ranges from 2.8 x 10 6 to 1.5 x 10 8 cm/s in the above mentioned temperature and density regions. (2) The coefficient of attenuation constant with respect to ω 2 /2ρu 3 plotted versus temperature with the parameter of density shows a minimum. At temperatures below this minimum, the attenuation comes mainly from the bulk viscosity due to ion-ion interaction and the shear viscosity due to free electron gas. At temperatures above this minimum, the sound is attenuated mainly by the thermal conductivity due to electrons. (3) The condition for the existence of such adiabatic sound wave, is satisfied with the frequency less than 10 10 Hz. But, as for the pellet design, the wave length of sound with frequency less than 10 10 Hz is longer than the diameter of pellet when compressed highly. (author)

Self-weldability of various materials in high temperature sodium

International Nuclear Information System (INIS)

Mizobuchi, Syotaro; Kano, Shigeki; Nakayama, Kohichi; Atsumo, Hideo

1980-01-01

Self-Weldability of Various Materials in High Temperature Sodium. The self-welding behavior of various materials was evaluated by measuring the tensile breakaway force of the specimen which had been self-welded in high temperature sodium. Experiments were carried out to investigate the influence of the sodium temperature and the contact stress on the self-welding behavior. The results obtained are as follows: (1) The self-welding behavior in sodium was recognized to initiate by the diffusion of the principal element through the real contact area. (2) Remarkable self-welding behavior was observed for SUS 316 material at 650 0 C, and for 2 1/4Cr-1Mo steel at a sodium temperature of 600 0 C. The self-welding force acting on the real contact area corresponds to the tensile strength of each material. (3) Hard chrome plating or hardfacing material showed good self-weld resistance, but the different combinations of SUS 316 with either of these materials were observed to easily cause self-welding. (4) The self-weldability of Cr 3 C 2 /Ni-Cr material varied with the preparing methods, especially, with the distribution of the binder composition contained in this material. (5) A derived equation was proposed to evaluate the self-welding force. It was found that the measured breakaway force was relatively equal to the self-welding force derived from this equation. (author)

Fatigue Crack Propagation Behavior of RC Beams Strengthened with CFRP under High Temperature and High Humidity Environment

Directory of Open Access Journals (Sweden)

Dongyang Li

2017-01-01

Full Text Available Numerical and experimental methods were applied to investigate fatigue crack propagation behavior of reinforced concrete (RC beams strengthened with a new type carbon fiber reinforced polymer (CFRP named as carbon fiber laminate (CFL subjected to hot-wet environment. J-integral of a central crack in the strengthened beam under three-point bending load was calculated by ABAQUS. In finite element model, simulation of CFL-concrete interface was based on the bilinear cohesive zone model under hot-wet environment and indoor atmosphere. And, then, fatigue crack propagation tests were carried out under high temperature and high humidity (50°C, 95% R · H environment pretreatment and indoor atmosphere (23°C, 78% R · H to obtain a-N curves and crack propagation rate, da/dN, of the strengthened beams. Paris-Erdogan formula was developed based on the numerical analysis and environmental fatigue tests.

Synthesis of TiC/Ni cermets via mechanically activated self-propagating high-temperature synthesis

Energy Technology Data Exchange (ETDEWEB)

Dubois, S.; Heian, E.; Karnatak, N.; Beaufort, M.F. [Lab. de Metallurgie Physique, Futuroscope (France); Vrel, D. [Lab. d' Ingenierie des Materiaux et des Hautes Pressions, Villetaneuse (France)

2003-07-01

Stoichiometric mixtures of Ti and C were milled in a high-energy vibratory mill for varying times and the results carefully characterized via X-ray diffraction and TEM. Cermets of stoichiometric TiC and 20 w% Ni were combustion synthesized from non-milled and milled reactant powders, resulting in porous solids composed of roughly spherical TiC particles surrounded by a layer of Ni. Time resolved infrared analysis shows that the kinetics of the reaction performed with milled reactant powders are drastically enhanced over non-milled reactants. This result may be attributed to the microstructure and uniformity of the milled reactant mixtures. It is also demonstrated that mechanical milling of Ti and C powders strongly affects the TiC grain size in the products, most likely due to a reduction in TiC crystal growth as a consequence of the increase in the reaction kinetics. (orig.)

Multiple cracks initiation and propagation behavior of stainless steel in high temperature water environment

International Nuclear Information System (INIS)

Kamaya, Masayuki; Chiba, Goro; Nakajima, Nobuo; Totsuka, Nobuo

2001-01-01

Environmentally assisted crack initiation behavior is greatly affected by applied stress and environmental factors, such as water temperature, contained impurities and so on. On the other hand, crack initiation behavior also influences crack propagation. A typical example of this influence can be observed as the interference effects of multiple cracks, such as the coalescence of approaching crack tips or the arrest phenomena in the relaxation zone of an adjacent crack. To understand these effects of crack initiation on crack propagation behavior is very important to predict the lifetime of components, in which quite a few cracks tend to occur. This study aimed at revealing the crack initiation behavior and the influence of this behavior on propagation. At first, to evaluate the effect of applied stress on crack initiation behavior, sensitized stainless steel was subjected to a four-point bending test in a high temperature water environment at the constant potentials of ECP +50 mV and ECP +150 mV. Secondly, a crack initiation and growth simulation model was developed, in which the interference effect of multiple cracks is evaluated by the finite element method, based on the experimental results. Using this model, the relationship between crack initiation and propagation was studied. From the model, it was revealed that the increasing number of the cracks accelerates crack propagation and reduces life. (author)

Initiation and propagation of multiple cracks of stainless steel in high temperature water environment

Energy Technology Data Exchange (ETDEWEB)

Kamaya, Masayuki; Chiba, Goro; Nakajima, Nobuo; Totsuka, Nobuo [Institute of Nuclear Safety System Inc., Mihama, Fukui (Japan)

2001-09-01

Environmentally assisted crack initiation behavior is greatly affected by applied stress and environmental factors, such as water temperature, contained impurities and so on. Crack initiation behavior also influences crack propagation. A typical example of this influence can be observed as the interference effects of multiple cracks, such as the coalescence of approaching crack tips or the arrest phenomena in the relaxation zone of an adjacent crack. To understand these effects of crack initiation on crack propagation behavior is very important to predict the lifetime of components, in which relatively large number of cracks tend to occur. This study aimed at revealing the crack initiation behavior and the influence of this behavior on propagation. At first, to evaluate the effect of applied stress on crack initiation behavior, sensitized stainless steel was subjected to a four-point bending test in high temperature water environment at the constant potentials of +50 mV SHE and +150 mV SHE Secondly, a crack initiation and growth simulation model was developed, in which the interference effect of multiple cracks is evaluated by the finite element method, based on the experimental results. Using this model, the relationship between crack initiation and propagation was investigated, and it was revealed that the increasing number of the cracks accelerates crack propagation and reduces life. (author)

Universal self-similarity of propagating populations.

Science.gov (United States)

Eliazar, Iddo; Klafter, Joseph

2010-07-01

This paper explores the universal self-similarity of propagating populations. The following general propagation model is considered: particles are randomly emitted from the origin of a d-dimensional Euclidean space and propagate randomly and independently of each other in space; all particles share a statistically common--yet arbitrary--motion pattern; each particle has its own random propagation parameters--emission epoch, motion frequency, and motion amplitude. The universally self-similar statistics of the particles' displacements and first passage times (FPTs) are analyzed: statistics which are invariant with respect to the details of the displacement and FPT measurements and with respect to the particles' underlying motion pattern. Analysis concludes that the universally self-similar statistics are governed by Poisson processes with power-law intensities and by the Fréchet and Weibull extreme-value laws.

Universal self-similarity of propagating populations

Science.gov (United States)

Eliazar, Iddo; Klafter, Joseph

2010-07-01

This paper explores the universal self-similarity of propagating populations. The following general propagation model is considered: particles are randomly emitted from the origin of a d -dimensional Euclidean space and propagate randomly and independently of each other in space; all particles share a statistically common—yet arbitrary—motion pattern; each particle has its own random propagation parameters—emission epoch, motion frequency, and motion amplitude. The universally self-similar statistics of the particles’ displacements and first passage times (FPTs) are analyzed: statistics which are invariant with respect to the details of the displacement and FPT measurements and with respect to the particles’ underlying motion pattern. Analysis concludes that the universally self-similar statistics are governed by Poisson processes with power-law intensities and by the Fréchet and Weibull extreme-value laws.

ACBC to Balcite: Bioinspired Synthesis of a Highly Substituted High-Temperature Phase from an Amorphous Precursor

Energy Technology Data Exchange (ETDEWEB)

Whittaker, Michael L.; Joester, Derk (NWU)

2017-04-28

Energy-efficient synthesis of materials locked in compositional and structural states far from equilibrium remains a challenging goal, yet biomineralizing organisms routinely assemble such materials with sophisticated designs and advanced functional properties, often using amorphous precursors. However, incorporation of organics limits the useful temperature range of these materials. Herein, the bioinspired synthesis of a highly supersaturated calcite (Ca0.5Ba0.5CO3) called balcite is reported, at mild conditions and using an amorphous calcium–barium carbonate (ACBC) (Ca1- x Ba x CO3·1.2H2O) precursor. Balcite not only contains 50 times more barium than the solubility limit in calcite but also displays the rotational disorder on carbonate sites that is typical for high-temperature calcite. It is significantly harder (30%) and less stiff than calcite, and retains these properties after heating to elevated temperatures. Analysis of balcite local order suggests that it may require the formation of the ACBC precursor and could therefore be an example of nonclassical nucleation. These findings demonstrate that amorphous precursor pathways are powerfully enabling and provide unprecedented access to materials far from equilibrium, including high-temperature modifications by room-temperature synthesis.

Self propagating high temperature synthesis (SHS) of the Fe(TiMo)C master alloy using ferroalloys

International Nuclear Information System (INIS)

Erauskin, J. I.; Sargyan, A.; Arana, J. L.

2009-01-01

Titanium monocarbide TiC is very hard, stable both at high and low temperatures and relatively easy to synthesize from its constituent elements by SHS. Nevertheless, it is difficult to use, as alloying element, in the reinforcement of steels manufactured by liquid metallurgy due to its low wettability by molten steel. To achieve this purpose and due to its better wettability, it is more appropriate to use a master alloy formed by the complex carbide (TiMo)C bonded in Fe. The simplest and most economic way to fabricate such a master alloy Fe(TiMo)C is, again, by SHS, with the added advantage that it can be manufactured using the commercial ferroalloys FeTi and FeMo instead of the individual elements Fe, Ti and Mo. In this work, we describe such a process as well as the characteristics of the master alloy obtained. (Author) 13 refs

Preparation of MoB and MoB-MoSi2 composites by combustion synthesis in SHS mode

International Nuclear Information System (INIS)

Yeh, C.L.; Hsu, W.S.

2007-01-01

Combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) was carried out in the Mo-B and Mo-B-Si systems for the preparation of molybdenum boride MoB and the composite of MoB-MoSi 2 from elemental powder compacts. Under a preheating temperature above 150 deg. C , the reaction of Mo with boron in the sample compact of Mo:B = 1:1 is characterized by a planar combustion front propagating in a self-sustaining and steady manner. As the preheating temperature or sample compaction density increased, combustion temperature was found to increase and the propagation rate of the combustion front was correspondingly enhanced. Moreover, the XRD analysis provides evidence of yielding nearly single-phase α-MoB from the Mo-B sample at equiatomic stoichiometry. In the synthesis of MoB-MoSi 2 composites, the starting stoichiometry of the Mo-B-Si powder compact was varied so as to produce the final composites containing 20-80 mol% MoB. It was also found the increase of flame-front velocity and combustion temperature with increasing MoB content formed in the composite. The composition analysis by XRD shows excellent conversion from the Mo-B-Si powder compact to the MoB-MoSi 2 composite through the SHS reaction; that is, in addition to a small amount of Mo 5 Si 3 , the as-synthesized composite is composed entirely of MoB and MoSi 2

High temperature bismuth cuprate superconductors synthesis and characterization

International Nuclear Information System (INIS)

Mansori, M.; Satre, P.; Breandon, C.; Roubin, M.; Sebaoun, A.

1993-01-01

High temperature superconductor phases synthesis by coprecipitation in alkaline solution is reported. (Bi 1.6 Pb 0.4 )Sr 2 Ca 1 Cu 2 O 8+x and (Bi 1.6 Pb 0.4 )Sr 2 Ca 2 Cu 3 O 10+y noted (2212) and (2223) have been prepared and studied. From aqueous nitrate solutions of Bi, Pb, Sr, Ca and Cu and oxalic acid aqueous solution as well as ethylene glycol, using an organic base (the triethylamine), the pH was increased up to the path of the precipitation zone (pH = 10.5-11.2). This method assures a good granulometric homogeneity of powders. Thermal analysis and characterization of the different components produced during the synthesis have been studied by DTA (differential thermal analysis)- TGA (thermogravimetric analysis), X-ray diffraction at different temperatures and by Infrared spectroscopy with a Fourier transformation. The measurements of magnetic susceptibility for the 2212 (with and without lead) and 2223 (with lead) phases have permitted us to observe the critical temperatures of 84 K, 87 K and 114 K. (author). 29 refs., 2 figs., 4 tabs

Dielectric constant and laser beam propagation in an underdense collisional plasma: effects of electron temperature

International Nuclear Information System (INIS)

Xia Xiongping; Qin Zhen; Xu Bin; Cai Zebin

2011-01-01

Dielectric constant and laser beam propagation in an underdense collisional plasma are investigated, using the wave and dielectric function equations, for their dependence on the electron temperature. Simulation results show that, due to the influence of the ponderomotive force there is a nonlinear variation of electron temperature in an underdense collisional plasma, and this leads to a complicated and interesting nonlinear variation of dielectric constant; this nonlinear variation of dielectric constant directly affects the beam propagation and gives rise to laser beam self-focusing in some spatial-temporal regions; in particular, the beam width and the beam intensity present an oscillatory variation in the self-focusing region. The influence of several parameters on the dielectric function and beam self-focusing is discussed.

Studies on synthesis of diamond at high pressure and temperature

Science.gov (United States)

Kailath, Ansu J.

Diamond is an essential material of modern industry and probably the most versatile abrasive available today. It also has many other industrial applications attributable to its unique mechanical, optical, thermal and electrical properties. Its usage has grown to the extent that there is hardly a production process in modern industry in which industrial diamond does not play a part. Bulk diamond production today is a major industry. Diamonds can be produced in its thermodynamically stable regions either by direct static conversion, or shock-wave conversion. The pressures and temperatures required for direct static conversion are very high. In the catalyst-solvent method, the material used establishes a reaction path with lower activation energy than for direct transformation. This helps in a quicker transformation under more benign conditions. Hence, catalyst-solvent synthesis is readily accomplished and is now a viable and successful industrial process. Diamonds produced by shock wave are very small (approximately 60mu). Therefore this diamond is limited to applications such as polishing compounds only. The quality, quantity, size and morphology of the crystals synthesized by catalyst-solvent process depend on different conditions employed for synthesis. These details, because of commercial reasons are not disclosed in published literature. Hence, systematic studies have been planned to investigate the effect of various growth parameters on the synthesized crystals. During the growth of synthetic diamond crystals, some catalyst-solvent is retained into the crystals in some form and behaves like an impurity. Several physico-mechanical properties of the crystals are found to depend on the total quantity and distribution of these inclusions. Thus, detailed investigation of the crystallization medium and inclusions in synthesized diamonds was also undertaken in the present work. The work incorporated in this thesis has been divided into seven chapters. The first

Suppression of small-scale self-focusing of high-power laser beams due to their self-filtration during propagation in free space

Science.gov (United States)

Ginzburg, V. N.; Kochetkov, A. A.; Potemkin, A. K.; Khazanov, E. A.

2018-04-01

It has been experimentally confirmed that self-cleaning of a laser beam from spatial noise during propagation in free space makes it possible to suppress efficiently the self-focusing instability without applying spatial filters. Measurements of the instability increment by two independent methods have demonstrated quantitative agreement with theory and high efficiency of small-scale self-focusing suppression. This opens new possibilities for using optical elements operating in transmission (frequency doublers, phase plates, beam splitters, polarisers, etc.) in beams with intensities on the order of a few TW cm‑2.

Ratiometric highly sensitive luminescent nanothermometers working in the room temperature range. Applications to heat propagation in nanofluids

Science.gov (United States)

Brites, Carlos D. S.; Lima, Patrícia P.; Silva, Nuno J. O.; Millán, Angel; Amaral, Vitor S.; Palacio, Fernando; Carlos, Luís D.

2013-07-01

There is an increasing demand for accurate, non-invasive and self-reference temperature measurements as technology progresses into the nanoscale. This is particularly so in micro- and nanofluidics where the comprehension of heat transfer and thermal conductivity mechanisms can play a crucial role in areas as diverse as energy transfer and cell physiology. Here we present two luminescent ratiometric nanothermometers based on a magnetic core coated with an organosilica shell co-doped with Eu3+ and Tb3+ chelates. The design of the hybrid host and chelate ligands permits the working of the nanothermometers in a nanofluid at 293-320 K with an emission quantum yield of 0.38 +/- 0.04, a maximum relative sensitivity of 1.5% K-1 at 293 K and a spatio-temporal resolution (constrained by the experimental setup) of 64 × 10-6 m/150 × 10-3 s (to move out of 0.4 K - the temperature uncertainty). The heat propagation velocity in the nanofluid, (2.2 +/- 0.1) × 10-3 m s-1, was determined at 294 K using the nanothermometers' Eu3+/Tb3+ steady-state spectra. There is no precedent of such an experimental measurement in a thermographic nanofluid, where the propagation velocity is measured from the same nanoparticles used to measure the temperature.There is an increasing demand for accurate, non-invasive and self-reference temperature measurements as technology progresses into the nanoscale. This is particularly so in micro- and nanofluidics where the comprehension of heat transfer and thermal conductivity mechanisms can play a crucial role in areas as diverse as energy transfer and cell physiology. Here we present two luminescent ratiometric nanothermometers based on a magnetic core coated with an organosilica shell co-doped with Eu3+ and Tb3+ chelates. The design of the hybrid host and chelate ligands permits the working of the nanothermometers in a nanofluid at 293-320 K with an emission quantum yield of 0.38 +/- 0.04, a maximum relative sensitivity of 1.5% K-1 at 293 K and a spatio

Combined scale effects for effective brazing at low temperatures

Directory of Open Access Journals (Sweden)

Bartout D.

2012-12-01

Full Text Available In modern joining technology, the focus is on effective brazing and soldering of temperature sensitive materials. Here, as well as in diffusion welding processes the needed thermal energy is externally realized in the joint zone. This produces a heating of the whole joining parts, since in laminar joining the thermal energy is transported in interior by thermal conduction. An excess of critical temperatures or tolerable impact periods in wide parts of materials and respectively components is often not avoidable. This leads to thermal damages. In this point of view nanotechnology shows promising possibilities as scale effects and their resulting thermophysical effects such as melting temperature reduction and high diffusion rates can be used for providing a self-propagating high-temperature synthesis at room temperature. After ignition by an external energy source a self-propagating exothermic reaction is started. By producing a multilayer system with alternately arranged nanoscaled layers of e.g. Al and Ni the resulting thin foil can be used as heat source for melting the braze or solder material within the joining zone without any external preheating. Due to the high process velocities up to 30 m/s and the local heat input significant thermal influences on the joined parts are not detectable.

Study of ultrasonic propagation through vortices for acoustic monitoring of high-temperature and turbulent fluid

International Nuclear Information System (INIS)

Massacret, Nicolas; Moysan, Joseph; Ploix, Marie-Aude; Chaouch, Naim; Jeannot, Jean-Philippe

2016-01-01

Ultrasonic monitoring in high temperature fluids with turbulences requires the knowledge of wave propagation in such media and the development of simulation tools. Applications could be the monitoring of sodium-cooled fast reactors. The objectives are mainly acoustic telemetry and thermometry, which involve the propagation of ultrasounds in turbulent and heated sodium flows. We developed a ray-tracing model to simulate the wave propagation and to determine wave deviations and delays due to an inhomogeneous medium. In previous work we demonstrated the sensitivity of ultrasounds to temperature gradients in liquid sodium. To complete that study, we need to investigate the sensitivity of ultrasounds to vortices created in a moving fluid. We designed a specific experimental setup called IKHAR (Instabilities of Kelvin-Helmholtz for Acoustic Research) in order to assess the validity of the ray-tracing model and the potential of ultrasounds for monitoring such fluid. In this experiment, Von Karman instabilities were created in a flow of water. Fluid temperature was homogeneous in our experimental setup. Through a careful choice of the parameters, periodic vortices were generated. The experiment was also simulated using Comsol registered to allow discussion about repeatability. The throughtransmission method was used to measure wave delays due to the vortices. Arrays of transducers were used to measure time of flight variations of several nanoseconds with a high spatial resolution. Results were similar to simulation results. They demonstrate that beam delays due to vortices can be measured and confirm the potential of ultrasounds in monitoring very inhomogeneous fluid media such as liquid sodium used as coolant fluid in nuclear fast reactors.

Propagating self-sustained annealing of radiation-induced interstitial complexes

International Nuclear Information System (INIS)

Bokov, P M; Selyshchev, P A

2016-01-01

A propagating self-sustained annealing of radiation induced defects as a result of thermal-concentration instability is studied. The defects that are considered in the model are complexes. Each of them consists of one atom of impunity and of one interstitial atom. Crystal with defects has extra energy which is transformed into heat during defect annealing. Simulation of the auto-wave of annealing has been performed. The front and the speed of the auto-wave have been obtained. It is shown that annealing occurs in a narrow region of time and space. There are two kinds of such annealing behaviour. In the first case the speed of the auto-wave oscillates near its constant mean value and the front of temperature oscillates in a complex way. In the second case the speed of propagation is constant and fronts of temperature and concentration look like sigmoid functions. (paper)

Self-propagating high-temperature synthesis of LaMO{sub 3} perovskite-type oxide using heteronuclearcyano metal complex precursors

Energy Technology Data Exchange (ETDEWEB)

Sánchez-Rodríguez, Daniel, E-mail: daniel.sanchez@udg.edu [GRMT, Department of Physics, University of Girona, Campus Montilivi, Edif.PII, E17071 Girona, Catalonia (Spain); Wada, Hiroki; Yamaguchi, Syuhei [Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577 (Japan); Farjas, Jordi [GRMT, Department of Physics, University of Girona, Campus Montilivi, Edif.PII, E17071 Girona, Catalonia (Spain); Yahiro, Hidenori, E-mail: yahiro.hidenori.me@ehime-u.ac.jp [Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577 (Japan)

2015-11-15

The decomposition of La[Fe(CN){sub 6}]·5H{sub 2}O and La[Co(CN){sub 6}]·5H{sub 2}O under different atmospheres has been analyzed by thermogravimetry (TG) and differential thermal analysis (DTA). In addition, the decomposition temperature at different sample locations was monitored for sample masses around 2 g of La[Fe(CN){sub 6}]·5H{sub 2}O and La[Co(CN){sub 6}]·5H{sub 2}O, when they were calcined for 1 h at temperatures ranging from 200 to 400 °C in a controlled gas-flow system. Results showed that, the large enough of the cyano complex precursors undergo combustion when they are decomposed under oxygen atmosphere. X-ray diffraction results revealed that perovskite-type oxides crystallize due to the overheating of the process. As a result, it has been possible to produce LaFeO{sub 3} and LaCoO{sub 3} perovskite-type oxide powders by SHS under oxygen atmosphere using La[Fe(CN){sub 6}]·5H{sub 2}O and La[Co(CN){sub 6}]·5H{sub 2}O as a precursor. The effect of the ignition temperature has been investigated. The specific surface area of the perovskite-type oxides produced via SHS using heteronuclearcyano metal complex as a precursor is significantly higher than that of other LaMO{sub 3} produced using the same technique but obtained from other type of precursors. - Highlights: • The decomposition of La[Fe(CN){sub 6}] and La[Co(CN){sub 6}] precursors was analyzed. • The combustion process proceeded under oxygen when sample was large enough. • Perovskite oxides via SHS from the cyano complex precursors were synthesized. • LaMO{sub 3} perovskite oxides via SHS was obtained with high specific surface area.

Shock-induced synthesis of high temperature superconducting materials

Science.gov (United States)

Ginley, D.S.; Graham, R.A.; Morosin, B.; Venturini, E.L.

1987-06-18

It has now been determined that the unique features of the high pressure shock method, especially the shock-induced chemical synthesis technique, are fully applicable to high temperature superconducting materials. Extraordinarily high yields are achievable in accordance with this invention, e.g., generally in the range from about 20% to about 99%, often in the range from about 50% to about 90%, lower and higher yields, of course, also being possible. The method of this invention involves the application of a controlled high pressure shock compression pulse which can be produced in any conventional manner, e.g., by detonation of a high explosive material, the impact of a high speed projectile or the effect of intense pulsed radiation sources such as lasers or electron beams. Examples and a discussion are presented.

The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells

International Nuclear Information System (INIS)

Nishimura, Akira; Kawahara, Nobuhiro; Takagi, Hiroshi

2013-01-01

Highlights: ► NO is produced from L-arginine in response to elevated temperature in yeast. ► Tah18 was first identified as the yeast protein involved in NO synthesis. ► Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiological role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe–S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.

SHS-produced intermetallides as catalysts for hydrocarbons synthesis from CO and H{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Eliseev, O.L.; Kazantsev, R.V.; Davydov, P.E.; Lapidus, A.L. [Russian Academy of Sciences, Moscow (Russian Federation). N.D. Zelinsky Institute of Organic Chemistry; Borshch, V.N.; Pugacheva, E.V. [Russian Academy of Sciences, Chernogolovka (Russian Federation). Inst. of Structural Macrokinetics and Materials Science

2012-07-01

Raney-type polymetallic alloys were prepared by Self-Propagating High-Temperature Synthesis followed by alkaline treating. Surface morphology and composition of were studied using XRD, BET, SEM and EMPA techniques. The samples were tested in Fischer-Tropsch synthesis demonstrated rather high activity and very high selectivity to heavy paraffins. High selectivity to C{sub 5+} hydrocarbons is attributed to high thermal conductivity of alloys which prevents hot spots formation and therefore suppresses formation of methane and light hydrocarbons. Selectivity can be further improved by adding some d-metals in catalyst composition. Promotion with La seems to be particularly suitable for lowering methane formation while doping with Ni enhances methane yield greatly. (orig.)

Propagation of Measurement-While-Drilling Mud Pulse during High Temperature Deep Well Drilling Operations

OpenAIRE

Li, Hongtao; Meng, Yingfeng; Li, Gao; Wei, Na; Liu, Jiajie; Ma, Xiao; Duan, Mubai; Gu, Siman; Zhu, Kuanliang; Xu, Xiaofeng

2013-01-01

Signal attenuates while Measurement-While-Drilling (MWD) mud pulse is transmited in drill string during high temperature deep well drilling. In this work, an analytical model for the propagation of mud pulse was presented. The model consists of continuity, momentum, and state equations with analytical solutions based on the linear perturbation analysis. The model can predict the wave speed and attenuation coefficient of mud pulse. The calculated results were compared with the experimental dat...

The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells

Energy Technology Data Exchange (ETDEWEB)

Nishimura, Akira; Kawahara, Nobuhiro [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan); Takagi, Hiroshi, E-mail: hiro@bs.naist.jp [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)

2013-01-04

Highlights: Black-Right-Pointing-Pointer NO is produced from L-arginine in response to elevated temperature in yeast. Black-Right-Pointing-Pointer Tah18 was first identified as the yeast protein involved in NO synthesis. Black-Right-Pointing-Pointer Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiological role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe-S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.

Synthesis of ultrasmall CsPbBr3 nanoclusters and their transformation to highly deep-blue-emitting nanoribbons at room temperature.

Science.gov (United States)

Xu, Yibing; Zhang, Qiang; Lv, Longfei; Han, Wenqian; Wu, Guanhong; Yang, Dong; Dong, Angang

2017-11-16

Discretely sized semiconductor clusters have attracted considerable attention due to their intriguing optical properties and self-assembly behaviors. While lead halide perovskite nanostructures have been recently intensively explored, few studies have addressed perovskite clusters and their self-assembled superstructures. Here, we report the room-temperature synthesis of sub-2 nm CsPbBr 3 clusters and present strong evidence that these ultrasmall perovskite species, obtained under a wide range of reaction conditions, possess a specific size, with optical properties and self-assembly characteristics resembling those of well-known II-VI semiconductor magic-sized clusters. Unlike conventional CsPbBr 3 nanocrystals, the as-synthesized CsPbBr 3 nanoclusters spontaneously self-assemble into a hexagonally packed columnar mesophase in solution, which can be further converted to single-crystalline CsPbBr 3 quantum nanoribbons with bright deep-blue emission at room temperature. Such a conversion of CsPbBr 3 nanoclusters to nanoribbons is found to be driven by a ligand-destabilization-induced crystallization and mesophase transition process. Our study will facilitate the investigation of perovskite nanoclusters and offer new possibilities in the low-temperature synthesis of anisotropic perovskite nanostructures.

A self-assembly SHS approach to form silicon carbide nanofibres

International Nuclear Information System (INIS)

Huczko, A; Osica, M; Rutkowska, A; Bystrzejewski, M; Lange, H; Cudzilo, S

2007-01-01

β-SiC nanofibres were efficiently produced using the thermal-explosion mode of self-propagating high-temperature synthesis from elemental Si and poly(tetrafluoroethylene) powder mixtures combusted under different operational parameters. The averaged combustion temperatures were evaluated using emission spectroscopy to be above 2000 K. The solid products were characterized by scanning and transmission electron microscopy, chemical analysis, and x-ray diffraction. Under optimum conditions the conversion of starting elemental Si into products exceeded 90%. To obtain pure (about 90%) SiC nanofibres the solid products were processed by wet chemistry

Synthesis and characterization of strontium carboxylates at room temperature and at high temperature in autoclave vessels

DEFF Research Database (Denmark)

Christgau, Stephan; Ståhl, Kenny; Andersen, Jens Enevold Thaulov

2006-01-01

A novel method was developed for synthesis of strontium coordination compounds in high yields. The synthesis proceeded along three pathways that provided strontium salts in high purity and high yields, close to 100%, as confirmed by flame atomic absorption spectroscopy (FAAS) and powder x......-ray crystallography. Optimum conditions were found at T = 120-1400C, a base-to-acid ratio of 1.2 and 15 min. of reaction-time in an autoclave vessel. Large crystals were readily obtained within a time period of hours. The crystal structures of strontium D-glutamate hexahydrate (I) and strontium di-(hydrogen L......-glutamate) pentahydrate (II) were confirmed by X-ray powder diffraction at 295 K and Rietveld refinements (I: Space group P212121, Z=4, a=7.3519(2), b=8.7616(2), c=20.2627(5) Å, and II: Space group P21, Z=2, a=8.7243(1), b=7.2635(1), c=14.6840(2) Å, β=100.5414(7) °). Synthesis at room temperature provided four additional...

Analytic properties of finite-temperature self-energies

International Nuclear Information System (INIS)

Weldon, H. Arthur

2002-01-01

The analytic properties in the energy variable k 0 of finite-temperature self-energies are investigated. A typical branch cut results from n particles being emitted into the heat bath and n ' being absorbed from the heat bath. There are three main results: First, in addition to the branch points at which the cuts terminate, there are also branch points attached to the cuts along their length. Second, branch points at k 0 =±k are ubiquitous and for massive particles they are essential singularities. Third, in a perturbative expansion using free particle propagators or in a resummed expansion in which the propagator pole occurs at a real energy, the self-energy will have a branch point at the pole location

High temperature behaviour of self-consolidating concrete

International Nuclear Information System (INIS)

Fares, Hanaa; Remond, Sebastien; Noumowe, Albert; Cousture, Annelise

2010-01-01

This paper presents an experimental study on the properties of self-compacting concrete (SCC) subjected to high temperature. Two SCC mixtures and one vibrated concrete mixture were tested. These concrete mixtures come from the French National Project B-P. The specimens of each concrete mixture were heated at a rate of 1 deg. C/min up to different temperatures (150, 300, 450 and 600 deg. C). In order to ensure a uniform temperature throughout the specimens, the temperature was held constant at the maximum temperature for 1 h before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. In this paper, the physicochemical properties and the microstuctural characteristics are presented. Thermogravimetric analysis, thermodifferential analysis, X-ray diffraction and SEM observations were used. The aim of these studies was in particular to explain the observed residual compressive strength increase between 150 and 300 deg. C.

Analysis on High Temperature Aging Property of Self-brazing Aluminum Honeycomb Core at Middle Temperature

Directory of Open Access Journals (Sweden)

ZHAO Huan

2016-11-01

Full Text Available Tension-shear test was carried out on middle temperature self-brazing aluminum honeycomb cores after high temperature aging by micro mechanical test system, and the microstructure and component of the joints were observed and analyzed using scanning electron microscopy and energy dispersive spectroscopy to study the relationship between brazing seam microstructure, component and high temperature aging properties. Results show that the tensile-shear strength of aluminum honeycomb core joints brazed by 1060 aluminum foil and aluminum composite brazing plate after high temperature aging(200℃/12h, 200℃/24h, 200℃/36h is similar to that of as-welded joints, and the weak part of the joint is the base metal which is near the brazing joint. The observation and analysis of the aluminum honeycomb core microstructure and component show that the component of Zn, Sn at brazing seam is not much affected and no compound phase formed after high temperature aging; therefore, the main reason for good high temperature aging performance of self-brazing aluminum honeycomb core is that no obvious change of brazing seam microstructure and component occurs.

Stable and unstable fatigue crack propagation during high temperature creep-fatigue in austenitic steels: the role of precipitation

International Nuclear Information System (INIS)

Lloyd, G.J.; Wareing, J.

1979-01-01

The distinction between stable and unstable fatigue crack propagation during high temperature creep-fatigue in austenitic stainless steels is introduced. The transition from one class of behavior to the other is related to the precipitate distribution and to the nature of the prevailing crack path. It is shown by reference to new studies and examples drawn from the literature that this behavior is common to both high strain and predominantly elastic fatigue in austenitic stainless steels. The relevance of this distinction to a mechanistic approach to high temperature plant design is discussed

REACTION KINETICS SELF-PROPOGATION REGIME DURING PRE-IGNITION PERIOD

Directory of Open Access Journals (Sweden)

D. D. Polishchuk

2015-11-01

Full Text Available Self-propagation high temperature synthesis (SHS technological regulations application is mainly limited by transformation processes taking place in the pre-ignition period. Zn-S, Zn-Se, Ti-C and 3Ni-Al small sample systems ignition experimental study was carried out under heating conditions in inert atmosphere with temperature values T = 1200K.It was shown that at this temperature level a chemical reaction can be initiated, turning into a self-sustaining mode. Wherein the reaction limiting factors can be mass transfer processes. Ignition temperatures were determined and plotted via the samples size. A physical ignition model was developed assuming the pre-ignition period limiting reaction Arrhenius law.The inverse combustion problem solution made it possible to calculate the low-temperature (T = 800 ÷ 1200K reaction kinetic constant values. Comparison thus obtained values  with the known data of other researchers showed their good agreement.Activation energy values for the Zn-S system were used to calculate the heat wave propagation speed. This value appeared to coincide with experimental values.Obtained results analysis leads to the conclusion about the availability and justification for the proposed method of express-analysis of presupposed, but previously not studied SHS systems. The results thus obtained allow us to estimate conditions for the SHS technology implementation, the reactor characteristic sizes and the thermal wave’s propagation speed.

In situ observation of self-propagating high temperature syntheses of Ta5Si3, Ti5Si3 and TiB2 by proton and X-ray radiography

Science.gov (United States)

Bernert, T.; Winkler, B.; Haussühl, E.; Trouw, F.; Vogel, S. C.; Hurd, A. J.; Smilowitz, L.; Henson, B. F.; Merrill, F. E.; Morris, C. L.; Mariam, F. G.; Saunders, A.; Juarez-Arellano, E. A.

2013-08-01

Self-propagating high temperature reactions of tantalum and titanium with silicon and titanium with boron were studied using proton and X-ray radiography, small-angle neutron scattering, neutron time-of-flight, X-ray and neutron diffraction, dilatometry and video recording. We show that radiography allows the observation of the propagation of the flame front in all investigated systems and the determination of the widths of the burning zones. X-ray and neutron diffraction showed that the reaction products consisted of ≈90 wt% of the main phase and one or two secondary phases. For the reaction 5Ti + 3Si → Ti5Si3 flame front velocities of 7.1(3)-34.2(4) mm/s were determined depending on the concentration of a retardant added to the starting material, the geometry and the green density of the samples. The flame front width was determined to be 1.17(4)-1.82(8) mm and depends exponentially on the flame front velocity. Similarly, for the reaction Ti + 2B → TiB2 flame front velocities of 15(2)-26.6(4) mm/s were determined, while for a 5Ta + 3Si → Ta5Si3 reaction the flame front velocity was 7.05(4) mm/s. The micro structure of the product phase Ta5Si3 shows no texture. From SANS measurements the dependence of the specific surface of the product phase on the particle sizes of the starting materials was studied.

Selection of Compositions in Ti-Cr-C-Steel, Ti-B, Ti-B-Me Systems and Establishing Synthesis Parameters for Obtaining Product by “SHS-Electrical Rolling”

Science.gov (United States)

Aslamazashvili, Zurab; Tavadze, Giorgi; Chikhradze, Mikheil; Namicheishvili, Teimuraz; Melashvili, Zaqaria

2017-12-01

For the production materials by the proposed Self-propagating High-Temperature Synthesis (SHS) - Electric Rolling method, there are no limitations in the length of the material and the width only depends on the length of rolls. The innovation method enables to carry out the process in nonstop regime, which is possible by merging energy consuming SHS method and Electrical Rolling. For realizing the process it is mandatory and sufficient, that initial components, after initiation by thermal pulse, could interaction with the heat emission, which itself ensures the self-propagation of synthesis front in lieu of heat transfer in the whole sample. Just after that process, the rolls instantly start rotation with the set speed to ensure the motion of material. This speed should be equal to the speed of propagation of synthesis front. The synthesized product in hot plastic condition is delivered to the rolls in nonstop regime, simultaneously, providing the current in deformation zone in order to compensate the energy loses. As a result by using the innovation SHS -Electrical Rolling technology we obtain long dimensional metal-ceramic product. In the presented paper optimal compositions of SHS chasms were selected in Ti-Cr-C-Steel, Ti-B and Ti-B-Me systems. For the selection of the compounds the thermodynamic analysis has been carried out which enabled to determine adiabatic temperature of synthesis theoretically and to determine balanced concentrations of synthesized product at synthesis temperature. Thermodynamic analysis also gave possibility to determine optimal compositions of chasms and define the conditions, which are important for correct realization of synthesis process. For obtaining non porous materials and product by SHS-Electrical Rolling, it is necessary to select synthesis and compacting parameters correctly. These parameters are the pressure and the time. In Ti-Cr-C-Steel, Ti-B and Ti-B-Me systems the high quality (nonporous or low porosity values are defined

Nonuniqueness of self-propagating spiral galaxy models

International Nuclear Information System (INIS)

Freedman, W.L.; Madore, B.F.

1984-01-01

We demonstrate the nonuniqueness of the basic assumptions leading to spiral structure in self-propagating star formation models. Even in the case where star formation occurs purely spontaneously and does not propagate, we have generated spiral structure by adopting the radically different assumption where star formation is systematically inhibited

Evaluation of crack propagation of alloy 600 tube in high temperature water, (1)

International Nuclear Information System (INIS)

Hirano, Hideo; Kawamura, H.; Kawamura, Kohji; Matsubara, Masaaki

1990-01-01

This report describes the analysis of stress intensity factors at cracks in alloy 600 steam generator tubes. Based on the results of the analysis, IGA/SCC tests were carried out to examine the effect of stress intensity and water quality on the crack propagation rate. The main test result are as follows: (1) Hoop stress was caused by the pressure difference between the internal and external surface of the steam generator tube. The calculated hoop stress was about 7 kg/mm 2 . In addition, the temperature difference between the internal and external surface caused thermal stress. The thermal stress was about 10 kg/mm 2 at the external surface and the one at the internal surface was about -10 kg/mm 2 . Total stress at the external and internal surface was 17 kg/mm 2 and -3 kg/mm 2 , respectively. (2) The stress intensity factor at the crack tip increased with increasing crack length. For a long crack, the stress intensity factor decreased with increasing crack number. However, for a short crack, the stress intensity factor decreased little with increasing crack number. (3) Under high stress-intensity conditions, i.e. 40∼50 kg·mm -3/2 , the IGA/SCC test showed that IGA/SCC propagated in AVT and AVT/boric-acid solution at 320degC and 350degC. However, the propagation rate was low. (author)

Burning velocity of the heterogeneous flame propagation in the SHS process expressed in explicit form

International Nuclear Information System (INIS)

Makino, A.; Law, C.K.

1995-01-01

The combustion behavior of the self-propagating high-temperature synthesis (SHS) process has been the subject of many analytical and experimental investigations. Recently, a theory based on spray combustion was proposed for the SHS flame structure and propagation. In contrast to previous studies based on the homogeneous premixed flame, this theory accounts for the premixed-mode of propagation of the bulk flame and the non-premixed reaction of the dispersed nonmetal (or higher melting-point metal) particles which supports the bulk flame. Finite-rate reaction at the particle surface and the temperature-dependent, Arrhenius nature of mass diffusion are both incorporated. The heterogeneous nature of the theory has satisfactorily captured the effects of particle size on the flame propagation speed. The final solution of Makino and Law was obtained numerically and hence presented parametrically. The authors have since then derived an approximate analytical expression for the burning velocity, which explicitly displays the functional dependence of the burning velocity on the various system parameters. This result is presented herein. Applicability of this expression is examined by comparing it with the numerical results for Ti-C, Ti-B, Zr-B, Hf-B, and Co-Ti systems. A fair degree of agreement has been shown as far as the general trend and approximate magnitude are concerned

Propagation and diffusion-limited extinction of nonadiabatic heterogeneous flame in the SHS process

International Nuclear Information System (INIS)

Makino, Atsushi

1994-01-01

Nonadiabatic heterogeneous flame propagation and extinction in self-propagating high-temperature synthesis (SHS) are analyzed based on a premixed mode of propagation for the bulk flame supported by the nonpremixed reaction of dispersed nonmetals in the liquid metal. The formulation allows for volumetric heat loss throughout the bulk flame, finite-rate Arrhenius reaction at the particle surface, and temperature-sensitive Arrhenius mass diffusion in the liquid. Results show that, subsequent to melting of the metal, the flame structure consists of a relatively thin diffusion-consumption/convection zone followed by a relatively thick convection-loss zone, that the flame propagation rate decreases with increasing heat loss, that at a critical heat-loss rate the flame extinguishes as indicated by the characteristic turning-point behavior, that the surface reaction is diffusion limited such that the nonlinear, temperature-sensitive nature of the system is actually a consequence of the Arrhenius mass diffusion, and that extinction is sensitively affected by the mixture ratio, the degree of dilution, the initial temperature of the compact, and the size of the nonmetal particles. An explicit expression is derived for the normalized mass burning rate, which exhibits the characteristic turning point and shows that extinction occurs when this value is reduced to e -1/2 , which is the same as that for the nonadiabatic gaseous premixed flame. It is further shown that the theoretical results agree well with available experimental data, indicating that the present formulation captures the essential features of the nonadiabatic heterogeneous SHS processes and its potential for extension to describe other SHS phenomena

Enhanced oxygen dissociation in a propagating constricted discharge formed in a self-pulsing atmospheric pressure microplasma jet

Science.gov (United States)

Schröder, Daniel; Burhenn, Sebastian; Kirchheim, Dennis; Schulz-von der Gathen, Volker

2013-11-01

We report on the propagation of a constricted discharge feature in a repetitively self-pulsing microplasma jet operated in helium with a 0.075 vol% molecular oxygen admixture in ambient air environment. The constricted discharge is about 1 mm in width and repetitively ignites at the point of smallest electrode distance in a wedge-shaped electrode configuration, propagates through the discharge channel towards the nozzle, extinguishes, and re-ignites at the inlet at frequencies in the kHz range. It co-exists with a homogeneous, volume-dominated low temperature (T ⋍ 300 K) α-mode glow. Time-resolved measurements of nitrogen molecule C-state and nitrogen molecule ion B-state emission bands reveal an increase of the rotational temperature within the constricted discharge to about 600 K within 50 µs. Its propagation velocity was determined by phase-resolved diagnostics to be similar to the gas velocity, in the order of 40 m s-1. Two-photon absorption laser-induced fluorescence spectroscopy synchronized to the self-pulsing reveals spatial regions of increased oxygen atom densities co-propagating with the constricted discharge feature. The generated oxygen pulse density is about ten times higher than in the co-existing homogeneous α-mode. Densities reach about 1.5 × 1016 cm-3 at average temperatures of 450 K at the nozzle. This enhanced dissociation of about 80% is attributed to the continuous interaction of the constricted discharge to the co-propagating gas volume.

Self propagating high temperature synthesis of mixed carbide and boride powder systems for cutting tools manufacturing

International Nuclear Information System (INIS)

Vallauri, D.; Cola, P.L. de; Piscone, F.; Amato, I.

2001-01-01

TiC-TiB 2 composites have been produced via SHS technique starting from low cost raw materials like TiO 2 , B 4 C, Mg. The influence of the diluent phase (Mg, TiC) content on combustion temperature has been investigated. The use of magnesium as the reductant phase allowed acid leaching of the undesired oxide product (MgO), leaving pure hard materials with fine particle size suitable to be employed in cutting tools manufacturing through cold pressing and sintering route. The densification has shown to be strongly dependent on the wetting additions. The influence of the metal binder and wetting additions on the sintering process has been investigated. A characterization of the obtained materials was performed by the point of view of cutting tools life (hardness, toughness, strength). (author)

The contact-temperature ignition (CTI) criteria for propagating chemical reactions including the effect of moisture and application to Hanford waste

International Nuclear Information System (INIS)

Cash, R.J.

1995-01-01

To assure the continued absence of uncontrolled condensed-phase chemical reactions in connection with the Hanford waste materials, efforts have been underway including both theoretical and experimental investigations to clarify the requirements for such reactions. This document defines the differences and requirements for homogeneous runaway and propagating chemical reactions incuding a discussion of general contact-temperature ignition (CTI) condition for propagating reactions that include the effect of moisture. The CTI condition implies that the contact temperature or interface temperature between reacted and unreacted materials must exceed the ignition temperature and is compared to experimental data including both synthetic ferrocyanide and surrogate organic materials. In all cases, the occurrences of ignition accompanied by self-propagating reactions are consistent with the theoretical anticipations of the CTI condition

Science for Materials in the Frontier of Centuries: Advantages and Challenges. Volume I

National Research Council Canada - National Science Library

Skorokhod, Valery

2002-01-01

... materials, hard alloys and cermets. III. Materials processing routes including materials synthesis in the bulk and dispersed states, self-propagating high- temperature synthesis, powder formation, sintering, joining, and coating. IV...

Science for Materials in the Frontier of Centuries: Advantages and Challenges, Volume 2

National Research Council Canada - National Science Library

2002-01-01

... materials, hard alloys and cermets. III. Materials processing routes including materials synthesis in the bulk and dispersed states, self-propagating high- temperature synthesis, powder formation, sintering, joining, and coating. IV...

Frequency up-conversion and spectral breaking of a high power microwave pulse propagation in a self-generated plasma

International Nuclear Information System (INIS)

Kuo, S.P.; Ren, A.

1993-01-01

The main concern of the propagation of high power microwave pulse is the energy loss of the pulse before reaching the destination. The loss is caused by self-generated plasma. There are two processes which are responsible for the energy loss (so called tail erosion). They are collisional damping and cutoff reflection. In very high power region, the cutoff reflection is much more severe than the collisional damping. A frequency up-conversion process may help to avoid the cutoff reflection of powerful electromagnetic pulse propagating in a self-generated plasma. Both chamber experiments and numerical simulation are performed. When the field amplitude only slightly exceeds the breakdown threshold field of the background gas, the result shows that the carrier frequency ω of the pulse shifts upward during the growth of local plasma frequency ωpe 2 . Thus, the self-generated plasma remains underdense to the pulse. However, the spectrum of the pulse starts to break up into two major peaks when the amplitude of the pulse is further increased. The frequency of one of the peaks is lower than the original carrier frequency and that of the other peak is higher than the original carrier frequency. These phenomena are observed both experimentally and numerically. The frequency down shift result is believed to be caused by damping mechanisms. Good agreement between the experimental results and the numerical simulation is obtained

Temperature dependency of external stress corrosion crack propagation of 304 stainless steel

International Nuclear Information System (INIS)

Hayashibara, Hitoshi; Mizutani, Yoshihiro; Mayuzumi, Masami; Tani, Jun-ichi

2010-01-01

Temperature dependency of external stress corrosion cracking (ESCC) of 304 stainless steel was examined with CT specimens. Maximum ESCC propagation rates appeared in the early phase of ESCC propagation. ESCC propagation rates generally became smaller as testing time advance. Temperature dependency of maximum ESCC propagation rate was analyzed with Arrhenius plot, and apparent activation energy was similar to that of SCC in chloride solutions. Temperature dependency of macroscopic ESCC incubation time was different from that of ESCC propagation rate. Anodic current density of 304 stainless steel was also examined by anodic polarization measurement. Temperature dependency of critical current density of active state in artificial sea water solution of pH=1.3 was similar to that of ESCC propagation rate. (author)

Flame propagation in two-dimensional solids: Particle-resolved studies with complex plasmas

Science.gov (United States)

Yurchenko, S. O.; Yakovlev, E. V.; Couëdel, L.; Kryuchkov, N. P.; Lipaev, A. M.; Naumkin, V. N.; Kislov, A. Yu.; Ovcharov, P. V.; Zaytsev, K. I.; Vorob'ev, E. V.; Morfill, G. E.; Ivlev, A. V.

2017-10-01

Using two-dimensional (2D) complex plasmas as an experimental model system, particle-resolved studies of flame propagation in classical 2D solids are carried out. Combining experiments, theory, and molecular dynamics simulations, we demonstrate that the mode-coupling instability operating in 2D complex plasmas reveals all essential features of combustion, such as an activated heat release, two-zone structure of the self-similar temperature profile ("flame front"), as well as thermal expansion of the medium and temperature saturation behind the front. The presented results are of relevance for various fields ranging from combustion and thermochemistry, to chemical physics and synthesis of materials.

Self-propagating combustion synthesis of Pb1–x Srx ZrO3 (0≤ x≤ 0 ...

Indian Academy of Sciences (India)

Lead strontium zirconate, Pb1–SrZrO3 (0 ≤ ≤ 0.20) ceramics, were prepared by novel glycine–nitrate self-propagating combustion technique. The crystal structure of the ceramics was investigated as a function of composition via X-ray diffraction (XRD). The XRD patterns obtained on these powders showed the ...

Application of low-temperature plasma for the synthesis of hydrogenated graphene (graphane)

Science.gov (United States)

Shavelkina, M. B.; Amirov, R. H.; Katarzhis, V. A.; Kiselev, V. I.

2017-12-01

The possibility of a direct synthesis of hydrogenated graphene in decomposition of methane by means of low-temperature plasma was investigated. A DC plasma torch with an expanding channel-anode, a vortex gas supply and a self-setting arc length was used as a generator of low-temperature plasma. Argon was used as the plasma-forming gas. The temperatures of argon plasma and with methane addition to it were determined on the basis of spectral measurements. The synthesis products were characterized by electron microscopy and thermogravimetry. The effect of hydrogenated graphene as a nanomodifier on the properties of the cubic boron nitride based functional ceramics was investigated.

Comparison of Reactive and Non-Reactive Spark Plasma Sintering Routes for the Fabrication of Monolithic and Composite Ultra High Temperature Ceramics (UHTC Materials

Directory of Open Access Journals (Sweden)

Roberto Orrù

2013-04-01

Full Text Available A wider utilization of ultra high temperature ceramics (UHTC materials strongly depends on the availability of efficient techniques for their fabrication as dense bodies. Based on recent results reported in the literature, it is possible to state that Spark Plasma Sintering (SPS technology offers a useful contribution in this direction. Along these lines, the use of two different SPS-based processing routes for the preparation of massive UHTCs is examined in this work. One method, the so-called reactive SPS (R-SPS, consists of the synthesis and densification of the material in a single step. Alternatively, the ceramic powders are first synthesized by Self-propagating High-temperature Synthesis (SHS and then sintered by SPS. The obtained results evidenced that R-SPS method is preferable for the preparation of dense monolithic products, while the sintering of SHS powders requires relatively milder conditions when considering binary composites. The different kinetic mechanisms involved during R-SPS of the monolithic and composite systems, i.e., combustion-like or gradual solid-diffusion, respectively, provides a possible explanation. An important role is also played by the SHS process, particularly for the preparation of composite powders, since stronger interfaces are established between the ceramic constituents formed in situ, thus favoring diffusion processes during the subsequent SPS step.

Photon propagators at finite temperature

International Nuclear Information System (INIS)

Yee, J.H.

1982-07-01

We have used the real time formalism to compute the one-loop finite temperature corrections to the photon self energies in spinor and scalar QED. We show that, for a real photon, only the transverse components develop the temperature-dependent masses, while, for an external static electromagnetic field applied to the finite temperature system, only the static electric field is screened by thermal fluctuations. After showing how to compute systematically the imaginary parts of the finite temperature Green functions, we have attempted to give a microscopic interpretation of the imaginary parts of the self energies. (author)

Propagation stability of self-reconstructing Bessel beams enables contrast-enhanced imaging in thick media.

Science.gov (United States)

Fahrbach, Florian O; Rohrbach, Alexander

2012-01-17

Laser beams that can self-reconstruct their initial beam profile even in the presence of massive phase perturbations are able to propagate deeper into inhomogeneous media. This ability has crucial advantages for light sheet-based microscopy in thick media, such as cell clusters, embryos, skin or brain tissue or plants, as well as scattering synthetic materials. A ring system around the central intensity maximum of a Bessel beam enables its self-reconstruction, but at the same time illuminates out-of-focus regions and deteriorates image contrast. Here we present a detection method that minimizes the negative effect of the ring system. The beam's propagation stability along one straight line enables the use of a confocal line principle, resulting in a significant increase in image contrast. The axial resolution could be improved by nearly 100% relative to the standard light-sheet techniques using scanned Gaussian beams, while demonstrating self-reconstruction also for high propagation depths.

Barium hexaferrite nanoparticles: Synthesis and magnetic properties

International Nuclear Information System (INIS)

Martirosyan, K.S.; Galstyan, E.; Hossain, S.M.; Wang Yiju; Litvinov, D.

2011-01-01

Carbon combustion synthesis is applied to rapid and energy efficient fabrication of crystalline barium hexaferrite nanoparticles with the average particle size of 50-100 nm. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm with a surface area of 80 m 2 /g generates a self-propagating thermal wave with maximum temperatures of up to 1000 deg. C. The thermal front rapidly propagates through the mixture of solid reactants converting it to the hexagonal barium ferrite. Carbon is not incorporated in the product and is emitted from the reaction zone as a gaseous CO 2 . The activation energy for carbon combustion synthesis of BaFe 12 O 19 was estimated to be 98 kJ/mol. A complete conversion to hexagonal barium ferrite is obtained for carbon concentration exceeding 11 wt.%. The magnetic properties H c ∼3000 Oe and M s ∼50.3 emu/g of the compact sintered ferrites compare well with those produced by other synthesis methods.

Ion temperature effects on magnetotail Alfvén wave propagation and electron energization: ION TEMPERATURE EFFECTS ON ALFVÉN WAVES

Energy Technology Data Exchange (ETDEWEB)

Damiano, P. A. [Princeton Center for Heliophysics, Princeton Plasma Physics Laboratory, Princeton University, Princeton New Jersey USA; Johnson, J. R. [Princeton Center for Heliophysics, Princeton Plasma Physics Laboratory, Princeton University, Princeton New Jersey USA; Chaston, C. C. [Space Sciences Laboratory, University of California, Berkeley California USA; School of Physics, University of Sydney, Sydney New South Wales Australia

2015-07-01

A new 2-D self-consistent hybrid gyrofluid-kinetic electron model in dipolar coordinates is presented and used to simulate dispersive-scale Alfvén wave pulse propagation from the equator to the ionosphere along an L = 10 magnetic field line. The model is an extension of the hybrid MHD-kinetic electron model that incorporates ion Larmor radius corrections via the kinetic fluid model of Cheng and Johnson (1999). It is found that consideration of a realistic ion to electron temperature ratio decreases the propagation time of the wave from the plasma sheet to the ionosphere by several seconds relative to a ρi=0 case (which also implies shorter timing for a substorm onset signal) and leads to significant dispersion of wave energy perpendicular to the ambient magnetic field. Additionally, ion temperature effects reduce the parallel current and electron energization all along the field line for the same magnitude perpendicular electric field perturbation.

Microwave-Assisted Rapid Synthesis of Self-Assembled T-Nb2 O5 Nanowires for High-Energy Hybrid Supercapacitors.

Science.gov (United States)

Yang, Huiling; Xu, Henghui; Wang, Libin; Zhang, Lei; Huang, Yunhui; Hu, Xianluo

2017-03-23

Recently ion-intercalation hybrid supercapacitors, with high energy density at high power density, have been widely investigated to meet ever-increasing practical demands. Here, a unique hybrid supercapacitor has been designed and fabricated using self-assembled orthorhombic-phase niobium oxide@carbon (T-Nb 2 O 5 @C) nanowires as an anode and commercially available activated carbon as a cathode. The 3D-interconnected T-Nb 2 O 5 @C nanowires have been synthesized through a highly efficient microwave-solvothermal method, combined with subsequent thermal treatment. The experimental parameters (e.g., time and temperature) can be easily programmed, and the synthesis time can be significantly shortened, thus enabling the buildup of abundant recipes for the engineering of scaled-up production. The Li-ion intercalation pseudocapacitance electrode, made from the as-formed self-assembled T-Nb 2 O 5 @C nanowires, shows excellent charge storage and transfer capability. When assembled into a hybrid supercapacitor with a cathode of activated carbon, a high energy density of 60.6 Wh kg -1 and a high power density of 8.5 kW kg -1 with outstanding stability are achieved. In virtue of easy optimization and programmability of the synthetic strategy, and the remarkable electrochemical performance, the self-assembled T-Nb 2 O 5 @C nanowires offer a promising anode for asymmetric hybrid supercapacitors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Depletion of microglia and inhibition of exosome synthesis halt tau propagation

Science.gov (United States)

Asai, Hirohide; Ikezu, Seiko; Tsunoda, Satoshi; Medalla, Maria; Luebke, Jennifer; Haydar, Tarik; Wolozin, Benjamin; Butovsky, Oleg; Kügler, Sebastian; Ikezu, Tsuneya

2015-01-01

Accumulation of pathological tau protein is a major hallmark of Alzheimer’s disease. Tau protein spreads from the entorhinal cortex to the hippocampal region early in the disease. Microglia, the primary phagocytes in the brain, are positively correlated with tau pathology, but their involvement in tau propagation is unknown. We developed an adeno-associated virus–based model exhibiting rapid tau propagation from the entorhinal cortex to the dentate gyrus in 4 weeks. We found that depleting microglia dramatically suppressed the propagation of tau and reduced excitability in the dentate gyrus in this mouse model. Moreover, we demonstrate that microglia spread tau via exosome secretion, and inhibiting exosome synthesis significantly reduced tau propagation in vitro and in vivo. These data suggest that microglia and exosomes contribute to the progression of tauopathy and that the exosome secretion pathway may be a therapeutic target. PMID:26436904

Analysis of ultrasound propagation in high-temperature nuclear reactor feedwater to investigate a clamp-on ultrasonic pulse doppler flowmeter

International Nuclear Information System (INIS)

Tezuka, Kenichi; Mori, Michitsugu; Wada, Sanehiro; Aritomi, Masanori; Kikura, Hiroshige; Sakai, Yukihiro

2008-01-01

The flow rate of nuclear reactor feedwater is an important factor in the operation of a nuclear power reactor. Venturi nozzles are widely used to measure the flow rate. Other types of flowmeters have been proposed to improve measurement accuracy and permit the flow rate and reactor power to be increased. The ultrasonic pulse Doppler system is expected to be a candidate method because it can measure the flow profile across the pipe cross section, which changes with time. For accurate estimation of the flow velocity, the incidence angle of ultrasound entering the fluid should be estimated using Snell's law. However, evaluation of the ultrasound propagation is not straightforward, especially for a high-temperature pipe with a clamp-on ultrasonic Doppler flowmeter. The ultrasound beam path may differ from what is expected from Snell's law due to the temperature gradient in the wedge and variation in the acoustic impedance between interfaces. Recently, simulation code for ultrasound propagation has come into use in the nuclear field for nondestructive testing. This article analyzes and discusses ultrasound propagation, using 3D-FEM simulation code plus the Kirchhoff method, as it relates to flow profile measurement in nuclear reactor feedwater with the ultrasonic pulse Doppler system. (author)

The Effect of Gravity on the Combustion Synthesis of Porous Biomaterials

Science.gov (United States)

Castillo, M.; Zhang, X.; Moore, J. J.; Schowengerdt, F. D.; Ayers, R. A.

2003-01-01

Production of highly porous composite materials by traditional materials processing is limited by difficult processing techniques. This work investigates the use of self propagating high temperature (combustion) synthesis (SHS) to create porous tricalcium phosphate (Ca3(PO4)2), TiB-Ti, and NiTi in low and microgravity. Combustion synthesis provides the ability to use set processing parameters to engineer the required porous structure suitable for bone repair or replacement. The processing parameters include green density, particle size, gasifying agents, composition, and gravity. The advantage of the TiB-Ti system is the high level of porosity achieved together with a modulus that can be controlled by both composition (TiB-Ti) and porosity. At the same time, NiTi exhibits shape memory properties. SHS of biomaterials allows the engineering of required porosity coupled with resorbtion properties and specific mechanical properties into the composite materials to allow for a better biomaterial.

Self-interacting scalar fields at high-temperature

Energy Technology Data Exchange (ETDEWEB)

Deur, Alexandre [University of Virginia, Charlottesville, VA (United States)

2017-06-15

We study two self-interacting scalar field theories in their high-temperature limit using path integrals on a lattice. We first discuss the formalism and recover known potentials to validate the method. We then discuss how these theories can model, in the high-temperature limit, the strong interaction and General Relativity. For the strong interaction, the model recovers the known phenomenology of the nearly static regime of heavy quarkonia. The model also exposes a possible origin for the emergence of the confinement scale from the approximately conformal Lagrangian. Aside from such possible insights, the main purpose of addressing the strong interaction here - given that more sophisticated approaches already exist - is mostly to further verify the pertinence of the model in the more complex case of General Relativity for which non-perturbative methods are not as developed. The results have important implications on the nature of Dark Matter. In particular, non-perturbative effects naturally provide flat rotation curves for disk galaxies, without need for non-baryonic matter, and explain as well other observations involving Dark Matter such as cluster dynamics or the dark mass of elliptical galaxies. (orig.)

On immobilization of high-level waste in an Y–Al garnet-based cermet matrix in SHS conditions

OpenAIRE

Konovalov, E.E.; Lastov, A.I.; Nerozin, N.A.

2015-01-01

A method of high-level waste (HLW) radionuclide immobilization in a long-life matrix based on Y–Al garnet, a material highly chemically resistant to natural environments, has been developed for the ultimate HLW isolation from the environment. Model systems containing Ce, Nd, Sm, Zr, Mo, 238U, and 241Am were used in the study as simulators of HLW radionuclides. An energy-saving technology of self-propagating high-temperature synthesis (SHS) was employed to synthesize the matrix material with f...

Fatigue crack propagation under elastic plastic medium at elevated temperature

International Nuclear Information System (INIS)

Asada, Y.; Yuuki, R.; Sakon, T.; Sunamoto, D.; Tokimasa, K.; Makino, Y.; Kitagawa, M; Shingai, K.

1980-01-01

The purposes of the present study are to establish the testing method to obtain compatible data on the low cycle fatigue crack propagation at elevated temperature, and to investigate the parameter controlling the crack propagation rate. In the present study, the preliminary experiments have been carried out on low cycle fatigue crack propagation behaviour in type 304 stainless steel in air at 550 0 C, using two types of specimen with a through thickness notch. Both strain controlled and stress controlled fatigue tests have been done under a fully reversed strain or stress cycling. The data obtained are correlated with some fracture mechanics parameters and are discussed with the appropriate parameter for evaluating the low cycle fatigue crack propagation behaviour at elevated temperature. (author)

Mechanical-thermal synthesis of chromium carbides

International Nuclear Information System (INIS)

Cintho, Osvaldo Mitsuyuki; Favilla, Eliane Aparecida Peixoto; Capocchi, Jose Deodoro Trani

2007-01-01

The present investigation deals with the synthesis of chromium carbides (Cr 3 C 2 and Cr 7 C 3 ), starting from metallic chromium (obtained from the reduction of Cr 2 O 3 with Al) and carbon (graphite). The synthesis was carried out via high energy milling, followed by heat-treating of pellets made of different milled mixtures at 800 o C, for 2 h, under an atmosphere of argon. A SPEX CertPrep 8000 Mixer/Mill was used for milling under argon atmosphere. A tool steel vat and two 12.7 mm diameter chromium steel balls were used. The raw materials used and the products were characterized by differential thermal analysis, thermo gravimetric analysis, X-ray diffraction, electronic microscopy and X-ray fluorescence chemical analysis. The following variables were investigated: the quantity of carbon in the mixture, the milling time and the milling power. Mechanical activation of the reactant mixture depends upon the milling power ratio used for processing. The energy liberated by the reduction of the chromium oxide with aluminium exhibits a maximum for milling power ratio between 5:1 and 7.5:1. Self-propagating reaction occurred for all heat-treated samples whatever the carbon content of the sample and the milling power ratio used. Bearing carbon samples exhibited hollow shell structures after the reaction. The level of iron contamination of the milled samples was kept below 0.3% Fe. The self-propagated reaction caused high temperatures inside the samples as it may be seen by the occurrence of spherules, dendrites and whiskers. The carbon content determines the type of chromium carbide formed

Preparation of molybdenum borides by combustion synthesis involving solid-phase displacement reactions

International Nuclear Information System (INIS)

Yeh, C.L.; Hsu, W.S.

2008-01-01

Preparation of molybdenum borides of five different phases in the Mo-B binary system (including Mo 2 B, MoB, MoB 2 , Mo 2 B 5 , and MoB 4 ) was performed by self-propagating high-temperature synthesis (SHS) with two kinds of the reactant samples. When elemental powder compacts with an exact stoichiometry corresponding to the boride phase were employed, self-sustaining reaction was only achieved in the sample with Mo:B = 1:1 and nearly single-phase MoB was yielded. Therefore, the other four boride compounds were prepared from the reactant compacts composed of MoO 3 , Mo, and B powders, within which the displacement reaction of MoO 3 with boron was involved in combustion synthesis. Experimental evidence shows that the extent of displacement reaction in the overall reaction has a significant impact on sustainability of the synthesis reaction, combustion temperature, reaction front velocity, and composition of the end product. An increase in the solid-phase displacement reaction taking place during the SHS process contributes more heat flux to the synthesis reaction, thus resulting in the increase of combustion temperature and enhancement of the reaction front velocity. Based upon the XRD analysis, formation of Mo 2 B, MoB 2 , and Mo 2 B 5 as the dominant boride phase in the end product was successful through the SHS reaction with powder compacts under appropriate stoichiometries between MoO 3 , Mo, and B. However, a poor conversion was observed in the synthesis of MoB 4 . The powder compact prepared for the production of MoB 4 yielded mostly Mo 2 B 5

High-temperature expansion along the self-dual line of three-dimensional Z(2) spin-gauge theory

International Nuclear Information System (INIS)

Bhanot, G.

1981-01-01

We exploit the self-duality of the three-dimensional Ising spin-gauge theory to develop an eighth-order high-temperature expansion for the partition function along the self-dual line. This generates a high-temperature series for the gauge-invariant, nearest-neighbor spin-spin correlation function. A Pade analysis of this series reveals a pole along the self-dual line. Recent Monte Carlo simulations indicate that this theory has a first-order self-dual line emerging from a triple point. We interpret the Pade pole as a theoretical estimate of the end point of this self-dual line

Mechanically activated SHS reaction in the Fe-Al system: in-situ time resolved diffraction using synchrotron radiation

International Nuclear Information System (INIS)

Gaffet, E.; Charlot, F.; Klein, D.; Bernard, F.; Niepce, J.C.

1998-01-01

The mechanical activation self propagating high temperature synthesis (M.A.S.H.S.) processing is a new way to produce nanocrystalline iron aluminide intermetallic compounds. This process is maily the combination of two steps; in the one hand, a mechanical activation where the Fe - Al powder mixture was milled during a short time at given energy and frequency of shocks and in the other hand, a self propagating high temperature synthesis (S.H.S.) reaction, for which the exothermicity of the Fe + Al reaction is used. This fast propagated MASHS reaction has been in-situ investigated using the time resolved X-ray diffraction (TRXRD) using a X-ray synchrotron beam and an infrared thermography camera, allowing the coupling of the materials structure and the temperature field. The effects of the initial mean compositions, of the milling conditions as well as of the compaction parameters on the MASHS reaction are reported. (orig.)

SCC crack propagation behavior in 316L weld metal under high temperature water

International Nuclear Information System (INIS)

Nakade, Katsuyuki; Hirasaki, Toshifumi; Suzuki, Shunichi; Takamori, Kenro; Kumagai, Katsuhiko; Tanaka, Yoshihiko; Umeoka, Kuniyoshi

2008-01-01

Intergranular stress corrosion cracking (SCC) of 316L weld metal is of concern to the BWR plants. PLR pipes in commercial BWR plants have shown SCC in almost HAZ area in high temperature water, whereas, SCC has been arrested around fusion boundary for long time in the actual PLR pipe. The SCC behavior could be characterized in terms of dendrite direction, which was defined as the angle between dendrite growth direction and macro-SCC direction. In this study, the relationship between dendrite growth direction and macro-SCC direction was clearly showed on the fracture surface. The relative large difference of SCC susceptibility of 316L HAZ and weld metal was observed on the fracture surface. In the case of 0 degree, SCC has rapidly propagated into the weld metal parallel to the dendrite structure. In the case of more than 30 degree SCC direction, SCC was arrested around fusion area, and 60 degree SCC was drastically arrested around the fusion area. The large inclined dendrite structure for SCC is highly resistant to SCC. (author)

Method of synthesis of abstract images with high self-similarity

Science.gov (United States)

Matveev, Nikolay V.; Shcheglov, Sergey A.; Romanova, Galina E.; Koneva, Ð.¢atiana A.

2017-06-01

Abstract images with high self-similarity could be used for drug-free stress therapy. This based on the fact that a complex visual environment has a high affective appraisal. To create such an image we can use the setup based on the three laser sources of small power and different colors (Red, Green, Blue), the image is the pattern resulting from the reflecting and refracting by the complicated form object placed into the laser ray paths. The images were obtained experimentally which showed the good therapy effect. However, to find and to choose the object which gives needed image structure is very difficult and requires many trials. The goal of the work is to develop a method and a procedure of finding the object form which if placed into the ray paths can provide the necessary structure of the image In fact the task means obtaining the necessary irradiance distribution on the given surface. Traditionally such problems are solved using the non-imaging optics methods. In the given case this task is very complicated because of the complicated structure of the illuminance distribution and its high non-linearity. Alternative way is to use the projected image of a mask with a given structure. We consider both ways and discuss how they can help to speed up the synthesis procedure for the given abstract image of the high self-similarity for the setups of drug-free therapy.

Synthesis and high (pressure, temperature) stability of ZnTiO3 polymorphs studied by Raman spectroscopy

Science.gov (United States)

Bernert, T.; Ruiz-Fuertes, J.; Bayarjargal, L.; Winkler, B.

2015-05-01

The phase-purity of ilmenite-type ZnTiO3 prepared by the ceramic method was investigated in dependence of the conditions during ball milling. The previously proposed addition of 2 ml ethanol to the starting materials led to a significant contamination of the product phase after a subsequent sintering process at 1073 K. However, by omitting ethanol this synthesis route led to a phase-pure sample of ZnTiO3 as confirmed by X-ray powder diffraction and Raman spectroscopy. High-temperature high-pressure experiments gave an ilmenite-type to perovskite-type phase boundary with a slope of dT/dP∼-135 K GPa-1 crossing ambient temperature conditions at ∼ 24 GPa in good agreement with previous calculations. Room-temperature high-pressure Raman spectroscopy experiments have shown the stability of the ilmenite-type phase up to a pressure of at least 38.5 GPa, the highest pressure applied in this study, indicating the presence of a kinetic barrier in this phase transition. The synthesis of ferroelectric LiNbO3-type ZnTiO3 was confirmed by second harmonic generation.

Effects of temperature variations on guided waves propagating in composite structures

Science.gov (United States)

Shoja, Siavash; Berbyuk, Viktor; Boström, Anders

2016-04-01

Effects of temperature on guided waves propagating in composite materials is a well-known problem which has been investigated in many studies. The majority of the studies is focused on effects of high temperature. Understanding the effects of low temperature has major importance in composite structures and components which are operating in cold climate conditions such as e.g. wind turbines operating in cold climate regions. In this study first the effects of temperature variations on guided waves propagating in a composite plate is investigated experimentally in a cold climate chamber. The material is a common material used to manufacture rotor blades of wind turbines. The temperature range is 25°C to -25°C and effects of temperature variations on amplitude and phase shift of the received signal are investigated. In order to apply the effects of lowering the temperature on the received signal, the Baseline Signal Stretch (BSS) method is modified and used. The modification is based on decomposing the signal into symmetric and asymmetric modes and applying two different stretch factors on each of them. Finally the results obtained based on the new method is compared with the results of application of BSS with one stretch factor and experimental measurements. Comparisons show that an improvement is obtained using the BSS with the mode decomposition method at temperature variations of more than 25°C.

The use of an electric field as a processing parameter in the combustion synthesis of ceramics and composites

International Nuclear Information System (INIS)

Munir, Z.A.

1996-01-01

The imposition of an electric field is shown to activate self-propagating combustion reactions and thus makes possible the synthesis of a variety of ceramic and composite phases. Experimental observations and modeling studies indicated that activation is accomplished by the localized effect of the current. The relationship between wave propagation and the direction of the applied field was investigated. The synthesis of composites by field-activated combustion synthesis (FACS) was demonstrated. It was shown that the imposition of a field during the combustion synthesis of MoSi 2 results in a decrease /in the product particle size. The results suggest that the field can be used as a processing parameter in self-propagating combustion synthesis

Synthesis of high luminescent carbon nanoparticles

Science.gov (United States)

Gvozdyuk, Alina A.; Petrova, Polina S.; Goryacheva, Irina Y.; Sukhorukov, Gleb B.

2017-03-01

In this article we report an effective and simple method for synthesis of high luminescent carbon nanodots (CDs). In our work as a carbon source sodium dextran sulfate (DS) was used because it is harmless, its analogs are used in medicine as antithrombotic compounds and blood substitutes after hemorrhage. was used as a substrate We investigated the influence of temperature parameters of hydrothermal synthesis on the photoluminescence (PL) intensity and position of emission maxima. We discovered that the PL intensity can be tuned by changing of synthesis temperature and CD concentration.

Hydroxide Self-Feeding High-Temperature Alkaline Direct Formate Fuel Cells.

Science.gov (United States)

Li, Yinshi; Sun, Xianda; Feng, Ying

2017-05-22

Conventionally, both the thermal degradation of the anion-exchange membrane and the requirement of additional hydroxide for fuel oxidation reaction hinder the development of the high-temperature alkaline direct liquid fuel cells. The present work addresses these two issues by reporting a polybenzimidazole-membrane-based direct formate fuel cell (DFFC). Theoretically, the cell voltage of the high-temperature alkaline DFFC can be as high as 1.45 V at 90 °C. It has been demonstrated that a proof-of-concept alkaline DFFC without adding additional hydroxide yields a peak power density of 20.9 mW cm -2 , an order of magnitude higher than both alkaline direct ethanol fuel cells and alkaline direct methanol fuel cells, mainly because the hydrolysis of formate provides enough OH - ions for formate oxidation reaction. It was also found that this hydroxide self-feeding high-temperature alkaline DFFC shows a stable 100 min constant-current discharge at 90 °C, proving the conceptual feasibility. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Towards room temperature, direct, solvent free synthesis of tetraborohydrides

International Nuclear Information System (INIS)

Remhof, A; Yan, Y; Friedrichs, O; Kim, J W; Mauron, Ph; Borgschulte, A; Züttel, A; Wallacher, D; Buchsteiner, A; Hoser, A; Oh, K H; Cho, Y W

2012-01-01

Due to their high hydrogen content, tetraborohydrides are discussed as potential synthetic energy carriers. On the example of lithium borohydride LiBH 4 , we discuss current approaches of direct, solvent free synthesis based on gas solid reactions of the elements or binary hydrides and/or borides with gaseous H 2 or B 2 H 6 . The direct synthesis from the elements requires high temperature and high pressure (700°C, 150bar D 2 ). Using LiB or AlB 2 as boron source reduces the required temperature by more than 300 K. Reactive milling of LiD with B 2 H 6 leads to the formation of LiBD 4 already at room temperature. The reactive milling technique can also be applied to synthesize other borohydrides from their respective metal hydrides.

Facile room-temperature solution-phase synthesis of a spherical covalent organic framework for high-resolution chromatographic separation.

Science.gov (United States)

Yang, Cheng-Xiong; Liu, Chang; Cao, Yi-Meng; Yan, Xiu-Ping

2015-08-07

A simple and facile room-temperature solution-phase synthesis was developed to fabricate a spherical covalent organic framework with large surface area, good solvent stability and high thermostability for high-resolution chromatographic separation of diverse important industrial analytes including alkanes, cyclohexane and benzene, α-pinene and β-pinene, and alcohols with high column efficiency and good precision.

Self-Propagating Reactive Fronts in Compacts of Multilayered Particles

International Nuclear Information System (INIS)

Sraj, I.; Vohra, M.; Alawieh, L.; Weihs, T.P.; Knio, O.M.

2013-01-01

Reactive multilayered foils in the form of thin films have gained interest in various applications such as joining, welding, and ignition. Typically, thin film multilayers support self-propagating reaction fronts with speeds ranging from 1 to 20 m/s. In some applications, however, reaction fronts with much smaller velocities are required. This recently motivated Fritz et al. (2011) to fabricate compacts of regular sized/shaped multilayered particles and demonstrate self-sustained reaction fronts having much smaller velocities than thin films with similar layering. In this work, we develop a simplified numerical model to simulate the self-propagation of reactive fronts in an idealized compact, comprising identical Ni/Al multilayered particles in thermal contact. The evolution of the reaction in the compact is simulated using a two-dimensional transient model, based on a reduced description of mixing, heat release, and thermal transport. Computed results reveal that an advancing reaction front can be substantially delayed as it crosses from one particle to a neighboring particle, which results in a reduced mean propagation velocity. A quantitative analysis is thus conducted on the dependence of these phenomena on the contact area between the particles, the thermal contact resistance, and the arrangement of the multilayered particles.

Self-Propagating Reactive Fronts in Compacts of Multilayered Particles

Directory of Open Access Journals (Sweden)

Ihab Sraj

2013-01-01

Full Text Available Reactive multilayered foils in the form of thin films have gained interest in various applications such as joining, welding, and ignition. Typically, thin film multilayers support self-propagating reaction fronts with speeds ranging from 1 to 20 m/s. In some applications, however, reaction fronts with much smaller velocities are required. This recently motivated Fritz et al. (2011 to fabricate compacts of regular sized/shaped multilayered particles and demonstrate self-sustained reaction fronts having much smaller velocities than thin films with similar layering. In this work, we develop a simplified numerical model to simulate the self-propagation of reactive fronts in an idealized compact, comprising identical Ni/Al multilayered particles in thermal contact. The evolution of the reaction in the compact is simulated using a two-dimensional transient model, based on a reduced description of mixing, heat release, and thermal transport. Computed results reveal that an advancing reaction front can be substantially delayed as it crosses from one particle to a neighboring particle, which results in a reduced mean propagation velocity. A quantitative analysis is thus conducted on the dependence of these phenomena on the contact area between the particles, the thermal contact resistance, and the arrangement of the multilayered particles.

Catalytic chemical amide synthesis at room temperature: one more step toward peptide synthesis.

Science.gov (United States)

Mohy El Dine, Tharwat; Erb, William; Berhault, Yohann; Rouden, Jacques; Blanchet, Jérôme

2015-05-01

An efficient method has been developed for direct amide bond synthesis between carboxylic acids and amines via (2-(thiophen-2-ylmethyl)phenyl)boronic acid as a highly active bench-stable catalyst. This catalyst was found to be very effective at room temperature for a large range of substrates with slightly higher temperatures required for challenging ones. This methodology can be applied to aliphatic, α-hydroxyl, aromatic, and heteroaromatic acids as well as primary, secondary, heterocyclic, and even functionalized amines. Notably, N-Boc-protected amino acids were successfully coupled in good yields with very little racemization. An example of catalytic dipeptide synthesis is reported.

Self-assembled 3D zinc borate florets via surfactant assisted synthesis under moderate pressures: Process temperature dependent morphology study

Science.gov (United States)

Mahajan, Dhiraj S.; Deshpande, Tushar; Bari, Mahendra L.; Patil, Ujwal D.; Narkhede, Jitendra S.

2018-04-01

In the present study, we prepared zinc borates using aqueous phase synthesis under moderate pressures (MP) (ethanol as a co-solvent in the presence of a quaternary ammonium surfactant-Cetyltrimethylammonium bromide (CTAB). 3D morphologies of self-assembled zinc borate (Zn(H2O)B2O4 · 0.12 H2O, Zn3B6O12 · 3.5H2O, ZnB2O4) resembling flower-like structures were obtained by varying temperature under moderate pressure conditions. Synthesized zinc borates’ florets were morphologically characterized by Field Emission Scanning Electron Microscopy. The x-ray diffractions of borate species reveal rhombohydra, monoclinic and cubic phases of zinc borate crystals as a function of process temperature. Additionally, thermal analysis confirms excellent dehydration/degradation behavior for the zinc borate crystals synthesized at moderate pressures and elevated temperatures and could be utilized as potential flame retardant fillers in the polymer matrices.

Purification of gas and liquid media by metal-ceramic SHS-filters

OpenAIRE

Geyneman, A. A.; Goncharov, V. D.; Novoselov, A. L.; Shchetinkina, N. Yu.

2007-01-01

Industrial samples of fine filters of gas and liquid media from mechanical microparticles have been developed. Porous permeable cermets obtained by self-propagating high-temperature synthesis are the basis of filters

Investigation into boron reaction with titanium at extreme temperature gradients

International Nuclear Information System (INIS)

Korchagin, M.A.; Gusenko, S.N.; Aleksandrov, V.V.; Neronov, V.A.

1981-01-01

The mechanism of self-propagation high-temperature synthesis of titanium boride is studied using the translucent electron microscopy. Titanium interaction with boron film (approximately 1000 A thick) starts with the metal partial melting. A twozone layer of the reaction products, separating the reagents, is formed. In the zone adjacent to B, Ti 3 B 4 and fusible liquid phases are present. The second zone consists of TiB. The subsequent interaction is realized by Means of the dissolving and absorption by titanium of the layer of products during its continuous increase in boron. TiB 2 formation takes place at subsequent stages of interaction inside Ti liquid particles during their saturation by boron from the products absorbed [ru

Reactive Ni/Ti nanolaminates

International Nuclear Information System (INIS)

Adams, D. P.; Bai, M. M.; Rodriguez, M. A.; McDonald, J. P.; Jones, E. Jr.; Brewer, L.; Moore, J. J.

2009-01-01

Nickel/titanium nanolaminates fabricated by sputter deposition exhibited rapid, high-temperature synthesis. When heated locally, self-sustained reactions were produced in freestanding Ni/Ti multilayer foils characterized by average propagation speeds between ∼0.1 and 1.4 m/s. The speed of a propagating reaction front was affected by total foil thickness and bilayer thickness (layer periodicity). In contrast to previous work with compacted Ni-Ti powders, no preheating of Ni/Ti foils was required to maintain self-propagating reactions. High-temperature synthesis was also stimulated by rapid global heating demonstrating low ignition temperatures (T ig )∼300-400 deg. C for nanolaminates. Ignition temperature was influenced by bilayer thickness with more coarse laminate designs exhibiting increased T ig . Foils reacted in a vacuum apparatus developed either as single-phase B2 cubic NiTi (austenite) or as a mixed-phase structure that was composed of monoclinic B19 ' NiTi (martensite), hexagonal NiTi 2 , and B2 NiTi. Single-phase, cubic B2 NiTi generally formed when the initial bilayer thickness was made small.

Numerical investigation of high temperature synthesis gas premixed combustion via ANSYS Fluent

Directory of Open Access Journals (Sweden)

Pashchenko Dmitry

2018-01-01

Full Text Available A numerical model of the synthesis gas pre-mixed combustion is developed. The research was carried out via ANSYS Fluent software. Verification of the numerical results was carried out using experimental data. A visual comparison of the flame contours that obtained by the synthesis gas combustion for Re = 600; 800; 1000 was performed. A comparison of the wall temperature of the combustion chamber, obtained with the help of the developed model, with the results of a physical experiment was also presented. For all cases, good convergence of the results is observed. It is established that a change in the temperature of the syngas/air mixture at the inlet to the combustion chamber does not significantly affect the temperature of the combustion products due to the dissipation of the H2O and CO2 molecules. The obtained results are of practical importance for the design of heat engineering plants with thermochemical heat recovery.

Nanometric solid solutions of the fluorite and perovskite type crystal structures: Synthesis and properties

Directory of Open Access Journals (Sweden)

Snežana Bošković

2012-09-01

Full Text Available In this paper a short review of our results on the synthesis of nanosized CeO2, CaMnO3 and BaCeO3 solid solutions are presented. The nanopowders were prepared by two innovative methods: self propagating room temperature synthesis (SPRT and modified glycine/nitrate procedure (MGNP. Different types of solid solutions with rare earth dopants in concentrations ranging from 0–0.25 mol% were synthesized. The reactions forming solid solutions were studied. In addition, the characteristics of prepared nanopowders, phenomena during sintering and the properties of sintered samples are discussed.

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH2/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H2 Generation.

Science.gov (United States)

Amin, Mohammed A; Fadlallah, Sahar A; Alosaimi, Ghaida S; Ahmed, Emad M; Mostafa, Nasser Y; Roussel, Pascal; Szunerits, Sabine; Boukherroub, Rabah

2017-09-06

Self-supported electrocatalysts are a new class of materials exhibiting high catalytic performance for various electrochemical processes and can be directly equipped in energy conversion devices. We present here, for the first time, sparse Au NPs self-supported on etched Ti (nanocarved Ti substrate self-supported with TiH 2 ) as promising catalysts for the electrochemical generation of hydrogen (H 2 ) in KOH solutions. Cleaned, as-polished Ti substrates were etched in highly concentrated sulfuric acid solutions without and with 0.1 M NH 4 F at room temperature for 15 min. These two etching processes yielded a thin layer of TiH 2 (the corrosion product of the etching process) self-supported on nanocarved Ti substrates with different morphologies. While F - -free etching process led to formation of parallel channels (average width: 200 nm), where each channel consists of an array of rounded cavities (average width: 150 nm), etching in the presence of F - yielded Ti surface carved with nanogrooves (average width: 100 nm) in parallel orientation. Au NPs were then grown in situ (self-supported) on such etched surfaces via immersion in a standard gold solution at room temperature without using stabilizers or reducing agents, producing Au NPs/TiH 2 /nanostructured Ti catalysts. These materials were characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), grazing incidence X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS). GIXRD confirmed the formation of Au 2 Ti phase, thus referring to strong chemical interaction between the supported Au NPs and the substrate surface (also evidenced from XPS) as well as a titanium hydride phase of chemical composition TiH 2 . Electrochemical measurements in 0.1 M KOH solution revealed outstanding hydrogen evolution reaction (HER) electrocatalytic activity for our synthesized catalysts, with Au NPs/TiH 2 /nanogrooved Ti catalyst being the best one among them. It exhibited fast kinetics

Ruthenium(V) oxides from low-temperature hydrothermal synthesis

Energy Technology Data Exchange (ETDEWEB)

Hiley, Craig I.; Walton, Richard I. [Department of Chemistry, University of Warwick, Coventry (United Kingdom); Lees, Martin R. [Department of Physics, University of Warwick, Coventry (United Kingdom); Fisher, Janet M.; Thompsett, David [Johnson Matthey Technology Centre, Reading (United Kingdom); Agrestini, Stefano [Max-Planck Institut, CPfS, Dresden (Germany); Smith, Ronald I. [ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Harwell Oxford, Didcot (United Kingdom)

2014-04-22

Low-temperature (200 C) hydrothermal synthesis of the ruthenium oxides Ca{sub 1.5}Ru{sub 2}O{sub 7}, SrRu{sub 2}O{sub 6}, and Ba{sub 2}Ru{sub 3}O{sub 9}(OH) is reported. Ca{sub 1.5}Ru{sub 2}O{sub 7} is a defective pyrochlore containing Ru{sup V/VI}; SrRu{sub 2}O{sub 6} is a layered Ru{sup V} oxide with a PbSb{sub 2}O{sub 6} structure, whilst Ba{sub 2}Ru{sub 3}O{sub 9}(OH) has a previously unreported structure type with orthorhombic symmetry solved from synchrotron X-ray and neutron powder diffraction. SrRu{sub 2}O{sub 6} exhibits unusually high-temperature magnetic order, with antiferromagnetism persisting to at least 500 K, and refinement using room temperature neutron powder diffraction data provides the magnetic structure. All three ruthenates are metastable and readily collapse to mixtures of other oxides upon heating in air at temperatures around 300-500 C, suggesting they would be difficult, if not impossible, to isolate under conventional high-temperature solid-state synthesis conditions. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Fungal prion HET-s as a model for structural complexity and self-propagation in prions.

Science.gov (United States)

Wan, William; Stubbs, Gerald

2014-04-08

The highly ordered and reproducible structure of the fungal prion HET-s makes it an excellent model system for studying the inherent properties of prions, self-propagating infectious proteins that have been implicated in a number of fatal diseases. In particular, the HET-s prion-forming domain readily folds into a relatively complex two-rung β-solenoid amyloid. The faithful self-propagation of this fold involves a diverse array of inter- and intramolecular structural features. These features include a long flexible loop connecting the two rungs, buried polar residues, salt bridges, and asparagine ladders. We have used site-directed mutagenesis and X-ray fiber diffraction to probe the relative importance of these features for the formation of β-solenoid structure, as well as the cumulative effects of multiple mutations. Using fibrillization kinetics and chemical stability assays, we have determined the biophysical effects of our mutations on the assembly and stability of the prion-forming domain. We have found that a diversity of structural features provides a level of redundancy that allows robust folding and stability even in the face of significant sequence alterations and suboptimal environmental conditions. Our findings provide fundamental insights into the structural interactions necessary for self-propagation. Propagation of prion structure seems to require an obligatory level of complexity that may not be reproducible in short peptide models.

Room-temperature Electrochemical Synthesis of Carbide-derived Carbons and Related Materials

Energy Technology Data Exchange (ETDEWEB)

Gogotsi, Yury [Drexel Univ., Philadelphia, PA (United States). Nanomaterials Group. Materials Science and Engineering Dept.

2015-02-28

This project addresses room-temperature electrochemical etching as an energy-efficient route to synthesis of 3D nanoporous carbon networks and layered 2D carbons and related structures, as well as provides fundamental understanding of structure and properties of materials produced by this method. Carbide-derived-carbons (CDCs) are a growing class of nanostructured carbon materials with properties that are desirable for many applications, such as electrical energy and gas storage. The structure of these functional materials is tunable by the choice of the starting carbide precursor, synthesis method, and process parameters. Moving from high-temperature synthesis of CDCs through vacuum decomposition above 1400°C and chlorination above 400°C, our studies under the previous DOE BES support led to identification of precursor materials and processing conditions for CDC synthesis at temperatures as low as 200°C, resulting in amorphous and highly reactive porous carbons. We also investigated synthesis of monolithic CDC films from carbide films at 250-1200°C. The results of our early studies provided new insights into CDC formation, led to development of materials for capacitive energy storage, and enabled fundamental understanding of the electrolyte ions confinement in nanoporous carbons.

Low-Temperature Synthesis Routes to Intermetallic Superconductors

Energy Technology Data Exchange (ETDEWEB)

Schaak, Raymond E

2008-01-08

Over the past few years, our group has gained expertise at developing low-temperature solution-based synthetic pathways to complex nanoscale solids, with particular emphasis on nanocrystalline intermetallic compounds. Our synthetic capabilities are providing tools to reproducibly generate intermetallic nanostructures with simultaneous control over crystal structure, composition, and morphology. This DOE-funded project aims to expand these capabilities to intermetallic superconductors. This could represent an important addition to the tools that are available for the synthesis and processing of intermetallic superconductors, which traditionally utilize high-temperature, high-pressure, thin film, or gas-phase vacuum deposition methods. Our current knowledge of intermetallic superconductors suggests that significant enhancements could result from the inherent benefits of low-temperature solution synthesis, e.g. metastable phase formation, control over nanoscale morphology to facilitate size-dependent property studies, robust and inexpensive processability, low-temperature annealing and consolidation, and impurity incorporation (for doping, stoichiometry control, flux pinning, and improving the critical fields). Our focus is on understanding the superconducting properties as a function of synthetic route, crystal structure, crystallite size, and morphology, and developing the synthetic tools necessary to accomplish this. This research program can currently be divided into two classes of superconducting materials: intermetallics (transition metal/post transition metal) and metal carbides/borides. Both involve the development and exploitation of low-temperature synthesis routes followed by detailed characterization of structures and properties, with the goal of understanding how the synthetic pathways influence key superconducting properties of selected target materials. Because of the low-temperature methods used to synthesize them and the nanocrystalline morphologies

Rotating and propagating LIB stabilized by self-induced magnetic field

International Nuclear Information System (INIS)

Murakami, H.; Aoki, T.; Kawata, S.; Niu, K.

1984-01-01

Rotating motion of a propagating LIB is analyzed in order to suppress the mixed mode of the Kelvin-Helmholtz instability, the tearing instability and the sausage instability by the action of a self-induced magnetic field in the axial direction. The beams are assumed to be charge-neutralized but not current-neutralized. The steady-state solutions of a propagating LIB with rotation are first obtained numerically. Through the dispersion relation with respect to the ikonal type of perturbations, which are added to the steady-state solutions, the growth rates of instabilities appearing in an LIB are obtained. It is concluded that if the mean rotating velocity of an LIB is comparable to the propagation velocity, the instability disappears in the propagating ion beam. (author)

Self-propagating exothermic reaction analysis in Ti/Al reactive films using experiments and computational fluid dynamics simulation

Energy Technology Data Exchange (ETDEWEB)

Sen, Seema, E-mail: seema.sen@tu-ilmenau.de [Technical University of Ilmenau, Department of Materials for Electronics, Gustav-Kirchhoff-Str. 5, 98693 Ilmenau (Germany); Niederrhein University of Applied Science, Department of Mechanical and Process Engineering, Reinarzstraße 49, 47805 Krefeld (Germany); Lake, Markus; Kroppen, Norman; Farber, Peter; Wilden, Johannes [Niederrhein University of Applied Science, Department of Mechanical and Process Engineering, Reinarzstraße 49, 47805 Krefeld (Germany); Schaaf, Peter [Technical University of Ilmenau, Department of Materials for Electronics, Gustav-Kirchhoff-Str. 5, 98693 Ilmenau (Germany)

2017-02-28

Highlights: • Development of nanoscale Ti/Al multilayer films with 1:1, 1:2 and 1:3 molar ratios. • Characterization of exothermic reaction propagation by experiments and simulation. • The reaction velocity depends on the ignition potentials and molar ratios of the films. • Only 1Ti/3Al films exhibit the unsteady reaction propagation with ripple formation. • CFD simulation shows the time dependent atom mixing and temperature flow during exothermic reaction. - Abstract: This study describes the self-propagating exothermic reaction in Ti/Al reactive multilayer foils by using experiments and computational fluid dynamics simulation. The Ti/Al foils with different molar ratios of 1Ti/1Al, 1Ti/2Al and 1Ti/3Al were fabricated by magnetron sputtering method. Microstructural characteristics of the unreacted and reacted foils were analyzed by using electronic and atomic force microscopes. After an electrical ignition, the influence of ignition potentials on reaction propagation has been experimentally investigated. The reaction front propagates with a velocity of minimum 0.68 ± 0.4 m/s and maximum 2.57 ± 0.6 m/s depending on the input ignition potentials and the chemical compositions. Here, the 1Ti/3Al reactive foil exhibits both steady state and unsteady wavelike reaction propagation. Moreover, the numerical computational fluid dynamics (CFD) simulation shows the time dependent temperature flow and atomic mixing in a nanoscale reaction zone. The CFD simulation also indicates the potentiality for simulating exothermic reaction in the nanoscale Ti/Al foil.

Glass fabrics self-cracking catalytic growth of boron nitride nanotubes

Science.gov (United States)

Wang, Jilin; Peng, Daijang; Long, Fei; Wang, Weimin; Gu, Yunle; Mo, Shuyi; Zou, Zhengguang; Fu, Zhengyi

2017-02-01

Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.

Mechanically Activated Combustion Synthesis of MoSi₂-Based Composites

Energy Technology Data Exchange (ETDEWEB)

Shafirovich, Evgeny [Univ. of Texas, El Paso, TX (United States)

2015-09-30

The thermal efficiency of gas-turbine power plants could be dramatically increased by the development of new structural materials based on molybdenum silicides and borosilicides, which can operate at temperatures higher than 1300 °C with no need for cooling. A major challenge, however, is to simultaneously achieve high oxidation resistance and acceptable mechanical properties at high temperatures. One approach is based on the fabrication of MoSi2-Mo5Si3 composites that combine high oxidation resistance of MoSi2 and good mechanical properties of Mo5Si3. Another approach involves the addition of boron to Mo-rich silicides for improving their oxidation resistance through the formation of a borosilicate surface layer. In particular, materials based on Mo5SiB2 phase are promising materials that offer favorable combinations of high temperature mechanical properties and oxidation resistance. However, the synthesis of Mo-Si-B multi-phase alloys is difficult because of their extremely high melting temperatures. Mechanical alloying has been considered as a promising method, but it requires long milling times, leading to large energy consumption and contamination of the product by grinding media. In the reported work, MoSi2-Mo5Si3 composites and several materials based on Mo5SiB2 phase have been obtained by mechanically activated self-propagating high-temperature synthesis (MASHS). Short-term milling of Mo/Si mixture in a planetary mill has enabled a self-sustained propagation of the combustion front over the mixture pellet, leading to the formation of MoSi2-T1 composites. Combustion of Mo/Si/B mixtures for the formation of T2 phase becomes possible if the composition is designed for the addition of more exothermic reactions leading to the formation of MoB, TiC, or TiB2. Upon ignition, Mo/Si/B and Mo/Si/B/Ti mixtures exhibited spin combustion, but the products were porous, contained undesired secondary phases, and had low oxidation resistance. It has been shown that use of

A self-consistency check for unitary propagation of Hawking quanta

Science.gov (United States)

Baker, Daniel; Kodwani, Darsh; Pen, Ue-Li; Yang, I.-Sheng

2017-11-01

The black hole information paradox presumes that quantum field theory in curved space-time can provide unitary propagation from a near-horizon mode to an asymptotic Hawking quantum. Instead of invoking conjectural quantum-gravity effects to modify such an assumption, we propose a self-consistency check. We establish an analogy to Feynman’s analysis of a double-slit experiment. Feynman showed that unitary propagation of the interfering particles, namely ignoring the entanglement with the double-slit, becomes an arbitrarily reliable assumption when the screen upon which the interference pattern is projected is infinitely far away. We argue for an analogous self-consistency check for quantum field theory in curved space-time. We apply it to the propagation of Hawking quanta and test whether ignoring the entanglement with the geometry also becomes arbitrarily reliable in the limit of a large black hole. We present curious results to suggest a negative answer, and we discuss how this loss of naive unitarity in QFT might be related to a solution of the paradox based on the soft-hair-memory effect.

Gluon and ghost propagator studies in lattice QCD at finite temperature

International Nuclear Information System (INIS)

Aouane, Rafik

2013-01-01

Gluon and ghost propagators in quantum chromodynamics (QCD) computed in the infrared momentum region play an important role to understand quark and gluon confinement. They are the subject of intensive research thanks to non-perturbative methods based on Dyson-Schwinger (DS) and functional renormalization group (FRG) equations. Moreover, their temperature behavior might also help to explore the chiral and deconfinement phase transition or crossover within QCD at non-zero temperature. Our prime tool is the lattice discretized QCD (LQCD) providing a unique ab-initio non-perturbative approach to deal with the computation of various observables of the hadronic world. We investigate the temperature dependence of Landau gauge gluon and ghost propagators in pure gluodynamics and in full QCD. Regarding the gluon propagator, we compute its longitudinal D L as well its transversal D T components. The aim is to provide a data set in terms of fitting formulae which can be used as input for DS (or FRG) equations. We deal with full (N f =2) LQCD with the twisted mass fermion discretization. We employ gauge field configurations provided by the tmfT collaboration for temperatures in the crossover region and for three fixed pion mass values in the range [300,500] MeV. Finally, within SU(3) pure gauge theory (at T=0) we compute the Landau gauge gluon propagator according to different gauge fixing criteria. Our goal is to understand the influence of gauge copies with minimal (non-trivial) eigenvalues of the Faddeev-Popov operator.

The temperature pulse propagation in interacting nuclear slabs

International Nuclear Information System (INIS)

Kozlowski, M.; Zurich Univ.

1989-01-01

Following the method developed by R.J. Swenson a non-Fourier equation for heat transfer in nuclear matter is obtained. The velocity of heat propagation is calculated and the value υ s = υ F /√3 is obtained. For two interacting nuclear slabs the temperature as a function of time is calculated. For a nucleon mean free path λ ≅ 3 fm the temperature saturation time is calculated and the value ≅ 160 fm/c is obtained. (orig.)

Bulletin of Materials Science | News

Indian Academy of Sciences (India)

Home; Journals; Bulletin of Materials Science; Volume 25; Issue 4 ... were synthesized by self-propagating high temperature synthesis (SHS) method. ... Structure determination at room temperature and phase transition studies above T c in .... Hyperfine field distributions in disordered Mn2CoSn and Mn2NiSn Heusler alloys.

Fatigue crack propagation in self-assembling nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Klingler, Andreas; Wetzel, Bernd [Institute for Composite Materials (IVW GmbH) Technical University of Kaiserslautern, 67633 Kaiserslautern (Germany)

2016-05-18

Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

Fatigue crack propagation in self-assembling nanocomposites

Science.gov (United States)

Klingler, Andreas; Wetzel, Bernd

2016-05-01

Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

Fatigue crack propagation in self-assembling nanocomposites

International Nuclear Information System (INIS)

Klingler, Andreas; Wetzel, Bernd

2016-01-01

Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

Study of Temperature Wave Propagation in Superfluid Helium Focusing on Radio-Frequency Cavity Cooling

CERN Document Server

Koettig, T; Avellino, S; Junginger, T; Bremer, J

2015-01-01

Oscillating Superleak Transducers (OSTs) can be used to localize quenches of superconducting radio-frequency cavities. Local hot spots at the cavity surface initiate temperature waves in the surrounding superfluid helium that acts as cooling fluid at typical temperatures in the range of 1.6 K to 2 K. The temperature wave is characterised by the properties of superfluid helium such as the second sound velocity. For high heat load densities second sound velocities greater than the standard literature values are observed. This fast propagation has been verified in dedicated small scale experiments. Resistors were used to simulate the quench spots under controlled conditions. The three dimensional propagation of second sound is linked to OST signals. The aim of this study is to improve the understanding of the OST signal especially the incident angle dependency. The characterised OSTs are used as a tool for quench localisation on a real size cavity. Their sensitivity as well as the time resolution was proven to b...

High-deposition-rate ceramics synthesis

Energy Technology Data Exchange (ETDEWEB)

Allendorf, M.D.; Osterheld, T.H.; Outka, D.A. [Sandia National Laboratories, Livermore, CA (United States)] [and others

1995-05-01

Parallel experimental and computational investigations are conducted in this project to develop validated numerical models of ceramic synthesis processes. Experiments are conducted in the High-Temperature Materials Synthesis Laboratory in Sandia`s Combustion Research Facility. A high-temperature flow reactor that can accommodate small preforms (1-3 cm diameter) generates conditions under which deposition can be observed, with flexibility to vary both deposition temperature (up to 1500 K) and pressure (as low as 10 torr). Both mass spectrometric and laser diagnostic probes are available to provide measurements of gas-phase compositions. Experiments using surface analytical techniques are also applied to characterize important processes occuring on the deposit surface. Computational tools developed through extensive research in the combustion field are employed to simulate the chemically reacting flows present in typical industrial reactors. These include the CHEMKIN and Surface-CHEMKIN suites of codes, which permit facile development of complex reaction mechanisms and vastly simplify the implementation of multi-component transport and thermodynamics. Quantum chemistry codes are also used to estimate thermodynamic and kinetic data for species and reactions for which this information is unavailable.

Synthesis of high saturation magnetic iron oxide nanomaterials via low temperature hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Bhavani, P.; Rajababu, C.H. [Department of Materials Science & Nanotechnology, Yogivemana University, Vemanapuram 516003, Kadapa (India); Arif, M.D. [Environmental Magnetism Laboratory, Indian Institute of Geomagnetism (IIG), Navi Mumbai 410218, Mumbai (India); Reddy, I. Venkata Subba [Department of Physics, Gitam University, Hyderabad Campus, Rudraram, Medak 502329 (India); Reddy, N. Ramamanohar, E-mail: manoharphd@gmail.com [Department of Materials Science & Nanotechnology, Yogivemana University, Vemanapuram 516003, Kadapa (India)

2017-03-15

Iron oxide nanoparticles (IONPs) were synthesized through a simple low temperature hydrothermal approach to obtain with high saturation magnetization properties. Two series of iron precursors (sulfates and chlorides) were used in synthesis process by varying the reaction temperature at a constant pH. The X-ray diffraction pattern indicates the inverse spinel structure of the synthesized IONPs. The Field emission scanning electron microscopy and high resolution transmission electron microscopy studies revealed that the particles prepared using iron sulfate were consisting a mixer of spherical (16–40 nm) and rod (diameter ~20–25 nm, length <100 nm) morphologies that synthesized at 130 °C, while the IONPs synthesized by iron chlorides are found to be well distributed spherical shapes with size range 5–20 nm. On other hand, the IONPs synthesized at reaction temperature of 190 °C has spherical (16–46 nm) morphology in both series. The band gap values of IONPs were calculated from the obtained optical absorption spectra of the samples. The IONPs synthesized using iron sulfate at temperature of 130 °C exhibited high saturation magnetization (M{sub S}) of 103.017 emu/g and low remanant magnetization (M{sub r}) of 0.22 emu/g with coercivity (H{sub c}) of 70.9 Oe{sub ,} which may be attributed to the smaller magnetic domains (d{sub m}) and dead magnetic layer thickness (t). - Highlights: • Comparison of iron oxide materials prepared with Fe{sup +2}/Fe{sup +3} sulfates and chlorides at different temperatures. • We prepared super-paramagnetic and soft ferromagnetic magnetite nanoparticles. • We report higher saturation magnetization with lower coercivity.

Thermal propagation and stability in superconducting films

International Nuclear Information System (INIS)

Gray, K.E.; Kampwirth, R.T.; Zasadzinski, J.F.; Ducharme, S.P.

1983-01-01

Thermal propagation and stable hot spots (normal domains) are studied in various high Tsub(c) superconducting films (Nb 3 Sn, Nb, NbN and Nb 3 Ge). A new energy balance is shown to give reasonable quantitative agreement of the dependence of the propagation velocity on the length of short normal domains. The steady state (zero velocity) measurements indicate the existence of two distinct situations for films on high thermal conductivity (sapphire) substrates. For low power per unit area the film and substrate have the same temperature, and the thermal properties of the substrate dominate. However, for higher power densities in short hot spots, the coupling is relatively weak and the thermal properties of the film alone are important. Here a connection is made between the critical current stability of superconducting films and a critical hot spot size for thermal propagation. As a result efficient heat removal is shown to dominate the stabilisation of superconducting films. The strong and weak coupling situations also lead to modifications of the models for propagation velocities on sapphire substrates. Self-healing of hot spots and other phenomena in superconducting film are explained. The potential use of the thermal propagation model in applications of superconductors, especially switches is discussed. (author)

Jiecai Han

Indian Academy of Sciences (India)

Home; Journals; Bulletin of Materials Science. Jiecai Han. Articles written in Bulletin of Materials Science. Volume 25 Issue 4 August 2002 pp 263-266 Synthesis. Self-propagating high temperature synthesis and magnetic properties of Ni0.35Zn0.65Fe2O4 powders · Yao Li Jiupeng Zhao Jiecai Han · More Details Abstract ...

Gluon and ghost propagator studies in lattice QCD at finite temperature

Energy Technology Data Exchange (ETDEWEB)

Aouane, Rafik

2013-04-29

Gluon and ghost propagators in quantum chromodynamics (QCD) computed in the infrared momentum region play an important role to understand quark and gluon confinement. They are the subject of intensive research thanks to non-perturbative methods based on Dyson-Schwinger (DS) and functional renormalization group (FRG) equations. Moreover, their temperature behavior might also help to explore the chiral and deconfinement phase transition or crossover within QCD at non-zero temperature. Our prime tool is the lattice discretized QCD (LQCD) providing a unique ab-initio non-perturbative approach to deal with the computation of various observables of the hadronic world. We investigate the temperature dependence of Landau gauge gluon and ghost propagators in pure gluodynamics and in full QCD. Regarding the gluon propagator, we compute its longitudinal D{sub L} as well its transversal D{sub T} components. The aim is to provide a data set in terms of fitting formulae which can be used as input for DS (or FRG) equations. We deal with full (N{sub f}=2) LQCD with the twisted mass fermion discretization. We employ gauge field configurations provided by the tmfT collaboration for temperatures in the crossover region and for three fixed pion mass values in the range [300,500] MeV. Finally, within SU(3) pure gauge theory (at T=0) we compute the Landau gauge gluon propagator according to different gauge fixing criteria. Our goal is to understand the influence of gauge copies with minimal (non-trivial) eigenvalues of the Faddeev-Popov operator.

A novel contra propagating ultrasonic flowmeter using glad buffer rods for high temperature measurement. Application to the oil and gas industries

Energy Technology Data Exchange (ETDEWEB)

Franca, Demartonne R. [Brasilia Univ., DF (Brazil). Dept. de Engenharia Eletrica; Cheng-Kuei Jen; Yuu Ono [National Research Council (NRC), Quebec (Canada). Industrial Materials Institute

2005-07-01

Ultrasonic techniques are attractive for process monitoring and control because they are non-intrusive, robust and inexpensive. Two common concerns limiting the high temperature performance of conventional ultrasonic systems for flow measurement are related to transducers and couplants. A suitable approach to overcoming this drawback is to insert a thermal isolating buffer rod with good ultrasonic performance (e.g., high signal-to-noise ratio). This requirement is important because, a priori, the noises generated in the buffer rod may bury the desired signals, so that no meaningful information is extracted. Besides protecting the ultrasonic transducers from overheating in applications such as high temperature flow measurements, buffer rods are also a solution for the couplant between the probe and tested sample, since their probing end can be directly wetted by fluids. Here, we propose clad buffer rods driven by shear transducers as the main building block of contra propagating ultrasonic flowmeters for high temperature application. It is demonstrated that the superior signal-to-noise ratio exhibit by clad buffer rods compared to the reported non-clad counterparts improve precision in transit-time measurement, leading to more accurate flow speed determination. In addition, it is shown that clad buffer rods generate specific ultrasonic signals for temperature calibration of flowmeters, allowing temperature variation while still measuring accurately the flow speed. These results are of interest for the oil and gas industries. (author)

Unirradiated cladding rip-propagation tests

International Nuclear Information System (INIS)

Hu, W.L.; Hunter, C.W.

1981-04-01

The size of cladding rips which develop when a fuel pin fails can affect the subassembly cooling and determine how rapidly fuel escapes from the pin. The object of the Cladding Rip Propagation Test (CRPT) was to quantify the failure development of cladding so that a more realistic fuel pin failure modeling may be performed. The test results for unirradiated 20% CS 316 stainless steel cladding show significantly different rip propagation behavior at different temperatures. At room temperature, the rip growth is stable as the rip extension increases monotonically with the applied deformation. At 500 0 C, the rip propagation becomes unstable after a short period of stable rip propagation. The rapid propagation rate is approximately 200 m/s, and the critical rip length is 9 mm. At test temperatures above 850 0 C, the cladding exhibits very high failure resistances, and failure occurs by multiple cracking at high cladding deformation. 13 figures

Obtención de Si3N4 mediante SHS

Directory of Open Access Journals (Sweden)

Rodríguez, M. A.

2003-04-01

Full Text Available In the present paper results obtained during synthesis of Silicon Nitride by Self-propagating High-temperature Synthesis (SHS are shown. Self-propagating High-temperature Synthesis is based on the high enthalpy of certain reactions able to be self-sustained. One of the most important advantages of the method is its very low energy consumption. The synthesis is carried out with a mixture of silicon powder with some additions of diluents and other synthesis aids (ammonium salts. The influence of the mixture composition on reaction parameters and characteristics of the obtained products has been studied. The use of new synthesis aids has been also studied in order to decrease the environmental impact of the process. Microstructural study, XRD and reaction parameters are shown. Finally a mechanism of Silicon Nitride synthesis is proposed.En el presente trabajo se presentan los resultados obtenidos en el estudio de las reacciones de Síntesis Autopropagada a Alta Temperatura (Self-propagating High-temperature Synthesis, SHS de Nitruro de Silicio. La síntesis autopropagada a alta temperatura consiste básicamente en la generación de reacciones altamente exotérmicas capaces de automantenerse. Se puede considerar como principal ventaja del método el ahorro energético que supone. La síntesis se realiza sobre una mezcla inicial de silicio metálico sobre la cual se realizan adiciones de diluyente y otros aditivos (sales amónicas que afectan al desarrollo de la reacción. Se ha estudiado la influencia que en este sistema pueden tener las proporciones de las distintas incorporaciones en la mezcla, tanto en el material resultante como en las condiciones de reacción. Igualmente se ha estudiado la posibilidad de utilización de nuevos aditivos que puedan minimizar el impacto medio ambiental. Se presentan los estudios microestructurales del material obtenido, la identificación cristalográfica de las fases presentes así como los comportamientos de los

A Self-Propagating Foaming Process of Porous Al-Ni Intermetallics Assisted by Combustion Reactions

Directory of Open Access Journals (Sweden)

Makoto Kobashi

2009-12-01

Full Text Available The self-propagating foaming process of porous Al-Ni intermetallics was investigated. Aluminum and nickel powders were blended, and titanium and boron carbide powders were added as reactive exothermic agents. The blended powder was extruded to make a rod-shape precursor. Only one end of the rod precursor was heated to ignite the reaction. The reaction propagated spontaneously throughout the precursor. Pore formation took place at the same time as the reaction occurred. Adding the exothermic agent was effective to increase the porosity. Preheating the precursor before the ignition was also very effective to produce porous Al-Ni intermetallics with high porosity.

High-temperature synthesis of highly hydrothermal stable mesoporous silica and Fe-SiO2 using ionic liquid as a template

International Nuclear Information System (INIS)

Liu, Hong; Wang, Mengyang; Hu, Hongjiu; Liang, Yuguang; Wang, Yong; Cao, Weiran; Wang, Xiaohong

2011-01-01

Mesoporous silicas and Fe-SiO 2 with worm-like structures have been synthesized using a room temperature ionic liquid, 1-hexadecane-3-methylimidazolium bromide, as a template at a high aging temperature (150-190 o C) with the assistance of NaF. The hydrothermal stability of mesoporous silica was effectively improved by increasing the aging temperature and adding NaF to the synthesis gel. High hydrothermally stable mesoporous silica was obtained after being aged at 190 o C in the presence of NaF, which endured the hydrothermal treatment in boiling water at least for 10 d or steam treatment at 600 o C for 6 h. The ultra hydrothermal stability could be attributed to its high degree of polymerization of silicate. Furthermore, highly hydrothermal stable mesoporous Fe-SiO 2 has been synthesized, which still remained its mesostructure after being hydrothermally treated at 100 o C for 12 d or steam-treated at 600 o C for 6 h. -- Graphical abstract: Worm-like mesoporous silica and Fe-SiO 2 with high hydrothermal stability have been synthesized using ionic liquid 1-hexadecane-3-methylimidazolium bromide as a template under the assistance of NaF at high temperature. Display Omitted Research highlights: → Increasing aging temperature improved the hydrothermal stability of materials. →Addition of NaF enhanced the polymerization degree of silicates. → Mesoporous SiO 2 and Fe-SiO 2 obtained have remarkable hydrothermal stability.

Combustion synthesis as a novel approach in preparation of polycrystalline Y{sub 2}Cu{sub 2}O{sub 5}

Energy Technology Data Exchange (ETDEWEB)

Gebrel, Z., E-mail: z_gebrel@yahoo.com; Blanusa, J.; Spasojevic, V.; Kusigerski, V.; Mrakovic, A.; Alqat, A.; Perovic, M.

2013-08-15

Highlights: •Y{sub 2}Cu{sub 2}O{sub 5} was successfully synthesized by both the glycine–nitrate and SHS method. •The reduction of synthesis duration down to 12 h has been achieved. •The detailed crystal structure and magnetic analyses of obtained material are provided. -- Abstract: Polycrystalline samples of Y{sub 2}Cu{sub 2}O{sub 5} were for the first time sintered from precursors obtained by two combustion routes – the glycine–nitrate method (sample S1) and a modified self-propagating high-temperature synthesis (sample S2). The detailed X-ray diffraction analysis has confirmed that both samples are well crystallized and single phase, with the high crystallization degree and cation ordering within a Cu sublattice. Magnetic characterization has shown magnetic behavior typical of pure Y{sub 2}Cu{sub 2}O{sub 5}. The distinctive advantages of these new synthesis routes in comparison to the ceramic sintering are in simplification of the overall procedure as well as in a significant reduction of synthesis duration from several days down to 31 h (S1) or 12 h (S2)

Preparation of high temperature superconductor ceramics using cuban reactives. Optimization of the synthesis method

International Nuclear Information System (INIS)

Leyva Fabelo, A.; Cruz, C.; Aragon, B.; Suarez, J.C.; Mora, M.

1991-01-01

Results of the crystallographic characterization of a group of Cuban Products, which are evaluated to be employed in HTSC fabrication are presented in this paper. The first results on the synthesis of HTSC (RBa 2 Cu 3 0 7δ , R= Y, La, Nd) using Cuban reactives, are presented. The so called 'solid state reaction method of synthesis' was optimized, obtaining a critical temperature of more than 93 k

Memory retrieval as a self-propagating process.

Science.gov (United States)

Bäuml, Karl-Heinz T; Schlichting, Andreas

2014-07-01

Retrieval of a subset of studied items and the presentation of those items as retrieval cues typically impair retrieval of the other items. Previous research on this self-limiting property of memory retrieval has relied heavily on short retention intervals and similar context between encoding and test. Here, we examined retrieval dynamics also after a prolonged retention interval with different spatial and social context between encoding and test, conditions that mimic people's remembering in many situations of daily life. For both unrelated word lists and more integrated prose material, we found retrieval and cuing to impair recall of other studied items after a short retention interval, but to improve recall in the prolonged retention interval condition. The results demonstrate that retrieval dynamics depend critically on situation, indicating that quite often in daily life, retrieval may be a self-propagating, rather than a self-limiting process. Copyright © 2014 Elsevier B.V. All rights reserved.

Effects of storage temperature on the physiological characteristics and vegetative propagation of desiccation-tolerant mosses

Science.gov (United States)

Guo, Yuewei; Zhao, Yunge

2018-02-01

Mosses, as major components of later successional biological soil crusts (biocrusts), play many critical roles in arid and semiarid ecosystems. Recently, some species of desiccation-tolerant mosses have been artificially cultured with the aim of accelerating the recovery of biocrusts. Revealing the factors that influence the vegetative propagation of mosses, which is an important reproductive mode of mosses in dry habitats, will benefit the restoration of moss crusts. In this study, three air-dried desiccation-tolerant mosses (Barbula unguiculata, Didymodon vinealis, and Didymodon tectorum) were hermetically sealed and stored at five temperature levels (0, 4, 17, 25, and 30 °C) for 40 days. Then, the vegetative propagation and physiological characteristics of the three mosses were investigated to determine the influence of storage temperature on the vegetative propagation of desiccation-tolerant mosses and the mechanism. The results showed that the vegetative propagation of the three mosses varied with temperature. The most variation in vegetative propagation among storage temperatures was observed in D. tectorum, followed by the variation observed in B. unguiculata. In contrast, no significant difference in propagation among temperatures was found in D. vinealis. The regenerative capacity of the three mosses increased with increasing temperature from 0 to 17 °C, accompanied by a decrease in malondialdehyde (MDA) content, and decreased thereafter. As the temperature increased, the chlorophyll and soluble protein contents increased in B. unguiculata but decreased in D. vinealis and D. tectorum. As to storage, the MDA and soluble sugar contents increased after storage. The MDA content of the three mosses increased at each of the investigated temperatures by more than 50 % from the initial values, and the soluble sugar content became higher than before in the three mosses. The integrity of cells and cell membranes is likely the most important factor influencing the

Propagation of seasonal temperature signals into an aquifer upon bank infiltration.

Science.gov (United States)

Molina-Giraldo, Nelson; Bayer, Peter; Blum, Philipp; Cirpka, Olaf A

2011-01-01

Infiltrating river water carries the temperature signal of the river into the adjacent aquifer. While the diurnal temperature fluctuations are strongly dampened, the seasonal fluctuations are much less attenuated and can be followed into the aquifer over longer distances. In one-dimensional model with uniform properties, this signal is propagated with a retarded velocity, and its amplitude decreases exponentially with distance. Therefore, time shifts in seasonal temperature signals between rivers and groundwater observation points may be used to estimate infiltration rates and near-river groundwater velocities. As demonstrated in this study, however, the interpretation is nonunique under realistic conditions. We analyze a synthetic test case of a two-dimensional cross section perpendicular to a losing stream, accounting for multi-dimensional flow due to a partially penetrating channel, convective-conductive heat transport within the aquifer, and heat exchange with the underlying aquitard and the land surface. We compare different conceptual simplifications of the domain in order to elaborate on the importance of different system elements. We find that temperature propagation within the shallow aquifer can be highly influenced by conduction through the unsaturated zone and into the underlying aquitard. In contrast, regional groundwater recharge has no major effect on the simulated results. In our setup, multi-dimensionality of the flow field is important only close to the river. We conclude that over-simplistic analytical models can introduce substantial errors if vertical heat exchange at the aquifer boundaries is not accounted for. This has to be considered when using seasonal temperature fluctuations as a natural tracer for bank infiltration. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.

Manufacturing Demonstration Facility: Low Temperature Materials Synthesis

International Nuclear Information System (INIS)

Graham, David E.; Moon, Ji-Won; Armstrong, Beth L.; Datskos, Panos G.; Duty, Chad E.; Gresback, Ryan; Ivanov, Ilia N.; Jacobs, Christopher B.; Jellison, Gerald Earle; Jang, Gyoung Gug; Joshi, Pooran C.; Jung, Hyunsung; Meyer, Harry M.; Phelps, Tommy

2015-01-01

The Manufacturing Demonstration Facility (MDF) low temperature materials synthesis project was established to demonstrate a scalable and sustainable process to produce nanoparticles (NPs) for advanced manufacturing. Previous methods to chemically synthesize NPs typically required expensive, high-purity inorganic chemical reagents, organic solvents and high temperatures. These processes were typically applied at small laboratory scales at yields sufficient for NP characterization, but insufficient to support roll-to-roll processing efforts or device fabrication. The new NanoFermentation processes described here operated at a low temperature (~60 C) in low-cost, aqueous media using bacteria that produce extracellular NPs with controlled size and elemental stoichiometry. Up-scaling activities successfully demonstrated high NP yields and quality in a 900-L pilot-scale reactor, establishing this NanoFermentation process as a competitive biomanufacturing strategy to produce NPs for advanced manufacturing of power electronics, solid-state lighting and sensors.

Manufacturing Demonstration Facility: Low Temperature Materials Synthesis

Energy Technology Data Exchange (ETDEWEB)

Graham, David E. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Moon, Ji-Won [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Armstrong, Beth L. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Datskos, Panos G. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Duty, Chad E. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Gresback, Ryan [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Ivanov, Ilia N. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jacobs, Christopher B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jellison, Gerald Earle [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jang, Gyoung Gug [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Joshi, Pooran C. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jung, Hyunsung [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Meyer, III, Harry M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Phelps, Tommy [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2015-06-30

The Manufacturing Demonstration Facility (MDF) low temperature materials synthesis project was established to demonstrate a scalable and sustainable process to produce nanoparticles (NPs) for advanced manufacturing. Previous methods to chemically synthesize NPs typically required expensive, high-purity inorganic chemical reagents, organic solvents and high temperatures. These processes were typically applied at small laboratory scales at yields sufficient for NP characterization, but insufficient to support roll-to-roll processing efforts or device fabrication. The new NanoFermentation processes described here operated at a low temperature (~60 C) in low-cost, aqueous media using bacteria that produce extracellular NPs with controlled size and elemental stoichiometry. Up-scaling activities successfully demonstrated high NP yields and quality in a 900-L pilot-scale reactor, establishing this NanoFermentation process as a competitive biomanufacturing strategy to produce NPs for advanced manufacturing of power electronics, solid-state lighting and sensors.

自蔓延高温合成Ti3AlC2材料及其摩擦磨损性能%Fabrication of Ti3AlC2 by self-propagating high-temperature synthesis and its friction and wear behavior

Institute of Scientific and Technical Information of China (English)

2013-01-01

　　以TiC，Ti，Al，C粉末为反应物原料，采用自蔓延高温反应按照质量分数为15% TiC，50% Ti，28% Al，7% C的配比合成了纯度为96.76%、气孔率为9.45%的高纯Ti3AlC2块体材料。研究添加TiC对合成产物Ti3AlC2材料纯度的影响，并对其摩擦磨损性能进行分析。结果表明：当添加 TiC 的质量分数小于15%，Ti3AlC2含量随 TiC 含量的增加而增加；当添加TiC质量分数大于15%，Ti3AlC2含量随TiC含量的增加而降低。当载荷较小，Ti3AlC2材料以磨粒磨损为主；而载荷较大，其以磨粒磨损为主并伴随有轻微黏着磨损。%High purity Ti3AlC2 was synthesized by self⁃propagating high⁃temperature synthesis method using TiC,Ti,Al and C powders as raw materials. Ti3AlC2 material with high density was successfully fabricated when the mass fraction of TiC/Ti/Al/C is equal to 15%/50%/28%/7%. The content of Ti3AlC2 in the material reaches as high as 96.76%,and the porosity is only 9.45%. The effects of TiC on the purity of sintered Ti3AlC2 were studied. When the addition content of TiC is less than 15%,Ti3AlC2 percentage content firstly increases with the increase of TiC content,but when the addition content of TiC is greater than 15%,it will decrease with continuously increasing amount of TiC. When the load is low,the main wear mechanism is abrasive wear. Under a higher load,the wear mechanism transforms to abrasive wear and light adhesive wear.

Low-temperature synthesis of silicon carbide powder using shungite

International Nuclear Information System (INIS)

Gubernat, A.; Pichor, W.; Lach, R.; Zientara, D.; Sitarz, M.; Springwald, M.

2017-01-01

The paper presents the results of investigation the novel and simple method of synthesis of silicon carbide. As raw material for synthesis was used shungite, natural mineral rich in carbon and silica. The synthesis of SiC is possible in relatively low temperature in range 1500–1600°C. It is worth emphasising that compared to the most popular method of SiC synthesis (Acheson method where the temperature of synthesis is about 2500°C) the proposed method is much more effective. The basic properties of products obtained from different form of shungite and in wide range of synthesis temperature were investigated. The process of silicon carbide formation was proposed and discussed. In the case of synthesis SiC from powder of raw materials the product is also in powder form and not requires any additional process (crushing, milling, etc.). Obtained products are pure and after grain classification may be used as abrasive and polishing powders. (Author)

Low-temperature synthesis of silicon carbide powder using shungite

Energy Technology Data Exchange (ETDEWEB)

Gubernat, A.; Pichor, W.; Lach, R.; Zientara, D.; Sitarz, M.; Springwald, M.

2017-07-01

The paper presents the results of investigation the novel and simple method of synthesis of silicon carbide. As raw material for synthesis was used shungite, natural mineral rich in carbon and silica. The synthesis of SiC is possible in relatively low temperature in range 1500–1600°C. It is worth emphasising that compared to the most popular method of SiC synthesis (Acheson method where the temperature of synthesis is about 2500°C) the proposed method is much more effective. The basic properties of products obtained from different form of shungite and in wide range of synthesis temperature were investigated. The process of silicon carbide formation was proposed and discussed. In the case of synthesis SiC from powder of raw materials the product is also in powder form and not requires any additional process (crushing, milling, etc.). Obtained products are pure and after grain classification may be used as abrasive and polishing powders. (Author)

Self-propagating synthesis and aqueous durability of Nd-bearing zirconolite-rich composites using Ca(NO{sub 3}){sub 2} as the oxidant

Energy Technology Data Exchange (ETDEWEB)

Zhang, Kuibao, E-mail: xiaobao320@163.com [State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials, Southwest University of Science and Technology, Mianyang, Sichuan 621010 (China); National Defense Key Discipline Lab of Nuclear Waste and Environmental Safety, Southwest University of Science and Technology, Mianyang 621010 (China); He, Shihong [State Nuclear Power Research Institute, Beijing 100029 (China); Yin, Dan; Peng, Le; Wu, Jingjun [State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials, Southwest University of Science and Technology, Mianyang, Sichuan 621010 (China)

2016-09-15

Synroc is recognized as the second-generation waste form for safety disposal of high-level radioactive waste (HLW). In this study, zirconolite-rich Synroc waste form was readily synthesized by self-propagating high-temperature plus quick pressing (SHS/QP) using Ca(NO{sub 3}){sub 2} as the oxidant and Ti as the reductant. As the surrogate of trivalent actinides, Nd{sub 2}O{sub 3} was introduced to equally substitute the Ca and Zr sites of zirconolite with nominal stoichiometry of Ca{sub 1−x}Zr{sub 1−x}Nd{sub 2x}Ti{sub 2}O{sub 7}. The results demonstrate that zirconolite, perovskite and pyrochlore (Ca{sub 2}Ti{sub 2}O{sub 6}) coexist as the ceramic components after SHS reaction. The introduction of Nd{sub 2}O{sub 3} promotes the formation of perovskite. Nd is mostly incorporated into the Ca sites of these phases. The normalized elemental leaching rates of Ca and Nd are fairly constant in low values of 1.80 × 10{sup −2} g m{sup −2} d{sup −1} and 6.12 × 10{sup −4} g m{sup −2} d{sup −1} after 42 days. - Highlights: • Zirconolite-rich composite was synthesized by SHS using Ca(NO{sub 3}){sub 2} as the oxidant. • Nd{sub 2}O{sub 3} was successfully immobilized into the crystal structure of this waste form. • Nd was mostly incorporated into the Ca sites of zirconolite, perovskite and pyrochlore. • The normalized leaching rates of Ca and Nd are in relatively low values.

Morse oscillator propagator in the high temperature limit II: Quantum dynamics and spectroscopy

Science.gov (United States)

Toutounji, Mohamad

2018-04-01

This paper is a continuation of Paper I (Toutounji, 2017) of which motivation was testing the applicability of Morse oscillator propagator whose analytical form was derived by Duru (1983). This is because the Morse oscillator propagator was reported (Duru, 1983) in a triple-integral form of a functional of modified Bessel function of the first kind, which considerably limits its applicability. For this reason, I was prompted to find a regime under which Morse oscillator propagator may be simplified and hence be expressed in a closed-form. This was well accomplished in Paper I. Because Morse oscillator is of central importance and widely used in modelling vibrations, its propagator applicability will be extended to applications in quantum dynamics and spectroscopy as will be reported in this paper using the off-diagonal propagator of Morse oscillator whose analytical form is derived.

Propagation of Measurement-While-Drilling Mud Pulse during High Temperature Deep Well Drilling Operations

Directory of Open Access Journals (Sweden)

Hongtao Li

2013-01-01

Full Text Available Signal attenuates while Measurement-While-Drilling (MWD mud pulse is transmited in drill string during high temperature deep well drilling. In this work, an analytical model for the propagation of mud pulse was presented. The model consists of continuity, momentum, and state equations with analytical solutions based on the linear perturbation analysis. The model can predict the wave speed and attenuation coefficient of mud pulse. The calculated results were compared with the experimental data showing a good agreement. Effects of the angular frequency, static velocity, mud viscosity, and mud density behavior on speed and attenuation coefficients were included in this paper. Simulated results indicate that the effects of angular frequency, static velocity, and mud viscosity are important, and lower frequency, viscosity, and static velocity benefit the transmission of mud pulse. Influenced by density behavior, the speed and attenuation coefficients in drill string are seen to have different values with respect to well depth. For different circulation times, the profiles of speed and attenuation coefficients behave distinctly different especially in lower section. In general, the effects of variables above on speed are seen to be small in comparison.

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

International Nuclear Information System (INIS)

Mamun, A.A.

1999-07-01

Obliquely propagating ultra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfven mode propagating parallel to the external magnetic field and dust-magnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that these effects of self-gravitational field and dust/ion fluid temperature play no role in parallel propagating dust-Alfven mode, but in obliquely propagating dust-Alfven mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays a destabilizing role whereas the effect of dust/ion fluid temperature plays a stabilizing role. (author)

On the Temperature Behavior of Pulse Propagation and Relaxation in Worms, Nerves and Gels.

Directory of Open Access Journals (Sweden)

Christian Fillafer

Full Text Available The effect of temperature on pulse propagation in biological systems has been an important field of research. Environmental temperature not only affects a host of physiological processes e.g. in poikilotherms but also provides an experimental means to investigate the thermodynamic phenomenology of nerves and muscle. In the present work, the temperature dependence of blood vessel pulsation velocity and frequency was studied in the annelid Lumbriculus variegatus. The pulse velocity was found to vary linearily between 0°C and 30°C. In contrast, the pulse frequency increased non-linearly in the same temperature range. A heat block ultimately resulted in complete cessation of vessel pulsations at 37.2±2.7°C (lowest: 33°C, highest: 43°C. However, quick cooling of the animal led to restoration of regularly propagating pulses. This experimentally observed phenomenology of pulse propagation and frequency is interpreted without any assumptions about molecules in the excitable membrane (e.g. ion channels or their temperature-dependent behaviour. By following Einstein's approach to thermodynamics and diffusion, a relation between relaxation time τ and compressibility κ of the excitable medium is derived that can be tested experimentally (for κT ∼ κS. Without fitting parameters this theory predicts the temperature dependence of the limiting (i.e. highest pulse frequency in good agreement with experimental data. The thermodynamic approach presented herein is neither limited to temperature nor to worms nor to living systems. It describes the coupling between pulse propagation and relaxation equally well in nerves and gels. The inherent consistency and universality of the concept underline its potential to explain the dependence of pulse propagation and relaxation on any thermodynamic observable.

Low temperature spalling of silicon: A crack propagation study

Energy Technology Data Exchange (ETDEWEB)

Bertoni, Mariana; Uberg Naerland, Tine; Stoddard, Nathan; Guimera Coll, Pablo

2017-06-08

Spalling is a promising kerfless method for cutting thin silicon wafers while doubling the yield of a silicon ingot. The main obstacle in this technology is the high total thickness variation of the spalled wafers, often as high as 100% of the wafer thickness. It has been suggested before that a strong correlation exists between low crack velocities and a smooth surface, but this correlation has never been shown during a spalling process in silicon. The reason lies in the challenge associated to measuring such velocities. In this contribution, we present a new approach to assess, in real time, the crack velocity as it propagates during a low temperature spalling process. Understanding the relationship between crack velocity and surface roughness during spalling can pave the way to attain full control on the surface quality of the spalled wafer.

Synthesis of MIL-100(Fe at Low Temperature and Atmospheric Pressure

Directory of Open Access Journals (Sweden)

Jing Shi

2013-01-01

Full Text Available MIL-100(Fe, a mesoporous metal-organic framework (MOF, has a large BET specific surface area and pore volume with the presence of a significant amount of accessible Lewis acid metal sites upon dehydration. The structural characteristics of MIL-100(Fe make it a good candidate for potential applications in gas storage, separation, and heterogeneous catalysis. Mainly, this MOF is obtained by the hydrothermal synthesis in a Teflon-lined autoclave at high temperature (>150°C under static conditions. However, this method has several disadvantages such as high temperature, high (autogenous pressure, long time, and comparable low MOF yield. Therefore, development of a facile method for synthesis of MIL-100(Fe is vitally important for fundamental understanding and practical application. Herein, MIL-100(Fe is synthesized by a facile low-temperature (90% still could be achieved, suggesting that this simple and energy saving method has the potential to be used practically.

Single-source-precursor Synthesis and High-temperature Behavior of SiC Ceramics Containing Boron

Science.gov (United States)

Gui, Miaomiao; Fang, Yunhui; Yu, Zhaoju

2014-12-01

In this paper, a hyperbranched polyborocarbosilane (HPBCS) was prepared by a one-pot synthesis with Cl2Si(CH3)CH2Cl, Cl3SiCH2Cl and BCl3 as the starting materials. The obtained HPBCS was characterized by GPC, FT-IR and NMR, and was confirmed to have hyperbranched structures. The thermal property of the resulting HPBCS was investigated by TGA. The ceramic yield of the HPBCS is about 84% and that of the counterpart hyperbranched hydridopolycarbosilane is only 45%, indicating that the introduction of boron into the preceramic polymer significantly improved the ceramic yield. With the polymer-derived ceramic route, the final ceramics were annealed at 1800 °C in argon atmosphere for 2 h in order to characterize the microstructure and to evaluate the high-temperature behavior. The final ceramic microstructure was studied by XRD and SEM, indicating that the introduction of boron dramatically inhibits SiC crystallization. The boron-containing SiC ceramic shows excellent high-temperature behavior against decomposition and crystallization at 1800 °C.

Effects of increasing temperature due to aquatic climate change on the self-fertility and the sexual development of the hermaphrodite fish, Kryptolebias marmoratus.

Science.gov (United States)

Park, Chang-Beom; Kim, Young Jun; Soyano, Kiyoshi

2017-01-01

In order to assess the effects of increasing temperature on the reproductive performance of fish, different thermal conditions (i.e., 25.0, 26.5, 27.5, 28.5, 30.0 °C) were used in this study and the self-fertilizing hermaphrodite fish, Kryptolebias marmoratus, was exposed to these different thermal conditions. During an exposure period of 30 to 150 days, the gonadosomatic index (GSI), gonadal development, the levels of plasma 17β-estradial (E2) and testosterone (T), hepatic vitellogenin (VTG) mRNA abundance, and the number of self-fertilized eggs were analyzed. This study confirmed that a high water temperature above 27.5 °C led to the suppression of self-fertility of hermaphroditic fish from 30 days after exposure. The oocyte quality and maturation would be affected by the disruption of hepatic VTG synthesis at a high water temperature of 30 °C, which resulted in the reduced the self-fertility in K. marmoratus. Consequently, this study suggests that elevated water temperature due to aquatic climate change prior to sexual maturation and the onset of spawning can lead to the reproductive dysfunction of hermaphroditic K. marmoratus.

Self-channeling of high-power laser pulses through strong atmospheric turbulence

Science.gov (United States)

Peñano, J.; Palastro, J. P.; Hafizi, B.; Helle, M. H.; DiComo, G. P.

2017-07-01

We present an unusual example of truly long-range propagation of high-power laser pulses through strong atmospheric turbulence. A form of nonlinear self-channeling is achieved when the laser power is close to the self-focusing power of air and the transverse dimensions of the pulse are smaller than the coherence diameter of turbulence. In this mode, nonlinear self-focusing counteracts diffraction, and turbulence-induced spreading is greatly reduced. Furthermore, the laser intensity is below the ionization threshold so that multiphoton absorption and plasma defocusing are avoided. Simulations show that the pulse can propagate many Rayleigh lengths (several kilometers) while maintaining a high intensity. In the presence of aerosols, or other extinction mechanisms that deplete laser energy, the pulse can be chirped to maintain the channeling.

High-pressure high-temperature experiments: Windows to the Universe

International Nuclear Information System (INIS)

Santaria-Perez, D.

2011-01-01

From Earth compositional arguments suggested by indirect methods, such as the propagation of seismic waves, is possible to generate in the laboratory pressure and temperature conditions similar to those of the Earth or other planet interiors and to study how these conditions affect to a certain metal or mineral. These experiments are, therefore, windows to the Universe. The aim of this chapter is to illustrate the huge power of the experimental high-pressure high-temperature techniques and give a global overview of their application to different geophysical fields. Finally, we will introduce the MALTA Consolider Team, which gather most of the Spanish high-pressure community, and present their available high-pressure facilities. (Author) 28 refs.

Low Temperature Synthesis and Properties of Gadolinium-Doped Cerium Oxide Nanoparticles

DEFF Research Database (Denmark)

Machado, M. F. S.; Moraes, L. P. R.; Monteiro, N. K.

2017-01-01

Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte and in composite electrodes operating at low and intermediate temperatures. GDC exhibits high oxygen ion conductivity at a wide range of temperatures and displays a high...... resistance to carbon deposition when hydrocarbons are used as fuels. However, an inconvenience of ceria-based oxides is the high sintering temperature needed to obtain a fully dense ceramic body. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. The aqueous...

Experiences of self-practice/self-reflection in cognitive behavioural therapy: a meta-synthesis of qualitative studies.

Science.gov (United States)

Gale, Corinne; Schröder, Thomas

2014-12-01

Self-practice/self-reflection is a valuable training strategy which involves therapists applying therapeutic techniques to themselves, and reflecting on the process. To undertake a meta-synthesis of qualitative studies exploring therapists' experiences of self-practice/self-reflection in cognitive behavioural therapy (CBT). This would integrate, and interpret, the current literature in order to develop a new understanding, and contribute to the development of CBT training programmes. The meta-synthesis encompassed three distinct phases: undertaking a comprehensive and systematic literature search; critically appraising the papers; and synthesising the data using the meta-ethnographic method. The literature search identified 378 papers, ten met the criteria for inclusion. After critical appraisal, all were included in the synthesis. The synthesis identified 14 constructs, which fell into three broad categories: 'experience of self-practice/self-reflection'; 'outcomes of self-practice/self-reflection'; and 'implications for training'. This synthesis found that self-practice allows therapists to put themselves into their clients' shoes, experiencing the benefits that therapy can bring but also the problems that clients can run in to. This experience increases therapists' empathy for their clients, allowing them to draw on their own experiences in therapy. As a result, therapists tend to feel both more confident in themselves and more competent as a therapist. The self-practice/self-reflection process was facilitated by reflective writing and working with others, particularly peers. Self-practice/self-reflection is a valuable training strategy in CBT, which has a range of beneficial outcomes. It can also be used as a means of continuing personal and professional development. Self-practice of CBT techniques, and reflecting on the process, can be a useful training strategy and helpful for ongoing development Therapists could consider developing a 'self-case' study

Room temperature chemical synthesis of highly oriented PbSe nanotubes based on negative free energy of formation

Energy Technology Data Exchange (ETDEWEB)

Sankapal, B.R., E-mail: brsankapal@rediffmail.com [Thin Film and Nano Science Laboratory, Department of Physics, School of Physical Sciences, North Maharashtra University, Jalgaon 425 001 (MS) (India); Ladhe, R.D.; Salunkhe, D.B.; Baviskar, P.K. [Thin Film and Nano Science Laboratory, Department of Physics, School of Physical Sciences, North Maharashtra University, Jalgaon 425 001 (MS) (India); Gupta, V.; Chand, S. [Organic and Hybrid Solar Cell, Physics of Energy Harvesting Division, Dr. K.S. Krishnan Marg, National Physical Laboratory, New Delhi 110012 (India)

2011-10-13

Highlights: > Simple, inexpensive and room temperature chemical synthesis route. > Highly oriented PbSe nanotubes from Cd(OH){sub 2} nanowires through lead hydroxination. > The process was template free without the use of any capping agent. > Reaction kinetics was accomplished due to more negative free energy of formation. > The ion exchange mechanism due to difference in the solubility products. - Abstract: The sacrificial template free chemical synthesis of PbSe nanotubes at room temperature has been performed by lead hydroxination from cadmium hydroxide nanowires. This process was based on the ion exchange reaction to replace Cd{sup 2+} with Pb{sup 2+} ions from hydroxyl group followed by replacement of hydroxyl group with selenium ions. The reaction kinetics was accomplished due to more negative free energy of formation and thus the difference in the solubility products. The formed nanotubes were inclusive of Pb and Se with proper inter-chemical bonds with preferred orientations having diameter in tens of nanometer. These nanotubes can have future applications in electronic, optoelectronics and photovoltaic's as well.

Room temperature chemical synthesis of highly oriented PbSe nanotubes based on negative free energy of formation

International Nuclear Information System (INIS)

Sankapal, B.R.; Ladhe, R.D.; Salunkhe, D.B.; Baviskar, P.K.; Gupta, V.; Chand, S.

2011-01-01

Highlights: → Simple, inexpensive and room temperature chemical synthesis route. → Highly oriented PbSe nanotubes from Cd(OH) 2 nanowires through lead hydroxination. → The process was template free without the use of any capping agent. → Reaction kinetics was accomplished due to more negative free energy of formation. → The ion exchange mechanism due to difference in the solubility products. - Abstract: The sacrificial template free chemical synthesis of PbSe nanotubes at room temperature has been performed by lead hydroxination from cadmium hydroxide nanowires. This process was based on the ion exchange reaction to replace Cd 2+ with Pb 2+ ions from hydroxyl group followed by replacement of hydroxyl group with selenium ions. The reaction kinetics was accomplished due to more negative free energy of formation and thus the difference in the solubility products. The formed nanotubes were inclusive of Pb and Se with proper inter-chemical bonds with preferred orientations having diameter in tens of nanometer. These nanotubes can have future applications in electronic, optoelectronics and photovoltaic's as well.

Impact of High-Temperature, High-Pressure Synthesis Conditions on the Formation of the Grain Structure and Strength Properties of Intermetallic Ni3Al

Science.gov (United States)

Ovcharenko, V. E.; Ivanov, K. V.; Boyangin, E. N.; Krylova, T. A.; Pshenichnikov, A. P.

2018-01-01

The impact of the preliminary load on 3Ni+Al powder mixture and the impact of the duration of the delay in application of compacting pressure to synthesis product under the conditions of continuous heating of the mixture up to its self-ignition on the grain size and strength properties of the synthesized Ni3Al intermetallide material have been studied. The grain structure of the intermetallide synthesized under pressure was studied by means of metallography, transmission electron microscopy and EBSD analysis, with the dependence of ultimate tensile strength on the grain size in the synthesized intermetallide having been investigated at room temperature and at temperatures up to 1000°C. It is shown that an increase in the pressure preliminarily applied to the initial mixture compact results in reduced grain size of the final intermetallide, whereas an increase in pre-compaction time makes the grain size increased. A decrease in the grain size increases the ultimate tensile strength of the intermetallide. The maximum value of the ultimate tensile strength in the observed anomalous temperature dependence of this strength exhibits a shift by 200°C toward higher temperatures, and the ultimate strength of the synthesized intermetallide at 1000°C increases roughly two-fold.

High temperature ceramic-tubed reformer

Science.gov (United States)

Williams, Joseph J.; Rosenberg, Robert A.; McDonough, Lane J.

1990-03-01

The overall objective of the HiPHES project is to develop an advanced high-pressure heat exchanger for a convective steam/methane reformer. The HiPHES steam/methane reformer is a convective, shell and tube type, catalytic reactor. The use of ceramic tubes will allow reaction temperature higher than the current state-of-the-art outlet temperatures of about 1600 F using metal tubes. Higher reaction temperatures increase feedstock conversion to synthesis gas and reduce energy requirements compared to currently available radiant-box type reformers using metal tubes. Reforming of natural gas is the principal method used to produce synthesis gas (primarily hydrogen and carbon monoxide, H2 and CO) which is used to produce hydrogen (for refinery upgrading), methanol, as well as several other important materials. The HiPHES reformer development is an extension of Stone and Webster's efforts to develop a metal-tubed convective reformer integrated with a gas turbine cycle.

HIGH TEMPERATURE EROSION WEAR OF CERMET PARTICLES REINFORCED SELF-FLUXING ALLOY MATRIX HVOF SPRAYED COATINGS

Directory of Open Access Journals (Sweden)

Andrei Surzhenkov

2015-09-01

Full Text Available In the present paper, the resistance of high velocity oxy-fuel (HVOF sprayed TiC-NiMo and Cr3C2-Ni cermet particles reinforced NiCrSiB self-fluxing alloy matrix coatings to high temperature erosion wear is studied. Microstructure of the coatings was examined by SEM, phase composition was determined by XRD. A four-channel centrifugal particle accelerator was applied to study the high temperature erosion wear of the coatings. The impact angles were 30 and 90 degrees, initial particle velocity was 50 m/s, temperature of the test - 650 degrees. Volume wear of the coatings was calculated and compared to the respective values of the reference materials. Wear mechanisms were studied by SEM.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7617

Effect of temperature on the rate of fatigue crack propagation in some steels during low cycle fatigue

International Nuclear Information System (INIS)

Taira, S.; Fujino, M.; Maruyama, S.

Temperature dependence of the rate of fatigue crack propagation in steels was examined, and compared with the temperature dependence of tensile ductility. Microcracks initiate and affect the propagation behavior of the main crack at elevated temperatures. Factors found to be elucidated include initiation rate of microcracks, reduction of ductility of the material in the vicinity of the main crack tip, and relaxation of concentrated strain by multi-cracks. It was found that during a strain controlled low cycle fatigue test at 1 cpm, the rate of crack propagation is largest at the blue-brittleness temperature range (200 to 300 0 C) in a low carbon steel. On the other hand, it is largest at above 700 0 C in austenite stainless steels. The temperature dependence of the rate of fatigue crack propagation is opposite to that of tensile ductility. Microcracks formed in the vicinity of the main crack tip were calculated, by considering the strain concentration and strain cycles imposed. Then, the local fracture strain was evaluated. Good correlation was found between the rate of crack propagation and the local fracture strain. (U.S.)

A new combustion route to γ-Fe2O3 synthesis

Indian Academy of Sciences (India)

A new combustion route for the synthesis of -Fe2O3 is reported by employing purified -Fe2O3 as aprecursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves fewer steps, a shorter overall processing time, is a low energy reaction without the need of any ...

Direct recovery of boiler residue by combustion synthesis.

Science.gov (United States)

Nourbaghaee, Homan; Ghaderi Hamidi, Ahmad; Pourabdoli, Mahdi

2018-04-01

Boiler residue (BR) of thermal power plants is one of the important secondary sources for vanadium production. In this research, the aluminothermic self-propagating high-temperature synthesis (SHS) was used for recovering the transition metals of BR for the first time. The effects of extra aluminum as reducing agent and flux to aluminum ratio (CaO/Al) were studied and the efficiency of recovery and presence of impurities were measured. Aluminothermic reduction of vanadium and other metals was carried out successfully by SHS without any foreign heat source. Vanadium, iron, and nickel principally were reduced and gone into metallic master alloy as SHS product. High levels of efficiency (>80%) were achieved and the results showed that SHS has a great potential to be an industrial process for BR recovery. SHS produced two useful products. Metallic master alloy and fused glass slag that is applicable for ceramic industries. SHS can also neutralize the environmental threats of BR by a one step process. Copyright © 2018 Elsevier Ltd. All rights reserved.

High-Temperature Self-Healing and Re-Adhering Geothermal Well Cement Composites

Science.gov (United States)

Pyatina, T.; Sugama, T.; Boodhan, Y.; Nazarov, L.

2017-12-01

Self-healing cementitious materials are particularly attractive for the cases where damaged areas are difficult to locate and reach. High-temperature geothermal wells with aggressive environments impose most difficult conditions on cements that must ensure durable zonal isolation under repeated thermal, chemical and mechanical stresses. The present work evaluates matrix and carbon steel (CS) - cement interface self-healing and re-adhering properties of various inorganic cementitious composites under steam, alkali carbonate or brine environments at 270-300oC applicable to geothermal wells. The composite materials included blends based on Ordinary Portland Cement (OPC) and natural zeolites and alkali or phosphate activated composites of Calcium Aluminate Cement (CAC) with fly ash, class F. Class G cement blend with crystalline silica was used as a baseline. Compressive-strength and bond-strength recoveries were examined to evaluate self-healing and re-adhering properties of the composites after repeated crush tests followed by 5-day healing periods in these environments. The optical and scanning electron microscopes, X-ray diffraction, Fourier Transform infrared, Raman spectroscopy and EDX measurements were used to identify phases participating in the strengths recoveries and cracks filling processes. Amorphous silica-rich- and small-size crystalline phases played an important role in the healing of the tested composites in all environments. Possible ways to enhance self-healing properties of cementitious composites under conditions of geothermal wells were identified.

Variation of Quench Propagation Velocities in YBCO Cables

CERN Document Server

Härö, E.; Stenvall, A.; 10.1007/s10948-015-2976-y

2015-01-01

changes during the quench. Due to the large temperature margin between the operation and the current sharing temperatures, the normal zone does not propagate with the temperature front. This means that the temperature will rise in a considerably larger volume when compared to the quenched volume. Thus, the evolution of the temperature distribution below current sharing temperature Tcs after the quench onset affects the normal zone propagation velocity in HTS more than in LTS coils. This can be seen as an acceleration of the quench propagation velocities while the quench evolves when margin to Tcs is high. In this paper we scrutinize quench propagation in a stack of YBCO cables with an in-house finite element method software which solves the heat diffusion equation. We compute the longitudinal and transverse normal zone propagation velocities at various distances from the hot spot to demonstrate the distance-variation...

Processing of high-temperature superconductors at high strain rates

International Nuclear Information System (INIS)

Mamalis, A.G.; Pantazsopoulos, G.; Manolakos, D.E.; Szalay, A.

2000-01-01

This new book provides, for the first time, a systematic, unified presentation of all steps in the processing of high-temperature superconductor materials, ranging from synthesis of various systems to fabrication and industrial applications. Also covered are characterization techniques and current directions in research and development. The authors are leading specialists who bring to this new book their many years of experience in research, education and industrial engineering work in superconductor materials. This book is primarily focused on the bulk-fabrication techniques of high-temperature ceramic superconducting components, especially on the combination of dynamic powder-consolidation and subsequent deformation processing. The properties of these ceramics, which are difficult-to-form materials by applying conventional techniques, are combined for the net-shape manufacturing of such components for the construction of HTS deviceshor e llipsis. However, very important topics such as superconducting structures, chemical synthesis, film fabrication and characterization techniques are also reviewedhor e llipsis to provide a complete, comprehensive view of superconductors engineering

Low Temperature Synthesis of Magnesium Aluminate Spinel

International Nuclear Information System (INIS)

Lebedovskaya, E.G.; Gabelkov, S.V.; Litvinenko, L.M.; Logvinkov, D.S.; Mironova, A.G.; Odejchuk, M.A.; Poltavtsev, N.S.; Tarasov, R.V.

2006-01-01

The low-temperature synthesis of magnesium-aluminum spinel is carried out by a method of thermal decomposition in combined precipitated hydrates. The fine material of magnesium-aluminium spinel with average size of coherent dispersion's area 4...5 nanometers is obtained. Magnesium-aluminum spinel and initial hydrates were investigated by methods of the differential thermal analysis, the x-ray phase analysis and measurements of weight loss during the dehydration and thermal decomposition. It is established that synthesis of magnesium-aluminum spinel occurs at temperature 300 degree C by method of the x-ray phase analysis

Quench propagation in High Temperature Superconducting materials integrated in high current leads

CERN Document Server

Milani, D

2001-01-01

High temperature superconductors (HTS) have been integrated in the high current leads for the Large Hadron Collider (LHC), under construction at CERN, in order to reduce the heat leak into the liquid helium bath due to the joule effect. The use of the HTS technology in the lower part of the current leads allowed to significantly reduce the heat charge on the cryogenic system. Hybrid current leads have been designed to fulfill the LHC requirements with respect to thermal load; several tests have been performed to study the lead behavior especially during a quench transient. Quench experiments have been performed at CERN on 13 kA prototypes to determine the adequate design and protection. In all the tests it is possible to know the temperature profile of the HTS only with the help of quench simulations that model the thermo-hydraulic processes during quench. The development of a theoretical model for the simulation allows reducing the number of test to perform and to scale the experimental result to other curre...

Self-assembly of gas-phase synthesized magnesium nanoparticles on room temperature substrates

International Nuclear Information System (INIS)

Venturi, F; Calizzi, M; Pasquini, L; Bals, S; Perkisas, T

2015-01-01

Magnesium nanoparticles (NPs) with initial size in the 10–50 nm range were synthesized by inert gas condensation under helium flow and deposited on room temperature substrates. The morphology and crystal structure of the NPs ensemble were investigated as a function of the deposition time by complementary electron microscopy techniques, including high resolution imaging and chemical mapping. With increasing amount of material, strong coarsening phenomena were observed at room temperature: small NPs disappeared while large faceted NPs developed, leading to a 5-fold increase of the average NPs size within a few minutes. The extent of coarsening and the final morphology depended also on the nature of the substrate. Furthermore, large single-crystal NPs were seen to arise from the self-organization of primary NPs units, providing a mechanism for crystal growth. The dynamics of the self-assembly process involves the basic steps of NPs sticking, diffusion on substrate, coordinated rotation and attachment/coalescence. Key features are the surface energy anisotropy, reflected by the faceted shape of the NPs, and the low melting point of the material. The observed phenomena have strong implications in relation to the synthesis and stability of nanostructures based on Mg or other elements with similar features. (paper)

High rate flame synthesis of highly crystalline iron oxide nanorods

International Nuclear Information System (INIS)

Merchan-Merchan, W; Taylor, A M; Saveliev, A V

2008-01-01

Single-step flame synthesis of iron oxide nanorods is performed using iron probes inserted into an opposed-flow methane oxy-flame. The high temperature reacting environment of the flame tends to convert elemental iron into a high density layer of iron oxide nanorods. The diameters of the iron oxide nanorods vary from 10 to 100 nm with a typical length of a few microns. The structural characterization performed shows that nanorods possess a highly ordered crystalline structure with parameters corresponding to cubic magnetite (Fe 3 O 4 ) with the [100] direction oriented along the nanorod axis. Structural variations of straight nanorods such as bends, and T-branched and Y-branched shapes are frequently observed within the nanomaterials formed, opening pathways for synthesis of multidimensional, interconnected networks

Propagators in magnetic string background and the problem of self-adjoint extensions

International Nuclear Information System (INIS)

Kaiser, H.J.

1993-01-01

Ghost and gluon propagators of a non-Abelian gauge theory in the background of a magnetic string are calculated. A simple technique to derive the ghost propagator is presented which makes use of the fact that the presence of a magnetic string of strength β shifts the differential operators ∂/∂φ to ∂/∂φ - iβ. In the case of a gluon propagator in the magnetic string background a difficulty arises from the presence of the magnetic field strength term involving a δ function. Here the ambiguities of a self-adjoint extension of the differential operator must be met. A proper treatment demands the specification of a limiting process starting from a string of finite thickness and well-defined structure and leading to the δ function string. Without this additional structure information about the background string the gauge field propagator is undetermined. (orig.)

Low temperature solution synthesis of zinc antimonide, manganese antimonide, and strontium ruthenate compounds

Science.gov (United States)

Noblitt, Jennifer Lenkner

2011-12-01

Increasing energy demands are fueling research in the area of renewable energy and energy storage. In particular, Li-ion batteries and superconducting wires are attractive choices for energy storage. Improving safety, simplifying manufacturing processes, and advancing technology to increase energy storage capacity is necessary to compete with current marketed energy storage devices. These advancements are accomplished through the study of new materials and new morphologies. Increasing dependence on and rising demand for portable electronic devices has continued to drive research in the area of Li-ion batteries. In order to compete with existing batteries and be applicable to future energy needs such as powering hybrid vehicles, the drawbacks of Li-ion batteries must be addressed including (i) low power density, (ii) safety, and (iii) high manufacturing costs. These drawbacks can be addressed through new materials and morphologies for the anode, cathode, and electrolyte. New intermetallic anode materials such as ZnSb, MnSb, and Mn2Sb are attractive candidates to replace graphite, the current industry standard anode material, because they are safer while maintaining comparable theoretical capacity. Electrodeposition is an inexpensive method that could be used for the synthesis of these electrode materials. Direct electrodeposition allows for excellent electrical contact to the current collector without the use of a binder. To successfully electrodeposit zinc and manganese antimonides, metal precursors with excellent solubility in water were needed. To promote solubility, particularly for the antimony precursor, coordinating ligands were added to the deposition bath solutions. This work shows that the choice of coordinating ligand and metal-ligand speciation can alter both the electrochemistry and the film composition. This work focuses on the search for appropriate coordinating ligands, solution pH, and bath temperatures so that high quality films of ZnSb, MnSb, and

Synthesis and Characterization of Stimuli Responsive Block Copolymers, Self-Assembly Behavior and Applications

Energy Technology Data Exchange (ETDEWEB)

Determan, Michael Duane [Iowa State Univ., Ames, IA (United States)

2005-12-17

The central theme of this thesis work is to develop new block copolymer materials for biomedical applications. While there are many reports of stimuli-responsive amphiphilic [19-21] and crosslinked hydrogel materials [22], the development of an in situ gel forming, pH responsive pentablock copolymer is a novel contribution to the field, Figure 1.1 is a sketch of an ABCBA pentablock copolymer. The A blocks are cationic tertiary amine methacrylates blocked to a central Pluronic F127 triblock copolymer. In addition to the prerequisite synthetic and macromolecular characterization of these new materials, the self-assembled supramolecular structures formed by the pentablock were experimentally evaluated. This synthesis and characterization process serves to elucidate the important structure property relationships of these novel materials, The pH and temperature responsive behavior of the pentablock copolymer were explored especially with consideration towards injectable drug delivery applications. Future synthesis work will focus on enhancing and tuning the cell specific targeting of DNA/pentablock copolymer polyplexes. The specific goals of this research are: (1) Develop a synthetic route for gel forming pentablock block copolymers with pH and temperature sensitive properties. Synthesis of these novel copolymers is accomplished with ATRP, yielding low polydispersity and control of the block copolymer architecture. Well defined macromolecular characteristics are required to tailor the phase behavior of these materials. (2) Characterize relationship between the size and shape of pentablock copolymer micelles and gel structure and the pH and temperature of the copolymer solutions with SAXS, SANS and CryoTEM. (3) Evaluate the temperature and pH induced phase separation and macroscopic self-assembly phenomenon of the pentablock copolymer. (4) Utilize the knowledge gained from first three goals to design and formulate drug delivery formulations based on the multi

High pressure direct synthesis of adipic acid from cyclohexene and hydrogen peroxide via capillary microreactors

NARCIS (Netherlands)

Shang, M.; Noël, T.; Su, Y.; Hessel, V.

2016-01-01

The direct synthesis of adipic acid from hydrogen peroxide and cyclohexene was investigated in capillary microreactors at high temperature (up to 115°C ) and pressure (up to 70 bar). High temperature was already applied in micro-flow packed-bed reactors for the direct adipic acid synthesis. In our

High temperature cracking of steels: effect of geometry on creep crack growth laws; Fissuration des aciers a haute temperature: effet de la geometrie sur la transferabilite des lois de propagation

Energy Technology Data Exchange (ETDEWEB)

Kabiri, M.R

2003-12-01

This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C{sup *} and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C{sup *} parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C{sup *} parameter, a second non singular term, denoted here as Q{sup *}, is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C{sup *} parameter (da/dt - C{sup *}), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C{sup *} type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C{sup *}), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical

Small-scale, self-propagating combustion realized with on-chip porous silicon.

Science.gov (United States)

Piekiel, Nicholas W; Morris, Christopher J

2015-05-13

For small-scale energy applications, energetic materials represent a high energy density source that, in certain cases, can be accessed with a very small amount of energy input. Recent advances in microprocessing techniques allow for the implementation of a porous silicon energetic material onto a crystalline silicon wafer at the microscale; however, combustion at a small length scale remains to be fully investigated, particularly with regards to the limitations of increased relative heat loss during combustion. The present study explores the critical dimensions of an on-chip porous silicon energetic material (porous silicon + sodium perchlorate (NaClO4)) required to propagate combustion. We etched ∼97 μm wide and ∼45 μm deep porous silicon channels that burned at a steady rate of 4.6 m/s, remaining steady across 90° changes in direction. In an effort to minimize the potential on-chip footprint for energetic porous silicon, we also explored the minimum spacing between porous silicon channels. We demonstrated independent burning of porous silicon channels at a spacing of 0.5 m on a chip surface area of 1.65 cm(2). Smaller porous silicon channels of ∼28 μm wide and ∼14 μm deep were also utilized. These samples propagated combustion, but at times, did so unsteadily. This result may suggest that we are approaching a critical length scale for self-propagating combustion in a porous silicon energetic material.

Selection and Clonal Propagation of High Artemisinin Genotypes of Artemisia annua

Science.gov (United States)

Wetzstein, Hazel Y.; Porter, Justin A.; Janick, Jules; Ferreira, Jorge F. S.; Mutui, Theophilus M.

2018-01-01

Artemisinin, produced in the glandular trichomes of Artemisia annua L. is a vital antimalarial drug effective against Plasmodium falciparum resistant to quinine-derived medicines. Although work has progressed on the semi-synthetic production of artemisinin, field production of A. annua remains the principal commercial source of the compound. Crop production of artemisia must be increased to meet the growing worldwide demand for artemisinin combination therapies (ACTs) to treat malaria. Grower artemisinin yields rely on plants generated from seeds from open-pollinated parents. Although selection has considerably increased plant artemisinin concentration in the past 15 years, seed-generated plants have highly variable artemisinin content that lowers artemisinin yield per hectare. Breeding efforts to produce improved F1 hybrids have been hampered by the inability to produce inbred lines due to self-incompatibility. An approach combining conventional hybridization and selection with clonal propagation of superior genotypes is proposed as a means to enhance crop yield and artemisinin production. Typical seed-propagated artemisia plants produce less than 1% (dry weight) artemisinin with yields below 25 kg/ha. Genotypes were identified producing high artemisinin levels of over 2% and possessing improved agronomic characteristics such as high leaf area and shoot biomass production. Field studies of clonally-propagated high-artemisinin plants verified enhanced plant uniformity and an estimated gross primary productivity of up to 70 kg/ha artemisinin, with a crop density of one plant m-2. Tissue culture and cutting protocols for the mass clonal propagation of A. annua were developed for shoot regeneration, rooting, acclimatization, and field cultivation. Proof of concept studies showed that both tissue culture-regenerated plants and rooted cutting performed better than plants derived from seed in terms of uniformity, yield, and consistently high artemisinin content. Use of

Recent advances in design procedures for high temperature plant

International Nuclear Information System (INIS)

1988-01-01

Thirteen papers cover several aspects of design for high temperature plant. These include design codes, computerized structural analysis and mechanical properties of materials at high temperatures. Seven papers are relevant for fast reactors and these are indexed separately. These cover shakedown design, design codes for thin shells subjected to cyclic thermal loading, the inelastic behaviour of stainless steels and creep and crack propagation in reactor structures under stresses caused by thermal cycling loading. (author)

Microscopic Observation of Self-Propagation of Calcifying Nanoparticles (Nanobacteria)

Science.gov (United States)

Mathew, Grace; McKay, David S.; Ciftcioglu, Neva

2007-01-01

Biologists typically define living organisms as carbon and water-based cellular forms with :self-replication" as the fundamental trait of the life process. However, this standard dictionary definition of life does not help scientists to categorize self-replicators like viruses, prions, proteons and artificial life. CNP also named nanobacteria were discovered in early 1990s as about 100 nanometer-sized bacteria-like particles with unique apatite mineral-shells around them, and found to be associated with pathological-calcification related diseases. Although CNP have been isolated and cultured from mammalian blood and diseased calcified tissues, and their biomineralizing properties well established, their biological nature and self-replicating capability have always been severely challenged. The terms "self-replication", "self-assembly" or "self-propagation" have been widely used for all systems including nanomachines, crystals, computer viruses and memes. In a simple taxonomy, all biological and non-biological "self replicators", have been classified into "living" or "nonliving" based on the properties of the systems and the amount of support they require to self-replicate. To enhance our understanding about self-replicating nature of CNP, we have investigated their growth in specific culture conditions using conventional inverted light microscope and BioStation IM, Nikon s latest time-lapse imaging system. Their morphological structure was examined using scanning (SEM) and transmission (TEM) electron microscopy. This present study, in conjunction with previous findings of metabolic activity, antibiotic sensitivity, antibody specificity, morphological aspects and infectivity, all concomitantly validate CNP as living self-replicators.

Simulation and Prediction of Weather Radar Clutter Using a Wave Propagator on High Resolution NWP Data

DEFF Research Database (Denmark)

Benzon, Hans-Henrik; Bovith, Thomas

2008-01-01

for prediction of this type of weather radar clutter is presented. The method uses a wave propagator to identify areas of potential non-standard propagation. The wave propagator uses a three dimensional refractivity field derived from the geophysical parameters: temperature, humidity, and pressure obtained from......Weather radars are essential sensors for observation of precipitation in the troposphere and play a major part in weather forecasting and hydrological modelling. Clutter caused by non-standard wave propagation is a common problem in weather radar applications, and in this paper a method...... a high-resolution Numerical Weather Prediction (NWP) model. The wave propagator is based on the parabolic equation approximation to the electromagnetic wave equation. The parabolic equation is solved using the well-known Fourier split-step method. Finally, the radar clutter prediction technique is used...

Effect of temperature upon the fatigue-crack propagation behavior of Inconel 625

International Nuclear Information System (INIS)

James, L.A.

1977-03-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of mill-annealed Inconel 625 in an air environment over the range 75 0 - 1200 0 F (24 0 - 649 0 C). In general, fatigue-crack growth rates increased with increasing test temperature. Two different specimen sizes were employed at each test temperature, and no effects of specimen size upon crack growth were noted

Nonequilibrium temperatures and second-sound propagation along nanowires and thin layers

International Nuclear Information System (INIS)

Jou, D.; Cimmelli, V.A.; Sellitto, A.

2009-01-01

It is shown that the dispersion relation of heat waves along nanowires or thin layers could allow to compare two different definitions of nonequilibrium temperature, since thermal waves are predicted to propagate with different phase speed depending on the definition of nonequilibrium temperature being used. The difference is small, but it could be in principle measurable in nanosystems, as for instance nanowires and thin layers, in a given frequency range. Such an experiment could provide a deeper view on the problem of the definition of temperature in nonequilibrium situations.

Optical diagnostics of diesel spray injections and combustion in a high-pressure high-temperature cell

NARCIS (Netherlands)

Bougie, H.J.T.; Tulej, M.; Dreier, T.; Dam, N.J.; Meulen, J.J. ter; Gerber, T.

2005-01-01

We report on spatially and temporally resolved optical diagnostic measurements of propagation and combustion of diesel sprays introduced through a single-hole fuel injector into a constant volume, high-temperature, high-pressure cell. From shadowgraphy images in non-reacting environments of pure

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

International Nuclear Information System (INIS)

Banerjee, A.K.; Alam, M.N.; Mamun, A.A.

2001-01-01

Obliquely propagating ultra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfven mode propagating parallel to the external magnetic field and dust- magnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfven mode these effects play no role, but in obliquely propagating dust-Alfven mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role. (author)

Tribological properties of PM212: A high-temperature, self-lubricating, powder metallurgy composite

Science.gov (United States)

Dellacorte, Christopher; Sliney, Harold E.

1989-01-01

This paper describes a research program to develop and evaluate a new high temperature, self-lubricating powder metallurgy composite, PM212. PM212 has the same composition as the plasma-sprayed coating, PS212, which contains 70 wt percent metal-bonded chromium carbide, 15 wt percent silver and 15 wt percent barium fluoride/calcium fluoride eutectic. The carbide acts as a wear resistant matrix and the silver and fluorides act as low and high temperature lubricants, respectively. The material is prepared by sequential cold press, cold isostatic pressing and sintering techniques. In this study, hemispherically tipped wear pins of PM212 were prepared and slid against superalloy disks at temperatures from 25 to 850 C in air in a pin-on-disk tribometer. Friction coefficients range from 0.29 to 0.38 and the wear of both the composite pins and superalloy disks was moderate to low in the 10(exp -5) to 10(exp -6) cubic mm/N-m range. Preliminary tests indicate that the material has a compressive strength of at least 130 MPa over the entire temperature range of 25 to 900 C. This material has promise for use as seal inserts, bushings, small inside diameter parts and other applications where plasma-sprayed coatings are impractical or too costly.

Tribological properties of PM212 - A high temperature, self-lubricating, powder metallurgy composite

Science.gov (United States)

Dellacorte, Christopher; Sliney, Harold E.

1990-01-01

This paper describes a research program to develop and evaluate a new high temperature, self-lubricating powder metallurgy composite, PM212. PM212 has the same composition as the plasma-sprayed coating, PS212, which contains 70 wt percent metal-bonded chromium carbide, 15 wt percent silver and 15 wt percent barium fluoride/calcium fluoride eutectic. The carbide acts as a wear resistant matrix and the silver and fluorides act as low and high temperature lubricants, respectively. The material is prepared by sequential cold press, cold isostatic pressing and sintering techniques. In this study, hemispherically tipped wear pins of PM212 were prepared and slid against superalloy disks at temperatures from 25 to 850 C in air in a pin-on-disk tribometer. Friction coefficients range from 0.29 to 0.38 and the wear of both the composite pins and superalloy disks was moderate to low in the 10(exp -5) to 10(exp -6) cubic mm/N-m range. Preliminary tests indicate that the material has a compressive strength of at least 130 MPa over the entire temperature range of 25 to 900 C. This material has promise for use as seal inserts, bushings, small inside diameter parts and other applications where plasma-sprayed coatings are impractical or too costly.

Synthesis and studies of Y-Ba-Cu-O high temperature superconductor prepared by sol-gel method

International Nuclear Information System (INIS)

Grigoryan, S.G.; Manukyan, A.L.; Hayrapetyan, A.G.; Arzumanyan, A.M.; Rashidyan, L.H.; Mkrtichyan, N.Y.; Mkrtchyan, A.A.; Kurginyan, K.A.; Trozyan, A.H.; Vardanyan, R.S.

2004-01-01

The method of preparation of Y-Ba-Cu-O high temperature superconducting materials by sol-gel processing technique both for powders and thin films are described. All these methods are based on using yttrium alkoxides as precursors, which are not ready available reagents, besides the majority of these methods use copper alkoxides, which show low solubility in organic solvents, moreover they are very sensitive to hydrolysis in air. The new method of preparation of Y-Ba-Cu-O ceramic materials by sol-gel processing technique based on new and convenient precursors stable in air, having high compatibility with each other is offered. Basic scientific and technological issues related to the synthesis of bulk materials, their structure and electrical conductivity are discussed

Low-temperature synthesis of graphene on nickel foil by microwave plasma chemical vapor deposition

International Nuclear Information System (INIS)

Kim, Y.; Song, W.; Lee, S. Y.; Jeon, C.; Jung, W.; Kim, M.; Park, C.-Y.

2011-01-01

Microwave plasma chemical vapor deposition (MPCVD) was employed to synthesize high quality centimeter scale graphene film at low temperatures. Monolayer graphene was obtained by varying the gas mixing ratio of hydrogen and methane to 80:1. Using advantages of MPCVD, the synthesis temperature was decreased from 750 deg. C down to 450 deg. C. Optical microscopy and Raman mapping images exhibited that a large area monolayer graphene was synthesized regardless of the temperatures. Since the overall transparency of 89% and low sheet resistances ranging from 590 to 1855 Ω/sq of graphene films were achieved at considerably low synthesis temperatures, MPCVD can be adopted in manufacturing future large-area electronic devices based on graphene film.

Low-temperature synthesis of graphene on nickel foil by microwave plasma chemical vapor deposition

Science.gov (United States)

Kim, Y.; Song, W.; Lee, S. Y.; Jeon, C.; Jung, W.; Kim, M.; Park, C.-Y.

2011-06-01

Microwave plasma chemical vapor deposition (MPCVD) was employed to synthesize high quality centimeter scale graphene film at low temperatures. Monolayer graphene was obtained by varying the gas mixing ratio of hydrogen and methane to 80:1. Using advantages of MPCVD, the synthesis temperature was decreased from 750 °C down to 450 °C. Optical microscopy and Raman mapping images exhibited that a large area monolayer graphene was synthesized regardless of the temperatures. Since the overall transparency of 89% and low sheet resistances ranging from 590 to 1855 Ω/sq of graphene films were achieved at considerably low synthesis temperatures, MPCVD can be adopted in manufacturing future large-area electronic devices based on graphene film.

Characterisation of high-temperature damage mechanisms of oxide dispersion strengthened (ODS) ferritic steels

International Nuclear Information System (INIS)

Salmon-Legagneur, Hubert

2017-01-01

The development of the fourth generation of nuclear power plants relies on the improvement of cladding materials, in order to achieve resistance to high temperature, stress and irradiation dose levels. Strengthening of ferritic steels through nano-oxide dispersion allows obtaining good mechanical strength at high temperature and good resistance to irradiation induced swelling. Nonetheless, studies available from open literature evidenced an unusual creep behavior of these materials: high anisotropy in time to rupture and flow behavior, low ductility and quasi-inexistent tertiary creep stage. These phenomena, and their still unclear origin are addressed in this study. Three 14Cr ODS steels rods have been studied. Their mechanical behavior is similar to those of other ODS steels from open literature. During creep tests, the specimens fractured by through crack nucleation and propagation from the lateral surfaces, followed by ductile tearing once the critical stress intensity factor was reached at the crack tip. Tensile and creep properties did not depend on the chemical environment of specimens. Crack propagation tests performed at 650 C showed a low value of the stress intensity factor necessary to start crack propagation. The cracks followed an intergranular path through the smaller-grained regions, which partly explains the anisotropy of high temperature strength. Notched specimens have been used to study the impact of the main loading parameters (deformation rate, temperature, stress triaxiality) on macroscopic crack initiation and stable propagation, from the central part of the specimens. These tests allowed revealing cavities created during high temperature loading, but unexposed to the external environment. These cavities showed a high chemical reactivity of the free surfaces in this material. The performed tests also evidenced different types of grain boundaries, which presented different damage development behaviors, probably due to differences in local

Nanocrystalline Ni-Co Alloy Synthesis by High Speed Electrodeposition

Directory of Open Access Journals (Sweden)

Jamaliah Idris

2013-01-01

Full Text Available Electrodeposition of nanocrystals is economically and technologically viable production path for the synthesis of pure metals and alloys both in coatings and bulk form. The study presents nanocrystalline Ni-Co alloy synthesis by high speed electrodeposition. Nanocrystalline Ni-Co alloys coatings were prepared by direct current (DC and deposited directly on steel and aluminum substrates without any pretreatment, using high speed electrodeposition method. The influence of the electrolysis parameters, such as cathodic current density and temperature at constant pH, on electrodeposition and microstructure of Ni-Co alloys were examined. A homogeneous surface morphology was obtained at all current densities of the plated samples, and it was evident that the current density and temperature affect the coating thickness of Ni-Co alloy coatings.

Root Growth Optimizer with Self-Similar Propagation

Directory of Open Access Journals (Sweden)

Xiaoxian He

2015-01-01

Full Text Available Most nature-inspired algorithms simulate intelligent behaviors of animals and insects that can move spontaneously and independently. The survival wisdom of plants, as another species of biology, has been neglected to some extent even though they have evolved for a longer period of time. This paper presents a new plant-inspired algorithm which is called root growth optimizer (RGO. RGO simulates the iterative growth behaviors of plant roots to optimize continuous space search. In growing process, main roots and lateral roots, classified by fitness values, implement different strategies. Main roots carry out exploitation tasks by self-similar propagation in relatively nutrient-rich areas, while lateral roots explore other places to seek for better chance. Inhibition mechanism of plant hormones is applied to main roots in case of explosive propagation in some local optimal areas. Once resources in a location are exhausted, roots would shrink away from infertile conditions to preserve their activity. In order to validate optimization effect of the algorithm, twelve benchmark functions, including eight classic functions and four CEC2005 test functions, are tested in the experiments. We compared RGO with other existing evolutionary algorithms including artificial bee colony, particle swarm optimizer, and differential evolution algorithm. The experimental results show that RGO outperforms other algorithms on most benchmark functions.

Fabrication of Ni-Ti Alloy by Self-Propagating High-Temperature Synthesis and Spark Plasma Sintering Technique

Czech Academy of Sciences Publication Activity Database

Salvetr, P.; Kubatík, Tomáš František; Pignol, D.; Novák, P.

2017-01-01

Roč. 48, č. 2 (2017), s. 772-778 ISSN 1073-5615 Institutional support: RVO:61389021 Keywords : powder metallurgy * Spark plasma sintering Subject RIV: JJ - Other Materials OBOR OECD: Materials engineering Impact factor: 1.642, year: 2016

Synthesis and high temperature stability of amorphous Si(B)CN-MWCNT composite nanowires

Science.gov (United States)

Bhandavat, Romil; Singh, Gurpreet

2012-02-01

We demonstrate synthesis of a hybrid nanowire structure consisting of an amorphous polymer-derived silicon boron-carbonitride (Si-B-C-N) shell with a multiwalled carbon nanotube core. This was achieved through a novel process involving preparation of a boron-modified liquid polymeric precursor through a reaction of trimethyl borate and polyureasilazane under atmospheric conditions; followed by conversion of polymer to glass-ceramic on carbon nanotube surfaces through controlled heating. Chemical structure of the polymer was studied by liquid-NMR while evolution of various ceramic phases was studied by Raman spectroscopy, solid-NMR, Fourier transform infrared and X-ray photoelectron spectroscopy. Electron microscopy and X-ray diffraction confirms presence of amorphous Si(B)CN coating on individual nanotubes for all specimen processed below 1400 degree C. Thermogravimetric analysis, followed by TEM revealed high temperature stability of the carbon nanotube core in flowing air up to 1300 degree C.

Bioinspired synthesis and self-assembly of hybrid organic–inorganic nanomaterials

Energy Technology Data Exchange (ETDEWEB)

Zhang, Honghu [Iowa State Univ., Ames, IA (United States)

2016-12-17

Nature is replete with complex organic–inorganic hierarchical materials of diverse yet specific functions. These materials are intricately designed under physiological conditions through biomineralization and biological self-assembly processes. Tremendous efforts have been devoted to investigating mechanisms of such biomineralization and biological self-assembly processes as well as gaining inspiration to develop biomimetic methods for synthesis and self-assembly of functional nanomaterials. In this work, we focus on the bioinspired synthesis and self-assembly of functional inorganic nanomaterials templated by specialized macromolecules including proteins, DNA and polymers. The in vitro biomineralization process of the magnetite biomineralizing protein Mms6 has been investigated using small-angle X-ray scattering. Templated by Mms6, complex magnetic nanomaterials can be synthesized on surfaces and in the bulk. DNA and synthetic polymers have been exploited to construct macroscopic two- and three-dimensional (2D and 3D) superlattices of gold nanocrystals. Employing X-ray scattering and spectroscopy techniques, the self-assembled structures and the self-assembly mechanisms have been studied, and theoretical models have been developed. Our results show that specialized macromolecules including proteins, DNA and polymers act as effective templates for synthesis and self-assembly of nanomaterials. These bottom-up approaches provide promising routes to fabricate hybrid organic–inorganic nanomaterials with rationally designed hierarchical structures, targeting specific functions.

Ultra-large scale synthesis of high electrochemical performance SnO{sub 2} quantum dots within 5 min at room temperature following a growth self-termination mechanism

Energy Technology Data Exchange (ETDEWEB)

Cui, Hongtao, E-mail: htcui@ytu.edu.cn; Xue, Junying; Ren, Wanzhong; Wang, Minmin

2015-10-05

Highlights: • SnO{sub 2} quantum dots were prepared at an ultra-large scale at room temperature within 5 min. • The grinding of SnCl{sub 2}⋅2H{sub 2}O and ammonium persulphate with morpholine produces quantum dots. • The reactions were self-terminated through the rapid consumption of water. • The obtained SnO{sub 2} quantum dots own high electrochemical performance. - Abstract: SnO{sub 2} quantum dots are prepared at an ultra-large scale by a productive synthetic procedure without using any organic ligand. The grinding of solid mixture of SnCl{sub 2}⋅2H{sub 2}O and ammonium persulphate with morpholine in a mortar at room temperature produces 1.2 nm SnO{sub 2} quantum dots within 5 min. The formation of SnO{sub 2} is initiated by the reaction between tin ions and hydroxyl groups generated from hydrolysis of morpholine in the released hydrate water from SnCl{sub 2}⋅2H{sub 2}O. It is considered that as water is rapidly consumed by the hydrolysis reaction of morpholine, the growth process of particles is self-terminated immediately after their transitory period of nucleation and growth. As a result of simple procedure and high toleration to scaling up of preparation, at least 50 g of SnO{sub 2} quantum dots can be produced in one batch in our laboratory. The as prepared quantum dots present high electrochemical performance due to the effective faradaic reaction and the alternative trapping of electrons and holes.

Effect of temperature upon the fatigue-crack propagation behavior of Inconel X-750

International Nuclear Information System (INIS)

James, L.A.

1976-05-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of precipitation heat-treated Inconel X-750 in an air environment over the range 75-1200 0 F. In general, fatigue-crack growth rates increased with increasing test temperature

A model for high-cycle fatigue crack propagation

Energy Technology Data Exchange (ETDEWEB)

Balbi, Marcela Angela [Rosario National Univ. (Argentina); National Council of Scientific Research and Technology (CONICET) (Argentina)

2017-02-01

This paper deals with the prediction of high-cycle fatigue behavior for four different materials (7075-T6 alloy, Ti-6Al-4 V alloy, JIS S10C steel and 0.4 wt.-% C steel) using Chapetti's approach to estimate the fatigue crack propagation curve. In the first part of the paper, a single integral equation for studying the entire propagation process is determined using the recent results of Santus and Taylor, which consider a double regime of propagation (short and long cracks) characterized by the model of El Haddad. The second part of the paper includes a comparison of the crack propagation behavior model proposed by Navarro and de los Rios with the one mentioned in the first half of this work. The results allow us to conclude that the approach presented in this paper is a good and valid estimation of high-cycle fatigue crack propagation using a single equation to describe the entire fatigue crack regime.

Carbon Isotope Systematics in Mineral-Catalyzed Hydrothermal Organic Synthesis Processes at High Temperature and Pressures

Science.gov (United States)

Fu, Qi; Socki, R. A.; Niles, Paul B.

2011-01-01

Observation of methane in the Martian atmosphere has been reported by different detection techniques. Reduction of CO2 and/or CO during serpentization by mineral surface catalyzed Fischer-Tropsch Type (FTT) synthesis may be one possible process responsible for methane generation on Mars. With the evidence a recent study has discovered for serpentinization in deeply buried carbon rich sediments, and more showing extensive water-rock interaction in Martian history, it seems likely that abiotic methane generation via serpentinization reactions may have been common on Mars. Experiments involving mineral-catalyzed hydrothermal organic synthesis processes were conducted at 750 C and 5.5 Kbars. Alkanes, alcohols and carboxylic acids were identified as organic compounds. No "isotopic reversal" of delta C-13 values was observed for alkanes or carboxylic acids, suggesting a different reaction pathway than polymerization. Alcohols were proposed as intermediaries formed on mineral surfaces at experimental conditions. Carbon isotope data were used in this study to unravel the reaction pathways of abiotic formation of organic compounds in hydrothermal systems at high temperatures and pressures. They are instrumental in constraining the origin and evolution history of organic compounds on Mars and other planets.

New insight of high temperature oxidation on self-exfoliation capability of graphene oxide

Science.gov (United States)

Liu, Yuhang; Zeng, Jie; Han, Di; Wu, Kai; Yu, Bowen; Chai, Songgang; Chen, Feng; Fu, Qiang

2018-05-01

The preparation of graphene oxide (GO) via Hummers method is usually divided into two steps: low temperature oxidation at 35 °C (step I oxidation) and high temperature oxidation at 98 °C (step II oxidation). However, the effects of these two steps on the exfoliation capability and chemical structure of graphite oxide remain unclear. In this study, both the functional group content of graphite oxide and the entire evolution of interlayer spacing were investigated during the two steps. Step I oxidation is a slowly inhomogeneous oxidation step to remove unoxidized graphite flakes. The prepared graphite oxide can be easily self-exfoliated but contains a lot of organic sulfur. During the first 20 min of step II oxidation, the majority of organic sulfur can be efficiently removed and graphite oxide still remains a good exfoliation capability due to sharp increasing of carboxyl groups. However, with a longer oxidation time at step II oxidation, the decrease of organic sulfur content is slowed down apparently but without any carboxyl groups forming, then graphite oxide finally loses self-exfoliation capability. It is concluded that a short time of step II oxidation can produce purer and ultralarge GO sheets via self-exfoliation. The pure GO is possessed with better thermal stability and liquid crystal behavior. Besides, reduced GO films prepared from step II oxidation show better mechanical and electric properties after reducing compared with that obtained only via step I oxidation.

CDSD-4000: High-resolution, high-temperature carbon dioxide spectroscopic databank

International Nuclear Information System (INIS)

Tashkun, S.A.; Perevalov, V.I.

2011-01-01

We present a high-resolution, high-temperature version of the Carbon Dioxide Spectroscopic Databank called CDSD-4000. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths, coefficients of temperature dependence of air- and self-broadened half-widths, and air-broadened pressure shifts) of the four most abundant isotopologues of CO 2 . A reference temperature is 296 K and an intensity cutoff is 10 -27 cm -1 /molecule cm -2 at 4000 K. The databank has 628,324,454 entries, covers the 226-8310 cm -1 spectral range and designed for the temperature range 2500-5000 K. Format of CDSD-4000 is similar to that of HITRAN-2008. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. The databank is useful for studying high-temperature radiative properties of CO 2 , including exoplanets atmospheres, aerothemal modeling for Mars entry missions, high-temperature laboratory spectra, and industrial applications. CDSD-4000 is freely accessible via the Internet site (ftp://ftp.iao.ru/pub/CDSD-4000).

Mineralizer-assisted high-pressure high-temperature synthesis and characterization of novel phosphorus nitride imides and luminescent alkaline earth metal (oxo)nitridophosphates

International Nuclear Information System (INIS)

Marchuk, Alexey

2016-01-01

The main objectives of this thesis were the synthesis, identification and structural characterization of new alkaline earth metal (oxo)nitridophopshates and phosphorus nitrides. Furthermore, luminescence properties of the resulting materials should be investigated and a connection between these properties and the respective structures should be established. For this purpose, a range of synthesis strategies was employed, including conventional solid-state syntheses in silica ampoules and high-pressure high-temperature syntheses using the multianvil technique. The emphasis of the synthetic part of this thesis lies on the development of new synthetic strategies in order to increase crystallinity of alkaline earth metal (oxo)nitridophosphates and thus accelerate their structure determination. This involves the selection of a suitable mineralizer and the investigation of its interaction with the respective starting materials. In addition, the analytical methods applied in this thesis in order to identify and characterize the compounds are just as essential as the synthesis strategies. X-ray diffraction on single crystals and on powders was carried out as the main analytical method while being supported by quantitative and qualitative 1 H and 31 P solid-state NMR measurements, FTIR and energy-dispersive X-ray (EDX) spectroscopy, as well as electron microscopy methods including both imaging and diffraction techniques. Implied by the large number of novel structures investigated, theoretical studies including topological analysis, calculations of lattice energies and bond-valence sums also played a major role in this thesis. Optical analysis methods such as reflectance spectroscopy, luminescence microscopy and photoluminescence measurements helped to determine the luminescence properties of some of the presented compounds.

Low temperature fatigue crack propagation in neutron irradiated Type 316 steel and weld metal

International Nuclear Information System (INIS)

Lloyd, G.J.; Walls, J.D.; Gravenor, J.

1981-02-01

The fast cycling fatigue crack propagation characteristics of Type 316 steel and weld metal have been investigated at 380 0 C after irradiation to 1.72-1.92x10 20 n/cm 2 (E>1MeV) and 2.03x10 21 n/cm 2 (E>1MeV) at the same temperature. With mill-annealed Type 316 steel, modest decreases in the rates of crack propagation were observed for both dose levels considered, whereas for cold-worked Type 316 steel irradiation to 2.03x10 21 n/cm 2 (E>1MeV) caused increases in the rate of crack propagation. For Type 316 weld metal, increases in the rate of crack propagation were observed for both dose levels considered. The diverse influences of irradiation upon fatigue crack propagation in these materials are explained by considering a simple continuum mechanics model of crack propagation together with the results of control tensile experiments made on similarly irradiated materials. (author)

THERMAL STABILITY OF Al-Cu-Fe QUASICRYSTALS PREPARED BY SHS METHOD

OpenAIRE

Pavel Novák; Alena Michalcová; Milena Voděrová; Ivo Marek; Dalibor Vojtěch

2013-01-01

Quasicrystal-containing materials are usually prepared by rapid solidification of the melt (e.g. by melt spinning) or mechanical alloying. In this work, the method using exothermic reactions between compressed metallic powders called SHS (Self-propagating High-temperature Synthesis) was tested. The microstructure and phase composition of the product was described in dependence on cooling regime from the reaction temperature. Thermal stability of prepared Al-Cu-Fe quasicrystals was studied by...

Ultrafast Self-Assembly of Sub-10 nm Block Copolymer Nanostructures by Solvent-Free High-Temperature Laser Annealing.

Science.gov (United States)

Jiang, Jing; Jacobs, Alan G; Wenning, Brandon; Liedel, Clemens; Thompson, Michael O; Ober, Christopher K

2017-09-20

Laser spike annealing was applied to PS-b-PDMS diblock copolymers to induce short-time (millisecond time scale), high-temperature (300 to 700 °C) microphase segregation and directed self-assembly of sub-10 nm features. Conditions were identified that enabled uniform microphase separation in the time frame of tens of milliseconds. Microphase ordering improved with increased temperature and annealing time, whereas phase separation contrast was lost for very short annealing times at high temperature. PMMA brush underlayers aided ordering under otherwise identical laser annealing conditions. Good long-range order for sub-10 nm cylinder morphology was achieved using graphoepitaxy coupled with a 20 ms dwell laser spike anneal above 440 °C.

Mechanical strength and thermophysical properties of PM212: A high temperature self-lubricating powder metallurgy composite

Science.gov (United States)

Edwards, Phillip M.; Sliney, Harold E.; Dellacorte, Christopher; Whittenberger, J. Daniel; Martineau, Robert R.

1990-01-01

A powder metallurgy composite, PM212, composed of metal bonded chromium carbide and solid lubricants is shown to be self-lubricating to a maximum application temperature of 900 C. The high temperature compressive strength, tensile strength, thermal expansion and thermal conductivity data needed to design PM212 sliding contact bearings and seals are reported for sintered and isostatically pressed (HIPed) versions of PM212. Other properties presented are room temperature density, hardness, and elastic modulus. In general, both versions appear to have adequate strength to be considered as sliding contact bearing materials, but the HIPed version, which is fully dense, is much stronger than the sintered version which contains about 20 percent pore volume. The sintered material is less costly to make, but the HIPed version is better where high compressive strength is important.

High quality aluminium doped zinc oxide target synthesis from nanoparticulate powder and characterisation of sputtered thin films

Energy Technology Data Exchange (ETDEWEB)

Isherwood, P.J.M., E-mail: P.J.M.Isherwood@lboro.ac.uk [Centre for Renewable Energy Systems Technology, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom); Neves, N. [Innovnano, S. A., Rua Coimbra Inovação Parque, IParque Lote 13, 3040-570 Antanhol, Coimbra (Portugal); Bowers, J.W. [Centre for Renewable Energy Systems Technology, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom); Newbatt, P. [Innovnano, S. A., Rua Coimbra Inovação Parque, IParque Lote 13, 3040-570 Antanhol, Coimbra (Portugal); Walls, J.M. [Centre for Renewable Energy Systems Technology, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom)

2014-09-01

Nanoparticulate aluminium-doped zinc oxide powder was synthesised through detonation and subsequent rapid quenching of metallic precursors. This technique allows for precise compositional control and rapid nanoparticle production. The resulting powder was used to form sputter targets, which were used to deposit thin films by radio frequency sputtering. These films show excellent sheet resistance and transmission values for a wide range of deposition temperatures. Crystal structure analysis shows that crystals in the target have a random orientation, whereas the crystals in the films grow perpendicular to the substrate surface and propagate preferentially along the (002) axis. Higher temperature deposition reduces crystal quality with a corresponding decrease in refractive index and an increase in sheet resistance. Films deposited between room temperature and 300 °C were found to have sheet resistances equivalent to or better than indium tin oxide films for a given average transmission value. - Highlights: • Nanoparticulate AZO powder was used to produce sputter targets. • The powder synthesis technique allows for precise compositional control. • Sputtered films show excellent optical, electronic and structural properties. • High temperature films show reduced electrical and structural quality. • For a given transmission, films show equivalent sheet resistances to ITO.

Self-ignition combustion synthesis of TiFe in hydrogen atmosphere

Energy Technology Data Exchange (ETDEWEB)

Wakabayashi, R. [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan)], E-mail: ryuta@eng.hokudai.ac.jp; Sasaki, S. [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan); Saita, I. [National Institute of Advanced Industrial Science and Technology (AIST), AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 (Japan); Sato, M. [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan); Uesugi, H. [Bio Coke Lab., Ltd., 5-34-20 Hirato, Totsuka-ku, Yokohama, Kanagawa 244-0802 (Japan); Akiyama, T. [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan)

2009-07-08

This paper describes the self-ignition combustion synthesis (SICS) of highly active titanium iron (TiFe) in a high-pressure hydrogen atmosphere without employing an activation process. In the experiments, well-mixed powders of Ti and Fe in the molar ratio of 1:1 were uniformly heated up to 1085 deg. C, the eutectic temperature of Ti-Fe binary system, in pressurized hydrogen at 0.9 MPa. The electric source was disconnected immediately after the ignition between Ti and Fe, and the mixture was cooled naturally. In this study, the exothermic reaction Ti + Fe = TiFe + 40 kJ occurred at around 1085 deg. C after the hydrogenation and decomposition of Ti. X-ray diffraction analysis showed that the final product had only one phase-TiFeH{sub 0.06}-which can store hydrogen of 1.55 mass% under hydrogen pressure of 4 MPa. The product obtained by SICS contained considerably more hydrogen quickly as compared to the commercially available product; this fact can be explained by the porous structure of the obtained product, which was observed using a scanning electron microscope. In conclusion, the SICS of TiFe saved time and energy, yields products with high porosity and small crystals, enabled easy hydrogenation, and did not require activation processes.

Insitu synthesis of self-assembled gold nanoparticles on glass or silicon substrates through reactive inkjet printing

KAUST Repository

Abulikemu, Mutalifu

2013-12-18

A facile and low cost method for the synthesis of self-assembled nanoparticles (NPs) with minimal size variation and chemical waste by using reactive inkjet printing was developed. Gold NPs with diameters as small as (8±2)nm can be made at low temperature (120 °C). The size of the resulting NPs can be readily controlled through the concentration of the gold precursor and oleylamine ink. The pure gold composition of the synthesized NPs was confirmed by energy-dispersive X-ray spectroscopy (EDXS) analysis. High-resolution SEM (HRSEM) and TEM (HRTEM), and X-ray diffraction revealed their size and face-centered cubic (fcc) crystal structure, respectively. Owing to the high density of the NP film, UV/Vis spectroscopy showed a red shift in the intrinsic plasmonic resonance peak. We envision the extension of this approach to the synthesis of other nanomaterials and the production of tailored functional nanomaterials and devices. Midas touch: The use of low-cost manufacturing approaches in the synthesis of nanoparticles is critical for many applications. Reactive inkjet printing, along with a judicious choice of precursor/solvent system, was used to synthesize a relatively uniform assembly of crystalline gold nanoparticles, with diameters as small as (8±2)nm, over a given substrate surface. © 2014 WILEY-VCH Verlag GmbH.

Effect of service exposure on fatigue crack propagation of Inconel 718 turbine disc material at elevated temperatures

Energy Technology Data Exchange (ETDEWEB)

Jeong, Dae-Ho [Department of Materials Science and Engineering, RECAPT, Gyeongsang National University, Chinju (Korea, Republic of); Choi, Myung-Je [Korea Aerospace Industry, Sacheon (Korea, Republic of); Goto, Masahiro [Department of Mechanical Engineering, Oita University, Oita (Japan); Lee, Hong-Chul [Republic of Korea Air Force (Korea, Republic of); Kim, Sangshik, E-mail: sang@gnu.ac.kr [Department of Materials Science and Engineering, RECAPT, Gyeongsang National University, Chinju (Korea, Republic of)

2014-09-15

In this study, the fatigue crack propagation behavior of Inconel 718 turbine disc with different service times from 0 to 4229 h was investigated at 738 and 823 K. No notable change in microstructural features, other than the increase in grain size, was observed with increasing service time. With increasing service time from 0 to 4229 h, the fatigue crack propagation rates tended to increase, while the ΔK{sub th} value decreased, in low ΔK regime and lower Paris' regime at both testing temperatures. The fractographic observation using a scanning electron microscope suggested that the elevated temperature fatigue crack propagation mechanism of Inconel 718 changed from crystallographic cleavage mechanism to striation mechanism in the low ΔK regime, depending on the grain size. The fatigue crack propagation mechanism is proposed for the crack propagating through small and large grains in the low ΔK regime, and the fatigue crack propagation behavior of Inconel 718 with different service times at elevated temperatures is discussed. - Highlights: • The specimens were prepared from the Inconel 718 turbine disc used for 0 to 4229 h. • FCP rates were measured at 738 and 823 K. • The ΔK{sub th} values decreased with increasing service time. • The FCP behavior showed a strong correlation with the grain size of used turbine disc.

Synthesis of indium nanoparticles at ambient temperature; simultaneous phase transfer and ripening

Energy Technology Data Exchange (ETDEWEB)

Aghazadeh Meshgi, Mohammad; Kriechbaum, Manfred [Graz University of Technology, Institute of Inorganic Chemistry (Austria); Biswas, Subhajit; Holmes, Justin D., E-mail: j.holmes@ucc.ie [University College Cork, Materials Chemistry and Analysis Group, Department of Chemistry and the Tyndall National Institute (Ireland); Marschner, Christoph, E-mail: christoph.marschner@tugraz.at [Graz University of Technology, Institute of Inorganic Chemistry (Austria)

2016-12-15

The synthesis of size-monodispersed indium nanoparticles via an innovative simultaneous phase transfer and ripening method is reported. The formation of nanoparticles occurs in a one-step process instead of well-known two-step phase transfer approaches. The synthesis involves the reduction of InCl{sub 3} with LiBH{sub 4} at ambient temperature and although the reduction occurs at room temperature, fine indium nanoparticles, with a mean diameter of 6.4 ± 0.4 nm, were obtained directly in non-polar n-dodecane. The direct synthesis of indium nanoparticles in n-dodecane facilitates their fast formation and enhances their size-monodispersity. In addition, the nanoparticles were highly stable for more than 2 months. The nanoparticles were characterised by dynamic light scattering (DLS), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared (FT-IR) spectroscopy to determine their morphology, structure and phase purity.

Thermochemistry of some binary lead and transition metal compounds by high temperature direct synthesis calorimetry

Energy Technology Data Exchange (ETDEWEB)

Meschel, S.V., E-mail: meschel@jfi.uchicago.edu [Illinois Institute of Technology,Thermal Processing Technology Center, 10 W. 32nd Street, Chicago, Illinois 60615 (United States); Gordon Center for Integrated Science, 929 E. 57th Street, Chicago, Illinois 60637 (United States); Nash, P. [Illinois Institute of Technology,Thermal Processing Technology Center, 10 W. 32nd Street, Chicago, Illinois 60615 (United States); Chen, X.Q.; Wei, P. [Materials processing Modeling Division, Shenyang National Laboratory for Materials Science, Institute of Metals Research, 72 Wenhua Road, Shenyang City (China)

2015-06-05

Highlights: • Studied binary lead-transition metal alloys by high temperature calorimetry. • Determined the enthalpies of formation of 8 alloys. • Compared the measurements with predictions by the model of Miedema and by the ab initio method. - Abstract: The standard enthalpies of formation of some binary lead and transition metal compounds have been measured by high temperature direct synthesis calorimetry. The reported results are: Pb{sub 3}Sc{sub 5}(−61.3 ± 2.9); PbTi{sub 4}(−16.6 ± 2.4); Pb{sub 3}Y{sub 5}(−64.8 ± 3.6); Pb{sub 3}Zr{sub 5}(−50.6 ± 3.1); PbNb{sub 3}(−10.4 ± 3.4); PbRh(−16.5 ± 3.3); PbPd{sub 3}(−29.6 ± 3.1); PbPt(−34.7 ± 3.3) kJ/mole of atoms. We will compare our results with previously published measurements. We will also compare the experimental measurements with enthalpies of formation of transition metal compounds with elements in the same vertical column in the periodic table. We will compare our measurements with predicted values on the basis of the semi empirical model of Miedema and coworkers and with ab initio values when available.

Asymptotic analysis to the effect of temperature gradient on the propagation of triple flames

Science.gov (United States)

Al-Malki, Faisal

2018-05-01

We study asymptotically in this paper the influence of the temperature gradient across the mixing layer on the propagation triple flames formed inside a porous wall channel. The study begins by formulating the problem mathematically using the thermo-diffusive model and then presents a thorough asymptotic analysis of the problem in the limit of large activation energy and thin flames. Analytical formulae for the local burning speed, the flame shape and the propagation speed in terms of the temperature gradient parameter have been derived. It was shown that varying the feed temperatures can significantly enhance the burning of the reactants up to a critical threshold, beyond which no solutions can be obtained. In addition, the study showed that increasing the temperature at the boundaries will modify the usual triple structure of the flame by inverting the upper premixed branch and extending it to the boundary, which may have great implications on the safety of the adopted combustion chambers.

Structural determinants of HIV-1 nucleocapsid protein for cTAR DNA binding and destabilization, and correlation with inhibition of self-primed DNA synthesis.

Science.gov (United States)

Beltz, Hervé; Clauss, Céline; Piémont, Etienne; Ficheux, Damien; Gorelick, Robert J; Roques, Bernard; Gabus, Caroline; Darlix, Jean-Luc; de Rocquigny, Hugues; Mély, Yves

2005-05-20

The nucleocapsid protein (NC) of human immunodeficiency virus type 1 (HIV-1) is formed of two highly conserved CCHC zinc fingers flanked by small basic domains. NC is required for the two obligatory strand transfers in viral DNA synthesis through its nucleic acid chaperoning properties. The first DNA strand transfer relies on NC's ability to bind and destabilize the secondary structure of complementary transactivation response region (cTAR) DNA, to inhibit self-priming, and to promote the annealing of cTAR to TAR RNA. To further investigate NC chaperone properties, our aim was to identify by fluorescence spectroscopy and gel electrophoresis, the NC structural determinants for cTAR binding and destabilization, and for the inhibition of self-primed DNA synthesis on a model system using a series of NC mutants and HIV-1 reverse transcriptase. NC destabilization and self-priming inhibition properties were found to be supported by the two fingers in their proper context and the basic (29)RAPRKKG(35) linker. The strict requirement of the native proximal finger suggests that its hydrophobic platform (Val13, Phe16, Thr24 and Ala25) is crucial for binding, destabilization and inhibition of self-priming. In contrast, only partial folding of the distal finger is required, probably for presenting the Trp37 residue in an appropriate orientation. Also, Trp37 and the hydrophobic residues of the proximal finger appear to be essential for the propagation of the melting from the cTAR ends up to the middle of the stem. Finally, both N-terminal and C-terminal basic domains contribute to cTAR binding but not to its destabilization.

Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history

International Nuclear Information System (INIS)

Stout, R.B.

2001-01-01

An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)

Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history

Energy Technology Data Exchange (ETDEWEB)

Stout, R.B. [California Univ., Livermore, CA (United States). Lawrence Livermore National Lab

2001-07-01

An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)

The influence of defects on the transport properties of AgSbPb18Te20 prepared at high pressure and high temperature

International Nuclear Information System (INIS)

Wang Yi; Zhu Pinwen; Jiao Hujun; Chen Haiyong; Ma Yanming; Niu Yingli; Li Yingai; Zhang Lijun; Zhang Tiechen; Gao Chunxiao; Zou Guangtian

2007-01-01

We synthesized polycrystal AgSbPb 18 Te 20 by using the method of high pressure and high temperature, and found that the defects produced by high pressure and high temperature caused the changes of transport properties. X-ray diffraction patterns showed that the cell parameters did not change obviously with synthesis at high pressure, apart from a small fluctuation. The electrical resistivity first increased, and then decreased to one quarter of the original value, as the synthesis pressure changed from low to high. The Seebeck coefficient decreased with the increase of synthesis pressure, and then changed from positive to negative. High pressure and high temperature could cause AgSbPb 18 Te 20 to change from a p-type to n-type semiconductor, increase the carrier concentration at maximum by two orders of magnitude, and shift the infrared absorption edge to a higher energy range. All of these phenomena were regarded as showing that high pressure and high temperature favored the formation of certain defects which could change the band structure and thereby change the transport properties

Facile and green synthesis of highly stable L-cysteine functionalized copper nanoparticles

International Nuclear Information System (INIS)

Kumar, Nikhil; Upadhyay, Lata Sheo Bachan

2016-01-01

Highlights: • A facile and eco-friendly method for the synthesis of L-cysteine functionalized copper nanoparticles is reported. • Synthesis of Highly stable L-cysteine functionalized copper nanoparticles (∼40 nm) was done in an aqueous medium. • FTIR analysis shows that L-cysteine bound to the nanoparticle surface via thiol group. - Abstract: A simple eco-friendly method for L-cysteine capped copper nanoparticles (CCNPs) synthesis in aqueous solution has been developed. Glucose and L-cysteine were used as reducing agent and capping/functionalizing agent, respectively. Different parameters such as capping agent concentration, pH, reaction temperature, and reducing agent concentration were optimized during the synthesis. The L-cysteine capped copper nanoparticle were characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Particle size and zeta potential analyser, and high resolution transmission electron microscopy. Spherical shaped cysteine functionalized/capped copper nanoparticles with an average size of 40 nm were found to be highly stable at room temperature (RT) for a period of 1 month

Facile and green synthesis of highly stable L-cysteine functionalized copper nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Kumar, Nikhil, E-mail: nkumar.phd2011.bt@nitrr.ac.in; Upadhyay, Lata Sheo Bachan, E-mail: contactlataupadhyay@gmail.com

2016-11-01

Highlights: • A facile and eco-friendly method for the synthesis of L-cysteine functionalized copper nanoparticles is reported. • Synthesis of Highly stable L-cysteine functionalized copper nanoparticles (∼40 nm) was done in an aqueous medium. • FTIR analysis shows that L-cysteine bound to the nanoparticle surface via thiol group. - Abstract: A simple eco-friendly method for L-cysteine capped copper nanoparticles (CCNPs) synthesis in aqueous solution has been developed. Glucose and L-cysteine were used as reducing agent and capping/functionalizing agent, respectively. Different parameters such as capping agent concentration, pH, reaction temperature, and reducing agent concentration were optimized during the synthesis. The L-cysteine capped copper nanoparticle were characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Particle size and zeta potential analyser, and high resolution transmission electron microscopy. Spherical shaped cysteine functionalized/capped copper nanoparticles with an average size of 40 nm were found to be highly stable at room temperature (RT) for a period of 1 month.

Analysis of normal zone propagation and hot spot temperature on ITER CS insert coil

International Nuclear Information System (INIS)

Suwa, Tomone; Ozeki, Hidemasa; Nabara, Yoshihiro; Saito, Toru; Kawano, Katsumi; Takahashi, Yoshikazu; Isono, Takaaki; Nunoya, Yoshihiko

2016-01-01

The Central Solenoid (CS) insert coil consists of a 42-m-long CS conductor, of which the specifications are the same as that of the ITER CS. In order to investigate normal zone propagation and hot spot temperature, a quench test was carried out on the CS insert under End-of-Burn condition at 12.5 T and 45.1 kA of after 16,000 cycles. External heat was applied at nearly the center of the CS insert using an inductive heater, and quench was induced. A current of 45.1 kA was dumped 9.5 s (7 s) after voltage generation (Quench detection, QD). The Normal zone propagation length reached 23.4 m, and the maxim propagation velocity was 3.1 m/s just before dumping. Considering the distribution of temperature, which is calculated by GANDALF, hot spot temperature was expected to reach 227 K. As the result, it was found that the hot spot temperature exceeded the criteria of 150 K which is designed on ITER. However, heating the CS insert to 227 K did not influence conductor performance, because the current sharing temperature was maintained after the quench test. Therefore, the quench detection has a margin of approximately 9.5 s (7 s) after voltage generation (QD) in view of the conductor performance under the conditions applied in this quench test. If the hot spot temperature is kept to less than 150 K, the current should be dumped 7.5 s (5 s) before voltage generation (QD). These results are very useful for designing quench protection of the ITER CS. (author)

ASD-1000: High-resolution, high-temperature acetylene spectroscopic databank

Science.gov (United States)

Lyulin, O. M.; Perevalov, V. I.

2017-11-01

We present a high-resolution, high-temperature version of the Acetylene Spectroscopic Databank called ASD-1000. The databank contains the line parameters (position, intensity, Einstein coefficient for spontaneous emission, term value of the lower states, self- and air-broadening coefficients, temperature dependence exponents of the self- and air-broadening coefficients) of the principal isotopologue of C2H2. The reference temperature for line intensity is 296 K and the intensity cutoff is 10-27 cm-1/(molecule cm-2) at 1000 K. The databank has 33,890,981 entries and covers the 3-10,000 cm-1 spectral range. The databank is based on the global modeling of the line positions and intensities performed within the framework of the method of effective operators. The parameters of the effective Hamiltonian and the effective dipole moment operator have been fitted to the observed values of the line positions and intensities collected from the literature. The broadening coefficients as well as their temperature dependence exponents were calculated using the empirical equations. The databank is useful for studying high-temperature radiative properties of C2H2. ASD-1000 is freely accessible via the Internet site of V.E. Zuev Institute of Atmospheric Optics SB RAS ftp://ftp.iao.ru/pub/ASD1000/.

An Investigation of Porous Structure of TiNi-Based SHS-Materials Produced at Different Initial Synthesis Temperatures

Science.gov (United States)

Khodorenko, V. N.; Anikeev, S. G.; Kokorev, O. V.; Yasenchuk, Yu. F.; Gunther, V. É.

2018-02-01

An investigation of structural characteristics and behavior of TiNi-based pore-permeable materials manufactured by the methods of selfpropagating high-temperature synthesis (SHS) at the initial synthesis temperatures T = 400 and 600°C is performed. It is shown that depending on the temperature regime, the resulting structure and properties of the material can differ. It is found out that the SHS-material produced at the initial synthesis temperature T = 400°C possesses the largest number of micropores in the pore wall surface structure due to a high phase inhomogeneity of the alloy. The regime of structure optimization of the resulting materials is described and the main stages of formation of the pore wall microporous surfaces are revealed. It is demonstrated that after optimization of the surface structure of a TiNi-based fine-pore alloy by its chemical etching, the fraction of micropores measuring in size less than 50 nm increased from 59 to 68%, while the number of pores larger than 1 μm increased twofold from 11 to 22%. In addition, peculiar features of interaction between certain cell cultures with the surface of the SHS-material manufactured at different initial synthesis temperatures are revealed. It is found out that the dynamics of the cell material integration depends on the pore wall surface morphology and dimensions of macropores.

Self-reflection of intense electromagnetic waves in plasmas

Energy Technology Data Exchange (ETDEWEB)

Tewari, D P; Kumar, A; Sharma, J K [Indian Inst. of Tech., New Delhi. Dept. of Physics

1977-10-01

A uniform electromagnetic wave of high power density, propagating in a collisional plasma gives rise to a modification in temperature-dependent collision frequency and in turn induces a gradient in the complex refractive index of the medium. A WKB solution of the problem predicts a backward propagating wave on account of the self-induced inhomogeneity. The amplitude of the backward (i.e. reflected) wave increases with increasing power density of the wave. This is a volume nonlinear effect and is appreciable for usually employed power densities.

Amplification due to two-stream instability of self-electric and magnetic fields of an ion beam propagating in background plasma

Science.gov (United States)

Tokluoglu, Erinc K.; Kaganovich, Igor D.; Carlsson, Johan A.; Hara, Kentaro; Startsev, Edward A.

2018-05-01

Propagation of charged particle beams in background plasma as a method of space charge neutralization has been shown to achieve a high degree of charge and current neutralization and therefore enables nearly ballistic propagation and focusing of charged particle beams. Correspondingly, the use of plasmas for propagation of charged particle beams has important applications for transport and focusing of intense particle beams in inertial fusion and high energy density laboratory plasma physics. However, the streaming of beam ions through a background plasma can lead to the development of two-stream instability between the beam ions and the plasma electrons. The beam electric and magnetic fields enhanced by the two-stream instability can lead to defocusing of the ion beam. Using particle-in-cell simulations, we study the scaling of the instability-driven self-electromagnetic fields and consequent defocusing forces with the background plasma density and beam ion mass. We identify plasma parameters where the defocusing forces can be reduced.

Self-Healing Phase Change Salogels with Tunable Gelation Temperature.

Science.gov (United States)

Karimineghlani, Parvin; Palanisamy, Anbazhagan; Sukhishvili, Svetlana A

2018-04-19

Chemically cross-linked polymer matrices have demonstrated strong potential for shape stabilization of molten phase change materials (PCM). However, they are not designed to be fillable and removable from a heat exchange module for an easy replacement with new PCM matrices and lack self-healing capability. Here, a new category of shapeable, self-healing gels, "salogels", is introduced. The salogels reversibly disassemble in a high-salinity environment of a fluid inorganic PCM [lithium nitrate trihydrate (LNH)], at a preprogrammed temperature. LNH was employed as a high latent heat PCM and simultaneously as a solvent, which supported the formation of a network of polyvinyl alcohol (PVA) chains via physical cross-linking through poly(amidoamine) dendrimers of various generations. The existence of hydrogen bonding and the importance of low-hydration state of PVA for the efficient gelation were experimentally confirmed. The thermal behavior of PCM salogels was highly reversible and repeatable during multiple heating/cooling cycles. Importantly, the gel-sol transition temperature could be precisely controlled within a range of temperature above LNH's melting point by the choice of dendrimer generation and their concentration. Shape stabilization and self-healing properties of the salogels, taken together with tunability of their temperature-induced fluidization make these materials attractive for thermal energy storage applications that require on-demand removal and replacement of used inorganic PCM salt hydrates.

Monitoring Moisture Damage Propagation in GFRP Composites Using Carbon Nanoparticles

Directory of Open Access Journals (Sweden)

Ahmed Al-Sabagh

2017-03-01

Full Text Available Glass fiber reinforced polymer (GFRP composites are widely used in infrastructure applications including water structures due to their relatively high durability, high strength to weight ratio, and non-corrosiveness. Here we demonstrate the potential use of carbon nanoparticles dispersed during GFRP composite fabrication to reduce water absorption of GFRP and to enable monitoring of moisture damage propagation in GFRP composites. GFRP coupons incorporating 2.0 wt % carbon nanofibers (CNFs and 2.0 wt % multi-wall carbon nanotubes (MWCNTs were fabricated in order to study the effect of moisture damage on mechanical properties of GFRP. Water absorption tests were carried out by immersing the GFRP coupons in a seawater bath at two temperatures for a time period of three months. Effects of water immersion on the mechanical properties and glass transition temperature of GFRP were investigated. Furthermore, moisture damage in GFRP was monitored by measuring the electrical conductivity of the GFRP coupons. It was shown that carbon nanoparticles can provide a means of self-sensing that enables the monitoring of moisture damage in GFRP. Despite the success of the proposed technique, it might not be able to efficiently describe moisture damage propagation in GFRP beyond a specific threshold because of the relatively high electrical conductivity of seawater. Microstructural investigations using Fourier Transform Infrared (FTIR explained the significance of seawater immersion time and temperature on the different levels of moisture damage in GFRP.

Protein synthesis during the initial phase of the temperature-induced bleaching response in Euglena gracilis

International Nuclear Information System (INIS)

Ortiz, W.

1990-01-01

Growing cultures of photoheterotrophic Euglena gracilis experience an increase in chlorophyll accumulation during the initial phase of the temperature-induced bleaching response suggesting an increase in the synthesis of plastid components at the bleaching temperature of 33 degree C. A primary goal of this work was to establish whether an increase in the synthesis of plastid proteins accompanies the observed increase in chlorophyll accumulation. In vivo pulse-labeling experiments with [ 35 S]sodium sulfate were carried out with cells grown at room temperature or at 33 degree C. The synthesis of a number of plastid polypeptides of nucleocytoplasmic origin, including some presumably novel polypeptides, increased in cultures treated for 15 hours at 33 degree C. In contrast, while synthesis of thylakoid proteins by the plastid protein synthesis machinery decreased modestly, synthesis of the large subunit of the enzyme ribulosebisphosphate carboxylase was strongly affected at the elevated temperature. Synthesis of novel plastid-encoded polypeptides was not induced at the bleaching temperature. It is concluded that protein synthesis in plastids declines during the initial phase of the temperature response in Euglena despite an overall increase in cellular protein synthesis and an increase in chlorophyll accumulation per cell

Flame Speed and Self-Similar Propagation of Expanding Turbulent Premixed Flames

Science.gov (United States)

Chaudhuri, Swetaprovo; Wu, Fujia; Zhu, Delin; Law, Chung K.

2012-01-01

In this Letter we present turbulent flame speeds and their scaling from experimental measurements on constant-pressure, unity Lewis number expanding turbulent flames, propagating in nearly homogeneous isotropic turbulence in a dual-chamber, fan-stirred vessel. It is found that the normalized turbulent flame speed as a function of the average radius scales as a turbulent Reynolds number to the one-half power, where the average radius is the length scale and the thermal diffusivity is the transport property, thus showing self-similar propagation. Utilizing this dependence it is found that the turbulent flame speeds from the present expanding flames and those from the Bunsen geometry in the literature can be unified by a turbulent Reynolds number based on flame length scales using recent theoretical results obtained by spectral closure of the transformed G equation.

Formulation and catalytic performance of MOF-derived Fe@C/Al composites for high temperature Fischer–Tropsch synthesis

KAUST Repository

Oar-Arteta, Lide; Valero-Romero, Marí a José ; Wezendonk, Tim; Kapteijn, Freek; Gascon, Jorge

2017-01-01

High productivity towards C-2-C-4 olefins together with high catalyst stability are key for optimum operation in high temperature Fischer-Tropsch synthesis (HT-FTS). Here, we report the fabrication of Fe@C/Al composites that combine both the outstanding catalytic properties of the Fe-BTC MOF-derived Fe catalyst and the excellent mechanical resistance and textural properties provided by the inorganic AlOOH binder. The addition of AlOOH to Fe-BTC followed by pyrolysis in N-2 atmosphere at 500 degrees C results in composites with a large mesoporosity, a high Fe/Fe3O4 ratio, 10-35 nm average Fe crystallite size and coordinatively unsaturated Al3+ sites. In catalytic terms, the addition of AlOOH binder gives rise to enhanced C-2-C-4 selectivity and catalyst mechanical stability in HT-FTS, but at high Al contents the activity decreases. Altogether, the productivity of these Fe@C/Al composites is well above most known Fe catalysts for this process.

Formulation and catalytic performance of MOF-derived Fe@C/Al composites for high temperature Fischer–Tropsch synthesis

KAUST Repository

Oar-Arteta, Lide

2017-11-15

High productivity towards C-2-C-4 olefins together with high catalyst stability are key for optimum operation in high temperature Fischer-Tropsch synthesis (HT-FTS). Here, we report the fabrication of Fe@C/Al composites that combine both the outstanding catalytic properties of the Fe-BTC MOF-derived Fe catalyst and the excellent mechanical resistance and textural properties provided by the inorganic AlOOH binder. The addition of AlOOH to Fe-BTC followed by pyrolysis in N-2 atmosphere at 500 degrees C results in composites with a large mesoporosity, a high Fe/Fe3O4 ratio, 10-35 nm average Fe crystallite size and coordinatively unsaturated Al3+ sites. In catalytic terms, the addition of AlOOH binder gives rise to enhanced C-2-C-4 selectivity and catalyst mechanical stability in HT-FTS, but at high Al contents the activity decreases. Altogether, the productivity of these Fe@C/Al composites is well above most known Fe catalysts for this process.

Phase distribution and microstructural changes of self-compacting cement paste at elevated temperature

International Nuclear Information System (INIS)

Ye, G.; Liu, X.; De Schutter, G.; Taerwe, L.; Vandevelde, P.

2007-01-01

Self-compacting concrete, as a new smart building material with various advanced properties, has been used for a wide range of structures and infrastructures. However little investigation have been reported on the properties of Self-compacting when it is exposed to elevated temperatures. Previous experiments on fire test have shown the differences between high performance concrete and traditional concrete at elevated temperature. This difference is largely depending on the microstructural properties of concrete matrix, i.e. the cement paste, especially on the porosity, pore size distribution and the connectivity of pores in cement pastes. In this contribution, the investigations are focused on the cement paste. The phase distribution and microstructural changes of self-compacting cement paste at elevated temperatures are examined by mercury intrusion porosimetry and scanning electron microscopy. The chemical decomposition of self-compacting cement paste at different temperatures is determined by thermogravimetric analysis. The experimental results of self-compacting cement paste are compared with those of high performance cement paste and traditional cement paste. It was found that self-compacting cement paste shows a higher change of the total porosity in comparison with high performance cement paste. When the temperature is higher than 700 deg. C, a dramatic loss of mass was observed in the self-compacting cement paste samples with addition of limestone filler. This implies that the SCC made by this type of self-compacting cement paste will probably show larger damage once exposed to fire. Investigation has shown that 0.5 kg/m 3 of Polypropylene fibers in the self-compacting cement paste can avoid the damage efficiently

Structural analysis technology for high-temperature design

International Nuclear Information System (INIS)

Greenstreet, W.L.

1977-01-01

Results from an ongoing program devoted to the development of verified high-temperature structural design technology applicable to nuclear reactor systems are described. The major aspects addressed by the program are (1) deformation behavior; (2) failure associated with creep rupture, brittle fracture, fatigue, creep-fatigue interactions, and crack propagation; and (3) the establishment of appropriate design criteria. This paper discusses information developed in the deformation behavior category. The material considered is type 304 stainless steel, and the temperatures range to 1100 0 F (593 0 C). In essence, the paper considers the ingredients necessary for predicting relatively high-temperature inelastic deformation behavior of engineering structures under time-varying temperature and load conditions and gives some examples. These examples illustrate the utility and acceptability of the computational methods identified and developed for prediting essential features of complex inelastic behaviors. Conditions and responses that can be encountered under nuclear reactor service conditions and invoked in the examples. (Auth.)

Propagation of 1-THz bandwidth electrical pulses on high Tc superconducting transmission lines

International Nuclear Information System (INIS)

Nuss, M.C.; Mankiewich, P.M.; Howard, R.E.; Harvey, T.E.; Brandle, C.D.; Straugh, B.L.; Smith, P.R.

1989-01-01

The new high temperature superconductors have triggered enormous interest not only because of the unique physics involved but also because of their technical potentials, such as the promise for propagation of extremely short electrical pulses. Superconducting band caps of --20TH z are predicted assuming BCS theory for the superconductor, making lossless propagation of electrical pulses as short as 50 fs possible. Despite microwave measurements at low frequencies of several gigahertz first studies at higher frequencies by Dykaar et al have shown distortion-free propagation of 100-GHz electrical pulses on YBa 2 Cu 3 O 3 (YBCO) lines for --5-mm propagation distance. Results were also reported for aluminum coplanar lines and a YBCO ground plane. The authors report on the propagation of 1-ps electrical pulses (1-THz bandwidth) on YBCO coplanar transmission lines defined on lanthanum gallate (LaGaO 3 ) as a substrate. On LaGaO 3 , YBCO grows highly oriented as on SrTiO 3 . However, unlike SrTiO 3 , LaGaO 3 has a much lower dielectric constant and small losses in the terahertz frequency range. Electrical pulses of --750-fs duration are generated in a radiation-damaged silicon-on-sapphire photoconductive switch integrated into a 20-μm coplanar stripline with 10-μm spacing and excited with 100-fs optical pulses from a CPM laser. An μ1-THz bandwidth electrical contact is made to the YBCO coplanar stripline defined on LaGaO 3 using a flip-chip geometry. They find that electrical pulses broaden only from 750 fs to 1 ps with little loss in amplitude on traveling through their flip-chip input and propagated electrical pulses are probed by electooptic sampling in two small LiTaO 3 crystals separated by 3 mm

Changes in the pattern of protein synthesis of prosopis chilensis induced by high temperatures

Energy Technology Data Exchange (ETDEWEB)

Medina, C.; Cardemil, L. (Univ. de Chile, Santiago (USA))

1989-04-01

Seeds of Prosopis chilensis, a leguminous tree from semi-arid regions of Central Chile, were germinated at temperatures of 25-30-35-40-45 and 50{degree}C. Germination was 100% between 25 and 40{degree}C, being faster at 35{degree}C. The best temperature for root growth was also 35{degree}C. There was not germination at 50{degree}C. However, seedlings coming from seeds germinated at 35{degree}C were capable of growing at higher temperatures of 45 and 50{degree}C. Pattern of protein synthesis was followed in roots incubated with {sup 35}S-methionine at increasing temperatures between 35 and 50{degree}C. SDS-PAGE of the proteins followed by fluorography shows that at temperatures above 35{degree}C, new protein bands appear while others become thicker. Most of the protein bands have decreased at 50{degree}C, with the exception of the new bands. A band of 70 KD, that is present at 35{degree}C, is more prominent at 50{degree}C. These proteins may have an important role in the thermotolerance of Prosopis chilensis to stressing temperatures.

Changes in the pattern of protein synthesis of prosopis chilensis induced by high temperatures

International Nuclear Information System (INIS)

Medina, C.; Cardemil, L.

1989-01-01

Seeds of Prosopis chilensis, a leguminous tree from semi-arid regions of Central Chile, were germinated at temperatures of 25-30-35-40-45 and 50 degree C. Germination was 100% between 25 and 40 degree C, being faster at 35 degree C. The best temperature for root growth was also 35 degree C. There was not germination at 50 degree C. However, seedlings coming from seeds germinated at 35 degree C were capable of growing at higher temperatures of 45 and 50 degree C. Pattern of protein synthesis was followed in roots incubated with 35 S-methionine at increasing temperatures between 35 and 50 degree C. SDS-PAGE of the proteins followed by fluorography shows that at temperatures above 35 degree C, new protein bands appear while others become thicker. Most of the protein bands have decreased at 50 degree C, with the exception of the new bands. A band of 70 KD, that is present at 35 degree C, is more prominent at 50 degree C. These proteins may have an important role in the thermotolerance of Prosopis chilensis to stressing temperatures

Excitation temperature of a solution plasma during nanoparticle synthesis

Energy Technology Data Exchange (ETDEWEB)

Saito, Genki, E-mail: genki@eng.hokudai.ac.jp; Nakasugi, Yuki; Akiyama, Tomohiro [Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo 060-8628 (Japan)

2014-08-28

Excitation temperature of a solution plasma was investigated by spectroscopic measurements to control the nanoparticle synthesis. In the experiments, the effects of edge shielding, applied voltage, and electrode material on the plasma were investigated. When the edge of the Ni electrode wire was shielded by a quartz glass tube, the plasma was uniformly generated together with metallic Ni nanoparticles. The emission spectrum of this electrode contained OH, H{sub α}, H{sub β}, Na, O, and Ni lines. Without an edge-shielded electrode, the continuous infrared radiation emitted at the edge created a high temperature on the electrode surface, producing oxidized coarse particles as a result. The excitation temperature was estimated from the Boltzmann plot. When the voltages were varied at the edge-shielded electrode with low average surface temperature by using different electrolyte concentrations, the excitation temperature of current-concentration spots increased with an increase in the voltage. The size of the Ni nanoparticles decreased at high excitation temperatures. Although the formation of nanoparticles via melting and solidification of the electrode surface has been considered in the past, vaporization of the electrode surface could occur at a high excitation temperature to produce small particles. Moreover, we studied the effects of electrodes of Ti, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Pd, Ag, W, Pt, Au, and various alloys of stainless steel and Cu–Ni alloys. With the exception of Ti, the excitation temperatures ranged from 3500 to 5500 K and the particle size depended on both the excitation temperature and electrode-material properties.

A Novel Strategy for Synthesis of Gold Nanoparticle Self Assemblies

NARCIS (Netherlands)

Verma, Jyoti; Lal, Sumit; van Veen, Henk A.; van Noorden, Cornelis J. F.

2014-01-01

Gold nanoparticle self assemblies are one-dimensional structures of gold nanoparticles. Gold nanoparticle self assemblies exhibit unique physical properties and find applications in the development of biosensors. Methodologies currently available for lab-scale and commercial synthesis of gold

Observational evidence for westward propagation of temperature inversions in the southeastern Arabian Sea

Digital Repository Service at National Institute of Oceanography (India)

Shankar, D.; Gopalakrishna, V.V.; Shenoi, S.S.C.; Durand, F.; Shetye, S.R.; Rajan, C.K.; Johnson, Z.; Araligidad, N.; Michael, G.S.

2002 to April 2003 show that temperature inversions occur off the southwest coast of India in early December with the arrival of low-salinity waters from the Bay of Bengal. The low-salinity waters and the inversions propagate westward along...

Covariant gauges at finite temperature

CERN Document Server

Landshoff, Peter V

1992-01-01

A prescription is presented for real-time finite-temperature perturbation theory in covariant gauges, in which only the two physical degrees of freedom of the gauge-field propagator acquire thermal parts. The propagators for the unphysical degrees of freedom of the gauge field, and for the Faddeev-Popov ghost field, are independent of temperature. This prescription is applied to the calculation of the one-loop gluon self-energy and the two-loop interaction pressure, and is found to be simpler to use than the conventional one.

Facile synthesis of graphene on dielectric surfaces using a two-temperature reactor CVD system

International Nuclear Information System (INIS)

Zhang, C; Man, B Y; Yang, C; Jiang, S Z; Liu, M; Chen, C S; Xu, S C; Sun, Z C; Gao, X G; Chen, X J

2013-01-01

Direct deposition of graphene on a dielectric substrate is demonstrated using a chemical vapor deposition system with a two-temperature reactor. The two-temperature reactor is utilized to offer sufficient, well-proportioned floating Cu atoms and to provide a temperature gradient for facile synthesis of graphene on dielectric surfaces. The evaporated Cu atoms catalyze the reaction in the presented method. C atoms and Cu atoms respectively act as the nuclei for forming graphene film in the low-temperature zone and the zones close to the high-temperature zones. A uniform and high-quality graphene film is formed in an atmosphere of sufficient and well-proportioned floating Cu atoms. Raman spectroscopy, scanning electron microscopy and atomic force microscopy confirm the presence of uniform and high-quality graphene. (paper)

Self-propagating solar light reduction of graphite oxide in water

Energy Technology Data Exchange (ETDEWEB)

Todorova, N.; Giannakopoulou, T.; Boukos, N.; Vermisoglou, E. [Institute of Nanoscience and Nanotechnology, NCSR “Demokritos”, 153 41 Attikis (Greece); Lekakou, C. [Division of Mechanical, Medical, and Aerospace Engineering, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford (United Kingdom); Trapalis, C., E-mail: c.trapalis@inn.demokritos.gr [Institute of Nanoscience and Nanotechnology, NCSR “Demokritos”, 153 41 Attikis (Greece)

2017-01-01

Highlights: • Graphite oxide was partially reduced by solar light irradiation in water media. • No addition of catalysts nor reductive agent were used for the reduction. • Specific capacitance increased stepwise with increase of irradiation time. • Self-propagating reduction of graphene oxide by solar light is suggested. - Abstract: Graphite Oxide (GtO) is commonly used as an intermediate material for preparation of graphene in the form of reduced graphene oxide (rGO). Being a semiconductor with tunable band gap rGO is often coupled with various photocatalysts to enhance their visible light activity. The behavior of such rGO-based composites could be affected after prolonged exposure to solar light. In the present work, the alteration of the GtO properties under solar light irradiation is investigated. Water dispersions of GtO manufactured by oxidation of natural graphite via Hummers method were irradiated into solar light simulator for different periods of time without addition of catalysts or reductive agent. The FT-IR analysis of the treated dispersions revealed gradual reduction of the GtO with the increase of the irradiation time. The XRD, FT-IR and XPS analyses of the obtained solid materials confirmed the transition of GtO to rGO under solar light irradiation. The reduction of the GtO was also manifested by the CV measurements that revealed stepwise increase of the specific capacitance connected with the restoration of the sp{sup 2} domains. Photothermal self-propagating reduction of graphene oxide in aqueous media under solar light irradiation is suggested as a possible mechanism. The self-photoreduction of GtO utilizing solar light provides a green, sustainable route towards preparation of reduced graphene oxide. However, the instability of the GtO and partially reduced GO under irradiation should be considered when choosing the field of its application.

Low temperature synthesis of carbon encapsulated Fe7S8 nanocrystals as high performance anode for lithium-ion batteries

International Nuclear Information System (INIS)

Liu, Boyang; Zhang, Fuhua; Wu, Qianlin; Wang, Junhua; Li, Wenge; Dong, Lihua; Yin, Yansheng

2015-01-01

A novel method is developed for low temperature synthesis of carbon encapsulated spherical Fe 7 S 8 nanocrystals with core–shell structure (Fe 7 S 8 @C) by the reaction of ferrocene with ammonium persulphate. The phase structure, morphology, specific surface area and composition of the nanocomposite are systematically characterized. It is found that the Fe 7 S 8 nanocrystals with a weight percent of 33.5% have a median size of 25.2 nm. The Fe 7 S 8 @C electrodes retain a reversible capacity of 815 and 539 mAh g −1 after 50 cycles at a current density of 200 and 2284 mA g −1 , respectively. The high capacity, good cycling behavior and rate capability of Fe 7 S 8 @C electrodes are attributed to the good protection and electrical conductivity of carbon shell. - Highlights: • Large scale and low temperature synthesis of Fe 7 S 8 @C with core–shell structure. • The Fe 7 S 8 @C electrodes retain a capacity of 815 mAh g −1 after 50 cycles at 200 mA g −1 . • The Fe 7 S 8 @C electrodes show good cycling behavior and rate capability

Multi-Temperature Zone, Droplet-based Microreactor for Increased Temperature Control in Nanoparticle Synthesis

KAUST Repository

Erdem, E. Yegân

2013-12-12

Microreactors are an emerging technology for the controlled synthesis of nanoparticles. The Multi-Temperature zone Microreactor (MTM) described in this work utilizes thermally isolated heated and cooled regions for the purpose of separating nucleation and growth processes as well as to provide a platform for a systematic study on the effect of reaction conditions on nanoparticle synthesis. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of self-powered wireless high temperature electrochemical sensor for in situ corrosion monitoring of coal-fired power plant.

Science.gov (United States)

Aung, Naing Naing; Crowe, Edward; Liu, Xingbo

2015-03-01

Reliable wireless high temperature electrochemical sensor technology is needed to provide in situ corrosion information for optimal predictive maintenance to ensure a high level of operational effectiveness under the harsh conditions present in coal-fired power generation systems. This research highlights the effectiveness of our novel high temperature electrochemical sensor for in situ coal ash hot corrosion monitoring in combination with the application of wireless communication and an energy harvesting thermoelectric generator (TEG). This self-powered sensor demonstrates the successful wireless transmission of both corrosion potential and corrosion current signals to a simulated control room environment. Copyright © 2014 ISA. All rights reserved.

Crack growth by micropore coalescence at high temperatures

International Nuclear Information System (INIS)

Beere, W.

1981-01-01

At high temperatures in the creep regime the stress distribution around a crack is different from the low temperature elastically generated distribution. The stress distribution ahead of the crack is calculated for a crack preceded by an array of growing cavities. The cavities maintain a displacement wedge ahead of the crack. When the displacement wedge is less than one-tenth the crack length the driving force for crack growth is similar to an all elastically loaded crack. When the deforming wedge exceeds the crack length the net section stress controls crack growth. An expression is derived for a crack growing by the growth and coalescence of cavities situated in the crack plane. It is predicted that at high temperatures above a critical stress intensity, the crack propagates in a brittle fashion. (author)

Nanostructured metal foams: synthesis and applications

Energy Technology Data Exchange (ETDEWEB)

Luther, Erik P [Los Alamos National Laboratory; Tappan, Bryce [Los Alamos National Laboratory; Mueller, Alex [Los Alamos National Laboratory; Mihaila, Bogdan [Los Alamos National Laboratory; Volz, Heather [Los Alamos National Laboratory; Cardenas, Andreas [Los Alamos National Laboratory; Papin, Pallas [Los Alamos National Laboratory; Veauthier, Jackie [Los Alamos National Laboratory; Stan, Marius [Los Alamos National Laboratory

2009-01-01

Fabrication of monolithic metallic nanoporous materials is difficult using conventional methodology. Here they report a relatively simple method of synthesizing monolithic, ultralow density, nanostructured metal foams utilizing self-propagating combustion synthesis of novel metal complexes containing high nitrogen energetic ligands. Nanostructured metal foams are formed in a post flame-front dynamic assembly with densities as low as 0.011 g/cc and surface areas as high as 270 m{sup 2}/g. They have produced metal foams via this method of titanium, iron, cobalt, nickel, zirconium, copper, palladium, silver, hafnium, platinum and gold. Microstructural features vary as a function of composition and process parameters. Applications for the metal foams are discussed including hydrogen absorption in palladium foams. A model for the sorption kinetics of hydrogen in the foams is presented.

Finding the energy source for self-propagating high-temperature synthesis production of NiTi shape memory alloy

Czech Academy of Sciences Publication Activity Database

Novák, P.; Školáková, A.; Pignol, D.; Průša, F.; Salvetr, P.; Kubatík, Tomáš František; Perriere, L.; Karlík, M.

2016-01-01

Roč. 181, September (2016), s. 295-300 ISSN 0254-0584 Institutional support: RVO:61389021 Keywords : NiTi * Shape memory alloys * Powder metallurgy * Microstructure Subject RIV: JG - Metallurgy Impact factor: 2.084, year: 2016 http://www.sciencedirect.com/science/article/pii/S025405841630476X

Synthesis and self-assembly of complex hollow materials

KAUST Repository

Zeng, Hua Chun

2011-01-01

aspects of this field of development. The synthetic methodologies can be broadly divided into three major categories: (i) template-assisted synthesis, (ii) self-assembly with primary building blocks, and (iii) induced matter relocations. In most cases

Laser beam trapping and propagation in cylindrical plasma columns

International Nuclear Information System (INIS)

Feit, M.D.; Fleck, J.A. Jr.

1976-01-01

An analysis of the scheme to heat magnetically confined plasma columns to kilovolt temperatures with a laser beam requires consideration of two propagation problems. The first question to be answered is whether stable beam trapping is possible. Since the laser beam creates its own density profile by heating the plasma, the propagation of the beam becomes a nonlinear phenomenon, but not necessarily a stable one. In addition, the electron density at a given time depends on the preceding history of both the medium and the laser pulse. A self-consistent time dependent treatment of the beam propagation and the medium hydrodynamics is consequently required to predict the behavior of the laser beam. Such calculations have been carried out and indicate that propagation of a laser beam in an initially uniform plasma can form a stable filament which alternately focuses and defocuses. An additional question that is discussed is whether diffractive losses associated with long propagation paths are significant

Dietary self-selection by broilers at normal and high temperature changes feed intake behavior, nutrient intake, and performance

NARCIS (Netherlands)

Syafwan, W.; Wermink, G.J.D.; Kwakkel, R.P.; Verstegen, M.W.A.

2012-01-01

Self-selection assumes that at high ambient temperature, birds are able to select a diet from different sources to minimize the heat load associated with the ingested nutrient metabolism. The objective was to test the hypothesis that young chickens are able to compose an adequate ration by adjusting

Synthesis and Self-Assembly of Block Copolymers Containing Temperature Sensitive and Degradable Chain Segments.

Science.gov (United States)

Gong, Hong-Liang; Lei, Lei; Shi, Shu-Xian; Xia, Yu-Zheng; Chen, Xiao-Nong

2018-05-01

In this work, polylactide-b-poly(N-isopropylacrylamide) were synthesized by the combination of controlled ring-opening polymerization and reversible addition fragmentation chain transfer polymerization. These block copolymers with molecular weight range from 7,900 to 12,000 g/mol and narrow polydispersity (≤1.19) can self-assemble into micelles (polylactide core, poly(N-isopropylacrylamide) shell) in water at certain temperature range, which have been evidenced by laser particle size analyzer proton nuclear magnetic resonance and transmission electron microscopy. Such micelles exhibit obvious thermo-responsive properties: (1) Poly(N-isopropylacrylamide) blocks collapse on the polylactide core as system temperature increase, leading to reduce of micelle size. (2) Micelles with short poly(N-isopropylacrylamide) blocks tend to aggregate together when temperature increased, which is resulted from the reduction of the system hydrophilicity and the decreased repulsive force between micelles.

Polarity-specific high-level information propagation in neural networks.

Science.gov (United States)

Lin, Yen-Nan; Chang, Po-Yen; Hsiao, Pao-Yueh; Lo, Chung-Chuan

2014-01-01

Analyzing the connectome of a nervous system provides valuable information about the functions of its subsystems. Although much has been learned about the architectures of neural networks in various organisms by applying analytical tools developed for general networks, two distinct and functionally important properties of neural networks are often overlooked. First, neural networks are endowed with polarity at the circuit level: Information enters a neural network at input neurons, propagates through interneurons, and leaves via output neurons. Second, many functions of nervous systems are implemented by signal propagation through high-level pathways involving multiple and often recurrent connections rather than by the shortest paths between nodes. In the present study, we analyzed two neural networks: the somatic nervous system of Caenorhabditis elegans (C. elegans) and the partial central complex network of Drosophila, in light of these properties. Specifically, we quantified high-level propagation in the vertical and horizontal directions: the former characterizes how signals propagate from specific input nodes to specific output nodes and the latter characterizes how a signal from a specific input node is shared by all output nodes. We found that the two neural networks are characterized by very efficient vertical and horizontal propagation. In comparison, classic small-world networks show a trade-off between vertical and horizontal propagation; increasing the rewiring probability improves the efficiency of horizontal propagation but worsens the efficiency of vertical propagation. Our result provides insights into how the complex functions of natural neural networks may arise from a design that allows them to efficiently transform and combine input signals.

Quench propagation in the SSC dipole magnets

International Nuclear Information System (INIS)

Lopez, G.; Snitchler, G.

1990-09-01

The effects of quench propagation are modeled in 40mm and 50mm diameter collider dipole magnet designs. A comparative study of the cold diode (passive) and quench heater (active) protection schemes will be presented. The SSCQ modeling program accurately simulates the axial quench velocity and uses phenomenological time delays for turn-to-turn transverse propagation. The axial quench velocity is field dependent and consequently, each conductor's quench profile is tracked separately. No symmetry constraints are employed and the distribution of the temperatures along the conductor differs from the adiabatic approximation. A single magnet has a wide margin of self protection which suggests that passive protection schemes must be considered. 6 refs., 3 figs., 1 tab

Highly reproducible polyol synthesis for silver nanocubes

Science.gov (United States)

Han, Hye Ji; Yu, Taekyung; Kim, Woo-Sik; Im, Sang Hyuk

2017-07-01

We could synthesize the Ag nanocubes highly reproducibly by conducting the polyol synthesis using HCl etchant in dark condition because the photodecomposition/photoreduction of AgCl nanoparticles formed at initial reaction stage were greatly depressed and consequently the selective self-nucleation of Ag single crystals and their selective growth reaction could be promoted. Whereas the reproducibility of the formation of Ag nanocubes were very poor when we synthesize the Ag nanocubes in light condition due to the photoreduction of AgCl to Ag.

SHS synthesis of Si-SiC composite powders using Mg and reactants from industrial waste

Science.gov (United States)

Chanadee, Tawat

2017-11-01

Si-SiC composite powders were synthesized by self-propagating high-temperature synthesis (SHS) using reactants of fly ash-based silica, sawdust-based activated carbon, and magnesium. Fly ash-based silica and sawdust-based activated carbon were prepared from coal mining fly ash and Para rubber-wood sawdust, respectively. The work investigated the effects of the synthesis atmosphere (air and Ar) on the phase and morphology of the SHS products. The SHS product was leached by a two-step acid leaching processes, to obtain the Si-SiC composite powder. The SHS product and SHS product after leaching were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectrometry. The results indicated that the SHS product synthesized in air consisted of Si, SiC, MgO, and intermediate phases (SiO2, Mg, Mg2SiO4, Mg2Si), whereas the SHS product synthesized in Ar consisted of Si, SiC, MgO and a little Mg2SiO4. The SiC content in the leached-SHS product was higher when Ar was used as the synthesis atmosphere. As well as affecting the purity, the synthesis atmospheres also affected the average crystalline sizes of the products. The crystalline size of the product synthesized in Ar was smaller than that of the product synthesized in air. All of the results showed that fly ash and sawdust could be effective waste-material reactants for the synthesis of Si-SiC composite powders.

Hydrazine-mediated construction of nanocrystal self-assembly materials.

Science.gov (United States)

Zhou, Ding; Liu, Min; Lin, Min; Bu, Xinyuan; Luo, Xintao; Zhang, Hao; Yang, Bai

2014-10-28

Self-assembly is the basic feature of supramolecular chemistry, which permits to integrate and enhance the functionalities of nano-objects. However, the conversion of self-assembled structures to practical materials is still laborious. In this work, on the basis of studying one-pot synthesis, spontaneous assembly, and in situ polymerization of aqueous semiconductor nanocrystals (NCs), NC self-assembly materials are produced and applied to design high performance white light-emitting diode (WLED). In producing self-assembly materials, the additive hydrazine (N2H4) is curial, which acts as the promoter to achieve room-temperature synthesis of aqueous NCs by favoring a reaction-controlled growth, as the polyelectrolyte to weaken inter-NC electrostatic repulsion and therewith facilitate the one-dimensional self-assembly, and in particular as the bifunctional monomers to polymerize with mercapto carboxylic acid-modified NCs via in situ amidation reaction. This strategy is versatile for mercapto carboxylic acid-modified aqueous NCs, for example CdS, CdSe, CdTe, CdSe(x)Te(1-x), and Cd(y)Hg(1-y)Te. Because of the multisite modification with carboxyl, the NCs act as macromonomers, thus producing cross-linked self-assembly materials with excellent thermal, solvent, and photostability. The assembled NCs preserve strong luminescence and avoid unpredictable fluorescent resonance energy transfer, the main problem in design WLED from multiple NC components. These advantages allow the fabrication of NC-based WLED with high color rendering index (86), high luminous efficacy (41 lm/W), and controllable color temperature.

Thermal stability of Al-Cu-Fe quasicrystals prepared by SHS method

Directory of Open Access Journals (Sweden)

Pavel Novak

2013-02-01

Full Text Available Quasicrystal-containing materials are usually prepared by rapid solidification of the melt (e.g. by melt spinning or mechanical alloying. In this work, the method using exothermic reactions between compressed metallic powders called SHS (Self-propagating High-temperature Synthesis was tested. The microstructure and phase composition of the product was described in dependence on cooling regime from the reaction temperature. Thermal stability of prepared Al-Cu-Fe quasicrystals was studied by annealing at the temperatures of 300 and 500 °C.

THERMAL STABILITY OF Al-Cu-Fe QUASICRYSTALS PREPARED BY SHS METHOD

Directory of Open Access Journals (Sweden)

Pavel Novák

2013-04-01

Full Text Available Quasicrystal-containing materials are usually prepared by rapid solidification of the melt (e.g. by melt spinning or mechanical alloying. In this work, the method using exothermic reactions between compressed metallic powders called SHS (Self-propagating High-temperature Synthesis was tested. The microstructure and phase composition of the product was described in dependence on cooling regime from the reaction temperature. Thermal stability of prepared Al-Cu-Fe quasicrystals was studied by annealing at the temperatures of 300 and 500 °C.

Synthesis of high-temperature viscosity stabilizer used in drilling fluid

Science.gov (United States)

Zhang, Yanna; Luo, Huaidong; Shi, Libao; Huang, Hongjun

2018-02-01

Abstract For a well performance drilling fluid, when it operates in deep wells under high temperature, the most important property required is the thermal stability. The drilling fluid properties under high temperature can be controlled by proper selection of viscosity stabilizer, which can capture oxygen to protect polymer agent in the drilling fluid. In this paper a viscosity stabilizer PB-854 is described, which was synthesized by 4-phenoxybutyl bromide, paraformaldehyde, and phloroglucinol using etherification method and condensation reaction. We studied the effect of catalyst dosage, temperature, time, and stirring rate on the synthetic yield. Under this condition: molar ratio of 2-tert-Butylphenol, paraformaldehyde and phloroglucinol of 2:1:2.5, reacting temperature of 100 °C, stirring rate of 100 r min-1, and mass content of catalyst of 15 %, char yield of 5-bromine-3-tert-butyl salicylaldehyde reached 86 %. Under this condition: molar ratio of 5-bromine-3-tert-butyl salicylaldehyde and phloroglucinol of 4, reacting temperature of 60 °C, reacting time of 30 min, volume content of sulphuric acid of 80 %, char yield of the target product viscosity stabilizer PB-854 is 86%. Finally, in this paper, infrared spectroscopy is adopted to analyse the structure of the synthetic product PB-854.The improvement in the stability of drilling fluid was further shown after adding the viscosity stabilizer in the common polymer drilling fluid under high temperature conditions of 120 °C ˜ 180 °C. The results show significant change in terms of fluid stability in the presence of this new stabilizer as it provides better stability.

Crack propagation studies and bond coat properties in thermal

Indian Academy of Sciences (India)

High threshold load at the interface between the ceramic layer and the bond coat was required to propagate the crack further into the bond coat. Once the threshold load was surpassed the crack propagated into the brittle bond coat without an appreciable increase in the load. At temperatures of 800°C the crack propagated ...

Facile and green synthesis of highly stable L-cysteine functionalized copper nanoparticles

Science.gov (United States)

Kumar, Nikhil; Upadhyay, Lata Sheo Bachan

2016-11-01

A simple eco-friendly method for L-cysteine capped copper nanoparticles (CCNPs) synthesis in aqueous solution has been developed. Glucose and L-cysteine were used as reducing agent and capping/functionalizing agent, respectively. Different parameters such as capping agent concentration, pH, reaction temperature, and reducing agent concentration were optimized during the synthesis. The L-cysteine capped copper nanoparticle were characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Particle size and zeta potential analyser, and high resolution transmission electron microscopy. Spherical shaped cysteine functionalized/capped copper nanoparticles with an average size of 40 nm were found to be highly stable at room temperature (RT) for a period of 1 month

Low temperature synthesis of InP nanocrystals

International Nuclear Information System (INIS)

Ung Thi Dieu Thuy; Tran Thi Thuong Huyen; Nguyen Quang Liem; Reiss, Peter

2008-01-01

We present a simple method for the chemical synthesis of InP nanocrystals, which comprises several advantages: (i) the use of simple reagents, namely InCl 3 .4H 2 O and yellow P as the In and P precursors, respectively, and NaBH 4 as the reducing agent in a mixed solvent of ethanol and toluene; (ii) a short reaction time (1-5 h) and low temperature (<75 deg. C); (iii) a high reaction yield approaching 100%. InP NCs in the zinc-blende structure have been obtained as confirmed by powder X-ray diffraction and Raman scattering measurements. Their mean size of 4 nm has been determined by transmission electron microscopy, Raman scattering and absorption spectroscopy

Magnetic dipole self-organization of charge carriers in high-temperature superconductors and kinetics of phase transformation

CERN Document Server

Voronov, A V; Shuvalov, V V

2001-01-01

The phenomenological model, describing the magnetic dipole self-organization of charge carriers (formation of so-called stripe-structures and energy gap in the states spectrum), is designed for interpreting the data on the nonstationary nonlinear spectroscopy of the high-temperature superconductors. It is shown that after fast heating of the superconducting sample the kinetics of the subsequent phase transition depends on the initial temperature T. The destruction of the stripe-structures at low overheating T* < T < T sub m approx = (1.4-1.5)T*, whereby T sub c and T* approx = T sub c are the temperatures of transition into the superconducting state and formation of the stripe-structures occurs slowly (the times above 10 sup - sup 9 s) in spite of practically instantaneous disappearance of the superconductivity

Antagonistic effects of high and low temperature pretreatments on the germination and pregermination ethylene synthesis of lettuce seeds.

Science.gov (United States)

Burdett, A N

1972-08-01

Red light-induced germination of Grand Rapids lettuce seeds (Lactuca sativa L.) incubated at 20 C was inhibited if the seeds were first imbibed at 30 C for 36 hours. This effect was counteracted by exogenous ethylene and associated with a reduction in the rate at which the seeds produced ethylene throughout the pregermination period. A chilling treatment reversed the effect of a prior imbibition at 30 C on both germination and ethylene production. The possibility that the pretreatments influence germination through their effects on ethylene production is discussed.Other evidence presented indicates that the inability of seeds to germinate at supraoptimal temperature is not due either to a rapid loss of far red-absorbing phytochrome or to an inadequate capacity for ethylene synthesis. It was also shown that a chilling treatment potentiated germination at high temperature without affecting the ethylene synthetic capacity of the seeds.

Wave propagation through an electron cyclotron resonance layer

International Nuclear Information System (INIS)

Westerhof, E.

1997-01-01

The propagation of a wave beam through an electron cyclotron resonance layer is analysed in two-dimensional slab geometry in order to assess the deviation from cold plasma propagation due to resonant, warm plasma changes in wave dispersion. For quasi-perpendicular propagation, N ' 'parallel to'' ≅ v t /c, an O-mode beam is shown to exhibit a strong wiggle in the trajectory of the centre of the beam when passing through the fundamental electron cyclotron resonance. The effects are largest for low temperatures and close to perpendicular propagation. Predictions from standard dielectric wave energy fluxes are inconsistent with the trajectory of the beam. Qualitatively identical results are obtained for the X-mode second harmonic. In contrast, the X-mode at the fundamental resonance shows significant deviations form cold plasma propagation only for strongly oblique propagation and/or high temperatures. On the basis of the obtained results a practical suggestion is made for ray tracing near electron cyclotron resonance. (Author)

Robust Temperature Control of a Thermoelectric Cooler via μ -Synthesis

Science.gov (United States)

Kürkçü, Burak; Kasnakoğlu, Coşku

2018-02-01

In this work robust temperature control of a thermoelectric cooler (TEC) via μ -synthesis is studied. An uncertain dynamical model for the TEC that is suitable for robust control methods is derived. The model captures variations in operating point due to current, load and temperature changes. A temperature controller is designed utilizing μ -synthesis, a powerful method guaranteeing robust stability and performance. For comparison two well-known control methods, namely proportional-integral-derivative (PID) and internal model control (IMC), are also realized to benchmark the proposed approach. It is observed that the stability and performance on the nominal model are satisfactory for all cases. On the other hand, under perturbations the responses of PID and IMC deteriorate and even become unstable. In contrast, the μ -synthesis controller succeeds in keeping system stability and achieving good performance under all perturbations within the operating range, while at the same time providing good disturbance rejection.

Ignition and wave processes in combustion of solids

CERN Document Server

Rubtsov, Nickolai M; Alymov, Michail I

2017-01-01

This book focuses on the application of classical combustion theory to ignition and flame propagation in solid-solid and gas-solid systems. It presents experimental investigations in the areas of local ignition, filtration combustion, self-propagating high temperature synthesis and nanopowders protection. The authors highlight analytical formulas used in different areas of combustion in solids and propose an approach based on classical combustion theory. The book attempts to analyze the basic approaches to understanding of solid-solid and solid - gas combustion presented in contemporary literature in a unified approach based on classical combustion theory. .

Solution-phase synthesis of nanomaterials at low temperature

Science.gov (United States)

Zhu, Yongchun; Qian, Yitai

2009-01-01

This paper reviews the solution-phase synthesis of nanoparticles via some routes at low temperatures, such as room temperature route, wave-assisted synthesis (γ-irradiation route and sonochemical route), directly heating at low temperatures, and hydrothermal/solvothermal methods. A number of strategies were developed to control the shape, the size, as well as the dispersion of nanostructures. Using diethylamine or n-butylamine as solvent, semiconductor nanorods were yielded. By the hydrothermal treatment of amorphous colloids, Bi2S3 nanorods and Se nanowires were obtained. CdS nanowires were prepared in the presence of polyacrylamide. ZnS nanowires were obtained using liquid crystal. The polymer poly (vinyl acetate) tubule acted as both nanoreactor and template for the CdSe nanowire growth. Assisted by the surfactant of sodium dodecyl benzenesulfonate (SDBS), nickel nanobelts were synthesized. In addition, Ag nanowires, Te nanotubes and ZnO nanorod arrays could be prepared without adding any additives or templates.

Synchrotron diffraction studies of TiC/FeTi cermets obtained by SHS

International Nuclear Information System (INIS)

Contreras, L.; Turrillas, X.; Mas-Guindal, M.J.; Vaughan, G.B.M.; Kvick, A.; Rodriguez, M.A.

2005-01-01

TiC/FeTi composites have been obtained in situ by Self-propagating High-temperature Synthesis (SHS) of an intimate mixture of compacted powders of elemental carbon, titanium and iron. The reaction has been followed in real time by X-ray diffraction at the ESRF. The mechanism of the reaction is discussed in terms of the formation of a liquid phase corresponding to the eutectic of the Fe/Ti system prior to the TiC synthesis. Temperatures of reaction have been estimated by correlating thermal expansion coefficients with diffraction peaks shifts. The microstructures obtained by this method, suitable for cutting tools and wear resistant applications, are presented

Laser beam propagation in nematic liquid crystals at the temperature close to the nematicisotropic critical point.

Science.gov (United States)

Chen, Yu-Jen; Lin, Yu-Sung; Jiang, I-Min; Tsai, Ming-Shan

2008-03-17

This study investigates the optical nonlinearity of beam propagation in homogeneously aligned nematic liquid crystal (NLC) cells at a temperature close to the nematic-isotropic temperature (TNI). The undulate propagation mode with convergent and divergent loops appearing alternately is reported and the thermally enhanced optical reorientation nonlinearity at the focus is described. The optically induced phase transition exists along the pump beam direction. With the application of the conscopic technique, the arrangements of LC at the focus are proposed in this study. Results of this study demonstrate that the evolution of the LC configuration was affected by the pump beam based on the analysis of conoscopic patterns.

Self-assembled GaInNAs/GaAsN quantum dot lasers: solid source molecular beam epitaxy growth and high-temperature operation

Directory of Open Access Journals (Sweden)

Yoon SF

2006-01-01

Full Text Available AbstractSelf-assembled GaInNAs quantum dots (QDs were grown on GaAs (001 substrate using solid-source molecular-beam epitaxy (SSMBE equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were extensively investigated using atomic-force microscopy (AFM, photoluminescence (PL, and transmission electron microscopy (TEM measurements. Self-assembled GaInNAs/GaAsN single layer QD lasers grown using SSMBE have been fabricated and characterized. The laser worked under continuous wave (CW operation at room temperature (RT with emission wavelength of 1175.86 nm. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm2from a GaInNAs QD laser (50 × 1,700 µm2 at 10 °C. High-temperature operation up to 65 °C was demonstrated from an unbonded GaInNAs QD laser (50 × 1,060 µm2, with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C.

Multi-Temperature Zone, Droplet-based Microreactor for Increased Temperature Control in Nanoparticle Synthesis

KAUST Repository

Erdem, E. Yegâ n; Cheng, Jim C.; Doyle, Fiona M.; Pisano, Albert P.

2013-01-01

Microreactors are an emerging technology for the controlled synthesis of nanoparticles. The Multi-Temperature zone Microreactor (MTM) described in this work utilizes thermally isolated heated and cooled regions for the purpose of separating

High intensity pulse self-compression in short hollow core capillaries

OpenAIRE

Butcher, Thomas J.; Anderson, Patrick N.; Horak, Peter; Frey, Jeremy G.; Brocklesby, William S.

2011-01-01

The drive for shorter pulses for use in techniques such as high harmonic generation and laser wakefield acceleration requires continual improvement in post-laser pulse compression techniques. The two most commonly used methods of pulse compression for high intensity pulses are hollow capillary compression via self-phase modulation (SPM) [1] and the more recently developed filamentation [2]. Both of these methods can require propagation distances of 1-3 m to achieve spectral broadening and com...

Organic titanates: a model for activating rapid room-temperature synthesis of shape-controlled CsPbBr3 nanocrystals and their derivatives.

Science.gov (United States)

Fang, Shaofan; Li, Guangshe; Li, Huixia; Lu, Yantong; Li, Liping

2018-04-12

The application of lead halide perovskite nanocrystals is challenged by the lack of strategies in rapid room-temperature synthesis with controlled morphologies. Here, we report on an initial study of adopting organic titanates as a model activator that promotes rapid room-temperature synthesis of shape-controlled, highly luminescent CsPbBr3 nanocrystals and their derivatives.

Room temperature synthesis of biodiesel using sulfonated ...

Science.gov (United States)

Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature. Prepared for submission to Royal Society of Chemistry (RSC) journal, Green Chemistry as a communication.

Low-temperature synthesis and characterization of helical carbon fibers by one-step chemical vapour deposition

Energy Technology Data Exchange (ETDEWEB)

Jin, Yongzhong [Department of Materials and Chemistry Engineering, Sichuan University of Science and Engineering, 643000 Zigong, Sichuan (China); Chen, Jian, E-mail: wuhangzs@163.com [Department of Materials and Chemistry Engineering, Sichuan University of Science and Engineering, 643000 Zigong, Sichuan (China); Fu, Qingshan [Department of Materials and Chemistry Engineering, Sichuan University of Science and Engineering, 643000 Zigong, Sichuan (China); Li, Binghong [China Rubber Group Carbon Black Industry Research and Design Institute, 643000 Zigong, Sichuan (China); Zhang, Huazhi; Gong, Yong [Department of Materials and Chemistry Engineering, Sichuan University of Science and Engineering, 643000 Zigong, Sichuan (China)

2015-01-01

Graphical abstract: - Highlights: • HCNFs were synthesized by one-step CVD using cupric tartrate as a catalyst at temperature below 500 °C. • The synthesis of HCNFs is highly temperature-dependent at the synthesis temperature of 280–480 °C. • The addition of HCNFs makes a noticeable contribution to the reinforcement of NR/CB system. - Abstract: Helical carbon fibers (HCNFs) were synthesized by one-step chemical vapour deposition using cupric tartrate as a catalyst at temperature below 500 °C. The bound rubber of natural rubber (NR)/HCNFs were also prepared in this study. The results of thermogravimetry–differential scanning calorimetry (TG/DSC) for cupric tartrate nanoparticles show that the transformation of C{sub 4}H{sub 4}CuO{sub 6} → Cu reaction occurs at ∼250–310 °C. The characterization of scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectrum for the synthesized products confirms that the synthesis of HCNFs is highly temperature-dependent. The straight fibers with the fiber diameter of 100–400 nm are obtained at 280 °C and HCNFs can be synthesized at higher temperature, with the coil diameter of 0.5–1 μm and fiber diameter of 100–200 nm at 380 °C, and the coil diameter of ∼100 nm and fiber diameter of ∼80 nm at 480 °C. The maximum of the bound-rubber content (37%) can be obtained with the addition of 100 wt.% HCNFs in NR, which indicates that the coiled configuration of HCNFs makes a noticeable contribution to the reinforcement of NR/CB system.

Low-temperature synthesis and characterization of helical carbon fibers by one-step chemical vapour deposition

International Nuclear Information System (INIS)

Jin, Yongzhong; Chen, Jian; Fu, Qingshan; Li, Binghong; Zhang, Huazhi; Gong, Yong

2015-01-01

Graphical abstract: - Highlights: • HCNFs were synthesized by one-step CVD using cupric tartrate as a catalyst at temperature below 500 °C. • The synthesis of HCNFs is highly temperature-dependent at the synthesis temperature of 280–480 °C. • The addition of HCNFs makes a noticeable contribution to the reinforcement of NR/CB system. - Abstract: Helical carbon fibers (HCNFs) were synthesized by one-step chemical vapour deposition using cupric tartrate as a catalyst at temperature below 500 °C. The bound rubber of natural rubber (NR)/HCNFs were also prepared in this study. The results of thermogravimetry–differential scanning calorimetry (TG/DSC) for cupric tartrate nanoparticles show that the transformation of C 4 H 4 CuO 6 → Cu reaction occurs at ∼250–310 °C. The characterization of scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectrum for the synthesized products confirms that the synthesis of HCNFs is highly temperature-dependent. The straight fibers with the fiber diameter of 100–400 nm are obtained at 280 °C and HCNFs can be synthesized at higher temperature, with the coil diameter of 0.5–1 μm and fiber diameter of 100–200 nm at 380 °C, and the coil diameter of ∼100 nm and fiber diameter of ∼80 nm at 480 °C. The maximum of the bound-rubber content (37%) can be obtained with the addition of 100 wt.% HCNFs in NR, which indicates that the coiled configuration of HCNFs makes a noticeable contribution to the reinforcement of NR/CB system

Evaluation of the real parts of fermion and boson propagators using dispersion relations

International Nuclear Information System (INIS)

Davies, K.T.R.; Davies, R.W.

1991-01-01

General methods are developed for efficiently evaluating principal-value integrals containing fermion and boson causal propagators. These methods are particularly applicable to integrals containing step functions which appear in the zero temperature limit of infinite nuclear matter. Examples are given for the Green functions that occur in the solution of Dyson's equations, with the inclusion of nucleon-delta-mesonic interactions. It is shown how to discretize in order to evaluate numerically the real parts of the propagators. If the real and purely imaginary self-energies of a propagator obey a dispersion relation, then the propagator itself satisfies such a relation. Finally, we discuss the two types of resonances occurring in the pion Green function. (orig.)

One-step synthesis of dimethyl ether from the gas mixture containing CO2 with high space velocity

International Nuclear Information System (INIS)

Chen, Wei-Hsin; Lin, Bo-Jhih; Lee, How-Ming; Huang, Men-Han

2012-01-01

Highlights: ► A bifunctional catalyst for DME synthesis is prepared using a coprecipitation method. ► The DME synthesis from syngas at a high space velocity of is investigated. ► The reaction is dominated by chemical kinetics at lower reaction temperatures. ► Thermodynamic equilibrium governs the reaction at higher temperatures. ► 0.2 g of ZSM5 is sufficient to be blended with 1 g of the catalyst for DME synthesis. -- Abstract: Dimethyl ether (DME) has been considered as a potential hydrogen carrier used in fuel cells; it can also be consumed as a diesel substitute or chemicals. To develop the technique of DME synthesis, a bifunctional Cu–ZnO–Al 2 O 3 /ZSM5 catalyst is prepared using a coprecipitation method. The reaction characteristics of DME synthesis from syngas at a high space velocity of 15,000 mL (g cat h) −1 are investigated and the effects of reaction temperature, pressure, CO 2 concentration and ZSM5 amount on the synthesis are taken into account. The results suggest that an increase in CO 2 concentration in the feed gas substantially decreases the DME formation. The optimum reaction temperature always occurs at 225 °C, regardless of what the pressure is. It is thus recognized that the DME synthesis is governed by two different mechanisms when the reaction temperature varies. At lower reaction temperatures ( 225 °C). For the CO 2 content of 5 vol.% and the pressure of 40 atm, the maximum DME yield is 1.89 g (g cat h) −1 . It is also found that 0.2 g of ZSM5 is sufficient to be blended with 1 g of the catalyst for DME synthesis.

High-temperature flaw assessment procedure: A state-of-the-art survey

International Nuclear Information System (INIS)

Ruggles, M.B.; Takahashi, Y.

1989-05-01

High-temperature crack growth under cyclic, static, and combined loading is received with an emphasis on fracture mechanics aspects. Experimental studies of the effects of loading history, microstructure, temperature, and environment on crack growth behavior are described and interpreted. The experimental evidence is used to examine crack growth parameters and theoretical models for fatigue, creep, and creep-fatigue crack propagation at elevated temperatures. The limitations of both elastic and elastic-plastic fracture mechanics for high-temperature subcritical crack growth are assessed. Existing techniques for modeling critical crack growth/ligament instability failure are also presented. Related topics of defect modeling and engineering flaw assessment procedures, nondestructive evaluation methods, and probabilistic failure analysis are briefly discussed. 142 refs., 33 figs

Synthesis and Characterization of Nanostructured ZnO Thick Film Gas Sensors Prepared by Screen Printing Method

Directory of Open Access Journals (Sweden)

R. Y. BORSE

2010-12-01

Full Text Available Nanosized ZnO was prepared by self propagating solution combustion synthesis method. The synthesized ZnO thick films were deposited on alumina substrate by using standard screen printing technique and fired at 700 0C. The films were characterized by X-ray diffractometer (XRD, Scanning Electron Microscopy (SEM and energy dispersive analysis of X-ray (EDAX. The electrical behaviors of ZnO thick films were investigated. From XRD spectra it is revealed that ZnO films are polycrystalline in nature. The average grain size of 87.44 nm has been estimated for the film fired at 700 0C using Scherrer’s formula. EDAX clearly shows the peaks corresponding to Zn and O element which confirms the successful growth of ZnO films. Gas sensing study for these samples shows high sensitivity and selectivity towards NO2 at all operating temperatures. The resistivity, TCR and activation energy of the ZnO films have been evaluated and discussed.

Kinetics of the ammonia synthesis at low temperatures. II. Sources of discrepancies

International Nuclear Information System (INIS)

Kuchaev, V.L.; Shapatina, E.N.; Temkin, M.I.

1988-01-01

A method is developed for calculating the degree of conversion during the synthesis of ammonia in a continuous flow, tubular reactor, taking longitudinal diffusion into account. Such a calculation shows that the available data in the literature on the rate of ammonia synthesis at low temperatures in a tubular reactor agree with the rate equation based on the idea that the predominant intermediate substance is adsorbed ammonia (and not imide). The seeming conflict between this idea and the ratio of the rates of synthesis of ammonia and deuteroammonia at low temperatures is explained

Nonlinear propagation of ultrashort laser pulses in transparent media

International Nuclear Information System (INIS)

Vincotte, A.

2006-10-01

We present different aspects of the propagation of ultrashort laser pulses in transparent media. First, we derive the propagation equations starting from the Maxwell equations. We remind of the main physical phenomena undergone by ultrashort and powerful laser pulses. First self-focusing occurs, owing to the Kerr response of the medium. This self-focusing is stopped by plasma generation from the laser-induced ionization of the ambient atoms. The propagation of the wave generates a super-continuum through self-phase modulation. We recall the main results concerning the simple and multiple filamentation of an intense wave, induced by the beam inhomogeneities and which take place as soon as the beam power is above critical. In a second part, we investigate the influence of high-order nonlinearities on the propagation of the beam and especially on its filamentation pattern. To control the multi-filamentation process, we investigate in a third part the propagation of beams with special designs, namely; Gradient- and vortex-shaped beams. We justify the robustness of this latter kind of optical objects. Eventually, we investigate multi-filamentation patterns of femtosecond pulses in a fog tube and in cells of ethanol doped with coumarin, for different beam configurations. (author)

The measurement for level of marine high-temperature and high-pressure vessels

International Nuclear Information System (INIS)

Lin Jie.

1986-01-01

The various error factors in measurement for level of marine high-temperature and high-pressure vessels are anslysed. The measuring method of error self compensation and its simplification for land use are shown

Three-dimensional propagation and absorption of high frequency Gaussian beams in magnetoactive plasmas

International Nuclear Information System (INIS)

Nowak, S.; Orefice, A.

1994-01-01

In today's high frequency systems employed for plasma diagnostics, power heating, and current drive the behavior of the wave beams is appreciably affected by the self-diffraction phenomena due to their narrow collimation. In the present article the three-dimensional propagation of Gaussian beams in inhomogeneous and anisotropic media is analyzed, starting from a properly formulated dispersion relation. Particular attention is paid, in the case of electromagnetic electron cyclotron (EC) waves, to the toroidal geometry characterizing tokamak plasmas, to the power density evolution on the advancing wave fronts, and to the absorption features occurring when a beam crosses an EC resonant layer

Low temperature synthesis of InP nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Ung Thi Dieu Thuy [Institute of Materials Science (IMS), Vietnamese Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Tran Thi Thuong Huyen [Institute of Materials Science (IMS), Vietnamese Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); National University of Thai Nguyen, 2 Luong Ngoc Quyen, Thai Nguyen (Viet Nam); Nguyen Quang Liem [Institute of Materials Science (IMS), Vietnamese Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam)], E-mail: liemnq@ims.vast.ac.vn; Reiss, Peter [DSM/INAC/SPrAM, UMR 5819 CEA-CNRS-Universite Joseph Fourier/LEMOH, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France)

2008-12-20

We present a simple method for the chemical synthesis of InP nanocrystals, which comprises several advantages: (i) the use of simple reagents, namely InCl{sub 3}.4H{sub 2}O and yellow P as the In and P precursors, respectively, and NaBH{sub 4} as the reducing agent in a mixed solvent of ethanol and toluene; (ii) a short reaction time (1-5 h) and low temperature (<75 deg. C); (iii) a high reaction yield approaching 100%. InP NCs in the zinc-blende structure have been obtained as confirmed by powder X-ray diffraction and Raman scattering measurements. Their mean size of 4 nm has been determined by transmission electron microscopy, Raman scattering and absorption spectroscopy.

High Temperature coatings based on β-NiAI

Energy Technology Data Exchange (ETDEWEB)

Severs, Kevin [Iowa State Univ., Ames, IA (United States)

2012-01-01

High temperature alloys are reviewed, focusing on current superalloys and their coatings. The synthesis, characerization, and oxidation performance of a NiAl–TiB₂ composite are explained. A novel coating process for Mo–Ni–Al alloys for improved oxidation performance is examined. The cyclic oxidation performance of coated and uncoated Mo–Ni–Al alloys is discussed.

Stress-corrosion cracking of Inconel alloy 600 in high-temperature water: an update

International Nuclear Information System (INIS)

Bandy, R.; van Rooyen, D.

1983-01-01

Inconel 600 has been tested in high-temperature aqueous media (without oxygen) in several tests. Data are presented to relate failure times to periods of crack initiation and propagation. Quantitative relationships have been developed from tests in which variations were made in temperature, applied load, strain rate, water chemistry, and the condition of the test alloy

High speed photography for studying the shock wave propagation at high Mach numbers through a reflection nozzle

International Nuclear Information System (INIS)

Zaytsev, S.G.; Lazareva, E.V.; Mikhailova, A.V.; Nikolaev-Kozlov, V.L.; Chebotareva, E.I.

1979-01-01

Propagation of intensive shock waves with a temperature of about 1 eV has been studied in a two-dimensional reflection nozzle mounted at the exit of a shock tube. The Toepler technique has been involved along with the interference scheme with a laser light source allowing the multiple-frame recording to be done. Density distribution in the nozzle as well as the wave pattern occurring at the shock propagation are presented. (author)

Nanofluid based on self-nanoencapsulated metal/metal alloys phase change materials with tuneable crystallisation temperature.

Science.gov (United States)

Navarrete, Nuria; Gimeno-Furio, Alexandra; Mondragon, Rosa; Hernandez, Leonor; Cabedo, Luis; Cordoncillo, Eloisa; Julia, J Enrique

2017-12-14

Nanofluids using nanoencapsulated Phase Change Materials (nePCM) allow increments in both the thermal conductivity and heat capacity of the base fluid. Incremented heat capacity is produced by the melting enthalpy of the nanoparticles core. In this work two important advances in this nanofluid type are proposed and experimentally tested. It is firstly shown that metal and metal alloy nanoparticles can be used as self-encapsulated nePCM using the metal oxide layer that forms naturally in most commercial synthesis processes as encapsulation. In line with this, Sn/SnOx nanoparticles morphology, size and thermal properties were studied by testing the suitability and performance of encapsulation at high temperatures and thermal cycling using a commercial thermal oil (Therminol 66) as the base fluid. Secondly, a mechanism to control the supercooling effect of this nePCM type based on non-eutectic alloys was developed.

Propagation environments [Chapter 4

Science.gov (United States)

Douglass F. Jacobs; Thomas D. Landis; Tara Luna

2009-01-01

An understanding of all factors influencing plant growth in a nursery environment is needed for the successful growth and production of high-quality container plants. Propagation structures modify the atmospheric conditions of temperature, light, and relative humidity. Native plant nurseries are different from typical horticultural nurseries because plants must be...

Optical evidence for a self-propagating molten buried layer in germanium films upon nanosecond laser irradiation

International Nuclear Information System (INIS)

Vega, F.; Chaoui, N.; Solis, J.; Armengol, J.; Afonso, C.N.

2005-01-01

This work describes the phase transitions occurring at the film-substrate interface of amorphous germanium films upon nanosecond laser-pulse-induced melting of the surface. Films with thickness ranging from 50 to 130 nm deposited on glass substrates were studied. Real-time reflectivity measurements with subnanosecond time resolution performed both at the air-film and film-substrate interfaces were used to obtain both surface and in-depth information of the process. In the thicker films (≥80 nm), the enthalpy released upon solidification of a shallow molten surface layer induces a thin buried liquid layer that self-propagates in-depth towards the film-substrate interface. This buried liquid layer propagates with a threshold velocity of 16±1 m/s and causes, eventually, melting at the film-substrate interface. In the thinnest film (50 nm) there is no evidence of the formation of the buried layer. The presence of the self-propagating buried layer for films thicker than 80 nm at low and intermediate laser fluences is discussed in terms of the thermal gradient in the primary melt front and the heat released upon solidification

Synthesis and Characterization of High Aluminum Zeolite X from Technical Grade Materials

Directory of Open Access Journals (Sweden)

Seyed Kamal Masoudian

2013-06-01

Full Text Available Zeolites are widely used as ion exchangers, adsorbents, separation materials and catalyst due to their well-tailored and highly-reproducible structures; therefore, the synthesis of zeolite from low grade resources can be interested. In the present work, high aluminum zeolite X was prepared from mixing technical grade sodium aluminate and sodium silicate solutions at temperatures between 70°C and 100°C. The synthesized zeolite X was characterized by SEM and X-ray methods according to ASTM standard procedures. The results showed that aging of the synthesis medium at the room temperature considerably increased the selectivity of zeolite X formation. On the other hand, high temperature of reaction mixture during crystallization formed zeolite A in the product; therefore, it decreased the purity of zeolite X. In addition, it was found that increasing H2O/Na2O and decreasing Na2O/SiO2 molar ratios in the reaction mixture resulted product with higher purity. © 2013 BCREC UNDIP. All rights reservedReceived: 7th January 2013; Revised: 7th April 2013; Accepted: 19th April 2013[How to Cite: Masoudian, S. K., Sadighi, S., Abbasi, A. (2013. Synthesis and Characterization of High Alu-minum Zeolite X from Technical Grade Materials. Bulletin of Chemical Reaction Engineering & Catalysis, 8 (1: 54-60. (doi:10.9767/bcrec.8.1.4321.54-60][Permalink/DOI: http://dx.doi.org/10.9767/bcrec.8.1.4321.54-60] | View in  |

Graphene synthesis on SiC: Reduced graphitization temperature by C-cluster and Ar-ion implantation

International Nuclear Information System (INIS)

Zhang, R.; Li, H.; Zhang, Z.D.; Wang, Z.S.; Zhou, S.Y.; Wang, Z.; Li, T.C.; Liu, J.R.; Fu, D.J.

2015-01-01

Thermal decomposition of SiC is a promising method for high quality production of wafer-scale graphene layers, when the high decomposition temperature of SiC is substantially reduced. The high decomposition temperature of SiC around 1400 °C is a technical obstacle. In this work, we report on graphene synthesis on 6H–SiC with reduced graphitization temperature via ion implantation. When energetic Ar, C 1 and C 6 -cluster ions implanted into 6H–SiC substrates, some of the Si–C bonds have been broken due to the electronic and nuclear collisions. Owing to the radiation damage induced bond breaking and the implanted C atoms as an additional C source the graphitization temperature was reduced by up to 200 °C

Dipolon theory of energy gap parameters at finite temperature and transition temperatures Tc and T* in high-temperature superconductors

International Nuclear Information System (INIS)

Sharma, R.R.

2006-01-01

First temperature dependent regular and pseudo-energy gap parameters and regular and pseudo-transition temperatures arising from the same physical origin have been calculated in the strong coupling formalism. Temperature dependent many-body field-theoretic techniques have been developed, as an extension of our previous zero-temperature formalism, to derive temperature dependent general expressions for the renormalized energy gap parameter Δ(k->,ω), the gap renormalization parameter Z(k->,ω) and energy band renormalization parameter χ(k->,ω) for momentum k-> and frequency ω making use of dipolon propagator and electron Green's function taking into account explicitly the dressed dipolons as mediators of superconductivity, the screened Coulomb repulsion and nonrigid electron energy bands considering retardation and damping effects and electron-hole asymmetry. The theory takes into account all necessary and important correlations. Our self-consistent calculations utilize the previously symmetry predicted two energy gap parameters for superconducting cuprates, one being antisymmetric (''as'') with respect to the exchange of the k x and k y components of vector k-> and the other being symmetric (''s'') with respect to the exchange of k x and k y . Our present temperature dependent self-consistent solutions of the real and imaginary parts of the Δ(k->,ω), Z(k->,ω) and χ(k->,ω) confirm the existence of these two (different) solutions and conclude that the antisymmetric solution of the gap parameter corresponds to the observed regular (''reg'') superconducting energy gap whereas the symmetric solution corresponds to the observed pseudo-(''pse-'') energy gap. Explicit temperature dependent self-consistent calculations have been performed here for Bi 2 Sr 2 CaCu 2 O 8+δ as well as Bi 2 Sr 2 CaCu 2 O 8 giving temperature dependent energy gap parameters and corresponding transition temperatures. The calculated results are consistent with the available experimental

Synthesis and self-assembling of responsive polysaccharide-based copolymers in aqueous media

Energy Technology Data Exchange (ETDEWEB)

Marques, Nivia do N.; Balaban, Rosangela de C. [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil); Halila, Sami; Borsali, Redouane, E-mail: borsali@cermav.cnrs.fr, E-mail: halila@cermav.cnrs.fr [Centre de Recherche sur les Macromolecules Vegetales (CERMAV), Grenoble (France)

2015-07-01

This work reports the synthesis and the thermoresponsive self-assembly behavior of carboxymethylcellulose-g-JeffamineM2070 and carboxymethylcellulose-g-JeffamineM600 copolymers in aqueous media. They were prepared through the grafting of two different types of amino-terminated poly(ethylene oxide-co-propylene oxide) chains onto the carboxylate groups of carboxymethylcellulose, by using water-soluble carbodiimide derivative and N-hydroxysuccinimide as coupling reagents. The grafting efficiency was confirmed by infrared and the degree of substitution by {sup 1}H NMR integrations. The salt effect on cloud point temperature was evaluated into different solvents (Milli-Q water, 0.5M NaCl, synthetic sea water (SSW) and 0.5M K{sub 2}CO{sub 3}) by UV-Vis and dynamic light scattering (DLS) measurements. Both copolymers showed lower cloud point temperature in 0.5M K2CO3 than in 0.5M NaCl and in SSW, which was attributed to the higher ionic strength for K{sub 2}CO{sub 3} combined to the ability of CO{sub 3}{sup 2-} to decrease polymer-water interactions. Copolymers chains displayed higher hydrodynamic radii than CMC precursor at 25 and 60 °C in saline solutions, and self-associations changed as a function of the environment and copolymer composition. (author)

Synthesis and self-assembling of responsive polysaccharide-based copolymers in aqueous media

International Nuclear Information System (INIS)

Marques, Nivia do N.; Balaban, Rosangela de C.; Halila, Sami; Borsali, Redouane

2015-01-01

This work reports the synthesis and the thermoresponsive self-assembly behavior of carboxymethylcellulose-g-JeffamineM2070 and carboxymethylcellulose-g-JeffamineM600 copolymers in aqueous media. They were prepared through the grafting of two different types of amino-terminated poly(ethylene oxide-co-propylene oxide) chains onto the carboxylate groups of carboxymethylcellulose, by using water-soluble carbodiimide derivative and N-hydroxysuccinimide as coupling reagents. The grafting efficiency was confirmed by infrared and the degree of substitution by "1H NMR integrations. The salt effect on cloud point temperature was evaluated into different solvents (Milli-Q water, 0.5M NaCl, synthetic sea water (SSW) and 0.5M K_2CO_3) by UV-Vis and dynamic light scattering (DLS) measurements. Both copolymers showed lower cloud point temperature in 0.5M K2CO3 than in 0.5M NaCl and in SSW, which was attributed to the higher ionic strength for K_2CO_3 combined to the ability of CO_3"2"- to decrease polymer-water interactions. Copolymers chains displayed higher hydrodynamic radii than CMC precursor at 25 and 60 °C in saline solutions, and self-associations changed as a function of the environment and copolymer composition. (author)

Effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280

International Nuclear Information System (INIS)

James, L.A.

1976-05-01

The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280 in an air environment. Also included in this study are survey tests to determine the effects of thermal aging and stress ratio upon crack growth behavior in this alloy

Catalytic activity of metal borides in the reaction of decomposition

International Nuclear Information System (INIS)

Labodi, I.; Korablev, L.I.; Tavadyan, L.A.; Blyumberg, Eh.A.

1982-01-01

Catalytic effect of CoB, MoB 2 , ZrB 2 and NbB 2 , prepared by the method of self-propagating high-temperature synthesis, on decomposition of tertiary butyl hydroperoxide has been studied. A technigue of determination of action mechanism of heterogeneous catalysts in liquid-phase process is suggested. It is established that CoB in contrast to other metal borides catalyzes only hydroperoxide decomposition into radicals

Numerical study of the propagation of high power microwave pulses in air breakdown environment

International Nuclear Information System (INIS)

Kim, J.; Kuo, S.P.

1992-01-01

A theoretical model based on a set of two modal equations has been developed to describe self-consistently the propagation of an intense microwave pulse in an air breakdown environment. It includes Poynting's equation for the continuity of the power flux of the pulse and the rate equation of the electron density. A forward wave approximation is used to simplify Poynting's equation and a semi-empirical formula for the ionization frequency as a function of the wave field amplitude is adopted for this model. In order to improve the numerical efficiency of the model in terms of the required computation time and available subroutines for numerical analysis of pulse propagation over a long distance, a transformation to the frame of local time of the pulse is introduced. The effect of space-time dependence of the group velocity of the pulse is included in this properly designed transformation. The inhomogeneous feature of the background pressure is also preserved in the model. The resultant equations are reduced to the forms which can be solved directly by the available subroutine of ODE solver. In this work, a comprehensive numerical analysis of the propagation of high power microwave pulse through the atmosphere is performed. It is shown that the pulse energy can severely be attenuated by the self-generated plasma. Therefore, the aim of the present study is to identify the optimum parameters of the pulse so that the energy loss of the pulse before reaching the destination can be minimized. These parameters include the power, frequency, shape and length of the pulse. The conditions for maximizing the ionization at a destinated region in the upper atmosphere will also be determined

Product engineering by high-temperature flame synthesis

DEFF Research Database (Denmark)

Johannessen, Tue; Johansen, Johnny; Mosleh, Majid

product gas can be applied directly in additional product engineering concepts. A brief overview of on-going product developments and product engineering projects is outlined below. These projects, which are all founded on flame synthesis of nano-structured materials, include: • Preparation of catalyzed...... hardware by direct deposition of catalysts on process equipment • Modifications of the substrate surfaces to obtain good adhesion during flame-coating • Formation of membrane layers by gas-phase deposition of nano-particles • Catalyst deposition in micro-reactors for rapid catalyst screening...

Synthesis and solution self-assembly of side-chain cobaltocenium-containing block copolymers.

Science.gov (United States)

Ren, Lixia; Hardy, Christopher G; Tang, Chuanbing

2010-07-07

The synthesis of side-chain cobaltocenium-containing block copolymers and their self-assembly in solution was studied. Highly pure monocarboxycobaltocenium was prepared and subsequently attached to side chains of poly(tert-butyl acrylate)-block-poly(2-hydroxyethyl acrylate), yielding poly(tert-butyl acrylate)-block-poly(2-acryloyloxyethyl cobaltoceniumcarboxylate). The cobaltocenium block copolymers exhibited vesicle morphology in the mixture of acetone and water, while micelles of nanotubes were formed in the mixture of acetone and chloroform.

Synthesis, characterization and magnetic properties of highly monodispersed PtNi nanoparticles

International Nuclear Information System (INIS)

Du, Juan-Juan; Yang, Yi; Zhang, Rong-Hua; Zhou, Xin-Wen

2015-01-01

In this paper, we report the controlled-synthesis of PtNi nanoparticles through galvanic displacement reaction and chemical reduction. The size, composition and morphology of the products are characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), energy dispersed X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses. The structure and composition of the PtNi nanoparticles can be controlled by adjusting the synthetic conditions. The possible formation mechanism is obtained from the academic analysis and experimental studies. The results of the magnetic measurement illustrate that the PtNi nanoparticles show a superparamagnetic behavior with a blocking temperature (T B ) about 8.0 K. - Highlights: • Highly monodispersed PtNi nanoparticles were synthesized by galvanic displacement reaction. • The formation of Pt nanocrystals was the foremost step because of its self-catalysis effect. • The PtNi nanoparticles show a superparamagnetic behavior with a T B about 8.0 K

Effect of temperature and time on solvothermal synthesis of ...

Indian Academy of Sciences (India)

Effect of temperature and time study on solvothermal synthesis of BaTiO3 revealed that a moderate reaction temperature i.e. 185◦C and longer reaction time favour tetragonal phase stabiliza- tion. Dissolution–precipitation appears to be the transformation mechanism for the crystallization of BaTiO3 from particulate TiO2 ...

Differential chromosomal and mitochondrial DNA synthesis in temperature-sensitive mutants of Ustilago maydis

Energy Technology Data Exchange (ETDEWEB)

Unrau, P.

1977-01-01

The amount and type of residual DNA synthesis was determined in eight temperature-sensitive mutants of the smut fungus Ustilago maydis after incubation at the restrictive temperature (32/sup 0/C) for eight hours. Mutants ts-220, ts-207, ts-432 and ts-346 were found to have an overall reduction in the synthesis of both nuclear and mitochondrial DNA in comparison to the wild-type. In mutants ts-20, tsd 1-1, ts-84 and pol 1-1 nuclear DNA synthesis was depressed relative to mitochondrial synthesis. The DNA-polymerase mutant pol 1-1 had persistent nuclear synthesis at about 50% of the rate of synthesis of mitochondrial DNA and similar behavior was observed in a diploid homozygous strain. Mutant ts-84 had an initial burst of DNA synthesis which was reduced for nuclear but not mitochondrial synthesis after three hours preincubation at 32/sup 0/C. tsd 1-1 and ts-20 had nuclear residual synthesis amounting to about 25% of the relative rate of mitochondrial synthesis which correlates to increasing UV sensitivity of these strains on incubation at 32/sup 0/C. A pol 1-1 ts-84 double mutant had an additive loss of nuclear DNA synthesis which indicates that the steps of replication involved may be sequential.

Ammonia synthesis at low temperatures

DEFF Research Database (Denmark)

Rod, Thomas Holm; Logadottir, Ashildur; Nørskov, Jens Kehlet

2000-01-01

have been carried out to evaluate its feasibility. The calculations suggest that it might be possible to catalytically produce ammonia from molecular nitrogen at low temperatures and pressures, in particular if energy is fed into the process electrochemically. (C) 2000 American Institute of Physics.......Density functional theory (DFT) calculations of reaction paths and energies for the industrial and the biological catalytic ammonia synthesis processes are compared. The industrial catalyst is modeled by a ruthenium surface, while the active part of the enzyme is modeled by a MoFe6S9 complex...

Development of fatigue crack propagation models for engineering applications at elevated temperatures

Energy Technology Data Exchange (ETDEWEB)

Tomkins, B.

1975-05-01

The value of modelling the fatigue crack propagation process is discussed and current models are examined in the light of increasing knowledge of crack tip deformation. Elevated temperature fatigue is examined in detail as an area in which models could contribute significantly to engineering design. A model is developed which examines the role of time-dependent creep cavitation on the failure process in an interactive creep-fatigue situation. (auth)

Low-temperature, high yield synthesis, and convenient isolation of the high-electron-density cluster compound Ta6Br14.8H2O for use in biomacromolecular crystallographic phase determination.

Science.gov (United States)

Hay, Daniel N T; Messerle, Louis

2002-09-01

Reduction of TaBr(5) with Ga in the presence of KBr in a sealed borosilicate ampule at 400 degrees, followed by aqueous Soxhlet extraction and addition of stannous bromide and hydrobromic acid to the extract, yielded Ta(6)Br(14).8H(2)O in 80-84% yield. The new procedure provides a convenient, low temperature, high yield route to the synthesis of the title compound from inexpensive precursors.

Some new fatigue tests in high temperature water and liquid sodium environment

International Nuclear Information System (INIS)

Hattori, Takahiro; Yamauchi, Takayoshi; Kanasaki, Hiroshi; Kondo, Yoshiyuki; Endo, Tadayoshi.

1987-01-01

To evaluate the fatigue strength of structural materials for PWR or FBR plants, fatigue test data must be obtained in an environment of simulated primary and secondary water for PWR or of high temperature liquid sodium for FBR. Generally, such tests make it necessary to prepare expensive facilities, so when large amount of fatigue data are required, it is necessary to rationalize and simplify the fatigue tests while maintaining high accuracy. At the Takasago Research Development Center, efforts to rationalize facilities and maintain accuracy in fatigue tests have been made by developing new test methods and improving conventional techniques. This paper introduces a new method of low cycle fatigue test in high temperature water, techniques for automatic measurement of crack initiation and propagation in high temperature water environment and a multiple type fatigue testing machine for high temperature liquid sodium. (author)

Preparation of Fe-Al Intermetallic / TiC-Al2O3 Ceramic Composites from Ilmenite by SHS

Institute of Scientific and Technical Information of China (English)

无

2007-01-01

Fe-Al intermetallic/TiC-Al2O3 ceramic composites were successfully prepared by self-propagating high-temperature synthesis (SHS) from natural ilmenite, aluminium and carbon as the raw materials. The effects of carbon sources, preheating time and heat treatment temperature on synthesis process and products were investigated in detail, and the reaction process of the FeTiO3-Al-C system was also discussed.It is shown that the temperature and velocity of the combustion wave are higher when graphite is used as the carbon source, which can reflect the effect of the carbon source structure on the combustion synthesis;Prolonging the preheating time or heat treatment temperature is beneficial to the formation of the ordered intermetallics; The temperature and velocity of the combustion wave arc improved, but the disordered alloys are difficult to eliminate with the preheating time prolonged. The compound powders mainly containing ordered Fe3Al intermetallic can be prepared through heat treatment at 750 ℃.

GPU-based local interaction simulation approach for simplified temperature effect modelling in Lamb wave propagation used for damage detection

International Nuclear Information System (INIS)

Kijanka, P; Radecki, R; Packo, P; Staszewski, W J; Uhl, T

2013-01-01

Temperature has a significant effect on Lamb wave propagation. It is important to compensate for this effect when the method is considered for structural damage detection. The paper explores a newly proposed, very efficient numerical simulation tool for Lamb wave propagation modelling in aluminum plates exposed to temperature changes. A local interaction approach implemented with a parallel computing architecture and graphics cards is used for these numerical simulations. The numerical results are compared with the experimental data. The results demonstrate that the proposed approach could be used efficiently to produce a large database required for the development of various temperature compensation procedures in structural health monitoring applications. (paper)

Self-induced temperature gradients in Brownian dynamics

Science.gov (United States)

Devine, Jack; Jack, M. W.

2017-12-01

Brownian systems often surmount energy barriers by absorbing and emitting heat to and from their local environment. Usually, the temperature gradients created by this heat exchange are assumed to dissipate instantaneously. Here we relax this assumption to consider the case where Brownian dynamics on a time-independent potential can lead to self-induced temperature gradients. In the same way that externally imposed temperature gradients can cause directed motion, these self-induced gradients affect the dynamics of the Brownian system. The result is a coupling between the local environment and the Brownian subsystem. We explore the resulting dynamics and thermodynamics of these coupled systems and develop a robust method for numerical simulation. In particular, by focusing on one-dimensional situations, we show that self-induced temperature gradients reduce barrier-crossing rates. We also consider a heat engine and a heat pump based on temperature gradients induced by a Brownian system in a nonequilibrium potential.

Temperature lowering in cryogenic chemical-synthesis techniques and system

International Nuclear Information System (INIS)

Martinez, H.E.; Nelson, T.O.; Vikdal, L.N.

1993-01-01

When evaluating a chemical synthesis process for a reaction that occurs on the cryogenically cooled walls, it is sometimes necessary to reduce the wall temperatures to enhance the chemical process. To evaluate the chemical process at lower than atmospheric boiling of liquid nitrogen, we built a system and used it to reduce the temperature of the liquid nitrogen. The technique of lowering the liquid nitrogen temperature by reducing the pressure of the boil-off is established knowledge. This paper presents the engineering aspects of the system, design features, equipment requirements, methods of control, and results of the chemical synthesis. The heat input to the system was ∼400 watts, placing a relatively large demand on the pumping system. Our system is a scale-up of the small laboratory experiment, and it provides the information needed to design an effective system. The major problem encountered was the large quantity of liquid escaping the system during the processing, placing a large gas load on the vacuum system

High frequency guided wave propagation in monocrystalline silicon wafers

Science.gov (United States)

Pizzolato, Marco; Masserey, Bernard; Robyr, Jean-Luc; Fromme, Paul

2017-04-01

Monocrystalline silicon wafers are widely used in the photovoltaic industry for solar panels with high conversion efficiency. The cutting process can introduce micro-cracks in the thin wafers and lead to varying thickness. High frequency guided ultrasonic waves are considered for the structural monitoring of the wafers. The anisotropy of the monocrystalline silicon leads to variations of the wave characteristics, depending on the propagation direction relative to the crystal orientation. Full three-dimensional Finite Element simulations of the guided wave propagation were conducted to visualize and quantify these effects for a line source. The phase velocity (slowness) and skew angle of the two fundamental Lamb wave modes (first anti-symmetric mode A0 and first symmetric mode S0) for varying propagation directions relative to the crystal orientation were measured experimentally. Selective mode excitation was achieved using a contact piezoelectric transducer with a custom-made wedge and holder to achieve a controlled contact pressure. The out-of-plane component of the guided wave propagation was measured using a noncontact laser interferometer. Good agreement was found with the simulation results and theoretical predictions based on nominal material properties of the silicon wafer.

Temperature Dependence on The Synthesis of Jatropha Biolubricant

International Nuclear Information System (INIS)

Resul, Muhammad Faiz M Gunam; Ghazi, Tinia Idaty Mohd; Idris, Azni

2011-01-01

Jatropha oil has good potential as the renewable energy as well as lubricant feedstock. The synthesis of jatropha biolubricant was performed by transesterification of jatropha methyl ester (JME) with trimethyl-ol-propane (TMP) with sodium methoxide (NaOCH3) catalyst. The effects of temperature on the synthesis were studied at a range between 120 deg. C and 200 deg. C with pressure kept at 10mbar. The conversion of JME to jatropha biolubricant was found to be the highest (47%) at 200 deg. C. However, it was suggested that the optimum temperature of the reaction is at 150 deg. C due to insignificant improvement in biolubricant production. To maintain forward reaction, the excess amount of JME was maintained at 3.9:1 ratios to TMP. Kinetic study was done and compared. The synthesis was found to follow a second order reaction with overall rate constant of 1.49 x 10-1 (%wt/wt.min.deg. C)-1. The estimated activation energy was 3.94 kJ/mol. Pour point for jatropha biolubricant was at -3 deg. C and Viscosity Index (VI) ranged from 178 to 183. The basic properties of jatropha biolubricant, pour point and viscosities are found comparable to other plant based biolubricant, namely palm oil and soybean based biolubricant.

Crack propagation of brittle rock under high geostress

Science.gov (United States)

Liu, Ning; Chu, Weijiang; Chen, Pingzhi

2018-03-01

Based on fracture mechanics and numerical methods, the characteristics and failure criterions of wall rock cracks including initiation, propagation, and coalescence are analyzed systematically under different conditions. In order to consider the interaction among cracks, adopt the sliding model of multi-cracks to simulate the splitting failure of rock in axial compress. The reinforcement of bolts and shotcrete supporting to rock mass can control the cracks propagation well. Adopt both theory analysis and simulation method to study the mechanism of controlling the propagation. The best fixed angle of bolts is calculated. Then use ansys to simulate the crack arrest function of bolt to crack. Analyze the influence of different factors on stress intensity factor. The method offer more scientific and rational criterion to evaluate the splitting failure of underground engineering under high geostress.

Effect of temperature on the plastic zone in near-threshold fatigue crack propagation in Nb-H alloys

International Nuclear Information System (INIS)

Lin, C.C.; Polvanich, N.; Salama, K.

1987-01-01

The effect of temperature on the formation of plastic zone in near-threshold fatigue crack propagation is investigated in niobium-hydrogen alloys. The study was made with the ultimate goal of determining the role of hydrogen related to test temperatures on the embrittlement and fracture processes of niobium. Fatigue tests were performed at the two temperatures 220 and 350 K on a hydrogen-free specimen as well as specimens containing hydrogen in solid solution and in the form of hydride. Microhardness was measured on the fatigued specimens in order to determine the plastic zone size at positions where the crack propagation was in the near-threshold region. The results show that at both temperatures, the plastic zone size in hydrogen-free niobium decreases as the amount of hydrogen is increased until it reaches a minimum value and then increases as the amount of hydrogen is further increased. The hydrogen concentrations at the minimum plastic zone are found to be approximately equal to those where the maximum embrittlement occurs for each temperature

Propagation of high power electromagnetic beam in relativistic magnetoplasma: Higher order paraxial ray theory

Science.gov (United States)

Gill, Tarsem Singh; Kaur, Ravinder; Mahajan, Ranju

2010-09-01

This paper presents an analysis of self-consistent, steady-state, theoretical model, which explains the ring formation in a Gaussian electromagnetic beam propagating in a magnetoplasma, characterized by relativistic nonlinearity. Higher order terms (up to r4) in the expansion of the dielectric function and the eikonal have been taken into account. The condition for the formation of a dark and bright ring derived earlier by Misra and Mishra [J. Plasma Phys. 75, 769 (2009)] has been used to study focusing/defocusing of the beam. It is seen that inclusion of higher order terms does significantly affect the dependence of the beam width on the distance of propagation. Further, the effect of the magnetic field and the nature of nonlinearity on the ring formation and self-focusing of the beam have been explored.

Propagation of high power electromagnetic beam in relativistic magnetoplasma: Higher order paraxial ray theory

International Nuclear Information System (INIS)

Gill, Tarsem Singh; Kaur, Ravinder; Mahajan, Ranju

2010-01-01

This paper presents an analysis of self-consistent, steady-state, theoretical model, which explains the ring formation in a Gaussian electromagnetic beam propagating in a magnetoplasma, characterized by relativistic nonlinearity. Higher order terms (up to r 4 ) in the expansion of the dielectric function and the eikonal have been taken into account. The condition for the formation of a dark and bright ring derived earlier by Misra and Mishra [J. Plasma Phys. 75, 769 (2009)] has been used to study focusing/defocusing of the beam. It is seen that inclusion of higher order terms does significantly affect the dependence of the beam width on the distance of propagation. Further, the effect of the magnetic field and the nature of nonlinearity on the ring formation and self-focusing of the beam have been explored.

What works with worked examples: Extending self-explanation and analogical comparison to synthesis problems

Science.gov (United States)

Badeau, Ryan; White, Daniel R.; Ibrahim, Bashirah; Ding, Lin; Heckler, Andrew F.

2017-12-01

The ability to solve physics problems that require multiple concepts from across the physics curriculum—"synthesis" problems—is often a goal of physics instruction. Three experiments were designed to evaluate the effectiveness of two instructional methods employing worked examples on student performance with synthesis problems; these instructional techniques, analogical comparison and self-explanation, have previously been studied primarily in the context of single-concept problems. Across three experiments with students from introductory calculus-based physics courses, both self-explanation and certain kinds of analogical comparison of worked examples significantly improved student performance on a target synthesis problem, with distinct improvements in recognition of the relevant concepts. More specifically, analogical comparison significantly improved student performance when the comparisons were invoked between worked synthesis examples. In contrast, similar comparisons between corresponding pairs of worked single-concept examples did not significantly improve performance. On a more complicated synthesis problem, self-explanation was significantly more effective than analogical comparison, potentially due to differences in how successfully students encoded the full structure of the worked examples. Finally, we find that the two techniques can be combined for additional benefit, with the trade-off of slightly more time on task.

The effects of strain-induced martensitic transformation and temperature on impact fatigue crack propagation behavior of SUS 304 at low temperature

International Nuclear Information System (INIS)

Murakami, Ri-ichi; Akizono, Koichi; Kusukawa, Kazuhiro.

1988-01-01

The fatigue crack propagation behavior in fatigue impact at room temperature and 103 K was investigated by means of fracture mechanics, X-ray diffraction analysis and fractography for an austenitic stainless steel, SUS 304. The crack growth rate in fatigue impact decreased with decreasing temperature. The crack growth rate at room temperature was scarcely influenced by the microstructure, while at low temperature it was markedly influenced by the microstructure. The effects of microstructure and temperature on the crack growth rate were closely related to the strain-induced martensitic transformation. The martensitic transformation was influenced by the microstructure, the temperature, the fracture morphology and the stress intensity level and resulted in a decrease in crack growth rate with increasing crack opening level. (author)

Rapid self-heating and internal temperature sensing of lithium-ion batteries at low temperatures

International Nuclear Information System (INIS)

Zhang, Guangsheng; Ge, Shanhai; Xu, Terrence; Yang, Xiao-Guang; Tian, Hua; Wang, Chao-Yang

2016-01-01

Highlights: • Self-heating lithium-ion battery (SHLB) structure provided a practical solution to the poor performance at subzero temperatures. • We report an improved SHLB that heats from −20 °C to 0 °C in 12.5 seconds, or 56% more rapidly, while consuming 24% less energy than previously reported. • The nickel foil heating element embedded inside a SHLB cell plays a dominant role in rapid self-heating. • The embedded nickel foil can simultaneously perform as an internal temperature sensor (ITS). • 2-sheet design self-heats faster than 1-sheet design due to more uniform internal temperature distribution. - Abstract: The recently discovered self-heating lithium-ion battery structure provided a practical solution to the poor performance at subzero temperatures that has hampered battery technology for decades. Here we report an improved self-heating lithium-ion battery (SHLB) that heats from −20 °C to 0 °C in 12.5 seconds, or 56% more rapidly, while consuming 24% less energy than that reported previously. We reveal that a nickel foil heating element embedded inside a SHLB cell plays a dominant role in self-heating and we experimentally demonstrate that a 2-sheet design can achieve dramatically accelerated self-heating due to more uniform internal temperature distribution. We also report, for the first time, that this embedded nickel foil can simultaneously perform as an internal temperature sensor (ITS) due to the perfectly linear relationship between the foil’s electrical resistance and temperature.

Theoretical Studies on the SAW Properties of LGS at High-Temperature in Optimal Cuts

Institute of Scientific and Technical Information of China (English)

Xiaojun JI; Tao HAN; Wenkang SHI; Guowei ZHANG

2004-01-01

Surface acoustic wave (SAW) devices play a significant role in signal processing, frequency control and sensing applications. In general, they cannot operate at elevated temperature. The new crystal of langasite provides possibility for surface acoustic wave devices applied at high temperature. This paper studies the SAW properties of single and doubly rotated cuts of LGS at high temperature. The calculated SAW properties of LGS are analyzed in space with aid of contour plots, and two promising SAW orientation regions at high temperature are presented. For some typical cuts and propagating directions within the two optimal regions, their SAW characteristics vs temperature are discussed. Based on the experimental evidence in some literatures, the reliability of calculated results is verified.

Low Temperature Synthesis and Properties of Gadolinium-Doped Cerium Oxide Nanoparticles

DEFF Research Database (Denmark)

Machado, Marina F. S.; P. R. Moraes, Leticia; Monteiro, Natalia K.

2017-01-01

Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte or in composite electrodes. The Ni/GDC cermet can be tuned as a catalytic layer, added to the conventional Ni/yttria-stabilized zirconia (YSZ), for the internal steam...... sintering temperature needed to obtain a fully dense ceramic body, which can result in undesired reactions with YSZ. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. Such a low temperature synthesis provides control over particle size and sinterability...

Self-propagative replication of Aβ oligomers suggests potential transmissibility in Alzheimer disease.

Directory of Open Access Journals (Sweden)

Amit Kumar

Full Text Available The aggregation of amyloid-β (Aβ peptide and its deposition in parts of the brain form the central processes in the etiology of Alzheimer disease (AD. The low-molecular weight oligomers of Aβ aggregates (2 to 30 mers are known to be the primary neurotoxic agents whose mechanisms of cellular toxicity and synaptic dysfunction have received substantial attention in the recent years. However, how these toxic agents proliferate and induce widespread amyloid deposition throughout the brain, and what mechanism is involved in the amplification and propagation of toxic oligomer species, are far from clear. Emerging evidence based on transgenic mice models indicates a transmissible nature of Aβ aggregates and implicates a prion-like mechanism of oligomer propagation, which manifests as the dissemination and proliferation of Aβ toxicity. Despite accumulating evidence in support of a transmissible nature of Aβ aggregates, a clear, molecular-level understanding of this intriguing mechanism is lacking. Recently, we reported the characterization of unique replicating oligomers of Aβ42 (12-24 mers in vitro called Large Fatty Acid-derived Oligomers (LFAOs (Kumar et al., 2012, J. Biol. Chem. In the current report, we establish that LFAOs possess physiological activity by activating NF-κB in human neuroblastoma cells, and determine the experimental parameters that control the efficiency of LFAO replication by self-propagation. These findings constitute the first detailed report on monomer - oligomer lateral propagation reactions that may constitute potential mechanism governing transmissibility among Aβ oligomers. These data support the previous reports on transmissible mechanisms observed in transgenic animal models.

Synthesis of pure ozone by nanosecond discharge at cryogenic temperatures

International Nuclear Information System (INIS)

Amirov, R.H.; Asinovsky, E.I.; Samoilov, I.S.

1996-01-01

Synthesis of pure ozone by nanosecond discharge at cryogenic temperatures was experimentally examined. The average ozone concentration in the volume of the discharge tube was less at cryogenic temperatures than at room temperatures. The production of condensed ozone have been determined by measuring the ozone concentration when the walls was heated and ozone evaporated. The energy yield of ozone generation at cryogenic temperatures has been calculated. The maximum value was 200 g/kWh

High-temperature operation of self-assembled GaInNAs/GaAsN quantum-dot lasers grown by solid-source molecular-beam epitaxy

International Nuclear Information System (INIS)

Liu, C.Y.; Yoon, S.F.; Sun, Z.Z.; Yew, K.C.

2006-01-01

Self-assembled GaInNAs/GaAsN single layer quantum-dot (QD) lasers grown using solid-source molecular-beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm 2 from a GaInNAs QD laser (50x1700 μm 2 ) at 10 deg. C. High-temperature operation up to 65 deg. C was also demonstrated from an unbonded GaInNAs QD laser (50x1060 μm 2 ), with high characteristic temperature of 79.4 K in the temperature range of 10-60 deg. C

Facile synthesis of highly active PdAu nanowire networks as self-supported electrocatalyst for ethanol electrooxidation.

Science.gov (United States)

Hong, Wei; Wang, Jin; Wang, Erkang

2014-06-25

In recent years, direct ethanol fuel cells (DEFCs) are attracting increasing attention owing to their wide applications. However, a significant challenge in the development of DEFC technology is the urgent need for highly active anode catalysts for the ethanol oxidation reaction. In this work, a facile and reproducible method for the high-yield synthesis of PdAu nanowire networks is demonstrated. The whole synthetic process is very simple, just mixing Na2PdCl4, HAuCl4, and KBr in an aqueous solution and using polyvinylpyrrolidone as a protective reagent while sodium borohydride as a reductant. The whole synthetic process can be simply performed at room temperature and completed in 30 min, which can greatly simplify the synthetic process and lower the preparation cost. Electrochemical catalytic measurement results prove that the as-prepared catalysts exhibit dramatically enhanced electrocatalytic activity for ethanol electrooxidation in alkaline solution. The facile synthetic process and excellent catalytic performance of the as-prepared catalysts demonstrate that they can be used as a promising catalyst for DEFCs.

Synthesis of a new hardener agent for self-healing epoxy resins

Science.gov (United States)

Raimondo, Marialuigia; Guadagno, Liberata; Naddeo, Carlo; Longo, Pasquale; Mariconda, Annaluisa; Agovino, Anna

2014-05-01

Actually, the development of smart composites capable of self-repair in aeronautical structures is still at the planning stage owing to complex issues to overcome. One of the critical points in the development of self-healing epoxy resin is related to the impossibility to employ primary amines as hardeners. In this paper, the synthesis of a new hardener for self-healing resins is shown together with applicability conditions/ranges.

P25-graphene hydrogels: room-temperature synthesis and application for removal of methylene blue from aqueous solution.

Science.gov (United States)

Hou, Chengyi; Zhang, Qinghong; Li, Yaogang; Wang, Hongzhi

2012-02-29

Herein we report a room-temperature synthesis of chemically bonded TiO2 (P25)-graphene composite hydrogels and their use as high performance visible light photocatalysts. The three-dimensional (3D) TiO2-carbon composite exhibits a significant enhancement in the reaction rate in the decontamination of methylene blue, compared to the bare P25. The 3D P25-graphene hydrogel is much easier to prepare and apply as a macroscopic device, compared to the 2D P25-graphene sheets. This work could provide new insights into the room-temperature synthesis of graphene-based materials. As a kind of the novel 3D graphene-based composite, the obtained high performance P25-graphene gel could be widely used in the environmental protection issues. Copyright © 2012. Published by Elsevier B.V.

Self-learning fuzzy controllers based on temporal back propagation

Science.gov (United States)

Jang, Jyh-Shing R.

1992-01-01

This paper presents a generalized control strategy that enhances fuzzy controllers with self-learning capability for achieving prescribed control objectives in a near-optimal manner. This methodology, termed temporal back propagation, is model-insensitive in the sense that it can deal with plants that can be represented in a piecewise-differentiable format, such as difference equations, neural networks, GMDH structures, and fuzzy models. Regardless of the numbers of inputs and outputs of the plants under consideration, the proposed approach can either refine the fuzzy if-then rules if human experts, or automatically derive the fuzzy if-then rules obtained from human experts are not available. The inverted pendulum system is employed as a test-bed to demonstrate the effectiveness of the proposed control scheme and the robustness of the acquired fuzzy controller.

The propagation of high power CW scanning electron beam in air

International Nuclear Information System (INIS)

Korenev, Sergey; Korenev, Ivan

2002-01-01

The question of propagation of high power electron beam in air presents the scientific and applied interests. The high power (80 kW) CW electron accelerator 'Rhodotron' with kinetic energy of electrons 5 and 10 MeV was used in the experiments. The experimental results for propagation of scanning electron beams in air are presented and discussed

Relativistically Self-Channeled Femtosecond Terawatt Lasers for High-Field Physics and X-Ray Generation

Energy Technology Data Exchange (ETDEWEB)

Borisov, A.B.; Boyer, K.; Cameron, S.M.; Luk, T.S.; McPherson, A.; Nelson, T.; Rhodes, C.K.

1999-01-01

Optical channeling or refractive guiding processes involving the nonlinear interaction of intense femtosecond optical pulses with matter in the self-focussing regime has created exciting opportunities for next-generation laser plasma-based x-ray sources and directed energy applications. This fundamentally new form of extended paraxial electromagnetic propagation in nonlinear dispersive media such as underdense plasma is attributed to the interplay between normal optical diffraction and intensity-dependent nonlinear focussing and refraction contributions in the dielectric response. Superposition of these mechanisms on the intrinsic index profile acts to confine the propagating energy in a dynamic self-guiding longitudinal waveguide structure which is stable for power transmission and robust compression. The laser-driven channels are hypothesized to support a degree of solitonic transport behavior, simultaneously stable in the space and time domains (group velocity dispersion balances self-phase modulation), and are believed to be self-compensating for diffraction and dispersion over many Rayleigh lengths in contrast with the defining characteristics of conventional diffractive imaging and beamforming. By combining concentrated power deposition with well-ordered spatial localization, this phenomena will also create new possibilities for production and regulation of physical interactions, including electron beams, enhanced material coupling, and self-modulated plasma wakefields, over extended gain distances with unprecedented energy densities. Harmonious combination of short-pulse x-ray production with plasma channeling resulting from a relativistic charge displacement nonlinearity mechanism in the terawatt regime (10{sup 18} W/cm{sup 2}) has been shown to generate high-field conditions conducive to efficient multi-kilovolt x-ray amplification and peak spectral brightness. Channeled optical propagation with intense short-pulse lasers is expected to impact several

The propagation property of ion-acoustic soliton in an inhomogeneous plasma

International Nuclear Information System (INIS)

Zhu Jiazhen; Wang Gengguo.

1990-01-01

The propagation property of ion-acoustic soliton in a weakly inhomogeneous plamsa caused by ionization is studied. Finite ion temperature and ion-neutral collisions are considered the self consistent stationary distribution N(x), v(x) and the corresponding soliton solution are obtained, numerical results of soliton amplitude, speed and width dependent on position are given, which are reasonable and consistent with experiments

The high temperature impact response of tungsten and chromium

Science.gov (United States)

Zaretsky, E. B.; Kanel, G. I.

2017-09-01

The evolution of elastic-plastic shock waves has been studied in pure polycrystalline tungsten and chromium at room and elevated temperatures over propagation distances ranging from 0.05 to 3 mm (tungsten) and from 0.1 to 2 mm (chromium). The use of fused silica windows in all but one experiment with chromium and in several high temperature experiments with tungsten led to the need for performing shock and optic characterization of these windows over the 300-1200 K temperature interval. Experiments with tungsten and chromium samples showed that annealing of the metals transforms the initial ramping elastic wave into a jump-like wave, substantially increasing the Hugoniot elastic limits of the metals. With increased annealing time, the spall strength of the two metals slightly increases. Both at room and at high temperatures, the elastic precursor in the two metals decays in two distinct regimes. At propagation distances smaller than ˜1 mm (tungsten) or ˜0.5 mm (chromium), decay is fast, with the dislocation motion and multiplication being controlled by phonon viscous drag. At greater distances, the rate of decay becomes much lower, with control of the plastic deformation being passed to the thermally activated generation and motion of dislocation double-kinks. The stress at which this transition takes place virtually coincides with the Peierls stress τP of the active glide system. Analysis of the annealing effects in both presently and previously studied BCC metals (i.e., Ta, V, Nb, Mo, W, and Cr) and of the dependencies of their normalized Peierls stresses τP(θ) /τP(0 ) on the normalized temperature θ=T /Tm allows one to conclude that the non-planar, split into several glide planes, structure of the dislocation core in these metals is mainly responsible for their plastic deformation features.

High concentration agglomerate dynamics at high temperatures.

Science.gov (United States)

Heine, M C; Pratsinis, S E

2006-11-21

The dynamics of agglomerate aerosols are investigated at high solids concentrations that are typical in industrial scale manufacture of fine particles (precursor mole fraction larger than 10 mol %). In particular, formation and growth of fumed silica at such concentrations by chemical reaction, coagulation, and sintering is simulated at nonisothermal conditions and compared to limited experimental data and commercial product specifications. Using recent chemical kinetics for silica formation by SiCl4 hydrolysis and neglecting aerosol polydispersity, the evolution of the diameter of primary particles (specific surface area, SSA), hard- and soft-agglomerates, along with agglomerate effective volume fraction (volume occupied by agglomerate) is investigated. Classic Smoluchowski theory is fundamentally limited for description of soft-agglomerate Brownian coagulation at high solids concentrations. In fact, these high concentrations affect little the primary particle diameter (or SSA) but dominate the soft-agglomerate diameter, structure, and volume fraction, leading to gelation consistent with experimental data. This indicates that restructuring and fragmentation should affect product particle characteristics during high-temperature synthesis of nanostructured particles at high concentrations in aerosol flow reactors.

An analysis of superluminal propagation becoming subluminal in highly dispersive media

Science.gov (United States)

Nanda, L.

2018-05-01

In this article the time-moments of the Poynting vector associated with an electromagnetic pulse are used to characterize the traversal time and the pulse width as the pulse propagates through highly dispersive media. The behaviour of these quantities with propagation distance is analyzed in two physical cases: Lorentz absorptive medium, and Raman gain doublet amplifying medium. It is found that the superluminal pulse propagation in these two cases with anomalous dispersion is always accompanied by pulse compression and eventually the pulse becomes subluminal with increasing distance of propagation.

Room temperature growth of ZnO nanorods by hydrothermal synthesis

Science.gov (United States)

Tateyama, Hiroki; Zhang, Qiyan; Ichikawa, Yo

2018-05-01

The effect of seed layer morphology on ZnO nanorod growth at room temperature was studied via hydrothermal synthesis on seed layers with different thicknesses and further annealed at different temperatures. The change in the thickness and annealing temperature enabled us to control over a diameter of ZnO nanorods which are attributed to the changing of crystallinity and roughness of the seed layers.

Propagation Characteristics of High-Power Vortex Laguerre-Gaussian Laser Beams in Plasma

Directory of Open Access Journals (Sweden)

Zhili Lin

2018-04-01

Full Text Available The propagation characteristics of high-power laser beams in plasma is an important research topic and has many potential applications in fields such as laser machining, laser-driven accelerators and laser-driven inertial confined fusion. The dynamic evolution of high-power Laguerre-Gaussian (LG beams in plasma is numerically investigated by using the finite-difference time-domain (FDTD method based on the nonlinear Drude model, with both plasma frequency and collision frequency modulated by the light intensity of laser beam. The numerical algorithms and implementation techniques of FDTD method are presented for numerically simulating the nonlinear permittivity model of plasma and generating the LG beams with predefined parameters. The simulation results show that the plasma has different field modulation effects on the two exemplified LG beams with different cross-sectional patterns. The self-focusing and stochastic absorption phenomena of high-power laser beam in plasma are also demonstrated. This research also provides a new means for the field modulation of laser beams by plasma.

Analytic structure of ρ meson propagator at finite temperature

International Nuclear Information System (INIS)

Ghosh, Sabyasachi; Sarkar, Sourav; Mallik, S.

2010-01-01

We analyse the structure of one-loop self-energy graphs for the ρ meson in real time formulation of finite temperature field theory. We find the discontinuities of these graphs across the unitary and the Landau cuts. These contributions are identified with different sources of medium modification discussed in the literature. We also calculate numerically the imaginary and the real parts of the self-energies and construct the spectral function of the ρ meson, which are compared with an earlier determination. A significant contribution arises from the unitary cut of the πω loop, that was ignored so far in the literature. (orig.)

Role of Self-Interstitial Atoms on the High Temperature Properties of Metals

International Nuclear Information System (INIS)

Nordlund, K.; Averback, R.S.

1998-01-01

Equilibrium concentrations of self-interstitial atoms and divacancies have been determined in Cu by molecular dynamics computer simulations using embedded atom potentials. Near the melting temperature these concentrations are both ∼10 -6 . Owing to the higher mobility of the interstitial atoms, however, they contribute more to diffusion. In perfect, or pulse-heated crystals, spontaneous Frenkel pair production results in even higher interstitial concentrations. copyright 1998 The American Physical Society

Ultra-High Temperature Distributed Wireless Sensors

Energy Technology Data Exchange (ETDEWEB)

May, Russell; Rumpf, Raymond; Coggin, John; Davis, Williams; Yang, Taeyoung; O' Donnell, Alan; Bresnahan, Peter

2013-03-31

Research was conducted towards the development of a passive wireless sensor for measurement of temperature in coal gasifiers and coal-fired boiler plants. Approaches investigated included metamaterial sensors based on guided mode resonance filters, and temperature-sensitive antennas that modulate the frequency of incident radio waves as they are re-radiated by the antenna. In the guided mode resonant filter metamaterial approach, temperature is encoded as changes in the sharpness of the filter response, which changes with temperature because the dielectric loss of the guided mode resonance filter is temperature-dependent. In the mechanically modulated antenna approach, the resonant frequency of a vibrating cantilever beam attached to the antenna changes with temperature. The vibration of the beam perturbs the electrical impedance of the antenna, so that incident radio waves are phase modulated at a frequency equal to the resonant frequency of the vibrating beam. Since the beam resonant frequency depends on temperature, a Doppler radar can be used to remotely measure the temperature of the antenna. Laboratory testing of the guided mode resonance filter failed to produce the spectral response predicted by simulations. It was concluded that the spectral response was dominated by spectral reflections of radio waves incident on the filter. Laboratory testing of the mechanically modulated antenna demonstrated that the device frequency shifted incident radio waves, and that the frequency of the re-radiated waves varied linearly with temperature. Radio wave propagation tests in the convection pass of a small research boiler plant identified a spectral window between 10 and 13 GHz for low loss propagation of radio waves in the interior of the boiler.

Demonstration of slow light propagation in an optical fiber under dual pump light with co-propagation and counter-propagation

Science.gov (United States)

Qiu, Wei; Liu, Jianjun; Wang, Yuda; Yang, Yujing; Gao, Yuan; Lv, Pin; Jiang, Qiuli

2018-04-01

In this paper, a general theory of coherent population oscillation effect in an Er3+ -doped fiber under the dual-frequency pumping laser with counter-propagation and co-propagation at room temperature is presented. Using the numerical simulation, in case of dual frequency light waves (1480 nm and 980 nm) with co-propagation and counter-propagation, we analyze the effect of the pump optical power ratio (M) on the group speed of light. The group velocity of light can be varied with the change of M. We research the time delay and fractional delay in an Er3+-doped fiber under the dual-frequency pumping laser with counter-propagation and co-propagation. Compared to the methods of the single pumping, the larger time delay can be got by using the technique of dual-frequency laser pumped fiber with co-propagation and counter-propagation.

High-energy few-cycle pulse compression through self-channeling in gases

International Nuclear Information System (INIS)

Hauri, C.; Merano, M.; Trisorio, A.; Canova, F.; Canova, L.; Lopez-Martens, R.; Ruchon, T.; Engquist, A.; Varju, K.; Gustafsson, E.

2006-01-01

Complete test of publication follows. Nonlinear spectral broadening of femtosecond optical pulses by intense propagation in a Kerr medium followed by temporal compression constitutes the Holy Grail for ultrafast science since it allows the generation of intense few-cycle optical transients from longer pulses provided by now commercially available femtosecond lasers. Tremendous progress in high-field and attosecond physics achieved in recent years has triggered the need for efficient pulse compression schemes producing few-cycle pulses beyond the mJ level. We studied a novel pulse compression scheme based on self-channeling in gases, which promises to overcome the energy constraints of hollow-core fiber compression techniques. Fundamentally, self-channeling at high laser powers in gases occurs when the self-focusing effect in the gas is balanced through the dispersion induced by the inhomogeneous refractive index resulting from optically-induced ionization. The high nonlinearity of the ionization process poses great technical challenges when trying to scale this pulse compression scheme to higher energies input energies. Light channels are known to be unstable under small fluctuations of the trapped field that can lead to temporal and spatial beam breakup, usually resulting in the generation of spectrally broad but uncompressible pulses. Here we present experimental results on high-energy pulse compression of self-channeled 40-fs pulses in pressure-gas cells. In the first experiment, performed at the Lund Laser Center in Sweden, we identified a particular self-channeling regime at lower pulse energies (0.8 mJ), in which the ultrashort pulses are generated with negative group delay dispersion (GDD) such that they can be readily compressed down to near 10-fs through simple material dispersion. Pulse compression is efficient (70%) and exhibits exceptional spatial and temporal beam stability. In a second experiment, performed at the LOA-Palaiseau in France, we

Engineering the propagation of high-k bulk plasmonic waves in multilayer hyperbolic metamaterials by multiscale structuring

DEFF Research Database (Denmark)

Zhukovsky, Sergei; Lavrinenko, Andrei; Sipe, J. E.

2013-01-01

, wavelength scale, the propagation of bulk plasmon polaritons in the resulting multiscale HMM is subject to photonic band gap phenomena. A great degree of control over such plasmons can be exerted by varying the superstructure geometry. As an example, Bragg reflection and Fabry-Pérot resonances...... are demonstrated in multiscale HMMs with periodic superstructures. More complicated, aperiodically ordered superstructures are also considered, with fractal Cantor-like multiscale HMMs exhibiting characteristic self-similar spectral signatures in the high-k band. The multiscale HMM concept is shown...

De novo centriole formation in human cells is error-prone and does not require SAS-6 self-assembly.

Science.gov (United States)

Wang, Won-Jing; Acehan, Devrim; Kao, Chien-Han; Jane, Wann-Neng; Uryu, Kunihiro; Tsou, Meng-Fu Bryan

2015-11-26

Vertebrate centrioles normally propagate through duplication, but in the absence of preexisting centrioles, de novo synthesis can occur. Consistently, centriole formation is thought to strictly rely on self-assembly, involving self-oligomerization of the centriolar protein SAS-6. Here, through reconstitution of de novo synthesis in human cells, we surprisingly found that normal looking centrioles capable of duplication and ciliation can arise in the absence of SAS-6 self-oligomerization. Moreover, whereas canonically duplicated centrioles always form correctly, de novo centrioles are prone to structural errors, even in the presence of SAS-6 self-oligomerization. These results indicate that centriole biogenesis does not strictly depend on SAS-6 self-assembly, and may require preexisting centrioles to ensure structural accuracy, fundamentally deviating from the current paradigm.

Low temperature synthesis & characterization of lead-free BCZT ceramics using molten salt method

Science.gov (United States)

Jai Shree, K.; Chandrakala, E.; Das, Dibakar

2018-04-01

Piezoelectric properties are greatly influenced by the synthesis route, microstructure, stoichiometry of the chemical composition, purity of the starting materials. In this study, molten salt method was used to prepare lead-free BCZT ceramics. Molten salt method is one of the simplestmethods to prepare chemically-purified, single phase powders in high yield often at lower temperatures and shorten reaction time. Calcination of the molten salt synthesized powders resulted in asingle-phase perovskite structure at 1000 °C which is ˜ 350 °C less than the conventional solid-sate reaction method. With increasing calcination temperature the average template size was increased (˜ 0.5-2 µm). Formation of well dispersive templates improves the sinterability at lower temperatures. Lead-free BCZT ceramics sintered at 1500 °C for 2 h resulted in homogenous and highly dense microstructure with ˜92% of the theoretical density and a grain size of ˜ 35 µm. This highly dense microstructure could enhance the piezoelectric properties of the system.

The effect of temperature in flux-assisted synthesis of SnNb2O6

KAUST Repository

Noureldine, Dalal

2014-10-03

A flux-assisted method was used to synthesize SnNb2O6 as a visible-light-responsive metal oxide photocatalyst. The role of synthesis temperature was investigated in detail using different reaction temperatures (300, 500, 600, 800, 1000 °C). The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET). The synthesis with SnCl2 as a flux led to tin niobate particles in the platelet morphology with smooth surfaces. The synthesized crystal showed 2D anisotropic growth along the (600) plane as the flux ratio increased. The particles synthesized with a high reactant to flux ratio (1:10 or higher) exhibited improved photocatalytic activity for hydrogen evolution from an aqueous methanol solution under visible radiation (λ > 420 nm). © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Size Tunable Synthesis of Highly Crystalline BaTiO3 Nanoparticles using Salt-Assisted Spray Pyrolysis

International Nuclear Information System (INIS)

Itoh, Yoshifumi; Lenggoro, I. Wuled; Okuyama, Kikuo; Maedler, Lutz; Pratsinis, Sotiris E.

2003-01-01

Highly crystalline, dense BaTiO 3 nanoparticles in a size range from 30 to 360nm with a narrow size distribution (σ g = 1.2-1.4) were prepared at various synthesis temperatures using a salt-assisted spray pyrolysis (SASP) method without the need for post-annealing. The effect of synthesis temperature on particle size, crystallinity and surface morphology of the nanoparticles were characterized by X-ray diffraction and scanning/transmission electron microscopy. The nature of the crystalline structure was analyzed by Rietveld refinement and Raman spectroscopy. The particle size decreased with decreasing operation temperature. The crystal phase was transformed from tetragonal to cubic at a particles size of about 50nm at room temperature. SASP can be used to produce high weight fraction of tetragonal BaTiO 3 nanoparticles down to 64nm in a single step

Electron thermal conductivity from heat wave propagation in Wendelstein 7-AS

Energy Technology Data Exchange (ETDEWEB)

Giannone, L.; Erckmann, V; Gasparino, U; Hartfuss, H J; Kuehner, G; Maassberg, H; Stroth, U; Tutter, M [Association Euratom-Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); W7-AS Team; ECRH Group IPF Stuttgart; Gyrotron Group KFK Karlsruhe

1992-11-01

Heat wave propagation experiments have been carried out on the Wendelstein 7-AS stellarator. The deposition of electron cyclotron resonance heating power is highly localized in the plasma centre, so that power modulation produces heat waves which propagate away from the deposition volume. Radiometry of the electron cyclotron emission is used to measure the generated temperature perturbation. The propagation time delay of the temperature perturbation as a function of distance to the power deposition region is used to determine the electron thermal conductivity [chi][sub e]. This value is then compared with the value determined by global power balance. In contrast to sawtooth propagation experiments in tokamaks, it is found that the value of [chi][sub e] from heat wave propagation is comparable to that calculated by power balance. In addition, inward propagating waves were produced by choosing a power deposition region away from the plasma centre. Experiments were carried out at 70 GHz in the ordinary mode and at 140 GHz in the extraordinary mode. Variations of the modulation power amplitude have demonstrated that the inferred value of [chi][sub e] is independent of the amplitude of the induced temperature perturbations. (author). 29 refs, 11 figs, 5 tabs.

Direct numerical simulation of ignition front propagation in a constant volume with temperature inhomogeneities. I. Fundamental analysis and diagnostics

Energy Technology Data Exchange (ETDEWEB)

Chen, Jacqueline H.; Hawkes, Evatt R.; Sankaran, Ramanan [Reacting Flow Research Department, Combustion Research Facility, Sandia National Laboratories, P.O. Box 969 MS 9051, Livermore, CA 94551-0969 (United States); Mason, Scott D. [Lockheed Martin Corporation, Sunnyvale, CA 94089 (United States); Im, Hong G. [Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2125 (United States)

2006-04-15

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry with a view to providing better understanding and modeling of combustion processes in homogeneous charge compression-ignition engines. Numerical diagnostics are developed to analyze the mode of combustion and the dependence of overall ignition progress on initial mixture conditions. The roles of dissipation of heat and mass are divided conceptually into transport within ignition fronts and passive scalar dissipation, which modifies the statistics of the preignition temperature field. Transport within ignition fronts is analyzed by monitoring the propagation speed of ignition fronts using the displacement speed of a scalar that tracks the location of maximum heat release rate. The prevalence of deflagrative versus spontaneous ignition front propagation is found to depend on the local temperature gradient, and may be identified by the ratio of the instantaneous front speed to the laminar deflagration speed. The significance of passive scalar mixing is examined using a mixing timescale based on enthalpy fluctuations. Finally, the predictions of the multizone modeling strategy are compared with the DNS, and the results are explained using the diagnostics developed. (author)

Thermo-optical effects in high-power Ytterbium-doped fiber amplifiers

DEFF Research Database (Denmark)

Hansen, Kristian Rymann; Alkeskjold, Thomas Tanggaard; Broeng, Jes

2011-01-01

We investigate the effect of temperature gradients in high-power Yb-doped fiber amplifiers by a numerical beam propagation model, which takes thermal effects into account in a self-consistent way. The thermally induced change in the refractive index of the fiber leads to a thermal lensing effect...

Gribov gap equation at finite temperature

International Nuclear Information System (INIS)

Canfora, Fabrizio; Pais, Pablo; Salgado-Rebolledo, Patricio

2014-01-01

In this paper the Gribov gap equation at finite temperature is analyzed. The solutions of the gap equation (which depend explicitly on the temperature) determine the structure of the gluon propagator within the semi-classical Gribov approach. The present analysis is consistent with the standard confinement scenario for low temperatures, while for high enough temperatures, deconfinement takes place and a free gluon propagator is obtained. An intermediate regime in between the confined and free phases can be read off from the resulting gluon propagator, which appears to be closely related to partial deconfinement. (orig.)

Gribov gap equation at finite temperature

Energy Technology Data Exchange (ETDEWEB)

Canfora, Fabrizio; Pais, Pablo [Centro de Estudios Cientificos (CECS), Valdivia (Chile); Universidad Andres Bello, Santiago (Chile); Salgado-Rebolledo, Patricio [Centro de Estudios Cientificos (CECS), Valdivia (Chile); Universidad de Concepcion, Departamento de Fisica, Concepcion (Chile); Universite Libre de Bruxelles and International Solvay Insitutes, Physique Theorique et Mathematique, Bruxelles (Belgium)

2014-05-15

In this paper the Gribov gap equation at finite temperature is analyzed. The solutions of the gap equation (which depend explicitly on the temperature) determine the structure of the gluon propagator within the semi-classical Gribov approach. The present analysis is consistent with the standard confinement scenario for low temperatures, while for high enough temperatures, deconfinement takes place and a free gluon propagator is obtained. An intermediate regime in between the confined and free phases can be read off from the resulting gluon propagator, which appears to be closely related to partial deconfinement. (orig.)

Low-temperature synthesis of superconducting nanocrystalline MgB2

International Nuclear Information System (INIS)

Lu, J.; Xiao, Z.; Lin, Q.; Claus, H.; Fang, Z.Z.

2010-01-01

Magnesium diboride (MgB 2 ) is considered a promising material for practical application in superconducting devices, with a transition temperature near 40 K. In the present paper, nanocrystalline MgB 2 with an average particle size of approximately 70 nm is synthesized by reacting LiBH 4 with MgH 2 at temperatures as low as 450 C. This synthesis approach successfully bypasses the usage of either elemental boron or toxic diborane gas. The superconductivity of the nanostructures is confirmed by magnetization measurements, showing a superconducting critical temperature of 38.7 K.

Precipitation synthesis and magnetic properties of self-assembled magnetite-chitosan nanostructures

Energy Technology Data Exchange (ETDEWEB)

Bezdorozhev, Oleksii; Kolodiazhnyi, Taras; Vasylkiv, Oleg, E-mail: oleg.vasylkiv@nims.go.jp

2017-04-15

This paper reports the synthesis and magnetic properties of unique magnetite-chitosan nanostructures synthesized by the chemical precipitation of magnetite nanoparticles in the presence of chitosan. The influence of varying synthesis parameters on the morphology of the magnetic composites is determined. Depending on the synthesis parameters, magnetite-chitosan nanostructures of spherical (9–18 nm), rice-seed-like (75–290 nm) and lumpy (75–150 nm) shapes were obtained via self-assembly. Spherical nanostructures encapsulated by a 9–15 nm chitosan layer were assembled as well. The prospective morphology of the nanostructures is combined with their excellent magnetic characteristics. It was found that magnetite-chitosan nanostructures are ferromagnetic and pseudo-single domain. Rice-seed-like nanostructures exhibited a coercivity of 140 Oe and saturation magnetization of 56.7 emu/g at 300 K. However, a drop in the magnetic properties was observed for chitosan-coated spherical nanostructures due to the higher volume fraction of chitosan. - Highlights: • Magnetite-chitosan nanostructures are synthesized via self-assembly. • Different morphology can be obtained by adjusting the synthesis parameters. • An attractive combination of magnetic properties and morphology is obtained. • Magnetite-chitosan nanostructures are ferrimagnetic and pseudo-single domain.

Precipitation synthesis and magnetic properties of self-assembled magnetite-chitosan nanostructures

International Nuclear Information System (INIS)

Bezdorozhev, Oleksii; Kolodiazhnyi, Taras; Vasylkiv, Oleg

2017-01-01

This paper reports the synthesis and magnetic properties of unique magnetite-chitosan nanostructures synthesized by the chemical precipitation of magnetite nanoparticles in the presence of chitosan. The influence of varying synthesis parameters on the morphology of the magnetic composites is determined. Depending on the synthesis parameters, magnetite-chitosan nanostructures of spherical (9–18 nm), rice-seed-like (75–290 nm) and lumpy (75–150 nm) shapes were obtained via self-assembly. Spherical nanostructures encapsulated by a 9–15 nm chitosan layer were assembled as well. The prospective morphology of the nanostructures is combined with their excellent magnetic characteristics. It was found that magnetite-chitosan nanostructures are ferromagnetic and pseudo-single domain. Rice-seed-like nanostructures exhibited a coercivity of 140 Oe and saturation magnetization of 56.7 emu/g at 300 K. However, a drop in the magnetic properties was observed for chitosan-coated spherical nanostructures due to the higher volume fraction of chitosan. - Highlights: • Magnetite-chitosan nanostructures are synthesized via self-assembly. • Different morphology can be obtained by adjusting the synthesis parameters. • An attractive combination of magnetic properties and morphology is obtained. • Magnetite-chitosan nanostructures are ferrimagnetic and pseudo-single domain.

High temperature induced disruption of the cell wall integrity and structure in Pleurotus ostreatus mycelia.

Science.gov (United States)

Qiu, Zhiheng; Wu, Xiangli; Gao, Wei; Zhang, Jinxia; Huang, Chenyang

2018-05-30

Fungal cells are surrounded by a tight cell wall to protect them from harmful environmental conditions and to resist lysis. The synthesis and assembly determine the shape, structure, and integrity of the cell wall during the process of mycelial growth and development. High temperature is an important abiotic stress, which affects the synthesis and assembly of cell walls. In the present study, the chitin and β-1,3-glucan concentrations in the cell wall of Pleurotus ostreatus mycelia were changed after high-temperature treatment. Significantly higher chitin and β-1,3-glucan concentrations were detected at 36 °C than those incubated at 28 °C. With the increased temperature, many aberrant chitin deposition patches occurred, and the distribution of chitin in the cell wall was uneven. Moreover, high temperature disrupts the cell wall integrity, and P. ostreatus mycelia became hypersensitive to cell wall-perturbing agents at 36 °C. The cell wall structure tended to shrink or distorted after high temperature. The cell walls were observed to be thicker and looser by using transmission electron microscopy. High temperature can decrease the mannose content in the cell wall and increase the relative cell wall porosity. According to infrared absorption spectrum, high temperature broke or decreased the glycosidic linkages. Finally, P. ostreatus mycelial cell wall was easily degraded by lysing enzymes after high-temperature treatment. In other words, the cell wall destruction caused by high temperature may be a breakthrough for P. ostreatus to be easily infected by Trichoderma.

1/Nc expansion of the quark condensate at finite temperature

International Nuclear Information System (INIS)

Blaschke, D.; Kalinovsky, Y.L.; Roepke, G.; Schmidt, S.; Volkov, M.K.

1996-01-01

Previously the quark and meson properties in a many quark system at finite temperature have been studied within effective QCD approaches in the Hartree approximation. In the present paper we consider the influence of the mesonic correlations on the quark self-energy and on the quark propagator within a systematic 1/N c expansion. Using a general separable ansatz for the nonlocal interaction, we derive a self-consistent equation for the 1/N c correction to the quark propagator. For a separable model with cutoff form factor, we obtain a decrease of the condensate of the order of 20% at zero temperature. A lowering of the critical temperature for the onset of the chiral restoration transition due to the inclusion of mesonic correlations is obtained with results that seem to be closer to those from lattice calculations. copyright 1996 The American Physical Society

Theoretical and Experimental Study on Vibration Propagation in PMMA Components in Ultrasonic Bonding Process

Directory of Open Access Journals (Sweden)

Yibo Sun

2017-03-01

Full Text Available Ultrasonic bonding has an increasing application in the micro assembly of polymeric micro-electro mechanical systems (MEMS with high requirements for fusion precision. In the ultrasonic bonding process, the propagation of ultrasonic vibration in polymer components is related to the interfacial fusion, which can be used as a monitoring parameter to control ultrasonic energy. To study the vibration propagation in viscoelastic polymer components, finite element analysis on the bonding of poly methyl methacrylate (PMMA micro connector to substrate for microfluidic system is carried out. Curves of propagated vibration amplitude corresponding to interfacial temperatures are obtained. The ultrasonic vibration propagated in PMMA components are measured through experiments. The theoretical and experimental results are contrasted to analyze the change mechanism of vibration propagation related to temperature. Based on the ultrasonic bonding process controlled by the feedback of vibration propagation, interfacial fusions at different vibration propagation states are obtained through experiments. Interfacial fusion behavior is contrasted to the propagated vibration amplitude in theoretical and experimental studies. The relation between vibration propagation and fusion degree is established with the proper parameter range for the obtained high quality bonding.

ON THE HIGH TEMPERATURE BENDING STRENGTH OF CASTABLES

Directory of Open Access Journals (Sweden)

JIŘÍ HAMÁČEK

2012-09-01

Full Text Available The hot moduli of rupture (HMOR measurements have been performed for the low-cement castable (LCC, the ultra-low cement castable (ULCC, and the no-cement castable (NCC. All castables contained SiO2-Al2O3 based aggregates (burned fireclay and kaolin. The experimental data points have been described using the model based on the Varshni approach within the temperature region 1000-1200°C and by the model based on the Adam-Gibbs theory above 1400°C. A smooth but distinct transition between both temperature regions has been observed. The limits and applicability of the models have been analyzed. At lower temperature the loss of strength of castables was attributed to weakening of bonds most probably in the frontal process zone of cracking. At higher temperature, the liquid phase causes slowing down of the crack propagation by formation of the viscous bridging in the following wake region. And finally, at very high temperatures, the castable behaves as very viscous suspension which can be described using models originally developed for molten glasses.

Synthesis and self-assembly of complex hollow materials

KAUST Repository

Zeng, Hua Chun

2011-01-01

Hollow materials with interiors or voids and pores are a class of lightweight nanostructured matters that promise many future technological applications, and they have received significant research attention in recent years. On the basis of well-known physicochemical phenomena and principles, for example, several solution-based protocols have been developed for the general preparation of these complex materials under mild reaction conditions. This article is thus a short introductory review on the synthetic aspects of this field of development. The synthetic methodologies can be broadly divided into three major categories: (i) template-assisted synthesis, (ii) self-assembly with primary building blocks, and (iii) induced matter relocations. In most cases, both synthesis and self-assembly are involved in the above processes. Further combinations of these methodologies appear to be very important, as they will allow one to prepare functional materials at a higher level of complexity and precision. The synthetic strategies are introduced through some simple case studies with schematic illustrations. Salient features of the methods developed have been summarized, and some urgent issues of this field have also been indicated. © 2011 The Royal Society of Chemistry.

Temperature and doping dependence of the high-energy kink in cuprates.

Science.gov (United States)

Zemljic, M M; Prelovsek, P; Tohyama, T

2008-01-25

It is shown that spectral functions within the extended t-J model, evaluated using the finite-temperature diagonalization of small clusters, exhibit the high-energy kink in single-particle dispersion consistent with recent angle-resolved photoemission results on hole-doped cuprates. The kink and waterfall-like features persist up to large doping and to temperatures beyond J; hence, the origin can be generally attributed to strong correlations and incoherent hole propagation at large binding energies. In contrast, our analysis predicts that electron-doped cuprates do not exhibit these phenomena in photoemission.

A SIMPLE ANALYSIS OF THE PROPAGATING ACOUSTOELECTRIC HIGH-FIELD DOMAIN

DEFF Research Database (Denmark)

Mosekilde, Erik

1968-01-01

An analytical treatment of the uniformly propagating acoustoelectric high-field domain is presented in the limit of zero diffusion. Expressions for the electron density and the acoustic energy density as functions of the electric field are given. The domain velocity is determined. ©1968 The Ameri......An analytical treatment of the uniformly propagating acoustoelectric high-field domain is presented in the limit of zero diffusion. Expressions for the electron density and the acoustic energy density as functions of the electric field are given. The domain velocity is determined. ©1968...

Initial Self-Healing Temperatures of Asphalt Mastics Based on Flow Behavior Index.

Science.gov (United States)

Li, Chao; Wu, Shaopeng; Tao, Guanyu; Xiao, Yue

2018-05-29

Increasing temperature is a simple and convenient method to accelerate the self-healing process of bitumen. However, bitumen may not achieve the healing capability at lower temperature, and may be aged if temperature is too high. In addition, the bitumen is mixed with mineral filler and formed as asphalt mastic in asphalt concrete, so it is more accurate to study the initial self-healing from the perspective of asphalt mastic. The primary purpose of this research was to examine the initial self-healing temperature of asphalt mastic, which was determined by the flow behavior index obtained from the flow characteristics. Firstly, the texture and geometry characteristics of two fillers were analyzed, and then the initial self-healing temperature of nine types of asphalt mastic, pure bitumen (PB) and styrene-butadiene-styrene (SBS) modified bitumen were determined by the flow behavior index. Results demonstrate that the average standard deviation of gray-scale texture value of limestone filler (LF) is 21.24% lower than that of steel slag filler (SSF), showing that the steel slag filler has a better particle distribution and geometry characteristics. Also the initial self-healing temperatures of asphalt mastics with 0.2, 0.4 and 0.6 LF-PB volume ratio are 46.5 °C, 47.2 °C and 49.4 °C, which are 1.4 °C, 0.8 °C and 0.4 °C higher than that of asphalt mastics with SSF-PB, but not suitable for the evaluation of asphalt mastic contained SBS modified bitumen because of unique structure and performance of SBS.

High temperature XRD of Cu2GeSe3

International Nuclear Information System (INIS)

Premkumar, D. S.; Malar, P.; Chetty, Raju; Mallik, Ramesh Chandra

2015-01-01

The Cu 2 GeSe 3 is prepared by solid state synthesis method. The high temperature XRD has been done at different temperature from 30 °C to 450 °C. The reitveld refinement confirms Cu 2 GeSe 3 phase and orthorhombic crystal structure. The lattice constants are increasing with increase in the temperature and their rate of increase with respect to temperature are used for finding the thermal expansion coefficient. The calculation of the linear and volume coefficient of thermal expansion is done from 30 °C to 400 °C. Decrease in the values of linear expansion coefficients with temperature are observed along a and c axis. Since thermal expansion coefficient is the consequence of the distortion of atoms in the lattice; this can be further used to find the minimum lattice thermal conductivity at given temperature

Radio Wave Propagation Scene Partitioning for High-Speed Rails

Directory of Open Access Journals (Sweden)

Bo Ai

2012-01-01

Full Text Available Radio wave propagation scene partitioning is necessary for wireless channel modeling. As far as we know, there are no standards of scene partitioning for high-speed rail (HSR scenarios, and therefore we propose the radio wave propagation scene partitioning scheme for HSR scenarios in this paper. Based on our measurements along the Wuhan-Guangzhou HSR, Zhengzhou-Xian passenger-dedicated line, Shijiazhuang-Taiyuan passenger-dedicated line, and Beijing-Tianjin intercity line in China, whose operation speeds are above 300 km/h, and based on the investigations on Beijing South Railway Station, Zhengzhou Railway Station, Wuhan Railway Station, Changsha Railway Station, Xian North Railway Station, Shijiazhuang North Railway Station, Taiyuan Railway Station, and Tianjin Railway Station, we obtain an overview of HSR propagation channels and record many valuable measurement data for HSR scenarios. On the basis of these measurements and investigations, we partitioned the HSR scene into twelve scenarios. Further work on theoretical analysis based on radio wave propagation mechanisms, such as reflection and diffraction, may lead us to develop the standard of radio wave propagation scene partitioning for HSR. Our work can also be used as a basis for the wireless channel modeling and the selection of some key techniques for HSR systems.