High-temperature Mode Research Articles

Symmetries in dissipation-free linear mode conversion

From properties of wave energy flow conservation and wave energy flow under time reversal, we derive the symmetries in dissipation-free mode conversion in an inhomogeneous plasma. These are applied to high-temperature plasma mode conversions near the ion–ion hybrid and upper hybrid resonances.

Steady state experiments on current profile control and long sustainment of high performance LHCD plasmas on the superconducting tokamak TRIAM-1M

The main purpose of TRIAM-1M (R0 = 0.8 m, a × b = 0.12 m × 0.18 m, B = 8 T) is to study the route towards a high field compact steady state fusion reactor. In the advanced steady state operation programme, a heating mechanism for the high ion temperature mode with an internal transport barrier has been studied, an enhanced current drive mode in an extended (higher power and higher density) operation regime has been obtained, current density profile control experiments using multicurrent drive systems have been performedand the effects of wall recycling, wall pumping and wall saturation on particle controlhave been investigated.

Monolithically integrated 780-nm-band high-power and 650-nm-band laser diodes with real refractive index guided self-aligned structure

780-nm-band high-power and 650-nm-band laser diodes (LDs) with real refractive index guided self-aligned (RISA) structures are monolithically integrated for the first time. High-power and fundamental transverse mode operation at an output power of 100-mW continuous wave (CW) up to 80/spl deg/C is attained for the 780-nm-band LD. For the 650-nm-band LD, high temperature and fundamental transverse mode operation at an output power of 10-mW CW up to 80/spl deg/C is obtained.

Nonlinear Optical Properties and Crystalline Orientation of 2-Methyl-4-nitroaniline Layers Grown on Nanostructured Poly(tetrafluoroethylene) Substrates

A new methodology to study the second-order nonlinear optical coefficients of organic materials was developed. The combination of oriented crystal growth (epitaxy or grapho-epitaxy) with grazing incidence X-ray diffraction and second harmonic ellipsometry gives an overview of the relations between the molecular hyperpolarizability and the crystalline nonlinear susceptibility tensor. Thin organic layers of 2-methyl-4-nitroaniline (MNA) were grown on nanostructured poly(tetrafluoroethylene) (PTFE) substrates prepared by the friction transfer method. The investigations show that MNA crystallizes with two definite single-crystal-like orientations depending on the substrate temperature. The low- and high-temperature modes of growth correspond to a deposit of the aromatic ring more or less flat ((11−2) orientation) or edge ((010) orientation) on the substrate, respectively, the transition temperature corresponding to the first order−disorder transition of PTFE (∼19 °C). Two different orientation mechanisms were then proposed. At low temperature, the intermolecular interactions at the overlayer−substrate interface induce a coincident epitaxy that corresponds to a specific physisorption of aromatic molecules on the polymer surface, whereas above the PTFE order−disorder phase transition, the drastic decrease of the nucleation rate strongly suggests that the orientation is achieved via a grapho-epitaxy that occurs on topological defects of the surface. From the second harmonic ellipsometry measurements, the ratio between the nonvanishing components of the first nonlinear susceptibility tensor (χijk or dij) was measured. Finally, the experimental observations were discussed in relation to the oriented gas model and the components of the molecular hyperpolarizability tensor (βijk).

Temperature-dependent linewidth of singleInP/GaxIn1−xPquantum dots: Interaction with surrounding charge configurations

We have investigated individual metal-organic vapor phase epitaxy-grown self-assembled InP quantum-dots in a ${\mathrm{Ga}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{P}$ matrix by means of photoluminescence with high spatial resolution as a function of temperature and excitation density. We observe an abrupt change from the well-known but yet unclear relatively broad emission band at low temperatures to narrow lines at $T>~45 \mathrm{K}.$ The high-temperature mode is the one expected for a fully confined quantum system. The ubiquitous broadening at low temperature is discussed in the framework of spectral diffusion, i.e., fluctuating charge configurations surrounding the quantum dot influence its transition energies. We conclude that the interacting charges are most probably trapped in connection with thickness variation in the wetting layer. Their release at higher temperatures removes the perturbation and leads to the expected appearance of sharp single dot spectra.

Characterisation of elastin and collagen in aortic bioprostheses.

Porcine aortic valves used as cardiac valve bioprostheses are well adapted to physiological functions in the short term, but they lack long-term durability. Several multi-step extractions have been performed to obtain a perfectly acellular matrix. A new physical methodology is proposed to evaluate the resulting fibrous protein damage after biochemical extraction (TRI-COL and SDS). Thermal analysis techniques are adapted to collagen and elastin characterisation in the solid state. The aortic tissue thermal transitions are determined by differential scanning calorimetry (DSC): elastin glass transition is observed around 200 degrees C, and collagen denaturation is observed around 230 degrees C. These parameters are characteristic of the elastin network arrangement and of collagen triple-helix stability. The technique of thermostimulated currents (TSC) is well suited to specify the chain dynamics of proteins. The low-temperature relaxations observed in both collagen and elastin are associated with localised motions, whereas the high-temperature modes are attributed to more delocalized motions of the chains. Therefore TSC and DSC spectrometries allow physical parameters specific to collagen and elastin to be obtained and their interaction in aortic tissues to be determined. According to the significant evolution of these parameters on SDS samples, the destabilizing effect of this detergent is highlighted.

Study of a high-temperature Raman-sensitive mode of TBDA at the solid-smectic G transition

Raman spectra of terephthal-bis-p-n-decylaniline (TBDA) were recorded in the wavenumber region 900– 1050 cm−1 at room temperature and higher temperatures up to 473 K. The Raman-sensitive mode at ca 975 cm−1 splits into two bands, the new band appearing at ca 968 cm−1. The variation of the deconvoluted linewidths of these two bands with temperature exhibits clearly a phase transition at 346 K. The dynamics of the phase transition are discussed in terms of large-amplitude vibration of the alkyl tail causing a strain on the core consisting of three staggered benzene rings and hence reduces the inter-planar spacing. The study reveals that the selection of a suitable Raman mode to characterize and study a phase transition is crucial. Copyright © 2000 John Wiley & Sons, Ltd.

Alterations in the chain dynamics of insoluble elastin upon proteolysis by serine elastases.

The high temperature dielectric relaxations of purified and elastolized ligamentum nuchae elastin in the dry state have been investigated by thermally stimulated depolarization current spectrometry, with an equivalent frequency comprised between 10(-2) and 10(-3) Hz. A main relaxation mode, located close to 150 degrees C and attributed to the dielectric manifestation of a glass transition, is found for all samples. After decomposition by the fractional polarization method, the analysis of the high temperature mode shows the existence of two relaxation mechanisms: a cooperative one, associated with flexible zones of the protein, and an isoenthalpic one, corresponding to more ordered and constrained zones. The activation parameters of the two mechanisms are dependent on the extent of elastolysis and on the nature of enzyme (pancreatic elastase vs leukocyte elastase). Both enzymes influence the dielectric behavior of elastin in a similar way: the activation enthalpy maximum of the relaxing units located in the flexible zones, characteristic of the cooperative length, decreases with increasing hydrolysis. Moreover, the isoenthalpic mechanism becomes cooperative at the highest extent of elastolysis, which highlights release of constraints in ordered zones. Nevertheless, the differences found between the two enzymatic hydrolyses are characteristic of distinct sites of cleavage in the elastin network.

Regularities of self-propagating high-temperature synthesis in the solid 8-hydroxyquinoline—chloramine B system

The regularities of chemical reactions in solid 8-hydroxyquinoline—chloramine B mixtures were studied under conditions of organic self-propagating high-temperature synthesis (SHS), isothermal reaction, and thermal explosion in the 20–220 °C temperature range. Comprehensive physicochemical analysis and microstructural study of the reaction products were carried out. The temperature of SHS initiation (58 °C), the heat of the reaction (129±9 kJ mol−1), the stoichiometric coefficient (1), the maximum temperature (Tmax=98–140 °C), and the velocity of SHS wave propagation (u=0.15–0.55 mm s−1) were determined. Depending on the ratio of the reactants (n), a low-temperature non-degeerate stable gasless mode (n≤1,Tmax=115 °C,Ea=42 kcal mol−1) and a high-temperature mode (n>1,Tmax=140 °C,Ea=0.4 kcal mol−1) are possible for SHS. The SHS affords monohydroxy and monochloro derivatives of 8-hydroxyquinoline, benzenesulfonamide, NaCl, NaOH, and H2O. The mechanism of the solid-phase reaction at temperatures below 58 °C includes surface, solid-phase, and gas-phase diffusion; that for SHS is capillary spreading of the hydroxyquinoline melt.

Observations and Design Considerations for In Situ Combustion Projects

Abstract An important part of any engineer's tool box is a set of simple equations thatwill allow one to quickly assess the performance potential of a given project. For many years, the model of Nelson and McNeil, as well as that of Gates and Ramey, have remained the standards for the preliminary design of in situcombustion projects. However, advances have been made in our understanding ofthe fundamental mechanisms and reaction kinetics of the combustion process, both for heavy and light oils. Combining established procedures with animproved interpretation of the mechanisms forms the basis for this paper. Theinclusion of the negative temperature gradient region, which affects thetransition to the high-temperature combustion mode, is one of the key elementsof these advances. The paper also addresses the sizing of air injection capacity and itsimportance, as well as the monitoring and analysis of gas-phase combustionproducts. In summary, the paper will provide the engineer with some realisticguidelines for estimating the oil recovery performance of an in situ combustionproject. Background In situ combustion is an enhanced recovery process with tremendous theoreticalpotential, but it has failed to perform up to expectations in many of its fieldimplementations. Two decades of research work at the University of Calgary onin situ combustion has focussed on the question "What makes in situ combustionfail?" While many mechanisms have been identified, the most critical withregard to heavy oil is the temperature of the oxidation (combustion)reactions. Figures 1 and 2 illustrate the importance of the oxidation zone temperature onthe residual oil and oil production for Athabasca bitumen (8 ° API). Figure 1shows high residual hydrocarbon concentrations for temperatures of less than300 ° C, while Figure 2 shows that no tests exhibited significant levels of oilrecovery for reaction temperatures of less than 350 ° C. These data, which werepreviously reported by Moore et al.(1), were determined by heatingpre-mixed Athabasca Oil Sands cores in a one dimensional core holder at a rateof 40 ° C/hr. while flowing an oxygen containing gas. Maximum oil recoveriesfor these ramped temperature oxidation tests were significantly lower thanthose for combustion tube tests due to the oxidation of the oil during theperiod of heating when temperatures were less than 300 ° C. However, thequalitative behaviour was similar in both types of tests. What these ramped temperature oxidation data show is that the mobilizationefficiency of air is low for oxidation temperatures of less than 300 ° C. However, reaction temperatures in excess of 350 ° C, while necessary, are not asufficient condition to mobilize oil from the region swept by the oxidationzone. It was found that elevated levels of oil recovery were associated with arapid transition of the leading edge temperatures to a value in excess of 350 °C.

Transition from L mode to high ion temperature mode in CHSheliotron/torsatron plasmas

A high ion temperature (Ti) mode is observed for neutral beam heated plasmas in the Compact Helical System (CHS) heliotron/torsatron. The high Ti mode plasma is characterized by a high central ion temperature, Ti(0), and is associated with a peaked electron density profile produced by neutral beam fuelling with low wall recycling. Transition from L mode to high Ti mode has been studied in CHS. Ti(0) in the high Ti mode discharges reaches 1 keV, which is 2.5 times higher than that in the L mode discharges. The ion thermal diffusivity is significantly reduced by a factor of more than 2-3 in the high Ti mode plasma. The ion loss cone is observed in neutral particle flux in the energy range 1-6 keV with a narrow range of pitch angle (90° ±20°) in the high Ti mode. However, the degradation of ion energy confinement due to this loss cone is negligible.

High ion temperature discharge and its long sustainment in both limiter and single null configurations on TRIAM-1M

A high ion temperature discharge in the lower hybrid current drive scheme has been obtained for the first time in the world in the TRIAM-1M superconducting tokamak. The high ion temperature mode is triggered by a transition which occurs within an operation window for the density, horizontal plasma position and antenna phasing. A steep ion temperature gradient (>80 keV/m) is formed near the core region at the transition. Long duration operation of this discharge has beensuccessfully demonstrated in both the limiter and single null configurations by multiple controltechniques.

超伝導強磁場トカマクTRIAM-1Mにおける高性能·定常プラズマ研究の最近の進展

On the superconducting high-field tokamak TRIAM-1M, the high performance plasmas has been demonstrated. A high ion temperature (HIT) mode with Ti2.5 keV was sustained for longer than 70 s in the limiter configuration. In the single null divertor configuration, the ion temperature has been achieved at 5 keV as the results of the improvement of plasma-wall interaction. By improvement of the time response of position control, the single null divertor configuration with κ=1.5 can be also sustained successfully for I min. These high performance plasmas have been obtained using 2.45 GHz lower hybrid current drive (LHCD). The current density profile can be controlled sufficiently longer than the current diffusion time using both 2.45 GHz and 8.2 GHz LHCD. The effects on the plasma wall of high energy neutral produced via charge exchange process has been also made clear in the HIT plasma.

Josephson plasma resonance in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} under parallel magnetic field

Josephson plasma resonance in under-doped Bi 2 Sr 2 CaCu 2 O 8+δ single crystals has been observed when magnetic field is applied parallel to the ab plane and its vicinity. The resonance mode splits into two branches at higher and lower temperature regions, and a definite gap appears in the temperature region between them. As the magnetic field is tilted from the ab plane, these branches come closer and finally merge to a single mode. This leads to a general interpretation that the resonance mode observed in a parallel field may be due to continuous extension of the c axis plasma mode. However, splitting of the mode as well as the peculiar temperature dependence of the resonance field, the line shape, and its intensity strongly imply that these behaviors may originate from the inherent resonance modes in parallel field. In particular, the high temperature mode fields goes even higher in temperature beyond the zero field resonance as the field increases, suggesting that a new explanation may be required for the case of parallel magnetic field.

Formation and termination of high ion temperature mode in heliotron/torsatron plasmas

The physics of the formation and termination of high ion temperature mode (high mode) is studied by controlling density profiles and radial electric field. High ion temperature mode is observed for neutral beam heated plasmas in heliotron/torsatron plasmas (Heliotron-E). This high mode plasma is characterized by a peaked ion temperature profile and is associated with a peaked electron density profile produced by neutral beam fuelling with low wall recycling. This high mode is terminated by flattening of the electron density caused either by gas puffing or by second-harmonic ECH (core density `pump out').

The criteria for the transitions between the various oxidation modes of binary solid-solution alloys forming immiscible oxides at high oxidant pressures

The possible high-temperature corrosion modes of binary solid-solution alloys forming two immiscible compounds by a single oxidant include (1) the exclusive growth of external scales of the most-noble component, which may or may not be associated with the internal oxidation of the most-reactive component, (2) the formation of composite external scales containing a mixture of the two compounds, or finally (3) the exclusive growth of the most-stable compound as an external scale. The conditions for the stability of each scale structure depend on a number of thermodynamic and kinetics parameters, whose effects are examined quantitatively in this paper. The conditions for the stability of the various structures and the criteria for the transitions among them are also examined. The maximum number of possible scale structures is four, but it can reduce to three and, in some cases, only to two. In particular, the internal oxidation of the most-reactive component may not occur if the stabilities of the two oxides are not sufficiently different from each other.

Vibrational modes and structures of lanthanide halide–alkali halide binary melts LnBr3–KBr (Ln=La, Nd, Gd) and NdCl3–ACl (A=Li, Na, K, Cs)

Raman spectra of the following rare earth halide–alkali halide binary molten salt systems have been measured: LnBr3–KBr (Ln=La, Nd, Gd) and NdCl3–ACl (A=Li, Na, K, Cs). The complete composition range has been studied at temperatures up to 850°C. The spectral changes occurring upon melting the elpasolite compounds Cs2NaLnBr6 (Ln=La, Nd, Gd) and Cs2NaNdCl6 and the pure crystalline solids LnBr3 (Ln=La, Nd, Gd) and NdCl3 were also measured. The data indicate that the behavior of these melt mixtures is similar to those of the YX3–KX (X=F, Cl, Br) binaries studied before. In molten mixtures rich in alkali halide with lanthanide halide mole fractions less than 0.25, the predominant species are the LnX63- octahedra giving rise to two main bands P1 (polarized) and D1 (depolarized) which are assigned to the ν1(A1g) and ν5(F2g) octahedral modes. In molten mixtures rich in LnX3 the spectra are characterized by the P1 and D1 bands plus two new bands D2 (depolarized) and P2 (polarized). The P2 band shifts continuously to higher frequencies with increasing LnX3 content. These four bands are attributed to the D3 distortions of the LnX63- octahedra bound by edges in the melt. The room temperature Raman spectra of the LnX3 solid compounds were characterized by bands due to the vibrational modes of the different crystalline structures: hexagonal for LaBr3 and NdCl3, orthorhombic for NdBr3 and rhombohedral for GdBr3 having the Ln3+ coordination number (CN) or 9, 8 and 6, respectively. With increasing temperature the spectra of the GdBr3 solid are dominated by six Raman bands which are assigned to the vibrational modes of a triple layer of ions consisting of distorted octahedra GdBr63- (CN=6) which share edges with neighboring octahedra. Upon melting, the molar volume of GdBr3 does not change much and the spectra are characterized by the above-mentioned P1, P2, D1 and D2 bands and can be correlated to the triple layer modes of the solid. The high temperature spectra of the hexagonal LaBr3, NdCl3 and the orthorhombic NdBr3 show that the structure and CN remain the same up to melting. However, upon melting, the compact orthorhombic (CN=8) and hexagonal (CN=9) forms increase drastically their molar volume and give spectra similar to those of molten GdBr3, YBr3 and YCl3 where the Ln3+ is in a six-fold coordination (CN=6). It appears that the structures of all the LnX3 melts are similar and independent of the structure of the solids. The frequency changes upon melting the LnX3 solids, the presence and assignment of the P1, P2, D1 and D2 bands in the spectra, the continuous shift of the P2 band with composition in the LnX3–AX binaries and the correlation of the high temperature modes of the rhombohedral LnX3 solid (CN=6) to the liquid suggest that the loose network structure proposed for the LnX3 melts is more likely to arise from ‘triple layer’ like structures composed of distorted octahedra. The rigidity of the network is related to the splitting of the P1 and P2 band and increases with increasing distortion of the octahedra in the sequence La–Y; F–Br. Fast interchange of ions leads to short lifetimes for the octahedra and weak intralayer interactions.

A time-resolved x-ray diffraction study of Ti5Si3 product formation during combustion synthesis

Time-resolved x-ray diffraction (TRXRD) was performed during Ti5Si3 synthesis by the self-propagating high-temperature synthesis mode for different Ti size fractions. It was determined that the time for product formation (ca. 15 s) was independent of Ti particle size. However, the formation of Ti5Si4 phase occurred when relatively large titanium particles were used. A simultaneous measurement of the temperature and TRXRD allowed us to attribute the shifting of XRD peaks at high temperature to thermal expansion of the Ti5Si3 product. The thermal expansion coefficients differ for different crystal planes, and their numerical values compare well with those reported previously in the literature.

Combustion modes in the titanium-nitrogen system at low nitrogen pressures

The macroscopic combustion regimes, as well as the dynamics of phase formation, for the titanium-nitrogen system at low nitrogen pressures (0.1 kPa < p < 50 kPa) have been studied. Several combustion modes, including planar surface (high-temperature), surface spot, and planar layer-by-layer (low-temperature) mode, have been observed. Also, a chaotic spot mode was found at pressures below 2 kPa for conditions of high heat loss. Using the time-resolved x-ray diffraction method previously developed by the authors, it was shown in situ that different mechanisms of phase formation correspond to these combustion modes. For the high-temperature mode, titanium nitride appeared in the combustion front as the initial product. However, only solid solutions of nitrogen in titanium were formed during the low-temperature mode. A complex sequence of phase formation was observed for spot combustion.

Synthesis of novel compounds by hydrogen combustion

The combustion of metals and intermetallic compounds in hydrogen and deuterium were studied. The products of synthesis in this technique are the hydrides and deuterides of transition metals and their alloys. We determined the formation mechanism in self-propagating high-temperature synthesis mode; the effect of second non-metal (C, N) and metal (VA, VIIIA groups) components on the combustion of IVA group metals in hydrogen was established.