Two-temperature accretion around rotating black holes: a description of the general advective flow paradigm in the presence of various cooling processes to explain low to high luminous sources

We investigate viscous two-temperature accretion disc flows around rotating black holes. We describe the global solution of accretion flows with a sub-Keplerian angular momentum profile, by solving the underlying conservation equations including explicit cooling processes self-consistently. Bremsstrahlung, synchrotron and inverse Comptonization of soft photons are considered as possible cooling mechanisms. We focus on the set of solutions for sub-Eddington, Eddington and super-Eddington mass accretion rates around Schwarzschild and Kerr black holes with a Kerr parameter of 0.998. It is found that the flow, during its infall from the Keplerian to sub-Kepleria transition region to the black hole event horizon, passes through various phases of advection: the general advective paradigm to the radiatively inefficient phase, and vice versa. Hence, the flow governs a much lower electron temperature similar to 10(8)-10(9.5) K, in the range of accretion rate in Eddington units 0.01 less than or similar to (M) over dot less than or similar to 100, compared to the hot protons of temperature similar to 10(10.2)-10(11.8) K. Therefore, the solution may potentially explain the hard X-rays and gamma-rays emitted from active galactic nuclei (AGNs) and X-ray binaries. We then compare the solutions for two different regimes of viscosity. We conclude that a weakly viscous flow is expected to be cooling dominated, particularly at the inner region of the disc, compared to its highly viscous counterpart, which is radiatively inefficient. With all the solutions in hand, we finally reproduce the observed luminosities of the underfed AGNs and quasars (e. g. Sgr A*) to ultraluminous X-ray sources (e. g. SS433), at different combinations of input parameters, such as the mass accretion rate and the ratio of specific heats. The set of solutions also predicts appropriately the luminosity observed in highly luminous AGNs and ultraluminous quasars (e. g. PKS 0743-67).

Ce0.67Cr0.33O2.11: A New Low-Temperature O-2 Evolution Material and H-2 Generation Catalyst by Thermochemical Splitting of Water

Ce0.67Cr0.33O2.11 was synthesized by hydrothermal method using diethylenetriamine as complexing agent (Chem. Mater. 2008, 20, 7268). Ce0.67Cr0.33O2.11 being the only compound likes UO2+delta to have excess oxygen, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) at relatively low temperature (465 degrees C) directly and it has been utilized for generation of H-2 by thermo-splitting of water. An almost stoichiometric amount of H-2 (0.152 M/Mole of compound) is generated at much lower temperature (65 degrees C). There is an almost comparable amount of oxygen release and hydrogen generation over this material at very low temperature comparedto other CeO2-MOx (Mn, Fe, Cu, and Ni) mixed-oxide solid solutions (O-2 evolution >= 1300 degrees C and H-2 generation at 1000 degrees C). The reversible nature of oxygen release and intake of this material is attributed to its fluorite Structure and coupling between the Ce4+/Ce3+ and Cr4+/6+/Cr3+ redox couples. Compound shows reversible oxygen release and intake by H2O absorption and subsequent hydrogen release to gain parent structure and hence this material can be utilized for generation of H-2 at very low temperature by thermo-chemical splitting of water.

Mechanism of failure in a free-standing Pt-aluminide bond coat during tensile testing at room temperature

The room temperature (RT) tensile behaviour of a free-standing high activity Pt-aluminide bond coat has been evaluated by microtensile testing technique. The coating had a typical three-layer microstructure. The stress-strain plot for the free-standing coating was linear, indicating the coating to be brittle at RT. Different fracture features were observed across the coating layers, namely quasi-cleavage in the outer layer and inner interdiffusion zone, and cleavage in the intermediate layer. By employing interrupted tensile test and observing the cross-sectional microstructure of the tested specimens, it was determined that failure of the microtensile samples occurred by the initiation of a single crack in the intermediate layer of the coating and its subsequent inside-out propagation. Such a mechanism of failure has been explained in terms of the fracture features observed across the sample thickness. This mechanism of failure is consistent with fracture toughness values of the individual coating layers. (C) 2009 Elsevier B.V. All rights reserved.

Microsphere Bouquets of Bismuth Telluride Nanoplates: Room-Temperature Synthesis and Thermoelectric Properties

We report the synthesis and properties of sphere-shaped microscale aggregates of bismuth telluride nanoplates. We obtain porous microspheres by reducing bismuth chloride and orthotelluric acid with hydrazine in the presence of thioglycolic acid-which serves as the shape-and size-directing agent-followed by room-temperature aging-which promotes nanoplate aggregation. Thin film assemblies of the nanoplate microspheres exhibit n-type behavior due to sulfur doping and a Seebeck coefficient higher than that reported for assemblies of chalcogenide nanostructures. Adaptation of our scalable approach to synthesize and hierarchically assemble nanostructures with controlled doping could be attractive for tailoring novel thermoelectric materials for applications in high-efficiency refrigeration and harvesting electricity from heat.

Apparent shortening of the Csp(3)-Csp(3) bond analysed via a variable-temperature X-ray diffraction study in racemic 1,1 '-binaphthalene-2,2 '-diyl diethyl bis(carbonate)

Crystal structure determination at room temperature [292 (2) K] of racemic 1,1'-binaphthalene-2,2'-diyl diethyl bis(carbonate), C26H22O6, showed that one of the terminal carbon-carbon bond lengths is very short [Csp(3)-Csp(3) = 1.327 (6) angstrom]. The reason for such a short bond length has been analysed by collecting data sets on the same crystal at 393, 150 and 90 K. The values of the corrected bond lengths clearly suggest that the shortening is mainly due to positional disorder at two sites, with minor perturbations arising as a result of thermal vibrations. The positional disorder has been resolved in the analysis of the 90 K data following the changes in the unit-cell parameters for the data sets at 150 and 90 K, which appear to be an artifact of a near centre of symmetry relationship between the two independent molecules in the space group P (1) over bar at these temperatures. Indeed, the unit cell at low temperature (150 and 90 K) is a supercell of the room-temperature unit cell.

Electrochemical properties and intermediate-temperature fuel cell performance of dense yttrium-doped barium zirconate with calcium addition

Although BaZr 0.8Y 0.2O 3-δ(BZY) possesses large bulk proton conductivity and excellent chemical stability, its poor sinterability and grain boundaries block proton conduction. In this work, the effect of Ca as a co-dopant and as a sintering aid (as CaO), on the sinterability, proton conductivity, and fuel cell performance of BZY was investigated. The addition of 4 mol% CaO significantly improved the BZY sinterability: BZY pellets with densities of 92.7% and 97.5% with respect to the theoretical density were obtained after sintering at 1500°C and 1600°C, respectively. The improved BZY sinterability by CaO addition resulted also in a large proton conductivity; at 600°C, the total conductivity of BZY-CaO was 2.14 × 10 -3 S/cm, in wet Ar. Anode-supported fuel cells with 25 μm-thick BZY-CaO electrolyte membranes were fabricated by a dual-layer co-firing technique. The peak power density of the fuel cell with a BZY-Ni/BZY-4CaO/BZY-LSCF (La 0.6Sr 0.4Fe 0.8Co 0.2O 3-δ) configuration was 141 mW/cm 2 at 700°C, several times larger than the reported values of BZY electrolyte membrane fuel cells sintered with the addition of CuO or ZnO, demonstrating promising features for practical fuel cell applications.

Electrophoretic deposition of Ti3Si(Al)C2 from aqueous suspension

Ti3Si(Al)C2 films were electrophoretically deposited at 3 V on indium-tin-oxide (ITO) conductive glass from Ti3Si(Al) C2 aqueous suspension with 1 vol% solid loading at pH 9 in the absence of any dispersant. The surface morphology, cross section microstructure, and preferred orientation of the films were investigated by scanning electron microscopy and X-ray diffraction. The as-deposited Ti3Si(Al)C 2 films exhibited (00l) preferred orientation and the thickness can be controlled by the deposition-drying-deposition method. These results demonstrate that electrophoretic deposition is a simple and feasible method to prepare MAX-phases green films at room temperature.

Low-temperature synthesis and sintering of γ-Y2Si2O7

In this article, a novel pressureless solid-liquid reaction method is presented for preparation of yttrium disilicate (γ-Y2Si2O7). Single-phase γ-Y2Si2O7 powder was synthesized by calcination of SiO2 and Y2O3 powders with the addition of LiYO2 at 1400 °C for 4 h. The addition of LiYO2 significantly decreased the synthesis temperature, shortened the calcination time, and enhanced the stability of γ-Y2Si2O7. The sintering of these powders in air and O2 was studied by means of thermal mechanical analyzer. It is shown that the γ-Y2Si2O7 sintered in oxygen had a faster densification rate and a higher density than that sintered in air. Furthermore, single-phase γ-Y2Si2O7 with a density of 4.0 g/cm3 (99% of the theoretical density) was obtained by pressureless sintering at 1400 °C for 2 h in oxygen. Microstructures of the sintered samples are studied by scanning electron microscope.

Constitutive equation for elevated temperature flow behavior of plain carbon steels using dimensional analysis

Dimensional analysis using π-theorem is applied to the variables associated with plastic deformation. The dimensionless groups thus obtained are then related and rewritten to obtain the constitutive equation. The constants in the constitutive equation are obtained using published flow stress data for carbon steels. The validity of the constitutive equation is tested for steels with up to 1.54 wt%C at temperatures: 850–1200 °C and strain rates: 6 × 10−6–2 × 10−2 s−1. The calculated flow stress agrees favorably with experimental data.

Analytical modelling of integrated solar drying system

The drying of fruit and vegetables is a subject of great importance. Dried fruit and vegetables have gained commercial importance, and their growth on a commercial scale has become an important sector of the agricultural industry. However, food drying is one of the most energy intensive processes of the major industrial process and accounts for up to 15 % of all industrial energy usage. Due to increasingly high electricity prices and environmental concern, a dryer using traditional energy sources is not a feasible option anymore. Therefore, an alternative/renewable energy source is needed. In this regard, an integrated solar drying system that includes highly efficient double-pass counter flow v-groove solar collector, conical-shaped rock-bed thermal storage, auxiliary heater, the centrifugal fan and the drying chamber has been designed and constructed. Mathematical model for all the individual components as well as an integrated model combining all components of the drying system has been developed. Mathematical equations were solved using MATLAB program. This paper presents the analytical model and key finding of the simulation.

Modelling conical rock-bed solar thermal storage tank

An important application of solar thermal storage is for power generation or process heating. Low-temperature thermal storage in a packed rock bed is considered the best option for thermal storage for solar drying applications. In this chapter, mathematical formulations for conical have been developed. The model equations are solved numerically for charging/discharging cycles utilizing MATLAB. Results were compared with rock-bed storage with standard straight tank. From the simulated results, the temperature distribution was found to be more uniform in the truncated conical rock-bed storage. Also, the pressure drop over a long period of time in the conical thermal storage was as low as 25 Pa. Hence, the amount of power required from a centrifugal fan would be significantly lower. The flow of air inside the tank is simulated in SolidWorks software. From flow simulation, 3D modelling of flow is obtained to capture the actual scenario inside the tank.

Mathematical modelling of rock-bed solar thermal storage tank

An important application of thermal storage is solar energy for power generation or process heating. Low temperature thermal storage in a packed rock bed is considered best option for thermal storage for solar drying applications. In this paper, mathematical formulations for conical and cylindrical rock bed storage tanks have been developed. The model equations are solved numerically for charging/discharging cycles. From the simulated results, it was observed that for the same aspect ratio between the diameter and the length of the thermal storages, the conical thermal storage had better performance. The temperature distribution was found to be more uniform in the truncated conical shape rock bed storage. Also, the pressure drop over long period of time in the conical thermal storage was lower than that of the cylindrical thermal storage. Hence, the amount of power required from a centrifugal fan was lower.

Low-temperature Er3+ emission in Ge-S-Ga glasses excited by host absorption

The photoluminescence (PL) of a series of (GeS2)(80)(Ga2S3)(20) glasses doped with different amounts of Er (0.17, 0.35, 0.52, 1.05 and 1.39 at.%) at 77 and 4.2 K has been studied. The influence of the temperature on the emission cross-section of the PL bands at -> 1540, 980 and 820 nm under host excitation has been defined. A quenching effect of the host photoluminescence has been established from the compositional dependence of the PL intensity. It has been found that the present Er3+-doped Ge-S-Ga glasses posses PL lifetime values about 3.25 ms. (C) 2007 Elsevier B.V. All rights reserved.

Temperature monitoring of nonanaesthetised patients in a cardiac catheterisation laboratory

Aim and objectives To identify the prevalence that temperature reduced by more than 1°C from pre to post-procedure in a sample of non-anaesthetised patients undergoing procedures in a cardiac catheterisation laboratory. Background Advances in medical technology are minimising the invasiveness of diagnostic tests and treatments for disease, which is correspondingly increasing the number of medical procedures performed without sedation or anaesthesia. Procedural areas in which medical procedures are performed without anaesthesia are typically kept at a cool temperature for staff comfort. As such, there is a need to inform nursing practices in regard to the thermal management of non-anaesthetised patients undergoing procedures in surgical or procedural environments. Design Single-site observational study Methods Patients were included if they had undergone an elective procedure without sedation or anaesthesia in a cardiac catheterisation laboratory. Ambient room temperature was maintained between 18°C and 20°C. Passive warming with heated cotton blankets was applied. Nurses measured body temperature and thermal comfort before and after 342 procedures. Results Mean change in temperature was -0.08°C (Standard deviation 0.43). The reduction in temperature was more than 1°C after 11 procedures (3.2%). One patient whose temperature had reduced more than 1°C after their procedure reported thermal discomfort. A total of 12 patients were observed to be shivering post-procedure (3.6%). No demographic or clinical characteristics were associated with reduction in temperature of more than 1°C from pre to post-procedure. Conclusions Significant reduction in body temperature was rare in our sample of non-anaesthetised patients. Relevance to clinical practice Similar results would likely be found in other procedural contexts during procedures conducted in settings with comparable room temperatures where passive warming can also be applied with limited skin exposure.

Temperature-dependent infrared reflectivity studies of multiferroic TbMnO3: Evidence for spin-phonon coupling

We have measured near normal incidence far-infrared (FIR) reflectivity spectra of a single crystal of TbMnO3 from 10 K to 300 K in the spectral range of 50 cm(-1)-700 cm(-1). Fifteen transverse optic (TO) and longitudinal optic (LO) modes are identified in the imaginary part of the dielectric function epsilon(2)(omega) and energy loss function Im(-1/epsilon(omega)), respectively. Some of the observed phonon modes show anomalous softening below the magnetic transition temperature T-N (similar to 46 K). We attribute this anomalous softening to the spin-phonon coupling caused by phonon modulation of the superexchange integral between the Mn3+ spins. The effective charge of oxygen (Z(O)) calculated using the measured LO-TO splitting increases below TN.