Dielectric Ba(Ti1?xSnx)O3 (x?=?0.13) ceramics, sintered by spark plasma and conventional methods

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti_0.87Sn_0.13)O₃ ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti_0.87Sn_0.13)O₃ ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were ~92% of the theoretical value of Ba(Ti_0.87Sn_0.13)O₃. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature of 63 °C and 10 Hz.     

A meta-index for querying distributed moving object database servers

Distributed moving object database servers offer a feasible solution to the scalability problems of centralized database systems. In these potentially large-scale systems, querying about the time-varying location of specific moving objects can be particularly expensive in terms of running time. This work proposes a meta-index   based strategy that can significantly speed up the processing of these queries. The meta-index acts as an entry point for spatio-temporal queries and quickly drives the search process to the database servers that contain solutions. It also enables very fast approximated solutions to queries such as top-k$k$ and spatio-temporal range queries.     

Thermal images generated by a line-scanning technique: statistical properties

The analysis of statistical parameters of computer-generated therfial images by a line-scanning technique indicates an approach to efficient image transmission.     

Cyclosporine A decreases kallikrein and BK2 mRNA expression in the rat renal cortex

The effect of subcutaneous injection of cyclosporine (20 mg/kg/day for 3 days) on the expression of kallikrein (Kal) and bradykinin 2 receptor (BK2) mRNA in the rat renal cortex was examined. CsA decreased significantly Kal and BK2 mRNA expression in the kidney cortex. These results indicate that the kallikrein-kinin system may participate in the genesis or the aggravation of the renal haemodynamic effect induced by long term administration of CsA.     

Synthesis,Pharmacological Evaluation,and Docking Studies of Novel Pyridazinone‐Based Cannabinoid Receptor Type 2 Ligands

In recent years, cannabinoid type 2 receptors (CB₂R) have emerged as promising therapeutic targets in a wide variety of diseases. Selective ligands of CB₂R are devoid of the psychoactive effects typically observed for CB₁R ligands. Based on our recent studies on a class of pyridazinone 4‐carboxamides, further structural modifications of the pyridazinone core were made to better investigate the structure–activity relationships for this promising scaffold with the aim to develop potent CB₂R ligands. In binding assays, two of the new synthesized compounds [6‐(3,4‐dichlorophenyl)‐2‐(4‐fluorobenzyl)‐cis‐N‐(4‐methylcyclohexyl)‐3‐oxo‐2,3‐dihydropyridazine‐4‐carboxamide ( 2 ) and 6‐(4‐chloro‐3‐methylphenyl)‐cis‐N‐(4‐methylcyclohexyl)‐3‐oxo‐2‐pentyl‐2,3‐dihydropyridazine‐4‐carboxamide ( 22 )] showed high CB₂R affinity, with K_i values of 2.1 and 1.6 nm , respectively. In addition, functional assays of these compounds and other new active related derivatives revealed their pharmacological profiles as CB₂R inverse agonists. Compound 22 displayed the highest CB₂R selectivity and potency, presenting a favorable in silico pharmacokinetic profile. Furthermore, a molecular modeling study revealed how 22 produces inverse agonism through blocking the movement of the toggle‐switch residue, W6.48.     

Natural fermentation of lentils Influence of time, temperature and flour concentration on the kinetics of thiamin, riboflavin and niacin

 Lentils (Lens culinaris, var. vulgaris cultivar Magda-20) were naturally fermented for 96 h at different lentil flour concentrations (79, 150 and 221 g/l) and temperatures (28, 35 and 42°C). During fermentation, samples were taken at 24-h intervals and the changes in thiamin (vitamin B₁), riboflavin (vitamin B₂) and total and available niacin (vitamin B₃) were investigated. Preparation of the lentil flour suspension to be fermented (i.e. the process of mixing the flour and sterilized tap water) caused an increase of the available niacin content in all batches, while changes in thiamin and riboflavin content were related to the conditions in which the preparation of the suspensions was carried out. The whole natural fermentation process (from the raw state to after 96 h of fermentation), either did not affect or produced a slight decrease in the thiamin content of lentils. In contrast, riboflavin, available niacin and total niacin contents increased throughout the 96 h period, which ended with a 35 – 82% increase of riboflavin, a 24 – 91% increase of available niacin and a 20 – 58% increase of total niacin. The temperature during the fermentation procedure had significant effect on the levels of thiamin and riboflavin in fermented lentils. To obtain lentil flours with an improved amount of riboflavin and available niacin with a minimum loss of thiamin, the natural fermentation of lentils should be carried out for 96 h at 42°C and with a lentil flour concentration of 221 g/l. Received: 21 February 1997     

EMP response of aircraft antennas

The responses of aircraft antennas to a broad-band electromagnetic wave such as the nuclear electromagnetic pulse (EMP) are analyzed. For convenience of analysis the antennas are divided into five classes: blades, loops, slots, bowls, and long wires. From each class a few specific antennas are selected as examples for detailed discussion. For each exemplary antenna the detailed equivalent circuit, input impedance, and effective height at the antenna's connector are given. Measurements of input impedance on some antennas are compared with the corresponding calculated results.     

Experimental and theoretical investigation on unburned coal char burnout in a pilot-scale rotary kiln

Oxidation reactivity studies are imperative for improving carbon re-burn technologies and valuing the heat content of unburned carbon within coal combustion ashes. Non-isothermal, thermal gravimetric analysis (TGA) was used to examine the oxidation kinetics of unburned carbon in coal combustion fly ashes having different particle size distributions; TGA results were related to combustion efficiencies as measured in a bench-scale rotary kiln. The activation energy and pre-exponential factor were determined for the chemically-controlled reaction regime; the transition temperatures between chemically-controlled and partially diffusion-controlled combustion regimes were obtained for unburned carbon particles of different sizes. After the oxidation reaction rates were evaluated, the residence time distribution (RTD) of fly ashes in the rotary kiln were experimentally measured and the mean residence times related to process parameters, including the rotating velocity and kiln inclination. By comparing these results with an advective-dispersive model, the axial dispersion coefficient of fly ashes was determined. The reaction rates obtained by thermal analyses and the RTDs were used to predict combustion efficiencies within the kiln and oxidation conditions of unburned carbon using various processing options.     

Towards integration of hydrolysis,decomposition and electrolysis processes of the Cu–Cl thermochemical water splitting cycle

The thermochemical copper–chlorine (Cu–Cl) cycle is a promising technology that can utilize various energy sources such as nuclear and solar energy to produce hydrogen with minimal or no emissions of greenhouse gases. Past investigations have primarily focused on the design and testing of individual unit operations of the Cu–Cl cycle. This paper investigates the chemical streams flowing through each individual process from the aspect of system integration. The interactions between each of the two immediate upstream and downstream processes are examined. Considering the integration of electrolytic hydrogen production and cupric chloride hydrolysis steps, it is evident that an intermediate step to concentrate CuCl₂ and reduce HCl composition is required. Spray drying and crystallization, serving as the intermediate steps, are examined from the aspects of energy requirements and viability of engineering. Regarding the integration of the hydrolysis and oxygen production steps, thermodynamic and XRD analysis results are presented to study the mutual impacts of these two steps on each other. Within the hydrolysis reactor, high conversion of CuCl₂ to Cu₂OCl₂ is preferable for the integration because it reduces the release of chlorine gas during the oxygen production. Considering the integration of the oxygen production step and electrolysis of CuCl, pulverization is needed for the solidified CuCl. The recovery of CuCl vapour entrained in oxygen gas requires further research. Residual CuCl₂ introduced from the hydrolysis step into the oxygen production step may be further entrained by CuCl into the electrolytic hydrogen production cell. Additionally, thermal energy integration patterns are briefly discussed while integrating the various chemical streams of the Cu–Cl cycle. Steam generated from the heat recovery of cuprous chloride can be introduced into the hydrolysis reactor to serve as a reactant.