High Q-factor microwave Fabry-Perot resonator with distributed Bragg reflectors

A Fabry-Perot resonator operating at 39 GHz, with two pairs of quarter-wavelength single-crystal quartz Bragg reflectors has been realized. For the length of 98.26 mm, its Q-factor is about 560,000, which is 4.3 times better than for the same resonator without Bragg reflectors. Rigorous finite-difference frequency-domain analysis has been applied to the problem and is compared with simplified semi-analytical solutions. Good agreement between theoretical and experimental resonant frequency and Q-factors has been obtained. Thermal compensation of the resonant frequency of the Fabry-Perot has been proposed employing rods and cylinders made of metals with different thermal expansion coefficients.     

The contribution of blood-flow-induced conductivity changes to measured impedance

The paper considers the contribution of conductivity changes undergone in an anisotropical medium to measured resistance. This was achieved by extending the relationship proposed by Geselowitz to anisotropical materials described, therefore, by a conductivity tensor. It was found that each element of a conductivity change tensor contributed to the measured resistance only if a corresponding component of the electrical field was nonzero. Numerical calculations were performed for blood-flow-associated conductivity changes. A special experiment stand was developed which allowed experiments to be performed proving the theoretical results. It was found that the absolute value of resistance change measured in the direction perpendicular to the vessel axis was much smaller than that measured along the vessel axis. The results obtained may explain the fact that the actual change of measured resistance created by changes of conductivity induced by aortic blood flow is lower than expected from simplified models.     

The switch mechanism of the cell death mode from apoptosis to necrosis in menadione-treated human osteosarcoma cell line 143B cells

Time-dependent changes in the cell death mode from apoptosis to necrosis were studied in cultured 143B cells treated with menadione, an anti-cancerous drug, excluding a possible involvement of "secondary necrosis." The population of apoptotic cells judged by FITC-Annexin V and propidium iodide (PI) double staining reached its maximum at 6 hours after 100 microM menadione treatment followed by an abrupt decrease thereafter, while that of necrotic cells continuously increased reaching 90% at 24 hours. Electron microscopically, cells attached to the culture dish at 6 hours after the treatment consisted of two different types of cells: cells with typical apoptotic features occupying the major population and those with condensed nuclei and swollen cytoplasm. Cells attached to the culture dish at 8 hours after the treatment consisted exclusively of those with condensed nuclei and swollen cytoplasm. Mitochondria in these cells showed various structural changes: those swollen to various degrees with deposition of flocculent densities, or those with highly condensed matrix. Distinct decreases both in intracellular levels of ATP and caspase-3-like activities and remarkable elevations of intracellular levels of superoxide, which were partly suppressed by NAD(P)H oxidase inhibitors, occurred at 6 hours after the treatment. These results may suggest that distinct increases of the intracellular level of superoxide derived from plasma membrane NAD(P)H oxidase besides that from mitochondria have triggered the transition of cell death mode from apoptosis to necrosis. Transition of highly condensed mitochondria to extremely swollen ones may reflect necrotic processes in menadione-treated cells. The present study strongly suggests that time-dependent study is essential using the electron microscopic technique to analyze detailed processes in the changes of the cell death mode.     

Whispering-gallery mode technique applied to the measurement of the dielectric properties of Langasite between 4 K and 300 K

We report new measurements of dielectric properties of Lanthanum gallium silicate (Langasite or LGS) conducted with the whispering-gallery mode technique at microwave frequencies and between 4.2 K and 300 K. The real part of the permittivity tensor of LGS presents two components having temperature coefficients of opposite sign. This unique property enables the design of a temperature compensated resonator that may be useful in building stable microwave oscillators or filters. We report also the first measurements of the two independent components of the imaginary part of the permittivity tensor. It appears LGS is a relatively high-loss dielectric material compared with sapphire or quartz.     

Modeling benzene sorption and diffusion in a γAl2O3catalyst

The behavior of the benzene--Pt--Sn/-Al₂O₃ catalytic system was simulated with the software Cerius² from Accelrys Inc. The Grand Canonical Monte Carlo (GCMC) method was used to assess the adsorption isotherms under conditions of constant pressure and an equilibrium number of benzene molecules. With the results of GCMC simulation it was possible to locate the adsorption centers on the micropore surface at low temperature and a homogeneous benzene monolayer surface at elevated temperature. The results obtained with the GCMC method were then used to simulate the molecular dynamics of the catalytic system and to assess the coefficients of benzene diffusion. Elevated temperature was found to limit molecular motion across the micropore to a large extent. From the temperature-dependence plots of the diffusion coefficients it can be inferred that if the number of molecules is constant, the diffusion in the micropore is a molecular one.     

Nonlinear Faraday rotation for optical limitation

The possible use of the nonlinear Faraday effect for optical limitation of the laser power is investigated in a resonant Faraday medium placed between two crossed polarizers. The results are comparable with those obtained at strong magnetic fields as a result of the linear Faraday effect. Advantages of the method are the narrow bandwidth and the wide field of view. The investigations are interesting from the viewpoint of applications for optical sensor protection and automation of the experiment. All measurements are performed at the F(g) = 2 --> F(e) = 1 hyperfine structure transition of the 87Rb D1 line.     

C60(Cg) and C70(g): A computational study of the pressure and temperature dependence of their populations

Equilibrium mixtures of pure carbon gas-phase aggregates, C_n(g). are treated combining all available observational as well as computational thermodynamical data for n = 1, 2, 3, 4, 5, 60 and 70. A considerable sensitivity to temperature and pressure is pointed out, showing that there are both regions of a higher relative population of C₆₀(g) as well as of C₇₀(g). There can be significant competition between the formation of small and large clusters. Relations between the full-equilibrium situation (i.e., including graphite), gas-phase equilibrium, and the nonequilibrium situation are discussed.     

Second order sensitivity analysis of lumped mechanical systems in the frequency domain

This paper presents a method for determining the second order sensitivity matrix and logarithmic sensitivity functions in the frequency domain. The procedure described is applicable to any discrete and viscously damped mechanical system. A definition of the second order logarithmic sensitivity function has been proposed. The examples shown indicate that logarithmic sensitivity functions of the second order preserve the qualitative character of first order sensitivity functions and are more sensitive to changes of system parameters. The influence of large parameter changes on second order sensitivity functions has also been investigated.     

The effect of water on the reduction of nickel/alumina catalysts

The crucial role of water in the reduction of calcined nickel/alumina catalysts is demonstrated. A fraction of nickel oxide in the catalysts is reduced as NiO powder in the absence of water vapour, and as a nickel aluminate in the presence of water. A much higher dispersion of nickel is attained when the reduction is carried out at low concentration of water vapour.     

One Copernican Table

Hand-written notes attached to a volume from the personal library of Copernicus contain a short untitled table of unknown purpose¹ which gave rise to a centennial sequence of publications and comments, somewhat out of proportion to its intrinsic value. Once more let us come back to the subject, this time in the hope to settle the question. For this purpose, it will be necessary to quote a few sample lines of the table which extends from 11;30 to 15;30 (of unspecified units) in the argument. The tabular function decreases linearly by 0;23° per unit of argument: