Far-Infrared Reflection Spectra of Dielectric Ceramics for Microwave Applications

Far-infrared reflection spectra of dielectric ceramics, BaSm₂Ti₅O₁₄, BaTi₄O₉, and some pcrovskites such as Ba(Zn_1/3Nb_2/3)O₃, have been measured at room temperature using a Fourier transform infrared spectrometer in order to investigate the effect of the crystal structure on the dielectric properties. As for perovskites, Sr(Zn_1/3Nb_2/3)O₃ and Sr(Mg_1/3Nb_2/3)O₃, in which B site ions are ordered, were also measured. Reflectance data were analyzed by means of a factorized form of dielectric functions instead of the classical dispersion theory, and all of the spectra were well fitted. The values of dielectric constants and tan δ calculated from the reflectance data were in good agreement with resonant cavity measurements at 5 GHz. Furthermore, results of this study have shown that the main contribution to the microwave dielectric properties is caused by low-frequency optically active modes located at 50 to about 300 cm⁻¹, and for perovskite structures it is suggested that the ordering of B site ions is significant in obtaining low dielectric losses.     

Kinetics of the reaction of hypobromous acid and organic matters in water treatment processes.

The fate of bromine species from human activity is affected by the bromination reaction in water treatment processes. In this study, kinetic information of the reaction between hypobromous acid (HOBr) and seven different natural organic matters (NOM) was collected by sequential stopped-flow techniques. Multiple reaction phases were found in the reaction between HOBr and NOM. The number of reaction sites for the faster reaction phase ranged from 0.26 to 0.92 micromole (mg DOC)(-1), and was correlated to both SUVA and specific phenolic content at pH 7.0. The apparent second-order rate constants for the faster reaction phase at pH 7.0 ranged from 5.4 x 10(5) to 1.4 x 10(6) M(-1) x s(-1), indicating that vanillin-like structures are involved in this reaction phase.     

Solid-state high-resolution 13C-NMR studies of regenerated cellulose samples with different crystallinities

Summary CP/DD/MASS ¹³C-NMR spectra have been obtained for regenerated cellulose samples with different crystallinities as well as for cotton, -D-glucose, -D-cellobiose, and cellopentaose. The spectra of the regenerated cellulose samples exhibit broad multiplicities of the C-4 and C-6 resonance lines in a similar manner as those of native cellulose samples such as cotton and ramie, and, in addition, another broad tailing of the C-1 resonance. Since these multiplicities change linearly with crystallinity, it is concluded that they are ascribed to the contributions from the crystalline and noncrystalline components. Effects of hydrogen bonds and conformations of the -1,4-glycosidic linkage on the chemical shifts are also discussed.     

Multiple robust H∞ controller design using the nonsmooth optimization method

This paper proposes a systematic technique to design multiple robust H_∞ controllers. The proposed technique achieves a desired robust performance objective, which is impossible to achieve with a single robust controller, by dividing the uncertainty set into several subsets and by designing a robust controller to each subset. To achieve this goal with a small number of divisions of the uncertainty set, an optimization problem is formulated. Since the cost function of this optimization problem is not a smooth function, a numerical nonsmooth optimization algorithm is proposed to solve this problem. This method avoids the use of Lyapunov variables, and therefore it leads to a moderate size optimization problem. A numerical example shows that the proposed multiple robust control method can improve the closed‐loop performance when a single robust controller cannot achieve satisfactory performance. Copyright © 2009 John Wiley & Sons, Ltd.     

Seismic proof test of a reinforced concrete containment vessel (RCCV): Part 2: Results of shaking table tests

A 1/8-scale model was constructed of a reinforced concrete containment vessel (RCCV) used in the latest advanced boiling water reactors (ABWR). Shaking table tests were conducted on it with input motions corresponding to or exceeding a design earthquake assumed for a real Nuclear Power Plant.The objectives of the tests were to verify the structural integrity and the leak-proof functional soundness of the RCCV subjected to design earthquakes, and to determine the ultimate strength and seismic margin by an excitation that led to the model's collapse. The model, the test sequence and the pressure and leak test results were addressed in Part 1. The shaking table test method, the input motions and the test results, including the transition of the model's stiffness, natural frequencies and damping factors and the effects of vertical input motions and internal pressure on the model's characteristics and behavior, the load–deformation, the ultimate strength, the failure mode of the reinforced concrete portion and the liner plate are described here. The seismic safety margin that was evaluated by the energy input during the failure test to a design basis earthquake will be described in Part 3. The analytical results of simulation using the multi-lumped mass model will be described in Part 4.     

CFD analysis of pollutant dispersion around buildings: Effect of cell geometry

The choice of the best mesh in terms of cost, time and accuracy of computational solutions in the CFD industry is a challenging topic and a subject of some controversy. Generating meshes based on hexahedral elements requires significant time and effort, however, these meshes are claimed to produce high quality solutions. Meshes that employ tetrahedral elements can be constructed much faster in complex geometries, but may increase the levels of numerical diffusion. The objective of this study is to better establish quantitative assessment of the influence of cell geometry in the computational mesh on the CFD results of pollutant dispersion around buildings in order to help modelers to choose the most effective mesh type for their applications. In order to achieve this objective, two widely used mesh styles, i.e., hexahedral-based and tetrahedral-based meshes, are considered in the simulation of this flow problem. Quantitative grid convergence was calculated based on a grid convergence index (GCI). The mesh style was found to have an observable effect on the calculated pollutant concentrations. For instance, the hexahedral-based mesh was observed to have GCI values that were in an order of magnitude below the tetrahedral-based mesh values for all resolutions considered, even in the very fine tetrahedral-based mesh. Furthermore, the GCI value, and hence the truncation error, remains high compared to conventional hexahedral cases. The study recommends taking special care when employing an unstructured tetrahedral-based mesh to ensure that the mesh is fine enough and any numerical errors should be documented for selected variables reported analogous to experimental uncertainty in order to assess the quality of the numerical solution.     

Magnetic Torque Measurements on Bi2201 Single Crystal in High Magnetic Fields

The magnetic field direction dependence of the magnetic torque in the superconducting state of Bi ₂ Sr _1.65 La _0.35 CuO ₆₊ (Bi2201) single crystal has been measured in several static magnetic fields up to 200 kOe. The applied field dependence of the anisotropy parameter, , defined by the square root of the effective mass ratio has been obtained by fitting the magnetic torque curves at 17 K by means of the effective mass model. For Bi ₂ Sr ₂ CaCu ₂ O ₈₊ (Bi2212), the values up to 210 kOe were reported previously. At each field, for Bi2201 is larger than that for Bi2212. Since the value decreases as the field increases both for Bi2201 and Bi2212, the reduction of by the application of the high magnetic field is considered to be common for Bi-based layered superconductors.     

Out-of-Plane Negative Magnetoresistance of Bi2Sr1.6La0.4CuO6+δ Single Crystals in the Underdoped Region

In order to investigate a relationship between the carrier concentration and negative magnetoresistance in the underdoped region, we have performed out-of-plane electrical resistivity measurements for underdoped Bi ₂ Sr _1.6 La _0.4 CuO ₆₊ single crystals. Giant negative magnetoresistance has been observed in the most abundant carrier sample with = 0.12 in our experiment. The negative magnetoresistance reduces with decreasing carrier concentration.     

Dipolar-decoupled carbon-13 NMR study of highly oriented polyethylene films

Summary High-resolution solid-state ¹³C NMR spectra and ¹³C relaxation times T₁ and T₁ have been measured at 40–100° C for uniaxially oriented polyethylene films with the drawing direction parallel to the magnetic field; this sample has a unique morphological structure that the noncrystalline chains are nearly disordered irrespective of the high degree of drawing. A sharp resonance line(line A) appears at the position corresponding to the principal value ₃₃ of the chemical shift tensor for the CH₂ carbons with the trans-trans conformation. Another sharp linedine B) is observed at almost the same chemical shift as for the CH₂ carbons of polyethylene in solution. Although these observations are similar to those for a cold-drawn polyethylene sample reported previously, line B is much enhanced in intensity and the linewidth is narrower in the present sample, reflecting the disorientation of the noncrystalline component. It is found from T₁ measurements that line A contains two components with different molecular mobility, both being assigned to the crystalline components. On the other hand, the line B is composed of a single component assignable to the noncrystalline component with liquid-like molecular mobility.     

Spectral estimation by least-squares optimization based on rational covariance extension

This paper proposes a new spectral estimation technique based on rational covariance extension with degree constraint. The technique finds a rational spectral density function that approximates given spectral density data under constraint on a covariance sequence. Spectral density approximation problems are formulated as nonconvex optimization problems with respect to a Schur polynomial. To formulate the approximation problems, the least-squares sum is considered as a distance. Properties of optimization problems and numerical algorithms to solve them are explained. Numerical examples illustrate how the methods discussed in this paper are useful in stochastic model reduction and stochastic process modeling.