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Active control of sound radiation from a vibrating plate excited by a harmonic line moment is analytically investigated. This model of simply supported rectangular plate with a line moment excitation is used to simulate the vibration of a ship hull or aircraft fuselage from the flutter of ship deck or aircraft wing, respectively. The control is achieved using various configurations of piezoelectric actuators, and the strategy of radiated power minimization is used to obtain the optimal control input voltage. The efficiency of the active control is dependent on the location of the line moment and the actuators, and the attenuation of radiated sound power is related to two physical mechanisms that are modal suppression and modal restructuring. The numerical result shows that significant attenuation of radiated sound power for volumetric modes (odd, 1) in the low frequency range can be achieved with one control actuator located at the center of plate. Irrespective of whether the excitation is on or off resonance, more actuators result in higher attenuation of radiated sound power. more...

The dual integral formulation for the Helmholtz equation for use in solving the acoustic modes of a two-dimensional square cavity is derived, and a general dual boundary element method (BEM) program is developed. Numerical experiments for the degenerate acoustic modes of a square cavity are performed. It is found that the degenerate modes can be distinguished by specifying the normalized boundary data at different boundary points using either the singular integral equation (UT method) or the hypersingular integral equation (LM method). This technique can be employed to determine the multiplicity of the eigenvalue. Two examples with Dirichlet and Neumann boundary conditions are given to show the validity of the proposed technique. Sensitivity and failure in determining the acoustic modes by specifying the normalized data at the boundary locations near and on the node are examined, respectively. Also, numerical results are obtained using finite element method (FEM) and analytical solutions for comparison. Good agreement between them is obtained. more...

The starting material was prepared by heating amounts of SmOCl/Ta 2 O 5 /Ta/Se in an evacuated quartz tube. Sm 2 Ta 2 Cl 2 O 7 single crystals were obtained by chemical transport reactions using NH 4 Cl as transport agent. It crystallizes in the monoclinic space group C 2/ m with a = 15.290(4) A, b = 3.903(2) A, c = 6.862(2) A, and β = 113.92(2)°. The structure was refined to a final R value of 2.8% using 1123 reflections. The structure shows a three-dimensional arrangement and is built up from layers of Ta octahedral dimers alternating with layers of Sm face-capped trigonal prismatic dimers. more...

A dual integral formulation with a hypersingular integral is derived to solve the boundary value problem with singularity arising from a degenerate boundary. A seepage flow under a dam with sheet piles is analyzed to check the validity of the mathematical model. The closed-form integral formulae containing the four kernel functions in the dual integral equations are presented and clearly reveal the properties of the single- and double-layer potentials and their derivatives. The field and boundary quantities of the potential heads and normal fluxes can thus be expressed in terms of both boundary potentials and boundary normal fluxes through the dual boundary integral equations. To facilitate the computation of the seepage flow along and near the boundary, an expression for the flux tangential to the boundary is also derived. The numerical implementations are compared with analytical solutions and the results of a general purpose commercial finite element program. Finally, four design cases of sheet piles are examined, and the best choice among them is suggested. more...

M.-J. Lee and J.-T. Chen, 1994. Vapor-liquid equilibrium for carbon dioxide/alcohol systems. Fluid Phase Equilibria, 92: 215-231. Equilibrium phase compositions were measured for the binary systems of carbon dioxide/2-methy1-1-pentanol, carbon dioxide/1-octanol, and carbon dioxide/1-decanol at temperatures from 348.15 to 453.15 K and pressures up to 50 bar. Henry's constants and the second virial cross coefficients were reported. The equilibrium vaporization ratios of nine carbon dioxide/alcohol systems were correlated by using four cubic equations of state. It is likely that the Soave equation yields better results and the binary interaction constant increases linearly with the critical volume and normal boiling point of the alcohol. Moreover, an artificial neural network was developed for correlating the equilibrium ratios of those systems. Some promising results have been obtained. more...

The frequency of K-ras point mutation(PM) at codon 12 was studied in 45 patients with endometrial carcinoma. In vitro amplification of target sequences of DNA extracted from endometrial cancer tissues by polymerase chain reaction and dot blotting with oligonucleotide hybridization were performed. Ten of 45 endometrial carcinomas disclosed K-ras PM at codon 12 (22.2%). Transition from GGT to GAT was most frequent in PM(41.7%). Simultaneously, double PM (GAT/GCT) were also detected in 2 cases. No relationship appeared to be present between PM and clinical prognosis such as clinical stage, histological type, histological grade of differentiation, depth of myometrial invasion, and ascitic cytology. The positive rates of lymph node metastasis tended to be higher in the group with positive PM than in the group without PM. K-ras and C-myc gene amplifications were found in 2 (5.1%) and 3 (7.7%) of 39 cases, respectively. No PM of H-ras at codons 12 and 61 was detected. Our results showed that the PM of K-ras gene at codon 12 was a fairly common event in genetic abnormality and suggested it would have some role in the progression of carcinogenesis in endometrial carcinoma. more...

Measurements of the complex AC susceptibility χ′ −jχ″ as a function of temperature and oscillatory magnetic field amplitude for a Y1Ba2Cu3O7 superconductor are reported. By observing the time-dependent analog signal produced in the AC susceptometer coils directly, the nonlinear magnetic response is demonstrated to arise from a nonsinusoidal waveform that is also phase-shifted from a purely inductive waveform. These observed waveforms are quantitatively interpreted within a weakly-connected loop model. more...

The superconducting and normal-state properties of YBa 2 Cu 3 O 7 :Y 2 BaCuO 5 composites with varying mass ratios and final sintering temperatures were investigated by using electrical resistivity and AC susceptibility techniques. By increasing the Y 2 BaCuO 5 concentration, the normal-state resistivity of the composites changes from a metallic-like behavior to a semiconducting-like behavior. Although the onset temperature of the superconductivity was unaffected by the presence of Y 2 BaCuO 5 , the zero-resistance temperature decreased with increasing Y 2 BaCuO 5 content. Increasing the Y 2 BaCuO 5 fraction also leads to a stronger AC magnetic field dependence, implying weaker intergranular coupling. By increasing the final sintering temperature from 900°C to 1050°C, the intergranular coupling can be improved. These results indicate that the presence of insulating Y 2 BaCuO 5 does not affect the intrinsic superconducting properties of the YBa 2 Cu 3 O 7 grains but has a strong effect on the intergranular coupling. more...

The diamagnetic shielding and flux expulsion in a Nb disk have been studied as a function of temperature and magnetic field. Both the zero-field-cooled (ZFCM) and the field-cooled (FCM) magnetizations show diamagnetic responses for fields parallel to the surface of the disk and indicate two different transition temperatures, 9.26 K and 9.06 K. Whereas for fields perpendicular to the surface, the ZFCM shows an additional diamagnetic transition at 9.17 K which is strongly field dependent while the FCM shows a positive magnetization for temperatures below 9.17 K. These features are qualitatively similar to the so-called paramagnetic Meissner effect observed in granular high-T c superconductors. more...

Microwave induced dc voltages in a YBa 2 Cu 3 O 7−δ single crystal have been observed along its c -axis with or without a dc bias current by utilizing standing waves near the end of an X-band (8–12 GHz) waveguide. With a dc bias current, the effect is larger when the single crystal is coupled to the maximum of the microwave H-field, suggesting that the induced dc voltages are due to vortes flow. Without a dc bias current, the induced voltages resemble the inverse ac Josephson effect and require the presence of both the E- and H-fields of the microwave. The temperature and the bias current dependences of the induced voltages both show several peak structures indicating the existence of multiple Josephson junctions inside a single crystal sample. more...

Two drastically different transition temperatures have been observed in a nonhomogeneous single crystal of YBa2Cu3O7−δ. The resistance measured perpendicular to the platelet surface (along the c-axis) has the well-known superconducting transition associated with YBa2Cu3O7. In the direction parallel to the platelet surface, a sharp resistive change of more than 4 orders of magnitude was observed near 265 K. Several other samples have shown transitions near 330 K. Various electrical measurements and the material analyses suggest that these resistive transitions are associated with the defect-filled regions localized in the samples. The transitions became more reproducible in time and finally stabilized after the sample was kept in oxygen environment for more than one month. more...

We have observed a resistive state in a long Josephson tunnel junction in the presence of applied microwaves when the microwave power is greater than a certaib threshold value. At the threshold power, the dc cutoff voltage of the resistive state, V co , and the microwave frequency, f, were found to satisfy the quantum relation 2eV co = nhf. more...

Electrical and magnetic measurements on oxygen-deficient Y 1 Ba 2 Cu 3 O 7−δ single crystals show three distinct superconducting phases. The properties of the 60 K superconducting phase suggest a Josephson coupling of a two-dimensional superconducting structure, probably associated with the double [CuO 2 ] layers. more...

Films of BiSrCaCuO have been deposited on MgO, ZrO 2 , Si, SiO 2 , and sapphire by rf triode sputtering from a single target made by hot-pressing an unreacted powder mixture of Bi 2 O 3 , SrCO 3 , CaO, and CuO. After a two-step post-growth anneal, films of Bi 4 Sr 3 Ca 3 Cu 4 O 16 on (100) MgO are highly oriented with the c-axis perpendicular to the substrate. These films attain zero resistance at 83K and have critical current densities of 2×10 5 A/cm 2 at 65K. more...

We have observed well defined current steps superimposed on the resistive branches associated with non-resonant vortex propagation in a long Sn-oxide-Sn junction. Experimental data suggest that these step structures are due to the interaction between the traveling vortex and the cavity modes whose frequencies are given by νn = nνc, where νc is the frequency of the fundamental cavity mode and n is an integer. The voltage-frequency relation for those steps are found to be 2eV = (n/m)hνc, where m is an integer greater than n. This is different from that of the Fiske steps and the zero field steps of a short junction for which the fraction n/m is replaced by an integer equal to or greater than unity. more...

Films of YBa 2 Cu 3 O y have been prepared on sapphire substrates by rf sputtering from a single nonconducting target made by hot-pressing unreacted powders of Y 2 O 3 , BaCO 3 and CuO and by e-beam deposition of multilayers of Cu, Y and BaF 2 . After post-growth annealing in oxygen, these films exhibited superconducting properties with T c onsets above 90 K and with zero resistances and diamagnetic susceptibilities above 60 K. Resistivity, ac magnetic susceptibility and reverse ac Josephson effect measurements indicate a very weak Josephson coupling between the superconducting grains of these polycrystalline films. more...

The superconducting and normal state properties of Y 1 Ba 2 Cu 3 O 7 : Y 2 Ba 1 Cu 1 O 5 composites have been measured as a function of the mass ratio of the 1-2-3 to 2-1-1 oxide materials and of the sintering temperatures. As the fraction of 1-2-3 material decreases or as the sintering temperature decreases, the normal state resistivity increases from a metallic-like behavior to a semiconducting-like behavior and the magnetic-field dependence of the diamagnetic susceptibility becomes greater even though the onset of the superconductivity in the 1-2-3 material is unchanged. These results indicate that the intergrain coupling plays an important role in the physical properties and that the compositional variation in this admixture of oxide materials is a method to vary the coupling in these granular structures. more...

A systematic investigation of the microwave effects on YBaCuO films show that there are several possible mechanisms involved. By properly coupling an unbiased film to the rf magnetic field, the microwave-induced dc voltage is shown to be oscillatory as a function of microwave power and dc magnetic field as well as to reverse its sign upon changing the magnetic field's direction. These results are in agreement with the nonlinear dynamic responses associated with the Josephson effects. more...