A tapered beam finite element for rotor dynamics analysis

The stiffness, mass and gyroscopic matrices of a rotating beam element are developed, a cubic function being used for the transverse displacement. Shear deflection is included by use of end nodal variables of shear strain, along with transverse displacement and cross-section rotation; rotatory inertia effects are included in the energy functional to provide a Timoshenko beam formulation. The gyroscopic effects for small perturbations are linearized as a skew symmetric damping matrix. The formulation is implemented by numerical integration for a linearly tapered circular beam. A technique of reduction of the shear nodal variable prior to global assembly is shown to provide little loss in accuracy with reduced system bandwidth. Numerical comparisons for three previously published beam models are included, with results presented for the case of forward and reverse precession to verify the gyroscopic effects. The utility of the element in a general program for rotor dynamics analysis is identified.     

Electroluminescence in anthracene crystals under time-varying electric fields

Electroluminescence in anthracene crystals has been systematically measured under time varying electric fields at various temperatures using a sodium electrode as the electron-injecting contact and a silver electrode as the hole-injecting contact. The results show that the electroluminescent brightness decreases with increasing frequency over the temperature range from ? 20 to 60°C; and that for a given frequency the brightness increases with increasing temperature, reaches a peak at a critical temperature, and then decreases with increasing temperature. The electroluminescence under a half-wave rectified sinusoidal a.c. field is brighter than that under a sinusoidal a.c. field of the same peak amplitude. There is a delay time between the application of the field and the appearance of electroluminescence, and this delay time decreases with increasing frequency and saturates at a value which may be associated with the transit time of the injected electrons across the specimen. All these results can be explained on the basis of the model that electroluminescence occurs when an electron space charge built up near the anode is sufficient to enhance hole injection from the anode.     

An optically thin radiating gas jet

A radiating gas jet near the optically thin limit is examined. The gas is assumed to be inviscid, optically grey, and in the state of chemical equilibrium or to obey the ideal gas law. The jet is assumed to be plane-symmetric or axi-symmetric and is fully expanded. Under these conditions and by the method of quasi-one-dimensional flow, the problem is analyzed. In addition to this, numerical examples are also included to illustrate the radiative effects.

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Zusammenfassung Es wird ein strahlender Gasstrahl untersucht, nahe zum optisch dünnen Grenzfall. Das Gas wird reibungsfrei, optisch grau und im chemischen Gleichgewicht (oder als ideales Gas) vorausgesetzt. Der Strahl wird eben oder axisymmetrisch angenommen und ist voll expandiert. Unter diesen Voraussetzungen und mit der Methode der fast-eindimensionalen Strömung wird das Problem analysiert. Zudem sind numerische Beispiele angegeben, um den Strahlungseffekt zu veranschaulichen.

     

S42+ and S42− : an ab initio study

The structures of S₄²⁺ and S₄^2? have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S₄^2? was also investigated. The anti chain form of S₄²⁺ was found to be 78.3 kJ mol^? more stable than the square form, in contrast to previous experimental data. S₄^2?is predicted to adopt the chain structure with the anti conformation.     

Transmission measurements of soft X-ray absorption fine structure in solids by a new scintillation technique

Transmission measurements of the extended X-ray absorption fine structure above the oxygen K-edge have been made by using a new scintillation detection technique. The absorption spectrum is in close resemblance with the total electron yield spectrum recorded at the same time. This new technique is of interest for studies of soft X-ray absorption spectroscopy for thin films of solid materials.     

Low-energy charge-density excitations in MgB2: Striking interplay between single-particle and collective behavior for large momenta

A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2.     

Effects of preannealing temperature of ZnO thin films on the performance of dye-sensitized solar cells

The preferred (002) orientation zinc oxide (ZnO) nanocrystalline thin films have been deposited on FTO-coated glass substrates by sol–gel spin-coating technology and rapid thermal annealing for use in dye-sensitized solar cells (DSSC). The effects of preannealing temperature (100 and 300°C) on the microstructure, morphology and optical properties of ZnO thin films were studied. The ZnO thin films were characterized by X-ray diffraction (XRD), scanning electron microscopic (SEM) and Brunauer–Emmett–Teller (BET) analysis. The photoelectric performance of DSSC was studied by I–V curve and the incident photon-to-current conversion efficiency (IPCE), respectively. From the results, the intensities of (002) peaks of ZnO thin films increases with increasing preannealing temperature from 100°C to 300°C. The increase in pore size and surface area of ZnO films crystallized at the increased preannealing temperature contributed to the improvement on the absorption of N3 dye onto the films, the short-circuit photocurrent (J _sc) and open-circuit voltage (V _oc) of DSSC. The higher efficiency (η) of 2.5% with J _sc and V _oc of 8.2 mA/cm² and 0.64 V, respectively, was obtained by the ZnO film preannealed at 300°C.     

Optical encoder based on Fractional-Talbot effect using two-dimensional phase grating

This work presents an optical encoder that uses a two-dimensional phase grating. Rather than using a four-windowed scanning grating, this design with a special two-dimensional phase index grating generates two sinusoidal signals that are mutually phase-shifted by 180°. Afterwards, two large-areas, specially structured index grating generates the four 90° electrically phase-shifted scanning signals. The special design of the two-dimensional phase index grating provides more accuracy of phase-shift by using the fact that the  + 1 and −1 diffraction orders are intrinsically phase-shifted from one another by 180°. The gap between the phase index grating and mail scale was increased to three quarters of Talbot distance. The tolerance of gap between the index and main grating is 0.1 mm. The tolerance of yaw motion is ± 0.25°.