Thermoelectric power of vacuum evaporated PbTe films

Variation of thermoelectric power with thickness of the vacuum evaporated PbTe films has been investigated. The films were deposited on mica, glass, quartz and LiF substrates, under identical conditions. Attempts have been made to derive a relation which represents the variation of thermoelectric power with thickness of the film. The temperature variation of thermoelectric power has also bsen studied.     

Identification and quantitative analysis of the intermediate phase in a linear high-density polyethylene

The observation of chain conformation and mobility in polyethylene by solid-state ¹³C magic angle spinning (MAS) nuclear magnetic resonance (NMR) permits unambiguous identification and quantitative analysis of an intermediate phase. The carbon-carbon bonds in the intermediate phase adopt, on the average, an all-trans conformation and are more mobile than in the crystalline state (room temperature rate of reorientation ≈ 10⁷ Hz). Comparisons of crystallinities by differential scanning calorimetry, wide-angle x-ray diffraction, and NMR support the high orientation of the intermediate phase and suggest a lower heat of fusion than for the crystals. Results from ¹³C spin-lattice relaxation and ¹H spin diffusion show that the mass fractions are ≈ 20% and the domain sizes ≈ 36 Å. Both change with crystallization and annealing conditions. © 1994 John Wiley & Sons, Inc.     

Total electron-scattering cross-section for molecular hydrogen at low energies by photoelectron spectroscopy

The relative total electron-scattering cross-section for molecular hydrogen has been measured in the energy region 0.02–1.14 eV. In general the Ramsauer technique is used for such a measurement, but in the present experiment the relative cross-sections have been measured by photoelectron spectroscopy. This is the first time that this technique has been put to such a use. The results in this energy region seem to match better the results of Ramsauer and Kollath than those of Golden et al.     

High-field magnetoresistance and magnetothermal e.m.f. in many-valley semiconductors with ellipsoidal energy surface

Thermomagnetic coefficients appropriate to a many-valley model of a semiconductor of the n -Germanium type are evaluated in the framework of the density matrix formalism developed earlier. These coefficients are determined for arbitrary values of the magnetic field, within the effective mass approximation. The phonon-drag contribution is not included in this work. An application is made to the four-ellipsoidal model of n-Ge under the conditions where elastic-acoustic phonon scattering is the predominant mechanism of scattering and the high-temperature limit of the phonon distribution is valid. The thermoelectric power (magneto-Seebeck effect) is found to increase with increasing values of the magnetic field except for a small region of low magnetic field values where it decreases in the longitudinal configuration only.     

Conductivity in intrinsic quantum well wires: Semimetal-semiconductor transition

The effect of size quantization on the conductivity of semimetallic and semiconducting rectangular quantum well wires (QWW) is studied. A semimental-semiconductor transition is predicted to occur at a critical thickness of the wire. For wires of smaller thickness than the critical thickness, semiconducting behavior will occur with the conductivity decreasing exponentially with decreasing transverse dimensions of the wire. That is due to carrier freeze-out because of the increase in effective bandgap resulting from the size quantization. The effect dominates any thickness dependence of the mobility resulting from scattering interactions.     

Hydrodynamics of a bubble formed at vent pipe exit

In this paper, the hydrodynamics of a bubble formed during transient injection of air through a tube submerged in a pool of water has been studied. The experiments were performed by injecting air through vertical tubes varying in diameter from 0.9 to 9.5 cm and located in the middle of a 45 cm dia. and 120 cm high plexiglas chamber. The plexiglas chamber was partly filled with water and was open at the top to the outside. Data for bubble growth and vent line pressure histories are obtained under different upstream pressure conditions. Effect of presence of an orifice in the vent line on bubble growth has also been investigated.A theoretical model describing the bubble growth at the exit of a vent pipe submerged in a pool of water is developed. Predictions of bubble radius, line static pressure and uplift on the bottom of the test chamber have been made and are found to compare well with the data. Insertion of an orifice in the pipe line between the solenoid valve and the vent exit has been found to inhibit the bubble expansion as well as alter the bubble oscillation characteristics.     

A simple extrusion method for the synthesis of aligned silica nanowires using the template of a rigid surfactant mesophase

Long range alignment of silica nanowires has been accomplished by extrusion of a novel surfactant mesophase prior to silica synthesis.     

Diethylene glycol ether-linked 3,4,5-trihydroxybenzamides as triply branched dendritic anchors to CdSe/ZnS core/shell type nanoparticles: potential hydrophilic fluorescent probes

Functionalized N-2-mercaptoethyl-gallamides bearing three or five hydroxyl units that are tethered with diethylene glycol ether(s) allow for transferring hydrophobically pyridine-capped CdSe/ZnS core/shell nanoparticles from an organic to an aqueous layer with intact fluorescent profiles.     

Segregation at alloy surfaces

We present a theory for segregation at alloy surfaces, where both the bond breaking and strain theories have been combined into one. The formulation can be applied to alloys of any concentration. In addition to it we present some ideas which should be considered while dealing with polycrystalline samples. Good agreement is obtained with Auger electron spectroscopy data on a Ni-Au system.     

Finite element implementation of boundary conditions for the pressure Poisson equation of incompressible flow

In this paper we address the problem of the implementation of boundary conditions for the derived pressure Poisson equation of incompressible flow. It is shown that the direct Galerkin finite element formulation of the pressure Poisson equation automatically satisfies the inhomogeneous Neumann boundary conditions, thus avoiding the difficulty in specifying boundary conditions for pressure. This ensures that only physically meaningful pressure boundary conditions consistent with the Navier-Stokes equations are imposed. Since second derivatives appear in this formulation, the conforming finite element method requires C¹ continuity. However, for many problems of practical interest (i.e. high Reynolds numbers) the second derivatives need not be included, thus allowing the use of more conventional C⁰ elements. Numerical results using this approach for a wall-driven contained flow within a square cavity verify the validity of the approach. Although the results were obtained for a two-dimensional problem using the p-version of the finite element method, the approach presented here is general and remains valid for the conventional h-version as well as three-dimensional problems.