Rapid initiation of reactions in Al/Ni multilayers with nanoscale layering

Research into nanoenergetic materials is enabling new capabilities for controlling exothermic reaction rates and energy output, as well as new methods for integrating these materials with conventional electronics fabrication techniques. Many reactions produce primarily heat, and in some cases it is desirable to increase the rate of heat release beyond what is typically observed. Here we investigate the Al-Ni intermetallic reaction, which normally propagates across films or foils at rates lower than 10 m/s. However, models and experiments indicate that local heating rates can be very high (10⁷ K/s), and uniform heating of such a multilayer film can lead to a rapid, thermally explosive type of reaction. With the hopes of using a device to transduce electrical energy to kinetic energy of a flyer plate in the timescale of 100's of nanoseconds, we have incorporated a Ni/Al nanolayer film that locally heats upon application of a large electrical current. We observed flyer plate velocities in the 2-6 km/s range, corresponding to 4-36 kJ/g in terms of specific kinetic energy. Several samples containing Ni/Al films with different bilayer thicknesses were tested, and many produced additional kinetic energy in the 1.1-2.3 kJ/g range, as would be expected from the Ni-Al intermetallic reaction. These results provide evidence that nanoscale Ni/Al layers reacted in the timescale necessary to contribute to device output.     

Output polarization states of a corner cube reflector irradiated at non-normal incidence

A method has been developed for determining the polarization state of the retro-reflected beam from a corner cube irradiated with an input beam of arbitrary polarization state and of arbitrary tilt angle to the cube. Experimentally, the output beam consists of six distinct beamlets of different polarization states that are focused into six non-overlapping regions in the active area of the detector. The overall polarization state of the beam as measured by the photodetector can thus be represented by the incoherent superposition of the polarization states of the six beamlets. Experiments have been performed that verify the theory for a linearly polarized input beam irradiating the corner cube.     

The influence of large-scale seafloor slope and average bottom sound speed on low-grazing-angle monostatic acoustic scattering

Variations in large-scale seafloor slope and average seabed sound speed account for a significant portion of the variations in scattering intensity observed in low-grazing-angle monostatic reverberation. Numerical modeling using a finite-difference solution to the elastic wave equation is used to quantify the effect of these large-scale parameters in interpretations of reverberation data. For hard rough seafloor (e.g., basalt), the results of the modeling suggest that the monostatic backscattering strength increases with increasing large-scale seafloor slope up to a slope of about 15 degrees dipping toward the incident direction. Once the grazing angle of the incident wavefield exceeds the critical grazing angle for the flat reference seafloor the backscattering intensity increases only slowly with increasing grazing angle. Similarly, average subseafloor sound speed has a significant effect. Seafloor with low sound speeds characteristic of soft bottoms (e.g., sediment) generate significantly weaker backscatter signals than seafloor with sound speeds characteristic of hard bottoms (e.g., basalt). The difference is that the shear waves can always be passed into soft bottoms because even for a flat seafloor there is no shear wave critical grazing angle.     

Scalar-type spectral operators and holomorphic semigroups

We show that a linear operator (possibly unbounded), A, on a reflexive Banach space, X, is a scalar-type spectral operator, with non-negative spectrum, if and only if the following conditions hold.

1. A generates a uniformly bounded holomorphic semigroup {e?^zA}_Re(z)≥0.
2. If \(F_N (s) \equiv \int_{ - N}^N {\tfrac{{\sin (sr)}}{r}} e^{irA} dr\) , then {‖F_N‖} _N=1 ^∞ is uniformly bounded on [0,∞) and, for all x in X, the sequence {F_N(s)x} _N=1 ^∞ converges pointwise on [0, ∞) to a vector-valued function of bounded variation.

The projection-valued measure, E, for A, may be constructed from the holomorphic semigroup {e^?zA}_Re(z)≥0 generated by A, as follows. $$\frac{1}{2}(E\{ s\} )x + (E[0,s)) x = \mathop {\lim }\limits_{N \to \infty } \int_{ - N}^N {\frac{{\sin (sr)}}{r}} e^{irA} x\frac{{dr}}{\pi }$$ for any x in X.     

ESR identification of a new N2− defect in X-ray irradiated NaN3

A relatively weak ESR spectrum is observed in single crystals of NaN₃ after X-ray irradiation at 77 K. This spectrum, which has an anisotropic g value and exhibits a resolved 5-line hyperfine structure with components in the ratio 1:2:3:2:1, corresponds to a single unpaired electron interacting symmetrically with two spin-one nuclei, in three inequivalent sites. The spin-Hamiltonian parameters are: g_x = 2.0054 ± 0.0005, g_y = 2.0045 ± 0.0005, g_z = 1.9688 ± 0.0005, |A_x| = 4.0 ± 0.2 G, |A_y| = 20.0 ± 0.2 G, and |A_z| = 4.9 ± 0.2 G, c-axis, and y is perpendicular to the c-axis. This spectrum, which is clearly different from that of substitutional N₂^?reported by Gelerinter and Silsbee, is attributed to interstitial N₂^?.     

An elementaryU(2) theory of radiation fields with spinJ

An elementary theory for a radiation field with any spinJ is presented. This is a natural extension of Maxwell's equations for the electromagnetic field. The idea is to use the generators for theU(2) group in a multidimensional representation. These generators are a linear combination of the ones for infinitesimal Lorentz transformations. The constants of the motion in this formalism are discussed. As an example, angular distributions of the Poynting vector are given.Supported in part by grants from the Research Corporation and the Mitsubishi Fund.Parts of this work were done in partial fulfilment of the requirements for the M.A. Degree at Western Michigan University.     

Synthesis and mesogenic properties of several homologous series of aldose dialkyl dithioacetals. A model for their behaviour

Abstract

Ten homologous series (n-butyl through n-decyl) of aldose S,S-acetals (D-glucose, D-galactose, D-mannose, L-rhamnose, 2-deoxy-D-glucose, D-xylose, D-lyxose, D- or L-arabinose, D-ribose and 2-deoxy-D-ribose) have been prepared. Most of these compounds form thermotropic liquid crystals, the exceptions being the entire L-rhamnose series and some of the derivatives with the shortest alkyl chains. All of the compounds have been investigated with differential scanning calorimetry and polarization microscopy. Some temperature dependent powder X-ray data are also presented. A model is proposed which correlates the carbohydrate configuration with the melting behaviour. On the basis of now available behaviourial characteristics, visual inspection, mixing experiments and precedent, the mesophase is identified as smectic A_d, the partially overlapping carbohydrate moieties being in the centre and the aliphatic chains pointing outward at an angle of about 62°. Despite the intrinsic chirality of all the carbohydrate mesogens, no evidence for chiral mesophases was found, not even after introduction of a homochiral branched alkyl chain.     

Spin torque, tunnel-current spin polarization, and magnetoresistance in MgO magnetic tunnel junctions

We employ the spin-torque response of magnetic tunnel junctions with ultrathin MgO tunnel barrier layers to investigate the relationship between spin transfer and tunnel magnetoresistance (TMR) under finite bias, and find that the spin torque per unit current exerted on the free layer decreases by < 10% over a bias range where the TMR decreases by > 40%. This is inconsistent with free-electron-like spin-polarized tunneling and reduced-surface-magnetism models of the TMR bias dependence, but is consistent with magnetic-state-dependent decay lengths in the tunnel barrier.     

Solvation dynamics in methanol: Experimental and molecular dynamics simulation studies

We have investigated the ultrafast dynamics of methanol by time dependent fluorescent shift experiments and molecular dynamic simulations. The experiments were performed with two different probe molecules, 1-aminonaphthalene and coumarin 153. The molecular dynamic simulations employed these probes as well as small atomic and diatomic solutes. We find a previously unobserved fast decay component in the solvation response of methanol. The molecular dynamics results are in good agreement with this experimental result. The origin of this fast response and the linearity of the solvent response are discussed.     

Interpolation of nonlinear positive or order preserving operators on Banach lattices

Positivity - We study the relationship between exact interpolation spaces for positive, linear operators, for order preserving, Lipschitz continuous operators, and for positive...