Materials Literature
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A theory of multiphonon relaxation for electronically or vibrationally excited impurities in crystals is developed. Two alternative approaches within the static-coupling scheme are presented and their relative importance is discussed. For each approach a closed-form analytical expression for the relaxation rate is giv…
We present here an optimized united atom model that is able to reproduce properties of melts of n-alkane chains of varying molecular weights. This model differs from previous models in that the Lennard-Jones well depth for the terminal methyl group (0.2264 kcal/mol) differs from that of the methylene units (0.093 kcal…
Our environment is largely one of polymers and all polymers burn whether natural or synthetic. The issue is not whether polymers burn but rather if a given polymer has a property profile appropriate to provide for an acceptable level of risk in a given application. How we make polymers flame retardant, what flame reta…
The roots of the Hankel determinant built with the Taylor coefficients of the regularized logarithmic derivative of the eigenfunction give both the bound-state and Siegert eigenvalues (resonances) of separable quantum-mechanical systems. We obtain accurate positions and widths for the resonances of some commonly chose…
Our environment is largely one of polymers and all polymers burn whether natural or synthetic. The issue is not whether polymers burn but rather if a given polymer has a property profile appropriate to provide for an acceptable level of risk in a given application. How we make polymers flame retardant, what flame reta…
The fundamental condensed phase processes which lead to char formation during the fire-like pyrolysis of poly(vinyl alcohol), PVA, and PVA-containing maleimides were characterized using CP/MAS 13 C NMR. In addition to evidence of the well known chain-stripping elimination of H 2 O and the chain-scission reactions, whi…
The authors report an all solid state, VLSI compatible, electroluminescent device based on porous silicon with an external quantum efficiency greater than 0.1% under CW operation. The emission, which is broadband and peaks at 600 nm, is detected above a low threshold current density and voltage of 0.01 Am-2 and 2.3 V,…
Tm(3+)-doped heavy metal oxide glasses in the PbO-Bi(2)O(3)-Ga(2)O(3) system were prepared, and their emission characteristics were examined. Three emission bands at the infrared wavelength region were observed, at 1.46, 1.79, and 2.36 µm, which are associated with the (3)H(4) ? (3)F(4), (3)F(4) ? (3)H(6), and (3)H(4)…
We consider the swelling kinetics of layered structures. We focus on the case of triblock copolymer mesogels, although our results are applicable to other layered structures including clays. We assume the mesogels are swollen by a solvent that is good for the bridging block but poor for the non-bridging block. At long…
Abstract Rubbers of different kind were tested as toughening agents of poly(ethylene terephthalate) (PET), noting significant morphological and mechanical differences. In particular, good results were obtained by using an ethylene–ethyl acrylate–glycidyl methacrylate copolymer. The resulting blend evidenced good parti…
Abstract A commercial linear low density polyethylene (1‐hexene comonomer) was reacted with dicumyl peroxide at appropriate levels to initiate chain extension without crosslinking. The peroxide modification was carried out both in the presence and absence of a common hindered phenolic antioxidant. Thermal treatment of…
Abstract This article begins by briefly reviewing the more important contributions to the area of modeling heat and mass transfer, and particle growth during the polymerization of olefins on Ziegler–Natta catalysts. It is shown that these models are capable of identifying the critical areas involved in heat and mass t…
In this paper I review the ways in which the glassy state is obtained both in nature and in materials science and highlight a "new twist"--the recent recognition of polymorphism within the glassy state. The formation of glass by continuous cooling (viscous slowdown) is then examined, the strong/fragile liquids classif…
Elastic singularities such as crack tips, when in motion through a medium that is itself vibrating, are subject to forces orthogonal to the direction of motion and thus impossible to determine by energy considerations alone. This fact is used to propose a universal scenario, in which three dimensionality is essential,…
DTA and ESR methods were applied for studying photostimulated changes in molecular arsenic (y-As). It is shown that under the effect of illumination/irradiation the stability of y-As decreases, which is due to the formation of stable fragments of the polymeric phase (a-As). Using the principles of orbital symmetry con…
We present a theoretical study of magnetic relaxation of big molecules, M${\mathrm{n}}_{12}$${\mathrm{O}}_{12}$, at low temperature, when the relaxation time $\ensuremath{\tau}$ is temperature independent. If the magnetic field ${h}_{z}$ is not too low, tunneling can only take place if energy is exchanged with phonons…
AC susceptibility, zero-field-cooled (ZFC) magnetization and field-cooled (FC) magnetization have been reported for the Zn 0.5 Co 0.5 Fe 1.1 Cr 0.9 O 4 disordered ferrite system. A polarization analysis of the transmitted neutron beam in both ZFC and FC conditions has also been reported for Zn 0.5 Co 0.5 Fe 2-x Cr x O…
Vincristine is used clinically for the treatment of various types of cancer. Recent significant therapeutic improvements obtained by entrapping anthracyclines in sterically stabilized liposomes raised the question whether the therapeutic index of vincristine can be similarly increased by formulation into such long-cir…
Coarsening in three-dimensional polycrystalline systems such as foams, magnetic bubbles, metal crystals, and ceramics is poorly understood because of the absence of data describing the interior of these materials. We introduce magnetic resonance imaging to probe the interior of a foam, providing information on topolog…
Ablation of diamond by short UV pulses is reported. The ablation threshold for 500 fs pulses at 248 nm was found to be 0.6 J/cm2 (equal to a peak intensity of 1.1 TW/cm2). Intensity-dependent transmission measurements from low intensities to 100 GW/cm2 showed that two-photon absorption is the dominant nonlinearity in…