Materials Literature
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In this article we report on the temperature dependencies of the longitudinal and shear sound velocities in Ti4AlN3, Ti3Al1.1C1.8, and Ti3SiC2. The velocities are measured using a phase sensitive pulse-echo ultrasonic technique in the 90–300 K temperature range. At room temperature, Young’s, ERT, and shear, μRT, modul…
High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal l…
Single molecule confocal microscopy is used to study fluorescence intermittency of individual ZnS overcoated CdSe quantum dots (QDs) excited at 488 nm. The confocal apparatus permits the distribution of “on” and “off” times (i.e., periods of sustained fluorescence emission and darkness) to be measured over an unpreced…
Scanning tunneling microscopy, spectroscopy, and tight-binding calculations have been used to elucidate the unique structural and electronic properties of single-walled carbon nanotubes (SWNTs). First, the unique relationship between SWNT atomic structure and electronic properties, and the richness of structures obser…
The cooperative Jahn-Teller coupling between the Mn e(g) electrons and the oxygen octahedral distortions in LaMnO3 is studied using ab initio density-functional calculations and tight-binding models. The linear and quadratic vibronic coupling parameters are calculated using density-functional methods. It is shown that…
We have developed the ability to grow reproducible La0.67Sr0.33MnO3/SrTiO3/Al tunnel junctions with high quality gap characteristics for spin-polarization measurements. A YBa2Cu3O7 counterelectrode was required to prevent current crowding. In order to fit our data, we have numerically solved Maki’s equations which inc…
The loss from polypropylene (PP) of sterically hindered amines with molecular weight ranging from 1364 to 2758 in heptane, chloroform, and methanol at room temperature was studied. The additives leak from polymer in heptane and in chloroform and some residual concentration remains in the polymer; the stabilizers show…
Results of the dynamic mechanical behavior of atactic polystyrene (PS) and high-impact polystyrene (HIPS) for temperatures between 300 and 425 K at a frequency of the order of 50 kHz are presented. The storage Young's modulus, (E′), of the HIPS is lower than the PS value, being the relationship between them a function…
The general behavior of the magnetostriction coefficients for Fe, Co, and Ni and their alloys is reproduced by first-principles theory. It is shown that the low magnetostriction coefficient of soft magnetic materials, observed for specific alloy concentrations, such as permalloy, can be explained theoretically by empl…
The kinetics of the bulk polymerization reaction of 1-iso-cyan-a-to-3-isocyanato methyl-3,5,5-trimethylcyclohexane or isophorone diisocyanate (IPDI) with poly(oxytetramethylene) glycol (POTM) was studied by 13C nuclear magnetic resonance (13C-NMR). The difference of reactivity of the NCO groups in this unsymmetrical d…
The optical properties of a new family of neodymium doped BPG (Bi2O3-PbO-Ga2O3 ) glasses are presented. We measured a high refractive index, of 2.5, and a transmission cutoff in the far infrared at 8microm. Three intense emission bands are observed centered at 877nm, 1066nm and 1341nm. The emission cross-section is 10…
During the plastic deformation of crystalline material the dislocations, being the carriers of the plastic flow, tend to form different patterns. Because of the long range nature of dislocation-dislocation interaction, the origin of this self-ordering phenomenon is still an open question. The paper presents a stochast…
A new class of biodegradable poly(ester-amide)s was prepared by a two step method. At first isosorbide or isomannide were esterified with α-amino acids in the presence of p-toluenesulfonic acid, and the resulting esters bisammonium tosylates were isolated. Second, the amino groups were liberated and polycondensed with…
Copolymers of ε-caprolactone and L-lactide (PCLLA) with different monomer ratio were synthesized by ring opening polymerization, and drug-loaded nanoparticles of poly-ε-caprolactone (PCL), poly-L-lactide (PLLA), and their copolymers were prepared by precipitation method, respectively. The results of differential scann…
A new technique for characterization of linear low-density polyethylene (LLDPE) is presented in this report. The molecular structure of two commercial LLDPEs, produced by copolymerization of ethylene with 1-butene over a Ziegler-Natta and a metallocene catalyst, was investigated. The LLDPE resins were fractionated by…
Slow structural relaxation ("aging") observed in many atomic, molecular, and polymeric glasses substantially alters their stress-strain relations and can produce a distinctive yield point. Using Monte Carlo simulation for a binary Lennard-Jones mixture, we have observed these phenomena and their cooling-rate dependenc…
New experimental data obtained mainly at the GSI/FRS facility allow one to modify the empirical parametrization of fragmentation cross sections. It will be shown that minor modifications of the parameters lead to a much better reproduction of measured cross sections. The most significant changes refer to the descripti…
We develop a variational mean-field theory of the ferromagnetic transition in compounds like Lanthanum-Manganite within the framework of the Double-Exchange Model supplemented by modest disorder. We obtain analytical expressions for the transition temperature, its variation with the valence electron-density and its de…
We present a new technique which allows the fully {\em ab initio} calculation of the chemical potential of a substitutional impurity in a high-temperature crystal, including harmonic and anharmonic lattice vibrations. The technique uses the combination of thermodynamic integration and reference models developed recent…
We develop a finite-element-based nodal dislocation dynamics model to simulate the structure and strength of dislocation junctions in fcc crystals. The model is based on anisotropic elasticity theory supplemented by the explicit inclusion of the separation of perfect dislocations into partial dislocations bounding a s…