Pattern Effect Removal Technique for Semiconductor-Optical-Amplifier-Based Wavelength Conversion

A technique to overcome pattern dependence in semiconductor-optical-amplifier-based wavelength converters is presented. The technique is based on a careful selection of red- and blue-shifted spectral components having complementary pattern effects in the output spectrum of a wavelength-converted signal. Significant signal quality improvements are reported at a bit rate of 40 Gb/s.     

Feasibility Study of Batteryless Temperature Transponders Using Miniature Microwave Cavity Resonators

Batteryless temperature transponders have been constructed and tested. The design employs a sensing element consisting of a miniature cavity resonator loaded with a ceramic material of high dielectric constant and large temperature coefficient of resonant frequency. This is connected by thin coaxial cable to a small dipole or sector antenna. Prototypes with sensors 3 mm in diameter have been fabricated and can resolve temperature differences of 0.1°C in air. Signals have been obtained from transponders implanted in anesthetized rats, but antenna orientation is a critical and limiting factor that will require further efforts before a system is capable of operating in freely roaming animals.     

Trends in metal-biradical exchange interaction for first-row M(II)(nitronyl nitroxide-semiquinone) complexes

We report molecular structures and temperature-dependent magnetic susceptibility data for several new metal complexes of heterospin triplet ground-state biradical ligands. The ligands are comprised of both nitronyl-nitroxide (NN) and semiquinone (SQ) spin carriers. Five compounds are five-coordinate M(II) complexes (M = Mn, Co, Ni, Cu, and Zn), and one is a six-coordinate Ni(II) complex. Five compounds were structurally characterized. During copper complex formation a reaction with methanol occurs to form a unique methoxy-substituted SQ ring. Variable-temperature magnetic susceptibility studies are consistent with strong intraligand (NN-SQ and NN-PhSQ) ferromagnetic exchange coupling. For the five-coordinate Mn, Co, and Ni complexes, the S = 1 ligand is antiferromagnetically coupled to the metal. For both the five-coordinate Cu complex and the six-coordinate Ni complex, the ligand is ferromagnetically coupled to the metal spins in accordance with orbital symmetry arguments. Despite the low molecular symmetries, the predicted trend in metal-ligand exchange interactions is supported by spin dimer analysis based on extended Hückel calculations. For (NN-SQ)NiTp(Cum,Me)() (Tp(Cum,Me)() = hydro-tris(3-cumenyl-5-methylpyrazolyl)borate), an antisymmetric exchange term was required for the best fit of the magnetic susceptibility data. Antisymmetric exchange was less important for the other complexes due to inherently smaller Deltag. Finally, it is shown that intraligand exchange coupling is of paramount importance in stabilizing high-spin states of mixed metal-biradical complexes.     

Nondiverging algebraically special ℋ-spaces

All nondiverging algebraically special -spaces are found by means of the complexified spin-coefficient formalism. The solutions are found to group naturally into two classes according to whether or not the optical-rotation spin coefficient vanishes.Research supported in part by a grant from the National Science Foundation.     

Quantum dot-in-a-well (QDWELL) laser dynamics under optical injection

We investigated theoretically the optical injection influence on the dynamics of a quantum dot in a quantum well (QDWELL) laser. The carrier dynamics is synchronized due to the optical injection, and QDWELL laser manifests a high performance at repetition frequencies up to 30 GHz.     

Distribution of Methoxyl Groups in the Methylation of Starch Alkoxides Obtained by Metallation with Alkali Metal Naphthalene

Abstract

The distribution of the alkoxide groups obtained in the metallation of starch in dimethyl sulfoxide solution by alkali metal naphthalenes was studied. The starch alkoxide was reacted with methyl iodide, and the methylated starch was hydrolyzed and analyzed for glucose and O-methyl glucose derivatives. The metallation reaction was found to be random, as seen from the fact that at low alkoxide concentration (D.S = 0.6), 2,3,6-tri-O-methyl glucose was formed, while at relatively high alkoxide concentration (D.S. = 1.5) unreacted glucose was still present. At low alkoxide concentration (D.S. ? 0.6) there was, to a certain extent, preferential metallation at the C₂ hydroxyl groups, and to a lesser extent at the C₆ hydroxyl groups, as seen from the relative molar ratios of about 10:4:1 of the 2-, 6-, and 3-O-methyl glucose derivatives obtained, respectively. An increase in the metallation at the C₃ hydroxyl occurred with increasing alkoxide concentration. The distribution of the methoxyl groups with the three alkali metals potassium, sodium, and lithium was similar; there were differences only in the ease of metallation of the starch by the various alkali metal naphthalenes and in the efficiency of the coupling reaction with methyl iodide.     

A novel cacalolide from Psacalium decompositum

A new cacalolide sesquiterpenoid, named as Romo-A, was isolated from the roots of Psacalium decompositum, Asteraceae, a Mexican medicinal shrub with antidiabetic properties. Its structure was elucidated by NMR, MS, IR, UV, and confirmed by X-ray diffraction studies.     

The adiabatic approximation for coupled oscillators

The adiabatic approximation is applied to determine the quantum states of coupled oscillators described by a generalized Hénon-Heiles hamiltonian. Comparison with exact quantum and other results show that numerically calculated adiabatic energy levels are accurate even for excited states.