Intermolecular charge-transfer complexes of macrocyclic polyethers with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

The interactions of benzo-15-crown-5, dibenzo-18-crown-6, and dibenzo-24-crown-8 with 2,3-dichloro-5,6-dicyano- 1,4-benzoquinone have been studied in methylene chloride by using spectroscopic methods. These crown ethers from 1:l molecular complexes with the acceptor. The magnitudes of association constants and thermodynamic parameters of complexation are indicative of cooperative interaction of oxygens with the acceptor.

Improved optical character recognition by matched filtering

The effectiveness of linear matched filters for improved character discrimination in presence of random noise and poorly defined characters has been investigated. We have found that although the performance of the filter in presence of random noise is reasonably good (16 dB gain in signal-to-noise-ratio) its performance is poor when the unknown character is distorted (linear shift and rotation).

Paraxial Maxwell beams: transformation by general linear optical systems

Extending the work of earlier papers on the relativistic-front description of paraxial optics and the formulation of Fourier optics for vector waves consistent with the Maxwell equations, we generalize the Jones calculus of axial plane waves to describe the action of the most general linear optical system on paraxial Maxwell fields. Several examples are worked out, and in each case it is shown that the formalism leads to physically correct results. The importance of retaining the small components of the field vectors along the axis of the system for a consistent description is emphasized.

Studies on the fractionation of total transfer ribonucleic acid and purification of an alanine transfer ribonucleic acid from chick embryo

Chick embryo tRNA, prepared by a simple large-scale method, was fractionated on three different ion-exchange columns. In all cases simple chromatographic patterns for various tRNA species were observed, indicating the presence of only a few major species of tRNA for each amino acid. By repeated chromatography one species of alanine tRNA was purified to approx. 80% purity. T1 ribonuclease digest of this purified tRNA gave a simple chromatographic pattern. Because of the simplicity of the method of preparation of tRNA from this readily available source and the presence of only a few species of tRNA for each amino acid, chick embryo is suited for the study of tRNA and its various functions in higher systems.

spin Precession of a Charged Particle in a Magnetic Field Including the Effects of General Relativity

Abstract is not available.

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr14−xCaxCu24O41 (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr14Cu24O41 show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. Tc onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with Tc max=9.4 K and TN=5 K at 56 kbars.

Study of linear and nonlinear optical properties of dendrimers using density matrix renormalization group method

We have used the density matrix renormalization group (DMRG) method to study the linear and nonlinear optical responses of first generation nitrogen based dendrimers with donor acceptor groups. We have employed Pariser–Parr–Pople Hamiltonian to model the interacting pi electrons in these systems. Within the DMRG method we have used an innovative scheme to target excited states with large transition dipole to the ground state. This method reproduces exact optical gaps and polarization in systems where exact diagonalization of the Hamiltonian is possible. We have used a correction vector method which tacitly takes into account the contribution of all excited states, to obtain the ground state polarizibility, first hyperpolarizibility, and two photon absorption cross sections. We find that the lowest optical excitations as well as the lowest excited triplet states are localized. It is interesting to note that the first hyperpolarizibility saturates more rapidly with system size compared to linear polarizibility unlike that of linear polyenes.

Number and proportion of selenocucleosides in the transfer RNA of escherichia-coli

tRNA isolated from escherichia-coli grown in a medium containing [75Se] sodium selenosulfate was converted to nucleosides and analysed for selenonucleosides on a phosphocellulose column. Upon chromatography of the nucleosides on phosphocellulose column, the radioactivity resolved into three peaks. The first peak consisted of free selenium and traces of undigested nucleotides. The second peak was identified as 4-selenouridine by co-chromatographing with an authentic sample of 4-selenouridine. The identity of the third peak was not established. The second and third peaks represented 93% and 7% of the selenium present in nucleosides respectively.

Improved optical character recognition by matched filtering

The effectiveness of linear matched filters for improved character discrimination in presence of random noise and poorly defined characters has been investigated. We have found that although the performance of the filter in presence of random noise is reasonably good (16 dB gain in signal-to-noise-ratio) its performance is poor when the unknown character is distorted (linear shift and rotation).

Microprocessor Based Sinusoidal PWM Inverter by DMA Transfer

The implementation of three-phase sinusoidal pulse-width-modulated inverter control strategy using microprocessor is discussed in this paper. To save CPU time, the DMA technique is used for transferring the switching pattern from memory to the pulse amplifier and isolation circuits of individual thyristors in the inverter bridge. The method of controlling both voltage and frequency is discussed here.

Stress-optical dispersion in rubidium chloride and rubidium bromide crystals

The stress-optical coefficients C = (n3/2) (q11−q12) and C′ = (n3/2)q44 of RbCl and RbBr crystals have been measured at room temperature (26°C) over the wave length range 5750-2500 A.

Unique presence of 2-methylthio-ribosylzeatin in the transfer ribonucleic acid of the bacterium Pseudomonas-Aeruginosa

Analysis of 35S labled nucleosides prepared from tRNA of Pseudomonas aeruginosa by phosphocellulose column chromatography, thin layer chromatography and Sephadex LH-20 column chromatography revealed the presence of 2-methylthioribosylzeatin in it. 2iPA, 6-(3-methyl-2-butenylamino)-9-β-D-ribofuranosyl purine; ms-2iPA, 6-(3-methyl-2-butenylamino)-2-methylthio-9-β-D-ribofuranosylpurine; ribosyl-cis-zeatin, 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-β-D-ribofuranosylpurine; ribosyl-trans-zeatin, 6-(4-hydroxy-3-methyl-trans-2-butenylamino)-9-β-D-ribofuranosylpurine; ms-ribosylzeatin, 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-β-D-ribofuranosylpurine; s4U2, 4-thiouridine; s2U*, 5-methylaminomethyl-2-thiouridine; s2C, 2-thiocytidine; TLC — thin layer chromatography.