Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

The dependence of the beam propagation factor (M ² parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M ₂ parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M ² parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd³⁺ -doped GdVO₄ crystal and the values of α and β parameters were estimated from the experimentally measured data points.     

Some empirical relations for electron mobility in II–VI compound semiconductors

Electron mobility has been calculated in a number of binary II–VI compound semiconductors using a displaced Maxwellian distribution function and taking the various scattering mechanisms into consideration at different lattice temperatures and for various amounts of ionized impurity concentrations. It is observed that the low field mobility values can be expressed by a cubic power relationship with lattice temperature and with ionized impurity concentration using a least mean square fit technique with an accuracy better than 5 per cent. Similarly, the field dependence of mobility can also be expressed as a power series of the applied electric field. It is suggested that these equations can be profitably used for a quick estimation of mobility values as a check on experiments and also as sufficiently accurate formulae for simulation and modelling purposes.     

Thermoelastic interactions without energy dissipation in an unbounded body with a spherical cavity subjected to harmonically varying temperature

The present work is concerned with the thermally induced vibration in a homogeneous and isotropic unbounded body with a spherical cavity. The Green and Nagdhi model of thermoelasticity without energy dissipation is employed. The closed form solutions for distributions of displacement, temperature and stresses are obtained. The solutions valid in the case of small frequency are deduced and the results are compared with the corresponding results obtained in other generalized thermoelasticity theories. Numerical results applicable to a copper-like material are also presented graphically and the nature of variations of the physical quantities with radial coordinate and with frequency of vibration is analyzed.     

Non-protein amino acids in peptide design

An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from the author’s laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the useα-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments and^DPro-Xxx segments for nucleating ofβ-hairpin structures.β- andγ-amino acid residues have been used to expand the range of designed polypeptide structures. Dedicated to Professor C N R Rao on his 70th birthday     

Effect of benzophenone on the H2O2-induced photopolymerization of methyl methacrylate

Benzophenone (BP) in low concentrations (<0.001 mol 1^?1) produces a rate enhancing effect in the H₂O₂-induced bulk photopolymerization of MMA. R_p is proportional to [H₂O₂]^0.4 and [BP]^0.4, and $\text{k}{}_{\mathrm{p}}{}^2\text{k}{}_1$ at 30° is 1.00 × 10^?2 1.mol^?1 sec^?1. In diluted systems, different solvents produce different kinetic effects, reaction order with respect to monomer being negative for IPA and THF as solvent, positive but <1.0 for benzene and chloroform, 1.2 for acetonitrile, CCl₄ and t-butanol and 1.8 for DMA. The variable solvent effect is attributed to modification of the initiation process by the various solvents to different extents. Kinetic analysis of data for bulk photopolymerization gives evidence for primary radical termination and degradative initiator transfer.     

Far-infrared spectroscopy of CH3OD in highly excited torsional states and the atlas of the Fourier transform spectra in the range 200-350 cm(-1)

The high resolution Fourier transform far-infrared (FIR) spectrum of the torsion rotation band of CH3OD has been analyzed for the highly excited torsion states (n > or = 2) in the vibrational ground state. The spectrum shows splitting of the lines due to strong torsional-rotational-vibrational interactions in the molecule. Assignments were possible for rotational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to approximately 30 in most cases, for all the symmetry species. For the third excited torsional state n = 3 assignments were possible to K = 10. The data were analyzed with the help of the energy expansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters were able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coefficients should prove valuable in the calculation of precise energy values for excited torsional states up to n = 4, which is way above the torsional barrier. The detailed high-resolution spectral atlas of CH3OD has been presented in the range 200-350 cm(-1). This atlas is an extension of our earlier atlas in the range 20-205 cm(-1). The availability of this atlas in the journal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer space.     

Aromatic-aromatic interactions in crystal structures of helical peptide scaffolds containing projecting phenylalanine residues

Aromatic-aromatic interactions between phenylalanine side chains in peptides have been probed by the structure determination in crystals of three peptides: Boc-Val-Ala-Phe-Aib-Val-Ala-Phe-Aib-OMe, I; Boc-Val-Ala-Phe-Aib-Val-Ala-Phe-Aib-Val-Ala-Phe-Aib-OMe, II; Boc-Aib-Ala-Phe-Aib-Phe-Ala-Val-Aib-OMe, III. X-ray diffraction studies reveal that all three peptides adopt helical conformations in the solid state with the Phe side chains projecting outward. Interhelix association in the crystals is promoted by Phe-Phe interactions. A total of 15 unique aromatic pairs have been characterized in the three independent crystal structures. In peptides I and II, the aromatic side chains lie on the same face of the helix at i/i + 4 positions resulting in both intrahelix and interhelix aromatic interactions. In peptide III, the Phe side chains are placed on the opposite faces of the helix, resulting in exclusive intermolecular aromatic interactions. The distances between the centroids of aromatic pair ranges from 5.11 to 6.86 A, while the distance of closest approach of ring carbon atoms ranges from 3.27 to 4.59 A. Examples of T-shaped and parallel-displaced arrangements of aromatic pairs are observed, in addition to several examples of inclined arrangements. The results support the view that the interaction potential for a pair of aromatic rings is relatively broad and rugged with several minima of similar energies, separated by small activation barriers.     

A one-pot synthesis of novel sugar derived 5,6-dihydro-quinazolino[4,3-b]quinazolin-8-ones: an entry towards highly functionalized sugar-heterocyclic hybrids

An efficient and practical one-pot method for the synthesis of novel diversified sugar derived dihydro-quinazolino[4,3-b]quinazolin-8-ones has been reported. Various protected sugar hemiacetals were used to synthesize the hybrid tetracyclic ring system. The one-step reductive transformation of 2-(2-nitrophenyl)-3H-quinazolin-4-one with different sugar hemiacetals furnished the desired tetracyclic product in good yields and with high purity.