Sensitive intracavity absorption at reduced pressures

A broadband continuous-wave dye laser has been enclosed to eliminate interfering atmospheric absorption, and has been run at pressures as low as 50 Torr of various gases. Detection of peak absorption coefficients as small as 10^-8 cm^-1 has been verified, and lines spaced by 0.1 cm^-1 have been resolved.     

Statistical description of a paired nucleus with the inclusion of angular momentum

The effect of angular momentum on an excited paired nucleus has been studied. The BCS Hamiltonian, modified to include the z-projection of angular momentum has been diagonalized and expressed in terms of the quasiparticle occupation numbers. The grand partition function and all the relevant thermodynamical functions as well as the level-density expression have been derived for the general case of an arbitrary set of single-particle levels. Furthermore, the formalism has been applied to the uniform model and, whenever possible, analytical expressions have been derived. In particular the zero-temperature angular momentum dependence of the gap parameter, the critical angular momentum as well as the yrast line have been calculated. The critical temperature as a function of angular momentum, which defines the phase transition between paired and unpaired systems, has been calculated. A new effect called the thermally assisted pairing correlation, involving an increase of pairing with increasing temperature has been predicted. The completeness of the formalism as applied to spherical or deformed nuclei has been discussed.     

Intensity measurements on Σ-hyperonic and kaonic atoms

σ-hyperonic X-ray lines have been observed in 8 elements and their intensities as well as those of the accompaning kaonic X-ray lines have been determined. The σ-atomic cascade has been found to be similar to those of other exotic atoms. The production of σ^? hyperons per stoppedK ^? has been measured by comparing their X-ray intensities. For the first time the intensity attenuation due to the strong absorptive σN interaction could be measured in four cases, and simple optical model calculations have been performed in order to reproduce the data.     

Neon ion irradiation studies on MgB2 superconductor

160 MeV of neon ion irradiation has been carried out on MgB₂ polycrystalline pellets at various doses. There has not been any significant change in T_c except at the highest dose of 1×10¹⁵ ions/cm². Increase in resistivity has been noticed. Resistivity data have been fitted with Bloch-Grüneisen function to extract the values of Debye temperature, residual resistivity and temperature coefficient of resistivity for irradiated as well as unirradiated samples. There has not been any significant effect on electron-phonon coupling due to irradiation as evident from Debye temperature and the electron-phonon coupling constant.     

Centrifugal distortion effects in SF2: Calculation of the force field and infrared spectrum

Measurements of the microwave spectrum of SF₂ have been extended up to J = 43 in order to account for the effects of centrifugal distortion. Seventy-five transitions have been included in a weighted least squares fit of the measured spectrum with an rms deviation of 0.078 MHz. The force field for SF₂ has been determined from the centrigufal distortion constants. The vibrational spectrum, as yet unobserved, has been predicted from the force field as have been the Coriolis coupling constants and the average structure.     

Performance of 2-hole YBCO rf SQUID in flux-locked-loop mode at 77 K

A 2-hole rf SQUID has been fabricated using naturally present grain boundary Josephson weaklinks in a microbridge of bulk Y-Ba-Cu-O superconductor. Periodic oscillations in voltage-flux characteristics have been observed up to 80.5 K. The spectral density of flux noise of the SQUID is 8 × 10⁻⁴ Φ₀/√Hz at 100 Hz and 77 K for open-loop mode. The SQUID has been successfully operated in flux-locked-loop mode at 77 K, demonstrating the feasiblity of the device for practical applications. In the flux-locked-loop mode the stability as well as flux noise of the SQUID has been found to improve considerably as compared to that in the open-loop mode. Various SQUID parameters have also been estimated and reported here.     

Study of surface morphology of ferrofluid deposited etched ion tracks in dielectric layers

An AFM study is reported on swift heavy irradiated Si/SiO₂ substrates which have been etched by aqueous hydrofluoric acid solution leading to ion tracks in which ferrofluids have been deposited leading to tunable electronic materials with pores in oxide on silicon (TEMPOS) structure. Two ferrofluids with different carrier fluids (aqueous and non-aqueous) have been deposited in the tracks. Atomic force microscopy has been used to study the empty as well as filled tracks. Since the ferrofluids contain iron oxide particles, there is a possibility of agglomeration of these particles inside and outside the tracks. Surface area and pore volume of the tracks have been measured by Brunauer-Emmett-Teller (BET) method. The track properties (empty and filled) as observed by AFM have been correlated with BET measurements.     

Tunable diode laser measurements of water vapour absorption line parameters

Tunable diode laser measurements of water vapour lines in the 5 μm region have been extended to include oxygen as well as nitrogen broadening. Positive pressure shifts of line positions have been observed for the first time in the v ₂ band. Absolute calibration of a line position using the CO laser as a reference has also been carried out.     

Cinchona alkaloid-based polymer-bound phase-transfer catalysts: Efficient enantioselective alkylation of benzophenone imine of glycine esters

Summary Cross-linked polystyrene-bound and poly(ethylene glycol)-bound phase-transfer catalysts as well as homopolymers of cinchona alkaloid derivatives have been synthesised. Both soluble and insoluble polymers have been investigated. The enantioselective alkylation of N-diphenyl methylene glycine t-butyl ester has been successfully carried out in heterogeneous and homogeneous systems. High enantioselectivities (up to 96%) have been obtained. The polymer-bound catalysts have been easily recovered and conditions for efficient recycling have been studied.     

Specific features of the EPR spectra of KTaO<Subscript>3</Subscript>: Mn nanopowders

The electron paramagnetic resonance spectra of KTaO₃: Mn nanocrystalline powders in the temperature range from 77 to 620 K have been measured and studied for the first time. The change observed in the spectra has been investigated as a function of the doping level. The doping regions in which Mn²⁺ ions are individual paramagnetic impurities have been established, as well as the regions where the dipole-dipole and exchange interactions of these ions begin to occur. The spin-Hamiltonian constants for the spectrum of non-interacting individual Mn²⁺ ions have been determined as follows: g = 2.0022, D = 0.0170 cm⁻¹, and A = 85 × 10⁻⁴ cm⁻¹. A significant decrease in the axial constant D in the KTaO₃: Mn nanopowder, as compared to the single crystal, has been explained by the remoteness of the charge compensator from the paramagnetic ion and by the influence of the surface of the nanoparticle. It has been assumed that the Mn²⁺ ions are located near the surface and do not penetrate deep into the crystallites.     

Ionic conductance behaviour of plasticized polymer electrolytes containing different plasticizers

The effect of different plasticizers on the properties of PEO-NH₄F polymer electrolytes has been studied. Aprotic organic solvents like propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (γ-BL), dimethylacetamide (DMA), dimethylformamide (DMF), diethylcarbonate (DEC) and dimethylcarbonate (DMC) having different values of donor number, dielectric constant, viscosity etc. have been used as plasticizers in the present study. The addition of plasticizer has been found to modify the conductivity of polymer electrolytes by increasing the amorphous content as well as by dissociating the ion aggregates present in polymer electrolytes at higher salt concentrations. The conductivity enhancement with different plasticizers has been found to be closely related to the donor number of the plasticizer used rather than its dielectric constant. The increase in conductivity with the addition of plasticizer has further been found to be dependent upon the level of ion association present in the electrolytes. The variation of conductivity as a function of plasticizer concentration and temperature has also been studied and maximum conductivity of ∼ 10⁻³ S /cm at room temperature has been obtained. X-ray diffraction studies show an increase of amorphous content in polymer electrolytes with the addition of plasticizers.     

Geometrical Model for Phenylthallium Dihalides

The geometry of the phenylthallium dihalides, PhTlX₂(X=F, Cl or Br) which has heitherto been unknown, has been proposed on the basis of several qualitative aspects and quantitative arguments. These molecules have a planar structure with C_2v symmetry and the ring geometry has been assumed to be the same as that of benzene. The ring-substituent bond length has been taken to be 2.218 A° in all the three molecules, and the Tl-F, Tl-Cl and Tl-Br bond lengths in respective molecules have been estimated to be 1.878, 2.366 and 2.520 A°. The remaining parameter inter-bond angle, F-Tl-F has been taken to be 116° in PhTlF₂, whereas, angles Cl-Tl-Cl and Br-Tl-Br in respective molecules have been taken to be 120°, as expected in the case of a pure sp² hybridization.     

Phase diagram of a thin film of the Fe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloy with the “bulk” or “planar” magnetoelastic interaction

Concentration-induced reorientation phase transitions in thin magnetic films of FeCo alloys have been investigated taking into account “planar” or “bulk” magnetoelastic interaction. The critical concentrations of Co corresponding to the phase transition points, as well as the types of the phase transitions, have been determined. The phase diagrams have been plotted.     

A band-mixing Hartree-Fock model for62Zn

Energy levels and electromagnetic transitions in⁶²Zn have been calculated using band-mixing formalism in the framework of deformed Hartree-Fock theory. Matrix elements of Adjusted-Surface Delta Interaction (ASDI) and of Tabakin interaction have been used. Detailed structure of various nuclear states in terms of bands has been discussed. Although the calculated spectra for both the interactions are somewhat compressed as compared to the observed spectra, the ASDI results are in substantially better agreement with experiments. Several additional states of high spin (J>4) have been predicted.B(E2) transitions between inter-band as well as some of the intraband states are calculated to stimulate further experiments.     

Microwave spectra and structure of an isoxazole-water complex

The rotational spectrum of a hydrogen-bonded isoxazole-water complex has been measured between 6–18 GHz with a pulsed nozzle Fourier transform microwave spectrometer. In addition to isoxazole-H₂O, the complexes with HDO and D₂O as well as isoxazole-¹⁵ N-H₂O have been investigated in order to determine the structure of the complex. Rotational constants, quartic centrifugal distortion constants and quadrupole coupling constants, where applicable, have been fitted to the measured transition frequencies of the isotopomers. Structural data, which have been deduced from the planar moments of inertia and the quadrupole coupling constants of the isotopomers, have established conclusively that water binds to nitrogen in the ring plane of isoxazole. Ab initio calculations have revealed that complexes with a hydrogen-bond to nitrogen or to oxygen are both stable. The complex with water attached to nitrogen has been found to be more strongly bound than that with water attached to oxygen. Small splittings of the rotational transitions of the two complexes with H₂O have been interpreted as being the result of an internal rotation of water with respect to isoxazole.     

Ugi–Smiles couplings: new entries to N-aryl carboxamide derivatives

The scope of the Ugi reaction has been extended by the use of phenols as carboxylic acid surrogates to afford N-aryl carboxamides. A Smiles rearrangement occurs as the last step of the mechanism instead of the classical final Mumm process. Various parameters concerning the nature of these inputs have been studied: the use of heteroaromatic derivatives, the substitution of the hydroxyl moiety by a thio entity (to afford functionalized thioamides), as well as the influence of the nature and position of substituents on the phenol. A three-component version (Passerini–Smiles) of this coupling has been developed as well. Following these couplings, various post-condensation transformations have been performed to reach more complex heteroaromatic fused systems. The easy functionalizations of phenols offer many opportunities for cyclization strategies: the reduction of the nitro group allows the formation of o-phenylenediamine derivatives, which, in turn, can be transformed into quinoxalines, benzotriazoles, and benzimidazoles. Various organometallic reactions of the Ugi–Smiles adducts have been successfully carried out, either from iodophenols (Heck couplings to give indoles, Ullmann reaction to form quinoxalines), or from allyl pyrimidines (azepine formation by RCM strategy) as starting phenol inputs. Finally, a new palladium-mediated oxidative cyclization led to the formation of tricyclic systems.     

Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis

Diclofenac sodium, a widely detected pharmaceutical drug in wastewater samples, has been selected as a model pollutant for degradation using novel combined approach of hydrodynamic cavitation and heterogeneous photocatalysis. A slit venturi has been used as cavitating device in the hydrodynamic cavitation reactor. The effect of various operating parameters such as inlet fluid pressure (2–4 bar) and initial pH of the solution (4–7.5) on the extent of degradation have been studied. The maximum extent of degradation of diclofenac sodium was obtained at inlet fluid pressure of 3 bar and initial pH as 4 using hydrodynamic cavitation alone. The loadings of TiO₂ and H₂O₂ have been optimised to maximise the extent of degradation of diclofenac sodium. Kinetic study revealed that the degradation of diclofenac sodium fitted first order kinetics over the selected range of operating protocols. It has been observed that combination of hydrodynamic cavitation with UV, UV/TiO₂ and UV/TiO₂/H₂O₂ results in enhanced extents of degradation as compared to the individual schemes. The maximum extent of degradation as 95% with 76% reduction in TOC has been observed using hydrodynamic cavitation in conjunction with UV/TiO₂/H₂O₂ under the optimised operating conditions. The diclofenac sodium degradation byproducts have been identified using LC/MS analysis.     

Magnetic properties of FeSiB thin films displaying stripe domains

FeSiB amorphous thin films with thicknesses from 25 to 600 nm have been produced by rf sputtering on Si₃N₄ substrates. A spin reorientation transition has been observed on the as-prepared samples, as a function of thickness and temperature. Spin reorientation transition is shown to depend on the thermal treatments to which the as-prepared samples have been submitted. Static hysteresis loops obtained as a function of temperature, and magnetic force microscopy images taken at room temperature at the remanence and as a function of an applied magnetic field, have been employed to study the magnetic domain configuration of all the samples, and to see how it is affected by sample thickness, measurement temperature and annealing conditions.     

Analyse perturbative des caractéristiques de propagation des fibres optiques à gradient d'indice quasi-parabolique

A simple perturbation theory, based on the scalar wave analysis, has been used to study the propagation characteristics of radially inhomogeneous lossless fibres. The formalism has been developed with a truncated parabolic-index profile as the zero-order solution and the perturbation approach is valid for azimuthally symmetric or anti-symmetric modes near cut-off as well as far from cut-off. In addition, numerical calculations have been carried out for-profiles and have been found to be in good agreement with more rigorous calculations reported by previous authors.