Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Assessment of the quality of reedbeds using holomicroscopic moiré

Holographic interferometry is proposed to detect the change in the mechanical responses of reed stems growing in eutrophic, as compared with those in healthy, water bodies. The detection of the difference in behaviour could be a sensitive way to index the degree of eutrophication. An interferometric method based on holomicroscopic moiré is developed and preliminary results obtained are presented.     

Analysis of Corrugated Long-Period Gratings in Planar Waveguides and Their Polarization Dependence

We present a theoretical analysis of corrugated long-period gratings in planar waveguides. In particular, we calculate the transmission spectra for both the TE and TM polarizations and highlight the polarization-independence conditions.     

Study on the extraction of U(IV) relevant to PUREX process

The paper presents a radiokinetic study on the appearance and growth of^*Fe₂S₃,^*Fe(OH)₃,^*Fe₂(C₂O₄)₃,^*Fe(IO₃)₃ crystals in a colloidal medium of agar and gelatine. The values of the diffusion constants through gels of⁵⁵⁺⁵⁹Fe³⁺ radioactive cations and of the rate of global growth process of these crystals in agar or gelatine were calculated using the experimental data. A new method for the determination of the starting time for the complex nucleation process was proposed. The formation rate of crystals under study decreases in the order:^*Fe(OH)₃>^*Fe(IO₃)₃>^*Fe₂S₃>^*Fe₂(C₂O₄)₃, in agar medium and^*Fe(OH)₃>^*Fe(IO₃)₃>^*FeC₂O₄)₃>^*FeS₃, in gelatine medium.     

Studies on electroosmotic and electrophoretic behavior of cholesterol in aqueous solutions

Electrical properties of cholesterol interfaces have been investigated. For this purpose electroosmotic and hydrodynamic permeation of water, sodium chloride, barium chloride, aluminum chloride, and urea solutions across a cholesterol plug have been investigated. Dependence of electroosmotic permeability on concentration of electrolytes has also been studied. Electrophoretic mobility of cholesterol particles of known size distribution and dispersed in solutions of varying concentrations of electrolytes and urea has also been studied. The data have been used to estimate ζ potentials in order to have a plausible picture of the electrical double layer at the cholesterol/ solution interfaces.     

Interaction between organophosphorous hydrolase and paraoxon studied by surface chemistry in situ at air-water interface

Subphase conditions have been optimized to obtain stable organophosphorous hydrolase (OPH-EC 3.1.8.1) as Langmuir films. The Langmuir film was characterized by surface pressure and surface potential-area isotherms and UV-Vis spectroscopy in situ. The interaction of an organophosphorous compound, namely Paraoxon, with the OPH film was investigated for various surface pressures. The stability of the monolayer and the evidence of the enzyme activity at air-water interface support the use of enzyme LB films as biosensor.     

Dispersion characteristics of broadside coupled dielectric image guide at millimeter wave frequencies

Dispersion characteristics and wave impedance for the even and odd modes of the broad side coupled dielectric image guides are computed by using mode matching techniques. Dispersion curves for broadside image guide are plotted for various dielectric materials and dimensional parameters as a function of frequency. Normalized electric field for dominant electric field component E of TM even and odd modes for various half spacings between two dielectric slabs of broadside coupled image guide have been plotted. Polysterene ( r=2.56) and Stycast ( r=3.4) have been used as dielectric materials in fabricating broadside coupled image guide. This broadside coupled dielectric guide is very convenient as compared to the other dielectric guides. Since in case of broadside coupled image guide the dielectric slab can be bonded to the side metallic walls using some low loss adhesive material, while in other coupled dielectric guides the dielectric slab have to be supported by some low dielectric constant material (Eccofoam with r=1.02) to maintain the proper distance of side metallic walls from the dielectric slab. Since this structure is symmetrical, this configuration can be analysed in terms of even and odd mode phase velocities. The difference in these even and off mode phase velocities can be used to determine the coupling between coupled dielectric slab. Various couplers in this configuration can be realised.     

The molecular structure of 4a, 5, 8, 8a-tetrahydro-11, 14-dimethoxy-7-methyl-4a-(3-methyl-2-butenyl)-5, 8a-o-benzeno-1, 4-naphthoquinone

A novel natural product, microphyllone, has been isolated from Ehretia microphylla² together with baurenol and ursolic acid. Spectroscopic techniques, derivative formation and finally X-ray diffraction have been utilized in the structure elucidation of microphyllone. The structure appears to be 4a, 5, 8,8a - tetrahydro -11,14- dihydroxy-7-methyl-4a-(3-methyl-2-butenyl)-5, 8a-o-benzeno-1, 4-naphthoquinone.     

Substitution reactions under NH3 chemical ionization conditions in cis-/trans-1,2-dihydroxybenzosuberans

The nucleophilic substitution reaction under NH₃ chemical ionization (CI) conditions in cis- and trans-1,2-dihydroxybenzosuberans (1–4) has been studied with the help of ND₃ CI and metastable data. The results indicate that in the parent diols 1 (cis) and 2 (trans), the substitution ion [M_sH]⁺, is produced mainly by the loss of H₂O from the [MNH₄]⁺ ion (S_Ni reaction) while in their 7-methoxy derivatives 3 and 4, the ion-molecule reaction between [M? OH]⁺ and NH₃ seems to be the major pathway for the formation of [M_sH]⁺. The substitution ion from 1 and 2 and the [MH]⁺ ion from trans-1-amino-2-hydroxybenzosuberan give similar collision-induced dissociation mass-analysed ion kinetic energy spectra. Interestingly, their diacetates do not undergo the substitution reaction.