Measurement of optical constants of thin polymer films using spectrally resolved white light interferometry

Using the spectrally resolved white light interferometry we present our experimental results on the measurement of the optical constants of thin polymer films coated on a transparent substrate. As an extension to our previous work (J. Opt. Soc. Am. B12, 1559 (1995)) on thick glass plates, we have shown here that this technique can be effectively applied to very thin polymer films also. We have improved the accuracy of our results by using the Sellmeier dispersion formula for fitting the data. From the width and position of the zero-order fringe and the frequency of modulations in the white light spectrum, the refractive indexn(λ) and thicknesst of the thin polymer films are calculated. To study the accuracies involved in the technique, PVA, PMMA and PS films of varied thicknesses are coated on glass plates and the measured values are compared with ellipsometer studies.     

A Graphical Approach to Price-Break Analysis—3

The price-break problem is a non-linear discrete problem of two variables and three parameters which is not solvable analytically. As such, a graphical solution is suggested here by re-formulating the problem in two stages: first, as an equivalent non-linear, and next, as a linear problem of two variables and a single parameter. The later formulation affords an efficient graphical solution which was not possible earlier. In addition, useful procedures for plotting iso-cost curves and deriving approximate numerical solutions are also discussed.     

Anomalous conversion of 127 keV (E3) transition in134Cs

The total conversion coefficient of the 127.49 keV E3 isomeric transition in the decay of^134mCs was measured using the gamma intensity balance method with the help of a high resolution low energy photon detector. Theα _Tvalue was found to be 5.84±0.47 as against the theoretical value of 6.96, thus showing an anomaly of (16.1±6.7)%. TheK-conversion coefficient,α _kwas also measured using the X-ray peak to gamma ray intensity method and found to be 2.24±0.04 as against the theoretical value of 2.72, which shows an anomaly of (17.6±1.4)% consistent with the experimental anomaly inα _T. TheE3 hindrance factor of the isomeric transition was estimated to be (3.44±0.23) ·10⁴.     

Laser Raman spectroscopic study of ferroelastic LiCsSO4

Lithium caesium sulphate has been reported to undergo a phase transition from the room temperature orthorhombic phase with space groupP cmn to a final phase with space groupP 2₂/n. Though a sharp anomaly in its physical properties has been found at 202.0;K, it was found that there was a need for careful investigations in the vicinity of 240 and 210.0;K. Since the changes in the crystal structure involve primarily a rotation of the SO₄ tetrahedron about thec-axis and as this may be reflected both in the intensity and polarisation of the internal as well as external phonon modes, the laser Raman spectra of oriented single crystals of LiCsSO₄ at different temperatures were investigated. For correlation and definite identification of the spectral features, its infrared absorption spectrum was also studied. An analysis of the intensities and polarizations of the internal modes of the sulphate ions reveals the change in symmetry of the crystal. The integrated intensity and peak height of thev ₁ line, plotted against temperature show anomalous peaks in the region of the phase transition. Differential scanning calorimetric study gives the enthalpy change ΔH across the phase transition to be 0.213 kJ/mol.     

First total synthesis of (−)-diospongin B

The first total synthesis of (−)-diospongin B has been achieved starting from benzaldehyde using chiral allylation, a base catalyzed conjugate addition of an α,β-unsaturated ester and an intramolecular oxy-Michael reaction as the key steps in 16% overall yield.     

Utilization of potassium ethyl xanthate as a substoichiometric reagent for the determination of indium

A sensitive and rapid radiochemical method has been developed for the determination of microgram amounts of indium(III) based on the substoichiometric extraction of its 13 complex with potassium ethyl xanthate from pH 7 ammonia buffer into chloroform. 5–50 g of indium was determined with an average error of 1.56%. The effect of associated species on the extraction was studied.     

London field penetration in heavy fermion superconductors

We present results of a series of high resolution, low fielddc-magnetization measurements on the heavy fermion superconductors UPt₃, UBe₁₃, U_1–x Th _X Be₁₃ and CeCu₂Si₂, from which values of the magnetic penetration depth can be extracted. A study of the temperature variation reveals aT ² power law in all cases. This can not be reconciled with a BCS-like isotropic energy gap but may be explained by the presence of low energy quasiparticle states inside the gap. In the case of very pure superconductors, one such possibility is the assumption of point-nodes in the gap function. We argue, however, that an interpretation in terms of resonant impurity scattering in various anisotropic superconducting states is more likely to explain a broad range of experimental data. The results on differently oriented single crystals of UBe₁₃ and UPt₃ reveal no pronounced anisotropy related to the crystal lattice. Absolute values of atT=0 are deduced by a novel method in which the field is first screened out from the sample by means of an evaporated superconducting film (of lowerT _c ). Above this lowerT _c the sudden penetration of field into the sample can then be measured absolutely.