CONDENSING HEAT TRANSFER IN VERTICAL CYCLONE

The heat transfer coefficient for condensation of steam has been determined experimentally for a cyclone surface. Ambient air is used as the coolant and the outer surface is maintained in a free-convection condition. A twofold increase in heat transfer coefficient is observed over a cyclone surface in comparison with a vertical tube.     

Optical properties of polyvinyl alcohol doped (Se80Te20)100–xAgx (0 ≤ x ≤ 4) composites

Polyvinyl alcohol (PVA) doped (Se₈₀Te₂₀)_100–xAg_x (0 ≤ x ≤ 4) thin films were prepared by the spin-coating technique on a quartz substrate. The optical parameters of PVA-doped (Se₈₀Te₂₀)_100–xAg_x (0 ≤ x ≤ 4) composites at the same chalcogen concentration (S₀ = 0.1 mg ml^?1) and PVA/(Se₈₀Te₂₀)₉₆Ag₄ composites at three different chalcogen concentrations viz. S₁ = 0.3 mg ml^?1, S₂ = 0.6 mg ml^?1 and S₃ = 1 mg ml^?1 have been studied. The semi-crystalline nature of the as-deposited thin filmsisdetermined by X-ray diffraction. The transmission and reflection spectra of PVA-doped Se–Te–Ag thin films were obtained in a 350–650 nm spectral region. The optical-band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical-band gap increases, but the refractive index, extinction coefficient, and the real and imaginary parts of the dielectric constant decrease, with increase in Agcontent in PVA-doped (Se₈₀Te₂₀)_100–xAg_x (0 ≤ x ≤ 4) thin films. Such type of behavior is explained on the basis of decrease in density of the defect states. However, the optical-band gap has been found to be decreased and all other optical parameters show increase in their values with increase in concentration of (Se₈₀Te₂₀)₉₆Ag₄ glass in PVA-doped composites. The results have been explained on the basis of cluster-size formation at the time of dissolution. This study shows that the optical properties of new composites are affected by the change in silver and chalcogen concentration.     

Crystallographic and microstructural aspects of the superconductor YBa2Cu3O7-y —an overview

Crystal structures and structural inhomogeneities observed in YBa₂Cu₃O_7-y are reviewed. It is brought out that a proper understanding of the nature of the structural inhomogeneities is essential for exploiting the technological potential of this material. The need for an adequate characterization of specimens used for experiments is emphasized. Practical implications of the ferroelastic nature of the material are discussed.     

Generation of excess minority carriers in mos devices due to gamma irradiation

The effect of gamma irradiation on MOS devices prepared under different oxidation conditions Is investigated. The C-V characteristics of the devices are studied before and after exposing the latter with gamma radiations of CO⁶⁰ (1.17 and 1.33 MeV gamma rays). For MOS transistor (n-channel depletion type devices) the C-V characteristics change slightly towards the negative voltage axis and the C_min also decreases after Irradiation. For MOS capacitor (wet oxide) there is a change from high frequency C-V characteristics to low frequency C-V characteristics. In the case of a MOS capacitor (HCl grown) breakdown occurs relatively at lower voltage.     

Mossbauer study of ferrite systems Co x Mn1−x Fe2O4 and Ni x Mn1−x Fe2O4

Mössbauer spectra of Co _x Mn_1?x Fe₂O₄ and Ni _x Mn_1?x Fe₂O₄ ferrites withx values ranging from 0·1 to 0·8 in steps of 0·1 have been recorded at room temperature. All spectra exhibit well-defined Zeeman hyperfine patterns. It has been observed that hyperfine field at Fe³⁺ nucleus increases more rapidly by nickel substitution than by cobalt substitution. This has been explained in terms of exchange interactions and cation distribution in the spinels. Hyperfine fields, isomer shifts and quadrupole splittings have been determined.     

Low-lying levels in103Rh from Coulomb excitation

Five low-lying negative parity states of¹⁰³Rh up to 1277 keV excitation energy were observed to be Coulomb excited with 2·5–4·5 MeV protons. The de-excitation gamma rays from these levels were identified in the singles spectra recorded with a 57 cc Ge(Li) detector. The level energies, branching ratios, reduced transition probabilitiesB(E2) and the multipole mixing ratios () were obtained. The 880, 1106 and 1277 keV levels have been Coulomb excited with protons for the first time. The ambiguity in theJ values for 803 and 1106 keV levels have been resolved using ²-fits, the assigned spin values are 1/2^– and 5/2^–, respectively. The-values for 474·1 and 811·2 keV transitions were obtained for the first time. The results have been discussed in the light of previously reported results.The authors wish to thank Professor I. M. Govil for his active interest at various stages of this work. One of us (DCT) acknowledges the financial support from U.G.C., New Delhi, under Faculty Improvement Programme.