Showing papers by "Cochin University of Science and Technology published in 1987"

Reflector-backed perfectly blazed strip gratings simulate corrugated reflector effects

Abstract: Perfect blazing of reflector-backed thin strip gratings to n = ? 1 spectral order for both TE and TM polarisations is compared with corrugated reflection gratings. The strip gratings are shown to be simulating effects of rectangular corrugations in conducting surfaces.

Low backscattered TM-polarised strip gratings

Abstract: The development of reflector-backed strip gratings exhibiting properties like the elimination of specular reflections from a conducting surface for normal and near-normal incidence is reported. This is not possibly by conventional corrugated metallic surfaces. Perfect blazing to n = −1 spectral order is also provided by the developed system. This technique offers a simple and inexpensive method for the simulation of corrugated horns.

Optical Properties of β-Bi2O3 Thin Films

Abstract: Optical properties of β-Bi2O3 films prepared by activated reactive evaporation are studied from 0.5 to 3.5 eV. It is shown that β-Bi2O3 is an indirect band gap semiconductor with a band gap of (1.74 ± 0.5) eV and the optical transition leading to this is an allowed one. The direct gap of β-Bi2O3 is 2.6 eV. Zwischen 0,5 und 3,5 eV werden die optischen Eigenschaften von β-Bi2O3-Schichten aus aktivierter reaktiver Aufdampfung untersucht. Es wird gezeigt, das β-Bi2O3 ein Halbleiter mit indirekter Bandlucke ist mit einem Gap von (1,74 ± 0,5) eV und der dazu fuhrende optische Ubergang erlaubt ist. Das direkte Gap von β-Bi2O3 betragt 2,6 eV.

Preparation of heat mirrors using bismuth oxide films

Abstract: Heat mirrors with structure Bi2O3AuBi2O3 are prepared. Thin films of bismuth oxide are deposited by activated reactive evaporation for the dielectric-metal-dielectric layer and the experimental set-up is also given. The optimum combination of layer thicknesses and the optimum conditions of heat treatment are determined for maximum transmission in the visible region with minimum transmission in IR region. Hitzespiegel mit der Struktur Bi2O3AuBi2O3 werden hergestellt. Dunne Schichten von Wismutoxid werden mittels reaktiver Aufdampfung fur die Dielektrikum-Metall-Dielektrikum-Schicht abgeschieden und auch der experimentelle Aufbau angegeben. Die optimale Kombination der Schichtdicke und der optimalen Bedingungen der Warmebehandlung fur maximale Transmission im sichtbaren Bereich und minimale Transmission im IR-Bereich werden bestimmt.

Platelet MAO activity in clinical subtypes of depression and DST suppression.

Abstract: Platelet MAO activity was measured in 75 hospitalized depressed patients and in 31 healthy subjects. Plasmas post dexamethasone cortisol levels were examined in 73 patients. Results indicate that higher platelet MAO activity does not occur in all, but only in male major depressed patients. No relationship between changes of MAO activity and specific clinical subtypes was found. Platelet MAO activity is not different between DST suppressors and DST non suppressors. The authors suggest that platelet MAO activity may be related to non specific factors such as sex, age, but not to diagnosis of depression.

Diffraction effects from h.c.p. crystals with random growth faults undergoing transformation to the f.c.c. phase by the deformation mechanism

Abstract: Hexagonally close-packed cobalt crystals often contain a random distribution of growth faults. The h.c.p. to f.c.c. transformation is effected by a non-random insertion of deformation faults at two layer separations. The kinematical theory is developed of diffraction from h.c.p. crystals containing randomly distributed growth faults undergoing a transformation to the f.c.c. phase. The presence of a small amount of random growth faults give rise to an additional broadening of some of the reflections. Hexagonal dicht gepackte Kobalt-Kristalle enthalten oft eine statistische Verteilung von eingewachsenen Stapelfehlern. Der ubergang h.d.p. nach k.f.z. wird durch einen, nichtstatistischen Einbau von Deformationsstapelfehlern mit dem Abstand zweier Lagen beeinflust. Die kinematisch Theorie der Beugung von h.d.p.-Kristallen mit statistisch verteilten Wachstumsfehlern, die einen ubergang zur k.f.z.-Phase durchlaufen, wird entwickelt. Die Anwesenheit von geringen Mengen von statistischen Wachstumsfehlern fuhrt zu einer zusatzlichen Verbreiterung einiger Reflexe.

Bifurcation structure and Lyapunov exponents of a modulated logistic map

Abstract: We have studied the bifurcation structure of the logistic map with a time dependant control parameter. By introducing a specific nonlinear variation for the parameter, we show that the bifurcation structure is modified qualitatively as well as quantitatively from the first bifurcation onwards. We have also computed the two Lyapunov exponents of the system and find that the modulated logistic map is less chaotic compared to the logistic map.

Modification of butadiene‐acrylonitrile rubber/poly(vinyl chloride) blend using natural rubber, styrene‐butadiene rubber, and polybutadiene rubber

Abstract: Natural rubber, styrene-butadiene rubber, and polybutadiene rubber were used to replace part of the butadiene-acrylonitrile rubber in a 70/30 butadiene-acrylonitrile rubber/poly(vinyl chloride) blend. Such replacement up to 15% of the total weight of the blend improved the mechanical properties, while decreasing the cost of the blend. Styrenebutadiene rubber could replace butadiene-acrylonitrile rubber up to 30% of the total weight of the blend without deterioration in the mechanical properties.

X-Ray Diffraction Effects from 2H Crystals Undergoing Transformation to the 3C Structure by the Layer Displacement Mechanism

Abstract: On annealing at elevated temperatures 2H silicon carbide crystals transform to a disordered twinned 3C structure. It is suggested that the transformation proceeds by nucleation and propagation of stacking faults causing layer-displacement in the solid state. The theory of X-ray diffraction for 2H crystals is developed undergoing transformation to the 3C phase by such a mechanism. The different diffraction effects such as peak breadth and peak broadening are predicted. Nach Temperung bei erhohten Temperaturen gehen die 2H-Siliziumkarbidkristalle in eine fehlgeordnete 3C-Zwillingsstruktur uber. Es wird angenommen, das der Ubergang durch Keimbildung und Ausbreitung von Stapelfehlern fortschreltet, die eine Schichtverlagerung im festen Zustand verursachen. Eine Theorie der Rontgenbeugung fur 2H-Kristalle, die in die 3C-Phase mit einem derartigen Mechanismus ubergehen, wird entwickelt. Verschiedene Beugungseffekte, wie Peakweite und Peakverbreiterung werden vorausgesagt.

Studies on 50/50 natural rubber/styrene butadiene copolymer blend†

Abstract: A carbon black filled 50/50 natural rubber (NR)/styrene-butadiene rubber (SBR) blend is vulcanized using several conventional curing systems designed by varying the amounts of sulphur and accelerator. The cure characteristics and the properties of the vulcanizates are compared. The quantity and quality of crosslinks in each case are evaluated by chemical probes to correlate them with the vulcanizate properties. Ein mit Rus gefulltes 50/50 NR/SBR-Blend (Naturkautschuk/Styrol-Butadien-Copolymer) wurde unter Verwendung verschiedener konventioneller Vernetzungssysteme, die durch unterschiedliche Schwefel- und Beschleunigeranteile gekennzeichnet sind, vulkanisiert. Die Vulkanisationscharakteristiken und die Eigenschaften der Vulkanisate wurden verglichen. Das Ausmas und die Qualitat der Vernetzungsstellen wurden fur jeden Fall durch chemische Testmethoden ermittelt, um sie mit den Vulkanisateigenschaften zu vergleichen.

Effect of blending techniques on the curing of elastomer blends

Abstract: Compounding of styrene-butadiene copolymer/polybutadiene, natural rubber/ethylene-propylene-diene terpolymer and natural rubber/butadiene-acrylonitrile copolymer blends was done in three different ways and their curing behaviour and the tensile properties of the vulcanizates are compared. Mischungen aus Poly(styrol-co-butadien)/Polybutadien, Naturkautschuk/Poly-(ethylen-co-propylen-co-dien und Naturkautschuk/Poly(butadien-co-acrylnitril)) wurden nach drei unterschiedlichen Verfahren compoundiert und Hartungsverhalten sowie Zugfestigkeit und Bruchdehnung der Vulkanisate wurden verglichen.

X‐ray diffraction effects from 2H crystals undergoing transformation to the 4H structure by the shear mechanism

Abstract: The 2H or ABAB… structure may be transformed to the 4H or ABCB… structure if deformation faults occur in a non-random manner. The theory of X-ray diffraction from one-dimensionally disordered crystals undergoing the 2H 4H structural transformation by the deformation mechanism is developed. For this it is necessary to consider that the faults are not distributed entirely at random but tend to occur in such a manner as to statistically create a 4H structure. The X-ray diffraction effects are predicted.

Tribasic lead sulphate as efficient curing agent for polychloroprene

Abstract: Tribasic lead sulphate is tried as a practical curing agent for polychloroprene. The cure characteristics of the compounds as well as the technical properties of the vulcanizates show that it can act as a potential curative. Dreibasisches Bleisulfat wurde als fur die Praxis geeignetes Vernetzungsmittel fur Polychloropren gepruft. Sowohl die Vernetzungscharakteristika als auch die technischen Eigenschaften der Vulkanisate zeigen, das es als Vulkanisierungsmittel eingesetzt werden kann.

On the role of acoustic plasmons in highT c superconductors

Abstract: The role of acoustic plasmons in the recently discovered highTc superconductors is discussed. It is shown that the exchange of acoustic plasmons together with the usual phonon exchange between electrons can give rise to aTc ∼ 100 K.

Ultrasonic attenuation of longitudinal and shear waves in superconducting lead

Abstract: Longitudinal and shear wave ultrasonic attenuations have been measured in high-purity Pb on two single crystals obtained from the same ingot. The measurements were done at low temperatures, at different frequencies, and in transverse magnetic fields, up to a field of 7.3 kG. The propagation directions in the two crystals were along [100] and [110]. For some propagation and polarization directions the α s /α n ratio is found to be frequency-independent, while for others, large divergences in the α s /α n ratios at different frequencies are observed. A sharp decrease of α s /α n nearT c is observed for a particular longitudinal wave propagation, but not in any shear wave propagation. In some cases α s /α n is found to be abnormally high and this feature is associated with a peak in attenuation α n and a relatively high α n at 7.2 K. None of the α s /α n curves fits closely to any BCS energy gap. For longitudinal waves the high magnetic field (H) dependence of the normal state attenuation was found to agree qualitatively with the free electron theory for propagation along [100], but not for propagation along [110]. For shear waves the high-field attenuations do not extrapolate to zero asH tends to infinity. For all propagation and polarization directions the high-field attenuations show 1/H 2 field dependence.

Synergism in electron gas in crossed fields

Abstract: An electron gas in crossed electric and magnetic fields of arbitrary strength is considered in the framework of nonequilibrium statistical mechanics. It is known that more than one independent frequency existing in a system, which are of comparable magnitude, can generate coherent synergic radiation. In the present system three independent frequencies exist: viz the synchrotron frequency due to the magnetic field, the hopping frequency due to the electric field, and the plasma frequency. It is shown that all these can combine to generate a new synergic coherent radiation. The results also show the possibility of interpreting the quantum nature of Hall conductance as due to density function alone. Besides these, the solution admits the Schubnikov-de Haas oscillation of the electrical conductivity due to change in the fields.

Trajectory approach to the calculation of sticking probability

Abstract: Using a path integral approach, we propose a method for the calculation of sticking probability of atoms on solid surfaces. The method makes use of a sticking trajectory for the calculation. The formalism is illustrated by applying it to the collision of an atom with a solid, the solid being modelled as a collection of bosons, the interaction term in the Hamiltonian being linear in the boson coordinates.

Research note An improved stabilization circuit for high current magnets used in NMR experiments

Abstract: A high current stabilization circuit which entirely eliminates the need for a separate current sensing unit is described. The circuit employs a novel current sensing technique which is not only more convenient to implement than earlier circuits, but also keeps the power dissipation involved in the current sensing process to a minimum. The method offers greater advantage for stabilizing fields produced by high current electromagnets used for wideline nuclear magnetic resonance (NMR) studies.

A high voltage solid state power supply system for a CW CO2 laser with current stabilization

Abstract: The design and fabrication of a solid state current regulated high voltage power supply system which incorporates a few protective features suitable for a 30 W dual section CW C02 laser are described.

Elastic nonlinearity parameters of tetragonal crystals

Abstract: The equations of motion for the propagation of finite amplitude elastic waves in crystals of tetragonal symmetry have been derived starting from the expression for the elastic strain energy. The equations have been solved for a finite amplitude sinusoidal wave propagating along the pure mode directions which are [100], [110] and [001] for the tetragonal group TI. The solutions corresponding to longitudinal wave propagation yield expressions for the amplitudes of the fundamental and generated second harmonic for these directions in terms of certain combinations of second and third order elastic constants of the medium. The results will aid the experimenter to determine these constants using ultrasonic harmonic generation technique.