Natural Convection on a Horizontal Cone in a Porous Medium with Non-Uniform Wall Temperature/Concentration or Heat/Mass Flux and Suction/Injection

The steady natural convection flow on a horizontal cone embedded in a saturated porous medium with non-uniform wall temperature/concentration or heat/mass flux and suction/injection has been investigated. Non-similar solutions have been obtained. The nonlinear couple differential equations under boundary layer approximations governing the flow have been numerically solved. The Nusselt and Sherwood numbers are found to depend on the buoyancy forces, suction/injection rates, variation of wall temperature/concentration or heat/mass flux, Lewis number and the non-Darcy parameter.

Influence of crossed electric and quantizing magnetic fields on the Einstein relation in nonlinear optical, optoelectronic and related materials: Simplified theory, relative comparison and suggestion for experimental determination

An attempt is made to study the Einstein relation for the diffusivity-to-mobility ratio (DMR) under crossed fields' configuration in nonlinear optical materials on the basis of a newly formulated electron dispersion law by incorporating the crystal field in the Hamiltonian and including the anisotropies of the effective electron mass and the spin-orbit splitting constants within the framework of kp formalisms. The corresponding results for III-V, ternary and quaternary compounds form a special case of our generalized analysis. The DMR has also been investigated for II-VI and stressed materials on the basis of various appropriate dispersion relations. We have considered n-CdGeAs2, n-Hg1-xCdxTe, n-In1-xGaxAsyP1-y lattice matched to InP, p-CdS and stressed n-InSb materials as examples. The DMR also increases with increasing electric field and the natures of oscillations are totally band structure dependent with different numerical values. It has been observed that the DMR exhibits oscillatory dependences with inverse quantizing magnetic field and carrier degeneracy due to the Subhnikov-de Haas effect. An experimental method of determining the DMR for degenerate materials in the present case has been suggested. (C) 2010 Elsevier B.V. All rights reserved.

Photo induced optical changes in Sb/As2S3 multilayered film and (As2S3)(0.93)Sb-0.07 film of equal thickness

The increase in optical band gap (photo bleaching) due to light illumination was studied at room temperature as well as at low (4.2 K) temperature for Sb/As2S3 multilayered film of 640 nm thickness by Fourier Transform Infrared Technique. The interdiffusion of Sb into As2S3 matrix results the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap (E-g), absorption coefficient (alpha), Tauc parameter (B-1/2), Urbach edge (E-e). At the same time, photo darkening phenomena was observed in (As2S3)(0.93)Sb-0.07 film of same thickness both at low and room temperatures. From our X-ray Photoelectron Spectroscopy measurements,we are able to show that some of the As-As, S-S and Sb-Sb bonds are converted into As-S and S-Sb bonds in case of multilayers. We found that the energetically favoured heteropolar bond formation take place by a phonon-assisted mechanism using the lone pair pi electrons of S-2(0). But in case of (As2S3)(0.93)Sb-0.02 film, the homopolar bonds are playing a major role. (C) 2010 Elsevier B.V. All rights reserved.

ESR and optical studies of Mo5+ and W5+ ions in phosphomolybdate and phosphotungstate glasses

ESR and optical studies of phosphomolybdate and phosphotungstate glasses are discussed. Both the ESR and optical results indicate that molybdenum or tungsten ions are present in distorted octahedral environments in these glasses. In addition, ESR spectra of Mo5+ and W5+ ions show that the d electrons are localized on molybdenum and tungsten sites respectively. The variation of gperpendicular and gshort parallel values has been examined using appropriate structural models of these glasses.

Studies on follicular growth in the immature rat and hamster: Effect of a single injection of gonadotropin or estrogen on the rate of3H-thymidine incorporation into ovarian DNAin vitro

Initiation of follicular growth by specific hormonal stimuli in ovaries of immature rats and hamsters was studied by determining the rate of incorporation of3H-thymidine into ovarian DNAin vitro. Incorporation was considered as an index of DNA synthesis and cell multiplication. A single injection of pregnant mare serum gonadotropin could thus maximally stimulate by 18 hr3H-thymidine incorporation into DNA of the ovary of immature hamsters. Neutralization of pregnant mare serum gonadotropin by an antiserum to ovine follicle stimulating hormone only during the initial 8–10 hr and not later could inhibit the increase in3H-thymidine incorporationin vitro observed at 18 hr, suggesting that the continued presence of gonadotropin stimulus was not necessary for this response. The other indices of follicular growth monitored such as ovarian weight, serum estradiol and uterine weight showed discernible increase at periods only after the above initial event. A single injection of estrogen (diethyl stilbesterol or estradiol-l7β) could similarly cause 18 hr later, a stimulation in the rate of incorporation of3H-thymidine into DNAin vitro in ovaries of immature rats. The presence of endogenous gonadotropins, however, was obligatory for observing this response to estrogen. Evidence in support of the above was two-fold: (i) administration of antiserum to follicle stimulating hormone or luteinizing hormone along with estrogen completely inhibited the increase in3H-thymidine incorporation into ovarian DNAin vitro; (ii) a radioimmunological measurement revealed following estrogen treatment, the presence of a higher concentration of endogenous follicle stimulating hormone in the ovary. Finally, administration of varying doses of ovine follicle stimulating hormone along with a constant dose of estrogen to immature rats produced a dose-dependent increment in the incorporation of3H-thymidine into ovarian DNAin vitro. These observations suggested the potentiality of this system for developing a sensitive bioassay for follicle stimulating hormone.

Optical trapping and transportation of carbon nanotubes made easy by decorating with palladium

Individual carbon nanotubes being substantially smaller than the wavelength of light, are not much responsive to optical manipulation. Here we demonstrate how decorating single-walled carbon nanotubes with palladium particles makes optical trapping and manipulation easier. Palladium decorated nanotubes (Pd/SWNTs) have higher effective dielectric constant and are trapped at much lower laser power level with greater ease. In addition, we report the transportation of Pd/SWNTs using an asymmetric line trap. Using this method carbon nanotubes can be transported in any desired direction with high transportation speed. (c) 2006 Optical Society of America.

Studies in nonlinear optical materials: structure of di-2-menthyl 2-(N,N'-dimethyl-2-imidazolidinylidene)malonate monohydrate

C28H48N2Oa.H2 O, Mr=494.7, orthorhombic,P2~2~2~, a = 7.634 (2), b = 11.370 (2), c=34. 167 (4) A, V = 2966 (2) A 3, Z = 4, D m = 1.095,D x -- 1. 108 g cm -3, Mo Kct, 2 -- 0.7107 ,/k, ~ =0.43 cm -~, F(000) = 1088.0, T= 293 K, R = 0.061 for 1578 significant reflections. The second-harmonicgeneration (SHG) efficiency of this compound is negligible (1/100th of the urea standard). The observed low second-order nonlinear response has been attributed to the unfavourable packing of the molecules in the crystal lattice.

Optical absorption and photoluminescence studies on heavily doped (Ga,Mn)Sb crystals

Ga1-xMnxSb crystals are grown with different Mn doping concentrations by the horizontal Bridgman method (x = 0 - 0.04). Optical absorption and photoluminescence studies are carried out in the temperature range 3-300 K. Optical absorption studies reveal that the inter-valence band transition from the spin-orbit split-off band to the light/heavy hole bands is dominant over the fundamental valence band to conduction band absorption. In higher doped crystals, the fundamental absorption peak is merged with the inter-valence band transition and could not be resolved. Photoluminescence measurements in heavily doped crystals reveal the band gap narrowing and band filling effects due to the Fermi level shifting into the valence band.

Optical nonlinearity in lead sulfide microtowers

Lead sulfide (PbS) microtowers on silicon substrates, having the physical properties of bulk PbS, have been synthesized. Optical nonlinearity studies using the open aperture z-scan technique employing 5 ns and 100 fs laser pulses reveal effective two-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (beta(eff)) are in the order of 10(-11) m W-1, two orders of magnitude less than the values reported for quantum confined PbS nanocrystals. For femtosecond excitation beta(eff) is of the order of 10(-14) m W-1. These results obtained in bulk PbS experimentally confirm the importance of quantum confinement in the enhancement of optical nonlinearities in semiconductor materials.

Synthesis, Structure and Optical Studies of a Family of Three-Dimensional Rare-Earth Aminoisophthalates M(mu(2)-OH)(C8H5NO4)] (M = Y3+, La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, and Er3+)

A hydrothermal reaction of the acetate salts of the rare-earths, 5-aminoisophthalic acid (H(2)AIP), and NaOH at 150 degrees C for 3 days gave rise to a new family of three-dimensional rare-earth aminoisophthalates, M(mu(2)-OH)(C8H5NO4)] M = Y3+ (I), La3+ (II), Pr3+ (III), Nd3+ (IV), Sm3+ (V), Eu3+ (VI), Gd3+ (VII), Dy3+ (VIII), and Er3+ (IX)]. The structures contain M-O(H)-M chains connected by AIP anions. The AIP ions are connected to five metal centers and each metal center is connected with five AIP anions giving rise to a unique (5,5) net. To the best of our knowledge, this is the first observation of a (5,5) net in metal-organic frameworks that involve rare-earth elements. The doping of Eu3+/(3+) ions in place of Y3+/ La3+ in the parent structures gave rise to characteristic metal-centered emission (red = Eu3+, green = Tb3+). Life-time studies indicated that the excited emission states in the case of Eu3+ (4 mol-% doped) are in the range 0.287-0.490 ms and for Tb3+ (4 mol-% doped) are in the range of 1.265-1.702 ms. The Nd3+-containing compound exhibits up-conversion behavior based on two-photon absorption when excited using lambda = 580 nm.

Effect of sintering on optical, structural and photoluminescence properties of ZnO thin films prepared by sol-gel process

Zinc oxide (ZnO) thin films have been deposited on glass substrates via sol-gel technique using zinc acetate dihydrate as precursor by spin coating of the sol at 2000 rpm. Effects of annealing temperature on optical, structural and photo luminescence properties of the deposited ZnO films have been investigated. The phase transition from amorphous to polycrystalline hexagonal wurtzite structure was observed at an annealing temperature of 400 degrees C. An average transmittance of 87% in the visible region has been obtained at room temperature. The optical transmittance has slightly increased with increase of annealing temperature. The band gap energy was estimated by Tauc's method and found to be 3.22 eV at room temperature. The optical band gap energy has decreased with increasing annealing temperature. The photoluminescence (PL) intensity increased with annealing temperature up to 200 degrees C and decreased at 300 degrees C. (c) 2010 Elsevier B.V. All rights reserved.

Multiple imaging and multichannel optical processing with split lenses

The use of split lenses for multiple imaging and multichannel optical processing is demonstrated. Conditions are obtained for nonoverlapping of multipled images and avoiding crosstalk in the multichannel processing. Almost uniform intensity across the multipled images is an advantage here, while the low ƒ/No. of the split lens segments puts a limit in the resolution in image processing. Experimental results of multiple imaging and of a few multichannel processing are presented.