Crystal chemistry of a new solid solution in the BaO-Bi2O3-Nb2O5 system: Ba-5x/2-Bi(1-x)5/3Nb5O15

A solid solution of the type Ba5x/2Bi(1-x)5/3Nb5O15 has been identified in the BaO-Bi2O3-Nb2O5 system for the first time. The limits of the solid solution are within the range 0.52 <= x <= 0.80. The compositions x = 0.52, 0.60, 0.72, 0.77, 0.78, and 0.80 were synthesized by the solid-state technique from the starting materials in stoichiometric quantities. The powder X-ray patterns of all the phases in the domain indicate a structural similarity to tetragonal tungsten bronzes (TTBs). The compositions below x = 0.52 and those above x = 0.80 exhibit barium niobate and bismuth niobate impurities, respectively. Single crystals of the composition x = 0.77 were obtained by the melt cooling technique. The crystal structure of Ba3.85/2Bi1.15/3Nb5O15 (x = 0.77) was solved in the tetragonal space group P4bm (No. 100) with a = 12.4938 (14) angstrom, c = 3.9519 (2) A, V = 616.87 (10) angstrom(3), and Z = 2 and was refined to an R index of 0.034. Dielectric measurements on all the phases indicate a typical relaxor behavior with a broad phase transition at T-m approximate to 300 K.

Crystal structure and ionic conductivity of a new bismuth tungstate,Bi3W2O10.5

The compound Bi3W2O10.5 was synthesized by the solid-state technique from Bi2O3 and WO3 in stoichiometric quantities. Single crystals were grown by the melt-cooling technique and the crystal structure was solved in the tetragonal 141in space group with a = 3.839 (1) A, c = 16-3S2 (5) A, V = 241.4 (1) angstrom(3), Z = 4 and was refined to an R index of 0.0672. The structure represents a modification of the Aurivillius phase and consists of [Bi2O2](2+) units separated by WO8 polyhedra. a.c. impedance studies indicate oxide ion conductivity of 2.91 10(-5) cm(-1) at 600 degrees C.

Retrieval of dust aerosols during night: improved assessment of long wave dust radiative forcing over Afro-Asian regions

Several investigators in the past have used the radiance depression (with respect to clear-sky infrared radiance), resulting from the presence of mineral dust aerosols in the atmosphere, as an index of dust aerosol load in the atmosphere during local noon. Here, we have used a modified approach to retrieve dust index during night since assessment of diurnal average infrared dust forcing essentially requires information on dust aerosols during night. For this purpose, we used infrared radiance (10.5-12.5 mu m), acquired from the METEOSAT-5 satellite (similar to 5 km resolution). We found that the `dust index' algorithm, valid for daytime, will no longer hold during the night because dust is then hotter than the theoretical dust-free reference. Hence we followed a `minimum reference' approach instead of a conventional `maximum reference' approach. A detailed analysis suggests that the maximum dust load occurs during the daytime. Over the desert regions of India and Africa, maximum change in dust load is as much as a factor of four between day and night and factor of two variations are commonly observed. By realizing the consequent impact on long wave dust forcing, sensitivity studies were carried out, which indicate that utilizing day time data for estimating the diurnally averaged long-wave dust radiative forcing results in significant errors (as much as 50 to 70%). Annually and regionally averaged long wave dust radiative forcing (which account for the diurnal variation of dust) at the top of the atmosphere over Afro-Asian region is 2.6 +/- 1.8 W m(-2), which is 30 to 50% lower than those reported earlier. Our studies indicate that neglecting diurnal variation of dust while assessing its radiative impact leads to an overestimation of dust radiative forcing, which in turn result in underestimation of the radiative impact of anthropogenic aerosols.

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.

Terahertz Time Domain Spectroscopy to Detect Low-Frequency Vibrations of Double-Walled Carbon Nanotubes

We have measured the frequency-dependent real index of refraction and extinction coefficient (and hence the complex dielectric function) of a free-standing double-walled carbon nanotube film of thickness 200 nm by using terahertz time domain spectroscopy in the frequency range 0.1 to 2.5 THz. The real index of refraction and extinction coefficient have very high values of approximately 52 and 35, respectively, at 0.1 THz, which decrease at higher frequencies. Two low-frequency phonon modes of the carbon nanotubes at 0.45 and 0.75 THz were clearly observed for the first time in the real and imaginary parts of the complex dielectric function along with a broad resonance centred at around 1.45 THz, the latter being similar to that in single-walled carbon nanotubes assigned to electronic excitations. Our experiments bring out a possible application of double-walled carbon nanotube films as a neutral density filter in the THz range.

High-precision diode-laser-based temperature measurement for air refractive index compensation

We present a laser-based system to measure the refractive index of air over a long path length. In optical distance measurements it is essential to know the refractive index of air with high accuracy. Commonly, the refractive index of air is calculated from the properties of the ambient air using either Ciddor or Edlén equations, where the dominant uncertainty component is in most cases the air temperature. The method developed in this work utilises direct absorption spectroscopy of oxygen to measure the average temperature of air and of water vapor to measure relative humidity. The method allows measurement of temperature and humidity over the same beam path as in optical distance measurement, providing spatially well matching data. Indoor and outdoor measurements demonstrate the effectiveness of the method. In particular, we demonstrate an effective compensation of the refractive index of air in an interferometric length measurement at a time-variant and spatially non-homogenous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.

Properties of ion assisted deposited titania films

Thin films of titanium dioxide have been deposited using ion assisted deposition with oxygen ions in the energy range 100�500 eV and current densities up to 100 ?A/cm2. It has been observed that the refractive index of the films increases up to 300 eV and the extinction coefficient increased only nominally up to 300 eV. Optical band gap calculations have shown a strong dependence of the gap on the energy of incident ions. Beyond a critical energy and current density of the ions the refractive index and extinction coefficient of the films start deteriorating. It has also been found that beyond the critical values the optical band gap value decreases. The maximum refractive index obtained was 2.49 at an energy of 300 eV and 50 ?A/cm2 current density. Post?deposition annealing of the films at 500?°C resulted in a slight increase in refractive index without affecting the extinction coefficient. X?ray diffraction studies revealed a monophasic anatase structure in these films. ?

Structural and optical properties of RF sputtered Bi2VO5.5 thin films

Thin films of Bismuth Vanadate Bi2VO5.5 (BiV) have been deposited on amorphous quartz and polycrystalline silicon substrates by r.f. sputtering technique and characterised for their structural and optical properties. The os-deposited films at room temperature are found to be amorphous and transparent over the spectral range of 0.55 mu m to 12 mu m. Post-deposition annealing at 400 degrees C in air shows the formation of the BiV crystalline phase. The optical constants namely refractive index. extinction coefficient and optical bandgap of both amorphous and crystalline films have been determined. The refractive index of the as-deposited film is around 2.4 at 0.7 mu m and drops to 2.26 at 1.56 mu m. The optical bandgap of the material has been determined from the computed values of the absorption coefficients.

Reactivity Of Silica From Rice Husk With Lime

The paper correlates the reactivity of rice husk ash with its physicochemical properties such as crystallinity, surface area, microstructure, particle size distribution, porosity and solubility. These properties, in tum, are dependent on the time-temperature conditions under which the ash is prepared. It is found that the reactivity of the ash cannot be quantified by any one of these parameters alone, though they all indicate it qualitatively. Therefore, a method for quantifying this property was developed, by which the Reactivity Index is obtained. There is only a gradual change in the reactivity index of RHA with ashing temperature, as in many other properties, like surface area, porosity and total volume of gas absorbed by unit mass of the silica ash. This reactive index is found to be useful in determining the optimum ash/lime ratios required to give the best performance for RHA-lime composites.

Structure and composition related properties of titania thin films

The dependence of optical constants, structure and composition of titania thin films on the process parameters has been investigated. Films were deposited using both reactive electron beam evaporation and ion Assisted Deposition(IAD). If has been observed that the refractive index of IAD films is higher than that for the reactively deposited films, without much difference in the extinction coefficient. Electron paramagnetic resonance has been used to estimate qualitatively the presence of non-stoichiometry in the films. It has been found that these spectra correlate very well the optical behaviour of the films. X-ray diffraction studies revealed that the neutral oxygen deposited films were stress free, while the IAD films showed tensile stress. The lattice parameters showed anisotropic change with ion beam parameters.

Optical and structural properties of reactive ion beam sputter deposited CeO2 films

Optical and structural properties of reactive ion beam sputter deposited CeO2 films as a function of oxygen partial pressures (P-O2) and substrate temperatures (T-s) have been investigated. The films deposited at ambient temperature with P-O2 of 0.01 Pa have shown a refractive index of 2.36 which increased to 2.44 at 400 degrees C. Refractive index and extinction coefficient are sensitive up to a T-s of similar to 200 degrees C. Raman spectroscopy and X-ray diffraction (XRD) have been used to characterise the structural properties. A preferential orientation of (220) was observed up to a T-s of 200 degrees C and it changed to (200) at 400 degrees C: and above. Raman line broadening, peak shift and XRD broadening indicate the formation of nanocrystalline phase for the films deposited up to a substrate temperature of 300 degrees C. However, crystallinity of the films were better for T-s values above 300 degrees C. In general both optical and structural properties were unusual compared to the films deposited by conventional electron beam evaporation, but were similar in some aspects to those deposited by ion-assisted deposition. Apart from thermal effects, this behavior is also attributed to the bombardment of backscattered ions/neutrals on the growing film as well as the higher kinetic energy of the condensing species, together resulting in increased packing density. (C) 1997 Elsevier Science S.A.

Acyclic Edge-Coloring of Planar Graphs

A proper edge-coloring with the property that every cycle contains edges of at least three distinct colors is called an acyclic edge-coloring. The acyclic chromatic index of a graph G, denoted. chi'(alpha)(G), is the minimum k such that G admits an acyclic edge-coloring with k colors. We conjecture that if G is planar and Delta(G) is large enough, then chi'(alpha) (G) = Delta (G). We settle this conjecture for planar graphs with girth at least 5. We also show that chi'(alpha) (G) <= Delta (G) + 12 for all planar G, which improves a previous result by Fiedorowicz, Haluszczak, and Narayan Inform. Process. Lett., 108 (2008), pp. 412-417].

A method for the calculation of the adsorbed phase volume and pseudo-saturation pressure from adsorption isotherm data on activated carbon

We propose a new method for evaluating the adsorbed phase volume during physisorption of several gases on activated carbon specimens. We treat the adsorbed phase as another equilibrium phase which satisfies the Gibbs equation and hence assume that the law of rectilinear diameters is applicable. Since invariably the bulk gas phase densities are known along measured isotherms, the constants of the adsorbed phase volume can be regressed from the experimental data. We take the Dubinin-Astakhov isotherm as the model for verifying our hypothesis since it is one of the few equations that accounts for adsorbed phase volume changes. In addition, the pseudo-saturation pressure in the supercritical region is calculated by letting the index of the temperature term in Dubinin's equation to be temperature dependent. Based on over 50 combinations of activated carbons and adsorbates (nitrogen, oxygen, argon, carbon dioxide, hydrocarbons and halocarbon refrigerants) it is observed that the proposed changes fit experimental data quite well.

Structural, optical and nanomechanical properties of (1 1 1) oriented nanocrystalline ZnTe thin films

Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from load-displacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4.

Structural, optical and nanomechanical properties of (1 1 1) oriented nanocrystalline ZnTe thin films

Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from load-displacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4.