An update on the thermodynamics of Ta2O5

Using a solid-state electrochemical cell incorporating yttria-doped thoria (YDT) as the electrolyte and a mixture of (Mn + MnO) as the reference electrode, standard Gibbs free energy of formation of beta-Ta2O5 has been determined as a function of temperature in the range (1000 to 1300) K. The solid-state electrochemical cell used can be represented as (-)Pt,Ta +Ta2O5//(Y2O3)ThO2//Mn + MnO, Pt(+) Combining the reversible e.m.f. of the cell with recent data on the free energy of formation of MnO, standard Gibbs free energy of formation of Ta2O5 from Ta metal and diatomic oxygen gas (O-2) in the temperature range (1000 to 1300) K is obtained: Delta fG degrees +/- 0.35/(kJ.mol(-1)) = -2004.376 + 0.40445(T/K). Because of the significant solid solubility of oxygen in tantalum, a small correction for the activity of Ta in the metal phase in equilibrium with Ta2O5 is applied. An analysis of the results obtained in this study and other free energy data reported in the literature by the "third law" method suggests the need for refining data for Ta2O5 reported in thermodynamic compilations. Used in the analysis is a revised value for standard entropy of Ta2O5 based on more recent low-temperature heat capacity measurements. An improved set of thermodynamic properties of ditantalum pentoxide (Ta2O5) are presented in the temperature range (298.15 to 2200) K. (C) 2008 Elsevier Ltd. All rights reserved.

Binding of nucleobases with single-walled carbon nanotubes: Theory and experiment

We report the binding energy of various nucleobases (guanine (G), adenine (A), thymine (T) and cytosine (C)) with (5,5) single-walled carbon nanotube (SWNT) calculated using first-principle Hartre–Fock method (HF) together with classical force field. The binding energy without including the solvation effects of water decreases in the order G>A>T>C. The inclusion of solvation energy changes the order of binding preference to be G>T>A>C. Using isothermal titration (micro) calorimetry experiments, we also show the relative binding affinity to be T>A>C, in agreement with our calculations.

Determination of the thermodynamic stability of TiB2

The standard free energy of formation of titanium boride (TiB2) Was measured by the Electro Motive Force (EMF) method (by using yttria doped thoria (YDT) as the solid electrolyte). Two galvanic cells viz. Cell (I): Pt, TiB2 (s), TiO2 (s), B (s) vertical bar YDT vertical bar NiO (s), Ni (s), Pt and cell (II): Pt, TiB2 (s), TiO2 (s), B (s) vertical bar YDT vertical bar FeO (s). Fe (s), Pt were constructed in order to determine the Delta(f)G degrees, of TiB2. Enthalpy increments on TiB2 were measured by using inverse drop calorimetry over the temperature range 583-1769 K. The heat capacity, entropy and the free energy function have been derived from these experimental data in the temperature range 298-1800 K. The mean value of the standard enthalpy of formation of TiB2 (Delta H-f(298)degrees (TiB2)) was obtained by combining these Delta(f)G degrees, values and the free energy functions of TiB2 derived from the drop calorimetry data. The mean values of Delta H-f(298)degrees (TiB2) derived from the Delta(f)G degrees, data obtained from cell I and II were -322 +/- 1.2 kJ mol(-1) and -323.3 +/- 2.1 kJ mol(-1), respectively. These values were found to be in very good agreement with the assessed data. (C) 2009 Elsevier B.V. All rights reserved.

Hanle-Zeeman redistribution matrix. I. Classical theory expressions in the laboratory frame

Polarized scattering in spectral lines is governed by a 4; 4 matrix that describes how the Stokes vector is scattered and redistributed in frequency and direction. Here we develop the theory for this redistribution matrix in the presence of magnetic fields of arbitrary strength and direction. This general magnetic field case is called the Hanle- Zeeman regime, since it covers both of the partially overlapping weak- and strong- field regimes in which the Hanle and Zeeman effects dominate the scattering polarization. In this general regime, the angle-frequency correlations that describe the so-called partial frequency redistribution (PRD) are intimately coupled to the polarization properties. We develop the theory for the PRD redistribution matrix in this general case and explore its detailed mathematical properties and symmetries for the case of a J = 0 -> 1 -> 0 scattering transition, which can be treated in terms of time-dependent classical oscillator theory. It is shown how the redistribution matrix can be expressed as a linear superposition of coherent and noncoherent parts, each of which contain the magnetic redistribution functions that resemble the well- known Hummer- type functions. We also show how the classical theory can be extended to treat atomic and molecular scattering transitions for any combinations of quantum numbers.

Impact resistance and evaluation of retained strength on geotextiles

Over the last few decades, geotextiles have progressively been incorporated into geotechnical applications, especially in the field of coastal engineering. Geotextile materials often act as separator and a filter layer between rocks laid above and subgrade beneath. This versatile material has gradually substituted traditional granular materials because of its ease of installation, consistent quality and labour costefficiency. However, geotextiles often suffer damage during installation due to high dynamic bulk loading of rock placement. This can degrade geotextiles' mechanical strength. The properties considered in this paper include the impact resistance and retained strength of geotextiles. In general, the greater the impact energy applied to geotextiles, the greater the potential for damage. Results highlight the inadequacy of using index derived values as an indicator to determine geotextile performance on site because test results shows that geotextiles (staple fibre (SF) and continuous filament (CF)) with better mechanical properties did not outperform lower mechanical strength materials. The toughest CF product with a CBR index value of 9696N shows inferior impact resistance compared to SF product with the least CBR strength (2719N) given the same impact energy of 9.02 kJ. Test results also indicated that the reduction of strength for CF materials were much greater (between 20 and 50%) compared to SF materials (between 0 and 5%) when subjected to the same impact energy of 4.52 kJ.

Electromagnetic signatures of lightning near the HF frequency band

The dissertation deals with remote narrowband measurements of the electromagnetic radiation emitted by lightning flashes. A lightning flash consists of a number of sub-processes. The return stroke, which transfers electrical charge from the thundercloud to to the ground, is electromagnetically an impulsive wideband process; that is, it emits radiation at most frequencies in the electromagnetic spectrum, but its duration is only some tens of microseconds. Before and after the return stroke, multiple sub-processes redistribute electrical charges within the thundercloud. These sub-processes can last for tens to hundreds of milliseconds, many orders of magnitude longer than the return stroke. Each sub-process causes radiation with specific time-domain characteristics, having maxima at different frequencies. Thus, if the radiation is measured at a single narrow frequency band, it is difficult to identify the sub-processes, and some sub-processes can be missed altogether. However, narrowband detectors are simple to design and miniaturize. In particular, near the High Frequency band (High Frequency, 3 MHz to 30 MHz), ordinary shortwave radios can, in principle, be used as detectors. This dissertation utilizes a prototype detector which is essentially a handheld AM radio receiver. Measurements were made in Scandinavia, and several independent data sources were used to identify lightning sub-processes, as well as the distance to each individual flash. It is shown that multiple sub-processes radiate strongly near the HF band. The return stroke usually radiates intensely, but it cannot be reliably identified from the time-domain signal alone. This means that a narrowband measurement is best used to characterize the energy of the radiation integrated over the whole flash, without attempting to identify individual processes. The dissertation analyzes the conditions under which this integrated energy can be used to estimate the distance to the flash. It is shown that flash-by-flash variations are large, but the integrated energy is very sensitive to changes in the distance, dropping as approximately the inverse cube root of the distance. Flashes can, in principle, be detected at distances of more than 100 km, but since the ground conductivity can vary, ranging accuracy drops dramatically at distances larger than 20 km. These limitations mean that individual flashes cannot be ranged accurately using a single narrowband detector, and the useful range is limited to 30 kilometers at the most. Nevertheless, simple statistical corrections are developed, which enable an accurate estimate of the distance to the closest edge of an active storm cell, as well as the approach speed. The results of the dissertation could therefore have practical applications in real-time short-range lightning detection and warning systems.

Photocatalytic degradation of methyl methacrylate copolymers

The photolytic and photocatalytic degradation of the copolymers poly(methyl methacrylate-co-butyl methacrylate) (MMA–BMA), poly(methyl methacrylate-co-ethyl acrylate) (MMA–EA) and poly(methyl methacrylate-co-methacrylic acid) (MMA–MAA) have been carried out in solution in the presence of solution combustion synthesized TiO2 (CS TiO2) and commercial Degussa P-25 TiO2 (DP 25). The degradation rates of the copolymers were compared with the respective homopolymers. The copolymers and the homopolymers degraded randomly along the chain. The degradation rate was determined using continuous distribution kinetics. For all the polymers, CS TiO2 exhibited superior photo-activity compared to the uncatalysed and DP 25 systems, owing to its high surface hydroxyl content and high specific surface area. The time evolution of the hydroxyl and hydroperoxide stretching vibration in the Fourier transform-infrared (FT-IR) spectra of the copolymers indicated that the degradation rate follows the order MMA–MAA > MMA–EA > MMA–BMA. The same order is observed for the rate coefficients of photocatalytic degradation. The photodegradation rate coefficients were compared with the activation energy of pyrolytic degradation. In degradation by pyrolysis, it was observed that MMA–BMA was the least stable followed by MMA–EA and MMA–MAA. The observed contrast in the order of thermal stability compared to the photo-stability of these copolymers was attributed to the two different mechanisms governing the scission of the polymer and the evolution of the products.

Excitation energy transfer from a fluorophore to single-walled carbon nanotubes

We study the process of electronic excitation energy transfer from a fluorophore to the electronic energy levels of a single-walled carbon nanotube. The matrix element for the energy transfer involves the Coulombic interaction between the transition densities on the donor and the acceptor. In the Foumlrster approach, this is approximated as the interaction between the corresponding transition dipoles. For energy transfer from a dye to a nanotube, one can use the dipole approximation for the dye, but not for the nanotube. We have therefore calculated the rate using an approach that avoids the dipole approximation for the nanotube. We find that for the metallic nanotubes, the rate has an exponential dependence if the energy that is to be transferred, h is less than a threshold and a d(-5) dependence otherwise. The threshold is the minimum energy required for a transition other than the k(i,perpendicular to)=0 and l=0 transition. Our numerical evaluation of the rate of energy transfer from the dye pyrene to a (5,5) carbon nanotube, which is metallic leads to a distance of similar to 165 A degrees up to which energy transfer is appreciable. For the case of transfer to semiconducting carbon nanotubes, apart from the process of transfer to the electronic energy levels within the one electron picture, we also consider the possibility of energy transfer to the lowest possible excitonic state. Transfer to semiconducting carbon nanotubes is possible only if>=epsilon(g)-epsilon(b). The long range behavior of the rate of transfer has been found to have a d(-5) dependence if h >=epsilon(g). But, when the emission energy of the fluorophore is in the range epsilon(g)>h >=epsilon(g)-epsilon(b), the rate has an exponential dependence on the distance. For the case of transfer from pyrene to the semiconducting (6,4) carbon nanotube, energy transfer is found to be appreciable up to a distance of similar to 175 A degrees.

Impedance studies on high energy Li3+ irradiated PZT thin films

The ferroelectric Pb(Zr0.48Ti0.52)O-3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiatedfilms, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25 eV of unirradiated film to 1.62 eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss.

Impact of riparian land use on stream insects of Kudremukh National Park, Karnataka state, India

The impact of riparian land use on the stream insect communities was studied at Kudremukh National Park located within Western Ghats, a tropical biodiversity hotspot in India. The diversity and community composition of stream insects varied across streams with different riparian land use types. The rarefied family and generic richness was highest in streams with natural semi evergreen forests as riparian vegetation. However, when the streams had human habitations and areca nut plantations as riparian land use type, the rarefied richness was higher than that of streams with natural evergreen forests and grasslands. The streams with scrub lands and iron ore mining as the riparian land use had the lowest rarefied richness. Within a landscape, the streams with the natural riparian vegetation had similar community composition. However, streams with natural grasslands as the riparian vegetation, had low diversity and the community composition was similar to those of paddy fields. We discuss how stream insect assemblages differ due to varied riparian land use patterns, reflecting fundamental alterations in the functioning of stream ecosystems. This understanding is vital to conserve, manage and restore tropical riverine ecosystems.

Studies on the ionic transport and structural investigations of La0.5Li0.5TiO3 perovskite synthesized by wet chemical methods and the effect of Ce, Zr substitution at Ti site

La0.5Li0.5TiO3 perovskite was synthesized by various wet chemical methods. By adopting low temperature methods of preparation lithium loss from the material is prevented. La0.5Li0.5TiO3 (LLTO) was formed with cubic symmetry at 1473 K. LLTO was formed at relatively lower temperature by using hydrothermal preparation method. PVA gel-decomposition route yield tetragonal LLTO on annealing the dried gel at 1473 K. By using gel-carbonate route LiTi2O4 minor phase was found to remain even after heat-treatment at 1473 K. The hydroxylation of LLTO was done in deionized water as well as in dilute acetic acid medium. By hydroxylation process incorporation of hydroxyls and leaching out of Li+ was observed from the material. The Li+ concentration of these compositions was examined by AAS. The electrical conductivities of these compositions were measured by dc and ac impedance techniques at elevated temperatures. The activation energies of electrical conduction for these compositions were estimated from the experimental results. The measured activation energy of Li+ conduction is 0.34 eV. Unhydroxylated samples exhibit only Li+ conduction, whereas, the hydroxylated LLTO show proton conductivity at 298-550 K in addition to Li+ conductivity. The effect of Zr or Ce substitution in place of Ti were attempted. La0.5Li0.5ZrO3 Perovskite was not formed; instead pyrochlore phase (La2Zr2O7) along with monoclinic ZrO2 phases was observed above 1173 K; below 1173 K cubic ZrO2 is stable. (La0.5Li0.5)(2)CeO4 solid solution was formed in the case of Ce substitution at Ti sublattice on heat-treatment up to 1673 K. (c) 2005 Springer Science + Business Media, Inc.

Enzymatic Degradation of Poly(soybean oil-g-methyl methacrylate)

This study discusses grafting of methyl methacrylate units from thepolymeric soybean oil peroxide to produce poly(soybean oil-graft-methyl methacrylate) (PSO-g-PMMA). The degradation of this copolymer in solution was evaluated in the presence of different lipases, viz Candida rugosa (CR), Lipolase 100T (LP), Novozym 435 (N435) and Porcine pancreas (PP), at different temperatures The copolymer degraded by specific chain end scission and the mass fraction of the specific product evolved was determined The degradation was modeled using continuous distribution kinetics to determine the rate coefficients ofmenzymatic chain end scission and deactivation of the enzyme The enzymes, CR. LP and N435 exhibited maximum activity for the degradation of PSO-g-PMMA at 60 degrees C, while PP was most active at 50 degrees C. The thermal degradability of the copolymer, assessed by thermo-gravimetry, indicated that the activation energy of degradation of the copolymer was 154 kJ mol(-1), which was lesser than that of the PMMA homopolymer.

Propagation of a spherical shock in an inhomogeneous self-gravitating or nongravitating system

The propagation of a shock wave of finite strength due to an explosion into inhomogeneous nongravitating and self-gravitating systems has been considered, using similarity principles, supposing that the density varies as an inverse power of distance from the centre of explosion. A large number of systems, characterised by different density exponents and different adiabatic coefficients of the gas have been considered for different shock strengths. The numerical integration from the shock inward has been continued to the surface of singularity where density tends to infinity and which acts like a piston in the self-gravitating case and to the surface where the velocity gradient tends to infinity in the nongravitating case. The effect of variation of shock strength, density exponent and adiabatic coefficient on the location of these singularities and on the distribution of flow parameters behind the shock has been studied. The initial energy of the system and the manner of release of the explosion energy influence strongly the flow behind the shock. The results have been graphically depicted.

Diffractive W and Z production at the Fermilab Tevatron

We report on a measurement of the fraction of events with a W or Z boson produced diffractively in antiproton-proton collisions at a center of mass energy of 1.96 TeV, using data from 0.6 inverse femtobarns of integrated luminosity collected with the CDF-II detector equipped with a Roman-pot spectrometer that detects the antiproton (pbar) from pbar+p --> pbar+[X+W/Z]. We find that (0.97 +/- 0.11)% of Ws and (0.85 +/- 0.22)% of Zs are produced diffractively in a region of (anti)proton fractional momentum loss (\xi) of 0.03-1t p+[X+W/Z]+pbar, and on exclusive Z production, pbar+p-->pbar+Z+p. No signal is seen above background for these processes, and comparisons are made with expectations.

The emission spectrum of bismuth monofluoride BiF—‘A’ system

The observation of (A-X) system of BiF has been extended up to λ 5316 and twenty new bands belonging to this system have been recorded. The band heads could be represented by the following equation: {Mathematical expression} Seven other faint bands in the region λ 5316-5492 have also been reported, which, however, could not be classified. By our analysis of the present data and from known thermochemical data it has been deduced that the ground state dissociation energy is, in all probability, around 20000 cm.-1 (∼2·5 ev.) and that the dissociation products are the normal Bi and F atoms. The dissociation energy of the upper state and the correlation rules have been used to show that the dissociation products in the upper state are very likely to be Bi atom in the excited state2D3/2 and F atom in its ground state (2P3/2).