Anatase-rutile transformation in Fe/TiO2, Th/TiO2 and Cu/TiO2 catalysts and its possible role in metal-support interaction

Based on in-situ Mossbauer and X-ray diffraction studies, it is shown that in the Fe/TiO2 catalyst, the anatase-rutile transformation of the TiO2 support is facilitated by the Fe2+ ions formed during the reduction. The transformation occurs at lower temperatures in Th/TiO2 and Cu/TiO2 compared to pure TiO2. In general, the transformation of anatase to rutile seems to occur at or below the temperature (approximately 770 K) at which strong-metal-support-interaction manifests itself.

An in situ EXAFS investigation of bimetallic Cu---Ni/γ-Al2O3 catalysts

In situ EXAFS investigations have been carried out on Ni/γ-Al2O3 and Cu---Ni/γ-Al2O3 catalysts with different metal loadings, and prepared by different procedures. As-prepared Ni/γ-Al2O3 on calcination gives NiO and NiAl2O4-like phases on the surface, the proportion of the latter increasing with the increase in calcination temperature; the proportion of the NiO-like phase, on the other hand, increases with the metal loading. The reducibility of Ni/γ-Al2O3 to give metallic Ni on the surface directly depends on the proportion of the NiO-like phase present before reduction. Co-impregnating with Cu suppresses the formation of the surface aluminate and thereby favours the reduction to metallic Ni. This conclusion is clearly substantiated by our studies of bimetallic catalysts containing varying Cu/Ni ratios and also those prepared by the two-stage impregnation procedure.

Dominant role of the Cu---O charge-transfer energy, electronic polarizability and associated factors in the superconductivity of cuprates

Although it is believed that there is strong hybridization between the Cu(3d) and O(2p) orbitals in the layered cuprates and that the parent compounds such as La2CuO4 are charge-transfer gap insulators, very few models consider the Cu---O charge-transfer energy, Δ, or the hybridization strength, tpd, to be the important factors responsible for the superconductivity of these materials. Based on the crucial experimental observation that the relative intensity of the features in Cu(2p) photoemission of several families of cuprates varies systematically with the hole concentration, nh, we have been able to show that both these properties vary smoothly with Δ /tpd. More importantly, we show that the electronic polarizability of the CuO2 sheets, α , is sufficiently large to favour hole pairing and that the value α also depends on Δ/tpd. Both nh and α increase smoothly with decreasing Δ /tpd. Considering that the maximum Tc in the various cuprate families containing the same number of CuO2 sheets occurs around the same nh value (e.g., nh≈ 0.2 in cuprates with two CuO2 sheets). The present study demonstrates how Δ /tpd, α and such chemical bonding characteristics have an important bearing on the superconducting properties of the cuprates.

Theoretical gain‐optimization studies in CO2–N2 gasdynamic lasers. I. Theory

Based on a method proposed by Reddy and Daum, the equations governing the steady inviscid nonreacting gasdynamic laser (GDL) flow in a supersonic nozzle are reduced to a universal form so that the solutions depend on a single parameter which combines all the other parameters of the problem. Solutions are obtained for a sample case of available data and compared with existing results to validate the present approach. Also, similar solutions for a sample case are presented.

Molecular hydrodynamic theory of non‐Markovian collective orientational relaxation in dense dipolar liquids

A microscopic study of the non‐Markovian (or memory) effects on the collective orientational relaxation in a dense dipolar liquid is carried out by using an extended hydrodynamic approach which provides a reliable description of the dynamical processes occuring at the molecular length scales. Detailed calculations of the wave‐vector dependent orientational correlation functions are presented. The memory effects are found to play an important role; the non‐Markovian results differ considerably from that of the Markovian theory. In particular, a slow long‐time decay of the longitudinal orientational correlation function is observed for dense liquids which becomes weaker in the presence of a sizeable translational contribution to the collective orientational relaxation. This slow decay can be attributed to the intermolecular correlations at the molecular length scales. The longitudinal component of the orientational correlation function becomes oscillatory in the underdamped limit of momenta relaxations and the frequency dependence of the friction reduce the frictional resistance on the collective excitations (commonly known as dipolarons) to make them long lived. The theory predicts that these dipolarons can, therefore, be important in chemical relaxation processes, in contradiction to the claims of some earlier theoretical studies.

Molecular theory of dielectric relaxation in a dense binary dipolar liquid

A molecular theory of dielectric relaxation in a dense binary dipolar liquid is presented. The theory takes into account the effects of intra- and interspecies intermolecular interactions. It is shown that the relaxation is, in general, nonexponential. In certain limits, we recover the biexponential form traditionally used to analyze the experimental data of dielectric relaxation in a binary mixture. However, the relaxation times are widely different from the prediction of the noninteracting rotational diffusion model of Debye for a binary system. Detailed numerical evaluation of the frequency-dependent dielectric function epsilon-(omega) is carried out by using the known analytic solution of the mean spherical approximation (MSA) model for the two-particle direct correlation function for a polar mixture. A microscopic expression for both wave vector (k) and frequency (omega) dependent dielectric function, epsilon-(k,omega), of a binary mixture is also presented. The theoretical predictions on epsilon-(omega) (= epsilon-(k = 0, omega)) have been compared with the available experimental results. In particular, the present theory offers a molecular explanation of the phenomenon of fusing of the two relaxation channels of the neat liquids, observed by Schallamach many years ago.

Path-integral derivation of the superconformal anomaly for the N=1 supersymmetric Yang-Mills theory

Fujikawa's method of evaluating the supercurrent and the superconformal current anomalies, using the heat-kernel regularization scheme, is extended to theories with gauge invariance, in particular, to the off-shell N=1 supersymmetric Yang-Mills (SSYM) theory. The Jacobians of supersymmetry and superconformal transformations are finite. Although the gauge-fixing term is not supersymmetric and the regularization scheme is not manifestly supersymmetric, we find that the regularized Jacobians are gauge invariant and finite and they can be expressed in such a way that there is no one-loop supercurrent anomaly for the N=1 SSYM theory. The superconformal anomaly is nonzero and the anomaly agrees with a similar result obtained using other methods.

Preparation, characterization, spectral and thermal analyses of (N2H5)2MCl4·2H2O (M = Fe, Co, Ni and Cu); crystal structure of the iron complex

Hydrazinium metal chlorides, (N2H5)2MCl4·2H2O (where M = Fe, Co, Ni and Cu), have been prepared from the aqueous solutions of the respective metal chlorides and hydrazine hydrochloride (N2H4·HCl or N2H4·2HCl) and investigated by spectral and thermal analyses. The crystal structure of the iron complex has been determined by direct methods and refined by full-matrix least-squares to an R of 0.023 and Rw of 0.031 for 1495 independent reflections. The structure shows ferrous ion in an octahedral environment bonded by two hydrazinium cations, two chloride anions and two water molecules. In the complex cation [Fe(N2H5)2(H2O)2Cl2]2+, the coordinated groups are in trans positions.

Quasicrystals and their crystalline homologues in the Al-Mn-Cu ternary alloys

Electron diffraction and high-resolution electron microscopy have been employed to differentiate among icosahedral, decagonal and crystalline particles that occur in as-cast and rapidly solidified Al-Mn-Cu alloys. The resemblance between decagonal quasicrystals and crystals in their electron diffraction patterns is striking. The crystalline structure is based on the orthorhombic 'Al3Mn' structure, but also a new monoclinic phase called 'X' has been discovered and described here. The present observations are also closely related to the orthorhombic structures in Al60Mn11Ni4. The occurrence of fine-scale twinning and fragmentation into domains explains the complex diffraction effects.

Reactivity with hydrogen of pure iron oxide and of iron oxides doped with oxides of Mn, Co, Ni and Cu

Using dynamic TG in H2, X-ray powder diffraction and Mössbauer Spectroscopy the reactivities fot hydrogen reduction of Fe2O3 prepared at different temperatures, Fe2O3 doped with oxides of Mn, Co, Ni and Cu prepared at 300DaggerC from nitrate precursors and intermediate spinels derived from above samples during reduction have been explored. The reactivity is higher for finely divided Fe2O3 prepared at 250DaggerC. The reduction is retarded by Mn, marginally affected by Co and accelerated by Ni and Cu, especially at higher (5 at.%) dopant concentration. These reactivities confirmed also by isothermal experiments, are ascribed to the nature of disorder in the metastable intermediate spinels and to hydrogen rsquospill overrsquo effects.

Scaling theory of quantum resistance distributions in disordered systems

We have derived explicitly, the large scale distribution of quantum Ohmic resistance of a disordered one-dimensional conductor. We show that in the thermodynamic limit this distribution is characterized by two independent parameters for strong disorder, leading to a two-parameter scaling theory of localization. Only in the limit of weak disorder we recover single parameter scaling, consistent with existing theoretical treatments.

Structure of a monochloro bridged polymeric copper(II)-di-2-pyridylamine complex: [Cu(dipyam)Cl(NO3)].0.5H2O

Di-2-pyridylaminechloronitratocopper(II) hemihydrate, [CuCl(NO3)(C10H9N3)].0.5H2O, M(r) = 341.21, monoclinic, P2(1)/a, a = 7.382 (1), b = 21.494 (4), c = 8.032 (1) angstrom, beta = 94.26 (1)-degrees, V = 1270.9 angstrom 3, Z = 4, D(m) = 1.78, D(x) = 1.782 g cm-3, lambda(Mo K-alpha) = 0.7107 angstrom, mu(Mo K-alpha) = 19.47 cm-1, F(000) = 688. The structure was solved by the heavy-atom method and refined to a final R value of 0.034 for 2736 reflections collected at 294 K. The structure consists of polymeric [Cu(dipyam)Cl(NO3)] units bridged by a chloride ion.