Dependence of photoconductivity on the crystallite orientations and porosity of polycrystalline ZnO films

Hexagonal ZnO films deposited on quartz glass, sapphire and glass substrates by sol–gel coating are found to be randomly oriented; maximum randomness is found in the film on quartz glass substrate. All the films are ultra-violet (UV) sensitive at around 360 nm sensitivity being maximum for the film with maximum randomness in the crystallite orientations. The film on quartz showed the lowest dark current and maximum photoresponse, which is related to the lowering of the barrier heights, introduced by the adsorbed oxygen at the grain boundaries. Faster decay in photocurrent is observed for the film deposited on glass, which is attributed due to the smaller crystallite sizes with porous microstructure of the film. PACS 73.61.Ga; 68.55.Jk; 73.50.Pz     

The effect of solutal undercooling on double‐diffusive convection and macrosegregation during binary alloy solidification: a numerical investigation

In this paper, we present a macroscopic numerical model that is capable of capturing the interaction between the double‐diffusive convective field and a localized fluid flow on account of solutal undercooling during non‐equilibrium solidification of binary alloys. The model is essentially based on a fixed‐grid enthalpy based control volume approach. In the present model, microscopic features pertaining to non‐equilibrium effects on account of solutal undercooling are incorporated through the formulation of a modified partition‐coefficient. The effective partition‐coefficient is numerically modelled by means of a number of macroscopically observable parameters related to the solidifying domain. This feature has made the present treatment different from micro‐macro modelling of alloy solidification, which involves certain parameters that may not be macroscopically resolvable. Numerical simulations are performed for the case of two‐dimensional transient solidification of Pb–Sn alloys (both hypoeutectic and hypereutectic) in a rectangular cavity, employing the present model. The simulation results are also compared with the corresponding experimental results quoted in the literature, and the agreement is excellent. From the results, it can be concluded that non‐equilibrium effects on account of solutal undercooling result in a more enhanced macrosegregation. Copyright © 2002 John Wiley & Sons, Ltd.     

Growth of Bi-Sb alloy thin films and their characterization by TEM, PIXE and RBS

Polycrystalline bulk materials of Bi₉₃Sb₇ Bi₈₈Sb₁₂, Bi₈₅Sb₁₅ and Bi₈₀Sb₂₀ were synthesized by melt-quench technique starting from the stoichiometric mixture of constituent elements. The phase purity and compositional uniformity of bulk materials were investigated using powder X-ray diffraction (XRD) and proton induced X-ray emission (PIXE) experiments. The single phase formation and the compositional analysis of thin films were confirmed by transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). X-ray diffraction studies confirmed the phase homogeneity of the materials. Atomic concentration ratio of constituent elements (Bi and Sb) determined by PIXE and RBS revealed that near-stoichiometric composition is nearly the same in the bulk as well as in thin film forms.     

Acylation of aromatic alcohols and phenols over InCl3/montmorillonite K-10 catalysts

Montmorillonite K-10 clay supported InCl₃ is a highly active catalyst for the acylation of aromatic alcohols and phenols with different acyl chlorides. This catalyst can be reused in reactions a number of times without very significant loss of catalytic activity     

Scattering amplitude and shift in self-energy in medium

Two simple proofs are presented for the first order virial expansion of the self-energy of a particle moving through a medium, characterised by temperature and/or chemical potential(s). One is based on the virial expansion of the self-energy operator itself, while the other is based on the analysis of its Feynman diagrams in configuration space. Received: 26 December 2001 / Published online: 5 April 2002     

$$\mathcal{P}\mathcal{T}$$ -supersymmetric partner of a short-range square well

In a box of size L, a spatially antisymmetric square-well potential of a purely imaginary strength ig and size l < L is interpreted as an initial element of the SUSY hierarchy of solvable Hamiltonians, the energies of which are all real for g < g _c (l). The first partner potential is constructed in closed form and discussed. Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22, 2005.     

Non-invasive diagnosis of type 2 diabetes in Helicobacter pylori infected patients using isotope-specific infrared absorption measurements

Helicobacter pylori causes several gastrointestinal diseases and may also contribute to the development of type 2 diabetes (T2D). Several studies suggest that there might be a potential link between H. pylori infection and T2D, but it still remains the subject of debate. Here, we first report the cumulative effect of H. pylori infection and T2D by exploiting the excretion kinetics of ¹³C/¹²C and ¹⁸O/¹⁶O isotope ratios of exhaled breath CO₂ in response to an oral dose of ¹³C-enriched glucose in individuals with T2D and non-diabetic controls (NDC) harbouring the H. pylori infection. Using a high-resolution integrated cavity output spectroscopy (ICOS) technique in the infrared region, we observed that the isotopic fractionations of ¹³C and ¹⁸O in breath CO₂ are distinctly altered in H. pylori infected T2D patients as well as in H. pylori infected NDC. Several optimal diagnostic cut-off points of ¹³C and ¹⁸O isotopes of breath CO₂ were also determined which exhibited the diagnostic sensitivity and specificity of ～97?% and thus suggesting that breath ¹³C and ¹⁸O isotopes might be considered as potential biomarkers for the non-invasive assessment of the gastric pathogen prior to the onset of T2D. This may open a new diagnostic strategy for treating these common diseases in an alternative way.     

Morphology induced magnetic instabilities on oxide antiferromagnetic surfaces

The role of interfacial disorder and roughness has been pointed out several times in ferromagnetic-antiferromagnetic exchange coupled systems. However, effect of surface morphology on magnetic properties of bare antiferromagnetic material has been mostly ignored. Here we report our experimental observations of magnetic instabilities on high temperature air annealed NiO(100) surfaces through treatment of successive vacuum and oxygen annealing above Néel temperature. Preferential spin-orientations are found to be governed by surface morphology with enhanced roughness and oxygen diffusion process. Stable domain distribution has been observed on smoother surfaces, which are found to be mostly inactive to these annealing treatments.