Electrical conduction and size effect in bismuth films

The size effect on electrical conduction is observed in bismuth films in the region of film thickness above 2000 Å. Applying Fuchs-Sondheimer theory and assuming specularity parameterp = 0·8, the value of bulk resistivity and mean free path are obtained as 6·692 × 10⁴ ohm-cm and 6000 Å respectively.     

Inequivalence of substitution pairs in hydroxynaphthaldehyde: A theoretical measurement by intramolecular hydrogen bond strength,aromaticity, and excited‐state intramolecular proton transfer reaction

The inequivalence of substitution pair positions of naphthalene ring has been investigated by a theoretical measurement of hydrogen bond strength, aromaticity, and excited state intramolecular proton transfer (ESIPT) reaction as the tools in three substituted naphthalene compounds viz 1‐hydroxy‐2‐naphthaldehyde (HN12), 2‐hydroxy‐1‐naphthaldehyde (HN21), and 2‐hydroxy‐3‐naphthaldehyde (HN23). The difference in intramolecular hydrogen bond (IMHB) strength clearly reflects the inequivalence of substitution pairs where the calculated IMHB strength is found to be greater for HN12 and HN21 than HN23. The H‐bonding interactions have been explored by calculation of electron density ρ(r) and Laplacian ?²ρ(r) at the bond critical point using atoms in molecule method and by calculation of interaction between σ* of OH with lone pair of carbonyl oxygen atom using NBO analysis. The ground and excited state potential energy surfaces (PESs) for the proton transfer reaction at HF (6‐31G**) and DFT (B3LYP/6‐31G**) levels are similar for HN12, HN21 and different for HN23. The computed aromaticity of the two rings of naphthalene moiety at B3LYP/6‐31G** method also predicts similarity between HN12 and HN21, but different for HN23. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

A new window towards multidimensional sensing of transition metal cations through dual mode sensing ability of N-benzyl-(3-hydoxy-2-naphthalene): emission enhancement coupled remarkable spectral shift

A structurally simple Schiff base N-benzyl-(3-hydroxy-2-naphthalene) (NBHN32) has been synthesized and characterized by (1)H NMR, (13)C NMR, and DEPT spectroscopy. The photophysical behaviour of NBHN32 in response to the presence of various transition metal cations has been explored by means of steady-state absorption, emission and time-resolved emission spectroscopy techniques. Efficient through space intramolecular photoinduced electron transfer (PET) between the naphthalene fluorophore and the imine group has been argued for extremely low fluorescence yield of NBHN32 compared to the parent molecule 3-hydroxy-2-naphthaldehyde (HN32) containing the same fluorophore but lacking the receptor moiety. Transition metal ion-induced emission enhancement is thus addressed on the lexicon of perturbation of the PET by the metal ions. Apart from fluorescence enhancement, transition metal ion imparts remarkable shift of the emission maxima of NBHN32, which is another unique aspect on the proposed ability of NBHN32 to function as a fluorescence chemosensor.     

Novel fusion method for direct determination of uranium in ilmenite,rutile, columbite,tantalite, and xenotime minerals by laser induced fluorimetry

A simple, rapid, effective and eco-friendly decomposition method is developed for the determination of uranium (U) by laser induced fluorimetry (LIF). The salts of sodium di-hydrogen phosphate (NaH₂PO₄) and di-sodium hydrogen phosphate (Na₂HPO₄) were used in the ratio of 1:1 (phosphate flux) for the decomposition and dissolution of refractory, non silicate minerals like ilmenite, rutile, columbite, tantalite, and xenotime. The effect of associated matrix elements (Ti, Fe, Nb, Ta, Mn and Y present in the sample) on quenching of uranyl fluorescence was studied. The flux used for the sample decomposition has several advantages. In the reported sample decomposition methods, α-hydroxy acids are used as complexing agents to prevent hydrolysis and to get clear and stable solution. This solution can not be directly used for U determination by LIF as α-hydroxy acids quench uranyl fluorescence, hence separation is required. In the present method no such separation is required. The flux itself acts as fluorescence enhancing reagent and buffer (maintaining the optimum pH of 7.1 ± 0.1). The fused melt of the flux mixture, when disintegrated in water, gives clear and stable solution and has high tolerance for most of inorganic quenchers compared to reported phosphate buffers. Also just by dilution (due to high sensitivity of LIF), the concentration of quenchers could be brought down well within the tolerance limit. The accuracy and precision of the method was evaluated by analyzing Certified Reference Materials (IGS-33 and IGS-34 of Institute of Geological Sciences, UK) and Synthetic Minerals. The accuracy of the data is further evaluated by comparing with standard decomposition methods. The results are well within the experimental error. The RSD of the method is ±10% (n = 6) at 10 ppm level for Ilmenite and for other minerals the RSD of the method is ±5% (n = 6) at 50 ppm level. The method is being routinely applied to various refractory samples received from Rare Metal and Rare Earth Investigations for determination of uranium by laser fluorimetry.     

Composite nonlinear feedback based discrete integral sliding mode controller for uncertain systems

In this paper, a discrete integral sliding mode (ISM) controller based on composite nonlinear feedback (CNF) method is proposed. The aim of the controller is to improve the transient performance of uncertain systems. The CNF based discrete ISM controller consists of a linear and a nonlinear term. The linear control law is used to decrease the damping ratio of the closed-loop system for yielding a quick transient response. The nonlinear feedback control law is used to increase the damping ratio with an aim to reduce the overshoot of the closed-loop system as it approaches the desired reference position. It is observed that the discrete CNF-ISM controller produces superior transient performance as compared to the discrete ISM controller. The closed-loop control system remains stable during the sliding condition. Simulation results demonstrate the effectiveness of the proposed controller.     

Implications of BNL measurement of \delta a_{\mu} on a class of scalar leptoquark interactions

Recently BNL have measured the muon magnetic moment anomaly with increased precision. The world average experimental value at present shows a discrepancy of from the standard model (SM) value. In this paper we investigate the implications of this difference on a class of scalar leptoquark interactions to SM quark–lepton pair. We find that for a leptoquark mass of a few hundred GeV the BNL muon anomaly can arise from couplings much smaller than even the electromagnetic coupling. We also find that the BNL value for the muon anomaly leads to an unambiguous prediction for the electric dipole moment of the muon and a bound on the flavor changing leptoquark coupling relevant for the rare decay . Received: 15 April 2001 / Published online: 6 July 2001     

Growth morphology of zinc tris(thiourea) sulphate crystals

The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc tris(thiourea) ions and sulphate ions.