On the convergence of the Zassenhaus formula

The domain of convergence of the Zassenhaus formula in a Banach algebra is studied. This domain is shown to be strictly larger than the one which was already known.     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Synthesis of polypyrrole nanoparticles and its grafting with silica gel for selective binding of chromium(VI)

Polypyrrole nanoparticles of desired structure have been synthesized through simple micelle technique. It is then grafted with functionalized silica gel to develop a novel organic-inorganic hybrid material. The role of dimethyl dichloro silane (coupling agent) in grafting is demonstrated. The nanoparticles are characterized by TEM, SEM and TGA. Grafting reactions are evaluated by spectral (FTIR) analysis and chemical test. The Cr(VI) binding behavior of the composite is studied in various pH of the medium. The selectivity in binding Cr(VI) is monitored. The metal ion adsorption capacity and surface area of the material are found to be 38 mg/g and 235 m²/g, respectively.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Localizability of massless particles in the framework of the conformal group

Localizability of massless particles in the framework of the conformal group is given by means of imprimitivity systems for particular representations of the Sitter groupSO ₀(4, 1).Dedicated to Professor Ivan Úlehla on the ocassion of his sixtieth birthday.The authors wish to thank Professors M. Flato and W. Schmid for stimulating discussions.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Facile synthesis of polyacrylate directed silver nanoparticles for pH sensing through naked eye

Poly(acrylic acid) (PAA) and its salt poly(acrylate) (PA) have been synthesized through modified free radical polymerization in environmentally begin aqueous medium under ultrasound to make the process robust. The synthesized polymer is well-characterized through conventional techniques. Its salt is employed to produce highly stable and stimuli sensitive colloidal silver (Ag-PA sol) without using any additional reducing chemical reagents like sodium borohydride, ascorbic acid, hydrazine, etc or UV/Gamma radiation. A detailed mechanistic path of the polymerization and reduction of Ag⁺ on polyacrylate chains has been evaluated. Finally Ag-PA sol is used for pH sensing through naked eye to eliminate the need for sophisticated instrument for data collection. The present work focuses mainly the development of a low cost pH sensing system based on colorimetric ‘smart polymer’ having high practical utility. The unique structural and photo-physical features of nano-scaled materials open new opportunities for the applications of colorimetric pH sensor. In the present work, Ag nano-clusters capped by PA^? are employed as an effective colorimetric pH sensor for the first time, requiring no further functionalization.     

The permeation liquid membrane as a sensor for free nickel in aqueous samples

There are currently a limited number of techniques to study nickel speciation in aqueous samples. This work reports on the use of the permeation liquid membrane (PLM) for that objective. In this paper, the composition of the organic phase was studied to maximize the Ni flux (thus the sensitivity of the device) over a wide Ni2+ concentration range (50 nM to 100 microM) in order to verify its ability to determine free Ni2+ in the presence of Ni complexes. A mixture containing 1,10-didecyl-1,10-diaza-18-crown-6 ether (22DD) and di(2-ethylhexyl)phosphoric acid (D2EHPA) in toluene/phenylhexane was selected as the optimized organic phase for the PLM. The PLM was shown to be a reliable tool to measure free nickel concentrations down to 10(-7) M. The effect of pH on Ni transport was also studied. Fluxes below pH 6 were reduced significantly, i.e. an order of magnitude smaller than fluxes above pH 7.8. Finally, as part of a broader study examining the ability of trace metals to induce antibiotic resistance in bacteria, we used the PLM to quantify the formation, at pH = 7.2, of a weak complex between Ni and Imipenem (a member of the carbapenem class of beta-lactam antibiotics) or its hydrolysis product(s).