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Kolkata, India

We investigate theoretically the coupling optics involving a laser diode and an elliptic core monomode step index fiber via an upside down tapered lens on the tip of the fiber in absence and presence of possible transverse and angular misalignments. By employing Gaussian field distributions for both the source and the fiber and also the derived ABCD matrix for upside down tapered lens, we formulate analytical expressions for the concerned coupling efficiencies with and without transverse and angular mismatches. Our formalism is very simple in comparison to the other existing methods involving cumbersome numerical integrations. Elliptic core single-mode fiber has already emerged as a potential candidate in polarization conserving fiber optic sensor, coherent fiber optical communication, etc. The investigations have been performed for two different emitting wavelengths of the laser diodes for the said elliptic core monomode fibers. Therefore, such analysis which as per our knowledge is the first theoretical investigation in the context, can also be treated as simple and novel prescription for choosing suitable parameters for the design of upside down tapered lens on the tip of elliptic core single-mode fiber for optimum launch optics. In addition, this analysis will be useful in case of inherent non-circularity that may arise due to fabrication problem in circular core fiber and thereby generates interests among the experimentalists for verification and future investigations on upside down tapered lens. © 2008. Source


Peng S.-M.,National Taiwan University | Lee G.H.,National Taiwan University | Butcher R.J.,Howard University | Lu T.-H.,National Tsing Hua University | And 2 more authors.
Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry | Year: 2011

Two cobalt(III) complexes [Co(L1)2]ClO4 (1) [HL 1= N-ethyl-2-((5-methyl-1H-pyrazol-3-yl)methylidene) hydrazinecarbothioamide] and [Co(L2)2]ClO 4.CH3OH.H2O (2) [HL2=N,N-dimethyl-2- ((5-methyl-1H-pyrazol-3-yl)methylidene) hydrazinecarbothioamide] and one nickel(II) complex [Ni(HL3)2](ClO4)2.2H 2O (3) [HL3=(2E)-N-ethyl-2-((6-methyl-2-(methylsulfanyl) pyrimidin-4-yl)methylidene)-hydrazinecarbothioamide] have been prepared and characterized by spectroscopic studies and X-ray diffraction measurements. Structural study reveals that the coordination environment around each metal center is distorted octahedral. The two tridentate (NNS) uninegative pyrazole derived ligands in the cobalt(III) complexes (1 and 2) and the two similar neutral pyrimidine derived ligands in the nickel(II) complex (3) are coordinated to the central metal ions in the meridional fashion. The pyrazole N and thiolato S in (1) and (2) and pyrimidine N and thione S in (3) are cis to each other while azomethine N atoms are trans coordinated. Source


Gupta K.K.S.,Jadavpur University | Bhattacharjee J.,Jadavpur University | Pal B.,St Pauls Cm College
Asian Journal of Chemistry | Year: 2015

The oxidation of thiosulfate ion by tris (pyridine-2-carboxylato) manganese(III) in picolinate-picolinic acid buffer occurs according to the equation 2S2O3 2- + 2MnIII → S4O6 2- + 2MnII. The reaction was studied under pseudo-first order conditions. The rate of the reaction is first order with respect to [S2O3 2-] and [MnIII] with no evidence of 1:1 complex formation between the reactants. The influence of pH on the reaction rate is insignificant. The rate of the reaction decreases with the increase in acrylamide concentration. The influence of temperature was studied in the temperature range 288-303 K. The values of ΔH# and ΔS# have been calculated to be 33 ± 2 kJ mol-1 and -137 ± 7 J K-1 mol-1, respectively. A one-equivalent electron transfer from S2O3 2- to MnIII takes place to give MnII and free radical, the latter subsequently is transformed to S4O6 2-. An attempt has been made to compare the results of the oxidation of some other sulfur, phosphorous and nitrogen containing inorganic compounds by this oxidant. Source


Sen P.K.,Jadavpur University | Bera R.N.,Jadavpur University | Pal B.,St Pauls Cm College
Asian Journal of Chemistry | Year: 2015

The reduction of toluidine blue (TB+) by sulfite [S(IV)] was studied spectrophtometrically in acetic acid-sodium acetate buffer medium in the temperature range 293-308 K. The reaction showed first order dependence on toluidine blue. The reaction was found to be first order in S(IV) at lower substrate concentration ([S(IV)] ≤ 0.07 mol dm-3) but the reaction became second order in S(IV) at high substrate concentration ([S(IV)] > 0.07 mol dm-3). H+ ions were found to inhibit the reaction in the pH range 4.0-5.4. The rate decreased with increase in the ionic strength of the medium, but remained unchanged with decreasing dielectric constant of the medium. The oxidation reaction possibly involved a one-electron transfer step via a free radical mechanism. An overall enthalpy and entropy of activation were computed. A plausible mechanism and rate law corroborating the experimental results have been put forward. Source


Das K.,Haldia Government College | Jana A.,University of Calcutta | Konar S.,University of Calcutta | Chatterjee S.,Serampore College | And 3 more authors.
Journal of Molecular Structure | Year: 2013

The new N6 donor hexadentate Schiff base 2,4-bis [2-(pyridine-2-ylmethylidene) hydrazinyl] pyrimidine (L), its trinuclear Zn(II) complex, [Zn3(L)2Cl6] (1) and mononuclear heptacoordinate Cd(II) complex [Cd(L)(H2O)2](ClO 4)2 (2) have been synthesised and characterised by crystallographically and spectroscopically. Complex 1 is featured by the triangular arrangement of three zinc atoms where the neighbouring Zn atoms are linked via half portion (N3 chromophore) of the same ligand molecule. In 1, the ligand molecules behave as hexadentate ones (employing both pyrimidine nitrogen atoms as active donor centres) to create the octahedral environment around Zn(II). The central and terminal Zn(II) atom has N 6 and N3Cl3 chromophores respectively. In 2 the same ligand (L) behaves as pentadentate one (ignoring one pyrimidine nitrogen in the coordination process) to produce a pentagonal bipyramidal geometry with two apical water molecules. The geometries of both complexes were optimised in the singlet state by DFT method. The TDDFT calculations have been done on the optimised geometries to understand the electronic structure and spectral transition in the complexes. Complex 1 exhibits intraligand 1(π→π*) fluorescence in aqueous methanol solvent at room temperature. © 2013 Elsevier B.V. All rights reserved. Source

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