A method of reducing the half wave voltage (Vπ) of an electro-optic modulator by multi passing a light through the modulator

Electro-optic material has several applications in optical communication, integrated optics and in data processing. The modulator is generally used for the purpose of amplitude and phase modulation of optical wave by the electrical message signal. Again the V_π voltage of an electro-optic modulator is an important parameter for the modulator. For the application of the V_π amount of electrical signal in the modulator the phase difference between two specific orthogonally polarized light waves changes from 0 to π. Thus the increase of V_π relates with the increase of electrical power requirement for modulation. Here in this paper the authors propose a new and novel concept for reduction of V_π voltage for the modulator. To reduce the value of the V_π voltage the multi passing technique of the beam through the modulator is used. If V_π is reduced the power requirement as well as the modulation cost will be greatly reduced to achieve a faithful and a meaningful optical communication. This paper describes also the necessary optical systems required for the multi passing technique.     

Polypyrrole–polyvinyl alcohol stable nanodispersion: A prospective conducting black ink

Chemical polymerization of pyrrole within aqueous polyvinyl alcohol (PVA) solution gives rise to a nanodispersion with unique stability and monodispersity. The nanodispersion has shown uniform distribution of perfectly spherical ～110 nm polypyrrole particles (from transmission electron microscopy and dynamic light scattering) with high doping level (from UV‐Vis analysis) and sufficient electrical conductivity (10^?3 S/cm). The dispersion with optimum stability and conductivity was subjected to viscoelastic studies. The viscosity of the system was adjusted by dilution with water and shear thinning (under steady shear) was generally observed. Dynamic mechanical studies have shown that the dispersion behaves like a semidiluted polymeric solution that roughly follows the Zimm model of viscoelasticity. This behavior accounts for its unique stability and miscibility with water at any proportion without precipitation. On drying or leaving the sample for 7 days, Fe³⁺ induced partial crosslinking of PVA chains takes place via –OH groups, although complete gelling does not occur. The dispersion forms flexible and uniform films on glass and metal surfaces that does not dissolve after complete drying; this observation combined with shear thinning encourages its application as ink or paint. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Adsorption and kinetic behavior of uranium and thorium in seawater-sediment system

The adsorption and kinetic mechanism of uranium (U) and thorium (Th) in seawater-sediments system of Mumbai Harbour Bay (MHB) has been studied by K _d values of two sets of experimental determinations using a batch experiment. After equilibrium time (7 days), under static conditions, K _d for U and Th ranged from 25,030 to 55,662 mL/g (mean: 42,140 mL/g) and 24,926 to 38,561 mL/g (mean: 34,256 L/kg), respectively. Extraction studies showed that both U and Th were strongly bound to sediment components due to insignificant difference in their mean concentration in equilibrium solution. Rate constants (k) for transfer between seawater and the exchangeable fraction were found to be similar for the sediments as 1.02 ± 0.03 day^?1 for uptake of U and Th. The resulting adsorption data were fitted to Freundlich, linear and Langmuir isotherm models. All the three models showed a significant correlation (R ² >0.9), indicating that there is more complex relationships with adsorption behavior of U and Th on sediment surface. Since, the Freundlich constant (n) for U and Th was found to be closer to unity. Therefore linear model was observed to be highly suitable. Based on the linear model, the distribution coefficient (k _d) of Th was about 1.5 times higher than U. According to Freundlich model, sorption of U in sediments observed to be higher than Th. However, Langmuir model considered in opposite to Freundlich and showed a higher value of K _L constant for Th than U. The pH (water) of the sediments ranged from 7.8 to 8.2 and the estimated total carbon (determined by C H N S–O elemental analyser) ranged from 1.7 to 3.4 %.     

Synthesis,spectral characterization,and evaluation of antimicrobial activity of O,O′-alkanediyl S-(N-phthalimidomethyl) dithiophosphates and zinc bis(O,O′-alkanediyl) dithiophosphates

The synthesis of novel dithiophosphate derivatives has been achieved. Two O,O′-alkanediyl S-(N-phthalimidomethyl) dithiophosphates and two Zinc bis(O,O′-alkanediyl) dithiophosphates are synthesized by an easy and facile chemical synthetic route. Zinc bis[O,O′-(2-methylpentane-2,4-diyl) dithiophosphate] L¹, Zinc bis[O,O′-(2-ethylhexane-1,3-diyl) dithiophosphate] L², O,O′-(2-methylpentane-2,4-diyl) S-(N-phthalimidomethyl) dithiophosphate L³ and O,O′-(2-ethylhexane-1,3-diyl) S-(N-phthalimidomethyl) dithiophosphate L⁴ are synthesized from the respective ammonium salts. Compounds L¹, L², L³, and L⁴ are characterized by (CHN) elemental analysis, ESI mass, FT-IR, ¹H, ¹³C, and ³¹P NMR techniques. The crystal structure of ammonium O,O′-(2-methylpentane-2,4-diyl) dithiophosphate is discussed. L¹, L², L³, and L⁴ were evaluated for antimicrobial activity. It was found that the phthalimide derivatives L³ and L⁴ showed much better antifungal potential against some species of fungus. The Zinc dithiophosphates L¹ and L² showed good antibacterial activity against Bacillus cereus and Escherichia coli.     

A concise enantioselective synthesis of 1,4-dideoxy-1,4-imino-d-arabinitol using Co(III)(salen)-catalyzed hydrolytic kinetic resolution of a two-stereocentered anti-azido epoxide

A concise enantioselective synthesis of 1,4-dideoxy-1,4-imino-d-arabinitol, (+)-DAB-1, has been described in good overall yield (18.1%) and with high enantiomeric purity (up to 98% ee) starting from a simple raw material, cis-2-butene-1,4-diol. The Co-catalyzed hydrolytic kinetic resolution of a two-stereocentered racemic azido epoxide followed by asymmetric dihydroxylation of the alkene and ‘one pot’ reductive cyclisation of the azido diol are key reactions in the synthetic sequence.     

Surface arsenic speciation of a drinking-water treatment residual using X-ray absorption spectroscopy

Drinking-water treatment residuals (WTRs) present a low-cost geosorbent for As-contaminated waters and soils. Previous work has demonstrated the high affinity of WTRs for As, but data pertaining to the stability of sorbed As is missing. Sorption/desorption and X-ray absorption spectroscopy (XAS), both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) studies, were combined to determine the stability of As sorbed by an Fe-based WTR. Arsenic(V) and As(III) sorption kinetics were biphasic in nature, sorbing >90% of the initial added As (15,000 mg kg(-1)) after 48 h of reaction. Subsequent desorption experiments with a high P load (7500 mg kg(-1)) showed negligible As desorption for both As species, approximately <3.5% of sorbed As; the small amount of desorbed As was attributed to the abundance of sorption sites. XANES data showed that sorption kinetics for either As(III) or As(V) initially added to solution had no effect on the sorbed As oxidation state. EXAFS spectroscopy suggested that As added either as As(III) or as As(V) formed inner-sphere mononuclear, bidentate complexes, suggesting the stability of the sorbed As, which was further corroborated by the minimum As desorption from the Fe-WTR.     

Development of a Liquid‐liquid Extraction System for Rhodium(III) by 2‐octylaminopyridine from Weak Malonate Media

We have developed the extraction method of rhodium(III) from malonate media with 2‐octylaminopyridine (2‐OAP) in xylene at pH 8.0. The quantitative extraction of rhodium(III) with extractant was found by screening of different physicochemical parameters like malonate concentration, extractant concentration, pH, diluents, effect of temperature, aq: org phase ratio, loading capacity of 2‐OAP. The optimum condition was malonate=0.025 M, pH=8.0, 2‐OAP=0.05 M in xylene. The complete stripping of rhodium(III) from the loaded organic phase was carried out with 2 M HCl. Log‐log plot was investigated to determine the stoichiometry of the extracted species and it was found to be 1 : 2 : 1 (metal : acid :extractant). The versatility of the proposed method was checked for extraction and separation of rhodium(III) from binary, ternary mixture of associated metal ions as well as platinum group metals and from the synthetic solution of rhodium minerals and alloys.     

Structure and Dynamic of Three Indole Alkaloids from the Campylospermum Genus (Ochnaceae)

A new indole alkaloid, calanthumindole ( 4 ), and three known biflavonoids, amentoflavone, sequoiaflavone, and podoscarpusflavone B, were isolated from Campylospermum calanthum (Ochnaceae). Calanthumindole is a new indole alkaloid of the serotobenine family characterized by the presence of a C?C bond between atoms C(7′) and C(8′) of the furan ring. This is the first compound to have a fully unsaturated furan ring among the members of this family. The combination of NMR and DFT allowed the determination and comparison of the 3D structures and relevant conformational characteristics of serotobenine ( 1 ), flavumindole ( 2 ), and calanthumindole ( 4 ).     

Formation of ZnO@Cd(OH)2 core-shell nanoparticles by sol-gel method: An approach to modify surface chemistry for stable and enhanced green emission

We report the formation of highly stable and luminescent ZnO@Cd(OH)₂ core-shell nanoparticles by simple introduction of cadmium salt in the initial precursor solution, used to synthesize ZnO nanoparticles by sol-gel route. The cadmium to zinc salt concentration ratio has been also varied to control the growth of ZnO nanoparticles at the smaller particle size. Formation of ZnO@Cd(OH)₂ core-shell nanostructure has been confirmed by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). UV-vis absorption spectroscopy exhibits blue-shift in absorption edge on increasing cadmium concentrations. The photoluminescence emission spectra showed the remarkably stable and enhanced visible (green) emission from suspended ZnO@Cd(OH)₂ nanoparticles in comparison to bare ZnO nanoparticles. It is postulated that Cd(OH)₂ layer at the surface of ZnO nanoparticles prevents the agglomeration of nanoparticles and efficiently assists the trapping of hole at the surface site, a first step necessary for visible emission. The Fourier transform infrared spectroscopy (FTIR) also supports our assumption about surface chemistry.