Emission properties of manganese-doped ZnS nanocrystals

We have performed steady-state and time-resolved fluorescence studies on undoped and Mn-doped ZnS nanocrystals with approximately 16 A diameter. While there is no band-edge emission, the intensity of the steady-state blue fluorescence from ZnS surface states decreases upon Mn incorporation, which gives rise to an orange emission. These results show that Mn incorporation competes very effectively with the donor-acceptor surface states for the energy transfer from the electron-hole pair excited across the band gap. In both undoped and doped samples, the time-resolved fluorescence studies establish the presence of a distribution of decay lifetimes possibly due to a number of emission centers in the nanocrystals. A faster short-time decay of the blue emission in the Mn-doped samples compared to that in the undoped sample suggests an additional decay channel for the surface states via an energy transfer from these states to the dopant levels.     

Complexation/speciation studies of Ni2+ion with ortho silicic acid in perchlorate media

Summary The complexation behavior of Ni²⁺with ortho-silicic acid (o-SA) has been studied as a function of ionic strength (I) from 0.20 to 1.00M (NaClO₄) at pcH 4.55±0.05 and 25 °C by a solvent extraction technique with bis(2-ethylhexyl) phosphoric acid (HDEHP) as the extractant. The stoichiometry of the extracted species was determined to be Ni(DEHP)₂(HDEHP)₂. Ni²⁺forms a 1:1 complex, Ni(OSi(OH)₃)⁺, as the predominant species withconcentrations of 1.00^. 10^-3to 1.00^. 10^-2M o-SA. The stability constant (logb₁) values for Ni(OSi(OH)₃)⁺complex formation decrease with increased ionic strength. These values have been fitted with the extended Debye-Huckel expression to obtain the value of logb₁=6.34±0.03 at I=0.00M. The data allowed the calculation of speciation of the Ni²⁺- silicate system as a function of ionic strength.     

A modified stochastic model for closed birth interval

"Based on some simple assumptions regarding [the] human reproduction process, a continuous time stochastic model for describing the variation in any closed birth interval of a woman of marital duration (t) has been developed. The model incorporates the possibility of the variation of the amenorrhea period among the women under observation. For illustration, the model is applied to an observed closed birth interval between first and second births of the women with marital duration of seven years."     

Silicate complexation of NpO<Subscript>2</Subscript><Superscript>+</Superscript> ion in perchlorate media

Complexation behavior of NpO₂ ⁺ with ortho-silicic acid (o-SA) has been studied using solvent extraction at ionic strengths varying from 0.10 to 1.00M (NaClO₄) at pcH 3.68±0.08 and 25 °C with bis-(2-ethylhexyl) phosphoric acid (HDEHP) as the extractant. The stability constant value (log β₁) for the 1:1 complex, NpO₂(OSi(OH)₃), was found to decrease with increase in ionic strength of the aqueous phase [6.83±0.01 at I=0.10M to 6.51±0.02 at I = 1.00M]. These values have been fitted in the SIT model expression and compared with similar values of complexation of the metal ions Am³⁺, Eu³⁺, UO₂ ²⁺, PuO₂ ²⁺, Np⁴⁺, Ni²⁺ and Co²⁺. The speciation of NpO₂ ⁺-o-silicate/carbonate system has been calculated as a function of pcH under ground water conditions. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Synthesis of some new fluorine-containing 5-amino-1,3-disubstituted pyrazoles and 1H-pyrazolo[3,4-b]pyridines

Nine new fluorine containing 5-amino-1,3-disubstituted pyrazoles have been synthesized and characterized by spectral studies. Condensation reactions of these 5-amino-1,3-disubstituted pyrazoles with fluorinated 1,3-diketones in the presence of glacial acetic acid have been studied and the structures of the resulting 1H-pyrazolo[3,4-b]pyridines have been confirmed by ir, pmr and ¹⁹F nmr spectral studies.     

Sorption of neptunyl(V) cations on suspended silicate: Effects of pH, ionic strength, complexing anions, humic acid, and metal ions

Sorption of NpO₂ ⁺ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase in ionic strength from 0.20M to 1.00M (NaClO₄), increased the NpO₂ ⁺ sorption, which then decreased at 1.50M (NaClO₄) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO₂ ⁺ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate (ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO₂ ⁺/silicate/ligand complexes. The effects of Ca(II) (1.00·10⁻³M) and Eu(III) (1.00·10⁻⁴ and 1.00·10⁻³M) ions on NpO₂ ⁺ sorption to suspended silicate were also investigated. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Continuation of functionals on ultradifferentiable function spaces

, c _k b _k . . . .

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This work is supported by N.B.H.M. grant No. 48/1/94-R&D-II.     

Towards a biosynthetic infochemical communication system

By exploiting recent advances in the understanding of both pheromone biosynthesis pathways and the detection of molecules in the insect nervous system, we are developing a new class of technology for biosynthetic infochemical communication. Here we present a prototype instrument that comprises an integrated chemotransmitter, an odour pathway and a chemoreceiver controlled by a laptop computer. Our initial studies show that the system can transmit, receive and decode a set of volatiles commonly found in fruits. The system is capable of ratiometrically encoding information by releasing complex blends of compounds in specific ratios, detecting the transmitted blends with a sensor array and decoding the infochemical information using neuromorphic algorithms representing ratio processing in the macroglomerular complex (MGC) of the antennal lobe of the moth (e.g. Manduca sexta).     

Compatible mappings of type (B) and common fixed point theorems in Saks spaces

In this paper we first introduce the concept of compatible mappings of type (B) and compare these mappings with compatible mappings and compatible mappings of type (A) in Saks spaces. In the sequel, we derive some relations between these mappings. Secondly, we prove a coincidence point theorem and common fixed point theorem for compatible mappings of type (B) in Saks spaces.     

Effect of Cd1−xZnxS/ZnS core/shell quantum dot on the optical response and relaxation behaviour of ferroelectric liquid crystal

Dielectrics, polarizing optical microscopic and electro-optical measurements have been carried out on a core/shell quantum dot Cd_1?xZn_xS/ZnS dispersed ferroelectric liquid crystal (FLC). In the present study, quantum dots were dispersed into two different concentrations of 0.1 and 0.25 wt./wt.% in pure FLC. The electro-optical parameters of pure and QDs dispersed FLC were carried out as a function of applied voltage. A significant improvement in optical response time of QDs dispersed FLC system is one of the major finding of the present study which may be useful for fabrication of faster liquid crystal system.