Electrochemical Determination of the Stability of Mono- and Dicalcium Stannates

he thermodynamic properties of mono- and dicalcium stannates have been determined in the temperature range 973–-1423°K from the electromotive force measurements on solid oxide galvanic cells[dformula Pt, Ni + NiO//CaO - ZrO[sub 2]/Y[sub 2]0[sub 3] - ThO[sub 2]//SnO[sub 2] + Sn, W, Pt][dformula Pt, Ni + NiO//CaO - ZrO[sub 2]/Y[sub 2]O[sub 3] - ThO[sub 2]//CaSnO[sub 3] + SnO[sub 2] + Sn, W, Pt][dformula Pt, Ni + NiO//CaO - ZrO[sub 2]/Y[sub 2]O[sub 3] - ThO[sub 2]/Ca[sub 2]SnO[sub 4] + CaSnO[sub 3] + Sn, W, Pt]and [dformula Pt, Ni + NiO//CaO - ZrO[sub 2]sol;Y[sub 2]O[sub 3] - ThO[sub 2]//Ca[sub 2]SnO[sub 4] + CaO, W, Pt] The Gibbs free energy changes accompanying the formation of the stannates from component oxides may be represented by the equations[dformula 2CaO + SnO[sub 2] --> Ca[sub 2]SnO[sub 4]][dformula Delta G[degree] = - 17,040 + 0.85T ([plus-minus]300) cal][dformula CaO + SnO[sub 2] --> CaSnO[sub 3]][dformula Delta G[degree] = - 17,390 + 2.0T ([plus-minus]300) cal]The partial pressures of the tin bearing oxide species resulting from the decomposition of the stannates have been calculated as a function of the oxygen partial pressure by combining the results of this study with published information on the partial pressures and composition of oxide species over stannic oxide.

Potentiometric determination of the Gibbs free energy of formation of cadmium and magnesium chromites

The standard Gibbs free energy of formation of magnesium and cadmiumchromites have been determined by potentiometric measurements on reversiblesolid-state electrochemical cells [dformula (Au-5%Cd, , Au-5%Cd; Pt, + , CaO-ZrO[sub 2], + ,Pt; CdO, , CdCr[sub 2]O[sub 4] + Cr[sub 2]O[sub 3])] in the temperature range 500°–730°C, and [dformula Pt, Cr + Cr[sub 2]O[sub 3]/Y[sub 2]O[sub 3]-ThO[sub 2]/Cr + MgCr[sub 2]O[sub 4] + MgO, Pt] in the temperature range 800°–1200°C. The temperature dependence of the freeenergies of formation of the ternary compounds can be represented by theequations [dformula CdO(r.s.) + Cr[sub 2]O[sub 3](cor) --> CdCr[sub 2]O[sub 4](sp)] [dformula Delta G[sup 0] = - 42,260 + 7.53T ([plus-minus]400) J] and [dformula MgO(r.s.) + Cr[sub 2]O[sub 3](cor) --> MgCr[sub 2]O[sub 4](sp)] [dformula Delta G[sup 0] = - 45,200 + 5.36T ([plus-minus]400) J] The entropies of formation of these spinels are discussed in terms of cationdisorder and extent of reduction of Cr3+ ions to Cr2+ ions. Thermodynamicdata on the chromates of cadmium and magnesium are derived by combiningthe results obtained in this study with information available in the literatureon high temperature, high pressure phase equilibria in the systems CdO-Cr2O3-O2 and MgO-Cr2O3-O2.

Electrochemical determination of activities in Cr2O3 Al2O3 solid solutions

The activity of Cr20~ in Cr20~-A12Oa solid solution has been determined in the temperature range 800~176 from electromotive force measurements on the solid oxide galvanic cell Pt,Cr + Cr2OJY~O~-ThO2/Cr + Cr~A12-xO~,Pt The activities of Cr203 and A120~ in the solid solution show both positive and negative deviations from Raoult's law. The heat and entropy of mixing of the solid Solution obtained from the temperature dependence of the emf can be expressed as AH = XCr203XA1203 [31,700Xcrzo3 -}- 37,470XA1203] J mole -I hS = -- 1.8R [Xcr2o3 In Xcr2o3 + XA12o3 In XAaos]The entropy of mixing is 10% lower than that predicted by the Temkin model.The large positive heat of mixing in the Cr2Os-A12Oa solid solution, however, suggests that this apparent: entropy discrepancy originates with the clustering of positive ions on the cation sublattice. The asymmetric miscibility gap exhibited in the CrzOa-A12Oa system below 900~ is consistent with the thermodynamic data trends recorded at the more elevated temperatures.

Allosteric Communication in Cysteinyl tRNA Synthetase A NETWORK OF DIRECT AND INDIRECT READOUT

Protein structure networks are constructed for the identification of long-range signaling pathways in cysteinyl tRNA synthetase (CysRS). Molecular dynamics simulation trajectory of CysRS-ligand complexes were used to determine conformational ensembles in order to gain insight into the allosteric signaling paths. Communication paths between the anticodon binding region and the aminoacylation region have been identified. Extensive interaction between the helix bundle domain and the anticodon binding domain, resulting in structural rigidity in the presence of tRNA, has been detected. Based on the predicted model, six residues along the communication paths have been examined by mutations (single and double) and shown to mediate a coordinated coupling between anticodon recognition and activation of amino acid at the active site. This study on CysRS clearly shows that specific key residues, which are involved in communication between distal sites in allosteric proteins but may be elusive in direct structure analysis, can be identified from dynamics of protein structure networks.

Potentiometric determination of the Gibbs energies of formation of lead aluminates

The Gibbs energies of formation of three compounds in the PbO-Al2O3 system—2PbO · Al2O3, PbO · Al2O3, andPbO· 6Al2O3—have been determined from potentiometric measurements on reversible solid-state galvanic cells [dformula Pt, Ir | Pb, alpha-Al[sub 2]O[sub 3], PbO [center-dot] 6Al[sub 2]O[sub 3] | ZrO[sub 2]-CaO | NiO, Ni | Pt] [dformula Pt | NiO, Ni | ZrO[sub 2]-CaO | Pb, PbO [center-dot] 6Al[sub 2]O[sub 3], PbO [center-dot] Al[sub 2]O[sub 3] | Ir, Pt] and [dformula Pt | NiO, Ni | ZrO[sub 2]-CaO | Pb, PbO [center-dot] Al[sub 2]O[sub 3], 2PbO [center-dot] Al[sub 2]O[sub 3] | Ir, Pt] in the temperature range 850–1375 K. The results are discussed in the light of reported phase diagrams for the PbO-Al2O3system. The partial pressures of different lead oxide species, PbnOn, n = 1–6, in the gas phase in equilibrium withthe aluminates are calculated by combining the results of this study with the mass-spectrometric data of Drowart et al.(1) for polymerization equilibria in the gas phase. The concentration of oxygen in lead in equilibrium with the aluminatesare also derived from the results and the literature data on the Gibbs energy of solution of oxygen in liquid lead.

Detection and determination of manganese concentration in water using a fiber Bragg grating coupled with nanotechnology

Through this paper we experimentally demonstrate the fabrication of a fiber Bragg grating (FBG) chemical sensor to detect and determine the manganese concentration in water and compare our results with sophisticated spectroscopic methods, such as atomic absorption spectrometry and the inductively coupled plasma method. Here we propose a simple method to develop a thin layer of gold nanoparticles above the etched grating region to enhance the sensitivity of the reflected spectrum of the FBG. By doing so, we achieve a sensitivity of 1.26 nm/parts per million in determining the trace level of Mn in water. Proper reagents are used to detect manganese in water. (C) 2011 Optical Society of America

Potentiometric determination of the stability of BaCu2O2

The thermodynamic stability of the compound BaCu2O2 was determined using a solid-state galvanic cell: View the MathML source as a function of temperature in the range 970–1170 K. Single crystal BaF2 was used as the solid electrolyte. The partial pressure of oxygen in the argon gas flowing over the electrodes was 1.27 Pa. The reversible e.m.f. of the cell can be expressed by View the MathML source. The Gibbs free energy of formation of barium cuprite from component oxides according to the reaction View the MathML source is View the MathML source.

Electrochemical determination of the Gibbs energy of formation of MgAl2O4

The standard Gibbs energy of formation of the spinel MgAl2O4 from component oxides, MgO and α-Al2O3, has been determined in the temperature range 900 to 1250 K using a solid-state cell incorporating single-crystal CaF2 as the solid electrolyte. The cell can be represented as—Pt,O2,MgO+MgF2|CaF2|MgF2+MgAl2O4+α-Al2O3,O2,Pt—The standard Gibbs energy of formation from binary oxides, computed from the reversible emf, can be represented by the expression—capdeltaG°f,ox=−23600 − 5.91T(±150) J/mol—The ‘second-law’ enthalpy of formation of MgAl2O4 obtained in this study is in good agreement with high-temperature solution calorimetric studies reported in the literature.

Determination of surge-diverter voltage/current characteristic

A mathematical model has been proposed to determine the voltage/current characteristic of the surge diverter for a wide range of currents of short duration of 8/20 and 4/10ÿs waveshapes. Experimental data agree well with the proposed model.

Determination of the follow current in surge diverters

Using a suitable mathematical model, computations of power/follow current in surge diverters (lightning arresters) have been made from the known short-circuit capacity of the power-frequency source and the nonlinear resistor characteristics. Also the effect of the initiation angle is studied. Typical verifications with the available data have been carried out. The influence of arc drop in the surge-diverter spark gap is neglected.

A tropical oviparous lizard, Calotes versicolor, exhibiting a potentially novel FMFM pattern of temperature-dependent sex determination

Among squamate reptiles, lizards exhibit an impressive array of sex-determining modes viz. genotypic sex determination, temperature-dependent sex determination, co-occurrence of both these and those that reproduce parthenogenetically. The oviparous lizard, Calotes versicolor, lacks heteromorphic sex chromosomes and there are no reports on homomorphic chromosomes. Earlier studies on this species presented little evidence to the sex-determining mechanism. Here we provide evidences for the potential role played by incubation temperature that has a significant effect (P<0.01) on gonadal sex and sex ratio. The eggs were incubated at 14 different incubation temperatures. Interestingly, 100% males were produced at low (25.5 +/- 0.5 degrees C) as well as high (34 +/- 0.5 degrees C) incubation temperatures and 100% females were produced at low (23.5 +/- 0.5 degrees C) and high (31.5 +/- 0.5 degrees C) temperatures, clearly indicating the occurrence of TSD in this species. Sex ratios of individual clutches did not vary at any of the critical male-producing or female-producing temperatures within as well as across the seasons. However, clutch sex ratios were female- or male-biased at intermediate temperatures. Thermosensitive period occurred during the embryonic stages 3033. Three pivotal temperatures operate producing 1:1 sex ratio. Histology of gonad and accessory reproductive structures provide additional evidence for TSD. The sex-determining pattern, observed for the first time in this species, that neither compares to Pattern I [Ia (MF) and Ib (FM)] nor to Pattern II (FMF), is being referred to as FMFM pattern of TSD. This novel FMFM pattern of sex ratio exhibited by C. versicolor may have an adaptive significance in maintaining sex ratio. J. Exp. Zool. 317:3246, 2012. (c) 2011 Wiley Periodicals, Inc.

Fast Direct Torque Control of an Open-End Induction Motor Drive Using 12-Sided Polygonal Voltage Space Vectors

A torque control scheme, based on a direct torque control (DTC) algorithm using a 12-sided polygonal voltage space vector, is proposed for a variable speed control of an open-end induction motor drive. The conventional DTC scheme uses a stator flux vector for the sector identification and then the switching vector to control stator flux and torque. However, the proposed DTC scheme selects switching vectors based on the sector information of the estimated fundamental stator voltage vector and its relative position with respect to the stator flux vector. The fundamental stator voltage estimation is based on the steady-state model of IM and the synchronous frequency of operation is derived from the computed stator flux using a low-pass filter technique. The proposed DTC scheme utilizes the exact positions of the fundamental stator voltage vector and stator flux vector to select the optimal switching vector for fast control of torque with small variation of stator flux within the hysteresis band. The present DTC scheme allows full load torque control with fast transient response to very low speeds of operation, with reduced switching frequency variation. Extensive experimental results are presented to show the fast torque control for speed of operation from zero to rated.

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH(4)) and ammonia borane (NH(3)BH(3)) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH(4) as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm(-2) at a load current density of 83 mA cm(-2) is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm(-2) at 105 mA cm(-2) is obtained in the case of AB-based fuel cell at 353 K. (C) 2011 Elsevier Ltd. All rights reserved.