Determination of the Gibbs energy of diamond using a solid state cell

he chemical potential of carbon in diamond, relative to its value in graphite, has been directly determined using a solid state electrochemical cell incorporating single crystal CaF2 as the solid electrolyte. The cell can be represented as Pt, C(graphite) + CaC2 + CaF2double vertical barCaF2double vertical barCaF2 + CaC2 + C(diamond), Pt The reversible emf of this cell is directly related by the Nernst equation to the Gibbs free energy change for the conversion of diamond to graphite. The difference in the chemical potential of carbon in the two crystal structures varies linearly with temperature in the range 940 to 1260 K ?C(diamond) ? ?C(graphite) = 1100 + 4.64T (±50) J mol?1 On the average, the values given by the equation are 320 J mol?1 less positive than the currently accepted ones based on calorimetric studies. The difference is primarily in the enthalpy term.

Room temperature giant magnetoresistance in La1-xPbxMnO3

Oxides of the La1-xPbxMnO3 system show giant magnetoresistance around 300 K. In La1-xPbxMnO3 the magnitude of the magnetoresistance (MR) at 320 K is 85% at 6 T and it is nearly temperature independent over a temperature range 40-320 K. All the compositions (0.1 less than or equal to x less than or equal to 0.5) show a peak in resistivity around 300-340 K and the magnitude of the MR also shows a peak around the same temperatures. This investigation suggests how to hole dope LaMnO3 in order to achieve maximum MR around 300 K so that these materials can have practical applications.

Coordination driven self-assembly of metallamacrocycles using ambidentate linkers and self-selection of single linkage isomer

Nicotinate-N-oxide and isonicotinate-N-oxide have been employed to synthesize four heterometallic metallamacrocycles (dppf)(2)Pd-2(nicotinate-N-oxide)(2)](OTf)(2) (1), (dppf)(2)Pt-2(nicotinate-N-oxide)(2)](OTf)(2) (2), (dppf) 2Pd2(isonicotinate-N-oxide)(2)](OTf)(2) (3) and (dppf)(2)Pt-2(isonicotinate-N-oxide)(2)](OTf)(2) (4). The complexes represent the first examples of metallamacrocycles driven by solely Pd(II)/Pt(II)-O coordination using carboxylate-N-oxide donor. All the complexes 1-4 are characterized by IR, UV-Vis, multinuclear NMR spectroscopic and ESI-MS studies. The molecular structures of the complexes 1 and 3 are unambiguously determined by single crystal X-ray diffraction analysis. Despite the possibility of formation of several linkage isomers due to ambidentate nature of the donors, exclusive formation of 2 + 2] self-assembled single isomeric metallamacrocycle in each case is interesting observation. (C) 2011 Elsevier B.V. All rights reserved.

Solution of a hypersingular integral equation of the second kind

A straightforward analysis involving the complex function-theoretic method is employed to determine the closed-form solution of a special hypersingular integral equation of the second kind, and its known solution is recovered.

Mean-field theory of charge ordering and phase transitions in the colossal-magnetoresistive manganites

We study phase transitions in the colossal-magnetoresistive manganites by using a mean-field theory both at zero and non-zero temperatures. Our Hamiltonian includes double-exchange, superexchange, and Hubbard terms with on-site and nearest-neighbour Coulomb interaction, with the parameters estimated from earlier density-functional calculations. The phase diagrams show magnetic and charge-ordered (or charge-disordered) phases as a result of the competition between the double-exchange, superexchange, and Hubbard terms, the relative effects of which are sensitively dependent on parameters such as doping, bandwidth, and temperature. In accord with the experimental observations, several important features are reproduced from our model, namely, (i) a phase transition from an insulating, charge-ordered antiferromagnetic to a metallic, charge-disordered ferromagnetic state near dopant concentration x = 1/2, (ii) the reduction of the transition temperature TAF-->F by the application of a magnetic field, (iii) melting of the charge order by a magnetic field, and (iv) phase coexistence for certain values of temperature and doping. An important feature, not reproduced in our model, is the antiferromagnetism in the electron-doped systems, e.g., La1-xCaxMnO3 over the entire range of 0.5 less than or equal to x less than or equal to 1, and we suggest that a multi-band model which includes the unoccupied t(2g) orbitals might be an important ingredient for describing this feature.

Mossbauer study of La1-xCaxMn1-y (57)FeyO(3) with x = 0, 0.25; y=0.01

Temperature dependent Mossbauer measurements are done on the samples of La1- xCaxMn1-y (FeyO3)-Fe-57 with x=0 and 0.25, and y=0.01. With decreasing temperature, the specimen with x=0.25 shows a paramagnetic to ferromagnetic transition around 175 K. In the specimen x=0.0, the temperature dependence of both the center shift (delta) and the recoilless fraction (f) can be fitted very well with the Debye theory with a theta(D)=320+/-50 K. But for the specimens with x=0.25, f and delta show distinct deviations from the Debye behavior in the temperature range in which the resistivity shows a sharp decrease. Dips observed in both the f and delta around the transition temperature suggest that the Jahn-Teller distortion observed in these systems is dynamic in nature.

Synthesis of acicular hydrogoethite (alpha-FeOOH center dot xH(2)O; 0.1 < x < 0.22) particles using morphology controlling cationic additives and magnetic properties of maghemite derived from hydrogoethite

A method for the preparation of acicular hydrogoethite (alpha -FeOOH.xH(2)O, 0.1 < x < 0.22) particles of 0.3-1 mm length has been optimized by air oxidation of Fe( II) hydroxide gel precipitated from aqueous (NH4)(2)Fe(SO4)(2) solutions containing 0.005-0.02 atom% of cationic Pt, Pd or Rh additives as morphology controlling agents. Hydrogoethite particles are evolved from the amorphous ferrous hydroxide gel by heterogeneous nucleation and growth. Preferential adsorption of additives on certain crystallographic planes thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shapes with high aspect ratios of 8-15. Synthetic hydrogoethite showed a mass loss of about 14% at similar to 280 degreesC, revealing the presence of strongly coordinated water of hydration in the interior of the goethite crystallites. As evident from IR spectra, excess H2O molecules (0.1- 0.22 per formula unit) are located in the strands of channels formed in between the double ribbons of FeO6 octahedra running parallel to the c- axis. Hydrogoethite particles constituted of multicrystallites are formed with Pt as additive, whereas single crystallite particles are obtained with Pd (or Rh). For both dehydroxylation as well as H-2 reduction, a lower reaction temperature (similar to 220 degreesC) was observed for the former (Pt treated) compared to the latter (Pd or Rh) (similar to 260 degreesC). Acicular magnetite (Fe3O4) was prepared either by reducing hydrogoethite (magnetite route) or dehydroxylating hydrogoethite to hematite and then reducing it to magnetite (hematite- magnetite route). According to TEM studies, preferential dehydroxylation of hydrogoethite along < 010 > leads to microporous hematite. Maghemite (gamma -Fe2O3 (-) (delta), 0 < < 0.25) was obtained by reoxidation of magnetite. The micropores are retained during the topotactic transformation to magnetite and finally to maghemite, whereas cylindrical mesopores are formed due to rearrangement of the oxygen sublattice from hexagonal to cubic close packing during the conversion of hydrogoethite to magnetite and then to maghemite. Accordingly, three different types of maghemite particles are realized: strongly oriented multicrystalline particles, single crystalline acicular particles with micropores or crystallites having mesopores. Higher values of saturation magnetization ((s) = 74 emu g(-1)) and coercivity (H-c = 320 Oe) are obtained for single crystalline mesoporous particles. In the other cases, the smaller size of particles and larger distribution of micropores decreases sigma (s) considerably ( < 60 emu g(-1)) due to relaxation effects of spins on the surface atoms as revealed by Mossbauer spectroscopy.

Through ring umbrella inversion of a molecular rattle

We report theoretical investigations on some [Ring]Li--(+) compounds, which can exhibit a through ring umbrella like inversion. Our studies predict cyclononatetraenyllithium to be molecular rattle, in which such inversions can occur. The potential energy for the motion is a double well, with an activation barrier of 11.50 kcal/mol. We find that the lithium should go through the ring easily by an excitation to nu = 17 vibrational level. (C) 2002 Elsevier Science B.V. All rights reserved.

Variable temperature x-ray crystal structure analysis of a type I langbeinite: Rb2Cd2(SO4)(3)

The structure of a type I langbeinite, Rb2Cd2(SO4)(3), displays three different phases, cubic with a = 10.378(5) Angstrom (space group P2(1)3) at room temperature, monoclinic at 120 K with a = 10.328(3), b = 10.322(3), c = 10.325(3) Angstrom, beta = 89.975(1)degrees (space group P2(1)), and orthorhombic at 85 K with a = 10.319(2), b = 10.321(2), c = 10.320(2) Angstrom (space group P2(1)2(1)2(1)), respectively. Precise single-crystal analyses of these phases indicate that Rb2Cd2(SO4)(3) distorts initially from cubic to monoclinic upon cooling followed by a significant reorientation of the SO4 tetrahedra, resulting in an orthorhombic symmetry upon further cooling. The three structures have been established unequivocally using the same crystal. There is no indication of the formation of an intermediate triclinic phase or any lattice disorder as conjectured in several earlier reports on compounds belonging to the type I langbeinite. The bond valence sum analyses of the coordination around the Rb sites indicate asymmetry in the bond strengths which could be the driving force of the ferroelectric behavior in these materials.

Identification of a core promoter and a novel isoform of the human TSCI gene transcript and structural comparison with mouse homolog

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder with loci on chromosome 9q34.12 (TSC1) and chromosome 16p13.3 (TSC2). Genes for both loci have been isolated and characterized. The promoters of both genes have not been characterized so far and little is known about the regulation of these genes. This study reports the characterization of the human TSC1 promoter region for the first time. We have identified a novel alternative isoform in the 5' untranslated region (UTR) of the TSC1 gene transcript involving exon 1. Alternative isoforms in the 5' UTR of the mouse Tsc1 gene transcript involving exon I and exon 2 have also been identified. We have identified three upstream open reading frames (uORFs) in the 5' UTR of the TSC1/Tsc1 gene. A comparative study of the 5' UTR of TSC1/Tsc1 gene has revealed that there is a high degree of similarity not only in the sequence but also in the splicing pattern of both human and mouse TSC1 genes. We have used PCR methodology to isolate approximately 1.6 kb genomic DNA 5' to the TSC1 cDNA. This sequence has directed a high level of expression of luciferase activity in both HeLa and HepG2 cells. Successive 5' and 3' deletion analysis has suggested that a -587 bp region, from position +77 to -510 from the transcription start site (TSS), contains the promoter activity. Interestingly, this region contains no consensus TATA box or CAAT box. However, a 521-bp fragment surrounding the TSS exhibits the characteristics of a CpG island which overlaps with the promoter region. The identification of the TSC1 promoter region will help in designing a suitable strategy to identify mutations in this region in patients who do not show any mutations in the coding regions. It will also help to study the regulation of the TSC1 gene and its role in tumorigenesis. (C) 2003 Elsevier B.V. All rights reserved.

Groundwater Management in India:Physical, Institutional and Policy Alternatives

Groundwater constitutes a vital natural resource for sustaining India’s agricultural economy and meeting the country’s social, ecological and environmental goals. It is a unique resource, widely available, providing security against droughts and yet it is closely linked to surface-water resources and the hydrological cycle. Its availability depends on geo-hydrological conditions and characteristics of aquifers, from deep to alluvium, sediment crystalline rocks to basalt formations; and agro-climate from humid to subhumid and semi-arid to arid. Its reliable supply, uniform quality and temperature, relative turbidity, pollution-safe, minimal evaporation losses, and low cost of development are attributes making groundwater more attractive compared to other resources. It plays a key role in the provision of safe drinking water to rural populations. For example, already almost 80% of domestic water use in rural areas in India is groundwater-supplied, and much of it is being supplied to farms, villages and small towns. Inadequate control of the use of groundwater, indiscriminate application of agrochemicals and unrestrained pollution of the rural environment by other human activities make groundwater usage unsustainable, necessitating proper management in the face of the twin demand for water of good quality for domestic supply and adequate supply for irrigation, ensuring equity, efficiency and sustainability of the resource. Groundwater irrigation has overtaken surface irrigation in the early 1980s, supported by well energization. It is estimated that there are about 24 million energised wells and tube wells now and it is driven by demand rather than availability, evident through the greater occurrence of wells in districts with high population densities. Apart from aquifer characteristics, land fragmentation and landholding size are the factors that decide the density of wells. The ‘rise and fall’ of local economies dependent on groundwater can be summarized as: the green revolution of 1980s, groundwaterbased agrarian boom, early symptoms of groundwater overdraft, and decline of the groundwater socio-ecology. The social characteristics and policy interventions typical of each stage provide a fascinating insight into the human-resource dynamics. This book is a compilation of nine research papers discussing various aspects of groundwater management. It attempts to integrate knowledge about the physical system, the socio-economic system, the institutional set-up and the policy environment to come out with a more realistic analysis of the situation with regard to the nature, characteristics and intensity of resource use, the size of the economy the use generates, and the negative socioeconomic consequences. Complex variables addressed in this regard focusing on northern Gujarat are the stock of groundwater available in the region, its hydrodynamics, its net outflows against inflows, the economics of its intensive use (particularly irrigation in semi-arid and arid regions), its criticality in the regional hydroecological regime, ethical aspects and social aspects of its use. The first chapter by Dinesh Kumar and Singh, dwells on complex groundwater socio-ecology of India, while emphasizing the need for policy measures to address indiscriminate over-exploitation of dwindling resources. The chapter also explores the nature of groundwater economy and the role of electricity prices on it. The next chapter on groundwater issue in north Gujarat provides a description of groundwater resource characteristics followed by a detailed analysis of the groundwater depletion and quality deterioration problems in the region and their undesirable consequences on the economy, ecosystem health and the society. Considering water-buyers and wellowning farmers individually, a methodology for economic valuation of groundwater in regions where its primary usage is in agriculture, and as assessment of the groundwater economy based on case studies from north Gujarat is presented in the fourth chapter. The next chapter focuses on the extent of dependency of milk production on groundwater, which includes the water embedded in green and dry fodder and animal feed. The study made a realistic estimate of irrigation water productivity in terms of the physics and economics of milk production. The sixth chapter analyses the extent of reduction in water usage, increase in yield and overall increase in physical productivity of alfalfa with the use of the drip irrigation system. The chapter also provides a detailed synthesis of the costs and benefits associated with the use of drip irrigation systems. A linear programmingbased optimization model with the objective to minimize groundwater use taking into account the interaction between two distinct components – farming and dairying under the constraints of food security and income stability for different scenarios, including shift in cropping pattern, introduction of water-efficient crops, water- saving technologies in addition to the ‘business as usual’ scenario is presented in the seventh chapter. The results show that sustaining dairy production in the region with reduced groundwater draft requires crop shifts and adoption of water-saving technologies. The eighth chapter provides evidences to prove that the presence of adequate economic incentive would encourage farmers to adopt water-saving irrigation devices, based on the findings of market research with reference to the level of awareness among farmers of technologies and the factors that decide the adoption of water-saving technologies. However, now the marginal cost of using electricity for agricultural pumping is almost zero. The economic incentives are strong and visible only when the farmers are either water-buyers or have to manage irrigation with limited water from tube-well partnerships. The ninth chapter explores the socio-economic viability of increasing the power tariff and inducing groundwater rationing as a tool for managing energy and groundwater demand, considering the current estimate of the country’s annual economic loss of Rs 320 billion towards electricity subsidy in the farm sector. The tenth chapter suggests private tradable property rights and development of water markets as the institutional tool for achieving equity, efficiency and sustainability of groundwater use. It identifies the externalities for local groundwater management and emphasizes the need for managing groundwater by local user groups, supported by a thorough analysis of groundwater socio-ecology in India. An institutional framework for managing the resource based on participatory approach that is capable of internalizing the externalities, comprising implementation of institutional and technical alternatives for resource management is also presented. Major findings of the analyses and key arguments in each chapter are summarized in the concluding chapter. Case studies of the social and economic benefits of groundwater use, where that use could be described as unsustainable, are interesting. The benefits of groundwater use are outlined and described with examples of social and economic impacts of groundwater and the negative aspects of groundwater development with the compilation of environmental problems based on up-to-date research results. This publication with a well-edited compilation of case studies is informative and constitutes a useful publication for students and professionals.

Heat of Mixing and Activities in Liquid Al-Sn Alloys

The microscopic electron theory based on the pseudopotential formalism has been applied to the calculation of the heats of mixing and of activities in liquid Al·Sn alloys. The calculated values for both quantities were found to be in reasonable agreement with ,the experimental data.

Three phase equilibria for activity determinations: system Co Mn

A solid state e.m.f. cell with yttria-doped thoria as the electrolyte and a mixture of Cr + Cr sub 2 O sub 3 as the reference electrode, was employed for the measurement of the activity of manganese in the Co--Mn system at 1760 deg K, for 0.3 > X sub Mn > 0.05. The liquid alloy was contained in an alumina crucible and saturated with MnAl sub 2+2x O sub 4+3x . The cell can be represented by Pt, W, (Co--Mn) + MnAl sub 2+2x O sub 4+3x + Al sub 2 O sub 3 /ThO sub 2 --Y sub 2 O sub 3 /Cr + Cr sub 2 O sub 3 , Pt. The activity of manganese shows negative deviations from Raoult's law. The activities in the Co--Mn system are intermediate between those in the Fe--Mn and Ni--Mn systems. The Gibbs' energies of mixing in these systems follow the trends given by Miedema's model. 14 ref.--AA.

Alloy/Oxide Equilibria in Iron--Vanadium--Oxygen and Iron--Niobium--Oxygen Systems

An experimental characterization of three-phase equilibria in Fe--V--O and Fe--Nb--O systems at 1823, 1873 and 1923K has been carried out using a solid state cell and by analysis of quenched samples. The oxygen potentials corresponding to these three-phase equilibria were monitored by a solid state cell incorporating Y sub 2 O sub 3 doped ThO sub 2 with Cr + Cr sub 2 O sub 3 as reference electrode. Similar measurements were carried out for Fe--Nb--O alloys in equilibrium with a mixture of FeNb sub 2 O sub 6 and NbO sub 2 . These measurements permit evaluation of interaction parameters (e exp V sub O = --6590/T + 2.892 and e exp Nb sub O = --4066/T + 1.502) and activity coefficients of vanadiun and niobium in dilute solution (ln gamma exp O sub V = --35 320/T + 12.68 and ln gamma sub Nb exp O = --12 386/T + 4.34) in liquid iron. The results obtained in this study resolve a number of discrepancies in thermodynamic data reported in the literature, especially regarding the activity coefficients of V and Nb and the stability ranges for V sub 2 O sub 3 and VO sub 1+x . 18 ref.--AA

An advanced design of the solid-state cell for accurate thermodynamic measurements on ternary oxides: system Sm–Pd–O

An advanced design of the solid-state cell incorporating a buffer electrode has been developed for high temperature thermodynamic measurements. The function of the buffer electrode, placed between reference and working electrodes, was to absorb the electrochemical flux of the mobile species through the solid electrolyte caused by trace electronic conductivity. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The application of the novel design and its advantages have been demonstrated by measuring the standard Gibbs energies of formation of ternary oxides of the system Sm–Pd–O. Yttria-stabilized zirconia was used as the solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the design of appropriate working electrodes, phase relations in the ternary system Sm–Pd–O were investigated at 1273 K. The two ternary oxides, Sm4PdO7 and Sm2Pd2O5, compositions of which fall on the Sm2O3–PdO join, were found to coexist with pure metal Pd. The thermodynamic properties of the ternary oxides were measured using three-phase electrodes in the temperature range 950–1425 K. During electrochemical measurements a third ternary oxide, Sm2PdO4, was found to be stable at low temperature. The standard Gibbs energies of formation (Δf(ox)Go) of the compounds from their component binary oxides Sm2O3 and PdO, can be represented by the equations: Sm4PdO7: Δf(ox)Go (J mol−1)=−34,220+0.84T(K) (±280); Sm2PdO4: Δf(ox)Go (J mol−1)=−33,350+2.49T(K) (±230); Sm2Pd2O5: Δf(ox)Go (J mol−1)=−59,955+1.80T(K) (±320). Based on the thermodynamic information, three-dimensional P–T–C and chemical potential diagrams for the system Sm–Pd–O were developed.