Spin State Selective Excitation of Single Quantum Transitions Using Multiple Quantum Spectroscopy- an Aid to Analyse Complex Proton NMR spectra of Oriented Molecules

NMR spectra of molecules oriented in liquid-crystalline matrix provide information on the structure and orientation of the molecules. Thermotropic liquid crystals used as an orienting media result in the spectra of spins that are generally strongly coupled. The number of allowed transitions increases rapidly with the increase in the number of interacting spins. Furthermore, the number of single quantum transitions required for analysis is highly redundant. In the present study, we have demonstrated that it is possible to separate the subspectra of a homonuclear dipolar coupled spin system on the basis of the spin states of the coupled heteronuclei by multiple quantum (MQ)−single quantum (SQ) correlation experiments. This significantly reduces the number of redundant transitions, thereby simplifying the analysis of the complex spectrum. The methodology has been demonstrated on the doubly 13C labeled acetonitrile aligned in the liquid-crystal matrix and has been applied to analyze the complex spectrum of an oriented six spin system.

Effective thermal conductivity of a heat generating rod bundle dissipating heat by natural convection and radiation

A numerical study of conjugate natural convection and surface radiation in a horizontal hexagonal sheath housing 19 solid heat generating rods with cladding and argon as the fill gas, is performed. The natural convection in the sheath is driven by the volumetric heat generation in the solid rods. The problem is solved using the FLUENT CFD code. A correlation is obtained to predict the maximum temperature in the rod bundle for different pitch-to-diameter ratios and heat generating rates. The effective thermal conductivity is related to the heat generation rate, maximum temperature and the sheath temperature. Results are presented for the dimensionless maximum temperature, Rayleigh number and the contribution of radiation with changing emissivity, total wattage and the pitch-to-diameter ratio. In the simulation of a larger system that contains a rod bundle, the effective thermal conductivity facilitates simplified modelling of the rod bundle by treating it as a solid of effective thermal conductivity. The parametric studies revealed that the contribution of radiation can be 38-65% of the total heat generation, for the parameter ranges chosen. Data for critical Rayleigh number above which natural convection comes into effect is also presented. (C) 2011 Elsevier B.V. All rights reserved.

Crystal Structure, Thermal Expansion and ElectricaH Conductivity of Yo.sCao.2Fel-x Mnx03+o (0 < x < 1.0)

The crystal structure, thennal expansion and electrical conductivity of the solid solutions YOgCao.2Fel-x MnxOJ+c5 (0 ~ x ~ 1.0) were investigated. All compositions had the GdFeOrtype orthorhombic perovskite structure with trace amounts of a second phase present in case of x = 0.8 and 1.0. The lattice parameters were detennined at room tempe'rature by using X-ray powder diffraction (XRPD). The pseudocubic lattice constant decreased with increasing x. The average I inear thermal expansion coefficient (anv) in the temperature range from 673 to 973 K showed negligible change with x up to x = 0.4. The thennal expansion curve for x = I had a slope approaching zero in the temperature range from 648 to 948 K. The calculated activation energy values for electrical conduction indicate that conduction occurs primarily by the small polaron hopping mechanism. The drastic drop in electrical conductivity for a small addition of Mn (0 ~ x ~ 0.2) is caused by the preferential fonnation of Mn4t ion~ (rather than Fe4 +) which act as carrier traps. This continues till the charge compensation for the divalent ions on the A-site is complete. The results indicate that with further increase in manganese content (beyond x =0.4) in the solid solutions, there is an increase in exc :::ss oxygen and consequently, a small increase in Mn'll il>I1~, which are charge compensated by the formation of cation vancancies.

La-Doped Ba2In2O5 Electrolyte: Pechini Synthesis, Microstructure, Electrical Conductivity, and Application for CO Gas Sensing

Dense (Ba1―xLax)2In2O5+x (BLIO) electrolytes with different compositions (x = 0.4, 0.5, 0.6) were fabricated using powders obtained by the Pechini method. The formation of BLIO powders was investigated by using X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The calcination temperature and time were optimized. The sintered (Ba1―xLax)2In2O5+x electrolytes showed a relative density greater than ∼97%, and the major phase of three electrolyte compositions was indexed as a cubic perovskite. The electrical conductivity of BLIO ceramics at elevated temperatures in air was measured by ac-impedance spectroscopy. The activation energies for conduction in BLIO were 102 kJ mol―1 between 473 and 666 K and 118 kJ mol―1 between 769 and 873 K, which are comparable to that for 8 mol % yttria-stabilized cubic zirconia. Mixed-potential gas sensors utilizing BLIO-based electrolytes exhibited good sensitivity to different CO concentrations from ∼100 to ∼500 ppm and excellent selectivity to methane at around 873 K.

Structure and temperature dependence of conductivity of Ag2.5Se‐Se composite

Rapid solidification of Ag‐53 at. % Se alloy resulted in the formation of a composite mixture of Ag2.5Se and Se. The microstructure consists of spherical Se grains of 2–20 μm size, randomly distributed in a matrix of Ag2.5 Se. The Se grains were found to be layered hexagonal while the Ag2.5 Se had an orthorhombic crystal structure. The unit cell size of this phase, however, was twice that reported for the equilibrium orthorhombic Ag2 Se compound. The conductivity σ variation with temperature in the range 80–320 K was found to be similar to that observed in degenerate semiconductors. The σ decreased from 295 Ω−1 cm−1 at room temperature to a saturation value of 70 Ω−1 cm−1 for temperatures <80 K. The results are discussed in terms of percolation conduction in the Ag2.5 Se phase.

Effect of pore medium chemistry on hydraulic conductivity of fine grained soils

Hydraulic conductivity of fine-grained soils has assumed greater importance in waste disposal facilities. It is necessary to understand better the factors controlling hydraulic conductivity of fine-grained soils which are used as liners in waste disposal facilities. Hydraulic Conductivity study with ten soils with two fluids having extreme dielectric constants(epsilon) namely water and CCl4 has shown that intrinsic permeability (K) increases drastically with decrease in epsilon. These changes are attributed to the significant reduction in the thickness of diffuse double layer which in turn mainly dependent on the epsilon of the permeant. Hydraulic Conductivity with water of each pair of soils having nearly same liquid limit but different plasticity properties is found to be vastly different, but found to correlate well with shrinkage index, defined as difference between the liquid and the shrinkage limits. Also the ratio Kccl(4)/K-w is found to significantly increase with the increase in the shrinkage index.

Selective double quantum resolved correlation experiment for the complete separation of entire proton NMR spectra of enantiomers

The present study reports a two dimensional NMR experiment which separates single quantum spectra of enantiomers from that of a racemic mixture. This is a blend of selective double quantum refocusing, for resolving couplings and chemical shift interactions along two dimensions followed by correlation of the selectively excited protons to the entire coupled spin network. The concept is solely based on the presence of distinct intra methyl dipolar couplings of different enantiomers when dissolved in chiral orienting media. The analysis of single enantiomer spectrum obtained from respective F-2 cross sections yield all the spectral information. (C) 2011 Elsevier Inc. All rights reserved.

Electrical conductivity of Ca-doped YFeO3

Electrical conductivity and Seebeck coefficient of calcium-doped YFeO3, a potential cathode material in solid oxide fuel cells (SOFC), are measured as function of temperature and composition in air to resolve conflicts in the literature both on the nature of conduction (n- or p-type) and the types of defects (majority and the minority) present. Compositions of Y1-xCaxFeO3-delta with x = 0.0, 0.025, 0.05 and 0.1 are studied in the temperature range from 625 to 1250 K. All Y1-xCaxFeO3-delta samples show p-type semiconducting behaviour. Addition of Ca up to 5% dramatically increases the conductivity of YFeO3; increase is more gradual up to 10%. A second phase Ca2Fe2O5 appears in the microstructure for Ca concentrations in excess of 11%.

Ionic conductivity of bis(2-cyanoethyl) ether-lithium salt and poly(propylether imine)-lithium salt liquid electrolytes

We report here a multiple-nitrile based lithium-salt liquid electrolyte. The ionic conductivity of poly (propyl ether imine) (abbreviated as PETIM) lithium salt dendrimer liquid electrolyte was observed to be a function of dendrimer generation number, n=0 (monomer)-3. While the highest room temperature ionic conductivity value (similar to 10(-1) Sm-1) was recorded for the bis-2cyanoethyl ether monomer (i.e. zeroth generation; G(0)-CN), conductivity decreased progressively to lower values (similar to 10(-3) Sm-1) with increase in generation number (G(1)-CN -> G(3)-CN). The G(0)-CN and higher dendrimer generations showed high thermal stability (approximate to 150 to 200 degrees C), low moisture sensitivity and tunable viscosity (similar to 10(-2) (G(0)-CN) to 3 (G(3)-CN) Pa s). The linker ether group was found to be crucial for ion transport and also eliminated a large number of detrimental features, chiefly moisture sensitivity, chemical instability associated typically with prevalent molecular liquid solvents. Based on the combination of several beneficial physicochemical properties, we presently envisage that the PETIM dendrimers especially the G(0)-CN electrolytes hold promise as electrolytes in electrochemical devices such as lithium-ion batteries.

Effect of cryogenic treatment on thermal conductivity properties of copper

Copper exhibits high thermal conductivity properties and hence it is extensively used in cryogenic applications like cold fingers, heat exchangers, etc. During the realization of such components, copper undergoes various machining operations from the raw material stage to the final component. During these machining processes, stresses are induced within the metal resulting in internal stresses, strains and dislocations. These effects build up resistance paths for the heat carriers which transfer heat from one location to the other. This in turn, results in reduction of thermal conductivity of the conducting metal and as a result the developed component will not perform as per expectations. In the process of cryogenic treatment, the metal samples are exposed to cryogenic temperature for extended duration of time for 24 hours and later tempered. During this process, the internal stresses and strains are reduced with refinement of the atomic structure. These effects are expected to favourably improve thermal conductivity properties of the metal. In this experimental work, OFHC copper samples were cryotreated for 24 hours at 98 K and part of them were tempered at 423K for one hour. Significant enhancement of thermal conductivity values were observed after cryotreating and tempering the copper samples.

Effect of pressure on the ionic conductivity of Li+ and Cl- ions in water

A molecular dynamics simulation study of aqueous solution of LiCl is reported as a function of pressure. Experimental measurements of conductivity of Li+ ion as a function of pressure shows an increase in conductivity with pressure. Our simulations are able to reproduce the observed trend in conductivity. A number of relevant properties have been computed in order to understand the reasons for the increase in conductivity with pressure. These include radial distribution function, void and neck distributions, hydration or coordination numbers, diffusivity, velocity autocorrelation functions, angles between ion-oxygen and dipole of water as well as OH vector, mean residence time for water in the hydration shell, etc. These show that the increase in pressure acts as a structure breaker. The decay of the self part of the intermediate scattering function at small wave number k shows a bi-exponential decay at 1 bar which changes to single exponential decay at higher pressures. The k dependence of the ratio of the self part of the full width at half maximum of the dynamic structure factor to 2Dk(2) exhibits trends which suggest that the void structure of water is playing a role. These support the view that the changes in void and neck distributions in water can account for changes in conductivity or diffusivity of Li+ with pressure. These results can be understood in terms of the levitation effect. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4756909]

Synthesis, characterisation, and DC conductivity of polyaniline-lead oxide composites

The polyaniline-PbO composites of various mass fractions were prepared by in situ polymerisation. The prepared samples were characterised by FTIR, and the dominant peaks confirmed the formation of polyaniline-PbO composites. The SEM study shows a granular agglomerated morphology, and increases with an increase in the lead oxide mass % in polyaniline. Direct current (DC) conductivity (sigma (DC)) was studied as a function of temperature (T). From these studies, it was found that conductivity increased at higher temperatures due to the polarons hopping from one localised state to another. DSC studies reveal, the decrease in peak temperature from 273A degrees C (pure PANI) to 169.2A degrees C, 193.5A degrees C, 218.4A degrees C, 235.2A degrees C, and 224.2A degrees C, respectively for the various mass fractions (10 %, 30 %, 20 %, 40 %, and 50 %) of polyaniline-PbO composites.