Stability constraints in the design of galvanic cells using composite electrolytes and auxiliary electrodes

Recent trends in the use of dispersed solid electrolytes and auxiliary electrodes in galvanic cells have increased the need for assessment of materials compatibility. In the design of dispersed solid electrolytes, the potential reactions between the dispersoid and the matrix must be considered. In galvanic cells, possible interactions between the dispersoid and the electrode materials must also be considered in addition to ion exchange between the matrix and the electrode. When auxiliary electrodes, which convert the chemical potential of a component present at the electrode into an equivalent chemical potential of the neutral form of the migrating species in the solid electrolyte are employed, displacement reactions between phases in contact may limit the range of applicability of the cell. Examples of such constraints in the use of oxide dispersoids in fluoride solid electrolytes and NASICON/Na2S couple for measurement of sulphur potential are illustrated with the aid of Ellingham and stability field diagrams.

A general procedure for generation of curved DNA molecules.

A general method for generation of base-pairs in a curved DNA structure, for any prescribed values of helical parameters--unit rise (h), unit twist (theta), wedge roll (theta R) and wedge tilt (theta T), propeller twist (theta p) and displacement (D) is described. Its application for generation of uniform as well curved structures is also illustrated with some representative examples. An interesting relationship is observed between helical twist (theta), base-pair parameters theta x, theta y and the wedge parameters theta R, theta T, which has important consequences for the description and estimation of DNA curvature.

Molecular structure-activity relationship study of some non-steroidal antiinflammatory agents using electrostatic potential mapping

A series of 6,11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acids (DOAA) which are known to be anti-inflammatory agents were studied. The geometries of some of the molecules obtained from X-ray crystallography were used in the calculations as such while the geometries of their derivatives were obtained by local, partial geometry optimization around the Sites of substitution employing the AMI method, keeping the remaining parts of the geometries the same as those in the parent molecules. Molecular electrostatic potential (MEP) mapping was performed for the molecules using optimized hybridization displacement charges (HDC) combined with Lowdin charges, as this charge distribution has been shown earlier to yield near ab initio quality results. A good correlation has been found between the MEP values near the oxygen atoms of the hydroxyl groups of the carboxy groups of the molecules and their anti-inflammatory activities. The result is broadly in agreement with the model proposed earlier by other authors regarding the structure-activity relationship for other similar molecules.

Communication: Evidence of dynamic heterogeneity in glassy polymer monolayers from interface microrheology measurements

We have developed a novel nanoparticle tracking based interface microrheology technique to perform in situ studies on confined complex fluids. To demonstrate the power of this technique, we show, for the first time, how in situ glass formation in polymers confined at air-water interface can be directly probed by monitoring variation of the mean square displacement of embedded nanoparticles as a function of surface density. We have further quantified the appearance of dynamic heterogeneity and hence vitrification in polymethyl methacrylate monolayers above a certain surface density, through the variation of non-Gaussian parameter of the probes. (C) 2010 American Institute of Physics. [doi:10.1063/1.3471584].

On the admittance of lipid bilayer membranes: Part I. Membrane-permeable ions

The modular formalism of Rangarajan [J. Electroanal. Chem., 55 (1974) 297] has been applied to the admittance of lipid bilayer membranes. The method leads to equations which clearly show the interrelations between the various partial processes involved in ion transport, and which allow examination of model assumptions without the need for a complete rederivation of the membrane admittance. Explicit expressions are given for both the continuum and single jump models. The former includes the ionic displacement component, important mostly at high frequencies.

On the admittance of lipid bilayer membranes: Part I. Membrane-permeable ions

The modular formalism of Rangarajan [J. Electroanal. Chem., 55 (1974) 297] has been applied to the admittance of lipid bilayer membranes. The method leads to equations which clearly show the interrelations between the various partial processes involved in ion transport, and which allow examination of model assumptions without the need for a complete rederivation of the membrane admittance. Explicit expressions are given for both the continuum and single jump models. The former includes the ionic displacement component, important mostly at high frequencies.

A rectangular laminated anisotropic shallow thin shell finite element

This report contains the details of the development of the stiffness matrix for a rectangular laminated anisotropic shallow thin shell finite element. The derivation is done under linear thin shell assumptions. Expressing the assumed displacement state over the middle surface of the shell as products of one-dimensional first-order Hermite interpolation polynomials, it is possible to insure that the displacement state for the assembled set of such elements, to be geometrically admissible. Monotonic convergence of the total potential energy is therefore possible as the modelling is successively refined. The element is systematically evaluated for its performance considering various examples for which analytical or other solutions are available

Prediction of Specimen Strain from Extensometer Deflection Measurements in a Direct Stress Fatigue Test Specimen under Static Tensile Loading

The displacement between the ridges situated outside the filleted test section of an axially loaded unnotched specimen is computed from the axial load and shape of the specimen and compared with extensometer deflection data obtained from experiments. The effect of prestrain on the extensometer deflection versus specimen strain curve has been studied experimentally and analytically. An analytical study shows that an increase in the slope of the stress-strain curve in the inelastic region increases the slope of the corresponding computed extensometer deflection versus specimen strain curve. A mathematical model has been developed which uses a modified length ¯ℓef in place of the actual length of the uniform diameter test section of the specimen. This model predicts the extensometer deflection within 5% of the corresponding experimental value. This method has been successfully used by the authors to evolve an iterative procedure for predicting the cyclic specimen strain in axial fatigue tests on unnotched specimens.

Static and dynamic properties of incommensurate smectic-AIC liquid crystals

We study the elasticity, topological defects, and hydrodynamics of the recently discovered incommensurate smectic (AIC) phase, characterized by two collinear mass density waves of incommensurate spatial frequency. The low-energy long-wavelength excitations of the system can be described by a displacement field u(x) and a ��phason�� field w(x) associated, respectively, with collective and relative motion of the two constituent density waves. We formulate the elastic free energy in terms of these two variables and find that when w=0, its functional dependence on u is identical to that of a conventional smectic liquid crystal, while when u=0, its functional dependence on w is the same as that for the angle variable in a slightly anisotropic XY model. An arbitrariness in the definition of u and w allows a choice that eliminates all relevant couplings between them in the long-wavelength elastic energy. The topological defects of the system are dislocations with nonzero u and w components. We introduce a two-dimensional Burgers lattice for these dislocations, and compute the interaction between them. This has two parts: one arising from the u field that is short ranged and identical to the interaction between dislocations in an ordinary smectic liquid crystal, and one arising from the w field that is long ranged and identical to the logarithmic interaction between vortices in an XY model. The hydrodynamic modes of the AIC include first- and second-sound modes whose direction-dependent velocities are identical to those in ordinary smectics. The sound attenuations have a different direction dependence, however. The breakdown of hydrodynamics found in conventional smectic liquid crystals, with three of the five viscosities diverging as 1/? at small frequencies ?, occurs in these systems as well and is identical in all its details. In addition, there is a diffusive phason mode, not found in ordinary smectic liquid crystals, that leads to anomalously slow mechanical response analogous to that predicted in quasicrystals, but on a far more experimentally accessible time scale.

Use of metastable equilibria for determination of Gibbs energy of solids

Attempts are made to measure activities of both components of a binary alloy (A�B) at 650 K using a solid-state galvanic cell incorporating a new composite solid electrolyte. Since the ionic conductivity of the composite solid electrolyte is three orders of magnitude higher than that of pure CaF2, the cell can be operated at lower temperatures. The alloy phase is equilibrated in separate experiments with flourides of each component and fluorine potential is measured. The mixture of the alloy (A�B) and the fluoride of the more reactive component (BF2) is stable, while (A�B) + AF2 mixture is metastable, Factors governing the possible use of metastable equilibria have been elucidated in this study. In the Co�Ni system, where the difference in Gibbs energies of formation of the fluorides is 21.4 kJ/mol, emf of the cell with metastable phases at the electrode is constant for periods ranging from 90 to 160 ks depending on alloy composition. Subsequently, the emf decreases because of the onset of the displacement reaction. In the Ni�Mn system, measurement of the activity of Ni using metastable equilibria is not fully successful at 650 K because of the large driving force for the displacement reaction (208.8 kJ/mol). Critical factors in the application of metastable equilibria are the driving force for displacement reaction and diffusion coefficients in both the alloy and fluoride solid solution.

Modelling of symmetric laminates under extension

A higher-order theory of laminated composites under in-plane loads is developed. The displacement field is expanded in terms of the thickness co-ordinate, satisfying the zero shear stress condition at the surfaces of the laminate. Using the principle of virtual displacement, the governing equations and boundary conditions are established. Numerical results for interlaminar stresses arising in the case of symmetric laminates under uniform extension have been obtained and are compared with similar results available in the literature.

Mean square displacements of hydrogen interstitial and its neighbours in the intermetallic compound Fe0.5Ti0.5

A Green's function technique is used in the scattering matrix formalism to compute the mean square displacement of hydrogen and deuterium interstitials in the intermetallic compound Fe0.5Ti0.5 for low hydrogen/deuterium concentration. The mean square amplitudes of the metal atoms surrounding the interstitial are found to be smaller than those for the host crystal. This anomalous effect is due to the stiffening of the lattice by the dissolved hydrogen or deuterium at low concentration. This type of effect is experimentally observed in the case of NbHx at low hydrogen concentration.

Mechanical Anisotropy in Crystalline Saccharin: Nanoindentation Studies

The nanoindentation technique has been employed to relate the mechanical properties of saccharin single crystals with their internal structure. Indentations were performed on (100) and (011) faces to assess the mechanical anisotropy. The load-displacement (P-h) curves indicate significant differences in the nature of the plastic deformation on the two faces. The P-h curves obtained on the (011) plane are smooth, reflecting homogeneous plasticity. However, displacement bursts (pop-ins) are observed in the P-h curves obtained on the (100) plane suggesting a discrete deformation mechanism. Marginal differences exist in the hardness and modulus on the two faces that may, in part, be rationalized, although one notes that saccharin has a largely three-dimensional close-packed structure. The structural origins of the fundamentally different deformation mechanisms on (100) and (011) are discussed in terms of the dimensionality of the hydrogen bonding networks. Down the (100) planes, the saccharin dimers are stacked and are stabilized by nonspecific van der Wants interactions mostly between aromatic rings. However, down the (011) planes, the molecules are stabilized by more directional and cross-linked C-H ... O hydrogen bonds. This anisotropy in crystal packing and interactions is reflected in the mechanical behavior on these faces. The displacements associated with the pop-ins were found to he integral multiples oldie molecule separation distances. Nanoindentation offers an opportunity to compare experimentally, and in a quantitative way, the various intermolecular interactions that fire present in a molecular crystal.

Nonlinear fracture properties of concrete-concrete interfaces

The fracture properties of different concrete-concrete interfaces are determined using the Bazant's size effect model. The size effect on fracture properties are analyzed using the boundary effect model proposed by Wittmann and his co-workers. The interface properties at micro-level are analyzed through depth sensing micro-indentation and scanning electron microscopy. Geometrically similar beam specimens of different sizes having a transverse interface between two different strengths of concrete are tested under three-point bending in a closed loop servo-controlled machine with crack mouth opening displacement control. The fracture properties such as, fracture energy (G(f)), length of process zone (c(f)), brittleness number (beta), critical mode I stress intensity factor (K-ic), critical crack tip opening displacement CTODc (delta(c)), transitional ligament length to free boundary (a(j)), crack growth resistance curve and micro-hardness are determined. It is seen that the above fracture properties decrease as the difference between the compressive strength of concrete on either side of the interface increases. (C) 2010 Elsevier Ltd. All rights reserved.

Improved hybrid elements for structural analysis

Hybrid elements, which are based on a two-field variational formulation with the displacements and stresses interpolated separately, are known to deliver very high accuracy, and to alleviate to a large extent problems of locking that plague standard displacement-based formulations. The choice of the stress interpolation functions is of course critical in ensuring the high accuracy and robustness of the method. Generally, an attempt is made to keep the stress interpolation to the minimum number of terms that will ensure that the stiffness matrix has no spurious zero-energy modes, since it is known that the stiffness increases with the increase in the number of terms. Although using such a strategy of keeping the number of interpolation terms to a minimum works very well in static problems, it results either in instabilities or fails to converge in transient problems. This is because choosing the stress interpolation functions merely on the basis of removing spurious energy modes can violate some basic principles that interpolation functions should obey. In this work, we address the issue of choosing the interpolation functions based on such basic principles of interpolation theory and mechanics. Although this procedure results in the use of more number of terms than the minimum (and hence in slightly increased stiffness) in many elements, we show that the performance continues to be far superior to displacement-based formulations, and, more importantly, that it also results in considerably increased robustness.