Stress-state-permeability relations for overconsolidated clays

Analysis of experimental data of soils in both the normally consolidated and overconsolidated states reveal that the proposed relationships are tenable. Preconsolidation stress level influences the level of permeability.

Levitation Effect: Role of Symmetry and Dependence of Diffusivity on the Bond Length of Homonuclear and Heteronuclear Diatomic Species

Molecular dynamics investigation of model diatomic species confined to the alpha-cages of zeolite NaY is reported. The dependence of self-diffusivity on the bond length of the diatomic species has been investigated. Three different sets of runs have been carried out. In the first set, the two atoms of the diatomic molecule interact with the zeolite atoms with equal strength (example, O-2, the symmetric case). In the second and third sets which correspond to asymmetric cases, the two atoms of the diatomic molecule interact with unequal strengths (example, CO). The result for the symmetric case exhibits a well-defined maximum in self-diffusivity for an intermediate bond length. In contrast to this, the intermediate asymmetry leads to a less pronounced maximum. For the large asymmetric case, the maximum is completely absent. These findings are analyzed by computing a number of related properties. These results provide a direct confirmation at the microscopic level of the suggestion by Derouane that the supermobility observed experimentally by Kemball has its origin in the mutual cancellation of forces. The maximum in diffusivity from molecular dynamics is seen at the value predicted by the levitation effect. Further, these findings suggest a role for symmetry in the existence of a diffusivity maximum as a function of diameter of the diffusant often referred to as the levitation effect. The nature of the required symmetry for the existence of anomalous diffusivity is interaction symmetry which is different from that normally encountered in crystallography.

Reflections on the Hydrogen Bond in Crystal Engineering

Comments on aspects of the new definition of the hydrogen bond specific to crystal engineering are given.

Diagrammatic valence bond studies on hemocyanin

The Diagrammatic Valence Bond studies on the active sites of hemocyanin, consisting of two Cu(I) ions and an oxygen molecule, are performed to find out the stable geometrical pattern and electronic structure. Different parameters used in this theoretical approach are taken from existing literature on high T-c superconductors. Attempts have been made to find out the differences in electronic structure of [Cu2O2](+2) and [Cu2O2N4](+2) as it is observed that coordination of nitrogen ligand do affect electronic structure i.e. spin excitation gaps and charge and spin density distribution. A comparison of our results with earlier theoretical results are also presented.

Effect of open joint on stress wave propagation

Stress wave characteristics are drastically altered by joints and other inhomogenities. This paper addresses the effect of an open joint on stress wave transmission. An elastodynamic analysis is developed to supplement and explain some recent observations by Fourney and Dick(1995) on open as well as filled joints. The analytical model developed here assuming spherical symmetry can be extended to filled joints between dissimilar media, but results are presented only for open joints separating identical materials. As a special case, stress wave transmission across a joint with no gap is also addressed.

Elasto-plastic contact stress analysis of joints subjected to cyclic loading

Rigorous elastic-plastic finite element analysis of joints subjected to cyclic loading is carried out. An incremental-iterative algorithm is developed in a modular form combining elasto-plastic material behaviour and contact stress analysis. For the case of the interference fit, the analysis sequentially carries out insertion of the pin and application of the load on the joint, covering possible initiation of separation (and/or yielding) and progressively the receding/advancing contact at the pin-plate interface. Deformations of both the plate and the pin are considered in the analysis. Numerical examples are presented for the case of an interference fit pin in a large plate under remote cyclic tension, and for an interference fit pin lug joint subjected to cyclic loading. A detailed study is carried out for the latter problem considering the effect of change in contact/separation at the pin-plate interface on local stresses, strains and redistribution of these stresses with the spread of a plastic zone. The results of the study are a useful input for the estimation of the fatigue life of joints. Copyright (C) 1996 Elsevier Science Ltd

Flexural bond strength of masonry using various blocks and mortars

This paper deals with an experimental study on flexural bond strength of masonry using various blocks in combination with different mortars. Flexural bond strength of masonry has been determined by testing stack-bonded prisms using a modified bond wrench test set-up. The effect of mortar composition and strength on the masonry's. flexural bond strength using three types of masonry units (stabilized mud blocks, stabilized soil-sand blocks and burnt brick) has been examined. The effect of the masonry unit's moisture content on flexural bond strength has also been studied. Increases in mortar strength lead to increased flexural bond strength for cement mortar, irrespective of the type of masonry unit. It has been found that combination mortars, such as soil-cement mortar and cement-lime mortar, lead to better bond strength compared to cement mortars. The moisture content of the masonry unit at the time of casting has displayed significant influence on the flexural bond strength of the masonry. It has been found that for each type of masonry unit, an optimum moisture content exists, beyond which the flexural bond strength falls off quickly.

Brownian dynamics simulation of dense binary colloidal mixtures. II. Translational and bond-orientational order

We report the Brownian dynamics simulation results on the translational and bond-angle-orientational correlations for charged colloidal binary suspensions as the interparticle interactions are increased to form a crystalline (for a volume fraction phi = 0.2) or a glassy (phi = 0.3) state. The translational order is quantified in terms of the two- and four-point density autocorrelation functions whose comparisons show that there is no growing correlation length near the glass transition. The nearest-neighbor orientational order is determined in terms of the quadratic rotational invariant Q(l) and the bond-orientational correlation functions g(l)(t). The l dependence of Q(l) indicates that icosahedral (l = 6) order predominates at the cost of the cubic order (l = 4) near the glass as well as the crystal transition. The density and orientational correlation functions for a supercooled liquid freezing towards a glass fit well to the streched-exponential form exp[-(t/tau)(beta)]. The average relaxation times extracted from the fitted stretched-exponential functions as a function of effective temperatures T* obey the Arrhenius law for liquids freezing to a crystal whereas these obey the Vogel-Tamman-Fulcher law exp[AT(0)*/(T* - T-0*)] for supercooled Liquids tending towards a glassy state. The value of the parameter A suggests that the colloidal suspensions are ''fragile'' glass formers like the organic and molecular liquids.

Influence of strain rate and state-of-stress on the formation of ferrite in stainless steel type AISI 304 during hot working

The influence of strain rate and state-of-stress on the formation of ferrite in stainless steel type AISI 304L, 304 and 304 as-cast, during hot working has been studied. Compression and torsion tests were conducted in the temperature range 1100 to 1250 degrees C and strain rate range 0.001 to 100 s(-1) on these materials, Ferrite formation occurs during deformation at temperatures above 1150 degrees C and strain rates above 10 s(-1), in stainless steel type AISI 304L and 304. The tendency for the formation of ferrite is more in as-cast 304 than in wrought 304, In as-cast 304 the ferrite forms at lower temperatures and strain rates, The tendency for the ferrite formation is more in torsion than in compression.

Glutathione peroxidase3 of Saccharomyces cerevisiae protects phospholipids during cadmium-induced oxidative stress

The present study was undertaken to determine the role of glutathione peroxidase3 (gpx3) in phospholipid protection in cells. Wild-type (WT) cells showed an overall increase in phospholipids upon 50 mu M cadmium (Cd)-treatment, whereas an untreated gpx3 Delta strain showed a drastic reduction in overall phospholipids which was further reduced with 50 mu M Cd. In WT cells, Cd-exposure increased the short chain fatty acids and decreased the unsaturated fatty acids and the magnitude was high in Cd-treated gpx3 Delta cells. Purified recombinant gpx3p showed higher activity with phospholipid hydroperoxides than shorter hydroperoxides. An increase in gpx activity was observed in Cd-treated WT cells and no such alteration was observed in gpx3 Delta. WT cells treated with Cd showed an increase in MDA over untreated, while untreated gpx3 Delta cells themselves showed a higher level of MDA which was further enhanced with Cd-treatment. Iron, zinc and calcium levels were significantly altered in WT and gpx3 Delta cells during Cd-treatment.

Effect of Strain Rate on Ductile-to-Brittle Transition Temperature of a Free-Standing Pt-Aluminide Bond Coat

The ductile-to-brittle transition temperature (DBTT) of a free-standing Pt-aluminide (PtAl) bondcoat was determined using the microtensile testing method and the effect of strain rate variation, in the range 10(-5) to 10(-1) s(-1), on the DBTT studied. The DBTT increased appreciably with the increase in strain rate. The activation energy determined for brittle-to-ductile transition, suggested that such transition is most likely associated with vacancy diffusion. Climb of aOE (c) 100 > dislocations observed in analysis of dislocation structure using a transmission electron microscope (TEM) supported the preceding mechanism.

Synthesis of new transition metal nitrides, MWN2 (Mtriple bond; length as m-dashMn, Co, Ni)

We report the synthesis of ternary transition metal nitrides of the formula MWN(2) for M=Mn, Co, Ni by reaction of the corresponding MWO(4) with NH3 gas at 600-700 degrees C. MnWN2 is isostructural with the already-known FeWN2, crystallizing in a hexagonal structure (a=2.901(2), b=16.48(5) Angstrom) related to LiMoN2. CoWN2 and NiWN2 (which are isostructural amongst themselves) adopt a different hexagonal structure with a smaller c parameter. While the Mn and Fe nitrides are semiconducting, the Co and Ni nitrides are semimetallic.