Effect of Various Impurities on the Hardness of NaCl Crystals

The hardness of NaCl crystal in the presence of mono, divalent and polyvalent ions were measured. Measurements were made in the indentation load range from 5 x 10^‐3 to 20 x 10^‐3 N. The measured data showed that there is an indentation size effect. Classical Meyer's law was used for the characterization of crystal hardness f NaCl. The Meyer index was found to be smaller than 2 indicating brittle material characteristic. The PRS model was also used for the determination of the load‐independent microhardness value. It was found that the crystal hardness of NaCl is chancing depending on the type of impurity and the concentration.     

Polynomial time approximation of dense weighted instances of MAX‐CUT

We give the first polynomial time approximability characterization of denseweighted instances of MAX‐CUT, and some other dense weighted 𝒩𝒫‐hard problems in terms of their empirical weight distributions. This also gives the first almost sharp characterization of inapproximability of unweighted 0, 1 MAX‐BISECTION instances in terms of their density parameter. © 2000 John Wiley & Sons, Inc. Random Struct. Alg., 16: 314–332, 2000     

Nanomechanical and optical studies on polymeric membranes

The nanomechanical properties of poly(ethylene terephthalate) (PET) membranes, were examined in light of nanoindentation experiments under conditions of maximum contact load in the range of 0.5-12 m?. Spectroscopic Ellipsometry (SE) from 1.5 to 6.5 ev (Vis-FUV range) was also applied to probe the dielectric function (ϵ(ω) of the industrially supplied membranes, as well as their geometrical structure. Mechanical stretching (uniaxial or biaxial) procedures are usually applied for the elongation of the polymeric membranes, their thickness reduction and enhancement of their mechanical and optical performance, causing a preferable orientation of the macromolecules close to the surface. Nanoindentation and se testing have revealed the existence of a two-layer geometrical structure of the pet membranes, consisting of a thick amorphous pet layer and a thin crystalline-like pet overlayer, with increased hardness (elastic modulus). The analyses of the experimental dataprovides quantitative information on the formed overlayer, which is ascribed to the processing history of the membrane.     

Metal cations toxicity: An inorganic interpretation

Chemical hardness is one of the useful parameters giving information about the toxic nature of the structures. In the present work, absolute chemical hardness imparted to the science by Pearson, the hydration enthalpies, the element's electronegativity, as calculated by Batsanov (using the force constants of the bonds), the calculated electrostatic charge on the hydrated cations, the absolute radii for the metals and the effective nuclear charges, were correlated with available toxicology data for a series of metal cations (namely Hg²⁺, Cd²⁺, Cu²⁺ and K⁺) in order to obtain, from a physicochemical point of view, a better understanding of the deleterious actions of metal cations on living organisms. A series of linear curves and empirical equations were obtained, providing a convincing picture of the correlation toxicity-physical inorganic chemistry.     

Inference of Mechanical Properties from Instrumented Depth Sensing Indentation at Tiny Loads and Indentation Depths

Different hardness measures as Vickers, Brinell and Meyer hardness are discussed with respect to their physical interpretation. Meyer hardness is found to be best suited as a measure of plastic properties. The outline of a depth sensing nanoindentation experiment is described, and particular emphasis is given to the correct deduction of the contact area from indenter penetration data. Experimental complications, as phase transformations, finite machine compliance, thermal and pieco drift, and sample creep are detailed with, and their impact on the calculation of hardness and elastic modulus is shown. Furthermore the onset of yielding in dependence on critical load, indenter curvature and yield strength is discussed.