Anomalous elasticity and anelasticity of GdCu at low temperatures

The temperature dependence of the single crystal and polycrystalline elastic constants of GdCu compound have been determined between the ambient and 77 K, the interval in which the structural instability occurs. From the shear constants, C' and C₄₄ the magnitude of the elastic anisotropy was calculated, and found to be close to unity over the whole temperature range. This is in contrast with the expected behavior of the elastic anisotropy in the vicinity of martensitic transformations, where the anisotropy attains appreciable values. The large changes of the shear elastic constants, relative to the compressional constant suggests that the structural instability in GdCu is induced by a mechanism of isotropic shear. The peak in the ultrasonic attenuation is symmetric, typical of a relaxational process. The behavior of the elastic properties and ultrasonic attenuation in the temperature interval of the structural instability of GdCu is discussed.     

The static character of prematter particles

It is shown that all spherically symmetric distributions of prematter in the framework of general relativity are static. These results provide a justification for the models of elementary particles proposed previously.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

A quadratic assignment formulation of the molecular conformation problem

The molecular conformation problem is discussed, and a concave quadratic global minimization approach for solving it is described. This approach is based on a quadratic assignment formulation of a discrete approximation to the original problem.     

Librational modes and the structure of ammonium nitrate in its high temperature phases

We have measured the temperature dependence of the low frequency Raman spectrum of ammonium nitrate in its solid phases IV, II and I and also in its melt. Librational modes are observed in phases IV and II but disappear in both phase I and the melt. Our results indicate that the NO₃ group is almost freely rotating in the solid phase I.     

A bi-metric theory of gravitation

A bi-metric theory of gravitation is proposed, satisfying the covariance and equivalence principles. It is based on a simple form of Lagrangian and has a simpler mathematical structure than that of the general theory of relativity. The theory agrees with general relativity up to the accuracy of the observations made up to now. The static spherically symmetric solution of the present field equations does not involve any 'black hole'.     

Support properties of the free measure for Boson fields

Let μ be the measure onI′ (? ^d ) corresponding to the Gaussian process with mean zero and covariance (f,(?Δ+1)^?1 g) onI (? ^d ). It is proven that the set $$( - \Delta _{d - 1} + 1)^{d/4 - \tfrac{1}{2} + \alpha } (1 + x^2 )^{d/4} [\log (2 + x^2 )]^\beta L^2 (\mathbb{R}^d )$$ has μ measure one if α>0 and β>1/2 and μ measure zero if α>0 and β<1/2; here Δ _d?1 is the Laplacian in anyd?1 dimensions whend>1 and Δ₀=Δ.     

Photon splitting into two photons in a Coulomb field

We explore the possibility of using neutral weak interactions to see whether neutrinos may flip their helicity. Experiments ranging from low-energy neutrino-nucleus scattering to high-energy inclusive reactions are discussed as tests for the presence of helicity-flipping scalar, pseudoscalar and tensor interactions.