The Effect of Configurational Entropy of Mixing on the Design and Development of Novel Materials

The configurational entropy of mixing (∆Smix) has a profound influence on the stability of various phases in different materials at intermediate and high temperatures. Recently, it has been observed that ∆Smix can be used as an important tool to design novel multicomponent materials with fascinating properties. ∆Smix affects ∆Gmix and tends to stabilize the FCC/ BCC/HCP multicomponent solid solutions over brittle phases including compounds. This opens up vistas to design novel solid solution-based materials with improved mechanical, functional properties. Accordingly, multicomponent and multiprinciple alloys were developed in 2004, and subsequently, novel ceramics and polymers have been designed. The present paper is intended to provide an insight into the role of ∆Smix to design novel metallic, ceramic as well as polymeric materials

Investigation of Shallow Sedimentary Structure of the Anchorage Basin, Alaska, Using Simulated Annealing Inversion of Site Response

This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SR(f)] data in the frequency range 0.5-11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity (beta), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L-2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter beta was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SR(f) in the Anchorage basin. In the uppermost part of the basin, the beta values of fine-grain Quaternary sediments mainly lie in the range of 180-500 m/sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80-200 m) coarse-grain Quaternary sediments with beta values in the range of 600-900 m/sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with beta > 1000 m/sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SR(f) in the Anchorage basin for the frequency band 0.5-11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.GIEnvironment and Natural Resources InstituteSchool of Engineering of the University of Alaska, AnchorageGeological Science

Low-energy quenching of positronium by helium

Very low-energy scattering of orthopositronium by helium has been investigated for simultaneous study of elastic cross section and pick-off quenching rate using a model exchange potential. The present calculational scheme, while agrees with the measured cross section of Skalsey et al, reproduces successfully the parameter ^ 1Z_{\makebox{eff}}, the effective number of electrons per atom in a singlet state relative to the positron. Together with the fact that this model potential also leads to an agreement with measured medium energy cross sections of this system, this study seems to resolve the long-standing discrepancy at low energies among different theoretical calculations and experimental measurements.Comment: 4 latex pages, 3 postscript figure

Truncated Harmonic Osillator and Parasupersymmetric Quantum Mechanics

We discuss in detail the parasupersymmetric quantum mechanics of arbitrary order where the parasupersymmetry is between the normal bosons and those corresponding to the truncated harmonic oscillator. We show that even though the parasusy algebra is different from that of the usual parasusy quantum mechanics, still the consequences of the two are identical. We further show that the parasupersymmetric quantum mechanics of arbitrary order p can also be rewritten in terms of p supercharges (i.e. all of which obey $Q_i^{2} = 0$). However, the Hamiltonian cannot be expressed in a simple form in terms of the p supercharges except in a special case. A model of conformal parasupersymmetry is also discussed and it is shown that in this case, the p supercharges, the p conformal supercharges along with Hamiltonian H, conformal generator K and dilatation generator D form a closed algebra.Comment: 9 page

Green synthesis of Ag nanoparticles in large quantity by cryomilling

Most of the synthetic methods for the preparation of Ag nanoparticles (Ag NPs) involve wet chemical synthesis, in which hazardous chemicals are used and the NPs are further stabilized by a surfactant. The presence of a surfactant is detrimental to the purity as well as to the native properties of the Ag NPs. The present study reports a unique technique to prepare ultrapure free-standing Ag NPs in large quantities without the use of any hazardous chemicals. This has been achieved by cryomilling. Note that cryomilling is a cost effective method to prepare metal NPs, involving ball milling below 160 ± 10 °C under a protective Ar atmosphere. The experimental results reveal that it is possible to obtain Ag NPs with a narrow size distribution (4–8 nm). The level of contamination (34 ppb of W) in the nanoparticles was estimated by EPMA, whereas the ultra-high purity of the Ag NPs was confirmed by ICP-OES and XPS. The surfactant-free Ag NPs were also stable at elevated temperatures (400 °C) and exhibited free-standing nature in liquids including ethanol, methanol, and water. The results have been discussed based on the low-temperature deformation behaviour of Ag and the electrostatic stabilization of highly pure Ag NPs in different polar liquids

Direct images of bundles under Frobenius morphisms

Let $X$ be a smooth projective variety of dimension $n$ over an algebraically closed field $k$ with ${\rm char}(k)=p>0$ and $F:X\to X_1$ be the relative Frobenius morphism. For any vector bundle $W$ on $X$, we prove that instability of $F_*W$ is bounded by instability of $W\otimes{\rm T}^{\ell}(\Omega^1_X)$ ($0\le \ell\le n(p-1)$)(Corollary \ref{cor3.8}). When $X$ is a smooth projective curve of genus $g\ge 2$, it implies $F_*W$ being stable whenever $W$ is stable.Comment: the final version to appear in Invent. math. (2008

Preparation of nanocrystalline high-entropy alloys via cryomilling of cast ingots

The advancement of nanotechnology demands large-scale preparation of nanocrystalline powder of innovative materials. High-entropy alloys (HEAs) exhibit unique properties: mechanical, thermal, magnetic etc., making them potentials candidates for applications in energy, environment and biomaterials etc. Thus, there is a need to develop novel synthesis methods to prepare nanocrystalline high-purity HEAs in large quantity. Conventional mechanical alloying of the multicomponent metallic powder mixture requires larger milling time and it is prone to contaminations and phase transformation. The present investigation reports a unique approach, involving casting followed by cryomilling, leading to formation of nanocrystalline HEAs powder, which are relatively contaminations free with narrow size distribution. Using examples of two FCC and one BCC single-phase HEAs, it has been shown that large-scale nanocrystalline HEAs powder can be prepared after few hours of cryomilling at 123 K. The formation of nanocrystalline HEAs during cryomilling has been discussed using theoretically available approaches

On bouncing solutions in non-local gravity

A non-local modified gravity model with an analytic function of the d'Alembert operator is considered. This model has been recently proposed as a possible way of resolving the singularities problem in cosmology. We present an exact bouncing solution, which is simpler compared to the already known one in this model in the sense it does not require an additional matter to satisfy all the gravitational equations.Comment: 5 pages; v2: matching the jounral versio