Analysis of the contributions of three-body potentials in the equation of state of 4He

The effect of three-body interatomic contributions in the equation of state of 4He are investigated. A recent two-body potential together with the Cohen and Murrell (Chem. Phys. Lett. 260, 371 (1996)) three-body potential are applied to describe bulk helium. The triple-dipole dispersion and exchange energies are evaluated subjected only to statistical uncertainties. An extension of the diffusion Monte Carlo method is applied in order to compute very small energies differences. The results show how the three-body contributions affects the ground-state energy, the equilibrium, melting and freezing densities.Comment: 18 pages, 3 figures, 4 table

Superplasticity in Aeroengine Titanium Alloy VT-9 and its Modified Compositions

The alloy (Ti-6.5AL-3.3 Mo-1.6Zr-O.3Si) is a Soviet composition designated VT-9. Excellent superplastic characteristics found by us in this alloy prompted us to explore the possibility of use of Si-free VT-9 in sheet form for superplastic forming. An optimum thermomechanical processing produced a microstructure that resulted in an elongation of 1700 per cent at a fairly high deformation rate (2 X 10-3 set-1). Thus, the same aeroengine alloy (VT-9) can be used for superplastically formed airframe parts in the Si-free condition. The present study also shows that for making the forming process commercially viable, deformation temperature could be lowered by temporarily alloying with hydrogen in a particular concentration range (0.1 to 0.2 wt per cent)

Aspects of Horava-Lifshitz cosmology

We review some general aspects of Horava-Lifshitz cosmology. Formulating it in its basic version, we extract the cosmological equations and we use observational data in order to constrain the parameters of the theory. Through a phase-space analysis we extract the late-time stable solutions, and we show that eternal expansion, and bouncing and cyclic behavior can arise naturally. Concerning the effective dark energy sector we show that it can describe the phantom phase without the use of a phantom field. However, performing a detailed perturbation analysis, we see that Horava-Lifshitz gravity in its basic version suffers from instabilities. Therefore, suitable generalizations are required in order for this novel theory to be a candidate for the description of nature.Comment: 10 pages, 4 figures, invited talk given at the 2nd International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Assymetry, National Tsing Hua University, Hsinchu, Taiwan, November 5-6, 201

Prolific Generation of Williamson Type Matrices

A new method of generating Williamson type Matrices A, B, C, D is described such that (i) A, B, C, D are symmetric. (ii) A, B, C are circulant matrices and D is a back circulant matrix. All such Williamsom type matrices of order n = 7, 9, 11, 13, 15, 17 are obtained by exhaustive computer search. The number of Williamson type Matrices constructed here is much greater than that of Williamson Matrices of same order. For example there are only 4 Williamson Matrices of order 17 but by our method we have obtained 504 Williamson type Matrices of order 17

Double Time Window Targeting Technique: Real time DMRG dynamics in the PPP model

We present a generalized adaptive time-dependent density matrix renormalization group (DMRG) scheme, called the {\it double time window targeting} (DTWT) technique, which gives accurate results with nominal computational resources, within reasonable computational time. This procedure originates from the amalgamation of the features of pace keeping DMRG algorithm, first proposed by Luo {\it et. al}, [Phys.Rev. Lett. {\bf 91}, 049701 (2003)], and the time-step targeting (TST) algorithm by Feiguin and White [Phys. Rev. B {\bf 72}, 020404 (2005)]. Using the DTWT technique, we study the phenomena of spin-charge separation in conjugated polymers (materials for molecular electronics and spintronics), which have long-range electron-electron interactions and belong to the class of strongly correlated low-dimensional many-body systems. The issue of real time dynamics within the Pariser-Parr-Pople (PPP) model which includes long-range electron correlations has not been addressed in the literature so far. The present study on PPP chains has revealed that, (i) long-range electron correlations enable both the charge and spin degree of freedom of the electron, to propagate faster in the PPP model compared to Hubbard model, (ii) for standard parameters of the PPP model as applied to conjugated polymers, the charge velocity is almost twice that of the spin velocity and, (iii) the simplistic interpretation of long-range correlations by merely renormalizing the {\it U} value of the Hubbard model fails to explain the dynamics of doped holes/electrons in the PPP model.Comment: Final (published) version; 39 pages, 13 figures, 1 table; 2 new references adde

Cosmological perturbations in f(T) gravity

We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbien, we extract the corresponding dispersion relation, which provides a constraint on the f(T) ansatzes that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from LCDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.Comment: 11 pages, 4 figures. Analysis of the vector and tensor sectors adde

Struggling to a monumental triumph : Re-assessing the final stages of the smallpox eradication program in India, 1960-1980

The global smallpox program is generally presented as the brainchild of a handful of actors from the WHO headquarters in Geneva and at the agency's regional offices. This article attempts to present a more complex description of the drive to eradicate smallpox. Based on the example of India, a major focus of the campaign, it is argued that historians and public health officials should recognize the varying roles played by a much wider range of participants. Highlighting the significance of both Indian and international field officials, the author shows how bureaucrats and politicians at different levels of administration and society managed to strengthen—yet sometimes weaken—important program components. Centrally dictated strategies developed at WHO offices in Geneva and New Delhi, often in association with Indian federal authorities, were reinterpreted by many actors and sometimes changed beyond recognition

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO2 and CH4 to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH2, H2PO3, NO2, and CH3. Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO2 to exceed that of CH4 by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH2, H2PO3, NO2, and COOH functional groups can significantly enhance gas binding with respect to a hydrogen-passivated edge, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO2/CH4 selectivity are discussed.Comment: 12 pages, 7 figure