Impurity Substitution in Bismuth and Thallium Cuprates: Suppression of T_c and Estimation of Pseudogap

Suppression of T_c in bilayer bismuth and thallium cuprates, by substitution of Co impurities at Cu sites, are taken for examination. T_c suppression data on differently doped Bi2212 and Tl2212 are analysed within the unitary pair-breaking formalism due to Abrikosov and Gorkov, by fitting data points to a phenomenological relation valid for weak coupling d-wave superconductors. Values of the pseudogap magnitude at each doping are thereby estimated within a "fermi-level density of states suppression" picture. Pseudogap magnitude from our estimation is observed to have a correspondence with a related characteristic temperature T^\star obtained by thermoelectric power measurements. Effects of pseudogap, on the density of states, is studied by calculating the susceptibility which shows a broad peak at high temperature. This peak feature in susceptibility is indicative of an unusual metallic state which could further be explored by systematic other measurements.Comment: Latex file, 14 pages, 3 figures (ps files included). To appear in Physica

The Role of Antioxidants on Cellular Aging

Aging is the multidimensional process of changes in physical, physiological and behavioral condition of a cell over time. It is characterized by decline of multiple physiological functions that increase the probability of homeostatic imbalance and cellular death. Various free radicals are produced due to endogenous oxidative reactions. These highly reactive atoms cause oxidative damage and shorten lifespan of a cell. The antioxidants are the molecules, which neutralize free radicals and delay the cellular aging

Environment assisted entanglement enhancement

We consider dissipative atom-cavity systems and show that their collective dynamics leads to the maximization of entanglement for intermediate values of the cavity leakage parameter $\kappa$. We discuss possible ways the reservoir influences entanglement. We first consider the entanglement of a single two-level atom with a microwave cavity that is coupled to another cavity. We show that the atom-cavity entanglement can be made to increase with cavity leakage. We next show that the entanglement between two atoms passing successively through a cavity can be maximised for intermediate values of $\kappa$. We finally consider the micromaser where the increase of two-atom entanglement for stronger cavity-environment coupling is demonstrated for experimentally attainable values of the micromaser parameters.Comment: 4 pages, Revtex, 1 eps figure; minor changes to match with published versio

Information transfer through a one-atom micromaser

We consider a realistic model for the one-atom micromaser consisting of a cavity maintained in a steady state by the streaming of two-level Rydberg atoms passing one at a time through it. We show that it is possible to monitor the robust entanglement generated between two successive experimental atoms passing through the cavity by the control decoherence parameters. We calculate the entanglement of formation of the joint two-atom state as a function of the micromaser pump parameter. We find that this is in direct correspondence with the difference of the Shannon entropy of the cavity photons before and after the passage of the atoms for a reasonable range of dissipation parameters. It is thus possible to demonstrate information transfer between the cavity and the atoms through this set-up.Comment: Revtex, 5 pages, 2 encapsulated ps figures; added discussion on information transfer in relation with cavity photon statistics; typos corrected; Accepted for Publicaiton in Europhysics Letter

Phase Diagram of the Half-Filled Extended Hubbard Model in Two Dimensions

We consider an extended Hubbard model of interacting fermions on a lattice. The fermion kinetic energy corresponds to a tight binding Hamiltonian with nearest neighbour (-t) and next nearest neighbour (t') hopping matrix elements. In addition to the onsite Hubbard interaction (U) we also consider a nearest neighbour repulsion (V). We obtain the zero temperature phase diagram of our model within the Hartree-Fock approximation. We consider ground states having charge and spin density wave ordering as well as states with orbital antiferromagnetism or spin nematic order. The latter two states correspond to particle-hole binding with $d_{x^2-y^2}$ symmetry in the charge and spin channels respectively. For $t' = 0$, only the charge density wave and spin density wave states are energetically stable. For non-zero t', we find that orbital antiferromagnetism (or spin nematic) order is stable over a finite portion of the phase diagram at weak coupling. This region of stability is seen to grow with increasing values of t'.Comment: Latex file, 10 output pages, 3 Figures (available on request to [email protected]), to appear in Phys. Rev. B (BR

A novel wear-resistant magnetic thin film material based on a Ti1−xFexC1−yTi_{1-x}Fe_xC_{1-y} nanocomposite alloy

In this study we report on the film growth and characterization of thin (approximately 50 nm thick) Ti-Fe-C films deposited on amorphous quartz. The experimental studies have been complemented by first principles density functional theory (DFT) calculations. Upon annealing of as-prepared films, the composition of the metastable Ti-Fe-C film changes. An iron-rich phase is first formed close to the film surface, but with increasing annealing time this phase is gradually displaced toward the film-substrate interface where its position stabilizes. Both the magnetic ordering temperature and the saturation magnetization changes significantly upon annealing. The DFT calculations show that the critical temperature and the magnetic moment both increase with increasing Fe and C-vacancy concentration. The formation of the metastable iron-rich Ti-Fe-C compound is reflected in the strong increase of the magnetic ordering temperature. Eventually, after enough annealing time ($\geq 10$ minutes), nano-crystalline $\alpha$-Fe starts to precipitate and the amount and size of these precipitates can be controlled by the annealing procedure; after 20 minutes of annealing, the experimental results indicate a nano-crystalline iron-film embedded in a wear resistant TiC compound. This conclusion is further supported by transmission electron microscopy studies on epitaxial Ti-Fe-C films deposited on single crystalline MgO substrates where, upon annealing, an iron film embedded in TiC is formed. Our results suggest that annealing of metastable Ti-Fe-C films can be used as an efficient way of creating a wear-resistant magnetic thin film material.Comment: 23 pages, 13 figure

Carbon release by selective alloying of transition metal carbides

We have performed first principles density functional theory calculations on TiC alloyed on the Ti sublattice with 3d transition metals ranging from Sc to Zn. The theory is accompanied with experimental investigations, both as regards materials synthesis as well as characterization. Our results show that by dissolving a metal with a weak ability to form carbides, the stability of the alloy is lowered and a driving force for the release of carbon from the carbide is created. During thin film growth of a metal carbide this effect will favor the formation of a nanocomposite with carbide grains in a carbon matrix. The choice of alloying elements as well as their concentrations will affect the relative amount of carbon in the carbide and in the carbon matrix. This can be used to design the structure of nanocomposites and their physical and chemical properties. One example of applications is as low-friction coatings. Of the materials studied, we suggest the late 3d transition metals as the most promising elements for this phenomenon, at least when alloying with TiC.Comment: 9 pages, 6 figure

An augmented space recursion study of the electronic structure of rough epitaxial overlayers

In this communication we propose the use of the Augmented Space Recursion as an ideal methodology for the study of electronic and magnetic structures of rough surfaces, interfaces and overlayers. The method can take into account roughness, short-ranged clustering effects, surface dilatation and interdiffusion. We illustrate our method by an application of Fe overlayer on Ag (100) surface.Comment: 22 pages, Latex, 6 postscript figure

Novel approach of association rule mining for tree canopy assessment

The evolution of technology and availability of voluminous satellite images are bringing a new scenario in satellite image classification where a performance efficient method for predictive analysis of satellite images for land cover classification needs to be devised. As urban areas are growing at faster rate, special attention needs to be given to solve tree canopy assessment problem. Vegetation indices are calculated from spectral information of satellite images. Hundreds of such vegetation indices are available to detect vegetation from a satellite image. The contribution of this paper is designing an improved Apriori algorithm to select optimal number of vegetation indices for tree canopy assessment. In this research, we propose a novel computational approach that allows the improvement of results. It selects optimal combination of vegetation indices and applies principal component analysis on it. It uses a greedy approach based on Apriori algorithm. This study emphasizes on assessment of tree canopy using GPU-enabled environment for performance-efficient assessment. The results achieved, are comparable to state-of-the-art techniques, with an accuracy of 96%. The research has considered 4 years data for Mumbai city of India. This research is useful for Green India Mission of India to assess tree canopy of urban region