The effect of Pressure in Higher Dimensional Quasi-Spherical Gravitational Collapse

We study gravitational collapse in higher dimensional quasi-spherical Szekeres space-time for matter with anisotropic pressure. Both local and global visibility of central curvature singularity has been studied and it is found that with proper choice of initial data it is possible to show the validity of CCC for six and higher dimensions. Also the role of pressure in the collapsing process has been discussed.Comment: 11 pages, 6 figures, RevTeX styl

Gas-Phase Cryogenic Vibrational Spectroscopy of Metal Oxide Cluster Ions: Structure-Reactivity Relationship

Gas phase cryogenic ion trap vibrational spectroscopy in combination with high level quantum chemical calculations provides an ideal arena to investigate structure- reactivity relationships of pure- and bi- metallic oxide clusters as a function of size, charge-state and coordination environment. In the last decades, characterization of binary metal oxide nanomaterials has received special attention, mainly because catalytically inactive materials can be activated by doping with a second metal. Precisely controlled conditions and the absence of perturbing interactions with an environment allow the gas phase clusters to serve as powerful model systems for nanomaterials. Moreover, the active site(s) of these reactive intermediates can be unambiguously identified by their characteristic vibrational signatures. Such insights ultimately allow for a molecular level understanding of the reaction mechanisms at play at reactive surfaces in heterogeneous catalysis. Iron is the most common impurity in naturally occurring zeolites. Atomic Fe- substituted small Al-oxide clusters [(Al2O3)nFeO]+ function as model system for Fe- doped zeolites. The influence of an Fe-atom in an Al-oxide network is investigated in terms of structural change and preferred coordination site in Chapter 4. The results demonstrate that the Fe-atom prefers to occupy a position in the outer ring of the cluster and induces substantial change in the cluster structure for the smallest cluster studied (n=1), but not for the larger ones. Furthermore, a structural evolution from planar (n=1) over quasi-2D (n=2) to cage type (n≥3) structures is observed with increasing cluster size. The insights correlate with reported results of Fe-doped nanoparticles and nanocrystals, where the dopant Fe-atom is mostly found to replace the under-coordinated surface Al-atoms of the Al2O3 network. In Chapter 5 the active site(s) of heteronuclear metal oxide clusters towards oxygen atom transfer (OAT) reactions is identified. [AlVOx=3,4]●+ and [VPOx=3,4]●+ radical cations are studied in the context of CO to CO2 conversion (chapter 5.1) and ethylene to formaldehyde oxidation (chapter 5.2), respectively. In both cases, the oxygen atom bound to the main group atom, either Al or P, in contrast to the transition metal atom (V) takes part in the OAT cycle. The results presented in Chapter 6 reveal that the oxygen-deficient Ti3+ centre, which represents a model system for an oxygen vacancy at a titania surface, is the active site for CO2 adsorption. The first two CO2 molecules adsorb chemically on [Ti3O6] ̅, forming asymmetric bidentate-bridged and symmetric tridentate-bridged binding motifs. The tridentate-bridged binding motif, which is reported here for the first time, plays a central role in the oxygen exchange mechanism on a defective anatase surface and activation of CO2 on wet titania surfaces

Shell Crossing Singularities in Quasi-Spherical Szekeres Models

We investigate the occurrence of shell crossing singularities in quasi-spherical Szekeres dust models with or without a cosmological constant. We study the conditions for shell crossing singularity both from physical and geometrical point of view and they are in agreement.Comment: 10 latex pages, RevTex style, no figure

Edge Detecting New Physics the Voronoi Way

We point out that interesting features in high energy physics data can be determined from properties of Voronoi tessellations of the relevant phase space. For illustration, we focus on the detection of kinematic "edges" in two dimensions, which may signal physics beyond the standard model. After deriving some useful geometric results for Voronoi tessellations on perfect grids, we propose several algorithms for tagging the Voronoi cells in the vicinity of kinematic edges in real data. We show that the efficiency is improved by the addition of a few Voronoi relaxation steps via Lloyd's method. By preserving the maximum spatial resolution of the data, Voronoi methods can be a valuable addition to the data analysis toolkit at the LHC.Comment: 6 pages, 7 figure

The study of gravitational collapse model in higher dimensional space-time

We investigate the end state of the gravitational collapse of an inhomogeneous dust cloud in higher dimensional space-time. The naked singularities are shown to be developing as the final outcome of non-marginally bound collapse. The naked singularities are found to be gravitationally strong in the sense of Tipler .Comment: 6 Latex pages, No figure, Revtex styl

Tripartite Entanglement versus Tripartite Nonlocality in Three-Qubit Greenberger-Horne-Zeilinger-Class States

We analyze the relationship between tripartite entanglement and genuine tripartite nonlocality for three-qubit pure states in the Greenberger-Horne-Zeilinger class. We consider a family of states known as the generalized Greenberger-Horne-Zeilinger states and derive an analytical expression relating the three-tangle, which quantifies tripartite entanglement, to the Svetlichny inequality, which is a Bell-type inequality that is violated only when all three qubits are nonlocally correlated. We show that states with three-tangle less than 1/2 do not violate the Svetlichny inequality. On the other hand, a set of states known as the maximal slice states does violate the Svetlichny inequality, and exactly analogous to the two-qubit case, the amount of violation is directly related to the degree of tripartite entanglement.We discuss further interesting properties of the generalized Greenberger-Horne-Zeilinger and maximal slice states

Quasi-spherical gravitational collapse and the role of initial data, anisotropy and inhomogeneity

In this paper, the role of anisotropy and inhomogeneity has been studied in quasi-spherical gravitational collapse. Also the role of initial data has been investigated in characterizing the final state of collapse. Finally, a linear transformation on the initial data set has been presented and its impact has been discussed.Comment: RevTex, 7 Latex pages, No figure