Comment on "Relativistic extension of shape-invariant potentials"

This comment directs attention to some fails of the Alhaidari approach to solve relativistic problems. It is shown that his gauge considerations are way off the mark and that the class of exactly solvable relativistic problems is not so enlarged as Alhaidari thinks it is

S-Matrix on the Moyal Plane: Locality versus Lorentz Invariance

Twisted quantum field theories on the Groenewold-Moyal plane are known to be non-local. Despite this non-locality, it is possible to define a generalized notion of causality. We show that interacting quantum field theories that involve only couplings between matter fields, or between matter fields and minimally coupled U(1) gauge fields are causal in this sense. On the other hand, interactions between matter fields and non-abelian gauge fields violate this generalized causality. We derive the modified Feynman rules emergent from these features. They imply that interactions of matter with non-abelian gauge fields are not Lorentz- and CPT-invariant.Comment: 15 pages, LaTeX, 1 figur

Spectrum of the three dimensional fuzzy well

We develop the formalism of quantum mechanics on three dimensional fuzzy space and solve the Schr\"odinger equation for a free particle, finite and infinite fuzzy wells. We show that all results reduce to the appropriate commutative limits. A high energy cut-off is found for the free particle spectrum, which also results in the modification of the high energy dispersion relation. An ultra-violet/infra-red duality is manifest in the free particle spectrum. The finite well also has an upper bound on the possible energy eigenvalues. The phase shifts due to scattering around the finite fuzzy potential well have been calculated

The role of social tags in web resource discovery: an evaluation of user-generated keywords

Social tags are user generated metadata and play vital role in Information Retrieval (IR) of web resources. This study is an attempt to determine the similarities between social tags extracted from LibraryThing and Library of Congress Subject Headings (LCSH) for the titles chosen for study by adopting Cosine similarity method. The result shows that social tags and controlled vocabularies are not quite similar due to the free nature of social tags mostly assigned by users whereas controlled vocabularies are attributed by subject experts. In the context of information retrieval and text mining, the Cosine similarity is most commonly adopted method to evaluate the similarity of vectors as it provides an important measurement in terms of degree to know how similar two documents are likely to be in relation to their subject matter. The LibraryThing tags and LCSH are represented in vectors to measure Cosine similarity between them

Unusual occurrence of large size oilsardine (Sardinella longiceps) at Karwar, Uttar Kannada coast of Karnataka

The oilsardine, Sardinella longiceps (Valenciennes, 1847), is a major pelagic fishery resource of Malabar and Konkan coast. At Karwar, the fishing season for oilsardine is from August-May and the peak season is from October to March. During the current year, after the ban period, the oilsardine fishery by the purseseine boats started from the first of August, 2011

E-cordial Labeling for Cartesian Product of Some Graphs

We investigate E-cordial labeling for some cartesian product of graphs. We prove that the graphs Kn × P2 and Pn × P2 are E-cordial for n even while Wn × P2 andK1,n × P2 are E-cordial for n odd. Key words: E-Cordial labeling; Edge graceful labeling; Cartesian produc

Domination Integrity of Some Path Related Graphs

The stability of a communication network is one of the important parameters for network designers and users. A communication network can be considered to be highly vulnerable if the destruction of a few elements cause large damage and only few members are able to communicate. In a communication network several vulnerability measures like binding number, toughness, scattering number, integrity, tenacity, edge tenacity and rupture degree are used to determine the resistance of network to the disruption after the failure of certain nodes (vertices) or communication links (edges). Domination theory also provides a model to measure the vulnerability of a graph network. The domination integrity of a simple connected graph is one such measure. Here we determine the domination integrity of square graph of path as well as the graphs obtained by composition (lexicographic product) of two paths

Relativistic Green functions in a plane wave gravitational background

We consider a massive relativistic particle in the background of a gravitational plane wave. The corresponding Green functions for both spinless and spin 1/2 cases, previously computed by A. Barducci and R. Giachetti \cite{Barducci3}, are reobtained here by alternative methods, as for example, the Fock-Schwinger proper-time method and the algebraic method. In analogy to the electromagnetic case, we show that for a gravitational plane wave background a semiclassical approach is also sufficient to provide the exact result, though the lagrangian involved is far from being a quadratic one.Comment: Last paper by Professor Arvind Narayan Vaidya, 18 pages, no figure

Asymptotically Flat Radiating Solutions in Third Order Lovelock Gravity

In this paper, we present an exact spherically symmetric solution of third order Lovelock gravity in $n$ dimensions which describes the gravitational collapse of a null dust fluid. This solution is asymptotically (anti-)de Sitter or flat depending on the choice of the cosmological constant. Using the asymptotically flat solution for $n \geq 7$ with a power-law form of the mass as a function of the null coordinate, we present a model for a gravitational collapse in which a null dust fluid radially injects into an initially flat and empty region. It is found that a naked singularity is inevitably formed whose strength is different for the $n = 7$ and $n \geq 8$ cases. In the $n=7$ case, the limiting focusing condition for the strength of curvature singularity is satisfied. But for $n \geq 8$, the strength of curvature singularity depends on the rate of increase of mass of the spacetime. These considerations show that the third order Lovelock term weakens the strength of the curvature singularity.Comment: 15 pages, no figure, references added, two appendix adde

Energy and momentum of cylindrical gravitational waves. II

Recently Nathan Rosen and the present author obtained the energy and momentum densities of cylindrical gravitational waves in Einstein's prescription and found them to be finite and reasonable. In the present paper we calculate the same in prescriptions of Tolman as well as Landau and Lifshitz and discuss the results.Comment: 8 pages, LaTex, To appear in Pramana- J. Physic