Intermediate Asymptotics of the Kerr Quasinormal Spectrum

We study analytically the quasinormal mode spectrum of near-extremal (rotating) Kerr black holes. We find an analytic expression for these black-hole resonances in terms of the black-hole physical parameters: its Bekenstein-Hawking temperature T_{BH} and its horizon's angular velocity \Omega, which is valid in the intermediate asymptotic regime 1<<\omega<<1/T_{BH}.Comment: 4 page

First-order formalism and dark energy

This work deals with cosmological models driven by real scalar field, described by standard dynamics in generic spherical, flat, and hyperbolic geometries. We introduce a first-order formalism, which shows how to relate the potential that specifies the scalar field model to Hubble's parameter in a simple and direct manner. Extensions to tachyonic dynamics, and to two or more real scalar fields are also presented.Comment: 7 pages, 3 figure

f(R)-Brane

We investigate the existence of brane solutions in braneworld scenarios described by real scalar field in the presence of modified $f(R)$ gravity with a single extra dimension. In the case of constant curvature, we obtain first-order differential equations which solve the equations of motion and ease the search for explicit analytical solutions. Several examples of current interest are investigated to illustrate the results of the present work.Comment: 10 pages, accepted to Phys. Lett.

Perturbations of Dark Matter Gravity

Until recently the study of the gravitational field of dark matter was primarily concerned with its local effects on the motion of stars in galaxies and galaxy clusters. On the other hand, the WMAP experiment has shown that the gravitational field produced by dark matter amplifies the higher acoustic modes of the CMBR power spectrum, more intensely than the gravitational field of baryons. Such a wide range of experimental evidences from cosmology to local gravity suggests the necessity of a comprehensive analysis of the dark matter gravitational field per se, regardless of any other attributes that dark matter may eventually possess. In this paper we introduce and apply Nash's theory of perturbative geometry to the study of the dark matter gravitational field alone, in a higher-dimensional framework. It is shown that the dark matter gravitational perturbations in the early universe can be explained by the extrinsic curvature of the standard cosmology. Together with the estimated presence of massive neutrinos, such geometric perturbation is compatible not only with the observed power spectrum in the WMAP experiment but also with the most recent data on the accelerated expansion of the universe. It is possible that the same structure formation exists locally, such as in the cases of young galaxies or in cluster collisions. In most other cases it seems to have ceased when the extrinsic curvature becomes negligible, leading to Einstein's equations in four dimensions. The slow motion of stars in galaxies and the motion of plasma substructures in nearly colliding clusters are calculated with the geodesic equation for a slowly moving object in a gravitational field of arbitrary strength.Comment: 10 pages, 5 figure

The earliest settlers' antiquity and evolutionary history of Indian populations: evidence from M2 mtDNA lineage

BACKGROUND: The "out of Africa" model postulating single "southern route" dispersal posits arrival of "Anatomically Modern Human" to Indian subcontinent around 66–70 thousand years before present (kyBP). However the contributions and legacy of these earliest settlers in contemporary Indian populations, owing to the complex past population dynamics and later migrations has been an issue of controversy. The high frequency of mitochondrial lineage "M2" consistent with its greater age and distribution suggests that it may represent the phylogenetic signature of earliest settlers. Accordingly, we attempted to re-evaluate the impact and contribution of earliest settlers in shaping the genetic diversity and structure of contemporary Indian populations; using our newly sequenced 72 and 4 published complete mitochondrial genomes of this lineage. RESULTS: The M2 lineage, harbouring two deep rooting subclades M2a and M2b encompasses approximately one tenth of the mtDNA pool of studied tribes. The phylogeographic spread and diversity indices of M2 and its subclades among the tribes of different geographic regions and linguistic phyla were investigated in detail. Further the reconstructed demographic history of M2 lineage as a surrogate of earliest settlers' component revealed that the demographic events with pronounced regional variations had played pivotal role in shaping the complex net of populations phylogenetic relationship in Indian subcontinent. CONCLUSION: Our results suggest that tribes of southern and eastern region along with Dravidian and Austro-Asiatic speakers of central India are the modern representatives of earliest settlers of subcontinent. The Last Glacial Maximum aridity and post LGM population growth mechanised some sort of homogeneity and redistribution of earliest settlers' component in India. The demic diffusion of agriculture and associated technologies around 3 kyBP, which might have marginalized hunter-gatherer, is coincidental with the decline of earliest settlers' population during this period

First-order formalism for dark energy and dust

This work deals with first-order formalism for dark energy and dust in standard cosmology, for models described by real scalar field in the presence of dust in spatially flat space. The field dynamics may be standard or tachyonic, and we show how the equations of motion can be solved by first-order differential equations. We investigate a model to illustrate how the dustlike matter may affect the cosmic evolution using this framework.Comment: 5 pages, 1 figure; title changed, new author included, discussions extended, references added, version to appear in EPJ

Teratogenicity of depleted uranium aerosols: A review from an epidemiological perspective

BACKGROUND: Depleted uranium is being used increasingly often as a component of munitions in military conflicts. Military personnel, civilians and the DU munitions producers are being exposed to the DU aerosols that are generated. METHODS: We reviewed toxicological data on both natural and depleted uranium. We included peer reviewed studies and gray literature on birth malformations due to natural and depleted uranium. Our approach was to assess the "weight of evidence" with respect to teratogenicity of depleted uranium. RESULTS: Animal studies firmly support the possibility that DU is a teratogen. While the detailed pathways by which environmental DU can be internalized and reach reproductive cells are not yet fully elucidated, again, the evidence supports plausibility. To date, human epidemiological data include case examples, disease registry records, a case-control study and prospective longitudinal studies. DISCUSSION: The two most significant challenges to establishing a causal pathway between (human) parental DU exposure and the birth of offspring with defects are: i) distinguishing the role of DU from that of exposure to other potential teratogens; ii) documentation on the individual level of extent of parental DU exposure. Studies that use biomarkers, none yet reported, can help address the latter challenge. Thoughtful triangulation of the results of multiple studies (epidemiological and other) of DU teratogenicity contributes to disentangling the roles of various potentially teratogenic parental exposures. This paper is just such an endeavor. CONCLUSION: In aggregate the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU

Laser surface texturing of gray cast iron for improving tribological behavior

Laser surface texturing process involves creation of microfeatures, e.g., tiny dimples, usually distributed in a certain pattern, covering only a fraction of the surface of the material that is being treated. The process offers several advantages for tribological applications, including improved load capacity, wear resistance, lubrication lifetime, and reduced friction coefficient. In the present study, the surface modification of gray cast iron, using millisecond (\u3bb\ua0=\ua01,064\ua0nm), nanosecond (\u3bb\ua0=\ua01,064\ua0nm) and femtosecond (\u3bb\ua0=\ua0800\ua0nm) pulse duration laser irradiation, is adopted to establish a particular geometrical pattern with dimple features and dimensions, to improve wear and friction behavior. The effect of various laser processing parameters, including laser pulse energy, pulse duration and processing speed, on the performance characteristics of the laser-treated samples is investigated. The microtextured surfaces were produced on gray cast iron using different millisecond (0.5\ua0ms), nanosecond (40\ua0ns) and femtosecond (120\ua0fs) laser source with the dimple depth between 3 and 15\ua0\u3bcm. The coefficient of friction for the untextured surface was ~0.55, millisecond laser textured ~0.31, nanosecond laser textured ~0.02 and femtosecond laser ~0.01, under normal force of 50\ua0N and sliding speed of 63\ua0mm/s. Surface texturing of the gray cast iron surface using femtosecond pulse duration resulted in significant improvement in wear resistance in comparison to the untextured as well as millisecond and nanosecond laser-textured surface. \ua9 2014 Springer-Verlag Berlin Heidelberg.Peer reviewed: YesNRC publication: Ye

Assessment of the Reliability of the Indian Tsunami Early Warning System

This paper analyses the reliability of the Indian Tsunami Early Warning System (ITEWS), comprising a 24 × 7 manned and automated center capable of monitoring the seismic, open sea water level and coastal tide levels and disseminating tsunami bulletins with the aid of proven prerun scenario models during a tsunamigenic earthquake. Since its inception in 2007, the ITEWS has undergone technological maturity with reliability as the prime objective. The system is expected to be in operation throughout the year and alerting the entire Indian Ocean rim countries in the event of a tsunami. Based on International Electrotechnical Commission (IEC) 61508 standards and field failure data, quantitative reliability modeling is done for the subsystems, and it is found that the seismic network, tsunami buoy network, and distress information dissemination systems conform to Safety Integrity Level SIL4, while tide gauge stations conform to SIL4 with a maintenance interval of 45 days. In case of the tsunami buoy network, the failure of one tsunami buoy degrades the network to SIL3 and needs to be restored within 8 months. The study provides confidence on ITEWS’s reliable support to tsunami early warning