Quaternionic Hyperbolic Fenchel-Nielsen Coordinates

Let $Sp(2,1)$ be the isometry group of the quaternionic hyperbolic plane ${{\bf H}_{\mathbb H}}^2$. An element $g$ in $Sp(2,1)$ is `hyperbolic' if it fixes exactly two points on the boundary of ${{\bf H}_{\mathbb H}}^2$. We classify pairs of hyperbolic elements in $Sp(2,1)$ up to conjugation. A hyperbolic element of $Sp(2,1)$ is called `loxodromic' if it has no real eigenvalue. We show that the set of $Sp(2,1)$ conjugation orbits of irreducible loxodromic pairs is a $(\mathbb C {\mathbb P}^1)^4$-bundle over a topological space that is locally a semi-analytic subspace of ${\mathbb R}^{13}$. We use the above classification to show that conjugation orbits of `geometric' representations of a closed surface group (of genus $g \geq 2$) into $Sp(2,1)$ can be determined by a system of $42g-42$ real parameters. Further, we consider the groups $Sp(1,1)$ and $GL(2, {\mathbb H})$. These groups also act by the orientation-preserving isometries of the four and five dimensional real hyperbolic spaces respectively. We classify conjugation orbits of pairs of hyperbolic elements in these groups. These classifications determine conjugation orbits of `geometric' surface group representations into these groups.Comment: major structural revision. Restructured the exposition. Introduction re-writte

Recent Techniques in Echocardiography: Two-Dimensional Echocardiography

Conventional M-mode echocardiography is a widely used noninvasive diagnostic technique. It allows bedside assessment of cardiac chamber dimensions, valve motion and left ventricular function. The limitations of this technique are that it (1) provides only a one-dimensional (icepick) view of the heart, (2) displays cardiac structures in an unfamiliar form that bears no resemblance to cardiac anatomy, and (3) does not provide information regarding spatial orientation of cardiac structures. These limitations led to the development of two-dimensional (2-D) real-time echocardiography in the last decade. The 2-D echo allows simultaneous visualization of cardiac structures in real time through multiple planes

On the highly reddened members in 6 young galactic star clusters - a multiwavelength study

The spectral and reddening properties of 211 highly reddened proper motion members with $V < 15$ mag in 6 young galactic star clusters are investigated using low resolution spectroscopic, broad-band $UBVRIJHK$ and mid-IR data. We report emission features in CaII HK and HI lines for a sample of 29 stars including 11 stars reported for the first time and also provide either a new or more reliable spectral class for a sample of 24 stars. CaII triplet width measurements are used to indicate the presence of an accretion disk for a dozen stars and to hint luminosity for a couple of stars. On the basis of spectral features, near-IR excesses, dereddened color-color diagrams and mid-IR spectral indices we identify a group of 28 pre-main sequence cluster members including 5 highly probable Herbig Ae/Be and 6 classical T Tauri star. A total of 25 non-emission MS stars, amounting to $\sim$ 10 % early type MS members, appears to show Vega-like characteristics or are precursors to such a phenomenon. The various membership indicators suggest that $\sim$ 16% of the PM members are non-members. A significant fraction ($>$70%) of program stars in NGC 1976, NGC 2244, NGC 6530 and NGC 6611 show anomalous reddening with $R_{V}$ = $5.11\pm0.11$, $3.60\pm0.05$, $3.87\pm0.05$ and $3.56\pm 0.02$, respectively, indicating the presence of grain size dust larger than that typical to the diffuse medium. A small number of stars in NGC 1976, NGC 2244 and NGC 6611 also show normal behavior while the cluster NGC 6823 appears to have a normal reddening. Three highly luminous late type giants, one in NGC 2244 and two in NGC 6530, appears to be member and are in post-hydrogen-core-burning stages suggesting a prolonged duration ($\sim$ 25 Myrs) of star formation.Comment: 12 pages, 13 figures, submitted to MNRA

Estimation of the Extragalactic Background Light using TeV Observations of BL~Lacs

The very high energy (VHE) gamma ray spectral index of high energy peaked blazars correlates strongly with its corresponding redshift whereas no such correlation is observed in the X-ray or the GeV bands. We attribute this correlation to a result of photon-photon absorption of TeV photons with the extragalactic background light (EBL) and utilizing this, we compute the allowed flux range for the EBL, which is independent of previous estimates. The observed VHE spectrum of the sources in our sample can be well approximated by a power-law, and if the de-absorbed spectrum is also assumed to be a power law, then we show that the spectral shape of EBL will be $\epsilon n(\epsilon) \sim k log(\frac{\epsilon}{\epsilon_p})$. We estimate the range of values for the parameters defining the EBL spectrum, $k$ and $\epsilon_p$, such that the correlation of the intrinsic VHE spectrum with redshift is nullified. The estimated EBL depends only on the observed correlation and the assumption of a power law source spectrum. Specifically, it does not depend on the spectral modeling or radiative mechanism of the sources, nor does it depend on any theoretical shape of the EBL spectrum obtained through cosmological calculations. The estimated EBL spectrum is consistent with the upper and lower limits imposed by different observations. Moreover, it also agrees closely with the theoretical estimates obtained through cosmological evolution models.Comment: 28 pages, 5 figures, Accepted for publication in The Astrophysical Journa

Co-citation Analysis: An Overview

This article gives an overview of co-citation analysis and its applications in tracking the linkages among the intellectual works and mapping the evolutionary structure of scientific disciplines. It also focuses on the features, interface, terminology used, merits and demerits of co-citation based online database applications

Marketing System and Efficiency of Indian Major Carps in India

The Kolleru Lake area (KLA) in Andhra Pradesh being a predominant centre for carp culture is known as the ‘Carp Pocket of India’. This paper has described the highly efficient fish marketing system prevalent in the KLA and has compared it with the marketing of Indian Major Carps (IMC) in other major aquaculture states like West Bengal and Orissa and marine states like Maharashtra and Tamil Nadu. The marketing channels, market intermediaries, price spread and marketing efficiency have been presented. A comparison of the marketing channels at several fish markets has revealed that the price spread for IMC from Kolleru is highest at the Mumbai market and lowest at the Coimbatore market. Consequently, fishermen’s share in consumer price has been found highest for Coimbatore at 61.54 per cent and lowest for Mumbai at 47.06 per cent. Similarly, the marketing efficiency was the highest for Coimbatore at 2.60 and lowest for Mumbai at 1.89. Retail price for KLA carps has been found lower than locally cultured carps at various areas, reflecting the efficiency of the marketing channel in providing cheap fish transported over large distances and through a large number of intermediaries. The reasons for the efficient IMC marketing system at KLA have been discussed and the study has recommended the development of efficient fish marketing system in other parts of the country.Agricultural and Food Policy,

Discrete simulations of spatio-temporal dynamics of small water bodies under varied stream flow discharges

International audienceSpatio-temporal patterns of small water bodies (SWBs) under the influence of temporally varied stream flow discharge are simulated in discrete space by employing geomorphologically realistic expansion and contraction transformations. Cascades of expansion-contraction are systematically performed by synchronizing them with stream flow discharge simulated via the logistic map. Templates with definite characteristic information are defined from stream flow discharge pattern as the basis to model the spatio-temporal organization of randomly situated surface water bodies of various sizes and shapes. These spatio-temporal patterns under varied parameters (?s) controlling stream flow discharge patterns are characterized by estimating their fractal dimensions. At various ?s, nonlinear control parameters, we show the union of boundaries of water bodies that traverse the water body and non-water body spaces as geomorphic attractors. The computed fractal dimensions of these attractors are 1.58, 1.53, 1.78, 1.76, 1.84, and 1.90, respectively, at ?s of 1, 2, 3, 3.46, 3.57, and 3.99. These values are in line with general visual observations

Optical Observations and Multiband Modelling of the Afterglow of GRB 041006: Evidence of A Hard Electron Energy Spectrum

We present the CCD Cousins R band photometric observations of the afterglow of GRB 041006. The multiband afterglow evolution is modelled using an underlying `hard' electron energy spectrum with a $p_1 \sim 1.3$. The burst appears to be of very low energy ($E \sim 10^{48}$ ergs) confined to a narrow cone of opening angle $\theta \sim 2.3^{\circ}$. The associated supernova is compared with SN1998bw and is found to be brighter.Comment: Accepted for publication in Bull. Astr. Soc. India (BASI