Black Hole Mass Limits for Optically Dark X-ray Bright Sources in Elliptical Galaxies

Estimation of the black hole mass in bright X-ray sources of nearby galaxies is crucial to the understanding of these systems and their formation. However, the present allowed black hole mass range spans five order of magnitude (10Msun < M < 10^5 Msun) with the upper limit obtained from dynamical friction arguments. We show that the absence of a detectable optical counterpart for some of these sources, can provide a much more stringent upper limit. The argument is based only on the assumption that the outer regions of their accretion disks is a standard one. Moreover, such optically dark X-ray sources cannot be foreground stars or background active galactic nuclei, and hence must be accreting systems residing within their host galaxies. As a demonstration we search for candidates among the point-like X-ray sources detected with Chandra in thirteen nearby elliptical galaxies. We use a novel technique to search for faint optical counterparts in the HST images whereby we subtract the bright galaxy light based on isophotal modeling of the surface brightness. We show that for six sources with no detectable optical emission at the 3$-$sigma level, their black hole masses M_{BH} < 5000Msun. In particular, an ultra-luminous X-ray source (ULX) in NGC 4486 has M_{BH} < 1244 Msun. We discuss the potential of this method to provide stringent constraints on the black hole masses, and the implications on the physical nature of these sources.Comment: 11 Pages, 1 figure, Accepted for publication in Ap

Comparison of History Effects in Magnetization in Weakly pinned Crystals of high-TcT_c and low-Tc_c Superconductors

A comparison of the history effects in weakly pinned single crystals of a high $T_c$ YBa$_2$Cu$_3$O$_{7 - \delta}$ (for H $\parallel$ c) and a low $T_c$ Ca$_3$Rh$_4$Sn$_{13}$, which show anomalous variations in critical current density $J_c(H)$ are presented via tracings of the minor magnetization hysteresis loops using a vibrating sample magnetometer. The sample histories focussed are, (i) the field cooled (FC), (ii) the zero field cooled (ZFC) and (iii) an isothermal reversal of field from the normal state. An understanding of the results in terms of the modulation in the plastic deformation of the elastic vortex solid and supercooling across order-disorder transition is sought.Comment: Presented in IWCC-200

Renewable energy based microgrid system sizing and energy management for green buildings

The objective of this paper is to model a hybrid power system for buildings, which is technically feasible and economically optimal. With a view to promote renewable energy sources, photovoltaics and wind turbines are integrated with the grid connected building. The system is modeled and the optimal system configuration is estimated with the help of hybrid optimization model for electric renewables (HOMER). The logic is illustrated with a case study based on the practical data of a building located in southern India. This building is associated with 3.4 MWh/day priority load (peak load as 422 kW), as well as 3.3 MWh/day deferrable load (peak load as 500 kW). Sensitivity analysis is performed to deal with uncertainties such as the increase in electricity consumption and grid tariff, environmental changes, etc. From the simulation result, it is observed that the designed system is cost effective and environment friendly, which leads to 6.18 % annual cost savings and reduces CO2 emissions by 38.3 %. Sensitivity results indicate that the system is optimal and adaptable in a certain range of unanticipated variances with respect to best estimated value. Finally, an energy management strategy is developed for the optimal system to ensure reliable power during contingency and disturbances. The green and hybrid power system designed can be adaptable to any critical and large consumers of urban buildings

Key Aspects of Smart Grid Design for Distribution System Automation: Architecture and Responsibilities ☆

In the conventional distribution network, systems designed for the control of individual constituents are autonomous with each other with respect to architectures and controlling. Thus, centralized control and integrated functionality are the major challenges faced by the distribution system operators. To overcome these issues, the term “distribution system automation” came into picture by using information and communications technology (ICT)as a resolution that integrate all the critical constituents of a distribution system. This develops a smart environment at power distribution level, called as “smart microgrid” that can optimize the system economy and improve the system resiliency. The major challenge lies in distribution system automation is the selection of proper architecture and communications. In view of all these aspects, this paper present an overview of distribution system automation as a part of smartgrid initiatives and its important features viz., architecture layout and responsibilities

Association of telomere shortening with impaired glucose tolerance and diabetic macroangiopathy

Objective: Shortening of telomere length has been reported in several conditions including Type 2 diabetes and atherosclerosis. The aims of this study were (1) to assess whether telomere shortening occurs at the stage of pre-diabetes, i.e., impaired glucose tolerance (IGT) and (2) whether telomere shortening was greater in Type 2 diabetic subjects with atherosclerotic plaques. Methods: Subjects with impaired glucose tolerance (IGT) (n = 30), non-diabetic control subjects (n = 30), Type 2 diabetic patients without (n = 30) and with atherosclerotic plaques (n = 30) were selected from the Chennai Urban Rural Epidemiology Study (CURES), an ongoing epidemiological population-based study. Southern-blot analysis was used to determine mean terminal restriction fragment (TRF) length, a measure of average telomere size, in leukocyte DNA. Levels of thiobarbituric acid reactive substances (TBARS), protein carbonyl content (PCO) and high sensitive C-reactive protein (hs-CRP) were measured by standard methodologies. Carotid intima-media thickness (IMT) was assessed by high resolution B-mode ultrasonography. Results: The mean (±S.E.) TRF lengths were significantly lower in IGT subjects (6.97 ± 0.3 kb; p = 0.002) and lower still in Type 2 diabetic subjects without plaques (6.21 ± 0.2; p = 0.0001) and lowest in Type 2 diabetic subjects with atherosclerotic plaques (5.39 ± 0.2; p = 0.0001) when compared to control subjects (8.7 ± 0.5). In IGT subjects, TRF length was positively correlated to HDL cholesterol and negatively correlated to glycated hemoglobin (HbA1c), TBARS, PCO, HOMA-IR and IMT. In multiple linear regression analysis, presence of diabetes, HDL cholesterol and increased TBARS levels appear as significant determinants of telomere shortening. Conclusion: Telomere shortening is seen even at the stage of IGT. Among subjects with Type 2 diabetes, those with atherosclerotic plaques had greater shortening of telomere length compared to those without plaques

Stable and Metastable vortex states and the first order transition across the peak effect region in weakly pinned 2H-NbSe_2

The peak effect in weakly pinned superconductors is accompanied by metastable vortex states. Each metastable vortex configuration is characterized by a different critical current density J_c, which mainly depends on the past thermomagnetic history of the superconductor. A recent model [G. Ravikumar, et al, Phys. Rev. B 61, R6479 (2000)] proposed to explain the history dependent J_c postulates a stable state of vortex lattice with a critical current density J_c^{st}, determined uniquely by the field and temperature. In this paper, we present evidence for the existence of the stable state of the vortex lattice in the peak effect region of 2H-NbSe_2. It is shown that this stable state can be reached from any metastable vortex state by cycling the applied field by a small amplitude. The minor magnetization loops obtained by repeated field cycling allow us to determine the pinning and "equilibrium" properties of the stable state of the vortex lattice at a given field and temperature unambiguously. The data imply the occurence of a first order phase transition from an ordered phase to a disordered vortex phase across the peak effect.Comment: 20 pages, 10 figures. Corresponding author: S. Ramakrishna

Estimation and Testing in Type I Generalized Half Logistic Distribution

A generalization of the half logistic distribution is developed through exponentiation of its cumulative distribution function and termed the Type I Generalized Half Logistic Distribution (GHLD). GHLD’s distributional characteristics and parameter estimation using maximum likelihood and modified maximum likelihood methods are presented with comparisons. Comparison of Type I GHLD and the exponential distribution is conducted via likelihood ratio criterion