Investigating the cores of fossil systems with Chandra

We investigate the cores of fossil galaxy groups and clusters (`fossil systems') using archival Chandra data for a sample of 17 fossil systems. We determined the cool-core fraction for fossils via three observable diagnostics, the central cooling time, cuspiness, and concentration parameter. We quantified the dynamical state of the fossils by the X-ray peak/brightest cluster galaxy (BCG), and the X-ray peak/emission weighted centre separations. We studied the X-ray emission coincident with the BCG to detect the presence of potential thermal coronae. A deprojection analysis was performed for z < 0.05 fossils to obtain cooling time and entropy profiles, and to resolve subtle temperature structures. We investigated the Lx-T relation for fossils from the 400d catalogue to see if the scaling relation deviates from that of other groups. Most fossils are identified as cool-core objects via at least two cool-core diagnostics. All fossils have their dominant elliptical galaxy within 50 kpc of the X-ray peak, and most also have the emission weighted centre within that distance. We do not see clear indications of a X-ray corona associated with the BCG unlike that has been observed for some other objects. Fossils do not have universal temperature profiles, with some low-temperature objects lacking features that are expected for ostensibly relaxed objects with a cool-core. The entropy profiles of the z < 0.05 fossil systems can be well-described by a power law model, albeit with indices smaller than 1. The 400d fossils Lx-T relation shows indications of an elevated normalisation with respect to other groups, which seems to persist even after factoring in selection effects.Comment: Accepted for publication in Astronomy and Astrophysic

HI Fluctuations at Large Redshifts: II - the Signal Expected for GMRT

For the GMRT, we calculate the expected signal from redshifted HI emission at two frequency bands centered at 610 and 325 MHz. The study focuses on the visibility-visibility cross-correlations, proposed earlier as the optimal statistical estimator for detecting and analyzing this signal. These correlations directly probe the power spectrum of density fluctuations at the redshift where the radiation originated, and thereby provide a method for studying the large scale structures at large redshifts. We present detailed estimates of the correlations expected between the visibilities measured at different baselines and frequencies. Analytic fitting formulas representing the salient features of the expected signal are also provided. These will be useful in planning observations and deciding an optimal strategy for detecting this signal.Comment: 16 pages including 7 figures, published in JAp

Inheritance of parthenocarpy in gynoecious cucumber (Cucumis sativus L.) cultivar PPC-2

The gynoecious and parthenocarpic inbred line, Pant Parthenocarpic Cucumber-2 (PPC- 2) was crossed with Indian monoecious and non-parthenocarpic cultivar Pusa Uday to develop F1, F2, B1 and B2 to determine the inheritance of parthenocarpy.The crop was grown under insect proof net house of 40 mesh. The pistillate buds were covered using butter paper bags before anthesis to prevent out-crossing.The observations were recorded separately for the development of early parthenocarpic fruits (i.e.1-7th nodes), late parthenocarpy (8th and above nodes) and non-parthenocarpic fruits. In F1 generation, out of 40 plants screened, 2 plants produced parthenocarpic fruits at lower nodes (1-7th nodes), 37 plants produced parthenocarpic fruits at upper nodes (8th and above), whereas,only 1 plant that did not produced any fruit was considered as non-parthenocarpic. The segregation of F2 population and test crosses for parthenocarpic fruit development suggested that parthenocarpy in gynoecious and parthenocarpic cucumber line PPC-2 is under the control of incomplete dominant gene

Estimating Wind Stress at the Ocean Surface From Scatterometer Observations

Abstract—Wind stress is the most important ocean forcing for driving tropical surface currents. Stress can be estimated from scatterometer-reported wind measurements at 10 m that have been extrapolated to the surface, assuming a neutrally stable atmosphere and no surface current. Scatterometer calibration is designed to account for the assumption of neutral stability; however, the assumption of a particular sea state and negligible current often introduces an error in wind stress estimations. Since the fundamental scatterometer measurement is of the surface radar backscatter (sigma-0) which is related to surface roughness and, thus, stress, we develop a method to estimate wind stress directly from the scatterometer measurements of sigma-0 and their associated azimuth angle and incidence angle using a neural network approach. We compare the results with in situ estimations and observe that the wind stress estimations from this approach are more accurate compared with those obtained from the conventional estimations using 10-m-height wind measurements. Index Terms—Atmospheric stability, neutral stability, scatterometer, wind stress. I

HI Fluctuations at Large Redshifts: I--Visibility correlation

We investigate the possibility of probing the large scale structure in the universe at large redshifts by studying fluctuations in the redshifted 1420 MHz emission from the neutral hydrogen (HI) at early epochs. The neutral hydrogen content of the universe is known from absorption studies for z<4.5. The HI distribution is expected to be inhomogeneous in the gravitational instability picture and this inhomogeneity leads to anisotropy in the redshifted HI emission. The best hope of detecting this anisotropy is by using a large low-frequency interferometric instrument like the Giant Meter-Wave Radio Telescope (GMRT). We calculate the visibility correlation function <V_nu(u) V_nu'(u)> at two frequencies nu and nu' of the redshifted HI emission for an interferometric observation. In particular we give numerical results for the two GMRT channels centered around nu =325 and 610 MHz from density inhomogeneity and peculiar velocity of the HI distribution. The visibility correlation is ~10^-9 to 10^-10 Jy^2. We calculate the signal-to-noise for detecting the correlation signal in the presence of system noise and show that the GMRT might detect the signal for integration times ~ 100 hrs. We argue that the measurement of visibility correlation allows optimal use of the uncorrelated nature of the system noise across baselines and frequency channels.Comment: 17 pages, 2 figures, Submitted to JA

HI power spectrum of the spiral galaxy NGC628

We have measured the HI power spectrum of the nearly face-on spiral galaxy NGC628 (M74) using a visibility based estimator. The power spectrum is well fitted by a power law $P(U)=AU^{\alpha}$, with $\alpha =- 1.6\pm0.2$ over the length scale $800 {\rm pc} {\rm to} 8 {\rm kpc}$. The slope is found to be independent of the width of the velocity channel. This value of the slope is a little more than one in excess of what has been seen at considerably smaller length scales in the Milky-Way, Small Magellanic Cloud (LMC), Large Magellanic Cloud (SMC) and the dwarf galaxy DDO210. We interpret this difference as indicating a transition from three dimensional turbulence at small scales to two dimensional turbulence in the plane of the galaxy's disk at length scales larger than galaxy's HI scale height. The slope measured here is similar to that found at large scales in the LMC. Our analysis also places an upper limit to the galaxy's scale height at $800\ {\rm pc}$ .Comment: 4 Pages, 2 Figures, 1 Table. Accepted for Publication in MNRAS LETTER

Foregrounds for redshifted 21 cm studies of reionization: GMRT 153 MHz observations

Foreground subtraction is the biggest challenge for future redshifted 21 cm observations to probe reionization. We use a short GMRT observation at 153 MHz to characterize the statistical properties of the background radiation across ~ one degree to sub-arcminutes angular scales, and across a frequency band of 5 MHz with 62.5 kHz resolution. The statistic we use is the visibility correlation function, or equivalently the angular power spectrum C_l. We present the results obtained from using relatively unsophisticated, conventional data calibration procedures. We find that even fairly simple minded calibration allows one to estimate the visibility correlation function at a given frequency V_2(U,0). From our observations we find that V_2(U,0) is consistent with foreground model predictions at all angular scales except the largest ones probed by our observations where the the model predictions are somewhat in excess. On the other hand the visibility correlation between different frequencies kappa(U, Delta nu), seems to be much more sensitive to calibration errors. We find a rapid decline in kappa(U, Delta nu), in contrast with the prediction of less than 1 % variation across 2.5 MHz. In this case however, it seems likely that a substantial part of the discrepancy may be due to limitations of data reduction procedures.Comment: 10 pages, 7 figures, 1 table, Accepted for Publication in MNRA

Negotiating Access Control Policies Between Autonomous Domains

Autonomous policy domains often need to share resources to accomplish a common task. To do this they must negotiate a common access control policy to the shared resources. We use mathematical techniques from game theory to show that the outcome of such negotiations can often be predicted from the distribution of power among the participants, independent of the actual mechanics of negotiation. We discuss the axiomatic derivation of some game theoretic solution concepts, and illustrate our techniques with examples

Probing neutrino decays with the cosmic microwave background

We investigate in detail the possibility of constraining neutrino decays with data from the cosmic microwave background radiation (CMBR). Two generic decays are considered \nu_H -> \nu_L \phi and \nu_H -> \nu_L \nu_L_bar \nu_L. We have solved the momentum dependent Boltzmann equation in order to account for possible relativistic decays. Doing this we estimate that any neutrino with mass m > 1 eV decaying before the present should be detectable with future CMBR data. Combining this result with other results on stable neutrinos, any neutrino mass of the order 1 eV should be detectable.Comment: 8 pages, 4 figures, to appear in Phys. Rev.

Probing Unstable Massive Neutrinos with Current Cosmic Microwave Background Observations

The pattern of anisotropies in the Cosmic Microwave Background depends upon the masses and lifetimes of the three neutrino species. A neutrino species of mass greater than 10 eV with lifetime between 10^{13} sec and 10^{17} sec leaves a very distinct signature (due to the integrated Sachs-Wolfe effect): the anisotropies at large angles are predicted to be comparable to those on degree scales. Present data exclude such a possibility and hence this region of parameter space. For $m_\nu \simeq 30$ eV, $\tau \simeq 10^{13}$ sec, we find an interesting possibility: the Integrated Sachs Wolfe peak produced by the decaying neutrino in low-$\Omega$ models mimics the acoustic peak expected in an $\Omega = 1$ model.Comment: 5 pages, 4 figure