Compressor and fan wake characteristics

A triaxial probe and a rotating conventional probe, mounted on a traverse gear operated by two step motors were used to measure the mean velocities and turbulence quantities across a rotor wake at various radial locations and downstream stations. The data obtained was used in an analytical model developed to study how rotor flow and blade parameters and turbulence properties such as energy, velocity correlations, and length scale affect the rotor wake characteristics and its diffusion properties. The model, includes three dimensional attributes, can be used in predicting the discrete as well as broadband noise generated in a fan rotor, as well as in evaluating the aerodynamic losses, efficiency and optimum spacing between a rotor and stator in turbomachinery

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

Leveraging Program Analysis to Reduce User-Perceived Latency in Mobile Applications

Reducing network latency in mobile applications is an effective way of improving the mobile user experience and has tangible economic benefits. This paper presents PALOMA, a novel client-centric technique for reducing the network latency by prefetching HTTP requests in Android apps. Our work leverages string analysis and callback control-flow analysis to automatically instrument apps using PALOMA's rigorous formulation of scenarios that address "what" and "when" to prefetch. PALOMA has been shown to incur significant runtime savings (several hundred milliseconds per prefetchable HTTP request), both when applied on a reusable evaluation benchmark we have developed and on real applicationsComment: ICSE 201

Domestic fish marketing in India - changing structure, conduct, performance and policies

This study has been conducted in all the major coastal states and some selected inland states to understand the domestic marketing of fish in India. The total marketing costs of auctioneer, wholesaler, retailer, vendor, marine fishermen cooperative society and contractor/freshwater fishermen cooperative society have been found to be Re 0.98, Rs 8.89, Rs 6.61, Rs 4.50, Rs 6.00 and Rs 3.51, respectively. The marketing efficiencies for Indian major carps (IMC), sardine and seer fish have been found to vary from 34 per cent to 74 per cent, depending on the length of market channel. The marketing efficiency has been found more in the case of marine species than freshwater species, since the latter travel longer distances from the point of production to consumption centre, passing many intermediaries as compared to the former. The fisherman’s share in consumer’s rupee has shown variations across species, marketing channels and markets. The infrastructure facilities at most of the surveyed landing centres, fishing harbours and wholesale and retail markets have been found grossly inadequate and poorly maintained. The study has highlighted the need for formulating a uniform market policy for fishes for easy operation and regulation so that the country’s fish production is efficiently managed and delivered to the consuming population, ensuring at the same time remunerative prices to the fishers.Marketing,

Evolution of the Gas Mass Fraction of Progenitors to Today's Massive Galaxies: ALMA Observations in the CANDELS GOODS-S Field

We present an ALMA survey of dust continuum emission in a sample of 70 galaxies in the redshift range z=2-5 selected from the CANDELS GOODS-S field. Multi-Epoch Abundance Matching (MEAM) is used to define potential progenitors of a z = 0 galaxy of stellar mass 1.5 10^11 M_sun. Gas masses are derived from the 850um luminosity. Ancillary data from the CANDELS GOODS-S survey are used to derive the gas mass fractions. The results at z<=3 are mostly in accord with expectations: The detection rates are 75% for the z=2 redshift bin, 50% for the z=3 bin and 0% for z>=4. The average gas mass fraction for the detected z=2 galaxies is f_gas = 0.55+/-0.12 and f_gas = 0.62+/-0.15 for the z=3 sample. This agrees with expectations for galaxies on the star-forming main sequence, and shows that gas fractions have decreased at a roughly constant rate from z=3 to z=0. Stacked images of the galaxies not detected with ALMA give upper limits to f_gas of <0.08 and <0.15, for the z=2 and z=3 redshift bins. None of our galaxies in the z=4 and z=5 sample are detected and the upper limit from stacked images, corrected for low metallicity, is f_gas<0.66. We do not think that lower gas-phase metallicities can entirely explain the lower dust luminosities. We briefly consider the possibility of accretion of very low-metallicity gas to explain the absence of detectable dust emission in our galaxies at z>4.Comment: Accepted for publication in the Astrophysical Journal. 33 pages; 11 figure

Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56

Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we have studied the spatially-resolved dynamics in the z=3.2 strongly lensed galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy (seen at a spatial resolution of about 200 pc in the source plane), whereas the fainter ``arc'' is a more strongly magnified peripheral region of the same galaxy at about a half-light radius, which otherwise appears to be a typical z=3 Lyman break galaxy. The overall shape of the position-velocity diagram resembles the ``rotation curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected velocities rise rapidly to 75 km/s within the core. This implies a dynamical mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this system the equivalent of the mass of a present-day L* bulge at the same radius was already in place by z>=3. Approximating the circular velocity of the halo by the measured asymptotic velocity of the rotation curve, we estimate a dark matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with large-scale clustering studies of Lyman break galaxies. The baryonic collapse fraction is low compared to actively star-forming ``BX'' and low-redshift galaxies around z=2, perhaps implying comparatively less gas infall to small radii or efficient feedback. Even more speculatively, the high central mass density might indicate highly dissipative gas collapse in very early stages of galaxy evolution, in approximate agreement with what is expected for ``inside-out'' galaxy formation models.Comment: Accepted for publication in the Astrophysical Journa

Decomposition of AGN host galaxy images

We describe an algorithm to decompose deep images of Active Galactic Nuclei into host galaxy and nuclear components. Currently supported are three galaxy models: A de-Vaucouleurs spheroidal, an exponential disc, and a two-component disc+bulge model. Key features of the method are: (semi-)analytic representation of a possibly spatially variable point-spread function; full two-dimensional convolution of the model galaxy using gradient-controlled adaptive subpixelling; multiple iteration scheme. The code is computationally efficient and versatile for a wide range of applications. The quantitative performance is measured by analysing simulated imaging data. We also present examples of the application of the method to small test samples of nearby Seyfert 1 galaxies and quasars at redshifts z < 0.35.Comment: 12 pages, 15 figures, accepted for publication in MNRA