High Resolution Infrared Imaging of the Compact Nuclear Source in NGC4258

We present high resolution imaging of the nucleus of NGC4258 from 1 micron to 18 microns. Our observations reveal that the previously discovered compact source of emission is unresolved even at the near-infrared resolution of about 0.2 arcsec FWHM which corresponds to about 7 pc at the distance of the galaxy. This is consistent with the source of emission being the region in the neighborhood of the purported 3.5*10^7 M_sun black hole. After correcting for about 18 mags of visual extinction, the infrared data are consistent with a F_nu \propto nu^(-1.4+/-0.1) spectrum from 1.1 micron to 18 micron, implying a non-thermal origin. Based on this spectrum, the total extinction corrected infrared luminosity (1-20 micron) of the central source is 2*10^8 L_sun. We argue that the infrared spectrum and luminosity of the central source obviates the need for a substantial contribution from a standard, thin accretion disk at these wavelengths and calculate the accretion rate through an advection dominated accretion flow to be Mdot \sim 10^(-3) M_sun/yr. The agreement between these observations and the theoretical spectral energy distribution for advection dominated flows provides evidence for the existence of an advection dominated flow in this low luminosity AGN.Comment: 21 pages, 5 figures, Appearing in Mar 2000 ApJ vol. 53

Refined procedures for accurate determination of solution structures of nucleic acids by two dimensional nuclear magnetic resonance spectroscopy

New procedures have been described for accurate determination of solution structures of nucleic acids. These are two fold; new two dimensional nuclear magnetic resonance techniques and better approaches for interpretation of nuclear magnetic resonance data for structure determination purposes. The significant development in two dimensional nuclear magnetic resonance techniques for this purpose are ω1 -scaling and recording of pure phase spectra. Use ofω1-scaled correlated and nuclear Overhauser effect spectra for estimation of interproton distances and 1H-1H coupling constants has been described. Computer simulation procedures for exact determination of structure have been described. Experimental spectra demonstrating the application of new procedures have been presented

Application of Resonance Perturbation Theory to Dynamics of Magnetization in Spin Systems Interacting with Local and Collective Bosonic Reservoirs

We apply our recently developed resonance perturbation theory to describe the dynamics of magnetization in paramagnetic spin systems interacting simultaneously with local and collective bosonic environments. We derive explicit expressions for the evolution of the reduced density matrix elements. This allows us to calculate explicitly the dynamics of the macroscopic magnetization, including characteristic relaxation and dephasing time-scales. We demonstrate that collective effects (i) do not influence the character of the relaxation processes but merely renormalize the relaxation times, and (ii) significantly modify the dephasing times, leading in some cases to a complicated (time inhomogeneous) dynamics of the transverse magnetization, governed by an effective time-dependent magnetic field

The SED of Low-Luminosity AGNs at high-spatial resolution

The inner structure of AGNs is expected to change below a certain luminosity limit. The big blue bump, footprint of the accretion disk, is absent for the majority of low-luminosity AGNs (LLAGNs). Moreover, recent simulations suggest that the torus, a keystone in the Unified Model, vanishes for nuclei with L_bol < 10^42 erg/s. However, the study of LLAGN is a complex task due to the contribution of the host galaxy, which light swamps these faint nuclei. This is specially critical in the IR range, at the maximum of the torus emission, due to the contribution of the old stellar population and/or dust in the nuclear region. Adaptive optics imaging in the NIR (VLT/NaCo) together with diffraction limited imaging in the mid-IR (VLT/VISIR) permit us to isolate the nuclear emission for some of the nearest LLAGNs in the Southern Hemisphere. These data were extended to the optical/UV range (HST), radio (VLA, VLBI) and X-rays (Chandra, XMM-Newton, Integral), in order to build a genuine spectral energy distribution (SED) for each AGN with a consistent spatial resolution (< 0.5") across the whole spectral range. From the individual SEDs, we construct an average SED for LLAGNs sampled in all the wavebands mentioned before. Compared with previous multiwavelength studies of LLAGNs, this work covers the mid-IR and NIR ranges with high-spatial resolution data. The LLAGNs in the sample present a large diversity in terms of SED shapes. Some of them are very well described by a self-absorbed synchrotron (e.g. NGC 1052), while some other present a thermal-like bump at ~1 micron (NGC 4594). All of them are significantly different when compared with bright Seyferts and quasars, suggesting that the inner structure of AGNs (i.e. the torus and the accretion disk) suffers intrinsic changes at low luminosities.Comment: 8 pages, 5 figures. To appear in the proceedings of "Astrophysics at High Angular Resolution" (AHAR 2011

Development of a novel 3D culture system for screening features of a complex implantable device for CNS repair

Tubular scaffolds which incorporate a variety of micro- and nanotopographies have a wide application potential in tissue engineering especially for the repair of spinal cord injury (SCI). We aim to produce metabolically active differentiated tissues within such tubes, as it is crucially important to evaluate the biological performance of the three-dimensional (3D) scaffold and optimize the bioprocesses for tissue culture. Because of the complex 3D configuration and the presence of various topographies, it is rarely possible to observe and analyze cells within such scaffolds in situ. Thus, we aim to develop scaled down mini-chambers as simplified in vitro simulation systems, to bridge the gap between two-dimensional (2D) cell cultures on structured substrates and three-dimensional (3D) tissue culture. The mini-chambers were manipulated to systematically simulate and evaluate the influences of gravity, topography, fluid flow, and scaffold dimension on three exemplary cell models that play a role in CNS repair (i.e., cortical astrocytes, fibroblasts, and myelinating cultures) within a tubular scaffold created by rolling up a microstructured membrane. Since we use CNS myelinating cultures, we can confirm that the scaffold does not affect neural cell differentiation. It was found that heterogeneous cell distribution within the tubular constructs was caused by a combination of gravity, fluid flow, topography, and scaffold configuration, while cell survival was influenced by scaffold length, porosity, and thickness. This research demonstrates that the mini-chambers represent a viable, novel, scale down approach for the evaluation of complex 3D scaffolds as well as providing a microbioprocessing strategy for tissue engineering and the potential repair of SCI

Revisiting the Cosmic Star Formation History: Caution on the Uncertainties in Dust Correction and Star Formation Rate Conversion

The cosmic star formation rate density (CSFRD) has been observationally investigated out to redshift z~10. However, most of theoretical models for galaxy formation underpredict the CSFRD at z>1. Since the theoretical models reproduce the observed luminosity functions (LFs), luminosity densities (LDs), and stellar mass density at each redshift, this inconsistency does not simply imply that theoretical models should incorporate some missing unknown physical processes in galaxy formation. Here, we examine the cause of this inconsistency in UV wavelengths by using a mock catalog of galaxies generated by a semi-analytic model of galaxy formation. We find that this inconsistency is due to two observational uncertainties: dust obscuration correction and conversion from UV luminosity to star formation rate (SFR). The methods for correction of obscuration and SFR conversion used in observational studies result in the overestimation of CSFRD by ~ 0.1-0.3 dex and ~ 0.1-0.2 dex, respectively, compared to the results obtained directly from our mock catalog. We present new empirical calibrations for dust attenuation and conversion from observed UV LFs and LDs into CSFRD.Comment: 12 pages including 11 figures. matches the published version (ApJ 2013 Jan. 20 issue

Assessment of spatio-temporal vegetation dynamics in tropical arid ecosystem of India using MODIS time-series vegetation indices

In the present study, we analyzed spatio-temporal vegetation dynamics to identify and delineate the vegetation stress zones in tropical arid ecosystem of Anantapuramu district, Andhra Pradesh, India, using Normalized Difference Vegetation Index (NDVI), Vegetation Condition Index (VCI), and Vegetation Anomaly Index (VAI) derived from time-series Moderate Resolution Imaging Spectroradiometer (MODIS) 16-day products (MOD13Q1) at 250 m spatial resolution for the growing season (June to September) of 19 years during 2000 to 2018. The 1-month Standardized Precipitation Index (SPI) was computed for 30 years (1989 to 2018) to quantify the precipitation deficit/surplus regions and assess its influence on vegetation dynamics. The growing season mean NDVI and VCI were correlated with growing season mean 1-month SPI of dry (2003) and wet (2007) years to analyze the spatio-temporal vegetation dynamics. The correlation analysis between SPI and NDVI for dry year (2003) showed strong positive correlation (r = 0.89). Analysis of VAI for dry year (2003) indicates that the central, western, and southwestern parts of the district reported high vegetation stress with VAI of less than − 2.0. This might be due to the fact that central and south-western parts of the district are more prone to droughts than the other parts of the district. The correlation analysis of SPI, NDVI, and VCI distinctly shows the impact of rainfall on vegetation dynamics. The study clearly demonstrates the robustness of NDVI, VCI, and VAI derived from time-series MODIS data in monitoring the spatio-temporal vegetation dynamics and delineate vegetation stress zones in tropical arid ecosystem of India

What fraction of stars formed in infrared galaxies at high redshift?

Star formation happens in two types of environment: ultraviolet-bright starbursts (like 30 Doradus and HII galaxies at low redshift and Lyman-break galaxies at high redshift) and infrared-bright dust-enshrouded regions (which may be moderately star-forming like Orion in the Galaxy or extreme like the core of Arp 220). In this work I will estimate how many of the stars in the local Universe formed in each type of environment, using observations of star-forming galaxies at all redshifts at different wavelengths and of the evolution of the field galaxy population.Comment: 7 pages, 0 figs, to appear in proceedings of "Starbursts - From 30 Doradus to Lyman break galaxies", edited by Richard de Grijs and Rosa M. Gonzalez Delgado, published by Kluwe

The Hawk-I UDS and GOODS Survey (HUGS): Survey design and deep K-band number counts

We present the results of a new, ultra-deep, near-infrared imaging survey executed with the Hawk-I imager at the ESO VLT, of which we make all the data public. This survey, named HUGS (Hawk-I UDS and GOODS Survey), provides deep, high-quality imaging in the K and Y bands over the CANDELS UDS and GOODS-South fields. We describe here the survey strategy, the data reduction process, and the data quality. HUGS delivers the deepest and highest quality K-band images ever collected over areas of cosmological interest, and ideally complements the CANDELS data set in terms of image quality and depth. The seeing is exceptional and homogeneous, confined to the range 0.38"-0.43". In the deepest region of the GOODS-S field, (which includes most of the HUDF) the K-band exposure time exceeds 80 hours of integration, yielding a 1-sigma magnitude limit of ~28.0 mag/sqarcsec. In the UDS field the survey matches the shallower depth of the CANDELS images reaching a 1-sigma limit per sq.arcsec of ~27.3mag in the K band and ~28.3mag in the Y-band, We show that the HUGS observations are well matched to the depth of the CANDELS WFC3/IR data, since the majority of even the faintest galaxies detected in the CANDELS H-band images are also detected in HUGS. We present the K-band galaxy number counts produced by combining the HUGS data from the two fields. We show that the slope of the number counts depends sensitively on the assumed distribution of galaxy sizes, with potential impact on the estimated extra-galactic background light (abridged).Comment: Accepted for publication on Astronomy and Astrophysic