Effects of dietary diludine supplementation on growth, proximate composition, muscle and texture structure of rainbow trout juveniles

A feeding trial which lasted for eight weeks was conducted to investigate the effects of diludine, a growth promoter, on feed efficiency, muscle structure and proximate composition of juvenile rainbow trout. Diludine was added at 0.0(D0) 0.2(D1), 0.5(D2) and 1(D3) g kg^-1 to a casein-based diet, and every diet was given to the triplicated groups of juvenile rainbow trout. At the end of experiment, it was determined that a significant improvability existed for both growth and feed utilization in fish fed diets supplemented with diludine (p<0.05). Similarly, different concentrations of diludine affected the densitometric quantification of myofibrillar proteins in fish muscle according to results obtained by Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The mean value of fiber diameters significantly increased in skeletal muscle with increasing concentrations of diludine. The histological results also showed hypertrophic adipocytes in skeletal muscle of fish fed D2 and D3 diets. The lowest elasticity values were observed in fish fed the control diet while those fed D3 diet had highest elasticity values. On the other hand, no differences were found between fish fed experimental diets in terms of survival rate and all fish exhibited similar proximate composition for protein, lipid, moisture and ash. Consequently, it may be suggested that dietary diludine supplementation up to 1 g kg^-1 concentration in the diets have positive impacts on growth of rainbow trout juveniles and the better growth in the fish fed with diludine supplements could be arise from muscle characteristics, in particular changes in fibres than proximate composition of the muscles

Stellar collisions in accreting protoclusters: a Monte Carlo dynamical study

We explore the behaviour of accreting protoclusters with a Monte Carlo dynamical code in order to evaluate the relative roles of accretion, two body relaxation and stellar collisions in the cluster evolution. We corroborate the suggestion of Clarke & Bonnell that the number of stellar collisions should scale as $N^{5/3} \dot M^{2/3}$ (independent of other cluster parameters, where N is the number of stars in the cluster and $\dot M$ the rate of mass accretion) and thus strengthen the argument that stellar collisions are more likely in populous (large N) clusters. We however find that the estimates of Clarke & Bonnell were pessimistic in the sense that we find that more than 99 % of the stellar collisions occur within the post-adiabatic regime as the cluster evolves towards core collapse, driven by a combination of accretion and two-body relaxation. We discuss how the inclusion of binaries may reduce the number of collisions through the reversal of core collapse but also note that it opens up another collisional channel involving the merger of stars within hard binaries; future Nbody simulations are however required in order to explore this issue.Comment: 9 pages, 9 figures; accepted for publication in MNRAS. This version contains minor revisions after referee's comments

Star formation in the central 0.5 pc of the Milky Way

The supermassive black hole candidate at the Galactic Center is surrounded by a parsec-scale star cluster, which contains a number of early type stars. The presence of such stars has been called a "paradox of youth" as star formation in the immediate vicinity of a supermassive black hole seemed difficult, as well as the transport of stars from far out in a massive-star lifetime. I will recall 30 years of technological developments which led to the current understanding of the nuclear cluster stellar population. The number of early type stars known at present is sufficient to access the 3D structure of this population and its dynamics, which in turn allows discriminating between the various possible origins proposed along the years.Comment: 8 pages, invited review for the conference "The Universe under the Microscope" (AHAR 2008), to be published in Journal of Physics: Conference Series by Institute of Physics Publishin

LOFAR MSSS: Flattening low-frequency radio continuum spectra of nearby galaxies

Accepted for publication in Astronomy and AstrophysicsAims. The shape of low-frequency radio continuum spectra of normal galaxies is not well understood, the key question being the role of physical processes such as thermal absorption in shaping them. In this work we take advantage of the LOFAR Multifrequency Snapshot Sky Survey (MSSS) to investigate such spectra for a large sample of nearby star-forming galaxies. Methods. Using the measured 150 MHz flux densities from the LOFAR MSSS survey and literature flux densities at various frequencies we have obtained integrated radio spectra for 106 galaxies characterised by different morphology and star formation rate. The spectra are explained through the use of a three-dimensional model of galaxy radio emission, and radiation transfer dependent on the galaxy viewing angle and absorption processes. Results. Our galaxies' spectra are generally flatter at lower compared to higher frequencies: the median spectral index α low measured between ≈ 50 MHz and 1.5 GHz is -0.57 ± 0.01 while the high-frequency one α high, calculated between 1.3 GHz and 5 GHz, is -0.77 ± 0.03. As there is no tendency for the highly inclined galaxies to have more flattened low-frequency spectra, we argue that the observed flattening is not due to thermal absorption, contradicting the suggestion of Israel & Mahoney (1990, ApJ, 352, 30). According to our modelled radio maps for M 51-like galaxies, the free-free absorption effects can be seen only below 30 MHz and in the global spectra just below 20 MHz, while in the spectra of starburst galaxies, like M 82, the flattening due to absorption is instead visible up to higher frequencies of about 150 MHz. Starbursts are however scarce in the local Universe, in accordance with the weak spectral curvature seen in the galaxies of our sample. Locally, within galactic disks, the absorption effects are distinctly visible in M 51-like galaxies as spectral flattening around 100-200 MHz in the face-on objects, and as turnovers in the edge-on ones, while in M 82-like galaxies there are strong turnovers at frequencies above 700 MHz, regardless of viewing angle. Conclusions. Our modelling of galaxy spectra suggests that the weak spectral flattening observed in the nearby galaxies studied here results principally from synchrotron spectral curvature due to cosmic ray energy losses and propagation effects. We predict much stronger effects of thermal absorption in more distant galaxies with high star formation rates. Some influence exerted by the Milky Way's foreground on the spectra of all external galaxies is also expected at very low frequencies.Peer reviewedFinal Accepted Versio

LOFAR MSSS: The Scaling Relation between AGN Cavity Power and Radio Luminosity at Low Radio Frequencies

This article has been accepted for publication in a forthcoming issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.We present a new analysis of the widely used relation between cavity power and radio luminosity in clusters of galaxies with evidence for strong AGN feedback. We study the correlation at low radio frequencies using two new surveys - the First Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) at 148 MHz and LOFAR's first all-sky survey, the Multifrequency Snapshot Sky Survey (MSSS) at 140 MHz. We find a scaling relation $P_{\rm cav} \propto L_{148}^{\beta}$, with a logarithmic slope of $\beta = 0.51 \pm 0.14$, which is in good agreement with previous results based on data at 327 MHz. The large scatter present in this correlation confirms the conclusion reached at higher frequencies that the total radio luminosity at a single frequency is a poor predictor of the total jet power. We show that including measurements at 148 MHz alone is insufficient to reliably compute the bolometric radio luminosity and reduce the scatter in the correlation. For a subset of four well-resolved sources, we examine the detected extended structures at low frequencies and compare with the morphology known from higher frequency images and Chandra X-ray maps. In Perseus we discuss details in the structures of the radio mini-halo, while in the 2A 0335+096 cluster we observe new diffuse emission associated with multiple X-ray cavities and likely originating from past activity. For A2199 and MS 0735.6+7421, we confirm that the observed low-frequency radio lobes are confined to the extents known from higher frequencies. This new low-frequency analysis highlights the fact that existing cavity power to radio luminosity relations are based on a relatively narrow range of AGN outburst ages. We discuss how the correlation could be extended using low frequency data from the LOFAR Two-metre Sky Survey (LoTSS) in combination with future, complementary deeper X-ray observations.Peer reviewe

Evidence for Warped Disks of Young Stars in the Galactic Center

The central parsec around the super-massive black hole in the Galactic Center hosts more than 100 young and massive stars. Outside the central cusp (R~1") the majority of these O and Wolf-Rayet (WR) stars reside in a main clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the Galactic Center with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured WR/O stars in the central 12" and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of four compared to our earlier work. We develop a detailed statistical analysis of their orbital properties and orientations. Half of the WR/O stars are compatible with being members of a clockwise rotating system. The rotation axis of this system shows a strong transition as a function of the projected distance from SgrA*. The main clockwise system either is either a strongly warped single disk with a thickness of about 10 degrees, or consists of a series of streamers with significant radial variation in their orbital planes. 11 out of 61 clockwise moving stars have an angular separation of more than 30 degrees from the clockwise system. The mean eccentricity of the clockwise system is 0.36+/-0.06. The distribution of the counter-clockwise WR/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young stars.Comment: ApJ in pres

Intermediate and extreme mass-ratio inspirals — astrophysics, science applications and detection using LISA

Black hole binaries with extreme (gtrsim104:1) or intermediate (~102–104:1) mass ratios are among the most interesting gravitational wave sources that are expected to be detected by the proposed laser interferometer space antenna (LISA). These sources have the potential to tell us much about astrophysics, but are also of unique importance for testing aspects of the general theory of relativity in the strong field regime. Here we discuss these sources from the perspectives of astrophysics, data analysis and applications to testing general relativity, providing both a description of the current state of knowledge and an outline of some of the outstanding questions that still need to be addressed. This review grew out of discussions at a workshop in September 2006 hosted by the Albert Einstein Institute in Golm, Germany