1,153 research outputs found
Measuring gravitational lens time delays using low-resolution radio monitoring observations
Obtaining lensing time delay measurements requires long-term monitoring
campaigns with a high enough resolution (< 1 arcsec) to separate the multiple
images. In the radio, a limited number of high-resolution interferometer arrays
make these observations difficult to schedule. To overcome this problem, we
propose a technique for measuring gravitational time delays which relies on
monitoring the total flux density with low-resolution but high-sensitivity
radio telescopes to follow the variation of the brighter image. This is then
used to trigger high-resolution observations in optimal numbers which then
reveal the variation in the fainter image. We present simulations to assess the
efficiency of this method together with a pilot project observing radio lens
systems with the Westerbork Synthesis Radio Telescope (WSRT) to trigger Very
Large Array (VLA) observations. This new method is promising for measuring time
delays because it uses relatively small amounts of time on high-resolution
telescopes. This will be important because instruments that have high
sensitivity but limited resolution, together with an optimum usage of followup
high-resolution observations from appropriate radio telescopes may in the
future be useful for gravitational lensing time delay measurements by means of
this new method.Comment: 10 pages, 7 figures, accepted by MNRA
Vascular variations of the kidney, retrospective analysis of computed tomography images of ninety-one laparoscopic donor nephrectomies, and comparison of computed tomography images with perioperative findings
Background: In this retrospective study, we aimed to determine the variations of kidney arteries and veins in kidney donor patients who underwent preoperative, computed tomography angiography (CTA).Materials and methods: We analysed kidney CTA findings of 91 donor nephrectomy patients operated from July 2016 through December 2017. Demographics, vascular diameters, abnormalities, numbers, branching variations, routing variations of arteries, and veins were assessed according to CTA images. We also compared the radiological findings with perioperative findings. Two radiologists evaluated CTA images, and the same surgical team performed all donor nephrectomies by laparoscopic approach.Results: Ninety-one of the 96 patients involved to study. Forty-six (50.5%) patients were female. Thirty-five (38.4%) of 91 cases had accessory arteries. Seven (7.6%) right, 1 (1.1%) left and 8 (8.7%) bilateral double hilar artery was observed on CTA. No statistically significant difference was observed in the evaluation of the side of accessory/polar arteries (p > 0.05), and in the evaluation of the distribution of arterial/venous variations according to perioperative findings (p > 0.05). However, in the evaluation of CTA images, we found that the diameter of the kidney artery and vein differed according to gender and side.Conclusions: The knowledge of the vascular variations of the kidney is essential for surgeons performing kidney transplantation. It is also essential for urologist and vascular surgeons. Incompatible with the literature, the right kidney has more vascular variations and, one kidney artery is found in the majority of Turkish kidneydonor patients
Improving the Surface Quality and Mechanical Properties of Selective Laser Sintered PA2200 Components by the Vibratory Surface Finishing Process
This paper attempts to improve the physical and mechanical properties of selective laser sintered polyamide PA2200
components through a vibratory surface finishing process by inducing severe plastic deformation at the outer surface
layers. The industrial target of additive manufacturing components is to obtain structures having surface roughness,
hardness, and other mechanical properties equivalent to or better than those produced conventionally. Compared to
the as-built SLS PA2200 samples, vibratory surface finishing treated specimens exhibited a smooth surface microstructure
and more favorable roughness, hardness, and tensile strength. Also, the duration of the vibratory surface finishing
process showed a further improvement in the surface roughness and hardness of the SLS samples. Compared to the asbuilt
state, the roughness and hardness of the surface-treated samples improved by almost 90% and 15%, respectively.
Consequently, microstructural analysis indicates that lower surface roughness and enhanced surface hardness is a crucial
factor in influencing the overall tensile strength of SLS-PA2200 components. We consider that the combination of VSF
and SLS processes can successfully handle a wide range of potential applications. This study also highlights the efficiency
and applicability of the vibratory surface finishing process to other additive manufacturing processes and materials
An evolutionary missing link? A modest-mass early-type galaxy hosting an oversized nuclear black hole
SAGE1C J053634.78-722658.5 is a galaxy at redshift z = 0.14, discovered behind the Large Magellanic Cloud in the Spitzer Space Telescope`Surveying the Agents of Galaxy Evolution' Spectroscopy survey. It has very strong silicate emission at 10 μm but negligible far-IR and UV emission. This makes it a candidate for a bare active galactic nuclei (AGN) source in the IR, perhaps seen pole-on, without significant IR emission from the host galaxy. In this paper we present optical spectra taken with the Southern African Large Telescope to investigate the nature of the underlying host galaxy and its AGN. We find broad H α emission characteristic of an AGN, plus absorption lines associated with a mature stellar population (>9 Gyr), and refine its redshift determination to z = 0.1428 ± 0.0001. There is no evidence for any emission lines associated with star formation. This remarkable object exemplifies the need for separating the emission from any AGN from that of the host galaxy when employing IR diagnostic diagrams. We estimate the black hole mass, MBH = 3.5 ± 0.8 × 108 M⊙, host galaxy mass, M_stars=2.5^{2.5}_{1.2}× 10^{10} M⊙, and accretion luminosity, Lbol(AGN) = 5.3 ± 0.4 × 1045 erg s-1 (≈12 per cent of the Eddington luminosity), and find the AGN to be more prominent than expected for a host galaxy of this modest size. The old age is in tension with the downsizing paradigm in which this galaxy would recently have transformed from a star-forming disc galaxy into an early-type, passively evolving galaxy
A temporal approach for morphological indices of the common sole (Solea solea Linnaeus 1758) from the coast of the Aegean Sea, Turkey
Temporal changes of the morphological indices (Relative Gut Length (RGL), Fullness Index (FI), Hepatosomatic Index (HSI), Visceral Index (VSI), Gonadosomatic Index (GSI) and Fulton condition)) in 122 (♀: 94, ♂: 19, immature: 9) common sole were evaluated. Total length-weight relationships were calculated as W = 0.085TL3.01 and W = 0.0547TL2.40 in females and males, respectively, whereby isometric growth was observed in females and negative allometric growth was observed in males. While there was no statistically significant difference was observed between the FI, HSI, Viscerosomatic Index (VSI), RGL and GSI values of both sexes, however, there was a statistically significant difference in terms of Fulton K values (P < 0.05). In addition, there are statistical differences between the sexes total lengths and the values of RGL, FI, HSI, VSI, and Fulton-K (P < 0.05), as it is discernible in their HSI and VSI index values according to the month the specimens were obtained (P < 0.05). According to the results of the analysis, it has been determined that the female common sole along the Aegean coast adjust their energy temporally and store the energy they obtain from vegetative and carnivorous feeding. Contrary to the situation seen in females, the male individuals invest in energy through omnivorous feeding, according to the diet in the active process. Based on the results, it can be stated that the VSI and HSI are both important indicators of fish condition status. The results found here may be useful in both fishery research and fishery management
Radio observations of NGC 6388: an upper limit on the mass of its central black hole
We present the results of deep radio observations with the Australia
Telescope Compact Array (ATCA) of the globular cluster NGC 6388. We show that
there is no radio source detected (with a r.m.s. noise level of 27 uJy) at the
cluster centre of gravity or at the locations of the any of the Chandra X-ray
sources in the cluster. Based on the fundamental plane of accreting black holes
which is a relationship between X-ray luminosity, radio luminosity and black
hole mass, we place an upper limit of 1500 M_sun on the mass of the putative
intermediate-mass black hole located at the centre of NGC 6388. We discuss the
uncertainties of this upper limit and the previously suggested black hole mass
of 5700 M_sun based on surface density profile analysis.Comment: 6 pages, 2 figures, accepted for publication in MNRA
Bovine oocytes in secondary follicles grow and acquire meiotic competence in severe combined immunodeficient mice
A rigorous methodology is developed
that addresses numerical and
statistical issues when developing group contribution (GC) based property
models such as regression methods, optimization algorithms, performance
statistics, outlier treatment, parameter identifiability, and uncertainty
of the prediction. The methodology is evaluated through development
of a GC method for the prediction of the heat of combustion (Δ<i>H</i><sub>c</sub><sup>o</sup>) for pure components. The results showed that robust regression
lead to best performance statistics for parameter estimation. The
bootstrap method is found to be a valid alternative to calculate parameter
estimation errors when underlying distribution of residuals is unknown.
Many parameters (first, second, third order group contributions) are
found unidentifiable from the typically available data, with large
estimation error bounds and significant correlation. Due to this poor
parameter identifiability issues, reporting of the 95% confidence
intervals of the predicted property values should be mandatory as
opposed to reporting only single value prediction, currently the norm
in literature. Moreover, inclusion of higher order groups (additional
parameters) does not always lead to improved prediction accuracy for
the GC-models; in some cases, it may even increase the prediction
error (hence worse prediction accuracy). However, additional parameters
do not affect calculated 95% confidence interval. Last but not least,
the newly developed GC model of the heat of combustion (Δ<i>H</i><sub>c</sub><sup>o</sup>) shows predictions of great accuracy and quality (the most data
falling within the 95% confidence intervals) and provides additional
information on the uncertainty of each prediction compared to other
Δ<i>H</i><sub>c</sub><sup>o</sup> models reported in literature
Dynamics of massive stellar black holes in young star clusters and the displacement of ultra-luminous X-ray sources
In low-metallicity environments, massive stars might avoid supernova
explosion and directly collapse, forming massive (~25-80 solar masses) stellar
black holes (MSBHs), at the end of their life. MSBHs, when hosted in young
massive clusters, are expected to form binaries and to strongly interact with
stars, mainly via three-body encounters. We simulate various realizations of
young star clusters hosting MSBHs in hard binaries with massive stars. We show
that a large fraction (~44 per cent) of MSBH binaries are ejected on a short
timescale (<=10 Myr). The offset of the ejected MSBHs with respect to the
parent cluster is consistent with observations of X-ray binaries and
ultra-luminous X-ray sources. Furthermore, three-body encounters change the
properties of MSBH binaries: the semi-major axis changes by <=50 per cent and
the eccentricity of the system generally increases. We shortly discuss the
implications of our simulations on the formation of high-mass X-ray binaries
hosting MSBHs.Comment: 10 pages, 9 figures, accepted for publication in MNRA
Central kinematics of the globular cluster NGC 2808: Upper limit on the mass of an intermediate-mass black hole
Globular clusters are an excellent laboratory for stellar population and
dynamical research. Recent studies have shown that these stellar systems are
not as simple as previously assumed. With multiple stellar populations as well
as outer rotation and mass segregation they turn out to exhibit high
complexity. This includes intermediate-mass black holes which are proposed to
sit at the centers of some massive globular clusters. Today's high angular
resolution ground based spectrographs allow velocity-dispersion measurements at
a spatial resolution comparable to the radius of influence for plausible IMBH
masses, and to detect changes in the inner velocity-dispersion profile.
Together with high quality photometric data from HST, it is possible to
constrain black-hole masses by their kinematic signatures. We determine the
central velocity-dispersion profile of the globular cluster NGC 2808 using
VLT/FLAMES spectroscopy. In combination with HST/ACS data our goal is to probe
whether this massive cluster hosts an intermediate-mass black hole at its
center and constrain the cluster mass to light ratio as well as its total mass.
We derive a velocity-dispersion profile from integral field spectroscopy in the
center and Fabry Perot data for larger radii. High resolution HST data are used
to obtain the surface brightness profile. Together, these data sets are
compared to dynamical models with varying parameters such as mass to light
ratio profiles and black-hole masses. Using analytical Jeans models in
combination with variable M/L profiles from N-body simulations we find that the
best fit model is a no black hole solution. After applying various Monte Carlo
simulations to estimate the uncertainties, we derive an upper limit of the back
hole mass of M_BH < 1 x 10^4 M_SUN (with 95 % confidence limits) and a global
mass-to-light ratio of M/L_V = (2.1 +- 0.2) M_SUN/L_SUN.Comment: 12 pages, 9 figures, 2 tables, accepted for publication in A&
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 , with a logarithmic slope of , 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
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