1,356 research outputs found
Runaway collisions in young star clusters. II. Numerical results
We present a new study of the collisional runaway scenario to form an
intermediate-mass black hole (IMBH, MBH > 100 Msun) at the centre of a young,
compact stellar cluster. The first phase is the formation of a very dense
central core of massive stars (Mstar =~ 30-120 Msun) through mass segregation
and gravothermal collapse. Previous work established the conditions for this to
happen before the massive stars evolve off the main sequence (MS). In this and
a companion paper, we investigate the next stage by implementing direct
collisions between stars. Using a Monte Carlo stellar dynamics code, we follow
the core collapse and subsequent collisional phase in more than 100 models with
varying cluster mass, size, and initial concentration. Collisions are treated
either as ideal, ``sticky-sphere'' mergers or using realistic prescriptions
derived from 3-D hydrodynamics computations. In all cases for which the core
collapse happens in less than the MS lifetime of massive stars (~3 Myr), we
obtain the growth of a single very massive star (VMS, Mstar =~ 400-4000 Msun)
through a runaway sequence of mergers. Mass loss from collisions, even for
velocity dispersions as high as sigma1D ~ 1000 km/s, does not prevent the
runaway. The region of cluster parameter space leading to runaway is even more
extended than predicted in previous work because, in clusters with sigma1D >
300 km/s, collisions accelerate (and, in extreme cases, drive) core collapse.
Although the VMS grows rapidly to > 1000 Msun in models exhibiting runaway, we
cannot predict accurately its final mass. This is because the termination of
the runaway process must eventually be determined by a complex interplay
between stellar dynamics, hydrodynamics, and the stellar evolution of the VMS.
[abridged]Comment: 23 pages, 24 figures. For publication in MNRAS. Paper revised to
follow requests and suggestions of referee. Companion paper to Freitag, Rasio
& Baumgardt 200
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
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The presence of organophosphorus compounds (OPs) in the environmental counterparts has become an important problem because of their toxicity. In this study, the photocatalytic degradation reactions of the three OPs with hydroxyl radical were investigated by both experimental and quantum chemical methods. Photocatalytic degradation kinetics of the examined organophosphorus compounds were investigated under UV-A irradiation using TiO2 as the photocatalyst. The effects of the initial concentrations on the degradation rate have been examined. There was an observable loss of OPs in the presence of TiO2 photocatalyst under UV-A at 0.2 g TiO2 per 100 mL. The quantum chemical calculations have been carried out by the density functional theory (DFT) at B3LYP/6-31g(d) level. The reaction pathways were modelled to find the most probable mechanism for OPs with the OH radical and to determine the primary intermediates. The rate constants of the eight reaction paths were calculated by the transition state theory. Conductor-like polarizable continuum model (CPCM) was used as the solvation model with the intention of understanding the water effect. The theoretical results were in agreement with experimental ones. © 2021 Serbian Chemical Society. All rights reserved.18,164Acknowledgement. The authors of this research has greatfully acknowledgemented to financially support of Tekirdag Namık Kemal University Research Project with the project number of NKUBAP.01.GA.18.164
THE ORGANIZATIONAL ATTRACTIVENESS AND JOB SATISFACTION OF INSTRUCTORS OF PHYSICAL EDUCATION AND SPORTS WHO WORKS IN DIFFERENT REGIONS
In our research which is made in order to examine the organizational attractiveness and job satisfaction of instructors of physical education and sports who works in different regions in terms of different factors, there are 60 instructors who are 12 women and 48 men and have different academic title and work in 7 universities in different regions of Turkey. According to the variance of academic title of instructors, they ,distribute as 5 associate professor (% 8,5), 18 assistant professor (%30,0), 17 instructors (%28,3), 8 lecturers (% 13,3), 12 research assistant (% 20,0). While choosing of the universities, it is looked youngest universities and the number of instructors is least. “Minessota Job Satisfaction Scale”, “Organizational Attractiveness” and “Demographic Information Form” are used. The points which are located of scale dimensions are evaluated between 1 and 5. According to the test results which are done in order to find out if there is a meaningful difference in terms of the variances of academic title, age, years of service, duration of administration, administrative task, lesson hours, marital status of the averages points of the organizational attractiveness, internal satisfaction, external satisfaction, general satisfaction of the instructors who participate the research, a meaningful difference has not been found. There is a weak, positive directional relation among the internal, external satisfaction and organizational attractiveness. There is a weak, positive directional relation between general satisfaction and organizational attractiveness. Article visualizations
Interpreting radiative efficiency in radio-loud AGNs
Author submitted version of unrefereed Nature Astronomy comment. Version in journal format available at https://rdcu.be/KH6WRadiative efficiency in radio-loud active galactic nuclei is governed by the accretion rate onto the central black hole rather than directly by the type of accreted matter; while it correlates with real differences in host galaxies and environments, it does not provide unambiguous information about particular objects.Non peer reviewedFinal Accepted Versio
An integrated knowledge-based and optimization tool for the sustainable selection of wastewater treatment process concepts
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