11,780 research outputs found
A Supernova Factory in the Merger System Arp 299
We have imaged the nearby galaxy merger Arp 299 at arcsecond and
milliarcsecond resolution, using both the Very Large Array and the Very Long
Baseline Array. The large-scale radio emission from the merger contains 5
bright, compact radio sources embedded in diffuse emission, with diameters less
than 200 pc. Supernova rates of 0.1 to 1 per year are required to produce the
VLA-detected radio emission in these sources. Two of the compact VLA radio
sources, designated Source A and Source D, also have been detected and imaged
at milliarcsecond scales. Source A, which is associated with the nucleus of one
of the merging galaxies, contains five milliarcsecond-scale sources, each with
a radio power between 100 and 1000 times that of the Galactic supernova remnant
Cassiopeia A. Four of these have flat or inverted spectra and appear to be
young supernovae. Three of the VLBI-scale sources are located within 10 pc
(projected) of one another, and two are separated by less than 3 pc, indicating
that they all may be within the same super starcluster or complex of such
clusters. The brightest VLBI-scale source, A0, has an extremely inverted
pectrum, with alpha larger than +2 at gigahertz frequencies. It seems to be the
youngest supernova, which has not yet broken out of its circumstellar shell.
The milliarcsecond radio sources within Source A appear to constitute a
upernova factory, confirming the presence of an extreme starburst that peaked
at least a few million years ago.Comment: Accepted for the Astrophysical Journal, 22 pages, 10 figure
Challenges of Primary Frequency Control and Benefits of Primary Frequency Response Support from Electric Vehicles
As the integration of wind generation displaces conventional plants, system inertia provided by rotating mass declines, causing concerns over system frequency stability. This paper implements an advanced stochastic scheduling model with inertia-dependent fast frequency response requirements to investigate the challenges on the primary frequency control in the future Great Britain electricity system. The results suggest that the required volume and the associated cost of primary frequency response increase significantly along with the increased capacity of wind plants. Alternative measures (e.g. electric vehicles) have been proposed to alleviate these concerns. Therefore, this paper also analyses the benefits of primary frequency response support from electric vehicles in reducing system operation cost, wind curtailment and carbon emissions
Experimental behaviour of FRP-confined large-scale curvilinearized rectangular RC columns under axial compression
Existing research has shown that strengthening through fibre-reinforced polymer (FRP) confinement is highly effective for circular columns but much less so for sTuare and rectangular columns due to the flat sides and sharp corners in the latter. Rounding the corners in the latter columns can enhance the effectiveness of confinement, but its benefit is limited. To overcome this problem, an alternative strengthening techniTue has recently been proposed by some researchers, in which the flat sides of a sTuarerectangular section are modified into slightly curved sides before FRP confinement (referred to as section curvilinearization). The resulting columns, referred to as curvilinearized sTuare rectangular columns, are much more effectively confined by an FRP jacket than the original sTuarerectangular columns with only corner rounding, and the associated column size increase is limited. While this section curvilinearization techniTue is highly attractive, there has been only very limited research on the behaviour of FRP-confined curvilinearized sTuare rectangular columns. In particular, all the existing experimental work has been limited to small-scale sTuare columns (with section widths being around or below 1 mm) under axial compression. Against the above background, a large experimental programme has been under way at The Hong Kong Polytechnic University to study the behaviour of large-scale curvilinearized RC columns under both concentric and eccentric compression. Both sTuare and rectangular columns have been considered in the experimental programme. This paper presents a systematic experimental study on the behaviour of FRP-confined curvilinearized rectangular RC columns under axial compression to study the effects of the following parameters: rise-to-span ratio of the edge profile, sectional aspect ratio and corner radius. In addition to the presentation of experimental results, two existing stress-strain models for FRP-confined concrete in these columns are assessed to reveal their limitations
High pressure effect on structure, electronic structure and thermoelectric properties of MoS
We systematically study the effect of high pressure on the structure,
electronic structure and transport properties of 2H-MoS, based on
first-principles density functional calculations and the Boltzmann transport
theory. Our calculation shows a vanishing anisotropy in the rate of structural
change at around 25 GPa, in agreement with the experimental data. A conversion
from van der Waals(vdW) to covalent-like bonding is seen. Concurrently, a
transition from semiconductor to metal occurs at 25 GPa from band structure
calculation. Our transport calculations also find pressure-enhanced electrical
conductivities and significant values of the thermoelectric figure of merit
over a wide temperature range. Our study supplies a new route to improve the
thermoelectric performance of MoS and of other transition metal
dichalcogenides by applying hydrostatic pressure.Comment: 6 pages, 6 figures; published in JOURNAL OF APPLIED PHYSICS 113, xxxx
(2013
Metabolism of ticagrelor in patients with acute coronary syndromes.
© The Author(s) 2018Ticagrelor is a state-of-the-art antiplatelet agent used for the treatment of patients with acute coronary syndromes (ACS). Unlike remaining oral P2Y12 receptor inhibitors ticagrelor does not require metabolic activation to exert its antiplatelet action. Still, ticagrelor is extensively metabolized by hepatic CYP3A enzymes, and AR-C124910XX is its only active metabolite. A post hoc analysis of patient-level (n = 117) pharmacokinetic data pooled from two prospective studies was performed to identify clinical characteristics affecting the degree of AR-C124910XX formation during the first six hours after 180 mg ticagrelor loading dose in the setting of ACS. Both linear and multiple regression analyses indicated that ACS patients presenting with ST-elevation myocardial infarction or suffering from diabetes mellitus are more likely to have decreased rate of ticagrelor metabolism during the acute phase of ACS. Administration of morphine during ACS was found to negatively influence transformation of ticagrelor into AR-C124910XX when assessed with linear regression analysis, but not with multiple regression analysis. On the other hand, smoking appears to increase the degree of ticagrelor transformation in ACS patients. Mechanisms underlying our findings and their clinical significance warrant further research.Peer reviewedFinal Published versio
Unified cyclic stress-strain model for normal and high strength concrete confined with FRP
Fiber reinforced polymer (FRP) has become increasingly popular as a confining material for concrete, both in the strengthening of existing columns where FRP wraps with fibers oriented completely or predominantly in the hoop direction are typically used, and in new construction where filament-wound FRP tubes with fibers oriented at desired angles to the longitudinal axis are typically used. For both types of applications, the stress-strain behavior of FRP-confined concrete under cyclic axial compression needs to be properly understood and modeled for the accurate simulation of such columns under seismic loading. This paper presents an improved cyclic stress-strain model for FRP-confined concrete on the basis of a critical assessment of an earlier model proposed by Lam and Teng in 2009 by making use of a database containing new test results of both concrete-filled FRP tubes (CFFTs) and concrete cylinders confined with an FRP wrap. The assessment reveals several deficiencies of Lam and Teng\u27s model due to the limited test results available to them. The proposed model corrects these deficiencies and is shown to provide reasonably accurate predictions for both concrete in CFFTs and concrete confined with an FRP wrap and for both normal strength concrete (NSC) and high strength concrete (HSC)
First-principles study on the effective masses of zinc-blend-derived Cu_2Zn-IV-VI_4 (IV = Sn, Ge, Si and VI = S, Se)
The electron and hole effective masses of kesterite (KS) and stannite (ST)
structured Cu_2Zn-IV-VI_4 (IV = Sn, Ge, Si and VI = S, Se) semiconductors are
systematically studied using first-principles calculations. We find that the
electron effective masses are almost isotropic, while strong anisotropy is
observed for the hole effective mass. The electron effective masses are
typically much smaller than the hole effective masses for all studied
compounds. The ordering of the topmost three valence bands and the
corresponding hole effective masses of the KS and ST structures are different
due to the different sign of the crystal-field splitting. The electron and hole
effective masses of Se-based compounds are significantly smaller compared to
the corresponding S-based compounds. They also decrease as the atomic number of
the group IV elements (Si, Ge, Sn) increases, but the decrease is less notable
than that caused by the substitution of S by Se.Comment: 14 pages, 6 figures, 2 table
A Storm in a "T" Cup
We revisit the process of transversification and agglomeration of particle
momenta that are often performed in analyses at hadron colliders, and show that
many of the existing mass-measurement variables proposed for hadron colliders
are far more closely related to each other than is widely appreciated, and
indeed can all be viewed as a common mass bound specialized for a variety of
purposes.Comment: 3 pages, 2 figures, presented by K.C. Kong at the 19th Particles and
Nuclei International Conference, PANIC 2011, MIT, Cambridge, MA (July 24-29,
2011
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