1,228 research outputs found
X-ray haloes and star formation in early-type galaxies
High resolution 2D hydrodynamical simulations describing the evolution of the
hot ISM in axisymmetric two-component models of early-type galaxies well
reproduced the observed trends of the X-ray luminosity () and
temperature () with galaxy shape and rotation, however they also
revealed the formation of an exceedingly massive cooled gas disc in rotating
systems. In a follow-up of this study, here we investigate the effects of star
formation in the disc, including the consequent injection of mass, momentum and
energy in the pre-existing interstellar medium. It is found that subsequent
generations of stars originate one after the other in the equatorial region;
the mean age of the new stars is Gyr, and the adopted recipe for star
formation can reproduce the empirical Kennicutt-Schmidt relation. The results
of the previous investigation without star formation, concerning
and of the hot gas, and their trends with galactic shape and
rotation, are confirmed. At the same time, the consumption of most of the cold
gas disc into new stars leads to more realistic final systems, whose cold gas
mass and star formation rate agree well with those observed in the local
universe. In particular, our models could explain the observation of
kinematically aligned gas in massive, fast-rotating early-type galaxies.Comment: 20 pages, 10 figures, 5 tables. Accepted for publication in MNRA
The effects of stellar dynamics on the X-ray emission of flat early-type galaxies
Observational and numerical studies gave hints that the hot gaseous haloes of
ETGs may be sensitive to the galaxy internal kinematics. By using high
resolution 2D hydro simulations, and realistic two-component (stars plus dark
matter) axisymmetric galaxy models, we study the evolution of the hot haloes in
a suite of flat ETGs of fixed mass distribution, but with variable amounts of
azimuthal velocity dispersion and rotational support, including the possibility
of a counter-rotating inner stellar disc. The hot halo is fed by stellar mass
losses and heated by SNIa explosions and thermalization of stellar motions. We
measure the value of the thermalization parameter gamma (the ratio between the
heating due to the relative velocity between the stellar streaming and the ISM
bulk flow, and the heating attainable by complete thermalization of the stellar
streaming motions). We find that 1) the X-ray emission and the average
temperature are larger in fully velocity dispersion supported systems; 2)
0.1<gamma<0.2 for isotropic rotators (with a trend for being larger for lower
dark mass models); 3) systems that are isotropic rotators at large radii with
an inner counter-rotating disc, or fully velocity dispersion supported systems
with an inner rotating disc, have gamma=1, again with a trend to increase for
lower dark mass contents. We also find that the lower X-ray luminosities of
isotropic rotators cannot be explained just by their low gamma, but are due to
the complicated flow structure, consequence of the angular momentum stored at
large radii. X-ray emission weighted temperatures and luminosities nicely match
observed values; the X-ray isophotes are boxy in case of significant galaxy
rotation. Overall, it is found that rotation has an important role to explain
the observational result that more rotationally supported ETGs on average show
a lower X-ray emission [abridged].Comment: 22 pages, 13 figures, accepted for publication in MNRAS. Comments
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Disk dynamics and the X-ray emission of S0 and flat early-type galaxies
With 2D hydrodynamical simulations, we study the evolution of the hot gas
flows in early-type galaxies, focussing on the effects of galaxy rotation on
the thermal and dynamical status of the ISM. The galaxy is modelled as a
two-component axisymmetric system (stars and dark matter), with a variable
amount of azimuthal velocity dispersion and rotational support; the presence of
a counter rotating stellar disk is also considered. It is found that the ISM of
the rotationally supported (isotropic) model is more prone to thermal
instabilities than the fully velocity dispersion counterpart, while its ISM
temperature and X-ray luminosity are lower. The model with counter rotation
shows an intermediate behaviour.Comment: 2 pages, 2 figures. Proceedings of the International Conference
"X-ray Astronomy: towards the next 50 years!", Milan, 1-5 Oct 201
A Non-blocking Buddy System for Scalable Memory Allocation on Multi-core Machines
Common implementations of core memory allocation components handle concurrent allocation/release requests by synchronizing threads via spin-locks. This approach is not prone to scale with large thread counts, a problem that has been addressed in the literature by introducing layered allocation services or replicating the core allocators - the bottom most ones within the layered architecture. Both these solutions tend to reduce the pressure of actual concurrent accesses to each individual core allocator. In this article we explore an alternative approach to scalability of memory allocation/release, which can be still combined with those literature proposals. We present a fully non-blocking buddy-system, that allows threads to proceed in parallel, and commit their allocations/releases unless a conflict is materialized while handling its metadata. Beyond improving scalability and performance it is resilient to performance degradation in face of concurrent accesses independently of the current level of fragmentation of the handled memory blocks
NBBS: A Non-blocking Buddy System for Multi-core Machines
Common implementations of core memory allocation components, like the Linux buddy system, handle concurrent allocation/release requests by synchronizing threads via spinlocks. This approach is not prone to scale with large thread counts, a problem that has been addressed in the literature by introducing layered allocation services or replicating the core allocators—the bottom most ones within the layered architecture. Both these solutions tend to reduce the pressure of actual concurrent accesses to each individual core allocator. In this article we explore an alternative approach to scalability of memory allocation/release, which can be still combined with those literature proposals. We present a fully non-blocking buddy-system, where threads performing concurrent allocations/releases do not undergo any spinlock based synchronization. Our solution allows threads to proceed in parallel, and commit their allocations/releases unless a conflict is materialized while handling its metadata. Conflict detection relies on conventional atomic machine instructions in the Read-Modify-Write (RMW) class. Beyond improving scalability and performance, our solution can also avoid wasting clock cycles for spin-lock operations by threads that could in principle carry out their memory allocation/release in full concurrency. Thus, it is resilient to performance degradation—in face of concurrent accesses—independently of the current level of fragmentation of the handled memory blocks
Machine Learning-Based Elastic Cloud Resource Provisioning in the Solvency II Framework
The Solvency II Directive (Directive 2009/138/EC) is a European Directive issued in November 2009 and effective from January 2016, which has been enacted by the European Union to regulate the insurance and reinsurance sector through the discipline of risk management. Solvency II requires European insurance companies to conduct consistent evaluation and continuous monitoring of risks—a process which is computationally complex and extremely resource-intensive. To this end, companies are required to equip themselves with adequate IT infrastructures, facing a significant outlay.
In this paper we present the design and the development of a Machine Learning-based approach to transparently deploy on a cloud environment the most resource-intensive portion of the Solvency II-related computation. Our proposal targets DISAR®, a Solvency II-oriented system initially designed to work on a grid of conventional computers. We show how our solution allows to reduce the overall expenses associated with the computation, without hampering the privacy of the companies’ data (making it suitable for conventional public cloud environments), and allowing to meet the strict temporal requirements required by the Directive. Additionally, the system is organized as a self-optimizing loop, which allows to use information gathered from actual (useful) computations, thus requiring a shorter training phase. We present an experimental study conducted on Amazon EC2 to assess the validity and the efficiency of our proposal
Charger-mediated energy transfer in exactly-solvable models for quantum batteries
We present a systematic analysis and classification of several models of
quantum batteries involving different combinations of two level systems and
quantum harmonic oscillators. In particular, we study energy transfer processes
from a given quantum system, termed charger, to another one, i.e. the proper
battery. In this setting, we analyze different figures of merit, including the
charging time, the maximum energy transfer, and the average charging power. The
role of coupling Hamiltonians which do not preserve the number of local
excitations in the charger-battery system is clarified by properly accounting
them in the global energy balance of the model.Comment: 11 page
Photocurrent-based detection of Terahertz radiation in graphene
Graphene is a promising candidate for the development of detectors of
Terahertz (THz) radiation. A well-known detection scheme due to Dyakonov and
Shur exploits the confinement of plasma waves in a field-effect transistor
(FET), whereby a dc photovoltage is generated in response to a THz field. This
scheme has already been experimentally studied in a graphene FET [L. Vicarelli
et al., Nature Mat. 11, 865 (2012)]. In the quest for devices with a better
signal-to-noise ratio, we theoretically investigate a plasma-wave photodetector
in which a dc photocurrent is generated in a graphene FET. The rectified
current features a peculiar change of sign when the frequency of the incoming
radiation matches an even multiple of the fundamental frequency of plasma waves
in the FET channel. The noise equivalent power per unit bandwidth of our device
is shown to be much smaller than that of a Dyakonov-Shur detector in a wide
spectral range.Comment: 5 pages, 4 figure
Model of murine ventricular cardiac tissue for in vitro kinematic-dynamic studies of electromagnetic and beta2-adrenergic stimulation
In a model of murine ventricular cardiac tissue in vitro, we have studied the inotropic effects of electromagnetic stimulation (frequency, 75 Hz), isoproterenol administration (10 μM), and their combination. In particular, we have performed an image processing analysis to evaluate the kinematics and the dynamics of beating cardiac syncytia starting from the video registration of their contraction movement. We have found that the electromagnetic stimulation is able to counteract the β-adrenergic effect of isoproterenol and to elicit an antihypertrophic response
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