86,805 research outputs found
On Mitigation of Side-Channel Attacks in 3D ICs: Decorrelating Thermal Patterns from Power and Activity
Various side-channel attacks (SCAs) on ICs have been successfully
demonstrated and also mitigated to some degree. In the context of 3D ICs,
however, prior art has mainly focused on efficient implementations of classical
SCA countermeasures. That is, SCAs tailored for up-and-coming 3D ICs have been
overlooked so far. In this paper, we conduct such a novel study and focus on
one of the most accessible and critical side channels: thermal leakage of
activity and power patterns. We address the thermal leakage in 3D ICs early on
during floorplanning, along with tailored extensions for power and thermal
management. Our key idea is to carefully exploit the specifics of material and
structural properties in 3D ICs, thereby decorrelating the thermal behaviour
from underlying power and activity patterns. Most importantly, we discuss
powerful SCAs and demonstrate how our open-source tool helps to mitigate them.Comment: Published in Proc. Design Automation Conference, 201
On the ICS interpretation of the Hard X-Ray Excesses in Galaxy Clusters: the case of Ophiuchus
(Abridged) High-E electrons produce Hard X-Ray (HXR) emission in galaxy
clusters by via Inverse Compton Scattering (ICS) of CMB photons. We derive the
ICS HXR emission of Ophiuchus under various scenarios: primary cosmic ray
model, secondary cosmic rays model and neutralino DM annihilation scenario. We
further discuss the predictions of the Warming Ray model for the cluster
atmosphere. Under the assumption to fit the observed HXR emission, we find that
the high-E electrons induce various consequences on the cluster atmosphere: i)
primary electrons can be marginally consistent with the data provided that
their spectrum is cutoff at E~30(90) MeV for spectral index of 3.5 (4.4); ii)
secondary electron models from pp collisions are inconsistent with gamma-ray
limits, cosmic ray protons produce too much heating of the IC gas and their
pressure at the cluster center largely exceeds the thermal one; iii) secondary
electron models from DM annihilation are inconsistent with gamma-ray and radio
limits and electrons produce too much heating of the IC gas at the cluster
center, unless the neutralino annihilation cross section is much lower than the
proposed value. We conclude that ICS by secondary electrons from both
neutralino DM annihilation and pp collisions cannot be the mechanism
responsible for the HXR excess emission; primary electrons are still a
marginally viable solution provided that their spectrum has a low-energy cutoff
at E~30-90 MeV. The WR model offers, so far, the best description of the
cluster in terms of temperature distribution, heating, pressure and spectral
energy distribution. Fermi observations of Ophiuchus will set further
constraints to this model.Comment: 10 pages, 9 figures, A&A in pres
Warming rays in cluster cool cores
We present a model of cosmic ray heating of clusters' cores that reproduces
the observed temperature distribution in clusters by using an energy balance
condition in which the emitted X-ray energy is supplied by the hadronic cosmic
rays, which act as warming rays (WRs). The temperature profile of the IC gas is
correlated with the WR pressure distribution and, consequently, with the
non-thermal emission (radio, hard X-ray and gamma-ray) induced by the
interaction of the WRs with the IC gas and magnetic field. The temperature
distribution of the IC gas in both cool-core and non cool-core clusters is
successfully predicted from the measured IC gas density distribution. Under
this contraint, the WR model is also able to reproduce the thermal and
non-thermal pressure distribution in clusters, as well as their radial entropy
distribution. The WR model provides other observable features: a correlation of
the pressure ratio (WRs to thermal IC gas) with the inner cluster temperature
T_{inner}, a correlation of the gamma-ray luminosity with T_{inner}, a
substantial number of cool-core clusters observable with the GLAST-LAT
experiment, a surface brightness of radio halos in cool-core clusters that
recovers the observed one, a hard X-ray emission from cool-core clusters that
is systematically lower than the observed limits and yet observable with the
next generation HXR experiments like Simbol-X. The specific theoretical
properties and the multi-frequency distribution of the e.m. signals predicted
in the WR model render it quite different from the other models proposed for
the heating of clusters' cool-cores. Such differences make it possible to prove
or disprove our model as an explanation of the cooling-flow problems on the
basis of multi-frequency observations of galaxy clusters.Comment: 19 pages, 17 figures, A&A in pres
Disentangling the gamma-ray emission of NGC1275 and that of the Perseus cluster
(Abridged). The gamma-ray emission from galaxy clusters hosting active
galaxies is a complex combination of diffuse and point-like emission with
different spectral and spatial properties. We discuss the case of the Perseus
cluster containing the radio-galaxy NGC 1275 that has been detected as a bright
gamma-ray source by the Fermi-LAT experiment. We provide a detailed study of
the gamma-ray emission coming from the core of Perseus by modeling the central
AGN emission with a multiple plasma blob model, and the emission from the
cluster atmosphere with both a Warming Ray (WR) model and Dark Matter (DM)
neutralino annihilation models. We set constraints on both the central galaxy
and cluster SED models by using multi-frequency data including the observations
obtained by Fermi and MAGIC. We find that: i) in all the viable models for the
cluster gamma-ray emission, the emission detected by Fermi from the Perseus
core is dominated by the active galaxy NGC 1275, that is found in a
high-emission state; ii) the diffuse gamma-ray emission of the cluster, in the
WR model and in the DM models with the highest allowed normalization, could be
detected by Fermi if the central emission from NGC1275 is in a low-emission
state; iii) Fermi can have the possibility to resolve and detect the diffuse
gamma-ray flux coming from the outer corona of the Perseus atmosphere at r> 800
kpc. Our results show that a simultaneous study of the various emission
mechanisms that produce diffuse gamma-rays from galaxy clusters and those
producing gamma-rays from active galaxies residing in the cluster atmospheres
is crucial first to disentangle the spectral and spatial characteristics of the
gamma-ray emission and secondly to assess the optimal observational strategy in
the attempt to reveal the still elusive diffuse gamma-ray emission widely
predicted for the atmospheres of large-scale structures.Comment: 14 pages, 14 figures, A&A in pres
SZ effect from radio-galaxy lobes: astrophysical and cosmological relevance
We derive the SZ effect arising in radio-galaxy lobes that are filled with
high-energy, non-thermal electrons. We provide here quantitative estimates for
SZ effect expected from the radio galaxy lobes by normalizing it to the
Inverse-Compton light, observed in the X-ray band, as produced by the
extrapolation to low energies of the radio emitting electron spectrum in these
radio lobes. We compute the spectral and spatial characteristics of the SZ
effect associated to the radio lobes of two distant radio galaxies (3C294 and
3C432) recently observed by Chandra, and we further discuss its detectability
with the next generation microwave and sub-mm experiments with arcsec and K sensitivity. We finally highlight the potential use of the SZE from
radio-galaxy lobes in the astrophysical and cosmological context.Comment: 8 pages, 5 figures, MNRAS in pres
Dark Matter in Modern Cosmology
The presence of Dark Matter (DM) is required in the universe regulated by the
standard general relativistic theory of gravitation. The nature of DM is
however still elusive to any experimental search. We discuss here the process
of accumulation of evidence for the presence of DM in the universe, the
astrophysical probes for the leading DM scenarios that can be obtained through
a multi-frequency analysis of cosmic structures on large scales, and the
strategies related to the multi-messenger and multi-experiment astrophysical
search for the nature of the DM.Comment: 25 pages, 9 figures. Updated version of the review included in
ASTROPHYSICS AND COSMOLOGY AFTER GAMOW: Proceedings of the 4th Gamow
International Conference on Astrophysics and Cosmology After Gamow and the
9th Gamow Summer School "Astronomy and Beyond: Astrophysics, Cosmology, Radio
Astronomy, High Energy Physics and Astrobiology". AIP Conference Proceedings,
Volume 1206, p.
Bayesian semi-blind component separation for foreground removal in interferometric 21-cm observations
We present in this paper a new Bayesian semi-blind approach for foreground
removal in observations of the 21-cm signal with interferometers. The
technique, which we call HIEMICA (HI Expectation-Maximization Independent
Component Analysis), is an extension of the Independent Component Analysis
(ICA) technique developed for two-dimensional (2D) CMB maps to
three-dimensional (3D) 21-cm cosmological signals measured by interferometers.
This technique provides a fully Bayesian inference of power spectra and maps
and separates the foregrounds from signal based on the diversity of their power
spectra. Only relying on the statistical independence of the components, this
approach can jointly estimate the 3D power spectrum of the 21-cm signal and,
the 2D angular power spectrum and the frequency dependence of each foreground
component, without any prior assumptions about foregrounds. This approach has
been tested extensively by applying it to mock data from interferometric 21-cm
intensity mapping observations under idealized assumptions of instrumental
effects. We also discuss the impact when the noise properties are not known
completely. As a first step toward solving the 21 cm power spectrum analysis
problem we compare the semi-blind HIEMICA technique with the commonly used
Principal Component Analysis (PCA). Under the same idealized circumstances the
proposed technique provides significantly improved recovery of the power
spectrum. This technique can be applied straightforwardly to all 21-cm
interferometric observations, including epoch of reionization measurements, and
can be extended to single-dish observations as well.Comment: 18 pages, 7 figures, added some discussions about the impact of noise
misspecificatio
Solar flares and Kelvin-Helmholtz instabilities: A parameter survey
Hard X-ray (HXR) sources are frequently observed near the top of solar flare
loops, and the emission is widely ascribed to bremsstrahlung. We here revisit
an alternative scenario which stresses the importance of inverse Compton
processes and the Kelvin- Helmholtz instability (KHI) proposed by Fang et al.
(2016). This scenario adds a novel ingredient to the standard flare model,
where evaporation flows from flare-impacted chromospheric foot-points interact
with each other near the loop top and produce turbulence via KHI. The
turbulence can act as a trapping region and as an efficient accelerator to
provide energetic electrons, which scatter soft X-ray (SXR) photons to HXR
photons via the inverse Compton mechanism. This paper focuses on the trigger of
the KHI and the resulting turbulence in this new scenario. We perform a
parameter survey to investigate the necessary ingredients to obtain KHI through
interaction of chromospheric evaporation flows. When turbulence is produced in
the loop apex, an index of -5/3 can be found in the spectra of velocity and
magnetic field fluctuations. The KHI development and the generation of
turbulence are controlled by the amount of energy deposited in the
chromospheric foot-points and the time scale of its energy deposition, but
typical values for M class flares show the KHI development routinely. Asymmetry
of energy deposition determines the location where the turbulence is produced,
and the synthesized SXR light curve shows a clear periodic signal related to
the sloshing motion of the vortex pattern created by the KHI.Comment: 12 pages, 14 figure
A multi-frequency study of the SZE in giant radio galaxies
Radio-galaxy (RG) lobes contain relativistic electrons embedded in a tangled
magnetic field that produce, in addition to low-frequency synchrotron radio
emission, inverse-Compton scattering (ICS) of the cosmic microwave background
(CMB) photons. This produces a relativistic, non-thermal Sunyaev-Zel'dovich
effect (SZE). We study the spectral and spatial properties of the non-thermal
SZE in a sample of radio galaxies and make predictions for their detectability
in both the negative and the positive part of the SZE, with space experiments
like Planck, OLIMPO, and Herschel-SPIRE. These cover a wide range of
frequencies, from radio to sub-mm. We model the SZE in a general formalism that
is equivalent to the relativistic covariant one and describe the electron
population contained in the lobes of the radio galaxies with parameters derived
from their radio observations, namely, flux, spectral index, and spatial
extension. We further constrain the electron spectrum and the magnetic field of
the RG lobes using X-ray, gamma-ray, and microwave archival observations. We
determine the main spectral features of the SZE in RG lobes, namely, the
minimum, the crossover, and the maximum of the SZE. We show that these typical
spectral features fall in the frequency ranges probed by the available space
experiments. We provide the most reliable predictions for the amplitude and
spectral shape of the SZE in a sample of selected RGs with extended lobes. In
three of these objects, we also derive an estimate of the magnetic field in the
lobe at the muG level by combining radio (synchrotron) observations and X-ray
(ICS) observations. These data, together with the WMAP upper limits, set
constraints on the minimum momentum of the electrons residing in the RG lobes
and allow realistic predictions for the visibility of their SZE to be derived
with Planck, OLIMPO, and Herschel-SPIRE. [abridged]Comment: 26 pages, 21 figures; Astronomy and Astrophysics, in pres
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