178 research outputs found
Impact of indentor sliding velocity and loading repetition factor on shear strain and structure dispersion in nanostructuring burnishing
The article probes into a relationship of the shear strain intensity and the shear strain rate in the surface layer and the sliding velocity of a spherical indentor and its loading repetition factor. It brings forward an experimental procedure to evaluate the shear strain intensity and rate by analyzing the geometrical parameters of the bulge of plastically edged metal and the thickness of the shifted layer relative to different sliding velocities and feed rates. © 2019 by University of Niš, Serbia
Experimental Analysis of the Laser-Induced Instruction Skip Fault Model
International audienceMicrocontrollers storing valuable data or using security functions are vulnerable to fault injection attacks. Among the various types of faults, instruction skips induced at runtime proved to be effective against identification routines or encryption algorithms. Several research works assessed a fault model that consists in a single instruction skip, i.e. the ability to prevent one chosen instruction in a program from being executed. This assessment is used to design countermeasures able to withstand a single instruction skip. We question this fault model on experimental basis and report the possibility to induce with a laser an arbitrary number of instruction skips. This ability to erase entire sections of a firmware has strong implications regarding the design of counter- measures
Noncommutative geometry and stochastic processes
The recent analysis on noncommutative geometry, showing quantization of the
volume for the Riemannian manifold entering the geometry, can support a view of
quantum mechanics as arising by a stochastic process on it. A class of
stochastic processes can be devised, arising as fractional powers of an
ordinary Wiener process, that reproduce in a proper way a stochastic process on
a noncommutative geometry. These processes are characterized by producing
complex values and so, the corresponding Fokker-Planck equation resembles the
Schroedinger equation. Indeed, by a direct numerical check, one can recover the
kernel of the Schroedinger equation starting by an ordinary Brownian motion.
This class of stochastic processes needs a Clifford algebra to exist. In four
dimensions, the full set of Dirac matrices is needed and the corresponding
stochastic process in a noncommutative geometry is easily recovered as is the
Dirac equation in the Klein-Gordon form being it the Fokker--Planck equation of
the process.Comment: 16 pages, 2 figures. Updated a reference. A version of this paper
will appear in the proceedings of GSI2017, Geometric Science of Information,
November 7th to 9th, Paris (France
Random Forest identification of the thin disk, thick disk and halo Gaia-DR2 white dwarf population
Gaia-DR2 has provided an unprecedented number of white dwarf candidates of
our Galaxy. In particular, it is estimated that Gaia-DR2 has observed nearly
400,000 of these objects and close to 18,000 up to 100 pc from the Sun. This
large quantity of data requires a thorough analysis in order to uncover their
main Galactic population properties, in particular the thin and thick disk and
halo components. Taking advantage of recent developments in artificial
intelligence techniques, we make use of a detailed Random Forest algorithm to
analyse an 8-dimensional space (equatorial coordinates, parallax, proper motion
components and photometric magnitudes) of accurate data provided by Gaia-DR2
within 100 pc from the Sun. With the aid of a thorough and robust population
synthesis code we simulated the different components of the Galactic white
dwarf population to optimize the information extracted from the algorithm for
disentangling the different population components. The algorithm is first
tested in a known simulated sample achieving an accuracy of 85.3%. Our
methodology is thoroughly compared to standard methods based on kinematic
criteria demonstrating that our algorithm substantially improves previous
approaches. Once trained, the algorithm is then applied to the Gaia-DR2 100 pc
white dwarf sample, identifying 12,227 thin disk, 1,410 thick disk and 95 halo
white dwarf candidates, which represent a proportion of 74:25:1, respectively.
Hence, the numerical spatial densities are , and
for the thin disk, thick disk and
halo components, respectively. The populations thus obtained represent the most
complete and volume-limited samples to date of the different components of the
Galactic white dwarf population.Comment: 18 pages, 11 figures and 3 tables. Accepted for publication in MNRA
The Gaia white dwarf population within 100 pc of the Sun
The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018The recent Gaia Data Release 2 has provided an
unprecedented sample of the local white dwarf
population. The high astrometric resolution and
the photometry provided by Gaia allows to build a
clean magnitude-color diagram that, with the aid
of the most updated population synthesis simulator,
permit us to select the sample of white dwarf
candidates. Our analysis shows that Gaia has virtually
identified all white dwarfs within 100 pc from
the Sun. Additionally, we use the Virtual Observatory
tool VOSA to derive effective temperatures and
luminosities for our sources by fitting their spectral
energy distributions. The Gaia 100 pc white dwarf
population is clearly dominated by cool (~8,000
K) objects and reveals a significant population of
massive (M ~ 0:8M ) white dwarfs, of which
no more than ~30 - 40% can be attributed to
hydrogen-deficient atmospheres. Preliminary results
including white dwarf mergers seem not to
explain this excess unless some ad hoc hypothesis
are adopted. Finally, we use an Intelligent Artificial
algorithm based on the Random Forest method to
disentangle the different Galactic components of
the white dwarf population. Our results show that
the thin, thick and halo ratio in the 100 pc sample
is 89:11:1, identifying 97 halo white dwarf candidates.Astronom
Crystal Undulator As A Novel Compact Source Of Radiation
A crystalline undulator (CU) with periodically deformed crystallographic
planes is capable of deflecting charged particles with the same strength as an
equivalent magnetic field of 1000 T and could provide quite a short period L in
the sub-millimeter range. We present an idea for creation of a CU and report
its first realization. One face of a silicon crystal was given periodic
micro-scratches (grooves), with a period of 1 mm, by means of a diamond blade.
The X-ray tests of the crystal deformation have shown that a sinusoidal-like
shape of crystalline planes goes through the bulk of the crystal. This opens up
the possibility for experiments with high-energy particles channeled in CU, a
novel compact source of radiation. The first experiment on photon emission in
CU has been started at LNF with 800 MeV positrons aiming to produce 50 keV
undulator photons.Comment: Presented at PAC 2003 (Portland, May 12-16
The analysis of speed increase perspectives of nanostructuring burnishing with heat removal from the tool
The work deals with investigation of opportunities of speed increase of nanostructuring burnishing due to heat removal from the contact area of severe plastic deformation using friction via the tool. The work has analyzed changes of the structure, thickness and quality of the modified layer, while increasing treatment speed of the tool without heat removal and with heat-cooling system. It is established that the cooling system of the tool indenter with a cooling capacity of 10 W allows for the two-times increase of the critical speed of burnishing, and when exceeding this speed, the deformable material does not turn into a nanostructuring state. It is shown that heat removal provides for a stable maintenance of the indenter temperature, an increase in thickness of the nanostructured layer up to 5 μm and roughness up to Ra=150 nanometers at processing speed up to 0.17 m/s
Effects of interatomic interaction on cooperative relaxation of two-level atoms
We study effects of direct interatomic interaction on cooperative processes
in atom-photon dynamics. Using a model of two-level atoms with Ising-type
interaction as an example, it is demonstrated that interparticle interaction
combined with atom-field coupling can introduce additional interatomic
correlations acting as a phase synchronizing factor. For the case of weakly
interacting atoms with , where is the interparticle
coupling constant and is the atomic frequency, dynamical regimes of
cooperative relaxation of atoms are analyzed in Born-Markov approximation both
numerically and using the mean field approximation. We show that interparticle
correlations induced by the direct interaction result in inhibition of
incoherent spontaneous decay leading to the regime of collective pulse
relaxation which differs from superradiance in nature. For superradiant
transition, the synchronizing effect of interatomic interaction is found to
manifest itself in enhancement of superradiance. When the interaction is strong
and , one-partice one-photon transitions are excluded and
transition to the regime of multiphoton relaxation occurs. Using a simple model
of two atoms in a high-Q single mode cavity we show that such transition is
accompanied by Rabi oscillations involving many-atom multiphoton states.
Dephasing effect of dipole-dipole interaction and solitonic mechanism of
relaxation are discussed.Comment: 34 pages, 8 figure
The UA9 experimental layout
The UA9 experimental equipment was installed in the CERN-SPS in March '09
with the aim of investigating crystal assisted collimation in coasting mode.
Its basic layout comprises silicon bent crystals acting as primary
collimators mounted inside two vacuum vessels. A movable 60 cm long block of
tungsten located downstream at about 90 degrees phase advance intercepts the
deflected beam.
Scintillators, Gas Electron Multiplier chambers and other beam loss monitors
measure nuclear loss rates induced by the interaction of the beam halo in the
crystal. Roman pots are installed in the path of the deflected particles and
are equipped with a Medipix detector to reconstruct the transverse distribution
of the impinging beam. Finally UA9 takes advantage of an LHC-collimator
prototype installed close to the Roman pot to help in setting the beam
conditions and to analyze the efficiency to deflect the beam. This paper
describes in details the hardware installed to study the crystal collimation
during 2010.Comment: 15pages, 11 figure, submitted to JINS
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