5,977 research outputs found
Thermal boundary resistance at Si/Ge interfaces determined by approach-to-equilibrium molecular dynamics simulations
The thermal boundary resistance of Si/Ge interfaces as been determined using
approach-to-equilibrium molecular dynamics simulations. Assuming a reciprocal
linear dependence of the thermal boundary resistance, a length-independent bulk
thermal boundary resistance could be extracted from the calculation resulting
in a value of 3.76x10 m K/W for a sharp Si/Ge interface and thermal
transport from Si to Ge. Introducing an interface with finite thickness of 0.5
nm consisting of a SiGe alloy, the bulk thermal resistance slightly decreases
compared to the sharp Si/Ge interface. Further growth of the boundary leads to
an increase in the bulk thermal boundary resistance. When the heat flow is
inverted (Ge to Si), the thermal boundary resistance is found to be higher.
From the differences in the thermal boundary resistance for different heat flow
direction, the rectification factor of the Si/Ge has been determined and is
found to significantly decrease when the sharp interface is moderated by
introduction of a SiGe alloy in the boundary layer.Comment: 7 pages, 6 figure
TG, FT-IR and NMR characterization of n-C16H34 contaminated alumina and silica after mechanochemical treatment
This paper deals with the application of mechanochemistry to model systems composed of alumina or silica artificially contaminated with n-C16H34. The mechanochemical treatment was carried out by means of a ring mill for times ranging from 10 to 40 h. Thermogravimetry and infrared and nuclear magnetic resonance spectroscopies were used for the characterization of the mechanochemical products. The results have indicated that, in the case of alumina, almost all the contaminant n-C16H34 undergoes a complex oxidative reaction path whose end products are strongly held on the surface. These end products are most likely made of crosslinked, partially oxidized hydrocarbon chains bond to the solid surface via COO− groups. In the case of silica, the hydrocarbon undergoes a different, equally complex reaction path, but to a lower extent. In this case the end products are most probably carbonylic compounds and graphitic carbon. Then, for both solid matrices, the mechanochemical treatment promotes significant modification of the chemical nature of the polluting hydrocarbon with end products much more difficult to remove from the surface. As the systems studied are models of sites contaminated by aliphatic hydrocarbon, the results are worthy of consideration in relation to the mobility of the contaminants in the environment
Polarized Proton Pionic Capture in Deuterium as a Probe of 3N Dynamics
The proton analyzing power Ay in pion production reaction pd --> pi0 3He has
been calculated including one- and two-body meson production mechanisms with a
proper treatment of the three-nucleon dynamics and an accurate solution of the
3N bound-state problem for phenomenological two-nucleon potentials. In the
region around the Delta resonance, the structure of the analyzing power can be
understood once interference effects among amplitudes describing intermediate
Delta N formation in different orbital states are considered along with the
additional interference with the S-wave pion production amplitudes. Then, the
inclusion of three-nucleon dynamics in the initial state produces the structure
of the analyzing power that has been observed experimentally.Comment: 9 pages, 5 figure
Accurate evolutions of inspiralling and magnetized neutron-stars: equal-mass binaries
By performing new, long and numerically accurate general-relativistic
simulations of magnetized, equal-mass neutron-star binaries, we investigate the
role that realistic magnetic fields may have in the evolution of these systems.
In particular, we study the evolution of the magnetic fields and show that they
can influence the survival of the hypermassive-neutron star produced at the
merger by accelerating its collapse to a black hole. We also provide evidence
that even if purely poloidal initially, the magnetic fields produced in the
tori surrounding the black hole have toroidal and poloidal components of
equivalent strength. When estimating the possibility that magnetic fields could
have an impact on the gravitational-wave signals emitted by these systems
either during the inspiral or after the merger we conclude that for realistic
magnetic-field strengths B<~1e12 G such effects could be detected, but only
marginally, by detectors such as advanced LIGO or advanced Virgo. However,
magnetically induced modifications could become detectable in the case of
small-mass binaries and with the development of gravitational-wave detectors,
such as the Einstein Telescope, with much higher sensitivities at frequencies
larger than ~2 kHz.Comment: 18 pages, 10 figures. Added two new figures (figures 1 and 7). Small
modifications to the text to match the version published on Phys. Rev.
GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?
On the basis of the recent understanding of GRB050315 and GRB060218, we
return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow.
We proposed it as the prototype for a new class of GRBs with "an occasional
softer extended emission lasting tenths of seconds after an initial spikelike
emission". Detailed theoretical computation of the GRB970228 light curves in
selected energy bands for the prompt emission are presented and compared with
observational BeppoSAX data. From our analysis we conclude that GRB970228 and
likely the ones of the above mentioned new class of GRBs are "canonical GRBs"
have only one peculiarity: they exploded in a galactic environment, possibly
the halo, with a very low value of CBM density. Here we investigate how
GRB970228 unveils another peculiarity of this class of GRBs: they do not
fulfill the "Amati relation". We provide a theoretical explanation within the
fireshell model for the apparent absence of such correlation for the GRBs
belonging to this new class.Comment: 5 pages, 3 figures, in the Proceedings of the "4th Italian-Sino
Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28,
2007, C.L. Bianco, S.-S. Xue, Editor
A Fast and Accurate Nonlinear Spectral Method for Image Recognition and Registration
This article addresses the problem of two- and higher dimensional pattern
matching, i.e. the identification of instances of a template within a larger
signal space, which is a form of registration. Unlike traditional correlation,
we aim at obtaining more selective matchings by considering more strict
comparisons of gray-level intensity. In order to achieve fast matching, a
nonlinear thresholded version of the fast Fourier transform is applied to a
gray-level decomposition of the original 2D image. The potential of the method
is substantiated with respect to real data involving the selective
identification of neuronal cell bodies in gray-level images.Comment: 4 pages, 3 figure
Elastic properties of hydrogenated graphene
There exist three conformers of hydrogenated graphene, referred to as chair-,
boat-, or washboard-graphane. These systems have a perfect two-dimensional
periodicity mapped onto the graphene scaffold, but they are characterized by a
orbital hybridization, have different crystal symmetry, and otherwise
behave upon loading. By first principles calculations we determine their
structural and phonon properties, as well as we establish their relative
stability. Through continuum elasticity we define a simulation protocol
addressed to measure by a computer experiment their linear and nonlinear
elastic moduli and we actually compute them by first principles. We argue that
all graphane conformers respond to any arbitrarily-oriented extention with a
much smaller lateral contraction than the one calculated for graphene.
Furthermore, we provide evidence that boat-graphane has a small and negative
Poisson ratio along the armchair and zigzag principal directions of the carbon
honeycomb lattice (axially auxetic elastic behavior). Moreover, we show that
chair-graphane admits both softening and hardening hyperelasticity, depending
on the direction of applied load.Comment: submitted on Phys.Rev.
The approach to typicality in many-body quantum systems
The recent discovery that for large Hilbert spaces, almost all (that is,
typical) Hamiltonians have eigenstates that place small subsystems in thermal
equilibrium, has shed much light on the origins of irreversibility and
thermalization. Here we give numerical evidence that many-body lattice systems
generically approach typicality as the number of subsystems is increased, and
thus provide further support for the eigenstate thermalization hypothesis. Our
results indicate that the deviation of many-body systems from typicality
decreases exponentially with the number of systems. Further, by averaging over
a number of randomly-selected nearest-neighbor interactions, we obtain a
power-law for the atypicality as a function of the Hilbert space dimension,
distinct from the power-law possessed by random Hamiltonians.Comment: 6 pages, 2 png figures, revtex
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