13,572 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
A novel CMB polarization likelihood package for large angular scales built from combined WMAP and Planck LFI legacy maps
We present a CMB large-scale polarization dataset obtained by combining WMAP
Ka, Q and V with Planck 70 GHz maps. We employ the legacy frequency maps
released by the WMAP and Planck collaborations and perform our own Galactic
foreground mitigation technique, which relies on Planck 353 GHz for polarized
dust and on Planck 30 GHz and WMAP K for polarized synchrotron. We derive a
single, optimally-noise-weighted, low-residual-foreground map and the
accompanying noise covariance matrix. These are shown, through
analysis, to be robust over an ample collection of Galactic masks. We use this
dataset, along with the Planck legacy Commander temperature solution, to build
a pixel-based low-resolution CMB likelihood package, whose robustness we test
extensively with the aid of simulations, finding excellent consistency. Using
this likelihood package alone, we constrain the optical depth to reionazation
at C.L., on 54\% of the sky. Adding the
Planck high- temperature and polarization legacy likelihood, the Planck
lensing likelihood and BAO observations we find
in a full CDM exploration. The
latter bounds are slightly less constraining than those obtained employing
\Planck\ HFI CMB data for large angle polarization, that only include EE
correlations. Our bounds are based on a largely independent dataset that does
include also TE correlations. They are generally well compatible with Planck
HFI preferring slightly higher values of . We make the low-resolution
Planck and WMAP joint dataset publicly available along with the accompanying
likelihood code.Comment: The WMAP+LFI likelihood module is available on
\http://www.fe.infn.it/u/pagano/low_ell_datasets/wmap_lfi_legacy
Interplay between bending and stretching in carbon nanoribbons
We investigate the bending properties of carbon nanoribbons by combining
continuum elasticity theory and tight-binding atomistic simulations. First, we
develop a complete analysis of a given bended configuration through continuum
mechanics. Then, we provide by tight-binding calculations the value of the
bending rigidity in good agreement with recent literature. We discuss the
emergence of a stretching field induced by the full atomic-scale relaxation of
the nanoribbon architecture. We further prove that such an in-plane strain
field can be decomposed into a first contribution due to the actual bending of
the sheet and a second one due to edge effects.Comment: 5 pages, 6 figure
Nanofriction behavior of cluster-assembled carbon films
We have characterized the frictional properties of nanostructured (ns) carbon
films grown by Supersonic Cluster Beam Deposition (SCBD) via an Atomic
Force-Friction Force Microscope (AFM-FFM). The experimental data are discussed
on the basis of a modified Amonton's law for friction, stating a linear
dependence of friction on load plus an adhesive offset accounting for a finite
friction force in the limit of null total applied load. Molecular Dynamics
simulations of the interaction of the AFM tip with the nanostructured carbon
confirm the validity of the friction model used for this system. Experimental
results show that the friction coefficient is not influenced by the
nanostructure of the films nor by the relative humidity. On the other hand the
adhesion coefficient depends on these parameters.Comment: 22 pages, 6 figures, RevTex
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