Phonon Transport in Asymmetric Sawtooth Nanowires

2011 ◽  
Author(s):  
N. A. Roberts ◽  
D. G. Walker
Keyword(s):  
Monte Carlo ◽  
Aspect Ratio ◽  
Monte Carlo Simulations ◽  
Free Path ◽  
Thermal Management ◽  
Strong Dependence ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Specular Reflections ◽  
Size Scales

Thermal transport in asymmetric sawtooth nanowires was investigated. The boundaries reflect phonons differently depending on the frequency and momentum of the phonon. These systems show thermally rectifying behavior when the boundary reflections are a function of both the direction the phonon is traveling and the frequency of the phonon. This rectifying effect could be useful for thermal management applications at all size scales, but would have to be built up from the nanoscale because of a strong dependence on the device aspect ratio and the Knudsen number of the system. Monte Carlo simulations show an accumulation of phonons at the boundary which emits phonons in a perceived rough direction where those phonons have some probability of diffuse reflections at the boundary while phonons emitted in the smooth direction only experience specular reflections at the boundary and are eventually thermalized at the opposite boundary. In this study the level of rectification of the system was linearly dependent on the device aspect ratio as long as the length of the device was near or below the phonon mean free path of the phonons.

Monte Carlo Simulations Of Elastic Scattering With Applications To Dc And High Power Pulsed Magnetron Sputtering For Ti3SIC2

2012 ◽  
Vol 11 (5) ◽  
pp. 1618-1642 ◽  
Author(s):  
Jürgen Geiser ◽  
Sven Blankenburg
Keyword(s):  
Monte Carlo ◽  
Magnetron Sputtering ◽  
Monte Carlo Simulations ◽  
Free Path ◽  
High Power ◽  
Mean Free Path ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Dc Sputtering ◽  
The Mean

AbstractWe simulate the particle transport in a thin film deposition process made by PVD (physical vapor deposition) and present several models for projectile and tar-get collisions in order to compute the mean free path and the differential cross section (angular distribution of scattered projectiles) of the scattering process. A detailed description of collision models is of the highest importance in Monte Carlo simulations of high power impulse magnetron sputtering and DC sputtering. We derive an equation for the mean free path for arbitrary interactions (cross sections) that includes the relative velocity between the particles. We apply our results to two major interaction models: hard sphere interaction & screened Coulomb interaction. Both types of interaction separate DC sputtering from HIPIMS.

scholarly journals Monte Carlo simulations of fast Newtonian and mildly relativistic shock breakout from a stellar wind

2020 ◽  
Vol 499 (4) ◽  
pp. 4961-4971
Author(s):  
Hirotaka Ito ◽  
Amir Levinson ◽  
Ehud Nakar
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Stellar Wind ◽  
Compact Star ◽  
Strong Dependence ◽  
Shock Velocity ◽  
Light Curves ◽  
Ultraviolet Emission ◽  
Relativistic Shocks ◽  
Strong Explosion

ABSTRACT Strong explosion of a compact star surrounded by a thick stellar wind drives a fast (>0.1c) radiation mediated shock (RMS) that propagates in the wind, and ultimately breaks out gradually once photons start escaping from the shock transition layer. In exceptionally strong or aspherical explosions, the shock velocity may even be relativistic. The properties of the breakout signal depend on the dynamics and structure of the shock during the breakout phase. Here we present, for the first time, spectra and light curves of the breakout emission of fast Newtonian and mildly relativistic shocks, that were calculated using self-consistent Monte Carlo simulations of finite RMS with radiative losses. We find a strong dependence of the νFν peak on shock velocity, ranging from ∼1 keV for vs/c = 0.1 to ∼100 keV for vs/c = 0.5, with a shift to lower energies as losses increase. For all cases studied the spectrum below the peak exhibits a nearly flat component (Fν ∼ ν0) that extends down to the break frequency below which absorption becomes important. This implies much bright optical/ultraviolet emission than hitherto expected. The computed light curves show a gradual rise over tens to hundreds of seconds for representative conditions. The application to SN 2008D/XRT 080109 and the detectability limits are also discussed. We predict a detection rate of about one per year with eROSITA.

scholarly journals Substitution Rates Under Stabilizing Selection

Genetics ◽  
1987 ◽  
Vol 116 (3) ◽  
pp. 479-486
Author(s):  
Alan Hastings
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Quantitative Traits ◽  
Strong Dependence ◽  
Phenotypic Selection ◽  
Analytical Models ◽  
Stabilizing Selection ◽  
Substitution Rates ◽  
Quantitative Characters ◽  
Selection For

ABSTRACT Allelic substitutions under stabilizing phenotypic selection on quantitative traits are studied in Monte Carlo simulations of 8 and 16 loci. The results are compared and contrasted to analytical models based on work of M. Kimura for two and "infinite" loci. Selection strengths of S = 4Nes approximately four (which correspond to reasonable strengths of selection for quantitative characters) can retard substitution rates tenfold relative to rates under neutrality. An important finding is a strong dependence of per locus substitution rates on the number of loci.

Mean Free Path of Gas Molecules in Organic Nanochannels Using Molecular Simulations

SPE Journal ◽  
2019 ◽  
Vol 24 (06) ◽  
pp. 2555-2573
Author(s):  
Seunghwan Baek ◽  
I.. Yucel Akkutlu
Keyword(s):  
Free Path ◽  
Average Length ◽  
Strong Dependence ◽  
Fluid Pressure ◽  
Molecular Simulations ◽  
Mean Free Path ◽  
Computational Method ◽  
Fluid Composition ◽  
Bulk Fluid ◽  
Gas Molecules

Summary A computational method using molecular–simulation data is introduced to estimate the average mean–free–path length of multicomponent hydrocarbon molecules in an organic nanochannel. Grand–canonical Monte Carlo (MC) simulation is used first to construct the equilibrium distribution of the gas molecules in the channel. These results show that the smaller the channel is, the denser the gas mixture becomes because of nanoconfinement effects. Capillary condensation occurs in the smaller channels. The fluid composition inside a channel becomes progressively heavier when the bulk–fluid pressure outside the nanopore is reduced and the lighter hydrocarbons leave the channel. The mean–free–path lengths of the confined molecules are computed using the trajectories of the molecules displaced over time in the equilibrium molecular–dynamics (MD) simulation. The average length of the confined molecules is estimated to be an order of magnitude smaller than the theoretical value. Further, the length does not show a strong dependence on the channel width and the pressure. Consequently, the predicted Knudsen–number value does not vary significantly, as anticipated by the kinetic theory of gases and by the molecular simulations of pure fluids. This invariance indicates that compositional change caused by nanoconfinement eliminates transition into other transport regimes where continuum mechanics is no longer valid.

scholarly journals Monte Carlo simulations of phonon transport in Si nanowires with constrictions

2015 ◽  
Vol 86 ◽  
pp. 648-655 ◽  
Author(s):  
V. Jean ◽  
S. Fumeron ◽  
K. Termentzidis ◽  
X. Zianni ◽  
D. Lacroix
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Phonon Transport ◽  
Si Nanowires
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