1,948 research outputs found
Test code for the assessment and improvement of Reynolds stress models
An existing two-dimensional, compressible flow, Navier-Stokes computer code, containing a full Reynolds stress turbulence model, was adapted for use as a test bed for assessing and improving turbulence models based on turbulence simulation experiments. To date, the results of using the code in comparison with simulated channel flow and over an oscillating flat plate have shown that the turbulence model used in the code needs improvement for these flows. It is also shown that direct simulation of turbulent flows over a range of Reynolds numbers are needed to guide subsequent improvement of turbulence models
Path integral analysis of Jarzynski's equality: Analytical results
We apply path integrals to study nonequilibrium work theorems in the context
of Brownian dynamics, deriving in particular the equations of motion governing
the most typical and most dominant trajectories. For the analytically soluble
cases of a moving harmonic potential and a harmonic oscillator with
time-dependent natural frequency, we find such trajectories, evaluate the
work-weighted propagators, and validate Jarzynski's equality.Comment: 10 pages, 1 figur
Transport properties in Simplified Double Exchange model
Transport properties of the manganites by the double-exchange mechanism are
considered. The system is modeled by a simplified double-exchange model, i.e.
the Hund coupling of the itinerant electron spins and local spins is simplified
to the Ising-type one. The transport properties such as the electronic
resistivity, the thermal conductivity, and the thermal power are calculated by
using Dynamical mean-field theory. The transport quantities obtained
qualitatively reproduce the ones observed in the manganites. The results
suggest that the Simplified double exchange model underlies the key properties
of the manganites.Comment: 5 pages, 5 eps figure
The Infrared Properties of Submillimeter Galaxies: Clues From Ultra-Deep 70 Micron Imaging
We present 70 micron properties of submillimeter galaxies (SMGs) in the Great
Observatories Origins Deep Survey (GOODS) North field. Out of thirty
submillimeter galaxies (S_850 > 2 mJy) in the central GOODS-N region, we find
two with secure 70 micron detections. These are the first 70 micron detections
of SMGs. One of the matched SMGs is at z ~ 0.5 and has S_70/S_850 and S_70/S_24
ratios consistent with a cool galaxy. The second SMG (z = 1.2) has
infrared-submm colors which indicate it is more actively forming stars. We
examine the average 70 micron properties of the SMGs by performing a stacking
analysis, which also allows us to estimate that S_850 > 2 mJy SMGs contribute 9
+- 3% of the 70 micron background light. The S_850/S_70 colors of the SMG
population as a whole is best fit by cool galaxies, and because of the
redshifting effects these constraints are mainly on the lower z sub-sample. We
fit Spectral Energy Distributions (SEDs) to the far-infrared data points of the
two detected SMGs and the average low redshift SMG (z_{median}= 1.4). We find
that the average low-z SMG has a cooler dust temperature than local
ultraluminous infrared galaxies (ULIRGs) of similar luminosity and an SED which
is best fit by scaled up versions of normal spiral galaxies. The average low-z
SMG is found to have a typical dust temperature T = 21 -- 33 K and infrared
luminosity L_{8-1000 micron} = 8.0 \times 10^11 L_sun. We estimate the AGN
contribution to the total infrared luminosity of low-z SMGs is less than 23%.Comment: Accepted by ApJ. 14 pages, 6 figures. Minor revisions 20th Dec 200
Evaluation of drilling parameters of a PDC bit
A drilling model for PDC bit is presented herein within steady bit advance hypothesis, with taking into account influence of wear and its evolution. First, friction mechanism on cutter wear flats, is studied by experimental and numerical approach. It is shown to correspond to a relationship between the normal applied pressure to the cutter wear flat, and its subsequent dip angle α into the rock surface. It is shown that frictional wear is directly influenced by bit profile. Typical results are exhibited for elliptic profiles and compared with literature
From Quantum Mechanics to Quantum Field Theory: The Hopf route
We show that the combinatorial numbers known as {\em Bell numbers} are
generic in quantum physics. This is because they arise in the procedure known
as {\em Normal ordering} of bosons, a procedure which is involved in the
evaluation of quantum functions such as the canonical partition function of
quantum statistical physics, {\it inter alia}. In fact, we shall show that an
evaluation of the non-interacting partition function for a single boson system
is identical to integrating the {\em exponential generating function} of the
Bell numbers, which is a device for encapsulating a combinatorial sequence in a
single function. We then introduce a remarkable equality, the Dobinski
relation, and use it to indicate why renormalisation is necessary in even the
simplest of perturbation expansions for a partition function. Finally we
introduce a global algebraic description of this simple model, giving a Hopf
algebra, which provides a starting point for extensions to more complex
physical systems
sFuzz: An efficient adaptive fuzzer for solidity smart contracts
Ministry of Education, Singapore under its Academic Research Funding Tier
Fermi arc reconstruction in synthetic photonic lattice
The chiral surface states of Weyl semimetals have an open Fermi surface
called Fermi arc. At the interface between two Weyl semimetals, these Fermi
arcs are predicted to hybridize and alter their connectivity. In this letter,
we numerically study a one-dimensional (1D) dielectric trilayer grating where
the relative displacements between adjacent layers play the role of two
synthetic momenta. The lattice emulates 3D crystals without time-reversal
symmetry, including Weyl semimetal, nodal line semimetal, and Chern insulator.
Besides showing the phase transition between Weyl semimetal and Chern insulator
at telecom wavelength, this system allows us to observe the Fermi arc
reconstruction between two Weyl semimetals, confirming the theoretical
predictions.Comment: Main text: 4 pages, 4 figures. Supplemental materials: 19 pages, 18
figure
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