34,382 research outputs found
Solutions of Conformal Turbulence on a Half Plane
Exact solutions of conformal turbulence restricted on a upper half plane are
obtained. We show that the inertial range of homogeneous and isotropic
turbulence with constant enstrophy flux develops in a distant region from the
boundary. Thus in the presence of an anisotropic boundary, these exact
solutions of turbulence generalize Kolmogorov's solution consistently and
differ from the Polyakov's bulk case which requires a fine tunning of
coefficients. The simplest solution in our case is given by the minimal model
of and moreover we find a fixed point of solutions when
become large.Comment: 10pages, KHTP-93-07, SNUCTP-93-3
Analytical Results For The Steady State Of Traffic Flow Models With Stochastic Delay
Exact mean field equations are derived analytically to give the fundamental
diagrams, i.e., the average speed - car density relations, for the
Fukui-Ishibashi one-dimensional traffic flow cellular automaton model of high
speed vehicles with stochastic delay. Starting with the basic
equation describing the time evolution of the number of empty sites in front of
each car, the concepts of inter-car spacings longer and shorter than are
introduced. The probabilities of having long and short spacings on the road are
calculated. For high car densities , it is shown that
inter-car spacings longer than will be shortened as the traffic flow
evolves in time, and any initial configurations approach a steady state in
which all the inter-car spacings are of the short type. Similarly for low car
densities , it can be shown that traffic flow approaches an
asymptotic steady state in which all the inter-car spacings are longer than
. The average traffic speed is then obtained analytically as a function of
car density in the asymptotic steady state. The fundamental diagram so obtained
is in excellent agreement with simulation data.Comment: 12 pages, latex, 2 figure
Carrier-mediated antiferromagnetic interlayer exchange coupling in diluted magnetic semiconductor multilayers GaMnAs/GaAs:Be
We use neutron reflectometry to investigate the interlayer exchange coupling
between GaMnAs ferromagnetic semiconductor layers separated
by non-magnetic Be-doped GaAs spacers. Polarized neutron reflectivity measured
below the Curie temperature of GaMnAs reveals a
characteristic splitting at the wave vector corresponding to twice the
multilayer period, indicating that the coupling between the ferromagnetic
layers are antiferromagnetic (AFM). When the applied field is increased to
above the saturation field, this AFM coupling is suppressed. This behavior is
not observed when the spacers are undoped, suggesting that the observed AFM
coupling is mediated by charge carriers introduced via Be doping. The behavior
of magnetization of the multilayers measured by DC magnetometry is consistent
with the neutron reflectometry results.Comment: 4 pages, 4 figure
DEMAND FOR NUTRIENTS: THE HOUSEHOLD PRODUCTION APPROACH
The household production approach is used to characterize the household's preference toward nutrients in food consumption. Elasticities of substitution and Hicksian price elasticities are estimated, price- and expenditure-nutrient elasticities are calculated. Results show that protein is the most expensive nutrient, and that nutrients played an important role in determining households' food consumption.Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety,
Diameters in preferential attachment models
In this paper, we investigate the diameter in preferential attachment (PA-)
models, thus quantifying the statement that these models are small worlds. The
models studied here are such that edges are attached to older vertices
proportional to the degree plus a constant, i.e., we consider affine PA-models.
There is a substantial amount of literature proving that, quite generally,
PA-graphs possess power-law degree sequences with a power-law exponent \tau>2.
We prove that the diameter of the PA-model is bounded above by a constant
times \log{t}, where t is the size of the graph. When the power-law exponent
\tau exceeds 3, then we prove that \log{t} is the right order, by proving a
lower bound of this order, both for the diameter as well as for the typical
distance. This shows that, for \tau>3, distances are of the order \log{t}. For
\tau\in (2,3), we improve the upper bound to a constant times \log\log{t}, and
prove a lower bound of the same order for the diameter. Unfortunately, this
proof does not extend to typical distances. These results do show that the
diameter is of order \log\log{t}.
These bounds partially prove predictions by physicists that the typical
distance in PA-graphs are similar to the ones in other scale-free random
graphs, such as the configuration model and various inhomogeneous random graph
models, where typical distances have been shown to be of order \log\log{t} when
\tau\in (2,3), and of order \log{t} when \tau>3
Numerical framework for transcritical real-fluid reacting flow simulations using the flamelet progress variable approach
An extension to the classical FPV model is developed for transcritical
real-fluid combustion simulations in the context of finite volume, fully
compressible, explicit solvers. A double-flux model is developed for
transcritical flows to eliminate the spurious pressure oscillations. A hybrid
scheme with entropy-stable flux correction is formulated to robustly represent
large density ratios. The thermodynamics for ideal-gas values is modeled by a
linearized specific heat ratio model. Parameters needed for the cubic EoS are
pre-tabulated for the evaluation of departure functions and a quadratic
expression is used to recover the attraction parameter. The novelty of the
proposed approach lies in the ability to account for pressure and temperature
variations from the baseline table. Cryogenic LOX/GH2 mixing and reacting cases
are performed to demonstrate the capability of the proposed approach in
multidimensional simulations. The proposed combustion model and numerical
schemes are directly applicable for LES simulations of real applications under
transcritical conditions.Comment: 55th AIAA Aerospace Sciences Meeting, Dallas, T
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