313 research outputs found
The Effects of Density, Spatial Pattern, and Competitive Symmetry on Size Variation in Simulated Plant Populations
Monte Carlo Simulation of a Random-Field Ising Antiferromagnet
Phase transitions in the three-dimensional diluted Ising antiferromagnet in
an applied magnetic field are analyzed numerically. It is found that random
magnetic field in a system with spin concentration below a certain threshold
induces a crossover from second-order phase transition to first-order
transition to a new phase characterized by a spin-glass ground state and
metastable energy states at finite temperatures.Comment: 10 pages, 11 figure
Numerical study of thermoviscous effects in ultrasound-induced acoustic streaming in microchannels
New Formulation of Causal Dissipative Hydrodynamics: Shock wave propagation
The first 3D calculation of shock wave propagation in a homogeneous QGP has
been performed within the new formulation of relativistic dissipative
hydrodynamics which preserves the causality. We found that the relaxation time
plays an important role and also affects the angle of Mach cone.Comment: 4 pages, 1 figure, Proceedings of Quark Matter 200
Equilibrium Relativistic Mass Distribution for Indistinguishable Events
A manifestly covariant relativistic statistical mechanics of the system of
indistinguishable events with motion in space-time parametrized by an
invariant ``historical time'' is considered. The relativistic mass
distribution for such a system is obtained from the equilibrium solution of the
generalized relativistic Boltzmann equation by integration over angular and
hyperbolic angular variables. All the characteristic averages are calculated.
Expressions for the pressure and the density of events are found and the
relativistic equation of state is obtained. The Galilean limit is considered;
the theory is shown to pass over to the usual nonrelativistic statistical
mechanics of indistinguishable particles.Comment: TAUP-2115-9
Coulomb drag in mesoscopic rings
We develop a Luttinger liquid theory of the Coulomb drag of persistent
currents flowing in concentric mesoscopic rings, by incorporating non-linear
corrections to the electron dispersion relation. We demonstrate that at low
temperatures, interactions between electrons in different rings generate an
additional phase and thus alter the period of Aharonov-Bohm oscillations. The
resulting nondissipative drag depends strongly on the relative parity of the
electron numbers. We also show that interactions set a new temperature scale
below which the linear response theory does not apply at certain values of
external flux.Comment: Latex 10 pages + 2 Figure
Theoretical study of time-dependent, ultrasound-induced acoustic streaming in microchannels
Based on first- and second-order perturbation theory, we present a numerical
study of the temporal build-up and decay of unsteady acoustic fields and
acoustic streaming flows actuated by vibrating walls in the transverse
cross-sectional plane of a long straight microchannel under adiabatic
conditions and assuming temperature-independent material parameters. The
unsteady streaming flow is obtained by averaging the time-dependent velocity
field over one oscillation period, and as time increases, it is shown to
converge towards the well-known steady time-averaged solution calculated in the
frequency domain. Scaling analysis reveals that the acoustic resonance builds
up much faster than the acoustic streaming, implying that the radiation force
may dominate over the drag force from streaming even for small particles.
However, our numerical time-dependent analysis indicates that pulsed actuation
does not reduce streaming significantly due to its slow decay. Our analysis
also shows that for an acoustic resonance with a quality factor Q, the
amplitude of the oscillating second-order velocity component is Q times larger
than the usual second-order steady time-averaged velocity component.
Consequently, the well-known criterion v << c for the validity of the
perturbation expansion is replaced by the more restrictive criterion v << c/Q.
Our numerical model is available in the supplemental material in the form of
Comsol model files and Matlab scripts.Comment: 14 pages, Revtex, 8 eps figure
Tropical tree height and crown allometries for the Barro Colorado Nature Monument, Panama: a comparison of alternative hierarchical models incorporating interspecific variation in relation to life history traits
Tree allometric relationships are widely employed for estimating forest biomass
and production and are basic building blocks of dynamic vegetation models.
In tropical forests, allometric relationships are often modeled by fitting
scale-invariant power functions to pooled data from multiple species, an
approach that fails to capture changes in scaling during ontogeny and
physical limits to maximum tree size and that ignores interspecific
differences in allometry. Here, we analyzed allometric relationships of tree
height (9884 individuals) and crown area (2425) with trunk diameter for 162
species from the Barro Colorado Nature Monument, Panama. We fit
nonlinear, hierarchical models informed by species traits –
wood density, mean sapling growth, or sapling mortality – and assessed the
performance of three alternative functional forms: the scale-invariant power
function and the saturating Weibull and generalized Michaelis–Menten (gMM)
functions. The relationship of tree height with trunk diameter was best fit
by a saturating gMM model in which variation in allometric parameters was
related to interspecific differences in sapling growth rates, a measure of
regeneration light demand. Light-demanding species attained taller heights at
comparatively smaller diameters as juveniles and had shorter asymptotic
heights at larger diameters as adults. The relationship of crown area with
trunk diameter was best fit by a power function model incorporating a weak
positive relationship between crown area and species-specific wood density.
The use of saturating functional forms and the incorporation of functional
traits in tree allometric models is a promising approach for improving estimates
of forest biomass and productivity. Our results provide an improved basis for
parameterizing tropical plant functional types in vegetation models.</p
Random-phase Approximation Treatment Of Edge Magnetoplasmons: Edge-state Screening And Nonlocality
A random-phase approximation (RPA) treatment of edge magnetoplasmons (EMP) is
presented for strong magnetic fields, low temperatures, and integer filling
factors \nu. It is valid for negligible dissipation and lateral confining
potentials smooth on the scale of the magnetic length \ell_{0} but sufficiently
steep that the Landau-level (LL) flattening can be neglected. LL coupling,
screening by edge states, and nonlocal contributions to the current density are
taken into account. In addition to the fundamental mode with typical dispersion
relation \omega\sim q_x \ln(q_{x}), fundamental modes with {\it acoustic}
dispersion relation \omega\sim q_x are obtained for \nu>2. For \nu=1,2 a {\bf
dipole} mode exists, with dispersion relation \omega\sim q_x^3, that is
directly related to nonlocal responses.Comment: Text 12 pages in Latex/Revtex format, 4 Postscript figure
Topography and instability of monolayers near domain boundaries
We theoretically study the topography of a biphasic surfactant monolayer in
the vicinity of domain boundaries. The differing elastic properties of the two
phases generally lead to a nonflat topography of ``mesas'', where domains of
one phase are elevated with respect to the other phase. The mesas are steep but
low, having heights of up to 10 nm. As the monolayer is laterally compressed,
the mesas develop overhangs and eventually become unstable at a surface tension
of about K(dc)^2 (dc being the difference in spontaneous curvature and K a
bending modulus). In addition, the boundary is found to undergo a
topography-induced rippling instability upon compression, if its line tension
is smaller than about K(dc). The effect of diffuse boundaries on these features
and the topographic behavior near a critical point are also examined. We
discuss the relevance of our findings to several experimental observations
related to surfactant monolayers: (i) small topographic features recently found
near domain boundaries; (ii) folding behavior observed in mixed phospholipid
monolayers and model lung surfactants; (iii) roughening of domain boundaries
seen under lateral compression; (iv) the absence of biphasic structures in
tensionless surfactant films.Comment: 17 pages, 9 figures, using RevTeX and epsf, submitted to Phys Rev
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