470 research outputs found
Simulation of hurricane response to suppression of warm rain by sub-micron aerosols
The feasibility of hurricane modification was investigated for hurricane Katrina using the Weather Research and Forecasting Model (WRF). The possible impact of seeding of clouds with submicron cloud condensation nuclei (CCN) on hurricane structure and intensity as measured by nearly halving of the area covered by hurricane force winds was simulated by "turning&ndash;off" warm rain formation in the clouds at Katrina's periphery (where wind speeds were less than 22 m s<sup>&minus;1</sup>). This simplification of the simulation of aerosol effects is aimed at evaluating the largest possible response. This resulted in the weakening of the hurricane surface winds compared to the "non-seeded" simulated storm during the first 24 h within the entire tropical cyclone (TC) area compared to a control simulation without warm rain suppression. Later, the seeding-induced evaporative cooling at the TC periphery led to a shrinking of the eye and hence to some increase in the wind within the small central area of the TC. Yet, the overall strength of the hurricane, as defined by the area covered by hurricane force winds, decreased in response to the suppressed warm rain at the periphery, as measured by a 25% reduction in the radius of hurricane force winds. In a simulation with warm rain suppression throughout the hurricane, the radius of the hurricane force winds was reduced by more than 42%, and although the diameter of the eye shrunk even further the maximum winds weakened. This shows that the main mechanism by which suppressing warm rain weakens the TC is the low level evaporative cooling of the un-precipitated cloud drops and the added cooling due to melting of precipitation that falls from above
Pattern Formation of Glioma Cells: Effects of Adhesion
We investigate clustering of malignant glioma cells. \emph{In vitro}
experiments in collagen gels identified a cell line that formed clusters in a
region of low cell density, whereas a very similar cell line (which lacks an
important mutation) did not cluster significantly. We hypothesize that the
mutation affects the strength of cell-cell adhesion. We investigate this effect
in a new experiment, which follows the clustering dynamics of glioma cells on a
surface. We interpret our results in terms of a stochastic model and identify
two mechanisms of clustering. First, there is a critical value of the strength
of adhesion; above the threshold, large clusters grow from a homogeneous
suspension of cells; below it, the system remains homogeneous, similarly to the
ordinary phase separation. Second, when cells form a cluster, we have evidence
that they increase their proliferation rate. We have successfully reproduced
the experimental findings and found that both mechanisms are crucial for
cluster formation and growth.Comment: 6 pages, 6 figure
Trading particle shape with fluid symmetry: on the mobility matrix in 3D chiral fluids
Chiral fluids - such as fluids under rotation or a magnetic field as well as
synthetic and biological active fluids - flow in a different way than ordinary
ones. Due to symmetries broken at the microscopic level, chiral fluids may have
asymmetric stress and viscosity tensors, for example giving rise to a
hydrostatic torque or non-dissipative (odd) and parity-violating viscosities.
In this article, we investigate the motion of rigid bodies in such an
anisotropic fluid in the incompressible Stokes regime through the mobility
matrix, which encodes the response of a solid body to forces and torques. We
demonstrate how the form of the mobility matrix, which is usually determined by
particle geometry, can be analogously controlled by the symmetries of the
fluid. By computing the mobility matrix for simple shapes in a
three-dimensional anisotropic chiral fluid, we predict counter-intuitive
phenomena such as motion perpendicular to applied forces and spinning under the
force of gravity.Comment: 31 pages, 7 figure
The Role of Atmospheric Aerosol Concentration on Deep Convective Precipitation: Cloud-resolving Model Simulations
Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 20011. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds NRC [2001]." The aerosol effect on clouds is often categorized into the traditional "first indirect (i.e., Twomey)" effect on the cloud droplet sizes for a constant liquid water path and the "semi-direct" effect on cloud coverage. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect, is even more complex, especially for mixed-phase convective clouds. ln this paper, a cloud-resolving model (CRM) with detailed spectral-bin microphysics was used to examine the effect of aerosols on three different deep convective cloud systems that developed in different geographic locations: South Florida, Oklahoma and the Central Pacific. In all three cases, rain reaches the ground earlier for the low CCN (clean) case. Rain suppression is also evident in all three cases with high CCN (dirty) case. However, this suppression only occurs during the first hour of the simulations. During the mature stages of the simulations, the effects of increasing aerosol concentration range from rain suppression in the Oklahoma case, to almost no effect in the Florida case, to rain enhancement in the Pacific case. These results show the complexity of aerosol interactions with convection
The role of cell-cell adhesion in wound healing
We present a stochastic model which describes fronts of cells invading a
wound. In the model cells can move, proliferate, and experience cell-cell
adhesion. We find several qualitatively different regimes of front motion and
analyze the transitions between them. Above a critical value of adhesion and
for small proliferation large isolated clusters are formed ahead of the front.
This is mapped onto the well-known ferromagnetic phase transition in the Ising
model. For large adhesion, and larger proliferation the clusters become
connected (at some fixed time). For adhesion below the critical value the
results are similar to our previous work which neglected adhesion. The results
are compared with experiments, and possible directions of future work are
proposed.Comment: to appear in Journal of Statistical Physic
Non-homogeneous random walks, subdiffusive migration of cells and anomalous chemotaxis
This paper is concerned with a non-homogeneous in space and non-local in time
random walk model for anomalous subdiffusive transport of cells. Starting with
a Markov model involving a structured probability density function, we derive
the non-local in time master equation and fractional equation for the
probability of cell position. We show the structural instability of fractional
subdiffusive equation with respect to the partial variations of anomalous
exponent. We find the criteria under which the anomalous aggregation of cells
takes place in the semi-infinite domain.Comment: 18 pages, accepted for publicatio
A generalized Cahn-Hilliard equation for biological applications
Recently we considered a stochastic discrete model which describes fronts of
cells invading a wound \cite{KSS}. In the model cells can move, proliferate,
and experience cell-cell adhesion. In this work we focus on a continuum
description of this phenomenon by means of a generalized Cahn-Hilliard equation
(GCH) with a proliferation term. As in the discrete model, there are two
interesting regimes. For subcritical adhesion, there are propagating "pulled"
fronts, similarly to those of Fisher-Kolmogorov equation. The problem of front
velocity selection is examined, and our theoretical predictions are in a good
agreement with a numerical solution of the GCH equation. For supercritical
adhesion, there is a nontrivial transient behavior, where density profile
exhibits a secondary peak. To analyze this regime, we investigated relaxation
dynamics for the Cahn-Hilliard equation without proliferation. We found that
the relaxation process exhibits self-similar behavior. The results of continuum
and discrete models are in a good agreement with each other for the different
regimes we analyzed.Comment: 11 figures, submitted to PR
A toy model of fractal glioma development under RF electric field treatment
A toy model for glioma treatment by a radio frequency electric field is
suggested. This low-intensity, intermediate-frequency alternating electric
field is known as the tumor-treating-field (TTF). In the framework of this
model the efficiency of this TTF is estimated, and the interplay between the
TTF and the migration-proliferation dichotomy of cancer cells is considered.
The model is based on a modification of a comb model for cancer cells, where
the migration-proliferation dichotomy becomes naturally apparent. Considering
glioma cancer as a fractal dielectric composite of cancer cells and normal
tissue cells, a new effective mechanism of glioma treatment is suggested in the
form of a giant enhancement of the TTF. This leads to the irreversible
electroporation that may be an effective non-invasive method of treating brain
cancer.Comment: Submitted for publication in European Physical Journal
Symmetry-breaking instability in a prototypical driven granular gas
Symmetry-breaking instability of a laterally uniform granular cluster (strip
state) in a prototypical driven granular gas is investigated. The system
consists of smooth hard disks in a two-dimensional box, colliding inelastically
with each other and driven, at zero gravity, by a "thermal" wall. The limit of
nearly elastic particle collisions is considered, and granular hydrodynamics
with the Jenkins-Richman constitutive relations is employed. The hydrodynamic
problem is completely described by two scaled parameters and the aspect ratio
of the box. Marginal stability analysis predicts a spontaneous symmetry
breaking instability of the strip state, similar to that predicted recently for
a different set of constitutive relations. If the system is big enough, the
marginal stability curve becomes independent of the details of the boundary
condition at the driving wall. In this regime, the density perturbation is
exponentially localized at the elastic wall opposite to the thermal wall. The
short- and long-wavelength asymptotics of the marginal stability curves are
obtained analytically in the dilute limit. The physics of the symmetry-breaking
instability is discussed.Comment: 11 pages, 14 figure
Evaluation of Cloud Microphysics Simulated using a Meso-Scale Model Coupled with a Spectral Bin Microphysical Scheme through Comparison with Observation Data by Ship-Borne Doppler and Space-Borne W-Band Radars
Equivalent radar reflectivity factors (Ze) measured by W-band radars are directly compared with the corresponding values calculated from a three-dimensional non-hydrostatic meso-scale model coupled with a spectral-bin-microphysical (SBM) scheme for cloud. Three case studies are the objects of this research: one targets a part of ship-borne observation using 95 GHz Doppler radar over the Pacific Ocean near Japan in May 2001; other two are aimed at two short segments of space-borne observation by the cloud profiling radar on CloudSat in November 2006. The numerical weather prediction (NWP) simulations reproduce general features of vertical structures of Ze and Doppler velocity. A main problem in the reproducibility is an overestimation of Ze in ice cloud layers. A frequency analysis shows a strong correlation between ice water contents (IWC) and Ze in the simulation; this characteristic is similar to those shown in prior on-site studies. From comparing with the empirical correlations by the prior studies, the simulated Ze is overestimated than the corresponding values in the studies at the same IWC. Whereas the comparison of Doppler velocities suggests that large-size snowflakes are necessary for producing large velocities under the freezing level and hence rules out the possibility that an overestimation of snow size causes the overestimation of Ze. Based on the results of several sensitivity tests, we conclude that the source of the overestimation is a bias in the microphysical calculation of Ze or an overestimation of IWC. To identify the source of the problems needs further validation research with other follow-up observations
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