2,466 research outputs found
Large deformation of spherical vesicle studied by perturbation theory and Surface evolver
With tangent angle perturbation approach the axial symmetry deformation of a
spherical vesicle in large under the pressure changes is studied by the
elasticity theory of Helfrich spontaneous curvature model.Three main results in
axial symmetry shape: biconcave shape, peanut shape, and one type of myelin are
obtained. These axial symmetry morphology deformations are in agreement with
those observed in lipsome experiments by dark-field light microscopy [Hotani,
J. Mol. Biol. 178, (1984) 113] and in the red blood cell with two thin
filaments (myelin) observed in living state (see, Bessis, Living Blood Cells
and Their Ultrastructure, Springer-Verlag, 1973). Furthermore, the biconcave
shape and peanut shape can be simulated with the help of a powerful software,
Surface Evolver [Brakke, Exp. Math. 1, 141 (1992) 141], in which the
spontaneous curvature can be easy taken into account.Comment: 16 pages, 6 EPS figures and 2 PS figure
On classical string configurations
Equations which define classical configurations of strings in are
presented in a simple form. General properties as well as particular classes of
solutions of these equations are considered.Comment: 10 pages, Latex, no figures, trivial corrections, submitted to Modern
Physics Letters
Counting White Blood Cells from a Blood Smear Using Fourier Ptychographic Microscopy
White blood cell (WBC) count is a valuable metric for assisting with diagnosis or prognosis of various diseases such as coronary heart disease, type 2 diabetes, or infection. Counting WBCs can be done either manually or automatically. Automatic methods are capable of counting a large number of cells to give a statistically more accurate reading of the WBC count of a sample, but the specialized equipment tends to be expensive. Manual methods are inexpensive since they only involve a conventional light microscope setup. However, it is more laborious and error-prone because the small field-of-view (FOV) of the microscope necessitates mechanical scanning of a specimen for counting an adequate number of WBCs. Here, we investigate the use of Fourier ptychographic microscopy (FPM) to bypass these issues of the manual methods. With a 2x objective, FPM can provide a FOV of 120 mm^2 with enhanced resolution comparable to that of a 20x objective, which is adequate for non-differentially counting WBCs in just one FOV. A specialist was able to count the WBCs in FPM images with 100% accuracy compared to the count as determined from conventional microscope images. An automatic counting algorithm was also developed to identify WBCs from FPM’s captured images with 95% accuracy, paving the way for a cost-effective WBC counting setup with the advantages of both the automatic and manual counting methods
Simulating the collapse transition of a two-dimensional semiflexible lattice polymer
It has been revealed by mean-field theories and computer simulations that the
nature of the collapse transition of a polymer is influenced by its bending
stiffness . In two dimensions, a recent analytical work
demonstrated that the collapse transition of a partially directed lattice
polymer is always first-order as long as is positive
[H. Zhou {\em et al.}, Phys. Rev. Lett. {\bf 97}, 158302 (2006)]. Here we
employ Monte Carlo simulation to investigate systematically the effect of
bending stiffness on the static properties of a 2D lattice polymer. The
system's phase-diagram at zero force is obtained. Depending on and the temperature , the polymer can be in one of three phases:
crystal, disordered globule, or swollen coil. The crystal-globule transition is
discontinuous, the globule-coil transition is continuous. At moderate or high
values of the intermediate globular phase disappears and the
polymer has only a discontinuous crystal-coil transition. When an external
force is applied, the force-induced collapse transition will either be
continuous or discontinuous, depending on whether the polymer is originally in
the globular or the crystal phase at zero force. The simulation results also
demonstrate an interesting scaling behavior of the polymer at the force-induced
globule-coil transition.Comment: 16 page
Numerical observation of non-axisymmetric vesicles in fluid membranes
By means of Surface Evolver (Exp. Math,1,141 1992), a software package of
brute-force energy minimization over a triangulated surface developed by the
geometry center of University of Minnesota, we have numerically searched the
non-axisymmetric shapes under the Helfrich spontaneous curvature (SC) energy
model. We show for the first time there are abundant mechanically stable
non-axisymmetric vesicles in SC model, including regular ones with intrinsic
geometric symmetry and complex irregular ones. We report in this paper several
interesting shapes including a corniculate shape with six corns, a
quadri-concave shape, a shape resembling sickle cells, and a shape resembling
acanthocytes. As far as we know, these shapes have not been theoretically
obtained by any curvature model before. In addition, the role of the
spontaneous curvature in the formation of irregular crenated vesicles has been
studied. The results shows a positive spontaneous curvature may be a necessary
condition to keep an irregular crenated shape being mechanically stable.Comment: RevTex, 14 pages. A hard copy of 8 figures is available on reques
Theory on quench-induced pattern formation: Application to the isotropic to smectic-A phase transitions
During catastrophic processes of environmental variations of a thermodynamic
system, such as rapid temperature decreasing, many novel and complex patterns
often form.
To understand such phenomena, a general mechanism is proposed based on the
competition between heat transfer and conversion of heat to other energy forms.
We apply it to the smectic-A filament growth process during quench-induced
isotropic to smectic-A phase transition. Analytical forms for the buckling
patterns are derived and we find good agreement with experimental observation
[Phys. Rev. {\bf E55} (1997) 1655]. The present work strongly indicates that
rapid cooling will lead to structural transitions in the smectic-A filament at
the molecular level to optimize heat conversion. The force associated with this
pattern formation process is estimated to be in the order of
piconewton.Comment: 9 pages in RevTex form, with 3 postscript figures. Accepted by PR
Dynamical description of vesicle growth and shape change
We systematize and extend the description of vesicle growth and shape change
using linear nonequilibrium thermodynamics. By restricting the study to shape
changes from spheres to axisymmetric ellipsoids, we are able to give a
consistent formulation which includes the lateral tension of the vesicle
membrane. This allows us to generalize and correct a previous calculation. Our
present calculations suggest that, for small growing vesicles, a prolate
ellipsoidal shape should be favored over oblate ellipsoids, whereas for large
growing vesicles oblates should be favored over prolates. The validity of this
prediction is examined in the light of the various assumptions made in its
derivation.Comment: 6 page
A generalized integral fluctuation theorem for general jump processes
Using the Feynman-Kac and Cameron-Martin-Girsanov formulas, we obtain a
generalized integral fluctuation theorem (GIFT) for discrete jump processes by
constructing a time-invariable inner product. The existing discrete IFTs can be
derived as its specific cases. A connection between our approach and the
conventional time-reversal method is also established. Different from the
latter approach that was extensively employed in existing literature, our
approach can naturally bring out the definition of a time-reversal of a
Markovian stochastic system. Additionally, we find the robust GIFT usually does
not result into a detailed fluctuation theorem
Interpretation of AIRS Data in Thin Cirrus Atmospheres Based on a Fast Radiative Transfer Model
A thin cirrus cloud thermal infrared radiative transfer model has been developed for application to cloudy
satellite data assimilation. This radiation model was constructed by combining the Optical Path Transmittance
(OPTRAN) model, developed for the speedy calculation of transmittances in clear atmospheres, and
a thin cirrus cloud parameterization using a number of observed ice crystal size and shape distributions.
Numerical simulations show that cirrus cloudy radiances in the 800–1130-cm^(-1) thermal infrared window are
sufficiently sensitive to variations in cirrus optical depth and ice crystal size as well as in ice crystal shape
if appropriate habit distribution models are selected a priori for analysis. The parameterization model has
been applied to the Atmospheric Infrared Sounder (AIRS) on board the Aqua satellite to interpret clear
and thin cirrus spectra observed in the thermal infrared window. Five clear and 29 thin cirrus cases at
nighttime over and near the Atmospheric Radiation Measurement program (ARM) tropical western Pacific
(TWP) Manus Island and Nauru Island sites have been chosen for this study. A X^2-minimization program
was employed to infer the cirrus optical depth and ice crystal size and shape from the observed AIRS
spectra. Independent validation shows that the AIRS-inferred cloud parameters are consistent with those
determined from collocated ground-based millimeter-wave cloud radar measurements. The coupled thin
cirrus radiative transfer parameterization and OPTRAN, if combined with a reliable thin cirrus detection
scheme, can be effectively used to enhance the AIRS data volume for data assimilation in numerical
weather prediction models
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