773 research outputs found
BRST quantization of quasi-symplectic manifolds and beyond
We consider a class of \textit{factorizable} Poisson brackets which includes
almost all reasonable Poisson structures. A particular case of the factorizable
brackets are those associated with symplectic Lie algebroids. The BRST theory
is applied to describe the geometry underlying these brackets as well as to
develop a deformation quantization procedure in this particular case. This can
be viewed as an extension of the Fedosov deformation quantization to a wide
class of \textit{irregular} Poisson structures. In a more general case, the
factorizable Poisson brackets are shown to be closely connected with the notion
of -algebroid. A simple description is suggested for the geometry underlying
the factorizable Poisson brackets basing on construction of an odd Poisson
algebra bundle equipped with an abelian connection. It is shown that the
zero-curvature condition for this connection generates all the structure
relations for the -algebroid as well as a generalization of the Yang-Baxter
equation for the symplectic structure.Comment: Journal version, references and comments added, style improve
Effect of fluid-colloid interactions on the mobility of a thermophoretic microswimmer in non-ideal fluids
Janus colloids propelled by light, e.g., thermophoretic particles, offer
promising prospects as artificial microswimmers. However, their swimming
behavior and its dependence on fluid properties and fluid-colloid interactions
remain poorly understood. Here, we investigate the behavior of a thermophoretic
Janus colloid in its own temperature gradient using numerical simulations. The
dissipative particle dynamics method with energy conservation is used to
investigate the behavior in non-ideal and ideal-gas like fluids for different
fluid-colloid interactions, boundary conditions, and temperature-controlling
strategies. The fluid-colloid interactions appear to have a strong effect on
the colloid behavior, since they directly affect heat exchange between the
colloid surface and the fluid. The simulation results show that a reduction of
the heat exchange at the fluid-colloid interface leads to an enhancement of
colloid's thermophoretic mobility. The colloid behavior is found to be
different in non-ideal and ideal fluids, suggesting that fluid compressibility
plays a significant role. The flow field around the colloid surface is found to
be dominated by a source-dipole, in agreement with the recent theoretical and
simulation predictions. Finally, different temperature-control strategies do
not appear to have a strong effect on the colloid's swimming velocity
Stability of heterogeneous parallel-bond adhesion clusters under static load
Adhesion interactions mediated by multiple bond types are relevant for many
biological and soft matter systems, including the adhesion of biological cells
and functionalized colloidal particles to various substrates. To elucidate
advantages and disadvantages of multiple bond populations for the stability of
heterogeneous adhesion clusters of receptor-ligand pairs, a theoretical model
for a homogeneous parallel adhesion bond cluster under constant loading is
extended to several bond types. The stability of the entire cluster can be
tuned by changing densities of different bond populations as well as their
extensional rigidity and binding properties. In particular, bond extensional
rigidities determine the distribution of total load to be shared between
different sub-populations. Under a gradual increase of the total load, the
rupture of a heterogeneous adhesion cluster can be thought of as a multistep
discrete process, in which one of the bond sub-populations ruptures first,
followed by similar rupture steps of other sub-populations or by immediate
detachment of the remaining cluster. This rupture behavior is qualitatively
independent of involved bond types, such as slip and catch bonds.
Interestingly, an optimal stability is generally achieved when the total
cluster load is shared such that loads on distinct bond populations are equal
to their individual critical rupture forces. We also show that cluster
heterogeneity can drastically affect cluster lifetime.Comment: 11 pages, 8 figure
Sharp-edged geometric obstacles in microfluidics promote deformability-based sorting of cells
Sorting cells based on their intrinsic properties is a highly desirable
objective, since changes in cell deformability are often associated with
various stress conditions and diseases. Deterministic lateral displacement
(DLD) devices offer high precision for rigid spherical particles, while their
success in sorting deformable particles remains limited due to the complexity
of cell traversal in DLDs. We employ mesoscopic hydrodynamics simulations and
demonstrate prominent advantages of sharp-edged DLD obstacles for probing
deformability properties of red blood cells (RBCs). By consecutive sharpening
of the pillar shape from circular to diamond to triangular geometry, a
pronounced cell bending around an edge is achieved, serving as a deformability
sensor. Bending around the edge is the primary mechanism, which governs the
traversal of RBCs through such DLD device. This strategy requires an
appropriate degree of cell bending by fluid stresses, which can be controlled
by the flow rate, and exhibits good sensitivity to moderate changes in cell
deformability. We expect that similar mechanisms should be applicable for the
development of novel DLD devices that target intrinsic properties of many other
cells.Comment: 16 pages, 9 figure
Higher order relations in Fedosov supermanifolds
Higher order relations existing in normal coordinates between affine
extensions of the curvature tensor and basic objects for any Fedosov
supermanifolds are derived. Representation of these relations in general
coordinates is discussed.Comment: 11 LaTex pages, no figure
- …