128 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
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Behaviour of the von Willebrand Factor in Blood Flow
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The von Willebrand factor (vWF), a large multimeric protein, is essential in hemostasis. Under
normal conditions, vWF is present in blood as a globular polymer. However, in case of an injury, vWF is able
to unwrap and bind to the vessel wall and to flowing platelets. Thus, platelets are significantly slowed down
and can adhere to the wall and close the lesion. Nevertheless, it is still not clear how the unwrapping of the
vWF is triggered. To better understand these complex processes, we employ a particle-based hydrodynamic
simulation method to study the behaviour of vWF in blood flow. The vWF is modelled as a chain of beads
(monomers) connected by springs. In addition, the monomers are subject to attractive interactions in order to
represent characteristic properties of the vWF. The behaviour of vWF is investigated under different conditions
including a freely-suspended polymer in shear flow and a polymer attached to a wall. We also examine the
migration of vWF to a wall (margination) depending on shear rate and volume fraction of red blood cells
(RBCs). Furthermore, the stretching of the vWF in flow direction depending on its radial position in a capillary
is monitored. Our results show that attractive interactions between monomer beads increase margination
efficiency and significantly affect the extension of vWF at different radial positions in blood vessels
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Blood Flow in silico: From Single Cells to Blood Rheology
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Mesoscale hydrodynamics simulations of red blood cells under flow have provided much new
insight into their shapes and dynamics in microchannel flow. The presented results range from the behavior
of single cells in confinement and the shape changes in sedimentation, to the clustering and arrangement of
many cells in microchannels and the viscosity of red blood cell suspensions under shear flow. The interaction
of red blood cells with other particles and cells, such as white blood cells, platelets, and drug carriers, shows
an essential role of red blood cells in the margination of other blood components
Red blood cells (RBCs) visualisation in bifurcations and bends
Bifurcating networks are commonly found in nature. One example is the microvascular system, composed of blood vessels consecutively branching into daughter vessels, driving the blood into the capillaries, where the red blood cells (RBCs) are responsible for delivering O 2 and up taking cell waste and CO 2 . In this preliminary study, we explore a microfluidic bifurcating geometry inspired by such biological models, for investigating RBC partitioning as well as RBC-plasma separation favored by the consecutive bifurcating channels. A biomimetic design rule [1] based on Murray’s law [2] was used to set the channels’ dimensions along the network, which consists of consecutive bifurcating channels of reducing diameter. The ability to apply differential flow resistances by controlling the flow rates at the end of the network allowed us to monitor the formation of a cell-free layer (CFL) for different flow conditions at haematocrits of 1% and 5%. We have also compared the values of CFL thickness determined directly by the measurement on the projection image created from a stack of images or indirectly by analyzing the intensity profile in the same projection. The results obtained from this study confirm the potential to study RBC partitioning along bifurcating networks, which could be of particular interest for the separation of RBCs from plasma in point-of-care devices.JF would like to thank Professor Graça Minas and her coworkers for
providing the laboratory facilities and technical help during the experiments.info:eu-repo/semantics/publishedVersio
Multiscale Modeling of Red Blood Cell Mechanics and Blood Flow in Malaria
Red blood cells (RBCs) infected by a Plasmodium parasite in malaria may lose their membrane deformability with a relative membrane stiffening more than ten-fold in comparison with healthy RBCs leading to potential capillary occlusions. Moreover, infected RBCs are able to adhere to other healthy and parasitized cells and to the vascular endothelium resulting in a substantial disruption of normal blood circulation. In the present work, we simulate infected RBCs in malaria using a multiscale RBC model based on the dissipative particle dynamics method, coupling scales at the sub-cellular level with scales at the vessel size. Our objective is to conduct a full validation of the RBC model with a diverse set of experimental data, including temperature dependence, and to identify the limitations of this purely mechanistic model. The simulated elastic deformations of parasitized RBCs match those obtained in optical-tweezers experiments for different stages of intra-erythrocytic parasite development. The rheological properties of RBCs in malaria are compared with those obtained by optical magnetic twisting cytometry and by monitoring membrane fluctuations at room, physiological, and febrile temperatures. We also study the dynamics of infected RBCs in Poiseuille flow in comparison with healthy cells and present validated bulk viscosity predictions of malaria-infected blood for a wide range of parasitemia levels (percentage of infected RBCs with respect to the total number of cells in a unit volume).United States. National Institutes of Health (Grant R01HL094270)National Science Foundation (U.S.). (Grant CBET-0852948)Singapore-MIT Alliance for Research and Technology Cente
The Weyl bundle as a differentiable manifold
Construction of an infinite dimensional differentiable manifold not modelled on any Banach space is proposed. Definition, metric
and differential structures of a Weyl algebra and a Weyl algebra bundle are
presented. Continuity of the -product in the Tichonov topology is
proved. Construction of the -product of the Fedosov type in terms of theory
of connection in a fibre bundle is explained.Comment: 31 pages; revised version - some typoes have been eliminated,
notation has been simplifie
Formal Deformations of Dirac Structures
In this paper we set-up a general framework for a formal deformation theory
of Dirac structures. We give a parameterization of formal deformations in terms
of two-forms obeying a cubic equation. The notion of equivalence is discussed
in detail. We show that the obstruction for the construction of deformations
order by order lies in the third Lie algebroid cohomology of the Dirac
structure. However, the classification of inequivalent first order deformations
is not given by the second Lie algebroid cohomology but turns out to be more
complicated.Comment: LaTeX 2e, 26 pages, no figures. Minor changes and improvement
Groupoids and an index theorem for conical pseudo-manifolds
We define an analytical index map and a topological index map for conical
pseudomanifolds. These constructions generalize the analogous constructions
used by Atiyah and Singer in the proof of their topological index theorem for a
smooth, compact manifold . A main ingredient is a non-commutative algebra
that plays in our setting the role of . We prove a Thom isomorphism
between non-commutative algebras which gives a new example of wrong way
functoriality in -theory. We then give a new proof of the Atiyah-Singer
index theorem using deformation groupoids and show how it generalizes to
conical pseudomanifolds. We thus prove a topological index theorem for conical
pseudomanifolds
The geometry of a bi-Lagrangian manifold
This is a survey on bi-Lagrangian manifolds, which are symplectic manifolds
endowed with two transversal Lagrangian foliations. We also study the
non-integrable case (i.e., a symplectic manifold endowed with two transversal
Lagrangian distributions). We show that many different geometric structures can
be attached to these manifolds and we carefully analyse the associated
connections. Moreover, we introduce the problem of the intersection of two
leaves, one of each foliation, through a point and show a lot of significative
examples.Comment: 30 page
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