46 research outputs found
Geometry of non-holonomic diffusion
We study stochastically perturbed non-holonomic systems from a geometric
point of view. In this setting, it turns out that the probabilistic properties
of the perturbed system are intimately linked to the geometry of the constraint
distribution. For -Chaplygin systems, this yields a stochastic criterion for
the existence of a smooth preserved measure. As an application of our results
we consider the motion planning problem for the noisy two-wheeled robot and the
noisy snakeboard
Geometric analysis of noisy perturbations to nonholonomic constraints
We propose two types of stochastic extensions of nonholonomic constraints for
mechanical systems. Our approach relies on a stochastic extension of the
Lagrange-d'Alembert framework. We consider in details the case of invariant
nonholonomic systems on the group of rotations and on the special Euclidean
group. Based on this, we then develop two types of stochastic deformations of
the Suslov problem and study the possibility of extending to the stochastic
case the preservation of some of its integrals of motion such as the Kharlamova
or Clebsch-Tisserand integrals
Symmetry reduction of Brownian motion and Quantum Calogero-Moser systems
Let be a Riemannian -manifold. This paper is concerned with the
symmetry reduction of Brownian motion in and ramifications thereof in a
Hamiltonian context. Specializing to the case of polar actions we discuss
various versions of the stochastic Hamilton-Jacobi equation associated to the
symmetry reduction of Brownian motion and observe some similarities to the
Schr\"odinger equation of the quantum free particle reduction as described by
Feher and Pusztai. As an application we use this reduction scheme to derive
examples of quantum Calogero-Moser systems from a stochastic setting.Comment: V2 contains some improvements thanks to referees' suggestions; to
appear in Stochastics and Dynamic
Integrable Euler top and nonholonomic Chaplygin ball
We discuss the Poisson structures, Lax matrices, -matrices, bi-hamiltonian
structures, the variables of separation and other attributes of the modern
theory of dynamical systems in application to the integrable Euler top and to
the nonholonomic Chaplygin ball.Comment: 25 pages, LaTeX with AMS fonts, final versio
Collisionless kinetic theory of rolling molecules
We derive a collisionless kinetic theory for an ensemble of molecules
undergoing nonholonomic rolling dynamics. We demonstrate that the existence of
nonholonomic constraints leads to problems in generalizing the standard methods
of statistical physics. In particular, we show that even though the energy of
the system is conserved, and the system is closed in the thermodynamic sense,
some fundamental features of statistical physics such as invariant measure do
not hold for such nonholonomic systems. Nevertheless, we are able to construct
a consistent kinetic theory using Hamilton's variational principle in
Lagrangian variables, by regarding the kinetic solution as being concentrated
on the constraint distribution. A cold fluid closure for the kinetic system is
also presented, along with a particular class of exact solutions of the kinetic
equations.Comment: Revised version; 31 pages, 1 figur
LR and L+R Systems
We consider coupled nonholonomic LR systems on the product of Lie groups. As
examples, we study -dimensional variants of the spherical support system and
the rubber Chaplygin sphere. For a special choice of the inertia operator, it
is proved that the rubber Chaplygin sphere, after reduction and a time
reparametrization becomes an integrable Hamiltonian system on the
--dimensional sphere. Also, we showed that an arbitrary L+R system
introduced by Fedorov can be seen as a reduced system of an appropriate coupled
LR system.Comment: 18 pages, 1 figur
Oligodendrocyte heterogeneity in the mouse juvenile and adult central nervous system
Oligodendrocytes have been considered as a functionally homogeneous population in the central nervous system (CNS). We performed single-cell RNA sequencing on 5072 cells of the oligodendrocyte lineage from 10 regions of the mouse juvenile and adult CNS. Thirteen distinct populations were identified, 12 of which represent a continuum from Pdgfra(+) oligodendrocyte precursor cells (OPCs) to distinct mature oligodendrocytes. Initial stages of differentiation were similar across the juvenile CNS, whereas subsets of mature oligodendrocytes were enriched in specific regions in the adult brain. Newly formed oligodendrocytes were detected in the adult CNS and were responsive to complex motor learning. A second Pdgfra(+) population, distinct from OPCs, was found along vessels. Our study reveals the dynamics of oligodendrocyte differentiation and maturation, uncoupling them at a transcriptional level and highlighting oligodendrocyte heterogeneity in the CNS
Classes and continua of hippocampal CA1 inhibitory neurons revealed by single-cell transcriptomics
Understanding any brain circuit will require a categorization of its constituent neurons. In hippocampal area CA1, at least 23 classes of GABAergic neuron have been proposed to date. However, this list may be incomplete; additionally, it is unclear whether discrete classes are sufficient to describe the diversity of cortical inhibitory neurons or whether continuous modes of variability are also required. We studied the transcriptomes of 3,663 CA1 inhibitory cells, revealing 10 major GABAergic groups that divided into 49 fine-scale clusters. All previously described and several novel cell classes were identified, with three previously described classes unexpectedly found to be identical. A division into discrete classes, however, was not sufficient to describe the diversity of these cells, as continuous variation also occurred between and within classes. Latent factor analysis revealed that a single continuous variable could predict the expression levels of several genes, which correlated similarly with it across multiple cell types. Analysis of the genes correlating with this variable suggested it reflects a range from metabolically highly active faster-spiking cells that proximally target pyramidal cells to slower-spiking cells targeting distal dendrites or interneurons. These results elucidate the complexity of inhibitory neurons in one of the simplest cortical structures and show that characterizing these cells requires continuous modes of variation as well as discrete cell classes.</p