934 research outputs found
MultiBodySync: Multi-Body Segmentation and Motion Estimation via 3D Scan Synchronization
We present MultiBodySync, a novel, end-to-end trainable multi-body motion
segmentation and rigid registration framework for multiple input 3D point
clouds. The two non-trivial challenges posed by this multi-scan multibody
setting that we investigate are: (i) guaranteeing correspondence and
segmentation consistency across multiple input point clouds capturing different
spatial arrangements of bodies or body parts; and (ii) obtaining robust
motion-based rigid body segmentation applicable to novel object categories. We
propose an approach to address these issues that incorporates spectral
synchronization into an iterative deep declarative network, so as to
simultaneously recover consistent correspondences as well as motion
segmentation. At the same time, by explicitly disentangling the correspondence
and motion segmentation estimation modules, we achieve strong generalizability
across different object categories. Our extensive evaluations demonstrate that
our method is effective on various datasets ranging from rigid parts in
articulated objects to individually moving objects in a 3D scene, be it
single-view or full point clouds.Comment: Contact: huang-jh18mailstsinghuaeduc
Markov chain models of calcium puffs and sparks
Localized cytosolic Ca2+ elevations known as puffs and sparks are important regulators of cellular function that arise due to the cooperative activity of Ca2+-regulated inositol 1,4,5-trisphosphate receptors (IP3Rs) or ryanodine receptors (RyRs) co-localized at Ca2+ release sites on the surface of the endoplasmic reticulum or sarcoplasmic reticulum. Theoretical studies have demonstrated that the cooperative gating of a cluster of Ca2+-regulated Ca 2+ channels modeled as a continuous-time discrete-state Markov chain may result in dynamics reminiscent of Ca2+ puffs and sparks. In such simulations, individual Ca2+-release channels are coupled via a mathematical representation of the local [Ca2+] and exhibit stochastic Ca2+ excitability where channels open and close in a concerted fashion. This dissertation uses Markov chain models of Ca 2+ release sites to advance our understanding of the biophysics connecting the microscopic parameters of IP3R and RyR gating to the collective phenomenon of puffs and sparks.;The dynamics of puffs and sparks exhibited by release site models that include both Ca2+ coupling and nearest-neighbor allosteric coupling are studied. Allosteric interactions are included in a manner that promotes the synchronous gating of channels by stabilizing neighboring closed-closed and/or open-open channel pairs. When the strength of Ca2+-mediated channel coupling is systematically varied, simulations that include allosteric interactions often exhibit more robust Ca2+ puffs and sparks. Interestingly, the changes in puff/spark duration, inter-event interval, and frequency observed upon the random removal of allosteric couplings that stabilize closed-closed channel pairs are qualitatively different than the changes observed when open-open channel pairs, or both open-open and closed-closed channel pairs are stabilized. The validity of a computationally efficient mean-field reduction applicable to the dynamics of a cluster of Ca2+-release Ca2+ channels coupled via the local [Ca2+] and allosteric interactions is also investigated.;Markov chain models of Ca2+ release sites composed of channels that are both activated and inactivated by Ca2+ are used to clarify the role of Ca2+ inactivation in the generation and termination of puffs and sparks. It is found that when the average fraction of inactivated channels is significant, puffs and sparks are often less sensitive to variations in the number of channels at release sites and the strength of Ca2+ coupling. While excessively fast Ca2+ inactivation can preclude puffs and sparks moderately fast Ca2+ inactivation often leads to time-irreversible puff/sparks whose termination is facilitated by the recruitment of inactivated channels throughout the duration of the puff/spark event. On the other hand, Ca2+ inactivation may be an important negative feedback mechanism even when its time constant is much greater than the duration of puffs and sparks. In fact, slow Ca 2+ inactivation can lead to release sites with a substantial fraction of inactivated channels that exhibit nearly time-reversible puffs and sparks that terminate without additional recruitment of inactivated channels
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Scheduling and stability analysis of Cambridge Ring
textMulticlass queueing networks are widely used to model complex manufacturing systems and communications networks. In this dissertation we describe and analyze a multiclass queueing network model known as the Cambridge Ring. As the name suggest this network has a circular topology with unidirectional routing. In many cases the analysis of a stochastic model is a difficult task. For a few special cases of this network we show that all non-idling policies are throughput optimal for this system. One of the major differences between this work and precious literature is that we prove throughput optimality of all non-idling policies, whereas most of the previous work has been on establishing throughput optimality for a specific policy (usually First-In-First-Out). We use a macroscopic technique known as fluid model to identify optimal policies with respect to work in process. In one case we consider, the discrete scheduling policy motivated by the optimal fluid policy is indeed optimal in the discrete network. For the other special case we show by means of a deterministic counterexample that the discrete policy most naturally suggested by the fluid optimal policy may not be optimal for the queueing network. We also formulate the fluid holding cost optimization problem and present its solution for a simple version of the Cambridge Ring. Further we establish that the optimal policy under a class of policies known as "non-ejective" policies may be an idling policy. We use an example of the Cambridge Ring with a single vehicle to show that the optimal policy for this example has to be an idling policy.Operations Research and Industrial Engineerin
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