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1.
In practice, the clearances of joints in a great number of mechanical systems are well under control. In these cases, some
of the existing methods become unpractical because of the little differences in the order of magnitude between relative movements
and computational errors. Assuming that the effects of impacts are negligible, we proved that both locations and forces of
contacts in joints can be fully determined by parts of joint reaction forces. Based on this fact, a method particularly suited
for multibody systems possessing frictional joints with tiny clearances is presented. In order to improve the efficiency of
computation, recursive formulations are proposed based on the interactions between bodies. The proposed recursive formulations
can improve the computation of joint reaction forces. With the methodology presented in this paper, not only the motion of
bodies in a multibody system but also the details about the contacts in joints, such as forces of contacts and locations of
contact points, can be obtained. Even with the assumption of impact free, the instants of possible impacts can be detected
without relying upon any ambiguous parameters, as indicated by numerical examples in this paper. 相似文献
2.
Ishay Goldin Jean-Marc Delosme Alfred M. Bruckstein 《Journal of Mathematical Imaging and Vision》2010,37(2):112-131
Modeling the deformation of shapes under constraints on both perimeter and area is a challenging task due to the highly nontrivial
interaction between the need for flexible local rules for manipulating the boundary and the global constraints. We propose
several methods to address this problem and generate “random walks” in the space of shapes obeying quite general possibly
time varying constraints on their perimeter and area. Design of perimeter and area preserving deformations are an interesting
and useful special case of this problem. The resulting deformation models are employed in annealing processes that evolve
original shapes toward shapes that are optimal in terms of boundary bending-energy or other functionals. Furthermore, such
models may find applications in the analysis of sequences of real images of deforming objects obeying global constraints as
building blocks for registration and tracking algorithms. 相似文献
3.
In this paper, a new lattice Boltzmann model based on the rebuilding-divergency method for the Poisson equation is proposed.
In order to translate the Poisson equation into a conservation law equation, the source term and diffusion term are changed
into divergence forms. By using the Chapman-Enskog expansion and the multi-scale time expansion, a series of partial differential
equations in different time scales and several higher-order moments of equilibrium distribution functions are obtained. Thus,
by rebuilding the divergence of the source and diffusion terms, the Laplace equation and the Poisson equation with the second
accuracy of the truncation errors are recovered. In the numerical examples, we compare the numerical results of this scheme
with those obtained by other classical method for the Green-Taylor vortex flow, numerical results agree well with the classical
ones. 相似文献
4.
In this paper we continue the study, which was initiated in (Ben-Artzi et al. in Math. Model. Numer. Anal. 35(2):313–303,
2001; Fishelov et al. in Lecture Notes in Computer Science, vol. 2667, pp. 809–817, 2003; Ben-Artzi et al. in J. Comput. Phys. 205(2):640–664, 2005 and SIAM J. Numer. Anal. 44(5):1997–2024, 2006) of the numerical resolution of the pure streamfunction formulation of the time-dependent two-dimensional Navier-Stokes equation.
Here we focus on enhancing our second-order scheme, introduced in the last three afore-mentioned articles, to fourth order
accuracy. We construct fourth order approximations for the Laplacian, the biharmonic and the nonlinear convective operators.
The scheme is compact (nine-point stencil) for the Laplacian and the biharmonic operators, which are both treated implicitly
in the time-stepping scheme. The approximation of the convective term is compact in the no-leak boundary conditions case and
is nearly compact (thirteen points stencil) in the case of general boundary conditions. However, we stress that in any case
no unphysical boundary condition was applied to our scheme. Numerical results demonstrate that the fourth order accuracy is
actually obtained for several test-cases. 相似文献
5.
Eiichi Yoshida Mathieu Poirier Jean-Paul Laumond Oussama Kanoun Florent Lamiraux Rachid Alami Kazuhito Yokoi 《Autonomous Robots》2010,28(1):77-88
In this paper we address whole-body manipulation of bulky objects by a humanoid robot. We adopt a “pivoting” manipulation
method that allows the humanoid to displace an object without lifting, but by the support of the ground contact. First, the
small-time controllability of pivoting is demonstrated. On its basis, an algorithm for collision-free pivoting motion planning
is established taking into account the naturalness of motion as nonholonomic constraints. Finally, we present a whole-body
motion generation method by a humanoid robot, which is verified by experiments. 相似文献
6.
Given a data set in a metric space, we study the problem of hierarchical clustering to minimize the maximum cluster diameter,
and the hierarchical k-supplier problem with customers arriving online.
We prove that two previously known algorithms for hierarchical clustering, one (offline) due to Dasgupta and Long and the
other (online) due to Charikar, Chekuri, Feder and Motwani, output essentially the same result when points are considered
in the same order. We show that the analyses of both algorithms are tight and exhibit a new lower bound for hierarchical clustering.
Finally we present the first constant factor approximation algorithm for the online hierarchical k-supplier problem. 相似文献
7.
In this paper, the Minimum Polynomial Extrapolation method (MPE) is used to accelerate the convergence of the Characteristic–Based–Split
(CBS) scheme for the numerical solution of steady state incompressible flows with heat transfer. The CBS scheme is a fractional
step method for the solution of the Navier–Stokes equations while the MPE method is a vector extrapolation method which transforms
the original sequence into another sequence converging to the same limit faster then the original one without the explicit
knowledge of the sequence generator. The developed algorithm is tested on a two-dimensional benchmark problem (buoyancy–driven
convection problem) where the Navier–Stokes equations are coupled with the temperature equation. The obtained results show
the feature of the extrapolation procedure to the CBS scheme and the reduction of the computational time of the simulation. 相似文献
8.
We first present a method to rule out the existence of parameter non-increasing polynomial kernelizations of parameterized
problems under the hypothesis P≠NP. This method is applicable, for example, to the problem Sat parameterized by the number of variables of the input formula. Then we obtain further improvements of corresponding results
in (Bodlaender et al. in Lecture Notes in Computer Science, vol. 5125, pp. 563–574, Springer, Berlin, 2008; Fortnow and Santhanam in Proceedings of the 40th ACM Symposium on the Theory of Computing (STOC’08), ACM, New York, pp. 133–142,
2008) by refining the central lemma of their proof method, a lemma due to Fortnow and Santhanam. In particular, assuming that
the polynomial hierarchy does not collapse to its third level, we show that every parameterized problem with a “linear OR”
and with NP-hard underlying classical problem does not have polynomial self-reductions that assign to every instance x with parameter k an instance y with |y|=k
O(1)⋅|x|1−ε
(here ε is any given real number greater than zero). We give various applications of these results. On the structural side we prove
several results clarifying the relationship between the different notions of preprocessing procedures, namely the various
notions of kernelizations, self-reductions and compressions. 相似文献
9.
Cloud Computing refers to the notion of outsourcing on-site available services, computational facilities, or data storage
to an off-site, location-transparent centralized facility or “Cloud.” Gang Scheduling is an efficient job scheduling algorithm
for time sharing, already applied in parallel and distributed systems. This paper studies the performance of a distributed
Cloud Computing model, based on the Amazon Elastic Compute Cloud (EC2) architecture that implements a Gang Scheduling scheme.
Our model utilizes the concept of Virtual Machines (or VMs) which act as the computational units of the system. Initially,
the system includes no VMs, but depending on the computational needs of the jobs being serviced new VMs can be leased and
later released dynamically. A simulation of the aforementioned model is used to study, analyze, and evaluate both the performance
and the overall cost of two major gang scheduling algorithms. Results reveal that Gang Scheduling can be effectively applied
in a Cloud Computing environment both performance-wise and cost-wise. 相似文献
10.
Communication and coordination are the main cores for reaching a constructive agreement among multi-agent systems (MASs). Dividing the overall performance of MAS to individual agents may lead to group learning as opposed to individual learning, which is one of the weak points of MASs. This paper proposes a recursive genetic framework for solving problems with high dynamism. In this framework, a combination of genetic algorithm and multi-agent capabilities is utilised to accelerate team learning and accurate credit assignment. The argumentation feature is used to accomplish agent learning and the negotiation features of MASs are used to achieve a credit assignment. The proposed framework is quite general and its recursive hierarchical structure could be extended. We have dedicated one special controlling module for increasing convergence time. Due to the complexity of blackjack, we have applied it as a possible test bed to evaluate the system’s performance. The learning rate of agents is measured as well as their credit assignment. The analysis of the obtained results led us to believe that our robust framework with the proposed negotiation operator is a promising methodology to solve similar problems in other areas with high dynamism. 相似文献
11.
Christophe Vandekerckhove Ioannis Kevrekidis Dirk Roose 《Journal of scientific computing》2009,39(2):167-188
The long-term dynamic behavior of many dynamical systems evolves on a low-dimensional, attracting, invariant slow manifold,
which can be parameterized by only a few variables (“observables”). The explicit derivation of such a slow manifold (and thus,
the reduction of the long-term system dynamics) is often extremely difficult or practically impossible. For this class of
problems, the equation-free framework has been developed to enable performing coarse-grained computations, based on short
full model simulations. Each full model simulation should be initialized so that the full model state is consistent with the
values of the observables and close to the slow manifold. To compute such an initial full model state, a class of constrained
runs functional iterations was proposed (Gear and Kevrekidis, J. Sci. Comput. 25(1), 17–28, 2005; Gear et al., SIAM J. Appl. Dyn. Syst. 4(3), 711–732, 2005). The schemes in this class only use the full model simulator and converge, under certain conditions, to an approximation
of the desired state on the slow manifold. In this article, we develop an implementation of the constrained runs scheme that
is based on a (preconditioned) Newton-Krylov method rather than on a simple functional iteration. The functional iteration
and the Newton-Krylov method are compared in detail using a lattice Boltzmann model for one-dimensional reaction-diffusion
as the full model simulator. Depending on the parameters of the lattice Boltzmann model, the functional iteration may converge
slowly or even diverge. We show that both issues are largely resolved by using the Newton-Krylov method, especially when a
coarse grid correction preconditioner is incorporated. 相似文献
12.
Alireza Pourshahid Daniel Amyot Liam Peyton Sepideh Ghanavati Pengfei Chen Michael Weiss Alan J. Forster 《Electronic Commerce Research》2009,9(4):269-316
A number of recent initiatives in both academia and industry have sought to achieve improvements in e-businesses through the
utilization of Business Process Management (BPM) methodologies and tools. However there are still some inadequacies that need
to be addressed when it comes to achieving alignment between business goals and business processes. The User Requirements
Notation (URN), recently standardized by ITU-T, has some unique features and capabilities beyond what is available in other
notations that can help address alignment issues. In this paper, a URN-based framework and its supporting toolset are introduced
which provide business process monitoring and performance management capabilities integrated across the BPM lifecycle. The
framework extends the URN notation with Key Performance Indicators (KPIs) and other concepts to measure and align processes
and goals. An example process for controlling access to a healthcare data warehouse is used to illustrate and evaluate the
framework. Early results indicate the feasibility of the approach. 相似文献
13.
We consider the problem of preemptive scheduling on uniformly related machines. We present a semi-online algorithm which,
if the optimal makespan is given in advance, produces an optimal schedule. Using the standard doubling technique, this yields
a 4-competitive deterministic and an e≈2.71-competitive randomized online algorithm. In addition, it matches the performance of the previously known algorithms
for the offline case, with a considerably simpler proof. Finally, we study the performance of greedy heuristics for the same
problem. 相似文献
14.
Yoshifumi Sakai 《Theory of Computing Systems》2011,48(1):189-210
The sparse spliced alignment problem consists of finding a chain of zero or more exons from O(n) prescribed candidate exons of a DNA sequence of length O(n) that is most similar to a known related gene sequence of length n. This study improves the running time of the fastest known algorithm for this problem to date, which executes in O(n
2.25) time, or very recently, in O(n
2log 2
n) time, by proposing an O(n
2log n)-time algorithm. 相似文献
15.
This paper presents a robot architecture with spatial cognition and navigation capabilities that captures some properties of the rat brain structures involved in learning and memory. This architecture relies on the integration of kinesthetic and visual information derived from artificial landmarks, as well as on Hebbian learning, to build a holistic topological-metric spatial representation during exploration, and employs reinforcement learning by means of an Actor-Critic architecture to enable learning and unlearning of goal locations. From a robotics perspective, this work can be placed in the gap between mapping and map exploitation currently existent in the SLAM literature. The exploitation of the cognitive map allows the robot to recognize places already visited and to find a target from any given departure location, thus enabling goal-directed navigation. From a biological perspective, this study aims at initiating a contribution to experimental neuroscience by providing the system as a tool to test with robots hypotheses concerned with the underlying mechanisms of rats’ spatial cognition. Results from different experiments with a mobile AIBO robot inspired on classical spatial tasks with rats are described, and a comparative analysis is provided in reference to the reversal task devised by O’Keefe in 1983. 相似文献
16.
We describe a method of representing human activities that allows a collection of motions to be queried without examples,
using a simple and effective query language. Our approach is based on units of activity at segments of the body, that can
be composed across space and across the body to produce complex queries. The presence of search units is inferred automatically
by tracking the body, lifting the tracks to 3D and comparing to models trained using motion capture data. Our models of short
time scale limb behaviour are built using labelled motion capture set. We show results for a large range of queries applied
to a collection of complex motion and activity. We compare with discriminative methods applied to tracker data; our method
offers significantly improved performance. We show experimental evidence that our method is robust to view direction and is
unaffected by some important changes of clothing. 相似文献
17.
Marta Mesquita Margarida Moz Ana Paias José Paixão Margarida Pato Ana Respício 《Journal of Scheduling》2011,14(4):319-334
Operational planning within public transit companies has been extensively tackled but still remains a challenging area for
operations research models and techniques. This phase of the planning process comprises vehicle-scheduling, crew-scheduling
and rostering problems. In this paper, a new integer mathematical formulation to describe the integrated vehicle-crew-rostering
problem is presented. The method proposed to obtain feasible solutions for this binary non-linear multi-objective optimization
problem is a sequential algorithm considered within a preemptive goal programming framework that gives a higher priority to
the integrated vehicle-crew-scheduling goal and a lower priority to the driver rostering goals. A heuristic approach is developed
where the decision maker can choose from different vehicle-crew schedules and rosters, while respecting as much as possible
management’s interests and drivers’ preferences. An application to real data of a Portuguese bus company shows the influence
of vehicle-crew-scheduling optimization on rostering solutions. 相似文献
18.
The convergence to steady state solutions of the Euler equations for high order weighted essentially non-oscillatory (WENO)
finite difference schemes with the Lax-Friedrichs flux splitting (Jiang and Shu, in J. Comput. Phys. 126:202–228, 1996) is investigated. Numerical evidence in Zhang and Shu (J. Sci. Comput. 31:273–305, 2007) indicates that there exist slight post-shock oscillations when we use high order WENO schemes to solve problems containing
shock waves. Even though these oscillations are small in their magnitude and do not affect the “essentially non-oscillatory”
property of the WENO schemes, they are indeed responsible for the numerical residue to hang at the truncation error level
of the scheme instead of settling down to machine zero. Differently from the strategy adopted in Zhang and Shu (J. Sci. Comput.
31:273–305, 2007), in which a new smoothness indicator was introduced to facilitate convergence to steady states, in this paper we study the
effect of the local characteristic decomposition on steady state convergence. Numerical tests indicate that the slight post-shock
oscillation has a close relationship with the local characteristic decomposition process. When this process is based on an
average Jacobian at the cell interface using the Roe average, as is the standard procedure for WENO schemes, such post-shock
oscillation appears. If we instead use upwind-biased interpolation to approximate the physical variables including the velocity
and enthalpy on the cell interface to compute the left and right eigenvectors of the Jacobian for the local characteristic
decomposition, the slight post-shock oscillation can be removed or reduced significantly and the numerical residue settles
down to lower values than other WENO schemes and can reach machine zero for many test cases. This new procedure is also effective
for higher order WENO schemes and for WENO schemes with different smoothness indicators. 相似文献
19.
This article considers the global robust output regulation problem via output feedback for a class of cascaded nonlinear systems with input-to-state stable inverse dynamics. The system uncertainties depend not only on the measured output but also all the unmeasurable states. By introducing an internal model, the output regulation problem is converted into a stabilisation problem for an appropriately augmented system. The designed dynamic controller could achieve the global asymptotic tracking control for a class of time-varying reference signals for the system output while keeping all other closed-loop signals bounded. It is of interest to note that the developed control approach can be applied to the speed tracking control of the fan speed control system. The simulation results demonstrate its effectiveness. 相似文献
20.
In recent years we have seen a tremendous growth in the amount of freely available 3D content, in part due to breakthroughs for 3D model design and acquisition. For example, advances in range sensor technology and design software have dramatically reduced the manual labor required to construct 3D models. As collections of 3D content continue to grow rapidly, the ability to perform fast and accurate retrieval from a database of models has become a necessity. At the core of this retrieval task is the fundamental challenge of defining and evaluating similarity between 3D shapes. Some effective methods dealing with this challenge consider similarity measures based on the visual appearance of models. While collections of rendered images are discriminative for retrieval tasks, such representations come with a few inherent limitations such as restrictions in the image viewpoint sampling and high computational costs. In this paper we present a novel algorithm for model similarity that addresses these issues. Our proposed method exploits techniques from spherical signal processing to efficiently evaluate a visual similarity measure between models. Extensive evaluations on multiple datasets are provided. 相似文献