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991.
Segment-based adaptive hyper-Erlang model for long-tailed network traffic approximation 总被引:1,自引:1,他引:0
Modeling the long-tailedness property of network traffic with phase-type distributions is a powerful means to facilitate the consequent performance evaluation and queuing based analysis. This paper
improves the recently proposed Fixed Hyper-Erlang model (FHE) by introducing an adaptive framework (Adaptive Hyper-Erlang
model, AHE) to determine the crucially performance-sensitive model parameters. The adaptive model fits long-tailed traffic
data set directly with a mixed Erlang distribution in a new divide-and-conquer manner. Compared with the well-known hyperexponential based models and the Fixed Hyper-Erlang model, the Adaptive Hyper-Erlang
model is more flexible and practicable in addition to its accuracy in fitting the tail behavior.
相似文献
Junfeng WangEmail: |
992.
This paper presents an adaptive robust control method for trajectory tracking and path following of an omni-directional wheeled
mobile platform with actuators’ uncertainties. The polar-space kinematic model of the platform with three independent driving
omnidirectional wheels equally spaced at 120 from one another is briefly introduced, and the dynamic models of the three
uncertain servomotors mounted on the driving wheels are also described. With the platform’s kinematic model and the motors’
dynamic model associated two unknown parameters, the adaptive robust controller is synthesized via the integral backstepping
approach. Computer simulations and experimental results are conducted to show the effectiveness and merits of the proposed
control method in comparison with a conventional PI feedback control method. 相似文献
993.
Jan Rosell Carlos Vázquez Alexander Pérez Pedro Iñiguez 《Journal of Intelligent and Robotic Systems》2008,53(3):223-245
Haptic devices allow a user to feel either reaction forces from virtual interactions or reaction forces reflected from a remote
site during a bilateral teleoperation task. Also, guiding forces can be exerted to train the user in the performance of a
virtual task or to assist him/her to safely teleoperate a robot. The generation of guiding forces relies on the existence
of a motion plan that provides the direction to be followed to reach the goal from any free configuration of the configuration
space (-space). This paper proposes a method to obtain such a plan that interleaves a sampling-based exploration of -space with an efficient computation of harmonic functions. A deterministic sampling sequence (with a bias based on harmonic
function values) is used to obtain a hierarchical cell decomposition model of -space. A harmonic function is iteratively computed over the partially known model using a novel approach. The harmonic function
is the navigation function used as motion plan. The approach has been implemented in a planner (called the Kautham planner) that, given an initial and a goal configuration, provides: (a) a channel of cells connecting the cell that contains
the initial configuration with the cell that contains the goal configuration; (b) two harmonic functions over the whole -space, one that guides motions towards the channel and another that guides motions within the channel towards the goal; and
(c) a path computed over a roadmap built with the free samples of the channel. The harmonic functions and the solution path
are then used to generate the guiding forces for the haptic device. The planning approach is illustrated with examples on
2D and 3D workspaces.
This work was partially supported by the CICYT projects DPI2005-00112 and DPI2007-63665. 相似文献
994.
Uniprocessor schedulability theory made great strides, in part, due to the simplicity of composing the delay of a job from
the execution times of higher-priority jobs that preempt it. In this paper, we bound the end-to-end delay of a job in a multistage
pipeline as a function of job execution times on different stages under preemptive as well as non-preemptive scheduling. We
show that the end-to-end delay is bounded by that of a single virtual “bottleneck” stage plus a small additive component. This contribution effectively transforms the pipeline into a
single stage system. The wealth of schedulability analysis techniques derived for uniprocessors can then be applied to decide
the schedulability of the pipeline. The transformation does not require imposing artificial per-stage deadlines, but rather
models the pipeline as a whole and uses the end-to-end deadlines directly in the single-stage analysis. It also does not make
assumptions on job arrival patterns or periodicity and thus can be applied to periodic and aperiodic tasks alike. We show
through simulations that this approach outperforms previous pipeline schedulability tests except for very short pipelines
or when deadlines are sufficiently large. The reason lies in the way we account for execution overlap among stages. We discuss
how previous approaches account for overlap and point out interesting differences that lead to different performance advantages
in different cases. Further, we also show that in certain cases non-preemptive scheduling can result in higher system utilization
than preemptive scheduling in pipelined systems. We hope that the pipeline delay composition rule, derived in this paper,
may be a step towards a general schedulability analysis foundation for large distributed systems.
相似文献
Tarek AbdelzaherEmail: |
995.
Dynamic memory allocation has been used for decades. However, it has seldom been used in real-time systems since the worst
case of spatial and temporal requirements for allocation and deallocation operations is either unbounded or bounded but with
a very large bound.
In this paper, a new allocator called TLSF (Two Level Segregated Fit) is presented. TLSF is designed and implemented to accommodate
real-time constraints. The proposed allocator exhibits time-bounded behaviour, O(1), and maintains a very good execution time. This paper describes in detail the data structures and functions provided by
TLSF. We also compare TLSF with a representative set of allocators regarding their temporal cost and fragmentation.
Although the paper is mainly focused on timing analysis, a brief study and comparative analysis of fragmentation incurred
by the allocators has been also included in order to provide a global view of the behaviour of the allocators.
The temporal and spatial results showed that TLSF is also a fast allocator and produces a fragmentation close to that caused
by the best existing allocators.
相似文献
Alfons Crespo (Corresponding author)Email: |
996.
This research introduces a new optimality criterion for motion planning of wheeled mobile robots based on a cost index that assesses the nearness to singularity of forward and
inverse kinematic models. Slip motions, infinite estimation error and impossible control actions are avoided escaping from singularities. In addition, high amplification of wheel velocity errors and high wheel velocity values are
also avoided by moving far from the singularity. The proposed cost index can be used directly to complement path-planning and motion-planning techniques (e.g. tree graphs, roadmaps, etc.) in order to select the optimal collision-free path or trajectory among several possible solutions. To illustrate the applications of the proposed
approach, an industrial forklift, equivalent to a tricycle-like mobile robot, is considered in a simulated environment. In particular, several results are
validated for the proposed optimality criterion, which are extensively compared to those obtained with other classical optimality criteria, such as shortest-path, time-optimal and minimum-energy. 相似文献
997.
Cheng-Jian Lin Yong-Cheng Liu Chi-Yung Lee 《Journal of Intelligent and Robotic Systems》2008,52(2):285-312
This study presents a wavelet-based neuro-fuzzy network (WNFN). The proposed WNFN model combines the traditional Takagi–Sugeno–Kang
(TSK) fuzzy model and the wavelet neural networks (WNN). This study adopts the non-orthogonal and compactly supported functions
as wavelet neural network bases. A novel supervised evolutionary learning, called WNFN-S, is proposed to tune the adjustable
parameters of the WNFN model. The proposed WNFN-S learning scheme is based on dynamic symbiotic evolution (DSE). The proposed
DSE uses the sequential-search-based dynamic evolutionary (SSDE) method. In some real-world applications, exact training data
may be expensive or even impossible to obtain. To solve this problem, the reinforcement evolutionary learning, called WNFN-R,
is proposed. Computer simulations have been conducted to illustrate the performance and applicability of the proposed WNFN-S
and WNFN-R learning algorithms. 相似文献
998.
Robert F. Hadley 《Minds and Machines》2008,18(1):1-15
It is well understood and appreciated that Gödel’s Incompleteness Theorems apply to sufficiently strong, formal deductive systems. In particular, the theorems apply to systems which are adequate for conventional number theory. Less well known is that there exist algorithms which can be applied to such a system to generate a gödel-sentence for that system. Although the generation of a sentence is not equivalent to proving its truth, the present paper argues that the existence of these algorithms, when conjoined with Gödel’s results and accepted theorems of recursion theory, does provide the basis for an apparent paradox. The difficulty arises when such an algorithm is embedded within a computer program of sufficient arithmetic power. The required computer program (an AI system) is described herein, and the paradox is derived. A solution to the paradox is proposed, which, it is argued, illuminates the truth status of axioms in formal models of programs and Turing machines. 相似文献
999.
Over the last two decades, artificial neural networks (ANN) have been applied to solve a variety of problems such as pattern
classification and function approximation. In many applications, it is desirable to extract knowledge from trained neural
networks for the users to gain a better understanding of the network’s solution. In this paper, we use a neural network rule
extraction method to extract knowledge from 2222 dividend initiation and resumption events. We find that the positive relation
between the short-term price reaction and the ratio of annualized dividend amount to stock price is primarily limited to 96
small firms with high dividend ratios. The results suggest that the degree of short-term stock price underreaction to dividend
events may not be as dramatic as previously believed. The results also show that the relations between the stock price response
and firm size is different across different types of firms. Thus, drawing the conclusions from the whole dividend event data
may leave some important information unexamined. This study shows that neural network rule extraction method can reveal more
knowledge from the data. 相似文献
1000.
Behaviour based on decision matrices for a coordination between agents in a urban traffic simulation
René Mandiau Alexis Champion Jean-Michel Auberlet Stéphane Espié Christophe Kolski 《Applied Intelligence》2008,28(2):121-138
This paper describes a multi-agent coordination mechanism applied to intersection simulation situations. In a goal of urban
traffic simulation, we must consider the dynamic interactions between autonomous vehicles. The field of multi-agent systems
provides us some studies for such systems, in particular on the coordination mechanisms. Conflicts between vehicles (i.e.
agents) are very frequent in such applications, and they may cause deadlocks, particularly at intersections such as crossroads.
Our approach is based on the solving of two player games/decision matrices which characterize three basic situations. An aggregation
method generalizes to n-player games for complex crossroads. The objective of this approach consists in searching basic two-player
matrices for solving n-agent problems. To explain the principle, we describe our approach for a particular case of crossroad
with three agents. Finally, the obtained results have been examined via a tool of road traffic simulation, ARCHISIM. We assume
also that the global traffic replicates the behavior of agents in different situations. 相似文献