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81.
This paper addresses the problem of autonomous navigation of a micro air vehicle (MAV) in GPS‐denied environments. We present experimental validation and analysis for our system that enables a quadrotor helicopter, equipped with a laser range finder sensor, to autonomously explore and map unstructured and unknown environments. The key challenge for enabling GPS‐denied flight of a MAV is that the system must be able to estimate its position and velocity by sensing unknown environmental structure with sufficient accuracy and low enough latency to stably control the vehicle. Our solution overcomes this challenge in the face of MAV payload limitations imposed on sensing, computational, and communication resources. We first analyze the requirements to achieve fully autonomous quadrotor helicopter flight in GPS‐denied areas, highlighting the differences between ground and air robots that make it difficult to use algorithms developed for ground robots. We report on experiments that validate our solutions to key challenges, namely a multilevel sensing and control hierarchy that incorporates a high‐speed laser scan‐matching algorithm, data fusion filter, high‐level simultaneous localization and mapping, and a goal‐directed exploration module. These experiments illustrate the quadrotor helicopter's ability to accurately and autonomously navigate in a number of large‐scale unknown environments, both indoors and in the urban canyon. The system was further validated in the field by our winning entry in the 2009 International Aerial Robotics Competition, which required the quadrotor to autonomously enter a hazardous unknown environment through a window, explore the indoor structure without GPS, and search for a visual target. © 2011 Wiley Periodicals, Inc. 相似文献
82.
Classical Cartesian domain decompositions for parallel lattice Boltzmann simulations of fluid flow through heterogeneous porous media are doomed to workload imbalance as the number of processors increases, thus leading to decreasing parallel performance. A one-lattice lattice Boltzmann method (LBM) implementation with vector data structure combined with even fluid node partitioning domain decomposition and fully-optimized data transfer layout is presented. It is found to provide nearly-optimal workload balance, lower memory usage and better computational performance than classical slice decomposition techniques using sparse matrix data structures. Predictive memory usage and parallel performance models are also established and observed to be in very good agreement with data corresponding to numerical fluid flow simulations performed through 3-dimensional packings of cylinders and polydisperse spheres. 相似文献
83.
We present an efficient implementation of the Modified SParse Approximate Inverse (MSPAI) preconditioner. MSPAI generalizes the class of preconditioners based on Frobenius norm minimizations, the class of modified preconditioners such as MILU, as well as interface probing techniques in domain decomposition: it adds probing constraints to the basic SPAI formulation, and one can thus optimize the preconditioner relative to certain subspaces. We demonstrate MSPAI’s qualities for iterative regularization problems arising from image deblurring.Such applications demand for a fast and parallel preconditioner realization. We present such an implementation introducing two new optimization techniques: First, we avoid redundant calculations using a dictionary. Second, our implementation reduces the runtime spent on the most demanding numerical parts as the code switches to sparse QR decomposition methods wherever profitable. The optimized code runs in parallel with a dynamic load balancing. 相似文献
84.
Benjamin Van Roy 《Discrete Event Dynamic Systems》2010,20(3):307-324
We study approaches that fit a linear combination of basis functions to the continuation value function of an optimal stopping
problem and then employ a greedy policy based on the resulting approximation. We argue that computing weights to maximize
expected payoff of the greedy policy or to minimize expected squared-error with respect to an invariant measure is intractable.
On the other hand, certain versions of approximate value iteration lead to policies competitive with those that would result
from optimizing the latter objective. 相似文献
85.
The present study was designed to examine the correlation between five personality traits (empathy, imagination, immersive
tendencies, dissociation tendencies and locus of control) and presence. Moreover, this study aimed to identify an optimal
virtual reality user’s profile. Eighty-four students (66 women, 18 men) completed personality questionnaires, experienced
exposure in a virtual environment and completed a presence questionnaire. Twenty-three women, among them 13 non-Jewish women
and no men, neglected to look out the virtual window, and reported lower levels of presence. Presence correlated with immersive
tendencies and empathy. However, empathy and internal locus of control were the best predictors for the sense of presence.
A correlation between imagination and presence was only found in the group that avoided viewing the virtual window. This study
revealed the importance of empathy and internal locus of control in the sense of presence. In addition, our findings suggest
that the subject’s imagination has an important role when the virtual environment is restricted and that we must attend to
cultural and gender-related factors when investigating therapy using virtual reality technology. 相似文献
86.
We propose an adaptive neuro‐fuzzy inference system (ANFIS) for stock portfolio return prediction. Previous work has shown that portfolio optimization can be improved by using predicted stock earnings rather than historical earnings. We show that predicted portfolio returns can be improved by using ANFIS and taking as input a variety of technical and fundamental attributes about various indices of the stock market. To generate membership functions, we use a robust noise rejection‐clustering algorithm. The neuro‐fuzzy model is tested on portfolios constituted from the Tehran Stock Exchange. In our experiments, the proposed method performs better in predicting the portfolio return than the classical Markowitz portfolio optimization method, a multiple regression, a neural network, and the Sugeno–Yasukawa method. © 2010 Wiley Periodicals, Inc. 相似文献
87.
We constructed a class of non-maximally entangled mixed states (Adhikari et al. in Quantum Inf Comput 10:0398, 2010) and extensively studied their entanglement properties and also their usefulness as teleportation channels. In this article, we have revisited our constructed state and have studied it from three different perspectives. Since every entangled state is associated with a witness operator, we have found a suitable entanglement as well as teleportation witness operator for our non-maximally entangled mixed states. We considered the noisy channel’s effects on our constructed states to see how much it affects the states’ capacities as teleportation channels. For this purpose, we have mainly focussed on amplitude damping channel. A comparative study on concurrence and quantum discord of our constructed state of Adhikari et al. (2010) has also been carried out here. 相似文献
88.
Rapid scalar value classification and volume clipping for?interactive 3D medical image visualization
In many clinical scenarios, medical data visualization and interaction are important to physicians for exploring inner anatomical
structures and extracting meaningful diagnostic information. Real-time high-quality volume rendering, artifact-free clipping,
and rapid scalar value classification are important techniques employed in this process. Unfortunately, in practice, it is
still difficult to achieve an optimal balance. In this paper, we present some strategies to address this issue, which are
based on the calculation of segment-based post color attenuation and dynamic ray–plane intersection (RPI) respectively. When
implemented within our visualization system, the new classification algorithm can deliver real-time performance while avoiding
the “color over-accumulation” artifacts suffered by the commonly used acceleration algorithms that employ pre-integrated classification.
Our new strategy can achieve an optimized balance between image quality and classification speed. Next, the RPI algorithm
is used with opacity adjustment technique to effectively remove the “striping” artifacts on the clipping plane caused by the
nonuniform integration length. Furthermore, we present techniques for multiple transfer function (TF) based anatomical feature
enhancement and “keyhole” based endoscopic inner structure view. Finally, the algorithms are evaluated subjectively by radiologists
and quantitatively compared using image power spectrum analysis. 相似文献
89.
OBJECTIVES: We investigated whether context or different speech rates could improve older adult performance on identification of synthetically generated words. BACKGROUND: Synthetic speech systems can potentially improve the daily functioning of older adults. However, research must determine whether older adults can effectively implement current text-to-speech technologies, which few studies have examined. Older adults' sensory and cognitive declines may cause difficulties in identifying words in synthetic speech. METHODS: Ninety-six participants (young, middle-aged, and older adults) identified auditory monosyllabic words (half natural, half synthetic) presented in isolation or at the ends of sentences. Participants heard speech at either normal or slower rates. RESULTS: We found an interaction of age, context, and voice type and that slower speech rates worsened performance for all groups. Contrasts revealed that context reduced age differences, though only for natural speech. Hearing acuity was highly correlated with age and fully accounts for the interaction. CONCLUSIONS: Context improves performance for everyone in natural speech. However, whereas context improves performance for synthetic speech, it does not differentially reduce the age impairment for older adults. Slower speed generally impairs everyone's performance compared with the normal rate. APPLICATIONS: Systems using synthetic speech should avoid presenting words in isolation, and rich contextual support should be consistently adopted. Synthetic speech fidelity must be improved significantly before becoming truly useful for older adult populations. 相似文献
90.
Benjamin S. Kirk John W. Peterson Roy H. Stogner Graham F. Carey 《Engineering with Computers》2006,22(3-4):237-254
In this paper we describe the libMesh (http://libmesh.sourceforge.net) framework for parallel adaptive finite element applications. libMesh is an open-source software library that has been developed to facilitate serial and parallel simulation of multiscale, multiphysics applications using adaptive mesh refinement and coarsening strategies. The main software development is being carried out in the CFDLab (http://cfdlab.ae.utexas.edu) at the University of Texas, but as with other open-source software projects; contributions are being made elsewhere in the US and abroad. The main goals of this article are: (1) to provide a basic reference source that describes libMesh and the underlying philosophy and software design approach; (2) to give sufficient detail and references on the adaptive mesh refinement and coarsening (AMR/C) scheme for applications analysts and developers; and (3) to describe the parallel implementation and data structures with supporting discussion of domain decomposition, message passing, and details related to dynamic repartitioning for parallel AMR/C. Other aspects related to C++ programming paradigms, reusability for diverse applications, adaptive modeling, physics-independent error indicators, and similar concepts are briefly discussed. Finally, results from some applications using the library are presented and areas of future research are discussed. 相似文献