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81.
Montesinos CA Tse ZT Chan YJ Elhawary H Rea M Hamed A Young I Lamperth M 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2012,226(1):49-54
The static magnetic field of a magnetic resonance imaging scanner can be distorted by the presence of materials, perturbing the spatial encoding process in magnetic resonance imaging and often resulting in image artifacts. The relationship between the image artifact size and magnetic susceptibility of the material specimen is of interest to engineers for the design of devices that are to be compatible with the imaging volume of the scanner. In this study, a finite-element method was used to simulate the distorted magnetic field of samples with different susceptibilities. With the knowledge of the external- and self- magnetic field interactions, a Lorentz correction was applied to compute the magnetic field deviation. The simulated results were then validated by the corresponding experimental magnetic resonance images. 相似文献
82.
Andrew J. Berry Jeremy Howitt Da-Wei Gu Ian Postlethwaite 《Journal of Intelligent and Robotic Systems》2012,66(4):477-494
As the complexity of an unmanned vehicle’s operational environment increases so does the need to consider the obstacle space
continually, and this is aided by splitting the motion planning functionality into distinct global and local layers. This
paper presents a new continuous local motion planning framework, where the output and control space elements of the traditional
receding horizon control problem are separated into distinct layers. This separation reduces the complexity of the local motion
trajectory optimisation, enabling faster design and increased horizon length. The focus of this paper is on the output space
component of this framework. Bezier polynomial functions are used to describe local motion trajectories which are constrained
to vehicle performance limits and optimised to track a global trajectory. Development and testing is in simulation, targeted
at a nonlinear model of a quadrotor unmanned air vehicle. The defined framework is used to provide situation-aware tracking of a global trajectory in the presence of static and dynamic obstacles, as well as realistic turbulence and gusts.
Also demonstrated is the immediate-term decentralised deconfliction of multiple unmanned vehicles, and multiple formations of unmanned vehicles. 相似文献
83.
In this paper, we seek to eliminate the noise caused by caustic paths during progressive Monte Carlo path tracing. We employ a filtering strategy over path space, handling each subspace using specialized derivations of path tracing and progressive photon mapping. Evaluating diffuse paths with path tracing allows the use of sample stratification over both pixels and the image as a whole, whilst sharp detailed caustics are produced using progressive photon mapping. This is an efficient, low noise progressive algorithm with vanishing bias combining the advantages of both Monte Carlo methods, and particle tracing. 相似文献
84.
In many applications, the properties of an object being modeled are stored as labels on vertices or edges of a graph. In this paper, we consider succinct representation of labeled graphs. Our main results are the succinct representations of labeled and multi-labeled graphs (we consider planar triangulations, planar graphs and k-page graphs) to support various label queries efficiently. The additional space cost to store the labels is essentially the information-theoretic minimum. As far as we know, our representations are the first succinct representations of labeled graphs. We also have two preliminary results to achieve the main contribution. First, we design a succinct representation of unlabeled planar triangulations to support the rank/select of edges in ccw (counter clockwise) order in addition to the other operations supported in previous work. Second, we design a succinct representation for a k-page graph when k is large to support various navigational operations more efficiently. In particular, we can test the adjacency of two vertices in O(lg?k) time, while previous work uses O(k) time. 相似文献
85.
In this article, we described a simple and rapid method for fabrication of droplet microfluidic devices on polystyrene substrate
using a CO2 laser system. The effects of the laser power and the cutting speed on the depth, width and aspect ratio of the microchannels
fabricated on polystyrene were investigated. The polystyrene microfluidic channels were encapsulated using a hot press bonding
technique. The experimental results showed that both discrete droplets and laminar flows could be obtained in the device. 相似文献
86.
Haptic and audio cues now appear commonly in computer interfaces, partially due to inherent advantages such as their support for eyes-free interaction. Their invisible, unobservable nature also makes them ideal candidates for security interfaces in which users have to enter secret information such as passwords. In particular, researchers have explored this idea through the design of PIN entry authentication systems based on multi-modal combinations of visual and non-visual content or on the recognition of small sets of unimodal haptic or audio stimuli. This paper highlights the benefits and performance limitations of these approaches and introduces an alternative based on unimodal audio or haptic temporal numerosity – the ability to accurately and rapidly determine the number of cues presented in rapid temporal succession. In essence, in a numerosity interface, rather than recognizing distinct cues, users must count the number of times that a single cue occurs. In an iterative process of design and evaluation, three prototypes implementing this concept are presented and studies of their use reported. The results show the fastest PIN entry times and lowest error rates to be 8 s and 2%, figures that improve substantially on previous research. These results are attained while maintaining low levels of workload and substantial resistance to observation attack (as determined via camera attack security studies). In sum, this paper argues that unimodal audio and haptic numerosity is a valuable and relatively unexplored metaphor for non-visual input and demonstrates the validity of this claim in the demanding task of unobservable authentication systems. 相似文献
87.
88.
A general simulation model of market competition is developed to explore the effectiveness of and interactions between different types of product exploration and exploitation strategies, that is, innovation, imitation and process improvement. The model, like real markets, is highly non-linear such that analytical solutions are not possible. We use simulation experiments to examine firm survival and the effectiveness of different strategies under different market conditions including competitors' strategies, how long it takes for each strategy to bear fruit and how costly it is, and the timing, growth and duration of product life cycles. The model is implemented on the Internet and provides the basis for further experiments to examine the impact of different combinations of firm strategies on survival and performance. 相似文献
89.
Joormann Jutta; Hertel Paula T.; Brozovich Faith; Gotlib Ian H. 《Canadian Metallurgical Quarterly》2005,114(4):640
The authors examined intentional forgetting of negative material in depression. Participants were instructed to not think about emotional nouns that they had learned to associate with a neutral cue word. The authors provided participants with multiple occasions to suppress the unwanted words. Overall, depressed participants successfully forgot negative words. Moreover, the authors obtained a clear practice effect. However, forgetting came at a cost: Compared with the nondepressed participants and with the depressed participants who were instructed to forget positive words, depressed participants who were instructed to forget negative words showed significantly worse recall of the baseline words. These results indicate that training depressed individuals in intentional forgetting could prove to be an effective strategy to counteract automatic ruminative tendencies and mood-congruent biases. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
Comparative optimism has been studied extensively in adults and is a significant component of social- cognitive models about health. In contrast, little is known about comparative optimism in children or about the wider social- cognitive processes that underpin their health-related behavior. This study investigated comparative optimism for health- and nonhealth-related topics in 101 children 8 or 9 years of age, the youngest ages that have been investigated so far. Children were shown to be unrealistically optimistic for health and nonhealth events. The implications of these findings for understanding comparative optimism in children are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献