Background： Attention deficit hyperactivity disorder （ADHD） is a common childhood disorder that affects approximately 11% of children in the United States. Research supports that a single session of exercise benefi...Background： Attention deficit hyperactivity disorder （ADHD） is a common childhood disorder that affects approximately 11% of children in the United States. Research supports that a single session of exercise benefits cognitive performance by children, and a limited number of studies have demonstrated that these effects can also be realized by children with ADHD. The purpose of this study was to examine the effect of acute exercise on cognitive performance by children with and without ADHD. Methods： Children with and without ADHD were asked to perform cognitive tasks on 2 days following treatment conditions that were assigned in a random, counterbalanced order. The treatment conditions consisted of a 30-min control condition on 1 day and a moderate intensity exercise condition on the other day. Results： Exercise significantly benefited performance on all three conditions of the Stroop Task, but did not significantly affect performance on the Tower of London or the Trail Making Test. Conclusion： children with and without ADHD realize benefits in speed of processing and inhibitory control in response to a session of acute exercise, but do not experience benefits in planning or set shifting.展开更多
This paper investigates the controllability problem of time-variant linear stochastic controlsystems.A sufficient and necessary condition is established for stochastic exact controllability,whichprovides a useful alge...This paper investigates the controllability problem of time-variant linear stochastic controlsystems.A sufficient and necessary condition is established for stochastic exact controllability,whichprovides a useful algebraic criterion for stochastic control systems.Furthermore,when the stochasticsystems degenerate to deterministic systems,the algebraic criterion becomes the counterpart for thecomplete controllability of deterministic control systems.展开更多
A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil...A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root sys- tems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excava- tion/drilling location is of prime importance. Ground penetrating radar （GPR） provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the perfor- mance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled envi- ronment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radar- grams were subject to the influence of the following factors： size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T2 （p〈0.001, t=0.795）. Because GPR root detection is highly site-specific, this study provides a local refer- ence for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.展开更多
This paper discusses the properties of the storage functions for a class of nonlinear stochastic systems. Some necessary and sufficient conditions for a function to be a storage function are derived. As applications, ...This paper discusses the properties of the storage functions for a class of nonlinear stochastic systems. Some necessary and sufficient conditions for a function to be a storage function are derived. As applications, the finite and infinite horizon nonlinear stochastic H∞ controls for systems with state, control, and external disturbance dependent noise are investigated, which generalize the previous results.展开更多
This paper is concerned with the effects of redundant control inputs on the quadratic optimal performance index in finite-time optimal control.Actually,the effects of redundant control input on quadratic performance i...This paper is concerned with the effects of redundant control inputs on the quadratic optimal performance index in finite-time optimal control.Actually,the effects of redundant control input on quadratic performance index is equal to study the effects of the redundant control input on the solution of Riccati differential equation(RDE).Hence,some sufficient conditions are presented to strictly decrease the solution of RDE with the column of input matrix increased.Especially,a necessary and sufficient condition is derived to strictly decrease the solution of the homogeneous RDE after control input extensions.Moreover,one sufficient condition is obtained,which guarantees that the minimum control energy index strictly decreases with input extension.It is shown that redundant control inputs can improve the system performance based on these results.Some examples are taken to illustrate the effectiveness of related problems.展开更多
文摘Background： Attention deficit hyperactivity disorder （ADHD） is a common childhood disorder that affects approximately 11% of children in the United States. Research supports that a single session of exercise benefits cognitive performance by children, and a limited number of studies have demonstrated that these effects can also be realized by children with ADHD. The purpose of this study was to examine the effect of acute exercise on cognitive performance by children with and without ADHD. Methods： Children with and without ADHD were asked to perform cognitive tasks on 2 days following treatment conditions that were assigned in a random, counterbalanced order. The treatment conditions consisted of a 30-min control condition on 1 day and a moderate intensity exercise condition on the other day. Results： Exercise significantly benefited performance on all three conditions of the Stroop Task, but did not significantly affect performance on the Tower of London or the Trail Making Test. Conclusion： children with and without ADHD realize benefits in speed of processing and inhibitory control in response to a session of acute exercise, but do not experience benefits in planning or set shifting.
基金supported by the National Natural Science Foundation under Grant Nos.60904029 and 60704002the State Key Laboratory under Grant No.RCS2008ZT002
文摘This paper investigates the controllability problem of time-variant linear stochastic controlsystems.A sufficient and necessary condition is established for stochastic exact controllability,whichprovides a useful algebraic criterion for stochastic control systems.Furthermore,when the stochasticsystems degenerate to deterministic systems,the algebraic criterion becomes the counterpart for thecomplete controllability of deterministic control systems.
基金the Research Grants Council of the Hong Kong Special Administrative Region (HKSAR) (Grant Nos. HKUST9/CRF/ 09, HKUST6/CRF/12R)
文摘A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root sys- tems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excava- tion/drilling location is of prime importance. Ground penetrating radar （GPR） provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the perfor- mance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled envi- ronment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radar- grams were subject to the influence of the following factors： size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T2 （p〈0.001, t=0.795）. Because GPR root detection is highly site-specific, this study provides a local refer- ence for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.
基金This research is supported by the National Natural Science Foundation of China under Grant Nos. 10921101 and 60874032, the National Basic Research Program of China （973 Program） under Grant No. 2007CB814904, the Key Project of Natural Science Foundation of Shandong Province under Grant No. ZR2009GZ001, and the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No. 20103718110006.
文摘This paper discusses the properties of the storage functions for a class of nonlinear stochastic systems. Some necessary and sufficient conditions for a function to be a storage function are derived. As applications, the finite and infinite horizon nonlinear stochastic H∞ controls for systems with state, control, and external disturbance dependent noise are investigated, which generalize the previous results.
基金supported by the National Natural Science Foundation of China under Grant Nos.61174038 and 61203129
文摘This paper is concerned with the effects of redundant control inputs on the quadratic optimal performance index in finite-time optimal control.Actually,the effects of redundant control input on quadratic performance index is equal to study the effects of the redundant control input on the solution of Riccati differential equation(RDE).Hence,some sufficient conditions are presented to strictly decrease the solution of RDE with the column of input matrix increased.Especially,a necessary and sufficient condition is derived to strictly decrease the solution of the homogeneous RDE after control input extensions.Moreover,one sufficient condition is obtained,which guarantees that the minimum control energy index strictly decreases with input extension.It is shown that redundant control inputs can improve the system performance based on these results.Some examples are taken to illustrate the effectiveness of related problems.
