Discrete time optimal control of linear time-delay systems

A discrete time optimal control for linear time-delay systems is developed to ensure that all closed-loop eigenvalues will lie inside a circular region centred at (β;, 0) with radius α. It is shown that by suitable manipulations the problem can be reduced to a standard discrete time quadratic regulator problem. An illustrative example is included to demonstrate the applicability of the proposed method.     

颅内破裂动脉瘤手术时机的探讨(附237例分析)

目的探讨颅内破裂动脉瘤手术时机与临床预后的关系。方法回顾性分析2005年我院收治的237例颅内破裂动脉瘤，其中196例行手术治疗。按入院时Hunt—Hess分级将手术病人分为A组（Ⅰ～Ⅲ级）162例，B组（Ⅳ、Ⅴ级）34例；根据手术时间分为早期手术组（SAH3d内手术）19例，延期手术组（SAH4～10d手术）82例，晚期手术组（SAH11d之后手术）95例。比较不同手术期别动脉瘤术中破裂率、术后1个月GOS评分及术后主要并发症（脑血管痉挛、脑积水）发生率，并进行统计学分析。结果24例（10．1％）因再出血丧失治疗机会。术中动脉瘤破裂早期手术组3例（15，8％），延期手术组8例（9．8％），晚期手术组6例（613％）。术后脑血管痉挛发生率早期手术组为15，8％，延期手术组为19，5％，晚期手术组为17，9％。脑积水发生率以晚期手术组最高（14，7％）。对术后1个月GOS评分Ridit分析结果显示：A、B两组中均以早期手术组治疗效果最佳．延期手术次之．晚期手术最差。结论早期手术可规避颅内破裂动脉瘤再出血的风险，降低主要并发症发生率。对于各个级别（包括Ⅳ、Ⅴ级）的SAH病人，均应根据治疗者的手术经验与技巧和所在医院的条件，及早诊断，尽早手术。     

Optimal response in siso ripple-free deadbeat systems

The ripple-free deadbeat control problem for SISO plants subjected to arbitrary reference signals is considered. The trade-off between the settling time and the integral square error between the system output and reference signal is investigated. Given a specific order of the controller, it is shown how to design an optimal ripple-free deadbeat controller. An illustrative example is presented to show the feasibility of the proposed algorithm.     

An optimal dynamic output feedback controller for a flexible spacecraft

The design of a low-order dynamic output feedback controller for a flexible spacecraft is carried out using modified linear quadratic Gaussian (LQG) theory. The necessary conditions for optimization are given. The linear equations governing a flexible spacecraft with a central rigid body and two sun-tracking solar panels are presented. The parameters of the Solar Electric Propulsion Spacecraft (SEPS) are selected for analysis and simulation. The optimal gains for the dynamic controller are estimated using an iterative algorithm. The sequential procedure which assures convergence is selected. The initial gains which stabilize the system are chosen on the basis of the principle of a PD controller. A third-order controller for pitch, roll and yaw axes of the 18th-order system, which includes sensor and actuator dynamics, is designed. Numerical simulations carried out to ascertain the performance of the controller show the performance to be satisfactory.     

A multi-input/multi-output optimal PI controller for redundant robots in the presence of flexible disturbances

The two-stage synthesis of a multi-input/multi-output optimal proportional-integral (PI) controller is described for linear, time-invariant systems. In the first stage the PI controller is designed by solving a steady state algebraic Riccati equation. As a result, the optimal cost is expressed in terms of the system's constant output set-points. In the second stage the cost is further reduced by optimally selecting the output set-points to minimize a static quadratic performance index subject to linear algebraic constraints. The design framework is applied to a planar redundant robotic manipulator equipped with four joints and mounted at the tip of a long flexible arm. We then address the problem of self-motion control in the presence of vibratory disturbances.     

大鼠脑震荡c-fos癌基因的表达及其法医病理学意义

目的 探讨原癌基因c-fos的表达和脑震荡性损伤的关系,同时寻找脑震荡后法医病理学的诊断依据。方法 55只实验大鼠随机分为脑震荡组和对照组。c-fos-mRNA表达采用原位杂交法观察。结果 对照组大鼠未见c-fos-mRNA的表达,然而脑震荡组在损伤后15min即可在神经元和胶质细胞观察到c-fos-mRNA的表达,至30min c-fos-mRNA的阳性反应达最高峰,以后逐渐下降。结论 c-fos原癌基因的检测可成为诊断脑震荡和推断脑震荡后经过时间的一项敏感指标。     

Work at sea: a study of sleep,and of circadian rhythms in physiological and psychological functions,in watchkeepers on merchant vessels

Summary Sleep length and sleep quality scores were collected on board ships over periods of up to two weeks from 38 watchkeepers working a 4-on/8-off routine and 29 dayworkers. All watchkeepers exhibited fragmented sleeping patterns, which indicated a lack of adaptation of the sleep/wakefulness cycle to the hours of work. There were only slight differences in total sleep length between watchkeepers and dayworkers, however, both groups did not obtain an adequate amount of sleep. Within the watchkeeping crews the 3rd Officers had by far the shortest sleep length. Concerning sleep quality, daytime sleep was generally given the lowest ratings, whereas sleep starting before midnight was on average evaluated as the best, both by watchkeepers and dayworkers. Watchkeeping personnel do not normally have any days off during a voyage so that missed sleep might even amount to a sleep deficit. A solution for this problem could perhaps be a new, stabilized system that allows a single uninterrupted sleep, which is required for full recuperation, to be taken each day.Dedicated to Professor J. Aschoff on the occasion of his 75th birthdayPartly supported by a grant from the Ministry for Technology and Research, Federal Republic of Germany, Project Schiff der Zukunft, Part ET83b     

The development of goal-directed reaching in infants: hand trajectory formation and joint torque control

Nine young infants were followed longitudinally from 4 to 15 months of age. We recorded early spontaneous movements and reaching movements to a stationary target. Time-position data of the hand (endpoint), shoulder, and elbow were collected using an optoelectronic measurement system (ELITE). We analyzed the endpoint kinematics and the intersegmental dynamics of the shoulder and elbow joint to investigate how changes in proximal torque control determined the development of hand trajectory formation. Two developmental phases of hand trajectory formation were identified: a first phase of rapid improvements between 16 and 24 weeks of age, the time of reaching onset for all infants. During that time period the number of movement units per reach and movement time decreased dramatically. In a second phase (28–64 weeks), a period of fine-tuning of the sensorimotor system, we saw slower, more gradual changes in the endpoint kinematics. The analysis of the underlying intersegmental joint torques revealed the following results: first, the range of muscular and motiondependent torques (relative to body weight) did not change significantly with age. That is, early reaching was not confined by limitations in producing task-adequate levels of muscular torque. Second, improvements in the endpoint kinematics were not accomplished by minimizing amplitude of muscle and reactive torques. Third, the relative timing of muscular and motion-dependent torque peaks showed a systematic development toward an adult timing profile with increasing age. In conclusion, the development toward invariant characteristics of the hand trajectory is mirrored by concurrent changes in the control of joint forces. The acquisition of stable patterns of intersegmental coordination is not achieved by simply regulating force amplitude, but more so by modulating the correct timing of joint force production and by the system's use of reactive forces. Our findings support the view that development of reaching is a process of unsupervised learning with no external or innate teacher prescribing the desired kinematics or kinetics of the movement.     

Temporal discrimination in the cerebellar cortex during conditioned eyelid responses

Little is known about mechanisms used by the nervous system to encode time. In light of recent evidence, cerebellar cortex involvement in the learned timing of conditioned eyelid responses shows promise as an area of investigation into neural timing mechanisms. Lesion studies indicate that the cerebellar cortex is necessary for response timing, but do not rule out the possibility that response timing is encoded afferent to the cerebellum. To differentiate between precerebellar and cerebellar cortical timing mechanisms, rabbits were trained by pairing direct stimulation of mossy fibers in the cerebellum as the conditioned stimulus (CS) with an eyeshock unconditioned stimulus (US). We find that individual animals can produce diffently timed conditioned responses when trained with a mossy fiber CS that has been paired with the US at various interstimulus intervals. The fact that differently timed responses can be conditioned using constant-frequency stimulation of an invariant subset of mossy fibers as the CS suggests that timing information in the afferent input to the cerebellum is not essential. Two rabbits trained with single-pulse stimulation in the cerebellum as the CS also learned differently timed conditioned responses; suggesting that fiber recruitment during a stimulus train does not convey the necessary temporal coding to the cerebellar cortex. Together with the lesion data, these findings suggest that the learned timing of conditioned eyelid responses occurs in the cerebellar cortex. Received: 25 August 1997 / Accepted: 12 January 1998