We analysed the effects of semaphorin D on axons from the developing rat entorhinal-hippocampal formation. Explants from superficial layers of the entorhinal cortex and of the hippocampus anlage were obtained from var...
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We analysed the effects of semaphorin D on axons from the developing rat entorhinal-hippocampal formation. Explants from superficial layers of the entorhinal cortex and of the hippocampus anlage were obtained from various developmental stages and co-cultured with cell aggregates expressing semaphorin D. Neurites extending from entorhinal explants that had been isolated from early embryonic stages (E16 and E17) were not affected by semaphorin D, but were repelled at later stages (E20 and E21). Axons from hippocampal neurons explanted at E21 were also repelled by semaphorin D, In situ hybridization studies revealed expression of the semaphorin D receptor neuropilin-1 in the entorhinal cortex from stage E17 to stage P7, and in the dentate gyrus and CA1-3 regions between E17 and adulthood. These data suggest that semaphorin D is involved in the formation of the perforant pathway and acts, via the neuropilin-1 receptor, as a repulsive signal that prevents entorhinal fibres from growing into the granular layer of the dentate gyrus. These data also suggest a role for semaphorin D in the development of intrahippocampal connections.
Binding of basic fibroblast growth factor (bFGF) and cell adhesion molecules to the nerve cell membrane promotes axon outgrowth. This response can be blocked by antagonists of voltage-gated calcium channels, yet no ch...
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Binding of basic fibroblast growth factor (bFGF) and cell adhesion molecules to the nerve cell membrane promotes axon outgrowth. This response can be blocked by antagonists of voltage-gated calcium channels, yet no change of cytosolic calcium concentration in the growth cone can be detected upon binding of the growth factor bFGF or the cell adhesion molecule L1. Using barium as a charge carrier, we show that bFGF and L1 open a calcium influx pathway in growth cones of rat sensory neurons without changing the membrane voltage. L1 does not activate influx in cells expressing a dominant negative mutant of the fibroblast growth factor receptor (FGFR) tyrosine kinase. FGFR-activated influx is blocked by specific antagonists of L- and N-type voltage-gated calcium channels and by an inhibitor of diacylglycerol lipase. We propose that both L1 and bFGF act via the FGFR to generate polyunsaturated fatty acids which in turn cause calcium channels to flicker open and shut. Short-lived domains of raised calcium at the cytosolic mouth of open channels activate axon outgrowth without raising bulk cytosolic calcium concentration. In confirmation of this model, the rapidly-acting calcium buffer BAPTA is significantly more effective at blocking FGF-induced axon outgrowth when compared with the slower buffer EGTA. Generation of short-lived calcium domains may provide a crucial mechanism for axon guidance during development and for promoting regeneration of damaged axons.
Chemotherapy and radiation therapy are ineffective against primary and secondary malignant hepatic tumors. Surgical resection has been considered the only potentially curative option, but few patients with hepatic tum...
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Chemotherapy and radiation therapy are ineffective against primary and secondary malignant hepatic tumors. Surgical resection has been considered the only potentially curative option, but few patients with hepatic tumors are candidates for surgery. Recent results suggest that radiofrequency thermal ablation may be an effective, minimally invasive technique for treating malignant hepatic tumors. Sonography is the primary technique for guiding percutaneous ablative procedures. We review the current research and clinical experience with radiofrequency thermal ablation for treating malignant hepatic tumors. (C) 1999 John Wiley & Sons, Inc.
This paper presents a number of new approach for ground vehicle to improve the positioning, guidance, navigation, multi-vehicle system approach and communication system regarding all function by using laser and light ...
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ISBN:
(纸本)0780342690
This paper presents a number of new approach for ground vehicle to improve the positioning, guidance, navigation, multi-vehicle system approach and communication system regarding all function by using laser and light beams and corner cubes. Regarding the positioning, guidance and navigation, two types of method, active and passive are presented with effective, useful experiments and also commented on commercial availability. On multi-vehicle system, passing control and blocking control systems are presented using optical scanning beam and corner cubes. On vehicle to vehicle communication, focused are two types of attenuated total reflection of corner cube prism and reflector-mirror movement control for modulation of the incident light beam. These proposed and experimentally confirmed prototypes are useful and attractive for intelligent vehicle transportation system and also will be applicable to all types of automation and intelligent guidance system on AGV in factory and off road vehicle as well as terrain vehicle like agricultural and constriction systems.
This paper presents an experimental mobile robot designed to operate autonomously within both indoor and outdoor environments. A sensor-based autonomous navigation architecture for a dynamically changing environment i...
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ISBN:
(纸本)0818681748
This paper presents an experimental mobile robot designed to operate autonomously within both indoor and outdoor environments. A sensor-based autonomous navigation architecture for a dynamically changing environment is described. Emphasis is placed on two important issues: autonomous navigation and smooth guidance of the robot. Several trajectory models are adopted to generate continuous-curvature paths in order to cope with the nonhonolomic constraint of the robot and unexpected obstacles. A smooth guidance algorithm has been used to track the planned path. Experimental results demonstrate its performance.
This paper presents a control system for guidance and navigation of a mobile planetary rover. The control system is composed of three subsystems. The path tracking is accomplished using the LQR algorithm. The position...
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This paper presents a control system for guidance and navigation of a mobile planetary rover. The control system is composed of three subsystems. The path tracking is accomplished using the LQR algorithm. The position and orientation errors are feedback using optimal gains. The disturbances are feedforward to improve the transient responses of the rover. Position and orientation errors are measured using odometry and inertial navigation system (INS). The collision avoidance is performed using the artificial potential field method. The data for that control loop is acquired using a scanning rangefinder. Dead reckoning is improved by using filtering and fusing signals from INS and odometry. Extensive simulation results and partial experimental results have been shown.
As part of the process of automatically guiding an aircraft, we have been successful in using stable inversion to compute a desired bounded state trajectory and corresponding bounded control. In addition to this feedf...
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As part of the process of automatically guiding an aircraft, we have been successful in using stable inversion to compute a desired bounded state trajectory and corresponding bounded control. In addition to this feedforward control, we must also construct a regulator to address modeling errors and disturbances. With respect to modeling errors we find that the stable inversion procedures used are so accurate that the regulator can assume a simple form, say a linear regulator about the desired trajectory. We show that under the appropriate assumptions, the bounded state trajectory and bounded control computed through stable inversion depend continuously on the parameters of the system. This is a consequence of a mathematical result that we prove about the continuous dependence of the "particular solution" of a time varying nonlinear system driven by a bounded input. This is distinct from the usual continuous dependence of the initial value problem for systems. (C) 1998 Elsevier Science B.V. All rights reserved.
This paper is intended to investigate the electromagnetic flux: distribution and side-force characteristics of a transverse flux linear switched-reluctance machine (TFLSRM) by three-dimensional finite element method. ...
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This paper is intended to investigate the electromagnetic flux: distribution and side-force characteristics of a transverse flux linear switched-reluctance machine (TFLSRM) by three-dimensional finite element method. With the flux path perpendicular to its moving direction, results showed that the TFLSRM is quite suitable for high speed linear motion applications, due to the generated electromagnetic side-force which enhance the overall system guidance. From comparison analysis, conceptual design suggestions on the machine pole shapes will also be supplied.
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