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排序方式: 共有558条查询结果,搜索用时 15 毫秒
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Functional electrical stimulation (FES) enables restoration of movement in individuals with spinal cord injury. FES-based devices use electric current pulses to stimulate and excite the intact peripheral nerves. They produce muscle contractions, generate joint torques, and thus, joint movements. Since the underlying neuromuscular-skeletal system is highly nonlinear and time-varying, feedback control is necessary for accurate control of the generated movement. However, classical feedback/closed-loop control algorithms have so far failed to provide satisfactory performance and were not able to guarantee stability of the closed-loop system. Because of this, only open-loop controlled FES devices are in clinical use in spite of their limitations. The purpose of the reported research was to design a novel closed-loop FES controller that achieves good tracking performance and guarantees closed-loop stability. Such a controller was designed based on a mathematical neuromuscular-skeletal model and is founded on a sliding mode control theory. The controller was used to control shank movement and was tested in computer simulations as well as in actual experiments on healthy and spinal cord injured subjects. It demonstrated good robustness, stability, and tracking performance properties. 相似文献
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Sheets made from readily available conventional materials containing diamond or star shaped perforations are shown to exhibit various Poisson's ratio values which could also be negative (auxetic). This behavior may be exhibited in both tension and compression and can be explained through models based on “rotating rigid units.” This provides an easy manner for the manufacture of auxetic or conventional systems at any scale which can be tailor made to exhibit particular values of the Poisson's ratio. 相似文献
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George Ruben Ph.D. 《Microscopy research and technique》1986,4(1):75-75
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Or Raifman Dr. Sofiya Kolusheva Dr. Said El Kazzouli Dr. Dina M. Sigano Dr. Noemi Kedei Dr. Nancy E. Lewin Ruben Lopez‐Nicolas Ana Ortiz‐Espin Juan C. Gomez‐Fernandez Dr. Peter M. Blumberg Dr. Victor E. Marquez Prof. Senena Corbalan‐Garcia Prof. Raz Jelinek 《Chembiochem : a European journal of chemical biology》2010,11(14):2003-2009
Synthetic diacylglycerol‐lactones (DAG‐lactones) are effective modulators of critical cellular signaling pathways, downstream of the lipophilic second messenger diacylglycerol, that activate a host of protein kinase C (PKC) isozymes and other nonkinase proteins that share similar C1 membrane‐targeting domains with PKC. A fundamental determinant of the biological activity of these amphiphilic molecules is the nature of their interactions with cellular membranes. This study examines the biological properties of charged DAG‐lactones exhibiting different alkyl groups attached to the heterocyclic nitrogen of an α‐pyridylalkylidene chain, and particularly the relationship between membrane interactions of the substituted DAG‐lactones and their respective biological activities. Our results suggest that bilayer interface localization of the N‐alkyl chain in the R2 position of the DAG‐lactones inhibits translocation of PKC isoenzymes onto the cellular membrane. However, the orientation of a branched alkyl chain at the bilayer surface facilitates PKC binding and translocation. This investigation emphasizes that bilayer localization of the aromatic side residues of positively charged DAG‐lactone derivatives play a central role in determining biological activity, and that this factor contributes to the diversity of biological actions of these synthetic biomimetic ligands. 相似文献
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Soraya Plaza Jose A. Sanchez Endika Perez Ruben Gil Borja Izquierdo Naiara Ortega Iñigo Pombo 《Precision Engineering》2014
There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V. 相似文献
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Sackeim Harold A.; Nordlie Johanna W.; Gur Ruben C. 《Canadian Metallurgical Quarterly》1979,88(5):474
Reviews clinical and experimental analyses of hysterical conversion reactions of blindness. A model is offered to account for the visually controlled behavior of the psychogenically blind. The model attributes a central role to motivational factors in determining selective nonawareness of cognition. A case study of hypnotic blindness is presented that illustrates the utility of the model. The model has implications for interpretations of other hypnotic phenomena and for views concerning the relations between cognition and awareness. (79 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献