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Intraoperative transcranial electrical motor evoked potential monitoring during spinal surgery under intravenous ketamine or etomidate anaesthesia (1994)

Yang, L. -H. ; Lin, S. -M. ; Lee, W. -Y. ; [et al.]

Springer

Acta neurochirurgica 127 (1994), S. 191-198

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ISSN: 0942-0940

Keywords: Intraoperative MEP ; SSEP ; ketamine ; etomidate

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Summary Motor evoked potentials (MEPs), monitoring the motor function directly, are superior to somatosensory evoked potentials (SSEPs) in monitoring the motor system during spinal surgery. Reliable MEPs are difficult to elicit under normal anaesthesia. Using intravenous anaesthesia with either ketamine or etomidate infusion, we performed intraoperative MEP monitoring in 12 spinal operations for 11 cases from February 1992 to May 1992. For anaesthesia, ketamine was used in 5, etomidate in 7, fentanyl was supplemented in all, muscle relaxation at 30% to 50% of pre-anaesthetic muscle power was maintained with atracurium or vencuronium infusion. Transcranial bipolar electrical stimulation was used to induce MEPs. Concomitant SSEP monitoring was performed in 3. No significant anaesthesia related side effects were noted except one episode of unpleasant dream occurred in the ketamine anaesthesia group. Successful monitoring was achieved in 10 sessions. In 5 of which warning to the surgeons was made due to sudden MEP deterioration, which recovered followed by definite management in four and persisted in one. In the other 5 sessions, no warning was made due to stationary or gradual change in MEPs. Bilateral two-channel recordings were used in 3 sessions. In 2 of which unilateral transient change was noted. Loss of SSEPs was noted in one despite unchanged MEPs, in whom only new sensory deficits occurred postoperatively. Compared to the baseline MEPs in terms of latency and amplitude, the final MEPs improved in 5 sessions, did not change significantly in 4 sessions, deteriorated in one session, and were correlated well with the immediate postoperative motor status. In our small series, the intraoperative MEP monitoring showed neither false negative nor false positive result. It is concluded that the intraoperative MEP monitoring is feasible under intravenous ketamine or etomidate anaesthesia and valuable in spinal surgery.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01808765

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Submillimeter and microwave residual losses in epitaxial films of Y-Ba-Cu-O and Tl-Ca-Ba-Cu-O (1992)

Miller, D. ; Richards, P. L. ; Garrison, S. M. ; [et al.]

Springer

Journal of superconductivity 5 (1992), S. 379-388

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ISSN: 1572-9605

Keywords: Superconductivity ; ac losses ; Y-Ba-Cu-O ; Tl-Ca-Ba-Cu-O

Source: Springer Online Journal Archives 1860-2000

Topics: Electrical Engineering, Measurement and Control Technology , Physics

Notes: Abstract We have used a novel bolometric technique and a resonant technique to obtain accurate submillimeter and microwave residual loss data for epitaxial thin films of YBa2Cu3O7, Tl2Ca2Ba2Cu3O10, and Tl2CaBa2Cu2O8. For all films we obtain good agreement between the submillimeter and microwave data, with the residual losses in both the Y-Ba-Cu-O and Tl-Ca-Ba-Cu-O films scaling approximately as frequency squared below ∼1 THz. We are able to fit the losses in the Y-Ba-Cu-O films to a weakly coupled grain model for thea-b plane conductivity, in good agreement with results from a Kramers-Kronig analysis of the loss data. We observe strong phonon structure in the Tl-Ca-Ba-Cu-O films for frequencies between 2 and 21 THz, and are unable to fit these losses to the simple weakly coupled grain model. This is in strong contrast to the case for other high-T c superconductors such as YBa2Cu3O7, where phonon structure observed in ceramic samples is absent in epitaxial oriented films and crystals because of the electronic screening due to the high conductivity of thea-b planes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00618138

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Optimal trajectories for aeroassisted, coplanar orbital transfer (1987)

Miele, A. ; Basapur, V. K. ; Lee, W. Y.

Springer

Journal of optimization theory and applications 52 (1987), S. 1-24

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ISSN: 1573-2878

Keywords: Orbital transfer ; coplanar orbital transfer ; aeroassisted orbital transfer ; transfer between circular orbits ; grazing trajectories ; nearly-grazing trajectories ; optimal trajectories ; lift modulation ; Bolza problems ; Chebyshev problems ; minimax problems ; numerical methods ; computing methods ; transformation techniques ; sequential gradient-restoration algorithm

Source: Springer Online Journal Archives 1860-2000

Topics: Mathematics

Notes: Abstract This paper considers both classical and minimax problems of optimal control which arise in the study of aeroassisted, coplanar orbital transfer. The maneuver considered involves the coplanar transfer from a high planetary orbit to a low planetary orbit. An example is the HEO-to-LEO transfer of a spacecraft, where HEO denotes high Earth orbit and LEO denotes low Earth orbit. In particular, HEO can be GEO, a geosynchronous Earth orbit. The basic idea is to employ the hybrid combination of propulsive maneuvers in space and aerodynamic maneuvers in the sensible atmosphere. Hence, this type of flight is also called synergetic space flight. With reference to the atmospheric part of the maneuver, trajectory control is achieved by means of lift modulation. The presence of upper and lower bounds on the lift coefficient is considered. Within the framework of classical optimal control, the following problems are studied: (P1) minimize the energy required for orbital transfer; (P2) minimize the time integral of the heating rate; (P3) minimize the time of flight during the atmospheric portion of the trajectory; (P4) maximize the time of flight during the atmospheric portion of the trajectory; (P5) minimize the time integral of the square of the path inclination; and (P6) minimize the sum of the squares of the entry and exit path inclinations. Problems (P1) through (P6) are Bolza problems of optimal control. Within the framework of minimax optimal control, the following problems are studied: (Q1) minimize the peak heating rate; (Q2) minimize the peak dynamic pressure; and (Q3) minimize the peak altitude drop. Problems (Q1) through (Q3) are Chebyshev problems of optimal control, which can be converted into Bolza problems by suitable transformations. Numerical solutions for Problems (P1)–(P6) and Problems (Q1)–(Q3) are obtained by means of the sequential gradient-restoration algorithm for optimal control problems. The engineering implications of these solutions are discussed. In particular, the merits of nearly-grazing trajectories are considered.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00938462

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