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SELECTIVE ACTIVATION OF SMALL MOTOR AXONS BY QUASITRAPEZOIDAL current PULSES

IEEE TRANSACTIONS ON BIOMEDICAL engineering 1991年第2期38卷 168-174页

作者： FANG, ZP MORTIMER, JT CASE WESTERN RESERVE UNIV DEPT NEUROSCICLEVELANDOH 44106

We have found a method to activate electrically smaller nerve fibers without activating larger fibers in the same nerve trunk. The method takes advantage of the fact that action potentials are blocked with less membrane hyperpolarization in larger fibers than in smaller fibers. In our nerve stimulation system, quasitrapezoidal-shaped current pulses were delivered through a tripolar cuff electrode to effect differential block by membrane hyperpolarization. The quasitrapezoidal-shaped pulses with a square leading edge, a 350-mu-s plateau, and an exponential trailing phase ensured the block of propagating action potentials and prevented the occurrence of anodal break excitation. The tripolar cuff electrode design restricted current flow inside the cuff and thus eliminated the undersired nerve stimulation due to a "virtual cathode." Experiments were performed on 13 cats. The cuff electrode was placed on the medial gastrocnemius nerve. Both compound and single fiber action potentials were recorded from L7 ventral root filaments. The results demonstrated that larger alpha motor axons could be blocked at lower current levels than smaller alpha motor axons, and that all alpha fibers could be blocked at lower current levels than gamma fibers. A statistical analysis indicated that the blocking threshold was correlated with the axonal conduction velocity or fiber diameter. This method could be used in physiological experiments and neural prostheses to achieve a small-to-large recruitment order in motor or sensory systems.

关键词： Nerve fibers Biomembranes Spirals optical fiber sensors Prosthetics Animals Biomedical electrodes Pulse shaping methods Cats Statistical analysis

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Latest developments in crystal growth and characterization of efficient acousto-optic materials

Latest developments in crystal growth and characterization o...

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Inorganic Crystals for Optics, Electro-Optics, and Frequency Conversion

作者： Paradies, C.J. Glicksman, M.E. Jones, O.C. Kim, G.T. Lin, Jen T. Gottlieb, Milton S. Singh, N.B. Rensselaer Polytechnic Inst. Troy NY USA

ISBN: (纸本)0819406899

Mercurous halides have become the subject of great interest because of their very high acousto-optic figure of merit and large transmission range. These crystals have unique acousto-optic properties that make possible a variety of high performance devices for signal processing and spectral processing and analysis, particularly in the mid- and long-wavelength infrared region. Mercurous chloride is the most developed in this class and large crystals have been grown by the physical vapor transport method. current research is attempting to extend the efficiency of devices using the mercurous halides. The authors' research centers on purification methods, determining the factors that affect optical quality and improving the process of single crystal growth.

关键词： Crystals

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design and analysis of a Water Window Imaging X-Ray Microscope

Design and analysis of a Water Window Imaging X-Ray Microsco...

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optical Methods for Tumor Treatment and Early Diagnosis: Mechanisms and Techniques

作者： Hoover, Richard B. Baker, Phillip C. Shealy, David L. Brinkley, B.R. Walker Jr., Arthur B. Barbee Jr., Troy W. NASA/Marshall Space Flight Cent. Huntsville AL USA

ISBN: (纸本)0819405167

The authors have theoretically designed and analyzed the optical components and mechanical structures for an imaging x-ray microscope which will be configured to operate in the water window. This instrument affords new and noninvasive strategies for examining living tumor cells without the use of dyes, stains or other exogenous chemicals, which can produce limiting artifacts. The Water Window Imaging X-Ray Microscope is based on doubly reflecting, normal incidence multilayer optical technology, such as has been previously employed in telescopes for high resolution x-ray imaging of the sun. Multilayer coatings have now been fabricated with near theoretical reflectivities and perfect bandpass matching for the new rocket-borne solar observatory, the Multi-Spectral Solar Telescope Array (MSSTA). These telescopes employ multilayer mirror substrates with sub-angstrom (rms) smoothness which are made possible by Advanced Flow Polishing. Recent developments in multilayer coating technology and Advanced Flow Polishing methods used with Zerodur and Hemlite grade sapphire have paved the way for the development of the Water Window Imaging X-Ray Microscope.

关键词： Microscopes

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Infrared optical response of superconducting YBaCuO thin films

Infrared optical response of superconducting YBaCuO thin fil...

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Superconductivity Applications for Infrared and Microwave Devices II

作者： Sun, Han D. Zhou, Fang Q. Zhao, Xing R. Wang, Lingjie Yi, Xin J. Huazhong Univ. of Science & Technology Wuhan Hubei China

ISBN: (纸本)0819405868

Results of measurements of the optical response of high Tc superconducting infrared detectors fabricated from YBaCuO thin films for wavelengths of 3-5 μm and 8-14 μm at an operating temperature above liquid nitrogen. The measurements of a meander line detector yield a noise equivalent power (NEP) of 2 × 10-9 w Hz-1/2 and a detectivity (D*) of 1.5 × 108 cmHz1/2W-1 for radiation of 8-14 μm at a chopping frequency of 50 Hz. The response for 3-5 μm radiation is lower than that for 8-14 μm for the same detector. The authors have investigated the dependence of the optical response of these detectors on several parameters, including bias current, chopping frequency, substrate material, and film quality (associated with different fabricating methods). In addition, the device design and methods to improve the sensitivity have been discussed.

关键词： High Temperature Superconductors

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New analytic formulas for the design of metal-clad ridge-waveguide lasers

New analytic formulas for the design of metal-clad ridge-wav...

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Fiber Optic Components and Reliability 1991

作者： Yu, Tong Beijing Glass Research Institute 1 Dong Dadi Chong Wen Men Wai Beijing100062 China

The waveguide characteristics of metal-clad ridge-waveguide (MCRW) lasers are analyzed by the equivalent current theory associated with the effective index method. The enhanced lateral mode confinement, and increased mode loss are calculated for different metals. All these results are in analytic form, which has not been published before and makes us easy to get the waveguide characteristics calculation. The optimum design of MCRW lasers is discussed by using these analytic formulas. © 1991 SPIE. All rights reserved.

关键词： Ridge waveguides

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A 1.25 Gb/s LED-based optical transmitter

A 1.25 Gb/s LED-based optical transmitter

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Fiber Optic Components and Reliability 1991

作者： Rosen, W.A. Herman, W.N. Daryoush, A.S. Daniel, T. Naval Air Development Center WarminsterPA18974 United States Dept. of ECE Drexel University PhiladelphiaPA19104 United States

An optical transmitter is described which uses a commercial LED coupled to an external modulator to achieve a 1.25 Gb/s data rate. Both a Mach-Zehnder modulator and a reverse Δβ directional coupler were evaluated for modulation of the optical signal. Analytical expressions are derived for the extinction ratio in each device as a function of spectral width of the source. Experimentally, both devices produced an extinction ratio > 20 dB with peak output powers of -20.1 and -23.9 dBm respectively. We estimate that by minimizing losses in the system, peak output powers of -12.5 and -15.1 dBm respectively can be achieved with the two devices using the available LED. We also discuss design improvements which can reduce the wavelength sensitivity of the Aft switch and describe a drive circuit capable of extending the upper frequency limit of the current switch from 200 to 1250 MHz. © 1991 SPIE. All rights reserved.

关键词： optical transmitters

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Advanced sensor systems for theapplication of LIME technologies in the process industry: a review

Industrial Metrology

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Industrial Metrology 1991年第1期2卷 1-31页

作者： Heitor, Manuel V. Instituto Superior Tecnico Technical University of Lisbon Av. Rovisco Pais 1096 LISBOACodex Portugal

Modern computer-integrated manufacturing and engineering (CIME) technologieshave been developed and implemented to improve plant and process design, measurement and control design, and plant operation, together with the economic optimization of flow processes. Almost irrespective of which approach is selected for obtaining these results, success or otherwise is based on some process measurements, involving predominantly either temperature, pressure or flow. optical sensors are often being adopted for these tasks not only because of their non-intrusive nature, but also in view of their reliability, together with their high response speed, intrinsic resolution and increasing ruggedness. In addition, the development of new measurement capabilities such as easy adjustment for operating range, compensation for effects of environmental conditions and self-diagnosis, has given a considerable level of "intelligence" to current sensors, which are smarter, smaller and cheaper than ever before. This paper reviews and discusses the implementation of advanced sensor systems for onlinemeasurements of process streams with emphasis on hot, dirty, hostile and multiphase environments. The requirements for the integration of the information from the sensors in a CIME environment are considered, taking into account the different levels of automation of typical processes. Novel methodologies, such as fiber-optic sensors, semiconductor materials, image processing and data analysis are discussed, as well as the use of "intelligent" instruments as part of the push towards higher quality. © 1991 Elsevier Science Publishers B.V.

关键词： Applied metrology optical diagnostics process control smart sensors

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The design and performance of a dynamically-aligned step-scan interferometer 8

The design and performance of a dynamically-aligned step-sca...

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8th International Conference on Fourier Transform Spectroscopy 1991

作者： Crocombe, Richard A. Curbelo, Raul Leonardi, John Johnson, David B. Bio-Rad Digilab Division 37 Putnam Avenue CambridgeMA02139 United States

In the past decade advances in microprocessors have been applied in FT-IR spectrometers to deliver higher data system performance at substantially reduced cost. Now, advances in microprocessors and signal processing technology are being applied to overcome current performance limits in the FT-IR optical bench, and considerably expand their functionality. This paper describes the design and performance of a new generation of research-grade interferometer, the 896, using state-ofthe art technology. The major enhancements are: rapid auto-align (allowing interchanging of beamsplitters);dynamic alignment (giving active stabilization and allowing high performance operation over a wide variety of scan conditions);enhanced stability rapid-scan mode with general purpose kinetic software;step-scan mode (0.004 Hz to 800 Hz) with variable phase modulation;and dynamic range extension. © 1991 SPIE. All rights reserved.

关键词： Interferometers

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Fabrication of light-guiding devices and fiber-coupling structures by the LIGA process

Fabrication of light-guiding devices and fiber-coupling stru...

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Micro-Optics II

作者： Rogner, Arnd Ehrfeld, Wolfgang MicroParts Gesellschaft fuer Mikrostrukturtechnik mbH Karlsruhe 21 Federal Republic of Germany

ISBN: (纸本)0819406155

The LIGA process which is based on deep-etch lithography in combination with high-precision electroforming and moulding processes is a particularly promising method for the fabrication of three-dimensional microstructures. Some interesting applications can be seen in the field of integrated optics. Passive waveguide structures can be fabricated by deep-etch synchrotron radiation lithography of multilayer resist systems. Using this technique, multimode strip waveguides with a PMMA core and a P (TFPMA/MMA) cladding as well as a planar grating spectrograph have been realized. The attenuation of 0.18 dB/cm measured at a wavelength of 850 nm can be reduced, especially in the near IR-region, by the use of deuterated PMMA as a core material. For plastic fiber LAN applications, moulding processes for the replication of passive multimode waveguide components like Y-couplers or star couplers are under investigation. The advantages of the LIGA process - unrestricted design in the cross-sectional shape and a small surface roughness in the range of 10 - 20 nm - are of special interest for these developments. For coupling fibers to integrated-optical chips, structures of a coupling array have been fabricated. The fibers are guided by exactly positioned stop faces and then precisely located and prefixed by integrated spring elements. The main advantages are as follows: the thermal expansion coefficient of the array can be matched to the optical chip material, the use of spring elements for prefixing simplifies the handling, and adhesives and the connected problems can be avoided.

关键词： Waveguides, optical

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New developments in mass-transport fabrication for reliable high-performance integrated optoelectronic devices

New developments in mass-transport fabrication for reliable ...

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Integrated Optoelectronics for Communication and Processing 1991

作者： Liau, Z.L. Lincoln Laboratory Massachusetts Institute of Technology LexingtonMA02173-9108 United States

current investigations of material issues in mass-transport fabrication are reviewed. Evaporation loss and resulting surface roughness have been identified and simple techniques developed for effective prevention. Photoluminescence intensity degradation and improvement were observed under different experimental conditions. Evidence of defect generation associated with high transport rate has also been observed. Extension of mass transport to GaAs-based heterostructure lasers showed considerable promise for advanced integrated siructures with high performance and improved reliability. © 1991 SPIE. All rights reserved.

关键词： Fabrication

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