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Johnson, J.

Publications and source records attributed to Johnson, J..

86 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Evaluation of a telerobotic system to assist surgeons in microsurgery

A tool was developed that assists surgeons in manipulating surgical instruments more precisely than is possible manually. The tool is a telemanipulator that scales down the surgeon's hand motion and filters tremor in the motion. The signals measured from the surgeon's hand are transformed and used to drive a six-degrees-of-freedom robot to position the surgical instrument mounted on its tip. A pilot study comparing the performance of the telemanipulator system against manual instrument positioning was conducted at the University of Southern California School of Medicine. The results show that a telerobotic tool can improve the performance of a microsurgeon by increasing the precision with which he can position surgical instruments, but this is achieved at the cost of increased time in performing the task. We believe that this technology will extend the capabilities of microsurgeons and allow more surgeons to perform highly skilled procedures currently performed only by the best surgeons. It will also enable performance of new surgical procedures that are beyond the capabilities of even the most skilled surgeons. Copyright 1999 Wiley-Liss, Inc.

Microsurgery/instrumentation/methods↗
NASA NTRS1997

Energy Calibration of the Scintillating Optical Fiber Calorimeter Chamber (SOFCAL)

The Scintillating Optical Fiber Calorimeter (SOFCAL) detector is designed to make direct measures of the primary cosmic ray spectrum from -200 GeV/amu - 20 TeV/amu. The primary particles are resolved into groups according to their charge (p, He, CNO, Medium Z, Heavy Z) using both active and passive components integrated into the detector. The principal part of SOFCAL is a thin ionization calorimeter that measures the electromagnetic cascades that result from these energetic particles interacting in the detector. The calorimeter is divided into two sections: a thin passive emulsion/x-ray film calorimeter, and a fiber calorimeter that uses crossing layers of small scintillating optical fibers to sample the energy deposition of the cascades. The energy determination is made by fitting the fiber data to transition curves generated by Monte Carlo simulations. The fiber data must first be calibrated using the electron counts from the emulsion plates in the calorimeter for a small number of events. The technique and results of this calibration will be presented together with samples of the data from a balloon flight.

Christl, M. C.↗
NASA NTRS1993

Distribution of small volcanic cones on the surface of Venus by size and elevation: Implications for differential deposition of volcanic features

It appears that volcanic features are not evenly distributed on the surface of Venus. Head et. al. theorizes that the sparcity of volcanic features in the lowlands may be due to an altitude dependent inhibition of volatile exsolution and the resulting products of neutral buoyancy zones sufficient to form magma reservoirs and favoring flood lavas at lower elevation. The astronomy research classes of Evergreen and Sahuaro High Schools surveyed a cross-section of different elevation topography to investigate size and distribution of small volcanic cones by elevation. The results from this survey are presented.

Lockwood, J. F.↗
NASA NTRS1992

HST Servicing Mission Planning and Replanning Tool

An overview is presented of the Hubble Space Telescope (HST) Service Mission Planning and Replanning Tool (SM/PART) and the approach that was employed to develop the system. SM/PART is an AI expert system utilized by NASA to rapidly build complex timelines and command plans to control HST activities. HST servicing missions are Space Shuttle/Orbiter missions expected to occur every three to five years to rendezvous with the HST in orbit and replace, upgrade, or repair HST components. SM/PART runs on a UNIX-based workstation and is implemented in the C language with a Motif-based graphical user interface.

Johnson, J.↗
NASA NTRS1992

An object-oriented approach for supporting both X and terminal interfaces

While the X Window System is clearly becoming the dominant user interface between display system, there is still a continuing need to support character cell terminal devices. For a user interface application which must support both, it is desirable to be able to use them to their fullest extent, as opposed to simply providing a character-based display within an X window. An object-oriented application framework is presented here which allows the full capabilities of each system to be used while minimizing and isolating the amount of device-dependent code. Every user interface application consists of two parts: the various components used to display information and accept user input, and the processing of the interaction between these components. Many user interfaces are built around a core set of components such as menus, text entry fields, and forms. For a given application, the interaction between these components is the same regardless of the display system in use. Our approach is to implement each component as an object, accessible via a single public interface. All of the code necesary to implement the component for the desired display system is completely encapsulated within the object. The application is then written as a collection of objects interacting in a device-independent manner with one another. If a display system provides additional capabilities, the application can be extended by adding objects (e.g. for image display in X). We are currently implementing StarView, the user interface to the HST science archive (STDADS) using this approach. StarView will be written in C++ and will use Vermont Views for the terminal interface and OSF/Motif for the X Window interface.

Johnson, J.↗
NASA NTRS1988

Horizontal electric fields from lightning return strokes

An experiment to measure simultaneously the wideband horizontal and vertical electric fields from lightning return strokes is described. Typical wave shapes of the measured horizontal and vertical fields are presented, and the horizontal fields are characterized. The measured horizontal fields are compared with calculated horizontal fields obtained by applying the wavetilt formula to the vertical fields. The limitations and sources of error in the measurement technique are discussed.

Thomson, E. M.↗
NASA NTRS1978

Microcrater and solar-flare track maturation of the lunar regolith

The microcrater, pancake and cosmic ray track record in the 100-200 microns feldspar fraction of a variety of surface soils and Apollo and Luna 16-24 cores have been studied. In Luna 24, a study of the glassy agglutinates plus breccias in 9 levels revealed this core was deposited as discrete layers, most of which are immature. Luna 16 and 20 cores were found respectively mature and immature. Glassy agglutinates and impact microcraters, absent to rare in immature soils such as 12033 and 14141, are present in similar abundances on crystals from submature to mature soils. In submature and mature soils, pancakes are present on 60 to 100 percent of crystals and craters on 50 to 70 percent. Microcrater, track and solar wind gas data suggest feldspar crystals in the size range considered reach an equilibrium maturity grade faster than bulk soils. This is interpreted as due to the limited lifetime of these crystals in the lunar regolith.

Poupeau, G.↗
NASA NTRS1976

Advanced supersonic propulsion study, phase 3

The variable stream control engine is determined to be the most promising propulsion system concept for advanced supersonic cruise aircraft. This concept uses variable geometry components and a unique throttle schedule for independent control of two flow streams to provide low jet noise at takeoff and high performance at both subsonic and supersonic cruise. The advanced technology offers a 25% improvement in airplane range and an 8 decibel reduction in takeoff noise, relative to first generation supersonic turbojet engines.

Howlett, R. A.↗