Special Coverage

Iodine-Compatible Hall Effect Thruster
Precision Assembly of Systems on Surfaces (PASS)
Development of a Novel Electrospinning System with Automated Positioning and Control Software
2016 Create The Future Design Contest Open For Entries
Clamshell Sampler
Shape Memory Alloy Rock Splitter
Deployable Extra-Vehicular Activity Platform (DEVAP) for Planetary Surfaces
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Study of Fusion-Driven Plasma Thruster With Magnetic Nozzle

A report presents a computational study of a proposed plasma thruster for a spacecraft. The behavior of the plasma was computationally simulated by use of a mathematical model of magnetohydrodynamic flow implemented in the previously developed MACH2 computer program. To increase the accuracy of modeling of the magnetic field, MACH2 was modified by providing for an arbitrary number of current loops used to generate the applied magnetic field and by splitting the total magnetic field into applied and plasma-induced components. The results of the computational simulations contribute to understanding of the appropriate parameter regimes for the electron beam, the in-flowing working fluid, and the applied magnetic field.

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Magnetostrictively Actuated Valves for Cryosurgical Probes

Probes could be made smaller and lighter, with better regulation of temperature. In cryosurgical probes of a type now undergoing development, the flow of coolant (typically, liquid nitrogen) would be regulated by magnetostrictively actuated needle valves controlled by use of superconductive electromagnet coils. In comparison with cryosurgical probes now in use, the developmental probes would be smaller and lighter, and would afford better regulation of temperature. This concept is made feasible by two recent advances:

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Remote Sensing of Electric Fields in Clouds

Radar and radiometry would provide data on bulk orientation of ice crystals. A proposed method for remote sensing of the electric field in a cloud that contains ice crystals would exploit the relationship between (1) the polarization-dependent radiometric or radar brightness of the cloud and (2) the average or bulk orientation of the crystals as affected by the electric field. The proposed method would complement other methods now used to measure natural electric fields in efforts to forecast lightning. A major advantage of the proposed method is that a few ground-based and/or airborne instruments could quickly survey a fairly large region of the sky.

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Improved Infrared Imaging of Bulk Defects in CdZnTe Wafers

Images would guide the "mining" of large wafers for fabricating x-ray detectors. An improved method of infrared imaging of bulk defects in cadmium zinc telluride (CdZnTe) wafers has been developed. The method is intended primarily to be a means of identifying those portions of large CdZnTe wafers that are suitable to be "mined" for use in fabricating focal-plane arrays of photodetectors for x-ray and g-ray astronomy. Suitable portions are those that exhibit acceptably high degrees of uniformity of x-ray spectral response. The present method of infrared imaging is useful for identifying the suitable portions because, as described below, there is a correlation between (1) x-ray spectral responses and (2) infrared images of bulk defects that affect those responses.

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Image Generators With Compact Optics

These devices can be used for head-mounted, helmet-mounted, and eyeglass-mounted displays. Compact image generators that contain illumination sources and electronically controlled spatial light modulators have been invented. Compactness is achieved by folding of the optical paths that link the illumination sources, the spatial light modulators, and the viewing regions into which images are projected. The optical configuration of a device of this type ensures that a large proportion of the light from the illumination source is directed into the viewing region; consequently, the device is unusually energy-efficient for a display device and can, therefore, be operated at a relatively low power (possibly even battery power) for a given display brightness. By virtue of their compactness and low power consumption, these image generators are suitable for head-mounted, helmet-mounted, and eyeglass-mounted displays.

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Hand-Held Instrument for Imaging Hydrogen Fires

Hydrogen fires can be seen even in full daylight. A hand-held instrument that contains two silicon-based charge-coupled-device (CCD) video cameras (see figure) has been developed for imaging hydrogen fires. This or a similar instrument is needed because the visible light emitted by a hydrogen fire is so dim that the fire cannot be seen by the unaided human eye — at least, not in bright daylight. Like some other CCD-camera-based instruments developed previously for the same purpose, this instrument is designed to operate at infrared wavelengths where hydrogen fires appear bright, relative to solar background light. One CCD camera is called the "cloudy" camera, while the other is called the "sunny" camera, to indicate the different lighting conditions under which the cameras are designed to operate. In front of the "cloudy" camera is a long-wavelength-pass filter with a cutoff wavelength of 800 nm; during overcast, this filter blocks enough background light to make a hydrogen flame appear bright against the background. In front of the "sunny" camera there is a long-wavelength-pass filter with a cutoff wavelength of 1,100 nm; this filter blocks the solar background in the presence of full sunshine, such that a hydrogen flame is brighter than the solar background. The infrared images in the cameras are converted electronically and displayed to the instrument operator as visible images on miniature cathode-ray tubes in electronic viewfinders. A switch enables the operator to select the camera depending on the current light conditions. Optionally, both cameras and their viewfinders can be used simultaneously for binocular viewing.

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Improvements in Computed-Tomography Imaging Spectrometry

CGHs are used for dispersion, and a modified calibration procedure saves time. Two major improvements, described below, have been made in the construction and operation of a computed-tomography imaging spectrometer (CTIS). These plus future improvements can be expected to enhance the practicality and commercial viability of CTISs, which, in principle, offer unprecedented capabilities for imaging with spatial, spectral, and temporal resolution. For example, the CTIS in its present form could be used in medical and pharmaceutical applications to perform spectral imaging of transient scenes that contain fluorescent dyes. With increases in spectral accuracy and spatial resolution, it could be used for remote sensing.

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