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This invention is associated with fluid heating devices which operate by circulating fluid past an electronically controlled heater element in a flow conduit. The efficiency of such devices is increased by placing the heater control components in the conduit, upstream from the heater element, thereby utilizing the heat generated in the control components for preheating the fluid anterior to the principal heater element.

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Apparatus for synchronizing a satellite time division multiplex system so that signals can be transmitted or received between any of the stations. The system constantly compensates for Doppler shift so that a medium altitude satellite is always in synchronization. Additionally, a system is provided for centering a slave station in an empty slot in the time division multiplex format.

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INVERTER WITH MEANS FOR BASE CURRENT
SHAPING FOR SWEEPING CHARGE CARRIERS
FROM BASE REGION

NASA Case No. XGS-06226

Canada

Address inquiries to:
Goddard Space Flight Centér

Attn: Patent Counsel

Mail Code: 204

Greenbelt, MD 20771
U.S.A.

[Corresponding to U.S. Patent No. 3,466,570]

Inverters are utilized for converting a source of direct current to alternating current, or alternately for converting a source of direct current to a first voltage level alternating current and then to a second desired direct current voltage level. The concept employed in the inverters of this invention employs semiconductors and utilizes means for base current shaping for sweeping charge carriers from the base region. More specifically, the provision of both an inductance and a saturable reactor in the frequency determining network of a push-pull transformer coupled oscillator-inverter drastically improves performance. The circuit inhibits abnormal surges, spikes or ripples which are usually present at an energy source output. Short circuit protection is provided and increased reliability and efficiency is obtained by reducing the switching transistor overlap without requiring the application of a high inverse base to emitter voltage. A further feature is the provision of a means for controllably separating the base drive current reduction (switching-off transistor) and base drive current overdrive (switching-on transistor) into two distinct and separate time intervals.

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THERMAL CONTROL PANEL

NASA Case No. XLA-07728

Canada

Address inquiries to:
Langley Research Center
Attn: Patent Counsel
Mail Code: 313
Langley Station
Hampton, VA 23665
U.S.A.

[Corresponding to U.S. Patent No. 3,374,830]

It is necessary to protect the interior of space vehicles from the extreme environmental temperature changes encountered in space missions. For this purpose a thermo-sensitive panel construction has been developed for achieving selectively changeable and controllable surface solar absorptivity/emissivity ratios. The result is obtained by altering the molecular structure of the panel construction through such changes as electroluminescence, semiconductivity, photovoltaic effect and electro-optical polarization.

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MICROWAVE FLAW DETECTOR

NASA Case No. ARC-10009

Canada

Address inquiries to:
Ames Research Center
Attn: Patent Counsel
Mail Code: 200-11A
Moffett Field, CA 94035
U.S.A.

[Corresponding to U.S. Patent No. 3,532,973]

The basic theory of a microwave metal surface flaw detector is that irradiation of a flawed metal surface by electromagnetic microwave energy results in re-emission of electromagnetic energy from the surface in a pattern of eigenmodes different from those of the original irradiating signal. The incident microwave signal must satisfy the electromagnetic boundary conditions on the surface of the specimen. In accordance with the present invention, there is provided a flaw detection system utilizing microwave energy which is radiated to the test surface and which varies in a cyclic or return-to-zero manner. The test surface modifies the reflected electromagnetic energy, in accordance with the surface condition, so that the reflected energy provides a measure of the surface condition as a function of the cyclic scan angle. This reflected energy is demodulated and then correlated, either with itself or with a reference pattern, to provide an indication of irregularities in the surface.

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