Use, Operation and Maintenance of Renewable Energy Systems:Experiences and Future Approaches

The aim of this book is to put the reader in contact with real experiences, current and future trends in the context of the use, exploitation and maintenance of renewable energy systems around the world. Today the constant increase of production plants of renewable energy is guided by important social, economical, environmental and technical considerations. The substitution of traditional methods of energy production is a challenge in the current context. New strategies of exploitation, new uses of energy and new maintenance procedures are emerging naturally as isolated actions for solving the integration of these new aspects in the current systems of energy production. This book puts together different experiences in order to be a valuable instrument of reference to take into account when a system of renewable energy production is in operation

NASA Tech Briefs, April 1992

Topics covered include: New Product Ideas; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences

Ultra-Low Phase Noise Atomic Clock using Coherent Population Trapping (CPT) in Rubidium

This thesis describes the design and implementation of a complete atomic clock system from first principles. The system is based on Coherent Population Trapping (CPT) in 85Rb and incorporates an ultra-low phase noise multi-element local oscillator, consisting of a 10MHz crystal oscillator and 1.5GHz Dielectric Resonator Oscillator (DRO) in a phase locked configuration. It is shown that the crystal oscillator can achieve excellent close to carrier phase noise performance of -122dBc/Hz at 1Hz offset and -147.7dBc/Hz at 10Hz offset, as well as Allan deviation of 3×10^(-13) at 100ms averaging time. The DRO exhibits excellent medium offset and far from carrier performance with a noise floor of about -180dBc/Hz. When phase locked to the crystal oscillator, the phase noise at 1Hz is shown to approach that of the crystal oscillator (scaled up to 1.5GHz). A frequency synthesis chain, incorporating a Direct Digital Synthesizer (DDS), low noise digital divider, single sideband mixer and notch filter is used to upconvert the 1.5GHz local oscillator frequency to the ground state hyperfine splitting frequency of 85Rb (1.5178GHz). The DDS is controlled by a microcontroller and used to produce an offset frequency of 17.8MHz, which can be tuned, modulated or swept. The single sideband mixer is used to mix the 1.5GHz and 17.8MHz signals and suppress the lower sideband of the output. The notch filter is used to further suppress the LO feedthrough of the mixer by another >30dB. A Rb CPT physics package incorporates a vertical cavity surface-emitting laser, which is modulated by the output of the synthesizer and used to interrogate the atomic resonance in a 85Rb vapour cell. The package was built with custom made optical mounts, low noise laser driving electronics and temperature control loops. The parameters affecting the shape, amplitude and stability of the atomic resonance were experimentally investigated and the construction of the physics package was adjusted for the optimal conditions. A digital frequency locked loop is used to lock the local oscillator to the atomic resonance and the performance of the full system is tested

Energy: A continuing bibliography with indexes, February 1975

Reports, articles, and other documents introduced into the NASA scientific and technical information system from July 1, 1974 through September 30, 1974 are cited. Regional, national, and international energy systems; research and development on fuels and other sources of energy; energy conversion, transport, transmission, distribution, and storage, with emphasis on the use of hydrogen and solar energy are included along with methods of locating or using new energy resources. Emphasis is placed on energy for heating, lighting, and powering aircraft, surface vehicles, or other machinery

NASA Tech Briefs, June 1989

Topics include: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Doherty amplifier structures for modern microwave communication systems

The Power Amplifier (PA) is a critical component in any mobile communications system with performance that is very sensitive to RF envelope dynamics. Achieving the required linearity demanded by evolving communications systems invariably involves increasing PA complexity at the cost of reducing PA efficiency the consequences of which are severe and include for example reduced operational time for portable communications devices and perhaps less obviously the significant running, capital and thermal management costs associated with mobile communication system base-stations. The Doherty PA is one of a number of elegant architectures that have been developed to address this problem, and although conceived and patented in the 1930's, has only recently become established as a means of enhancing efficiency in microwave PA applications. The Doherty is renowned for its elegant simplicity however, the realisation of functional Doherty PAs using modern microwave devices is problematical and hindered by many hidden complexities, which are in general brought about by the complex, 'load-pulling' action of two active devices that conspire to cause a variety of performance related problems. Although harmonic behaviour is important, understanding device interaction at a fundamental level has been found to be the critical factor in achieving good overall Doherty performance. With this in mind, this thesis concentrates initially on developing an extensive understanding of fundamental device interaction through the use of a novel Doherty measurement approach which involves replacing the classical Doherty's symmetrical input power division arrangement with independent, phase-coherent excitations. The resulting insight has meant that it has been possible to introduce more focused measurement techniques including harmonic analysis and waveform engineering in order to further explore individual device behaviour. The extensive use of harmonic load-pull measurement systems and the direct synthesis of the impedance environments that exist within the Doherty have allowed a number of device technologies to be considered within the application environment resulting in the realisation of GaAs and GaN Doherty prototypes. As a direct result of this analysis, a number of optimisation approaches have been identified that involve the dynamic adjustment of relative input magnitude, relative input phase and relative device bias, which has in turn exposed the various design trade-offs that exist between linearity and efficiency within the Doherty. Other work includes the development of modulated measurement systems and specialised excitations that allow the meaningful comparison between measured single-tone and modulated performance, as well as allowing more comprehensive investigations into Doherty linearity under varying IF impedance conditions

Postlaunch Report for Mission AS-201 (APOLLO Spacecraft 009)

No abstract availabl

Far-Infrared Photometry with an 0.4-Meter Liquid Helium Cooled Balloon-Borne Telescope

A 0.4-meter aperture, liquid helium cooled multichannel far-infrared balloon-borne telescope was constructed to survey the galactic plane. Nine new sources, above a 3-sigma confidence level of 1300 Jy, were identified. Although two-thirds of the scanned area was more than 10 degrees from the galactic plane, no sources were detected in that region; all nine fell within 10 degrees and eight of those within 4 degrees of the galactic equator. Correlations with visible, compact H lines associated with radio continuum and with sources displaying spectra steeply rising between 11 and 20 microns were noted, while stellar objects were not detected