Controls-structures-electromagnetics interaction program

A technology development program is described involving Controls Structures Electromagnetics Interaction (CSEI) for large space structures. The CSEI program was developed as part of the continuing effort following the successful kinematic deployment and RF tests of the 15 meter Hoop/Column antenna. One lesson learned was the importance of making reflector surface adjustment after fabrication and deployment. Given are program objectives, ground based test configuration, Intelsat adaptive feed, reflector shape prediction model, control experiment concepts, master schedule, and Control Of Flexible Structures-II (COFS-II) baseline configuration

Combined effect of wind-forcing and isobath divergence on upwelling at Cape Bathurst, Beaufort Sea

Cape Bathurst is at the northeastern end of the Canadian Beaufort Shelf in the southeastern Beaufort Sea where the continental shelf abruptly ends at Amundsen Gulf. In this area, the steep slope east of the cape joins the relatively flat shelf immediately north of the cape leading to strong isobath divergence at the cape. Hydrographic and satellite data show upwelling of nutrient-rich, Pacific-origin water to the surface at Cape Bathurst when surface stress is upwelling-favorable for the Canadian Beaufort Shelf. We suggest that this enhanced upwelling is forced by the adjustment of the along-shelf flow (that is part of upwelling circulation) to the isobath divergence at the cape. Mooring and drifter data near Cape Bathurst also support this, showing swift, surface-intensified along-isobath flow during upwelling-favorable surface stress. Benthic samples near the cape show high numbers and diversity of organisms which suggest that nutrients brought to the surface by upwelling allow additional primary production in the region that ultimately feeds the benthos

As pastagens e seu manejo no Centro-Sul do Brasil

Although the cattle industry of south-central Brazil is of great importance to the economy of the country and the nutrition of the people, present pasture practices have only short term viability. The continuing decrease in productivity of pasture lands has led to consideration of legumes and fertilization to satisfy the primary need for nitrogen. Both alternatives are examined and in conclusion the establishment of legumes is economically viable depending on site conditions and distance from market. Adequate provisions for seasonal shortages, and the establishment of rotational grazing systems are also essential.A indústria pecuária do centro-sul brasileiro constitui importante contribuição para a economia nacional e para a alimentação das populações. Contudo, percebe-se que os atuais métodos de pastoreio não podem continuar por muito tempo. A produtividade das pastagens vem diminuindo constantemente; e isso levou a pensar no uso das leguminosas e na fertilização das terras, para suprir a necessidade primária de nitrogênio. Ambas as alternativas foram examinadas, concluindo-se que o estabelecimento de leguminosas é economicamente viável, dependendo das condições da localização e distância do mercado; mas é necessário também fazer provisões para os períodos de escassez, bem como implantar o sistema da rotatividade dos pastos

Design for validation: An approach to systems validation

Every complex system built is validated in some manner. Computer validation begins with review of the system design. As systems became too complicated for one person to review, validation began to rely on the application of adhoc methods by many individuals. As the cost of the changes mounted and the expense of failure increased, more organized procedures became essential. Attempts at devising and carrying out those procedures showed that validation is indeed a difficult technical problem. The successful transformation of the validation process into a systematic series of formally sound, integrated steps is necessary if the liability inherent in the future digita-system-based avionic and space systems is to be minimized. A suggested framework and timetable for the transformtion are presented. Basic working definitions of two pivotal ideas (validation and system life-cyle) are provided and show how the two concepts interact. Many examples are given of past and present validation activities by NASA and others. A conceptual framework is presented for the validation process. Finally, important areas are listed for ongoing development of the validation process at NASA Langley Research Center

Merged ionization/dissociation fronts in planetary nebulae

The hydrogen ionization and dissociation front around an ultraviolet radiation source should merge when the ratio of ionizing photon flux to gas density is sufficiently low and the spectrum is sufficiently hard. This regime is particularly relevant to the molecular knots that are commonly found in evolved planetary nebulae, such as the Helix Nebula, where traditional models of photodissociation regions have proved unable to explain the high observed luminosity in H_2 lines. In this paper we present results for the structure and steady-state dynamics of such advection-dominated merged fronts, calculated using the Cloudy plasma/molecular physics code. We find that the principal destruction processes for H_2 are photoionization by extreme ultraviolet radiation and charge exchange reactions with protons, both of which form H_2^+, which rapidly combines with free electrons to undergo dissociative recombination. Advection moves the dissociation front to lower column densities than in the static case, which vastly increases the heating in the partially molecular gas due to photoionization of He^0, H_2, and H^0. This causes a significant fraction of the incident bolometric flux to be re-radiated as thermally excited infrared H_2 lines, with the lower excitation pure rotational lines arising in 1000 K gas and higher excitation H_2 lines arising in 2000 K gas, as is required to explain the H_2 spectrum of the Helix cometary knots.Comment: 4 pages, accepted by ApJL, scheduled December 20 issu

Pulsed Triple Frequency Modulation for Frequency Stabilization and Control of Two Lasers to an Optical Cavity

We present a method to stabilize two lasers to an optical cavity using pulsed triple frequency modulation. The setup allows simultaneous Pound–Drever–Hall stabilization, as well as independent frequency control, while removing interference terms that limit the frequency scan range and allowing for smaller modulation depths. A review of single, dual, and triple frequency modulation is also presented in addition to a discussion of how to effectively turn pulsed triple frequency modulation into independent dual frequency modulation for each laser. This method would increase the scan range to half the free spectral range

Absolute Frequency Measurement of the lLevel of Neutral Using Two-Photon Spectroscopy

We report absolute frequency measurements on the level of neutral using sub-Doppler two-photon spectroscopy. The absolute center-of-gravity energy for the level is determined to be , a factor of 170 times improvement over the previous measurement from 1964 of . This measurement also corrects a discrepancy with the previously measured value. The hyperfine coefficients were found to be and , which are consistent with previous results