The infrared synthetic spectrum of comet Halley

In order to prepare infrared sounding of comet Halley from the flyby VEGA probes, we have computed the synthetic spectrum between 2.5 and 15 μ of a typical comet at a heliocentric distance of ～ 0.8 AU. The present paper is particularly devoted to the contribution from the cometary gases. For a selection of 20 possible parent molecules, the most efficient excitation process is resonant fluorescence by the solar radiation field. The H₂O, CO, CO₂, CH₄, NH₃ and H₂CO molecules are the best candidates for detection by the IKS infrared spectrometers aboard the VEGA probes. For the water molecule, collisions are too rare to ensure thermal equilibrium in the whole coma ; therefore a limited number of fluorescence lines are expected to be present in the H₂O vibrational bands.     

Adaptive Pulse Doppler Ambiguity Resolution

This paper demonstrates and tests a new algorithm for extracting velocity information from a pulse Doppler radar signal. The system is adaptive and performs weil in the presence of target scintillation. This paper also shows a special steady-state version of the adaptive algorithm. lt is computationally attractive and produces near optimal velocity estimates.     

A Note on Dynamic Range of Quantizers

Based on the relationship between the inputand output correlation functions for a symmetric2N step optimum quantizer withGaussian noise inputs a computer programwas generated to obtain plots of the inputnumber of levels versus dynamic range of thequantizer. For it to be physically useful thedynamic range should be related to the distortionin the fundamental band and thedesired harmonic suppression. A definitionbased upon these considerations is suggestedand curves are plotted for two different fundamentaldistortion levels and three differentlevels of harmonic suppression. It is foundthat, for low levels of harmonic suppression(0-20 dB range), the dynamic range can beincreased by tolerating a higher level of fundamentaldistortion. In the medium range ofharmonic suppression (20-35 dB), any increasein the dynamic range due to higherfundamental distortion levels disappearsfor high level quantizers (typically 4 bitsor more). For still higher harmonic suppression(40 dB or higher), the dynamic range ofthe quantizer is independent of the acceptablefundamental distortion.     

Switchless Control Strategies for Minimum Time Frequency Transitions in Phase-Locked Loops

The problem of minimum time frequency transitions in phase-locked loops with both phase and frequency controls applied is investigated using Pontryagin's maximum principle. Typically, a type II secondorder loop with a damping ratio of 0.707 subjected to a step change in the frequency of its input signal is considered and switchless control strategies that force the transients in the loop to settle down in minimum time are obtained.     

Stable mid-latitude red arcs: Observations and theory

Summary The observational features of the arc are fairly well established. At present, the thermal conduction model appears to explain the red arc features most consistently, but it must be noted that a soft electron flux would give very similar results. Ion temperature measurements in the vicinity of an arc, which should be forthcoming in the very near future, can establish conclusively whether transverse electric fields play any important role in the formation of the arcs. Accepting the assumption that the arcs are the result of energy flowing down from the plasmasphere, the major remaining question is: where does the energy come from and how does it get into the plasmasphere? The various proposed mechanisms discussed in the previous chapter appear feasible, but much work needs to be done before this problem is completely resolved.On leave from the Department of Electrical Engineering, The University of Michigan, Ann Arbor.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Evaluation of Multipoint Interaction in the Design of a Thin Diffraction-Limited Active Mirror

Active control of a thin, deformable mirror is one approach to obtaining diffraction-limited performance from large orbiting telescopes. The control system design requires knowledge of the mirror reaction to the multiple forces used to maintain the desired mirror figure. A structural analysis program is used to obtain estimates of the static deflections of a point-loaded, thin, shallow, spherical primary mirror. The calculated deflections are compared to experimentally measured deflections for a specific configuration.     

Some Comments on the Dynamics of Urban Structural Development

The suggestion is made that the aerospace industry examine the dynamics of urban structural development, that it identify the forces which act on the elements comprising the structure of the city, and that it describe the relationship between and the relative movements of those elements. By formulating such a general theory of urban structural development, urban political, social, and economic leadership may be given the means by which permanent remedies?including technological?may be devised and applied. This paper presents examples of such means and explains their application and effects.     

Hydroelectrolytic and hormonal modifications related to prolonged bedrest in antiorthostatic position

The effects of prolonged bedrest in antiorthostatic position (-4 degrees head down) on electrolyte balance were studied in 4 young volunteers. An increase was noted in sodium excretion during the first 4 days. Plasma renin activity and plasma aldosterone varied in parallel manner during the same period. Potassium balance and creatinine clearance were not significantly modified. In light of these data we feel that prolonged bedrest in antiorthostatic position constitutes an effective way to simulate on earth metabolic and hormonal modifications occurring in man under weightlessness conditions.     

Soil and crop management experiments in the Laboratory Biosphere: an analogue system for the Mars on Earth(R) facility.

During the years 2002 and 2003, three closed system experiments were carried out in the "Laboratory Biosphere" facility located in Santa Fe, New Mexico. The program involved experimentation of "Hoyt" Soy Beans, (experiment #1) USU Apogee Wheat (experiment #2) and TU-82-155 sweet potato (experiment #3) using a 5.37 m2 soil planting bed which was 30 cm deep. The soil texture, 40% clay, 31% sand and 28% silt (a clay loam), was collected from an organic farm in New Mexico to avoid chemical residues. Soil management practices involved minimal tillage, mulching, returning crop residues to the soil after each experiment and increasing soil biota by introducing worms, soil bacteria and mycorrhizae fungi. High soil pH of the original soil appeared to be a factor affecting the first two experiments. Hence, between experiments #2 and #3, the top 15 cm of the soil was amended using a mix of peat moss, green sand, humates and pumice to improve soil texture, lower soil pH and increase nutrient availability. This resulted in lowering the initial pH of 8.0-6.7 at the start of experiment #3. At the end of the experiment, the pH was 7.6. Soil nitrogen and phosphorus has been adequate, but some chlorosis was evident in the first two experiments. Aphid infestation was the only crop pest problem during the three experiments and was handled using an introduction of Hyppodamia convergens. Experimentation showed there were environmental differences even in this 1200 cubic foot ecological system facility, such as temperature and humidity gradients because of ventilation and airflow patterns which resulted in consequent variations in plant growth and yield. Additional humidifiers were added to counteract low humidity and helped optimize conditions for the sweet potato experiment. The experience and information gained from these experiments are being applied to the future design of the Mars On Earth(R) facility (Silverstone et al., Development and research program for a soil-based bioregenerative agriculture system to feed a four person crew at a Mars base, Advances in Space Research 31(1) (2003) 69-75; Allen and Alling, The design approach for Mars On Earth(R), a biospheric closed system testing facility for long-term space habitation, American Institute of Aeronautics and Astronautics Inc., IAC-02-IAA.8.2.02, 2002).