An experiment to study solar flare effects on radio-communication signals

The occurrence of radio signal fading events caused by ionospheric absorption plays an important role in the performance of radio-communication systems. It is necessary to know the magnitude and time-scale of such events in order to specify technical parameters of the communication system to be used. Generally, fading events are associated with solar flares, which are characterized by sudden increase in the solar X-ray flux that causes an increase in the ionization in the lower ionosphere. The abrupt increase of ionization causes the absorption of radio waves propagating in the Earth–ionosphere wave-guide and is reported as radio signal fading events. A simple experiment to monitor the behavior of lower ionosphere has been carried out at the Southern Space Observatory-SSO/INPE (29.43°S, 53.8°W), located in southern Brazil. The experiment is basically a computer controlled radio receiver that records the received signal strength of Amplitude Modulated (AM) radio signals in the HF (High Frequencies) range. We analyzed data of the 6 MHz beacon signal that has been transmitted by a broadcasting radio station located about 400 km from the observation site. In this work we present initial results of daily variation of the received signal strength and fading events associated with solar flares observed in the 6 MHz signal monitored by the experiment during 2001. X-ray solar flux data from the GOES-8 satellite were used to identify X-ray solar bursts associated with solar flares. Based on the one-year data collected by the experiment, a statistical summary of fading occurrences and their correlation with solar flares, as well as the distributions of time-scales and magnitudes of such events are presented.     

Evaluation of an anaerobic digestion system for processing CELSS crop residues for resource recovery.

Three bioreactors, connected in series, were used to process CELSS potato residues for recovery of resources. The first stage was an anaerobic digestor (8 L working volume; cow rumen contents inoculum; fed-batch; 8 day retention time; feed rate 25 gdw day-1) that converted 33% of feed (dry weight loss) to CO2 and "volatile fatty acids" (vfa, 83:8:8 mmolar ratio acetic:propionic:butyric). High nitrate-N in the potato residue feed was absent in the anaerobic effluent, with a high portion converted to NH4(+)-N and the remainder unaccounted and probably lost to denitrification and NH4+ volatilization. Liquid anaerobic effluent was fed to an aerobic, yeast biomass production vessel (2 L volume; Candida ingens inoculum; batch [pellicle] growth; 2 day retention time) where the VFAs and some NH4(+)-N were converted into yeast biomass. Yeast yields accounted for up to 8% of potato residue fed into the anaerobic bioreactor. The third bioreactor (0.5 L liquid working volume; commercial nitrifier inoculum; packed-bed biofilm; continuous yeast effluent feed; recirculating; constant volume; 23 day hydraulic retention time) was used to convert successfully the remaining NH4(+)-N into nitrate-N (preferred form of N for CELSS crop production) and to remove the remaining degradable soluble organic carbon. Effluents from the last two stages were used for partial replenishment of minerals for hydroponic potato production.     

Near-Infrared Mapping Spectrometer experiment on Galileo

The Galileo Near-Infrared Mapping Spectrometer (NIMS) is a combination of imaging and spectroscopic methods. Simultaneous use of these two methods yields a powerful combination, far greater than when used individually. For geological studies of surfaces, it can be used to map morphological features, while simultaneously determining their composition and mineralogy, providing data to investigate the evolution of surface geology. For atmospheres, many of the most interesting phenomena are transitory, with unpredictable locations. With concurrent mapping and spectroscopy, such features can be found and spectroscopically analyzed. In addition, the spatial/compositional aspects of known features can be fully investigated. The NIMS experiment will investigate Jupiter and the Galilean satellites during the two year orbital operation period, commencing December 1995. Prior to that, Galileo will have flown past Venus, the Earth/Moon system (twice), and two asteroids; obtaining scientific measurements for all of these objects.The NIMS instrument covers the spectral range 0.7 to 5.2 , which includes the reflected-sunlight and thermal-radiation regimes for many solar system objects. This spectral region contains diagnostic spectral signatures, arising from molecular vibrational transitions (and some electronic transitions) of both solid and gaseous species. Imaging is performed by a combination of one-dimensional instrument spatial scanning, coupled with orthogonal spacecraft scan-platform motion, yielding two-dimensional images for each of the NIMS wavelengths.The instrument consists of a telescope, with one dimension of spatial scanning, and a diffraction grating spectrometer. Both are passively cooled to low temperatures in order to reduce background photon shot noise. The detectors consist of an array of indium antimonide and silicon photovoltaic diodes, contained within a focal-plane-assembly, and cooled to cryogenic temperatures using a radiative cooler. Spectral and spatial scanning is accomplished by electro-mechanical devices, with motions executed using commandable instrument modes.Particular attention was given to the thermal and contamination aspects of the Galileo spacecraft, both of which could profoundly affect NIMS performance. Various protective measures have been implemented, including shades to protect against thruster firings as well as thermal radiation from the spacecraft.The Near Infrared Mapping Spectrometer (NIMS) Engineering and Science Teams consist of I. Aptaker (Instrument Manager), G. Bailey (Detectors), K. Baines (Science Coordinator), R. Burns (Digital Electronics), R. Carlson (Principal Investigator), E. Carpenter (Structures), K. Curry (Radiative Cooler), G. Danielson (Co-Investigator), T. Encrenaz (Co-Investigator), H. Enmark (Instrument Engineer), F. Fanale (Co-Investigator), M. Gram (Mechanisms), M. Hernandez (NIMS Orbiter Engineering Team), R. Hickok (Support Equipment Software), G. Jenkins (Support Equipment), T. Johnson (Co-Investigator), S. Jones (Optical-Mechanical Assembly), H. Kieffer (Co-Investigator), C. LaBaw (Spacecraft Calibration Targets), R. Lockhart (Instrument Manager), S. Macenka (Optics), J. Mahoney (Instrument Engineer), J. Marino (Instrument Engineer), H. Masursky (Co-Investigator), D. Matson (Co-Investigator), T. McCord (Co-Investigator), K. Mehaffey (Analog Electronics), A. Ocampo (Science Coordinator), G. Root (Instrument System Analysis), R. Salazar (Radiative Cooler and Thermal Design), D. Sevilla (Cover Mechanisms), W. Sleigh (Instrument Engineer), W. Smythe (Co-Investigator and Science Coordinator), L. Soderblom (Co-Investigator), L. Steimle (Optics), R. Steinkraus (Digital Electronics), F. Taylor (Co-Investigator), P. Weissman (Co-Investigator and Science Coordinator), and D. Wilson (Manufacturing Engineer).     

Status of TiOx Antireflective Coating in the United States

The performance of glassed and unglassed Ti0x-coated silicon cells is compared to Si0-coated cells for coating thicknesses from 100 to 200 nm. The experiment was made on cells having initially the same quantum efficiency allowing complete separation of coating induced effects. U.S. cells only showed an adusted improvement of 2.6% for Ti0x-coatings over Si0-coatings as compared to an expected range of 4.8 to 5.5% as based on European investigations. Spectral reflectance analysis showed some destinct differences between the various cell types. This may be related to cell crystal orientation. All cells showed much higher reflectance at the minimum than predicted by theoretical analyses.     

Book reviews

Space Science Reviews -     

Optimal Detection of a Signala with Time-Varying Carrier Phase

The problem considered in this paper is the detection of a signal known except for time-varying carrier phase in white Gaussian noise. The method of attacking this problem is to model the time-varying carrier phase as a Markov process. Fourier transform techniques are then applies to yield a simple time-wise adaptive form for the phasetracking detector. Optimal accounting for the time variations in phase is accomplished via a simple algorithm which serves to update the detector memory. Furthermore, it is shown that this memory updating operation is a discrete linear filter whose impulse response is a simple function of the previous memory state and the Markov transitional statistics on the phase. A priori knowledge regarding the phase is summarized in the initial impulse response of the updating filter.     

A Study of Pilot Reaction Capability to Sound Stimulus

An experiment is described which was used to evaluate a typical pilot's ability to activate a switch in response to a sound stimulus. Regularly spaced voice countdown, irregular voice countdown, initiation of a tone, and termination of a tone were each used as the stimulus. The individual under test was given a task similar to that involved in maintaining accurate flight conditions to occupy his attention. The regular voice countdown is shown to be least accurate in defining the switching time, providing a mean delay of approximately -0.09 second (actually a stimulus anticipation) and a standard deviation of a bit more than 0.2 second. In each of the other cases, a mean delay of approximately 0.25 second and a standard deviation of approximately 0.09 second were obtained. This compares favorably with previous experimental results.     

Molecular diversity of cyanobacteria inhabiting coniform structures and surrounding mat in a Yellowstone hot spring

Lithified coniform structures are common within cyanobacterial mats in Yellowstone National Park hot springs. It is unknown whether these structures and the mats from which they develop are inhabited by the same cyanobacterial populations. Denaturing gradient gel electrophoresis and sequencing and phylogenetic analysis of 16S rDNA was used to determine whether (1) three different morphological types of lithified coniform structures are inhabited by different cyanobacterial species, (2) these species are partitioned along a vertical gradient of these structures, and (3) lithified and non-lithified sections of mat are inhabited by different cyanobacterial species. Our results, based on multiple samplings, indicate that the cyanobacterial community compositions in the three lithified morphological types were identical and lacked any vertical differentiation. However, lithified and non-lithified portions of the same mat were inhabited by distinct and different populations of cyanobacteria. Cyanobacteria inhabiting lithified structures included at least one undefined Oscillatorialean taxon, which may represent the dominant cyanobacteria genus in lithified coniform stromatolites, Phormidium, three Synechococcus-like species, and two unknown cyanobacterial taxa. In contrast, the surrounding mats contained four closely related Synechococcus-like species. Our results indicate that the distribution of lithified coniform stromatolites may be dependent on the presence of one or more microorganisms, which are phylogenetically different from those inhabiting surrounding non-lithified mats.     

Plant molecular biology in the space station era: utilization of KSC fixation tubes with RNAlater

Spaceflight experiments involving biological specimens face unique challenges with regard to the on orbit harvest and preservation of material for later ground-based analyses. Preserving plant material for gene expression analyses requires that the tissue be prepared and stored in a manner that maintains the integrity of RNA. The liquid preservative RNAlater (Ambion) provides an effective alternative to conventional freezing strategies, which are limited or unavailable in current spaceflight experiment scenarios. The spaceflight use of RNAlater is enabled by the Kennedy space center fixation tube (KFT), hardware designed to provide the necessary containment of fixatives during the harvest and stowage of biological samples in space. Pairing RNAlater with the KFT system provides a safe and effective strategy for preserving plant material for subsequent molecular analyses, a strategy that has proven effective in several spaceflight experiments. Possible spaceflight scenarios for the use of RNAlater and KFTs are explored and discussed.