Aqueous alteration on main belt primitive asteroids: results from visible spectroscopy

This work focuses on the study of the aqueous alteration process which acted in the main belt and produced hydrated minerals on the altered asteroids. The aqueous alteration is particularly important for unraveling the processes occurring during the earliest times of the Solar System history, as it can give information both on the asteroids thermal evolution and on the localization of water sources in the asteroid belt. We present new spectral observations in the visible region of 80 asteroids belonging to the primitive classes C, G, F, B and P. We combine the present observations with the visible spectra of asteroids available in the literature for a total of 600 primitive main belt asteroids. Our analysis shows that the aqueous alteration sequence starts from the P-type objects, practically unaltered, and increases through the F, B, C, and G asteroids. Around 50% of the observed C-type asteroids show absorption features in the vis. range due to hydrated silicates, implying that more than 70% of them will have a 3 $\mu$m absorption band and thus hydrated minerals on their surfaces. The process dominates in primitive asteroids located between 2.3 and 3.1 AU, that is at smaller heliocentric distances than previously suggested. The aqueous alteration process dominates in the 50--240 km sized primitive asteroids, while it is less effective for bodies smaller than 50 km. No correlation is found between the aqueous alteration process and the asteroids albedo or orbital elements. Comparing the $\sim$ 0.7 $\mu$m band parameters of hydrated silicates and CM2 carbonaceous chondrites, we see that the band center of meteorites is at longer wavelengths than that of asteroids. This difference on center positions may be attributed to different minerals abundances, and to the fact that CM2 available on Earth might not be representative of the whole aqueous altered asteroids population.Comment: Icarus, accepted for publication on 28 January 2014 Manuscript pages: 38; Figures: 13 ; Tables:

A Survey Course in the Biological Sciences

A review of a Survey course in the biological sciences which is being given at Iowa State Teachers College. It is a course extending over a period of twelve weeks, meeting five times a week including two double periods. The following five points are considered: (1) objectives of the course, (2) the major units, (3) methods of presentation, (4) some results obtained, (5) criticism of the course by the students

The Survey Courses in Science

What should be the nature of the beginning courses in science in our colleges? There has been much criticism directed at these courses. The criticism is usually to the effect that they are too technical and are planned to meet the needs of those who are going to be specialists in some field of science whereas relatively few will continue in a particular field of science. The courses are said to be unrelated to everyday life, whereas what is needed are courses that will give an understanding and an appreciation of modern science as it applies to everyday life in a world so largely dominated by science situations. It is difficult for us who are specialists in some field of science to realize that we are not primarily training specialists in a field of science. Such beginning courses should not be planned for those who specialize but for the average student who needs a knowledge of science in his life and in his chosen vocation

The Status of the Biological Sciences in the High Schools of Iowa

In the germination tests of alfalfa seed in the spring of 1930, one seed was discovered with two embryos. They were both normal in all structures, equal in size and behaved normally in germination. Multiple embryo sacs in the ovules of alfalfa are frequent, but it has been supposed that not more than one is able to mature and function. The presence of two embryos is evidence that two embryo sacs may mature and function

Temperature and Catalase Activity in Germinating Corn

Catalase is an enzyme almost universally present in living cells and has the power of breaking hydrogen peroxide into water and molecular oxygen. The various theories as to the significance of catalase in metabolism are conflicting. Catalase has been considered by some as an enzyme directly correlated with respiration, others have failed to find such a correlation

The Clay Prairie in Butler County, Iowa

The Clay Prairie is a small area of 2.64 acres of native prairie belonging to the University of Northern Iowa. It is located in Butler County, 15 miles northeast of Parkersburg, Iowa. A list of the species of the vascular plants found in this area is given, representing 33 families

Vegetation Succession and Environmental Conditions following Catastrophic Lake Drainage in Old Crow Flats, Yukon

Increases in the frequency and magnitude of disturbances associated with the thawing of ice-rich permafrost highlight the need to understand long-term vegetation succession in permafrost environments. This study uses field sampling and remote sensing to explore vegetation development and soil conditions following catastrophic lake drainage in Old Crow Flats (OCF). The data presented show that vegetation on drained lake basins in OCF is characterized by two distinct assemblages: tall willow stands and sedge swards. Field sampling indicates that these alternative successional trajectories result from variation in soil moisture following drainage. Increased willow mortality on older drained basins suggests that intraspecific competition drives self-thinning in shrub thickets. This finding, combined with data from paleoecological studies and contemporary vegetation in OCF, suggests that willow stands on drained lake basins are seral communities. These results also indicate that the increase in number of catastrophic drainages that occurred between 1972 and 2010 will alter regional vegetation in ways that affect wildlife habitat, permafrost conditions, and local hydrology.L’accroissement de la fréquence et de l’ampleur des perturbations liées au dégel du pergélisol à forte teneur en glace fait ressortir la nécessité de comprendre la succession de la végétation à long terme en milieu de pergélisol. Grâce à des travaux d’échantillonnage sur le terrain et à des données obtenues par télédétection, cette étude explore le développement de la végétation et les conditions du sol suivant le drainage catastrophique du lac de la plaine Old Crows (POC). Selon les données obtenues, la végétation des bassins lacustres drainés de la POC relève de deux assemblages distincts : des peuplements de grands saules et des peuplements de foin plat. L’échantillonnage sur le terrain indique que ces trajectoires de succession différents découlent de la variation de l’humidité du sol après le drainage. Le taux de mortalité accru des saules dans les bassins drainés plus anciens suggère que la compétition intraspécifique entraîne l’autoréduction dans les taillis d’arbustes. Alliée aux données émanant d’études paléoécologiques et aux données sur la végétation contemporaine de la POC, cette observation suggère que les peuplements de saules des bassins lacustres drainés sont des communautés de succession. Ces résultats indiquent aussi que l’augmentation du nombre de drainages catastrophiques qui se sont produits entre 1972 et 2010 aura pour effet d’altérer la végétation régionale, ce qui aura des incidences sur l’habitat de la faune, les conditions du pergélisol et l’hydrologie de la région

Spectral variability on primitive asteroids of the Themis and Beagle families: space weathering effects or parent body heterogeneity?

Themis is an old and statistically robust asteroid family populating the outer main belt, and resulting from a catastrophic collision that took place 2.5$\pm$1.0 Gyr ago. Within the old Themis family a young sub-family, Beagle, formed less than 10 Myr ago, has been identified. We present the results of a spectroscopic survey in the visible and near infrared range of 22 Themis and 8 Beagle families members. The Themis members investigated exhibit a wide range of spectral behaviors, while the younger Beagle family members look spectrally bluer with a smaller spectral slope variability. The best meteorite spectral analogues found for both Themis and Beagle families members are carbonaceous chondrites having experienced different degrees of aqueous alteration, prevalently CM2 but also CV3 and CI, and some of them are chondrite samples being unusual or heated. We extended the spectral analysis including the data available in the literature on Themis and Beagle families members, and we looked for correlations between spectral behavior and physical parameters using the albedo and size values derived from the WISE data. The analysis of this larger sample confirm the spectral diversity within the Themis family and that Beagle members tend to be bluer and to have an higher albedo. The differences between the two family may be partially explained by space weathering processes, which act on these primitive surfaces in a similar way than on S-type asteroids, i.e. producing reddening and darkening. However we see several Themis members having albedos and spectral slopes similar to the young Beagle members. Alternative scenarios are proposed including heterogeneity in the parent body having a compositional gradient with depth, and/or the survival of projectile fragments having a different composition than the parent body.Comment: Manuscript pages: 40; Figures: 15 ; Tables: 4 Icarus (2016),in pres

Advanced combined iodine dispenser and detector

A total weight of 1.23 kg (2.7 lb), a total volume of 1213 cu m (74 cu in), and an average power consumption of 5.5W was achieved in the advanced combined iodine dispenser/detector by integrating the detector with the iodine source, arranging all iodinator components within a compact package and lowering the parasitic power to the detector and electronics circuits. These achievements surpassed the design goals of 1.36 kg (3.0 lb), 1671 cu m (102 cu in) and 8W. The reliability and maintainability were improved by reducing the detector lamp power, using an interchangeable lamp concept, making the electronic circuit boards easily accessible, providing redundant water seals and improving the accessibility to the iodine accumulator for refilling. The system was designed to iodinate (to 5 ppm iodine) the fuel cell water generated during 27 seven-day orbiter missions (equivalent to 18,500 kg (40,700 lb) of water) before the unit must be recharged with iodine crystals

Detector Channel Combining Results from a High Photon Efficiency Optical Communications Link Test Bed

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is developing a low cost, scalable, photon-counting receiver prototype for space-to-ground optical communications links. The receiver is being tested in a test bed that emulates photon-starved space-to-ground optical communication links. The receiver uses an array of single-pixel fiber-coupled superconducting nanowire single-photon detectors. The receiver is designed to receive the high photon efficiency serially concatenated pulse position modulation (SCPPM) waveform specified in the Consultative Committee for Space Data Systems (CCSDS) Optical Communications Coding and Synchronization Blue Book Standard. The optical receiver consists of an array of single-pixel superconducting nanowire detectors, analog phase shifters for channel alignment, digitizers for each detector channel, and digital processing of the received signal. An overview of the test bed and arrayed receiver system is given. Simulation and system characterization results are presented. The data rate increase of using a four-channel arrayed detector system over using one single pixel nanowire detector is characterized. Results indicate that a single-pixel detector is capable of receiving data at a rate of 40 Mbps and a four-channel arrayed detector system is capable of receiving data at a rate of 130 Mbps