Notes on the Morphology and Genesis of Mud Polygons on Mount Kenya, East Africa

Mud polygons forming in a valley train deposit in Teleki Valley on Mount Kenya were studied with respect to their physical, mineralogical, chemical and biological characteristics. Developing in fine-grained alluvium of postglacial age, those polygonal systems are composed of numerous, and nearly isomorphous units, that appear close to existing drainages in areas stripped of vegetation cover. Stream erosion and animal activity (particularly rodents and Mount Kenya hyrax, e.g. cony) appear to be primarily responsible for the loss of plant cover. Field tests show that periodic wetting and drying results in closure and reopening of polygonal cracks; freeze thaw activity was not observed to assist in developing polygonal ground shape. Subsequent laboratory tests on several samples confirm that the lack of expandable clay minerals might inhibit wetting-drying activity in individual polygon samples.Les polygones de boue, qui se forment dans les dépôts fluvio-glaciaires dans la vallée de Teleki sur le mont Kenya, ont été étudiés en fonction de leurs caractéristiques physiques, minéralogiques, chimiques et biologiques. Ces réseaux polygonaux, qui se développent dans des alluvions postglaciaires fins, sont composés de plusieurs unités presque isomorphes qui apparaissent près des chenaux d'écoulement là où il n'y a plus de couvert végétal. L'érosion fluviatile et l'activité animale (en particulier celle des rongeurs et le daman du mont Kenya) semblent être les principales causes de la perte du couvert végétal. Les expériences de terrain démontrent que les cycles mouillage-assèchement provoquent la fermeture et la réouverture des fissures polygonales; le phénomène gel-dégel ne semble pas contribuer au développement des sols polygonaux. Les tests de laboratoire subséquents faits sur plusieurs échantillons confirment le fait que l'absence de minéraux argileux dilatables peut empêcher l'opération mouillage-séchage de se produire dans les échantillons de polygones pris isolément

Evaluation of Amino Acid Composition as a Geochronometer in Buried Soils on Mount Kenya, East Africa

A sequence of surface and buried paleosols from the slopes of Mount Kenya, East Africa, has been identified and dated by radiocarbon and amino acid dating techniques in order to elucidate the Quaternary history of the area. Buried paleosols vary in radiocarbon age from 900 to > 40,000 yrs BP. They have developed in glacial and periglacial deposits of variable texture, consisting of a high percentage of clasts of phonolite, basalt and syenite. All but two paleosols are located in the Afroalpine zone (above 3200 m). D/L ratios of amino acids in Ab horizons were determined in order to establish their reliability for relative age dating. Alanine, aspartic acid, glutamic acid, leucine, valine, and phenylalanine were routinely analyzed. Aspartic acid, as in other cases, proved reliable yielding remarkably consistent results, with higher ratios corresponding to increasing age. Other acids analyzed showed distinct trends, although not as convincing as aspartic acid. In most cases, the aspartic acid ratio/ age relationships were supported by radiocarbon dates. D/L ratios of aspartic acid varied from approximately 0.07 for modern samples, to approximately 0.45 in samples > 40,000 years old.On a identifié et daté, au radiocarbone et à l'aide de techniques de datations à l'acide aminé, des paléosols enfouis et de surface afin de comprendre l'évolution quaternaire de la région. Les datations au radiocarbone des paléosols enfouis varient de 900 à plus de 40 000 BP. Les sols se sont développés dans des dépôts glaciaires et périglaciaires de différentes textures, constitués de fragments de roches détritiques, de phonolite, de basalte et de syénite. Tous les paléosols, sauf deux, sont situés dans la zone afroalpine (au-dessus de 3200 m). On a déterminé par racémisation les rapports D/L des acides aminés dans les horizons Ab en vue d'évaluer leur fiabilité pour la datation des âges relatifs. On a fait l'analyse de l'alaline, de l'acide aspartique, de l'acide glutamique, de la leucine, de la valine et du phénylalaline. L'acide aspartique, comme dans d'autres cas, a donné des résultats particulièrement satisfaisants, les quotients plus élevés correspondant aux âges les plus anciens. D'autres acides montraient des tendances bien distinctes, mais moins convaincantes que dans le cas de l'acide aspartique. Ainsi, dans la plupart des cas, les relations quotients/âges de l'acide aspartique étaient corroborées par les datations au radiocarbone. Les rapports D/L de l'acide aspartique variaient d'environ 0,07 pour les échantillons modernes à environ 0,45 pour les échantillons de plus de 40 000 ans.Eine Série von an der Oberflâche Negenden und begrabenen Palàobôden von den Hàngen des Mount Kenya, Ost-Afrika, wurde mittels Radiokarbon- und Aminosâuredatierungs-techniken identifiziert und datiert, um die Geschichte dieses Gebiets im Quaternàr zu erhellen. Das durch Radiokarbon bestimmte Alter der begrabenen Palàobôden variiert von 900 bis > 40,000 Jahren v.u.Z. Dièse Bôden haben sich in glazialen und periglazialen Ablagerungen verschiedener Beschaffenheit entwickelt, welche zu einem hohen Prozentsatz aus Trùmmern von Phonolith, Basait und Syenit bestehen. AuBer zweien befinden sich aile Palàobôden in der afroalpinen Zone (oberhalb 3200 m). Die D/L Anteile der Aminosâuren in den Ab-Horizonten wurden bestimmt, um ihre Verlâpiichkeit bei der relativen Altersbestimmung festzustellen. Alamin, aspartische Sàure, Glutamin-Sàure, Leuzin, Valin und Phenylalanin wurden laufend analysiert. Wie in anderen Fallen erwies sich die aspartische Sàure als verlàpiich, indem sie bemerkenswert bestàndige Ergebnisse ergab, bei denen die hôheren Quotienten dem hôheren Alter entsprachen. Andere analysierte Sàuren zeigten ausgepràgte Trends, wenn auch nicht so ùberzeugend wie die aspartische Sàure. In den meisten Fallen wurden die Beziehungen Quotient/Alter der aspartischen Sàure durch Radiokarbondatierungen gestùtzt. Die D/L Anteile der aspartischen Sàure variierten von ungefâhr 0.07 fur moderne Proben bis ungefâhr 0.45 in Proben, die > 40,000 Jahre ait sind

An auxiliary capacitor based ultra-fast drive circuit for shear piezoelectric motors

Shear piezoelectric motors frequently require large voltage changes on very short time scales. Since piezos behave electrically as capacitors, this requires a drive circuit capable of quickly sourcing or sinking a large amount of current at high voltages. Here we describe a novel circuit design using a high voltage amplifier, transistor switching stage, and auxiliary capacitor. This circuit can drive piezoelectric motors at higher speeds and lower costs than conventional methods and with greater flexibility for computer automation. We illustrate its application in a controller for a scanning tunneling microscope coarse approach mechanism and discuss other possible applications and modifications of this circuit.National Science Foundation CAREER programNational Science Foundation MRSEC ProgramResearch Corporation Cottrell Scholarshi

"Making Safety Happen" Through Probabilistic Risk Assessment at NASA

NASA is using Probabilistic Risk Assessment (PRA) as one of the tools in its Safety & Mission Assurance (S&MA) tool belt to identify and quantify risks associated with human spaceflight. This paper discusses some of the challenges and benefits associated with developing and using PRA for NASA human space programs. Some programs have entered operation prior to developing a PRA, while some have implemented PRA from the start of the program. It has been observed that the earlier a design change is made in the concept or design phase, the less impact it has on cost and schedule. Not finding risks until the operation phase yields much costlier design changes and major delays, which can result in discussions of just accepting the risk. Risk contributors identified by PRA are not just associated with hardware failures. They include but are not limited to crew fatality due to medical causes, the environment the vehicle and crew are exposed to, the software being used, and the reliability of the crew performing required actions. Some programs have entered operation prior to developing a PRA, and while PRA can still provide a benefit for operations and future design trades, the benefit of implementing PRA from the start of the program provides the added benefit of informing design and reducing risk early in program development. Currently, NASAs International Space Station (ISS) program is in its 20th year of on-orbit operations around the Earth and has several new programs in the design phase preparing to enter the operation phase all of which have active (or living) PRAs. These programs incorporate PRA as part of their Risk-Informed, Decision-Making (RIDM) process. For new NASA human spaceflight programs discussion begins with mission concept, establishing requirements, forming the PRA team, and continues through the design cycles into the operational phase. Several examples of PRA related applications and observed lessons are included

A note on monopole moduli spaces

We discuss the structure of the framed moduli space of Bogomolny monopoles for arbitrary symmetry breaking and extend the definition of its stratification to the case of arbitrary compact Lie groups. We show that each stratum is a union of submanifolds for which we conjecture that the natural $L^2$ metric is hyperKahler. The dimensions of the strata and of these submanifolds are calculated, and it is found that for the latter, the dimension is always a multiple of four.Comment: 17 pages, LaTe

Modeling the Risk of U.S. Offshore Oil & Gas Exploration-Well Drilling, Commercial Nuclear Plants, and Human Spaceflight

Probabilistic Risk Assessment (PRA) has been applied in different industries for many years. Each industry and technology area presents varying challenges and priorities, and the risk models therefore need to be somewhat different. This paper compares aspects of risk modeling of offshore drilling, nuclear plant operation, and human spaceflight. Risk models in all three technology areas have certain high-level similarities: (1) they employ redundancy and diversity in their means to prevent or mitigate risk, including a mix of active and passive systems designed to respond to off-normal evolutions; (2) they are affected by human reliability; (3) their models require consideration of coupling between scenario structure and scenario phenomenology. But in examining the models in more detail, one sees important differences in methodology and emphasis. For purposes of comparison, this paper discusses aspects of a risk model of an offshore drilling operation in the U.S. Gulf of Mexico, focusing on where such a development differs in important ways from models of commercial U.S. nuclear plants and models developed for human spaceflight

The Role of Low-Energy (≤ 20 eV) Electrons in Astrochemistry

UV photon-driven condensed phase cosmic ice reactions have been the main focus in understanding the extraterrestrial synthesis of complex organic molecules. Low-energy (≤20 eV) electron-induced reactions, on the other hand, have been largely ignored. In this article, we review studies employing surface science techniques to study low-energy electron-induced condensed phase reactions relevant to astrochemistry. In particular, we show that low-energy electron irradiation of methanol ices leads to the synthesis of many of the same complex molecules formed through UV irradiation. Moreover, our results are qualitatively consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. In addition, due to the numbers of available low-energy secondary electrons resulting from the interaction of high-energy radiation with matter as well as differences between electron- and photon-induced processes, low-energy electron-induced reactions are perhaps as, or even more, effective than photon-induced reactions in initiating condensed-phase chemical reactions in the interstellar medium. Consequently, we illustrate a need for astrochemical models to include the details of electron-induced reactions in addition to those driven by UV photons. Finally, we show that low-energy electron-induced reactions may lead to the production of unique molecular species that could serve as tracer molecules for electron-induced condensed phase reactions in the interstellar medium

Water rate structure: A tool for water conservation in Oklahoma

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