Stratigraphy of the PB-1 well, Nopal I uranium deposit, Sierra Pena Blanca, Chihuahua, Mexico

The Nopal I site in the Pena Blanca uranium district has a number of geologic and hydrologic similarities to the proposed high-level radioactive waste repository at Yucca Mountain, making it a useful analogue to evaluate process models for radionuclide transport. The PB-1 well was drilled in 2003 at the Nopal I uranium deposit as part of a DOE-sponsored natural analogue study to constrain processes affecting radionuclide transport. The well penetrates through the Tertiary volcanic section down to Cretaceous limestone and intersects the regional aquifer system. The well, drilled along the margin of the Nopal I ore body, was continuously cored to a depth of 250 m, thus providing an opportunity to document the local stratigraphy. Detailed observations of these units were afforded through petrographic description and rock-property measurements of the core, together with geophysical logs of the well. The uppermost unit encountered in the PB-1 well is the Nopal Formation, a densely welded, crystal-rich, rhyolitic ash-flow tuff. This cored section is highly altered and devitrified, with kaolinite, quartz, chlorite, and montmorillonite replacing feldspars and much of the groundmass. Breccia zones within the tuff contain fracture fillings of hematite, limonite, goethite, jarosite, and opal. A zone of intense clay alteration encountered in the depth interval 17.45-22.30 m was interpreted to represent the basal vitrophyre of this unit. Underlying the Nopal Formation is the Coloradas Formation, which consists of a welded lithic-rich rhyolitic ash-flow tuff. The cored section of this unit has undergone devitrification and oxidation, and has a similar alteration mineralogy to that observed in the Nopal tuff. A sharp contact between the Coloradas tuff and the underlying Pozos Formation was observed at a depth of 136.38 m. The Pozos Formation consists of poorly sorted conglomerate containing clasts of subangular to subrounded fragments of volcanic rocks, limestone, and chert. Three thin (2-6 m) intervals of intercalated pumiceous tuffs were observed within this unit. The contact between the Pozos Formation and the underlying Cretaceous limestone basement was observed at a depth of 244.40 m. The water table is located at a depth of {approx}223 m. Several zones with elevated radioactivity in the PB-1 core are located above the current water table. These zones may be associated with changes in redox conditions that could have resulted in the precipitation of uraninite from downward flowing waters transporting U from the overlying Nopal deposit. All of the intersected units have low (typically submillidarcy) matrix permeability, thus fluid flow in this area is dominated by fracture flow. These stratigraphic and rock-property observations can be used to constrain flow and transport models for the Pena Blanca natural analogue

Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo.

Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth's Hadean liquid iron core

Using a Blackboard to Integrate Multiple Activities and Achieve Strategic Reasoning for Mobile-Robot Navigation

This article discusses some of the associated difficulties in designing system architecture for the autonomous control of a mobile robot, in particular the problem associated with using strategic reasoning for selecting a set of "activities". An activity is designed as a stand alone sub-system capable of performing a particular focused task. Strategic reasoning is coded as a set of production rules and interaction between the activities and the strategic reasoning knowledgebase occurs through blackboard style architecture. The system architecture described in this article is known as a blackboard activity-based system and came about from a study of desired attributes for mobile robot system architecture. A definition of these attributes is given along with a qualitative comparison of several classical system architectures. The blackboard activity-based system is a hybrid system incorporating advantages of the three classical systems. It is designed with two hierarchical layers for strategic and reactive reasoning, a blackboard database for keeping track of the global state of the world, and a set of reactive behaviour-like activities. The feasibility of the approach is demonstrated by an actual implementation on a mobile platform which has the ability of real-time reactive navigation, detection of floor anomalies, and dynamic path planning. An example of strategic reasoning is demonstrated when information posted on the blackboard by the passageway activity is used to guide the floor anomaly activity.Cet article aborde quelques-unes des difficult\ue9s associ\ue9es \ue0 la conception d'une architecture de syst\ue8me pour le contr\uf4le autonome d'un robot mobile, en particulier le probl\ue8me li\ue9 \ue0 l'utilisation d'un raisonnement strat\ue9gique pour la s\ue9lection d'un ensemble "d'activit\ue9s". Une activit\ue9 est con\ue7ue comme un sous-syst\ue8me autonome qui peut effectuer une t\ue2che ayant un focus particulier. Le raisonnement strat\ue9gique est cod\ue9 comme un ensemble de r\ue8gles de production et l'interaction entre la base de connaissances du raisonnement strat\ue9gique et les activit\ue9s se produit gr\ue2ce \ue0 une architecture de style tableau noir. L'architecture d\ue9crite dans le pr\ue9sent article est connue comme celle d'un syst\ue8me bas\ue9 sur des activit\ue9s tableau noir et elle d\ue9coule d'une \ue9tude des attributs voulus pour une architecture de syst\ue8me de robots mobiles. On donne une d\ue9finition de ces attributs avec une comparaison qualitative de plusieurs architectures classiques de syst\ue8me. Le syst\ue8me bas\ue9 sur les activit\ue9s tableau noir est un syst\ue8me hybride int\ue9grant les avantages des trois syst\ue8mes classiques. Il est con\ue7u avec deux couches hi\ue9rarchiques pour le raisonnement strat\ue9gique et le raisonnement r\ue9actif, avec une base de donn\ue9es tableau noir qui tient registre de l'\ue9tat global du monde et avec un ensemble d'activit\ue9s de type comportement r\ue9actif. La faisabilit\ue9 de l'approche est d\ue9montr\ue9e par la mise en oeuvre r\ue9elle d'une plate-forme mobile qui a la capacit\ue9 de navigation r\ue9active en temps r\ue9el, de d\ue9tection des anomalies de plancher et de planification de chemin dynamique. On donne un exemple de raisonnement strat\ue9gique o\uf9 l'information affich\ue9e au tableau noir par l'activit\ue9 de la voie de passage sert \ue0 guider l'activit\ue9 de d\ue9tection d'anomalies de plancher.NRC publication: Ye

MACDONALD CODES OVER THE RING

MACDONALD CODES OVER THE RIN

Effect of various treatments on the production of first grade grafts of Thompson Seedless grapevine on Vitis solonis x V. riparia 1616 rootstock

Soaking Solonis X Riparia 1616 vine rootstock cuttings in 50 ppm NAA for 24 hours before grafting gave the highest rate of Thompson Seedless graftage success. Cold stratification of cuttings gave superior results than other treatments. However, IAA, IBA, GA, thiamin and sucrose reduced the percentage of success. Steeping the basal portion of rootstock cuttings in water at 14-16 °C for 6 or 12, and 12 hours for cold-stored and freshly prepared cuttings respectively improved the grafting success. Basal soaking for 24 hours and then removing the lower 3 cm or 24 hours' soaking upside-down were advantageous for precooled rootstock cuttings. Yet, waxing the grafting zone increased only the success rate of directly grafted cuttings.Einfluß verschiedener Behandlungsverfahren auf die Erzeugung pflanzfähiger Pfropfreben aus Thompson Seedless auf der Unterlage Vitis solonis X Vitis riparia 1616Durch 24stündiges Eintauchen des Unterlagenschnittholzes von Vitis solonis X V. riparia 1616 in 50 ppm NES vor der Veredlung mit Thompson Seedless wurde der höchste Prozentsatz pflanzfähiger Pfropfreben erzielt. Kältestratifikation des Schnittholzes erbrachte bessere Ergebnisse als die anderen Behandlungen. IES, IBS, GS, Thiamin und Saccharose verringerten die Anwuchsprozente. Wurden die Unterlagen mit dem basalen Ende in 14-16 °C warmes Wasser eingetaucht, und zwar kalt gelagertes Schnittholz 6 oder 12 Stunden, frisch geschnittenes Holz 12 Stunden lang, so war der Pfropferfolg beträchtlich verbessert. Bei vorgekühltem Unterlagenschnittholz waren auch 24stündiges Quellen des basalen Endes mit anschließendem Entfernen der unteren 3 cm oder 24stündiges Eintauchen des oberen Endes von Vorteil. überziehen der Pfropfstelle mit Paraffin erhöhte die Anwuchsrate nur im Falle des unmittelbar vor der Pfropfung geernteten Holzes