Tensile stresses around boreholes due to transient fluid flow

We present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production.     

Quick-look assessments to identify optimal CO2 EOR storage sites

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO₂ enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO₂ EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO₂ EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO₂ sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO₂ EOR. The second stage provides quick estimates of CO₂ EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites.     

Multi-AUV Control and Adaptive Sampling in Monterey Bay

Operations with multiple autonomous underwater vehicles (AUVs) have a variety of underwater applications. For example, a coordinated group of vehicles with environmental sensors can perform adaptive ocean sampling at the appropriate spatial and temporal scales. We describe a methodology for cooperative control of multiple vehicles based on virtual bodies and artificial potentials (VBAP). This methodology allows for adaptable formation control and can be used for missions such as gradient climbing and feature tracking in an uncertain environment. We discuss our implementation on a fleet of autonomous underwater gliders and present results from sea trials in Monterey Bay in August, 2003. These at-sea demonstrations were performed as part of the Autonomous Ocean Sampling Network (AOSN) II project     

Phytolith analysis from the archaeological site of Kush, Ras al-Khaimah, United Arab Emirates

Despite the wealth of archaeological sites and excellent conditions for preservation, few phytolith investigations have been undertaken from the Arabian Gulf region. The results from the Sasanian and Islamic archaeological tell of Kush, Ras al-Khaimah, United Arab Emirates, are presented. Kush is situated just inside the Gulf on an important trade route. The occupation sequence dates from the 4^th century A.D. until the 13^th century A.D., recording the development of the site in the Sasanian period, followed by the arrival of Islam in the 7^th century A.D. and the final abandonment of the site in the late 13^th century when the nearby site of al-Mataf (Julfar) began to develop closer to the present day coastline. All the samples analyzed contained abundant phytoliths (short cells, elongated cells, and groups of elongated cells) of various types. They included date palm (Phoenix dactylifera), papillae (possibly from barley (Hordeum)), and hair cells possibly from species of canary grass (Phalaris spp.). Some researchers have suggested that groups of elongated cells may indicate the presence of irrigation in semiarid environments. The present results for this class of phytoliths appeared to imply that intensive irrigation was unlikely to have taken place around Kush.     

Structural chemistry of synthetic cordierite: Evidence for solid solutions and disordered compositional domains in Bi-flux-grown Mg-cordierites

The structure, crystal chemistry, and microstructure of disordered and ordered Mg-cordierites synthesized in a bismuth oxide flux system have been studied by a combination of x-ray and neutron powder diffraction and quantitative x-ray microanalysis using analytical electron microscopy. Microchemical data obtained on Bi-flux cordierites using energy-dispersive x-ray analysis is interpreted through comparison with data collected on stoichiometric Mg₂Al₄Si₅O₁₈ glass and α- and β-cordierite samples synthesized by subsolidus crystallization of the glass. Bi-flux cordierites crystallize in both the hexagonal and orthorhombic polymorphs and contain 5 to 10 at% occupancy of bismuth on the C1 and C2 channel sites. The microstructure of Bi-flux α-cordierite is characterized by the existence of local domains of disordered cordierite solid solutions with variable composition and significant vacancy concentrations on the octahedral site. The β-cordierites have a more homogeneous microstructure but are still Al-deficient, Si-rich solid solutions.     

西天山喇嘛苏成矿斑岩年代学、地球化学特征与成因初探

近东西走向的天山造山带位于中亚造山带或阿尔泰构造拼贴体的最南端,是哈萨克斯坦和塔里木板块的汇聚地带,也是一个重要的铜一金等多金属成矿带[1].天山造山带是在古生代由塔里木和西伯利亚板块之间的古亚洲洋的消减闭合,塔里木、准噶尔、哈萨克斯坦等板块的俯冲-碰撞-增生所形成[2].     

A paper with an interest in rhythm

This paper is a performative effort to move with and through the expressive and theoretical spaces of an interest in rhythm. This interest emerges initially from the middle of an encounter with the 5 Rhythms™, a contemporary somatic practice that uses rhythm to facilitate and catalyse expressive movement. Rather than seeking to excavate representational meaning from an encounter with the practice or using it to critically diagnose the corporeal politics of contemporary society, this paper apprehends the creative movement emerging from an encounter with/in the non-representational, performative potential of the 5 Rhythms™. By becoming a deliberately playful effort to hold onto the lines of movement emergent from the affective, kinaesthetic territories of this practice, the paper works to avoid either falling back upon a representational ethics that stops this movement dead in its tracks or becoming seduced by an aesthetics of weightless escape. This effort draws particular support from Deleuze and Guattari's writing on the refrain, a concept that provides a vehicle through which the lines of an interest in rhythm gain expressive and theoretical consistency. Because the territories of the refrain open onto lines of movement that are as much figural as discursive, the paper works to animate the lines of movement emerging from an encounter with the 5 Rhythms™ through a series of non-representational diagrammatic interventions. Finally, in drawing the diagrammatic lines of this movement in-between, the paper becomes not so much a series of lines about moving, but a series of lines moving about.     

Mass-independent fractionation of oxygen isotopes in the mesostasis of a chondrule from the Semarkona LL3.0 ordinary chondrite

A large chondrule from Semarkona, the most primitive ordinary chondrite known, has been discovered to contain a record of mass transport during its formation. In most respects, it is a normal Type I, group A1, low-FeO chondrule that was produced by reduction and mass-loss during the unidentified flash-heating event that produced the chondrules, the most abundant structural component in primitive meteorites. We have previously measured elemental abundances and abundance profiles in this chondrule. We here report oxygen isotope ratio abundances and ratio abundance profiles. We have found that the mesostasis is zoned in oxygen isotope ratio, with the center of the chondrule containing isotopically heavier oxygen than the outer regions, the outer regions being volatile rich from the diffusion of volatiles into the chondrule during cooling. The δ¹⁷O values range from −2.0‰ to 9.9‰, while δ¹⁸O range from −1.9‰ to 9.6‰. More importantly, a plot of δ¹⁷O against δ¹⁸O has a slope of 1.1 ± 0.2 (1σ) and 0.88 ± 0.10 (1σ) when measured by two independent methods. Co-variation of δ¹⁷O with δ¹⁸O that does not follow mass-dependent fractionation has often been seen in primitive solar system materials and is usually ascribed to the mixing of different oxygen reservoirs. We argue that petrographic and compositional data indicate that this chondrule was completely melted at the time of its formation so that relic grains could not have survived. Furthermore, there is petrographic and compositional evidence that there was no aqueous alteration of this chondrule subsequent to its formation. Although it is possible to formulate a series of exchanges between the chondrule and external ¹⁶O-rich and ¹⁶O-poor reservoirs that may explain the detailed oxygen isotope systematics of this chondrule, such a sequence of events looks very contrived. We therefore hypothesize that reduction, devolatilization, and crystallization of the chondrule melt may have produced ¹⁶O-rich olivines and ¹⁶O-poor mesostasis plotting on a slope-one line as part of the chondrule-forming process in an analogous fashion to known chemical mass-independent isotopic fractionation mechanisms. During cooling, volatiles and oxygen near the terrestrial line in oxygen isotope composition produced the outer zone of volatile rich and ¹⁶O-rich mesostasis. The chondrule therefore not only retains a record of considerable mass transport accompanying formation, but also may indicate that the isotopes of oxygen underwent mass-independent fractionation during the process.