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Search Results: 1 - 10 of 53012 matches for " David Clague "
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The Geological History of Deep-Sea Volcanoes: Biosphere, Hydrosphere, and Lithosphere Interactions
Hubert Staudigel,David A. Clague
Oceanography , 2010,
Abstract: The geological evolution of seamounts has distinct influence on their interactions with the ocean, their hydrology, geochemical fluxes, biology, resources, and geohazards. There are six geological evolutionary stages of seamounts: (1) small seamounts (100–1000-m height), (2) mid-sized seamounts (>1000-m height, > 700-m eruption depth), (3) explosive seamounts (< 700-m eruption depth), (4) ocean islands, (5) extinct seamounts, and (6) subducting seamounts. Throughout their lifetimes, seamounts offer major passageways for fluid circulation that promotes geochemical exchange between seawater and the volcanic oceanic crust, and seamounts likely host significant microbial communities. Water circulation may be promoted by hydrothermal siphons in conjunction with the underlying oceanic crust, or it may be driven by intrusions inside seamounts from Stage 2 onward. Geochemical fluxes are likely to be very large, primarily because of the very large number of Stage 1 seamounts. Intrusive growth of seamounts also initiates internal deformation that ultimately may trigger volcano sector collapse that likely peaks at the end of the main volcanic activity at large seamounts or islands. Explosive activity at seamounts may begin at abyssal depth, but it is most pronounced at eruption depths shallower than 700 m. Wave erosion inhibits the emergence of islands and shortens their lifespans before they subside due to lithosphere cooling. Once volcanism ends and a seamount is submerged, seamounts are largely unaffected by collapse or erosion. Throughout their histories, seamounts offer habitats for diverse micro- and macrobiological communities, culminating with the formation of coral reefs in tropical latitudes. Geological hazards associated with seamounts are responsible for some of the largest natural disasters recorded in history and include major explosive eruptions and large-scale landslides that may trigger tsunamis.
Spotlight 6: Davidson Seamount
David Clague,Lonny Lundsten,James Hein,Jennifer Paduan
Oceanography , 2010,
Abstract: Davidson Seamount is located about 80 km off the central California coast in the Monterey Bay National Marine Sanctuary. It is one of the better-explored seamounts in the world, having been sampled and observed during 32 dives by the remotely operated vehicle (ROV) Tiburon. These dives mapped the bottom substrate and biological communities, and collected over 280 rock samples and nearly as many benthic animals.
Publishing Student Work on the Web: The Living Music Project and the Imperatives of the New Literacy
Mark Clague
Journal of Music History Pedagogy , 2011,
Abstract: To be effective in enhancing learning in the music history classroom, technology must be applied judiciously toward specific goals. The Web presents opportunities to broaden and deepen the impact of traditional research assignments, primarily through online publication, which increases motivation and brings a host of thorny issues of representation and quality to bear upon student work. One such assignment is an oral history project the author has developed titled Living Music in which students interview an informant involved with the music world (a concept akin to Howard Becker’s notion of “Art World”) and present their findings through the Living Music website. In completing this work, students have the opportunity to grow on several levels: as historical researchers, as writers, as editors, and most importantly as readers and users of historical research. As a guided experience in original research and publication, Living Music teaches students traditional skills in musicology, shares the joys of discovery and publication, and offers insights into the way the Web has augmented and shifted the character and values of publication itself.
Endeavour Segment of the Juan de Fuca Ridge: One of the Most Remarkable Places on Earth
Deborah S. Kelley,Suzanne M. Carbotte,David W. Caress,David A. Clague
Oceanography , 2012,
Abstract: Endeavour Segment of the Juan de Fuca Ridge is one of three Integrated Study Sites for the Ridge 2000 Program. It is a remarkable, dynamic environment hosting five major hydrothermal fields, numerous smaller fields, and myriad diffuse-flow sites; magma chambers underlie all fields. Over 800 individual extinct and active chimneys have been documented within the central ~ 15 km portion of the ridge, with some edifices reaching 50 m across and up to 45 m tall. Fluid flow is focused along faults within the rift zone, and seismically active faults along the western axial valley wall have been used by both magmas and upwelling hydrothermal fluids. There is significant chemical heterogeneity in basalt compositions within the axial rift valley, with the greatest diversity occurring near the base of the western axial valley wall where normal, transitional, and enriched type mid-ocean ridge basalts occur within tens of meters of each other. Endeavour is the only site where seismic intensity has been linked directly to heat flux at the individual vent field scale. Installation of the world's first high-power and high-bandwidth cabled observatory at Endeavour via NEPTUNE Canada ensures that new discoveries along the Juan de Fuca Ridge will continue into the future.
XRF Standardless Comparison of Mining Head and Tail Grades to Screen and Display Ore Processing Recoveries  [PDF]
Nicholas E. Pingitore Jr, Juan W. Clague, Daniel Gorski
American Journal of Analytical Chemistry (AJAC) , 2016, DOI: 10.4236/ajac.2016.711070
Abstract: Separation of target elements or minerals from their host rock or ore is essential to successful mining operation. The inevitable loss of a portion of the desired material that accompanies each step in the extraction process must be documented to develop the operational protocol. Superposition of the characteristic X-ray fluorescence spectra of head (crushed rock ore particles, pre-processing) and tail (post-processing particles) samples provides a direct visual comparison of relative peak sizes, and thereby the relative concentrations, of elements of interest. If the head and tail peaks are identical, none of the element was recovered in the extraction process. At the other extreme if the tail peak “flat lines”, i.e., there is no peak, there was 100% recovery of that element. Standardless visual comparison is valid if the same mass of identical starting material is incorporated into the head and tail sample analysis pucks, and XRF analytical conditions are identical. The considerable time and expense of acquiring and calibrating the standards associated with XRF analysis of 75 or more elements are avoided, a significant advantage during initial broad screening of an experimental extraction procedure. Full quantitation by XRF or an alternate technique can proceed at a later project stage, if desired. The approach retains and presents all features of the original data, thus eliminating questions about data quality, standards and their calibration, and data manipulation in processing from raw counts to concentrations in printout tables. This form of display is ideal for both the mining professional and such less technical groups as corporate staff, investors, regulators, and the public. Examples presented herein are for heap leaching; the protocol can be applied as well to any of the other traditional ore processing and beneficiation procedures, e.g., gravity concentration, magnetic and electrical separation, froth flotation, and ore sorting.
Remarkably Consistent Rare Earth Element Grades at Round Top Yttrofluorite Deposit  [PDF]
Nicholas E. Pingitore Jr., Juan W. Clague, Daniel Gorski
Advances in Materials Physics and Chemistry (AMPC) , 2018, DOI: 10.4236/ampc.2018.81001
Abstract: The peraluminous rhyolite that forms Round Top Mountain (approximately 375 m high × nearly 2 km in diameter), near Sierra Blanca, Hudspeth County, west Texas, USA, is enriched in yttrium and heavy rare earth elements (YHREEs), as well as Li, Be, U, Th, Sn, F, Rb, Cs, Nb, and Ta. Texas Mineral Resources Corp. (USA) proposes to release the YHREEs from their unique yttrofluorite host via heap leaching with dilute sulfuric acid. The inexpensive process also releases portions of valuable byproduct Be, Li, and U from accessory minerals amid the insoluble feldspars and quartz that comprise 90% - 95% of the surface-exposed rhyolite mountain. The objective of this study is to determine the consistency of mineralization grade, an important consideration in mine planning and preliminary economic analysis. The method is to plot elemental analyses of Y, Dy, Ho, Tm, Yb, Ce, Pr, Nd, Eu, Gd, Tb, U, and Nb from more than 1400 reverse circulation cuttings taken from 64 exploration drill holes against sample depth. The result of inspection of the plots reveals a remarkably homogeneous distribution of minor and trace elements throughout the sampled portion of the massive, 1.6-billion-tonne laccolith. The plots drive the conclusion that Round Top mine feedstock should remain constant for the life of the mine (multiple decades). Thus mining mechanics could be optimized at the start of operations and not require expensive later changes. The physical and chemical design of the heap leach and recovery and purification of target elements from pregnant leach solution also could be perfected during early development.
Major clinical and angiographic outcome of drug eluting stents in native ostial coronary artery disease  [PDF]
Khaled R. Abd El Meguid, Hesham B. Mahmoud, Fouad R. Amin, Jonathan R. Clague
World Journal of Cardiovascular Diseases (WJCD) , 2013, DOI: 10.4236/wjcd.2013.33051
Abstract:

Objectives: The study was designed to evaluate the efficacy and safety of drug eluting stents (DESs) in aorto-ostial (A-O) coronary artery lesions, in terms of early and late restenosis rate; including clinical assessment, non-invasive stress testing and angiographic follow-up. Also, the study was aimed to compare the results of implantation of drug eluting stents (DES) to that of bare metal stents (BMS) in aortoostial lesions done over a previous 5 years in Royal Brompton Hospital. Background: The safety and effectiveness of DESs for the treatment of aortoostial lesions. Methods: We included 161 consecutive patients with symptoms subjective of angina pectoris or objective evidence of myocardial ischemia; who underwent percutaneous coronary interventions (PCI) in coronary ostial lesions using DES. The patients were divided into two groups based on the site of ostial lesion. The control group consisted of 125 consecutive patients who underwent percutaneous coronary intervention for ostial lesions using bare metal stents (BMS) implantation in the period immediately before the introduction of DES. The incidence of major adverse cardiac events (MACE), including death or Q-wave myocardial infarction (MI), need for repeated revascularization procedure CABG or angioplasty, were recorded in-hospital and at twelve months ± 3 months. Follow-up angiography was only performed in case of recurrent symptoms subjective of myocardial ischemia or if there was objective evidence of myocardial ischemia by stress testing. Results: The initial procedure was successful in 149 patients (92.5%) in the DES arm. There were no statistically significant major in-hospital complications in the DES group, compared to BMS group which showed 4 cases of in-hospital deaths (p = 0.017). At Twelve months ± 3 months follow-up, MACE were significantly less frequent in the DES group compared to the BMS group, including death (0.8% vs. 6.4%, p = 0.004) and need for CABG (1.7% vs. 10%, p = 0.012). Conclusions: The main finding of our study is that, compared to the BMS, implantation

Regulation of ErbB2 Receptor Status by the Proteasomal DUB POH1
Han Liu, Richard Buus, Michael J. Clague, Sylvie Urbé
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005544
Abstract: Understanding the factors, which control ErbB2 and EGF receptor (EGFR) status in cells is likely to inform future therapeutic approaches directed at these potent oncogenes. ErbB2 is resistant to stimulus-induced degradation and high levels of over-expression can inhibit EGF receptor down-regulation. We now show that for HeLa cells expressing similar numbers of EGFR and ErbB2, EGFR down-regulation is efficient and insensitive to reduction of ErbB2 levels. Deubiquitinating enzymes (DUBs) may extend protein half-lives by rescuing ubiquitinated substrates from proteasomal degradation or from ubiquitin-dependent lysosomal sorting. Using a siRNA library directed at the full complement of human DUBs, we identified POH1 (also known as Rpn11 or PSMD14), a component of the proteasome lid, as a critical DUB controlling the apparent ErbB2 levels. Moreover, the effects on ErbB2 levels can be reproduced by administration of proteasomal inhibitors such as epoxomicin used at maximally tolerated doses. However, the extent of this apparent loss and specificity for ErbB2 versus EGFR could not be accounted for by changes in transcription or degradation rate. Further investigation revealed that cell surface ErbB2 levels are only mildly affected by POH1 knock-down and that the apparent loss can at least partially be explained by the accumulation of higher molecular weight ubiquitinated forms of ErbB2 that are detectable with an extracellular but not intracellular domain directed antibody. We propose that POH1 may deubiquitinate ErbB2 and that this activity is not necessarily coupled to proteasomal degradation.
Deciphering histone 2A deubiquitination
Michael J Clague, Judy M Coulson, Sylvie Urbé
Genome Biology , 2008, DOI: 10.1186/gb-2008-9-1-202
Abstract: Ubiquitination is a reversible posttranslational modification of proteins that could rival phosphorylation in its scope and complexity. Removal of ubiquitin is accomplished through the action of deubiquitinating enzymes (DUBs), which fall into five distinct families in the human genome, containing about 84 active members [1,2]. Post-translational modifications of histones include methylation, acetylation, sumoylation and ubiquitination, enabling a combinatorial code to regulate chromatin structure [3] and recruit protein complexes [4]. An example of the interplay between these modifications is provided by the activity of Ubp8, a yeast deubiquitinating enzyme which regulates the methylation of histone 3 (H3) on lysine 4 (K4 methylation) by deubiquitinating histone 2B (H2B) [5]. About 5-15% of histone 2A (H2A) is monoubiquitinated in mammalian cells, making it the most abundant ubiquitinated protein in the nucleus; in fact, it was the first example of a ubiquitinated protein to be described [6]. Monoubiquitination is not linked to protein degradation, but instead plays a role in transcriptional control, DNA repair and other processes. It has also long been known that deubiquitination of histones occurs during metaphase of the cell cycle, coincident with complete condensation of the chromosomes [7,8]. Monoubiquitination of H2A has been linked to Polycomb group complex-dependent gene silencing [9] and X-chromosome inactivation [10]. Furthermore, DNA damage induces monoubiquitination of H2A in the vicinity of DNA lesions after incision of the damaged strand [11].Three recent papers identify distinct DUBs with activity towards H2A and begin to unravel their cellular functions (Figure 1). Zhu et al. [12] identified MYSM1/KIAA1915 (belonging to the JAMM/MPN+ family of metalloprotease DUBs [13]) in a screen for factors regulating androgen-controlled gene expression. The authors argue that MYSM1 is an H2A-specific DUB on the basis of decreased ubiquitination following overexp
Climate change and hazardous processes in high mountains Cambio climático y peligros naturales en altas monta as
John J Clague,Christian Huggel,Oliver Korup,Bill McGuire
Revista de la Asociación Geológica Argentina , 2012,
Abstract: The recent and continuing reduction in glacier ice cover in high mountains and thaw of alpine permafrost may have an impact on many potentially hazardous processes. As glaciers thin and retreat, existing ice- and moraine-dammed lakes can catastrophically empty, generating large and destructive downstream floods and debris flows. New ice-dammed lakes will form higher in mountain catchments, posing additional hazards in the future. The magnitude or frequency of shallow landslides and debris flows in some areas will increase because of the greater availability of unconsolidated sediment in new deglaciated terrain. Continued permafrost degradation and glacier retreat probably will decrease the stability of rock slopes. La reciente y continua reducción de la cobertura glaciaria en alta monta a y el deshielo del permafrost pueden tener un impacto negativo en muchos procesos potencialmente peligrosos. A medida que los glaciares reducen su espesor y retroceden, los lagos formados por diques de hielo o morenas pueden vaciarse catastróficamente, resultando en grandes y destructivas inundaciones o flujos detríticos río abajo. Nuevos diques de hielo van a formarse en zonas más altas de las cuencas monta osas, generando peligros adicionales en el futuro. La magnitud o frecuencia de movimientos en masa superficiales y flujos detríticos va a aumentar en algunas áreas debido a la mayor disponibilidad de materiales no consolidados en nuevos terrenos desglasados. La degradación continua del permafrost y el retiro de glaciares probablemente va a disminuir la estabilidad de laderas rocosas.
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