6,756 research outputs found
High precision Cl, Br and I determinations in mineral standards using the noble gas method
No full textFew techniques are available for analysis of the heavy halogens (Br and I) and characterisation of mineral standards for inter-laboratory comparison is desirable. This study illustrates the noble gas method for precise halogen measurement in neutron-activated samples by laser characterisation of four scapolite gems. The scapolites have Cl concentrations of 3.1-4.1wt.% and a range of Br/Cl and I/Cl ratios that are typical of crustal fluids. Each of the scapolites exhibits some heterogeneity which limits reproducibility to levels beneath the analytical precision of ~2% (2σ). However, the most uniform scapolite, sample SY, has Br/Cl of 11.2×10 ±4.5% and I/Cl of 9.3×10 ±10% (molar ratios, 2σ uncertainties), and all the scapolites have sufficiently reproducible compositions to be useful Cl, Br, I standards. Biotite and hornblende Ar- Ar flux monitors (GA1550 and Hb3Gr) and the Durango fluorapatite were also investigated. These minerals are not suitable as halogen standards for the noble gas method, but help further illustrate the technique, and their analyses represent the first Br and I abundance data reported for biotite and amphibole
Slab-derived halogens and noble gases illuminate closed system processes controlling volatile element transport into the mantle wedge
No full textHalogen and noble gas systematics are powerful tracers of volatile recycling in subduction zones. We present halogen and noble gas compositions of mantle peridotites containing H2O-rich fluid inclusions collected at volcanic fronts from two contrasting subduction zones (the Avacha volcano of Kamchatka arc and the Pinatubo volcano of Luzon arcs) and orogenic peridotites from a peridotite massif (the Horoman massif, Hokkaido, Japan) which represents an exhumed portion of the mantle wedge. The aims are to determine how volatiles are carried into the mantle wedge and how the subducted fluids modify halogen and noble gas compositions in the mantle. The halogen and noble gas signatures in the H2O-rich fluids are similar to those of marine sedimentary pore fluids and forearc and seafloor serpentinites. This suggests that marine pore fluids in deep-sea sediments are carried by serpentine and supplied to the mantle wedge, preserving their original halogen and noble gas compositions. We suggest that the sedimentary pore fluid-derived water is incorporated into serpentine through hydration in a closed system along faults at the outer rise of the oceanic, preserving Cl/H2O and 36Ar/H2O values of sedimentary pore fluids. Dehydration–hydration process within the oceanic lithospheric mantle maintains the closed system until the final stage of serpentine dehydration. The sedimentary pore fluid-like halogen and noble gas signatures in fluids released at the final stage of serpentine dehydration are preserved due to highly channelized flow, whereas the original Cl/H2O and 36Ar/H2O ratios are fractionated by the higher incompatibility of halogens and noble gases in hydrous minerals
Strong Binding of Noble Gases to [B12X11]˗: A Theoretical Study
No full textWe systematically explore the stability and properties
of [B12X11Ng]− adducts resulting
from the capture reaction of noble gas atoms (Ng) by anionic [B12X11]− clusters in the ion
trap. [B12X11]− can be obtained by
stripping one X− ligand
off the icosahedral closo-dodecaborate
dianion [B12X12]2−. We study the
binding of the noble gas atoms He, Ne, Kr, Ar and Xe to [B12X11]− with ligands X =
F, Cl, Br, I, CN. While He cannot be captured by these clusters and Ne only
binds at low temperatures, the complexes with the heavier Kr, Ar and Xe show
appreciable complexation energies and exceed 1 eV at room temperature in
the case of [B12(CN)11Xe]−. For the latter
three noble gases, we observe a significant charge transfer from the Ng to the icosahedral
B12 cage
Subduction zone fluxes of halogens and noble gases in seafloor and forearc serpentinites
No full textSerpentinites form by hydration of ultramafic lithologies in a range of seafloor and shallow subduction zone settings. Serpentinites are recognised as major reservoirs of fluid mobile elements and HO in subducting oceanic lithosphere, and together with forearc serpentinites formed in the mantle wedge, provide critical information about shallow-level volatile fluxes during subduction. The current study provides new Cl, as well as the first comprehensive Br, I and noble gas analyses reported for seafloor and forearc chrysotile-lizardite serpentinites. The samples were recovered from IODP drilling campaigns of mid-ocean ridge, passive margin and forearc settings (n=17), and ophiolites in the Italian Alps and Apennines (n=10). The aims of this study were to determine the compositional variability of noble gases and halogens in serpentinites entering subduction zones and evaluate the efficiency of gas loss during the early stages of serpentinite subduction.The chrysotile-lizardite serpentinites and serpentised peridotites contain 43-2300ppm Cl and 3×10-2×10molg Ar, with the concentrations of these elements broadly related to the estimated degree of serpentinisation. The serpentinites have extremely variable Br/Cl and I/Cl ratios with many samples preserving compositions similar to organic-rich sedimentary marine pore fluids. Serpentinites from the Marianas Forearc have very high I concentrations of up to 45ppm I and I/Cl ratios of ~14,000 times the seawater value that is even higher than the maximum I/Cl enrichment observed in sedimentary marine pore fluids. The serpentinites have Xe/Ar and Kr/Ar ratios that are mostly close to or above seawater values, and Ne/Ar ratios that range from seawater to lower values. The serpentinites contain 200km, imply that serpentinites could dominate the deep recycling budgets of both the heavy halogens and atmospheric noble gases
New constraints on the release of noble gases during in vacuo crushing and application to scapolite Br-Cl-I and 40Ar/39Ar age determinations
No full textThe release of irradiation-produced noble gas isotopes (Ar, Kr, Xe and Ar) during in vacuo crushing scapolite has been investigated and is compared to quartz. Three thousand crushing strokes released ∼98% of fluid inclusion-hosted noble gas from quartz. In comparison, 3000 crushing strokes released only ∼4% of the lattice-hosted Ar from a scapolite gem. In vacuo crushing released lattice Ar preferentially relative to lattice Kr or Xe and prolonged crushing released ∼88% of the lattice-hosted noble gas in 96,000 crushing strokes. We suggest fast diffusion pathways generated by crushing are an important noble gas release mechanism and we demonstrate two applications of prolonged in vacuo crushing on irradiated scapolite. Firstly, scapolite molar Br/Cl and I/Cl values are shown to vary over a similar range as crustal fluids. The Cl-rich scapolite gem from Hunza, Pakistan has Br/Cl of 0.5-0.6 × 10 and I/Cl values of 0.3-2 × 10, that are similar to fluids that have dissolved evaporites. In contrast, three out of four skarn-related scapolites from the Canadian Grenville Province have molar Br/Cl values of 1.5-2.4 × 10, and I/Cl values of 11-24 × 10, that are broadly consistent with skarn formation by magmatic fluids. The fourth Grenvillian scapolite, with only 0.02 wt% Cl, has an exceptionally elevated molar Br/Cl value of up to ∼54 × 10 and I/Cl of 284 × 10. It is unclear if these values reflect the composition of fluids formed during metamorphism or preferential incorporation of Br and I in Cl-poor meionitic scapolite. Secondly, the Grenvillian scapolites give plateau ages of between 830 Ma and 400 Ma. The oldest ages post-date regional skarn formation by ∼200 Myr, but are similar to feldspar cooling ages in the Province. The age variation in these samples is attributed to a combination of factors including variable thermal history and the presence of mineral sub-grains in some of the samples. These sub-grains control the release of Ar, Ar and Ar* during in vacuo crushing as well as the samples Ar* retentivity in nature. Scapolite is suggested as a possible analogue for K-feldspar in thermochronologic studies
Si(Cl)H
No full textThe perfluorinated alkoxy silanes {(F3C)(3)CO}(3)SiH (1) and {(F5C6)(3)CO}(2)Si(Cl)H (2) were prepared and fully characterized. Despite the high calculated Bronsted acidities, all attempts to deprotonate 1 and 2 to give the conjugate silanide ions failed due to the exceptionally short and strong Si-H bonds. In the solid state, the Si-H units are not involved in any intermolecular interactions, but instead the crystal packing consists of exceptionally short and strong F...F interactions. The cohesive energies are entirely comprised of London dispersion interactions, similarly as in the crystal structures of noble gases
Epidemiology and pathophysiology of cancer-associated thrombosis
No full textVenous thromboembolism (VTE) is a common complication in patients with malignant disease. First recognised by Bouillard in 1823 and later described by Trousseau in 1844, multiple studies have since provided considerable evidence for a clinical association between VTE and cancer. Across all cancers, the risk for VTE is elevated 7-fold; in certain malignancies, the risk for VTE may be increased up to 28-fold. Venous thromboembolism is the second leading cause of death in patients with cancer; among survivors, complications commonly include recurrent VTE and post-thrombotic syndrome, and (more rarely) chronic thromboembolic pulmonary hypertension, which are costly, and have a profound impact on the patient's quality of life. Tumour cells can activate blood coagulation through multiple mechanisms, including production of procoagulant, fibrinolytic, and proaggregating activities, release of proinflammatory and proangiogenic cytokines, and interacting directly with host vascular and blood cells (e.g., endothelial cells, leukocytes, and platelets) through adhesion molecules. Increasing evidence suggests that elements of the haemostatic system also have a direct role in eliciting or enhancing angiogenesis, cell survival, and metastasis. Despite the problem posed by VTE in the setting of cancer, it is evident that a significant number of oncologists do not recognise the link between cancer, its treatment, and thrombogenesis. On 22 May 2009, a group of UK-based physicians met in London, UK, to evaluate recent data on cancer thrombosis. This article (1 of 4) briefly reviews key data on the epidemiology and pathophysiology of VTE as a context for a discussion and consensus statement developed by meeting attendees, on the implications of this information for UK clinical practice
Microstructure Characterization of Noble Metal-Silica Nanocomposites
No full textThe presence of highly dispersed metal particles on solid supports with well-defined microstructure is important in the field of functional materials, active catalysts as well as bionanomaterials for medical applications. Noble metal nanostructures, in particular silver, palladium, and platinum nanoparticles were formed from ammine complexes ([Pt(NH₃)₄]Cl₂, [Ag(NH₃)₂]OH, and [Pd(NH₃)₄]Cl₂) and supported on high ordered mesoporous silica (SBA-15) and aluminosilica matrix. In this work, the distribution, composition and crystal structure of supported noble metal nanoparticles were determined and characterized. Finally the stability of incorporated nanostructures was confirmed. The microstructures of the obtained samples were analyzed by high resolution transmission electron microscopy. Obtained results indicated that developed procedures of synthesis and modification of mesoporous ordered silica or their derivate by proposed nanostructures are effective and allow to obtain new nanocomposites and nanocatalysts in repeatable and controlled way
Open access self-archiving: An author study
No full textThis, our second author international, cross-disciplinary study on open access had 1296 respondents. Its focus was on self-archiving. Almost half (49%) of the respondent population have self-archived at least one article during the last three years. Use of institutional repositories for this purpose has doubled and usage has increased by almost 60% for subject-based repositories. Self-archiving activity is greatest amongst those who publish the largest number of papers. There is still a substantial proportion of authors unaware of the possibility of providing open access to their work by self-archiving. Of the authors who have not yet self-archived any articles, 71% remain unaware of the option. With 49% of the author population having self-archived in some way, this means that 36% of the total author population (71% of the remaining 51%), has not yet been appraised of this way of providing open access. Authors have frequently expressed reluctance to self-archive because of the perceived time required and possible technical difficulties in carrying out this activity, yet findings here show that only 20% of authors found some degree of difficulty with the first act of depositing an article in a repository, and that this dropped to 9% for subsequent deposits. Another author worry is about infringing agreed copyright agreements with publishers, yet only 10% of authors currently know of the SHERPA/RoMEO list of publisher permissions policies with respect to self-archiving, where clear guidance as to what a publisher permits is provided. Where it is not known if permission is required, however, authors are not seeking it and are self-archiving without it. Communicating their results to peers remains the primary reason for scholars publishing their work; in other words,
researchers publish to have an impact on their field. The vast majority of authors (81%) would willingly comply with a mandate from their employer or research funder to deposit copies of their articles in an institutional or subject-based repository. A further 13% would comply reluctantly; 5% would not comply with such a mandate
Progress of international hydrogen production network for the thermochemical Cu–Cl cycle
No full textThis paper presents recent advances by an international team which is developing the thermochemical copper–chlorine (Cu–Cl) cycle for hydrogen production. Development of the Cu–Cl cycle has been pursued by several countries within the framework of the Generation IV International Forum (GIF) for hydrogen production with the next generation of nuclear reactors. Due to its lower temperature requirements in comparison with other thermochemical cycles, the Cu–Cl cycle is particularly well matched with Canada's Generation IV reactor, SCWR (Super-Critical Water Reactor), as well as other heat sources such as solar energy or industrial waste heat. In this paper, recent developments of the Cu–Cl cycle are presented, specifically involving unit operation experiments, corrosion resistant materials and system integration.Atomic Energy of Canada LimitedOntario Research Excellence FundNatural Sciences and Engineering Research Council of CanadaUniversity Network of Excellence in Nuclear Engineering (UNENE)Canada Research Chairs progra
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