The availability of future fusion devices, such as a fusion nuclear science facility or demonstration fusion power station, greatly depends on long operating lifetimes of plasma facing components in ...their divertors. ORNL is designing the Material Plasma Exposure eXperiment (MPEX), a superconducting magnet, steady-state device to address the plasma material interactions of fusion reactors. MPEX will utilize a new highintensity plasma source concept based on RF technology. This source concept will allow the experiment to cover the entire expected plasma conditions in the divertor of a future fusion reactor. It will be able to study erosion and redeposition for relevant geometries with relevant electric and magnetic fields in-front of the target. MPEX is being designed to allow for the exposure of a priori neutron-irradiated samples. The target exchange chamber has been designed to undock from the linear plasma generator such that it can be transferred to diagnostics stations for more detailed surface analysis. MPEX is being developed in a staged approach with successively increased capabilities. After the initial development step of the helicon source and electron cyclotron heating system, the source concept is being tested in the Proto-MPEX device. Proto-MPEX has achieved electron densities of more than 4×10 19 m -3 with a large diameter (13 cm) helicon antenna at 100 kW power. First heating with microwaves resulted in a higher ionization represented by higher electron densities on axis, when compared with the helicon plasma only without microwave heating.
ABSTRACT We present the first results from an ongoing survey to characterize the circumgalactic medium (CGM) of massive high-redshift galaxies detected as submillimeter galaxies (SMGs). We ...constructed a parent sample of 163 SMG-QSO pairs with separations less than ∼36″ by cross-matching far-infrared-selected galaxies from Herschel with spectroscopically confirmed QSOs. The Herschel sources were selected to match the properties of the SMGs. We determined the sub-arcsecond positions of six Herschel sources with the Very Large Array and obtained secure redshift identification for three of those with near-infrared spectroscopy. The QSO sightlines probe transverse proper distances of 112, 157, and 198 kpc at foreground redshifts of 2.043, 2.515, and 2.184, respectively, which are comparable to the virial radius of the ∼1013 M halos expected to host SMGs. High-quality absorption-line spectroscopy of the QSOs reveals systematically strong H i Ly absorption around all three SMGs, with rest-frame equivalent widths of ∼2-3 . However, none of the three absorbers exhibit compelling evidence for optically thick H i gas or metal absorption, in contrast to the dominance of strong neutral absorbers in the CGM of luminous z ∼ 2 QSOs. The low covering factor of optically thick H i gas around SMGs tentatively indicates that SMGs may not have as prominent cool gas reservoirs in their halos as the coeval QSOs and that they may inhabit less massive halos than previously thought.
The Wendelstein 7-X stellarator is in final stages of commissioning, and will begin operation in late 2015. In the first phase, the machine will operate with a limiter, and will be restricted to low ...power and short pulse. But in 2019, plans are for an actively cooled divertor to be installed, and the machine will operate in steady state at full power. Recently, plasma simulations have indicated that, in this final operational phase, a bootstrap current will evolve in certain scenarios. This will cause the sensitive ends of the divertor target to be overloaded beyond their qualified limit. A high heat flux scraper element (HHF-SE) has been proposed in order to take up some of the convective flux and reduce the load on the divertor. In order to examine whether the HHF-SE will be able to effectively reduce the plasma flux in the divertor region of concern, and to determine how the pumping effectiveness will be affected by such a component, it is planned to include a test divertor unit scraper element (TDU-SE) in 2017 during an earlier operational phase. Several U.S. fusion energy science laboratories have been involved in the design, analysis (structural and thermal finite element, as well as computational fluid dynamics), plasma simulation, planning, prototyping, and diagnostic development around the scraper element program (both TDU-SE and HHF-SE). This paper presents an overview of all of these activities and their current status.
The function of the high heat flux scraper element is to reduce the heat loads on the element ends of the actively cooled divertor of Wendelstein 7-X. The scraper element is actively water cooled to ...remove up to 550kW steady state power load, with localized heat fluxes as high as 20MW/m2. Its surface area, 0.17m2, is contoured to optimally intercept both upstream and downstream particle fluxes. The plasma facing surface is made of 24 individual scraper fingers based on the monoblock technology. Each scraper finger is 247mm long and 28mm wide and has 13 monoblocks made of CFC NB31 bonded by hot isostatic pressing onto a CuCrZr cooling tube equipped with a copper twisted tape. Development activities, described here, include the design and fabrication of prototypes to validate the different technologies selected for the scraper element design to prepare a possible production.
What the bubble knows Langenegger, T.; Vachon, D.; Donis, D. ...
Limnology and oceanography,
07/2019, Letnik:
64, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Atmospheric methane (CH₄) concentrations have more than doubled in the past ~ 250 yr, although the sources of this potent greenhouse gas remain poorly constrained. Freshwaters contribute ~ 20% of ...natural CH₄ emissions, about half attributed to ebullition. Estimates remain uncertain as ebullition is stochastic, making measurements difficult, time consuming, and costly with current methods (e.g., floating chambers, funnel gas traps, and hydroacoustics). We present a novel approach to quantify basin-wide hypolimnetic CH₄ fluxes at the sediment level based on measurements of bubble gas content and modeling of dissolved pore-water gases. We show that the relative ebullition flux pathway can be resolved by knowledge of only bubble gas content. As sediment CH₄ production, diffusion, and ebullition are interrelated, the addition of a second observation allows closing the entire sediment CH₄ balance. Such measurements could include bubble formation depth, sediment diffusive fluxes, ebullition, sediment CH₄ production, or the hypolimnetic CH₄ mass balance. The measurement of bubble gas content is particularly useful for identifying local ebullitive hotspots and integrating spatial heterogeneity of CH₄ fluxes. Our results further revealed the crucial effect of water column depth, production rates, and hypolimnetic dissolved CH₄ concentrations on sediment CH₄ dynamics. Although we apply the model to cohesive sediments in an anoxic hypolimnion, the model can be applied to shallow, oxic settings by altering the CH₄ production rate curve to account for oxidation. Utilizing our approach will provide a deeper understanding of in-lake CH₄ budgets, and thus improve CH₄ emission estimates from inland freshwaters at the regional and global scales.
We studied the methane (CH4) budget of Lake Baikal, the most voluminous lake in the world and the only freshwater body with known occurrences of methane hydrates in the sediments. CH4 concentrations ...were measured in water samples taken during six expeditions between October 2002 and June 2004; these expeditions covered the entire lake volume. A one-dimensional model was applied to (1) estimate the large-scale vertical CH4 fluxes within the South Basin of Lake Baikal, (2) determine the exchange with the atmosphere, and (3) constrain the CH4 inputs from seeps and mud volcanoes to the deep water. Fluxes were generally several orders of magnitude below previous estimates. The annual internal source of CH4 to the pelagic surface mixed layer was roughly estimated to be $40 Mg CH_4$. A large part of this input diffuses downwards and is consumed in the water column, with a CH4 residence time of about 4 yr. The input of CH4 from deep gas seeps and mud volcanoes is less than a few $10 Mg CH_{4} yr^{-1}$, most of which is oxidized before reaching the surface. The net CH4 flux between the atmosphere and the main waterbody distant from shallow areas is negligible and not significantly different from zero. However, occasional high CH4 concentrations, both in the surface water and in the atmosphere, indicate that the region near the Selenga delta is a local CH4 source to the atmosphere. CH4 fluxes in the Central Basin are very similar to those in the South Basin, whereas in the North Basin, the shallow CH4 sources are weaker.
The National Center for Biotechnology Information (NCBI) hosts 39 literature and molecular biology databases containing almost half a billion records. As the complexity of these data and associated ...resources and tools continues to expand, so does the need for educational resources to help investigators, clinicians, information specialists and the general public make use of the wealth of public data available at the NCBI. This review describes the educational resources available at NCBI via the NCBI Education page (www.ncbi.nlm.nih.gov/Education/). These resources include materials designed for new users, such as About NCBI and the NCBI Guide, as well as documentation, Frequently Asked Questions (FAQs) and writings on the NCBI Bookshelf such as the NCBI Help Manual and the NCBI Handbook. NCBI also provides teaching materials such as tutorials, problem sets and educational tools such as the Amino Acid Explorer, PSSM Viewer and Ebot. NCBI also offers training programs including the Discovery Workshops, webinars and tutorials at conferences. To help users keep up-to-date, NCBI produces the online NCBI News and offers RSS feeds and mailing lists, along with a presence on Facebook, Twitter and YouTube.
HLA and KIR are diverse and rapidly evolving gene complexes that work together in human immunity mediated by cytolytic lymphocytes. Understanding their complex immunogenetic interaction requires ...study of both HLA and KIR diversity in the same human population. Here a panel of 72 unrelated north Indian Hindus was analyzed. HLA- A, B, C, DRB1, DQA1, and DQB1 alleles and their frequencies were determined by sequencing or high-resolution typing of genomic DNA; KIR genotypes were determined by gene-specific typing and by allele-level DNA typing for KIR2DL1, 2DL3, 2DL5, 3DL1, and 3DL2. From HLA analysis, the north Indian population is seen to have several characteristics shared either with Caucasian or East Asian populations, consistent with the demographic history of north India, as well as specific features, including several alleles at high frequency that are rare or absent in other populations. A majority of the north Indian KIR gene profiles have not been seen in Caucasian and Asian populations. Most striking is a higher frequency of the B group of KIR haplotypes, resulting in equal frequencies for A and B group haplotypes in north Indians. All 72 members of the north Indian panel have different HLA genotype and different KIR genotype.
Elinor Ostrom's IAD and SES frameworks are widely used among social scientists, but each framework suffers from significant problems not shared by the other. The IAD framework lacks detail in terms ...of the specific social and ecological variables that influence social interactions, resulting in inconsistent applications of a supposedly common framework. The SES framework was designed specifically to resolve that problem, but has lost the dynamic character of the IAD framework. As a result it excels at identifying configurations of social, ecological and institutional factors associated with outcomes, but cannot explain the process by which these factors interact across action situations to generate those outcomes, let alone predict or prescribe changes to social-ecological conditions over time. This article seeks to remedy the problems of each framework by combining them to facilitate detailed and process-oriented studies of social-ecological systems. We then demonstrate the utility of the combined IAD-SES framework by applying it to describe the historical development of Maine's lobster fishery. Future applications of the framework have the potential to address several longstanding questions in the literature on common-pool resources regarding the role of history, power and dynamic social and ecological processes in influencing prospects for environmental sustainability.
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