1,840,914 research outputs found

    Models of Hawaiian volcano growth and plume structure: Implications of results from the Hawaii Scientific Drilling Project

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    The shapes of typical Hawaiian volcanoes are simply parameterized, and a relationship is derived for the dependence of lava accumulation rates on volcano volume and volumetric growth rate. The dependence of lava accumulation rate on time is derived by estimating the eruption rate of a volcano as it traverses the Hawaiian plume, with the eruption rate determined from a specified radial dependence of magma generation in the plume and assuming that a volcano captures melt from a circular area centered on the volcano summit. The timescale of volcano growth is t = 2 R/Ī½_plate where R is the radius of the melting zone of the (circular) plume and Ī½plate is the velocity of the Pacific plate. The growth progress of a volcano can be described by a dimensionless time tā€² = tĪ½_plate/2R, where tā€² = 0 is chosen to be the start of volcano growth and tā€² = 1 approximates the end of ā€œshieldā€ growth. Using a melt generation rate for the whole plume of 0.2 km^(3)/yr, a plume diameter of 50 km, and a plate velocity of 10 cm/yr, we calculate that the lifetime of a typical volcano is 1000 kyr. For a volcano that traverses the axis of the plume, the ā€œstandardā€ dimensions are a volume of 57,000 km^3, a summit thickness of 18 km, a summit elevation of 3.6 km, and a basal radius of 60 km. The volcano first breaches the sea surface at tā€² ā‰ˆ 0.22 when it has attained only 5% of its eventual volume; 80% of the volume accumulates between tā€² = 0.3 and tā€² = 0.7. Typical lava accumulation rates start out over 50 m/kyr in the earliest stages of growth from the seafloor, and level out at āˆ¼35 m/kyr from tā€² ā‰ˆ 0.05 until tā€² = 0.4. From tā€² = 0.4 to tā€² = 0.9, the submarine lava accumulation rates decrease almost linearly from 35 m/kyr to āˆ¼0; subaerial accumulation rates are about 30% lower. The lava accumulation rate is a good indicator of volcano age. A volcano that passes over the plume at a distance 0.4R off to the side of the plume axis is predicted to have a volume of about 60% of the standard volcano, a lifetime about 8% shorter, and lava accumulation rates about 15ā€“20% smaller. The depth-age data for Mauna Kea lavas cored by the Hawaii Scientific Drilling Project are a good fit to the model parameters used, given that Mauna Kea appears to have crossed the plume about 15ā€“20 km off-axis. The lifetime of Mauna Kea is estimated to be 920 kyr. Mauna Loa is predicted to be at a stage corresponding to tā€² ā‰ˆ 0.8, Kilauea is at tā€² ā‰ˆ 0.6, and Loihi is at tā€² ā‰ˆ0.16. The model also allows the subsurface structure of the volcanoes (the interfaces between lavas from different volcanoes) to be modeled. Radial geochemical structure in the plume may be blurred in the lavas because the volcanoes capture magma from a sizeable cross-sectional area of the plume; this inference is qualitatively born out by available isotopic data. The model predicts that new Hawaiian volcanoes are typically initiated on the seafloor near the base of the next older volcano but generally off the older volcano's flank

    Estimating drizzle drop size and precipitation rate using two-colour lidar measurements

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    A method to estimate the size and liquid water content of drizzle drops using lidar measurements at two wavelengths is described. The method exploits the differential absorption of infrared light by liquid water at 905 nm and 1.5 Ī¼m, which leads to a different backscatter cross section for water drops larger than ā‰ˆ50 Ī¼m. The ratio of backscatter measured from drizzle samples below cloud base at these two wavelengths (the colour ratio) provides a measure of the median volume drop diameter D0. This is a strong effect: for D0=200 Ī¼m, a colour ratio of ā‰ˆ6 dB is predicted. Once D0 is known, the measured backscatter at 905 nm can be used to calculate the liquid water content (LWC) and other moments of the drizzle drop distribution. The method is applied to observations of drizzle falling from stratocumulus and stratus clouds. High resolution (32 s, 36 m) profiles of D0, LWC and precipitation rate R are derived. The main sources of error in the technique are the need to assume a value for the dispersion parameter Ī¼ in the drop size spectrum (leading to at most a 35% error in R) and the influence of aerosol returns on the retrieval (ā‰ˆ10% error in R for the cases considered here). Radar reflectivities are also computed from the lidar data, and compared to independent measurements from a colocated cloud radar, offering independent validation of the derived drop size distributions

    Characterisation of microstructure and creep properties of alloy 617 for high-temperature applications

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    Current energy drivers are pushing research in power generation materials towards improved efficiency and improved environmental impact. In the context of new generation ultra-supercritical (USC) power plant, this is represented by increased efficiency, service temperature reaching 750. Ā°C, pressures in the range of 35-37.5. MPa and associated carbon capture technology. Ni base alloys are primary candidate materials for long term high temperature applications such as boilers. The transition from their current applications, which have required lower exposure times and milder corrosive environments, requires the investigation of their microstructural evolution as a function of thermo-mechanical treatment and simulated service conditions, coupled with modelling activities that are able to forecast such microstructural changes. The lack of widespread microstructural data in this context for most nickel base alloys makes this type of investigation necessary and novel. Alloy INCONEL 617 is one of the Ni-base candidate materials. The microstructures of four specimens of this material crept at temperatures in the 650-750. Ā°C range for up to 20,000. h have been characterised and quantified. Grain structure, precipitate type and location, precipitate volume fraction, size and inter-particle spacing have been determined. The data obtained are used both as input for and validation of a microstructurally-based CDM model for forecasting creep properties

    Some Environmental Policy Implications of Recycling Paper Products in Western Europe

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    We live in a wasteful society, and are becoming increasingly aware of this fact. Our concern for conservation of our natural resources and about the deleterious effects on the environment of disposal of waste products is increasingly reflected in proposed legislation aimed at reducing waste. The preferred technique is recycling of waste products. While laudable in its objectives, a narrow focus on recycling is also limited, and can result in unexpected effects that can at least partially offset the expected benefits. This is particularly true of paper for at least three basic reasons. First, paper is a major component, about 35%, of household waste volume. Second, unlike most waste, paper has a very high energy content. And third, unlike coal or oil, paper is a renewable resource, and in Europe is produced mostly from forests managed on sustainable principles. This report summarizes a forthcoming feasibility study of large-scale paper recycling in Europe which investigated the entire production and disposal process using a "life-cycle" methodology and data base developed at IIASA

    Biological sulphate reduction with primary sewage sludge in an upflow anaerobic sludge bed reactor ā€“ Part 6: Development of a kinetic model for BSR

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    A 2-phase (aqueous-gas) kinetic model for biological sulphate reduction (BSR) using primary sewage sludge (PSS) as carbon source is presented. The methanogenic anaerobic digestion (AD) model of Sƶtemann et al. (2005) is extended by adding the biological, chemical and physical processes associated with BSR, i.e. propionic acid degrading sulphate-reducing bacteria (SRB), acetoclastic SRB and hydrogenotrophic SRB, the aqueous weak acid/base chemistry processes of the sulphate and sulphide systems and an aqueous-gas sulphide exchange process. The model is validated with experimental data from 2 upflow anaerobic sludge bed (UASB) reactors fed various PSS COD/SO42- ratios under constant flow and load conditions at 35Ā°C and 20Ā°C. The kinetic model results, including the reactor pH (within 0.1 pH unit) compare well with the experimental results and with those calculated from a steady-state BSR model. The kinetic model confirms that: (1) at ambient temperature (20Ā°C), the hydrolysis rate is significantly reduced compared with that at 35Ā°C, which requires a longer sludge age (larger bed volume) in the UASB reactor; (2) the hydrolysis rate of the PSS biodegradable particulate organics (BPO) is the same under methanogenic and sulphidogenic conditions; (3) the PSS BPO are carbon deficient for BSR in that more electrons are donated than carbon supplied for the required alkalinity increase, with the result that the sulphide system supplies the alkalinity deficit; and (4) due to (3) there is zero CO2 gas generation and in effect the sulphide system establishes the reactor pH. This observation allows the carbon content of the utilised organics to be determined from the H2CO3* alkalinity increase in the reactor, which can be simply measured by titration methods. Keywords: biological sulphate reduction, primary sewage sludge, upflow anaerobic sludge bed reactor, dynamic model, kinetics, stoichiometry, mixed weak acid/base chemistr

    Analysis of the particulate emissions and combustion performance of a direct injection spark ignition engine using hydrogen and gasoline mixtures

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    Three different fractions (2%, 5%, and 10% of stoichiometric, or 2.38%, 5.92%, and 11.73% by energy fraction) of hydrogen were aspirated into a gasoline direct injection engine under two different load conditions. The base fuel was 65% iso-octane, and 35% toluene by volume fraction. Ignition sweeps were conducted for each operation point. The pressure traces were recorded for further analysis, and the particulate emission size distributions were measured using a Cambustion DMS500. The results indicated a more stable and faster combustion as more hydrogen was blended. Meanwhile, a substantial reduction in particulate emissions was found at the low load condition (more than 95% reduction either in terms of number concentration or mass concentration when blending 10% hydrogen). Some variation in the results occurred at the high load condition, but the particulate emissions were reduced in most cases, especially for nucleation mode particulate matter. Retarding the ignition timing generally reduced the particulate emissions. An engine model was constructed using the Ricardo WAVE package to assist in understanding the data. The simulation reported a higher residual gas fraction at low load, which explained the higher level of cycle-by-cycle variation at the low load

    Targeted Treatment With Radio Frequency Ablation for Lingual Tonsil

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    Objectives:Benign enlargement of the lingual tonsils due to various causes may cause symptoms that warrant treatment. Conventional lingual tonsillectomy remains a challenging procedure, and there is no established standard procedure. We aimed to review the patients receiving different methods of lingual tonsil surgery for various indications at our institute.Methods:Retrospective clinical data on all patients with an ablative operation of the tongue base during the 8-year period between 2007 and 2014 at the Helsinki University Hospital, Helsinki, Finland, were reviewed. The larger cohort comprised 35 patients, of whom 26 were men (74%). Ten patients had undergone solely lingual tonsil radio frequency ablation (LTRFA). The minimum follow-up time for all patients was 2 years.Results:Of the 10 patients, 5 patients with LTRFA had been operated on because of symptomatic lingual tonsil hypertrophy and 5 because of periodic fever associated with possible lingual tonsil involvement. In 2 of the 5 patients with periodic fever, the fever cycles ended after the operation. Of the 5 patients, 3 patients with symptomatic lingual tonsil hypertrophy have been non-symptomatic after 1 to 3 treatment sessions. The last 2 patients continue to have persistent symptoms. There were no major complications.Conclusions:Development of new approaches for the management of various lingual tonsil conditions is warranted. Lingual tonsil volume reduction by LTRFA seems to be a treatment alternative with low morbidity but with limited curative effect only.Peer reviewe

    Dynamic capillary pressure analysis of tight sandstone based on digital rock model

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    In recent studies, dynamic capillary pressure has shown signiļ¬cant impacts on the ļ¬‚ow behaviors in porous media under transient ļ¬‚ow condition. However, the effect of dynamic capillary pressure effect on tight sandstone is still not very clear. Since lattice Boltzmann method (LBM) is a very promising and widely used method in analyzing ļ¬‚ow behaviors, therefore, a two-phase D3Q27 LBM model is adopted in this paper to simulate the ļ¬‚ow behaviors and analyze the dynamic capillary pressure effect in tight sandstone. Moreover, a new pore segmentation method for tight sandstone base on U-net deep learning model is implemented in this study to improve the pore boundary qualities of pore space, which is crucial for two-phase LBM simulation of tight sandstone. A total of 3800 3D sub-volume data sets extracted from computed tomography data of 19 tight sandstone samples are selected as ground truth data to train the network and segment the pore space afterward. The simulation results based on the segmented digital rock model, show that nonwetting phase ļ¬‚uid prefer the path with lower dynamic capillary pressure in the seepage process before breaking through the porous model. Furthermore, the increase of injection rate causes the saturation changes more quickly, injection rate also shows apparent positive correlation relationship with capillary pressure, which implies that dynamic capillary pressure effect also exists in tight sandstone, and LBM based two-phase ļ¬‚ow simulation could be used to quantitatively analyze such effect in tight sandstone.Cited as: Cao, Y., Tang, M., Zhang, Q., Tang, J., Lu, S. Dynamic capillary pressure analysis of tight sandstone based on digital rock model. Capillarity, 2020, 3(2): 28-35, doi: 10.46690/capi.2020.02.0

    Towards greener horizontal-axis wind turbines: Analysis of carbon emissions, energy and costs at the early design stage

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    This paper describes the development of a quantitative analysis system as a platform for rapidly estimate energy, costs and carbon emission to facilitate the comparison of different wind turbine concept designs. This system aimed specifically at wind turbine manufacturing processes due to the fact that a large proportion of the environmental, costs and energy impacts would occur at this stage. The proposed method supports an initial assessment of multiple design concepts which allows the selection and development of a ā€œgreenerā€ wind turbine. The developed system enables concept design of commercial wind turbine towers of hub heights between 44 and 135 m. The method supports an accurate estimation in regards to the dimension, energy consumed, maximum power output, costs and carbon emission in the early design phases of a wind turbine. As a result of the development, the proposed approach could potentially be used to minimise the carbon footprints of major engineering projects such as wind farms

    Energy Consumption Reduction Strategies for Plug-in Hybrid Electric Vehicles with Connected Vehicle Technology in an Urban Environment

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    Automobile manufacturers have introduced plug-in hybrid electric vehicles (PHEVs) to reduce fossil fuel consumption. This paper details three optimization strategies that can be utilized to further minimize energy consumption of PHEVs through an information exchange between PHEVs and infrastructure agents supported by the connected vehicle technology (CVT). While an earlier research by the authors focused on a freeway scenario, this study developed strategies for an urban scenario in which frequent ā€˜stop-and-goā€™ conditions exist. Three strategies were considered in this study based on different types of information availability using CVT; only signal timing information was available in Strategy One, only headway information was available in Strategy Two, and both signal timing and headway information were available in Strategy Three. The performance of PHEVs that received no real-time information was used as the base case for Strategies One, Two or Three to evaluate each strategy. The optimization strategies resulted in energy consumption savings ranging from 60% to 76%. An analysis with various levels of penetration of CVT-supported PHEVs in the traffic was conducted to demonstrate the impact of these optimization strategies with their increased market share. For a case study network, the authors found a linear trend between energy savings and penetration rate of CVT supported PHEVs. The Strategy Three in which signal timing and headway data were provided to CVT supported PHEVs, resulted in about 31% to 35% energy savings with 30% penetration of CVT supported PHEVs at the peak hour volume
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