2,046 research outputs found
Kinetics of helium bubble formation in nuclear materials
The formation and growth of helium bubbles due to self-irradiation in
plutonium has been modelled by a discrete kinetic equations for the number
densities of bubbles having atoms. Analysis of these equations shows that
the bubble size distribution function can be approximated by a composite of:
(i) the solution of partial differential equations describing the continuum
limit of the theory but corrected to take into account the effects of
discreteness, and (ii) a local expansion about the advancing leading edge of
the distribution function in size space. Both approximations contribute to the
memory term in a close integrodifferential equation for the monomer
concentration of single helium atoms.
The present boundary layer theory for discrete equations is compared to the
numerical solution of the full kinetic model and to previous approximation of
Schaldach and Wolfer involving a truncated system of moment equations.Comment: 24 pages, 6 figures, to appear in Physica
A systematic study of element mobilisation from gas shales during hydraulic fracturing
The large quantities of wastewater produced throughout the lifetime of a shale gas well can contain heavy metals and other regulated potentially toxic elements. These can be mobilised from the target formation by some of the additives present in the hydraulic fracturing fluids (HFF). High levels of inorganic geogenic chemicals may pose a hazard to the environment through accidental releases such as spills of untreated wastewater. The concentration of mobilised elements and the hazard they pose is uncertain and is likely dependant on the chemical agents used in HFF, groundwater composition and the trace element content of targeted shale gas formation. Laboratory protocols were developed to investigate the release of inorganic contaminants of potential concern (e.g. As, Co, Cu, Pb, Se) from shale gas formations around the world. Powdered rock samples were leached for up to 360 hours at elevated temperature (80Ā°C) and a range of pressures (1-200 bar), with synthetic HFF and synthetic groundwater (SGW). Elemental concentrations released into solution were generally much higher in the HFF leachates than in the SGW treatments, indicating that the chemical additives in the HFF influenced element mobilisation. SEM and EDX images show substantial mineral etching and precipitation of secondary phases on shale chips leached for 360 hours with HFF at 80Ā°C and ~180 bar when compared to the SGW experiment. Time-series data also show evidence of mineral dissolution and subsequent precipitation of new phases, which resulted in sequestration of a number of trace elements that were initially mobilised into the solution. We also observed that the carbonate content of the unreacted shale sample had a strong control on the final pH of the HFF leachates. This study shows that additives can enhance the release of geogenic chemicals, but also that subsequent precipitation within the fracture system could limit ultimate release to surface
Design Aspects on Winding of an MgB<sub>2</sub> Superconducting Generator Coil
AbstractGenerators based on superconducting rotor coils are considered for future large off-shore wind turbines for their low weight and compact design, and for their possibility to reduce costs. In the 10-20 K temperature range, MgB2 superconductors carry current densities 100 times higher than standard copper conductors at room temperature at one tenth of the wire cost per unit carried current. In the framework of the European project INNWIND.EU, an MgB2 superconducting generator pole will be designed, built and tested. Some of the design aspects of this work with emphasis on the winding process and associated coil insulation are discussed. An overall high current density in the coil is of crucial importance to obtain clear benefits compared to conventional solutions. The wire itself may be the most important parameter in that respect. However, the overall current density of the coil is also influenced by the thickness of the turn-to-turn electrical insulation. Here we discuss the impact of the insulation and suggest the use of a one-step winding process, employing wet-winding, where the applied epoxy also constitutes the insulation layer between turns. In this way the coil is densified by approximately 10% compared to the use of an additional, dedicated, electrical insulation like Kapton for wet-winding or glass-fibre for dry-winding followed by vacuum impregnation. We show the results of a trial winding of 500 m of MgB2 superconducting wire into a double pancake coil using the wet-winding technique. The coil is tested for contacts between the turns to evaluate the suggested one-step wet-winding process
Comparison of site-specific and conventional uniform irrigation management for potatoes
Site-Specific Irrigation Management (SSIM) can be defined as irrigation management (depth, timing) based on
crop need to defined sub-areas of a field referred to as management zones. Implementation of SSIM will require additional
irrigation system hardware, labor, and information on soil and/or plant water status in each management zone. Costs
associated with these additional requirements will need to be offset by increased receipts from improved crop yield and quality
in order for the technology to be adopted by producers. The potential for SSIM to increase crop yield, quality, and economic
return has not been evaluated in field studies. Crops such as potatoes, for which yield and quality are highly sensitive to soil
water availability, are most likely to show an economic benefit from site-specific irrigation management. A two-year field
study was conducted to evaluate the potential for SSIM to increase yield and quality of potatoes relative to Conventional
Uniform Irrigation Management (CUIM). Near real-time soil water content was used to schedule irrigations under both
irrigation management treatments. Field average water application was nearly the same for the irrigation management
treatments, 503 mm (19.8 in.) in 2001 and 445 mm (17.5 in.) in 2002. In both study years, tuber yield distributions trended
4% greater under site-specific irrigation management but were not significantly different (p < 0.05). Total tuber yield per
unit of water applied from irrigation and precipitation was 4% greater in 2001 and 6% greater in 2002 under SSIM. Based
on a local tuber quality adjusted potato processing contract price structure, the trend in gross income averaged across the
field site was 65/acre) greater with SSIM. This increase in gross income is likely about half the actual cost of
commercial site-specific irrigation technology. The required 3- to 5-year crop rotation for potato disease management means
that the site-specific irrigation system needs to be mobile or an economic benefit must also be realized from other crops in
the rotation. The economic benefit of SSIM needs to be increased or realized for other crops in the rotation for it to be an
economically viable technology in potato production systems in Idaho
Potato Irrigation Management
Potato yield and quality are sensitive to both excess and deficit soil water. This sensitivity, coupled with a relatively shallow root zone and medium- to coarse -textured soils common in many production areas, makes economically efficient irrigated potato production challenging. Potato is grown under all types of irrigation systems worldwide, but irrigation systems capable of light, frequent, uniform water application are best. Optimum potato irrigation management requires a working knowledge of soil water relations and irrigation system characteristics. This chapter introduces both in the context of potato production in arid areas of the Pacific Northwest U.S. General guidelines and irrigation management aids are presented along with examples for implementing quantitative irrigation management of potato in an arid environment
Heat transfer enhancement in single impinging jets due to surface cavities
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This paper presents an assessment of a novel technique that
further enhances the heat transfer potential of a single
impinging jet. The method entails a geometrical modification
to the jet impingement surface wherein the jet is directed into a
cylindrical cavity located coaxially beneath the jet orifice.
A numerical study is performed to examine the parametric
influence on heat dissipation and flow characteristics of this
modified jet impingement process. The results indicate a very
significant increase in heat transfer, which is primarily
dependent on cavity depth and jet Reynolds number.cs201
Stellar contents and Star formation in the young cluster Stock 18
We have carried out deep (V21 mag) \ubvri photometric study of the star
cluster Stock 18. These along with archival Infrared data have been used to
derive the basic cluster parameters and also to study the star formation
processes in and around the cluster region. The distance to the cluster is
derived as 2.80.2 kpc while its age is estimated as Myr.
Present study indicates that interstellar reddening is normal in the direction
of the cluster. The mass function slope is found to be -1.370.27 for the
mass range 111.9. There is no evidence found for the effect of
mass segregation in main-sequence stars of the cluster. A young stellar
population with age between 1-2 Myr have been found in and around the cluster
region. The presence of IRAS and AKARI sources with MSX intensity map also show
the youth of the Sh2-170 region.Comment: 25 pages, 11 figures, 3 tables (Accepted for publication in New
Astronomy
An open extensible tool environment for Event-B
Abstract. We consider modelling indispensable for the development of complex systems. Modelling must be carried out in a formal notation to reason and make meaningful conjectures about a model. But formal modelling of complex systems is a difficult task. Even when theorem provers improve further and get more powerful, modelling will remain difficult. The reason for this that modelling is an exploratory activity that requires ingenuity in order to arrive at a meaningful model. We are aware that automated theorem provers can discharge most of the onerous trivial proof obligations that appear when modelling systems. In this article we present a modelling tool that seamlessly integrates modelling and proving similar to what is offered today in modern integrated development environments for programming. The tool is extensible and configurable so that it can be adapted more easily to different application domains and development methods.
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