22,365 research outputs found
Experimental investigation of open-ended microwave oven assisted encapsulation process
An open ended microwave oven is presented with improved uniform heating, heating rates and power conversion efficiency. This next generation oven produces more uniform EM fields in the evanescent region forming part of the heating area of the oven. These fields are vital for the rapid and uniform heating of various electromagnetically lossy materials. A fibre optic temperature sensor and an IR pyrometer are used to measure in situ and in real-time the temperature of the curing materials. An automatic computer controlled closed feedback loop measures the temperature in the curing material and drives the microwave components to
obtain predetermined curing temperature cycles for efficient curing. Uniform curing of the lossy encapsulants
is achieved with this oven with typical cure cycle of 270
seconds with a ramp rate of 1oC/s and a hold period of 2
minutes. Differential scanning calorimeter based measurement for the pulsed microwave based curing of
the polymer dielectric indicates a ~ 100% degree of cure
Fine Structure of the 1s3p ^3P_J Level in Atomic ^4He: Theory and Experiment
We report on a theoretical calculation and a new experimental determination
of the 1s3p ^3P_J fine structure intervals in atomic ^4He. The values from the
theoretical calculation of 8113.730(6) MHz and 658.801(6) MHz for the nu_{01}
and nu_{12} intervals, respectively, disagree significantly with previous
experimental results. However, the new laser spectroscopic measurement reported
here yields values of 8113.714(28) MHz and 658.810(18) MHz for these intervals.
These results show an excellent agreement with the theoretical values and
resolve the apparent discrepancy between theory and experiment.Comment: 9 pages, 3 figure
RR LYRAE VARIABLE STARS: PULSATIONAL CONSTRAINTS RELEVANT TO THE OOSTERHOFF CONTROVERSY
A solution to the old Oosterhoff controversy is proposed on the basis of a
new theoretical pulsational scenario concerning RR Lyrae cluster variables
(Bono and coworkers). We show that the observed constancy of the lowest
pulsation period in both Oosterhoff type I (OoI) and Oosterhoff type II (OoII)
prototypes (M3, M15) can be easily reproduced only by assuming the canonical
evolutionary horizontal-branch luminosity levels of these Galactic globular
clusters and therefore by rejecting the Sandage period shift effect (SPSE).Comment: postscript file of 7 pages and 2 figures; one non postcript figure is
available upon request; for any problem please write to
[email protected]
Climatically driven loss of calcium in steppe soil as a sink for atmospheric carbon
During the last several thousand years the semiâarid, cold climate of the Russian steppe formed highly fertile soils rich in organic carbon and calcium (classified as Chernozems in the Russian system). Analysis of archived soil samples collected in Kemannaya Steppe Preserve in 1920, 1947, 1970, and fresh samples collected in 1998 indicated that the native steppe Chernozems, however, lost 17â28 kg mâ2 of calcium in the form of carbonates in 1970â1998. Here we demonstrate that the loss of calcium was caused by fundamental shift in the steppe hydrologic balance. Previously unleached soils where precipitation was less than potential evapotranspiration are now being leached due to increased precipitation and, possibly, due to decreased actual evapotranspiration. Because this region receives low levels of acidic deposition, the dissolution of carbonates involves the consumption of atmospheric CO2. Our estimates indicate that this climatically driven terrestrial sink of atmospheric CO2 is âŒ2.1â7.4 g C mâ2 aâ1. In addition to the net sink of atmospheric carbon, leaching of pedogenic carbonates significantly amplified seasonal amplitude of CO2 exchange between atmosphere and steppe soil
Response to âAssessing the energy requirements and global warming potential of the production of rare earth elementsâ
This is the final version. Available on open access from Elsevier via the DOI in this recordIn this letter, we respond to the article in this journal by Weng et al. (2016) which performs a cradle to gate scale life cycle impact assessment for 26 operating and potential rare earth element (REE) mining projects. The work focuses on gross energy requirement and the global warming impacts of the primary REE production stage. The results suggest that the declining ore grades of REE significantly increase the environmental impact of REE production. We agree that a life cycle impact approach can be useful in comparing proposed REE production routes in the various different deposits currently under exploration, and were pleased to see a range of deposit types included in this work. However, we would like to make five points to clarify some of the results, which if taken at âface valueâ from the graphs presented by Weng et al. (2016) may be misleading.Research was funded by SoS RARE NERC consortium (NE/
M011429/1), www.sosrare.org with University of Exeter cofunding
for R. Pellâs PhD project. Mkango Resources Ltd, owners
of the Songwe Hill exploration project, are one of the industry partners
on this project
Applying and advancing the economic resource scarcity potential (ESP) method for rare earth elements
This is the author accepted manuscript. The final version is available on open access from Elsevier via the DOI in this record.A number of studies have identified rare earth elements (REE) as critical metals due to their
high economic importance combined with a high risk of supply disruption (Du et al, 2011;
Nassar et al, 2015; Schneider et al, 2014). The current methods used to calculate resource
depletion in life cycle assessments (LCA) neglect socio-economic, regulatory and
geopolitical aspects, nor do they include functionalities such as material recycling or reuse
that control the supply of raw materials. These are important factors in determining criticality
and are the controlling factors on REE availability rather than geological availability. The
economic scarcity potential (ESP) method introduced by Schneider et al. (2014) provides a
framework to calculate criticality. This paper reviews the ESP method and advances the
method based on recent developments in material criticality. ESP criticality scores for 15
REE with the addition of Au, Cu, platinum-group metals (PGM), Fe and Li are measured.
The results highlight that Nd and Dy are the most critical REE, owing mainly to the high
demand growth forecast for these two elements. A pathway is presented for incorporating
these calculated scores into the ReCiPe life cycle impact assessment (LCIA) method of a
LCA.Research was funded by NERC SoS RARE consortium (NE/M011429/1), www.sosrare.org with University of Exeter co-funding for R. Pellâs PhD project. The authors appreciate the funding assistance from the Camborne School of Mines Trust to visit and present this research in USA and gain insight from the Critical Metals team from Yale University and Nedal Nassar and his team at USGS
Asymptotic defectiveness of manufacturing plants: an estimate based on process learning curves
The paper describes a method for a preliminary estimation of asymptotic defectiveness of a manufacturing plant based on the prediction of its learning curve estimated during a p-chart setting up. The proposed approach provides process managers with the possibility of estimating the asymptotic variability of the process and the period of revision of p-chart control limits. An application of the method is also provided
Peeled film GaAs solar cells for space power
Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg
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