2,142 research outputs found
Testing isomorphism of graded algebras
We present a new algorithm to decide isomorphism between finite graded
algebras. For a broad class of nilpotent Lie algebras, we demonstrate that it
runs in time polynomial in the order of the input algebras. We introduce
heuristics that often dramatically improve the performance of the algorithm and
report on an implementation in Magma
Effect of pre-milking teat disinfection on new mastitis infection rates of dairy cows
peer-reviewedBackground
The practise of teat disinfection prior to cluster attachment for milking is being adopted by farmers in Ireland, particularly where there are herd issues with new infection rates. Pre-milking teat disinfection has been shown to reduce bacterial numbers on teat skin and to be most effective against environmental bacteria such as Escherichia coli and Streptococcus uberis. A split udder design experiment was undertaken on two research herds (Aβ=β96 cows: Bβ=β168 cows) to test the benefit of pre-milking teat disinfection on new mastitis infection levels. The disinfectant was applied to the left front and right hind teats of all cows in each herd and the right front and left hind teats received no disinfectant treatment prior to milking over a complete lactation. Individual quarter foremilk samples were taken on 5 occasions during the lactation and all clinical cases were recorded. The presence and number of staphylococcus and streptococcus bacteria on teat skin of a random sample of experimental cows (nβ=β20) was measured on 3 occasions during lactation (April, June, and October).
Results
Pre-milking teat disinfection had no significant impact on quarter SCC and new infection rates (Pβ>β0.05). The median SCC was 169 (95% CIβ=β144β198) Γβ103 cells/mL and 170 (95% CIβ=β145β199)βΓβ103 cells/mL for disinfected teats and non-disinfected teats, respectively. There were no differences in SCC observed between herds (Aβ=β161 (95% CIβ=β127β205)βΓβ103 cells/mL; Bβ=β169 (95% CIβ=β144β198)βΓβ103 cells/mL) over the complete lactation. Bacterial levels on teat skin were reduced significantly with pre-milking teat disinfection compared to teats receiving no disinfectant (Pβ<β0.001). Total infections (clinical and sub-clinical) were similar for disinfected teats (nβ=β36) and not disinfected teats (nβ=β40), respectively. Staphylococcus aureus (nβ=β47) and Strep. uberis (nβ=β9) were identified as the predominant bacteria in quarter foremilk samples with both clinical and sub-clinical infections.
Conclusion
SCC and new infection rates were similar in non-disinfected teats and disinfected (pre-milking) teats. The routine application of pre-milking teat disinfectant in pasture-grazed herds is unlikely to be of benefit where herd SCC is below 200βΓβ103 cells/mL
System Evaluation and Life-Cycle Cost Analysis of a Commercial-Scale High-Temperature Electrolysis Hydrogen Production Plant
Results of a system evaluation and lifecycle cost analysis are presented for a commercial-scale high-temperature electrolysis (HTE) central hydrogen production plant. The plant design relies on grid electricity to power the electrolysis process and system components, and industrial natural gas to provide process heat. The HYSYS process analysis software was used to evaluate the reference central plant design capable of producing 50,000 kg/day of hydrogen. The HYSYS software performs mass and energy balances across all components to allow optimization of the design using a detailed process flow sheet and realistic operating conditions specified by the analyst. The lifecycle cost analysis was performed using the H2A analysis methodology developed by the Department of Energy (DOE) Hydrogen Program. This methodology utilizes Microsoft Excel spreadsheet analysis tools that require detailed plant performance information (obtained from HYSYS), along with financial and cost information to calculate lifecycle costs. The results of the lifecycle analyses indicate that for a 10% internal rate of return, a large central commercial-scale hydrogen production plant can produce 50,000 kg/day of hydrogen at an average cost of 0.40/kg to $3.08/kg
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3D CFD Electrochemical and Heat Transfer Model of an Integrated-Planar Solid Oxide Electrolysis Cells
A three-dimensional computational fluid dynamics (CFD) electrochemical model has been created to model high-temperature electrolysis cell performance and steam electrolysis in a new novel integrated planar porous-tube supported solid oxide electrolysis cell (SOEC). The model is of several integrated planar cells attached to a ceramic support tube. This design is being evaluated with modeling at the Idaho National Laboratory. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, activation over-potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean per-cell area-specific-resistance (ASR) values decrease with increasing current density. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Effects of variations in operating temperature, gas flow rate, cathode and anode exchange current density, and contact resistance from the base case are presented. Contour plots of local electrolyte temperature, current density, and Nernst potential indicated the effects of heat transfer, reaction cooling/heating, and change in local gas composition. Results are discussed for using this design in the electrolysis mode. Discussion of thermal neutral voltage, enthalpy of reaction, hydrogen production, cell thermal efficiency, cell electrical efficiency, and Gibbs free energy are discussed and reported herein
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TEST RESULTS OF HIGH TEMPERATURE STEAM/CO2 CO-ELECTROLYSIS IN A 10-CELL STACK
High temperature coelectrolysis experiments with CO2 / H2O mixtures were performed in a 10-cell planar solid oxide stack. Results indicated that stack apparent ASR values were shown not to vary significantly between pure steam electrolysis and steam / CO2 coelectrolysis values. Product gas compositions measured via an online micro gas chromatograph (GC) showed excellent agreement to predictions obtained from a chemical equilibrium coelectrolysis model developed for this study. Experimentally determined open cell potentials and thermal neutral voltages for coelectrolysis compared favorably to predictions obtained from a chemical equilibrium coelectrolysis and energy balance model, also developed for this study
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Results Of Recent High Temperature Co-Electrolysis Studies At The Idaho National Laboratory
For the past several years, the Idaho National Laboratory and Ceramatec, Inc. have been studying the feasibility of high temperature solid oxide electrolysis for large-scale, nuclear-powered hydrogen production. Parallel to this effort, the INL and Ceramatec have been researching high temperature solid oxide co-electrolysis of steam/CO2 mixtures to produce syngas, the raw material for synthetic fuels production. When powered by nuclear energy, high temperature co-electrolysis offers a carbon-neutral means of syngas production while consuming CO2. The INL has been conducting experiments to characterize the electrochemical performance of co-electrolysis, as well as validate INL-developed computer models. An inline methanation reactor has also been tested to study direct methane production from co-electrolysis products. Testing to date indicate that high temperature steam electrolysis cells perform equally well under co-electrolysis conditions. Process model predictions compare well with measurements for outlet product compositions. The process appears to be a promising technique for large-scale syngas production
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Test Plan for Long-Term Operation of a Ten-Cell High Temperature Electrolysis Stack
This document defines a test plan for a long-term (2500 Hour) test of a ten-cell high-temperature electrolysis stack to be performed at INL during FY09 under the Nuclear Hydrogen Initiative. This test was originally planned for FY08, but was removed from our work scope as a result of the severe budget cuts in the FY08 NHI Program. The purpose of this test is to evaluate stack performance degradation over a relatively long time period and to attempt to identify some of the degradation mechanisms via post-test examination. This test will be performed using a planar ten-cell Ceramatec stack, with each cell having dimensions of 10 cm Γ 10 cm. The specific makeup of the stack will be based on the results of a series of shorter duration ten-cell stack tests being performed during FY08, funded by NGNP. This series of tests was aimed at evaluating stack performance with different interconnect materials and coatings and with or without brazed edge rails. The best performing stack from the FY08 series, in which five different interconnect/coating/edge rail combinations were tested, will be selected for the FY09 long-term test described herein
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SYNGAS PRODUCTION VIA HIGH-TEMPERATURE CO-ELECTROLYSIS OF STEAM AND CARBON DIOXIDE IN A SOLID-OXIDE STACK
This paper presents results of recent experiments conducted at the INL studying coelectrolysis of steam and carbon dioxide in a 10-cell high-temperature solid-oxide electrolysis stack. Coelectrolysis is complicated by the fact that the reverse shift reaction occurs concurrently with the electrolytic reduction reactions. All reactions must be properly accounted for when evaluating results. Electrochemical performance of the stack was evaluated over a range of temperatures, compositions, and flow rates. The apparatus used for these tests is heavily instrumented, with precision mass-flow controllers, on-line dewpoint and CO2 sensors, and numerous pressure and temperature measurement stations. It also includes a gas chromatograph for analyzing outlet gas compositions. Comparisons of measured compositions to predictions obtained from a chemical equilibrium co-electrolysis model are presented, along with corresponding polarization curves. Results indicate excellent agreement between predicted and measured outlet compositions. Coelectrolysis significantly increases the yield of syngas over the reverse water gas shift reaction equilibrium composition. The process appears to be a promising technique for large-scale syngas production
System Evaluations and Life-Cycle Cost Analyses for High-Temperature Electrolysis Hydrogen Production Facilities
This report presents results of system evaluations and lifecycle cost analyses performed for several different commercial-scale high-temperature electrolysis (HTE) hydrogen production concepts. The concepts presented in this report rely on grid electricity and non-nuclear high-temperature process heat sources for the required energy inputs. The HYSYS process analysis software was used to evaluate both central plant designs for large-scale hydrogen production (50,000 kg/day or larger) and forecourt plant designs for distributed production and delivery at about 1,500 kg/day. The HYSYS software inherently ensures mass and energy balances across all components and it includes thermodynamic data for all chemical species. The optimized designs described in this report are based on analyses of process flow diagrams that included realistic representations of fluid conditions and component efficiencies and operating parameters for each of the HTE hydrogen production configurations analyzed. As with previous HTE system analyses performed at the INL, a custom electrolyzer model was incorporated into the overall process flow sheet. This electrolyzer model allows for the determination of the average Nernst potential, cell operating voltage, gas outlet temperatures, and electrolyzer efficiency for any specified inlet steam, hydrogen, and sweep-gas flow rates, current density, cell active area, and external heat loss or gain. The lifecycle cost analyses were performed using the H2A analysis methodology developed by the Department of Energy (DOE) Hydrogen Program. This methodology utilizes spreadsheet analysis tools that require detailed plant performance information (obtained from HYSYS), along with financial and cost information to calculate lifecycle costs. There are standard default sets of assumptions that the methodology uses to ensure consistency when comparing the cost of different production or plant design options. However, these assumptions may also be varied within the spreadsheets when better information is available or to allow the performance of sensitivity studies. The selected reference plant design for this study was a 1500 kg/day forecourt hydrogen production plant operating in the thermal-neutral mode. The plant utilized industrial natural gas-fired heaters to provide process heat, and grid electricity to supply power to the electrolyzer modules and system components. Modifications to the reference design included replacing the gas-fired heaters with electric resistance heaters, changing the operating mode of the electrolyzer (to operate below the thermal-neutral voltage), and considering a larger 50,000 kg/day central hydrogen production plant design. Total H2A-calculated hydrogen production costs for the reference 1,500 kg/day forecourt hydrogen production plant were 3.55/kg and 2.89/kg
The role of molecular testing and enzyme analysis in the management of hypomorphic citrullinemia
No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69185/1/33256_ftp.pd
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