544 research outputs found
Recommended from our members
Subfreezing operation of polymer electrolyte fuel cells: Ice formation and cell performance loss
In this work, we investigate the cold-start operation of polymer electrolyte fuel cells (PEFCs) through high-resolution neutron radiography, experimental testing, theoretical evaluation, and comparison with model prediction. Ice formation location, voltage evolution, and loss of the electro-catalyst surface area (ECSA) are examined. A dimensionless parameter , characterizing the spatial variation of the reaction rate across the cathode catalyst layer, is discussed at subfreezing temperature using newly determined membrane ionic conductivity. The evaluation identifies the operating range that the reaction rate can be treated uniform across the catalyst layer, in which the model is valid. © 2012 Elsevier Ltd. All rights reserved
Recommended from our members
An experimental study of polymer electrolyte fuel cell operation at sub-freezing temperatures
The ability of polymer electrolyte fuel cells (PEFCs) to startup at subfreezing temperatures is governed by whether it is able to overcome the freezing point (0°C) before product ice prevents the electrochemical reactions. In this work, we experimentally investigated the coulombs of charge Qc transferred in PEFCs under subfreezing operation before the output voltage drops to 0.0V. PEFCs with various membranes and catalyst-layer thicknesses, ionomer-carbon ratios, operating current density, and initial hydration of PEFCs were studied, and their influences on cold-start performance and coulombs of charge were experimentally measured. We find that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness, significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. © 2013 The Electrochemical Society
Energy innovation and competitiveness indicators. A contribution to Work Package 8 of the MEI project
Ph.d.-afhandling om Myōshinji
“Er du dybest set ikke bare en turist?”, spurgte en rinzai zen-mester (shike) mig engang, da jeg interviewede ham om forskellige ting vedrørende hans liv. En så udtalt mistænkeliggørelse af, hvad jeg i det mindste selv betragtede som en plausibel, akademisk metode, er naturligvis ikke ny. At studere levende religion ved at inddrage andet og mere end klassiske og ‘rigtige’ tekster anses ofte som helligbrøde ikke blot på universitære institutioner, men også hos skolastisk sindede buddhister. De fleste feltarbejdere inden for buddhismen vil på et eller andet tidspunkt blive dirigeret hen mod helligteksterne, for der står sandhederne. Eller de vil blive præsenteret for meditationsmesteren, der ....
Comparison of nuclear imaging techniques and volumetric imaging for the prediction of postoperative mortality and liver failure in patients undergoing localized liver-directed treatments:a systematic review
BACKGROUND/AIMS: Although volumetric imaging by computed tomography (CT) is the gold standard for preoperative assessment of the future liver remnant, nuclear imaging studies have shown promising data. This systematic review summarized the results from trials investigating volumetric and nuclear medicine imaging for the prediction of postoperative mortality and liver failure (LF). METHODS: MEDLINE and Web of Science were searched for papers investigating nuclear imaging methods for the prediction of postoperative clinical outcomes in patients undergoing local, liver-directed treatments. Only papers investigating both preoperative nuclear imaging and CT or magnetic resonance imaging (MR) for the prediction of postoperative mortality and/or LF were included. RESULTS: Twenty-five trials were qualified for this review. All trials but two used technetium-based tracers for the nuclear imaging examination. Four papers used MR imaging and the remaining used CT for the volumetric evaluation. Overall, the studies were heterogeneous both in terms of methodology and imaging technique. Of the thirteen studies reporting on postoperative mortality, most were descriptive without detailed diagnostic data. A few with detailed data found that nuclear imaging had better predictive value than volumetric imaging. Nineteen studies investigated the prediction of postoperative LF of which seven papers investigated the predictive value of both modalities in multivariable regression analysis. Two papers found that only nuclear imaging parameters were predictive of LF, one paper found that the CT parameter was predictive, and four papers found that combined nuclear and CT/MR imaging parameters were predictive of LF. CONCLUSION: Both methodologies were useful in the preoperative assessment of patients scheduled for liver interventions, especially in combination, but nuclear imaging demonstrated better predictive value for postoperative mortality and LF in a few trials. The overall technical and methodological heterogeneity of the included studies complicates the ability to directly compare the clinical utility of the two imaging techniques
Tetrapotassium cis-dioxido-trans-bis(sulfato-κO)sulfato(κ2 O,O′)molybdate(VI)
The title compound, K4[MoVIO2(SO4)3], was precipitated from a melt of molybdenum(VI) oxide and potassium sulfate in potassium disulfate. The compound contains monomeric [MoVIO2(SO4)3]4− anions, with the MoVI atom, both oxide ligands, and the S atom and both ligating O atoms of the bidentate sulfate group lying on a crystallographic mirror plane. One of the potassium cations is nine-coordinate, while the other is eight-coordinate
- …