Towards Validation of Advanced Accelerated Stress Testing Protocols through Failure Analysis and Materials Characterization

Development of mathematical transfer functions correlating Solid Oxide Fuel Cell degradation to operating conditions for Accelerated Stress Test protocols design

Nanostructured α‐hematite (Fe 2 O 3 ) is a widely studied material for photoanode applications, particularly for driving the oxygen evolution reaction (OER) under visible light irradiation in photoelectrochemical (PEC) cells. Our recent work has shown that Fe 2 O 3 suffers from photocorrosion in alkaline and neutral electrolytes, with a noticeable decline in performance after 5 h of operation. This highlights the need for strategies that enhance the stability of Fe 2 O 3 ‐based photoanodes. To enhance the stability of Fe 2 O 3 nanorods (NR), we employed atomic layer deposition (ALD) to coat the NR with a well‐defined, controlled TiO 2 overlayer designed to protect the photoanode from photocorrosion during PEC operation. The influence of overlayer thickness is evaluated regarding the PEC activity, stability, and photocurrent retention in alkaline electrolyte using a PEC scanning flow cell coupled to an inductively coupled plasma mass spectrometer (PEC‐ICP‐MS). This setup can quantify metal dissolution during PEC OER, allowing the characterization of the photo‐degradation under realistic illumination conditions. An accelerated stress test (AST) protocol was designed to drive degradation faster and obtain insightful information about the stability of the TiO 2 @Fe 2 O 3 heterostructures using in situ PEC‐ICP‐MS. PEC‐ICP‐MS measurements demonstrate that the TiO 2 coating significantly enhances the photocorrosion resistance of Fe 2 O 3 NR in alkaline electrolytes during operation. A TiO 2 thickness of 2.8 nm (50 ALD cycles) offered the most favorable compromise between activity, photocurrent retention, and decrease of Fe dissolution. The proposed methodology combines in situ stability quantification and ASTs as a powerful tool to advance material development and can be extended to other protected photoanodes.

The impeding ban on per- and polyfluoroalkyl substances (PFAS) prompted researchers to focus on hydrocarbon-based materials as constituents of next-generation proton exchange membranes (PEMs) for polymer electrolyte fuel cells (PEFCs). Here, we report on the fuel cell performance and durability of fluorine-lean PEMs prepared by the post-sulfonation of co-grafted α-methylstyrene (AMS) and 2-methylene glutaronitrile (MGN) monomers into preirradiated 12 µm polyvinylidene fluoride (PVDF) base film. The membranes were subjected to two distinctly different accelerated stress test (AST) protocols performed at open-circuit voltage (OCV): the US Department of Energy-similar chemical AST (90 °C, 30% relative humidity (RH), H2/air, 1 bara), developed originally for perfluoroalkylsulfonic acid (PFSA) membranes, and the high relative humidity AST (80 °C, 100% RH, H2/O2, 2.5 bara), designed for aromatic hydrocarbon membranes. We found that doping the grafted membranes with a metalated porphyrin antioxidant can simultaneously reduce membrane aging and improve fuel cell performance.

Proton Exchange Membrane Fuel Cells (PEMFC) are high-efficiency energy converters that can be deployed for mobile, transport and stationary applications in an eco-friendly manner. Nevertheless, their large-scale development requires further improvements, specifically regarding their lifetime in operation1. In abnormal PEMFC operating conditions, e.g. start-up/shutdown events2 or localized fuel starvation3, the positive electrode may reach potentials of 1.5 V vs the reversible hydrogen electrode (RHE), which triggers extensive carbon support corrosion at the cathode side.To tackle this problem, one of the solution studied in the literature is to use (more robust) carbon-free catalyst supports based on metal oxides4-6. To represent viable alternatives to conventional carbon blacks, metal-oxide substrates must fulfill three criteria: be electron-conducting, resist corrosion and possess an opened porous structure compatible with facile ionomer insertion and efficient mass-transport properties.This study focuses on aerogel structures obtained using a sol-gel route, based on antimony-doped tin dioxide (ATO) with different doping levels (0, 5, 10 and 15 at.%). A Pt nanoparticles colloidal solution, obtained via a modified polyol route, was deposited on the ATO (Pt/ATO) featuring the best properties (10 at.% Sb-doped SnO2), and, for comparison, on Vulcan XC72 carbon (Pt/C) and on an undoped tin dioxide aerogel (Pt/SnO2). This strategy allowed the straightforward comparison of the Pt/ATO, Pt/C and Pt/SnO2 electrocatalysts in terms of catalytic activity for the oxygen reduction reaction (ORR) and durability. A 2-fold enhancement in specific activity for the ORR was measured on Pt/ATO over the reference Pt/C, suggesting strong metal support interactions between the Pt nanoparticles and the ATO support. An accelerated stress test (AST) protocol (5,000 or 10,000 potential cycles between 1.0 and 1.5 V vs RHE) enabled to determine the robustness of the Pt/ATO and the Pt/C electrocatalysts during model start-up/shut-down events. Figure 1 illustrates that Pt/C did not withstand operation in these conditions, as observed from the massive detachment of Pt nanoparticles from the carbon support following its corrosion. On the contrary, the Pt nanoparticles did not detach from the ATO support during ageing. However, evidences were provided that a core@shell structure with a Sb-poor surface covering a core with a Sb content close to the nominal forms during the AST. This core@shell structure restricts the capacity of the Pt nanoparticles to exchange electrons, as evidenced by the attenuated Pt surface oxide formation/reduction features, and the decreased catalytic activity for the ORR.

Background A variety of exercise stress testing protocols with various workloads are available. The test protocol is typically selected according to patient's expected exercise performance. Purpose We sought to assess whether the choice of the protocol is by itself independently associated with mortality even after adjusting for clinical variables and estimated workload achieved in metabolic equivalents of task (METS). Methods In a 25-year stress testing registry spanning from 1991 to 2015, we identified 120,705 patients who underwent 7 different standardized exercise protocols: Bruce, Modified Bruce, Cornell 0%, 5%, and 10%, Naughton, and modified Naughton. The choice of the protocol was dependent on the supervising exercise physiologist, mainly according to patient's expected exercise performance. The primary outcome was all-cause mortality. Results Mean age was 53.3±12.5 years and 59% were male. There were 74953 Bruce, 8368 modified Bruce, 2648 Cornell 0%, 9972 Cornell 5%, 20425 Cornell 10% 1226 Naughton, and 3113 modified Naughton protocols. A total of 8426 death occurred over 8.7 years of mean follow-up duration. Table 1 presents the baseline characteristics by protocol. After adjusting for the number of METs, age, gender, hypertension, diabetes, coronary disease, end-stage renal disease, smoking, and statin use, the protocol selected remained predictive of mortality. Figure 1 shows the adjusted HR for death by protocol selected when compared to Bruce. Baseline characteristics by protocol Variable Bruce (n=74953) Modified Bruce (n=8368) Cornell 0% (n=2648) Cornell 5% (n=9972) Cornell 10% (n=20425) Naughton (n=1226) Modified Naughton (n=3113) Age, mean ± SD 49.4±11.3 61.3±10.3 66.4±11.7 62.5±11.8 57.2±11.5 67.5±9.8 55.5±11.9 Male, % 64.6 51.8 37.8 42.3 51.7 49 66.7 Coronary disease, % 8.7 32.5 31.7 26.7 21.1 49.7 45.6 Diabetes mellitus, % 7.6 16.5 25.3 20 14.2 27.2 26.2 Hypertension, % 41.7 64 85.4 77.9 67.1 82.5 97.5 Smoker, % 40.9 55 50.7 50.9 50.8 56.9 60.6 ESRD, % 0.7 1 3.7 2.4 1.6 2.7 8.1 Mets, mean ± SD 10.3±2.4 7.2±1.7 5.2±1.6 6.7±1.5 8.3±1.9 4.8±1.5 4.6±1.5 Statin use, % 22.4 15.2 41.8 38.3 35.1 19 40.1 ESRD = end-stage renal disease; METS = metabolic equivalents of task. Adjusted HR by protocol selected Conclusion The choice of the stress testing protocol, which is in large part dependent on patient's expected exercise performance is in itself independently associated with mortality even after adjustment for METs achieved and patients' demographics and comorbidities. The choice of the modified-Naughton is associated with the greatest risk of mortality, likely chosen based on limited functional capacity

To compete with well-established fossil fuel-based power sources and to maximize their potential as environmental friendly alternative, proton exchange membrane (PEM) fuel cells have to meet several technical criteria, as described by the US Department of Energy’s Multi Year Research, Development and Demonstration Plan (MYRD&D) [1]. Those criteria include long-term durability under normal operation conditions and stability to external disturbances, both of which are strongly related to the aging processes of fuel cell electrocatalysts. Proposed degradation mechanisms for the most commonly used platinum group metal nanoparticles supported on a carbon support material include [2]: Ostwald ripening, coalescence via particle migration, particle detachment from the carbon support, and Pt dissolution into the electrolyte. These catalyst aging processes significantly depend on the robustness of the metal nanoparticles and support material as well as the stabilizing particle – carbon interactions [3, 4]. As all of the degradation processes result in a loss of electrochemically active surface area and often appear simultaneously, differentiating between these aging processes is a highly complicated task which we track in our comprehensive project. In our work, we provide a deeper understanding about the degradation mechanisms occurring on carbon-supported platinum nanoparticles (Pt/C) as electrocatalyst for PEM fuel cells. Thin film electrodes made from Pt/C were electrochemically analyzed by exposing them to accelerated stress test (AST) protocols using a rotating disc electrode (RDE) setup. Our protocols include (i) potential cycling between 0.5 – 1.0 V vs. RHE (10,000 cycles) to resemble normal operation conditions in a fuel cell, (ii) 0.5 – 1.5 V vs. RHE (2,000 cycles) to simulate more extreme conditions e.g. during start-up and shutdown of the cell, and finally (iii) 1.0 – 1.5 V vs. RHE (2,000 cycles) to analyze corrosion effects on the carbon support material. As indicators for the catalyst degradation we monitored the electrochemically active surface area (ECSA), as well as the specific and mass activities at 0.9V vs. RHE of the Pt nanoparticles over the course of the AST experiments. Furthermore, the catalysts were characterized using various techniques such as transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The losses of ECSA and ORR activity were then correlated to the structural changes such as particle size and carbon structure as well as to the experimental parameters such as number of cycles and potential range of the AST protocols. We observed a strong decrease in ECSA by up to 70% during simulated “start/stop” experiments, while “lifetime” and “carbon corrosion” protocols showed relatively small losses of ~30% and ~10%, respectively. These observations were accompanied by a strong growth in particle size during “start/stop” and less particle growth during “lifetime” and “carbon corrosion” protocols. Since the degradation rates of the Pt/C altered during the runs of these AST protocols in different manners, we performed intermediate stops to monitor the changes in structure and morphology of the Pt nanoparticles as well as of the carbon. Based on our results, we developed a model to clarify the degradation mechanisms during different types of accelerated stress tests and to identify the critical parameters for maintaining the catalytic performance of the Pt/C catalysts under operating fuel cell conditions.

A mechanistic understanding of carbon corrosion in polymer electrolyte fuel cells (PEFCs) is required to design catalyst layers that are durable. Electrochemical oxidation of carbon occurs during uncontrolled startup and shutdown events of PEFCs leading to multitude of degradation events, including loss of electrochemical surface area (ECSA), pore structure collapse, Pt detachment, loss in ionomer and others. To understand carbon corrosion physics and resulting degradation mechanisms a detailed electrochemical characterization is needed to probe interfaces between Pt-ionomer, carbon-ionomer and to measure transport properties and the ECSA in the catalyst layer. In this presentation we will provide an overview of carbon corrosion understanding and our approaches to quantify the sequence of events. In these studies, PEFCs were subjected to the Department of Energy carbon corrosion accelerated stress test (AST) protocol. Various electrochemical techniques were used to describe interfaces and morphology, as well as transport properties for the cells at different stages of the AST. ECSA measurements, polarization curves, CO-displacement/stripping to determine sulfonic acid group coverage in dry and wet conditions, electrochemical impedance spectroscopy, oxygen transport resistance measurements and other techniques were used. In addition, physical characterization methods at the beginning of life (BOL) and end of life (EOL) were used, such as micro x-ray fluorescence mapping, focused ion beam scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and Raman spectroscopy. A combination of electrochemical and physicochemical methods revealed that amorphous carbon oxidizes first, after which Pt detach resulting in the loss of the ECSA, followed by severe structure collapse, resulting in a poor oxygen transport resistance. We extend the study to carbon supports that are more graphitized to alleviate some of the issues observed with amorphous carbon support.

FUEL CELLS – PROTON-EXCHANGE MEMBRANE FUEL CELLS | Life-Limiting Considerations

Their is significantly growing interests in a polymer electrolyte membrane fuel cell (PEMFC)as a promising alternative electric power generation system for stationary, backup power, and automotive applications because of high power density, low operating temperature, and reduced release of environmental pollutants relative to converntional energy conversion and storage devices [1]. In this regard, a high level of activities in materials science and engineering research for the PEMFC have been made to realize its potential applications as the advanced sustainable energy sourcecs.For realizing the widespread commercialization of the PEMFC, there are still technical hurdles including high cost, performance loss, and insufficient durability with long-term cycles [2]. Especially in automotive condition, startup/shutdown and load-cycling cause a significant degradation of Pt nanoparticles supported on high surface area carbon. Although several types of Pt-based catalysts with enhanced catalytic activity and/or durability have emerged, they are still in development [3]. Therefore,it is still of great importance to develop efficient electro-catalysts with enhancing stability as well as sustaining catalytic acitvity under the wide ranges of operating conditions.The development of a functional carbon supported Pt catalyst that has both high oxygen reduction activity and high durability would significantly contribute to the commercialization of automotive PEMFC. Herein we report a diazonium-functionalized graphitized carbon (DFGC) support prepared by grafting different types of end-functional groups on a GC support via simple diazonium chemistry that can improve the dispersion of Pt nanoparticles and reduce their sintering phenomena, resulting in higher electrochemical durability with enhanced catalytic activity as compared to the unmodified GC support. The membrane-electrode assembly (MEA) fabricated with the Pt/DFGC series as the cathode catalysts shows a power density higher than 1.0 W/cm2 under an automotivce operating condition at a low catalyst loading of 0.25 mgPt/cm2. The durability of the MEA was measured by electrocatalyst cycling and catalytst support cycling tests according to the procedures of DOE-FCTT accelerated stress test (AST) protocols. THe AST results reveal that the MEA series with the Pt/DFGC catalysts exhibit higher durability event at 30% lower catalyst loading compared to a commercial MEA. These results demonstrate that the catalyst design strategy based on simple diazonium chemistry is an effective way to fabricate highly durable catalysts with enhanced catalytic activity for the PEMFC, providing a design guide of a high performance MEA for automotive applications.We also present current development status of our developed MEA for automotive applications. Our research and development focus on the fabrication of a cost-competitive MEA with high power performance and longer durability even at lower Pt amount for automotive PEMFC systems. To achieve these goals, a high level of activities have been made to develop the MEA design for high temperature and low humidified operation including the design of highly active catalyst layer, the functionalization of polymer electrolyte membrane and interfaces in the MEA, and cost-effective manufacturing process. The development of a cost-competitive MEA with high power output, long durability, and operation flexibility is expected to contribute the widespread commercialization of automotive PEMFC systems. Further development of the MEA for automotive applications would be performed by balancing high performance against long-term durability and manufacturing cost.

The successful use of plasma-sprayed hydroxyapatite (HA) coatings on Ti-alloy implants for implant-to-bone fixation requires strong adherence of the ceramic coating to the underlying metal substrate. In this study, the metal-ceramic interface was evaluated using mechanical, chemical, and structural characterization methods. Evaluations of an HA-coated Ti-6Al-4V implant system using a modified short bar technique for interfacial fracture toughness determination revealed relatively low fracture toughness values. Additionally, conventional tensile bond strength testing indicated much lower values than previously reported. Using high resolution electron spectroscopic imaging, evidence of chemical bonding was revealed at the plasma-sprayed HA/Ti-6Al-4V interface, though bonding was primarily due to mechanical interlock at the interface. This study illustrates the benefits of, and the need for, a multilevel approach to evaluate and improve these plasma-sprayed ceramic-metal substrate interfaces.

In multi-layer printed wiring boards (PWBs), electrical connections between different layers are accomplished with plated through holes (PTHs). The reliability of the PTH barrel and the PTH-inner plane (IP) connection depends not only on the design but also on the conditions of manufacturing and assembly processes of the board. The concerns associated with manufacturing arise from drilling which heats up and smears the surrounding epoxy onto the copper inner plane surfaces and also from subsequent chemical hole-clean operations which desmear the drilled holes. Good adhesion of the PTH copper to the desmeared PTH wall and to the copper inner planes is important for the reliability of the PTHs during assembly and field service. PWB coupons consisting of resin-glass bundle areas as well as resin filled clearance areas surrounding the PTH have been considered for a series of experiments and tests. On these coupons, accelerated stress tests and failure analysis of the PTHs at the end of these tests have been conducted. An elasto-plastic finite element analysis of the PTH strains for a temperature excursion of 102°C has been carried out for signal PTHs without and with IP connections. A peel test, using a micro-mechanical tester, has also been carried out to assess the adhesion of PTH copper to different regions along the drilled hole. All of the testing techniques have been supplemented by suitable analytical techniques for studying the distribution of smear on the copper inner planes. A birefringence technique to estimate the temperature of the hole wall during drilling has been described. All of the fails observed during stress testing are in the form of cracks in the PTH barrel, the plane of the crack being perpendicular to the barrel axis. The cracks are localized near the glass bundle-resin rich interface. It has also been observed in the failure analysis that the PTH/IP connections are not susceptible to failure during the accelerated stress testing conditions considered. These observations are also supported by the results of stress analysis. The results of stress analysis show that the interior clearance holes show higher strains than those closer to board surfaces, suggesting that the PTH barrel failure is likely to occur at the clearance hole and that the likelihood of failure at the interior clearance holes is higher than those closer to the PWB surfaces. The results of the peel test reveal that in the glass bundle-resin regions, the adhesion along the PTH wall is determined by the mechanical interlocking between the plated copper and the glass bundles and is relatively insensitive to desmear operations. However, adhesion in the resin-rich areas is a strong function of the desmear operation, which enhances the adhesion of the PTH to the resin. Finally, it is shown that the birefringence technique may be used effectively to estimate the drilling temperature and, hence, the degree of smearing and PTH quality. It is concluded that while smear may play an important role in the failure of PTHs in PWBs, for thick packaging boards with high aspect ratio PTHs, the predominant failure mechanism is less likely to be smear related. Such a failure mechanism would be preceded by failure in the PTH barrels as a result of the large strain concentrations imposed at specific locations within the cross-section.

Introduction: Lactate Minimum Test (LMT) identifies a sustainable exercise intensity, in which an equilibrium is observed between production and clearance of blood lactate and the hormone influence during this physiological moment. Objective: The present study aimed to identify the levels of LM and hormones after caffeine consumption and exercise Stress Test (ST) in diabetic rats. Methods: This study was composed of 24 animals, of 60 days, allocated into four groups: Control, Diabetic, Caffeine, and Diabetes+Caffeine. The Diabetes model was induced by intraperitoneal administration of 120 mg/kg of alloxan. On the test day, 6 mg/kg of caffeine were administrated 30 minutes before the exercise Stress Test (ST) protocol. During the ST animals underwent a Stress Test (ST), in which they performed forced swimming (until exhaustion) tie to loads of 13% Body’s Weight (BW). The incremental phase of LM began with an initial load of 4% Body’s Weight (BW) and increased 0.5% every 5 min. Lactate concentration was measured 5, 7 and 9 min (mmol/L) after ST. The Incremental Progressive Test (IPT) involved swimming with loads of 4.0, 4.5, 5.0, 5.5, 6.0, and 7.0% of BW, for 5min with each. Blood samples were collected by a caudal puncture to subsequent lactate and hormone assay. Results: Performance time and lactate concentration of hyperlactatemia test, as well as Lactate Minimum (LM) and Lactate (LAC) concentration after the progressive test presented a significant difference when comparing the levels of the control group with caffeine and diabetic group (p<0.05). Conclusion: It is suggested that caffeine improves lactate clearance and hormonal steady state condition of diabetic animals after hyperlactacidemia and physical exercise maintenance.

Results of a program to investigate the reliability characteristics of unencapsulated low-cost terrestrial solar cells using accelerated stress testing are presented. A total of seven types of cells were investigated. Results of extended (~ 1 year) bias-temperature stress testing of four cell types were obtained. An additional three cell types, including cells fabricated using the advanced technologies of ribbon-grown silicon and polycrystalline silicon, were subjected to various combinations of bias, temperature cycling stress tests. The spectrum of tests used was based on previous years' work, but differs from that used earlier. An electrical measurement procedure capable of distinguishing small changes in cell electrical parameters was used. Significant degradation was shown by some cell types in some stress tests. Other combinations of cell types and stress tests resulted in no detectable cell degradation. Analysis of the origins of the differences in degradation is continuing. Second quadrant characteristics of some cell types were also investigated in order to establish the electrical behavior of cells which may be exposed to this stress condition in modules deployed in the field.

Proton Exchange Membrane (PEM) failure is one of the key criteria in deciding the durability of the PEM fuel cell system. Physical properties such as ionic conductivity and mechanical properties depend on the microstructure. The microstructure is itself strongly dependent on the water content of the membrane (1, 2). It is therefore important to fully understand the effect of degradation stressors on the morphological changes and water-uptake characteristics in order to improve membrane durability.In this work, standard perfluorosulfonic acid (PFSA) ionomer membranes are subjected to a combined chemical and mechanical accelerated stress test (AST) used for rapid benchmarking of in-situ membrane stability. The degradation stressors in the combined chemical/mechanical AST was previously shown by our group to change the molecular structure and lead to membrane material loss (3). The chemical phase of the AST generates hydroxyl radicals that attack both the side chain and main chain of the polymer, while the mechanically generated stresses due to humidity cycling accelerate mechanical failures. The observed structural changes are anticipated to alter the water-uptake properties of the membrane, as shown previously for ex-situ testing (4). The degradation also alters the morphology, ion exchange capacity, mechanical properties, and proton conductivity of the membrane (5). Water-uptake measurements of partially AST degraded catalyst coated membrane (CCM) samples are carried out at room temperature using a dynamic vapor sorption system. In spite of severe fluoride release and membrane thinning, the water-uptake per unit mass of the AST degraded CCMs is found to be relatively constant. Since the test specimens are CCMs which contain a significant amount of catalyst layer material, an attempt is made to measure and separate the mass of the ionomer by thermogravimetric analysis (TGA). The ionomer material loss throughout the AST process is significant due to fluoride release and ionomer degradation, up to roughly 50% at end-of-life (3). The water-uptake per unit mass of ionomer in the CCM is determined by extracting the ionomer weight obtained by heating the CCM in the TGA chamber. In contrast to the previous results normalized by specimen dry weight, the water-uptake increases significantly per unit mass of the ionomer in the CCM, as shown in Fig. 1. Although the increased water-uptake may indicate enlarged solvated hydrophilic domains in the membrane, which is good for enhanced proton mobility, the proton conductivity is found to decrease (Fig. 1). This may be attributed to a decay in proton concentration due to sulfonic acid functional group loss during side chain degradation. The overall effects of the combined chemical/mechanical AST on the membrane morphology and properties are presented and compared to provide additional insight into the complex degradation mechanism.ACKNOWLEDGMENTSResearch funding provided by Automotive Partnership Canada (APC), Natural Sciences and Engineering Research Council of Canada (NSERC) and Ballard Power Systems (BPS) is gratefully acknowledged. BPS is also acknowledged for providing access to experimental facilities, material samples and technical support. REFERENCES1. J.Benziger, A. Bocarsly, M. J. Cheah, P. Majsztrik, B. Satterfield, and Q. Zhao, in Fuel Cells and Hydrogen Storage 141, Bocarly and Mingos, Editors, p. 85 Springer, Berlin Heidelberg 141 (2011).2. Y. Yang, A. Siu, T. J. Peckham, S. Holdcroft, in Advances in Polymer Sciences 215: Fuel cells 1, G. G. Scherer, Editor p. 55 Springer, Berlin Heidelberg 215 (2008).3. C. Lim, L. Ghassemzadeh, F. Van Hove, M. Lauritzen, J. Kolodziej, G.G. Wang, S. Holdcroft, E. Kjeang, J. Power Sources 257 102 (2014).4. L. Ghassemzadeh and S. Holdcroft, J.Am.Chem.Soc. 135 8181 (2013).5. S. V. Venkatesan and E. Kjeang, 11th International Fuel Cell Science, Engineering and Technology Conference, ASME, Minneapolis, MN (2013).

American Society of Echocardiography Recommendations for Performance, Interpretation, and Application of Stress Echocardiography