Natural Sciences And Engineering Research Council Of Canada Research Articles

Polynomial Upper Bounds on the Number of Differing Columns of Δ-Modular Integer Programs

We study integer-valued matrices with bounded determinants. Such matrices appear in the theory of integer programs (IPs) with bounded determinants. For example, an IP can be solved in strongly polynomial time if the constraint matrix is bimodular: that is, the determinants are bounded in absolute value by two. Determinants are also used to bound the [Formula: see text] distance between IP solutions and solutions of its linear relaxation. One of the first to quantify the complexity of IPs with bounded determinants was Heller, who identified the maximum number of differing columns in a totally unimodular matrix. Each extension of Heller’s bound to general determinants has been superpolynomial in the determinants or the number of equations. We provide the first column bound that is polynomial in both values. For integer programs with box constraints, our result gives the first [Formula: see text] distance bound that is polynomial in the determinants and the number of equations. Our result can also be used to derive a bound on the height of Graver basis elements that is polynomial in the determinants and the number of equations. Furthermore, we show a tight bound on the number of differing columns in a bimodular matrix; this is the first tight bound since Heller. Our analysis reveals combinatorial properties of bimodular IPs that may be of independent interest. Funding: J. Lee was supported in part by the Office of Naval Research [Grant N00014-21-1-2135] and the Air Force Office of Scientific Research [Grant FA9550-19-1-0175]. J. Paat was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant [Grant RGPIN-2021-02475].

Effect of Cobalt Cation Concentration on PEMFC Electrode Performance

Metal alloy catalysts, such as Pt-Co, reduce the activation energy of oxygen reduction reaction, leading to improved proton exchange membrane fuel cell (PEMFC) performance. However, leaching of non-noble elements contaminates the ionomer and membrane, which has a negative impact on the durability of PEMFCs [1,2]. For the commercial success of metal alloy catalysts, understanding the mechanisms of how cation contamination affects PEMFC performance is crucial. Here, we investigate the effect of cobalt cation contamination effects through intentional doping of decal electrodes. Electrochemical testing results are coupled with membrane conductivity and water uptake measurements, as well as impedance modeling to identify the mechanisms of performance loss. Our results provide a comprehensive understanding of how cation contamination affects performance, which can inform mitigation strategies and new materials development that can enable the use of metal alloy catalysts in PEMFCs. Acknowledgement This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos. Financial support for this work from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) is gratefully acknowledged (Projects 2020200DR and 20210915PRD2). ChungHyuk Lee acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC). References Cai et al., ECS Trans., 69, 1047 (2015)P. Braaten et al., J. Electrochem. Soc., 166, F1337 (2019) Figure 1

The Acute Effect Of A Laboratory Shame Induction Protocol On Endothelial Function

Shame is a self-conscious emotion that arises when one internalizes social devaluations from others. Increased shame in a laboratory setting is associated with increased cortisol and tumor necrosis factor alpha activity, however, no studies have investigated the acute effects of shame on important indices of cardiovascular disease risk such as endothelial function. The endothelium is a single layer of cells which lines the inside of all arteries and acts as a vasoprotective and vasoactive agent by inhibiting the development of atherosclerosis and adjusting vessel diameter in response to changes in blood flow associated shear stress (flow-mediated dilation). PURPOSE: The objective of this study was to examine the impact of a shame induction protocol on endothelial function. METHODS: Fifteen, young (23 ± 2 years), healthy participants (n = 7 men, n = 8 women) completed both a 20-min written shame induction and control protocol on two different experimental days. Pre- and post-protocol we assessed: 1) Endothelial function via a standard brachial artery reactive hyperemia flow-mediated dilation (RH-FMD) test which was characterized as the peak % and absolute change in diameter following release of 5 min of forearm occlusion, and; 2) Perceived shame via the Experiential Shame Scale (ESS). RESULTS: Shame increased in response to the shame induction protocol (pre: 2.9 ± 0.6 vs. post: 3.7 ± .5, p < 0.001) but not the control protocol (pre: 3.0 ± 0.5 vs. post: 2.8 ± 0.5, p = 0.15). %RH-FMD significantly decreased in response to the shame protocol (pre: 4.8 ± 1.9 vs. post: 3.2 ± 1.6, p < 0.001) but not the control protocol (4.2 ± 1.8 vs. post: 3.8 ± 1.5, p = 0.45). Covariation of the shear stress stimulus for RH-FMD did not alter the RH-FMD results. Increased shame was significantly associated with decreased absolute RH-FMD (r = -0.37, p = 0.046). CONCLUSIONS: The shame induction protocol caused a significant increase in shame and reduction in RH-FMD. This suggests that temporary increases in shame cause transient endothelial dysfunction which, if chronically repeated, could manifest as reduced vasoprotection against atherosclerosis. Supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) discovery grant.

Critical Pitting Temperature of Stainless Steel: Deterministic Vs. Probabilistic Behavior

The concept of the critical pitting temperature (CPT), which is described as the temperature below which stable pits are not formed regardless of applied potential and exposure time, has received considerable attention in the literature. Over the past few decades, many attempts have been made to assess the CPT of stainless steel as a function of alloy composition, alloy microstructure, bulk solution composition, and surface roughness. In contrast to the pitting potential, which is known to be probabilistic in nature, CPT is believed by most to be a deterministic phenomenon that can be measured within a few degrees Celsius [1]. This notion has been validated by many authors who have observed a narrow range of CPT for several alloy/environment combinations [2,3]. Some authors have recently challenged this idea by reporting scattered CPT values [4]. This work seeks to determine whether the CPT falls within a narrow or wide temperature range (i.e., is CPT a deterministic or probabilistic phenomenon?).To answer this question, potentiostatic CPT measurements were performed using 1 cm² 904L stainless steel electrodes and an applied potential of 750 mV (Ag/AgCl). Temperature was increased at a rate of 1 °C/min, and the CPT was determined using the temperature at which current density rapidly increased. The CPT of 904L stainless steel was measured in four different conditions to evaluate the effect of bulk Cl⁻ concentration (0.05 and 1.0 M NaCl), passivation in 20 vol.% HNO3, and the presence of a corrosion inhibitor (0.02 M NaNO3).Figure 1 shows a cumulative graph of the CPT values of 904L obtained using the four different conditions. In this graph, n is the number of the n th pitted sample and N is the total number of experiments (i.e., 10). For all test conditions, the CPT was measured within ± 1.8 °C, which is in agreement with the reproducible CPT values reported by others [3]. Figure 1 shows that the CPT of 904L is independent of passivation in HNO₃. Further, decreasing bulk solution aggressiveness from 1.0 M NaCl to 0.05 M NaCl does not result in scattered CPT values. However, some authors have reported a considerably broader range (i.e., ± 10 °C) for the CPT of stainless steel (AISI 316L and 2205), as discussed previously. One possible explanation for their larger reported CPT range is the occurrence of crevice corrosion at the interface of the alloy/inert support (e.g., epoxy mount), which results in an inaccurate CPT measurement. To evaluate this hypothesis, the current density vs. temperature curves for two conditions were compared (see Figure 2). The blue and red curves show potentiostatic polarization results for pure pitting corrosion (i.e., crevice-free CPT measurement) and pitting + crevice corrosion, respectively. The gradual increase of the current density with temperature for the red curve suggests the presence of a crevice at the alloy/epoxy interface, which was confirmed using SEM to characterize the electrode post-polarization. On the other hand, when no crevice corrosion occurs, the current density shows a sudden increase at the CPT.The results of this study reveal that the CPT of 904L can be measured to within ± 1.8 °C, regardless of bulk solution aggressiveness (e.g., 1.0 M NaCl and 0.05 M NaCl solution) or passive state before polarization. This finding is in contrast to what some authors have suggested recently. The scattered CPT values reported in the literature are most likely due to contributions from both pitting + crevice corrosion rather than pitting corrosion alone. Acknowledgments Financial support provided by Natural Sciences and Engineering Research Council of Canada (NSERC) is gratefully acknowledged.

Mixing of X and Y states from QCD sum rules analysis * *Supported by NSFC (11175153, 11205093) and the Natural Sciences and Engineering Research Council of Canada (NSERC)

We study and states as mixed states in QCD sum rules. By calculating the two-point correlation functions of pure states of their corresponding currents, we review the mass and coupling constant predictions of , , and states. By calculating the two-point mixed correlation functions of and currents, we estimate the mass and coupling constants of the corresponding "physical state" that couples to both and currents. Our results suggest that for states, the and components are more likely to mix, while for and states, there is less mixing between and . Our results suggest the Y series of states have more complicated components.

Modulatory role of prenatal alcohol exposure and adolescent stress on the response to arthritis challenge in adult female rats.

SummaryBackgroundThere are known environmental risk factors associated with rheumatoid arthritis; however, less is known regarding how the prenatal environment impacts later-life risk for rheumatoid arthritis. Based on preliminary clinical data suggesting that individuals with fetal alcohol spectrum disorder (FASD) are at higher risk for autoimmune disorders, this study investigated the modulatory impact of prenatal alcohol exposure (PAE) on the inflammatory disease profile in an adjuvant-induced arthritis rat model.MethodsPregnant rats received liquid ethanol or control diet throughout gestation. To model the increased exposure to stressors often experienced by individuals with FASD, adolescent offspring were exposed to chronic mild stress (CMS) or remained undisturbed. In adulthood, experimental arthritis was initiated and rats terminated either at the peak or following resolution from inflammation to assess endocrine, immune, and histopathological outcomes.FindingsPAE rats had an increased incidence and severity of, and impaired recovery from, arthritis. Increased joint damage was observed in PAE animals, even in the face of apparent recovery from the clinical signs of arthritis, while it appeared that oestradiol may have a protective role. Moreover, with the combination of PAE and adolescent stress, increased macrophage density was detected in the synovium of PAE but not control rats.InterpretationThese findings demonstrate that PAE alters the severity and course of arthritis, highlighting the potential immunomodulatory impact of adverse prenatal exposures. In particular, these data have implications for understanding preliminary data that suggest a heightened propensity for autoimmune disorders in individuals with FASD.

P.167: Gene Expression and Function in Pig Islets From One-day-old Pigs

Introduction: Islet transplantation is a budding alternative treatment for type 1 diabetics. A potential solution to the limited number of human pancreas donors is pig islet xenotransplantation. Limited study has been performed on pig islet cell signaling pathways, which may differ from the mechanisms seen in humans. We have identified molecules involved in the insulin secretion pathway, including the glucose transporter GLUT2, GTPase RAC1, which is involved in F-actin remodeling in islet cells, and SNAP25, a protein involved in insulin release. We evaluated these molecules across different days of culture in neonatal pig islets. We also quantified the gene expression of common cadherins associated with cell-cell adhesion and islet function as determined by insulin secretion. Method: Islets from 1-day-old pigs (n=3) were isolated and samples collected on days 0, 3, 5 and 7 of culture to quantify GLUT2, SNAP25, RAC1, E-, N- and VE-cadherin gene expression by qRT-PCR. Immunofluorescence staining was performed to localize protein expression. Static glucose stimulation insulin secretion assays (GSIS) and ELISA were used to quantify the ability of these islets to secrete insulin under conditions containing low glucose, high glucose and high glucose with KCl. Kruskal-Wallis testing was completed with GraphPad Prism software. Results: Qualitatively, the islets developed visible membranes and had fewer contaminating exocrine cells as they moved from 0 to 7 days in culture. E-cadherin, SNAP25 and GLUT2 all peaked on day 5 of culture, correlating with when islets formed a distinct spherical structure in-vitro. N-cadherin consistently rose, peaking at day 7 of culture. VE-cadherin was highest at day 0 and decreased with a linear trend. RAC1 gene expression decreased from day 0, remaining stable between days 5 and 7. P-values are indicated in Figure 1. Preliminary immunofluorescence staining showed co-localization of SNAP25 and insulin at all-time points. The amount of insulin secreted in low vs high glucose settings was similar without KCl, and as expected, the amount of insulin secreted when islets were cultured in high glucose with KCl was greater. Kruskal-Wallis testing demonstrated significant differences amongst GSIS groups (Figure 2). Discussion/Conclusion: Our data demonstrates variation in the gene expression of our molecules of interest across 7 days of culture. Our immunofluorescence results demonstrate that SNAP25 colocalized with insulin, suggesting their proximity in islet cells. Our results also demonstrate the limited ability of glucose to stimulate islets from 1-day-old pigs at 7 days of culture. This is different than results seen previously in our lab suggesting islets from 7-day-old pigs at 7 days of culture secrete greater amounts of insulin when exposed to high glucose conditions. These findings may be important for the development of pig islets in vitro and warrant further investigation.Royal College of Physicians and Surgeons of Canada (RCPSC) - Clinician Investigator Program. Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant. Canadian Institutes of Health Research (CIHR) - Canadian Graduate Scholarships - Master’s Program. Walter H. John’s Graduate Fellowship (University of Alberta). Alberta Graduate Excellence Scholarship (AGES).

Fission accomplished: Uncovering the role of Drp1 in regulating mitochondrial dysfunction and age-related muscle atrophy.

Fission accomplished: Uncovering the role of Drp1 in regulating mitochondrial dysfunction and age-related muscle atrophy.

SARS-CoV-2 shedding dynamics across the respiratory tract, sex, and disease severity for adult and pediatric COVID-19.

Previously, we conducted a systematic review and analyzed the respiratory kinetics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (Chen et al., 2021). How age, sex, and coronavirus disease 2019 (COVID-19) severity interplay to influence the shedding dynamics of SARS-CoV-2, however, remains poorly understood. We updated our systematic dataset, collected individual case characteristics, and conducted stratified analyses of SARS-CoV-2 shedding dynamics in the upper (URT) and lower respiratory tract (LRT) across COVID-19 severity, sex, and age groups (aged 0-17 years, 18-59 years, and 60 years or older). The systematic dataset included 1266 adults and 136 children with COVID-19. Our analyses indicated that high, persistent LRT shedding of SARS-CoV-2 characterized severe COVID-19 in adults. Severe cases tended to show slightly higher URT shedding post-symptom onset, but similar rates of viral clearance, when compared to nonsevere infections. After stratifying for disease severity, sex and age (including child vs. adult) were not predictive of respiratory shedding. The estimated accuracy for using LRT shedding as a prognostic indicator for COVID-19 severity was up to 81%, whereas it was up to 65% for URT shedding. Virological factors, especially in the LRT, facilitate the pathogenesis of severe COVID-19. Disease severity, rather than sex or age, predicts SARS-CoV-2 kinetics. LRT viral load may prognosticate COVID-19 severity in patients before the timing of deterioration and should do so more accurately than URT viral load. Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant, NSERC Senior Industrial Research Chair, and the Toronto COVID-19 Action Fund.

Potential Mechanical Ventilation System For Emergency Care During Spaceflight Missions

Neurally Adjusted Ventilation Assist (NAVA) technology is an autonomous mechanical ventilator that is triggered by diaphragm activity (EAdi) to provide the necessary assisted breath required by the patient. This technology could be an asset toward medical autonomy during spaceflight missions. PURPOSE: To test if NAVA has potential for increasing medical autonomy during spaceflights and to test ventilatory assist with NAVA at rest and during steady state physical exercise. METHODS: EAdi, respiratory frequency (RF), tidal volume (VT) and pulmonary ventilation (VE) were measured on 5 participants (males, age: 24.8 ± 2.8 yrs, height: 1.74 ± 0.07 m, weight: 71.8 ± 11.9 kg, V02max: 51.42 ± 5.32 ml/kg/min) during 6 minutes of resting breathing (T0) and during 10 minutes at 70% of V02max on an ergocycle (T1: minutes 1-3 and T2: minutes 8-10). This protocol was performed without (WO) and with NAVA (W) 30 minutes later. Paired T-tests were performed between both conditions. RESULTS: A slightly lower EAdi was observed with NAVA at T0 (WO: 3.52 ± 1.04 μV, W: 2.67 ± 0.88 μV, p = 0.2761), T1 (WO: 15.74 ± 4.79 μV, W: 15.34 ± 6.16 μV, p = 0.9190) and T2 (WO:23.42 ± 4.4 μV, W:23.19 ± 2.83 μV, p = 0.9105). However, NAVA was activated at every inspiration meaning that the electrodes on the naso-gastric tube can capture EAdi at high RF; T0 (WO: 13 ± 3, W: 14 ± 6 breaths/min), T1 (WO: 21 ± 2, W: 18 ± 4) and T2 (WO: 27 ± 4 and W: 23 ± 4). VE was also slightly lower with NAVA at T2 (WO: 63.17 ± 7.72, W: 59.78 ± 7.52 L/min), but these results were not significant. VT was slightly higher with NAVA at T0 (WO:1.08 ± 0.3, W: 1.22 ± 0.75 L/breath), T1 (WO:2.11 ± 0.46, W:2.32 ± 0.8 L/breath) and T2 (WO:2.43 ± 0.47, W: 2.67 ± 0.76 L/breath), but these results were not statistically significant. Also, the mechanical ventilator portion triggered by NAVA was unable to offer sufficient positive pressure to maintain inspiratory flow during exercise (peaked during first minute of exercise). CONCLUSION: NAVA is light, portable, and auto adjustable, which are desirable characteristics for medical equipment for spaceflight missions. It provided assisted breathing at rest but was unable to offered limited mechanical ventilation airflow during exercise. Funding: Annie Martin received a scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC) for this project.

Molecular protectors: Superheroes for nanostructures

Molecular protectors: Superheroes for nanostructures

Overview of Canada's energy storage related research activities: A perspective

Overview of Canada's energy storage related research activities: A perspective

Heterogeneity in transmissibility and shedding SARS-CoV-2 via droplets and aerosols.

Which virological factors mediate overdispersion in the transmissibility of emerging viruses remains a long-standing question in infectious disease epidemiology. Here, we use systematic review to develop a comprehensive dataset of respiratory viral loads (rVLs) of SARS-CoV-2, SARS-CoV-1 and influenza A(H1N1)pdm09. We then comparatively meta-analyze the data and model individual infectiousness by shedding viable virus via respiratory droplets and aerosols. The analyses indicate heterogeneity in rVL as an intrinsic virological factor facilitating greater overdispersion for SARS-CoV-2 in the COVID-19 pandemic than A(H1N1)pdm09 in the 2009 influenza pandemic. For COVID-19, case heterogeneity remains broad throughout the infectious period, including for pediatric and asymptomatic infections. Hence, many COVID-19 cases inherently present minimal transmission risk, whereas highly infectious individuals shed tens to thousands of SARS-CoV-2 virions/min via droplets and aerosols while breathing, talking and singing. Coughing increases the contagiousness, especially in close contact, of symptomatic cases relative to asymptomatic ones. Infectiousness tends to be elevated between 1 and 5 days post-symptom onset. Intrinsic case variation in rVL facilitates overdispersion in the transmissibility of emerging respiratory viruses. Our findings present considerations for disease control in the COVID-19 pandemic as well as future outbreaks of novel viruses. Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant program, NSERC Senior Industrial Research Chair program and the Toronto COVID-19 Action Fund.

NSERC discovery grants and a tribute to Leo A. Behie

AbstractThe scope of chemical engineering continues to evolve and has become ever more multifaceted. It encompasses traditional fields like polymers, thermodynamics, transport processes, control, and environmental science, but has expanded to include biotechnology, biomedical, food technology, materials, and numerical techniques like artificial neural networks and discrete element methods. In fact, the Natural Sciences and Engineering Research Council of Canada (NSERC) combines chemical engineering and materials in the same evaluation group to award competitive funding for the Discovery Grant. Prof. Leo Behie's career reflected the change in the scope of chemical engineering. In the 1970s and early 1980s, Prof. Behie's research included hydrodynamics of fluidized beds and deriving the kinetics of the Claus reaction. In the late 1980s and into the 1990s, he contributed to biotechnology. In the 2000s and 2010s, his areas of expertise related to biomedical engineering comprising stem cell research and a focus on Parkinson's and Huntington's diseases. The common denominator for most of his research was reactor technology. In 2014, Prof. Behie quipped that chemical engineering was dead and many North American departments shared this tenet and added various scientific fields to recognize the emerging synergies. Here, we show that chemical engineering is a vibrant and growing field. We demonstrate in what way it is changing and describe how NSERC evaluates research dossiers for the Discovery Grants. We describe the relationship between the hindex and the number of citations and confirm that bibliometrics has only a minor role in the Discovery Grant award.

Relevance of differential control of sympathorespiratory response magnitudes in clinical assessments.

Relevance of differential control of sympathorespiratory response magnitudes in clinical assessments.

The Effect of Persuasive Design on the Adoption of Exposure Notification Apps: A Case Study of COVID Alert

Background: The COVID-19 pandemic began in the first quarter of 2020 necessitated the imposition of public health restrictions and the shutting down of the global economy. To slow down the spread of the coronavirus, governments worldwide rolled out nationwide contact tracing apps (CTAs) to notify people that may have been exposed to COVID-19. The emergence of new variants of COVID-19, which can cause breakthrough infections, necessitate the continued use of CTAs. However, the uptake of these apps has been low and slow worldwide. Some experts have argued that the low adoption rate of CTAs can be attributed to their minimalist design and lack of motivational features, trust- and privacy-related issues aside. However, there is little to no research to show that the incorporation of persuasive principles in the design of CTAs has the potential of increasing their effectiveness and adoption. Method: To bridge the gap in the extant literature, we conducted an empirical study on Amazon Mechanical Turk to investigate the effect of persuasive design in CTAs using the Government of Canada’s exposure notification app (“COVID Alert”) as a case study. Our study is based on 204 participants (comprising adopters and non-adopters) resident in Canada and two app designs: persuasive and control.Findings: Regarding the willingness to download the COVID Alert app, our three-way analysis of variance (ANOVA) shows there is an interaction between adoption status and app design. Among adopters, there is no significant difference between the persuasive and the control design. However, among non-adopters, there is an effect of app design (p p Interpretation: The results of our study show that non-adopters are more likely to download the persuasive version of a CTA (equipped with self-monitoring) than the control version. Moreover, adopters are more likely to report their COVID-19 diagnosis using the persuasive version of a CTA (equipped with social-learning) than the control version. Overall, the study shows that that CTAs are more likely to be effective if equipped with persuasive features.Funding Information: Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (RGPIN-2017-05310) and Cybersecurity and Privacy Institute, University of Waterloo.Declaration of Interests: None to declare. Ethics Approval Statement: Our survey was approved by the Research Ethics Board of our university.

An Accelerated Mechanical Stress Test for Evaluating Fatigue Durability of Reinforced Fuel Cell Membranes

For evaluating the durability of membranes in polymer electrolyte fuel cells (PEFCs) within relatively short time, accelerated stress tests (AST) are used for applying chemical and mechanical stressors by means of current density, cell voltage, temperature, and relative humidity (RH) cycling. The U.S. Department of Energy (DOE) standardized RH cycling test is considered as a routine screening test for evaluating the mechanical durability under cyclic mechanical stresses [1]. Due to limitation in diffusion kinetics of water in the membrane, each RH cycle often takes several minutes that consequently restricts the magnitude of the induced mechanical stress. Therefore, conventional mechanical ASTs become time-consuming and expensive, especially as more durable membranes are being adopted.A typical mechanical degradation mitigation strategy is to insert an insulating and chemically-inert reinforcement layer, e.g., a thin microporous expanded polytetrafluoroethylene (ePTFE) mesh in the membrane to improve dimensional stability in response to RH-induced membrane expansion and contraction. The reinforcement layer provides additional mechanical strength and enables the use of thinner and more conductive ionomer that would otherwise have insufficient strength. When tested using mechanical ASTs, reinforced membranes possessed longer lifetime [2,3].Experimental work on application of ASTs to fuel cell membranes was previously performed [4] where an accelerated membrane durability test (AMDT) was developed to characterize membrane stability when subjected to chemical and mechanical degradation relevant to field operation. In another work [5], mechanical ASTs were performed via in situ RH cycling with longer dry cycles (for maximizing the fatigue stress amplitude) and at a higher temperature than the DOE protocol. Using these conventional protocols, it is expected that tests with reinforced membranes will continue beyond 20,000 cycles (as defined by DOE [1]) without reaching failure. An ex situ blister test method was used for bi-axial fatigue-creep testing by cycling air pressure [6,7]. In this case, the inherent hygroscopic membrane properties, i.e., water uptake and dimensional changes, which are the actual source of in situ fatigue and mechanical degradation in the constrained fuel cell environment, were not considered.In this work, a custom-developed mechanical AST procedure, based in part on the DOE-standardized AST for mechanical membrane degradation [1], was developed and used for evaluating the mechanical fatigue durability of reinforced membranes in a shorter time. Here, mechanical stressors were applied to the membrane using a sustained pressure differential (ΔP) combined with RH cycling at 80oC in a bi-axial, fuel cell inspired configuration. For validation of the developed method, denoted as ΔP-AMST, ePTFE-reinforced membranes were cycled using 4 min dry (0% RH) and 2 min wet (100% RH) cycles along with a ΔP ranging from 7 to 14 kPa. When the ΔP was applied, a transparent polycarbonate spacer, placed between the cathode and anode, allowed inflation of the membrane by means of a through-thickness hole, as shown in Figure 1. In order to prevent chemical degradation, nitrogen was used as the carrier gas in the ΔP-AMST instead of air, which is used in the DOE method [1]. Depending on the applied ΔP, reinforced membranes failed within ~10 to 10,000 RH cycles, the failure criterion being the loss of ΔP, indicative of major gas leakage through the degraded membrane. Therefore, compared to conventional mechanical ASTs, this novel mechanical AST could be used as a rapid and economical in situ alternative for evaluating the mechanical durability of advanced fuel cell membranes. Acknowledgements This research was supported by Mitacs, Automotive Fuel Cell Cooperation (AFCC), Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, and Simon Fraser University. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

A Maturation Process or Binders Based on Coordination Chemistry to Boost the Mechanical Strength and Cyclability of Si-Based Electrodes

Silicon is attractive as negative electrode material for Li-ion batteries (LIBs) to increase their energy density [1]. The main challenge is to deal with the large silicon volume expansion induced by its lithiation, which damages the mechanical integrity of the electrode, and produces an unstable solid electrolyte interphase (SEI).Recently, we have discovered a post-processing treatment, called maturation, which very significantly improves the mechanical and electrochemical stabilities of silicon-based electrodes made with polycarboxylic acid binders [2-4]. It consists of storing the electrode in a humid atmosphere for a few days before drying and cell assembly. We found that during maturation, the atmospheric-induced corrosion of the current collector releases oxidized copper species that migrate into the electrode to physically crosslink the binder phase, substantially modifying its resiliency to the silicon volume variation as shown by various in situ and operando characterizations. The pre-addition of a small amount of copper or zinc salt in the electrode slurry allows to reach similar improvement of electrochemical performance than maturation [5]. This reveals that there is great potential to explore coordination chemistry to design new, more efficient binders through the medium strength and dynamic nature of coordination bonds [6]. Acknowledgments The authors thank the Natural Sciences and Engineering Research Council of Canada (NSERC) (grant RGPIN-2016-04524) and Transition Énergétique Québec (TEQ) (grant Techno-0040-0001) for financial support of this work.

(Invited) Examining Catalyst Layer Design Strategies for Improved Fuel Cell Performance and Durability

Introduction The commercialization of fuel cell products for a variety of applications including forklifts, buses, cars and other heavy duty transport is well underway. Recent studies suggest that over the next 10 years, the total cost of ownership of fuel cell vehicles will become more favourable than both battery electric vehicles and internal combustion engine commercial vehicles1,2. This is driven, in part, by a forecasted almost 50% decrease in the cost of fuel cell systems. While this achievement is mainly due to product volume increases and related economies of scale, further improvements of fuel cell technology can be achieved through next generation catalyst layer designs.Design approaches related to the individual component characteristics, optimization of the component interactions to obtain enhanced morphology and microstructure, as well as processing techniques are currently being developed. Strategies to lower catalyst loadings and move to higher current operation and power densities include incorporating high activity catalysts and improving proton conductivity and oxygen transport by integrating advanced ionomers. Advanced cathode catalysts3 such as Pt alloy (de-alloy), core-shell and shape controlled nanocrystals show more promise in achieving higher mass activity than conventional carbon supported platinum catalyst, although durability or technology maturity challenges remain. Alternatively, while performance gains through ohmic improvements can be achieved by utilizing high proton conductivity ionomers4, additional opportunities such as incorporating novel ionomer materials5, with increased oxygen permeability to allow for reduction of the oxygen thin film transport resistance are of interest.In addition to maximizing the catalyst and ionomer attributes, catalyst-ionomer interaction understanding at the molecular scale and its influence on catalyst layer morphology and transport properties is crucial. Earlier studies of ionomer thin films6, molecular dynamics modeling7 as well as catalyst layer characterization by XPS8, indicate that the ionomer morphology within confined thin films, as well as the resulting film properties, are not only dependent on the surface properties of the substrate / catalyst material and water content, but can be altered in situ as those parameters change. Therefore, the catalyst-ionomer interaction and morphology must be better understood and controlled. Although it can be optimized through design choices, processing parameters during catalyst layer fabrication can also be effective. For example, Figure 1a) shows changes to the cathode catalyst layer pore size distribution with four different processes, incorporating changes to the ink preparation, coating and drying parameters, while keeping the same catalyst layer composition and loading. The optimized process resulted in improved catalyst and ionomer dispersion, lower ionic resistivity and improved performance. Moreover, Figure 1b) shows a clear relationship of improved performance with larger catalyst layer pore size.In addition to microstructural characteristics, macroscopic non-uniformities of the catalyst layer, such as cracks and roughness variations, can also affect the performance and durability of the MEA and are an area of focus for quality control tools9. Recent four dimensional X-ray computed tomography studies have shown how pre-existing cracks within the catalyst layer grow with accelerated stress testing and can be detrimental to both the voltage and membrane durability of the MEA10-11. All in all, a multiscale research approach to gain understanding focussed on nanoscale, microscale and macroscale features of the catalyst layer for next generation designs is recommended and will be the focus of the presentation. Acknowledgement The authors would like to acknowledge Natural Sciences and Engineering Research Council of Canada (NSERC), Mitacs, Automotive Partnership Canada (APC), and the US Department of Energy (DOE) for funding various aspects of this work. References Deloitte and Ballard. (2020). Fueling the Future of Mobility: Hydrogen and fuel cell solutions for transportation. Volume 1 [White paper]. 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Machine learning for predicting AF ablation outcomes using daily heart rhythm data at baseline

Abstract Background While numerous studies have shown that catheter ablation is superior to antiarrhythmic drug (AAD) in treating atrial fibrillation (AF), the long term outcomes have been limited by arrhythmia recurrence. Reliable data and methods to predict ablation outcomes will thus be valuable for treatment planning. Objective To evaluate the utility of machine learning and various types of input variables, viz. patient characteristics at baseline, and daily heart rhythm data recorded prior to ablation for outcome prediction. Methods We acquired permission to analyze data collected from a randomized clinical trial that recorded daily biomeasures from &amp;gt;345 patients who were referred for first catheter ablation due to AF refractory to at least one AAD. After standardizing the dataset, each patient sample is characterized by a set of daily measures, viz. heart rate variability (HRV) and AF burden (AFB), which is the total minutes in AF per day. We next performed comparative analyses on 19 candidate model variants to evaluate each model's ability in identifying patients who were to experience at least one episode of AF recurrence during post-ablation period starting from day 91 up to day 365 post-ablation, per standard guidelines. We examined: i) use of a set of daily biomeasures jointly with baseline sex and age; and ii) observation lengths of the pre-ablation period. We also examined the use of baseline CHA2DS2-VASc scores, left-atrial volume (LAV), atrial diameter, medical history. We conducted multiple sets of 3-fold cross validation (CV) experiments, each fold independently trained a candidate model with 236 samples (two thirds of the dataset) and performed evaluation on the left-out samples. About 50% of cohort belongs to one class. Each fold scored a model and its input variables in terms of sensitivity (SEN), specificity (SPEC), area under receiver operating characteristic curve (AUC), etc. To circumvent risks of overfitting highly parameterized models to our training subset, we shortlisted 19 models that have few hyper-parameters, e.g. stepwise regression, random forest (RF), linear discriminant analysis (LDA). Results CV results demonstrated that LDA and RF gave comparable performances, with RF achieving highest AUC of 0.68±0.06 using 30 days of rhythm data prior to ablation (SEN of 65.9±7.82; SPEC of 66.3±0.57). When observation period extended to 90 days prior, AUC improved to 0.691±0.02. In contrast, use of LAV alone was not adequate to predict outcome (AUC∼0.5), and when combined with all aforementioned baseline variables, the best model achieved AUC of 0.58±0.05. Feature analyses from the trained models suggest that AFB had highest relevance in predicting outcome. Using only daily AFB, RF and LDA respectively achieved AUC of 0.608±0.04 and 0.652±0.04. Conclusions Our results suggest the value of pre-ablation rhythm data for improving outcome-prediction. Future work will validate these findings using large public datasets. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): Huawei-Data Science Institute Research Program; Natural Sciences and Engineering Research Council of Canada (NSERC)