585 results on '"Friedrich K"'
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2. Stabilizing Pure Water-Fed Anion Exchange Membrane Water Electrolyzers through Membrane–Electrode Interface Engineering
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Kang, Sinwoo, Kim, Yeongin, Wilke, Vincent, Bae, Sooan, Chmielarz, Jagoda J., Sanchez, Daniel G., Ham, Kahyun, Gago, Aldo S., Friedrich, K. Andreas, and Lee, Jaeyoung
- Abstract
Nickel–iron (oxy)hydroxide (NiFeOxHy) stands as a cutting-edge nonprecious electrocatalyst for the oxygen evolution reaction (OER). However, the intrinsic thermodynamic instability of nickel and iron as anode materials in pure water-fed electrolyzers poses a significant durability challenge. In this study, an anion exchange ionomer coating was applied to NiFeOxHyto modify the local pH between a membrane and an electrode. This effectively extended the diffusion length of hydroxide anions toward the electrode, establishing an alkaline local pH environment. Stability tests with the ionomer coating showed reduced Ni dissolution. Moreover, locally resolved current density measurements were used to demonstrate a notably lower degradation rate during stability testing, revealing a 6-fold increase in stability with the ionomer on NiFeOxHy. In situ Raman spectroscopy in a neutral pH electrolyte confirmed inhibited Ni oxidation with the ionomer, mitigating Ni dissolution and enhancing stability of state-of-the-art NiFeOxHycatalysts in pure water-fed water electrolyzers.
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- 2024
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3. Der Operationsplan für die polnischen Streitkräfte von 1964
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Jeschonnek, Friedrich K.
- Abstract
Im Rahmen der Warschauer Vertragsorganisation (WVO) wurde hinsichtlich der Operationsplanung für den Kriegsfall unter sowjetischer Führung bi- und multinational zusammengearbeitet. Hierzu gehörte, dass der Einsatz der Polnischen Küstenfront vom Gebiet der DDR aus vorgesehen war. Dies erforderte besondere Abstimmungen und weitergehende Unterstützungsleistungen durch die DDR. Anfänge bildeten polnische Erkundungen des Einsatzraumes, im Weiteren war die Unterstützung des polnischen Angriffs durch Kräfte des 5. Armeekorps (bzw. ab 1983 der 5. Armee) der NVA und die Raumordnung für die Küstenfront zu koordinieren. Diese Abstimmungen erfolgten dann, wenn sich erhebliche und gravierende Änderungen in der polnischen Planung ergaben. Weitere Unterstützungsleistungen wurden im Rahmen der Operativen Vorbereitung des Territoriums für den Kriegsfall von der DDR vorbereitet. Auf Basis der operativen Planungen führten die NVA und die PVA im Rahmen der WVO über Jahrzehnte militärische Übungen in Anlehnung an ihre Einsatzoptionen durch. Das Zusammenwirken war in den 1980er Jahren aufgrund der politischen und militärischen Veränderungen nicht immer frei von Irritationen. Viele der polnischen Forderungen zur Einsatzvorbereitung des Territoriums wurden trotz immer knapper werdender Ressourcen der DDR erfüllt oder zugesagt. Die Kooperation mündete 1986 in ein gemeinsames Protokoll über die Unterstützung der Küstenfront durch die NVA. Aufgrund der Geheimhaltung und anderer Konsultationswege in der WVO war das bilaterale operative Zusammenwirken sporadisch und bedarfsorientiert.
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- 2024
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4. Preoperative Midazolam and Patient-Centered Outcomes of Older Patients: The I-PROMOTE Randomized Clinical Trial
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Kowark, Ana, Keszei, András P., Schneider, Gerhard, Pilge, Stefanie, Schneider, Frederick, Obert, David P., Georgii, Marie-Therese, Heim, Markus, Rossaint, Rolf, Ziemann, Sebastian, van Waesberghe, Julia, Czaplik, Michael, Pühringer, Friedrich K., Minarski, Christian, May, Verena, Malisi, Tobias, Drexler, Berthold, Ring, Carmen Maria, Engler, Phillip, Tilly, Roman, Bischoff, Petra, Frey, Ulrich, Wittmann, Maria, Soehle, Martin, Saller, Thomas, Kienbaum, Peter, Kretzschmar, Moritz, and Coburn, Mark
- Abstract
IMPORTANCE: The effect of oral midazolam premedication on patient satisfaction in older patients undergoing surgery is unclear, despite its widespread use. OBJECTIVE: To determine the differences in global perioperative satisfaction in patients with preoperative administration of oral midazolam compared with placebo. DESIGN, SETTING, AND PARTICIPANTS: This double-blind, parallel-group, placebo-controlled randomized clinical trial was conducted in 9 German hospitals between October 2017 and May 2019 (last follow-up, June 24, 2019). Eligible patients aged 65 to 80 years who were scheduled for elective inpatient surgery for at least 30 minutes under general anesthesia and with planned extubation were enrolled. Data were analyzed from November 2019 to December 2020. INTERVENTIONS: Patients were randomized to receive oral midazolam, 3.75 mg (n = 309), or placebo (n = 307) 30 to 45 minutes prior to anesthesia induction. MAIN OUTCOMES AND MEASURES: The primary outcome was global patient satisfaction evaluated using the self-reported Evaluation du Vécu de l’Anesthésie Generale (EVAN-G) questionnaire on the first postoperative day. Key secondary outcomes included sensitivity and subgroup analyses of the primary outcome, perioperative patient vital data, adverse events, serious complications, and cognitive and functional recovery up to 30 days postoperatively. RESULTS: Among 616 randomized patients, 607 were included in the primary analysis. Of these, 377 (62.1%) were male, and the mean (SD) age was 71.9 (4.4) years. The mean (SD) global index of patient satisfaction did not differ between the midazolam and placebo groups (69.5 [10.7] vs 69.6 [10.8], respectively; mean difference, −0.2; 95% CI, −1.9 to 1.6; P = .85). Sensitivity (per-protocol population, multiple imputation) and subgroup analyses (anxiety, frailty, sex, and previous surgical experience) did not alter the primary results. Secondary outcomes did not differ, except for a higher proportion of patients with hypertension (systolic blood pressure ≥160 mm Hg) at anesthesia induction in the placebo group. CONCLUSION AND RELEVANCE: A single low dose of oral midazolam premedication did not alter the global perioperative patient satisfaction of older patients undergoing surgery or that of patients with anxiety. These results may be affected by the low dose of oral midazolam. Further trials—including a wider population with commonplace low-dose intravenous midazolam and plasma level measurements—are needed. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03052660
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- 2024
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5. Magnesium Anode Protection by an Organic Artificial Solid Electrolyte Interphase for Magnesium-Sulfur Batteries.
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Häcker, Joachim, Rommel, Tobias, Lange, Pia, Zhao-Karger, Zhirong, Morawietz, Tobias, Biswas, Indro, Wagner, Norbert, Nojabaee, Maryam, and Friedrich, K. Andreas
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- 2023
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6. Explaining International Trends in Mortality on Hemodialysis Through Changes in Hemodialysis Practices in the Dialysis Outcomes and Practice Patterns Study (DOPPS)
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McCullough, Keith P., Morgenstern, Hal, Rayner, Hugh C., Port, Friedrich K., Jadoul, Michel Y., Akizawa, Tadao, Pisoni, Ronald L., Herman, William H., Robinson, Bruce M., Al-Aradi, Dr. Ali, Jadoul, Michel, Evenepoel, Pieter, Sood, Manish, Suri, Rita, Zuo, Li, Chen, Yuqing, Ni, Zhaohui, Chen, Xiaonong, Hou, Fanfan, Liang, Xinling, Combe, Christian, Guebre-Egziabher, Fitsum, Antonio Ureña Torres, Pablo, Kleophas, Werner, Schaeffner, Elke, Weinreich, Thomas, Brunori, Giuliano, Messa, Piergiorio, Nitta, Kosaku, Inaba, Masaaki, Fukagawa, Masafumi, Sakai, Ken, Tsuruya, Kazuhiko, Hamano, Takayuki, Honda, Hirokazu, Hoshino, Junichi, Komaba, Hirotaka, Nakano, Toshiaki, Al Helal, Bassam, Alkandari, Naser, AlRajab, Heba, Alyousef, Anas, Al Maimani, Yacoub, Alsalmi, Issa, Al Ali, Fadwa, Hamad, Abdulla, Al-Ghamdi, Saeed, Al Ghonaim, Mohammed, Al Wakeel, Jamal, Hejaili, Fayez, Karkar, Ayman, Shaheen, Faissal, Jacobson, Stefan, Christensson, Anders, Cases, Aleix, Vega Martínez, Almudena, Abdulkarim Al Obaidli, Ali, Al Rukhaimi, Mona, Hassan, Mohamed, Kareem Saleh, Abdul, Asgari, Elham, and Dasgupta, Indranil
- Abstract
Case-mix adjusted hemodialysis mortality has decreased since 1998. Many factors that influence mortality may have contributed to this trend, and these associations may differ by continental region. We studied changes in hemodialysis facility practices over time and their potential role in mediating changes in patient survival.
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- 2025
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7. Fluid volume management in hemodialysis: never give up!
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Hecking, Manfred, Madero, Magdalena, Port, Friedrich K., Schneditz, Daniel, Wabel, Peter, and Chazot, Charles
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Every hemodialysis session starts with the question of how much fluid should be removed, which can currently not be answered precisely. Herein, we first revisit the “probing-dry-weight” concept, using the historical example of Tassin/France (practicing also “long, slow dialysis”): Mortality outcomes were, in the 1980s, better than registry data, but are nowadays similar to European average. In view of the negative primary end point in a recent trial on dry weight assessment, based on lung ultrasound-guided evaluation of fluid excess in the lungs, and a meta-analysis of prospective studies failing to show that bioimpedance-based interventions for correction of volume overload had a direct effect on all-cause mortality, we ask how to ever move forward. Clinical reasoning demands that as much information as possible should be gathered on the fluid status of patients undergoing dialysis. Besides body weight and blood pressure, measurements of bioimpedance and dialysate bolus–derived absolute blood volume can in principle be automatized, whereas lung ultrasound can be obtained routinely. In the era of machine learning, fluid management could consist of flexible target weight prescriptions, adjusted on a daily basis and accounting even for fluctuations in fluid-free body mass. In view of all the negative prospective results surrounding fluid management in hemodialysis, we propose this as a “never-give-up” approach.
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- 2023
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8. Operational Aspects of a Perovskite Chromite-Based Fuel Electrode in Solid Oxide Electrolysis Cells (SOEC).
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Amaya-Dueñas, Diana M., Riegraf, Matthias, Nenning, Andreas, Opitz, Alexander K., Costa, Rémi, and Friedrich, K. Andreas
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- 2022
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9. Dialysate Sodium and Mortality
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Hecking, Manfred, Karaboyas, Angelo, Krenn, Simon, Mussnig, Sebastian, Beige, Joachim, Chazot, Charles, Pecoits-Filho, Roberto, Rayner, Hugh, and Port, Friedrich K.
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- 2024
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10. Deciphering the Exceptional Performance of NiFe Hydroxide for the Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyzer.
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Wang, Li, Saveleva, Viktoriia A., Eslamibidgoli, Mohammad J., Antipin, Denis, Bouillet, Corinne, Biswas, Indro, Gago, Aldo S., Hosseiny, Seyed S., Gazdzicki, Pawel, Eikerling, Michael H., Savinova, Elena R., and Friedrich, K. Andreas
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- 2022
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11. Operando UV/vis Spectroscopy Providing Insights into the Sulfur and Polysulfide Dissolution in Magnesium-Sulfur Batteries.
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Häcker, Joachim, Duc Hien Nguyen, Rommel, Tobias, Zhirong Zhao-Karger, Wagner, Norbert, and Friedrich, K. Andreas
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- 2022
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12. PEM Single Cells under Differential Conditions: Full Factorial Parameterization of the ORR and HOR Kinetics and Loss Analysis.
- Author
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Gerling, Christophe, Hanauer, Matthias, Berner, Ulrich, and Friedrich, K. Andreas
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FACTORIALS ,PARAMETERIZATION ,PARTIAL pressure ,HYDROGEN oxidation ,OXYGEN reduction ,ACTIVATION energy - Abstract
The anode and cathode kinetics are parameterized based on differential cell measurements. Systematic parameter variations are evaluated to disentangle the dependencies of the electrochemical impedance spectroscopy (EIS) signatures in H
2 /H2 mode. We introduce a new CO recovery protocol for both electrodes that enables to accurately characterize the hydrogen oxidation reaction (HOR) kinetics. Then, we demonstrate that a compact Tafel kinetics law captures the oxygen reduction reaction (ORR) kinetics for a full factorial grid of conditions, covering a wide range of relative humidities (rH), temperatures, oxygen partial pressures and current densities. This yields the characteristic activation energy and effective reaction order, and we reconcile models that make different assumptions regarding the rH dependency. Moreover, we analyze O2 transport contributions by steady-state and transient limiting current techniques and heliox measurements. Although the rising uncertainty of loss corrections at high current densities makes it impossible to unambiguously identify an intrinsic potential-dependent change of the Tafel slope, our data support that such effect needs not be considered for steady-state cathodic half-cell potentials above 0.8 V. [ABSTRACT FROM AUTHOR]- Published
- 2022
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13. Full Factorial In Situ Characterization of Ionomer Properties in Differential PEM Fuel Cells.
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Gerling, Christophe, Hanauer, Matthias, Berner, Ulrich, and Friedrich, K. Andreas
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PROTON exchange membrane fuel cells ,FACTORIALS ,GAS analysis ,ELECTRIC lines ,IMPEDANCE spectroscopy - Abstract
The performance optimization of membrane electrode assemblies of PEM fuel cells requires accurate characterization and modelling of the relevant mechanisms. In this paper, the ionomer conductivities and permeation properties are characterized in situ in a differential cell setup by varying the operating conditions in a full factorial fashion in H
2 /N2 mode. Voltammetry methods are validated against online gas analysis and then used to record H2 crossover. The membrane and cathode catalyst layer (CCL) resistances are deconvoluted by fitting transmission line models (TLM) to electrochemical impedance spectroscopy (EIS) data. Based on this, we estimate activation energies of 20 kJ mol-1 for the H2 permeation, 7 kJ mol-1 for the membrane resistance and 9 kJ mol-1 for the ionomer resistance in the CCL. Through EIS measurements under load (H2 /O2 ), we also evaluate the change in the ionomer resistances in course of water production. This effect is most pronounced under cold and dry conditions and implies that a subtraction of the protonic loss contributions from polarization curves only based on EIS measurements obtained in H2 /N2 mode is not possible. [ABSTRACT FROM AUTHOR]- Published
- 2021
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14. Insights into Self-Discharge of Lithium– and Magnesium–Sulfur Batteries.
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Richter, Raphael, Häcker, Joachim, Zhirong Zhao-Karger, Danner, Timo, Wagner, Norbert, Fichtner, Maximilian, Friedrich, K. Andreas, and Latz, Arnulf
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- 2020
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15. Influence of Cycling Profile, Depth of Discharge and Temperature on Commercial LFP/C Cell Ageing: Cell Level Analysis with ICA, DVA and OCV Measurement.
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Simolka, M., Heger, J.-F., Traub, N., Kaess, H., and Friedrich, K. A.
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CELLULAR aging ,CELL analysis ,TEMPERATURE ,LITHIUM cell electrodes - Abstract
This paper uses several techniques to monitor the ageing of commercial LiFePO
4 cells, which are cycled at 55 °C and −20 °C at various depths of discharge. Ageing at lower depth of discharge leads to higher capacity fading, as compared to higher depth of discharge. The highest capacity fading is observed using 50% depth of discharge for cycling at 55 °C, while the lowest capacity fading is observed for the cells aged at 100% depth of discharge when cycled at −20 °C. Using incremental capacity analysis and differential voltage analysis the capacity fading is monitored and underlying ageing mechanisms are described. The loss of lithium inventory and the loss of active material, especially on the cathode side, are the major degradation mechanisms for the cells. The first incremental capacity analysis peak of the discharge process can be used in our case to predict remaining life and cell capacity. [ABSTRACT FROM AUTHOR]- Published
- 2020
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16. Early Postoperative Basal Insulin Therapy versus Standard of Care for the Prevention of Diabetes Mellitus after Kidney Transplantation: A Multicenter Randomized Trial
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Schwaiger, Elisabeth, Krenn, Simon, Kurnikowski, Amelie, Bergfeld, Leon, Pérez-Sáez, María José, Frey, Alexander, Topitz, David, Bergmann, Michael, Hödlmoser, Sebastian, Bachmann, Friederike, Halleck, Fabian, Kron, Susanne, Hafner-Giessauf, Hildegard, Eller, Kathrin, Rosenkranz, Alexander R., Crespo, Marta, Faura, Anna, Tura, Andrea, Song, Peter X. K., Port, Friedrich K., Pascual, Julio, Budde, Klemens, Ristl, Robin, Werzowa, Johannes, and Hecking, Manfred
- Published
- 2021
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17. Bowel dysfunction after elective spinal surgery: etiology, diagnostics and management based on the medical literature and experience in a university hospital
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Jaber, A., Hemmer, S., Klotz, R., Ferbert, T., Hensel, C., Eisner, C., Ryang, Y. M., Obid, P., Friedrich, K., Pepke, W., and Akbar, M.
- Abstract
Background: Bowel dysfunction after spinal surgery is often underestimated and if not treated in a timely manner can lead to undesirable surgical interventions or fatal complications. The current medical literature primarily focuses on bowel dysfunction as a result of spinal injury. Objective: The purpose of this review is to explore this topic in evaluating current evidence regarding the causes of acute bowel dysfunction after elective spinal surgery, primarily the thoracolumbar spine. Since available evidence for recommendations of treatment is scarce, an interdisciplinary management approach for treatment of bowel dysfunction following spinal surgery is also formulated. Material and methods: An extensive literature search was carried out on PubMed. Keywords that were used in the search included bowel dysfunction, obstruction, postoperative ileus, spinal surgery, spinal fusion, constipation, opioid-induced constipation, colonic pseudo-obstruction, ischemic colitis, immobility-induced bowel changes, epidural anesthesia and diet. Relevant studies were chosen and included in the review. The treatment approach used in the spine center of a university hospital was included. Results: Current research mainly focuses on investigating the nature and symptomatology of chronic bowel dysfunction after spinal cord injury. Emphasis on the acute phase of bowel dysfunction in patients after elective spinal surgery is lacking. The comorbidities that exacerbate bowel dysfunction postoperatively are well-defined. There has been refinement and expansion of the pharmacological and nonpharmacological treatment that could be implemented. Enough evidence exists to provide sufficient care. Conclusion: Management of acute bowel dysfunction after spinal surgery requires a comprehensive and individualized approach, encompassing comorbidities, behavioral changes, medications and surgery. Close supervision and timely treatment could minimize further complications. Research is required to identify patients who are at a higher risk of developing bowel dysfunction after specific spinal procedures.
- Published
- 2021
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18. Von der Kurvendiskussion zum Internet der Dinge
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Jondral, Friedrich K.
- Abstract
Ausgehend von der Schulmathematik, skizzieren wir einen leicht nachvollziehbaren Weg zum Verständnis des Internet der Dinge und von Industrie 4.0. Mit Hilfe des Bits als Informationsquant wird die Digitalisierung, d. h. die Überführung analoger Größen in diskrete Werte, anschaulich am Beispiel des maschinellen Lesens erklärt. Die Digitalisierung als eine notwendige Voraussetzung für den Einsatz der Mikroelektronik ist Motor des rasanten technologischen Fortschritts der vergangenen 50 Jahre, der seinerseits an der Entwicklung des zellularen Mobilfunks von der Analogtechnik bis zur 5. Generation nachvollzogen werden kann.**
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- 2021
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19. Insight into the Mechanisms of High Activity and Stability of Iridium Supported on Antimony-Doped Tin Oxide Aerogel for Anodes of Proton Exchange Membrane Water Electrolyzers.
- Author
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Saveleva, V. A., Wang, L., Kasian, O., Batuk, M., Hadermann, J., Gallet, J.-J., Bournel, F., Alonso-Vante, N., Ozouf, G., Beauger, C., Mayrhofer, K. J. J., Cherevko, S., Gago, A. S., Friedrich, K. A., Zafeiratos, S., and Savinova, E. R.
- Published
- 2020
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20. Experimental Analysis of the Co-Electrolysis Operation under Pressurized Conditions with a 10 Layer SOC Stack.
- Author
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Riedel, M., Heddrich, M. P., and Friedrich, K. A.
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OPEN-circuit voltage ,THERMODYNAMIC equilibrium ,HIGH temperature electrolysis ,PROTON exchange membrane fuel cells ,ELECTROLYSIS ,DENSITY currents ,LOW temperatures - Abstract
This study examines the performance of a solid oxide cell (SOC) stack during co-electrolysis of CO2 and H2O at elevated pressures up to 8 bar. Steady-state and dynamically recorded U(i)-curves were performed in order to evaluate the performance over a wide temperature range and to quantify the area specific resistance (ASR) at different pressure levels. Furthermore, the outlet gas composition at various current densities was analyzed and compared with the thermodynamic equilibrium. The open circuit voltage (OCV) was found to increase with higher pressure due to well known thermodynamic relations. An increase of the limiting current density at elevated pressure was not observed for the investigated stack with electrolyte supported cells. The ASR of the stack was found to decrease slightly with higher pressure. It revealed an increase of the cell resistance with lower H/C ratios in the feed at lower temperatures, whereas the performance of the co-electrolysis was very similar to steam electrolysis for temperatures above 820 °C. Within an impedance study for steam, co- and CO2 electrolysis operation it was shown that pure CO2 electrolysis exhibits a higher pressure sensitivity compared to pure steam or co-electrolysis due to significantly increased activation and diffusion resistances. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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21. Die Rolle von Streitkräften während der Berlinkrise 1948/49.
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Jeschonnek, Friedrich K.
- Abstract
Copyright of Österreichische Militarische Zeitschrift is the property of Bundesministerium fuer Landesverteidigung, Landesverteidigungsakademie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2020
22. High Performance Anion Exchange Membrane Electrolysis Using Plasma-Sprayed, Non-Precious-Metal Electrodes.
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Li Wang, Weissbach, Thomas, Reissner, Regine, Ansar, Asif, Gago, Aldo S., Holdcroft, Steven, and Friedrich, K. Andreas
- Published
- 2019
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23. Electrochemical Impedance Analysis of Symmetrical Ni/Gadolinium-Doped Ceria (CGO10) Electrodes in Electrolyte-Supported Solid Oxide Cells.
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Riegraf, Matthias, Costa, Rémi, Schiller, Günter, Friedrich, K. Andreas, Dierickx, Sebastian, and Weber, André
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ELECTROCHEMICAL analysis ,SUPERIONIC conductors ,CERIUM oxides ,ELECTRODES ,ACTIVATION energy ,IMPEDANCE spectroscopy ,GADOLINIUM - Abstract
One of the most powerful tools in solid oxide cell (SOC) characterization is electrochemical impedance spectroscopy, which can unfold important insights into SOC performance characteristics and degradation behavior. To obtain a better understanding of the electrochemical behavior of Ni/CGO fuel electrodes, this work presents a comprehensive investigation of state-of-the-art Ni/CGO10-based electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10 symmetrical cells were characterized between 550-975°C at pH
2 = 0.8 bar and pH2 O = 0.2 bar, and for different H2/H2O gas mixtures at 550°C. (i) Small electrode area, (ii) thin electrodes and (iii) large gas flowrates were used to minimize mass transport contributions. Based on distribution of relaxation times (DRT) analysis an equivalent circuit model was derived. Electrode process contributions on Ni/CGO were determined bymeans of a complex non-linear least square fit of the equivalent circuit model to the experimental data. One lowfrequency process at 0.1-1 Hz and one middle frequency process at 10-100 Hz were identified and correlated to a surface and a bulk process, respectively. Values for the apparent activation energy barriers and reaction orders with respect to steam and hydrogen content were determined. [ABSTRACT FROM AUTHOR]- Published
- 2019
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24. About the Necessity to Consider Membrane Electrolyte Degradation Statistically
- Author
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Dlugosch, Thomas, Friedrich, K. Andreas, and Kirsch, Sebastian
- Abstract
Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are subjected to aging under pure mechanical, pure chemical and the combination of both stressors. Progression of degradation leads to membrane failures. In this study, seven different accelerated stress test (AST) protocols are applied to degrade two types of commercially available membrane electrode assemblies (MEAs) to demonstrate the necessity to evaluate lifetime of this system with statistical methods. In total, data from 56 samples is reported. Membrane lifetime is derived from hydrogen crossover and open circuit voltage (OCV) which is tracked over the course of degradation. The characteristic membrane lifetime distribution of each AST protocol is described via a cumulative Weibull distribution function (CDF). As a result, the scatter of lifetime distribution correlates with the lifetime itself and thus conclude that less repeats are required for ASTs creating short lifetimes compared to those causing long lifetimes. As the latter is required especially for membrane lifetime prediction, these conclusions are relevant for anybody designing the lifetime of PEMFC stacks.
- Published
- 2024
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25. Understanding the Role of Water Flow and the Porous Transport Layer on the Performance of Proton Exchange Membrane Water Electrolyzers.
- Author
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Garcia-Navarro, J., Schulze, M., and Friedrich, K. A.
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- 2019
- Full Text
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26. Operatives Denken, Planen und Führen als Forschungsgegenstand der Militärwissenschaft.
- Author
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Jeschonnek, Friedrich K.
- Abstract
Copyright of Österreichische Militarische Zeitschrift is the property of Bundesministerium fuer Landesverteidigung, Landesverteidigungsakademie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2018
27. High-Resolution Analysis of Ionomer Loss in Catalytic Layers after Operation.
- Author
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Morawietz, T., Handl, M., Oldani, C., Gazdzicki, P., Hunger, Jürgen, Wilhelm, Florian, Blake, John, Friedrich, K. A., and Hiesgen, R.
- Subjects
IONOMERS ,PROTON exchange membrane fuel cells ,CATALYTIC activity - Abstract
The function of catalytic layers in fuel cells and electrolyzers depends on the properties of the ionically conductive phase, which are most commonly perfluorinated ionomers based on Nafion and Aquivion. An analysis by atomic force microscopy reveals that the ultrathin ionomer films around Pt/C agglomerates have a thickness distribution ranging from 3.5 nm to 20 nm. Their conductivity and gas permeation properties determine the fuel cell performance to a large extend. For electrodes in Aquivion-based membrane-electrode-assemblies operation-induced structure changes were investigated by means of material- and conductivity-sensitive atomic force microscopy, infrared spectroscopy and electron-dispersive X-ray analysis. The observed thinning of the ultrathin ionomer films was mainly caused by polymer degradation deduced from reduced swelling after long-time operation and a significant loss of ionomer with operation time detected by infrared spectroscopy. From the linear thickness increase of the ultrathin films with rising humidity, a mainly layered structure of the ionomer was deduced. An influence of thickness of such ultrathin ionomer films on fuel cell lifetime was found by analysis of differently prepared membrane-electrode-assemblies, where a linear increase of irreversible degradation rate with ionomer film thickness in the electrodes of unused membrane-electrode-assemblies was found. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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- View/download PDF
28. International variation in dialysis discontinuation in patients with advanced kidney disease
- Author
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Jassal, Sarbjit V., Larkina, Maria, Jager, Kitty J., Murtagh, Fliss E.M., O’Hare, Ann M., Hanafusa, Norio, Morgenstern, Hal, Port, Friedrich K., McCullough, Keith, Pisoni, Ronald, Tentori, Francesca, Perlman, Rachel, and Swartz, Richard D.
- Abstract
BACKGROUND:Decisions about dialysis for advanced kidney disease are often strongly shaped by sociocultural and system-level factors rather than the priorities and values of individual patients. We examined international variation in the uptake of conservative approaches to the care of patients with advanced kidney disease, in particular discontinuation of dialysis.METHODS:We employed an observational cohort study design using data collected from patients maintained on long-term hemodialysis between 1996 and 2015 in facilities across 12 developed countries participating in the Dialysis Outcomes and Practice Patterns Study (DOPPS). The main outcome was discontinuation of dialysis therapy. We analyzed the association between several patient characteristics and time to dialysis discontinuation by country and phase of study entry.RESULTS:A total of 259 343 DOPPS patients contributed data to the study, of whom 48 519 (18.7%) died during the study period. Of the decedents, 5808 (12.0%) discontinued dialysis before death. Rates of discontinuation were higher within the first few months after initiation of dialysis, among older adults, among those with a greater number of comorbidities and among those living in an institution. After adjustment for age, sex, dialysis duration, diabetes and dialysis era, rates of discontinuation were highest in Canada, the United States and Australia/New Zealand (33.8, 31.4 and 21.5 per 1000/yr, respectively) and lowest in Japan and Italy (< 0.1 per 1000/yr). Crude discontinuation rates were highest in dialysis facilities that were more likely to offer comprehensive conservative renal care to older adults.INTERPRETATION:We found persistent international variation in average rates of dialysis discontinuation not explained by differences in patient case-mix. These differences may reflect physician-, facility- and society-level differences in clinical practice. There may be opportunities for international cross-collaboration to improve support for patients with end-stage renal disease who prefer a more conservative approach.
- Published
- 2020
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29. Stellar mergers as the origin of magnetic massive stars
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Schneider, Fabian R. N., Ohlmann, Sebastian T., Podsiadlowski, Philipp, Röpke, Friedrich K., Balbus, Steven A., Pakmor, Rüdiger, and Springel, Volker
- Abstract
About ten per cent of ‘massive’ stars (those of more than 1.5 solar masses) have strong, large-scale surface magnetic fields1–3. It has been suggested that merging of main-sequence and pre-main-sequence stars could produce such strong fields4,5, and the predicted fraction of merged massive stars is also about ten per cent6,7. The merger hypothesis is further supported by a lack of magnetic stars in close binaries8,9, which is as expected if mergers produce magnetic stars. Here we report three-dimensional magnetohydrodynamical simulations of the coalescence of two massive stars and follow the evolution of the merged product. Strong magnetic fields are produced in the simulations, and the merged star rejuvenates such that it appears younger and bluer than other coeval stars. This can explain the properties of the magnetic ‘blue straggler’ star τSco in the Upper Scorpius association that has an observationally inferred, apparent age of less than five million years, which is less than half the age of its birth association10. Such massive blue straggler stars seem likely to be progenitors of magnetars, perhaps giving rise to some of the enigmatic fast radio bursts observed11, and their supernovae may be affected by their strong magnetic fields12.
- Published
- 2019
- Full Text
- View/download PDF
30. Self-reported Urine Volume in Hemodialysis Patients: Predictors and Mortality Outcomes in the International Dialysis Outcomes and Practice Patterns Study (DOPPS)
- Author
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Hecking, Manfred, McCullough, Keith P., Port, Friedrich K., Bieber, Brian, Morgenstern, Hal, Yamamoto, Hiroyasu, Suri, Rita S., Jadoul, Michel, Gesualdo, Loreto, Perl, Jeffrey, and Robinson, Bruce M.
- Published
- 2019
- Full Text
- View/download PDF
31. In Memoriam: Hubertus Schulte Herbrueggen
- Author
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Unterweg, Friedrich-K.
- Published
- 2021
- Full Text
- View/download PDF
32. Upscaling of Reactive Mass Transport through Porous Electrodes in Aqueous Flow Batteries
- Author
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Wlodarczyk, Jakub K., Schärer, Roman P., Friedrich, K. Andreas, and Schumacher, Jürgen O.
- Abstract
Porous electrodes (PEs) are an important component of modern energy storage devices, such as lithium-ion batteries, flow batteries or fuel cells. Their complicated multiphase structure presents a considerable challenge to modeling and simulation. In this paper, we apply the volume-averaging method (VAM) as an efficient approach for the evaluation of effective macroscopic transport parameters in PEs. We consider the transport of electro-active species coupled to heterogeneous Butler-Volmer type reactions at the electrode surface. We identify the characteristic scales and dimensionless groups for the application to aqueous flow batteries. We validate the VAM-based model with direct numerical simulation results and literature data showing excellent agreement. Subsequently, we characterize several simplified periodic PE structures in 2D and 3D in terms of hydraulic permeability, effective dispersion and the effective kinetic number. We apply the up-scaled transport parameters to a simple macroscopic porous electrode to compare the overall efficiency of different pore-scale structures and material porosity values over a wide range of energy dissipation values. This study also reveals that the Bruggeman correction, commonly used in macroscopic porous electrode models, becomes inaccurate for realistic kinetic numbers in flow battery applications and should be used with care.
- Published
- 2024
- Full Text
- View/download PDF
33. Astrophysics with the Laser Interferometer Space Antenna
- Author
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Amaro-Seoane, Pau, Andrews, Jeff, Arca Sedda, Manuel, Askar, Abbas, Baghi, Quentin, Balasov, Razvan, Bartos, Imre, Bavera, Simone S., Bellovary, Jillian, Berry, Christopher P. L., Berti, Emanuele, Bianchi, Stefano, Blecha, Laura, Blondin, Stéphane, Bogdanović, Tamara, Boissier, Samuel, Bonetti, Matteo, Bonoli, Silvia, Bortolas, Elisa, Breivik, Katelyn, Capelo, Pedro R., Caramete, Laurentiu, Cattorini, Federico, Charisi, Maria, Chaty, Sylvain, Chen, Xian, Chruślińska, Martyna, Chua, Alvin J. K., Church, Ross, Colpi, Monica, D’Orazio, Daniel, Danielski, Camilla, Davies, Melvyn B., Dayal, Pratika, De Rosa, Alessandra, Derdzinski, Andrea, Destounis, Kyriakos, Dotti, Massimo, Duţan, Ioana, Dvorkin, Irina, Fabj, Gaia, Foglizzo, Thierry, Ford, Saavik, Fouvry, Jean-Baptiste, Franchini, Alessia, Fragos, Tassos, Fryer, Chris, Gaspari, Massimo, Gerosa, Davide, Graziani, Luca, Groot, Paul, Habouzit, Melanie, Haggard, Daryl, Haiman, Zoltan, Han, Wen-Biao, Istrate, Alina, Johansson, Peter H., Khan, Fazeel Mahmood, Kimpson, Tomas, Kokkotas, Kostas, Kong, Albert, Korol, Valeriya, Kremer, Kyle, Kupfer, Thomas, Lamberts, Astrid, Larson, Shane, Lau, Mike, Liu, Dongliang, Lloyd-Ronning, Nicole, Lodato, Giuseppe, Lupi, Alessandro, Ma, Chung-Pei, Maccarone, Tomas, Mandel, Ilya, Mangiagli, Alberto, Mapelli, Michela, Mathis, Stéphane, Mayer, Lucio, McGee, Sean, McKernan, Berry, Miller, M. Coleman, Mota, David F., Mumpower, Matthew, Nasim, Syeda S., Nelemans, Gijs, Noble, Scott, Pacucci, Fabio, Panessa, Francesca, Paschalidis, Vasileios, Pfister, Hugo, Porquet, Delphine, Quenby, John, Ricarte, Angelo, Röpke, Friedrich K., Regan, John, Rosswog, Stephan, Ruiter, Ashley, Ruiz, Milton, Runnoe, Jessie, Schneider, Raffaella, Schnittman, Jeremy, Secunda, Amy, Sesana, Alberto, Seto, Naoki, Shao, Lijing, Shapiro, Stuart, Sopuerta, Carlos, Stone, Nicholas C., Suvorov, Arthur, Tamanini, Nicola, Tamfal, Tomas, Tauris, Thomas, Temmink, Karel, Tomsick, John, Toonen, Silvia, Torres-Orjuela, Alejandro, Toscani, Martina, Tsokaros, Antonios, Unal, Caner, Vázquez-Aceves, Verónica, Valiante, Rosa, van Putten, Maurice, van Roestel, Jan, Vignali, Christian, Volonteri, Marta, Wu, Kinwah, Younsi, Ziri, Yu, Shenghua, Zane, Silvia, Zwick, Lorenz, Antonini, Fabio, Baibhav, Vishal, Barausse, Enrico, Bonilla Rivera, Alexander, Branchesi, Marica, Branduardi-Raymont, Graziella, Burdge, Kevin, Chakraborty, Srija, Cuadra, Jorge, Dage, Kristen, Davis, Benjamin, de Mink, Selma E., Decarli, Roberto, Doneva, Daniela, Escoffier, Stephanie, Gandhi, Poshak, Haardt, Francesco, Lousto, Carlos O., Nissanke, Samaya, Nordhaus, Jason, O’Shaughnessy, Richard, Portegies Zwart, Simon, Pound, Adam, Schussler, Fabian, Sergijenko, Olga, Spallicci, Alessandro, Vernieri, Daniele, and Vigna-Gómez, Alejandro
- Abstract
The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.
- Published
- 2023
- Full Text
- View/download PDF
34. Simulations of common-envelope evolution in binary stellar systems: physical models and numerical techniques
- Author
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Röpke, Friedrich K. and De Marco, Orsola
- Abstract
When the primary star in a close binary system evolves into a giant and engulfs its companion, its core and the companion temporarily orbit each other inside a common envelope. Drag forces transfer orbital energy and angular momentum to the envelope material. Depending on the efficiency of this process, the envelope may be ejected leaving behind a tight remnant binary system of two stellar cores, or the cores merge retaining part of the envelope material. The exact outcome of common-envelope evolution is critical for in the formation of X-ray binaries, supernova progenitors, the progenitors of compact-object mergers that emit detectable gravitational waves, and many other objects of fundamental astrophysical relevance. The wide ranges of spatial and temporal timescales that characterize common-envelope interactions and the lack of spatial symmetries present a substantial challenge to generating consistent models. Therefore, these critical phases are one of the largest sources for uncertainty in classical treatments of binary stellar evolution. Three-dimensional hydrodynamic simulations of at least part of the common-envelope interaction are the key to gain predictive power in modeling common-envelope evolution. We review the development of theoretical concepts and numerical approaches for such three-dimensional hydrodynamic simulations. The inherent multi-physics, multi-scale challenges have resulted in a wide variety of approximations and numerical techniques to be exercised on the problem. We summarize the simulations published to date and their main results. Given the recent rapid progress, a sound understanding of the physics of common-envelope interactions is within reach and thus there is hope that one of the remaining fundamental problems of stellar astrophysics may be solved before long.
- Published
- 2023
- Full Text
- View/download PDF
35. Tolerance of Silicon Oxide‐Coated Pt/C Catalyst Toward CO and H2S Contamination in Hydrogen for Proton Exchange Membrane Fuel Cells
- Author
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Prass, Sebastian, Nerlich, Leon, Singh, Rajveer, Godoy, Andres O., Jankovic, Jasna, Friedrich, K. Andreas, and Zamel, Nada
- Abstract
Platinum on graphitized low surface area carbon (Pt/C) is coated with a silicon oxide thin film and is employed as anode catalyst to manipulate the tolerance of proton exchange membrane fuel cells toward carbon monoxide and hydrogen sulfide contamination. The SiO2coating, prepared by successive hydrolysis of 3‐aminopropyl‐triethoxisilane and tetraethoxysilane, forms clusters in proximity to Pt in sizes comparable to the catalyst particles, leaving most of the carbon surfaces free. The performance with and without CO is investigated in situ at relative humidities (RH) of 100%, 70%, and 40%. When operated with neat hydrogen, SiO2‐Pt/C shows marginally better performance owing to an improved protonic conduction due to the water retaining hydrophilic SiO2. Upon operation with CO‐contaminated fuel, the SiO2‐Pt/C performs worse than that of Pt/C particularly at high RH. CO stripping measurements reveal an increase in CO oxidation potential for the SiO2‐Pt/C, suggesting an increased CO coverage and consequently higher anode overpotentials during operation with CO‐contaminated fuel. Upon operation with H2S in the fuel, the SiO2coating extends the lifetime until the cell voltage broke down, which is attributed to the enhanced water retention due to SiO2and the solubility of sulfuric species. To manipulate the tolerance of proton exchange membrane fuel cells versus fuel impurities, a silicon oxide coating is applied on the carbon supported platinum catalyst. Although this type of coating is known to improve the electrocatalysts stability, it shows mixed results when it comes to the tolerance versus carbon monoxide and hydrogen sulfide in the fuel.
- Published
- 2023
- Full Text
- View/download PDF
36. Investigation of the Influence of Nanostructured LiNi0.33Co0.33Mn0.33O2 Lithium-Ion Battery Electrodes on Performance and Aging.
- Author
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Dreizler, Andreas M., Bohn, Nicole, Geßwein, Holger, Müller, Marcus, Binder, Joachim R., Wagner, Norbert, and Friedrich, K. Andreas
- Subjects
LITHIUM-ion batteries ,AGING of materials (Library science) ,IMPEDANCE spectroscopy - Abstract
The paper focuses on the performance and aging behavior of lithium nickel cobalt manganese oxide commercial standard material (NCM-111) which is improved with a post synthesis process in order to enhance the cathode active material of lithium-ion pouch cells regarding their capacity and cyclic stability. The aging behavior of the cells is analyzed with electrochemical impedance spectroscopy (EIS) during long-term electrochemical load cycling tests based on the Common Artemis Driving Cycle (CADC). Additionally, post-mortem investigations using scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed. The results demonstrate that post-processing of electrode active material is an effective tool to improve the properties of lithium-ion electrode materials, especially regarding high energy applications and lifetime optimization. The paper bridges the gap between lithium-ion battery electrode material development and the necessary cell testing under automotive relevant conditions which is important for the evaluation of new lithium-ion battery materials for automotive applications. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
37. Highly active anode electrocatalysts derived from electrochemical leaching of Ru from metallic Ir0.7Ru0.3 for proton exchange membrane electrolyzers.
- Author
-
Wang, Li, Saveleva, Viktoriia A., Zafeiratos, Spyridon, Savinova, Elena R., Lettenmeier, Philipp, Gazdzicki, Pawel, Gago, Aldo S., and Friedrich, K. Andreas
- Abstract
Hydrogen produced by water splitting is a promising solution for a sustained economy from renewable energy sources. Proton exchange membrane (PEM) electrolysis is the utmost suitable technology for this purpose, although the quest for low cost, highly active and durable catalysts is persistent. Here we develop a nanostructured iridium catalyst after electrochemically leaching ruthenium from metallic iridium-ruthenium, Ir 0.7 Ru 0.3 O x (EC), and compare its physical and electrochemical properties to the thermally treated counterpart: Ir 0.7 Ru 0.3 O 2 (TT). Ir 0.7 Ru 0.3 O x (EC) shows an unparalleled 13-fold higher oxygen evolution reaction (OER) activity compared to the Ir 0.7 Ru 0.3 O 2 (TT). PEM electrolyzer tests at 1 A cm −2 show no increase of cell voltage for almost 400 h, proving that Ir 0.7 Ru 0.3 O x (EC) is one of the most efficient anodes so far developed. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
38. Funktechnik in der Fabrik
- Author
-
Jondral, Friedrich K.
- Abstract
Mit der Funktechnik ist es wie mit dem Strom: Genauso, wie dieser zuverlässig aus der Steckdose kommt, ist die stets funktionierende drahtlose Kommunikation aus unserem Alltag nicht mehr wegzudenken. Wenn im Rahmen von Industrie 4.0 die Funktechnik in die Fabrik verstärkt Einzug hält [1], sollten weitere Kreise der für die Produktion Verantwortlichen zumindest einen Überblick über die Physik der drahtlosen Kommunikation und die grundlegenden Tatsachen der Nachrichtentechnik besitzen. Hierzu möchte der vorliegende Aufsatz einen Beitrag leisten, indem er kurz, prägnant und ohne sich mit technischen Einzelheiten aufzuhalten, die wesentlichen Grundbegriffe der Funktechnik erklärt und einen Überblick über die dahinter liegende Physik vermittelt.
- Published
- 2019
- Full Text
- View/download PDF
39. Dialysate Calcium Concentration below 3.0 mEq/L Is Not Associated with Improved Outcomes in the Japanese Dialysis Outcomes and Practice Patterns Study
- Author
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Iseki, Kunitoshi, Henn, Lisa L., Nomura, Takanobu, Kanda, Eiichiro, Tsuruya, Kazuhiko, Hirakata, Hideki, Port, Friedrich K., Pisoni, Ronald L., Tentori, Francesca, and Robinson, Bruce M.
- Abstract
Background:Abnormal chronic kidney disease-mineral and bone disorder (CKD-MBD) markers have been associated with adverse outcomes in hemodialysis (HD) patients. Dialysate calcium concentration (D-Ca) likely influences serum calcium and phosphorus levels. Optimal D-Ca level remains unclear. We hypothesized that higher D-Ca is associated with cardiovascular events and mortality among Japanese HD patients. Methods:Enrollment data of chronic HD patients in the prospective observational study JDOPPS, phases 1–5 (1999–2015), provided exposures and covariates. All-cause mortality, non-arrhythmic cardiovascular events (NonAR-CVE), or their composites were analyzed by D-Ca, and divided into 2.5, 2.75, and 3.0 mEq/L. To minimize confounding by indication, analyses were restricted to facilities in which at least 90% of patients received the same D-Ca prescription. Association of D-Ca level with outcomes was evaluated in Cox models stratified by phase and accounting for facility clustering. Covariates describing patient demographics, comorbidities, laboratory values, CKD-MBD therapy, and facility attributes provided adjustment. Results:Of 9,201 patients included, 25.0% had D-Ca of 2.5 mEq/L; 6.8% D-Ca 2.75; and 68.2% D-Ca 3.0. Median follow-up time was 2.03 years. D-Ca was not associated with all-cause mortality, with hazards ratios for 2.5 vs. 3.0 mEq/L of 0.90 and 95% CI (0.73–1.11), nor with other outcomes. One effect modification occurred, protective for lower D-Ca on NonAR-CVE in the absence of cardiovascular comorbidities (p= 0.032), although corresponding D-Ca effects were not significant after multiple comparisons adjustment (p= 0.261 [D-Ca 2.5] and 0.125 [D-Ca 2.75]). Conclusion:Lowering D-Ca level below 3.0 mEq/L seems not to have a meaningful effect on patient outcomes.
- Published
- 2018
- Full Text
- View/download PDF
40. Missed Hemodialysis Treatments: International Variation, Predictors, and Outcomes in the Dialysis Outcomes and Practice Patterns Study (DOPPS)
- Author
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Al Salmi, Issa, Larkina, Maria, Wang, Mia, Subramanian, Lalita, Morgenstern, Hal, Jacobson, Stefan H., Hakim, Raymond, Tentori, Francesca, Saran, Rajiv, Akiba, Takashi, Tomilina, Natalia A., Port, Friedrich K., Robinson, Bruce M., and Pisoni, Ronald L.
- Published
- 2018
- Full Text
- View/download PDF
41. DOPPS data suggest a possible survival benefit of renin angiotensin-aldosterone system inhibitors and other antihypertensive medications for hemodialysis patients
- Author
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Karaboyas, Angelo, Xu, Hairong, Morgenstern, Hal, Locatelli, Francesco, Jadoul, Michel, Nitta, Kosaku, Dasgupta, Indranil, Tentori, Francesca, Port, Friedrich K., and Robinson, Bruce M.
- Abstract
The benefits of renin angiotensin-aldosterone system inhibitors (RAASi) are well-established in the general population, particularly among those with diabetes, congestive heart failure (CHF), or coronary artery disease (CAD). However, conflicting evidence from trials and concerns about hyperkalemia limit RAASi use in hemodialysis patients, relative to other antihypertensive agents, including beta blockers and calcium channel blockers. Therefore, we investigated prescription patterns and associations with mortality for RAASi and other antihypertensive agents using data from the international Dialysis Outcomes and Practice Patterns Study (DOPPS). Cox regression was used to estimate the effect of the prescription of RAASi and other antihypertensive agents at study entry on mortality in 11,421 incident (120 days or less) hemodialysis and 37,124 prevalent (over 120 days) hemodialysis patients from DOPPS phases 2-5 (2002-2015). Over 95% of RAASi were angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. RAASi prevalence was 39% and varied minimally by CHF and CAD. The adjusted hazard ratio for RAASi (vs. no RAASi) was 0.89 (95% confidence interval 0.80-0.99) among incident and 0.94 (0.90-0.99) among prevalent hemodialysis patients, with no convincing evidence of interaction with diabetes, CAD or CHF. Inverse associations with mortality were also observed for beta blockers and calcium channel blockers, and were stronger for angiotensin receptor blockers than angiotensin-converting enzyme inhibitors, but this latter finding requires further study. Thus, our observations suggest a relatively small survival benefit of RAASi and other antihypertensive agents in hemodialysis patients, though randomized prospective studies are needed to potentially change prescribing criteria.
- Published
- 2018
- Full Text
- View/download PDF
42. White Gaussian Noise – Models for Engineers
- Author
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Jondral, Friedrich K.
- Abstract
This paper assembles some information about white Gaussian noise (WGN) and its applications. It starts from a description of thermal noise, i. e. the irregular motion of free charge carriers in electronic devices. In a second step, mathematical models of WGN processes and their most important parameters, especially autocorrelation functions and power spectrum densities, are introduced. In order to proceed from mathematical models to simulations, we discuss the generation of normally distributed random numbers. The signal-to-noise ratio as the most important quality measure used in communications, control or measurement technology is accurately introduced. As a practical application of WGN, the transmission of quadrature amplitude modulated (QAM) signals over additive WGN channels together with the optimum maximum likelihood (ML) detector is considered in a demonstrative and intuitive way.
- Published
- 2018
- Full Text
- View/download PDF
43. An Investigation of PEFC Sub-Zero Startup: Evidence of Local Freezing Effects.
- Author
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Stahl, P., Biesdorf, J., Boillat, P., and Friedrich, K. A.
- Subjects
NEUTRON radiography ,FREEZING ,TEMPERATURE - Abstract
Starting PEFCs from sub-zero temperatures can be challenging as generated product water runs the risk to freeze, causing cell failure by blocking the gas pathways for the reactant gases in the porous layers. Hence a fundamental understanding of the cell failure mechanisms is essential to enable robust system functionalities even at temperatures far below 0°C. In this work we set a focus on analysis of water transport processes during isothermal startup at temperatures between -10 and -2.5 °C. Neutron radiography was applied in order to analyze spatial heterogeneities of water production during a cold start and also to verify phase transitions from water to ice. The latter was facilitated by a recently developed dual spectrum neutron radiography method, which was applied for the first time to a 50 cm test cell. Our results reveal that at -5 °C and above freezing can occur in a limited region while the rest of the cell continues generating liquid product water. But as temperature is shifted downwards, water distribution tends to be more uniform and freezing mechanisms seem to proceed more homogeneously over the cell plane. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
44. Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Electrolyzers.
- Author
-
Lettenmeier, P., Wang, R., Abouatallah, R., Burggraf, F., Gago, A. S., and Friedrich, K. A.
- Subjects
PROTONS ,WATER electrolysis ,STAINLESS steel ,VAPOR-plating ,SURFACE coatings - Abstract
Given its rapid response to fluctuating currents and wide operation range, proton exchange membrane (PEM) water electrolysis is utmost suitable for generation of hydrogen from renewable power. However, it is still hindered by the high cost of the stack components compared to those used in the alkaline technology. In particular, the titanium bipolar plates (BPP) are an issue and the replacement of this metal by stainless steel is a challenge, due to the highly corrosive environment inside PEM electrolyzer stack. Herein, we coat stainless steel BPPs with 50-60 μm Ti and 1.5 μm Pt coatings by vacuum plasma spraying (VPS) and magnetron sputtering physical vapor deposition (PVD), respectively. The BPPs are evaluated at constant 1 A cm
-2 for more than 1000 h. The thermally sprayed Ti coatings fully protect the stainless steel substrate during this period of time, and the Pt surface modification allows achieving a cell performance comparable to the baseline. [ABSTRACT FROM AUTHOR]- Published
- 2016
- Full Text
- View/download PDF
45. In Situ Studies of Solid Electrolyte Interphase (SEI) Formation on Crystalline Carbon Surfaces by Neutron Reflectometry and Atomic Force Microscopy
- Author
-
Steinhauer, Miriam, Stich, Michael, Kurniawan, Mario, Seidlhofer, Beatrix-Kamelia, Trapp, Marcus, Bund, Andreas, Wagner, Norbert, and Friedrich, K. Andreas
- Abstract
The solid electrolyte interphase (SEI) is a complex and fragile passivation layer with crucial importance for the functionality of lithium-ion batteries. Due to its fragility and reactivity, the use of in situ techniques is preferable for the determination of the SEI’s true structure and morphology during its formation. In this study, we use in situ neutron reflectometry (NR) and in situ atomic force microscopy (AFM) to investigate the SEI formation on a carbon surface. It was found that a lithium-rich adsorption layer is already present at the open circuit voltage on the carbon sample surface and that the first decomposition products start to deposit close to this potential. During the negative potential sweep, the growth of the SEI can be observed in detail by AFM and NR. This allows precise monitoring of the morphology evolution and the resulting heterogeneities of individual SEI features. NR measurements show a maximum SEI thickness of 192 Å at the lower cutoff potential (0.02 V vs Li/Li+), which slightly decreases during the positive potential scan. The scattering length density (SLD) obtained by NR provides additional information on the SEI’s chemical nature and structural evolution.
- Published
- 2017
- Full Text
- View/download PDF
46. Highly active anode electrocatalysts derived from electrochemical leaching of Ru from metallic Ir0.7Ru0.3for proton exchange membrane electrolyzers
- Author
-
Wang, Li, Saveleva, Viktoriia A., Zafeiratos, Spyridon, Savinova, Elena R., Lettenmeier, Philipp, Gazdzicki, Pawel, Gago, Aldo S., and Friedrich, K. Andreas
- Abstract
Hydrogen produced by water splitting is a promising solution for a sustained economy from renewable energy sources. Proton exchange membrane (PEM) electrolysis is the utmost suitable technology for this purpose, although the quest for low cost, highly active and durable catalysts is persistent. Here we develop a nanostructured iridium catalyst after electrochemically leaching ruthenium from metallic iridium-ruthenium, Ir0.7Ru0.3Ox(EC), and compare its physical and electrochemical properties to the thermally treated counterpart: Ir0.7Ru0.3O2(TT). Ir0.7Ru0.3Ox(EC) shows an unparalleled 13-fold higher oxygen evolution reaction (OER) activity compared to the Ir0.7Ru0.3O2(TT). PEM electrolyzer tests at 1Acm−2show no increase of cell voltage for almost 400h, proving that Ir0.7Ru0.3Ox(EC) is one of the most efficient anodes so far developed.
- Published
- 2017
- Full Text
- View/download PDF
47. Interdialytic Weight Gain: Trends, Predictors, and Associated Outcomes in the International Dialysis Outcomes and Practice Patterns Study (DOPPS)
- Author
-
Wong, Michelle M.Y., McCullough, Keith P., Bieber, Brian A., Bommer, Juergen, Hecking, Manfred, Levin, Nathan W., McClellan, William M., Pisoni, Ronald L., Saran, Rajiv, Tentori, Francesca, Tomo, Tadashi, Port, Friedrich K., and Robinson, Bruce M.
- Abstract
High interdialytic weight gain (IDWG) is associated with adverse outcomes in hemodialysis (HD) patients. We identified temporal and regional trends in IDWG, predictors of IDWG, and associations of IDWG with clinical outcomes.
- Published
- 2017
- Full Text
- View/download PDF
48. Full Parameterization Study of a High-Energy and High-Power Li-Ion Cell for Physicochemical Models
- Author
-
Schmitt, Christina, Gerle, Martina, Kopljar, Dennis, and Friedrich, K. Andreas
- Abstract
For physicochemical modelling of lithium ion batteries, an extensive parametrization is necessary. These parameters need to be derived cell specifically as they vary with cell design. In this study, two cells from the same manufacturer are investigated which are optimized for high power and high energy applications. After opening the cells under argon atmosphere, the battery materials are extracted to conduct various chemical and physical measurements to define the active material type, microstructure, conductivity and mass loading of the electrodes. Furthermore, laboratory cells were built from the extracted materials to evaluate tortuosity and exchange current density by electrochemical impedance spectroscopy, open circuit voltages and solid diffusion coefficient by galvanostatic intermittent titration technique (GITT). The differences and similarities of these parameters for both cell types are discussed and compared to literature. Main differences are the electrode area, thickness, porosity, and thus, mass loading and areal capacity of the electrodes. Both cells have a NCA cathode, but only the high energy cell has a blend anode consisting of graphite and Si/SiOxwhereas the anode active material of the high power cell is only made of graphite. The derived parameters are finally used for the parameterization of a P2D model.
- Published
- 2023
- Full Text
- View/download PDF
49. The US Renal Data System at 30 Years: A Historical Perspective
- Author
-
Port, Friedrich K. and Held, Philip J.
- Published
- 2019
- Full Text
- View/download PDF
50. The Influence of Sulfur Formation on Performance and Reforming Chemistry of SOFC Anodes Operating on Methane Containing Fuel.
- Author
-
Riegraf, Matthias, Yurkiv, Vitaliy, Schiller, Günter, Costa, Rémi, Latz, Arnulf, and Friedrich, K. Andreas
- Subjects
SULFUR ,SOLID oxide fuel cells ,METHANE as fuel ,ANODES ,CHARGE transfer - Abstract
This paper presents a detailed analysis of the influence of sulfur formation on performance and efficiency of Solid Oxide Fuel Cells (SOFC) operating on methane containing fuels. Our previously developed multi-step reaction mechanism of sulfur formation and oxidation is coupled with a complex heterogeneous mechanism of methane reforming, channel gas-flow, porous-media transport and elementary kinetic charge transfer and is used to describe sulfur-induced degradation and performance drops of Ni/YSZ anodes. Experimental literature data is used to validate the model and to interpret important aspects of cell performance degradation. Comparisons of the model predictions to the experiments illustrate that the developed model, without any modifications, reproduces the observed voltage decrease well and is able to capture the changes in fuel conversion and selectivity for different gas mixtures. It is shown that atomically adsorbed sulfur significantly influences heterogeneous reforming chemistry, causing substantial voltage degradation. At constant current densities, cell voltage decreases in a non-linear way with faster recovery than in H
2 /H2 O mixtures. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
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