Electrical switching of antiferromagnetic Mn2_2Au and the role of thermal activation

Electrical manipulation of antiferromagnets with specific symmetries offers the prospect of creating novel, antiferromagnetic spintronic devices. Such devices aim to make use of the insensitivity to external magnetic fields and the ultrafast dynamics at the picosecond timescale intrinsic to antiferromagnets. The possibility to electrically switch antiferromagnets was first predicted for Mn2Au and then experimentally observed in tetragonal CuMnAs. Here, we report on the electrical switching and detection of the Neel order in epitaxial films of Mn2Au. The exponential dependences of the switching amplitude on the current density and the temperature are explained by a macroscopic thermal activation model taking into account the effect of the Joule heating in Hall cross devices and we observe that the thermal activation plays a key role in the reorientation process of the Neel order. Our model analysis shows that the electrically set Neel-state is long-term stable at room temperature, paving the way for practical applications in memory devices.Comment: 8 pages, 6 figure

Spin-orbit torque induced electrical switching of antiferromagnetic MnN

Electrical switching and readout of antiferromagnets allows to exploit the unique properties of antiferromagnetic materials in nanoscopic electronic devices. Here we report experiments on the spin-orbit torque induced electrical switching of a polycrystalline, metallic antiferromagnet with low anisotropy and high N\'eel temperature. We demonstrate the switching in a Ta / MnN / Pt trilayer system, deposited by (reactive) magnetron sputtering. The dependence of switching amplitude, efficiency, and relaxation are studied with respect to the MnN film thickness, sample temperature, and current density. Our findings are consistent with a thermal activation model and resemble to a large extent previous measurements on CuMnAs and Mn$_2$Au, which exhibit similar switching characteristics due to an intrinsic spin-orbit torque.Comment: 7 pages, 5 figure

Hyperspectral Imaging (HSI) of Human Kidney Allografts

Zusammenfassung der Arbeit /Dissertation zur Erlangung des akademischen Grades Dr. med. Hyperspectral Imaging (HSI) of Human Kidney Allografts Die HSI Bildgebung ist ein nichtinvasives Instrument zur quantitativen Bewertung der Sauerstoffanreicherung parenchymatöser Organe, der Mikroperfusion von Transplantaten sowie zur Messung der Hämoglobin- und Wasserkonzentration von Organen. Aktuell wird die HSI Bildgebung bereits in der neuronalen Funktionsdiagnostik zur detaillierten Gewebedifferenzierung genutzt18 und dient zur Überprüfung der Perfusion komplexer Anastomosen im Bereich der Ösophagus- und der Leberchirurgie31,32. Die ersten Ergebnisse zur Tumordetektion konnten ebenfalls erfolgversprechend publiziert werden20. Ziel unserer Studie war es das Potenzial dieser neuartigen Bildgebungstechnik im Rahmen der Transplantationsmedizin vorzustellen und zu beschreiben. Es sollte gezeigt werden, ob die HSI Analyse für die intraoperative Qualitäts- und Lebensfähigkeitsbewertung bei Nierentransplantationen verwendet werden kann. Generell hat sich die Komplikationsrate nach erfolgter Nierentransplantation in den letzten Jahrzehnten von bis zu 30% auf weniger als 6% verringert6. Die Einschätzung der Organqualität während der Organentnahme oder Implantation, die potentiellen Funktionalität einer Transplantatniere im Rahmen einer postmortal oder auch lebend gespendeten Niere ist jedoch fortwährend schwer33. Im Rahmen der aktuellen Studie, wurden zur Erläuterung der beschriebenen Zielsetzung 17 postmortale Nierentransplantationen mit der hyperspektralen Kamera 15 und 45 Minuten nach Reperfusion fotografiert. Hierbei wurden mithilfe der HSI- Kamera die Gewebeoxygenierung (StO2), die Perfusion (NIR-Perfusionsindex), der OHI (Organ Hämoglobin Index) und der TWI (Tissue-Water-Index, Gehalt des Wassers des Gewebes) erfasst19,31. Revisionseingriffe, wie die Ureterneuimplantation und eine Thrombektomie wurden ebenfalls begleitet und analysiert. Zwei Patienten (11,8%) entwickelten eine Delayed Graft Function (DGF). Als Ergebnis zeigte sich, dass die optisch ermittelte Oxygenierung und Mikroperfusion bei Patienten mit einer DGF in unserer Studie signifikant verringert war. Gleiches galt für den NIR Perfusionsindex. Bei einer postoperativen Ureternekrose wurde ein deutliches NIR-Perfusionsdefizite des nekrotischen Teils dargestellt. Die Bestätigung erfolgte durch die Histopathologie. Wir konnten zeigen, dass eine genaue, quantifizierbare Aussage über die Mikroperfusion im arteriellen sowie venösen Stromgebiet möglich ist. Eine sichere und nicht invasive Untersuchungsmethode ist somit während einer Nierentransplantation integrierbar ohne den Ablauf der Operation zu beeinflussen. Die hyperspektrale Bildgebung ermöglicht somit intraoperativ die Organfunktion während der Transplantation zu bewerten und eine verzögerte Transplantatfunktion vorherzusagen. Als Kritikpunkt an der neuen Methode könnte angeführt werden, dass die Technik der HSI Visualisierung eine direkte Sicht auf die Niere erfordert. Grund dafür ist, dass die derzeitige maximale Eindringtiefe für Mikrozirkulationsmessungen 4 bis 6 Millimeter beträgt. Die intraoperative Sonographie ist aktuell das Einzige vergleichbare, bildgebende, zugelassene und nicht invasive Verfahren zur Bewertung der Organe. Mit der Ultraschalldiagnostik ist die Makroperfusion darstellbar und Vasospasmen sowie Perfusionsdefizite können frühzeitige detektiert werden34. Auf die Mikrozirkulation und die Oxygenierung und mögliche noch chirurgisch behandelbare Perfusionsdefizite, kann jedoch nur bedingt eingegangen werden35. Grundsätzlich hat die Bedeutung der Ultraschalldiagnostik im prä- und postoperativen Verlauf bei Patienten nach Nierentransplantation einen hohen Stellwert. Nichtsdestotrotz könnte die Kombination von Sonographie und HSI die genaue Beschreibung von Mikro- und Makroperfusion optimieren und das Erfassen und Beschreiben der Organqualität verbessern. Grundsätzlich stünde als weitere Alternative zu Bewertung des Organs die Indocyaningrün-Angiographie zur Verfügung. Hier besticht die hyperspektrale Bildgebung jedoch, da keine intravenöse Gabe von Floreszenzen wie Indocyaningrün (ICG) benötigt wird. So sind Wechselwirkungen und allergische Reaktionen ausgeschlossen28. Zusammenfassend wäre die mögliche Weiterentwicklung der Bildgebung in ein video- gestütztes operatives Tool zur Überwachung der Reperfusion und Fertigung diverser Anastomosen ein Meilenstein in der operativen Bildgebung und könnte wegweisenden Erkenntnisse der vaskulären Versorgung generieren. Nach unseren erfolgversprechenden Ergebnissen könnte es bald möglich sein, die Maschinenperfusion, die eine Verbesserung der Graft-Funktion und auch Verbesserung des Gesamtüberlebens bei Nieren- und Lebertransplantation zeigt5,36, mit hyperspektraler Bildgebung zu observieren und noch feiner zu justieren. Die Erkenntnis der HSI Bildgebung ist in Zeiten der Organknappheit7,11 essentiell und unseren Erachtens nur vorteilhaft zu beschreiben

Impact of asset usage preferences on parallel replacement decisions

Data from a state department of transportation fleet shows that the usage of a typical asset decreases as it ages. One possible explanation for decreasing asset usage with age is operator preference for using the newest available asset. In this research the long-term cost and replacement implications of such a "newest first" usage practice are investigated for a fleet of similar assets with a fixed replacement age (age standard). Capital constraints on replacement are not considered. Comparisons are made to a "random" usage practice that results in constant expected usage as an asset ages. For most major cost categories, the newest first usage practice results in greater or equal costs. It is also shown that asset usage and fixed replacement age are interdependent under the newest first usage practice. The implications of this are that simple approaches found in the literature to address decreasing usage with age give incorrect results

Priority asset utilization in parallel replacement analysis

Two policies for allocating individual assets from a pool of assets to incoming requests were contrasted within the context of replacement analysis. Assets within a pool are considered similar in the service they provide, but may differ in age and cumulative usage. The two policies considered for allocating assets to incoming requests were random and newest first (or priority). Scenarios using fixed replacement ages and no budget limitations were analyzed and also simulated. Random allocation results in constant utilization over asset lifetime, while newest first allocation results in decreasing utilization. Random allocation is more economical than newest first allocation for most of the cost types investigated. Assuming replacement candidates are identified using a fixed age standard, the optimal pool-wide replacement age standard is shorter for the newest first allocation policy. This is opposite to the results obtained if the optimal pool-wide replacement age is computed using single asset replacement analysis with pool-wide average data representing a single “average” asset

Resistive contribution in electrical switching experiments with antiferromagnets

Recent research demonstrated the electrical switching of antiferromagnets via intrinsic spin-orbit torque or the spin Hall effect of an adjacent heavy metal layer. The electrical readout is typically realized by measuring the transverse anisotropic magnetoresistance at planar cross- or star-shaped devices with four or eight arms, respectively. Depending on the material, the current density necessary to switch the magnetic state can be large, often close to the destruction threshold of the device. We demonstrate that the resulting electrical stress changes the film resistivity locally and thereby breaks the fourfold rotational symmetry of the conductor. This symmetry breaking due to film inhomogeneity produces signals, that resemble the anisotropic magnetoresistance and is experimentally seen as a "saw-tooth"-shaped transverse resistivity. This artifact can persist over many repeats of the switching experiment and is not easily separable from the magnetic contribution. We discuss the origin of the artifact, elucidate the role of the film crystallinity, and propose approaches how to separate the resistive contribution from the magnetic contribution.Comment: 9 pages, 7 figure

Resistive contribution in electrical switching experiments with antiferromagnets

Recent research demonstrated the electrical switching of antiferromagnets via intrinsic spin-orbit torque or the spin Hall effect of an adjacent heavy metal layer. The electrical readout is typically realized by measuring the transverse anisotropic magnetoresistance at planar cross- or star-shaped devices with four or eight arms, respectively. Depending on the material, the current density necessary to switch the magnetic state can be large, often close to the destruction threshold of the device. We demonstrate that the resulting electrical stress changes the film resistivity locally and thereby breaks the fourfold rotational symmetry of the conductor. This symmetry breaking due to film inhomogeneity produces signals, that resemble the anisotropic magnetoresistance and is experimentally seen as a "saw-tooth"-shaped transverse resistivity. This artifact can persist over many repeats of the switching experiment and is not easily separable from the magnetic contribution. We discuss the origin of the artifact, elucidate the role of the film crystallinity, and propose approaches how to separate the resistive contribution from the magnetic contribution.Comment: 9 pages, 7 figure

Influence of Multiple Donor Renal Arteries on the Outcome and Graft Survival in Deceased Donor Kidney Transplantation

Aim: Complex arterial reconstruction in kidney transplantation (KT) using kidneys from deceased donors (DD) warrants additional study since little is known about the effects on the mid- and long-term outcome and graft survival. Methods: A total of 451 patients receiving deceased donor KT in our department between 1993 and 2017 were included in our study. Patients were divided into three groups according to the number of arteries and anastomosis: (A) 1 renal artery, 1 arterial anastomosis (N = 369); (B) >1 renal artery, 1 arterial anastomosis (N = 47); and (C) >1 renal artery, >1 arterial anastomosis (N = 35). Furthermore, the influence of localization of the arterial anastomosis (common iliac artery (CIA), versus non-CIA) was analyzed. Clinicopathological characteristics, outcome, and graft and patient survival of all groups were compared retrospectively. Results: With growing vascular complexity, the time of warm ischemia increased significantly (groups A, B, and C: 40 ± 19 min, 45 ± 19 min, and 50 ± 17 min, respectively; p = 0.006). Furthermore, the duration of operation was prolonged, although this did not reach significance (groups A, B, and C: 175 ± 98 min, 180 ± 35 min, and 210 ± 43 min, respectively; p = 0.352). There were no significant differences regarding surgical complications, post-transplant kidney function (delayed graft function, initial non-function, episodes of acute rejection), or long-term graft survival. Regarding the localization of the arterial anastomosis, non-CIA was an independent prognostic factor for deep vein thrombosis in multivariate analysis (CIA versus non-CIA: OR 11.551; 95% CI, 1.218–109.554; p = 0.033). Conclusion: Multiple-donor renal arteries should not be considered a contraindication to deceased KT, as morbidity rates and long-term outcomes seem to be comparable with grafts with single arteries and less complex anastomoses

Electrical N\'eel-order switching in magnetron-sputtered CuMnAs thin films

Antiferromagnetic materials as active components in spintronic devices promise insensitivity against external magnetic fields, the absence of own magnetic stray fields, and ultrafast dynamics at the picosecond time scale. Materials with certain crystal-symmetry show an intrinsic N\'eel-order spin-orbit torque that can efficiently switch the magnetic order of an antiferromagnet. The tetragonal variant of CuMnAs was shown to be electrically switchable by this intrinsic spin-orbit effect and its use in memory cells with memristive properties has been recently demonstrated for high-quality films grown with molecular beam epitaxy. Here, we demonstrate that the magnetic order of magnetron-sputtered CuMnAs films can also be manipulated by electrical current pulses. The switching efficiency and relaxation as a function of temperature, current density, and pulse width can be described by a thermal-activation model. Our findings demonstrate that CuMnAs can be fabricated with an industry-compatible deposition technique, which will accelerate the development cycle of devices based on this remarkable material.Comment: 6 + 4 pages, 4 + 4 figures (main + appendix

Effect of glucose and insulin supplementation on the isolation of primary human hepatocytes

Primary human hepatocytes (PHHs) remain the gold standard for in vitro investigations of xenobiotic metabolism and hepatotoxicity. However, scarcity of liver tissue and novel developments in liver surgery has limited the availability and quality of tissue samples. In particular, warm ischemia shifts the intracellular metabolism from aerobic to anaerobic conditions, which increases glycogenolysis, glucose depletion and energy deficiency. Therefore, the aim of the present study was to investigate whether supplementation with glucose and insulin during PHH isolation could reconstitute intracellular glycogen storage and beneficially affect viability and functionality. Furthermore, the study elucidated whether the susceptibility of the tissue’s energy status correlates with body mass index (BMI). PHHs from 12 donors were isolated from human liver tissue obtained from partial liver resections using a two-step EDTA/collagenase perfusion technique. For a direct comparison of the influence of glucose/insulin supplementation, we modified the setup, enabling the parallel isolation of two pieces of one tissue sample with varying perfusate. Independent of the BMI of the patient, the glycogen content in liver tissue was notably low in the majority of samples. Furthermore, supplementation with glucose and insulin had no beneficial effect on the glycogen concentration of isolated PHHs. However, an indirect improvement of the availability of energy was shown by increased viability, plating efficiency and partial cellular activity after supplementation. The plating efficiency showed a striking inverse correlation with increasing lipid content of PHHs. However, 60 h of cultivation time revealed no significant impact on the maintenance of albumin and urea synthesis or xenobiotic metabolism after supplementation. In conclusion, surgical procedures and tissue handling may decrease hepatic energy resources and lead to cell stress and death. Consequently, PHHs with low energy resources die during the isolation process without supplementation of glucose/insulin or early cell culture, while their survival rates are improved with glucose/insulin supplementation