Variational free energy based macroscopical modeling of ferroelectroelasticity

In this paper, a thermodynamically consistent minimum-type variational model for ferroelectric materials in a macroscopical continuum approach is presented. The motivation for this results from the lack of models in the literature that have on the one hand a Helmholtz free energy based variational structure and on the other hand are able to represent all important characteristic phenomena of ferroelectrics under quasi-static conditions. First of all, a unified variational theory for the material response of dissipative electro-mechanical solids in line with the framework of the generalized standard materials (GSM) is outlined. A macroscopic ferroelectric model with microscopically motivated internal state variables representing the switching processes taking place at the material microscale is adapted to the above mentioned variational structure. Additionally, a mixed variational principle for the global electro-mechanical boundary value problem is introduced in order to embed the Helmholtz free energy based local theory in a suitable finite element formulation. The solution processes for the resulting local and global variational problems is described in detail to enable easy implementation. The capability of the presented methods to reproduce the real behavior of ferroelectric systems is demonstrated by numerical examples. Here, a comparison to experimental results from the literature is a particular focus

Materiell nichtlineare Kontinuumsmodellierung ferroelektrischer Funktionskeramiken mit piezoelektrischen und flexoelektrischen Eigenschaften

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung eines makroskopischen Kontinuumsmodells zur Untersuchung des Einflusses des flexoelektrischen Effekts auf mikrostrukturelle Domänenumklappprozesse in ferroelektrischen Funktionskeramiken. Durch die zunehmende Miniaturisierung moderner mikroelektromechanischer Systeme (MEMS) spielt die Berücksichtigung von größenabhängigen Effekten wie der Flexoelektrizität bei der computergestützten Modellierung ihres Materialverhaltens eine immer größere Rolle. Die häufig eingesetzte Materialklasse der ferroelektrischen Funktionskeramiken zeigt zudem bei hinreichend großer elektrischer oder mechanischer Beanspruchung ein stark nichtlineares Materialverhalten aufgrund irreversibler Umklappvorgänge ihrer Domänenstruktur. Für die Entwicklung eines Modells, das die genannten Effekte vereint, wird zunächst eine elektro-mechanische Kontinuumstheorie höherer Ordnung in einer variationellen Struktur eingeführt. Zur Berücksichtigung der dissipativen Domänenumklappprozesse wird ein mikroskopisch motiviertes phänomenologisches Materialmodell in den zuvor bereitgestellten makroskopischen Modellierungsrahmen integriert. Im Zuge der numerischen Lösung der elektro-mechanisch gekoppelten Randwertprobleme werden geeignete Variationsformulierungen eingeführt und diskutiert sowie zugehörige Finite-Elemente-Formulierungen vorgestellt. Die Leistungsfähigkeit des entwickelten Modells zur Abbildung des charakteristischen nichtlinearen Materialverhaltens von Ferroelektrika und der Wechselwirkung mit dem flexoelektrischen Effekt wird anhand von numerischen Beispielen demonstriert. Im Mittelpunkt der numerischen Untersuchungen steht zudem, soweit möglich, der Vergleich mit experimentellen Ergebnissen. Darüber hinaus wird die Möglichkeit untersucht, in Piezokeramiken einen Polungsvorgang allein durch den flexoelektrischen Effekt zu induzieren

Materiell nichtlineare Kontinuumsmodellierung ferroelektrischer Funktionskeramiken mit piezoelektrischen und flexoelektrischen Eigenschaften

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung eines makroskopischen Kontinuumsmodells zur Untersuchung des Einflusses des flexoelektrischen Effekts auf mikrostrukturelle Domänenumklappprozesse in ferroelektrischen Funktionskeramiken. Dabei ist von Interesse, ob in Piezokeramiken durch direkte Flexoelektrizität ein Polungsprozess in Gang gesetzt werden kann und ob durch indirekte Flexoelektrizität eine Verbesserung der aktorischen Eigenschaften eines IDE-Wafers möglich ist

Electrical and magnetic properties of FM/MgO/FM (FM = Co90Fe10, Fe20Ni80) heterostructures

In this paper we present the development and characterization of FM/MgO/FM (FM = Co90Fe10, Fe20Ni80) heterostructures. The magnetic order of the structures, magnetic anisotropy and interlayer exchange coupling were characterized by magnetization measurements. The influence of the substrate temperature during growth on the magnetic properties and topographical features of the bottom electrode was also explored. Higher values of the coercive field were achieved increasing the substrate temperature during deposition of the bottom electrode. Patterned magnetic tunnel junctions were grown on Si(1 0 0) and MgO(1 0 0). The junctions consist of square pillars with different areas (1600, 625, 100 and 25 μm2) fabricated by optical lithography. I(V) curves obtained with conducting atomic force microscopy of the patterned junctions were performed at room temperature in order to explore the reproducibility of the transport properties of the insulating barrier. The results show a more insulating behavior of the junctions grown on Si(1 0 0), with very good control and a high reproducibility of the transport properties of the MgO insulating barrier.Fil: Aviles Felix, Luis Steven. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Gonzalez Sutter, Jesus Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Gomez, Javier Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

Increased surface expression of CD18 and CD11b in leukocytes after tourniquet ischemia during elective hand surgery

The surface expression of β2-integrins was investigated in leukocytes from patients undergoing ischemia induced by tourniquet application for elective hand surgery. Blood samples were obtained before initiation, at the end of ischemia, and after 15 minutes of reperfusion from ischemic and contralateral arms of five patients. Comparable expression of CD18, CD11a, CD11b, and CD11c could be detected by immunofluorescence in leukocytes from samples drawn from either arm before tourniquet application. In contrast, a significant increase in the expression of CD18 was detectable in monocytes, granulocytes, and lymphocytes from the ischemic arm compared with that in the nonischemic contralateral control, at the end of the ischemia time (80 ± 16 minutes). A significantly increased expression of CD11b, but not CD11a or CD11c, determinants was also observed in granulocytes and monocytes. Concomitantly, a significant reduction in the percentages of granulocytes in samples from ischemic areas was detectable. After 15 minutes of reperfusion, differences in the expression of these adhesion molecules were no longer significant. The expression of the genes encoding interleukins IL-1α, IL-1β, and IL-6 and tumor necrosis factor alpha (TNFα) proinflammatory cytokines was also studied by reverse polymerase chain reaction (rPCR) in peripheral blood mononuclear cells (PBMCs) obtained from the same samples in three patients. IL-1β or IL-6 gene expression was never observed. Expression of IL-1α and TNFα genes, as detected in two patients, was not related with induction of ischemia. However, in these patients expression of one or both these genes was observed in samples derived from the ischemic but not the control arm after 15 minutes of reperfusion. These data document that overexpression of adhesion molecules and sequestration of leukocytes take place following short ischemia times, as routinely applied clinically for minor surgical procedure

Current Developments and Challenges in the Recycling of Key Components of (Hybrid) Electric Vehicles

The introduction of electromobility causes major challenges as new components and materials enter vehicle recycling. This paper discusses the current developments in the recycling of traction batteries, electric motors, and power electronics, which constitute the key components of (hybrid) electric vehicles. Both technical and ecological aspects are addressed. Beside base metals, all components contain metals that are considered critical by the EU (European Union), e.g., rare earth elements, cobalt, antimony, and palladium. As electromobility is a new trend, no recycling routes have been established at an industrial scale for these components. The implementation is complicated by small return flows and a great variety of vehicle concepts as well as components. Furthermore, drastic changes regarding design and material compositions can be expected over the next decades. Due to hazards and high weights, there is a strong research emphasis on battery recycling. Most pilot-scale or semi-industrial processes focus on the recovery of cobalt, nickel, and copper due to their high value. Electric motors and power electronics can be fed into established recycling routes if they are extracted from the vehicle before shredding. However, these processes are not capable of recovering some minor metals such as rare earth elements and antimony

The interplay of landscape composition and configuration: new pathways to manage functional biodiversity and agroecosystem services across Europe

Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and non‐crop habitats, and species’ dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7‐ and 1.4‐fold respectively. Arable‐dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield‐enhancing ecosystem services

CropPol: a dynamic, open and global database on crop pollination

Seventy five percent of the world's food crops benefit from insect pollination. Hence, there has been increased interest in how global change drivers impact this critical ecosystem service. Because standardized data on crop pollination are rarely available, we are limited in our capacity to understand the variation in pollination benefits to crop yield, as well as to anticipate changes in this service, develop predictions, and inform management actions. Here, we present CropPol, a dynamic, open and global database on crop pollination. It contains measurements recorded from 202 crop studies, covering 3,394 field observations, 2,552 yield measurements (i.e. berry weight, number of fruits and kg per hectare, among others), and 47,752 insect records from 48 commercial crops distributed around the globe. CropPol comprises 32 of the 87 leading global crops and commodities that are pollinator dependent. Malus domestica is the most represented crop (32 studies), followed by Brassica napus (22 studies), Vaccinium corymbosum (13 studies), and Citrullus lanatus (12 studies). The most abundant pollinator guilds recorded are honey bees (34.22% counts), bumblebees (19.19%), flies other than Syrphidae and Bombyliidae (13.18%), other wild bees (13.13%), beetles (10.97%), Syrphidae (4.87%), and Bombyliidae (0.05%). Locations comprise 34 countries distributed among Europe (76 studies), Northern America (60), Latin America and the Caribbean (29), Asia (20), Oceania (10), and Africa (7). Sampling spans three decades and is concentrated on 2001-05 (21 studies), 2006-10 (40), 2011-15 (88), and 2016-20 (50). This is the most comprehensive open global data set on measurements of crop flower visitors, crop pollinators and pollination to date, and we encourage researchers to add more datasets to this database in the future. This data set is released for non-commercial use only. Credits should be given to this paper (i.e., proper citation), and the products generated with this database should be shared under the same license terms (CC BY-NC-SA). This article is protected by copyright. All rights reserved