The Intrinsic Magnetization of Antiferromagnetic Textures

Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order parameter spatially varies. This intrinsic spin is present even at equilibrium and can be interpreted as a twisting of the homogeneous AFM into a state with a finite spin. Because magnetic moments couple directly to external magnetic fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic textures under such influence. Starting from the discrete Heisenberg model, we derive the continuum limit of the free energy of AFMs in the exchange approximation and explicitly rederive that the spatial variation of the antiferromagnetic order parameter is associated with an intrinsic magnetization density. We calculate the magnetization profile of a domain wall and discuss how the intrinsic magnetization reacts to external forces. We show conclusively, both analytically and numerically, that a spatially inhomogeneous magnetic field can move and control the position of domain walls in AFMs. By comparing our model to a commonly used alternative parametrization procedure for the continuum fields, we show that the physical interpretations of these fields depend critically on the choice of parametrization procedure for the discrete-to-continuous transition. This can explain why a significant amount of recent studies of the dynamics of AFMs, including effective models that describe the motion of antiferromagnetic domain walls, have neglected the intrinsic spin of the textured order parameter.Comment: 12 pages, 7 figure

Extending solid-state calculations to ultra long-range length scales

We present a method which enables solid-state density functional theory calculations to be applied to systems of almost unlimited size. Computations of physical effects up to the micron length scale but which nevertheless depend on the microscopic details of the electronic structure, are made possible. Our approach is based on a generalization of the Bloch state which involves an additional sum over a finer grid in reciprocal space around each ${\bf k}$-point. We show that this allows for modulations in the density and magnetization of arbitrary length on top of a lattice-periodic solution. Based on this, we derive a set of ultra long-range Kohn-Sham equations. We demonstrate our method with a sample calculation of bulk LiF subjected to an arbitrary external potential containing nearly 3500 atoms. We also confirm the accuracy of the method by comparing the spin density wave state of bcc Cr against a direct supercell calculation starting from a random magnetization density. Furthermore, the spin spiral state of $\gamma$-Fe is correctly reproduced and the screening by the density of a saw-tooth potential over 20 unit cells of silicon is verified

On the hypothesis of an inverted Z-gradient inside Jupiter

Models of Jupiter s interior struggle to agree with measurements of the atmospheric composition. Interior models favour a subsolar or solar abundance of heavy elements Z while atmospheric measurements suggest a supersolar abundance. One potential solution may be the presence of an inverted Z-gradient, namely an inward decrease of Z, which implies a larger heavy element abundance in the atmosphere than in the outer envelope. We investigate two scenarios in which the inverted Z gradient is located either where helium rain occurs (Mbar level) or at upper levels (kbar level) where a radiative region could exist. We aim to assess how plausible these scenarios are. We calculate interior and evolution models of Jupiter with such inverted Z-gradient and use constraints on the stability and the formation of an inverted Z-gradient. We find that an inverted Z-gradient at the location of helium rain cannot work as it requires a late accretion and of too much material. We find interior models with an inverted Z-gradient at upper levels, due to a radiative zone preventing downward mixing, that could satisfy the present gravity field of the planet. However, our evolution models suggest that this second scenario might not be in place. An inverted Z-gradient in Jupiter could be stable. Yet, its presence either at the Mbar level or kbar level is rather unlikely.Comment: Accepted for publication in A&

Does Exchange Splitting persist above TCT_C? A spin-resolved photoemission study of EuO

The electronic structure of the ferromagnetic semiconductor EuO is investigated by means of spin- and angle-resolved photoemission spectroscopy and density functional theory (GGA+$U$). Our spin-resolved data reveals that, while the macroscopic magnetization of the sample vanishes at the Curie temperature, the exchange splitting of the O 2$p$ band persists up to $T_{C}$. Thus, we provide evidence for short-range magnetic order being present at the Curie temperature

Reduced expression of C/EBPβ-LIP extends health- and lifespan in mice

Ageing is associated with physical decline and the development of age-related diseases such as metabolic disorders and cancer. Few conditions are known that attenuate the adverse effects of ageing, including calorie restriction (CR) and reduced signalling through the mechanistic target of rapamycin complex 1 (mTORC1) pathway. Synthesis of the metabolic transcription factor C/EBPβ-LIP is stimulated by mTORC1, which critically depends on a short upstream open reading frame (uORF) in the Cebpb-mRNA. Here we describe that reduced C/EBPβ-LIP expression due to genetic ablation of the uORF delays the development of age-associated phenotypes in mice. Moreover, female C/EBPβΔuORF mice display an extended lifespan. Since LIP levels increase upon aging in wild type mice, our data reveal an important role for C/EBPβ in the aging process and suggest that restriction of LIP expression sustains health and fitness. Thus, therapeutic strategies targeting C/EBPβ-LIP may offer new possibilities to treat age-related diseases and to prolong healthspan

A formally verified compiler back-end

This article describes the development and formal verification (proof of semantic preservation) of a compiler back-end from Cminor (a simple imperative intermediate language) to PowerPC assembly code, using the Coq proof assistant both for programming the compiler and for proving its correctness. Such a verified compiler is useful in the context of formal methods applied to the certification of critical software: the verification of the compiler guarantees that the safety properties proved on the source code hold for the executable compiled code as well

Navigieren

Prof. Dr. Jens Schröter, Christoph Borbach, Max Kanderske und Prof. Dr. Benjamin Beil sind Herausgeber der Reihe. Die Herausgeber*innen der einzelnen Hefte sind renommierte Wissenschaftler*innen aus dem In- und Ausland.Navigieren ist längst kein Unikum professionalisierter Seefahrer:innen mehr, sondern als Smartphone- und Browser-Praktik fester Bestandteil des vernetzten digitalen Alltags. Da Wegfindungen durch On- und Offline-Räume navigationsspezifische Formen von Medienkompetenz voraussetzen und hervorbringen, fordern sie die Intensivierung der medienkulturwissenschaftlichen Beschäftigung mit den situierten und technisierten Medienpraktiken der Navigation geradezu heraus. Die Ausgabe nimmt diesen Befund zum Anlass, polyperspektivische Zugänge zum »Navigieren« vorzustellen. Die körper-, kultur- und medientechnischen Facetten des Navigierens stehen dabei ebenso im Fokus wie ihre historischen Ausgestaltungen, die Arbeit am und im Datenmaterial von Navigationsmedien und die Theoretisierung postdigitaler Sensor-Medien-Kulturen, die dem Umstand Rechnung trägt, dass es nicht allein Daten, Dinge und Körper sind, die es zu navigieren gilt, sondern zunehmend nicht-menschliche Akteure selbst zielgerichtete Raumdurchquerungen praktizieren. Fehlte es in der (deutschsprachigen) Medienkulturwissenschaft bislang an einer Bündelung heterogener navigationsspezifischer Forschungsarbeiten, gibt diese Ausgabe einen Überblick über das Feld, seine Forscher:innen und Fragestellungen. Denn trotz des Spatial Turns in den Humanities und der gegenwärtigen Konjunktur geomedialer Arbeiten, scheint die synthetisierende Fokussierung auf Medien und Praktiken des Navigierens in historischer, ethnografischer, technischer und theoretischer Perspektive bislang ein Desiderat darzustellen.Navigation is no longer unique to the context of professional seafaring, but has become an integral part of networked digital everyday life enabled through smartphones and web browsers. Indeed, finding one’s way through online and offline spaces increasingly presupposes and produces specific forms of media competence one could call »navigational«. In this, a ›media cultural studies‹ perspective on the situated and ›technologized‹ media practices of navigation becomes imperative to understanding the contemporary media landscape. Issue 1/22 of Navigationen answers this call by presenting polyperspectival approaches to »navigating«. The contributions discuss the bodily, cultural, and media-technical facets of navigation, as well as its historical forms, the work on and in the data produced by and with navigational media, and the theorization of post-digital ›sensor media cultures‹. In doing so, the issue acknowledges that not only do data, things, and bodies need to be ›navigated‹ in the context of logistics, but that the increasingly autonomous wayfinding processes of non-human actors change the notion of navigation itself. As (German language) media cultural studies has so far lacked a convincing compilation of heterogeneous approaches to studying navigation, this issue provides an overview of the field, its researchers and questions. Despite the spatial turn in the humanities and a recent surge in geomedia studies, an approach towards the media and practices of navigation that combines historical, ethnographic, technical and theoretical perspectives, has remained a desideratum until now. The issue fills this gap