Defect-induced phase transition in the asymmetric simple exclusion process

We reconsider the long-standing question of the critical defect hopping rate $r_c$ in the one-dimensional totally asymmetric exclusion process (TASEP) with a slow bond (defect). For $r< r_c$ a phase separated state is observed due to queuing at the defect site whereas for $r\geq r_c$ the defect site has only local effects on the stationary state of the homogeneous system. Mean-field theory predicts $r_c=1$ (when hopping rates outside the defect bond are equal to 1) but numerical investigations seem to indicate $r_c \approx 0.80(2)$. Here we improve the numerics to show that $r_c > 0.99$ and give strong evidence that indeed $r_c=1$ as predicted by mean-field theory, and anticipated by recent theoretical findings.Comment: 5 pages, 6 Figs, version as accepted by Europhysics Letter

Fibonacci family of dynamical universality classes

Universality is a well-established central concept of equilibrium physics. However, in systems far away from equilibrium a deeper understanding of its underlying principles is still lacking. Up to now, a few classes have been identified. Besides the diffusive universality class with dynamical exponent $z=2$ another prominent example is the superdiffusive Kardar-Parisi-Zhang (KPZ) class with $z=3/2$. It appears e.g. in low-dimensional dynamical phenomena far from thermal equilibrium which exhibit some conservation law. Here we show that both classes are only part of an infinite discrete family of non-equilibrium universality classes. Remarkably their dynamical exponents $z_\alpha$ are given by ratios of neighbouring Fibonacci numbers, starting with either $z_1=3/2$ (if a KPZ mode exist) or $z_1=2$ (if a diffusive mode is present). If neither a diffusive nor a KPZ mode are present, all dynamical modes have the Golden Mean $z=(1+\sqrt{5})/2$ as dynamical exponent. The universal scaling functions of these Fibonacci modes are asymmetric L\'evy distributions which are completely fixed by the macroscopic current-density relation and compressibility matrix of the system and hence accessible to experimental measurement.Comment: 8 pages, 5 Figs (2 Figure revised, one new Figure added), revised introductio

Exact scaling solution of the mode coupling equations for non-linear fluctuating hydrodynamics in one dimension

We obtain the exact solution of the one-loop mode-coupling equations for the dynamical structure function in the framework of non-linear fluctuating hydrodynamics in one space dimension for the strictly hyperbolic case where all characteristic velocities are different. All solutions are characterized by dynamical exponents which are Kepler ratios of consecutive Fibonacci numbers, which includes the golden mean as a limiting case. The scaling form of all higher Fibonacci modes are asymmetric L\'evy-distributions. Thus a hierarchy of new dynamical universality classes is established. We also compute the precise numerical value of the Pr\"ahofer-Spohn scaling constant to which scaling functions obtained from mode coupling theory are sensitive.Comment: PACS classification: \pacs{05.60.Cd, 05.20.Jj, 05.70.Ln, 47.10.-g

Effekte von Glukokortikoiden,gonadalen Steroiden und Interleukinen auf antioxidativ wirksame Substanzen und Enzymsysteme in neuronalen und glialen Zellsystemen

Zusammenfassung In Zusammenhang mit fast allen neurologischen und psychiatrischen Krankheitsbildern und dem normalen Alterungsprozess existieren heute Untersuchungen über biochemische Veränderungen von Komponenten des antioxidativen Systems. Dieses System ist für die Entgiftung von reaktiven Sauerstoffspezies verantwortlich. Unter diesem Oberbegriff werden freie Radikale und Substanzen wie Wasserstoffperoxid zusammengefasst, die Moleküle wie DNA, Membranlipide und Proteine schädigen können. Wesentliche Bestandteile dieses Stoffwechsel-Systems sind Enzyme wie Superoxid Dismutase, Glutathion Peroxidase und Katalase, sowie Substanzen wie Glutathion und verschiedene Vitamine. Die Superoxid Dismutase-Isoformen wandeln das Superoxidradikal in Wasserstoffperoxid um, das dann von der Katalase und der Glutathion Peroxidase mit Glutathion als Substrat in Wasser umgewandelt wird. Es existiert eine Vielzahl von Untersuchungen über Effekte von Steroidhormonen und Interleukinen auf das antioxidative System in peripheren Organsystemen wie z. B. Leber oder Niere. Im Zusammenhang mit dem zentralen Nervensystem gibt es bis jetzt nur wenige Studien. Der pharmakologische Einsatz von Steroiden ist im Falle des 6-Methylprednisolon bei Rückenmarksverletzungen ein Standardtherapieverfahren und wird für Östrogenen in der Therapie neurodegenerativer Erkrankungen wie z. B. der Alzheimerschen Demenz diskutiert. Weiterhin existieren eine Reihe von Studien, die den Einsatz von Östrogenen und Androgenen zur Verbesserung der kognitiven Fähigkeiten im Alter vorschlagen. Fasst man die bisher geschilderten Erkenntnisse zusammen, so ist es von großem Interesse, Wirkungen von Steroiden und Interleukinen auf das antioxidative System im zentralen Nervensystem zu untersuchen. Ziel der vorliegenden Arbeit war es deshalb, Effekte von Glukortikoiden (Kortikosteron, Dexamethason, 6-Methylprednisolon), gonadalen Steroiden (17β-Östradiol, Progesteron, Testosteron) und Interleukinen (Interleukin-6) auf den Glutathion-Gehalt in verschiedenen neuronalen (HT22 Zellen, hippokampale und neokortikale Primärkulturen) und glialen (C6 Zellen) und von Interleukin-6 in hippokampalen Zellsystemen in verschiedenen Konzentrationen und nach unterschiedlichen Inkubationszeiten zu untersuchen. Die Steroide und das Interleukin-6 entfalteten eine Vielzahl unterschiedlicher Effekte. Zu den wesentlichsten Effekten zählt der höchste gemessene Anstieg des Glutathion-Gehaltes nach einer Behandlung von HT22 Zellen für 24 Stunden mit 6-Methylprednisolon. In primären hippokampalen Kulturen wurde eine signifikante Erhöhung des Glutathion-Spiegels nach 48 Stunden beobachtet. Die Beteiligung des Glutathion-Systems an der Wirkung von 6-Methylprednisolon in Zusammenhang mit Rückenmarksverletzungen wird in der Literatur diskutiert. Der 6-Methylprednisolon induzierte Anstieg des Glutathion-Gehalts in neuronalen Zellsystemen könnte hierbei eine große Rolle spielen. Eine Inkubation aller verwendeter neuronaler Zellsysteme wie auch der C6 Zelllinie mit 17β-Östradiol (10-7 M) für 24 Stunden führte zu einem signifikanten Anstieg des Glutathion-Spiegels. Eine Beteiligung dieser Wirkung an den vielfach diskutierten neuroprotektiven Effekten dieses Hormons liegt nahe. Auch von Androgenen werden in letzter Zeit protektive Effekte zunehmend diskutiert. In Zusammenhang mit der Katalase gibt es Arbeiten, die zeigen, dass Testosteron in der Lage ist die Katalase-Aktivität zu erhöhen. In der vorliegenden Arbeit konnte gezeigt werden, dass mit einem durch Testosteron induzierten Anstieg der Katalase-Aktivität in HT22 Zellen eine Neuroprotektion gegenüber der Schädigung durch Wasserstoffperoxid verbunden ist. Die Ergebnisse dieser Studien haben gezeigt, dass sowohl Steroide wie auch Interleukine in der Lage sind, auf vielfache Weise den Spiegel von antioxidativ wirksamen Substanzen sowie die Aktivität antioxidativer Enzyme zu beeinflussen. Weitere Untersuchungen werden ergeben müssen, ob auch die Veränderungen des Glutathion-Spiegels mit protektiven Effekten verbunden sind und sich im Tierversuch nachvollziehen lassen

Bose-Hubbard model on two-dimensional line graphs

We construct a basis for the many-particle ground states of the positive hopping Bose-Hubbard model on line graphs of finite 2-connected planar bipartite graphs at sufficiently low filling factors. The particles in these states are localized on non-intersecting vertex-disjoint cycles of the line graph which correspond to non-intersecting edge-disjoint cycles of the original graph. The construction works up to a critical filling factor at which the cycles are close-packed.Comment: 9 pages, 5 figures, figures and conclusions update

Focus Alignment Method for Laser Manufacturing at Sub-micron Positional Accuracy

AbstractAccurate positioning of a sample is one of the major challenges in the laser micro manufacturing – especially if the requirements on tolerances are high as in ultrafast laser micromachining. There are a number of methods that allow detection of the surface position, however only few of them use the beam of the processing laser as a basis for the measurement. These methods have an advantage that any changes in the structuring beam will be inherently accommodated for. This work describes a direct contact free method to accurately determine the surface position with respect to the structuring beam focal plane. The method makes alignment of unique samples precise and time efficient due to ease of automation and provides a reproducibility of surface detection of less than 1μm

Slow and fast single photons from a quantum dot interacting with the excited state hyperfine structure of the Cesium D1-line

Hybrid interfaces between distinct quantum systems play a major role in the implementation of quantum networks. Quantum states have to be stored in memories to synchronize the photon arrival times for entanglement swapping by projective measurements in quantum repeaters or for entanglement purification. Here, we analyze the distortion of a single-photon wave packet propagating through a dispersive and absorptive medium with high spectral resolution. Single photons are generated from a single In(Ga)As quantum dot with its excitonic transition precisely set relative to the Cesium D1 transition. The delay of spectral components of the single-photon wave packet with almost Fourier-limited width is investigated in detail with a 200 MHz narrow-band monolithic Fabry-Pérot resonator. Reflecting the excited state hyperfine structure of Cesium, “slow light” and “fast light” behavior is observed. As a step towards room-temperature alkali vapor memories, quantum dot photons are delayed for 5 ns by strong dispersion between the two 1.17 GHz hyperfine-split excited state transitions. Based on optical pumping on the hyperfine-split ground states, we propose a simple, all-optically controllable delay for synchronization of heralded narrow-band photons in a quantum network.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/H2020/679183/EU/Entanglement distribution via Semiconductor-Piezoelectric Quantum-Dot Relays/SPQRe

Pathogenicity of Pythium species to maize

AbstractPythium isolates from diseased and dead bait plants of maize and cress grown in compost or various soils (maize fields, parkland under deciduous trees, grassland) were characterised and tested for pathogenicity to maize (Zea mays L.). In pot tests performed under controlled conditions, pathogenicity of the isolates to maize was apparent by reduction of root and shoot growth, whereas damping-off of maize seedlings was less frequent. Contrarily, pea seedlings were killed by pathogenic Pythium isolates. Pythium isolates from diseased maize seedlings and pathogenic strains from other gramineous plants (P. phragmitis, P. aff.phragmitis, P. catenulatum) were not necessarily more virulent to maize compared to isolates originating from dicotyledonous plants (cress). The most virulent isolates originated from compost and caused a reduction of maize shoot growth of up to 60%. Phylogenetic analysis revealed that they were very closely related to P. ultimum var. ultimum and P. arrhenomanes, respectively. Isolates originating from maize fields, grassland and parkland under deciduous trees, a reference culture of P. arrhenomanes and strains of P. phragmitis, P. aff. phragmitis and P. catenulatum with known pathogenicity on reed were non-pathogenic on maize. Isolates from compost, and from maize fields generally had a higher temperature optimum for mycelial growth (30 °C) and a faster growth rate (1.5–2.0 mm h−1) compared to the isolates from parkland under deciduous trees and grassland soil (20–25 °C, ~1.0 mm h−1), respectively. This study indicates a potential impact of pathogenic Pythium on maize plants even in the absence of visible symptoms

An Educated Warm Start For Deep Image Prior-Based Micro CT Reconstruction

Deep image prior (DIP) was recently introduced as an effective unsupervised approach for image restoration tasks. DIP represents the image to be recovered as the output of a deep convolutional neural network, and learns the network's parameters such that the output matches the corrupted observation. Despite its impressive reconstructive properties, the approach is slow when compared to supervisedly learned, or traditional reconstruction techniques. To address the computational challenge, we bestow DIP with a two-stage learning paradigm: (i) perform a supervised pretraining of the network on a simulated dataset; (ii) fine-tune the network's parameters to adapt to the target reconstruction task. We provide a thorough empirical analysis to shed insights into the impacts of pretraining in the context of image reconstruction. We showcase that pretraining considerably speeds up and stabilizes the subsequent reconstruction task from real-measured 2D and 3D micro computed tomography data of biological specimens. The code and additional experimental materials are available at https://educateddip.github.io/docs.educated_deep_image_prior/