672 research outputs found
COMPLETE SOLUTION OF THE XXZ-MODEL ON FINITE RINGS. DYNAMICAL STRUCTURE FACTORS AT ZERO TEMPERATURE.
The finite size effects of the dynamical structure factors in the XXZ-model
are studied in the euclidean time -representation. Away from the
critical momentum finite size effects turn out to be small except for
the large limit. The large finite size effects at the critical momentum
signal the emergence of infrared singularities in the spectral
-representation of the dynamical structure factors.Comment: PostScript file with 12 pages + 11 figures uuencoded compresse
Transcriptional networks specifying homeostatic and inflammatory programs of gene expression in human aortic endothelial cells.
Endothelial cells (ECs) are critical determinants of vascular homeostasis and inflammation, but transcriptional mechanisms specifying their identities and functional states remain poorly understood. Here, we report a genome-wide assessment of regulatory landscapes of primary human aortic endothelial cells (HAECs) under basal and activated conditions, enabling inference of transcription factor networks that direct homeostatic and pro-inflammatory programs. We demonstrate that 43% of detected enhancers are EC-specific and contain SNPs associated to cardiovascular disease and hypertension. We provide evidence that AP1, ETS, and GATA transcription factors play key roles in HAEC transcription by co-binding enhancers associated with EC-specific genes. We further demonstrate that exposure of HAECs to oxidized phospholipids or pro-inflammatory cytokines results in signal-specific alterations in enhancer landscapes and associate with coordinated binding of CEBPD, IRF1, and NFκB. Collectively, these findings identify cis-regulatory elements and corresponding trans-acting factors that contribute to EC identity and their specific responses to pro-inflammatory stimuli
Tiefendifferenzierte Untersuchung der mikrobiellen Gemeinschaft und Benetzungseigenschaften von Regenwurmröhrenwänden von Lumbricus terrestris
Regenwürmer sind essentiell an der Strukturierung des Oberbodens beteiligt, wobei ein verzweigtes Gangsystem entsteht, dessen Porenwände (PW) vor allem durch die Aktivitäten von anözischen Regenwürmern mit organischem Material (OM) angereichert sind. Das leicht verfügbare Nährstoffangebot stimuliert die dortigen Mikroorganismen, wodurch sich eine einzigartige mikrobielle Gemeinschaft (MG) etabliert. Die erhöhte mikrobielle Biomasse (MB) und Aktivität an den PW führt zu einem Überzug der Oberflächen mit einem Biofilm, welcher wiederum mit pflanzlichen Abbauprodukten zu Hydrophobie führen kann. Die Benetzungseigenschaften der PW können einen entscheidenden Einfluss auf Infiltration und Stofftransport besitzen und bedürfen daher genauerer Betrachtung. Ziel dieser Studie ist es, Unterschiede in der MG zum umgebenden Boden (BS) darzustellen und die Zusammensetzung des OM sowie das Benetzungsverhalten der PW tiefendifferenziert zu charakterisieren.
Ungestörte Bodensäulen wurden mit PVC-Rohren auf einem Wiesenstandort im Hainich, einem Höhenrücken auf Muschelkalkbasis im NW Thüringens, genommen und tiefendifferenziert (0-20 cm) PW und Referenzmaterial des BS freipräpariert. Die MG wurde mit einer PLFA-Analyse charakterisiert, die Zusammensetzung des OM mit FTIR und die Benetzung mit dem Water Drop Penetration Time (WDPT) Test untersucht und anschließend statistisch ausgewertet (PCA, Split-Plot-Modell).
Die MG der PW unterschied sich signifikant zu der des BS. Pilze waren an den PW prozentual stärker präsent, wohingegen der Anteil gram-positiver Bakterien geringer war. Die signifikant höhere absolute MB sowie aliphatische Komponenten der PW verursachten stark hydrophobe Oberflächen, die im Vergleich zum BS eine neunfach erhöhte Benetzungszeit aufwiesen. Die Daten zeigen, dass die PW in Hinblick auf OM-Zusammensetzung und Benetzungseigenschaften deutlich von denen der BS zu unterscheiden sind und somit das Infiltrationsverhalten von der PW in den BS beeinflusst werden kann
Direct Observation of Quantum Coherence in Single-Molecule Magnets
Direct evidence of quantum coherence in a single-molecule magnet in frozen
solution is reported with coherence times as long as T2 = 630 ns. We can
strongly increase the coherence time by modifying the matrix in which the
single-molecule magnets are embedded. The electron spins are coupled to the
proton nuclear spins of both the molecule itself and interestingly, also to
those of the solvent. The clear observation of Rabi oscillations indicates that
we can manipulate the spin coherently, an essential prerequisite for performing
quantum computations.Comment: 5 Pages, 4 Figures, final version published in PR
Resistive transition of hydrogen-rich superconductors
Critical temperature, Tc, and transition width, ΔTc, are two primary parameters of the superconducting transition. The latter parameter reflects the superconducting state disturbance originating from the thermodynamic fluctuations, atomic disorder, applied magnetic field, the presence of secondary crystalline phases, applied pressure, etc. Recently, Hirsch and Marsiglio (2021 Phys. Rev. B 103 134505, doi: 10.1103/PhysRevB.103.134505) performed an analysis of the transition width in several near-room-temperature superconductors and reported that the reduced transition width, ΔTc/Tc, in these materials does not follow the conventional trend of transition width broadening in applied magnetic field observed in low- and high-Tc superconductors. Here, we present a thorough mathematical analysis of the magnetoresistive data, R(T, B), for the high-entropy alloy (ScZrNb)0.65[RhPd]0.35 and hydrogen-rich superconductors of Im-3m-H3S, C2/m-LaH10 and P63/mmc-CeH9. We found that the reduced transition width, ΔTc/Tc, in these materials follows a conventional broadening trend in applied magnetic field. © 2021 IOP Publishing Ltd
Disorder Induced Quantum Phase Transition in Random-Exchange Spin-1/2 Chains
We investigate the effect of quenched bond-disorder on the anisotropic
spin-1/2 (XXZ) chain as a model for disorder induced quantum phase transitions.
We find non-universal behavior of the average correlation functions for weak
disorder, followed by a quantum phase transition into a strongly disordered
phase with only short-range xy-correlations. We find no evidence for the
universal strong-disorder fixed point predicted by the real-space
renormalization group, suggesting a qualitatively different view of the
relationship between quantum fluctuations and disorder.Comment: 4 pages, 4 postscript figures, needs RevTeX
Dynamic properties of the spin-1/2 XY chain with three-site interactions
We consider a spin-1/2 XY chain in a transverse (z) field with multi-site
interactions. The additional terms introduced into the Hamiltonian involve
products of spin components related to three adjacent sites. A Jordan-Wigner
transformation leads to a simple bilinear Fermi form for the resulting
Hamiltonian and hence the spin model admits a rigorous analysis. We point out
the close relationships between several variants of the model which were
discussed separately in previous studies. The ground-state phases (ferromagnet
and two kinds of spin liquid) of the model are reflected in the dynamic
structure factors of the spin chains, which are the main focus in this study.
First we consider the zz dynamic structure factor reporting for this quantity a
closed-form expression and analyzing the properties of the two-fermion
(particle-hole) excitation continuum which governs the dynamics of transverse
spin component fluctuations and of some other local operator fluctuations. Then
we examine the xx dynamic structure factor which is governed by many-fermion
excitations, reporting both analytical and numerical results. We discuss some
easily recognized features of the dynamic structure factors which are
signatures for the presence of the three-site interactions.Comment: 28 pages, 10 fugure
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