A generalisation of Amitsur's A-polynomials

summary:We find examples of polynomials $f\in D[t;\sigma ,\delta ]$ whose eigenring $\mathcal {E}(f)$ is a central simple algebra over the field $F = C \cap \mathrm {Fix}(\sigma ) \cap \mathrm {Const}(\delta )$

The eigenspaces of twisted polynomials over cyclic field extensions

Let $K$ be a field and $\sigma$ an automorphism of $K$ of order $n$. We study the eigenspace of a bounded skew polynomial $f\in K[t;\sigma]$, with emphasis on the case of a cyclic field extension $K/F$ of degree $n$, where $\sigma$ generates the Galois group. We obtain lower bounds on its dimension, and compute it in special cases.Comment: Rewritten and streamlined new version, some results are improve

Surface Reconstructions in Molecular Beam Epitaxy of SrTiO3

We show that reflection high-energy electron diffraction (RHEED) can be used as a highly sensitive tool to track surface and resulting film stoichiometry in adsorption-limited molecular beam epitaxy of (001) SrTiO3 thin films. Even under growth conditions that yield films with a lattice parameter that is identical to that of stoichiometric bulk crystals within the detection limit of high-resolution x-ray diffraction (XRD), changes in surface reconstruction occur from (1x1) to (2x1) to c(4x4) as the equivalent beam pressure of the Ti metalorganic source is increased. These surface reconstructions are correlated with a shift from mixed SrO/TiO2 termination to pure TiO2 termination. The crossover to TiO2 surface termination is also apparent in a phase shift in RHEED oscillations observed at the beginning of growth. Comparison with prior results for carrier mobilities of doped films shows that the best films are grown under conditions of a TiO2-saturated surface [c(4x4) reconstruction] within the XRD growth window.Comment: Accepted for publication in Applied Physics Letter

Fire in the Heart: A Characterization of the High Kinetic Temperatures and Heating Sources in the Nucleus of NGC253

The nuclear starburst within the central $\sim 15^{\prime\prime}$ ($\sim 250$ pc; $1^{\prime\prime} \simeq 17$ pc) of NGC253 has been extensively studied as a prototype for the starburst phase in galactic evolution. Atacama Large Millimeter/submillimeter Array (ALMA) imaging within receiver Bands 6 and 7 have been used to investigate the dense gas structure, kinetic temperature, and heating processes which drive the NGC253 starburst. Twenty-nine transitions from fifteen molecular species/isotopologues have been identified and imaged at $1.^{\prime\prime}5$ to $0.^{\prime\prime}4$ resolution, allowing for the identification of five of the previously-studied giant molecular clouds (GMCs) within the central molecular zone (CMZ) of NGC253. Ten transitions from the formaldehyde (H$_2$CO) molecule have been used to derive the kinetic temperature within the $\sim 0.^{\prime\prime}5$ to $5^{\prime\prime}$ dense-gas structures imaged. On $\sim 5^{\prime\prime}$ scales we measure $T_K \gtrsim 50$ K, while on size scales $\lesssim 1^{\prime\prime}$ we measure $T_K \gtrsim 300$ K. These kinetic temperature measurements further delineate the association between potential sources of dense gas heating. We have investigated potential heating sources by comparing our measurements to models which predict the physical conditions associated with dense molecular clouds that possess a variety of heating mechanisms. This comparison has been supplemented with tracers of recently-formed massive stars (Br$\gamma$) and shocks ([FeII]). Derived molecular column densities point to a radially-decreasing abundance of molecules with sensitivity to cosmic ray and mechanical heating within the NGC253 CMZ. These measurements are consistent with radio spectral index calculations which suggest a higher concentration of cosmic ray producing supernova remnants within the central 10 pc of NGC253.Comment: 60 pages, 25 figures (whew!), Accepted for publication in ApJ, Latest version includes minor corrections following proof submissio

Die Rolle der Aldehyd-Dehydrogenase 1A1 (ALDH1A1) als Markerenzym der astrozytären Differenzierung sowie als prognostischer Biomarker im Glioblastoma multiforme

Das Glioblastom stellt den häufigsten bösartigen Hirntumor dar und ist mit einem raschen Krankheitsfortschreiten und infauster Prognose innerhalb kurzer Zeit vergesellschaftet. Die Aldehyddehydrogenase A1 (ALDH1A1) ist in zahlreichen soliden Neoplasien als Marker für Tumorstammzellen beschrieben. Dabei korreliert die Expression des Enzyms häufig mit einer ungünstigen Prognose. Über die Expression der ALDH1A1 im sich entwickelnden Gehirn ist wenig bekannt. Wir untersuchten daher in der hier vorliegenden Arbeit die Expression der ALDH1A1 in Gewebeproben aus gesunden menschlichen Gehirnen verschiedener Entwicklungsstufen sowie in verschiedenen Hirntumoren, darunter 93 Glioblastome. Wir zeigen, dass ALDH1A1 in reifen Astrozyten exprimiert wird, in den Stammzellnischen des sich entwickelnden Gehirns jedoch keine ALDH1A1- Expression nachweisbar ist. Fast alle untersuchten Glioblastome zeigten eine kräftige Expression des Enzyms, wobei die ALDH1A1-positiven Zellen keine Expression von Nestin, Olig2 oder SOX2 und kaum proliferative Aktivität zeigten. Eine starke Expression von ALDH1A1 korrelierte mit einem längeren Überleben von Glioblastompatienten unabhängig von der Gabe einer Chemotherapie oder dem MGMT-Methylierungsstatus, was auf eine mögliche Bedeutung der ALDH1A1- Immunhistochemie als prognostischen Biomarker für das Glioblastom hindeutet. Wir zeigen daher, dass die ALDH1A1 ein Marker für die astrogliale Differenzierung bei der Hirnentwicklung ist und dass eine starke Expression des Enzyms ein günstiger prognostischer Biomarker für ein längeres Überleben von Glioblastompatienten ist

Carrier-controlled ferromagnetism in SrTiO3

Magnetotransport and superconducting properties are investigated for uniformly La-doped SrTiO3 films and GdTiO3/SrTiO3 heterostructures, respectively. GdTiO3/SrTiO3 interfaces exhibit a high-density two-dimensional electron gas on the SrTiO3-side of the interface, while for the SrTiO3 films carriers are provided by the dopant atoms. Both types of samples exhibit ferromagnetism at low temperatures, as evidenced by a hysteresis in the magnetoresistance. For the uniformly doped SrTiO3 films, the Curie temperature is found to increase with doping and to coexist with superconductivity for carrier concentrations on the high-density side of the superconducting dome. The Curie temperature of the GdTiO3/SrTiO3 heterostructures scales with the thickness of the SrTiO3 quantum well. The results are used to construct a stability diagram for the ferromagnetic and superconducting phases of SrTiO3.Comment: Revised version that is closer to the published version; Fig. 2 correcte

Tuning bad metal and non-Fermi liquid behavior in a Mott material: rare earth nickelate thin films

Resistances that exceed the Mott-Ioffe-Regel limit, known as bad metal behavior, and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. Here we establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype, bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of the Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to non-Fermi liquid metal phase and provide a predictive criterion for strong localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices.Comment: Manuscript text, 5 figures and supplemen