1,617 research outputs found
Aurorae of Io and Europa: Observations and Modeling
In the present dissertation we study the auroral emissions emanating from the tenuous atmospheres of Jupiter's satellites Io and Europa. The satellites are embedded in a dense magnetospheric plasma environment. Due to Jupiter's fast rotation the corotating magnetospheric plasma particles constantly flow past Io and Europa causing a complex interaction and triggering auroral emission in the atmospheres. Therefore, aurora observations are a useful tool to explore both the magnetospheric environment and the neutral gas clouds of the satellites. For our analysis, images of Io's and Europa's ultraviolet (UV) emissions are extracted from a large data set of observations by the Space Telescope Imaging Spectrograph (STIS) of the Hubble Space Telescope (HST). Additionally, high-resolution images taken by the Long-Range Reconnaissance Imager (LORRI) of the New Horizons spacecraft of Io's visible aurora and a simultaneous observation by the HST Advanced Camera for Surveys (ACS) are examined.
Io's aurora is characterized by bright emissions on the sub-Jovian and anti-Jovian flanks close to the equator and a fainter limb glow around the polar regions. Analyzing the STIS images we demonstrate that the variations of Io's UV aurora observed over a period of five years can be attributed to changes in the magnetospheric environment as well as to the varying viewing perspective. Based on these findings, an analytical model for the three-dimensional distribution of the UV emission around Io is developed. By fitting the parameters of this phenomenological model to the STIS observations, we are able to derive universal, quantitative properties of the emission distribution. Thereby, we find that the aurora above the sunlit part of Io's surface is brighter than on the night side or during an eclipse event, when Io moves through Jupiter's shadows. By comparing the LORRI and ACS observations of Io's aurora in eclipse to results from a three-dimensional two-fluid plasma simulation model, we show that the reduced auroral brightness originates from a lowered atmospheric density. Our results are a strong indication, that Io's atmosphere is driven by sublimation of SO2 frost rather than direct volcanic outgassing. The ultimate source for Io's atmospheric gas is widely debated for many years.
We also investigate the observed variation or rocking of the bright auroral spots around Io's equator. The location of the spots has been shown to be correlated to the Jovian magnetic field orientation at Io. The exact correlation is, however, not 1:1, but is presumably affected by local perturbations of the magnetic field. Therefore, we analyze the influence of the magnetic field perturbations due to the plasma interaction as well as due to induced fields from Io's interior on the expected variations of the aurora spots. According to our calculations, the observed rocking of the aurora is not consistent with a conductive magma ocean below Io's surface. A rough estimation of the plasma interaction effects on the auroral spots does not yield conclusive results.
Furthermore, we examine the morphology and brightness of oxygen emissions in the STIS observations of Europa's UV aurora. We find that most emission is observed on the disk of Europa rather than around the limb like in comparable observations of Io's aurora. We show that an increasing O2 density towards the sub-solar point possibly explains the observed morphology as well as previous observations. While the OI] 1356 Ã… emission pattern appears to vary periodically in correlation with the changing magnetospheric environment, the OI 1304 Ã… morphology is clearly dominated by a very bright locally confined emission in the northern, anti-Jovian quadrant of Europa's disk. The location of this anomaly coincides exactly with the longitude, where a peak in water vapor production is predicted due to increased shear heating at the surface cracks. Estimating the emission brightnesses expected for a local water plume, we find that the observed UV emission intensities are principally consistent with a locally confined abundance of water vapor. However, due to observational uncertainties and since we have neglected the effects of the plasma interaction for the approximation of the H2O abundance, our results can not be seen as prove for the existence of water plumes on Europa. To accurately determine the effects of an asymmetric O2 atmosphere and the influence of a local water plume, the plasma interaction has to be simulated
Spin-orbital excitation continuum and anomalous electron-phonon interaction in the Mott insulator LaTiO
Raman scattering experiments on stoichiometric, Mott-insulating LaTiO
over a wide range of excitation energies reveal a broad electronic continuum
which is featureless in the paramagnetic state, but develops a gap of cm upon cooling below the N\'eel temperature K. In the
antiferromagnetic state, the spectral weight below the gap is transferred to
well-defined spectral features due to spin and orbital excitations. Low-energy
phonons exhibit pronounced Fano anomalies indicative of strong interaction with
the electron system for , but become sharp and symmetric for . The electronic continuum and the marked renormalization of the phonon
lifetime by the onset of magnetic order are highly unusual for Mott insulators
and indicate liquid-like correlations between spins and orbitals.Comment: to appear in Phys. Rev. Let
Mott-Hubbard exciton in the optical conductivity of YTiO3 and SmTiO3
In the Mott-Hubbard insulators YTiO3 and SmTiO3 we study optical excitations
from the lower to the upper Hubbard band, d^1d^1 -> d^0d^2. The multi-peak
structure observed in the optical conductivity reflects the multiplet structure
of the upper Hubbard band in a multi-orbital system. Absorption bands at 2.55
and 4.15 eV in the ferromagnet YTiO3 correspond to final states with a triplet
d^2 configuration, whereas a peak at 3.7 eV in the antiferromagnet SmTiO3 is
attributed to a singlet d^2 final state. A strongly temperature-dependent peak
at 1.95 eV in YTiO3 and 1.8 eV in SmTiO3 is interpreted in terms of a Hubbard
exciton, i.e., a charge-neutral (quasi-)bound state of a hole in the lower
Hubbard band and a double occupancy in the upper one. The binding to such a
Hubbard exciton may arise both due to Coulomb attraction between
nearest-neighbor sites and due to a lowering of the kinetic energy in a system
with magnetic and/or orbital correlations. Furthermore, we observe anomalies of
the spectral weight in the vicinity of the magnetic ordering transitions, both
in YTiO3 and SmTiO3. In the G-type antiferromagnet SmTiO3, the sign of the
change of the spectral weight at T_N depends on the polarization. This
demonstrates that the temperature dependence of the spectral weight is not
dominated by the spin-spin correlations, but rather reflects small changes of
the orbital occupation.Comment: Strongly extended version; new data of SmTiO3 included; detailed
discussion of temperature dependence include
Genetic and Phenotypic Diversity of Morganella morganii Isolated From Cheese
The bacterium Morganella morganii can produce the biogenic amines (BA) cadaverine, putrescine, and histamine in vitro and is responsible for high histamine concentrations in fish products. These BA can have toxic effects upon ingestion and are undesired in food. The purpose of this study was to characterize the phenotype and genotype of 11 M. morganii isolated from cheese in regard to the BA formation. In addition, we investigated the phylogeny, trehalose fermentation ability, and antibiotic resistance of the cheese isolates. To do so, we sequenced their genomes using both long and short read technologies. Due to the presence of the trehalose operon and the ability to ferment trehalose, the cheese isolates can be assigned to the subsp. sibonii. Comparative genomics with public available M. morganii genomes shows that the genomes of the cheese isolates cluster together with other subsp. sibonii genomes. All genomes between subsp. morganii and subsp. sibonii are separated by an average nucleotide identity (ANI) of less than 95.0%. Therefore, the subspecies could represent two distinct species. Nine of the strains decarboxylated lysine yielding cadaverine in vitro. This metabolic activity is linked to a previously unknown gene cluster comprising genes encoding a lysine-tRNA ligase (lysS), an HTH-transcriptional regulator (argP), a cadaverine-lysine antiporter (cadB), and a lysine decarboxylase (cadA). The formation of putrescine is linked to the speF gene encoding an ornithine decarboxylase. The gene is disrupted in five strains by an insertion sequence, and these strains only exhibit a weak putrescine production. Antimicrobial susceptibility profiling revealed that all cheese strains are resistant to tetracycline, chloramphenicol, tigecycline, colistin, and ampicillin. These phenotypes, except for colistin which is intrinsic, could be linked to antimicrobial resistance genes located on the chromosome
Dynamic critical behavior of the chiral phase transition from the real-time functional renormalization group
In the chiral limit the complicated many-body dynamics around the
second-order chiral phase transition of two-flavor QCD can be understood by
appealing to universality. We present a novel formulation of the real-time
functional renormalization group that describes the stochastic hydrodynamic
equations of motion for systems in the same dynamic universality class, which
corresponds to Model G in the Halperin-Hohenberg classification. Our approach
preserves all relevant symmetries of such systems with reversible mode
couplings. We show that the calculations indeed produce the non-trivial value
for the dynamic critical exponent, where is the number of spatial
dimensions. From the momentum and temperature dependence of the diffusion
coefficient of the conserved charge densities, we extract the dimensionless
universal scaling function.Comment: 80 pages, 13 figure
Magnetoelastic coupling in RETiO3 (RE = La, Nd, Sm, Gd, Y)
A detailed analysis of the crystal structure in RETiO3 with RE = La, Nd, Sm,
Gd, and Y reveals an intrinsic coupling between orbital degrees of freedom and
the lattice which cannot be fully attributed to the structural deformation
arising from bond-length mismatch. The TiO6 octahedra in this series are all
irregular with the shape of the distortion depending on the RE ionic radius.
These octahedron distortions vary more strongly with temperature than the tilt
and rotation angles. Around the Ti magnetic ordering all compounds exhibit
strong anomalies in the thermal-expansion coefficients, these anomalies exhibit
opposite signs for the antiferromagnetic and ferromagnetic compounds.
Furthermore the strongest effects are observed in the materials close to the
magnetic cross-over from antiferromagnetic to ferromagnetic order
Hyper-N-glycosylated SAMD14 and neurabin-I as driver autoantigens of primary central nervous system lymphoma
To address the role of chronic antigenic stimulation in primary central nervous system lymphoma (PCNSL), we searched for autoantigens and identified sterile α-motif domain containing protein 14 (SAMD14) and neural tissue-specific F-actin binding protein I (neurabin-I) as autoantigenic targets of the B-cell receptors (BCRs) from 8/12 PCNSLs. In the respective cases, SAMD14 and neurabin-I were atypically hyper--glycosylated (SAMD14 at ASN339 and neurabin-I at ASN1277), explaining their autoimmunogenicity. SAMD14 and neurabin-I induced BCR pathway activation and proliferation of aggressive lymphoma cell lines transfected with SAMD14- and neurabin-I-reactive BCRs. Moreover, the BCR binding epitope of neurabin-I conjugated to truncated exotoxin-killed lymphoma cells expressing the respective BCRs. These results support the role of chronic antigenic stimulation by posttranslationally modified central nervous system (CNS) driver autoantigens in the pathogenesis of PCNSL, serve as an explanation for their CNS tropism, and provide the basis for a novel specific treatment approach
Momentum dependence of orbital excitations in Mott-insulating titanates
High-resolution resonant inelastic x-ray scattering has been used to
determine the momentum dependence of orbital excitations in Mott-insulating
LaTiO and YTiO over a wide range of the Brillouin zone. The data are
compared to calculations in the framework of lattice-driven and
superexchange-driven orbital ordering models. A superexchange model in which
the experimentally observed modes are attributed to two-orbiton excitations
yields the best description of the data.Comment: to appear in PR
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