170 research outputs found
Tumor im Dünndarm bei Peutz-Jeghers-Syndrom
Zusammenfassung: Epithelverschleppung ("epithelial misplacement") kommt in Peutz-Jeghers-Polypen des Jejunum und Ileum vor. Sie kann zur Fallstrickdiagnose eines invasiven Adenokarzinoms verleiten. Hilfreich ist der Nachweis der erhaltenen Lamina propria um die verlagerten Epithelkomplexe, die selten auch Dysplasien aufweisen können. Epithelverschleppungen sind häufig mit intramuralem Schleim assoziier
Magnetic-field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compound Ce(1-x)La(x)B(6)
CeB(6) is a model compound exhibiting antiferroquadrupolar (AFQ) order, its
magnetic properties being typically interpreted within localized models. More
recently, the observation of strong and sharp magnetic exciton modes forming in
its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors
suggested a significant contribution of itinerant electrons to the spin
dynamics. Here we investigate the evolution of the AFQ excitation upon the
application of an external magnetic field and the substitution of Ce with
non-magnetic La, both parameters known to suppress the AFM phase. We find that
the exciton energy decreases proportionally to T_N upon doping. In field, its
intensity is suppressed, while its energy remains constant. Its disappearance
above the critical field of the AFM phase is preceded by the formation of two
modes, whose energies grow linearly with magnetic field upon entering the AFQ
phase. These findings suggest a crossover from itinerant to localized spin
dynamics between the two phases, the coupling to heavy-fermion quasiparticles
being crucial for a comprehensive description of the magnon spectrum.Comment: Extended version with a longer introduction and an additional figure.
6 pages and 5 figure
One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6
Using inelastic neutron scattering, we have observed a quasi-one-dimensional
dispersive magnetic excitation in the frustrated triangular-lattice spin-2
chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
characterized by a large zone-center spin gap of ~27 meV, which we attribute to
the large single-ion anisotropy, and disperses along the chain direction with a
bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
measurable dispersion was found. With increasing temperature, the magnon
dispersion shifts towards lower energies, yet persists up to at least 150 K,
indicating that the ferromagnetic intrachain correlations survive up to 6 times
higher temperatures than the long-range interchain antiferromagnetic order. The
magnon dispersion can be well described within the predictions of linear
spin-wave theory for a system of weakly coupled ferromagnetic chains with large
single-ion anisotropy, enabling the direct quantitative determination of the
magnetic exchange and anisotropy parameters.Comment: 7 pages, 6 figures including one animatio
Magnetic Resonant Mode in the Low-Energy Spin-Excitation Spectrum of Superconducting Rb2Fe4Se5 Single Crystals
We have studied the low-energy spin-excitation spectrum of the
single-crystalline Rb2Fe4Se5 superconductor (Tc = 32 K) by means of inelastic
neutron scattering. In the superconducting state, we observe a magnetic
resonant mode centered at an energy of 14 meV and at the (0.5 0.25 0.5) wave
vector (unfolded Fe-sublattice notation), which differs from the ones
characterizing magnetic resonant modes in other iron-based superconductors. Our
finding suggests that the 245-iron-selenides are unconventional superconductors
with a sign-changing order parameter, in which bulk superconductivity coexists
with the sqrt(5) x sqrt(5) magnetic superstructure. The estimated ratios of the
resonance energy to Tc and the superconducting gap indicate moderate pairing
strength in this compound, similar to that in optimally doped 1111- and
122-pnictides.Comment: To be published in Phys. Rev. Lett. Figures and references have been
updated in v
Similar zone-center gaps in the low-energy spin-wave spectra of NaFeAs and BaFe2As2
We report results of inelastic-neutron-scattering measurements of low-energy
spin-wave excitations in two structurally distinct families of iron-pnictide
parent compounds: Na(1-{\delta})FeAs and BaFe2As2. Despite their very different
values of the ordered magnetic moment and N\'eel temperatures, T_N, in the
antiferromagnetic state both compounds exhibit similar spin gaps of the order
of 10 meV at the magnetic Brillouin-zone center. The gap opens sharply below
T_N, with no signatures of a precursor gap at temperatures between the
orthorhombic and magnetic phase transitions in Na(1-{\delta})FeAs. We also find
a relatively weak dispersion of the spin-wave gap in BaFe2As2 along the
out-of-plane momentum component, q_z. At the magnetic zone boundary (q_z = 0),
spin excitations in the ordered state persist down to 20 meV, which implies a
much smaller value of the effective out-of-plane exchange interaction, J_c, as
compared to previous estimates based on fitting the high-energy spin-wave
dispersion to a Heisenberg-type model.Comment: 5 pages, 4 figures, 1 tabl
Magnetic field dependence of the neutron spin resonance in CeB6
In zero magnetic field, the famous neutron spin resonance in the f-electron
superconductor CeCoIn5 is similar to the recently discovered exciton peak in
the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5
into two components, indicating that it is a doublet. Here we employ inelastic
neutron scattering (INS) to scrutinize the field dependence of spin
fluctuations in CeB6. The exciton shows a markedly different behavior without
any field splitting. Instead, we observe a second field-induced magnon whose
energy increases with field. At the ferromagnetic zone center, however, we find
only a single mode with a non-monotonic field dependence. At low fields, it is
initially suppressed to zero together with the antiferromagnetic order
parameter, but then reappears at higher fields inside the hidden-order phase,
following the energy of an electron spin resonance (ESR). This is a unique
example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR
and INS consistently over a broad range of magnetic fields.Comment: 7 pages, 6 figures including one animation, accepted to Phys. Rev.
The omega-3 fatty acid docosahexaenoic acid attenuates organic dust-induced airway inflammation.
Workers exposed to organic dusts from concentrated animal feeding operations (CAFOs) are at risk for developing airway inflammatory diseases. Available preventative and therapeutic measures for alleviating dust-induced lung disease are inadequate. Because omega-3 fatty acids can mitigate inflammatory processes, we aimed to determine whether nutritional supplementation with the omega-3 fatty acid docosahexaenoic acid (DHA) could reduce the airway inflammatory consequences of exposures to organic dust. Aqueous extracts of organic dusts from swine CAFOs (ODE) were utilized. In DHA-pretreated human bronchial epithelial cells, lung fibroblasts, monocyte cell cultures, and precision-cut murine lung slices, we found that DHA pretreatment dose-dependently decreased ODE-induced inflammatory cytokine production. To determine the in vivo significance of DHA, C57BL/6 mice were orally administered DHA for seven days prior to treatment with intranasal ODE or saline inhalations. Animals treated with 2 mg DHA demonstrated significant reductions in ODE-induced bronchial alveolar lavage neutrophil influx and pro-inflammatory cytokine/chemokine production compared to mice exposed to ODE alone. Collectively, these data demonstrate that DHA affects several lung cells to reduce the airway inflammatory response to organic dust exposures. Dietary supplementation with DHA may be an effective therapeutic strategy to reduce the airway inflammatory consequences in individuals exposed to agriculture dust environments
Evolution of prokaryotic SPFH proteins
BACKGROUND: The SPFH protein superfamily is a diverse family of proteins whose eukaryotic members are involved in the scaffolding of detergent-resistant microdomains. Recently the origin of the SPFH proteins has been questioned. Instead, convergent evolution has been proposed. However, an independent, convergent evolution of three large prokaryotic and three eukaryotic families is highly unlikely, especially when other mechanisms such as lateral gene transfer which could also explain their distribution pattern have not yet been considered.To gain better insight into this very diverse protein family, we have analyzed the genomes of 497 microorganisms and investigated the pattern of occurrence as well as the genomic vicinity of the prokaryotic SPFH members. RESULTS: According to sequence and operon structure, a clear division into 12 subfamilies was evident. Three subfamilies (SPFH1, SPFH2 and SPFH5) show a conserved operon structure and two additional subfamilies are linked to those three through functional aspects (SPFH1, SPFH3, SPFH4: interaction with FtsH protease). Therefore these subgroups most likely share common ancestry. The complex pattern of occurrence among the different phyla is indicative of lateral gene transfer. Organisms that do not possess a single SPFH protein are almost exclusively endosymbionts or endoparasites. CONCLUSION: The conserved operon structure and functional similarities suggest that at least 5 subfamilies that encompass almost 75% of all prokaryotic SPFH members share a common origin. Their similarity to the different eukaryotic SPFH families, as well as functional similarities, suggests that the eukaryotic SPFH families originated from different prokaryotic SPFH families rather than one. This explains the difficulties in obtaining a consistent phylogenetic tree of the eukaryotic SPFH members. Phylogenetic evidence points towards lateral gene transfer as one source of the very diverse patterns of occurrence in bacterial species
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