Anatomie von Kommunikationsrollen: Methoden zur Identifizierung von Akteursrollen in gerichteten Netzwerken

Zusammenfassung: Die Identifizierung von generalisierbaren Akteursrollen in sozialen Systemen ist seit jeher ein zentrales Anliegen der Sozialwissenschaften. Dies gilt insbesondere für die Identifizierung von Kommunikationsrollen, um die überaus komplexen Prozesse der interpersonalen und massenmedialen Kommunikation systematisch zu beschreiben und zu verstehen. Der vorliegende Beitrag zeigt auf, welche theoretischen und methodischen Überlegungen bei der Operationalisierung von Akteursrollen in gerichteten Netzwerken zu berücksichtigen sind. Basierend auf einer netzwerkanalytischen Betrachtung werden zum einen Unzulänglichkeiten in bestehenden Operationalisierungen von Kommunikationsrollen aufgezeigt und zum anderen neue Konzepte vorgeschlagen. Die diskutierten Konzepte lassen sich zwei unterschiedlichen Ansätzen zuordnen. Einerseits können Mikrostrukturen wie dyadische und triadische Ego-Rollen als Basis für die Operationalisierung verwendet werden und andererseits kann man von der Gesamtstruktur des Netzwerks ausgehen. Für den ersten Fall werden unterschiedliche Aggregationsregeln diskutiert, welche eine Anwendung in komplexeren Netzwerken ermöglichen. Beim zweiten Ansatz, der Berücksichtigung der Gesamtstruktur, werden die Eignung unterschiedlicher Zentralitätsmaße, das Konzept des Blockmodelling und die hierarchische Strukturanalyse besprochen. Zwecks Anschaulichkeit beschränkt sich dieser Beitrag auf Rollen in Kommunikationsnetzwerken. Die vorgestellten Konzepte sind jedoch auch auf andere Netzwerke übertragbar, die aus gerichteten Beziehungen bestehe

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

Function of survivin in trophoblastic cells of the placenta

Background: Preeclampsia is one of the leading causes of maternal and perinatal mortality and morbidity worldwide and its pathogenesis is not totally understood. As a member of the chromosomal passenger complex and an inhibitor of apoptosis, survivin is a well-characterized oncoprotein. Its roles in trophoblastic cells remain to be defined. Methods: The placental samples from 16 preeclampsia patients and 16 well-matched controls were included in this study. Real-time PCR, immunohistochemistry and Western blot analysis were carried out with placental tissues. Primary trophoblastic cells from term placentas were isolated for Western blot analysis. Cell proliferation, cell cycle analysis and immunofluorescence staining were performed in trophoblastic cell lines BeWo, JAR and HTR-8/SVneo. Results: The survivin gene is reduced but the protein amount is hardly changed in preeclamptic placentas, compared to control placentas. Upon stress, survivin in trophoblastic cells is phosphorylated on its residue serine 20 by protein kinase A and becomes stabilized, accompanied by increased heat shock protein 90. Depletion of survivin induces chromosome misalignment, abnormal centrosome integrity, and reduced localization and activity of Aurora B at the centromeres/kinetochores in trophoblastic metaphase cells. Conclusions: Our data indicate that survivin plays pivotal roles in cell survival and proliferation of trophoblastic cells. Further investigations are required to define the function of survivin in each cell type of the placenta in the context of proliferation, differentiation, apoptosis, angiogenesis, migration and invasion

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