2,002 research outputs found
„Gar heilsam ist´s, wenn dem Gehirn man gute Düfte bringen kann" : Ein Kapitel aus der Geschichte des Riechens
Chemoattractant-controlled accumulation of coronin at the leading edge of Dictyostelium cells monitored using a green fluorescent protein–coronin fusion protein
AbstractBackground: The highly motile cells of Dictyostelium discoideum rapidly remodel their actin filament system when they change their direction of locomotion either spontaneously or in response to chemoattractant. Coronin is a cytoplasmic actin-associated protein that accumulates at the cortical sites of moving cells and contributes to the dynamics of the actin system. It is a member of the WD-repeat family of proteins and is known to interact with actin–myosin complexes. In coronin null mutants, cell locomotion is slowed down and cytokinesis is impaired.Results We have visualized the redistribution of coronin by fluorescence imaging of motile cells that have been transfected with an expression plasmid containing the coding sequence of coronin fused to the sequence encoding the green fluorescent protein (GFP). This coronin–GFP fusion protein transiently accumulates in the front regions of growth-phase cells, reflecting the changing positions of leading edges and the competition between them. During the aggregation stage, local accumulation of coronin–GFP is biased by chemotactic orientation of the cells in gradients of cAMP. The impairment of cell motility in coronin null mutants shows that coronin has an important function at the front region of the cells. The mutant cells are distinguished by the formation of extended particle-free zones at their front regions, from where pseudopods often break out as blebs. Cytochalasin A reduces the size of these zones, indicating that actin filaments prevent entry of the particles.Conclusion These data demonstrate that coronin is reversibly recruited from the cytoplasm and is incorporated into the actin network of a nascent leading edge, where it participates in the reorganization of the cytoskeleton. Monitoring the dynamics of protein assembly using GFP fusion proteins and fluorescence microscopy promises to be a generally applicable method for studying the dynamics of cytoskeletal proteins in moving and dividing cells
Risk attitudes and informal employment in a developing economy
© 2012 Bennett et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License(http://creativecommons.org/licenses/by/2.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.We model an urban labour market in a developing economy, incorporating workers’ risk attitudes. Trade-offs between risk aversion and ability determine worker allocation across formal and informal wage employment, and voluntary and involuntary self employment. Greater risk of informal wage non-payment can raise or lower informal wage employment, depending on the source of risk. Informal wage employment can be reduced by increasing detection efforts or by strengthening contract enforcement for informal wage payment. As the average ability of workers rises, informal wage employment first rises, then falls. Greater demand for formal production may lead to more involuntary self employment
Impaired evoked and resting-state brain oscillations in patients with liver cirrhosis as revealed by magnetoencephalography
AbstractA number of studies suggest that the clinical manifestation of neurological deficits in hepatic encephalopathy results from pathologically synchronized neuronal oscillations and altered oscillatory coupling. In the present study spontaneous and evoked oscillatory brain activities were analyzed jointly with established behavioral measures of altered visual oscillatory processing. Critical flicker and fusion frequencies (CFF, FUF) were measured in 25 patients diagnosed with liver cirrhosis and 30 healthy controls. Magnetoencephalography (MEG) data were collected at rest and during a visual task employing repetitive stimulation. Resting MEG and evoked fields were analyzed. CFF and FUF were found to be reduced in patients, providing behavioral evidence for deficits in visual oscillatory processing. These alterations were found to be related to resting brain activity in patients, namely that the lower the dominant MEG frequency at rest, the lower the CFF and FUF. An analysis of evoked fields at sensor level indicated that in comparison to normal controls, patients were not able to dynamically adapt to flickering visual stimulation. Evoked activity was also analyzed based on independent components (ICs) derived by independent component analysis. The similarity between the shape of each IC and an artificial sine function representing the stimulation frequency was tested via magnitude squared coherence. In controls, we observed a small number of components that correlated strongly with the sine function and a high number of ICs that did not correlate with the sine function. Interestingly, patient data were characterized by a high number of moderately correlating components. Taken together, these results indicate a fundamental divergence of the cerebral resonance activity in cirrhotic patients
Magnetic and vibrational properties of the covalent chain antiferromagnet RbFeS2
Ternary rubidium-iron sulfide, RbFeS2, belongs to a family of quasi-one-dimensional compounds with the general chemical composition AFeCh2 (where A – K, Rb, Cs, Tl; Ch – S, Se). Understanding the magnetic properties of these compounds is a challenge. The controversy concerning the spin-state of the iron ion needs to be resolved to build the proper model of magnetism. Single crystals of RbFeS2 were grown and characterized by powder x-ray diffraction. QD MPMS-5 SQUID magnetometry was used to measure the magnetic susceptibility, and specific heat was measured utilizing QD PPMS-9 setup. Above the transition to three-dimensional antiferromagnetic order at the Néel temperature of TN = 188 K, the susceptibility exhibits unusual quasi-linear increase up to the highest measured temperature of 500 K. The specific heat was measured in the temperature range 1.8 – 300 K. Ab initio phonon dispersion and density-of-states calculations were performed by means of density functional theory (DFT), and the calculated lattice specific heat was subtracted from the measured one giving the magnetic contribution to the specific heat. Our results suggest that the features of the magnetic specific heat are general for the whole family of the covalent chain ternary iron chalcogenides of the AFeCh2 structure and indicate an intermediate S = 3/2 spin state of the iron ion
Vorbericht über die Untersuchungen an der Faustkeilstation Şehremuz in der südöstlichen Türkei
Nach Vorarbeiten 1977 und 1979 wurden im Bereich der paläolithischen Fundstelle Şehremuz im Jahre 1982 zwei Grabungskampagnen von je zwei Monaten durchgeführt. Es konnten zwei archäologische Komplexe in unterschiedlicher geologischer Lagerung festgestellt werden: a) Silexabschläge und Faustkeile im obersten aufgeschlossenen Schotter des Keluşk-Baches, eines Euphratzuflusses. Dieser Seitentalschotter ist korrelierbar mit einem etwa 60 m über der heutigen Talaue liegenden Euphratschotter. b) „Mittelpaläolithische" Inventare in einem über den Keluşk-Schottern liegenen Glacis, weitgehend nur aus Oberflächenfunden bekannt. Sie sind aufgrund ihrer Einlagerung jünger als der "Faustkeilkomplex".
Die Inventare mit Faustkeilen sind einem entwickelten faustkeilführenden Paläolithikum zuzurechnen. Auf sie ist die vorliegende Untersuchung konzentriert. Die durch die Silexartefakte belegten zahlreichen Begehungen des alten Keluşk-Bettes durch den paläolithischen Menschen haben ihre Ursache u.a. in einem hohen natürlichen Anteil von Silex im Schotter. Neben vollständigen Knollen liegt zahlreicher Naturbruch vor, der gegen die Stücke mit anthropogenen Bearbeitungsspuren abgegrenzt werden muß. Dabei kommt der Konfiguration der Einzelmerkmale — Dimensionen; Abbaufläche und Schlagmerkmale — die größte Bedeutung zu. Die Bearbeitung der Steinartefakte unter funktionalen Gesichtspunkten ist ein wichtiger Teil der Untersuchungen: Die Methoden werden beschrieben. Form und Zurichtung der Faustkeile lassen makroskopisch mögliche Funktionsflächen zum tiefen Einschneiden etwa in Fleisch und mögliche Funktionskanten zum Ritzen oder flach Einschneiden erkennen. Im mikroskopischen Bereich werden an Artefakten punktuell Gebrauchsspuren faßbar, die z.B. die Benutzung eines Faustkeils sowohl zum Einschneiden in Fleisch wie auch zum Zertrümmern von Knochen belegen.researc
Quantification of trace element contents in frozen fluid inclusions by UV-fs-LA-ICP-MS analysis
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