1,721,014 research outputs found
Escape rate of an active Brownian particle over a potential barrier
No full textWe study the dynamics of an active Brownian particle with a nonlinear friction function located in a spatial cubic potential. For strong but finite damping, the escape rate of the particle over the spatial potential barrier shows a nonmonotonic dependence on the noise intensity. We relate this behavior to the fact that the active particle escapes from a limit cycle rather than from a fixed point and that a certain amount of noise can stabilize the sojourn of the particle on this limit cycle
Aufbau einer quantitativen massenspektrometrischen Analytik zur Untersuchung der Lipidzusammensetzung zellulärer Membranen und ihre Anwendung auf Membranmikrodomänen
No full textThe lipopolysaccharide of the mastitis isolate Escherichia coli strain 1303 comprises a novel O-antigen and the rare K-12 core type
No full textMastitis represents one of the most significant health problems of dairy herds. The two major causative agents of this disease areEscherichia coliandStaphylococcus aureus. Of the first, its lipopolysaccharide (LPS) is thought to play a prominent role during infection. Here, we report the O-antigen (OPS, O-specific polysaccharide) structure of the LPS from bovine mastitis isolateE. coli1303. The structure was determined utilizing chemical analyses, mass spectrometry, and 1D and 2D NMR spectroscopy methods. The O-repeating unit was characterized as -[→4)-β-d-Quip3NAc-(1→3)-α-l-Fucp2OAc-(1→4)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→]- in which theO-acetyl substitution was non-stoichiometric. The nucleotide sequence of the O-antigen gene cluster ofE. coli1303 was also determined. This cluster, located between thegndandgalFgenes, contains 13 putative open reading frames, most of which represent unknown nucleotide sequences that have not been described before. The O-antigen ofE. coli1303 was shown to substitute O-7 of the terminalld-heptose of the K-12 core oligosaccharide. Interestingly, the non-OPS-substituted core oligosaccharide represented a truncated version of the K-12 outer core – namely terminalld-heptose and glucose were missing; however, it possessed a third Kdo residue in the inner core. On the basis of structural and genetic data we show that the mastitis isolateE. coli1303 represents a new serotype and possesses the K-12 core type, which is rather uncommon among human and bovine isolates.</jats:p
Aufbau und Kopplung einer Kapillarelektrophorese an ein hochauflösendes Massenspektrometer zur Analyse amphiphiler Zellmembrankomponenten
Get PDFLipopolysaccharid (LPS) ist der Hauptbestandteil der äußeren Membran Gram-negativer Bakterien. Gringe Substanzmengen in Verbindung mit der großen Heterogenität aufgrund ihrer physiko-chemischen Eigenschaften erschweren die Strukturanalytik von LPS-Isolaten, sodass die Massenspektrometrie für deren Analyse ein unverzichtbares Werkzeug ist. In der vorliegenden Arbeit wurde eine selbst gebaute Kapillarelektrophorese-Anlage (CE) an ein an ein hochauflösendes Fourier transform ion cyclotron resonance Massenspektrometer (FT-ICR MS) mittels eines sheath liquid Interfaces gekoppelt. Mit diesem Aufbau konnte erstmals die Auftrennung verschiedener, nativer R-Form LPS-Isolate einschließlich Lipid A sowie auch von Mischungen dieser Isolate in einem online CE-MS Experiment gezeigt werden. Die Nachweisgrenze für die Substanzen lag dabei im Femtomol-Bereich. Des weiteren wurde die entwickelte Methodik auf weitere Zellmembranbestandteile wie Glykosphingolipide und Glycerophospholipide angewendet, wobei eine Trennung für einen Teil der getesteten Substanzen beobachtet wurde. Die Auswertung von Massenspektren von Glycerophospho- und Glykolipiden konnte mit Hilfe einer selbst entwickelten Software erheblich vereinfacht und beschleunigt werden
Physikalische Analyse des Freisetzungsmechanismus von Chemotherapeutika aus dotiertem Polymethylmethacrylat
No full textPhysikalische Analyse des Freisetzungsmechanismus von Chemotherapeutika aus dortiertem Polymethylmethacrylat
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Structural Investigation of the Oligosaccharide Portion Isolated from the Lipooligosaccharide of the Permafrost Psychrophile Psychrobacter arcticus 273-4
No full textPsychrophilic microorganisms have successfully colonized all permanently cold environments from the deep sea to mountain and polar regions. The ability of an organism to survive and grow in cryoenviroments depends on a number of adaptive strategies aimed at maintaining vital cellular functions at subzero temperatures, which include the structural modifications of the membrane. To understand the role of the membrane in the adaptation, it is necessary to characterize the cell-wall components, such as the lipopolysaccharides, that represent the major constituent of the outer membrane. The aim of this study was to investigate the structure of the carbohydrate backbone of the lipooligosaccharide (LOS) isolated from the cold-adapted Psychrobacter arcticus 273-4. The strain, isolated from a 20,000-to-30,000-year-old continuously frozen permafrost in Siberia, was cultivated at 4 °C. The LOS was isolated from dry cells and analyzed by means of chemical methods. In particular, it was degraded either by mild acid hydrolysis or by hydrazinolysis and investigated in detail by (1)H and (13)C NMR spectroscopy and by ESI FT-ICR mass spectrometry. The oligosaccharide was characterized by the substitution of the heptose residue, usually linked to Kdo in the inner core, with a glucose, and for the unusual presence of N-acetylmuramic acid
Physikalische Analyse des Freisetzungsmechanismus von Chemotherapeutika aus dotiertem Polymethylmethacrylat
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