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Search Results: 1 - 10 of 10765 matches for " Claudia Schirra "
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Vesicle Pools: Lessons from Adrenal Chromaffin Cells
David R. Stevens,Claudia Schirra,Ute Becherer,Jens Rettig
Frontiers in Synaptic Neuroscience , 2011, DOI: 10.3389/fnsyn.2011.00002
Abstract: The adrenal chromaffin cell serves as a model system to study fast Ca2+-dependent exocytosis. Membrane capacitance measurements in combination with Ca2+ uncaging offers a temporal resolution in the millisecond range and reveals that catecholamine release occurs in three distinct phases. Release of a readily releasable (RRP) and a slowly releasable (SRP) pool are followed by sustained release, due to maturation, and release of vesicles which were not release-ready at the start of the stimulus. Trains of depolarizations, a more physiological stimulus, induce release from a small immediately releasable pool of vesicles residing adjacent to calcium channels, as well as from the RRP. The SRP is poorly activated by depolarization. A sequential model, in which non-releasable docked vesicles are primed to a slowly releasable state, and then further mature to the readily releasable state, has been proposed. The docked state, dependent on membrane proximity, requires SNAP-25, synaptotagmin, and syntaxin. The ablation or modification of SNAP-25 and syntaxin, components of the SNARE complex, as well as of synaptotagmin, the calcium sensor, and modulators such complexins and Snapin alter the properties and/or magnitudes of different phases of release, and in particular can ablate the RRP. These results indicate that the composition of the SNARE complex and its interaction with modulatory molecules drives priming and provides a molecular basis for different pools of releasable vesicles.
In the Crosshairs: Investigating Lytic Granules by High-Resolution Microscopy and Electrophysiology
Varsha Pattu,Mahantappa Halimani,Min Ming,Claudia Schirra,Ulrike Hahn,Hawraa Bzeih,Hsin-Fang Chang,Lisa Weins,Elmar Krause,Jens Rettig
Frontiers in Immunology , 2013, DOI: 10.3389/fimmu.2013.00411
Abstract: Cytotoxic T lymphocytes (CTLs) form an integral part of the adaptive immune system. Their main function is to eliminate bacteria- and virus-infected target cells by releasing perforin and granzymes (the lethal hit) contained within lytic granules (LGs), at the CTL-target-cell interface [the immunological synapse (IS)]. The formation of the IS as well as the final events at the IS leading to target-cell death are both highly complex and dynamic processes. In this review we highlight and discuss three high-resolution techniques that have proven invaluable in the effort to decipher key features of the mechanism of CTL effector function and in particular lytic granule maturation and fusion. Correlative light and electron microscopy allows the correlation between organelle morphology and localization of particular proteins, while total internal reflection fluorescence microscopy (TIRFM) enables the study of lytic granule dynamics at the IS in real time. The combination of TIRFM with patch-clamp membrane capacitance measurements finally provides a tool to quantify the size of fusing LGs at the IS.
Investigating Potential Mechanisms of Obesity by Metabolomics
Baogang Xie,Michael J. Waters,Horst Joachim Schirra
Journal of Biomedicine and Biotechnology , 2012, DOI: 10.1155/2012/805683
Abstract: Obesity is a serious health problem with an increased risk of several common diseases including diabetes, cardiovascular disease, and cancer. Metabolomics is an emerging analytical technique for systemic determination of metabolite profiles, which is useful for understanding the biochemical changes in obesity or related diseases both in individual organs and at the organism level. Increasingly, this technology has been applied to the study of obesity, complementing transcriptomics and/or proteomics analyses. Indeed, the alterations of metabolites in biofluids/tissues are direct indicators of variations in physiology or pathology. In this paper, we will examine the obesity-related alterations in significant metabolites that have been identified by metabolomics as well as their metabolic pathway associations. Issues concerning the screening of biologically significant metabolites related to obesity will also be discussed.
NMRDyn: A Program for NMR Relaxation Studies of Protein Association
Conan K. Wang, Horst Joachim Schirra, David J. Craik
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003820
Abstract: Self-association is an important biological phenomenon that is associated with many cellular processes. NMR relaxation measurements provide data about protein molecular dynamics at the atomic level and are sensitive to changes induced by self-association. Thus, measurements and analysis of NMR relaxation data can provide structurally resolved information on self-association that would not be accessible otherwise. Here, we present a computer program, NMRdyn, which analyses relaxation data to provide parameters defining protein self-association. Unlike existing relaxation analysis software, NMRdyn can explicitly model the monomer-oligomer equilibrium while fitting measured relaxation data. Additionally, the program is packaged with a user-friendly interface, which is important because relaxation data can often be large and complex. NMRdyn is available from http://research1t.imb.uq.edu.au/nmr/NMRd?yn.
Fachkommunikation, Popularisierung, übersetzung: Empirische Vergleiche am Beispiel der Nominalphrase im Englischen und Deutschen
Hansen-Schirra, Silvia,Hansen, Sandra,Wolfer, Sascha,Konieczny, Lars
Linguistik Online , 2009,
Abstract: This article examines the contrasts and commonalities between languages for specific purposes (LSP) and their popularizations on the one hand and the frequency patterns of LSP register features in English and German on the other. For this purpose corpora of expert-expert and expert-lay communication are annotated for part-of-speech and phrase structure information. On this basis, the frequencies of pre- and post-modifications in complex noun phrases are statistically investigated and compared for English and German. Moreover, using parallel and comparable corpora it is tested whether English-German translations obey the register norms of the target language or whether the LSP frequency patterns of the source language shine throughì. The results provide an empirical insight into language contact phenomena involving specialized communication.
On the rheology of red blood cell suspensions with different amounts of dextran: separating the effect of aggregation and increase in viscosity of the suspending phase
Daniel Flormann,Katharina Schirra,Thomas Podgorski,Christian Wagner
Physics , 2015,
Abstract: We investigate the shear thinning of red blood cell - dextran suspensions. Microscopic images show that at low polymer concentration, aggregation increases with increasing concentration until it reaches a maximum and then decreases again to non-aggregation. This bell shape dependency is also deduced from the rheological measurements, if the data are correctly normalized by the viscosity of the suspending phase since a significant amount of polymers adsorb to the cell surfaces. We find that the position of the maximum of this shear rate dependent bell shape increases with increasing viscosity of the suspending phase, which indicates a that the dynamic process of aggregation and disaggregation is coupled via hydrodynamic interactions. This hydrodynamic coupling can be suppressed by characterizing a suspension of 80% hematrocrit which yields good agreement with the results from the microscopical images.
Markers for Detection of Prostate Cancer
Raymond A. Clarke,Horst J. Schirra,James W. Catto,Martin F. Lavin,Robert A. Gardiner
Cancers , 2010, DOI: 10.3390/cancers2021125
Abstract: Early detection of prostate cancer is problematic, not just because of uncertainly whether a diagnosis will benefit an individual patient, but also as a result of the imprecise and invasive nature of establishing a diagnosis by biopsy. Despite its low sensitivity and specificity for identifying patients harbouring prostate cancer, serum prostate specific antigen (PSA) has become established as the most reliable and widely-used diagnostic marker for this condition. In its wake, many other markers have been described and evaluated. This review focuses on the supporting evidence for the most prominent of these for detection and also for predicting outcome in prostate cancer.
Caracterización mecánica y microestructural de aceros de baja activación candidatos como primera pared en los reactores de fusión por confinamiento magnético
Hernández, M. T.,Lape?a, J.,de Diego, G.,Schirra, M.
Revista de Metalurgia , 1996,
Abstract: Currently, the design development of fusion reactors and the possible materials to use in them are being studied in parallel. One of the most critical problems in this research is the structural material selection for the first wall and blanket. The aim of the present work is to study three low activation alloys designed in Germany in which niobium has been substituted by tantalum or cerium. The mechanical results show that the alloys containing cerium are in the same order of the low activation materials known to date, but the tantalum doped alloy produces TaC3 precipitation that destabilizes the matrix and provokes large microstructural changes. This causes a decrease of the mechanical properties at about 600 °C. This fact makes this alloy unsuitable for the first wall on fusion reactors, because the working temperature is near 550 °C. Actualmente, se está estudiando de forma paralela al desarrollo del dise o de los reactores de fusión los posibles materiales a emplear en estos. Una de las cuestiones más críticas en esta investigación es la selección del material estructural a emplear como primera pared y envoltura. En el presente trabajo se estudian tres aleaciones de dise o alemán de baja activación, en las que se ha sustituido el niobio por tantalio o por cerio. Los resultados mecánicos muestran que las aleaciones, en las que se ha a adido cerio de forma controlada, están en la línea de las de baja activación existentes hasta ahora, pero la adición de tantalio presenta problemas al provocar una precipitación primaria y masiva de carburos TaC3 que desestabiliza la matriz y origina cambios microestructurales muy acusados. Así, ocurre un descenso en las propiedades mecánicas en torno a los 600 °C, que la incapacita para la aplicación como primera pared, ya que la temperatura de trabajo de ésta se halla en torno a los 550 °C.
Eye-Tracker-Guided Non-Mechanical Excimer Laser Assisted Penetrating Keratoplasty
Edgar Janunts,Frank Schirra,Nora Szentmáry,Berthold Seitz,Achim Langenbucher
Sensors , 2013, DOI: 10.3390/s130303753
Abstract: Purpose: The purpose of the study was to implement a new eye tracking mask which could be used to guide the laser beam in automated non-mechanical excimer laser assisted penetrating keratoplasty. Materials and methods: A new trephination mask design with an elevated surface geometry has been proposed with a step formation between conical and flat interfaces. Two recipient masks of 7.5/8.0 mm have been manufactured and tested. The masks have outer diameter of 12.5 mm, step formation at 10.5 mm, and slope of conical surfaces 15°. Its functionality has been tested in different lateral positions and tilts on a planar surface, and pig eye experiments. After successful validation on porcine eyes, new masks have been produced and tested on two patients. Results: The build-in eye tracking software of the MEL 70 was always able to capture the masks. It has been shown that the unwanted pigmentation/pattern induced by the laser pulses on the mask surface does not influence the eye-tracking efficiency. The masks could be tracked within the 18 × 14 mm lateral displacement and up to 12° tilt. Two patient cases are demonstrated. No complications were observed during the surgery, although it needs some attention for aligning the mask horizontally before trephination. Stability of eye tracking masks is emphasized by inducing on purpose movements of the patient head. Conclusion: Eye-tracking-guided penetrating keratoplasty was successfully applied in clinical practice, which enables robust tracking criteria within an extended range. It facilitates the automated trephination procedure of excimer laser-assisted penetrating keratoplasty.
Self consistent kinetic simulations of SPT and HEMP thrusters including the near-field plume region
K. Matyash,R. Schneider,A. Mutzke,O. Kalentev,F. Taccogna,N. Koch,M. Schirra
Physics , 2009, DOI: 10.1109/TPS.2010.2056936
Abstract: The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.
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