54 research outputs found
Lipid-protein interactions in lipid membranes
West B. Lipid-protein interactions in lipid membranes. Bielefeld (Germany): Bielefeld University; 2008.In dieser Arbeit werden Lipid-Protein-Wechselwirkungen und lipidvermittelte Protein-Protein-Wechselwirkungen mittels Monte-Carlo-Simulationen eines generischen vergröberten Modells für Lipiddoppelschichten mit hydrophoben Einschlüssen untersucht. Die Ergebnisse werden mit den Vorhersagen zweier analytischer Theorien verglichen: Der Landau-de-Gennes-Theorie und der elastischen Theorie.In this thesis lipid-protein interactions and lipid-mediated protein-protein interactions are studied by Monte Carlo simulations of a generic coarse-grained model for lipid bilayer with hydrophobic inclusions. The results are compared with predictions of two analytical theories: The Landau-de Gennes theory and the elastic theory
Coarse-Grained Simulations of Membranes under Tension
We investigate the properties of membranes under tension by Monte-Carlo
simulations of a generic coarse-grained model for lipid bilayers. We give a
comprising overview of the behavior of several membrane characteristics, such
as the area per lipid, the monolayer overlap, the nematic order, and pressure
profiles. Both the low-temperature regime, where the membranes are in a gel
phase, and the high-temperature regime, where they are in the fluid phase, are
considered. In the gel state, the membrane is hardly influenced by tension. In
the fluid state, high tensions lead to structural changes in the membrane,
which result in different compressibility regimes. The ripple state, which is
found at tension zero in the transition regime between the fluid and the gel
phase, disappears under tension and gives way to an interdigitated phase. We
also study the membrane fluctuations in the fluid phase. In the low tension
regime the data can be fitted nicely to a suitably extended elastic theory. At
higher tensions the elastic fit consistently underestimates the strength of
long-wavelength fluctuations. Finally, we investigate the influence of tension
on the effective interaction between simple transmembrane inclusions and show
that tension can be used to tune the hydrophobic mismatch interaction between
membrane proteins.Comment: 14 pages, 14 figures, accepted for publication in The Journal of
Chemical Physic
A generic model for lipid monolayers, bilayers, and membranes
We describe a simple coarse-grained model which is suited to study lipid
layers and their phase transitions. Lipids are modeled by short semiflexible
chains of beads with a solvophilic head and a solvophobic tail component. They
are forced to self-assemble into bilayers by a computationally cheap `phantom
solvent' environment. The model reproduces the most important phases and phase
transitions of monolayers and bilayers. Technical issues such as Monte Carlo
parallelization schemes are briefly discussed.Comment: 4 pages, 4 figures conference paper for the CCP 2006 (Gyeongju,
Korea
Warming the early Earth - CO2 reconsidered
Despite a fainter Sun, the surface of the early Earth was mostly ice-free.
Proposed solutions to this so-called "faint young Sun problem" have usually
involved higher amounts of greenhouse gases than present in the modern-day
atmosphere. However, geological evidence seemed to indicate that the
atmospheric CO2 concentrations during the Archaean and Proterozoic were far too
low to keep the surface from freezing. With a radiative-convective model
including new, updated thermal absorption coefficients, we found that the
amount of CO2 necessary to obtain 273 K at the surface is reduced up to an
order of magnitude compared to previous studies. For the late Archaean and
early Proterozoic period of the Earth, we calculate that CO2 partial pressures
of only about 2.9 mb are required to keep its surface from freezing which is
compatible with the amount inferred from sediment studies. This conclusion was
not significantly changed when we varied model parameters such as relative
humidity or surface albedo, obtaining CO2 partial pressures for the late
Archaean between 1.5 and 5.5 mb. Thus, the contradiction between sediment data
and model results disappears for the late Archaean and early Proterozoic.Comment: 53 pages, 4 tables, 11 figures, published in Planetary and Space
Scienc
SCARLET – A European Effort to Develop HTS and MgB2 Based MVDC Cables
Superconducting cables have been proven in a variety of pilot projects and utility installations, demonstrating several of their advantages, including compact size and low energy losses, which can make the technology economically attractive for certain applications. It is clear though that different applications impose different requirements and challenges, but also opportunities for the cables. An interesting application is high-power DC transfer at medium voltage (MVDC). The high-current capability of the superconductor allows for a reduction in voltage while maintaining or increasing the power transfer level. In this way, one MVDC superconducting cable can replace one or more conventional high-voltage DC cables. In the European project SCARLET (Superconducting cables for sustainable energy transition), two types of MVDC cables will be developed, one based on HTS and one on MgB2 materials. Additionally, protection requirements will be considered, including the development of a modular DC fault current limiter for 10 kA. A main motivation for the development is the elimination of costly high-voltage converter stations when going from high to medium voltage, e.g., for offshore wind power plants. Another feature is the combined hydrogen and electricity transmission from generation sites to industry or mobility end users. This paper describes the superconducting MVDC cable concept as well as the main challenges and research needed to develop and type test the cables.SCARLET – A European Effort to Develop HTS and MgB2 Based MVDC CablesacceptedVersio
Membrane-Protein Interactions in a Generic Coarse-Grained Model for Lipid Bilayers
We study membrane-protein interactions and membrane-mediated protein-protein
interactions by Monte Carlo simulations of a generic coarse-grained model for
lipid bilayers with cylindrical hydrophobic inclusions. The strength of the
hydrophobic force and the hydrophobic thickness of the proteins are
systematically varied. The results are compared with analytical predictions of
two popular analytical theories: The Landau-de Gennes theory and the elastic
theory. The elastic theory provides an excellent description of the fluctuation
spectra of pure membranes and successfully reproduces the deformation profiles
of membranes around single proteins. However, its prediction for the potential
of mean force between proteins is not compatible with the simulation data for
large distances. The simulations show that the lipid-mediated interactions are
governed by five competing factors: Direct interactions, lipid-induced
depletion interactions, lipid bridging, lipid packing, and a smooth long-range
contribution. The mechanisms leading to "hydrophobic mismatch" interactions are
critically analyzed.Comment: 16 pages, 8 figures, accepted for publication in Biophysical Journa
Reporting bias in medical research - a narrative review
Reporting bias represents a major problem in the assessment of health care interventions. Several prominent cases have been described in the literature, for example, in the reporting of trials of antidepressants, Class I anti-arrhythmic drugs, and selective COX-2 inhibitors. The aim of this narrative review is to gain an overview of reporting bias in the medical literature, focussing on publication bias and selective outcome reporting. We explore whether these types of bias have been shown in areas beyond the well-known cases noted above, in order to gain an impression of how widespread the problem is. For this purpose, we screened relevant articles on reporting bias that had previously been obtained by the German Institute for Quality and Efficiency in Health Care in the context of its health technology assessment reports and other research work, together with the reference lists of these articles
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