The Experts below are selected from a list of 864648 Experts worldwide ranked by ideXlab platform
Matthias Weiss - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Structure Formation of Membrane Proteins
Biophysical Journal, 2011Co-Authors: Gernot Guigas, Diana Morozova, Matthias WeissAbstract:Cellular membranes are not mere passive envelopes but act as a reaction space for a multitude of vital cellular processes. While it is generally anticipated that biomembranes are highly dynamic and self-organizing entities, molecular mechanisms that underlie Structure Formation on lipid bilayers are still far from being fully understood. Here, we show by means of coarse-grained membrane simulations that proteins can form higher-order Structures due to membrane-mediated interactions. Structure Formation originates from characteristic protein-induced bilayer perturbations that particularly affect the coupling between membrane leaflets. Examining transmembrane proteins as well as peripheral membrane proteins, we observe the Formation of protein oligomers and templates, even between proteins residing in different membrane leaflets. Also raft-like cross-leaflet associations of proteins and lipid patches are observed. Key parameter of this Structure Formation is the protein geometry. Apart from their potential influence on the organization of biomembranes, these effects may also support the Formation of templates for signaling processes, the assembly of transport intermediates, or protein sorting events.
Aseem Paranjape - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Structure Formation, Backreaction and Weak Gravitational Fields
EAS Publications Series, 2009Co-Authors: Aseem ParanjapeAbstract:There is an ongoing debate in the literature concerning the effects of averaging out inhomogeneities (``backreaction'') in cosmology. In particular, some simple models of Structure Formation studied in the literature seem to indicate that the backreaction can play a significant role at late times, and it has also been suggested that the standard perturbed FLRW framework is no longer a good approximation during Structure Formation, when the density contrast becomes nonlinear. In this work we use Zalaletdinov's covariant averaging scheme (macroscopic gravity or MG) to show that as long as the metric of the Universe can be described by the perturbed FLRW form, the corrections due to averaging remain negligibly small. Further, using a fully relativistic and reasonably generic model of pressureless spherical collapse, we show that as long as matter velocities remain small (which is true in our model), the perturbed FLRW form of the metric can be explicitly recovered. Together, these results imply that the backreaction remains small even during nonlinear Structure Formation, and we confirm this within the toy model with a numerical calculation.
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Structure Formation, Backreaction and Weak Gravitational Fields
Journal of Cosmology and Astroparticle Physics, 2008Co-Authors: Aseem Paranjape, Tejinder P. SinghAbstract:There is an ongoing debate in the literature as to whether the effects of averaging out inhomogeneities (``backreaction'') in Cosmology can be large enough to account for the acceleration of the scale factor in the FLRW models. In particular, some simple models of Structure Formation studied in the literature seem to indicate that this is indeed possible, and it has also been suggested that the perturbed FLRW framework is no longer a good approximation during Structure Formation, when the density contrast becomes nonlinear. In this work we attempt to clarify the situation to some extent, using a fully relativistic model of pressureless spherical collapse. We find that whereas averaging during Structure Formation can lead to acceleration via a selective choice of averaging domains, the acceleration is not present when more generic domains are used for averaging. Further, we show that for most of the duration of the collapse, matter velocities remain small, and the perturbed FLRW form of the metric can be explicitly recovered, in the Structure Formation phase. We also discuss the fact that the magnitude of the average effects of inhomogeneities depends on the scale of averaging, and while it may not be completely negligible on intermediate scales, it is expected to remain small when averaging on suitably large scales.
Tejinder P. Singh - One of the best experts on this subject based on the ideXlab platform.
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Structure Formation, Backreaction and Weak Gravitational Fields
Journal of Cosmology and Astroparticle Physics, 2008Co-Authors: Aseem Paranjape, Tejinder P. SinghAbstract:There is an ongoing debate in the literature as to whether the effects of averaging out inhomogeneities (``backreaction'') in Cosmology can be large enough to account for the acceleration of the scale factor in the FLRW models. In particular, some simple models of Structure Formation studied in the literature seem to indicate that this is indeed possible, and it has also been suggested that the perturbed FLRW framework is no longer a good approximation during Structure Formation, when the density contrast becomes nonlinear. In this work we attempt to clarify the situation to some extent, using a fully relativistic model of pressureless spherical collapse. We find that whereas averaging during Structure Formation can lead to acceleration via a selective choice of averaging domains, the acceleration is not present when more generic domains are used for averaging. Further, we show that for most of the duration of the collapse, matter velocities remain small, and the perturbed FLRW form of the metric can be explicitly recovered, in the Structure Formation phase. We also discuss the fact that the magnitude of the average effects of inhomogeneities depends on the scale of averaging, and while it may not be completely negligible on intermediate scales, it is expected to remain small when averaging on suitably large scales.
Gernot Guigas - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Structure Formation of Membrane Proteins
Biophysical Journal, 2011Co-Authors: Gernot Guigas, Diana Morozova, Matthias WeissAbstract:Cellular membranes are not mere passive envelopes but act as a reaction space for a multitude of vital cellular processes. While it is generally anticipated that biomembranes are highly dynamic and self-organizing entities, molecular mechanisms that underlie Structure Formation on lipid bilayers are still far from being fully understood. Here, we show by means of coarse-grained membrane simulations that proteins can form higher-order Structures due to membrane-mediated interactions. Structure Formation originates from characteristic protein-induced bilayer perturbations that particularly affect the coupling between membrane leaflets. Examining transmembrane proteins as well as peripheral membrane proteins, we observe the Formation of protein oligomers and templates, even between proteins residing in different membrane leaflets. Also raft-like cross-leaflet associations of proteins and lipid patches are observed. Key parameter of this Structure Formation is the protein geometry. Apart from their potential influence on the organization of biomembranes, these effects may also support the Formation of templates for signaling processes, the assembly of transport intermediates, or protein sorting events.
Ruth Durrer - One of the best experts on this subject based on the ideXlab platform.
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Large-scale Structure Formation with global topological defects.
Physical review. D Particles and fields, 1996Co-Authors: Ruth Durrer, Zhi-hong ZhouAbstract:We investigate cosmological Structure Formation seeded by topological defects which may form during a phase transition in the early universe. First we derive a partially new, local and gauge invariant system of perturbation equations to treat microwave background and dark matter fluctuations induced by topological defects or any other type of seeds. We then show that this system is well suited for numerical analysis of Structure Formation by applying it to seeds induced by fluctuations of a global scalar field. Our numerical results are complementary to previous investigations since we use substantially different methods. The resulting microwave background fluctuations are compatible with older simulations. We also obtain a scale invariant spectrum of fluctuations with about the same amplitude. However, our dark matter results yield a smaller bias parameter compatible with b\sim 2 on a scale of 20 Mpc in contrast to previous work which yielded to large bias factors. Our conclusions are thus more positive. According to the aspects analyzed in this work, global topological defect induced fluctuations yield viable scenarios of Structure Formation and do better than standard CDM on large scales.
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Cosmological Structure Formation with topological defects
1996Co-Authors: Ruth DurrerAbstract:Structure Formation with topological defects is described. The main differences from inflationary models are highlighted. The results are compared with recent observations. It is concluded that all the defect models studied so far are in disagreement with recent observations of CMB anisotropies. Furthermore, present observations do not support 'decoherence', a generic feature of Structure Formation from topological defects.
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Structure Formation in the universe from texture induced fluctuations.
Physical review letters, 1995Co-Authors: Ruth Durrer, Zhi-hong ZhouAbstract:The topic of this letter is Structure Formation with topological defects. We first present a partially new, fully local and gauge invariant system of perturbation equations to treat microwave background and dark matter fluctuations induced by topological defects (or any other type of seeds). We show that this treatment is extremly well suited for linear numerical analysis of Structure Formation by applying it to the texture scenario. Our numerical results cover a larger dynamical range than previous investigations and are complementary since we use substantially different methods.
