Diagrammatic analysis of correlations in polymer fluids: Cluster diagrams via Edwards' field theory

A straightforward expansion of Edwards' functional integral representation of the grand partition function for a polymer liquid as an infinite set of Feynman diagrams is shown to yield a cluster expansion that is closely related to the corresponding Mayer cluster expansion developed for flexible molecules by Chandler and coworkers. The procedure initially yields a perturbative cluster expansion in which all free energies and correlation functions are expressed diagrammatically as functionals of single-molecule correlation functions of non-interacting molecules. Topological reduction yields several renormalized expansions for collective correlation functions of all orders as functionals of single-molecule correlation functions in the interacting fluid. Renormalized expansions are also obtained for a generalized Ornstein-Zernicke (OZ) direct correlation function and for intramolecular correlation functions. The application of the formalism to coarse-grained models of polymer fluids is discussed, and a loop expansion about self-consistent field theory is shown to converge for sufficiently coarse-grained models, in which monomers are strongly overlapping. The formalism is used to derive a new expression for the OZ direct correlation function and to recover known results for the 2-point intramolecular correlation function to first order in a loop expansion, for binary blends and diblock copolymer melts.Comment: 98 pages, 13 figures, accepted by Annals of Physic

Charge Isomers of Myelin Basic Protein: Structure and Interactions with Membranes, Nucleotide Analogues, and Calmodulin

As an essential structural protein required for tight compaction of the central nervous system myelin sheath, myelin basic protein (MBP) is one of the candidate autoantigens of the human inflammatory demyelinating disease multiple sclerosis, which is characterized by the active degradation of the myelin sheath. In this work, recombinant murine analogues of the natural C1 and C8 charge components (rmC1 and rmC8), two isoforms of the classic 18.5-kDa MBP, were used as model proteins to get insights into the structure and function of the charge isomers. Various biochemical and biophysical methods such as size exclusion chromatography, calorimetry, surface plasmon resonance, small angle X-ray and neutron scattering, Raman and fluorescence spectroscopy, and conventional as well as synchrotron radiation circular dichroism were used to investigate differences between these two isoforms, both from the structural point of view, and regarding interactions with ligands, including calmodulin (CaM), various detergents, nucleotide analogues, and lipids. Overall, our results provide further proof that rmC8 is deficient both in structure and especially in function, when compared to rmC1. While the CaM binding properties of the two forms are very similar, their interactions with membrane mimics are different. CaM can be used to remove MBP from immobilized lipid monolayers made of synthetic lipids - a phenomenon, which may be of relevance for MBP function and its regulation. Furthermore, using fluorescently labelled nucleotides, we observed binding of ATP and GTP, but not AMP, by MBP; the binding of nucleoside triphosphates was inhibited by the presence of CaM. Together, our results provide important further data on the interactions between MBP and its ligands, and on the differences in the structure and function between MBP charge isomers

Ancestral sleep.

While we do not yet understand all the functions of sleep, its critical role for normal physiology and behaviour is evident. Its amount and temporal pattern depend on species and condition. Humans sleep about a third of the day with the longest, consolidated episode during the night. The change in lifestyle from hunter-gatherers via agricultural communities to densely populated industrialized centres has certainly affected sleep, and a major concern in the medical community is the impact of insufficient sleep on health [1,2]. One of the causal mechanisms leading to insufficient sleep is altered exposure to the natural light-dark cycle. This includes the wide availability of electric light, attenuated exposure to daylight within buildings, and evening use of light-emitting devices, all of which decrease the strength of natural light-dark signals that entrain circadian systems [3]

Ancestral sleep

While we do not yet understand all the functions of sleep, its critical role for normal physiology and behaviour is evident. Its amount and temporal pattern depend on species and condition. Humans sleep about a third of the day with the longest, consolidated episode during the night. The change in lifestyle from hunter-gatherers via agricultural communities to densely populated industrialized centres has certainly affected sleep, and a major concern in the medical community is the impact of insufficient sleep on health [1,2]. One of the causal mechanisms leading to insufficient sleep is altered exposure to the natural light-dark cycle. This includes the wide availability of electric light, attenuated exposure to daylight within buildings, and evening use of light-emitting devices, all of which decrease the strength of natural light-dark signals that entrain circadian systems [3].Fil: de la Iglesia, Daniel Horacio. University of Washington; Estados UnidosFil: Moreno, Claudia. Stockholms Universitet; Suecia. Universidade de Sao Paulo; Brasil. Stockholms Universitet; SueciaFil: Lowden, Arne. Stockholms Universitet; SueciaFil: Louzada, Fernando. Universidade Federal do Paraná; BrasilFil: Marqueze, Elaine. Universidade de Sao Paulo; Brasil. Universidade Católica de Santos; BrasilFil: Levandovski, Rosa. Universidade Federal do Rio Grande do Sul; BrasilFil: Pilz, Luisa K.. Universidade Federal do Rio Grande do Sul; Brasil. Ludwig Maximilians Universitat; AlemaniaFil: Valeggia, Claudia Rita. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Yale; Estados UnidosFil: Fernandez Duque, Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Yale; Estados UnidosFil: Golombek, Diego Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; ArgentinaFil: Czeisler, Charles A.. Brigham and Women’s Hospital; Estados Unidos. Harvard Medical School; Estados UnidosFil: Skene, Debra J.. University of Surrey. Faculty of Health & Medical Sciences; Reino UnidoFil: Duffy, Jeanne F.. Brigham and Women’s Hospital; Estados Unidos. Harvard Medical School; Estados UnidosFil: Roenneberg, Till. Ludwig Maximilians Universitat; Alemani