Membrane curvature at a glance.
McMahon, Harvey T; Boucrot, Emmanuel
2015-03-15
Membrane curvature is an important parameter in defining the morphology of cells, organelles and local membrane subdomains. Transport intermediates have simpler shapes, being either spheres or tubules. The generation and maintenance of curvature is of central importance for maintaining trafficking and cellular functions. It is possible that local shapes in complex membranes could help to define local subregions. In this Cell Science at a Glance article and accompanying poster, we summarize how generating, sensing and maintaining high local membrane curvature is an active process that is mediated and controlled by specialized proteins using general mechanisms: (i) changes in lipid composition and asymmetry, (ii) partitioning of shaped transmembrane domains of integral membrane proteins or protein or domain crowding, (iii) reversible insertion of hydrophobic protein motifs, (iv) nanoscopic scaffolding by oligomerized hydrophilic protein domains and, finally, (v) macroscopic scaffolding by the cytoskeleton with forces generated by polymerization and by molecular motors. We also summarize some of the discoveries about the functions of membrane curvature, where in addition to providing cell or organelle shape, local curvature can affect processes like membrane scission and fusion as well as protein concentration and enzyme activation on membranes. PMID:25774051
Monomeric Synucleins Generate Membrane Curvature*
Westphal, Christopher H.; Chandra, Sreeganga S.
2013-01-01
Synucleins are a family of presynaptic membrane binding proteins. α-Synuclein, the principal member of this family, is mutated in familial Parkinson disease. To gain insight into the molecular functions of synucleins, we performed an unbiased proteomic screen and identified synaptic protein changes in αβγ-synuclein knock-out brains. We observed increases in the levels of select membrane curvature sensing/generating proteins. One of the most prominent changes was for the N-BAR protein endophilin A1. Here we demonstrate that the levels of synucleins and endophilin A1 are reciprocally regulated and that they are functionally related. We show that all synucleins can robustly generate membrane curvature similar to endophilins. However, only monomeric but not tetrameric α-synuclein can bend membranes. Further, A30P α-synuclein, a Parkinson disease mutant that disrupts protein folding, is also deficient in this activity. This suggests that synucleins generate membrane curvature through the asymmetric insertion of their N-terminal amphipathic helix. Based on our findings, we propose to include synucleins in the class of amphipathic helix-containing proteins that sense and generate membrane curvature. These results advance our understanding of the physiological function of synucleins. PMID:23184946
Anisotropic Membrane Curvature Sensing by Amphipathic Peptides.
Gómez-Llobregat, Jordi; Elías-Wolff, Federico; Lindén, Martin
2016-01-01
Many proteins and peptides have an intrinsic capacity to sense and induce membrane curvature, and play crucial roles for organizing and remodeling cell membranes. However, the molecular driving forces behind these processes are not well understood. Here, we describe an approach to study curvature sensing by simulating the interactions of single molecules with a buckled lipid bilayer. We analyze three amphipathic antimicrobial peptides, a class of membrane-associated molecules that specifically target and destabilize bacterial membranes, and find qualitatively different sensing characteristics that would be difficult to resolve with other methods. Our findings provide evidence for direction-dependent curvature sensing mechanisms in amphipathic peptides and challenge existing theories of hydrophobic insertion. The buckling approach is generally applicable to a wide range of curvature-sensing molecules, and our results provide strong motivation to develop new experimental methods to track position and orientation of membrane proteins. PMID:26745422
Membrane Curvature Sensing by Amphipathic Helices
Jensen, Martin Borch; Bhatia, Vikram Kjøller; Jao, Christine C.; Rasmussen, Jakob Ewald; Pedersen, Søren L.; Jensen, Knud J.; Langen, Ralf; Stamou, Dimitrios
2011-01-01
Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues. PMID:21953452
Intrinsically disordered proteins drive membrane curvature
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-01-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures. PMID:26204806
Intrinsically disordered proteins drive membrane curvature
NASA Astrophysics Data System (ADS)
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-07-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures.
Renormalization of curvature elastic constants for elastic and fluid membranes
NASA Astrophysics Data System (ADS)
Ami, S.; Kleinert, H.
1987-02-01
We study the fluctuations of membranes with area and curvature elasticity and calculate the renormalization of the curvature elastic constants due to thermal fluctuations. For the mean curvature elastic constant the result is the same as obtained previously for “ideal membranes” which resist only to curvature deformations. The renormalization of the gaussian curvature, on the other hand, depends on the elastic contants. In an incompressible membrane, it is five times weaker than in an ideal membrane.
On the curvature effect of thin membranes
NASA Astrophysics Data System (ADS)
Wang, Duo; Jiao, Xiangmin; Conley, Rebecca; Glimm, James
2013-01-01
We investigate the curvature effect of a thin, curved elastic interface that separates two subdomains and exerts a pressure due to a curvature effect. This pressure, which we refer to as interface pressure, is similar to the surface tension in fluid mechanics. It is important in some applications, such as the canopy of parachutes, biological membranes of cells, balloons, airbags, etc., as it partially balances a pressure jump between the two sides of an interface. In this paper, we show that the interface pressure is equal to the trace of the matrix product of the curvature tensor and the Cauchy stress tensor in the tangent plane. We derive the theory for interfaces in both 2-D and 3-D, and present numerical discretizations for computing the quality over triangulated surfaces.
Protein-Induced Membrane Curvature Alters Local Membrane Tension
Rangamani, Padmini; Mandadap, Kranthi K.; Oster, George
2014-01-01
Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface properties of the membrane, such as membrane tension, change in response to protein adsorption. In this article, we show that the partial differential equations arising from classical elastic model of lipid membranes, which account for simultaneous changes in shape and membrane tension due to protein adsorption in a local region, cannot be solved for nonaxisymmetric geometries using straightforward numerical techniques; instead, a viscous-elastic formulation is necessary to fully describe the system. Therefore, we develop a viscous-elastic model for inhomogeneous membranes of the Helfrich type. Using the newly available viscous-elastic model, we find that the lipids flow to accommodate changes in membrane curvature during protein adsorption. We show that, at the end of protein adsorption process, the system sustains a residual local tension to balance the difference between the actual mean curvature and the imposed spontaneous curvature. We also show that this change in membrane tension can have a functional impact such as altered response to pulling forces in the presence of proteins. PMID:25099814
Preference for Curvature: A Historical and Conceptual Framework
Gómez-Puerto, Gerardo; Munar, Enric; Nadal, Marcos
2016-01-01
That people find curved contours and lines more pleasurable than straight ones is a recurrent observation in the aesthetic literature. Although such observation has been tested sporadically throughout the history of scientific psychology, only during the last decade has it been the object of systematic research. Recent studies lend support to the idea that human preference for curved contours is biologically determined. However, it has also been argued that this preference is a cultural phenomenon. In this article, we review the available evidence, together with different attempts to explain the nature of preference for curvature: sensoriomotor-based and valuation-based approaches. We also argue that the lack of a unifying framework and clearly defined concepts might be undermining our efforts towards a better understanding of the nature of preference for curvature. Finally, we point to a series of unresolved matters as the starting point to further develop a consistent research program. PMID:26793092
Transmembrane protein sorting driven by membrane curvature
NASA Astrophysics Data System (ADS)
Strahl, H.; Ronneau, S.; González, B. Solana; Klutsch, D.; Schaffner-Barbero, C.; Hamoen, L. W.
2015-11-01
The intricate structure of prokaryotic and eukaryotic cells depends on the ability to target proteins to specific cellular locations. In most cases, we have a poor understanding of the underlying mechanisms. A typical example is the assembly of bacterial chemoreceptors at cell poles. Here we show that the classical chemoreceptor TlpA of Bacillus subtilis does not localize according to the consensus stochastic nucleation mechanism but accumulates at strongly curved membrane areas generated during cell division. This preference was confirmed by accumulation at non-septal curved membranes. Localization appears to be an intrinsic property of the protein complex and does not rely on chemoreceptor clustering, as was previously shown for Escherichia coli. By constructing specific amino-acid substitutions, we demonstrate that the preference for strongly curved membranes arises from the curved shape of chemoreceptor trimer of dimers. These findings demonstrate that the intrinsic shape of transmembrane proteins can determine their cellular localization.
Transmembrane protein sorting driven by membrane curvature
Strahl, H.; Ronneau, S.; González, B. Solana; Klutsch, D.; Schaffner-Barbero, C.; Hamoen, L. W.
2015-01-01
The intricate structure of prokaryotic and eukaryotic cells depends on the ability to target proteins to specific cellular locations. In most cases, we have a poor understanding of the underlying mechanisms. A typical example is the assembly of bacterial chemoreceptors at cell poles. Here we show that the classical chemoreceptor TlpA of Bacillus subtilis does not localize according to the consensus stochastic nucleation mechanism but accumulates at strongly curved membrane areas generated during cell division. This preference was confirmed by accumulation at non-septal curved membranes. Localization appears to be an intrinsic property of the protein complex and does not rely on chemoreceptor clustering, as was previously shown for Escherichia coli. By constructing specific amino-acid substitutions, we demonstrate that the preference for strongly curved membranes arises from the curved shape of chemoreceptor trimer of dimers. These findings demonstrate that the intrinsic shape of transmembrane proteins can determine their cellular localization. PMID:26522943
Nanoscale Membrane Curvature detected by Polarized Localization Microscopy
NASA Astrophysics Data System (ADS)
Kelly, Christopher; Maarouf, Abir; Woodward, Xinxin
Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology.
Curvature-undulation coupling as a basis for curvature sensing and generation in bilayer membranes.
Bradley, Ryan P; Radhakrishnan, Ravi
2016-08-30
We present coarse-grained molecular dynamics simulations of the epsin N-terminal homology domain interacting with a lipid bilayer and demonstrate a rigorous theoretical formalism and analysis method for computing the induced curvature field in varying concentrations of the protein in the dilute limit. Our theory is based on the description of the height-height undulation spectrum in the presence of a curvature field. We formulated an objective function to compare the acquired undulation spectrum from the simulations to that of the theory. We recover the curvature field parameters by minimizing the objective function even in the limit where the protein-induced membrane curvature is of the same order as the amplitude due to thermal undulations. The coupling between curvature and undulations leads to significant predictions: (i) Under dilute conditions, the proteins can sense a site of spontaneous curvature at distances much larger than their size; (ii) as the density of proteins increases the coupling focuses and stabilizes the curvature field to the site of the proteins; and (iii) the mapping of the protein localization and the induction of a stable curvature is a cooperative process that can be described through a Hill function. PMID:27531962
The Hydrophobic Insertion Mechanism of Membrane Curvature Generation by Proteins
Campelo, Felix; McMahon, Harvey T.; Kozlov, Michael M.
2008-01-01
A wide spectrum of intracellular processes is dependent on the ability of cells to dynamically regulate membrane shape. Membrane bending by proteins is necessary for the generation of intracellular transport carriers and for the maintenance of otherwise intrinsically unstable regions of high membrane curvature in cell organelles. Understanding the mechanisms by which proteins curve membranes is therefore of primary importance. Here we suggest, for the first time to our knowledge, a quantitative mechanism of lipid membrane bending by hydrophobic or amphipathic rodlike inclusions which simulate amphipathic α-helices—structures shown to sculpt membranes. Considering the lipid monolayer matrix as an anisotropic elastic material, we compute the intramembrane stresses and strains generated by the embedded inclusions, determine the resulting membrane shapes, and the accumulated elastic energy. We characterize the ability of an inclusion to bend membranes by an effective spontaneous curvature, and show that shallow rodlike inclusions are more effective in membrane shaping than are lipids having a high propensity for curvature. Our computations provide experimentally testable predictions on the protein amounts needed to generate intracellular membrane shapes for various insertion depths and membrane thicknesses. We also predict that the ability of N-BAR domains to produce membrane tubules in vivo can be ascribed solely to insertion of their amphipathic helices. PMID:18515373
Intermembrane Docking Reactions Are Regulated by Membrane Curvature
Kunding, Andreas H.; Mortensen, Michael W.; Christensen, Sune M.; Bhatia, Vikram K.; Makarov, Ivan; Metzler, Ralf; Stamou, Dimitrios
2011-01-01
The polymorphism of eukaryotic cellular membranes is a tightly regulated and well-conserved phenotype. Recent data have revealed important regulatory roles of membrane curvature on the spatio-temporal localization of proteins and in membrane fusion. Here we quantified the influence of membrane curvature on the efficiency of intermembrane docking reactions. Using fluorescence microscopy, we monitored the docking of single vesicle–vesicle pairs of different diameter (30–200 nm) and therefore curvature, as mediated by neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and streptavidin-biotin. Surprisingly, the intermembrane docking efficiency exhibited an ∼30–60 fold enhancement as a function of curvature. In comparison, synaptotagmin and calcium accelerate SNARE-mediated fusion in vitro by a factor of 2–10. To explain this finding, we formulated a biophysical model. On the basis of our findings, we propose that membrane curvature can regulate intermembrane tethering reactions and consequently any downstream process, including the fusion of vesicles and possibly viruses with their target membranes. PMID:22261058
Kegulian, Natalie C; Sankhagowit, Shalene; Apostolidou, Melania; Jayasinghe, Sajith A; Malmstadt, Noah; Butler, Peter C; Langen, Ralf
2015-10-23
Islet amyloid polypeptide (IAPP) is a 37-amino acid amyloid protein intimately associated with pancreatic islet β-cell dysfunction and death in type II diabetes. In this study, we combine spectroscopic methods and microscopy to investigate α-helical IAPP-membrane interactions. Using light scattering and fluorescence microscopy, we observe that larger vesicles become smaller upon treatment with human or rat IAPP. Electron microscopy shows the formation of various highly curved structures such as tubules or smaller vesicles in a membrane-remodeling process, and spectrofluorometric detection of vesicle leakage shows disruption of membrane integrity. This effect is stronger for human IAPP than for the less toxic rat IAPP. From CD spectra in the presence of different-sized vesicles, we also uncover the membrane curvature-sensing ability of IAPP and find that it transitions from inducing to sensing membrane curvature when lipid negative charge is decreased. Our in vivo EM images of immunogold-labeled rat IAPP and human IAPP show both forms to localize to mitochondrial cristae, which contain not only locally curved membranes but also phosphatidylethanolamine and cardiolipin, lipids with high spontaneous negative curvature. Disruption of membrane integrity by induction of membrane curvature could apply more broadly to other amyloid proteins and be responsible for membrane damage observed in other amyloid diseases as well. PMID:26283787
Spatial Control of Epsin-induced Clathrin Assembly by Membrane Curvature.
Holkar, Sachin S; Kamerkar, Sukrut C; Pucadyil, Thomas J
2015-06-01
Epsins belong to the family of highly conserved clathrin-associated sorting proteins that are indispensable for clathrin-mediated endocytosis, but their precise functions remain unclear. We have developed an assay system of budded supported membrane tubes displaying planar and highly curved membrane surfaces to analyze intrinsic membrane curvature preference shown by clathrin-associated sorting proteins. Using real-time fluorescence microscopy, we find that epsin preferentially partitions to and assembles clathrin on highly curved membrane surfaces. Sorting of epsin to regions of high curvature strictly depends on binding to phosphatidylinositol 4,5-bisphosphate. Fluorescently labeled clathrins rapidly assemble as foci, which in turn cluster epsin, while maintaining tube integrity. Clathrin foci grow in intensity with a typical time constant of ∼75 s, similar to the time scales for coated pit formation seen in cells. Epsin therefore effectively senses membrane curvature to spatially control clathrin assembly. Our results highlight the potential role of membrane curvature in orchestrating the myriad molecular interactions necessary for the success of clathrin-mediated membrane budding. PMID:25837255
Spatial Control of Epsin-induced Clathrin Assembly by Membrane Curvature*♦
Holkar, Sachin S.; Kamerkar, Sukrut C.; Pucadyil, Thomas J.
2015-01-01
Epsins belong to the family of highly conserved clathrin-associated sorting proteins that are indispensable for clathrin-mediated endocytosis, but their precise functions remain unclear. We have developed an assay system of budded supported membrane tubes displaying planar and highly curved membrane surfaces to analyze intrinsic membrane curvature preference shown by clathrin-associated sorting proteins. Using real-time fluorescence microscopy, we find that epsin preferentially partitions to and assembles clathrin on highly curved membrane surfaces. Sorting of epsin to regions of high curvature strictly depends on binding to phosphatidylinositol 4,5-bisphosphate. Fluorescently labeled clathrins rapidly assemble as foci, which in turn cluster epsin, while maintaining tube integrity. Clathrin foci grow in intensity with a typical time constant of ∼75 s, similar to the time scales for coated pit formation seen in cells. Epsin therefore effectively senses membrane curvature to spatially control clathrin assembly. Our results highlight the potential role of membrane curvature in orchestrating the myriad molecular interactions necessary for the success of clathrin-mediated membrane budding. PMID:25837255
Membrane tension controls the assembly of curvature-generating proteins
Simunovic, Mijo; Voth, Gregory A.
2015-01-01
Proteins containing a Bin/Amphiphysin/Rvs (BAR) domain regulate membrane curvature in the cell. Recent simulations have revealed that BAR proteins assemble into linear aggregates, strongly affecting membrane curvature and its in-plane stress profile. Here, we explore the opposite question: do mechanical properties of the membrane impact protein association? By using coarse-grained molecular dynamics simulations, we show that increased surface tension significantly impacts the dynamics of protein assembly. While tensionless membranes promote a rapid formation of long-living linear aggregates of N-BAR proteins, increase in tension alters the geometry of protein association. At high tension, protein interactions are strongly inhibited. Increasing surface density of proteins leads to a wider range of protein association geometries, promoting the formation of meshes, which can be broken apart with membrane tension. Our work indicates that surface tension may play a key role in recruiting proteins to membrane-remodelling sites in the cell. PMID:26008710
Membrane curvature in cell biology: An integration of molecular mechanisms.
Jarsch, Iris K; Daste, Frederic; Gallop, Jennifer L
2016-08-15
Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists. PMID:27528656
Curvature Sorting of Peripheral Proteins on Solid-Supported Wavy Membranes
Hsieh, Wan-Ting; Hsu, Chih-Jung; Capraro, Benjamin R.; Wu, Tingting; Chen, Chi-Mon; Yang, Shu; Baumgart, Tobias
2013-01-01
Cellular membrane deformation and the associated redistribution of membrane-bound proteins are important aspects of membrane function. Current model membrane approaches for studying curvature sensing are limited to positive curvatures, and often require complex and delicate experimental setups. To overcome these challenges, we fabricated a wavy substrate imposing a range of curvatures onto an adhering lipid bilayer membrane. We examined the curvature sorting of several peripheral proteins binding to the wavy membrane and observed them to partition into distinct regions of curvature. Furthermore, single molecule imaging experiments suggested that curvature sensing of proteins on low-curvature substrates requires cooperative interactions. PMID:22881196
Curvature Forces in Membrane Lipid-Protein Interactions
NASA Astrophysics Data System (ADS)
Brown, Michael F.
2012-02-01
Membrane protein conformational changes, folding, and stability may all involve elastic deformation of the bilayer. Non-specific properties of the bilayer play a significant role in modulating protein conformational energetics. A flexible-surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. The FSM describes elastic coupling of membrane lipids to integral membrane proteins. Curvature and hydrophobic matching to the lipid bilayer entails a stress field that explains membrane protein stability. Rhodopsin provides an important example, where solid-state NMR and FTIR spectroscopy characterize the energy landscape of the dynamically activated receptor. Time-resolved UV-visible and FTIR spectroscopic studies show how membrane lipids affect the metarhodopsin equilibrium due to non-specific material properties. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress on rhodopsin function are all explained by the new biomembrane model. By contrast, the older fluid-mosaic model fails to account for such effects on membrane protein activity. According to the FSM proteins are regulated by membrane lipids whose spontaneous curvature most closely matches the activated state within the lipid membrane.
Micron-scale plasma membrane curvature is recognized by the septin cytoskeleton.
Bridges, Andrew A; Jentzsch, Maximilian S; Oakes, Patrick W; Occhipinti, Patricia; Gladfelter, Amy S
2016-04-11
Cells change shape in response to diverse environmental and developmental conditions, creating topologies with micron-scale features. Although individual proteins can sense nanometer-scale membrane curvature, it is unclear if a cell could also use nanometer-scale components to sense micron-scale contours, such as the cytokinetic furrow and base of neuronal branches. Septins are filament-forming proteins that serve as signaling platforms and are frequently associated with areas of the plasma membrane where there is micron-scale curvature, including the cytokinetic furrow and the base of cell protrusions. We report here that fungal and human septins are able to distinguish between different degrees of micron-scale curvature in cells. By preparing supported lipid bilayers on beads of different curvature, we reconstitute and measure the intrinsic septin curvature preference. We conclude that micron-scale curvature recognition is a fundamental property of the septin cytoskeleton that provides the cell with a mechanism to know its local shape. PMID:27044896
Bcl-2 apoptosis proteins, mitochondrial membrane curvature, and cancer
NASA Astrophysics Data System (ADS)
Hwee Lai, Ghee; Schmidt, Nathan; Sanders, Lori; Mishra, Abhijit; Wong, Gerard; Ivashyna, Olena; Christenson, Eric; Schlesinger, Paul; Akabori, Kiyotaka; Santangelo, Christian
2012-02-01
Critical interactions between Bcl-2 family proteins permeabilize the outer mitochondrial membrane, a common decision point early in the intrinsic apoptotic pathway that irreversibly commits the cell to death. However, a unified picture integrating the essential non-passive role of lipid membranes with the contested dynamics of Bcl-2 regulation remains unresolved. Correlating results between synchrotron x-ray diffraction and microscopy in cell-free assays, we report activation of pro-apoptotic Bax induces strong pure negative Gaussian membrane curvature topologically necessary for pore formation and membrane remodeling events. Strikingly, Bcl-xL suppresses not only Bax-induced pore formation, but also membrane remodeling by disparate systems including cell penetrating, antimicrobial or viral fusion peptides, and bacterial toxin, none of which have BH3 allosteric domains to mediate direct binding. We propose a parallel mode of Bcl-2 pore regulation in which Bax and Bcl-xL induce antagonistic and mutually interacting Gaussian membrane curvatures. The universal nature of curvature-mediated interactions allows synergy with direct binding mechanisms, and potentially accounts for the Bcl-2 family modulation of mitochondrial fission/fusion dynamics.
Membrane curvature and its generation by BAR proteins
Mim, Carsten; Unger, Vinzenz M
2012-01-01
Membranes are flexible barriers that surround the cell and its compartments. To execute vital functions such as locomotion or receptor turnover, cells need to control the shapes of their membranes. In part, this control is achieved through membrane-bending proteins, such as the bin/amphiphysin/rvs domain (BAR) proteins. Many open questions remain about the mechanisms by which membrane-bending proteins function. Addressing this shortfall, recent structures of BAR protein:membrane complexes support existing mechanistic models, but also produced novel insights into how BAR-domain proteins sense, stabilize and generate curvature. Here we review these recent findings, focusing on how BAR proteins interact with the membrane, and how the resulting scaffold structures might aid the recruitment of other proteins to the sites where membranes are bent. PMID:23058040
Curvature-mediated interactions between membrane proteins.
Kim, K S; Neu, J; Oster, G
1998-01-01
Membrane proteins can deform the lipid bilayer in which they are embedded. If the bilayer is treated as an elastic medium, then these deformations will generate elastic interactions between the proteins. The interaction between a single pair is repulsive. However, for three or more proteins, we show that there are nonpairwise forces whose magnitude is similar to the pairwise forces. When there are five or more proteins, we show that the nonpairwise forces permit the existence of stable protein aggregates, despite their pairwise repulsions. PMID:9788923
Exo70 Generates Membrane Curvature for Morphogenesis and Cell Migration
Zhao, Yuting; Liu, Jianglan; Yang, Changsong; Capraro, Benjamin R.; Baumgart, Tobias; Bradley, Ryan P.; Ramakrishnan, N.; Xu, Xiaowei; Radhakrishnan, Ravi; Svitkina, Tatyana; Guo, Wei
2013-01-01
Dynamic shape changes of the plasma membrane are fundamental to many processes ranging from morphogenesis and cell migration to phagocytosis and viral propagation. Here we demonstrate that Exo70, a component of the exocyst complex, induces tubular membrane invaginations towards the lumen of synthetic vesicles in vitro and generates protrusions on the surface of cells. Biochemical analyses using Exo70 mutants and independent molecular dynamics simulations based on Exo70 structure demonstrate that Exo70 generates negative membrane curvature through an oligomerization-based mechanism. In cells, the membrane-deformation function of Exo70 is required for protrusion formation and directional cell migration. Exo70 thus represents a membrane-bending protein that may couple actin dynamics and plasma membrane remodeling for morphogenesis. PMID:23948253
NASA Astrophysics Data System (ADS)
RóŻycki, Bartosz; Lipowsky, Reinhard
2015-02-01
Biomimetic and biological membranes consist of molecular bilayers with two leaflets which are typically exposed to different aqueous environments and may differ in their molecular density or composition. Because of these asymmetries, the membranes prefer to curve in a certain manner as quantitatively described by their spontaneous curvature. Here, we study such asymmetric membranes via coarse-grained molecular dynamics simulations. We consider two mechanisms for the generation of spontaneous curvature: (i) different lipid densities within the two leaflets and (ii) leaflets exposed to different concentrations of adsorbing particles. We focus on membranes that experience no mechanical tension and describe two methods to compute the spontaneous curvature. The first method is based on the detailed structure of the bilayer's stress profile which can hardly be measured experimentally. The other method starts from the intuitive view that the bilayer represents a thin fluid film bounded by two interfaces and reduces the complexity of the stress profile to a few membrane parameters that can be measured experimentally. For the case of asymmetric adsorption, we introduce a simulation protocol based on two bilayers separated by two aqueous compartments with different adsorbate concentrations. The adsorption of small particles with a size below 1 nm is shown to generate large spontaneous curvatures up to about 1/(24 nm). Our computational approach is quite general: it can be applied to any molecular model of bilayer membranes and can be extended to other mechanisms for the generation of spontaneous curvatures as provided, e.g., by asymmetric lipid composition or depletion layers of solute molecules.
Lipid membrane-mediated attraction between curvature inducing objects.
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J
2016-01-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (-3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles. PMID:27618764
Geometrical Membrane Curvature as an Allosteric Regulator of Membrane Protein Structure and Function
Tonnesen, Asger; Christensen, Sune M.; Tkach, Vadym; Stamou, Dimitrios
2014-01-01
Transmembrane proteins are embedded in cellular membranes of varied lipid composition and geometrical curvature. Here, we studied for the first time the allosteric effect of geometrical membrane curvature on transmembrane protein structure and function. We used single-channel optical analysis of the prototypic transmembrane β-barrel α-hemolysin (α-HL) reconstituted on immobilized single small unilamellar liposomes of different diameter and therefore curvature. Our data demonstrate that physiologically abundant geometrical membrane curvatures can enforce a dramatic allosteric regulation (1000-fold inhibition) of α-HL permeability. High membrane curvatures (1/diameter ∼1/40 nm−1) compressed the effective pore diameter of α-HL from 14.2 ± 0.8 Å to 11.4 ± 0.6 Å. This reduction in effective pore area (∼40%) when combined with the area compressibility of α-HL revealed an effective membrane tension of ∼50 mN/m and a curvature-imposed protein deformation energy of ∼7 kBT. Such substantial energies have been shown to conformationally activate, or unfold, β-barrel and α-helical transmembrane proteins, suggesting that membrane curvature could likely regulate allosterically the structure and function of transmembrane proteins in general. PMID:24411252
Research on stretched membrane with electrostatic curvature (SMEC) mirrors
NASA Astrophysics Data System (ADS)
Sun, X. W.; Jin, G.
Stretched Membrane with Electrostatic Curvature SMEC Mirrors is a new spatial optical technology recently developed in foreign countries which performed modification of figuration of SMEC Mirror in control of Electrostatic With the folding property of membrane when it was loaded this technology have taken on important prospect in system of spatial remote sensing in the future In this paper the fundamental of SMEC Mirror was introduced the more deeply analyzing of cybernetic model completed and at present research method based on synthesis of foreign development in the field was put forward
Solvent-exposed lipid tail protrusions depend on lipid membrane composition and curvature.
Tahir, Mukarram A; Van Lehn, Reid C; Choi, S H; Alexander-Katz, Alfredo
2016-06-01
The stochastic protrusion of hydrophobic lipid tails into solution, a subclass of hydrophobic membrane defects, has recently been shown to be a critical step in a number of biological processes like membrane fusion. Understanding the factors that govern the appearance of lipid tail protrusions is critical for identifying membrane features that affect the rate of fusion or other processes that depend on contact with solvent-exposed lipid tails. In this work, we utilize atomistic molecular dynamics simulations to characterize the likelihood of tail protrusions in phosphotidylcholine lipid bilayers of varying composition, curvature, and hydration. We distinguish two protrusion modes corresponding to atoms near the end of the lipid tail or near the glycerol group. Through potential of mean force calculations, we demonstrate that the thermodynamic cost for inducing a protrusion depends on tail saturation but is insensitive to other bilayer structural properties or hydration above a threshold value. Similarly, highly curved vesicles or micelles increase both the overall frequency of lipid tail protrusions as well as the preference for splay protrusions, both of which play an important role in driving membrane fusion. In multi-component bilayers, however, the incidence of protrusion events does not clearly depend on the mismatch between tail length or tail saturation of the constituent lipids. Together, these results provide significant physical insight into how system components might affect the appearance of protrusions in biological membranes, and help explain the roles of composition or curvature-modifying proteins in membrane fusion. PMID:26828121
Nonlinear Sorting, Curvature Generation, and Crowding of Endophilin N-BAR on Tubular Membranes
Zhu, Chen; Das, Sovan L.; Baumgart, Tobias
2012-01-01
The curvature of biological membranes is controlled by membrane-bound proteins. For example, during endocytosis, the sorting of membrane components, vesicle budding, and fission from the plasma membrane are mediated by adaptor and accessory proteins. Endophilin is a peripherally binding membrane protein that functions as an endocytic accessory protein. Endophilin's membrane tubulation capacity is well known. However, to understand the thermodynamic and mechanical aspects of endophilin function, experimental measurements need to be compared to quantitative theoretical models. We present measurements of curvature sorting and curvature generation of the endophilin A1 N-BAR domain on tubular membranes pulled from giant unilamellar vesicles. At low concentration, endophilin functions primarily as a membrane curvature sensor; at high concentrations, it also generates curvature. We determine the spontaneous curvature induced by endophilin and observe sigmoidal curvature/composition coupling isotherms that saturate at high membrane tensions and protein solution concentrations. The observation of saturation is supported by a strong dependence of lateral diffusion coefficients on protein density on the tether membrane. We develop a nonlinear curvature/composition coupling model that captures our experimental observations. Our model predicts a curvature-induced phase transition among two states with varying protein density and membrane curvature. This transition could act as a switch during endocytosis. PMID:22768939
Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers.
Tourdot, Richard W; Ramakrishnan, N; Radhakrishnan, Ravi
2014-08-01
Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane-in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer
Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers
NASA Astrophysics Data System (ADS)
Tourdot, Richard W.; Ramakrishnan, N.; Radhakrishnan, Ravi
2014-08-01
Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane—in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer
Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers
Tourdot, Richard W.; Ramakrishnan, N.; Radhakrishnan, Ravi
2015-01-01
Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane—in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer
Thermodynamics and Mechanics of Membrane Curvature Generation and Sensing by Proteins and Lipids
Baumgart, Tobias; Capraro, Benjamin R.; Zhu, Chen; Das, Sovan L.
2014-01-01
Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations. PMID:21219150
Thermodynamics and Mechanics of Membrane Curvature Generation and Sensing by Proteins and Lipids
NASA Astrophysics Data System (ADS)
Baumgart, Tobias; Capraro, Benjamin R.; Zhu, Chen; Das, Sovan L.
2011-05-01
Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations.
IRSp53 senses negative membrane curvature and phase separates along membrane tubules
Prévost, Coline; Zhao, Hongxia; Manzi, John; Lemichez, Emmanuel; Lappalainen, Pekka; Callan-Jones, Andrew; Bassereau, Patricia
2015-01-01
BAR domain proteins contribute to membrane deformation in diverse cellular processes. The inverted-BAR (I-BAR) protein IRSp53, for instance, is found on the inner leaflet of the tubular membrane of filopodia; however its role in the formation of these structures is incompletely understood. Here we develop an original assay in which proteins are encapsulated in giant unilamellar vesicles connected to membrane nanotubes. Our results demonstrate that I-BAR dimers sense negative membrane curvature. Experiment and theory reveal that the I-BAR displays a non-monotonic sorting with curvature, and expands the tube at high imposed tension while constricting it at low tension. Strikingly, at low protein density and tension, protein-rich domains appear along the tube. This peculiar behaviour is due to the shallow intrinsic curvature of I-BAR dimers. It allows constriction of weakly curved membranes coupled to local protein enrichment at biologically relevant conditions. This might explain how IRSp53 contributes in vivo to the initiation of filopodia. PMID:26469246
Dymond, Marcus K
2016-08-01
Several theories of phospholipid homeostasis have postulated that cells regulate the molecular composition of their bilayer membranes, such that a common biophysical membrane parameter is under homeostatic control. Two commonly cited theories are the intrinsic curvature hypothesis, which states that cells control membrane curvature elastic stress, and the theory of homeoviscous adaptation, which postulates cells control acyl chain packing order (membrane order). In this paper, we present evidence from data-driven modelling studies that these two theories correlate in vivo. We estimate the curvature elastic stress of mammalian cells to be 4-7 × 10(-12) N, a value high enough to suggest that in mammalian cells the preservation of membrane order arises through a mechanism where membrane curvature elastic stress is controlled. These results emerge from analysing the molecular contribution of individual phospholipids to both membrane order and curvature elastic stress in nearly 500 cellular compositionally diverse lipidomes. Our model suggests that the de novo synthesis of lipids is the dominant mechanism by which cells control curvature elastic stress and hence membrane order in vivo These results also suggest that cells can increase membrane curvature elastic stress disproportionately to membrane order by incorporating polyunsaturated fatty acids into lipids. PMID:27534697
Measuring the composition-curvature coupling in binary lipid membranes by computer simulations
Barragán Vidal, I. A. Müller, M.; Rosetti, C. M.; Pastorino, C.
2014-11-21
The coupling between local composition fluctuations in binary lipid membranes and curvature affects the lateral membrane structure. We propose an efficient method to compute the composition-curvature coupling in molecular simulations and apply it to two coarse-grained membrane models—a minimal, implicit-solvent model and the MARTINI model. Both the weak-curvature behavior that is typical for thermal fluctuations of planar bilayer membranes as well as the strong-curvature regime corresponding to narrow cylindrical membrane tubes are studied by molecular dynamics simulation. The simulation results are analyzed by using a phenomenological model of the thermodynamics of curved, mixed bilayer membranes that accounts for the change of the monolayer area upon bending. Additionally the role of thermodynamic characteristics such as the incompatibility between the two lipid species and asymmetry of composition are investigated.
Influenza M2 Transmembrane Domain Senses Membrane Heterogeneity and Enhances Membrane Curvature.
Ho, Chian Sing; Khadka, Nawal K; She, Fengyu; Cai, Jianfeng; Pan, Jianjun
2016-07-01
Targeting host cell membranes by M2 of influenza A virus is important for virus invasion and replication. We study the transmembrane domain of M2 (M2TM) interacting with mica-supported planar bilayers and free-standing giant unilamellar vesicles (GUVs). Using solution atomic force microscopy (AFM), we show that the size of M2TM oligomers is dependent on lipid composition. The addition of M2TM to lipid bilayers containing liquid-ordered (Lo) and liquid-disordered (Ld) phases reveals that M2TM preferentially partitions into the Ld phase; phase-dependent partitioning results in a larger rigidity of the Ld phase. We next use fluorescence microscopy to study the effects of M2TM on phase-coexisting GUVs. In particular, M2TM is found to increase GUVs' miscibility transition temperature Tmix. The augmented thermodynamic stability can be accounted for by considering an enhanced energy barrier of lipid mixing between coexisting phases. Our GUV study also shows that M2TM can elicit an array of vesicle shapes mimicking virus budding. M2TM enhanced membrane curvature is consistent with our AFM data, which show altered membrane rigidity and consequently line tension at domain edges. Together, our results highlight that in addition to conducting protons, M2TM can actively regulate membrane heterogeneity and augment membrane curvature. PMID:27285399
Membrane Curvature Sensing by Amphipathic Helices Is Modulated by the Surrounding Protein Backbone
Doucet, Christine M.; Esmery, Nina; de Saint-Jean, Maud; Antonny, Bruno
2015-01-01
Membrane curvature is involved in numerous biological pathways like vesicle trafficking, endocytosis or nuclear pore complex assembly. In addition to its topological role, membrane curvature is sensed by specific proteins, enabling the coordination of biological processes in space and time. Amongst membrane curvature sensors are the ALPS (Amphipathic Lipid Packing Sensors). ALPS motifs are short peptides with peculiar amphipathic properties. They are found in proteins targeted to distinct curved membranes, mostly in the early secretory pathway. For instance, the ALPS motif of the golgin GMAP210 binds trafficking vesicles, while the ALPS motif of Nup133 targets nuclear pores. It is not clear if, besides curvature sensitivity, ALPS motifs also provide target specificity, or if other domains in the surrounding protein backbone are involved. To elucidate this aspect, we studied the subcellular localization of ALPS motifs outside their natural protein context. The ALPS motifs of GMAP210 or Nup133 were grafted on artificial fluorescent probes. Importantly, ALPS motifs are held in different positions and these contrasting architectures were mimicked by the fluorescent probes. The resulting chimeras recapitulated the original proteins localization, indicating that ALPS motifs are sufficient to specifically localize proteins. Modulating the electrostatic or hydrophobic content of Nup133 ALPS motif modified its avidity for cellular membranes but did not change its organelle targeting properties. In contrast, the structure of the backbone surrounding the helix strongly influenced targeting. In particular, introducing an artificial coiled-coil between ALPS and the fluorescent protein increased membrane curvature sensitivity. This coiled-coil domain also provided membrane curvature sensitivity to the amphipathic helix of Sar1. The degree of curvature sensitivity within the coiled-coil context remains correlated to the natural curvature sensitivity of the helices. This suggests
Curvature sensing MARCKS-ED peptides bind to membranes in a stereo-independent manner.
Yan, Lei; de Jesus, Armando Jerome; Tamura, Ryo; Li, Victoria; Cheng, Kui; Yin, Hang
2015-07-01
Membrane curvature and lipid composition plays a critical role in interchanging of matter and energy in cells. Peptide curvature sensors are known to activate signaling pathways and promote molecular transport across cell membranes. Recently, the 25-mer MARCKS-ED peptide, which is derived from the effector domain of the myristoylated alanine-rich C kinase substrate protein, has been reported to selectively recognize highly curved membrane surfaces. Our previous studies indicated that the naturally occurring L-MARCKS-ED peptide could simultaneously detect both phosphatidylserine and curvature. Here, we demonstrate that D-MARCKS-ED, composed by unnatural D-amino acids, has the same activities as its enantiomer, L-MARCKS-ED, as a curvature and lipid sensor. An atomistic molecular dynamics simulation suggests that D-MARCKS-ED may change from linear to a boat conformation upon binding to the membrane. Comparable enhancement of fluorescence intensity was observed between D- and L-MARCKS-ED peptides, indicating similar binding affinities. Meanwhile, circular dichroism spectra of D- and L-MARCKS-ED are almost symmetrical both in the presence and absence of liposomes. These results suggest similar behavior of artificial D- and natural L-MARCKS-ED peptides when binding to curved membranes. Our studies may contribute to further understanding of how MARCKS-ED senses membrane curvature as well as provide a new direction to develop novel membrane curvature probes. PMID:25851418
A cost-benefit analysis of the physical mechanisms of membrane curvature
Stachowiak, Jeanne C.; Brodsky, Frances M.; Miller, Elizabeth A.
2013-01-01
Many cellular membrane-bound structures exhibit distinct curvature that is driven by the physical properties of their lipid and protein constituents. Here we review how cells manipulate and control this curvature in the context of dynamic events such as vesicle-mediated membrane traffic. Lipids and cargo proteins each contribute energetic barriers that must be overcome during vesicle formation. In contrast, protein coats and their associated accessory proteins drive membrane bending using a variety of interdependent physical mechanisms. We survey the energetic costs and drivers involved in membrane curvature, drawing a contrast between the stochastic contributions of molecular crowding and the deterministic assembly of protein coats. These basic principles also apply to other cellular examples of membrane bending events, including important disease-related problems like viral egress. PMID:23999615
Membrane curvature induced by Arf1-GTP is essential for vesicle formation
Beck, Rainer; Sun, Zhe; Adolf, Frank; Rutz, Chistoph; Bassler, Jochen; Wild, Klemens; Sinning, Irmgard; Hurt, Ed; Brügger, Britta; Béthune, Julien; Wieland, Felix
2008-01-01
The GTPase Arf1 is considered as a molecular switch that regulates binding and release of coat proteins that polymerize on membranes to form transport vesicles. Here, we show that Arf1-GTP induces positive membrane curvature and find that the small GTPase can dimerize dependent on GTP. Investigating a possible link between Arf dimerization and curvature formation, we isolated an Arf1 mutant that cannot dimerize. Although it was capable of exerting the classical role of Arf1 as a coat receptor, it could not mediate the formation of COPI vesicles from Golgi-membranes and was lethal when expressed in yeast. Strikingly, this mutant was not able to deform membranes, suggesting that GTP-induced dimerization of Arf1 is a critical step inducing membrane curvature during the formation of coated vesicles. PMID:18689681
Quantifying Membrane Curvature Generation of Drosophila Amphiphysin N-BAR Domains
Heinrich, Michael C.; Capraro, Benjamin R.; Tian, Aiwei; Isas, Jose M.; Langen, Ralf; Baumgart, Tobias
2012-01-01
Biological membrane functions are coupled to membrane curvature, the regulation of which often involves membrane-associated proteins. The membrane-binding N-terminal amphipathic helix-containing BIN/Amphiphysin/Rvs (N-BAR) domain of amphiphysin is implicated in curvature generation and maintenance. Improving the mechanistic understanding of membrane curvature regulation by N-BAR domains requires quantitative experimental characterization. We have measured tube pulling force modulation by the N-BAR domain of Drosophila amphiphysin (DA-N-BAR) bound to tubular membranes pulled from micropipette-aspirated giant vesicles. We observed that fluorescently-labeled DA-N-BAR showed significantly higher protein density on tubules compared to the connected low-curvature vesicle membrane. Furthermore, we found the equilibrium tube pulling force to be systematically dependent on the aqueous solution concentration of DA-N-BAR, thereby providing the first quantitative assessment of spontaneous curvature generation. At sufficiently high protein concentrations, pulled tubes required no external force to maintain mechanical equilibrium, in agreement with the qualitative spontaneous tubulation previously reported for amphiphysin. PMID:23772271
Calculation of free energies in fluid membranes subject to heterogeneous curvature fields
NASA Astrophysics Data System (ADS)
Agrawal, Neeraj J.; Radhakrishnan, Ravi
2009-07-01
We present a computational methodology for incorporating thermal effects and calculating relative free energies for elastic fluid membranes subject to spatially dependent intrinsic curvature fields using the method of thermodynamic integration. Based on a simple model for the intrinsic curvature imposed only in a localized region of the membrane, we employ thermodynamic integration to calculate the free-energy change as a function of increasing strength of the intrinsic curvature field and a thermodynamic cycle to compute free-energy changes for different sizes of the localized region. By explicitly computing the free-energy changes and by quantifying the loss of entropy accompanied with increasing membrane deformation, we show that the membrane stiffness increases with increasing intrinsic field, thereby, renormalizing the membrane bending rigidity. The second main conclusion of this work is that the entropy of the membrane decreases with increasing size of the localized region subject to the curvature field. Our results help to quantify the free-energy change when a planar membrane deforms under the influence of curvature-inducing proteins at a finite temperature.
When physics takes over: BAR proteins and membrane curvature
Simunovic, Mijo; Voth, Gregory A.; Callan-Jones, Andrew; Bassereau, Patricia
2016-01-01
Cell membranes become highly curved during membrane trafficking, cytokinesis, infection, immune response or cell motion. Bin/amphiphysin/Rvs (BAR) domain proteins with their intrinsically curved and anisotropic shape are involved in many of these processes, but with a large spectrum of modes of action. In vitro experiments and multiscale computer simulations have contributed in identifying a minimal set of physical parameters, namely protein density on the membrane, membrane tension, and membrane shape, that control how bound BAR domain proteins behave on the membrane. In this review, we summarize the multifaceted coupling of BAR proteins to membrane mechanics and propose a simple phase diagram that recapitulates the effects of these parameters. PMID:26519988
Curvature sorting of proteins on a cylindrical lipid membrane tether connected to a reservoir
Singh, Pankaj; Mahata, Paritosh; Baumgart, Tobias; Das, Sovan Lal
2012-01-01
Membrane curvature of a biological cell is actively involved in various fundamental cell biological functions. It has been discovered that membrane curvature and binding of peripheral membrane proteins follow a symbiotic relationship. The exact mechanism behind this interplay of protein binding and membrane curvature has not yet been properly understood. To improve understanding of the mechanism, we study curvature sorting of proteins in a model system consisting of a tether pulled from a giant unilamellar vesicle using mechanical-thermodynamic models. The concentration of proteins bound to the membrane changes significantly due to curvature. This has also been observed in experiments by other researchers. We also find that there is a phase transition based on protein concentration and we discuss the coexistence of phases and stability of solutions. Furthermore, when sorting is favorable, the increase in protein concentration stabilizes the tether in the sense that less pulling force is required to maintain the tether. A similar mechanism may be in place, when motor proteins pull tethers from donor membranes. PMID:23004787
Curvature sorting of proteins on a cylindrical lipid membrane tether connected to a reservoir
NASA Astrophysics Data System (ADS)
Singh, Pankaj; Mahata, Paritosh; Baumgart, Tobias; Das, Sovan Lal
2012-05-01
Membrane curvature of a biological cell is actively involved in various fundamental cell biological functions. It has been discovered that membrane curvature and binding of peripheral membrane proteins follow a symbiotic relationship. The exact mechanism behind this interplay of protein binding and membrane curvature has not yet been properly understood. To improve understanding of the mechanism, we study curvature sorting of proteins in a model system consisting of a tether pulled from a giant unilamellar vesicle using mechanical-thermodynamic models. The concentration of proteins bound to the membrane changes significantly due to curvature. This has also been observed in experiments by other researchers. We also find that there is a phase transition based on protein concentration and we discuss the coexistence of phases and stability of solutions. Furthermore, when sorting is favorable, the increase in protein concentration stabilizes the tether in the sense that less pulling force is required to maintain the tether. A similar mechanism may be in place, when motor proteins pull tethers from donor membranes.
Tarahovsky, Yury S.; Koynova, Rumiana; MacDonald, Robert C.
2010-01-18
DNA release from lipoplexes is an essential step during lipofection and is probably a result of charge neutralization by cellular anionic lipids. As a model system to test this possibility, fluorescence resonance energy transfer between DNA and lipid covalently labeled with Cy3 and BODIPY, respectively, was used to monitor the release of DNA from lipid surfaces induced by anionic liposomes. The separation of DNA from lipid measured this way was considerably slower and less complete than that estimated with noncovalently labeled DNA, and depends on the lipid composition of both lipoplexes and anionic liposomes. This result was confirmed by centrifugal separation of released DNA and lipid. X-ray diffraction revealed a clear correlation of the DNA release capacity of the anionic lipids with the interfacial curvature of the mesomorphic structures developed when the anionic and cationic liposomes were mixed. DNA release also correlated with the rate of fusion of anionic liposomes with lipoplexes. It is concluded that the tendency to fuse and the phase preference of the mixed lipid membranes are key factors for the rate and extent of DNA release. The approach presented emphasizes the importance of the lipid composition of both lipoplexes and target membranes and suggests optimal transfection may be obtained by tailoring lipoplex composition to the lipid composition of target cells.
Fluid lipid membranes: from differential geometry to curvature stresses.
Deserno, Markus
2015-01-01
A fluid lipid membrane transmits stresses and torques that are fully determined by its geometry. They can be described by a stress- and torque-tensor, respectively, which yield the force or torque per length through any curve drawn on the membrane's surface. In the absence of external forces or torques the surface divergence of these tensors vanishes, revealing them as conserved quantities of the underlying Euler-Lagrange equation for the membrane's shape. This review provides a comprehensive introduction into these concepts without assuming the reader's familiarity with differential geometry, which instead will be developed as needed, relying on little more than vector calculus. The Helfrich Hamiltonian is then introduced and discussed in some depth. By expressing the quest for the energy-minimizing shape as a functional variation problem subject to geometric constraints, as proposed by Guven (2004), stress- and torque-tensors naturally emerge, and their connection to the shape equation becomes evident. How to reason with both tensors is then illustrated with a number of simple examples, after which this review concludes with four more sophisticated applications: boundary conditions for adhering membranes, corrections to the classical micropipette aspiration equation, membrane buckling, and membrane mediated interactions. PMID:24835737
Smrt, Sean T.; Draney, Adrian W.; Lorieau, Justin L.
2015-01-01
The highly conserved N-terminal 23 residues of the hemagglutinin glycoprotein, known as the fusion peptide domain (HAfp23), is vital to the membrane fusion and infection mechanism of the influenza virus. HAfp23 has a helical hairpin structure consisting of two tightly packed amphiphilic helices that rest on the membrane surface. We demonstrate that HAfp23 is a new class of amphipathic helix that functions by leveraging the negative curvature induced by two tightly packed helices on membranes. The helical hairpin structure has an inverted wedge shape characteristic of negative curvature lipids, with a bulky hydrophobic region and a relatively small hydrophilic head region. The F3G mutation reduces this inverted wedge shape by reducing the volume of its hydrophobic base. We show that despite maintaining identical backbone structures and dynamics as the wild type HAfp23, the F3G mutant has an attenuated fusion activity that is correlated to its reduced ability to induce negative membrane curvature. The inverted wedge shape of HAfp23 is likely to play a crucial role in the initial stages of membrane fusion by stabilizing negative curvature in the fusion stalk. PMID:25398882
Membrane curvature sensing by the C-terminal domain of complexin
NASA Astrophysics Data System (ADS)
Snead, David; Wragg, Rachel T.; Dittman, Jeremy S.; Eliezer, David
2014-09-01
Complexin functions at presynaptic nerve terminals to inhibit spontaneous SNARE-mediated synaptic vesicle (SV) exocytosis, while enhancing stimulated neurotransmitter release. The C-terminal domain (CTD) of complexin is essential for its inhibitory function and has been implicated in localizing complexin to SVs via direct membrane interactions. Here we show that complexin’s CTD is highly sensitive to membrane curvature, which it senses via tandem motifs, a C-terminal motif containing a mix of bulky hydrophobic and positively charged residues, and an adjacent amphipathic region that can bind membranes in either a disordered or a helical conformation. Helix formation requires membrane packing defects found on highly curved membrane surfaces. Mutations that disrupt helix formation without disrupting membrane binding compromise complexin’s inhibitory function in vivo. Thus, this membrane curvature-dependent conformational transition, combined with curvature-sensitive binding by the adjacent C-terminal motif, constitute a novel mechanism for activating complexin’s inhibitory function on the surface of SVs.
NASA Astrophysics Data System (ADS)
Junesch, Juliane; Emilsson, Gustav; Xiong, Kunli; Kumar, Shailabh; Sannomiya, Takumi; Pace, Hudson; Vörös, Janos; Oh, Sang-Hyun; Bally, Marta; Dahlin, Andreas B.
2015-09-01
The biochemical processes of cell membranes are sensitive to the geometry of the lipid bilayer. We show how plasmonic ``nanowells'' provide label-free real-time analysis of molecules on membranes with detection of preferential binding at negative curvature. It is demonstrated that norovirus accumulate in invaginations due to multivalent interactions with glycosphingolipids.The biochemical processes of cell membranes are sensitive to the geometry of the lipid bilayer. We show how plasmonic ``nanowells'' provide label-free real-time analysis of molecules on membranes with detection of preferential binding at negative curvature. It is demonstrated that norovirus accumulate in invaginations due to multivalent interactions with glycosphingolipids. Electronic supplementary information (ESI) available: Additional plasmonic sensing results, numerical electromagnetic simulations, quartz crystal microbalance data, fluorescence recovery after photobleaching, additional electron microscopy images, experimental methodology and materials used. See DOI: 10.1039/c5nr04208a
Bavi, Omid; Cox, Charles D.; Vossoughi, Manouchehr; Naghdabadi, Reza; Jamali, Yousef; Martinac, Boris
2016-01-01
Mechanosensitive (MS) channels are ubiquitous molecular force sensors that respond to a number of different mechanical stimuli including tensile, compressive and shear stress. MS channels are also proposed to be molecular curvature sensors gating in response to bending in their local environment. One of the main mechanisms to functionally study these channels is the patch clamp technique. However, the patch of membrane surveyed using this methodology is far from physiological. Here we use continuum mechanics to probe the question of how curvature, in a standard patch clamp experiment, at different length scales (global and local) affects a model MS channel. Firstly, to increase the accuracy of the Laplace’s equation in tension estimation in a patch membrane and to be able to more precisely describe the transient phenomena happening during patch clamping, we propose a modified Laplace’s equation. Most importantly, we unambiguously show that the global curvature of a patch, which is visible under the microscope during patch clamp experiments, is of negligible energetic consequence for activation of an MS channel in a model membrane. However, the local curvature (RL < 50) and the direction of bending are able to cause considerable changes in the stress distribution through the thickness of the membrane. Not only does local bending, in the order of physiologically relevant curvatures, cause a substantial change in the pressure profile but it also significantly modifies the stress distribution in response to force application. Understanding these stress variations in regions of high local bending is essential for a complete understanding of the effects of curvature on MS channels. PMID:26861405
Sar1 GTPase Activity Is Regulated by Membrane Curvature*♦
Hanna, Michael G.; Mela, Ioanna; Wang, Lei; Henderson, Robert M.; Chapman, Edwin R.; Edwardson, J. Michael; Audhya, Anjon
2016-01-01
The majority of biosynthetic secretory proteins initiate their journey through the endomembrane system from specific subdomains of the endoplasmic reticulum. At these locations, coated transport carriers are generated, with the Sar1 GTPase playing a critical role in membrane bending, recruitment of coat components, and nascent vesicle formation. How these events are appropriately coordinated remains poorly understood. Here, we demonstrate that Sar1 acts as the curvature-sensing component of the COPII coat complex and highlight the ability of Sar1 to bind more avidly to membranes of high curvature. Additionally, using an atomic force microscopy-based approach, we further show that the intrinsic GTPase activity of Sar1 is necessary for remodeling lipid bilayers. Consistent with this idea, Sar1-mediated membrane remodeling is dramatically accelerated in the presence of its guanine nucleotide-activating protein (GAP), Sec23-Sec24, and blocked upon addition of guanosine-5′-[(β,γ)-imido]triphosphate, a poorly hydrolysable analog of GTP. Our results also indicate that Sar1 GTPase activity is stimulated by membranes that exhibit elevated curvature, potentially enabling Sar1 membrane scission activity to be spatially restricted to highly bent membranes that are characteristic of a bud neck. Taken together, our data support a stepwise model in which the amino-terminal amphipathic helix of GTP-bound Sar1 stably penetrates the endoplasmic reticulum membrane, promoting local membrane deformation. As membrane bending increases, Sar1 membrane binding is elevated, ultimately culminating in GTP hydrolysis, which may destabilize the bilayer sufficiently to facilitate membrane fission. PMID:26546679
Blood, Philip D.; Swenson, Richard D.; Voth, Gregory A.
2008-01-01
N-BAR domains are protein modules that bind to and induce curvature in membranes via a charged concave surface and N-terminal amphipathic helices. Recently, molecular dynamics simulations have demonstrated that the N-BAR domain can induce a strong local curvature that matches the curvature of the BAR domain surface facing the bilayer. Here we present further molecular dynamics simulations that examine in greater detail the roles of the concave surface and amphipathic helices in driving local membrane curvature. We find that the strong curvature induction observed in our previous simulations requires the stable presentation of the charged concave surface to the membrane and is not driven by the membrane-embedded amphipathic helices. Nevertheless, without these amphipathic helices embedded in the membrane, the N-BAR domain does not maintain a close association with the bilayer, and fails to drive membrane curvature. Increasing the membrane negative charge through the addition of PIP2 facilitates closer association with the membrane in the absence of embedded helices. At sufficiently high concentrations, amphipathic helices embedded in the membrane drive membrane curvature independently of the BAR domain. PMID:18469070
NASA Astrophysics Data System (ADS)
Lee, Sin-Doo
2015-10-01
Soft matters such as liquid crystals and biological molecules exhibit a variety of interesting physical phenomena as well as new applications. Recently, in mimicking biological systems that have the ability to sense, regulate, grow, react, and regenerate in a highly responsive and self-adaptive manner, the significance of the liquid crystal order in living organisms, for example, a biological membrane possessing the lamellar order, is widely recognized from the viewpoints of physics and chemistry of interfaces and membrane biophysics. Lipid bilayers, resembling cell membranes, provide primary functions for the transport of biological components of ions and molecules in various cellular activities, including vesicle budding and membrane fusion, through lateral organization of the membrane components such as proteins. In this lecture, I will describe how the liquid crystal-analog curvature elasticity of a lipid bilayer plays a critical role in developing a new platform for understanding diverse biological functions at a cellular level. The key concept is to manipulate the local curvature at an interface between a solid substrate and a model membrane. Two representative examples will be demonstrated: one of them is the topographic control of lipid rafts in a combinatorial array where the ligand-receptor binding event occurs and the other concerns the reconstitution of a ring-type lipid raft in bud-mimicking architecture within the framework of the curvature elasticity.
Henne, William Mike; Kent, Helen M; Ford, Marijn G J; Hegde, Balachandra G; Daumke, Oliver; Butler, P Jonathan G; Mittal, Rohit; Langen, Ralf; Evans, Philip R; McMahon, Harvey T
2007-07-01
A spectrum of membrane curvatures exists within cells, and proteins have evolved different modules to detect, create, and maintain these curvatures. Here we present the crystal structure of one such module found within human FCHo2. This F-BAR (extended FCH) module consists of two F-BAR domains, forming an intrinsically curved all-helical antiparallel dimer with a Kd of 2.5 microM. The module binds liposomes via a concave face, deforming them into tubules with variable diameters of up to 130 nm. Pulse EPR studies showed the membrane-bound dimer is the same as the crystal dimer, although the N-terminal helix changed conformation on membrane binding. Mutation of a phenylalanine on this helix partially attenuated narrow tubule formation, and resulted in a gain of curvature sensitivity. This structure shows a distant relationship to curvature-sensing BAR modules, and suggests how similar coiled-coil architectures in the BAR superfamily have evolved to expand the repertoire of membrane-sculpting possibilities. PMID:17540576
NASA Astrophysics Data System (ADS)
Manukovsky, Nurit; Sanders, Ella; Matalon, Erez; Wolf, Sharon G.; Goldfarb, Daniella
2013-10-01
Nitroxide spin-labelled lipid analogues are often used to study model membrane properties using EPR spectroscopy. Whereas in liquid phase membranes the spin label assumes, on average, its putative location, in gel phases and frozen membrane, depending on its position along the acyl chain, it may exhibit a different average location. Here we used 2H three-pulse Electron Spin Echo Envelope Modulation (ESEEM) of phospholipid spin probes, combined with various deuteration schemes to detect the effect of the model membrane curvature and cholesterol on vertical migrations of the spin label. We compared large and small unilamellar 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles with and without cholesterol (10%). The vertical displacement of the spin label was manifested as an apparently flat trans-membrane profile of water concentration and of label proximity to the head group choline. The spin-label propensity to migrate was found to increase with vesicle curvature and decrease in the presence of cholesterol. This in turn reflects the effect of packing and ordering of the membrane lipids. The results show that in curved vesicles lacking cholesterol, the label attached to carbon 16 may travel as far high along the membrane normal as the location of the label on carbon 5, due to the presence of U-shaped lipid conformations. This phenomenon must be taken into account when using spin-labelled lipids as membrane depth markers or to trace trans-membrane profiles.
A PH domain in ACAP1 possesses key features of the BAR domain in promoting membrane curvature.
Pang, Xiaoyun; Fan, Jun; Zhang, Yan; Zhang, Kai; Gao, Bingquan; Ma, Jun; Li, Jian; Deng, Yuchen; Zhou, Qiangjun; Egelman, Edward H; Hsu, Victor W; Sun, Fei
2014-10-13
The BAR (Bin-Amphiphysin-Rvs) domain undergoes dimerization to produce a curved protein structure, which superimposes onto membrane through electrostatic interactions to sense and impart membrane curvature. In some cases, a BAR domain also possesses an amphipathic helix that inserts into the membrane to induce curvature. ACAP1 (Arfgap with Coil coil, Ankyrin repeat, and PH domain protein 1) contains a BAR domain. Here, we show that this BAR domain can neither bind membrane nor impart curvature, but instead requires a neighboring PH (Pleckstrin Homology) domain to achieve these functions. Specific residues within the PH domain are responsible for both membrane binding and curvature generation. The BAR domain adjacent to the PH domain instead interacts with the BAR domains of neighboring ACAP1 proteins to enable clustering at the membrane. Thus, we have uncovered the molecular basis for an unexpected and unconventional collaboration between PH and BAR domains in membrane bending. PMID:25284369
Koller, Daniel; Lohner, Karl
2014-09-01
Research on antimicrobial peptides is in part driven by urgent medical needs such as the steady increase in pathogens being resistant to antibiotics. Despite the wealth of information compelling structure-function relationships are still scarce and thus the interfacial activity model has been proposed to bridge this gap. This model also applies to other interfacially active (membrane active) peptides such as cytolytic, cell penetrating or antitumor peptides. One parameter that is strongly linked to interfacial activity is the spontaneous lipid curvature, which is experimentally directly accessible. We discuss different parameters such as H-bonding, electrostatic repulsion, changes in monolayer surface area and lateral pressure that affect induction of membrane curvature, but also vice versa how membrane curvature triggers peptide response. In addition, the impact of membrane lipid composition on the formation of curved membrane structures and its relevance for diverse mode of action of interfacially active peptides and in turn biological activity are described. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova. PMID:24853655
Poxviruses Encode a Reticulon-Like Protein that Promotes Membrane Curvature
Erlandson, Karl J.; Bisht, Himani; Weisberg, Andrea S.; Hyun, Seong-In; Hansen, Bryan T.; Fischer, Elizabeth R.; Hinshaw, Jenny E.; Moss, Bernard
2016-01-01
Poxviruses are enveloped DNA viruses that replicate within the cytoplasm. The first viral structures are crescents and spherical particles with a lipoprotein membrane bilayer thought to be derived from the endoplasmic reticulum (ER). We determined that A17, a conserved viral transmembrane protein essential for crescent formation, forms homo-oligomers and shares topological features with cellular reticulon-like proteins, which promote membrane curvature and contribute to the tubular structure of the ER. When the purified A17 protein was incorporated into liposomes, 25 nm diameter vesicles and tubules formed at low and high A17 concentrations, respectively. In addition, intracellular expression of A17, in the absence of other viral structural proteins, transformed the ER into aggregated 3-dimensional tubular networks. We suggest that A17 is a viral reticulon-like protein that contributes to curvature during biogenesis of the poxvirus membrane. PMID:26923595
Membrane nanotubes induced by aqueous phase separation and stabilized by spontaneous curvature
Li, Yanhong; Lipowsky, Reinhard; Dimova, Rumiana
2011-01-01
Tubular membrane structures are widespread in eukaryotic cells, but the mechanisms underlying their formation and stability are not well understood. Previous work has focused on tube extrusion from cells and model membranes under the application of external forces. Here, we present novel membrane/polymer systems, where stable tubes form in the absence of externally applied forces. Solutions of two water-soluble polymers, polyethylene glycol and dextran, were encapsulated in giant lipid vesicles, cell-size model systems. Hypertonic deflation induced phase separation of the enclosed solution. The excess membrane area created during the deflation process was stored in a large number of membrane nanotubes inside the vesicle. The tubes had a diameter below optical resolution and became visible only when fluorescently labeled. The tubes were rather stable: In the absence of external forces, they existed for several days. A theoretical analysis of the shapes of the deflated vesicles reveals that these shapes would be unstable if the membranes had no spontaneous curvature. Using the large separation of length scales between the tube diameter and the overall size of the vesicles, the spontaneous curvature can be calculated and is found to be about -1/(240 nm) for a certain range of polymer concentrations. The nanotubes could also be retracted back into the mother vesicle by increasing the membrane tension via micropipette aspiration of the vesicle. Membrane tubes, which can form and be retracted easily, should be relevant for lipid storage in cells. PMID:21383120
Mészáros, Noémi; Cibulka, Jakub; Mendiburo, Maria Jose; Romanauska, Anete; Schneider, Maren; Köhler, Alwin
2015-01-01
Summary Nuclear pore complexes (NPCs) are selective transport channels embedded in the nuclear envelope. The cylindrical NPC core forms a protein coat lining a highly curved membrane opening and has a basket-like structure appended to the nucleoplasmic side. How NPCs interact with lipids, promoting membrane bending and NPC integrity, is poorly understood. Here we show that the NPC basket proteins Nup1 and Nup60 directly induce membrane curvature by amphipathic helix insertion into the lipid bilayer. In a cell-free system, both Nup1 and Nup60 transform spherical liposomes into highly curved membrane structures. In vivo, high levels of the Nup1/Nup60 amphipathic helices cause deformation of the yeast nuclear membrane, whereas adjacent helical regions contribute to anchoring the basket to the NPC core. Basket amphipathic helices are functionally linked to distinct transmembrane nucleoporins of the NPC core, suggesting a key contribution to the membrane remodeling events that underlie NPC assembly. PMID:25942622
The role of Gauss curvature in a membrane phase separation problem
NASA Astrophysics Data System (ADS)
Gillmor, Susan; Lee, Jieun; Ren, Xiaofeng
2011-12-01
Consider a two-phase lipid vesicle. Below the transition temperature, the phases separate into non-connecting domains that coarsen into larger areas. The free energy of phase properties determines the length of the boundaries separating the regions. The two phases correspond to different lipid compositions, and in cells, this fluctuation in composition is a dynamic process vital to its function. We prove that a small patch of the minority lipids forms at a point of the membrane where the Gauss curvature attains a maximum. This patch has a round shape approximately and its boundary has a constant geodesic curvature. The proof consists of three steps. The construction of a family of good approximate solutions, an improvement of the approximate solutions so that their geodesic curvature is a constant modulo translation, and the identification of an exact solution from the family of the improved approximate solutions. Our theoretical results are supported by vesicle experiments.
Różycki, Bartosz; Lipowsky, Reinhard
2016-08-21
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
Yoo, Jejoong; Cui, Qiang
2009-01-01
Abstract Although many membrane additives are known to modulate the activities of membrane proteins via perturbing the properties of lipid membrane, the underlying mechanism is often not precisely understood. In this study, we investigate the impact of asymmetrically incorporating single-tailed lysophosphatidylcholine (LPC) into a membrane bilayer using coarse-grained molecular dynamics simulations. Using a simple computational protocol designed to approximately mimic a micropipette setting, we show that asymmetric incorporation of LPC can lead to significant curvature in a bilayer. Detailed analysis of geometrical and mechanical properties (pressure profile) of the resulting mound structure indicates that the degree of pressure profile perturbation is determined not by the local curvature per se but by the packing of lipid headgroups (i.e., area-per-lipid). The findings help provide a concrete basis for understanding the activation mechanism of mechanosensitive channels by asymmetric incorporation of LPC into membrane patches in patch-clamp experiments. The calculated local pressure profiles are valuable to the construction of realistic membrane models for the analysis of mechanosensation in a continuum mechanics framework. PMID:19843459
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins.
Ramakrishnan, N; Sunil Kumar, P B; Radhakrishnan, Ravi
2014-10-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
NASA Astrophysics Data System (ADS)
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-10-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham-Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this description, the
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-01-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this
Stachowiak, Jeanne C.; Hayden, Carl C.; Negrete, Oscar A.; Davis, Ryan Wesley; Sasaki, Darryl Yoshio
2013-10-01
Pathogenic viruses are a primary threat to our national security and to the health and economy of our world. Effective defense strategies to combat viral infection and spread require the development of understanding of the mechanisms that these pathogens use to invade the host cell. We present in this report results of our research into viral particle recognition and fusion to cell membranes and the role that protein affinity and confinement in lipid domains plays in membrane curvature in cellular fusion and fission events. Herein, we describe 1) the assembly of the G attachment protein of Nipah virus using point mutation studies to define its role in viral particle fusion to the cell membrane, 2) how lateral pressure of membrane bound proteins induce curvature in model membrane systems, and 3) the role of membrane curvature in the selective partitioning of molecular receptors and specific affinity of associated proteins.
Sankhagowit, Shalene; Lee, Ernest Y; Wong, Gerard C L; Malmstadt, Noah
2016-03-15
Oxidation is associated with conditions related to chronic inflammations and aging. Cubic structures have been observed in the smooth endoplasmic reticulum and mitochondrial membranes of cells under oxidative stress (e.g., tumor cells and virus-infected cells). It has been previously suspected that oxidation can result in the rearrangement of lipids from a fluid lamellar phase to a cubic structure in organelles containing membranes enriched with amphiphiles that have nonzero intrinsic curvature, such as phosphatidylethanolamine (PE) and cardiolipin. This study focuses on the oxidation of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), a lipid that natively forms an inverted hexagonal phase at physiological conditions. The oxidized samples contain an approximately 3:2 molar ratio of nonoxidized to oxidized DOPE. Optical microscopy images collected during the hydration of this mixture from a dried film suggest that the system evolves into a coexistence of a stable fluid lamellar phase and transient square lattice structures with unit cell sizes of 500-600 nm. Small-angle X-ray scattering of the same lipid mixture yielded a body-centered Im3m cubic phase with the lattice parameter of 14.04 nm. On average, the effective packing parameter of the oxidized DOPE species was estimated to be 0.657 ± 0.069 (standard deviation). This suggests that the oxidation of PE leads to a group of species with inverted molecular intrinsic curvature. Oxidation can create amphiphilic subpopulations that potently impact the integrity of the membrane, since negative Gaussian curvature intrinsic to cubic phases can enable membrane destabilization processes. PMID:26866900
Picard, G.; Schneider-Henriquez, J.E.; Fendler, J.H. )
1990-01-25
Two-exposure interferometric holograms have been shown to sensitively report ultrasmall-pressure (10 natm)-induced curvature changes in glyceryl monooleate (GMO) bilayer lipid membranes (BLMs). The number of concentric fringes observed, and hence the lateral distance between the plane of the Teflon and the BLM, increased linearly with increasing transmembrane pressure and led to a value of 1.1 {plus minus} 0.05 dyn/cm for the surface tension of the BLM. BLMs with appreciable Plateau-Gibbs borders have been shown to undergo nonuniform deformation; the bilayer portion is distorted less than the surrounding Plateau-Gibbs border upon the application of a transmembrane pressure gradient.
van Duyl, Bianca Y; Meeldijk, Hans; Verkleij, Arie J; Rijkers, Dirk T S; Chupin, Vladimir; de Kruijff, Ben; Killian, J Antoinette
2005-03-22
The aim of this study was to gain insight into the structural consequences of hydrophobic mismatch for membrane proteins in lipid bilayers that contain cholesterol. For this purpose, tryptophan-flanked peptides, designed to mimic transmembrane segments of membrane proteins, were incorporated in model membranes of unsaturated phosphatidylcholine bilayers of varying thickness and containing varying amounts of cholesterol. Analysis of the lipid organization by (31)P NMR and cryo-TEM demonstrated the formation of an isotropic phase, most likely representing a cubic phase, which occurred exclusively in mixtures containing lipids with relatively long acyl chains. Formation of this phase was inhibited by incorporation of lysophosphatidylcholine. These results indicate that the isotropic phase is formed as a consequence of negative hydrophobic mismatch and that its formation is related to a negative membrane curvature. When either peptide or cholesterol was omitted from the mixture, isotropic-phase formation did not occur, not even when the concentrations of these compounds were significantly increased. This suggests that formation of the isotropic phase is the result of a synergistic effect between the peptides and cholesterol. Interestingly, isotropic-phase formation was not observed when the tryptophans in the peptide were replaced by either lysines or histidines. We propose a model for the mechanism of this synergistic effect, in which its dependence on the flanking residues is explained by preferential interactions between cholesterol and tryptophan residues. PMID:15766283
The effect of curvature on the undulation spectrum of Red Blood Cell membranes
NASA Astrophysics Data System (ADS)
Kuriabova, Tatiana; Henle, Mark L.; Levine, Alex J.
2009-03-01
The human red blood cell (RBC) membrane has a composite structure of a fluid lipid bilayer tethered to an elastic 2D spectrin network. The study of the mechanical properties of RBCs is crucial to our understanding of their ability withstand large amplitude deformations during their passage through the microvasculature. The linear mechanical response of this composite membrane can be measured by observing its undulatory dynamics in thermal equilibrium, i.e. microrheology. Previous models of these dynamics postulated an effective surface tension. In this talk, we show that surface tension is not necessary. Rather, the coupling of membrane bending to spectrin network compression by curvature can account for the observed dynamics. We use a simplified theoretical model to describe the undulatory dynamics of RBCs, measured experimentally by the Popescu group.ootnotetextG. Popescu et al. ``Imaging red blood cell dynamics by quantitative phase microscopy, Blood Cells, Molecules, and Diseases, (2008), in print'' Analyzing their data using our model, we observe dramatic changes in RBC membrane elasticity associated with cells' morphological transition from discocytes to echinocyte to spherocyte.
Xu, Peng; Baldridge, Ryan D.; Chi, Richard J.; Burd, Christopher G.
2013-01-01
Vesicle-mediated protein transport between organelles of the secretory and endocytic pathways is strongly influenced by the composition and organization of membrane lipids. In budding yeast, protein transport between the trans-Golgi network (TGN) and early endosome (EE) requires Drs2, a phospholipid translocase in the type IV P-type ATPase family. However, downstream effectors of Drs2 and specific phospholipid substrate requirements for protein transport in this pathway are unknown. Here, we show that the Arf GTPase-activating protein (ArfGAP) Gcs1 is a Drs2 effector that requires a variant of the ArfGAP lipid packing sensor (+ALPS) motif for localization to TGN/EE membranes. Drs2 increases membrane curvature and anionic phospholipid composition of the cytosolic leaflet, both of which are sensed by the +ALPS motif. Using mutant forms of Drs2 and the related protein Dnf1, which alter their ability to recognize phosphatidylserine, we show that translocation of this substrate to the cytosolic leaflet is essential for +ALPS binding and vesicular transport between the EE and the TGN. PMID:24019533
NASA Astrophysics Data System (ADS)
Golushko, I. Yu.; Rochal, S. B.
2016-01-01
Conditions of joint equilibrium and stability are derived for a spherical lipid vesicle and a tubular lipid membrane (TLM) pulled from this vesicle. The obtained equations establish relationships between the geometric and physical characteristics of the system and the external parameters, which have been found to be controllable in recent experiments. In particular, the proposed theory shows that, in addition to the pressure difference between internal and external regions of the system, the variable spontaneous average curvature of the lipid bilayer (forming the TLM) also influences the stability of the lipid tube. The conditions for stability of the cylindrical phase of TLMs after switching off the external force that initially formed the TLM from a vesicle are discussed. The loss of system stability under the action of a small axial force compressing the TLM is considered.
NASA Astrophysics Data System (ADS)
Lowengrub, John; Allard, Jun; Aland, Sebastian
2016-03-01
The formation of membrane vesicles from a larger membrane that occurs during endocytosis and other cell processes is typically orchestrated by curvature-inducing molecules attached to the membrane. Recent reports demonstrate that vesicles can form de novo in a few milliseconds. Membrane dynamics at these scales are strongly influenced by hydrodynamic interactions. To study this problem, we develop new diffuse interface models for the dynamics of inextensible vesicles in a viscous fluid with stiff, curvature-inducing molecules. The model couples the Navier-Stokes equations with membrane-induced bending forces that incorporate concentration-dependent bending stiffness coefficients and spontaneous curvatures, with equations for molecule transport and for a Lagrange multiplier to enforce local inextensibility. Two forms of surface transport equations are considered: Fickian surface diffusion and Cahn-Hilliard surface dynamics, with the former being more appropriate for small molecules and the latter being better for large molecules. The system is solved using adaptive finite element methods in 3D axisymmetric geometries. The results demonstrate that hydrodynamics can indeed enable the rapid formation of a small vesicle attached to the membrane by a narrow neck. When the Fickian model is used, this is a transient state with the steady state being a flat membrane with a uniformly distributed molecule concentration due to diffusion. When the Cahn-Hilliard model is used, molecule concentration gradients are sustained, the neck stabilizes and the system evolves to a steady-state with a small, compact vesicle attached to the membrane. By varying the membrane coverage of molecules in the Cahn-Hilliard model, we find that there is a critical (smallest) neck radius and a critical (fastest) budding time. These critical points are associated with changes in the vesicle morphology from spherical to mushroom-like as the molecule coverage on the membrane is increased.
Pannuzzo, Martina; Raudino, Antonio; Böckmann, Rainer A
2014-07-14
Peptide- or protein-induced curvatures of lipid membranes may be studied in molecular dynamics (MD) simulations. In these, membranes are usually modeled as infinitely extended bilayers by using periodic boundary conditions. However, the enforced periodicity results in an underestimation of the bending power of peptides, unless the patch size is much larger than the induced curvature radii. In this letter, we propose a novel approach to evaluate the bending power of a given distribution and/or density of peptides based on the use of flat open-edged lipid patches. To ensure long-lived metastable structures, the patch rim is stabilized in MD simulations by a local enrichment with short-chain lipids. By combining the theory of continuum elastic media with MD simulations, we prove that open-edged patches evolve from a planar state to a closed vesicle, with a transition rate that strongly depends on the concentration of lipid soluble peptides. For close-to-critical values for the patch size and edge energy, the response to even small changes in peptide concentration adopts a transition-like behavior (buckling instability). The usage of open-edged membrane patches amplifies the bending power of peptides, thereby enabling the analysis of the structural properties of membrane-peptide systems. We applied the presented method to investigate the curvature induced by aggregating β -amyloid peptides, unraveling a strong sensitivity of membrane deformation to the peptide concentration. PMID:25028040
NASA Astrophysics Data System (ADS)
Pannuzzo, Martina; Raudino, Antonio; Böckmann, Rainer A.
2014-07-01
Peptide- or protein-induced curvatures of lipid membranes may be studied in molecular dynamics (MD) simulations. In these, membranes are usually modeled as infinitely extended bilayers by using periodic boundary conditions. However, the enforced periodicity results in an underestimation of the bending power of peptides, unless the patch size is much larger than the induced curvature radii. In this letter, we propose a novel approach to evaluate the bending power of a given distribution and/or density of peptides based on the use of flat open-edged lipid patches. To ensure long-lived metastable structures, the patch rim is stabilized in MD simulations by a local enrichment with short-chain lipids. By combining the theory of continuum elastic media with MD simulations, we prove that open-edged patches evolve from a planar state to a closed vesicle, with a transition rate that strongly depends on the concentration of lipid soluble peptides. For close-to-critical values for the patch size and edge energy, the response to even small changes in peptide concentration adopts a transition-like behavior (buckling instability). The usage of open-edged membrane patches amplifies the bending power of peptides, thereby enabling the analysis of the structural properties of membrane-peptide systems. We applied the presented method to investigate the curvature induced by aggregating β -amyloid peptides, unraveling a strong sensitivity of membrane deformation to the peptide concentration.
Sugiura, Yuuki; Ikeda, Keisuke; Nakano, Minoru
2015-10-27
Aggregation of the amyloid-β (Aβ) protein and the formation of toxic aggregates are the possible pathogenic pathways in Alzheimer's disease. Accumulating evidence suggests that lipid membranes play key roles in protein aggregation, although the intermolecular forces that drive the interactions between Aβ-(1-40) and the membranes vary in different membrane systems. Here, we observed that a high positive curvature of lipid vesicles with diameters of ∼30 nm enhanced the association of Aβ with anionic phosphatidylglycerol membranes in the liquid-crystalline phase and with zwitterionic phosphatidylcholine membranes in the gel phase. The binding modes of Aβ to these membranes differ in terms of the location of the protein on the membrane and of the protein secondary structure. The fibrillation of Aβ was accelerated in the presence of the vesicles and at high protein-to-lipid ratios. Under these conditions, the protein accumulated on the surfaces, as demonstrated by a high (10(7) M(-1)) binding constant. Our findings suggest that packing defects on membranes with high curvatures, such as the intraluminal vesicles in multivesicular bodies and the exosomes, might result in the accumulation of toxic protein aggregates. PMID:26474149
Wu, Tingting; Baumgart, Tobias
2014-11-25
In striated muscles, invaginations from the plasma membrane, termed transverse tubules (T-tubule), function in the excitation-contraction coupling machinery. BIN1 (isoform8) plays a critical role in the biogenesis of T-tubules. BIN1 contains an N-terminal BAR domain to sense and induce membrane curvature, an isoform8-specific polybasic motif (exon10) as the phosphoinositide binding module and a C-terminal Src homology 3 (SH3) domain for the recruitment of downstream proteins such as dynamin 2. Previous studies of N-BAR domains focused on elucidating mechanisms of membrane curvature sensing and generation (MC-S&G). Less is known about how MC-S&G is regulated. We found that the SH3 domain binds to the exon10 motif more strongly compared to the proline-rich domain (PRD) of dynamin 2. Furthermore, we found that the MC-S&G ability of full-length BIN1 is inhibited on membranes lacking PI(4,5)P2. Addition of PI(4,5)P2 in the membrane activates BIN1 to sense and induce membrane curvature. Co-presence of the SH3 domain and exon10 motif leads to the strongest phosphoinositide-mediated control of BIN1 function. Addition of SH3 domain ligand (such as PRD peptides), as well as addition of the water-soluble PI(4,5)P2 analogue, can both enhance the MC-S&G ability of BIN1 on membranes without PI(4,5)P2, indicating that the key to activate BIN1 is to disrupt the exon10-SH3 interaction. The nonsense mutation K436X, found in centronuclear myopathy (CNM) patients, abolishes SH3 domain binding with either exon10 or the PRD motif, resulting in increased membrane deformation capacity. Our results suggest an autoinhibition model for BIN1 that involves a synergistic regulation by membrane composition and protein-protein interactions. PMID:25350771
Miller, Sharon E.; Mathiasen, Signe; Bright, Nicholas A.; Pierre, Fabienne; Kelly, Bernard T.; Kladt, Nikolay; Schauss, Astrid; Merrifield, Christien J.; Stamou, Dimitrios; Höning, Stefan; Owen, David J.
2015-01-01
Summary The size of endocytic clathrin-coated vesicles (CCVs) is remarkably uniform, suggesting that it is optimized to achieve the appropriate levels of cargo and lipid internalization. The three most abundant proteins in mammalian endocytic CCVs are clathrin and the two cargo-selecting, clathrin adaptors, CALM and AP2. Here we demonstrate that depletion of CALM causes a substantial increase in the ratio of “open” clathrin-coated pits (CCPs) to “necked”/“closed” CCVs and a doubling of CCP/CCV diameter, whereas AP2 depletion has opposite effects. Depletion of either adaptor, however, significantly inhibits endocytosis of transferrin and epidermal growth factor. The phenotypic effects of CALM depletion can be rescued by re-expression of wild-type CALM, but not with CALM that lacks a functional N-terminal, membrane-inserting, curvature-sensing/driving amphipathic helix, the existence and properties of which are demonstrated. CALM is thus a major factor in controlling CCV size and maturation and hence in determining the rates of endocytic cargo uptake. PMID:25898166
Takano, Kazunari; Toyooka, Kiminori; Suetsugu, Shiro
2008-01-01
Extended Fer-CIP4 homology (EFC)/FCH-BAR (F-BAR) domains generate and bind to tubular membrane structures of defined diameters that are involved in the formation and fission of endocytotic vesicles. Formin-binding protein 17 (FBP17) and Toca-1 contain EFC/F-BAR domains and bind to neural Wiskott–Aldrich syndrome protein (N-WASP), which links phosphatidylinositol (4,5)-bisphosphate (PIP2) and the Rho family GTPase Cdc42 to the Arp2/3 complex. The N-WASP–WASP-interacting protein (WIP) complex, a predominant form of N-WASP in cells, is known to be activated by Toca-1 and Cdc42. Here, we show that N-WASP–WIP complex-mediated actin polymerization is activated by phosphatidylserine-containing membranes depending on membrane curvature in the presence of Toca-1 or FBP17 and in the absence of Cdc42 and PIP2. Cdc42 further promoted the activation of actin polymerization by N-WASP–WIP. Toca-1 or FBP17 recruited N-WASP–WIP to the membrane. Conserved acidic residues near the SH3 domain of Toca-1 and FBP17 positioned the N-WASP–WIP to be spatially close to the membrane for activation of actin polymerization. Therefore, curvature-dependent actin polymerization is stimulated by spatially appropriate interactions of EFC/F-BAR proteins and the N-WASP–WIP complex with the membrane. PMID:18923421
Kawamoto, Shuhei; Klein, Michael L; Shinoda, Wataru
2015-12-28
The effects of membrane curvature on the free energy barrier for membrane fusion have been investigated using coarse-grained molecular dynamics (CG-MD) simulations, assuming that fusion takes place through a stalk intermediate. Free energy barriers were estimated for stalk formation as well as for fusion pore formation using the guiding potential method. Specifically, the three different geometries of two apposed membranes were considered: vesicle-vesicle, vesicle-planar, and planar-planar membranes. The free energy barriers for the resulting fusion were found to depend importantly on the fusing membrane geometries; the lowest barrier was obtained for vesicular membranes. Further, lipid sorting was observed in fusion of the mixed membranes of dimyristoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine (DOPE). Specifically, DOPE molecules were found to assemble around the stalk to support the highly negative curved membrane surface. A consistent result for lipid sorting was observed when a simple continuum model (CM) was used, where the Helfrich energy and mixing entropy of the lipids were taken into account. However, the CM predicts a much higher free energy barrier than found using CG-MD. This discrepancy originates from the conformational changes of lipids, which were not considered in the CM. The results of the CG-MD simulations reveal that a large conformational change in the lipid takes place around the stalk region, which results in a reduction of free energy barriers along the stalk mechanism of membrane fusion. PMID:26723597
Kawamoto, Shuhei; Shinoda, Wataru; Klein, Michael L.
2015-12-28
The effects of membrane curvature on the free energy barrier for membrane fusion have been investigated using coarse-grained molecular dynamics (CG-MD) simulations, assuming that fusion takes place through a stalk intermediate. Free energy barriers were estimated for stalk formation as well as for fusion pore formation using the guiding potential method. Specifically, the three different geometries of two apposed membranes were considered: vesicle–vesicle, vesicle–planar, and planar–planar membranes. The free energy barriers for the resulting fusion were found to depend importantly on the fusing membrane geometries; the lowest barrier was obtained for vesicular membranes. Further, lipid sorting was observed in fusion of the mixed membranes of dimyristoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine (DOPE). Specifically, DOPE molecules were found to assemble around the stalk to support the highly negative curved membrane surface. A consistent result for lipid sorting was observed when a simple continuum model (CM) was used, where the Helfrich energy and mixing entropy of the lipids were taken into account. However, the CM predicts a much higher free energy barrier than found using CG-MD. This discrepancy originates from the conformational changes of lipids, which were not considered in the CM. The results of the CG-MD simulations reveal that a large conformational change in the lipid takes place around the stalk region, which results in a reduction of free energy barriers along the stalk mechanism of membrane fusion.
2015-01-01
In striated muscles, invaginations from the plasma membrane, termed transverse tubules (T-tubule), function in the excitation–contraction coupling machinery. BIN1 (isoform8) plays a critical role in the biogenesis of T-tubules. BIN1 contains an N-terminal BAR domain to sense and induce membrane curvature, an isoform8-specific polybasic motif (exon10) as the phosphoinositide binding module and a C-terminal Src homology 3 (SH3) domain for the recruitment of downstream proteins such as dynamin 2. Previous studies of N-BAR domains focused on elucidating mechanisms of membrane curvature sensing and generation (MC-S&G). Less is known about how MC-S&G is regulated. We found that the SH3 domain binds to the exon10 motif more strongly compared to the proline-rich domain (PRD) of dynamin 2. Furthermore, we found that the MC-S&G ability of full-length BIN1 is inhibited on membranes lacking PI(4,5)P2. Addition of PI(4,5)P2 in the membrane activates BIN1 to sense and induce membrane curvature. Co-presence of the SH3 domain and exon10 motif leads to the strongest phosphoinositide-mediated control of BIN1 function. Addition of SH3 domain ligand (such as PRD peptides), as well as addition of the water-soluble PI(4,5)P2 analogue, can both enhance the MC-S&G ability of BIN1 on membranes without PI(4,5)P2, indicating that the key to activate BIN1 is to disrupt the exon10–SH3 interaction. The nonsense mutation K436X, found in centronuclear myopathy (CNM) patients, abolishes SH3 domain binding with either exon10 or the PRD motif, resulting in increased membrane deformation capacity. Our results suggest an autoinhibition model for BIN1 that involves a synergistic regulation by membrane composition and protein–protein interactions. PMID:25350771
Yang, L.; Gordon, V.D.; Trinkle, D.R.; Schmidt, N.W.; Davis, M.A.; DeVries, C.; Som, A.; Cronan, J.E., Jr.; Tew, G.N.; Wong, G.C.L.
2009-05-28
Phenylene ethynylenes comprise a prototypical class of synthetic antimicrobial compounds that mimic antimicrobial peptides produced by eukaryotes and have broad-spectrum antimicrobial activity. We show unambiguously that bacterial membrane permeation by these antimicrobials depends on the presence of negative intrinsic curvature lipids, such as phosphatidylethanolamine (PE) lipids, found in high concentrations within bacterial membranes. Plate-killing assays indicate that a PE-knockout mutant strain of Escherichia coli drastically out-survives the wild type against the membrane-active phenylene ethynylene antimicrobials, whereas the opposite is true when challenged with traditional metabolic antibiotics. That the PE deletion is a lethal mutation in normative environments suggests that resistant bacterial strains do not evolve because a lethal mutation is required to gain immunity. PE lipids allow efficient generation of negative curvature required for the circumferential barrel of an induced membrane pore; an inverted hexagonal HII phase, which consists of arrays of water channels, is induced by a small number of antimicrobial molecules. The estimated antimicrobial occupation in these water channels is nonlinear and jumps from {approx}1 to 3 per 4 nm of induced water channel length as the global antimicrobial concentration is increased. By comparing to exactly solvable 1D spin models for magnetic systems, we quantify the cooperativity of these antimicrobials.
2015-01-01
Viral fusion proteins catalyze the merger of the virus envelope and the target cell membrane through multiple steps of protein conformational changes. The fusion peptide domain of these proteins is important for membrane fusion, but how it causes membrane curvature and dehydration is still poorly understood. We now use solid-state NMR spectroscopy to investigate the conformation, topology, and lipid and water interactions of the fusion peptide of the PIV5 virus F protein in three lipid membranes, POPC/POPG, DOPC/DOPG, and DOPE. These membranes allow us to investigate the effects of lipid chain disorder, membrane surface charge, and intrinsic negative curvature on the fusion peptide structure. Chemical shifts and spin diffusion data indicate that the PIV5 fusion peptide is inserted into all three membranes but adopts distinct conformations: it is fully α-helical in the POPC/POPG membrane, adopts a mixed strand/helix conformation in the DOPC/DOPG membrane, and is primarily a β-strand in the DOPE membrane. 31P NMR spectra show that the peptide retains the lamellar structure and hydration of the two anionic membranes. However, it dehydrates the DOPE membrane, destabilizes its inverted hexagonal phase, and creates an isotropic phase that is most likely a cubic phase. The ability of the β-strand conformation of the fusion peptide to generate negative Gaussian curvature and to dehydrate the membrane may be important for the formation of hemifusion intermediates in the membrane fusion pathway. PMID:24428385
MARCKS-ED Peptide as a Curvature and Lipid Sensor
Morton, Leslie A.; Yang, Hengwen; Saludes, Jonel P.; Fiorini, Zeno; Beninson, Lida; Chapman, Edwin R.; Fleshner, Monika; Xue, Ding; Yin, Hang
2012-01-01
Membrane curvature and lipid composition regulate important biological processes within a cell. Currently, several proteins have been reported to sense and/or induce membrane curvatures, e.g. Synaptotagmin-1 and Amphiphysin. However, the large protein scaffold of these curvature sensors limits their applications in complex biological systems. Our interest focuses on identifying and designing peptides that can sense membrane curvature based on established elements observed in natural curvature-sensing proteins. Membrane curvature remodeling also depends on their lipid composition, suggesting strategies to specifically target membrane shape and lipid components simultaneously. We have successfully identified a 25-mer peptide, MARCKS-ED, based on the effector domain sequence of the intracellular membrane protein myristoylated alanine-rich C-kinase substrate that can recognize PS with preferences for highly curved vesicles in a sequence specific manner. These studies further contribute to the understanding of how proteins and peptides sense membrane curvature, as well as provide potential probes for membrane shape and lipid composition. PMID:23075500
Gardner, Jasmine M; Deserno, Markus; Abrams, Cameron F
2016-08-21
We use a combination of coarse-grained molecular dynamics simulations and theoretical modeling to examine three-junctions in mixed lipid bilayer membranes. These junctions are localized defect lines in which three bilayers merge in such a way that each bilayer shares one monolayer with one of the other two bilayers. The resulting local morphology is non-lamellar, resembling the threefold symmetric defect lines in inverse hexagonal phases, but it regularly occurs during membrane fission and fusion events. We realize a system of junctions by setting up a honeycomb lattice, which in its primitive cell contains two hexagons and four three-line junctions, permitting us to study their stability as well as their line tension. We specifically consider the effects of lipid composition and intrinsic curvature in binary mixtures, which contain a fraction of negatively curved lipids in a curvature-neutral background phase. Three-junction stability results from a competition between the junction and an open edge, which arises if one of the three bilayers detaches from the other two. We show that the stable phase is the one with the lower defect line tension. The strong and opposite monolayer curvatures present in junctions and edges enhance the mole fraction of negatively curved lipids in junctions and deplete it in edges. This lipid sorting affects the two line tensions and in turn the relative stability of the two phases. It also leads to a subtle entropic barrier for the transition between junction and edge that is absent in uniform membranes. PMID:27544120
Molecular Modeling of Lipid Membrane Curvature Induction by a Peptide: More than Simply Shape
Sodt, Alexander J.; Pastor, Richard W.
2014-01-01
Molecular dynamics simulations of an amphipathic helix embedded in a lipid bilayer indicate that it will induce substantial positive curvature (e.g., a tube of diameter 20 nm at 16% surface coverage). The induction is twice that of a continuum model prediction that only considers the shape of the inclusion. The discrepancy is explained in terms of the additional presence of specific interactions described only by the molecular model. The conclusion that molecular shape alone is insufficient to quantitatively model curvature is supported by contrasting molecular and continuum models of lipids with large and small headgroups (choline and ethanolamine, respectively), and of the removal of a lipid tail (modeling a lyso-lipid). For the molecular model, curvature propensity is analyzed by computing the derivative of the free energy with respect to bending. The continuum model predicts that the inclusion will soften the bilayer near the headgroup region, an effect that may weaken curvature induction. The all-atom predictions are consistent with experimental observations of the degree of tubulation by amphipathic helices and variation of the free energy of binding to liposomes. PMID:24806928
Curvature-driven pore growth in charged membranes during charge-pulse and voltage-clamp experiments.
Kroeger, Jens H; Vernon, Dan; Grant, Martin
2009-02-01
We find that curvature-driven growth of pores in electrically charged membranes correctly reproduces charge-pulse experiments. Our model, consisting of a Langevin equation for the time dependence of the pore radius coupled to an ordinary differential equation for the number of pores, captures the statistics of the pore population and its effect on the membrane conductance. The calculated pore radius is a linear, and not an exponential, function of time, as observed experimentally. Two other important features of charge-pulse experiments are recovered: pores reseal for low and high voltages but grow irreversibly for intermediate values of the voltage. Our set of coupled ordinary differential equations is equivalent to the partial differential equation used previously to study pore dynamics, but permits the study of longer timescales necessary for the simulations of voltage-clamp experiments. An effective phase diagram for such experiments is obtained. PMID:19186129
Curvature-Driven Pore Growth in Charged Membranes during Charge-Pulse and Voltage-Clamp Experiments
Kroeger, Jens H.; Vernon, Dan; Grant, Martin
2009-01-01
We find that curvature-driven growth of pores in electrically charged membranes correctly reproduces charge-pulse experiments. Our model, consisting of a Langevin equation for the time dependence of the pore radius coupled to an ordinary differential equation for the number of pores, captures the statistics of the pore population and its effect on the membrane conductance. The calculated pore radius is a linear, and not an exponential, function of time, as observed experimentally. Two other important features of charge-pulse experiments are recovered: pores reseal for low and high voltages but grow irreversibly for intermediate values of the voltage. Our set of coupled ordinary differential equations is equivalent to the partial differential equation used previously to study pore dynamics, but permits the study of longer timescales necessary for the simulations of voltage-clamp experiments. An effective phase diagram for such experiments is obtained. PMID:19186129
Khattree, Nidhi; Ritter, Linda M.; Goldberg, Andrew F. X.
2013-01-01
Summary Vertebrate vision requires photon absorption by photoreceptor outer segments (OSs), structurally elaborate membranous organelles derived from non-motile sensory cilia. The structure and function of OSs depends on a precise stacking of hundreds of membranous disks. Each disk is fully (as in rods) or partially (as in cones) bounded by a rim, at which the membrane is distorted into an energetically unfavorable high-curvature bend; however, the mechanism(s) underlying disk rim structure is (are) not established. Here, we demonstrate that the intrinsically disordered cytoplasmic C-terminus of the photoreceptor tetraspanin peripherin-2/rds (P/rds) can directly generate membrane curvature. A P/rds C-terminal domain and a peptide mimetic of an amphipathic helix contained within it each generated curvature in liposomes with a composition similar to that of OS disks and in liposomes generated from native OS lipids. Association of the C-terminal domain with liposomes required conical phospholipids, and was promoted by membrane curvature and anionic surface charge, results suggesting that the P/rds C-terminal amphipathic helix can partition into the cytosolic membrane leaflet to generate curvature by a hydrophobic insertion (wedging) mechanism. This activity was evidenced in full-length P/rds by its induction of small-diameter tubulovesicular membrane foci in cultured cells. In sum, the findings suggest that curvature generation by the P/rds C-terminus contributes to the distinctive structure of OS disk rims, and provide insight into how inherited defects in P/rds can disrupt organelle structure to cause retinal disease. They also raise the possibility that tethered amphipathic helices can function for shaping cellular membranes more generally. PMID:23886945
Dorn, Jonas F; Zhang, Li; Phi, Tan-Trao; Lacroix, Benjamin; Maddox, Paul S; Liu, Jian; Maddox, Amy Shaub
2016-04-15
During cytokinesis, the cell undergoes a dramatic shape change as it divides into two daughter cells. Cell shape changes in cytokinesis are driven by a cortical ring rich in actin filaments and nonmuscle myosin II. The ring closes via actomyosin contraction coupled with actin depolymerization. Of interest, ring closure and hence the furrow ingression are nonconcentric (asymmetric) within the division plane across Metazoa. This nonconcentricity can occur and persist even without preexisting asymmetric cues, such as spindle placement or cellular adhesions. Cell-autonomous asymmetry is not explained by current models. We combined quantitative high-resolution live-cell microscopy with theoretical modeling to explore the mechanistic basis for asymmetric cytokinesis in theCaenorhabditis eleganszygote, with the goal of uncovering basic principles of ring closure. Our theoretical model suggests that feedback among membrane curvature, cytoskeletal alignment, and contractility is responsible for asymmetric cytokinetic furrowing. It also accurately predicts experimental perturbations of conserved ring proteins. The model further suggests that curvature-mediated filament alignment speeds up furrow closure while promoting energy efficiency. Collectively our work underscores the importance of membrane-cytoskeletal anchoring and suggests conserved molecular mechanisms for this activity. PMID:26912796
Dorn, Jonas F.; Zhang, Li; Phi, Tan-Trao; Lacroix, Benjamin; Maddox, Paul S.; Liu, Jian; Maddox, Amy Shaub
2016-01-01
During cytokinesis, the cell undergoes a dramatic shape change as it divides into two daughter cells. Cell shape changes in cytokinesis are driven by a cortical ring rich in actin filaments and nonmuscle myosin II. The ring closes via actomyosin contraction coupled with actin depolymerization. Of interest, ring closure and hence the furrow ingression are nonconcentric (asymmetric) within the division plane across Metazoa. This nonconcentricity can occur and persist even without preexisting asymmetric cues, such as spindle placement or cellular adhesions. Cell-autonomous asymmetry is not explained by current models. We combined quantitative high-resolution live-cell microscopy with theoretical modeling to explore the mechanistic basis for asymmetric cytokinesis in the Caenorhabditis elegans zygote, with the goal of uncovering basic principles of ring closure. Our theoretical model suggests that feedback among membrane curvature, cytoskeletal alignment, and contractility is responsible for asymmetric cytokinetic furrowing. It also accurately predicts experimental perturbations of conserved ring proteins. The model further suggests that curvature-mediated filament alignment speeds up furrow closure while promoting energy efficiency. Collectively our work underscores the importance of membrane–cytoskeletal anchoring and suggests conserved molecular mechanisms for this activity. PMID:26912796
Ogunyankin, Maria O; Huber, Dale L; Sasaki, Darryl Y; Longo, Marjorie L
2013-05-21
This work describes a technique for forming high-density arrays and patterns of membrane-bound proteins through binding to a curvature-organized compositional pattern of metal-chelating lipids (Cu(2+)-DOIDA or Cu(2+)-DSIDA). In this bottom-up approach, the underlying support is an e-beam formed, square lattice pattern of hemispheres. This curvature pattern sorts Cu(2+)-DOIDA to the 200 nm hemispherical lattice sites of a 600 nm × 600 nm unit cell in Ld - Lo phase separated lipid multibilayers. Binding of histidine-tagged green fluorescent protein (His-GFP) creates a high density array of His-GFP-bound pixels localized to the square lattice sites. In comparison, the negative pixel pattern is created by sorting Cu(2+)-DSIDA in Ld - Lβ' phase separated lipid multibilayers to the flat grid between the lattice sites followed by binding to His-GFP. Lattice defects in the His-GFP pattern lead to interesting features such as pattern circularity. We also observe defect-free arrays of His-GFP that demonstrate perfect arrays can be formed by this method suggesting the possibility of using this approach for the localization of various active molecules to form protein, DNA, or optically active molecular arrays. PMID:23642033
Lee, Il-Hyung; Kai, Hiroyuki; Carlson, Lars-Anders; Groves, Jay T; Hurley, James H
2015-12-29
The endosomal sorting complexes required for transport (ESCRT) machinery functions in HIV-1 budding, cytokinesis, multivesicular body biogenesis, and other pathways, in the course of which it interacts with concave membrane necks and bud rims. To test the role of membrane shape in regulating ESCRT assembly, we nanofabricated templates for invaginated supported lipid bilayers. The assembly of the core ESCRT-III subunit CHMP4B/Snf7 is preferentially nucleated in the resulting 100-nm-deep membrane concavities. ESCRT-II and CHMP6 accelerate CHMP4B assembly by increasing the concentration of nucleation seeds. Superresolution imaging was used to visualize CHMP4B/Snf7 concentration in a negatively curved annulus at the rim of the invagination. Although Snf7 assemblies nucleate slowly on flat membranes, outward growth onto the flat membrane is efficiently nucleated at invaginations. The nucleation behavior provides a biophysical explanation for the timing of ESCRT-III recruitment and membrane scission in HIV-1 budding. PMID:26668364
Galic, Milos; Jeong, Sangmoo; Tsai, Feng-Chiao; Joubert, Lydia-Marie; Wu, Yi I.; Hahn, Klaus M.; Cui, Yi; Meyer, Tobias
2012-01-01
Many of the more than 20 mammalian proteins with N-BAR domains1-2 control cell architecture3 and endocytosis4-5 by associating with curved sections of the plasma membrane (PM)6. It is not well understood whether N-BAR proteins are recruited directly by processes that mechanically curve the PM or indirectly by PM-associated adaptor proteins that recruit proteins with N-BAR domains that then induce membrane curvature. Here, we show that externally-induced inward deformation of the PM by cone-shaped nanostructures (Nanocones) and internally-induced inward deformation by contracting actin cables both trigger recruitment of isolated N-BAR domains to the curved PM. Markedly, live-cell imaging in adherent cells showed selective recruitment of full length N-BAR proteins and isolated N-BAR domains to PM sub-regions above Nanocone stripes. Electron microscopy confirmed that N-BAR domains are recruited to local membrane sites curved by Nanocones. We further showed that N-BAR domains are periodically recruited to curved PM sites during local lamellipodia retraction in the front of migrating cells. Recruitment required Myosin II-generated force applied to PM connected actin cables. Together, our study shows that N-BAR domains can be directly recruited to the PM by external push or internal pull forces that locally curve the PM. PMID:22750946
NASA Astrophysics Data System (ADS)
Sun, Yiwei; Davidovitch, Benny; Grason, Gregory M.
2014-03-01
A crystalline membrane with an isolated disclination buckles below a critical thickness. Examples include mechanical models of viral capsids-pentavalent and hexavalent units assembled into triangulated shells-that show a pronounced faceting above a critical size. While buckling from the planar state has been studied previously in coarse-grained simulations, questions remain regarding the organization of structure and mechanics of the buckled state. Specifically, how is elastic stress distributed within the membrane; more precisely - how does this mechanical state evolve from the buckling threshold to the asymptotic limit of vanishing thickness, where the shape is expected to be isometric (conical) nearly everywhere? We employ a combination of numerical and analytic approaches to studying the solutions of the Föppl-von Kármán equations describing the shape of and stress in circular sheets possessing a 5-fold defect. Despite the complexity underlying the solution of these highly nonlinear relations, we search for much simpler set of mechanical principles to quantitatively capture the inhomogeneous concentration of stress and shape deformation throughout the full range of the von Kármán number.
Preferred dialysis fluid for the high-performance membrane.
Tomo, Tadashi
2011-01-01
In the present study, we investigated the effect of hemodialysis (HD) with high-performance membrane filter (HPM-HD) using acetate-free bicarbonate dialysis (AFD) fluid on bioincompatibility as represented by inflammatory markers in patients undergoing maintenance HD therapy and compared it with conventional acetate-containing bicarbonate dialysis (ACD) fluid. A total of 36 maintenance HD patients were registered for study during the 4-month study period (22 males and 14 females, aged 63.5 ± 10.2 years, mean duration of dialysis 12.2 ± 8.6 years, chronic glomerular nephritis in 27 patients, diabetic nephropathy in 6 patients, and nephrosclerosis in 3 patients). These patients were subjected to ACD for the first 2 months followed by AFD fluid for the latter 2 months. Predialysis blood pH and bicarbonate were examined after each of the first and latter 2-month period. Blood variables of C-reactive protein (CRP) and interleukin-6 (IL-6) or fetuin-A were also determined. The filters (membrane surface area, raw material), the conditions of HD (blood flow rate, dialysate flow rate, dialysis time, dry weight) and drug regimen including erythrocyte-simulating agent (drug type, dosage) were unchanged throughout the study. There appeared to be significantly higher levels of predialysis blood pH and bicarbonate in the AFD phase than in the ACD phase. Blood CRP and IL-6 levels were significantly decreased in the AFD group as compared with those seen in the ACD group. From these results, it can be suggested that HPM-HD using AFD fluid contributes to correcting metabolic acidosis and alleviating microinflammation in HD patients. PMID:21865775
Wang, Tuo; Hong, Mei
2015-01-01
A wide variety of membrane proteins induce membrane curvature for function, thus it is important to develop new methods to simultaneously determine membrane curvature and protein binding sites in membranes with multiple curvatures. We introduce solid-state NMR methods based on magnetically oriented bicelles and off-magic-angle spinning (OMAS) to measure membrane curvature and the binding site of proteins in mixed-curvature membranes. We demonstrate these methods on the influenza virus M2 protein, which not only acts as a proton channel but also mediates virus assembly and membrane scission. An M2 peptide encompassing the transmembrane (TM) domain and an amphipathic helix, M2(21-61), was studied and compared with the TM peptide (M2TM). Static 31P NMR spectra of magnetically oriented DMPC/DHPC bicelles exhibit a temperature-independent isotropic chemical shift in the presence of M2(21-61) but not M2TM, indicating that the amphipathic helix confers the peptide with the ability to generate a high-curvature phase. 2D 31P spectra indicate that this high-curvature phase is associated with the DHPC bicelle edges, suggestive of the structure of budding viruses from the host cell. 31P- and 13C-detected 1H relaxation times of the lipids indicate that the majority of M2(21-61) is bound to the high-curvature phase. Using OMAS experiments, we resolved the 31P signals of lipids with identical headgroups based on their distinct chemical shift anisotropies. Based on this resolution, 2D 1H-31P correlation spectra show that the amide protons in M2(21-61) correlate with the DMPC but not the DHPC 31P signal of the bicelle, indicating that a small percentage of M2(21-61) partitions into the planar region of the bicelles. These results show that the M2 amphipathic helix induces high membrane curvature and localizes the protein to this phase, in excellent agreement with the membrane-scission function of the protein. These bicelle-based relaxation and OMAS solid-state NMR techniques are
Khakshoor, Hamid; Eslampoor, Alireza; Rad, Saeed Shokoohi; Vejdani, Amirhossein
2014-01-01
Aims: To determine the clinical efficacy of modified deep anterior lamellar keratoplasty (DALK) for the treatment of advanced-stage keratoconus with steep curvature. Materials and Methods: In this interventional, non-comparative case series, 30 patients with advanced stages of keratoconus and curvature of more than 60 D underwent a modified DALK procedure. In this technique, after big-bubble formation, posterior stromal lamella was cut and removed 5 mm centrally (baring Descemet's membrane completely) with posterior stromal layer remaining peripherally. Results: The study included 30 eyes (30 patients with a mean ± SD age of 25 ± 5.4 years). The follow-up examination was performed for all participants up to 12 months after the surgery. The mean uncorrected visual acuity (UCVA) increased from 20/800 before the surgery to a subsequent 3/10 (P =0.12). Likewise, best spectacle corrected visual acuity (BSCVA) improved, reaching 6/10 postoperatively (former quantity 20/200) (P =0.18). In addition, mean keratometry and keratometric astigmatism managed to achieve considerable improvement, from 58.8 ± 5.4 D to 46.5 ± 2.1 D and 7.8 ± 2.1 to 4.54 ± 1.54 D, respectively (P =0.52). Descemet's membrane wrinkling was not seen in any patient postoperatively. Conclusions: This technique is effective in restoring acceptable vision and corneal regularity in advanced cases of keratoconus with a curvature more than 60 D who are also at risk of Descemet's membrane wrinkling after DALK. Therefore, this procedure could prevent from Descemet membrane wrinkling in such cases. PMID:24817742
Lähdesmäki, Katariina; Ollila, O H Samuli; Koivuniemi, Artturi; Kovanen, Petri T; Hyvönen, Marja T
2010-05-01
Phospholipids are key components of biological membranes and their lipolysis with phospholipase A(2) (PLA(2)) enzymes occurs in different cellular pH environments. Since no studies are available on the effect of pH on PLA(2)-modified phospholipid membranes, we performed 50-ns atomistic molecular dynamics simulations at three different pH conditions (pH 9.0, 7.5, and 5.5) using a fully PLA(2)-hydrolyzed phosphatidylcholine (PC) bilayer which consists solely of lysophosphatidylcholine and free fatty acid molecules. We found that a decrease in pH results in lateral squeezing of the membrane, i.e. in decreased surface area per headgroup. Thus, at the decreased pH, the lipid hydrocarbon chains had larger S(CD) order parameter values, and also enhanced membrane thickness, as seen in the electron density profiles across the membrane. From the lateral pressure profiles, we found that the values of spontaneous curvature of the two opposing monolayers became negative when the pH was decreased. At low pH, protonation of the free fatty acid headgroups reduces their mutual repulsion and accounts for the pH dependence of all the above-mentioned properties. The altered structural characteristics may significantly affect the overall surface properties of biomembranes in cellular vesicles, lipid droplets, and plasma lipoproteins, play an important role in membrane fission and fusion, and modify interactions between membrane lipids and the proteins embedded within them. PMID:20132791
Shi, Junli; Xia, Yonggao; Yuan, Zhizhang; Hu, Huasheng; Li, Xianfeng; Zhang, Huamin; Liu, Zhaoping
2015-01-01
Separators with high reliability and security are in urgent demand for the advancement of high performance lithium ion batteries. Here, we present a new and practical porous membrane with three-dimension (3D) heat-resistant skeleton and high curvature pore structure as a promising separator candidate to facilitate advances in battery safety and performances beyond those obtained from the conventional separators. The unique material properties combining with the well-developed structural characteristics enable the 3D porous skeleton to own several favorable properties, including superior thermal stability, good wettability with liquid electrolyte, high ion conductivity and internal short-circuit protection function, etc. which give rise to acceptable battery performances. Considering the simply and cost-effective preparation process, the porous membrane is deemed to be an interesting direction for the future lithium ion battery separator. PMID:25653104
Shi, Junli; Xia, Yonggao; Yuan, Zhizhang; Hu, Huasheng; Li, Xianfeng; Zhang, Huamin; Liu, Zhaoping
2015-01-01
Separators with high reliability and security are in urgent demand for the advancement of high performance lithium ion batteries. Here, we present a new and practical porous membrane with three-dimension (3D) heat-resistant skeleton and high curvature pore structure as a promising separator candidate to facilitate advances in battery safety and performances beyond those obtained from the conventional separators. The unique material properties combining with the well-developed structural characteristics enable the 3D porous skeleton to own several favorable properties, including superior thermal stability, good wettability with liquid electrolyte, high ion conductivity and internal short-circuit protection function, etc. which give rise to acceptable battery performances. Considering the simply and cost-effective preparation process, the porous membrane is deemed to be an interesting direction for the future lithium ion battery separator. PMID:25653104
Murayama, Tomo; Pujals, Sílvia; Hirose, Hisaaki; Nakase, Ikuhiko; Futaki, Shiroh
2016-11-01
The N-terminal amphipathic helical segment of adenovirus internal protein VI (AdVpVI) plays a critical role in viral infection. Here, we report that the peptide segment corresponding to AdVpVI (positions 33-55) can induce positive membrane curvature together with membrane perturbation. The enhanced perturbation ability of the peptide was observed for membranes containing negatively charged phospholipids. Based on the liposome leakage assay, substitution of leucine at position 40 to other aliphatic (isoleucine) and aromatic (phenylalanine and tryptophan) residues yielded a similar degree of membrane perturbation by the peptides, which was considerably diminished by the substitution to glutamine. Further studies using the wild-type AdVpVI (33-55) (WT) and phenylalanine-substituted peptides (L40F) demonstrated that both peptides have positive membrane-curvature-inducing ability. These peptides showed higher binding affinity to 50-nm large unilamellar vesicles (LUVs) than to 200-nm LUVs. However, no enhanced perturbation by these peptides was observed for 50-nm LUVs compared to 200-nm LUVs, suggesting that both the original membrane curvature and the additional strain due to peptide insertion affect the membrane perturbation ability of these peptides. In the case of L40F, this peptide rather had a lower membrane perturbation ability for 50-nm LUVs than for 200-nm LUVs, which can be attributed to possible shallower binding of L40F on membranes. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 430-439, 2016. PMID:27271816
Galic, Milos; Tsai, Feng-Chiao; Collins, Sean R; Matis, Maja; Bandara, Samuel; Meyer, Tobias
2014-01-01
In the vertebrate central nervous system, exploratory filopodia transiently form on dendritic branches to sample the neuronal environment and initiate new trans-neuronal contacts. While much is known about the molecules that control filopodia extension and subsequent maturation into functional synapses, the mechanisms that regulate initiation of these dynamic, actin-rich structures have remained elusive. Here, we find that filopodia initiation is suppressed by recruitment of ArhGAP44 to actin-patches that seed filopodia. Recruitment is mediated by binding of a membrane curvature-sensing ArhGAP44 N-BAR domain to plasma membrane sections that were deformed inward by acto-myosin mediated contractile forces. A GAP domain in ArhGAP44 triggers local Rac-GTP hydrolysis, thus reducing actin polymerization required for filopodia formation. Additionally, ArhGAP44 expression increases during neuronal development, concurrent with a decrease in the rate of filopodia formation. Together, our data reveals a local auto-regulatory mechanism that limits initiation of filopodia via protein recruitment to nanoscale membrane deformations. DOI: http://dx.doi.org/10.7554/eLife.03116.001 PMID:25498153
Clancy, Eileen K.; Barry, Chris; Ciechonska, Marta; Duncan, Roy
2010-02-05
The reovirus fusion-associated small transmembrane (FAST) proteins evolved to induce cell-cell, rather than virus-cell, membrane fusion. It is unclear whether the FAST protein fusion reaction proceeds in the same manner as the enveloped virus fusion proteins. We now show that fluorescence-based cell-cell and cell-RBC hemifusion assays are unsuited for detecting lipid mixing in the absence of content mixing during FAST protein-mediated membrane fusion. Furthermore, membrane curvature agents that inhibit hemifusion or promote pore formation mediated by influenza hemagglutinin had no effect on p14-induced cell-cell fusion, even under conditions of limiting p14 concentrations. Standard assays used to detect fusion intermediates induced by enveloped virus fusion proteins are therefore not applicable to the FAST proteins. These results suggest the possibility that the nature of the fusion intermediates or the mechanisms used to transit through the various stages of the fusion reaction may differ between these distinct classes of viral fusogens.
Jespersen, Henrik; Andersen, Jonas H; Ditzel, Henrik J; Mouritsen, Ole G
2012-01-01
Molecular shape and its impact on bilayer curvature stress are powerful concepts for describing the effects of lipids and fatty acids on fundamental membrane properties, such as passive permeability and derived properties like drug transport across liposomal membranes. We illustrate these relationships by studying the effects of fatty acids and lysolipids on the permeation of a potent anti-cancer drug, doxorubicin, across the bilayer of a liposome in which the drug is encapsulated. Using a simple fluorescence assay, we have systematically studied the passive permeation of doxorubicin across liposomal membranes in different lipid phases: the solid-ordered phase (DPPC bilayers), the liquid-disordered phase (POPC lipid bilayers), and the liquid-ordered phase induced by high levels of cholesterol (DOPC + cholesterol lipid bilayers). The effect of different free fatty acids (FA) and lysolipids (LL), separately and in combination, on permeability was assessed to elucidate the possible mechanism of phospholipase A(2)-triggered release in cancer tissue of liposomal doxorubicin formulations. In all cases, FAs applied separately lead to significant enhancement of permeability, most pronounced in liquid-disordered bilayers and less pronounced in solid and solid-ordered bilayers. LLs applied separately had only a marginal effect on permeability. FA and LL applied in combination lead to a synergistic enhancement of permeability in solid bilayers, whereas in liquid-disordered bilayers, the combined effect suppressed the otherwise strong permeability enhancement due to the FAs. PMID:21839138
Soubias, Olivier; Teague, Walter E.; Hines, Kirk G.; Gawrisch, Klaus
2014-01-01
The human genome encodes about 800 different G protein-coupled receptors (GPCR). They are key molecules in signal transduction pathways that transmit signals of a variety of ligands such as hormones and neurotransmitters to the cell interior. Upon ligand binding, the receptors undergo structural transitions that either enhance or inhibit transmission of a specific signal to the cell interior. Here we discuss results which indicate that transmission of such signals can be strongly modulated by the composition of the lipid matrix into which GPCR are imbedded. Experimental results have been obtained on rhodopsin, a prototype GPCR whose structure and function is representative for the great majority of GPCR in humans. The data shed light on the importance of curvature elastic stress in the lipid domain for function of GPCR. PMID:25447139
NASA Astrophysics Data System (ADS)
Noguchi, Hiroshi
2016-05-01
The assembly of curved protein rods on fluid membranes is studied using implicit-solvent meshless membrane simulations. As the rod curvature increases, the rods on a membrane tube assemble along the azimuthal direction first and subsequently along the longitudinal direction. Here, we show that both transition curvatures decrease with increasing rod stiffness. For comparison, curvature-inducing isotropic inclusions are also simulated. When the isotropic inclusions have the same bending rigidity as the other membrane regions, the inclusions are uniformly distributed on the membrane tubes and vesicles even for large spontaneous curvature of the inclusions. However, the isotropic inclusions with much larger bending rigidity induce shape deformation and are concentrated on the region of a preferred curvature. For high rod density, high rod stiffness, and/or low line tension of the membrane edge, the rod assembly induces vesicle rupture, resulting in the formation of a high-genus vesicle. A gradual change in the curvature suppresses this rupture. Hence, large stress, compared to the edge tension, induced by the rod assembly is the key factor determining rupture. For rod curvature with the opposite sign to the vesicle curvature, membrane rupture induces inversion of the membrane, leading to division into multiple vesicles as well as formation of a high-genus vesicle.
Boumann, Henry A.; Gubbens, Jacob; Koorengevel, Martijn C.; Oh, Chan-Seok; Martin, Charles E.; Heck, Albert J.R.; Patton-Vogt, Jana; Henry, Susan A.; de Kruijff, Ben; de Kroon, Anton I.P.M.
2006-01-01
To study the consequences of depleting the major membrane phospholipid phosphatidylcholine (PC), exponentially growing cells of a yeast cho2opi3 double deletion mutant were transferred from medium containing choline to choline-free medium. Cell growth did not cease until the PC level had dropped below 2% of total phospholipids after four to five generations. Increasing contents of phosphatidylethanolamine (PE) and phosphatidylinositol made up for the loss of PC. During PC depletion, the remaining PC was subject to acyl chain remodeling with monounsaturated species replacing diunsaturated species, as shown by mass spectrometry. The remodeling of PC did not require turnover by the SPO14-encoded phospholipase D. The changes in the PC species profile were found to reflect an overall shift in the cellular acyl chain composition that exhibited a 40% increase in the ratio of C16 over C18 acyl chains, and a 10% increase in the degree of saturation. The shift was stronger in the phospholipid than in the neutral lipid fraction and strongest in the species profile of PE. The shortening and increased saturation of the PE acyl chains were shown to decrease the nonbilayer propensity of PE. The results point to a regulatory mechanism in yeast that maintains intrinsic membrane curvature in an optimal range. PMID:16339082
Boumann, Henry A; Gubbens, Jacob; Koorengevel, Martijn C; Oh, Chan-Seok; Martin, Charles E; Heck, Albert J R; Patton-Vogt, Jana; Henry, Susan A; de Kruijff, Ben; de Kroon, Anton I P M
2006-02-01
To study the consequences of depleting the major membrane phospholipid phosphatidylcholine (PC), exponentially growing cells of a yeast cho2opi3 double deletion mutant were transferred from medium containing choline to choline-free medium. Cell growth did not cease until the PC level had dropped below 2% of total phospholipids after four to five generations. Increasing contents of phosphatidylethanolamine (PE) and phosphatidylinositol made up for the loss of PC. During PC depletion, the remaining PC was subject to acyl chain remodeling with monounsaturated species replacing diunsaturated species, as shown by mass spectrometry. The remodeling of PC did not require turnover by the SPO14-encoded phospholipase D. The changes in the PC species profile were found to reflect an overall shift in the cellular acyl chain composition that exhibited a 40% increase in the ratio of C16 over C18 acyl chains, and a 10% increase in the degree of saturation. The shift was stronger in the phospholipid than in the neutral lipid fraction and strongest in the species profile of PE. The shortening and increased saturation of the PE acyl chains were shown to decrease the nonbilayer propensity of PE. The results point to a regulatory mechanism in yeast that maintains intrinsic membrane curvature in an optimal range. PMID:16339082
Siegel, D. P.; Kozlov, M. M.
2004-01-01
The energy of intermediates in fusion of phospholipid bilayers is sensitive to \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}},\\end{equation*}\\end{document} the saddle splay (Gaussian curvature) elastic modulus of the lipid monolayers. The value \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}}\\end{equation*}\\end{document} is also important in understanding the stability of inverted cubic (QII) and rhombohedral (R) phases relative to the lamellar (Lα) and inverted hexagonal (HII) phases in phospholipids. However, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}}\\end{equation*}\\end{document} cannot be measured directly. It was previously measured by observing changes in QII phase lattice dimensions as a function of water content. Here we use observations of the phase behavior of N-mono-methylated dioleoylphosphatidylethanolamine (DOPE-Me) to determine \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}}.\\end{equation*}\\end{document} At the temperature of the Lα/QII phase transition, TQ, the partial energies of the two phases are equal, and we can express \\documentclass[12pt
Curvature Sensing by a Viral Scission Protein.
Martyna, Agnieszka; Gómez-Llobregat, Jordi; Lindén, Martin; Rossman, Jeremy S
2016-06-28
Membrane scission is the final step in all budding processes wherein a membrane neck is sufficiently constricted so as to allow for fission and the release of the budded particle. For influenza viruses, membrane scission is mediated by an amphipathic helix (AH) domain in the viral M2 protein. While it is known that the M2AH alters membrane curvature, it is not known how the protein is localized to the center neck of budding virions where it would be able to cause membrane scission. Here, we use molecular dynamics simulations on buckled lipid bilayers to show that the M2AH senses membrane curvature and preferentially localizes to regions of high membrane curvature, comparable to that seen at the center neck of budding influenza viruses. These results were then validated using in vitro binding assays to show that the M2AH senses membrane curvature by detecting lipid packing defects in the membrane. Our results show that the M2AH senses membrane curvature and suggest that the AH domain may localize the protein at the viral neck where it can then mediate membrane scission and the release of budding viruses. PMID:27299375
Preferred conformation of endomorphin-1 in aqueous and membrane-mimetic environments.
Fiori, S; Renner, C; Cramer, J; Pegoraro, S; Moroder, L
1999-08-01
The newly discovered endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2) are potent opioid peptides with the highest affinity and selectivity for the mu receptor among all known endogenous ligands. To investigate a possible correlation between these biological properties and the conformational preferences of the small peptides, a comparative structural analysis was performed of endomorphin-1 in aqueous buffer and in membrane-mimicking SDS and AOT normal and reverse micelles by the use of CD, FT-IR, fluorescence and(1)H-NMR spectroscopy. It is well established for opioid peptides that, independently of the receptor selectivity, the Tyr1 residue plays the role of the primary pharmacophore and that the orientation of the second aromatic pharmacophore relative to the tyrosine side-chain dictates the mu or delta-receptor selectivity. By varying the environment of endomorphin-1 from water to the amphipathic SDS micelles and even more efficiently to the AOT reverse micelles, the display of the aromatic side-chains changes from an interaction of the Tyr1 and Phe4 residues to a switch of the Trp3 indole group into close contact with the phenolic moiety to prevent this type of interaction and to force an orientation of the Phe4 side-chain into the opposite direction. This conformational switch is accompanied by a stabilization of the cis -Pro2 isomer and the resulting spatial array of the pharmacophoric groups correlate well with the structural model of mu receptor-bound opioid peptides. The results indicate that AOT reverse micelles with a woof 10, where almost exclusively ordered water is secluded in the cavity, constitute with their electrostatic and hydrophobic potential an excellent mimetic of amphipathic surfaces as present on lipid bilayers and on ligand-recognition and ligand-binding sites of proteins. PMID:10438613
Campanacci, Valérie; Bishop, Russell E.; Blangy, Stéphanie; Tegoni, Mariella; Cambillau, Christian
2016-01-01
Lipocalins, a widespread multifunctional family of small proteins (15–25 kDa) have been first described in eukaryotes and more recently in Gram-negative bacteria. Bacterial lipocalins belonging to class I are outer membrane lipoproteins, among which Blc from E. coli is the better studied. Blc is expressed under conditions of starvation and high osmolarity, conditions known to exert stress on the cell envelope. The structure of Blc that we have previously solved (V. Campanacci, D. Nurizzo, S. Spinelli, C. Valencia, M. Tegoni, C. Cambillau, FEBS Lett. 562 (2004) 183–188.) suggested its possible role in binding fatty acids or phospholipids. Both physiological and structural data on Blc, therefore, point to a role in storage or transport of lipids necessary for membrane maintenance. In order to further document this hypothesis for Blc function, we have performed binding studies using fluorescence quenching experiments. Our results indicate that dimeric Blc binds fatty acids and phospholipids in a micromolar Kd range. The crystal structure of Blc with vaccenic acid, an unsaturated C18 fatty acid, reveals that the binding site spans across the Blc dimer, opposite to its membrane anchored face. An exposed unfilled pocket seemingly suited to bind a polar group attached to the fatty acid prompted us to investigate lyso-phospholipids, which were found to bind in a nanomolar Kd range. We discuss these findings in terms of a potential role for Blc in the metabolism of lysophospholipids generated in the bacterial outer membrane. PMID:16920109
Curvature constraints from the causal entropic principle
Bozek, Brandon; Albrecht, Andreas; Phillips, Daniel
2009-07-15
Current cosmological observations indicate a preference for a cosmological constant that is drastically smaller than what can be explained by conventional particle physics. The causal entropic principle (Bousso et al.) provides an alternative approach to anthropic attempts to predict our observed value of the cosmological constant by calculating the entropy created within a causal diamond. We have extended this work to use the causal entropic principle to predict the preferred curvature within the 'multiverse'. We have found that values larger than {rho}{sub k}=40{rho}{sub m} are disfavored by more than 99.99% peak value at {rho}{sub {lambda}}=7.9x10{sup -123} and {rho}{sub k}=4.3{rho}{sub m} for open universes. For universes that allow only positive curvature or both positive and negative curvature, we find a correlation between curvature and dark energy that leads to an extended region of preferred values. Our universe is found to be disfavored to an extent depending on the priors on curvature. We also provide a comparison to previous anthropic constraints on open universes and discuss future directions for this work.
Nath, Sangeeta; Dancourt, Julia; Shteyn, Vladimir; Puente, Gabriella; Fong, Wendy M.; Nag, Shanta; Bewersdorf, Joerg; Yamamoto, Ai; Antonny, Bruno; Melia., Thomas J.
2014-01-01
The protein biochemistry supporting autophagosome growth on the cup-like isolation membrane is likely different from the biochemistry on the closed and maturing autophagosome. Thus, the highly curved rim of the cup may serve as a functionally-required surface for transiently-associated components of the early-acting autophagic machinery. Here we demonstrate that the E2-like enzyme, Atg3, facilitates LC3/GABARAPlipidation only on membranes exhibiting local lipid-packing defects. This activity requires an amino-terminal amphipathic helix similar to motifs found on proteins targeting highly curved intracellular membranes. By tuning the hydrophobicity of this motif, we can promote or inhibit lipidation in vitro and in rescue experiments in Atg3 knockout cells, implying a physiologic role for this stress detection. The need for extensive lipid-packing defects suggests that Atg3 is designed to work at highly-curved membranes perhaps including the limiting edge of the growing phagophore. PMID:24747438
Spatial curvature, spacetime curvature, and gravity
NASA Astrophysics Data System (ADS)
Price, Richard H.
2016-08-01
The belief that curved spacetime gravity cannot be simply and correctly presented results in such misleading presentations as elastic two-dimensional sheets deformed as they support heavy objects. This article attempts to show that the conceptual basis of curved spacetime gravity can be simply and correctly presented, and that the spatial curvature of a deformed elastic sheet is very different from the spacetime curvature underlying gravity. This article introduces the idea of a "splittable" spacetime that has spatial curvature, but is missing most of the manifestations of gravity. A section in which no mathematics is used is directed at students who have studied no more than introductory physics. A separate section, for students who have taken only an introductory course in general relativity, gives mathematical arguments centering on splittable spacetimes.
Lipids, curvature, and nano-medicine*
Mouritsen, Ole G
2011-01-01
The physical properties of the lamellar lipid-bilayer component of biological membranes are controlled by a host of thermodynamic forces leading to overall tensionless bilayers with a conspicuous lateral pressure profile and build-in curvature-stress instabilities that may be released locally or globally in terms of morphological changes. In particular, the average molecular shape and the propensity of the different lipid and protein species for forming non-lamellar and curved structures are a source of structural transitions and control of biological function. The effects of different lipids, sterols, and proteins on membrane structure are discussed and it is shown how one can take advantage of the curvature-stress modulations brought about by specific molecular agents, such as fatty acids, lysolipids, and other amphiphilic solutes, to construct intelligent drug-delivery systems that function by enzymatic triggering via curvature. Practical applications: The simple concept of lipid molecular shape and how it impacts on the structure of lipid aggregates, in particular the curvature and curvature stress in lipid bilayers and liposomes, can be exploited to construct liposome-based drug-delivery systems, e.g., for use as nano-medicine in cancer therapy. Non-lamellar-forming lysolipids and fatty acids, some of which may be designed to be prodrugs, can be created by phospholipase action in diseased tissues thereby providing for targeted drug release and proliferation of molecular entities with conical shape that break down the permeability barrier of the target cells and may hence enhance efficacy. PMID:22164124
Curvature of the penis is an abnormal bend in the penis that occurs during erection. It is also called Peyronie's disease. ... tissue develops in the deep tissues of the penis. The cause of this fibrous tissue is often ...
Wang, Wangchen; Yang, Lin; Huang, Huey W.
2007-01-01
Recent experiments suggested that cholesterol and other lipid components of high negative spontaneous curvature facilitate membrane fusion. This is taken as evidence supporting the stalk-pore model of membrane fusion in which the lipid bilayers go through intermediate structures of high curvature. How do the high-curvature lipid components lower the free energy of the curved structure? Do the high-curvature lipid components modify the average spontaneous curvature of the relevant monolayer, thereby facilitate its bending, or do the lipid components redistribute in the curved structure so as to lower the free energy? This question is fundamental to the curvature elastic energy for lipid mixtures. Here we investigate the lipid distribution in a monolayer of a binary lipid mixture before and after bending, or more precisely in the lamellar, hexagonal, and distorted hexagonal phases. The lipid mixture is composed of 2:1 ratio of brominated di18:0PC and cholesterol. Using a newly developed procedure for the multiwavelength anomalous diffraction method, we are able to isolate the bromine distribution and reconstruct the electron density distribution of the lipid mixture in the three phases. We found that the lipid distribution is homogenous and uniform in the lamellar and hexagonal phases. But in the distorted hexagonal phase, the lipid monolayer has nonuniform curvature, and cholesterol almost entirely concentrates in the high curvature region. This finding demonstrates that the association energies between lipid molecules vary with the curvature of membrane. Thus, lipid components in a mixture may redistribute under conditions of nonuniform curvature, such as in the stalk structure. In such cases, the spontaneous curvature depends on the local lipid composition and the free energy minimum is determined by lipid distribution as well as curvature. PMID:17259270
Hybrid curvature and modal wavefront sensor
NASA Astrophysics Data System (ADS)
Dong, Shihao; Haist, Tobias; Dietrich, Tom; Osten, Wolfgang
2014-09-01
The crosstalk effect considerably limits the capability of holography-based modal wavefront sensing (HMWS) when measuring wavefronts with large aberrations. In this contribution, we introduce a curvature-based measurement technique into HMWS to extend the dynamic range and the sensitivity of HMWS via a compact holographic design. If the input aberrations are large, the dominating aberration modes are first detected via curvature sensing and compensated using a wavefront correcting device, e.g. a membrane mirror. The system then switches to HMWS to obtain better sensitivity and accuracy with reduced aberrations. Different approaches for the reconstruction of the wavefront have been tested and extensive simulations for different aberrations have been analyzed.
NASA Astrophysics Data System (ADS)
Wasnik, Vaibhav; Wingreen, Ned; Mukhopadhyay, Ranjan
2012-02-01
Recent experiments suggest that in the bacterium, B. subtilis, the cue for the localization of small sporulation protein, SpoVM, that plays a central role in spore coat formation, is curvature of the bacterial plasma membrane. This curvature-dependent localization is puzzling given the orders of magnitude difference in lengthscale of an individual protein and radius of curvature of the membrane. Here we develop a minimal model to study the relationship between curvature-dependent membrane absorption of SpoVM and clustering of membrane-associated SpoVM and compare our results with experiments.
Spontaneous curvature of phosphatidic acid and lysophosphatidic acid.
Kooijman, Edgar E; Chupin, Vladimir; Fuller, Nola L; Kozlov, Michael M; de Kruijff, Ben; Burger, Koert N J; Rand, Peter R
2005-02-15
The formation of phosphatidic acid (PA) from lysophosphatidic acid (LPA), diacylglycerol, or phosphatidylcholine plays a key role in the regulation of intracellular membrane fission events, but the underlying molecular mechanism has not been resolved. A likely possibility is that PA affects local membrane curvature facilitating membrane bending and fission. To examine this possibility, we determined the spontaneous radius of curvature (R(0p)) of PA and LPA, carrying oleoyl fatty acids, using well-established X-ray diffraction methods. We found that, under physiological conditions of pH and salt concentration (pH 7.0, 150 mM NaCl), the R(0p) values of PA and LPA were -46 A and +20 A, respectively. Thus PA has considerable negative spontaneous curvature while LPA has the most positive spontaneous curvature of any membrane lipid measured to date. The further addition of Ca(2+) did not significantly affect lipid spontaneous curvature; however, omitting NaCl from the hydration buffer greatly reduced the spontaneous curvature of PA, turning it into a cylindrically shaped lipid molecule (R(0p) of -1.3 x 10(2) A). Our quantitative data on the spontaneous radius of curvature of PA and LPA at a physiological pH and salt concentration will be instrumental in developing future models of biomembrane fission. PMID:15697235
Curvature calculations with GEOCALC
NASA Astrophysics Data System (ADS)
Moussiaux, A.; Tombal, Ph.
1987-04-01
A new method for calculating the curvature tensor has been recently proposed by D. Hestenes. This method is a particular application of geometric calculus, which has been implemented in an algebraic programming language on the form of a package called GEOCALC. We show how to apply this package to the Schwarzchild case and we discuss the different results.
Curvature calculations with GEOCALC
Moussiaux, A.; Tombal, P.
1987-04-01
A new method for calculating the curvature tensor has been recently proposed by D. Hestenes. This method is a particular application of geometric calculus, which has been implemented in an algebraic programming language on the form of a package called GEOCALC. They show how to apply this package to the Schwarzchild case and they discuss the different results.
Improving the Sensitivity of Astronomical Curvature Wavefront Sensor Using Dual-Stroke Curvature
NASA Astrophysics Data System (ADS)
Guyon, Olivier; Blain, Celia; Takami, Hideki; Hayano, Yutaka; Hattori, Masayuki; Watanabe, Makoto
2008-06-01
Curvature wavefront sensors measure wavefront phase aberration by acquiring two intensity images on either side of the pupil plane. Low-order adaptive optics (AO) systems using curvature wavefront sensing (CWFS) have proved to be highly efficient for astronomical applications: they are more sensitive, use fewer detector elements, and achieve, for the same number of actuators, higher Strehl ratios than AO systems using more traditional Shack-Hartmann wavefront sensors. In higher-order systems, however, curvature wavefront sensors lose sensitivity to low spatial frequencies wavefront aberrations. This effect, often described as "noise propagation," limits the usefulness of curvature wavefront sensing for high-order AO systems and/or large telescopes. In this paper, we first explain how this noise propagation effect occurs and then show that this limitation can be overcome by acquiring four defocused images of the pupil instead of two. This solution can be implemented without significant technology development and can run with a simple linear wavefront reconstruction algorithm at >kHz speed. We have successfully demonstrated in the laboratory that the four conjugation planes can be sequentially obtained at >kHz speed using a speaker-vibrating membrane assembly commonly used in current curvature AO systems. Closed loop simulations show that implementing this scheme is equivalent to making the guide star 1 to 1.5 magnitude brighter for the configuration tested (188 actuator elements on 8-m telescope). Higher sensitivity gains are expected on curvature systems with higher number of actuators.
Surface precision of optical membranes with curvature.
Marker, D; Jenkins, C
1997-11-24
Space-based inflatable technology is of current interest to NASA and DOD, and in particular to the Air Force and Phillips Laboratory. Potentially large gains in lowering launch costs, through reductions in structure mass and volume, are driving this activity. Diverse groups are researching and developing this technology for radio and radar antennae, optical telescopes, and solar power and propulsion applications. Regardless of the use, one common requirement for successful application is the accuracy of the inflated surface shape. The work reported here concerns the shape control of an inflated thin circular disk through use of a nonlinear finite element analysis. First, a review of the important associated Hencky problem is given. Then we discuss a shape modification, achieved through enforced boundary displacements, which resulted in moving the inflated shape towards a desired parabolic profile. Minimization of the figure error is discussed and conclusions are drawn. PMID:19377552
de Jesus, Armando J.; Espinoza, Arianna; Yin, Hang
2014-01-01
Curved membranes are a common and important attribute in cells. Protein and peptide curvature sensors are known to activate signaling pathways, initiate vesicle budding, trigger membrane fusion, and facilitate molecular transport across cell membranes. Nonetheless, there is little understanding how these proteins and peptides achieve preferential binding of different membrane curvatures. The current study is to elucidate specific factors required for curvature sensing. As a model system, we employed a recently identified peptide curvature sensor, MARCKS-ED, derived from the effector domain of the myristoylated alanine-rich C-kinase substrate protein, for these biophysical investigations. An atomistic molecular dynamics (MD) simulation suggested an important role played by the insertion of the Phe residues within MARCKS-ED. To test these observations from our computational simulations, we performed electron paramagnetic resonance (EPR) studies to determine the insertion depth of MARCKS-ED into differently curved membrane bilayers. Next, studies with varied lipid compositions revealed their influence on curvature sensing by MARCKS-ED, suggesting contributions from membrane fluidity, rigidity, as well as various lipid structures. Finally, we demonstrated that the curvature sensing by MARCKS-ED is configuration independent. In summary, our studies have shed further light to the understanding of how MARCKS-ED differentiates between membrane curvatures, which may be generally applicable to protein curvature sensing behavior. PMID:25195712
Forman curvature for complex networks
NASA Astrophysics Data System (ADS)
Sreejith, R. P.; Mohanraj, Karthikeyan; Jost, Jürgen; Saucan, Emil; Samal, Areejit
2016-06-01
We adapt Forman’s discretization of Ricci curvature to the case of undirected networks, both weighted and unweighted, and investigate the measure in a variety of model and real-world networks. We find that most nodes and edges in model and real networks have a negative curvature. Furthermore, the distribution of Forman curvature of nodes and edges is narrow in random and small-world networks, while the distribution is broad in scale-free and real-world networks. In most networks, Forman curvature is found to display significant negative correlation with degree and centrality measures. However, Forman curvature is uncorrelated with clustering coefficient in most networks. Importantly, we find that both model and real networks are vulnerable to targeted deletion of nodes with highly negative Forman curvature. Our results suggest that Forman curvature can be employed to gain novel insights on the organization of complex networks.
Constant mean curvature foliations in cosmological spacetimes.
NASA Astrophysics Data System (ADS)
Rendall, A. D.
1996-11-01
Foliations by constant mean curvature hypersurfaces provide a possibility of defining a preferred time coordinate in general relativity. In the following various conjectures are made about the existence of foliations of this kind in spacetimes satisfying the strong energy condition and possessing compact Cauchy hypersurfaces. Recent progress on proving these conjectures under supplementary assumptions is reviewed. The method of proof used is explained and the prospects for generalizing it discussed. The relations of these questions to cosmic censorship and the closed universe recollapse conjecture are pointed out.
Bacterial cell curvature through mechanical control of cell growth
Cabeen, Matthew T; Charbon, Godefroid; Vollmer, Waldemar; Born, Petra; Ausmees, Nora; Weibel, Douglas B; Jacobs-Wagner, Christine
2009-01-01
The cytoskeleton is a key regulator of cell morphogenesis. Crescentin, a bacterial intermediate filament-like protein, is required for the curved shape of Caulobacter crescentus and localizes to the inner cell curvature. Here, we show that crescentin forms a single filamentous structure that collapses into a helix when detached from the cell membrane, suggesting that it is normally maintained in a stretched configuration. Crescentin causes an elongation rate gradient around the circumference of the sidewall, creating a longitudinal cell length differential and hence curvature. Such curvature can be produced by physical force alone when cells are grown in circular microchambers. Production of crescentin in Escherichia coli is sufficient to generate cell curvature. Our data argue for a model in which physical strain borne by the crescentin structure anisotropically alters the kinetics of cell wall insertion to produce curved growth. Our study suggests that bacteria may use the cytoskeleton for mechanical control of growth to alter morphology. PMID:19279668
On the edge energy of lipid membranes and the thermodynamic stability of pores
Pera, H.; Kleijn, J. M.; Leermakers, F. A. M.
2015-01-21
To perform its barrier function, the lipid bilayer membrane requires a robust resistance against pore formation. Using a self-consistent field (SCF) theory and a molecularly detailed model for membranes composed of charged or zwitterionic lipids, it is possible to predict structural, mechanical, and thermodynamical parameters for relevant lipid bilayer membranes. We argue that the edge energy in membranes is a function of the spontaneous lipid monolayer curvature, the mean bending modulus, and the membrane thickness. An analytical Helfrich-like model suggests that most bilayers should have a positive edge energy. This means that there is a natural resistance against pore formation. Edge energies evaluated explicitly in a two-gradient SCF model are consistent with this. Remarkably, the edge energy can become negative for phosphatidylglycerol (e.g., dioleoylphosphoglycerol) bilayers at a sufficiently low ionic strength. Such bilayers become unstable against the formation of pores or the formation of lipid disks. In the weakly curved limit, we study the curvature dependence of the edge energy and evaluate the preferred edge curvature and the edge bending modulus. The latter is always positive, and the former increases with increasing ionic strength. These results point to a small window of ionic strengths for which stable pores can form as too low ionic strengths give rise to lipid disks. Higher order curvature terms are necessary to accurately predict relevant pore sizes in bilayers. The electric double layer overlap across a small pore widens the window of ionic strengths for which pores are stable.
Representation of tactile curvature in macaque somatosensory area 2
Connor, Charles E.; Hsiao, Steven S.
2013-01-01
Tactile shape information is elaborated in a cortical hierarchy spanning primary (SI) and secondary somatosensory cortex (SII). Indeed, SI neurons in areas 3b and 1 encode simple contour features such as small oriented bars and edges, whereas higher order SII neurons represent large curved contour features such as angles and arcs. However, neural coding of these contour features has not been systematically characterized in area 2, the most caudal SI subdivision in the postcentral gyrus. In the present study, we analyzed area 2 neural responses to embossed oriented bars and curved contour fragments to establish whether curvature representations are generated in the postcentral gyrus. We found that many area 2 neurons (26 of 112) exhibit clear curvature tuning, preferring contours pointing in a particular direction. Fewer area 2 neurons (15 of 112) show preferences for oriented bars. Because area 2 response patterns closely resembled SII patterns, we also compared area 2 and SII response time courses to characterize the temporal dynamics of curvature synthesis in the somatosensory system. We found that curvature representations develop and peak concurrently in area 2 and SII. These results reveal that transitions from orientation tuning to curvature selectivity in the somatosensory cortical hierarchy occur within SI rather than between SI and SII. PMID:23536717
Wallace, John Paul; Myneni, Ganapati Rao; Pike, Robert
2011-03-31
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Cosmic curvature and condensation
NASA Technical Reports Server (NTRS)
Harwit, Martin
1992-01-01
It is shown that the universe may consist of a patchwork of domains with different Riemann curvature constants k = 0, +/-1. Features of a phase transition in which flat space breaks up in a transition 2k0 - k(-) + k(+) with initial scale factors R(-) = R(+) are postulated and explored. It is shown that such a transition is energetically permitted, has the equivalent of a Curie temperature, and can lead in a natural way to the formation of voids and galaxies. It is predicted that, if the ambient universe on average is well fitted by a purely k(-) space, with only occasional domains of k(+) containing galaxies, a density parameter of (A(z sub c + 1)) super -1 should be expected, where z sub c represents the redshift of the earliest objects to have condensed, and A takes on values ranging from about 5 to 3. Present observations of quasars would suggest a density of about 0.03 or 0.05, respectively, but it could be lower if earlier condensation took place.
John Paul Wallace, Ganapati Rao Myneni, and Robert Pike
2011-03-01
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Particles and curvatures in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Serra, Francesca; Luo, Yimin; Yang, Shu; Kamien, Randall D.; Stebe, Kathleen J.
Elastic interactions in anisotropic fluids can be harnessed to direct particle interactions. A strategy to smoothly manipulate the director field in nematic liquid crystals is to vary the topography of the bounding surfaces. A rugged landscape with peaks and valleys create local deformations of the director field which can interact with particles in solution. We study this complex interaction in two different settings. The first consists of an array of shallow pores in a poly-dimethyl-siloxane (PDMS) membrane, whose curvature can be tuned either by swelling the PDMS membrane or by mechanical stretching. The second is a set of grooves with wavy walls, fabricated by photolithography, with various parameters of curvature and shapes. In this contexts we study how the motion of colloidal particles in nematic liquid crystals can be influenced by their interaction with the peaks and valleys of the bottom substrate or of the side walls. Particles with different associated topological defects (hedgehogs or Saturn rings) behave differently as they interact with the topographical features, favoring the docking on peaks or valleys. These experimental systems are also ideal to study the ``lock and key'' mechanism of particles in holes and to investigate a possible route for particle sorting.
Sigma models with negative curvature
NASA Astrophysics Data System (ADS)
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-05-01
We construct Higgs Effective Field Theory (HEFT) based on the scalar manifold Hn, which is a hyperbolic space of constant negative curvature. The Lagrangian has a non-compact O (n , 1) global symmetry group, but it gives a unitary theory as long as only a compact subgroup of the global symmetry is gauged. Whether the HEFT manifold has positive or negative curvature can be tested by measuring the S-parameter, and the cross sections for longitudinal gauge boson and Higgs boson scattering, since the curvature (including its sign) determines deviations from Standard Model values.
On the Weyl curvature hypothesis
NASA Astrophysics Data System (ADS)
Stoica, Ovidiu Cristinel
2013-11-01
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity.
Curvature calculations with spacetime algebra
Hestenes, D.
1986-06-01
A new method for calculating the curvature tensor is developed and applied to the Scharzschild case. The method employs Clifford algebra and has definite advantages over conventional methods using differential forms or tensor analysis.
Endoplasmatic reticulum shaping by generic mechanisms and protein-induced spontaneous curvature.
Sackmann, Erich
2014-06-01
The endoplasmatic reticulum (ER) comprises flattened vesicles (cisternae) with worm holes dubbed with ribosomes coexisting with a network of interconnected tubes which can extend to the cell periphery or even penetrate nerve axons. The coexisting topologies enclose a continuous luminal space. The complex ER topology is specifically controlled by a group of ER-shaping proteins often called reticulons (discovered by the group of Tom Rapoport). They include atlastin, reticulon, REEP and the MT severing protein spastin. A generic ER shape controlling factor is the necessity to maximize the area-to-volume ratio of ER membranes in the highly crowded cytoplasmic space. I present a model of the ER-shaping function of the reticulons based on the Helfrich bending elasticity concept of soft shell shape changes. Common structural motifs of the reticulons are hydrophobic sequences forming wedge shaped hairpins which penetrate the lipid bilayer of the cell membranes. The wedge-like hydrophobic anchors can both induce the high curvature of the tubular ER fraction and ensure the preferred distribution of the reticulons along the tubules. Tubular junctions may be stabilized by the reticulons forming two forceps twisted by 90°. The ER extensions to the cell periphery and the axons are mediated by coupling of the tubes to the microtubules which is mediated by REEP and spastin. At the end I present a model of the tension driven homotype fusion of ER-membranes by atlastin, based on analogies to the SNARE-complexin-SNARE driven heterotype fusion process. PMID:24607001
Spatial curvature endgame: Reaching the limit of curvature determination
NASA Astrophysics Data System (ADS)
Leonard, C. Danielle; Bull, Philip; Allison, Rupert
2016-07-01
Current constraints on spatial curvature show that it is dynamically negligible: |ΩK|≲5 ×10-3 (95% C.L.). Neglecting it as a cosmological parameter would be premature however, as more stringent constraints on ΩK at around the 10-4 level would offer valuable tests of eternal inflation models and probe novel large-scale structure phenomena. This precision also represents the "curvature floor," beyond which constraints cannot be meaningfully improved due to the cosmic variance of horizon-scale perturbations. In this paper, we discuss what future experiments will need to do in order to measure spatial curvature to this maximum accuracy. Our conservative forecasts show that the curvature floor is unreachable—by an order of magnitude—even with Stage IV experiments, unless strong assumptions are made about dark energy evolution and the Λ CDM parameter values. We also discuss some of the novel problems that arise when attempting to constrain a global cosmological parameter like ΩK with such high precision. Measuring curvature down to this level would be an important validation of systematics characterization in high-precision cosmological analyses.
Lateral organization of membranes and cell shapes.
Markin, V S
1981-01-01
The relations among membrane structure, mechanical properties, and cell shape have been investigated. The fluid mosaic membrane models used contains several components that move freely in the membrane plane. These components interact with each other and determine properties of the membrane such as curvature and elasticity. A free energy equation is postulated for such a multicomponent membrane and the condition of free energy minimum is used to obtain differential equations relating the distribution of membrane components and the local membrane curvature. The force that moves membrane components along the membrane in a variable curvature field is calculated. A change in the intramembrane interactions can bring about phase separation or particle clustering. This, in turn, may strongly affect the local curvature. The numerical solution of the set of equations for the two dimensional case allows determination of the cell shape and the component distribution along the membrane. The model has been applied to describe certain erythrocytes shape transformations. PMID:7284547
van den Brink-van der Laan, Els; Killian, J Antoinette; de Kruijff, Ben
2004-11-01
Nonbilayer lipids can be defined as cone-shaped lipids with a preference for nonbilayer structures with a negative curvature, such as the hexagonal phase. All membranes contain these lipids in large amounts. Yet, the lipids in biological membranes are organized in a bilayer. This leads to the question: what is the physiological role of nonbilayer lipids? Different models are discussed in this review, with a focus on the lateral pressure profile within the membrane. Based on this lateral pressure model, predictions can be made for the effect of nonbilayer lipids on peripheral and integral membrane proteins. Recent data on the catalytic domain of Leader Peptidase and the potassium channel KcsA are discussed in relation to these predictions and in relation to the different models on the function of nonbilayer lipids. The data suggest a general mechanism for the interaction between nonbilayer lipids and membrane proteins via the membrane lateral pressure. PMID:15519321
NASA Astrophysics Data System (ADS)
Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D.; Yoon, Dong Ki
2016-01-01
Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air-smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales.
Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D.; Yoon, Dong Ki
2016-01-01
Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air–smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales. PMID:26725975
Di Natale, Giuseppe; Pappalardo, Giuseppe; Milardi, Danilo; Sciacca, Michele F M; Attanasio, Francesco; La Mendola, Diego; Rizzarelli, Enrico
2010-11-01
The flexible N-terminal domain of the prion protein (PrP(c)) is believed to play a pivotal role in both trafficking of the protein through the cell membrane and its pathogenic conversion into the β sheet-rich scrapie isoform (PrP(sc)). Unlike mammalian PrP(c), avian prion proteins are not known to undergo any pathogenic conformational conversions. Consequently, some critical advances in our understanding of the molecular mechanisms underlying prion pathogenesis are expected from comparative studies of the biophysical properties of the N-terminal domains of the two proteins. The present study addresses the role played by different environmental factors, i.e., copper(II), pH, and membrane-mimicking environments, in assisting the conformational preferences of huPrP60-91 and chPrP53-76, two soluble peptides encompassing the N-terminal copper(II) binding domains of the human and chicken prion proteins, respectively. Moreover, the membrane interactions of huPrP60-91, chPrP53-76, and their copper(II) complexes were evaluated by Trp fluorescence in conjunction with measurements of the variation in thermotropic properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles. Circular dichroism experiments revealed that huPrP60-91 adopts a predominant polyproline II conformation in aqueous solution that is destabilized at basic pH or in the presence of trifluoroethanol (TFE). Unlike anionic sodium dodecyl sulfate (SDS), which seems to stabilize the polyproline II conformation further, zwitterionic dodecylphosphocholine (DPC) micelles do not affect the peptide structure. On the contrary, copper(II) promptly promotes an increase in β-turn-rich structures. Differential scanning calorimetry (DSC) and Trp fluorescence assays carried out on DPPC model membranes after incubation with huPrP60-91 showed a marked tendency of the peptide to slowly penetrate the lipid bilayer with a concomitant conformational transition toward an extended β-sheet-like structure
Determinants of Curvature-Sensing Behavior for MARCKS-Fragment Peptides.
de Jesus, Armando J; White, Ormacinda R; Flynn, Aaron D; Yin, Hang
2016-05-10
It is increasingly recognized that membrane curvature plays an important role in various cellular activities such as signaling and trafficking, as well as key issues involving health and disease development. Thus, curvature-sensing peptides are essential to the study and detection of highly curved bilayer structures. The effector domain of myristoylated alanine-rich C-kinase substrate (MARCKS-ED) has been demonstrated to have curvature-sensing ability. Research of the MARCKS-ED has further revealed that its Lys and Phe residues play an essential role in how MARCKS-ED detects and binds to curved bilayers. MARCKS-ED has the added property of being a lower-molecular-weight curvature sensor, which offers advantages in production. With that in mind, this work investigates peptide-sequence-related factors that influence curvature sensing and explores whether peptide fragments of even shorter length can function as curvature sensors. Using both experimental and computational methods, we studied the curvature-sensing capabilities of seven fragments of MARCKS-ED. Two of the longer fragments were designed from approximately the two halves of the full-length peptide whereas the five shorter fragments were taken from the central stretch of MARCKS-ED. Fully atomistic molecular dynamics simulations show that the fragments that remain bound to the bilayer exhibit interactions with the bilayer similar to that of the full-length MARCKS-ED peptide. Fluorescence enhancement and anisotropy assays, meanwhile, reveal that five of the MARCKS fragments possess the ability to sense membrane curvature. Based on the sequences of the curvature-sensing fragments, it appears that the ability to sense curvature involves a balance between the numbers of positively charged residues and hydrophobic anchoring residues. Together, these findings help crystallize our understanding of the molecular mechanisms underpinning the curvature-sensing behaviors of peptides, which will prove useful in the
On the Weyl curvature hypothesis
Stoica, Ovidiu Cristinel
2013-11-15
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity. In previous papers it has been proposed an equivalent form of Einstein’s equation, which extends it and remains valid at an important class of singularities (including in particular the Schwarzschild, FLRW, and isotropic singularities). Here it is shown that if the Big-Bang singularity is from this class, it also satisfies the Weyl curvature hypothesis. As an application, we study a very general example of cosmological models, which generalizes the FLRW model by dropping the isotropy and homogeneity constraints. This model also generalizes isotropic singularities, and a class of singularities occurring in Bianchi cosmologies. We show that the Big-Bang singularity of this model is of the type under consideration, and satisfies therefore the Weyl curvature hypothesis. -- Highlights: •The singularities we introduce are described by finite geometric/physical objects. •Our singularities have smooth Riemann and Weyl curvatures. •We show they satisfy Penrose’s Weyl curvature hypothesis (Weyl=0 at singularities). •Examples: FLRW, isotropic singularities, an extension of Schwarzschild’s metric. •Example: a large class of singularities which may be anisotropic and inhomogeneous.
Spontaneous Curvature of Polymer Brushes
NASA Astrophysics Data System (ADS)
Sheiko, Sergei; da Silva, Marcelo; Shirvaniants, David; Rodrigues, Carlos; Beers, Kathryn; Matyjaszewski, Krzysztof; Potemkin, Igor; Moeller, Martin
2003-03-01
Experimental studies of cylindrical brushes on surfaces revealed peculiar shape of brush molecules with a curved backbone. According to scaling analysis, spontaneous bending of the backbone can be driven by entropic elasticity of the side chains: smaller extension of the chains is attained due to their asymmetric distribution with respect to the backbone. An equilibrium, i.e. spontaneous curvature results from the balance of the elasticity of the side chains and the elasticity of the interface. The curvature is predicted to increase with the side chain length. The system is of general interest because cylindrical brushes confined to a flat surface represent a two-dimensional cross-section of a planar brush grafted on both sides. Here we present systematic studies of cylindrical brushes with different length of the side chains. The curvature of cylindrical brushes confined to a flat substrate was investigated by atomic force microscopy. The method allowed visualization of individual molecules and quantitative analysis of their conformation. In agreement with theory, adsorbed brushes demonstrated spontaneous curvature, however the curvature was shown to decrease with the side chain length.
Spatial curvature falsifies eternal inflation
NASA Astrophysics Data System (ADS)
Kleban, Matthew; Schillo, Marjorie
2012-06-01
Inflation creates large-scale cosmological density perturbations that are characterized by an isotropic, homogeneous, and Gaussian random distribution about a locally flat background. Even in a flat universe, the spatial curvature measured within one Hubble volume receives contributions from long wavelength perturbations, and will not in general be zero. These same perturbations determine the Cosmic Microwave Background (CMB) temperature fluctuations, which are Script O(10-5). Consequently, the low-l multipole moments in the CMB temperature map predict the value of the measured spatial curvature Ωk. On this basis we argue that a measurement of |Ωk| > 10-4 would rule out slow-roll eternal inflation in our past with high confidence, while a measurement of Ωk < -10-4 (which is positive curvature, a locally closed universe) rules out false-vacuum eternal inflation as well, at the same confidence level. In other words, negative curvature (a locally open universe) is consistent with false-vacuum eternal inflation but not with slow-roll eternal inflation, and positive curvature falsifies both. Near-future experiments will dramatically extend the sensitivity of Ωk measurements and constitute a sharp test of these predictions.
Incisor crown bending strength correlates with diet and incisor curvature in anthropoid primates.
Deane, Andrew S
2015-02-01
Anthropoid incisors are large relative to the postcanine dentition and function in the preprocessing of food items. Previous analyses of anthropoid incisor allometry and shape demonstrate that incisor morphology is correlated with preferred foods and that more frugivorous anthropoids have larger and more curved incisors. Although the relationship between incisal crown curvature and preferred foods has been well documented in extant and fossil anthropoids, the functional significance of curvature variation has yet to be conclusively established. Given that an increase in crown curvature will increase maximum linear crown dimensions, and bending resistance is a function of linear crown dimensions, it is hypothesized that incisor crown curvature functons to increase incisor crown resistance to bending forces. This study uses beam theory to calculate the mesiodistal and labiolingual bending strengths of the maxillary and mandibular incisors of hominoid and platyrrhine taxa with differing diets and variable degrees of incisal curvature. Results indicate that bending strength correlates with incisal curvature and that frugivores have elevated incisor bending resistance relative to folivores. Maxillary central incisor bending strengths further discriminate platyrrhine and hominoid hard- and soft-object frugivores suggesting this crown is subjected to elevated occlusal loading relative to other incisors. These results are consistent with the hypothesis that incisor crown curvature functions to increase incisor crown resistance to bending forces but does not preclude the possibility that incisor bending strength is a composite function of multiple dentognathic variables including, but not limited to, incisor crown curvature. PMID:25156755
Curvature generation in nematic surfaces
NASA Astrophysics Data System (ADS)
Mostajeran, Cyrus
2015-06-01
In recent years there has been a growing interest in the study of shape formation using modern responsive materials that can be preprogrammed to undergo spatially inhomogeneous local deformations. In particular, nematic liquid crystalline solids offer exciting possibilities in this context. Considerable recent progress has been made in achieving a variety of shape transitions in thin sheets of nematic solids by engineering isolated points of concentrated Gaussian curvature using topological defects in the nematic director field across textured surfaces. In this paper, we consider ways of achieving shape transitions in thin sheets of nematic glass by generation of nonlocalized Gaussian curvature in the absence of topological defects in the director field. We show how one can blueprint any desired Gaussian curvature in a thin nematic sheet by controlling the nematic alignment angle across the surface and highlight specific patterns which present feasible initial targets for experimental verification of the theory.
Niramitranon, Jitti; Sansom, Mark Sp; Pongprayoon, Prapasiri
2016-04-01
Porins are water-filled protein channels across the outer membrane of gram-negative bacteria. They facilitate the uptake of nutrients and essential ions. Solutes are filtered by a constriction loop L3 at the mid of a pore. Porins are heat-stable and resistant to toxic agents and detergents. Most porins are trimer, but no clear explanation why trimeric form is preferable. In this work, we thus studied effects of oligomerization on porin structure and function in microscopic detail. A well-studied OmpF (general porin from Escherichia coli) and well-characterised OprP (phosphate-specific pore from Pseudomonas aeruginosa) are used as samples from 2 types of porins found in gram-negative bacteria. MD simulations of trimeric and monomeric pores in pure water and 1M NaCl solution were performed. With a salt solution, the external electric field was applied to mimic a transmembrane potential. Expectedly, OprP is more stable than OmpF. Interestingly, being a monomer turns OmpF into an anion-selective pore. The dislocation of D113's side chain on L3 in OmpF causes the disruption of cation pathway resulting in the reduction of cation influx. In contrast, OprP's structure and function are less dependent on oligomeric states. Both monomeric and trimeric OprP can maintain their anion selectivity. Our findings suggest that trimerization is crucial for both structure and function of general porin OmpF, whereas being trimer in substrate-specific channel OprP supports a pore function. PMID:26895142
Cosmic strings with curvature corrections
NASA Astrophysics Data System (ADS)
Boisseau, Bruno; Letelier, Patricio S.
1992-08-01
A generic model of string described by a Lagrangian density that depends on the extrinsic curvature of the string worldsheet is studied. Using a system of coordinates adapted to the string world sheet the equation of motion and the energy-momentum tensor are derived for strings evolving in curved spacetime. We find that the curvature corrections may change the relation between the string energy density and the tension. It can also introduce heat propagation along the string. We also find for the Polyakov as well as Nambu strings with a topological term that the open string end points can travel with a speed less than the velocity of light.
Ménager, Christine; Guemghar, Dihya; Cabuil, Valérie; Lesieur, Sylviane
2010-10-01
The present study deals with the morphological modifications of giant dioleoyl phosphatidylcholine vesicles (DOPC GUVs) induced by the nonionic surfactant n-octyl β,D-glucopyranoside at sublytic levels, i.e., in the first steps of the vesicle-to-micelle transition process, when surfactant inserts into the vesicle bilayer without disruption. Experimental conditions were perfected to exactly control the surfactant bilayer composition of the vesicles, in line with former work focused on the mechanical properties of the membrane of magnetic-fluid-loaded DOPC GUVs submitted to a magnetic field. The purpose here was to systematically examine, in the absence of any external mechanical constraint, the dynamics of giant vesicle shape and membrane deformations as a function of surfactant partitioning between the aqueous phase and the lipid membrane, beforehand established by turbidity measurements from small unilamellar vesicles. PMID:20825201
Modeling of closed membrane shapes
NASA Astrophysics Data System (ADS)
Penič, S.; Mesarec, L.; Fošnarič, M.; Kralj Iglič, V.; Kralj, S.; Góźdź, W.; Iglič, A.
2014-12-01
Closed biological membranes were considered within the spontaneous curvature model. Ground state membrane shapes were compared with Monte Carlo simulations in the thermal equilibrium, where membranes are subject to thermal fluctuations. The results of the two approaches correspond well with each other. The oblate discocyte membrane shapes are obtained in the ground state but can become metastable when thermal fluctuations are taken into account. The nematic ordering in oblate and stomatocyte vesicle membranes was also studied. It was confirmed that the net topological charge on the surfaces with the topology of a sphere was 2. On the oblate vesicle four topological defects, each with charge 1/2, assembled in the region exhibiting the highest Gaussian curvature. On the stomatocyte vesicle with six topological defects, each with charge 1/2, and two topological antidefects, each with charge -1/2, the latter assembled in the region with a negative Gaussian curvature. The position of topological defects is strongly curvature dependent.
Space Curvature and the "Heavy Banana 'Paradox.'"
ERIC Educational Resources Information Center
Gruber, Ronald P.; And Others
1991-01-01
Two ways to visually enhance the concept of space curvature are described. Viewing space curvature as a meterstick contraction and the heavy banana "paradox" are discussed. The meterstick contraction is mathematically explained. (KR)
Barenboim, Gabriela; Martínez, Enrique Fernández; Mena, Olga; Verde, Licia E-mail: enfmarti@mppmu.mpg.de E-mail: liciaverde@icc.ub.edu
2010-03-01
Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d{sub A}(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Ω{sub k} in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d{sub A}(z) up to sufficiently high redshifts z ∼ 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z)−Ω{sub k} degeneracy.
Classification and quantification of leaf curvature
Liu, Zhongyuan; Jia, Liguo; Mao, Yanfei; He, Yuke
2010-01-01
Various mutants of Arabidopsis thaliana deficient in polarity, cell division, and auxin response are characterized by certain types of leaf curvature. However, comparison of curvature for clarification of gene function can be difficult without a quantitative measurement of curvature. Here, a novel method for classification and quantification of leaf curvature is reported. Twenty-two mutant alleles from Arabidopsis mutants and transgenic lines deficient in leaf flatness were selected. The mutants were classified according to the direction, axis, position, and extent of leaf curvature. Based on a global measure of whole leaves and a local measure of four regions in the leaves, the curvature index (CI) was proposed to quantify the leaf curvature. The CI values accounted for the direction, axis, position, and extent of leaf curvature in all of the Arabidopsis mutants grown in growth chambers. Comparison of CI values between mutants reveals the spatial and temporal variations of leaf curvature, indicating the strength of the mutant alleles and the activities of the corresponding genes. Using the curvature indices, the extent of curvature in a complicated genetic background becomes quantitative and comparable, thus providing a useful tool for defining the genetic components of leaf development and to breed new varieties with leaf curvature desirable for the efficient capture of sunlight for photosynthesis and high yields. PMID:20400533
Proteins interacting with Membranes: Protein Sorting and Membrane Shaping
NASA Astrophysics Data System (ADS)
Callan-Jones, Andrew
2015-03-01
Membrane-bound transport in cells requires generating membrane curvature. In addition, transport is selective, in order to establish spatial gradients of membrane components in the cell. The mechanisms underlying cell membrane shaping by proteins and the influence of curvature on membrane composition are active areas of study in cell biophysics. In vitro approaches using Giant Unilamellar Vesicles (GUVs) are a useful tool to identify the physical mechanisms that drive sorting of membrane components and membrane shape change by proteins. I will present recent work on the curvature sensing and generation of IRSp53, a protein belonging to the BAR family, whose members, sharing a banana-shaped backbone, are involved in endocytosis. Pulling membrane tubes with 10-100 nm radii from GUVs containing encapsulated IRSp53 have, unexpectedly, revealed a non-monotonic dependence of the protein concentration on the tube as a function of curvature. Experiments also show that bound proteins alter the tube mechanics and that protein phase separation along the tube occurs at low tensions. I will present accompanying theoretical work that can explain these findings based on the competition between the protein's intrinsic curvature and the effective rigidity of a membrane-protein patch.
Schmeiser, Christian; Winkler, Christoph
2015-09-01
The crawling motility of many cell types relies on lamellipodia, flat protrusions spreading on flat substrates but (on cells in suspension) also growing into three-dimensional space. Lamellipodia consist of a plasma membrane wrapped around an oriented actin filament meshwork. It is well known that the actin density is controlled by coordinated polymerization, branching, and capping processes, but the mechanisms producing the small aspect ratios of lamellipodia (hundreds of nm thickness vs. several μm lateral and inward extension) remain unclear. The main hypothesis of this work is a strong influence of the local geometry of the plasma membrane on the actin dynamics. This is motivated by observations of co-localization of proteins with I-BAR domains (like IRSp53) with polymerization and branching agents along the membrane. The I-BAR domains are known to bind to the membrane and to prefer and promote membrane curvature. This hypothesis is translated into a stochastic mathematical model where branching and capping rates, and polymerization speeds depend on the local membrane geometry and branching directions are influenced by the principal curvature directions. This requires the knowledge of the deformation of the membrane, being described in a quasi-stationary approximation by minimization of a modified Helfrich energy, subject to the actin filaments acting as obstacles. Simulations with this model predict pieces of flat lamellipodia without any prescribed geometric restrictions. PMID:26002996
Effect of Gaussian curvature modulus on the shape of deformed hollow spherical objects.
Quilliet, C; Farutin, A; Marmottant, P
2016-06-01
A popular description of soft membranes uses the surface curvature energy introduced by Helfrich, which includes a spontaneous curvature parameter. In this paper we show how the Helfrich formula can also be of interest for a wider class of spherical elastic surfaces, namely with shear elasticity, and likely to model other deformable hollow objects. The key point is that when a stress-free state with spherical symmetry exists before subsequent deformation, its straightforwardly determined curvature ("geometrical spontaneous curvature") differs most of the time from the Helfrich spontaneous curvature parameter that should be considered in order to have the model being correctly used. Using the geometrical curvature in a set of independent parameters unveils the role of the Gaussian curvature modulus, which appears to play on the shape of an elastic surface even though this latter is closed, contrary to what happens for surfaces without spontaneous curvature. In appendices, clues are given to apply this alternative and convenient formulation of the elastic surface model to the particular case of thin spherical shells of isotropic material (TSSIMs). PMID:27255647
SLED phenomenology: curvature vs. volume
NASA Astrophysics Data System (ADS)
Niedermann, Florian; Schneider, Robert
2016-03-01
We assess the question whether the SLED (Supersymmetric Large Extra Dimensions) model admits phenomenologically viable solutions with 4D maximal symmetry. We take into account a finite brane width and a scale invariance (SI) breaking dilaton-brane coupling, both of which should be included in a realistic setup. Provided that the brane tension and the microscopic size of the brane take generic values set by the fundamental bulk Planck scale, we find that either the 4D curvature or the size of the extra dimensions is unacceptably large. Since this result is independent of the dilaton-brane couplings, it provides the biggest challenge to the SLED program.
The curvature elastic-energy function of the lipid-water cubic mesophase
NASA Astrophysics Data System (ADS)
Chung, Hesson; Caffrey, Martin
1994-03-01
CELL and lipid membranes are able to bend, as manifested during membrane fusion and the formation of non-lamellar lyotropic mesopbases in water. But there is an energy cost to bending of lipid layers, called the curvature elastic energy. Although the functional form of this energy is known1, a complete quantitative knowledge of the curvature elastic energy, which is central to predicting the relative stability of the large number of phases that lipid membranes can adopt, has been lacking. Here we use X-ray synchrotron diffraction measurements of the variation of lattice parameter with pressure and temperature for the periodic Ia3d (Q230) cubic phase of hydrated monoolein to calculate the complete curvature elastic-energy function for the lipid cubic mesophase. This allows us to predict the stabilities of different cubic and lamellar phases for this system as a function of composition.
Adsorbate-induced curvature and stiffening of graphene.
Svatek, Simon A; Scott, Oliver R; Rivett, Jasmine P H; Wright, Katherine; Baldoni, Matteo; Bichoutskaia, Elena; Taniguchi, Takashi; Watanabe, Kenji; Marsden, Alexander J; Wilson, Neil R; Beton, Peter H
2015-01-14
The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon-carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625
Spontaneous curvature in chiral polar filaments near interfaces
NASA Astrophysics Data System (ADS)
Olmsted, Peter D.; Riley, Emily E.; Jordens, Sophia; Usov, Ivan; Isa, Lucio; Mezzenga, Raffaele
2015-03-01
Chiral filaments (actin, DNA, alpha helical strands, ...) are ubiquitous in biology, and they frequently come into contact with interfaces or inhomogeneous environments, either in biology (e.g. actin on membranes) or use and processing of biomaterials (fibrils at solvent boundaries or nanoparticle surfaces). Recent experiments have shown that amyloid fibrils can develop unusual curvatures at the air-water interface. Here we show that spontaneous curvature follows, on symmetry grounds, for chiral polar filaments placed in inhomgeneous environments such as near surfaces. We demonstrate this for simple model surface-fibril interactions, and discuss some of the implications. Financial support is acknowledged from: ETH Zurich (ETHIIRA TH 32-1), SNF (2-77002-11), and SNSF (IZK072_141955, PP00P2_144646/1, PZ00P2_142532/1).
Multiscale Simulation of Protein Mediated Membrane Remodeling
Ayton, Gary S.; Voth, Gregory A.
2009-01-01
Proteins interacting with membranes can result in substantial membrane deformations and curvatures. This effect is known in its broadest terms as membrane remodeling. This review article will survey current multiscale simulation methodologies that have been employed to examine protein-mediated membrane remodeling. PMID:19922811
Mirror with thermally controlled radius of curvature
Neil, George R.; Shinn, Michelle D.
2010-06-22
A radius of curvature controlled mirror for controlling precisely the focal point of a laser beam or other light beam. The radius of curvature controlled mirror provides nearly spherical distortion of the mirror in response to differential expansion between the front and rear surfaces of the mirror. The radius of curvature controlled mirror compensates for changes in other optical components due to heating or other physical changes. The radius of curvature controlled mirror includes an arrangement for adjusting the temperature of the front surface and separately adjusting the temperature of the rear surface to control the radius of curvature. The temperature adjustment arrangements can include cooling channels within the mirror body or convection of a gas upon the surface of the mirror. A control system controls the differential expansion between the front and rear surfaces to achieve the desired radius of curvature.
x-y curvature wavefront sensor.
Cagigal, Manuel P; Valle, Pedro J
2015-04-15
In this Letter, we propose a new curvature wavefront sensor based on the principles of optical differentiation. The theoretically modeled setup consists of a diffractive optical mask placed at the intermediate plane of a classical two-lens coherent optical processor. The resulting image is composed of a number of local derivatives of the entrance pupil function whose proper combination provides the wavefront curvature. In contrast to the common radial curvature sensors, this one is able to provide the x and y wavefront curvature maps simultaneously. The sensor offers other additional advantages like having high spatial resolution, adjustable dynamic range, and not being sensitive to misalignment. PMID:25872040
Radius of curvature controlled mirror
Neil, George R.; Rathke, John Wickham; Schultheiss, Thomas John; Shinn, Michelle D.; Dillon-Townes, Lawrence A.
2006-01-17
A controlled radius of curvature mirror assembly comprising: a distortable mirror having a reflective surface and a rear surface; and in descending order from the rear surface; a counter-distortion plate; a flow diverter having a flow diverter aperture at the center thereof; a flow return plate having a flow return aperture at the center thereof; a thermal isolation plate having a thermal isolation plate aperture at the center thereof and a flexible heater having a rear surface and a flexible heater aperture at the center thereof; a double walled tube defining a coolant feed chamber and a coolant return chamber; said coolant feed chamber extending to and through the flow diverter aperture and terminating at the counter-distortion plate and the coolant return chamber extending to and through the thermal isolation backplate and terminating at the flow diverter; and a coolant feed and a coolant return exit at the rear of said flexible heater.
Monolayer curvature stabilizes nanoscale raft domains in mixed lipid bilayers
Meinhardt, Sebastian; Vink, Richard L. C.; Schmid, Friederike
2013-01-01
According to the lipid raft hypothesis, biological lipid membranes are laterally heterogeneous and filled with nanoscale ordered “raft” domains, which are believed to play an important role for the organization of proteins in membranes. However, the mechanisms stabilizing such small rafts are not clear, and even their existence is sometimes questioned. Here, we report the observation of raft-like structures in a coarse-grained molecular model for multicomponent lipid bilayers. On small scales, our membranes demix into a liquid ordered (lo) phase and a liquid disordered (ld) phase. On large scales, phase separation is suppressed and gives way to a microemulsion-type state that contains nanometer-sized lo domains in an ld environment. Furthermore, we introduce a mechanism that generates rafts of finite size by a coupling between monolayer curvature and local composition. We show that mismatch between the spontaneous curvatures of monolayers in the lo and ld phases induces elastic interactions, which reduce the line tension between the lo and ld phases and can stabilize raft domains with a characteristic size of the order of a few nanometers. Our findings suggest that rafts in multicomponent bilayers might be closely related to the modulated ripple phase in one-component bilayers. PMID:23487780
Membrane Bending by Protein Crowding
NASA Astrophysics Data System (ADS)
Stachowiak, Jeanne
2014-03-01
From endosomes and synaptic vesicles to the cristae of the mitochondria and the annulus of the nuclear pore, highly curved membranes are fundamental to the structure and physiology of living cells. The established view is that specific families of proteins are able to bend membranes by binding to them. For example, inherently curved proteins are thought to impose their structure on the membrane surface, while membrane-binding proteins with hydrophobic motifs are thought to insert into the membrane like wedges, driving curvature. However, computational models have recently revealed that these mechanisms would require specialized membrane-bending proteins to occupy nearly 100% of a curved membrane surface, an improbable physiological situation given the immense density and diversity of membrane-bound proteins, and the low expression levels of these specialized proteins within curved regions of the membrane. How then does curvature arise within the complex and crowded environment of cellular membranes? Our recent work using proteins involved in clathrin-mediated endocytosis, as well as engineered protein-lipid interactions, has suggested a new hypothesis - that lateral pressure generated by collisions between membrane-bound proteins can drive membrane bending. Specifically, by correlating membrane bending with quantitative optical measurements of protein density on synthetic membrane surfaces and simple physical models of collisions among membrane-bound proteins, we have demonstrated that protein-protein steric interactions can drive membrane curvature. These findings suggest that a simple imbalance in the concentration of membrane-bound proteins across a membrane surface can drive a membrane to bend, providing an efficient mechanism by which essentially any protein can contribute to shaping membranes.
Curvature recognition and force generation in phagocytosis
2010-01-01
Background The uptake of particles by actin-powered invagination of the plasma membrane is common to protozoa and to phagocytes involved in the immune response of higher organisms. The question addressed here is how a phagocyte may use geometric cues to optimize force generation for the uptake of a particle. We survey mechanisms that enable a phagocyte to remodel actin organization in response to particles of complex shape. Results Using particles that consist of two lobes separated by a neck, we found that Dictyostelium cells transmit signals concerning the curvature of a surface to the actin system underlying the plasma membrane. Force applied to a concave region can divide a particle in two, allowing engulfment of the portion first encountered. The phagosome membrane that is bent around the concave region is marked by a protein containing an inverse Bin-Amphiphysin-Rvs (I-BAR) domain in combination with an Src homology (SH3) domain, similar to mammalian insulin receptor tyrosine kinase substrate p53. Regulatory proteins enable the phagocyte to switch activities within seconds in response to particle shape. Ras, an inducer of actin polymerization, is activated along the cup surface. Coronin, which limits the lifetime of actin structures, is reversibly recruited to the cup, reflecting a program of actin depolymerization. The various forms of myosin-I are candidate motor proteins for force generation in particle uptake, whereas myosin-II is engaged only in retracting a phagocytic cup after a switch to particle release. Thus, the constriction of a phagocytic cup differs from the contraction of a cleavage furrow in mitosis. Conclusions Phagocytes scan a particle surface for convex and concave regions. By modulating the spatiotemporal pattern of actin organization, they are capable of switching between different modes of interaction with a particle, either arresting at a concave region and applying force in an attempt to sever the particle there, or extending the cup
Determining wave direction using curvature parameters.
de Queiroz, Eduardo Vitarelli; de Carvalho, João Luiz Baptista
2016-01-01
The curvature of the sea wave was tested as a parameter for estimating wave direction in the search for better results in estimates of wave direction in shallow waters, where waves of different sizes, frequencies and directions intersect and it is difficult to characterize. We used numerical simulations of the sea surface to determine wave direction calculated from the curvature of the waves. Using 1000 numerical simulations, the statistical variability of the wave direction was determined. The results showed good performance by the curvature parameter for estimating wave direction. Accuracy in the estimates was improved by including wave slope parameters in addition to curvature. The results indicate that the curvature is a promising technique to estimate wave directions.•In this study, the accuracy and precision of curvature parameters to measure wave direction are analyzed using a model simulation that generates 1000 wave records with directional resolution.•The model allows the simultaneous simulation of time-series wave properties such as sea surface elevation, slope and curvature and they were used to analyze the variability of estimated directions.•The simultaneous acquisition of slope and curvature parameters can contribute to estimates wave direction, thus increasing accuracy and precision of results. PMID:27408830
Bender, Ruben R.; Muth, Anke; Schneider, Irene C.; Friedel, Thorsten; Hartmann, Jessica; Plückthun, Andreas; Maisner, Andrea; Buchholz, Christian J.
2016-01-01
Receptor-targeted lentiviral vectors (LVs) can be an effective tool for selective transfer of genes into distinct cell types of choice. Moreover, they can be used to determine the molecular properties that cell surface proteins must fulfill to act as receptors for viral glycoproteins. Here we show that LVs pseudotyped with receptor-targeted Nipah virus (NiV) glycoproteins effectively enter into cells when they use cell surface proteins as receptors that bring them closely enough to the cell membrane (less than 100 Å distance). Then, they were flexible in receptor usage as demonstrated by successful targeting of EpCAM, CD20, and CD8, and as selective as LVs pseudotyped with receptor-targeted measles virus (MV) glycoproteins, the current standard for cell-type specific gene delivery. Remarkably, NiV-LVs could be produced at up to two orders of magnitude higher titers compared to their MV-based counterparts and were at least 10,000-fold less effectively neutralized than MV glycoprotein pseudotyped LVs by pooled human intravenous immunoglobulin. An important finding for NiV-LVs targeted to Her2/neu was an about 100-fold higher gene transfer activity when particles were targeted to membrane-proximal regions as compared to particles binding to a more membrane-distal epitope. Likewise, the low gene transfer activity mediated by NiV-LV particles bound to the membrane distal domains of CD117 or the glutamate receptor subunit 4 (GluA4) was substantially enhanced by reducing receptor size to below 100 Å. Overall, the data suggest that the NiV glycoproteins are optimally suited for cell-type specific gene delivery with LVs and, in addition, for the first time define which parts of a cell surface protein should be targeted to achieve optimal gene transfer rates with receptor-targeted LVs. PMID:27281338
Bender, Ruben R; Muth, Anke; Schneider, Irene C; Friedel, Thorsten; Hartmann, Jessica; Plückthun, Andreas; Maisner, Andrea; Buchholz, Christian J
2016-06-01
Receptor-targeted lentiviral vectors (LVs) can be an effective tool for selective transfer of genes into distinct cell types of choice. Moreover, they can be used to determine the molecular properties that cell surface proteins must fulfill to act as receptors for viral glycoproteins. Here we show that LVs pseudotyped with receptor-targeted Nipah virus (NiV) glycoproteins effectively enter into cells when they use cell surface proteins as receptors that bring them closely enough to the cell membrane (less than 100 Å distance). Then, they were flexible in receptor usage as demonstrated by successful targeting of EpCAM, CD20, and CD8, and as selective as LVs pseudotyped with receptor-targeted measles virus (MV) glycoproteins, the current standard for cell-type specific gene delivery. Remarkably, NiV-LVs could be produced at up to two orders of magnitude higher titers compared to their MV-based counterparts and were at least 10,000-fold less effectively neutralized than MV glycoprotein pseudotyped LVs by pooled human intravenous immunoglobulin. An important finding for NiV-LVs targeted to Her2/neu was an about 100-fold higher gene transfer activity when particles were targeted to membrane-proximal regions as compared to particles binding to a more membrane-distal epitope. Likewise, the low gene transfer activity mediated by NiV-LV particles bound to the membrane distal domains of CD117 or the glutamate receptor subunit 4 (GluA4) was substantially enhanced by reducing receptor size to below 100 Å. Overall, the data suggest that the NiV glycoproteins are optimally suited for cell-type specific gene delivery with LVs and, in addition, for the first time define which parts of a cell surface protein should be targeted to achieve optimal gene transfer rates with receptor-targeted LVs. PMID:27281338
Conversion of radius of curvature to power (and vice versa)
NASA Astrophysics Data System (ADS)
Wickenhagen, Sven; Endo, Kazumasa; Fuchs, Ulrike; Youngworth, Richard N.; Kiontke, Sven R.
2015-09-01
Manufacturing optical components relies on good measurements and specifications. One of the most precise measurements routinely required is the form accuracy. In practice, form deviation from the ideal surface is effectively low frequency errors, where the form error most often accounts for no more than a few undulations across a surface. These types of errors are measured in a variety of ways including interferometry and tactile methods like profilometry, with the latter often being employed for aspheres and general surface shapes such as freeforms. This paper provides a basis for a correct description of power and radius of curvature tolerances, including best practices and calculating the power value with respect to the radius deviation (and vice versa) of the surface form. A consistent definition of the sagitta is presented, along with different cases in manufacturing that are of interest to fabricators and designers. The results make clear how the definitions and results should be documented, for all measurement setups. Relationships between power and radius of curvature are shown that allow specifying the preferred metric based on final accuracy and measurement method. Results shown include all necessary equations for conversion to give optical designers and manufacturers a consistent and robust basis for decision-making. The paper also gives guidance on preferred methods for different scenarios for surface types, accuracy required, and metrology methods employed.
Gao, Dengliang
2013-03-01
In 3D seismic interpretation, curvature is a popular attribute that depicts the geometry of seismic reflectors and has been widely used to detect faults in the subsurface; however, it provides only part of the solutions to subsurface structure analysis. This study extends the curvature algorithm to a new curvature gradient algorithm, and integrates both algorithms for fracture detection using a 3D seismic test data set over Teapot Dome (Wyoming). In fractured reservoirs at Teapot Dome known to be formed by tectonic folding and faulting, curvature helps define the crestal portion of the reservoirs that is associated with strong seismic amplitude and high oil productivity. In contrast, curvature gradient helps better define the regional northwest-trending and the cross-regional northeast-trending lineaments that are associated with weak seismic amplitude and low oil productivity. In concert with previous reports from image logs, cores, and outcrops, the current study based on an integrated seismic curvature and curvature gradient analysis suggests that curvature might help define areas of enhanced potential to form tensile fractures, whereas curvature gradient might help define zones of enhanced potential to develop shear fractures. In certain fractured reservoirs such as at Teapot Dome where faulting and fault-related folding contribute dominantly to the formation and evolution of fractures, curvature and curvature gradient attributes can be potentially applied to differentiate fracture mode, to predict fracture intensity and orientation, to detect fracture volume and connectivity, and to model fracture networks.
Programming curvature using origami tessellations
NASA Astrophysics Data System (ADS)
Dudte, Levi H.; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L.
2016-05-01
Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures--we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.
Ionic liquid tunes microemulsion curvature.
Liu, Liping; Bauduin, Pierre; Zemb, Thomas; Eastoe, Julian; Hao, Jingcheng
2009-02-17
Middle-phase microemulsions formed from cationic dioctadecyldimethylammonium chloride (DODMAC), anionic sodium dodecylsulfate (SDS), n-butanol, and n-heptane were studied. An ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), was employed as the electrolyte in the aqueous media instead of inorganic salts usually used in microemulsion formulation. Studies have been carried out as a function of the concentrations of [bmim][BF4], n-butanol, total surfactant (cDODMAC+SDS), and temperature on the phase behavior and the ultralow interfacial tensions in which the anionic component is present in excess in the catanionic film. Ultralow interfacial tension measurements confirmed the formation of middle-phase microemulsions and the necessary conditions for stabilizing middle-phase microemulsions. Electrical conductivity, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments were also performed, indicating that the typical heptane domain size has an average radius of 360 A and the ionic liquid induces softening of the charged catanionic film. Most interestingly, the IL concentration (cIL) is shown to act as an effective interfacial curvature-control parameter, representing a new approach to tuning the formulation of microemulsions and emulsions. The results expand the potential uses of ILs but also point to the design of new ILs that may achieve superefficient control over interfacial and self-assembly systems. PMID:19161325
Magnetophoretic Induction of Root Curvature
NASA Technical Reports Server (NTRS)
Hasenstein, Karl H.
1997-01-01
The last year of the grant period concerned the consolidation of previous experiments to ascertain that the theoretical premise apply not just to root but also to shoots. In addition, we verified that high gradient magnetic fields do not interfere with regular cellular activities. Previous results have established that: (1) intracellular magnetophoresis is possible; and (2) HGMF lead to root curvature. In order to investigate whether HGMF affect the assembly and/or organization of structural proteins, we examined the arrangement of microtubules in roots exposed to HGMF. The cytoskeletal investigations were performed with fomaldehyde-fixed, nonembedded tissue segments that were cut with a vibratome. Microtubules (MTs) were stained with rat anti-yeast tubulin (YOL 1/34) and DTAF-labeled antibody against rat IgG. Microfilaments (MFs) were visualized by incubation in rhodamine-labeled phalloidin. The distribution and arrangement of both components of the cytoskeleton were examined with a confocal microscope. Measurements of growth rates and graviresponse were done using a video-digitizer. Since HGMF repel diamagnetic substances including starch-filled amyloplasts and most The second aspect of the work includes studies of the effect of cytoskeletal inhibitors on MTs and MFs. The analysis of the effect of micotubular inhibitors on the auxin transport in roots showed that there is very little effect of MT-depolymerizing or stabilizing drugs on auxin transport. This is in line with observations that application of such drugs is not immediately affecting the graviresponsiveness of roots.
Conformation of charged vesicles: the Debye-Hückel and the low-curvature limit.
Priti Sinha, Kumari; M Thaokar, Rochish
2016-07-01
The shape as well as tension and pressure inside an uncharged vesicle are understood to be determined by the reduced volume of a vesicle. These parameters are important for a vesicle or a biological cell, since they can affect bio-physical processes such as osmosis and permeation, interaction with external agents such as bio-macromolecules as well as thermal fluctuations in a bilayer membrane of a vesicle. Charged membranes are ubiquitous in nature, most biological cell bio-membranes are charged, and therefore the knowledge of shape, tension and pressure of charged vesicles is critical. Additionally, the distribution of charges in the inner and outer leaflets is also important as it can affect the spatial interaction of a bilayer membrane with proteins and other micro and macromolecular species. This work addresses these issues in the low-charge and low-curvature limit. Our analysis indicates that despite a very strong two-way coupling between the charge and the curvature, the shapes of charged vesicles remain similar to that of uncharged vesicles at comparable reduced volumes, even for reasonable values of total charge. However, the tension and pressure values are higher, and are accurately estimated in our analysis. The charge distribution on the outer and inner leaflet which is strongly affected by the curvature is calculated. The value of spontaneous curvature due to charge redistribution is also estimated. The insensitivity of the shape to charges persists even when only the outer leaflet is charged instead of charged inner and outer leaflets. PMID:27450654
Conformation of charged vesicles: the Debye Huckel and the low curvature limit
NASA Astrophysics Data System (ADS)
Sinha, Kumari Priti; Thaokar, Rochish M., , Prof.
The shape as well as tension and pressure inside an uncharged vesicle are determined by the reduced volume. These parameters are important for a vesicle or a biological cell, since it can affect bio-physical processes such as osmosis and permeation, interaction with external agents such as bio- macromolecules and thermal fluctuations of the bilayer membrane of a vesicle. Charged membranes are ubiquitous in nature, most biological cell bio-membranes are charged, and therefore the knowledge of shape, tension and pressure of charged vesicles is critical. Additionally, the distribution of charges in the inner and outer leaflets is also important as it can affect the spatial interaction of a bilayer membrane with proteins. This work addresses these issues in the low charge and curvature limit. Our analysis indicates that despite a very strong two-way coupling between the charge and the curvature, the shapes of charged vesicles remain similar to that of uncharged vesicles at comparable reduced volumes, even for reasonable values of total charge. However, the tension and pressure values are higher, and are accurately estimated. Similarly the charge distribution on the outer and inner leaflet is strongly affected by the curvature. The value of spontaneous curvature due to charge redistribution is estimated. The insensitivity of the shape to charges persists even when only the outer leaflet is charged instead of charged inner and outer leaflets
Soliton curvatures of surfaces and spaces
Konopelchenko, B.G.
1997-01-01
An intrinsic geometry of surfaces and three-dimensional Riemann spaces is discussed. In the geodesic coordinates the Gauss equation for two-dimensional Riemann spaces (surfaces) is reduced to the one-dimensional Schr{umlt o}dinger equation, where the Gaussian curvature plays a role of potential. The use of this fact provides an infinite set of explicit expressions for curvature and metric of surface. A special case is governed by the KdV equation for the Gaussian curvature. Integrable dynamics of curvature via the KdV equation, higher KdV equations, and 2+1-dimensional integrable equations with breaking solitons is considered. For a special class of three-dimensional Riemann spaces the relation between metric and scalar curvature is given by the two-dimensional stationary Schr{umlt o}dinger or perturbed string equations. This provides us an infinite family of Riemann spaces with explicit scalar curvature and metric. Particular class of spaces and their integrable evolutions are described by the Nizhnik{endash}Veselov{endash}Novikov equation and its higher analogs. Surfaces and three-dimensional Riemann spaces with large curvature and slow dependence on the variable are considered. They are associated with the Burgers and Kadomtsev{endash}Petviashvili equations, respectively. {copyright} {ital 1997 American Institute of Physics.}
Curvature and torsion in growing actin networks
NASA Astrophysics Data System (ADS)
Shaevitz, Joshua W.; Fletcher, Daniel A.
2008-06-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque.
Distributed curvature and stability of fullerenes.
Fowler, Patrick W; Nikolić, Sonja; De Los Reyes, Rasthy; Myrvold, Wendy
2015-09-21
Energies of non-planar conjugated π systems are typically described qualitatively in terms of the balance of π stabilisation and the steric strain associated with geometric curvature. Curvature also has a purely graph-theoretical description: combinatorial curvature at a vertex of a polyhedral graph is defined as one minus half the vertex degree plus the sum of reciprocal sizes of the faces meeting at that vertex. Prisms and antiprisms have positive combinatorial vertex curvature at every vertex. Excluding these two infinite families, we call any other polyhedron with everywhere positive combinatorial curvature a PCC polyhedron. Cubic PCC polyhedra are initially common, but must eventually die out with increasing vertex count; the largest example constructed so far has 132 vertices. The fullerenes Cn have cubic polyhedral molecular graphs with n vertices, 12 pentagonal and (n/2 - 10) hexagonal faces. We show that there are exactly 39 PCC fullerenes, all in the range 20 ≤n≤ 60. In this range, there is only partial correlation between PCC status and stability as defined by minimum pentagon adjacency. The sum of vertex curvatures is 2 for any polyhedron; for fullerenes the sum of squared vertex curvatures is linearly related to the number of pentagon adjacencies and hence is a direct measure of relative stability of the lower (n≤ 60) fullerenes. For n≥ 62, non-PCC fullerenes with a minimum number of pentagon adjacencies minimise mean-square curvature. For n≥ 70, minimum mean-square curvature implies isolation of pentagons, which is the strongest indicator of stability for a bare fullerene. PMID:26283188
Magnetic curvature effects on plasma interchange turbulence
NASA Astrophysics Data System (ADS)
Li, B.; Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-01
The magnetic curvature effects on plasma interchange turbulence and transport in the Z-pinch and dipole-like systems are explored with two-fluid global simulations. By comparing the transport levels in the systems with a different magnetic curvature, we show that the interchange-mode driven transport strongly depends on the magnetic geometry. For the system with large magnetic curvature, the pressure and density profiles are strongly peaked in a marginally stable state and the nonlinear evolution of interchange modes produces the global convective cells in the azimuthal direction, which lead to the low level of turbulent convective transport.
Wasnik, Vaibhav; Wingreen, Ned S.; Mukhopadhyay, Ranjan
2015-01-01
Recent in vivo experiments suggest that in the bacterium, Bacillus subtilis, the cue for the localization of the small sporulation protein, SpoVM, an essential factor in spore coat formation, is curvature of the bacterial plasma membrane. In vitro measurements of SpoVM adsorption to vesicles of varying sizes also find high sensitivity of adsorption to vesicle radius. This curvature-dependent adsorption is puzzling given the orders of magnitude difference in length scale between an individual protein and the radius of curvature of the cell or vesicle, suggesting protein clustering on the membrane. Here we develop a minimal model to study the relationship between curvature-dependent membrane adsorption and clustering of SpoVM. Based on our analysis, we hypothesize that the radius dependence of SpoVM adsorption observed in vitro is governed primarily by membrane tension, while for in-vivo localization of SpoVM, we propose a highly sensitive mechanism for curvature sensing based on the formation of macroscopic protein clusters on the membrane. PMID:25625300
Membrane with supported internal passages
NASA Technical Reports Server (NTRS)
Gonzalez-Martin, Anuncia (Inventor); Salinas, Carlos E. (Inventor); Cisar, Alan J. (Inventor); Hitchens, G. Duncan (Inventor); Murphy, Oliver J. (Inventor)
2000-01-01
The invention provides an improved proton exchange membrane for use in electrochemical cells having internal passages parallel to the membrane surface comprising permanent tubes preferably placed at the ends of the fluid passages. The invention also provides an apparatus and process for making the membrane, membrane and electrode assemblies fabricated using the membrane, and the application of the membrane and electrode assemblies to a variety of devices, both electrochemical and otherwise. The passages in the membrane extend from one edge of the membrane to another and allow fluid flow through the membrane and give access directly to the membrane.
Gravitropic basis of leaf blade nastic curvatures
NASA Technical Reports Server (NTRS)
Hayes, A. B.
1982-01-01
The curvatures produced in leaf blades by auxin treatment have been described as nastic curvatures because the initial differential growth is always enhanced on the lower side, regardless of the side of application. It is now known, however, that blades can show differential growth of either the upper or the lower side depending on the conditions of treatment. The dorsiventrality of the blade therefore influences but does not limit the direction of curvature. The dorsiventral directionality of response to growth regulators and the response to changes in the orientation to gravity are seen as indicating that blade curvatures are analogous to negative or positive gravitropism. It is noted that neither blade hyponasty or epinasty can be accounted for by ethylene alone. Petiole responses, however, are not directional, and the leaf angle changes induced by rotation or auxin treatment can be accounted for by ethylene production.
Visually discerning the curvature of the Earth.
Lynch, David K
2008-12-01
Reports and photographs claiming that visual observers can detect the curvature of the Earth from high mountains or high-flying commercial aircraft are investigated. Visual daytime observations show that the minimum altitude at which curvature of the horizon can be detected is at or slightly below 35,000 ft, providing that the field of view is wide (60 degrees ) and nearly cloud free. The high-elevation horizon is almost as sharp as the sea-level horizon, but its contrast is less than 10% that of the sea-level horizon. Photographs purporting to show the curvature of the Earth are always suspect because virtually all camera lenses project an image that suffers from barrel distortion. To accurately assess curvature from a photograph, the horizon must be placed precisely in the center of the image, i.e., on the optical axis. PMID:19037349
Spline-Based Smoothing of Airfoil Curvatures
NASA Technical Reports Server (NTRS)
Li, W.; Krist, S.
2008-01-01
Constrained fitting for airfoil curvature smoothing (CFACS) is a splinebased method of interpolating airfoil surface coordinates (and, concomitantly, airfoil thicknesses) between specified discrete design points so as to obtain smoothing of surface-curvature profiles in addition to basic smoothing of surfaces. CFACS was developed in recognition of the fact that the performance of a transonic airfoil is directly related to both the curvature profile and the smoothness of the airfoil surface. Older methods of interpolation of airfoil surfaces involve various compromises between smoothing of surfaces and exact fitting of surfaces to specified discrete design points. While some of the older methods take curvature profiles into account, they nevertheless sometimes yield unfavorable results, including curvature oscillations near end points and substantial deviations from desired leading-edge shapes. In CFACS as in most of the older methods, one seeks a compromise between smoothing and exact fitting. Unlike in the older methods, the airfoil surface is modified as little as possible from its original specified form and, instead, is smoothed in such a way that the curvature profile becomes a smooth fit of the curvature profile of the original airfoil specification. CFACS involves a combination of rigorous mathematical modeling and knowledge-based heuristics. Rigorous mathematical formulation provides assurance of removal of undesirable curvature oscillations with minimum modification of the airfoil geometry. Knowledge-based heuristics bridge the gap between theory and designers best practices. In CFACS, one of the measures of the deviation of an airfoil surface from smoothness is the sum of squares of the jumps in the third derivatives of a cubicspline interpolation of the airfoil data. This measure is incorporated into a formulation for minimizing an overall deviation- from-smoothness measure of the airfoil data within a specified fitting error tolerance. CFACS has been
Induced gravity from curvature density preserving diffeomorphisms
NASA Astrophysics Data System (ADS)
Oda, Ichiro
2016-08-01
We construct not only an induced gravity model with restricted diffeomorphisms, that is, transverse diffeomorphisms that preserve the curvature density, but also with full diffeomorphisms. By solving the equations of motion, it turns out that these models produce Einstein's equations with a certain Newton constant in addition to the constraint for the curvature density. In the limit of the infinite Newton constant, the models give rise to induced gravity. Moreover, we discuss cosmological solutions on the basis of the gravitational models at hand.
Curvature tensors unified field equations on SEXn
NASA Astrophysics Data System (ADS)
Chung, Kyung Tae; Lee, Il Young
1988-09-01
We study the curvature tensors and field equations in the n-dimensional SE manifold SEXn. We obtain several basic properties of the vectors S λ and U λ and then of the SE curvature tensor and its contractions, such as a generalized Ricci identity, a generalized Bianchi identity, and two variations of the Bianchi identity satisfied by the SE Einstein tensor. Finally, a system of field equations is discussed in SEXn and one of its particular solutions is constructed and displayed.
The role of curvature in entanglement
NASA Astrophysics Data System (ADS)
Buck, Gregory
2015-10-01
Which tangles more readily: curly hair or straight hair? A perhaps natural thought, supported by some theoretical evidence, is to associate curvature and entanglement, and assume that they would grow together-that an increase in one fosters an increase in the other. However we have biological examples such as DNA in the chromosome, and mechanical examples such as coiled telephone cords, in which much more curvature is employed than is required for the packing, and in which tangling is presumably detrimental. We offer a resolution to this conundrum. We show, that at least for simple but generally applicable models, the relationship between curvature and entanglement is subtle: if we keep filament density constant and increase curvature, the entanglement initially increases, passes through a maximum, then decreases, so there is a regime where increasing curvature increases entanglement, and there is also a regime where increasing curvature decreases entanglement. This has implications for filament packing in many circumstances, and in particular for the compaction structure of DNA in the cell-it provides a straightforward argument for the view that one purpose of DNA coiling and supercoiling is to inhibit entanglement. It also tells us to expect that wavy hair-neither the straightest nor the curliest-tangles most readily.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-08-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
Cosmological attractor models and higher curvature supergravity
NASA Astrophysics Data System (ADS)
Cecotti, Sergio; Kallosh, Renata
2014-05-01
We study cosmological α-attractors in superconformal/supergravity models, where α is related to the geometry of the moduli space. For α = 1 attractors [1] we present a generalization of the previously known manifestly superconformal higher curvature supergravity model [2]. The relevant standard 2-derivative supergravity with a minimum of two chiral multiplets is shown to be dual to a 4-derivative higher curvature supergravity, where in general one of the chiral superfields is traded for a curvature superfield. There is a degenerate case when both matter superfields become non-dynamical and there is only a chiral curvature superfield, pure higher derivative supergravity. Generic α-models [3] interpolate between the attractor point at α = 0 and generic chaotic inflation models at large α, in the limit when the inflaton moduli space becomes flat. They have higher derivative duals with the same number of matter fields as the original theory or less, but at least one matter multiplet remains. In the context of these models, the detection of primordial gravity waves will provide information on the curvature of the inflaton submanifold of the Kähler manifold, and we will learn if the inflaton is a fundamental matter multiplet, or can be replaced by a higher derivative curvature excitation.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-05-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
Formation, Stability, and Mobility of One-Dimensional Lipid Bilayer on High Curvature Substrates
Huang, J; Martinez, J; Artyukhin, A; Sirbuly, D; Wang, Y; Ju, J W; Stroeve, P; Noy, A
2007-03-23
Curved lipid membranes are ubiquitous in living systems and play an important role in many biological processes. To understand how curvature and lipid composition affect membrane formation and fluidity we have assembled and studied mixed 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine (DOPC) and 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine (DOPE) supported lipid bilayers on amorphous silicon nanowires with controlled diameters ranging from 20 nm to 200 nm. Addition of cone-shaped DOPE molecules to cylindrical DOPC molecules promotes vesicle fusion and bilayer formation on smaller diameter nanowires. Our experiments demonstrate that nanowire-supported bilayers are mobile, exhibit fast recovery after photobleaching, and have low concentration of defects. Lipid diffusion coefficients in these high-curvature tubular membranes are comparable to the values reported for flat supported bilayers and increase with decreasing nanowire diameter.
Does a methionine-to-norleucine substitution in PGLa influence peptide-membrane interactions?
Radchenko, Dmytro S; Kattge, Saskia; Kara, Sezgin; Ulrich, Anne S; Afonin, Sergii
2016-09-01
Yes. To understand the molecular mechanisms of amphiphilic membrane-active peptides, it is essential to study their interactions with lipid bilayers under near-native conditions. Amino acid composition largely determines the non-specific properties of peptides, on the basis of the physicochemical properties of the side chains. The resultant effects on peptides' functional properties include influences on the conformation, structural dynamics and binding affinities within the peptide interactome. Here, we studied the effect of substituting oxidation-prone methionine (Met) with non-oxidizable norleucine (Nle) in the model α-helical antimicrobial peptide PGLa, through systematic comparison of PGLa with the (2)Met/(2)Nle mutant. Both peptides were evaluated for their bacteriostatic and hemolytic activities (using in situ assays), for their conformational preferences in isotropic solutions (using circular dichroism spectropolarimetry) and for their abilities to modulate membrane curvature (using a solid-state (31)P NMR assay). We determined the membrane-bound states in detail and characterized the orientational dynamics of both peptides in oriented phospholipid membranes by solid-state (19)F NMR spectroscopy. On the one hand, the bioactivity results, the structure in the diluted membrane-mimicking environments and the strong inhibition of the negative membrane curvature were comparable between PGLa and the mutant. On the other hand, the alignments in DMPC bilayer were qualitatively the same but differed in absolute values - the more hydrophobic Nle residue inserted deeper in the membrane core. Furthermore, the mutant peptide displayed a significantly reduced ability to re-orient from the monomeric, surficial to the putative dimeric, tilted state. Overall, these results confirm the functional isosterism of Nle and Met in the helical membrane-active peptides but highlight differences in the ways in which the two residues affect non-specific binding to the lipid bilayer
Brannigan, Grace; Brown, Frank L. H.
2007-01-01
An elastic model for membrane deformations induced by integral membrane proteins is presented. An earlier theory is extended to account for nonvanishing saddle splay modulus within lipid monolayers and perturbations to lipid volume proximal to the protein. Analytical results are derived for the deformation profile surrounding a single cylindrical protein inclusion, which compare favorably to coarse-grained simulations over a range of protein sizes. Numerical results for multi-protein systems indicate that membrane-mediated interactions between inclusions are strongly affected by Gaussian curvature and display nonpairwise additivity. Implications for the aggregation of proteins are discussed. PMID:17098794
Strong curvature effects in Neumann wave problems
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-15
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schroedinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
Hydrophobic surfactant proteins strongly induce negative curvature.
Chavarha, Mariya; Loney, Ryan W; Rananavare, Shankar B; Hall, Stephen B
2015-07-01
The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism. PMID:26153706
Strong curvature effects in Neumann wave problems
NASA Astrophysics Data System (ADS)
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-01
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schrödinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
Membrane shape instabilities induced by BAR domain proteins
NASA Astrophysics Data System (ADS)
Baumgart, Tobias
2014-03-01
Membrane curvature has developed into a forefront of membrane biophysics. Numerous proteins involved in membrane curvature sensing and membrane curvature generation have recently been discovered, including proteins containing the crescent-shaped BAR domain as membrane binding and shaping module. Accordingly, the structure determination of these proteins and their multimeric complexes is increasingly well-understood. Substantially less understood, however, are thermodynamic and kinetic aspects and the detailed mechanisms of how these proteins interact with membranes in a curvature-dependent manner. New experimental approaches need to be combined with established techniques to be able to fill in these missing details. Here we use model membrane systems in combination with a variety of biophysical techniques to characterize mechanistic aspects of BAR domain protein function. This includes a characterization of membrane curvature sensing and membrane generation. We also establish kinetic and thermodynamic aspects of BAR protein dimerization in solution, and investigate kinetic aspects of membrane binding. We present two new approaches to investigate membrane shape instabilities and demonstrate that membrane shape instabilities can be controlled by protein binding and lateral membrane tension. This work is supported through NIH grant GM-097552 and NSF grant CBET-1053857.
A new algorithm for evaluating 3D curvature and curvature gradient for improved fracture detection
NASA Astrophysics Data System (ADS)
Di, Haibin; Gao, Dengliang
2014-09-01
In 3D seismic interpretation, both curvature and curvature gradient are useful seismic attributes for structure characterization and fault detection in the subsurface. However, the existing algorithms are computationally intensive and limited by the lateral resolution for steeply-dipping formations. This study presents new and robust volume-based algorithms that evaluate both curvature and curvature gradient attributes more accurately and effectively. The algorithms first instantaneously fit a local surface to seismic data and then compute attributes using the spatial derivatives of the built surface. Specifically, the curvature algorithm constructs a quadratic surface by using a rectangle 9-node grid cell, whereas the curvature gradient algorithm builds a cubic surface by using a diamond 13-node grid cell. A dip-steering approach based on 3D complex seismic trace analysis is implemented to enhance the accuracy of surface construction and to reduce computational time. Applications to two 3D seismic surveys demonstrate the accuracy and efficiency of the new curvature and curvature gradient algorithms for characterizing faults and fractures in fractured reservoirs.
Curvature constraints from large scale structure
NASA Astrophysics Data System (ADS)
Di Dio, Enea; Montanari, Francesco; Raccanelli, Alvise; Durrer, Ruth; Kamionkowski, Marc; Lesgourgues, Julien
2016-06-01
We modified the CLASS code in order to include relativistic galaxy number counts in spatially curved geometries; we present the formalism and study the effect of relativistic corrections on spatial curvature. The new version of the code is now publicly available. Using a Fisher matrix analysis, we investigate how measurements of the spatial curvature parameter ΩK with future galaxy surveys are affected by relativistic effects, which influence observations of the large scale galaxy distribution. These effects include contributions from cosmic magnification, Doppler terms and terms involving the gravitational potential. As an application, we consider angle and redshift dependent power spectra, which are especially well suited for model independent cosmological constraints. We compute our results for a representative deep, wide and spectroscopic survey, and our results show the impact of relativistic corrections on spatial curvature parameter estimation. We show that constraints on the curvature parameter may be strongly biased if, in particular, cosmic magnification is not included in the analysis. Other relativistic effects turn out to be subdominant in the studied configuration. We analyze how the shift in the estimated best-fit value for the curvature and other cosmological parameters depends on the magnification bias parameter, and find that significant biases are to be expected if this term is not properly considered in the analysis.
Unfolding the Berry curvature of supercell calculations
NASA Astrophysics Data System (ADS)
Bianco, Raffaello; Resta, Raffaele; Souza, Ivo
2014-03-01
Unfolding band structures of supercell calculations has become a valuable tool for visualizing the influence of point impurities on the electronic states in crystals. In the same spirit, we introduce a procedure which maps the k-space Berry curvature of the occupied states from the small BZ of a supercell onto the normal BZ of the perfect (or virtual) crystal. As an application, we analyze the k-space distribution of the unfolded curvature of bcc Fe1-xCox ordered alloys, to better understand the influence of alloying on the anomalous Hall conductivity. Comparing with the ordinary curvature calculated in the virtual-crystal approximation, we find that the lowering of translational symmetry by the Co ``impurities'' introduces ``extrinsic'' contributions, which correlate with changes in the spectral function near the Fermi surface. In particular, the unfolded curvature displays additional sharp peaks associated with low-energy pseudovertical transitions. These occur in regions of k-space where two unfolded bands, which in the virtual crystal would be separated in k-space (and therefore would not jointly contribute to its Berry curvature), lie on either side of the Fermi level and are coupled by the impurity potential.
Zhao, Chunyu; Burge, James H
2013-12-16
Zernike polynomials are an orthonormal set of scalar functions over a circular domain, and are commonly used to represent wavefront phase or surface irregularity. In optical testing, slope or curvature of a surface or wavefront is sometimes measured instead, from which the surface or wavefront map is obtained. Previously we derived an orthonormal set of vector polynomials that fit to slope measurement data and yield the surface or wavefront map represented by Zernike polynomials. Here we define a 3-element curvature vector used to represent the second derivatives of a continuous surface, and derive a set of orthonormal curvature basis functions that are written in terms of Zernike polynomials. We call the new curvature functions the C polynomials. Closed form relations for the complete basis set are provided, and we show how to determine Zernike surface coefficients from the curvature data as represented by the C polynomials. PMID:24514717
The Induction of Negative Curvature as a Mechanism of Cell Toxicity by Amyloidogenic Peptides
Smith, Pieter E. S.; Brender, Jeffrey R.; Ramamoorthy, Ayyalusamy
2009-01-01
The death of insulin-producing β-cells is a key step in the pathogenesis of type 2 diabetes. The amyloidogenic peptide Islet Amyloid Polypeptide (IAPP, also known as amylin) has been shown to disrupt β-cell membranes leading to β-cell death. Despite the strong evidence linking IAPP to the destruction of β-cell membrane integrity and cell death, the mechanism of IAPP toxicity is poorly understood. In particular, the effect of IAPP on the bilayer structure has largely been uncharacterized. In this study, we have determined the effect of the amyloidogenic and toxic hIAPP1-37 peptide and the non-toxic and non-amyloidogenic rIAPP1-37 peptide on membranes by a combination of DSC and solid-state NMR spectroscopy. We also characterized the toxic but largely non-amyloidogenic rIAPP1-19 and hIAPP1-19 fragments. DSC shows that both amyloidogenic (hIAPP1-37) and largely non-amyloidogenic (hIAPP1-19 and rIAPP1-19) toxic versions of the peptide strongly favor the formation of negative curvature in lipid bilayers, while the non-toxic full-length rat IAPP1-37 peptide does not. This result was confirmed by solid-state NMR spectroscopy which shows that in bicelles composed of regions of high curvature and low curvature, non-toxic rIAPP1-37 binds to the regions of low curvature while toxic rIAPP1-19 binds to regions of high curvature. Similarly, solid-state NMR spectroscopy shows that the toxic rIAPP1-19 peptide significantly disrupts the lipid bilayer structure, whereas the non-toxic rIAPP1-37 does not have a significant effect. These results indicate IAPP may induce the formation of pores by the induction of excess membrane curvature and can be used to guide the design of compounds that can prevent the cell-toxicity of IAPP. This mechanism may be important to understand the toxicity of other amyloidogenic proteins. Our solid-state NMR results also demonstrate the possibility of using bicelles to measure the affinity of biomolecules for negatively or positively curved regions of
Curvature corrections and Kac Moody compatibility conditions
NASA Astrophysics Data System (ADS)
Damour, Thibault; Hanany, Amihay; Henneaux, Marc; Kleinschmidt, Axel; Nicolai, Hermann
2006-10-01
We study possible restrictions on the structure of curvature corrections to gravitational theories in the context of their corresponding Kac Moody algebras, following the initial work on E 10 in Damour and Nicolai [Class Quant Grav 22:2849 (2005)]. We first emphasize that the leading quantum corrections of M-theory can be naturally interpreted in terms of (non-gravity) fundamental weights of E 10. We then heuristically explore the extent to which this remark can be generalized to all over-extended algebras by determining which curvature corrections are compatible with their weight structure, and by comparing these curvature terms with known results on the quantum corrections for the corresponding gravitational theories.
Substrate Curvature Gradient Drives Rapid Droplet Motion
NASA Astrophysics Data System (ADS)
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-01
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces.
Substrate curvature gradient drives rapid droplet motion.
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-11
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces. PMID:25062213
Superintegrable systems on spaces of constant curvature
NASA Astrophysics Data System (ADS)
Gonera, Cezary; Kaszubska, Magdalena
2014-07-01
Construction and classification of two-dimensional (2D) superintegrable systems (i.e. systems admitting, in addition to two global integrals of motion guaranteeing the Liouville integrability, the third global and independent one) defined on 2D spaces of constant curvature and separable in the so-called geodesic polar coordinates are presented. The method proposed is applicable to any value of curvature including the case of Euclidean plane, sphere and hyperbolic plane. The main result is a generalization of Bertrand's theorem on 2D spaces of constant curvature and covers most of the known separable and superintegrable models on such spaces (in particular, the so-called Tremblay-Turbine-Winternitz (TTW) and Post-Winternitz (PW) models which have recently attracted some interest).
Extrinsic and intrinsic curvatures in thermodynamic geometry
NASA Astrophysics Data System (ADS)
Hosseini Mansoori, Seyed Ali; Mirza, Behrouz; Sharifian, Elham
2016-08-01
We investigate the intrinsic and extrinsic curvatures of a certain hypersurface in thermodynamic geometry of a physical system and show that they contain useful thermodynamic information. For an anti-Reissner-Nordström-(A)de Sitter black hole (Phantom), the extrinsic curvature of a constant Q hypersurface has the same sign as the heat capacity around the phase transition points. The intrinsic curvature of the hypersurface can also be divergent at the critical points but has no information about the sign of the heat capacity. Our study explains the consistent relationship holding between the thermodynamic geometry of the KN-AdS black holes and those of the RN (J-zero hypersurface) and Kerr black holes (Q-zero hypersurface) ones [1]. This approach can easily be generalized to an arbitrary thermodynamic system.
NASA Astrophysics Data System (ADS)
Breidenich, Markus
2000-11-01
The surface of biological cells consists of a lipid membrane and a large amount of various proteins and polymers, which are embedded in the membrane or attached to it. We investigate how membranes are influenced by polymers, which are anchored to the membrane by one end. The entropic pressure exerted by the polymer induces a curvature, which bends the membrane away from the polymer. The resulting membrane shape profile is a cone in the vicinity of the anchor segment and a catenoid far away from it. The perturbative calculations are confirmed by Monte-Carlo simulations. An additional attractive interaction between polymer and membrane reduces the entropically induced curvature. In the limit of strong adsorption, the polymer is localized directly on the membrane surface and does not induce any pressure, i.e. the membrane curvature vanishes. If the polymer is not anchored directly on the membrane surface, but in a non-vanishing anchoring distance, the membrane bends towards the polymer for strong adsorption. In the last part of the thesis, we study membranes under the influence of non-anchored polymers in solution. In the limit of pure steric interactions between the membrane and free polymers, the membrane curves towards the polymers (in contrast to the case of anchored polymers). In the limit of strong adsorption the membrane bends away from the polymers. Die Oberfläche biologischer Zellen besteht aus einer Lipidmembran und einer Vielzahl von Proteinen und Polymeren, die in die Membran eingebaut sind. Die Beeinflussung der Membran durch Polymere, die mit einem Ende an der Membran verankert sind, wird im Rahmen dieser Arbeit anhand eines vereinfachten biomimetischen Systems studiert. Der entropische Druck, den das Polymer durch Stöße auf die Membran ausübt, führt dazu, dass sich die Membran vom Polymer weg krümmt. Die resultierende Membranform ist ein Kegel in der Nähe des Ankers und ein Katenoid in grossem Abstand vom Ankerpunkt. Monte Carlo-Simulationen best
Wavefront reconstruction from tangential and sagittal curvature.
Canales, Javier; Barbero, Sergio; Portilla, Javier; López-Alonso, José Manuel
2014-12-10
In a previous contribution [Appl. Opt.51, 8599 (2012)], a coauthor of this work presented a method for reconstructing the wavefront aberration from tangential refractive power data measured using dynamic skiascopy. Here we propose a new regularized least squares method where the wavefront is reconstructed not only using tangential but also sagittal curvature data. We prove that our new method provides improved quality reconstruction for typical and also for highly aberrated wavefronts, under a wide range of experimental error levels. Our method may be applied to any type of wavefront sensor (not only dynamic skiascopy) able to measure either just tangential or tangential plus sagittal curvature data. PMID:25608069
Scaling of curvature in subcritical gravitational collapse
NASA Astrophysics Data System (ADS)
Garfinkle, David; Duncan, G. Comer
1998-09-01
We perform numerical simulations of the gravitational collapse of a spherically symmetric scalar field. For those data that just barely do not form black holes we find the maximum curvature at the position of the central observer. We find a scaling relation between this maximum curvature and distance from the critical solution. The scaling relation is analogous to that found by Choptuik for the black hole mass for those data that do collapse to form black holes. We also find a periodic wiggle in the scaling exponent.
NASTRAN modifications for recovering strains and curvatures
NASA Technical Reports Server (NTRS)
Hennrich, C. W.
1975-01-01
Modifications to the NASTRAN structural analysis computer program are described. The modifications allow the recovery of strain and curvature data for the general two-dimensional elements, in addition to the usual stress data. Option features allow the transformation of the strain/curvature (or stress) data to a common coordinate system and representation at the grid points of the structural model rather than at the conventional element center locations. Usage information is provided which will allow present users of NASTRAN to easily utilize the new capability.
Modulus stabilization in higher curvature dilaton gravity
NASA Astrophysics Data System (ADS)
Choudhury, Sayantan; Mitra, Joydip; SenGupta, Soumitra
2014-08-01
We propose a framework of modulus stabilization in two brane warped geometry scenario in presence of higher curvature gravity and dilaton in bulk space-time. In the prescribed setup we study various features of the stabilized potential for the modulus field, generated by a bulk scalar degrees of freedom with quartic interactions localized on the two 3-branes placed at the orbifold fixed points. We determine the parameter space for the gravidilaton and Gauss-Bonnet couplings required to stabilize the modulus in such higher curvature dilaton gravity setup.
A methodology for quantifying seated lumbar curvatures.
Leitkam, Samuel T; Bush, Tamara Reid; Li, Mingfei
2011-11-01
To understand the role seating plays in the support of posture and spinal articulation, it is necessary to study the interface between a human and the seat. However, a method to quantify lumbar curvature in commercially available unmodified seats does not currently exist. This work sought to determine if the lumbar curvature for normal ranges of seated posture could be documented by using body landmarks located on the anterior portion of the body. The development of such a methodology will allow researchers to evaluate spinal articulation of a seated subject while in standard, commercially available seats and chairs. Anterior measurements of boney landmarks were used to quantify the relative positions of the ribcage and pelvis while simultaneous posterior measurements were made of lumbar curvature. The relationship between the anterior and the posterior measures was compared. The predictive capacity of this approach was evaluated by determining linear and second-order regressions for each of the four postures across all subjects and conducting a leave-one-out cross validation. The relationships between the anterior and posterior measures were approximated by linear and second-order polynomial regressions (r(2 ) = 0.829, 0.935 respectively) across all postures. The quantitative analysis showed that openness had a significant relationship with lumbar curvature, and a first-order regression was superior to a second-order regression. Average standard errors in the prediction were 5.9° for the maximum kyphotic posture, 9.9° for the comfortable posture, 12.8° for the straight and tall, and 22.2° for the maximum lordotic posture. These results show predictions of lumbar curvature are possible in seated postures by using a motion capture system and anterior measures. This method of lumbar curvature prediction shows potential for use in the assessment of seated spinal curvatures and the corresponding design of seating to accommodate those curvatures; however
Rossman, Jeremy S.; Lamb, Robert A.
2014-01-01
Virus budding is a complex, multistep process in which viral proteins make specific alterations in membrane curvature. Many different viral proteins can deform the membrane and form a budding virion, but very few can mediate membrane scission to complete the budding process. As a result, enveloped viruses have developed numerous ways of facilitating membrane scission, including hijacking host cellular scission machinery and expressing their own scission proteins. These proteins mediate scission in very different ways, though the biophysical mechanics underlying their actions may be similar. In this review, we explore the mechanisms of membrane scission and the ways in which enveloped viruses use these systems to mediate the release of budding virions. PMID:24099087
Regulation of membrane-shape transitions induced by I-BAR domains.
Chen, Zhiming; Shi, Zheng; Baumgart, Tobias
2015-07-21
I-BAR proteins are well-known actin-cytoskeleton adaptors and have been observed to be involved in the formation of plasma membrane protrusions (filopodia). I-BAR proteins contain an all-helical, crescent-shaped IRSp53-MIM domain (IMD) dimer that is believed to be able to couple with a membrane shape. This coupling could involve the sensing and even the generation of negative plasma membrane curvature. Indeed, the in vitro studies have shown that IMDs can induce inward tubulation of liposomes. While N-BAR domains, which generate positive membrane curvature, have received a considerable amount of attention from both theory and experiments, the mechanisms of curvature coupling through IMDs are comparatively less studied and understood. Here we used a membrane-shape stability assay developed recently in our lab to quantitatively characterize IMD-induced membrane-shape transitions. We determined a membrane-shape stability diagram for IMDs that reveals how membrane tension and protein density can comodulate the generation of IMD-induced membrane protrusions. From comparison to analytical theory, we determine three key parameters that characterize the curvature coupling of IMD. We find that the curvature generation capacity of IMDs is significantly stronger compared to that of endophilin, an N-BAR protein known to be involved in plasma membrane shape transitions. Contrary to N-BAR domains, where amphipathic helix insertion is known to promote its membrane curvature generation, for IMDs we find that amphipathic helices inhibit membrane shape transitions, consistent with the inverse curvature that IMDs generate. Importantly, in both of these types of BAR domains, electrostatic interactions affect membrane-binding capacity, but do not appear to affect the curvature generation capacity of the protein. These two types of BAR domain proteins show qualitatively similar membrane shape stability diagrams, suggesting an underlying ubiquitous mechanism by which peripheral proteins
Photon Drag Effect due to Berry Curvature
NASA Astrophysics Data System (ADS)
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-01
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results.
Constraining inverse curvature gravity with supernovae
Mena, Olga; Santiago, Jose; Weller, Jochen; /University Coll., London /Fermilab
2005-10-01
We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.
Geometrical constraint on curvature with BAO experiments
NASA Astrophysics Data System (ADS)
Takada, Masahiro; Doré, Olivier
2015-12-01
The spatial curvature (K or ΩK) is one of the most fundamental parameters of an isotropic and homogeneous universe and has a close link to the physics of the early Universe. Combining the radial and angular diameter distances measured via the baryon acoustic oscillation (BAO) experiments allows us to unambiguously constrain the curvature. The method is primarily based on the metric theory, and is less sensitive to the theory of structure formation (other than the existence of the BAO scale) and is free of any model of dark energy. In this paper, we estimate a best achievable accuracy of constraining the curvature with the BAO experiments. We show that an all-sky, cosmic-variance-limited galaxy survey covering the Universe up to z ≳4 enables a precise determination of the curvature to an accuracy of σ (ΩK)≃1 0-3. When we assume a model of dark energy—either the cosmological constraint or the (w0,wa) model—it can achieve a precision of σ (ΩK)≃a few×10-4. These forecasts require a high sampling density of galaxies, and are degraded by up to a factor of a few for a survey with a finite number density of ˜10-3 (h /Mpc )3 .
Photon Drag Effect due to Berry Curvature.
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-19
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results. PMID:27588858
Graph Curvature for Differentiating Cancer Networks
Sandhu, Romeil; Georgiou, Tryphon; Reznik, Ed; Zhu, Liangjia; Kolesov, Ivan; Senbabaoglu, Yasin; Tannenbaum, Allen
2015-01-01
Cellular interactions can be modeled as complex dynamical systems represented by weighted graphs. The functionality of such networks, including measures of robustness, reliability, performance, and efficiency, are intrinsically tied to the topology and geometry of the underlying graph. Utilizing recently proposed geometric notions of curvature on weighted graphs, we investigate the features of gene co-expression networks derived from large-scale genomic studies of cancer. We find that the curvature of these networks reliably distinguishes between cancer and normal samples, with cancer networks exhibiting higher curvature than their normal counterparts. We establish a quantitative relationship between our findings and prior investigations of network entropy. Furthermore, we demonstrate how our approach yields additional, non-trivial pair-wise (i.e. gene-gene) interactions which may be disrupted in cancer samples. The mathematical formulation of our approach yields an exact solution to calculating pair-wise changes in curvature which was computationally infeasible using prior methods. As such, our findings lay the foundation for an analytical approach to studying complex biological networks. PMID:26169480
Graph Curvature for Differentiating Cancer Networks
NASA Astrophysics Data System (ADS)
Sandhu, Romeil; Georgiou, Tryphon; Reznik, Ed; Zhu, Liangjia; Kolesov, Ivan; Senbabaoglu, Yasin; Tannenbaum, Allen
2015-07-01
Cellular interactions can be modeled as complex dynamical systems represented by weighted graphs. The functionality of such networks, including measures of robustness, reliability, performance, and efficiency, are intrinsically tied to the topology and geometry of the underlying graph. Utilizing recently proposed geometric notions of curvature on weighted graphs, we investigate the features of gene co-expression networks derived from large-scale genomic studies of cancer. We find that the curvature of these networks reliably distinguishes between cancer and normal samples, with cancer networks exhibiting higher curvature than their normal counterparts. We establish a quantitative relationship between our findings and prior investigations of network entropy. Furthermore, we demonstrate how our approach yields additional, non-trivial pair-wise (i.e. gene-gene) interactions which may be disrupted in cancer samples. The mathematical formulation of our approach yields an exact solution to calculating pair-wise changes in curvature which was computationally infeasible using prior methods. As such, our findings lay the foundation for an analytical approach to studying complex biological networks.
How to calculate normal curvatures of sampled geological surfaces
NASA Astrophysics Data System (ADS)
Bergbauer, Stephan; Pollard, David D.
2003-02-01
Curvature has been used both to describe geological surfaces and to predict the distribution of deformation in folded or domed strata. Several methods have been proposed in the geoscience literature to approximate the curvature of surfaces; however we advocate a technique for the exact calculation of normal curvature for single-valued gridded surfaces. This technique, based on the First and Second Fundamental Forms of differential geometry, allows for the analytical calculation of the magnitudes and directions of principal curvatures, as well as Gaussian and mean curvature. This approach is an improvement over previous methods to calculate surface curvatures because it avoids common mathematical approximations, which introduce significant errors when calculated over sloped horizons. Moreover, the technique is easily implemented numerically as it calculates curvatures directly from gridded surface data (e.g. seismic or GPS data) without prior surface triangulation. In geological curvature analyses, problems arise because of the sampled nature of geological horizons, which introduces a dependence of calculated curvatures on the sample grid. This dependence makes curvature analysis without prior data manipulation problematic. To ensure a meaningful curvature analysis, surface data should be filtered to extract only those surface wavelengths that scale with the feature under investigation. A curvature analysis of the top-Pennsylvanian horizon at Goose Egg dome, Wyoming shows that sampled surfaces can be smoothed using a moving average low-pass filter to extract curvature information associated with the true morphology of the structure.
Lipid exchange between membranes.
Jähnig, F
1984-01-01
The exchange of lipid molecules between vesicle bilayers in water and a monolayer forming at the water surface was investigated theoretically within the framework of thermodynamics. The total number of exchanged molecules was found to depend on the bilayer curvature as expressed by the vesicle radius and on the boundary condition for exchange, i.e., whether during exchange the radius or the packing density of the vesicles remains constant. The boundary condition is determined by the rate of flip-flop within the bilayer relative to the rate of exchange between bi- and monolayer. If flip-flop is fast, exchange is independent of the vesicle radius; if flip-flop is slow, exchange increases with the vesicle radius. Available experimental results agree with the detailed form of this dependence. When the theory was extended to exchange between two bilayers of different curvature, the direction of exchange was also determined by the curvatures and the boundary conditions for exchange. Due to the dependence of the boundary conditions on flip-flop and, consequently, on membrane fluidity, exchange between membranes may partially be regulated by membrane fluidity. PMID:6518251
Dynamics and instabilities of lipid bilayer membrane shapes.
Shi, Zheng; Baumgart, Tobias
2014-06-01
Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a 'slipping mode' in addition to the conventional 'bending mode' for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions. PMID:24529968
Dynamics and instabilities of lipid bilayer membrane shapes
Shi, Zheng; Baumgart, Tobias
2014-01-01
Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a ‘slipping mode’ in addition to the conventional ‘bending mode’ for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions. PMID:24529968
An Optical Method For Surface Curvature Testing
NASA Astrophysics Data System (ADS)
Jarisch, W.
1985-01-01
Inspection and measurement of surface quality play increasingly an important role in most machining and polishing processes. A typical example is the manufacturing of magnetic disks. The quality of a disk file essentially depends on the surface flatness of the substrate material. For many measurement aspects largearea topography variations are of less interest than high local changes of slope and curvature of the surface to be tested. Mathematically, the surface curvature is expressed as the second derivative of the profile function of the substrate, while the first derivative is known as the slope. Rapid local variations of the slope, that means high curvature values, cause high vertical accelerations of the magnetic head flying over the disk surface in fractions of a micrometer flight-height. Such irregularities of the substrate in the azimuthal disk direction would lead to uncontrolled fluctuations of the air gap between disk and head causing an attenuation of the write/read signal, to head vibrations, or even to a direct contact of the head with the disk (head crash). In the radial direction, the high-speed radial positioning of the head by voice coil driven motors also may cause a head crash at high local changes of the disk slope. Limits of the tolerable head accelerations, found by experience and theoretically by calculations, are listed in manufacturing specifications. For a fast, large area disk quality inspection and evaluation, a compact and highly sensitive measuring method has been developed. A testing tool based on this method displays the test area superimposed with a clear fringe pattern on a TV screen. The fringe pattern represents the surface curvature. From this, both components of the disk curvature, the azimuthal as well as the radial component, can be measured. Coherent optical interference and Moire techniques are the basic principles of the method providing the fringe pattern of the surface area under test. Each fringe interconnects
Sehgal, Rakesh; Brinker, Charles Jeffrey
1998-01-01
Supported inorganic membranes capable of molecular sieving, and methods for their production, are provided. The subject membranes exhibit high flux and high selectivity. The subject membranes are substantially defect free and less than about 100 nm thick. The pores of the subject membranes have an average critical pore radius of less than about 5 .ANG., and have a narrow pore size distribution. The subject membranes are prepared by coating a porous substrate with a polymeric sol, preferably under conditions of low relative pressure of the liquid constituents of the sol. The coated substrate is dried and calcined to produce the subject supported membrane. Also provided are methods of derivatizing the surface of supported inorganic membranes with metal alkoxides. The subject membranes find use in a variety of applications, such as the separation of constituents of gaseous streams, as catalysts and catalyst supports, and the like.
Membrane tension and peripheral protein density mediate membrane shape transitions
Shi, Zheng; Baumgart, Tobias
2015-01-01
Endocytosis is a ubiquitous eukaryotic membrane budding, vesiculation, and internalization process fulfilling numerous roles including compensation of membrane area increase after bursts of exocytosis. The mechanism of the coupling between these two processes to enable homeostasis is not well understood. Recently, an ultrafast endocytosis (UFE) pathway was revealed with a speed significantly exceeding classical clathrin-mediated endocytosis (CME). Membrane tension reduction is a potential mechanism by which endocytosis can be rapidly activated at remote sites. Here we provide experimental evidence for a mechanism whereby membrane tension reduction initiates membrane budding and tubulation mediated by endocytic proteins such as endophilin A1. We find that shape instabilities occur at well-defined membrane tensions and surface densities of endophilin. From our data, we obtain a membrane shape stability diagram that shows remarkable consistency with a quantitative model. This model applies to all laterally diffusive curvature coupling proteins and therefore a wide range of endocytic proteins. PMID:25569184
Membrane tension and peripheral protein density mediate membrane shape transitions.
Shi, Zheng; Baumgart, Tobias
2015-01-01
Endocytosis is a ubiquitous eukaryotic membrane budding, vesiculation and internalization process fulfilling numerous roles including compensation of membrane area increase after bursts of exocytosis. The mechanism of the coupling between these two processes to enable homeostasis is not well understood. Recently, an ultrafast endocytosis (UFE) pathway was revealed with a speed significantly exceeding classical clathrin-mediated endocytosis (CME). Membrane tension reduction is a potential mechanism by which endocytosis can be rapidly activated at remote sites. Here, we provide experimental evidence for a mechanism whereby membrane tension reduction initiates membrane budding and tubulation mediated by endocytic proteins, such as endophilin A1. We find that shape instabilities occur at well-defined membrane tensions and surface densities of endophilin. From our data, we obtain a membrane shape stability diagram that shows remarkable consistency with a quantitative model. This model applies to all laterally diffusive curvature-coupling proteins and therefore a wide range of endocytic proteins. PMID:25569184
Membrane tension and peripheral protein density mediate membrane shape transitions
NASA Astrophysics Data System (ADS)
Shi, Zheng; Baumgart, Tobias
2015-01-01
Endocytosis is a ubiquitous eukaryotic membrane budding, vesiculation and internalization process fulfilling numerous roles including compensation of membrane area increase after bursts of exocytosis. The mechanism of the coupling between these two processes to enable homeostasis is not well understood. Recently, an ultrafast endocytosis (UFE) pathway was revealed with a speed significantly exceeding classical clathrin-mediated endocytosis (CME). Membrane tension reduction is a potential mechanism by which endocytosis can be rapidly activated at remote sites. Here, we provide experimental evidence for a mechanism whereby membrane tension reduction initiates membrane budding and tubulation mediated by endocytic proteins, such as endophilin A1. We find that shape instabilities occur at well-defined membrane tensions and surface densities of endophilin. From our data, we obtain a membrane shape stability diagram that shows remarkable consistency with a quantitative model. This model applies to all laterally diffusive curvature-coupling proteins and therefore a wide range of endocytic proteins.
Curvature Dependence of Hydrophobic Hydration Dynamics
NASA Astrophysics Data System (ADS)
Weiß, R. Gregor; Heyden, Matthias; Dzubiella, Joachim
2015-05-01
We investigate the solute curvature dependence of water dynamics in the vicinity of hydrophobic spherical solutes using molecular dynamics simulations. For both the lateral and perpendicular diffusivity, as well as for H-bond kinetics of water in the first hydration shell, we find a nonmonotonic solute-size dependence, exhibiting extrema close to the well-known structural crossover length scale for hydrophobic hydration. Additionally, we find an apparent anomalous diffusion for water moving parallel to the surface of small solutes, which, however, can be explained by topology effects. Our findings regarding the intimate connection between solute curvature and water dynamics has implications for our understanding of hydration dynamics at heterogeneous biomolecular surfaces.
Cosmological signatures of anisotropic spatial curvature
NASA Astrophysics Data System (ADS)
Pereira, Thiago S.; Mena Marugán, Guillermo A.; Carneiro, Saulo
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Coarse-grained modeling of DNA curvature
NASA Astrophysics Data System (ADS)
Freeman, Gordon S.; Hinckley, Daniel M.; Lequieu, Joshua P.; Whitmer, Jonathan K.; de Pablo, Juan J.
2014-10-01
The interaction of DNA with proteins occurs over a wide range of length scales, and depends critically on its local structure. In particular, recent experimental work suggests that the intrinsic curvature of DNA plays a significant role on its protein-binding properties. In this work, we present a coarse grained model of DNA that is capable of describing base-pairing, hybridization, major and minor groove widths, and local curvature. The model represents an extension of the recently proposed 3SPN.2 description of DNA [D. M. Hinckley, G. S. Freeman, J. K. Whitmer, and J. J. de Pablo, J. Chem. Phys. 139, 144903 (2013)], into which sequence-dependent shape and mechanical properties are incorporated. The proposed model is validated against experimental data including melting temperatures, local flexibilities, dsDNA persistence lengths, and minor groove width profiles.
Tube curvature measuring probe and method
Sokol, George J.
1990-01-01
The present invention is directed to a probe and method for measuring the radius of curvature of a bend in a section of tubing. The probe includes a member with a pair of guide means, one located at each end of the member. A strain gauge is operatively connected to the member for detecting bending stress exrted on the member as the probe is drawn through and in engagement with the inner surface of a section of tubing having a bend. The method of the present invention includes steps utilizing a probe, like the aforementioned probe, which can be made to detect bends only in a single plane when having a fixed orientation relative the section of tubing to determine the maximum radius of curvature of the bend.
Transformation optics, curvature and beyond (Conference Presentation)
NASA Astrophysics Data System (ADS)
McCall, Martin W.
2016-04-01
Although the transformation algorithm is very well established and implemented, some intriguing questions remain unanswered. 1) In what precise mathematical sense is the transformation optics algorithm `exact'? The invariance of Maxwell's equations is well understood, but in what sense does the same principle not apply to acoustics (say)? 2) Even if the fields are transformed in a way that apparently mimic vacuum perfectly, it is easy to construct very simple examples where the impedance of the transformed medium is no longer isotropic and homogeneous. This would seem to imply a fundamental shortcoming in any claim that electromagnetic cloaking has been reduced to technology. 3) Transformations are known to exist that introduce a discrepancy between the Poynting vector and the wave-vector. Does this distinction carry any physical significance? We have worked extensively on understanding a commonality between transformation theories that operates at the level of rays - being interpreted as geodesics of an appropriate manifold. At this level we now understand that the *key* problem underlying all attempts to unify the transformational approach to disparate areas of physics is how to relate the transformation of the base metric (be it Euclidean for spatial transformation optics, or Minkowskian for spacetime transformation optics) to the medium parameters of a given physical domain (e.g. constitutive parameters for electromagnetism, bulk modulus and mass density for acoustics, diffusion constant and number density for diffusion physics). Another misconception we will seek to address is the notion of the relationship between transformation optics and curvature. Many have indicated that transformation optics evinces similarities with Einstein's curvature of spacetime. Here we will show emphatically that transformation optics cannot induce curvature. Inducing curvature in an electromagnetic medium requires the equivalent of a gravitational source. We will propose a scheme
Multiple Manifold Clustering Using Curvature Constrained Path
Babaeian, Amir; Bayestehtashk, Alireza; Bandarabadi, Mojtaba
2015-01-01
The problem of multiple surface clustering is a challenging task, particularly when the surfaces intersect. Available methods such as Isomap fail to capture the true shape of the surface near by the intersection and result in incorrect clustering. The Isomap algorithm uses shortest path between points. The main draw back of the shortest path algorithm is due to the lack of curvature constrained where causes to have a path between points on different surfaces. In this paper we tackle this problem by imposing a curvature constraint to the shortest path algorithm used in Isomap. The algorithm chooses several landmark nodes at random and then checks whether there is a curvature constrained path between each landmark node and every other node in the neighborhood graph. We build a binary feature vector for each point where each entry represents the connectivity of that point to a particular landmark. Then the binary feature vectors could be used as a input of conventional clustering algorithm such as hierarchical clustering. We apply our method to simulated and some real datasets and show, it performs comparably to the best methods such as K-manifold and spectral multi-manifold clustering. PMID:26375819
Effects of wall curvature on turbulence statistics
NASA Technical Reports Server (NTRS)
Moser, R. D.; Moin, P.
1985-01-01
A three-dimensional, time-dependent, direct numerical simulation of low-Reynolds number turbulent flow in a mildly curved channel was performed, and the results examined to determine the mechanism by which curvature affects wall-bounded turbulent shear flows. A spectral numerical method with about one-million modes was employed, and no explicit subgrid scale model was used. The effects of curvature on this flow were determined by comparing the concave and convex sides of the channel. The observed effects are consistent with experimental observations for mild curvature. The most significant difference in the turbulence statistics between the concave and convex sides is in the Reynolds shear stress. This is accompanied by significant differences in the terms of the Reynolds shear stress balance equations. In addition, it was found that stationary Taylor-Goertler vortices were present and that they had a significant effect on the flow by contributing to the mean Reynolds shear stress, and by enhancing the difference between the wall shear stresses.
Superintegrable systems on spaces of constant curvature
Gonera, Cezary Kaszubska, Magdalena
2014-07-15
Construction and classification of two-dimensional (2D) superintegrable systems (i.e. systems admitting, in addition to two global integrals of motion guaranteeing the Liouville integrability, the third global and independent one) defined on 2D spaces of constant curvature and separable in the so-called geodesic polar coordinates are presented. The method proposed is applicable to any value of curvature including the case of Euclidean plane, sphere and hyperbolic plane. The main result is a generalization of Bertrand’s theorem on 2D spaces of constant curvature and covers most of the known separable and superintegrable models on such spaces (in particular, the so-called Tremblay–Turbiner–Winternitz (TTW) and Post–Winternitz (PW) models which have recently attracted some interest). -- Highlights: •Classifying 2D superintegrable, separable (polar coordinates) systems on S{sup 2}, R{sup 2}, H{sup 2}. •Construction of radial, angular potentials leading to superintegrability. •Generalization of Bertrand’s theorem covering known models, e.g. Higgs, TTW, PW, and Coulomb.
Beshears, John; Choi, James J.; Laibson, David; Madrian, Brigitte C.
2009-01-01
Revealed preferences are tastes that rationalize an economic agent’s observed actions. Normative preferences represent the agent’s actual interests. It sometimes makes sense to assume that revealed preferences are identical to normative preferences. But there are many cases where this assumption is violated. We identify five factors that increase the likelihood of a disparity between revealed preferences and normative preferences: passive choice, complexity, limited personal experience, third-party marketing, and intertemporal choice. We then discuss six approaches that jointly contribute to the identification of normative preferences: structural estimation, active decisions, asymptotic choice, aggregated revealed preferences, reported preferences, and informed preferences. Each of these approaches uses consumer behavior to infer some property of normative preferences without equating revealed and normative preferences. We illustrate these issues with evidence from savings and investment outcomes. PMID:24761048
Stable hypersurfaces with zero scalar curvature in Euclidean space
NASA Astrophysics Data System (ADS)
Alencar, Hilário; do Carmo, Manfredo; Neto, Gregório Silva
2016-04-01
In this paper we prove some results concerning stability of hypersurfaces in the four dimensional Euclidean space with zero scalar curvature. First we prove there is no complete stable hypersurface with zero scalar curvature, polynomial growth of integral of the mean curvature, and with the Gauss-Kronecker curvature bounded away from zero. We conclude this paper giving a sufficient condition for a regular domain to be stable in terms of the mean and the Gauss-Kronecker curvatures of the hypersurface and the radius of the smallest extrinsic ball which contains the domain.
Distributed mean curvature on a discrete manifold for Regge calculus
NASA Astrophysics Data System (ADS)
Conboye, Rory; Miller, Warner A.; Ray, Shannon
2015-09-01
The integrated mean curvature of a simplicial manifold is well understood in both Regge Calculus and Discrete Differential Geometry. However, a well motivated pointwise definition of curvature requires a careful choice of the volume over which to uniformly distribute the local integrated curvature. We show that hybrid cells formed using both the simplicial lattice and its circumcentric dual emerge as a remarkably natural structure for the distribution of this local integrated curvature. These hybrid cells form a complete tessellation of the simplicial manifold, contain a geometric orthonormal basis, and are also shown to give a pointwise mean curvature with a natural interpretation as the fractional rate of change of the normal vector.
The crack problem in a specially orthotropic shell with double curvature
NASA Technical Reports Server (NTRS)
Delale, F.; Erdogan, F.
1982-01-01
The crack problem of a shallow shell with two nonzero curvatures is considered. It is assumed that the crack lies in one of the principal planes of curvature and the shell is under Mode I loading condition. The material is assumed to be specially orthotropic. After giving the general formulation of the problem the asymptotic behavior of the stress state around the crack tip is examined. The analysis is based on Reissner's transverse shear theory. Thus, as in the bending of cracked plates, the asymptotic results are shown to be consistent with that obtained from the plane elasticity solution of crack problems. Rather extensive numerical results are obtained which show the effect of material orthotropy on the stress intensity factors in cylindrical and spherical shells and in shells with double curvature. Other results include the stress intensity factors in isotropic toroidal shells with positive or negative curvature ratio, the distribution of the membrane stress resultant outside the crack, and the influence of the material orthotropy on the angular distribution of the stresses around the crack tip.
The crack problem in a specially orthotropic shell with double curvature
NASA Technical Reports Server (NTRS)
Delale, F.; Erdogan, F.
1983-01-01
The crack problem of a shallow shell with two nonzero curvatures is considered. It is assumed that the crack lies in one of the principal planes of curvature and the shell is under Mode I loading condition. The material is assumed to be specially orthotropic. After giving the general formulation of the problem the asymptotic behavior of the stress state around the crack tip is examined. The analysis is based on Reissner's transverse shear theory. Thus, as in the bending of cracked plates, the asymptotic results are shown to be consistent with that obtained from the plane elasticity solution of crack problems. Rather extensive numerical results are obtained which show the effect of material orthotropy on the stress intensity factors in cylindrical and spherical shells and in shells with double curvature. Other results include the stress intensity factors in isotropic toroidal shells with positive or negative curvature ratio, the distribution of the membrane stress resultant outside the crack, and the influence of the material orthotropy on the angular distribution of the stresses around the crack tip. Previously announced in STAR as N83-16782
Mechanical model for fiber-laden membranes
NASA Astrophysics Data System (ADS)
Rey, Alejandro D.; Murugesan, Yogesh K.
2011-01-01
An integrated mechanical model for fiber-laden membranes is presented and representative predictions of relevance to cellulose ordering and orientation in the plant cell wall are presented. The model describes nematic liquid crystalline self-assembly of rigid fibers on an arbitrarily curved fluid membrane. The mechanics of the fluid membrane is described by the Helfrich bending-torsion model, the fiber self-assembly is described by the 2D Landau-de Gennes quadrupolar Q-tensor order parameter model, and the fiber-membrane interactions (inspired by an extension of the 2D Maier-Saupe model to curved surfaces) include competing curvo-philic (curvature-seeking) and curvo-phobic (curvature-avoiding) effects. Analysis of the free energy reveals three fiber orientation regimes: (a) along the major curvature, (b) along the minor curvature, (c) away from the principal curvatures, according to the competing curvo-philic and curvo-phobic interactions. The derived shape equation (normal stress balance) now includes curvature-nematic ordering contributions, with both bending and torsion renormalizations. Integration of the shape and nematic order equations gives a complete model whose solution describes the coupled membrane shape/fiber order state. Applications to cylindrical membranes, relevant to the plant cell wall, shows how growth decreases the fiber order parameter and moves the fibers' director from the axial direction towards the azimuthal orientation, eventually leading to a state of stress predicted by pure membranes. The ubiquitous 54.7° cellulose fibril orientation with respect to the long axis in a cylindrical plant cell wall is shown to be predicted by the preset model when the ratio of curvo-phobic and curvo-philic interactions is in the range of the cylinder radius.
Interaction between bending and tension forces in bilayer membranes.
Secomb, T W
1988-01-01
A theoretical analysis is presented of the bending mechanics of a membrane consisting of two tightly-coupled leaflets, each of which shears and bends readily but strongly resists area changes. Structures of this type have been proposed to model biological membranes such as red blood cell membrane. It is shown that when such a membrane is bent, anisotropic components of resultant membrane tension (shear stresses) are induced, even when the tension in each leaflet is isotropic. The induced shear stresses increase as the square of the membrane curvature, and become significant for moderate curvatures (when the radius of curvature is much larger than the distance between the leaflets). This effect has implications for the analysis of shape and deformation of freely suspended and flowing red blood cells. PMID:3224154
Crystallizing Membrane Proteins in Lipidic Mesophases. A Host Lipid Screen
Li, Dianfan; Lee, Jean; Caffrey, Martin
2011-11-30
The default lipid for the bulk of the crystallogenesis studies performed to date using the cubic mesophase method is monoolein. There is no good reason, however, why this 18-carbon, cis-monounsaturated monoacylglycerol should be the preferred lipid for all target membrane proteins. The latter come from an array of biomembrane types with varying properties that include hydrophobic thickness, intrinsic curvature, lateral pressure profile, lipid and protein makeup, and compositional asymmetry. Thus, it seems reasonable that screening for crystallizability based on the identity of the lipid creating the hosting mesophase would be worthwhile. For this, monoacylglycerols with differing acyl chain characteristics, such as length and olefinic bond position, must be available. A lipid synthesis and purification program is in place in the author's laboratory to serve this need. In the current study with the outer membrane sugar transporter, OprB, we demonstrate the utility of host lipid screening as a means for generating diffraction-quality crystals. Host lipid screening is likely to prove a generally useful strategy for mesophase-based crystallization of membrane proteins.
Schell, William J.
1979-01-01
A dry, fabric supported, polymeric gas separation membrane, such as cellulose acetate, is prepared by casting a solution of the polymer onto a shrinkable fabric preferably formed of synthetic polymers such as polyester or polyamide filaments before washing, stretching or calendering (so called griege goods). The supported membrane is then subjected to gelling, annealing, and drying by solvent exchange. During the processing steps, both the fabric support and the membrane shrink a preselected, controlled amount which prevents curling, wrinkling or cracking of the membrane in flat form or when spirally wound into a gas separation element.
FtsZ Protofilament Curvature Is the Opposite of Tubulin Rings.
Housman, Max; Milam, Sara L; Moore, Desmond A; Osawa, Masaki; Erickson, Harold P
2016-07-26
FtsZ protofilaments (pfs) form the bacterial cytokinetic Z ring. Previous work suggested that a conformational change from straight to curved pfs generated the constriction force. In the simplest model, the C-terminal membrane tether is on the outside of the curved pf, facing the membrane. Tubulin, a homologue of FtsZ, also forms pfs with a curved conformation. However, it is well-established that tubulin rings have the C terminus on the inside of the ring. Could FtsZ and tubulin rings have the opposite curvature? In this study, we explored the FtsZ curvature direction by fusing large protein tags to the FtsZ termini. Thin section electron microscopy showed that the C-terminal tag was on the outside, consistent with the bending pf model. This has interesting implications for the evolution of tubulin. Tubulin likely began with the curvature of FtsZ, but evolution managed to reverse direction to produce outward-curving rings, which are useful for pulling chromosomes. PMID:27368355
The curvature adaptive optics system modeling
NASA Astrophysics Data System (ADS)
Yang, Qiang
A curvature adaptive optics (AO) simulation system has been built. The simulation is based on the Hokupa'a-36 AO system for the NASA IRTF 3m telescope and the Hokupa'a-85 AO system for the Gemini Near Infrared Coronagraphic Imager. Several sub-models are built separately for the AO simulation system, and they are: (1) generation and propagation of atmospheric phase screens, (2) the bimorph deformable mirror (DM), (3) the curvature wave-front sensor (CWFS), (4) generation of response functions, interaction matrices and calculation of command matrices, (5) Fresnel propagation from the DM pupil to the lenslet pupil, (6) AO servo loop, and (7) post processing. The AO simulation system is then applied to the effects of DM hysteresis, and to the optimization of DM actuator patterns for the Hokupa'a-85 and Hokupa'a-36 AO systems. In the first application, an enhancing Coleman-Hodgdon model is introduced to approximate the hysteresis curves, and then the Lambert W function is introduced to calculate the inverse of the Coleman-Hodgdon equation. Step response, transfer functions and Strehl Ratios from the AO system have been compared under the cases with/without DM hysteresis. The servo-loop results show that the bandwidth of an AO system is improved greatly after the DM hysteresis is corrected. In the second application, many issues of the bimorph mirror will be considered to optimize the DM patterns, and they include the type and length of the edge benders, gap size of electrodes, DM size, and DM curvature limit.
Curvature sensors: noise and its propagation.
Kellerer, Aglae
2010-11-01
The signal measured with a curvature sensor is analyzed. At the outset, we derive the required minimum number of sensing elements at the pupil edges, depending on the total number of sensing elements. The distribution of the sensor signal is further characterized in terms of its mean, variance, kurtosis, and skewness. It is established that while the approximation in terms of a Gaussian distribution is correct down to fairly low photon numbers, much higher numbers are required to obtain meaningful sensor measurements for small wavefront distortions. Finally, we indicate a closed expression for the error propagation factor and for the photon-noise-induced Strehl loss. PMID:21045888
Negative Gaussian curvature from induced metric changes.
Modes, Carl D; Warner, Mark
2015-07-01
We revisit the light or heat-induced changes in topography of initially flat sheets of a solid that elongate or contract along patterned in-plane director fields. For radial or azimuthal directors, negative Gaussian curvature is generated-so-called "anticones." We show that azimuthal material displacements are required for the distorted state to be stretch free and bend minimizing. The resultant shapes are smooth and asterlike and can become reentrant in the azimuthal coordinate for large deformations. We show that care is needed when considering elastomers rather than glasses, although the former offer huge deformations. PMID:26274106
Curvature and temperature of complex networks
NASA Astrophysics Data System (ADS)
Krioukov, Dmitri; Papadopoulos, Fragkiskos; Vahdat, Amin; Boguñá, Marián
2009-09-01
We show that heterogeneous degree distributions in observed scale-free topologies of complex networks can emerge as a consequence of the exponential expansion of hidden hyperbolic space. Fermi-Dirac statistics provides a physical interpretation of hyperbolic distances as energies of links. The hidden space curvature affects the heterogeneity of the degree distribution, while clustering is a function of temperature. We embed the internet into the hyperbolic plane and find a remarkable congruency between the embedding and our hyperbolic model. Besides proving our model realistic, this embedding may be used for routing with only local information, which holds significant promise for improving the performance of internet routing.
Curvature sensor for ocular wavefront measurement.
Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O
2006-08-01
We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes. PMID:16832447
Amplification of curvature perturbations in cyclic cosmology
Zhang Jun; Liu Zhiguo; Piao Yunsong
2010-12-15
We analytically and numerically show that through the cycles with nonsingular bounce, the amplitude of curvature perturbation on a large scale will be amplified and the power spectrum will redden. In some sense, this amplification will eventually destroy the homogeneity of the background, which will lead to the ultimate end of cycles of the global universe. We argue that for the model with increasing cycles, it might be possible that a fissiparous multiverse will emerge after one or several cycles, in which the cycles will continue only at corresponding local regions.
Double curvature mirrors for linear concentrators
NASA Astrophysics Data System (ADS)
Lance, Tamir; Ackler, Harold; Finot, Marc
2012-10-01
Skyline Solar's medium concentration photovoltaic system uses quasi-parabolic mirrors and one axis tracking. Improvements in levelized cost of energy can be achieved by effective management of non-uniformity of the flux line on the panels. To reduce non uniformity of the flux line due to mirror to mirror gaps, Skyline developed a dual curvature mirror that stretches the flux line along the panel. Extensive modeling and experiments have been conducted to analyze the impact of this new design and to optimize the design.
Holographic entropy increases in quadratic curvature gravity
NASA Astrophysics Data System (ADS)
Bhattacharjee, Srijit; Sarkar, Sudipta; Wall, Aron C.
2015-09-01
Standard methods for calculating the black hole entropy beyond general relativity are ambiguous when the horizon is nonstationary. We fix these ambiguities in all quadratic curvature gravity theories, by demanding that the entropy be increasing at every time, for linear perturbations to a stationary black hole. Our result matches with the entropy formula found previously in holographic entanglement entropy calculations. We explicitly calculate the entropy increase for Vaidya-like solutions in Ricci-tensor gravity to show that (unlike the Wald entropy) the holographic entropy obeys a second law.
Spacetime Curvature and Higgs Stability after Inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2015-12-11
We investigate the dynamics of the Higgs field at the end of inflation in the minimal scenario consisting of an inflaton field coupled to the standard model only through the nonminimal gravitational coupling ξ of the Higgs field. Such a coupling is required by renormalization of the standard model in curved space, and in the current scenario also by vacuum stability during high-scale inflation. We find that for ξ≳1, rapidly changing spacetime curvature at the end of inflation leads to significant production of Higgs particles, potentially triggering a transition to a negative-energy Planck scale vacuum state and causing an immediate collapse of the Universe. PMID:26705621
Steering electromagnetic beams with conical curvature singularities.
Zhang, Yong-Liang; Dong, Xian-Zi; Zheng, Mei-Ling; Zhao, Zhen-Sheng; Duan, Xuan-Ming
2015-10-15
We describe how the transformation-optics technique can be used to design an effective medium mimicking the conical curvature singularity. Anholonomic coordinate transformation gives rise to linear topological defects that break the rotational symmetry. The bending and splitting of the optical beams are found analytically and numerically, depending on the incident direction and the topological charge. Beyond their practical applications to omnidirectional beam steering for photonics, our findings set forth an attractive realm to simulate the relevant physical phenomena in the optical laboratory. PMID:26469619
ERIC Educational Resources Information Center
Regenwetter, Michel; Dana, Jason; Davis-Stober, Clintin P.
2011-01-01
Transitivity of preferences is a fundamental principle shared by most major contemporary rational, prescriptive, and descriptive models of decision making. To have transitive preferences, a person, group, or society that prefers choice option "x" to "y" and "y" to "z" must prefer "x" to "z". Any claim of empirical violations of transitivity by…
Charge transfer and negative curvature energy in magnesium boride nanotubes
NASA Astrophysics Data System (ADS)
Tang, Hui; Ismail-Beigi, Sohrab
2016-07-01
Using first-principles calculations based on density functional theory, we study the energetics and charge transfer effects in MgBx nanotubes and two-dimensional (2D) sheets. The behavior of adsorbed Mg on 2D boron sheets is found to depend on the amount of electron transfer between the two subsystems. The amount is determined by both the density of adsorbed Mg as well as the atomic-scale structure of the boron subsystem. The degree of transfer can lead to repulsive or attractive Mg-Mg interactions. In both cases, model MgBx nanotubes built from 2D MgBx sheets can display negative curvature energy: a relatively unusual situation in nanosystems where the energy cost to curve the parent 2D sheet into a small-diameter nanotube is negative. Namely, the small-diameter nanotube is energetically preferred over the corresponding flat sheet. We also discuss how these findings may manifest themselves in experimentally synthesized MgBx nanotubes.
Force-control at cellular membranes
Galic, Milos; Begemann, Isabell; Viplav, Abhiyan; Matis, Maja
2014-01-01
Force-regulation at cellular membranes relies on dynamic molecular platforms that integrate intra- and extracellular signals to control cell shape and function. To correctly respond to a continuously changing environment, activity of these platforms needs to be tightly controlled in space and time. Over the last few years, curvature-dependent mechano-chemical signal translation—a receptor-independent signaling mechanism where physical forces at the plasma membrane trigger nanoscale membrane deformations that are then translated into chemical signal transduction cascades—has emerged as a new signaling principle that cells use to regulate forces at the membrane. However, until recently, technical limitations have precluded studies of this force-induced curvature-dependent signaling at the physiological scale. Here, we comment on recent advancements that allow studying curvature-dependent signaling at membranes, and discuss processes where it may be involved in. Considering its general impact on cell function, a particular focus will be put on the curvature-dependence of feedback loops that control actin-based forces at cellular membranes. PMID:25715331
Turbulent boundary layers subjected to multiple curvatures and pressure gradients
NASA Technical Reports Server (NTRS)
Bandyopadhyay, Promode R.; Ahmed, Anwar
1993-01-01
The effects of abruptly applied cycles of curvatures and pressure gradients on turbulent boundary layers are examined experimentally. Two two-dimensional curved test surfaces are considered: one has a sequence of concave and convex longitudinal surface curvatures and the other has a sequence of convex and concave curvatures. The choice of the curvature sequences were motivated by a desire to study the asymmetric response of turbulent boundary layers to convex and concave curvatures. The relaxation of a boundary layer from the effects of these two opposite sequences has been compared. The effect of the accompaying sequences of pressure gradient has also been examined but the effect of curvature dominates. The growth of internal layers at the curvature junctions have been studied. Measurements of the Gortler and corner vortex systems have been made. The boundary layer recovering from the sequence of concave to convex curvature has a sustained lower skin friction level than in that recovering from the sequence of convex to concave curvature. The amplification and suppression of turbulence due to the curvature sequences have also been studied.
The role of cholesterol in membrane fusion.
Yang, Sung-Tae; Kreutzberger, Alex J B; Lee, Jinwoo; Kiessling, Volker; Tamm, Lukas K
2016-09-01
Cholesterol modulates the bilayer structure of biological membranes in multiple ways. It changes the fluidity, thickness, compressibility, water penetration and intrinsic curvature of lipid bilayers. In multi-component lipid mixtures, cholesterol induces phase separations, partitions selectively between different coexisting lipid phases, and causes integral membrane proteins to respond by changing conformation or redistribution in the membrane. But, which of these often overlapping properties are important for membrane fusion?-Here we review a range of recent experiments that elucidate the multiple roles that cholesterol plays in SNARE-mediated and viral envelope glycoprotein-mediated membrane fusion. PMID:27179407
Detonation Front Curvatures and Detonation Rates
NASA Astrophysics Data System (ADS)
Lauderbach, Lisa M.; Lorenz, K. Thomas; Lee, Edward L.; Souers, P. Clark
2015-06-01
We have normalized the LLNL library of detonation front curvatures by dividing lags by the edge lag and radii by the edge radius. We then fit the normalized data to the equation L = AR2 + BR8, where L is the normalized lag and R is the normalized radius. We attribute the quadratic term to thermal processes and the 8th-power term to shock processes. We compare the % of the quadratic term J at the edge with detonation rates obtained from the size effect. One class of results is made up of fine-grained, uniform explosives with large lags, where a low detonation rate leads to a high J and vice versa. This provides a rough way of estimating unknown rates if the unknown explosive is of high quality. The other, equally-large class contains rough-grained materials, often with small lags and small radii. These have curves that do not fit the equation but superfically often look quadratic. Some HMX and PETN curvatures even show a ``sombrero'' effect. Code models show that density differences of 0.03 g/cc in ram-pressed parts can cause pseudo-quadratic curves and even sombreros. Modeling is used to illustrate J at the lowest and highest possible detonation rates. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Kinetic information from detonation front curvature
Souers, P. C., LLNL
1998-06-15
The time constants for time-dependent modeling may be estimated from reaction zone lengths, which are obtained from two sources One is detonation front curvature, where the edge lag is close to being a direct measure The other is the Size Effect, where the detonation velocity decreases with decreasing radius as energy is lost to the cylinder edge A simple theory that interlocks the two effects is given A differential equation for energy flow in the front is used, the front is described by quadratic and sixth-power radius terms The quadratic curvature comes from a constant power source of energy moving sideways to the walls Near the walls, the this energy rises to the total energy of detonation and produces the sixth-power term The presence of defects acting on a short reaction zone can eliminate the quadratic part while leaving the wall portion of the cuvature A collection of TNT data shows that the reaction zone increases with both the radius and the void fraction
Effects of streamline curvature on separation prediction
NASA Astrophysics Data System (ADS)
Arolla, Sunil K.; Durbin, Paul A.
2009-11-01
In this study, the effects of streamline curvature on prediction of flow separation are investigated. The geometry is a circulation control airfoil, a high-lift configuration that has been under extensive research for more than two decades. A tangential jet is blown over a thick, rounded trailing edge, using the Coanda effect to delay separation. An attempt is made to understand, through numerical simulations, the dynamics of turbulent separation and reattachment on the Coanda surface. Highly curved, attached recirculation regions are seen to form. A physics based curvature correction proposed by Pettersson-Reif et al. (1999) is used in conjunction with ζ-f turbulence model. The chord-based Reynolds number is Re = 10^6. Two jet momentum coefficients of Cμ=0.03 and 0.1 are computed. In this paper, comparisons between the computed and experimental pressure distributions, velocity profiles and the position of flow detachment are presented. Comparisons with other closures such as Menter's SST model are also discussed.
Vortex motion on surfaces of small curvature
Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.
2013-12-15
We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.
Iori, F.; Grechy, L.; Gedroyc, W.; Duncan, N.; Caro, C. G.; Vincent, P. E.
2015-01-01
Arterio-Venous Fistulae (AVF) are the preferred method of vascular access for patients with end stage renal disease who need hemodialysis. In this study, simulations of blood flow and oxygen transport were undertaken in various idealized AVF configurations. The objective of the study was to understand how arterial curvature affects blood flow and oxygen transport patterns within AVF, with a focus on how curvature alters metrics known to correlate with vascular pathology such as Intimal Hyperplasia (IH). If one subscribes to the hypothesis that unsteady flow causes IH within AVF, then the results suggest that in order to avoid IH, AVF should be formed via a vein graft onto the outer-curvature of a curved artery. However, if one subscribes to the hypothesis that low wall shear stress and/or low lumen-to-wall oxygen flux (leading to wall hypoxia) cause IH within AVF, then the results suggest that in order to avoid IH, AVF should be formed via a vein graft onto a straight artery, or the inner-curvature of a curved artery. We note that the recommendations are incompatible—highlighting the importance of ascertaining the exact mechanisms underlying development of IH in AVF. Nonetheless, the results clearly illustrate the important role played by arterial curvature in determining AVF hemodynamics, which to our knowledge has been overlooked in all previous studies. PMID:25829837
Asymptotic behavior of curvature of surface elements in isotropic turbulence
NASA Technical Reports Server (NTRS)
Girimaji, S. S.
1991-01-01
The asymptotic behavior of the curvature of material elements in turbulence is investigated using Lagrangian velocity-gradient time series obtained from direct numerical simulations of isotropic turbulence. Several material-element ensembles of different initial curvatures and shapes are studied. It is found that, at long times, the (first five) moments of the logarithm of characteristic curvature and shape factor asymptote to values that are independent of the initial curvature or shape. This evidence strongly suggests that the asymptotic pdf's of the curvature and shape of material elements are stationary and independent of initial conditions. Irrespective of initial curvature or shape, the asymptotic shape of a material surface is cylindrical with a high probability.
Substituted polyacetylene separation membrane
Pinnau, Ingo; Morisato, Atsushi
1998-01-13
A separation membrane useful for gas separation, particularly separation of C.sub.2+ hydrocarbons from natural gas. The invention encompasses the membrane itself, methods of making it and processes for using it. The membrane comprises a polymer having repeating units of a hydrocarbon-based, disubstituted polyacetylene, having the general formula: ##STR1## wherein R.sub.1 is chosen from the group consisting of C.sub.1 -C.sub.4 alkyl and phenyl, and wherein R.sub.2 is chosen from the group consisting of hydrogen and phenyl. In the most preferred embodiment, the membrane comprises poly(4-methyl-2-pentyne) ›PMP!. The membrane exhibits good chemical resistance and has super-glassy properties with regard to separating certain large, condensable permeant species from smaller, less-condensable permeant species. The membranes may also be useful in other fluid separations.
Substituted polyacetylene separation membrane
Pinnau, I.; Morisato, Atsushi
1998-01-13
A separation membrane is described which is useful for gas separation, particularly separation of C{sub 2+} hydrocarbons from natural gas. The invention encompasses the membrane itself, methods of making it and processes for using it. The membrane comprises a polymer having repeating units of a hydrocarbon-based, disubstituted polyacetylene, having the general formula shown in the accompanying diagram, wherein R{sub 1} is chosen from the group consisting of C{sub 1}-C{sub 4} alkyl and phenyl, and wherein R{sub 2} is chosen from the group consisting of hydrogen and phenyl. In the most preferred embodiment, the membrane comprises poly(4-methyl-2-pentyne) [PMP]. The membrane exhibits good chemical resistance and has super-glassy properties with regard to separating certain large, condensable permeant species from smaller, less-condensable permeant species. The membranes may also be useful in other fluid separations. 4 figs.
Compact surfaces of constant Gaussian curvature in Randers manifolds
NASA Astrophysics Data System (ADS)
Cui, Ningwei
2016-08-01
The flag curvature of a Finsler surface is called the Gaussian curvature in Finsler geometry. In this paper, we characterize the surfaces of constant Gaussian curvature (CGC) in the Randers 3-manifold. Then we give a classification of the orientable closed CGC surfaces in two Randers space forms, which are the non-Euclidean Minkowski-Randers 3-space (K = 0) and the Bao-Shen sphere (K = 1).
Eddy-Current Measurement Of Turning Or Curvature
NASA Technical Reports Server (NTRS)
Chern, Engmin J.
1993-01-01
Rotatable conductive plate covers sensing coil to varying degree. Curvature of pipe at remote or otherwise inaccessible location inside pipe measured using relatively simple angular-displacement eddy-current probe. Crawler and sensor assemblies move along inside of pipe on wheels. Conductive plate pivots to follow curvature of pipe, partly covering one of eddy-current coils to degree depending on local curvature on pipe.
Wrinkles and splay conspire to give positive disclinations negative curvature.
Matsumoto, Elisabetta A; Vega, Daniel A; Pezzutti, Aldo D; García, Nicolás A; Chaikin, Paul M; Register, Richard A
2015-10-13
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
Wrinkles and splay conspire to give positive disclinations negative curvature
Matsumoto, Elisabetta A.; Vega, Daniel A.; Pezzutti, Aldo D.; García, Nicolás A.; Chaikin, Paul M.; Register, Richard A.
2015-01-01
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
Calcium-actin waves and oscillations of cellular membranes.
Veksler, Alex; Gov, Nir S
2009-09-16
We propose a mechanism for the formation of membrane oscillations and traveling waves, which arise due to the coupling between the actin cytoskeleton and the calcium flux through the membrane. In our model, the fluid cell membrane has a mobile but constant population of proteins with a convex spontaneous curvature, which act as nucleators of actin polymerization and adhesion. Such a continuum model couples the forces of cell-substrate adhesion, actin polymerization, membrane curvature, and the flux of calcium through the membrane. Linear stability analysis shows that sufficiently strong coupling among the calcium, membrane, and protein dynamics may induce robust traveling waves on the membrane. This result was checked for a reduced feedback scheme and is compared to the results without the effects of calcium, where permanent phase separation without waves or oscillations is obtained. The model results are compared to the published observations of calcium waves in cell membranes, and a number of testable predictions are proposed. PMID:19751660
Evolution of the curvature perturbations during warm inflation
Matsuda, Tomohiro
2009-06-15
This paper considers warm inflation as an interesting application of multi-field inflation. Delta-N formalism is used for the calculation of the evolution of the curvature perturbations during warm inflation. Although the perturbations considered in this paper are decaying after the horizon exit, the corrections to the curvature perturbations sourced by these perturbations can remain and dominate the curvature perturbations at large scales. In addition to the typical evolution of the curvature perturbations, inhomogeneous diffusion rate is considered for warm inflation, which may lead to significant non-Gaussianity of the spectrum.
Mean Curvature Flow in a Ricci Flow Background
NASA Astrophysics Data System (ADS)
Lott, John
2012-07-01
Following work of Ecker (Comm Anal Geom 15:1025-1061, 2007), we consider a weighted Gibbons-Hawking-York functional on a Riemannian manifold-with-boundary. We compute its variational properties and its time derivative under Perelman's modified Ricci flow. The answer has a boundary term which involves an extension of Hamilton's differential Harnack expression for the mean curvature flow in Euclidean space. We also derive the evolution equations for the second fundamental form and the mean curvature, under a mean curvature flow in a Ricci flow background. In the case of a gradient Ricci soliton background, we discuss mean curvature solitons and Huisken monotonicity.
Plane wave gravitons, curvature singularities and string physics
Brooks, R. . Center for Theoretical Physics)
1991-03-21
This paper discusses bounded (compactifying) potentials arising from a conspiracy between plane wave graviton and dilaton condensates. So are string propagation and supersymmetry in spacetimes with curvature singularities.
Rotational preference in gymnastics.
Heinen, Thomas; Jeraj, Damian; Vinken, Pia M; Velentzas, Konstantinos
2012-06-01
In gymnastics, most skills incorporate rotations about one or more body axes. At present, the question remains open if factors such as lateral preference and/or vestibulo-spinal asymmetry are related to gymnast's rotational preference. Therefore, we sought to explore relationships in gymnast's rotation direction between different gymnastic skills. Furthermore, we sought to explore relationships between rotational preference, lateral preference, and vestibulo-spinal asymmetry. In the experiment n = 30 non-experts, n = 30 near-experts and n = 30 experts completed a rotational preference questionnaire, a lateral preference inventory, and the Unterberger-Fukuda Stepping Test. The results revealed, that near-experts and experts more often rotate rightward in the straight jump with a full turn when rotating leftward in the round-off and vice versa. The same relationship was found for experts when relating the rotation preference in the handstand with a full turn to the rotation preference in the straight jump with a full turn. Lateral preference was positively related to rotational preference in non-expert gymnasts, and vestibulo-spinal asymmetry was positively related to rotational preference in experts. We suggest, that gymnasts should explore their individual rotational preference by systematically practicing different skills with a different rotation direction, bearing in mind that a clearly developed structure in rotational preference between different skills may be appropriate to develop more complex skills in gymnastics. PMID:23486362
Rotational Preference in Gymnastics
Heinen, Thomas; Jeraj, Damian; Vinken, Pia M.; Velentzas, Konstantinos
2012-01-01
In gymnastics, most skills incorporate rotations about one or more body axes. At present, the question remains open if factors such as lateral preference and/or vestibulo-spinal asymmetry are related to gymnast’s rotational preference. Therefore, we sought to explore relationships in gymnast’s rotation direction between different gymnastic skills. Furthermore, we sought to explore relationships between rotational preference, lateral preference, and vestibulo-spinal asymmetry. In the experiment n = 30 non-experts, n = 30 near-experts and n = 30 experts completed a rotational preference questionnaire, a lateral preference inventory, and the Unterberger-Fukuda Stepping Test. The results revealed, that near-experts and experts more often rotate rightward in the straight jump with a full turn when rotating leftward in the round-off and vice versa. The same relationship was found for experts when relating the rotation preference in the handstand with a full turn to the rotation preference in the straight jump with a full turn. Lateral preference was positively related to rotational preference in non-expert gymnasts, and vestibulo-spinal asymmetry was positively related to rotational preference in experts. We suggest, that gymnasts should explore their individual rotational preference by systematically practicing different skills with a different rotation direction, bearing in mind that a clearly developed structure in rotational preference between different skills may be appropriate to develop more complex skills in gymnastics. PMID:23486362
Nonminimal coupling of perfect fluids to curvature
Bertolami, Orfeu; Lobo, Francisco S. N.; Paramos, Jorge
2008-09-15
In this work, we consider different forms of relativistic perfect fluid Lagrangian densities that yield the same gravitational field equations in general relativity (GR). A particularly intriguing example is the case with couplings of the form [1+f{sub 2}(R)]L{sub m}, where R is the scalar curvature, which induces an extra force that depends on the form of the Lagrangian density. It has been found that, considering the Lagrangian density L{sub m}=p, where p is the pressure, the extra-force vanishes. We argue that this is not the unique choice for the matter Lagrangian density, and that more natural forms for L{sub m} do not imply the vanishing of the extra force. Particular attention is paid to the impact on the classical equivalence between different Lagrangian descriptions of a perfect fluid.
Natural curvature for manifest T-duality
NASA Astrophysics Data System (ADS)
Poláček, Martin; Siegel, Warren
2014-01-01
We reformulate the manifestly T-dual description of the massless sector of the closed bosonic string, directly from the geometry associated with the (left and right) affine Lie algebra of the coset space Poincaré/Lorentz. This construction initially doubles not only the (spacetime) coordinates for translations but also those for Lorentz transformations (and their "dual"). As a result, the Lorentz connection couples directly to the string (as does the vielbein), rather than being introduced ad hoc to the covariant derivative as previously. This not only reproduces the old definition of T-dual torsion, but automatically gives a general, covariant definition of T-dual curvature (but still with some undetermined connections).
Hawking temperature of constant curvature black holes
Cai Ronggen; Myung, Yun Soo
2011-05-15
The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of M{sub D-1}xS{sup 1}, where D is the spacetime dimension and M{sub D-1} stands for a conformal Minkowski spacetime in D-1 dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both the static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.
Canards and curvature: nonsmooth approximation by pinching
NASA Astrophysics Data System (ADS)
Desroches, M.; Jeffrey, M. R.
2011-05-01
In multiple time-scale (singularly perturbed) dynamical systems, canards are counterintuitive solutions that evolve along both attracting and repelling invariant manifolds. In two dimensions, canards result in periodic oscillations whose amplitude and period grow in a highly nonlinear way: they are slowly varying with respect to a control parameter, except for an exponentially small range of values where they grow extremely rapidly. This sudden growth, called a canard explosion, has been encountered in many applications ranging from chemistry to neuronal dynamics, aerospace engineering and ecology. Canards were initially studied using nonstandard analysis, and later the same results were proved by standard techniques such as matched asymptotics, invariant manifold theory and parameter blow-up. More recently, canard-like behaviour has been linked to surfaces of discontinuity in piecewise-smooth dynamical systems. This paper provides a new perspective on the canard phenomenon by showing that the nonstandard analysis of canard explosions can be recast into the framework of piecewise-smooth dynamical systems. An exponential coordinate scaling is applied to a singularly perturbed system of ordinary differential equations. The scaling acts as a lens that resolves dynamics across all time-scales. The changes of local curvature that are responsible for canard explosions are then analysed. Regions where different time-scales dominate are separated by hypersurfaces, and these are pinched together to obtain a piecewise-smooth system, in which curvature changes manifest as discontinuity-induced bifurcations. The method is used to classify canards in arbitrary dimensions, and to derive the parameter values over which canards form either small cycles (canards without head) or large cycles (canards with head).
Novel imaging system for measuring microscale curvatures at high temperatures
NASA Astrophysics Data System (ADS)
Tada, Haruna; Kumpel, Amy E.; Lathrop, Richard E.; Slanina, John B.; Nieva, Patricia; Zavracky, Paul; Miaoulis, Ioannis N.; Wong, Peter Y.
2000-01-01
An innovative system was designed to optically measure the curvature of microelectromechanical system at high temperatures. The system takes advantage of the limited numerical aperture of the imaging system to detect the curvature of cantilever beams. Images of the beam are used to determine beam curvature at high temperatures of up to 850 °C by analyzing the apparent change in beam length as seen by the camera during an experimental trial. The system is designed to operate at very high temperatures, which is difficult in conventional microscale curvature measurement techniques such as scanning electron microscopy or stylus profilometry due to excess heating of peripheral equipment. The system can measure curvatures as small as 300 m-1, which corresponds to tip deflections of 1.5 μm for a 100 μm beam. The resolution of the system is limited by the image resolution of the charge-coupled device camera, and increases at large curvatures. The maximum curvature that can be measured by the system is limited by the increase in system resolution, and is estimated to be 4500 m-1, corresponding to 22 μm deflection for a 100 μm beam. The apparatus was demonstrated to measure the thermally induced curvature of multilayered thin-film cantilever beams. The beams bend at high temperatures due to mismatch in thermal expansion coefficients between the layers. One innovative application of such curvature measurement is the determination of thermophysical properties of thin films at elevated temperatures. This article presents the experimental setup and operational theory of apparatus, as well as curvature measurements obtained by the system. The thermal expansion coefficient of polycrystalline silicon, determined from the curvature measurements, are also discussed.
Applications of variable focus liquid lenses for curvature wave-front sensors in astronomy
NASA Astrophysics Data System (ADS)
Fuentes-Fernández, J.; Cuevas, S.; Alvarez-Nuñez, L. C.; Watson, A. M.
2014-08-01
Curvature wavefront sensors obtain the wave-front aberrations from two defocused intensity images at each side of the pupil plane. Typically, when high modulation speeds are required, as it is the case with Adaptive Optics, that defocusing is done with a fast vibrating membrane mirror. We propose an alternative defocusing mechanism based on an electrowetting variable focus liquid lens. The use of such lenses may perform the required focus modulation without the need of extra moving parts, reducing the overall size of the system.
Measuring Children's Food Preferences.
ERIC Educational Resources Information Center
Birch, Leann L.; Sullivan, Susan A.
1991-01-01
Measures of preference are useful predictors of children's food consumption patterns. The paper discusses children's affective response to food and describes the preference assessment procedure which obtains information on children's likes and dislikes. The methodology helps investigate factors influencing development of preferences and food…
Coherent gradient sensing method and system for measuring surface curvature
NASA Technical Reports Server (NTRS)
Rosakis, Ares J. (Inventor); Singh, Ramen P. (Inventor); Kolawa, Elizabeth (Inventor); Moore, Jr., Nicholas R. (Inventor)
2000-01-01
A system and method for determining a curvature of a specularly reflective surface based on optical interference. Two optical gratings are used to produce a spatial displacement in an interference field of two different diffraction components produced by one grating from different diffraction components produced by another grating. Thus, the curvature of the surface can be determined.
Effects of curvature on asymmetric steady states in catalyst particles
Lucier, B J
1981-02-01
The effects of curvature on steady states of chemical catalytic reactions are investigated by studying the cases of the catalytic particle being a spherical or cylindrical shell. Existence and stability of solutions are studied. It is shown that the solutions converge to the solutions for the catalytic slab when the curvature goes to 0 in each case.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-06-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of co-seismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth, the other with a larger radius can approximate a half-space model. Then, we calculate the co-seismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum co-seismic displacement. The results show that the maximum curvature effect is about 4% for source depths of less than 100 km, and about 30% for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100%. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Determination of Radius of Curvature for Teeth With Cycloid Profile
NASA Astrophysics Data System (ADS)
Shatalov, E. V.; Efremenkov, E. A.; Shibinskiy, K. G.
2016-04-01
In the article the geometric determination of curvature radius is considered for teeth with cycloid profile. The equations are obtained for the determination of a radius of curvature with point coordinates of a cycloid profile. The conditions of convexo-concavity of a teeth profile are defined for transmission with intermediate rollers.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-08-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of coseismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth and the other with a larger radius can approximate a half-space model. Then, we calculate the coseismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum coseismic displacement. The results show that the maximum curvature effect is about 4 per cent for source depths of less than 100 km, and about 30 per cent for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100 per cent. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Interaction of peptides with cell membranes: insights from molecular modeling
NASA Astrophysics Data System (ADS)
Li, Zhen-lu; Ding, Hong-ming; Ma, Yu-qiang
2016-03-01
The investigation of the interaction of peptides with cell membranes is the focus of active research. It can enhance the understanding of basic membrane functions such as membrane transport, fusion, and signaling processes, and it may shed light on potential applications of peptides in biomedicine. In this review, we will present current advances in computational studies on the interaction of different types of peptides with the cell membrane. Depending on the properties of the peptide, membrane, and external environment, the peptide-membrane interaction shows a variety of different forms. Here, on the basis of recent computational progress, we will discuss how different peptides could initiate membrane pores, translocate across the membrane, induce membrane endocytosis, produce membrane curvature, form fibrils on the membrane surface, as well as interact with functional membrane proteins. Finally, we will present a conclusion summarizing recent progress and providing some specific insights into future developments in this field.
Tests and evaluation of a variable focus liquid lens for curvature wavefront sensors in astronomy.
Fuentes-Fernández, Jorge; Cuevas, Salvador; Álvarez-Nuñez, Luis C; Watson, Alan
2013-10-20
Curvature wavefront sensors (WFSs), which obtain the wavefront aberrations from two defocused intensity images at each side of the pupil plane, have shown to be highly efficient for astronomical applications. We propose here an alternative defocusing mechanism for curvature sensors, based on an electrowetting-based variable focus liquid lens. Typically, the sampling rates of a WFS for active optics are of the order of 0.01 Hz, and the focus modulation can be done by simply moving the detector back and forth. On the other hand, adaptive optics may require speeds of up to several hundred hertz, and the modulation is then done by using a fast vibrating membrane mirror. We believe variable focus liquid lenses may be able to perform this focus modulation, reducing the overall size of the system and without the need of extra moving parts. We have done a full characterization of the Varioptic Arctic 416 liquid lens, and we have evaluated its potential performance in different curvature configurations. PMID:24216579
Use of autologous grafts in the treatment of acquired penile curvature: An experience of 33 cases
Khawaja, Abdul Rouf; Dar, Tanveer Iqbal; Zahur, Suhael; Tariq, Sheikh; Hamid, Arf; Wani, M. S.; Wazir, B. S.; Iqbal, Arsheed
2016-01-01
Aim: The objective was to compare the use of autologous dermal and temporalis fascia grafts in the treatment of acquired penile curvatures. Materials and Methods: It was a prospective observational study of 33 cases, conducted in Sher-i-Kashmir Institute of Medical Sciences, Srinagar from March 2007 to September 2013. All the patients had stable Peyronies disease (PD). Dorsal, dorsolateral and vental curvatures with good preoperative erections were included. PD index with visual analog scales for curvature was used preoperatively. An informed written consent was taken from all the patients with main emphasis on erectile dysfunction. Results: After an average follow up of 2 years, complete straightening of penis was observed in all patients with satisfactory sexual intercourse in 30 patients (90%). Three patients (10%) required frequent use of type 5 phosphodiesterase inhibitors for adequate erections. Overall 91% of patients and partners were satisfied with the procedure and cosmetically donor site was better in temporalis fascia graft site. No rejection of any graft was noted and glans hypoesthesia was noticed in 4 patients (12%). None of the patients required penile prosthesis. Total operative time for harvesting and application of the graft was more in dermal grafts (>3 hrs) than for temporalis fascia graft (2 hrs). Conclusion: Tunical lengthening procedures by autologous free grafts represents a safe and reproducible technique. A good preoperative erectile function is required for tunical lengthening procedure. Temporalis fascia graft is thin, tough membrane and effective graft for PD with good cosmetic and functional results. PMID:27141196
Actin-Based Transport Adapts Polarity Domain Size to Local Cellular Curvature.
Bonazzi, Daria; Haupt, Armin; Tanimoto, Hirokazu; Delacour, Delphine; Salort, Delphine; Minc, Nicolas
2015-10-19
Intracellular structures and organelles such as the nucleus, the centrosome, or the mitotic spindle typically scale their size to cell size [1]. Similarly, cortical polarity domains built around the active form of conserved Rho-GTPases, such as Cdc42p, exhibit widths that may range over two orders of magnitudes in cells with different sizes and shapes [2-6]. The establishment of such domains typically involves positive feedback loops based on reaction-diffusion and/or actin-mediated vesicle transport [3, 7, 8]. How these elements may adapt polarity domain size to cellular geometry is not known. Here, by tracking the width of successive oscillating Cdc42-GTP domains in fission yeast spores [9], we find that domain width scales with local cell-surface radii of curvature over an 8-fold range, independently of absolute cell volume, surface, or Cdc42-GTP concentration. This local scaling requires formin-nucleated cortical actin cables and the fusion of secretory vesicles transported along these cables with the membrane. These data suggest that reaction-diffusion may set a minimal domain size and that secretory vesicle transport along actin cables may dilute and extend polarity domains to adapt their size to local cell-surface curvature. This work reveals that actin networks may act as micrometric curvature sensors and uncovers a generic morphogenetic principle for how polarity domains define their size according to cell morphologies. PMID:26441355
Effects of Iris Surface Curvature on Iris Recognition
Thompson, Joseph T; Flynn, Patrick J; Bowyer, Kevin W; Santos-Villalobos, Hector J
2013-01-01
To focus on objects at various distances, the lens of the eye must change shape to adjust its refractive power. This change in lens shape causes a change in the shape of the iris surface which can be measured by examining the curvature of the iris. This work isolates the variable of iris curvature in the recognition process and shows that differences in iris curvature degrade matching ability. To our knowledge, no other work has examined the effects of varying iris curvature on matching ability. To examine this degradation, we conduct a matching experiment across pairs of images with varying degrees of iris curvature differences. The results show a statistically signi cant degradation in matching ability. Finally, the real world impact of these ndings is discussed
Nastic curvatures of wheat coleoptiles that develop in true microgravity
NASA Technical Reports Server (NTRS)
Heathcote, D. G.; Chapman, D. K.; Brown, A. H.
1995-01-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Elliptic inflation: generating the curvature perturbation without slow-roll
NASA Astrophysics Data System (ADS)
Matsuda, Tomohiro
2006-09-01
There are many inflationary models in which the inflaton field does not satisfy the slow-roll condition. However, in such models, it is always difficult to generate the curvature perturbation during inflation. Thus, to generate the curvature perturbation, one must introduce another component into the theory. To cite a case, curvatons may generate the dominant part of the curvature perturbation after inflation. However, we question whether it is realistic to consider the generation of the curvature perturbation during inflation without slow-roll. Assuming multifield inflation, we encounter the generation of curvature perturbation during inflation without slow-roll. The potential along the equipotential surface is flat by definition and thus we do not have to worry about symmetry. We also discuss KKLT (Kachru Kallosh Linde Trivedi) models, in which corrections lifting the inflationary direction may not become a serious problem if there is a symmetry enhancement at the tip (not at the moving brane) of the inflationary throat.
Robust pupil center detection using a curvature algorithm
NASA Technical Reports Server (NTRS)
Zhu, D.; Moore, S. T.; Raphan, T.; Wall, C. C. (Principal Investigator)
1999-01-01
Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.
Curvature-processing network in macaque visual cortex
Yue, Xiaomin; Pourladian, Irene S.; Tootell, Roger B. H.; Ungerleider, Leslie G.
2014-01-01
Our visual environment abounds with curved features. Thus, the goal of understanding visual processing should include the processing of curved features. Using functional magnetic resonance imaging in behaving monkeys, we demonstrated a network of cortical areas selective for the processing of curved features. This network includes three distinct hierarchically organized regions within the ventral visual pathway: a posterior curvature-biased patch (PCP) located in the near-foveal representation of dorsal V4, a middle curvature-biased patch (MCP) located on the ventral lip of the posterior superior temporal sulcus (STS) in area TEO, and an anterior curvature-biased patch (ACP) located just below the STS in anterior area TE. Our results further indicate that the processing of curvature becomes increasingly complex from PCP to ACP. The proximity of the curvature-processing network to the well-known face-processing network suggests a possible functional link between them. PMID:25092328
NASA Astrophysics Data System (ADS)
Tourdot, Richard W.; Ramakrishnan, N.; Baumgart, Tobias; Radhakrishnan, Ravi
2015-10-01
We investigate the phenomenon of protein-induced tubulation of lipid bilayer membranes within a continuum framework using Monte Carlo simulations coupled with the Widom insertion technique to compute excess chemical potentials. Tubular morphologies are spontaneously formed when the density and the curvature-field strength of the membrane-bound proteins exceed their respective thresholds and this transition is marked by a sharp drop in the excess chemical potential. We find that the planar to tubular transition can be described by a micellar model and that the corresponding free-energy barrier increases with an increase in the curvature-field strength (i.e., of protein-membrane interactions) and also with an increase in membrane tension.
Tourdot, Richard W; Ramakrishnan, N; Baumgart, Tobias; Radhakrishnan, Ravi
2015-10-01
We investigate the phenomenon of protein-induced tubulation of lipid bilayer membranes within a continuum framework using Monte Carlo simulations coupled with the Widom insertion technique to compute excess chemical potentials. Tubular morphologies are spontaneously formed when the density and the curvature-field strength of the membrane-bound proteins exceed their respective thresholds and this transition is marked by a sharp drop in the excess chemical potential. We find that the planar to tubular transition can be described by a micellar model and that the corresponding free-energy barrier increases with an increase in the curvature-field strength (i.e., of protein-membrane interactions) and also with an increase in membrane tension. PMID:26565280
Tourdot, Richard W.; Ramakrishnan, N.; Baumgart, Tobias; Radhakrishnan, Ravi
2016-01-01
We investigate the phenomenon of protein-induced tubulation of lipid bilayer membranes within a continuum framework using Monte Carlo simulations coupled with the Widom insertion technique to compute excess chemical potentials. Tubular morphologies are spontaneously formed when the density and the curvature-field strength of the membrane-bound proteins exceed their respective thresholds and this transition is marked by a sharp drop in the excess chemical potential. We find that the planar to tubular transition can be described by a micellar model and that the corresponding free-energy barrier increases with an increase in the curvature-field strength (i.e., of protein-membrane interactions) and also with an increase in membrane tension. PMID:26565280
Masel, Richard L.; Chen, Qingmei; Liu, Zengcai; Kutz, Robert
2016-06-21
An ion conducting polymeric composition mixture comprises a copolymer of styrene and vinylbenzyl-R.sub.s. R.sub.s is selected from the group consisting of imidazoliums and pyridiniums. The composition contains 10%-90% by weight of vinylbenzyl-R.sub.s. The composition can further comprise a polyolefin comprising substituted polyolefins, a polymer comprising cyclic amine groups, a polymer comprising at least one of a phenylene group and a phenyl group, a polyamide, and/or the reaction product of a constituent having two carbon-carbon double bonds. The composition can be in the form of a membrane. In a preferred embodiment, the membrane is a Helper Membrane that increases the faradaic efficiency of an electrochemical cell into which the membrane is incorporated, and also allows product formation at lower voltages than in cells without the Helper Membrane.
Clinical Assessment of Lamina Cribrosa Curvature in Eyes with Primary Open-Angle Glaucoma
Kim, Yong Woo; Jeoung, Jin Wook; Kim, Dai Woo; Girard, Michael J. A.; Mari, Jean Martial; Park, Ki Ho; Kim, Dong Myung
2016-01-01
Purpose Quantitative evaluation of lamina cribrosa (LC) posterior bowing in primary open-angle glaucoma (POAG) eyes using swept-source optical coherence tomography. Methods Patients with POAG (n = 123 eyes) and healthy individuals of a similar age (n = 92 eyes) were prospectively recruited. Anterior laminar insertion depth (ALID) was defined as the vertical distance between the anterior laminar insertion and a reference plane connecting the Bruch’s membrane openings (BMO). The mean LC depth (mLCD) was approximated by dividing the area enclosed by the anterior LC, the BMO reference plane, and the two vertical lines for ALID measurement by the length between those two vertical lines. The LC curvature index was defined as the difference between the mLCD and the ALID. The factors influencing the LC curvature index were evaluated. Results The ALID and mLCD were significantly larger in POAG eyes than in healthy controls (P < 0.05). The LC curvature index was significantly larger in POAG eyes than in healthy controls on both the horizontal (85.8 ± 34.1 vs. 68.2 ± 32.3 μm) and vertical meridians (49.8 ± 38.5 vs. 32.2 ± 31.1 μm, all P < 0.001). Multivariate regression showed significant associations of greater disc area (P < 0.001), vertical C/D ratio (P < 0.001) and mLCD (P < 0.001), smaller rim area (P = 0.001), thinner average RNFLT (P < 0.001), and myopic refraction (P = 0.049) with increased LC curvature index. There was no difference in the LC curvature index between mild (MD > –6 dB) and moderate-to-advanced glaucoma (MD < –6 dB, P = 0.95). Conclusions LC posterior bowing was increased in POAG eyes, and was significantly associated with structural optic nerve head (ONH) changes but not with functional glaucoma severity. Quantitative evaluation of LC curvature can facilitate assessment of glaucomatous ONH change. PMID:26963816
Cosmological spatial curvature probed by microwave polarization
Matzner, R.A.; Tolman, B.W.
1982-11-15
If there is a large-scale anisotropy in the expansion of the universe, the microwave background radiation is expected to be linearly polarized. This communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary ina complicated way over the celestial sphere (type VII/sub h/). These facts suggest a clear observational test of the closure of the universe. Also, an ambiguity inherent in the homogeneity of the universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called ''handedness.''
Actin filament curvature biases branching direction
NASA Astrophysics Data System (ADS)
Wang, Evan; Risca, Viviana; Chaudhuri, Ovijit; Chia, Jia-Jun; Geissler, Phillip; Fletcher, Daniel
2012-02-01
Actin filaments are key components of the cellular machinery, vital for a wide range of processes ranging from cell motility to endocytosis. Actin filaments can branch, and essential in this process is a protein complex known as the Arp2/3 complex, which nucleate new ``daughter'' filaments from pre-existing ``mother'' filaments by attaching itself to the mother filament. Though much progress has been made in understanding the Arp2/3-actin junction, some very interesting questions remain. In particular, F-actin is a dynamic polymer that undergoes a wide range of fluctuations. Prior studies of the Arp2/3-actin junction provides a very static notion of Arp2/3 binding. The question we ask is how differently does the Arp2/3 complex interact with a straight filament compared to a bent filament? In this study, we used Monte Carlo simulations of a surface-tethered worm-like chain to explore possible mechanisms underlying the experimental observation that there exists preferential branch formation by the Arp2/3 complex on the convex face of a curved filament. We show that a fluctuation gating model in which Arp2/3 binding to the actin filament is dependent upon a rare high-local-curvature shape fluctuation of the filament is consistent with the experimental data.
Geodesic Curvature Effects in the WCMs
NASA Astrophysics Data System (ADS)
Zhou, Tianchun
2015-11-01
The favorable features of the steady state I-Regime discovered on Alcator C-Mod recently make this regime a hopeful working regime for future burning plasma experiments. Accompanying the I-regime are the weakly coherent modes (WCMs) with frequency around 200 kHz that propagate poloidally in the electron diamagnetic drift direction in the lab frame. The WCMs were interpreted as certain type of heavy impurity modes in the 3-fluid framework in a 1-D plane magnetic field geometry. Once considering in a simplified toroidal magnetic field geometry, the geodesic curvature will play important roles in that the contribution of the geodesic compression may catch up with or outweighs that of the parallel compression in the plasma edge region where the fluctuations are highly localized. This geodesic coupling to the neighboring bands modifies the marginal stability condition and mode profiles in Refs.. In the same framework, attempts will be made to interpret the concomitant low frequency (~ 20kHz) fluctuations as a type of impurity drift wave-like modes propagating in the ion diamagnetic drift direction. Supported by China National MCFE Research Program under Grant No. 2015GB11000.
BICEP2, the curvature perturbation and supersymmetry
NASA Astrophysics Data System (ADS)
Lyth, David H.
2014-11-01
The tensor fraction r simeq 0.16 found by BICEP2 corresponds to a Hubble parameter H simeq 1.0 × 1014 GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index ns. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Characterizing repulsive gravity with curvature eigenvalues
NASA Astrophysics Data System (ADS)
Luongo, Orlando; Quevedo, Hernando
2014-10-01
Repulsive gravity has been investigated in several scenarios near compact objects by using different intuitive approaches. Here, we propose an invariant method to characterize regions of repulsive gravity, associated to black holes and naked singularities. Our method is based upon the behavior of the curvature tensor eigenvalues, and leads to an invariant definition of a repulsion radius. The repulsion radius determines a physical region, which can be interpreted as a repulsion sphere, where the effects due to repulsive gravity naturally arise. Further, we show that the use of effective masses to characterize repulsion regions can lead to coordinate-dependent results whereas, in our approach, repulsion emerges as a consequence of the spacetime geometry in a completely invariant way. Our definition is tested in the spacetime of an electrically charged Kerr naked singularity and in all its limiting cases. We show that a positive mass can generate repulsive gravity if it is equipped with an electric charge or an angular momentum. We obtain reasonable results for the spacetime regions contained inside the repulsion sphere whose size and shape depend on the value of the mass, charge and angular momentum. Consequently, we define repulsive gravity as a classical relativistic effect by using the geometry of spacetime only.
Gradient expansion, curvature perturbations, and magnetized plasmas
Giovannini, Massimo; Rezaei, Zahra
2011-04-15
The properties of magnetized plasmas are always investigated under the hypothesis that the relativistic inhomogeneities stemming from the fluid sources and from the geometry itself are sufficiently small to allow for a perturbative description prior to photon decoupling. The latter assumption is hereby relaxed and predecoupling plasmas are described within a suitable expansion where the inhomogeneities are treated to a given order in the spatial gradients. It is argued that the (general relativistic) gradient expansion shares the same features of the drift approximation, customarily employed in the description of cold plasmas, so that the two schemes are physically complementary in the large-scale limit and for the low-frequency branch of the spectrum of plasma modes. The two-fluid description, as well as the magnetohydrodynamical reduction, is derived and studied in the presence of the spatial gradients of the geometry. Various solutions of the coupled system of evolution equations in the anti-Newtonian regime and in the quasi-isotropic approximation are presented. The relation of this analysis to the so-called separate universe paradigm is outlined. The evolution of the magnetized curvature perturbations in the nonlinear regime is addressed for the magnetized adiabatic mode in the plasma frame.
BICEP2, the curvature perturbation and supersymmetry
Lyth, David H.
2014-11-01
The tensor fraction r ≅ 0.16 found by BICEP2 corresponds to a Hubble parameter H ≅ 1.0 × 10{sup 14} GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index n{sub s}. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Nonlinear diffusion filtering influenced by mean curvature
NASA Astrophysics Data System (ADS)
Kollár, Michal; Mikula, Karol; Čunderlík, Róbert
2016-04-01
The presentation introduces a new nonlinear diffusion filtering method on closed surfaces such as a sphere, ellipsoid or the Earth's surface. Our new model extends the regularized surface Perona-Malik model by including a local extrema detector based on a mean curvature of processed data. The model is thus represented by a nonlinear diffusion equation which filters noise while preserves main edges, local extrema and details important for a correct interpretation of data. We define a surface finite-volume method to approximate numerically the nonlinear parabolic partial differential equation on a closed surface. The closed surface is approximated by a polyhedral surface created by planar triangles representing subdivision of an initial icosahedron grid and we use a piece-wise linear approximation of a solution in space and the backward Euler time discretization. Numerical experiments present nonlinear diffusion filtering of artificial data and real measurements, namely the GOCE satellite observations. They aim to point out a main advantage of the new nonlinear model which, on the contrary of Perona-Malik model, preserves local extremal values of filtered data.
Curvature-tuned preparation of nanoliposomes.
Genç, Rükan; Ortiz, Mayreli; O'Sullivan, Ciara K
2009-11-01
Numerous methods have been reported for the preparation of liposomes, many of which, in addition to requiring time-consuming preparative steps and the use of organic solvents, result in heterogeneous liposome populations of incontrollable size. Taking into consideration the phenomenon of spontaneous vesiculation and the theory of curvature, here we present an extremely rapid and simple, solvent-free method for the preparation of monodisperse solutions of highly stable small unilamellar vesicles using both charged and zwitterionic lipids mixed with lyso-palmitoylphosphatidylcholine, exploiting a combination of a rapid pH change followed by a defined period of equilibration. Various experimental parameters and their interactions were evaluated in terms of their effect on resulting liposome size and shape, as well as on liposome stability and size distribution, with transmission electron microscope imaging being used to visualize the formed liposomes, and photon correlation spectroscopy to obtain statistical data on mean diameter and monodispersity of the liposome population. zeta potential measurements also provided information about the interpretation of vesiculation kinetics and liposome stability. The time interval of pH jump, operation temperature, equilibration time, and lipid type were shown to be the determining factors controlling the size, shape, and monodispersity of the liposomes. Buffer type was also found to be important for the long-term storage of the liposomes. Ongoing work is looking at the application of the developed method for encapsulation of bioactive molecules, such as drugs, genetic materials, and enzymes. PMID:19856992
Small scale membrane mechanics
Rangamani, Padmini; Benjamini, Ayelet; Agrawal, Ashutosh; Smit, Berend; Oster, George
2014-01-01
Large scale changes to lipid bilayer shapes are well represented by the Helfrich model. However, there are membrane processes that take place at smaller length scales that this model cannot address. In this work, we present a one-dimensional continuum model that captures the mechanics of the lipid bilayer membrane at the length scale of the lipids themselves. The model is developed using the Cosserat theory of surfaces with lipid orientation, or ‘tilt’, as the fundamental degree of freedom. The Helfrich model can be recovered as a special case when the curvatures are small and the lipid tilt is everywhere zero. We use the tilt model to study local membrane deformations in response to a protein inclusion. Parameter estimates and boundary conditions are obtained from a coarse-grained molecular model using dissipative particle dynamics (DPD) to capture the same phenomenon. The continuum model is able to reproduce the membrane bending, stretch and lipid tilt as seen in the DPD model. The lipid tilt angle relaxes to the bulk tilt angle within 5–6 nm from the protein inclusion. Importantly, for large tilt gradients induced by the proteins, the tilt energy contribution is larger than the bending energy contribution. Thus, the continuum model of tilt accurately captures behaviors at length scales shorter than the membrane thickness. PMID:24081650
On 3-gauge transformations, 3-curvatures, and Gray-categories
Wang, Wei
2014-04-15
In the 3-gauge theory, a 3-connection is given by a 1-form A valued in the Lie algebra g, a 2-form B valued in the Lie algebra h, and a 3-form C valued in the Lie algebra l, where (g,h,l) constitutes a differential 2-crossed module. We give the 3-gauge transformations from one 3-connection to another, and show the transformation formulae of the 1-curvature 2-form, the 2-curvature 3-form, and the 3-curvature 4-form. The gauge configurations can be interpreted as smooth Gray-functors between two Gray 3-groupoids: the path 3-groupoid P{sub 3}(X) and the 3-gauge group G{sup L} associated to the 2-crossed module L, whose differential is (g,h,l). The derivatives of Gray-functors are 3-connections, and the derivatives of lax-natural transformations between two such Gray-functors are 3-gauge transformations. We give the 3-dimensional holonomy, the lattice version of the 3-curvature, whose derivative gives the 3-curvature 4-form. The covariance of 3-curvatures easily follows from this construction. This Gray-categorical construction explains why 3-gauge transformations and 3-curvatures have the given forms. The interchanging 3-arrows are responsible for the appearance of terms with the Peiffer commutator (, )
Influence of Coanda surface curvature on performance of bladeless fan
NASA Astrophysics Data System (ADS)
Li, Guoqi; Hu, Yongjun; Jin, Yingzi; Setoguchi, Toshiaki; Kim, Heuy Dong
2014-10-01
The unique Coanda surface has a great influence on the performance of bladeless fan. However, there is few studies to explain the relationship between the performance and Coanda surface curvature at present. In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan, numerical studies are performed in this paper. Firstly, three-dimensional numerical simulation is done by Fluent software. For the purpose to obtain detailed information of the flow field around the Coanda surface, two-dimensional numerical simulation is also conducted. Five types of Coanda surfaces with different curvature are designed, and the flow behaviour and the performance of them are analyzed and compared with those of the prototype. The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance, It is found that there is an optimal curvature of Coanda surfaces among the studied models. Simulation result shows that there is a special low pressure region. With increasing curvature in Y direction, several low pressure regions gradually enlarged, then begin to merge slowly, and finally form a large area of low pressure. From the analyses of streamlines and velocity angle, it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall. Thus, it leads to that the curvature of the streamlines is consistent with that of Coanda surface. Meanwhile, it also causes the fluid movement towards the most suitable direction. This study will provide useful information to performance improvements of bladeless fans.
Geometry-specific scaling of detonation parameters from front curvature
Jackson, Scott I; Short, Mark
2011-01-20
It has previously been asserted that classical detonation curvature theory predicts that the critical diameter and the diameter-effect curve of a cylindrical high-explosive charge should scale with twice the thickness of an analogous two-dimensional explosive slab. The varied agreement of experimental results with this expectation have led some to question the ability of curvature-based concepts to predict detonation propagation in non-ideal explosives. This study addresses such claims by showing that the expected scaling relationship (hereafter referred to d = 2w) is not consistent with curvature-based Detonation Shock Dynamics (DSD) theory.
Dynamic Curvature Steering Control for Autonomous Vehicle: Performance Analysis
NASA Astrophysics Data System (ADS)
Aizzat Zakaria, Muhammad; Zamzuri, Hairi; Amri Mazlan, Saiful
2016-02-01
This paper discusses the design of dynamic curvature steering control for autonomous vehicle. The lateral control and longitudinal control are discussed in this paper. The controller is designed based on the dynamic curvature calculation to estimate the path condition and modify the vehicle speed and steering wheel angle accordingly. In this paper, the simulation results are presented to show the capability of the controller to track the reference path. The controller is able to predict the path and modify the vehicle speed to suit the path condition. The effectiveness of the controller is shown in this paper whereby identical performance is achieved with the benchmark but with extra curvature adaptation capabilites.
Complete manifolds with bounded curvature and spectral gaps
NASA Astrophysics Data System (ADS)
Schoen, Richard; Tran, Hung
2016-08-01
We study the spectrum of complete noncompact manifolds with bounded curvature and positive injectivity radius. We give general conditions which imply that their essential spectrum has an arbitrarily large finite number of gaps. In particular, for any noncompact covering of a compact manifold, there is a metric on the base so that the lifted metric has an arbitrarily large finite number of gaps in its essential spectrum. Also, for any complete noncompact manifold with bounded curvature and positive injectivity radius we construct a metric uniformly equivalent to the given one (also of bounded curvature and positive injectivity radius) with an arbitrarily large finite number of gaps in its essential spectrum.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed. PMID:25615464
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
Motion on constant curvature spaces and quantization using Noether symmetries.
Bracken, Paul
2014-12-01
A general approach is presented for quantizing a metric nonlinear system on a manifold of constant curvature. It makes use of a curvature dependent procedure which relies on determining Noether symmetries from the metric. The curvature of the space functions as a constant parameter. For a specific metric which defines the manifold, Lie differentiation of the metric gives these symmetries. A metric is used such that the resulting Schrödinger equation can be solved in terms of hypergeometric functions. This permits the investigation of both the energy spectrum and wave functions exactly for this system. PMID:25554048
Motion on constant curvature spaces and quantization using noether symmetries
NASA Astrophysics Data System (ADS)
Bracken, Paul
2014-12-01
A general approach is presented for quantizing a metric nonlinear system on a manifold of constant curvature. It makes use of a curvature dependent procedure which relies on determining Noether symmetries from the metric. The curvature of the space functions as a constant parameter. For a specific metric which defines the manifold, Lie differentiation of the metric gives these symmetries. A metric is used such that the resulting Schrödinger equation can be solved in terms of hypergeometric functions. This permits the investigation of both the energy spectrum and wave functions exactly for this system.
Curvature perturbation and waterfall dynamics in hybrid inflation
Abolhasani, Ali Akbar; Firouzjahi, Hassan; Sasaki, Misao E-mail: firouz@mail.ipm.ir
2011-10-01
We investigate the parameter spaces of hybrid inflation model with special attention paid to the dynamics of waterfall field and curvature perturbations induced from its quantum fluctuations. Depending on the inflaton field value at the time of phase transition and the sharpness of the phase transition inflation can have multiple extended stages. We find that for models with mild phase transition the induced curvature perturbation from the waterfall field is too large to satisfy the COBE normalization. We investigate the model parameter space where the curvature perturbations from the waterfall quantum fluctuations vary between the results of standard hybrid inflation and the results obtained here.
LPG-based sensor for curvature and vibration
NASA Astrophysics Data System (ADS)
Nascimento, I. M.; Chesini, G.; Baptista, J. M.; Cordeiro, Cristiano M. B.; Jorge, P. A. S.
2016-05-01
A long-period grating (LPG) written on a standard single mode fiber is investigated as a curvature and vibration sensor. It is demonstrated a high sensitivity to applied curvature and the possibility to monitor vibration in a wide range of frequencies from 30 Hz to 2000 Hz. The system was tested using an intensity based interrogation scheme with the LPG sensor operating in the curvature regime. Results have shown a reproducible frequency discrimination in the 30 Hz to 2000 Hz, with resolutions between 11 mHz and 913 mHz. Frequency retrieval could be performed independent of temperature up to 86 °C.
Curvature-driven assembly in soft matter.
Liu, Iris B; Sharifi-Mood, Nima; Stebe, Kathleen J
2016-07-28
Control over the spatial arrangement of colloids in soft matter hosts implies control over a wide variety of properties, ranging from the system's rheology, optics, and catalytic activity. In directed assembly, colloids are typically manipulated using external fields to form well-defined structures at given locations. We have been developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. Such potential fields allow particles to interact with each other. If the soft matter host is deformed in some way, the potential allows the particles to interact with the global system distortion. One important example is capillary assembly of colloids on curved fluid interfaces. Upon attaching, the particle distorts that interface, with an associated energy field, given by the product of its interfacial area and the surface tension. The particle's capillary energy depends on the local interface curvature. We explore this coupling in experiment and theory. There are important analogies in liquid crystals. Colloids in liquid crystals elicit an elastic energy response. When director fields are moulded by confinement, the imposed elastic energy field can couple to that of the colloid to define particle paths and sites for assembly. By improving our understanding of these and related systems, we seek to develop new, parallelizable routes for particle assembly to form reconfigurable systems in soft matter that go far beyond the usual close-packed colloidal structures.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298434
Curvature instability of a vortex ring
NASA Astrophysics Data System (ADS)
Fukumoto, Yasuhide; Hattori, Yuji
2005-03-01
A global stability analysis of Kelvin's vortex ring to three-dimensional disturbances of infinitesimal amplitude is made. The basic state is a steady asymptotic solution of the Euler equations, in powers of the ratio ɛ of the core radius to the ring radius, for an axisymmetric vortex ring with vorticity proportional to the distance from the symmetric axis. The effect of ring curvature appears at first order, in the form of a dipole field, and a local straining field, which is a quadrupole field, follows at second order. The eigenvalue problem of the Euler equations, retaining the terms to first order, is solved in closed form, in terms of the Bessel and the modified Bessel functions. We show that the dipole field causes a parametric resonance instability between a pair of Kelvin waves whose azimuthal wavenumbers are separated by 1. The most unstable mode occurs in the short-wavelength limit, under the constraint that the radial and the azimuthal wavenumbers are of the same magnitude, and the limiting value of maximum growth rate coincides with the value 165/256 ɛ obtained by Hattori & Fukumoto (Phys. Fluids, vol. 15, 2003, p. 3151) by means of the geometric optics method. The instability mechanism is traced to stretching of disturbance vorticity in the toroidal direction. In the absence of viscosity, the dipole effect outweighs the straining field effect of O(ɛ2) known as the Moore-Saffman-Tsai-Widnall instability. The viscosity acts to damp the former preferentially and these effects compete with each other.
Trans-Membrane Area Asymmetry Controls the Shape of Cellular Organelles
Beznoussenko, Galina V.; Pilyugin, Sergei S.; Geerts, Willie J. C.; Kozlov, Michael M.; Burger, Koert N. J.; Luini, Alberto; Derganc, Jure; Mironov, Alexander A.
2015-01-01
Membrane organelles often have complicated shapes and differ in their volume, surface area and membrane curvature. The ratio between the surface area of the cytosolic and luminal leaflets (trans-membrane area asymmetry (TAA)) determines the membrane curvature within different sites of the organelle. Thus, the shape of the organelle could be critically dependent on TAA. Here, using mathematical modeling and stereological measurements of TAA during fast transformation of organelle shapes, we present evidence that suggests that when organelle volume and surface area are constant, TAA can regulate transformation of the shape of the Golgi apparatus, endosomal multivesicular bodies, and microvilli of brush borders of kidney epithelial cells. Extraction of membrane curvature by small spheres, such as COPI-dependent vesicles within the Golgi (extraction of positive curvature), or by intraluminal vesicles within endosomes (extraction of negative curvature) controls the shape of these organelles. For instance, Golgi tubulation is critically dependent on the fusion of COPI vesicles with Golgi cisternae, and vice versa, for the extraction of membrane curvature into 50–60 nm vesicles, to induce transformation of Golgi tubules into cisternae. Also, formation of intraluminal ultra-small vesicles after fusion of endosomes allows equilibration of their TAA, volume and surface area. Finally, when microvilli of the brush border are broken into vesicles and microvilli fragments, TAA of these membranes remains the same as TAA of the microvilli. Thus, TAA has a significant role in transformation of organelle shape when other factors remain constant. PMID:25761238
NASA Astrophysics Data System (ADS)
Ma, Shuang; Yi, Shengzhen; Chen, Shenghao; Wang, Zhanshan
2014-11-01
Monochromatic energy multilayer Kirkpatrick-Baez microscope is one of key diagnostic tools for researches on inertial confinement fusion. It is composed by two orthogonal concave spherical mirrors with small curvature and aperture, and produce the image of an object by collecting X-rays in each orthogonal direction, independently. Accurate measurement of radius of curvature of concave spherical mirrors is very important to achieve its design optical properties including imaging quality, optical throughput and energy resolution. However, it is difficult to measure the radius of curvature of spherical optical surfaces with small curvature and aperture by conventional methods, for the produced reflective intensity of glass is too low to correctly test. In this paper, we propose an improved measuring method of optical profiler to accomplish accurate measurement of radius of curvature of spherical optical surfaces with small curvature and aperture used in the monochromatic energy multilayer Kirkpatrick-Baez microscope. Firstly, we use a standard super-smooth optical flat to calibrate reference mirror before each experiment. Following, deviation of central position between measurement area and interference pattern is corrected by the theory of Newton's rings, and the zero-order fringe position is derived from the principle of interference in which surface roughness has minimum values in the position of zero light path difference. Measured results by optical profiler show the low relative errors and high repeatability. Eventually, an imaging experiment of monochromatic energy multilayer Kirkpatrick-Baez microscope determines the measurement accuracy of radius of curvature.
Reflectors Made from Membranes Stretched Between Beams
NASA Technical Reports Server (NTRS)
Dooley, Jennifer; Dragovan, Mark; Tolomeo, Jason
2009-01-01
Lightweight cylindrical reflectors of a proposed type would be made from reflective membranes stretched between pairs of identically curved and identically oriented end rails. In each such reflector, the curvature of the two beams would define the reflector shape required for the intended application. For example, the beams could be curved to define a reflector of parabolic cross section, so that light incident along the axis of symmetry perpendicular to the cylindrical axis would be focused to a line. In addition, by applying suitable forces to the ends of the beams, one could bend the beams to adjust the reflector surface figure to within a precision of the order of the wavelength of the radiation to be reflected. The figure depicts an example of beams shaped so that in the absence of applied forces, each would be flat on one side and would have a radius of curvature R on the opposite side. Alternatively, the curvature of the reflector-membrane side could be other than circular. In general, the initial curvature would be chosen to optimize the final reflector shape. Then by applying forces F between the beam ends in the positions and orientations shown in the figure, one could bend beams to adjust their shape to a closer approximation of the desired precise circular or noncircular curvature.
Thermodynamics of protein driven self assembly in membranes
NASA Astrophysics Data System (ADS)
Natesan, Ramakrishnan; Tourdot, Richard; Bradley, Ryan; Radhakrishnan, Ravi
2013-03-01
Recent experimental evidences strongly point to the role of proteins and other membrane binding macromolecules in reshaping biological membranes, at length scales of the molecule and the structure enclosed by the membrane. In this work, we investigate the interplay between the membrane curvature induced at the molecular scale, mainly due to peripheral membrane proteins, and the resulting membrane morphologies, of varying complexity, observed at the mesoscale. The biological membrane, in our approach, is represented by a dynamically triangulated surface while the proteins are modeled as curvature fields on the membrane, which can either be isotropic or anisotropic. Thermal undulations in the membrane and cooperativity in the curvature field, due to the stabilization of a nematic phase, drives the membrane into conformations that resembles those in experiments in vivo and vitro. The stability of these structures are examined by two approaches to compute the free energy of the system: (i) Widom insertion technique to compute excess chemical potentials and (ii) thermodynamic integration using the Kirkwood coupling parameter to compute absolute free energies. Building on these methods, we propose a hybrid scheeme that couples both the approaches for computing free energies.
Dynamic sorting of lipids and proteins in membrane tubes with a moving phase boundary
Heinrich, Michael; Tian, Aiwei; Esposito, Cinzia; Baumgart, Tobias
2010-01-01
Cellular organelle membranes maintain their integrity, global shape, and composition despite vigorous exchange among compartments of lipids and proteins during trafficking and signaling. Organelle homeostasis involves dynamic molecular sorting mechanisms that are far from being understood. In contrast, equilibrium thermodynamics of membrane mixing and sorting, particularly the phase behavior of binary and ternary model membrane mixtures and its coupling to membrane mechanics, is relatively well characterized. Elucidating the continuous turnover of live cell membranes, however, calls for experimental and theoretical membrane models enabling manipulation and investigation of directional mass transport. Here we introduce the phenomenon of curvature-induced domain nucleation and growth in membrane mixtures with fluid phase coexistence. Membrane domains were consistently observed to nucleate precisely at the junction between a strongly curved cylindrical (tube) membrane and a pipette-aspirated giant unilamellar vesicle. This experimental geometry mimics intracellular sorting compartments, because they often show tubular-vesicular membrane regions. Nucleated domains at tube necks were observed to present diffusion barriers to the transport of lipids and proteins. We find that curvature-nucleated domains grow with characteristic parabolic time dependence that is strongly curvature-dependent. We derive an analytical model that reflects the observed growth dynamics. Numerically calculated membrane shapes furthermore allow us to elucidate mechanical details underlying curvature-dependent directed lipid transport. Our observations suggest a novel dynamic membrane sorting principle that may contribute to intracellular protein and lipid sorting and trafficking. PMID:20368457
Lee H-t; Choe, E H
1982-12-01
This paper provides a brief overview of not yet fully analyzed 1974 World Fertility Survey for Korea data on sex preference, and also parental gender role stereotyping and gender preference, as they relate to sex preference and fertility behavior of the individual parents of childbearing age. The data includes the mother's background and numbers of children desired. Fertility preferences reflect sociocultural, economic and psychological aspects of individual parents' habits and perceptions of the world. Attitude, which is difficult to measure, is often connected to and can predict behavior. Age, residence, educational level, and spouse's occupation are related. Sex preference for sons is affected by how many parents hope to send a son to college (75.2%), compared to those hoping to send a daughter to college (52%). Parents under 25 also prefer boys. Gender preference is the pattern of sociocultural behavior associated with the awareness of being masculine or feminine. Sex preference is the patterns arising from the biological fact of being male or female. A 1981 son preference survey covered the province of Kyongbuk, conservative in gender preference, polling 832 women, ages 15 to 49. The survey covered questions about gender associated activities, occupations and personality traits. These items were divided into 4 gender role discriminant scales, covering most and least masculine or feminine degrees within each category. Respondents with less extreme gender role stereotyping are less sex biased; extreme sex preference is closely related to the respondents' extreme gender role stereotypic traits. Korean society has conferred differential value upon gender specific work and the main criterion for the division of labor is gender, not biological sex. This contributes to a parent's sex preferential attitude, which is unlikely to change without a modification of premodern neoconfucian gender based behaviors. PMID:12264918
Curvature Control of Silicon Microlens for THz Dielectric Antenna
NASA Technical Reports Server (NTRS)
Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran
2012-01-01
We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.
16. Detail of curvature of northern parapet, with 1932 concrete ...
16. Detail of curvature of northern parapet, with 1932 concrete extension of parapet in foreground, facing east. - Dubbs Bridge, Spinnerstown Road (State Route 2031) spanning Hosensack Creek, Dillingerville, Lehigh County, PA
Wavefront curvature of an opticaly pumped waveguide laser
Tacke, M.
1983-05-01
The influence of inhomogeneous gain on the wavefront shape is discussed for waveguide lasers. As an example, the curvature of the EH(11) mode of an optically pumped FIR laser is computed, its influence on the output beam is discussed.
Curvature-Squared Cosmology In The First-Order Formalism
NASA Technical Reports Server (NTRS)
Shahid-Saless, Bahman
1993-01-01
Paper presents theoretical study of some of general-relativistic ramifications of gravitational-field energy density proportional to R - alpha R(exp 2) (where R is local scalar curvature of space-time and alpha is a constant).
Curvature and bow of bulk GaN substrates
NASA Astrophysics Data System (ADS)
Foronda, Humberto M.; Romanov, Alexey E.; Young, Erin C.; Roberston, Christian A.; Beltz, Glenn E.; Speck, James S.
2016-07-01
We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.
Electric current measurement using fiber-optic curvature sensor
NASA Astrophysics Data System (ADS)
Di, Haiting; Xin, Ying; Sun, Suping
2016-02-01
A novel fiber-optic curvature sensor, which can measure curvature directly, has been developed in recent years. The electric current measurements system based on fiber-optic curvature sensor and electromagnetic principle is developed. A fiber-optic curvature sensor is bonded to a thin-walled cantilever and two circular magnet targets with the same parameters are configured at the tip of the cantilever symmetrically. In this case, the throughput of the sensor will be changed due to the bending deformation of cantilever, which is proportional to the electromagnetic force caused by measured electric current. Direct and alternate characteristics of the proposed measurement system are studied experimentally. The results show that the measurement errors are within the range of ±5.5 mA and the corresponding accuracy is within 1% at the current measurement range from -300 mA to 300 mA, which indicate the feasibility of the proposed measurement system.
Constraints on the geometric and dynamic spatial curvature
NASA Astrophysics Data System (ADS)
Yu, Bo
2015-10-01
In this paper, the geometric and dynamic spatial curvature parameters of the Universe are constrained by type Ia supernova, baryon acoustic oscillation, and cosmic microwave background data. Compared with the previous result, a more stringent constraint is obtained, especially for the dynamic spatial curvature in the case of variable dark energy. No evidence is found that the geometric spatial curvature deviates from the dynamic spatial curvature, which is consistent with general relativity. In the case of dark energy with constant equation of state, it is found that -8.4 ×1 0-3≤ΩKgeo≤6.6 ×1 0-3 (95% C.L.). This supports the hypothesis of a flat Universe in a very general meaning.
ERIC Educational Resources Information Center
Richards, Irving E.; And Others
In order to ascertain students' preferences for the number of times a class should meet each week, 375 questionnaires administered to students during the 1989 summer session at Cuyahoga Community College, Western Campus (Ohio) were evaluated. Results indicated that 49% of respondents preferred classes meeting twice each week, and 29% preferred…
The Learning Preference Inventory.
ERIC Educational Resources Information Center
Rezler, Agnes G.; Rezmovic, Victor
1981-01-01
Describes the development, validity, and reliability of the Learning Preference Inventory (LPI) and its use with health professions students and practitioners. Use of the LPI allows identification of individual learning preferences with a fair degree of accuracy. Ways to improve motivation for learning are suggested. (JOW)
NASA Astrophysics Data System (ADS)
Montazami, Reza; Liu, Sheng; Liu, Yang; Wang, Dong; Zhang, Qiming; Heflin, James R.
2011-05-01
Ionic electroactive polymer (IEAP) actuators containing porous conductive network composites (CNCs) and ionic liquids can result in high strain and fast response times. Incorporation of spherical gold nanoparticles in the CNC enhances conductivity and porosity, while maintaining relatively small thickness. This leads to improved mechanical strain and bending curvature of the actuators. We have employed the layer-by-layer self-assembly technique to fabricate a CNC with enhanced curvature (0.43 mm-1) and large net intrinsic strain (6.1%). The results demonstrate that curvature and net strain of IEAP actuators due to motion of the anions increase linearly with the thickness of the CNC as a result of the increased volume in which the anions can be stored. In addition, after subtracting the curvature of a bare Nafion actuator without a CNC, it is found that the net intrinsic strain of the CNC layer is independent of thickness for the range of 20-80 nm, indicating that the entire CNC volume contributes equivalently to the actuator motion. Furthermore, the response time of the actuator due to anion motion is independent of CNC thickness, suggesting that traversal through the Nafion membrane is the limiting factor in the anion motion.
Understanding the Role of Amphipathic Helices in N-BAR Domain Driven Membrane Remodeling
Cui, Haosheng; Mim, Carsten; Vázquez, Francisco X.; Lyman, Edward; Unger, Vinzenz M.; Voth, Gregory A.
2013-01-01
Endophilin N-BAR (N-terminal helix and Bin/amphiphysin/Rvs) domain tubulates and vesiculates lipid membranes in vitro via its crescent-shaped dimer and four amphipathic helices that penetrate into membranes as wedges. Like F-BAR domains, endophilin N-BAR also forms a scaffold on membrane tubes. Unlike F-BARs, endophilin N-BARs have N-terminal H0 amphipathic helices that are proposed to interact with other N-BARs in oligomer lattices. Recent cryo-electron microscopy reconstructions shed light on the organization of the N-BAR lattice coats on a nanometer scale. However, because of the resolution of the reconstructions, the precise positioning of the amphipathic helices is still ambiguous. In this work, we applied a coarse-grained model to study various membrane remodeling scenarios induced by endophilin N-BARs. We found that H0 helices of N-BARs prefer to align in an antiparallel manner at two ends of the protein to form a stable lattice. The deletion of H0 helices causes disruption of the lattice. In addition, we analyzed the persistence lengths of the protein-coated tubes and found that the stiffness of endophilin N-BAR-coated tubules qualitatively agrees with previous experimental work studying N-BAR-coated tubules. Large-scale simulations on membrane liposomes revealed a systematic relation between H0 helix density and local membrane curvature fluctuations. The data also suggest that the H0 helix is required for BARs to form organized structures on the liposome, further illustrating its important function. PMID:23442862
A novel curvature-controllable steerable needle for percutaneous intervention.
Bui, Van Khuyen; Park, Sukho; Park, Jong-Oh; Ko, Seong Young
2016-08-01
Over the last few decades, flexible steerable robotic needles for percutaneous intervention have been the subject of significant interest. However, there still remain issues related to (a) steering the needle's direction with less damage to surrounding tissues and (b) increasing the needle's maximum curvature for better controllability. One widely used approach is to control the fixed-angled bevel-tip needle using a "duty-cycle" algorithm. While this algorithm has shown its applicability, it can potentially damage surrounding tissue, which has prevented the widespread adoption of this technology. This situation has motivated the development of a new steerable flexible needle that can change its curvature without axial rotation, while at the same time producing a larger curvature. In this article, we propose a novel curvature-controllable steerable needle. The proposed robotic needle consists of two parts: a cannula and a stylet with a bevel-tip. The curvature of the needle's path is controlled by a control offset, defined by the offset between the bevel-tip and the cannula. As a result, the necessity of rotating the whole needle's body is decreased. The duty-cycle algorithm is utilized to a limited degree to obtain a larger radius of curvature, which is similar to a straight path. The first prototype of 0.46 mm (outer diameter) was fabricated and tested with both in vitro gelatin phantom and ex vivo cow liver tissue. The maximum curvatures measured 0.008 mm(-1) in 6 wt% gelatin phantom, 0.0139 mm(-1) in 10 wt% gelatin phantom, and 0.0038 mm(-1) in cow liver. The experimental results show a linear relationship between the curvature and the control offset, which can be utilized for future implementation of this control algorithm. PMID:27206444
Layered devices having surface curvature and method of constructing same
Woodbury, Richard C.; Perkins, Raymond T.; Thorne, James M.
1989-01-01
A method of treating a substrate having first and second sides with corresponding oppositely facing first and second surfaces, to produce curvature in the first surface. The method includes the steps of removing material, according to a predetermined pattern, from the second side of the substrate, and applying a stress-producing film of material to at least one surface of the substrate to thereby cause the substrate to bend to produce the desired curvature in the first surface.
Topology of codimension-one foliations of nonnegative curvature
Bolotov, Dmitry V
2013-05-31
We show that a transversely oriented C{sup 2}-foliation of codimension one with nonnegative Ricci curvature on a closed orientable manifold is a foliation with almost no holonomy. This allows us to decompose the manifold into blocks on which this foliation has a simple structure. We also show that a manifold homeomorphic to a 5-dimensional sphere does not admit a codimension-one C{sup 2}-foliation with nonnegative sectional curvature. Bibliography: 29 titles.
Hedgehogs in higher dimensional gravity with curvature self-interactions
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2001-04-01
Static solutions of the higher dimensional Einstein-Hilbert gravity supplemented by quadratic curvature self-interactions are discussed in the presence of hedgehog configurations along the transverse dimensions. The quadratic part of the action is parametrized in terms of the (ghost-free) Euler-Gauss-Bonnet curvature invariant. Spherically symmetric profiles of the transverse metric admit exponentially decaying warp factors both for positive and negative bulk cosmological constants.
Mundschau, Michael V.
2005-05-31
Composite hydrogen transport membranes, which are used for extraction of hydrogen from gas mixtures are provided. Methods are described for supporting metals and metal alloys which have high hydrogen permeability, but which are either too thin to be self supporting, too weak to resist differential pressures across the membrane, or which become embrittled by hydrogen. Support materials are chosen to be lattice matched to the metals and metal alloys. Preferred metals with high permeability for hydrogen include vanadium, niobium, tantalum, zirconium, palladium, and alloys thereof. Hydrogen-permeable membranes include those in which the pores of a porous support matrix are blocked by hydrogen-permeable metals and metal alloys, those in which the pores of a porous metal matrix are blocked with materials which make the membrane impervious to gases other than hydrogen, and cermets fabricated by sintering powders of metals with powders of lattice-matched ceramic.
Fuel cell membrane humidification
Wilson, Mahlon S.
1999-01-01
A polymer electrolyte membrane fuel cell assembly has an anode side and a cathode side separated by the membrane and generating electrical current by electrochemical reactions between a fuel gas and an oxidant. The anode side comprises a hydrophobic gas diffusion backing contacting one side of the membrane and having hydrophilic areas therein for providing liquid water directly to the one side of the membrane through the hydrophilic areas of the gas diffusion backing. In a preferred embodiment, the hydrophilic areas of the gas diffusion backing are formed by sewing a hydrophilic thread through the backing. Liquid water is distributed over the gas diffusion backing in distribution channels that are separate from the fuel distribution channels.
Elastic deformations of bolalipid membranes.
Galimzyanov, Timur R; Kuzmin, Peter I; Pohl, Peter; Akimov, Sergey A
2016-02-17
Archaeal membranes have unique mechanical properties that enable these organisms to survive under extremely aggressive environmental conditions. The so-called bolalipids contribute to this exceptional stability. They have two polar heads joined by two hydrocarbon chains. The two headgroups can face different sides of the membrane (O-shape conformation) or the same side (U-shape conformation). We have developed an elasticity theory for bolalipid membranes and show that the energetic contributions of (i) tilt deformations, (ii) area compression/stretching deformations, (iii) as well as those of Gaussian splay from the two membrane surfaces are additive, while splay deformations yield a cross-term. The presence of a small fraction of U-shaped molecules resulted in spontaneous membrane curvature. We estimated the tilt modulus to be approximately equal to that of membranes in eukaryotic cells. In contrast to conventional lipids, the bolalipid membrane possesses two splay moduli, one of which is estimated to be an order of magnitude larger than that of conventional lipids. The projected values of elastic moduli act to hamper pore formation and to decelerate membrane fusion and fission. PMID:26791255
Gas phase fractionation method using porous ceramic membrane
Peterson, Reid A.; Hill, Jr., Charles G.; Anderson, Marc A.
1996-01-01
Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.
Mingenbach, William A.
1988-01-01
A device is provided for stabilizing a flexible membrane secured within a frame, wherein a plurality of elongated arms are disposed radially from a central hub which penetrates the membrane, said arms imposing alternately against opposite sides of the membrane, thus warping and tensioning the membrane into a condition of improved stability. The membrane may be an opaque or translucent sheet or other material.
Focus control system for stretched-membrane mirror module
Butler, Barry L.; Beninga, Kelly J.
1991-01-01
A focus control system dynamically sets and controls the focal length of a reflective membrane supported between a perimeter frame. A rear membrane is also supported between the perimeter frame rearward and spaced apart from a back side of the reflective membrane. The space between the membranes defines a plenum space into which a mass of gas at a first pressure is inserted. The pressure differential between the first pressure and an external pressure, such as the atmospheric pressure, causes the reflective membrane to assume a first curvature relative to a reference plane associated with the perimeter frame. This curvature defines the focal length of the reflective membrane. The focal length is dynamically controlled by changing the volume of the plenum space, thereby changing the first pressure. The system can be used to change or maintain the pressure differential and hence the front membrane curvature. The plenum volume is changed by pushing or pulling on a central section of the rear membrane using a suitable actuator. Sensing means continuously sense the location of the reflective membrane relative to the reference plane. This sensed position is compared to a reference position, and a resulting error signal, comprising the difference between the sensed position and reference position, drives the actuator in a direction to minimize the difference. A vent value compensates for temperature changes or leaks in the closed volume by allowing the pressure differential to be adjusted as required to center the working range of the actuator about the desired focal length.
Focus control system for stretched-membrane mirror module
Butler, B.L.; Beninga, K.J.
1991-05-21
A focus control system dynamically sets and controls the focal length of a reflective membrane supported between a perimeter frame. A rear membrane is also supported between the perimeter frame rearward and spaced apart from a back side of the reflective membrane. The space between the membranes defines a plenum space into which a mass of gas at a first pressure is inserted. The pressure differential between the first pressure and an external pressure, such as the atmospheric pressure, causes the reflective membrane to assume a first curvature relative to a reference plane associated with the perimeter frame. This curvature defines the focal length of the reflective membrane. The focal length is dynamically controlled by changing the volume of the plenum space, thereby changing the first pressure. The system can be used to change or maintain the pressure differential and hence the front membrane curvature. The plenum volume is changed by pushing or pulling on a central section of the rear membrane using a suitable actuator. Sensing means continuously sense the location of the reflective membrane relative to the reference plane. This sensed position is compared to a reference position, and a resulting error signal, comprising the difference between the sensed position and reference position, drives the actuator in a direction to minimize the difference. A vent value compensates for temperature changes or leaks in the closed volume by allowing the pressure differential to be adjusted as required to center the working range of the actuator about the desired focal length. 13 figures.
Overriding plate thickness control on subducting slab curvature
NASA Astrophysics Data System (ADS)
Holt, A.; Buffett, B. A.; Becker, T. W.
2014-12-01
The curvature of subducting lithosphere controls deformation due to bending at the trench, which results in a force that dissipates gravitational potential energy and may affect seismic coupling. We use 2-D, thermo-mechanical subduction models to explore the dependence of the radius of curvature on the thickness of the subducting and overriding plates for models with both viscous and effectively plastic lithospheric rheologies. Such a plastic rheology has been shown to reproduce the bending stresses/moment computed using a kinematic strain rate description and a laboratory derived composite rheology. Laboratory and numerical models show that the bending geometry of subducting slabs with a viscous rheology is strongly dependent on slab thickness; thicker plates have a larger radius of curvature. However, the curvature of subducting plates on Earth, illuminated by the distribution of earthquake hypocenters, shows little to no dependence on the plate thickness or age. Such an observation is instead compatible with plates that have a plastic rheology. Indeed, our numerical models show that the radius of curvature of viscous plates has a stronger dependence on subducting plate thickness than in equivalent plastic models. In viscous plates, the bending moment produces a torque, which balances the torque exerted by buoyancy. However, for the plastic plate case the bending moment saturates at a maximum value and so cannot balance the gravitational torque. The saturation of bending moment means that, (a) the radius of curvature of the bending region is not constrained by this torque balance, and, (b) other forces are required to balance the gravitational torque. We explore the role that the overriding plate could play in controlling the subducting plate curvature in plastic plate models where the bending stresses have saturated. For such plates, we find that increasing the thickness of the overriding plate causes the radius of curvature to increase. The same correlation is
Topological Transitions in Mitochondrial Membranes controlled by Apoptotic Proteins
NASA Astrophysics Data System (ADS)
Hwee Lai, Ghee; Sanders, Lori K.; Mishra, Abhijit; Schmidt, Nathan W.; Wong, Gerard C. L.; Ivashyna, Olena; Schlesinger, Paul H.
2010-03-01
The Bcl-2 family comprises pro-apoptotic proteins, capable of permeabilizing the mitochondrial membrane, and anti-apoptotic members interacting in an antagonistic fashion to regulate programmed cell death (apoptosis). They offer potential therapeutic targets to re-engage cellular suicide in tumor cells but the extensive network of implicated protein-protein interactions has impeded full understanding of the decision pathway. We show, using synchrotron x-ray diffraction, that pro-apoptotic proteins interact with mitochondrial-like model membranes to generate saddle-splay (negative Gaussian) curvature topologically required for pore formation, while anti-apoptotic proteins can deactivate curvature generation by molecules drastically different from Bcl-2 family members and offer evidence for membrane-curvature mediated interactions general enough to affect very disparate systems.
Clinical workflow for spinal curvature measurement with portable ultrasound
NASA Astrophysics Data System (ADS)
Tabanfar, Reza; Yan, Christina; Kempston, Michael; Borschneck, Daniel; Ungi, Tamas; Fichtinger, Gabor
2016-03-01
PURPOSE: Spinal curvature monitoring is essential in making treatment decisions in scoliosis. Monitoring entails radiographic examinations, however repeated ionizing radiation exposure has been shown to increase cancer risk. Ultrasound does not emit ionizing radiation and is safer for spinal curvature monitoring. We investigated a clinical sonography protocol and challenges associated with position-tracked ultrasound in spinal curvature measurement in scoliosis. METHODS: Transverse processes were landmarked along each vertebra using tracked ultrasound snapshots. The transverse process angle was used to determine the orientation of each vertebra. We tested our methodology on five patients in a local pediatric scoliosis clinic, comparing ultrasound to radiographic curvature measurements. RESULTS: Despite strong correlation between radiographic and ultrasound curvature angles in phantom studies, we encountered new challenges in the clinical setting. Our main challenge was differentiating transverse processes from ribs and other structures during landmarking. We observed up to 13° angle variability for a single vertebra and a 9.85° +/- 10.81° difference between ultrasound and radiographic Cobb angles for thoracic curvatures. Additionally, we were unable to visualize anatomical landmarks in the lumbar region where soft tissue depth was 25-35mm. In volunteers with large Cobb angles (greater than 40° thoracic and 60° lumbar), we observed spinal protrusions resulting in incomplete probe-skin contact and partial ultrasound images not suitable for landmarking. CONCLUSION: Spinal curvature measurement using tracked ultrasound is viable on phantom spine models. In the clinic, new challenges were encountered which must be resolved before a universal sonography protocol can be developed.
A novel approach in assessment of root canal curvature
Sadeghi, Shiva; Poryousef, Vahideh
2009-01-01
Introduction: The purpose of this in vitro study was to introduce a new method to describe root canal curvatures and to assess the degree of curvature of human permanent mandibular teeth with curved root canals. Materials and Methods: One hundred and thirty five mesial root canals of mandibular first and second molar teeth were selected. Access cavities were prepared. After inserting a K-file size #10 into each canal, radiographs were taken. Canal curvature was determined by measuring the Schneider angle, canal access angle, as well as the canal radius, length, height and curvature starting distance on scanned radiographs using a computerized image processing system. Data was evaluated statistically using Pearson correlation. Results: The mean canal access angle (CAA) and Schneider angle (S) were 8.04◦ (3.46) and 19◦ (6.99), respectively. The Pearson correlation analysis found significant positive correlation between S and CAA (r=0.826, P<0.0001). Negative correlations were found between radius and length (r= –0.4, P<0.0001), radius and Schneider angle (r= –0.4, P<0.0001), radius and CAA (r= –0.24, P=0.004) and CAA and curvature starting distance (r= 0.4, P<0.0001). There was no correlation between height and distance (r=0.013, P=0.789), as well as CAA and height (r=0.654, P=0.001). Conclusion: Under the limitations of this study, the results indicated that the shape of root canal curvature can be more accurately described using two angles, Schneider in combination with Canal access angle. The related parameters included radius, length, distance and height of curvature. [Iranian Endodontic Journal 2009;4(4):131-4] PMID:24019833
Bending membranes on demand: fluid phospholipid bilayers on topographically deformable substrates.
Sanii, Babak; Smith, Andreia Michelle; Butti, Ravichandra; Brozell, Adrian M; Parikh, Atul N
2008-03-01
We combine hierarchical surface wrinkling of elastomers with lipid membrane deposition techniques to dynamically template complex three-dimensional topographies onto supported lipid bilayers. The real-time introduction of corresponding nano- to micrometer scale curvatures triggers spatially periodic, elastic bending of the bilayer, accompanied by molecular-level reorganizations. This ability to dynamically impose curvatures on supported bilayers and the ensuing re-equilibration promises fundamental material and biophysical investigations of curvature-dependent, static heterogeneities and dynamic reorganizations pervasive in biological membranes. PMID:18271562
NON-GAUSSIANITIES IN THE LOCAL CURVATURE OF THE FIVE-YEAR WMAP DATA
Rudjord, Oeystein; Groeneboom, Nicolaas E.; Hansen, Frode K.; Cabella, Paolo
2010-07-20
Using the five-year WMAP data, we re-investigate claims of non-Gaussianities and asymmetries detected in local curvature statistics of the one-year WMAP data. In Hansen et al., it was found that the northern ecliptic hemisphere was non-Gaussian at the {approx}1% level testing the densities of hill, lake, and saddle points based on the second derivatives of the cosmic microwave background temperature map. The five-year WMAP data have a much lower noise level and better control of systematics. Using these, we find that the anomalies are still present at a consistent level. Also the direction of maximum non-Gaussianity remains. Due to limited availability of computer resources, Hansen et al. were unable to calculate the full covariance matrix for the {chi}{sup 2}-test used. Here, we apply the full covariance matrix instead of the diagonal approximation and find that the non-Gaussianities disappear and there is no preferred non-Gaussian direction. We compare with simulations of weak lensing to see if this may cause the observed non-Gaussianity when using a diagonal covariance matrix. We conclude that weak lensing does not produce non-Gaussianity in the local curvature statistics at the scales investigated in this paper. The cause of the non-Gaussian detection in the case of a diagonal matrix remains unclear.
Membrane Compartment Occupied by Can1 (MCC) and Eisosome Subdomains of the Fungal Plasma Membrane
Douglas, Lois M.; Wang, Hong X.; Li, Lifang; Konopka, James B.
2011-01-01
Studies on the budding yeast Saccharomyces cerevisiae have revealed that fungal plasma membranes are organized into different subdomains. One new domain termed MCC/eisosomes consists of stable punctate patches that are distinct from lipid rafts. The MCC/eisosome domains correspond to furrows in the plasma membrane that are about 300 nm long and 50 nm deep. The MCC portion includes integral membrane proteins, such as the tetraspanners Sur7 and Nce102. The adjacent eisosome includes proteins that are peripherally associated with the membrane, including the BAR domains proteins Pil1 and Lsp1 that are thought to promote membrane curvature. Genetic analysis of the MCC/eisosome components indicates these domains broadly affect overall plasma membrane organization. The mechanisms regulating the formation of MCC/eisosomes in model organisms will be reviewed as well as the role of these plasma membrane domains in fungal pathogenesis and response to antifungal drugs. PMID:22368779
Membranes, mechanics, and intracellular transport
NASA Astrophysics Data System (ADS)
Parthasarathy, Raghuveer
2012-10-01
Cellular membranes are remarkable materials -- self-assembled, flexible, two-dimensional fluids. Understanding how proteins manipulate membrane curvature is crucial to understanding the transport of cargo in cells, yet the mechanical activities of trafficking proteins remain poorly understood. Using an optical-trap based assay involving dynamic deformation of biomimetic membranes, we have examined the behavior of Sar1, a key component of the COPII family of transport proteins. We find that Sar1 from yeast (S. cerevisiae) lowers membrane rigidity by up to 100% as a function of its concentration, thereby lowering the energetic cost of membrane deformation. Human Sar1 proteins can also lower the mechanical rigidity of the membranes to which they bind. However, unlike the yeast proteins, the rigidity is not a monotonically decreasing function of concentration but rather shows increased rigidity and decreased mobility at high concentrations that implies interactions between proteins. In addition to describing this study of membrane mechanics, I'll also discuss some topics relevant to a range of biophysical investigations, such as the insights provided by imaging methods and open questions in the dynamics of multicellular systems.
The weighted curvature approximation in scattering from sea surfaces
NASA Astrophysics Data System (ADS)
Guérin, Charles-Antoine; Soriano, Gabriel; Chapron, Bertrand
2010-07-01
A family of unified models in scattering from rough surfaces is based on local corrections of the tangent plane approximation through higher-order derivatives of the surface. We revisit these methods in a common framework when the correction is limited to the curvature, that is essentially the second-order derivative. The resulting expression is formally identical to the weighted curvature approximation, with several admissible kernels, however. For sea surfaces under the Gaussian assumption, we show that the weighted curvature approximation reduces to a universal and simple expression for the off-specular normalized radar cross-section (NRCS), regardless of the chosen kernel. The formula involves merely the sum of the NRCS in the classical Kirchhoff approximation and the NRCS in the small perturbation method, except that the Bragg kernel in the latter has to be replaced by the difference of a Bragg and a Kirchhoff kernel. This result is consistently compared with the resonant curvature approximation. Some numerical comparisons with the method of moments and other classical approximate methods are performed at various bands and sea states. For the copolarized components, the weighted curvature approximation is found numerically very close to the cut-off invariant two-scale model, while bringing substantial improvement to both the Kirchhoff and small-slope approximation. However, the model is unable to predict cross-polarization in the plane of incidence. The simplicity of the formulation opens new perspectives in sea state inversion from remote sensing data.
Nonlinear Development of Goertler Vortices Over Variable Curvature Walls.
NASA Astrophysics Data System (ADS)
Benmalek, Ali
The development of Gortler vortices over walls of variable curvature is studied. This is of interest because of stability and transition studies of boundary layers over surfaces which may have a combination of concave and convex or flat regions such as the lower surface of supercritical low drag suction laminar flow airfoils. The question arises regarding the nature of stabilization of the convex and zero curvature of the wall and whether it is sufficient to overcome the destabilization of the concave region. The parabolized disturbance equations governing the problem for small curvature, high Reynolds number and order one Gortler number are integrated numerically. Cases with concave, convex and zero curvatures are analyzed. The results show significant stabilization of the disturbances in the convex region, where new sets of vortices are successively created with opposite rotation to the preceding set. The "mushroom-shaped" distributions of low-momentum fluid riding above high-momentum fluid that are subject to secondary instability are predicted. The convex curvature tends to eliminate the inflection points from the spanwise and normal profiles of the streamwise velocity and, hence, suppresses the oscillatory secondary instability that leads to turbulence. Stabilization of Gortler vortices in a flat region is found to be less significant than in a convex region. Finally, the question as to whether the Gortler -Witting mechanism is important in boundary-layer transition is addressed.
Zhang, Meng; Huang, Rui; Im, Sang-Choul; Waskell, Lucy; Ramamoorthy, Ayyalusamy
2015-01-01
Mammalian cytochrome P450 (P450) is a membrane-bound monooxygenase whose catalytic activities require two electrons to be sequentially delivered from its redox partners: cytochrome b5 (cytb5) and cytochrome P450 reductase, both of which are membrane proteins. Although P450 functional activities are known to be affected by lipids, experimental evidence to reveal the effect of membrane on P450-cytb5 interactions is still lacking. Here, we present evidence for the influence of phospholipid bilayers on complex formation between rabbit P450 2B4 (CYP2B4) and rabbit cytb5 at the atomic level, utilizing NMR techniques. General line broadening and modest chemical shift perturbations of cytb5 resonances characterize CYP2B4-cytb5 interactions on the intermediate time scale. More significant intensity attenuation and a more specific protein-protein binding interface are observed in bicelles as compared with lipid-free solution, highlighting the importance of the lipid bilayer in stabilizing stronger and more specific interactions between CYP2B4 and cytb5, which may lead to a more efficient electron transfer. Similar results observed for the interactions between CYP2B4 lacking the transmembrane domain (tr-CYP2B4) and cytb5 imply interactions between tr-CYP2B4 and the membrane surface, which might assist in CYP2B4-cytb5 complex formation by orienting tr-CYP2B4 for efficient contact with cytb5. Furthermore, the observation of weak and nonspecific interactions between CYP2B4 and cytb5 in micelles suggests that lipid bilayer structures and low curvature membrane surface are preferable for CYP2B4-cytb5 complex formation. Results presented in this study provide structural insights into the mechanism behind the important role that the lipid bilayer plays in the interactions between P450s and their redox partners. PMID:25795780
Govindarajan, Sutharsan; Elisha, Yair; Nevo-Dinur, Keren; Amster-Choder, Orna
2013-01-01
ABSTRACT The bacterial cell poles are emerging as subdomains where many cellular activities take place, but the mechanisms for polar localization are just beginning to unravel. The general phosphotransferase system (PTS) proteins, enzyme I (EI) and HPr, which control preferential use of carbon sources in bacteria, were recently shown to localize near the Escherichia coli cell poles. Here, we show that EI localization does not depend on known polar constituents, such as anionic lipids or the chemotaxis receptors, and on the cell division machinery, nor can it be explained by nucleoid occlusion or localized translation. Detection of the general PTS proteins at the budding sites of endocytotic-like membrane invaginations in spherical cells and their colocalization with the negative curvature sensor protein DivIVA suggest that geometric cues underlie localization of the PTS system. Notably, the kinetics of glucose uptake by spherical and rod-shaped E. coli cells are comparable, implying that negatively curved “pole-like” sites support not only the localization but also the proper functioning of the PTS system in cells with different shapes. Consistent with the curvature-mediated localization model, we observed the EI protein from Bacillus subtilis at strongly curved sites in both B. subtilis and E. coli. Taken together, we propose that changes in cell architecture correlate with dynamic survival strategies that localize central metabolic systems like the PTS to subcellular domains where they remain active, thus maintaining cell viability and metabolic alertness. PMID:24129255
Zhou, Zhou; Munteanu, Emilia Laura; He, Jun; Ursell, Tristan; Bathe, Mark; Huang, Kerwyn Casey; Chang, Fred
2015-01-01
The functions of the actin-myosin–based contractile ring in cytokinesis remain to be elucidated. Recent findings show that in the fission yeast Schizosaccharomyces pombe, cleavage furrow ingression is driven by polymerization of cell wall fibers outside the plasma membrane, not by the contractile ring. Here we show that one function of the ring is to spatially coordinate septum cell wall assembly. We develop an improved method for live-cell imaging of the division apparatus by orienting the rod-shaped cells vertically using microfabricated wells. We observe that the septum hole and ring are circular and centered in wild-type cells and that in the absence of a functional ring, the septum continues to ingress but in a disorganized and asymmetric manner. By manipulating the cleavage furrow into different shapes, we show that the ring promotes local septum growth in a curvature-dependent manner, allowing even a misshapen septum to grow into a more regular shape. This curvature-dependent growth suggests a model in which contractile forces of the ring shape the septum cell wall by stimulating the cell wall machinery in a mechanosensitive manner. Mechanical regulation of the cell wall assembly may have general relevance to the morphogenesis of walled cells. PMID:25355954
Kinetics for phototropic curvature by etiolated seedlings of Arabidopsis thaliana
NASA Technical Reports Server (NTRS)
Orbovic, V.; Poff, K. L.
1991-01-01
An infrared-imaging system has been used to study the influence of gravity on the kinetics of first positive phototropism. The development of phototropic curvature of etiolated seedlings of Arabidopsis thaliana was measured in the absence of visible radiation. Following a pulse of blue light, stationary seedlings curved to a maximum of approximately 16 degrees about 80 minutes after stimulation. The seedlings then curved upward again or straightened by about 6 degrees during the subsequent 100 minutes. Seedlings rotated on a clinostat reached a similar maximum curvature following photostimulation. These seedlings maintained that curvature for 30 to 40 minutes before subsequently straightening to the same extent as the stationary seedlings. It is concluded that straightening is not a consequence of gravitropism, although gravity has some effect on the phototropism kinetics.
Robust disparity estimation based on color monogenic curvature phase.
Zang, Di; Li, Jie; Zhang, Dongdong; Zhang, Junqi
2012-07-01
Disparity estimation for binocular images is an important problem for many visual tasks such as 3D environment reconstruction, digital hologram, virtual reality, robot navigation, etc. Conventional approaches are based on brightness constancy assumption to establish spatial correspondences between a pair of images. However, in the presence of large illumination variation and serious noisy contamination, conventional approaches fail to generate accurate disparity maps. To have robust disparity estimation in these situations, we first propose a model - color monogenic curvature phase to describe local features of color images by embedding the monogenic curvature signal into the quaternion representation. Then a multiscale framework to estimate disparities is proposed by coupling the advantages of the color monogenic curvature phase and mutual information. Both indoor and outdoor images with large brightness variation are used in the experiments, and the results demonstrate that our approach can achieve a good performance even in the conditions of large illumination change and serious noisy contamination. PMID:22772192
Numerical Estimation of the Curvature of Biological Surfaces
NASA Technical Reports Server (NTRS)
Todd, P. H.
1985-01-01
Many biological systems may profitably be studied as surface phenomena. A model consisting of isotropic growth of a curved surface from a flat sheet is assumed. With such a model, the Gaussian curvature of the final surface determines whether growth rate of the surface is subharmonic or superharmonic. These properties correspond to notions of convexity and concavity, and thus to local excess growth and local deficiency of growth. In biological models where the major factors controlling surface growth are intrinsic to the surface, researchers thus gained from geometrical study information on the differential growth undergone by the surface. These ideas were applied to an analysis of the folding of the cerebral cortex, a geometrically rather complex surface growth. A numerical surface curvature technique based on an approximation to the Dupin indicatrix of the surface was developed. A metric for comparing curvature estimates is introduced, and considerable numerical testing indicated the reliability of this technique.
Tensor analysis and curvature in quantum space-time
Namsrai, K.
1987-03-01
Introducing quantum space-time into physics by means of the transformation language of noncommuting coordinates gives a simple scheme of generalizing the tensor analysis. The general covariance principle for the quantum space-time case is discussed, within which one can obtain the covariant structure of basic tensor quantities and the motion equation for a particle in a gravitational field. Definitions of covariant derivatives and curvature are also generalized in the give case. It turns out that the covariant structure of the Riemann-Christoffel curvature tensor is not preserved in quantum space-time. However, if the curvature tensor R/sub ..mu.. nu lambda chi/(z) is redetermined up to the value of the L/sup 2/ term, then its covariant structure is achieved, and it, in turn, allows them to reconstruct the Einstein equation in quantum space-time.
Exploiting cantilever curvature for noise reduction in atomic force microscopy.
Labuda, Aleksander; Grütter, Peter H
2011-01-01
Optical beam deflection is a widely used method for detecting the deflection of atomic force microscope (AFM) cantilevers. This paper presents a first order derivation for the angular detection noise density which determines the lower limit for deflection sensing. Surprisingly, the cantilever radius of curvature, commonly not considered, plays a crucial role and can be exploited to decrease angular detection noise. We demonstrate a reduction in angular detection shot noise of more than an order of magnitude on a home-built AFM with a commercial 450 μm long cantilever by exploiting the optical properties of the cantilever curvature caused by the reflective gold coating. Lastly, we demonstrate how cantilever curvature can be responsible for up to 45% of the variability in the measured sensitivity of cantilevers on commercially available AFMs. PMID:21280834
Studies of the effects of curvature on dilution jet mixing
NASA Astrophysics Data System (ADS)
Holdeman, James D.; Srinivasan, Ram; Reynolds, Robert S.; White, Craig D.
1992-02-01
An analytical program was conducted using both three-dimensional numerical and empirical models to investigate the effects of transition liner curvature on the mixing of jets injected into a confined crossflow. The numerical code is of the TEACH type with hybrid numerics; it uses the power-law and SIMPLER algorithms, an orthogonal curvilinear coordinate system, and an algebraic Reynolds stress turbulence model. From the results of the numerical calculations, an existing empirical model for the temperature field downstream of single and multiple rows of jets injected into a straight rectangular duct was extended to model the effects of curvature. Temperature distributions, calculated with both the numerical and empirical models, are presented to show the effects of radius of curvature and inner and outer wall injection for single and opposed rows of cool dilution jets injected into a hot mainstream flow.
An Experimental Study of Laminarization Induced by Acceleration and Curvature
NASA Astrophysics Data System (ADS)
Jackson, R. Brian
The Generation IV Very High Temperature Reactor (VHTR) design is being actively studied in various countries for application due to its inherent passive safe design, higher thermal efficiencies, and proposed capability of providing high temperature process heat. The pebble bed core is one of two core designs used in gas reactors. In the pebble bed core there are mechanisms present which can cause the flow to laminarize, thus reducing its heat transfer effectiveness. Wind tunnel experiments were conducted using Particle Image Velocimetry (PIV) to investigate boundary layer laminarization due to flow acceleration and convex curvature effects. The flow was subject to acceleration and curvature both separately and together and the flow behavior characterized with velocity flow profiles, mean boundary layer parameters, and turbulence quantities. Laminarization was identified and the influence of acceleration and curvature was characterized.
Curvature-Controlled Defect Localization in Elastic Surface Crystals
NASA Astrophysics Data System (ADS)
Jiménez, Francisco López; Stoop, Norbert; Lagrange, Romain; Dunkel, Jörn; Reis, Pedro M.
2016-03-01
We investigate the influence of curvature and topology on crystalline dimpled patterns on the surface of generic elastic bilayers. Our numerical analysis predicts that the total number of defects created by adiabatic compression exhibits universal quadratic scaling for spherical, ellipsoidal, and toroidal surfaces over a wide range of system sizes. However, both the localization of individual defects and the orientation of defect chains depend strongly on the local Gaussian curvature and its gradients across a surface. Our results imply that curvature and topology can be utilized to pattern defects in elastic materials, thus promising improved control over hierarchical bending, buckling, or folding processes. Generally, this study suggests that bilayer systems provide an inexpensive yet valuable experimental test bed for exploring the effects of geometrically induced forces on assemblies of topological charges.
[Frequency and most common localisation of root canal curvature].
Blasković-Subat, V
1991-01-01
The root canal therapy of the curved canals is a complex operative procedure. Therefore 260 root canals were analysed radiologically to determine the frequency and the most common localisation of the root canal curvature. The frequency of the curved canals averaged at 59%, being greater in the sample of posterior than in the anterior teeth (p less than 0.05). The root canal curvature was most frequently localised at the apical third part (53.9%), followed by the cervical (33.3%) and the middle (12.8%) third part. The apical curvature was predominant in the sample of the anterior, while the cervical predominant (45.2%) in the sample of the posterior teeth. This study pointed out that the frequency of the curved canals is rather high. Consequently, the necessity for practising the modern root canal preparation techniques, bearing in mind their potential danger, is emphasized. PMID:1819932
DNA origami with complex curvatures in three-dimensional space.
Han, Dongran; Pal, Suchetan; Nangreave, Jeanette; Deng, Zhengtao; Liu, Yan; Yan, Hao
2011-04-15
We present a strategy to design and construct self-assembling DNA nanostructures that define intricate curved surfaces in three-dimensional (3D) space using the DNA origami folding technique. Double-helical DNA is bent to follow the rounded contours of the target object, and potential strand crossovers are subsequently identified. Concentric rings of DNA are used to generate in-plane curvature, constrained to 2D by rationally designed geometries and crossover networks. Out-of-plane curvature is introduced by adjusting the particular position and pattern of crossovers between adjacent DNA double helices, whose conformation often deviates from the natural, B-form twist density. A series of DNA nanostructures with high curvature--such as 2D arrangements of concentric rings and 3D spherical shells, ellipsoidal shells, and a nanoflask--were assembled. PMID:21493857
Waterfall field in hybrid inflation and curvature perturbation
Gong, Jinn-Ouk; Sasaki, Misao E-mail: misao@yukawa.kyoto-u.ac.jp
2011-03-01
We study carefully the contribution of the waterfall field to the curvature perturbation at the end of hybrid inflation. In particular we clarify the parameter dependence analytically under reasonable assumptions on the model parameters. After calculating the mode function of the waterfall field, we use the δN formalism and confirm the previously obtained result that the power spectrum is very blue with the index 4 and is absolutely negligible on large scales. However, we also find that the resulting curvature perturbation is highly non-Gaussian and hence we calculate the bispectrum. We find that the bispectrum is at leading order independent of momentum and exhibits its peak at the equilateral limit, though it is unobservably small on large scales. We also present the one-point probability distribution function of the curvature perturbation.
Characterization of inherent curvature in DNA lacking polyadenine runs.
McNamara, P T; Harrington, R E
1991-07-01
Sequence-directed DNA curvature is most commonly associated with AA dinucleotides in the form of polyadenine runs. We demonstrate inherent curvature in DNA which lacks AA/TT dinucleotides using the criteria of polyacrylamide gel mobility and efficiency of DNA cyclization. These studies are based upon two 21-base pair synthetic DNA fragments designed to exhibit fixed curvature according to deflections made to the helical axis by non-AA dinucleotide stacks. Repeats of these sequences display anomalously slow migration in polyacrylamide gels. Moreover, both sequences describe helical conformations that are closed into circles by DNA ligase at much smaller sizes than is typical of nondeformed DNA. Chemical cleavage of these DNA molecules with hydroxyl radical is also consistent with local variation in helical conformation at specific dinucleotide steps. PMID:1648100
IFITM Proteins Restrict Viral Membrane Hemifusion
Golfetto, Ottavia; Bungart, Brittani; Li, Minghua; Ding, Shilei; He, Yuxian; Liang, Chen; Lee, James C.; Gratton, Enrico; Cohen, Fredric S.; Liu, Shan-Lu
2013-01-01
The interferon-inducible transmembrane (IFITM) protein family represents a new class of cellular restriction factors that block early stages of viral replication; the underlying mechanism is currently not known. Here we provide evidence that IFITM proteins restrict membrane fusion induced by representatives of all three classes of viral membrane fusion proteins. IFITM1 profoundly suppressed syncytia formation and cell-cell fusion induced by almost all viral fusion proteins examined; IFITM2 and IFITM3 also strongly inhibited their fusion, with efficiency somewhat dependent on cell types. Furthermore, treatment of cells with IFN also markedly inhibited viral membrane fusion and entry. By using the Jaagsiekte sheep retrovirus envelope and influenza A virus hemagglutinin as models for study, we showed that IFITM-mediated restriction on membrane fusion is not at the steps of receptor- and/or low pH-mediated triggering; instead, the creation of hemifusion was essentially blocked by IFITMs. Chlorpromazine (CPZ), a chemical known to promote the transition from hemifusion to full fusion, was unable to rescue the IFITM-mediated restriction on fusion. In contrast, oleic acid (OA), a lipid analog that generates negative spontaneous curvature and thereby promotes hemifusion, virtually overcame the restriction. To explore the possible effect of IFITM proteins on membrane molecular order and fluidity, we performed fluorescence labeling with Laurdan, in conjunction with two-photon laser scanning and fluorescence-lifetime imaging microscopy (FLIM). We observed that the generalized polarizations (GPs) and fluorescence lifetimes of cell membranes expressing IFITM proteins were greatly enhanced, indicating higher molecularly ordered and less fluidized membranes. Collectively, our data demonstrated that IFITM proteins suppress viral membrane fusion before the creation of hemifusion, and suggested that they may do so by reducing membrane fluidity and conferring a positive spontaneous
Zhi-Qiang, Chen; Jun-Wen, Li; Yi-Hong, Zhang; Xuan, Wang; Bin, Zhang
2012-01-01
The goal of this study is to investigate the effect of inoculating granules on reducing membrane fouling. In order to evaluate the differences in performance between flocculent sludge and aerobic granular sludge in membrane reactors (MBRs), two reactors were run in parallel and various parameters related to membrane fouling were measured. The results indicated that specific resistance to the fouling layer was five times greater than that of mixed liquor sludge in the granular MBR. The floc sludge more easily formed a compact layer on the membrane surface, and increased membrane resistance. Specifically, the floc sludge had a higher moisture content, extracellular polymeric substances concentration, and negative surface charge. In contrast, aerobic granules could improve structural integrity and strength, which contributed to the preferable permeate performance. Therefore, inoculating aerobic granules in a MBR presents an effective method of reducing the membrane fouling associated with floc sludge the perspective of from the morphological characteristics of microbial aggregates. PMID:22859954
Effect of curvature on the backscattering from leaves
NASA Technical Reports Server (NTRS)
Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.
1988-01-01
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.
Effect of curvature on the backscattering from a leaf
NASA Technical Reports Server (NTRS)
Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.
1988-01-01
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross-section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.
Electron energy transport and magnetic curvature driven modes
Coppi, B.; Tang, W.M.
1984-10-01
A transport coefficient for anomalous electron thermal conduction is constructed on the basis of the so-called Principle of Profile Consistency. It is assumed that the relevant modes in plasma where a substantial fraction of the electron population is magnetically trapped produce magnetic reconnection at a microscopic level and are driven by the combined effects of the plasma pressure gradient and the magnetic field curvature. Consequently, the scaling for the electron energy confinement time exhibits a strongly favorable dependence on the radius of magnetic curvature.
Constant curvature solutions of Grassmannian sigma models: (1) Holomorphic solutions
NASA Astrophysics Data System (ADS)
Delisle, L.; Hussin, V.; Zakrzewski, W. J.
2013-04-01
We present a general procedure for constructing constant curvature holomorphic maps of 2-spheres into Grassmannian manifolds G(m,n). Our procedure allows us to make a couple of conjectures as to the possible values of this curvature. We prove our conjectures for G(2,4), G(2,5), present explicit formulae for the relevant maps and show that they agree with those found by other methods. We also make some comments about the maps into G(2,n) for n≥6.
Focal Length Controllable Ultrasonic Array Transducer with Adjustable Curvature
NASA Astrophysics Data System (ADS)
Kim, Jungsoon; Kim, Moojoon; Ha, Kanglyel
2012-07-01
In the underwater imaging field, the control of the focal length of a transducer is very useful. As one of the control methods, we suggested an ultrasonic array transducer with adjustable curvature by using air pressure. The curvature of the transducer was investigated according to the air pressure level in the back space of the transducer. Concave-, planar-, and convex-type transducers were obtained with different air pressure levels. The acoustic fields of the transducer were measured for different shapes of the radiation surface.
Composite oxygen transport membrane
Christie, Gervase Maxwell; Lane, Jonathan A.
2014-08-05
A method of producing a composite oxygen ion membrane and a composite oxygen ion membrane in which a porous fuel oxidation layer and a dense separation layer and optionally, a porous surface exchange layer are formed on a porous support from mixtures of (Ln.sub.1-xA.sub.x).sub.wCr.sub.1-yB.sub.yO.sub.3-.delta. and a doped zirconia. In the porous fuel oxidation layer and the optional porous surface exchange layer, A is Calcium and in the dense separation layer A is not Calcium and, preferably is Strontium. Preferred materials are (La.sub.0.8Ca.sub.0.2).sub.0.95Cr.sub.0.5Mn.sub.0.5O.sub.3-.delta. for the porous fuel oxidation and optional porous surface exchange layers and (La.sub.0.8Sr.sub.0.2).sub.0.95Cr.sub.0.5Fe.sub.0.5O.sub.3-.delta. for the dense separation layer. The use of such materials allows the membrane to sintered in air and without the use of pore formers to reduce membrane manufacturing costs. The use of materials, as described herein, for forming the porous layers have application for forming any type of porous structure, such as a catalyst support.
Mechano-capacitive properties of polarized membranes.
Mosgaard, Lars D; Zecchi, Karis A; Heimburg, Thomas
2015-10-28
Biological membranes are capacitors that can be charged by applying a field across the membrane. The charges on the capacitor exert a force on the membrane that leads to electrostriction, i.e. a thinning of the membrane. Since the force is quadratic in voltage, negative and positive voltage have an identical influence on the physics of symmetric membranes. However, this is not the case for a membrane with an asymmetry leading to a permanent electric polarization. Positive and negative voltages of identical magnitude lead to different properties. Such an asymmetry can originate from a lipid composition that is different on the two monolayers of the membrane, or from membrane curvature. The latter effect is called 'flexoelectricity'. As a consequence of permanent polarization, the membrane capacitor is discharged at a voltage different from zero. This leads to interesting electrical phenomena such as outward or inward rectification of membrane permeability. Here, we introduce a generalized theoretical framework, that treats capacitance, polarization, flexoelectricity, piezoelectricity and thermoelectricity in the same language. We show applications to electrostriction, membrane permeability and piezoelectricity and thermoelectricity close to melting transitions, where such effects are especially pronounced. PMID:26324950
Tormala, Zakary L; Jia, Jayson S; Norton, Michael I
2012-10-01
When people seek to impress others, they often do so by highlighting individual achievements. Despite the intuitive appeal of this strategy, we demonstrate that people often prefer potential rather than achievement when evaluating others. Indeed, compared with references to achievement (e.g., "this person has won an award for his work"), references to potential (e.g., "this person could win an award for his work") appear to stimulate greater interest and processing, which can translate into more favorable reactions. This tendency creates a phenomenon whereby the potential to be good at something can be preferred over actually being good at that very same thing. We document this preference for potential in laboratory and field experiments, using targets ranging from athletes to comedians to graduate school applicants and measures ranging from salary allocations to online ad clicks to admission decisions. PMID:22775472
[Food preferences among students].
Maldonado, R; Villalbí, J R
1993-07-01
The results of a food preference survey using a questionnaire on 2,567 schoolchildren of sixth, seventh and eighth grade (11 to 14 years of age) from 26 public schools in the city of Barcelona (Spain) are presented. Foods based on potatoes and cereals have the maximum acceptability, followed by dairy and meat products. Chicken is the meat with highest acceptance. Fish has a medium acceptance, and preference for dry beans and peas, fruits and vegetables is lower, although it is high for some specific foods. Important differences among sexes are observed. Boys have higher preference for meat, milk and yogurt, and girls for fish and some vegetables. Differences among genders increase with increasing age. These results are relevant for planning interventions on diet in schools from a health promotion perspective, and for the planning of school lunch programs. PMID:8363142
Mingenbach, W.A.
1988-02-09
A device is provided for stabilizing a flexible membrane secured within a frame, wherein a plurality of elongated arms are disposed radially from a central hub which penetrates the membrane, said arms imposing alternately against opposite sides of the membrane, thus warping and tensioning the membrane into a condition of improved stability. The membrane may be an opaque or translucent sheet or other material. 10 figs.
NASA Technical Reports Server (NTRS)
Bagshaw, S. L.; Cleland, R. E.
1990-01-01
Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates could be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower (Helianthus annuus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.
Metal Preferences and Metallation*
Foster, Andrew W.; Osman, Deenah; Robinson, Nigel J.
2014-01-01
The metal binding preferences of most metalloproteins do not match their metal requirements. Thus, metallation of an estimated 30% of metalloenzymes is aided by metal delivery systems, with ∼25% acquiring preassembled metal cofactors. The remaining ∼70% are presumed to compete for metals from buffered metal pools. Metallation is further aided by maintaining the relative concentrations of these pools as an inverse function of the stabilities of the respective metal complexes. For example, magnesium enzymes always prefer to bind zinc, and these metals dominate the metalloenzymes without metal delivery systems. Therefore, the buffered concentration of zinc is held at least a million-fold below magnesium inside most cells. PMID:25160626
Nonlinear dynamics of a double bilipid membrane.
Sample, C; Golovin, A A
2007-09-01
The nonlinear dynamics of a biological double membrane that consists of two coupled lipid bilayers, typical of some intracellular organelles such as mitochondria or nuclei, is studied. A phenomenological free-energy functional is formulated in which the curvatures of the two parts of the double membrane and the distance between them are coupled to the lipid chemical composition. The derived nonlinear evolution equations for the double-membrane dynamics are studied analytically and numerically. A linear stability analysis is performed, and the domains of parameters are found in which the double membrane is stable. For the parameter values corresponding to an unstable membrane, numerical simulations are performed that reveal various types of complex dynamics, including the formation of stationary, spatially periodic patterns. PMID:17930289
Nonlinear dynamics of a double bilipid membrane
NASA Astrophysics Data System (ADS)
Sample, C.; Golovin, A. A.
2007-09-01
The nonlinear dynamics of a biological double membrane that consists of two coupled lipid bilayers, typical of some intracellular organelles such as mitochondria or nuclei, is studied. A phenomenological free-energy functional is formulated in which the curvatures of the two parts of the double membrane and the distance between them are coupled to the lipid chemical composition. The derived nonlinear evolution equations for the double-membrane dynamics are studied analytically and numerically. A linear stability analysis is performed, and the domains of parameters are found in which the double membrane is stable. For the parameter values corresponding to an unstable membrane, numerical simulations are performed that reveal various types of complex dynamics, including the formation of stationary, spatially periodic patterns.
Electrokinetic effects near a membrane
NASA Astrophysics Data System (ADS)
Lacoste, David
2009-03-01
We discuss the electrostatic and electrokinetic contribution to the elastic moduli of a cell or artificial membrane placed in an electrolyte and driven by a DC electric field. The field drives ion currents across the membrane, through specific channels, pumps or natural pores. In steady state, charges accumulate in the Debye layers close to the membrane, modifying the membrane elastic moduli. We first study a model of a membrane of zero thickness, later generalizing this treatment to allow for a finite thickness and finite dielectric constant. Our results clarify and extend the results presented in [D. Lacoste, M. Cosentino Lagomarsino, and J. F. Joanny, Europhys. Lett., 77, 18006 (2007)], by providing a physical explanation for a destabilizing term proportional to kps^3 in the fluctuation spectrum, which we relate to a nonlinear (E^2) electro-kinetic effect called induced-charge electro-osmosis (ICEO). Recent studies of ICEO have focused on electrodes and polarizable particles, where an applied bulk field is perturbed by capacitive charging of the double layer and drives flow along the field axis toward surface protrusions; we predict similar ICEO flows around driven membranes, due to curvature-induced tangential fields within a non-equilibrium double layer, which hydrodynamically enhance protrusions.
Complex Dynamic Development of Poliovirus Membranous Replication Complexes
Nair, Vinod; Hansen, Bryan T.; Hoyt, Forrest H.; Fischer, Elizabeth R.; Ehrenfeld, Ellie
2012-01-01
Replication of all positive-strand RNA viruses is intimately associated with membranes. Here we utilize electron tomography and other methods to investigate the remodeling of membranes in poliovirus-infected cells. We found that the viral replication structures previously described as “vesicles” are in fact convoluted, branching chambers with complex and dynamic morphology. They are likely to originate from cis-Golgi membranes and are represented during the early stages of infection by single-walled connecting and branching tubular compartments. These early viral organelles gradually transform into double-membrane structures by extension of membranous walls and/or collapsing of the luminal cavity of the single-membrane structures. As the double-membrane regions develop, they enclose cytoplasmic material. At this stage, a continuous membranous structure may have double- and single-walled membrane morphology at adjacent cross-sections. In the late stages of the replication cycle, the structures are represented mostly by double-membrane vesicles. Viral replication proteins, double-stranded RNA species, and actively replicating RNA are associated with both double- and single-membrane structures. However, the exponential phase of viral RNA synthesis occurs when single-membrane formations are predominant in the cell. It has been shown previously that replication complexes of some other positive-strand RNA viruses form on membrane invaginations, which result from negative membrane curvature. Our data show that the remodeling of cellular membranes in poliovirus-infected cells produces structures with positive curvature of membranes. Thus, it is likely that there is a fundamental divergence in the requirements for the supporting cellular membrane-shaping machinery among different groups of positive-strand RNA viruses. PMID:22072780
Preferring the Contemporary Look.
ERIC Educational Resources Information Center
Springer, Marc
1980-01-01
Describes a study that indicated that readers of college newspapers prefer a front page style that is contemporary and emphasizes a horizontal layout to either an avant-garde style that features an entirely horizontal layout or a traditional layout having a vertical page. (TJ)
Cognitive Preferences and Ethnicity.
ERIC Educational Resources Information Center
O'Donnell, William J.; O'Donnell, Teresa Flores
This document reports on a study into the relationships between cognitive preferences, achievement, and ethnicity of first year algebra students. The sample consisted of 175 students from two high schools in the Denver (Colorado) metropolitan area. The two schools were chosen because of the diversity of ethnic groups in the student populations.…
Controlling Protein Oligomerization with Surface Curvature on the Nanoscale
NASA Astrophysics Data System (ADS)
Kurylowicz, Marty; Dutcher, John
2011-03-01
We investigate the effect of surface curvature on the conformation of beta-lactoglobulin (β LG) using Single Molecule Force Spectroscopy. β LG is a model interfacial protein which stabilizes oil droplets in milk and is known to undergo structural rearrangement when adsorbed onto a surface. We reliably control nanoscale surface curvature by creating close-packed monolayers of monodisperse polystyrene (PS) nanoparticles with diameters of 20, 40, 60, 80 and 140 nm, which are stable in aqueous buffer. By adsorbing β LG onto these hydrophobic surfaces and collecting force-extension curves in the fluid phase we can compare the conformation of β LG on 5 different surface curvatures with that on a flat PS film. We demonstrate a transition from oligomeric to monomeric β LG as the surface curvature is increased. Histograms of contour length from fits to peaks in the force-extension curves show a single maximum near 30 nm for β LG adsorbed onto nanoparticles with diameters less than 80 nm. For the larger nanoparticles, the histogram approaches that observed for β LG adsorbed onto a flat PS film, with maxima indicative of β LG dimers and trimers.
Stiffness, not inertial coupling, determines path curvature of wrist motions.
Charles, Steven K; Hogan, Neville
2012-02-01
When humans rotate their wrist in flexion-extension, radial-ulnar deviation, and combinations, the resulting paths (like the path of a laser pointer on a screen) exhibit a distinctive pattern of curvature. In this report we show that the passive stiffness of the wrist is sufficient to account for this pattern. Simulating the dynamics of wrist rotations using a demonstrably realistic model under a variety of conditions, we show that wrist stiffness can explain all characteristics of the observed pattern of curvature. We also provide evidence against other possible causes. We further demonstrate that the phenomenon is robust against variations in human wrist parameters (inertia, damping, and stiffness) and choice of model inputs. Our findings explain two previously observed phenomena: why faster wrist rotations exhibit more curvature and why path curvature rotates with pronation-supination of the forearm. Our results imply that, as in reaching, path straightness is a goal in the planning and control of wrist rotations. This requires humans to predict and compensate for wrist dynamics, but, unlike reaching, nonlinear inertial coupling (e.g., Coriolis acceleration) is insignificant. The dominant term to be compensated is wrist stiffness. PMID:22131378
Effect of asymmetric auxin application on Helianthus hypocotyl curvature
NASA Technical Reports Server (NTRS)
Migliaccio, F.; Rayle, D. L.
1989-01-01
Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution.
Wormhole geometries supported by a nonminimal curvature-matter coupling
Garcia, Nadiezhda Montelongo; Lobo, Francisco S. N.
2010-11-15
Wormhole geometries in curvature-matter coupled modified gravity are explored, by considering an explicit nonminimal coupling between an arbitrary function of the scalar curvature, R, and the Lagrangian density of matter. It is the effective stress-energy tensor containing the coupling between matter and the higher order curvature derivatives that is responsible for the null energy condition violation, and consequently for supporting the respective wormhole geometries. The general restrictions imposed by the null energy condition violation are presented in the presence of a nonminimal R-matter coupling. Furthermore, obtaining exact solutions to the gravitational field equations is extremely difficult due to the nonlinearity of the equations, although the problem is mathematically well defined. Thus, we outline several approaches for finding wormhole solutions, and deduce an exact solution by considering a linear R nonmiminal curvature-matter coupling and by considering an explicit monotonically decreasing function for the energy density. Although it is difficult to find exact solutions of matter threading the wormhole satisfying the energy conditions at the throat, an exact solution is found where the nonminimal coupling does indeed minimize the violation of the null energy condition of normal matter at the throat.
Special-holonomy manifolds and quartic-curvature string corrections
NASA Astrophysics Data System (ADS)
Stelle, K. S.
2004-06-01
The quartic-curvature corrections derived from string theory have a very specific impact on the geometry of target-space manifolds of special holonomy. In the cases of Calabi-Yau manifolds and D = 7 manifolds of G2 holonomy, we show how the corrections conspire to preserve the unbroken supersymmetry of these backgrounds.
Three-dimensional ultrasound palmprint recognition using curvature methods
NASA Astrophysics Data System (ADS)
Iula, Antonio; Nardiello, Donatella
2016-05-01
Palmprint recognition systems that use three-dimensional (3-D) information of the palm surface are the most recently explored techniques to overcome some two-dimensional palmprint difficulties. These techniques are based on light structural imaging. In this work, a 3-D ultrasound palmprint recognition system is proposed and evaluated. Volumetric images of a region of the human hand are obtained by moving an ultrasound linear array along its elevation direction and one by one acquiring a number of B-mode images, which are then grouped in a 3-D matrix. The acquisition time was contained in about 5 s. Much information that can be exploited for 3-D palmprint recognition is extracted from the ultrasound volumetric images, including palm curvature and other under-skin information as the depth of the various traits. The recognition procedure developed in this work is based on the analysis of the principal curvatures of palm surface, i.e., mean curvature image, Gaussian curvature image, and surface type. The proposed method is evaluated by performing verification and identification experiments. Preliminary results have shown that the proposed system exhibits an acceptable recognition rate. Further possible improvements of the proposed technique are finally highlighted and discussed.
On a modified streamline curvature method for the Euler equations
NASA Technical Reports Server (NTRS)
Cordova, Jeffrey Q.; Pearson, Carl E.
1988-01-01
A modification of the streamline curvature method leads to a quasilinear second-order partial differential equation for the streamline coordinate function. The existence of a stream function is not required. The method is applied to subsonic and supersonic nozzle flow, and to axially symmetric flow with swirl. For many situations, the associated numerical method is both fast and accurate.
Effect of track asymmetry and curvature on shingle writing scheme
NASA Astrophysics Data System (ADS)
Liu, Feng; Li, Shaoping; Bai, Daniel; Mendez, Hector; Pan, Tao; Han, Dehua; Mao, Sining
2011-04-01
Written transition curvature in perpendicular magnetic recording is generally understood to result in increased transition jitter noise and degraded signal to noise ratio or byte error rate (BER) performance. For the shingle writing scheme, asymmetry or curvature in written tracks is considered inherent due to the erasure and track edge writing characteristics. It is proposed that such a track asymmetry is more prominent at high track density/smaller track pitch recording conditions. In this report we present spin stand experimental results to study the effect of the possible track asymmetry or curvature by shingle writing and reading back in different skews. By comparing shingle writing BER bathtub profiles in different writing skew conditions 0°, +/-2°, +/-4°, +/-6°, the effect of varying shingle track asymmetry and curvature is analyzed via subsequent skewed reading process. The shingle writing BER bathtub profiles as well as the read back amplitude cross track profile are generally symmetric upon one sided erasure at different track pitches. We found that the 0° skew writing and reading process provides both the maximum BER and amplitude.
The influence of curvature on film cooling performance
NASA Astrophysics Data System (ADS)
Schwarz, S. G.; Goldstein, R. J.; Eckert, E. R. G.
1990-06-01
The effects of injection rate and strength of curvature on film cooling performance of gas injected through a row of holes on a convex surface is studied. Comparisons are made to film cooling of concave and flat surfaces. Three different relative strengths of curvature (ratio of radius of curvature to radius of injection hole), two density ratios (0.95 and 2.0), and a wide range of blowing rates (0.3 to 2.7) are considered. A foreign gas injection technique (mass transfer analogy) is used. The strength of curvature was controlled by varying the injection hole diameter. At low blowing rates, film cooling is more effective on the convex surface than on a flat or a concave surface. The cross stream pressure gradient present in curved flows tends to push the jet into the convex wall. As the injection rate is increased, normal and tangential jet momentum promote lift-off from the convex surface, thereby lowering performance. In contrast, previous studies show that a concave surface, tangential jet momentum, flow instabilities, and blockage improve performance on a concave surface as blowing rate is increased.
Negative voltage bandgap reference with multilevel curvature compensation technique
NASA Astrophysics Data System (ADS)
Xi, Liu; Qian, Liu; Xiaoshi, Jin; Yongrui, Zhao; Lee, Jong-Ho
2016-05-01
A novel high-order curvature compensation negative voltage bandgap reference (NBGR) based on a novel multilevel compensation technique is introduced. Employing an exponential curvature compensation (ECC) term with many high order terms in itself, in a lower temperature range (TR) and a multilevel curvature compensation (MLCC) term in a higher TR, a flattened and better effect of curvature compensation over the TR of 165 °C (‑40 to 125 °C) is realised. The MLCC circuit adds two convex curves by using two sub-threshold operated NMOS. The proposed NBGR implemented in the Central Semiconductor Manufacturing Corporation (CSMC) 0.5 μm BCD technology demonstrates an accurate voltage of ‑1.183 V with a temperature coefficient (TC) as low as 2.45 ppm/°C over the TR of 165 °C at a ‑5.0 V power supply; the line regulation is 3 mV/V from a ‑5 to ‑2 V supply voltage. The active area of the presented NBGR is 370 × 180 μm2. Project supported by the Fund of Liaoning Province Education Department (No. L2013045).
Frustration and curvature - Glasses and the cholesteric blue phase
NASA Technical Reports Server (NTRS)
Sethna, J. P.
1983-01-01
An analogy is drawn between continuum elastic theories of the blue phase of cholesteric liquid crystals and recent theories of frustration in configurational glasses. Both involve the introduction of a lattice of disclination lines to relieve frustration; the frustration is due to an intrinsic curvature in the natural form of parallel transport. A continuum theory of configurational glasses is proposed.
Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy
NASA Astrophysics Data System (ADS)
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Equilibrium models of coronal loops that involve curvature and buoyancy
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Simple partitions of a hyperbolic plane of positive curvature
Romakina, Lyudmila N
2012-09-30
We construct special monohedral isotropic partitions with symmetries of the hyperbolic plane H of positive curvature with a simple 4-contour as a cell. An analogue of mosaic in these partitions called a tiling is introduced. Also we consider some fractal tilings. The existence of band tilings in each homological series with code (m, n) is proved. Bibliography: 14 titles.
Intracellular magnetophoresis of amyloplasts and induction of root curvature
NASA Technical Reports Server (NTRS)
Kuznetsov, O. A.; Hasenstein, K. H.
1996-01-01
High-gradient magnetic fields (HGMFs) were used to induce intracellular magnetophoresis of amyloplasts. The HGMFs were generated by placing a small ferromagnetic wedge into a uniform magnetic field or at the gap edge between two permanent magnets. In the vicinity of the tip of the wedge the dynamic factor of the magnetic field, delta(H2/2), was about 10(9) Oe2.cm-1, which subjected the amyloplasts to a force comparable to that of gravity. When roots of 2-d-old seedlings of flax (Linum usitatissimum L.) were positioned vertically and exposed to an HGMF, curvature away from the wedge was transient and lasted approximately 1 h. Average curvature obtained after placing magnets, wedge and seedlings on a 1-rpm clinostat for 2 h was 33 +/- 5 degrees. Roots of horizontally placed control seedlings without rotation curved about 47 +/- 4 degrees. The time course of curvature and changes in growth rate were similar for gravicurvature and for root curvature induced by HGMFs. Microscopy showed displacement of amyloplasts in vitro and in vivo. Studies with Arabidopsis thaliana (L.) Heynh. showed that the wild type responded to HGMFs but the starchless mutant TC7 did not. The data indicate that a magnetic force can be used to study the gravisensing and response system of roots.
The flow curvature method applied to canard explosion
NASA Astrophysics Data System (ADS)
Ginoux, Jean-Marc; Llibre, Jaume
2011-11-01
The aim of this work is to establish that the bifurcation parameter value leading to a canard explosion in dimension 2 obtained by the so-called geometric singular perturbation method can be found according to the flow curvature method. This result will be then exemplified with the classical Van der Pol oscillator.
A requirement for epsin in mitotic membrane and spindle organization
2009-01-01
Eukaryotic cells possess a sophisticated membrane system to facilitate diverse functions. Whereas much is known about the nature of membrane systems in interphase, the organization and function of the mitotic membrane system are less well understood. In this study, we show that epsin, an endocytic adapter protein, regulates mitotic membrane morphology and spindle integrity in HeLa cells. Using epsin that harbors point mutations in the epsin NH2-terminal homology domain and spindle assembly assays in Xenopus laevis egg extracts, we show that epsin-induced membrane curvature is required for proper spindle morphogenesis, independent of its function in endocytosis during interphase. Although several other membrane-interacting proteins, including clathrin, AP2, autosomal recessive hypercholesterolemia, and GRASP65, are implicated in the regulation of mitosis, whether they participate through regulation of membrane organization is unclear. Our study of epsin provides evidence that mitotic membrane organization influences spindle integrity. PMID:19704019
TOPICAL REVIEW: Stability of macroion-decorated lipid membranes
NASA Astrophysics Data System (ADS)
May, Sylvio
2005-08-01
Adsorption of macroions such as colloidal particles, proteins, or other rigid biopolymers onto oppositely charged, mixed lipid membranes is a ubiquitous phenomenon encountered in biotechnology, drug delivery, and cellular biology. The softness and self-assembled nature of the membrane enable the macroion-membrane complex to laterally reorganize via forming macroion clusters, lipid domains, or separate phases, and to exhibit curvature modulations or even morphological transitions. Almost always, the lateral organization of the membrane and associated macroion layer mutually depend on each other so that neither of the two extreme views—macroion-induced membrane domain formation or membrane-mediated macroion clustering—strictly accounts for the underlying energetics. We review and discuss some recent efforts to describe the lateral organization and stability of macroion-decorated lipid membranes using different levels of mean-field electrostatics, thereby focusing on binary membranes and the destabilizing role of compositional gradients.
NASA Technical Reports Server (NTRS)
Khurana, J. P.; Best, T. R.; Poff, K. L.
1989-01-01
Phototropic and gravitropic curvature by hypocotyls of Arabidopsis thaliana is minimal when the side of the hook with the cotyledons attached is positioned toward the direction of tropistic curvature, and maximal when that side of the hook is positioned away from the direction of tropistic curvature. Based on these data, it is proposed that the position of the hook with attached cotyledons affects curvature and not stimulus perception. A randomly oriented population of plants exhibited considerable heterogeneity in tropistic curvature. This heterogeneity arises at least in part from the dependence of curvature on the position of the hook.
Stimulation of root elongation and curvature by calcium
NASA Technical Reports Server (NTRS)
Takahashi, H.; Scott, T. K.; Suge, H.
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms.
Separation of metals by supported liquid membranes
Takigawa, D.Y.
1990-12-31
A supported liquid membrane system for the separation of a preselected chemical species within a feedstream, preferably an aqueous feedstream, includes a feed compartment containing a feed solution having at least one preselected chemical species therein, a stripping compartment containing a stripping solution therein, and a microporous polybenzimidazole membrane situated between the compartments, the microporous polybenzimidazole membrane containing an extractant mixture selective for the preselected chemical species within the membrane pores is disclosed along with a method of separating preselected chemical species from a feedstream with such a system, and a supported liquid membrane for use in such a system.
Separation of metals by supported liquid membrane
Takigawa, Doreen Y.
1992-01-01
A supported liquid membrane system for the separation of a preselected chemical species within a feedstream, preferably an aqueous feedstream, includes a feed compartment containing a feed solution having at least one preselected chemical species therein, a stripping compartment containing a stripping solution therein, and a microporous polybenzimidazole membrane situated between the compartments, the microporous polybenzimidazole membrane containing an extractant mixture selective for the preselected chemical species within the membrane pores is disclosed along with a method of separating preselected chemical species from a feedstream with such a system, and a supported liquid membrane for use in such a system.
Physical basis of some membrane shaping mechanisms.
Simunovic, Mijo; Prévost, Coline; Callan-Jones, Andrew; Bassereau, Patricia
2016-07-28
In vesicular transport pathways, membrane proteins and lipids are internalized, externalized or transported within cells, not by bulk diffusion of single molecules, but embedded in the membrane of small vesicles or thin tubules. The formation of these 'transport carriers' follows sequential events: membrane bending, fission from the donor compartment, transport and eventually fusion with the acceptor membrane. A similar sequence is involved during the internalization of drug or gene carriers inside cells. These membrane-shaping events are generally mediated by proteins binding to membranes. The mechanisms behind these biological processes are actively studied both in the context of cell biology and biophysics. Bin/amphiphysin/Rvs (BAR) domain proteins are ideally suited for illustrating how simple soft matter principles can account for membrane deformation by proteins. We review here some experimental methods and corresponding theoretical models to measure how these proteins affect the mechanics and the shape of membranes. In more detail, we show how an experimental method employing optical tweezers to pull a tube from a giant vesicle may give important quantitative insights into the mechanism by which proteins sense and generate membrane curvature and the mechanism of membrane scission.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298443
Dimer ribbons of ATP synthase shape the inner mitochondrial membrane
Strauss, Mike; Hofhaus, Götz; Schröder, Rasmus R; Kühlbrandt, Werner
2008-01-01
ATP synthase converts the electrochemical potential at the inner mitochondrial membrane into chemical energy, producing the ATP that powers the cell. Using electron cryo-tomography we show that the ATP synthase of mammalian mitochondria is arranged in long ∼1-μm rows of dimeric supercomplexes, located at the apex of cristae membranes. The dimer ribbons enforce a strong local curvature on the membrane with a 17-nm outer radius. Calculations of the electrostatic field strength indicate a significant increase in charge density, and thus in the local pH gradient of ∼0.5 units in regions of high membrane curvature. We conclude that the mitochondrial cristae act as proton traps, and that the proton sink of the ATP synthase at the apex of the compartment favours effective ATP synthesis under proton-limited conditions. We propose that the mitochondrial ATP synthase organises itself into dimer ribbons to optimise its own performance. PMID:18323778
Membrane tension and membrane fusion.
Kozlov, Michael M; Chernomordik, Leonid V
2015-08-01
Diverse cell biological processes that involve shaping and remodeling of cell membranes are regulated by membrane lateral tension. Here we focus on the role of tension in driving membrane fusion. We discuss the physics of membrane tension, forces that can generate the tension in plasma membrane of a cell, and the hypothesis that tension powers expansion of membrane fusion pores in late stages of cell-to-cell and exocytotic fusion. We propose that fusion pore expansion can require unusually large membrane tensions or, alternatively, low line tensions of the pore resulting from accumulation in the pore rim of membrane-bending proteins. Increase of the inter-membrane distance facilitates the reaction. PMID:26282924
Chia, Pei Zhi Cheryl
2014-01-01
Membrane trafficking depends on transport vesicles and carriers docking and fusing with the target organelle for the delivery of cargo. Membrane tethers and small guanosine triphosphatases (GTPases) mediate the docking of transport vesicles/carriers to enhance the efficiency of the subsequent SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-mediated fusion event with the target membrane bilayer. Different classes of membrane tethers and their specific intracellular location throughout the endomembrane system are now well defined. Recent biochemical and structural studies have led to a deeper understanding of the mechanism by which membrane tethers mediate docking of membrane carriers as well as an appreciation of the role of tethers in coordinating the correct SNARE complex and in regulating the organization of membrane compartments. This review will summarize the properties and roles of membrane tethers of both secretory and endocytic systems. PMID:25343031
Cohen, J
1996-01-01
Quality Adjusted Life Years (QALYs) have become a household word among health economists. Their use as a means of comparing the value of health programmes and medical interventions has stirred up controversy in the medical profession and the academic community. In this paper, I argue that QALY analysis does not adequately take into account the differentiated nature of the health state values it measures. Specifically, it does not distinguish between needs and preferences with respect to its valuation of health states. I defend the view that needs and preferences are clearly distinguishable, and that the concept of needs cannot be dispensed with, as many health economists suggest. It is argued that the scale along which health states are measured in QALY analysis is not a continuous interval scale, but one which concerns two distinctly different value dimensions. Measuring the values of health state intervals may reveal the weighting attached to the different value dimensions. PMID:8910777
Haughton, J; Haughton, D
1995-01-01
This article assesses the strength of son preference in Vietnam, as reflected in fertility behavior. It formulates and estimates a proportional hazards model applied to birth intervals, and a contraceptive prevalence model, using household survey data from 2,636 ever-married women aged 15-49 with at least one living child who were interviewed for the Vietnam Living Standards Survey 1992-1993. Son preference is found to be strong by world standards, but nevertheless, it has a minor effect on fertility; in its absence, the total fertility rate would fall by roughly 10 percent from the current level of about 3.2 children per woman of reproductive age. PMID:8826072
Membrane Tension Inhibits Deformation by Coat Proteins in Clathrin-Mediated Endocytosis
NASA Astrophysics Data System (ADS)
Hassinger, Julian; Drubin, David; Oster, George; Rangamani, Padmini
2016-02-01
In clathrin-mediated endocytosis (CME), clathrin and various adaptor proteins coat a patch of the plasma membrane, which is reshaped to form a budded vesicle. Experimental studies have demonstrated that elevated membrane tension can inhibit bud formation by a clathrin coat. In this study, we investigate the impact of membrane tension on the mechanics of membrane budding by simulating clathrin coats that either grow in area or progressively induce greater curvature. At low membrane tension, progressively increasing the area of a curvature-generating coat causes the membrane to smoothly evolve from a flat to budded morphology, whereas the membrane remains essentially flat at high membrane tensions. Interestingly, at physiologically relevant, intermediate membrane tensions, the shape evolution of the membrane undergoes a snapthrough instability in which increasing coat area causes the membrane to "snap" from an open, U-shaped bud to a closed, $\\Omega$-shaped bud. This instability is accompanied by a large energy barrier, which could cause a developing endocytic pit to stall if the binding energy of additional coat is insufficient to overcome this barrier. Similar results were found for a coat of constant area in which the spontaneous curvature progressively increases. Additionally, a pulling force on the bud, simulating a force from actin polymerization, is sufficient to drive a transition from an open to closed bud, overcoming the energy barrier opposing this transition.
Coaching preferences of athletes.
Terry, P C; Howe, B L
1984-12-01
The study examined the coaching preferences of 80 male and 80 female athletes, as measured by the Leadership Scale for Sports (Chelladurai and Saleh, 1978, 1980). In addition, it attempted to assess the applicability to sport of the Life-cycle and Path-goal theories of leadership. Comparisons between groups were made on the basis of sex, age, and type of sport. A MANOVA indicated that athletes in independent sports preferred more democratic behaviour (p less than .001) and less autocratic behaviour (p = .028) than athletes in interdependent sports. No differences in coaching preferences were found which could be attributed to the age or sex of the athlete, or the variability of the sports task. These results partially supported the Path-goal theory, but did not support the Life-cycle theory. Athletes of all groups tended to favour coaches who displayed training behaviour and rewarding behaviour "often", democratic behaviour and social support behaviour "occasionally", and autocratic behaviour "seldom". This consistency may be a useful finding for those organizations and institutions interested in preparing coaches. PMID:6525751
Perspectives on Preference Aggregation.
Regenwetter, Michel
2009-07-01
For centuries, the mathematical aggregation of preferences by groups, organizations, or society itself has received keen interdisciplinary attention. Extensive theoretical work in economics and political science throughout the second half of the 20th century has highlighted the idea that competing notions of rational social choice intrinsically contradict each other. This has led some researchers to consider coherent democratic decision making to be a mathematical impossibility. Recent empirical work in psychology qualifies that view. This nontechnical review sketches a quantitative research paradigm for the behavioral investigation of mathematical social choice rules on real ballots, experimental choices, or attitudinal survey data. The article poses a series of open questions. Some classical work sometimes makes assumptions about voter preferences that are descriptively invalid. Do such technical assumptions lead the theory astray? How can empirical work inform the formulation of meaningful theoretical primitives? Classical "impossibility results" leverage the fact that certain desirable mathematical properties logically cannot hold in all conceivable electorates. Do these properties nonetheless hold true in empirical distributions of preferences? Will future behavioral analyses continue to contradict the expectations of established theory? Under what conditions do competing consensus methods yield identical outcomes and why do they do so? PMID:26158988
Clay Mineral Preferred Orientation
NASA Astrophysics Data System (ADS)
Day-Stirrat, R. J.
2014-12-01
Anisotropy of the orientation of clay minerals, often referred to as texture, may be unique to sediments' deposition, composition, deformation or diagenetic history. The literature is rich with studies that include preferred orientation generation in fault gouge, low-grade metamorphic rocks, sediments with variable clay content and during the smectite-to-illite transformation. Untangling the interplay between many competing factors in any one geologic situation has proven a significant challenge over many years. Understanding how, where and when clay minerals develop a preferred orientation has significant implications for permeability anisotropy in shallow burial, the way mechanical properties are projected from shallower to deeper settings in basin modeling packages and the way velocity anisotropy is accounted for in seismic data processing. The assessment of the anisotropic properties of fine-grained siliciclastic rocks is gaining significant momentum in rock physics research. Therefore, a fundamental understanding of how clay minerals develop a preferred orientation in space and time is crucial to the understanding of anisotropy of physical properties. The current study brings together a wealth of data that may be used in a predictive sense to account for fabric anisotropy that may impact any number of rock properties.
Organelle morphogenesis by active membrane remodeling
NASA Astrophysics Data System (ADS)
Ramakrishnan, N.; Ipsen, John H.; Rao, Madan; Kumar, P. B. Sunil
Intracellular organelles are subject to a steady flux of lipids and proteins through active, energy consuming transport processes. Active fission and fusion are promoted by GTPases, e.g., Arf-Coatamer and the Rab-Snare complexes, which both sense and generate local membrane curvature. Here we investigate through Dynamical Triangulation Monte Carlo simulations, the role that these active processes play in determining the morphology and compositional segregation in closed membranes. Our results suggest that the ramified morphologies of organelles observed in-vivo are a consequence of driven nonequilibrium processes rather than equilibrium forces.
A classification result for helix surfaces with parallel mean curvature in product spaces
NASA Astrophysics Data System (ADS)
Fetcu, Dorel
2015-10-01
We determine all helix surfaces with parallel mean curvature vector field which are not minimal or pseudo-umbilical in spaces of type , where M n ( c) is a simply connected n-dimensional manifold with constant sectional curvature c.
Membrane Mechanics of Endocytosis in Cells with Turgor
Dmitrieff, Serge; Nédélec, François
2015-01-01
Endocytosis is an essential process by which cells internalize a piece of plasma membrane and material from the outside. In cells with turgor, pressure opposes membrane deformations, and increases the amount of force that has to be generated by the endocytic machinery. To determine this force, and calculate the shape of the membrane, we used physical theory to model an elastic surface under pressure. Accurate fits of experimental profiles are obtained assuming that the coated membrane is highly rigid and preferentially curved at the endocytic site. The forces required from the actin machinery peaks at the onset of deformation, indicating that once invagination has been initiated, endocytosis is unlikely to stall before completion. Coat proteins do not lower the initiation force but may affect the process by the curvature they induce. In the presence of isotropic curvature inducers, pulling the tip of the invagination can trigger the formation of a neck at the base of the invagination. Hence direct neck constriction by actin may not be required, while its pulling role is essential. Finally, the theory shows that anisotropic curvature effectors stabilize membrane invaginations, and the loss of crescent-shaped BAR domain proteins such as Rvs167 could therefore trigger membrane scission. PMID:26517669
Do adult men with untreated ventral penile curvature have adverse outcomes?
Menon, Vani; Breyer, Benjamin; Copp, Hillary L.; Baskin, Laurence; Disandro, Michael; Schlomer, Bruce J.
2016-01-01
Summary Introduction Congenital ventral penile curvature without hypospadias is often treated surgically in childhood. The history of untreated ventral curvature is unknown. Objective This study’s aim was to examine the association of untreated ventral penile curvature with various sexual and psychosexual outcomes. Study design An electronic survey was advertised to men older than 18 years on Facebook. Men with possible ventral penile curvature identified themselves by choosing sketches that most closely represented their anatomy. Outcomes assessed included: Sexual Health Inventory for Men, difficulty of intercourse because of curvature, International Prostate Symptom Score, Penile Perception Score, psychosexual milestones, paternity, infertility, sitting to urinate, and the CDC HRQOL-4 module. Results Among participants, 81 out of 684 men (11.8%) reported untreated ventral penile curvature. Participants with self-reported curvature noted more difficulty with intercourse because of curvature (4.5 vs 4.9, p < 0.001), more unhealthy mental days (8.6 vs 6.2, p = 0.02), and increased dissatisfaction with penile self-perception compared with men without reported curvature (8.6 vs 9.5, p < 0.001). Discussion Men with possible untreated ventral curvature reported worse penile perception scores, more mentally unhealthy days, and increased difficulty with intercourse secondary to curvature compared with men without curvature. A limitation to this study is selection bias; responses collected were self-reported from survey volunteers. Additionally, the question identifying ventral penile curvature is not validated but performed well in pretesting. Most questions were from validated surveys, but some were modeled after validated surveys and/or contained high face validity types of questions. Conclusion Men with possible untreated ventral penile curvature reported more dissatisfaction with penile appearance, increased difficulty with intercourse, and more unhealthy mental
Constructing Graphs over with Small Prescribed Mean-Curvature
NASA Astrophysics Data System (ADS)
Carley, Holly; Kiessling, Michael K.-H.
2015-12-01
In this paper nonlinear Hodge theory and Banach algebra estimates are employed to construct a convergent series expansion which solves the prescribed mean curvature equation for n-dimensional hypersurfaces in (+ sign) and (- sign) which are graphs of a smooth function , and whose mean curvature function H is α-Hölder continuous and integrable, with small norm. The radius of convergence is estimated explicitly from below. Our approach is inspired by, and applied to, the Maxwell-Born-Infeld theory of electromagnetism in , for which our method yields the first systematic way of explicitly computing the electrostatic potential for regular charge densities and small Born parameter, with explicit error estimates at any order of truncation of the series. In particular, our results level the ground for a controlled computation of Born-Infeld effects on the Hydrogen spectrum.
Generating ekpyrotic curvature perturbations before the big bang
Lehners, Jean-Luc; Turok, Neil; McFadden, Paul; Steinhardt, Paul J.
2007-11-15
We analyze a general mechanism for producing a nearly scale-invariant spectrum of cosmological curvature perturbations during a contracting phase preceding a big bang, which can be entirely described using 4D effective field theory. The mechanism, based on first producing entropic perturbations and then converting them to curvature perturbations, can be naturally incorporated in cyclic and ekpyrotic models in which the big bang is modeled as a brane collision, as well as other types of cosmological models with a pre-big bang phase. We show that the correct perturbation amplitude can be obtained and that the spectral tilt n{sub s} tends to range from slightly blue to red, with 0.97
Curvature boundary condition for a moving contact line
NASA Astrophysics Data System (ADS)
Luo, J.; Hu, X. Y.; Adams, N. A.
2016-04-01
Effective wall boundary conditions are very important for simulating multi-phase flows involving a moving contact line. In this paper we present a curvature boundary condition to circumvent the difficulties of previous approaches on explicitly imposing the contact angle and with respect to mass-loss artifacts near the wall boundary. While employing the asymptotic theory of Cox for imposing an effective curvature directly at the wall surface, the present method avoids a mismatch between the exact and the numerical contact angles. Test simulations on drop spreading and multi-phase flow in a channel show that the present method achieves grid-convergent results and ensures mass conservation, and delivers good agreement with theoretical, numerical and experimental data.
Curvature effects on carbon nanomaterials: Exohedral versus endhohedral supercapacitors
Huang, J; Sumpter, B. G.; Meunier, V.; Yushin, G.; Portet, C.; Gogotsi, Y.
2011-01-31
Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.
Curvature effects in carbon nanomaterials: Exohedral versus endohedral supercapacitors
Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Gogotsi, Yury G.; Yushin, Gleb; Portet, Cristelle
2010-01-01
Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.
Confinement for Thin Film on Substrates with Different Geometric Curvatures
NASA Astrophysics Data System (ADS)
Xu, Jie; Chen, Jiao; Xue, Gi
2014-03-01
Molecular chain conformation in thin polymer film on substrates with different geometric curvature was examined using fluorescence non-radiative energy transfer (NRET) spectroscopy. We find that thin film on concave substrate exihibits significant differences in vitrification behavior, in both magnitude and thickness dependence, from the planar film. NRET measured a more compact morphology, while dynamical scanning calorimetry detected an increased glass transition temperature (Tg) for the concave thin film, with respect to bulk film. In contrast to planar film where properties are thickness dependent, polymer concave film shows that its conformation and Tg are solely dependent on curvature radius. Surprisingly, these properties converted back to the bulk values when the substrate was removed, indicating the crucial importance of interaction imposed by the concave hard wall. These spectroscopic data matched perfectly the calorimetric results and provided a new implication to understanding geometric confinement on dynamics.
Dynamic Chord-wise Tip Curvature on Flexible Flapping Plates
NASA Astrophysics Data System (ADS)
Martin, Nathan; Gharib, Morteza
2014-11-01
The aerodynamic characteristics of long rectangular flapping plates are strongly influenced by the interaction between tip and edge vortices. This has led to the development of many tip actuation mechanisms to independently bend or rotate the tip towards the root of the plate in the span-wise direction. In our current work, the influence of dynamically altering the chord-wise curvature of the tip on the generation of aerodynamic forces is investigated; for this case, the two free corners of the flat plate bend towards each other. The parameters of actuation timing, maximum curvature, Reynolds number, flexibility, and tip speed are independently varied to determine their influence. These results will further the fundamental understanding of unsteady aerodynamics. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship and the Gordon and Betty Moore foundation.
Robust contour decomposition using a constant curvature criterion
NASA Technical Reports Server (NTRS)
Wuescher, Daniel M.; Boyer, Kim L.
1991-01-01
The problem of decomposing an extended boundary or contour into simple primitives is addressed with particular emphasis on Laplacian-of-Gaussian (LoG) zero-crossing contours. A technique is introduced for partitioning such contours into constant curvature segments. A nonlinear `blip' filter matched to the impairment signature of the curvature computation process, an overlapped voting scheme, and a sequential contiguous segment extraction mechanism are used. This technique is insensitive to reasonable changes in algorithm parameters and robust to noise and minor viewpoint-induced distortions in the contour shape, such as those encountered between stereo image pairs. The results vary smoothly with the data, and local perturbations induce only local changes in the result. Robustness and insensitivity are experimentally verified.
Control of repeat protein curvature by computational protein design
Park, Keunwan; Shen, Betty W.; Parmeggiani, Fabio; Huang, Po-Ssu; Stoddard, Barry L.; Baker, David
2014-01-01
Shape complementarity is an important component of molecular recognition, and the ability to precisely adjust the shape of a binding scaffold to match a target of interest would greatly facilitate the creation of high affinity protein reagents and therapeutics. Here we describe a general approach to control the shape of the binding surface on repeat protein scaffolds, and apply it to leucine rich repeat proteins. First, a set of self-compatible building block modules are designed that when polymerized each generate surfaces with unique but constant curvatures. Second, a set of junction modules that connect the different building blocks are designed. Finally, new proteins with custom designed shapes are generated by appropriately combining building block and junction modules. Crystal structures of the designs illustrate the power of the approach in controlling repeat protein curvature. PMID:25580576
DNA Origami with Complex Curvatures in Three-Dimensional Space
Han, Dongran; Pal, Suchetan; Nangreave, Jeanette; Deng, Zhengtao; Liu, Yan; Yan, Hao
2011-04-14
We present a strategy to design and construct self-assembling DNA nanostructures that define intricate curved surfaces in three-dimensional (3D) space using the DNA origami folding technique. Double-helical DNA is bent to follow the rounded contours of the target object, and potential strand crossovers are subsequently identified. Concentric rings of DNA are used to generate in-plane curvature, constrained to 2D by rationally designed geometries and crossover networks. Out-of-plane curvature is introduced by adjusting the particular position and pattern of crossovers between adjacent DNA double helices, whose conformation often deviates from the natural, B-form twist density. A series of DNA nanostructures with high curvature—such as 2D arrangements of concentric rings and 3D spherical shells, ellipsoidal shells, and a nanoflask—were assembled.
Effect of curvature on three-dimensional boundary layer stability
NASA Technical Reports Server (NTRS)
Malik, M. R.; Poll, D. I. A.
1984-01-01
The problem of the stability of a three-dimensional laminar boundary layer formed on a curved surface is considered. A calculation scheme, which takes account of the curvature of the flow streamlines and of the surface is proposed for the prediction of the development of small amplitude temporal disturbances. Computations have been performed for the flow over the windward face of an infinitely long yawed cylinder and comparisons have been made with experimental data. These indicate that the theory correctly predicts many of the features of the unstable laminar flow. The theory also suggests that transition, in this particular situation, is dominated by traveling disturbance waves and that, at the experimentally observed transition location, the wave which has undergone greatest total amplification has an amplitude ratio of approximately e to the 11th. When the effects of curvature are omitted the maximum amplitude ratio at transition is about e to the 17th.
On the breakdown of the curvature perturbation ζ during reheating
NASA Astrophysics Data System (ADS)
Tarman Algan, Merve; Kaya, Ali; Seyma Kutluk, Emine
2015-04-01
It is known that in single scalar field inflationary models the standard curvature perturbation ζ, which is supposedly conserved at superhorizon scales, diverges during reheating at times 0dot phi=, i.e. when the time derivative of the background inflaton field vanishes. This happens because the comoving gauge 0varphi=, where varphi denotes the inflaton perturbation, breaks down when 0dot phi=. The issue is usually bypassed by averaging out the inflaton oscillations but strictly speaking the evolution of ζ is ill posed mathematically. We solve this problem in the free theory by introducing a family of smooth gauges that still eliminates the inflaton fluctuation varphi in the Hamiltonian formalism and gives a well behaved curvature perturbation ζ, which is now rigorously conserved at superhorizon scales. At the linearized level, this conserved variable can be used to unambiguously propagate the inflationary perturbations from the end of inflation to subsequent epochs. We discuss the implications of our results for the inflationary predictions.
A three-dimensional validation of crack curvature in muscovite mica
J. C. Hill; J. W. Foulk III; P. A. Klein; E. P. Chen
2001-01-07
Experimental and computational efforts focused on characterizing crack tip curvature in muscovite mica. Wedge-driven cracks were propagated under monochromatic light. Micrographs verified the subtle curvature of the crack front near the free surface. A cohesive approach was employed to model mixed-mode fracture in a three-dimensional framework. Finite element calculations captured the crack curvature observed in experiment.
Digital elevation model visibility including Earth's curvature and atmosphere refraction
NASA Astrophysics Data System (ADS)
Santossilva, Ewerton; Vieiradias, Luiz Alberto
1990-03-01
There are some instances in which the Earth's curvature and the atmospheric refraction, optical or electronic, are important factors when digital elevation models are used for visibility calculations. This work deals with this subject, suggesting a practical approach to solve this problem. Some examples, from real terrain data, are presented. The equipment used was an IBM-PC like computer with a SITIM graphic card.
Global and local curvature in density functional theory
NASA Astrophysics Data System (ADS)
Zhao, Qing; Ioannidis, Efthymios I.; Kulik, Heather J.
2016-08-01
Piecewise linearity of the energy with respect to fractional electron removal or addition is a requirement of an electronic structure method that necessitates the presence of a derivative discontinuity at integer electron occupation. Semi-local exchange-correlation (xc) approximations within density functional theory (DFT) fail to reproduce this behavior, giving rise to deviations from linearity with a convex global curvature that is evidence of many-electron, self-interaction error and electron delocalization. Popular functional tuning strategies focus on reproducing piecewise linearity, especially to improve predictions of optical properties. In a divergent approach, Hubbard U-augmented DFT (i.e., DFT+U) treats self-interaction errors by reducing the local curvature of the energy with respect to electron removal or addition from one localized subshell to the surrounding system. Although it has been suggested that DFT+U should simultaneously alleviate global and local curvature in the atomic limit, no detailed study on real systems has been carried out to probe the validity of this statement. In this work, we show when DFT+U should minimize deviations from linearity and demonstrate that a "+U" correction will never worsen the deviation from linearity of the underlying xc approximation. However, we explain varying degrees of efficiency of the approach over 27 octahedral transition metal complexes with respect to transition metal (Sc-Cu) and ligand strength (CO, NH3, and H2O) and investigate select pathological cases where the delocalization error is invisible to DFT+U within an atomic projection framework. Finally, we demonstrate that the global and local curvatures represent different quantities that show opposing behavior with increasing ligand field strength, and we identify where these two may still coincide.
Entropy production and curvature perturbation from dissipative curvatons
Matsuda, Tomohiro
2010-09-01
Considering the curvaton field that follows dissipative slow-roll equation, we show that the field can lead to entropy production and generation of curvature perturbation after reheating. Spectral index is calculated to discriminate warm and thermal scenarios of dissipative curvatons from the standard curvaton model. In contrast to the original curvaton model, quadratic potential is not needed in the dissipative scenario, since the growth in the oscillating period is not essential for the model.
Higher Curvature Effects in the ADD and RS Models
Rizzo, Thomas G.; /SLAC
2006-07-05
Over the last few years several extra-dimensional models have been introduced in attempt to deal with the hierarchy problem. These models can lead to rather unique and spectacular signatures at Terascale colliders such as the LHC and ILC. The ADD and RS models, though quite distinct, have many common feature including a constant curvature bulk, localized Standard Model(SM) fields and the assumption of the validity of the EH action as a description of gravitational interactions.
Global and local curvature in density functional theory.
Zhao, Qing; Ioannidis, Efthymios I; Kulik, Heather J
2016-08-01
Piecewise linearity of the energy with respect to fractional electron removal or addition is a requirement of an electronic structure method that necessitates the presence of a derivative discontinuity at integer electron occupation. Semi-local exchange-correlation (xc) approximations within density functional theory (DFT) fail to reproduce this behavior, giving rise to deviations from linearity with a convex global curvature that is evidence of many-electron, self-interaction error and electron delocalization. Popular functional tuning strategies focus on reproducing piecewise linearity, especially to improve predictions of optical properties. In a divergent approach, Hubbard U-augmented DFT (i.e., DFT+U) treats self-interaction errors by reducing the local curvature of the energy with respect to electron removal or addition from one localized subshell to the surrounding system. Although it has been suggested that DFT+U should simultaneously alleviate global and local curvature in the atomic limit, no detailed study on real systems has been carried out to probe the validity of this statement. In this work, we show when DFT+U should minimize deviations from linearity and demonstrate that a "+U" correction will never worsen the deviation from linearity of the underlying xc approximation. However, we explain varying degrees of efficiency of the approach over 27 octahedral transition metal complexes with respect to transition metal (Sc-Cu) and ligand strength (CO, NH3, and H2O) and investigate select pathological cases where the delocalization error is invisible to DFT+U within an atomic projection framework. Finally, we demonstrate that the global and local curvatures represent different quantities that show opposing behavior with increasing ligand field strength, and we identify where these two may still coincide. PMID:27497541
Reheating via a generalized nonminimal coupling of curvature to matter
Bertolami, Orfeu; Frazao, Pedro; Paramos, Jorge
2011-02-15
In this work, one shows that a generalized nonminimal coupling between geometry and matter is compatible with Starobinsky inflation and leads to a successful process of preheating, a reheating scenario based on the production of massive particles via parametric resonance. The model naturally extends the usual preheating mechanism, which resorts to an ad hoc scalar curvature-dependent mass term for a scalar field {chi}, and also encompasses a previously studied preheating channel based upon a nonstandard kinetic term.
Resolution of curvature singularities from quantum mechanical and loop perspective
NASA Astrophysics Data System (ADS)
Tahamtan, T.; Svítek, O.
2014-08-01
We analyze the persistence of curvature singularities when analyzed using quantum theory. First, quantum test particles obeying the Klein-Gordon and Chandrasekhar-Dirac equation are used to probe the classical timelike naked singularity. We show that the classical singularity is felt even by our quantum probes. Next, we use loop quantization to resolve a singularity hidden beneath the horizon. The singularity is resolved in this case.
CURVATURE-DRIFT INSTABILITY FAILS TO GENERATE PULSAR RADIO EMISSION
Kaganovich, Alexander; Lyubarsky, Yuri
2010-10-01
The curvature-drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing the propagation of short electromagnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity; therefore, this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.
Toward assessing the effects of crack front curvature /CFC/.
NASA Technical Reports Server (NTRS)
Swedlow, J. L.; Ritter, M. A.
1972-01-01
Consideration of the effect of crack front curvature (CFC) on the K calibration of five special geometries in which CFC occurs. The five cases considered include an elliptical crack in an infinite medium, an internal annular crack in a thick-walled cylinder, a through crack in a flat plate, a part-through crack in a plate, and an irregularly shaped crack in a solid. It is shown that K depends on CFC differently in each case.
Membrane-Mediated Interaction between Strongly Anisotropic Protein Scaffolds
Schweitzer, Yonatan; Kozlov, Michael M.
2015-01-01
Specialized proteins serve as scaffolds sculpting strongly curved membranes of intracellular organelles. Effective membrane shaping requires segregation of these proteins into domains and is, therefore, critically dependent on the protein-protein interaction. Interactions mediated by membrane elastic deformations have been extensively analyzed within approximations of large inter-protein distances, small extents of the protein-mediated membrane bending and small deviations of the protein shapes from isotropic spherical segments. At the same time, important classes of the realistic membrane-shaping proteins have strongly elongated shapes with large and highly anisotropic curvature. Here we investigated, computationally, the membrane mediated interaction between proteins or protein oligomers representing membrane scaffolds with strongly anisotropic curvature, and addressed, quantitatively, a specific case of the scaffold geometrical parameters characterizing BAR domains, which are crucial for membrane shaping in endocytosis. In addition to the previously analyzed contributions to the interaction, we considered a repulsive force stemming from the entropy of the scaffold orientation. We computed this interaction to be of the same order of magnitude as the well-known attractive force related to the entropy of membrane undulations. We demonstrated the scaffold shape anisotropy to cause a mutual aligning of the scaffolds and to generate a strong attractive interaction bringing the scaffolds close to each other to equilibrium distances much smaller than the scaffold size. We computed the energy of interaction between scaffolds of a realistic geometry to constitute tens of kBT, which guarantees a robust segregation of the scaffolds into domains. PMID:25710602
A Usual G-Protein-Coupled Receptor in Unusual Membranes.
Chawla, Udeep; Jiang, Yunjiang; Zheng, Wan; Kuang, Liangju; Perera, Suchithranga M D C; Pitman, Michael C; Brown, Michael F; Liang, Hongjun
2016-01-11
G-protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and constitute about 50% of all known drug targets. They offer great potential for membrane protein nanotechnologies. We report here a charge-interaction-directed reconstitution mechanism that induces spontaneous insertion of bovine rhodopsin, the eukaryotic GPCR, into both lipid- and polymer-based artificial membranes. We reveal a new allosteric mode of rhodopsin activation incurred by the non-biological membranes: the cationic membrane drives a transition from the inactive MI to the activated MII state in the absence of high [H(+)] or negative spontaneous curvature. We attribute this activation to the attractive charge interaction between the membrane surface and the deprotonated Glu134 residue of the rhodopsin-conserved ERY sequence motif that helps break the cytoplasmic "ionic lock". This study unveils a novel design concept of non-biological membranes to reconstitute and harness GPCR functions in synthetic systems. PMID:26633591
Stress and fold localization in thin elastic membranes
Pocivavsek, Luka; Dellsy, Robert; Kern, Andrew; Johnson, Sebastián; Lin, Binhua; Lee, Ka Yee C.; Cerda, Enrique
2010-11-08
Thin elastic membranes supported on a much softer elastic solid or a fluid deviate from their flat geometries upon compression. We demonstrate that periodic wrinkling is only one possible solution for such strained membranes. Folds, which involve highly localized curvature, appear whenever the membrane is compressed beyond a third of its initial wrinkle wavelength. Eventually the surface transforms into a symmetry-broken state with flat regions of membrane coexisting with locally folded points, reminiscent of a crumpled, unsupported membrane. We provide general scaling laws for the wrinkled and folded states and proved the transition with numerical and experimental supported membranes. Our work provides insight into the interfacial stability of such diverse systems as biological membranes such as lung surfactant and nanoparticle thin films.
NASA Astrophysics Data System (ADS)
Noguchi, Hiroshi
2014-11-01
BAR superfamily proteins have a banana-shaped domain that causes the local bending of lipid membranes. We study as to how such a local anisotropic curvature induces effective interaction between proteins and changes the global shape of vesicles and membrane tubes using meshless membrane simulations. The proteins are modeled as banana-shaped rods strongly adhered to the membrane. Our study reveals that the rods assemble via two continuous directional phase separations unlike a conventional two-dimensional phase separation. As the rod curvature increases, in the membrane tube the rods assemble along the azimuthal direction and subsequently along the longitudinal direction accompanied by shape transformation of the tube. In the vesicle, in addition to these two assembly processes, further increase in the rod curvature induces tubular scaffold formation.
Nanolaminate Membranes as Cylindrical Telescope Reflectors
NASA Technical Reports Server (NTRS)
Dooley, Jennifer; Dragovan, Mark; Hickey, Gregory; Lih, Shyh-Shiu Lih
2010-01-01
A document discusses a proposal to use axially stretched metal nanolaminate membranes as lightweight parabolic cylindrical reflectors in the Dual Anamorphic Reflector Telescope (DART) - a planned spaceborne telescope in which the cylindrical reflectors would be arranged to obtain a point focus. The discussion brings together a combination of concepts reported separately in several prior NASA Tech Briefs articles, the most relevant being "Nanolaminate Mirrors With Integral Figure-Control Actuators" NPO -30221, Vol. 26, No. 5 (May 2002), page 90; and "Reflectors Made From Membranes Stretched Between Beams" NPO -30571, Vol. 33, No. 10 (October 2009), page 11a. The engineering issues receiving the greatest emphasis in the instant document are (1) the change in curvature associated with the Poisson contraction of a stretched nanolaminate reflector membrane and (2) the feasibility of using patches of poly(vinylidene fluoride) on the rear membrane surface as piezoelectric actuators to correct the surface figure for the effect of Poisson contraction and other shape errors.
Curvature wavefront sensing for the large synoptic survey telescope.
Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian
2015-10-20
The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing. PMID:26560396
Isolating Curvature Effects in Computing Wall-Bounded Turbulent Flows
NASA Technical Reports Server (NTRS)
Rumsey, Christopher L.; Gatski, Thomas B.
2001-01-01
The flow over the zero-pressure-gradient So-Mellor convex curved wall is simulated using the Navier-Stokes equations. An inviscid effective outer wall shape, undocumented in the experiment, is obtained by using an adjoint optimization method with the desired pressure distribution on the inner wall as the cost function. Using this wall shape with a Navier-Stokes method, the abilities of various turbulence models to simulate the effects of curvature without the complicating factor of streamwise pressure gradient can be evaluated. The one-equation Spalart-Allmaras turbulence model overpredicts eddy viscosity, and its boundary layer profiles are too full. A curvature-corrected version of this model improves results, which are sensitive to the choice of a particular constant. An explicit algebraic stress model does a reasonable job predicting this flow field. However, results can be slightly improved by modifying the assumption on anisotropy equilibrium in the model's derivation. The resulting curvature-corrected explicit algebraic stress model possesses no heuristic functions or additional constants. It lowers slightly the computed skin friction coefficient and the turbulent stress levels for this case (in better agreement with experiment), but the effect on computed velocity profiles is very small.
Curvature wavefront sensing for the large synoptic survey telescope
NASA Astrophysics Data System (ADS)
Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian
2015-10-01
The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from 4 curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1mm on either side of focus. In this paper we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intra- and extra-focal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing.
Berry Curvature and Chiral Plasmons in Massive Dirac Materials
NASA Astrophysics Data System (ADS)
Song, Justin; Rudner, Mark
2015-03-01
In the semiclassical model of carrier dynamics, quasiparticles are described as nearly free electrons with modified characteristics modified characteristics such as effective masses which may differ significantly from those of an electron in vacuum. In addition to being influenced by external electric and magnetic fields, the trajectories of electrons in topological materials are also affected by the presence of an interesting quantum mechanical field - the Berry curvature - which is responsible for a number of anomalous transport phenomena recently observed in Dirac materials including G/hBN, and MoS2. Here we discuss how Berry curvature can affect the collective behavior of electrons in these systems. In particular, we show that the collective electronic excitations in metallic massive Dirac materials can feature a chirality even in the absence of an applied magnetic field. The chirality of these plasmons arises from the Berry curvature of the massive Dirac bands. The corresponding dispersion is split between left- and right-handed modes. We also discuss experimental manifestations.
Curvature-dependent excitation propagation in cultured cardiac tissue
NASA Astrophysics Data System (ADS)
Kadota, S.; Kay, M. W.; Magome, N.; Agladze, K.
2012-02-01
The geometry of excitation wave front may play an important role on the propagation block and spiral wave formation. The wave front which is bent over the critical value due to interaction with the obstacles may partially cease to propagate and appearing wave breaks evolve into rotating waves or reentry. This scenario may explain how reentry spontaneously originates in a heart. We studied highly curved excitation wave fronts in the cardiac tissue culture and found that in the conditions of normal, non-inhibited excitability the curvature effects do not play essential role in the propagation. Neither narrow isthmuses nor sharp corners of the obstacles, being classical objects for production of extremely curved wave front, affect non-inhibited wave propagation. The curvature-related phenomena of the propagation block and wave detachment from the obstacle boundary were observed only after partial suppression of the sodium channels with Lidocaine. Computer simulations confirmed the experimental observations. The explanation of the observed phenomena refers to the fact that the heart tissue is made of finite size cells so that curvature radii smaller than the cardiomyocyte size loses sense, and in non-inhibited tissue the single cell is capable to transmit excitation to its neighbors.
Damage identification techniques via modal curvature analysis: Overview and comparison
NASA Astrophysics Data System (ADS)
Dessi, Daniele; Camerlengo, Gabriele
2015-02-01
This paper aims to compare several damage identification methods based on the analysis of modal curvature and related quantities (natural frequencies and modal strain energy) by evaluating their performances on the same test case, a damaged Euler-Bernoulli beam. Damage is modelled as a localized and uniform reduction of stiffness so that closed-form expressions of the mode-shape curvatures can be analytically computed and data accuracy, which affects final results, can be controlled. The selected techniques belong to two categories: one includes several methods that need reference data for detecting structural modifications due to damage, the second group, including the modified Laplacian operator and the fractal dimension, avoids the knowledge of the undamaged behavior for issuing a damage diagnosis. To explain better the different performances of the methods, the mathematical formulation has been revised in some cases so as to fit into a common framework where the underlying hypotheses are clearly stated. Because the various damage indexes are calculated on 'exact' data, a sensitivity analysis has been carried out with respect to the number of points where curvature information is available, to the position of damage between adjacent points, to the modes involved in the index computation. In this way, this analysis intends to point out comparatively the capability of locating and estimating damage of each method along with some critical issues already present with noiseless data.
Instability in bacterial populations and the curvature tensor
NASA Astrophysics Data System (ADS)
Melgarejo, Augusto; Langoni, Laura; Ruscitti, Claudia
2016-09-01
In the geometry associated with equilibrium thermodynamics the scalar curvature Rs is a measure of the volume of correlation, and therefore the singularities of Rs indicates the system instabilities. We explore the use of a similar approach to study instabilities in non-equilibrium systems and we choose as a test example, a colony of bacteria. In this regard we follow the proposal made by Obata et al. of using the curvature tensor for studying system instabilities. Bacterial colonies are often found in nature in concentrated biofilms, or other colony types, which can grow into spectacular patterns visible under the microscope. For instance, it is known that a decrease of bacterial motility with density can promote separation into bulk phases of two coexisting densities; this is opposed to the logistic law for birth and death that allows only a single uniform density to be stable. Although this homogeneous configuration is stable in the absence of bacterial interactions, without logistic growth, a density-dependent swim speed v(ρ) leads to phase separation via a spinodal instability. Thus we relate the singularities in the curvature tensor R to the spinodal instability, that is the appearance of regions of different densities of bacteria.
Stress-induced curvature engineering in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Aksyuk, Vladimir A.; Pardo, Flavio; Bishop, David J.
1999-03-01
Residual stress and stress gradients play an important role in determining equilibrium shape and behavior of various Si surface-micromachined devices under applied loads. This is particularly true for system having large-area plates and long beams where curvature resulting from stress can lead to significant deviations from stress-free shape. To gain better understanding of these properties, we have measured the equilibrium shapes of various structures built on the MCNC MUMPs using an interferometric profiler. The structures were square plates and long beams composed of various combinations of polysilicon an oxide layers. Some of the structures had additional MUMPs metal layer on top, while on others in-house chromium-gold stacks of varying thickness have been deposited. Temperature dependence of the curvature was measured for some plates. We have used these data in conjunction with simple models to significantly improve the performance of our micromachined devices. While for some structures such as large area reflectors the curvature had to be minimized, it could be advantageously exploited by others, for example vertical actuators for self-assembly.
Effect of Interface Curvature on Super-Hydrophobic Drag Reduction
NASA Astrophysics Data System (ADS)
Rastegari, Amirreza; Akhavan, Rayhaneh
2015-11-01
The effect of interface curvature on Super-Hydrophobic (SH) Drag Reduction (DR) has been investigated using DNS with lattice Boltzmann methods in laminar (Rebulk = 50) and turbulent (Rebulk = 3600 , Reτ0 ~ 223) channel flows. SH surfaces with longitudinal arrays of micro-grooves (MG) of size 0 . 1 <= g / h <= 0 . 47 & g / w = 1 , 7 were investigated, where g and w denote the width of the MG and the separation in between them, respectively, and h denotes the channel half-height. The liquid/gas interfaces on the SH MG were modeled as `idealized', stationary, curved, shear-free boundaries, with the interface curvatures determined from the Young-Laplace equation. The presence of interface curvature leads to enhancements of DR by up to 10% in laminar flow, and more modest enhancements or even decreases in DR in turbulent flow, compared to flat, shear-free interfaces. These enhancements or decreases in DR, relative to flat, shear-free interfaces, in both laminar and turbulent flow, are shown to arise primarily from the modified shape of the cross section of the channel in the presence of the curved interface.
Encoding Gaussian curvature in glassy and elastomeric liquid crystal solids
Mostajeran, Cyrus; Ware, Taylor H.; White, Timothy J.
2016-01-01
We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains. PMID:27279777
Formation of Curvature Subunit of Carbon in Combustion.
Wu, Xin-Zhou; Yao, Yang-Rong; Chen, Miao-Miao; Tian, Han-Rui; Xiao, Jun; Xu, Yun-Yan; Lin, Min-Song; Abella, Laura; Tian, Cheng-Bo; Gao, Cong-Li; Zhang, Qianyan; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun
2016-08-01
Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5-C18 that are online produced in the flame of acetylene-cyclopentadiene-oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process. PMID:27377559
Finger vein extraction using gradient normalization and principal curvature
NASA Astrophysics Data System (ADS)
Choi, Joon Hwan; Song, Wonseok; Kim, Taejeong; Lee, Seung-Rae; Kim, Hee Chan
2009-02-01
Finger vein authentication is a personal identification technology using finger vein images acquired by infrared imaging. It is one of the newest technologies in biometrics. Its main advantage over other biometrics is the low risk of forgery or theft, due to the fact that finger veins are not normally visible to others. Extracting finger vein patterns from infrared images is the most difficult part in finger vein authentication. Uneven illumination, varying tissues and bones, and changes in the physical conditions and the blood flow make the thickness and brightness of the same vein different in each acquisition. Accordingly, extracting finger veins at their accurate positions regardless of their thickness and brightness is necessary for accurate personal identification. For this purpose, we propose a new finger vein extraction method which is composed of gradient normalization, principal curvature calculation, and binarization. As local brightness variation has little effect on the curvature and as gradient normalization makes the curvature fairly uniform at vein pixels, our method effectively extracts finger vein patterns regardless of the vein thickness or brightness. In our experiment, the proposed method showed notable improvement as compared with the existing methods.
Sensitivity to curvatures in orientation-based texture segmentation.
Ben-Shahar, Ohad; Zucker, Steven W
2004-02-01
Texture segregation has long been attributed to changes in the distribution of elementary features across the visual field [Nature 290 (12) (1981) 91; Biol. Cybernet. 54 (1986) 245]. The study of orientation, a conspicuous feature, has led to models of orientation-based texture segmentation (OBTS) that depend on the magnitude of one or two orientation gradients [Vis. Res. 31 (4) (1991) 679; Vis. Res. 31 (6) (1991) 1073] and influenced further by the relative configuration between the orientation textons and the global orientation edge [Percept. Psychophys. 52 (4) (1992) 255; Vis. Res. 35 (20) (1995) 2863]. Here we show that these models are at best partial and that the notion of orientation gradient has been incompletely used in the study of OBTS. To do so, we first study the behavior of orientation in orientation-defined texture patches. Geometrical analysis identifies two texture curvatures and reveals the incompleteness of previous stimuli. Psychophysical experimentation then demonstrates that segmentation is strongly affected by discontinuities in these curvatures. Importantly, we show that this sensitivity to curvature is independent of the orientation gradients and inconsistent with the simple configural considerations proposed in the past. PMID:14642898
Generic Properties of Curvature Sensing through Vision and Touch
2013-01-01
Generic properties of curvature representations formed on the basis of vision and touch were examined as a function of mathematical properties of curved objects. Virtual representations of the curves were shown on a computer screen for visual scaling by sighted observers (experiment 1). Their physical counterparts were placed in the two hands of blindfolded and congenitally blind observers for tactile scaling. The psychophysical data show that curvature representations in congenitally blind individuals, who never had any visual experience, and in sighted observers, who rely on vision most of the time, are statistically linked to the same mathematical properties of the curves. The perceived magnitude of object curvature, sensed through either vision or touch, is related by a mathematical power law, with similar exponents for the two sensory modalities, to the aspect ratio of the curves, a scale invariant geometric property. This finding supports biologically motivated models of sensory integration suggesting a universal power law for the adaptive brain control and balance of motor responses to environmental stimuli from any sensory modality. PMID:24454538
Shifting Preferences in Pornography Consumption.
ERIC Educational Resources Information Center
Zillmann, Dolf; Bryant, Jennings
1986-01-01
Concludes that subjects with considerable prior exposure to common, nonviolent pornography preferred to watch uncommon pornography. Male nonstudents preferred it almost exclusively, as did male students to a lesser extent. Females also exhibited this consumption preference, though it was far less pronounced, especially in female students. (JD)
Non-uniform dispersion of the source-sink relationship alters wavefront curvature.
Romero, Lucia; Trenor, Beatriz; Ferrero, Jose M; Starmer, C Frank
2013-01-01
The distribution of cellular source-sink relationships plays an important role in cardiac propagation. It can lead to conduction slowing and block as well as wave fractionation. It is of great interest to unravel the mechanisms underlying evolution in wavefront geometry. Our goal is to investigate the role of the source-sink relationship on wavefront geometry using computer simulations. We analyzed the role of variability in the microscopic source-sink relationship in driving changes in wavefront geometry. The electrophysiological activity of a homogeneous isotropic tissue was simulated using the ten Tusscher and Panfilov 2006 action potential model and the source-sink relationship was characterized using an improved version of the Romero et al. safety factor formulation (SFm2). Our simulations reveal that non-uniform dispersion of the cellular source-sink relationship (dispersion along the wavefront) leads to alterations in curvature. To better understand the role of the source-sink relationship in the process of wave formation, the electrophysiological activity at the initiation of excitation waves in a 1D strand was examined and the source-sink relationship was characterized using the two recently updated safety factor formulations: the SFm2 and the Boyle-Vigmond (SFVB) definitions. The electrophysiological activity at the initiation of excitation waves was intimately related to the SFm2 profiles, while the SFVB led to several counterintuitive observations. Importantly, with the SFm2 characterization, a critical source-sink relationship for initiation of excitation waves was identified, which was independent of the size of the electrode of excitation, membrane excitability, or tissue conductivity. In conclusion, our work suggests that non-uniform dispersion of the source-sink relationship alters wavefront curvature and a critical source-sink relationship profile separates wave expansion from collapse. Our study reinforces the idea that the safety factor