CURVATURE-DRIVEN MOLECULAR FLOW ON MEMBRANE SURFACE.
Mikucki, Michael; Zhou, Y C
2017-01-01
This work presents a mathematical model for the localization of multiple species of diffusion molecules on membrane surfaces. Morphological change of bilayer membrane in vivo is generally modulated by proteins. Most of these modulations are associated with the localization of related proteins in the crowded lipid environments. We start with the energetic description of the distributions of molecules on curved membrane surface, and define the spontaneous curvature of bilayer membrane as a function of the molecule concentrations on membrane surfaces. A drift-diffusion equation governs the gradient flow of the surface molecule concentrations. We recast the energetic formulation and the related governing equations by using an Eulerian phase field description to define membrane morphology. Computational simulations with the proposed mathematical model and related numerical techniques predict (i) the molecular localization on static membrane surfaces at locations with preferred mean curvatures, and (ii) the generation of preferred mean curvature which in turn drives the molecular localization.
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 remodelling cell membranes. However, the molecular driving forces behind these processes are not well understood. Here, we describe a new approach to study curvature sensing, by simulating the direction-dependent interactions of single molecules with a buckled lipid bilayer. We analyse three amphipathic antimicrobial peptides, a class of membrane-associated m...
Anisotropic Membrane Curvature Sensing by Amphipathic Peptides.
Gómez-Llobregat, Jordi; Elías-Wolff, Federico; Lindén, Martin
2016-01-05
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. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Intrinsically disordered proteins drive membrane curvature.
Busch, David J; Houser, Justin R; Hayden, Carl C; Sherman, Michael B; Lafer, Eileen M; Stachowiak, Jeanne C
2015-07-24
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.
Membrane Curvature Affects the Formation of α-Hemolysin Nanopores.
Fujii, Satoshi; Matsuura, Tomoaki; Yomo, Tetsuya
2015-07-17
Membrane proteins perform their functions within or on the lipid membrane, and lipid compositions are known to affect membrane protein integration and activity. Recently, the geometric aspect of membrane curvature was shown to play an important role in membrane protein behavior. Certain membrane proteins are known to sense the curvature of the membrane and to preferentially bind to highly curved membranes. However, although numerous membrane proteins assemble to form homo- or heterocomplexes and perform their biological functions, the dependence of membrane protein assembly on membrane curvature remains elusive. In this study, we analyzed the effect of the membrane curvature on the nanopore formation of α-hemolysin (AH), which is a toxic membrane protein derived from Staphylococcus aureus. The AH protein binds to the membrane as a monomer, assembles to form a heptamer, and forms a nanopore. By simultaneously measuring the molecules bound to the membrane and the activities of the nanopore on the membrane, we determined the nanopore formation ratio of AH. We used various sizes of liposomes and analyzed the dependence on the membrane curvature by using flow cytometry. Combining the results for positive and negative curvature, we found that the nanopore formation ratio of AH was curvature sensitive and was higher in a flat membrane than in a curved membrane. Furthermore, the nanopore formation ratio was almost identical or relatively higher in membranes with negative curvature than those with positive curvature.
Transmembrane protein sorting driven by membrane curvature
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.
Curvature-driven effective attraction in multicomponent membranes.
Demers, Matthew F; Sknepnek, Rastko; Olvera de la Cruz, Monica
2012-08-01
We study closed liquid membranes that segregate into three phases due to differences in the chemical and physical properties of its components. The shape and in-plane membrane arrangement of the phases are coupled through phase-specific bending energies and line tensions. We use simulated annealing Monte Carlo simulations to find low-energy structures, allowing both phase arrangement and membrane shape to relax. The three-phase system is the simplest one in which there are multiple interface pairs, allowing us to analyze interfacial preferences and pairwise distinct line tensions. We observe the system's preference for interface pairs that maximize differences in spontaneous curvature. From a pattern selection perspective, this acts as an effective attraction between phases of most disparate spontaneous curvature. We show that this effective attraction is robust enough to persist even when the interface between these phases is the most penalized by line tension. This effect is driven by geometry and not by any explicit component-component interaction.
Novel tilt-curvature coupling in lipid membranes
Terzi, M. Mert; Deserno, Markus
2017-08-01
On mesoscopic scales, lipid membranes are well described by continuum theories whose main ingredients are the curvature of a membrane's reference surface and the tilt of its lipid constituents. In particular, Hamm and Kozlov [Eur. Phys. J. E 3, 323 (2000)] have shown how to systematically derive such a tilt-curvature Hamiltonian based on the elementary assumption of a thin fluid elastic sheet experiencing internal lateral pre-stress. Performing a dimensional reduction, they not only derive the basic form of the effective surface Hamiltonian but also express its emergent elastic couplings as trans-membrane moments of lower-level material parameters. In the present paper, we argue, though, that their derivation unfortunately missed a coupling term between curvature and tilt. This term arises because, as one moves along the membrane, the curvature-induced change of transverse distances contributes to the area strain—an effect that was believed to be small but nevertheless ends up contributing at the same (quadratic) order as all other terms in their Hamiltonian. We illustrate the consequences of this amendment by deriving the monolayer and bilayer Euler-Lagrange equations for the tilt, as well as the power spectra of shape, tilt, and director fluctuations. A particularly curious aspect of our new term is that its associated coupling constant is the second moment of the lipid monolayer's lateral stress profile—which within this framework is equal to the monolayer Gaussian curvature modulus, κ¯ m. On the one hand, this implies that many theoretical predictions now contain a parameter that is poorly known (because the Gauss-Bonnet theorem limits access to the integrated Gaussian curvature); on the other hand, the appearance of κ¯ m outside of its Gaussian curvature provenance opens opportunities for measuring it by more conventional means, for instance by monitoring a membrane's undulation spectrum at short scales.
Pattern formation by curvature-inducing proteins on spherical membranes
Agudo-Canalejo, Jaime; Golestanian, Ramin
2017-12-01
Spatial organisation is a hallmark of all living cells, and recreating it in model systems is a necessary step in the creation of synthetic cells. It is therefore of both fundamental and practical interest to better understand the basic mechanisms underlying spatial organisation in cells. In this work, we use a continuum model of membrane and protein dynamics to study the behaviour of curvature-inducing proteins on membranes of spherical shape, such as living cells or lipid vesicles. We show that the interplay between curvature energy, entropic forces, and the geometric constraints on the membrane can result in the formation of patterns of highly-curved/protein-rich and weakly-curved/protein-poor domains on the membrane. The spontaneous formation of such patterns can be triggered either by an increase in the average density of curvature-inducing proteins, or by a relaxation of the geometric constraints on the membrane imposed by the membrane tension or by the tethering of the membrane to a rigid cell wall or cortex. These parameters can also be tuned to select the size and number of the protein-rich domains that arise upon pattern formation. The very general mechanism presented here could be related to protein self-organisation in many biological processes, ranging from (proto)cell division to the formation of membrane rafts.
Membrane curvature enables N-Ras lipid anchor sorting to liquid-ordered membrane phases
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Larsen, Jannik Bruun; Jensen, Martin Borch; Bhatia, Vikram Kjøller
2015-01-01
Trafficking and sorting of membrane-anchored Ras GTPases are regulated by partitioning between distinct membrane domains. Here, in vitro experiments and microscopic molecular theory reveal membrane curvature as a new modulator of N-Ras lipid anchor and palmitoyl chain partitioning. Membrane curva...... curvature was essential for enrichment in raft-like liquid-ordered phases; enrichment was driven by relief of lateral pressure upon anchor insertion and most likely affects the localization of lipidated proteins in general....
Bcl-2 apoptosis proteins, mitochondrial membrane curvature, and cancer
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.
Annexin A4 and A6 induce membrane curvature and constriction during cell membrane repair
DEFF Research Database (Denmark)
Boye, Theresa Louise; Maeda, Kenji; Pezeshkian, Weria
2017-01-01
that annexin A4 binds to artificial membranes and generates curvature force initiated from free edges, whereas annexin A6 induces constriction force. In cells, plasma membrane injury and Ca2+ influx recruit annexin A4 to the vicinity of membrane wound edges where its homo-trimerization leads to membrane......Efficient cell membrane repair mechanisms are essential for maintaining membrane integrity and thus for cell life. Here we show that the Ca2+- and phospholipid-binding proteins annexin A4 and A6 are involved in plasma membrane repair and needed for rapid closure of micron-size holes. We demonstrate...... curvature near the edges. We propose that curvature force is utilized together with annexin A6-mediated constriction force to pull the wound edges together for eventual fusion. We show that annexin A4 can counteract various plasma membrane disruptions including holes of several micrometers indicating...
Lipid membrane-mediated attraction between curvature inducing objects
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.
2016-09-01
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.
DEFF Research Database (Denmark)
Bhatia, Vikram Kjøller; Hatzakis, Nikos; Stamou, Dimitrios
2010-01-01
itself. We thus anticipate that membrane curvature will promote the redistribution of proteins that are anchored in membranes through any type of hydrophobic moiety, a thesis that broadens tremendously the implications of membrane curvature for protein sorting, trafficking and signaling in cell biology....
Amphipathic motifs in BAR domains are essential for membrane curvature sensing
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Bhatia, Vikram K; Madsen, Kenneth L; Bolinger, Pierre-Yves
2009-01-01
BAR (Bin/Amphiphysin/Rvs) domains and amphipathic alpha-helices (AHs) are believed to be sensors of membrane curvature thus facilitating the assembly of protein complexes on curved membranes. Here, we used quantitative fluorescence microscopy to compare the binding of both motifs on single...... nanosized liposomes of different diameters and therefore membrane curvature. Characterization of members of the three BAR domain families showed surprisingly that the crescent-shaped BAR dimer with its positively charged concave face is not able to sense membrane curvature. Mutagenesis on BAR domains showed...... that membrane curvature sensing critically depends on the N-terminal AH and furthermore that BAR domains sense membrane curvature through hydrophobic insertion in lipid packing defects and not through electrostatics. Consequently, amphipathic motifs, such as AHs, that are often associated with BAR domains...
Yamamoto, Hikaru; Kondo, Akihiro; Itoh, Toshiki
2018-01-01
Tyrosine kinases are important enzymes that mediate signal transduction at the plasma membrane. While the significance of membrane localization of tyrosine kinases has been well evaluated, the role of membrane curvature in their regulation is unknown. Here, we demonstrate that an intrinsically disordered region in the tyrosine kinase Fer acts as a membrane curvature sensor that preferentially binds to highly curved membranes in vitro. This region forms an amphipathic α-helix upon interaction with curved membranes, aligning hydrophobic residues on one side of the helical structure. Further, the tyrosine kinase activity of Fer is significantly enhanced by the membrane in a manner dependent on curvature. We propose a model for the regulation of Fer based on an intramolecular interaction and the curvature-dependent membrane binding mediated by its intrinsically disordered region. Copyright © 2017 Elsevier Inc. All rights reserved.
Curvature of double-membrane organelles generated by changes in membrane size and composition.
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Roland L Knorr
Full Text Available Transient double-membrane organelles are key players in cellular processes such as autophagy, reproduction, and viral infection. These organelles are formed by the bending and closure of flat, double-membrane sheets. Proteins are believed to be important in these morphological transitions but the underlying mechanism of curvature generation is poorly understood. Here, we describe a novel mechanism for this curvature generation which depends primarily on three membrane properties: the lateral size of the double-membrane sheets, the molecular composition of their highly curved rims, and a possible asymmetry between the two flat faces of the sheets. This mechanism is evolutionary advantageous since it does not require active processes and is readily available even when resources within the cell are restricted as during starvation, which can induce autophagy and sporulation. We identify pathways for protein-assisted regulation of curvature generation, organelle size, direction of bending, and morphology. Our theory also provides a mechanism for the stabilization of large double-membrane sheet-like structures found in the endoplasmic reticulum and in the Golgi cisternae.
DEFF Research Database (Denmark)
Madsen, Kenneth Lindegaard; Bhatia, V K; Gether, U
2010-01-01
The internal membranes of eukaryotic cells are all twists and bends characterized by high curvature. During recent years it has become clear that specific proteins sustain these curvatures while others simply recognize membrane shape and use it as "molecular information" to organize cellular proc...... on curved membranes instead of higher affinity as assumed so far. Finally, we integrate these new insights into the debate about which motifs are involved in sensing versus induction of membrane curvature and what role MCS proteins may play in biology....
Nontopological Saddle-Splay and Curvature Instabilities from Anisotropic Membrane Inclusions
Fournier, J. B.
1996-06-01
Anisotropic inclusions are shown to induce spontaneous deviatoric bendings in lipidic membranes, by orienting at right angles across the bilayer. In the limit of strong membrane curvatures, a nonanalytical bending energy term is generated that favors saddlelike and cylindrical shapes, without penalizing spherical ones. An ``egg-carton'' instability results in flat membranes as well as a wormlike shape instability for vesicles.
A cost-benefit analysis of the physical mechanisms of membrane curvature.
Stachowiak, Jeanne C; Brodsky, Frances M; Miller, Elizabeth A
2013-09-01
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 energy 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 energy costs and drivers involved in membrane curvature, and draw 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 such as viral egress.
Curvature-electric effects in artificial and natural membranes studied using patch-clamp techniques.
Petrov, A G; Ramsey, R L; Usherwood, P N
1989-01-01
Methods for applying sound pressure to membrane patches formed at the tips of patch-clamp pipettes have been developed. Artificial membrane patches were formed from diphytanoyl phosphatidylcholine using a pipette dipping technique. Natural membrane patches were excised (inside-out mode) from collagenase-treated locust muscle membrane. Curvature-electric signals were registered under both voltage clamp and current clamp conditions. The phenomenon of flexoelectricity in membranes has previously been attributed to curvature-induced polarization originating from the liquid crystalline properties of membranes. The estimated magnitude (2 x 10(-18) C) of the flexoelectric coefficient of the artificial lipid bilayers is consistent with previous findings while that of the muscle membrane was in certain cases several times larger. The present study is the first to report on flexoelectricity in a natural membrane and raises the question of the biological significance of this phenomenon.
Spontaneous Behaviors and Wall-Curvature Lead to Apparent Wall Preference in Planarian.
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Yoshitaro Akiyama
Full Text Available The planarian Dugesia japonica tends to stay near the walls of its breeding containers and experimental dishes in the laboratory, a phenomenon called "wall preference". This behavior is thought to be important for environmental adaptation, such as hiding by planarians in nature. However, the mechanisms regulating wall-preference behavior are not well understood, since this behavior occurs in the absence of any particular stimulation. Here we show the mechanisms of wall-preference behavior. Surprisingly, planarian wall-preference behavior was also shown even by the head alone and by headless planarians. These results indicate that planarian "wall-preference" behavior only appears to be a "preference" behavior, and is actually an outcome of spontaneous behaviors, rather than of brain function. We found that in the absence of environmental cues planarians moved basically straight ahead until they reached a wall, and that after reaching a wall, they changed their direction of movement to one tangential to the wall, suggesting that this spontaneous behavior may play a critical role in the wall preference. When we tested another spontaneous behavior, the wigwag movement of the planarian head, using computer simulation with various wigwag angles and wigwag intervals, large wigwag angle and short wigwag interval reduced wall-preference behavior. This indicated that wigwag movement may determine the probability of staying near the wall or leaving the wall. Furthermore, in accord with this simulation, when we tested planarian wall-preference behavior using several assay fields with different curvature of the wall, we found that concavity and sharp curvature of walls negatively impacted wall preference by affecting the permissible angle of the wigwag movement. Together, these results indicate that planarian wall preference may be involuntarily caused by the combination of two spontaneous planarian behaviors: moving straight ahead until reaching a wall and
Membrane heterogeneity : from lipid domains to curvature effects
Semrau, Stefan
2009-01-01
Membrane heterogeneity on the micro- and nanometer scale plays an important role for a large number of biological processes. In parallel to the conception of refined membrane models, new experimental techniques to determine membrane microstructure were developed in recent years. Single molecule
Spontaneous Behaviors and Wall-Curvature Lead to Apparent Wall Preference in Planarian
Akiyama, Yoshitaro; Agata, Kiyokazu; Inoue, Takeshi
2015-01-01
The planarian Dugesia japonica tends to stay near the walls of its breeding containers and experimental dishes in the laboratory, a phenomenon called “wall preference”. This behavior is thought to be important for environmental adaptation, such as hiding by planarians in nature. However, the mechanisms regulating wall-preference behavior are not well understood, since this behavior occurs in the absence of any particular stimulation. Here we show the mechanisms of wall-preference behavior. Surprisingly, planarian wall-preference behavior was also shown even by the head alone and by headless planarians. These results indicate that planarian “wall-preference” behavior only appears to be a “preference” behavior, and is actually an outcome of spontaneous behaviors, rather than of brain function. We found that in the absence of environmental cues planarians moved basically straight ahead until they reached a wall, and that after reaching a wall, they changed their direction of movement to one tangential to the wall, suggesting that this spontaneous behavior may play a critical role in the wall preference. When we tested another spontaneous behavior, the wigwag movement of the planarian head, using computer simulation with various wigwag angles and wigwag intervals, large wigwag angle and short wigwag interval reduced wall-preference behavior. This indicated that wigwag movement may determine the probability of staying near the wall or leaving the wall. Furthermore, in accord with this simulation, when we tested planarian wall-preference behavior using several assay fields with different curvature of the wall, we found that concavity and sharp curvature of walls negatively impacted wall preference by affecting the permissible angle of the wigwag movement. Together, these results indicate that planarian wall preference may be involuntarily caused by the combination of two spontaneous planarian behaviors: moving straight ahead until reaching a wall and then
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. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.
Steric confinement of proteins on lipid membranes can drive curvature and tubulation.
Stachowiak, Jeanne C; Hayden, Carl C; Sasaki, Darryl Y
2010-04-27
Deformation of lipid membranes into curved structures such as buds and tubules is essential to many cellular structures including endocytic pits and filopodia. Binding of specific proteins to lipid membranes has been shown to promote membrane bending during endocytosis and transport vesicle formation. Additionally, specific lipid species are found to colocalize with many curved membrane structures, inspiring ongoing exploration of a variety of roles for lipid domains in membrane bending. However, the specific mechanisms by which lipids and proteins collaborate to induce curvature remain unknown. Here we demonstrate a new mechanism for induction and amplification of lipid membrane curvature that relies on steric confinement of protein binding on membrane surfaces. Using giant lipid vesicles that contain domains with high affinity for his-tagged proteins, we show that protein crowding on lipid domain surfaces creates a protein layer that buckles outward, spontaneously bending the domain into stable buds and tubules. In contrast to previously described bending mechanisms relying on local steric interactions between proteins and lipids (i.e. helix insertion into membranes), this mechanism produces tubules whose dimensions are defined by global parameters: domain size and membrane tension. Our results suggest the intriguing possibility that confining structures, such as lipid domains and protein lattices, can amplify membrane bending by concentrating the steric interactions between bound proteins. This observation highlights a fundamental physical mechanism for initiation and control of membrane bending that may help explain how lipids and proteins collaborate to create the highly curved structures observed in vivo.
The Role of Membrane Curvature in Nanoscale Topography-Induced Intracellular Signaling.
Lou, Hsin-Ya; Zhao, Wenting; Zeng, Yongpeng; Cui, Bianxiao
2018-04-12
Over the past decade, there has been growing interest in developing biosensors and devices with nanoscale and vertical topography. Vertical nanostructures induce spontaneous cell engulfment, which enhances the cell-probe coupling efficiency and the sensitivity of biosensors. Although local membranes in contact with the nanostructures are found to be fully fluidic for lipid and membrane protein diffusions, cells appear to actively sense and respond to the surface topography presented by vertical nanostructures. For future development of biodevices, it is important to understand how cells interact with these nanostructures and how their presence modulates cellular function and activities. How cells recognize nanoscale surface topography has been an area of active research for two decades before the recent biosensor works. Extensive studies show that surface topographies in the range of tens to hundreds of nanometers can significantly affect cell functions, behaviors, and ultimately the cell fate. For example, titanium implants having rough surfaces are better for osteoblast attachment and host-implant integration than those with smooth surfaces. At the cellular level, nanoscale surface topography has been shown by a large number of studies to modulate cell attachment, activity, and differentiation. However, a mechanistic understanding of how cells interact and respond to nanoscale topographic features is still lacking. In this Account, we focus on some recent studies that support a new mechanism that local membrane curvature induced by nanoscale topography directly acts as a biochemical signal to induce intracellular signaling, which we refer to as the curvature hypothesis. The curvature hypothesis proposes that some intracellular proteins can recognize membrane curvatures of a certain range at the cell-to-material interface. These proteins then recruit and activate downstream components to modulate cell signaling and behavior. We discuss current technologies
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Omid Bavi
2016-02-01
Full Text Available 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.
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.
Electrostatic field in terms of geometric curvature in membrane MEMS devices
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Di Barba Paolo
2017-03-01
Full Text Available In this paper we present, in a framework of 1D-membrane Micro-Electro-Mechanical- Systems (MEMS theory, a formalization of the problem of existence and uniqueness of a solution related to the membrane deformation u for electrostatic actuation in the steady- state case. In particular, we propose a new model in which the electric field magnitude E is proportional to the curvature of the membrane and, for it, we obtain results of existence by Schauder-Tychono's fixed point application and subsequently we establish conditions of uniqueness. Finally, some numerical tests have been carried out to further support the analytical results.
Yoo, Jejoong; Cui, Qiang
2009-10-21
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.
Energy Technology Data Exchange (ETDEWEB)
Stachowiak, Jeanne C.; Hayden, Carl C.; Negrete, Oscar.; Davis, Ryan Wesley; Sasaki, Darryl Y
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.
The effect of curvature on the undulation spectrum of Red Blood Cell membranes
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.
Directory of Open Access Journals (Sweden)
Elena Beltrán-Heredia
2017-05-01
Full Text Available Many cell division processes have been conserved throughout evolution and are being revealed by studies on model organisms such as bacteria, yeasts, and protozoa. Cellular membrane constriction is one of these processes, observed almost universally during cell division. It happens similarly in all organisms through a mechanical pathway synchronized with the sequence of cytokinetic events in the cell interior. Arguably, such a mechanical process is mastered by the coordinated action of a constriction machinery fueled by biochemical energy in conjunction with the passive mechanics of the cellular membrane. Independently of the details of the constriction engine, the membrane component responds against deformation by minimizing the elastic energy at every constriction state following a pathway still unknown. In this paper, we address a theoretical study of the mechanics of membrane constriction in a simplified model that describes a homogeneous membrane vesicle in the regime where mechanical work due to osmotic pressure, surface tension, and bending energy are comparable. We develop a general method to find approximate analytical expressions for the main descriptors of a symmetrically constricted vesicle. Analytical solutions are obtained by combining a perturbative expansion for small deformations with a variational approach that was previously demonstrated valid at the reference state of an initially spherical vesicle at isotonic conditions. The analytic approximate results are compared with the exact solution obtained from numerical computations, getting a good agreement for all the computed quantities (energy, area, volume, constriction force. We analyze the effects of the spontaneous curvature, the surface tension and the osmotic pressure in these quantities, focusing especially on the constriction force. The more favorable conditions for vesicle constriction are determined, obtaining that smaller constriction forces are required for positive
A Theoretical Characterization of Curvature Controlled Adhesive Properties of Bio-Inspired Membranes
DEFF Research Database (Denmark)
Afferante, Luciano; Heepe, Lars; Casdorff, Kirstin
2016-01-01
Some biological systems, such as the tree frog, Litoria caerulea, and the bush-cricket, Tettigonia viridissima, have developed the ability to control adhesion by changing the curvature of their pads. Active control systems of adhesion inspired by these biological models can be very attractive...
Nonadditive Compositional Curvature Energetics of Lipid Bilayers
Sodt, A. J.; Venable, R. M.; Lyman, E.; Pastor, R. W.
2016-09-01
The unique properties of the individual lipids that compose biological membranes together determine the energetics of the surface. The energetics of the surface, in turn, govern the formation of membrane structures and membrane reshaping processes, and thus they will underlie cellular-scale models of viral fusion, vesicle-dependent transport, and lateral organization relevant to signaling. The spontaneous curvature, to the best of our knowledge, is always assumed to be additive. We describe observations from simulations of unexpected nonadditive compositional curvature energetics of two lipids essential to the plasma membrane: sphingomyelin and cholesterol. A model is developed that connects molecular interactions to curvature stress, and which explains the role of local composition. Cholesterol is shown to lower the number of effective Kuhn segments of saturated acyl chains, reducing lateral pressure below the neutral surface of bending and favoring positive curvature. The effect is not observed for unsaturated (flexible) acyl chains. Likewise, hydrogen bonding between sphingomyelin lipids leads to positive curvature, but only at sufficient concentration, below which the lipid prefers negative curvature.
Molecular View of the Role of Fusion Peptides in Promoting Positive Membrane Curvature
Fuhrmans, Marc; Marrink, Siewert J.
2012-01-01
Fusion peptides are moderately hydrophobic segments of viral and nonviral membrane fusion proteins that enable these proteins to fuse two closely apposed biological membranes. In vitro assays furthermore show that even isolated fusion peptides alone can support membrane fusion in model systems. In
Takemura, Kazuhiro; Hanawa-Suetsugu, Kyoko; Suetsugu, Shiro; Kitao, Akio
2017-07-28
The BAR domain superfamily proteins sense or induce curvature in membranes. The inverse-BAR domain (I-BAR) is a BAR domain that forms a straight "zeppelin-shaped" dimer. The mechanisms by which IRSp53 I-BAR binds to and deforms a lipid membrane are investigated here by all-atom molecular dynamics simulation (MD), binding energy analysis, and the effects of mutation experiments on filopodia on HeLa cells. I-BAR adopts a curved structure when crystallized, but adopts a flatter shape in MD. The binding of I-BAR to membrane was stabilized by ~30 salt bridges, consistent with experiments showing that point mutations of the interface residues have little effect on the binding affinity whereas multiple mutations have considerable effect. Salt bridge formation increases the local density of lipids and deforms the membrane into a concave shape. In addition, the point mutations that break key intra-molecular salt bridges within I-BAR reduce the binding affinity; this was confirmed by expressing these mutants in HeLa cells and observing their effects. The results indicate that the stiffness of I-BAR is important for membrane deformation, although I-BAR does not act as a completely rigid template.
Van Rijn, P.
2010-01-01
We have designed and synthesised a new class of molecules which self-assemble based on hydrophobic interactions with an additional driving force for influencing the overall aggregate morphology, namely, molecular curvature. The structure is build from subunits which are substituted with either
Membrane curvature induction and tubulation are common features of synucleins and apolipoproteins
DEFF Research Database (Denmark)
Varkey, Jobin; Isas, Jose Mario; Mizuno, Naoko
2010-01-01
Synucleins and apolipoproteins have been implicated in a number of membrane and lipid trafficking events. Lipid interaction for both types of proteins is mediated by 11 amino acid repeats that form amphipathic helices. This similarity suggests that synucleins and apolipoproteins might have compar...... density of tubulating proteins may be important. How cellular safeguarding mechanisms prevent such potentially toxic events and whether they go awry in disease remains to be determined....
Effects of membrane curvature and pH on proton pumping activity of single cytochrome bo3 enzymes
DEFF Research Database (Denmark)
Li, Mengqiu; Khan, Sanobar; Rong, Honglin
2017-01-01
Escherichia coli, cytochrome bo3, for hundreds of seconds on the single enzyme level (Li et al. J Am Chem Soc 137 (2015) 16055–16063). Here, we have extended these studies by additional experiments and analyses of the proton transfer rate as a function of proteoliposome size and pH at the N- and P...... that the pH optimum is related to proton release from the proton exit site. Our previous single-enzyme experiments identified rare, long-lived conformation states of cytochrome bo3 where protons leak back under turn-over conditions. Here, we analyzed and found that ~ 23% of cytochrome bo3 proteoliposomes......-side of single HCOs. Proton transport activity of cytochrome bo3 was found to decrease with increased curvature of the membrane. Furthermore, proton uptake at the N-side (proton entrance) was insensitive to pH between pH 6.4–8.4, while proton release at the P-side had an optimum pH of ~ 7.4, suggesting...
Effects of membrane curvature and pH on proton pumping activity of single cytochrome bo3enzymes.
Li, Mengqiu; Khan, Sanobar; Rong, Honglin; Tuma, Roman; Hatzakis, Nikos S; Jeuken, Lars J C
2017-09-01
The molecular mechanism of proton pumping by heme-copper oxidases (HCO) has intrigued the scientific community since it was first proposed. We have recently reported a novel technology that enables the continuous characterisation of proton transport activity of a HCO and ubiquinol oxidase from Escherichia coli, cytochrome bo 3 , for hundreds of seconds on the single enzyme level (Li et al. J Am Chem Soc 137 (2015) 16055-16063). Here, we have extended these studies by additional experiments and analyses of the proton transfer rate as a function of proteoliposome size and pH at the N- and P-side of single HCOs. Proton transport activity of cytochrome bo 3 was found to decrease with increased curvature of the membrane. Furthermore, proton uptake at the N-side (proton entrance) was insensitive to pH between pH6.4-8.4, while proton release at the P-side had an optimum pH of ~7.4, suggesting that the pH optimum is related to proton release from the proton exit site. Our previous single-enzyme experiments identified rare, long-lived conformation states of cytochrome bo 3 where protons leak back under turn-over conditions. Here, we analyzed and found that ~23% of cytochrome bo 3 proteoliposomes show ΔpH half-lives below 50s after stopping turnover, while only ~5% of the proteoliposomes containing a non-pumping mutant, E286C cytochrome bo 3 exhibit such fast decays. These single-enzyme results confirm our model in which HCO exhibit heterogeneous pumping rates and can adopt rare leak states in which protons are able to rapidly flow back. Copyright © 2017 Elsevier B.V. All rights reserved.
Katayama, Sayaka; Nakase, Ikuhiko; Yano, Yoshiaki; Murayama, Tomo; Nakata, Yasushi; Matsuzaki, Katsumi; Futaki, Shiroh
2013-09-01
Arginine-rich cell-penetrating peptides, including octaarginine (R8) and HIV-1 TAT peptides, have the ability to translocate through cell membranes and transport exogenous bioactive molecules into cells. Hydrophobic counteranions such as pyrenebutyrate (PyB) have been reported to markedly promote the membrane translocation of these peptides. In this study, using model membranes having liquid-ordered (Lo) and liquid-disordered (Ld) phases, we explored the effects of PyB on the promotion of R8 translocation. Confocal microscopic observations of giant unilamellar vesicles (GUVs) showed that PyB significantly accelerated the accumulation of R8 on membranes containing negatively charged lipids, leading to the internalization of R8 without collapse of the GUV structures. PyB displayed an alternative activity, increasing the fluidity of the negatively charged membranes, which diminished the distinct Lo/Ld phase separation on GUVs. This was supported by the decrease in fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH). Additionally, PyB induced membrane curvature, which has been suggested as a possible mechanism of membrane translocation for R8. Taken together, our results indicate that PyB may have multiple effects that promote R8 translocation through cell membranes. Copyright © 2013 Elsevier B.V. All rights reserved.
Cholera toxin B subunit induces local curvature on lipid bilayers
DEFF Research Database (Denmark)
Pezeshkian, Weria; Nåbo, Lina J.; Ipsen, John H.
2017-01-01
B induces a local membrane curvature that is essential for its clathrin-independent uptake. Using all-atom molecular dynamics, we show that CTxB induces local curvature, with the radius of curvature around 36 nm. The main feature of the CTxB molecular structure that causes membrane bending is the protruding...... alpha helices in the middle of the protein. Our study points to a generic protein design principle for generating local membrane curvature through specific binding to their lipid anchors....
DEFF Research Database (Denmark)
(geodesic) triangles and negative curvatures slim triangles. Some basic ideas from metric (length-)space geometry and from the geometric analysis of the Laplacian will be surveyed and applied. Via the Laplacian the curvature tensor is in control of a variety of very natural phenomena ranging from heat......This talk is essentially concerned with the shape molding forces of curvature and with the old question of how to detect the presence of curvature in manifolds and length spaces at various scales ranging from global to local to microlocal. As the old saying goes: Positive curvatures produce fat...... diffusion to volume growth. We are e.g. interested in obtaining precise bounds for mean exit times for Brownian motions and for isoperimetric inequalities. One way to obtain such bounds are via curvature controlled comparison with corresponding values in constant curvature spaces and in other tailor-made so...
DEFF Research Database (Denmark)
Bendix, Pól Martin
2015-01-01
Current topics include membrane-protein interactions with regard to membrane deformation or curvature sensing by BAR domains. Also, we study the dynamics of membrane tubes of both cells and simple model membrane tubes. Finally, we study membrane phase behavior which has important implications...
Youssef, Nermeen; Campbell, Scott; Barr, Amy; Gandhi, Manoj; Hunter, Beth; Dolinsky, Vernon; Dyck, Jason R B; Clanachan, Alexander S; Light, Peter E
2017-09-01
Cardiac ATP-sensitive K + (K ATP ) channels couple changes in cellular metabolism to membrane excitability and are activated during metabolic stress, although under basal aerobic conditions, K ATP channels are thought to be predominately closed. Despite intense research into the roles of K ATP channels during metabolic stress, their contribution to aerobic basal cardiac metabolism has not been previously investigated. Hearts from Kir6.2 +/+ and Kir6.2 -/- mice were perfused in working mode, and rates of glycolysis, fatty acid oxidation, and glucose oxidation were measured. Changes in activation/expression of proteins regulating metabolism were probed by Western blot analysis. Despite cardiac mechanical function and metabolic efficiency being similar in both groups, hearts from Kir6.2 -/- mice displayed an approximately twofold increase in fatty acid oxidation and a 0.45-fold reduction in glycolytic rates but similar glucose oxidation rates compared with hearts from Kir6.2 +/+ mice. Kir6.2 -/- hearts also possessed elevated levels of activated AMP-activated protein kinase (AMPK), higher glycogen content, and reduced mitochondrial density. Moreover, activation of AMPK by isoproterenol or diazoxide was significantly blunted in Kir6.2 -/- hearts. These data indicate that K ATP channel ablation alters aerobic basal cardiac metabolism. The observed increase in fatty acid oxidation and decreased glycolysis before any metabolic insult may contribute to the poor recovery observed in Kir6.2 -/- hearts in response to exercise or ischemia-reperfusion injury. Therefore, K ATP channels may play an important role in the regulation of cardiac metabolism through AMPK signaling. NEW & NOTEWORTHY In this study, we show that genetic ablation of plasma membrane ATP-sensitive K + channels results in pronounced changes in cardiac metabolic substrate preference and AMP-activated protein kinase activity. These results suggest that ATP-sensitive K + channels may play a novel role in
Curvature-Induced Instabilities of Shells
Pezzulla, Matteo; Stoop, Norbert; Steranka, Mark P.; Bade, Abdikhalaq J.; Holmes, Douglas P.
2018-01-01
Induced by proteins within the cell membrane or by differential growth, heating, or swelling, spontaneous curvatures can drastically affect the morphology of thin bodies and induce mechanical instabilities. Yet, the interaction of spontaneous curvature and geometric frustration in curved shells remains poorly understood. Via a combination of precision experiments on elastomeric spherical shells, simulations, and theory, we show how a spontaneous curvature induces a rotational symmetry-breaking buckling as well as a snapping instability reminiscent of the Venus fly trap closure mechanism. The instabilities, and their dependence on geometry, are rationalized by reducing the spontaneous curvature to an effective mechanical load. This formulation reveals a combined pressurelike term in the bulk and a torquelike term in the boundary, allowing scaling predictions for the instabilities that are in excellent agreement with experiments and simulations. Moreover, the effective pressure analogy suggests a curvature-induced subcritical buckling in closed shells. We determine the critical buckling curvature via a linear stability analysis that accounts for the combination of residual membrane and bending stresses. The prominent role of geometry in our findings suggests the applicability of the results over a wide range of scales.
Substrate curvature regulates cell migration.
He, Xiuxiu; Jiang, Yi
2017-05-23
Cell migration is essential in many aspects of biology. Many basic migration processes, including adhesion, membrane protrusion and tension, cytoskeletal polymerization, and contraction, have to act in concert to regulate cell migration. At the same time, substrate topography modulates these processes. In this work, we study how substrate curvature at micrometer scale regulates cell motility. We have developed a 3D mechanical model of single cell migration and simulated migration on curved substrates with different curvatures. The simulation results show that cell migration is more persistent on concave surfaces than on convex surfaces. We have further calculated analytically the cell shape and protrusion force for cells on curved substrates. We have shown that while cells spread out more on convex surfaces than on concave ones, the protrusion force magnitude in the direction of migration is larger on concave surfaces than on convex ones. These results offer a novel biomechanical explanation to substrate curvature regulation of cell migration: geometric constrains bias the direction of the protrusion force and facilitates persistent migration on concave surfaces.
Introducing quantum Ricci curvature
Klitgaard, N.; Loll, R.
2018-02-01
Motivated by the search for geometric observables in nonperturbative quantum gravity, we define a notion of coarse-grained Ricci curvature. It is based on a particular way of extracting the local Ricci curvature of a smooth Riemannian manifold by comparing the distance between pairs of spheres with that of their centers. The quantum Ricci curvature is designed for use on non-smooth and discrete metric spaces, and to satisfy the key criteria of scalability and computability. We test the prescription on a variety of regular and random piecewise flat spaces, mostly in two dimensions. This enables us to quantify its behavior for short lattices distances and compare its large-scale behavior with that of constantly curved model spaces. On the triangulated spaces considered, the quantum Ricci curvature has good averaging properties and reproduces classical characteristics on scales large compared to the discretization scale.
Equi-Gaussian curvature folding
Indian Academy of Sciences (India)
curvature kf (p) i.e., kp = kf (p). In this case f will map curves to curves with equal equi-. Gaussian curvature at corresponding points. It will also map area with sectional curvature k(σ, p) into areas with the same sectional curvature, and so on. The set of all equi-Gaussian curvature foldings of M into N will be denoted by.
Wolf, Joseph A
2010-01-01
This book is the sixth edition of the classic Spaces of Constant Curvature, first published in 1967, with the previous (fifth) edition published in 1984. It illustrates the high degree of interplay between group theory and geometry. The reader will benefit from the very concise treatments of riemannian and pseudo-riemannian manifolds and their curvatures, of the representation theory of finite groups, and of indications of recent progress in discrete subgroups of Lie groups. Part I is a brief introduction to differentiable manifolds, covering spaces, and riemannian and pseudo-riemannian geomet
Rainaldi, Mario; Moretto, Alessandro; Peggion, Cristina; Formaggio, Fernando; Mammi, Stefano; Peggion, Evaristo; Galvez, José Antonio; Díaz-de-Villegas, Maria Dolores; Cativiela, Carlos; Toniolo, Claudio
2003-08-04
We have synthesized by solution methods and characterized the lipopeptaibol metabolite LP237-F8 extracted from the fungus Tolypocladium geodes and five selected analogues with the Etn-->Aib or Etn-->Nva replacement at position 8 and/or a triple Gln-->Glu(OMe) replacement at positions 5, 6, and 9 (Etn=Calpha-ethylnorvaline, Aib=alpha-aminoisobutyric acid, Nva=norvaline). Conformation analysis, performed by FT-IR absorption, NMR, and CD techniques, strongly supports the view that the six terminally blocked decapeptides are highly helical in solution. Helix topology and amphiphilic character are responsible for their remarkable membrane activity. At position 8 the combination of high hydrophobicity and Calpha tetrasubstitution, as in the Etn-containing LP237-F8 metabolite, has a positive effect on membrane interaction.
Surgical wound management with adhesive polyurethane membrane: a preferred method for routine usage.
Tinckler, L.
1983-01-01
The author gives an account of his experience of the use in some 1600 patients of adhesive polyurethane membrane, marketed as Op-site, both for skin closure and wound dressing, in combination, as a routine method of surgical wound management in a wide variety of surgical operations. The technique of utilising this method is described in detail, as also are the advantages for patients, nursing and medical staff. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 PMID:6870136
The curvature coordinate system
DEFF Research Database (Denmark)
Almegaard, Henrik
2007-01-01
hyperbolas. This means that when a plane orthogonal system of curves for which the vertices in a mesh always lie on a circle is mapped on a surface with positive Gaussian curvature using inverse mapping, and the mapped vertices are connected by straight lines, this network will form a faceted surface...
Brane cosmology with curvature corrections
International Nuclear Information System (INIS)
Kofinas, Georgios; Maartens, Roy; Papantonopoulos, Eleftherios
2003-01-01
We study the cosmology of the Randall-Sundrum brane-world where the Einstein-Hilbert action is modified by curvature correction terms: a four-dimensional scalar curvature from induced gravity on the brane, and a five-dimensional Gauss-Bonnet curvature term. The combined effect of these curvature corrections to the action removes the infinite-density big bang singularity, although the curvature can still diverge for some parameter values. A radiation brane undergoes accelerated expansion near the minimal scale factor, for a range of parameters. This acceleration is driven by the geometric effects, without an inflation field or negative pressures. At late times, conventional cosmology is recovered. (author)
Quantifying the Relationship between Curvature and Electric Potential in Lipid Bilayers.
Bruhn, Dennis S; Lomholt, Michael A; Khandelia, Himanshu
2016-06-02
Cellular membranes mediate vital cellular processes by being subject to curvature and transmembrane electrical potentials. Here we build upon the existing theory for flexoelectricity in liquid crystals to quantify the coupling between lipid bilayer curvature and membrane potentials. Using molecular dynamics simulations, we show that headgroup dipole moments, the lateral pressure profile across the bilayer, and spontaneous curvature all systematically change with increasing membrane potentials. In particular, there is a linear dependence between the bending moment (the product of bending rigidity and spontaneous curvature) and the applied membrane potentials. We show that biologically relevant membrane potentials can induce biologically relevant curvatures corresponding to radii of around 500 nm. The implications of flexoelectricity in lipid bilayers are thus likely to be of considerable consequence both in biology and in model lipid bilayer systems.
DEFF Research Database (Denmark)
Brumm, T.; Jørgensen, Kent; Mouritsen, Ole G.
1996-01-01
The phase transition behavior of a lipid bilayer of dimyristoyl-sn-glycero-3-phosphalidylcholine/distearoyl-sn- glycero-3-phosphatidylcholine (DMPC-d54/DSPC) (1:1) on a solid support with varying curvatures was investigated with differential scanning calorimetry, infrared spectroscopy, and model...... of the liquidus point can be understood as a reduction of the lateral pressure in the bilayer with increasing curvature. The shift of the solidus line is interpreted as a result of the increased demixing of the two components in the two-phase region with increasing curvature due to lowering of the lateral...
Quantifying the Relationship Between Curvature and Electric Potential in Lipid Bilayers
DEFF Research Database (Denmark)
Bruhn, Dennis Skjøth; Lomholt, Michael Andersen; Khandelia, Himanshu
2016-01-01
Cellular membranes mediate vital cellular processes by being subject to curvature and transmembrane electrical potentials. Here we build upon the existing theory for flexoelectricity in liquid crystals to quantify the coupling between lipid bilayer curvature and membrane potentials. Using molecular...... and spontaneous curvature) and the applied membrane potentials. We show that biologically relevant membrane potentials can induce biologically relevant curva- tures corresponding to radii of around 500nm. The implications of flexoelectricity in lipid bilayers are thus likely to be of considerable consequence both...
Directory of Open Access Journals (Sweden)
Mohammed Larbi Labbi
2007-12-01
Full Text Available The $(2k$-th Gauss-Bonnet curvature is a generalization to higher dimensions of the $(2k$-dimensional Gauss-Bonnet integrand, it coincides with the usual scalar curvature for $k = 1$. The Gauss-Bonnet curvatures are used in theoretical physics to describe gravity in higher dimensional space times where they are known as the Lagrangian of Lovelock gravity, Gauss-Bonnet Gravity and Lanczos gravity. In this paper we present various aspects of these curvature invariants and review their variational properties. In particular, we discuss natural generalizations of the Yamabe problem, Einstein metrics and minimal submanifolds.
A Curvature Flow Unifying Symplectic Curvature Flow And Pluriclosed Flow
Dai, Song
2013-01-01
Streets and Tian introduced pluriclosed flow and symplectic curvature flow in recent years. Here we construct a curvature flow to unify these two flows. We show the short time existence of our flow and exhibit an obstruction to long time existence.
Bacterial cell curvature through mechanical control of cell growth
DEFF Research Database (Denmark)
Cabeen, M.; Charbon, Godefroid; Vollmer, W.
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...
Lectures on mean curvature flows
Zhu, Xi-Ping
2002-01-01
"Mean curvature flow" is a term that is used to describe the evolution of a hypersurface whose normal velocity is given by the mean curvature. In the simplest case of a convex closed curve on the plane, the properties of the mean curvature flow are described by Gage-Hamilton's theorem. This theorem states that under the mean curvature flow, the curve collapses to a point, and if the flow is diluted so that the enclosed area equals \\pi, the curve tends to the unit circle. In this book, the author gives a comprehensive account of fundamental results on singularities and the asymptotic behavior of mean curvature flows in higher dimensions. Among other topics, he considers in detail Huisken's theorem (a generalization of Gage-Hamilton's theorem to higher dimension), evolution of non-convex curves and hypersurfaces, and the classification of singularities of the mean curvature flow. Because of the importance of the mean curvature flow and its numerous applications in differential geometry and partial differential ...
Discrete Curvature Theories and Applications
Sun, Xiang
2016-08-25
Discrete Di erential Geometry (DDG) concerns discrete counterparts of notions and methods in di erential geometry. This thesis deals with a core subject in DDG, discrete curvature theories on various types of polyhedral surfaces that are practically important for free-form architecture, sunlight-redirecting shading systems, and face recognition. Modeled as polyhedral surfaces, the shapes of free-form structures may have to satisfy di erent geometric or physical constraints. We study a combination of geometry and physics { the discrete surfaces that can stand on their own, as well as having proper shapes for the manufacture. These proper shapes, known as circular and conical meshes, are closely related to discrete principal curvatures. We study curvature theories that make such surfaces possible. Shading systems of freeform building skins are new types of energy-saving structures that can re-direct the sunlight. From these systems, discrete line congruences across polyhedral surfaces can be abstracted. We develop a new curvature theory for polyhedral surfaces equipped with normal congruences { a particular type of congruences de ned by linear interpolation of vertex normals. The main results are a discussion of various de nitions of normality, a detailed study of the geometry of such congruences, and a concept of curvatures and shape operators associated with the faces of a triangle mesh. These curvatures are compatible with both normal congruences and the Steiner formula. In addition to architecture, we consider the role of discrete curvatures in face recognition. We use geometric measure theory to introduce the notion of asymptotic cones associated with a singular subspace of a Riemannian manifold, which is an extension of the classical notion of asymptotic directions. We get a simple expression of these cones for polyhedral surfaces, as well as convergence and approximation theorems. We use the asymptotic cones as facial descriptors and demonstrate the
Mixed lipid bilayers with locally varying spontaneous curvature and bending.
Gueguen, Guillaume; Destainville, Nicolas; Manghi, Manoel
2014-08-01
A model of lipid bilayers made of a mixture of two lipids with different average compositions on both leaflets, is developed. A Landau Hamiltonian describing the lipid-lipid interactions on each leaflet, with two lipidic fields ψ 1 and ψ 2, is coupled to a Helfrich one, accounting for the membrane elasticity, via both a local spontaneous curvature, which varies as C 0 + C 1(ψ 1 - ψ 2/2), and a bending modulus equal to κ 0 + κ 1(ψ 1 + ψ 2)/2. This model allows us to define curved patches as membrane domains where the asymmetry in composition, ψ 1 - ψ 2, is large, and thick and stiff patches where ψ 1 + ψ 2 is large. These thick patches are good candidates for being lipidic rafts, as observed in cell membranes, which are composed primarily of saturated lipids forming a liquid-ordered domain and are known to be thick and flat nano-domains. The lipid-lipid structure factors and correlation functions are computed for globally spherical membranes and planar ones and for a whole set of parameters including the surface tension and the coupling in the two leaflet compositions. Phase diagrams are established, within a Gaussian approximation, showing the occurrence of two types of Structure Disordered phases, with correlations between either curved or thick patches, and an Ordered phase, corresponding to the divergence of the structure factor at a finite wave vector. The varying bending modulus plays a central role for curved membranes, where the driving force κ 1 C 0 (2) is balanced by the line tension, to form raft domains of size ranging from 10 to 100 nm. For planar membranes, raft domains emerge via the cross-correlation with curved domains. A global picture emerges from curvature-induced mechanisms, described in the literature for planar membranes, to coupled curvature- and bending-induced mechanisms in curved membranes forming a closed vesicle.
Introduction of curvature in amphipathic oligothiophenes for defined aggregate formation.
van Rijn, Patrick; Janeliunas, Dainius; Brizard, Aurélie M A; Stuart, Marc C A; Eelkema, Rienk; van Esch, Jan H
2010-12-03
In this study the possibility to control the size and shape of self-assembled structures through the local curvature of their molecular building blocks has been investigated. To this end a series of amphipathic conjugated oligothiophenes with a well-defined curvature of their backbone has been designed and synthesized. The molecular (local) curvature of these oligothiophenes resulted from a preference for cis instead of trans conformations at specific positions along the oligothiophene backbone, which can be controlled by the sequence of hydrophilic and hydrophobic groups, while their ratio was kept constant. The self-assembly of ter-, sexi-, and dodecathiophenes appeared to be a low-cooperative process, involving the formation of premicellar aggregates at sub-millimolar concentrations, which at concentrations in the millimolar regime transformed into micelles and cylindrical micelles. The aggregates display fine structures with dimensions reminiscent of the thiophene molecules. The structure-morphology relationship of the ter- and sexithiophenes could be described by conventional packing theory. However, with the dodecathiophene, the backbone curvature governed the formation of cylindrical aggregates with a well-defined diameter. These results demonstrate that it is possible to control the aggregation morphology of simple amphipathic oligothiophenes by implementation of an additional structural motif namely, the curvature.
The role of curvature in silica mesoporous crystals
Miyasaka, Keiichi
2012-02-08
Silica mesoporous crystals (SMCs) offer a unique opportunity to study micellar mesophases. Replication of non-equilibrium mesophases into porous silica structures allows the characterization of surfactant phases under a variety of chemical and physical perturbations, through methods not typically accessible to liquid crystal chemists. A poignant example is the use of electron microscopy and crystallography, as discussed herein, for the purpose of determining the fundamental role of amphiphile curvature, namely mean curvature and Gaussian curvature, which have been extensively studied in various fields such as polymer, liquid crystal, biological membrane, etc. The present work aims to highlight some current studies devoted to the interface curvature on SMCs, in which electron microscopy and electron crystallography (EC) are used to understand the geometry of silica wall surface in bicontinuous and cage-type mesostructures through the investigation of electrostatic potential maps. Additionally, we show that by altering the synthesis conditions during the preparation of SMCs, it is possible to isolate particles during micellar mesophase transformations in the cubic bicontinuous system, allowing us to view and study epitaxial relations under the specific synthesis conditions. By studying the relationship between mesoporous structure, interface curvature and micellar mesophases using electron microscopy and EC, we hope to bring new insights into the formation mechanism of these unique materials but also contribute a new way of understanding periodic liquid crystal systems. © 2012 The Royal Society.
Surface meshing with curvature convergence
Li, Huibin
2014-06-01
Surface meshing plays a fundamental role in graphics and visualization. Many geometric processing tasks involve solving geometric PDEs on meshes. The numerical stability, convergence rates and approximation errors are largely determined by the mesh qualities. In practice, Delaunay refinement algorithms offer satisfactory solutions to high quality mesh generations. The theoretical proofs for volume based and surface based Delaunay refinement algorithms have been established, but those for conformal parameterization based ones remain wide open. This work focuses on the curvature measure convergence for the conformal parameterization based Delaunay refinement algorithms. Given a metric surface, the proposed approach triangulates its conformal uniformization domain by the planar Delaunay refinement algorithms, and produces a high quality mesh. We give explicit estimates for the Hausdorff distance, the normal deviation, and the differences in curvature measures between the surface and the mesh. In contrast to the conventional results based on volumetric Delaunay refinement, our stronger estimates are independent of the mesh structure and directly guarantee the convergence of curvature measures. Meanwhile, our result on Gaussian curvature measure is intrinsic to the Riemannian metric and independent of the embedding. In practice, our meshing algorithm is much easier to implement and much more efficient. The experimental results verified our theoretical results and demonstrated the efficiency of the meshing algorithm. © 2014 IEEE.
Cosmic curvature tested directly from observations
Denissenya, Mikhail; Linder, Eric V.; Shafieloo, Arman
2018-03-01
Cosmic spatial curvature is a fundamental geometric quantity of the Universe. We investigate a model independent, geometric approach to measure spatial curvature directly from observations, without any derivatives of data. This employs strong lensing time delays and supernova distance measurements to measure the curvature itself, rather than just testing consistency with flatness. We define two curvature estimators, with differing error propagation characteristics, that can crosscheck each other, and also show how they can be used to map the curvature in redshift slices, to test constancy of curvature as required by the Robertson-Walker metric. Simulating realizations of redshift distributions and distance measurements of lenses and sources, we estimate uncertainties on the curvature enabled by next generation measurements. The results indicate that the model independent methods, using only geometry without assuming forms for the energy density constituents, can determine the curvature at the ~6×10‑3 level.
Curvature Entropy for Curved Profile Generation
Ujiie, Yoshiki; Kato, Takeo; Sato, Koichiro; Matsuoka, Yoshiyuki
2012-01-01
In a curved surface design, the overall shape features that emerge from combinations of shape elements are important. However, controlling the features of the overall shape in curved profiles is difficult using conventional microscopic shape information such as dimension. Herein two types of macroscopic shape information, curvature entropy and quadrature curvature entropy, quantitatively represent the features of the overall shape. The curvature entropy is calculated by the curvature distribu...
Model-independent Constraints on Cosmic Curvature and Opacity
Wang, Guo-Jian; Wei, Jun-Jie; Li, Zheng-Xiang; Xia, Jun-Qing; Zhu, Zong-Hong
2017-09-01
In this paper, we propose to estimate the spatial curvature of the universe and the cosmic opacity in a model-independent way with expansion rate measurements, H(z), and type Ia supernova (SNe Ia). On the one hand, using a nonparametric smoothing method Gaussian process, we reconstruct a function H(z) from opacity-free expansion rate measurements. Then, we integrate the H(z) to obtain distance modulus μ H, which is dependent on the cosmic curvature. On the other hand, distances of SNe Ia can be determined by their photometric observations and thus are opacity-dependent. In our analysis, by confronting distance moduli μ H with those obtained from SNe Ia, we achieve estimations for both the spatial curvature and the cosmic opacity without any assumptions for the cosmological model. Here, it should be noted that light curve fitting parameters, accounting for the distance estimation of SNe Ia, are determined in a global fit together with the cosmic opacity and spatial curvature to get rid of the dependence of these parameters on cosmology. In addition, we also investigate whether the inclusion of different priors for the present expansion rate (H 0: global estimation, 67.74 ± 0.46 km s-1 Mpc-1, and local measurement, 73.24 ± 1.74 km s-1 Mpc-1) exert influence on the reconstructed H(z) and the following estimations of the spatial curvature and cosmic opacity. Results show that, in general, a spatially flat and transparent universe is preferred by the observations. Moreover, it is suggested that priors for H 0 matter a lot. Finally, we find that there is a strong degeneracy between the curvature and the opacity.
Fine-Tuning of Photosynthesis Requires CURVATURE THYLAKOID1-Mediated Thylakoid Plasticity
DEFF Research Database (Denmark)
Pribil, Mathias; Sandoval Ibáñez, Omar Alejandro; Xu, Wenteng
2018-01-01
The thylakoid membrane system of higher plant chloroplasts consists of interconnected subdomains of appressed and nonappressed membrane bilayers, known as grana and stroma lamellae, respectively. CURVATURE THYLAKOID1 (CURT1) protein complexes mediate the shape of grana stacks in a dosage-dependen...... plays an important role in fine-tuning photosynthesis and plant fitness during challenging growth conditions....
International Nuclear Information System (INIS)
Barenboim, Gabriela; Martínez, Enrique Fernández; Mena, Olga; Verde, Licia
2010-01-01
Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d A (z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Ω 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 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 k degeneracy
Modern approaches to discrete curvature
Romon, Pascal
2017-01-01
This book provides a valuable glimpse into discrete curvature, a rich new field of research which blends discrete mathematics, differential geometry, probability and computer graphics. It includes a vast collection of ideas and tools which will offer something new to all interested readers. Discrete geometry has arisen as much as a theoretical development as in response to unforeseen challenges coming from applications. Discrete and continuous geometries have turned out to be intimately connected. Discrete curvature is the key concept connecting them through many bridges in numerous fields: metric spaces, Riemannian and Euclidean geometries, geometric measure theory, topology, partial differential equations, calculus of variations, gradient flows, asymptotic analysis, probability, harmonic analysis, graph theory, etc. In spite of its crucial importance both in theoretical mathematics and in applications, up to now, almost no books have provided a coherent outlook on this emerging field.
Equi-Gaussian curvature folding
Indian Academy of Sciences (India)
have the same equi-Gaussian curvature 1/a2, where a is the radius of the sphere. Now let f : S2 → Pn be a cellular folding. Then we have the following possibilities: Firstly, there are no cellular foldings f : S2 → Pn, for any n > 3 [2]. Secondly, any cellular folding f : S2 → P3 for which Gf forms a regular graph is equivalent to ...
Lipid shape is a key factor for membrane interactions of amphipathic helical peptides.
Strandberg, Erik; Tiltak, Deniz; Ehni, Sebastian; Wadhwani, Parvesh; Ulrich, Anne S
2012-07-01
The membrane alignment of the amphiphilic alpha-helical model peptide MSI-103 (sequence [KIAGKIA]3-NH2) was examined by solid state 2H-NMR in different lipid systems by systematically varying the acyl chain length and degree of saturation, the lipid head group type, and the peptide-to-lipid molar ratio. In liquid crystalline phosphatidylcholine (PC) lipids with saturated chains, the amphiphilic helix changes its orientation from a surface-bound "S-state" to a tilted "T-state" with increasing peptide concentration. In PC lipids with unsaturated chains, on the other hand, the S-state is found throughout all concentrations. Using phosphatidylethanolamine lipids with a small head group or by addition of lyso-lipids with only one acyl chain, the spontaneous curvature of the bilayer was purposefully changed. In the first case with a negative curvature only the S-state was found, whereas in systems with a positive curvature the peptide preferred the obliquely immersed T-state at high concentration. The orientation of MSI-103 thus correlates very well with the shape of the lipid molecules constituting the membrane. Lipid charge, on the other hand, was found to affect only the initial electrostatic attraction to the membrane surface but not the alignment preferences. In bilayers that are "sealed" with 20% cholesterol, MSI-103 cannot bind in a well-oriented manner and forms immobilized aggregates instead. We conclude that the curvature properties of a membrane are a key factor in the interactions of amphiphilic helical peptides in general, whose re-alignment and immersion preferences may thus be inferred in a straightforward manner from the lipid-shape concept.
Curvature Entropy for Curved Profile Generation
Directory of Open Access Journals (Sweden)
Koichiro Sato
2012-03-01
Full Text Available In a curved surface design, the overall shape features that emerge from combinations of shape elements are important. However, controlling the features of the overall shape in curved profiles is difficult using conventional microscopic shape information such as dimension. Herein two types of macroscopic shape information, curvature entropy and quadrature curvature entropy, quantitatively represent the features of the overall shape. The curvature entropy is calculated by the curvature distribution, and represents the complexity of a shape (one of the overall shape features. The quadrature curvature entropy is an improvement of the curvature entropy by introducing a Markov process to evaluate the continuity of a curvature and to approximate human cognition of the shape. Additionally, a shape generation method using a genetic algorithm as a calculator and the entropy as a shape generation index is presented. Finally, the applicability of the proposed method is demonstrated using the side view of an automobile as a design example.
Dynamic Double Curvature Mould System
DEFF Research Database (Denmark)
Jepsen, Christian Raun; Kristensen, Mathias Kræmmergaard; Kirkegaard, Poul Henning
2011-01-01
The present paper describes a concept for a reconfigurable mould surface which is designed to fit the needs of contemporary architecture. The core of the concept presented is a dynamic surface manipulated into a given shape using a digital signal created directly from the CAD drawing of the design....... This happens fast, automatic and without production of waste, and the manipulated surface is fair and robust, eliminating the need for additional, manual treatment. Limitations to the possibilities of the flexible form are limited curvature and limited level of detail, making it especially suited for larger...
Edges, curvature, and primal sketches.
Watt, Roger
2012-01-01
Marr described two versions of the primal sketch: the basic image-processing level in human vision. In line with his broader view of how one should construct explanatory theories in vision, he provided some details of the computational theory for this stage, the algorithms used, and how they might be implemented in neural systems. In this paper I consider how Marr ideas have continued over the past 30 years. In this regard, I pay particular attention to three stages: locating edges; describing edge curvature; linking local edge segments into elongated contours.
DEFF Research Database (Denmark)
Madsen, Kenneth Lindegaard; Herlo, Rasmus
2017-01-01
The shape and composition of a membrane directly regulate the localization, activity, and signaling properties of membrane associated proteins. Proteins that both sense and generate membrane curvature, e.g., through amphiphilic insertion motifs, potentially engage in recursive binding dynamics......, where the recruitment of the protein itself changes the properties of the membrane substrate. Simple geometric models of membrane curvature interactions already provide prediction tools for experimental observations, however these models are treating curvature sensing and generation as separated...
Curvature-Controlled Topological Defects
Directory of Open Access Journals (Sweden)
Luka Mesarec
2017-05-01
Full Text Available Effectively, two-dimensional (2D closed films exhibiting in-plane orientational ordering (ordered shells might be instrumental for the realization of scaled crystals. In them, ordered shells are expected to play the role of atoms. Furthermore, topological defects (TDs within them would determine their valence. Namely, bonding among shells within an isotropic liquid matrix could be established via appropriate nano-binders (i.e., linkers which tend to be attached to the cores of TDs exploiting the defect core replacement mechanism. Consequently, by varying configurations of TDs one could nucleate growth of scaled crystals displaying different symmetries. For this purpose, it is of interest to develop a simple and robust mechanism via which one could control the position and number of TDs in such atoms. In this paper, we use a minimal mesoscopic model, where variational parameters are the 2D curvature tensor and the 2D orientational tensor order parameter. We demonstrate numerically the efficiency of the effective topological defect cancellation mechanism to predict positional assembling of TDs in ordered films characterized by spatially nonhomogeneous Gaussian curvature. Furthermore, we show how one could efficiently switch among qualitatively different structures by using a relative volume v of ordered shells, which represents a relatively simple naturally accessible control parameter.
LOCALIZATION OF POINT VORTICES UNDER CURVATURE PERTURBATIONS
Roberto, Garra
2013-01-01
International audience; We discuss the effect of curvature on the dynamics of a two-dimensional inviscid incompressible fluid with initial vorticity concentrated in N small disjoint regions, that is, the classical point vortex system. We recall some results about point vortex dynamics on simply connected surfaces with constant curvature K, that is, plane, spherical, and hyperbolic surfaces. We show that the effect of curvature can be treated as a smooth perturbation to the Green's function of...
SLED phenomenology: curvature vs. volume
International Nuclear Information System (INIS)
Niedermann, Florian; Schneider, Robert
2016-01-01
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. In addition, to quantify its potential with respect to the cosmological constant problem, we infer the amount of tuning on model parameters required to obtain a sufficiently small 4D curvature. A first answer was recently given in http://dx.doi.org/10.1007/JHEP02(2016)025, showing that 4D flat solutions are only ensured in the SI case by imposing a tuning relation, even if a brane-localized flux is included. In this companion paper, we find that the tuning can in fact be avoided for certain SI breaking brane-dilaton couplings, but only at the price of worsening the phenomenological problem. Our results are obtained by solving the full coupled Einstein-dilaton system in a completely consistent way. The brane width is implemented using a well-known ring regularization. In passing, we note that for the couplings considered here the results of http://dx.doi.org/10.1007/JHEP02(2016)025 (which only treated infinitely thin branes) are all consistently recovered in the thin brane limit, and how this can be reconciled with the concerns about their correctness, recently brought up in http://dx.doi.org/10.1007/JHEP01(2016)017.
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. Copyright © 2014 Elsevier B.V. All rights reserved.
Curvature recognition and force generation in phagocytosis
Directory of Open Access Journals (Sweden)
Prassler Jana
2010-12-01
Full Text Available Abstract 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
Optimal Transportation and Curvature of Metric Spaces
Eskin, Thomas
2013-01-01
In this thesis we study the notion of non-negative Ricci curvature for compact metric measure spaces introduced by Lott and Villani in their article (2009): Ricci curvature for metric measure spaces via optimal transport. We also define and prove the required prerequisites concerning length spaces, convex analysis, measure theory, and optimal transportation.
Weyl tensors for asymmetric complex curvatures
International Nuclear Information System (INIS)
Oliveira, C.G.
Considering a second rank Hermitian field tensor and a general Hermitian connection the associated complex curvature tensor is constructed. The Weyl tensor that corresponds to this complex curvature is determined. The formalism is applied to the Weyl unitary field theory and to the Moffat gravitational theory. (Author) [pt
Fermion localization in higher curvature spacetime
Choudhury, Sayantan; Mitra, Joydip; SenGupta, Soumitra
2018-01-01
Fermion localization in a braneworld model in presence of dilaton coupled higher curvature Gauss–Bonnet bulk gravity is discussed. It is shown that the lowest mode of left handed fermions can be naturally localized on the visible brane due to the dilaton coupled higher curvature term without the necessity of any external localizing bulk field.
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.
Importance of plan curvature in watershed modeling
Boll, J.; Ribail, J.; Zhao, M.
2016-12-01
A hillslope's hydrologic response to precipitation events is largely controlled by the topographic features of a given hillslope, specifically the profile and plan curvature. Many models simplify hillslope topography and ignore the curvature properties, and some use alternate measures such as a topographic index or the hillslope width function. Models that ignore curvature properties may be calibrated to produce the statistically acceptable integrated response of runoff at a watershed outlet, but incorporating these properties is necessary to model accurately hydrologic processes such as surface flow, erosion, subsurface lateral flow, location of runoff generation and drainage response. In this study, we evaluated the sensitivity of rainfall-runoff modelling to profile and plan curvature in two models. In the first model, the Water Erosion Prediction Project (WEPP) model, hillslope uses a representative width to the hillslope by dividing the drainage area by the average surface channel length. Profile curvature is preserved with a limited spatial resolution due to the number of overland flow elements. In the second model, the distributed Soil Moisture Routing (SMR) model, the geographic information system uses the D8 algorithm to capture profile and plan curvature. Sensitivity to topographic features was tested for three profile curvatures (convex, concave, straight) combined with three plan curvatures (diverging, converging, uniform) resulting in a total of nine hillslopes. Each hillslope was subjected to different rainfall events to detect threshold behavior for when topographic features cannot be ignored. Our findings indicate that concave and convex plan curvature need to be included when subsurface flow processes are the dominant flow process for surface flow runoff generation. We present thresholds for acceptable cases when profile and plan curvature can be simplified in larger spatial hydrologic units.
Energy Technology Data Exchange (ETDEWEB)
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.
Curvature function and coarse graining
International Nuclear Information System (INIS)
Diaz-Marin, Homero; Zapata, Jose A.
2010-01-01
A classic theorem in the theory of connections on principal fiber bundles states that the evaluation of all holonomy functions gives enough information to characterize the bundle structure (among those sharing the same structure group and base manifold) and the connection up to a bundle equivalence map. This result and other important properties of holonomy functions have encouraged their use as the primary ingredient for the construction of families of quantum gauge theories. However, in these applications often the set of holonomy functions used is a discrete proper subset of the set of holonomy functions needed for the characterization theorem to hold. We show that the evaluation of a discrete set of holonomy functions does not characterize the bundle and does not constrain the connection modulo gauge appropriately. We exhibit a discrete set of functions of the connection and prove that in the abelian case their evaluation characterizes the bundle structure (up to equivalence), and constrains the connection modulo gauge up to ''local details'' ignored when working at a given scale. The main ingredient is the Lie algebra valued curvature function F S (A) defined below. It covers the holonomy function in the sense that expF S (A)=Hol(l=∂S,A).
Curvature of Indoor Sensor Network: Clustering Coefficient
Directory of Open Access Journals (Sweden)
2009-03-01
Full Text Available We investigate the geometric properties of the communication graph in realistic low-power wireless networks. In particular, we explore the concept of the curvature of a wireless network via the clustering coefficient. Clustering coefficient analysis is a computationally simplified, semilocal approach, which nevertheless captures such a large-scale feature as congestion in the underlying network. The clustering coefficient concept is applied to three cases of indoor sensor networks, under varying thresholds on the link packet reception rate (PRR. A transition from positive curvature (“meshed” network to negative curvature (“core concentric” network is observed by increasing the threshold. Even though this paper deals with network curvature per se, we nevertheless expand on the underlying congestion motivation, propose several new concepts (network inertia and centroid, and finally we argue that greedy routing on a virtual positively curved network achieves load balancing on the physical network.
Higher Curvature Supergravity, Supersymmetry Breaking and Inflation
Ferrara, Sergio
2017-01-01
In these lectures, after a short introduction to cosmology, we discuss the supergravity embedding of higher curvature models of inflation. The supergravity description of such models is presented for the two different formulations of minimal supergravity.
GDP growth and the yield curvature
DEFF Research Database (Denmark)
Møller, Stig Vinther
2014-01-01
This paper examines the forecastability of GDP growth using information from the term structure of yields. In contrast to previous studies, the paper shows that the curvature of the yield curve contributes with much more forecasting power than the slope of yield curve. The yield curvature also...... predicts bond returns, implying a common element to time-variation in expected bond returns and expected GDP growth....
Cosmological attractor models and higher curvature supergravity
International Nuclear Information System (INIS)
Cecotti, Sergio; Kallosh, Renata
2014-01-01
We study cosmological α-attractors in superconformal/supergravity models, where α is related to the geometry of the moduli space. For α=1 attractors http://dx.doi.org/10.1088/1475-7516/2013/07/002 we present a generalization of the previously known manifestly superconformal higher curvature supergravity model http://dx.doi.org/10.1016/0370-2693(87)90844-6. 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 http://dx.doi.org/10.1007/JHEP11(2013)198 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
Cosmological attractor models and higher curvature supergravity
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.
Strong curvature effects in Neumann wave problems
International Nuclear Information System (INIS)
Willatzen, M.; Pors, A.; Gravesen, J.
2012-01-01
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.
DEFF Research Database (Denmark)
Johannes, Ludger; Pezeshkian, Weria; Ipsen, John H
2018-01-01
Clustering of extracellular ligands and proteins on the plasma membrane is required to perform specific cellular functions, such as signaling and endocytosis. Attractive forces that originate in perturbations of the membrane's physical properties contribute to this clustering, in addition to direct...... protein-protein interactions. However, these membrane-mediated forces have not all been equally considered, despite their importance. In this review, we describe how line tension, lipid depletion, and membrane curvature contribute to membrane-mediated clustering. Additional attractive forces that arise...... from protein-induced perturbation of a membrane's fluctuations are also described. This review aims to provide a survey of the current understanding of membrane-mediated clustering and how this supports precise biological functions....
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.
Cosmic curvature from de Sitter equilibrium cosmology.
Albrecht, Andreas
2011-10-07
I show that the de Sitter equilibrium cosmology generically predicts observable levels of curvature in the Universe today. The predicted value of the curvature, Ω(k), depends only on the ratio of the density of nonrelativistic matter to cosmological constant density ρ(m)(0)/ρ(Λ) and the value of the curvature from the initial bubble that starts the inflation, Ω(k)(B). The result is independent of the scale of inflation, the shape of the potential during inflation, and many other details of the cosmology. Future cosmological measurements of ρ(m)(0)/ρ(Λ) and Ω(k) will open up a window on the very beginning of our Universe and offer an opportunity to support or falsify the de Sitter equilibrium cosmology.
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.
Longitudinal surface curvature effect in magnetohydrodynamics
International Nuclear Information System (INIS)
Bodas, N.G.
1975-01-01
The two-dimensional motion of an incompressible and electrically conducting fluid past an electrically insulated body surface (having curvature) is studied for a given O(1) basic flow and magnetic field, when (i) the applied magnetic field is aligned with the velocity in the basic flow, and (ii) the applied magnetic field is within the body surface. 01 and 0(Re sup(1/2)) mean the first and second order approximations respectively in an exansion scheme in powers of Resup(-1/2), Re being the Reynolds number). The technique of matched asymptotic expansions is used to solve the problem. The governing partial differential equations to 0(Resup(-1/2)) boundary layer approximation are found to give similarity solutions for a family of surface curvature and pressure gradient distributions in case (i), and for uniform basic flow with analytic surface curvature distributions in case (ii). The equations are solved numerically. In case (i) it is seen that the effect of the magnetic field on the skin-friction- correction due to the curvature is very small. Also the magnetic field at the wall is reduced by the curvature on the convex side. In case (ii) the magnetic field significantly increases the skin-friction-correction due to the curvature. The effect of the magnetic field on the O(1) and O(Resup(-1/2)) skin friction coefficients increases with the increase of the electrical conductivity of the fluid. Also, at higher values of the magnetic pressure, moderate changes in the electrical conductivity do not influence the correction to the skin-friction significantly. (Auth.)
Membrane bending by protein-protein crowding.
Stachowiak, Jeanne C; Schmid, Eva M; Ryan, Christopher J; Ann, Hyoung Sook; Sasaki, Darryl Y; Sherman, Michael B; Geissler, Phillip L; Fletcher, Daniel A; Hayden, Carl C
2012-09-01
Curved membranes are an essential feature of dynamic cellular structures, including endocytic pits, filopodia protrusions and most organelles. It has been proposed that specialized proteins induce curvature by binding to membranes through two primary mechanisms: membrane scaffolding by curved proteins or complexes; and insertion of wedge-like amphipathic helices into the membrane. Recent computational studies have raised questions about the efficiency of the helix-insertion mechanism, predicting that proteins must cover nearly 100% of the membrane surface to generate high curvature, an improbable physiological situation. Thus, at present, we lack a sufficient physical explanation of how protein attachment bends membranes efficiently. On the basis of studies of epsin1 and AP180, proteins involved in clathrin-mediated endocytosis, we propose a third general mechanism for bending fluid cellular membranes: protein-protein crowding. By correlating membrane tubulation with measurements of protein densities on membrane surfaces, we demonstrate that lateral pressure generated by collisions between bound proteins drives bending. Whether proteins attach by inserting a helix or by binding lipid heads with an engineered tag, protein coverage above ~20% is sufficient to bend membranes. Consistent with this crowding mechanism, we find that even proteins unrelated to membrane curvature, such as green fluorescent protein (GFP), can bend membranes when sufficiently concentrated. These findings demonstrate a highly efficient mechanism by which the crowded protein environment on the surface of cellular membranes can contribute to membrane shape change.
Positive scalar curvature and the Euler class
Yu, Jianqing; Zhang, Weiping
2018-03-01
We prove the following generalization of the classical Lichnerowicz vanishing theorem: if F is an oriented flat vector bundle over a closed spin manifold M such that TM carries a metric of positive scalar curvature, then 〈 A ̂ (TM) e(F) , [ M ] 〉 = 0, where e(F) is the Euler class of F.
Timelike Constant Mean Curvature Surfaces with Singularities
DEFF Research Database (Denmark)
Brander, David; Svensson, Martin
2014-01-01
We use integrable systems techniques to study the singularities of timelike non-minimal constant mean curvature (CMC) surfaces in the Lorentz–Minkowski 3-space. The singularities arise at the boundary of the Birkhoff big cell of the loop group involved. We examine the behavior of the surfaces...
Norm of the Riemannian Curvature Tensor
Indian Academy of Sciences (India)
We consider the Riemannian functional R p ( g ) = ∫ M | R ( g ) | p d v g defined on the space of Riemannian metrics with unit volume on a closed smooth manifold where R ( g ) and d v g denote the corresponding Riemannian curvature tensor and volume form and p ∈ ( 0 , ∞ ) . First we prove that the Riemannian metrics ...
Zero curvature conditions and conformal covariance
International Nuclear Information System (INIS)
Akemann, G.; Grimm, R.
1992-05-01
Two-dimensional zero curvature conditions were investigated in detail, with special emphasis on conformal properties, and the appearance of covariant higher order differential operators constructed in terms of a projective connection was elucidated. The analysis is based on the Kostant decomposition of simple Lie algebras in terms of representations with respect to their 'principal' SL(2) subalgebra. (author) 27 refs
On Mass, Spacetime Curvature, and Gravity
Janis, Allen I.
2018-01-01
The frequently used analogy of a massive ball distorting an elastic sheet, which is used to illustrate why mass causes spacetime curvature and gravitational attraction, is criticized in this article. A different analogy that draws on the students' previous knowledge of spacetime diagrams in special relativity is suggested.
Resolving curvature singularities in holomorphic gravity
Mantz, C.L.M.; Prokopec, T.
2011-01-01
We formulate a holomorphic theory of gravity and study how the holomorphy symmetry alters the two most important singular solutions of general relativity: black holes and cosmology. We show that typical observers (freely) falling into a holomorphic black hole do not encounter a curvature
Gaussian curvature on hyperelliptic Riemann surfaces
Indian Academy of Sciences (India)
Indian Acad. Sci. (Math. Sci.) Vol. 124, No. 2, May 2014, pp. 155–167. c Indian Academy of Sciences. Gaussian curvature on hyperelliptic Riemann surfaces. ABEL CASTORENA. Centro de Ciencias Matemáticas (Universidad Nacional Autónoma de México,. Campus Morelia) Apdo. Postal 61-3 Xangari, C.P. 58089 Morelia,.
Curvature driven instabilities in toroidal plasmas
International Nuclear Information System (INIS)
Andersson, P.
1986-11-01
The electromagnetic ballooning mode, the curvature driven trapped electron mode and the toroidally induced ion temperature gradient mode have been studies. Eigenvalue equations have been derived and solved both numerically and analytically. For electromagnetic ballooning modes the effects of convective damping, finite Larmor radius, higher order curvature terms, and temperature gradients have been investigated. A fully toroidal fluid ion model has been developed. It is shown that a necessary and sufficient condition for an instability below the MHD limit is the presence of an ion temperature gradient. Analytical dispersion relations giving results in good agreement with numerical solutions are also presented. The curvature driven trapped electron modes are found to be unstable for virtually all parameters with growth rates of the order of the diamagnetic drift frequency. Studies have been made, using both a gyrokinetic ion description and the fully toroidal ion model. Both analytical and numerical results are presented and are found to be in good agreement. The toroidally induced ion temperature gradients modes are found to have a behavior similar to that of the curvature driven trapped electron modes and can in the electrostatic limit be described by a simple quadratic dispersion equation. (author)
Modulation of saccade curvature by ocular counterroll.
Weber, Konrad P; Bockisch, Christopher J; Olasagasti, Itsaso; Straumann, Dominik
2009-03-01
On close inspection, it can be seen that most saccadic trajectories are not straight but curve slightly; in other words, they are not single-axis ocular rotations. The authors asked whether saccade curvatures are systematically influenced by static ocular counterroll (OCR). OCR was elicited by static whole-body roll position. Eight healthy human subjects performed horizontal and vertical saccades (10 degrees amplitude; 0 degrees and 10 degrees eccentricity; head-fixed coordinate system) in upright and ear-down whole-body roll positions (45 degrees right, 45 degrees left). Three-dimensional eye movements were recorded with modified dual-search coils at 1000 Hz. Saccade curvature was systematically modulated by OCR depending on saccade direction. In the horizontal-vertical plane, primarily vertical saccades were modulated with downward saccades curving toward the upper ear and upward saccades curving toward the lower ear. Modulation of saccade curvature in the torsional direction correlated significantly with OCR only in abducting saccades. No universal mechanism, such as visual-motor coordinate transformation or kinematic characteristics of the saccadic burst generator, alone could explain the complex modulation pattern of saccade curvature. OCR-induced changes of the ocular motor plant, including transient force imbalances between agonist eye muscles (vertical rectus and oblique muscles) and shifting eye muscle pulleys, are suitable to explain the found direction-dependent modulation pattern.
Curvature controlled wetting in two dimensions
DEFF Research Database (Denmark)
Gil, Tamir; Mikheev, Lev V.
1995-01-01
. As the radius of the substrate r0→∞, the leading effect of the curvature is adding the Laplace pressure ΠL∝r0-1 to the pressure balance in the film. At temperatures and pressures under which the wetting is complete in planar geometry, Laplace pressure suppresses divergence of the mean thickness of the wetting...
Constraining inverse curvature gravity with supernovae
Energy Technology Data Exchange (ETDEWEB)
Mena, Olga; Santiago, Jose; /Fermilab; 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.
Leal-Junior, Arnaldo G.; Frizera, Anselmo; José Pontes, Maria
2018-03-01
Polymer optical fibers (POFs) are suitable for applications such as curvature sensors, strain, temperature, liquid level, among others. However, for enhancing sensitivity, many polymer optical fiber curvature sensors based on intensity variation require a lateral section. Lateral section length, depth, and surface roughness have great influence on the sensor sensitivity, hysteresis, and linearity. Moreover, the sensor curvature radius increase the stress on the fiber, which leads on variation of the sensor behavior. This paper presents the analysis relating the curvature radius and lateral section length, depth and surface roughness with the sensor sensitivity, hysteresis and linearity for a POF curvature sensor. Results show a strong correlation between the decision parameters behavior and the performance for sensor applications based on intensity variation. Furthermore, there is a trade-off among the sensitive zone length, depth, surface roughness, and curvature radius with the sensor desired performance parameters, which are minimum hysteresis, maximum sensitivity, and maximum linearity. The optimization of these parameters is applied to obtain a sensor with sensitivity of 20.9 mV/°, linearity of 0.9992 and hysteresis below 1%, which represent a better performance of the sensor when compared with the sensor without the optimization.
How curved membranes recruit amphipathic helices and protein anchoring motifs.
Hatzakis, Nikos S; Bhatia, Vikram K; Larsen, Jannik; Madsen, Kenneth L; Bolinger, Pierre-Yves; Kunding, Andreas H; Castillo, John; Gether, Ulrik; Hedegård, Per; Stamou, Dimitrios
2009-11-01
Lipids and several specialized proteins are thought to be able to sense the curvature of membranes (MC). Here we used quantitative fluorescence microscopy to measure curvature-selective binding of amphipathic motifs on single liposomes 50-700 nm in diameter. Our results revealed that sensing is predominantly mediated by a higher density of binding sites on curved membranes instead of higher affinity. We proposed a model based on curvature-induced defects in lipid packing that related these findings to lipid sorting and accurately predicted the existence of a new ubiquitous class of curvature sensors: membrane-anchored proteins. The fact that unrelated structural motifs such as alpha-helices and alkyl chains sense MC led us to propose that MC sensing is a generic property of curved membranes rather than a property of the anchoring molecules. We therefore anticipate that MC will promote the redistribution of proteins that are anchored in membranes through other types of hydrophobic moieties.
Cosmological signatures of anisotropic spatial curvature
Energy Technology Data Exchange (ETDEWEB)
Pereira, Thiago S. [Departamento de Física, Universidade Estadual de Londrina, 86057-970, Londrina – PR (Brazil); Marugán, Guillermo A. Mena [Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006, Madrid (Spain); Carneiro, Saulo, E-mail: tspereira@uel.br, E-mail: mena@iem.cfmac.csic.es, E-mail: saulo.carneiro@pq.cnpq.br [Instituto de Física, Universidade Federal da Bahia, 40210-340, Salvador – BA (Brazil)
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.
Weyl curvature tensor in static spherical sources
International Nuclear Information System (INIS)
Ponce de Leon, J.
1988-01-01
The role of the Weyl curvature tensor in static sources of the Schwarzschild field is studied. It is shown that in general the contribution from the Weyl curvature tensor (the ''purely gravitational field energy'') to the mass-energy inside the body may be positive, negative, or zero. It is proved that a positive (negative) contribution from the Weyl tensor tends to increase (decrease) the effective gravitational mass, the red-shift (from a point in the sphere to infinity), as well as the gravitational force which acts on a constituent matter element of a body. It is also proved that the contribution from the Weyl tensor always is negative in sources with surface gravitational potential larger than (4/9. It is pointed out that large negative contributions from the Weyl tensor could give rise to the phenomenon of gravitational repulsion. A simple example which illustrates the results is discussed
On a curvature-statistics theorem
Energy Technology Data Exchange (ETDEWEB)
Calixto, M [Departamento de Matematica Aplicada y Estadistica, Universidad Politecnica de Cartagena, Paseo Alfonso XIII 56, 30203 Cartagena (Spain); Aldaya, V [Instituto de Astrofisica de Andalucia, Apartado Postal 3004, 18080 Granada (Spain)], E-mail: Manuel.Calixto@upct.es
2008-08-15
The spin-statistics theorem in quantum field theory relates the spin of a particle to the statistics obeyed by that particle. Here we investigate an interesting correspondence or connection between curvature ({kappa} = {+-}1) and quantum statistics (Fermi-Dirac and Bose-Einstein, respectively). The interrelation between both concepts is established through vacuum coherent configurations of zero modes in quantum field theory on the compact O(3) and noncompact O(2; 1) (spatial) isometry subgroups of de Sitter and Anti de Sitter spaces, respectively. The high frequency limit, is retrieved as a (zero curvature) group contraction to the Newton-Hooke (harmonic oscillator) group. We also make some comments on the physical significance of the vacuum energy density and the cosmological constant problem.
Strong curvature effects in Neumann wave problems
DEFF Research Database (Denmark)
Willatzen, Morten; Pors, A.; Gravesen, Jens
2012-01-01
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 Schro¨dinger 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...
Scaling up the curvature of mammalian metabolism
Directory of Open Access Journals (Sweden)
Juan eBueno
2014-10-01
Full Text Available A curvilinear relationship between mammalian metabolic rate and body size on a log-log scale has been adopted in lieu of thelongstanding concept of a 3/4 allometric relationship (Kolokotrones et al. 2010. The central tenet of Metabolic Ecology (ME states that metabolism at the individual level scales-up to drive the ecology of populations, communities and ecosystems. If this tenet is correct, the curvature of metabolism should be perceived in other ecological traits. By analyzing the size scaling allometry of eight different mammalian traits including basal and field metabolic rate, offspring biomass production, ingestion rate, costs of locomotion, life span, population growth rate and population density we show that the curvature affects most ecological rates and
Discrete Curvatures and Discrete Minimal Surfaces
Sun, Xiang
2012-06-01
This thesis presents an overview of some approaches to compute Gaussian and mean curvature on discrete surfaces and discusses discrete minimal surfaces. The variety of applications of differential geometry in visualization and shape design leads to great interest in studying discrete surfaces. With the rich smooth surface theory in hand, one would hope that this elegant theory can still be applied to the discrete counter part. Such a generalization, however, is not always successful. While discrete surfaces have the advantage of being finite dimensional, thus easier to treat, their geometric properties such as curvatures are not well defined in the classical sense. Furthermore, the powerful calculus tool can hardly be applied. The methods in this thesis, including angular defect formula, cotangent formula, parallel meshes, relative geometry etc. are approaches based on offset meshes or generalized offset meshes. As an important application, we discuss discrete minimal surfaces and discrete Koenigs meshes.
Harmonic curvatures and generalized helices in En
International Nuclear Information System (INIS)
Camci, Cetin; Ilarslan, Kazim; Kula, Levent; Hacisalihoglu, H. Hilmi
2009-01-01
In n-dimensional Euclidean space E n , harmonic curvatures of a non-degenerate curve defined by Ozdamar and Hacisalihoglu [Ozdamar E, Hacisalihoglu HH. A characterization of Inclined curves in Euclidean n-space. Comm Fac Sci Univ Ankara, Ser A1 1975;24:15-23]. In this paper, we give some characterizations for a non-degenerate curve α to be a generalized helix by using its harmonic curvatures. Also we define the generalized Darboux vector D of a non-degenerate curve α in n-dimensional Euclidean space E n and we show that the generalized Darboux vector D lies in the kernel of Frenet matrix M(s) if and only if the curve α is a generalized helix in the sense of Hayden.
Collineations of the curvature tensor in general relativity
Indian Academy of Sciences (India)
Curvature collineations for the curvature tensor, constructed from a fundamental Bianchi Type-V metric, are studied. We are concerned with a symmetry property of space-time which is called curvature collineation, and we briefly discuss the physical and kinematical properties of the models.
On hypersurfaces with two distinct principal curvatures in space forms
Indian Academy of Sciences (India)
Abstract. We investigate the immersed hypersurfaces in space forms Nn+1(c), n ≥4 with two distinct non-simple principal curvatures without the assumption that the (high order) mean curvature is constant. We prove that any immersed hypersurface in space forms with two distinct non-simple principal curvatures is locally ...
DEFF Research Database (Denmark)
Ramesh, Pradeep; Baroji, Younes F.; Seyyed Reihani, Seyyed Nader
2013-01-01
brain lipid vesicles and show that it senses membrane curvature at low density whereas it induces and reinforces tube stiffness at higher density. FBAR strongly up-concentrates on the high curvature tubes pulled out of Giant Unilamellar lipid Vesicles (GUVs), this sorting behavior is strongly amplified...... at low protein densities. Interestingly, FBAR from syndapin 1 has a large affinity for tubular membranes with curvatures larger than its own intrinsic concave curvature. Finally, we studied the effect of FBAR on membrane relaxation kinetics with high temporal resolution and found that the protein...... increases relaxation time of the tube holding force in a density-dependent fashion....
Generating the primordial curvature perturbation from inflation
Lyth, David H.
2002-01-01
The scale--independence of the primordial curvature perturbation suggests that it comes from the vacuum fluctuation during inflation of a light scalar field. This field may be the inflaton, or a different `curvaton' field. The observation of primordial non--gaussianity would be a smoking gun for the curvaton model, while the observation of gravitational waves originating during slow--roll inflation would rule out the model.
Gravitational curvature an introduction to Einstein's theory
Frankel, Theodore Thomas
1979-01-01
This classic text and reference monograph applies modern differential geometry to general relativity. A brief mathematical introduction to gravitational curvature, it emphasizes the subject's geometric essence, replacing the often-tedious analytical computations with geometric arguments. Clearly presented and physically motivated derivations express the deflection of light, Schwarzchild's exterior and interior solutions, and the Oppenheimer-Volkoff equations. A perfect choice for advanced students of mathematics, this volume will also appeal to mathematicians interested in physics. It stresses
Mixed 3-Sasakian structures and curvature
Caldarella, Angelo V.; Pastore, Anna Maria
2008-01-01
In this paper we deal with two classes of mixed metric 3-structures, namely the mixed 3-Sasakian structures and the mixed metric 3-contact structures. Firstly we study some properties of the curvature of mixed 3-Sasakian structures, proving that any manifold endowed with such a structure is Einstein. Then we prove the identity between the class of mixed 3-Sasakian structures and the class of mixed metric 3-contact structures.
Inflationary scenario from higher curvature warped spacetime
Energy Technology Data Exchange (ETDEWEB)
Banerjee, Narayan [Indian Institute of Science Education and Research Kolkata, Department of Physical Sciences, Nadia, West Bengal (India); Paul, Tanmoy [Indian Association for the Cultivation of Science, Department of Theoretical Physics, Kolkata (India)
2017-10-15
We consider a five dimensional warped spacetime, in presence of the higher curvature term like F(R) = R + αR{sup 2} in the bulk, in the context of the two-brane model. Our universe is identified with the TeV scale brane and emerges as a four dimensional effective theory. From the perspective of this effective theory, we examine the possibility of ''inflationary scenario'' by considering the on-brane metric ansatz as an FRW one. Our results reveal that the higher curvature term in the five dimensional bulk spacetime generates a potential term for the radion field. Due to the presence of radion potential, the very early universe undergoes a stage of accelerated expansion and, moreover, the accelerating period of the universe terminates in a finite time. We also find the spectral index of curvature perturbation (n{sub s}) and the tensor to scalar ratio (r) in the present context, which match with the observational results based on the observations of Planck (Astron. Astrophys. 594, A20, 2016). (orig.)
Directory of Open Access Journals (Sweden)
Ruben R Bender
2016-06-01
Full Text Available 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.
A curvature theory for discrete surfaces based on mesh parallelity
Bobenko, Alexander Ivanovich
2009-12-18
We consider a general theory of curvatures of discrete surfaces equipped with edgewise parallel Gauss images, and where mean and Gaussian curvatures of faces are derived from the faces\\' areas and mixed areas. Remarkably these notions are capable of unifying notable previously defined classes of surfaces, such as discrete isothermic minimal surfaces and surfaces of constant mean curvature. We discuss various types of natural Gauss images, the existence of principal curvatures, constant curvature surfaces, Christoffel duality, Koenigs nets, contact element nets, s-isothermic nets, and interesting special cases such as discrete Delaunay surfaces derived from elliptic billiards. © 2009 Springer-Verlag.
Distributed mean curvature on a discrete manifold for Regge calculus
International Nuclear Information System (INIS)
Conboye, Rory; Miller, Warner A; Ray, Shannon
2015-01-01
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. (paper)
Free-streaming radiation in cosmological models with spatial curvature
Wilson, M. L.
1982-01-01
The effects of spatial curvature on radiation anisotropy are examined for the standard Friedmann-Robertson-Walker model universes. The effect of curvature is found to be very important when considering fluctuations with wavelengths comparable to the horizon. It is concluded that the behavior of radiation fluctuations in models with spatial curvature is quite different from that in spatially flat models, and that models with negative curvature are most strikingly different. It is therefore necessary to take the curvature into account in careful studies of the anisotropy of the microwave background.
How curved membranes recruit amphipathic helices and protein anchoring motifs
DEFF Research Database (Denmark)
Hatzakis, Nikos; Bhatia, Vikram Kjøller; Larsen, Jannik
2009-01-01
Lipids and several specialized proteins are thought to be able to sense the curvature of membranes (MC). Here we used quantitative fluorescence microscopy to measure curvature-selective binding of amphipathic motifs on single liposomes 50-700 nm in diameter. Our results revealed that sensing...
Analysis of interfacial curvature during drainage and imbibition
Armstrong, R. T.; Porter, M. L.; Wildenschild, D.
2011-12-01
Recent synchrotron-based tomographic data sets of oil-water drainage and imbibition scenarios have been analyzed to quantify phase saturations, interfacial curvature, and separate connected from disconnected fluid phases. This allows us to follow the drainage and imbibition processes in great detail, assess equilibrium states, and understand the effects of fluid phase disconnection and re-connection on the resulting capillary pressures and interfacial curvatures. This analysis also allows for estimating capillary pressure (Pc) based on calculated curvatures and comparison to Pc measured externally with a transducer. Results indicate good agreement between curvature-based and transducer-based measurements when the connected phase interfaces are considered. Curvature measurements show a strong dependence on whether an interface is formed by connected or disconnected phases. Assuming that at equilibrium curvature is constant, curvature differences between the connected and disconnected phase interfaces can be used as a metric to asses equilibrium. Over longer equilibration, the average curvature value, for all interfaces, approaches the average curvature value predicted by the pressure transducer. Overall, the results indicate good agreement between curvature -based and transducer-based Pc measurements and allow for a detailed assessment of interfacial curvature during drainage and imbibition.
Constraining inverse-curvature gravity with supernovae.
Mena, Olga; Santiago, José; Weller, Jochen
2006-02-03
We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07baryonic matter component.
Curvature, zero modes and quantum statistics
Energy Technology Data Exchange (ETDEWEB)
Calixto, M [Departamento de Matematica Aplicada y EstadIstica, Universidad Politecnica de Cartagena, Paseo Alfonso XIII 56, 30203 Cartagena (Spain); Aldaya, V [Instituto de AstrofIsica de AndalucIa, Apartado Postal 3004, 18080 Granada (Spain)
2006-08-18
We explore an intriguing connection between the Fermi-Dirac and Bose-Einstein statistics and the thermal baths obtained from a vacuum radiation of coherent states of zero modes in a second quantized (many-particle) theory on the compact O(3) and noncompact O(2, 1) isometry subgroups of the de Sitter and anti-de Sitter spaces, respectively. The high frequency limit is retrieved as a (zero-curvature) group contraction to the Newton-Hooke (harmonic oscillator) group. We also make some comments on the vacuum energy density and the cosmological constant problem. (letter to the editor)
Lecture Notes on Mean Curvature Flow
Mantegazza, Carlo
2011-01-01
This book is an introduction to the subject of mean curvature flow of hypersurfaces with special emphasis on the analysis of singularities. This flow occurs in the description of the evolution of numerous physical models where the energy is given by the area of the interfaces. These notes provide a detailed discussion of the classical parametric approach (mainly developed by R. Hamilton and G. Huisken). They are well suited for a course at PhD/PostDoc level and can be useful for any researcher interested in a solid introduction to the technical issues of the field. All the proofs are carefully
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.
Electricity and mechanics of biomembrane systems: Flexoelectricity in living membranes
International Nuclear Information System (INIS)
Petrov, Alexander G.
2006-01-01
Flexoelectricity provides a reciprocal relationship between electricity and mechanics in membranes, i.e., between membrane curvature and polarization. Experimental evidence of biomembrane flexoelectricity (including direct and converse flexoelectric effect) is reviewed. Biological implications of flexoelectricity in membrane transport, membrane contact, mechanosensitivity, electromotility and hearing are underlined. Flexoelectricity enables membrane structures to function like soft micro- and nano-machines, sensors and actuators, thus providing important input to molecular electronics applications
Electricity and mechanics of biomembrane systems: Flexoelectricity in living membranes
Energy Technology Data Exchange (ETDEWEB)
Petrov, Alexander G. [Biomolecular Layers Department, Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia (Bulgaria)]. E-mail: director@issp.bas.bg
2006-05-24
Flexoelectricity provides a reciprocal relationship between electricity and mechanics in membranes, i.e., between membrane curvature and polarization. Experimental evidence of biomembrane flexoelectricity (including direct and converse flexoelectric effect) is reviewed. Biological implications of flexoelectricity in membrane transport, membrane contact, mechanosensitivity, electromotility and hearing are underlined. Flexoelectricity enables membrane structures to function like soft micro- and nano-machines, sensors and actuators, thus providing important input to molecular electronics applications.
Electricity and mechanics of biomembrane systems: flexoelectricity in living membranes.
Petrov, Alexander G
2006-05-24
Flexoelectricity provides a reciprocal relationship between electricity and mechanics in membranes, i.e., between membrane curvature and polarization. Experimental evidence of biomembrane flexoelectricity (including direct and converse flexoelectric effect) is reviewed. Biological implications of flexoelectricity in membrane transport, membrane contact, mechanosensitivity, electromotility and hearing are underlined. Flexoelectricity enables membrane structures to function like soft micro- and nano-machines, sensors and actuators, thus providing important input to molecular electronics applications.
Emergent gravity in spaces of constant curvature
Energy Technology Data Exchange (ETDEWEB)
Alvarez, Orlando; Haddad, Matthew [Department of Physics, University of Miami,1320 Campo Sano Ave, Coral Gables, FL 33146 (United States)
2017-03-07
In physical theories where the energy (action) is localized near a submanifold of a constant curvature space, there is a universal expression for the energy (or the action). We derive a multipole expansion for the energy that has a finite number of terms, and depends on intrinsic geometric invariants of the submanifold and extrinsic invariants of the embedding of the submanifold. This is the second of a pair of articles in which we try to develop a theory of emergent gravity arising from the embedding of a submanifold into an ambient space equipped with a quantum field theory. Our theoretical method requires a generalization of a formula due to by Hermann Weyl. While the first paper discussed the framework in Euclidean (Minkowski) space, here we discuss how this framework generalizes to spaces of constant sectional curvature. We focus primarily on anti de Sitter space. We then discuss how such a theory can give rise to a cosmological constant and Planck mass that are within reasonable bounds of the experimental values.
Emergent gravity in spaces of constant curvature
Alvarez, Orlando; Haddad, Matthew
2017-03-01
In physical theories where the energy (action) is localized near a submanifold of a constant curvature space, there is a universal expression for the energy (or the action). We derive a multipole expansion for the energy that has a finite number of terms, and depends on intrinsic geometric invariants of the submanifold and extrinsic invariants of the embedding of the submanifold. This is the second of a pair of articles in which we try to develop a theory of emergent gravity arising from the embedding of a submanifold into an ambient space equipped with a quantum field theory. Our theoretical method requires a generalization of a formula due to by Hermann Weyl. While the first paper discussed the framework in Euclidean (Minkowski) space, here we discuss how this framework generalizes to spaces of constant sectional curvature. We focus primarily on anti de Sitter space. We then discuss how such a theory can give rise to a cosmological constant and Planck mass that are within reasonable bounds of the experimental values.
Biesheuvel, P.M.; Biesheuvel, Pieter Maarten
2000-01-01
Synthetic membranes are increasingly used for energy-efficient separation of liquid and gaseous mixtures in household applications, environmental technology and the chemical and energy industry. Besides, membranes are used in component-specific sensors in gas and liquid streams, preferably combined
Ricci Curvature on Polyhedral Surfaces via Optimal Transportation
Directory of Open Access Journals (Sweden)
Benoît Loisel
2014-03-01
Full Text Available The problem of correctly defining geometric objects, such as the curvature, is a hard one in discrete geometry. In 2009, Ollivier defined a notion of curvature applicable to a wide category of measured metric spaces, in particular to graphs. He named it coarse Ricci curvature because it coincides, up to some given factor, with the classical Ricci curvature, when the space is a smooth manifold. Lin, Lu and Yau and Jost and Liu have used and extended this notion for graphs, giving estimates for the curvature and, hence, the diameter, in terms of the combinatorics. In this paper, we describe a method for computing the coarse Ricci curvature and give sharper results, in the specific, but crucial case of polyhedral surfaces.
The curvature calculation mechanism based on simple cell model.
Yu, Haiyang; Fan, Xingyu; Song, Aiqi
2017-07-20
A conclusion has not yet been reached on how exactly the human visual system detects curvature. This paper demonstrates how orientation-selective simple cells can be used to construct curvature-detecting neural units. Through fixed arrangements, multiple plurality cells were constructed to simulate curvature cells with a proportional output to their curvature. In addition, this paper offers a solution to the problem of narrow detection range under fixed resolution by selecting an output value under multiple resolution. Curvature cells can be treated as concrete models of an end-stopped mechanism, and they can be used to further understand "curvature-selective" characteristics and to explain basic psychophysical findings and perceptual phenomena in current studies.
Lecture notes on mean curvature flow, barriers and singular perturbations
Bellettini, Giovanni
2013-01-01
The aim of the book is to study some aspects of geometric evolutions, such as mean curvature flow and anisotropic mean curvature flow of hypersurfaces. We analyze the origin of such flows and their geometric and variational nature. Some of the most important aspects of mean curvature flow are described, such as the comparison principle and its use in the definition of suitable weak solutions. The anisotropic evolutions, which can be considered as a generalization of mean curvature flow, are studied from the view point of Finsler geometry. Concerning singular perturbations, we discuss the convergence of the Allen–Cahn (or Ginsburg–Landau) type equations to (possibly anisotropic) mean curvature flow before the onset of singularities in the limit problem. We study such kinds of asymptotic problems also in the static case, showing convergence to prescribed curvature-type problems.
Estimates and nonexistence of solutions of the scalar curvature ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
Introduction. Let M be an n-dimensional complete Riemannian manifold with metric g0 and scalar curvature k(x). The problem of the conformal deformation of scalar curvature is to find conditions on the function K(x) so that K(x) is the scalar curvature of a conformally related metric g = ρ(x)g0, here ρ(x) is some positive ...
Statistical mechanics of paths with curvature dependent action
International Nuclear Information System (INIS)
Ambjoern, J.; Durhuus, B.; Jonsson, T.
1987-01-01
We analyze the scaling limit of discretized random paths with curvature dependent action. For finite values of the curvature coupling constant the theory belongs to the universality class of simple random walk. It is possible to define a non-trivial scaling limit if the curvature coupling tends to infinity. We compute exactly the two point function in this limit and discuss the relevance of our results for random surfaces and string theories. (orig.)
On Riemannian manifolds (Mn, g) of quasi-constant curvature
International Nuclear Information System (INIS)
Rahman, M.S.
1995-07-01
A Riemannian manifold (M n , g) of quasi-constant curvature is defined. It is shown that an (M n , g) in association with other class of manifolds gives rise, under certain conditions, to a manifold of quasi-constant curvature. Some observations on how a manifold of quasi-constant curvature accounts for a pseudo Ricci-symmetric manifold and quasi-umbilical hypersurface are made. (author). 10 refs
Hair curvature: a natural dialectic and review.
Nissimov, Joseph N; Das Chaudhuri, Asit Baran
2014-08-01
Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one-to-one correspondences between them and their genetic causes do not exist. Current hair-curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross-sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair-form phenotypes. As such they suggest dialectic for hair-curvature development. We define a natural-dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top-down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca(2+) and planar cell polarity (PCP) pathways
3D face recognition with asymptotic cones based principal curvatures
Tang, Yinhang
2015-05-01
The classical curvatures of smooth surfaces (Gaussian, mean and principal curvatures) have been widely used in 3D face recognition (FR). However, facial surfaces resulting from 3D sensors are discrete meshes. In this paper, we present a general framework and define three principal curvatures on discrete surfaces for the purpose of 3D FR. These principal curvatures are derived from the construction of asymptotic cones associated to any Borel subset of the discrete surface. They describe the local geometry of the underlying mesh. First two of them correspond to the classical principal curvatures in the smooth case. We isolate the third principal curvature that carries out meaningful geometric shape information. The three principal curvatures in different Borel subsets scales give multi-scale local facial surface descriptors. We combine the proposed principal curvatures with the LNP-based facial descriptor and SRC for recognition. The identification and verification experiments demonstrate the practicability and accuracy of the third principal curvature and the fusion of multi-scale Borel subset descriptors on 3D face from FRGC v2.0.
Mariani, María Elisa; Madoery, Ricardo Román; Fidelio, Gerardo Daniel
2015-01-01
Two secretory phospholipase A2 (sPLA2s) from Glycine max, GmsPLA2-IXA-1 and GmsPLA2-XIB-2, have been purified as recombinant proteins and the activity was evaluated in order to obtain the optimum conditions for catalysis using mixed micelles and lipid monolayers as substrate. Both sPLA2s showed a maximum enzyme activity at pH 7 and a requirement of Ca(2+) in the micromolar range. These parameters were similar to those found for animal sPLA2s but a surprising optimum temperature for catalysis at 60 °C was observed. The effect of negative interfacial charges on the hydrolysis of organized substrates was evaluated through initial rate measurements using short chain phospholipids with different head groups. The enzymes showed subtle differences in the specificity for phospholipids with different head groups (DLPC, DLPG, DLPE, DLPA) in presence or absence of NaCl. Both recombinant enzymes showed lower activity toward anionic phospholipids and a preference for the zwitterionic ones. The values of the apparent kinetic parameters (Vmax and KM) demonstrated that these enzymes have more affinity for phosphatidylcholine compared with phosphatidylglycerol, in contrast with the results observed for pancreatic sPLA2. A hopping mode of catalysis was proposed for the action of these sPLA2 on mixed phospholipid/triton micelles. On the other hand, Langmuir-monolayers assays indicated an optimum lateral surface pressure for activity in between 13 and 16 mN/m for both recombinant enzymes. Copyright © 2014 Elsevier B.V. and Société française de biochimie et biologie Moléculaire (SFBBM). All rights reserved.
Membrane fission by protein crowding.
Snead, Wilton T; Hayden, Carl C; Gadok, Avinash K; Zhao, Chi; Lafer, Eileen M; Rangamani, Padmini; Stachowiak, Jeanne C
2017-04-18
Membrane fission, which facilitates compartmentalization of biological processes into discrete, membrane-bound volumes, is essential for cellular life. Proteins with specific structural features including constricting rings, helical scaffolds, and hydrophobic membrane insertions are thought to be the primary drivers of fission. In contrast, here we report a mechanism of fission that is independent of protein structure-steric pressure among membrane-bound proteins. In particular, random collisions among crowded proteins generate substantial pressure, which if unbalanced on the opposite membrane surface can dramatically increase membrane curvature, leading to fission. Using the endocytic protein epsin1 N-terminal homology domain (ENTH), previously thought to drive fission by hydrophobic insertion, our results show that membrane coverage correlates equally with fission regardless of the hydrophobicity of insertions. Specifically, combining FRET-based measurements of membrane coverage with multiple, independent measurements of membrane vesiculation revealed that fission became spontaneous as steric pressure increased. Further, fission efficiency remained equally potent when helices were replaced by synthetic membrane-binding motifs. These data challenge the view that hydrophobic insertions drive membrane fission, suggesting instead that the role of insertions is to anchor proteins strongly to membrane surfaces, amplifying steric pressure. In line with these conclusions, even green fluorescent protein (GFP) was able to drive fission efficiently when bound to the membrane at high coverage. Our conclusions are further strengthened by the finding that intrinsically disordered proteins, which have large hydrodynamic radii yet lack a defined structure, drove fission with substantially greater potency than smaller, structured proteins.
A Field Theory with Curvature and Anticurvature
Directory of Open Access Journals (Sweden)
M. I. Wanas
2014-01-01
Full Text Available The present work is an attempt to construct a unified field theory in a space with curvature and anticurvature, the PAP-space. The theory is derived from an action principle and a Lagrangian density using a symmetric linear parameterized connection. Three different methods are used to explore physical contents of the theory obtained. Poisson’s equations for both material and charge distributions are obtained, as special cases, from the field equations of the theory. The theory is a pure geometric one in the sense that material distribution, charge distribution, gravitational and electromagnetic potentials, and other physical quantities are defined in terms of pure geometric objects of the structure used. In the case of pure gravity in free space, the spherical symmetric solution of the field equations gives the Schwarzschild exterior field. The weak equivalence principle is respected only in the case of pure gravity in free space; otherwise it is violated.
Differential geometry connections, curvature, and characteristic classes
Tu, Loring W
2017-01-01
This text presents a graduate-level introduction to differential geometry for mathematics and physics students. The exposition follows the historical development of the concepts of connection and curvature with the goal of explaining the Chern–Weil theory of characteristic classes on a principal bundle. Along the way we encounter some of the high points in the history of differential geometry, for example, Gauss' Theorema Egregium and the Gauss–Bonnet theorem. Exercises throughout the book test the reader’s understanding of the material and sometimes illustrate extensions of the theory. Initially, the prerequisites for the reader include a passing familiarity with manifolds. After the first chapter, it becomes necessary to understand and manipulate differential forms. A knowledge of de Rham cohomology is required for the last third of the text. Prerequisite material is contained in author's text An Introduction to Manifolds, and can be learned in one semester. For the benefit of the reader and to establ...
Nonminimal coupling of perfect fluids to curvature
International Nuclear Information System (INIS)
Bertolami, Orfeu; Lobo, Francisco S. N.; Paramos, Jorge
2008-01-01
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 2 (R)]L 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 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 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.
Hawking temperature of constant curvature black holes
International Nuclear Information System (INIS)
Cai Ronggen; Myung, Yun Soo
2011-01-01
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 D-1 xS 1 , where D is the spacetime dimension and M 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
International Nuclear Information System (INIS)
Desroches, M; Jeffrey, M R
2011-01-01
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)
Slope and curvature of microbreaking wind waves
Caulliez, G.
2009-04-01
Microscale breaking is commonly observed at sea for steep waves less than 30 cm in wavelength. This phenomenon generates high surface slope and curvature roughness at the water surface, which has numerous implications for air-sea exchange and remote-sensing studies. In particular, microbreaking affects momentum transfer from wind to waves, leads to formation of vortices in water, and plays a key role in scattering of electromagnetic and acoustic waves by the air-sea interface. The geometric properties of the parasitic capillaries generated upon steep steady gravity-capillary waves have been well studied over the last decades, both experimentally and numerically. However, owing to their variability, the basic features of naturally occurring wind wave breakers as observed at sea or even in laboratory are far from being identified up to now. To this end, an experimental investigation of microbreaking wind waves was made in a large wind wave tank which combined visualizations of wave breaker profiles with single-point wave elevation and slope measurements. We show that microscale breakers exhibit a characteristic signature in slope and curvature suggesting formation of a bulge on the forward face of the wave crest. Parasitic ripples however are not necessarily generated ahead the bulge. Such breakers are observed for a wide range of wave steepness and wave slope skewness, their structure being only weakly dependent on wavelength and wind forcing. The geometric properties of microbreakers are analysed statistically and compared with the results of the recent numerical simulations by Hung and Tsai (J. Phys. Oceanogr., 2009).
Endogenous Time Preference and Strategic Growth
Carmen CAMACHO; Cagri SAGLAM; Agah TURAN
2010-01-01
This paper presents a strategic growth model that analyzes the impact of Endogenous preferences on equilibrium dynamics by employing the tools provided by lattice theory and supermodular games. Supermodular game structure of the model let us provide monotonicity results on the greatest and the least equilibrium without making any assumptions regarding the curvature of the production function. We also sharpen these results by showing the differentiability of the value function and the uniquene...
Loubet, Bastien; Hansen, Per Lyngs; Lomholt, Michael Andersen
2013-12-01
We investigate the electrostatic contribution to the lipid membrane mechanical parameters: tension, bending rigidity, spontaneous curvature, and flexocoefficient, using an approach where stress in the membrane is explicitly balanced. Our model includes an applied electrostatic potential as well as a charge distribution in the membrane. We apply our theory to membranes having surface charges and electric dipoles at the surface.
Liquid crystal model of membrane flexoelectricity.
Rey, Alejandro D
2006-07-01
An interfacial liquid crystal model is formulated and used to derive a membrane shape equation that takes into account pressure, tension, bending, torsion, and flexoelectric forces. Flexoelectricity introduces electric field-induced curvature and is of relevance to the study and characterization of biological membranes. It is shown that flexoelectricity renormalizes the membrane mechanical tension, shear, and bending effects, and hence it offers diverse pathways to manipulate the membrane's shape. The derived electroelastic shape equation provides systematic guidance on how to use electric fields in membrane studies.
Collineations of the curvature tensor in general relativity
Indian Academy of Sciences (India)
physics pp. 43–48. Collineations of the curvature tensor in general relativity. RISHI KUMAR TIWARI. Department of Mathematics and Computer Application, ... and kinematical properties of the models. Keywords. Collineation; Killing vectors; Ricci tensor; Riemannian curvature tensor. PACS No. 98.80. 1. Introduction.
Estimates and nonexistence of solutions of the scalar curvature ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
We derive some estimates and properties of supersolutions of the scalar curvature equation, and obtain some nonex- ... The problem of the conformal deformation of scalar curvature is to find conditions on the function ..... that the condition (b) of Theorem 3.4 is satisfied since r = (n−1)c coth(cr), and hence for any C2 positive ...
Introduction of Curvature in Amphipathic Oligothiophenes for Defined Aggregate Formation
van Rijn, Patrick; Janeliunas, Dainius; Brizard, Aurelie M. A.; Stuart, Marc C. A.; Eelkema, Rienk; van Esch, Jan H.
2010-01-01
In this study the possibility to control the size and shape of self-assembled structures through the local curvature of their molecular building blocks has been investigated. To this end a series of amphipathic conjugated oligothiophenes with a well-defined curvature of their backbone has been
Finsler metrics with constant (or scalar) flag curvature
Indian Academy of Sciences (India)
The very special relativity is an interesting theory of investigating the violation of Lorentz invariance which is developed by Cohen and Glashow [5]. In [9], the authors showed that the Killing navi- gation representation has the flag curvature preserving property. In particular, it preserves scalar (or constant) flag curvature.
Determination of Radius of Curvature for Teeth With Cycloid Profile
Shatalov, E. V.; Efremenkov (Ephremenkov), Egor Alekseevich; Shibinskiy, Konstantin Grigorievich
2016-01-01
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.
Determination of Radius of Curvature for Teeth With Cycloid Profile
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.
Automatic quantification of local and global articular cartilage surface curvature
DEFF Research Database (Denmark)
Folkesson, Jenny; Dam, Erik B; Olsen, Ole F
2008-01-01
The objective of this study was to quantitatively assess the surface curvature of the articular cartilage from low-field magnetic resonance imaging (MRI) data, and to investigate its role in populations with varying radiographic signs of osteoarthritis (OA), cross-sectionally and longitudinally. ...... curvature estimates from low-field MRI at different scales could potentially become biomarkers targeted at different stages of OA....
Curvature collineations for the field of gravitational waves
International Nuclear Information System (INIS)
Singh, K.P.; Singh, Gulab
1981-01-01
It has been shown that the space-times formed from a plane-fronted gravity wave and from a plane sandwich wave with constant polarisation admit proper curvature collineation in general. The curvature collineation vectors have been determined explicitly. (author)
Robust modal curvature features for identifying multiple damage in beams
Ostachowicz, Wiesław; Xu, Wei; Bai, Runbo; Radzieński, Maciej; Cao, Maosen
2014-03-01
Curvature mode shape is an effective feature for damage detection in beams. However, it is susceptible to measurement noise, easily impairing its advantage of sensitivity to damage. To deal with this deficiency, this study formulates an improved curvature mode shape for multiple damage detection in beams based on integrating a wavelet transform (WT) and a Teager energy operator (TEO). The improved curvature mode shape, termed the WT - TEO curvature mode shape, has inherent capabilities of immunity to noise and sensitivity to damage. The proposed method is experimentally validated by identifying multiple cracks in cantilever steel beams with the mode shapes acquired using a scanning laser vibrometer. The results demonstrate that the improved curvature mode shape can identify multiple damage accurately and reliably, and it is fairly robust to measurement noise.
Nastic curvatures of wheat coleoptiles that develop in true microgravity.
Heathcote, D G; Chapman, D K; Brown, A H
1995-07-01
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.
Energy Technology Data Exchange (ETDEWEB)
None
1978-12-01
The project's first objective is to establish, analytically, the cost and performance of design choices within the boundaries of the basic proposed concept. With these cost and performance measures as a guide, the second project objective is to design a cost-effective Dual Curvature collector module and collector field array. The third objective is to establish technical and economic concept feasibility through prototype fabrication and test. The final objective is to define the Dual Curvature collector commercialization requirements. The Dual Curvature collector uses a unique reflector module consisting of a reflective film that is tensioned on a reflector support frame. The tensioned membrane (film) surface approximates a hyperbolic paraboloid that is capable of linear focusing when the surface tracks the sun's apparent motion in one axis. The reflective film can be backed by polystyrene foam with an air space between the film and the foam surfaces. This provides damping of the reflector surface to minimize the effect of wind gusts and physical impacts. The baseline collector is intended to operate at a concentration of ten (10) or greater with a nominal absorber temperature of 150/sup 0/C (300/sup 0/F). The Component Research and Analysis tasks which lead to the selection of a baseline collector configuration are discussed. Also, some preliminary results of the Collector Module Design task are presented.
Clinical Assessment of Lamina Cribrosa Curvature in Eyes with Primary Open-Angle Glaucoma.
Directory of Open Access Journals (Sweden)
Yong Woo Kim
Full Text Available Quantitative evaluation of lamina cribrosa (LC posterior bowing in primary open-angle glaucoma (POAG eyes using swept-source optical coherence tomography.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.The ALID and mLCD were significantly larger in POAG eyes than in healthy controls (P -6 dB and moderate-to-advanced glaucoma (MD < -6 dB, P = 0.95.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.
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
The objective was to compare the use of autologous dermal and temporalis fascia grafts in the treatment of acquired penile curvatures. 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. 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). 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.
Haptic perception of object curvature in Parkinson's disease.
Directory of Open Access Journals (Sweden)
Jürgen Konczak
2008-07-01
Full Text Available The haptic perception of the curvature of an object is essential for adequate object manipulation and critical for our guidance of actions. This study investigated how the ability to perceive the curvature of an object is altered by Parkinson's disease (PD.Eight healthy subjects and 11 patients with mild to moderate PD had to judge, without vision, the curvature of a virtual "box" created by a robotic manipulandum. Their hands were either moved passively along a defined curved path or they actively explored the curved curvature of a virtual wall. The curvature was either concave or convex (bulging to the left or right and was judged in two locations of the hand workspace--a left workspace location, where the curved hand path was associated with curved shoulder and elbow joint paths, and a right workspace location in which these joint paths were nearly linear. After exploring the curvature of the virtual object, subjects had to judge whether the curvature was concave or convex. Based on these data, thresholds for curvature sensitivity were established. The main findings of the study are: First, 9 out 11 PD patients (82% showed elevated thresholds for detecting convex curvatures in at least one test condition. The respective median threshold for the PD group was increased by 343% when compared to the control group. Second, when distal hand paths became less associated with proximal joint paths (right workspace, haptic acuity was reduced substantially in both groups. Third, sensitivity to hand trajectory curvature was not improved during active exploration in either group.Our data demonstrate that PD is associated with a decreased acuity of the haptic sense, which may occur already at an early stage of the disease.
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.
Characterizing repulsive gravity with curvature eigenvalues
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.
Cosmic acceleration from matter-curvature coupling
Zaregonbadi, Raziyeh; Farhoudi, Mehrdad
2016-10-01
We consider f( {R,T} ) modified theory of gravity in which, in general, the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy-momentum tensor. We indicate that in this type of the theory, the coupling energy-momentum tensor is not conserved. However, we mainly focus on a particular model that matter is minimally coupled to the geometry in the metric formalism and wherein, its coupling energy-momentum tensor is also conserved. We obtain the corresponding Raychaudhuri dynamical equation that presents the evolution of the kinematic quantities. Then for the chosen model, we derive the behavior of the deceleration parameter, and show that the coupling term can lead to an acceleration phase after the matter dominated phase. On the other hand, the curvature of the universe corresponds with the deviation from parallelism in the geodesic motion. Thus, we also scrutinize the motion of the free test particles on their geodesics, and derive the geodesic deviation equation in this modified theory to study the accelerating universe within the spatially flat FLRW background. Actually, this equation gives the relative accelerations of adjacent particles as a measurable physical quantity, and provides an elegant tool to investigate the timelike and the null structures of spacetime geometries. Then, through the null deviation vector, we find the observer area-distance as a function of the redshift for the chosen model, and compare the results with the corresponding results obtained in the literature.
Face recognition based on depth maps and surface curvature
Gordon, Gaile G.
1991-09-01
This paper explores the representation of the human face by features based on the curvature of the face surface. Curature captures many features necessary to accurately describe the face, such as the shape of the forehead, jawline, and cheeks, which are not easily detected from standard intensity images. Moreover, the value of curvature at a point on the surface is also viewpoint invariant. Until recently range data of high enough resolution and accuracy to perform useful curvature calculations on the scale of the human face had been unavailable. Although several researchers have worked on the problem of interpreting range data from curved (although usually highly geometrically structured) surfaces, the main approaches have centered on segmentation by signs of mean and Gaussian curvature which have not proved sufficient in themselves for the case of the human face. This paper details the calculation of principal curvature for a particular data set, the calculation of general surface descriptors based on curvature, and the calculation of face specific descriptors based both on curvature features and a priori knowledge about the structure of the face. These face specific descriptors can be incorporated into many different recognition strategies. A system that implements one such strategy, depth template comparison, giving recognition rates between 80% and 90% is described.
Compensation of Gaussian curvature in developable cones is local
Wang, Jin W.; Witten, Thomas A.
2009-10-01
We use the angular deficit scheme [V. Borrelli, F. Cazals, and J.-M. Morvan, Comput. Aided Geom. Des. 20, 319 (2003)] to determine the distribution of Gaussian curvature in developable cones (d-cones) [E. Cerda, S. Chaieb, F. Melo, and L. Mahadevan, Nature (London) 401, 46 (1999)] numerically. These d-cones are formed by pushing a thin elastic sheet into a circular container. Negative Gaussian curvatures are identified at the rim where the sheet touches the container. Around the rim there are two narrow bands with positive Gaussian curvatures. The integral of the (negative) Gaussian curvature near the rim is almost completely compensated by that of the two adjacent bands. This suggests that the Gauss-Bonnet theorem which constrains the integral of Gaussian curvature globally does not explain the spontaneous curvature cancellation phenomenon [T. Liang and T. A. Witten, Phys. Rev. E 73, 046604 (2006)]. The locality of the compensation seems to increase for decreasing d-cone thickness. The angular deficit scheme also provides a way to confirm the curvature cancellation phenomenon.
Planck-Scale Dual-Curvature Lensing and Spacetime Noncommutativity
Directory of Open Access Journals (Sweden)
Giovanni Amelino-Camelia
2017-01-01
Full Text Available It was recently realized that Planck-scale momentum-space curvature, which is expected in some approaches to the quantum-gravity problem, can produce dual-curvature lensing, a feature which mainly affects the direction of observation of particles emitted by very distant sources. Several gray areas remain in our understanding of dual-curvature lensing, including the possibility that it might be just a coordinate artifact and the possibility that it might be in some sense a by-product of the better studied dual-curvature redshift. We stress that data reported by the IceCube neutrino telescope should motivate a more vigorous effort of investigation of dual-curvature lensing, and we observe that studies of the recently proposed “ρ-Minkowski noncommutative spacetime” could be valuable from this perspective. Through a dedicated ρ-Minkowski analysis, we show that dual-curvature lensing is not merely a coordinate artifact and that it can be present even in theories without dual-curvature redshift.
National Oceanic and Atmospheric Administration, Department of Commerce — Curvature was calculated from the bathymetry surface for each raster cell using the ArcGIS 3D Analyst "Curvature" Tool. Curvature describes the rate of change of...
National Oceanic and Atmospheric Administration, Department of Commerce — Profile curvature was calculated from the bathymetry surface for each raster cell using the ArcGIS 3D Analyst "Curvature" Tool. Profile curvature describes the rate...
Membrane Shape Instability Induced by Protein Crowding.
Chen, Zhiming; Atefi, Ehsan; Baumgart, Tobias
2016-11-01
Peripheral proteins can bend membranes through several different mechanisms, including scaffolding, wedging, oligomerization, and crowding. The crowding effect in particular has received considerable attention recently, in part because it is a colligative mechanism-implying that it could, in principle, be explored by any peripheral protein. Here we sought to clarify to what extent this mechanism is exploited by endocytic accessory proteins. We quantitatively investigate membrane curvature generation by means of a GUV shape stability assay. We found that the amount of crowding required to induce membrane curvature is correlated with membrane tension. Importantly, we also revealed that at the same membrane tension, the crowding mechanism requires far higher protein coverage to induce curvature changes compared to those observed for the endophilin BAR domain, serving here as an example of an endocytic accessory protein. Our results are important for the design of membrane-targeted biosensors as well as the understanding of mechanisms of biological membrane shaping. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Correlation between thoracolumbar curvatures and respiratory function in older adults
Directory of Open Access Journals (Sweden)
Rahman NNAA
2017-03-01
Full Text Available Nor Najwatul Akmal Ab Rahman,1 Devinder Kaur Ajit Singh,1 Raymond Lee2 1Physiotherapy Programme, School of Rehabilitation Sciences, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, Kuala Lumpur, Malaysia; 2School of Applied Sciences, London South Bank University, London, UK Abstract: Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation age of 66.63 (5.16 years participated in this cross-sectional study. The results showed that mean (standard deviation thoracic curvature angle and lumbar curvature angles were -46.30° (14.66° and 14.10° (10.58°, respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=-0.23, P<0.05; forced vital capacity: r=-0.32, P<0.05, quiet expiration intercostal thickness (r=-0.22, P<0.05 and deep expiration diaphragm muscle thickness (r=-0.21, P<0.05. The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=-0.29, P<0.05 and diaphragm muscle thickness at deep inspiration (r=-0.22, P<0.05. However, respiratory rate
On the transverse Scalar Curvature of a Compact Sasaki Manifold
Directory of Open Access Journals (Sweden)
He Weiyong
2014-09-01
Full Text Available We show that the standard picture regarding the notion of stability of constant scalar curvature metrics in Kähler geometry described by S.K. Donaldson [10, 11], which involves the geometry of infinitedimensional groups and spaces, can be applied to the constant scalar curvature metrics in Sasaki geometry with only few modification. We prove that the space of Sasaki metrics is an infinite dimensional symmetric space and that the transverse scalar curvature of a Sasaki metric is a moment map of the strict contactomophism group
Public and private space curvature in Robertson-Walker universes.
Rindler, W.
1981-05-01
The question is asked: what space curvature would a fundamental observer in an ideal Robertson-Walker universe obtain by direct local spatial measurements, i.e., without reference to the motion pattern of the other galaxies? The answer is that he obtains the curvatureK of his “private” space generated by all the geodesics orthogonal to his world line at the moment in question, and that ˜K is related to the usual curvatureK=k/R 2 of the “public” space of galaxies byK=K+H 2/c2, whereH is Hubble's parameter.
Energy Technology Data Exchange (ETDEWEB)
Masel, Richard I.; Sajjad, Syed Dawar; Gao, Yan; Liu, Zengcai; Chen, Qingmei
2017-12-26
An anion-conducting polymeric membrane comprises a terpolymer of styrene, vinylbenzyl-R.sub.s and vinylbenzyl-R.sub.x. R.sub.s is a positively charged cyclic amine group. R.sub.x is at least one constituent selected from the group consisting Cl, OH and a reaction product between an OH or Cl and a species other than a simple amine or a cyclic amine. The total weight of the vinylbenzyl-R.sub.x groups is greater than 0.3% of the total weight of the 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.
Large Deformation Mechanics of Plasma Membrane Chained Vesicles in Cells
Kosawada, Tadashi; Sanada, Kouichi; Takano, Tetsuo
The clathrin-coated pits, vesicles and chained vesicles on the inner surface of the plasma membrane facilitate the cell to transport specific extracellular macromolecules. This cellular process is strongly involved with large mechanical deformations of the plasma membrane accompanied by changes in membrane curvature. The assembly of the clathrin coat is thought to provide curvature into the membrane. Hence, effects of in-plane shear elasticity due to these coat structure may be significant on the vesicular mechanics. In this study, large deformation mechanics of plasma membrane chained vesicles in cells have been formulated based on minimization of bending and in-plane shear strain energy of the membrane. Effects of outer surrounding cytoplasmic flat membrane upon mechanically stable shapes of the vesicles were revealed, while effects of in-plane shear elasticity were partly discussed.
Sequential effects in preference decision: Prior preference assimilates current preference.
Directory of Open Access Journals (Sweden)
Seah Chang
Full Text Available An important factor affecting preference formation is the context in which that preference decision takes place. The current research examined whether one's preference formed for a previously presented stimulus influences the processing of a subsequent preference decision, henceforth referred to as the preference sequence effect. Using a novel sequential rating/judgment paradigm, the present study demonstrated the presence of a preference sequence effect using artistic photographs and face stimuli: A neutral stimulus was preferred more following a preferable stimulus than a less preferable stimulus. Furthermore, a similar trend was found even when the potential influence of response bias was controlled. These results suggest that an assimilative sequential effect exists even when sequential judgments are made solely based on one's subjective feeling; preference formed for a preceding stimulus modulates preference for a subsequent stimulus. This implies the need for a consideration of trial sequence as a factor creating a psychological context affecting the subsequent preference decisions.
Membrane Buckling Induced by Curved Filaments
Lenz, Martin; Crow, Daniel J. G.; Joanny, Jean-François
2009-07-01
We present a novel buckling instability relevant to membrane budding in eukaryotic cells. In this mechanism, curved filaments bind to a lipid bilayer without changing its intrinsic curvature. As more and more filaments adsorb, newly added ones are more and more strained, which destabilizes the flat membrane. We perform a linear stability analysis of filament-dressed membranes and find that the buckling threshold is within reasonable in vivo parameter values. We account for the formation of long tubes previously observed in cells and in purified systems. We study strongly deformed dressed membranes and their bifurcation diagram numerically. Our mechanism could be validated by a simple experiment.
On hypersurfaces with two distinct principal curvatures in space forms
Indian Academy of Sciences (India)
simple principal curvatures is locally conformal to the. Riemannian product of two constant curved manifolds. We also obtain some charac- terizations for the Clifford hypersurfaces in terms of the trace free part of the second fundamental form.
Abnormalities of Penile Curvature: Chordee and Penile Torsion
Directory of Open Access Journals (Sweden)
Sylvia Montag
2011-01-01
Full Text Available Congenital chordee and penile torsion are commonly observed in the presence of hypospadias, but can also be seen in boys with the meatus in its orthotopic position. Varying degrees of penile curvature are observed in 4–10% of males in the absence of hypospadias. Penile torsion can be observed at birth or in older boys who were circumcised at birth. Surgical management of congenital curvature without hypospadias can present a challenge to the pediatric urologist. The most widely used surgical techniques include penile degloving and dorsal plication. This paper will review the current theories for the etiology of penile curvature, discuss the spectrum of severity of congenital chordee and penile torsion, and present varying surgical techniques for the correction of penile curvature in the absence of hypospadias.
Curvature and bow of bulk GaN substrates
Energy Technology Data Exchange (ETDEWEB)
Foronda, Humberto M.; Young, Erin C.; Robertson, Christian A.; Speck, James S. [Materials Department, UCSB, Santa Barbara, California 93106 (United States); Romanov, Alexey E. [Materials Department, UCSB, Santa Barbara, California 93106 (United States); Ioffe Physico-Technical Institute RAS, St. Petersburg 194021 (Russian Federation); ITMO University, St. Petersburg 197101 (Russian Federation); Beltz, Glenn E. [Mechanical Engineering Department, UCSB, Santa Barbara, California 93106 (United States)
2016-07-21
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.
Stability of the cylindrical shell of variable curvature
Marguerre, Karl
1951-01-01
This report is a first attempt to devise a calculation method for representing the buckling behavior of cylindrical shells of variable curvature. The problem occurs, for instance, in dimensioning wing noses, the stability of which is decisively influenced by the variability of curvature. The calculation is made possible by simplifying the stability equations (permissible for the shell of small curvature) and by assuming that the curvature 1/R as a function of the arc lengths can be represented by a very few Fourier terms. The formulas for the special case of an ellipse-like half oval with an axis ratio 1/3 ?= e ?= 1 under compression in longitudinal direction,shear, and a combination of shear and compression were evaluated. However, the results can also be applied approximately to an unsymmetrical oval-shell segment under compression, shear, and bending so that the numerical values contained in the diagrams 10 to 12 represent directly dimensioning data for the wing nose.
On the projective curvature tensor of generalized Sasakian-space ...
African Journals Online (AJOL)
space-forms under some conditions regarding projective curvature tensor. All the results obtained in this paper are in the form of necessary and sufficient conditions. Keywords: Generalized Sasakian-space-forms; projectively flat; ...
Flow derivatives and curvatures for a normal shock
Emanuel, G.
2018-03-01
A detached bow shock wave is strongest where it is normal to the upstream velocity. While the jump conditions across the shock are straightforward, many properties, such as the shock's curvatures and derivatives of the pressure, along and normal to a normal shock, are indeterminate. A novel procedure is introduced for resolving the indeterminacy when the unsteady flow is three-dimensional and the upstream velocity may be nonuniform. Utilizing this procedure, normal shock relations are provided for the nonunique orientation of the flow plane and the corresponding shock's curvatures and, e.g., the downstream normal derivatives of the pressure and the velocity components. These algebraic relations explicitly show the dependence of these parameters on the shock's shape and the upstream velocity gradient. A simple relation, valid only for a normal shock, is obtained for the average curvatures. Results are also obtained when the shock is an elliptic paraboloid shock. These derivatives are both simple and proportional to the average curvature.
Translating Solitons of Mean Curvature Flow of Noncompact Submanifolds
International Nuclear Information System (INIS)
Li Guanghan; Tian Daping; Wu Chuanxi
2011-01-01
We prove the existence and asymptotic behavior of rotationally symmetric solitons of mean curvature flow for noncompact submanifolds in Euclidean and Minkowski spaces, which generalizes part of the corresponding results for hypersurfaces of Jian.
Gauge and non-gauge curvature tensor copies
International Nuclear Information System (INIS)
Srivastava, P.P.
1982-10-01
A procedure for constructing curvature tensor copies is discussed using the anholonomic geometrical framework. The corresponding geometries are compared and the notion of gauge copy is elucidated. An explicit calculation is also made. (author)
Higher-order curvature terms and extended inflation
International Nuclear Information System (INIS)
Wang Yun
1990-01-01
We consider higher-order curvature terms in context of the Brans-Dicke theory of gravity, and investigate the effects of these terms on extended inflationary theories. We find that the higher-order curvature terms tend to speed up inflation, although the original extended-inflation solutions are stable when these terms are small. Analytical solutions are found for two extreme cases: when the higher-order curvature terms are small, and when they dominate. A conformal transformation is employed in solving the latter case, and some of the subtleties in this technique are discussed. We note that percolation is less likely to occur when the higher-order curvature terms are present. An upper bound on α is expected if we are to avoid excessive and inadequate percolation of true-vacuum bubbles
Constant scalar curvature hypersurfaces in extended Schwarzschild space-time
International Nuclear Information System (INIS)
Pareja, M. J.; Frauendiener, J.
2006-01-01
We present a class of spherically symmetric hypersurfaces in the Kruskal extension of the Schwarzschild space-time. The hypersurfaces have constant negative scalar curvature, so they are hyperboloidal in the regions of space-time which are asymptotically flat
Inverse curvature flows in asymptotically Robertson Walker spaces
Kröner, Heiko
2018-04-01
In this paper we consider inverse curvature flows in a Lorentzian manifold N which is the topological product of the real numbers with a closed Riemannian manifold and equipped with a Lorentzian metric having a future singularity so that N is asymptotically Robertson Walker. The flow speeds are future directed and given by 1 / F where F is a homogeneous degree one curvature function of class (K*) of the principal curvatures, i.e. the n-th root of the Gauss curvature. We prove longtime existence of these flows and that the flow hypersurfaces converge to smooth functions when they are rescaled with a proper factor which results from the asymptotics of the metric.
Correlation between thoracolumbar curvatures and respiratory function in older adults.
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were -46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r =-0.23, P <0.05; forced vital capacity: r =-0.32, P <0.05), quiet expiration intercostal thickness ( r =-0.22, P <0.05) and deep expiration diaphragm muscle thickness ( r =-0.21, P <0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength ( r =-0.29, P <0.05) and diaphragm muscle thickness at deep inspiration ( r =-0.22, P <0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and
Curvature-driven acceleration: a utopia or a reality?
International Nuclear Information System (INIS)
Das, Sudipta; Banerjee, Narayan; Dadhich, Naresh
2006-01-01
The present work shows that a combination of nonlinear contributions from the Ricci curvature in Einstein field equations can drive a late time acceleration of expansion of the universe. The transit from the decelerated to the accelerated phase of expansion takes place smoothly without having to resort to a study of asymptotic behaviour. This result emphasizes the need for thorough and critical examination of models with nonlinear contribution from the curvature
Curvature-driven acceleration: a utopia or a reality?
Energy Technology Data Exchange (ETDEWEB)
Das, Sudipta [Relativity and Cosmology Research Centre, Department of Physics, Jadavpur University, Calcutta-700 032 (India); Banerjee, Narayan [Relativity and Cosmology Research Centre, Department of Physics, Jadavpur University, Calcutta-700 032 (India); Dadhich, Naresh [Inter University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007 (India)
2006-06-21
The present work shows that a combination of nonlinear contributions from the Ricci curvature in Einstein field equations can drive a late time acceleration of expansion of the universe. The transit from the decelerated to the accelerated phase of expansion takes place smoothly without having to resort to a study of asymptotic behaviour. This result emphasizes the need for thorough and critical examination of models with nonlinear contribution from the curvature.
Inflation in a shear-or curvature-dominated universe
International Nuclear Information System (INIS)
Steigman, G.; Turner, M.S.
1983-01-01
We show that new inflation occurs even if the universe is shear-or (negative) curvature-dominated when the phase transition begins. In such situations the size of a causally coherent region, after inflation, is only slightly smaller (by powers, but not by exponential factors) than the usual result. The creation and evolution of density perturbations is unaffected. This result is marked contrast to 'old' inflation, where shear- or curvature-domination could quench inflation. (orig.)
New energy definition for higher-curvature gravities
International Nuclear Information System (INIS)
Deser, S.; Tekin, Bayram
2007-01-01
We propose a novel but natural definition of conserved quantities for gravity models of quadratic and higher order in curvature. Based on the spatial asymptotics of curvature rather than of metric, it avoids the more egregious problems - such as zero-energy 'theorems' and failure in flat backgrounds--in this fourth-derivative realm. In D>4, the present expression indeed correctly discriminates between second-derivative Gauss-Bonnet and generic, fourth-derivative actions
Curvature reduces bending strains in the quokka femur
Directory of Open Access Journals (Sweden)
Kyle McCabe
2017-03-01
Full Text Available This study explores how curvature in the quokka femur may help to reduce bending strain during locomotion. The quokka is a small wallaby, but the curvature of the femur and the muscles active during stance phase are similar to most quadrupedal mammals. Our hypothesis is that the action of hip extensor and ankle plantarflexor muscles during stance phase place cranial bending strains that act to reduce the caudal curvature of the femur. Knee extensors and biarticular muscles that span the femur longitudinally create caudal bending strains in the caudally curved (concave caudal side bone. These opposing strains can balance each other and result in less strain on the bone. We test this idea by comparing the performance of a normally curved finite element model of the quokka femur to a digitally straightened version of the same bone. The normally curved model is indeed less strained than the straightened version. To further examine the relationship between curvature and the strains in the femoral models, we also tested an extra-curved and a reverse-curved version with the same loads. There appears to be a linear relationship between the curvature and the strains experienced by the models. These results demonstrate that longitudinal curvature in bones may be a manipulable mechanism whereby bone can induce a strain gradient to oppose strains induced by habitual loading.
Design of a curvature sensor using a flexoelectric material
Yan, X.; Huang, W. B.; Kwon, S. R.; Yang, S. R.; Jiang, X. N.; Yuan, F. G.
2013-04-01
A curvature sensor based on flexoelectricity using Ba0.64Sr0.36TiO3 (BST) material is proposed and developed in this paper. The working principle of the sensor is based on the flexoelectricity, exhibiting coupling between mechanical strain gradient and electric polarization. A BST curvature sensor is lab prepared using a conventional solid state processing method. The curvature sensing is demonstrated in four point bending tests of the beam under harmonic loads. BST sensors are attached on both side surfaces of an aluminum beam, located symmetrically with respect to its neutral axis. Analyses have shown that the epoxy bonding layer plays a critical role for curvature transfer. Consequently a shear lag effect is taken into account for extracting actual curvature from the sensor measurement. Experimental results demonstrated good linearity from the charge outputs under the frequencies tests and showed a sensor sensitivity of 30.78pC•m in comparison with 32.48pC•m from theoretical prediction. The BST sensor provides a direct curvature measure instead of using traditional strain gage through interpolation and may offer an optional avenue for on-line and in-situ structural health monitoring.
Reconstitutions of mitochondrial inner membrane remodeling.
Barbot, Mariam; Meinecke, Michael
2016-10-01
Biological membranes exhibit function-related shapes, leading to a plethora of complex and beautiful cell and cell organellar morphologies. Most if not all of these structures have evolved for a particular physiological reason. The shapes of these structures are formed by physical forces that operate on membranes. To create particular shaped cells and cell organelles, membranes must undergo deformations which are determined by the structure and elasticity of the membrane and this process is most probable driven by proteins, lipids and/or interplay of both Zimmerberg and Kozlov (2006). Therefore, an important question of current cell biology in conjunction with physics and mathematics is to elucidate the functional cause for these different membrane morphologies as well as how they are formed. One of the most peculiar membrane shapes is observed in mitochondria. These organelles are surrounded by two membranes and especially the convoluted inner membrane displays a complex ultra-structure. A molecular understanding of how this membrane is shaped is missing to a large extent. Unlike membrane remodeling in classical curvature-dependent processes like clathrin-mediated endocytosis, mitochondria are most likely shaped by integral membrane proteins. Following, we will review the current knowledge of inner mitochondrial membrane architecture and discuss recent findings and advances in understanding the factors that shape this membrane. We will address pending questions especially with regard to the experimentally challenging nature of investigating membrane bending by hydrophobic integral membrane proteins. Copyright © 2016 Elsevier Inc. All rights reserved.
DEFF Research Database (Denmark)
Gulløv, Eva
2014-01-01
The focus of this article is social divisions among preschool children in daycare centers. Based on ethnographic fieldwork in three daycare centers in Denmark, the analysis concerns young children’s social preferences. The ethnographic material shows that despite an explicit political ambition...... indicates that children’s choices of playmates run along lines of ethnic and class divisions. The article will address this pattern and analyze its causes in order to understand why such lines of divisions are to be found in an institutional context designed to overcome social inequality and prevent social...
Reflectors Made from Membranes Stretched Between Beams
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.
The Egg Carton: Theory of a Periodic Superstructure of Some Lipid Membranes
Goetz, Rüdiger; Helfrich, Wolfgang
1996-02-01
A model calculation of the square membrane superstructure of some mixed lipid bilayers is presented. It involves bending elasticity of higher than quadratic order in the principal curvatures and employs Monte Carlo simulation.
Spinal curvature and characteristics of postural change in pregnant women.
Okanishi, Natsuko; Kito, Nobuhiro; Akiyama, Mitoshi; Yamamoto, Masako
2012-07-01
Pregnant women often report complaints due to physiological and postural changes. Postural changes during pregnancy may cause low back pain and pelvic girdle pain. This study aimed to compare the characteristics of postural changes in pregnant compared with non-pregnant women. Prospective case-control study. Pregnancy care center. Fifteen women at 17-34 weeks pregnancy comprised the study group, while 10 non-pregnant female volunteers comprised the control group. Standing posture was evaluated in the sagittal plane with static digital pictures. Two angles were measured by image analysis software: (1) between the trunk and pelvis; and (2) between the trunk and lower extremity. Spinal curvature was measured with Spinal Mouse® to calculate the means of sacral inclination, thoracic and lumbar curvature and inclination. The principal components were calculated until eigenvalues surpassed 1. Three distinct factors with eigenvalues of 1.00-2.49 were identified, consistent with lumbosacral spinal curvature and inclination, thoracic spine curvature, and inclination of the body. These factors accounted for 77.2% of the total variance in posture variables. Eleven pregnant women showed postural characteristics of lumbar kyphosis and sacral posterior inclination. Body inclination showed a variety of patterns compared with those in healthy women. Spinal curvature demonstrated a tendency for lumbar kyphosis in pregnant women. Pregnancy may cause changes in spinal curvature and posture, which may in turn lead to relevant symptoms. Our data provide a basis for investigating the effects of spinal curvature and postural changes on symptoms during pregnancy. © 2012 The Authors Acta Obstetricia et Gynecologica Scandinavica© 2012 Nordic Federation of Societies of Obstetrics and Gynecology.
The speed-curvature power law of movements: a reappraisal.
Zago, Myrka; Matic, Adam; Flash, Tamar; Gomez-Marin, Alex; Lacquaniti, Francesco
2018-01-01
Several types of curvilinear movements obey approximately the so called 2/3 power law, according to which the angular speed varies proportionally to the 2/3 power of the curvature. The origin of the law is debated but it is generally thought to depend on physiological mechanisms. However, a recent paper (Marken and Shaffer, Exp Brain Res 88:685-690, 2017) claims that this power law is simply a statistical artifact, being a mathematical consequence of the way speed and curvature are calculated. Here we reject this hypothesis by showing that the speed-curvature power law of biological movements is non-trivial. First, we confirm that the power exponent varies with the shape of human drawing movements and with environmental factors. Second, we report experimental data from Drosophila larvae demonstrating that the power law does not depend on how curvature is calculated. Third, we prove that the law can be violated by means of several mathematical and physical examples. Finally, we discuss biological constraints that may underlie speed-curvature power laws discovered in empirical studies.
Surface Curvatures and Diffraction Profiles of Sagittaly Bent Laue Crystals
Energy Technology Data Exchange (ETDEWEB)
Shi, X.; Takacs, P.; Ghose, S.; Zhong, Z.; Rehak, M.L.; Kaznatcheev, K.; Dooryhee, E.
2011-05-17
The performance of a bent Laue crystal monochromator crucially depends on the sagittal and meridional bending curvatures of the crystal. To optimize the design of monochromator crystals, the surface curvatures and diffraction profiles of a set of sagittally bent Laue crystals with different aspect ratios have been studied experimentally by optical metrology and X-ray measurements. The results were confirmed with finite-element analysis using large-deformation theory. The nonlinear relationship between the curvatures necessitates an experimentally determined parameter in the theoretical modeling of the diffraction profiles. By taking into account the local stress and the aspect ratio of the sagittally bent Laue crystal, the modified analytical approach successfully predicts the rocking-curve width and the integrated reflecting power. The effect of extreme sagittal bending on the rocking curve is also discussed. To retain high reflectivity, the bending curvature should not exceed its critical value for the specified crystal geometry. Furthermore, the uniformity of the bending curvatures across the crystal surface has been examined, which suggests that the minimum crystal dimension should be approximately twice the size of the beam footprint.
Geometric curvature and phase of the Rabi model
Energy Technology Data Exchange (ETDEWEB)
Mao, Lijun; Huai, Sainan; Guo, Liping; Zhang, Yunbo, E-mail: ybzhang@sxu.edu.cn
2015-11-15
We study the geometric curvature and phase of the Rabi model. Under the rotating-wave approximation (RWA), we apply the gauge independent Berry curvature over a surface integral to calculate the Berry phase of the eigenstates for both single and two-qubit systems, which is found to be identical with the system of spin-1/2 particle in a magnetic field. We extend the idea to define a vacuum-induced geometric curvature when the system starts from an initial state with pure vacuum bosonic field. The induced geometric phase is related to the average photon number in a period which is possible to measure in the qubit–cavity system. We also calculate the geometric phase beyond the RWA and find an anomalous sudden change, which implies the breakdown of the adiabatic theorem and the Berry phases in an adiabatic cyclic evolution are ill-defined near the anti-crossing point in the spectrum.
Revisiting the curvature cancellation in forced thin sheets
Wang, Jin; Witten, Thomas
2011-03-01
We revisit the numerically observed spontaneous vanishing of mean curvature on a developable cone or ``d-cone'' made by pushing a thin elastic sheet into a circular container. The deflection of the d-cone is the distance by which the sheet is pushed into the container. We investigate the ratio of the two principal curvatures versus sheet thickness h over a wider dynamic range than was used previously, holding the deflection and radius fixed. Instead of tending towards 1 as suggested by previous work, we find that the ratio scales as h 1 / 3 . Scaling arguments and geometric variants support this h 1 / 3 finding. Thus the mean curvature does not vanish for very thin sheets as previously claimed. Supported by NSF award DMR 0820054.
Curvature affects Doppler investigation of vessels: implications for clinical practice.
Balbis, S; Roatta, S; Guiot, C
2005-01-01
In clinical practice, blood velocity estimations from Doppler examination of curved vascular segments are normally different from those of nearby straight segments. The observed "accelerations," sometimes considered as a sort of stochastic disturbances, can actually be related to very specific physical effects due to vessel curvature (i.e., the development of nonaxial velocity [NAV] components) and the spreading of the axial velocity direction in the Doppler sample volume with respect to the insonation axis. The relevant phenomena and their dependence on the radius of curvature of the vessels and on the insonation angle are investigated with a beam-vessel geometry as close as possible to clinical setting, with the simplifying assumptions of steady flow, mild vessel curvature, uniform ultrasonic beam and complete vessel insonation. The insonation angles that minimize the errors are provided on the basis of the study results.
Spinor description of the curvatures of D = 5 gauge fields
Uvarov, D. V.
2017-03-01
Spinor description of the curvatures of D = 5 Yang-Mills, Rarita-Schwinger and gravitational fields is considered. Restrictions imposed on the curvature spinors by the dynamical equations and Bianchi identities are studied. In the absence of sources symmetric curvature spinors with 2 s indices obey first-order equations that in the linearized limit reduce to Dirac-type equations for massless free fields. These equations allow for a higher-spin generalization similarly to 4 d case. Their solution in the form of the integral over Lorentz-harmonic variables parametrizing coset manifold SO(1, 4)/( SO(1,1) × ISO(3)) isomorphic to the three-sphere is considered.
a Curvature Based Adaptive Neighborhood for Individual Point Cloud Classification
He, E.; Chen, Q.; Wang, H.; Liu, X.
2017-09-01
As a key step in 3D scene analysis, point cloud classification has gained a great deal of concerns in the past few years. Due to the uneven density, noise and data missing in point cloud, how to automatically classify the point cloud with a high precision is a very challenging task. The point cloud classification process typically includes the extraction of neighborhood based statistical information and machine learning algorithms. However, the robustness of neighborhood is limited to the density and curvature of the point cloud which lead to a label noise behavior in classification results. In this paper, we proposed a curvature based adaptive neighborhood for individual point cloud classification. Our main improvement is the curvature based adaptive neighborhood method, which could derive ideal 3D point local neighborhood and enhance the separability of features. The experiment result on Oakland benchmark dataset shows that the proposed method can effectively improve the classification accuracy of point cloud.
Curvature-induced electron localization in developable Moebius-like nanostructures
Energy Technology Data Exchange (ETDEWEB)
Korte, A P; Van der Heijden, G H M, E-mail: a.korte@ucl.ac.u, E-mail: g.heijden@ucl.ac.u [Centre for Nonlinear Dynamics, University College London, Chadwick Building, Gower Street, London WC1E 6BT (United Kingdom)
2009-12-02
We study curvature effects and localization of non-interacting electrons confined to developable one-sided elastic sheets motivated by recent nanostructured origami techniques for creating and folding extremely thin membrane structures. The most famous one-sided sheet is the Moebius strip but the theory we develop allows for arbitrary linking number. Unlike previous work in the literature we do not assume a shape for the elastic structures. Rather, we find the shape by minimizing the elastic energy, i.e., solving the Euler-Lagrange equations for the bending energy functional. This shape varies with the aspect ratio of the sheet and affects the potential experienced by the particles. Depending on the link there is a number of singular points on the edge of the structure where the bending energy density goes to infinity, leading to deep potential wells. The inverse participation ratio is used to show that electrons are increasingly localized to the higher-curvature regions of the higher-width structures, where sharp creases radiating out from the singular points could form channels for particle transport. Our geometric formulation could be used to study transport properties of Moebius strips and other components in nanoscale devices.
Curvature-induced electron localization in developable Moebius-like nanostructures
International Nuclear Information System (INIS)
Korte, A P; Van der Heijden, G H M
2009-01-01
We study curvature effects and localization of non-interacting electrons confined to developable one-sided elastic sheets motivated by recent nanostructured origami techniques for creating and folding extremely thin membrane structures. The most famous one-sided sheet is the Moebius strip but the theory we develop allows for arbitrary linking number. Unlike previous work in the literature we do not assume a shape for the elastic structures. Rather, we find the shape by minimizing the elastic energy, i.e., solving the Euler-Lagrange equations for the bending energy functional. This shape varies with the aspect ratio of the sheet and affects the potential experienced by the particles. Depending on the link there is a number of singular points on the edge of the structure where the bending energy density goes to infinity, leading to deep potential wells. The inverse participation ratio is used to show that electrons are increasingly localized to the higher-curvature regions of the higher-width structures, where sharp creases radiating out from the singular points could form channels for particle transport. Our geometric formulation could be used to study transport properties of Moebius strips and other components in nanoscale devices.
Some curvature properties of quarter symmetric metric connections
International Nuclear Information System (INIS)
Rastogi, S.C.
1986-08-01
A linear connection Γ ji h with torsion tensor T j h P i -T i h P j , where T j h is an arbitrary (1,1) tensor field and P i is a 1-form, has been called a quarter-symmetric connection by Golab. Some properties of such connections have been studied by Rastogi, Mishra and Pandey, and Yano and Imai. In this paper based on the curvature tensor of quarter-symmetric metric connection we define a tensor analogous to conformal curvature tensor and study some properties of such a tensor. (author)
Vertex Normals and Face Curvatures of Triangle Meshes
Sun, Xiang
2016-08-12
This study contributes to the discrete differential geometry of triangle meshes, in combination with discrete line congruences associated with such meshes. In particular we discuss when a congruence defined by linear interpolation of vertex normals deserves to be called a ŉormal’ congruence. Our main results are a discussion of various definitions of normality, a detailed study of the geometry of such congruences, and a concept of curvatures and shape operators associated with the faces of a triangle mesh. These curvatures are compatible with both normal congruences and the Steiner formula.
The effect of anterior cruciate ligament injury on bone curvature
DEFF Research Database (Denmark)
Hunter, D J; Lohmander, Stefan; Makovey, J
2014-01-01
OBJECTIVE: Investigate the 5-year longitudinal changes in bone curvature after acute anterior cruciate ligament (ACL) injury, and identify predictors of such changes. METHODS: In the KANON-trial (ISRCTN 84752559), 111/121 young active adults with an acute ACL tear to a previously un-injured knee...... had serial 1.5 T MR images from baseline (within 5 weeks from injury) to 5 years after injury. Of these, 86 had ACL reconstruction (ACLR) performed early or delayed, 25 were treated with rehabilitation alone. Measures of articulating bone curvature were obtained from computer-assisted segmentation...
Understanding Detergent Effects on Lipid Membranes: A Model Study of Lysolipids
DEFF Research Database (Denmark)
Henriksen, Jonas Rosager; Andresen, Thomas Lars; Feldborg, Lise Nørkjær
2010-01-01
in terms of a phenomenological model based on continuum elastic theory, which yields information about the curvature-inducing properties of the LPC molecule. The results reveal: 1), an increase in the partition coefficient with increasing LPC acyl-chain length; and 2), that the degree of acyl-chain...... mismatch between LPC and POPC determines the magnitude of the membrane mechanical perturbation per LPC molecule in the membrane. Finally, the three-stage model describing detergent membrane interaction has been extended by a parameter D-MCI, which governs the membrane curvature stability in the detergent...... concentration range below the cmc-value of the LPC molecule....
Cosmological models with positive scalar spatial curvature and Λ>0
Ponce de Leon, J.
1987-12-01
Some exact spherically symmetric solutions of the Einstein field equations with Λ>0 and positive three-curvature are given. They have reasonable physical properties and represent universes which do not undergo inflation but have a non-de Sitter behaviour for large times. This paper extends some previous results in the literature. Permanent address: Apartado 2816, Caracas 1010-A, Venezuela.
Three-dimensional ultrasound palmprint recognition using curvature methods
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.
Curvature Effect and the Spectral Softening Phenomenon Detected ...
Indian Academy of Sciences (India)
1999; Kumar & Panaitescu 2000; Qin 2002; Ryde & Petrosian 2002; Kocevski et al. 2003; Qin et al. 2004). Several factors influence the curvature effect in distinct aspects. (a) The expanding motion of the fireball influences the time contraction, the Doppler effect factor, the growth of the fireball radius or enhancement of the ...
The infinite curvature limit of AdS/CFT
Alvarez, Enrique
2004-01-01
Some kinematical speculations on the infinite curvature limit of the conjectured duality of Maldacena between ten-dimensional strings living in $AdS_5\\times S_5$ and a ordinary four-dimensional quantum field theory, namely ${\\cal{N}}=4$ super Yang-Mills with gauge group SU(N) are given.
Effect of track asymmetry and curvature on shingle writing scheme
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.
Phase error correction in wavefront curvature sensing via phase retrieval
DEFF Research Database (Denmark)
Almoro, Percival; Hanson, Steen Grüner
2008-01-01
Wavefront curvature sensing with phase error correction system is carried out using phase retrieval based on a partially-developed volume speckle field. Various wavefronts are reconstructed: planar, spherical, cylindrical, and a wavefront passing through the side of a bare optical fiber. Spurious...
Frustration and curvature - Glasses and the cholesteric blue phase
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.
Axial Length/Corneal Radius of Curvature Ratio and Refractive ...
African Journals Online (AJOL)
2017-12-05
Dec 5, 2017 ... variously described as determined by the ocular biometric variables. There have been many studies on the relationship between refractive error and ocular axial length (AL), anterior chamber depth, corneal radius of curvature (CR), keratometric readings as well as other ocular biometric variables such as ...
Temperature insensitive curvature sensor based on cascading photonic crystal fiber
Fu, Guangwei; Li, Yunpu; Fu, Xinghu; Jin, Wa; Bi, Weihong
2018-03-01
A temperature insensitive curvature sensor is proposed based on cascading photonic crystal fiber. Using the arc fusion splicing method, this sensor is fabricated by cascading together a single-mode fiber (SMF), a three layers air holes structure of photonic crystal fiber (3PCF), a five layers air holes structure of photonic crystal fiber (5PCF) and a SMF in turn. So the structure SMF-3PCF-5PCF-SMF can be obtained with a total length of 20 mm. During the process of fabrication, the splicing machine parameters and the length of each optical fiber are adjusted to obtain a high sensitivity curvature sensor. The experimental results show that the curvature sensitivity is -8.40 nm/m-1 in the curvature variation range of 0-1.09 m-1, which also show good linearity. In the range of 30-90 °C, the temperature sensitivity is only about 3.24 pm/°C, indicating that the sensor is not sensitive to temperature. The sensor not only has the advantages of easy fabricating, simple structure, high sensitivity but also can solve the problem of temperature measurement cross sensitivity, so it can be used for different areas including aerospace, large-scale bridge, architectural structure health monitoring and so on.
Curvature Effect and the Spectral Softening Phenomenon Detected ...
Indian Academy of Sciences (India)
soft spectral evolution, indicating that ... this definition of observation time, basic formulas of the full curvature effect are as follows: fν(t) = 2πc2. D2( v/c) ... (d) In most cases, the temporal power law index α and the spectral power law index β will be ...
Zero mean curvature surfaces of mixed type in Minkowski space
International Nuclear Information System (INIS)
Klyachin, V A
2003-01-01
We investigate zero mean curvature surfaces in the Minkowski space R 3 1 such that their first fundamental quadratic form changes signature. Part of such a surface is space-like and part is time-like. We obtain complete information about the structure of the set of points where the surface changes type and prove the related existence and uniqueness theorems
Curvature-induced symmetry breaking in nonlinear Schrodinger models
DEFF Research Database (Denmark)
Gaididei, Yuri Borisovich; Mingaleev, S. F.; Christiansen, Peter Leth
2000-01-01
We consider a curved chain of nonlinear oscillators and show that the interplay of curvature and nonlinearity leads to a symmetry breaking when an asymmetric stationary state becomes energetically more favorable than a symmetric stationary state. We show that the energy of localized states decrea...
A quasifibration of spaces of positive scalar curvature metrics
Chernysh, Vladislav
2004-01-01
In this paper we show that for Riemannian manifolds with boundary the natural restriction map is a quasifibration between spaces of metrics of positive scalar curvature. We apply this result to study homotopy properties of spaces of such metrics on manifolds with boundary.
Axial Length/Corneal Radius of Curvature Ratio and Refractive ...
African Journals Online (AJOL)
2018-02-07
Feb 7, 2018 ... Aim/Background: Associations between axial length (AL) to corneal radius of curvature (CR) ratio and refractive status in a healthy Nigerian adult population were studied. Materials and Methods: Healthy students and members of staff of Obafemi Awolowo Teaching Hospitals Complex, Ile-Ife, South West ...
Other Earths: Search for Life and the Constant Curvature
Directory of Open Access Journals (Sweden)
Khoshyaran M. M.
2015-07-01
Full Text Available The objective of this paper is to propose a search methodology for finding other exactly similar earth like planets (or sister earths. The theory is based on space consisting of Riemann curves or highways. A mathematical model based on constant curvature, a moving frame bundle, and gravitational dynamics is introduced.
Generalized Curvature-Matter Couplings in Modified Gravity
Directory of Open Access Journals (Sweden)
Tiberiu Harko
2014-07-01
Full Text Available In this work, we review a plethora of modified theories of gravity with generalized curvature-matter couplings. The explicit nonminimal couplings, for instance, between an arbitrary function of the scalar curvature R and the Lagrangian density of matter, induces a non-vanishing covariant derivative of the energy-momentum tensor, implying non-geodesic motion and, consequently, leads to the appearance of an extra force. Applied to the cosmological context, these curvature-matter couplings lead to interesting phenomenology, where one can obtain a unified description of the cosmological epochs. We also consider the possibility that the behavior of the galactic flat rotation curves can be explained in the framework of the curvature-matter coupling models, where the extra terms in the gravitational field equations modify the equations of motion of test particles and induce a supplementary gravitational interaction. In addition to this, these models are extremely useful for describing dark energy-dark matter interactions and for explaining the late-time cosmic acceleration.
Axial Length/Corneal Radius of Curvature Ratio and Refractive ...
African Journals Online (AJOL)
Aim/Background: Associations between axial length (AL) to corneal radius of curvature (CR) ratio and refractive status in a healthy Nigerian adult population were studied. Materials and Methods: Healthy students and members of staff of Obafemi Awolowo Teaching Hospitals Complex, Ile‑Ife, South West Nigeria, free of ...
Curvature Properties of Lorentzian Manifolds with Large Isometry Groups
Energy Technology Data Exchange (ETDEWEB)
Batat, Wafaa [Ecole Normale Superieure de L' Enseignement Technique d' Oran, Departement de Mathematiques et Informatique (Algeria)], E-mail: wafa.batat@enset-oran.dz; Calvaruso, Giovanni, E-mail: giovanni.calvaruso@unile.it; Leo, Barbara De [University of Salento, Dipartimento di Matematica ' E. De Giorgi' (Italy)], E-mail: barbara.deleo@unile.it
2009-08-15
The curvature of Lorentzian manifolds (M{sup n},g), admitting a group of isometries of dimension at least 1/2n(n - 1) + 1, is completely described. Interesting behaviours are found, in particular as concerns local symmetry, local homogeneity and conformal flatness.
On the Curvature and Heat Flow on Hamiltonian Systems
Directory of Open Access Journals (Sweden)
Ohta Shin-ichi
2014-01-01
Full Text Available We develop the differential geometric and geometric analytic studies of Hamiltonian systems. Key ingredients are the curvature operator, the weighted Laplacian, and the associated Riccati equation.We prove appropriate generalizations of the Bochner-Weitzenböck formula and Laplacian comparison theorem, and study the heat flow.
The influence of curvature on film cooling performance
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.
Effect of curvature on structures and vibrations of zigzag carbon ...
Indian Academy of Sciences (India)
By determining the correlation between vibrational modes of a graphene sheet and of the nanotube, we understand how rolling of the sheet results in mixing between modes and changes in vibrational spectrum of graphene. We find that the radial breathing mode softens with decreasing curvature. We estimate thermal ...
The flow curvature method applied to canard explosion
Energy Technology Data Exchange (ETDEWEB)
Ginoux, Jean-Marc [Laboratoire Protee, IUT de Toulon, Universite du Sud, BP 20132, F-83957 La Garde cedex (France); Llibre, Jaume, E-mail: ginoux@univ-tln.fr, E-mail: jllibre@mat.uab.cat [Departament de Matematiques, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain)
2011-11-18
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. (paper)
The flow curvature method applied to canard explosion
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.
Draping Double-Layer Woven Fabrics Onto Double-Curvature ...
African Journals Online (AJOL)
Draping woven fabrics to complex parts with double curvature leads to complex redistribution and reorientation of the yarns in composites reinforced with woven preforms. To reduce the risk of fabric tearing or wrinkling we propose to use double-layer woven fabrics. This paper presents a simulation model for draping
Independent encoding of surface orientation and surface curvature.
Johnston, A; Passmore, P J
1994-11-01
Marr [(1982) Vision, San Francisco, Calif.: Freeman] proposed that we represent surface geometry in terms of a viewer-centred description of surface orientation and distance. This description is computed by a range of independent processing systems which take as input particular kinds of information present in images, like surface texture, shading, retinal disparity and motion parallax. The outputs of these modules are integrated in order to provide a unitary representation of the layout of visible surfaces. Higher order properties of surface geometry, like surface curvature, might be computed from this symbolic representation or might be encoded independently from the visual information available at the retinae. We measured surface slant and surface curvature discrimination thresholds for surface patches defined by shading, texture and retinal disparity as a function of the elevation of the illumination. We found that observers judgements about the curvature of local surface patches were too precise to be based on a symbolic representation of surface orientation and we conclude that surface curvature is computed directly from depth cues present in the retinal images.
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.
Anionic lipids and the maintenance of membrane electrostatics in eukaryotes.
Platre, Matthieu Pierre; Jaillais, Yvon
2017-02-01
A wide range of signaling processes occurs at the cell surface through the reversible association of proteins from the cytosol to the plasma membrane. Some low abundant lipids are enriched at the membrane of specific compartments and thereby contribute to the identity of cell organelles by acting as biochemical landmarks. Lipids also influence membrane biophysical properties, which emerge as an important feature in specifying cellular territories. Such parameters are crucial for signal transduction and include lipid packing, membrane curvature and electrostatics. In particular, membrane electrostatics specifies the identity of the plasma membrane inner leaflet. Membrane surface charges are carried by anionic phospholipids, however the exact nature of the lipid(s) that powers the plasma membrane electrostatic field varies among eukaryotes and has been hotly debated during the last decade. Herein, we discuss the role of anionic lipids in setting up plasma membrane electrostatics and we compare similarities and differences that were found in different eukaryotic cells.
Quantum charged rigid membrane
International Nuclear Information System (INIS)
Cordero, Ruben; Molgado, Alberto; Rojas, Efrain
2011-01-01
The early Dirac proposal to model the electron as a charged membrane is reviewed. A rigidity term, instead of the natural membrane tension, involving linearly the extrinsic curvature of the worldvolume swept out by the membrane is considered in the action modeling the bubble in the presence of an electromagnetic field. We set up this model as a genuine second-order derivative theory by considering a non-trivial boundary term which plays a relevant part in our formulation. The Lagrangian in question is linear in the bubble acceleration and by means of the Ostrogradski-Hamiltonian approach, we observed that the theory comprises the management of both first- and second-class constraints. We thus show that our second-order approach is robust allowing for a proper quantization. We found an effective quantum potential which permits us to compute bounded states for the system. We comment on the possibility of describing brane world universes by invoking this kind of second-order correction terms.
Quantum charged rigid membrane
Energy Technology Data Exchange (ETDEWEB)
Cordero, Ruben [Departamento de Fisica, Escuela Superior de Fisica y Matematicas del I.P.N., Unidad Adolfo Lopez Mateos, Edificio 9, 07738 Mexico, D.F. (Mexico); Molgado, Alberto [Unidad Academica de Fisica, Universidad Autonoma de Zacatecas, Zacatecas Zac. (Mexico); Rojas, Efrain, E-mail: cordero@esfm.ipn.mx, E-mail: amolgado@fisica.uaz.edu.mx, E-mail: efrojas@uv.mx [Departamento de Fisica, Facultad de Fisica e Inteligencia Artificial, Universidad Veracruzana, 91000 Xalapa, Veracruz (Mexico)
2011-03-21
The early Dirac proposal to model the electron as a charged membrane is reviewed. A rigidity term, instead of the natural membrane tension, involving linearly the extrinsic curvature of the worldvolume swept out by the membrane is considered in the action modeling the bubble in the presence of an electromagnetic field. We set up this model as a genuine second-order derivative theory by considering a non-trivial boundary term which plays a relevant part in our formulation. The Lagrangian in question is linear in the bubble acceleration and by means of the Ostrogradski-Hamiltonian approach, we observed that the theory comprises the management of both first- and second-class constraints. We thus show that our second-order approach is robust allowing for a proper quantization. We found an effective quantum potential which permits us to compute bounded states for the system. We comment on the possibility of describing brane world universes by invoking this kind of second-order correction terms.
VIERS- User Preference Service
Department of Veterans Affairs — The Preferences service provides a means to store, retrieve, and manage user preferences. The service supports definition of enterprise wide preferences, as well as...
Broaden Students' Music Preferences.
Le Blanc, Albert
1983-01-01
A model of music preference theory suggests ways that teachers can broaden their students' musical preferences. Teachers can change preferences by changing something in the listener, the social environment, the music, or the ways that the listener processes information. (AM)
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.
Physical and Geometric Interpretations of the Riemann Tensor, Ricci Tensor, and Scalar Curvature
Loveridge, Lee C.
2004-01-01
Various interpretations of the Riemann Curvature Tensor, Ricci Tensor, and Scalar Curvature are described. Also, the physical meanings of the Einstein Tensor and Einstein's Equations are discussed. Finally a derivation of Newtonian Gravity from Einstein's Equations is given.
Deciphering the BAR code of membrane modulators.
Salzer, Ulrich; Kostan, Julius; Djinović-Carugo, Kristina
2017-07-01
The BAR domain is the eponymous domain of the "BAR-domain protein superfamily", a large and diverse set of mostly multi-domain proteins that play eminent roles at the membrane cytoskeleton interface. BAR domain homodimers are the functional units that peripherally associate with lipid membranes and are involved in membrane sculpting activities. Differences in their intrinsic curvatures and lipid-binding properties account for a large variety in membrane modulating properties. Membrane activities of BAR domains are further modified and regulated by intramolecular or inter-subunit domains, by intermolecular protein interactions, and by posttranslational modifications. Rather than providing detailed cell biological information on single members of this superfamily, this review focuses on biochemical, biophysical, and structural aspects and on recent findings that paradigmatically promote our understanding of processes driven and modulated by BAR domains.
DEFF Research Database (Denmark)
Bendix, Pól Martin
2015-01-01
At Stanford University, Boxer lab, I worked on membrane fusion of small unilamellar lipid vesicles to flat membranes tethered to glass surfaces. This geometry closely resembles biological systems in which liposomes fuse to plasma membranes. The fusion mechanism was studied using DNA zippering...... between complementary strands linked to the two apposing membranes closely mimicking the zippering mechanism of SNARE fusion complexes....
Koenders, E.A.B.; Zlopasa, J.; Picken, S.J.
2015-01-01
The present invention is in the field of a composition for forming a bio-compatible membrane applicable to building material, such as concrete, cement, etc., to a meth od of applying said composition for forming a bio-compatible membrane, a biocompatible membrane, use of said membrane for various
A 1 + 5-dimensional gravitational-wave solution. Curvature singularity and spacetime singularity
International Nuclear Information System (INIS)
Chen, Yu-Zhu; Li, Wen-Du; Dai, Wu-Sheng
2017-01-01
We solve a 1 + 5-dimensional cylindrical gravitational-wave solution of the Einstein equation, in which there are two curvature singularities. Then we show that one of the curvature singularities can be removed by an extension of the spacetime. The result exemplifies that the curvature singularity is not always a spacetime singularity; in other words, the curvature singularity cannot serve as a criterion for spacetime singularities. (orig.)
A 1 + 5-dimensional gravitational-wave solution. Curvature singularity and spacetime singularity
Energy Technology Data Exchange (ETDEWEB)
Chen, Yu-Zhu [Tianjin University, Department of Physics, Tianjin (China); Li, Wen-Du [Tianjin University, Department of Physics, Tianjin (China); Nankai University, Theoretical Physics Division, Chern Institute of Mathematics, Tianjin (China); Dai, Wu-Sheng [Nankai University, Theoretical Physics Division, Chern Institute of Mathematics, Tianjin (China); Nankai University and Tianjin University, LiuHui Center for Applied Mathematics, Tianjin (China)
2017-12-15
We solve a 1 + 5-dimensional cylindrical gravitational-wave solution of the Einstein equation, in which there are two curvature singularities. Then we show that one of the curvature singularities can be removed by an extension of the spacetime. The result exemplifies that the curvature singularity is not always a spacetime singularity; in other words, the curvature singularity cannot serve as a criterion for spacetime singularities. (orig.)
Constant curvature black hole and dual field theory
Cai, Rong-, Gen
2002-09-01
We consider a five-dimensional constant curvature black hole, which is constructed by identifying some points along a Killing vector in a five-dimensional AdS space. The black hole has the topology M4×S1, its exterior is time-dependent and its boundary metric is of the form of a three-dimensional de Sitter space times a circle, which means that the dual conformal field theory resides on a dynamical spacetime. We calculate the quasilocal stress-energy tensor of the gravitational background and then the stress-energy tenor of the dual conformal field theory. It is found that the trace of the tensor does indeed vanish, as expected. Further we find that the constant curvature black hole spacetime is just the “bubble of nothing” resulting from Schwarzschild-AdS black holes when the mass parameter of the latter vanishes.
Substrate Curvature Regulates Cell Migration -A Computational Study
He, Xiuxiu; Jiang, Yi
Cell migration in host microenvironment is essential to cancer etiology, progression and metastasis. Cellular processes of adhesion, cytoskeletal polymerization, contraction, and matrix remodeling act in concert to regulate cell migration, while local extracellular matrix architecture modulate these processes. In this work we study how stromal microenvironment with native and cell-derived curvature at micron-meter scale regulate cell motility pattern. We developed a 3D model of single cell migration on a curved substrate. Mathematical analysis of cell morphological adaption to the cell-substrate interface shows that cell migration on convex surfaces deforms more than on concave surfaces. Both analytical and simulation results show that curved surfaces regulate the cell motile force for cell's protruding front through force balance with focal adhesion and cell contraction. We also found that cell migration on concave substrates is more persistent. These results offer a novel biomechanical explanation to substrate curvature regulation of cell migration. NIH 1U01CA143069.
On M-theory fourfold vacua with higher curvature terms
Directory of Open Access Journals (Sweden)
Thomas W. Grimm
2015-04-01
Full Text Available We study solutions to the eleven-dimensional supergravity action, including terms quartic and cubic in the Riemann curvature, that admit an eight-dimensional compact space. The internal background is found to be a conformally Kähler manifold with vanishing first Chern class. The metric solution, however, is non-Ricci-flat even when allowing for a conformal rescaling including the warp factor. This deviation is due to the possible non-harmonicity of the third Chern-form in the leading order Ricci-flat metric. We present a systematic derivation of the background solution by solving the Killing spinor conditions including higher curvature terms. These are translated into first-order differential equations for a globally defined real two-form and complex four-form on the fourfold. We comment on the supersymmetry properties of the described solutions.
Generating ekpyrotic curvature perturbations before the big bang
International Nuclear Information System (INIS)
Lehners, Jean-Luc; Turok, Neil; McFadden, Paul; Steinhardt, Paul J.
2007-01-01
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 s tends to range from slightly blue to red, with 0.97 s <1.02 for the simplest models, a range compatible with current observations but shifted by a few percent towards the blue compared to the prediction of the simplest, large-field inflationary models
Non-linear realizations and higher curvature supergravity
Energy Technology Data Exchange (ETDEWEB)
Farakos, F. [Dipartimento di Fisica e Astronomia ' ' Galileo Galilei' ' , Universita di Padova (Italy); INFN, Sezione di Padova (Italy); Ferrara, S. [Department of Theoretical Physics, Geneva (Switzerland); INFN - Laboratori Nazionali di Frascati, Frascati (Italy); Department of Physics and Astronomy, Mani L. Bhaumik Institute for Theoretical Physics, U.C.L.A., Los Angeles, CA (United States); Kehagias, A. [Physics Division, National Technical University of Athens (Greece); Luest, D. [Arnold Sommerfeld Center for Theoretical Physics, Muenchen (Germany); Max-Planck-Institut fuer Physik, Muenchen (Germany)
2017-12-15
We focus on non-linear realizations of local supersymmetry as obtained by using constrained superfields in supergravity. New constraints, beyond those of rigid supersymmetry, are obtained whenever curvature multiplets are affected as well as higher derivative interactions are introduced. In particular, a new constraint, which removes a very massive gravitino is introduced, and in the rigid limit it merely reduces to an explicit supersymmetry breaking. Higher curvature supergravities free of ghosts and instabilities are also obtained in this way. Finally, we consider direct coupling of the goldstino multiplet to the super Gauss-Bonnet multiplet and discuss the emergence of a new scalar degree of freedom. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Curvature effects in carbon nanomaterials: Exohedral versus endohedral supercapacitors
Energy Technology Data Exchange (ETDEWEB)
Huang, Jingsong [ORNL; Sumpter, Bobby G [ORNL; Meunier, Vincent [ORNL; Gogotsi, Yury G. [Drexel University; Yushin, Gleb [Georgia Institute of Technology; Portet, Cristelle [Drexel University
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.
Curvature effects on carbon nanomaterials: Exohedral versus endhohedral supercapacitors
Energy Technology Data Exchange (ETDEWEB)
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.
Thermodynamic curvature of soft-sphere fluids and solids
Brańka, A. C.; Pieprzyk, S.; Heyes, D. M.
2018-02-01
The influence of the strength of repulsion between particles on the thermodynamic curvature scalar R for the fluid and solid states is investigated for particles interacting with the inverse power (r-n) potential, where r is the pair separation and 1 /n is the softness. Exact results are obtained for R in certain limiting cases, and the R behavior determined for the systems in the fluid and solid phases. It is found that in such systems the thermodynamic curvature can be positive for very soft particles, negative for steeply repulsive (or large n ) particles across almost the entire density range, and can change sign between negative and positive at a certain density. The relationship between R and the form of the interaction potential is more complex than previously suggested, and it may be that R is an indicator of the relative importance of energy and entropy contributions to the thermodynamic properties of the system.
DNA Origami with Complex Curvatures in Three-Dimensional Space
Energy Technology Data Exchange (ETDEWEB)
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.
The Lp Lp Lp-curvature images of convex bodies and Lp Lp Lp ...
Indian Academy of Sciences (India)
Associated with the Lp-curvature image defined by Lutwak, some inequali- ties for extended mixed p-affine surface areas of ... p = 1, this definition of curvature image differs from the definition used by him in [6–8]. The p-curvature image plays an .... unique up to translation, such thatSL = μ. Thus, given a continuous function f ...
Remarks on the boundary curve of a constant mean curvature topological disc
DEFF Research Database (Denmark)
Brander, David; Lopéz, Rafael
2017-01-01
We discuss some consequences of the existence of the holomorphic quadratic Hopf differential on a conformally immersed constant mean curvature topological disc with analytic boundary. In particular, we derive a formula for the mean curvature as a weighted average of the normal curvature...
On Ricci curvature of C-totally real submanifolds in Sasakian space ...
Indian Academy of Sciences (India)
Springer Verlag Heidelberg #4 2048 1996 Dec 15 10:16:45
Keywords. Ricci curvature; C-totally real submanifold; Sasakian space form. 1. Introduction. Let Mn be a Riemannian n-manifold isometrically immersed in a Riemannian m-manifold. ¯Mm(c) of constant sectional curvature c. Denote by g, R and h the metric tensor, Riemann curvature tensor and the second fundamental form ...
Two-Sided Gravitational Mirror: Sealing off Curvature Singularities
Davidson, Aharon; Yellin, Ben
2011-01-01
A gravitational mirror is a non-singular finite redshift surface which bounces all incident null geodesics. While a white mirror (outward bouncing) resembles 't Hooft's brick wall, a black mirror (inward bouncing) offers a novel mechanism for sealing off curvature singularities. The geometry underlying a two-sided mirror is characterized by a single signature change, to be contrasted with the signature flip which governs the black hole geometry. To demonstrate the phenomenon analytically, we ...
On the concircular curvature tensor of Riemannian manifolds
International Nuclear Information System (INIS)
Rahman, M.S.; Lal, S.
1990-06-01
Definition of the concircular curvature tensor, Z hijk , along with Z-tensor, Z ij , is given and some properties of Z hijk are described. Tensors identical with Z hijk are shown. A necessary and sufficient condition that a Riemannian V n has zero Z-tensor is found. A number of theorems on concircular symmetric space, concircular recurrent space (Z n -space) and Z n -space with zero Z-tensor are deduced. (author). 6 refs
The primordial curvature perturbation in the ekpyrotic Universe
Lyth, David H
2002-01-01
In the ekpyrotic scenario the Universe is initially collapsing, the energy density coming from a scalar field with a negative exponential potential. On the basis of a calculation ignoring the gravitational back-reaction the authors of the scenario claim that during collapse the vacuum fluctuation creates a perturbation in the comoving curvature, which has a flat spectrum in accordance with observation. In this note the back-reaction is included, and it is found that the spectrum during collap...
Intrinsic DNA curvature of double-crossover tiles.
Kim, Seungjae; Kim, Junghoon; Qian, Pengfei; Shin, Jihoon; Amin, Rashid; Ahn, Sang Jung; LaBean, Thomas H; Kim, Moon Ki; Park, Sung Ha
2011-06-17
A theoretical model which takes into account the structural distortion of double-crossover DNA tiles has been studied to investigate its effect on lattice formation sizes. It has been found that a single vector appropriately describes the curvature of the tiles, of which a higher magnitude hinders lattice growth. In conjunction with these calculations, normal mode analysis reveals that tiles with relative higher frequencies have an analogous effect. All the theoretical results are shown to be in good agreement with experimental data.
Abdus Salam and quadratic curvature gravity: Classical solutions
Stelle, K. S.
2017-03-01
In 1978, Salam and Strathdee suggested on the basis of Froissart boundedness that curvature-squared terms should be included in the gravitational Lagrangian. Despite the presence of ghosts in such theories, the subject has remained a persistent topic in approaches to quantum gravity and cosmology. In this article, the space of spherically symmetric solutions to such theories is explored, highlighting horizonless solutions, wormholes and non-Schwarzschild black holes.
The Imaginary Starobinsky Model and Higher Curvature Corrections
Ferrara, Sergio; Riotto, Antonio
2015-01-01
We elaborate on the predictions of the imaginary Starobinsky model of inflation coupled to matter, where the inflaton is identified with the imaginary part of the inflaton multiplet suggested by the Supergravity embedding of a pure R + R^2 gravity. In particular, we study the impact of higher-order curvature terms and show that, depending on the parameter range, one may find either a quadratic model of chaotic inflation or monomial models of chaotic inflation with fractional powers between 1 and 2.
Curvature of super Diff(S1)/S1
International Nuclear Information System (INIS)
Oh, P.; Ramond, P.
1987-01-01
Motivated by the work of Bowick and Rajeev, we calculate the curvature of the infinite-dimensional flag manifolds Diff(S 1 )/S 1 and Super Diff(S 1 )/S 1 using standard finite-dimensional coset space techniques. We regularize the infinite by ζ-function regularization and recover the conformal and superconformal anomalies respectively for a specific choice of the torsion. (orig.)
Torsion and curvature in higher dimensional supergravity theories
International Nuclear Information System (INIS)
Smith, A.W.; Pontificia Univ. Catolica do Rio de Janeiro
1983-01-01
This work is an extension of Dragon's theorems to higher dimensional space-time. It is shown that the first set of Bianchi identities allow us to express the curvature components in terms of torsion components and its covariant derivatives. It is also shown that the second set of Bianchi identities does not give any new information which is not already contained in the first one. (Author) [pt
Boundary curvature effects on gas bubble oscillations in underwater explosion
Matsumoto, Kazuhiro
1996-01-01
The oscillation of a gas bubble produced as a result of underwater explosion could cause the severe whipping damage on nearby marine vehicle. The effects of rigid boundary curvatures to explosive gas bubble oscillation behavior in underwater were investigated. The analyses were conducted using a multimaterial Lagrangian-Eulerian finite element code, MSC/DYTRAN. The incident shock wave pressure, bubble pulse pressure, gas bubble radius and period were calculated for the case of detonation of a...
Mechanosensitivity of cell membranes. Ion channels, lipid matrix and cytoskeleton.
Petrov, A G; Usherwood, P N
1994-01-01
Physical and biophysical mechanisms of mechano-sensitivity of cell membranes are reviewed. The possible roles of the lipid matrix and of the cytoskeleton in membrane mechanoreception are discussed. Techniques for generation of static strains and dynamic curvatures of membrane patches are considered. A unified model for stress-activated and stress-inactivated ion channels under static strains is described. A review of work on stress-sensitive pores in lipid-peptide model membranes is presented. The possible role of flexoelectricity in mechano-electric transduction, e.g. in auditory receptors is discussed. Studies of flexoelectricity in model lipid membranes, lipid-peptide membranes and natural membranes containing ion channels are reviewed. Finally, possible applications in molecular electronics of mechanosensors employing some of the recognized principles of mechano-electric transduction in natural membranes are discussed.
Factors affecting root curvature of mandibular first molar
International Nuclear Information System (INIS)
Choi, Hang Moon; Yi, Won Jin; Heo, Min Suk; Kim, Jung Hwa; Choi, Soon Chul; Park, Tae Won
2006-01-01
To find the cause of root curvature by use of panoramic and lateral cephalometric radiograph. Twenty six 1st graders whose mandibular 1st molars just emerged into the mouth were selected. Panoramic and lateral cephalometric radiograph were taken at grade 1 and 6, longitudinally. In cephalometric radio graph, mandibular plane angle, ramus-occlusal place angle, gonial angle, and gonion-gnathion distance(Go-Gn distance) were measured. In panoramic radiograph, elongated root length and root angle were measured by means of digital subtraction radiography. Occlusal plane-tooth axis angle was measured, too. Pearson correlations were used to evaluate the relationships between root curvature and elongated length and longitudinal variations of all variables. Multiple regression equation using related variables was computed. The pearson correlation coefficient between curved angle and longitudinal variations of occlusal plane-tooth axis angle and ramus-occlusal plane angle was 0.350 and 0.401, respectively (p 1 +0.745X 2 (Y: root angle, X 1 : variation of occlusal plane-tooth axis angle, X 2 : variation of ramus-occlusal plane angle). It was suspected that the reasons of root curvature were change of tooth axis caused by contact with 2nd deciduous tooth and amount of mesial and superior movement related to change of occlusal plane
Curvature profiles as initial conditions for primordial black hole formation
International Nuclear Information System (INIS)
Polnarev, Alexander G; Musco, Ilia
2007-01-01
This work is part of an ongoing research programme to study possible primordial black hole (PBH) formation during the radiation-dominated era of the early universe. Working within spherical symmetry, we specify an initial configuration in terms of a curvature profile, which represents initial conditions for the large amplitude metric perturbations, away from the homogeneous Friedmann-Robertson-Walker model, which are required for PBH formation. Using an asymptotic quasi-homogeneous solution, we relate the curvature profile with the density and velocity fields, which at an early enough time, when the length scale of the configuration is much larger than the cosmological horizon, can be treated as small perturbations of the background values. We present general analytic solutions for the density and velocity profiles. These solutions enable us to consider in a self-consistent way the formation of PBHs in a wide variety of cosmological situations with the cosmological fluid being treated as an arbitrary mixture of different components with different equations of state. We obtain the analytical solutions for the density and velocity profiles as functions of the initial time. We then use two different parametrizations for the curvature profile and follow numerically the evolution of initial configurations
Patterned Cell Alignment in Response to Macroscale Curvature
Bade, Nathan; Kamien, Randall; Assoian, Richard; Stebe, Kathleen
The formation of spatial behavior patterns in tissues is a long-standing problem in biology. Decades of research have focused on understanding how biochemical signaling and morphogen gradients establish cell patterns during development and tissue morphogenesis. Here, we show that geometry and physical cues can drive organization and pattern formation. We find that mouse embryonic fibroblasts and human vascular smooth muscle cells sense curvature differently when in monolayers than when isolated on surfaces with various amounts of Gaussian curvature. While the long, apical stress fibers within these cells align in the direction of minimum curvature on cylindrical substrates, a subpopulation of stress fibers beneath the nucleus aligns in the circumferential direction and is bent maximally. We find dramatic reorganization of the actin cytoskeleton upon activation of RhoA, which is associated with increased contractility of the fibers. Thus, stress fiber alignment is likely a result of a complex balance between energy penalties associated with stress fiber bending, contractility, and the dynamics of F-actin assembly.
Anteroposterior curvatures of the spine in adolescent athletes.
Grabara, Małgorzata
2014-01-01
To assess the shape of anteroposterior vertebral curvatures in adolescents who practice team sports. 57 females and 104 males aged 14-17 years, playing volleyball, basketball or handball, and 63 females and 99 males as a control group. A Rippstein plurimeter was used to measure the angles of thoracic kyphosis and lumbar lordosis. The study has revealed significant differences in lumbar lordosis in male athletes compared to the control (p=0.01). Male volleyball players had greater thoracic kyphosis (p=0.002) than basketball players. Female athletes had lower thoracic kyphosis than the control group (p < 0.01). Normal values of thoracic kyphosis were more frequent in female athletes and male handball players whereas normal lumbar lordosis was more frequently seen in female volleyball players and male control group. Our investigations revealed significant (p < 0.05) correlations between the anteroposterior curvature of the spine and somatic parameters. Differences in thoracic kyphosis or lumbar lordosis among the athletes and the control group might be due to postural muscles strengthening as a result of regular engagement in intensive exercise. The variability of anteroposterior spine curvatures may not only be associated with directional physical activity; some contribution of the somatic structure is also possible.
Generic Properties of Curvature Sensing through Vision and Touch
Directory of Open Access Journals (Sweden)
Birgitta Dresp-Langley
2013-01-01
Full Text Available 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.
Curvature dependance of blob dynamics in TJ-K
Energy Technology Data Exchange (ETDEWEB)
Garland, Stephen; Ramisch, Mirko [Institut fuer Grenzflaechenverfahrenstechnik und Plasmatechnologie, Universitaet Stuttgart (Germany); Fuchert, Golo [Institut Jean Lamour, Universite de Lorraine (France)
2014-07-01
Turbulent transport in the scrape-off layer (SOL) is an important area of investigation in magnetic confinement fusion research. Relatively dense and hot, field-aligned, filament-like structures (blobs) have been observed to propagate radially through the SOL in many fusion devices, and contribute significantly to SOL transport. The torsatron TJ-K operates with a low-temperature plasma, allowing Langmuir probe measurements in the entire plasma volume. Despite the low temperature, investigations are relevant to fusion research due to dimensionless plasma parameters similar to those in the edge region of fusion plasmas. Analytical blob models link blob velocity in the SOL to blob polarisation, which can be driven by magnetic field line curvature. In TJ-K, average blob dynamics can be studied in detail using a 2D movable probe and a conditional averaging technique. In addition, a fast camera can be used to supplement probe data, and provide information on individual blob trajectories. With these tools, the connection between magnetic field line curvature and the poloidal component of blob velocity has been studied. Taking into account background E x B flows, initial investigations suggest a correlation between the poloidal component of blob velocity and averaged geodesic magnetic field line curvature.
Localized tearing modes in the magnetotail driven by curvature effects
Energy Technology Data Exchange (ETDEWEB)
Sundaram, A.K.; Fairfield, D.H. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)
1995-03-01
The stability of collisionless tearing modes is examined in the presence of curvature drift resonances and the trapped particle effects. A kinetic description for both electrons and ions is employed to investigate the stability of a two-dimensional equilibrium model. The main features of the study are to treat the ion dynamics properly by incorporating effects associated with particle trajectories in the tail fields and to include the linear coupling of trapped particle modes. Generalized dispersion relations are derived in several parameter regimes by considering two important sublayers of the reconnecting region. For a typical choice of parameters appropriate to the current sheet region, the authors demonstrate that localized tearing modes driven by ion curvature drift resonance effects are excited in the current sheet region with growth time of the order of a few seconds. Also, they examine nonlocal characteristics of tearing modes driven by curvature effects and show that modes growing in a fraction of a second arise when mode widths are larger than the current sheet width. Further, they show that trapped particle effects, in an interesting frequency regime, significantly enhance the growth rate of the tearing mode. The relevance of this theory for substorm onset phase and other features of the substorms is briefly discussed. 38 refs.
DEFF Research Database (Denmark)
Loubet, Bastien; Hansen, Per Lyngs; Lomholt, Michael Andersen
2013-01-01
We investigate the electrostatic contribution to the lipid membrane mechanical parameters: tension, bending rigidity, spontaneous curvature, and ﬂexocoefﬁcient, using an approach where stress in the membrane is explicitly balanced. Our model includes an applied electrostatic potential as well as ...
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…
Directory of Open Access Journals (Sweden)
Wang Jing-Feng
Full Text Available 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.
A sensor for the direct measurement of curvature based on flexoelectricity
International Nuclear Information System (INIS)
Yan, Xiang; Huang, Wenbin; Ryung Kwon, Seol; Yang, Shaorui; Jiang, Xiaoning; Yuan, Fuh-Gwo
2013-01-01
A direct curvature sensing measurement based on the flexoelectricity of Ba 0.64 Sr 0.36 TiO 3 (BST) material through electromechanical coupling is proposed and developed in this paper. The curvature sensing was demonstrated in four point bending tests of a beam with bonded BST curvature sensors under different applied loads with low time-harmonic frequencies from 0.5 to 3 Hz. A shear lag concept which describes the efficiency of the loading transfer from the epoxy bonding layer was taken into account in extracting the actual curvature from the sensor measurement. A finite element analysis has been performed to estimate the curvature transfer efficiency and the bonding layer thickness is found to be a critical parameter in determining the curvature transfer. Experimental results showed a good linearity of charge output dependence on curvature inputs in a limited frequency range and showed a curvature sensitivity of 30.78 pC m, in comparison with 32.48 pC m from theoretical predictions. Using the measured curvature, the bending stiffness of the beam was then obtained from the experimentally obtained moment–curvature curve. This work demonstrated that the flexoelectric BST sensor provides a direct curvature measurement instead of using a traditional strain gage sensor through interpolation, and thus offers an important avenue for on-line and in situ structural health monitoring. (paper)
A sensor for the direct measurement of curvature based on flexoelectricity
Yan, Xiang; Huang, Wenbin; Ryung Kwon, Seol; Yang, Shaorui; Jiang, Xiaoning; Yuan, Fuh-Gwo
2013-08-01
A direct curvature sensing measurement based on the flexoelectricity of Ba0.64Sr0.36TiO3 (BST) material through electromechanical coupling is proposed and developed in this paper. The curvature sensing was demonstrated in four point bending tests of a beam with bonded BST curvature sensors under different applied loads with low time-harmonic frequencies from 0.5 to 3 Hz. A shear lag concept which describes the efficiency of the loading transfer from the epoxy bonding layer was taken into account in extracting the actual curvature from the sensor measurement. A finite element analysis has been performed to estimate the curvature transfer efficiency and the bonding layer thickness is found to be a critical parameter in determining the curvature transfer. Experimental results showed a good linearity of charge output dependence on curvature inputs in a limited frequency range and showed a curvature sensitivity of 30.78 pC m, in comparison with 32.48 pC m from theoretical predictions. Using the measured curvature, the bending stiffness of the beam was then obtained from the experimentally obtained moment-curvature curve. This work demonstrated that the flexoelectric BST sensor provides a direct curvature measurement instead of using a traditional strain gage sensor through interpolation, and thus offers an important avenue for on-line and in situ structural health monitoring.
Spreading and contraction in phagocytosis: The role of actin organization and curvature
Curtis, Jennifer E.
Phagocytosis is the process used by immune cells to engulf and remove foreign objects from the body. The engulfment is realized by the formation of an actin-driven `phagocytic cup' of the cell membrane, which quickly crawls up and then surrounds the object via constriction. In this study, we resolve the paradox of how actin-driven protrusion of the plasma membrane can co-exist with a contractile actin belt proposed to mechanically-drive the closure of the phagocytic cup. To do this we quantitatively assessed macrophage phagocytic behavior in a planar geometry, a process known as frustrated phagocytosis. Our results reveal that phagocytosis occurs in a binary manner, such that once it is initiated, frustrated phagocytosis proceeds at a prescribed rate, resulting in peak contact areas that correspond to a roughly 225% increase in apparent cell surface area. Upon reaching their maximum area, the majority of macrophages enter a period of late-stage contraction. During the contraction phase, cells exert significant stress on the underlying substrate. Contraction also corresponds with dramatic reorganization of the F-actin cytoskeleton, in particular the formation of a bundled contractile belt around the cell perimeter. In contrast to other studies of phagocytosis, our work definitively illustrates that whatever signals trigger late-stage phagocytic contraction must be independent of particle size and curvature. Mounting evidence suggests that membrane tension is involved in late-stage signaling. The idea that tension is linked to late-stage contraction is reinforced by our finding that the peak-contact area roughly corresponds to the area threshold that results in increased cortical tension, as measured by Lam et al., and that reducing tension through hypertonic buffer shock enables the cells to spread further before the onset of contraction. Supported by NSF Grants #PHYS-0848797 and SRN-POLS 1205878.
... check for hepatitis B, hepatitis C, and syphilis Complement levels Cryoglobulin test Treatment The goal of treatment ... not as helpful for people with membranous nephropathy. Medicines used treat membranous nephropathy include: Angiotensin-converting enzyme ( ...
Spheres of influence: Porphyromonas gingivalis outer membrane vesicles.
Gui, M J; Dashper, S G; Slakeski, N; Chen, Y-Y; Reynolds, E C
2016-10-01
Outer membrane vesicles (OMVs) are asymmetrical single bilayer membranous nanostructures produced by Gram-negative bacteria important for bacterial interaction with the environment. Porphyromonas gingivalis, a keystone pathogen associated with chronic periodontitis, produces OMVs that act as a virulence factor secretion system contributing to its pathogenicity. Despite their biological importance, the mechanisms of OMV biogenesis have not been fully elucidated. The ~14 times more curvature of the OMV membrane than cell outer membrane (OM) indicates that OMV biogenesis requires energy expenditure for significant curvature of the OMV membrane. In P. gingivalis, we propose that this may be achieved by upregulating the production of certain inner or outer leaflet lipids, which causes localized outward curvature of the OM. This results in selection of anionic lipopolysaccharide (A-LPS) and associated C-terminal domain (CTD) -family proteins on the outer surface due to their ability to accommodate the curvature. Deacylation of A-LPS may further enable increased curvature leading to OMV formation. Porphyromonas gingivalis OMVs that are selectively enriched in CTD-family proteins, largely the gingipains, can support bacterial coaggregation, promote biofilm development and act as an intercessor for the transport of non-motile bacteria by motile bacteria. The P. gingivalis OMVs are also believed to contribute to host interaction and colonization, evasion of immune defense mechanisms, and destruction of periodontal tissues. They may be crucial for both micro- and macronutrient capture, especially heme and probably other assimilable compounds for its own benefit and that of the wider biofilm community. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
Membrane-mediated interaction between strongly anisotropic protein scaffolds.
Directory of Open Access Journals (Sweden)
Yonatan Schweitzer
2015-02-01
Full Text Available 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.
An Improved Method to Measure the Cosmic Curvature
Energy Technology Data Exchange (ETDEWEB)
Wei, Jun-Jie; Wu, Xue-Feng, E-mail: jjwei@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
2017-04-01
In this paper, we propose an improved model-independent method to constrain the cosmic curvature by combining the most recent Hubble parameter H ( z ) and supernovae Ia (SNe Ia) data. Based on the H ( z ) data, we first use the model-independent smoothing technique, Gaussian processes, to construct a distance modulus μ {sub H} ( z ), which is susceptible to the cosmic curvature parameter Ω{sub k}. In contrary to previous studies, the light-curve-fitting parameters, which account for the distance estimation of SN (μ {sub SN}( z )), are set free to investigate whether Ω {sub k} has a dependence on them. By comparing μ {sub H} ( z ) to μ {sub SN}(z), we put limits on Ω {sub k}. Our results confirm that Ω {sub k} is independent of the SN light-curve parameters. Moreover, we show that the measured Ω {sub k} is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat universe at the current observational data level. We also test the influence of different H(z) samples and different Hubble constant H {sub 0} values, finding that different H(z) samples do not have a significant impact on the constraints. However, different H {sub 0} priors can affect the constraints of Ω {sub k} to some degree. The prior of H {sub 0} = 73.24 ± 1.74 km s{sup −1} Mpc{sup −1} gives a value of Ω {sub k}, a little bit above the 1 σ confidence level away from 0, but H{sub 0} = 69.6 ± 0.7 km s{sup −1} Mpc{sup −1} gives it below 1 σ .
Pelvic Floor Symptoms and Spinal Curvature in Women
Meyer, Isuzu; McArthur, Tatum A; Tang, Ying; McKinney, Jessica L; Morgan, Sarah L; Richter, Holly E
2016-01-01
Objectives To characterize the association between thoracic (T) and lumbar (L) spinal curvature and pelvic floor (PF) symptoms (pelvic organ prolapse [POP], urinary incontinence [UI], fecal incontinence [FI]). Methods Of women undergoing a bone mineral density scan from 1/2007 to 10/2010, patients who completed PF symptom questionnaires and had T and/or L spine radiographs or computerized tomography (CT) exams within 3 years of questionnaire completion were included in this study. The spine angles were measured using the Cobb angle method. The T and L curvature were categorized as hypo-kyphosis (40°), hypo-lordosis (70°). The presence and type of UI were identified with the 3 Incontinence Questionnaire and FI with the Modified Manchester Questionnaire. POP was defined as a positive response to the presence of a bulge question from the PF Distress Inventory-20. Results Of 1665 eligible women, 824 and 302 (mean age 64±10 for both) had T and L spine images, respectively. No differences in PF symptoms were observed in the T or L spine groups categorized by hypo-, normal, and hyper-kyphosis/lordosis except for urgency UI being more prevalent in the hypo-lordosis group (p=0.01). However, upon further characterization using logistic regression, no association was noted between PF symptoms and T or L spine angles; no differences in the mean angles were found between women with versus without PF symptoms (p≥0.05). Conclusions The current study shows that the thoracic and lumbar spinal curvature is not associated with the presence of pelvic floor symptoms. PMID:27054800
Facial landmark localization by curvature maps and profile analysis.
Lippold, Carsten; Liu, Xiang; Wangdo, Kim; Drerup, Burkhard; Schreiber, Kristina; Kirschneck, Christian; Moiseenko, Tatjana; Danesh, Gholamreza
2014-12-08
Three-dimensional landmarks of the face are important for orthodontic examination, harmony assessment and treatment planning. Currently, facial landmarks are often measured by orthodontists via direct observation and manual soft tissue image analysis. This study wants to evaluate and present an objective method for measuring selected facial landmarks based on an analysis of curvature maps and of sagittal profile obtained by a laser-scanning method. The faces of 15 people were scanned in 3D by means of the laser scanner FastSCAN™. It allowed the recording of a curvature map of the face in under a minute, which depicted the distribution of Gaussian and mean curvatures. The median-sagittal profile line of the face was localized in this map, and a mathematical analysis comprising its first and second derivatives was performed. Anatomical landmarks were identified and facial measurements performed. To assess validity the obtained data were compared with manual measurements by orthodontists by means of Lin's concordance correlation CCC coefficient and reliability was determined by consecutive measurements. Facial landmarks, such as the soft tissue glabella and nasal tip, could be easily and accurately identified and located. Lin's CCC showed substantial agreement between digital and manual measurements for 4 of the 7 distances evaluated. Larger discrepancies were due to inadequate image quality and scanning errors. Reliability of consecutive measurements by the same operator was excellent. In our pilot study the three-dimensional laser-scanning method FastSCAN™ allowed a reliable and accurate identification of anatomical landmarks of the face. The obtained distances between certain landmarks, such as the intercanthal distance, were largely consistent with those from manual measurements. Due to its easy and rapid implementation, the method facilitates facial analysis and could be a clinically valid alternative to manual measurements, when remaining problems in
Nanolaminate Membranes as Cylindrical Telescope Reflectors
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.
The evolution of space curves by curvature and torsion
International Nuclear Information System (INIS)
Richardson, G; King, J R
2002-01-01
We apply Lie group based similarity methods to the study of a new, and widely relevant, class of objects, namely motions of a space curve. In particular, we consider the motion of a curve evolving with a curvature κ and torsion τ dependent velocity law. We systematically derive the Lie point symmetries of all such laws of motion and use these to catalogue all their possible similarity reductions. This calculation reveals special classes of law with high degrees of symmetry (and a correspondingly large number of similarity reductions). Of particular note is one class which is invariant under general linear transformations in space. This has potential applications in pattern and signal recognition
Geometry of manifolds with non-negative sectional curvature
Dearricott, Owen; Kennard, Lee; Searle, Catherine; Weingart, Gregor; Ziller, Wolfgang
2014-01-01
Providing an up-to-date overview of the geometry of manifolds with non-negative sectional curvature, this volume gives a detailed account of the most recent research in the area. The lectures cover a wide range of topics such as general isometric group actions, circle actions on positively curved four manifolds, cohomogeneity one actions on Alexandrov spaces, isometric torus actions on Riemannian manifolds of maximal symmetry rank, n-Sasakian manifolds, isoparametric hypersurfaces in spheres, contact CR and CR submanifolds, Riemannian submersions and the Hopf conjecture with symmetry. Also included is an introduction to the theory of exterior differential systems.
Static potential in a string model with extrinsic curvatures
International Nuclear Information System (INIS)
Olesen, P.; Yang, S.K.
1987-01-01
The static quark potential in a string model including extrinsix curvature effects is studied in the large d limit, where d is the dimensionality of euclidean space. At large distances it is explicitly shown that the physical string tension is dynamically generated. Examining the large-distance ''Coulomb'' term in the potential, we show that the non-perturbative effects in general generate non-gaussian efective theories in the infrared regime. At large distances the d → ∞ saddle point is stable for a large range of parameters. (orig.)
The imaginary Starobinsky model and higher curvature corrections
International Nuclear Information System (INIS)
Ferrara, Sergio; Kehagias, Alex; Riotto, Antonio
2015-01-01
We elaborate on the predictions of the imaginary Starobinsky model of inflation coupled to matter, where the inflaton is identified with the imaginary part of the inflaton multiplet suggested by the Supergravity embedding of a pure R + R 2 gravity. In particular, we study the impact of higher-order curvature terms and show that, depending on the parameter range, one may find either a quadratic model of chaotic inflation or monomial models of chaotic inflation with fractional powers between 1 and 2. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Curvature by design and on demand in liquid crystal elastomers
Kowalski, B. A.; Mostajeran, C.; Godman, N. P.; Warner, M.; White, T. J.
2018-01-01
The shape of liquid crystalline elastomers (LCEs) with spatial variation in the director orientation can be transformed by exposure to a stimulus. Here, informed by previously reported analytical treatments, we prepare complex spiral patterns imprinted into LCEs and quantify the resulting shape transformation. Quantification of the stimuli-induced shapes reveals good agreement between predicted and experimentally observed curvatures. We conclude this communication by reporting a design strategy to allow LCE films to be anchored at their external boundaries onto rigid substrates without incurring internal, mechanical-mismatch stresses upon actuation, a critical advance to the realization of shape transformation of LCEs in practical device applications.
Ashrafuzzaman, Mohammad
2013-01-01
Physics, mathematics and chemistry all play a vital role in understanding the true nature and functioning of biological membranes, key elements of living processes. Besides simple spectroscopic observations and electrical measurements of membranes we address in this book the phenomena of coexistence and independent existence of different membrane components using various theoretical approaches. This treatment will be helpful for readers who want to understand biological processes by applying both simple observations and fundamental scientific analysis. It provides a deep understanding of the causes and effects of processes inside membranes, and will thus eventually open new doors for high-level pharmaceutical approaches towards fighting membrane- and cell-related diseases.
Pinkbar is an epithelial-specific BAR domain protein that generates planar membrane structures
Energy Technology Data Exchange (ETDEWEB)
Pykäläinen, Anette; Boczkowska, Malgorzata; Zhao, Hongxia; Saarikangas, Juha; Rebowski, Grzegorz; Jansen, Maurice; Hakanen, Janne; Koskela, Essi V.; Peränen, Johan; Vihinen, Helena; Jokitalo, Eija; Salminen, Marjo; Ikonen, Elina; Dominguez, Roberto; Lappalainen, Pekka (Helsinki); (Penn)
2013-05-29
Bin/amphipysin/Rvs (BAR)-domain proteins sculpt cellular membranes and have key roles in processes such as endocytosis, cell motility and morphogenesis. BAR domains are divided into three subfamilies: BAR- and F-BAR-domain proteins generate positive membrane curvature and stabilize cellular invaginations, whereas I-BAR-domain proteins induce negative curvature and stabilize protrusions. We show that a previously uncharacterized member of the I-BAR subfamily, Pinkbar, is specifically expressed in intestinal epithelial cells, where it localizes to Rab13-positive vesicles and to the plasma membrane at intercellular junctions. Notably, the BAR domain of Pinkbar does not induce membrane tubulation but promotes the formation of planar membrane sheets. Structural and mutagenesis analyses reveal that the BAR domain of Pinkbar has a relatively flat lipid-binding interface and that it assembles into sheet-like oligomers in crystals and in solution, which may explain its unique membrane-deforming activity.
Mitra, Eshan D.; Whitehead, Samuel C.; Holowka, David; Baird, Barbara; Sethna, James P.
2018-01-01
Lipid phase heterogeneity in the plasma membrane is thought to be crucial for many aspects of cell signaling, but the physical basis of participating membrane domains such as "lipid rafts" remains controversial. Here we consider a lattice model yielding a phase diagram that includes several states proposed to be relevant for the cell membrane, including microemulsion - which can be related to membrane curvature - and Ising critical behavior. Using a neural network-based machine learning appro...
Zheng, Qing-hua; Zhou, Xue-dong; Jiang, Ying; Sun, Tuo-qi; Liu, Cheng-xia; Xue, Hui; Huang, Ding-ming
2009-02-01
Accurate knowledge of root canal curvature is a critical factor in successful root canal procedures. The objective of this study was to determine the degree of root canal curvature and the frequency of curvature identified in different radiographic views in permanent incisors from a Chinese population. The curvature of canals from 299 permanent mandibular incisors was investigated by measuring the angle, the radius of curvature, and the length of the curved part of the canals. These measurements were taken by inserting size 10 K-files into the canals and taking radiographs of the tooth-file assembly from both facial and proximal views by using a standardized parallel technique. All radiographs were analyzed with a computerized digital image processing system. Statistical analysis was performed with analysis of variance test at alpha = .05. Of the 299 teeth examined, 252 (84.3%) were curved, and 125 (41.8%) of the teeth had secondary curvature. Curvature was most frequently detected in the proximal views rather than in the facial lingual views (P < .05). The highest curvature among all samples tested was 44 degrees primary curvature and 36 degrees secondary curvature. The maximum and minimum radii of curvature for the sample set were 54.61 and 1.55 mm, respectively. The mean value of the radius of secondary curvature seen in proximal views was significantly less than that of the primary ones (P < .05). The length of the curved parts of canals measured maximum and minimum values of 14 and 0.33 mm, respectively. It is suggested that the canal curvature can start at either the middle third or apical third of the tooth.
Stark, Oded
2007-01-01
At least to some extent migration behavior is the outcome of a preference for migration. The pattern of migration as an outcome of a preference for migration depends on two key factors: imitation technology and migration feasibility. We show that these factors jointly determine the outcome of a preference for migration and we provide examples that illustrate how the prevalence and transmission of a migration-forming preference yield distinct migration patterns. In particular, the imitation of...
Semiclassical dynamics, Berry curvature, and spiral holonomy in optical quasicrystals
Spurrier, Stephen; Cooper, Nigel R.
2018-04-01
We describe the theory of the dynamics of atoms in two-dimensional quasicrystalline optical lattices. We focus on a regime of shallow lattice depths under which the applied force can cause Landau-Zener tunneling past a dense hierarchy of gaps in the quasiperiodic energy spectrum. We derive conditions on the external force that allow for a "semiadiabatic" regime in which semiclassical equations of motion can apply, leading to Bloch oscillations between the edges of a pseudo-Brillouin-zone. We verify this semiclassical theory by comparing to the results of an exact numerical solution. Interesting features appear in the semiclassical dynamics for the quasicrystal for a particle driven in a cyclic trajectory around the corner of the pseudo-Brillouin-zone: The particle fails to return to its initial state, providing a realization of a "spiral holonomy" in the dynamics. We show that there can appear anomalous velocity contributions, associated with nonzero Berry curvature. We relate these to the Berry phase associated with the spiral holonomy, and show how the Berry curvature can be accessed from the semiclassical dynamics. Finally, by identifying the pseudo-Brillouin-zone as a higher genus surface, we show that the Chern number classification for periodic systems can be extended to a quasicrystal, thereby determining a topological index for the system.
Memory for curvature of objects: haptic touch vs. vision.
Ittyerah, Miriam; Marks, Lawrence E
2007-11-01
The present study examined the role of vision and haptics in memory for stimulus objects that vary along the dimension of curvature. Experiment 1 measured haptic-haptic (T-T) and haptic-visual (T-V) discrimination of curvature in a short-term memory paradigm, using 30-second retention intervals containing five different interpolated tasks. Results showed poorest performance when the interpolated tasks required spatial processing or movement, thereby suggesting that haptic information about shape is encoded in a spatial-motor representation. Experiment 2 compared visual-visual (V-V) and visual-haptic (V-T) short-term memory, again using 30-second delay intervals. The results of the ANOVA failed to show a significant effect of intervening activity. Intra-modal visual performance and cross-modal performance were similar. Comparing the four modality conditions (inter-modal V-T, T-V; intra-modal V-V, T-T, by combining the data of Experiments 1 and 2), in a global analysis, showed a reliable interaction between intervening activity and experiment (modality). Although there appears to be a general tendency for spatial and movement activities to exert the most deleterious effects overall, the patterns are not identical when the initial stimulus is encoded haptically (Experiment 1) and visually (Experiment 2).
Constant curvature algebras and higher spin action generating functions
International Nuclear Information System (INIS)
Hallowell, K.; Waldron, A.
2005-01-01
The algebra of differential geometry operations on symmetric tensors over constant curvature manifolds forms a novel deformation of the sl(2,R)-bar R 2 Lie algebra. We present a simple calculus for calculations in its universal enveloping algebra. As an application, we derive generating functions for the actions and gauge invariances of massive, partially massless and massless (for both Bose and Fermi statistics) higher spins on constant curvature backgrounds. These are formulated in terms of a minimal set of covariant, unconstrained, fields rather than towers of auxiliary fields. Partially massless gauge transformations are shown to arise as degeneracies of the flat, massless gauge transformation in one dimension higher. Moreover, our results and calculus offer a considerable simplification over existing techniques for handling higher spins. In particular, we show how theories of arbitrary spin in dimension d can be rewritten in terms of a single scalar field in dimension 2d where the d additional dimensions correspond to coordinate differentials. We also develop an analogous framework for spinor-tensor fields in terms of the corresponding superalgebra
Curvature dependence of blob dynamics in TJ-K
Energy Technology Data Exchange (ETDEWEB)
Garland, Stephen; Ramisch, Mirko; Hirth, Thomas [Institut fuer Grenzflaechenverfahrenstechnik und Plasmatechnologie, Universitaet Stuttgart (Germany)
2015-05-01
Turbulent transport in the scrape-off layer (SOL) is an important area of investigation in magnetic confinement fusion research. Relatively dense and hot, field-aligned, filament-like structures (blobs) have been observed to propagate radially through the SOL in many fusion devices, and contribute significantly to SOL transport. The torsatron TJ-K is well suited to turbulence studies since it operates with a low-temperature plasma, allowing Langmuir probe measurements in the entire plasma volume. Despite the low temperature, investigations are relevant to fusion research due to dimensionless plasma parameters similar to those in the edge region of fusion plasmas. Blob dynamics have been studied in the SOL of TJ-K using a 2D movable probe and the conditional averaging technique. In addition, emissive probes have been used to determine equilibrium electric fields, allowing the calculation of background E x B flows. Experimentally deduced centre of mass radial and poloidal blob velocity components have been compared to an analytical blob model, which has been simplified to express blob velocity in terms of the magnetic field curvature vector. Experimental radial blob velocity components compare well to the model, confirming the normal curvature drive of blob polarisation. On the other hand, poloidal velocity components are comparable to the model only when background E x B flow is also taken into account.
A Global Poincaré inequality on Graphs via a Conical Curvature-Dimension Condition
Directory of Open Access Journals (Sweden)
Lakzian Sajjad
2018-02-01
Full Text Available We introduce and study the conical curvature-dimension condition, CCD(K, N, for finite graphs.We show that CCD(K, N provides necessary and sufficient conditions for the underlying graph to satisfy a sharp global Poincaré inequality which in turn translates to a sharp lower bound for the first eigenvalues of these graphs. Another application of the conical curvature-dimension analysis is finding a sharp estimate on the curvature of complete graphs
3D Curves With a Prescribed Curvature and Torsion for a Flying Robot
International Nuclear Information System (INIS)
Bestaoui, Yasmina
2008-01-01
The objective of this paper is to generate a desired flight path to be followed by an flying robot. A curve with discontinuous curvature and torsion is not appropriate for smooth motions for any vehicle architecture. Three different classes of curves are presented. First, constant curvature and torsion followed by a linear variation versus the curvilinear abscissa then a quadratic variation. Finally, the problem of maneuvers between two trim helices of different curvature and torsion is tackled with
Curvature-tuned InAs-based shells containing two-dimensional electron gas
Energy Technology Data Exchange (ETDEWEB)
Mutilin, S V; Vorobyova, Ju S; Vorob' ev, A B; Putyato, M A; Prinz, V Ya, E-mail: s.mutilin@gmail.com [AV Rzhanov Institute of Semiconductor Physics, 630090, acad. Lavrentyev ave., 13, Novosibirsk (Russian Federation)
2011-09-14
Conducting InAs/AlSb/GaSb shells of curvature radius {approx}10 {mu}m are fabricated on GaSb (1 0 0) substrates. In the InAs quantum well, the shells are shown to contain a two-dimensional electron gas. Controlled tuning of the curvature of the formed shells in excess of three times is demonstrated. The sequence of fabrication steps for forming curvature-tuned InAs-based shells with quantum well is described.
Consumers’ preferences for bread
DEFF Research Database (Denmark)
Edenbrandt, Anna Kristina; Gamborg, Christian; Thorsen, Bo Jellesmark
2018-01-01
Consumers are apprehensive about transgenic technologies, so cisgenics, which limit gene transfers to sexually compatible organisms, have been suggested to address consumer concerns. We study consumer preferences for rye bread alternatives based on transgenic or cisgenic rye, grown conventionally...... or without the use of pesticides, relative to traditionally bred rye, grown with conventional or organic farming methods. Stated preference (SP) data from a choice experiment are combined with revealed preference (RP) data from market purchases from the same respondents. Results show that respondents prefer...... pesticide-free production methods, and that while cisgenics is preferred over transgenics, the majority of respondents favour traditional breeding methods. The distribution in preferences suggests that some respondents prefer bread from cisgenic crops produced without pesticides over traditional crops...
DEFF Research Database (Denmark)
Harrison, Glenn W.; Lau, Morten; Rutström, E. Elisabet
2013-01-01
We elicit individual preferences over social risk. We identify the extent to which these preferences are correlated with preferences over individual risk and the well-being of others. We examine these preferences in the context of laboratory experiments over small, anonymous groups, although...... the methodological issues extend to larger groups that form endogenously (e.g., families, committees, communities). Preferences over social risk can be closely approximated by individual risk attitudes when subjects have no information about the risk preferences of other group members. We find no evidence...... that subjects systematically reveal different risk attitudes in a social setting with no prior knowledge about the risk preferences of others compared to when they solely bear the consequences of the decision. However, we also find that subjects are significantly more risk averse when they know the risk...
Curvature Continuous and Bounded Path Planning for Fixed-Wing UAVs.
Wang, Xiaoliang; Jiang, Peng; Li, Deshi; Sun, Tao
2017-09-19
Unmanned Aerial Vehicles (UAVs) play an important role in applications such as data collection and target reconnaissance. An accurate and optimal path can effectively increase the mission success rate in the case of small UAVs. Although path planning for UAVs is similar to that for traditional mobile robots, the special kinematic characteristics of UAVs (such as their minimum turning radius) have not been taken into account in previous studies. In this paper, we propose a locally-adjustable, continuous-curvature, bounded path-planning algorithm for fixed-wing UAVs. To deal with the curvature discontinuity problem, an optimal interpolation algorithm and a key-point shift algorithm are proposed based on the derivation of a curvature continuity condition. To meet the upper bound for curvature and to render the curvature extrema controllable, a local replanning scheme is designed by combining arcs and Bezier curves with monotonic curvature. In particular, a path transition mechanism is built for the replanning phase using minimum curvature circles for a planning philosophy. Numerical results demonstrate that the analytical planning algorithm can effectively generate continuous-curvature paths, while satisfying the curvature upper bound constraint and allowing UAVs to pass through all predefined waypoints in the desired mission region.
Femoral condyle curvature is correlated with knee walking kinematics in ungulates.
Sylvester, Adam D
2015-12-01
The knee has been the focus of many studies linking mammalian postcranial form with locomotor behaviors and animal ecology. A more difficult task has been linking joint morphology with joint kinematics during locomotor tasks. Joint curvature represents one opportunity to link postcranial morphology with walking kinematics because joint curvature develops in response to mechanical loading. As an initial examination of mammalian knee joint curvature, the curvature of the medial femoral condyle was measured on femora representing 11 ungulate species. The position of a region of low curvature was measured using a metric termed the "angle to low curvature". This low-curvature region is important because it provides the greatest contact area between femoral and tibial condyles. Kinematic knee angles during walking were derived from the literature and kinematic knee angles across the gait cycle were correlated with angle to low curvature values. The highest correlation between kinematic knee angle and the angle to low curvature metric occurred at 20% of the walking gait cycle. This early portion of the walking gait cycle is associated with a peak in the vertical ground reaction force for some mammals. The chondral modeling theory predicts that frequent and heavy loading of particular regions of a joint surface during ontogeny will result in these regions being flatter than the surrounding joint surface. The locations of flatter regions of the femoral condyles of ungulates, and their association with knee angles used during the early stance phase of walking provides support for the chondral modeling theory. © 2015 Wiley Periodicals, Inc.
Curvature Continuous and Bounded Path Planning for Fixed-Wing UAVs
Jiang, Peng; Li, Deshi; Sun, Tao
2017-01-01
Unmanned Aerial Vehicles (UAVs) play an important role in applications such as data collection and target reconnaissance. An accurate and optimal path can effectively increase the mission success rate in the case of small UAVs. Although path planning for UAVs is similar to that for traditional mobile robots, the special kinematic characteristics of UAVs (such as their minimum turning radius) have not been taken into account in previous studies. In this paper, we propose a locally-adjustable, continuous-curvature, bounded path-planning algorithm for fixed-wing UAVs. To deal with the curvature discontinuity problem, an optimal interpolation algorithm and a key-point shift algorithm are proposed based on the derivation of a curvature continuity condition. To meet the upper bound for curvature and to render the curvature extrema controllable, a local replanning scheme is designed by combining arcs and Bezier curves with monotonic curvature. In particular, a path transition mechanism is built for the replanning phase using minimum curvature circles for a planning philosophy. Numerical results demonstrate that the analytical planning algorithm can effectively generate continuous-curvature paths, while satisfying the curvature upper bound constraint and allowing UAVs to pass through all predefined waypoints in the desired mission region. PMID:28925960
Measurement of curvature and twist of a deformed object using digital holography
International Nuclear Information System (INIS)
Chen Wen; Quan Chenggen; Cho Jui Tay
2008-01-01
Measurement of curvature and twist is an important aspect in the study of object deformation. In recent years, several methods have been proposed to determine curvature and twist of a deformed object using digital shearography. Here we propose a novel method to determine the curvature and twist of a deformed object using digital holography and a complex phasor. A sine/cosine transformation method and two-dimensional short time Fourier transform are proposed subsequently to process the wrapped phase maps. It is shown that high-quality phase maps corresponding to curvature and twist can be obtained. An experiment is conducted to demonstrate the validity of the proposed method
The effects of out-of-plane curvature on the growth of epithelia
Yevick, Hannah; Duclos, Guillaume; Bonnet, Isabelle; Silberzan, Pascal
2015-03-01
Collective cell migration is at play in many well documented in vivo processes for example, wound re-epithelialization, cancer metastasis and dorsal closure. We present a study describing the effect of out of plane curvature on the collective properties of epithelial tissue. Microfabricated environments are used to deconstruct a monolayer's response to geometry. Specifically, fibers with a radius of curvature between 1um-100um are populated with MDCK cells, a model epithelial, kidney-derived, cell line. Migration dynamics as well as cell architecture are quantified and the effects of curvature compared with confinement alone. Large curvatures trigger specific cellular behaviors and organization that may shed light on tubulogenesis.
Curvature-driven bubbles or droplets on the spiral surface
Li, Shanpeng; Liu, Jianlin; Hou, Jian
2016-11-01
Directional motion of droplets or bubbles can often be observed in nature and our daily life, and this phenomenon holds great potential in many engineering areas. The study shows that droplets or bubbles can be driven to migrate perpetually on some special substrates, such as the Archimedean spiral, the logarithmic spiral and a cantilever sheet in large deflection. It is found that a bubble approaches or deviates from the position with highest curvature of the substrate, when it is on the concave or convex side. This fact is helpful to explain the repelling water capability of Nepenthes alata. Based on the force and energy analysis, the mechanism of the bubble migration is well addressed. These findings pave a new way to accurately manipulate droplet or bubble movement, which bring inspirations to the design of microfluidic and water harvesting devices, as well as oil displacement and ore filtration.
Cones in the Euclidean space with vanishing scalar curvature
Directory of Open Access Journals (Sweden)
João Lucas M. Barbosa
2004-12-01
Full Text Available Given a hypersurface M on a unit sphere of the Euclidean space, we define the cone based on M as the set of half-lines issuing from the origin and passing through M. By assuming that the scalar curvature of the cone vanishes, we obtain conditions under which bounded domains of such cone are stable or unstable.Dada uma hipersuperfície M de uma esfera unitária do espaço euclidiano, definimos o cone sobre M como o conjunto das semi-retas que saem da origem e passam por M. Admitindo que a curvatura escalar de um dado cone é nula, estabelecemos condições para que os seus domínios limitados sejam estáveis ou instáveis.
Higher Curvature Gravity in TeV-Scale Extra Dimensions
Energy Technology Data Exchange (ETDEWEB)
Rizzo, Thomas G.
2006-03-31
We begin a general exploration of the phenomenology of TeV-scale extra-dimensional models with gravitational actions that contain higher curvature terms. In particular, we examine how the classic collider signatures of the models of Arkani-Hamed, Dimopoulos and Dvali (missing energy and new dimension-8 contact interactions) and of Randall and Sundrum (TeV-scale graviton Kaluza-Klein resonances) are altered by these modifications to the usual Einstein-Hilbert action. We find that not only are the detailed signatures for these gravitationally induced processes altered but new contributions are found to arise due to the existence of additional scalar Kaluza-Klein states in the spectrum.
Observational constraints on the primordial curvature power spectrum
Emami, Razieh; Smoot, George F.
2018-01-01
CMB temperature fluctuation observations provide a precise measurement of the primordial power spectrum on large scales, corresponding to wavenumbers 10‑3 Mpc‑1 lesssim k lesssim 0.1 Mpc‑1, [1-7, 11]. Luminous red galaxies and galaxy clusters probe the matter power spectrum on overlapping scales (0.02 Mpc‑1 lesssim k lesssim 0.7 Mpc‑1 [10, 12-20]), while the Lyman-alpha forest reaches slightly smaller scales (0.3 Mpc‑1 lesssim k lesssim 3 Mpc‑1 [22]). These observations indicate that the primordial power spectrum is nearly scale-invariant with an amplitude close to 2 × 10‑9, [5, 23-28]. These observations strongly support Inflation and motivate us to obtain observations and constraints reaching to smaller scales on the primordial curvature power spectrum and by implication on Inflation. We are able to obtain limits to much higher values of k lesssim 105 Mpc‑1 and with less sensitivity even higher k lesssim 1019‑ 1023 Mpc‑1 using limits from CMB spectral distortions and other limits on ultracompact minihalo objects (UCMHs) and Primordial Black Holes (PBHs). PBHs are one of the known candidates for the Dark Matter (DM). Due to their very early formation, they could give us valuable information about the primordial curvature perturbations. These are complementary to other cosmological bounds on the amplitude of the primordial fluctuations. In this paper, we revisit and collect all the published constraints on both PBHs and UCMHs. We show that unless one uses the CMB spectral distortion, PBHs give us a very relaxed bounds on the primordial curvature perturbations. UCMHs, on the other hand, are very informative over a reasonable k range (3 lesssim k lesssim 106 Mpc‑1) and lead to significant upper-bounds on the curvature spectrum. We review the conditions under which the tighter constraints on the UCMHs could imply extremely strong bounds on the fraction of DM that could be PBHs in reasonable models. Failure to satisfy these conditions would
Discrete extrinsic curvatures and approximation of surfaces by polar polyhedra
Garanzha, V. A.
2010-01-01
Duality principle for approximation of geometrical objects (also known as Eu-doxus exhaustion method) was extended and perfected by Archimedes in his famous tractate “Measurement of circle”. The main idea of the approximation method by Archimedes is to construct a sequence of pairs of inscribed and circumscribed polygons (polyhedra) which approximate curvilinear convex body. This sequence allows to approximate length of curve, as well as area and volume of the bodies and to obtain error estimates for approximation. In this work it is shown that a sequence of pairs of locally polar polyhedra allows to construct piecewise-affine approximation to spherical Gauss map, to construct convergent point-wise approximations to mean and Gauss curvature, as well as to obtain natural discretizations of bending energies. The Suggested approach can be applied to nonconvex surfaces and in the case of multiple dimensions.
Converting entropy to curvature perturbations after a cosmic bounce
Energy Technology Data Exchange (ETDEWEB)
Fertig, Angelika; Lehners, Jean-Luc; Mallwitz, Enno; Wilson-Ewing, Edward [Max Planck Institute for Gravitational Physics, Albert Einstein Institute,14476 Potsdam-Golm (Germany)
2016-10-04
We study two-field bouncing cosmologies in which primordial perturbations are created in either an ekpyrotic or a matter-dominated contraction phase. We use a non-singular ghost condensate bounce model to follow the perturbations through the bounce into the expanding phase of the universe. In contrast to the adiabatic perturbations, which on large scales are conserved across the bounce, entropy perturbations can grow significantly during the bounce phase. If they are converted into adiabatic/curvature perturbations after the bounce, they typically form the dominant contribution to the observed temperature fluctuations in the microwave background, which can have several beneficial implications. For ekpyrotic models, this mechanism loosens the constraints on the amplitude of the ekpyrotic potential while naturally suppressing the intrinsic amount of non-Gaussianity. For matter bounce models, the mechanism amplifies the scalar perturbations compared to the associated primordial gravitational waves.
Curvature-driven morphing of non-Euclidean shells
Pezzulla, Matteo; Stoop, Norbert; Jiang, Xin; Holmes, D. P.
2017-05-01
We investigate how thin structures change their shape in response to non-mechanical stimuli that can be interpreted as variations in the structure's natural curvature. Starting from the theory of non-Euclidean plates and shells, we derive an effective model that reduces a three-dimensional stimulus to the natural fundamental forms of the mid-surface of the structure, incorporating expansion, or growth, in the thickness. Then, we apply the model to a variety of thin bodies, from flat plates to spherical shells, obtaining excellent agreement between theory and numerics. We show how cylinders and cones can either bend more or unroll, and eventually snap and rotate. We also study the nearly isometric deformations of a spherical shell and describe how this shape change is ruled by the geometry of a spindle. As the derived results stem from a purely geometrical model, they are general and scalable.
Magnetization of fluid phonons and large-scale curvature perturbations
Giovannini, Massimo
2014-01-01
The quasinormal mode of a gravitating and magnetized fluid in a spatially flat, isotropic and homogeneous cosmological background is derived in the presence of the fluid sources of anisotropic stress and of the entropic fluctuations of the plasma. The obtained gauge-invariant description involves a system of two coupled differential equations whose physical content is analyzed in all the most relevant situations. The Cauchy problem of large-scale curvature perturbations during the radiation dominated stage of expansion can be neatly formulated and its general solution is shown to depend on five initial data assigned when the relevant physical wavelengths are larger than the particle horizon. The consequences of this approach are explored.
Inflation in non-minimal matter-curvature coupling theories
Energy Technology Data Exchange (ETDEWEB)
Gomes, C.; Bertolami, O. [Departamento de Física e Astronomia and Centro de Física do Porto, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto (Portugal); Rosa, J.G., E-mail: claudio.gomes@fc.up.pt, E-mail: joao.rosa@ua.pt, E-mail: orfeu.bertolami@fc.up.pt [Departamento de Física da Universidade de Aveiro and CIDMA, Campus de Santiago, 3810-183 Aveiro (Portugal)
2017-06-01
We study inflationary scenarios driven by a scalar field in the presence of a non-minimal coupling between matter and curvature. We show that the Friedmann equation can be significantly modified when the energy density during inflation exceeds a critical value determined by the non-minimal coupling, which in turn may considerably modify the spectrum of primordial perturbations and the inflationary dynamics. In particular, we show that these models are characterised by a consistency relation between the tensor-to-scalar ratio and the tensor spectral index that can differ significantly from the predictions of general relativity. We also give examples of observational predictions for some of the most commonly considered potentials and use the results of the Planck collaboration to set limits on the scale of the non-minimal coupling.
A numerical shoreline model for shorelines with large curvature
DEFF Research Database (Denmark)
Kærgaard, Kasper Hauberg; Fredsøe, Jørgen
2013-01-01
This paper presents a new numerical model for shoreline change which can be used to model the evolution of shorelines with large curvature. The model is based on a one-line formulation in terms of coordinates which follow the shape of the shoreline, instead of the more common approach where the two...... orthogonal horizontal directions are used. The volume error in the sediment continuity equation which is thereby introduced is removed through an iterative procedure. The model treats the shoreline changes by computing the sediment transport in a 2D coastal area model, and then integrating the sediment...... transport field across the coastal profile to obtain the longshore sediment transport variation along the shoreline. The model is used to compute the evolution of a shoreline with a 90° change in shoreline orientation; due to this drastic change in orientation a migrating shoreline spit develops...
Palatini versus metric formulation in higher-curvature gravity
International Nuclear Information System (INIS)
Borunda, Mónica; Janssen, Bert; Bastero-Gil, Mar
2008-01-01
We compare the metric and the Palatini formalism to obtain the Einstein equations in the presence of higher-order curvature corrections that consist of contractions of the Riemann tensor, but not of its derivatives. We find that there is a class of theories for which the two formalisms are equivalent. This class contains the Palatini version of Lovelock theory, but also more Lagrangians that are not Lovelock, but respect certain symmetries. For the general case, we find that imposing the Levi-Civita connection as an ansatz, the Palatini formalism is contained within the metric formalism, in the sense that any solution of the former also appears as a solution of the latter, but not necessarily the other way around. Finally we give the conditions the solutions of the metric equations should satisfy in order to solve the Palatini equations
A new formula of the Gravitational Curvature for the prism
Grazia D'Urso, Maria
2017-04-01
Gravitational Curvatures (GC) are the components of the third-order gravitational tensor and physically represent the rate of change of the gravity gradient. While scalar, vector and second-order tensor quantities of the Earth's gravitational field have extensively been studied and their properties have been well understood [1], the first successful terrestrial measurements of the third-order vertical gravitational gradients have been recently performed in [2] by atom interferometry sensors in laboratory environment. Possible benefits of the airborne third-order gravitational gradients for exploration geophysics are discussed in [3] while Brieden et al. (2010) [4] have proposed a new satellite mission called OPTical Interferometry for global Mass change detection from space (OPTIMA) sensing the third-order gravitational gradients in space. Moreover, exploitation of GC for modelling the Earth's gravitational field has been object of recent studies [5-7]. We extend the approach presented by the author in previous papers [8-10] by evaluating the algebraic expression of the third-order gravitational tensor for a prism. Comparisons with previous results [11-12] are also included. [1] Freeden W, Schreiner M (2009) Spherical functions of mathematical geosciences. A scalar, vectorial, and tensorial setup. In: Advances in geophysical and environmental mechanics and mathematics. Springer, Berlin [2] Rosi G, Cacciapuoti L, Sorrentino F, Menchetti M, Prevedelli M, Tino GM (2015) Measurements of the gravity-field curvature by atom interferometry. Phys Rev Lett 114:013001 [3] Di Francesco D, Meyer T, Christensen A, FitzGerald D (2009) Gravity gradiometry - today and tomorrow. In: 11th SAGA Biennial technical meeting and exhibition, 13-18 September 2009, Switzerland, pp 80-83 [4] Brieden P, Müller J, Flury J, Heinzel G (2010) The mission OPTIMA - novelties and benefit. In: Geotechnologien science report No. 17, Potsdam, pp 134-139 [5] Šprlák M, Novák P (2015) Integral
Conditions on holographic entangling surfaces in higher curvature gravity
Energy Technology Data Exchange (ETDEWEB)
Erdmenger, Johanna; Flory, Mario; Sleight, Charlotte [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, D-80805, Munich (Germany)
2014-06-17
We study the extremal surfaces of functionals recently proposed for the holographic calculation of entanglement entropy in general higher curvature theories, using New Massive gravity and Gauss-Bonnet gravity as concrete examples. We show that the entropy functionals admit closed extremal surfaces, which for black hole backgrounds can encircle the event horizon of the black hole. In the examples considered, such closed surfaces correspond to a lower value of the entropy functional than expected from CFT calculations, implying a seeming mismatch between the bulk and boundary calculations. For Lorentzian settings we show that this problem can be resolved by imposing a causality constraint on the extremal surfaces. The possibility of deriving conditions from an alternative conical boundary condition method as proposed by Lewkowycz and Maldacena is explored.
Reachability by paths of bounded curvature in a convex polygon
Ahn, Heekap
2012-01-01
Let B be a point robot moving in the plane, whose path is constrained to forward motions with curvature at most 1, and let P be a convex polygon with n vertices. Given a starting configuration (a location and a direction of travel) for B inside P, we characterize the region of all points of P that can be reached by B, and show that it has complexity O(n). We give an O(n2) time algorithm to compute this region. We show that a point is reachable only if it can be reached by a path of type CCSCS, where C denotes a unit circle arc and S denotes a line segment. © 2011 Elsevier B.V.
Prachayasittikul, Virapong; Isarankura-Na-Ayudhya, Chartchalerm; Tantimongcolwat, Tanawut; Nantasenamat, Chanin; Galla, Hans-Joachim
2007-11-01
The molecular mechanism of ethylenediaminetetraacetic acid (EDTA)-induced membrane destabilization has been studied using a combination of four biophysical techniques on artificial lipid membranes. Data from Langmuir film balance and epifluorescence microscopy revealed the fluidization and expansion effect of EDTA on phase behavior of monolayers of either 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or mixtures of DPPC and metal-chelating lipids, such as N(alpha),N(alpha)-Bis[carboxymethyl]-N(epsilon)-[(dioctadecylamino)succinyl]-L-lysine or 1,2-dioleoyl-sn-glycero-3-[N-(5-amino-1-carboxypentyl iminodiacetic acid) succinyl]. A plausible explanation could be drawn from the electrostatic interaction between negatively charged groups of EDTA and the positively charged choline head group of DPPC. Intercalation of EDTA into the lipid membrane induced membrane curvature as elucidated by atomic force microscopy. Growth in size and shape of the membrane protrusion was found to be time-dependent upon exposure to EDTA. Further loss of material from the lipid membrane surface was monitored in real time using a quartz crystal microbalance. This indicates membrane restabilization by exclusion of the protrusions from the surface. Loss of lipid components facilitates membrane instability, leading to membrane permeabilization and lysis.
Nonlinear damping of drift waves by strong flow curvature
International Nuclear Information System (INIS)
Sidikman, K.L.; Carreras, B.A.; Garcia, L.; Diamond, P.H.
1993-01-01
A single-equation model has been used to study the effect of a fixed poloidal flow (V 0 ) on turbulent drift waves. The electron dynamics come from a laminar kinetic equation in the dissipative trapped-electron regime. In the past, the authors have assumed that the mode frequency is close to the drift-wave frequency. Trapped-electron density fluctuations are then related to potential fluctuations by an open-quotes iδclose quotes term. Flow shear (V 0 ') and curvature (V 0 double-prime) both have a stabilizing effect on linear modes for this open-quotes iδclose quotes model. However, in the nonlinear regime, single-helicity effects inhibit the flow damping. Neither V 0 ' nor V 0 double-prime produces a nonlinear damping effect. The above assumption on the frequency can be relaxed by including the electron time-response in the linear part of the evolution. In this time-dependent model, instability drive due to trapped electrons is reduced when mode frequency is greater than drift-wave frequency. Since V 0 double-prime produces such a frequency shift, its linear effect is enhanced. There is also nonlinear damping, since single-helicity effects do not eliminate the shift. Renormalized theory for this model predicts nonlinear stability for sufficiently large curvature. Single-helicity calculations have already shown nonlinear damping, and this strong V 0 double-prime regime is being explored. In the theory, the Gaussian shape of the nonlinear diffusivity is expanded to obtain a quadratic potential. The implications of this assumption will be tested by solving the full renormalized equation using a shooting method
Cross-section curvature effect in plasmonic ring lasers
Shi, Feifei; Liu, Xudong; Gong, Xin; Zhang, Zhaoyu
2013-09-01
Nanolasers have shown their potential in optical communication and information storage, due to their tiny footprint, potential high modulation rate and light spot under diffraction limit. In recent years, many structures use metal as whole or part of the cavity to achieve light confinement at subwavelength scale. In this paper, we propose and compare two novel types of hybrid plasmonic lasers, both with an ultrathin insulator layer sandwiched by a ring shape semiconductor and planar silver layer. The lasers differ in their cross-section curvature on the interface of metal and insulator. Finite difference time domain (FDTD) method is used to calculate and optimize these two ring laser structures. The resonant wavelength is set around 490 nm. The ultrathin thickness of the insulator layer makes photonic modes hybridize with surface plasmon plaritons (SPPs) at Ag-insulator interface, which confines the light field strongly in the ultrathin layer. The SPPs carry high momentum and high effective refractive index to TM mode. Whispering gallery mode is achieved according to strong feedback at the ring boundary by total internal reflection. The ring lasers have relatively high Q factors, approaching 100, at 250 nm radius and mode confinement around λ2/360. The mode volume can be shrunk to 0.1(λ/n)3 and 0.01(λ/n)3 respectively, which leads to Purcell factors around 70 for square cross-section and 380 for circle cross-section. We discuss the curvature effects on the mode volume and on the quality factor which accounts for the high Purcell factor for the circle cross-section.
Lee, Sang-Mok; Choi, Hyuk Jin; Choi, Heejin; Kim, Mee Kum; Wee, Won Ryang
2016-10-07
BACKGROUND: Though the development and fitting of scleral contact lenses are expanding steadily, there is no simple method to provide scleral metrics for scleral contact lens fitting yet. The aim of this study was to establish formulae for estimation of the axial radius of curvature (ARC) of the anterior sclera using ocular biometric parameters that can be easily obtained with conventional devices. A semi-automated stitching method and a computational analysis tool for calculating ARC were developed by using the ImageJ and MATLAB software. The ARC of all the ocular surface points were analyzed from the composite horizontal cross-sectional images of the right eyes of 24 volunteers; these measurements were obtained using anterior segment optical coherence tomography for a previous study (AS-OCT; Visante). Ocular biometric parameters were obtained from the same volunteers with slit-scanning topography and partial coherence interferometry. Correlation analysis was performed between the ARC at 8 mm to the axis line (ARC[8]) and other ocular parameters (including age). With ARC obtained on several nasal and temporal points (7.0, 7.5, 8.0, 8.5, and 9.0 mm from the axis line), univariate and multivariate linear regression analyses were performed to develop a model for estimating ARC with the help of ocular biometric parameters. Axial length, spherical equivalent, and angle kappa showed correlations with temporal ARC[8] (tARC[8]; Pearson's r = 0.653, -0.579, and -0.341; P = 0.001, 0.015, and 0.015, respectively). White-to-white corneal diameter (WTW) and anterior chamber depth (ACD) showed correlation with nasal ARC[8] (nARC[8]; Pearson's r = -0.492 and -0.461; P = 0.015 and 0.023, respectively). The formulae for estimating scleral curvatures (tARC, nARC, and average ARC) were developed as a function of axial length, ACD, WTW, and distance from the axis line, with good determinant power (72 - 80 %; SPSS ver. 22.0). Angle kappa showed strong
Radiographic evaluation of maxillary anterior teeth canal curvatures in an Iranian population.
Abesi, Farida; Ehsani, Maryam
2011-01-01
Complete knowledge of root canal curvature is a critical factor in successful endodontic treatment. The aim of this study was to investigate the direction, radius and degree of curvature of maxillary anterior teeth and the relationship between the radius and degree of curvature in Babol, a northern city of Iran. A total of 242 radiographs of maxillary anterior teeth (central, lateral and canine) were taken by periapical parallel technique and processed by automatic processing. The degree of canal curvature was measured only at mesiodistal direction with Schneider method and classified according to Seidberg method. Statistical analysis was performed with Kruskal Wallis and Mann-Whitney U tests. Overall, 153 (62%) teeth had curvatures; 35.3% were mesially inclined and 64.7% were distally inclined. The degree of canal curvature was categorized into small, intermediate, and severe, that is 39.3%, 44.6% and 16.1%, respectively. The mean value of root curvature angle was 7.24°±9.03° in central incisors, 12.08°±11.02° in lateral incisors, and 15.08°±12.02° in canines respectively. There was significant correlation between type of tooth and degree of curvature (P=0.000). Significant correlation was not found between the type of tooth and radius of curvature (P=0.365). In the present study, 62% of maxillary anterior teeth had some form of curvatures; highest degrees of curvature were attributed to the canine teeth.
International Nuclear Information System (INIS)
Price, R.H.; Thorne, K.S.
1986-01-01
The membrane paradigm is a modified frozen star approach to modeling black holes, with particles and fields assuming a complex, static, boundary-layer type structure (membrane) near the event horizon. The membrane has no effects on the present or future evolution of particles and fields above itself. The mathematical representation is a combination of a formalism containing terms for the shear and bulk viscosity, surface pressure, momentum, temperature, entropy, etc., of the horizon and the 3+1 formalism. The latter model considers a family of three-dimensional spacelike hypersurfaces in one-dimensional time. The membrane model considers a magnetic field threading the hole and undergoing torque from the hole rotation. The field is cleaned by the horizon and distributed over the horizon so that ohmic dissipation is minimized. The membrane paradigm is invalid inside the horizon, but is useful for theoretically probing the properties of slowly evolving black holes
Staszak, Katarzyna
2017-11-01
The membrane processes have played important role in the industrial separation process. These technologies can be found in all industrial areas such as food, beverages, metallurgy, pulp and paper, textile, pharmaceutical, automotive, biotechnology and chemical industry, as well as in water treatment for domestic and industrial application. Although these processes are known since twentieth century, there are still many studies that focus on the testing of new membranes' materials and determining of conditions for optimal selectivity, i. e. the optimum transmembrane pressure (TMP) or permeate flux to minimize fouling. Moreover the researchers proposed some calculation methods to predict the membrane processes properties. In this article, the laboratory scale experiments of membrane separation techniques, as well their validation by calculation methods are presented. Because membrane is the "heart" of the process, experimental and computational methods for its characterization are also described.
Association of microRNAs with Types of Leaf Curvature inBrassica rapa.
Ren, Wenqing; Wang, Han; Bai, Jinjuan; Wu, Feijie; He, Yuke
2018-01-01
Many vegetable crops of Brassica rapa are characterized by their typical types of leaf curvature. Leaf curvature in the right direction and to the proper degree is important for the yield and quality of green vegetable products, when cultivated under stress conditions. Recent research has unveiled some of the roles of miRNAs in Brassica crops such as how they regulate the timing of leafy head initiation and shape of the leafy head. However, the molecular mechanism underlying the variability in leaf curvature in B. rapa remains unclear. We tested the hypothesis that the leaf curvature of B. rapa is affected by miRNA levels. On the basis of leaf phenotyping, 56 B. rapa accessions were classified into five leaf curvature types, some of which were comparable to miRNA mutants of Arabidopsis thaliana in phenotype. Higher levels of miR166 and miR319a expression were associated with downward curvature and wavy margins, respectively. Overexpression of the Brp - MIR166g-1 gene caused rosette leaves to change from flat to downward curving and folding leaves to change from upward curving to flat, leading to the decrease in the number of incurved leaves and size of the leafy head. Our results reveal that miRNAs affect the types of leaf curvature in B. rapa . These findings provide insight into the relationship between miRNAs and variation in leaf curvature.
Curvature and position of nested tubes in hollow-core anti-resonant fibers
DEFF Research Database (Denmark)
Habib, Md Selim; Markos, Christos; Bang, Ole
2017-01-01
], especially when smaller tubes are “nested” inside the larger tubes [2, 3]. Here we investigate the role of curvature and position of the nested tube and we show that the position of the nested tube has a much more pronounced effect compared to the curvature on the overall performance and single...
The zero curvature formulation of the KP and the sKP equations
Energy Technology Data Exchange (ETDEWEB)
Barcelos-Neto, J.; Das, A. (Dept. of Physics and Astronomy, Univ. Rochester, NY (United States)); Panda, S.; Roy, S. (International Centre for Theoretical Physics, Trieste (Italy))
1992-05-28
The Kadomtsev-Petviashvili equation is derived from the zero curvature condition associated with the gauge group SL(2, R) in 2+1 dimensions. A fermionic extension of the KP equation is also obtained using the zero curvature condition of the supergroup OSp(2vertical stroke1), which reduces upon appropriate restriction to the Kupershmidt equation. (orig.).
Real-time GPU surface curvature estimation on deforming meshes and volumetric data sets.
Griffin, Wesley; Wang, Yu; Berrios, David; Olano, Marc
2012-10-01
Surface curvature is used in a number of areas in computer graphics, including texture synthesis and shape representation, mesh simplification, surface modeling, and nonphotorealistic line drawing. Most real-time applications must estimate curvature on a triangular mesh. This estimation has been limited to CPU algorithms, forcing object geometry to reside in main memory. However, as more computational work is done directly on the GPU, it is increasingly common for object geometry to exist only in GPU memory. Examples include vertex skinned animations and isosurfaces from GPU-based surface reconstruction algorithms. For static models, curvature can be precomputed and CPU algorithms are a reasonable choice. For deforming models where the geometry only resides on the GPU, transferring the deformed mesh back to the CPU limits performance. We introduce a GPU algorithm for estimating curvature in real time on arbitrary triangular meshes. We demonstrate our algorithm with curvature-based NPR feature lines and a curvature-based approximation for an ambient occlusion. We show curvature computation on volumetric data sets with a GPU isosurface extraction algorithm and vertex-skinned animations. We present a graphics pipeline and CUDA implementation. Our curvature estimation is up to ~18x faster than a multithreaded CPU benchmark.
Symmetric Extremal K"ahler metrics of Non-Constant Scalar Curvature
Indian Academy of Sciences (India)
58
METRICS OF NON-CONSTANT SCALAR CURVATURES. XIAOJUAN DUAN. Abstract. In this paper, we explicitly construct some rotationally symmetric extremal (pseudo-)Kähler metrics of non-constant scalar curvature, which de- pend on some parameters, on some line bundles over projective spaces. We also discuss the ...
3D FACE RECOGNITION FROM RANGE IMAGES BASED ON CURVATURE ANALYSIS
Directory of Open Access Journals (Sweden)
Suranjan Ganguly
2014-02-01
Full Text Available In this paper, we present a novel approach for three-dimensional face recognition by extracting the curvature maps from range images. There are four types of curvature maps: Gaussian, Mean, Maximum and Minimum curvature maps. These curvature maps are used as a feature for 3D face recognition purpose. The dimension of these feature vectors is reduced using Singular Value Decomposition (SVD technique. Now from calculated three components of SVD, the non-negative values of ‘S’ part of SVD is ranked and used as feature vector. In this proposed method, two pair-wise curvature computations are done. One is Mean, and Maximum curvature pair and another is Gaussian and Mean curvature pair. These are used to compare the result for better recognition rate. This automated 3D face recognition system is focused in different directions like, frontal pose with expression and illumination variation, frontal face along with registered face, only registered face and registered face from different pose orientation across X, Y and Z axes. 3D face images used for this research work are taken from FRAV3D database. The pose variation of 3D facial image is being registered to frontal pose by applying one to all registration technique then curvature mapping is applied on registered face images along with remaining frontal face images. For the classification and recognition purpose five layer feed-forward back propagation neural network classifiers is used, and the corresponding result is discussed in section 4.
The role of the epidermis and cortex in gravitropic curvature of maize roots
Bjorkman, T.; Cleland, R. E.
1988-01-01
In order to determine the role of the epidermis and cortex in gravitropic curvature of seedling roots of maize (Zea mays L. cv. Merit), the cortex on the two opposite flanks was removed from the meristem through the growing zone; gravitropic curvature was measured with the roots oriented horizontally with the cut flanks either on the upper and lower side, or on the lateral sides as a wound control. Curvature was slower in both these treatments (53 degrees in 5 h) than in intact roots (82 degrees), but there was no difference between the two orientations in extent and rate of curvature, nor in the latent time, showing that epidermis and cortex were not the site of action of the growth-regulating signal. The amount of cortex removed made no difference in the extent of curvature. Curvature was eliminated when the endodermis was damaged, raising the possibility that the endodermis or the stele-cortex interface controls gravitropic curvature in roots. The elongation rate of roots from which just the epidermis had been peeled was reduced by 0.01 mM auxin (indole-3-acetic acid) from 0.42 to 0.27 mm h-1, contradicting the hypothesis that only the epidermis responds to changes in auxin activity during gravistimulation. These observations indicate that gravitropic curvature in maize roots is not driven by differential cortical cell enlargement, and that movement of growth regulator(s) from the tip to the elongating zone is unlikely to occur in the cortex.
DEFF Research Database (Denmark)
Folkesson, Jenny; Dam, Erik B; Olsen, Ole F
2007-01-01
for intersubject comparisons. Digital phantoms were created to establish the accuracy of the curvature estimation methods. RESULTS: A comparison of the two curvature estimation methods to ground truth yielded absolute pairwise differences of 1.1%, and 4.8%, respectively. The interscan reproducibility for the two...
Association of microRNAs with Types of Leaf Curvature in Brassica rapa
Directory of Open Access Journals (Sweden)
Wenqing Ren
2018-02-01
Full Text Available Many vegetable crops of Brassica rapa are characterized by their typical types of leaf curvature. Leaf curvature in the right direction and to the proper degree is important for the yield and quality of green vegetable products, when cultivated under stress conditions. Recent research has unveiled some of the roles of miRNAs in Brassica crops such as how they regulate the timing of leafy head initiation and shape of the leafy head. However, the molecular mechanism underlying the variability in leaf curvature in B. rapa remains unclear. We tested the hypothesis that the leaf curvature of B. rapa is affected by miRNA levels. On the basis of leaf phenotyping, 56 B. rapa accessions were classified into five leaf curvature types, some of which were comparable to miRNA mutants of Arabidopsis thaliana in phenotype. Higher levels of miR166 and miR319a expression were associated with downward curvature and wavy margins, respectively. Overexpression of the Brp-MIR166g-1 gene caused rosette leaves to change from flat to downward curving and folding leaves to change from upward curving to flat, leading to the decrease in the number of incurved leaves and size of the leafy head. Our results reveal that miRNAs affect the types of leaf curvature in B. rapa. These findings provide insight into the relationship between miRNAs and variation in leaf curvature.
A note on curvature estimate of the Hermitian-Yang-Mills flow
Li, Jiayu; Zhang, Chuanjing; Zhang, Xi
2016-01-01
In this paper, we study the curvature estimate of the Hermitian-Yang-Mills flow on holomorphic vector bundles. In one simple case, we show that the curvature of the evolved Hermitian metric is uniformly bounded away from the analytic subvariety determined by the Harder-Narasimhan-Seshadri filtration of the holomorphic vector bundle.
Constant curvature surfaces of the supersymmetric ℂP{sup N−1} sigma model
Energy Technology Data Exchange (ETDEWEB)
Delisle, L., E-mail: delisle@dms.umontreal.ca [Département de Mathématiques et de Statistique, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, Québec H3C 3J7 (Canada); Hussin, V., E-mail: hussin@dms.umontreal.ca [Département de Mathématiques et de Statistique, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, Québec H3C 3J7 (Canada); Centre de Recherches Mathématiques, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, Québec H3C 3J7 (Canada); Yurduşen, İ., E-mail: yurdusen@hacettepe.edu.tr [Department of Mathematics, Hacettepe University, 06800 Beytepe, Ankara (Turkey); Zakrzewski, W. J., E-mail: w.j.zakrzewski@durham.ac.uk [Department of Mathematical Sciences, University of Durham, Durham DH1 3LE,United Kingdom (United Kingdom)
2015-02-15
Constant curvature surfaces are constructed from the finite action solutions of the supersymmetric ℂP{sup N−1} sigma model. It is shown that there is a unique holomorphic solution which leads to constant curvature surfaces: the generalized Veronese curve. We give a general criterion to construct non-holomorphic solutions of the model. We extend our analysis to general supersymmetric Grassmannian models.
On the mean curvature of semi-Riemannian graphs in semi ...
Indian Academy of Sciences (India)
Abstract. We investigate the mean curvature of semi-Riemannian graphs in the semi-. Riemannian warped product M × f Rε, where M is a semi-Riemannian manifold, Rε is the real line R with metric εdt2 (ε = ±1), and f : M → R+ is the warping function. We obtain an integral formula for mean curvature and some results ...
Biharmonic Submanifolds with Parallel Mean Curvature Vector in Pseudo-Euclidean Spaces
International Nuclear Information System (INIS)
Fu, Yu
2013-01-01
In this paper, we investigate biharmonic submanifolds in pseudo-Euclidean spaces with arbitrary index and dimension. We give a complete classification of biharmonic spacelike submanifolds with parallel mean curvature vector in pseudo-Euclidean spaces. We also determine all biharmonic Lorentzian surfaces with parallel mean curvature vector field in pseudo-Euclidean spaces
Chmyrov, Volodymyr; Spielmann, Thiemo; Hevekerl, Heike; Widengren, Jerker
2015-06-02
Membrane environment and fluidity can modulate the dynamics and interactions of membrane proteins and can thereby strongly influence the function of cells and organisms in general. In this work, we demonstrate that trans-cis isomerization of lipophilic dyes is a useful parameter to monitor packaging and fluidity of biomembranes. Fluorescence fluctuations, generated by trans-cis isomerization of the thiocarbocyanine dye Merocyanine 540 (MC540), were first analyzed by fluorescence correlation spectroscopy (FCS) in different alcohol solutions. Similar isomerization kinetics of MC540 in lipid vesicles could then also be monitored, and the influence of lipid polarity, membrane curvature, and cholesterol content was investigated. While no influence of membrane curvature and lipid polarity could be observed, a clear decrease in the isomerization rates could be observed with increasing cholesterol contents in the vesicle membranes. Finally, procedures to spatially map photoinduced and thermal isomerization rates on live cells by transient state (TRAST) imaging were established. On the basis of these procedures, MC540 isomerization was studied on live MCF7 cells, and TRAST images of the cells at different temperatures were found to reliably detect differences in the isomerization parameters. Our studies indicate that trans-cis isomerization is a useful parameter for probing membrane dynamics and that the TRAST imaging technique can provide spatial maps of photoinduced isomerization as well as both photoinduced and thermal back-isomerization, resolving differences in local membrane microviscosity in live cells.
DEFF Research Database (Denmark)
Hanczyc, Martin M; Monnard, Pierre-Alain
2017-01-01
Cellular membranes, which are self-assembled bilayer structures mainly composed of lipids, proteins and conjugated polysaccharides, are the defining feature of cell physiology. It is likely that the complexity of contemporary cells was preceded by simpler chemical systems or protocells during...... the various evolutionary stages that led from inanimate to living matter. It is also likely that primitive membranes played a similar role in protocell 'physiology'. The composition of such ancestral membranes has been proposed as mixtures of single hydrocarbon chain amphiphiles, which are simpler versions...
Inﬂuence of implant rod curvature on sagittal correction of scoliosis deformity
DEFF Research Database (Denmark)
Salmingo, Remel A.; Tadano, Shigeru; Abe, Yuichiro
2014-01-01
scoliosis patients underwent surgery. Average age at the time of operation was 14 years. OUTCOME MEASURES: The preoperative and postoperative implant rod angle of curvature expressed in degrees was obtained for each patient. METHODS: Two implant rods were attached to the concave and convex side...... of curvature between the implant rod extreme ends was measured before implantation and after surgery. The sagittal curvature between the corresponding spinal levels of healthy adolescents obtained by previous studies was compared with the implant rod angle of curvature to evaluate the sagittal curve correction...... significantly deformed after surgery. The average degree of rod deformation Dq at the concave and convex sides was 15.8 and 1.6, respectively. The average preoperative and postoperative implant rod angle of curvature at the concave side was 33.6 and 17.8, respectively. The average preoperative and postoperative...
von Neumann Morgenstern Preferences
DEFF Research Database (Denmark)
Vind, Karl
von Neumann Morgenstern utility is generalized to von Neumann Morgenstern preferences. The proof is an application of simple hyperplane theorems......von Neumann Morgenstern utility is generalized to von Neumann Morgenstern preferences. The proof is an application of simple hyperplane theorems...
von Neumann Morgenstern Preferences
DEFF Research Database (Denmark)
Vind, Karl
2000-01-01
von Neumann Morgenstern utility is generalized to von Neumann Morgenstern preferences. The proof is an application of simple hyperplane theorems......von Neumann Morgenstern utility is generalized to von Neumann Morgenstern preferences. The proof is an application of simple hyperplane theorems...
Eye tracking social preferences
Jiang, Ting; Potters, Jan; Funaki, Yukihiko
We hypothesize that if people are motivated by a particular social preference, then choosing in accordance with this preference will lead to an identifiable pattern of eye movements. We track eye movements while subjects make choices in simple three-person distribution experiments. We characterize
Versatile membrane deformation potential of activated pacsin.
Directory of Open Access Journals (Sweden)
Shih Lin Goh
Full Text Available Endocytosis is a fundamental process in signaling and membrane trafficking. The formation of vesicles at the plasma membrane is mediated by the G protein dynamin that catalyzes the final fission step, the actin cytoskeleton, and proteins that sense or induce membrane curvature. One such protein, the F-BAR domain-containing protein pacsin, contributes to this process and has been shown to induce a spectrum of membrane morphologies, including tubules and tube constrictions in vitro. Full-length pacsin isoform 1 (pacsin-1 has reduced activity compared to its isolated F-BAR domain, implicating an inhibitory role for its C-terminal Src homology 3 (SH3 domain. Here we show that the autoinhibitory, intramolecular interactions in pacsin-1 can be released upon binding to the entire proline-rich domain (PRD of dynamin-1, resulting in potent membrane deformation activity that is distinct from the isolated F-BAR domain. Most strikingly, we observe the generation of small, homogenous vesicles with the activated protein complex under certain experimental conditions. In addition, liposomes prepared with different methods yield distinct membrane deformation morphologies of BAR domain proteins and apparent activation barriers to pacsin-1's activity. Theoretical free energy calculations suggest bimodality of the protein-membrane system as a possible source for the different outcomes, which could account for the coexistence of energetically equivalent membrane structures induced by BAR domain-containing proteins in vitro. Taken together, our results suggest a versatile role for pacsin-1 in sculpting cellular membranes that is likely dependent both on protein structure and membrane properties.
Supported lipid bilayers with controlled curvature via colloidal lithography
DEFF Research Database (Denmark)
Sundh, Maria; Manandhar, Michal; Svedhem, Sofia
2011-01-01
monitoring (QCM-D) was used to confirm vesicle rupture onto such structured surfaces. Fluorescence microscopy was used to show fluidity of the supported membranes. The formation of confluent SLBs is demonstrated at the nanostructured surfaces from vesicles composed of POPC lipids. However, at surfaces...
Hamiltonian formulation of surfaces with constant Gaussian curvature
Energy Technology Data Exchange (ETDEWEB)
Trejo, Miguel; Amar, Martine Ben; Mueller, Martin Michael [Laboratoire de Physique Statistique de l' Ecole Normale Superieure (UMR 8550), associe aux Universites Paris 6 et Paris 7 et au CNRS, 24, rue Lhomond, 75005 Paris (France)
2009-10-23
Dirac's method for constrained Hamiltonian systems is used to describe surfaces of constant Gaussian curvature. A geometrical free energy, for which these surfaces are equilibrium states, is introduced and interpreted as an action. An equilibrium surface can then be generated by the evolution of a closed space curve. Since the underlying action depends on second derivatives, the velocity of the curve and its conjugate momentum must be included in the set of phase-space variables. Furthermore, the action is linear in the acceleration of the curve and possesses a local symmetry-reparametrization invariance-which implies primary constraints in the canonical formalism. These constraints are incorporated into the Hamiltonian through Lagrange multiplier functions that are identified as the components of the acceleration of the curve. The formulation leads to four first-order partial differential equations, one for each canonical variable. With the appropriate choice of parametrization, only one of these equations has to be solved to obtain the surface which is swept out by the evolving space curve. To illustrate the formalism, several evolutions of pseudospherical surfaces are discussed.
Terminal twist-induced writhe of DNA with intrinsic curvature.
Hu, Kai
2007-04-01
Supercoiling of a closed circular DNA rod may result from an application of terminal twist to the DNA rod by cutting the rod, rotating one of the cut faces as the other being fixed and then sealing the cut. According to White's formula, DNA supercoiling is probably accompanied by a writhe of the DNA axis. Deduced from the elastic rod model for DNA structure, an intrinsically straight closed circular DNA rod does not writhe as subject to a terminal twist, until the number of rotation exceeds a rod-dependent threshold. By contrast, a closed circular DNA rod with intrinsic curvature writhes instantly as subject to a terminal twist. This noteworthy character in fact belongs to many intrinsically curved DNA rods. By solving the dynamic equations, the linearization of the Euler-Lagrange equations governing intrinsically curved DNA rods, this paper shows that almost every clamped-end intrinsically curved DNA rod writhes instantly when subject to a terminal twist (clamped-end DNA rods include closed circular DNA rods and topological domains of open DNA rods). In terms of physical quantities, the exceptions are identified with points in R(6) whose projections onto R(5) (through ignoring the total energy density of a rod) form a subset of a quadratic hypersurface. This paper also suggests that the terminal twist induced writhe is due to the elasticity and the clamped-end boundary conditions of the DNA rods.
Berry curvature and dynamics of a magnetic bubble
Koshibae, Wataru; Nagaosa, Naoto
2016-04-01
Magnetic bubbles have been the subject of intensive studies aiming to investigate their applications to memory devices. A bubble can be regarded as the closed domain wall and is characterized by the winding number of the in-plane components or the skyrmion number N sk , which are related to the number of Bloch lines (BLs). For the magnetic bubbles without BLs, the Thiele equation assuming no internal distortion describes the center-of-mass motion of the bubbles very well. For the magnetic bubbles with BLs, on the other hand, their dynamics is affected seriously by that of BLs along the domain wall. Here we show theoretically, that the distribution of the Berry curvature b z , i.e., the solid angle formed by the magnetization vectors, in the bubble plays the key role in the dynamics of a bubble with {N}{sk}=0 in a dipolar magnet. In this case, the integral of b z over the space is zero, while the nonuniform distribution of b z and associated Magnus force induce several nontrivial coupled dynamics of the internal deformation and center-of-mass motion as explicitly demonstrated by numerical simulations of Landau-Lifshitz-Gilbert equation. These findings give an alternative view and will pave a new route to design the bubble dynamics.
Dual curvature acoustically damped concentrating collector. Final technical report
Energy Technology Data Exchange (ETDEWEB)
Smith, G.A.; Rausch, R.A.
1980-05-01
A development program was conducted to investigate the design and performance parameters of a novel, dual curvature, concentrating solar collector. The reflector of the solar collector is achieved with a stretched-film reflective surface that approximates a hyperbolic paraboloid and is capable of line-focusing at concentration ratios ranging from 10 to 20X. A prototype collector was designed based on analytical and experimental component trade-off activities as well as economic analyses of solar thermal heating and cooling systems incorporating this type of collector. A prototype collector incorporating six 0.66 x 1.22 m (2 x 4 ft) was fabricated and subjected to a limited thermal efficiency test program. A peak efficiency of 36% at 121/sup 0/C (250/sup 0/F) was achieved based upon the gross aperture area. Commercialization activities were conducted, including estimated production costs of $134.44/m/sup 2/ ($12.49/ft/sup 2/) for the collector assembly (including a local suntracker and controls) and $24.33/m/sup 2/ ($2.26/ft/sup 2/) for the reflector subassembly.
The hybrid inflation waterfall and the primordial curvature perturbation
International Nuclear Information System (INIS)
Lyth, David H.
2012-01-01
Without demanding a specific form for the inflaton potential, we obtain an estimate of the contribution to the curvature perturbation generated during the linear era of the hybrid inflation waterfall. The spectrum of this contribution peaks at some wavenumber k = k * , and goes like k 3 for k * , making it typically negligible on cosmological scales. The scale k * can be outside the horizon at the end of inflation, in which case ζ = −(g 2 −(g 2 )) with g gaussian. Taking this into account, the cosmological bound on the abundance of black holes is likely to be satisfied if the curvaton mass m much bigger than the Hubble parameter H, but is likely to be violated if m∼< H. Coming to the contribution to ζ from the rest of the waterfall, we are led to consider the use of the 'end-of-inflation' formula, giving the contribution to ζ generated during a sufficiently sharp transition from nearly-exponential inflation to non-inflation, and we state for the first time the criterion for the transition to be sufficiently sharp. Our formulas are applied to supersymmetric GUT inflation and to supernatural/running-mass inflation
The hybrid inflation waterfall and the primordial curvature perturbation
Energy Technology Data Exchange (ETDEWEB)
Lyth, David H., E-mail: d.lyth@lancaster.ac.uk [Consortium for Fundamental Physics, Cosmology and Astroparticle Group, Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom)
2012-05-01
Without demanding a specific form for the inflaton potential, we obtain an estimate of the contribution to the curvature perturbation generated during the linear era of the hybrid inflation waterfall. The spectrum of this contribution peaks at some wavenumber k = k{sub *}, and goes like k{sup 3} for k << k{sub *}, making it typically negligible on cosmological scales. The scale k{sub *} can be outside the horizon at the end of inflation, in which case ζ = −(g{sup 2}−(g{sup 2})) with g gaussian. Taking this into account, the cosmological bound on the abundance of black holes is likely to be satisfied if the curvaton mass m much bigger than the Hubble parameter H, but is likely to be violated if m∼
The hybrid inflation waterfall and the primordial curvature perturbation
Lyth, David H.
2012-05-01
Without demanding a specific form for the inflaton potential, we obtain an estimate of the contribution to the curvature perturbation generated during the linear era of the hybrid inflation waterfall. The spectrum of this contribution peaks at some wavenumber k = k*, and goes like k3 for k Lt k*, making it typically negligible on cosmological scales. The scale k* can be outside the horizon at the end of inflation, in which case ζ = -(g2-langg2rang) with g gaussian. Taking this into account, the cosmological bound on the abundance of black holes is likely to be satisfied if the curvaton mass m much bigger than the Hubble parameter H, but is likely to be violated if mlsimH. Coming to the contribution to ζ from the rest of the waterfall, we are led to consider the use of the `end-of-inflation' formula, giving the contribution to ζ generated during a sufficiently sharp transition from nearly-exponential inflation to non-inflation, and we state for the first time the criterion for the transition to be sufficiently sharp. Our formulas are applied to supersymmetric GUT inflation and to supernatural/running-mass inflation. A preliminary version of this paper appeared as arXiv:1107.1681.
Zecchi, Karis A.; Mosgaard, Lars D.; Heimburg, Thomas
2017-01-01
Biological membranes are capacitors that can be charged by applying an electric 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. This effect is especially strong close to chain melting transitions. A consequence is voltage induced pore formation in the lipid membrane. Since the force is quadratic in voltage, negative and positive voltages have an identical influence on the physics of symmetric membranes. 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 physical 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. It was investigated in detail by A.G. Petrov in the recent decades. 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. The changes in current-voltage relationships are consistent with the known magnitude of the flexoelectric effect.
Hamilton's equations for a fluid membrane: axial symmetry
International Nuclear Information System (INIS)
Capovilla, R; Guven, J; Rojas, E
2005-01-01
Consider a homogeneous fluid membrane, or vesicle, described by the Helfrich-Canham energy, quadratic in the mean curvature. When the membrane is axially symmetric, this energy can be viewed as an 'action' describing the motion of a particle; the contours of equilibrium geometries are identified with particle trajectories. A novel Hamiltonian formulation of the problem is presented which exhibits the following two features: (i) the second derivatives appearing in the action through the mean curvature are accommodated in a natural phase space and (ii) the intrinsic freedom associated with the choice of evolution parameter along the contour is preserved. As a result, the phase space involves momenta conjugate not only to the particle position but also to its velocity, and there are constraints on the phase space variables. This formulation provides the groundwork for a field theoretical generalization to arbitrary configurations, with the particle replaced by a loop in space
Modelling Protein-induced Membrane Deformation using Monte Carlo and Langevin Dynamics Simulations
Radhakrishnan, R.; Agrawal, N.; Ramakrishnan, N.; Kumar, P. B. Sunil; Liu, J.
2010-11-01
In eukaryotic cells, internalization of extracellular cargo via the cellular process of endocytosis is orchestrated by a variety of proteins, many of which are implicated in membrane deformation/bending. We model the energetics of deformations membranes by using the Helfrich Hamiltonian using two different formalisms: (i) Cartesian or Monge Gauge using Langevin dynamics; (ii) Curvilinear coordinate system using Monte Carlo (MC). Monge gauge approach which has been extensively studied is limited to small deformations of the membrane and cannot describe extreme deformations. Curvilinear coordinate approach can handle large deformation limits as well as finite-temperature membrane fluctuations; here we employ an unstructured triangular mesh to compute the local curvature tensor, and we evolve the membrane surface using a MC method. In our application, we compare the two approaches (i and ii above) to study how the spatial assembly of curvature inducing proteins leads to vesicle budding from a planar membrane. We also quantify how the curvature field of the membrane impacts the spatial segregation of proteins.
Colloidal membranes: The rich confluence of geometry and liquid crystals
Kaplan, Cihan Nadir
A simple and experimentally realizable model system of chiral symmetry breaking is liquid-crystalline monolayers of aligned, identical hard rods. In these materials, tuning the chirality at the molecular level affects the geometry at systems level, thereby inducing a myriad of morphological transitions. This thesis presents theoretical studies motivated by the rich phenomenology of these colloidal monolayers. High molecular chirality leads to assemblages of rods exhibiting macroscopic handedness. In the first part we consider one such geometry, twisted ribbons, which are minimal surfaces to a double helix. By employing a theoretical approach that combines liquid-crystalline order with the preferred shape, we focus on the phase transition from simple flat monolayers to these twisted structures. In these monolayers, regions of broken chiral symmetry nucleate at the interfaces, as in a chiral smectic A sample. The second part particularly focuses on the detailed structure and thermodynamic stability of two types of observed interfaces, the monolayer edge and domain walls in simple flat monolayers. Both the edge and "twist-walls" are quasi-one-dimensional bands of molecular twist deformations dictated by local chiral interactions and surface energy considerations. We develop a unified theory of these interfaces by utilizing the de Gennes framework accompanied by appropriate surface energy terms. The last part turns to colloidal "cookies", which form in mixtures of rods with opposite handedness. These elegant structures are essentially flat monolayers surrounded by an array of local, three dimensional cusp defects. We reveal the thermodynamic and structural characteristics of cookies. Furthermore, cookies provide us with a simple relation to determine the intrinsic curvature modulus of our model system, an important constant associated with topological properties of membranes. Our results may have impacts on a broader class of soft thin films.
Quantitative analysis and prediction of curvature in leucine-rich repeat proteins.
Hindle, K Lauren; Bella, Jordi; Lovell, Simon C
2009-11-01
Leucine-rich repeat (LRR) proteins form a large and diverse family. They have a wide range of functions most of which involve the formation of protein-protein interactions. All known LRR structures form curved solenoids, although there is large variation in their curvature. It is this curvature that determines the shape and dimensions of the inner space available for ligand binding. Unfortunately, large-scale parameters such as the overall curvature of a protein domain are extremely difficult to predict. Here, we present a quantitative analysis of determinants of curvature of this family. Individual repeats typically range in length between 20 and 30 residues and have a variety of secondary structures on their convex side. The observed curvature of the LRR domains correlates poorly with the lengths of their individual repeats. We have, therefore, developed a scoring function based on the secondary structure of the convex side of the protein that allows prediction of the overall curvature with a high degree of accuracy. We also demonstrate the effectiveness of this method in selecting a suitable template for comparative modeling. We have developed an automated, quantitative protocol that can be used to predict accurately the curvature of leucine-rich repeat proteins of unknown structure from sequence alone. This protocol is available as an online resource at http://www.bioinf.manchester.ac.uk/curlrr/.
International Nuclear Information System (INIS)
Yamasaki, K; Iwayama, T; Yajima, T
2011-01-01
The Okubo-Weiss field, frequently used for partitioning incompressible two-dimensional (2D) fluids into coherent and incoherent regions, corresponds to the Gaussian curvature of the stream function. Therefore, we consider the differential geometric structures of stream functions and calculate the Gaussian curvatures of some basic flows. We find the following. (I) The vorticity corresponds to the mean curvature of the stream function. Thus, the stream-function surface for an irrotational flow and that for a parallel shear flow correspond to the minimal surface and a developable surface, respectively. (II) The relationship between the coherency and the magnitude of the vorticity is interpreted by the curvatures. (III) Using the Gaussian curvature, stability of single and double point vortex streets is analyzed. The results of this analysis are compared with the well-known linear stability analysis. (IV) Conformal mapping in fluid mechanics is the physical expression of the geometric fact that the sign of the Gaussian curvature does not change in conformal mapping. These findings suggest that the curvatures of stream functions are useful for understanding the geometric structure of an incompressible 2D flow.
Changes of anterior and posterior corneal curvature and anterior chamber depth after SMILE
Directory of Open Access Journals (Sweden)
Li Li
2017-12-01
Full Text Available AIM: To observe the changes of anterior and posterior corneal curvature and anterior chamber depth after small incision lenticule extraction(SMILEfor low and high myopic astigmatism. METHODS: Sixty-three cases(88 eyesundergone SMILE in our hospital were included. The patients were divided into two groups based on astigmatism degree: the Group A: -2.00D to -4.00D astigmatism, the Group B: -0.25D to -1.00D astigmatism. Patients were examined at 1wk, 1 and 3mo after operations. Visual acuity, intraocular pressure, refraction, corneal curvature and anterior chamber depth were recorded. The change of anterior and posterior corneal curvature and anterior chamber depth was compared. Spearman correlation analysis and independent t test were used for statistical analysis. RESULTS: Surgery was done well in all patients without complications. No statistically significant difference was found between the two groups in posterior corneal curvature and anterior chamber depth preoperatively, postoperatively 7d,1 and 3mo(P>0.05. One week postoperatively, the anterior corneal curvature was statistically significant from that of preoperative in both groups(PP>0.05. CONCLUSION: No significant change of anterior and posterior corneal curvature and anterior chamber depth was found after SMILE for correcting low and high myopic astigmatism. One week after SMILE the anterior corneal curvature become stable.
Directory of Open Access Journals (Sweden)
Mehdi Safari
2016-09-01
Full Text Available In this work, laser forming of cylindrical surfaces with arbitrary radius of curvature is investigated experimentally and numerically. For laser forming of cylindrical surfaces with arbitrary radius of curvature, a new and comprehensive method is proposed in this paper. This method contains simple linear irradiating lines and using an analytical method, required process parameters for laser forming of a cylindrical surface with a specific radius of curvature is proposed. In this method, laser output power, laser scanning speed and laser beam diameter are selected based on laser machine and process limitations. As in the laser forming of a cylindrical surface, parallel irradiating lines are needed; therefore key parameter for production of a cylindrical surface with a specific radius of curvature is the number of irradiating lines. Hence, in the proposed analytical method, the required number of irradiating lines for production of a cylindrical surface with a specific radius of curvature is suggested. Performance of the proposed method for production of cylindrical surface with a specific radius of curvature is verified with experimental tests. The results show that using proposed analytical method, cylindrical surfaces with any radius of curvature can be produced successfully.
Revealed smooth nontransitive preferences
DEFF Research Database (Denmark)
Keiding, Hans; Tvede, Mich
2013-01-01
In the present paper, we are concerned with the behavioural consequences of consumers having nontransitive preference relations. Data sets consist of ﬁnitely many observations of price vectors and consumption bundles. A preference relation rationalizes a data set provided that for every observed...... many observations of price vectors, lists of individual incomes and aggregate demands. We apply our main result to characterize market data sets consistent with equilibrium behaviour of pure-exchange economies with smooth nontransitive consumers....... consumption bundle, all strictly preferred bundles are more expensive than the observed bundle. Our main result is that data sets can be rationalized by a smooth nontransitive preference relation if and only if prices can normalized such that the law of demand is satisﬁed. Market data sets consist of ﬁnitely...
Curvature effects in two-dimensional optical devices inspired by transformation optics
Yuan, Shuhao
2016-11-14
Light transport in curved quasi two-dimensional waveguides is considered theoretically. Within transformation optics and tensor theory, a concise description of curvature effects on transverse electric and magnetic waves is derived. We show that the curvature can induce light focusing and photonic crystal properties, which are confirmed by finite element simulations. Our results indicate that the curvature is an effective parameter for designing quasi two-dimensional optical devices in the fields of micro and nano photonics. Â© 2016 Author(s).
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-03-01
A geometric formulation of Higgs Effective Field Theory (HEFT) is presented. Experimental observables are given in terms of geometric invariants of the scalar sigma model sector such as the curvature of the scalar field manifold M. We show how the curvature can be measured experimentally via Higgs cross-sections, WL scattering, and the S parameter. The one-loop action of HEFT is given in terms of geometric invariants of M. The distinction between the Standard Model (SM) and HEFT is whether M is flat or curved, and the curvature is a signal of the scale of new physics.
Directory of Open Access Journals (Sweden)
Rodrigo Alonso
2016-03-01
Full Text Available A geometric formulation of Higgs Effective Field Theory (HEFT is presented. Experimental observables are given in terms of geometric invariants of the scalar sigma model sector such as the curvature of the scalar field manifold M. We show how the curvature can be measured experimentally via Higgs cross-sections, WL scattering, and the S parameter. The one-loop action of HEFT is given in terms of geometric invariants of M. The distinction between the Standard Model (SM and HEFT is whether M is flat or curved, and the curvature is a signal of the scale of new physics.
Estimation of current sheath curvature in plasma focus device using magnetic probes
International Nuclear Information System (INIS)
Li, Cai; Yujuan, Shi; Patran, A.; Rawat, R.S.
2002-01-01
The dynamics of current sheath, in terms of its speed and sheath curvature, in dense plasma focus device was investigated in its axial acceleration phase using multiple magnetic probes. The investigation was performed for different filling gas pressures of neon. The relative X-ray yields were estimated using a diode X-ray spectrometer. A possible correlation between the current sheath curvature and the X-ray emission was explored. The investigation demonstrates the effective use of relatively simple diagnostics tool, the magnetic probes, in the estimation of current sheath axial speeds and curvatures. (authors)
DEFF Research Database (Denmark)
Rask, Morten; Sørensen, Bent F.
2012-01-01
A new approach is proposed for measuring the J integral (and thus the fracture resistance) of interface cracks in multiply laminates. With this approach the J integral is found from beam curvatures and applied moments. Knowledge of ply layup and stiffness is not required. In order to test...... the accuracy of the proposed approach, double cantilever beam specimen loaded with uneven bending moments (DCB-UBM) specimens were tested and analysed using the curvature approach and a method based on laminate beam theory. Beam curvatures were determined using a configuration of strain gauges. Good agreement...
DEFF Research Database (Denmark)
van der Horst, Sander; van de Wiel, Jelmer E.; Ferreira, Carlos Simao
2016-01-01
Blades on a Vertical Axis Wind Turbine (VAWT) experience curved streamlines, caused by the rotation of the turbine. This phenomenon is known as flow curvature and has effects on the aerodynamic loading of the blades. Several authors have proposed methods to account for flow curvature, resulting...... errors remain that are intrinsic to the conformal methods used. It is shown that VAWT rotation is equivalent to an eternal pitching motion. Using this similarity, flow curvature modeling has been added to the airfoil analysis tool XFOIL. The various changes have been made in the inviscid solver, in a way...
Re-acceleration Model for Radio Relics with Spectral Curvature
Kang, Hyesung; Ryu, Dongsu
2016-05-01
Most of the observed features of radio gischt relics, such as spectral steepening across the relic width and a power-law-like integrated spectrum, can be adequately explained by a diffusive shock acceleration (DSA) model in which relativistic electrons are (re-)accelerated at shock waves induced in the intracluster medium. However, the steep spectral curvature in the integrated spectrum above ˜2 GHz detected in some radio relics, such as the Sausage relic in cluster CIZA J2242.8+5301, may not be interpreted by the simple radiative cooling of postshock electrons. In order to understand such steepening, we consider here a model in which a spherical shock sweeps through and then exits out of a finite-size cloud with fossil relativistic electrons. The ensuing integrated radio spectrum is expected to steepen much more than predicted for aging postshock electrons, since the re-acceleration stops after the cloud-crossing time. Using DSA simulations that are intended to reproduce radio observations of the Sausage relic, we show that both the integrated radio spectrum and the surface brightness profile can be fitted reasonably well, if a shock of speed {u}s ˜ 2.5-2.8 × {10}3 {km} {{{s}}}-1 and a sonic Mach number {M}s ˜ 2.7-3.0 traverses a fossil cloud for ˜45 Myr, and the postshock electrons cool further for another ˜10 Myr. This attempt illustrates that steep curved spectra of some radio gischt relics could be modeled by adjusting the shape of the fossil electron spectrum and adopting the specific configuration of the fossil cloud.
Villeneuve, Masumi; Tanaka, Mihoko; Saito, Natsumi; Sakamoto, Hiroyasu; Hayami, Yoshiteru
2018-01-01
Mixed micelles formed in a ternary-solute aqueous solution of NaOH, iron (III)-ethylenediamine-N, N, N', N'-tetraacetic acid complex (Fe-EDTA) and 1,2-diheptanoyl-sn-glycero-3-phosphatidyl choline (DHPC) were studied and compared with the mixed adsorbed film reported in Part I of this series to clarify the effect of the curvature of molecular assemblies on the interactions between their Fe-EDTA and DHPC constituents. The critical micelle concentrations (CMCs), surface tension at the CMC, and solution pH were measured as functions of the mole fractions of NaOH and DHPC. Rigorous thermodynamic equations were derived, in which the overall proton dissociation equilibria of Fe-EDTA and DHPC were taken into consideration, and applied to experimental data to obtain phase diagrams of micelle formation and the micelle-adsorbed film equilibrium. It was found that when the bulk solution was strongly acidic, Fe-EDTA was incorporated in the micelles. However, the adsorbed film was more Fe-EDTA-enriched than the micelle. These findings imply that a flat cell membrane is more permeable to an iron complex than a cell membrane with positive curvature. Copyright © 2017 Elsevier B.V. All rights reserved.
Flexoelectric effects in model and native membranes containing ion channels.
Petrov, A G; Miller, B A; Hristova, K; Usherwood, P N
1993-01-01
An experimental study of flexoelectricity in model membranes containing ion pores and native membranes containing ion channels has been undertaken with the objective of determining the relationship, if any, between flexoelectricity and ion transport. Model membrane patches containing ion pores induced by a blue-green algal toxin, microcystin-LR, and locust muscle membrane patches containing potassium channels were studied using patch-clamp techniques. A correspondence was established between the presence of open channels and pores and the amplitude of the 1st harmonic of the total membrane current when the membranes or patches were subjected to pressure oscillations. The 2nd harmonic of the membrane current provided a measure of the amplitude of a membrane curvature induced by pressure, thus making it possible to determine the membrane flexoelectric coefficient. This study shows that flexoelectricity could be an effective driving force for ion transport through membrane pores and channels, thus further highlighting the possible biological significance of this mechano-electric phenomenon.
Preference Handling for Artificial Intelligence
Goldsmith, Judy; University of Kentucky; Junker, Ulrich; ILOG
2009-01-01
This article explains the benefits of preferences for AI systems and draws a picture of current AI research on preference handling. It thus provides an introduction to the topics covered by this special issue on preference handling.
Age Preferences for Professional Helpers.
Furchtgott, Ernest; Busemeyer, Jerome R.
1981-01-01
For all occupations except clergyman, a relationship between the age of the respondent and preferred age of the professional existed. Older individuals preferred older service providers with one exception, their physician. Highly educated respondents preferred younger physicians. (Author)
DNA sequencing using fluorescence background electroblotting membrane
Caldwell, K.D.; Chu, T.J.; Pitt, W.G.
1992-05-12
A method for the multiplex sequencing on DNA is disclosed which comprises the electroblotting or specific base terminated DNA fragments, which have been resolved by gel electrophoresis, onto the surface of a neutral non-aromatic polymeric microporous membrane exhibiting low background fluorescence which has been surface modified to contain amino groups. Polypropylene membranes are preferably and the introduction of amino groups is accomplished by subjecting the membrane to radio or microwave frequency plasma discharge in the presence of an aminating agent, preferably ammonia. The membrane, containing physically adsorbed DNA fragments on its surface after the electroblotting, is then treated with crosslinking means such as UV radiation or a glutaraldehyde spray to chemically bind the DNA fragments to the membrane through amino groups contained on the surface. The DNA fragments chemically bound to the membrane are subjected to hybridization probing with a tagged probe specific to the sequence of the DNA fragments. The tagging may be by either fluorophores or radioisotopes. The tagged probes hybridized to the target DNA fragments are detected and read by laser induced fluorescence detection or autoradiograms. The use of aminated low fluorescent background membranes allows the use of fluorescent detection and reading even when the available amount of DNA to be sequenced is small. The DNA bound to the membranes may be reprobed numerous times. No Drawings
Ogunyankin, Maria O; Longo, Marjorie L
2013-07-07
Nanometer-scale curvature patterns of an underlying substrate are imposed on lipid multibilayers with each pattern imparting distinctly different sorting dynamics to a metastable pixelation pattern of coexisting liquid ordered (Lo)-liquid disordered (Ld) lipid phases. Therefore, this work provides pathways toward mechanical energy-based separations for analysis of biomembrane-associate species. The central design concept of the patterned sections of the silica substrate is a square lattice pattern of 100 nm projected radius poly(methyl methacrylate) (PMMA) hemispherical features formed by electron beam lithography which pixelates the coexisting phases in order to balance membrane bending and line energy. In one variation, we surround this pattern with three PMMA walls/fences 100 nm in height which substantially slows the loss of the high line energy pixelated Lo phase by altering the balance of two competing mechanism (Ostwald ripening vs. vesiculation). In another walled variation, we form a gradient of the spacing of the 100 nm features which forces partitioning of the Lo phase toward the end of the gradient with the most open (400 nm spacing) lattice pattern where a single vesicle could grow from the Lo phase. We show that two other variations distinctly impact the dynamics, demonstrating locally slowed loss of the high line energy pixelated Lo phase and spontaneous switching of the pixel location on the unit cell, respectively. Moreover, we show that the pixelation patterns can be regenerated and sharpened by a heating and cooling cycle. We argue that localized variations in the underlying curvature pattern have rather complex consequences because of the coupling and/or competition of dynamic processes to optimize mechanical energy such as lipid diffusion, vesiculation and growth, and phase/compositional partitioning.
Surfaces of Constant Mean Curvature in Euclidean 3-space Orthogonal to a Plane along its Boundary
Directory of Open Access Journals (Sweden)
HINOJOSA PEDRO A.
2002-01-01
Full Text Available We consider compact surfaces with constant nonzero mean curvature whose boundary is a convex planar Jordan curve. We prove that if such a surface is orthogonal to the plane of the boundary, then it is a hemisphere.
The Explicit Construction of Einstein Finsler Metrics with Non-Constant Flag Curvature
Directory of Open Access Journals (Sweden)
Enli Guo
2009-04-01
Full Text Available By using the Hawking Taub-NUT metric, this note gives an explicit construction of a 3-parameter family of Einstein Finsler metrics of non-constant flag curvature in terms of navigation representation.
Curvature effects on the electronic and transport properties of semiconductor films
Batista, F. F.; Chaves, Andrey; da Costa, D. R.; Farias, G. A.
2018-05-01
Within the effective mass approximation, we study the curvature effects on the electronic and transport properties of semiconductor films. We investigate how the geometry-induced potential resulting exclusively from periodic ripples in the film induces electronic confinement and a superlattice band structure. For fixed curvature parameters, such a confinement can be easily tuned by an external electric field, hence features of the superlattice band structure such as its energy gaps and band curvature can be controlled by an external parameter. We also show that, for some values of curvature and electric field, it is possible to obtain massless Dirac bands for a smooth curved structure. Moreover, we use a wave packet propagation method to demonstrate that the ripples are responsible for a significant inter-sub-band transition, specially for moderate values of the ripple height.
Phase-space curvature in spin-orbit-coupled ultracold atomic systems
Armaitis, J.; Ruseckas, J.; Anisimovas, E.
2017-04-01
We consider a system with spin-orbit coupling and derive equations of motion which include the effects of Berry curvatures. We apply these equations to investigate the dynamics of particles with equal Rashba-Dresselhaus spin-orbit coupling in one dimension. In our derivation, the adiabatic transformation is performed first and leads to quantum Heisenberg equations of motion for momentum and position operators. These equations explicitly contain position-space, momentum-space, and phase-space Berry curvature terms. Subsequently, we perform the semiclassical approximation and obtain the semiclassical equations of motion. Taking the low-Berry-curvature limit results in equations that can be directly compared to previous results for the motion of wave packets. Finally, we show that in the semiclassical regime, the effective mass of the equal Rashba-Dresselhaus spin-orbit-coupled system can be viewed as a direct effect of the phase-space Berry curvature.
Generalization of the swelling method to measure the intrinsic curvature of lipids
Barragán Vidal, I. A.; Müller, M.
2017-12-01
Via computer simulation of a coarse-grained model of two-component lipid bilayers, we compare two methods of measuring the intrinsic curvatures of the constituting monolayers. The first one is a generalization of the swelling method that, in addition to the assumption that the spontaneous curvature linearly depends on the composition of the lipid mixture, incorporates contributions from its elastic energy. The second method measures the effective curvature-composition coupling between the apposing leaflets of bilayer structures (planar bilayers or cylindrical tethers) to extract the spontaneous curvature. Our findings demonstrate that both methods yield consistent results. However, we highlight that the two-leaflet structure inherent to the latter method has the advantage of allowing measurements for mixed lipid systems up to their critical point of demixing as well as in the regime of high concentration (of either species).
Directory of Open Access Journals (Sweden)
Donghoon Kang
2013-01-01
Full Text Available This study is focused on the verification of the key idea of a newly developed steel-concrete composite bridge. The key idea of the proposed bridge is to reduce the design moment by applying vertical prestressing force to steel girders, so that a moment distribution of a continuous span bridge is formed in a simple span bridge. For the verification of the key technology, curvature changes of the bridge should be monitored sequentially at every construction stage. A pair of multiplexed FBG sensor arrays is proposed in order to measure curvature changes in this study. They are embedded in a full-scale test bridge and measured local strains, which are finally converted to curvatures. From the result of curvature changes, it is successfully ensured that the key idea of the proposed bridge, expected theoretically, is viable.
Estimation of the curvature of an interface from a digital 2D image
Energy Technology Data Exchange (ETDEWEB)
Frette, O.I.; Virnovsky, G.; Silin, D.
2008-10-15
In this paper a method for the estimation of the curvature along a condensed phase interface is presented. In a previous paper in this journal [1] a mathematical relationship was established between this curvature and a template disk located at a given point along the interface. The portion of the computed area of the template disk covering one of the phases was shown to be asymptotically linear in the mean curvature. Instead of utilizing this relationship, an empirical approach was proposed in [1] in order to compensate for discrete uncertainties. In this paper, we show that this linear relationship can be used directly along the interface avoiding the empirical approach proposed earlier. Modifications of the algorithm are however needed, and with good data smoothing techniques, our method provides good quantitative curvature estimates.
The effects of curvature on the flow field in rapidly rotating gas centrifuges
International Nuclear Information System (INIS)
Wood, H.G.; Jordan, J.A.
1984-01-01
The effects of curvature on the fluid dynamics of rapidly rotating gas centrifuges are studied. A governing system of a linear partial differential equation and boundary conditions is derived based on a linearization of the equations for viscous compressible flow. This system reduces to the Onsager pancake model if the effects of curvature are neglected. Approximations to the solutions of the governing equations with and without curvature terms are obtained via a finite-element method. Two examples are considered: first where the flow is driven by a thermal gradient at the wall of the centrifuge, and then for the flow being driven by the introduction and removal of mass through the ends of the centrifuge. Comparisons of the results obtained show that, especially for the second example, the inclusion of the terms due to curvature in the model can have an appreciable effect on the solution. (author)
Spinal curvatures of children and adolescents – a cross-sectional study
Directory of Open Access Journals (Sweden)
Grabara Małgorzata
2017-02-01
Full Text Available Study aim: The aim was to assess the spinal curvatures of primary and lower secondary male and female students from Silesia and to identify individual variations that can determine spinal posture.
Kvaternik, R. G.; Kaza, K. R. V.
1976-01-01
The nonlinear curvature expressions for a twisted rotor blade or a beam undergoing transverse bending in two planes, torsion, and extension were developed. The curvature expressions were obtained using simple geometric considerations. The expressions were first developed in a general manner using the geometrical nonlinear theory of elasticity. These general nonlinear expressions were then systematically reduced to four levels of approximation by imposing various simplifying assumptions, and in each of these levels the second degree nonlinear expressions were given. The assumptions were carefully stated and their implications with respect to the nonlinear theory of elasticity as applied to beams were pointed out. The transformation matrices between the deformed and undeformed blade-fixed coordinates, which were needed in the development of the curvature expressions, were also given for three of the levels of approximation. The present curvature expressions and transformation matrices were compared with corresponding expressions existing in the literature.
Directory of Open Access Journals (Sweden)
Amilal Bhat
2010-01-01
Conclusions : Preputioplasty with TIP is feasible in proximal hypospadias with curvature without increasing the complication rate. Postoperative phimosis can be prevented by on-table testing of the adequacy of preputial skin by 3 stay sutures.
Sartori, Pablo; Geyer, Veikko F; Scholich, Andre; Jülicher, Frank; Howard, Jonathon
2016-05-11
Cilia and flagella are model systems for studying how mechanical forces control morphology. The periodic bending motion of cilia and flagella is thought to arise from mechanical feedback: dynein motors generate sliding forces that bend the flagellum, and bending leads to deformations and stresses, which feed back and regulate the motors. Three alternative feedback mechanisms have been proposed: regulation by the sliding forces, regulation by the curvature of the flagellum, and regulation by the normal forces that deform the cross-section of the flagellum. In this work, we combined theoretical and experimental approaches to show that the curvature control mechanism is the one that accords best with the bending waveforms of Chlamydomonas flagella. We make the surprising prediction that the motors respond to the time derivative of curvature, rather than curvature itself, hinting at an adaptation mechanism controlling the flagellar beat.
Chemically triggered ejection of membrane tubules controlled by intermonolayer friction.
Fournier, J-B; Khalifat, N; Puff, N; Angelova, M I
2009-01-09
We report a chemically driven membrane shape instability that triggers the ejection of a tubule growing exponentially toward a chemical source. The instability is initiated by a dilation of the exposed monolayer, which is coupled to the membrane spontaneous curvature and slowed down by intermonolayer friction. Our experiments are performed by local delivery of a basic pH solution to a giant vesicle. Quantitative fits of the data give an intermonolayer friction coefficient b approximately 2x10;{9} J s/m;{4}. The exponential growth of the tubule may be explained by a Marangoni stress yielding a pulling force proportional to its length.
DEFF Research Database (Denmark)
Ramsgaard Thomsen, Mette
2008-01-01
, Vivisection and Strange Metabolisms, were developed at the Centre for Information Technology and Architecture (CITA) at the Royal Danish Academy of Fine Arts in Copenhagen as a means of engaging intangible digital data with tactile physical material. As robotic membranes, they are a dual examination...
Pre-Interpretation of Potential Fields by the Aid of Curvature Attributes
Schmidt, S.; Götze, H.-J.
2003-04-01
Algorithms which allow the processing of potential field data base on smoothing by bi-splines, edge detection and/or gradient calculations (e.g. shading). All these methods result in important "surface derived" (field derived) attributes, which will ease numerical interpretations by forward and/or inversion methods later. We introduce an supplementary set of numerical facilities to extract information which concerns with the gridded representation of gravity and magnetic fields and their derivatives: "curvature attributes" of fields which are given on an orthogonal grid (x- and y-coordinates and function value). Curvature can be calculated for curves and surfaces in a 3D space. For a particular point on a curve, its curvature is defined as the rate of change of direction of this curve. There exist a circle (osculating circle) having a common tangent at this point, which makes the greatest possible contact with the curve. The radius of the circle is defined as the "radius of curvature" and the reciprocal of this "radius of curvature" is curvature. It can also be expressed in terms of the second derivatives of the curve. In general this concept can easily extended into three dimensions of a "surface". First, with the help of curvature we can calculate a class of attributes which consists of "first derivation" attributes, which includes the "dip", "edge", "azimuth" or "trends" of the fields. More complex attributes e.g. minimum and maximum curvature, "shape index" of surfaces, "dip" and "strike curvature" can be calculated from normal curvatures. The interactive calculation and future visualization will be handled by the aid of a JAVA program. We present pre-interpretations of Bouguer- and magnetic fields and their gradients from the Andes, the Near East and the Northwest German Basin. "Dip curvature" and "shape index" calculations show most satisfying results. The first indicates the edge of causing bodies of different densities and susceptibilities the latter could
First contact: understanding the relationship between hominoid incisor curvature and diet.
Deane, Andrew
2009-03-01
Accurately interpreting fossil primate dietary behaviour is necessary to fully understand a species' ecology and connection to its environment. Traditional methods developed to infer diet from hominoid teeth successfully group taxa into broad dietary categories (i.e., folivore, frugivore) but often fail to represent the range of dietary variability characteristic of living apes. This oversimplification is not only a consequence of poor resolution, but may also reflect the use of similar fallback resources by closely related taxa with dissimilar diets. This study demonstrates that additional dietary specificity can be achieved using a morphometric approach to hominoid incisor curvature. High-resolution polynomial curve fitting (HR-PCF) was used to quantify the incisor curvatures of closely related hominoid taxa that have dissimilar diets but similar morphological adaptations to specific keystone resources (e.g., Gorilla gorilla beringei vs. G. g. gorilla). Given the key role of incisors in food processing, it is reasonable to assume that these teeth will be at least partially influenced by the unique selective pressures imposed by the mechanical loading specific to individual diets. Results from this study identify a strong correlation between hominoid dietary proportions and incisor linear dimensions and curvature, indicating that more pronounced incisor curvature is positively correlated with higher levels of frugivory. Hard-object frugivores have the greatest mesiodistal and cervico-incisal curvature and dedicated folivores have the least curved incisors. Mixed folivore/frugivores are morphological intermediates between dedicated folivores and hard- and soft-object frugivores. Mesiodistal curvature varied only in the degree of curvature; however, cervico-incisal curvature was shown to differ qualitatively between more frugivorous and more folivorous taxa. In addition to identifying a greater range of dietary variability among hominoids, this study also
Role of parallel flow curvature on the mitigation of Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Sarmah, D.; Sen, S.; Cairns, R.A.
2001-01-01
The effect of a radially varying parallel equilibrium flow on the stability of the Rayleigh-Taylor (RT) mode is studied analytically in the presence of a sheared magnetic field. It is shown that the parallel flow curvature can completely stabilize the RT mode. The flow curvature also has a robust effect on the radial structure of the mode. Possible implications of these theoretical findings to recent experiments are also discussed
Curvature and torsion of implicit hypersurfaces and the origin of charge
Kiehn, R. M.
2001-01-01
A formal correspondence is established between the curvature theory of generalized implicit hypersurfaces, electromagnetism as expressed in terms of exterior differential systems, and thermodynamics. Starting with a generalized implicit surface whose normal field is represented by an exterior differential 1-form, it is possible to deduce the curvature invariants of the implicit surface and to construct a globally closed vector density in terms of the Jacobian properties of the normal field. W...
Isometric surfaces with a common mean curvature and the problem of Bonnet pairs
International Nuclear Information System (INIS)
Sabitov, Idzhad Kh
2012-01-01
Simple methods are used to give new proofs, and sometimes to make them more precise, of basic theorems on isometric surfaces with a common mean curvature, which are usually called Bonnet pairs. The considerations are conducted under the assumption of minimally admissible smoothness of the objects in question, and certain necessary or sufficient criteria are given for the non-existence of Bonnet pairs with a common non-constant mean curvature among compact surfaces. Bibliography: 26 titles.
Measurements of the Curvature of Protrusions/Retrusions on Migrating Recrystallization Boundaries
DEFF Research Database (Denmark)
Zhang, Yubin; Godfrey, A.; Juul Jensen, Dorte
2009-01-01
Two methods to quantify protrusions/retrusions and to estimate local boundary curvature from sample plane sections are proposed. The methods are used to evaluate the driving force due to curvature of the protrusions/retrusions for partially recrystallized pure nickel cold rolled to 96% reduction...... for partially recrystallized pure aluminum cold rolled to 50%. The results show that the local deformed microstructure as well as local heterogeneities have to be analyzed in order to understand the formation of the protrusions....
Bhat, Amilal; Gandhi, Ajay; Saxena, Gajendra; Choudhary, Gautam Ram
2010-01-01
Aims : Objective of this study was to assess the feasibility and results of preputial reconstruction and tubularized incised plate urethroplasty (TIP) in patients of proximal hypospadias with ventral penile curvature. Materials and Methods : Twenty-seven patients of proximal hypospadias who underwent preputioplasty with TIP were evaluated retrospectively. Ventral curvature was corrected by mobilization of the urethral plate with the corpus spongiosum and the proximal urethra; dorsal plica...
ORNL Interim Progress Report on Static CIRFT Testing Curvature Data Update
Energy Technology Data Exchange (ETDEWEB)
Wang, Jy-An John [ORNL; Wang, Hong [ORNL
2016-10-10
Since the CIRFT tests reported in NUREG-7198 were generated, a number of factors that influence the recorded curvature measurement data were identified. In 2016, a data reanalysis task was undertaken to implement the lessons learned. This letter report provides the revised results of previous CIRFT tests, after implementing the following data reanalysis procedures: (A) experimental data smoothing and LVDT reset, (B) LVDT probe contact and sensor spacing correction for curvature data, and (C) LVDT probe dynamic vibration adjustment procedure development.
Femoral curvature in Neanderthals and modern humans: a 3D geometric morphometric analysis.
De Groote, Isabelle
2011-05-01
Since their discovery, Neanderthals have been described as having a marked degree of anteroposterior curvature of the femoral shaft. Although initially believed to be pathological, subsequent discoveries of Neanderthal remains lead femoral curvature to be considered as a derived Neanderthal feature. A recent study on Neanderthals and middle and early Upper Palaeolithic modern humans found no differences in femoral curvature, but did not consider size-corrected curvature. Therefore, the objectives of this study were to use 3D morphometric landmark and semi-landmark analysis to quantify relative femoral curvature in Neanderthals, Upper Palaeolithic and recent modern humans, and to compare adult bone curvature as part of the overall femoral morphology among these populations. Comparisons among populations were made using geometric morphometrics (3D landmarks) and standard multivariate methods. Comparative material involved all available complete femora from Neanderthal and Upper Palaeolithic modern human, archaeological (Mesolithic, Neolithic, Medieval) and recent human populations representing a wide geographical and lifestyle range. There are significant differences in the anatomy of the femur between Neanderthals and modern humans. Neanderthals have more curved femora than modern humans. Early modern humans are most similar to recent modern humans in their anatomy. Femoral curvature is a good indicator of activity level and habitual loading of the lower limb, indicating higher activity levels in Neanderthals than modern humans. These differences contradict robusticity studies and the archaeological record, and would suggest that femoral morphology, and curvature in particular, in Neanderthals may not be explained by adult behavior alone and could be the result of genetic drift, natural selection or differences in behavior during ontogeny. Copyright © 2010 Elsevier Ltd. All rights reserved.
Distal root curvatures in mandibular molars: analysis using digital panoramic X-rays.
Fuentes, R; Farfán, C; Astete, N; Navarro, P; Arias, A
2018-01-01
The aim of this study was to describe the degree of curvature in distal roots in the first and second permanent mandibular molars in a Chilean patient sample. A cross-sectional descriptive study was conducted in which digital panoramic X-rays were analysed. Examinations of patients under 18 years, with signs of distortion or alteration in the contrast or the presence of pathologies that affected visualisation of the roots and pulp-chamber floor of the teeth to be analysed were excluded. Using the AutoCad software, an angle was drawn to represent the curve of the root in its different thirds, drawing lines inside the root canal from the pulp-chamber floor to the dental apex. Using the classic definition of dilaceration (root curvature > 90°), its prevalence was established. 412 teeth and roots were analysed, finding a dilaceration prevalence of 0.73% (n = 3). 84.72% of the roots presented some type of curvature. The middle third had the highest percentage of curvatures and the greatest average of angular curvature, whereas the cervical third was the straightest. No significant differences were found between the degree of curvature and the gender of the subjects, except for the apical third of tooth 3.6. The analysis of curvature by root third offers to the clinician a better perspective of the directional change of the roots and does not limit it to just the presence of curves in the apical third. The report of the angular degree of the curvatures, in addition to the prevalence of dilacerations, informs to the clinicians about the likelihood of finding difficulties when treating root canals. (Folia Morphol 2018; 77, 1: 131-137).
Instability of elliptic equations on compact Riemannian manifolds with non-negative Ricci curvature
Directory of Open Access Journals (Sweden)
Arnaldo S. Nascimento
2010-05-01
Full Text Available We prove the nonexistence of nonconstant local minimizers for a class of functionals, which typically appear in scalar two-phase field models, over smooth N-dimensional Riemannian manifolds without boundary and non-negative Ricci curvature. Conversely, for a class of surfaces possessing a simple closed geodesic along which the Gauss curvature is negative, we prove the existence of nonconstant local minimizers for the same class of functionals.
Stress compensation for arbitrary curvature control in vanadium dioxide phase transition actuators
International Nuclear Information System (INIS)
Dong, Kaichen; Lou, Shuai; Choe, Hwan Sung; Yao, Jie; Wu, Junqiao; Liu, Kai; You, Zheng
2016-01-01
Due to its thermally driven structural phase transition, vanadium dioxide (VO 2 ) has emerged as a promising material for micro/nano-actuators with superior volumetric work density, actuation amplitude, and repetition frequency. However, the high initial curvature of VO 2 actuators severely obstructs the actuation performance and application. Here, we introduce a “seesaw” method of fabricating tri-layer cantilevers to compensate for the residual stress and realize nearly arbitrary curvature control of VO 2 actuators. By simply adjusting the thicknesses of the individual layers, cantilevers with positive, zero, or negative curvatures can be engineered. The actuation amplitude can be decoupled from the curvature and controlled independently as well. Based on the experimentally measured residual stresses, we demonstrate sub-micron thick VO 2 actuators with nearly zero final curvature and a high actuation amplitude simultaneously. This “seesaw” method can be further extended to the curvature engineering of other microelectromechanical system multi-layer structures where large stress-mismatch between layers are inevitable.
Schuurmann, Richte C L; van Noort, Kim; Overeem, Simon P; Ouriel, Kenneth; Jordan, William D; Muhs, Bart E; 't Mannetje, Yannick; Reijnen, Michel; Fioole, Bram; Ünlü, Çağdaş; Brummel, Peter; de Vries, Jean-Paul P M
2017-06-01
To evaluate the association between aortic curvature and other preoperative anatomical characteristics and late (>1 year) type Ia endoleak and endograft migration in endovascular aneurysm repair (EVAR) patients. Eight high-volume EVAR centers contributed 116 EVAR patients (mean age 81±7 years; 103 men) to the study: 36 patients (mean age 82±7 years; 31 men) with endograft migration and/or type Ia endoleak diagnosed >1 year after the initial EVAR and 80 controls without early or late complications. Aortic curvature was calculated from the preoperative computed tomography scan as the maximum and average curvature over 5 predefined aortic segments: the entire infrarenal aortic neck, aneurysm sac, and the suprarenal, juxtarenal, and infrarenal aorta. Other morphological characteristics included neck length, neck diameter, mural neck calcification and thrombus, suprarenal and infrarenal angulation, and largest aneurysm sac diameter. Independent risk factors were identified using backward stepwise logistic regression. Relevant cutoff values for each of the variables in the final regression model were determined with the receiver operator characteristic curve. Logistic regression identified maximum curvature over the length of the aneurysm sac (>47 m -1 ; p=0.023), largest aneurysm sac diameter (>56 mm; p=0.028), and mural neck thrombus (>11° circumference; pIa endoleak. Aortic curvature is a predictor for late type Ia endoleak and endograft migration after EVAR. These findings suggest that aortic curvature is a better parameter than angulation to predict post-EVAR failure and should be included as a hostile neck parameter.
Incorporating contact angles in the surface tension force with the ACES interface curvature scheme
Owkes, Mark
2017-11-01
In simulations of gas-liquid flows interacting with solid boundaries, the contact line dynamics effect the interface motion and flow field through the surface tension force. The surface tension force is directly proportional to the interface curvature and the problem of accurately imposing a contact angle must be incorporated into the interface curvature calculation. Many commonly used algorithms to compute interface curvatures (e.g., height function method) require extrapolating the interface, with defined contact angle, into the solid to allow for the calculation of a curvature near a wall. Extrapolating can be an ill-posed problem, especially in three-dimensions or when multiple contact lines are near each other. We have developed an accurate methodology to compute interface curvatures that allows for contact angles to be easily incorporated while avoiding extrapolation and the associated challenges. The method, known as Adjustable Curvature Evaluation Scale (ACES), leverages a least squares fit of a polynomial to points computed on the volume-of-fluid (VOF) representation of the gas-liquid interface. The method is tested by simulating canonical test cases and then applied to simulate the injection and motion of water droplets in a channel (relevant to PEM fuel cells).
Comparative effectiveness of metal ions in inducing curvature of primary roots of Zea mays
Hasenstein, K. H.; Evans, M. L.; Stinemetz, C. L.; Moore, R.; Fondren, W. M.; Koon, E. C.; Higby, M. A.; Smucker, A. J.
1988-01-01
We used five cultivars of Zea mays (Bear Hybrid WF9 * 38MS, B73 * Missouri 17, Yellow Dent, Merit, and Great Lakes Hybrid 422) to reinvestigate the specificity of metal ions for inducing root curvature. Of 17 cations tested, 6 (Al3+, Ba2+, Ca2+, Cd2+, Cu2+, Zn2+) induced curvature. Roots curved away from Al3+, Ba2+, and Cd2+. Roots curved away from low (0.1 millimolar) concentrations of Cu2+ but toward higher (1-5 millimolar) concentrations. Roots initially curved away from Zn2+ but the direction of the subsequent curvature was unpredictable. In most cases, roots of all cultivars curved towards calcium. However, in some tests there was no response to calcium or even (especially in the cultivars Merit and B73 * Missouri 17) substantial curvature away from calcium. The results indicate that the induction of root curvature is not specific for calcium. The results are discussed relative to the possible role of calmodulin as a mediator of ion-induced root curvature.
[Analysis and Correction of Spectral Curvature in Hadamard Transform Spectrometer with DMD].
Quan, Xiang-qian; Liu, Hua; Lu, Zhen-wu; Wang, Xiao-duo; Dang, Bo-shi; Chen, Xiang-zi; Wang, Fang
2016-02-01
Due to the advantages of its low cost and high utilization rate of light energy and no moving parts, Hadamard transform spectrometer with DMD has become a focus in the research of spectrometer. In order to solve the reduction of spectral resolution caused by the spectral curvature of Hadamard transform spectrometer with DMD (Digital Micro-mirror Device), the spectral aliasing in the spectrometer was investigated. Firstly, the mathematical relationship of spectral aliasing to radius of spectral curvature was deduced. Then, two procedures were proposed to solve the spectral aliasing. One is making the DMD encoded spectral band accordant with the standard spectral band as far as possible by adjusting the DMD-encoded stripe, and another is correcting remaining spectral aliasing by means of data processing. Finally, by analyzing and correcting spectral curvature in six situations of the curvature radius of 15.8 x 10⁴, 7.8 x 10⁴, 9.7 x 10⁴ µm and etc, we fit out the relationship of spectral aliasing and spectrum correction effect of spectral-curvature to the curvature radius. The simulation indicates that the spectral resolution increases to the resolution of optical system. It shows that the proposed methods are universal, simple and effective in the improvement of spectral resolution.
Dramatic effect of curvature on DW velocity in chiral domain walls
Garg, Chirag; Yang, See-Hun; Phung, Timothy; Pushp, Aakash; Parkin, Stuart S. P.; Magnetoelectronics Group, IBM Almaden Team
The use of current pulses to manipulate domain walls (DWs) in nanowires is one of the most exciting developments in spintronics over the past decade, promising a range of novel devices. However, even after more than 10 years of work on current induced DW motion it has not been realized that the curvature of the nanowire can affect the speed of chiral DWs. Here we show that simply changing the sign of the curvature of a nanowire, dramatically changes the speed of Néel DWs in perpendicularly magnetized nanowires, by up to a factor of 10. We find that, DWs have an increased or decreased velocity in wires of a given curvature, independent of the DW chirality and the sign of the current induced torques. The fundamental origin of this effect is due to a current induced tilting of the DW that breaks the symmetry of the DW's motion with respect to the curvature of the wire. Whilst the strong dependence of the DW velocity on the nanowire's curvature may offer added device functionalities, we find that in synthetic antiferromagnetic nanowires, the influence of the curvature on the DW's velocity can be completely removed.
Bioinspired model of mechanical energy harvesting based on flexoelectric membranes.
Rey, Alejandro D; Servio, P; Herrera-Valencia, E E
2013-02-01
Membrane flexoelectricity is an electromechanical coupling process that describes membrane electrical polarization due to bending and membrane bending under electric fields. In this paper we propose, formulate, and characterize a mechanical energy harvesting system consisting of a deformable soft flexoelectric thin membrane subjected to harmonic forcing from contacting bulk fluids. The key elements of the energy harvester are formulated and characterized, including (i) the mechanical-to-electrical energy conversion efficiency, (ii) the electromechanical shape equation connecting fluid forces with membrane curvature and electric displacement, and (iii) the electric power generation and efficiency. The energy conversion efficiency is cast as the ratio of flexoelectric coupling to the product of electric and bending elasticity. The device is described by a second-order curvature dynamics coupled to the electric displacement equation and as such results in mechanical power absorption with a resonant peak whose amplitude decreases with bending viscosity. The electric power generation is proportional to the conversion factor and the power efficiency decreases with frequency. Under high bending viscosity, the power efficiency increases with the conversion factor and under low viscosities it decreases with the conversion factor. The theoretical results presented contribute to the ongoing experimental efforts to develop mechanical energy harvesting from fluid flow energy through solid-fluid interactions and electromechanical transduction.
Hamilton's equations for a fluid membrane
International Nuclear Information System (INIS)
Capovilla, R; Guven, J; Rojas, E
2005-01-01
Consider a homogeneous fluid membrane described by the Helfrich-Canham energy, quadratic in the mean curvature of the membrane surface. The shape equation that determines equilibrium configurations is fourth order in derivatives and cubic in the mean curvature. We introduce a Hamiltonian formulation of this equation which dismantles it into a set of coupled first-order equations. This involves interpreting the Helfrich-Canham energy as an action; equilibrium surfaces are generated by the evolution of space curves. Two features complicate the implementation of a Hamiltonian framework. (i) The action involves second derivatives. This requires treating the velocity as a phase-space variable and the introduction of its conjugate momentum. The canonical Hamiltonian is constructed on this phase space. (ii) The action possesses a local symmetry-reparametrization invariance. The two labels we use to parametrize points on the surface are themselves physically irrelevant. This symmetry implies primary constraints, one for each label, that need to be implemented within the Hamiltonian. The two Lagrange multipliers associated with these constraints are identified as the components of the acceleration tangential to the surface. The conservation of the primary constraints implies two secondary constraints, fixing the tangential components of the momentum conjugate to the position. Hamilton's equations are derived and the appropriate initial conditions on the phase-space variables are identified. Finally, it is shown how the shape equation can be reconstructed from these equations
Measuring children's food preferences
DEFF Research Database (Denmark)
Olsen, Annemarie; Kildegaard, Heidi; Gabrielsen, Gorm
2012-01-01
juices (tangible products), chosen to span the preference spectrum, were hedonically evaluated for appearance and taste. Finally, an actual product choice was performed by having the children choose between two buns and two juices.Results showed that the computer evaluationswith pictures of foods...... provided reproducible information about the children’s visual food preferences, which were in concordance with both hedonic measures and products choices, and can thus be considered valid.......The aim of this study is to investigate if children’s food preferences can be reliable measured by using pictures of foods presented on a computer screen in a conjoint layout.We investigate reproducibility (test–retest) and infer validity by comparison with traditional hedonic evaluations...
Estimating exponential scheduling preferences
DEFF Research Database (Denmark)
Hjorth, Katrine; Börjesson, Maria; Engelson, Leonid
2015-01-01
distributed independent random variables: Assuming smooth preferences; this holds only for specifications with a constant marginal utility of time at the origin and an exponential or affine marginal utility of time at the destination. We apply a generalized version of this model to stated preference data...... utility of being at the origin. Another issue is that models with the exponential marginal utility formulation suffer from empirical identification problems. Though our results are not decisive, they partly support the constant-affine specification, in which the value of travel time variability...
Stress-sensor device based on flexoelectric liquid crystalline membranes.
Rey, Alejandro D; Servio, Phillip; Herrera Valencia, Edtson Emilio
2014-05-19
Membrane flexoelectricity is an electromechanical coupling process that describes membrane bending and membrane electrical polarization caused by bending under electric fields. In this paper we propose, formulate, and characterize a stress-sensor device for mechanically loaded solids, consisting of a soft flexoelectric thin membrane attached to the loaded deformed solid. Because the curvature of the deformed solid is transferred to the attached flexoelectric membrane, the electromechanical transduction of the latter produces a charge that is proportional to the stress of the solid. The model of the stress-sensor device is based on the integration of the thermodynamics of polarizable membranes with isotropic solid elasticity, leading to a transfer function that identifies the elastic, electromechanical, and geometrical parameters involved in electrical-signal generation. The model is applied to representative normal bending and then to more complex off-axis bending of elastic bars. In all cases, a common transfer function shows the generic material and its geometric contributions. The sensor sensitivity increases linearly with flexoelectricity and the membrane-solid interface, and the sensitivity decreases with increasing membrane thickness and Young's modulus of the solid. The theoretical results contribute to ongoing experimental efforts towards the development of anisotropic soft-matter-based stress-sensor devices through solid-membrane interactions and electromechanical transduction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Simulation of vacuum membrane distillation coupled with solar energy
International Nuclear Information System (INIS)
Zrelli, Adel; Chaouchi, Bechir; Gabsi, Slimane
2009-01-01
This work focuses on solar energy coupled with vacuum membrane distillation (VMD) for brackish water desalination. VMD is an evaporative process, using porous and hydrophobic membranes, permit to obtain the gaseous permeate, under vacuum, from the aqueous liquid feed. The aim of this work was to simulate the influence of operating conditions (feed flow, feed temperature, permeate pressure) and hollow fibres membrane characteristics (pitch, radius of curvature) on the permeate flux. In order to enhance the performance of the VMD process in desalination to get more permeate flux, we have choose a new module, placed in the absorber of the cylindro-parabolic concentrator, containing hollow fibres wrapped around rod in helical geometry. The model formulation allows for variation of the physical characteristics of brackish solution and the water permeability of membrane. The numerical results showed the important effect of the helical geometry on the enhancement of the permeate flux.
Membrane separation of ionic liquid solutions
Campos, Daniel; Feiring, Andrew Edward; Majumdar, Sudipto; Nemser, Stuart
2015-09-01
A membrane separation process using a highly fluorinated polymer membrane that selectively permeates water of an aqueous ionic liquid solution to provide dry ionic liquid. Preferably the polymer is a polymer that includes polymerized perfluoro-2,2-dimethyl-1,3-dioxole (PDD). The process is also capable of removing small molecular compounds such as organic solvents that can be present in the solution. This membrane separation process is suitable for drying the aqueous ionic liquid byproduct from precipitating solutions of biomass dissolved in ionic liquid, and is thus instrumental to providing usable lignocellulosic products for energy consumption and other industrial uses in an environmentally benign manner.
DEFF Research Database (Denmark)
Dahl, Sofia; Huron, David; Brod, Garvin
2014-01-01
In two experiments participants tuned a drum machine to their preferred dance tempo. Measurements of height, shoulder width, leg length, and weight were taken for each participant, and their sex recorded. Using a multiple regression analysis, height and leg length combined was found to be the bes...
Patterns of Environmental Preference
Kaplan, Rachel
1977-01-01
This study sought to evaluate components of the Environmental Preference Questionnaire (EPQ). The 267 teenagers who completed the EPQ in this study also responded to questions relating to facets of self esteem and the reasons for selecting their favorite activities. (BT)
Constructive Preference Elicitation
Directory of Open Access Journals (Sweden)
Paolo Dragone
2018-01-01
Full Text Available When faced with large or complex decision problems, human decision makers (DM can make costly mistakes, due to inherent limitations of their memory, attention, and knowledge. Preference elicitation tools assist the decision maker in overcoming these limitations. They do so by interactively learning the DM’s preferences through appropriately chosen queries and suggesting high-quality outcomes based on the preference estimates. Most state-of-the-art techniques, however, fail in constructive settings, where the goal is to synthesize a custom or entirely novel configuration rather than choosing the best option among a given set of candidates. Many wide-spread problems are constructive in nature: customizing composite goods such as cars and computers, bundling products, recommending touristic travel plans, designing apartments, buildings, or urban layouts, etc. In these settings, the full set of outcomes is humongous and can not be explicitly enumerated, and the solution must be synthesized via constrained optimization. In this article, we describe recent approaches especially designed for constructive problems, outlining the underlying ideas and their differences as well as their limitations. In presenting them, we especially focus on novel issues that the constructive setting brings forth, such as how to deal with sparsity of the DM’s preferences, how to properly frame the interaction, and how to achieve efficient synthesis of custom instances.
Arm chair perspective preferences
Koenderink, Jan; van Doorn, A.J.; Pinna, Baingio; Pepperell, Robert
2016-01-01
Do generic observers in their free-style viewing of postcard-size pictures have a preference for specific modes of perspective rendering? This most likely depends upon the phrasing of the question. Here we consider the feeling of ‘presence’: does the observer experience a sense of being ‘immersed in
Hormones and social preferences
Buser, T.
2011-01-01
We examine whether social preferences are determined by hormones. We do this by investigating whether markers for the strength of prenatal testosterone exposure (finger length ratios) and current exposure to progesterone and oxytocin (the menstrual cycle) are correlated with choices in social
DNA sequencing using fluorescence background electroblotting membrane
Caldwell, Karin D.; Chu, Tun-Jen; Pitt, William G.
1992-01-01
A method for the multiplex sequencing on DNA is disclosed which comprises the electroblotting or specific base terminated DNA fragments, which have been resolved by gel electrophoresis, onto the surface of a neutral non-aromatic polymeric microporous membrane exhibiting low background fluorescence which has been surface modified to contain amino groups. Polypropylene membranes are preferably and the introduction of amino groups is accomplished by subjecting the membrane to radio or microwave frequency plasma discharge in the presence of an aminating agent, preferably ammonia. The membrane, containing physically adsorbed DNA fragments on its surface after the electroblotting, is then treated with crosslinking means such as UV radiation or a glutaraldehyde spray to chemically bind the DNA fragments to the membrane through said smino groups contained on the surface thereof. The DNA fragments chemically bound to the membrane are subjected to hybridization probing with a tagged probe specific to the sequence of the DNA fragments. The tagging may be by either fluorophores or radioisotopes. The tagged probes hybridized to said target DNA fragments are detected and read by laser induced fluorescence detection or autoradiograms. The use of aminated low fluorescent background membranes allows the use of fluorescent detection and reading even when the available amount of DNA to be sequenced is small. The DNA bound to the membrances may be reprobed numerous times.
Model Answers to Lipid Membrane Questions
DEFF Research Database (Denmark)
Mouritsen, O. G.
2011-01-01
Ever since it was discovered that biological membranes have a core of a bimolecular sheet of lipid molecules, lipid bilayers have been a model laboratory for investigating physicochemical and functional properties of biological membranes. Experimental and theoretical models help the experimental ...... to pursue. Here we review some membrane models for lipid self-assembly, monolayers, bilayers, liposomes, and lipid-protein interactions and illustrate how such models can help answering questions in modern lipid cell biology....... scientist to plan experiments and interpret data. Theoretical models are the theoretical scientist's preferred toys to make contact between membrane theory and experiments. Most importantly, models serve to shape our intuition about which membrane questions are the more fundamental and relevant ones...
Young, L. M.; Evans, M. L.; Hertel, R.
1990-01-01
We compared the kinetics of auxin redistribution across the caps of primary roots of 2-day-old maize (Zea mays, cv Merit) seedlings with the time course of gravitropic curvature. [3H] indoleacetic acid was applied to one side of the cap in an agar donor and radioactivity moving across the cap was collected in an agar receiver applied to the opposite side. Upon gravistimulation the roots first curved upward slightly, then returned to the horizontal and began curving downward, reaching a final angle of about 67 degrees. Movement of label across the caps of gravistimulated roots was asymmetric with preferential downward movement (ratio downward/upward = ca. 1.6, radioactivity collected during the 90 min following beginning of gravistimulation). There was a close correlation between the development of asymmetric auxin movement across the root cap and the rate of curvature, with both values increasing to a maximum and then declining as the roots approached the final angle of curvature. In roots preadapted to gravity (alternate brief stimulation on opposite flanks over a period of 1 hour) the initial phase of upward curvature was eliminated and downward bending began earlier than for controls. The correlation between asymmetric auxin movement and the kinetics of curvature also held in comparisons between control and preadapted roots. Both downward auxin transport asymmetry and downward curvature occurred earlier in preadapted roots than in controls. These findings are consistent with suggestions that the root cap is not only the site of perception but also the location of the initial redistribution of effectors that ultimately leads to curvature.
Flexoelectric response in soft polyurethane films and their use for large curvature sensing
Merupo, V. I.; Guiffard, B.; Seveno, R.; Tabellout, M.; Kassiba, A.
2017-10-01
The flexoelectric effect is simply defined as the coupling between the strain gradient and polarization in solid dielectrics. It may be seen as an alternative transduction mechanism to the piezoelectric effect to directly sense the curvature of bent flexible thin structures. In the case of large curvatures, flexible and compliant sensors are required and soft polar elastomers may be suitable for curvature sensing. In this study, we report the flexoelectric characterization of soft semi-crystalline polyurethane (PU) films with thicknesses ranging from 1.7 μm to 350 μm. Dynamic bending experiments have been performed on PU films deposited onto rigid steel substrates in the vicinity of the mechanical resonance frequency of the cantilever beams. Quasi-static flexoelectric coefficients of PU films could be obtained by using a classical oscillating model. A global large increase of μ12 ' with the decreasing film thickness was found, especially for thicknesses lower than 25 μm. The variation of μ12 ' is explained by the presence of a Young's Modulus gradient through the thickness of PU films. Besides, a concomitant uncommon dramatic decrease in the dielectric constant is observed. The combination of these two effects contributes to enhancing the flexocoupling "F" constant with the decreasing thickness. At last, the potential use of a 6.6 μm-thick soft PU film as a large curvature sensor has been experimentally demonstrated by subjecting a flexible Aluminum foil/Polyethylene terephthalate bilayered cantilever to large deflections. A curvature of about 80 m-1 (radius of curvature of ˜1.2 cm) could be sensed under low frequency (3 Hz) bending motion. These results may pave the way for the development of low cost and easy to implement soft flexoelectric elastomer-based large curvature sensors on highly flexible metallic structures.
Annular force based variable curvature mirror aiming to realize non-moving element optical zooming
Zhao, Hui; Xie, Xiaopeng; Wei, Jingxuan; Ren, Guorui; Pang, Zhihai; Xu, Liang
2015-10-01
Recently, a new kind of optical zooming technique in which no moving elements are involved has been paid much attention. The elimination of moving elements makes optical zooming suitable for applications which has exacting requirements in space, power cost and system stability. The mobile phone and the space-borne camera are two typical examples. The key to realize non-moving elements optical zooming lies in the introduction of variable curvature mirror (VCM) whose radius of curvature could be changed dynamically. When VCM is about to be used to implement optical zoom imaging, two characteristics should be ensured. First, VCM has to provide large enough saggitus variation in order to obtain a big magnification ratio. Second, after the radius of curvature has been changed, the corresponding surface figure accuracy should still be maintained superior to a threshold level to make the high quality imaging possible. In this manuscript, based on the elasticity theory, the physical model of the annular force based variable curvature mirror is established and numerically analyzed. The results demonstrate that when the annular force is applied at the half-the-aperture position, the actuation force is reduced and a smaller actuation force is required to generate the saggitus variation and thus the maintenance of surface figure accuracy becomes easier during the variation of radius of curvature. Besides that, a prototype VCM, whose diameter and thickness are 100mm and 3mm respectively, have been fabricated and the maximum saggitus variation that could be obtained approaches more than 30 wavelengths. At the same time, the degradation of surface figure accuracy is weakly correlated to the curvature radius variation. Keywords: optical zooming; variable curvature mirror; surface figure accuracy; saggitus;
Sonntag, D; Stachniss-Carp, S; Stachniss, C; Stachniss, V
2006-04-01
The aim of this paper is to present a new method based on numeric calculus to provide data on any type of root canal curvature at any point of the long axis of the canal. Twenty severely curved, simulated root canals were prepared with rotary FlexMaster and Profile instruments in the crown-down technique and manually in the step-back technique. The inner and outer curvatures were registered in a system of coordinates before and after preparation in increments of 0.5 mm. Using an equalising function, the curvatures were first represented in graphic and algebraic form. The maximum and the mean curvature as well as the length of the arc from the apical foramen to the point of maximum curvature were determined mathematically. An increase in maximum curvature was registered for all four shaping systems investigated. The radius of the inner curvature decreased by 0.5-1.2 mm in the manual systems as a result of the preparation. The Profile system displayed the smallest changes in radius (-0.9 mm) even with the outer curvature, and manual preparation with stainless steel files the most pronounced change (-1.8 mm). The point of maximum curvature at the inner curvature was displaced by 1.6 mm to the apical foramen through manual preparation with Ni-Ti files. At the outer curvature, the maximum displacement (1.8 mm) recorded was also the result of preparation with Ni-Ti hand files, while a displacement of only 0.3 mm to the apical foramen was recorded with the other systems. The method offers a means of determining curvatures precisely without random specification of reference points. The method is also capable of registering only minor changes in curvature in the two-dimensional long axis of the canal.
Lee, J. S.; Evans, M. L.
1990-01-01
We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.
Membranes as separators of dispersed emulsion phases
Lefferts, A.G.
1997-01-01
The reuse or discharge of industrial waste waters, containing small fractions of dispersed oil, requires a purification treatment for which membranes can be used. If only little oil is present, removal of the dispersed phase might be preferable to the more commonly applied removal of the
Investigations concerning the use of membrane bioreactor systems
International Nuclear Information System (INIS)
Wenger-Oehn, H.; Universitaet fuer Bodenkulturen, Wien; Braun, R.; Universitaet fuer Bodenkulturen, Wien
1994-01-01
Membrane bioreactor systems are increasingly being used to clean leachates from landfills. Besides being compact they can, especially, be easily combined with further cleaning techniques. The paper first of all gives an overview on landfill leachate cleaning standards in Austria. A combination of processes is applied where the membrane bioreactor forms a preferred element. Finally, results are presented which should help with the dimensioning of membrane bioreactors. (orig.) [de
Anatomical study of the radius and center of curvature of the distal femoral condyle
Kosel, Jürgen
2010-01-01
In this anatomical study, the anteroposterior curvature of the surface of 16 cadaveric distal femurs was examined in terms of radii and center point. Those two parameters attract high interest due to their significance for total knee arthroplasty. Basically, two different conclusions have been drawn in foregoing studies: (1) The curvature shows a constant radius and (2) the curvature shows a variable radius. The investigations were based on a new method combining three-dimensional laser-scanning and planar geometrical analyses. This method is aimed at providing high accuracy and high local resolution. The high-precision laser scanning enables the exact reproduction of the distal femurs - including their cartilage tissue - as a three-dimensional computer model. The surface curvature was investigated on intersection planes that were oriented perpendicularly to the surgical epicondylar line. Three planes were placed at the central part of each condyle. The intersection of either plane with the femur model was approximated with the help of a b-spline, yielding three b-splines on each condyle. The radii and center points of the circles, approximating the local curvature of the b-splines, were then evaluated. The results from all three b-splines were averaged in order to increase the reliability of the method. The results show the variation in the surface curvatures of the investigated samples of condyles. These variations are expressed in the pattern of the center points and the radii of the curvatures. The standard deviations of the radii for a 90 deg arc on the posterior condyle range from 0.6 mm up to 5.1 mm, with an average of 2.4 mm laterally and 2.2 mm medially. No correlation was found between the curvature of the lateral and medial condyles. Within the range of the investigated 16 samples, the conclusion can be drawn that the condyle surface curvature is not constant and different for all specimens when viewed along the surgical epicondylar axis. For the portion
Experimental study of curvature effects on jet impingement heat transfer on concave surfaces
Directory of Open Access Journals (Sweden)
Ying Zhou
2017-04-01
Full Text Available Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects. The experiments were conducted by employing a piccolo tube with one single jet hole over a wide range of parameters: jet Reynolds number from 27000 to 130000, relative nozzle to surface distance from 3.3 to 30, and relative surface curvature from 0.005 to 0.030. Experimental results indicate that the surface curvature has opposite effects on heat transfer characteristics. On one hand, an increase of relative nozzle to surface distance (increasing jet diameter in fact enhances the average heat transfer around the surface for the same curved surface. On the other hand, the average Nusselt number decreases as relative nozzle to surface distance increases for a fixed jet diameter. Finally, experimental data-based correlations of the average Nusselt number over the curved surface were obtained with consideration of surface curvature effect. This work contributes to a better understanding of the curvature effects on heat transfer of a round jet impingement on concave surfaces, which is of high importance to the design of the aircraft anti-icing system.
Using Single-Scattering Albedo Spectral Curvature to Characterize East Asian Aerosol Mixtures
Li, Jing; Carlson, Barbara E.; Lacis, Andrew A.
2015-01-01
Spectral dependence of aerosol single-scattering albedo (SSA) has been used to infer aerosol composition. In particular, aerosol mixtures dominated by dust absorption will have monotonically increasing SSA with wavelength while that dominated by black carbon absorption has monotonically decreasing SSA spectra. However, by analyzing SSA measured at four wavelengths, 440, 675, 870, and 1020 nm from the Aerosol Robotic Network data set, we find that the SSA spectra over East Asia are frequently peaked at 675 nm. In these cases, we suggest that SSA spectral curvature, defined as the negative of the second derivative of SSA as a function of wavelength, can provide additional information on the composition of these aerosol mixtures. Aerosol SSA spectral curvatures for East Asia during fall and winter are considerably larger than those found in places primarily dominated by biomass burning or dust aerosols. SSA curvature is found to increase as the SSA magnitude decreases. The curvature increases with coarse mode fraction (CMF) to a CMF value of about 0.4, then slightly decreases or remains constant at larger CMF. Mie calculations further verify that the strongest SSA curvature occurs at approx. 40% dust fraction, with 10% scattering aerosol fraction. The nonmonotonic SSA spectral dependence is likely associated with enhanced absorption in the shortwave by dust, absorption by black carbon at longer wavelengths, and also the flattened absorption optical depth spectral dependence due to the increased particle size.
Curvature-driven stability of defects in nematic textures over spherical disks
Duan, Xiuqing; Yao, Zhenwei
2017-06-01
Stabilizing defects in liquid-crystal systems is crucial for many physical processes and applications ranging from functionalizing liquid-crystal textures to recently reported command of chaotic behaviors of active matters. In this work, we perform analytical calculations to study the curvature-driven stability mechanism of defects based on the isotropic nematic disk model that is free of any topological constraint. We show that in a growing spherical disk covering a sphere the accumulation of curvature effect can prevent typical +1 and +1/2 defects from forming boojum textures where the defects are repelled to the boundary of the disk. Our calculations reveal that the movement of the equilibrium position of the +1 defect from the boundary to the center of the spherical disk occurs in a very narrow window of the disk area, exhibiting the first-order phase-transition-like behavior. For the pair of +1/2 defects by splitting a +1 defect, we find the curvature-driven alternating repulsive and attractive interactions between the two defects. With the growth of the spherical disk these two defects tend to approach and finally recombine towards a +1 defect texture. The sensitive response of defects to curvature and the curvature-driven stability mechanism demonstrated in this work in nematic disk systems may have implications towards versatile control and engineering of liquid-crystal textures in various applications.
Numerical Investigation on Fluid Flow in a 90-Degree Curved Pipe with Large Curvature Ratio
Directory of Open Access Journals (Sweden)
Yan Wang
2015-01-01
Full Text Available In order to understand the mechanism of fluid flows in curved pipes, a large number of theoretical and experimental researches have been performed. As a critical parameter of curved pipe, the curvature ratio δ has received much attention, but most of the values of δ are very small (δ<0.1 or relatively small (δ≤0.5. As a preliminary study and simulation this research studied the fluid flow in a 90-degree curved pipe of large curvature ratio. The Detached Eddy Simulation (DES turbulence model was employed to investigate the fluid flows at the Reynolds number range from 5000 to 20000. After validation of the numerical strategy, the pressure and velocity distribution, pressure drop, fluid flow, and secondary flow along the curved pipe were illustrated. The results show that the fluid flow in a curved pipe with large curvature ratio seems to be unlike that in a curved pipe with small curvature ratio. Large curvature ratio makes the internal flow more complicated; thus, the flow patterns, the separation region, and the oscillatory flow are different.
Badial, Peres R; Cisneros-Àlvarez, Luis Emiliano; Brandão, Cláudia Valéria S; Ranzani, José Joaquim T; Tomaz, Mayana A R V; Machado, Vania M; Borges, Alexandre S
2015-09-01
The aim of this study was to compare ocular dimensions, corneal curvature, and corneal thickness between horses affected with hereditary equine regional dermal asthenia (HERDA) and unaffected horses. Five HERDA-affected quarter horses and five healthy control quarter horses were used. Schirmer's tear test, tonometry, and corneal diameter measurements were performed in both eyes of all horses prior to ophthalmologic examinations. Ultrasonic pachymetry was performed to measure the central, temporal, nasal, dorsal, and ventral corneal thicknesses in all horses. B-mode ultrasound scanning was performed on both eyes of each horse to determine the dimensions of the ocular structures and to calculate the corneal curvature. Each corneal region examined in this study was thinner in the affected group compared with the healthy control group. However, significant differences in corneal thickness were only observed for the central and dorsal regions. HERDA-affected horses exhibited significant increases in corneal curvature and corneal diameter compared with unaffected animals. The ophthalmologic examinations revealed mild corneal opacity in one eye of one affected horse and in both eyes of three affected horses. No significant between-group differences were observed for Schirmer's tear test, intraocular pressure, or ocular dimensions. Hereditary equine regional dermal asthenia-affected horses exhibit decreased corneal thickness in several regions of the cornea, increased corneal curvature, increased corneal diameter, and mild corneal opacity. Additional research is required to determine whether the increased corneal curvature significantly impacts the visual accuracy of horses with HERDA. © 2014 American College of Veterinary Ophthalmologists.
The geometric curvature of the lumbar spine during restricted and unrestricted squats.
Hebling Campos, Mário; Furtado Alaman, Laizi I; Seffrin-Neto, Aldo A; Vieira, Carlos A; Costa de Paula, Marcelo; Barbosa de Lira, Claudio A
2017-06-01
The main purpose of this study was to analyze the behavior of the geometric curvature of the lumbar spine during restricted and unrestricted squats, using a novel investigative method. The rationale for our hypothesis is that the lumbar curvature has different patterns at different spine levels depending on the squat technique used. Spine motion was collected via stereo-photogrammetric analysis in nineteen participants (11 males, 8 females). The reconstructed spine points at the upright neutral position and at the deepest position of the squat exercise were projected onto the sagittal plane of the trunk, a polynomial was fitted to the data, and were quantified the two-dimensional geometric curvature at lower, central and higher lumbar levels, besides the inclination of trunk and lumbosacral region, the overall geometric curvature and overall angle of the lumbar spine. The mean values for each variable were analysed with paired t-test (Psquat techniques and these effects are also reduced in unrestricted squats. The data collected in the study are evidence that during barbell squats the lumbar curvature has different patterns at different spinal levels depending on the exercise technique. The lower lumbar spine appears to be less overloaded during unrestricted squats.
Karimi, Davood; Ward, Rabab K.
2016-03-01
Reducing the radiation dose in computed tomography (CT) requires reducing the number or the energy of the photons that pass through the patient's body. An image reconstructed from such noisy or undersampled measurements will contain much noise and artifacts that can significantly reduce the diagnostic value of the image. Effective sinogram denoising or interpolation can reduce these noise and artifacts. In this paper, we present a novel approach to sinogram smoothing and interpolation. The proposed method iteratively estimates the local slope and curvature of the sinogam and forces the sinogram to follow the estimated slope and curvature. This is performed by projection onto the set of constraints that define the slope and the curvature. The constraints on the slope and curvature correspond to very simple convex sets. Projection onto these sets have simple analytical solutions. Moreover, these operations are highly parallelizable because the equations defining the slope and curvature constraints for all the points in a sinogram can be summarized as five convex sets, regardless of the length of the sinogram. We apply the proposed method on simulated and real data and examine its effect on the quality of the reconstructed image. Our results show that the proposed method is highly effective and can lead to a substantial improvement in the quality of the images reconstructed from noisy sinogram measurements. A comparison with the K-SVD denoising algorithm shows that the proposed algorithm achieves better results. We suggest that the proposed method can be a useful tool for low-dose CT.
Systems biology of cellular membranes: a convergence with biophysics.
Chabanon, Morgan; Stachowiak, Jeanne C; Rangamani, Padmini
2017-09-01
Systems biology and systems medicine have played an important role in the last two decades in shaping our understanding of biological processes. While systems biology is synonymous with network maps and '-omics' approaches, it is not often associated with mechanical processes. Here, we make the case for considering the mechanical and geometrical aspects of biological membranes as a key step in pushing the frontiers of systems biology of cellular membranes forward. We begin by introducing the basic components of cellular membranes, and highlight their dynamical aspects. We then survey the functions of the plasma membrane and the endomembrane system in signaling, and discuss the role and origin of membrane curvature in these diverse cellular processes. We further give an overview of the experimental and modeling approaches to study membrane phenomena. We close with a perspective on the converging futures of systems biology and membrane biophysics, invoking the need to include physical variables such as location and geometry in the study of cellular membranes. WIREs Syst Biol Med 2017, 9:e1386. doi: 10.1002/wsbm.1386 For further resources related to this article, please visit the WIREs website. © 2017 Wiley Periodicals, Inc.
Electrothermal technique for the alteration of corneal curvature
Energy Technology Data Exchange (ETDEWEB)
Doss, J.D.; Hutson, R.L.; Albillar, J.I.
1978-02-01
Extreme cases of refractive error, such as those caused by keratoconus, are often not correctable by the addition of external refraction. In such cases, corneal transplant is the usual remedy. Alternatives have recently included modification of the corneal shape by thermal techniques which exploit the dramatic shrinkage of corneal collagen at temperatures of 55 to 63/sup 0/C. The use of conventional thermal techniques has been limited by damage to the epithelium and Bowman's membrane, and by the observation that the change in corneal shape is often temporary. Each of these problems appears to be related to the thermal dose profile that is generated by the conductive heating method; temperature is relatively high in the epithelium, but is below the critical shrinkage temperature in the deeper stromal collagen. A wide variability in treatment results has also been reported; this may be due to unintentional variation in technique, especially in timing the treatment. An alternative heating technique will be discussed that has a more desirable thermal dose distribution. In addition, the technique allows precise electronic control of treatment duration, and other parameters that affect thermal dose to the cornea.
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.
Eickenscheidt, Max; Zeck, Günther
2014-06-01
The initiation of an action potential by extracellular stimulation occurs after local depolarization of the neuronal membrane above threshold. Although the technique shows remarkable clinical success, the site of action and the relevant stimulation parameters are not completely understood. Here we identify the site of action potential initiation in rabbit retinal ganglion cells (RGCs) interfaced to an array of extracellular capacitive stimulation electrodes. We determine which feature of the extracellular potential governs action potential initiation by simultaneous stimulation and recording RGCs interfaced in epiretinal configuration. Stimulation electrodes were combined to areas of different size and were presented at different positions with respect to the RGC. Based on stimulation by electrodes beneath the RGC soma and simultaneous sub-millisecond latency measurement we infer axonal initiation at the site of maximal curvature of the extracellular potential. Stimulation by electrodes at different positions along the axon reveals a nearly constant threshold current density except for a narrow region close to the cell soma. These findings are explained by the concept of the activating function modified to consider a region of lower excitability close to the cell soma. We present a framework how to estimate the site of action potential initiation and the stimulus required to cross threshold in neurons tightly interfaced to capacitive stimulation electrodes. Our results underscore the necessity of rigorous electrical characterization of the stimulation electrodes and of the interfaced neural tissue.
Eickenscheidt, Max; Zeck, Günther
2014-06-01
Objective. The initiation of an action potential by extracellular stimulation occurs after local depolarization of the neuronal membrane above threshold. Although the technique shows remarkable clinical success, the site of action and the relevant stimulation parameters are not completely understood. Approach. Here we identify the site of action potential initiation in rabbit retinal ganglion cells (RGCs) interfaced to an array of extracellular capacitive stimulation electrodes. We determine which feature of the extracellular potential governs action potential initiation by simultaneous stimulation and recording RGCs interfaced in epiretinal configuration. Stimulation electrodes were combined to areas of different size and were presented at different positions with respect to the RGC. Main results. Based on stimulation by electrodes beneath the RGC soma and simultaneous sub-millisecond latency measurement we infer axonal initiation at the site of maximal curvature of the extracellular potential. Stimulation by electrodes at different positions along the axon reveals a nearly constant threshold current density except for a narrow region close to the cell soma. These findings are explained by the concept of the activating function modified to consider a region of lower excitability close to the cell soma. Significance. We present a framework how to estimate the site of action potential initiation and the stimulus required to cross threshold in neurons tightly interfaced to capacitive stimulation electrodes. Our results underscore the necessity of rigorous electrical characterization of the stimulation electrodes and of the interfaced neural tissue.
Frame-Covariant Formulation of Inflation in Scalar-Curvature Theories
Burns, Daniel; Pilaftsis, Apostolos
2016-01-01
We develop a frame-covariant formulation of inflation in the slow-roll approximation by generalizing the inflationary attractor solution for scalar-curvature theories. Our formulation gives rise to new generalized forms for the potential slow-roll parameters, which enable us to examine the effect of conformal transformations and inflaton reparameterizations in scalar-curvature theories. We find that cosmological observables, such as the power spectrum, the spectral indices and their runnings, can be expressed in a concise manner in terms of the generalized potential slow-roll parameters which depend on the scalar-curvature coupling function, the inflaton wavefunction, and the inflaton potential. We show how the cosmological observables of inflation are frame-invariant in this generalized potential slow-roll formalism, as long as the end-of-inflation condition is appropriately extended to become frame-invariant as well. We then apply our formalism to specific scenarios, such as the induced gravity inflation, H...
Control of defect localization in crystalline wrinkling by curvature and topology
Lopez Jimenez, Francisco
We investigate the influence of curvature and topology on crystalline wrinkling patterns in 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. Joint work with Norbert Stoop, Romain Lagrange, Jorn Dunkel and Pedro M. Reis.
Controllable soliton propagation based on phase-front curvature in asymmetrical nonlocal media
Zhang, Huafeng; Lü, Hua; Luo, Jianghua; Sun, Lihui
2016-08-01
The influence of phase-front curvature on the dynamical behavior of the fundamental mode soliton during its transmission in asymmetrical nonlocal media is studied in detail and the phase-front curvature can be imposed on the fundamental mode soliton by reshaping or phase imprinting technologies. By changing the phase-front curvature or its imposed position, controllable soliton propagation in asymmetrical nonlocal media can be achieved. Project supported by the National Natural Science Foundation of China (Grants Nos. 11547007 and 11304024), the Innovation Personnel Training Plan for Excellent Youth of Guangdong University Project (Grant No. 2013LYM_0023), and the Yangtze Fund for Youth Teams of Science and Technology Innovation (Grant No. 2015cqt03).
Nonminimal curvature-matter coupled wormholes with matter satisfying the null energy condition
Energy Technology Data Exchange (ETDEWEB)
Garcia, Nadiezhda Montelongo; Lobo, Francisco S N, E-mail: nadiezhda@cosmo.fis.fc.ul.pt, E-mail: flobo@cii.fc.ul.pt [Centro de Astronomia e Astrofisica da Universidade de Lisboa, Campo Grande, Edificio C8 1749-016 Lisboa (Portugal)
2011-04-21
Recently, the exact solutions of wormhole geometries supported by a nonminimal curvature-matter coupling were found, where the nonminimal coupling minimizes the violation of the null energy condition of normal matter at the throat. In this brief report, we present a solution where normal matter satisfies the energy conditions at the throat and it is the higher order curvature derivatives of the nonminimal coupling that are responsible for the null energy condition violation, and consequently for supporting the respective wormhole geometries. For simplicity, we consider a linear R nonmiminal curvature-matter coupling and an explicit monotonically increasing function for the energy density. Thus, the solution found is not asymptotically flat, but may in principle be matched to an exterior vacuum solution.
Keller, Brad M.; Reeves, Anthony P.; Barr, R. Graham; Yankelevitz, David F.; Henschke, Claudia I.
2010-03-01
CT scans allow for the quantitative evaluation of the anatomical bases of emphysema. Recently, a non-density based geometric measurement of lung diagphragm curvature has been proposed as a method for the quantification of emphysema from CT. This work analyzes variability of diaphragm curvature and evaluates the effectiveness of a compensation methodology for the reduction of this variability as compared to emphysema index. Using a dataset of 43 scan-pairs with less than a 100 day time-interval between scans, we find that the diaphragm curvature had a trend towards lower overall variability over emphysema index (95% CI:-9.7 to + 14.7 vs. -15.8 to +12.0), and that the variation of both measures was reduced after compensation. We conclude that the variation of the new measure can be considered comparable to the established measure and the compensation can reduce the apparent variation of quantitative measures successfully.
Prescribing the mixed scalar curvature of a foliated Riemann-Cartan manifold
Rovenski, Vladimir Y.; Zelenko, Leonid
2018-03-01
The mixed scalar curvature is the simplest curvature invariant of a foliated Riemannian manifold. We explore the problem of prescribing the leafwise constant mixed scalar curvature of a foliated Riemann-Cartan manifold by conformal change of the structure in tangent and normal to the leaves directions. Under certain geometrical assumptions and in two special cases: along a compact leaf and for a closed fibered manifold, we reduce the problem to solution of a nonlinear leafwise elliptic equation for the conformal factor. We are looking for its solutions that are stable stationary solutions of the associated parabolic equation. Our main tool is using of majorizing and minorizing nonlinear heat equations with constant coefficients and application of comparison theorems for solutions of Cauchy's problem for parabolic equations.
International Nuclear Information System (INIS)
Catoni, Francesco; Cannata, Roberto; Zampetti, Paolo
2005-08-01
The Riemann and Lorentz constant curvature surfaces are investigated from an Euclidean point of view. The four surfaces (constant positive and constant negative curvatures with definite and non-definite fine elements) are represented as surfaces in a Riemannian or in a particular semi-Riemannian flat space and it is shown that the complex and the hyperbolic numbers allow to obtain the same equations for the corresponding Riemann and Lorentz surfaces, respectively. Moreover it is shown that the geodesics on the Lorentz surfaces states, from a physical point of view, a link between curvature and fields. This result is obtained just as a consequence of the space-time geometrical symmetry, without invoking the famous Einstein general relativity postulate [it
Polyunsaturation in cell membranes and lipid bilayers and its effects on membrane proteins.
Slater, S J; Kelly, M B; Yeager, M D; Larkin, J; Ho, C; Stubbs, C D
1996-03-01
The effect of variation of the degree of cis-unsaturation on cell membrane protein functioning was investigated using a model lipid bilayer system and protein kinase C (PKC). This protein is a key element of signal transduction. Furthermore it is representative of a class of extrinsic membrane proteins that show lipid dependent interactions with cell membranes. To test for dependence of activity on the phospholipid unsaturation, experiments were devised using a vesicle assay system consisting of phosphatidylcholine (PC) and phosphatidylserine (PS) in which the unsaturation was systematically varied. Highly purified PKC alpha and epsilon were obtained using the baculovirus-insect cell expression system. It was shown that increased PC unsaturation elevated the activity of PKC alpha. By contrast, increasing the unsaturation of PS decreased the activity of PKC alpha, and to a lesser extent PKC epsilon. This result immediately rules out any single lipid bilayer physical parameter, such as lipid order, underlying the effect. It is proposed that while PC unsaturation effects are explainable on the basis of a contribution to membrane surface curvature stress, the effects of PS unsaturation may be due to specific protein-lipid interactions. Overall, the results indicate that altered phospholipid unsaturation in cell membranes that occurs in certain disease states such as chronic alcoholism, or by dietary manipulations, are likely to have profound effects on signal transduction pathways involving PKC and similar proteins.
Solid polymer electrolyte composite membrane comprising laser micromachined porous support
Liu, Han [Waltham, MA; LaConti, Anthony B [Lynnfield, MA; Mittelsteadt, Cortney K [Natick, MA; McCallum, Thomas J [Ashland, MA
2011-01-11
A solid polymer electrolyte composite membrane and method of manufacturing the same. According to one embodiment, the composite membrane comprises a rigid, non-electrically-conducting support, the support preferably being a sheet of polyimide having a thickness of about 7.5 to 15 microns. The support has a plurality of cylindrical pores extending perpendicularly between opposing top and bottom surfaces of the support. The pores, which preferably have a diameter of about 5 microns, are made by laser micromachining and preferably are arranged in a defined pattern, for example, with fewer pores located in areas of high membrane stress and more pores located in areas of low membrane stress. The pores are filled with a first solid polymer electrolyte, such as a perfluorosulfonic acid (PFSA) polymer. A second solid polymer electrolyte, which may be the same as or different than the first solid polymer electrolyte, may be deposited over the top and/or bottom of the first solid polymer electrolyte.
Kristensen, A M; Nielsen, O B; Overgaard, K
2018-03-01
In dynamically contracting muscles, increased curvature of the force-velocity relationship contributes to the loss of power during fatigue. It has been proposed that fatigue-induced reduction in [Ca ++ ] i causes this increased curvature. However, earlier studies on single fibres have been conducted at low temperatures. Here, we investigated the hypothesis that curvature is increased by reductions in tetanic [Ca ++ ] i in isolated skeletal muscle at near-physiological temperatures. Rat soleus muscles were stimulated at 60 Hz in standard Krebs-Ringer buffer, and contraction force and velocity were measured. Tetanic [Ca ++ ] i was in some experiments either lowered by addition of 10 μmol/L dantrolene or use of submaximal stimulation (30 Hz) or increased by addition of 2 mmol/L caffeine. Force-velocity curves were constructed by fitting shortening velocity at different loading forces to the Hill equation. Curvature was determined as the ratio a/F 0 with increased curvature reflecting decreased a/F 0 . Compared to control levels, lowering tetanic [Ca ++ ] i with dantrolene or reduced stimulation frequency decreased the curvature slightly as judged from increase in a/F 0 of 13 ± 1% (P = reduced tetanic [Ca ++ ] i caused a decrease in curvature, while increasing tetanic [Ca ++ ] i increased the curvature. These results reject a simple causal relation between [Ca ++ ] i and curvature of the force-velocity relation during fatigue. © 2017 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.
Multi-scale curvature for automated identification of glaciated mountain landscapes☆
Prasicek, Günther; Otto, Jan-Christoph; Montgomery, David R.; Schrott, Lothar
2014-01-01
Erosion by glacial and fluvial processes shapes mountain landscapes in a long-recognized and characteristic way. Upland valleys incised by fluvial processes typically have a V-shaped cross-section with uniform and moderately steep slopes, whereas glacial valleys tend to have a U-shaped profile with a changing slope gradient. We present a novel regional approach to automatically differentiate between fluvial and glacial mountain landscapes based on the relation of multi-scale curvature and drainage area. Sample catchments are delineated and multiple moving window sizes are used to calculate per-cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides. Single-scale curvature can take similar values for glaciated and non-glaciated catchments but a comparison of multi-scale curvature leads to different results according to the typical cross-sectional shapes. To adapt these differences for automated classification of mountain landscapes into areas with V- and U-shaped valleys, curvature values are correlated with drainage area and a new and simple morphometric parameter, the Difference of Minimum Curvature (DMC), is developed. At three study sites in the western United States the DMC thresholds determined from catchment analysis are used to automatically identify 5 × 5 km quadrats of glaciated and non-glaciated landscapes and the distinctions are validated by field-based geological and geomorphological maps. Our results demonstrate that DMC is a good predictor of glacial imprint, allowing automated delineation of glacially and fluvially incised mountain landscapes. PMID:24748703
Casas, Jesús; Ibarguren, Maitane; Álvarez, Rafael; Terés, Silvia; Lladó, Victoria; Piotto, Stefano P; Concilio, Simona; Busquets, Xavier; López, David J; Escribá, Pablo V
2017-09-01
G proteins often bear myristoyl, palmitoyl and isoprenyl moieties, which favor their association with the membrane and their accumulation in G Protein Coupled Receptor-rich microdomains. These lipids influence the biophysical properties of membranes and thereby modulate G protein binding to bilayers. In this context, we showed here that geranylgeraniol, but neither myristate nor palmitate, increased the inverted hexagonal (H II ) phase propensity of phosphatidylethanolamine-containing membranes. While myristate and palmitate preferentially associated with phosphatidylcholine membranes, geranylgeraniol favored nonlamellar-prone membranes. In addition, Gαi 1 monomers had a higher affinity for lamellar phases, while Gβγ and Gαβγ showed a marked preference for nonlamellar prone membranes. Moreover, geranylgeraniol enhanced the binding of G protein dimers and trimers to phosphatidylethanolamine-containing membranes, yet it decreased that of monomers. By contrast, both myristate and palmitate increased the Gαi 1 preference for lamellar membranes. Palmitoylation reinforced the binding of the monomer to PC membranes and myristoylation decreased its binding to PE-enriched bilayer. Finally, binding of dimers and trimers to lamellar-prone membranes was decreased by palmitate and myristate, but it was increased in nonlamellar-prone bilayers. These results demonstrate that co/post-translational G protein lipid modifications regulate the membrane lipid structure and that they influence the physico-chemical properties of membranes, which in part explains why G protein subunits sort to different plasma membrane domains. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá. Copyright © 2017 Elsevier B.V. All rights reserved.
Deriving belief operators from preferences
Asheim, Geir B.
2000-01-01
A belief operator derived from preferences is presented. It generalizes ‘belief with probability1’ to incomplete preferences and satisﬁes minimal requirements for belief operators under weak conditions.
Zero-curvature formulation of asymptotic ordered flows of the Euler fluid
International Nuclear Information System (INIS)
Spineanu, Florin; Vlad, Madalina
2008-01-01
The two-dimensional ideal incompressible (Euler) fluid evolves at relaxation from turbulent states to large scale coherent structures. We review the field theoretical formalism for the description of the continuum limit of the discrete set of point-like vortices in plane. This formalism is used in the present work to show that the equation governing the asymptotic stationary coherent flows of the Euler fluid can be derived from the condition of zero-curvature. It is suggested that the self-duality can be represented, for this particular system, also as the Hodge duality. Key words: Euler fluids, ordered flows, fields theories, zero-curvature condition.(authors)
Energy Technology Data Exchange (ETDEWEB)
Wu, Jin-Yuan; Shi, Z.; /Fermilab
2004-12-01
Strong magnetic field in today's colliding detectors causes track recognition more difficult due to large track curvatures. In this document, we present a global track recognition scheme based on track angle measurements for circular tracks passing the collision point. It uses no approximations in the track equation and therefore is suitable for both large and small curvature tracks. The scheme can be implemented both in hardware for lower-level trigger or in software for higher-level trigger or offline analysis codes. We will discuss an example of FPGA implementations using ''hash sorter''.
The influence of road curvature on fatal crashes in New Zealand
DEFF Research Database (Denmark)
Haynes, Robin; Lake, Iain R.; Kingham, Simon
2008-01-01
of average road curvature. The best predictors of the number of fatal crashes on urban roads, rural state highways and other rural roads were traffic flow, speed limitation and socio-economic deprivation. Holding significant factors constant, there was no evidence that TLAs with the most curved roads had...... more crashes than elsewhere. Fatal crashes on urban roads were significantly and negatively related to two measures of road curvature: the ratio of road length to straight distance and the cumulative angle turned per kilometre. Weaker negative associations on rural state highways could have occurred...
FY 2016 Status Report: CIRFT Testing Data Analyses and Updated Curvature Measurements
Energy Technology Data Exchange (ETDEWEB)
Wang, Jy-An John [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Wang, Hong [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2016-08-01
This report provides a detailed description of FY15 test result corrections/analysis based on the FY16 Cyclic Integrated Reversible-Bending Fatigue Tester (CIRFT) test program methodology update used to evaluate the vibration integrity of spent nuclear fuel (SNF) under normal transportation conditions. The CIRFT consists of a U-frame testing setup and a real-time curvature measurement method. The three-component U-frame setup of the CIRFT has two rigid arms and linkages to a universal testing machine. The curvature of rod bending is obtained through a three-point deflection measurement method. Three linear variable differential transformers (LVDTs) are used and clamped to the side connecting plates of the U-frame to capture the deformation of the rod. The contact-based measurement, or three-LVDT-based curvature measurement system, on SNF rods has been proven to be quite reliable in CIRFT testing. However, how the LVDT head contacts the SNF rod may have a significant effect on the curvature measurement, depending on the magnitude and direction of rod curvature. It has been demonstrated that the contact/curvature issues can be corrected by using a correction on the sensor spacing. The sensor spacing defines the separation of the three LVDT probes and is a critical quantity in calculating the rod curvature once the deflections are obtained. The sensor spacing correction can be determined by using chisel-type probes. The method has been critically examined this year and has been shown to be difficult to implement in a hot cell environment, and thus cannot be implemented effectively. A correction based on the proposed equivalent gauge-length has the required flexibility and accuracy and can be appropriately used as a correction factor. The correction method based on the equivalent gauge length has been successfully demonstrated in CIRFT data analysis for the dynamic tests conducted on Limerick (LMK) (17 tests), North Anna (NA) (6 tests), and Catawba mixed oxide (MOX
Induction of Plant Curvature by Magnetophoresis and Cytoskeletal Changes during Root Graviresponse
Hasenstein, Karl H.; Kuznetsov, Oleg A.; Blancaflor, Eilson B.
1996-01-01
High gradient magnetic fields (HGMF) induce curvature in roots and shoots. It is considered that this response is likely to be based on the intracellular displacement of bulk starch (amyloplasts) by the ponderomotive force generated by the HGMF. This process is called magnetophoresis. The differential elongation during the curvature along the concave and convex flanks of growing organs may be linked to the microtubular and/or microfilament cytoskeleton. The possible existence of an effect of the HGMF on the cytoskeleton was tested for, but none was found. The application of cytoskeletal stabilizers or depolymerizers showed that neither microtubules, nor microfilaments, are involved in the graviresponse.
Curved nanocarbon materials: probing the curvature and topology effects using phonon spectra
Energy Technology Data Exchange (ETDEWEB)
Saxena, Avadh Baheri [Los Alamos National Laboratory; Gupta, Sanju [UNIV OF MISSOURI
2008-01-01
In spite of detailed structural characterization of nanoscale carbons, they still possess some features that are not entirely understood particularly in terms of topological characteristics. By means of resonance Raman spectroscopy, we elucidated the notion of global topology and curvature by determining the prominent Raman bands variation for various carbon nanostructures including tubular (single-, double- and multiwalled nanotubes, peapod), spherical (hypo- and hyperfullerenes, onion-like carbon) and complex (nanocones, nanohorns, nanodisks and nanorings) geometries. This knowledge points to an unprecedented emergent paradigm of global topology/curvature {yields} property {yields} functionality relationship.
Alonso, Rodrigo; Manohar, Aneesh V
2016-01-01
A geometric formulation of Higgs Effective Field Theory (HEFT) is presented. Experimental observables are given in terms of geometric invariants of the scalar sigma model sector such as the curvature of the scalar field manifold $\\mathcal M$. We show how the curvature can be measured experimentally via Higgs cross-sections, $W_L$ scattering, and the $S$ parameter. The one-loop action of HEFT is given in terms of geometric invariants of $\\mathcal M$. The distinction between the Standard Model (SM) and HEFT is whether $\\mathcal M$ is flat or curved, not whether the scalars transform linearly or non-linearly under the electroweak group.
Prediction of the Critical Curvature for LX-17 with the Time of Arrival Data from DNS
Energy Technology Data Exchange (ETDEWEB)
Yao, Jin [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Fried, Laurence E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Moss, William C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2017-01-10
We extract the detonation shock front velocity, curvature and acceleration from time of arrival data measured at grid points from direct numerical simulations of a 50mm rate-stick lit by a disk-source, with the ignition and growth reaction model and a JWL equation of state calibrated for LX-17. We compute the quasi-steady (D, κ) relation based on the extracted properties and predicted the critical curvatures of LX-17. We also proposed an explicit formula that contains the failure turning point, obtained from optimization for the (D, κ) relation of LX-17.
On the Effect of Curvature in Debonded Sandwich Panels Subjected to Compressive Loading
DEFF Research Database (Denmark)
Moslemian, Ramin; Berggreen, Christian; Branner, Kim
2008-01-01
with a circular debond. The Crack Surface Displacement Extrapolation (CSDE) method is used to calculate fracture parameters in the interface. Compression tests were carried out on two types of debonded curved panels with different curvature using Digital Image Correlation (DIC) measurements to determine the full......The aim of this study is to obtain an understanding of the effect of panel curvature on residual compressive strength in debond damaged sandwich panels. Finite element analysis and linear elastic fracture mechanics are employed to analyze the residual compressive strength of curved panels...
Large-scale magnetic fields, curvature fluctuations, and the thermal history of the Universe
International Nuclear Information System (INIS)
Giovannini, Massimo
2007-01-01
It is shown that gravitating magnetic fields affect the evolution of curvature perturbations in a way that is reminiscent of a pristine nonadiabatic pressure fluctuation. The gauge-invariant evolution of curvature perturbations is used to constrain the magnetic power spectrum. Depending on the essential features of the thermodynamic history of the Universe, the explicit derivation of the bound is modified. The theoretical uncertainty in the constraints on the magnetic energy spectrum is assessed by comparing the results obtained in the case of the conventional thermal history with the estimates stemming from less conventional (but phenomenologically allowed) post-inflationary evolutions
Recursion Formulae for Obtaining Surfaces with Constant Mean Curvature in R2,1
International Nuclear Information System (INIS)
Tian Yongbo; Nan Zhijie; Tian Chou
2007-01-01
Though the Baecklund transformation on time-like surfaces with constant mean curvature surfaces in R 2,1 has been obtained, it is not easy to obtain corresponding surfaces because the procedure of solving the related integrable system cannot be avoided when the Baecklund transformation is used. For sake of this, in this article, some special work is done to reform the Baecklund transformation to a recursion formula, by which we can construct time-like surfaces with constant mean curvature form known ones just by quadrature procedure.
The flag curvature of invariant (α, β)-metrics of type (α+β)2/α
International Nuclear Information System (INIS)
Moghaddam, H R Salimi
2008-01-01
In this paper, we study the flag curvature of invariant (α, β)-metrics of the form (α+β) 2 /α on homogeneous spaces and Lie groups. We give a formula for the flag curvature of invariant metrics of the form f=(α+β) 2 /α such that α is induced by an invariant Riemannian metric g on the homogeneous space and the Chern connection of F coincides to the Levi-Civita connection of g. Then some conclusions in the cases of naturally reductive homogeneous spaces and Lie groups are given
Large-scale magnetic fields, curvature fluctuations and the thermal history of the Universe
Giovannini, Massimo
2007-01-01
It is shown that gravitating magnetic fields affect the evolution of curvature perturbations in a way that is reminiscent of a pristine non-adiabatic pressure fluctuation. The gauge-invariant evolution of curvature perturbations is used to constrain the magnetic power spectrum. Depending on the essential features of the thermodynamic history of the Universe, the explicit derivation of the bound is modified. The theoretical uncertainty in the constraints on the magnetic energy spectrum is assessed by comparing the results obtained in the case of the conventional thermal history with the estimates stemming from less conventional (but phenomenologically allowed) post-inflationary evolutions.
Phase space localization for anti-de Sitter quantum mechanics and its zero curvature limit
Elgradechi, Amine M.
1993-01-01
Using techniques of geometric quantization and SO(sub 0)(3,2)-coherent states, a notion of optimal localization on phase space is defined for the quantum theory of a massive and spinning particle in anti-de Sitter space time. It is shown that this notion disappears in the zero curvature limit, providing one with a concrete example of the regularizing character of the constant (nonzero) curvature of the anti-de Sitter space time. As a byproduct a geometric characterization of masslessness is obtained.
The Gauss Map of Complete Minimal Surfaces with Finite Total Curvature
Directory of Open Access Journals (Sweden)
PEDRO A. HINOJOSA
2013-11-01
Full Text Available In this paper we are concerned with the image of the normal Gauss map of a minimal surface immersed in ℝ3 with finite total curvature. We give a different proof of the following theorem of R. Osserman: The normal Gauss map of a minimal surface immersed in ℝ3 with finite total curvature, which is not a plane, omits at most three points of2 Moreover, under an additional hypothesis on the type of ends, we prove that this number is exactly 2.