The Homeodomain Derived Peptide Penetratin Induces Curvature of Fluid Membrane Domains
Lamazière, Antonin; Wolf, Claude; Lambert, Olivier; Chassaing, Gérard; Trugnan, Germain; Ayala-Sanmartin, Jesus
2008-01-01
Background Protein membrane transduction domains that are able to cross the plasma membrane are present in several transcription factors, such as the homeodomain proteins and the viral proteins such as Tat of HIV-1. Their discovery resulted in both new concepts on the cell communication during development, and the conception of cell penetrating peptide vectors for internalisation of active molecules into cells. A promising cell penetrating peptide is Penetratin, which crosses the cell membranes by a receptor and metabolic energy-independent mechanism. Recent works have claimed that Penetratin and similar peptides are internalized by endocytosis, but other endocytosis-independent mechanisms have been proposed. Endosomes or plasma membranes crossing mechanisms are not well understood. Previously, we have shown that basic peptides induce membrane invaginations suggesting a new mechanism for uptake, “physical endocytosis”. Methodology/Principal Findings Herein, we investigate the role of membrane lipid phases on Penetratin induced membrane deformations (liquid ordered such as in “raft” microdomains versus disordered fluid “non-raft” domains) in membrane models. Experimental data show that zwitterionic lipid headgroups take part in the interaction with Penetratin suggesting that the external leaflet lipids of cells plasma membrane are competent for peptide interaction in the absence of net negative charges. NMR and X-ray diffraction data show that the membrane perturbations (tubulation and vesiculation) are associated with an increase in membrane negative curvature. These effects on curvature were observed in the liquid disordered but not in the liquid ordered (raft-like) membrane domains. Conclusions/Significance The better understanding of the internalisation mechanisms of protein transduction domains will help both the understanding of the mechanisms of cell communication and the development of potential therapeutic molecular vectors. Here we showed that
Penetratin-induced transdermal delivery from H(II) mesophases of sodium diclofenac.
Cohen-Avrahami, Marganit; Libster, Dima; Aserin, Abraham; Garti, Nissim
2012-05-10
Penetratin, a cell penetrating peptide is embedded within a reversed hexagonal (H(II)) mesophase for improved transdermal delivery of sodium diclofenac (Na-DFC). The H(II) mesophase serves as the solubilization reservoir and gel matrix whereas penetratin is the transdermal penetration enhancer for the drug. The systems were characterized and the interactions between the components were determined by SAXS, ATR-FTIR and SD-NMR. High affinity of Na-DFC to glycerol monooleate (GMO) was revealed, associated with increasing the order within the water channels. This affinity is enhanced upon heating and seems to be associated with GMO dehydration. Penetratin (PEN) is entrapped at the hydrophilic region of the H(II) mesophase, between the GMO headgroups, reducing the order of the system and decreasing the size of the hexagonal domains. The transdermal delivery rate of Na-DFC through porcine skin, from the H(II) mesophases, was enhanced by PEN and so also the cumulative transport crossing the skin. PEN induced accelerated drug diffusion through the stratum corneum, towards the different skin layers. The transdermal delivery enhancement is explained from the results of the ATR-FTIR analysis. It seems that PEN accelerates the structural transition of skin lipids from hexagonal to liquid. The disordering results in enhanced diffusion of Na-DFC through the stratum corneum, followed by enhanced overall penetration of the drug.
Induced gravity from curvature density preserving diffeomorphisms
NASA Astrophysics Data System (ADS)
Oda, Ichiro
2016-08-01
We construct not only an induced gravity model with restricted diffeomorphisms, that is, transverse diffeomorphisms that preserve the curvature density, but also with full diffeomorphisms. By solving the equations of motion, it turns out that these models produce Einstein's equations with a certain Newton constant in addition to the constraint for the curvature density. In the limit of the infinite Newton constant, the models give rise to induced gravity. Moreover, we discuss cosmological solutions on the basis of the gravitational models at hand.
Curvature-induced lipid segregation
NASA Astrophysics Data System (ADS)
Zheng, Bin; Meng, Qing-Tian; B. Selinger Robin, L.; V. Selinger, Jonathan; Ye, Fang-Fu
2015-06-01
We investigate how an externally imposed curvature influences lipid segregation on two-phase-coexistent membranes. We show that the bending-modulus contrast of the two phases and the curvature act together to yield a reduced effective line tension. On largely curved membranes, a state of multiple domains (or rafts) forms due to a mechanism analogous to that causing magnetic-vortex formation in type-II superconductors. We determine the criterion for such a multi-domain state to occur; we then calculate respectively the size of the domains formed on cylindrically and spherically curved membranes. Project supported by the Hundred-Talent Program of the Chinese Academy of Sciences (FY) and the National Science Foundation of USA via Grant DMR-1106014 (RLBS, JVS).
Hydrophobic surfactant proteins strongly induce negative curvature.
Chavarha, Mariya; Loney, Ryan W; Rananavare, Shankar B; Hall, Stephen B
2015-07-01
The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism. PMID:26153706
Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature
Chavarha, Mariya; Loney, Ryan W.; Rananavare, Shankar B.; Hall, Stephen B.
2015-01-01
The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism. PMID:26153706
Negative Gaussian curvature from induced metric changes
NASA Astrophysics Data System (ADS)
Modes, Carl D.; Warner, Mark
2015-07-01
We revisit the light or heat-induced changes in topography of initially flat sheets of a solid that elongate or contract along patterned in-plane director fields. For radial or azimuthal directors, negative Gaussian curvature is generated—so-called "anticones." We show that azimuthal material displacements are required for the distorted state to be stretch free and bend minimizing. The resultant shapes are smooth and asterlike and can become reentrant in the azimuthal coordinate for large deformations. We show that care is needed when considering elastomers rather than glasses, although the former offer huge deformations.
Curvature inducing macroion condensation driven shape changes of fluid vesicles.
Sreeja, K K; Ipsen, John H; Sunil Kumar, P B
2015-11-21
We study the effect of curvature inducing macroion condensation on the shapes of charged deformable fluid interfaces using dynamically triangulated Monte Carlo simulations. In the weak electrostatic coupling regime, surface charges are weakly screened and the conformations of a vesicle, with fixed spherical topology, depend on the charge-charge interaction on the surface. While in the strong coupling regime, condensation driven curvature induction plays a dominant role in determining the conformations of these surfaces. Condensation itself is observed to be dependent on the induced curvature, with larger induced curvatures favoring increased condensation. We show that both curvature generation and curvature sensing, induced by the interplay of electrostatics and curvature energy, contribute to determination of the vesicle configurations.
Curvature inducing macroion condensation driven shape changes of fluid vesicles.
Sreeja, K K; Ipsen, John H; Sunil Kumar, P B
2015-11-21
We study the effect of curvature inducing macroion condensation on the shapes of charged deformable fluid interfaces using dynamically triangulated Monte Carlo simulations. In the weak electrostatic coupling regime, surface charges are weakly screened and the conformations of a vesicle, with fixed spherical topology, depend on the charge-charge interaction on the surface. While in the strong coupling regime, condensation driven curvature induction plays a dominant role in determining the conformations of these surfaces. Condensation itself is observed to be dependent on the induced curvature, with larger induced curvatures favoring increased condensation. We show that both curvature generation and curvature sensing, induced by the interplay of electrostatics and curvature energy, contribute to determination of the vesicle configurations. PMID:26590553
Curvature inducing macroion condensation driven shape changes of fluid vesicles
NASA Astrophysics Data System (ADS)
Sreeja, K. K.; Ipsen, John H.; Sunil Kumar, P. B.
2015-11-01
We study the effect of curvature inducing macroion condensation on the shapes of charged deformable fluid interfaces using dynamically triangulated Monte Carlo simulations. In the weak electrostatic coupling regime, surface charges are weakly screened and the conformations of a vesicle, with fixed spherical topology, depend on the charge-charge interaction on the surface. While in the strong coupling regime, condensation driven curvature induction plays a dominant role in determining the conformations of these surfaces. Condensation itself is observed to be dependent on the induced curvature, with larger induced curvatures favoring increased condensation. We show that both curvature generation and curvature sensing, induced by the interplay of electrostatics and curvature energy, contribute to determination of the vesicle configurations.
Armbruster, Ute; Labs, Mathias; Pribil, Mathias; Viola, Stefania; Xu, Wenteng; Scharfenberg, Michael; Hertle, Alexander P.; Rojahn, Ulrike; Jensen, Poul Erik; Rappaport, Fabrice; Joliot, Pierre; Dörmann, Peter; Wanner, Gerhard; Leister, Dario
2013-01-01
Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. A granum consists of a core of appressed membranes, two stroma-exposed end membranes, and margins, which connect pairs of grana membranes at their lumenal sides. Multiple forces contribute to grana stacking, but it is not known how the extreme curvature at margins is generated and maintained. We report the identification of the CURVATURE THYLAKOID1 (CURT1) protein family, conserved in plants and cyanobacteria. The four Arabidopsis thaliana CURT1 proteins (CURT1A, B, C, and D) oligomerize and are highly enriched at grana margins. Grana architecture is correlated with the CURT1 protein level, ranging from flat lobe-like thylakoids with considerably fewer grana margins in plants without CURT1 proteins to an increased number of membrane layers (and margins) in grana at the expense of grana diameter in overexpressors of CURT1A. The endogenous CURT1 protein in the cyanobacterium Synechocystis sp PCC6803 can be partially replaced by its Arabidopsis counterpart, indicating that the function of CURT1 proteins is evolutionary conserved. In vitro, Arabidopsis CURT1A proteins oligomerize and induce tubulation of liposomes, implying that CURT1 proteins suffice to induce membrane curvature. We therefore propose that CURT1 proteins modify thylakoid architecture by inducing membrane curvature at grana margins. PMID:23839788
Relaxation and curvature-induced molecular flows within multicomponent membranes.
Morris, Richard G
2014-06-01
The quantitative understanding of membranes is still rooted in work performed in the 1970s by Helfrich and others, concerning amphiphilic bilayers. However, most biological membranes contain a wide variety of nonamphiphilic molecules too. Drawing analogy with the physics of nematic-non-nematic mixtures, we present a dynamical (out-of-equilibrium) description of such multicomponent membranes. The approach combines nematohydrodynamics in the linear regime and a proper use of (differential-) geometry. The main result is to demonstrate that one can obtain equations describing a cross-diffusion effect (similar to the Soret and Dufour effects) between curvature and the (in-membrane) flow of amphiphilic molecules relative to nonamphiphilic ones. Surprisingly, the shape of a membrane relaxes according to a simple heat equation in the mean curvature, a process that is accompanied by a simultaneous boost to the diffusion of amphiphiles away from regions of high curvature. The model also predicts the inverse process, by which the forced bending of a membrane induces a flow of amphiphilic molecules towards areas of high curvature. In principle, numerical values for the relevant diffusion coefficients should be verifiable by experiment. PMID:25019811
Adsorbate-induced curvature and stiffening of graphene.
Svatek, Simon A; Scott, Oliver R; Rivett, Jasmine P H; Wright, Katherine; Baldoni, Matteo; Bichoutskaia, Elena; Taniguchi, Takashi; Watanabe, Kenji; Marsden, Alexander J; Wilson, Neil R; Beton, Peter H
2015-01-14
The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon-carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625
Adsorbate-Induced Curvature and Stiffening of Graphene
2014-01-01
The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon–carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625
Sequence-induced curvature of Tenebrio molitor satellite DNA.
Plohl, M; Borstnik, B; Ugarković, D; Gamulin, V
1990-09-01
Single satellite DNA constitutes about 50% of the Tenebrio molitor genome. Electrophoresis of 142 base pair long satellite monomers on nondenaturating polyacrylamide gel shows retarded mobility, a characteristic of fragments with sequence-induced DNA curvature. Migrational analysis of circularly permuted satellite monomers revealed the existence of 2 bend centers in the monomer sequence. We calculated the trajectory of DNA helix axis according to the algorithm of De Santis et al. This model predicts that T molitor naked satellite DNA forms a solenoid structure with left-handed superhelix. One turn of the superhelix has approximately 310 base pairs and a 33 nm pitch. Point mutations found in the satellite DNA (1.8%) influence bending characteristics, but do not distort the general geometry of satellite superhelix.
Bera, Swapna; Kar, Rajiv K; Mondal, Susanta; Pahan, Kalipada; Bhunia, Anirban
2016-09-01
Cell-penetrating peptides (CPPs) have shown promise in nonpermeable therapeutic drug delivery, because of their ability to transport a variety of cargo molecules across the cell membranes and their noncytotoxicity. Drosophila antennapedia homeodomain-derived CPP penetratin (RQIKIWFQNRRMKWKK), being rich in positively charged residues, has been increasingly used as a potential drug carrier for various purposes. Penetratin can breach the tight endothelial network known as the blood-brain barrier (BBB), permitting treatment of several neurodegenerative maladies, including Alzheimer's disease, Parkinson's disease, and Huntington's disease. However, a detailed structural understanding of penetratin and its mechanism of action is lacking. This study defines structural features of the penetratin-derived peptide, DK17 (DRQIKIWFQNRRMKWKK), in several model membranes and describes a membrane-induced conformational transition of the DK17 peptide in these environments. A series of biophysical experiments, including high-resolution nuclear magnetic resonance spectroscopy, provides the three-dimensional structure of DK17 in different membranes mimicking the BBB or total brain lipid extract. Molecular dynamics simulations support the experimental results showing preferential binding of DK17 to particular lipids at atomic resolution. The peptide conserves the structure of the subdomain spanning residues Ile6-Arg11, despite considerable conformational variation in different membrane models. In vivo data suggest that the wild type, not a mutated sequence, enters the central nervous system. Together, these data highlight important structural and functional attributes of DK17 that could be utilized in drug delivery for neurodegenerative disorders.
Cosmology of a holographic induced gravity model with curvature effects
Bouhmadi-Lopez, Mariam; Errahmani, Ahmed; Ouali, Taoufiq
2011-10-15
We present a holographic model of the Dvali-Gabadadze-Porrati scenario with a Gauss-Bonnet term in the bulk. We concentrate on the solution that generalizes the normal Dvali-Gabadadze-Porrati branch. It is well known that this branch cannot describe the late-time acceleration of the universe even with the inclusion of a Gauss-Bonnet term. Here, we show that this branch in the presence of a Gauss-Bonnet curvature effect and a holographic dark energy with the Hubble scale as the infrared cutoff can describe the late-time acceleration of the universe. It is worthwhile to stress that such an energy density component cannot do the same job on the normal Dvali-Gabadadze-Porrati branch (without Gauss-Bonnet modifications) nor in a standard four-dimensional relativistic model. The acceleration on the brane is also presented as being induced through an effective dark energy which corresponds to a balance between the holographic one and geometrical effects encoded through the Hubble parameter.
An Experimental Study of Laminarization Induced by Acceleration and Curvature
NASA Astrophysics Data System (ADS)
Jackson, R. Brian
The Generation IV Very High Temperature Reactor (VHTR) design is being actively studied in various countries for application due to its inherent passive safe design, higher thermal efficiencies, and proposed capability of providing high temperature process heat. The pebble bed core is one of two core designs used in gas reactors. In the pebble bed core there are mechanisms present which can cause the flow to laminarize, thus reducing its heat transfer effectiveness. Wind tunnel experiments were conducted using Particle Image Velocimetry (PIV) to investigate boundary layer laminarization due to flow acceleration and convex curvature effects. The flow was subject to acceleration and curvature both separately and together and the flow behavior characterized with velocity flow profiles, mean boundary layer parameters, and turbulence quantities. Laminarization was identified and the influence of acceleration and curvature was characterized.
Protein-Induced Membrane Curvature Alters Local Membrane Tension
Rangamani, Padmini; Mandadap, Kranthi K.; Oster, George
2014-01-01
Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface properties of the membrane, such as membrane tension, change in response to protein adsorption. In this article, we show that the partial differential equations arising from classical elastic model of lipid membranes, which account for simultaneous changes in shape and membrane tension due to protein adsorption in a local region, cannot be solved for nonaxisymmetric geometries using straightforward numerical techniques; instead, a viscous-elastic formulation is necessary to fully describe the system. Therefore, we develop a viscous-elastic model for inhomogeneous membranes of the Helfrich type. Using the newly available viscous-elastic model, we find that the lipids flow to accommodate changes in membrane curvature during protein adsorption. We show that, at the end of protein adsorption process, the system sustains a residual local tension to balance the difference between the actual mean curvature and the imposed spontaneous curvature. We also show that this change in membrane tension can have a functional impact such as altered response to pulling forces in the presence of proteins. PMID:25099814
Comparative Effectivness of Metal Ions in Inducing Curvature of Primary Roots of Zea mays1
Hasenstein, Karl Heinz; Evans, Michael L.; Stinemetz, Charles L.; Moore, Randy; Fondren, W. Mark; Koon, E. Colin; Higby, Mary A.; Smucker, Alvin J. M.
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. PMID:11538239
Comparative effectiveness of metal ions in inducing curvature of primary roots of Zea mays
NASA Technical Reports Server (NTRS)
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.
Lipid membrane-mediated attraction between curvature inducing objects.
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J
2016-01-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (-3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles. PMID:27618764
Lipid membrane-mediated attraction between curvature inducing objects
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.
2016-01-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (−3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles. PMID:27618764
Membrane Curvature Induced by Aggregates of LH2s and Monomeric LH1s
Chandler, Danielle E.; Gumbart, James; Stack, John D.; Chipot, Christophe; Schulten, Klaus
2009-01-01
Abstract The photosynthetic apparatus of purple bacteria is contained within organelles called chromatophores, which form as extensions of the cytoplasmic membrane. The shape of these chromatophores can be spherical (as in Rhodobacter sphaeroides), lamellar (as in Rhodopseudomonas acidophila and Phaeospirillum molischianum), or tubular (as in certain Rb. sphaeroides mutants). Chromatophore shape is thought to be influenced by the integral membrane proteins Light Harvesting Complexes I and II (LH1 and LH2), which pack tightly together in the chromatophore. It has been suggested that the shape of LH2, together with its close packing in the membrane, induces membrane curvature. The mechanism of LH2-induced curvature is explored via molecular dynamics simulations of multiple LH2 complexes in a membrane patch. LH2s from three species—Rb. sphaeroides, Rps. acidophila, and Phsp. molischianum—were simulated in different packing arrangements. In each case, the LH2s pack together and tilt with respect to neighboring LH2s in a way that produces an overall curvature. This curvature appears to be driven by a combination of LH2's shape and electrostatic forces that are modulated by the presence of well-conserved cytoplasmic charged residues, the removal of which inhibits LH2 curvature. The interaction of LH2s and an LH1 monomer is also explored, and it suggests that curvature is diminished by the presence of LH1 monomers. The implications of our results for chromatophore shape are discussed. PMID:19948127
The cellular response to curvature-induced stress
NASA Astrophysics Data System (ADS)
Biton, Y. Y.; Safran, S. A.
2009-12-01
We present a theoretical model to explain recent observations of the orientational response of cells to unidirectional curvature. Experiments show that some cell types when plated on a rigid cylindrical surface tend to reorient their shape and stress fibers along the axis of the cylinder, while others align their stress fibers perpendicular to that axis. Our model focuses on the competition of the shear stress—that results from cell adhesion and active contractility—and the anisotropic bending stiffness of the stress fibers. We predict the cell orientation angle that results from the balance of these two forces in a mechanical equilibrium. The conditions under which the different experimental observations can be obtained are discussed in terms of the theory.
Curvature induced phase stability of an intensely heated liquid.
Sasikumar, Kiran; Liang, Zhi; Cahill, David G; Keblinski, Pawel
2014-06-21
We use non-equilibrium molecular dynamics simulations to study the heat transfer around intensely heated solid nanoparticles immersed in a model Lennard-Jones fluid. We focus our studies on the role of the nanoparticle curvature on the liquid phase stability under steady-state heating. For small nanoparticles we observe a stable liquid phase near the nanoparticle surface, which can be at a temperature well above the boiling point. Furthermore, for particles with radius smaller than a critical radius of 2 nm we do not observe formation of vapor even above the critical temperature. Instead, we report the existence of a stable fluid region with a density much larger than that of the vapor phase. We explain the stability in terms of the Laplace pressure associated with the formation of a vapor nanocavity and the associated effect on the Gibbs free energy. PMID:24952551
Flow-induced instabilities of shells of revolution with non-zero Gaussian curvatures conveying fluid
NASA Astrophysics Data System (ADS)
Chang, Gary Han; Modarres-Sadeghi, Yahya
2016-02-01
We study flow-induced instabilities of axis-symmetric shells of revolution with an arbitrary meridian and non-zero Gaussian curvatures. We consider a fluid-structure interaction (FSI) model based on an inviscid flow model and a thin shell theory. This FSI model is solved using a method that combines the Galerkin technique with the boundary element method (BEM). The present method is capable of investigating the dynamic behavior of doubly-curved shells in contact with flow without the need for an analytical solution of the perturbed flow potential. Shells of revolution with different values of non-zero Gaussian curvatures are investigated and their behavior is compared to shells with zero Gaussian curvature. It is found that the added mass natural frequencies of shells of revolution are larger than those of conical shells with the same inlet, outlet and length. Shells of revolution, with both positive and negative Gaussian curvatures, lose their instability by buckling, however, shells with negative Gaussian curvatures buckle at modes similar to those observed in uniform and conical shells, while shells with positive Gaussian curvatures buckle with localized deformations close to the area with higher local flow velocities.
NASA Astrophysics Data System (ADS)
Yang, Fan; Liu, Ren-Bao
2014-12-01
We propose a general framework of nonlinear optics induced by non-Abelian Berry curvature in time-reversal-invariant (TRI) insulators. We find that the third-order response of a TRI insulator under optical and terahertz light fields is directly related to the integration of the non-Abelian Berry curvature over the Brillouin zone. We apply the result to insulators with rotational symmetry near the band edge. Under resonant excitations, the optical susceptibility is proportional to the flux of the Berry curvature through the iso-energy surface, which is equal to the Chern number of the surface times 2 π . For the III-V compound semiconductors, microscopic calculations based on the six-band model give a third-order susceptibility with the Chern number of the iso-energy surface equal to 3.
Curvature-induced activation of a passive tracer in an active bath
NASA Astrophysics Data System (ADS)
Mallory, S. A.; Valeriani, C.; Cacciuto, A.
2014-09-01
We use numerical simulations to study the motion of a large asymmetric tracer immersed in a low-density suspension of self-propelled particles in two dimensions. Specifically, we analyze how the curvature of the tracer affects its translational and rotational motion in an active environment. We find that even very small amounts of curvature are sufficient for the active bath to impart directed motion to the tracer, which results in its effective activation. We propose simple scaling arguments to characterize this induced activity in terms of the curvature of the tracer and the strength of the self-propelling force. Our results suggest new ways of controlling the transport properties of passive tracers in an active medium by carefully tailoring their geometry.
Curvature-induced activation of a passive tracer in an active bath.
Mallory, S A; Valeriani, C; Cacciuto, A
2014-09-01
We use numerical simulations to study the motion of a large asymmetric tracer immersed in a low-density suspension of self-propelled particles in two dimensions. Specifically, we analyze how the curvature of the tracer affects its translational and rotational motion in an active environment. We find that even very small amounts of curvature are sufficient for the active bath to impart directed motion to the tracer, which results in its effective activation. We propose simple scaling arguments to characterize this induced activity in terms of the curvature of the tracer and the strength of the self-propelling force. Our results suggest new ways of controlling the transport properties of passive tracers in an active medium by carefully tailoring their geometry. PMID:25314448
Curvature-induced expulsion of actomyosin bundles during cytokinetic ring contraction
Huang, Junqi; Chew, Ting Gang; Kamnev, Anton; Martin, Douglas S; Carter, Nicholas J; Cross, Robert Anthony; Oliferenko, Snezhana; Balasubramanian, Mohan K
2016-01-01
Many eukaryotes assemble a ring-shaped actomyosin network that contracts to drive cytokinesis. Unlike actomyosin in sarcomeres, which cycles through contraction and relaxation, the cytokinetic ring disassembles during contraction through an unknown mechanism. Here we find in Schizosaccharomyces japonicus and Schizosaccharomyces pombe that, during actomyosin ring contraction, actin filaments associated with actomyosin rings are expelled as micron-scale bundles containing multiple actomyosin ring proteins. Using functional isolated actomyosin rings we show that expulsion of actin bundles does not require continuous presence of cytoplasm. Strikingly, mechanical compression of actomyosin rings results in expulsion of bundles predominantly at regions of high curvature. Our work unprecedentedly reveals that the increased curvature of the ring itself promotes its disassembly. It is likely that such a curvature-induced mechanism may operate in disassembly of other contractile networks. DOI: http://dx.doi.org/10.7554/eLife.21383.001 PMID:27734801
Molecular Characterization of Caveolin-induced Membrane Curvature*
Ariotti, Nicholas; Rae, James; Leneva, Natalya; Ferguson, Charles; Loo, Dorothy; Okano, Satomi; Hill, Michelle M.; Walser, Piers; Collins, Brett M.; Parton, Robert G.
2015-01-01
The generation of caveolae involves insertion of the cholesterol-binding integral membrane protein caveolin-1 (Cav1) into the membrane, however, the precise molecular mechanisms are as yet unknown. We have speculated that insertion of the caveolin scaffolding domain (CSD), a conserved amphipathic region implicated in interactions with signaling proteins, is crucial for caveola formation. We now define the core membrane-juxtaposed region of Cav1 and show that the oligomerization domain and CSD are protected by tight association with the membrane in both mature mammalian caveolae and a model prokaryotic system for caveola biogenesis. Cryoelectron tomography reveals the core membrane-juxtaposed domain to be sufficient to maintain oligomerization as defined by polyhedral distortion of the caveolar membrane. Through mutagenesis we demonstrate the importance of the membrane association of the oligomerization domain/CSD for defined caveola biogenesis and furthermore, highlight the functional significance of the intramembrane domain and the CSD for defined caveolin-induced membrane deformation. Finally, we define the core structural domain of Cav1, constituting only 66 amino acids and of great potential to nanoengineering applications, which is required for caveolin-induced vesicle formation in a bacterial system. These results have significant implications for understanding the role of Cav1 in caveola formation and in regulating cellular signaling events. PMID:26304117
Smrt, Sean T.; Draney, Adrian W.; Lorieau, Justin L.
2015-01-01
The highly conserved N-terminal 23 residues of the hemagglutinin glycoprotein, known as the fusion peptide domain (HAfp23), is vital to the membrane fusion and infection mechanism of the influenza virus. HAfp23 has a helical hairpin structure consisting of two tightly packed amphiphilic helices that rest on the membrane surface. We demonstrate that HAfp23 is a new class of amphipathic helix that functions by leveraging the negative curvature induced by two tightly packed helices on membranes. The helical hairpin structure has an inverted wedge shape characteristic of negative curvature lipids, with a bulky hydrophobic region and a relatively small hydrophilic head region. The F3G mutation reduces this inverted wedge shape by reducing the volume of its hydrophobic base. We show that despite maintaining identical backbone structures and dynamics as the wild type HAfp23, the F3G mutant has an attenuated fusion activity that is correlated to its reduced ability to induce negative membrane curvature. The inverted wedge shape of HAfp23 is likely to play a crucial role in the initial stages of membrane fusion by stabilizing negative curvature in the fusion stalk. PMID:25398882
Smrt, Sean T; Draney, Adrian W; Lorieau, Justin L
2015-01-01
The highly conserved N-terminal 23 residues of the hemagglutinin glycoprotein, known as the fusion peptide domain (HAfp23), is vital to the membrane fusion and infection mechanism of the influenza virus. HAfp23 has a helical hairpin structure consisting of two tightly packed amphiphilic helices that rest on the membrane surface. We demonstrate that HAfp23 is a new class of amphipathic helix that functions by leveraging the negative curvature induced by two tightly packed helices on membranes. The helical hairpin structure has an inverted wedge shape characteristic of negative curvature lipids, with a bulky hydrophobic region and a relatively small hydrophilic head region. The F3G mutation reduces this inverted wedge shape by reducing the volume of its hydrophobic base. We show that despite maintaining identical backbone structures and dynamics as the wild type HAfp23, the F3G mutant has an attenuated fusion activity that is correlated to its reduced ability to induce negative membrane curvature. The inverted wedge shape of HAfp23 is likely to play a crucial role in the initial stages of membrane fusion by stabilizing negative curvature in the fusion stalk.
Curvature induced by amyloplast magnetophoresis in protonemata of the moss Ceratodon purpureus
NASA Technical Reports Server (NTRS)
Kuznetsov, O. A.; Schwuchow, J.; Sack, F. D.; Hasenstein, K. H.
1999-01-01
After gravistimulation of Ceratodon purpureus (Hedw.) Brid. protonemata in the dark, amyloplast sedimentation was followed by upward curvature in the wild-type (WT) and downward curvature in the wwr mutant (wrong way response). We used ponderomotive forces induced by high-gradient magnetic fields (HGMF) to simulate the effect of gravity and displace the presumptive statoliths. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, close to the edge of a magnetized ferromagnetic wedge, or close to a small (<1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. WT cells curved toward the HGMF, and wwr cells curved away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g cm-3. Plastid density was similar for both genotypes, but the mutant contained larger plastids than the WT. The size difference might explain the stronger response of the wwr protonemata to the HGMF. Our data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can substitute for gravity.
Curvature induced by amyloplast magnetophoresis in protonemata of the moss Ceratodon purpureus.
Kuznetsov, O A; Schwuchow, J; Sack, F D; Hasenstein, K H
1999-02-01
After gravistimulation of Ceratodon purpureus (Hedw.) Brid. protonemata in the dark, amyloplast sedimentation was followed by upward curvature in the wild-type (WT) and downward curvature in the wwr mutant (wrong way response). We used ponderomotive forces induced by high-gradient magnetic fields (HGMF) to simulate the effect of gravity and displace the presumptive statoliths. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, close to the edge of a magnetized ferromagnetic wedge, or close to a small (<1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. WT cells curved toward the HGMF, and wwr cells curved away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g cm-3. Plastid density was similar for both genotypes, but the mutant contained larger plastids than the WT. The size difference might explain the stronger response of the wwr protonemata to the HGMF. Our data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can substitute for gravity. PMID:9952461
Bending-induced mode non-degeneracy and coupling in chalcogenide negative curvature fibers.
Wei, Chengli; Menyuk, Curtis R; Hu, Jonathan
2016-05-30
We study bend loss in chalcogenide negative curvature fibers with different polarizations, different tube wall thicknesses, and different bend directions relative to the mode polarization. The coupling between the core mode and tube modes induces bend loss peaks in the two non-degenerate modes at the same bend radius. There is as much as a factor of 28 difference between the losses of the two polarization modes. The fiber with a larger tube wall thickness, corresponding to a smaller inner tube diameter, can sustain a smaller bend radius. The bend loss is sensitive to the bend direction when coupling occurs between the core mode and tube modes. A bend loss of 0.2 dB/m at a bend radius of 16 cm, corresponding to 0.2 dB/turn, can be achieved in a chalcogenide negative curvature fiber. PMID:27410139
Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature.
Ershov, Dmitry; Sprakel, Joris; Appel, Jeroen; Cohen Stuart, Martien A; van der Gucht, Jasper
2013-06-01
Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together as a result of capillary attraction. This attraction arises from deformation of the liquid interface due to gravitational forces; these deformations cause excess surface area that can be reduced if the particles move closer together. For micrometer-sized colloids, however, the gravitational force is too small to produce significant interfacial deformations, so capillary forces between spherical colloids at a flat interface are negligible. Here, we show that this is different when the confining liquid interface has a finite curvature that is also anisotropic. In that case, the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature.
Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature.
Ershov, Dmitry; Sprakel, Joris; Appel, Jeroen; Cohen Stuart, Martien A; van der Gucht, Jasper
2013-06-01
Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together as a result of capillary attraction. This attraction arises from deformation of the liquid interface due to gravitational forces; these deformations cause excess surface area that can be reduced if the particles move closer together. For micrometer-sized colloids, however, the gravitational force is too small to produce significant interfacial deformations, so capillary forces between spherical colloids at a flat interface are negligible. Here, we show that this is different when the confining liquid interface has a finite curvature that is also anisotropic. In that case, the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature. PMID:23690591
Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature
Ershov, Dmitry; Sprakel, Joris; Appel, Jeroen; Cohen Stuart, Martien A.; van der Gucht, Jasper
2013-01-01
Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together as a result of capillary attraction. This attraction arises from deformation of the liquid interface due to gravitational forces; these deformations cause excess surface area that can be reduced if the particles move closer together. For micrometer-sized colloids, however, the gravitational force is too small to produce significant interfacial deformations, so capillary forces between spherical colloids at a flat interface are negligible. Here, we show that this is different when the confining liquid interface has a finite curvature that is also anisotropic. In that case, the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature. PMID:23690591
NASA Astrophysics Data System (ADS)
van der Gucht, Jasper; Ershov, Dmitry
2014-03-01
Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together in space-saving hexagons to minimize the disruption of the liquid interface. Micrometer-sized colloidal particles embedded in a liquid interface normally do not disrupt the interface, so that such clustering does not occur. Here, we show that this is different when the interface has a curvature that is anisotropic. We find that in this case the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature.
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-01-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
NASA Astrophysics Data System (ADS)
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-10-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham-Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this description, the
Ion beam induced surface patterns due to mass redistribution and curvature-dependent sputtering
NASA Astrophysics Data System (ADS)
Bobes, Omar; Zhang, Kun; Hofsäss, Hans
2012-12-01
Recently it was reported that ion-induced mass redistribution would solely determine nano pattern formation on ion-irradiated surfaces. We investigate the pattern formation on amorphous carbon thin films irradiated with Xe ions of energies between 200 eV and 10 keV. Sputter yield as well as number of displacements within the collision cascade vary strongly as function of ion energy and allow us to investigate the contributions of curvature-dependent erosion according to the Bradley-Harper model as well as mass redistribution according to the Carter-Vishnyakov model. We find parallel ripple orientations for an ion incidence angle of 60° and for all energies. A transition to perpendicular pattern orientation or a rather flat surface occurs around 80° for energies between 1 keV and 10 keV. Our results are compared with calculations based on both models. For the calculations we extract the shape and size of Sigmund's energy ellipsoid (parameters a, σ, μ), the angle-dependent sputter yield, and the mean mass redistribution distance from the Monte Carlo simulations with program SDTrimSP. The calculated curvature coefficients Sx and Sy describing the height evolution of the surface show that mass redistribution is dominant for parallel pattern formation in the whole energy regime. Furthermore, the angle where the parallel pattern orientation starts to disappear is related to curvature-dependent sputtering. In addition, we investigate the case of Pt erosion with 200 eV Ne ions, where mass redistribution vanishes. In this case, we observe perpendicular ripple orientation in accordance with curvature-dependent sputtering and the predictions of the Bradley-Harper model.
Picard, G.; Schneider-Henriquez, J.E.; Fendler, J.H. )
1990-01-25
Two-exposure interferometric holograms have been shown to sensitively report ultrasmall-pressure (10 natm)-induced curvature changes in glyceryl monooleate (GMO) bilayer lipid membranes (BLMs). The number of concentric fringes observed, and hence the lateral distance between the plane of the Teflon and the BLM, increased linearly with increasing transmembrane pressure and led to a value of 1.1 {plus minus} 0.05 dyn/cm for the surface tension of the BLM. BLMs with appreciable Plateau-Gibbs borders have been shown to undergo nonuniform deformation; the bilayer portion is distorted less than the surrounding Plateau-Gibbs border upon the application of a transmembrane pressure gradient.
Kristensen, Mie; Franzyk, Henrik; Klausen, Mia Thorne; Iversen, Anne; Bahnsen, Jesper Søborg; Skyggebjerg, Rikke Bjerring; Foderà, Vito; Nielsen, Hanne Mørck
2015-09-01
Penetratin is a widely used carrier peptide showing promising potential for mucosal delivery of therapeutic proteins. In the present study, the importance of specific penetratin residues and pH was investigated with respect to complexation with insulin and subsequent transepithelial insulin permeation. Besides penetratin, three analogues were studied. The carrier peptide-insulin complexes were characterized in terms of size and morphology at pH 5, 6.5, and 7.4 by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. At pH 7.4 mainly very large complexes were present, while much smaller complexes dominated at pH 5. Presence of arginine residues in the carrier peptide proved to be a prerequisite for complexation with insulin as well as for enhanced transepithelial insulin permeation in vitro. Rearrangement of tryptophan residues resulted in significantly increased insulin permeation as compared to that of the parent penetratin. In general, pre-complexation with penetratin and its analogues at pH 5 gave rise to increased insulin permeation as compared to that observed at pH 7.4; this finding was further supported by a preliminary in vivo study using the parent penetratin.
Lee, Hwankyu
2013-10-14
We performed coarse-grained (CG) molecular dynamics (MD) simulations of single-walled carbon nanotubes (SWNTs) with lipid bilayers to understand the effect of the SWNT diameter, length, and concentration on membrane curvature and penetration. Starting with different orientations of multiple SWNTs near lipid bilayers, simulations show that SWNTs insert into the bilayer and induce membrane curvature, which is much larger than that observed from previous simulations of a single SWNT. Longer and thicker SWNTs at higher concentration cause larger membrane curvature, indicating the effect of the SWNT size and concentration, in qualitative agreement with experiments. In particular, thicker SWNTs significantly increase the bilayer height and the difference of the projected and contour bilayer areas, decrease the area compressibility, and disorder lipids. When inserted into the bilayer, thinner SWNTs mainly contact the entire tails of lipids, while thicker SWNTs are wrapped mainly by the ending tail-carbons, leading to the larger membrane curvature. This indicates the effect of SWNT diameter on the SWNT-lipid interaction, yielding different extents of membrane curvature. These findings imply that the SWNT-induced membrane penetration and curvature are modulated by a combination of SWNT length, diameter, and concentration.
Gravitational induced particle production through a nonminimal curvature-matter coupling
NASA Astrophysics Data System (ADS)
Harko, Tiberiu; Lobo, Francisco S. N.; Mimoso, José P.; Pavón, Diego
2015-08-01
We consider the possibility of a gravitationally induced particle production through the mechanism of a nonminimal curvature-matter coupling. An interesting feature of this gravitational theory is that the divergence of the energy-momentum tensor is nonzero. As a first step in our study we reformulate the model in terms of an equivalent scalar-tensor theory, with two arbitrary potentials. By using the formalism of open thermodynamic systems, we interpret the energy balance equations in this gravitational theory from a thermodynamic point of view, as describing irreversible matter creation processes. The particle number creation rates, the creation pressure, and the entropy production rates are explicitly obtained as functions of the scalar field and its potentials, as well as of the matter Lagrangian. The temperature evolution laws of the newly created particles are also obtained. The cosmological implications of the model are briefly investigated, and it is shown that the late-time cosmic acceleration may be due to particle creation processes. Furthermore, it is also shown that due to the curvature-matter coupling, during the cosmological evolution a large amount of comoving entropy is also produced.
NASA Astrophysics Data System (ADS)
Shimazaki, Y.; Yamamoto, M.; Borzenets, I. V.; Watanabe, K.; Taniguchi, T.; Tarucha, S.
2015-12-01
The field of `Valleytronics’ has recently been attracting growing interest as a promising concept for the next generation electronics, because non-dissipative pure valley currents with no accompanying net charge flow can be manipulated for computational use, akin to pure spin currents. Valley is a quantum number defined in an electronic system whose energy bands contain energetically degenerate but non-equivalent local minima (conduction band) or maxima (valence band) due to a certain crystal structure. Specifically, spatial inversion symmetry broken two-dimensional honeycomb lattice systems exhibiting Berry curvature is a subset of possible systems that enable optical, magnetic and electrical control of the valley degree of freedom. Here we use dual-gated bilayer graphene to electrically induce and control broken inversion symmetry (or Berry curvature) as well as the carrier density for generating and detecting the pure valley current. In the insulating regime, at zero-magnetic field, we observe a large nonlocal resistance that scales cubically with the local resistivity, which is evidence of pure valley current.
Muto, Keiya; Kamei, Noriyasu; Yoshida, Mia; Takayama, Kozo; Takeda-Morishita, Mariko
2016-06-01
Nasal vaccination is considered an attractive strategy to prevent the infection and spread of viruses. However, the vaccine formulations available on the market remain imperfect on account of their limited effectiveness. In the present study, we hypothesized that the nasal coadministration of antigens with cell-penetrating peptides promotes antigen delivery immune response in the nasal mucosa, thereby enhancing the production of mucosal IgA and systemic IgG. The levels of ovalbumin (OVA)-specific IgG and IgA in plasma and nasal perfusate, respectively, increased after 2 or 4 weeks on nasal coadministration of OVA with l- or d-penetratin, suggesting that OVA antigen was effectively delivered by penetratin to the nasal epithelium. An additional study demonstrated that the production of systemic IgG and nasal mucosal IgA against influenza A virus was specifically promoted by nasal coadministration of influenza A virus with d-penetratin. The results of this study suggested that cell-penetrating peptides are a promising tool for the delivery of vaccines to the nasal mucosa and for the subsequent dual stimulation of systemic and mucosal immune responses. PMID:27155764
Penetratin-Membrane Association: W48/R52/W56 Shield the Peptide from the Aqueous Phase
Lensink, M. F.; Christiaens, B.; Vandekerckhove, J.; Prochiantz, A.; Rosseneu, M.
2005-01-01
Using molecular dynamics simulations, we studied the mode of association of the cell-penetrating peptide penetratin with both a neutral and a charged bilayer. The results show that the initial peptide-lipid association is a fast process driven by electrostatic interactions. The homogeneous distribution of positively charged residues along the axis of the helical peptide, and especially residues K46, R53, and K57, contribute to the association of the peptide with lipids. The bilayer enhances the stability of the penetratin helix. Oriented parallel to the lipid-water interface, the subsequent insertion of the peptide through the bilayer headgroups is significantly slower. The presence of negatively charged lipids considerably enhances peptide binding. Lateral side-chain motion creates an opening for the helix into the hydrophobic core of the membrane. The peptide aromatic residues form a π-stacking cluster through W48/R52/W56 and F49/R53, protecting the peptide from the water phase. Interaction with the penetratin peptide has only limited effect on the overall membrane structure, as it affects mainly the conformation of the lipids which interact directly with the peptide. Charge matching locally increases the concentration of negatively charged lipids, lateral lipid diffusion locally decreases. Lipid disorder increases, through decreased order parameters of the lipids interacting with the penetratin side chains. Penetratin molecules at the membrane surface do not seem to aggregate. PMID:15542560
Curvature-Induced Bunch Self-Interaction for an Energy-Chirped Bunch in Magnetic Bends
Li, Rui
2008-02-01
Within the realm of classical electrodynamics, the curvature-induced bunch collective interaction in magnetic bends can be studied using effective forces in the canonical formulation of the coherent synchrotron radiation (CSR) effect. As an application of this canonical formulation, in this paper, for an electron distribution moving ultrarelativistically in a bending system, the dynamics of the particles in the distribution is derived from the Hamiltonian of the particles in terms of the bunch internal coordinates. The consequent Vlasov equation manifests explicitly how the phase-space distribution is perturbed by the effective CSR forces. In particular, we study the impact of an initial linear energy chirp of the bunch on the behavior of the effective longitudinal CSR force, which arises due to the modification of the retardation relation as a result of the energy-chirping- induced longitudinal-horizontal correlation of the bunch distribution (bunch tilt) in dispersive regions. Our study demonstrates clearly the time delay (or retardation) of the behavior of the effective longitudinal CSR force on a bunch in responding to the change of the bunch length in a magnetic bend. Our result also shows that the effective longitudinal CSR force for a bunch under full compression can have sensitive dependence on the transverse position of the test particle in the bunch for certain parameter regimes.
Yin, Tiantian; Xie, Wenjie; Sun, Jing; Yang, Licong; Liu, Jie
2016-08-01
The structural changes of amyloid-beta (Aβ) from nontoxic monomers into neurotoxic aggregates are implicated with pathogenesis of Alzheimer's disease (AD). Over the past decades, weak disaggregation ability and low permeability to the blood-brain barrier (BBB) may be the main obstacles for major Aβ aggregation blockers. Here, we synthesized penetratin (Pen) peptide loaded poly(ethylene glycol) (PEG)-stabilized gold nanostars (AuNS) modified with ruthenium complex (Ru@Pen@PEG-AuNS), and Ru(II) complex as luminescent probes for tracking drug delivery. We revealed that Ru@Pen@PEG-AuNS could obviously inhibit the formation of Aβ fibrils as well as dissociate preformed fibrous Aβ under the irradiation of near-infrared (NIR) due to the NIR absorption characteristic of AuNS. More importantly, this novel design could be applied in medicine as an appropriate nanovehicle, being highly biocompatible and hemocompatible. In addition, Ru@Pen@PEG-AuNS had excellent neuroprotective effect on the Aβ-induced cellular toxicity by applying NIR irradiation. Meanwhile, Pen peptide could effectively improve the delivery of nanoparticles to the brain in vitro and in vivo, which overcame the major limitation of Aβ aggregation blockers. These consequences illustrated that the enhanced BBB permeability and efficient photothermolysis of Ru@Pen@PEG-AuNS are promising agents in AD therapy. PMID:27411476
Curvature-induced crosshatched order in two-dimensional semiflexible polymer networks
NASA Astrophysics Data System (ADS)
Vrusch, Cyril; Storm, Cornelis
2015-12-01
A recurring motif in the organization of biological tissues are networks of long, fibrillar protein strands effectively confined to cylindrical surfaces. Often, the fibers in such curved, quasi-two-dimensional (2D) geometries adopt a characteristic order: the fibers wrap around the central axis at an angle which varies with radius and, in several cases, is strongly bimodally distributed. In this Rapid Communication, we investigate the general problem of a 2D crosslinked network of semiflexible fibers confined to a cylindrical substrate, and demonstrate that in such systems the trade-off between bending and stretching energies, very generically, gives rise to crosshatched order. We discuss its general dependency on the radius of the confining cylinder, and present an intuitive model that illustrates the basic physical principle of curvature-induced order. Our findings shed new light on the potential origin of some curiously universal fiber orientational distributions in tissue biology, and suggests novel ways in which synthetic polymeric soft materials may be instructed or programmed to exhibit preselected macromolecular ordering.
Zamotaiev, Oleksandr M; Postupalenko, Viktoriia Y; Shvadchak, Volodymyr V; Pivovarenko, Vasyl G; Klymchenko, Andrey S; Mély, Yves
2014-09-28
A new fluorescent label N-[4′-(dimethylamino)-3-hydroxyflavone-7-yl]-N-methyl-β-alanine (7AF) was synthesized. Due to two electron donor groups at the opposite ends of the chromophore, an excited state intramolecular proton transfer (ESIPT) resulting in a dual emission was observed even in highly polar media and its fluorescence quantum yield was found to be remarkably high in a broad range of solvents including water. As a consequence, this label exhibits a remarkable sensitivity to the hydration of its environment, which is observed as a color switch between the emission of the ESIPT product (T* form) and that of the normal N* form. The 7AF label was coupled to the N-terminus of penetratin, a cell penetrating peptide, in order to study its interactions with lipid membranes and internalization inside the cells. As expected, the binding of penetratin to lipid membranes resulted in a dramatic switch in the relative intensity of its two emission bands as compared to its emission in buffer. Our studies with different lipid compositions confirmed the preference of penetratin to lipid membranes of the liquid disordered phase. After incubation of low concentrations of labeled penetratin with living cells, ratiometric imaging revealed, in addition to membrane-bound species, a significant fraction of free peptide in cytosol showing the characteristic emission from aqueous medium. At higher concentrations of penetratin, mainly peptides bound to cell membrane structures were observed. These observations confirmed the ability of penetratin to enter the cytosol by direct translocation through the cell plasma membrane, in addition to the classical entry by endocytosis. The present probe constitutes thus a powerful tool to study the interaction of peptides with living cells and their internalization mechanisms. PMID:25072870
Second Variation of Induced Curvature Term in Brane-World Action
NASA Astrophysics Data System (ADS)
Iofa, Mikhail Z.
In a 5D spacetime with a 3-brane embedded we calculate the second variation of the scalar 4D curvature term on the brane under variations of the 5D metric. It is shown that the second variation of the 4D scalar curvature term in adapted coordinates is expressed only through variations of the components of the 5D metric with 4D indices.
NASA Astrophysics Data System (ADS)
Pannuzzo, Martina; Raudino, Antonio; Böckmann, Rainer A.
2014-07-01
Peptide- or protein-induced curvatures of lipid membranes may be studied in molecular dynamics (MD) simulations. In these, membranes are usually modeled as infinitely extended bilayers by using periodic boundary conditions. However, the enforced periodicity results in an underestimation of the bending power of peptides, unless the patch size is much larger than the induced curvature radii. In this letter, we propose a novel approach to evaluate the bending power of a given distribution and/or density of peptides based on the use of flat open-edged lipid patches. To ensure long-lived metastable structures, the patch rim is stabilized in MD simulations by a local enrichment with short-chain lipids. By combining the theory of continuum elastic media with MD simulations, we prove that open-edged patches evolve from a planar state to a closed vesicle, with a transition rate that strongly depends on the concentration of lipid soluble peptides. For close-to-critical values for the patch size and edge energy, the response to even small changes in peptide concentration adopts a transition-like behavior (buckling instability). The usage of open-edged membrane patches amplifies the bending power of peptides, thereby enabling the analysis of the structural properties of membrane-peptide systems. We applied the presented method to investigate the curvature induced by aggregating β -amyloid peptides, unraveling a strong sensitivity of membrane deformation to the peptide concentration.
Jiang, Jinglong; Su, Miao; Wang, Liyan; Jiao, Chengjin; Sun, Zhengxi; Cheng, Wei; Li, Fengmin; Wang, Chongying
2012-04-01
During germination in distilled water (dH(2)O) on a horizontally positioned Petri dish, emerging primary roots of grass pea (Lathyrus sativus L.) grew perpendicular to the bottom of the Petri dish, due to gravitropism. However, when germinated in exogenous hydrogen peroxide (H(2)O(2)), the primary roots grew parallel to the bottom of the Petri dish and asymmetrically, forming a horizontal curvature. Time-course experiments showed that the effect was strongest when H(2)O(2) was applied prior to the emergence of the primary root. H(2)O(2) failed to induce root curvature when applied post-germination. Dosage studies revealed that the frequency of primary root curvature was significantly enhanced with increased H(2)O(2) concentrations. This curvature could be directly counteracted by dimethylthiourea (DMTU), a scavenger of H(2)O(2), but not by diphenylene iodonium (DPI) and pyridine, inhibitors of H(2)O(2) production. Exogenous H(2)O(2) treatment caused both an increase in the activities of H(2)O(2)-scavenging enzymes [including ascorbate peroxidase (APX: EC 1.11.1.11), catalase (CAT: EC 1.11.1.6) and peroxidase (POD: EC 1.11.1.7)] and a reduction in endogenous H(2)O(2) levels and root vitality. Although grass pea seeds absorbed exogenous H(2)O(2) during seed germination, DAB staining of paraffin sections revealed that exogenous H(2)O(2) only entered the root epidermis and not inner tissues. These data indicated that exogenously applied H(2)O(2) could lead to a reversible loss of the root gravitropic response and a horizontal curvature in primary roots during radicle emergence of the seedling.
Curvature-Induced Anomalous Enhancement in the Work Function of Nanostructures.
Kaur, Jasmin; Kant, Rama
2015-08-01
An analytical theory to estimate the electronic work function in curved geometries is formulated under Thomas-Fermi approximation. The work function is framed as the work against the electrostatic self-capacitive energy. The contribution of surface curvature is characterized by mean and Gaussian curvature (through multiple scattering expansion). The variation in work function of metal and semimetal nanostructures is shown as the consequence of surface radius of curvature comparable to electronic screening length. For ellipsoidal particles, the maximum value of work function is observed at the equator and poles for oblate and prolate particles, respectively, whereas triaxial ellipsoid shows nonuniform distribution of the work function over the surface. Similarly, theory predicts manifold increase in the work function for a particle with atomic scale roughness. Finally, the theory is validated with experimental data, and it is concluded that the work function of a nanoparticle can be tailored through its shape. PMID:26267172
Real-time transmembrane translocation of penetratin driven by light-generated proton pumping.
Björklund, Jörgen; Biverståhl, Henrik; Gräslund, Astrid; Mäler, Lena; Brzezinski, Peter
2006-08-15
Cell penetrating peptides (CPPs) are small peptides that are able to penetrate the plasma membrane of mammalian cells. Because these peptides can also carry large hydrophilic cargos such as proteins, they could potentially be used to transport biologically active drugs across cell membranes to modulate in vivo biology. One characteristic feature of the CPPs is that they typically have a net positive charge. Therefore, a key issue associated with the transport mechanism is the role of the transmembrane electrochemical potential in driving the peptides across the membrane. In this study, we have reconstituted bacteriorhodopsin (bR) in large unilamellar vesicles (LUVs) with fluorescein-labeled CPP penetratin enclosed within the LUVs under conditions when the fluorescence is quenched. Illumination of the bacteriorhodopsin-containing LUVs resulted in creation of a transmembrane proton electrochemical gradient (positive on the inside). Upon generation of this gradient, an increase in fluorescence was observed, which shows that the proton gradient drives the translocation of penetratin. The mechanism most likely can be generalized to other CPPs.
Chaudhary, Suman; Smith, Carol Anne; del Pino, Pablo; de la Fuente, Jesus M.; Mullin, Margaret; Hursthouse, Andrew; Stirling, David; Berry, Catherine C.
2013-01-01
Nanotechnology plays an increasingly important role in the biomedical arena. In particular, magnetic nanoparticles (mNPs) have become important tools in molecular diagnostics, in vivo imaging and improved treatment of disease, with the ultimate aim of producing a more theranostic approach. Due to their small sizes, the nanoparticles can cross most of the biological barriers such as the blood vessels and the blood brain barrier, thus providing ubiquitous access to most tissues. In all biomedical applications maximum nanoparticle uptake into cells is required. Two promising methods employed to this end include functionalization of mNPs with cell-penetrating peptides to promote efficient translocation of cargo into the cell and the use of external magnetic fields for enhanced delivery. This study aimed to compare the effect of both penetratin and a static magnetic field with regards to the cellular uptake of 200 nm magnetic NPs and determine the route of uptake by both methods. Results demonstrated that both techniques increased particle uptake, with penetratin proving more cell specific. Clathrin- medicated endocytosis appeared to be responsible for uptake as shown via PCR and western blot, with Pitstop 2 (known to selectively block clathrin formation) blocking particle uptake. Interestingly, it was further shown that a magnetic field was able to reverse or overcome the blocking, suggesting an alternative route of uptake. PMID:24275948
Toroidal curvature induced screening of external fields by a resistive plasma response
NASA Astrophysics Data System (ADS)
Liu, Yueqiang; Connor, J. W.; Cowley, S. C.; Ham, C. J.; Hastie, R. J.; Hender, T. C.
2012-07-01
Within the single fluid theory for a toroidal, resistive plasma, the favorable average curvature effect [Glasser et al., Phys. Fluids 18, 875 (1975)], which is responsible for the strong stabilization of the classical tearing mode at finite pressure, can also introduce a strong screening effect to the externally applied resonant magnetic field. Contrary to conventional understanding, this screening, occurring at slow plasma rotation, is enhanced when decreasing the plasma flow speed. The plasma rotation frequency, below which this screening effect is observed, depends on the plasma pressure and resistivity. For the simple toroidal case considered here, the toroidal rotation frequency has to be below ˜10-5ωA, with ωA being the Alfvén frequency. In addition, the same curvature effect leads to enhanced toroidal coupling of poloidal Fourier harmonics inside the resistive layer, as well as reversing the sign of the electromagnetic torque at slow plasma flow.
NASA Astrophysics Data System (ADS)
Lowengrub, John; Allard, Jun; Aland, Sebastian
2016-03-01
The formation of membrane vesicles from a larger membrane that occurs during endocytosis and other cell processes is typically orchestrated by curvature-inducing molecules attached to the membrane. Recent reports demonstrate that vesicles can form de novo in a few milliseconds. Membrane dynamics at these scales are strongly influenced by hydrodynamic interactions. To study this problem, we develop new diffuse interface models for the dynamics of inextensible vesicles in a viscous fluid with stiff, curvature-inducing molecules. The model couples the Navier-Stokes equations with membrane-induced bending forces that incorporate concentration-dependent bending stiffness coefficients and spontaneous curvatures, with equations for molecule transport and for a Lagrange multiplier to enforce local inextensibility. Two forms of surface transport equations are considered: Fickian surface diffusion and Cahn-Hilliard surface dynamics, with the former being more appropriate for small molecules and the latter being better for large molecules. The system is solved using adaptive finite element methods in 3D axisymmetric geometries. The results demonstrate that hydrodynamics can indeed enable the rapid formation of a small vesicle attached to the membrane by a narrow neck. When the Fickian model is used, this is a transient state with the steady state being a flat membrane with a uniformly distributed molecule concentration due to diffusion. When the Cahn-Hilliard model is used, molecule concentration gradients are sustained, the neck stabilizes and the system evolves to a steady-state with a small, compact vesicle attached to the membrane. By varying the membrane coverage of molecules in the Cahn-Hilliard model, we find that there is a critical (smallest) neck radius and a critical (fastest) budding time. These critical points are associated with changes in the vesicle morphology from spherical to mushroom-like as the molecule coverage on the membrane is increased.
On ripples and rafts: Curvature induced nanoscale structures in lipid membranes
NASA Astrophysics Data System (ADS)
Schmid, Friederike; Dolezel, Stefan; Lenz, Olaf; Meinhardt, Sebastian
2014-03-01
We develop an elastic theory that predicts the spontaneous formation of nanoscale structures in lipid bilayers which locally phase separate between two phases with different spontaneous monolayer curvature. The theory rationalizes in a unified manner the observation of a variety of nanoscale structures in lipid membranes: Rippled states in one-component membranes, lipid rafts in multicomponent membranes. Furthermore, we report on recent observations of rippled states and rafts in simulations of a simple coarse-grained model for lipid bilayers, which are compatible with experimental observations and with our elastic model.
Virialisation-induced curvature as a physical explanation for dark energy
Roukema, Boudewijn F.; Ostrowski, Jan J.; Buchert, Thomas E-mail: Jan.Ostrowski@astro.uni.torun.pl
2013-10-01
The geometry of the dark energy and cold dark matter dominated cosmological model (ΛCDM) is commonly assumed to be given by a Friedmann-Lemaître-Robertson-Walker (FLRW) metric, i.e. it assumes homogeneity in the comoving spatial section. The homogeneity assumption fails most strongly at (i) small distance scales and (ii) recent epochs, implying that the FLRW approximation is most likely to fail at these scales. We use the virialisation fraction to quantify (i) and (ii), which approximately coincide with each other on the observational past light cone. For increasing time, the virialisation fraction increases above 10% at about the same redshift ( ∼ 1–3) at which Ω{sub Λ} grows above 10% ( ≈ 1.8). Thus, instead of non-zero Ω{sub Λ}, we propose an approximate, general-relativistic correction to the matter-dominated (Ω{sub m}; = 1,Ω{sub Λ} = 0), homogeneous metric (Einstein-de Sitter, EdS). A low-redshift effective matter-density parameter of Ω{sub m}{sup eff}(0) = 0.26±0.05 is inferred. Over redshifts 0 < z < 3, the distance modulus of the virialisation-corrected EdS model approximately matches the ΛCDM distance modulus. This rough approximation assumes ''old physics'' (general relativity), not ''new physics''. Thus, pending more detailed calculations, we strengthen the claim that ''dark energy'' should be considered as an artefact of emerging average curvature in the void-dominated Universe, via a novel approach that quantifies the relation between virialisation and average curvature evolution.
Lee, Hwankyu
2013-02-01
Single-walled carbon nanotubes (SWNTs) wrapped with different types of lipids and polyethylene glycol (PEG)-grafted lipids were simulated with lipid bilayers. Simulations were carried out with the previously parametrized coarse-grained (CG) SWNT and PEG force fields that had captured the experimentally observed conformations of self-assembled SWNT-lipid complexes and phase behavior of PEG-grafted lipids. Simulations of multiple copies of the SWNT in water show that all pure SWNTs aggregate, lipid-wrapped SWNTs partially aggregate, but those wrapped with lipids grafted to PEG (M(w) = 550) completely disperse, indicating the effect of short PEG chains on interparticle aggregation, in agreement with experiment. Starting with initial SWNT orientation parallel to the bilayer surface, SWNTs wrapped with lysophospholipids and PEG (M(w) = 550)-grafted lipids insert into the hydrophobic region of the bilayer, while SWNTs wrapped with phospholipids and longer PEG (M(w) = 2000)-grafted lipids do not. These indicate that SWNTs insert because of the hydrophobic interaction with the bilayer tails, but the tight wrapping of charged lipid headgroups and long hydrophilic PEG chains can weaken the hydrophobic interaction and inhibit SWNT insertion. The inserted SWNTs contact the entire tails of neighboring lipids in one leaflet of the bilayer, which disorders the lipid bilayer and induces positive curvature. Our findings indicate that interparticle aggregation, SWNT penetration, and membrane curvature can be modulated by the SWNT-lipid structure and the PEG length.
Curvature and ionization-induced reversible hydrogen storage in metalized hexagonal B36.
Liu, Chun-Sheng; Wang, Xiangfu; Ye, Xiao-Juan; Yan, Xiaohong; Zeng, Zhi
2014-11-21
The synthesis of quasiplanar boron clusters (B36) with a central hexagonal hole provides the first experimental evidence that a single-atomic-layer borophene with hexagonal vacancies is potentially viable [Z. Piazza, H. Hu, W. Li, Y. Zhao, J. Li, and L. S. Wang, Nat. Commun. 5, 3113 (2014)]. However, owing to the hexagonal holes, tunning the electronic and physical properties of B36 through chemical modifications is not fully understood. Based on (van der Waals corrected-) density functional theory, we show that Li adsorbed on B36 and B36 (-) clusters can serve as reversible hydrogen storage media. The present results indicate that the curvature and ionization of substrates can enhance the bond strength of Li due to the energetically favorable B 2p-Li 2p orbitals hybridization. Both the polarization mechanism and the orbital hybridization between H-s orbitals and Li-2s2p orbitals contribute to the adsorption of H2 molecules and the resulting adsorption energy lies between the physisorbed and chemisorbed states. Interestingly, the number of H2 in the hydrogen storage medium can be measured by the appearance of the negative differential resistance behavior at different bias voltage regions. Furthermore, the cluster-assembled hydrogen storage materials constructed by metalized B36 clusters do not cause a decrease in the number of adsorbed hydrogen molecules per Li. The system reported here is favorable for the reversible hydrogen adsorption/desorption at ambient conditions. PMID:25416890
Curvature and ionization-induced reversible hydrogen storage in metalized hexagonal B36.
Liu, Chun-Sheng; Wang, Xiangfu; Ye, Xiao-Juan; Yan, Xiaohong; Zeng, Zhi
2014-11-21
The synthesis of quasiplanar boron clusters (B36) with a central hexagonal hole provides the first experimental evidence that a single-atomic-layer borophene with hexagonal vacancies is potentially viable [Z. Piazza, H. Hu, W. Li, Y. Zhao, J. Li, and L. S. Wang, Nat. Commun. 5, 3113 (2014)]. However, owing to the hexagonal holes, tunning the electronic and physical properties of B36 through chemical modifications is not fully understood. Based on (van der Waals corrected-) density functional theory, we show that Li adsorbed on B36 and B36 (-) clusters can serve as reversible hydrogen storage media. The present results indicate that the curvature and ionization of substrates can enhance the bond strength of Li due to the energetically favorable B 2p-Li 2p orbitals hybridization. Both the polarization mechanism and the orbital hybridization between H-s orbitals and Li-2s2p orbitals contribute to the adsorption of H2 molecules and the resulting adsorption energy lies between the physisorbed and chemisorbed states. Interestingly, the number of H2 in the hydrogen storage medium can be measured by the appearance of the negative differential resistance behavior at different bias voltage regions. Furthermore, the cluster-assembled hydrogen storage materials constructed by metalized B36 clusters do not cause a decrease in the number of adsorbed hydrogen molecules per Li. The system reported here is favorable for the reversible hydrogen adsorption/desorption at ambient conditions.
Curvature and ionization-induced reversible hydrogen storage in metalized hexagonal B{sub 36}
Liu, Chun-Sheng Wang, Xiangfu; Yan, Xiaohong; Ye, Xiao-Juan; Zeng, Zhi
2014-11-21
The synthesis of quasiplanar boron clusters (B{sub 36}) with a central hexagonal hole provides the first experimental evidence that a single-atomic-layer borophene with hexagonal vacancies is potentially viable [Z. Piazza, H. Hu, W. Li, Y. Zhao, J. Li, and L. S. Wang, Nat. Commun. 5, 3113 (2014)]. However, owing to the hexagonal holes, tunning the electronic and physical properties of B{sub 36} through chemical modifications is not fully understood. Based on (van der Waals corrected-) density functional theory, we show that Li adsorbed on B{sub 36} and B{sub 36}{sup −} clusters can serve as reversible hydrogen storage media. The present results indicate that the curvature and ionization of substrates can enhance the bond strength of Li due to the energetically favorable B 2p-Li 2p orbitals hybridization. Both the polarization mechanism and the orbital hybridization between H-s orbitals and Li-2s2p orbitals contribute to the adsorption of H{sub 2} molecules and the resulting adsorption energy lies between the physisorbed and chemisorbed states. Interestingly, the number of H{sub 2} in the hydrogen storage medium can be measured by the appearance of the negative differential resistance behavior at different bias voltage regions. Furthermore, the cluster-assembled hydrogen storage materials constructed by metalized B{sub 36} clusters do not cause a decrease in the number of adsorbed hydrogen molecules per Li. The system reported here is favorable for the reversible hydrogen adsorption/desorption at ambient conditions.
NASA Technical Reports Server (NTRS)
Hasenstein, K. H.; Kuznetsov, O. A.
1999-01-01
Shoots of the lazy-2 mutant of tomato (Lycopersicon esculentum Mill., cv. Ailsa Craig) exhibit negative gravitropism in the dark, but respond positively gravitropically in (red) light. In order to test whether high-gradient magnetic fields (HGMFs) exert only ponderomotive effects on amyloplasts or affect other physiological processes, we induced magnetophoretic curvature in wild-type (WT) and lazy-2 mutant seedlings. Straight hypocotyls of 4-d-old plants were selected and the tips of their hooks were placed in an HGMF near the edge of a magnetized ferromagnetic wedge [grad (H2/2) approximately 10(9)-10(10) Oe2/cm] and mounted on a 1-rpm clinostat. After 4 h in the dark, 85% of WT hypocotyls and 67% of mutant hypocotyls curved toward the wedge. When the seedlings were exposed to red light for 1 h prior to and during the application of the HGMF, 78% of the WT seedlings curved toward the magnetic gradient, but the majority of the lazy-2 seedlings (75%) curved away from the stronger field area. Intracellular amyloplast displacement in the HGMF was similar for both varieties and resembled the displacement after horizontal reorientation. The WT showed a distinct graviresponse pattern depending on the orientation of the hook, even after excision of the apex. Application of HGMFs to decapitated hypocotyls resulted in curvature consistent with that obtained after horizontal reorientation. After light exposure, decapitated lazy-2 seedlings did not respond positively gravitropically. The data imply that the lazy-2 mutants perceive the displacement of amyloplasts in a similar manner to the WT and that the HGMF does not affect the graviresponse mechanism. The study demonstrates that ponderomotive forces due to HGMFs are useful for the analysis of the gravity-sensing mechanism in plants.
NASA Astrophysics Data System (ADS)
Rahnavard, M. H.; Rusch, W. V. T.
1992-02-01
Using diffracted-field formulas, the slope of the field is evaluated at the reflection boundary of an edge-induced shadow. Retaining high-frequency terms, the wavelength dependency is (lambda) exp -1/2. Using a formula for the field near the turning point of an inflected surface, the slope of the field at the reflection boundary is evaluated. Retaining high-frequency terms, the wavelength dependency is (lambda) exp -5/6 in this case. That is, the shadow for the surface-curvature-induced case gets sharper nearly twice as fast as for the edge-induced case as the frequency increases. This slope is a measure of spillover into the shadow region.
Prosseda, Gianni; Mazzola, Alessia; Di Martino, Maria Letizia; Tielker, Denis; Micheli, Gioacchino; Colonna, Bianca
2010-04-01
Among the molecular strategies bacteria have set up to quickly match their transcriptional program to new environments, changes in sequence-mediated DNA curvature play a crucial role. Bacterial promoters, especially those of mesophilic bacteria, are in general preceded by a curved region. The marked thermosensitivity of curved DNA stretches allows bacteria to rapidly sense outer temperature variations and affects transcription by favoring the binding of activators or repressors. Curved DNA is also able to influence the transcriptional activity of a bacterial promoter directly, without the involvement of trans-acting regulators. This study attempts to quantitatively analyze the role of DNA curvature in thermoregulated gene expression using a real-time in vitro transcription model system based on a specific fluorescence molecular beacon. By analyzing the temperature-dependent expression of a reporter gene in a construct carrying a progressively decreasing bent sequence upstream from the promoter, we show that with a decrease in temperature a narrow curvature range accounts for a significant enhancement of promoter activity. This strengthens the view that DNA curvature-mediated regulation of gene expression is likely a strategy offering fine-tuning control possibilities and that, considering the widespread presence of curved sequences upstream from bacterial promoters, it may represent one of the most primitive forms of gene regulation.
NASA Astrophysics Data System (ADS)
Hromada, Ivan; Trubko, Raisa; Holmgren, William F.; Gregoire, Maxwell D.; Cronin, Alexander D.
2014-03-01
To improve precision measurements made with atom interferometers, the effect of de Broglie wave-front curvature induced by a lens inside an atom interferometer is experimentally demonstrated and theoretically analyzed. Electrostatic lenses shift, magnify, and distort atom interference fringes, which modifies the phase and the contrast of the interference signals. Informed by these observations, an improved method is presented for analyzing measurements of atomic beam velocity distributions using phase choppers [W. F. Holmgren, I. Hromada, C. E. Klauss, and A. D. Cronin, New J. Phys. 13, 115007 (2011), 10.1088/1367-2630/13/11/115007].
Chrometzka, P
1967-12-01
1. High atmospheric pressure causes an increase of the 3-indoleacetic-acid-induced curvature of Avena coleoptiles in the Went-test, regardless of whether the applied gas is nitrogen, hydrogen, oxygen, or air. 2. The highest increase was caused by high pressure of oxygen, the lowest by lack of oxygen. 3. The high pressure effect was also observed with coleoptiles which were treated 20 hours prior to the test and which were then kept under normal pressure. 4. High pressure of oxygen for a long period (20 hours) had a poisonous effect on the coleoptiles. They ceased to grow. Preliminary studies have shown that the respiration is enhanced if the coleoptiles have been kept under high pressure. PMID:24554325
NASA Astrophysics Data System (ADS)
Liu, Ruiwen; Jiao, Binbin; Kong, Yanmei; Li, Zhigang; Shang, Haiping; Lu, Dike; Gao, Chaoqun; Chen, Dapeng
2013-09-01
Micro-devices with a bi-material-cantilever (BMC) commonly suffer initial curvature due to the mismatch of residual stress. Traditional corrective methods to reduce the residual stress mismatch generally involve the development of different material deposition recipes. In this paper, a new method for reducing residual stress mismatch in a BMC is proposed based on various previously developed deposition recipes. An initial material film is deposited using two or more developed deposition recipes. This first film is designed to introduce a stepped stress gradient, which is then balanced by overlapping a second material film on the first and using appropriate deposition recipes to form a nearly stress-balanced structure. A theoretical model is proposed based on both the moment balance principle and total equal strain at the interface of two adjacent layers. Experimental results and analytical models suggest that the proposed method is effective in producing multi-layer micro cantilevers that display balanced residual stresses. The method provides a generic solution to the problem of mismatched initial stresses which universally exists in micro-electro-mechanical systems (MEMS) devices based on a BMC. Moreover, the method can be incorporated into a MEMS design automation package for efficient design of various multiple material layer devices from MEMS material library and developed deposition recipes.
Spatial curvature, spacetime curvature, and gravity
NASA Astrophysics Data System (ADS)
Price, Richard H.
2016-08-01
The belief that curved spacetime gravity cannot be simply and correctly presented results in such misleading presentations as elastic two-dimensional sheets deformed as they support heavy objects. This article attempts to show that the conceptual basis of curved spacetime gravity can be simply and correctly presented, and that the spatial curvature of a deformed elastic sheet is very different from the spacetime curvature underlying gravity. This article introduces the idea of a "splittable" spacetime that has spatial curvature, but is missing most of the manifestations of gravity. A section in which no mathematics is used is directed at students who have studied no more than introductory physics. A separate section, for students who have taken only an introductory course in general relativity, gives mathematical arguments centering on splittable spacetimes.
Lin, Sheng-Fong; Lin, Gong-Ru
2014-09-01
With the combining effects of the fiber birefringence induced round-trip phase variation and the gain profile reshaping induced spectral filtering in the Erbium-doped fiber laser (EDFL) cavity, the mechanism corresponding to the central wavelength tunability of the EDFL passively mode-locked by nonlinear polarization rotation is explored. Bending the intracavity fiber induces the refractive index difference between orthogonal axes, which enables the dual-band central wavelength shift of 2.9 nm at 1570 nm region and up to 10.2 nm at 1600 nm region. The difference between the wavelength shifts at two bands is attributed to the gain dispersion decided by the gain spectral curvature of the EDFA, and the spacing between two switchable bands is provided by the birefringence induced variation on phase delay which causes transmittance variation. In addition, the central wavelength shift can also be controlled by varying the pumping geometry. At 1570 nm regime, an offset of up to 5.9 nm between the central wavelengths obtained under solely forward or backward pumping condition is observed, whereas the bidirectional pumping scheme effectively compensates the gain spectral reshaping effects to minimize the central wavelength shift. In contrast, the wavelength offset shrinks to only 1.1 nm when mode-locking at 1600 nm under single-sided pumping, as the gain profile strongly depends on the spatial distribution of the excited erbium ions under different pumping schemes. Except the birefringence variation and the gain spectral filtering phenomena, the gain-saturation mechanism induced refractive index change and its influence to the dual-band central wavelength tunability are also observed and analyzed.
Curvature-undulation coupling as a basis for curvature sensing and generation in bilayer membranes.
Bradley, Ryan P; Radhakrishnan, Ravi
2016-08-30
We present coarse-grained molecular dynamics simulations of the epsin N-terminal homology domain interacting with a lipid bilayer and demonstrate a rigorous theoretical formalism and analysis method for computing the induced curvature field in varying concentrations of the protein in the dilute limit. Our theory is based on the description of the height-height undulation spectrum in the presence of a curvature field. We formulated an objective function to compare the acquired undulation spectrum from the simulations to that of the theory. We recover the curvature field parameters by minimizing the objective function even in the limit where the protein-induced membrane curvature is of the same order as the amplitude due to thermal undulations. The coupling between curvature and undulations leads to significant predictions: (i) Under dilute conditions, the proteins can sense a site of spontaneous curvature at distances much larger than their size; (ii) as the density of proteins increases the coupling focuses and stabilizes the curvature field to the site of the proteins; and (iii) the mapping of the protein localization and the induction of a stable curvature is a cooperative process that can be described through a Hill function. PMID:27531962
NASA Technical Reports Server (NTRS)
Dolgin, Benjamin P.
1992-01-01
Calculations are presented of the coefficient of thermal expansion (CTE) of the radius of curvature of the reflector face sheets made of a quasi-isotropic composite. It is shown that, upon cooling, the change of the CTE of the focal distance of the mirror is equal to that of the radius of the curvature of the reflector face sheet. The CTE of the radius of the curvature of a quasi-isotropic composite face sheet depends on both the in-plane and the out-of-plane CTEs. The zero in-plane CTE of a face sheet does not guarantee mirrors with no focal length changes.
Wrinkles and splay conspire to give positive disclinations negative curvature
Matsumoto, Elisabetta A.; Vega, Daniel A.; Pezzutti, Aldo D.; García, Nicolás A.; Chaikin, Paul M.; Register, Richard A.
2015-01-01
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
Analysis of microtubule curvature.
Bicek, Andrew D; Tüzel, Erkan; Kroll, Daniel M; Odde, David J
2007-01-01
The microtubule cytoskeleton in living cells generate and resist mechanical forces to mediate fundamental cell processes, including cell division and migration. Recent advances in digital fluorescence microscopy have enabled the direct observation of bending of individual microtubules in living cells, which has enabled quantitative estimation of the mechanical state of the microtubule array. Although a variety of mechanisms have been proposed, the precise origins of microtubule deformation in living cells remain largely obscure. To investigate these mechanisms and their relative importance in cellular processes, a method is needed to accurately quantify microtubule bending within living cells. Here we describe a method for quantification of bending, using digital fluorescence microscope images to estimate the distribution of curvature in the microtubule. Digital images of individual microtubules can be used to obtain a set of discrete x-y coordinates along the microtubule contour, which is then used to estimate the curvature distribution. Due to system noise and digitization error, the estimate will be inaccurate to some degree. To quantify the inaccuracy, a computational model is used to simulate both the bending of thermally driven microtubules and their observation by digital fluorescence microscopy. This allows for direct comparison between experimental and simulated images, a method which we call model convolution microscopy. We assess the accuracy of various methods and present a suitable method for estimating the curvature distribution for thermally driven semiflexible polymers. Finally, we discuss extensions of the method to quantify microtubule curvature in living cells. PMID:17613311
Diffraction with wavefront curvature
NASA Astrophysics Data System (ADS)
Nugent, K. A.; Peele, A. G.; Quiney, H. M.; Chapman, H. N.
2005-05-01
Modern X-ray optics can produce a focused synchrotron beam with curvature on a scale comparable to that of an isolated biomolecule or to the lattice spacing of a biomolecular crystal. It is demonstrated that diffraction of phase-curved beams from such systems allows unique and robust phase recovery.
Curvature calculations with GEOCALC
Moussiaux, A.; Tombal, P.
1987-04-01
A new method for calculating the curvature tensor has been recently proposed by D. Hestenes. This method is a particular application of geometric calculus, which has been implemented in an algebraic programming language on the form of a package called GEOCALC. They show how to apply this package to the Schwarzchild case and they discuss the different results.
Photon Drag Effect due to Berry Curvature
NASA Astrophysics Data System (ADS)
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-01
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results.
Photon Drag Effect due to Berry Curvature.
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-19
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results. PMID:27588858
Curvature perturbation and waterfall dynamics in hybrid inflation
Abolhasani, Ali Akbar; Firouzjahi, Hassan; Sasaki, Misao E-mail: firouz@mail.ipm.ir
2011-10-01
We investigate the parameter spaces of hybrid inflation model with special attention paid to the dynamics of waterfall field and curvature perturbations induced from its quantum fluctuations. Depending on the inflaton field value at the time of phase transition and the sharpness of the phase transition inflation can have multiple extended stages. We find that for models with mild phase transition the induced curvature perturbation from the waterfall field is too large to satisfy the COBE normalization. We investigate the model parameter space where the curvature perturbations from the waterfall quantum fluctuations vary between the results of standard hybrid inflation and the results obtained here.
Anisotropic cubic curvature couplings
NASA Astrophysics Data System (ADS)
Bailey, Quentin G.
2016-09-01
To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass-dimension-eight coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the weak equivalence principle for self-gravitating bodies. These coefficients can be measured in Solar-System tests, while binary-pulsar systems and short-range gravity tests are particularly sensitive.
Robust pupil center detection using a curvature algorithm
NASA Technical Reports Server (NTRS)
Zhu, D.; Moore, S. T.; Raphan, T.; Wall, C. C. (Principal Investigator)
1999-01-01
Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.
Wallace, John Paul; Myneni, Ganapati Rao; Pike, Robert
2011-03-31
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
John Paul Wallace, Ganapati Rao Myneni, and Robert Pike
2011-03-01
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Ionic liquid tunes microemulsion curvature.
Liu, Liping; Bauduin, Pierre; Zemb, Thomas; Eastoe, Julian; Hao, Jingcheng
2009-02-17
Middle-phase microemulsions formed from cationic dioctadecyldimethylammonium chloride (DODMAC), anionic sodium dodecylsulfate (SDS), n-butanol, and n-heptane were studied. An ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), was employed as the electrolyte in the aqueous media instead of inorganic salts usually used in microemulsion formulation. Studies have been carried out as a function of the concentrations of [bmim][BF4], n-butanol, total surfactant (cDODMAC+SDS), and temperature on the phase behavior and the ultralow interfacial tensions in which the anionic component is present in excess in the catanionic film. Ultralow interfacial tension measurements confirmed the formation of middle-phase microemulsions and the necessary conditions for stabilizing middle-phase microemulsions. Electrical conductivity, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments were also performed, indicating that the typical heptane domain size has an average radius of 360 A and the ionic liquid induces softening of the charged catanionic film. Most interestingly, the IL concentration (cIL) is shown to act as an effective interfacial curvature-control parameter, representing a new approach to tuning the formulation of microemulsions and emulsions. The results expand the potential uses of ILs but also point to the design of new ILs that may achieve superefficient control over interfacial and self-assembly systems. PMID:19161325
Compound curvature laser window development
NASA Technical Reports Server (NTRS)
Verhoff, Vincent G.
1993-01-01
The NASA Lewis Research Center has developed and implemented a unique process for forming flawless compound curvature laser windows. These windows represent a major part of specialized, nonintrusive laser data acquisition systems used in a variety of compressor and turbine research test facilities. This report summarizes the main aspects of compound curvature laser window development. It is an overview of the methodology and the peculiarities associated with the formulation of these windows. Included in this discussion is new information regarding procedures for compound curvature laser window development.
Sigma models with negative curvature
NASA Astrophysics Data System (ADS)
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-05-01
We construct Higgs Effective Field Theory (HEFT) based on the scalar manifold Hn, which is a hyperbolic space of constant negative curvature. The Lagrangian has a non-compact O (n , 1) global symmetry group, but it gives a unitary theory as long as only a compact subgroup of the global symmetry is gauged. Whether the HEFT manifold has positive or negative curvature can be tested by measuring the S-parameter, and the cross sections for longitudinal gauge boson and Higgs boson scattering, since the curvature (including its sign) determines deviations from Standard Model values.
Transformation optics, curvature and beyond (Conference Presentation)
NASA Astrophysics Data System (ADS)
McCall, Martin W.
2016-04-01
Although the transformation algorithm is very well established and implemented, some intriguing questions remain unanswered. 1) In what precise mathematical sense is the transformation optics algorithm `exact'? The invariance of Maxwell's equations is well understood, but in what sense does the same principle not apply to acoustics (say)? 2) Even if the fields are transformed in a way that apparently mimic vacuum perfectly, it is easy to construct very simple examples where the impedance of the transformed medium is no longer isotropic and homogeneous. This would seem to imply a fundamental shortcoming in any claim that electromagnetic cloaking has been reduced to technology. 3) Transformations are known to exist that introduce a discrepancy between the Poynting vector and the wave-vector. Does this distinction carry any physical significance? We have worked extensively on understanding a commonality between transformation theories that operates at the level of rays - being interpreted as geodesics of an appropriate manifold. At this level we now understand that the *key* problem underlying all attempts to unify the transformational approach to disparate areas of physics is how to relate the transformation of the base metric (be it Euclidean for spatial transformation optics, or Minkowskian for spacetime transformation optics) to the medium parameters of a given physical domain (e.g. constitutive parameters for electromagnetism, bulk modulus and mass density for acoustics, diffusion constant and number density for diffusion physics). Another misconception we will seek to address is the notion of the relationship between transformation optics and curvature. Many have indicated that transformation optics evinces similarities with Einstein's curvature of spacetime. Here we will show emphatically that transformation optics cannot induce curvature. Inducing curvature in an electromagnetic medium requires the equivalent of a gravitational source. We will propose a scheme
Solving higher curvature gravity theories
NASA Astrophysics Data System (ADS)
Chakraborty, Sumanta; SenGupta, Soumitra
2016-10-01
Solving field equations in the context of higher curvature gravity theories is a formidable task. However, in many situations, e.g., in the context of f( R) theories, the higher curvature gravity action can be written as an Einstein-Hilbert action plus a scalar field action. We show that not only the action but the field equations derived from the action are also equivalent, provided the spacetime is regular. We also demonstrate that such an equivalence continues to hold even when the gravitational field equations are projected on a lower-dimensional hypersurface. We have further addressed explicit examples in which the solutions for Einstein-Hilbert and a scalar field system lead to solutions of the equivalent higher curvature theory. The same, but on the lower-dimensional hypersurface, has been illustrated in the reverse order as well. We conclude with a brief discussion on this technique of solving higher curvature field equations.
Curvature Interaction in Collective Space
NASA Astrophysics Data System (ADS)
Herrmann, Richard
2012-12-01
For the Riemannian space, built from the collective coordinates used within nuclear models, an additional interaction with the metric is investigated, using the collective equivalent to Einstein's curvature scalar. The coupling strength is determined using a fit with the AME2003 ground state masses. An extended finite-range droplet model including curvature is introduced, which generates significant improvements for light nuclei and nuclei in the trans-fermium region.
Curvature capillary migration of microspheres.
Sharifi-Mood, Nima; Liu, Iris B; Stebe, Kathleen J
2015-09-14
We address the question: how does capillarity propel microspheres along curvature gradients? For a particle on a fluid interface, there are two conditions that can apply at the three phase contact line: either the contact line adopts an equilibrium contact angle, or it can be pinned by kinetic trapping, e.g. at chemical heterogeneities, asperities, or other pinning sites on the particle surface. We formulate the curvature capillary energy for both scenarios for particles smaller than the capillary length and far from any pinning boundaries. The scale and range of the distortion made by the particle are set by the particle radius; we use singular perturbation methods to find the distortions and to rigorously evaluate the associated capillary energies. For particles with equilibrium contact angles, contrary to the literature, we find that the capillary energy is negligible, with the first contribution bounded to fourth order in the product of the particle radius and the deviatoric curvature of the host interface. For pinned contact lines, we find curvature capillary energies that are finite, with a functional form investigated previously by us for disks and microcylinders on curved interfaces. In experiments, we show microspheres migrate along deterministic trajectories toward regions of maximum deviatoric curvature with curvature capillary energies ranging from 6 × 10(3)-5 × 10(4)kBT. These data agree with the curvature capillary energy for the case of pinned contact lines. The underlying physics of this migration is a coupling of the interface deviatoric curvature with the quadrupolar mode of nanometric disturbances in the interface owing to the particle's contact line undulations. This work is an example of the major implications of nanometric roughness and contact line pinning for colloidal dynamics.
Influence of Coanda surface curvature on performance of bladeless fan
NASA Astrophysics Data System (ADS)
Li, Guoqi; Hu, Yongjun; Jin, Yingzi; Setoguchi, Toshiaki; Kim, Heuy Dong
2014-10-01
The unique Coanda surface has a great influence on the performance of bladeless fan. However, there is few studies to explain the relationship between the performance and Coanda surface curvature at present. In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan, numerical studies are performed in this paper. Firstly, three-dimensional numerical simulation is done by Fluent software. For the purpose to obtain detailed information of the flow field around the Coanda surface, two-dimensional numerical simulation is also conducted. Five types of Coanda surfaces with different curvature are designed, and the flow behaviour and the performance of them are analyzed and compared with those of the prototype. The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance, It is found that there is an optimal curvature of Coanda surfaces among the studied models. Simulation result shows that there is a special low pressure region. With increasing curvature in Y direction, several low pressure regions gradually enlarged, then begin to merge slowly, and finally form a large area of low pressure. From the analyses of streamlines and velocity angle, it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall. Thus, it leads to that the curvature of the streamlines is consistent with that of Coanda surface. Meanwhile, it also causes the fluid movement towards the most suitable direction. This study will provide useful information to performance improvements of bladeless fans.
Spatial curvature endgame: Reaching the limit of curvature determination
NASA Astrophysics Data System (ADS)
Leonard, C. Danielle; Bull, Philip; Allison, Rupert
2016-07-01
Current constraints on spatial curvature show that it is dynamically negligible: |ΩK|≲5 ×10-3 (95% C.L.). Neglecting it as a cosmological parameter would be premature however, as more stringent constraints on ΩK at around the 10-4 level would offer valuable tests of eternal inflation models and probe novel large-scale structure phenomena. This precision also represents the "curvature floor," beyond which constraints cannot be meaningfully improved due to the cosmic variance of horizon-scale perturbations. In this paper, we discuss what future experiments will need to do in order to measure spatial curvature to this maximum accuracy. Our conservative forecasts show that the curvature floor is unreachable—by an order of magnitude—even with Stage IV experiments, unless strong assumptions are made about dark energy evolution and the Λ CDM parameter values. We also discuss some of the novel problems that arise when attempting to constrain a global cosmological parameter like ΩK with such high precision. Measuring curvature down to this level would be an important validation of systematics characterization in high-precision cosmological analyses.
Raft Formation in Lipid Bilayers Coupled to Curvature
Sadeghi, Sina; Müller, Marcus; Vink, Richard L.C.
2014-01-01
We present computer simulations of a membrane in which the local composition is coupled to the local membrane curvature. At high temperatures (i.e., above the temperature of macroscopic phase separation), finite-sized transient domains are observed, reminiscent of lipid rafts. The domain size is in the range of hundred nanometers, and set by the membrane elastic properties. These findings are in line with the notion of the membrane as a curvature-induced microemulsion. At low temperature, the membrane phase separates. The transition to the phase-separated regime is continuous and belongs to the two-dimensional Ising universality class when the coupling to curvature is weak, but becomes first-order for strong curvature-composition coupling. PMID:25296311
Raft formation in lipid bilayers coupled to curvature.
Sadeghi, Sina; Müller, Marcus; Vink, Richard L C
2014-10-01
We present computer simulations of a membrane in which the local composition is coupled to the local membrane curvature. At high temperatures (i.e., above the temperature of macroscopic phase separation), finite-sized transient domains are observed, reminiscent of lipid rafts. The domain size is in the range of hundred nanometers, and set by the membrane elastic properties. These findings are in line with the notion of the membrane as a curvature-induced microemulsion. At low temperature, the membrane phase separates. The transition to the phase-separated regime is continuous and belongs to the two-dimensional Ising universality class when the coupling to curvature is weak, but becomes first-order for strong curvature-composition coupling.
Nanoscale Membrane Curvature detected by Polarized Localization Microscopy
NASA Astrophysics Data System (ADS)
Kelly, Christopher; Maarouf, Abir; Woodward, Xinxin
Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology.
On the Weyl curvature hypothesis
Stoica, Ovidiu Cristinel
2013-11-15
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity. In previous papers it has been proposed an equivalent form of Einstein’s equation, which extends it and remains valid at an important class of singularities (including in particular the Schwarzschild, FLRW, and isotropic singularities). Here it is shown that if the Big-Bang singularity is from this class, it also satisfies the Weyl curvature hypothesis. As an application, we study a very general example of cosmological models, which generalizes the FLRW model by dropping the isotropy and homogeneity constraints. This model also generalizes isotropic singularities, and a class of singularities occurring in Bianchi cosmologies. We show that the Big-Bang singularity of this model is of the type under consideration, and satisfies therefore the Weyl curvature hypothesis. -- Highlights: •The singularities we introduce are described by finite geometric/physical objects. •Our singularities have smooth Riemann and Weyl curvatures. •We show they satisfy Penrose’s Weyl curvature hypothesis (Weyl=0 at singularities). •Examples: FLRW, isotropic singularities, an extension of Schwarzschild’s metric. •Example: a large class of singularities which may be anisotropic and inhomogeneous.
Spatial curvature falsifies eternal inflation
Kleban, Matthew; Schillo, Marjorie E-mail: mls604@nyu.edu
2012-06-01
Inflation creates large-scale cosmological density perturbations that are characterized by an isotropic, homogeneous, and Gaussian random distribution about a locally flat background. Even in a flat universe, the spatial curvature measured within one Hubble volume receives contributions from long wavelength perturbations, and will not in general be zero. These same perturbations determine the Cosmic Microwave Background (CMB) temperature fluctuations, which are O(10{sup −5}). Consequently, the low-l multipole moments in the CMB temperature map predict the value of the measured spatial curvature Ω{sub k}. On this basis we argue that a measurement of |Ω{sub k}| > 10{sup −4} would rule out slow-roll eternal inflation in our past with high confidence, while a measurement of Ω{sub k} < −10{sup −4} (which is positive curvature, a locally closed universe) rules out false-vacuum eternal inflation as well, at the same confidence level. In other words, negative curvature (a locally open universe) is consistent with false-vacuum eternal inflation but not with slow-roll eternal inflation, and positive curvature falsifies both. Near-future experiments will dramatically extend the sensitivity of Ω{sub k} measurements and constitute a sharp test of these predictions.
Cosmic strings with curvature corrections
NASA Astrophysics Data System (ADS)
Boisseau, Bruno; Letelier, Patricio S.
1992-08-01
A generic model of string described by a Lagrangian density that depends on the extrinsic curvature of the string worldsheet is studied. Using a system of coordinates adapted to the string world sheet the equation of motion and the energy-momentum tensor are derived for strings evolving in curved spacetime. We find that the curvature corrections may change the relation between the string energy density and the tension. It can also introduce heat propagation along the string. We also find for the Polyakov as well as Nambu strings with a topological term that the open string end points can travel with a speed less than the velocity of light.
Control of microelectromechanical systems membrane curvature by silicon ion implantation
NASA Astrophysics Data System (ADS)
Jin, S.; Mavoori, H.; Kim, J.; Aksyuk, V. A.
2003-09-01
Thin silicon membranes in microelectromechanical systems (MEMS) optical devices such as beam-steering, movable mirrors may exhibit undesirable curvature when their surface is metallized with light-reflecting metals to enhance optical performance. We have applied Si+ ion implantations at dose levels of 0.4-5×1016/cm2 into the gold metallization layer to successfully reduce the mirror curvature as well as the degree of its temperature-dependent changes. The curvature change as well as the temperature dependence is found to be dependent on the implantation dose. The mechanism of the observed curvature flattening effect is attributed mostly to the induced compressive stress in gold metallization caused by the insertion of foreign implanted atoms of silicon. Such a Si implantation approach can be useful as a means for post-fabrication correction of unwanted curvature in MEMS membranes, as well as a technique to intentionally introduce a desired degree of curvature if needed. A convenient blanket implantation process can be utilized with minimal contamination problems as Si is a common element already present in the MEMS.
Thermodynamic Curvature and Black Holes
NASA Astrophysics Data System (ADS)
Ruppeiner, George
In my talk, I will discuss black hole thermodynamics, particularly what happens when you add thermodynamic curvature to the mix. Although black hole thermodynamics is a little off the main theme of this workshop, I hope nevertheless that my message will be of some interest to researchers in supersymmetry and supergravity.
Meloni, Bruno P; Craig, Amanda J; Milech, Nadia; Hopkins, Richard M; Watt, Paul M; Knuckey, Neville W
2014-03-01
Cell-penetrating peptides (CPPs) are small peptides (typically 5-25 amino acids), which are used to facilitate the delivery of normally non-permeable cargos such as other peptides, proteins, nucleic acids, or drugs into cells. However, several recent studies have demonstrated that the TAT CPP has neuroprotective properties. Therefore, in this study, we assessed the TAT and three other CPPs (penetratin, Arg-9, Pep-1) for their neuroprotective properties in cortical neuronal cultures following exposure to glutamic acid, kainic acid, or in vitro ischemia (oxygen-glucose deprivation). Arg-9, penetratin, and TAT-D displayed consistent and high level neuroprotective activity in both the glutamic acid (IC50: 0.78, 3.4, 13.9 μM) and kainic acid (IC50: 0.81, 2.0, 6.2 μM) injury models, while Pep-1 was ineffective. The TAT-D isoform displayed similar efficacy to the TAT-L isoform in the glutamic acid model. Interestingly, Arg-9 was the only CPP that displayed efficacy when washed-out prior to glutamic acid exposure. Neuroprotection following in vitro ischemia was more variable with all peptides providing some level of neuroprotection (IC50; Arg-9: 6.0 μM, TAT-D: 7.1 μM, penetratin/Pep-1: >10 μM). The positive control peptides JNKI-1D-TAT (JNK inhibitory peptide) and/or PYC36L-TAT (AP-1 inhibitory peptide) were neuroprotective in all models. Finally, in a post-glutamic acid treatment experiment, Arg-9 was highly effective when added immediately after, and mildly effective when added 15 min post-insult, while the JNKI-1D-TAT control peptide was ineffective when added post-insult. These findings demonstrate that different CPPs have the ability to inhibit neurodamaging events/pathways associated with excitotoxic and ischemic injuries. More importantly, they highlight the need to interpret neuroprotection studies when using CPPs as delivery agents with caution. On a positive note, the cytoprotective properties of CPPs suggests they are ideal carrier molecules to
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.
Space Curvature and the "Heavy Banana 'Paradox.'"
ERIC Educational Resources Information Center
Gruber, Ronald P.; And Others
1991-01-01
Two ways to visually enhance the concept of space curvature are described. Viewing space curvature as a meterstick contraction and the heavy banana "paradox" are discussed. The meterstick contraction is mathematically explained. (KR)
Barenboim, Gabriela; Martínez, Enrique Fernández; Mena, Olga; Verde, Licia E-mail: enfmarti@mppmu.mpg.de E-mail: liciaverde@icc.ub.edu
2010-03-01
Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d{sub A}(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Ω{sub k} in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d{sub A}(z) up to sufficiently high redshifts z ∼ 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z)−Ω{sub k} degeneracy.
Classification and quantification of leaf curvature
Liu, Zhongyuan; Jia, Liguo; Mao, Yanfei; He, Yuke
2010-01-01
Various mutants of Arabidopsis thaliana deficient in polarity, cell division, and auxin response are characterized by certain types of leaf curvature. However, comparison of curvature for clarification of gene function can be difficult without a quantitative measurement of curvature. Here, a novel method for classification and quantification of leaf curvature is reported. Twenty-two mutant alleles from Arabidopsis mutants and transgenic lines deficient in leaf flatness were selected. The mutants were classified according to the direction, axis, position, and extent of leaf curvature. Based on a global measure of whole leaves and a local measure of four regions in the leaves, the curvature index (CI) was proposed to quantify the leaf curvature. The CI values accounted for the direction, axis, position, and extent of leaf curvature in all of the Arabidopsis mutants grown in growth chambers. Comparison of CI values between mutants reveals the spatial and temporal variations of leaf curvature, indicating the strength of the mutant alleles and the activities of the corresponding genes. Using the curvature indices, the extent of curvature in a complicated genetic background becomes quantitative and comparable, thus providing a useful tool for defining the genetic components of leaf development and to breed new varieties with leaf curvature desirable for the efficient capture of sunlight for photosynthesis and high yields. PMID:20400533
Curvature operator for loop quantum gravity
NASA Astrophysics Data System (ADS)
Alesci, E.; Assanioussi, M.; Lewandowski, J.
2014-06-01
We introduce a new operator in loop quantum gravity—the 3D curvature operator—related to the three-dimensional scalar curvature. The construction is based on Regge calculus. We define this operator starting from the classical expression of the Regge curvature, we derive its properties and discuss some explicit checks of the semiclassical limit.
Probing Persistence in DNA Curvature Properties with Atomic Force Microscopy
NASA Astrophysics Data System (ADS)
Moukhtar, J.; Fontaine, E.; Faivre-Moskalenko, C.; Arneodo, A.
2007-04-01
We elaborate on a mean-field extension of the wormlike chain model that accounts for the presence of long-range correlations (LRC) in the intrinsic curvature disorder of genomic DNA, the stronger the LRC, the smaller the persistence length. The comparison of atomic force microscopy imaging of straight, uncorrelated virus and correlated human DNA fragments with DNA simulations confirms that the observed decrease in persistence length for human DNA more likely results from a sequence-induced large-scale intrinsic curvature than from some increased flexibility.
Disformal invariance of curvature perturbation
NASA Astrophysics Data System (ADS)
Motohashi, Hayato; White, Jonathan
2016-02-01
We show that under a general disformal transformation the linear comoving curvature perturbation is not identically invariant, but is invariant on superhorizon scales for any theory that is disformally related to Horndeski's theory. The difference between disformally related curvature perturbations is found to be given in terms of the comoving density perturbation associated with a single canonical scalar field. In General Relativity it is well-known that this quantity vanishes on superhorizon scales through the Poisson equation that is obtained on combining the Hamiltonian and momentum constraints, and we confirm that a similar result holds for any theory that is disformally related to Horndeski's scalar-tensor theory so long as the invertibility condition for the disformal transformation is satisfied. We also consider the curvature perturbation at full nonlinear order in the unitary gauge, and find that it is invariant under a general disformal transformation if we assume that an attractor regime has been reached. Finally, we also discuss the counting of degrees of freedom in theories disformally related to Horndeski's.
On the collective curvature radiation
NASA Astrophysics Data System (ADS)
Istomin, Ya. N.; Philippov, A. A.; Beskin, V. S.
2012-05-01
In this paper, we study one possible mechanism of pulsar radio emission (i.e. with the collective curvature radiation of the relativistic particle stream moving along the curved magnetospheric magnetic field lines). We show that an electromagnetic wave that contains one cylindrical harmonic exp {isφ} cannot be radiated by the curvature radiation mechanism, which corresponds to the radiation of a charged particle moving along curved magnetic field lines. The point is that a particle in a vacuum radiates the triplex of harmonics (s, s± 1) in which the polarization of the emitted wave changes from one point to another on a circle of constant radius, while for one s-harmonic the polarization remains constant. So, for the collective curvature radiation, the wave polarization is very important and cannot be fixed a priori. For this reason, the polarization of real unstable waves must be determined directly from the solution of wave equations for the media. Its electromagnetic properties should be described by the dielectric permittivity tensor ?, which contains information on the reaction on all possible types of radiation.
Thermodynamic curvature and ensemble nonequivalence
NASA Astrophysics Data System (ADS)
Bravetti, Alessandro; Nettel, Francisco
2014-08-01
In this work we consider thermodynamic geometries defined as Hessians of different potentials and derive some useful formulas that show their complementary role in the description of thermodynamic systems with 2 degrees of freedom that show ensemble nonequivalence. From the expressions derived for the metrics, we can obtain the curvature scalars in a very simple and compact form. We explain here the reason why each curvature scalar diverges over the line of divergence of one of the specific heats. This application is of special interest in the study of changes of stability in black holes as defined by Davies. From these results we are able to prove on a general footing a conjecture first formulated by Liu, Lü, Luo, and Shao stating that different Hessian metrics can correspond to different behaviors in the various ensembles. We study the case of two thermodynamic dimensions. Moreover, comparing our result with the more standard turning point method developed by Poincaré, we obtain that the divergence of the scalar curvature of the Hessian metric of one potential exactly matches the change of stability in the corresponding ensemble.
Intracellular magnetophoresis of amyloplasts and induction of root curvature
NASA Technical Reports Server (NTRS)
Kuznetsov, O. A.; Hasenstein, K. H.
1996-01-01
High-gradient magnetic fields (HGMFs) were used to induce intracellular magnetophoresis of amyloplasts. The HGMFs were generated by placing a small ferromagnetic wedge into a uniform magnetic field or at the gap edge between two permanent magnets. In the vicinity of the tip of the wedge the dynamic factor of the magnetic field, delta(H2/2), was about 10(9) Oe2.cm-1, which subjected the amyloplasts to a force comparable to that of gravity. When roots of 2-d-old seedlings of flax (Linum usitatissimum L.) were positioned vertically and exposed to an HGMF, curvature away from the wedge was transient and lasted approximately 1 h. Average curvature obtained after placing magnets, wedge and seedlings on a 1-rpm clinostat for 2 h was 33 +/- 5 degrees. Roots of horizontally placed control seedlings without rotation curved about 47 +/- 4 degrees. The time course of curvature and changes in growth rate were similar for gravicurvature and for root curvature induced by HGMFs. Microscopy showed displacement of amyloplasts in vitro and in vivo. Studies with Arabidopsis thaliana (L.) Heynh. showed that the wild type responded to HGMFs but the starchless mutant TC7 did not. The data indicate that a magnetic force can be used to study the gravisensing and response system of roots.
Curvature–undulation coupling as a basis for curvature sensing and generation in bilayer membranes
Bradley, Ryan P.; Radhakrishnan, Ravi
2016-01-01
We present coarse-grained molecular dynamics simulations of the epsin N-terminal homology domain interacting with a lipid bilayer and demonstrate a rigorous theoretical formalism and analysis method for computing the induced curvature field in varying concentrations of the protein in the dilute limit. Our theory is based on the description of the height–height undulation spectrum in the presence of a curvature field. We formulated an objective function to compare the acquired undulation spectrum from the simulations to that of the theory. We recover the curvature field parameters by minimizing the objective function even in the limit where the protein-induced membrane curvature is of the same order as the amplitude due to thermal undulations. The coupling between curvature and undulations leads to significant predictions: (i) Under dilute conditions, the proteins can sense a site of spontaneous curvature at distances much larger than their size; (ii) as the density of proteins increases the coupling focuses and stabilizes the curvature field to the site of the proteins; and (iii) the mapping of the protein localization and the induction of a stable curvature is a cooperative process that can be described through a Hill function. PMID:27531962
Mirror with thermally controlled radius of curvature
Neil, George R.; Shinn, Michelle D.
2010-06-22
A radius of curvature controlled mirror for controlling precisely the focal point of a laser beam or other light beam. The radius of curvature controlled mirror provides nearly spherical distortion of the mirror in response to differential expansion between the front and rear surfaces of the mirror. The radius of curvature controlled mirror compensates for changes in other optical components due to heating or other physical changes. The radius of curvature controlled mirror includes an arrangement for adjusting the temperature of the front surface and separately adjusting the temperature of the rear surface to control the radius of curvature. The temperature adjustment arrangements can include cooling channels within the mirror body or convection of a gas upon the surface of the mirror. A control system controls the differential expansion between the front and rear surfaces to achieve the desired radius of curvature.
Canards and curvature: nonsmooth approximation by pinching
NASA Astrophysics Data System (ADS)
Desroches, M.; Jeffrey, M. R.
2011-05-01
In multiple time-scale (singularly perturbed) dynamical systems, canards are counterintuitive solutions that evolve along both attracting and repelling invariant manifolds. In two dimensions, canards result in periodic oscillations whose amplitude and period grow in a highly nonlinear way: they are slowly varying with respect to a control parameter, except for an exponentially small range of values where they grow extremely rapidly. This sudden growth, called a canard explosion, has been encountered in many applications ranging from chemistry to neuronal dynamics, aerospace engineering and ecology. Canards were initially studied using nonstandard analysis, and later the same results were proved by standard techniques such as matched asymptotics, invariant manifold theory and parameter blow-up. More recently, canard-like behaviour has been linked to surfaces of discontinuity in piecewise-smooth dynamical systems. This paper provides a new perspective on the canard phenomenon by showing that the nonstandard analysis of canard explosions can be recast into the framework of piecewise-smooth dynamical systems. An exponential coordinate scaling is applied to a singularly perturbed system of ordinary differential equations. The scaling acts as a lens that resolves dynamics across all time-scales. The changes of local curvature that are responsible for canard explosions are then analysed. Regions where different time-scales dominate are separated by hypersurfaces, and these are pinched together to obtain a piecewise-smooth system, in which curvature changes manifest as discontinuity-induced bifurcations. The method is used to classify canards in arbitrary dimensions, and to derive the parameter values over which canards form either small cycles (canards without head) or large cycles (canards with head).
Radius of curvature controlled mirror
Neil, George R.; Rathke, John Wickham; Schultheiss, Thomas John; Shinn, Michelle D.; Dillon-Townes, Lawrence A.
2006-01-17
A controlled radius of curvature mirror assembly comprising: a distortable mirror having a reflective surface and a rear surface; and in descending order from the rear surface; a counter-distortion plate; a flow diverter having a flow diverter aperture at the center thereof; a flow return plate having a flow return aperture at the center thereof; a thermal isolation plate having a thermal isolation plate aperture at the center thereof and a flexible heater having a rear surface and a flexible heater aperture at the center thereof; a double walled tube defining a coolant feed chamber and a coolant return chamber; said coolant feed chamber extending to and through the flow diverter aperture and terminating at the counter-distortion plate and the coolant return chamber extending to and through the thermal isolation backplate and terminating at the flow diverter; and a coolant feed and a coolant return exit at the rear of said flexible heater.
Classification of Hamilton-Jacobi separation in orthogonal coordinates with diagonal curvature
Rajaratnam, Krishan McLenaghan, Raymond G.
2014-08-15
We find all orthogonal metrics where the geodesic Hamilton-Jacobi equation separates and the Riemann curvature tensor satisfies a certain equation (called the diagonal curvature condition). All orthogonal metrics of constant curvature satisfy the diagonal curvature condition. The metrics we find either correspond to a Benenti system or are warped product metrics where the induced metric on the base manifold corresponds to a Benenti system. Furthermore, we show that most metrics we find are characterized by concircular tensors; these metrics, called Kalnins-Eisenhart-Miller metrics, have an intrinsic characterization which can be used to obtain them on a given space. In conjunction with other results, we show that the metrics we found constitute all separable metrics for Riemannian spaces of constant curvature and de Sitter space.
Robust contour decomposition using a constant curvature criterion
NASA Technical Reports Server (NTRS)
Wuescher, Daniel M.; Boyer, Kim L.
1991-01-01
The problem of decomposing an extended boundary or contour into simple primitives is addressed with particular emphasis on Laplacian-of-Gaussian (LoG) zero-crossing contours. A technique is introduced for partitioning such contours into constant curvature segments. A nonlinear `blip' filter matched to the impairment signature of the curvature computation process, an overlapped voting scheme, and a sequential contiguous segment extraction mechanism are used. This technique is insensitive to reasonable changes in algorithm parameters and robust to noise and minor viewpoint-induced distortions in the contour shape, such as those encountered between stereo image pairs. The results vary smoothly with the data, and local perturbations induce only local changes in the result. Robustness and insensitivity are experimentally verified.
Determining wave direction using curvature parameters.
de Queiroz, Eduardo Vitarelli; de Carvalho, João Luiz Baptista
2016-01-01
The curvature of the sea wave was tested as a parameter for estimating wave direction in the search for better results in estimates of wave direction in shallow waters, where waves of different sizes, frequencies and directions intersect and it is difficult to characterize. We used numerical simulations of the sea surface to determine wave direction calculated from the curvature of the waves. Using 1000 numerical simulations, the statistical variability of the wave direction was determined. The results showed good performance by the curvature parameter for estimating wave direction. Accuracy in the estimates was improved by including wave slope parameters in addition to curvature. The results indicate that the curvature is a promising technique to estimate wave directions.•In this study, the accuracy and precision of curvature parameters to measure wave direction are analyzed using a model simulation that generates 1000 wave records with directional resolution.•The model allows the simultaneous simulation of time-series wave properties such as sea surface elevation, slope and curvature and they were used to analyze the variability of estimated directions.•The simultaneous acquisition of slope and curvature parameters can contribute to estimates wave direction, thus increasing accuracy and precision of results. PMID:27408830
Bcl-2 apoptosis proteins, mitochondrial membrane curvature, and cancer
NASA Astrophysics Data System (ADS)
Hwee Lai, Ghee; Schmidt, Nathan; Sanders, Lori; Mishra, Abhijit; Wong, Gerard; Ivashyna, Olena; Christenson, Eric; Schlesinger, Paul; Akabori, Kiyotaka; Santangelo, Christian
2012-02-01
Critical interactions between Bcl-2 family proteins permeabilize the outer mitochondrial membrane, a common decision point early in the intrinsic apoptotic pathway that irreversibly commits the cell to death. However, a unified picture integrating the essential non-passive role of lipid membranes with the contested dynamics of Bcl-2 regulation remains unresolved. Correlating results between synchrotron x-ray diffraction and microscopy in cell-free assays, we report activation of pro-apoptotic Bax induces strong pure negative Gaussian membrane curvature topologically necessary for pore formation and membrane remodeling events. Strikingly, Bcl-xL suppresses not only Bax-induced pore formation, but also membrane remodeling by disparate systems including cell penetrating, antimicrobial or viral fusion peptides, and bacterial toxin, none of which have BH3 allosteric domains to mediate direct binding. We propose a parallel mode of Bcl-2 pore regulation in which Bax and Bcl-xL induce antagonistic and mutually interacting Gaussian membrane curvatures. The universal nature of curvature-mediated interactions allows synergy with direct binding mechanisms, and potentially accounts for the Bcl-2 family modulation of mitochondrial fission/fusion dynamics.
NASA Technical Reports Server (NTRS)
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.
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.
Magnetophoretic Induction of Root Curvature
NASA Technical Reports Server (NTRS)
Hasenstein, Karl H.
1997-01-01
The last year of the grant period concerned the consolidation of previous experiments to ascertain that the theoretical premise apply not just to root but also to shoots. In addition, we verified that high gradient magnetic fields do not interfere with regular cellular activities. Previous results have established that: (1) intracellular magnetophoresis is possible; and (2) HGMF lead to root curvature. In order to investigate whether HGMF affect the assembly and/or organization of structural proteins, we examined the arrangement of microtubules in roots exposed to HGMF. The cytoskeletal investigations were performed with fomaldehyde-fixed, nonembedded tissue segments that were cut with a vibratome. Microtubules (MTs) were stained with rat anti-yeast tubulin (YOL 1/34) and DTAF-labeled antibody against rat IgG. Microfilaments (MFs) were visualized by incubation in rhodamine-labeled phalloidin. The distribution and arrangement of both components of the cytoskeleton were examined with a confocal microscope. Measurements of growth rates and graviresponse were done using a video-digitizer. Since HGMF repel diamagnetic substances including starch-filled amyloplasts and most The second aspect of the work includes studies of the effect of cytoskeletal inhibitors on MTs and MFs. The analysis of the effect of micotubular inhibitors on the auxin transport in roots showed that there is very little effect of MT-depolymerizing or stabilizing drugs on auxin transport. This is in line with observations that application of such drugs is not immediately affecting the graviresponsiveness of roots.
Curvature and torsion in growing actin networks
NASA Astrophysics Data System (ADS)
Shaevitz, Joshua W.; Fletcher, Daniel A.
2008-06-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque.
Soliton curvatures of surfaces and spaces
Konopelchenko, B.G.
1997-01-01
An intrinsic geometry of surfaces and three-dimensional Riemann spaces is discussed. In the geodesic coordinates the Gauss equation for two-dimensional Riemann spaces (surfaces) is reduced to the one-dimensional Schr{umlt o}dinger equation, where the Gaussian curvature plays a role of potential. The use of this fact provides an infinite set of explicit expressions for curvature and metric of surface. A special case is governed by the KdV equation for the Gaussian curvature. Integrable dynamics of curvature via the KdV equation, higher KdV equations, and 2+1-dimensional integrable equations with breaking solitons is considered. For a special class of three-dimensional Riemann spaces the relation between metric and scalar curvature is given by the two-dimensional stationary Schr{umlt o}dinger or perturbed string equations. This provides us an infinite family of Riemann spaces with explicit scalar curvature and metric. Particular class of spaces and their integrable evolutions are described by the Nizhnik{endash}Veselov{endash}Novikov equation and its higher analogs. Surfaces and three-dimensional Riemann spaces with large curvature and slow dependence on the variable are considered. They are associated with the Burgers and Kadomtsev{endash}Petviashvili equations, respectively. {copyright} {ital 1997 American Institute of Physics.}
Distributed curvature and stability of fullerenes.
Fowler, Patrick W; Nikolić, Sonja; De Los Reyes, Rasthy; Myrvold, Wendy
2015-09-21
Energies of non-planar conjugated π systems are typically described qualitatively in terms of the balance of π stabilisation and the steric strain associated with geometric curvature. Curvature also has a purely graph-theoretical description: combinatorial curvature at a vertex of a polyhedral graph is defined as one minus half the vertex degree plus the sum of reciprocal sizes of the faces meeting at that vertex. Prisms and antiprisms have positive combinatorial vertex curvature at every vertex. Excluding these two infinite families, we call any other polyhedron with everywhere positive combinatorial curvature a PCC polyhedron. Cubic PCC polyhedra are initially common, but must eventually die out with increasing vertex count; the largest example constructed so far has 132 vertices. The fullerenes Cn have cubic polyhedral molecular graphs with n vertices, 12 pentagonal and (n/2 - 10) hexagonal faces. We show that there are exactly 39 PCC fullerenes, all in the range 20 ≤n≤ 60. In this range, there is only partial correlation between PCC status and stability as defined by minimum pentagon adjacency. The sum of vertex curvatures is 2 for any polyhedron; for fullerenes the sum of squared vertex curvatures is linearly related to the number of pentagon adjacencies and hence is a direct measure of relative stability of the lower (n≤ 60) fullerenes. For n≥ 62, non-PCC fullerenes with a minimum number of pentagon adjacencies minimise mean-square curvature. For n≥ 70, minimum mean-square curvature implies isolation of pentagons, which is the strongest indicator of stability for a bare fullerene. PMID:26283188
Magnetic curvature effects on plasma interchange turbulence
NASA Astrophysics Data System (ADS)
Li, B.; Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-01
The magnetic curvature effects on plasma interchange turbulence and transport in the Z-pinch and dipole-like systems are explored with two-fluid global simulations. By comparing the transport levels in the systems with a different magnetic curvature, we show that the interchange-mode driven transport strongly depends on the magnetic geometry. For the system with large magnetic curvature, the pressure and density profiles are strongly peaked in a marginally stable state and the nonlinear evolution of interchange modes produces the global convective cells in the azimuthal direction, which lead to the low level of turbulent convective transport.
Defect Motifs for Constant Mean Curvature Surfaces
NASA Astrophysics Data System (ADS)
Kusumaatmaja, Halim; Wales, David J.
2013-04-01
The energy landscapes of electrostatically charged particles embedded on constant mean curvature surfaces are analyzed for a wide range of system size, curvature, and interaction potentials. The surfaces are taken to be rigid, and the basin-hopping method is used to locate the putative global minimum structures. The defect motifs favored by potential energy agree with experimental observations for colloidal systems: extended defects (scars and pleats) for weakly positive and negative Gaussian curvatures, and isolated defects for strongly negative Gaussian curvatures. Near the phase boundary between these regimes, the two motifs are in strong competition, as evidenced from the appearance of distinct funnels in the potential energy landscape. We also report a novel defect motif consisting of pentagon pairs.
First Investigation on the Magnetic Curvature Distribution in the Magnetic Diffusion Region
NASA Astrophysics Data System (ADS)
Zhang, Y.; Shen, C.; Liu, Z.; Marchaudon, A.; Rong, Z.
2015-12-01
We report first results of magnetic curvature distribution in the diffusion region of a unique magnetic reconnection event. This event is exceptional since all four Cluster spacecraft are crossing the diffusion region. Magnetic curvature analysis shows that magnetic field lines are sharply curved with high curvature in the inner outflow regions between the two Hall regions and display nearly coplanar features of antiparallel reconnection. Combination of the decrease in curvature radius of magnetic field lines and the increase in electron gyro-radius induces curvature pitch angle scattering of initially trapped electrons, resulting in an isotropic electron distribution. In Hall regions, magnetic curvature decreases corresponding obviously to the presence of Y-directed Hall fields, which implies that the stress of reconnected field is released here, in agreement with whistler mediated-reconnection. The value and direction of curvature radius are not well organized due to the fluctuating Hall fields resulting from the temporal dynamical reconnection.Same analysis will be applied to MMS data to investigate the fine magnetic structure in diffusion region.
Curvature tensors unified field equations on SEXn
NASA Astrophysics Data System (ADS)
Chung, Kyung Tae; Lee, Il Young
1988-09-01
We study the curvature tensors and field equations in the n-dimensional SE manifold SEXn. We obtain several basic properties of the vectors S λ and U λ and then of the SE curvature tensor and its contractions, such as a generalized Ricci identity, a generalized Bianchi identity, and two variations of the Bianchi identity satisfied by the SE Einstein tensor. Finally, a system of field equations is discussed in SEXn and one of its particular solutions is constructed and displayed.
The role of curvature in entanglement
NASA Astrophysics Data System (ADS)
Buck, Gregory
2015-10-01
Which tangles more readily: curly hair or straight hair? A perhaps natural thought, supported by some theoretical evidence, is to associate curvature and entanglement, and assume that they would grow together-that an increase in one fosters an increase in the other. However we have biological examples such as DNA in the chromosome, and mechanical examples such as coiled telephone cords, in which much more curvature is employed than is required for the packing, and in which tangling is presumably detrimental. We offer a resolution to this conundrum. We show, that at least for simple but generally applicable models, the relationship between curvature and entanglement is subtle: if we keep filament density constant and increase curvature, the entanglement initially increases, passes through a maximum, then decreases, so there is a regime where increasing curvature increases entanglement, and there is also a regime where increasing curvature decreases entanglement. This has implications for filament packing in many circumstances, and in particular for the compaction structure of DNA in the cell-it provides a straightforward argument for the view that one purpose of DNA coiling and supercoiling is to inhibit entanglement. It also tells us to expect that wavy hair-neither the straightest nor the curliest-tangles most readily.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-08-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
Nonadditive Compositional Curvature Energetics of Lipid Bilayers
NASA Astrophysics Data System (ADS)
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.
Wu, Hao; Wang, Ruoxu; Liu, Deming; Fu, Songnian; Zhao, Can; Wei, Huifeng; Tong, Weijun; Shum, Perry Ping; Tang, Ming
2016-04-01
We proposed and demonstrated a few-mode fiber (FMF) based optical-fiber sensor for distributed curvature measurement through quasi-single-mode Brillouin frequency shift (BFS). By central-alignment splicing FMF and single-mode fiber (SMF) with a fusion taper, a SMF-components-compatible distributed curvature sensor based on FMF is realized using the conventional Brillouin optical time-domain analysis system. The distributed BFS change induced by bending in FMF has been theoretically and experimentally investigated. The precise BFS response to the curvature along the fiber link has been calibrated. A proof-of-concept experiment is implemented to validate its effectiveness in distributed curvature measurement. PMID:27192275
No large scale curvature perturbations during the waterfall phase transition of hybrid inflation
Abolhasani, Ali Akbar; Firouzjahi, Hassan
2011-03-15
In this paper the possibility of generating large scale curvature perturbations induced from the entropic perturbations during the waterfall phase transition of the standard hybrid inflation model is studied. We show that whether or not appreciable amounts of large scale curvature perturbations are produced during the waterfall phase transition depends crucially on the competition between the classical and the quantum mechanical backreactions to terminate inflation. If one considers only the classical evolution of the system, we show that the highly blue-tilted entropy perturbations induce highly blue-tilted large scale curvature perturbations during the waterfall phase transition which dominate over the original adiabatic curvature perturbations. However, we show that the quantum backreactions of the waterfall field inhomogeneities produced during the phase transition dominate completely over the classical backreactions. The cumulative quantum backreactions of very small scale tachyonic modes terminate inflation very efficiently and shut off the curvature perturbation evolution during the waterfall phase transition. This indicates that the standard hybrid inflation model is safe under large scale curvature perturbations during the waterfall phase transition.
Strong curvature effects in Neumann wave problems
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-15
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schroedinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
A new algorithm for evaluating 3D curvature and curvature gradient for improved fracture detection
NASA Astrophysics Data System (ADS)
Di, Haibin; Gao, Dengliang
2014-09-01
In 3D seismic interpretation, both curvature and curvature gradient are useful seismic attributes for structure characterization and fault detection in the subsurface. However, the existing algorithms are computationally intensive and limited by the lateral resolution for steeply-dipping formations. This study presents new and robust volume-based algorithms that evaluate both curvature and curvature gradient attributes more accurately and effectively. The algorithms first instantaneously fit a local surface to seismic data and then compute attributes using the spatial derivatives of the built surface. Specifically, the curvature algorithm constructs a quadratic surface by using a rectangle 9-node grid cell, whereas the curvature gradient algorithm builds a cubic surface by using a diamond 13-node grid cell. A dip-steering approach based on 3D complex seismic trace analysis is implemented to enhance the accuracy of surface construction and to reduce computational time. Applications to two 3D seismic surveys demonstrate the accuracy and efficiency of the new curvature and curvature gradient algorithms for characterizing faults and fractures in fractured reservoirs.
Curvature constraints from large scale structure
NASA Astrophysics Data System (ADS)
Di Dio, Enea; Montanari, Francesco; Raccanelli, Alvise; Durrer, Ruth; Kamionkowski, Marc; Lesgourgues, Julien
2016-06-01
We modified the CLASS code in order to include relativistic galaxy number counts in spatially curved geometries; we present the formalism and study the effect of relativistic corrections on spatial curvature. The new version of the code is now publicly available. Using a Fisher matrix analysis, we investigate how measurements of the spatial curvature parameter ΩK with future galaxy surveys are affected by relativistic effects, which influence observations of the large scale galaxy distribution. These effects include contributions from cosmic magnification, Doppler terms and terms involving the gravitational potential. As an application, we consider angle and redshift dependent power spectra, which are especially well suited for model independent cosmological constraints. We compute our results for a representative deep, wide and spectroscopic survey, and our results show the impact of relativistic corrections on spatial curvature parameter estimation. We show that constraints on the curvature parameter may be strongly biased if, in particular, cosmic magnification is not included in the analysis. Other relativistic effects turn out to be subdominant in the studied configuration. We analyze how the shift in the estimated best-fit value for the curvature and other cosmological parameters depends on the magnification bias parameter, and find that significant biases are to be expected if this term is not properly considered in the analysis.
Curvature constraints from the causal entropic principle
Bozek, Brandon; Albrecht, Andreas; Phillips, Daniel
2009-07-15
Current cosmological observations indicate a preference for a cosmological constant that is drastically smaller than what can be explained by conventional particle physics. The causal entropic principle (Bousso et al.) provides an alternative approach to anthropic attempts to predict our observed value of the cosmological constant by calculating the entropy created within a causal diamond. We have extended this work to use the causal entropic principle to predict the preferred curvature within the 'multiverse'. We have found that values larger than {rho}{sub k}=40{rho}{sub m} are disfavored by more than 99.99% peak value at {rho}{sub {lambda}}=7.9x10{sup -123} and {rho}{sub k}=4.3{rho}{sub m} for open universes. For universes that allow only positive curvature or both positive and negative curvature, we find a correlation between curvature and dark energy that leads to an extended region of preferred values. Our universe is found to be disfavored to an extent depending on the priors on curvature. We also provide a comparison to previous anthropic constraints on open universes and discuss future directions for this work.
Curvature effect on tearing modes in presence of neoclassical friction
NASA Astrophysics Data System (ADS)
Maget, Patrick; Mellet, Nicolas; Lütjens, Hinrich; Meshcheriakov, Dmytro; Garbet, Xavier
2013-11-01
Neoclassical physics (here associated to the poloidal variation of the magnetic field strength along field lines in a tokamak) is well known for driving self-generated plasma current and nonlinear magnetic islands associated to it in high performance, ITER relevant plasma discharges. It is demonstrated that the neoclassical friction between a magnetic perturbation and plasma flow already impacts magnetic islands in the linear regime, by inducing a weakening of curvature stabilization for tearing modes. This conclusion holds in particular for regimes where convection is influencing the pressure dynamics, as shown using a simple analytical model and confirmed in full Magneto-Hydro-Dynamics simulations.
Curvature effect on tearing modes in presence of neoclassical friction
Maget, Patrick; Mellet, Nicolas; Meshcheriakov, Dmytro; Garbet, Xavier; Lütjens, Hinrich
2013-11-15
Neoclassical physics (here associated to the poloidal variation of the magnetic field strength along field lines in a tokamak) is well known for driving self-generated plasma current and nonlinear magnetic islands associated to it in high performance, ITER relevant plasma discharges. It is demonstrated that the neoclassical friction between a magnetic perturbation and plasma flow already impacts magnetic islands in the linear regime, by inducing a weakening of curvature stabilization for tearing modes. This conclusion holds in particular for regimes where convection is influencing the pressure dynamics, as shown using a simple analytical model and confirmed in full Magneto-Hydro-Dynamics simulations.
Curvature and geometric modules of noncommutative spheres and tori
Arnlind, Joakim
2014-04-15
When considered as submanifolds of Euclidean space, the Riemannian geometry of the round sphere and the Clifford torus may be formulated in terms of Poisson algebraic expressions involving the embedding coordinates, and a central object is the projection operator, projecting tangent vectors in the ambient space onto the tangent space of the submanifold. In this note, we point out that there exist noncommutative analogues of these projection operators, which implies a very natural definition of noncommutative tangent spaces as particular projective modules. These modules carry an induced connection from Euclidean space, and we compute its scalar curvature.
Anomalous Coupling Between Topological Defects and Curvature
NASA Astrophysics Data System (ADS)
Vitelli, Vincenzo; Turner, Ari M.
2004-11-01
We investigate a counterintuitive geometric interaction between defects and curvature in thin layers of superfluids, superconductors, and liquid crystals deposited on curved surfaces. Each defect feels a geometric potential whose functional form is determined only by the shape of the surface, but whose sign and strength depend on the transformation properties of the order parameter. For superfluids and superconductors, the strength of this interaction is proportional to the square of the charge and causes all defects to be repelled (attracted) by regions of positive (negative) Gaussian curvature. For liquid crystals in the one elastic constant approximation, charges between 0 and 4π are attracted by regions of positive curvature while all other charges are repelled.
Cosmic curvature from de Sitter equilibrium cosmology.
Albrecht, Andreas
2011-10-01
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.
Detonation wave curvature of PBXN-111
NASA Astrophysics Data System (ADS)
Forbes, J. W.; Lemar, E. R.; Baker, R. N.
1994-07-01
Spherical curvatures of detonation waves were measured by streak photography over the center 50 percent of PBXN-111 charges. These curvatures range from 54 to 143 mm for charge diameters of 41 to 68 mm and are not spherical near the edges of the charges. The wave fronts appear linear over about the last 3 mm at the charges edges. The angle between the detonation wave front and the edge of the charge was about 62 degrees over this last 3 mm for all the charges. Detonation velocity and wave front curvature data of PBXN-111 were used to calculate CJ zone lengths of 2-4 mm using the Wood-Kirkwood theory.
Total positive curvature of circular DNA.
Bohr, Jakob; Olsen, Kasper W
2013-11-01
The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature are presented.
Total positive curvature of circular DNA
NASA Astrophysics Data System (ADS)
Bohr, Jakob; Olsen, Kasper W.
2013-11-01
The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature are presented.
Extrinsic and intrinsic curvatures in thermodynamic geometry
NASA Astrophysics Data System (ADS)
Hosseini Mansoori, Seyed Ali; Mirza, Behrouz; Sharifian, Elham
2016-08-01
We investigate the intrinsic and extrinsic curvatures of a certain hypersurface in thermodynamic geometry of a physical system and show that they contain useful thermodynamic information. For an anti-Reissner-Nordström-(A)de Sitter black hole (Phantom), the extrinsic curvature of a constant Q hypersurface has the same sign as the heat capacity around the phase transition points. The intrinsic curvature of the hypersurface can also be divergent at the critical points but has no information about the sign of the heat capacity. Our study explains the consistent relationship holding between the thermodynamic geometry of the KN-AdS black holes and those of the RN (J-zero hypersurface) and Kerr black holes (Q-zero hypersurface) ones [1]. This approach can easily be generalized to an arbitrary thermodynamic system.
Substrate Curvature Gradient Drives Rapid Droplet Motion
NASA Astrophysics Data System (ADS)
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-01
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces.
Substrate curvature gradient drives rapid droplet motion.
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-11
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces. PMID:25062213
Scaling of curvature in subcritical gravitational collapse
NASA Astrophysics Data System (ADS)
Garfinkle, David; Duncan, G. Comer
1998-09-01
We perform numerical simulations of the gravitational collapse of a spherically symmetric scalar field. For those data that just barely do not form black holes we find the maximum curvature at the position of the central observer. We find a scaling relation between this maximum curvature and distance from the critical solution. The scaling relation is analogous to that found by Choptuik for the black hole mass for those data that do collapse to form black holes. We also find a periodic wiggle in the scaling exponent.
Wavefront reconstruction from tangential and sagittal curvature.
Canales, Javier; Barbero, Sergio; Portilla, Javier; López-Alonso, José Manuel
2014-12-10
In a previous contribution [Appl. Opt.51, 8599 (2012)], a coauthor of this work presented a method for reconstructing the wavefront aberration from tangential refractive power data measured using dynamic skiascopy. Here we propose a new regularized least squares method where the wavefront is reconstructed not only using tangential but also sagittal curvature data. We prove that our new method provides improved quality reconstruction for typical and also for highly aberrated wavefronts, under a wide range of experimental error levels. Our method may be applied to any type of wavefront sensor (not only dynamic skiascopy) able to measure either just tangential or tangential plus sagittal curvature data.
Equal-Curvature X-Ray Telescopes
NASA Technical Reports Server (NTRS)
Saha, Timo T.; Zhang, William
2002-01-01
We introduce a new type of x-ray telescope design; an Equal-Curvature telescope. We simply add a second order axial sag to the base grazing incidence cone-cone telescope. The radius of curvature of the sag terms is the same on the primary surface and on the secondary surface. The design is optimized so that the on-axis image spot at the focal plane is minimized. The on-axis RMS (root mean square) spot diameter of two studied telescopes is less than 0.2 arc-seconds. The off-axis performance is comparable to equivalent Wolter type 1 telescopes.
Severe Penile Curvature following Otis Urethrotomy.
Karaguzel, Ersagun; Gur, Metin; Tok, Dogan S; Kazaz, Ilke O; Eren, Huseyin; Kutlu, Omer; Ozgur, Guner K
2013-01-01
Urethral stricture is a common urological pathology with a high recurrence rate after treatment. Urethral manipulations are among its main causes. In this paper, urethral stricture developed secondary to urethral catheterization and was treated with cold-knife internal urethrotomy and the Otis urethrotomy procedure. During the follow-up period, severe ventral penile curvature preventing sexual intercourse developed due to fibrosis of the corpus spongiosum and tunica albuginea of the penis. This ventral penile curvature was corrected with a separate operation using a tunica vaginalis flap harvested from the left scrotum.
Curvature-driven capillary migration and assembly of rod-like particles.
Cavallaro, Marcello; Botto, Lorenzo; Lewandowski, Eric P; Wang, Marisa; Stebe, Kathleen J
2011-12-27
Capillarity can be used to direct anisotropic colloidal particles to precise locations and to orient them by using interface curvature as an applied field. We show this in experiments in which the shape of the interface is molded by pinning to vertical pillars of different cross-sections. These interfaces present well-defined curvature fields that orient and steer particles along complex trajectories. Trajectories and orientations are predicted by a theoretical model in which capillary forces and torques are related to Gaussian curvature gradients and angular deviations from principal directions of curvature. Interface curvature diverges near sharp boundaries, similar to an electric field near a pointed conductor. We exploit this feature to induce migration and assembly at preferred locations, and to create complex structures. We also report a repulsive interaction, in which microparticles move away from planar bounding walls along curvature gradient contours. These phenomena should be widely useful in the directed assembly of micro- and nanoparticles with potential application in the fabrication of materials with tunable mechanical or electronic properties, in emulsion production, and in encapsulation.
Variable-curvature mirrors for the VLTI
NASA Astrophysics Data System (ADS)
Ferrari, Marc; Derie, Frederic
1998-07-01
A variable curvature mirror is a powerful device that can increase the field of view of optical interferometers. Such a mirror has being developed for the coherent combined focus of the European Southern Observatory Very Large Telescope Interferometer. The variable focal length permits positioning of the pupil image of an individual telescope at a precise location after the delay-line. This property is necessary to exactly remap homothetically the output pupil configuration at the image beam combiner. Given the large zoom range that is needed in the delay line, when the mirror is not stressed the optical surface is a plane while it is convex with f/2.5 at maximum stress. The mirror itself is a very small stainless steel meniscus, with a 300 micrometers thickness, because only the high elasticity of such material allows to achieve the full domain of curvature. The thickness distribution of the meniscus is calculated using elasticity theory in the case of a large deformation. The realization of this micro-optic active device requires advanced techniques in optical fabrication and in particular high precision manufacturing with numerical command lathe. This article also presents the testing of this highly variable curvature mirror and the surface quality obtained within the full curvature range.
Size effect and detonation front curvature
Souers, P. C., LLNL
1997-07-01
Heat flow in a cylinder with internal heating is used as a basis for deriving a simple theory of detonation front curvature, leading to the prediction of quadratic curve shapes. A thermal conductivity of 50 MW/mm{sup 2} is found for TATB samples.
Curvature instability in passive diffractive resonators.
Tlidi, M; Vladimirov, A G; Mandel, Paul
2002-12-01
We study the stability of localized structures in a passive optical bistable system. We show that there is a critical value of the input field intensity above which localized structures are unstable with respect to a curvature instability. Beyond this instability boundary, a transition from the localized branch of solutions to stable hexagons is found. PMID:12485009
Strong curvature singularities and causal simplicity
Krolak, A. )
1992-02-01
Techniques of differential topology in Lorentzian manifolds developed by Geroch, Hawking, and Penrose are used to rule out a class of locally naked strong curvature singularities in strongly causal space-times. This result yields some support to the validity of Penrose's strong cosmic censorship hypothesis.
Riemann curvature of a boosted spacetime geometry
NASA Astrophysics Data System (ADS)
Battista, Emmanuele; Esposito, Giampiero; Scudellaro, Paolo; Tramontano, Francesco
2016-10-01
The ultrarelativistic boosting procedure had been applied in the literature to map the metric of Schwarzschild-de Sitter spacetime into a metric describing de Sitter spacetime plus a shock-wave singularity located on a null hypersurface. This paper evaluates the Riemann curvature tensor of the boosted Schwarzschild-de Sitter metric by means of numerical calculations, which make it possible to reach the ultrarelativistic regime gradually by letting the boost velocity approach the speed of light. Thus, for the first time in the literature, the singular limit of curvature, through Dirac’s δ distribution and its derivatives, is numerically evaluated for this class of spacetimes. Moreover, the analysis of the Kretschmann invariant and the geodesic equation shows that the spacetime possesses a “scalar curvature singularity” within a 3-sphere and it is possible to define what we here call “boosted horizon”, a sort of elastic wall where all particles are surprisingly pushed away, as numerical analysis demonstrates. This seems to suggest that such “boosted geometries” are ruled by a sort of “antigravity effect” since all geodesics seem to refuse to enter the “boosted horizon” and are “reflected” by it, even though their initial conditions are aimed at driving the particles toward the “boosted horizon” itself. Eventually, the equivalence with the coordinate shift method is invoked in order to demonstrate that all δ2 terms appearing in the Riemann curvature tensor give vanishing contribution in distributional sense.
Graph Curvature for Differentiating Cancer Networks
Sandhu, Romeil; Georgiou, Tryphon; Reznik, Ed; Zhu, Liangjia; Kolesov, Ivan; Senbabaoglu, Yasin; Tannenbaum, Allen
2015-01-01
Cellular interactions can be modeled as complex dynamical systems represented by weighted graphs. The functionality of such networks, including measures of robustness, reliability, performance, and efficiency, are intrinsically tied to the topology and geometry of the underlying graph. Utilizing recently proposed geometric notions of curvature on weighted graphs, we investigate the features of gene co-expression networks derived from large-scale genomic studies of cancer. We find that the curvature of these networks reliably distinguishes between cancer and normal samples, with cancer networks exhibiting higher curvature than their normal counterparts. We establish a quantitative relationship between our findings and prior investigations of network entropy. Furthermore, we demonstrate how our approach yields additional, non-trivial pair-wise (i.e. gene-gene) interactions which may be disrupted in cancer samples. The mathematical formulation of our approach yields an exact solution to calculating pair-wise changes in curvature which was computationally infeasible using prior methods. As such, our findings lay the foundation for an analytical approach to studying complex biological networks. PMID:26169480
Constraining inverse curvature gravity with supernovae
Mena, Olga; Santiago, Jose; Weller, Jochen; /University Coll., London /Fermilab
2005-10-01
We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.
Curvature Elasticities of the Micellar Nematics.
NASA Astrophysics Data System (ADS)
Zhou, E.
This dissertation is concerned with the curvature elastic and viscous properties of two micellar nematic systems. The mixtures of the first system had a nematic phase (N_{rm L}) with a second order transition to a lamellar smectic phase. The second system has three different nematic phases, two uniaxial phases (N_{rm L} and N_{rm C}) and an intermediate biaxial nematic phase (N_ {rm bx}). The experimental procedures used in this research are modifications of the conventional method which is based on magnetic field induced deformations of surface aligned films. Modifications were required for measurements close to the nematic-lamellar smectic transition, where the elastic constants assume very large values, and for the biaxial nematic phase and the adjacent higher temperature uniaxial phase, where the surface by itself does not impose a homogeneous alignment. A theoretical study of limiting cases, of small deformations in general and of small deformations at high magnetic fields, proved useful to select the proper experimental conditions and to evaluate the data. The nematic-lamellar smectic transition was studied on mixtures of decylammoniumchloride (DACl), ammoniumchloride, and water. The bend elastic coefficient and the rotational viscosity were found to vary over more than three orders of magnitude due to an exponential divergence at the transition. We obtained an exponent of 1.07 +/- 0.05 for a weight ratio of DACl/NHL_4Cl = 20, and an exponent of 0.87 +/- 0.02 for a weight ratio of 10, but an unexpected thermal hysteresis interferes with a reliable determination of the critical properties. The three different nematic phases were studied on potassium laurate in mixtures with 1-decanol and D _2O. The elastic constants for bend and splay in the N_{rm L} phase are nearly equal. They are about one order of magnitude smaller than the lowest values measured in the nematic phase of the DACl system. Because of surface alignment problems, only one elastic constant could
How to calculate normal curvatures of sampled geological surfaces
NASA Astrophysics Data System (ADS)
Bergbauer, Stephan; Pollard, David D.
2003-02-01
Curvature has been used both to describe geological surfaces and to predict the distribution of deformation in folded or domed strata. Several methods have been proposed in the geoscience literature to approximate the curvature of surfaces; however we advocate a technique for the exact calculation of normal curvature for single-valued gridded surfaces. This technique, based on the First and Second Fundamental Forms of differential geometry, allows for the analytical calculation of the magnitudes and directions of principal curvatures, as well as Gaussian and mean curvature. This approach is an improvement over previous methods to calculate surface curvatures because it avoids common mathematical approximations, which introduce significant errors when calculated over sloped horizons. Moreover, the technique is easily implemented numerically as it calculates curvatures directly from gridded surface data (e.g. seismic or GPS data) without prior surface triangulation. In geological curvature analyses, problems arise because of the sampled nature of geological horizons, which introduces a dependence of calculated curvatures on the sample grid. This dependence makes curvature analysis without prior data manipulation problematic. To ensure a meaningful curvature analysis, surface data should be filtered to extract only those surface wavelengths that scale with the feature under investigation. A curvature analysis of the top-Pennsylvanian horizon at Goose Egg dome, Wyoming shows that sampled surfaces can be smoothed using a moving average low-pass filter to extract curvature information associated with the true morphology of the structure.
NASA Astrophysics Data System (ADS)
Shugurov, Artur
2015-10-01
The effect of curvature of the film/substrate interface on the fracture mechanisms of Si-Al-N coatings on Cu substrates subjected to uniaxial tension and alternating bending is studied. Local interface curvature due to substrate surface roughening caused by its plastic deformation in the course of the uniaxial tension is shown to have a profound effect on their delamination and buckling. Interface curvature induced by specimen bending promotes kinking of through-the-coating cracks at the interface that is followed by delamination and spalling of the coatings.
Measuring Intrinsic Curvature of Space with Electromagnetism
NASA Astrophysics Data System (ADS)
Mabin, Mason; Becker, Maria; Batelaan, Herman
2016-10-01
The concept of curved space is not readily observable in everyday life. The educational movie "Sphereland" attempts to illuminate the idea. The main character, a hexagon, has to go to great lengths to prove that her world is in fact curved. We present an experiment that demonstrates a new way to determine if a two-dimensional surface, the 2-sphere, is curved. The behavior of an electric field, placed on a spherical surface, is shown to be related to the intrinsic Gaussian curvature. This approach allows students to gain some understanding of Einstein's theory of general relativity, which relates the curvature of spacetime to the presence of mass and energy. Additionally, an opportunity is provided to investigate the dimensionality of Gauss's law.
Tube curvature measuring probe and method
Sokol, George J.
1990-01-01
The present invention is directed to a probe and method for measuring the radius of curvature of a bend in a section of tubing. The probe includes a member with a pair of guide means, one located at each end of the member. A strain gauge is operatively connected to the member for detecting bending stress exrted on the member as the probe is drawn through and in engagement with the inner surface of a section of tubing having a bend. The method of the present invention includes steps utilizing a probe, like the aforementioned probe, which can be made to detect bends only in a single plane when having a fixed orientation relative the section of tubing to determine the maximum radius of curvature of the bend.
Streamline curvature in supersonic shear layers
NASA Technical Reports Server (NTRS)
Kibens, V.
1992-01-01
Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.
Cosmological signatures of anisotropic spatial curvature
NASA Astrophysics Data System (ADS)
Pereira, Thiago S.; Mena Marugán, Guillermo A.; Carneiro, Saulo
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Coarse-grained modeling of DNA curvature
NASA Astrophysics Data System (ADS)
Freeman, Gordon S.; Hinckley, Daniel M.; Lequieu, Joshua P.; Whitmer, Jonathan K.; de Pablo, Juan J.
2014-10-01
The interaction of DNA with proteins occurs over a wide range of length scales, and depends critically on its local structure. In particular, recent experimental work suggests that the intrinsic curvature of DNA plays a significant role on its protein-binding properties. In this work, we present a coarse grained model of DNA that is capable of describing base-pairing, hybridization, major and minor groove widths, and local curvature. The model represents an extension of the recently proposed 3SPN.2 description of DNA [D. M. Hinckley, G. S. Freeman, J. K. Whitmer, and J. J. de Pablo, J. Chem. Phys. 139, 144903 (2013)], into which sequence-dependent shape and mechanical properties are incorporated. The proposed model is validated against experimental data including melting temperatures, local flexibilities, dsDNA persistence lengths, and minor groove width profiles.
Space-time curvature and cosmology
NASA Astrophysics Data System (ADS)
Nurgaliev, I. S.; Ponomarev, V. N.
1982-10-01
The possibility is considered of obtaining a steady-state cosmological solution in the framework of the Einstein-Cartan theory. It is found that the Einstein-Cartan equations without the cosmological constant admit a solution in the form of the static de Sitter metric for a specific value of the spin-spin gravitational interaction constant, whose introduction is required by gauge theory. It is shown that the steady-state solution might serve as a model for the pre-Friedmann stage of the expansion of the universe, when the spin-curvature interaction was comparable to the interaction between space-time curvature and energy-momentum. A value of about 10 to the -20th is obtained for the spin-spin interaction constant in the case where the de Sitter stage occurs at quantum densities (10 to the 94th g/cu cm).
Curvature continuity in arbitrary bicubic Bezier patches
NASA Technical Reports Server (NTRS)
Roach, Robert L.
1990-01-01
Two methods are outlined for imposing interpatch curvature continuity in existing Bezier bicubic patch surfaces. Each method assumes that coordinates of the corners of the patches can not be altered but the interior Bezier control point can. Each method also preserves outer edge slope and outer corner twist derivatives. Neither method requires intersection or C0 continuity nor slope or C1 continuity at the start. A computer program for each method is given in the appendices.
Induction of Plant Curvature by Magnetophoresis and Cytoskeletal Changes during Root Graviresponse
NASA Technical Reports Server (NTRS)
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.
Superintegrable systems on spaces of constant curvature
Gonera, Cezary Kaszubska, Magdalena
2014-07-15
Construction and classification of two-dimensional (2D) superintegrable systems (i.e. systems admitting, in addition to two global integrals of motion guaranteeing the Liouville integrability, the third global and independent one) defined on 2D spaces of constant curvature and separable in the so-called geodesic polar coordinates are presented. The method proposed is applicable to any value of curvature including the case of Euclidean plane, sphere and hyperbolic plane. The main result is a generalization of Bertrand’s theorem on 2D spaces of constant curvature and covers most of the known separable and superintegrable models on such spaces (in particular, the so-called Tremblay–Turbiner–Winternitz (TTW) and Post–Winternitz (PW) models which have recently attracted some interest). -- Highlights: •Classifying 2D superintegrable, separable (polar coordinates) systems on S{sup 2}, R{sup 2}, H{sup 2}. •Construction of radial, angular potentials leading to superintegrability. •Generalization of Bertrand’s theorem covering known models, e.g. Higgs, TTW, PW, and Coulomb.
Intrinsically disordered proteins drive membrane curvature
NASA Astrophysics Data System (ADS)
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-07-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures.
Multiple Manifold Clustering Using Curvature Constrained Path
Babaeian, Amir; Bayestehtashk, Alireza; Bandarabadi, Mojtaba
2015-01-01
The problem of multiple surface clustering is a challenging task, particularly when the surfaces intersect. Available methods such as Isomap fail to capture the true shape of the surface near by the intersection and result in incorrect clustering. The Isomap algorithm uses shortest path between points. The main draw back of the shortest path algorithm is due to the lack of curvature constrained where causes to have a path between points on different surfaces. In this paper we tackle this problem by imposing a curvature constraint to the shortest path algorithm used in Isomap. The algorithm chooses several landmark nodes at random and then checks whether there is a curvature constrained path between each landmark node and every other node in the neighborhood graph. We build a binary feature vector for each point where each entry represents the connectivity of that point to a particular landmark. Then the binary feature vectors could be used as a input of conventional clustering algorithm such as hierarchical clustering. We apply our method to simulated and some real datasets and show, it performs comparably to the best methods such as K-manifold and spectral multi-manifold clustering. PMID:26375819
Flow of an elastico-viscous liquid in a curved pipe of slowly varying curvature.
Sarin, V B
1993-03-01
Curvature forms an important feature of thoracic aorta and this paper deals with the flow of an idealized elastico-viscous liquid in a curved pipe of circular cross-section and slowly varying curvature, under a pressure gradient. The flow is assumed to be steady and at low Reynolds numbers. By using the series expansion method of Dean (Phil Mag 4 (1927) 208-223; Phil Mag 5 (1928) 673-693) in powers of a parameter L, which can be considered as the square of ratio of the centrifugal force induced by the circular motion of the fluid to the viscous force, it is shown that in a tube of increasing curvature, there will be delay in setting up of the secondary motion. The wall shear stress, an important parameter in physiological flows, is calculated. The flow of Newtonian fluid in a tube of circular cross section is discussed, as a particular case. PMID:8449591
The effect of tibial curvature and fibular loading on the tibia index.
Funk, James R; Rudd, Rodney W; Kerrigan, Jason R; Crandall, Jeff R
2004-06-01
The tibia index (TI) is commonly used to predict leg injury based on measurements taken by an anthropomorphic test device (ATD). The TI consists of an interaction formula that combines axial loading and bending plus a supplemental compressive force criterion. Current ATD lower limbs lack geometric biofidelity with regard to tibial curvature and fibular load-sharing. Due to differences in tibial curvature, the midshaft moments induced by axial loading are different in humans and ATDs. Midshaft tibial loading in the human is also reduced by load-sharing through the fibula, which is not replicated in current ATDs. In this study, tibial curvature and fibular load-sharing are quantified through CT imaging and biomechanical testing, and equations are presented to correct ATD measurements to reflect the loading that would be experienced by a human tibia.
Stable hypersurfaces with zero scalar curvature in Euclidean space
NASA Astrophysics Data System (ADS)
Alencar, Hilário; do Carmo, Manfredo; Neto, Gregório Silva
2016-10-01
In this paper we prove some results concerning stability of hypersurfaces in the four dimensional Euclidean space with zero scalar curvature. First we prove there is no complete stable hypersurface with zero scalar curvature, polynomial growth of integral of the mean curvature, and with the Gauss-Kronecker curvature bounded away from zero. We conclude this paper giving a sufficient condition for a regular domain to be stable in terms of the mean and the Gauss-Kronecker curvatures of the hypersurface and the radius of the smallest extrinsic ball which contains the domain.
Distributed mean curvature on a discrete manifold for Regge calculus
NASA Astrophysics Data System (ADS)
Conboye, Rory; Miller, Warner A.; Ray, Shannon
2015-09-01
The integrated mean curvature of a simplicial manifold is well understood in both Regge Calculus and Discrete Differential Geometry. However, a well motivated pointwise definition of curvature requires a careful choice of the volume over which to uniformly distribute the local integrated curvature. We show that hybrid cells formed using both the simplicial lattice and its circumcentric dual emerge as a remarkably natural structure for the distribution of this local integrated curvature. These hybrid cells form a complete tessellation of the simplicial manifold, contain a geometric orthonormal basis, and are also shown to give a pointwise mean curvature with a natural interpretation as the fractional rate of change of the normal vector.
Fiber Fabry-Perot interferometer for curvature sensing
NASA Astrophysics Data System (ADS)
Monteiro, Catarina S.; Ferreira, Marta S.; Silva, Susana O.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
2016-07-01
A curvature sensor based on an Fabry-Perot (FP) interferometer was proposed. A capillary silica tube was fusion spliced between two single mode fibers, producing an FP cavity. Two FP sensors with different cavity lengths were developed and subjected to curvature and temperature. The FP sensor with longer cavity showed three distinct operating regions for the curvature measurement. Namely, a linear response was shown for an intermediate curvature radius range, presenting a maximum sensitivity of 68.52 pm/m-1. When subjected to temperature, the sensing head produced a similar response for different curvature radii, with a sensitivity varying from 0.84 pm/°C to 0.89 pm/°C, which resulted in a small cross-sensitivity to temperature when the FP sensor was subjected to curvature. The FP cavity with shorter length presented low sensitivity to curvature.
Exo70 Generates Membrane Curvature for Morphogenesis and Cell Migration
Zhao, Yuting; Liu, Jianglan; Yang, Changsong; Capraro, Benjamin R.; Baumgart, Tobias; Bradley, Ryan P.; Ramakrishnan, N.; Xu, Xiaowei; Radhakrishnan, Ravi; Svitkina, Tatyana; Guo, Wei
2013-01-01
Dynamic shape changes of the plasma membrane are fundamental to many processes ranging from morphogenesis and cell migration to phagocytosis and viral propagation. Here we demonstrate that Exo70, a component of the exocyst complex, induces tubular membrane invaginations towards the lumen of synthetic vesicles in vitro and generates protrusions on the surface of cells. Biochemical analyses using Exo70 mutants and independent molecular dynamics simulations based on Exo70 structure demonstrate that Exo70 generates negative membrane curvature through an oligomerization-based mechanism. In cells, the membrane-deformation function of Exo70 is required for protrusion formation and directional cell migration. Exo70 thus represents a membrane-bending protein that may couple actin dynamics and plasma membrane remodeling for morphogenesis. PMID:23948253
Curvature and shape determination of growing bacteria
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Ranjan; Wingreen, Ned S.
2009-12-01
Bacterial cells come in a variety of shapes, determined by the stress-bearing cell wall. Though many molecular details about the cell wall are known, our understanding of how a particular shape is produced during cell growth is at its infancy. Experiments on curved Escherichia coli grown in microtraps, and on naturally curved Caulobacter crescentus, reveal different modes of growth: one preserving arc length and the other preserving radius of curvature. We present a simple model for curved cell growth that relates these two growth modes to distinct but related growth rules—“hooplike growth” and “self-similar growth”—and discuss the implications for microscopic growth mechanisms.
Curvature sensor for ocular wavefront measurement.
Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O
2006-08-01
We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes. PMID:16832447
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.
Amplification of curvature perturbations in cyclic cosmology
Zhang Jun; Liu Zhiguo; Piao Yunsong
2010-12-15
We analytically and numerically show that through the cycles with nonsingular bounce, the amplitude of curvature perturbation on a large scale will be amplified and the power spectrum will redden. In some sense, this amplification will eventually destroy the homogeneity of the background, which will lead to the ultimate end of cycles of the global universe. We argue that for the model with increasing cycles, it might be possible that a fissiparous multiverse will emerge after one or several cycles, in which the cycles will continue only at corresponding local regions.
Spacetime Curvature and Higgs Stability after Inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2015-12-11
We investigate the dynamics of the Higgs field at the end of inflation in the minimal scenario consisting of an inflaton field coupled to the standard model only through the nonminimal gravitational coupling ξ of the Higgs field. Such a coupling is required by renormalization of the standard model in curved space, and in the current scenario also by vacuum stability during high-scale inflation. We find that for ξ≳1, rapidly changing spacetime curvature at the end of inflation leads to significant production of Higgs particles, potentially triggering a transition to a negative-energy Planck scale vacuum state and causing an immediate collapse of the Universe. PMID:26705621
Holographic entropy increases in quadratic curvature gravity
NASA Astrophysics Data System (ADS)
Bhattacharjee, Srijit; Sarkar, Sudipta; Wall, Aron C.
2015-09-01
Standard methods for calculating the black hole entropy beyond general relativity are ambiguous when the horizon is nonstationary. We fix these ambiguities in all quadratic curvature gravity theories, by demanding that the entropy be increasing at every time, for linear perturbations to a stationary black hole. Our result matches with the entropy formula found previously in holographic entanglement entropy calculations. We explicitly calculate the entropy increase for Vaidya-like solutions in Ricci-tensor gravity to show that (unlike the Wald entropy) the holographic entropy obeys a second law.
Curvature sensor for ocular wavefront measurement.
Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O
2006-08-01
We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes.
A PH domain in ACAP1 possesses key features of the BAR domain in promoting membrane curvature.
Pang, Xiaoyun; Fan, Jun; Zhang, Yan; Zhang, Kai; Gao, Bingquan; Ma, Jun; Li, Jian; Deng, Yuchen; Zhou, Qiangjun; Egelman, Edward H; Hsu, Victor W; Sun, Fei
2014-10-13
The BAR (Bin-Amphiphysin-Rvs) domain undergoes dimerization to produce a curved protein structure, which superimposes onto membrane through electrostatic interactions to sense and impart membrane curvature. In some cases, a BAR domain also possesses an amphipathic helix that inserts into the membrane to induce curvature. ACAP1 (Arfgap with Coil coil, Ankyrin repeat, and PH domain protein 1) contains a BAR domain. Here, we show that this BAR domain can neither bind membrane nor impart curvature, but instead requires a neighboring PH (Pleckstrin Homology) domain to achieve these functions. Specific residues within the PH domain are responsible for both membrane binding and curvature generation. The BAR domain adjacent to the PH domain instead interacts with the BAR domains of neighboring ACAP1 proteins to enable clustering at the membrane. Thus, we have uncovered the molecular basis for an unexpected and unconventional collaboration between PH and BAR domains in membrane bending. PMID:25284369
Local curvature measurements of a lean, partially premixed swirl-stabilised flame
NASA Astrophysics Data System (ADS)
Bayley, Alan E.; Hardalupas, Yannis; Taylor, Alex M. K. P.
2012-04-01
A swirl-stabilised, lean, partially premixed combustor operating at atmospheric conditions has been used to investigate the local curvature distributions in lifted, stable and thermoacoustically oscillating CH4-air partially premixed flames for bulk cold-flow Reynolds numbers of 15,000 and 23,000. Single-shot OH planar laser-induced fluorescence has been used to capture instantaneous images of these three different flame types. Use of binary thresholding to identify the reactant and product regions in the OH planar laser-induced fluorescence images, in order to extract accurate flame-front locations, is shown to be unsatisfactory for the examined flames. The Canny-Deriche edge detection filter has also been examined and is seen to still leave an unacceptable quantity of artificial flame-fronts. A novel approach has been developed for image analysis where a combination of a non-linear diffusion filter, Sobel gradient and threshold-based curve elimination routines have been used to extract traces of the flame-front to obtain local curvature distributions. A visual comparison of the effectiveness of flame-front identification is made between the novel approach, the threshold binarisation filter and the Canny-Deriche filter. The novel approach appears to most accurately identify the flame-fronts. Example histograms of the curvature for six flame conditions and of the total image area are presented and are found to have a broader range of local flame curvatures for increasing bulk Reynolds numbers. Significantly positive values of mean curvature and marginally positive values of skewness of the histogram have been measured for one lifted flame case, but this is generally accounted for by the effect of flame brush curvature. The mean local flame-front curvature reduces with increasing axial distance from the burner exit plane for all flame types. These changes are more pronounced in the lifted flames but are marginal for the thermoacoustically oscillating flames. It is
The lemon illusion: seeing curvature where there is none
Strother, Lars; Killebrew, Kyle W.; Caplovitz, Gideon P.
2015-01-01
Curvature is a highly informative visual cue for shape perception and object recognition. We introduce a novel illusion—the Lemon Illusion—in which subtle illusory curvature is perceived along contour regions that are devoid of physical curvature. We offer several perceptual demonstrations and observations that lead us to conclude that the Lemon Illusion is an instance of a more general illusory curvature phenomenon, one in which the presence of contour curvature discontinuities lead to the erroneous extension of perceived curvature. We propose that this erroneous extension of perceived curvature results from the interaction of neural mechanisms that operate on spatially local contour curvature signals with higher-tier mechanisms that serve to establish more global representations of object shape. Our observations suggest that the Lemon Illusion stems from discontinuous curvature transitions between rectilinear and curved contour segments. However, the presence of curvature discontinuities is not sufficient to produce the Lemon Illusion, and the minimal conditions necessary to elicit this subtle and insidious illusion are difficult to pin down. PMID:25755640
Lauric, Alexandra; Hippelheuser, James; Safain, Mina G; Malek, Adel M
2014-09-22
Although high-impact hemodynamic forces are thought to lead to cerebral aneurysmal change, little is known about the aneurysm formation on the inner aspect of vascular bends such as the internal carotid artery (ICA) siphon where wall shear stress (WSS) is expected to be low. This study evaluates the effect of vessel curvature and hemodynamics on aneurysm formation along the inner carotid siphon. Catheter 3D-rotational angiographic volumes of 35 ICA (10 aneurysms, 25 controls) were evaluated in 3D for radius of curvature and peak curvature of the siphon bend, followed by univariate statistical analysis. Computational fluid dynamic (CFD) simulations were performed on patient-derived models after aneurysm removal and on synthetic variants of increasing curvature. Peak focal siphon curvature was significantly higher in aneurysm bearing ICAs (0.36 ± 0.045 vs. 0.30 ± 0.048 mm(-1), p=0.003), with no difference in global radius of curvature (p=0.36). In CFD simulations, increasing parametric curvature tightness (from 5 to 3mm radius) resulted in dramatic increase of WSS and WSS gradient magnitude (WSSG) on the inner wall of the bend. In patient-derived data, the location of aneurysms coincided with regions of low WSS (<4 Pa) flanked by high WSS and WSSG peaks. WSS peaks correlated with the aneurysm neck. In contrast, control siphon bends displayed low, almost constant, WSS and WSSG profiles with little spatial variation. High bend curvature induces dynamically fluctuating high proximal WSS and WSSG followed by regions of flow stasis and recirculation, leading to local conditions known to induce destructive vessel wall remodeling and aneurysmal initiation.
An Anionic Phospholipid Enables the Hydrophobic Surfactant Proteins to Alter Spontaneous Curvature
Chavarha, Mariya; Loney, Ryan W.; Rananavare, Shankar B.; Hall, Stephen B.
2013-01-01
The hydrophobic surfactant proteins, SP-B and SP-C, greatly accelerate the adsorption of the surfactant lipids to an air/water interface. Previous studies of factors that affect curvature suggest that vesicles may adsorb via a rate-limiting structure with prominent negative curvature, in which the hydrophilic face of the lipid leaflets is concave. To determine if SP-B and SP-C might promote adsorption by inducing negative curvature, we used small-angle x-ray scattering to test whether the physiological mixture of the two proteins affects the radius of cylindrical monolayers in the inverse hexagonal phase. With dioleoyl phosphatidylethanolamine alone, the proteins had no effect on the hexagonal lattice constant, suggesting that the proteins fail to insert into the cylindrical monolayers. The surfactant lipids also contain ∼10% anionic phospholipids, which might allow incorporation of the cationic proteins. With 10% of the anionic dioleoyl phosphatidylglycerol added to dioleoyl phosphatidylethanolamine, the proteins induced a dose-related decrease in the hexagonal lattice constant. At 30°C, the reduction reached a maximum of 8% relative to the lipids alone at ∼1% (w/w) protein. Variation of NaCl concentration tested whether the effect of the protein represented a strictly electrostatic effect that screening by electrolyte would eliminate. With concentrations up to 3 M NaCl, the dose-related change in the hexagonal lattice constant decreased but persisted. Measurements at different hydrations determined the location of the pivotal plane and proved that the change in the lattice constant produced by the proteins resulted from a shift in spontaneous curvature. These results provide the most direct evidence yet that the surfactant proteins can induce negative curvature in lipid leaflets. This finding supports the model in which the proteins promote adsorption by facilitating the formation of a negatively curved, rate-limiting structure. PMID:23442910
Particles and curvatures in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Serra, Francesca; Luo, Yimin; Yang, Shu; Kamien, Randall D.; Stebe, Kathleen J.
Elastic interactions in anisotropic fluids can be harnessed to direct particle interactions. A strategy to smoothly manipulate the director field in nematic liquid crystals is to vary the topography of the bounding surfaces. A rugged landscape with peaks and valleys create local deformations of the director field which can interact with particles in solution. We study this complex interaction in two different settings. The first consists of an array of shallow pores in a poly-dimethyl-siloxane (PDMS) membrane, whose curvature can be tuned either by swelling the PDMS membrane or by mechanical stretching. The second is a set of grooves with wavy walls, fabricated by photolithography, with various parameters of curvature and shapes. In this contexts we study how the motion of colloidal particles in nematic liquid crystals can be influenced by their interaction with the peaks and valleys of the bottom substrate or of the side walls. Particles with different associated topological defects (hedgehogs or Saturn rings) behave differently as they interact with the topographical features, favoring the docking on peaks or valleys. These experimental systems are also ideal to study the ``lock and key'' mechanism of particles in holes and to investigate a possible route for particle sorting.
Effects of streamline curvature on separation prediction
NASA Astrophysics Data System (ADS)
Arolla, Sunil K.; Durbin, Paul A.
2009-11-01
In this study, the effects of streamline curvature on prediction of flow separation are investigated. The geometry is a circulation control airfoil, a high-lift configuration that has been under extensive research for more than two decades. A tangential jet is blown over a thick, rounded trailing edge, using the Coanda effect to delay separation. An attempt is made to understand, through numerical simulations, the dynamics of turbulent separation and reattachment on the Coanda surface. Highly curved, attached recirculation regions are seen to form. A physics based curvature correction proposed by Pettersson-Reif et al. (1999) is used in conjunction with ζ-f turbulence model. The chord-based Reynolds number is Re = 10^6. Two jet momentum coefficients of Cμ=0.03 and 0.1 are computed. In this paper, comparisons between the computed and experimental pressure distributions, velocity profiles and the position of flow detachment are presented. Comparisons with other closures such as Menter's SST model are also discussed.
ODE/PDE analysis of corneal curvature.
Płociniczak, Lukasz; Griffiths, Graham W; Schiesser, William E
2014-10-01
The starting point for this paper is a nonlinear, two-point boundary value ordinary differential equation (BVODE) that defines corneal curvature according to a static force balance. A numerical solution to the BVODE is computed by first converting the BVODE to a parabolic partial differential equation (PDE) by adding an initial value (t, pseudo-time) derivative to the BVODE. A numerical solution to the PDE is then computed by the method of lines (MOL) with the calculation proceeding to a sufficiently large value of t such that the derivative in t reduces to essentially zero. The PDE solution at this point is also the solution for the BVODE. This procedure is implemented in R (an open source scientific programming system) and the programming is discussed in some detail. A series approximation to the solution is derived from which an estimate for the rate of convergence is obtained. This is compared to a fitted exponential model. Also, two linear approximations are derived, one of which leads to a closed form solution. Both provide solutions very close to that obtained from the full nonlinear model. An estimate for the cornea radius of curvature is also derived. The paper concludes with a discussion of the features of the solution to the ODE/PDE system.
Multidimensional integrable vacuum cosmology with two curvatures
NASA Astrophysics Data System (ADS)
Gavrilov, V. R.; Ivashchuk, V. D.; Melnikov, V. N.
1996-11-01
The vacuum cosmological model on the manifold 0264-9381/13/11/018/img1 describing the evolution of n Einstein spaces of non-zero curvatures is considered. For n = 2 the Einstein equations are reduced to the Abel (ordinary differential) equation and solved, when 0264-9381/13/11/018/img2. The Kasner-like behaviour of the solutions near the singularity 0264-9381/13/11/018/img3 is considered (0264-9381/13/11/018/img4 is synchronous time). The exceptional (`Milne-type') solutions are obtained for arbitrary n. For n = 2 these solutions are attractors for other ones, when 0264-9381/13/11/018/img5. For 0264-9381/13/11/018/img6 and 0264-9381/13/11/018/img7 certain two-parametric families of solutions are obtained from n = 2 ones using the `curvature-splitting' trick. In the case n = 2, 0264-9381/13/11/018/img8 a family of non-singular solutions with the topology 0264-9381/13/11/018/img9 is found.
Kinetic information from detonation front curvature
Souers, P. C., LLNL
1998-06-15
The time constants for time-dependent modeling may be estimated from reaction zone lengths, which are obtained from two sources One is detonation front curvature, where the edge lag is close to being a direct measure The other is the Size Effect, where the detonation velocity decreases with decreasing radius as energy is lost to the cylinder edge A simple theory that interlocks the two effects is given A differential equation for energy flow in the front is used, the front is described by quadratic and sixth-power radius terms The quadratic curvature comes from a constant power source of energy moving sideways to the walls Near the walls, the this energy rises to the total energy of detonation and produces the sixth-power term The presence of defects acting on a short reaction zone can eliminate the quadratic part while leaving the wall portion of the cuvature A collection of TNT data shows that the reaction zone increases with both the radius and the void fraction
Vortex motion on surfaces of small curvature
Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.
2013-12-15
We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.
Detonation Front Curvatures and Detonation Rates
NASA Astrophysics Data System (ADS)
Lauderbach, Lisa M.; Lorenz, K. Thomas; Lee, Edward L.; Souers, P. Clark
2015-06-01
We have normalized the LLNL library of detonation front curvatures by dividing lags by the edge lag and radii by the edge radius. We then fit the normalized data to the equation L = AR2 + BR8, where L is the normalized lag and R is the normalized radius. We attribute the quadratic term to thermal processes and the 8th-power term to shock processes. We compare the % of the quadratic term J at the edge with detonation rates obtained from the size effect. One class of results is made up of fine-grained, uniform explosives with large lags, where a low detonation rate leads to a high J and vice versa. This provides a rough way of estimating unknown rates if the unknown explosive is of high quality. The other, equally-large class contains rough-grained materials, often with small lags and small radii. These have curves that do not fit the equation but superfically often look quadratic. Some HMX and PETN curvatures even show a ``sombrero'' effect. Code models show that density differences of 0.03 g/cc in ram-pressed parts can cause pseudo-quadratic curves and even sombreros. Modeling is used to illustrate J at the lowest and highest possible detonation rates. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Curvature dependent modulation of fish fin stiffness
NASA Astrophysics Data System (ADS)
Nguyen, Khoi; Yu, Ning; Bandi, Mahesh; Venkadesan, Madhusudhan; Mandre, Shreyas
Propulsion and maneuvering ability of fishes depends on the stiffness of their fins. However, increasing stiffness by simply adding material to thicken the fin would incur a substantial energetic cost associated with flapping the fin. We propose that fishes increase stiffness of the fin not by building thicker fins, but by geometrically coupling out-of-plane bending of the fin's rays with in-plane stretching of a stiff membrane that connects the rays. We present a model of fin elasticity for ray-finned fish, where we decompose the fin into a series of elastic beams (rays) with springy interconnections (membrane). In one limit, where the membranes are infinitely extensible, the fin's stiffness is no more than the sum of the stiffness of individual rays. At the other limit of an inextensible membrane, fin stiffness reaches an asymptotic maximum. The asymptote value increases monotonically with curvature. We propose that musculature at the base of the fin controls fin curvature, and thereby modulates stiffness.
Polarized curvature radiation in pulsar magnetosphere
NASA Astrophysics Data System (ADS)
Wang, P. F.; Wang, C.; Han, J. L.
2014-07-01
The propagation of polarized emission in pulsar magnetosphere is investigated in this paper. The polarized waves are generated through curvature radiation from the relativistic particles streaming along curved magnetic field lines and corotating with the pulsar magnetosphere. Within the 1/γ emission cone, the waves can be divided into two natural wave-mode components, the ordinary (O) mode and the extraordinary (X) mode, with comparable intensities. Both components propagate separately in magnetosphere, and are aligned within the cone by adiabatic walking. The refraction of O mode makes the two components separated and incoherent. The detectable emission at a given height and a given rotation phase consists of incoherent X-mode and O-mode components coming from discrete emission regions. For four particle-density models in the form of uniformity, cone, core and patches, we calculate the intensities for each mode numerically within the entire pulsar beam. If the corotation of relativistic particles with magnetosphere is not considered, the intensity distributions for the X-mode and O-mode components are quite similar within the pulsar beam, which causes serious depolarization. However, if the corotation of relativistic particles is considered, the intensity distributions of the two modes are very different, and the net polarization of outcoming emission should be significant. Our numerical results are compared with observations, and can naturally explain the orthogonal polarization modes of some pulsars. Strong linear polarizations of some parts of pulsar profile can be reproduced by curvature radiation and subsequent propagation effect.
Magneto-reheating constraints from curvature perturbations
Ringeval, Christophe; Suyama, Teruaki; Yokoyama, Jun'ichi E-mail: suyama@resceu.s.u-tokyo.ac.jp
2013-09-01
As additional perturbative degrees of freedom, it is known that magnetic fields of inflationary origin can source curvature perturbations on super-Hubble scales. By requiring the magnetic generated curvature to remain smaller than its inflationary adiabatic counterpart during inflation and reheating, we derive new constraints on the maximal field value today, the reheating energy scale and its equation of state parameter. These bounds end up being stronger by a few order of magnitude than those associated with a possible backreaction of the magnetic field onto the background. Our results are readily applicable to any slow-roll single field inflationary models and any magnetic field having its energy density scaling as a{sup γ} during inflation. As an illustrative example, massive inflation is found to remain compatible with a magnetic field today B{sub 0} = 5 × 10{sup −15} G for some values of γ only if a matter dominated reheating takes place at energies larger than 10{sup 5} GeV. Conversely, assuming γ = −1, massive inflation followed by a matter dominated reheating cannot explain large scale magnetic fields larger than 10{sup −20} G today.
Compact surfaces of constant Gaussian curvature in Randers manifolds
NASA Astrophysics Data System (ADS)
Cui, Ningwei
2016-08-01
The flag curvature of a Finsler surface is called the Gaussian curvature in Finsler geometry. In this paper, we characterize the surfaces of constant Gaussian curvature (CGC) in the Randers 3-manifold. Then we give a classification of the orientable closed CGC surfaces in two Randers space forms, which are the non-Euclidean Minkowski-Randers 3-space (K = 0) and the Bao-Shen sphere (K = 1).
Eddy-Current Measurement Of Turning Or Curvature
NASA Technical Reports Server (NTRS)
Chern, Engmin J.
1993-01-01
Rotatable conductive plate covers sensing coil to varying degree. Curvature of pipe at remote or otherwise inaccessible location inside pipe measured using relatively simple angular-displacement eddy-current probe. Crawler and sensor assemblies move along inside of pipe on wheels. Conductive plate pivots to follow curvature of pipe, partly covering one of eddy-current coils to degree depending on local curvature on pipe.
The curvature index and synchronization of dynamical systems
NASA Astrophysics Data System (ADS)
Chen, Yen-Sheng; Chang, Chien-Cheng
2012-06-01
We develop a quantity, named the curvature index, for dynamical systems. This index is defined as the limit of the average curvature of the trajectory during evolution, which measures the bending of the curve on an attractor. The curvature index has the ability to differentiate the topological change of an attractor, as its alterations exhibit the structural changes of a dynamical system. Thus, the curvature index may indicate thresholds of some synchronization regimes. The Rössler system and a time-delay system are simulated to demonstrate the effectiveness of the index, respectively.
Evolving extrinsic curvature and the cosmological constant problem
NASA Astrophysics Data System (ADS)
Capistrano, Abraão J. S.; Cabral, Luis A.
2016-10-01
The concept of smooth deformation of Riemannian manifolds associated with the extrinsic curvature is explained and applied to the Friedmann-Lemaître-Robertson-Walker cosmology. We show that such deformation can be derived from the Einstein-Hilbert-like dynamical principle may produce an observable effect in the sense of Noether. As a result, we show how the extrinsic curvature compensates both quantitative and qualitative differences between the cosmological constant Λ and the vacuum energy {ρ }{vac} obtaining the observed upper bound for the cosmological constant problem at electroweak scale. The topological characteristics of the extrinsic curvature are discussed showing that the produced extrinsic scalar curvature is an evolving dynamical quantity.
Plane wave gravitons, curvature singularities and string physics
Brooks, R. . Center for Theoretical Physics)
1991-03-21
This paper discusses bounded (compactifying) potentials arising from a conspiracy between plane wave graviton and dilaton condensates. So are string propagation and supersymmetry in spacetimes with curvature singularities.
Curvature effects in thin magnetic shells.
Gaididei, Yuri; Kravchuk, Volodymyr P; Sheka, Denis D
2014-06-27
A magnetic energy functional is derived for an arbitrary curved thin shell on the assumption that the magnetostatic effects can be reduced to an effective easy-surface anisotropy; it can be used for solving both static and dynamic problems. General static solutions are obtained in the limit of a strong anisotropy of both signs (easy-surface and easy-normal cases). It is shown that the effect of the curvature can be treated as the appearance of an effective magnetic field, which is aligned along the surface normal for the case of easy-surface anisotropy and is tangential to the surface for the case of easy-normal anisotropy. In general, the existence of such a field excludes the solutions that are strictly tangential or strictly normal to the surface. As an example, we consider static equilibrium solutions for a cone surface magnetization.
Hawking temperature of constant curvature black holes
Cai Ronggen; Myung, Yun Soo
2011-05-15
The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of M{sub D-1}xS{sup 1}, where D is the spacetime dimension and M{sub D-1} stands for a conformal Minkowski spacetime in D-1 dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both the static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.
Natural curvature for manifest T-duality
NASA Astrophysics Data System (ADS)
Poláček, Martin; Siegel, Warren
2014-01-01
We reformulate the manifestly T-dual description of the massless sector of the closed bosonic string, directly from the geometry associated with the (left and right) affine Lie algebra of the coset space Poincaré/Lorentz. This construction initially doubles not only the (spacetime) coordinates for translations but also those for Lorentz transformations (and their "dual"). As a result, the Lorentz connection couples directly to the string (as does the vielbein), rather than being introduced ad hoc to the covariant derivative as previously. This not only reproduces the old definition of T-dual torsion, but automatically gives a general, covariant definition of T-dual curvature (but still with some undetermined connections).
Tight-binding approach to strain and curvature in monolayer transition-metal dichalcogenides
NASA Astrophysics Data System (ADS)
Pearce, Alexander J.; Mariani, Eros; Burkard, Guido
2016-10-01
We present a model of the electronic properties of monolayer transition-metal dichalcogenides based on a tight-binding approach which includes the effects of strain and curvature of the crystal lattice. Mechanical deformations of the lattice offer a powerful route for tuning the electronic structure of the transition-metal dichalcogenides, as changes to bond lengths lead directly to corrections in the electronic Hamiltonian while curvature of the crystal lattice mixes the orbital structure of the electronic Bloch bands. We first present an effective low-energy Hamiltonian describing the electronic properties near the K point in the Brillouin zone, then present the corrections to this Hamiltonian due to arbitrary mechanical deformations and curvature in a way which treats both effects on an equal footing. This analysis finds that local area variations of the lattice allow for tuning of the band gap and effective masses, while the application of uniaxial strain decreases the magnitude of the direct band gap at the K point. Additionally, strain induced bond length modifications create a fictitious gauge field with a coupling strength that is smaller than that seen in related materials like graphene. We also find that curvature of the lattice leads to the appearance of both an effective in-plane magnetic field which couples to spin degrees of freedom and a Rashba-like spin-orbit coupling due to broken mirror inversion symmetry.
Holographic curvature perturbations in a cosmology with a space-like singularity
NASA Astrophysics Data System (ADS)
Ferreira, Elisa G. M.; Brandenberger, Robert
2016-07-01
We study the evolution of cosmological perturbations in an anti-de-Sitter (AdS) bulk through a cosmological singularity by mapping the dynamics onto the boundary conformal fields theory by means of the AdS/CFT correspondence. We consider a deformed AdS space-time obtained by considering a time-dependent dilaton which induces a curvature singularity in the bulk at a time which we call t = 0, and which asymptotically approaches AdS both for large positive and negative times. The boundary field theory becomes free when the bulk curvature goes to infinity. Hence, the evolution of the fluctuations is under better controle on the boundary than in the bulk. To avoid unbounded particle production across the bounce it is necessary to smooth out the curvature singularity at very high curvatures. We show how the bulk cosmological perturbations can be mapped onto boundary gauge field fluctuations. We evolve the latter and compare the spectrum of fluctuations on the infrared scales relevant for cosmological observations before and after the bounce point. We find that the index of the power spectrum of fluctuations is the same before and after the bounce.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-08-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of coseismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth and the other with a larger radius can approximate a half-space model. Then, we calculate the coseismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum coseismic displacement. The results show that the maximum curvature effect is about 4 per cent for source depths of less than 100 km, and about 30 per cent for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100 per cent. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Coherent gradient sensing method and system for measuring surface curvature
NASA Technical Reports Server (NTRS)
Rosakis, Ares J. (Inventor); Singh, Ramen P. (Inventor); Kolawa, Elizabeth (Inventor); Moore, Jr., Nicholas R. (Inventor)
2000-01-01
A system and method for determining a curvature of a specularly reflective surface based on optical interference. Two optical gratings are used to produce a spatial displacement in an interference field of two different diffraction components produced by one grating from different diffraction components produced by another grating. Thus, the curvature of the surface can be determined.
Curvature sensor based on a Fabry-Perot interferometer
NASA Astrophysics Data System (ADS)
Monteiro, Catarina; Ferreira, Marta S.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
2016-05-01
A curvature sensor based on a Fabry-Perot interferometer is proposed. A capillary tube of silica is fusion spliced between two single mode fibers, producing a Fabry-Perot cavity. The light propagates in air, when passing through the capillary tube. Two different cavities are subjected to curvature and temperature. The cavity with shorter length shows insensitivity to both measurands. The larger cavity shows two operating regions for curvature measurement, where a linear response is shown, with a maximum sensitivity of 18.77pm/m-1 for the high curvature radius range. When subjected to temperature, the sensing head produces a similar response for different curvature radius, with a sensitivity of 0.87pm/°C.
Elliptic inflation: generating the curvature perturbation without slow-roll
NASA Astrophysics Data System (ADS)
Matsuda, Tomohiro
2006-09-01
There are many inflationary models in which the inflaton field does not satisfy the slow-roll condition. However, in such models, it is always difficult to generate the curvature perturbation during inflation. Thus, to generate the curvature perturbation, one must introduce another component into the theory. To cite a case, curvatons may generate the dominant part of the curvature perturbation after inflation. However, we question whether it is realistic to consider the generation of the curvature perturbation during inflation without slow-roll. Assuming multifield inflation, we encounter the generation of curvature perturbation during inflation without slow-roll. The potential along the equipotential surface is flat by definition and thus we do not have to worry about symmetry. We also discuss KKLT (Kachru Kallosh Linde Trivedi) models, in which corrections lifting the inflationary direction may not become a serious problem if there is a symmetry enhancement at the tip (not at the moving brane) of the inflationary throat.
Nastic curvatures of wheat coleoptiles that develop in true microgravity
NASA Technical Reports Server (NTRS)
Heathcote, D. G.; Chapman, D. K.; Brown, A. H.
1995-01-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Curvature-processing network in macaque visual cortex
Yue, Xiaomin; Pourladian, Irene S.; Tootell, Roger B. H.; Ungerleider, Leslie G.
2014-01-01
Our visual environment abounds with curved features. Thus, the goal of understanding visual processing should include the processing of curved features. Using functional magnetic resonance imaging in behaving monkeys, we demonstrated a network of cortical areas selective for the processing of curved features. This network includes three distinct hierarchically organized regions within the ventral visual pathway: a posterior curvature-biased patch (PCP) located in the near-foveal representation of dorsal V4, a middle curvature-biased patch (MCP) located on the ventral lip of the posterior superior temporal sulcus (STS) in area TEO, and an anterior curvature-biased patch (ACP) located just below the STS in anterior area TE. Our results further indicate that the processing of curvature becomes increasingly complex from PCP to ACP. The proximity of the curvature-processing network to the well-known face-processing network suggests a possible functional link between them. PMID:25092328
Effects of Iris Surface Curvature on Iris Recognition
Thompson, Joseph T; Flynn, Patrick J; Bowyer, Kevin W; Santos-Villalobos, Hector J
2013-01-01
To focus on objects at various distances, the lens of the eye must change shape to adjust its refractive power. This change in lens shape causes a change in the shape of the iris surface which can be measured by examining the curvature of the iris. This work isolates the variable of iris curvature in the recognition process and shows that differences in iris curvature degrade matching ability. To our knowledge, no other work has examined the effects of varying iris curvature on matching ability. To examine this degradation, we conduct a matching experiment across pairs of images with varying degrees of iris curvature differences. The results show a statistically signi cant degradation in matching ability. Finally, the real world impact of these ndings is discussed
NASA Astrophysics Data System (ADS)
Torgoev, Almaz; Havenith, Hans-Balder
2016-07-01
A 2D elasto-dynamic modelling of the pure topographic seismic response is performed for six models with a total length of around 23.0 km. These models are reconstructed from the real topographic settings of the landslide-prone slopes situated in the Mailuu-Suu River Valley, Southern Kyrgyzstan. The main studied parameter is the Arias Intensity (Ia, m/sec), which is applied in the GIS-based Newmark method to regionally map the seismically-induced landslide susceptibility. This method maps the Ia values via empirical attenuation laws and our studies investigate a potential to include topographic input into them. Numerical studies analyse several signals with varying shape and changing central frequency values. All tests demonstrate that the spectral amplification patterns directly affect the amplification of the Ia values. These results let to link the 2D distribution of the topographically amplified Ia values with the parameter called as smoothed curvature. The amplification values for the low-frequency signals are better correlated with the curvature smoothed over larger spatial extent, while those values for the high-frequency signals are more linked to the curvature with smaller smoothing extent. The best predictions are provided by the curvature smoothed over the extent calculated according to Geli's law. The sample equations predicting the Ia amplification based on the smoothed curvature are presented for the sinusoid-shape input signals. These laws cannot be directly implemented in the regional Newmark method, as 3D amplification of the Ia values addresses more problem complexities which are not studied here. Nevertheless, our 2D results prepare the theoretical framework which can potentially be applied to the 3D domain and, therefore, represent a robust basis for these future research targets.
Velocity-curvature relationship of colliding spherical calcium waves in rat cardiac myocytes.
Wussling, M H; Scheufler, K; Schmerling, S; Drygalla, V
1997-01-01
Colliding spherical calcium waves in enzymatically isolated rat cardiac myocytes develop new wavefronts propagating perpendicular to the original direction. When investigated by confocal laser scanning microscopy (CLSM), using the fluorescent Ca2+ indicator fluo-3 AM, "cusp"-like structures become visible that are favorably approximated by double parabolae. The time-dependent position of the vertices is used to determine propagation velocity and negative curvature of the wavefront in the region of collision. It is evident that negatively curved waves propagate faster than positively curved, single waves. Considering two perfectly equal expanding circular waves, we demonstrated that the collision of calcium waves is due to an autocatalytic process (calcium-induced calcium release), and not to a simple phenomenon of interference. Following the spatiotemporal organization in simpler chemical systems maintained under conditions far from the thermodynamic equilibrium (Belousov-Zhabotinskii reaction), the dependence of the normal velocity on the curvature of the spreading wavefront is given by a linear relation. The so-called velocity-curvature relationship makes clear that the velocity is enhanced by curvature toward the direction of forward propagation and decreased by curvature away from the direction of forward propagation (with an influence of the diffusion coefficient). Experimentally obtained velocity data of both negatively and positively curved calcium waves were approximated by orthogonal weighted regression. The negative slope of the straight line resulted in an effective diffusion coefficient of 1.2 x 10(-4) mm2/s. From the so-called critical radius, which must be exceeded to initiate a traveling calcium wave, a critical volume (with enhanced [Ca2+]i) of approximately 12 microm3 was calculated. This is almost identical to the volume that is occupied by a single calcium spark. Images FIGURE 2 FIGURE 4 FIGURE 5 FIGURE 6 PMID:9284291
Cosmological spatial curvature probed by microwave polarization
Matzner, R.A.; Tolman, B.W.
1982-11-15
If there is a large-scale anisotropy in the expansion of the universe, the microwave background radiation is expected to be linearly polarized. This communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary ina complicated way over the celestial sphere (type VII/sub h/). These facts suggest a clear observational test of the closure of the universe. Also, an ambiguity inherent in the homogeneity of the universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called ''handedness.''
Accelerated Transonic Flow past a curvature discontinuity
NASA Astrophysics Data System (ADS)
de Cointet, Thomas; Ruban, Anatoly
2014-11-01
The aim of this talk is to investigate High Reynolds number Transonic flow past a discontinuity in body curvature. Starting with the inviscid flow outside the boundary layer, our analysis will focus on the flow in a vicinity of the point of discontinuity, where a solution of the Euler equations will be sought in self-similar form. This reduces the Euler equations to an ordinary differential equation. The analysis of this equation shows that the pressure gradient on the airfoil surface develops a strong singularity, which is proportional to (x0 - x) - 1 / 3 as the discontinuity point x0 is approached. We then study the response of the boundary layer to this extremely favourable pressure gradient. We show that the boundary layer splits into two parts, the main body of the boundary layer that becomes inviscid on approach to the singularity, and a thin viscous sublayer situated near the wall. The analysis of the behaviour of the solution in the viscous sublayer shows that Prandtl's hierarchical concept breaks down in a small region surrounding the singular point, where the viscous-inviscid interaction model should be used. In the final part of this talk we present a full formulation of the viscous-inviscid interaction problem and discuss numerical results.
Mean curvature flow of a hyperbolic surface
Ovchinnikov, Yu. N.; Sigal, I. M.
2011-12-15
A four-parameter family of self-similar solutions is obtained to the mean curvature flow equation for a surface. This family is shown to be stable with respect to a small deformation of a hyperbolic surface. At time instant t*, a singular point is formed within a finite time interval, that is accompanied by a change in the topology of the surface. The solution is continued beyond the singular point. A relationship between the parameters describing the hyperbolic surface before and after the change in the surface topology is obtained. A particular case is analyzed when the unperturbed surface is a cylinder. A cylindrical surface is weakly unstable with respect to a perturbation in the form of a 'wide neck.' At the final stage of the development of the neck when its transverse size becomes much less than the cylinder radius at large distances from the neck, the surface flow in a wide region in the neighborhood of the neck is described by a universal two-parameter family of self-similar solutions. These solutions are stable with respect to small perturbations of the surface.
Cosmic acceleration from matter-curvature coupling
NASA Astrophysics Data System (ADS)
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.
Nonlinear diffusion filtering influenced by mean curvature
NASA Astrophysics Data System (ADS)
Kollár, Michal; Mikula, Karol; Čunderlík, Róbert
2016-04-01
The presentation introduces a new nonlinear diffusion filtering method on closed surfaces such as a sphere, ellipsoid or the Earth's surface. Our new model extends the regularized surface Perona-Malik model by including a local extrema detector based on a mean curvature of processed data. The model is thus represented by a nonlinear diffusion equation which filters noise while preserves main edges, local extrema and details important for a correct interpretation of data. We define a surface finite-volume method to approximate numerically the nonlinear parabolic partial differential equation on a closed surface. The closed surface is approximated by a polyhedral surface created by planar triangles representing subdivision of an initial icosahedron grid and we use a piece-wise linear approximation of a solution in space and the backward Euler time discretization. Numerical experiments present nonlinear diffusion filtering of artificial data and real measurements, namely the GOCE satellite observations. They aim to point out a main advantage of the new nonlinear model which, on the contrary of Perona-Malik model, preserves local extremal values of filtered data.
Dark energy, matter creation and curvature
NASA Astrophysics Data System (ADS)
Cárdenas, Víctor H.
2012-09-01
The most studied way to explain the current accelerated expansion of the universe is to assume the existence of dark energy; a new component that fills the universe, does not form clumps, currently dominates the evolution, and has a negative pressure. In this work I study an alternative model proposed by Lima et al. (Abramo and Lima in Class. Quantum Gravity 13:2953, 1996; Zimdahl in Phys. Rev. D 53:5483, 1996; Zimdahl and Pavón in Mon. Not. R. Astron. Soc. 266:872, 1994), which does not need an exotic equation of state, but assumes instead the existence of gravitational particle creation. Because this model fits the supernova observations as well as the ΛCDM model, I perform in this work a thorough study of this model, considering an explicit spatial curvature. I found that in this scenario we can alleviate the cosmic coincidence problem, basically showing that these two components, dark matter and dark energy, are of the same nature, but they act at different scales. I also shown the inadequacy of some particle creation models, and I study a previously proposed new model that overcomes these difficulties.
Geodesic Curvature Effects in the WCMs
NASA Astrophysics Data System (ADS)
Zhou, Tianchun
2015-11-01
The favorable features of the steady state I-Regime discovered on Alcator C-Mod recently make this regime a hopeful working regime for future burning plasma experiments. Accompanying the I-regime are the weakly coherent modes (WCMs) with frequency around 200 kHz that propagate poloidally in the electron diamagnetic drift direction in the lab frame. The WCMs were interpreted as certain type of heavy impurity modes in the 3-fluid framework in a 1-D plane magnetic field geometry. Once considering in a simplified toroidal magnetic field geometry, the geodesic curvature will play important roles in that the contribution of the geodesic compression may catch up with or outweighs that of the parallel compression in the plasma edge region where the fluctuations are highly localized. This geodesic coupling to the neighboring bands modifies the marginal stability condition and mode profiles in Refs.. In the same framework, attempts will be made to interpret the concomitant low frequency (~ 20kHz) fluctuations as a type of impurity drift wave-like modes propagating in the ion diamagnetic drift direction. Supported by China National MCFE Research Program under Grant No. 2015GB11000.
BICEP2, the curvature perturbation and supersymmetry
Lyth, David H.
2014-11-01
The tensor fraction r ≅ 0.16 found by BICEP2 corresponds to a Hubble parameter H ≅ 1.0 × 10{sup 14} GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index n{sub s}. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Curvature-induced and thermal strain in polyhedral gold nanocrystals
Kim, J. W.; Dietze, S. H.; Ulvestad, A.; Fohtung, E.; Shpyrko, O. G.; Manna, S.; Fullerton, E. E.; Harder, R.
2014-10-27
We use coherent x-ray diffractive imaging to map the local distribution of strain in gold (Au) polyhedral nanocrystals grown on a silicon (Si) substrate by a single-step thermal chemical vapor deposition process. The lattice strain at the surface of the octahedral nanocrystal agrees well with the predictions of the Young-Laplace equation quantitatively, but exhibits a discrepancy near the nanocrystal-substrate interface. We attribute this discrepancy to the dissimilar interfacial energies between Au/Air and Au/Si and to the difference in thermal expansion between the nanocrystal and the substrate during the cooling process.
Curvature-induced symmetry breaking determines elastic surface patterns.
Stoop, Norbert; Lagrange, Romain; Terwagne, Denis; Reis, Pedro M; Dunkel, Jörn
2015-03-01
Symmetry-breaking transitions associated with the buckling and folding of curved multilayered surfaces-which are common to a wide range of systems and processes such as embryogenesis, tissue differentiation and structure formation in heterogeneous thin films or on planetary surfaces-have been characterized experimentally. Yet owing to the nonlinearity of the underlying stretching and bending forces, the transitions cannot be reliably predicted by current theoretical models. Here, we report a generalized Swift-Hohenberg theory that describes wrinkling morphology and pattern selection in curved elastic bilayer materials. By testing the theory against experiments on spherically shaped surfaces, we find quantitative agreement with analytical predictions for the critical curves separating labyrinth, hybrid and hexagonal phases. Furthermore, a comparison to earlier experiments suggests that the theory is universally applicable to macroscopic and microscopic systems. Our approach builds on general differential-geometry principles and can thus be extended to arbitrarily shaped surfaces. PMID:25643032
Microinjected magnetic beads induce curvature in Chara rhizoids
NASA Astrophysics Data System (ADS)
Scherp, P.; Hasenstein, K.
The gravitropic response of the Chara rhizoid is based on the interaction between the statoliths and the actin network located in the rhizoid apex. The rhizoid represents a model system for the study of gravitropism, because its apical cell contains the gravity sensing and response mechanism. In order to study the function of the statoliths and the cytoskeleton, we supplemented the naturally occurring statoliths with magnetic beads. These beads can be moved by an external magnetic field and they can be coated to interact with the cytoskeleton. The magnetic beads (1μm diameter) were injected close to the tip of the rhizoid in the presence of an external osmoticum to offset turgor pressure. The injection caused the formation of a noticeable plug of dense material at the site of impalement. After a recovery period of ca. 2 - 4 hours, the whole plant was mounted on the rotatable stage of a custom- built horizontal microscope, equipped with a long-working distance objective and a video camera. This stage is designed to reorientate the cell and/or the injected beads. In order to study the effect of the displacement of magnetic beads, an external magnetic field was applied. This external field was capable of displacing the magnetic particles but did not affect the natural statoliths. Work is in progress to quantify the response, to study the effect of microinjection on wall formation, and utilize coating of the beads to investigate their possible interaction with the original statoliths and with the microfilament network. Supported by NASA grant NAG 2- 1423.
Curvature-induced symmetry breaking determines elastic surface patterns
NASA Astrophysics Data System (ADS)
Stoop, Norbert; Lagrange, Romain; Terwagne, Denis; Reis, Pedro M.; Dunkel, Jörn
2015-03-01
Symmetry-breaking transitions associated with the buckling and folding of curved multilayered surfaces—which are common to a wide range of systems and processes such as embryogenesis, tissue differentiation and structure formation in heterogeneous thin films or on planetary surfaces—have been characterized experimentally. Yet owing to the nonlinearity of the underlying stretching and bending forces, the transitions cannot be reliably predicted by current theoretical models. Here, we report a generalized Swift-Hohenberg theory that describes wrinkling morphology and pattern selection in curved elastic bilayer materials. By testing the theory against experiments on spherically shaped surfaces, we find quantitative agreement with analytical predictions for the critical curves separating labyrinth, hybrid and hexagonal phases. Furthermore, a comparison to earlier experiments suggests that the theory is universally applicable to macroscopic and microscopic systems. Our approach builds on general differential-geometry principles and can thus be extended to arbitrarily shaped surfaces.
Curvature-induced symmetry breaking selects elastic wrinkling patterns
NASA Astrophysics Data System (ADS)
Stoop, Norbert; Lagrange, Romain; Terwagne, Denis; Reis, Pedro; Dunkel, Joern
2015-03-01
Wrinkling in curved bilayer surfaces is a ubiquitous phenomenon, including embryogenesis, biological tissue differentiation or structure formation in heterogenous thin films. Due to curved substrate and the strong nonlinearities in the elastic strains, predictions for the wrinkling morphology are notoriously difficult to obtain using classical analysis. Here, we derive a generalized Swift-Hohenberg theory to describe these morphologies and their pattern selection. Testing the theory against experiments on spherically shaped surfaces, we find quantitative agreement with analytical predictions for the phase transition curves separating labyrinth, hybrid and hexagonal wrinkling phases. Our approach builds on general differential-geometric principles and can be extended to arbitrarily shaped surfaces. Present address: Universite Libre de Bruxelles.
NASA Astrophysics Data System (ADS)
Wang, Liang-Ji; Zhang, Shu-Ming; Wang, Yu-Tian; Jiang, De-Sheng; Zhu, Jian-Jun; Zhao, De-Gang; Liu, Zong-Shun; Wang, Hui; Shi, Yong-Sheng; Wang, Hai; Liu, Su-Ying; Yang, Hui
2009-07-01
A method for accurate determination of the curvature radius of semiconductor thin films is proposed. The curvature-induced broadening of the x-ray rocking curve (XRC) of a heteroepitaxially grown layer can be determined if the dependence of the full width at half maximum (FWHM) of XRC is measured as a function of the width of incident x-ray beam. It is found that the curvature radii of two GaN films grown on a sapphire wafer are different when they are grown under similar MOCVD conditions but have different values of layer thickness. At the same time, the dislocation-induced broadening of XRC and thus the dislocation density of the epitaxial film can be well calculated after the curvature correction.
Spontaneous curvature of phosphatidic acid and lysophosphatidic acid.
Kooijman, Edgar E; Chupin, Vladimir; Fuller, Nola L; Kozlov, Michael M; de Kruijff, Ben; Burger, Koert N J; Rand, Peter R
2005-02-15
The formation of phosphatidic acid (PA) from lysophosphatidic acid (LPA), diacylglycerol, or phosphatidylcholine plays a key role in the regulation of intracellular membrane fission events, but the underlying molecular mechanism has not been resolved. A likely possibility is that PA affects local membrane curvature facilitating membrane bending and fission. To examine this possibility, we determined the spontaneous radius of curvature (R(0p)) of PA and LPA, carrying oleoyl fatty acids, using well-established X-ray diffraction methods. We found that, under physiological conditions of pH and salt concentration (pH 7.0, 150 mM NaCl), the R(0p) values of PA and LPA were -46 A and +20 A, respectively. Thus PA has considerable negative spontaneous curvature while LPA has the most positive spontaneous curvature of any membrane lipid measured to date. The further addition of Ca(2+) did not significantly affect lipid spontaneous curvature; however, omitting NaCl from the hydration buffer greatly reduced the spontaneous curvature of PA, turning it into a cylindrically shaped lipid molecule (R(0p) of -1.3 x 10(2) A). Our quantitative data on the spontaneous radius of curvature of PA and LPA at a physiological pH and salt concentration will be instrumental in developing future models of biomembrane fission.
An intuitive approach to measuring protein surface curvature.
Coleman, Ryan G; Burr, Michael A; Souvaine, Diane L; Cheng, Alan C
2005-12-01
A natural way to measure protein surface curvature is to generate the least squares fitted (LSF) sphere to a surface patch and use the radius as the curvature measure. While the concept is simple, the sphere-fitting problem is not trivial and known means of protein surface curvature measurement use alternative schemes that are arguably less straightforward to interpret. We have developed an approach to solve the LSF sphere problem by turning the sphere-fitting problem into a solvable plane-fitting problem using a transformation known as geometric inversion. The approach works on any arbitrary surface patch, and returns a radius of curvature that has direct physical interpretation. Additionally, it is flexible in its ability to find the curvature of an arbitrary surface patch, and the "resolution" can be adjusted to highlight atomic features or larger features such as peptide binding sites. We include examples of applying the method to visualization of peptide recognition pockets and protein conformational change, as well as a comparison with a commonly used solid-angle curvature method showing that the LSF method produces more pronounced curvature results.
3D curvature of muscle fascicles in triceps surae
Hamarneh, Ghassan; Wakeling, James M.
2014-01-01
Muscle fascicles curve along their length, with the curvatures occurring around regions of high intramuscular pressure, and are necessary for mechanical stability. Fascicles are typically considered to lie in fascicle planes that are the planes visualized during dissection or two-dimensional (2D) ultrasound scans. However, it has previously been predicted that fascicles must curve in three-dimensional (3D) and thus the fascicle planes may actually exist as 3D sheets. 3D fascicle curvatures have not been explored in human musculature. Furthermore, if the fascicles do not lie in 2D planes, then this has implications for architectural measures that are derived from 2D ultrasound scans. The purpose of this study was to quantify the 3D curvatures of the muscle fascicles and fascicle sheets within the triceps surae muscles and to test whether these curvatures varied among different contraction levels, muscle length, and regions within the muscle. Six male subjects were tested for three torque levels (0, 30, and 60% maximal voluntary contraction) and four ankle angles (−15, 0, 15, and 30° plantar flexion), and fascicles were imaged using 3D ultrasound techniques. The fascicle curvatures significantly increased at higher ankle torques and shorter muscle lengths. The fascicle sheet curvatures were of similar magnitude to the fascicle curvatures but did not vary between contractions. Fascicle curvatures were regionalized within each muscle with the curvature facing the deeper aponeuroses, and this indicates a greater intramuscular pressure in the deeper layers of muscles. Muscle architectural measures may be in error when using 2D images for complex geometries such as the soleus. PMID:25324510
An antidamping spin-orbit torque originating from the Berry curvature
NASA Astrophysics Data System (ADS)
Kurebayashi, H.; Sinova, Jairo; Fang, D.; Irvine, A. C.; Skinner, T. D.; Wunderlich, J.; Novák, V.; Campion, R. P.; Gallagher, B. L.; Vehstedt, E. K.; Zârbo, L. P.; Výborný, K.; Ferguson, A. J.; Jungwirth, T.
2014-03-01
Magnetization switching at the interface between ferromagnetic and paramagnetic metals, controlled by current-induced torques, could be exploited in magnetic memory technologies. Compelling questions arise regarding the role played in the switching by the spin Hall effect in the paramagnet and by the spin-orbit torque originating from the broken inversion symmetry at the interface. Of particular importance are the antidamping components of these current-induced torques acting against the equilibrium-restoring Gilbert damping of the magnetization dynamics. Here, we report the observation of an antidamping spin-orbit torque that stems from the Berry curvature, in analogy to the origin of the intrinsic spin Hall effect. We chose the ferromagnetic semiconductor (Ga,Mn)As as a material system because its crystal inversion asymmetry allows us to measure bare ferromagnetic films, rather than ferromagnetic-paramagnetic heterostructures, eliminating by design any spin Hall effect contribution. We provide an intuitive picture of the Berry curvature origin of this antidamping spin-orbit torque as well as its microscopic modelling. We expect the Berry curvature spin-orbit torque to be of comparable strength to the spin-Hall-effect-driven antidamping torque in ferromagnets interfaced with paramagnets with strong intrinsic spin Hall effect.
Berry curvature and dynamics of a magnetic bubble
NASA Astrophysics Data System (ADS)
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.
Geometry of matrix product states: Metric, parallel transport, and curvature
Haegeman, Jutho Verstraete, Frank; Mariën, Michaël; Osborne, Tobias J.
2014-02-15
We study the geometric properties of the manifold of states described as (uniform) matrix product states. Due to the parameter redundancy in the matrix product state representation, matrix product states have the mathematical structure of a (principal) fiber bundle. The total space or bundle space corresponds to the parameter space, i.e., the space of tensors associated to every physical site. The base manifold is embedded in Hilbert space and can be given the structure of a Kähler manifold by inducing the Hilbert space metric. Our main interest is in the states living in the tangent space to the base manifold, which have recently been shown to be interesting in relation to time dependence and elementary excitations. By lifting these tangent vectors to the (tangent space) of the bundle space using a well-chosen prescription (a principal bundle connection), we can define and efficiently compute an inverse metric, and introduce differential geometric concepts such as parallel transport (related to the Levi-Civita connection) and the Riemann curvature tensor.
Berry curvature and dynamics of a magnetic bubble
NASA Astrophysics Data System (ADS)
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.
Dendritic growth tip velocities and radii of curvature in microgravity
Koss, M.B.; LaCombe, J.C.; Tennenhouse, L.A.; Glicksman, M.E.; Winsa, E.A.
1999-12-01
Dendritic growth is the common mode of solidification encountered when metals and alloys freeze under low thermal gradients. The growth of dendrites in pure melts depends on the transport of latent heat from the moving crystal-melt interface and the influence of weaker effects like the interfacial energy. Experimental data for critical tests of dendritic growth theories remained limited because dendritic growth can be complicated by convection. The Isothermal Dendritic Growth Experiment (IDGE) was developed specifically to test dendritic growth theories by performing measurements with succinonitrile (SCN) in microgravity, thus eliminating buoyancy-induced convection. The first flight of the IDGE in 1994 operated for 9 days at a mean quasi-static acceleration of 0.7 x 10{sup {minus}6} g{sub 0}. The velocity and radius data show that at supercoolings above approximately 0.4 K, dendritic growth in SCN under microgravity conditions is diffusion limited. By contrast, under terrestrial conditions, dendritic growth of SCN is dominated y convection for supercoolings below 1.7 K. The theoretical and experimental Peclet numbers exhibit modest disagreement, indicating that transport theories of dendritic solidification require some modification. Finally, the kinetic selection rule for dendritic growth, VR{sup 2} = constant, where V is the velocity of the tip and R is the radius of curvature at the tip, appears to be independent of the gravity environment, with a slight dependence on the supercooling.
Curvature and isocurvature perturbations in two-field inflation
NASA Astrophysics Data System (ADS)
Lalak, Z.; Langlois, D.; Pokorski, S.; Turzyński, K.
2007-07-01
We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, up to first order in the slow-roll parameters. We also compute numerically the evolution of the curvature and isocurvature modes from well within the Hubble radius until the end of inflation. We show explicitly for a few examples, including the recently proposed model of 'roulette' inflation, how isocurvature perturbations affect significantly the curvature perturbation between Hubble crossing and the end of inflation.
Dynamic Curvature Steering Control for Autonomous Vehicle: Performance Analysis
NASA Astrophysics Data System (ADS)
Aizzat Zakaria, Muhammad; Zamzuri, Hairi; Amri Mazlan, Saiful
2016-02-01
This paper discusses the design of dynamic curvature steering control for autonomous vehicle. The lateral control and longitudinal control are discussed in this paper. The controller is designed based on the dynamic curvature calculation to estimate the path condition and modify the vehicle speed and steering wheel angle accordingly. In this paper, the simulation results are presented to show the capability of the controller to track the reference path. The controller is able to predict the path and modify the vehicle speed to suit the path condition. The effectiveness of the controller is shown in this paper whereby identical performance is achieved with the benchmark but with extra curvature adaptation capabilites.
Complete manifolds with bounded curvature and spectral gaps
NASA Astrophysics Data System (ADS)
Schoen, Richard; Tran, Hung
2016-08-01
We study the spectrum of complete noncompact manifolds with bounded curvature and positive injectivity radius. We give general conditions which imply that their essential spectrum has an arbitrarily large finite number of gaps. In particular, for any noncompact covering of a compact manifold, there is a metric on the base so that the lifted metric has an arbitrarily large finite number of gaps in its essential spectrum. Also, for any complete noncompact manifold with bounded curvature and positive injectivity radius we construct a metric uniformly equivalent to the given one (also of bounded curvature and positive injectivity radius) with an arbitrarily large finite number of gaps in its essential spectrum.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed. PMID:25615464
Geometry-specific scaling of detonation parameters from front curvature
Jackson, Scott I; Short, Mark
2011-01-20
It has previously been asserted that classical detonation curvature theory predicts that the critical diameter and the diameter-effect curve of a cylindrical high-explosive charge should scale with twice the thickness of an analogous two-dimensional explosive slab. The varied agreement of experimental results with this expectation have led some to question the ability of curvature-based concepts to predict detonation propagation in non-ideal explosives. This study addresses such claims by showing that the expected scaling relationship (hereafter referred to d = 2w) is not consistent with curvature-based Detonation Shock Dynamics (DSD) theory.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
Nonlinear dynamics of the tearing mode with two-fluid and curvature effects in tokamaks
Meshcheriakov, Dmytro; Maget, Patrick; Garbet, Xavier; Lütjens, Hinrich; Beyer, Peter
2014-01-15
Curvature and diamagnetic effects are both known to have an influence on tearing mode dynamics. In this paper, we investigate the impact of these effects on the nonlinear stability and saturation of a (2, 1) island using non-linear two-fluid MHD simulations and we apply our results to Tore Supra experiments, where its behavior is not well understood from the single fluid MHD model. Simulations show that a metastable state induced by diamagnetic effect exists for this mode and that it also produces a reduction of the saturated island size, in presence of toroidal curvature. The mode is found to be nonlinearly destabilized by a seed island and it saturates at a macroscopic level causing a significant confinement degradation. The interpretation of dual states, with either no island on q = 2 or a large one, observed on discharges with high non inductive current source on Tore Supra, is revisited.
Curvature-driven assembly in soft matter.
Liu, Iris B; Sharifi-Mood, Nima; Stebe, Kathleen J
2016-07-28
Control over the spatial arrangement of colloids in soft matter hosts implies control over a wide variety of properties, ranging from the system's rheology, optics, and catalytic activity. In directed assembly, colloids are typically manipulated using external fields to form well-defined structures at given locations. We have been developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. Such potential fields allow particles to interact with each other. If the soft matter host is deformed in some way, the potential allows the particles to interact with the global system distortion. One important example is capillary assembly of colloids on curved fluid interfaces. Upon attaching, the particle distorts that interface, with an associated energy field, given by the product of its interfacial area and the surface tension. The particle's capillary energy depends on the local interface curvature. We explore this coupling in experiment and theory. There are important analogies in liquid crystals. Colloids in liquid crystals elicit an elastic energy response. When director fields are moulded by confinement, the imposed elastic energy field can couple to that of the colloid to define particle paths and sites for assembly. By improving our understanding of these and related systems, we seek to develop new, parallelizable routes for particle assembly to form reconfigurable systems in soft matter that go far beyond the usual close-packed colloidal structures.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298434
NASA Astrophysics Data System (ADS)
Ma, Shuang; Yi, Shengzhen; Chen, Shenghao; Wang, Zhanshan
2014-11-01
Monochromatic energy multilayer Kirkpatrick-Baez microscope is one of key diagnostic tools for researches on inertial confinement fusion. It is composed by two orthogonal concave spherical mirrors with small curvature and aperture, and produce the image of an object by collecting X-rays in each orthogonal direction, independently. Accurate measurement of radius of curvature of concave spherical mirrors is very important to achieve its design optical properties including imaging quality, optical throughput and energy resolution. However, it is difficult to measure the radius of curvature of spherical optical surfaces with small curvature and aperture by conventional methods, for the produced reflective intensity of glass is too low to correctly test. In this paper, we propose an improved measuring method of optical profiler to accomplish accurate measurement of radius of curvature of spherical optical surfaces with small curvature and aperture used in the monochromatic energy multilayer Kirkpatrick-Baez microscope. Firstly, we use a standard super-smooth optical flat to calibrate reference mirror before each experiment. Following, deviation of central position between measurement area and interference pattern is corrected by the theory of Newton's rings, and the zero-order fringe position is derived from the principle of interference in which surface roughness has minimum values in the position of zero light path difference. Measured results by optical profiler show the low relative errors and high repeatability. Eventually, an imaging experiment of monochromatic energy multilayer Kirkpatrick-Baez microscope determines the measurement accuracy of radius of curvature.
Curvature effect in grazing X-ray reflectometry
NASA Astrophysics Data System (ADS)
Bridou, F.
1994-09-01
Grazing X-ray reflectometry is currently used for the characterization of thin layer stacks. The parameters to be determined are thickness, roughness, and optical index. They can be worked out by fitting the recorded reflectivity curve, with a theoretical one calculated with the appropriate parameters. In such a calculation, the sample is supposed to be flat. It can be shown experimentally that the curvature of the sample modifies the expected reflectivity. An example of a saddle shaped sample, with opposite main curvature in two perpendicular directions shows typical differences on recorded curves for these two perpendicular directions. In order to make a quantitative study of the effect of the sample curvature, five pairs of spherical silica substrates have been made and coated with similar TiN layers. A theoretical study has also been made. It is shown that, for a given set-up, the sample curvature changes the aperture of the reflected beam with respect to that of the incident beam. At grazing incidence, the aperture change is significant in the incidence plane, while it can be neglected in the plane perpendicular to the incidence plane. As a consequence of the aperture change, the recorded intensity can be increased or decreased, depending on the position of the source image with respect to the position and width of the stop aperture in the image space. A calculation has been made, taking into account the geometrical characteristics of the equipment. The results have been compared with the reflectivity curves measured for the TiN layers deposited on the curved silica substrates. It can be seen that the anomalies in the reflectivity curves, induced by the substrate curvature in the plateau region are well accounted for by the model. La réflectométrie en X rasants est utilisée couramment pour la caractérisation d'empilements de couches minces. Les paramètres á déterminer sont : épaisseurs, rugosités et indices. On peut y accéder en ajustant la courbe
VLTI pupil transfer: variable curvature mirrors: II. Plasticity, hysteresis, and curvature control
NASA Astrophysics Data System (ADS)
Lemaitre, Gerard R.; Ferrari, Marc; Mazzanti, Silvio P.; Lanzoni, Patrick; Joulie, Patrice; Leduc, Denis; Copede, Myriam
2000-07-01
Progress in Active Optics Methods have led to the invention of Variable Curvature Mirrors. VCMs are useful to provide optical path compensations of the imaged field of view. Preliminarily developed for Fourier transform IR spectrometers, they are now used for the coherent beam recombination of the VLT array. With the VLT Interferometer, a highly flexible VCM will be installed at the focal surface of each cat's eye delay lines. The VCM developments led to the design choice of metal substrates in a quenched state which are at least 15 times more flexible--to external loading--than gloss or vitroceram substrates and thus, have provided accurately the large zoom-range from f/(infinity) to f/2.6. Due to the very large zoom range provided by such active mirrors, it has been found necessary to take under consideration the small plastical deformation as well as the small hysterese loop deformation of the metal substrate. With the four VCMs such as now built for the 8 m telescopes, a plastical deformation model and a hysterese loop model have been determined and are presently described. Including these compensations, the VCM optical figures have been improved and the control software now performs a curvature resolution in between 10-3 and 5 10-4.
NASA Astrophysics Data System (ADS)
Xu, Ning; Ding, Jian-Wen; Chen, Hong-Bo; Ma, Ming-Ming
2009-07-01
To accurately describe the persistent current for various toroidal carbon nanotubes (TCNs), a semiempirical sp3 tight-binding model is presented, in which the intrinsic curvature and hybridization have been fully taken into account. The calculations show that the curvature and hybridization can induce dramatic changes in the energy spectra of TCNs such as the Fermi energy EF shifting up, an energy gap opening at EF, and the energy spectrum symmetry about EF destroyed, which leads to a decrease of persistent current and changes in the shape of the flux-dependent current. In the presence of curvature and hybridization, the persistent current in non-armchair TCNs is nearly an order of magnitude lower than that obtained by using the Brillouin-zone folding approach, while it is of the same order of magnitude in armchair TCNs.
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.
16. Detail of curvature of northern parapet, with 1932 concrete ...
16. Detail of curvature of northern parapet, with 1932 concrete extension of parapet in foreground, facing east. - Dubbs Bridge, Spinnerstown Road (State Route 2031) spanning Hosensack Creek, Dillingerville, Lehigh County, PA
Shape Coherence and Finite-Time Curvature Evolution
NASA Astrophysics Data System (ADS)
Ma, Tian; Bollt, Erik M.
We introduce a definition of finite-time curvature evolution along with our recent study on shape coherence in nonautonomous dynamical systems. Comparing to slow evolving curvature preserving the shape, large curvature growth points reveal the dramatic change on shape such as the folding behaviors in a system. Closed trough curves of low finite-time curvature (FTC) evolution field indicate the existence of shape coherent sets, and troughs in the field indicate the most significant shape coherence. Here, we will demonstrate these properties of the FTC, as well as contrast to the popular Finite-Time Lyapunov Exponent (FTLE) computation, often used to indicate hyperbolic material curves as Lagrangian Coherent Structures (LCS). We show that often the FTC troughs are in close proximity to the FTLE ridges, but in other scenarios, the FTC indicates entirely different regions.
Curvature and bow of bulk GaN substrates
NASA Astrophysics Data System (ADS)
Foronda, Humberto M.; Romanov, Alexey E.; Young, Erin C.; Roberston, Christian A.; Beltz, Glenn E.; Speck, James S.
2016-07-01
We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.
Curvature-Squared Cosmology In The First-Order Formalism
NASA Technical Reports Server (NTRS)
Shahid-Saless, Bahman
1993-01-01
Paper presents theoretical study of some of general-relativistic ramifications of gravitational-field energy density proportional to R - alpha R(exp 2) (where R is local scalar curvature of space-time and alpha is a constant).
Curvature Control of Silicon Microlens for THz Dielectric Antenna
NASA Technical Reports Server (NTRS)
Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran
2012-01-01
We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.
Changes on the corneal thickness and curvature after orthokeratology
NASA Astrophysics Data System (ADS)
Mitsui, Iwane; Yamada, Yoshiya
2004-07-01
To evaluate the corneal thickness and curvature changes after Orthokeratology contact lens wear, using the ORBSCAN II corneal topography system, corneal thickness and corneal curvature were measured on one hundred and twenty eyes of sixty patients before and after wearing the custom rigid gas permeable contact lenses for Orthokeratology. The contact lenses were specially designed for each eye. The subjects wore the orthokeratology lenses for approximately Four hours with their eyes closed. The corneal thickness of the subjects was increased on fifty-five eyes at not only the peripheral zone but also the center of the cornea. The average increase of central and peripheral corneal thickness was 18 micrometer and 22micrometer, respectively. The mean anterior curvature of corneal surface changed 1.25D. The mean posterior curvature of corneal endothelium side changed 0.75D.
The probability equation for the cosmological comoving curvature perturbation
Riotto, Antonio; Sloth, Martin S. E-mail: sloth@cern.ch
2011-10-01
Fluctuations of the comoving curvature perturbation with wavelengths larger than the horizon length are governed by a Langevin equation whose stochastic noise arise from the quantum fluctuations that are assumed to become classical at horizon crossing. The infrared part of the curvature perturbation performs a random walk under the action of the stochastic noise and, at the same time, it suffers a classical force caused by its self-interaction. By a path-interal approach and, alternatively, by the standard procedure in random walk analysis of adiabatic elimination of fast variables, we derive the corresponding Kramers-Moyal equation which describes how the probability distribution of the comoving curvature perturbation at a given spatial point evolves in time and is a generalization of the Fokker-Planck equation. This approach offers an alternative way to study the late time behaviour of the correlators of the curvature perturbation from infrared effects.
Wang, Dan; Yin, Yajun; Wu, Jiye; Wang, Xugui; Zhong, Zheng
2016-01-01
The interaction potential between a curved surface body and a particle located on the surface of the body is studied in this paper. Based on the negative exponential pair potential (1/R(n)) between particles, the interaction potential is proved to be of the curvature-based form, i.e., it can be written as a function of curvatures of the surface. Idealized numerical experiments are designed to test the accuracy of curvature-based potential. Based on the curvature-based potential, propositions below are confirmed: a highly curved surface body will induce driving forces on the particle located on the surface, and curvatures and the gradients of curvatures are essential factors forming the driving forces. In addition, the tangent driving force acting on the particle from the curved surface body is studied. Based on duality, the following rule is proved: for a convex or concave curved body sharing the same curved surface, the curvature-based interaction potential between them and a particle on the surface can make up the potential of a particle in the whole space.
Ishikawa, H; Evans, M L
1992-01-01
We examined the response of primary roots of maize (Zea mays L. cv Merit) to unilateral application of calcium with particular attention to the site of application, the dependence on growth rate, and possible contributions of thigmotropic stimulation during application. Unilateral application of agar to the root cap induced negative curvature whether or not the agar contained calcium. This apparent thigmotropic response was enhanced by including calcium in the agar. Curvature away from objects applied unilaterally to the extreme root tip occurred both in intact and detipped roots. When agar containing calcium chloride was applied to one side of the postmitotic isodiametric growth zone ( a region between the apical meristem and the elongation zone), the root curved toward the side of application. This response could not be induced by plain agar. We conclude that curvature away from calcium applied to the root tip results from a thigmotropic response to stimulation during application. In contrast, curvature toward the calcium applied to the postmitotic isodiametric growth zone results from direct calcium-induced inhibition of growth. PMID:11537870
Ishikawa, H; Evans, M L
1992-01-01
We examined the response of primary roots of maize (Zea mays L. cv Merit) to unilateral application of calcium with particular attention to the site of application, the dependence on growth rate, and possible contributions of thigmotropic stimulation during application. Unilateral application of agar to the root cap induced negative curvature whether or not the agar contained calcium. This apparent thigmotropic response was enhanced by including calcium in the agar. Curvature away from objects applied unilaterally to the extreme root tip occurred both in intact and detipped roots. When agar containing calcium chloride was applied to one side of the postmitotic isodiametric growth zone ( a region between the apical meristem and the elongation zone), the root curved toward the side of application. This response could not be induced by plain agar. We conclude that curvature away from calcium applied to the root tip results from a thigmotropic response to stimulation during application. In contrast, curvature toward the calcium applied to the postmitotic isodiametric growth zone results from direct calcium-induced inhibition of growth.
NASA Technical Reports Server (NTRS)
Ishikawa, H.; Evans, M. L.
1992-01-01
We examined the response of primary roots of maize (Zea mays L. cv Merit) to unilateral application of calcium with particular attention to the site of application, the dependence on growth rate, and possible contributions of thigmotropic stimulation during application. Unilateral application of agar to the root cap induced negative curvature whether or not the agar contained calcium. This apparent thigmotropic response was enhanced by including calcium in the agar. Curvature away from objects applied unilaterally to the extreme root tip occurred both in intact and detipped roots. When agar containing calcium chloride was applied to one side of the postmitotic isodiametric growth zone ( a region between the apical meristem and the elongation zone), the root curved toward the side of application. This response could not be induced by plain agar. We conclude that curvature away from calcium applied to the root tip results from a thigmotropic response to stimulation during application. In contrast, curvature toward the calcium applied to the postmitotic isodiametric growth zone results from direct calcium-induced inhibition of growth.
Influence of curvature on the losses of doubly clad fibers.
Marcuse, D
1982-12-01
The loss increase of the HE(11) mode of a doubly clad (depressed-index) fiber due to constant curvature is considered. The calculations presented in this paper are based on a simplified theory. We find that for typical fibers the leakage loss of the HE(11) mode begins to increase significantly when the radius of curvature of the fiber axis reaches the 1-10-cm range.
Layered devices having surface curvature and method of constructing same
Woodbury, Richard C.; Perkins, Raymond T.; Thorne, James M.
1989-01-01
A method of treating a substrate having first and second sides with corresponding oppositely facing first and second surfaces, to produce curvature in the first surface. The method includes the steps of removing material, according to a predetermined pattern, from the second side of the substrate, and applying a stress-producing film of material to at least one surface of the substrate to thereby cause the substrate to bend to produce the desired curvature in the first surface.
Topology of codimension-one foliations of nonnegative curvature
Bolotov, Dmitry V
2013-05-31
We show that a transversely oriented C{sup 2}-foliation of codimension one with nonnegative Ricci curvature on a closed orientable manifold is a foliation with almost no holonomy. This allows us to decompose the manifold into blocks on which this foliation has a simple structure. We also show that a manifold homeomorphic to a 5-dimensional sphere does not admit a codimension-one C{sup 2}-foliation with nonnegative sectional curvature. Bibliography: 29 titles.
Fresnel diffractive imaging: Experimental study of coherence and curvature
NASA Astrophysics Data System (ADS)
Whitehead, L. W.; Williams, G. J.; Quiney, H. M.; Nugent, K. A.; Peele, A. G.; Paterson, D.; de Jonge, M. D.; McNulty, I.
2008-03-01
A Fresnel coherent diffractive imaging experiment is performed using a pinhole as a test object. The experimental parameters of the beam curvature and coherence length of the illuminating radiation are varied to investigate their effects on the reconstruction process. It is found that a sufficient amount of curvature across the sample strongly ameliorates the effects of low coherence, even when the sample size exceeds the coherence length.
FAST TRACK COMMUNICATION: Lorentzian manifolds and scalar curvature invariants
NASA Astrophysics Data System (ADS)
Coley, Alan; Hervik, Sigbjørn; Pelavas, Nicos
2010-05-01
We discuss (arbitrary-dimensional) Lorentzian manifolds and the scalar polynomial curvature invariants constructed from the Riemann tensor and its covariant derivatives. Recently, we have shown that in four dimensions a Lorentzian spacetime metric is either \\mathcal {I}-non-degenerate, and hence locally characterized by its scalar polynomial curvature invariants, or is a degenerate Kundt spacetime. We present a number of results that generalize these results to higher dimensions and discuss their consequences and potential physical applications.
Adhesive Nanoparticles as Local Probes of Membrane Curvature.
Agudo-Canalejo, Jaime; Lipowsky, Reinhard
2015-10-14
Biological and biomimetic membranes display complex shapes with nonuniform curvature. Because the interaction of adhesive nanoparticles with such membranes depends on the local membrane curvature, different segments of the same membrane can differ in their engulfment behavior. For a single vesicle in contact with many nanoparticles, we predict ten distinct engulfment patterns as well as morphological transitions between these patterns, which are directly accessible to experiment.
Design of a curvature sensor using a flexoelectric material
NASA Astrophysics Data System (ADS)
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.
Monolayer spontaneous curvature of raft-forming membrane lipids
NASA Astrophysics Data System (ADS)
Kollmitzer, Benjamin; Heftberger, Peter; Rappolt, Michael; Pabst, Georg
Monolayer spontaneous curvatures for cholesterol, DOPE, POPE, DOPC, DPPC, DSPC, POPC, SOPC, and egg sphingomyelin were obtained using small-angle X-ray scattering (SAXS) on inverted hexagonal phases (HII). Spontaneous curvatures of bilayer forming lipids were estimated by adding controlled amounts to a HII forming template following previously established protocols. Spontanous curvatures of both phosphatidylethanolamines and cholesterol were found to be at least a factor of two more negative than those of phosphatidylcholines, whose J0 are closer to zero. Interestingly, a significant positive J0 value (+0.1 1/nm) was retrieved for DPPC at 25 {\\deg}C. We further determined the temperature dependence of the spontaneous curvatures J0(T) in the range from 15 to 55 \\degC, resulting in a quite narrow distribution of -1 to -3 * 10^-3 1/nm{\\deg}C for most investigated lipids. The data allowed us to estimate the monolayer spontaneous curvatures of ternary lipid mixtures showing liquid ordered / liquid disordered phase coexistence. We report spontaneous curvature phase diagrams for DSPC/DOPC/Chol, DPPC/DOPC/Chol and SM/POPC/Chol and discuss effects on protein insertion and line tension.
Overriding plate thickness control on subducting slab curvature
NASA Astrophysics Data System (ADS)
Holt, A.; Buffett, B. A.; Becker, T. W.
2014-12-01
The curvature of subducting lithosphere controls deformation due to bending at the trench, which results in a force that dissipates gravitational potential energy and may affect seismic coupling. We use 2-D, thermo-mechanical subduction models to explore the dependence of the radius of curvature on the thickness of the subducting and overriding plates for models with both viscous and effectively plastic lithospheric rheologies. Such a plastic rheology has been shown to reproduce the bending stresses/moment computed using a kinematic strain rate description and a laboratory derived composite rheology. Laboratory and numerical models show that the bending geometry of subducting slabs with a viscous rheology is strongly dependent on slab thickness; thicker plates have a larger radius of curvature. However, the curvature of subducting plates on Earth, illuminated by the distribution of earthquake hypocenters, shows little to no dependence on the plate thickness or age. Such an observation is instead compatible with plates that have a plastic rheology. Indeed, our numerical models show that the radius of curvature of viscous plates has a stronger dependence on subducting plate thickness than in equivalent plastic models. In viscous plates, the bending moment produces a torque, which balances the torque exerted by buoyancy. However, for the plastic plate case the bending moment saturates at a maximum value and so cannot balance the gravitational torque. The saturation of bending moment means that, (a) the radius of curvature of the bending region is not constrained by this torque balance, and, (b) other forces are required to balance the gravitational torque. We explore the role that the overriding plate could play in controlling the subducting plate curvature in plastic plate models where the bending stresses have saturated. For such plates, we find that increasing the thickness of the overriding plate causes the radius of curvature to increase. The same correlation is
Arenavirus budding resulting from viral-protein-associated cell membrane curvature
Schley, David; Whittaker, Robert J.; Neuman, Benjamin W.
2013-01-01
Viral replication occurs within cells, with release (and onward infection) primarily achieved through two alternative mechanisms: lysis, in which virions emerge as the infected cell dies and bursts open; or budding, in which virions emerge gradually from a still living cell by appropriating a small part of the cell membrane. Virus budding is a poorly understood process that challenges current models of vesicle formation. Here, a plausible mechanism for arenavirus budding is presented, building on recent evidence that viral proteins embed in the inner lipid layer of the cell membrane. Experimental results confirm that viral protein is associated with increased membrane curvature, whereas a mathematical model is used to show that localized increases in curvature alone are sufficient to generate viral buds. The magnitude of the protein-induced curvature is calculated from the size of the amphipathic region hypothetically removed from the inner membrane as a result of translation, with a change in membrane stiffness estimated from observed differences in virion deformation as a result of protein depletion. Numerical results are based on experimental data and estimates for three arenaviruses, but the mechanisms described are more broadly applicable. The hypothesized mechanism is shown to be sufficient to generate spontaneous budding that matches well both qualitatively and quantitatively with experimental observations. PMID:23864502
Frame-covariant formulation of inflation in scalar-curvature theories
NASA Astrophysics Data System (ADS)
Burns, Daniel; Karamitsos, Sotirios; Pilaftsis, Apostolos
2016-06-01
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, Higgs inflation and F (R) models of inflation, and obtain more accurate results, without making additional approximations to the potential. Our results are shown to be consistent to lowest order with those presented in the literature. Finally, we outline how our frame-covariant formalism can be naturally extended beyond the tree-level approximation, within the framework of the Vilkovisky-DeWitt effective action.
Palmer, Antony L; Bradley, David A; Nisbet, Andrew
2015-03-08
This work considers a previously overlooked uncertainty present in film dosimetry which results from moderate curvature of films during the scanning process. Small film samples are particularly susceptible to film curling which may be undetected or deemed insignificant. In this study, we consider test cases with controlled induced curvature of film and with film raised horizontally above the scanner plate. We also evaluate the difference in scans of a film irradiated with a typical brachytherapy dose distribution with the film naturally curved and with the film held flat on the scanner. Typical naturally occurring curvature of film at scanning, giving rise to a maximum height 1 to 2 mm above the scan plane, may introduce dose errors of 1% to 4%, and considerably reduce gamma evaluation passing rates when comparing film-measured doses with treatment planning system-calculated dose distributions, a common application of film dosimetry in radiotherapy. The use of a triple-channel dosimetry algorithm appeared to mitigate the error due to film curvature compared to conventional single-channel film dosimetry. The change in pixel value and calibrated reported dose with film curling or height above the scanner plate may be due to variations in illumination characteristics, optical disturbances, or a Callier-type effect. There is a clear requirement for physically flat films at scanning to avoid the introduction of a substantial error source in film dosimetry. Particularly for small film samples, a compression glass plate above the film is recommended to ensure flat-film scanning. This effect has been overlooked to date in the literature.
Controlling carbon-nanotube-phospholipid solubility by curvature-dependent self-assembly.
Määttä, Jukka; Vierros, Sampsa; Sammalkorpi, Maria
2015-03-12
Control of aqueous dispersion is central in the processing and usage of nanoscale hydrophobic objects. However, selecting dispersive agents based on the size and form of the hydrophobic object and the role of coating morphology in dispersion efficiency remain important open questions. Here, the effect of the substrate and the dispersing molecule curvature, as well as, the influence of dispersant concentration on the adsorption morphology are examined by molecular simulations of graphene and carbon nanotube (CNT) substrates with phospholipids of varying curvature as the dispersing agents. Lipid spontaneous curvature is increased from close to zero (effectively cylindrical lipid) to highly positive (effectively conical lipid) by studying double tailed dipalmitoylphosphadidylcholine (DPPC) and single tailed lysophosphadidylcholine (LPC) which differ in the number of acyl chains but have identical headgroup. We find that lipids are good dispersion agents for both planar and curved nanoparticles and induce a dispersive barrier nonsize selectively. Differences in dispersion efficiency arise from lipid headgroup density and their extension from the hydrophobic substrate in the adsorption morphology. We map the packing morphology contributing factors and report that the aggregate morphologies depend on the competition of interactions rising from (1) hydrophobicity driven maximization of lipid-substrate contacts and lipid self-adhesion, (2) tail bending energy cost, (3) preferential alignment along the graphitic substrate principal axes, and (4) lipid headgroup preferential packing. Curved substrates adjust the morphology by changing the balance between the interaction strengths. Jointly, the findings show substrate curvature and dimensions are a way to tune lipid adsorption to desired, self-assembling patterns. Besides engineering dispersion efficiency, the findings could bear significance in designing materials with defined molecular scale, molecular coatings for
Clinical workflow for spinal curvature measurement with portable ultrasound
NASA Astrophysics Data System (ADS)
Tabanfar, Reza; Yan, Christina; Kempston, Michael; Borschneck, Daniel; Ungi, Tamas; Fichtinger, Gabor
2016-03-01
PURPOSE: Spinal curvature monitoring is essential in making treatment decisions in scoliosis. Monitoring entails radiographic examinations, however repeated ionizing radiation exposure has been shown to increase cancer risk. Ultrasound does not emit ionizing radiation and is safer for spinal curvature monitoring. We investigated a clinical sonography protocol and challenges associated with position-tracked ultrasound in spinal curvature measurement in scoliosis. METHODS: Transverse processes were landmarked along each vertebra using tracked ultrasound snapshots. The transverse process angle was used to determine the orientation of each vertebra. We tested our methodology on five patients in a local pediatric scoliosis clinic, comparing ultrasound to radiographic curvature measurements. RESULTS: Despite strong correlation between radiographic and ultrasound curvature angles in phantom studies, we encountered new challenges in the clinical setting. Our main challenge was differentiating transverse processes from ribs and other structures during landmarking. We observed up to 13° angle variability for a single vertebra and a 9.85° +/- 10.81° difference between ultrasound and radiographic Cobb angles for thoracic curvatures. Additionally, we were unable to visualize anatomical landmarks in the lumbar region where soft tissue depth was 25-35mm. In volunteers with large Cobb angles (greater than 40° thoracic and 60° lumbar), we observed spinal protrusions resulting in incomplete probe-skin contact and partial ultrasound images not suitable for landmarking. CONCLUSION: Spinal curvature measurement using tracked ultrasound is viable on phantom spine models. In the clinic, new challenges were encountered which must be resolved before a universal sonography protocol can be developed.
Variable Curvature Mirrors for ELT Laser Guide Star refocusing systems
NASA Astrophysics Data System (ADS)
Challita, Zalpha; Hugot, Emmanuel; Ferrari, Marc; Madec, Fabrice; Le Mignant, David; Cuby, Jean-Gabriel
2011-09-01
The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, LGS defocusing is one of the system issues that can be tackled using active refocusing mirrors such as Variable Curvature Mirrors (VCM). Indeed, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope, and induces a large defocusing at the LGS wave-front sensor focal plane. To compensate for that, we propose an original concept including a VCM specifically designed to keep a focused spot on the wave-front sensor: the mirror is made of a thin meniscus bend using a pressure applied on its back face. Due to the large defocusing, the LGS-VCM must be able to change its shape from F/12.5 to F/5, leading to more than 1 mm sag. The VCM benefits of a specific shape with a variable radial thickness distribution, allowing keeping an optical quality better than λ/5 over this very large range of deformation. The work presented here details the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Two prototypes have been manufactured to compare the real behaviour of the mirror and the simulations data. Results obtained on the prototypes show that the deformation of the VCM is very close to the simulation, and leads to a realistic concept.
Re-acceleration Model for Radio Relics with Spectral Curvature
NASA Astrophysics Data System (ADS)
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.
The formation of mountain range curvature by gravitational spreading
NASA Astrophysics Data System (ADS)
Copley, Alex
2012-10-01
This paper presents a mechanism by which mountain ranges can form curved range-fronts. Gravitational spreading of mountain ranges that have been thrust onto rigid lowlands will result in the formation of curvature, provided that enough gravity-driven flow occurs to dominate the shape of the topography. Whether this mechanism can operate during the lifetime of a given mountain range depends upon the viscosity of the range, the square of the along-strike length of the range, and the cube of the elevation of the range. The curvature of the southern edge of the Tibetan Plateau is consistent with formation by gravitational spreading provided that the viscosity is similar to that previously estimated using other, independent, methods. The low elevation and young age of the Zagros mountains mean that large-scale curvature has not had time to develop. The short along-strike extent and possibly low viscosity of the Sulaiman Ranges in Pakistan may have allowed the ranges to form their distinctive arcuate shape. The formation of range-front curvature plays an important role in controlling the tectonic evolution of the interiors of the ranges, with arc-parallel extension becoming progressively more important as range-front curvature develops.
Representation of tactile curvature in macaque somatosensory area 2
Connor, Charles E.; Hsiao, Steven S.
2013-01-01
Tactile shape information is elaborated in a cortical hierarchy spanning primary (SI) and secondary somatosensory cortex (SII). Indeed, SI neurons in areas 3b and 1 encode simple contour features such as small oriented bars and edges, whereas higher order SII neurons represent large curved contour features such as angles and arcs. However, neural coding of these contour features has not been systematically characterized in area 2, the most caudal SI subdivision in the postcentral gyrus. In the present study, we analyzed area 2 neural responses to embossed oriented bars and curved contour fragments to establish whether curvature representations are generated in the postcentral gyrus. We found that many area 2 neurons (26 of 112) exhibit clear curvature tuning, preferring contours pointing in a particular direction. Fewer area 2 neurons (15 of 112) show preferences for oriented bars. Because area 2 response patterns closely resembled SII patterns, we also compared area 2 and SII response time courses to characterize the temporal dynamics of curvature synthesis in the somatosensory system. We found that curvature representations develop and peak concurrently in area 2 and SII. These results reveal that transitions from orientation tuning to curvature selectivity in the somatosensory cortical hierarchy occur within SI rather than between SI and SII. PMID:23536717
Curvature properties of some class of warped product manifolds
NASA Astrophysics Data System (ADS)
Deszcz, Ryszard; Głogowska, Małgorzata; Jełowicki, Jan; Zafindratafa, Georges
2016-10-01
We prove that warped product manifolds with p-dimensional base, p = 1, 2, satisfy some pseudosymmetry type curvature conditions. These conditions are formed from the metric tensor g, the Riemann-Christoffel curvature tensor R, the Ricci tensor S and the Weyl conformal curvature C of the considered manifolds. The main result of the paper states that if p = 2 and the fiber is a semi-Riemannian space of constant curvature (when n is greater or equal to 5) then the (0, 6)-tensors R ṡ R - Q(S,R) and C ṡ C of such warped products are proportional to the (0, 6)-tensor Q(g,C) and the tensor C is a linear combination of some Kulkarni-Nomizu products formed from the tensors g and S. We also obtain curvature properties of this kind of quasi-Einstein and 2-quasi-Einstein manifolds, and in particular, of the Goedel metric, generalized spherically symmetric metrics and generalized Vaidya metrics.
Intermembrane Docking Reactions Are Regulated by Membrane Curvature
Kunding, Andreas H.; Mortensen, Michael W.; Christensen, Sune M.; Bhatia, Vikram K.; Makarov, Ivan; Metzler, Ralf; Stamou, Dimitrios
2011-01-01
The polymorphism of eukaryotic cellular membranes is a tightly regulated and well-conserved phenotype. Recent data have revealed important regulatory roles of membrane curvature on the spatio-temporal localization of proteins and in membrane fusion. Here we quantified the influence of membrane curvature on the efficiency of intermembrane docking reactions. Using fluorescence microscopy, we monitored the docking of single vesicle–vesicle pairs of different diameter (30–200 nm) and therefore curvature, as mediated by neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and streptavidin-biotin. Surprisingly, the intermembrane docking efficiency exhibited an ∼30–60 fold enhancement as a function of curvature. In comparison, synaptotagmin and calcium accelerate SNARE-mediated fusion in vitro by a factor of 2–10. To explain this finding, we formulated a biophysical model. On the basis of our findings, we propose that membrane curvature can regulate intermembrane tethering reactions and consequently any downstream process, including the fusion of vesicles and possibly viruses with their target membranes. PMID:22261058
Representation of tactile curvature in macaque somatosensory area 2.
Yau, Jeffrey M; Connor, Charles E; Hsiao, Steven S
2013-06-01
Tactile shape information is elaborated in a cortical hierarchy spanning primary (SI) and secondary somatosensory cortex (SII). Indeed, SI neurons in areas 3b and 1 encode simple contour features such as small oriented bars and edges, whereas higher order SII neurons represent large curved contour features such as angles and arcs. However, neural coding of these contour features has not been systematically characterized in area 2, the most caudal SI subdivision in the postcentral gyrus. In the present study, we analyzed area 2 neural responses to embossed oriented bars and curved contour fragments to establish whether curvature representations are generated in the postcentral gyrus. We found that many area 2 neurons (26 of 112) exhibit clear curvature tuning, preferring contours pointing in a particular direction. Fewer area 2 neurons (15 of 112) show preferences for oriented bars. Because area 2 response patterns closely resembled SII patterns, we also compared area 2 and SII response time courses to characterize the temporal dynamics of curvature synthesis in the somatosensory system. We found that curvature representations develop and peak concurrently in area 2 and SII. These results reveal that transitions from orientation tuning to curvature selectivity in the somatosensory cortical hierarchy occur within SI rather than between SI and SII.
Compensation for large tensor modes with iso-curvature perturbations in CMB anisotropies
Kawasaki, Masahiro; Yokoyama, Shuichiro E-mail: shu@icrr.u-tokyo.ac.jp
2014-05-01
Recently, BICEP2 has reported the large tensor-to-scalar ratio r = 0.2{sup +0.07}{sub −0.05} from the observation of the cosmic microwave background (CMB) B-mode at degree-scales. Since tensor modes induce not only CMB B-mode but also the temperature fluctuations on large scales, to realize the consistent temperature fluctuations with the Planck result we should consider suppression of scalar perturbations on corresponding large scales. To realize such a suppression, we consider anti-correlated iso-curvature perturbations which could be realized in the simple curvaton model.
Studies of the effects of curvature on dilution jet mixing
NASA Astrophysics Data System (ADS)
Holdeman, James D.; Srinivasan, Ram; Reynolds, Robert S.; White, Craig D.
1992-02-01
An analytical program was conducted using both three-dimensional numerical and empirical models to investigate the effects of transition liner curvature on the mixing of jets injected into a confined crossflow. The numerical code is of the TEACH type with hybrid numerics; it uses the power-law and SIMPLER algorithms, an orthogonal curvilinear coordinate system, and an algebraic Reynolds stress turbulence model. From the results of the numerical calculations, an existing empirical model for the temperature field downstream of single and multiple rows of jets injected into a straight rectangular duct was extended to model the effects of curvature. Temperature distributions, calculated with both the numerical and empirical models, are presented to show the effects of radius of curvature and inner and outer wall injection for single and opposed rows of cool dilution jets injected into a hot mainstream flow.
Numerical Estimation of the Curvature of Biological Surfaces
NASA Technical Reports Server (NTRS)
Todd, P. H.
1985-01-01
Many biological systems may profitably be studied as surface phenomena. A model consisting of isotropic growth of a curved surface from a flat sheet is assumed. With such a model, the Gaussian curvature of the final surface determines whether growth rate of the surface is subharmonic or superharmonic. These properties correspond to notions of convexity and concavity, and thus to local excess growth and local deficiency of growth. In biological models where the major factors controlling surface growth are intrinsic to the surface, researchers thus gained from geometrical study information on the differential growth undergone by the surface. These ideas were applied to an analysis of the folding of the cerebral cortex, a geometrically rather complex surface growth. A numerical surface curvature technique based on an approximation to the Dupin indicatrix of the surface was developed. A metric for comparing curvature estimates is introduced, and considerable numerical testing indicated the reliability of this technique.
Robust disparity estimation based on color monogenic curvature phase.
Zang, Di; Li, Jie; Zhang, Dongdong; Zhang, Junqi
2012-07-01
Disparity estimation for binocular images is an important problem for many visual tasks such as 3D environment reconstruction, digital hologram, virtual reality, robot navigation, etc. Conventional approaches are based on brightness constancy assumption to establish spatial correspondences between a pair of images. However, in the presence of large illumination variation and serious noisy contamination, conventional approaches fail to generate accurate disparity maps. To have robust disparity estimation in these situations, we first propose a model - color monogenic curvature phase to describe local features of color images by embedding the monogenic curvature signal into the quaternion representation. Then a multiscale framework to estimate disparities is proposed by coupling the advantages of the color monogenic curvature phase and mutual information. Both indoor and outdoor images with large brightness variation are used in the experiments, and the results demonstrate that our approach can achieve a good performance even in the conditions of large illumination change and serious noisy contamination. PMID:22772192
The role of membrane curvature for the wrapping of nanoparticles.
Bahrami, Amir Houshang; Lipowsky, Reinhard; Weikl, Thomas R
2016-01-14
Cellular internalization of nanoparticles requires the full wrapping of the nanoparticles by the cell membrane. This wrapping process can occur spontaneously if the adhesive interactions between the nanoparticles and the membranes are sufficiently strong to compensate for the cost of membrane bending. In this article, we show that the membrane curvature prior to wrapping plays a key role for the wrapping process, besides the size and shape of the nanoparticles that have been investigated in recent years. For membrane segments that initially bulge away from nanoparticles by having a mean curvature of the same sign as the mean curvature of the particle surface, we find strongly stable partially wrapped states that can prevent full wrapping. For membrane segments that initially bulge towards the nanoparticles, in contrast, partially wrapped states can constitute a significant energetic barrier for the wrapping process.
Waterfall field in hybrid inflation and curvature perturbation
Gong, Jinn-Ouk; Sasaki, Misao E-mail: misao@yukawa.kyoto-u.ac.jp
2011-03-01
We study carefully the contribution of the waterfall field to the curvature perturbation at the end of hybrid inflation. In particular we clarify the parameter dependence analytically under reasonable assumptions on the model parameters. After calculating the mode function of the waterfall field, we use the δN formalism and confirm the previously obtained result that the power spectrum is very blue with the index 4 and is absolutely negligible on large scales. However, we also find that the resulting curvature perturbation is highly non-Gaussian and hence we calculate the bispectrum. We find that the bispectrum is at leading order independent of momentum and exhibits its peak at the equilateral limit, though it is unobservably small on large scales. We also present the one-point probability distribution function of the curvature perturbation.
Characterization of inherent curvature in DNA lacking polyadenine runs.
McNamara, P T; Harrington, R E
1991-07-01
Sequence-directed DNA curvature is most commonly associated with AA dinucleotides in the form of polyadenine runs. We demonstrate inherent curvature in DNA which lacks AA/TT dinucleotides using the criteria of polyacrylamide gel mobility and efficiency of DNA cyclization. These studies are based upon two 21-base pair synthetic DNA fragments designed to exhibit fixed curvature according to deflections made to the helical axis by non-AA dinucleotide stacks. Repeats of these sequences display anomalously slow migration in polyacrylamide gels. Moreover, both sequences describe helical conformations that are closed into circles by DNA ligase at much smaller sizes than is typical of nondeformed DNA. Chemical cleavage of these DNA molecules with hydroxyl radical is also consistent with local variation in helical conformation at specific dinucleotide steps. PMID:1648100
Crystalline particle packings on constant mean curvature (Delaunay) surfaces
NASA Astrophysics Data System (ADS)
Bendito, Enrique; Bowick, Mark J.; Medina, Agustin; Yao, Zhenwei
2013-07-01
We investigate the structure of crystalline particle arrays on constant mean curvature (CMC) surfaces of revolution. Such curved crystals have been realized physically by creating charge-stabilized colloidal arrays on liquid capillary bridges. CMC surfaces of revolution, classified by Delaunay in 1841, include the 2-sphere, the cylinder, the vanishing mean curvature catenoid (a minimal surface), and the richer and less investigated unduloid and nodoid. We determine numerically candidate ground-state configurations for 1000 pointlike particles interacting with a pairwise-repulsive 1/r3 potential, with distance r measured in three-dimensional Euclidean space R3. We mimic stretching of capillary bridges by determining the equilibrium configurations of particles arrayed on a sequence of Delaunay surfaces obtained by increasing or decreasing the height at constant volume starting from a given initial surface, either a fat cylinder or a square cylinder. In this case, the stretching process takes one through a complicated sequence of Delaunay surfaces, each with different geometrical parameters, including the aspect ratio, mean curvature, and maximal Gaussian curvature. Unduloids, catenoids, and nodoids all appear in this process. Defect motifs in the ground state evolve from dislocations at the boundary to dislocations in the interior to pleats and scars in the interior and then isolated sevenfold disclinations in the interior as the capillary bridge narrows at the waist (equator) and the maximal (negative) Gaussian curvature grows. We also check theoretical predictions that the isolated disclinations are present in the ground state when the surface contains a geodesic disk with integrated Gaussian curvature exceeding -π/3. Finally, we explore minimal energy configurations on sets of slices of a given Delaunay surface, and we obtain configurations and defect motifs consistent with those seen in stretching.
Curvature of the spectral energy distributions of blazars
Chen, Liang
2014-06-20
In this paper, spectral energy distributions (SED) of both synchrotron and inverse Compton (IC) components of a sample of Fermi bright blazars are fitted by a log-parabolic law. The second-degree term of the log parabola measures the curvature of an SED. We find a statistically significant correlation between the synchrotron peak frequency and its curvature. This result is in agreement with the theoretical prediction and confirms previous studies that dealt with a single source with observations at various epochs or a small sample. If a broken power law is employed to fit the SED, the difference between the two spectral indices (i.e., |α{sub 2} – α{sub 1}|) can be considered a 'surrogate' of the SED curvature. We collect data from the literature and find a correlation between the synchrotron peak frequency and the spectral difference. We do not find a significant correlation between the IC peak frequency and its curvature, which may be caused by a complicated seed photon field. It is also found that the synchrotron curvatures are on average larger than those of IC curvatures, and there is no correlation between these two parameters. As suggested by previous works, both the log-parabolic law of the SED and the above correlation can be explained by statistical and/or stochastic particle accelerations. Based on a comparison of the slops of the correlation, our result seems to favor stochastic acceleration mechanisms and emission processes. Additional evidence, including SED modeling, particle acceleration simulation, and comparisons between some predictions and empirical relations/correlations, also seems to support the idea that the electron energy distribution (and/or synchrotron SED) may be log-parabolic.
Detonation wave velocity and curvature of brass encased PBXN-111
NASA Astrophysics Data System (ADS)
Forbes, J. W.; Lemar, E. R.
1996-05-01
Detonation velocities and wave front curvatures were measured for PBXN-111 charges encased in 5 mm thick brass tubes. In all the experiments (charge diameters from 19 to 47 mm) the brass case affected the detonation properties of PBXN-111. Steady detonation waves propagated in brass encased charges with diameters as small as 19 mm, which is about half of the unconfined failure diameter. The radii of curvature of the detonation waves at the center of the wave fronts ranged from 52 to 141 mm for charge diameters of 25 to 47 mm. The angles between the detonation wave fronts and the brass/charge interfaces were between 72 and 74 degrees.
Subaperture method for aspheric surface metrology using curvature data
NASA Astrophysics Data System (ADS)
Lee, SeongWon; Jeon, WooKyung; Park, TaeJin; Kim, ByoungChang; Kim, GeonHee; Hyun, SangWon; Kim, IJong; Kim, Seunghyun; Kim, ChangKyu; Lee, HyungSuk
2016-04-01
We present a profilometry for measuring aspheric surface, which determines the curvature from the sub-aperture topography along two orthogonal directions and then reconstructs the entire surface profile from the measured curvature data. The entire surface was divided into a number of sub-apertures with overlapping zones. Each sub-aperture was measured using white-light scanning interferometry to avoid any optical alignment error along an optical axis. Simulation studies are also presented based on the mathematical model. The proposed mathematical model was also experimentally tested on freeform surfaces using white-light scanning interferometry under deveolpment.
Effect of curvature on the backscattering from leaves
NASA Technical Reports Server (NTRS)
Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.
1988-01-01
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.
Effect of curvature on the backscattering from a leaf
NASA Technical Reports Server (NTRS)
Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.
1988-01-01
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross-section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.
Electron energy transport and magnetic curvature driven modes
Coppi, B.; Tang, W.M.
1984-10-01
A transport coefficient for anomalous electron thermal conduction is constructed on the basis of the so-called Principle of Profile Consistency. It is assumed that the relevant modes in plasma where a substantial fraction of the electron population is magnetically trapped produce magnetic reconnection at a microscopic level and are driven by the combined effects of the plasma pressure gradient and the magnetic field curvature. Consequently, the scaling for the electron energy confinement time exhibits a strongly favorable dependence on the radius of magnetic curvature.
NASA Astrophysics Data System (ADS)
Simon, F.; Zólyomi, V.; Pfeiffer, R.; Kuzmany, H.; Koltai, J.; Kürti, J.
2010-03-01
The defect-induced D line and its overtone are fundamental signatures in the Raman spectra of carbon nanomaterials. An analysis of these lines as a function of laser excitation energy is reported for double-walled carbon nanotubes where the inner tubes represent high-curvature nanotube species. From C13 substituted inner tubes it is demonstrated that the quasilinear relations between laser energy and line position (Raman dispersion) cross over unexpectedly for low-energy excitation for the inner and outer tube shells. The result is quantitatively explained by a curvature-induced phonon softening and first-principles calculations of the optical transition energies.
NASA Technical Reports Server (NTRS)
Bagshaw, S. L.; Cleland, R. E.
1990-01-01
Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates could be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower (Helianthus annuus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.
Jenkins, K.W.; Klein, M.; Chakraborty, N.; Cant, R.S.
2006-04-15
Strain rate and curvature effects on the propagation of turbulent premixed flame kernels have been investigated in the thin-reaction-zones regime using three-dimensional compressible direct numerical simulations (DNS) with single-step Arrhenius chemistry. An initially spherical laminar flame kernel is allowed to interact with the surrounding turbulent fluid motion to provide a propagating turbulent flame with a strong mean spherical curvature. The statistical behavior of the local displacement speed in response to strain and curvature is investigated in detail. The results demonstrate clearly that the mean curvature inherent to the flame kernel configuration has a significant influence on the propagation of the flame. It has been found that the mean density-weighted displacement speed rS{sub d} in the case of flame kernels varies significantly over the flame brush and remains different from r{sub 0}S{sub L} (where r{sub 0} is the reactant density and S{sub L} is laminar flame speed), unlike statistically planar flames. It is also shown that the magnitude of reaction progress variable gradient ||c| is negatively correlated with curvature in the case of flame kernels, in contrast to the weak correlation between ||c| and curvature in the case of planar flames. This correlation induces a net positive correlation between the combined reaction and normal diffusion components of displacement speed (S{sub r}+S{sub n}) and curvature in flame kernels, whereas the previous studies based on statistically planar flames did not observe any appreciable correlation between (S{sub r}+S{sub n}) and curvature. (author)
Equilibrium models of coronal loops that involve curvature and buoyancy
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Determination of light beam curvature in a rotating Luneburg lens
NASA Astrophysics Data System (ADS)
Gladyshev, V. O.; Bazleva, D. D.; Tereshin, A. A.; Gladysheva, T. M.
2016-09-01
We have determined the curvature of a beam of coherent electromagnetic radiation and its angular and linear deviation in a rotating microsatellite representing a Luneburg lens in the optical segment of accuracy augmentation for new-generation global navigation satellite systems.
Symmetric curvature descriptors for label-free analysis of DNA
NASA Astrophysics Data System (ADS)
Buzio, Renato; Repetto, Luca; Giacopelli, Francesca; Ravazzolo, Roberto; Valbusa, Ugo
2014-09-01
High-resolution microscopy techniques such as electron microscopy, scanning tunnelling microscopy and atomic force microscopy represent well-established, powerful tools for the structural characterization of adsorbed DNA molecules at the nanoscale. Notably, the analysis of DNA contours allows mapping intrinsic curvature and flexibility along the molecular backbone. This is particularly suited to address the impact of the base-pairs sequence on the local conformation of the strands and plays a pivotal role for investigations relating the inherent DNA shape and flexibility to other functional properties. Here, we introduce novel chain descriptors aimed to characterize the local intrinsic curvature and flexibility of adsorbed DNA molecules with unknown orientation. They consist of stochastic functions that couple the curvatures of two nanosized segments, symmetrically placed on the DNA contour. We show that the fine mapping of the ensemble-averaged functions along the molecular backbone generates characteristic patterns of variation that highlight all pairs of tracts with large intrinsic curvature or enhanced flexibility. We demonstrate the practical applicability of the method for DNA chains imaged by atomic force microscopy. Our approach paves the way for the label-free comparative analysis of duplexes, aimed to detect nanoscale conformational changes of physical or biological relevance in large sample numbers.
The influence of curvature on film cooling performance
NASA Astrophysics Data System (ADS)
Schwarz, S. G.; Goldstein, R. J.; Eckert, E. R. G.
1990-06-01
The effects of injection rate and strength of curvature on film cooling performance of gas injected through a row of holes on a convex surface is studied. Comparisons are made to film cooling of concave and flat surfaces. Three different relative strengths of curvature (ratio of radius of curvature to radius of injection hole), two density ratios (0.95 and 2.0), and a wide range of blowing rates (0.3 to 2.7) are considered. A foreign gas injection technique (mass transfer analogy) is used. The strength of curvature was controlled by varying the injection hole diameter. At low blowing rates, film cooling is more effective on the convex surface than on a flat or a concave surface. The cross stream pressure gradient present in curved flows tends to push the jet into the convex wall. As the injection rate is increased, normal and tangential jet momentum promote lift-off from the convex surface, thereby lowering performance. In contrast, previous studies show that a concave surface, tangential jet momentum, flow instabilities, and blockage improve performance on a concave surface as blowing rate is increased.
Directable weathering of concave rock using curvature estimation.
Jones, Michael D; Farley, McKay; Butler, Joseph; Beardall, Matthew
2010-01-01
We address the problem of directable weathering of exposed concave rock for use in computer-generated animation or games. Previous weathering models that admit concave surfaces are computationally inefficient and difficult to control. In nature, the spheroidal and cavernous weathering rates depend on the surface curvature. Spheroidal weathering is fastest in areas with large positive mean curvature and cavernous weathering is fastest in areas with large negative mean curvature. We simulate both processes using an approximation of mean curvature on a voxel grid. Both weathering rates are also influenced by rock durability. The user controls rock durability by editing a durability graph before and during weathering simulation. Simulations of rockfall and colluvium deposition further improve realism. The profile of the final weathered rock matches the shape of the durability graph up to the effects of weathering and colluvium deposition. We demonstrate the top-down directability and visual plausibility of the resulting model through a series of screenshots and rendered images. The results include the weathering of a cube into a sphere and of a sheltered inside corner into a cavern as predicted by the underlying geomorphological models.
Ultrasoft Electronics for Hyperelastic Strain, Pressure, and Direct Curvature Sensing
NASA Astrophysics Data System (ADS)
Majidi, Carmel; Kramer, Rebecca; Wood, Robert
2011-03-01
Progress in soft robotics, wearable computing, and programmable matter demands a new class of ultrasoft electronics for tactile control, contact detection, and deformation mapping. This next generation of sensors will remain electrically functional under extreme deformation without influencing the natural mechanics of the host system. Ultrasoft strain and pressure sensing has previously been demonstrated with elastomer sheets (eg. PDMS, silicone rubber) embedded with microchannels of conductive liquid (mercury, eGaIn). Building on these efforts, we introduce a novel method for direct curvature sensing that registers the location and intensity of surface curvature. An elastomer sheet is embedded with micropatterned cavities and microchannels of conductive liquid. Bending the elastomer or placing it on a curved surface leads to a change in channel cross-section and a corresponding change in its electrical resistance. In contrast to conventional methods of curvature sensing, this approach does not depend on semi-rigid components or differential strain measurement. Direct curvature sensing completes the portfolio of sensing elements required to completely map hyperelastic deformation for future soft robotics and computing. NSF MRSEC DMR-0820484.
Effect of Asymmetric Auxin Application on Helianthus Hypocotyl Curvature 1
Migliaccio, Fernando; Rayle, David L.
1989-01-01
Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution. PMID:11537460
Frustration and curvature - Glasses and the cholesteric blue phase
NASA Technical Reports Server (NTRS)
Sethna, J. P.
1983-01-01
An analogy is drawn between continuum elastic theories of the blue phase of cholesteric liquid crystals and recent theories of frustration in configurational glasses. Both involve the introduction of a lattice of disclination lines to relieve frustration; the frustration is due to an intrinsic curvature in the natural form of parallel transport. A continuum theory of configurational glasses is proposed.
Wormhole geometries supported by a nonminimal curvature-matter coupling
Garcia, Nadiezhda Montelongo; Lobo, Francisco S. N.
2010-11-15
Wormhole geometries in curvature-matter coupled modified gravity are explored, by considering an explicit nonminimal coupling between an arbitrary function of the scalar curvature, R, and the Lagrangian density of matter. It is the effective stress-energy tensor containing the coupling between matter and the higher order curvature derivatives that is responsible for the null energy condition violation, and consequently for supporting the respective wormhole geometries. The general restrictions imposed by the null energy condition violation are presented in the presence of a nonminimal R-matter coupling. Furthermore, obtaining exact solutions to the gravitational field equations is extremely difficult due to the nonlinearity of the equations, although the problem is mathematically well defined. Thus, we outline several approaches for finding wormhole solutions, and deduce an exact solution by considering a linear R nonmiminal curvature-matter coupling and by considering an explicit monotonically decreasing function for the energy density. Although it is difficult to find exact solutions of matter threading the wormhole satisfying the energy conditions at the throat, an exact solution is found where the nonminimal coupling does indeed minimize the violation of the null energy condition of normal matter at the throat.
Compound Schmidt telescope designs with nonzero Petzval curvatures.
Sigler, R D
1975-09-01
A variety of aplanatic and anastigmatic Schmidt Cassegrain and Schmidt Gregorian telescope designs with nonzero Petzval curvatures are investigated. Relaxing the Petzval constraint permits the development of high performance photo/visual instruments which are capable of diffraction limited imaging over fields of view of 1-2 degrees . PMID:20155004
Simple partitions of a hyperbolic plane of positive curvature
Romakina, Lyudmila N
2012-09-30
We construct special monohedral isotropic partitions with symmetries of the hyperbolic plane H of positive curvature with a simple 4-contour as a cell. An analogue of mosaic in these partitions called a tiling is introduced. Also we consider some fractal tilings. The existence of band tilings in each homological series with code (m, n) is proved. Bibliography: 14 titles.
Negative voltage bandgap reference with multilevel curvature compensation technique
NASA Astrophysics Data System (ADS)
Xi, Liu; Qian, Liu; Xiaoshi, Jin; Yongrui, Zhao; Lee, Jong-Ho
2016-05-01
A novel high-order curvature compensation negative voltage bandgap reference (NBGR) based on a novel multilevel compensation technique is introduced. Employing an exponential curvature compensation (ECC) term with many high order terms in itself, in a lower temperature range (TR) and a multilevel curvature compensation (MLCC) term in a higher TR, a flattened and better effect of curvature compensation over the TR of 165 °C (‑40 to 125 °C) is realised. The MLCC circuit adds two convex curves by using two sub-threshold operated NMOS. The proposed NBGR implemented in the Central Semiconductor Manufacturing Corporation (CSMC) 0.5 μm BCD technology demonstrates an accurate voltage of ‑1.183 V with a temperature coefficient (TC) as low as 2.45 ppm/°C over the TR of 165 °C at a ‑5.0 V power supply; the line regulation is 3 mV/V from a ‑5 to ‑2 V supply voltage. The active area of the presented NBGR is 370 × 180 μm2. Project supported by the Fund of Liaoning Province Education Department (No. L2013045).
Effect of asymmetric auxin application on Helianthus hypocotyl curvature
NASA Technical Reports Server (NTRS)
Migliaccio, F.; Rayle, D. L.
1989-01-01
Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution.
Curvature and torsion estimation for coronary-artery motion analysis
NASA Astrophysics Data System (ADS)
Medina, Ruben; Wahle, Andreas; Olszewski, Mark E.; Sonka, Milan
2004-04-01
The dynamics of curvature and torsion are important for the geometric description of arteries and for the distribution of accumulating plaque. In this research, two methods for estimating curvature and torsion are analyzed with respect to their accuracy. The first method is based on estimating the curvature and torsion of the artery centerline using the Fourier transform. Since the centerline always represents an open curve, extensions ensuring a minimal spectral energy are added on both ends to obtain a closed curve suitable for Fourier analysis. The second method has been previously used for analyzing the motion of coronary arteries and is based on the least squares fitting of a cubic polynomial to the centerline of the artery. Validation is performed using two mathematical, time-varying phantoms as well as 4-D (3-D plus time) in-vivo data of coronary arteries reconstructed by fusion of biplane angiograms and intravascular ultrasound images. Results show that both methods are accurate for estimating curvature and torsion, and that both methods have average errors below 2.15%.
Geometric optics radome analysis wall incorporating effects of wall curvature
NASA Astrophysics Data System (ADS)
Kozakoff, Dennis J.
1993-07-01
In this research, a principal unmodeled error contributor in radome analysis is identified as the local plane approximation at the ray intercept point. An improved approach to modeling and computing the effects of the radome wall was developed which improves the radome wall transmission wall analysis in three respects: use of surface integration, utilization of a divergence factor (DF) to account for wall curvature, and incorporation of the effects of multiple refraction (MR). Modeling an incident plane wave on an external reference plane as an ensemble of Huygen's sources, geometric optics is used to trace the fields from the reference plane through the radome wall to a receiving monopulse antenna, where the wall transmissions on each ray are collected. The fact that the integration of a bundle of rays through the radome wall, as opposed to a single ray, more densely samples the curvature variation results in a more robust model. A DF derived from Snell's law for spherical shells accounts for the local wall curvature at the ray intercept point. To validate the approach, a microwave measurement setup was assembled around a network analyzer. Swept frequency data were obtained for similar monolithic wall dielectric panels but with different wall curvatures. Comparisons were then with measured data and the predictions of the model herein.
Analysis of models for curvature driven motion of interfaces
NASA Astrophysics Data System (ADS)
Swartz, Drew E.
Interfacial energies frequently appear in models arising in materials science and engineering. To dissipate energy in these systems, the interfaces will often move by a curvature dependent velocity. The present work details the mathematical analysis of some models for curvature dependent motion of interfaces. In particular we focus on two types, thresholding schemes and phase field models. With regard to thresholding schemes, we give a new proof of the convergence of the Merriman-Bence-Osher thresholding algorithm to motion by mean curvature. This new proof does not rely on the scheme satisfying a comparison principle. The technique shows promise in proving the convergence of thresholding schemes for more general motions, such as fourth-order motions and motions of higher codimension interfaces. The application of the proof technique to these more general schemes is discussed, along with rigorous consistency estimates. With regard to phase-field models, we examine the L 2-gradient flow of a second order gradient model for phase transitions, introduced by Fonseca and Mantegazza. In the case of radial symmetry we demonstrate that the diffuse interfacial dynamics converge to motion by mean curvature as the width of the interface decreases to zero. This is in accordance with the first-order Allen-Cahn model for phase transitions. But unlike the Allen-Cahn model, the gradient flow for the Fonseca-Mantegazza model is a fourth-order parabolic PDE. This creates new and novel difficulties in its analysis.
On the Surprising Salience of Curvature in Grouping by Proximity
ERIC Educational Resources Information Center
Strother, Lars; Kubovy, Michael
2006-01-01
The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the…
Focus retrocollimated interferometry for long-radius-of-curvature measurement
NASA Astrophysics Data System (ADS)
Xiang, Yang
2001-12-01
Focus retrocollimated interferometry is described for measuring long radius of curvature (>1 m), and achievable accuracy is discussed. It is shown that this method can be applied to both concave and convex spherical surfaces and can provide measurement to accuracy of 0.01-0.1%.
Compound Schmidt telescope designs with nonzero Petzval curvatures.
Sigler, R D
1975-09-01
A variety of aplanatic and anastigmatic Schmidt Cassegrain and Schmidt Gregorian telescope designs with nonzero Petzval curvatures are investigated. Relaxing the Petzval constraint permits the development of high performance photo/visual instruments which are capable of diffraction limited imaging over fields of view of 1-2 degrees .
Effect of track asymmetry and curvature on shingle writing scheme
NASA Astrophysics Data System (ADS)
Liu, Feng; Li, Shaoping; Bai, Daniel; Mendez, Hector; Pan, Tao; Han, Dehua; Mao, Sining
2011-04-01
Written transition curvature in perpendicular magnetic recording is generally understood to result in increased transition jitter noise and degraded signal to noise ratio or byte error rate (BER) performance. For the shingle writing scheme, asymmetry or curvature in written tracks is considered inherent due to the erasure and track edge writing characteristics. It is proposed that such a track asymmetry is more prominent at high track density/smaller track pitch recording conditions. In this report we present spin stand experimental results to study the effect of the possible track asymmetry or curvature by shingle writing and reading back in different skews. By comparing shingle writing BER bathtub profiles in different writing skew conditions 0°, +/-2°, +/-4°, +/-6°, the effect of varying shingle track asymmetry and curvature is analyzed via subsequent skewed reading process. The shingle writing BER bathtub profiles as well as the read back amplitude cross track profile are generally symmetric upon one sided erasure at different track pitches. We found that the 0° skew writing and reading process provides both the maximum BER and amplitude.
The flow curvature method applied to canard explosion
NASA Astrophysics Data System (ADS)
Ginoux, Jean-Marc; Llibre, Jaume
2011-11-01
The aim of this work is to establish that the bifurcation parameter value leading to a canard explosion in dimension 2 obtained by the so-called geometric singular perturbation method can be found according to the flow curvature method. This result will be then exemplified with the classical Van der Pol oscillator.
Quasi-Maxwell interpretation of the spin-curvature coupling
NASA Astrophysics Data System (ADS)
Natário, José
2007-09-01
We write the Mathisson-Papapetrou equations of motion for a spinning particle in a stationary spacetime using the quasi-Maxwell formalism and give an interpretation of the coupling between spin and curvature. The formalism is then used to compute equilibrium positions for spinning particles in the NUT spacetime.
Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy
NASA Astrophysics Data System (ADS)
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
From M-theory higher curvature terms to α‧ corrections in F-theory
NASA Astrophysics Data System (ADS)
Grimm, Thomas W.; Keitel, Jan; Savelli, Raffaele; Weissenbacher, Matthias
2016-02-01
We perform a Kaluza-Klein reduction of eleven-dimensional supergravity on a Calabi-Yau fourfold including terms quartic and cubic in the Riemann curvature and determine the induced corrections to the three-dimensional two-derivative N = 2 effective action. We focus on the effective Einstein-Hilbert term and the kinetic terms for vectors. Dualizing the vectors into scalars, we derive the resulting Kähler potential and complex coordinates. The classical expressions for the Kähler coordinates are non-trivially modified by terms containing the third Chern form of the background Calabi-Yau fourfold, while the functional form of the Kähler potential is shown to be uncorrected. We omit terms proportional to the non-harmonic part of the third Chern form. For elliptically fibered Calabi-Yau fourfolds the corrections can be uplifted to a four-dimensional F-theory compactification. We argue that also the four-dimensional N = 1 Kähler coordinates receive non-trivial corrections. We find a simple expression for the induced corrections for different Abelian and non-Abelian seven-brane configurations by scanning over many Calabi-Yau fourfolds with resolved singularities. The interpretation of this expression leads us to conjecture that the higher-curvature corrections correspond to α‧2 corrections that arise from open strings at the self-intersection of seven-branes.
Phantomlike behavior in a brane-world model with curvature effects
Bouhmadi-Lopez, Mariam; Moniz, Paulo Vargas
2008-10-15
Recent observational evidence seems to allow the possibility that our Universe may currently be under a dark energy effect of a phantom nature. A suitable effective phantom fluid behavior can emerge in brane cosmology; in particular, within the normal non-self-accelerating Dvali-Gabadadze-Porrati branch, without any exotic matter and due to curvature effects from induced gravity. The phantomlike behavior is based in defining an effective energy density that grows as the brane expands. This effective description breaks down at some point in the past when the effective energy density becomes negative and the effective equation of state parameter blows up. In this paper we investigate if the phantomlike regime can be enlarged by the inclusion of a Gauss-Bonnet (GB) term into the bulk. The motivation is that such a GB component would model additional curvature effects on the brane setting. More precisely, our aim is to determine if the GB term, dominating and modifying the early behavior of the brane universe, may eventually extend the regime of validity of the phantom mimicry on the brane. However, we show that the opposite occurs: the GB effect seems instead to induce a breakdown of the phantomlike behavior at an even smaller redshift.
Stimulation of root elongation and curvature by calcium.
Takahashi, H; Scott, T K; Suge, H
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms. PMID:11537880
Stimulation of root elongation and curvature by calcium
NASA Technical Reports Server (NTRS)
Takahashi, H.; Scott, T. K.; Suge, H.
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms.
Detonation wave velocity and curvature of brass encased PBXN-111
Forbes, J.W.; Lemar, E.R.
1996-05-01
Detonation velocities and wave front curvatures were measured for PBXN-111 charges encased in 5 mm thick brass tubes. In all the experiments (charge diameters from 19 to 47 mm) the brass case affected the detonation properties of PBXN-111. Steady detonation waves propagated in brass encased charges with diameters as small as 19 mm, which is about half of the unconfined failure diameter. The radii of curvature of the detonation waves at the center of the wave fronts ranged from 52 to 141 mm for charge diameters of 25 to 47 mm. The angles between the detonation wave fronts and the brass/charge interfaces were between 72 and 74 degrees. {copyright} {ital 1996 American Institute of Physics.}
Turbulent boundary layers with large streamline curvature effects
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
1978-01-01
It has been shown that turbulent flows are greatly affected by streamline curvature. In spite of this and the fact that curved shear flows are frequently encountered in engineering applications, the predictions of such flows are relatively less developed than the predictions of two-dimensional plane flows. Recently, various attempts were made by different investigators; however, their methods are only successful when the product of the boundary layer thickness to the local surface curvature is approximately 0.05. The present paper investigates the more general case where this product is in the range from 0.1 to 0.5. Results show that the calculated boundary-layer characteristics for arbitrary free stream conditions are in good agreement with measurements.
Membrane curvature in cell biology: An integration of molecular mechanisms.
Jarsch, Iris K; Daste, Frederic; Gallop, Jennifer L
2016-08-15
Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists.
Generating ekpyrotic curvature perturbations before the big bang
Lehners, Jean-Luc; Turok, Neil; McFadden, Paul; Steinhardt, Paul J.
2007-11-15
We analyze a general mechanism for producing a nearly scale-invariant spectrum of cosmological curvature perturbations during a contracting phase preceding a big bang, which can be entirely described using 4D effective field theory. The mechanism, based on first producing entropic perturbations and then converting them to curvature perturbations, can be naturally incorporated in cyclic and ekpyrotic models in which the big bang is modeled as a brane collision, as well as other types of cosmological models with a pre-big bang phase. We show that the correct perturbation amplitude can be obtained and that the spectral tilt n{sub s} tends to range from slightly blue to red, with 0.97
Curvature effects on carbon nanomaterials: Exohedral versus endhohedral supercapacitors
Huang, J; Sumpter, B. G.; Meunier, V.; Yushin, G.; Portet, C.; Gogotsi, Y.
2011-01-31
Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.
Curvature effects in carbon nanomaterials: Exohedral versus endohedral supercapacitors
Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Gogotsi, Yury G.; Yushin, Gleb; Portet, Cristelle
2010-01-01
Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.
Spontaneous curvature in chiral polar filaments near interfaces
NASA Astrophysics Data System (ADS)
Olmsted, Peter D.; Riley, Emily E.; Jordens, Sophia; Usov, Ivan; Isa, Lucio; Mezzenga, Raffaele
2015-03-01
Chiral filaments (actin, DNA, alpha helical strands, ...) are ubiquitous in biology, and they frequently come into contact with interfaces or inhomogeneous environments, either in biology (e.g. actin on membranes) or use and processing of biomaterials (fibrils at solvent boundaries or nanoparticle surfaces). Recent experiments have shown that amyloid fibrils can develop unusual curvatures at the air-water interface. Here we show that spontaneous curvature follows, on symmetry grounds, for chiral polar filaments placed in inhomgeneous environments such as near surfaces. We demonstrate this for simple model surface-fibril interactions, and discuss some of the implications. Financial support is acknowledged from: ETH Zurich (ETHIIRA TH 32-1), SNF (2-77002-11), and SNSF (IZK072_141955, PP00P2_144646/1, PZ00P2_142532/1).
DNA Origami with Complex Curvatures in Three-Dimensional Space
Han, Dongran; Pal, Suchetan; Nangreave, Jeanette; Deng, Zhengtao; Liu, Yan; Yan, Hao
2011-04-14
We present a strategy to design and construct self-assembling DNA nanostructures that define intricate curved surfaces in three-dimensional (3D) space using the DNA origami folding technique. Double-helical DNA is bent to follow the rounded contours of the target object, and potential strand crossovers are subsequently identified. Concentric rings of DNA are used to generate in-plane curvature, constrained to 2D by rationally designed geometries and crossover networks. Out-of-plane curvature is introduced by adjusting the particular position and pattern of crossovers between adjacent DNA double helices, whose conformation often deviates from the natural, B-form twist density. A series of DNA nanostructures with high curvature—such as 2D arrangements of concentric rings and 3D spherical shells, ellipsoidal shells, and a nanoflask—were assembled.
The role of gravity in leaf blade curvatures
NASA Technical Reports Server (NTRS)
Hayes, A. B.
1984-01-01
In the past year we have gained useful information on several aspects of leaf blade growth. The most important observations are as follows: The C(14)-1AA moves preferentially in a gravipositive dorsiventral direction through the blade. This movement is inhibited by inversion of the blade. The responding cells in leaf blade hyponasty are in the lower epidermis and bundle sheath cells. Two additional responses in the leaf were characterized. In addition to blade curvature, the leaf shows petiole curvature and changes in the liminal angle subtended by the pulvinus. Ethylene production was studied under a number of conditions. The blade, rather than the petiole or pulvinus, is the principal site of auxin-promoted ethylene synthesis. The effects of a variety of agents on the blade, including gibberellic acid, abscisic acid, vanadate, low pH buffers, and blue light were reviewed.
Constructing Graphs over with Small Prescribed Mean-Curvature
NASA Astrophysics Data System (ADS)
Carley, Holly; Kiessling, Michael K.-H.
2015-12-01
In this paper nonlinear Hodge theory and Banach algebra estimates are employed to construct a convergent series expansion which solves the prescribed mean curvature equation for n-dimensional hypersurfaces in (+ sign) and (- sign) which are graphs of a smooth function , and whose mean curvature function H is α-Hölder continuous and integrable, with small norm. The radius of convergence is estimated explicitly from below. Our approach is inspired by, and applied to, the Maxwell-Born-Infeld theory of electromagnetism in , for which our method yields the first systematic way of explicitly computing the electrostatic potential for regular charge densities and small Born parameter, with explicit error estimates at any order of truncation of the series. In particular, our results level the ground for a controlled computation of Born-Infeld effects on the Hydrogen spectrum.
NASA Astrophysics Data System (ADS)
Reeves, Matthew; Stratford, Kevin; Thijssen, Job H. J.
Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity $L$ (average interfacial separation) of the bijel is controlled by varying the radius ($r$) and volume fraction ($\\phi$) of the colloids ($L \\propto r/\\phi$). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by $L$ alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.
Membrane curvature in cell biology: An integration of molecular mechanisms.
Jarsch, Iris K; Daste, Frederic; Gallop, Jennifer L
2016-08-15
Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists. PMID:27528656
On M-theory fourfold vacua with higher curvature terms
NASA Astrophysics Data System (ADS)
Grimm, Thomas W.; Pugh, Tom G.; Weißenbacher, Matthias
2015-04-01
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.
Control of repeat protein curvature by computational protein design
Park, Keunwan; Shen, Betty W.; Parmeggiani, Fabio; Huang, Po-Ssu; Stoddard, Barry L.; Baker, David
2014-01-01
Shape complementarity is an important component of molecular recognition, and the ability to precisely adjust the shape of a binding scaffold to match a target of interest would greatly facilitate the creation of high affinity protein reagents and therapeutics. Here we describe a general approach to control the shape of the binding surface on repeat protein scaffolds, and apply it to leucine rich repeat proteins. First, a set of self-compatible building block modules are designed that when polymerized each generate surfaces with unique but constant curvatures. Second, a set of junction modules that connect the different building blocks are designed. Finally, new proteins with custom designed shapes are generated by appropriately combining building block and junction modules. Crystal structures of the designs illustrate the power of the approach in controlling repeat protein curvature. PMID:25580576
Preference for Curvature: A Historical and Conceptual Framework
Gómez-Puerto, Gerardo; Munar, Enric; Nadal, Marcos
2016-01-01
That people find curved contours and lines more pleasurable than straight ones is a recurrent observation in the aesthetic literature. Although such observation has been tested sporadically throughout the history of scientific psychology, only during the last decade has it been the object of systematic research. Recent studies lend support to the idea that human preference for curved contours is biologically determined. However, it has also been argued that this preference is a cultural phenomenon. In this article, we review the available evidence, together with different attempts to explain the nature of preference for curvature: sensoriomotor-based and valuation-based approaches. We also argue that the lack of a unifying framework and clearly defined concepts might be undermining our efforts towards a better understanding of the nature of preference for curvature. Finally, we point to a series of unresolved matters as the starting point to further develop a consistent research program. PMID:26793092
On the breakdown of the curvature perturbation ζ during reheating
NASA Astrophysics Data System (ADS)
Tarman Algan, Merve; Kaya, Ali; Seyma Kutluk, Emine
2015-04-01
It is known that in single scalar field inflationary models the standard curvature perturbation ζ, which is supposedly conserved at superhorizon scales, diverges during reheating at times 0dot phi=, i.e. when the time derivative of the background inflaton field vanishes. This happens because the comoving gauge 0varphi=, where varphi denotes the inflaton perturbation, breaks down when 0dot phi=. The issue is usually bypassed by averaging out the inflaton oscillations but strictly speaking the evolution of ζ is ill posed mathematically. We solve this problem in the free theory by introducing a family of smooth gauges that still eliminates the inflaton fluctuation varphi in the Hamiltonian formalism and gives a well behaved curvature perturbation ζ, which is now rigorously conserved at superhorizon scales. At the linearized level, this conserved variable can be used to unambiguously propagate the inflationary perturbations from the end of inflation to subsequent epochs. We discuss the implications of our results for the inflationary predictions.
Effect of nano-scale curvature on the intrinsic blood coagulation system.
Kushida, Takashi; Saha, Krishnendu; Subramani, Chandramouleeswaran; Nandwana, Vikas; Rotello, Vincent M
2014-11-01
The intrinsic coagulation activity of silica nanoparticles strongly depends on their surface curvature. Nanoparticles with higher surface curvature do not denature blood coagulation factor XII on its surface, providing a coagulation 'silent' surface, while nanoparticles with lower surface curvature show denaturation and concomitant coagulation.
Impact of local vessel curvature on the circumferential plaque distribution in coronary arteries
NASA Astrophysics Data System (ADS)
Wahle, Andreas; Medina, Ruben; Braddy, Kathleen C.; Fox, James M.; Brennan, Theresa M. H.; Lopez, John J.; Rossen, James D.; Sonka, Milan
2003-05-01
Plaque in native coronary arteries is hypothesized to accumulate more likely along the inner curvature of a vessel segment as compared to its outer curvature. This behavior is likely associated with differences in local shear stress, which tends to be lower on the inner bend of a curved vessel than on the outer bend. The reported in-vivo study evaluated how the circumferential plaque distribution depends on local vessel curvature in coronaries from a limited set of 12 patients. Geometrically correct models of the vessel segments were generated utilizing fusion between biplane angiography and intravascular ultrasound. The plaque thickness was derived from the 3-D borders of the lumen/plaque and media/adventitia interfaces. Within each frame, plaque thickness was classified into "below-average" and "above-average" regions. A local curvature index was defined for each point: A positive value indicates the "inner" curvature, a negative value the "outer" curvature, with the magnitude determined from differential geometry. In the majority of the examined vessels, regions of "below-average/outer-curvature" and "above-average/inner-curvature" combined outweighed the "below-average/inner-curvature" and "above-average/outer-curvature" regions. The ratio increased with the threshold to exclude lower-curvature regions, confirming the hypothesis that plaque is more likely to accumulate on the luminal surface along the inner curvature of the coronary segment.
A three-dimensional validation of crack curvature in muscovite mica
J. C. Hill; J. W. Foulk III; P. A. Klein; E. P. Chen
2001-01-07
Experimental and computational efforts focused on characterizing crack tip curvature in muscovite mica. Wedge-driven cracks were propagated under monochromatic light. Micrographs verified the subtle curvature of the crack front near the free surface. A cohesive approach was employed to model mixed-mode fracture in a three-dimensional framework. Finite element calculations captured the crack curvature observed in experiment.
Chowdhury, Debashree Basu, B.
2013-02-15
We have studied the spin dependent force and the associated momentum space Berry curvature in an accelerating system. The results are derived by taking into consideration the non-relativistic limit of a generally covariant Dirac equation with an electromagnetic field present, where the methodology of the Foldy-Wouthuysen transformation is applied to achieve the non-relativistic limit. Spin currents appear due to the combined action of the external electric field, the crystal field and the induced inertial electric field via the total effective spin-orbit interaction. In an accelerating frame, the crucial role of momentum space Berry curvature in the spin dynamics has also been addressed from the perspective of spin Hall conductivity. For time dependent acceleration, the expression for the spin polarization has been derived. - Highlights: Black-Right-Pointing-Pointer We study the effect of acceleration on the Dirac electron in the presence of an electromagnetic field, where the acceleration induces an electric field. Black-Right-Pointing-Pointer Spin currents appear due to the total effective electric field via the total spin-orbit interaction. Black-Right-Pointing-Pointer We derive the expression for the spin dependent force and the spin Hall current, which is zero for a particular acceleration. Black-Right-Pointing-Pointer The role of the momentum space Berry curvature in an accelerating system is discussed. Black-Right-Pointing-Pointer An expression for the spin polarization for time dependent acceleration is derived.
Jao, Christine C.; Hegde, Balachandra G.; Gallop, Jennifer L.; Hegde, Prabhavati B.; McMahon, Harvey T.; Haworth, Ian S.; Langen, Ralf
2010-01-01
Control of membrane curvature is required in many important cellular processes, including endocytosis and vesicular trafficking. Endophilin is a bin/amphiphysin/rvs (BAR) domain protein that induces vesicle formation by promotion of membrane curvature through membrane binding as a dimer. Using site-directed spin labeling and EPR spectroscopy, we show that the overall BAR domain structure of the rat endophilin A1 dimer determined crystallographically is maintained under predominantly vesiculating conditions. Spin-labeled side chains on the concave surface of the BAR domain do not penetrate into the acyl chain interior, indicating that the BAR domain interacts only peripherally with the surface of a curved bilayer. Using a combination of EPR data and computational refinement, we determined the structure of residues 63–86, a region that is disordered in the crystal structure of rat endophilin A1. Upon membrane binding, residues 63–75 in each subunit of the endophilin dimer form a slightly tilted, amphipathic α-helix that directly interacts with the membrane. In their predominant conformation, these helices are located orthogonal to the long axis of the BAR domain. In this conformation, the amphipathic helices are positioned to act as molecular wedges that induce membrane curvature along the concave surface of the BAR domain. PMID:20418375
CURVATURE-DRIFT INSTABILITY FAILS TO GENERATE PULSAR RADIO EMISSION
Kaganovich, Alexander; Lyubarsky, Yuri
2010-10-01
The curvature-drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing the propagation of short electromagnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity; therefore, this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.
Global and local curvature in density functional theory
NASA Astrophysics Data System (ADS)
Zhao, Qing; Ioannidis, Efthymios I.; Kulik, Heather J.
2016-08-01
Piecewise linearity of the energy with respect to fractional electron removal or addition is a requirement of an electronic structure method that necessitates the presence of a derivative discontinuity at integer electron occupation. Semi-local exchange-correlation (xc) approximations within density functional theory (DFT) fail to reproduce this behavior, giving rise to deviations from linearity with a convex global curvature that is evidence of many-electron, self-interaction error and electron delocalization. Popular functional tuning strategies focus on reproducing piecewise linearity, especially to improve predictions of optical properties. In a divergent approach, Hubbard U-augmented DFT (i.e., DFT+U) treats self-interaction errors by reducing the local curvature of the energy with respect to electron removal or addition from one localized subshell to the surrounding system. Although it has been suggested that DFT+U should simultaneously alleviate global and local curvature in the atomic limit, no detailed study on real systems has been carried out to probe the validity of this statement. In this work, we show when DFT+U should minimize deviations from linearity and demonstrate that a "+U" correction will never worsen the deviation from linearity of the underlying xc approximation. However, we explain varying degrees of efficiency of the approach over 27 octahedral transition metal complexes with respect to transition metal (Sc-Cu) and ligand strength (CO, NH3, and H2O) and investigate select pathological cases where the delocalization error is invisible to DFT+U within an atomic projection framework. Finally, we demonstrate that the global and local curvatures represent different quantities that show opposing behavior with increasing ligand field strength, and we identify where these two may still coincide.
Relative stability and local curvature analysis in carbon nanotori
NASA Astrophysics Data System (ADS)
Chuang, Chern; Guan, Jie; Witalka, David; Zhu, Zhen; Jin, Bih-Yaw; Tománek, David
2015-04-01
We introduce a concise formalism to characterize nanometer-sized tori based on carbon nanotubes and to determine their stability by combining ab initio density functional calculations with a continuum elasticity theory approach that requires only shape information. We find that the high strain energy in nanotori containing only hexagonal rings is significantly reduced in nanotori containing also other polygons. Our approach allows to determine local curvature and link it to local strain energy, which is correlated with local stability and chemical reactivity.
Digital elevation model visibility including Earth's curvature and atmosphere refraction
NASA Astrophysics Data System (ADS)
Santossilva, Ewerton; Vieiradias, Luiz Alberto
1990-03-01
There are some instances in which the Earth's curvature and the atmospheric refraction, optical or electronic, are important factors when digital elevation models are used for visibility calculations. This work deals with this subject, suggesting a practical approach to solve this problem. Some examples, from real terrain data, are presented. The equipment used was an IBM-PC like computer with a SITIM graphic card.
Intrinsic DNA curvature of double-crossover tiles
NASA Astrophysics Data System (ADS)
Kim, Seungjae; Kim, Junghoon; Qian, Pengfei; Shin, Jihoon; Amin, Rashid; Ahn, Sang Jung; LaBean, Thomas H.; Kim, Moon Ki; Park, Sung Ha
2011-06-01
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.
Różycki, Bartosz; Lipowsky, Reinhard
2016-08-21
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
NASA Astrophysics Data System (ADS)
RóŻycki, Bartosz; Lipowsky, Reinhard
2016-08-01
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
Berry Curvature and Chiral Plasmons in Massive Dirac Materials
NASA Astrophysics Data System (ADS)
Song, Justin; Rudner, Mark
2015-03-01
In the semiclassical model of carrier dynamics, quasiparticles are described as nearly free electrons with modified characteristics modified characteristics such as effective masses which may differ significantly from those of an electron in vacuum. In addition to being influenced by external electric and magnetic fields, the trajectories of electrons in topological materials are also affected by the presence of an interesting quantum mechanical field - the Berry curvature - which is responsible for a number of anomalous transport phenomena recently observed in Dirac materials including G/hBN, and MoS2. Here we discuss how Berry curvature can affect the collective behavior of electrons in these systems. In particular, we show that the collective electronic excitations in metallic massive Dirac materials can feature a chirality even in the absence of an applied magnetic field. The chirality of these plasmons arises from the Berry curvature of the massive Dirac bands. The corresponding dispersion is split between left- and right-handed modes. We also discuss experimental manifestations.
Formation of Curvature Subunit of Carbon in Combustion.
Wu, Xin-Zhou; Yao, Yang-Rong; Chen, Miao-Miao; Tian, Han-Rui; Xiao, Jun; Xu, Yun-Yan; Lin, Min-Song; Abella, Laura; Tian, Cheng-Bo; Gao, Cong-Li; Zhang, Qianyan; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun
2016-08-01
Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5-C18 that are online produced in the flame of acetylene-cyclopentadiene-oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process.
Encoding Gaussian curvature in glassy and elastomeric liquid crystal solids
Mostajeran, Cyrus; Ware, Taylor H.; White, Timothy J.
2016-01-01
We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains. PMID:27279777
Voronoi-Based Curvature and Feature Estimation from Point Clouds.
Mérigot, Quentin; Ovsjanikov, Maks; Guibas, Leonidas
2011-06-01
We present an efficient and robust method for extracting curvature information, sharp features, and normal directions of a piecewise smooth surface from its point cloud sampling in a unified framework. Our method is integral in nature and uses convolved covariance matrices of Voronoi cells of the point cloud which makes it provably robust in the presence of noise. We show that these matrices contain information related to curvature in the smooth parts of the surface, and information about the directions and angles of sharp edges around the features of a piecewise-smooth surface. Our method is applicable in both two and three dimensions, and can be easily parallelized, making it possible to process arbitrarily large point clouds, which was a challenge for Voronoi-based methods. In addition, we describe a Monte-Carlo version of our method, which is applicable in any dimension. We illustrate the correctness of both principal curvature information and feature extraction in the presence of varying levels of noise and sampling density on a variety of models. As a sample application, we use our feature detection method to segment point cloud samplings of piecewise-smooth surfaces.
Generic properties of curvature sensing through vision and touch.
Dresp-Langley, Birgitta
2013-01-01
Generic properties of curvature representations formed on the basis of vision and touch were examined as a function of mathematical properties of curved objects. Virtual representations of the curves were shown on a computer screen for visual scaling by sighted observers (experiment 1). Their physical counterparts were placed in the two hands of blindfolded and congenitally blind observers for tactile scaling. The psychophysical data show that curvature representations in congenitally blind individuals, who never had any visual experience, and in sighted observers, who rely on vision most of the time, are statistically linked to the same mathematical properties of the curves. The perceived magnitude of object curvature, sensed through either vision or touch, is related by a mathematical power law, with similar exponents for the two sensory modalities, to the aspect ratio of the curves, a scale invariant geometric property. This finding supports biologically motivated models of sensory integration suggesting a universal power law for the adaptive brain control and balance of motor responses to environmental stimuli from any sensory modality.
Curvature wavefront sensing for the large synoptic survey telescope.
Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian
2015-10-20
The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing. PMID:26560396
Formation of Curvature Subunit of Carbon in Combustion.
Wu, Xin-Zhou; Yao, Yang-Rong; Chen, Miao-Miao; Tian, Han-Rui; Xiao, Jun; Xu, Yun-Yan; Lin, Min-Song; Abella, Laura; Tian, Cheng-Bo; Gao, Cong-Li; Zhang, Qianyan; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun
2016-08-01
Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5-C18 that are online produced in the flame of acetylene-cyclopentadiene-oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process. PMID:27377559
Curvature-dependent excitation propagation in cultured cardiac tissue
NASA Astrophysics Data System (ADS)
Kadota, S.; Kay, M. W.; Magome, N.; Agladze, K.
2012-02-01
The geometry of excitation wave front may play an important role on the propagation block and spiral wave formation. The wave front which is bent over the critical value due to interaction with the obstacles may partially cease to propagate and appearing wave breaks evolve into rotating waves or reentry. This scenario may explain how reentry spontaneously originates in a heart. We studied highly curved excitation wave fronts in the cardiac tissue culture and found that in the conditions of normal, non-inhibited excitability the curvature effects do not play essential role in the propagation. Neither narrow isthmuses nor sharp corners of the obstacles, being classical objects for production of extremely curved wave front, affect non-inhibited wave propagation. The curvature-related phenomena of the propagation block and wave detachment from the obstacle boundary were observed only after partial suppression of the sodium channels with Lidocaine. Computer simulations confirmed the experimental observations. The explanation of the observed phenomena refers to the fact that the heart tissue is made of finite size cells so that curvature radii smaller than the cardiomyocyte size loses sense, and in non-inhibited tissue the single cell is capable to transmit excitation to its neighbors.
Instability in bacterial populations and the curvature tensor
NASA Astrophysics Data System (ADS)
Melgarejo, Augusto; Langoni, Laura; Ruscitti, Claudia
2016-09-01
In the geometry associated with equilibrium thermodynamics the scalar curvature Rs is a measure of the volume of correlation, and therefore the singularities of Rs indicates the system instabilities. We explore the use of a similar approach to study instabilities in non-equilibrium systems and we choose as a test example, a colony of bacteria. In this regard we follow the proposal made by Obata et al. of using the curvature tensor for studying system instabilities. Bacterial colonies are often found in nature in concentrated biofilms, or other colony types, which can grow into spectacular patterns visible under the microscope. For instance, it is known that a decrease of bacterial motility with density can promote separation into bulk phases of two coexisting densities; this is opposed to the logistic law for birth and death that allows only a single uniform density to be stable. Although this homogeneous configuration is stable in the absence of bacterial interactions, without logistic growth, a density-dependent swim speed v(ρ) leads to phase separation via a spinodal instability. Thus we relate the singularities in the curvature tensor R to the spinodal instability, that is the appearance of regions of different densities of bacteria.
Finger vein extraction using gradient normalization and principal curvature
NASA Astrophysics Data System (ADS)
Choi, Joon Hwan; Song, Wonseok; Kim, Taejeong; Lee, Seung-Rae; Kim, Hee Chan
2009-02-01
Finger vein authentication is a personal identification technology using finger vein images acquired by infrared imaging. It is one of the newest technologies in biometrics. Its main advantage over other biometrics is the low risk of forgery or theft, due to the fact that finger veins are not normally visible to others. Extracting finger vein patterns from infrared images is the most difficult part in finger vein authentication. Uneven illumination, varying tissues and bones, and changes in the physical conditions and the blood flow make the thickness and brightness of the same vein different in each acquisition. Accordingly, extracting finger veins at their accurate positions regardless of their thickness and brightness is necessary for accurate personal identification. For this purpose, we propose a new finger vein extraction method which is composed of gradient normalization, principal curvature calculation, and binarization. As local brightness variation has little effect on the curvature and as gradient normalization makes the curvature fairly uniform at vein pixels, our method effectively extracts finger vein patterns regardless of the vein thickness or brightness. In our experiment, the proposed method showed notable improvement as compared with the existing methods.
Curvature wavefront sensing for the large synoptic survey telescope.
Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian
2015-10-20
The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing.
Encoding Gaussian curvature in glassy and elastomeric liquid crystal solids
NASA Astrophysics Data System (ADS)
Mostajeran, Cyrus; Warner, Mark; Ware, Taylor H.; White, Timothy J.
2016-05-01
We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains.
The geometric curvature of the spine of runners during maximal incremental effort test.
Campos, Mário Hebling; de Paula, Marcelo Costa; Deprá, Pedro Paulo; Brenzikofer, René
2015-04-13
This study sought to analyse the behaviour of the average spinal posture using a novel investigative procedure in a maximal incremental effort test performed on a treadmill. Spine motion was collected via stereo-photogrammetric analysis in thirteen amateur athletes. At each time percentage of the gait cycle, the reconstructed spine points were projected onto the sagittal and frontal planes of the trunk. On each plane, a polynomial was fitted to the data, and the two-dimensional geometric curvature along the longitudinal axis of the trunk was calculated to quantify the geometric shape of the spine. The average posture presented at the gait cycle defined the spine Neutral Curve. This method enabled the lateral deviations, lordosis, and kyphosis of the spine to be quantified noninvasively and in detail. The similarity between each two volunteers was a maximum of 19% on the sagittal plane and 13% on the frontal (p<0.01). The data collected in this study can be considered preliminary evidence that there are subject-specific characteristics in spinal curvatures during running. Changes induced by increases in speed were not sufficient for the Neutral Curve to lose its individual characteristics, instead behaving like a postural signature. The data showed the descriptive capability of a new method to analyse spinal postures during locomotion; however, additional studies, and with larger sample sizes, are necessary for extracting more general information from this novel methodology. PMID:25770754
Visualization of Secondary Flow Development in High Aspect Ratio Channels with Curvature
NASA Technical Reports Server (NTRS)
Meyer, Michael L.; Giuliani, James E.
1994-01-01
The results of an experimental project to visually examine the secondary flow structure that develops in curved, high aspect-ratio rectangular channels are presented. The results provide insight into the fluid dynamics within high aspect ratio channels. A water flow test rig constructed out of plexiglass, with an adjustable aspect ratio, was used for these experiments. Results were obtained for a channel geometry with a hydraulic diameter of 10.6 mm (0.417 in.), an aspect ratio of 5.0, and a hydraulic radius to curvature radius ratio of 0.0417. Flow conditions were varied to achieve Reynolds numbers up to 5,100. A new particle imaging velocimetry technique was developed which could resolve velocity information from particles entering and leaving the field of view. Time averaged secondary flow velocity vectors, obtained using this velocimetry technique, are presented for 30 degrees, 60 degrees, and 90 degrees into a 180 degrees bend and at a Reynolds number of 5,100. The secondary flow results suggest the coexistence of both the classical curvature induced vortex pair flow structure and the eddies seen in straight turbulent channel flow.
Curvature and nanoscale forces in controlling self-assembly of carbon nanotube-amphiphile complexes
NASA Astrophysics Data System (ADS)
Maatta, Jukka; van Tassel, Paul; Sammalkorpi, Maria
2014-03-01
In aqueous solution, carbon nanotubes (CNTs) bundle strongly via hydrophobicity induced aggregation, yet the extraordinary properties are best realized when CNTs are dispersed as individual tubes. As a result, pure and well isolated individual CNTs are typically desired and extensive effort has been devoted to achieving good aqueous dispersion of CNTs through covalent or non-covalent functionalization. Here, we examine by molecular simulations the non-covalent solubilization of CNTs with a special focus on curvature effects. We employ molecular dynamics simulations and theoretical models to systematically study the amphiphile interactions at the CNT surface. We report that micelle-forming amphiphiles form hemimicellar structures whereas bilayer-forming lipids form tubular coatings. We characterize the energetics of the underlying physical components - the electrostatic, hydration, and geometric effects on CNT dispersion to examine the efficiency of the various CNT solubilization strategies. The observed differences in amphiphile absorption provide a microscopic understanding on the curvature-dependence in amphiphile-coated CNTs solubility in the aqueous phase and will facilitate the bottom-up design of soft nanoscale materials for nanotechnology.
The geometric curvature of the spine of runners during maximal incremental effort test.
Campos, Mário Hebling; de Paula, Marcelo Costa; Deprá, Pedro Paulo; Brenzikofer, René
2015-04-13
This study sought to analyse the behaviour of the average spinal posture using a novel investigative procedure in a maximal incremental effort test performed on a treadmill. Spine motion was collected via stereo-photogrammetric analysis in thirteen amateur athletes. At each time percentage of the gait cycle, the reconstructed spine points were projected onto the sagittal and frontal planes of the trunk. On each plane, a polynomial was fitted to the data, and the two-dimensional geometric curvature along the longitudinal axis of the trunk was calculated to quantify the geometric shape of the spine. The average posture presented at the gait cycle defined the spine Neutral Curve. This method enabled the lateral deviations, lordosis, and kyphosis of the spine to be quantified noninvasively and in detail. The similarity between each two volunteers was a maximum of 19% on the sagittal plane and 13% on the frontal (p<0.01). The data collected in this study can be considered preliminary evidence that there are subject-specific characteristics in spinal curvatures during running. Changes induced by increases in speed were not sufficient for the Neutral Curve to lose its individual characteristics, instead behaving like a postural signature. The data showed the descriptive capability of a new method to analyse spinal postures during locomotion; however, additional studies, and with larger sample sizes, are necessary for extracting more general information from this novel methodology.
What can the observation of nonzero curvature tell us?
NASA Astrophysics Data System (ADS)
Guth, Alan H.; Nomura, Yasunori
2012-07-01
The eternally inflating multiverse provides a consistent framework to understand coincidences and fine-tuning in the Universe. As such, it provides the possibility of finding another coincidence: if the amount of slow-roll inflation in our past was only slightly more than the anthropic threshold, then spatial curvature might be measurable. We study this issue in detail, particularly focusing on the question: “If future observations reveal nonzero curvature, what can we conclude?” We find that whether an observable signal arises or not depends crucially on three issues: the cosmic history just before the observable inflation, the measure adopted to define probabilities in the eternally inflating spacetime, and the sign and strength of the correlation between the tunneling and slow-roll parts of the potential. We find that if future measurements find positive curvature at the level Ωk≲-10-4, then the framework of the eternally inflating multiverse, as currently understood, is excluded with high significance. If the measurements instead reveal negative curvature at the level Ωk≳10-4, then we can conclude that (1) diffusive (new or chaotic type) eternal inflation did not occur in our immediate past; (2) our pocket universe was born by a bubble nucleation; (3) the probability measure does not reward volume increase; and (4) the origin of the observed slow-roll inflation is an accidental feature of the potential, presumably selected by anthropic conditions, and not due to a theoretical mechanism ensuring the flatness of the potential. Discovery of Ωk≳10-4 would also give us nontrivial information about the correlation between the tunneling and slow-roll parts of the potential; for example, a strong correlation favoring large N would be ruled out in certain measures. We also address the question of whether the current constraint on Ωk is consistent with multiverse expectations; we find the answer to be yes, except that current observations, for many choices
A sensor for the direct measurement of curvature based on flexoelectricity
NASA Astrophysics Data System (ADS)
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.
Higher order statistics of curvature perturbations in IFF model and its Planck constraints
Fujita, Tomohiro; Yokoyama, Shuichiro E-mail: shu@icrr.u-tokyo.ac.jp
2013-09-01
We compute the power spectrum P{sub ζ} and non-linear parameters f{sub NL} and τ{sub NL} of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result of P{sub ζ},f{sub NL} and τ{sub NL} reported by the Planck collaboration, we study the constraint on the model comprehensively. Interestingly, if the single slow-rolling inflaton is responsible for the observed P{sub ζ}, the constraint from τ{sub NL} is most stringent. We also find a general relationship between f{sub NL} and τ{sub NL} generated in this model. Even if f{sub NL} ∼ O(1), a detectable τ{sub NL} can be produced.
Topologically stable magnetization states on a spherical shell: Curvature-stabilized skyrmions
NASA Astrophysics Data System (ADS)
Kravchuk, Volodymyr P.; Rößler, Ulrich K.; Volkov, Oleksii M.; Sheka, Denis D.; van den Brink, Jeroen; Makarov, Denys; Fuchs, Hagen; Fangohr, Hans; Gaididei, Yuri
2016-10-01
Topologically stable structures include vortices in a wide variety of matter, skyrmions in ferro- and antiferromagnets, and hedgehog point defects in liquid crystals and ferromagnets. These are characterized by integer-valued topological quantum numbers. In this context, closed surfaces are a prominent subject of study as they form a link between fundamental mathematical theorems and real physical systems. Here we perform an analysis on the topology and stability of equilibrium magnetization states for a thin spherical shell with easy-axis anisotropy in normal directions. Skyrmion solutions are found for a range of parameters. These magnetic skyrmions on a spherical shell have two distinct differences compared to their planar counterpart: (i) they are topologically trivial and (ii) can be stabilized by curvature effects, even when Dzyaloshinskii-Moriya interactions are absent. Due to its specific topological nature a skyrmion on a spherical shell can be simply induced by a uniform external magnetic field.
Golushko, I Yu; Rochal, S B; Lorman, V L
2015-10-01
Tubular lipid membranes (TLMs) are formed by an external pulling force from artificial or biological bilayer vesicles and can be subsequently stabilized by incorporating proteins or amphiphilic polymers into the lipid bilayer. The arising spontaneous curvature of the lipid sheet allows switching off the pulling force without TLM destabilization. However, here we show that during this process two different thermal fluctuation modes drastically increase their amplitudes making fluctuations of the TLM much greater than its radius. Due to the system's proximity to the critical fluctuation point, a weak axial compressive force is sufficient to destabilize the TLM. Its absolute value is shown to be much smaller than that of the pulling force required for the initial lipid nanotube formation. Induced complex instability was studied in the frame of Landau phase transition theory. The process involves two consecutive second-order phase transitions and leads to the tube deformation combining annular corrugation with completely unconventional chiral buckling.
Golushko, I Yu; Rochal, S B; Lorman, V L
2015-10-01
Tubular lipid membranes (TLMs) are formed by an external pulling force from artificial or biological bilayer vesicles and can be subsequently stabilized by incorporating proteins or amphiphilic polymers into the lipid bilayer. The arising spontaneous curvature of the lipid sheet allows switching off the pulling force without TLM destabilization. However, here we show that during this process two different thermal fluctuation modes drastically increase their amplitudes making fluctuations of the TLM much greater than its radius. Due to the system's proximity to the critical fluctuation point, a weak axial compressive force is sufficient to destabilize the TLM. Its absolute value is shown to be much smaller than that of the pulling force required for the initial lipid nanotube formation. Induced complex instability was studied in the frame of Landau phase transition theory. The process involves two consecutive second-order phase transitions and leads to the tube deformation combining annular corrugation with completely unconventional chiral buckling. PMID:26507403
Trench curvature and deformation of the subducting lithosphere
NASA Astrophysics Data System (ADS)
Schettino, Antonio; Tassi, Luca
2012-01-01
The subduction of oceanic lithosphere is generally accompanied by downdip and lateral deformation. The downdip component of strain is associated with external forces that are applied to the slab during its sinking, namely the gravitational force and the mantle resistance to penetration. Here, we present theoretical arguments showing that a tectonic plate is also subject to a predictable amount of lateral deformation as a consequence of its bending along an arcuate trench zone, independently from the long-term physical processes that have determined the actual curvature of the subduction zone. In particular, we show that the state of lateral strain and the lateral strain rate of a subducting slab depend from geometric and kinematic parameters, such as trench curvature, dip function and subduction velocity. We also demonstrate that the relationship between the state of lateral strain in a subducting slab and the geometry of bending at the corresponding active margin implies a small component of lateral shortening at shallow depths, and may include large extensional lateral deformation at intermediate depths, whereas a state of lateral mechanical equilibrium can only represent a localized exception. Our formulation overcomes the flaws of the classic 'ping-pong ball' model for the bending of the lithosphere at subduction zones, which lead to severe discrepancies with the observed geometry and style of deformation of the modern subducting slabs. A study of the geometry and seismicity of eight modern subduction zones is performed, to assess the validity of the theoretical relationship between trench curvature, slab dip function, and lateral strain rate. The strain pattern within the eight present-day slabs, which is reconstructed through an analysis of Harvard CMT solutions, shows that tectonic plates cannot be considered as flexible-inextensible spherical caps, whereas the lateral intraslab deformation which is accommodated through seismic slip can be explained in terms
Determination of biplane geometry and centerline curvature in vascular imaging
NASA Astrophysics Data System (ADS)
Nazareth, Daryl; Hoffmann, Kenneth R.; Walczak, Alan; Dmochowski, Jacek; Guterman, Lee R.; Rudin, Stephen; Bednarek, Daniel R.
2002-05-01
Three-dimensional (3-D) vessel trees can provide useful visual and quantitative information during interventional procedures. To calculate the 3-D vasculature from biplane images, the transformation relating the imaging systems (i.e., the rotation matrix R and the translation vector t) must be determined. We have developed a technique to calculate these parameters, which requires only the identification of approximately corresponding vessel regions in the two images. Initial estimates of R and t are generated based on the gantry angles, and then refined using an optimization technique. The objective function to be minimized is determined as follows. For each endpoint of each vessel in the first image, an epipolar line in the second image is generated. The intersection points between these two epipolar lines and the corresponding vessel centerline in the second image are determined. The vessel arclength between these intersection points is calculated as a fraction of the entire vessel region length in the image. This procedure is repeated for every vessel in each image. The value of the objective function is calculated from the sum of these fractions, and is smallest when the total fractional arclength is greatest. The 3-D vasculature is obtained from the optimal R and t using triangulation, and vessel curvature is then determined. This technique was evaluated using simulated curves and vessel centerlines obtained from clinical images, and provided rotational, magnification and relative curvature errors of 1 degree(s), 1% and 14% respectively. Accurate 3-D and curvature measures may be useful in clinical decision making, such as in assessing vessel tortuousity and access, during interventional procedures.
The influence of pipe organ reed curvature on tone quality.
Plitnik, George R; Angster, Judit
2012-11-01
Although organ flue pipes have been widely studied, the same claim cannot be made for pipe organ reed stops. Given certain design constraints, such as the type of reed stop being voiced and the desired tone quality, the reed voicer must use consummate skill to curve the reed tongue so as to produce the best and most stable tone as well as to guarantee that each pipe blends with its neighbors. The amount and type of curve given to a reed tongue influences not only the harmonic structure of the steady-state sound but also the attack. There are two fundamentally different types of curvature that can be given to a reed tongue, the trompette (chorus reed) curve (which gives a bright sound) and the smooth-toned curve employed for clarinet pipes. This study investigated the effect of reed curvature on the vibration and tone (as assessed by professionals) on reed tongues of both types. Two F2 (8'F, 87.3 Hz) pipes (a trompette and a clarinet) were constructed and voiced with differently curved tongues to produce a variety of tones. The vibration of the reed tongue was measured under typical conditions by laser vibrometer; the pressure waves in the boot and in the shallot were measured by means of one-quarter inch microphones, and the pipe's sound was recorded at the egress. By performing various measurements simultaneously, phase differences were also determined, the extreme sensitivity of tone to reed curvature was demonstrated, and a recently proposed theory of reed vibration was shown to be more accurate than the standard model. PMID:23145630
Curvature singularities from gravitational contraction in f(R) gravity
NASA Astrophysics Data System (ADS)
Reverberi, Lorenzo
2013-04-01
The discovery of the accelerated expansion of the Universe has had a vast resonance on a number of physical disciplines. In recent years several viable modified gravity models have been proposed, which naturally lead to a late-time de Sitter stage while basically reducing to General Relativity in the early Universe. We consider a contracting cloud of pressureless dust, having arbitrary mass and initial density, and study some aspects of these modified gravity models. We show how the increasing energy/mass density may lead to a curvature singularity and discuss the typical time scales for its development.
Curvature spectra and nongaussianities in the roulette inflation model
NASA Astrophysics Data System (ADS)
Vincent, Aaron C.; Cline, James M.
2008-10-01
Using the gradient expansion method of Rigopoulos, Shellard and van Tent which treats cosmological perturbations as gradients on top of a homogeneous and isotropic FRW background, we study the production of nongaussianities in the roulette model of inflation. Investigating a number of trajectories within this two-field model of inflation, we find that while the superhorizon influence of the isocurvature modes on the curvature bispectrum produces nonzero contribution to fNL, the effect is negligible next to the standard inflationary prediction |fNL| ~ ns-1. This is the case in both the squeezed and equilateral configurations of the bispectrum, although the former is slightly larger in the trajectories under consideration.
Closeness to spheres of hypersurfaces with normal curvature bounded below
Borisenko, A A; Drach, K D
2013-11-30
For a Riemannian manifold M{sup n+1} and a compact domain Ω⊂ M{sup n+1} bounded by a hypersurface ∂Ω with normal curvature bounded below, estimates are obtained in terms of the distance from O to ∂Ω for the angle between the geodesic line joining a fixed interior point O in Ω to a point on ∂Ω and the outward normal to the surface. Estimates for the width of a spherical shell containing such a hypersurface are also presented. Bibliography: 9 titles.
Detonation wave curvature of cast Comp B and PBXN-111
NASA Astrophysics Data System (ADS)
Lemar, E. R.; Forbes, J. W.
1994-07-01
Detonation wave profiles for cast Comp B and PBXN-111 have been fitted accurately over the entire wave fronts using a series expansion of the natural logarithm of a Bessel function. The fit equation has been used to obtain the angle of the detonation front as a function of position and the radii of curvature used in Wood-Kirkwood zone length calculations. The results obtained from the fit equation agree with results obtained previously for PBXN-111. Since the fit equation gives a functional form for the detonation wave across the whole charge diameter, it can be used to test the results obtained from detonation theories and code calculations.
Direct and alignment-insensitive measurement of cantilever curvature
Hermans, Rodolfo I.; Aeppli, Gabriel; Bailey, Joe M.
2013-07-15
We analytically derive and experimentally demonstrate a method for the simultaneous measurement of deflection for large arrays of cantilevers. The Fresnel diffraction patterns of a cantilever independently reveal tilt, curvature, cubic, and higher order bending of the cantilever. It provides a calibrated absolute measurement of the polynomial coefficients describing the cantilever shape, without careful alignment and could be applied to several cantilevers simultaneously with no added complexity. We show that the method is easily implemented, works in both liquid media and in air, for a broad range of displacements and is especially suited to the requirements for multi-marker biosensors.
Influence of curvature in regenerative cooling system of rocket engine
NASA Astrophysics Data System (ADS)
Torres, Y.; Stefanini, L.; Suslov, D.
2009-09-01
Thermomechanical loads in rocket engines can be drastically reduced by a reliable cooling system. The regenerative cooling system uses propellants as coolant which flows through milled cooling channels in the chamber walls. Due to centrifugal forces, dynamic secondary motions appear in cooling-channel curvatures, which strongly modify heat transfer. Three-dimensional (3D) numerical calculations have been performed in order to compare this heat flux modification with empirical correlations. Different turbulence models and wall treatments have been tested to develop a complete numerical data base about asymmetrical (concave side) heat transfer in curved cooling channels of rocket engine.
2008 ULTRASONIC BENCHMARK STUDIES OF INTERFACE CURVATURE--A SUMMARY
Schmerr, L. W.; Huang, R.; Raillon, R.; Mahaut, S.; Leymarie, N.; Lonne, S.; Spies, M.; Lupien, V.
2009-03-03
In the 2008 QNDE ultrasonic benchmark session researchers from five different institutions around the world examined the influence that the curvature of a cylindrical fluid-solid interface has on the measured NDE immersion pulse-echo response of a flat-bottom hole (FBH) reflector. This was a repeat of a study conducted in the 2007 benchmark to try to determine the sources of differences seen in 2007 between model-based predictions and experiments. Here, we will summarize the results obtained in 2008 and analyze the model-based results and the experiments.
New modes from higher curvature corrections in holography
NASA Astrophysics Data System (ADS)
Aksteiner, Steffen; Korovin, Yegor
2016-03-01
In gravitational theories involving higher curvature corrections the metric describes additional degrees of freedom beyond the graviton. Holographic duality maps these to operators in the dual CFT. We identify infinite families of theories for which these new modes cannot be truncated and the usual Fefferman-Graham expansion needs to be modified. New massive gravity in three dimensions and critical gravity in four dimensions are particular representatives of these families. We propose modified expansion, study the near-boundary behaviour of the metric and derive fall-off properties of the additional modes in theories involving higher derivative corrections.
Scattering of force-free electrodynamic waves by spacetime curvature
NASA Astrophysics Data System (ADS)
Zhang, Fan; McWilliams, Sean
2014-03-01
The electromagnetic fields E and B are vectors that couple to spacetime curvatures via Ricci identities, and so force-free electrodynamic waves will in general be scattered. However, Brennan, Gralla and Jacobson found a family of exact solutions that escape scattering. We analytically and numerically study these solutions and their alterations, in order to provide more details as to what features allow them to possess this property. We hope our results will be useful when searching for other solutions of this type. We also provide physical intuition for some commonly encountered theoretical constructs.
Constant mean curvature slicings of Kantowski-Sachs spacetimes
Heinzle, J. Mark
2011-04-15
We investigate existence, uniqueness, and the asymptotic properties of constant mean curvature (CMC) slicings in vacuum Kantowski-Sachs spacetimes with positive cosmological constant. Since these spacetimes violate the strong energy condition, most of the general theorems on CMC slicings do not apply. Although there are in fact Kantowski-Sachs spacetimes with a unique CMC foliation or CMC time function, we prove that there also exist Kantowski-Sachs spacetimes with an arbitrary number of (families of) CMC slicings. The properties of these slicings are analyzed in some detail.
Vorticity, gyroscopic precession, and spin-curvature force
NASA Astrophysics Data System (ADS)
Liang, Wei Chieh; Lee, Si Chen
2013-02-01
In investigating the relationship between vorticity and gyroscopic precession, we calculate the vorticity vector in Godel, Kerr, Lewis, Schwarzschild, and Minkowski metrics and find that the vorticity vector of the specific observers is the angular velocity of the gyroscopic precession. Furthermore, when space-time torsion is included, the vorticity and spin-curvature force change sign. This result is very similar to the behavior of the positive and negative helicities of quantum spin in the Stern-Gerlach force. It implies that the inclusion of torsion will lead to an analogous property of quantum spin even in classical treatment.
Information content in F (R ) brane models with nonconstant curvature
NASA Astrophysics Data System (ADS)
Correa, R. A. C.; Moraes, P. H. R. S.; Dutra, A. de Souza; da Rocha, Roldão
2015-12-01
In this work we investigate the entropic information measure in the context of braneworlds with nonconstant curvature. The braneworld entropic information is studied for gravity modified by the square of the Ricci scalar, besides the usual Einstein-Hilbert term. We showed that the minimum value of the brane configurational entropy provides a stricter bound on the parameter that is responsible for the F (R ) model differing from the Einstein-Hilbert standard one. Our results are moreover consistent to a negative bulk cosmological constant.
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. PMID:21543827
Classical and Quantum features of the spin-curvature coupling
NASA Astrophysics Data System (ADS)
Cianfrani, Francesco; Montani, Giovanni
2007-04-01
We analyze the behavior of a spinning particle in gravity, both from a quantum and a classical perspective point of view. We infer that, since the interaction between the space-time curvature and a spinning test particle is expected, then the main features of such an interaction can get light on which degrees of freedom have physical meaning in a quantum gravity theory with fermions. Finally, the dimensional reduction of Papapetrou equations is performed in a 5-dimensional Kaluza-Klein background and Dixon-Souriau results for the motion of a charged spinning body are obtained.
An algorithm for prescribed mean curvature using isogeometric methods
NASA Astrophysics Data System (ADS)
Chicco-Ruiz, Aníbal; Morin, Pedro; Pauletti, M. Sebastian
2016-07-01
We present a Newton type algorithm to find parametric surfaces of prescribed mean curvature with a fixed given boundary. In particular, it applies to the problem of minimal surfaces. The algorithm relies on some global regularity of the spaces where it is posed, which is naturally fitted for discretization with isogeometric type of spaces. We introduce a discretization of the continuous algorithm and present a simple implementation using the recently released isogeometric software library igatools. Finally, we show several numerical experiments which highlight the convergence properties of the scheme.
Extrinsic curvature, geometric optics, and lamellar order on curved substrates
NASA Astrophysics Data System (ADS)
Kamien, Randall D.; Nelson, David R.; Santangelo, Christian D.; Vitelli, Vincenzo
2009-11-01
When thermal energies are weak, two-dimensional lamellar structures confined on a curved substrate display complex patterns arising from the competition between layer bending and compression in the presence of geometric constraints. We present broad design principles to engineer the geometry of the underlying substrate so that a desired lamellar pattern can be obtained by self-assembly. Two distinct physical effects are identified as key factors that contribute to the interaction between the shape of the underlying surface and the resulting lamellar morphology. The first is a local ordering field for the direction of each individual layer, which tends to minimize its curvature with respect to the three-dimensional embedding. The second is a nonlocal effect controlled by the intrinsic geometry of the surface that forces the normals to the (nearly incompressible) layers to lie on geodesics, leading to caustic formation as in optics. As a result, different surface morphologies with predominantly positive or negative Gaussian curvature can act as converging or diverging lenses, respectively. By combining these ingredients, as one would with different optical elements, complex lamellar morphologies can be obtained. This smectic optometry enables the manipulation of lamellar configurations for the design of materials.
Grain boundary curvature and grain growth kinetics with particle pinning
NASA Astrophysics Data System (ADS)
Shahandeh, Sina; Militzer, Matthias
2013-08-01
Second-phase particles are used extensively in design of polycrystalline materials to control the grain size. According to Zener's theory, a distribution of particles creates a pinning pressure on a moving grain boundary. As a result, a limiting grain size is observed, but the effect of pinning on the detail of grain growth kinetics is less known. The influence of the particles on the microstructure occurs in multiple length scales, established by particle radius and the grain size. In this article, we use a meso-scale phase-field model that simulates grain growth in the presence of a uniform pinning pressure. The curvature of the grain boundary network is measured to determine the driving pressure of grain growth in 2D and 3D systems. It was observed that the grain growth continues, even under conditions where the average driving pressure is smaller than the pinning pressure. The limiting grain size is reached when the maximum of driving pressure distribution in the structure is equal to the pinning pressure. This results in a limiting grain size, larger than the one predicted by conventional models, and further analysis shows consistency with experimental observations. A physical model is proposed for the kinetics of grain growth using parameters based on the curvature analysis of the grain boundaries. This model can describe the simulated grain growth kinetics.
Polydimethylsiloxane bilayer films with an embedded spontaneous curvature.
Egunov, A I; Korvink, J G; Luchnikov, V A
2016-01-01
Elastomer polydimethylsiloxane (PDMS) films with embedded in-plane gradient stress are created by making PDMS/(PDMS + silicone oil) crosslinked bilayers and extracting the oil in a suitable organic solvent bath. The collapse of the elastomer after oil extraction generates differential stress in the films that is manifested through their out-of-plane deformation. The curvature κ of narrow stripes of the bilayer, which is composed of layers of approximately equal thicknesses and elasticity moduli, is satisfactorily described by the simple relationship κ = 1.5δH(-1), where δ is the mechanical strain, and H is the total thickness of the bilayer. Curvature mapping of triangular PDMS plates reveals the existence of spherical and cylindrical types of deformation at different locations of the plates. Various 3D-shaped objects can be formed by the self-folding of appropriately designed 2D patterns that are cut from the films, or by nonuniform distribution of the collapsing layer. Thin PDMS bilayers with embedded stress roll up into microtubes of almost perfect cylindrical shape when released in a controlled manner from a substrate. PMID:26539638
Using curvature extrema to track the evolution of axisymmetric interfaces
NASA Astrophysics Data System (ADS)
Vogel, M. J.; Nitsche, M.; Steen, P. H.
2003-11-01
The temporal evolution of the shape of an interface can exhibit phenomena such as break-up or pinch-off, which are fundamental events that must be controlled in many capillary systems of technological importance. For an axisymmetric surface, lemmas rooted in differential geometry dictate that curvature extrema coincide with curvature crossings or profile extrema. These features provide a convenient means to characterize the profiles of interfaces and to track their evolution even up to singularities, such as occurs at pinch-off. Being solely geometric in nature, this characterization is not limited by the physical properties of the system, e.g., Newtonian versus non-Newtonian behavior, viscous versus inviscid etc. We illustrate by tracking images from evolving soap-films (passive) and polymeric films (non-Newtonian), both observed in experiment, and a deforming mathematical surface predicted by the inviscid vortex-sheet model in simulation. We will discuss extensions of this approach that bring in some model of the flow (e.g. inviscid) and thereby lead to a dynamical system for the motion of the extrema.
PEAPOD regulates lamina size and curvature in Arabidopsis
White, Derek W. R.
2006-01-01
Although a complex pattern of interspersed cell proliferation and cell differentiation is known to occur during leaf blade development in eudicot plants, the genetic mechanisms coordinating this growth are unclear. In Arabidopsis, deletion of the PEAPOD (PPD) locus increases leaf lamina size and results in dome-shaped rather than flat leaves. Siliques are also altered in shape because of extra lamina growth. The curvature of a Δppd leaf reflects the difference between excess growth of the lamina and a limitation to the extension capacity of its perimeter. Excess lamina growth in Δppd plants is due to a prolonged phase of dispersed meristematic cell (DMC) proliferation (for example, the meristemoid and procambium cells that form stomatal stem cells and vascular cells, respectively) during blade development. The PPD locus is composed of two homologous genes, PPD1 and PPD2, which encode plant-specific putative DNA-binding proteins. Overexpression of PPD reduces lamina size by promoting the early arrest of DMC proliferation during leaf and silique development. Therefore, by regulating the arrest of DMC proliferation, the PPD genes coordinate tissue growth, modulate lamina size, and limit curvature of the leaf blade. I propose a revised model of leaf development with two cell-cycle arrest fronts progressing from the tip to the base: the known primary front, which determines arrest of general cell proliferation, followed by a secondary front that involves PPD and arrests DMC division. PMID:16916932
Characterizing Suspension Plasma Spray Coating Formation Dynamics through Curvature Measurements
NASA Astrophysics Data System (ADS)
Chidambaram Seshadri, Ramachandran; Dwivedi, Gopal; Viswanathan, Vaishak; Sampath, Sanjay
2016-10-01
Suspension plasma spraying (SPS) enables the production of variety of microstructures with unique mechanical and thermal properties. In SPS, a liquid carrier (ethanol/water) is used to transport the sub-micrometric feedstock into the plasma jet. Considering complex deposition dynamics of SPS technique, there is a need to better understand the relationships among spray conditions, ensuing particle behavior, deposition stress evolution and resultant properties. In this study, submicron yttria-stabilized zirconia particles suspended in ethanol were sprayed using a cascaded arc plasma torch. The stresses generated during the deposition of the layers (termed evolving stress) were monitored via the change in curvature of the substrate measured using an in situ measurement apparatus. Depending on the deposition conditions, coating microstructures ranged from feathery porous to dense/cracked deposits. The evolving stresses and modulus were correlated with the observed microstructures and visualized via process maps. Post-deposition bi-layer curvature measurement via low temperature thermal cycling was carried out to quantify the thermo-elastic response of different coatings. Lastly, preliminary data on furnace cycle durability of different coating microstructures were evaluated. This integrated study involving in situ diagnostics and ex situ characterization along with process maps provides a framework to describe coating formation mechanisms, process parametrics and microstructure description.
Reeves, Matthew; Stratford, Kevin; Thijssen, Job H J
2016-05-14
Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity L (average interfacial separation) of the bijel is controlled by varying the radius (r) and volume fraction (ϕ) of the colloids (L∝r/ϕ). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by L alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures; we further demonstrate that bijels are bicontinuous using an image-analysis technique known as 'region growing'. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding. PMID:27035101
Directing peptide crystallization through curvature control of nanotubes.
Gobeaux, Frédéric; Tarabout, Christophe; Fay, Nicolas; Meriadec, Cristelle; Ligeti, Melinda; Buisson, David-Alexandre; Cintrat, Jean-Christophe; Artzner, Franck; Paternostre, Maïté
2014-07-01
In the absence of efficient crystallization methods, the molecular structures of fibrous assemblies have so far remained rather elusive. In this paper, we present a rational method to crystallize the lanreotide octapeptide by modification of a residue involved in a close contact. Indeed, we show that it is possible to modify the curvature of the lanreotide nanotubes and hence their diameter. This fine tuning leads to crystallization because the radius of curvature of the initially bidimensional peptide wall can be increased up to a point where the wall is essentially flat and a crystal is allowed to grow along a third dimension. By comparing X-ray diffraction data and Fourier transform Raman spectra, we show that the nanotubes and the crystals share similar cell parameters and molecular conformations, proving that there is indeed a structural continuum between these two morphologies. These results illustrate a novel approach to crystallization and represent the first step towards the acquisition of an Å-resolution structure of the lanreotide nanotubes β-sheet assembly.
Diameter Effect Curve and Detonation Front Curvature Measurements for ANFO
NASA Astrophysics Data System (ADS)
Catanach, R. A.; Hill, L. G.
2002-07-01
Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium-nitrate/fuel-oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm (approximately failure diameter) to 205 mm, with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity Dn, and local total curvature kappa, were generated as a function of radius R, then plotted parametrically to generate a Dn(kappa) function. The observed behavior deviates substantially from that of previous explosives, for which curves for different diameters overlay well for small kappa but diverge for large kappa, and for which kappa increases monotonically with R. For ANFO, we find that Dn(kappa) curves for individual sticks 1) show little or no overlap--with smaller sticks lying to the right of larger ones, 2) exhibit a large velocity deficit with little kappa variation, and 3) reach a peak kappa at an intermediate R.
Diameter effect curve and detonation front curvature measurements for ANFO
Catanach, R. A.; Hill, L. G.
2001-01-01
Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium-nitrate/fuel-oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm ({approx} failure diameter) to 205 mm, with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity Dn, and local total curvature {kappa}, were generated as a function of radius R, then plotted parametrically to generate a Dn({kappa}) function. The observed behavior deviates substantially from that of previous explosives, for which curves for different diameters overlay well for small {kappa} but diverge for large {kappa}, and for which {kappa} increases monotonically with R. For ANFO, we find that Dn({kappa}) curves for individual sticks (1) show little or no overlap--with smaller sticks lying to the right of larger ones, (2) exhibit a large velocity deficit with little {kappa} variation, and (3) reach a peak {kappa} at an intermediate R.
Diameter Effect Curve and Detonation Front Curvature Measurements for ANFO
NASA Astrophysics Data System (ADS)
Catanach, R. A.; Hill, L. G.
2001-06-01
Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium nitrate-fuel oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm. (≈ failure diameter) to 200 mm., with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity Dn and total curvature κ were generated as a function of radius R, then plotted parametrically to generate a D_n(κ) function. The resulting behavior deviates substantially from that of previous explosives,(Hill,L.G., Bdzil,J.B., and Aslam,T.D., 11^th) Detonation Symposium, 1998^,(Hill,L.G., Bdzil,J.B., Davis,W.C., and Engelke,R., Shock Compression of Condensed Matter, 1999) in which curves for different stick sizes overlay well for small κ but diverge for large κ, and for which κ increases monotonically with R to achieve a maximum value at the charge edge. For ANFO, we find that κ achieves a maximum at an intermediate R and that D_n(κ) curves for different stick sizes are widely separated with no overlap whatsoever.
Residual stress determination from a laser-based curvature measurement
W. D. Swank; R. A. Gavalya; J. K. Wright; R. N. Wright
2000-05-08
Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.
Residual Stress Determination from a Laser-Based Curvature Measurement
Swank, William David; Gavalya, Rick Allen; Wright, Julie Knibloe; Wright, Richard Neil
2000-05-01
Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.
Dynamic cutaneous information is sufficient for precise curvature discrimination
Cheeseman, Jacob R.; Norman, J. Farley; Kappers, Astrid M. L.
2016-01-01
Our tactual perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration often enhances the tactual perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 28 younger (mean age was 23.1 years) and older adults (mean age was 71.4 years) to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. While dynamic cutaneous stimulation was therefore present in both conditions, active exploratory movements only occurred in one. The results indicated that there was a significant and large effect of age, such that the older participants’ thresholds were 43.8 percent higher than those of the younger participants. Despite the overall adverse effect of age, the pattern of results across the active and passive touch conditions was identical. For both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch. Curvature discrimination performance was therefore best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement. PMID:27137417
Dynamic cutaneous information is sufficient for precise curvature discrimination.
Cheeseman, Jacob R; Norman, J Farley; Kappers, Astrid M L
2016-01-01
Our tactual perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration often enhances the tactual perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 28 younger (mean age was 23.1 years) and older adults (mean age was 71.4 years) to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. While dynamic cutaneous stimulation was therefore present in both conditions, active exploratory movements only occurred in one. The results indicated that there was a significant and large effect of age, such that the older participants' thresholds were 43.8 percent higher than those of the younger participants. Despite the overall adverse effect of age, the pattern of results across the active and passive touch conditions was identical. For both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch. Curvature discrimination performance was therefore best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement. PMID:27137417
Conversion of radius of curvature to power (and vice versa)
NASA Astrophysics Data System (ADS)
Wickenhagen, Sven; Endo, Kazumasa; Fuchs, Ulrike; Youngworth, Richard N.; Kiontke, Sven R.
2015-09-01
Manufacturing optical components relies on good measurements and specifications. One of the most precise measurements routinely required is the form accuracy. In practice, form deviation from the ideal surface is effectively low frequency errors, where the form error most often accounts for no more than a few undulations across a surface. These types of errors are measured in a variety of ways including interferometry and tactile methods like profilometry, with the latter often being employed for aspheres and general surface shapes such as freeforms. This paper provides a basis for a correct description of power and radius of curvature tolerances, including best practices and calculating the power value with respect to the radius deviation (and vice versa) of the surface form. A consistent definition of the sagitta is presented, along with different cases in manufacturing that are of interest to fabricators and designers. The results make clear how the definitions and results should be documented, for all measurement setups. Relationships between power and radius of curvature are shown that allow specifying the preferred metric based on final accuracy and measurement method. Results shown include all necessary equations for conversion to give optical designers and manufacturers a consistent and robust basis for decision-making. The paper also gives guidance on preferred methods for different scenarios for surface types, accuracy required, and metrology methods employed.
Reeves, Matthew; Stratford, Kevin; Thijssen, Job H J
2016-05-14
Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity L (average interfacial separation) of the bijel is controlled by varying the radius (r) and volume fraction (ϕ) of the colloids (L∝r/ϕ). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by L alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures; we further demonstrate that bijels are bicontinuous using an image-analysis technique known as 'region growing'. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.
Magnetophoretic induction of curvature in coleoptiles and hypocotyls
NASA Technical Reports Server (NTRS)
Kuznetsov, O. A.; Hasenstein, K. H.
1997-01-01
Coleoptiles of barley (Hordeum vulgare) were positioned in a high gradient magnetic field (HGMF, dynamic factor gradient of H(2)/2 of 10(9)-10(10) Oe2 cm-1), generated by a ferromagnetic wedge in a uniform magnetic field and rotated on a 1 rpm clinostat. After 4 h 90% of coleoptiles had curved toward the HGMF. The cells affected by HGMF showed clear intracellular displacement of amyloplasts. Coleoptiles in a magnetic field next to a non-ferromagnetic wedge showed no preferential curvature. The small size of the area of nonuniformity of the HGMF allowed mapping of the sensitivity of the coleoptiles by varying the initial position of the wedge relative to the coleoptile apex. When the ferromagnetic wedge was placed 1 mm below the coleoptile tip only 58% of the coleoptiles curved toward the wedge indicating that the cells most sensitive to intracellular displacement of amyloplasts and thus gravity sensing are confined to the top 1 mm portion of barley coleoptiles. Similar experiments with tomato hypocotyls (Lycopersicum esculentum) also resulted in curvature toward the HGMF. The data strongly support the amyloplast-based gravity-sensing system in higher plants and the usefulness of HGMF to substitute gravity in shoots.
Gauss-Bonnet black holes with nonconstant curvature horizons
Maeda, Hideki
2010-06-15
We investigate static and dynamical n({>=}6)-dimensional black holes in Einstein-Gauss-Bonnet gravity of which horizons have the isometries of an (n-2)-dimensional Einstein space with a condition on its Weyl tensor originally given by Dotti and Gleiser. Defining a generalized Misner-Sharp quasilocal mass that satisfies the unified first law, we show that most of the properties of the quasilocal mass and the trapping horizon are shared with the case with horizons of constant curvature. It is shown that the Dotti-Gleiser solution is the unique vacuum solution if the warp factor on the (n-2)-dimensional Einstein space is nonconstant. The quasilocal mass becomes constant for the Dotti-Gleiser black hole and satisfies the first law of the black-hole thermodynamics with its Wald entropy. In the non-negative curvature case with positive Gauss-Bonnet constant and zero cosmological constant, it is shown that the Dotti-Gleiser black hole is thermodynamically unstable. Even if it becomes locally stable for the nonzero cosmological constant, it cannot be globally stable for the positive cosmological constant.
Spatio-temporal curvature measures for flow-field analysis
NASA Astrophysics Data System (ADS)
Zetzsche, Christoph; Barth, Erhardt; Berkmann, Joachim
1991-09-01
Intrinsic signal dimensionality, a property closely related to Gaussian curvature, is shown to be an important conceptual tool in multi-dimensional image processing for both biological and engineering sciences. Intrinsic dimensionality can reveal the relationship between recent theoretical developments in the definition of optic flow and the basic neurophysiological concept of 'end-stopping' of visual cortical cells. It is further shown how the concept may help to avoid certain problems typically arising from the common belief that an explicit computation of a flow field has to be the essential first step in the processing of spatio- temporal image sequences. Signals which cause difficulties in the computation of optic flow, mainly the discontinuities of the motion vector field, are shown to be detectable directly in the spatio-temporal input by evaluation of its three-dimensional curvature. The relevance of the suggested concept is supported by the fact that fast and efficient detection of such signals is of vital importance for ambulant observers in both the biological and the technical domain.
NASA Astrophysics Data System (ADS)
Dass, Sumit; Narayan Dash, Jitendra; Jha, Rajan
2016-03-01
We propose a highly sensitive curvature sensor based on cascaded single mode fiber (SMF) tapers with a microcavity. The microcavity is created by splicing a small piece of hollow core photonic crystal fiber (HCPCF) at the end of an SMF to obtain a sharp interference pattern. Experimental results show that two SMF tapers enhance the curvature sensitivity of the system and by changing the tapering parameters of the second taper, the curvature sensitivity of the system can be tailored, together with the fringe contrast of the interference pattern. A maximum curvature sensitivity of 10.4 dB/m-1 is observed in the curvature range 0 to 1 m-1 for a second taper diameter of 18 μm. The sensing setup is highly stable and shows very low temperature sensitivity. As the interrogation is intensity based, a low cost optical power meter can be utilized to determine the curvature.
Effect of nano-scale curvature on the intrinsic blood coagulation system
NASA Astrophysics Data System (ADS)
Kushida, Takashi; Saha, Krishnendu; Subramani, Chandramouleeswaran; Nandwana, Vikas; Rotello, Vincent M.
2014-11-01
The intrinsic coagulation activity of silica nanoparticles strongly depends on their surface curvature. Nanoparticles with higher surface curvature do not denature blood coagulation factor XII on its surface, providing a coagulation `silent' surface, while nanoparticles with lower surface curvature show denaturation and concomitant coagulation.The intrinsic coagulation activity of silica nanoparticles strongly depends on their surface curvature. Nanoparticles with higher surface curvature do not denature blood coagulation factor XII on its surface, providing a coagulation `silent' surface, while nanoparticles with lower surface curvature show denaturation and concomitant coagulation. Electronic supplementary information (ESI) available: Physical properties and scanning electron micrographs (SEM) of silica NPs, intrinsic coagulation activity after 3 h. See DOI: 10.1039/c4nr04128c
Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D; Yoon, Dong Ki
2016-01-01
Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air-smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales. PMID:26725975
Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D; Yoon, Dong Ki
2016-01-04
Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air-smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales.
Kim, Dae Seok; Cha, Yun Jeong; Kim, Mun Ho; Lavrentovich, Oleg D.; Yoon, Dong Ki
2016-01-01
Soft materials with layered structure such as membranes, block copolymers and smectics exhibit intriguing morphologies with nontrivial curvatures. Here, we report restructuring the Gaussian and mean curvatures of smectic A films with free surface in the process of sintering, that is, reshaping at elevated temperatures. The pattern of alternating patches of negative, zero and positive mean curvature of the air–smectic interface has a profound effect on the rate of sublimation. As a result of sublimation, condensation and restructuring, initially equilibrium smectic films with negative and zero Gaussian curvature are transformed into structures with pronounced positive Gaussian curvature of layers packing, which are rare in the samples obtained by cooling from the isotropic melt. The observed relationship between the curvatures, bulk elastic behaviour and interfacial geometries in sintering of smectic liquid crystals might pave the way for new approaches to control soft morphologies at micron and submicron scales. PMID:26725975
Determinants of Curvature-Sensing Behavior for MARCKS-Fragment Peptides.
de Jesus, Armando J; White, Ormacinda R; Flynn, Aaron D; Yin, Hang
2016-05-10
It is increasingly recognized that membrane curvature plays an important role in various cellular activities such as signaling and trafficking, as well as key issues involving health and disease development. Thus, curvature-sensing peptides are essential to the study and detection of highly curved bilayer structures. The effector domain of myristoylated alanine-rich C-kinase substrate (MARCKS-ED) has been demonstrated to have curvature-sensing ability. Research of the MARCKS-ED has further revealed that its Lys and Phe residues play an essential role in how MARCKS-ED detects and binds to curved bilayers. MARCKS-ED has the added property of being a lower-molecular-weight curvature sensor, which offers advantages in production. With that in mind, this work investigates peptide-sequence-related factors that influence curvature sensing and explores whether peptide fragments of even shorter length can function as curvature sensors. Using both experimental and computational methods, we studied the curvature-sensing capabilities of seven fragments of MARCKS-ED. Two of the longer fragments were designed from approximately the two halves of the full-length peptide whereas the five shorter fragments were taken from the central stretch of MARCKS-ED. Fully atomistic molecular dynamics simulations show that the fragments that remain bound to the bilayer exhibit interactions with the bilayer similar to that of the full-length MARCKS-ED peptide. Fluorescence enhancement and anisotropy assays, meanwhile, reveal that five of the MARCKS fragments possess the ability to sense membrane curvature. Based on the sequences of the curvature-sensing fragments, it appears that the ability to sense curvature involves a balance between the numbers of positively charged residues and hydrophobic anchoring residues. Together, these findings help crystallize our understanding of the molecular mechanisms underpinning the curvature-sensing behaviors of peptides, which will prove useful in the
3D Curves With a Prescribed Curvature and Torsion for a Flying Robot
Bestaoui, Yasmina
2008-06-12
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.
Radius of Curvature Measurements: An Independent Look at Accuracy Using Novel Optical Metrology
NASA Technical Reports Server (NTRS)
Taylor, Bryon; Kahan, Mark; Russell, Kevin (Technical Monitor)
2002-01-01
The AMSD (Advanced Mirror System Demonstrator) program mirror specifications include the ability to manufacture the mirror to a radius of curvature of 10 m +/- 1 mm and to control its radius at 30K to the same specification. Therefore, it is necessary for the Government Team to be able to measure mirror radius of curvature to an accuracy of better than 0.5 mm. This presentation discusses a novel optical metrology system for measuring radius of curvature.
Yang, L.; Gordon, V.D.; Trinkle, D.R.; Schmidt, N.W.; Davis, M.A.; DeVries, C.; Som, A.; Cronan, J.E., Jr.; Tew, G.N.; Wong, G.C.L.
2009-05-28
Phenylene ethynylenes comprise a prototypical class of synthetic antimicrobial compounds that mimic antimicrobial peptides produced by eukaryotes and have broad-spectrum antimicrobial activity. We show unambiguously that bacterial membrane permeation by these antimicrobials depends on the presence of negative intrinsic curvature lipids, such as phosphatidylethanolamine (PE) lipids, found in high concentrations within bacterial membranes. Plate-killing assays indicate that a PE-knockout mutant strain of Escherichia coli drastically out-survives the wild type against the membrane-active phenylene ethynylene antimicrobials, whereas the opposite is true when challenged with traditional metabolic antibiotics. That the PE deletion is a lethal mutation in normative environments suggests that resistant bacterial strains do not evolve because a lethal mutation is required to gain immunity. PE lipids allow efficient generation of negative curvature required for the circumferential barrel of an induced membrane pore; an inverted hexagonal HII phase, which consists of arrays of water channels, is induced by a small number of antimicrobial molecules. The estimated antimicrobial occupation in these water channels is nonlinear and jumps from {approx}1 to 3 per 4 nm of induced water channel length as the global antimicrobial concentration is increased. By comparing to exactly solvable 1D spin models for magnetic systems, we quantify the cooperativity of these antimicrobials.
NASA Astrophysics Data System (ADS)
Bars, Itzhak; Chen, Shih-Hung; Steinhardt, Paul J.; Turok, Neil
2012-10-01
We study a model of a scalar field minimally coupled to gravity, with a specific potential energy for the scalar field, and include curvature and radiation as two additional parameters. Our goal is to obtain analytically the complete set of configurations of a homogeneous and isotropic universe as a function of time. This leads to a geodesically complete description of the Universe, including the passage through the cosmological singularities, at the classical level. We give all the solutions analytically without any restrictions on the parameter space of the model or initial values of the fields. We find that for generic solutions the Universe goes through a singular (zero-size) bounce by entering a period of antigravity at each big crunch and exiting from it at the following big bang. This happens cyclically again and again without violating the null-energy condition. There is a special subset of geodesically complete nongeneric solutions which perform zero-size bounces without ever entering the antigravity regime in all cycles. For these, initial values of the fields are synchronized and quantized but the parameters of the model are not restricted. There is also a subset of spatial curvature-induced solutions that have finite-size bounces in the gravity regime and never enter the antigravity phase. These exist only within a small continuous domain of parameter space without fine-tuning the initial conditions. To obtain these results, we identified 25 regions of a 6-parameter space in which the complete set of analytic solutions are explicitly obtained.
NASA Astrophysics Data System (ADS)
Mondal, Rabindra Nath; Roy, Titob; Shaha, Poly Rani; Yanase, Shinichiro
2016-07-01
Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number -300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario `multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic', if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario `multi-periodic → periodic → steady-state', if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.
Finite element analysis of a femur to deconstruct the paradox of bone curvature.
Jade, Sameer; Tamvada, Kelli H; Strait, David S; Grosse, Ian R
2014-01-21
Most long limb bones in terrestrial mammals exhibit a longitudinal curvature and have been found to be loaded in bending. Bone curvature poses a paradox in terms of the mechanical function of limb bones, for many believe the curvature in these bones increases bending stress, potentially reducing the bone's load carrying capacity (i.e., its mechanical strength). The aim of this study is to investigate the role of longitudinal bone curvature in the design of limb bones. In particular, it has been hypothesized that bone curvature results in a trade-off between the bone's mechanical strength and its bending predictability. We employed finite element analysis (FEA) of abstract and realistic human femora to address this issue. Geometrically simplified human femur models with different curvatures were developed and analyzed with a commercial FEA tool to examine how curvature affects the bone's bending predictability and load carrying capacity. Results were post-processed to yield probability density functions (PDFs) describing the circumferential location of maximum equivalent stress for various curvatures in order to assess bending predictability. To validate our findings, a finite element model was built from a CT scan of a real human femur and compared to the simplified femur model. We found general agreement in trends but some quantitative differences most likely due to the geometric differences between the digitally reconstructed and the simplified finite element models. As hypothesized by others, our results support the hypothesis that bone curvature can increase bending predictability, but at the expense of bone strength.
Detecting curvatures in digital images using filters derived from differential geometry
NASA Astrophysics Data System (ADS)
Toro Giraldo, Juanita
2015-09-01
Detection of curvature in digital images is an important theoretical and practical problem in image processing. Many important features in an image are associated with curvature and the detection of such features is reduced to detection and characterization of curvatures. Differential geometry studies many kinds of curvature operators and from these curvature operators is possible to derive powerful filters for image processing which are able to detect curvature in digital images and videos. The curvature operators are formulated in terms of partial differential operators which can be applied to images via convolution with generalized kernels derived from the the Korteweg- de Vries soliton . We present an algorithm for detection of curvature in digital images which is implemented using the Maple package ImageTools. Some experiments were performed and the results were very good. In a future research will be interesting to compare the results using the Korteweg-de Vries soliton with the results obtained using Airy derivatives. It is claimed that the resulting curvature detectors could be incorporated in standard programs for image processing.
Wright, Anthony R; McKenzie, Ross H
2014-02-26
We show that in a layered metal, the angle dependent, finite frequency, interlayer magnetoresistance is altered due to the presence of a non-zero Berry curvature at the Fermi surface. At zero frequency, we find a conservation law which demands that the 'magic angle' condition for interlayer magnetoresistance extrema as a function of magnetic field tilt angle is essentially both field and Berry curvature independent. In the finite frequency case, however, we find that surprisingly large signatures of a finite Berry curvature occur in the periodic orbit resonances. We outline a method whereby the presence and magnitude of the Berry curvature at the Fermi surface can be extracted.
Identification of multiple damage in beams based on robust curvature mode shapes
NASA Astrophysics Data System (ADS)
Cao, Maosen; Radzieński, Maciej; Xu, Wei; Ostachowicz, Wiesław
2014-06-01
Multiple damage identification in beams using curvature mode shape has become a research focus of increasing interest during the last few years. On this topic, most existing studies address the sensitivity of curvature mode shape to multiple damage. A noticeable deficiency of curvature mode shape, however, is its susceptibility to measurement noise, easily impairing its advantage of sensitivity to multiple damage. To overcome this drawback, the synergy between a wavelet transform (WT) and a Teager energy operator (TEO) is explored, with the aim of ameliorating the curvature mode shape. The improved curvature mode shape, termed the TEO-WT curvature mode shape, has inherent capabilities of immunity to noise and sensitivity to multiple damage. The efficacy of the TEO-WT curvature mode shape is analytically verified by identifying multiple cracks in cantilever beams, with particular emphasis on its ability to locate multiple damage in noisy conditions; the applicability of the proposed curvature mode shape is experimentally validated by detecting multiple fairly thin slots in steel beams with mode shapes acquired by a scanning laser vibrometer. The proposed curvature mode shape appears sensitive to multiple damage and robust against noise, and therefore is well suited to identification of multiple damage in beams in noisy environments.
Ciulla, Carlo; Veljanovski, Dimitar; Rechkoska Shikoska, Ustijana; Risteski, Filip A.
2015-01-01
This research presents signal-image post-processing techniques called Intensity-Curvature Measurement Approaches with application to the diagnosis of human brain tumors detected through Magnetic Resonance Imaging (MRI). Post-processing of the MRI of the human brain encompasses the following model functions: (i) bivariate cubic polynomial, (ii) bivariate cubic Lagrange polynomial, (iii) monovariate sinc, and (iv) bivariate linear. The following Intensity-Curvature Measurement Approaches were used: (i) classic-curvature, (ii) signal resilient to interpolation, (iii) intensity-curvature measure and (iv) intensity-curvature functional. The results revealed that the classic-curvature, the signal resilient to interpolation and the intensity-curvature functional are able to add additional information useful to the diagnosis carried out with MRI. The contribution to the MRI diagnosis of our study are: (i) the enhanced gray level scale of the tumor mass and the well-behaved representation of the tumor provided through the signal resilient to interpolation, and (ii) the visually perceptible third dimension perpendicular to the image plane provided through the classic-curvature and the intensity-curvature functional. PMID:26644943
Linear stability of three-dimensional boundary layers - Effects of curvature and non-parallelism
NASA Technical Reports Server (NTRS)
Malik, M. R.; Balakumar, P.
1993-01-01
In this paper we study the effect of in-plane (wavefront) curvature on the stability of three-dimensional boundary layers. It is found that this effect is stabilizing or destabilizing depending upon the sign of the crossflow velocity profile. We also investigate the effects of surface curvature and nonparallelism on crossflow instability. Computations performed for an infinite-swept cylinder show that while convex curvature stabilizes the three-dimensional boundary layer, nonparallelism is, in general, destabilizing and the net effect of the two depends upon meanflow and disturbance parameters. It is also found that concave surface curvature further destabilizes the crossflow instability.
NASA Astrophysics Data System (ADS)
Byrum, Christopher Ronald
One of the biggest gaps of missing knowledge between accurate structural modeling of concrete pavement slab behavior and real pavement behavior is accounting for slab warping (locked-in curvature and moisture gradient effects) and curling (temperature gradient effects). Curling and warping are curvatures that can be present in a PCC slab that can cause corners and edges, or mid panel, of the slab to lift off of the ground resulting in relatively high deflection and stress in the system. The least understood type of curvature in slabs is apparent locked-in curvature, which can become excessive and control the overall behavior of the pavement system. This project is focused on quantifying slab curvatures and the effects of apparent locked-in curvature on the behavior and long-term performance of pavement systems. A high-speed profile analysis technique for detecting the amount of slab curvatures along pavement wheel paths is described. This signal processing technique can detect relatively small curvature variations in high-speed pavement elevation profiles obtained at normal highway operating speeds using special vehicles. A resulting curvature detection algorithm is applied to the Federal Highway Administration (FHWA) Long Term Pavement Performance (LTPP) database high-speed pavement profiles for jointed concrete pavements. The range and nature of slab curvatures detected in the profiles is described. The calculated locked-in curvature at the various pavement sites is compared to LTPP database information to evaluate curvature effects on pavement deterioration rates and the relation between site parameters and locked-in curvature. The significance of slab curvature is shown through statistics and predictive models developed for various pavement distress modes. It is shown that the amount of curvature locked into concrete slabs is one of the strongest factors in the FHWA LTPP data correlated to deterioration of pavements. This study shows that preventing locked
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.
A major QTL controls susceptibility to spinal curvature in the curveback guppy
2011-01-01
Background Understanding the genetic basis of heritable spinal curvature would benefit medicine and aquaculture. Heritable spinal curvature among otherwise healthy children (i.e. Idiopathic Scoliosis and Scheuermann kyphosis) accounts for more than 80% of all spinal curvatures and imposes a substantial healthcare cost through bracing, hospitalizations, surgery, and chronic back pain. In aquaculture, the prevalence of heritable spinal curvature can reach as high as 80% of a stock, and thus imposes a substantial cost through production losses. The genetic basis of heritable spinal curvature is unknown and so the objective of this work is to identify quantitative trait loci (QTL) affecting heritable spinal curvature in the curveback guppy. Prior work with curveback has demonstrated phenotypic parallels to human idiopathic-type scoliosis, suggesting shared biological pathways for the deformity. Results A major effect QTL that acts in a recessive manner and accounts for curve susceptibility was detected in an initial mapping cross on LG 14. In a second cross, we confirmed this susceptibility locus and fine mapped it to a 5 cM region that explains 82.6% of the total phenotypic variance. Conclusions We identify a major QTL that controls susceptibility to curvature. This locus contains over 100 genes, including MTNR1B, a candidate gene for human idiopathic scoliosis. The identification of genes associated with heritable spinal curvature in the curveback guppy has the potential to elucidate the biological basis of spinal curvature among humans and economically important teleosts. PMID:21269476
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. PMID:26414648
The X-Ray Transform for Connections in Negative Curvature
NASA Astrophysics Data System (ADS)
Guillarmou, Colin; Paternain, Gabriel P.; Salo, Mikko; Uhlmann, Gunther
2016-04-01
We consider integral geometry inverse problems for unitary connections and skew-Hermitian Higgs fields on manifolds with negative sectional curvature. The results apply to manifolds in any dimension, with or without boundary, and also in the presence of trapped geodesics. In the boundary case, we show injectivity of the attenuated ray transform on tensor fields with values in a Hermitian bundle (i.e., vector valued case). We also show that a connection and Higgs field on a Hermitian bundle are determined up to gauge by the knowledge of the parallel transport between boundary points along all possible geodesics. The main tools are an energy identity, the Pestov identity with a unitary connection, which is presented in a general form, and a precise analysis of the singularities of solutions of transport equations when there are trapped geodesics. In the case of closed manifolds, we obtain similar results modulo the obstruction given by twisted conformal Killing tensors, and we also study this obstruction.
Theory for the curvature dependence of delta front progradation
NASA Astrophysics Data System (ADS)
Ke, Wun-Tao; Capart, Hervé
2015-12-01
When Gilbert-type deltas respond to uneven sediment supply or advance over irregular basin bathymetry, they develop curved, creased fronts prograding at speeds that vary with location along the shoreline. Relations governing the progradation rate, however, have so far been proposed only for simple special cases. In this paper, we exploit the special properties of solutions to the eikonal equation to derive a general progradation relation, applicable to delta fronts of finite angle of repose and arbitrary shoreline planform. In these circumstances, the theory explicitly relates the progradation rate to the local shoreline curvature. We illustrate the resulting morphodynamics with numerical and analytical solutions for a sinuous delta front. The proposed relation can be used to model deltaic evolution or deduce spanwise distributions of sediment supply rates from observations of foreset evolution.
Thermodynamic curvature for attractive and repulsive intermolecular forces.
May, Helge-Otmar; Mausbach, Peter; Ruppeiner, George
2013-09-01
The thermodynamic curvature scalar R for the Lennard-Jones system is evaluated in phase space, including vapor, liquid, and solid state. We paid special attention to the investigation of R along vapor-liquid, liquid-solid, and vapor-solid equilibria. Because R is a measure of interaction strength, we traced out the line R=0 dividing the phase space into regions with effectively attractive (R<0) or repulsive (R>0) interactions. Furthermore, we analyzed the dependence of R on the strength of attraction applying a perturbation ansatz proposed by Weeks-Chandler-Anderson. Our results show clearly a transition from R>0 (for poorly repulsive interaction) to R<0 when loading attraction in the intermolecular potential.
Curvature condensation and bifurcation in an elastic shell.
Das, Moumita; Vaziri, Ashkan; Kudrolli, Arshad; Mahadevan, L
2007-01-01
We study the formation and evolution of localized geometrical defects in an indented cylindrical elastic shell using a combination of experiment and numerical simulation. We find that as a symmetric localized indentation on a semicylindrical shell increases, there is a transition from a global mode of deformation to a localized one which leads to the condensation of curvature along a symmetric parabolic defect. This process introduces a soft mode in the system, converting a load-bearing structure into a hinged, kinematic mechanism. Further indentation leads to twinning wherein the parabolic defect bifurcates into two defects that move apart on either side of the line of symmetry. A qualitative theory captures the main features of the phenomena but leads to further questions about the mechanism of defect nucleation.
Converting entropy to curvature perturbations after a cosmic bounce
NASA Astrophysics Data System (ADS)
Fertig, Angelika; Lehners, Jean-Luc; Mallwitz, Enno; Wilson-Ewing, Edward
2016-10-01
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.
Topological implications of negative curvature for biological and social networks
NASA Astrophysics Data System (ADS)
Albert, Réka; DasGupta, Bhaskar; Mobasheri, Nasim
2014-03-01
Network measures that reflect the most salient properties of complex large-scale networks are in high demand in the network research community. In this paper we adapt a combinatorial measure of negative curvature (also called hyperbolicity) to parametrized finite networks, and show that a variety of biological and social networks are hyperbolic. This hyperbolicity property has strong implications on the higher-order connectivity and other topological properties of these networks. Specifically, we derive and prove bounds on the distance among shortest or approximately shortest paths in hyperbolic networks. We describe two implications of these bounds to crosstalk in biological networks, and to the existence of central, influential neighborhoods in both biological and social networks.
Palatini versus metric formulation in higher-curvature gravity
NASA Astrophysics Data System (ADS)
Borunda, Mónica; Janssen, Bert; Bastero-Gil, Mar
2008-11-01
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.
Berry Phases and Curvatures in Electronic-Structure Theory.
NASA Astrophysics Data System (ADS)
Vanderbilt, David
2006-03-01
In the last fifteen years, Berry phases have been found to play an increasingly important role in electronic-structure theory. I will briefly review some of the important developments in which Berry phases have been involved, starting with the modern theory of polarization^1 and the closely related theory of Wannier functions and their Wannier centers.^2 Next, I will discuss the theory of insulators in finite electric fields,^3 in which the field is taken to couple linearly to the Berry-phase polarization. I will then conclude by discussing the role of Berry phases and Berry curvatures in systems in which time-reversal symmetry has been broken, and in particular, the theory of orbital magnetization^4 and the anomalous Hall effect in ferromagnets. *[[1
Curvature effects on the dynamics of tearing modes in tokamaks
NASA Astrophysics Data System (ADS)
Lütjens, Hinrich; Luciani, Jean-François; Garbet, Xavier
2001-10-01
The curvature effects on the dynamics of magnetic island evolution in tokamaks are investigated both theoretically and numerically. By taking into account perpendicular and parallel heat diffusion, a new dispersion relation is derived for tearing modes that match the linear and nonlinear results. This evolution equation allows a quantitative description over the whole range of island sizes. It predicts a nonlinear instability, i.e., growing magnetic islands in linearly stable magnetic configurations. All these predictions are in excellent agreement with full tridimensional linear and nonlinear magnetohydrodynamic (MHD) computations with the latest version of XTOR [K. Lerbinger and J. F. Luciani, J. Comput. Phys. 97, 444 (1991)]. These results have important consequences on the onset of neoclassical tearing modes because they predict a resistive MHD threshold.
Discrete extrinsic curvatures and approximation of surfaces by polar polyhedra
NASA Astrophysics Data System (ADS)
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.
DNA curvature and flexibility in vitro and in vivo
Peters, Justin P.; Maher, L. James
2014-01-01
It has been more than 50 years since the elucidation of the structure of double-helical DNA. Despite active research and progress in DNA biology and biochemistry, much remains to be learned in the field of DNA biophysics. Predicting the sequence-dependent curvature and flexibility of DNA is difficult. Applicability of the conventional worm-like chain polymer model of DNA has been challenged. The fundamental forces responsible for the remarkable resistance of DNA to bending and twisting remain controversial. The apparent “softening” of DNA measured in vivo in the presence of kinking proteins and superhelical strain is incompletely understood. New methods and insights are being applied to these problems. This review places current work on DNA biophysics in historical context and illustrates the ongoing interplay between theory and experiment in this exciting field. PMID:20478077
Synaptobrevin Transmembrane Domain Influences Exocytosis by Perturbing Vesicle Membrane Curvature
Chang, Che-Wei; Jackson, Meyer B.
2015-01-01
Membrane fusion requires that nearly flat lipid bilayers deform into shapes with very high curvature. This makes membrane bending a critical force in determining fusion mechanisms. A lipid bilayer will bend spontaneously when material is distributed asymmetrically between its two monolayers, and its spontaneous curvature (C0) will influence the stability of curved fusion intermediates. Prior work on Ca2+-triggered exocytosis revealed that fusion pore lifetime (τ) varies with vesicle content (Q), and showed that this relation reflects membrane bending energetics. Lipids that alter C0 change the dependence of τ on Q. These results suggested that the greater stability of an initial exocytotic fusion pore associated with larger vesicles reflects the need to bend more membrane during fusion pore dilation. In this study, we explored the possibility of manipulating C0 by mutating the transmembrane domain (TMD) of the vesicle membrane protein synaptobrevin 2 (syb2). Amperometric measurements of exocytosis in mouse chromaffin cells revealed that syb2 TMD mutations altered the relation between τ and Q. The effects of these mutations showed a striking periodicity, changing sign as the structural perturbation moved through the inner and outer leaflets. Some glycine and charge mutations also influenced the dependence of τ on Q in a manner consistent with expected changes in C0. These results suggest that side chains in the syb2 TMD influence the kinetics of exocytosis by perturbing the packing of the surrounding lipids. The present results support the view that membrane bending occurs during fusion pore expansion rather than during fusion pore formation. This supports the view of an initial fusion pore through two relatively flat membranes formed by protein. PMID:26153704
Non-Gaussianities and curvature perturbations from hybrid inflation
NASA Astrophysics Data System (ADS)
Clesse, Sébastien; Garbrecht, Björn; Zhu, Yi
2014-03-01
For the original hybrid inflation as well as the supersymmetric F-term and D-term hybrid models, we calculate the level of non-Gaussianities and the power spectrum of curvature perturbations generated during the waterfall, taking into account the contribution of entropic modes. We focus on the regime of mild waterfall, in which inflation continues for more than about 60 e-folds N during the waterfall. We find that the associated fNL parameter goes typically from fNL≃-1/Nexit in the regime with N ≫60, where Nexit is the number of e-folds between the time of Hubble exit of a pivot scale and the end of inflation, down to fNL˜-0.3 when N ≳60, i.e., much smaller in magnitude than the current bound from Planck. Considering only the adiabatic perturbations, the power spectrum is red, with a spectral index ns=1-4/Nexit in the case N ≫60, whereas in the case N≳60, it increases up to unity. Including the contribution of entropic modes does not change observable predictions in the first case, and the spectral index is too low for this regime to be viable. In the second case, entropic modes are a relevant source for the power spectrum of curvature perturbations, of which the amplitude increases by several orders of magnitude. When spectral index values are consistent with observational constraints, the primordial spectrum amplitude is much larger than the observed value and can even lead to black hole formation. We conclude that, due to the important contribution of entropic modes, the parameter space leading to a mild waterfall phase is excluded by cosmic microwave background observations for all the considered models.
NASA Astrophysics Data System (ADS)
Keller, Brad M.; Reeves, Anthony P.; Yankelevitz, David F.; Henschke, Claudia I.; Barr, R. Graham
2009-02-01
Emphysema is a disease of the lungs that destroys the alveolar air sacs and induces long-term respiratory dysfunction. CT scans allow for the imaging of the anatomical basis of emphysema and quantification of the underlying disease state. Several measures have been introduced for the quantification emphysema directly from CT data; most,however, are based on the analysis of density information provided by the CT scans, which vary by scanner and can be hard to standardize across sites and time. Given that one of the anatomical variations associated with the progression of emphysema is the flatting of the diaphragm due to the loss of elasticity in the lung parenchyma, curvature analysis of the diaphragm would provide information about emphysema from CT. Therefore, we propose a new, non-density based measure of the curvature of the diaphragm that would allow for further quantification methods in a robust manner. To evaluate the new method, 24 whole-lung scans were analyzed using the ratios of the lung height and diaphragm width to diaphragm height as curvature estimates as well as using the emphysema index as comparison. Pearson correlation coefficients showed a strong trend of several of the proposed diaphragm curvature measures to have higher correlations, of up to r=0.57, with DLCO% and VA than did the emphysema index. Furthermore, we found emphysema index to have only a 0.27 correlation to the proposed measures, indicating that the proposed measures evaluate different aspects of the disease.
How does relativity affect magnetically induced currents?
Berger, R J F; Repisky, M; Komorovsky, S
2015-09-21
Magnetically induced probability currents in molecules are studied in relativistic theory. Spin-orbit coupling (SOC) enhances the curvature and gives rise to a previously unobserved current cusp in AuH or small bulge-like distortions in HgH2 at the proton positions. The origin of this curvature is magnetically induced spin-density arising from SOC in the relativistic description.
How does relativity affect magnetically induced currents?
Berger, R J F; Repisky, M; Komorovsky, S
2015-09-21
Magnetically induced probability currents in molecules are studied in relativistic theory. Spin-orbit coupling (SOC) enhances the curvature and gives rise to a previously unobserved current cusp in AuH or small bulge-like distortions in HgH2 at the proton positions. The origin of this curvature is magnetically induced spin-density arising from SOC in the relativistic description. PMID:26243659
Equal-Curvature X-ray Telescope Designs for Constellation-X Mission
NASA Technical Reports Server (NTRS)
Saha, Timo T.; Content, David A.; Zhang, William W.
2003-01-01
We study grazing incidence Equal-Curvature telescope designs for the Constellation-X mission. These telescopes have nearly spherical axial surfaces. The telescopes are designed so that the axial curvature is the same on the primary and secondary. The optical performance of these telescopes is for all practical purposes identical to the equivalent Wolter telescopes.
Curvature energy effects on strange quark matter nucleation at finite density
Horvath, J.E. Department of Space Physics and Astronomy, Rice University, P.O. Box 1892, Houston, Texas 77251 )
1994-05-15
We consider the effects of the curvature energy term on thermal strange quark matter nucleation in dense neutron matter. Lower bounds on the temperature at which this process can take place are given and compared to those without the curvature term.
Intra- and intermanual curvature aftereffect can be obtained via tool-touch.
Denisova, Kristina; Kibbe, Melissa M; Cholewiak, Steven A; Kim, Sung-Ho
2014-03-01
We examined the perception of virtual curved surfaces explored with a tool. We found a reliable curvature aftereffect, suggesting neural representation of the curvature in the absence of direct touch. Intermanual transfer of the aftereffect suggests that this representation is somewhat independent of the hand used to explore the surface. PMID:24845746
Noriega, Arturo; Cervantes, Emilio; Tocino, Angel
2008-06-16
Recently, curvature was described as a new trait useful in the analysis of root apex shape. Treating the root profile as a geometric curve revealed that root apex curvature values are lower in ethylene-insensitive mutants (Cervantes E, Tocino A. Geometric analysis of Arabidopsis root apex reveals a new aspect of the ethylene signal transduction pathway in development. J Plant Physiol 2005;162:1038-45). This fact suggests that curvature is regulated by ethylene. In this work, we have determined the curvature values in embryonic roots of wild-type Columbia as well as in ethylene signal-transduction mutants, and found smaller values in embryos of the mutants. We also report on the evolution of root curvature during early development after seed germination. The line Lt16b that expresses GFP in the cell wall has allowed us to investigate the evolution of curvature values in three successive cell layers of seedling roots by confocal microscopy. Treatment of seedlings with norbornadiene resulted in lower curvature values. Our results show details illustrating the effect of ethylene in root curvature.
The effects of streamline curvature and swirl on turbulent flows in curved ducts
NASA Technical Reports Server (NTRS)
Cheng, Chih-Hsiung; Farokhi, Saeed
1990-01-01
A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows, the flow in a curved duct, and swirling flows are examples of flow fields where streamline curvature plays a dominant role. A comprehensive literature review on the effect of streamline curvature was conducted. New algebraic formulations for the eddy viscosity incorporating the kappa-epsilon turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the static pressure coefficients in an S-bend duct and in 180 degree turn-around ducts. The proposed turbulence model embedded with transverse curvature modification is substantiated by predicting the decay of the axial velocities in the confined swirling flows. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.
The role of the epidermis and cortex in gravitropic curvature of maize roots
NASA Technical Reports Server (NTRS)
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.
de Jesus, Armando J.; Espinoza, Arianna; Yin, Hang
2014-01-01
Curved membranes are a common and important attribute in cells. Protein and peptide curvature sensors are known to activate signaling pathways, initiate vesicle budding, trigger membrane fusion, and facilitate molecular transport across cell membranes. Nonetheless, there is little understanding how these proteins and peptides achieve preferential binding of different membrane curvatures. The current study is to elucidate specific factors required for curvature sensing. As a model system, we employed a recently identified peptide curvature sensor, MARCKS-ED, derived from the effector domain of the myristoylated alanine-rich C-kinase substrate protein, for these biophysical investigations. An atomistic molecular dynamics (MD) simulation suggested an important role played by the insertion of the Phe residues within MARCKS-ED. To test these observations from our computational simulations, we performed electron paramagnetic resonance (EPR) studies to determine the insertion depth of MARCKS-ED into differently curved membrane bilayers. Next, studies with varied lipid compositions revealed their influence on curvature sensing by MARCKS-ED, suggesting contributions from membrane fluidity, rigidity, as well as various lipid structures. Finally, we demonstrated that the curvature sensing by MARCKS-ED is configuration independent. In summary, our studies have shed further light to the understanding of how MARCKS-ED differentiates between membrane curvatures, which may be generally applicable to protein curvature sensing behavior. PMID:25195712
Fiber curvature sensor based on spherical-shape structures and long-period grating
NASA Astrophysics Data System (ADS)
Xiong, Mengling; Gong, Huaping; Wang, Zhiping; Zhao, Chun-Liu; Dong, Xinyong
2016-11-01
A novel curvature sensor based on optical fiber Mach-Zehnder interferometer (MZI) is demonstrated. It consists of two spherical-shape structures and a long-period grating (LPG) in between. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivity are -22.144 nm/m-1 in the measurement range of 5.33-6.93 m-1, -28.225 nm/m-1 in the range of 6.93-8.43 m- and -15.68 nm/m-1 in the range of 8.43-9.43 m-1, respectively. And the maximum curvature error caused by temperature is only -0.003 m-1/°C. The sensor exhibits the advantages of all-fiber structure, high mechanical strength, high curvature sensitivity and large measurement scales.
Sha, Haoyan; Faller, Roland
2016-07-20
Quantum chemistry calculations were performed to investigate the effect of the surface curvature of a Boron Nitride (BN) nanotube/nanosheet on gas adsorption. Curved boron nitride layers with different curvatures interacting with a number of different gases including noble gases, oxygen, and water on both their convex and concave sides of the surface were studied using density functional theory (DFT) with a high level dispersion corrected functional. Potential energy surfaces of the gas molecules interacting with the selected BN surfaces were investigated. In addition, the charge distribution and electrostatic potential contour of the selected BN surfaces are discussed. The results reveal how the curvature of the BN surfaces affects gas adsorption. In particular, small curvatures lead to a slight difference in the physisorption energy, while large curvatures present distinct potential energy surfaces, especially for the short-range repulsion. PMID:27399852
Non-perturbative approach for curvature perturbations in stochastic δ N formalism
Fujita, Tomohiro; Kawasaki, Masahiro; Tada, Yuichiro E-mail: kawasaki@icrr.u-tokyo.ac.jp
2014-10-01
In our previous paper [1], we have proposed a new algorithm to calculate the power spectrum of the curvature perturbations generated in inflationary universe with use of the stochastic approach. Since this algorithm does not need the perturbative expansion with respect to the inflaton fields on super-horizon scale, it works even in highly stochastic cases. For example, when the curvature perturbations are very large or the non-Gaussianities of the curvature perturbations are sizable, the perturbative expansion may break down but our algorithm enables to calculate the curvature perturbations. We apply it to two well-known inflation models, chaotic and hybrid inflation, in this paper. Especially for hybrid inflation, while the potential is very flat around the critical point and the standard perturbative computation is problematic, we successfully calculate the curvature perturbations.
Spinning particles in vacuum spacetimes of different curvature types
NASA Astrophysics Data System (ADS)
Semerák, O.; Šrámek, M.
2015-09-01
We consider the motion of spinning test particles with nonzero rest mass in the "pole-dipole" approximation, as described by the Mathisson-Papapetrou-Dixon (MPD) equations, and examine its properties in dependence on the spin supplementary condition added to close the system. In order to better understand the spin-curvature interaction, the MPD equation of motion is decomposed in the orthonormal tetrad whose time vector is given by the four-velocity Vμ chosen to fix the spin condition (the "reference observer") and the first spatial vector by the corresponding spin sμ; such projections do not contain the Weyl scalars Ψ0 and Ψ4 obtained in the associated Newman-Penrose (NP) null tetrad. One natural option of how to choose the remaining two spatial basis vectors is shown to follow "intrinsically" whenever Vμ has been chosen; it is realizable if the particle's four-velocity and four-momentum are not parallel. In order to see how the problem depends on the algebraic type of curvature, one first identifies the first vector of the NP tetrad kμ with the highest-multiplicity principal null direction of the Weyl tensor, and then sets Vμ so that kμ belong to the spin-bivector eigenplane. In spacetimes of any algebraic type but III, it is known to be possible to rotate the tetrads so as to become "transverse," namely so that Ψ1 and Ψ3 vanish. If the spin-bivector eigenplane could be made to coincide with the real-vector plane of any of such transverse frames, the spinning particle motion would consequently be fully determined by Ψ2 and the cosmological constant; however, this can be managed in exceptional cases only. Besides focusing on specific Petrov types, we derive several sets of useful relations that are valid generally and check whether/how the exercise simplifies for some specific types of motion. The particular option of having four-velocity parallel to four-momentum is advocated, and a natural resolution of nonuniqueness of the corresponding reference
Small Peptides Derived from Penetratin as Antibacterial Agents.
Parravicini, Oscar; Somlai, Csaba; Andujar, Sebastián A; Garro, Adriana D; Lima, Beatriz; Tapia, Alejandro; Feresin, Gabriela; Perczel, Andras; Tóth, Gabor; Cascales, Javier López; Rodríguez, Ana M; Enriz, Ricardo D
2016-04-01
The synthesis, in vitro evaluation and conformational study of several small-size peptides acting as antibacterial agents are reported. Among the compounds evaluated, the peptides Arg-Gln-Ile-Lys-Ile-Trp-Arg-Arg-Met-Lys-Trp-Lys-Lys-NH2 , Arg-Gln-Ile-Lys-Ile-Arg-Arg-Met-Lys-Trp-Arg-NH2 , and Arg-Gln-Ile-Trp-Trp-Trp-Trp-Gln-Arg-NH2 exhibited significant antibacterial activity. These were found to be very active antibacterial compounds, considering their small molecular size. In order to better understand the antibacterial activity obtained for these peptides, an exhaustive conformational analysis was performed, using both theoretical calculations and experimental measurements. Molecular dynamics simulations using two different media (water and trifluoroethanol/water) were employed. The results of these theoretical calculations were corroborated by experimental circular dichroism measurements. A brief discussion on the possible mechanism of action of these peptides at molecular level is also presented. Some of the peptides reported here constitute very interesting structures to be used as starting compounds for the design of new small-size peptides possessing antibacterial activity. PMID:26972341
NASA Technical Reports Server (NTRS)
Baker, David R.; Lynn, Barry H.; Boone, Aaron; Tao, Wei-Kuo; Simpson, Joanne
2000-01-01
Idealized numerical simulations are performed with a coupled atmosphere/land-surface model to identify the roles of initial soil moisture, coastline curvature, and land breeze circulations on sea breeze initiated precipitation. Data collected on 27 July 1991 during the Convection and Precipitation Electrification Experiment (CAPE) in central Florida are used. The 3D Goddard Cumulus Ensemble (GCE) cloud resolving model is coupled with the Goddard Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) land surface model, thus providing a tool to simulate more realistically land-surface/atmosphere interaction and convective initiation. Eight simulations are conducted with either straight or curved coast-lines, initially homogeneous soil moisture or initially variable soil moisture, and initially homogeneous horizontal winds or initially variable horizontal winds (land breezes). All model simulations capture the diurnal evolution and general distribution of sea-breeze initiated precipitation over central Florida. The distribution of initial soil moisture influences the timing, intensity and location of subsequent precipitation. Soil moisture acts as a moisture source for the atmosphere, increases the connectively available potential energy, and thus preferentially focuses heavy precipitation over existing wet soil. Strong soil moisture-induced mesoscale circulations are not evident in these simulations. Coastline curvature has a major impact on the timing and location of precipitation. Earlier low-level convergence occurs inland of convex coastlines, and subsequent precipitation occurs earlier in simulations with curved coastlines. The presence of initial land breezes alone has little impact on subsequent precipitation. however, simulations with both coastline curvature and initial land breezes produce significantly larger peak rain rates due to nonlinear interactions.
Turned head--adducted hip--truncal curvature syndrome.
Hamanishi, C; Tanaka, S
1994-01-01
One hundred and eight neonates and infants who showed the clinical triad of a head turned to one side, adduction contracture of the hip joint on the occipital side of the turned head, and truncal curvature, which we named TAC syndrome, were studied. These cases included seven with congenital and five with late infantile dislocations of the hip joint and 14 who developed muscular torticollis. Forty one were among 7103 neonates examined by one of the authors. An epidemiological analysis confirmed the aetiology of the syndrome to be environmental. The side to which the head was turned and that of the adducted hip contracture showed a high correlation with the side of the maternal spine on which the fetus had been lying. TAC syndrome is an important asymmetrical deformity that should be kept in mind during neonatal examination, and may be aetiologically related to the unilateral dislocation of the hip joint, torticollis, and infantile scoliosis which develop after a vertex presentation. Images PMID:8048823
Constructing empirical resolution diagnostics for kriging and minimum curvature gridding
NASA Astrophysics Data System (ADS)
Chiao, Ling-Yun; Chen, Ying-Nien; Gung, Yuancheng
2014-05-01
Resolution analysis is a crucial appraisal procedure in solving general estimation problems, especially for correctly interpreting the results of spatial analysis schemes. Resolution analyses based on the resolving kernels are typically applied to small inverse problems only when the inverse operators are explicitly accessible. Stochastic simulation schemes have been proposed to extract empirical resolution information for solving large inverse problem. In this study, we generalize the formulation of the empirical resolution length and derive the characteristic length of the point spread function for general estimation methods such as minimum curvature gridding and kriging interpolation schemes that are not equipped with explicitly accessible resolving kernels. The implementation of these resolution diagnostics has not been possible in the past and is demonstrated in this study to facilitate clarifying the advantages and limitations of these widely used methods. In addition, we compare these schemes, based on the resolution appraisal, with a multiscale gridding algorithm in the spatial analysis of the Pacific seafloor heat flow observations. By depicting the pattern of the resolution length variations of both the empirical averaging function and the point spread function for each of the estimated models, we demonstrate that schemes equipped with multiscale capability are more favorable for accommodating sparse, nonuniform data distribution than stationary schemes, such as the kriging method. Furthermore, the empirical resolution pattern constructed in this study facilitates the selection of an appropriate reference function and radii of influence for fitting the variogram, which is difficult but critical when using the kriging method.
Bond strength optimization between adherends with different curvatures
Randow, C.L.; Dillard, D.A.
1996-12-31
Due to the increasing use of adhesives in various industrial applications, the accurate prediction of bond behavior becomes more important. This information may also be used to optimize bond design. In particular, the following analysis focuses on bond geometries involving a curvature mismatch between adherends. For example, consider the profile view of a typical laminated counter-top. This involves bonding an initially flat adherend to a rigid substrate with a flat top, a curved corner of radius {rho}, and a flat landing at the bond edge. Questions arise regarding the behavior of the bond and how to optimize the design to minimize stresses resulting from the initially flat adherend being fixed to the rigid, curved substrate. The deflection of the adherend is modeled using beam on elastic foundation analysis. These results, which can be used to calculate peel stresses, are used to determine the optimal design of the laminated counter-top geometry as presented above. Experimental results are also correlated to the analytical solution.
Dual curvature acoustically damped concentrating collector. Final technical report
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.
Linear response to long wavelength fluctuations using curvature simulations
NASA Astrophysics Data System (ADS)
Baldauf, Tobias; Seljak, Uroš; Senatore, Leonardo; Zaldarriaga, Matias
2016-09-01
We study the local response to long wavelength fluctuations in cosmological N-body simulations, focusing on the matter and halo power spectra, halo abundance and non-linear transformations of the density field. The long wavelength mode is implemented using an effective curved cosmology and a mapping of time and distances. The method provides an alternative, more direct, way to measure the isotropic halo biases. Limiting ourselves to the linear case, we find generally good agreement between the biases obtained from the curvature method and the traditional power spectrum method at the level of a few percent. We also study the response of halo counts to changes in the variance of the field and find that the slope of the relation between the responses to density and variance differs from the naïve derivation assuming a universal mass function by approximately 8–20%. This has implications for measurements of the amplitude of local non-Gaussianity using scale dependent bias. We also analyze the halo power spectrum and halo-dark matter cross-spectrum response to long wavelength fluctuations and derive second order halo bias from it, as well as the super-sample variance contribution to the galaxy power spectrum covariance matrix.
Charge transfer and negative curvature energy in magnesium boride nanotubes
NASA Astrophysics Data System (ADS)
Tang, Hui; Ismail-Beigi, Sohrab
2016-07-01
Using first-principles calculations based on density functional theory, we study the energetics and charge transfer effects in MgBx nanotubes and two-dimensional (2D) sheets. The behavior of adsorbed Mg on 2D boron sheets is found to depend on the amount of electron transfer between the two subsystems. The amount is determined by both the density of adsorbed Mg as well as the atomic-scale structure of the boron subsystem. The degree of transfer can lead to repulsive or attractive Mg-Mg interactions. In both cases, model MgBx nanotubes built from 2D MgBx sheets can display negative curvature energy: a relatively unusual situation in nanosystems where the energy cost to curve the parent 2D sheet into a small-diameter nanotube is negative. Namely, the small-diameter nanotube is energetically preferred over the corresponding flat sheet. We also discuss how these findings may manifest themselves in experimentally synthesized MgBx nanotubes.
Modeling Normal Shock Velocity Curvature Relation for Heterogeneous Explosives
NASA Astrophysics Data System (ADS)
Yoo, Sunhee; Crochet, Michael; Pemberton, Steve
2015-06-01
The normal shock velocity and curvature, Dn(κ) , relation on a detonation shock surface has been an important functional quantity to measure to understand the shock strength exerted against the material interface between a main explosive charge and the case of an explosive munition. The Dn(κ) relation is considered an intrinsic property of an explosive, and can be experimentally deduced by rate stick tests at various charge diameters. However, experimental measurements of the Dn(κ) relation for heterogeneous explosives such as PBXN-111 are challenging due to the non-smoothness and asymmetry usually observed in the experimental streak records of explosion fronts. Out of the many possibilities, the asymmetric character may be attributed to the heterogeneity of the explosives, a hypothesis which begs two questions: (1) is there any simple hydrodynamic model that can explain such an asymmetric shock evolution, and (2) what statistics can be derived for the asymmetry using simulations with defined structural heterogeneity in the unreacted explosive? Saenz, Taylor and Stewart studied constitutive models for derivation of the Dn(κ) relation on porous `homogeneous' explosives and carried out simulations in a spherical coordinate frame. In this paper, we extend their model to account for `heterogeneity' and present shock evolutions in heterogeneous explosives using 2-D hydrodynamic simulations with some statistical examination. (96TW-2015-0004)
Curvature and Frontier Orbital Energies in Density Functional Theory
Stein, Tamar; Autschbach, Jochen; Govind, Niranjan; Kronik, Leeor; Baer, Roi
2012-12-20
Perdew et al. [Phys. Rev. Lett 49, 1691 (1982)] discovered and proved two different properties that exact Kohn-Sham density functional theory (DFT) must obey: (i) The exact total energy versus particle number must be a series of linear segments between integer electron points; (ii) Across an integer number of electrons, the exchange-correlation potential may ``jump’’ by a constant, known as the derivative discontinuity (DD). Here, we show analytically that in both the original and the generalized Kohn-Sham formulation of DFT, the two are in fact two sides of the same coin. Absence of a derivative discontinuity necessitates deviation from piecewise linearity, and the latter can be used to correct for the former, thereby restoring the physical meaning of the orbital energies. Using selected small molecules, we show that this results in a simple correction scheme for any underlying functional, including semi-local and hybrid functionals as well as Hartree-Fock theory, suggesting a practical correction for the infamous gap problem of density functional theory. Moreover, we show that optimally-tuned range-separated hybrid functionals can inherently minimize both DD and curvature, thus requiring no correction, and show that this can be used as a sound theoretical basis for novel tuning strategies.
The hybrid inflation waterfall and the primordial curvature perturbation
NASA Astrophysics Data System (ADS)
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.
Self-attraction and natural curvature in null DNA.
Manning, G S
1989-08-01
Forces of self-attraction inherent in DNA are unmasked when its ionic charge is neutralized. On the global level, self-attraction operates between segments to condense null (charge-neutralized) DNA into a segment-rich particle. Locally, self-attraction tends to contract an individual segment along its axis. If certain conditions are satisfied, the compressed segment buckles outward from the original line of the axis. Its most stable shape is then curved, or, as an extreme case, even completely folded. Buckling conditions are derived and shown to be met by DNA, thus explaining the high degree of ordered curvature and folding in the observed morphologies of condensed null DNA. The central concept employed is the buckling persistence length. It is evaluated for null DNA (40-50 bp) and agrees with experimental data (less than 60 bp). It helps in understanding the observed cooperative unit in the condensation/decondensation equilibrium (about 60 bp) and the observed size of digestion fragments unstable in the condensed phase (about 80 bp). The root-mean-square thermal compression/extension fluctuation in DNA is estimated at about 0.1 A/bp. PMID:2684222
Linear response to long wavelength fluctuations using curvature simulations
NASA Astrophysics Data System (ADS)
Baldauf, Tobias; Seljak, Uroš; Senatore, Leonardo; Zaldarriaga, Matias
2016-09-01
We study the local response to long wavelength fluctuations in cosmological N-body simulations, focusing on the matter and halo power spectra, halo abundance and non-linear transformations of the density field. The long wavelength mode is implemented using an effective curved cosmology and a mapping of time and distances. The method provides an alternative, more direct, way to measure the isotropic halo biases. Limiting ourselves to the linear case, we find generally good agreement between the biases obtained from the curvature method and the traditional power spectrum method at the level of a few percent. We also study the response of halo counts to changes in the variance of the field and find that the slope of the relation between the responses to density and variance differs from the naïve derivation assuming a universal mass function by approximately 8-20%. This has implications for measurements of the amplitude of local non-Gaussianity using scale dependent bias. We also analyze the halo power spectrum and halo-dark matter cross-spectrum response to long wavelength fluctuations and derive second order halo bias from it, as well as the super-sample variance contribution to the galaxy power spectrum covariance matrix.
Phase separation in artificial vesicles driven by light and curvature
NASA Astrophysics Data System (ADS)
Rinaldin, Melissa; Pomp, Wim; Schmidt, Thomas; Giomi, Luca; Kraft, Daniela; Physics of Life Processes Team; Soft; Bio Mechanics Collaboration; Self-Assembly in Soft Matter Systems Collaboration
The role of phase-demixing in living cells, leading to the lipid-raft hypothesis, has been extensively studied. Lipid domains of higher lipid chain order are proposed to regulate protein spatial organization. Giant Unilamellar Vesicles provide an artificial model to study phase separation. So far temperature was used to initiate the process. Here we introduce a new methodology based on the induction of phase separation by light. To this aim, the composition of the lipid membrane is varied by photo-oxidation of lipids. The control of the process gained by using light allowed us to observe vesicle shape fluctuations during phase-demixing. The presence of fluctuations near the critical mixing point resembles features of a critical process. We quantitatively analyze these fluctuations using a 2d elastic model, from which we can estimate the material parameters such as bending rigidity and surface tension, demonstrating the non-equilibrium critical behaviour. Finally, I will describe recent attempts toward tuning the membrane composition by controlling the vesicle curvature.
Damage Detection Using the Frequency-Response Curvature Method
NASA Astrophysics Data System (ADS)
SAMPAIO, R. P. C.; MAIA, N. M. M.; SILVA, J. M. M.
1999-10-01
Structural damage detection has gained increasing attention from the scientific community since unpredicted major hazards, most with human losses, have been reported. Aircraft crashes and the catastrophic bridge failures are some examples. Security and economy aspects are the important motivations for increasing research on structural health monitoring. Since damage alters the dynamic characteristics of a structure, namely its eigenproperties (natural frequencies, modal damping and modes of vibration), several techniques based on experimental modal analysis have been developed in recent years. A method that covers the four steps of the process of damage detection—existence, localization, extent and prediction—has not yet been recognized or reported. The frequency-response-function (FRF) curvature method encompasses the first three referred steps being based on only the measured data without the need for any modal identification. In this paper, the method is described theoretically and compared with two of the most referenced methods on literature. Numerically generated data, from a lumped-mass system, and experimental data, from a real bridge, are used for better illustration.
Primordial magnetic field and kinetic theory with Berry curvature
NASA Astrophysics Data System (ADS)
Bhatt, Jitesh R.; Pandey, Arun Kumar
2016-08-01
We study the generation of a magnetic field in primordial plasma of standard model particles at a temperature T >80 TeV —much higher than the electroweak scale. It is assumed that there is an excess number of right-handed electrons compared to left-handed positrons in the plasma. Using the Berry-curvature modified kinetic theory to incorporate the effect of the Abelian anomaly, we show that this chiral imbalance leads to the generation of a hypermagnetic field in the plasma in both the collision dominated and collisionless regimes. It is shown that, in the collision dominated regime, the chiral-vorticity effect can generate finite vorticity in the plasma together with the magnetic field. Typical strength of the generated magnetic field is 1 027 G at T ˜80 TeV with the length scale 1 05/T , whereas the Hubble length scale is 1 013/T . Furthermore, the instability can also generate a magnetic field of the order 1 031 G at a typical length scale 10 /T . But there may not be any vorticity generation in this regime. We show that the estimated values of the magnetic field are consistent with the bounds obtained from current observations.
Capillary-bridge–derived particles with negative Gaussian curvature
Wang, Liming; McCarthy, Thomas J.
2015-01-01
We report the preparation of millimeter-scale particles by thermal polymerization of liquid monomer capillary bridges to form catenoid-shaped particles that exhibit negative Gaussian curvature. The shape of the capillary bridges and resulting particles can be finely tuned using several addressable parameters: (i) the shape, size, and orientation of lithographic pinning features on the spanned surfaces; (ii) the distance between opposing support surfaces; and (iii) the lateral displacement (shear) of opposing features. The catenoid-shaped particles exhibit controllable optical properties as a result of their concave menisci, the shape of which can be easily manipulated. The particles self assemble in the presence of a condensing liquid (water) to form reversible neck-to-neck pairs and less reversible end-to-end aggregates. We argue that this approach could be scaled down to micrometer dimensions by fabricating an array of micrometer-scale particles. We also argue, with a discussion of dynamic wetting, that these particles will exhibit interesting anisotropic adhesive properties. PMID:25730873
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{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∼
Hong, J M; Chung, C-S; Bang, O Y; Yong, S W; Joo, I S; Huh, K
2009-01-01
Objectives: The diameters of the vertebral arteries (VAs) are very often unequal. Therefore, this study investigated if unequal VA flow contributes to the development of basilar artery (BA) curvature and if it is a link to the laterality of pontine or cerebellar infarcts occurring around the vertebrobasilar junction. Methods: Radiological factors were analysed (infarct laterality, VA dominance, BA curvature and their directional relationships) in 91 patients with acute unilateral pontine or posterior inferior cerebellar artery (PICA) territory infarcts. The “dominant” VA side was defined as either that the VA was larger in diameter or the VA was connected with the BA in more of a straight line, if both VAs looked similar in diameter on CT angiography. Multiple regression analysis was performed to predict moderate to severe BA curvature. Results: The dominant VA was more frequent on the left side (p<0.01). Most patients had an opposite directional relationship between the dominant VA and BA curvature (p<0.01). Pontine infarcts were opposite to the side of BA curvature (p<0.01) and PICA infarcts were on the same side as the non-dominant VA side (p<0.01). The difference in VA diameters was the single independent predictor for moderate to severe BA curvature (OR per 1 mm, 2.70; 95% CI 1.22 to 5.98). Conclusions: Unequal VA flow is an important haemodynamic contributor of BA curvature and development of peri-vertebrobasilar junctional infarcts. PMID:19414436
Dymond, Marcus K
2016-08-01
Several theories of phospholipid homeostasis have postulated that cells regulate the molecular composition of their bilayer membranes, such that a common biophysical membrane parameter is under homeostatic control. Two commonly cited theories are the intrinsic curvature hypothesis, which states that cells control membrane curvature elastic stress, and the theory of homeoviscous adaptation, which postulates cells control acyl chain packing order (membrane order). In this paper, we present evidence from data-driven modelling studies that these two theories correlate in vivo. We estimate the curvature elastic stress of mammalian cells to be 4-7 × 10(-12) N, a value high enough to suggest that in mammalian cells the preservation of membrane order arises through a mechanism where membrane curvature elastic stress is controlled. These results emerge from analysing the molecular contribution of individual phospholipids to both membrane order and curvature elastic stress in nearly 500 cellular compositionally diverse lipidomes. Our model suggests that the de novo synthesis of lipids is the dominant mechanism by which cells control curvature elastic stress and hence membrane order in vivo These results also suggest that cells can increase membrane curvature elastic stress disproportionately to membrane order by incorporating polyunsaturated fatty acids into lipids. PMID:27534697
Familial appearance of congenital penile curvature – case history of two brothers
Matuszewski, Marcin; Krajka, Kazimierz; Rębała, Krzysztof
2013-01-01
The true prevalence of congenital penile curvature (CPC) is difficult to determine. Some study reports suggests that this problem may occur in as many as 10% of the male population [1]. However, a literature search of the Medline database revealed no reference concerning familial appearance of congenital penile curvature. For that reason we would like to present our case series. Two brothers aged 25 and 26 respectively were admitted to the department of urology due to congenital penile curvature. Each patient was assessed by a history, physical examination, auto-photography of the erect penis, and a thorough sexual history. Concomitant anomalies of penile layers were absent in both cases. The Yachia [2] and Essed-Schroeder [3] corporoplasty technique were applied respectively. In follow-up both brothers reported straight erections. A survey of the fetal penis at different stages of development shows some degree of curvature in a considerable number of embryos [4]. Penile curvature may thus be considered almost physiological in embryos between 35 and 45 mm in length. Thus, it has also been proposed that penile curvature is secondary to an arrest in normal penile development [5]. Therefore, some form of congenital local androgen deficiency may be responsible for inherited penile curvature. PMID:24579033
Plan curvature and landslide probability in regions dominated by earth flows and earth slides
Ohlmacher, G.C.
2007-01-01
Damaging landslides in the Appalachian Plateau and scattered regions within the Midcontinent of North America highlight the need for landslide-hazard mapping and a better understanding of the geomorphic development of landslide terrains. The Plateau and Midcontinent have the necessary ingredients for landslides including sufficient relief, steep slope gradients, Pennsylvanian and Permian cyclothems that weather into fine-grained soils containing considerable clay, and adequate precipitation. One commonly used parameter in landslide-hazard analysis that is in need of further investigation is plan curvature. Plan curvature is the curvature of the hillside in a horizontal plane or the curvature of the contours on a topographic map. Hillsides can be subdivided into regions of concave outward plan curvature called hollows, convex outward plan curvature called noses, and straight contours called planar regions. Statistical analysis of plan-curvature and landslide datasets indicate that hillsides with planar plan curvature have the highest probability for landslides in regions dominated by earth flows and earth slides in clayey soils (CH and CL). The probability of landslides decreases as the hillsides become more concave or convex. Hollows have a slightly higher probability for landslides than noses. In hollows landslide material converges into the narrow region at the base of the slope. The convergence combined with the cohesive nature of fine-grained soils creates a buttressing effect that slows soil movement and increases the stability of the hillside within the hollow. Statistical approaches that attempt to determine landslide hazard need to account for the complex relationship between plan curvature, type of landslide, and landslide susceptibility. ?? 2007 Elsevier B.V. All rights reserved.
ERIC Educational Resources Information Center
Lim, Ik Soo; Leek, E. Charles
2012-01-01
Previous empirical studies have shown that information along visual contours is known to be concentrated in regions of high magnitude of curvature, and, for closed contours, segments of negative curvature (i.e., concave segments) carry greater perceptual relevance than corresponding regions of positive curvature (i.e., convex segments). Lately,…